The Effect of Tempering Temperature on Microstructure and the Mechanical Properties of Forged Steel Containing Chrome, Manganese and Molybdenum
Steel bearings have plenty of usages in manufacturing different kinds of ball bearings, bearings and cold rolling rollers. Heat treatment has an important role in the properties of this group of steels. Therefore, in current research the effect of tempering temperature on the microstructure, hardness, impact energy and wear resistance in forged steel containing Chrome, Manganese and Molybdenum will be studied. For this purpose, the samples were tempered after austenitizing at 900ºC and quenching in the oil at 6 temperatures of 150, 250, 350, 450, 550 and 650 ºC for an hour. Then microstructural studies and mechanical properties of the samples including hardness, impact energy and wear resistance were surveyed on the samples. The results showed that the hardness was gradually decreased (impact energy gradually increased) at the temperature range of 150 - 250 ˚C and at temperature range of 350 -650ºC, the hardness would decrease and the impact energy would increase. Also, the wear resistance would decrease with an increase in the tempering temperature. The result should be justified considering the softening of the structure and the reduction in martensite tetragonality which stems from an increase in the tempering temperature. The study of the wear surface of the samples indicated that the dominant wear mechanism was adhesive wear in which with an increase the tempering temperature due to a reduction in the hardness of the samples, more sever adhesive wear was observed.