Friction stir welding(FSW) was performed for 4mm thick T4003 ferritic stainless steel(FSS) with different welding parameters. The effect of welding parameters on microstructure, hardness distribution, and impact toughness of FS-welded joints at room temperature and low temperature was investigated. The results show that the stir zone(SZ) and the thermo-mechanically affected zone (TMAZ) consist of duplex structure of ferrite and martensite. The SZ is heterogeneous along the thickness of the joint and this trend gets more obvious with the decrease of rotational speed and increase of welding speed. In the heat affected zone(HAZ) of the advancing side, the microstructure transits smoothly and no obvious characteristics of deformation and elongation as the rotational speed increases to 250r/min from 150r/min. The hardness distribution of the weld is relatively uniform and the maximum hardness is 290HV, approximately 1.87 times than that of the base material(BM). The welding parameters and temperature exert great effect on the impact absorbing energy of the welded joint. The impact absorbing energy of HAZ and SZ are up to 90%-92%, and 85%-103% of BM, respectively, at room temperature(20℃). While at low temperature(-20℃), the impact absorbing energy of HAZ and SZ reaches 87%-97%, and 82%-95% of BM, respectively. It shows that the weld zone still has better matching between strength and toughness.
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