Physical simulation of low temperature phase separation during multipass welding of super duplex stainless steel

Abstract

This study aimed to investigate the degree of low-temperature phase separations and 475 °C -embrittlement in physically simulated multipass super duplex stainless steel (SDSS) welds. A single bead weld was produced using gas metal arc welding and multiple thermal cycles with different peak temperatures were applied using a Gleeble physical simulator with fixed and moving jaws to simulate the influence of constrained designs, to mimic the welding of thick SDSS components. The samples were studied using atom probe tomography and the results were correlated with toughness and ferrite microhardness. The results showed that the microhardness of the ferrite in the constrained simulated multipass reheated weld increased from 304 HV to 374 HV after 5 min aging at 475 °C. The amplitude of the Cr concentration of the same sample, showing the level of Fe-Cr phase separation, increased from 1.025 to 1.045 after 5 min aging at 475 °C. Despite the clear development of phase separation in the ferrite, the toughness did not drop. It can be concluded that reheated SDSS welds are not susceptible to 475 °C -embrittlement during short fabrication times of up to 5 min for the austenite level of 50%.

Keywords:

• super duplex stainless steel
• multipass welding
• 475 °C -embrittlement
• spinodal decomposition

Acknowledgment

The author would like to dedicate this article to Prof. Leif Karlsson for more than 30 years of his great contribution to welding science and technology of stainless steels.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors would like to thank Kjell Hurtig from University West for their support during heat treatment and welding. The authors would like to acknowledge University West, ESAB AB, Bodycote, and Outokumpu Stainless AB for partnership in “ALWAYS project” funded by KK-Stiftelsen. The APT was performed in Chalmers Materials Analysis Laboratory (CMAL).