The Effect of Hardening Conditions on Microstructure and Hardness of EN 21NiCrMo2 Steel
AbstractIn this study, the hardening process was performed in air, water and oil environment after austenitizing to 8620 steel which is used in parts, machines and automobiles, gear wheels, pins and spindles. The austenitization process was carried out in a Protherm brand oven with an electrical resistance for 1 hour at 900 °C. The cooling in air was carried out in a stagnant atmosphere at 25 °C. For engine cooling, the waste engine oil at room temperature was used, while for the cooling of the water environment, the tap water at room temperature was used. The sample thickness studied is approximately 20 mm. As a result of the optical microstructure studies, the air-cooled samples have a hardness of up to about 1 mm below the surface, and the hardness in the material center is about 400 HV. In the oil cooling process, the classrooms, which have 750 HV on the surface, have decreased down to 550 HV at 2,5 mm depths. In the hardening process, 800 HV hardness values on the surface are replaced by 600 HV values in the center.