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Vol.38, No.6, 857 ~ 863, 2000

Title

Pesearch Paper / Materials Processing : A study on the Fabrication of Ni - Cr / Steel Graded Boundary Material by Electron Beam

김재현Jae Hyun Kim,김도훈To Hoon Kim

Abstract

For a development purpose of thick metal/metal graded-boundary materials, a preliminary research on the fabrication of graded-boundary Ni-Cr/steel material was carried out by an electron beam and its mechanical properties and thermal characteristics were investigated. In order to produce a compositionally graded boundary region between substrate steel and added Ni-Cr alloy, a series of surface alloying treatments was performed with an electron beam. Ni-Cr sheet was placed on a low carbon steel plate(0.18%C), and then an electron beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer another Ni-Cr sheet was placed and then the electron beam was irradiated again to produce second surface-alloyed layer. Sequential repetitions of electron beam surface alloying treatment 4 times resulted in a graded-boundary region with the thickness of about 2.2 ㎜. Simultaneous concentration gradients of different kinds of alloying elements(Ni and Cr) showed from 28%Ni, 29%Cr and 43%Fe on surface region to 0%Ni 0%Cr and 99%Fe in substrate region. A thermal conductivity gradient resulted in graded-region and its value changed from 0.028 ㎈/㎝ s℃ in surface region to 0.1 ㎈/㎝ s℃ in substrate region. Microstructural observation showed that any visible root porosities and solidification shrinkage cracks were not formed in graded region between alloyed layers and substrate steel during rapid cooling.

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