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 delta-ferrite formation in the HAZ and showed changing characteristics with increasing delta-ferrite fraction. Pitting corrosion resistance was reduced by the formation of a Cr-depleted zone along the delta-ferrite/austenite phase boundary due to delta-ferrite formation. However, pitting corrosion resistance did not change with increased peak temperature in the HAZ despite the increasing delta-ferrite fraction. Sensitivity to interphase corrosion was strongly affected by the amount of delta-ferrite/austenite phase boundary and delta-ferrite area, gradually increasing with increasing delta-ferrite fraction. These dissimilar corrosion behaviors were carefully investigated and are discussed in terms of phase transformation and alloying element partitioning in the HAZ. (C) 2013 Elsevier B.V. All rights reserved.This project was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea. The authors wish to thank Min-Ho Jang and Kyutae Han for their valuable support of the experiments