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고탄소강 다단 신선 와이어의 표면 온도 상승에 의한 축방향 잔류응력 예측
김대운(Dae Woon Kim),이상곤(Sang Kon Lee),김병민(Byung Min Kim),정진영(Jin Young Jung),반덕영(Deok Young Ban) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.10
최근 와이어의 생산성 및 고강도화를 위한 고탄소강의 고속신선으로 인해 와이어 표면의 급격한 온도상승으로 잔류응력이 크게 증가하는 문제점이 발생되고 있다. 와이어의 다단 신선 공정시에는 소성변형과 마찰열에 의하여 와이어 내부의 온도가 더욱 크게 상승하게 된다. 특히, 고속 신선의 경우 마찰에 의한 온도구배가 더욱 크게 되어 와이어 표면층에 축방향 인장 잔류응력을 과도하게 발생시킨다. 따라서, 본 연구에서는 먼저 표면 온도 상승과 축방향 잔류응력과의 관계를 규명한 다음에 와이어의 평형온도 예측 모델을 제안하고, 이를 토대로 표면 온도 상승에 의한 축방향 잔류응력 예측식을 개발하였다. 고탄소강(0.82%C)소재의 다단신선 실험을 통해 얻어진 시편에 대하여 X 선 회절을 이용하여 잔류응력을 측정하여 제안된 예측식을 검증하였다. In recent times, due to wire drawing of high carbon steel at a high speed to ensure a high productivity and high strength, axial residual stress are generated because of rapid increase in surface temperature. In the process, the temperatures of the wires increased because of the deformation of the wires and the friction between the die and wire. In particular, in the case of the wire drawing at a high speed, friction leads to a large temperature gradient so that considerable axial residual stress is generated on the surface. In this study, the relationship between axial residual stress and increase in the surface temperature was investigated, and a prediction model of uniform temperature was proposed. Then, a prediction model for residual stress was developed. The proposed model was verified by measuring the residual stress by X-ray diffraction on drawn wires.
W의 첨가가 고강도 Si-Cr 스프링 강의 미세 조직 및 기계적 성질에 미치는 영향
남원종,이상래,반덕영 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
Effects of the W addition on the microstructure evolution and mechanical properties of high strength Si-Cr spring steels have been investigated. The W addition would reduce the coarsening rate of cementite due to the lower diffusion rate, resulting in a smaller size of cementite particles. The sag resistance depends on the distribution and the size of precipitates. Therefore, an abundance of precipitates at 350℃ tempering exhibits the maximum hysteresis loop area, i.e. the sag resistance. At the tempering temperature of 450℃-500℃, the W addition resulted in the improvement of the sag resistance through the suppression of the cementite coarsening.
Si-Cr 스프링 강에서의 Mo 및 W 첨가가 미세조직 및 기계적 성질에 미치는 영향
남원종,이상래,반덕영 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.2
Effects of the Mo and W additions to Si-Cr spring steels on the microstructural evolution and mechanical properties in spring steels were investigated. It was found that the Mo and/or W addition does not change the behavior of tempered carbide at low temperatures, such as the precipitation of ε-carbide and the conversion of ε-carbide to cementite, via dilatometry tests and the observation of microstructure using TEM. However, it would reduce the coarsening rate of cementite at high temperatures above 450℃, resulting in the smaller size of cementite particles due to the lower diffusion rate. Since the sag resistance depends on the distribution and the size of precipitates, steel C(0.2% W) showed the strongest sag resistance whereas steel A showed the weakest sag resistance, when tempered at 450℃. Also, an abundance of precipitates at 350℃ tempering exhibits the maximum loop area, i.e., the sag resistance for all the tested steels. The Mo and W additions to Si-Cr spring steels raised the ratio of loop area/tensile strength. Therefore, the Mo and W additions would be effective method to increase the sag resistance as well as strength in Si-Cr spring steels.