高强钢大型构件局部控温/控流整体模锻成形基础研究

The technological level of die forging for large components of high strength steel has been becoming a bottleneck that constraining the technological development of advanced equipment in such sectors as aerospace, aviation and express train manufacturing. During the die forging of large components, there exist multiple loops of heating, deformation and cooling. The materials deform so large overall and the differences of temperature and formability defer significantly. These barriers result in difficulties in die filling and poor grain size uniformity in the forgings, which causes performance failure. Therefore, the project proposes an idea to improve microstructure and formability of materials by controlling local temperature and facilitate complicated cavity filling by controlling local flow in the forgings. In order to implement the idea, the project, from the perspective of the whole processing chain from preforming to final die forging of high strength steel large components, tries to control the overall evolution of microstructure and flow behavior in the forging components by cooperatively controlling the local temperature, pattern and sequence of forming in different regions during forging to accomplish the requirements on shape, microstructure and performance of the forging components. For this purpose, several critical scientific issues should be addressed. The first issue is the influence rules of local temperature variation and deformation on evolution of microstructure and uniformity of grain size in the components. The second one is the influence rules of local flow control on the overall forming and filling behavior of the material. The last one is to get the inheritance mechanism of deformation and microstructure in the forgings among upstream and downstream operations. Based on the research results, the project tries to investigate the optimization method to integral die forging process by local control of temperature and flow pattern and establish the integral forming technology and processing guide for high strength steel large components to meet the manufacturing demands of advanced equipment for our country.

大型构件的模锻技术水平已成为制约我国航空航天、高铁等领域高端装备技术发展的瓶颈。由于模锻过程存在多道次的加热-变形-冷却工序，整体变形量大、不同部位温差及流动性能差别显著，导致大型锻件充模困难、晶粒均匀性差，性能难以满足要求。本项目提出以局部控温改善微观组织与材料流动、局部控流促进复杂区域充满的思想，从高强钢大型构件制坯-模锻成形全流程角度出发，协同控制锻造过程中锻件不同部位的温度和流动，实现对其组织演变和流动行为的控制，保证锻件的形状、组织结构和性能要求。主要研究：局部控温/控流对高强钢组织结构演化及晶粒均匀性的影响规律、局部流动控制对材料整体流动与充模行为的影响规律、及多工序间锻件变形和组织结构演变的宏微观继承机制等关键科学问题。在此基础上，探讨局部控温控流整体模锻成形制造工艺的优化方法，构建高强钢大型构件整体模锻成形制造技术体系和工艺规范，以满足我国高端装备的制造需求。

高强钢广泛应用于航空、航天、军工等行业的大型构件制造。由于高强钢大型构件形状复杂，材料变形抗力大，在模锻过程中，一般需要经过多次的加热、变形、降温等工序组合，才能完成最终锻件。这些工序对构件成形的流变行为、晶粒演变和产品性能产生影响，为准确预测高强钢大型构件在整个成形过程中的行为，需要对高强钢成形整个过程的所有环节进行建模。本项目围绕高强钢在全流程、大应变跨度、宽温度范围、复杂加载路径状态下的多道次成形过程的流动行为和动态再结晶、亚动态再结晶、静态再结晶、晶粒长大等多种形式的微观组织演化两个方面开展研究。本项目首次提出软化百分比概念，通过软化百分比来表征、传递多道次变形过程各种软化机制对材料变形行为的影响，构建了统一的宏微耦合的全流程本构模型，实现了复杂多道次变形过程的准确数值模拟分析。通过原位实验观测，首次发现常规认为仅发生在变形过程的应变诱导晶界迁移机制在变形后工件保温过程也存在，并且是晶粒形核后引起晶粒尺寸迅速增大的关键原因。通过开发，将这些模型集成于有限元模拟系统，以此为平台，开展了高强钢大型构件局部控温与控流成形方法的研究，基于大型构件锻造时会形成连皮和飞边的特点，将锻件局部连皮或飞边尺寸与材料分流面位置关联起来，通过改变它们的尺寸调节分流面位置，控制材料的定向流动，同时结合局部控温，促进材料优先流向难充满部位，并形成有利于细晶形成的工艺状态。研究成果已初步应用于高强钢起落架外筒模锻件全流程的工艺设计及优化，应用于B787、C919起落架锻件等的制造。在项目研究过程中，在材料科学、材料成形加工等领域的国内外重要期刊及重要会议上发表论文44篇，其中SCI源刊27篇、EI源刊4篇、中文核心期刊4篇；获发明专利授权4项、受理3项；部分成果作为 “多工位精锻净成形关键技术与装备”的内容获2016年国家技术发明二等奖。