钛微合金中锰钢强韧化机制研究

低碳中锰钢因为其优异的力学性能及低成本的成分设计逐渐被应用到海洋平台用厚板生产制备中,通过对钛微合金化低碳中锰钢进行控轧控冷工业试验,观察不同厚度位置的显微组织及析出物形貌,测定了室温拉伸及低温冲击韧性,并对其强韧化机制进行了分析。结果表明,试验钢基体为板条宽度200～400 nm的回火马氏体和宽度为50～100 nm的逆转变奥氏体复合层状组织,且全厚度方向组织性能均匀性较好,屈服强度均大于760 MPa、屈强比均小于等于0.88、伸长率均大于20%、-60℃冲击功均大于200 J。试验钢的主要强韧化机制有亚微米尺度的复合层状组织、大角度晶界韧化机制、亚稳态逆转变奥氏体TRIP效应、Ti(C,N)粒子的细晶强化及析出强化效应,多种强化机制叠加作用,最终获得高强韧的中锰钢厚板。

Study on strength- toughness mechanism of Ti microallyed medium manganese steel

Low- C medium- Mn steel has been gradually applied to the production and preparation of heavy plate for offshore platform usage due to its excellent mechanical properties and low- cost composition design. The industrial thermo- mechanical control process test was conducted on Ti microallyed low- C medium- Mn steel. The morphologies of microstructure and precipitates at different positions along thickness direction were studied，and tensile strength and impact toughness were measured. Moreover，the strength- toughness mechanism was investigated. The results show that the matrix of experimental steel is laminated structure composed of tempered martensite with strip width of 200-400nm and reversed austenite with strip width of 50-100nm. Moreover, excellent homogeneity of microstructures and properties are obtained. Results indicate that for all experimental steels, the yield strength exceeds 760MPa, yield ratio is no more than 0. 88, elongation rate are more than 20%, and the impact energy measured at -60℃ exceeds 200J. Sub- micron laminated of matrix structure, toughening mechanism of large angle grain boundary, transformation- induced plasticity effect of metastable austenite, as well as fine- grained strengthening and precipitation strengthening of Ti（C,N）are the major strengthening and toughening mechanisms, which work together and finally obtain the medium manganese thick plate with high strength and toughness.