Effects of strain rate and welding current mode on microstructural properties of SUS 304L PAW welds

This paper uses a compressive split-Hopkinson bar and transmission electron microscopy (TEM) to investigate the impact properties and residual microstructures of Plasma Arc Welded 304L SS weldments. The current specimens were fabricated using either a continuous current (CC) or a pulsed current (PC) welding mode and were then deformed at strain rates ranging from 10−3 s−1 to 7.7 × 103 s−1 at room temperature. The impacted specimens were polished and etched and then analysed using TEM to investigate the correlation between their dynamic mechanical response and the microstructural evolution of dislocations, mechanical twins and α′ martensite structures. The results showed that the microstructural characteristics of the weldments were influenced both by the strain rate and by the welding current mode. Comparing the evolution of the microstructure in the base metal and the fusion zone, it was found that a higher dislocation density existed in the fusion zone, while a larger volume fraction of α′ martensite and a greater twinning density were present in the base metal. Furthermore, for both welding current modes, the dislocation density and volume fraction of α′ martensite were found to increase with increasing strain rate, whereas the twinning density reduced. Microstructural analysis revealed that the number of dislocations, twins and α′ martensite structures varied as an increasing function of the work-hardening stress. Finally, it was determined that the microstructure of the PC weldments enhanced the dynamic impact response.