两相区位错增殖对低碳贝氏体/铁素体复相钢组织和性能的影响

利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、电子探针(EPMA)、X射线衍射仪(XRD)、室温拉伸等手段, 通过两相区保温-淬火(IQ)、两相区形变后保温-淬火(DIQ)、两相区保温-淬火-配分-贝氏体区等温(IQ&PB)及两相区形变后保温-淬火-配分-贝氏体区等温(DIQ&PB)热处理工艺, 研究高温形变对室温组织、性能、残余奥氏体稳定性的综合影响作用.结果表明, 经15%的压缩形变后铁素体中位错密度由0.290×1014增加至1.286×1014 m-2, 马氏体(原奥氏体)中C、Cu元素富集浓度提高, 高温形变产生位错增殖对元素配分有明显促进作用.DIQ&PB工艺下, 形变后贝氏体板条尺寸变短且宽度增加0.1 μm左右, 贝氏体转变量较未变形时增加14%, 多边形铁素体尺寸明显减小.力学性能方面, 两相区形变热处理后抗拉强度增加132.85 MPa, 断后伸长率增加7%, 强塑积可达25435 MPa·%.形变后残余奥氏体体积分数由7.8%提高到8.99%, 残余奥氏体中碳质量分数由1.05%提高到1.31%. 

Effect of dislocation multiplication in intercritical region on microstructure and properties of low-carbon bainite/ferrite multiphase steel

Hot deformation is a way to effectively improve strength and plasticity of multiphase steels simultaneously, thereby, improving mechanical properties of multiphase steels. Hot deformation affects martensitic transformation mechanism, microstructure, and mechanical properties because it increases retained austenite content and improves stability of multiphase steels. Moreover, hot deformation plays a role in dislocation multiplication, and fine grain strengthening; it can reduce bainite transformation driving force, reduce bainite transformation point, and result in small multiphase organization after quenching-partitioning process. The result can significantly improve the properties of materials. The effects of high-temperature deformation on the stability of room-temperature microstructure, mechanical property, and retained austenite under treatment of IQ&PB (intercritical annealing-quenching and partitioning within the bainitic region) and DIQ&PB (intercritical deformation-intercritical annealing-quenching and partitioning within the bainitic region) processes were studied using scanning electron microscopy (SEM), transmission electron microscope (TEM), electron probe X-ray microanalyser (EPMA), X-ray diffraction (XRD), and tensile testing machine. The results show that dislocation density increases from 0.290×1014 to 1.286×1014 m-2 after 15% compression deformation, and the respective concentrations of C and Cu element enrichment in martensite (the original austenite) increases. Overall, dislocation multiplication produced by high-temperature deformation significantly promotes elemental distribution. After the deformation, the size of bainite lath shortenes and its width increases by 0.1 μm, the volume of the bainite transition increased by 14%, and the size of the polygonal ferrite significantly decreases under the DIQ&PB treatment. In terms of mechanical properties, the tensile strength increases by 132.85 MPa, and the elongation increases by 7%; the strength and ductility product reaches 25435 MPa·% after intercritical deformation heat treatment. The volume fraction of retained austenite increases from 7.8% to 8.99%, and the mass fraction of carbon in the retained austenite increases from 1.05% to 1.31% after compression deformation.