Precipitation Strengthening in 16Cr–1.5Mo Ferritic Stainless Steel Enabled by Coherent B2 Cu Nanoprecipitates and Nb(C, N) Precipitates

Ferritic stainless steels (FSSs) are constrained by inherent low toughness and multiple embrittlement mechanisms. To address these limitations, we developed an Fe‐16Cr‐1.5Cu‐1.5Mo‐0.1Nb FSS processed by annealing at 950°C for 5 min followed by aging at 650°C for various durations (5, 10, 30, and 100 min). While annealing facilitated full recrystallization into a uniform equiaxed matrix, the subsequent aging precipitated Cu nanoparticles. Electron backscatter diffraction analyses confirmed complete recrystallization after annealing, as evidenced by the grain size increase from 13.5 μm to 28.4 μm and the markedly higher fraction of high‐angle grain boundaries. Crucially, grain growth during aging was effectively suppressed by thermally stable Nb(C, N) carbonitrides, ensuring microstructural stability. Transmission electron microscopy analyses demonstrated the existence of nanoscale Cu‐rich precipitates with B2‐ordered structure, which were coherent with the matrix. Through vacuum induction melting, forging, rolling, annealing, and aging at 650°C for 10 min, the alloy achieved a tensile strength of 658.7 MPa (a 180.7 MPa increment) with an elongation of 21.8% and impact toughness energy of 28.2 J at −40°C. The favorable combination of increased strength and stable toughness is attributed to the suitable grain size, the uniformly distributed B2‐ordered Cu‐ precipitates, and their pinning effect on dislocation motion.