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采用扫描电镜(SEM)、透射电镜(TEM)、拉伸试验及示波冲击试验研究了淬火和回火热处理对X100管线钢组织和性能的影响。结果表明:450℃回火后,实验钢的屈服强度(Rt0.5)由785 MPa降低至731 MPa,抗拉强度(Rm)由845 MPa提高至931 MPa,强度及塑韧性改善。板条贝氏体(LB)板条结构弱化,粒状贝氏体(GB)体积分数增加,马氏体/奥氏体(M/A)组元细化至亚微米级。针状铁素体(AF)的回火稳定性高于LB和GB;940℃淬火+450℃回火实验钢的Rt0.5为819 MPa,Rm为893 MPa,Rt0.5/Rm为0.92,A50为33.5%,强韧性提高。淬火和回火对实验钢冲击断裂过程的脆性裂纹扩展能(E3)和脆性裂纹扩展止裂能(E4)改善效果好于450℃回火。实验温度降低,止裂性的改善效果变差。LB、GB和平行排列的M/A组元将原始奥氏体晶粒分割细化,亚微米级M/A组元的分布差异使铁素体晶粒内不同区域呈现LB和GB组织形态。
The effects of quenching and tempering heat treatment on microstructure and properties of X100 pipeline steel were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile test and oscillometric impact test. The results show that after tempering at 450 ℃, the yield strength (Rt0.5) of the experimental steel decreases from 785 MPa to 731 MPa, the tensile strength (Rm) increases from 845 MPa to 931 MPa, and the strength and toughness of the steel decrease. The lath structure of lath bainite (LB) is weakened, the volume fraction of granular bainite (GB) increases, and the martensite / austenite (M / A) component is refined to submicron order. The tempering stability of acicular ferrite (AF) is higher than that of LB and GB. The tempering temperature of 940 ℃ and tempering at 450 ℃ is 819 MPa, Rm is 893 MPa, Rt0.5 / Rm is 0.92, A50 33.5%, increased toughness. The effect of quenching and tempering on brittle crack propagation energy (E3) and brittle crack arrest crack energy (E4) during impact fracture of experimental steels is better than that of 450 ℃ tempering. The experimental temperature is lowered, and the effect of improving the anti-cracking property is deteriorated. LB, GB and M / A elements arranged in parallel refine the original austenite grains. The distribution of submicron M / A elements presents the LB and GB morphologies in different regions of the ferrite grains.