Warm deep drawability in a square cup drawing was investigated using a newly developed high-strength steel sheet with retained austenite that was transformed into martensite during formation. For this investigation, six different temperatures between room temperature and 250℃, and five different drawing ratios ranging from 2.2 to 2.6 were considered. The results showed that the maximum drawing force and the drawing depth were affected by the change in temperature, and a more stable thickness strain distribution was observed at elevated temperatures. However, blue shortness occurred at over 200℃. FEM analysis using the LS-DYNA code was used to compare the experimental results with the numerical results for the thickness strain distribution.

The effects of intermediate annealing (IA) and the final cold rolling (CR) condition on the microstructure and sagging resistance during brazing were investigated using three layer clad sheets composed of the Al-7.5 wt.%Si alloy (filler, thickness: 10 ㎛)/Al-1.3 wt.%Mn based alloy (core, 80㎛)/Al-7.5 wt.%Si alloy (filler, 10㎛). Also, the effect of 1.2∼2 wt.% Zn addition into the core on the sagging resistance of the clad sheets was determined. It was revealed that all the clad sheets fabricated by the optimum condition (IA at 690 K and CR to 20∼45%) show excellent sagging resistance with a limited erosion due to the formation of a coarsely recrystallized grain structure in the core during brazing. It was also revealed that the recrystallization behavior of the Al-1.3 wt.%Mn based alloy is hardly affected by the addition of 1.2-2 wt.%Zn during the brazing cycle. Therefore, the sagging resistance of the clad sheets is found to be governed not by the Zn content added in the A1-1.3wt.%Mn based core, but by the intermediate annealing and final cold rolling condition.

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

The purpose of this research is for the development of a new type forging equipment. H.C.G.(Hyundai Continuous Grain-Flow), by using two virtual build-up tools, rigid viscoplastic FEM and downsized plasticine experiment. This forging method consists of only vertical pressuree. Therefore, high quality crankshafts can be forged with this method as it can maintain a continuous grain flow. The factors considered in the development of equipment are die geometry for flawless deformed shape, die reaction forces, stress/strain distributions and continuous material flow. We carried out several numerical simulations and downsized plasticine experiments for the proper design of the forging equipment. The validity of those simulation results is confirmed by checking with the actual test results. Based on these simulation results, the proper design of the H.C.G. forging equipment is enabled.

With the aim of assessing the degradation of Zr-2.5Nb pressure tubes operating in the Wolsong unit-1 nuclear power plant, characterization tests are being conducted on irradiated Zr-2.5Nb tubes removed after 10-year operation. The examined tube had been exposed to temperatures ranging from 264 to 306℃ and a neutron fluence of 8.9×$10^{21}$ n/cm²(E>1 MeV) at the maximum. Tensile tests were carried out at temperatures ranging from RT to 300℃. The density of a-type and c-type dislocations was examined on the irradiated Zr-2.5Nb tube using a transmission electron microscope. Neutron irradiation up to 8.9×$10^{21}$ n/cm²(E>1 MeV) yielded an increase in a-type dislocation density of the Zr-2.5Nb pressure tube to 7.5×$10^{14} m^{-2}$, which was highest at the inlet of the tube exposed to the low temperature of 275℃. In contrast, the c-component dislocation density did not change with irradiation, keeping an initial dislocation density of 0.8×$10^{14} m^{-2}$ over the whole length of the tube. As expected, the neutron irradiation increased mechanical strength by about 17-26% in the transverse direction and by 34-39% in the longitudinal direction compared to that of the unirradiated tube at 300℃. The change in the mechanical properties with irradiation is discussed in association with the microstructural change as a function of temperature and neutron fluence.

In this study, the experimental considerations of the friction factors are presented in a few cases. The friction factors in the cases of, first, the drawing quality material, SPC3C through the non-coated die of base material. GC30, secondly, SPCC through the Cr-coated GC30 die, and lastly. SPCC through the TD heat treated STD11 die, are measured experimentally both for the increasing die temperature and the blank holding forces. The results show no considerable variations of the value of friction coefficients according to the change of both the die temperature and the die treating conditions.

The segregation (distribution) of nickel and the composition of its constituents influence the low thermal expansion characteristics (Invar effect) in Fe-30 wt.% Ni-12.5 wt.% Co-xC Invar alloy. The change of coefficient of the thermal expansion and magnetic properties were studied as an aspect of carbon addition causing the segregation of Ni in primary austenite of as-cast Fe-30 wt.% Ni-12.5 wt.% Co Invar alloy. The coefficient of thermal expansion of Fe-30 wt.% Ni-12.5 wt.% Co-xC Invar alloy showed its lowest value at 0.08 wt.% carbon, increased with increasing carbon content in the range of 0.08-1.0 wt.%C, kept constant at 1.0-2.0 wt.%C and decreased at carbon higher than 2.0 wt.%. The effective distribution of the coefficient of nickel in as-cast Fe-30 wt.% Ni-12.5 wt.% Co-xC Invar alloy increased with increasing carbon content. The volume fraction of they phase of Fe-30 wt.% Ni-12.5 wt.% Co-xC alloy increased with increasing carbon content. The microstructure of Fe-30 wt.% Ni-12.5 wt.% Co-xC alloy changed with the carbon content was independent of the coefficient of thermal expansion. The Curie temperature changed linearly with the carbon content and was similar to the change of the coefficient of thermal expansion. Moreover, the coefficient of thermal expansion decreased when the ratio of saturation magnetization to Curie temperature ($\sigma_s/T_c$) increased, decreasing the Curie temperature and showed a specific relationship with the magnetic properties of the Fe-30 wt.% Ni-12.5 wt.% Co-xCInvar alloy.

The 3-dimensional finite element program is developed to analyze the non-isothermal forming processes of aluminum-alloy sheet metals. Bishop's method is introduced to solve the heat balance and force equilibrium equations. Also, Barlat's non-quadratic anisotropic yield function depicts the planar anisotropy of the aluminum-alloy sheet. To find an appropriate constitutive equation, four different forms are reviewed. For the verification of the reliability of the developed program, the computational try-outs of the non-isothermal cylindrical cupping processes of AL5052-H32 and Al1050-H16 are carried out. As results, the constitutive equation relating to strain and strain-rate, in which the constants are represented by the 5th-degree polynomials of temperature, is in good agreement with measurement. The computational try-outs can predict optimal forming conditions in non-isothermal forming processes.

Dense WC-10 vol.%Co composite was simultaneously synthesized with field-activated and pressure-assisted combustion synthesis (FAPACS) within several minutes in one step from elemental powders of W, C and Co. Combustion synthesis was carried out under the combined effect of an electric field and mechanical pressure. Under the application of 60MPa pressure and 3000A current on the reactants, the relative density of WC-10 vol.%Co composite was 98.4%. The fracture toughness and hardness of WC-10 vol.%Co were 8.6 MPa·$m^{1/2}$ and 1900 kg/mm², respectively.

TiC ceramic particulate-reinforced titanium matrix composites were fabricated and the resultant densification, microstructure, and static and dynamic mechanical properties were studied. Comparing Ti with TiH₂powders as host materials for TiC ceramic reinforcement by pressureless vacuum sintering, TiH₂-started composites showed better sinterability and resistance to both elastic and plastic deformation than Ti-started ones. When TiH₂and TiH₂-45 vol.%TiC samples were hot pressed, TiH₂matrices transformed to alpha prime Ti and alpha Ti phase, respectively. It is interpreted that the diffusion of an alpha stabilizer carbon from TiC into the matrix is one of the plausible reasons far such a microstructural difference. The 0.2% offset yield strengths of the hot pressed TiH₂and TiH₂-45 vol.%TiC samples were 1008 and 1446 MPa, respectively, in a static compressive mode (strain rate of 1×$10^{-3}$/s). Dynamic compressive strengths of the samples were 1600 and 2060 MPa, respectively, at a strain rate of 4×10³/s.

This paper reviews the rules for optimizing die design and the process variables such as die shoulder radius and punch to die clearance, which are important factors in drawing the sheet metal without failures during deep drawing. To find the optimum conditions for improving deep drawability, a series of the experiments are performed, and the wall thinning and thickening variations are investigated in each process of deep drawing for a complex cylindrical shell. From the results of this proposed experiment, the optimum values of process variables are examined and discussed, and the usefulness of the present suggestion is shown.

The development of mechanical alloying (MA)-oxide dispersion strengthened (ODS) heat-resistant ferritic alloys of Fe-12%Cr with W, Ti and Y₂O₃additions were carried out. Fe-12%Cr alloys with 3%W, 0.4%Ti and 0.25% Y₂O₃additions showed a much finer and more uniform dispersion of oxide particles among the alloy system studied. Nano-sized oxides dispersed in the alloys suppress the grain growth during annealing at a high temperature and resulted in the remarkable improvement of creep strength. The oxide phase was identified as a complex oxide type of Y-Ti-O.

A variable blank holding force method is proposed to improve deep drawing characteristics of sheet materials. In this method, the blank holding force (BHF) is controlled throughout a drawing process so that the punch load does not exceed a critical value, which is slightly less than the conventional process with the conforming process with the variable BHF is more flexible than the conventional process with the constant BHF and it could be used for improving the product's quality and drawability. In this paper we suggest a method controlling the BHF as a function of punch travel during the forming process. The optimization BHF curves are determined theoretically and experimentally. It is concluded that for the case of optimum BHF control methods the drawn cup height and the drawing formability achieved by this method are increased than those for constant BHF method. Also, as comparing the wall thickness distribution of the cup drawn by the constant BHF and the optimum BHF control, the BHF control reduce the wall thickness variation of the drawn cup at the cup wall and make the cup thickness distribution more uniformly than the constant BHF.

A concentration change during grade transition operation in thin slab casting is investigated through computer simulation and the results are compared with experimental measurements. Fluid flow and mixing patterns in various tundish levers and flow rates were analysed by a three-dimensional mathematical model. Based on the contained results, a simple, efficient and accurate computational model is suggested to predict the concentration profile at the outlet of the tundish. Based on the model, mixing in and below the mold was analyzed considering electromagnetic braking force. The predicted concentration profiles show good agreements with the measured values. It is found that the lower vortices in the mold are suppressed by the electromagnetic field and a plug-like flow region develops, which decreases the intermixing of two different grades of steel and shortens the length of transition region.

This study focuses on part quality and cycle times under gas-assisted injection molding (GIM) of box shape molded parts. The position of the gas channel was established near to parting line at the end of last locations to fill. Applied hot runner and valve gates, the gas was introduced directly into the mold cavity via gas pin. As GIM was applied, the conclusion reached as follows. I) The quality of appearance was improved by reducing sink marks and scratches of texture. ii) The reliability was improved by preventing warpages and reinforcing rigidity through optimum gas channel layout. iii) It is enable to use small size of injection molding machine step by step as GIM was accomplished low pressure and reduced clamp forces against CIM. iv) The productivity were improved by reducing cycle times.

In the present study, the effect of microporosity on the tensile properties of as-cast AZ91D magnesium alloy was investigated through experimental observation and numerical prediction. The test specimens were fabricated by die-casting and gravity-casting. For gravity-casting, the inoculation and use of various metallic moulds were applied to obtain a wide range of microporosity. The deficiency of the interdendritic feeding of the liquid phase acted as d dominant mechanism on the formation of the micropores in the Mg-Al-alloys, rather than the evolution of hydrogen gas. Although tensile strength and elongation has a nonlinear and very intensive dependence upon microporosity, the yield strength appeared to have a linear relationship with microporosity. However, it was possible to quantitatively estimate the linear contribution of microporosity on the individual tensile property far a range of microporosity, which was below about B %. The numerical prediction suggests that the effect of microporosity on fractured strength and elongation decreased as the strain hardening exponent increased. Furthermore. the shape and distribution of micropores may play a more dominant role than local plastic deformation on the tensile behavior of AZ9lD alloy.

The rigid-plastic finite element analysis requires a large amount of computation time due to its non-linearity. For economic computation, mismatching refinement, and efficient domain decomposition method with different mesh density for each sub domain, is developed. A modified velocity alternating scheme for the interface treatment is proposed in order to obtain good convergence and accuracy. As a numerical example, the axisymmetric extrusion process is analyzed. The results are discussed for the various velocity update schemes form the viewpoint of convergence and accuracy. The three-dimen-sional extrusion process with rectangular section is analyzed in order to verify the effectiveness of the proposed method. Comparing the results with those of the conventional method of full region analysis, the accuracy and the computational efficiency of the proposed method are then discussed.

This paper describes the investment casting of TiAl alloys. The effects of mold material and mold preheating temperature for the investment casting of TiAl on metal-mold interfacial reaction were investigated by means of optical micrography, hardness profiles and an electron probe microanalyzer. The mold materials examined were colloidal silica bonded ZrO₂, ZrSiO₄, A1₂O₃and CaO stabilized ZrO₂. When compared with conventional titanium a1loy, the high aluminum concentration of TiAl alloys helps to lower their reactivity in the molten state. The A1₂O₃mold is a promising mold material for the investment casting of TiAl in terms of the thermal stability, formability and cost. Special attention need to be paid to thermal stability and mold preheating when developing the investment calling of TiAl alloys.

A vision-based surface-strain measurement system has been still improved since the authors devel-oped the first version of it. New algorithms for the subpixel measurement and surface smoothing are introduced to improve the accuracy and precision in the present study. The effects of these algorithms are investigated by error analysis. And the equations required to calculate 3D surface-strain of a shell element are derived from the shape function of a linear solid finite-element. The influences of external factors on the measurement error are also examined, and several trials are made to obtain possible optimal condition which may minimize the error.

In the present study, the corrosion behavior of AZ91D as-cast alloy was investigated form the viewpoint of the distribution aspect of precipitate ($Mg_{17}Al_{12}$) and the variation of Al concentration in the Mg-rich matrix. The dendrite arm spacing (DAS) of an as-cast specimen was measured as a function of degree which describes the distribution aspect of the precipitate, and the salt spray test was conducted for various grain-sired specimens fur 20 days. The dendrite arm spacing increased as the grain size increased to about 150㎛, but a constant value is indicated when the grain size exceeds that range. Although the relationship between the corrosion rate and grain size is of a nonlinear type, the linear trend between the corrosion rate and the dendrite arm spacing is maintained for the overall range of dendrite arm spacing. Since the precipitate in the as-cast alloy is discontinuously distributed, this linear relationship means that the variation of Al-solute concentration in the Mg-rich matrix has a more potent effect than the protective action of the precipitate on the corrosion behavior of an as-cast alloy.

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0,4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.

In the recent sheet metal forming simulations, it increases to adopt the dynamic explicit method for an effective computation and the elastoplastic formulation for stress recovery. It is inevitable in the dynamic explicit method that some noises occur, which sometimes partly spoil results of simulations. This phenomenon becomes severer when complicate contact conditions are included in simulations. In commercial dynamic codes, the concept of contact damping is introduced. However, the formulation process of it is not revealed well. In this paper, a contact damping method is formulated in order for effectively suppressing noises occurring due to complicated contact conditions. This is checked by analyzing a simple sheet metal stamping process (U-draw bending). From the computational results, it is shown that the contact damping can effectively control the noises due to contacts, especially when considering the sheet thickness, and help to develop more reliable internal stress states, which result in more realistic shapes after springbank.

Effects of rare earth metals addition and aging treatment on corrosion resistance and mechanical properties of super duplex stainless steels were investigated using optical/SEM/TEM metallographic examination, an X-ray diffraction test, a potentiodynamic anodic polarization test and a tensile test. The performance of the experimental alloy with 0.32% REM addition was compared with commercial super duplex stainless steel such as SAF 2507 when they were exposed to solution annealing heat treatment and aging treatment. The corrosion resistance in CF environments and mechanical properties of the experimental alloy were found superior to those of the commercial duplex stainless steel. The REM with larger atomic radii than those of Cr, Mo and W may fill vacancies inside the matrix and around the grain boundaries, retarding formation of harmful intermetallic σ and χ phases. In addition, fine REM oxides/oxy-sulfides (1-3㎛) seemed to enhance the retardation effects. With REM additions, strength and ductility increased due to the phase and grain refinement caused by fine REM oxides and oxy-sulfides.

Many products related to automobile and airplane industry have been manufactured by semi-solid forging. In this paper finite element analysis of product by combined extrusion in semi-solid state was performed and its experimental verification using A356 was conducted. distribution of solid fraction was analyzed and compared with the experimental microstructure in the product. In addition, distribution of temperature in the product was analysed by finite element method.

From isothermal and cyclic oxidation tests on thermomechanically treated Ti-5%Al, Ti47%Al-4%Cr, and Ti-48%Al-2%Cr-2%Nb alloys at 800, 900, 1000℃ in air, it was found that Ti-48%Al-2%Cr-2%Nb and Ti-47%Al-4%Cr had the best and the worst oxidation resistance, respectively. The oxide scales consisted primarily of TiO₂and Al₂O₃, with and without a small amount of dissolved Cr and 7b ions, depending on the alloy composition. These ions were slightly enriched inside the inner oxide layer, and strongly enriched around the scale-matrix interface. The outer TiO₂-rich layer was formed by the outward diffusion of Ti ions, while the inner (TiO₂+A1₂O₃,) mixed layer was formed by the inward transport of oxygen. The outward movement of Al ions farmed the intermediate Al₂O₃-rich Iayer, above talc prepared alloys.

The oxidation behavior of 60%Cu-40%Zn brass haying small amounts of Zr, Cr, Mg, Al, and Si was studied between 873 and 1043 K in air. The alloying element of Mg was harmful, while other alloying elements were beneficial to oxidation resistance. Particularly, the simultaneous addition of Al and Si decreased the oxidation rate drastically. During oxidation, Zr formed ZrO₂, Cr formed CuCr₂O₄, Mg formed MgO, Al formed A1₂CuO₄, and Si formed amorphous SiO₂. These oxides were incorporated in the oxide scale composed predominantly of ZnO. The oxide scales formed on all the tested alloyswere prone to cracking, wrinkling, and spallation.