Influence of nitriding treatment on the microstructure and mechanical properties of AISI 422 martensitic stainless steel
Zhentong Xi, Qiong Jing, Yun Wang, Xiao Han, Ruijun He, Hongye Zhang
Abstract
This study investigates the microstructural evolution and residual stress mechanisms in plasma-nitrided AISI 422 martensitic stainless steel through integrated experiments and phase-field simulations. Plasma nitriding at 560 °C induced sequential phase transitions, initiating from Guinier-Preston (GP) zones that transformed into coherent CrN precipitates, followed by continuous coarsening growth. Advanced characterization techniques, including TEM, XRD, and geometric phase analysis (GPA), revealed depth-dependent structural gradients: CrN precipitates evolved from coherent needle-like morphologies (100 nm length, 5 nm width) near the matrix interface to coarser rod-like structures (50 nm length, 20 nm width) in shallower regions. Surface layers were dominated by γ′-Fe 4 N phases, exhibiting residual tensile stress, while peak compressive stress (−550 MPa) occurred at 150 μm depth due to coherent strain fields arising from CrN-matrix lattice mismatch. Phase-field simulations successfully replicated CrN nucleation, anisotropic growth, and coarsening, aligning closely with experimental observations. The saddle-shaped residual stress profile was attributed to nitrogen diffusion-induced lattice expansion, strain relaxation during precipitate coarsening, and contraction of the γ′-Fe 4 N phase. These findings establish a microstructure-property relationship, providing theoretical support for industrial-scale production of nitrided martensitic stainless steels.