Heat Treatment Effect on Super Duplex Stainless Steel UNS S32750 FCA Multipass Welds

Jang, Bok-Su; Moon, In-June; Lim, Myung-Jin; Kim, Se-Cheol; Kim, Soo-Sung; Lee, Jung-Won; Park, Hai-Woong; Koh, Jin-Hyun

doi:2014.32.2.174

JWJ > Volume 32(2); 2014 > Article

Research Paper

Journal of Welding and Joining 2014 April;32(2) :174-179.
Published online May 14, 2014.

doi:https://doi.org/10.5781/JWJ.2014.32.2.48

Heat Treatment Effect on Super Duplex Stainless Steel UNS S32750 FCA Multipass Welds

Bok-Su Jang^*, In-June Moon^*, Myung-Jin Lim^*, Se-Cheol Kim^*, Soo-Sung Kim^**, Jung-Won Lee^**, Hai-Woong Park^*, Jin-Hyun Koh^*

^*School of Energy․Materials․Chemical, Korea University of Technology and Education,Cheonan 330-708, Korea
^**Research Reactor Development Division, Korea Atomic Energy Research Institute, Daejeon 305-353, Korea

Correspondence: Jin-Hyun Koh Email: jhkoh@kut.ac.kr
Published online May 14, 2014

ABSTRACT

This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, 1230℃) on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the σ phase was formed in the welds heat treated at 930℃ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at 930℃ were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of 1050~1150℃.

Keywords: Super Duplex Stainless Steel | FCA multipass | PWHT | Pitting corrosicon | Mechanical properties