Effect of heat treatment on the microstructure and mechanical properties of low carbon steel

Shazreena , Samat (2013) Effect of heat treatment on the microstructure and mechanical properties of low carbon steel. Project Report. UTeM, Melaka. (Submitted)

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Abstract

A study of heat treatment of low carbon steel has been carried out in order to investigate the effect on its microstructure and mechanical properties. The study consists of metallurgy and mechanical investigation before and after heat treatment process. Various treatments were performed which were annealing, normalizing, quenching and carburizing at temperature 860, 900 and 940 ˚C with 1 hour soaking time. Metallurgical investigation was conducted and it was observed that quenched sample form a martensite microstructure due to rapid cooling. As for normalizing and annealing process, it formed pearlite and ferrite microstructure due to slow cooling rate. Then, hardness test was carried out highest hardness value was achieved by carburizing (water quenched) sample with 88.38 HRA at 940 ˚C. This is because of the existence of fine grain size and also the effect of carbon diffusion from the process. Meanwhile annealing process gave a lowest hardness value with 33.38 HRA compared to as-received sample with 53.62 HRA due to larger grain size. The grain size was measured according to ASTM E112, and its proof that annealed sample gave a coarse grain size while the quenched sample prompted ultrafine grain size since it gave more than 14 grain size number. Besides, the finding also found that heating energy and cooling rate effects the grain size where it became larger as increased in temperature thus it decreased the hardness value.

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