To clarify the possibility to maintain the retained austenite even in the joint area of the low-alloyed transformation induced plasticity-aided steel sheets, friction stir welding (FSW) was investigated with a special focus on the effects of the FSW tool rotation rate and initial microstructure on the microstructural evolution and mechanical properties. The experimental results clarified that the lower tool rotation rate and the use of a finer initial microstructure are preferable in order to obtain the retained austenite and the retained austenite obtained by FSW with preferable conditions contributed to maintaining both the strength and ductility of the joints.
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