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Si-Cr 스프링용강에서의 니오븀 및 바나듐 첨가 효과
남원종,최해창 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.3
The effects of Nb and V addition on mechanical properties and microstructures were investigated in conventionally heat treated(quenched and tempered) Si-Cr spring steels. The specimens were austenitized at 850℃ for 15min and tempered at 470℃ for 15min. The addition of vanadium raised tensile strength by about 5kg/㎟, while that of niobium did not show any influence on tensile strength. The addition of V and Nb increased the hardness over the entire tempering temperatures, but did not have an effect on softening resistance which occurred by the Si addition. The impact values were not changed by the addition of vanadium and niobium. When tempered at 470℃, all steels showed the cementite precipitation in addition to asquenched microstructures. (Received July 4, 1994)
고탄소 베어링강에서의 합금원소가 미세조직 및 피로수명에 미치는 영향
남원종,최해창 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.6
The effects of alloying elements on microstructures and fatigue life in STB2 bearing steel, were investigated through the measurements of particle distribution and alloy content in carbides for different chemical composition and manufacturing processes. Among alloying elements, chromium has a strong influence on the distribution of carbides. Finer spheroidized carbides and finer retained carbide particles were distributed after austenitizing and quenching. The microchemistry of carbides also changes during spheroidizing and austenitizing. The chromium content in carbides was decreased during spheroidizing and increased again during austenitizing. The effect of the chromium addition was found to increase fatigue life markedly, while those of other elements such as manganese and silicon, were found to be not so effective on the fatigue life.
남원종,최해창 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.4
The effect of the distribution of non-metallic inclusions on fatigue life in bearing steels was investigated. Most oxide inclusions observed in this work were globular oxides. The increase in the oxygen content has an effect of increasing the amount of oxides inclusions and decreasing fatigue life. But the direct relationship between the distribution of oxide inclusions and fatigue life could not be formulated. The increase in sulfur content results in the decrease in fatigue life. The phenomenon that the exis tence of MnS does not hinder the crack propagation during rolling contanct fatigue test was observed. And also the occurence of cracks and cavities at the MnS inclusion was observed.
김석우,남원종,최해창 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.5
Microstructural changes in STB2 bearing steel caused by rolling contact fatigue test, were investigated using optical and scanning electron microscopy. Dark area, butterfly structures and plate-like carbides were found in the area below the flaking. Rolling contact caused the formation of Dark area in the subsurface area of contact in the region of maximun Hertzian stress. Most subsurface cracks were initiated at the region of Dark area. Butterflies found only at the oxide inclusions, were frequently associated with cracks. Plate-like carbides acted as the potential crack initiation site responsible for the flaking. The growth of plate-like carbides was caused by the carbon diffusion by rolling stress between not only oxide inclusions but also fine residual carbides.
남원종,최해창 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.2
The effects of the alloy content of Si, Ni and V and tempering temperatures on mechanical properties, especially hardness and yield strength, of 0.6C-(1.0-2.5)Si-(0.7-1.8)Ni-(0.1-0.2)V steels were investigated by hardness tests, tensile tests and transmission electron microscopy. The results showed that tempering temperatures for the maximum yield strength and the softening resistance in hardness moved to higher temperatures due to the retardation of the conversion of ε-carbide to cementite within martensite laths by Si addition. Additionally, it was found that the temperatures of the conversion of ε-carbide to cementite was not changed by the addition of Ni or V addition in present steels. The contribution of Ni or V addition was limited only to the increase in hardness and yield strength.