钛微合金化高强钢的组织性能及强化机制

 为了掌握钛微合金化高强钢的组织性能、第二相粒子特性和析出规律以及强化机制，采用光学显微镜、扫描电镜、透射电镜、拉伸试验机等设备并结合热力学计算，对高强度汽车车厢板进行了系统研究。研究结果表明，试验钢的显微组织类型主要为多边形铁素体+针状铁素体+少量索氏体，平均有效晶粒尺寸约为3.5 μm。钢中存在大量的球形TiC和少量的不规则形状Ti4C2S2及方形TiN析出物，析出顺序为TiN→Ti4C2S2→TiC。第二相析出物以TiC的沉淀强化效果最为显著，TiN和Ti4C2S2的沉淀强化效果十分微弱。试验钢中所有强化方式对试验钢的强度贡献大小顺序为细晶强化＞沉淀强化＞位错强化＞固溶强化＞晶格点阵强化，其中细晶强化和沉淀强化的强化效果最为显著，对屈服强度的贡献超过50%。

Microstructure，mechanical properties and strengthening #br# mechanism of Ti microalloyed high strength steel

 In order to study the microstructure，mechanical properties，characteristics and precipitation behavior of the second phase precipitate as well as strengthening mechanism of Ti microalloyed high strength steel for automobile carriage，which were systematically investigated by means of the optical microscope，scanning electron microscope，transmission electron microscope and tensile testing machine combined with thermodynamic calculation. The results show that the microstructure of the experimental steel is mainly composed of polygonal ferrite+acicular ferrite+a small amount of sorbite，and the average effective grain size is about 3.5 μm. There are a large amount of spherical TiC and a small amount of irregular shape Ti4C2S2 and square TiN precipitates in steel. The precipitation sequence is TiN→Ti4C2S2→TiC. The precipitation strengthening effect of TiC is the most remarkable for the second phase precipitates，and the precipitation strengthening effects of TiN and Ti4C2S2 are very weak. The contribution order of all strengthening methods to the strength of experimental steel is as follow：fine grain strengthening>precipitation strengthening>dislocation strengthening>solid solution strengthening>lattice strengthening，in which the strengthening effects of fine grain strengthening and precipitation strengthening are the most significant，and the contribution to yield strength is more than 50%.