Study On The Deformation Permeability Of Large Size Bar Rolling

Large-size bar is widely used in national defense and military industry, shipbuilding industry, nuclear power equipment, large-scale shaft parts, metallurgical equipment, machinery manufacturing industry and other fields. With the rapid development of our country's economy,its demand and requirement are getting higher and higher. The traditional production method is forging for bar larger than ?250mm. With the development of continuous casting technique and rolling mill equipment, rolling becomes the main production method instead of forging,which realizes industrial producing and reduces production cost greatly. But the internal pore defects of billet affect the product quality seriously. The deformation is difficult to penetrate into billet core because of limited compression ratio and it results in the failure of pore defects' compaction and welding together.To solve this problem, using finite element analysis software MARC to analyze and research the rolling deformation situation of ?600mm round billet rolling to 300 mm square billet and 488mm×326mm rectangular billet rolling to 220 mm square billet in box pass rolling,metal deformation of rectangular billet in improved box pass, and rolling deformation of round billet in oblate hexangular and diamond pass.Calculate the strain distribution, stress state,section shape dimension, rolling force and other important parameters. Main conclusions are:(1)When round and rectangular billet are rolling in box pass, the stress state in deformation zone near billet core is two tensile stresses and one compressive stress. The residual stress state of round billet is three tensile stresses, while it's two tensile stresses and one compressive stress for rectangular billet after box pass rolling which is more conducive to deformation and penetration and rectangular billet fills the box better. Under the condition that the compression ratio is basically the same, round billet core total strain is 1.470, rectangular billet core total strain is 1.421, they are basically the same, and the equivalent strain of rectangular billet distributes more uniformly than that of round billet when rolling in the box. When the groove sidewalls serve to limit the broadening, tensile stress decreases and it even changes to compressive stress, and the stress state near billet core is two compressive stresses and one tensile stress, deformation penetrates to the core obviously.(2)When reducing the slope of sidewalls, increasing the depth of groove of box pass and using it to roll rectangular billet, residual stress changes from two tensile stresses and one compressive stress to two compressive stresses and one tensile stress, and billet fills the new box better. Equivalent strain in the billet core after each new box pass is larger than that of original pass, total strain increases from 1.421 to 1.732, and the deformation permeability isenhanced. The strain distribution in the improved pass is more uniform than that in the original pass, and the energy consumption is low, the rolling process is more stable.(3)When rolling round billet in oblate hexangular and diamond box, equivalent strain in the billet core after the first pass is 0.165 and 0.382. In deformation zone near billet core, the stress state in diamond box is two compressive stresses and one tensile stress, the stress state in oblate hexangular box is two tensile stresses and one compressive stress. After deformation, the residual stress state in diamond box is two compressive stresses and one tensile stress while that is two tensile stresses and one compressive stress in oblate hexangular box. The strain distribution in diamond box is uniform and the residual stress is small, and the deformation permeability is the best. But the diamond box is not suitable for large reduction rolling, and the oblate hexangular box can achieve better penetration of the deformation of round billet during rolling.