高端车用热成形钢CR300MB的研发与应用

Development and application of hot forming steel CR300MB for high-end vehicle

为开发高端车用CR300MB冷轧热成形钢,对经冶炼、连铸、热轧、酸轧的CR300MB冷硬卷取样并进行连续退火和罩式退火工艺模拟,结果表明,两种退火工艺模拟试样的力学性能均能满足某高端车企标准要求,但连续退火试样的强度偏高,断后伸长率偏低,组织晶粒粗大,多为细长的轧制变形晶粒并存在带状组织偏析,而罩式退火试样的力学性能更接近进口材料实物水平,组织晶粒比较细小,大部分为等轴晶。综合分析可知,680℃罩式退火工艺模拟试样的力学性能和显微组织均最佳,确定采用680℃退火、保温10 h的罩式退火工艺开发试制冷轧热成形钢CR300MB。工业试制的CR300MB热成形钢热冲压前的屈服强度、抗拉强度和断后伸长率均满足标准要求,且组织和性能均优于罩式退火模拟时的试样,基本达到进口材料实物水平。开发的CR300MB热成形钢采用加热温度930℃,保温时间300 s,保压压力8000 kN,保压时间10 s的热冲压工艺成功完成某高端车企零件试制,零件的力学性能、显微组织和脱碳层深度检测均合格,表明高端车用热成形钢CR300MB的研发和应用取得成功。

After smelting,continuous casting,hot rolling,pickling and cold rolling,the cold-rolled coil of CR300 MB steel was produced.In order to develop the hot forming steel CR300 MB for high-end vehicle,the spesimens cut from the cold-rolled CR300 MB steel coil were simulated by continuous annealing and batch annealing process.The results show that the mechanical properties of the two kinds of specrmens simulated by continuous annealing and batch annealing can satisfy the requirement of the high-end vehicle enterprise standards,however,for the specrmens simulated by continuous annealing,the yield strength and tensile strength are too high and the elongation is too low compared with that of the imported material,and the grains are coarse,most of them are elongated rolling deformed grains and there is banded segregation,while the mechanical properties of the specrmens simulated by batch annealing are closer to that of the imported material,and the grains are fine and most of them are equiaxed.Comprehensive analysis shows that the mechanical properties and microstructure of the specrmens simulated by 680℃batch annealing process are the best,and the batch annealing process with annealing at 680℃and holding for 10 h is adopted to develop the CR300 MB cold rolled hot forming steel.The yield strength,tensile strength and elongation of the CR300 MB steel before hot stamping meet the standard requirements,and the microstructure and mechanical properties are better than that of the specrmens simulated by batch annealing,basically reaching the level of the imported material.The developed CR300 MB steel adopts the hot stamping process of heating temperature 930℃with holding time 300 s,holding pressure 8000 kN with holding time 10 s to trial produce the parts for a high-end automotive company and gets success.The mechanical properties,microstructure and decarburization layer depth of the parts are qualified,which shows that the development and application of the CR300 MB hot forming steel for high-end vehicle is successful.