Effects of different laser welding parameters on the microstructural and mechanical properties of an advanced dual phase steel grade

Purpose: Effects of different laser welding parameters on microstructure and mechanical properties were investigated in order to observe the suitable welding parameter ranges for an advanced dual phase steel grade. Theory and Methods: Sheets of dual phase steel were welded with butt-joint using a 3kW fiber laser welding system. Tensile tests, microhardness measurements and microstructural investigation via optical and scanning electron microscopy were performed to examine the weld metal, heat affected zone and base metal. Results: Two laser welding trials resulted in weldments with full weld penetration and higher mechanical performance than the base metal. In other trials, in strong correlation with mechanical test results and microstructural examination findings, it is observed that the amount and fine grain structure of hard phases trigger the brittle fracture. Conclusion: All results are correlated with laser welding process parameters and parameter range towards optimum process is observed. It is also confirmed that laser power and laser weld speed are critical parameters which directly affect welded sheet product performance and should be determined correctly to obtain good quality welding. Laser welding in narrower process parameter ranges and investigation of the material performance under dynamic loading conditions might be suggested as future extensions of this study.