Predicting Hydrogen-Assisted Crack Initiation in Stretch-Formed AHSS Through a Coupled Diffusion–Mechanics Model and Process Window Map

Hydrogen-assisted cracking in advanced high-strength steels (AHSS) during or after stretch forming remains a critical barrier to lightweight automotive design. We present a predictive framework that couples finite-strain elastoplastic mechanics with trap-dominated hydrogen diffusion, accounts for stress-driven transport and strain-induced microstructural evolution, and is calibrated against operando/ ex-situ measurements of residual stress, plasticity proxies, and phase fraction. The model correctly predicts the experimentally observed first-crack locus at the foot/hillside region and reproduces the dependence of initiation on stretch height and charging severity. Using the validated model, we construct a process window map—a practitioner-ready diagram in the space of punch stroke, punch radius, and friction coefficient—that separates safe, delayed, and fast-crack regimes. The map yields quantitative guidance for tooling/lubrication choices and forms the basis for a pass/fail screening rule via a normalized risk index. This work operationalizes mechanism into design rules that can be deployed in forming process development.