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Fe-30 Ni-0.24C합금에서 역변태 오스테나이트의 기계적 성질에 미치는 이전가공도 및 역변태 Cycle수의 영향
김학신,이규복,홍순국 ( H . S . Kim,K . B . Lee,S . K . Hong ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.4
In this study, the ausformed martensite cooled to -196℃ with various deformation degrees in Fe-30%Ni-0.24%C alloy was transformed to reversed austenite at 500℃ by cyclic reverse martensitic transformation. The effects of prior deformation and the number of cyclic reverse transformation on the microstructure and the mechanical properities of reversed anstensite were investigated. Experimental results showed that the strength of reversed austenite was higer than that of original austenite. This is due to higher dislocation density and grain refining. The reversed austenite formed from ausformed martensite was highly strengthened by prior deformation. This strengthening effect of reversed austenite is attributed to higher dislocation density than grain fefining. The yield strength of reversed austenite below 30% prior deformation, but above 30% prior deformation the strength of reversed austenite is lower than that of deformed austenite. This is due to partly disappearance of strain hardening effect at higher deformation degree by reverse transformation. The strength of reversed austenite is increased with the number of cyclic transformation. Especially, it is principally strengthened by the first cyclic transformation and shows higher increase in yield strength than that of ultimate tensile strength.
급냉응고된 분말로부터 CAPA법으로 제조한 NdFeB 영구자석의 자기적 특성
김형태(H. T. Kim),김윤배(Y. B. Kim),전우용(W. Y. Jeon),김학신(H. S. Kim) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.6
Magnetic properties of the isotropic and anisotropic NdFeB magnets obtained by the Current-Applied Pressure-Assisted (CAPA) process from a melt-spun NdFeB powder were investigated using B-H loop analyser. The coercivity of the isotropic magnets is sensitive to the applied pressure in the CA-pressing and increases with increasing the pressure. The remanence of the anisotropic magnet increases with increasing the degree of deformation, and it results in the increase of a maximum energy product. The best magnetic properties of the isotropic and antistropic magnet are Br=8.7 kG, iHc= 16.9 kOe, (BH)max = 16.5 and Br=13.6 kG, iHc =10.9 kOe, (BH)max = 44.2 MGOe, respectively.
통전가압법으로 제조한 이방성 NdFeB 영구자석의 자기특성에 미치는 첨가제의 영향
김형태(H. T. Kim),조성호(S. H. Cho),김윤배(Y. B. Kim),김학신(H. S. Kim) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.3
Rapidly solidified NdFeB powders were mixed with fine powders of pure metal elements before CA-press employed to obtain a fully dense isotropic precursor. Subsequently, the precursor was deformed by CA-deformation to obtain an anisotropic magnet. The CA-deformed anisotropic NdFeB magnets with 0.3 wt.% Zn or Sn exhibited the coercivities about 80 % higher (11.4. and 11.2 kOe, respectively) than that (6.4 kOe) of the additive-free magnet.