Effect of Induction Hardening‐Tempering Process on Fatigue Performance of 34CrNiMo6 Crankshaft Steel

The strength and toughness of alloy steel are improved by the induction hardening–tempering process, which generates a hardened layer and relieves residual stress. However, the effect of structural evolution induced by this process on fatigue performance for crankshaft alloy steel remains unexplored. In this work, 34CrNiMo6 steel with a preoptimized microstructure in the quenched and tempered (Q&T) state is selected. Under the induction hardening conditions of a current of 400 mA, 4 s heating time, and 0.8 mm coating thickness, the microstructure of steel transforms from tempered sorbite to martensite, contributing to a near doubling of hardness compared to the Q&T specimen. After tempering at 330 °C for 2 h, the tempered martensite synergistically enhances tensile and fatigue properties. Carbide precipitation and grain refinement in tempered martensite lead to the increases of 11.7% in yield strength, 21.2% in tensile strength, 29.5% in elongation, and 46.7% in reduction of area. The finely dispersed carbides effectively optimize the residual stress distribution and inhibit fatigue crack propagation. Consequently, the maximum stress fatigue limit increases from 385 MPa to 440 MPa. The study clarifies the fatigue resistance of induction hardening–tempering for 34CrNiMo6 crankshaft steel and offers insights for designing fatigue‐resistant alloys.