Cast irons heat treatment effect

Carbon is the cheapest and most effective alloying element for hardening iron. We have already seen in Chapter 1 (Table 1.1) that carbon is added to iron in quantities ranging from 0.04 to 4 wt% to make low, medium and high carbon steels, and cast iron. The mechanical properties are strongly dependent on both the carbon content and on the type of heat treatment. Steels and cast iron can therefore be used in a very wide range of applications (see Table 1.1). 

Physical Properties.—Cobalt is a silver-white metal which, when pure, may be machined in a lathe as readily as pure nickel or pure iron. The commercial metal, containing small percentages of carbon, machines after the manner of mild steel. When under corresponding conditions cobalt is harder than nickel and iron.9 The effect of carbon between 0-06 and 0-37 per cent, is not sufficient to counteract that of slight variations in the heat treatment. The tensile strength of cobalt when pure, cast, and unannealed is 34,400 lb. per square inch, which value is increased to 59,700 lb. with a carbon content of 0 062 per cent. and to 61,900 lb. when the carbon reaches 0-25 per cent. 

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