Akira Azushima

Properties of ultrafine-grained steel by repeated shear deformation of side extrusion process

The development of an ultrafine grain size during repeated shear deformation of side extrusion of ultra-low-carbon steel with an initial grain size of approximately 150 μm and a tensile strength of 200 MPa was investigated. Experiments were carried out at room temperature and at a low extrusion speed of 2 mm min−1. Repeated side extrusions with lateral pressure were carried out for up to ten passes for the specimen extruded without rotation (route A). Uniform shear deformation was obtained by the side extrusion with the lateral pressure and an equivalent strain after a single side extrusion was 1.15. After ten passes of the side extrusions, an ultrafine-grained steel with a grain size of 0.5 μm×0.2 μm was realized and the tensile strength was over 1000 MPa.

Effects of Plastic Strain on Surface Roughness and Coefficient of Friction in Tension-Bending Test

In order to make investigation into the tribological behaviors at the interface between tool and workpiece in the die corner of deep drawing, a tension-bending type test was used. A new tension-bending type test in which constant back tensions were applied and the deformation of specimen was plastic was developed. The workpiece used was an aluminum sheet with a smooth surface. The tests were carried out at a constant speed under various back tensions using a lubricant. The drawing force was measured during test and after tests the surface roughness of specimen was measured. In the lower average contact pressure, the surface roughening was predominant and the coefficient of friction was constant. On the other hand, in the higher average contact pressure, the flattening of surface asperities is predominant and the coefficient of friction decreased with increasing average contact pressure.

Effect of carbide properties of roll materials on lubricity in cold sheet rolling of low-carbon steel

Abstract The prevention of friction pick-up, which often occurs under the condition of high reduction and/or high speed, is required to improve the productivity in cold sheet rolling of low-carbon steel. Therefore, rolls made of high-chromium steels and high-speed steels with different carbide contents are tested in order to evaluate the effect of various properties of the carbide component of the materials on the lubrication characteristics. Coefficients of friction for the reduction in thickness and the limit of the reduction of friction pick-up are measured using the sliding–rolling simulation testing machine developed by one of the authors. The experimental results show that carbides on the surface of the roll can stop the increase in friction pick-up, and that keeping the carbide spacing small is effective in preventing friction pick-up. Because of the effectiveness of carbides, a high-chromium steel roll with controlled carbide morphology is manufactured and applied in a cold tandem mill. The results of the application show that the carbide-controlled roll has an excellent antiseizure property and is effective in improving productivity.

Lubrication characteristics of physical vapor deposition Tin-coated roll for high productivity in cold rolling of low-carbon steel sheet

Abstract The prevention of friction pickup, which often occurs under the condition of high rolling reduction and/or high rolling speed, is required to improve productivity in the cold sheet rolling of low-carbon steel. Therefore, the lubrication characteristics of a TiN-coated steel roll treated by the physical vapor deposition (PVD) process are evaluated quantitatively and compared with those of a conventional steel roll. Coefficients of friction for the reduction in thickness and the limit of the reduction of friction pickup are measured using a sliding–rolling simulation testing machine. The experimental results show that the limit of the reduction of the TiN-coated roll is much higher than that of the conventional roll. Moreover, the maximum rolling speed of the TiN-coated roll used in an actual mill is calculated. The results show that the maximum rolling speed of the TiN-coated roll will be two times faster than that of the conventional roll.

Plating Out Oil Film Thickness on Roll and Workpiece During Cold Rolling with O/W Emulsion

The plating-out film thickness during rolling in cold rolling with emulsion is quantitatively estimated for the improvement of productivity and the precise control of surface qualities after rolling. The estimating method of the plating-out film thickness was investigated using the numerical method of the inlet oil film thickness under the starvation condition of emulsion. The estimation model was proposed using a new starvation model considering the plating-out film on the roll and strip surface proposed by Azushima, et al. Sheets and coil sheets of aluminum A1050H and mineral oil with a viscosity of 0.235 Pa · s were used. It is reasonable that the value of trapping ratio in the sheet rolling could be used as the value of the trapping ratio in the coil rolling. From the experimental results, the effect of the emulsion concentration and the emulsifier on the plating-out film thickness was examined using the numerical method. The plating-out film thickness increased with increasing emulsion concentration and the plating-out film thickness was relatively dependent on the affinity of the emulsion particle for the steel surface of the emulsifier.

Measurement and Analysis of Inlet Oil Film Thickness in Cold Sheet Rolling with Oil-in-Water Emulsion

A calculation system of the inlet oil film thickness in cold sheet rolling with oil droplets-in-water (O/W) emulsion was developed. The inlet oil film thicknesses in the case of sheet rolling and coil rolling were calculated using the estimation system. The inlet oil film thickness in the coil rolling was larger than in the sheet rolling. In order to estimate the inlet oil film thickness at the entrance to the interface between roll and workpiece in cold coil rolling with O/W emulsion, a numerical method was proposed using the starvation model. This model consisted of a combination of the conventional starvation model and the plate out model. The inlet oil film thicknesses were calculated, changing the tribological factors, using the numerical method of the new starvation model. By using the proposed numerical method, the inlet oil film thickness obtained experimentally using the estimation system could be reasonably estimated.

Permeation of Lubricant Trapped Within Pocket Into Real Contact Area on the End Surface of Cylinder

Knowledge on the behavior of lubricant trapped in a surface pocket is important for improving metal forming technology, since the trapped lubricant affects friction and surface finishing. The permeation phenomena at higher reduction in height were quantitatively observed during the upsetting of cylinders with a central conical dent using the new fluorescence direct observation apparatus developed by the authors. Moreover, the permeation phenomena were estimated using a rigid-plastic finite element analysis model incorporating the compressibility of the lubricant. From the experimental results, it was quantitatively observed that over a reduction in height of 37%, the outline of the central conical dent became blurred, and the lubricant trapped within the conical dent permeated into the peripheral real contact area. It was also quantitatively observed that the volume of the lubricant trapped within the conical dent decreased gradually and abruptly with increasing reduction in height up to and above 36%, respectively. From the numerical results, it was estimated that the trapped lubricant permeated when the hydrostatic pressure generated within the lubricant pocket exceeded the die pressure at higher reduction in height.

Development and Properties of High Strengthened Carbon Steels Produced by Repetitive Side Extrusion and Heat Treatment Process

In recent years, ultrafine grained steels have developed by the new thermo-mechanical control processing (TMCP) and the severe plastic deformation (SPD) processes. The minimum ferrite grain size obtained by the new TMCP is less than 1 μm. On the other hand, in the SPD processes such as the equal channel angular Extrusion (ECAE), the high pressure torsion process (HPT) and the accumulative roll bonding (ARB), steels with a sub-micron scaled grain size are developed. In order to obtain high-strengthened steel with ductility, carbon steels with various carbon contents were deformed by repetitive side extrusion process and heat treatment, and the properties of materials such as Vickers hardness, tensile strength and microstructure observation were investigated. Vickers hardness and tensile strength increased with increasing number of process. The microstructures of all steels were refined by deformed structure. After heat treatment, the tensile strength became lower and total elongation increased with decreasing hardness. Fatigue property was better than that of the as-received material after side extrusion and heat treatment.

Mechanical Properties of Ultrafine Grained Steel Produced by Repetitive Cold Side Extrusion

Abstract Ultrafine grained microstructure was produced by repetitive deformation using the cold side-extrusion method from carbon steels. The side-extrusions with lateral pressure were repeated up to 10 passes without rotation. Each sample was uniformly deformed by the side-extrusion, and the equivalent strain was 1.15 after a single pass of the side-extrusion. After 10 passes of side-extrusion an ultrafine grained steel with a tensile strength of over 1000MPa a grain size of 0.5μm × 0.2 μm was developed for the ultra low carbon steel. The uniform elongation in tensile test for the steels after repetitive side extrusions was very small, but the cold formability was very good. By the heat treatment, the uniform elongation became larger.

Lubrication in steel strip rolling in Japan

Abstract Research into, and the state of technology for, lubrication in steel strip rolling in Japan are reviewed. Both cold and hot strip rolling are discussed. Subjects covered include coefficient of friction and oil film thickness, friction pick-up, and roll wear.