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침질탄화처리한 고탄소 크롬 베어링강의 회전접촉 피로거동에 미치는 잔류오스테나이트의 영향
최병영,김동건,김창석,진재관 ( Byung Young Choi,Dong Keon Kim,Chang Seok Kim,Jai Koan Jin ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.3
Effect of retained austenite on rolling contact fatigue of nitrocarburized high-carbon chromium bearing steel has been investigated to develop surface-hardened bearing steel with imprved resistance to rolling contact fatigue. Fatigue tests were conducted in elesto-hydrodynamic lubricating conditions at a shaft speed of 5,000rpm, under max. hertzian stress of 492㎏/㎟. Volume fraction of retained austenite in austenitic nitrocarburized STB2 steel was controlled by tempering at various temperature, 200∼250℃. It was observed using TEM that decomposition of retained austenite during tempering at 250℃ was the highest in quantity, resulted in formation of lower bainite. Rolling contact fatigue life of the specimens with lower bainite, formed by decomposition of retained austenite, was improved in comparison with there of specimens with more amount of retained austenite.
온내장좌우바뀜증(situs inversus totalis) 1예 보고
최병영(Byoung Young Choi),윤상욱(Sang Wook Yoon),강호석(Ho Suck Kang),조병필(Byung Pil Cho),양영철(Young Chul Yang) 대한체질인류학회 2001 대한체질인류학회지 Vol.14 No.4
허리통증 및 다리부기로 인하여 정형외과 및 흉부외과 진료를 받은 55세 여성의 가슴 및 배 방사선 사진과 심전도에서 심장 및 허파의 좌우가 바뀐 모습을 우연히 발견하였다. 추가로 허파에 대한 허파관류주사 검사, 배속 장기에 대한 방사선사진 촬영, 도플러 초음파 검사, 자기공명사진 촬영을 시행하여 다른 기형과 동반 질환이 없이 가슴 및 배속 장기들의 위치가 좌우가 바뀌어 있는 오른심장증 동반 온내장좌우바뀜증을 진단하였다.
심리스 튜브 제조용 피어싱 플러그 공구강과 SA210C강의 고온 미끄럼 마모에 미치는 예비산화의 영향
최병영(Byung-Young Choi),구윤식(Yoon-Sik Gu) 한국표면공학회 2013 한국표면공학회지 Vol.46 No.6
Effects of preoxidation on high temperature wear of piercing plug tool steel sliding against SA210C steel used for production of seamless tube have been studied using a pin-on-disc CETR tribometer, under applied normal load of 20 N at 900oC in air. It was found in the preoxidized pin specimens of piercing plug tool steel that the coefficient of friction decreased to about 0.4 at an initial stage followed by showing nearly constant value of about 0.4 during high temperature wear testing. On the other hand, it was also found in the pin specimens without preoxidation that the coefficient of friction increased and fluctuated, ranging from about 0.3 to 0.6 during the tests until the running period of about 800 sec. The compact and continuous Fe-oxide layer was formed on the contact surface of the preoxidized pin specimens after high temperature wear testing followed by penetrating along the grain boundaries of coarse ferrite in the decarburized region beneath the oxide layer due to the lower hardness of the region.
열간단조 후 고주파 유도경화에 의해 제조된 휠 베어링 유니트용 0.52%C강의 특성과 변태거동
최병영 ( Byung Young Choi ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.12
We fabricated flanged outer races for wheel bearing units using 0.52%C clean steels, and then characterized and studied the transformation behavior. The outer races produced by hot forging and high frequency induction hardening in this study were analyzed through microstructural characterization using OM, SEM, TEM, and X-ray diffractometer and their microhardness depth profiles of the raceway contacted by balls were measured using MVH tester. The surface hardened layers with a uniform hardness profile in the raceway consisting of very fine martensite with sub-micron sized retained austenite could be formed for very short time during high frequency induction hardening after hot forging. The very fine martensite may be transformed on rapid cooling, from the inhomogeneous austenite nucleated on rapid heating in small particles of pearlitic cementite fragmentated by hot forging. On the other hand the sub-micron sized retained austenite may be chemically stabilized due to their extremely small size, from the small austenite nucleated at the grain boundaries.
화력발전용 심리스 튜브 제조에 쓰이는 피어싱 플러그 공구강의 미끄럼 접촉 고온마모거동
최병영 ( Byung Young Choi ),구윤식 ( Yoon Sik Gu ),( Qiang Zhu ),( Hongtao Zhu ),( Kiet Tieu ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.12
Sliding wear behaviors of piercing plug tool steels were investigated at 900 ℃ against low Cr ferritic steels containing 2 %Cr and 9 %Cr using a pin-on-disc CETR tribometer under condition of applied normal load of 20N in air. Formation of glaze layers consisting of porous Fe-oxides wear debris with rapid growth on worn surface of piercing plug tool and smooth surface of steels containing 2 % Cr resulted in decreased friction coefficient at an initial period followed by exhibited constant value of about 0.3 during the elevated temperature wear tests. It was found on the cross-section underneath the worn surface of the tool steels against the steels containing 2 %Cr that coarse ferrite with equiaxed grains by phase transformation and dynamic recrystallization was formed showing the decrease in hardness. On the other hand, formation of the glaze layers consisting of compact Cr-rich Fe-oxide wear debris on the worn surface of the tool steels at slow rates of materials transfer from the steels containing 9 %Cr resulted in the fluctuated friction coefficient ranging from about 1.0~1.1 to 0.4 followed by exhibited almost constant value of 0.2~0.3. It was also found on cross-section underneath worn surface of tool steels against the steels containing 9 %Cr that severely deformed microstructures by cyclic applied loading was formed below compact and continuous oxide layers. The results showed that the elevated temperature sliding wear of the piercing plug tool steels was dominated by oxidation, materials transfer and subsurface degradation such as dynamic recrystallization softening or severe deformation.