【作者】 岳重祥；

【导师】 张立文；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2010， 博士

【摘要】 轧制是金属塑性成型的重要方法,轧制成型的钢材是数量最大的金属材料制品。在诸多轧制产品中,棒线材由于断面形状简单,品种繁多,所以其用途非常广泛。随着现代工业的飞速发展,各领域对棒线材产品的质量要求越来越严格和专门化。这就要求各钢铁企业不断改进生产工艺,精确控制轧钢过程,生产多规格、高品质的棒线材产品。然而,由于轧钢过程涉及多阶段、多因素,是几何与材料高度非线性的复杂接触问题,要对其进行较全面的在线生产试验研究,需要耗费大量的人力、物力和财力。近年来,物理冶金和有限元理论的研究取得巨大进展,热力模拟实验设备日益普及,它们从理论和实验两个方面为轧钢过程的多场耦合数值模拟打下了坚实的基础。通过对轧钢过程进行多场耦合数值模拟,冶金工作者可以全面、细致地了解和掌握轧制过程中轧件内部各宏观场量和微观场量的分布与演变情况,从而达到缩短研发周期、降低生产成本和提高产品质量的目的。在前期工作的基础上,本文紧紧围绕棒线材轧制过程多场耦合数值模拟这一主题展开研究,主要研究内容和结论如下：1.基于大型非线性有限元软件MSC.Marc,开发了棒线材轧制过程的多场耦合数值模拟技术。借助该技术,对某特钢集团棒线材1号生产线采用150mm×150mm方坯生产Φ12.7mm、Φ15.4mm和φ22.4mm轴承钢、碳素钢及不锈钢棒线材的轧制过程与该特钢集团棒线材2号生产线采用180mm×180mm方坯生产Φ10.0mm、Φ17.5mm和φ25.0mm轴承钢棒线材的轧制过程进行多场耦合三维数值模拟,得到了轧制过程中轧件内部各宏观场量和微观场量的分布与演变情况。Φ15.4mm轴承钢棒线材轧制过程中,温度和晶粒尺寸的模拟结果与实验结果吻合较好,轧制速度的模拟值与工艺设定值吻合较好,验证了模拟的准确性。2.详细分析了轴承钢、碳素钢和不锈钢棒线材轧制过程中轧件内部温度和微观组织的演变情况。结果表明,轴承钢轧制过程中的微观组织演变情况非常复杂,轧件内的奥氏体晶粒尺寸在动态再结晶、亚动态再结晶、静态再结晶和晶粒长大的共同作用下,总体上不断减小；完全再结晶后的晶粒长大能够显著影响碳素钢轧件内部的奥氏体晶粒尺寸；而不锈钢轧制过程中奥氏体晶粒尺寸的变化主要取决于轧制时的动态再结晶。3.采用分段模拟的方法对不同工艺参数条件下Φ15.4mm轴承钢棒线材的轧制过程进行多场耦合三维数值模拟,分析了轧件温度、轧制速度、轧辊辊缝、轧辊辊径和初始奥氏体晶粒尺寸对轧件内部奥氏体晶粒尺寸演变的影响。结果表明,轧件温度的改变能够显著影响轧件内部奥氏体晶粒尺寸的演变；轧制速度的适当调整和轧辊辊径的适当减小基本不影响轧件内部奥氏体晶粒尺寸的演变；初始晶粒尺寸大小和轧辊辊缝的适当调整能够影响奥氏体晶粒尺寸的演变,但对多道次轧制后的晶粒尺寸影响较小。在实际轧制过程中,为了获得合格产品,可以在保证定径过程轧制温度的基础上；对其他各工艺参数进行适当调整。4.基于棒线材轧制过程的孔型设计原理,开发了采用300mm×300mm方坯轧制生产Φ70mm与Φ80mm轴承钢棒材的孔型系统。通过数值模拟,对设计的轧制工艺进行了优化。然后,根据优化后的轧制工艺,对该轧制过程进行多场耦合三维数值模拟,得到了轧制过程中轧件内部温度、应变、应变率和奥氏体晶粒尺寸的分布与演变情况,预测了各道次轧制时的轧制力和轧件变形情况。模拟结果表明,采用优化后的轧制工艺,能够获得合格的棒材产品,且内部组织比较均匀。更多还原

【Abstract】 Rolling is the major method of metal plastic forming. Rolled steel occupies considerable proportion of metal products. In all rolled products, rod and wire with simple shape and numerous varieties are widely used. With the rapid development of modern industry, industrial fields put forward stricter and more specialistic demands on the quality of rod and wire products. So iron and steel enterprises must optimize production technology, and accurately control rolling process to produce rod and wire products with numerous specifications and high quality. While rolling process which includes many phases and depends on many factors is a complicated contact problem with geometric nonlinear and material nonlinear. A detailed study on the problem by on-line experiments needs to consume a large amount of manpower, material resources and financial resources. In recent years, the universalization of thermo-mechanical simulation machines and great progress of physical metallurgy and finite element theories lay experimental and theoretical foundations for multi-field coupled numerical simulation of rolling process. The simulation can help metallurgists understand the distributions and evolutions of macroscopic and microscopic field-variables in the rolled piece during the rolling process in detail, then achieve the aim to shorten development time, reduce production costs and upgrade the quality of product. Based on previous work, the paper pays all attention to multi-field coupled numerical simulation of rod and wire rolling process. The main research contents and conclusions are as follows:1. Based on nonlinear finite element software MSC.Marc, the paper develops multi-field coupled numerical simulation technique of rod and wire rolling process. In a special steel group, rod and wire rolling production line-No.1 producesΦ12.7mm,Φ15.4mm and 022.4mm bearing steel, carbon steel and stainless steel rods and wires using 150mm×150mm square billets, and rod and wire rolling production line-No.2 producesΦ10.0mm,Φ17.5mm andΦ25.0mm bearing steel rods and wires using 180mm×180mm square billets. With the aid of the technique, the paper performs multi-field coupled numerical simulation on these rolling processes, and the distributions and evolutions of macroscopic and microscopic field-variables in the rolled pieces during these rolling processes are obtained. During the rolling process ofΦ15.4mm bearing steel rod and wire, the simulation results of temperature and grain size are in good agreement with measured ones, and the simulation values of mill speed quite agree with technological parameters. The comparisons show the validity of simulation results.2. The paper analyzes the evolutions of macroscopic and microscopic field-variables in the rolled pieces during the rolling processes of bearing steel, carbon steel and stainless steel rods and wires in detail. Results show that microstructure evolution during the rolling process of bearing steel is very complex, and the combined action of dynamic recrystallization, meta-dynamic recrystallization, static recrystallization and grain growth makes austenite grain size in the rolled piece decrease continuously. In addition, grain growth after complete recrystallization has an important effect on the grain size in the rolled piece of carbon steel, and the evolution of grain size during the rolling process of stainless steel depends mainly on dynamic recrystallization which occurs in deformation phases.3. The paper simulates the rolling processes ofΦ15.4mm bearing steel rod and wire under different technological parameters with the segmental simulation method, and analyzes the effects of temperature, mill speed, roller gap, roller diameter and initial grain size on the evolution of grain size in the rolled piece. Results show that the change of rolling temperature has an important effect on the evolution of grain size in the rolled piece. The appropriate adjustment of mill speed and the appropriate reduction of roller diameter have little influence on the evolution of grain size in the rolled piece. Initial grain size and the appropriate adjustment of roller gap can affect the evolution of grain size to a certain extent, but have no effect on the grain size after multi-pass rolling. When the temperature of rolled piece during the sizing process can be ensured, iron and steel enterprises can adjust other technological parameters in a certain range to produce qualified products.4. Based on pass design theory of rod and wire rolling process, the paper designs a pass system to produceΦ70mm andΦ80mm bearing steel rods using 300mm×300mm square billets. According to simulation results, the paper optimizes the rolling technology, and performs multi-field coupled numerical simulation on the rolling process with optimized technology. The distributions and evolutions of temperature, strain, strain rate and austenite grain size in the rolled piece during the rolling process are obtained, and rolling force and deformation of rolled piece in every pass are predicted. Simulation results show that qualified rod products can be obtained with optimized technology, and the uniformity of microstructure in rolled piece is good.更多还原