低屈强比石油套管用700 MPa级钢的开发

Development of 700 MPa-grade Steel of Low Yield Ratio for Oil Casing

研制了低屈强比石油套管用700 MPa级钢,其化学成分为0.10%~0.15%C、1.20%~1.60%Mn、0.25%~0.40%Si、0.03%~0.08%Ti、0.018%~0.030%N、≤0.012%S、≤0.020%P(质量分数),Fe含量。钢板的热轧工艺参数为:粗轧累计压下量70%~78%,精轧累计压下量70%~88%,终轧温度780~850℃。轧后两段冷却,以有效控制钢板的铁素体、贝氏体和珠光体含量。检测了钢板的显微组织、力学性能和焊接性能。结果表明:钢板的抗拉强度大于710 MPa,屈服强度大于420 MPa,屈强比不大于0.70,满足API Spec 5CT要求。钢板的显微组织由多边形铁素体、珠光体及贝氏体组成,焊接接头的焊缝组织均匀,焊接性能优良,可应用于实际工程。

A 700 MPa-grade steel of low yield ratio reserved for oil castings,containing 0.10%to 0.15%C,1.20%to 1.60%Mn,0.25%to 0.40%Si,0.03%to 0.08%Ti,0.018%to 0.030%N,≤0.012%S,≤0.020%P by mass,allowance of Fe was developed.Process parameters for hot-rolling were as follows:cumulative rough rolling reductions of 70%to 78%,cumulative finish rolling reductions of 70%to 88%,finishing temperatures of 780℃to 850℃.Two-stage cooling process was used after rolling to effectively control the contents of ferrite,bainite and pearlite in the finished steel plate.The steel plate was subjected to microstructure survey,mechanical property and weldability measurements.The results indicated that the tensile strength was higher than 710 MPa,the yield strength higher than 420 MPa,and the yield ratio up to 0.70,fitting with the API Spec 5CT requirements.In addition,the steel plate showed the microstructure consisting of polygonal ferrite,pearlite and bainite,uniform weld structure and excellent weldability,being applicable to practice.