冷却速度对SA508-3钢显微组织r与力学性能的影响

摘要

The thermal dilatometric curves of SA508-3 steel during the cooling process from 890℃ to room temperature with different cooling rates have been measured. The types of phase transformation at different cooling rates were determined by analyzing the thermal dilatometric curves and microstructure observed by optical microscopy (OM)and scanning electronic microscopy (SEM). It is found that ferrite,pearlite and bainite transformation occurs when cooling rate is during 0. 01 ～0. 05℃/s;Bainite transformation occurs when cooling rate is during 0. 1 ～5℃/s;Martensitic transformation occurs when cooling rate is during 10～50℃/s. Furnace cooling,sand cooling and oil cooling have been used to simu-late different cooling rates of different locations in a large forging,the microstructure and mechanical properties of the 3 specimens were tested after 880℃ × 1 h quenching+640℃ × 2h tempering. The experimental results indicate that with the increase of cooling rate,the type of microstructure changed from ferrite and pearlite to bainite and martensite. A good combination of strength and low temperature impact toughness can be obtained under the condition of faster cooling rate. However,both the strength and impact toughness of the ma-terial decrease as the cooling rate decreases.%利用快速热膨胀仪测得SA508-3钢奥氏体化后以不同冷速冷至室温的热膨胀曲线,通过切线法分析热膨胀曲线并结合金相显微镜(OM)、扫描电子显微镜(SEM)观察不同冷速下材料的显微组织,确定了不同冷速条件下SA508-3钢的相变类型.发现冷却速度在0.01～0.05℃/s时,发生铁素体相变、珠光体相变和贝氏体相变;冷却速度在0.1～5℃/s时,发生贝氏体相变;冷却速度在10～50℃/s时,发生马氏体相变.使用炉冷、砂冷、油冷三种冷却方式模拟大型锻件不同部位的冷却条件,并测试了不同冷却方式下材料经880℃ ×1 h淬火+640℃ ×2 h回火处理后的力学性能.结果表明:随着冷却速度的增加,显微组织的类型逐渐从铁素体、珠光体组织变为贝氏体和马氏体组织.较快冷速条件下,SA508-3钢可以达到强度和低温冲击韧性的良好结合,而随着冷速降低,材料的强度和冲击韧性同时下降.