Stressstrain state of metal at the initial stage of railway rails rolling

Abstract

Based on the studies of stress­strain metal formation during railway rails rolling in roughing stands of a universal rail­and­beam mill, carried out using the DEFORM­3D software package, the authors have determined the features of distribution of the Cockcroft­Latham criterion over the cross­section of the rolled stock of various shapes. An extremely uneven distribution of the Cockcroft­Latham criterion over the roll section has been established. According to the data obtained, values of the specifed criterion are minimal in the axial zone, and in the near­surface layers the greatest value of the Cockcroft­Latham criterion and, accordingly, the highest probability of defects formation occur near the gauge vertical axis. In gauges of complex shape (“trapezium”, “recumbent trapezium”, rail gauges), the authors have revealed the presence of local zones with maximum Cockcroft­Latham criterion, located in the places where the foot of the rail profle is formed. And rolling in gauge of the “trapezium” type is marked by the presence of such a zone in the near­surface area near the gauge vertical axis. Within the framework of determining formation regularities of the diagram of metal stress­strain state at the initial stage of rail rolling, direct relationship was established between the uneven temperature distribution over the section of rolling and the values (maximum and average over the section) of the Cockcroft­Latham criterion. At the same time, it was shown that uneven temperature distribution over the cross­section of the roll tends to decrease with an increase in the coefcients of extracts along the passes and increase in tilting frequency, regardless of the shape of the used gauges. For gauges of complex shape, in addition to the listed parameters, an increase in similarity of shape of the roll and gauge used also has a signifcant effect on reducing temperature inhomogeneity. Based on the results of theoretical studies, a new mode of railway rails rolling has been developed. Its pilot testing in the conditions of a universal rail­and­beam mill of JSC “EVRAZ ZSMK” has shown a decrease in rail rejection by 0.78 % compared to the previously used rolling mode.