超高强热成形钢TSCR中微米级Ti(Cx,N1-x)的析出演变

超高强热成型钢薄板坯连铸连轧(TSCR)工艺生产过程中,合理控制工艺参数,尽可能减少铸坯中粗大第二相的析出是保证产品质量和生产顺行的关键。明确粗大的微米级Ti(C_x,N_1-x)析出相在TSCR工艺流程中析出演变规律对实际生产中质量控制和工艺参数优化具有重要的指导意义。本研究通过热力学计算和试验研究相结合的方式,对超高强热成型钢TSCR工艺连铸及均热这一连续过程中微米Ti(C_x,N_1-x)析出相的析出演变行为进行了研究;明确了该过程中微米Ti(C_x,N_1-x)相“析出-回溶-粗化”的演变规律,并对其析出长大速度、回溶速度以及粗化速度做了定量分析。结果表明,22MnB5钢中粗大的微米级Ti(C_x,N_1-x)析出相在凝固末期液相中开始析出,开始析出的固相率为0.912。随着连铸温度不断降低,微米级Ti(C_x,N_1-x)相中x值由0.1增大到0.7,Ti(C_x,N_1-x)析出相逐渐由富氮相逐渐转变为富碳相。微米级Ti(C_x,N_1-x)相在连铸冷却过程中不断长大,在升温过程中又部分回溶于基体中,随后在保温阶段再次长大。在TSCR工艺连铸和均热过程降温、升温、保温阶段,微米级Ti(C_x,N_1-x)析出相颗粒生长、回溶、粗化的平均速度分别为0.007 2、-0.001 5、1.95×10-4 μm/s。

Evolution of micron Ti(Cx,N1-x) in TSCR process of ultra-high strength hot stamping steel

In the process of producing ultra-high strength hot stamping steel by thin slab continuous casting and rolling (TSCR) process, the key to ensure product quality and smooth production is to correctly control the process parameters and reduce the precipitation of coarse second phase in the slab as much as possible. Clarifying the precipitation evolution law of coarse micron Ti(C_x,N_1-x) precipitates in TSCR process has important guiding significance for quality control and process parameter optimization in actual production. Through the combination of thermodynamic calculation and experimental research, the precipitation evolution behavior of micron Ti(C_x,N_1-x) precipitates in the continuous process of TSCR continuous casting and soaking of ultra-high strength hot stamping steel was studied in detail. The evolution law of “precipitation-remelting-coarsening” of micron Ti(C_x,N_1-x) phase in this process is clarified, and its precipitation growth rate, remelting rate and coarsening rate are quantitatively analyzed. The results show that the coarse micron Ti(C_x,N_1-x) precipitates in 22MnB5 steel begin to precipitate in the liquid phase at the end of solidification, and the solid rate is 0.912. With the continuous reduction of continuous casting temperature, the x value in micron Ti(C_x,N_1-x) phase increases from 0.1 to 0.7, and the precipitated phase of Ti(C_x,N_1-x) gradually changes from N-rich phase to C-rich phase. Micron Ti(C_x,N_1-x) phase grows continuously during continuous casting cooling, partially dissolves in the matrix during heating up, and then grows again in the holding stage. In the cooling, heating and holding stages of continuous casting and soaking process of TSCR process, the average rates of particle growth, dissolution and coarsening of micron Ti(C_x,N_1-x) precipitates are respectively 0.007 2、-0.001 5、1.95×10-4 μm/s.