• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.188-197
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• 1999

Grain refinement of the structural steels was selected as the most effective method to meet improvement of strength and toughness without heat treatment. So, the future research and developing direction of ultra fine grain steels are more and more required to response to the production of eco - materials(environmental consciousness - materials) In this paper, the product of surface fine grain steels by CRCT and Inverse Transformation Method by warm deformation of martensite is carried out in order to improve the production process of Dowel Bar. It is possible to obtain surface ultra fine grain steel, when warm deformation of martensite formed after quenching is carried out from 730$^{\circ}C$ to 800$^{\circ}C$ in the finishing rolling step. The characters of surface with ultra fine grain steel is showing the cementite particles inside the ferrite grain and fine ferrite grain of about 1.2$\mu\textrm{m}$ in size.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.53-56
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• 2006

Magnesium alloy AZ31, which processed by conventional rolling or extrusion, has high anisotropy of mechanical properties in its strength and elongation at room temperature. We compared the influence of differential speed rolling with conventional rolling process on microstructure and mechanical properties of commercial AZ31 sheet. Commercial AZ31 alloy sheets were processed with conventional and differential speed rolling with thickness reduction ratio of 30% at a various temperature. The elongation of AZ31 alloy, warm-rolled by differential speed rolling is larger than those rolled by conventional rolling. Besides, grain size and distribution on microstructure of the conventional rolled materials were coarse and inhomogeneous, on the contrary, those of the differential speed rolled were fine and homogeneous.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.723-724
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• 2009

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.274-277
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• 2009

There have been a number of works on manufacturing ultrafine grained steels with average ferrite grain sizes of smaller than a few micrometers to develop beneficial high strength steels. Among microstructures in low carbon steels, lath martensite is known to be useful to produce an ultrafine grained ferrite matrix and finely globular cementite particle. Thus, severe plastic deformation and subsequent annealing at lower temperature of lath martensite would become an effective way to produce ultrafine grained steels. However, most ultrafine grained steels exhibited a total elongation of a few per cent in tensile tests. Such a defect is one of the primary factors restricting the potential applications of ultrafine grained steels. Therefore, the improvement of the strength-elongation balance is required for the application of ultrafine grained structural steels. In this study, the effect of deformation temperatures on microstructure, such as ferrite grain size and the distribution of cementite particles, and mechanical property of lath martensite steels, was investigated. Specimens were fabricated through cold rolling or warm rolling and subsequent annealing.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.409-412
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• 2006

Bulk metallic glass (BMG) strips of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ were produced by warm rolling of the amorphous powder canned with copper. Controlling of temperatures of the rolled sample and rolls was essential for the successive rolling process. Because improper controlling of the sample temperature gave rise to the crystallization of BMG loading to the catastrophic fracture of BMG strips, the temperature of rolls should be properly controlled for achieving successful powder rolling of BMG. The variations of the strain state and temperature in the roll gap was simulated by the finite element method(FEM) using various roll temperatures.

• Weed & Turfgrass Science
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• 제7권3호
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• pp.239-245
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• 2018

Comparative drought resistances of 11 perennial warm-season turfgrasses were evaluated in the field after withholding irrigation for 48 days in summer I and 57 days in summer II. There were significant variations among the grasses in their drought resistances. From two years study of field shoot recovery from drought stress, the relative rankings among the 11 warm-season turfgrasses was as follows. 'Arizona Common' and 'Texturf 10' bermudagrasses [Cynodon dactylon (L.) Pers.], 'Tifgreen' hybrid bermudagrass [C. dactylon (L.) Pers. ${\times}$ C. transvaalensis Davy], and 'Georgia Common' centipedegrass [Eremochloa ophiuroides (Munro.) Mack.] possessed good drought resistances, whereas 'Texas Common' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] and 'Tifway' hybrid bermudagrass [Cyndon dactylon (L.) Pers ${\times}$ C. transvaalensis Davy] possessed poor drought resistances. 'Texas Common' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], 'Pensacola' bahiagrass (Paspalum notatum Flugge.), and 'Adalayd' seashore paspalum (Paspalum vaginatum Swartz), 'Meyer' zoysiagrass (Zoysia japonica Steud.), 'Emerald' zoysiagrass (Z. japonica Steud. ${\times}$ Z. tenuifolia Willd. ex Trin.) were found to rank intermediate. Visual leaf firing showed the highest correlation (r=-0.84) to shoot recovery from drought stress. Visual leaf rolling (r=-0.59) and canopy-air temperature differential (r=-0.64) also showed very significant correlations, whereas leaf water potential (r=0.54) showed relatively lower correlation.

• 열처리공학회지
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• 제11권3호
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• pp.192-199
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• 1998

This study was carried out to investigate the influence of variations in the temperature and time of isothermal heat treatment, applied stresses and prestrain on the isothermal transformation behavior of ${\gamma}$ and ${\sigma}$ phases and mechanical properties of 25Cr-7Ni-3Mo duplex stainless steel. The precipitation of ${\gamma}$ and ${\sigma}$ phases through isothermal heat treatment showed the type curves with a certain incubation period, the curve migrated to in a short period of time and the amount of precipitation increased with decreasing isothermal heat treatment temperature. Under the state of isothermal transformation, the precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by applied stress, with increasing applied stress, the curves migrated to in a short period of time and also observed that the application of stress has a greater influence on the amount of ${\sigma}$ precipitation than that of ${\gamma}$ precipitation. The precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by cold and warm rolling before isothermal heat treatment and precipitation of ${\gamma}$ and ${\sigma}$ phases has a greater influence on the warm rolling than cold rolling. The tensile strength and hardness increased with increasing cold and warm rooling reduction ratio.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.80-81
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• 2009

Ti-6Al-4V alloy has been widely used for aerospace and power generation applications because of low density and attractive mechanical and corrosion resistant properties. However, the titanium alloy bolt is generally manufactured by cutting and rolling because of their poor workability. In order to achieve the mass production of titanium alloy bolts, it needs to be solved some manufacturing problems such as the sticking between workpiece and dies, the formation of the forming defects during the forging and so on. In this study, the manufacturing technology of titanium alloy bolts using warm forging process was introduced. The aim of present work is to develop a warm forging technology for high strength Ti-6Al-4V bolts.

• 열처리공학회지
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• 제18권2호
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• pp.91-98
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• 2005

Both commercially pure titanium and Ti-6Al-4V alloy have been widely used as biomaterials because of their excellent biocompatibility, corrosion resistance and mechanical properties. However, in recent years, vanadium has been found to cause cytotoxic effects and adverse tissue reactions, while aluminium has been associated with potential neurological disorders. A newly designed ${\alpha}+{\beta}$ type Ti alloy, Ti-10Ta-10Nb alloy showed superior properties to CP Ti and Ti-6Al-4V alloy in the point of biomaterial, and elucidated the future uses as a biomaterial. Microstructural changes of Ti-10Ta-10Nb alloy after hot-rolling, warm-rolling, solution and aging treatment were investigated. According to TEM results, the microstructures after solution treatment were composed of mostly ${\alpha}$ phase with a trace of ${\beta}$ phase due to adding ${\beta}$-phase stabilizer tantalum and niobium. The microstructures after warm-rolling is coarse and elongated ${\alpha}$ phase and hot rolling resulted in very fine ${\alpha}$ widmanst$\ddot{a}$tten. The highest value of hardness was obtained by aging treatment at $400^{\circ}C$ for 20hr in which microstructure consisted of very fine ${\alpha}$ phase in ${\beta}$ matrix.

• 한국분말재료학회지
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• 제19권4호
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• pp.264-270
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• 2012

In this study, we mainly focus on the study of densification of gas-atomized Cu-50 wt.%In-13 wt.%Ga alloy powder without occurrence of crack during the forming process. Cu-50 wt.%In-13 wt.%Ga alloy powder was consolidated by sintering and rolling processes in order to obtain high density. The phase and microstructure of formed materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM), respectively. Warm rolling using copper can result in the improvement of density. The specimen obtained with 80% of rolling reduction ratio at $140^{\circ}C$ using cooper can have the highest density of $8.039g/cm^3$.