Study on Microstructure and Properties of Cold Metal Transfer and Pulse Hybrid Welded Super Duplex Stainless Steel

• Published in: Steel research international Vol. 95; no. 7
• Main Authors: Zhang, Zhiqiang, He, Jiahuan, Lu, Xuecheng, Bai, Yujie, Xu, Lianyong, Wu, Dongquan, Qu, Sicheng, Han, Yongdian
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2024
• Subjects: Austenite; Base metal; Chromium nitride; cold metal transfer; Cold welding; Corrosion resistance; Duplex stainless steels; Ferrite; Fillers; Heat affected zone; Heat treating; Heating; Impact strength; impact toughnesses; Low temperature resistance; Microstructure; Numbering schemes; Phase ratio; Pitting (corrosion); pitting corrosion resistances; Precipitates; secondary phases; Stainless steel; Toughness; Weld metal; Welded joints
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202300846

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ2) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ2. Additionally, chromium nitride (Cr2N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr2N. Owing to the lower austenite content and Cr2N precipitation in the backing pass, its toughness (122.6 J cm−2) is found to be inferior to that of the filler pass (130.1 J cm−2). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number. In this article, the microstructure evolution, precipitation mechanism of γ2 and Cr2N, as well as the effect of microstructural difference on impact toughness and pitting corrosion resistance of duplex stainless steel welded joints are investigated. It is concluded that reheating is a crucial condition for the precipitation of γ2 and HAZ exhibits worst properties attributed to Cr2N and lower austenite content.