Abstract: 1 000 MPa high-strength steel plates for construction machinery are welded by metal active gas(MAG) welding method with GHS90 welding wire as filler material and the weld joints are treated at 250 ℃, 480 ℃, 600 ℃ for 2 h, respectively. Microstructure and mechanical properties of welded joints with different post weld heat treatment (PWHT) is analyzed by tensile test, microhardness measurement, optical microscope(OM), scanning electron microscope(SEM), transmission electron microscopy(TEM) and electron back-scattered diffraction(EBSD). The results show that with the increase of PWHT temperature from 250 ℃ to 600 ℃, the average strength of welded joint reduces from 1 014.5 MPa to 934.5 MPa and the average –20 ℃ impact absorbing energy of weld metals decreases from 66 J to 24 J. With higher PWHT temperature, larger bainitic lath and coarser carbide precipitates result in lower toughness of weld metal. Meanwhile, the size of effective grains becomes larger and the density of high-angle grain boundary is decreased, which led to the degradation of impact property of weld metal.

Key words: 1 000 MPa high-strength steel, carbide, high-angle grain boundary, impact property, post weld heat treatment