• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.172-175
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• 2003

Run-Out-Table is the region between EDT and CT. Hot killed strip is cooled by air and water in ROT. In this procedure, phase transformation and shape deformation occur due to temperature drop. Because of un-ideal cooling condition, deformation of strip and non-uniform phase distribution come into existence. This phenomenon affects the strip property and lead th the existence of residual stress. And it exerts effects on the Coiling process, Coil Cooling process, and Un-coiling process. Through these process, the residual stresses of strip are more larger and unbalance of these stresses become more severe. Finite element (FE) based models for the analysises of non-steady state heat transfer and elastoplastic deformation are described in this investigation. The analysises of thermodynamics and phase transformation kinetics are suggested also. Using the ROT simulation result coiling process and coil cooling process simulations are carried out.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.356-365
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• 1999

The present study is aimed at developing the TRIP(transformation induced plasticity) aided high strength low carbon steel using reversion process. An excellent combination of elongation over 40% and tensile strength abut 100kgf/$\textrm{mm}^2$ achieved in processing of 0.15C-0.5 Si-6Mn steel by slow heating to intercritial temperature region and accelerated cooling into room temperature. This good combination is caused by TRIP phenomena of retained austenite in steels during deformation. The stability of retained austenite is very important for the good ductility and it depends on the diffusion of carbon and manganeses during heat treatment. The accelerated cooling after holding at annealing temperature retards the formation of pearlite and provides the carbon enrichment in retained austenite in steel, resulting in the increase in elongation of the cold-rolled TRIP steel. On the other hand, heat treating the steel at 600$^{\circ}C$ for 5 hour before cold rolling increases elongation but reduces the amount of retained austenite after reversion processing. It is accounted that the heat treating is effective for the increase in the stability of retained austenite.

• Applied Microscopy
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• v.45 no.2
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• pp.52-57
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• 2015

Bulk metallic glass (BMG) shows higth strength, high elastic limit, corrosion resistance and good wear resistance and soft magnetic properties and has been considering as a candidate for new structural materials. But they show limited macroscopic plasticity and lack of tensile ductility due to highly localized shear deformation, which should be solved for real structural application. In this paper researches on the enhancement of plasticity of BMG were reviewed briefly. Introducing heterogeneous structure in glass is effective to induce more shear transformation zones (STZs) active for multiple shear band initiation and also to block the propagating shear band. Several methods such as BMG alloy design for high Poisson's ratio, addition of alloying element having positive heat of mixing, pre-straining BMG and variety of BMG composites have been developed for homogenous distribution of locally weak region, where local strain can be initiated. Therefore enhancement of plasticity of BMG is normally accompanied with some penalty of strength loss.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.156-160
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• 2001

The effects of TRansformation Induced Plasticity(TRIP) phenomena on the plastic deformation of 0.2C-1.5Si-1.5Mn multiphase steels have been investigated at various heat treatment and stress conditions. In order to estimate the formability, the hole expansion(HE) tests and the tensile tests were carried out. The formability evaluated from the uni-axial tensile tests was quite different from the formability measured from multi-axial HE-tests. Consequently, the formability in the multi-axial stress state decreased due to the extinction of the retained austenite relatively at earlier deformation stage and the production of irregular α' martensite. However, the defects of TRIP-steels were initiated exactly at the boundary between transformed martensite and ferrite matrix regardless of stress state. In addition, new experimental formula is proposed in order to predict the multi-axial formability of the TRIP steels from the results of uniaxial tensile test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.173-176
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• 2009

A great emphasis has been placed on the design of heat treatment process to achieve desired microstructure and mechanical property of final product. In this study, finite element analysis was carried out to predict temperature, microstructure and hardness of eutectoid steel after water quenching. Convective heat transfer coefficients were determined by inverse analysis using surface temperatures measured with three different installation methods of thermocouples. Finally, the effect of convective heat transfer coefficients on the prediction of temperature history and hardness was analyzed by comparing experimental and simulation results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.185-189
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• 2009

Recently, ultra high strength products can be manufactured by the hot press forming process of Boron steel in automotive and electronics industries. In order to get high strength, the hot press forming should be accompanied by quenching process inducing phase transformation. There are several types of the hot press forming processes according to the quenching method, water quenching and die quenching, etc. In the study, the process was numerically and physically simulated to compare the two types of quenching processes, and then the strength, hardness and dimensions of the products were compared with try-outs.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.465-467
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• 2004

Finite element analysis of welding processes, which entail phase evolution, heat transfer and deformation, is considered in this paper. Attention focuses on numerical implementation of the thermo-elastic-plastic constitutive equation proposed by Leblond et al in consideration of the transformation plasticity. Based upon the multiplicative decomposition of deformation gradient, hyperelastic formulation is employed for efficient numerical integration, and the algorithmic consistent moduli for elastic-plastic deformations including transformation plasticity are obtained in the closed form. The convergence behavior of the present implementation is demonstrated via a couple of numerical examples. Several locking phenomena removed by Solid-shell element.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.366-371
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• 2002

Because of the environmental problems, automotive companies are trying to reduce the weight of car body. Therefore, TRIP(TRansformation Induced Plasticity) steels, which have high strength and ductility have been developed. Welding process is a complex process; therefore deciding the optimal welding conditions on the basis of experimental data is an effective method. However, trial-and-error method to decide the optimal conditions requires too many experiments. To overcome these problems, response surface methodology was used. Response surface methodology is a collection of mathematical and statistical techniques that are used in the modeling and analysis of problems in which a response of interest is influenced by several variables and the objective is to optimize this response. This method was applied to the resistance spot welding process of the TRIP steel to optimize the welding parameters.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.77-80
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• 2006

Structural phase transformations of silicon during nanoindentation were investigated in detail at the atomic level. The molecular dynamics simulations of nanoindentation on the (100), (110) and (111) surface of single crystalline silicon were simulated, and this supported the theoretical prediction of the anisotropic behavior of structural phase transformations. Simulations showed that microscopic aspects of phase transformation varied according to the crystallographic orientation of the contact surface and were directly linked to the slip system.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.336-340
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• 2001

We propose an implicit numerical implementation for the Leblond's transformation plasticity constitutive equations, which are widely used in welded steel structure. We apply generalized trapezoidal rule to integrate the equations and determine the consistent tangent moduli. The implementation may be used with updated Lagrangian formulation. We test a simple butt-welding process to compare with SYSWELD and discuss the accuracy.