研究了在不同热处理工艺条件下,一种800MPa级低碳贝氏体钢组织性能的变化规律。通过对控轧控冷（TMCP）、TMCP＋水淬（WQ）、TMCP＋WQ＋回火（T）工艺的比较,发现试验钢在450℃时回火2h后,可以获得具有良好强韧性的组织,屈服强度为816MPa,伸长率大于16%。通过SEM和TEM观察可知,这种钢的室温组织主要是细小的板条状贝氏体、（准）多边形铁素体和少量过冷奥氏体转变相的复相组织,随着回火温度的升高,板条逐渐合并变宽,最终发生多边形化;基体内存在大量的位错以及细小、弥散分布的纳米级第二相粒子,其尺寸约为10～20nm,选区衍射花样标定确定是Nb、Ti的碳氮化物,纳米级第二相粒子与位错的相互作用对材料增强增韧起重要作用,450℃回火时因析出强化造成的强度增量约为233MPa。
The effects of thermal treatment on microstructure and mechanical properties of 800 MPa grade low carbon bainitic steels were investigated.After applying thermomechanical control process,water quenching and tempering at different temperatures,optimal comprehensive mechanical properties were obtained when tempered at 450 ℃.The yield strength achieves 816 MPa,simultaneously the elongation exceeds 16%.The morphology by SEM shows that the microstructure consists of fine lath-shape bainite,polygonal ferrite,quasi-polygonal ferrite and a small fraction of residual austenite or martensite-austenite constituents.A TEM study shows that plenty of Nb/Ti carbonitride precipitates with the size about 10-20 nm interacted with the existent dislocations,which is very significant for the improvement of strength and ductility.The strength increment caused by precipitation strenghthening can reach about 233 MPa,when the specimen tempered at 450 ℃.
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