Multi-Field Coupled Numerical Simulation And Technological Optimization Of Rod And Wire Rolling Process

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.