V. N. Peretyat’ko

Roller grooving in ball-rolling mills. Part 1

In ball rolling, the metal is deformed in rollers with helical grooves. Accordingly, the deformation zone may be dividing into the shaping section, where the blank is captured and rolled and the ball is formed, and the finishing section, where the ball is smoothed, its final dimensions are attained, and the links between balls are severed. For normal rolling, the shaping section is calibrated. In the present work, the roller grooving for a spherical blank is calculated, when the ball diameter is 125 mm. The initial data for grooving of the ball mill are presented.

Rolling of metal balls

The rolling of balls (diameter 93 and 125 mm) of precise mass in helical grooves is simulated by means of QForm-3D and DEFORM-3D software. A model of a virtual rolling mill is created. Analysis of the stress state at characteristic points along the rolling axis focuses on the effective stress, the components of the stress tensor, and the mean normal stress. The mass of balls rolled on new and worn rollers is measured. The quality of internal metal layers is verified, and the hardness of rolled balls over the vertical and horizontal symmetry axes is measured. Modeling of ball rolling shows that the hot blank (a rod of hot-rolled steel) is satisfactorily captured by the rollers. Rolling is stable, without slipping. The blank completely fills the grooves; no gaps are observed between the metal and the walls. The crosslinks between the balls are completely eliminated within the rollers. The crosslinks are cut by the rim of the rollers and pressed into the body of the ball. The individual balls continue to roll along the finishing section of the groove; the stubs of the crosslinks are smoothed; and a completely shaped ball with a smooth surface emerges from the rollers. In modeling the stress–strain state, all the components of the stress tensor are negative. In other words, all the components of the stress tensor are compressive in rolling of the balls. Statistical analysis of the data from weighing of the rolled balls (diameter 93 and 125 mm) shows that the mass deviates from the required value by no more than 1%. Measurement of the hardness over the diametric cross section of the balls shows that there is no decline in hardness in the internal layers. That indicates high quality of the ball core.

High-temperature plasticity of the solidification zones of continuous-cast Э76Φ rail-steel billet

The high-temperature plasticity of electrosmelted Э76Φ rail steel is investigated in the range 950–1250°C. The best plasticity is obtained at 1150°C, with satisfactory microstructure.

Inhomogeneity of the hot deformation of austenitic steel

By high-temperature metallography, the nonuniformity of deformation is studied for 08X18H10T steel with 28% δ ferrite. The mean strain of the ferrite is greater than for the austenite; this difference increases with rise in temperature. Correspondingly, the slip along phase boundaries increases. The hot-microhardness ratio of δ ferrite and austenite declines with increase in test temperature.

Stamping Axisymmetric Forgings

As a rule, cylindrical blanks are used in hot bulk stamping of axisymmetric parts. However, cutting the rod into measured lengths is associated with fluctuation in mass of the blank on account of distortion of its end geometry and change in its length. Therefore, seams arise in the stamping of such blanks. A promising approach to the deformation of axisymmetric parts (gears, disks, flanges, etc.) is stamping from spherical blanks obtained by hot rolling of rod on a ball-rolling mill. In the present work, experiments on the seamless stamping of axisymmetric forgings from a spherical blank (diameter 60 mm) are conducted for flanges and lids. The forgings are illustrated in Fig. 1, with the relevant dimensions. In the first stage of our research, the stamping of these forgings is simulated on a computer by the finiteelement method [1]. In the second stage, the model is verified. Computer simulation permits study of the filling of the die’s contours by metal and the deformation over the diametric cross section of the forging; evaluation of the nonuniformity of deformation; and the identification of points of possible defect formation in stamping. By computer simulation, new products may be introduced more rapidly, with smaller outlays. Simulation of the filling of the stamp cavity indicates that it is completely filled with metal; there is no burring. No pinching or cracking of the metal is observed. The distribution of the accumulated strain in the axial plane is shown on the right side of Figs. 1a and 1b for a flange and lid forging, respectively, in the form of lines of equal strain. As is evident from Fig. 1a, the strain distribution over the cross section of the forging is nonuniform. The surface layers of the upper and lower plates in the flange experience the least strain e i = 0.49. The central layers of the hub experience the greatest strain. In stamping the lid (Fig. 1b), the surface layer of the central projection experiences the least strain e i < 0.14, while the internal layers of the forging closer to the bottom experience the greatest strain e i = 1.7. On the basis of the computer simulation, the strain distribution in different cross sections of the forging is plotted. The continuous curves in Fig. 2a denote the strain intensity in cross sections A , B , and C . In cross section C , the least strain is observed in the upper region of the concave hub. In the central part of the hub, the strain rises to a maximum, beyond which it falls. In cross section B , the maximum strain is again in the central region. In horizontal cross section C , the strain falls from e i = 2.48 in the central region to e i = 0.72 in the crown at the edge of the forging.

Hot plastic deformation of 08X21H5T steel

The nonuniformity of hot plastic deformation of 08X21H5T steel is studied. Tensile tests are conducted in the vacuum chamber of the IMASH-20-75 Ala-Too machine. The samples are attached to a clamp in the chamber by means of straps. A junction of a platinorhodium–platinum thermocouple is soldered to the side surface of the sample. Air is pumped out of the chamber to a residual pressure of 5.0 × 10–5 mm Hg (6.7 × 10–3 Pa). The sample is heated to 800–1200°C by means of industrial-frequency current. The precision of temperature maintenance is ±5°C. The deformation of the austenite and ferrite phases is investigated as a function of the overall deformation of the steel and the temperature. The influence of these factors on the slip rate of the austenite and ferrite phases along the grain boundaries is also considered. The hot-microhardness ratio of the austenite and δ ferrite in 08X21H5T steel is investigated as a function of the temperature.

Energy-efficient rolling in four-roller grooves

Energy-efficient rolling in four-roller grooves is considered. The distribution of the effective stress and strain is established. The metal’s margin of plasticity is determined. The distribution of the rolling forces due to the vertical rollers is plotted. The applicability of mathematical simulation in industrial conditions is assessed.

New rolling technology for streetcar girder rail

Despite the very diverse types of rails in industrial use, practically the same groove configurations may be used in rolling. However, the system used for streetcar girder rail is somewhat different. Computer simulation and industrial experiments permit the investigation of the axial-porosity distribution and assessment of the deformed state of the rolled metal in roughing and finishing. On that basis, a new rolling technology for streetcar girder rail has been developed. In the industrial research, the axial-porosity distribution in rolling with box grooves of the BD-1 roughing cell and slotted grooves in the BD-2 cell is investigated. The macrostructure is investigated on templates taken from the continuous-cast billet after the second, seventh, and ninth passes in the BD-1 and BD-2 cells. The results of computer simulation and the industrial trials are in good agreement.

Broaching of Blanks for Forged Rollers

Research shows that most mechanical properties of cast steel are lower than those of forged steel, since castings are nonuniform and relatively low in plasticity [1, 2]. Accordingly, forging is generally used in manu� facturing to produce the required shape of the compo� nent and to eliminate casting defects. Hot deforma� tion converts the hot metal to forged metal, with cor� responding gain in quality. The nonuniform deformation over the cross sec� tion of forgings and in their axial zone may be analyzed

New Methods of Rolling and Straightening Rails from Continuous-Cast Billet at OAO NKMK

The structure of rail steel is mainly determined by the temperature and deformation in rolling. The required deformation conditions over the profile from the initial blank to its final cross section are ensured by the groove structure and configuration in the system. The grooves determine the stress‐strain state and physicomechanical properties of the rolled metal. Therefore, rail manufacturers pay particular attention to the groove configuration, which is fundamental to the rolling process. In this context, it is important to establish the change in shape of continuous-cast billet in rail rolling. In the present work, we analyze the change in shape of the metal in the rolling grooves during rail production from continuous-cast billet and improve the rolling technology developed for rail production from ingots.