Phase stability, microstructural evolution, and corrosion behavior of GTAW-welded AISI 316 L austenitic stainless steel

This work explores the phase changes in welded AISI 316 L stainless steel coated with a nickel-watts bath containing niobium microparticles. The CALPHAD method, using Thermo-Calc with TCFE7, TCFE12, and PRISMA, simulated phase changes during rapid cooling. Simulations identified amounts of austenite, delta ferrite, and a small amount of sigma phase during cooling from 1450 °C to 25 °C. The influence of the Ni-Nb coating on stability and element diffusion was assessed. Results were confirmed by microscopy, microhardness testing, ferritoscopy, and electrochemical testing. The CALPHAD model reliably predicted phase stability, supporting its use in alloy design and in the optimization of welded stainless steel. This study’s approach lays the groundwork for the detailed background and motivation discussed in the following introduction. • CALPHAD predicts δ-ferrite and σ-phase evolution in GTAW-welded AISI 316 L. • Ni–Nb coating slightly enhances corrosion and microstructural stability. • δ-ferrite formation validated by ferritoscopy and SEM–EDS mapping. • Welded joints retain ductility and hardness under rapid cooling cycles. • Integrated CALPHAD-experimental approach guides stainless-steel design.