Heat Treatment Effect on Pitting Corrosion of Super Duplex Stainless Steel UNS S32750 FCA Welds

Jang, Bok-Su; Moon, In-June; Kim, Se-Cheol; Koh, Jin-Hyun

doi:2013.31.5.20

J Weld Join > Volume 31(5); 2013 > Article

Research Paper

Journal of KWJS 2013;31(5):20-25.
DOI: https://doi.org/10.5781/KWJS.2013.31.5.20 Published online November 5, 2013.

Heat Treatment Effect on Pitting Corrosion of Super Duplex Stainless Steel UNS S32750 FCA Welds

Bok-Su Jang^1,2, In-June Moon², Se-Cheol Kim^2,3, Jin-Hyun Koh²

Correspondence: Jin-Hyun Koh,
Email: jhkoh@kut.ac.kr

Abstract

This study was carried out to investigate the influence of a sigma phase precipitation on the pitting corrosion resistance and microstructural change of super duplex stainless steels(UNS S32750). The welds made by FCAW (Flux Cored Arc Welding) were heat treated (930℃, 1080℃, 1230℃) and quenched. Based on the microstructural examination, it was found that the σ phase was formed in base metals and welds heat treated at 930℃ while there were little σphases formed in base metals and weld metal experienced the relatively fast cooling from 1080℃ and 1230℃. On the other hand, the most weight loss due to pitting corrosion occurred in base and weld metals heat treated at 930℃. It was confirmed that the pitting corrosion occurred in the phase boundaries of ferrite/sigma and austenite/sigma. The pitting corrosion resistance decreased owing to an increase in Cr, Mo depleted areas adjacent to the intermetallic phases such as σphase. The hardness was greatly increased due to the precipitation σphase.

Key Words: Pitting corrosion, FCAW, PWHT, Weight loss, Ferrite, Sigma-phase