Mathematical Modelling of the Influence of Powder Boriding Parameters on Surface Roughness and Electrochemical Behaviour of Austenitic Stainless Steel AISI 316

This study investigates the effect of powder-pack boriding on the microstructure, surface roughness, and corrosion behaviour of AISI 316 (EN X5CrNiMo17-12-2) stainless steel, with the aim of developing a mathematical model based on the obtained experimental results.

Boriding was performed at 850, 900, and 950 °C for durations of 2–4 h using commercial Durborid G powder. Surface roughness was measured before and after treatment, corrosion performance was assessed in 3.5 wt% NaCl solution by potentiodynamic polarisation with focus on corrosion current density (icorr), and boride layer thickness was analysed metallographically. Mathematical models were developed to describe the dependence of surface and electrochemical properties on process parameters.

Boride layer thickness value ranged from ~10 µm at 850 °C/2 h to nearly 95 µm at 950 °C/2 h. Surface roughness generally increased compared to the untreated steel, except for the 850 °C/3 h condition, which exhibited a smoother surface. Corrosion currents revealed a strong influence of boriding conditions. The untreated specimen showed icorr = 4.36 µA. At 850 °C, icorr ranged between 8.86 µA and 20.5 µA, indicating deterioration of corrosion resistance. At 900 °C, the best results were obtained: icorr decreased to 1.13 µA at 2 h and 3.17 µA at 3 h, representing up to a fourfold improvement compared to untreated steel. Boriding at 950 °C gave mixed results, with icorr values between 5.37 µA and 8.67 µA.

These findings demonstrate that optimised boriding, particularly at 900 °C for short to moderate durations, can markedly reduce corrosion current and improve the electrochemical stability of austenitic stainless steel in chloride environments.