Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni-Coated Martensitic Steels by Advanced Computational Modeling

Ultrahigh-strength steel (UHSS) structures are plated with Zn–Ni coatings because of their excellent corrosion resistance properties, but the plating process is accompanied by the production of hydrogen. The presence of hydrogen in steel results in hydrogen embrittlement. Hence, during the production of UHSS parts, dedicated outgassing steps are employed to remove the diffusible hydrogen from the steel. In a production environment, the real effect of the outgassing process and the outgassing efficiency is unknown for parts coated with Zn–Ni. Hence, a finite element model is developed to capture the evolution of the hydrogen concentration profile in coated UHSS parts during outgassing to study the influence of coating morphology and microstructural features of steel. In order to develop the geometry of the model, scanning electron microscope images are analyzed to understand the microstructure and morphology of the coating. Numerical samples are generated by combining different coating morphologies with steel substrates of varying microstructural features to attain a series of samples with varying features. The results of the outgassing simulations clearly demonstrate the major role of the coating morphology on the hydrogen flux.