Formation mechanism of heat treatment crack in 42CrMo automobile steering knuckle
Aiming at the problem of crack on the upper surface of a single branch of forging after heat treatment,the crack was analyzed based on the finite element numerical simulation of macro and micro heat treatment,and the forming mechanism of the crack was ex-plored.Optical microscope(OM)and energy dispersive spectrometer(EDS)analysis show that the crack is similar to the typical quenching crack,and there is no decarburization phenomenon near the crack but obvious oxidation phenomenon.It is determined that the crack is generated in quenching stage and oxidized in tempering stage.Combined with the stress simulation results,it can be concluded that the rapid cooling shrinkage of the single branch surface in the early stage is mainly due to the crack caused by the surface tensile stress in x direction.The distribution of the maximum tensile stress in x direction on the single branch surface during this period was ana-lyzed,and it is found that it basically coincides with the actual crack occurrence area,which further proves the correctness of the crack generation mechanism.
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