热冲压成形保温时间对SAF2507 SDSS微观组织和力学性能的影响

Effect of holding time on microstructure and mechanical properties of hot stamping forming SAF2507 SDSS

对SAF2507 SDSS板材进行1050℃下不同保温时间的热冲压成形,使用光学显微镜、扫描电镜和能谱仪观察其微观组织的变化,通过拉伸试验、硬度计和冲击试验等测试了不同保温时间下试验钢的力学性能。结果表明:在1050℃热冲压成形时,试验钢的微观组织中无析出相,只有条状平行分布的α相和γ相。当保温时间为2~5 min时,α相含量快速增加,γ相含量快速减少,微观组织发生γ→α转变;当保温时间超过10 min后,α相含量缓慢上升,γ相含量缓慢下降。随保温时间的增加,抗拉强度和硬度先上升后下降,伸长率、截面收缩率和冲击吸收能量一直下降,拉伸试样的断裂形式由韧窝断裂逐渐向准解理断裂转变;保温时间为5 min时,试验钢获得最佳的微观组织和力学性能。

SAF2507 SDSS sheet was formed by hot stamping at 1050 ℃ with different holding time. Microstructure variation of the tested steel was observed by means of optical microscope, scanning electron microscopy and energy dispersive spectrometer. Mechanical properties of the tested steel under different holding time were tested by tensile test, hardness meter and impact test. The results show that there is no precipitates in the microstructure of the tested steel during the hot stamping at 1050 ℃, only the α phase and the γ phase with parallel distribution in strip shape. When the holding time is 2-5 min, with the increase of holding time, the α phase content increases rapidly, the γ phase content decreases rapidly, and the microstructure occurs γ→α transformation. When the holding time exceeds 10 min, the α phase content increases slowly and the γ phase content decreases slowly. With the increase of holding time, the tensile strength and hardness of the tested steel increase first and then decrease, and the elongation, section shrinkage and impact absorbed energy decrease all the time, and the fracture mechanism of the tensile specimen changes gradually from dimple fracture to quasi-cleavage fracture. When the holding time is 5 min, the tested steel has the best microstructure and mechanical properties.