Insights into the effect of plasma nitriding on corrosion behavior of 304 stainless steel in liquid lead-bismuth eutectic

Abstract

The effect of plasma nitriding on the microstructure and corrosion behavior of 304 stainless steel in 550 °C lead-bismuth eutectic alloy (LBE) was investigated. A uniform nitriding layer was prepared on 304 steel, and the surface hardening process further made nitrogen concentrated on subsurface of nitriding layer. The results indicate that the nitriding exerted degradation effect on corrosion resistance of 304 steel. A thin oxide layer formed on the original 304 steel surface, around 1.0 μm in thickness. However, the oxide scales formed in nitrided steel were much thicker, approximately 20.0 μm. LBE penetration along grain boundaries were frequently observed in nitriding layer. The surface hardening process promoted the oxidation of nitrided steel while inhibited the LBE penetration, which is related to the precipitation of CrN at grain boundaries. This study provides reference to the application of nitriding technology in LBE-based reactors.