1500 MPa级低合金超高强钢的微观组织与力学性能

来源期刊：金属学报2010年第6期

论文作者：王立军 蔡庆伍 余伟 武会宾 雷爱娣

文章页码：687 - 694

关键词：低合金超高强钢； 直接淬火； 马氏体； 贝氏体； 残余奥氏体

Key words：ultra-high strength low alloy steel； direct quenching； martensite； bainite； retained austenite

摘    要：设计了一种新型1500 MPa级Si-Mn-Cr-Ni-Mo多组元系低合金超高强度结构钢,对比研究了控轧+控冷(TMCP)、控轧+空冷、控轧+直接淬火、控轧+直接淬火+250℃回火4种不同工艺对其微观组织和力学性能的影响.结果表明:直接淬火态钢板抗拉强度最高,可达1890 MPa,屈服强度为1280 MPa,延伸率为13%;250℃回火30 min后抗拉强度降低为1820 MPa,而屈服强度升高为1350 MPa,分析认为这归因于位错亚结构的回复软化过程与残余奥氏体分解为马氏体、析出ε-碳化物强化机制的综合作用;空冷与TMCP工艺获得板条贝氏体+马氏体+少量残余奥氏体的复相组织,贝氏体分割马氏体板条束,使实验钢具有良好的强塑性.低碳马氏体相变过程存在C扩散现象.研究发现,回火过程不仅包含残余奥氏体分解,也包含C从马氏体或贝氏体向奥氏体的分配过程.证明了立方结构的析出粒子在奥氏体中形核,在整个冷却过程长大、粗化,而相变后的马氏体或贝氏体未出现大量第二相析出核心.

Abstract: A novel sort of 1500 MPa grade ultra-high strength low alloy structural steel with multi-element of Si-Mn-Cr-Ni-Mo was designed.Effects of four different processes of TMCP(thermomechanical controlled processing),controlled rolling+air-cooled,controlled rolling + direct quenching and controlled rolling+direct quenching+tempering at 250℃ on the microstructure and mechanical properties were investigated.The results indicate that the directly quenched steel has a maximum tensile strength of 1890 MPa,yield strength of 1280 MPa and elongation of 13%.After tempered at 250℃ for 30 min,the tensile strength of the steel decreased to 1820 MPa,while the yield strength increased to 1350 MPa,which is ascribed to the comprehensive effect of the softening mechanism due to the recovery of dislocation sub-structure and the strengthening mechanism due to the decomposition of retained austenite andε-carbide precipitation.Duplex phase microstructure involving lath bainite, martensite segmented by bainite,and retained austenite was obtained by the process of air-cooling and TMCP,so that it has excellent strength and plasticity.Carbon diffusion phenomenon exists in the quenching process of low-carbon steel.Both the decomposition of retained austenite and the carbon partitioning into austenite from martensite or bainite were found during tempering process.The paper demonstrates that the precipitation particles of cubic structure nucleated in austenite,growing up and coarsening during the whole cooling process.Futhermore,the emergence of a large number of second-phase precipitation cores was not found in martensite or bainite after phase transformation.