The effects of heat treatment conditions on the microstructures and mechanical properties of low activation steel with Y, Zr and Ti were investigated. Two heat treatment processes are designed to control the microstructure and carbides in the steels, by pre-tempering and repetition of normalizing. The higher the pre-tempering temperature is, the higher the yield strength is. With the increase of pre-tempering temperature, the residual stress in steel decreases. The average diameter of M₂₃C₆ phase in the steel reduced from 141 to 130 nm, and the microstructure is full martensite. When the pre-tempering temperature is 500 °C, the yield strength of the steel is 663 MPa, the ductile-brittle transition temperature (DBTT) of the steel is − 61 °C. Double normalizing has a significant effect on the microstructure and precipitated phase of steel. The microstructure of the steel is sorbite, and the size of M₂₃C₆ in the steel is reduced to 93-102 nm. The size of MX increases to 23-26 nm. With the increase of the second normalizing temperature, the size of MX increases and the size of M₂₃C₆ decreases. MX preferentially precipitates, reducing the carbon in the matrix, thereby inhibiting the precipitation of M₂₃C₆. The yield strength of 1050 °C × 30 min (normalizing) + 950 °C × 30 min (normalizing) + 425 °C × 30 min (pre-tempering) + 750 °C × 90 min (tempering) experimental steel is 693 MPa, and the DBTT is − 99 °C. The refinement of M₂₃C₆ and the increase of MX volume fraction strengthen the precipitation strengthening effect. Double normalizing has a significant effect on the ductile-brittle transition temperature (DBTT) of the experimental steel. The change trend of DBTT of different heat treatment samples is consistent with the change trend of fracture strength caused by M₂₃C₆ calculated by improved Griffith model. M₂₃C₆ is the main reason for the change of impact property of steel.

研究了热处理条件对含Y、Zr、Ti低活化钢显微组织和力学性能的影响。设计了两种热处理工艺，通过预回火和重复正火来控制钢中的微观结构和碳化物。预回火温度越高，屈服强度越高。随着预回火温度的升高，钢中的残余应力减小。钢中M ₂₃ C ₆相平均直径由141 nm减小至130 nm，显微组织为全马氏体。当预回火温度为500℃时，钢的屈服强度为663MPa，钢的韧脆转变温度（DBTT）为-61℃。二次正火对钢的显微组织和析出相有显着影响。钢的显微组织为索氏体，钢中M ₂₃ C ₆尺寸减小至93-102 nm。 MX的尺寸增加到23-26 nm。随着第二次正火温度的升高，MX尺寸增大，M ₂₃ C ₆尺寸减小。 MX优先沉淀，减少基体中的碳，从而抑制M ₂₃ C ₆的沉淀。 1050℃×30min（正火）+950℃×30min（正火）+425℃×30min（预回火）+750℃×90min（回火）实验钢屈服强度为693MPa ，DBTT 为 − 99 °C。 M ₂₃ C ₆的细化和MX体积分数的增加增强了沉淀强化效果。二次正火对实验钢的韧脆转变温度（DBTT）有显着影响。不同热处理样品的DBTT变化趋势与改进Griffith模型计算的M ₂₃ C ₆引起的断裂强度变化趋势一致。 M ₂₃ C ₆是钢冲击性能变化的主要原因。