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이성학,김낙준,이희춘,이창길,손기선 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.3
The main objective of the present study is to clarify the microstructural factors such as tempered martensite matrix, coarse primary carbides, eutectic structures, and fine secondary carbides, which influence fracture properties of high speed steel (HSS) rolls. Three HSS rolls with different Cr content were manufactured by a centrifugal casting method, and the microstructures of their shell regions were investigated quantitatively. MC type primary carbides, together with eutectic ledeburite structures, were observed in the intercellular regions. The observation of fracture processes indicated that these primary carbides cleaved first to form microcracks at very low stress levels. These microcracks were easily propagated along the intercellular networks, leading to predominantly cleavage mode of fracture on fracture surfaces. To improve microstructures for use in the HSS rolls, therefore, it is suggested that the cell size must be minimized to achieve the homogeneous distribution of primary carbides
이호인,오규환,나형용,이희춘 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.9
A steady state model on the shape of rod during spray forming has been developed. Steady shape of the rod has been calculated numerically under the assumption of parallel spray density distribution and normal distribution. Time for reaching steady shape of rod during spray forming has been calculated numerically. The calculated steady shape of rod agrees well with the result of transient model, reported previously. The radius of the rod is proportional to square root of melt flow rate, and inverse to square root of substrate withdrawal velocity. Steady shape of the rod can be obtained at following condition : V$lt;a·cosφ, where V, a and φ is substrate withdrawal velocity, spray density constant and spray angle respectively.
고속도강 압연롤의 고온마모특성에 미치는 템퍼링 온도의 영향
이정호,박준욱,이성학,이희춘,오준철 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.2
This study is concerned with the effects of tempering temperature on wear properties and surface roughness of a high speed steel (HSS) roll manufactured by centrifugal casting method. Hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. The test results revealed that the peak-tampered roll specimen showed the best wear resistance because it contained a hard matrix. However, its surface roughness deteriorated as the scratching wear proceeded, thereby leading to increase in friction coefficient. In the over-tempered specimens containing a number of fine spherical carbides in the matrix, the abrasive wear occurred predominantly as fine carbides were fallen off from the worn surface, and thus the surface roughness was enhanced by more homogeneous wear of matrix and carbides. These findings suggested that over-tempering would be more desirable in order to improve wear resistance with consideration of the surface roughness of the HSS roll.