Improvements of fatigue and wear resistances of 20MnCr5 and 8620 materials used in tire protection chain for various heat treatment conditions

Carburizing is used commonly for increasing wear and fatigue strengths of low carbon steel by diffusing carbon to their surface. This technique has been also used for a long time in tire protection chains to increase wear and fatigue strengths. However, wear and fatigue performance of the rings are affected negatively due to the low case depth, as a result of which service life decreases. On the other hand, thicker case depth with respect of wear strength results in reduces in fatigue life/strength. It is therefore necessary to determine suitable case depth for the appropriate service life. Not only case depth, also retained austenite as well as martensite ratio are directly related to wear and fatigue performances of treated part. In this study, the effects of carburising case depth and sub-zero process on fatigue and wear resistances of 8620 and 20MnCr5 steels used in tire protection chain have been investigated. From the results of wear and fatigue tests, it was determined that the ratio of effective carburizing depth to diameter is most suitable for t/D:0.15. Application of subzero treatment enhanced 86% improvement in wear resistance for 8620 steel and 47% improvement in wear resistance for 20MnCr5 steel. It has been determined that this process also provides remarkable improvement in fatigue strength. Keywords: Carburizing, subzero processing, bending fatigue strength