Different aspect of pitting corrosion and interphase corrosion in the weld heat-affected zone of high-nitrogen Fe–18Cr–10Mn–N steel

Phase transformation and its effects on corrosion behavior in the weld heat-affected zone (HAZ) of a metastable high-nitrogen Fe–18Cr–10Mn–N austenitic stainless steel were investigated through electrochemical tests, electron probe micro analysis and electron microscopy analysis. Electrochemical tests showed that pitting corrosion and interphase corrosion were significantly affected by δ-ferrite formation in the HAZ and showed changing characteristics with increasing δ-ferrite fraction. Pitting corrosion resistance was reduced by the formation of a Cr-depleted zone along the δ-ferrite/austenite phase boundary due to δ-ferrite formation. However, pitting corrosion resistance did not change with increased peak temperature in the HAZ despite the increasing δ-ferrite fraction. Sensitivity to interphase corrosion was strongly affected by the amount of δ-ferrite/austenite phase boundary and δ-ferrite area, gradually increasing with increasing δ-ferrite fraction. These dissimilar corrosion behaviors were carefully investigated and are discussed in terms of phase transformation and alloying element partitioning in the HAZ.