In-service failure of disc used for stamping automatic transmission clutch housing

An early failure of an AISI D2 steel forming disc used for manufacturing automatic transmission clutch housings was investigated. The failed disc was characterized by optical emission spectroscopy, X-ray diffraction (XRD), and electron backscatter diffraction (EBSD), while fractographic and microstructural features were examined using stereomicroscopy, optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Hardness measurements, laboratory shearing and compression tests, and preliminary finite element analysis were also performed to clarify the role of carbides in the failure behavior. The results showed that the failed material satisfied the compositional requirements of AISI D2 steel and consisted of a tempered martensitic matrix containing carbides with different sizes, morphologies, and distributions. The carbides were mainly primary M7C3 carbides and secondary M23C6 carbides. Fractographic observations demonstrated that primary carbides fractured mainly by carbide cracking and interfacial decohesion, providing preferential paths for crack propagation. Small secondary carbides detached from the matrix and formed micropores, whereas large secondary carbides exhibited interfacial decohesion, intrinsic cracking, and composite structures with primary carbides that promoted crack initiation and propagation. To further quantify the influence of carbide characteristics, a multiparameter analysis approach based on Image-Pro Plus data was introduced, and ten machine-learning algorithms were evaluated. The results demonstrate the critical role of carbide characteristics in premature disc failure and the potential of carbide-feature-based prediction for engineering failure analysis.