Property Improvement of Subzero/Cryogenic Heat Treated Camshafts made of 8620H, 16MnCr5 and 100Cr6 Steels

B. Karacaa, T. Güna, A. Dayança, L.C. Kumruoğlub aESTAŞ Eksantrik San. ve Tic. A.Ş., 58060 Sivas, Turkey bCumhuriyet University, Department of Metallurgy and Materials Eng., 58100 Sivas, Turkey

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Several types of camshafts that made of 8620H, 16MnCr5 and 100Cr6 steel were subzero/cryogenic heat treated and the effect of these heat treatment parameters such holding duration and temperature on the microstructure, retained austenite volume ratio and hardness. 8620H and 16MnCr5 grade camshafts were carburized at 925° in endogas atmosphere (20% CO, 40% N2, 40% H2) for 1440 min. At the end of carburing process the diffusion temperature was decreased to 840°, which is the austenizing temperature, and held for 90 min. Next the samples were hardened in oil at 60° (held for 30 min). Samples were subzero treated at -100° for 210 minutes and were tempered at 185° for 120 minutes. The microstructure was revealed that the subzero/cryogenic heat treatment increased the hardness up to 62 HRc and increased the wear resistance of camshafts surface. The decrease in the retained austenite ratio was observed from 25% to 5-10% after cryogenic heat treatment. All of steels the hardness values were increased with the transformation of retained austenite into martensite. This increase is the result of the transformation of martensite from retained austenite and the carbide precipitation mechanism. In this study, the wear strength values of the hardened camshaft have been brought from the level of 2.2851 mg to 0.5239 mg and SEM analyzes were performed.

DOI:10.12693/APhysPolA.135.800 topics: machining, subzero/cryogenic heat treatment, retained austenite, wear, hardness