Effect of Heat Treatment on Hardness of Plain Carbon Steel

Generally, low carbon steel or mild steels contain 0.15% to 0.3% Carbon and do not respond to hardening heat treatment processes like quenching and tempering. Thus hardly any martensite is formed on quenching. Thus, to improve the surface hardness and wear resistance several casehardening methods like carburizing, nitriding, carbonitriding and cyaniding are normally used. Carburizing is the most common treatment among them in which the surface composition of the low carbon steel changes by diffusion of carbon and results in to hard outer case with good wear resistance. On the other hand, medium carbon steel contains higher percentage of carbon than low carbon steel and thus gives better response to the heat treatment. The hardness of medium carbon steel can be improved by quenching through different quenching mediums. The present investigation emphasizes on improving the hardness property of four different types of steel having varying carbon content. The mild steel was carburized at different temperatures ranging from 8000C to 9000C for 2 and 5 hours. After carburizing, annealing, normalizing, hardening and tempering treatments were given. The hardness values under all the process