Abstract: Using the Gleeble-3800 thermal simulation experimental machine, different over-aging temperature tests of 1.2 mm thick 1.2 GPa high-strength steel bearing C-Si-Mn-Cr-Mo-B were conducted on the cold-rolled hardening raw materials and the research of influencing law about different over-aging temperatures on mechanical properties and microstructure was focused on. The results show that, in the range of 260-340 ℃, as the over-aging temperature increases, the tensile strength monotonically decreases, while the yield strength and yield ratio monotonically increase, and the change in elongation after fracture is not obvious. Meanwhile, as the rapid cooling temperature increases with the aging temperature, the degree of undercooling during the cooling process decreases, resulting in the gradually decreases of martensite content, and even white granular second phase precipitates inside the grain and the convex features of martensite gradually weaken, and the large angle grain boundaries gradually increase. The amount of (Fe, Mn)_xC_y precipitates inside the ferrite grains gradually decreases. Under the trial production process with an annealing temperature of 800 ℃ and an over-aging temperature of 280 ℃, the mechanical properties of the finished product meet the national standard requirements. It is successfully applied to the roll forming of the front bumper crossbeam.

Key words: 1.2 GPa high strength steel, over-aging temperature, mechanical properties, microstructure, industrial trial, roll forming