退火工艺对超高强冷轧马氏体钢板力学性能的影响

Effects of annealing on mechanical properties of ultra-high strength cold-rolled martensite steel sheets

以C-Mn-Si系冷轧马氏体钢为研究对象,分析了退火工艺对超高强马氏体钢强度和冷弯性能的影响。由于碳含量高,试验用钢淬透性良好,当水淬入口温度在710℃及以上时,都能获得极高的抗拉强度和稳定的马氏体组织。随过时效温度升高,马氏体钢抗拉强度降低、延伸率升高;而屈服强度和冷弯性能则先升后降,在180℃过时效时具有最高的屈服强度和最优的冷弯性能。经扫描电镜和显微硬度分析发现,过时效温度的变化会直接影响马氏体钢中的碳化物析出及粗化,当过时效温度大于200℃时,试验用钢碳化物开始粗化,降低了马氏体钢的宏观冷弯性能。

As the cold-forming sheets having the highest strength up to now,the ultra-high strength martensitic steel attracts great interest by global car-makers. The effects of quenching temperature and over-aging temperature on the strength and cold bendability of the C-Mn-Si martensitic steel were studied. Due to a high carbon content,the C-Mn-Si martensitic has high quenching hardenability,and can obtain the ultra-high tensile strength and uniform martensitic morphology when the water quenching temperature is above 710 ℃. With increasing over-aging temperature,the tensile strength of the experimental steel decreases,the total elongation increases,and the yield point increases first and then declines and reaches the peak at 180 ℃ over-aging temperature. Besides,when increasing over-aging temperature,the bendability of the experimental steel improves first and then declines,which reaches the best bendability at over-aging temperature of 180 ℃. Based on the SEM analysis and micro-hardness distribution,it is found that the over-aging temperature affects the size of carbides and the micro-hardness difference in the experimental steel and therefore determines the bendability.