LEC 2_part 2_Ferrous Metal Alloys PDF

Properties and Testing of Electromechanical Materials MEC 147N Lecture 2 Ferrous Metal Alloys Presented by: Dr. Mohamed M. AbdelKader Hassan 1 Types of Met...

Properties and Testing of Electromechanical Materials MEC 147N Lecture 2 Ferrous Metal Alloys Presented by: Dr. Mohamed M. AbdelKader Hassan 1 Types of Metal Alloys Ferrous: iron as main constitute. Non ferrous: NOT BASED ON iron as main constitute. 2 A- Steels Alloys I – Low Alloys INTRODUCTION Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements; there are thousands of alloys that have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. Some of the more common steels are classified according to carbon concentration into low-, medium-, and high-carbon types. 3 Important Definitions 4 STRENGTH The ability of a material to resist the externally applied forces without breaking or yielding. 5  DUCTILITY The ability of a material to be deform plastically before rupture Note: Brittleness is the opposite of Ductility 6 HARDNESS A measure of a material’s resistance to localized plastic deformation (e.g., a small dent or a scratch). 7 i- Low-Carbon Steels These generally contain less than about 0.25 wt% C and are unresponsive to heat treatments intended to form martensite; strengthening is accomplished by cold work. As a consequence, these alloys are relatively soft and weak but have outstanding ductility and toughness; in addition, they are machinable, weldable, and, of all steels, are the least expensive to produce. Typical applications include automobile body components, structural shapes (e.g., I-beams, channel and angle iron), and sheets that are used in pipelines, buildings, bridges, and tin cans. 8 Tables 1 and 2 present the compositions and mechanical properties of several plain low carbon steels. They typically have a yield strength of 275 MPa, tensile strengths between 415 and 550 MPa, and a ductility of 25%EL. Table 1 9 NOTE: (AISI): codes used by the American Iron and Steel Institute. (SAE): codes used by the Society of Automotive Engineers. (ASTM): codes used by the American Society for Testing and Materials. (UNS): codes used by the Uniform Numbering System. The AISI/SAE designation for these steels is a four-digit number: The first two digits indicate the alloy content; the last two give the carbon concentration. For plain carbon steels, the first two digits are 1 and 0; alloy steels are designated by other initial two digit combinations (e.g., 13, 41, 43). The third and fourth digits represent the weight percent carbon multiplied by 100. For example, a 1060 steel is a plain carbon steel10 containing 0.60 wt% C. 11 Table 2 12  Plain carbon steels contain only residual concentrations of impurities other than carbon and a little manganese. For alloy steels, more alloying elements are intentionally added in specific concentrations.  high-strength, low-alloy (HSLA) steels They contain other alloying elements such as copper, vanadium, nickel, and molybdenum in combined concentrations as high as 10 wt%, and they possess higher strengths than the plain low-carbon steels. Most may be strengthened by heat treatment, giving tensile strengths in excess of 480 MPa; in addition, they are ductile, formable, and machinable. 13 Several are listed in Tables 1 and 2. In normal atmospheres, the HSLA steels are more resistant to corrosion than the plain carbon steels, which they have replaced in many applications where structural strength is critical (e.g., bridges, towers, support columns in high-rise buildings, pressure vessels). 14 ii- Medium-Carbon Steels The medium-carbon steels have carbon concentrations between about 0.25 and 0.60 wt%. These alloys may be heat-treated to improve their mechanical properties. Additions of chromium, nickel, and molybdenum improve the capacity of these alloys to be heat-treated, giving rise to a variety of strength–ductility combinations.  heat-treated alloys are stronger than the low-carbon steels, but at a sacrifice of ductility and toughness. Applications include railway wheels and tracks, gears, crankshafts, and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, 15 and toughness. iii- High-Carbon Steels The high-carbon steels, normally having carbon contents between 0.60 and 1.4 wt%, are the hardest, strongest, and yet least ductile of the carbon steels.  The tool and die steels are high-carbon alloys, usually containing chromium, vanadium, tungsten, and molybdenum. These alloying elements combine with carbon to form very hard and wear-resistant carbide compounds. These steels are used as cutting tools and dies for forming and shaping materials, as well as in knives, razors, hacksaw blades, springs, and high- strength wire. 16 II – High Alloys The stainless steels are highly resistant to corrosion (rusting) in a variety of environments, especially the ambient atmosphere. Their predominant alloying element is chromium; a concentration of at least 11 wt% Cr is required. Corrosion resistance may also be enhanced by nickel and molybdenum additions. Stainless steels are divided into three classes on the basis of the predominant phase constituent of the microstructure—martensitic, ferritic, or austenitic. A wide range of mechanical properties combined with excellent resistance to corrosion make stainless steels very versatile in their applicability. 17 18 19 B- Cast Irons Generically, cast irons are a class of ferrous alloys with carbon contents above 2.14 wt%; in practice, however, most cast irons contain between 3.0 and 4.5 wt% C and, in addition, other alloying elements. Furthermore, some cast irons are very brittle, and casting is the most convenient fabrication technique. 20 i- Gray Cast Iron The carbon content of gray cast irons vary between 2.5 and 4.0 wt%. For most of these cast irons, the graphite exists in the form of flakes (similar to corn flakes). These flakes are formed due to cooling the cast iron slowly during manufacturing. Because of these graphite flakes, a fractured surface takes on a gray appearance—hence its name. Microstructure of gray cast iron 21 They are very effective in damping vibrational energy; this is represented in following Figure, which compares the relative damping capacities of steel and gray iron. Furthermore, in the molten state they have a high fluidity at casting temperature, which permits casting pieces that have intricate shapes; also, casting shrinkage is low. Comparison of the relative vibrational damping capacities of (a) steel and (b) gray cast iron. 22 Applications of Gray Cast iron 23 ii- Ductile (or Nodular) Iron Adding a small amount of magnesium (Mg) and/or Ce or Ca to the gray iron before casting produces a distinctly different microstructure and set of mechanical properties. Graphite still forms, but as nodules or spherelike particles instead of flakes. The resulting alloy is called ductile or nodular iron. Advantages: High ductility and machinability. Microstructure of ductile cast iron 24 Applications of Ductile (Nodular) Cast iron 25 iii- White Cast Iron If the cast iron is cooled rapidly during manufacturing, the graphite flakes do not get the chance to form. Instead, white cast iron is formed with cementite (Fe3C) 26 Applications of white Cast iron Rail Car Brake shoes 27 iv- Malleable Cast Iron Generally, white iron is used as an intermediary in the production of yet another cast iron, malleable iron. NOTE Microstructure of Malleable cast iron 28  Applications of malleable Cast iron Representative applications include transmission gears, differential cases for the automotive industry, and also flanges, pipe fittings 29 Comparison between the microstructures of the four types of Cast Iron 30 Characteristics of some non-ferrous materials 31