Insight into the effect of weld pitch on the microstructure-properties relationships of St 37/AISI 316 steels dissimilar welds processed by friction stir welding

This research aims to evaluate the effect of weld pitch on the microstructure and properties of St 37/AISI 316 steels friction stir welds. The microstructure and microtexture of the samples were studied by means of electron backscatter diffraction analysis. The mechanical behaviors of the weldments were also investigated by microhardness, shear punch testing, and uniaxial tensile testing. In addition, the corrosion behavior of the welds was also evaluated. It was observed that the weld pitch of 0.0830 or 0.0625 mm/rotation resulted in producing defect-free welds with acceptable tensile strength level. Moreover, hardness and shear strength of the weld zone were improved up to 57% and 74%, respectively as compared to the base metals. It was due to the grain refinement which occurred within the stir zones by activating the dynamic recrystallization mechanism. Initial texture components of the base metals were replaced by recrystallized texture components in the stir zones. Orientation of grains in the stir zones was found to be highly dependent on the weld pitch. Regarding the corrosion resistance, the obtained results revealed that stir zone of St 37 steel was the weakest part of the weldments. Overall, the weldment employing the weld pitch of 0.0625 mm/rotation was found to achieve superior microstructural features and optimum properties.

Automated summary

The study demonstrated that selecting a weld pitch of 0.0625 mm/rotation resulted in defect-free welds with significantly improved hardness and shear strength in the weld zone. The grain refinement within the stir zones and reorganization of initial texture components of the base metals were key factors contributing to these enhancements.