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M3/2계 고속도 공구강 분말의 소결분위기와 탄소첨가가 소결밀도에 미치는 영향
안진환,허종서,주동원,정은,성장현,Ahn, Jin-Hwan,Heo, Jong-Seo,Joo, Dong-Won,Jung, Eun,Sung, Jang-Hyun 한국분말야금학회 1998 한국분말재료학회지 (KPMI) Vol.5 No.4
For the purpose of investigating the effect of sintering atmosphere and carbon addition on sintered density and microstructural characteristics, the M3/2 grade high speed steel powders with the addition of carbon are sintered in vacuum and $20%H_2/79%N_2/l%CH_4$ gas atmosphere. With the addition of 0 wt%C, 0.45wt%C and 1.15 wt%C the optimum sintering temperatures decrease down to $1260^{\circ}C$, $1210^{\circ}C$ and $1150^{\circ}C$ respectively for the vacuum sintered specimen, and also decrease down to $1130^{\circ}C$, $1120^{\circ}C$ and $1115^{\circ}C$ for the gas sintered specimen. The threshold temperatures for full densification decrease steeply with increasing carbon content of the sintered specimen, while this temperatures are slowly decreased at high carbon content. The vacuum sintered specimen shows the primary carbides of MC and $M_6C$ type at the optimum sintering temperature, and eutectic carbides of $M_2C$ and Fe-Cr type are produced in the oversintered specimen. The gas sintered specimen exhibits M6C and Fe-Cr type primary carbides at the optimum sintering temperature. The eutectic carbides of $M_6C$ and Fe-Cr type and MX type carbonitride are shown for the oversintered specimen in the gas atmosphere. The hardness of gas sintered specimen shows high value of 830-860 Hv due to the increment of carbide precipitation.
강창용,성장현,주동원,허종서 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3
After nitrogen permeation heat treating the Al and Cu alloyed 13wt%Cr stainless steels in the nitrogen gas pressure of 1㎏/㎟ mainly at 1200℃, the surface nitrogen content,, phase changes, hardness variations and corrosion properties were investigated. The nitrogen dissolution and exhaustion of Al owing to the nitride precipitation cause to $quot;change the microstructure of the nitrogen permeated surface layer from α+γ(martensite) phase to γ single phase. The surface austenite phase contains round type aluminum nitrides and needle type carbonitrides. The nitrogen content of the surface layer increases after showing low content at the outmost surface due to the hindrance effect of carbon diffusing from interiors to surface. The Al and Cu move from γ phase to precipitate and Cr moves from precipitate to γ phase during nitrogen permeation heat treatment. At the nitrogen permeation temperature, the specimen representing γ single phase shows gradual decrease in the hardness with increasing depth below surface. while the specimen representing α+γ phase shows abrupt decrease in hardness due to the obvious nitrogen permeation layer boundary. The corrosion resistance of nitrogen permeated surface layer increases and remarkablely decreases in the 5%HCl solution and the 5%H₂SO₄ solution, respectively. compared to that of matrix.