• 소성∙가공
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• 제7권6호
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• pp.530-538
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• 1998

Elimination of the heat treatment process is very important in automation of metal forming since controlling heat treatment by computer has many difficulties and it has bottle neck problem. non-heat-treated steels materials which are not in need of heat treatment have been developed for cold forging. However to apply non-heat-treated steel to structural parts. it is necessary to prove reliability of mechanical properties. In order to define the reliability of mechanical properties we have investigated microstructure, hardness, the tensile strength compressive strength and tensile fatigue strength for both steels. Considering the results of high cycle fatigue test for both specimen the characteristics of non-heat-treated steel are decided on the yield strength, It has same tendency for heat-treated steel. Therefore non-heat-treated steel which has the appropriate yield strength may be applied in cold forging.

• 소성∙가공
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• 제19권4호
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• pp.210-216
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• 2010

The importance and interests for saving of energy and cost in industry has grown up. Therefore, process optimization to reduce the process and energy become one of the most important things. The non-heat treated steel, post-heat-treated is no necessary, has attractive points as structural materials. However, establishment of mechanical properties is necessary to apply non-heat-treated steel to structural parts. In this study, for non-heat-treated steel and pre-heat-treated steel, we have investigated microstructure, hardness, the tensile strength, compressive strength. And the FE analysis technology to predict the hardness value of forged part is developed on micro-alloyed steel forged part.

• 대한치과교정학회지
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• 제16권1호
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• pp.133-144
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• 1986

This study was conducted to evaluate the effects of loop formation and heat treatment upon the elastic properties of orthodontic wires. The specimens selected were .016', .018', .016x.022', and .018x.022' sized stainless steel (standard) and cobalt-chromium-nickel wires, and were divided into 7 groups as; 1. straight non-heat treated 2. U looped non-heat treated 3. L looped non-heat treated 4. Circle looped non-heat treated 5. U looped heat treated 6. L looped heat treated 7. Circle looped heat treated Heat treatment was performed in Big Jane furnace at 850' F for 3 minutes. The elastic limit and the elastic range of each specimen were determined by bending test, and load deflection rate was computed from those values. The findings were as follows; 1. The formation of loop resulted in increased load-deflection rate for both stainless steel and cobalt-chromium-nickel wires. 2. The heat treated group showed higher load-deflection rate than non-heat treated group, which was more apparent in cobalt-chromiumnickel wire than in stainless steel wire. 3. L loop had the highest load-deflection rate among 3 types of loops, followed by U loop and circle loop. 4. The specimens with greater diameter displayed the more increase in load-deflection rate by looping and heat treatment.

• 소성∙가공
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• 제12권4호
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• pp.364-369
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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. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to study their mechanical properties and the cold formability. The cold formability of three steels was investigated by estimating the deformation resistance and the forming limit. The 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 strains of ultra low carbon bainitic steel and low-Si steel were higher than that of commercial SWRCH45F steel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.137-138
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• 2009

There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment in the steel-wire industry production. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the cold drawing process. In this presentation, non-heat treated steel wire rod produced by POSCO will be introduced and discussed on detail technical concepts.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.400-403
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• 2004

A non-heat기leafed steel does not need quenching and tempering processes that are called a heat treatment differently from conventional steel. Since the tensile strength of this steel is higher than 900MPa, a conventional forming process should be changed to incremental forming process such as a cross wedge rolling that requires lower load capacity than conventional ones. In this paper, the cold cross wedge rolling (CWR) die has been designed using CAD/CAE In order to produce near-net-shaped component of ball stud of non-heat-treated cold steel. Finite element analyses were applied in order to investigate process parameters of CWR. Results provide that the stretching angle and the forming angie at knifing zone in CWR process is important parameter to be the stable process under the low friction coefficient condition.

• 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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.771-772
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• 2009

• 대한치과교정학회지
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• 제19권1호
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• pp.245-256
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• 1989

Translational movement along an arch wire requires sufficient force to overcome frictional forces between bracket and arch wire. The orthodontist must appreciate the importance of friction in this process, and study out the influencing factors on the level of friction. The purpose of this study was to evaluate the effect of artificial saliva on frictional resistances generated between the bracket and arch wire. Independent variables of this study were arch wire material, angulation and environment. Static frictional forces of cobalt-chromium, heat-treated cobalt-chromium, beta-titanium, stainless steel wires were measured under non-angulated dry, angulated dry, non-angulated saliva, angulated saliva conditions. The results were as follows: 1. Stainless steel wires showed lower friction values in non-angulated dry condition, and heat-treated cobalt-chromium wires showed higher friction values in angulated dry condition. Higher friction values were showed in order of cobalt-chromium. stainless steel, heat-treated cobalt-chromium and beta-titanium wires in non-angulated saliva condition. and were showed in order of stainless steel, cobalt-chromium, heat-treated cobalt-chromium, beta-titanium wires in angulated saliva condition. 2. Angulation increased friction for stainless steel wires under dry condition. 3. Artificial saliva decreased friction for cobalt-chromium wires and increased friction for stainless steel wires under non-angulated condition. 4. Artificial saliva decreased friction for all wires except beta-titanium wires under angulated condition. 5. Regardless of angulation or environment. heat-treated cobalt-chromium and beta-titanium wires showed higher friction values, and stainless steel wires showed lower friction values.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.326-329
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• 2005

Since the required strength of forged part is achieved by work hardening with the accumulation of plastic strain during the cold working, severe load can be exerted on die system. So, dies are liable to the early fracture for the non-heat treated steel forging in comparison with the conventional mild steels. Therefore, it is necessary to lower the flow stress of steels as much as possible during forging steps. Bauschinger effect can be utilized to lower flow stress during forging steps by giving the tensile prestrain on the forging billet during wire drawing step. In the present study, the prestrain effect on Bauschinger phenomenon is studied to avoid difficulties with application of non-heat treated cold forging steels in practice.