• Korean Journal of Materials Research
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• v.2 no.5
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• pp.343-352
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• 1992

The high temperature deformation behavior of microalloyed hot forging steels has been examined as a function of the temperature, the strain rate, and the alloying element by using high temperature compression test. The high temperature deformation mechanism, which was obtained by analyzing the flow stress-strain curve and microstructure, could be considered to dynamic recrystallization. The peak stress of Nb-V-Mo steel was more increased and the dynamic recrystallization of Nb-V-Mo steel was faster than those of Nb-V steel. The peak stress of 1.2Mn-0.09Nb steel was more increased and the dynamic recrystallization of 1.2Mn-0.09Nb was delayed a little bit than those of 1.0Mn-0.05Nb. The peak stress of C-Nb-V steel was more increased and the dynamic recrystallization of C-Nb-V steel was delayed than those of C-steel. The constitutive equation of high temperature deformation had a power law type. The grain size of dynamic recrystallization was refined as the Zener-Hollomon parameter was increased. The relation of the dynamic recrystallization grain size and Zener-Hollomon parameter could be quantified to power law.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.77-80
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• 1997

The torsion tests in the range of 900~110$0^{\circ}C$, 5.0$\times$10-2~5.0$\times$100/sec were performed to study the recry stallization behavior of 304 stainless steel in the high temperature multistage deformation. The no-recrystallization temperature(Tnr) and fractional softening(FS) were determined by the change of flow curves. The inflection points of stress slope were moved to lower temperature area as the strain rate and the interrupt time were increased. From the multipass flow curve, the intersection between pass stress and FS curve was corresponding to the pass which the FS dropped abruptly and it was shown that the recrystallization area could be determined by the FS measurement in multipass deformation.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.39-44
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• 2008

Magnesium alloys have given high attention to the industry of light-weigh as automobile and electronics with aluminium, titanium and composite alloys due to their high strength, low specific density and good damping characteristics. But the magnesium contained structures under high temperature have the problems related to creep deformation and rupture life, which is a reason of developing the new material against creep deformation to use them safely. The purpose of this study is to predict the creep deformation mechanism and rupture time of AZ31 magnesium alloy. For this, creep tests of AZ31 magnesium alloy were done under constant creep load and temperature with the equipment including automatic temperature controller with acquisition computer. The apparent activation energy Qc and the applied stress exponent n, rupture life have been determined during creep of AZ31 Mg alloy over the temperature range of $150^{\circ}C$ to $300^{\circ}C$. In order to investigate the creep behavior. Constant load creep tests were carried out in the equipment including automatic temperature controller, whose data are sent to computer. At around the temperature of $150^{\circ}C{\sim}300^{\circ}C$ the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy for the creep deformation was nearly equal and a little low, respectively, to that of the self diffusion of Mg alloy.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.535-541
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• 2016

The present study deals with the effects of micro-alloying elements such as Ni, V, and Ti on the recrystallization behavior of carbon steels at different strain rates. Eight steel specimens were fabricated by varying the chemical composition and reheating temperature; then, a high-temperature compressive deformation test was conducted in order to investigate the relationship of the microstructure and the recrystallization behavior. The specimens containing micro-alloying elements had smaller prior austenite grain sizes than those of the other specimens, presumably due to the pinning effect of the formation of carbonitrides and AlN precipitates at the austenite grain boundaries. The high-temperature compressive deformation test results indicate that dynamic recrystallization behavior was suppressed in the specimens with micro-alloying elements, particularly at increased strain rate, because of the pinning effect of precipitates, grain boundary dragging and lattice misfit effects of solute atoms, although the strength increased with increasing strain rate.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.242-243
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• 2006

NiTiZrSiSn bulk metallic glass powder was produced using inert gas atomization and then was sprayed onto a SS 41 mild steel substrate using the kinetic spraying process. Through this study, the effects of thermal energy of in-flight particle and crystallization degree by powder preheating temperature were evaluated. The deformation behavior of bulk metallic glass is very interesting and it is largely dependent on the temperature. The crystalline phase formation at impact interface was dependent on the in-flight particle temperature. In addition, variations in the impact behavior need to be considered at high strain rate and in-flight particle temperature.

• Journal of Ocean Engineering and Technology
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• v.26 no.3
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• pp.55-60
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• 2012

This study was carried out to investigate the effect of the deformation temperature in high manganese austenitic stainless steel. ${\alpha}$'-martensite was formed with a specific direction by deformation. The volume fraction of the deformation induced martensite was increased by increasing the degree of deformation and decreasing the deformation temperature. With the increase in the deformation, the hardness and tensile strength were increased, while the elongation was rapidly decreased at the initial stage of the deformation, and then gradually decreased. The hardness and tensile strength were increased and the elongation was decreased with adecrease in the deformation temperature. The hardness and tensile strength were strongly controlled by the volume fraction of martensite, but the elongation was controlled by the transformation behavior of the deformation induced martensite.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.429-433
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• 2006

High Temperature deformation behavior of newly developed beta-gamma TiAl alloy was investigated in this study. The optimum processing condition was investigated with the aid of Dynamic Materials Model (DMM). Processing maps representing the efficiency of power dissipation for microstructural evolution and instability were constructed utilizing the results of hot compression test at temperatures ranging from $1000^{\circ}C$ to $1200^{\circ}C$ and strain rate ranging from $10^{-4}/s$ to $10^2/s$. The Artificial Neural Network (ANN) simulation was adopted to consider the deformation heating. With the help of processing map and microstructural analysis, the optimum processing condition was presented and the role of $\beta$ phase was also discussed in this study.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.491-492
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• 2008

The effect of B on the hot ductility of Fe-29Ni-17Co Kovar alloy and the mechanism of high temperature deformation behavior were investigated. Hot-tensile test was carried out at the temperature range of $900^{\circ}C-1200^{\circ}C$. Optical microscopy and scanning electron microscopy were used to investigate the microstructure and fracture during hot deformation. The hot ductility of Kovar alloy was drastically increased with the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range($900^{\circ}C$).

• Transactions of Materials Processing
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• v.7 no.4
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• pp.333-339
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• 1998

Hot torsion tests were conducted to investigate the high temperature deformation behavior of $Al_{85}Ni_{10}Y_5$ alloy extrudates fabricated with amorphous ribbons. The powder metallurgy routes, hot pressing and hot extrusion were used to fabricate the extrudates. Thermal properties of amorphous ribbons with different thickness as a function of aging temperature were studied by thin film x-ray dif-fraction (XRD) and differential scanning calorimetry(DSC). The Al phase crystallite firstly formed in the amorphous ribbons and its crystallization temperature($T_x$)Was ~210${\circ}C$ During the processings of consolidation and extrusion, nano-grained structure(~100 nm) was formed in the Al85Ni10Y5 alloy extrudates. The as-extrudated Al85Ni10Y5 alloy and the $Al_{85}Ni_{10}Y_5$ alloy annealed at 250${\circ}C$ for 1 hour showed a flow curve of DRV(dynamic recovery) during hot deformation at 400-550${\circ}C$. On the other hand, the $Al_{85}Ni_{10}Y_5$ alloy annealed at 400${\circ}C$ for 1 hour showed a flow curve of DRX(dynamic recrys-tallization) during hot deformation at 450-500${\circ}C$. Also the flow stress and flow strain of the $Al_{85}Ni_{10}Y_5$ alloy extrudate annealed at 400${\circ}C$ were higher than those at 250${\circ}C$.

• Design & Manufacturing
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• v.2 no.6
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• pp.43-48
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• 2008

Magnesium alloys have given high attention to the industry of light-weigh as automobile and electronics with aluminium, titanium and composite alloys due to their high strength, low specific density and good damping characteristics. But the magnesium contained structures under high temperature have the problems related to creep deformation and rupture life, which is a reason of developing the new material against creep deformation to use them safely. The purpose of this study is to predict the creep deformation mechanism and rupture time of AZ31 magnesium alloy. For this, creep tests of AZ31 magnesium alloy were done under constant creep load and temperature with the equipment including automatic temperature controller with acquisition computer. The apparent activation energy Qc, the applied stress exponent n and rupture life have been determined over the temperature range below 0.5Tm and stress range of 109~187MPa, respectively, in order to investigate the creep behavior. AZ31 Magnesium alloy identify the activation energy for creep deformation and the stress dependence to creep rate at below 0.5Tm, and then investigate the mechanism for creep deformation and creep rupture life of AZ31 Magnesium alloy.