Study On Controlling Of Dimensional Accuracy And Flatness And Residual Stress Of Rail For High Speed Railway

Combined with the 10th Five-Year national key scientific and technological project "the Advanced Technology of High-speed and Heavy-duty Steel", the process parameters affecting the quality of heavy rail were investigated in the present work in order to improve dimensional precision and flatness, and reduce the residual stress. The chief original work of this paper is as follows.(1) Hot rolling process of 60kg/m high precision heavy rail with full-universal pass was proposed based on the present widely used rolling process with the semi-universal pass. Quantity of pass and rolling passes, reduction of each pass, shape and dimension of each pass were determined according to the equipment capacity of the universal production line for heavy rail at Pan-steel Rail Beam Plant, and the section shape and dimension of the blank and the final product, as well as the requirements of products property.(2) Comparative analysis between full-universal pass and semi-universal pass for the production of 60kg/m heavy rail was conducted to investigate the difference of reduction coefficient and the rolling efficiency. The finishing rolling pass with two kinds of universal pass was simulated by FEM using the ANSYS/LS-DYNA software. The displacement along the X direction, and the distribution of stress and strain were comparatively investigated. It has suggested that the 60kg/m heavy rail could be feasibly produced with the full-universal pass, and the dimension precision on the tread and the fluctuation range of the rail height could be improved by the employment of full-universal pass at the finishing rolling pass.(3) The temperature field of heavy rail during cooling process at Walking beam cooling bed was simulated using ANSYS thermal analysis, and the temperature at rail bottom was continuously measured. The temperature distribution of cross section, the temperature difference, and the effect of heat transfer coefficient on the temperature difference were analyzed. The bending of heavy rail during the cooling process at the air cooling bed was simulated using the thermal-structure coupling analysis. And the magnitude and distribution of longitudinal residual stress after cooling process were also studied. By analyzing the pre-bending results of 100m length heavy rail at cooling bed, the pre-bending curve model was obtained in order to ensure the straightness of heavy rail after the cooling process.(4) The horizon straightening process of 60kg/m rail by straightening machine with eight rollers was simulated using the ANS YS/LS-DYNA software. The variation of stress and strain at different part of cross section when straightening, and the rail flatness and distribution of longitudinal residual stress after straightening were investigated. In addition to the effect of straightening process parameters on residual stress, the effect of the curvature degree on flatness and residual stress was also studied.(5) Based on the practical measurement and simulation result of dimensional change of cross section, the effects of straightening process parameters and curvature degree of heavy rail on the dimensional change of cross section were studied.