Effects of TIG Reheating on Duplex Stainless Steel Weld Microstructure

Abstract

Duplex stainless steels (DSS) gaining their excellent mechanical properties and corrosion resistance due to their austenitic-ferritic microstructure, ideally in the same amount. However, to keep this ideal phase ratio during arc welding is very difficult. Generally, the arc welding processes will result in more ferritic microstructure in the weld metal and in the heat affected zone, due to the rapid cooling. The ferritic microstructure can cause chromiumnitride precipitation, because the nitrogen solubility in ferrite phase is very low below 700 °C. These chromiumnitride precipitations can cause loss of corrosion resistance and mechanical properties. However, during subsequent reheating, the chromium-nitrides can dissolve and act as a secondary austenite nucleation site in the ferritic microstructure. In our research we welded DSS specimen autogenously, with tungsten inert gas welding using pure argon and 94 % argon + 6 % nitrogen as shielding gasses. In the first case the sub-sequent solid-state reheating caused 20 % increase in the austenite fraction of the weld metal but with the use of mixed shielding gas only 5 % increase.

Microstructure and mechanical properties of TOP-TIG-wire and arc additive manufactured super duplex stainless steel (ER2594)

“…A certain amount of work, in the field of welding duplex stainless steels, has devoted constructive research in the microstructure evolution after reheating the fusion region [25][26][27] and the heat affect zone (HAZ) [19,28,29]. It was found that secondary austenite generated both in the reheating fusion region and the reheating HAZ in the form of intragranular γ 2 and intergranular γ 2 .…”

Microstructural Evolution and Its Influence on Low‐Temperature Toughness of Simulated Heat‐Affected Zone in Super Duplex Stainless Steel Welded Joint

“…It has been reported by Chenhua, [15] Zhang, [4] and Ramirez [16] that the selective corrosion of γ 2 in the HAZ resulted from the lower Cr and Mo content of the γ 2 compared with the ferrite and γ 1 . Our research team [17][18][19] and other researchers [9,20,21] previously carried out lots of studies on how to promote more austenite formation and inhibit Cr 2 N and γ 2 precipitation in the HAZ of DSS welded joint by changing welding methods, optimizing welding DOI: 10.1002/srin.202300460…”

“…It has been reported by Chenhua, [ 15 ] Zhang, [ 4 ] and Ramirez [ 16 ] that the selective corrosion of γ 2 in the HAZ resulted from the lower Cr and Mo content of the γ 2 compared with the ferrite and γ 1 . Our research team [ 17–19 ] and other researchers [ 9,20,21 ] previously carried out lots of studies on how to promote more austenite formation and inhibit Cr 2 N and γ 2 precipitation in the HAZ of DSS welded joint by changing welding methods, optimizing welding process, and alloying treatment. The latest research [ 22–24 ] showed that the austenite content in the HAZ can be increased to above 30% by using hybrid welding technique, N 2 addition into shielding gas, or postweld heat treatment.…”