测试了低碳钢不同退火温度下烘烤态的应力-应变曲线和烘烤硬化(BH)值以及变形态和烘烤态的内耗曲线, 研究了不同退火温度下的烘烤硬化机制. 结果表明, 退火温度由750 ℃逐渐提高到880 ℃, 应力-应变曲线均表现不连续屈服现象, 且屈服平台的锯齿状越来越明显, 屈服点延伸量不断增大. 退火温度由750 ℃提高到780 ℃, BH值降低, 变形态和烘烤态的Snoek峰高差值增大, SKK峰高降低, Kê峰变化不大, 固溶强化对烘烤硬化起主导作用. 退火温度由780 ℃逐渐提高到880 ℃, BH值不断增大, 变形态和烘烤态的Snoek峰高差值逐渐减小, SKK峰的驰豫强度逐渐增大, Kê峰变化不大, Cottrell气团强化对烘烤硬化的作用逐渐增强. 烘烤硬化机制是固溶强化、Cottrell气团强化和沉淀强化的共同作用.

High strength steel plates are being applied more extensively in automobile industry under higher demands of weight reduction, safety and environmental protection. As one of the high strength steel plates for automobile body panel, bake-hardening steel plate is featured by low yield strength and good formability during stamping, and is particularly featured by improved yield strength through following paint baking process, exhibiting higher strength and anti-dent ability in service. Bake-hardening (BH) is closely related to interactions between interstitial atoms and crystal defects during baking process. In this work, BH mechanisms in low carbon steel are studied under different annealing temperatures by measuring and analyzing stress-strain curves and BH values in baked conditions, and internal friction curves in both deformed and baked conditions. The results show that when the annealing temperature increases gradually from 750 to 880 ℃, the stress-strain curves exhibit discontinuous yielding behavior with stronger serration of yield platform and continuous elongation of yield point. With the increase of the annealing temperature from 750 to 780 ℃, BH value decreases, difference between Snoek peak values in deformed and baked conditions increases, SKK peak value decreases, and Kê peak value does not change significantly, which indicates that solid solution strengthening dominates the BH. When the annealing temperature increases from 780 to 880 ℃, BH value continuously increases, difference between Snoek peak values in deformed and baked conditions gradually decreases, relaxation strength of SKK peak gradually increases, and Kê peak is stable, which indicates that Cottrell atmosphere strengthening is playing an increasing role in the BH. The BH is due to a combined mechanism contributed by solid solution strengthening Cottrell atmosphere strengthening and precipitation strengthening.