The effect of heat treatment routes on the retained austenite and Tribomechanical properties of carburized AISI 8620 steel

The objective of this study is to investigate the effect of heat treatment routes involving carburizing and quenching technique on the tribological behavior of carburized AISI 8620 steel. This particular material is commonly used in drivetrain components and undergoes sliding or rolling under high contact pressure conditions. Different levels of retained austenite (RA), hardness and residual stress were achieved by varying carbon potential (0.45% to 1.05%) during carburizing as well as by employing different end-quenching routes (from air-cooled to deep freezing). Wear tests were carried out using a ball on flat reciprocating micro-tribometer between a diamond probe and the samples under dry sliding conditions. Samples were subsequently analyzed using non-contact profilometry and field emission scanning electron microscopy to observe wear behavior and elucidate mechanisms. Hardness and RA had comparatively significant effect on wear resistance as compared to residual stress. It was observed that beyond a certain limiting Hertzian contact pressure level, higher carbon potential carburized sample resulted in increased abrasive wear resistance. This increased wear resistance is attributed to the higher hardness and conditions conducive to transformation of RA into martensite via ploughing-induced work-hardening. The findings indicate that surface treatments resulting in a combination of high hardness and moderately high RA levels result in enhanced abrasive wear resistance for AISI 8620 steel.