• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.281-284
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• 2003

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment is investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) are hot extruded to make I-shape bars at 380$^{\circ}C$, then the bars are solution treated at 480$^{\circ}C$ for 2hrs followed by artificial aging at 120$^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consists of elongated grains, however, fine equiaxed grains are mainly observed around surface. The microstructural gradient suggests that different restoration process can proceed during the hot extrusion. For B1 and B2, different grain growth behaviors are found around the surface during the post heat treatment. Rapid grain growth behavior around the surface is discussed related with the crystallographic orientation of the grain.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.21-24
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• 2003

In hot forming process of the backward end-bulkhead of a pressure hull, the blank diameter and the tool clearance are the critical factors which influence wrinkling defect, forming load and shape completeness of the product. Two F.E.A softwares with the elasto-plastic material model and rigid plastic model were utilized to predict the occurrence of wrinkling defect. Tool clearance was determined by considering the increase of blank thickness, die strength and the stretching effect. Heat treatment condition after the hot forming to recover the original properties of the material was estabilished by specimen-based heat treating experiment.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.307-310
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• 2003

Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to investigate their deformation resistance and forming limit. Deformation resistance was estimated by calculating the deformation energy and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strain was the highest in the ultra low carbon bainitic steel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.161-166
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• 2001

The distortion and fracture of heat treated components is a major industrial problem, which may considerably increase the costs of operations that involve high cooling rates. And also, thermal deformation would be generated during Heat Treatment. In this paper, the purpose is to check out the thermally deformed components during heat treatment and to analyze thermal deformation and thermal stress by two dimensional Finite Element Method. And two dimensional FEM program is evaluated for heat transfer and thermal deformation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.17-20
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• 2000

In order to improve the sheet formability of the ferritic stainless steel, the through-thickness textures of the recrystallized sample was modified by means of a thermomechanical treatment. An annealing process between the cold rolling reductions modified the preferred orientations throughout the thickness, which resulted in the modification of the final cold rolling texture as well as the final recrystallization texture. With the help of the modification of the recrystallization texture by the intermediate annealing, improvement of the sheet formability, i.e. an increase of the Lankford value.

• 소성∙가공
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• 제12권3호
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• pp.221-227
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• 2003

Heat treatment is widely used in various manufacturing Processes to enhance the quality of a Product such as strength, surface hardness, and service life. In the heat treatment, there is dimensional change or distortion of the product, which critically influences the dimensional accuracy of precision parts. In this study, the distortion of a straight bevel gear induced by heat treatment is investigated in two cases. In the first case, the distortion induced by heat treatment we compared between a forged bevel gear and a machined bevel gear. In the second case, the distortion of an annealed gen is compared with that of a quenched gear. And finite element analysis has been Performed to predict the distortion of a heat-treated and machined bevel gear. The predicted values are compared with the experimental values.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.166-169
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• 2004

Permalloys were successfully fabricated by melt drag casting in the present study, and their variation of microstructure and consequent magnetic properties were investigated as a function of Si contents and annealing temperature. The increases in Si content and annealing temperature resulted in the increases of grain size and amount of $FeNi_3$ ordered phase. Both the grain size and $FeNi_3$ ordered phase controlled by Si and annealing temperature had a important role on permeability of permalloys.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.178-181
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• 2004

Heat treatment is one of important manufacturing process that determine the quality of the products. Because of a difference of mechanical property by heat treatment, It is necessary to This papers presents flow stress and yield point through tensile test. The goal of this study is to obtain the data of flow stress and yield point at martensite, bainite, ferrite/pearlite phase structure using SCM420, SCr420. The result of tensile test is satisfied and is expected to develop an available FEM analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.172-175
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• 2006

Effects of deformation at austenite non-recrystallization region and cooling rate on the microstructure and mechanical properties of low carbon (0.06 wt. %) high strength low alloy steels have been investigated. Average grain size decreased and polygonal ferrite transformation promoted with increasing deformation amount due to increase of ferrite nucleation site. As cooling rate increased, the major microstructure changed from polygonal ferrite to acicular ferrite and the fraction of M/A constituents gradually increased. Discontinuous yielding occurred in highly deformed specimen due to the formation of polygonal ferrite. However, small grain size of highly deformed specimen caused lower ductile-to-brittle transition temperature than slightly deformed specimen.

• 소성∙가공
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• 제24권5호
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• pp.354-360
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• 2015

AHSS (Advanced High Strength Steels) has been increasingly employed by global automotive OEMs in order to satisfy strengthened regulations and reduce weight for fuel efficiency. Hot stamping using boron steels in AHSS increases not only formability but also strength. The typical hot-stamped automotive part is the center pillar that is critical for vehicle side impact. However, the hot-stamped part can be risky for the passenger safety caused by brittle fracture under a vehicle collision. The high power diode laser is suitable for the heat treatment giving AHSS increased elongation that prevents brittle fracture in car crash. Therefore, local softening by laser heat treatment for energy absorption area on the hot-stamped part improves crash-worthiness.