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The purpose of this study is to obtain a constitutive equation of high-accuracy flow stress in superalloy 718, which allows fabrication of highly reliable disks for gas turbine engines. Hot compression tests using superalloy 718 at deformation temperatures from 850 to 1100 °C, a 67% height reduction, and strain rates of 1, 10, and 25 s−1 were performed to investigate the flow stress behavior, which excludes environmental effects during hot working by inverse analysis. The effects of dynamic recrystallization and strain-induced dynamic precipitation on the flow stress were also investigated. The dynamically precipitated δ phases deformed at 1050 °C and γ″ phases deformed at 950 °C might affect the increase in the plastic modulus F1 and the decrease in the critical strain εc, deteriorating the accuracy of regression in terms of, for example, the strain rate sensitivity m and the temperature sensitivity A. A constitutive equation for a generalized flow curve for superalloy 718 is proposed by considering these effects.

Leaves of an obscure plant “oxalis deppei” are so hydrophobic that showered water droplets are almost completely repelled and hardly remained on their surfaces. For this reason, surface configurations were investigated. On the live leaves, there formed protrusions somewhat similar to those observed on lotus leaves which are well known as super hydrophobic leaves. However, in winter, it was found that even dead leaves were hydrophobic also. Because leaf tissues were shriveled and dried half, heights of protrusions with sizes of 20-50 μm were low, and undulations of surfaces were gentle and smooth, and pitches of undulations were as large as 30-70 μm. It was thought that such gentle lens-like protrusions would be probably formed on versatile stainless-steel plates using lithography and wet chemical etching. For this reason, arrays of protrusions with a size of 20 μm, a pitch of 35 μm, and heights of 6-7 μm were formed, and change of hydrophobic properties were investigated. As a result, the hydrophobic properties were effectively improved by forming even such gentle and smooth protrusions. It was also clarified that contact angles were improved almost in proportion to etched depths.

A process–microstructure–property database on forging and heat treatment of superalloy 720Li was established by high precision large-scale 1500 ton forging simulator and laboratory-scale forging simulator. The database was utilized to determine the parameters of flow stress, microstructure, and strength prediction models. The models were integrated to CAE software to predict process–microstructure–property relationships. In the integrated model, the stress, strain, and temperature distributions and their temporal development are calculated by using flow stress model and thermophysical properties. The calculated stress, strain, and temperature data are inputted into the microstructure model. The microstructure model considers grain growth, recrystallization, and precipitation of γ′ and calculates the temporal evolution of microstructural features. The strength model considers solution, grain boundary, and precipitation strengthening and calculates high-temperature 0.2% tensile proof stress, which is related to creep and low-cycle fatigue properties, from the calculated microstructural features. The integrated model successfully predicted the load, microstructure, and strength distribution of a prototype forging experiment conducted by the Hitachi Metals 6000 ton forging machine. The integrated model is a promising tool to design the forging and heat treatment process of the alloy.

It is desired that the amount of adhesion on the die surface becomes small in hot stamping of the aluminum-silicon (Al-Si) coated 22MnB5 steels, since regrinding of the die is reducing productivity. The effect of coating on the tool surface on the adhesion behavior under a dry condition was investigated by continuous flat drawing test up to 9 passes. The amount of adhesion is measured by laser scanning microscope with measuring volume function. The steady state coefficient of friction was 0.5 in the first pass and it gradually decreased to 0.48 with increasing pass for the non-coated and the AlCrN coated tool. The diamond‐like carbon (DLC) coating tool, the steady state coefficient of friction was 0.46 independent of the number of passes. The variation of adhesion height due to the number of passes was small, the average heights of the non-coated, the AlCrN coated and the DLC coated tool after 9 passes were 1.1 µm, 0.18 µm and 0.023 µm, respectively. For the coated tools, the amount of adhesion became significantly thinner.

Dispersion of the basal texture is effective to improve the formability. A repeated roll bending process (7 work rolls, work roll radius of 32 mm, roll pitch of 40 mm) was applied to AZ31 magnesium alloy sheets by activating the tensile twins. The larger applied bending strain per pass was effective to increase hardness at the surface of the sheet. The Erichsen value was slightly increased from 3.0 to 3.5 mm by subjected 2 passes repeated roll bending and subsequent at 180 °C for 12 hours annealing without decreasing the hardness of the sheet before bending (Hv=60). The Erichsen value of 3.3 and over hardness of Hv 65 through thickness were obtained by 2 passes bending and 160°C for 12 hours annealing. The tensile twins and texture randomizing were observed around center of thickness by electron backscatter diffraction (EBSD) analysis. It was possible to increase formability of AZ31 magnesium alloy by the repeated roll bending and subsequent low temperature annealing.

A new lithography optics designed and fabricated for printing 300-μm patterns on inside surfaces of pipes with an inner diameter of 10 mm and a length of 300 mm was investigated. Such patterning is required for giving textures to heat pipes, graving bearing grooves, and fabricating electrode and wiring patterns on inside surfaces of pipes. Although the pattern size is far larger than those used for semiconductor device fabrication, patterning onto non-flat surfaces in narrow spaces has hardly been researched anywhere else. Here, a linear optical fiber array composed of 500-μm fibers with squared ends were used for leading exposure light from light emitting diodes and designating pattern shapes. Then, the fiber array end was contacted to the inlet of a taper-conduit, and the pattern shapes were reduced in 1/2.25 at the outlet of the conduit. The conduit was composed of densely contacted fine optical fibers, and each fiber diameter was gradually reduced in the longitudinal direction keeping each fiber position invariably. The reduced pattern shapes were projected by a ratio of 1.25/1 using a simple convex lens on the inside surface of a pipe. Here, the performances of the projection optics were investigated by printing patterns on wafers used temporarily in place of the inside wall of a pipe. As a result, hole and linear space patterns with sizes or widths of approximately 300 μm were successfully formed.

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.

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.

The use of lubricants is effective for decreasing the forming load in hot stamping of Al-coated 22MnB5 steel. It is desired that new lubricants for hot stamping are developed. In this study, first, the coefficients of friction were measured using commercial lubricants for hot forging with the hot flat drawing simulator. The coefficient of friction of a commercial lubricant that consisted of a hydrophilic polymer and a mineral salt was the lowest. Second, lubricants with added different solid lubricants were newly developed and their coefficients of friction were measured. The coefficient of friction of the lubricant with added swellable mica was the lowest. Third, the formability of Al-coated 22MnB5 steel using the newly developed lubricant was examined with the hot deep drawing test machine and its formability was superior. A new high-performance lubricant for hot stamping was developed.

Intermetallics of TiFe were processed using three different routes: annealing, plastic deformation using groove rolling and severe plastic deformation using high-pressure torsion (HPT). Hydrogen absorption was less than 0.2 wt.% in the coarse-grained annealed sample because of difficult activation. The groove-rolled sample, with subgrain structure and high density of dislocations and cracks, absorbed 0.3, 1.0, 1.4 and 1.7 wt.% of hydrogen in the first, second, third and fourth hydrogenation cycles, respectively. The HPT-processed sample, containing nanograins, absorbed 1.7–2 wt.% of hydrogen in any hydrogenation cycles. Both samples activated by groove rolling and HPT were not deactivated by long time exposure to the air. No surface segregation was detected after groove rolling, while the HPT-processed sample exhibited surface segregation. The current study confirmed the significance of plastic deformation and formation of grain boundaries and cracks on activation for hydrogen storage.

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.

The material genome of type 316 austenitic stainless steel is presented. The material genome is a set of constitutive equations which describes the microstructure evolution during hot forming. Single- and double-compression tests at temperatures of 950–1150°C and with strain rates of 0.01–20 s−1 were performed to obtain the kinetics of dynamic and static events. Inverse analysis, which couples a thermomechanical finite element analysis with experimental data, is used to obtain the flow curves. It compensates the effect of inhomogeneous distributions of deformation and temperature during the compression tests. The sine-hyperbolic law, which relates the flow stress and the Zener–Hollomon parameter, is used to validate the accuracy of the solution. Regression analysis is applied on the coefficients of the flow curves in order to obtain the parameters of the constitutive equations. Microstructure investigations are used to demonstrate the validity of the newly obtained material genome.

An equal channel angular extrusion (ECAE) process equipment which enable a repetitive hot ECAE process without ejecting workpiece with route A and C are developed. This equipment has T-shape 3 actuator axis in horizontal plane and is capable of simulating the formation of fine grained steels in the transformation route. Each actuator (mechanical servo press unit) can be controlled by both position and load with programed motion. The outline of the developed ECAE equipment and the results of preliminary application of the ECAE equipment at an elevated temperature at various pressing speeds ranging from 2 to 32 mm/s for a Nb alloyed steel are present. 2 passes via route C at ram speed 16 mm/s are also conducted. The ferrite grain size of about 2 μm steel is obtained throughout the workpiece at ram speed of 32 mm/s, preheated temperature 960 o C.

The accumulative roll-bonding (ARB) process, which is a severe plastic deformation process, was simulated using finite element analysis, including the influence of friction, stress–strain relations, and roll diameter. The complicated distributions of equivalent strain through the thickness of ARB-processed sheets were quantified. These quantitative strain analyses would be useful for analyzing the evolution of ultrafine-grained structures in the ARB process.

A method of predicting the microstructure evolution and shape in the hot forming process is important for optimizing the process conditions. To develop a new analytical model that can be used to predict microstructure behavior in the actual process, a high-speed with multistage compression testing machine is required for physical simulation of the production process and to obtain material data for the prediction model. A high-speed uniform true strain rate (~300 s–1) was achieved by a servo-hydraulic computer-driven machine with a deviation control feedforward program. The effects of processing parameter and chemical composition of plane carbon and Nb alloyed steels on ferrite grain size were investigated. A grain size of about 1 μm was accomplished in this simulator by severe hot plastic deformation.

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.

T.M.C.P. (Thermo Mechanical Control Process) has been widely used in the steel industry. We have produced ultra low-carbon steel strip and ferritic stainless-steel strip through T.M.C.P. rolling method. Next, we analyze rolling texture and recrystallization texture of the ultra low-carbon strip and the ferritic stainless- steel strip using our developed texture prediction model. We can predict rolling texture accurately using the conventional Taylor model. Moreover, we precisely predict recrystallization texture classifying the total number of microscopic slips which are calculated using the Taylor model. We consider that these calculated results prove nucleation-oriented model and two types of recrystallization and grain growth mechanisms exit in our studies. One mechanism is that grains which had the lowest total number of microscopic slips are preferred orientation for the hot rolled and annealed ferritic stainless-steel strip. The other mechanism is that grains which had the highest total number of microscopic slips are preferred orientation for the cold rolled and annealed ultra low-carbon strip.

Coefficients of friction were measured at elevated temperatures using a hot flat strip drawing test machine newly developed by the authors for the purpose of confirming the coefficients of friction used for the FEM simulation of hot stamping. To examine the functions of the tribo-simulator, the coefficients of friction are measured using hot rolling oil with an emulsion, which is supplied continuously, while varying the drawing speed, drawing pressure and temperature. From the experimental results, it was shown that the coefficient of friction in hot stamping can be measured using this tribo-simulator. The measured coefficients of friction can be used as values in the FEM simulation of hot stamping. Moreover, the tribological behavior at the interface between the die and strip in hot stamping can be evaluated from the coefficient of friction, because it is one of the quantitative values used to represent the tribological behavior between the die and blank.

A hot extrusion system with controlled cooling is investigated in this study. This system is used with the aim of manufacturing steel and other metal products with ultrafine microstructures by single-pass heavy deformation followed by controlled cooling. The continuous formation of bulk materials with the desired geometry and microstructure could be realized using the proposed system or by adding hot rolling stands after processing using the proposed system. Microstructure evolution during and after heavy single-pass deformation is examined through a series of experiments involving the hot extrusion of plain carbon steel followed by controlled cooling. The effects of severe plastic deformation on grain refinement and the mechanical properties of the formed products are discussed. It is clear that the use of the proposed system is helpful for the grain refinement of a cast microstructure. Also, ultrafine-grain steel with a grain diameter of 3 μm can be formed using the proposed system. Finally, the formability of the ultrafine-grain steel manufactured using the proposed system is examined by a cold-forging experiment.

Various surface coating technologies have been applied to improve the tribological and mechanical properties of thin films. For the use of surface modified tools and parts under severe conditions, thin films with high adhesion strength are required. To quantitatively measure the adhesion of coating films on substrates a new method for the measurement of hard coating film was developed which consists of an indentation and an AE (Acoustic Emission) system. TiN coatings were deposited onto substrates using arc ion plating PVD. Indentation tests were conducted on substrates with different film thicknesses of 3, 5, and 7 μm. Two specific loads, denoted the “Critical load”, and the “Fracture load” were defined. The critical load and fracture load correlate to the initiation of delamination and film fracture. The critical load was calculated a finite element calculation and SEM observation.

An inverse analysis for obtaining a flow curve equation, which accounts for inhomogeneous strain and temperature distributions, is applied to the evaluation of the softening fraction in a double compression test. To obtain the set of equations in the first and second hits, two approaches are used. One is to determine different sets of coefficients for the first and second hits, independently. The other approach is to introduce the residual strain ɛR in the inverse analysis and to use the same set of coefficients in the first and second hits. Assuming both the rule of additivity for metallurgical strain and static recrystallization kinetics, which depends on temperature and applied strain, the residual strain after dwelling can be related to the recrystallized fraction. Under the above conditions, the effects of inhomogeneous strain and temperature distributions on softening behavior during the double compression test can be investigated. The distribution of softening behavior within a workpiece in plain carbon steel is investigated. The calculated softening fractions are compared with metallographically observed recrystallized fractions at three different observation points. Metallographically observed recrystallized volume fractions agree well with the calculated softening fractions, which accounts for inhomogeneous distributions of deformation and temperature, at higher fractions.

Extensive researches have been conducted on mechanical property and microstructure after severe plastic deformation (SPD) processes, i.e. ECAE, ARB, HPT and so on. The study on mechanical properties, such as the tensile strength, the hardness and the fatigue were conducted, however the formability of materials after SPD processes was little studied. Therefore we investigated the formability of steels subjected to different cold forming processes, the one is the ECAE process and the other is the cold rolling and followed swaging. The evaluation of formability was judged by forming micro screws (M1.6), whether it was possible or not. Four different materials, Ultra low Carbon, 0.15%C, 0.25%C steel and SWCH18A (0.16%C with spheroidizing treatment) were used. The formability test was conducted to product micro screws by a cold header that was commonly used in factory production. The formability was checked with eyes to examine crack or not at the first pre-forming and second recess forming. The materials subjected to ECAE process and as-received were able to manufacture the micro screw except ECAE processed 0.25%C steel. On the contrary no materials subjected to the cold rolling followed by swaging were able to manufacture the micro screw. It was found that formability of steel subjected to ECAE process was little decreased from as-received.

We developed an extrusion process with a cross-sectional area reduction as ‘single-pass severe plastic forming (S 2 PF)’ process for producing ultrafine-grained plain carbon steels. We investigated the microstructure and mechanical properties of fine-grained 0.2% carbon steels extruded at 1100–600 °C. Ultrafine ferrite grains with a grain size of 1.2 μm were generated at the surface of the materials extruded at 700 °C. The materials extruded at 800, 700 and 600 °C were investigated by scanning electron microscopy, electron backscattering diffraction analyses, tensile tests and compression tests. Extrusion at 700 °C, which is near the austenite–ferrite transformation temperature (A r3 ), produced a material sample with a diameter of 5 mm, an average ferrite grain size of approximately 2 μm, a tensile strength of about 700 MPa, a uniform elongation of about 15% and a good cold-forging property.

Processes of severe plastic deformation (SPD) are defined as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal. The objective of the SPD processes for creating ultra-fine grained metal is to produce lightweight parts by using high strength metal for the safety and reliability of micro-parts and for environmental harmony. In this keynote paper, the fabrication process of equal channel angular pressing (ECAP), accumulative roll-bonding (ARB), high pressure torsion (HPT), and others are introduced, and the properties of metals processed by the SPD processes are shown. Moreover, the combined processes developed recently are also explained. Finally, the applications of the ultra-fine grained (UFG) metals are discussed.

Bacterial communities in crude-oil samples from Japanese oil stockpiles were investigated by 16S rRNA gene cloning, followed by denaturing gradient gel electrophoresis (DGGE) analysis. 16S rRNA genes were successfully amplified by PCR after isooctane treatment from three kinds of crude-oil sample collected at four oil stockpiles in Japan. DGGE profiles showed that bacteria related to Ochrobactrum anthropi, Burkholderia cepacia, Stenotrophomonas maltophilia, Propionibacterium acnes, and Brevundimonas diminuta were frequently detected in most crude-oil samples. The bacterial communities differed in the sampling time and layer. Among the predominant bacteria detected in the crude oil, only three species were found for bacteria isolated on agar plates and were related to Burkholderia, Stenotrophomonas, and Propionibacterium, while Ochrobactrum sp. could not be isolated although this species seemed to be the most abundant bacterium in crude oil from the DGGE profiles. Using an archaea-specific primer set, methanogens were found in crude-oil sludge but not in crude-oil samples, indicating that methanogens might be involved in sludge formation in oil stockpiles.

A regression method of obtaining a generalized description of a flow curve is proposed in this paper. The flow curve of a metal at a constant temperature and a constant strain rate is precisely obtained by an inverse analysis of hot compression. To eliminate the error in the flow curve induced by the inhomogeneous distribution of temperature in the test piece, an electromagnetic analysis of induction heating is performed with thermal analysis throughout the heating and hot compression of a test piece. The coefficients embedded in the flow curve are determined by the inverse analysis associated with thermomechanical FE (Finite Element) analysis. The obtained coefficients, which cover wide ranges of hot-forming temperature and high strain rate, are regressed using the proposed regression method, and a generalized flow curve for a C-Si-Mn steel is obtained. Although the proposed regression method is demonstrated for only one type of C-Si-Mn steel, it could also be used to obtain a generalized description of a flow curve for other types of steel under dynamic recrystallization, which could be used to estimate the force characteristics of hot metals in bulk forming processes, such as forging and rolling.

A new method to estimate the kinetics of dynamic recrystallization is proposed in this paper. The proposed method enables the estimation of the kinetics of dynamic recrystallization directly from the flow curve of metal obtained by the hot compression test. Laborious hot compression tests to obtain frozen microstructures and image analyses of frozen microstructures to evaluate the kinetics for dynamic recrystallization can be replaced from the inverse analysis of the flow curve obtained by one hot compression test. The proposed method is applied to the hot compression test of plain carbon steel, and the kinetics of dynamic recrystallization are obtained successfully for a wide range of deformation rate at elevated temperature. The obtained kinetics for dynamic recrystallization are clarified by comparing them with those obtained by the conventional approach using image analyses of frozen microstructures. It is established that proposed method can give accurate kinetics for dynamic recrystallization with shorter time for experiment and computation. Finally, the kinetics for dynamic recrystallization obtained by the proposed method are compared with those in the literature obtained using the conventional approach.

A new method for determining flow curves of hot metal under dynamic recrystallization is proposed in this paper. Thermomechanical finite element analysis of a tool and a workpiece under hot compression is used to evaluate the upsetting force obtained by an experiment, as a function of the distributed flow stress of the workpiece. In order to compensate the effect of inhomogeneous distributions of deformation and temperature on the flow curve, inverse analysis for calculating coefficients in a flow stress curve under dynamic recrystallization is coupled with the thermomechanical finite element analysis. The discrepancy in upsetting force between the experiment and thermomechanical finite element analysis is used as an error estimator in the inverse analysis. A new regression formula of the flow curve, which includes four independent parameters, is introduced. It can express the flow curve of hot metal under dynamic recrystallization as well as dynamic recovery and work hardening. Also, four independent parameters included in the proposed formula have clear physical meanings. The proposed method is applied to the hot compression test of plain carbon steel at elevated temperatures. Flow curves are successfully determined for diversified conditions of strain rate and forming temperature. From the determined parameters of the flow curve by the proposed inverse analysis method, it can be concluded that 1) the critical strain for the onset of dynamic recrystallization is dependent on strain rate as well as temperature, 2) the stain rate sensitivity of m ¼ 0:13 is acceptable for plain carbon steel under testing conditions, and 3) the temperature sensitivity A is approximately 30003600 [K � 1 ]. Through investigation, it has become clearer that an accurate flow curve can be determined by the proposed method. In addition to a quantitative description of the flow curve as a function of strain, strain rate and temperature, metallurgical parameters such as the critical strain for the onset of dynamic recrystallization and steady-state stress could also be estimated directly by the proposed method.

To achieve microstructural refinement of ferrous alloys by using severe plastic deformation (SPD) methods, investigation of the microstructural evolution during hot deformation near the austenite–ferrite transformation temperature of ferrous alloys is necessary. In this study, a series of single and double-compression tests of cylindrical Fe–0.15C–0.2Si–1.4Mn–0.03Nb specimens are conducted in the temperature range from 750 to 900 °C. On the basis of experimental results, inverse analysis, micrographic investigation, finite element method (FEM) analysis, and regression analysis are carried out to obtain the material genome for Fe–0.15C–0.2Si–1.4Mn–0.03Nb alloy, which describes the static and dynamic kinetics of microstructural evolution of this alloy. The validity and feasibility of the proposed material genome are verified by compression tests of hourglass-shaped specimens and subsequent micrographic investigation.

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 © 2014 by ASME

Transition in austenite grain size distribution after hot forging, which is closely related to recrystallization, is investigated. Rapid change in grain size distribution just after hot bar stretching is experimentally obtained by hot compression test with controlled rapid quenching, and experimental results are examined by microstructure analysis using incremental approach with three-dimensional finite element analysis for plastic deformation. Through investigation, it has become clear that transient change in microstructure is very rapid with higher amount of plastic deformation. Microstructure analysis using incremental approach with three-dimensional finite element analysis for plastic deformation is helpful to evaluate rapid change in cross-sectional grain size distribution after hot bar stretching.