Journal of Welding Science

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Tehrani-Moghadam H, Jafarian H, Aghazadeh Ghomi M, Heidarzadeh A. Effect of friction stir welding on microstructure, phase transformations, and mechanical properties of austenitic Fe-24Ni-4Cr steel. JWSTI 2025; 11 (1) :111-121
URL: http://jwsti.iut.ac.ir/article-1-489-en.html

In this study, the effect of friction stir welding on the microstructure and mechanical properties of Fe-24Ni-4Cr austenitic steel was investigated. For this purpose, a sheet with a thickness of 1 mm was subjected to friction stir welding using a WC-5%Co tool at a traverse speed of 100 mm/min and a tool rotational speed of 450 rpm. Electron backscatter diffraction (EBSD) analysis revealed that this process led to grain refinement and an increase in high-angle grain boundaries in the stir zone, attributed to dynamic recrystallization during welding. Phase maps indicated an increase in the BCC phase fraction in the stir zone compared to the base metal. Given the high strain rate and the presence of stabilizing elements, this phase was primarily strain-induced martensite. Mechanical property assessments showed a significant increase in the tensile strength of the stir zone (450 MPa) compared to the base metal (350 MPa). Moreover, the yield strength of the stir zone (388 MPa) was substantially higher than that of the base metal (145 MPa), which can be attributed to grain refinement, an increase in high-angle grain boundaries, a higher dislocation density, and martensite formation. However, the ductility of the stir zone decreased due to higher stress concentration and dislocation density in this region. These findings suggest that friction stir welding can be an effective method for enhancing the strength and hardness of austenitic steels, but process conditions must be carefully controlled to prevent reductions in toughness and ductility.