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.