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함종오,남익희,한신호,조병일,박기덕 한국신뢰성학회 2021 한국신뢰성학회 학술대회논문집 Vol.2021 No.6
차량에 사용되는 CAM 샤프트 생산 중 총 출하수량 3,000 EA Lot에서 85 EA 제품이 중주파열처리/연마 후 크랙이 발생하여 그 원인을 분석하였다. 시험편은 단조 후 궨칭한 시험편, CAM 위치 #7에 크랙이 발생한 7번째 제품 및 39번째 제품에서 시험편을 채취하였다. 각각 채취한 시험편은 화학성분, 미세조직, 경화 깊이, 비금속 개재물 및 SEM/EDX 분석을 수행하였다. 경도프로파일 결과 크랙 시험편과 비크랙 시험편간의 약 60 HV 이상의 경도편차가 발생하였다. 미세조직 관찰 결과 중주파열처리 내의 조직은 마르텐사이트로 조직이 나타났으며, 크랙이 발생한 시험편의 경우 표면에서 약0.2 ~ 0.3 mm지점 까지는 템퍼드 마르텐사이트 조직이 나타났다. SEM/EDX 분석 결과 크랙부위에서는 Si성분이 다량 검출되었으나, 비 크랙부위에서 SI성분이 검출되지 않았다. 따라서 CAM의 크랙 발생원인은 중주파열처리 후 연마과정 중 표면이 과열냉각을 반복하여 경도가 상승되었고, 표면의 지속된 과열로인해 표면이 재템퍼링 되어 표면의 경도는 저하되었다. 이로 인해, 표면과 표면직하의 응력차이로 인한 잔류응력이 존재하였으며, 연하된 표면이 충격으로 인하여 크랙이 발생하고 응력이 집중된 곳에서 크랙이 계속적으로 전파된 것으로 판단된다.
다이아몬드 grit(흑연) / Cu-13Sn-12Ti 삽입금속 진공 브레이징 접합체의 젖음성 및 계면반응
함종오,이지환,Ham, Jong-Oh,Lee, Chi-Hwan 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.3
Various alloy system, such as Cu-Sn-Ti, Cu-Ag-Ti, and Ni-B-Cr-based alloy are used for the brazing of diamond grits. However, the problem of the adhesion strength between the diamond grits and the brazed alloy is presented. The adhesion strength between the diamond grits and the melting filler alloy is predicted by the contact angle, thereby, instead of diamond grit, the study on the wettability between the graphite and the brazing alloy has been indirectly executed. In this study, Cu-13Sn-12Ti filler alloy was manufactured, and the contact angles, the shear strengths and the interfacial area between the graphites (diamond grits) and braze matrix were investigated. The contact angle was decreased on increasing holding time and temperature. The results of shear strength of the graphite joints brazed filler alloys were observed that the joints applied Cu-13Sn-12Ti alloy at brazing temperature $940^{\circ}C$ was very sound condition indicating the shear tensile value of 23.8 MPa because of existing the widest carbide(TiC) reaction layers. The micrograph of wettability of the diamond grit brazed filler alloys were observed that the brazement applied Cu-13Sn-12Ti alloy at brazing temperature $990^{\circ}C$ was very sound condition because of existing a few TiC grains in the vicinity of the TiC layers.
발전소용 이중보온용 강관의 홈부식(Grooving Corrosion)에 의한 파손 분석
함종오(Jong-Oh Ham),박기덕(Ki-Duck Park),박성진(Sung-Jin Park),선일식(Il-Sik Sun) 한국신뢰성학회 2015 신뢰성응용연구 Vol.15 No.3
Failure analysis of pre-insulated pipe (SPPS 380, 400A) transporting high temperature water (95~110℃) for a plant was carried out. The damaged area (Ф 5㎜) of pre-insulated pipe was found only on welds. The chemical composition of damaged pipe meets specification of carbon steel pipes for pressure service (KS D 3562). As results of microstructure analysis, crack propagated from outer to inside after pitting corrosion occurred on the outside surface. The non-metallic inclusion existed on the end of crack. And the non-metallic inclusion continuously and linearly formed along with the bond line of welds. Based on SEM-EDS analysis, the nonmetallic inclusions have higher Manganese (Mn) and Oxygen (O) content but sulfur (S) was not detected. As results of water quality analysis, hydrogen ion concentration and minerals like Fe, Mg, Si were in low level. But the content of dissolved oxygen (11.2 ppm) was slightly higher than that of standard. It seems that the cause of damaged pipe is grooving corrosion due to MnO inclusion formed on bond line and corrosion took place nearby welds.
함종오 ( Jong Oh Ham ),김복기 ( Bok Gi Kim ),이선호 ( Sun Ho Lee ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
To measure the sensitivity of the hydrogen embrittlement from plated high strength bolts (SWCH18A, F11T), the bolt was stressed by a corresponding to the amount of tensile strain of 5% and 20%, and then the bolt developed a crack on the surface. The bolt that didn`t have concentrated hydrogen, even though it was stressed by a corresponding the amount of tensile strain of 5% and 20%, no crack developed. However, the bolt that had concentrated hydrogen, developed cracks from the thread crest to the root. It is impossible to measure the hydrogen amount from plated high strength bolts using Hydrogen-Determinator, because of the limitation of the minimum sample size (about 1g as a mass or 5 × 5 × 5 mm3 as a volume). Therefore, the sensitivity of hydrogen embrittlement can be measured by observing the presence of cracks on the surface of plated high strength bolts which are stressed by a corresponding to the amount of tensile strain of 5% and 20%.