On the Microstructural Transformations and Mechanical Performance of Laser Beam Welded UNS S43000 Ferritic Stainless Steel

As regards significance of phase transformations and nature of phases developed as well as their affective role in the physical and mechanical properties and also corrosion resistance of ferritic stainless steel (FSS) welds, this paper wishes to investigate phases identification by means of electron backscattered diffraction (EBSD) analysis and mechanical performance via tensile test. For this goal, the sheets of FSS were prepared for the lap joints and successively, were welded by laser beam welding process under different pulse durations. No welding defects such as porosity, crack, etc., were seen, exhibiting prosperous joining process. Optical microscopy and EBSD corroborated the attendance of low-temperature (LT) and high-temperature (HT) heat-affected zone (HAZ). Fine-grained ferrite, intergranular martensite, as well as carbide precipitates were characterized in the LTHAZ, because of rapid cooling from the \(\delta +\gamma +{{\text{C}}}_{1}\) $\delta +\gamma +{\text{C}}_1$ zone. Whereas, the HTHAZ was composed of coarse-grained ferrite and intergranular martensite by way of quenching from the \(\delta +\gamma\) $\delta +\gamma$ zone. Phases characterization could show that the fusion zone (FZ) also had extremely coarsened ferrite and martensite at the grain boundaries. Grain coarsening might be responsible for weak crystallographic texture in this zone. The minimum and maximum microhardness allocated to the FZ and LTHAZ which were 174 \(\pm\) $\pm$ 5 HV and 261 \(\pm\) $\pm$ 11 HV, respectively. Founded on the tensile testing, it was apprehended that an increase in the pulse duration from 12 to 15 ms promoted the failure load and energy absorption by almost 13 and 327%, respectively. This was caused by joints strengthening through enhancing the weld penetration. However, an increase in the pulse duration from 15 to 18 ms resulted in degrading the failure load and energy absorption by around 31 and 95%, respectively. This arose from joints weakening due to intensifying grain coarsening phenomenon in the weld zone.