Influence of laser power on weld formation, microstructure, and mechanical properties of Q235B steel joined by Laser-CMT hybrid welding process

This study investigates the influence of laser power on weld formation, microstructure, and mechanical performance of 6-mm-thick Q235B steel joints fabricated by laser–CMT hybrid welding, combined with finite element thermal simulations. Results showed that increasing laser power decreased the cooling rate and promoted grain coarsening in all weld regions. The WZ consisted mainly of FA, FSP, FP, and bainite; the CGHAZ was dominated by Widmanstätten; while the FGHAZ contained refined ferrite–pearlite compared with the BM. EBSD analysis indicated that higher laser power enhanced texture intensity, while the fraction of HAGBs decreased from 69.8 % to 54.2 % and the KAM value dropped from 0.68° to 0.53°, reflecting a reduction in geometrically necessary dislocation density. At 5100 W, the joint exhibited optimal properties, with tensile strength of 730 MPa, elongation of 13.12 %, strength-ductility balance of 9.6 × 10³ MPa% and peak microhardness of 204.6 HV. These superior properties were attributed to defect-free weld morphology, moderate grain size, and a favorable balance of texture and grain boundary characteristics. Numerical simulations accurately reproduced thermal cycles and weld profiles, confirming that higher power extends cooling time and reduces cooling rate, thereby accelerating grain growth. Overall, appropriate heat input is essential for controlling microstructural evolution and achieving a superior strength–ductility synergy in laser–CMT hybrid welded joints.