Experimental and statistical investigation of laser welding with different joint gap widths for HSLA steel

Automated Ytterbium (Yb) single pass fiber laser beam welding of High Strength Low Alloy (HSLA) steel is an expensive process, so it's a need for machining process for butt joint preparation (CNC Milling and Grinding Machining) to make it less expensive to get the same material strength after constant varying joint gap. This study aims to optimize input parameters (fixed (Power and Speed), variable (Butt Joint Gap, and Focal Length)) with respect to output parameters (Distortion, Ultimate Tensile Strength (UTS), Residual Stresses (RS)) for a 4.5 mm thick 30CrMnSiA steel. Experiments and statistical modelling (using Design of Experiment) has been performed on 0–0.5 mm butt joint gap with 0.1 mm incremental size and without filler wire. The results showed that less percentage error in distortion, UTS and RS, which are 8.19 %, 2.38 % and 6.08 % respectively. In addition, 0.2–0.4 mm joint gaps show better tensile properties and almost equal to 95 % of base material (BM), by failure appearing on the BM (aside weld) due to annealed material condition. Micro-hardness measured at the fusion zone (max. 617 HV) was almost 3 times that of the base metal (max. 208 HV). Metallography study shows that fusion zone is consisted of martensite structure due to high cooling rate during laser beam welding process, so it has more strength as compared to other two zones (Heat affected zone (HAZ) and base material). Moreover, fractured tensile sample fractography study shows the ductile behavior of failure due to presence of dimples and voids.