Fe-C-Si-Mn系超高强度贝氏体钢残余奥氏体控制及力学稳定化机理研究

Ultra-high strength bainitic steel with an excellent combination of strength and ductility has become a new generation steel. It has been widely researched in recent years. So far, there still exist some problems such as the addition of expensive alloying elements, long transformation time and so on. However, it is difficult to obtain ultra-high strength and good ductility simultaneously. Retained austenite (RA) surrounded by lath bainite can affect elongation, which is related to volume fraction of RA, morphology, size, distribution and carbon concentration. In order to achieve excellent synthetic mechanical properties, the microstructure of RA should be optimized reasonably, which is full of scientific significance and practical value. Therefore, a new idea is proposed to make an improvement on Fe-C-Si-Mn ultra-high strength bainitic steels. That is controlling the microstructure of RA by ausforming. The main purpose is to obtain a good combination of strength and elongation, contributing to produce a new generation bainitic steel. In addition, the effect of RA on elongation will be investigated and an optimized ausforming technology will be explored. From the theoretical point, the results can reveal the mechanism of controlling RA by deformation. And the relationship between RA and elongation in the ultra-high strength bainitic steel will also be clarified. From the practical point, the present work can provide valuable guidance for the production of ultra-high strength bainitic steels.

超高强度贝氏体钢是重点发展的新一代超高强钢，但目前还存在贝氏体低温转变周期长、大量贵重合金元素添加、强度和延伸率不匹配等问题，其中关键问题是高强度与高延伸率很难同时匹配。残余奥氏体对超高强度贝氏体钢延伸率起决定作用，如何优化残留奥氏体微观组织，实现超高强度和高延伸率良好匹配，具有重要的科学意义和应用价值。项目以Fe-C-Si-Mn系列超高强贝氏体钢为对象，提出通过奥氏体预变形调控超高强度贝氏体钢中残余奥氏体的微观组织这一新思路，目的是实现贝氏体钢超高强度和高延伸率良好匹配，制备综合性能优良的新一代超高强度贝氏体钢。此外，研究残余奥氏体对超高强贝氏体钢延伸率的影响规律，探索优化残余奥氏体微观组织的变形条件，不仅可以从理论上揭示变形控制残余奥氏体的微观机理，阐明残留奥氏体微结构控制与超高强度贝氏体钢延伸率关系，同时也能为生产兼具优良延伸率的超高强度贝氏体钢提供必要理论支持。

钢铁产业是国民经济建设、社会进步和国防安全的重要基础，我国已进入工业化中后期，开展先进新型钢铁材料研究，对支撑我国从钢铁制造大国向钢铁强国转变具有重要战略意义。超高强纳米结构贝氏体钢同时具备高耐磨、耐腐蚀等优点，可广泛应用于汽车、高速重载轨道、海洋船舶、工程机械等领域，符合新一代先进钢铁材料战略发展方向。但目前存在贝氏体低温转变周期长、强度和延伸率不匹配等问题。项目以Fe-C-Si-Mn系列超高强贝氏体钢为对象，提出通过奥氏体预变形调控超高强度贝氏体钢中残余奥氏体的微观组织这一新思路，目的是实现贝氏体钢超高强度和高延伸率良好匹配，制备综合性能优良的新一代超高强度贝氏体钢。主要研究内容包括：奥氏体预变形对等温贝氏体相变和组织的影响，变形条件下奥氏体力学稳定化研究，残余奥氏体稳定性与超高强贝氏体钢塑性内在关联。重要研究结论包括：（1）对于中碳超高强贝氏体钢，低温变形对贝氏体相变的促进效果随应变量呈非线性变化，存在一个应变使贝氏体体积分数达到最大，即峰值应变（PVS），PVS随变形温度增加而增大，且对应的最大贝氏体转变量减少，当应变量大于峰值应变时，贝氏体体积分数随应变量的增加而减小；（2）确定应变时，存在临界温度Tc，当变形温度超过Tc时，变形对贝氏体相变起到抑制作用；（3）MS点以下变形增加随后等温贝氏体相变孕育期，减弱初始等温贝氏体相变动力学，随先马氏体组织数量增加，弱化效果越明显；（4）低温变形促进残留奥氏体稳定化，有助于获得更多的残余奥氏体组织，采用热变形+等温贝氏体相变的方法，不仅可以提升超高强贝氏体钢强度，而且增加延伸率，制备的中碳超高强贝氏体钢抗拉强度为1755MPa，延伸率为18.1%。上述研究成果，从理论上揭示了变形控制残余奥氏体的微观机理，阐明了残留奥氏体微结构控制与超高强度贝氏体钢延伸率关系，同时也能为生产兼具优良延伸率的超高强度贝氏体钢提供必要理论支持。.项目研究结果已在国内外学术刊物上发表学术论文24篇，其中SCI 收录22 篇，授权国家发明专利3 项，帮助课题组培养硕士研究生2人，博士研究生1 人。