ABSTRACT

In this paper, thermal simulation testing machine (Gleeble3500) was used to investigate the mechanical properties and microstructure evolution of the 22MnB5 hot stamping steel under different interrupt quenching temperatures and cooling rates to explore the auto-tempering behaviour during discontinuous cooling process. The results demonstrated that the auto-tempering was distinctly promoted with the elevated interrupt quenching temperature and decreasing cooling rate. The tensile strength and hardness significantly decreased. The elongation of the test steel increased first and then slightly decreased ultimately increased. The test steel had the optimal combination of mechanical properties when quenched to 350°C and then cooled to room temperature with cooling rate of 8°C/s. The product of tensile strength and elongation was 24.34 GPa%. The auto-tempering effects led to the reduction of martensite variants and small-angle grain boundaries. The variation of the amount of small-angle grain boundaries and hardness were greater at 0.5°C/s, compared to that of 15°C/s.

摘要

本文利用热模拟试验机（Gleeble3500）研究了22MnB5热冲压钢在不同间断淬火温度和冷却速率下的力学性能和组织演变，以探索间断冷却过程中的自回火行为。结果表明，随着断续淬火温度的升高和冷却速度的降低，自动回火明显得到促进。抗拉强度和硬度明显下降。试验钢的伸长率先增加后略有下降，最终增加。试验钢在淬火至 350°C 然后以 8°C/s 的冷却速度冷却至室温时具有最佳的力学性能组合。拉伸强度和伸长率的乘积为 24.34 GPa%。自回火效应导致马氏体变体和小角度晶界的减少。与 15°C/s 相比，0.5°C/s 时小角晶界数量和硬度的变化更大。