高热强性低活化铁素体/马氏体钢组织设计及其搅拌摩擦焊接

With the promising development opportunity for nuclear power construction, the high-technology export with nuclear power as the representative has been turned into one key role to promote our country's economic development, which makes urgent requirements for the localization of key components for nuclear power equipment. Reduced activation ferritic/martensitic (RAFM) steels have been widely used as the candidate structural materials for cladding and outer tubes of fuel assemblies in advanced fast reactors, and the primary structural materials for cladding structure in future fusion reactors. To improve the thermal efficiency and safety of the nuclear power plants, it is essential to further improve the heat resistance and radiation stability of the RAFM steels. In this project, based on the previous completed studies on high Cr ferritic heat-resistant steel for power plants and the selection principle for reduced activation elements, regarding the composition design and optimization, attention would be focused on the combined effects of W and Ta on microstructure and mechanical performance of RAFM steels, as well as the trace addition of Zr, with respect to the microstructure modification, the strengthening mechanism combining sub-boundary hardening and precipitation hardening would be stressed, aimed at attaining the refined martensite laths that are pinned by the nano-scale precipitates with high thermal stability. Considering the limitations of diffusion bonding technology (adopted in the manufacture of cladding part of fusion plant) in joining large sized parts, the exploration and optimization of friction stir welding process for RAFM steels would be conducted, and the strength degradation mechanisms of the joints would be clarified. The strategies to improve the reliability of the friction stir welded joints would also be developed, to ensure the consistent high-temperature performance of the overall joined component and promote the development of nuclear advanced manufacturing industry.

核电建设正迎来战略发展机遇期，以核电为代表的高端科技出口已成为推动我国经济发展的重要力量，这其中迫切需要实现核电关键部件的国产化。低活化铁素体/马氏体钢广泛应用于先进快堆燃料组件包壳管和外套管，以及未来聚变堆包层结构，进一步提高其热强性和辐照稳定性对改善建设机组的热效率及安全可靠性具有重要意义。本项目拟在前期已完成的火电用高Cr铁素体耐热钢的研发基础上，依据低活化元素选取原则，在钢材合金成分设计中重点考虑W、Ta组元间的交互作用，以及痕量Zr组元的添加；在组织设计中突出亚晶强化和沉淀相复合强化机制，实现纳米级高热稳定性沉淀相对细化马氏体板条界的有效钉扎作用。由于已在核聚变包层模块应用的扩散连接技术受炉体尺寸限制，难以完成大工件连接，拟开展低活化铁素体/马氏体钢搅拌摩擦焊工艺探索及优化，阐明接头高温强度退化机制，提出相应强化方法，实现构件整体高温性能的一致性，从而为核电高端制造产业发展助力。

核电建设正迎来战略发展机遇期，以核电为代表的高端科技出口已成为推动我国经济发展的重要力量，这其中迫切需要实现核电关键部件的国产化。低活化铁素体/马氏体钢广泛应用于先进快堆燃料组件包壳管和外套管，以及未来聚变堆包层结构，进一步提高其热强性和辐照稳定性对改善建设机组的热效率及安全可靠性具有重要意义。本项目在前期已完成的火电用高Cr铁素体耐热钢的研发基础上，开展了相变行为及沉淀演化的研究，完成了合金优化设计，开发了微观组织设计与调控方法，在低活化铁素体/马氏体钢高温塑性变形机制研究的基础上形成了搅拌摩擦焊工艺优化指导方案，澄清了搅拌摩擦焊接头蠕变失效机制。取得的重要成果包括：澄清了低活化铁素体/马氏体钢中的板条马氏体非连续转变动力学，提出了板条马氏体相变的“局域应力场”理论，揭示了退火孪晶与冷却速率对板条马氏体非连续转变动力学的影响机制；开发了Ta/Zr复合强化的高热强性低活化铁素体/马氏体钢种，600℃、180MPa蠕变寿命相较于未添加Ta/Zr钢种提升30倍以上；探明了低活化铁素体/马氏体钢在中高温条件下的动态应变时效行为的机制，指出溶质原子在中温区间与可移动位错交互作用增强限制了可移动位错的移动性，塑性变形过程是通过位错“雪崩式”增殖进行，导致了塑性的降低；开发了“中温轧制&两步回火”工艺，实现了组织细化，从而使得强度与塑性同步提升；探明了摩擦搅拌焊工艺参数对焊接接头缺陷和性能的影响，澄清了焊接工艺参数对接头组织形成及演化的作用机制；发现了接头中的组织不均匀性对蠕变过程有重要影响，热影响区中存在的等轴晶粒及粗大第二相是导致接头蠕变失效的最关键因素。项目执行期间，累计发表标注资助的SCI收录论文54篇，授权中国科技发明专利11项。本项目的顺利实施将助于提升我国核电关键构件的整体制造水平，推进中国核聚变实验堆的研发进程。