Research On Kinematics And Forming Process And Evolution Rules Of Microstructure And Properties For Ring Rolling Of 50Mn Steel

The ring of slewing bearing made of 50 Mn steel is a new kind of mechanical parts and is widely applied to machinery manufacturing because of its higher values of plasticity, hardness, corrosion resistance and pressure resistance. Regarded as the main forming process of slewing bearing ring, radial-axial ring rolling, is restricted by the coupling impact of a plurality of nonlinear factors and the multi-variable effects, so it has an important role in forming quality of ring rolling process. By designing the reasonable hot ring rolling procedures, it can get controlling geometry and microstructure of ring blank precisely, and can offer scientific reference in quality improvement of ring blank. In fact, it is based on setting the available parameters of ring rolling to control forming process of ring blank.On the basis of the theory of ring rolling in this thesis, the formulas of increasing motion in ring diameter, rotational motion of ring, linear fed motion of mandrel roller and upper-roller, guiding motion of centering rollers are deduced by mathematical methods. The main factors of these motions are derived from the formulas of these motions. In analysis of the case of ring rolling process, the reason of the ring bent by the centering rolls is explained well, and some reasonable measures to avoid this situation are also offered. By combination of the theory of ring rolling and the method of finite element analysis, regularities of metal flow, displacement field and temperature field are studied. Influences on macro quality of ring forming from changing rotating speed of driving roll, initial temperature of ring blank and friction factor between driving roller and ring blank are studied by the software of Simufact.Forming 13.3.After studies on numerical simulation analysis of deformation and thermal transmission, regularities of metal flow, displacement and temperature fields are obtained: the metal in the region near outer diameter of ring blank flows quickly, the metal in the region near center diameter of ring blank flows moderately, the metal in the region near inner diameter of ring blank flows slowly. Equivalent plastic strain of ring blank gradually extended from the region near outer and inner diameter to middle diameter. The region of ring blank near outer diameter and inner diameter is bigger deformation zone, while the region of ring blank near middle diameter is slight deformation zones. The temperature of ring blank gradually decreases from the region near outer diameter and inner diameter to middle diameter. The higher temperature zones are in the region near middle diameter, while the lower temperature zones are in the region near outer diameter, inner diameter, upper surface and lower surface of ring blank. The method of variable change in a single parameter is used to study effects of different rotating speeds of driver roller, initial temperatures of ring blank and factors of shear friction on displacement field and temperature field of ring blank.When rotating speed of driver roller increases, the values of non-uniformity of equivalent plastic strain and temperature increase correspondingly. When initial temperature of ring blank increases, the values of non-uniformity of equivalent plastic strain decreases initially and increases afterwards; the values of non-uniformity of equivalent temperature increases initially and decreases afterwards. When shear friction factor increases, the values of non-uniformity of equivalent plastic strain and temperature increase correspondingly. Finally, evolution rules of microstructure and properties of 50 Mn steel in production process are obtained by experiments. Specimen in thermal refining state is a better combination of toughness and strength than specimen in rolling state, whereas specimen in forging state is a lot worse. Meanwhile, specimen in rolling state has finer grain than specimen in forging state, specimen in thermal refining state has coarser grain than others. The distributions of displacement field and temperature field on the ring rectangular cross –section in simulation result of FEM are verified by experiments. the distribution of displacement filed and temperature filed in the cross-section of ring blank are verified by experiments.According to the findings of this thesis, reference materials and technical support for ring rolling production of slewing bearing ring made of 50 Mn steel are provided. Meanwhile practical and scientific evidences for precisely controlling ring shape in ring rolling process are also provided.