富Cu析出强化贝氏体超高强钢的组织特征及强韧化机制

Microstructure characteristics and strengthening and toughening mechanism of Cu-rich precipitation strengthened ultra-high strength bainitic steel

由于传统超高强钢高的碳含量导致其焊接性严重恶化,低碳含量的含Cu超高强钢因具有优异的焊接性而受到广泛关注,在高载荷焊接结构中具有较好的应用前景。为了获得更为优异的强韧性,将铁素体低碳纳米富Cu超高强钢的基体组织优化为板条贝氏体,分析了优化后试验钢的微观组织及纳米富Cu析出相晶体结构的特征,并基于常温拉伸试验及示波冲击试验探究了试验钢的强韧化机制。结果表明:该板条贝氏体低碳纳米富Cu析出强化超高强钢的强韧性能匹配优异,其屈服强度为1334 MPa,-40℃冲击吸收能量为63.5 J。该试验钢贝氏体基体中含有大量1~5 nm尺寸的B_(2)型富Cu析出相。纳米富Cu相的析出强化是主要强化的机制,对屈服强度的贡献约700 MPa;而且细小的晶粒尺寸(3.11μm)、较高的位错密度(8.2×10^(13)m^(-2))也有效地提高了试验钢的屈服强度,细晶强化和位错强化增量分别约305和215 MPa。试验钢中的贝氏体板条束亚结构对裂纹扩展起到阻碍作用,使其在提高强度的同时仍具有良好的冲击韧性。

Due to the high carbon content of traditional ultra-high strength steel,its weldability is seriously deteriorated.Cu containing ultra-high strength steel with low carbon content has attracted extensive attention because of its excellent weldability,and has a good application prospect in high load welded structures.In order to obtain better strength and toughness,the matrix structure of ferritic low carbon nano Cu-rich ultra-high strength steel was optimized to lath bainite.The microstructure and the characteristics of the Cu-rich precipitates crystal structure of the optimized experimental steel were analyzed.The strengthening and toughening mechanism of the experimental steel was studied based on room temperature tensile test and oscillographic impact test.The results show that the lath bainite low carbon nano Cu-rich precipitation strengthened ultra high strength steel has excellent matching of strength and toughness,its yield strength is 1334 MPa,and the impact absorbed energy at-40℃is 63.5 J.The bainite matrix of the experimental steel contains a large number of B_(2) type Cu-rich precipitates with the size of 1-5 nm.The precipitation strengthening of nano Cu-rich precipitates is the main strengthening mechanism of the experimental steel,and its contribution to yield strength is about 700 MPa;the fine grain size(3.11μm)and high dislocation density(8.2×10^(13) m^(-2))also effectively improved the yield strength of the experimental steel,and the increment of fine grain strengthening and dislocation strengthening are about 305 MPa and 215 MPa,respectively.The lath bundle substructure of bainite in the experimental steel hinders the crack propagation,so the steel still has good impact toughness while the strength is improved.