摘要
Abstract
To investigate the microstructural and mechanical properties of 1 000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering,the microstructure of different regions of the welded joint was characterized using scanning electron microscopy(SEM).Mechanical properties of the welded joint were determined through tensile testing,impact testing,and bending testing.The results reveals that,the weld metal of the root pass and fill passes is composed of columnar,dendritic,and equiaxed grains,with a microstructure dominated by acicular ferrite and a small amount of granular bainite.The heat-affected zone(HAZ)exhibits multiple typical regions,including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction.Away from the weld,fine grain zones and critical zones are observed,with a microstructure primarily consisting of granular bainite,M-A constituents,and lath martensite.The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite.The HAZ of the cap pass includes coarse grain,fine grain,critical,and subcritical zones.Due to the absence of subsequent welding passes,no critical coarse grain zone is formed,and the microstructure is primarily composed of lath martensite,granular bainite,and M-A constituents.The average tensile strength of the welded joint reaches 980 MPa grade,the low-temperature impact absorption energy of the weld zone and the HAZ at-40℃is 118.7 J and 149.3 J(at T/4),67.0 J and 154.0 J(at T/2),respectively.No cracks appear in the lateral bending.关键词
埋弧焊焊接接头/扫描电镜/显微组织/力学性能Key words
submerged arc welded joints/SEM/microstructure/mechanical property
