Abstract：50CrV4 is a high-quality Cr-Mn-V series alloy spring steel. After isothermal quenching and tempering heat treatment, the duplex structure of lower bainite + tempered martensite + a small amount of retained austenite + dispersed granular carbide can be obtained. After heat treatment, the automotive timing toothed chain plate made of 50CrV4 strip steel can ensure high fatigue strength, and meanwhile, possess good wear resistance. However, due to the existence of Cr, Mn and V in 50CrV4, the undercooled austenite of 50CrV4 is relatively stable. During hot rolling, the cooling cannot be too fast, otherwise the martensite and bainite are prone to occur, leading to cracking in the process of coiling. Therefore, the residence time in the high temperature zone is relatively long, and there is inevitably grain boundary oxidation at different levels. 50CrV4 strips with different grain boundary oxidation levels were studied. The grain boundary oxidation depth was detected. Then the strips were punched to chain plates, which were prepared to the finished chains under same heat treatment conditions. The tension and fatigue strength of chains were measured, and the effects of different degrees of grain boundary oxidation were obtained. Through comparative analysis, it was found that the longitudinal grain boundary oxidation could cause the decrease of tensile strength and fatigue strength. Moreover, the transverse grain boundary oxidation had a severer impact on the tensile strength than the longitudinal grain boundary oxidation. The fatigue strength of the chains would be seriously reduced.
2024, Vol. 42 
