• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.179-182
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• 2000

The dynamic softening behavior of type 430 ferritic stainless steel could be characterized by the hot torsion test in the temperature range of 900-110$0^{\circ}C$ and the strain rate range of 0.05-5/sec. It is found that the continuous dynamic recrystallization (CDRX) was a major dynamic softening mechanism. The effects of process variables strain ($\varepsilon$) stain rate($\varepsilon$)and temperature (T) on CDRX could be individually established from the analysis of flow stress curves and microstructure. The effect of CDRX individually established from the analysis of flow stress curves and microstructure. The effect of CDRX increased with increasing strain rate and decreasing temperature in continuous deformation. The multipass deformation processes were performed with 10 pass deformations. The CDRX effect occurred in multipass deformatioon. The grain refinement could be achieved from multipass deformation The grain refinement increased with increasing strain rate and decreasing temperature. Also the CDRX in multipass deformation was affected by interpass time and pass strain. The total strain was to be found key parameter to occur CDRX.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.135-139
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• 1999

The static softening behavior of AISI 4140 could be characterized by the hot torsion test in the temperature ranges of 10$0^{\circ}C$~120$0^{\circ}C$ and strain rate ranges of 0.05/sec~5/sec. Deformation efficiency which was based on dynamic materials model was calculated from flow stress curves obtained continuous deformation. Interrupted deformation was performed with 2 pass deformation in the pass strain ranges of 0.25{{{{ epsilon _p}}}} ~3{{{{ epsilon _p}}}} and interrupted time ranges of 0.5~100sec. The dependences of process variables pass strain ({{{{ epsilon _i}}}}) stain rate ({{{{ {. } atop {$\varepsilon$ } }}}}) temperature (T) and interpass time ({{{{ {t }_{i } }}}}) on static recrystallization (SRX) and metadynamic recrystallization .(MDRX) could be indicidually predicted from the modified Avrami's equations. Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. Controlled multipass deformations were performed using deformation efficiency static and metadynamic recrystallization of AISI 4140.

• Transactions of Materials Processing
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• v.9 no.1
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• pp.80-87
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• 2000

The static softening behavior of SCM 440 could be characterized by the hot torsion test in the temperature ranges of 90$0^{\circ}C$~110$0^{\circ}C$and strain rate ranges of 0.05/sec~5/sec. Interrupted deformation was performed with 2 pass deformation in the pass strain ranges of 0.25$\varepsilon$p~3$\varepsilon$p and interrupted time ranges of 0.5~100sec. The dependences of process variables, pass strain ($\varepsilon$i), stain rate ($\varepsilon$), temperature (T) and interpass time (ti), on static recrystallization (SRX) and metadynamic recrystallization (MDRX)were individually predicted from the modified Avrami's equations, The dependence of pass strain on MDRX was neglectable. Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. Controlled multipass deformations were performed using static and metadynamic recrystallization of SCM 440.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.531-536
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• 2003

Equal channel angular pressing (ECAP) has been employed to produce materials with ultra-fine grains that have high strength and high corrosion resistance properties. In order to obtain super plastic deformation during ECAP, multipass angular pressing is frequently employed. In this paper, three-dimensional finite element analyses have been performed to investigate the deformation behavior of pure-Zr specimen and the effects of process parameters for equal channel multi-angular pressing (ECMAP) process. The results have been compared with some experimental results