750 MPa级Nb-Ti-Mo复合微合金化方管用钢显微组织和力学性能

Microstructure and mechanical properties of 750 MPa grade Nb-Ti-Mo microalloyed square tube steel

为了实现汽车车身骨架轻量化,研发了750 MPa级Nb-Ti-Mo复合微合金化方管用钢。采用OM、SEM和TEM等分析方法对750 MPa级Nb-Ti-Mo复合微合金化方管用钢的显微组织与性能进行了分析。结果表明,采用低C、低Mn、Nb、Ti和Mo复合微合金化成分体系,通过优化卷取工艺路线,得到的750 MPa级Nb-Ti-Mo复合微合金化方管用钢的显微组织为全铁素体和大量弥散分布的纳米级析出物,材料具有优异的综合力学性能。750 MPa级Nb-Ti-Mo复合微合金化方管用钢采用直接成方工艺制管后,材料性能与母材基本相当;采用圆变方工艺制管后,随着管径的下降,强度明显提高,塑性逐渐降低,伸长率依然大于14%。750 MPa级Nb-Ti-Mo复合微合金化方管用钢替代传统的Q235、345C、510L等低强度钢材应用于车身骨架,减重比例高达30%,减重效果显著。

In order to achieve lightweight of automobile body frame,75o MPa grade Nb-Ti-Mo composite microal-loyed square pipe steel was developed.The microstructure and properties of 75o MPa grade Nb-Ti-Mo composite microalloyed square tube steel were analyzed by OM,SEM and TEM.The results show that the microstructure of the 75o MPa grade Nb-Ti-Mo composite microalloyed square steel is full of total ferrite and a large number of dis-persed nanoscale precipitates,and the material has excellent comprehensive mechanical properties by adopting the low C,low Mn,Nb,Ti and Mo composite microalloyed composition system and optimizing the coiling process.The properties of 75o MPa grade Nb-Ti-Mo composite microalloyed square pipe steel are similar to those of the base ma-terial after direct square forming process.When the tube is made by the round to square process,with the decrease of pipe diameter,the strength is obviously increased,the plasticity is gradually decreased,and the elongation is still greater than 14%.When 750 MPa grade Nb-Ti-Mo composite microalloyed square pipe steel is instead of traditional Q235,345C,510L and other low strength steel to apply to the body skeleton,the weight reduction ratio is as high as30%,the weight reduction effect is remarkable.