Ductile-brittle Transition Behavior Of Heat-affected Zone In Copper Precipitation Strengthening Steel

Copper Precipitation Strengthening Steel is ship hull steel of high strength, high toughness and good weldability. It has lower carbon content (below 0.06%) and copper content exceeds 1%, which is different from quenched and tempered high tensile strength steel. Copper Precipitation Strengthening Steel mainly utilizes deposit strengthening ofε-Cu in aging process to cover loss of strength by carbon drop. By the mode of copper deposit aging strengthening changed traditional mode of carbon deposit strengthening, reduced carbon content and carbon equivalent of steel, and obviously improved weldability.Cu of heat-affected zone(HAZ) can be dissolved at high welding heat-input,which makes property of HAZ change. Variable trend of HAZ property of Copper Precipitation Strengthening Steel at different heat-input was investigated in this paper.Property influences of heat-input to simulated Coarse Grain HAZ and Incomplete Recrystallization HAZ of Copper Precipitation Strengthening Steel were also investigated by thermal simulation method, and mainly analyzed relation between toughness and microstructure of Coarse Grain HAZ. The results indicated emerging M-A constituent in ferrite matrix by increasing heat-input, which reduced low-temperature toughness in Coarse Grain HAZ of Copper Precipitation Strengthening Steel.TheⅡ-type groove was adopted in welding plates to obtain relative flat heat-affected zone, and separately adopted instrumented impact test and drop weigh tearing test to investigate the behavior of ductile-to-brittle transition in actual HAZ. The results indicated that low-temperature toughness of HAZ was reducing by increasing heat-input. But it still had relative high impact value at -40℃on condition of heat-input above 50KJ/cm and can meet operating requirements.