Chapter 8 : SteelsLearning Objectives :

1) Name four different types of steels and, for each, cite compositional differences, distinctive properties, and typical uses.

IntroductionBased on composition, metal alloys are grouped into two classes1) Ferrous – iron is the principal constituent e.g. steels and cast iron2) Nonferrous – alloys that are not iron based

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.

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

SteelsSteels are iron-carbon alloys that may contain trace of other alloying elements. Some of common steels are classified according to carbon concentration – namely, into low-, medium-, and high- carbon types.

Low Carbon Steels Of all the different steels, low carbon steels are produced in the greatest quantity. These contain less than about 0.25 wt % C and a little manganese

é Properties: nonresponsive to heat treatments; relatively soft and weak but have outstanding ductility and toughness; machinable and weldable

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é Typical applications: automobile body components, structural shapes (I-beams, channel and angle iron), sheets used in pipelines, buildings, bridges, and tin cans.

High-strength, low alloy (HSLA) steels are another group of low carbon steels. They contain other alloying element ( Cu, V, Ni, Mo) as high as 10% in combined concentration. HSLA steels posses higher strength, more corrosion resistance than plain carbon steels.

Medium Carbon Steels About 0.25 - 0.60 wt % C. The plain medium-carbon steels have low hardenabilities. The heat-treated medium- carbon steels contain Cr, Ni and Mo to improve the capacity to heat treatment thus, improving strength-ductility combinations. They are stronger than low-carbon steels

é Properties: heat treatable, relatively large combinations of mechanical characteristics.

é Typical applications: railway wheels and tracks, gears, crankshafts, and machine parts.

High Carbon Steels About 0.60 – 1.4 wt % C. The hardest, strongest, and yet least ductile of the carbon steels. They are used in a hardened and tampered condition (wear resistance). The tool and die steels are high carbon alloys contain (Cr, V, W, Mo). The combination with C will form very hard and wear resistance carbide compound (for cutting tools).

é Properties: hard, strong, and relatively brittle. é Typical applications: chisels, hammers, knives, and hacksaw blades.

High Alloy Steels / Stainless steel The major alloying element is Cr ≥ 11wt%. Corrosion resistant is enhanced by adding Ni and Mo

é Properties: hard and wear resistant; resistant to corrosion in a large variety of environments.

é Typical applications: cutting tools, drills, cutlery, food processing, and surgical tools

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