Akira Yanagida

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.

Microstructure and Mechanical Properties of Nb Alloyed Steel Processed by Hot Equal Channel Angular Extrusion

A Nb alloyed low carbon steel was processed by hot equal channel angular extrusion (ECAE) and following transformation. The workpieces were heated up to the 960°C in the furnace for 10 min within the container block. Before extrusion, the die was preheated to 400oC. The workpiece was cooled in the die after ECAE process. 1 pass and 2 pass via route C were conducted at a speed of 32mm/s, the inter-pass time is about 2 sec. The sample of average ferrite grain size of about 2μm, a tensile strength of 800MPa, a total elongation about 20% is produced after 2 pass ECAE processed and subsequent cooling.

Measurement of Coefficient of Friction in Hot Stamping by Hot Deep Drawing Test

Hot stamping process has been developed to produce the steel automobile parts with an ultra-high-strength of 1500 MPa. The effect of scale thickness on the formability in hot stamping was investigated by a hot deep drawing test in our previous research. The draw-in lengths of flange increased with decreasing the scale thickness. It is supposed that thin scale thickness resulted in low coefficient of friction at the flange area. The other reason is the temperature of wall zone would become low according to decreasing the scale thickness or increasing of the thermal transfer coefficient and it slightly inhibits local deformation at the wall area. It is difficult to separate these phenomena. To quantify the effect of scale thickness on the friction at the flange area during hot deep drawing, the coefficient of friction was directly measured. The coefficient of friction decreases with decreasing scale thickness.

On the development of a model predicting the recrystallization texture of aluminum using the Taylor model for rolling textures and the coincidence lattice site theory

First, hardening model in f.c.c. metals was formulated with collinear interactions slips, Hirth slips and Lomer-Cottrell slips. Using the Taylor and the Sachs rolling texture prediction model, the residual dislocation densities of cold-rolled commercial pure aluminum were estimated. Then, coincidence site lattice grains were investigated from observed cold rolling texture. Finally, on the basis of oriented nucleation theory and coincidence site lattice theory, the recrystallization texture of commercial pure aluminum after low-temperature annealing was predicted.

Application of Recrystallization Texture Evolution Model to Predict Plastic Formability in Steel Strips

T.M.C.P.(Thermo Mechanical Control Processing) has been widely used to improveplastic formability in steel strips. We have produced interstitial free steel(IF steel) strips and ferriticstainless-steel strips through T.M.C.P. rolling method. Optimizing conditions of hot rolling, hotrolled annealing, cold rolling and cold rolled annealing, we developed texture prediction model. Wecan predict rolling texture accurately using the conventional Taylor model. Moreover, we preciselypredict recrystallization texture classifying the total number of microscopic slips which arecalculated using the Taylor model. We consider that these calculated results provednucleation-oriented model and two types of recrystallization and grain growth mechanisms exit inour studies. One mechanism is that grains which had the small total number of microscopic slips arepreferred orientation for the hot rolled and annealed ferritic stainless-steel strip. The othermechanism is that grains which had the high total number of microscopic slips are preferredorientation for the cold rolled and annealed IF steel strip.

Modelling Static and Dynamic Kinetics of Microstructure Evolution in Type 316 Stainless Steel During Hot Rolling

In this study, the kinetics of microstructure evolution during hot rolling of type 316 austenitic stainless steel is investigated. First, its kinetics during the dynamic and static events, known as the material genome, is driven by single- and double-compression tests at several temperatures and strain rates. Inverse analysis is used to obtain the flow curves and regression analysis is applied on the coefficients of these flow curves in order to obtain the parameters of the constitutive equations. This new material genome is then used as the boundary condition on an incremental type formulation, taking the dislocation density as the representative variable, to estimate the flow stress and microstructural evolution after the transient changes during rolling schedules of seamless pipes. Actual rolling schedules are simulated and the microstructural changes are compared to industrial data. The outcome of the grain size evolution was reproduced reasonably well showing that proposed methodology can be used to simulate a complex thermomechanical process akin to the rolling schedules of seamless pipes.Copyright

Ferrite Transformation Kinetics of Severely Hot-Deformed Austenite

The ferrite transformation kinetics of severely hot-deformed austenite has been studiedby considering ferrite nucleation from dislocation cell blocks inside austenite grains. The size ofdislocation cell blocks and ferrite grain size just after phase transformation are acknowledged to beinversely proportional to the square root of dislocation density. It is found that the ferrite nucleationrate in this area can reach the saturated state at a high temperature just under Ae3, and the ferritetransformation finishes within a very short time. The kinetics of ferrite volume fraction and theferrite grain growth after phase transformation for plain carbon (0.1%C, 0.2%Si, 1.0%Mn) steelhave been studied using a THERMECMASTER hot-compression testing machine. These modelscan be applied to the hot and warm forming processes of plain carbon steel to predict the ferritetransformation from severely deformed austenite.