非调质生产Cr-Ni-Mo系低合金超高强度钢强化机制

The demand for low-alloy ultra-high strength steels in our national economy increased significantly in recent years due to the great press from the problems of resource, energy and environment. Therefore, trying to simplify the producing process of low-alloy ultra-high strength steels and decrease the production cost is significantly important for the iron and steel industry to develop sustainably. Limited by the present capacity of rolling mills, the advanced technology of thermo mechanical treatment is difficult to be applied in the production of low-alloy ultra-high strength steels, which is developed in the study of general low-alloy high strength steels. The traditional heat treatment of quenching followed by tempering after rolling is still used as the main strengthening method for low-alloy ultra-high strength steels, which is of high energy consumption. In the present project, the Cr-Ni-Mo low-alloy ultra-high strength steel was investigated to develop a new thermo mechanical treatment strengthening method for low-alloy ultra-high strength steels, in which the rolling mills are not needed to undertake great load, and thus the energy consuming quenching and tempering treatment can be successfully omitted. An innovative idea was put forward for the strengthening of low-alloy ultra-high strength steels, by combining the large deformation at austenite recrystallization temperature and the small deformation at austenite non-recrystallization temperature. The present project will focus on the effect of the deformation and stress, both at the austenite recrystallization zone and the non-recrystallization zone, on the phase transformation. The ideal microstructure exhibiting both ultra-high strength and enough toughness will be determined after the evaluation of mechanical properties. The key parameters to realize the ideal microstructure will be determined and optimized, and an instructive technology will finally be given.

资源、能源和环境的压力迫使国民经济对低合金超高强钢的需求量猛增，简化低合金超高强钢生产工艺、降低其生产成本对钢铁工业可持续发展具有重要意义。受现有轧机能力的限制，一般级别高强钢中发展起来的形变热处理工艺难以应用于低合金超高强钢的生产，从而传统的高能耗淬火、回火热处理工艺目前仍是此类钢主要强化手段。本项目拟以成分优化的Cr-Ni-Mo系低合金超高强钢为研究对象，探索一种全新的对轧机能力要求低、适应低合金超高强钢的热机械处理强化途径，从而实现低合金超高强钢的非调质生产。拟通过奥氏体再结晶区高温大变形联合未再结晶区低温小变形对Cr-Ni-Mo低合金超高强度钢组织进行控制并实现强化，围绕再结晶区和未再结晶区变形与应力对轧后组织形成过程的影响展开研究。在此基础上，结合力学性能评价，确定获得超高强度与良好韧性配合的理想组织，提出对理想组织进行控制的关键指标，并优化工艺参数、形成指导性工艺方案。

鉴于低合金超高强度钢的生产面临成本高、浪费资源和能源及环境污染方面的问题，探索通过非调质方法实现超高强度，简化生产工艺、降低生产成本，对扩大其在工业中的应用范围具有重要意义。本项目的核心内容探索一种全新的对轧机能力要求低、适应Cr-Ni-Mo低合金超高强钢的热机械处理强化途径，从而为实现非调质生产低合金超高强钢提供理论基础。在项目实施中，通过高精度差分膨胀测量对奥氏体晶粒长大动力学进行分析，以及对奥氏体化过程中碳化物溶解过程分析，确定了该钢奥氏体化条件对连续冷却过程中相变的影响规律；采用热模拟实验，通过分析不同变形条件下的真应力-应变曲线，确定了Cr-Ni-Mo系低合金超高强钢再结晶临界温度、临界形变量，并分析了变形参数对奥氏体再结晶动力学的影响。通过建立热加工图，确立了最佳热变形条件；利用相变动力学分析和多种显微组织分析手段，研究了高温大变形（1000℃）结合低温小变形（850℃）对连续冷却过程中相变行为及微合金碳化物析出行为的影响，确定了通过热机械处理获得均匀、强韧结合的贝氏体组织的强化机制；通过高温大变形控制再结晶和低温小变形控制轧后连续冷却相变，获得了低轧制力非调质生产低合金超高强度钢指导性工艺。项目研究计划圆满完成，并取得预期研究成果，完成了考核指标。课题组发表学术论文13篇，其中SCI检索8篇，EI检索2篇，并申请了相关科学技术发明专利3项。