退火温度对钒微合金化780 MPa级冷轧双相钢组织性能的影响

Effect of annealing temperature on microstructure and mechanical properties of vanadium microalloyed 780 MPa cold rolled dual phase steel

将钒微合金化试验钢分别加热至780、800、820℃和840℃保温一段时间后,依次经过缓慢冷却、快速冷却、模拟镀锌后,空冷至室温。研究结果表明,780℃退火时微观组织均匀性较差且发现未溶解的碳化物,导致强度和塑性均不佳。随着退火温度的升高,铁素体尺寸及分数逐渐降低,中低温转变产物含量逐步增加且其尺寸有所粗化。当退火温度为800℃时,马氏体含量达到最大,当退火温度进一步升高时,马氏体含量有所降低,而贝氏体含量则有所增加,导致抗拉强度在800~840℃范围内变化不大,而延伸率先升高后降低。当退火温度为820℃时,带钢获得较佳的力学性能,屈服强度、抗拉强度、屈强比、断后伸长率A80和扩孔率分别为486 MPa、835 MPa、0.58、16.0%和27%。

The vanadium microalloyed tested steel was heated to 780℃,800℃,820℃and 840℃,respectively and then held for a few minutes,followed by different cooling modes such as slow cooling,rapid cooling,simulated galvanizing,and air cooling to room temperature.Microstructure observation by SEM shows that microstructure uniformity is poor during annealing at 780℃and undissolved carbides are found,leading to a weak combination of strength and plasticity.With the increase of annealing temperature,the size and fraction of ferrite gradually decrease,the volume fraction of mid-low temperature transformation products gradually increases and its size becomes coarser.When the annealing temperature was 800℃,the fraction of martensite reaches the maximum.When the annealing temperature further increases,the fraction of martensite decreases,while the fraction of bainite increases,resulting in a relatively stable tensile strength when annealing temperature of 800~840℃range,however,the elongation firstly increases and then decreases.When the annealing temperature was 820℃,the steel strip obtains better mechanical properties.The yield strength,tensile strength,yield ratio,elongation after fracture A80 and hole expansion rate are 486 MPa,835 MPa,0.58,16.0%and 27%,respectively.