EMC Online Manual 2021 PDF

ENGINEERING, MATERIALS AND COMPONENTS (EMC) ONLINE COURSE MANUAL CANADIAN INSTITUTE FOR NON-DESTRUCTIVE EVALUATION 135 Fennell Avenue West Hamilton, Ontario L9C 0E5 Telephone: 905-387-1655 Fax: 905-574-6080 Emai...

ENGINEERING, MATERIALS AND COMPONENTS (EMC) ONLINE COURSE MANUAL CANADIAN INSTITUTE FOR NON-DESTRUCTIVE EVALUATION 135 Fennell Avenue West Hamilton, Ontario L9C 0E5 Telephone: 905-387-1655 Fax: 905-574-6080 Email: [email protected] Website: www.cinde.ca COPYRIGHT 2021 CANADIAN INSTITUTE FOR NDE Section 1 Engineering Materials and Processes Table of Contents 1. Materials 1.1 Nature of Matter ………………………………………….. 2 1.2 Metals ………………………………………….. 11 1.2.1 Introduction ……………………................................ 11 1.2.2 Cast Iron ……………………................................ 19 1.2.3 Steel ……………………................................ 24 1.2.4 Aluminum ……………………................................ 39 1.2.5 Nickel ……………………................................ 44 1.2.6 Copper ……………………................................ 46 1.3 Powder Metallurgy ………………………………………….. 49 1.4 Plastics ………………………………………….. 52 1.5 Ceramics ………………………………………….. 54 1.6 Concrete ………………………………………….. 57 1.7 Composites ………………………………………….. 60 2. Mechanical Testing of Materials 3. Manufacturing Processes 3.1 Heat Treatment ………………………………………….. 79 3.2 Welding, Brazing and Soldering ……………………………. 85 3.3 Forming ………………………………………….. 123 3.4 Bulk Forming ………………………………………….. 127 3.5 Casting ………………………………………….. 137 3.6 Manufacturing of Pipe ………………………………………. 152 3.7 Machining.............................................................154 4. In Service Deterioration of Materials 4.1 Fatigue............................................................ 161 4.2 Corrosion............................................................ 166 4.3 Wear and Erosion............................................................ 173 5. Other Sources of Discontinuities 6. Terminology Engineering, Materials and Components Revision Date: 9/17/19 -1- CANADIAN INSTITUTE FOR NDE Section 1 MATERIALS 1.1 NATURE OF MATTER Understanding the nature of materials plays an important role in our understanding of the materials or components that we non-destructively test (NDT). The discontinuities or material properties that we seek and study with NDT methods maybe associated with the initial processing of the material, subsequent processing or manufacturing, and/or service conditions in which they perform. An understanding of these processes or conditions enhances our ability to detect, measure and characterize these conditions. Understanding the nature of materials also aids in understanding the NDT methods. As an example, in the study of radiography why do isotopes decay and what energy is released? This is explained at the atomic and subatomic level. In the study of magnetic particle why can some metals be magnetized and others not? Why is a specific light given off from fluorescent magnetic particles and dyes when exposed to black light? Why do metals conduct electricity? Knowing the basic concepts of the atom plays an important role in this understanding. History The concept of the atom dates back to ancient Greece in the 5th Century BC. Democritus the “laughing philosopher” around 440 BC first coined the term “atomos” meaning the smallest particle of matter. This original concept of the atom was based in philosophy; the science of chemistry in 1661 first proposed all matter was made of atoms rather than the classical elements of earth, fire and water. John Dalton in 1803 was the first to propose each atom has a characteristic mass and remains unchanged in chemical processes as well as other additional features that have since been discarded. JJ Thompson (Nobel Prize in Physics 1906) first revealed through his work on cathode rays that subatomic particles (electrons) existed. Ernest Rutherford (1871-1937) received the Nobel Prize for Chemistry in 1908 and proposed the concept that the mass of an atom is concentrated at the centre (nucleus) with electrons that orbit the nucleus. Together with H.G. Moseley by bombarding atoms with cathode rays was able to characterize atoms in such a way that each could be assigned an atomic number. The periodic table could then be described as one atom existing for each element of the table. In 1913 Frederick Soddy (Nobel Prize in Chemistry 1921) discovered that there appeared to be more than one type of atom at each Engineering, Materials and Components Revision Date: 9/17/19 -2- CANADIAN INSTITUTE FOR NDE Section 1 position in the periodic table. The term isotope was introduced by Margaret Todd (Scottish writer and doctor) for different atoms of the same element. It was Niels Bohr (Nobel Prize in Physics 1922) in 1913 that introduced the principles of quantum mechanics to the study of electrons and the fact that they were confined to clearly defined orbits, could jump between orbits, and could not freely move between the orbits or reside in the intermediate states. Erwin Schrödinger (Nobel Prize in Physics 1933) and Louis de Broglie (Nobel Prize in Physics 1929) proposed that the electrons behaved like waves developing a three dimensional model in which it was impossible to determine the position and momentum of the particles. This came to be known as the “uncertainty principle”. Although difficult to visualize it did explain the behaviour of atoms that previous models could not, and could predict a range of position and momentum of the electrons. The planetary (Bohr Model) model was then discarded. The mass spectrometer an instrument developed to measure the exact mass of an atom was used by Francis William Aston (Nobel Prize in Chemistry 1922) to demonstrate that isotopes had different masses. He was able to determine that isotopes varied by integer amounts and was called the “whole number rule”. James Chadwick (Nobel Prize in Physics 1935) in 1932 explained isotopes as atoms with the same number of protons but different number of neutrons within the nucleus. In the 1950’s using particle accelerators and detectors scientists were able to determine that neutrons and protons were made of smaller particles called quarks. Atoms All matter such as solids, liquids, and gases are made up of atoms, the smallest particle of any element (refer to the periodic table in figure 1.1a). There are approximately 118 different atoms. This periodic table shows all 118 elements and specifies the chemical name, atomic number, chemical symbol, and atomic weight. Engineering, Materials and Components Revision Date: 9/17/19 -3- CANADIAN INSTITUTE FOR NDE Section 1 Figure 1.1a Engineering, Materials and Components Revision Date: 9/17/19 -4- CANADIAN INSTITUTE FOR NDE Section 1 Not all of the atoms in the periodic table will be of interest to us. Some elements’ chemical symbols appear on Mill Test Reports and may be routinely used in our day to day activities. Mill Test Reports (see figure1.1b) are used to communicate the actual properties of a piece of material. Among other information, is the chemical composition of the material expressed as percentages of weight. As an example (refer to figure 1.1b) the cast analysis of a specific piece of steel is: Carbon C.187% Manganese Mn 1.100% Phosphorus P.013% Sulphur S.010% Silicon Si.075% Aluminum Al.046% Nickel Ni.004% the remainder will be iron (Fe) Some of the most common elements that appear in Mill Test Reports and their symbols are: Al Aluminum C Carbon Cr Chromium Co Cobalt Cu Copper Fe Iron Pb Lead Mg Magnesium Mn Manganese Mo Molybdenum Ni Nickel Si Silicon S Sulphur Sn Tin Ti Titanium W Tungsten Zn Zinc Engineering, Materials and Components Revision Date: 9/17/19 -5- CANADIAN INSTITUTE FOR NDE Section 1 Engineering, Materials and Components Revision Date: 9/17/19 -6- CANADIAN INSTITUTE FOR NDE Section 1 Atoms of all elements consist of even smaller particles. The atom has a central mass called the nucleus which consists of protons and neutrons (except hydrogen that has 1 proton and no neutrons). The protons (positively charged) and the neutrons (electrically neutral) are composed of particles called quarks of which there are 6 types. A quark is a type of fermion one of two basic building blocks of all matter. Revolving around the nucleus in orbits (or "shells") are the electrons which are negatively charged. The electron is an example of the second building block; a lepton. In an electrically neutral atom, the number of electrons will equal the number of protons, thereby cancelling the electrical charge of each. Figure 1.1c Figure 1.1d The electrons in each atom are attracted to the nucleus by an electromagnetic force. Electrons have properties of both waves and particles and their attraction to the nucleus is based on their distance from the nucleus. The attraction to the nucleus is measured in electron volts (eV), the amount of energy needed to unbind it from the nucleus. The lowest energy of a bound electron is the ground Engineering, Materials and Components Revision Date: 9/17/19 -7- CANADIAN INSTITUTE FOR NDE Section 1 state and electrons at higher energy levels are in an excited state. In order for an electron to transition from one energy level to another it must absorb or emit a photon of energy matching the difference between the energy levels. When an electron emits a photon it drops to a lower energy level, the energy is proportional to its frequency and so appears as distinct bands in the electromagnetic spectrum. This is what happens when a fluorescent material is subjected to black light; the energy of the electron is raised to a higher level and as it drops back to its original energy level, energy is released in the form of visible light which our eyes see. Atoms are bound together in one of several ways. Either with the same type of atom to form a pure substance or with atoms of other elements to form compounds. The three methods of atomic bonding are: Ionic Bonding o Sodium Chloride (salt) is an example of this type of bond. Chlorine has 7 electrons in it’s third (outer, valence) shell, the capacity of that shell is 8. Atoms like to have a full valence shell, so chlorine will attempt to pickup one electron to fill this outer shell. Sodium has only one electron in its third shell. If sodium gives up this one electron, to have a full 2nd (valence) shell it will become positively charged. If chlorine picks up this electron given up by the sodium it will become negatively charged and they will have an attraction for each other. The resultant material, salt has very different chemical properties than either of the two elements that make it up. This type of bond occurs between a metal and a non-metal atom. Figure 1.1e, Ionic Bonding Engineering, Materials and Components Revision Date: 9/17/19 -8- CANADIAN INSTITUTE FOR NDE Section 1 Covalent Bonding o Two hydrogen atoms bond together through the sharing of an electron. Each atom has one electron. The first shell of an atom has a capacity for two electrons. To achieve full outer shells the hydrogen atoms share an electron. Covalent bonding can involve the sharing of more than one electron and occurs between two non- metal atoms. Sharing Electrons Figure 1.1f, Covalent Bonding Metallic Bonding o The metal atoms will be dealt with later in 1.2.1. States of Matter Matter can exist in four states: solid, liquid, gaseous or plasma. Within a given state atoms can be in different phases. As an Pressure SOLID example, carbon can exist as graphite or LIQUID diamond while in the solid state. Critical Point The state of the atom depends on the pressure and temperature to which the material is exposed. If pressure and Triple Point VAPOUR temperature are plotted showing the states for a given material the point at which solid, liquid and gas can exist in equilibrium is Temperature called the triple point. An example is that of Figure 1.1g, Triple Point Diagram an ice skate on ice. The pressure of a persons’ body applied over the area of the Engineering, Materials and Components Revision Date: 9/17/19 -9- CANADIAN INSTITUTE FOR NDE Section 1 skate blade increases the pressure on the ice. The increase in pressure favours the formation of a denser phase, which in this case is water. The film of water between the skate blade and the ice is what the person skating glides on. This is why the blades are designed with a particular width. It is also why people who skate on double bladed skates commonly find it more difficult as the pressure per unit area is cut in half. A metallurgical example using this information would be the plating of gold onto glass. To avoid damage to the glass and achieve a uniform coating, gold is taken to the vapour state and transitioned directly to the solid state by keeping the pressure below the triple point. Another point shown on these diagrams is the “critical point”. That is the point when liquids and gases cannot be distinguished. Above the critical point condensation does not occur at any pressure. Refer to figure1.1g for an example of a triple point diagram. The fourth state of matter is plasma which is typically an ionized gas but is considered a separate phase from gas because it has one or more free electrons which are not bound to the atom and thus the material is electrically conductive. The resulting mixture consists of neutral atoms, free electrons and charged ions. Artificially produced plasmas are used in plasma displays including televisions and in electric arc welding and cutting (plasma arc welding and plasma cutting). Properties of Materials Properties of solid materials can be divided into the following categories: Physical Properties include: melting point, boiling point and density. Mechanical properties include: elastic modulus, shear modulus, Poisson’s Ratio, and mechanical strength properties such as yield strength, ultimate tensile strength and elongation. Thermal properties include: coefficient of thermal expansion, and thermal conductivity. Electric properties include: electric conductivity and electric resistivity. Magnetic properties include: permeability, relative permeability, and retentivity. Acoustic Properties include: acoustic velocities and impedance. References: 1. Stanford Encyclopaedia of Philosophy (2004), http://plato.stanford.edu/entries/democritus/ 2. Cardwell, D, John Dalton and the Progress of Science (1968) 3. The Nobel Foundation, http://nobelprize.org/nobelfoundation/index.html Engineering, Materials and Components Revision Date: 9/17/19 - 10 - CANADIAN INSTITUTE FOR NDE Section 1 1.2 METALS 1.2.1 Introduction (metallic bonding) A chemist might describe a metal as a chemical element whose atoms readily lose electrons to form positive ions and form metallic bonds between other metals and ionic bonds with non-metals. Metals have a few common properties: In the solid state they exist in the form of crystals They have relatively high thermal and electrical conductivity They have the ability to be formed plastically They have relatively high reflectivity of light (metallic lustre) Metals are on the left side of the periodic table and constitute about three- quarters of the elements. Unlike ionic and covalent bonds; metal to metal bonds do not share electrons with other individual atoms, or do they depend upon the transfer of electrons and attraction of atoms through unlike electrical charges. Metals contribute their valence (highest energy electrons) to a negative electron cloud. The electrons are therefore not associated with any specific atom but are free to move among the positively charged metallic ions. The atoms are held together by their mutual attraction for the negatively charged cloud. The atoms tend to assume a relatively fixed position which gives rise to a crystalline structure. The atoms oscillate about the fixed location and are said to be in dynamic equilibrium, rather than statically fixed. The atoms are in a three dimensional network and the imaginary lines connecting the atoms are referred to as lattices. The three most important crystalline structures in the study of metals are: Body-centered Cubic A single cell of this structure consists of 9 atoms. The corner atoms each form the corner of the adjacent cells. Metals which crystallize in the body centered cubic structure include: Chromium Tungsten Alpha Iron Delta Iron Molybdenum Vanadium Sodium Figure 1.2a, BCC Engineering, Materials and Components Revision Date: 9/17/19 - 11 - CANADIAN INSTITUTE FOR NDE Section 1 Face-centered Cubic A single cell of this structure consists of 14 atoms, eight (one at each corner) plus 6 (one on each face). The external atoms each form the sides of the adjacent cell. Metals which crystallize in the face centered cubic structure include: Aluminum Nickel Copper Gold Silver Lead Platinum Gamma iron Figure 1.2b, FCC Hexagonal Close-packed A single cell of this structure consists of 17 atoms, seven on each end plus 3 in the middle. The external atoms each form the sides of the adjacent cell. Metals which crystallize in the hexagonal close-packed cubic structure include: Magnesium Beryllium Zinc Cadmium Hafnium Figure 1.2c, HCP Some metals (in particular iron), can exist in more than one type of lattice. This is referred to as polymorphism. If the process is reversible (as it is with iron) it is referred to as allotropy. The importance of this will be seen in the heat treatment of steel. In the liquid phase there is no orientation or crystalline structure, the atoms are only contained by the vessel in which the molten metal is held and the surface tension of the liquid. Crystal growth as the material freezes occurs in two stages: Nuclei formation Crystal growth Engineering, Materials and Components Revision Date: 9/17/19 - 12 - CANADIAN INSTITUTE FOR NDE Section 1 When a pure metal freezes the nuclei (starting points/seed) tend to gather on the mold surfaces and individual groups of atoms tend to form into their crystalline structure. Groups of atoms may break up and continue to grow as separate crystal formations. As the solid crystalline structures form, the energy must be given up; this is referred to as the latent heat of fusion. In pure metals some under cooling occurs to establish a stable situation between the solid and liquid boundaries. Impurities such as alloy elements may tend to reduce this under- cooling as they act as nuclei throughout the liquid to form other crystal growths. These crystal growths are referred to as dendrites Figure 1.2d shows a dendrite formation. The dendrites continue to grow until they start to interfere with each other. Each has a different orientation of growth and where they meet tends to have the highest concentration of impurities in the liquid. These are the last areas to freeze and make up what is known as the “grain boundaries”. The slower the rate of cooling the larger the grain will grow. Crystals will not form perfectly in their lattice structure, there maybe disturbed regions between otherwise perfectly aligned crystals. These disturbed regions are called dislocations. Also, defects such as Figure 1.2d, Dendrite shrinkage cavities and porosity which are large enough to be seen by the naked eye may form (refer to section 3.5 on castings for a more complete description of defects that occur on freezing of the metal). Other items that affect the grain size besides the rate of cooling are: Impurities (act as nucleation points) Stirring of the molten metal (breaks up the formation of dendrite) Relative position in the casting (centre tends to cool slower and therefore has larger grains) In general finer grained material has better toughness and resistance to shock and they usually are harder and stronger than coarse grained material. Engineering, Materials and Components Revision Date: 9/17/19 - 13 - CANADIAN INSTITUTE FOR NDE Section 1 Equilibrium Diagrams Equilibrium diagrams, also referred to as phase diagrams, are a type of graph that illustrates the phases that exist at various temperatures of a material or combination of materials. The simplest form is of a single simple substance e.g. water. This also maybe referred to as a triple point diagram as it highlights the point (triple point) where all three phases can coexist at equilibrium. As discussed previously, another point included on these diagrams is the “critical point”. The point when liquids and gases cannot be distinguished. Iron-Iron Carbide Equilibrium Diagram Iron is allotropic, that is it can exist in more than one type of lattice structure and depending upon temperature and the condition is reversible (polymorphism). Figure 1.2e is a cooling curve for pure iron. As we heat iron from room temperature up to the melting point, the structure of the iron changes. From room temperature up to 908°C the iron is in body centered cubic structure (BCC). From 908°C to 1400°C the iron is face centered cubic structure (FCC). From 1400°C up to the melting point (1538°C) the iron reverts back to BCC. Each of these phase changes is given a name for identification purposes: Alpha Iron, α Iron, (BCC) up to 908°C Gamma Iron, γ Iron, (FCC) from 908°C to 1400°C Figure 1.2e, Cooling Curve, Iron Delta Iron, δ Iron, (BCC) from 1400°C to 1538°C Liquid Iron above 1538°C Important to NDT practitioners is the fact that at above 768°C (1444°F) the iron becomes nonmagnetic. So that if heat treatment above this temperature is to Engineering, Materials and Components Revision Date: 9/17/19 - 14 - CANADIAN INSTITUTE FOR NDE Section 1 take place after magnetization it may not be necessary to demagnetize the material inspected. The above information is for pure iron, but of the ferrous metals it is usually steel that is of interest to us. Steel by definition is iron that has some carbon, not more than 2%. This has a very interesting impact on the phases that are formed by the steel as it is heated and cooled. This is best shown in an equilibrium diagram. The choice of the name “equilibrium” is made because it displays what happens during the heating and cooling at very slow rates of change of temperature. Refer to figure 1.2f. Figure 1.2f, Iron-Carbon Equilibrium Diagram The x-axis (horizontal) represents the percentage of carbon; we are seeing a small portion of the overall axis up to about 3% which includes the area of interest for steel. The y-axis (vertical) represents temperature and again we are looking at only the portion of the solid range, remembering that the melting Engineering, Materials and Components Revision Date: 9/17/19 - 15 - CANADIAN INSTITUTE FOR NDE Section 1 temperature is about 1500°C. Consider alloy 1 shown on the diagram as it cools from about 1100 C. It is first in the austenite phase (FCC) in this lattice structure the iron can dissolve up to 2% carbon, in other words all of the.2% carbon in this alloy is in solution (dissolved). As it cools it undergoes a phase change and consist of ferrite (BCC) and austenite (FCC). The ferrite can dissolve only a small portion of the carbon (.025%) in solution. Layers will start to form of ferrite and pearlite. Pearlite is a mixture of ferrite and cementite. Cementite is the phase which holds the carbon that cannot be held by the ferrite. If the composition was.8% instead of.2% the structure would be all pearlite and this would be referred to as the eutectic (figure 1.2i). Alloy 1 will have areas of pearlite plus areas of ferrite, because more ferrite is present than needed to form pure pearlite, see figure 1.2h, referred to as hypo-eutectoid steel. Alloy 2 (1.0% carbon) at the upper temperatures all of the carbon is in solution forming austenite as it cools a phase change to austenite and cementite occurs. As it cools down below the lower critical temperature a final phase change to pearlite and cementite occurs. Because.8% is the carbon content in a pearlite structure, additional islands of cementite form to hold the excess carbon. See figure 1.2g. The phases of plain carbon steel are: Cementite, (Fe3C) iron carbide with a maximum of 6.67% carbon. It is hard and very brittle, very low tensile strength but very high compressive strength. Figure 1.2g, Hyper-Eutectoid Steel Austenite is gamma iron, that exists between 908°C and 1400°C it is in face centered cubic lattice and can hold a maximum of 2.0% carbon in solution. Ferrite is relatively pure iron with carbon content up to a maximum of.025%. It is the softest phase shown on the equilibrium diagram and is a Figure 1.2h, very ductile material. Hypo-Eutectoid Steel Engineering, Materials and Components Revision Date: 9/17/19 - 16 - CANADIAN INSTITUTE FOR NDE Section 1 Pearlite is the eutectoid mixture which contains.8% carbon and is a lamellar mixture of ferrite and cementite. Figure 1.2i, Eutectoid Steel Phase diagrams that involve two elements such as carbon and iron are referred to as binary. A very interesting binary phase diagram is that of copper and nickel. Each is soluble in the other regardless of the percentages. There are only three phases: Liquid Liquid and Solid Solid Figure 1.2j, Copper-Nickel Phase Diagram Engineering, Materials and Components Revision Date: 9/17/19 - 17 - CANADIAN INSTITUTE FOR NDE Section 1 References: 1. Sidney H Avner; Introduction to Physical Metallurgy, McGraw-Hill Book Company 2. ASM, Handbook Volume 3, Alloy Phase Diagrams 3. ASM Handbook, Volume 9, Metallography and Microstructures 4. ASM Metals Handbook, 1960 Engineering, Materials and Components Revision Date: 9/17/19 - 18 - CANADIAN INSTITUTE FOR NDE Section 1 1.2.2 Cast Iron Cast iron is made by re-melting pig iron (the product from the blast furnace) with scrap iron and steel in a small vessel called a cupola or alternatively in a small electric arc furnace or coreless induction furnace. By definition cast iron contains between 2% and 4% carbon and 1% to 3% silicon and other elements to control specific properties. The ductility of cast iron is very low and it cannot be rolled, drawn or worked at room temperature. Since casting is the only suitable preliminary process that can be applied to these materials they are known as cast iron. There are several families of cast iron: White Cast Iron named because it exhibits a white crystalline fracture surface as a result of its metastable solidification. All of the carbon is in the form of cementite. See figure 1.2.2a which shows the microstructure of white cast iron. The material is hard and wear resistant but extremely brittle and difficult to machine. White cast irons are described in ASTM A532, Standard Specification for Abrasion-Resistant Cast Iron. These white cast irons have been alloyed to ensure high resistance to abrasion for applications in mining, Figure 1.2.2a, earth moving and heavy industry. There are three White Cast Iron (3) classes, consisting of four (4) types in the first two (2) classes and one (1) type in the third class. Other ASTM standards that describe applications of white cast iron include: A667, Standard Specification for Centrifugally Cast Dual Metal (Gray and White Cast Iron) Cylinders; A748, Standard Specification for Statically Cast Chilled White Iron-Gray Iron Dual Metal Rolls for Pressure Vessel Use; and A942, Standard Specification for Centrifugally Cast White Iron/Gray Iron Dual Metal Abrasion-Resistant Roll Shells. Gray Cast Iron is the most widely used of all cast irons and sometimes referred to as just “cast iron”. It contains between 2.5% and 4% carbon and 1% to 3% silicon and manganese from.1% to 1.2%. Sulphur and phosphorus are also present as small residual impurities. ASTM A48, Standard Specification for Gray Iron Castings classifies gray cast iron in terms of tensile strength from 140 MPa Figure 1.2.2b, to 410 MPa. Some typical applications would Gray Cast Iron include: clutch plates and brake drums. Lower Engineering, Materials and Components Revision Date: 9/17/19 - 19 - CANADIAN INSTITUTE FOR NDE Section 1 strength gray cast iron is used in machine basics particularly because of its ability to absorb vibration. The casting of gray iron is typically done between 1410° C to 1450° C, the fluidity of the gray iron is dependent upon the carbon content; so as the carbon content decreases the fluidity decreases at any given temperature. Misruns, cold shuts and rounded corners are often attributed to a lack of fluidity. The usual microstructure of gray iron is a matrix of pearlite with graphite flakes. The machinability of gray iron is superior to most other cast irons and steels. Figure 1.2.2c, Gray Cast Iron Housings Ductile Iron Ductile Iron previously known as nodular or spheroid-graphite cast iron is a cast iron in which the graphite is in the form of tiny spheres (nodules). Cast iron with nodular graphite is much stronger and has greater elongation than gray or malleable iron. Typical applications include gears, automotive crank shafts, chain links, chain sprockets, universal joints and dolly wheels. ASTM A897, Standard Specification for Austempered Ductile Iron Castings describes the properties of austempered ductile iron. Ductile iron can be alloyed with small amounts of nickel, molybdenum or copper to improve strength and hardenability. Large amounts of silicon, nickel, chromium or copper are added to improve corrosion resistance and for high temperature applications. The machinability of ductile iron is Figure 1.2.2d, similar to gray iron particularly at higher hardness Ductile Iron levels. Engineering, Materials and Components Revision Date: 9/17/19 - 20 - CANADIAN INSTITUTE FOR NDE Section 1 Compacted Graphite Cast Iron, some times referred to as “semi ductile cast iron”, was first inadvertently produced when making ductile iron as a result of under treatment with magnesium or cerium and was patented in 1965. The resultant graphite is thicker and shorter than other graphite flakes and 20% of the graphite is in a nodular form, yielding higher strengths and ductility than gray cast iron. It has good cast ability, good thermal conductivity and better vibration dampening than ductile iron. Figure 1.2.2e, Compacted Graphite Figure 1.2.2f, Compacted Graphite Cast Cast Iron Iron Engine Block Malleable Iron is produced from white cast iron in a two stage annealing process. It has irregular shaped graphite nodules as opposed to the flakes in grey cast iron or small spheroid shaped nodules in ductile iron. It has good ductility and toughness due to the relatively low carbon in the matrix. Malleable iron is preferred for thin section castings, parts that are to be cold formed; it has good machining ability, good impact resistance at low temperatures, good magnetic permeability, low magnetic retention and good fatigue strength. Ferritic malleable iron is specified in ASTM A47, Standard Specification for Ferritic Malleable Iron Castings; A197, Figure 1.2.2g, Standard Specification for Cupola Malleable Malleable Iron Iron and A338, Standard Specification for Malleable Iron Flanges, Pipe Fittings, and Valve Parts for Railroad, Marine, and Other Heavy Duty Service at Temperatures up to 650 Degrees F (345 Degrees C); pearlitic and martensitic variations are specified in ASTM A220, Standard Specification for Pearlitic Malleable Iron and for some automotive applications in ASTM A602, Standard Specification for Automotive Malleable Iron Castings. See figure1.2.2h for typical automotive applications. Engineering, Materials and Components Revision Date: 9/17/19 - 21 - CANADIAN INSTITUTE FOR NDE Section 1 Figure 1.2.2h, Automotive Applications of Malleable Iron Chilled Cast Iron is a white cast iron layer at the surface with a gray cast iron interior. The harder outer layer is achieved by rapid cooling of the outer surfaces and relatively slower cooling below the surface. Chromium is used to control the depth of the chill or hardened layer. A photomicrograph of the outer layer is shown in figure 1.2.2i. Chilled cast iron is used to produce railway wheels, crushing rolls and heavy duty machine parts that require the strength of white Figure 1.2.2i, cast iron and the wear or abrasion resistance of Chilled Cast Iron the hardened outer layer. Alloy Cast Irons are cast irons that have additional alloys intentionally added to enhance one or more of the properties. Small amounts of material (ferrosilicon, cerium or magnesium) are added to the cast iron to control graphite shape and distribution are not considered alloys but are termed inoculations. The affects of various alloys: Carbon in chilled cast irons decreases the depth of chill but increases the hardness. In white cast irons it tends to increase hardness and reduce breaking strength. It is generally used to increase hardness and wear resistance. Silicon is present in all cast irons, it controls the depth of chill in chilled cast irons. In amounts of 3.5% to 7%, silicon improves the high temperature properties. Engineering, Materials and Components Revision Date: 9/17/19 - 22 - CANADIAN INSTITUTE FOR NDE Section 1 Manganese and sulphur increases the depth of chill, manganese in amounts above 1.5% tends to decrease strength and toughness. Chromium in higher quantities improves abrasion resistance, toughness, and corrosion resistance and is used to improve high temperature properties. Nickel of more than 12% in cast iron improves heat and corrosion resistance; in smaller quantities it is used to produce a harder finer structure and improve abrasion resistance. Copper is used to improve high temperature properties and corrosion resistance. References: 1. ASM Handbooks, Volume 1, Properties and Selection, Irons, Steels and High Performance Alloys 2. Sydney H Avnor; Introduction to Physical Metallurgy, McGraw Hill Book Company 3. ASM Metals Handbook, 1960 4. ASTM A897, Standard Specification for Austempered Ductile Iron Castings Engineering, Materials and Components Revision Date: 9/17/19 - 23 - CANADIAN INSTITUTE FOR NDE Section 1 1.2.3 Steel All steels are alloys of iron and carbon in which the carbon percentage by weight is less than 2%. Plain carbon steel contains small percentages of manganese and silicon, plus small unavoidable amounts of sulphur and phosphorus. Steels vary widely in their properties and their applications and are used in both the cast and wrought conditions. Classification and Designations of Steels The term wrought implies the material has been worked (deformed as opposed to cast) into its shape. Carbon and low (less than 5%) alloy steels are classified in several ways. There are 8 general methods to classify steel: 1. Chemical composition 2. Manufacturing method e.g. BOF or Electric arc furnace 3. Finishing method e.g. hot rolled or cold rolled 4. Microstructure e.g. ferritic or martensitic 5. Required strength such as specified in ASTM 6. Heat treatment e.g. annealed or quench and tempered 7. Quality such as forging or structural quality 8. Product form e.g. bar, plate, strip, tubing or structural shape These broad categories are subdivided. For example, under chemical content, the carbon content is subdivided into low (up to.3% carbon), medium (.3% to.6% carbon) and high (.6% to 2.0% carbon). They may also be classified as rimmed, capped, semi-killed, or killed depending on the oxygen content (from high to low). Alloyed steels are classified by the principle alloy such as chromium, molybdenum, nickel, etc. Some important terms in understanding the classification of steel are: Designation is the specific identifier of grade, type, or class of steel and usually consists of a unique set of letters and numbers. Chemical composition is the most common method of designation (see the information related to the AISI-SAE, and the UNS systems). Quality does not imply that the material is better than steel from another mill but that it is particularly well suited for a specific application. See the information on quality descriptors. Specification is a written statement of the attributes of a particular steel. It usually contains a range of values that the steel must comply with and any restrictions on its production. Standard Specification is a published document that describes the attributes of the steel for a wide variety of applications. Engineering, Materials and Components Revision Date: 9/17/19 - 24 - CANADIAN INSTITUTE FOR NDE Section 1 Quality Descriptors have been developed to denote the steels that are well suited for specific applications. As an example, carbon steel plates have been grouped into the following fundamental quality descriptors: Regular quality Structural quality Cold-drawing quality Cold-pressing quality Forging quality Pressure vessel quality Alloy steels are also grouped by quality descriptors. As an example, alloy speciality steel tubular goods are grouped into the following quality descriptors: Pressure tubing Mechanical tubing Stainless and head resisting pipe, pressure tubing and mechanical tubing Aircraft tubing Pipe In North America Standard Specifications have been developed by these groups: AAR Association of American Railways ABS American Bureau of Ship Building API American Petroleum Institute AREA American Railway Engineering Association ASME American Society of Mechanical Engineers ASTM American Society for Testing Materials SAE Society of Automotive Engineers AMS Aerospace Materials Specification (of SAE) AISI American Iron and Steel Institute CSA Canadian Standards Association SAE-AISI System The SAE-AISI system is likely one of the most widely used systems for designating steels. It is applied to: semi-finished forgings, hot-rolled and cold finished bars, wire rod, seamless tubular goods, structural shapes, plates, sheet strip and welded tubing. The designation consists of four (4) digits, the first two (2) digits define the type and nominal alloy content and the last two (2) digits specify the number of points of carbon (carbon content in hundredths of a percent). Table 1.2.3a shows the most common designations. Engineering, Materials and Components Revision Date: 9/17/19 - 25 - CANADIAN INSTITUTE FOR NDE Section 1 Table 1.2.3a Alloy Designation Nominal Alloy Content Carbon Steel 10xx Plain carbon steel (Mn 1.00 max) 11xx Re-sulphurized steel 12xx Re-phosphorized steel 15xx Plain carbon (max Mn range 1.00 to 1.65) Manganese Steel 13xx Mn 1.75 Nickel Steel 23xx Ni 3.50 25xx Ni 5.00 Nickel-Chromium 31xx Ni 1.25, Cr.65-.80 Steel 32xx Ni.75, Cr 1.07 33xx Ni 3.50, Cr 1.50 – 1.57 34xx NI 3.00, Cr.77 Molybdenum Steel 40xx Mo.20 -.25 44xx Mo.40 -.52 Chromium - 41xx Cr.50 -.95, Mo.12-.30 Molybdenum Steel Nickel-Chromium- 43xx Ni 1.82, Cr.50-.80, Mo.25 Molybdenum Steel 47xx Ni 1.05, Cr.45, Mo.20-.35 Chromium steel 50xx Cr.27-.65 51xx Cr.80-1.05 50xxx Cr.50, C 1.00 min 51xxx Cr 1.02, C 1.00 min 52xxx Cr 1.45, C 1.00 min Chromium-vanadium 61xx Cr.60-.95, V.10-.15 steel Tungsten-chromium 72xx W 1.75, Cr.75 steel Nickel-chromium- 81xx Ni.30, Cr.40, Mo.12 molybdenum steel 86xx Ni.55, Cr.50, Mo.20 87xx Ni.55, Cr.50, Mo.25 88xx Ni.55, Cr.50, Mo.35 Silicon-manganese 92xx Si 1.40-2.00, Mn.65-.85, Cr 0-.65 steel Nickel-chromium- 93xx Ni 3.25, Cr 1.20, Mo.12 molybdenum steel 94xx Ni.45, Cr.40, Mo.12 97xx Ni.55, Cr.20, Mo.20 98xx Ni 1.00, Cr.80, Mo.25 Engineering, Materials and Components Revision Date: 9/17/19 - 26 - CANADIAN INSTITUTE FOR NDE Section 1 SAE AMS System The AMS system is published by the Society for Automotive Engineers (SAE) most of the materials designated in this system are intended for aerospace applications. Some of these specifications have mechanical property requirements significantly more severe than for other applications. Some of the acronyms used in conjunction with these specifications include: P Premium quality CVM Consumable vacuum melted CVAR Consumable vacuum arc remelted ESR Electroslag remelted DVM Double vacuum melted VAR Vacuum arc remelted CM Consumable electrode remelted VM Vacuum melted An example of an AMS specification: 6454D, P, CM; this material is similar to SAE-AISI 4340 and is a premium aircraft quality low-alloy steel, it comes in plate, strip sheet, it is premium quality and it is consumable electrode remelted. The letter D represents the 4th revision to this specification (dated 2007.02.01). To determine the properties of the material to this specification, you would need to consult the document AMS 6454D UNS System The UNS system was developed by ASTM and SAE and is a designation consisting of a letter and five (5) numerals that indicates the chemical composition and not the entire specification (Table 1.2.3b). It does permit easier comparisons to other specifications from around the world and is described in ASTM E 527 Standard Practice for Numbering Metals and Alloys in the Unified Numbering System (UNS). Engineering, Materials and Components Revision Date: 9/17/19 - 27 - CANADIAN INSTITUTE FOR NDE Section 1 Table 1.2.3b Designation Metals A00001-A99999 aluminum and aluminum alloys C00001-C99999 copper and copper alloys E00001-E99999 rare earths and like materials and alloys L00001-L99999 low melting metals and alloys M00001-M99999 miscellaneous nonferrous alloys N00001-N99999 nickel and nickel alloys P00001-P99999 precious metals and alloys R00001-R99999 reactive and refractory metals and alloys Z00001-Z99999 zinc and zinc alloys D00001-D99999 specified mechanical properties steels F00001-F99999 cast iron and cast steels G00001-G99999 AISI and SAE carbon and alloy steels H00001-H99999 AISI H-steels J00001-J99999 cast steels except tool steels K00001-K99999 miscellaneous steels and ferrous alloys S00001-S99999 heat and corrosion resistant (stainless) steels T00001-T99999 tool steels W00001-W99999 welding filler metals ASTM (ASME) System The most widely used standard in North America, published and maintained by the American Society for Testing and Materials. These are consensus standards developed by industry and in many cases include complete material specifications. ASTM standards are published annually in 15 sections: Table 1.2.3c Section Title 01 Iron and Steel Products 02 Nonferrous Metal Products 03 Metals Test Methods and Analytical Procedures 04 Construction 05 Petroleum Products, Lubricants and Fossil Fuels 06 Paints, Related Coatings and Aromatics 07 Textiles 08 Plastic 09 Rubber 10 Electrical Insulation and Electronics 11 Water and Environmental Technology 12 Nuclear, Solar, and Geothermal Energy 13 Medical Devises and Services 14 General Methods and Instrumentation 15 General Products, Chemical Specialties and End Use Products 00 Index Engineering, Materials and Components Revision Date: 9/17/19 - 28 - CANADIAN INSTITUTE FOR NDE Section 1 An individual standard will have a designation such as ASTM A709/A709M-08. The title of this standard is “Standard Specification for Structural Steel for Bridges”. The designation is a serialized number applied to this standard; “M” implies it has metric units as well as imperial units, “08” is the year of issue or last revision. If a date appears in brackets it is the date of last reapproval without revision. This standard references nine (9) other ASTM standards related to shape, mechanical properties, mechanical testing, chemical properties, and manufacturing methods which make it a nearly complete specification, by referencing other specifications that are also used for other purposes. ASME (American Society for Mechanical Engineers), adopted standards developed by ASTM and in doing so they inset the letter “S” in front of the ASTM designation. For example ASTM A36 Standard Specification for Carbon Structural Steel when adopted by ASME becomes SA36 within the ASME system. CSA System CSA Canadian Standards Association has only one standard directly related to metals and that is CSA G40.20/G40.21, The General Requirements for Rolled or Welded Structural Quality Steel/Structural Quality Steel. G40.20 deals with general specifications related to structural steel such as: Definitions How chemical analysis is conducted Permissible variations and tolerances Testing Heat treatment Marking Certification G40.21 deals with the specific properties of individual steels. There are seven (7) grades of structural steels in this standard W Weldable steel WT Weldable steel with notch toughness requirements R Atmospheric corrosion resistance steel A Atmospheric corrosion resistance weldable steel AT Atmospheric corrosion resistance weldable steel with notch toughness requirements Q Quench and tempered low alloy steel QT Quench and tempered low alloy steel with notch toughness requirements Engineering, Materials and Components Revision Date: 9/17/19 - 29 - CANADIAN INSTITUTE FOR NDE Section 1 Each of these steels is available with different nominal yield strengths. Table 1.2.3d is the Grades and Strengths table taken from CSA G40.21 Table 1.2.3d Engineering, Materials and Components Revision Date: 9/17/19 - 30 - CANADIAN INSTITUTE FOR NDE Section 1 AISI System for Stainless Steels One special family of steels are stainless steels which are most frequently identified by a three (3) digit AISI numbering system (Table 1.2.3e). Most stainless steels contain between 10.5% and 30% chromium and not less than 50% iron. The stainless property is due to a chromium rich oxide layer which forms on the surface and if damaged self heals in the presence of oxygen. Other alloys included in stainless steels are: nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur and selenium. There are five families of stainless steels: Martensitic, alloys of chromium and carbon with possible additions of small amounts of other alloying elements. They are ferromagnetic, hardenable by heat treatment and corrosion resistant only in relatively mild environments. In the hardened condition their structure is a distorted body-centered cubic (martensitic crystal structure). Ferritic, alloys of chromium (10.5% to 30%) with other minor alloys. They are also ferromagnetic, body centered cubic, have good ductility and formability but relatively poor strength at high temperatures and reduced toughness at low temperatures. Austenitic, have a face centered cubic structure because of the alloys nickel, manganese and nitrogen. They are nonmagnetic in the annealed condition and can be hardened only by cold working. Chromium content will be between 16% to 26% and nickel up to about 35%. Duplex stainless have a mixed structure of body- centered and face-centered. The alloying is principally nickel and chromium with small amounts of nitrogen, molybdenum, copper, silicon and tungsten. Similar corrosion resistance to austenitic stainless steels but with improved tensile and yield strengths as well as resistance to stress corrosion cracking. Precipitation hardening stainless steels are alloys of chromium and nickel with the addition of precipitation hardening elements such as copper, aluminum, or titanium. The original list of stainless steels was published by AISI (American Iron and Steel Institute), but ASTM and SAE include these standards in their specifications. Engineering, Materials and Components Revision Date: 9/17/19 - 31 - CANADIAN INSTITUTE FOR NDE Section 1 Table 1.2.3 e, Partial AISI Listing of Stainless Steels Type UNS C Mn Si Cr Ni P S Other Austenitic 201 S20100.15 5.5- 1.00 16.0- 3.5-.06.03.25 N 7.5 18.0 5.5 304 S30400.08 2.00 1.00 18.0- 8.0-.045.03 20.0 10.5 304L S30403.03 2.00 1.00 18.0- 8.0-.045.03 20.0 12.0 316 S31600.08 2.00 1.00 16.0- 10.0-.045.03 2.0- 18.0 14.0 3.0 Mo Ferritic 409 S40900.08 1.00 1.00 10.5-.50.045.045 Ti 11.75 444 S44400.025 1.00 1.00 17.5- 1.00.04.03 Mo, N, 19.5 Ti, Nb Duplex 329 S32900.20 1.00.75 23.0- 2.5-.04.03 1-2 28.0 5.0 Mo Martensitic 403 S40300.15 1.00.50 11.5-.04.03 13.0 420 S42000.15 1.00 1.00 12.0-.04.03 14.0 Precipitation Hardening 15-5 S15500.07 1.00 1.00 14.0- 3.5-.04.03 Cu, PH 15.5 5.5 Nb 17-4 S17400.07 1.00 1.00 15.5- 3.0-.04.03 Cu, PH 17.5 5.0 Nb 17-7 S17700.09 1.00 1.00 16.0- 6.5-.04.04 Al PH 18.0 7.75 Other standard systems that we should be aware of include: EN, European Committee for Standardization. They have 30 national members as of March 2009. As an example BSI (British Standards Institute) is the national standards body for the United Kingdom and represents their national interests in the development of European Standards. Engineering, Materials and Components Revision Date: 9/17/19 - 32 - CANADIAN INSTITUTE FOR NDE Section 1 As an example of one of their standards; BS EN 10111:2008 is a European standard adopted by the British Standards Institute, last approved or revised in 2008. “Continuously hot rolled low carbon steel sheet and strip for cold forming. Technical delivery conditions”. Primary Steel Making Steel is a commercial iron that contains no more than 2% carbon as an alloy and is malleable. It is distinguished from cast iron by its lower carbon content and malleability. “Primary steel production” is the production of steel from iron ore as the principle source of the iron constituent, as opposed to it being principally from steel scrap. The process of primary steel production has advanced significantly in the past several decades and continues to evolve. A brief description of the current technology: Metallurgical coal is a combustible rock containing more than 50%, by weight, of carbonaceous material formed from the compaction of altered plant remains. Coke is produced from coal by heating the coal to high temperatures (1100° C) in an oxygen deficient atmosphere. See the figure 1.2.3a which shows the coke oven battery. During this process the carbon is concentrated. The iron ore is either Fe 2 O 3 or Fe 3 O 4 and has an iron content of 50% to 70%, otherwise further processed and crushed before being put into the furnace. Sinter is produced from fine Figure 1.2.3a, Primary Steel Production raw ore, small coke, limestone, and Engineering, Materials and Components Revision Date: 9/17/19 - 33 - CANADIAN INSTITUTE FOR NDE Section 1 steel plant waste and charged to the furnace. Limestone melts in the blast furnace to become the slag which removes the sulphur and other impurities. The purpose of the blast furnace is to chemically reduce and convert iron oxides into liquid iron. The inputs are charged into the top of the blast furnace. The preheated blast air combines with the carbon to produce carbon monoxide and heat. The carbon monoxide reacts with the iron oxide to produce molten iron and carbon dioxide. The carbon dioxide, un-reacted carbon monoxide and nitrogen from the blast air, travel upward heating the feed material as it passes downward. The limestone is decomposed to produce calcium oxide and carbon dioxide which reduces the iron oxides. The calcium oxide reacts with the silica in the iron oxide to produce slag. The product from the blast furnace, molten pig iron, has relatively high carbon content (4% to 5%). Some of the pig iron maybe used to produce cast iron, but the majority is sent onto the basic oxygen furnace (BOF) to produce various grades of steel. In the basic oxygen furnace impurities such as sulphur and phosphorus are removed and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the grades of steel required. The basic oxygen process was developed in Austria and is sometimes referred to as the LD Converter (Linz- Donawitz). The term “basic” is used to describe the pH of the refractory lining of the furnace, made from calcium oxide and magnesium oxide. In addition to the pig iron; alloy elements, high purity oxygen, scrap steel, lime and fluxes are added to the BOF. This oxidizes the carbon and other unwanted elements. Carbon monoxide is produced and the rest of the unwanted elements are converted to acidic oxides which Figure 1.2.3b combine with the lime and fluxes to Primary Steel Production (continued) produce slag. BOFs range in sizes up to 350 tons and convert iron to steel in less than 40 minutes. In the past other Engineering, Materials and Components Revision Date: 9/17/19 - 34 - CANADIAN INSTITUTE FOR NDE Section 1 furnaces were used to convert pig iron to steel, they included: puddling furnaces, Bessemer converters and open hearth furnaces. From the basic oxygen furnace the molten steel goes by ladle to any secondary processing then onto a continuous casting process where the steel is solidified into semi finished blooms, slabs or billets. Recent developments continue to link the processes, in some cases the time from liquid metal to final shape is less than two hours. This results in highly efficient steel production. Hot rolling of steel is conducted above its upper critical temperature (recrystallization temperature). The metal is worked before the final crystalline structure is formed to shape the steel rather than change it’s mechanical properties. It is mainly used to produce sheet metal. After hot rolling and before any cold forming operations, steel is descaled usually by a process called pickling (either continuous or batch process). The process may involve hydrochloric acid and the objectives are; to improve die or roll life used in subsequent forming operations, promotes smoother surfaces, permits better coating adherence, and eliminates surface irregularities. Figure 1.2.3c, Hot Rolling The material may go on to other forming processes or may be sold as hot rolled product. Cold rolling is a metal working process that passes the steel through rolls at a temperature below the recrystallization temperature. It increases the yield strength and hardness by introducing microscopic defects into the crystalline structure to prevent further slip and can reduce grain size and increase hardness. Engineering, Materials and Components Revision Date: 9/17/19 - 35 - CANADIAN INSTITUTE FOR NDE Section 1 As the steel absorbs significant amounts of energy from the rolling process its hardness and tensile strength increase and ductility decreases. Metals which are subjected to cold rolling are more sensitive to cracks and are more prone to brittle failure. A material hardened by cold rolling can be tempered or annealed to relieve stress and partially return some of the original properties. The cold rolling process is also used to precisely control thickness or impart trade symbols into the sheet. Galvanizing is one of several processes to coat the steel with other metals usually to prevent corrosion. Hot dip galvanizing deposits a thick layer of zinc onto the steel, which acts as a sacrificial anode if the galvanizing is damaged. Zinc reacts with oxygen to form zinc oxide, which reacts with water in the atmosphere to form zinc hydroxide which reacts with carbon dioxide in the atmosphere to Figure 1.2.3d, Final Finishing produce zinc carbonate which provides further protection to the zinc and underlying steel in the damaged area. Secondary Steel Production Secondary refining is defined as any post steel making process performed in a separate station prior to casting, figure 1.2.3b. The purpose of secondary refining is to ensure temperature homogenization, chemical adjustment (carbon, sulphur, phosphorus, oxygen and precise alloying), inclusion control and degassing. The equipment and processes are varied and maybe performed at atmospheric pressure or under vacuum, with or without heating. Nine different vacuum processes are used throughout the world for carbon steel alone. Engineering, Materials and Components Revision Date: 9/17/19 - 36 - CANADIAN INSTITUTE FOR NDE Section 1 Mini-Mill Steel Production Mini –mill production is discussed here but its principle purpose is the reclaiming of scrap steel. A mini-mill is traditionally a secondary steel producer which usually obtains most of its iron from scrap steel. Iron directly reduced in a blast furnace can be used to supplement scrap steel or control chemistry of the steel. A mini-mill usually consists of an electric arc furnace, ladle or vacuum furnace, a continuous caster, a reheat furnace and rolling mill. Electric Arc Furnaces Electric arc furnaces used in iron and steel production range from one (1) ton to four hundred (400) ton capacities. It consists of a refractory lined vessel, often water cooled in larger sizes, with a retractable roof and graphite electrodes which penetrate the roof. A typical alternating current furnace uses three electrodes. The arc forms between the electrodes and material being melted in the furnace. The material is melted by the current flowing through the material and the radiant heat of the arc. The furnace control strives to maintain constant current flow by moving the electrodes up and down as the material moves into the melting bath. Additional energy maybe provided by injecting oxygen and carbon into the furnace. Ladle Furnace Ladle furnaces employ graphite electrodes to reheat the liquid steel, provide uniformity of temperature and chemistry through inert gas stirring, it removes inclusions and metal oxides through a slag layer and also desulphurizes the steel. Vacuum Tank Degassing A VTD is used to reduce dissolved gasses (hydrogen, nitrogen, and oxygen) in the liquid steel. The bath is stirred by percolating argon gas through the bath from the bottom of the ladle while in the vacuum tank. Vacuum Arc Remelting For highly critical applications such as critical aerospace components VIM- VAR (Vacuum induction melted, vacuum arc remelted) steels are specified. After initial melting in an electric arc furnace and alloying in an argon- oxygen decarburization vessel the steel is cast into ingots. The solidified ingots are melted in a vacuum induction melting furnace to rid the steel of inclusions and unwanted gasses and optimize the chemistry. The steel is cast into electrode molds and remains under vacuum until solidified. The surfaces of the electrodes are ground to remove impurities. The electrodes Engineering, Materials and Components Revision Date: 9/17/19 - 37 - CANADIAN INSTITUTE FOR NDE Section 1 are then placed into vacuum induction melting furnace where they melt drop by drop in the vacuum to further remove inclusions and gases. The steel produced is more resistant to fracture and fatigue than conventional steels and is suitable for such demanding applications as military helicopter rotor shafts. References: 1. ASM Handbook, Volume 1, Properties and Selection: Irons, Steels, and High Performance Alloys 2. ASTN International, http://www.astm.org/Standard/index.shtml 3. CSA G40.20/G40.21, The General Requirements for Rolled or Welded Structural Quality Steel/Structural Quality Steel 4. BSI British Standards Institute, http://www.bsigroup.com/en/ 5. LTV Steel Corporation, All About Steel, http://www.ltvsteel.com/htmfiles/about.htm 6. American Iron and Steel Institute, Learning Center, http://www.steel.org 7. Continuous Casting of Steel, Basic Principles http://www.energymanagertraining.com/iron_steel/cont_cast_steel.htm Engineering, Materials and Components Revision Date: 9/17/19 - 38 - CANADIAN INSTITUTE FOR NDE Section 1 1.2.4 Aluminum (chemical symbol “Al”) The Canadian Oxford Dictionary prefers the spelling aluminum as it is spelled in the USA; most other English speaking countries use the British spelling aluminium. It is the most abundant metal in the earth’s crust. The chief source of aluminum is bauxite ore. Aluminum (Table 1.2.4a) is soft, light weight, malleable and its appearance is silvery to light gray. Pure aluminum has a yield strength of 7 to 11 MPa and alloyed aluminum has a yield strength of 200 to 600 MPa. It has about one third the density of steel, it is easily cast, machined, or extruded. It has good thermal and electrical conductivity. Aluminum has good atmospheric corrosion resistance due to passivation by a thin aluminum oxide layer on the surface preventing further corrosion. Table 1.2.4a – Properties of Aluminum Property Value Atomic Number 13 Chemical Symbol Al Density [gm/cm3] 2.70 Melting Point [°C] 660 Crystal structure Face centered cubic Electrical resistivity (20°) [ nΩ/m] 28.2 Longitudinal Wave Sound Velocity [km/sec] 6.32 Transverse Wave Sound Velocity [km/sec] 3.13 Rayleigh Wave Sound Velocity [km/sec] 2.90 Acoustic Impedance [g/cm2-sec x 105] 17.10 Magnetic Ordering Paramagnetic Aluminum Production The stages in producing aluminum from bauxite are (figure 1.2.4a): Crushing and Grinding o The bauxite is screened crushed and ground. Grinding is conducted in rod mills where it is injected with sodium hydroxide to produce slurry. The residue (red mud), consisting of undissolved bauxite, iron, silicon and titanium, is allowed to settle out in tanks and is removed. Digesting o The digester is a pressure cooker (145°C @ 345 kPa) in which a chemical reaction occurs to dissolve the alumina and remove impurities. Engineering, Materials and Components Revision Date: 9/17/19 - 39 - CANADIAN INSTITUTE FOR NDE Section 1 Settling o Impurities settle to the bottom and the alumina liquor is recovered from the top and filtered. Precipitation o The filtered sodium aluminate is pumped into precipitators where fine particles of alumina are added. These particles act as seeds in the formation of alumina crystals. The crystals settle to the bottom and are removed and filtered. Calcination o The calcining process is conducted in heated kilns to drive off the water leaving pure alumina dried crystals. Smelting o Smelting takes place in graphite lined reduction pots where the alumina powder is converted to metallic aluminium (99.7%). Figure 1.2.4a, Aluminum Production 1. Bauxite 2. Crusher 3. Digester 4. Decantor 5. Filter Press 6. Precipitator 7. Calciner 8. Smelting Process starts 15. Aluminum Processing starts The Aluminum Association has developed an alloy identification system that is used most widely in North America. The system addresses wrought and cast compositions for pure aluminum and its alloys. Wrought alloys are designated by a four digit system (Table 1.2.4b), the first digit signifies the alloy group, the second digit refers to a modification of the original alloy and the remainder are assigned in sequence. Engineering, Materials and Components Revision Date: 9/17/19 - 40 - CANADIAN INSTITUTE FOR NDE Section 1 Table 1.2.4b Designation Principle Alloy(s) 1xxx Controlled unalloyed composition 2xxx Copper, and may also include other elements such as magnesium 3xxx Manganese 4xxx Silicon 5xxx Magnesium 6xxx Magnesium and silicon 7xxx Zinc, may also include other elements such as copper, magnesium, chromium, and zirconium 8xxx Tin and lithium 9xxx For future use Cast compositions are designated by a three digit number followed by a decimal and one digit (Table 1.2.4c). Table 1.2.4c Designation Principle Alloy(s) 1xx.x Controlled unalloyed composition 2xx.x Copper, and may also include other elements 3xx.x Silicon but may include other elements such as copper and manganese 4xx.x Silicon 5xx.x Magnesium 6xx.x Unused 7xx.x Zinc, may also include other elements such as copper, magnesium 8xx.x Unused The final digit:.0 pertains to casting alloy limits.1 and.2 pertain to ingot compositions A temper designation system is used for both wrought and cast aluminum and its alloys. The basic temper designations are: F, As fabricated the product is shaped by hot or cold working or as cast with no special thermal or stain hardening. Engineering, Materials and Components Revision Date: 9/17/19 - 41 - CANADIAN INSTITUTE FOR NDE Section 1 O, Annealed applies to wrought products that are annealed to obtain the lowest strength temper and cast products that are to improve ductility and dimensional stability. H, Strain-hardened applies to wrought products only that have been strengthened by working with no additional heat treatment. The H is always followed by a digit: 1 to 9 to indicate the degree of strain hardening. W, Solution heat-treated is an unstable temper that applies to alloys whose strength changes over time. T, Solution heat treated applies to alloys whose strength is stable within a few weeks. The T is followed by a digit(s) 1 to 10 which defines the sequence of heat treatment. Aluminum can be cast, extruded, forged, shaped by impact forming, formed by powder metallurgy processes, or used in metal-matrix composites. The machining properties of aluminum are excellent. Forging of aluminum is considered generally more difficult than steels although it varies by alloy, condition of the aluminum and the forging method. Aluminum alloys can be joined by: Fusion welding Resistance welding Brazing Soldering Adhesive bonding Mechanical methods (bolting, riveting, etc.) Aluminum can present challenges to welding operations because of: Surface oxide, if not removed, it can become entrapped in the weld and contribute to lack of ductility, lack of fusion and possible weld cracking. Thermal conductivity is about four times greater than carbon steel and therefore the rate of heat input must compensate for the thermal conductivity. Coefficient of expansion is also higher than for steel, approximately twice, and care must be taken in fit-up of the joints to be welded. Melting characteristics, the melting temperature of aluminum is lower than steel and must be adjusted for. Electrical conductivity has an effect on resistance welding of aluminum, because the resistance is lower more current is required than a similar weld in steel. Engineering, Materials and Components Revision Date: 9/17/19 - 42 - CANADIAN INSTITUTE FOR NDE Section 1 Cast aluminum alloys have several favourable characteristics as compared to other metals: Good fluidity and easily fill thin sections Low melting temperature Rapid heat transfer to the mold Hydrogen is the only soluble gas and it can be controlled Most alloys are relatively free from hot short cracks and tears It has good chemical stability Aluminum can be cast by many different methods. References: 1. “How aluminum is produced”, http://www.rocksandminerals.com/aluminum/process.htm, 2. ASM Desk Edition Metals Handbook 3. ASM Handbook, Volume 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials Engineering, Materials and Components Revision Date: 9/17/19 - 43 - CANADIAN INSTITUTE FOR NDE Section 1 1.2.5 Nickel Nickel (Table 1.2.5a) is a nonferrous, silver-white with a slight gold tinge metal. It is ferromagnetic at room temperature. Major sources of the metal are Sudbury, Ontario, Ragiln Quebec, and Voisey’s Bay Newfoundland and Labrador in Canada, and New Caledonia, Russia, and Australia. Table 1.2.5a – Properties of Nickel Property Value Atomic Number 28 Chemical Symbol Ni Density [gm/cm3] 8.908 Melting Point [°C] 1455 Crystal structure Face centered cubic Electrical resistivity (20°) [ nΩ/m] 69.3 Longitudinal Wave Sound Velocity [km/sec] 5.6 Transverse Wave Sound Velocity [km/sec] 3.0 Rayleigh Wave Sound Velocity [km/sec] 2.6 Acoustic Impedance [g/cm2-sec x 105] 47.2 Magnetic Ordering Ferro magnetic Over 60% of nickel is used to produce stainless steels, other applications include copper-nickel alloys, super-alloys, plating, alloying of cast iron (Figure 1.2.5a). Figure 1.2.5a, Usage of Nickel Nickel from sulphide ore is processed by first crushing and milling the ore. The first separation process is by flotation were a flocculent is added to the slurry causing the nickel and other metals to float to the surface and be skimmed off. This concentrate is dried and fed to a flash furnace and combined with oxygen to Engineering, Materials and Components Revision Date: 9/17/19 - 44 - CANADIAN INSTITUTE FOR NDE Section 1 ignite the concentrate and form a molten bath to remove iron and sulphur. Slag (iron and silica) is skimmed off and the matte is transferred in ladles to converters where air is blown through the liquid bath, to remove the remainder of iron as slag, and more of the sulphur as sulphur dioxide. The matte is then cast and allowed to solidify in molds. It is then crushed and ground. Nickel is separated from copper and other metals by magnetic separation. Further purification is accomplished by employing carbon monoxide combined with the nickel to form nickel carbonyl which is then decomposed on to seed pellets which form spherical nickel pellets of 99.99% pure nickel. The other process of nickel refining is by electro-winning to produce anodes or nickel rounds (on masked anodes) within a tank-house. Nickel is sold in several families: 1. Nickel used for plating 2. Nickel used for melting 3. As a part of other alloying packages 4. Specialty products (including powders and foams). Nickel is a versatile alloy with many metals. Nickel is often employed to take advantage of good performance in areas of high temperature, cryogenics, corrosion resistance, corrosion fatigue and low expansion. Super Alloys are used in high temperature applications such as gas turbines. They are heat resisting alloys based on nickel, nickel iron or cobalt that exhibit mechanical strength and resistance to degrading of the surface at high temperatures. Examples of super alloys are Inconel, Incoloy, Hasteloy, Waspaloy, and Rene Alloys. The alloy elements include: nickel, cobalt, chromium, iron, molybdenum and others. References: 1. ASM Handbook, Volume 1, Properties and Selection: Irons, Steels, and High Performance Alloys 2. Nickel Institute, http://www.nickelinstitute.org/ 3. Inco Copper Cliff Smelter Complex Video, Sudbury, Ontario Engineering, Materials and Components Revision Date: 9/17/19 - 45 - CANADIAN INSTITUTE FOR NDE Section 1 1.2.6 Copper Copper is the metal (Table 1.2.6a) which has been known the longest to man. For more than 10,000 years man has made use of this metal. A pendant dating 8700 BC was discovered in Iraq. One of the Dead Sea Scrolls, found in Israel, is made of copper. Table 1.2.6a – Properties of Copper Property Value Atomic Number 29 Chemical Symbol Cu Density [gm/cm3] 8.96 Melting Point [°C] 1084.6 Crystal structure Face Centered Cubic Electrical resistivity (20°) [ nΩ/m] 16.78 Longitudinal Wave Sound Velocity [km/sec] 4.75 Transverse Wave Sound Velocity [km/sec] 2.30 Rayleigh Wave Sound Velocity [km/sec] 1.93 Acoustic Impedance [g/cm2-sec x 105] 42.5 Magnetic Ordering Diamagnetic For the initial stages of copper production refer to the section on nickel. At the point where the copper and nickel streams separate, copper concentrate is dried and further finished to remove the remaining sulphur dioxide and impurities. At this stage the copper is 98% pure and referred to as blister copper. The copper is cast into anode shapes, figure 1.2.6a. Final refining is by electro-winning, the shapes are loaded into a tank containing an acidic solution of copper sulphate, and each anode is separated by a Figure 1.2.6a, Copper anode cathode starter sheet of pure copper. A direct current impressed upon the cathode (negative) and anode (positive). As the anode dissolves, the pure copper is deposited on the cathode and impurities and other metals fall to the bottom of the tank. Today many of the advantages of copper are taken in engineering use. In addition to its heat and electrical conducting properties, copper has antimicrobial properties and is used in the treatment of disease. It is also used as an alloy in water intake screens to prevent Zebra mussel attachment and impede growth. Engineering, Materials and Components Revision Date: 9/17/19 - 46 - CANADIAN INSTITUTE FOR NDE Section 1 Copper is both ductile and malleable and can be easily drawn into wire. It has excellent electrical properties. It has the second highest electrical conductivity after silver. Copper does not react with water but oxygen in the air will react slowly forming a copper oxide layer. Typical uses of copper include: Electronics: o Copper Wire o Electromagnets o Printed Circuit boards o Lead free solder Architecture: o Roofing o Statue of Liberty (81.3 tonnes) o Used as an alloy in ship building Household: o Plumbing o Cookware Coinage: o European Union o USA o Canada o Australia o United Kingdom Alloys of Copper There are more than 400 different alloys of copper. Alloys are specified by the Copper Development Association, their designations are identical to the UNS system, they begin with the letter C followed by 5 digits. ASTM also has over 200 specifications related to copper, some typical ASTM standards include: ASTM B1, Standard Specification for Hard-Drawn Copper Wire ASTM B30, Standard Specification for Copper Alloys in Ingot Form ASTM B49, Standard Specification for Copper Rod Drawing Stock for Electrical Purposes ASTM B75, Standard Specification for Seamless Copper Tube Engineering, Materials and Components Revision Date: 9/17/19 - 47 - CANADIAN INSTITUTE FOR NDE Section 1 In addition to pure copper, wrought alloys can be classified as follows: High-copper alloys o Contain more than 96% Cu Brasses (Zinc is the principle alloy) o Leaded brasses (Cu, Zn, Pb) o Tin Brasses (Cu, Zn, Sn, Pb) Bronzes (Zinc is not the principle alloy) o Phosphorous Bronze (Cu, Sn, P) o Aluminum Bronzes (Cu, Al, Ni, Fe, Si, Sn) o Silicon Bronzes (Cu, Si, Sn) Copper Nickels o (Cu, Ni, Fe) Nickel Silvers o (Cu, Ni, Zn) References: 1. Wikipedia 2. Canadian Copper, no. 155, pp8, 2008 3. World Wide Guide to Equivalent Nonferrous Metals and Alloys, ASM International, Second Edition. Engineering, Materials and Components Revision Date: 9/17/19 - 48 - CANADIAN INSTITUTE FOR NDE Section 1 1.3 POWDER METALLURGY Although powder metallurgy, the process of forming of parts from powder without remelting, was practiced in Egypt around 3000 BC and by the Incas in South America around 1200 AD not much continuous use was made in Europe until the 18th century. More recently it has been used for self-lubricating bearings since the 1920’s, super alloys since 1970’s, and inter-metallics and metal-matrix composites since the 1990’s A much wider variation in alloys can be produced from powder metallurgy than from conventional alloying methods. It is possible to form both metallic and ceramic powders. The process can be made continuous such as to produce rolled strip. Machining can be reduced or eliminated, scarp losses are substantially reduced and good surface finishes can be achieved. Metals can be further heat treated to improve properties and controlled porosity can be achieved for self lubricating bearings. Recent developments include adding ceramic fibres and inter-metallic compounds The process can be subdivided as follows (Figure 1.3a): Conventional Press and Sinter Powders are prepared by mixing them, often a solid lubricant is added to facilitate flow and reduce friction entering the dies. The pressing operation maybe warm or cold. For cold pressing the particles are irregular shapes which provides “green strength” until the sintering process occurs. Sintering is conducted in a furnace with a controlled atmosphere at a temperature below the melting point which causes the formation of metallurgical bonds between the powder particles. Higher temperatures and longer sintering times promote more dense materials and greater contraction. Figure 1.3a, Powder Metallurgy Process Engineering, Materials and Components Revision Date: 9/17/19 - 49 - CANADIAN INSTITUTE FOR NDE Section 1 Powder Forging This process forms the component as in the conventional process. The component at this stage is referred to as a “preform” as its shape is different than the final shape. After the sintering operation the components are then hot formed in closed dies to deform the material and eliminate all the porosity. Metal Injection Molding This process uses spherical shaped fine powder which is mixed with binders and injected into a mold. After removal from the mold the binders are removed and the part sintered. Part size is limited to parts not greater than 250 g and the process is very similar to high pressure die casting or plastic injection molding. Hot Isostatic Pressing This process is more expensive than the others, is used for tool steels and super alloys and allows much larger sizes of components than the other powder metallurgy methods. The powders are vibrated in a container which is then evacuated and sealed then placed in a furnace and pressurized with gas (argon or helium). The component takes up the shape of the container. The need for sintering is eliminated. Powder metallurgy often eliminates the need for machining operations and ferrous powder metallurgy products are used extensively in automotive manufacture. Typical parts include: connecting rods, oil pump gears and rotors, valve guides, water pump impeller, drive sprockets, ball joint bearings, brake pistons and exhaust flanges. Other materials used in powder metallurgy besides iron and steel include: Copper and copper based alloys Aluminum Molybdenum Tungsten Tungsten carbide Nickel Tin Defects which occur in powder metallurgy parts during manufacture include: Ejection cracks o During the pressing operation a residual stress is imparted into the green part. During the ejection process some of the stress maybe relieved and manifest itself as a crack. This can be reduced through improved die design and powder control. Density variation o Compaction density variations within the part, particularly low density areas around changes of section can lead to cracking. Engineering, Materials and Components Revision Date: 9/17/19 - 50 - CANADIAN INSTITUTE FOR NDE Section 1 Micro-laminations o Very small unsintered layers which develop as a result of micro- cracks which develop during ejection from the pressing operation remain unhealed during the sintering process. Improper sintering o Poor sintering can result from insufficient time or temperature as well as improper furnace atmosphere, improper removal of the lubricant Nondestructive testing can be applied to powder metallurgy parts at the green stage (prior to sintering) and after sintering. Refer to table 1.3a for methods applied and there purpose. Table 1.3a NDE Method Purpose Gamma-ray density Density variations Electrical resistivity Density variations, Degree of Sinter Eddy Current Density, hardness, chemistry Magnetic particle Surface and near surface cracks Ultrasonics Density variation and cracks References: 1. ASM Metals Handbook, Volume 7, Powder Metal Technologies and Applications 2. Wikipedia 3. Metals Powder Industries Federation (MPIF), http://www.pickpm.com/intropm/process.asp?locarr=1|1 Engineering, Materials and Components Revision Date: 9/17/19 - 51 - CANADIAN INSTITUTE FOR NDE Section 1 1.4 PLASTICS The term plastic is from the Greek word “plastikos” meaning molding. The term is used to describe a wide variety of synthetic and organic amorphous solid materials. The first man made plastic dates back to 1862 when Alexander Parkes a British metallurgist created Parkesine. There are two basic types of plastic: Thermoplastic Thermoplastic will change shape, and eventually melt if heated sufficiently and retain its new shape. Examples of this type of plastic include plastic grocery bags and some children’s toys. Thermosetting plastic When heated will char and burn but not undergo shape change. During manufacture upon formation into its shape it undergoes a chemical reaction and retains that shape. Examples of this type of plastic include circuit boards and bases of kitchen kettles. Types of thermoplastics: Polyethylene Used to produce plastic grocery bags and available in several categories based on density and branching of polymers. Polyvinyl chloride Abbreviated PVC, used in electrical conduit, window and door frames. Polypropylene Used to produce rope, automotive components, carpets and thermal underwear. Polystyrene Dow chemical trade name: Styrofoam, used as insulation, available in several other forms. Polyethylene Terephthalate Often abbreviated as PET, used in the production of plastic bottles and other liquid and food containers. Acrylonitrile Butadiene Styrene Often abbreviated as ABS, used in plastic pipe Polymethyl Methacrylate Known by many trade names such as Plexiglas, Perspex and Lucite, used for aircraft wind shields, ultrasonic shear wave transducers. Polyamide DuPont trade name: nylon Engineering, Materials and Components Revision Date: 9