• Journal of the Korean Society for Heat Treatment
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• v.3 no.4
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• pp.1-9
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• 1990

In this study, the ausformed martensite cooled to $-196^{\circ}C$ with various deformation degrees in Fe-30%Ni-0.24%C alloy was transformed to reversed austenite at $500^{\circ}C$ by cyclic reverse martensitic transformation. The effects of prior deformation and the number of cyclic reverse transformation on the microstructure and the mechanical properities of reversed anstensite were investigated. Experimental results showed that the strength of reversed austenite was higher than that of original austenite. This is due to higher dislocation density and grain refining. The reversed austenite formed from ausformed martensite was highly strengthened by prior deformation. This strengthening effect of reversed austenite is attributed to higher dislocation density than grain fefining. The yield strength of reversed austenite below 30% prior deformation, but above 30% prior deformation the strength of reversed austenite is lower than that of deformed austenite. This is due to partly disappearance of strain hardening effect at higher deformation degree by reverse transformation. The strength of reversed austenite is increased with the number of cyclic transformation. Especially, it is principally strengthened by the first cyclic transformation and shows higher increase in yield strength than that of ultimate tensile strength.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.5
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• pp.271-276
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• 2011

The effect of grain size on the deformation induced martensite transformation and mechanical properties in austenitic stainless steel with high amount of Mn was studied. a'-martensite was formed by deformation and deformation induced martensite was formed with surface relief. With increase of grain size, volume fraction of deformation induced martensite was increased. With the increase in degree of cold rolling, hardness, and tensile strength was rapidly increased with linear relationship, while, elongation was decreased rapidly and then decreased slowly. With increase of grain size, hardness and tensile strength was rapidly increased with linear relationship, while elongation was decreased rapidly. The hardness, tensile strengths, and elongation were more strongly influenced by deformation induced martensite than the grain size.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.2
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• pp.47-53
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• 1991

Recrystallization behaviors of ordered and disordered structures in $Ll_2$ type $Ni_3Fe$ alloy were studied through hardness measurement and differential thermal analysis. When the disordered structure was isothermally aged at $480^{\circ}C$ below order-disorder transition temperature, the hardness of the structure was increased due to progressive ordering with increasing aging time. The hardness of the disordered structure was increased rapidly with increasing deformation degree up to 10%, and then gradually increased with further deformation degree. while the hardness of the ordered structure was increased rapidly with increasing deformation degree up to 10%, showing a constant hardness value up to 50% and gradually decreased with further deformation degree. The hardness of the ordered structure was higher than that of the disordered structure at all same deformation degrees. The recrystallization temperature of the ordered and disordered structures were decreased with increasing deformation degree. At the same deformation degrees, the recrystallization temperature of the ordered structure was lower than that of the desordered structure.

• Journal of Ocean Engineering and Technology
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• v.22 no.1
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• pp.64-69
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• 2008

As it has been well appreciated from the viewpoint of efficiency, The weld-induced deformation control is one of the most important issues in marine structure production. In the case of thin plate block, weld-induced deformation is more serious than in the case of relatively thick plate block. The heat affect zone of thin plates is wider than that of thick plates with the same heat input. Among weld-induced deformations, the buckling deformation by the shrinkage and residual stress in the weld line direction is one of the most serious deformation types. This paper is concerned with controlling buckling deformations for the thin plate fillet welds, by using the tensioning method. A numerical analysis was carried out to illustrate several dominant buckling modes due to compressive residual stress in the fillet weldsof thin plates. Then, weld tests were carried out for 20 specimens with varying plate thickness, and with different magnitudes and directions for the tension load. The results graphically represented to shaw the effect of the tensioning method in reducing the weld-induced deformation. From the present findings, it was seen that the tensioning method is a useful way to control weld-induced deformations in the fillet welds of thin plates.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.127-130
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• 2004

In the recent years, lightweight components fabricated with aluminum alloys have been applied into building the automobiles. Among the several competing fabrication methods, hot forging is taken as the most reliable technique to produce suspension parts such as control arms. Generally, Al forging products have been used widely for the aircraft building with the extruded stock as a starting material. For the economical base, however, the cast stocks turn to be as the forging stocks recently after a continuously casting technique was developed to produce quite a uniform microstructure enough to use for the forging process. Even more, there is a tendency to omit the homogenization step before forging, which is considered to be an indispensable process for all kinds of Al alloy, In the present study, a series of compression test was carried out to find out how the cast structure and the following heat treatments influence the deformation behavior, that is, forging characteristic.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.339-343
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• 2000

Rapid prototyping for welding and milling is a hybrid approach that makes use of welding as additive and conventional milling as subtractive technique. For two years this concept has been used to verify manufacturing mold and mechanical parts successfully. In latest new fabrication methods. For example, manufacturing mold for two sort of materials and shell fabrication, have been applied to the concept in KIST. This methods will be an alternative proposal in rapid prototyping. Metal deposition for welding causes the part to deform. It is a handicap in our proceeding. To overcome this problem, in this paper, we represent an optimal welding path for FEM analysis. Eight paths are tried to this and the value of deformation is average and standard deviation in four points'. Then we can compare with eight cases and select the optimal path.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.209-212
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• 2006

Line heating with water cooling is generally adapted process in the shipyards for the forming hull surface. The purpose of this paper is to develop a model of thermal deformation in water cooling process after the line heating. In order to simulate the cooling process, heat transfer analysis was performed by assuming the effects of water cooling as a negative heat-source. Experiment for the line heating with water cooling was performed for 9 models of plates in order to verify the cooling model. By using the suggested model for the water cooling process, it could be observed that the present method predict the plate deformations in the line heating more accurately.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.139-144
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• 2003

Laser melting problems with deformed substrates are investigated by axisymmetric numerical simulations. Source-based method is used to solve the energy equation, and the momentum equations are solved in the liquid domain with SIMPLER algorithm. Using a laser beam with a top-hat heat flux distribution, this study is performed to examine the effect of surface deformation, beam power density and surface tension force on the melt pool during laser melting. Surface temperature decreases with increasing surface deformation, while surface velocity increases. It is found that surface deformation, beam power density and surface tension force have a very significant effect on heat transfer and fluid flow during laser melting.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.1-8
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• 2005

Laser melting problems with deformed substrates are investigated by axisymmetric numerical simulations. Source-based method is used to solve the energy equation, and the momentum equations are solved in the liquid domain with SIMPLER algorithm. Using a laser beam with a top-hat heat flux distribution, this study is performed to examine the effect of surface deformation, beam power density and surface tension force on the molten pool during laser melting. Surface temperature decreases with increasing surface deformation, while surface velocity increases. It is found that surface deformation, beam power density and surface tension force have a very significant effect on heat transfer and fluid flow during laser melting.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.3-11
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• 2005

Using various thermo-mechanical schedules characterized by varying reheating temperature, deformation temperature and strain, the austenite recrystallization and ferrite refinement of a Nb bearing low carbon steel(0.15C-0.25Si-1.11Mn-0.04Nb) were investigated. For single pass heavy deformations at $800^{\circ}C$, the 40% deformed austenite was not recrystallized while the 80% deformed one was fully recrystallized. Ferrite grains formed in the 80% deformed specimen was not very small compared with those in the 40% deformed specimen, which implied the recrystallized austenite was not more beneficial to ferrite refinement than the non-recrystallized one. In case of deformation in low temperature austenite region, a multi-pass deformation made finer ferrites than a single-pass deformation, as the total reduction was the same, due to more ferrite nucleation sites in the non-recrystallization of austenite for multi-pass deformation. When specimen was deformed at $775^{\circ}C$ that was $10^{\circ}C$ higher than $Ar_3$, the ferrite of about $1{\mu}m$ was formed through deformation induced ferrite transformation(DIFT), and the amount of ferrite was increased with increasing reduction. Dislocation density was very high and no carbides were observed in DIFT ferrites, presumably due to supersaturated carbon solution. By deformation in two phase(50% austenite+50% ferrite) region the very refined ferrite grains of less than $1{\mu}m$ were formed certainly by recovery and recrystallization of deformed ferrites and, a large portion of ferrites were divided by subgrain boundaries with misorientation angles smaller than 10 degrees.