55. Hard steel contains A.2 to 5 per cent carbon B.0.5 to 1.5 per cent carbon C.0.1 to 0.4 per cent carbon D.0.01 to 0.04 per cent carbon
Answer: Option B Solution: The term hardened steel is often used for a medium or high carbon steel that has been given the heat treatments of quenching followed by tempering. The quenching results in the formation of metastable martensite, the fraction of which is reduced to the desired amount during tempering. This is the most common state for finished articles such as tools and machine parts. In contrast, the same steel composition in annealed state will be softer as required for forming and machining. Carbon steels which can successfully undergo heat-treatment have carbon content in the range of 0.30–1.70% by weight. Trace impurities of various other elements can have a significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make the steel red-short.
