基于空心钢锭的大型厚壁筒形件轧制成形基础理论与关键技术

According to disadvantages of multi-process operations, low material utilization ratio, long manufacturing cycle and high manufacturing cost in the open die forging process with solid steel ingots for manufacturing large cylinders, a new short process of large thick-wall cylinder rolling with hollow ingots was put forward in this project. By taking 600-1000MW retaining rings as the research object, the new process will be investigated systematically by means of thermo-mechanical modeling experiments, microstructure analyzing and testing, physical and numerical simulation, process tests. In the proposed project, the characteristics of solidification structures in hollow ingots manufactured by conventional melting casting and ESR methods will be analyzed; microstructure evolution mechanisms and rules of casting microstructures in hollow ingots during hot working will be studied; cylinder rolling pattern in the radial-axial direction and deformation parameters for obtaining small uniform grain structure will be optimized. On the basis of ring rolling theory, the stress-strain state and metal flow pattern in the rolling area of large thick-wall cylinder will be analyzed; mechanical analysis, parameter design, rolling load calculation, rolling kinematics and dynamics of cylinder rolling will be carried out for establishing fundamental theory and key technologies of large thick-wall cylinder rolling process. The quality control method for configuration, dimensions and internal structure of the rolled cylinder will be put forward. And the short process of cylinder rolling with hollow ingots will be developed for manufacturing retaining-ring large thick-wall cylinders.

针对传统大型厚壁筒形件实心钢锭自由锻制造中存在的成形工序多、材料利用率低、生产周期长和成本高的弊病，本项目提出基于空心钢锭的大型厚壁筒形件轧制短流程新工艺。并拟以600-1000MW级护环为研究对象，采用热力模拟、组织分析测试、物理模拟、数值模拟及工艺试验相结合的研究方法，分析常规冶炼浇注空心钢锭和电渣重熔空心钢锭凝固组织特征，开展空心钢锭凝固组织轧制变形条件下的演变机理和规律的研究，优化获得细匀化组织的径轴向轧制变形方式和变形参数；在环件轧制理论和技术基础上，通过分析大型厚壁筒形件轧制变形区应力应变状态和金属流动规律，进行筒形件轧制力学分析与参数设计、轧制力能计算、轧制运动学和动力学分析研究，提出轧制过程中筒件外形尺寸和内部组织的质量控制方法，建立大型厚壁筒形件轧制成形理论与关键技术，开发我国大型护环类筒形件空心钢锭轧制成形短流程新工艺。

项目针对传统实心钢锭自由锻造大型厚壁筒形件中存在的成形工序多、材料利用率低、生产周期长和成本高等弊病，以大型厚壁筒形护环锻件为研究对象，开展了基于空心钢锭的大型厚壁筒形件轧制成形基础理论与关键技术研究。研究获得了常规冶炼浇注和电渣重熔制备空心钢锭孔隙性缺陷和凝固组织形貌尺寸与分布特征，及其工艺控制参数。研究得到了氮含量对该钢合金相图的影响规律，以及N含量和时效制度对Mn18Cr18N钢析出物、析出行为及其对力学性能的影响。研究了柱状晶凝固组织热变形行为与微观组织演变机理和规律。采用分子动力学模拟方法，揭示了柱状晶组织变形的各向异性行为，即加载方向对柱状晶变形的力学行为、变形位错和微观亚结构的影响规律。揭示了柱状晶凝固组织高温低应变速率下位错主导的动态再结晶机理和高温高应变速率下孪晶主导的动态再结晶机理。发现了孪晶控制的动态再结晶动力学演变规律有别于位错控制的经典动态再结晶演变规律。建立了位错控制机理的动态再结晶晶粒和动力学模型。研究获得了凝固组织热变形道次间的力学行为和静态再结晶演变规律，建立了静态再结晶晶粒和动力学模型。提出了采用罗德参数和应力三轴度函数的新的孔洞闭合模型，以及基于速度间断功率变化的孔洞闭合判据。提出了厚壁筒形件轧制锻透的修正模型和最小压下量修正计算方法；分析了厚壁筒轧制的辊系尺寸和速度对厚壁筒形件变形规律影响，优化了辊系速度的取值范围和匹配关系；研究了空心钢锭粗大凝固组织在轧制过程中的演变规律，优化了消除空心钢锭内部冶金缺陷的轧制工艺参数，形成了基于空心钢锭的厚壁筒形件轧制成形成性理论与关键技术。. 本项目所揭示的柱状晶凝固组织的变形各向异性行为以及孪晶控制的动态再结晶机理和规律具有重要的科学意义。基于空心钢锭的大型厚壁筒形件轧制短流程新工艺具有节能节材、简化流程、降低成本等优点，其理论、工艺和方法在能源、电力、冶金、重型装备等领域的厚壁筒形件制造方面具有良好的应用前景。