中文摘要：

对系列Si,Mn,Ni等合金元素合金化的低碳超高强度贝氏体钢（LUHSBS）,通过控制相变温度、冷却与回火参数,可明显提高其韧性.与同等强度（＞1500 MPa）的高级马氏体钢23MnNiCrMo相比,研制的LUHSBS冲击吸收能（AKV≥185J）提高3倍以上.强度与韧性优化结合的根本原因在于组织细化、贝氏体铁素体（BF）中含碳量增加、碳化物消除以及存在较高体积分数的稳定膜状残余奥氏体（AR）.原子力显微镜和扫描隧道显微镜分析证实：钢中不存在对韧性有损伤作用的块状AR;不仅切变单元超细化,而且超细晶粒的平均尺寸小于20 nm,部分切变单元的平均厚度仅约1.6 nm.这些精细组织是影响钢的强度、AR稳定性和AKV增加的主要原因.分析了强度与韧性改善的物理机制.

英文摘要：

Through adding Si, Mn and Ni into low alloy ultra-high strength bainitic steels （LUHSBS） and controlling the transformation temperature, cooling and tempering parameters the impact energy absorption （AKv ≥185 J） has been tripled compared to the martensitic steel 23MnNiCrMo with the same strength level （〉 1500 MPa）. The basic reasons of the excellent combination of strength and toughness consist in the refinement of microstructure, the increase of carbon content in the bainitic ferrite （BF）, the elimination of carbides and the thin film shaped retained austenite （AR） with high volume fraction and stability. AFM and STM revealed that no bulky AR existed in the structure which will reduce the impact toughness of bainitic steels. Not only the shear-units are significantly refined, but also the average size of super-fine grains is less than 20 nm and the average thickness of partial shear-units in a BF lath is only about 1.6 nm. The refinement of microstructure, the enrichment of carbon atom in BF and the increase of both the dislocation density and the volume fraction of AR are the factors affecting the ultimate tensile strength, the stability of AR and the impact toughness. Furthermore, the physical mechanism on the improvements of strength and toughness was discussed.