Effect of heat input on microstructure and properties of coarse-grain heat affected zone in duplex stainless steel

Against the backdrop of growing demand for high-efficiency welding technologies in large-scale manufacturing, economical S32101 duplex stainless steel has demonstrated significant potential in heavy equipment manufacturing due to its excellent performance. However, the challenge of achieving desirable strength-toughness balance in the welded joint caused by high welding heat input remains a key constraint on its application. In order to systematically reveal the effect of heat input on the microstructure and properties of coarse grain heat affected zone（CGHAZ） of economical S32101 duplex stainless steel, the microstructure evolution, strengthening and toughening mechanism of CGHAZ in economical S32101 duplex stainless steel under different heat input were analyzed by means of thermal simulation test machine, electron backscatter diffraction（EBSD） and transmission electron microscopy（TEM）. The results show that the microstructure of CGHAZ in economical S32101 duplex stainless steel consists of austenite（γ-Fe）, ferrite（α-Fe）, and Cr₂N precipitates. The austenite phase exhibits three morphologies, that is grain boundary austenite（GBA）, Widmanstätten austenite（WA）, and intragranular austenite（IGA）. As the heat input increases from 20 kJ/cm to 100 kJ/cm, the proportion of austenite phase shows an increasing trend, and its average grain size gradually increases. At heat input of 100 kJ/cm, the ratio of ferrite to austenite in the CGHAZ microstructure approaches balanced state of nearly 1∶1. The increase in austenite content promotes higher proportion of nitrogen atoms in solid solution, effectively suppressing the precipitation of Cr₂N. The CGHAZ of economic S32101 duplex stainless steel exhibits the best comprehensive mechanical properties at heat input of 100 kJ/cm, with product of strength and elongation of 19. 63 GPa·%, yield ratio of 0. 76, and low-temperature impact energy of 48 J. The strengthening mechanism of CGHAZ arises from the synergistic effects of grain refinement strengthening, dislocation strengthening, and second-phase strengthening, while the toughening mechanism is influenced by the combined effects of second-phase morphology, austenite morphology, and austenite grain size.