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研究了双相区保温温度对9Ni钢组织和力学性能演变的影响规律,分析了双相区热处理的增韧机理。结果表明:在双相区670℃左右保温淬火回火后,成品板的屈服强度可达到600 MPa以上,-196℃横向冲击功高达249 J且塑性最佳。显微组织分析结果发现,670℃条件下部分区域内的马氏体板条间形成了γ相,有利于淬火后提高材料平均晶界取向差并增加逆转奥氏体(γ’)的形核点。讨论了9Ni钢双相区热处理的增韧机理:材料平均取向差增加,晶粒得到有效细化,使得基体钝化裂纹和增加裂纹扩展路径作用强化;γ’量(体积分数)增加、碳过饱和度降低使得材料塑性增加,这有利于扩大裂纹前端塑性形变区以实现增韧。碳过饱和度降低时仍能保持高强度的原因在于双相区保温过程中细化了组织,通过细晶强化予以补偿。
The effect of holding temperature in two-phase zone on the microstructure and mechanical properties of 9Ni steel was studied. The toughening mechanism of heat treatment in two-phase zone was analyzed. The results show that after quenching and tempering at about 670 ℃ in the dual-phase zone, the yield strength of the finished plate can reach more than 600 MPa, and the transverse impact energy at -196 ℃ reaches as high as 249 J with the best plasticity. The results of microstructure analysis showed that the γ phase was formed between the martensite laths in some areas at 670 ℃, which was advantageous to improve the average grain boundary orientation difference and increase the nucleation of reversed austenite (γ ’) after quenching point. The toughening mechanism of the heat treatment in 9Ni steel is discussed: the average orientation difference of the material increases, the grains are effectively refined, the matrix passivation crack and the crack propagation path are strengthened, the γ ’content (volume fraction) Saturation decreases the material plasticity increases, which is conducive to expanding the crack front plastic deformation zone to achieve toughening. The reason why the high degree of carbon supersaturation decreases while maintaining high strength is that the microstructure is refined during the heat preservation in the dual phase zone and compensated by the grain refinement.