球化退火冷却速率对SR19热作模具钢组织和硬度的影响  

Effect of Spheroidization Annealing Cooling Rate on Microstructure and Hardness of SR19 Hot-Working Die Steel

作　　者：李奎岑 吴日铭 周光富 陈雨飞 许艺 LI Kuicen;WU Riming;ZHOU Guangfu;CHEN Yufei;XU Yi(School of Materials Science&Engineering,Shanghai University of Engineering Science,Shanghai 201600,China;Hubei Rising Steel Co.,Ltd.,Huangshi 435000,China)

机构地区：[1]上海工程技术大学材料工程学院,上海201600 [2]湖北日盛科技有限公司,黄石435000

出　　处：《机械工程材料》2024年第6期55-61,共7页Materials For Mechanical Engineering

摘　　要：利用DEFORM软件模拟得到大尺寸(200 mm×800 mm×2 000 mm)SR19热作模具钢在退火降温过程中不同深度位置的温度场,根据降温曲线设计该钢小尺寸试样的球化退火工艺,如下:将试样加热至860℃保温2 h,分别以不同速率(15,30,45,60℃·h^(-1))缓冷至740℃保温4 h,再炉冷至500℃后空冷至室温。分析了冷却速率对试样组织和硬度的影响。结果表明:随着冷却速率增大,试样中的先共析铁素体含量和碳化物分布均匀程度均先减小后增大,球化率先保持平稳后快速下降,退火硬度先减小后增大;当冷却速率为45℃·h-1时得到的显微组织最佳,碳化物分布均匀,球化率较高,先共析铁素体含量较少且出现了硬度的回落。先共析铁素体产生的原因主要是退火过程中冷却速率的控制不当导致奥氏体优先转变为铁素体并保留在最终组织中。Temperature field at different depth positions of the large size(200 mm×800 mm×2000 mm)SR19 hot-working die steel during the annealing cooling process was simulated by using DEFORM software.According to the cooling curve,the spheroidization annealing process of the small size steel specimens was designed,that was,heating the sample to 860℃and holding for 2 h,slow cooling at different rates(15,30,45,60℃·h^(−1))to 740℃,respectively,holding at 740℃for 4 h,then cooling to 500℃in furnace and then air cooling to room temperature.The effect of cooling rate on the microstructure and hardness of specimens was analyzed.The results show that with the increase of cooling rate,the content of proeutectoid ferrite and the uniformity of carbide distribution in the specimen both decreased first and then increased,the spheroidization rate first remained stable and then rapidly declined,and the annealed hardness first decreased and then increased.When the cooling rate was 45℃·h^(−1),the microstructure was the best;the distribution of carbides was uniform,the spheroidization rate was relatively high,the content of proeutectoid ferrite was relatively low and there was a fallback in the hardness.The reason for the precipitation of proeutectoid ferrite was mainly due to the improper control of the cooling rate during annealing,which led to the preferential transformation of austenite into ferrite and retention of ferrite in the final microstructure.

关 键 词：热作模具钢 球化退火 先共析铁素体 冷却速率 球化率 

分 类 号：TG161[金属学及工艺—热处理]