Engineering Materials and Metallurgy - Unit 1 PDF

ENGINEERING MATERIALS AND METALLURGY UNIT-1 SYLLABI SYLLABI SYLLABI Solid Solutions Structure of Alloys Phases in Alloys 1. Solid solutions Variation in composition Usually the crystal structure of the one of the solution is that of one of the co...

ENGINEERING MATERIALS AND METALLURGY UNIT-1 SYLLABI SYLLABI SYLLABI Solid Solutions Structure of Alloys Phases in Alloys 1. Solid solutions Variation in composition Usually the crystal structure of the one of the solution is that of one of the components 2. Compounds(Intermetallic Compounds) Solid Solutions A solid solution is a homogeneous mixture of 2 crystalline solids with similar crystal lattices. As in certain metal alloys, mixtures often consist of two or more forms of atoms or molecules that share a crystal lattice. The most abundant element or compound is referred to as a solvent. A tiny concentration of an element or compound is referred to as a solute. Solids have varying degrees of mutual solubility, similar to liquids, based on their chemical characteristics and crystalline structure, influencing how their atoms fit together in the mixed crystal lattice. Solid Solutions Combining the two solids after they have been melted into fluids at high temperatures but then cooling the result to produce the new solid or putting vapours of the precursors onto substrates to form thin films are two steps to complete mixing. Solid Solutions The mixed lattice can be substitutional, with atoms from one initial crystal changing those from the other, or interstitial, with atoms occupying locations in the lattice that are ordinarily vacant. Alloy is a metal made up of a variety of components. The majority of alloys are made up of a base metal and a few additions of alloying elements. Steel/cast iron (iron base alloys), bronze/brass (copper base alloys), aluminium alloys, nickel-based alloys, magnesium base alloys, and titanium alloys are typical examples of alloys. Solid Solutions Different technological procedures can be used to make alloys, such as melting, sintering a powder mixture, high-temperature diffusion of an alloying element into the base metal, plasma and vapour deposition of various elements, electroplating, and so on. The structure of an alloy might be single-phase or multi-phase. A phase is a uniform section of an alloy with certain chemical composition and structure, separated from the rest of the alloy by a phase boundary. An alloy phase can take the form of a valence compound (a substance made up of two or more elements in which a fixed ratio determines the composition) or a solid solution. Solid Solutions A solid solution refers to a state in which two or more elements are entirely soluble in one another. When two or more types of homogeneous atoms escape the solid state, it is known as a solid solution. Solid solutions are divided into two categories: Interstitial solid solution Substitutional solid solution Solid Solutions Interstitial solid solution: The interstitial solid solution comprises solid solutions with an angstrom number of less than one. And this is generated when the interstitial solid solution is formed by the space of lattice structure of a big solvent in which small atomic radii fit. The solubility of this solid solution is limited. The solid solution can be easily separated and has a high melting temperature. Example: carbon dissolves in iron. Solid Solutions Substitutional solid solution: The solute atoms in the crystal lattice are substituted for the solvent atoms in this form of solid solution. The crystal structure does not change, although the addition of atoms causes some deformation. There is a variation in diameter between the solute and the solvent. Ex: gold-silver alloy’s lattice structure remains unchanged. Two Types : 1. Ordered – Al in CU – Al takes corner position and Cu takes Face Centered Position 2. Random or Disordered – Most of the alloys Hume Rothery Rules The Hume-Rothery rules state that two elements will likely form a substitutional solid solution when these four conditions are met: The atomic size of the solute atoms is within 15% of the atomic size of the solvent atoms. The two elements have similar crystal structures. The two elements have similar electronegativities. The two elements have similar valences. Phase Diagram Phase Chemically homogeneous Physically distinct Mechanically separable Phase Diagram Relation of number of components Number of phases Degrees of freedom Components The composition in a material Ex(1) : H20 Hydrogen and Oxygen are the 2 components Where as the phase is 1(Liquid Phase) Ex (2) : Water + Ice Bar Hydrogen and Oxygen are the 2 components Where as the phase is 2(Liquid Phase + Solid Phase) Ex (3) : Mild Steel Fe & C In the room temperature – α,Fe3C Phase Diagram – Cu-Ni Reactions What is Steel? Steel is an alloy of Iron (the concept of alloy is explained below) and the principal or main alloying element is Carbon. Hence, The main or base element in steel is: Iron Main (principal) alloying element in steel is: Carbon Other alloying elements in steel are: Manganese, Silicon, Nickel, Chromium, Molybdenum, Vanadium, Titanium, Niobium, Aluminum, etc Types Of Steel Carbon Steel Carbon steel is the most utilized steel in industries and accounts for over 90% of the total steel production. Based on the carbon content, Carbon steels are further classified into three groups. Low Carbon Steel/Mild Steel Medium Carbon Steel High Carbon steel Carbon Steel Designation system - Carbon Steel American Iron and Steel Institute (AISI) together with Society of Automotive Engineers (SAE) have established four-digit (with additional letter prefixes) designation system: SAE 1XXX First digit 1 indicates carbon steel (2-9 are used for alloy steels); Second digit indicates modification of the steel. 0 - Plain carbon, non-modified 1 - Resulfurized 2 - Resulfurized and rephosphorized 5 - Non-resulfurized, Mn over 1.0% Last two digits indicate carbon concentration in 0.01%. Example: SAE 1030 means non modified carbon steel, containing 0.30% of carbon. Carbon Steel A letter prefix before the four-digit number indicates the steel making technology: A - Alloy, basic open hearth B - Carbon, acid Bessemer C - Carbon, basic open hearth D - Carbon, acid open hearth E - Electric furnace Example: AISI B1020 means non modified carbon steel, produced in acid Bessemer and containing 0.20% of carbon Stainless Steel Stainless steel is an alloy steel that contains 10.5% Chromium (Minimum). Stainless steel exhibits corrosion resistance properties, due to the formation of a very thin layer of Cr2O3 on its surface. This layer is also known as the passive layer. Increasing the amount of Chromium will further increase the material’s corrosion resistance. In addition to Chromium, Nickel, and Molybdenum are also added to impart desired (or improved) properties. Stainless steel also contains varying amounts of Carbon, Silicon, and Manganese. Stainless Steel Stainless steels are further classified as; 1. Ferritic Stainless Steel 2. Martensitic Stainless Steel 3. Austenitic Stainless Steel 4. Duplex Stainless Steel 5. Precipitation-Hardening (PH) Stainless Steel Stainless Steel Ferritic Stainless Steel: Ferritic steels consist of Iron-Chromium alloys with body-centered cubic crystal structures (BCC). These are generally magnetic and cannot be hardened by heat treatment but can be strengthened by cold working. Austenitic Stainless Steel: Austenitic steels are the most corrosion-resistant. It is non-magnetic and non-heat-treatable. Generally, austenitic steels are highly weldable. Martensitic Stainless Steel: Martensitic stainless steels are extremely strong and tough but not as corrosion-resistant as the other two classes. These steels are highly machinable, magnetic, and heat-treatable. Stainless Steel Duplex Stainless Steels: Duplex stainless steel consists of a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel (i.e Ferrite + Austenite). Duplex steels are about twice as strong as austenitic or ferritic stainless steels. Precipitation-Hardening (PH) Stainless Steels: Precipitation-Hardening (PH) Stainless Steels possess Ultra high strength due to precipitation hardening. Stainless Steel AISI has established three-digit system for the stainless steels: 2XX series – chromium-nickel-manganese austenitic stainless steels; 3XX series –chromium-nickel austenitic stainless steels; 4XXseries–chromium martensitic stainless steels or ferritic stainless steels; 5XX series – low chromium martensitic stainless steels; Alloy Steel In alloy steel, varying proportions of alloying elements are used, to achieve desired (improved) properties such as weldability, ductility, machinability, strength, hardenability, corrosion resistance, etc. Some of the most used alloying elements and their effects are as follows; Manganese – Increases strength and hardness, decreases ductility and weldability Silicon – Used as deoxidizers used in the steel-making process Alloy Steel Phosphorus – Increases strength and hardness and decreases ductility and notch impact toughness of steel. Sulphur –Decreases ductility, notch impact toughness, and weldability. Found in the form of sulfide inclusions. Copper – improved corrosion resistance Nickel – Increases hardenability and Impact strength of steels. Molybdenum – Increases hardenability and enhances the creep resistance of low-alloy steels Alloy Steel Low alloy steels (alloying elements ⇐ 8%); High alloy steels (alloying elements > 8%). First digit indicates the class of the alloy steel: 2- Nickel steels; 3- Nickel-chromium steels; 4- Molybdenum steels; 5- Chromium steels; 6- Chromium-vanadium steels; 7- Tungsten-chromium steels; 9- Silicon-manganese steels. Second digit indicates concentration of the major element in percents (1 means 1%). Last two digits indicate carbon concentration in 0,01%. Example: SAE 5130 means alloy chromium steel, containing 1% of chromium and 0.30% of carbon. Tool Steel or Die Steel Tool steels have high carbon content (0.5% to 1.5%). Higher carbon content provides higher hardness and strength. These steels are mostly used to make tools and dies. Tool steel contains various amounts of tungsten, cobalt, molybdenum, and vanadium to increase the heat and wear resistance, and durability of the metal. This makes tool steels very ideal for use as cutting and drilling tools. Tool Steel or Die Steel Designation system of one-letter in combination with a number is accepted for tool steels. The letter means: W - Water hardened plain carbon tool steels; O - Oil hardening cold work alloy steels; A - Air hardening cold work alloy steels; D -Diffused hardening cold work alloy steels; S – Shock resistant low carbon tool steels; T – High speed tungsten tool steels; M - High speed molybdenum tool steels; H – Hot work tool steels; P – Plastic mold tool steels. Classification of cast irons White cast irons - hard and brittle wear resistant cast irons consisting of pearlite and cementite. Grey cast irons - cast irons at slow cooling and consisting of ferrite and dispersed graphite flakes. Malleable cast irons - cast irons, produced by heat treatment of white cast irons and consisting of ferrite and particles of free graphite. Nodular (ductile) cast irons - grey cast iron in which Graphite particles are modified by magnesium added to the melt before casting. Nodular cast iron consists of spheroid nodular graphite particles in ferrite or pearlite matrix. Microstructure - CI Applications Steel Cast Iron Rail car wheels, frames, and bolsters Cast iron frying pans and other cookware Mining machinery, construction equipment, and heavy Automotive engine blocks, brake disks, and numerous trucks other parts Heavy duty pumps, valves, and fittings Residential fence gates, decorative light posts, fireplace Turbochargers, engine blocks, and other automotive elements, and other furnishings parts Valves, fittings, and manhole covers in water and sewer Turbines and other components in power station applications assemblies Chains, gears, shafts, linkages, and more MCQ Q O Which of the following is a) Metals a basic classification of b) Non-Metals Engineering Materials? c) Both Metals & Non- Metals d) None of the mentioned MCQ Q O Which of the following is a) Mechanical properties not a property of b) Chemical properties engineering materials? c) Polymorphism d) Electrical properties MCQ Q O Which of the following is a) Asbestos a type of Engineering b) Ferrous Metals Materials and is a Metal? c) Non-Ferrous Metals d) Both b & c MCQ Q O Which of the following a) Softness attributes explain why b) Hardness pure metals are not c) Brittleness frequently used in d) Luster engineering applications? MCQ Q O Which of the following a) Grain size factors don’t affect the b) Shape of material mechanical properties of c) Content of alloys a material under applied d) Imperfection and loads? defects MCQ Q O Which of these is not a a) Improves ductility function of alloy steels? b) Improves machinability c) Increases strength d) Reduces cost MCQ Q O Which of the following is a) Vanadium the primary element b) Indium used for making c) Chromium stainless steel alloy? d) Zirconium MCQ Q O Which of the following a) Chromium carbide carbides are used for b) Silicon carbide cutting tools? c) Tungsten carbide d) Vanadium carbide MCQ Q O What is the result of full a) Cementite annealing of b) Coarse pearlite hypoeutectoid steels? c) Silicon d) Bainite MCQ Q O White iron structure A) Pearlite consists of B) Cementite C) Ferrite D) Pearlite and Cementite MCQ Q O The reaction in which a 1. Eutectoid Reaction liquid phase transform 2. Peritectic Reaction into two different solid phases is called 3. Peritectoid Reaction 4. Eutectic Reaction MCQ Q O Which of the following 1. Ferrite phase of steel is not 2. Cementite present in the Fe-Fe3C Diagram? 3. Austenite 4. Martensite MCQ Q O The eutectic reaction of 1. 527’C Iron-Carbon occurs at 2. 1493’C 3. 1147’C 4. 723’C MCQ Q O The eutectic point in the a) 0.022 iron-iron carbide phase b) 0.77 diagram occurs at c) 2.11 __________ weight % d) 4.30 composition of carbon. MCQ Q O At what temperature a) 1674 F does δ ferrite melt? b) 1990 F c) 2541 F d) 2800 F MCQ Q O What is the solubility of a) 0.1% α ferrite at 0oC? b) 0.02% c) 0.005% d) 0.0004% MCQ Q O At what temperature a) 1778oC does peritectic reaction b) 1495oC occur? c) 1148oC d) 723oC