Study On The Laser Welding Technology Of Q890 Hsla Steel And Its Property

Low alloy high strength(HSLA)steel is widely used in engineering machinery for its excellent toughness and strength.Generally,the application of Q890 steel was about 16 mm thick and welded by multi-layer multi-pass electric arc welding which led to the low machining efficiency and produced multiple sandwich structures in welding joints.In this research,16 mm thick Q890 low alloy high strength steel plate was welded by multi-layer and multi-pass arc welding,laser welding and laser welding with filling wire respectively.By evaluating the microstructure,hardness,tensile and Charpy impact performance of the three joints,the optimum welding method and process were attempted to obtain the comprehensive performance of the joint.The sound joint was successfully made by adopting the multi-layer and multi-pass electrical arc welding(21passes).The weld formation was good and had no obvious defects.But the profile of the weld metal was quite wide(average 15.4 mm).The width of heat affected zone(HAZ)was 2.2 mm.Single pass laser welding with full penetration was directly conducted on the 16 mm thick plate.Welding bead with maximized 9.5mm width was obtained without obvious defects.But the total width of HAZ is pretty large(maximum 4.2 mm).The hardness presented large fluctuation with maximized 465 HV and minimum 338 HV respectively.The elongation rate of the laser welding joint were about 8% and the Charpy impact energy values of WM and HAZ were 16.4J and 18.5J respectively.The mechanical properties could meet the requirement.Laser welding with multi-pass filling wire was conducted based 2.5mm and 5mm gap size respectively instead of single laser welding.The size of hardening and softening zone was reduced by lower heat input laser welding with filling metal.The average width of HAZ was 1.2 mm in 2.5 gap and 1.9mm in 5mm gap.The maximized hardness was 485 HV and 482 HV and the minimum was 333 HV and 323 HV respectively.The average width of softening zone was 0.8 mm and minimum hardness was323 HV.The tensile properties could meet the standard requirement.The elongation rate was 10.5% and 7.6% respectively in 2.5mm and 5mm gap.The Charpy impact energy values of HAZ were 13.5J and 13.0J respectively.The weld seam was 19.1J and 17.8J separately.Comparably,the profile of weld seam was better in 2.5mm gap size.Finally,Laser welding with filling wire could both increase the elongation of the joint significantly and obtain better comprehensive performance without damage the impact of HAZ and tensile properties.The paper supplied the theory and technical evidence for Q890 HSLA application.