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Materials Science and Engineering: An Introduction

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259 microstructure will be totally pearlite--probably a reasonably fine pearlite. On the other hand, in Figure 10.20 is shown the CCT diagram for a 4340 steel. From this diagram it may be noted that a cooling rate of 10 ° C/s produces a totally martensitic structure. Pearlite is softer and more ductile than martensite, and, therefore, is most likely more desirable. 12.8 If a steel weld is cooled very rapidly, martensite may form, which is very brittle. In some situations, cracks may form in the weld region as it cools. 12.9 This question asks that we list four classifications of steels, and, for each, to describe properties and cite typical applications. Low Carbon Steels Properties: nonresponsive to heat treatments; relatively soft and weak; machinable and weldable. Typical applications: automobile bodies, structural shapes, pipelines, buildings, bridges, and tin cans. Medium Carbon Steels Properties: heat treatable, relatively large combinations of mechanical characteristics.
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Unformatted text preview: Typical applications: railway wheels and tracks, gears, crankshafts, and machine parts. High Carbon Steels Properties: hard, strong, and relatively brittle. Typical applications: chisels, hammers, knives, and hacksaw blades. High Alloy Steels (Stainless and Tool) Properties: hard and wear resistant; resistant to corrosion in a large variety of environments. Typical applications: cutting tools, drills, cutlery, food processing, and surgical tools. 12.10 (a) Ferrous alloys are used extensively because: 1) Iron ores exist in abundant quantities. 2) Economical extraction, refining, and fabrication techniques are available. 3) The alloys may be tailored to have a wide range of properties. (b) Disadvantages of ferrous alloys are: 1) They are susceptible to corrosion. 2) They have a relatively high density. 3) They have relatively low electrical conductivities....
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