• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.111-113
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• 2007

The Mechanical properties of steel in hot strip mill were associated with the alloy composition, plastic deformation, cooling history and so on. In the case of the same alloy composition and deformation conditions, cooling history on ROT (run out table) is the main factor in affecting mechanical properties of steel, especially, in carbon steel. On ROT, the steel undergoes under various kinds of cooling conditions such as radiation, convection by air, water and wetting zone. The coiling temperature (CT) of the steel is also important factor in affecting mechanical properties. But with the same CT, the mechanical properties of steel can be different because the temperature history of cooling is more important factor than CT itself. In this study, we have studied the relations between temperature history and mechanical properties of steel and then the predicted mechanical properties have compared with the measured values.

• Transactions of Materials Processing
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• v.23 no.6
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• pp.351-356
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• 2014

The current study aims to predict the forming limits considering the deformation characteristics of tailor rolled blank(TRB) during hot stamping. The formability of TRB is affected by the TRB line orientation because elongations change due to the intrinsic geometry within the sheet. To evaluate the forming limits, Nakazima tests were conducted at elevated temperatures with different TRB line orientations. Forming limit diagrams(FLD) of TRB can be predicted by an interpolating equation based on the Nakazima test. Predicted FLDs were used in FE-simulations of a rectangular drawing. The predicted limit drawing height was compared with experimental results. The simulation results show good agreement with the experimental ones with an error range of 3%.

• Journal of Welding and Joining
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• v.8 no.2
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• pp.70-79
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• 1990

Stainless clad steels were made through hot rolling process. Backing plates employed in this study were HSLA steel and mild steel. The shear bond strength increased with an increase of the soaking temperature and time. It was also found that the shear bond strength increased with an increase of the reduction ratio. The threshold deformation was observed to be 20% and 10% respectively when the soaking conditions of 15 min. at 900.deg. C and 30 min. at 1000.deg. C were applied. Either the rolling or the transverse direction did not give any significant difference in the shear bond strength. Stainless steel-HSLA steel was superior to stainless steel-mild steel in the same range of magnitude. Because the above experimental results were in contrary to the existing mechanisms, the new model was proposed to describe the bonding mechanism and the void formation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.326-329
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• 2009

In order to analyze the effect of leveling conditions on residual stress evolution of hot rolled high strength steels, a numerical algorithm was developed. It was able to implement the effect of plastic fraction (intermesh) in leveling, line tension, work roll bending, and initial residual stress and curl distribution. The effect of work roll bending on residual stress and curl were studied by using the developed program. The validity of simulated results was verified from comparison with the experimentally measured residual stress and curl in a sheet.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2003.12a
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• pp.207-211
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• 2003

In this study, the geometric modeling has been conducted for a new model of 12 inch hot-cold chuck using three-dimensional solid modeler, SolidWorks. Then, the heat transfer analysis and the thermal deformation analysis using FEM have been performed. The results of the analysis show the temperature distribution and the deformed shape of a new model of 12 inch hot-cold chuck. The evaluation for the surface flatness of a new model has been performed based on the deformed shape obtained from ANSYS.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.277-280
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• 2001

The effects of a -phase morphology on the static and dynamic deformation behavior of a Ti-6Al-4V alloy was investigated in this study. Static tension test, static and dynamic tension test and hot compression test were conducted on three microstructures of Ti-6Al-4V alloy, i.e., equiaxed, widmanstatten and bimodal microstructures. Fracture surfaces of all three microstructures represented ductile fracture appearance, though the formation of adiabatic shear bands was noticed at dynamic torsion test. The susceptibility of forming adiabatic shear bands was greatest in the equiaxed microsoucture and lowest in the bimodal microstructure, which was evidenced by hot compression test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.195-198
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• 2003

High temperature deformation and softening behavior of SAF 2507 super duplex stainless steel (SDSS) has been investigated in connection with an FEM analysis of hot forging process. Flow curves at various strain rates and temperatures were determined first from compression tests, and the kinetics of dynamic recrystallization were also formulated through the analysis of load relaxation test results. Applying the dynamic materials and proposed by Prasad et al., it was possible to determine the characteristics of deformation behavior effectively at a given condition of deformation. Constitutive relations and recrystallization kinetics formulated from the test results were then implemented in a commercial FEM code. Flow stress compensation formulated upon the volume fraction of recrystallization and adiabatic heating was found to improve significantly the FEA solutions in predicting the forming load and the distribution of recrystallized volume fraction after forging.

• Transactions of Materials Processing
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• v.25 no.1
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• pp.61-66
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• 2016

In the current study, we present a new model for the prediction of the strip profile and the residual stresses. This new approach is an analytical model that predicts the residual stresses from the effect of post-deformation. Since the residual stress cannot exceed the yield strength of the material, post-yielding may possibly occur in the post-deformation zone prior to the strip reaching the steady-state zone. The prediction accuracy of the proposed model is examined through comparison with the predictions from 3-D finite element (FE) simulations.

• Metals and materials international
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• v.24 no.6
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• pp.1249-1255
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• 2018

High temperature compression tests for newly developed Al-Zn-Mg alloy were carried out to investigate its hot deformation behavior and obtain deformation processing maps. In the compression tests, cylindrical specimens were deformed at high temperatures ($300-500^{\circ}C$) and strain rates of 0.001-1/s. Using the true stress-true strain curves obtained from the compression tests, processing maps were constructed by evaluating the power dissipation efficiency map and flow instability map. The processing map can be divided into three areas according to the microstructures of the deformed specimens: instability area with flow localization, instability area with mixed grains, and stable area with homogeneous grains resulting from continuous dynamic recrystallization (CDRX). The results suggest that the optimal processing conditions for the Al-Zn-Mg alloy are $450^{\circ}C$ and a strain rate of 0.001/s, having a stable area with homogeneous grains resulting from CDRX.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.614-622
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• 2003

In this paper, the stress-strain curves of bearing steels at hot working conditions are obtained by hot compression test with a computer controlled servo-hydraulic Gleeble 3800 testing machine and elongations and reductions of area of the bearing steels are also obtained by hot tensile test with a Gleeble 1500 testing machine. Experiments are conducted under the various strain-rates and temperatures and their results are used to obtain the flow stress information. A rigid thermo-viscoplastic finite element method is applied to the multi-stage hot forging process in order to predict temperature distribution of workpiece. The experimental results and the analysis results are used to obtain an optimal hot forging condition.