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研究了一种Mn-Nb-B系低碳贝氏体钢,在MMS-300多功能热力模拟试验机上模拟不同的TMCP工艺制度,分析试验钢的显微组织及硬度,从而确定该试验钢最佳TMCP参数组合。变形量为15%、30%和50%时,试验钢相变组织均为单相粒状贝氏体。变形量为50%时,其显微组织均匀细小,硬度较高;变形温度为880、850、820、780℃时,试验钢相变组织都是以粒状贝氏体为主,变形温度较高时,组织较粗大。变形温度较低时,组织中铁素体较多,中间变形温度为850℃时,组织为均匀细小的粒状贝氏体,硬度较高;终冷温度为600、550、500、400℃时,相变组织都是铁素体和粒状贝氏体。终冷温度越低,组织越细小,但在400℃出现板条贝氏体,在终冷温度为500℃时,组织为均匀细小的粒状贝氏体,硬度也较高。最终确定该试验钢最佳的TMCP工艺参数为:变形量50%、变形温度850℃、终冷温度500℃。
A kind of Mn-Nb-B series low-carbon bainitic steel was studied. Different TMCP process systems were simulated on a MMS-300 multi-functional thermal simulation machine to analyze the microstructure and hardness of the test steel. Good TMCP parameter combinations. When the deformation is 15%, 30% and 50%, the phase transformation microstructure of the test steel is single-phase granular bainite. When the deformation is 50%, the microstructure is fine and uniform, and the hardness is high. When the deformation temperature is 880, 850, 820 and 780 ℃, the phase transformation microstructure of the test steel is mainly granular bainite and the deformation temperature is high When the organization is larger. When the deformation temperature is lower, the ferrite is more in the microstructure. When the intermediate deformation temperature is 850 ℃, the microstructure is uniform fine granular bainite with higher hardness. When the final cooling temperature is 600, 550, 500 and 400 ℃, Variable organizations are ferrite and granular bainite. The lower the final cooling temperature, the finer the structure. However, the lath bainite appears at 400 ℃. When the final cooling temperature is 500 ℃, the microstructure is uniform and fine granular bainite with higher hardness. Finally, the optimum TMCP process parameters of this test steel are determined as follows: deformation amount 50%, deformation temperature 850 ℃ and final cooling temperature 500 ℃.