Analysis on joint softening for JFE980S high strength steel

The softening problems in the joints of low alloy high strength steel JFE980S by laser-MAG hybrid welding and MAG welding were studied.The softening law and mechanism for the quenched and tempered low alloy high strength steel joints were discussed according to the results of tensile test,hardness test and microstructure analysis.The result indicated that the joints by MAG welding are seriously softened,but the joints by laser-MAG hybrid welding only are softened a little.And the softened zone width and the softened degree of the joints by laser-MAG hybrid welding are both smaller and lower than those of the joints by MAG welding.The softening mainly appears in over-tempering zone and incomplete normalizing zone in the HAZ.And the distribution of granular or nubbly microstructure along the grain boundaries is the main reason of the softening.