20CrMo钢内齿圈跌落试验开裂失效分析OA

Aiming at the cracking failure of 20CrMo steel internal gear ring in drop test,comprehensive analysis is carried out on the cracked gear ring by means of macroscopic observation,microstructure analysis,mechanical property test and fracture morphology observation.The crack source of the failed gear ring originated at the inner side,and the final fracture occurred at the outer side.It is indicated that an instantaneous impact load is applied to the outer side when the gear ring dropped to the ground,inducing compressive stress on the outer surface and tensile stress on the inner surface.Under the effect of tensile stress,crack initiation firstly occurred at the inner side,and the crack then rapidly propagated outward,eventually causing integral cracking of the internal gear ring.Fracture characteristic analysis shows that large structural stress existed inside the material.Both cleavage fracture and dimple fracture are observed at the fracture core,where the dimple fracture corresponded to the unquenched low-strength microstructure,proving that the core is not fully quenched.Matrix microstructure analysis demonstrates that the tempering process during heat treatment is extremely inadequate.Meanwhile,serious non-martensitic microstructure appears on the sample surface,which reduces the surface strength of the gear ring.The superposition and combined action of the above microstructure defects and stress state are the main causes for the cracking of the internal gear ring in drop test,which provides a basis for proposing targeted improvement measures and schemes for cracked gear ring parts.