Cu, as an austenitic stable element, is added to steel in order to suppress the adverse effects of high content of C and Mn on welding. Based on C partitioning, Cu and Mn partitioning can further improve the stability of retained austenite in the intercritical annealing process. A sample of low carbon steel containing Cu was treated by the intercritical annealing, then quenching process（I＆Q）. Subsequently, another sample was treated by the intercritical annealing, subsequent austenitizing, then quenching and partitioning process（I＆Q＆P）. The effects of element partitioning behavior in intercritical region on the microstructure and mechanical properties of the steel were studied. The results showed that after the I＆Q process ferrite and martensite could be obtained, with C, Cu and Mn enriched in the martensite. When intercritically heated at 800 ℃, Cu and Mn were partitioned from ferrite to austenite, which was enhanced gradually as the heating time was increased. This partitioning effect was the most obvious when the sample was heated at 800 ℃ for 40 min. At the early stage of α→γ transformation, the formation of γ was controlled by the partitioning of carbon, while at the later stage, it was mainly affected by the partitioning of Cu and Mn. After the I＆Q＆P process, the partitioning effect of Cu and Mn element could be retained. C was assembled in retained austenite during the quenching and partitioning process. The strength and elongation of I＆Q＆P steel was increased by 5 305 MPa% compared with that subjected to Q＆P process. The volume fraction of retained autensite was increased from 8.5% to 11.2%. Hence, the content of retained austenite could be improved significantly by Mn and Cu partitioning, which increased the elongation of steel.
对专用车轻量化设计的重要性进行了分析,介绍了目前汽车轻量化的主要途径,针对专用汽车底盘横梁零件开展了包括材料和结构在内的轻量化设计。选用22MnB5高强钢和现役Q345碳钢两种材料,对横梁零件的受力情况进行理论分析,采用有限元仿真技术对横梁零件的尺寸和结构进行优化,综合应用CATIA、Hypermesh和MSC Marc 3种软件的优势完成几何建模、网格划分、计算分析和结果处理的整个过程,提高有限元分析的效率。结果表明,现役U型带孔结构横梁易产生应力集中倾向,使零件过早达到屈服,而采用高强钢W型结构横梁不仅安全性显著提高,而且重量比现役零件减少约69%,轻量化效果显著。
