Nb-V微合金化低钼型Q345耐火钢的开发

 为了推动耐火钢的市场应用,采用低碳、低钼(约0.2%)及铌、钒、钛的复合微合金化成分设计,成功开发出低成本Q345耐火钢。采用Formastor-Digital全自动相变测试仪测定了试验钢的连续冷却转变(CCT)曲线,利用Gleeble-1500热模拟试验机研究了变形后不同冷却工艺对试验钢组织及硬度的影响,并采用SEM、EBSD、TEM和物理化学相分析等手段对热轧及600 ℃高温拉伸试样基体组织及纳米第二相进行了详细表征,定量分析了试验钢室温及高温下的强度机制。结果表明,轧后760~780 ℃开始层流冷却、终冷温度为400~600 ℃,试验钢获得铁素体+贝氏体组织。经600 ℃高温拉伸后,试验钢中MC相的质量分数及处于18 nm以下的粒子质量百分比相对于热轧态试样分别提高了16.4%、9.8%,这些新析出的纳米级粒子在高温下起到了良好的沉淀强化作用,一定程度弥补了高温下因剪切模量下降和细晶强化失效导致的高温屈服强度的损失;固溶、沉淀强化为Q345耐火钢主要的高温强化方式。

Development of Nb-V microalloying and low Mo alloyed Q345 fire-resistant steel

In order to promote the market application of fire-resistant steel,the low-cost Q345 fire-resistant steel was successfully developed,adopting the composition design of low C,low Mo (about 0.2%)and Nb,V,Ti composite microalloying. The continuous cooling transformation (CCT)of experimental steel was measured by Formastor-Digital automatic transformation tester. The influence of different cooling processes on the microstructure and hardness of the experimental steel was studied by Gleeble-1500 thermal simulation test machine. The microstructure and nano second phase of hot rolled and high temperature tensile samples were characterized in detail by SEM,EBSD,TEM and physicochemical phase analysis. The strength mechanism of the experimental steel at room temperature and high temperature was quantitatively analyzed. The ferrite+bainite microstructure was obtained by laminar cooling started at 760-780 ℃ but finished at 400-600 ℃. After high temperature tensile test at 600 ℃,the mass percent of MC phase and the percentage of particles below 18 nm in the experimental steel are increased by 16.4% and 9.8% respectively,compared with those of the hot-rolled sample. These newly precipitated nano particles play a good role in precipitation strengthening at high temperature. It makes up to some extent for the loss of high-temperature yield strength,which is caused by the decrease of shear modulus at high temperature and by the failure of fine grain strengthening. The solid solution strengthening and precipitation strengthening are the main high-temperature strengthening methods of Q345 fire-resistant steel.