基于空心铸坯的大型厚壁管挤压成形工艺基础研究

As essential basal part of contemporary mechanical device, large diameter thick-walled seamless pipes have found wide application in the fields of thermal power, nuclear power and petrochemical industry. In recent years, the increasing market demand of large diameter thick-walled seamless pipes brings the rapid developing in the corresponding hot extrusion forming technology and equipment research. In order to solving the disadvantages of current production method in hot extrusion forming process, such as long production cycle, low production efficiency, more requirements of production equipments and power consumption, as well as waste materials and other problems. This project put forward a new short process of casting-extrusion composite forming technology, which directly employing the hollow blank with high depanning temperature through hot extrusion forming and then manufacture the large diameter thick-walled seamless pipes. Taking the typical heat-resisting material of T/P91 alloy steel as the research object, the present project will aim to investigate the plastic deformation behaviors, stress-strain relationship and constitutive model in hot extrusion of T/P91 alloy steel by means of theoretical analysis, experimental research and numerical simulation. Therefore, the deformation and metal flow behaviors of deformation zone in hollow blank during hot extrusion will be presented. The effects of hot extrusion parameters on microstructure evolution and forming properties during processing will be formulated. The regulatory mechanism with ‘combine shape forming and performance improving’ during large diameter thick-walled seamless pipes extrusion will be established. Furthermore this can lay a good theory foundation for the high efficient and new short processing technology, provided implementation and application for the forming process, naturally.

大口径厚壁无缝管是火电、核电和石油化工等行业关键、重要的基础部件。近年来我国大口径厚壁无缝管市场需求与日俱增，相应的热挤压成形工艺和装备的研究与开发也快速发展。本项目针对目前我国大口径厚壁无缝管热挤压成形生产工艺存在流程长、生产效率低、需要的装备多、能耗大和浪费材料等问题，提出和研究一种利用环形铸坯直接热挤压成形制造大口径厚壁无缝管的短流程铸挤复合成形新工艺。以厚壁管典型耐热材料T/P91钢为研究对象，通过理论分析、实验研究和数值模拟，研究铸态T/P91合金钢在挤压塑性变形条件下的应力应变关系、本构模型和热变形行为；揭示空心铸坯热挤压变形区材料变形特征和金属流动规律；探讨热挤压工艺参数对成形过程中材料组织演变和成形性能的影响；建立基于空心铸坯的大口径厚壁管热挤压成形过程“成形/成性”一体化调控机制。为这种新的大口径厚壁无缝管高效、短流程生产工艺的实施和推广应用提供理论基础。

大口径厚壁无缝管是火电、核电、石油化工等行业的关键核心构件，常用于高温高压流体的输送。我国大口径厚壁无缝管的生产水平一直较为落后，高性能、大尺寸厚壁管则长期依赖引进。现有的冲孔—热挤压生产工艺生产流程长、效率低、设备投资大、材料和能源浪费严重，为此提出了一种节能、节材、高效的短流程大口径厚壁管铸挤生产方法。本项目针对短流程工艺的关键科学问题展开研究，探究铸态组织向锻态组织转变的热力学行为和热力学条件，进而研究热挤压宏观工艺参数对合金微观组织演变的影响，最终制定合理的短流程工艺参数。. 研究主要针对大口径厚壁管材料铸态P91合金钢材料参数及模型建立、短流程热挤压多参数耦合数值模拟计算、热挤压模具参数化设计、热挤压管件热处理工艺制定、热挤压工厂试验五部分。建立了铸态P91合金的等温晶粒长大模型、两段式热变形本构模型、动态再结晶、亚动态再结晶模型以及静态再结晶的动力学及晶粒模型；将DEFORM数值模拟软件进行二次开发，建立多参数耦合数值模拟计算模型，通过数值模拟计算研究不同热挤压工艺参数对热挤压过程及成形管件晶粒大小的影响，制定短流程热挤压工艺参数：初始挤压温度为1200 ℃，挤压比为9，挤压速度为50 mm/s；热挤压模具挤压角角度为58°、过渡圆角半径R1为70-90 mm、过渡圆角半径R2为100-120 mm、定径带长度h为90-120 mm；热挤压管件的热处理工艺为正火+高温回火，正火温度1060℃、正火时间120min、回火温度750℃、回火时间180min；将制定的热挤压工艺参数进行热挤压工厂试验以及数值模拟计算，热挤压过程位移—载荷曲线、晶粒组织大小的对比结果误差较小，所建立数值挤压模型可靠，热处理后的管件各区域组织转变为性能优良的回火组织，塑韧性得到大幅提高，各项指标均达到相关国标要求，获得良好的综合力学性能。项目所建立的热挤压模型可用于大口径厚壁管短流程工艺的数值模拟研究，极大地降低了实验研究成本，为进一步的研究和工艺推广奠定研究基础，有力推动了我国绿色制造体系的建立进程。