基于凝固过程与固态相变双联调控的Cr13型马氏体不锈钢强韧化机理

The research on alloying with rare elements, solidification process and solid-state phase transformation is launched in order to develop a new way for preparing Cr13 martensitic stainless steel with high strength and toughness. By means of analyzing on the solidification path and the microstructure of multi-component Fe-Cr-Ni-Mo based alloys, and discussing phase formation rule of the steel based on computational materials science, the composition of the steel is determined. The nucleation and growth of the primary phase and the other phases, the distribution of solute elements caused by solute redistribution, the atomic diffusion and interaction are investigated during directional solidification, rapid solidification and microgravity solidification, respectively. The dynamic characteristics of the solid-state phase transformations with different cooling rates are achieved using JMAK model. According to this, the microstructure is further optimized by vacuum quenching and vacuum tempering. On the basis of analyzing solute diffusion, nucleation and growth of grain, lattice distortion, dislocation formation and grain/phase boundary movement, the strengthening mechanism of the second phase, the influence of rare earth elements and austenite on strength and toughness, the strengthening effect from martensitic grain refinement, are revealed. Consequently, a new method for preparing Cr13 martensitic stainless steel with high strength and toughness is proposed.

本项目将掺杂稀土元素微合金化、凝固过程与固态相变研究相结合，探求实现Cr13型马氏体不锈钢强韧化的新途径。通过分析多元Fe-Cr-Ni-Mo基模型合金的凝固路径和微观组织，并且基于计算材料科学方法探索掺杂稀土元素Cr13型马氏体不锈钢的相形成规律，从而优化设计钢材成分。采用定向凝固、快速凝固和微重力凝固三种方法对比研究钢材发生液固相变时初生相和第二相/多相析出物的形核与生长、溶质再分配引起的多溶质元素分布、多元素原子扩散与交互作用等。根据JMAK模型获取钢材在不同冷却速率下的固态相变动力学特征，并据此选取真空淬火和真空回火相结合的特种热处理方式对室温组织进一步优化调控。通过研究溶质扩散、晶粒形核长大、晶格畸变、位错胞形成、晶界/相界迁移等，阐明钢材中第二相/多相析出物的复相强化机理，揭示稀土元素和逆变奥氏体的增强增韧作用，发掘马氏体的细晶强化机制，最终提出一套钢材强韧化制备工艺方案。

Cr13型马氏体不锈钢主要被广泛应用于油气钢管、海上钻井平台、水轮机叶片等领域。基于其应用重要性和急需解决的科学研究问题，本项目选择Cr13型马氏体不锈钢及其模型合金为研究对象，将合金设计、凝固机制和固态相变相结合进行了多尺度协同研究。根据计算材料科学原理优化设计了材料成分，讨论了焓变等热力学参数随温度和成分的变化规律。采用多种凝固实验方法揭示了液固相变时元素原子的扩散与分布、初生相和第二相/多相析出物的形成以及微观偏析特征，获取了枝晶生长动力学规律。结合固态相变原理优化真空热处理工艺参数，对其室温组织及力学性能等进行了主动调控。发掘了掺杂稀土元素对Cr13型马氏体不锈钢凝固组织与力学性能的影响机制。研究结果为Cr13型马氏体不锈钢强韧化提供了一条新途径。