발간논문

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Vol.41, No.5, 297 ~ 306, 2003
Title
Microstructure and Thermal Fatigue Properties of High Speed Steel Rolls -2. Correlation of Microstructure and Thermal Fatigue Properties
박종일 Jong Il Park , 김창규 Chang Kyu Kim , 류재화 Jae Hwa Ryu , 이성학 Sung Hak Lee
Abstract
This is a study of thermal fatigue properties in five high speed steel (HSS) rolls. The thermal fatigue mechanism was investigated with focuses on the roll microstructure and the increase in tensile stress which led the specimens to fracture when it reached to the tensile strength. The thermal fatigue test results indicated that the thermal fatigue life decreased with increasing the maximum temperature of the thermal fatigue cycle. The results were then interpreted based on the amount of carbides and the cyclic softening phenomenon associated with the exposure time to elevated temperature. The coarse intercellular carbides on the specimen surface acted as fatigue crack initiation sites as they cleaved at a low stress level to form cracks. The roll having the lowest matrix hardness and the smallest amount of intercellular carbides thus showed better thermal fatigue properties than the other rolls. For the improvement of the thermal fatigue properties of the rolls, this study suggests a homogeneous distribution of carbides by reducing the carbide segregation formed along the solidification cell boundary and by optimizing the roll compositions.
Key Words
High speed steel roll, Thermal fatigue, Cyclic softening, Intercellular carbide, Solidification cell
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