特殊钢铸锻一体化制备及组织调控基础研究

Equipment manufacturing is the pillar industry of national economy. However, it needs urgently to transform and upgrade under present economic situation. The innovation on processing routine is an effective way to promote the development of the industry. Heavy forgings are fundamental elements of major equipment, but always have a long manufacturing routine which includes melting, casting, forging and heat treatment. What are even worse, severe defects such as macrosegregation, shrinkage cavity, and coarse grains are usually caused on final products. In this project, by breaking through the traditional routine of forging ingots after complete solidification, ingots are forged before solidification completed with a natural status of solidified shell and mushy core. By forging solidifying metal, the coarse dendrites in the mushy core are broken down into globular grains under the high pressure and deformation. The melt with suspending globular grains become thixotropic like the slurry of semisolid metal and is highly fluid, being able to feed the porosity and reduce segregations. Meanwhile, the routine is shorten, and thus the energy and resource consumptions are reduced. In this study, through combining simulations and experimental studies, we try to explore the behavior of solute transports, evolutions of defects and microstructure with heavy deformation at high temperature, as well as to reveal the mechanism of forced feeding, segregation lowering and grains refining under high pressure, finally to extend the research area of heavy deformation in both solid region and semisolid region. On basis of these studies, we will further develop the novel technology, offering technical supports to the forging steel industry by reducing cost over 15%.

装备制造业是国民经济的重要支柱，迫切需要转型升级，通过工艺流程创新是引领行业发展的有效途径。大锻件是重大装备的基础，但传统制备工艺流程长，偏析、疏松、粗晶等缺陷严重，制约产业发展。本项目突破钢锭完全凝固后再加热锻造的传统方法，利用铸坯凝固过程中表层处于固态而芯部仍处于两相区的自然条件，直接进行超高温“软芯”锻造，通过大应变破碎树枝晶获得球状晶，利用芯部半固态浆料的触变特性实现孔洞补缩并减少偏析，显著提升锻件中心质量，缩短加工流程，降低成本与能耗。项目拟通过铸锻一体化成形过程的模拟与实验研究，探索金属在超高温形变过程中的溶质传输、缺陷和组织演化行为，揭示高压下强制补缩、偏析减轻和组织细化机制，拓展金属在固液两相区与固相区协同大变形的新学科方向。在此基础上，开发短流程铸锻一体化成形原型技术，降低模具钢等锻件/锻材制造成本15%以上，为辽宁乃至全国重机与特钢企业的高品质清洁制造提供支撑。

大锻件是重大装备的基础，但传统制备工艺流程长，偏析、疏松、粗晶等缺陷严重，制约产业发展。本项目突破钢锭完全凝固后再加热锻造的传统方法，利用铸坯凝固过程中表层处于固态而芯部仍处于两相区的自然条件，直接进行超高温“软芯”锻造，通过大应变破碎树枝晶获得了球状晶，利用芯部半固态浆料的触变特性实现了孔洞补缩并减轻了偏析，显著提升了锻件中心质量。在基础研究方面，结合第一原理计算，建立了耦合固相晶粒运动/变形和溶质自然对流的凝固晶粒生长多晶相场模型，揭示了不同运动机制下枝晶生长过程中的流场演化规律，以及晶体生长、液体流动和晶体运动/变形之间的交互作用规律，阐明了枝晶生长形貌、生长动力学和枝晶间偏析等受自然对流和晶粒运动/变形的影响特点和作用机制。宏观尺度上，利用任意欧拉-拉格朗日方法建立了耦合固相变形和液相流动的宏观偏析有限元模型，对未完全凝固的工业钢坯挤压过程中的偏析行为进行了模拟，温度曲线、元素分布均与实验测量结果吻合良好。最后，成功实现了铸造-锻造全流程数据传递与数值模拟技术开发，能够准确确定钢锭自然冷却、冷封冒口、高温脱模以及“软芯”锻造的时间节点和变形工艺关键参数。在工程应用与技术开发方面，结合一系列Gleeble实验室研究、500kg级缩比件和20吨级等比件实验研究以及铸锻一体化模拟技术，确定了液相分数为10~20%的最佳两相区变形时刻，相继实现了加氢反应器、法兰、模具等产品的短流程制造，涉及钢种近10个。通过此技术生产出的锻件探伤合格，力学性能达标，相比传统工艺大大缩短了生产制造流程，节能30%，制造成本降低了15.9%，真正实现了铸锻一体化绿色短流程制备，开创了特殊钢和重机行业节能减排的新模式。通过本项目的开展，拓展了金属在固液两相区与固相区协同大变形的新学科方向。培养了相关领域的高层次人才若干，并建立了广泛的国际合作关系。