Microstructure evolution and mechanical properties of friction stir welding super-austenitic stainless steel S32654

Publication date: 15 March 2017
Source:Materials & Design, Volume 118
Author(s): Huabing Li, Shouxing Yang, Shucai Zhang, Binbin Zhang, Zhouhua Jiang, Hao Feng, Peide Han, Jizhong Li
Super-austenitic stainless steel S32654 sheets with 2.4mm thickness were successfully welded by friction stir welding (FSW) at the rotational speeds of 300 and 400rpm with a constant traverse speed of 100mm/min using W-Re tool. The sound joints with almost no nitrogen loss were successfully produced. The microstructure evolution was characterized by optical digital microscope (ODM), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron backscatter diffraction (EBSD) and transmission electron spectroscopy (TEM). The results suggest that the grain structure evolution in stir zone (SZ) is dominated by continuous dynamic recrystallization (CDRX). The strain rate plays a dominated effect on obvious grain refinement. The band structures containing W and Re are generated due to the wear between tool probe and steel in SZ. Furthermore, the microhardness measurements and transverse tensile tests indicate that the grain refinement combining with high density dislocations and substructures improves the hardness and strength, but greatly reduces the plastic deformation capacity of joints. The more suitable welding parameters are determined as 300rpm and 100mm/min for this steel.

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