Investigation on microstructure and mechanical properties of NV E690 steel joint by laser-MIG hybrid welding

Hybrid laser-arc welding (HLAW) was carried out on 690 MPa high strength NV E690 steel plates of 15 min thickness using single-pass and double-pass welding processes. Fine weld joints with good performance were successfully obtained by double-pass HLAW. The weld bead characteristics, microstructure and mechanical properties (hardness, tensile strength, low-temperature impact toughness) were investigated. The porosity morphology and distribution were detected by the micro-CT. The results showed that the fusion zone was composed of martensite and ferrite. The average hardness value of the fusion zone was higher than that of the base material, but lower than that of the heat affect zone. The tensile strength of the welded specimens matched the strength of the BM. The ultimate tensile strength of the fusion zone exceeded 1100 MPa. The fracture mode of the welded specimens was ductile fracture. The average absorbed energy in the fusion zone at - 40 degrees C reached 46.02% that of the base material, higher than the industrial standard (35.8%). The fracture surface of double pass HLAW specimens presented a typical brittle fracture mechanism. The correlation between the microstructure features and mechanical properties of the weld bead was analyzed.