Microstructure and microhardness evolution of thermal simulated HAZ of Q&P980 steel
Microstructure and microhardness evolution of thermal simulated HAZ of Q&P980 steel
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DOI：
10.1016/j.jmrt.2021.11.059
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
Xiaoyan Wu;Hongtao Lin;Wei-hong Luo;Haitao Jiang
中科院分区：
文献类型：
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作者：
Xiaoyan Wu;Hongtao Lin;Wei-hong Luo;Haitao Jiang
采用焊接热模拟技术，系统地研究了Q&P980钢热影响区的组织演变和显微硬度。用膨胀法测定了其相变温度。在高于150℃/S的升温速率下，Ac1和Ac3相当恒定，分别为750℃和935℃。在模拟实验中，通过改变峰值加热温度得到了不同的热影响区区域。当峰值温度从300℃升高到1350℃时，组织由马氏体/铁素体/残余奥氏体转变为回火马氏体/碳化物/铁素体，最后转变为板条细小或粗大的单一马氏体相。由于高温下的残余奥氏体相变，残余奥氏体体积分数从13%急剧下降到2%。亚临界热影响区显微硬度最低，为268 HV，细晶热影响区显微硬度最高，为485 HV。用膨胀法绘制了Q&P980钢对应粗晶HAZ的焊接连续冷却转变图。冷却速度在0.1~10 0℃/S范围内存在铁素体、贝氏体区和马氏体区，在较高的冷却速度(≥2 0°C/S)下，由于马氏体的形成，显微硬度保持在45 0~460HV的较高水平。根据所确定的CCT图，可以推断冷却速度对组织和显微硬度的影响，并将其用于优化焊接参数。
The microstructure evolution and microhardness of Q&P980 steel heat-affected zone (HAZ) was investigated systematically using weld thermal simulation technique. The phase transformation temperatures were determined by the dilatometry. Ac1and Ac3were observed to be quite constant, 750 and 935 °C, at the heating rates higher than 150 °C/s. The different regions of HAZ were obtained varying the peak heating temperature in the simulation experiments. With the peak temperature increased from 300 to 1350 °C, the microstructure evolved from martensite/ferrite/retained austenite to tempered martensite/carbides/ferrite, then finally turned to single martensite phase with fine lath or coarse lath morphology. The volume percentage of retained austenite reduced dramatically from 13% to 2% due to retained austenite transformation at high temperature. The lowest microhardness of 268 HV was obtained in sub-critical HAZ and the highest microhardness of 485 HV was obtained in fine grained HAZ. The welding continuous cooling transformation (CCT) diagram of Q&P980 steel corresponding coarse grained HAZ was constructed by dilatometric methods. There was ferrite, bainite and martensite transformation regions when the cooling rates ranged from 0.1 to 100 °C/s. The microhardness kept at a high certain level of 450–460 HV at high cooling rates (≥20 °C/s) because of the formation of martensite. By the CCT diagram determined, the effect of cooling rate on microstructure and microhardness can be deduced and utilized for optimizing the welding parameters.