Cr-Ni-Cu桥梁耐候钢的连续冷却相变及其组织和硬度

为了掌握Cr-Ni-Cu桥梁耐候钢在连续冷却过程中组织及硬度的变化及其原因，借助JMatPro软件模拟计算了连续冷却转变(CCT)曲线和等温转变(TTT)曲线，采用Gleeble-3800热模拟试验机、金相显微镜、扫描电镜和硬度计等试验手段研究了Cr-Ni-Cu桥梁耐候钢在不同冷却速度下的微观组织和硬度的变化，探讨了冷却速度对组织、硬度及相变行为的影响。结果表明，对Cr-Ni-Cu桥梁耐候钢进行1050℃和860℃两阶段高温变形后，随着冷却速度由0.1℃/s增加至30℃/s,组织依次为多边形铁素体+珠光体→多边形铁素体+贝氏体→粒状贝氏体→粒状贝氏体+马氏体，硬度由155 HV0.2增加至373 HV0.2。当冷却速度由0.1℃/s增加至3℃/s,硬度的增加主要是由于多边形铁素体晶粒的细化。当冷却速度由5℃/s增加至30℃/s,硬度的增大主要来自于贝氏体组织的不断细化和马氏体含量的不断增加。

Continuous cooling transformation of Cr-Ni-Cu bridge weathering steel and its microstructure and hardness

In order to understand the changes of microstructure and hardness of Cr-Ni-Cu bridge weathering steel during continuous cooling transformation (CCT) and the causes, the CCT curves and time-temperature-transformation(TTT) curves were simulated and calculated by the JMatPro software. Microstructure and hardness of the Cr-Ni-Cu bridge weathering steel during CCT process were investigated by means of Gleeble-3800 hot-simulated test machine, optical microscope (OM), scanning electron microscope (SEM) and hardness tester, and the influencing mechanisms of cooling rate on microstructure, hardness and phase transformation behavior were discussed. The results show that after 1050 ℃ and 860 ℃ two-stage high temperature deformation, as the cooling rate increases from 0.1 ℃/s to 30 ℃/s, the microstructures of Cr-Ni-Cu bridge weathering steel are successively evolving from polygonal ferrite+pearlite→polygonal ferrite+bainite→granular bainite→granular bainite+martensite, and the hardness increases gradually from 155 HV0.2 to 373 HV0.2. When the cooling rate increases from 0.1 ℃/s to 3 ℃/s, the increase of hardness is mainly due to the refinement of polygonal ferrite grains. While the cooling rate increases from 5 ℃/s to 30 ℃/s, the increase of hardness is attributed to the continuous refinement of bainite microstructure and the consistent increase of martensite content.