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구경희(Kyoung-Hee Gu),이기식(Ki-Sik Lee),강석희(Seok-Hee Kang),강창룡(Chang-Yong Kang),박상현(Sang-Hyun Park),남기우(Ki-Woo Nam) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Ultra-high-strength steel structures are exposed to corrosive environments in service, and there is a risk of hydrogen assisted cracking(HAC) due to stress corrosion cracking and hydrogen embrittlement. In this paper, the HAC threshold stress intensity factor (KIHAC) and fatigue life of ultra-high-strength steel were evaluated by applying stress in a corrosive environment to prevent structures fracture. On the surface of the crack, grain boundaries were embrittled by corrosion, and the grains were clearly observed, and cracks in the surface direction propagated slightly, but cracks in the depth direction did not. Therefore, the HAC threshold stress intensity factor of the depth was determined as 1.96MPa·m<SUP>0.5</SUP>. The static fatigue limit of ultra-high strength steel (SKD11:HV670) was determined as 400MPa.
레이저 및 초음파 피닝된 STS316L의 공식 부식에 관한 연구
구경희(Kyoung-Hee Gu),윤서현(Seo-Hyun Yun),남기우(Ki-Woo Nam) 대한기계학회 2022 大韓機械學會論文集A Vol.46 No.4
본 연구에서는 모재시험편, 초음파 피닝시험편, 레이저 피닝시험편을 FeCl3+HCl 용액에 침지하여 내공식성을 평가하였다. 초음파 피닝시험편은 초음파 해머핀의 충격에 의한 소성변형으로 표면 조직 입도가 작고, 깊이가 깊어질수록 모재의 조직 입도였다. 레이저 피닝시험편은 레이저 충격파에 의해 소성변형되었으나, 조직 입도의 크기 변화는 없었다. 모재시험편의 평균 비커스 경도는 약 153 HV, 초음파 피닝 및 레이저 피닝시험편의 표면 경도는 각각 약 290 및 250 HV였다. 세 가지 유형의 시험편에서 공식 부식이 관찰되었다. 레이저 피닝 및 초음파 피닝시험편은 모재보다 더 많은 공식 부식이 관찰되었다. The pitting resistance of as-received and laser and ultrasonically peened STS316L specimens was evaluated by immersion in FeCl₃ + HCl solution. The ultrasonically peened specimen had a smaller grain size owing to the plastic deformation caused by shocking induced via an ultrasonic hammer pin. However, the as-received grain size was observed at larger depths. The laser peening specimen was plastically deformed by the laser shock wave; however, no change in the grain size was observed. The average Vickers hardness of the as-received specimen was approximately 153 HV. The hardness values of the ultrasonically and laser peened specimens were approximately 290 and 250 HV, respectively. Pitting corrosion was observed for the three types of specimens. Notably, the laser and ultrasonically peened specimens exhibited a larger amount of pitting than that of the as-received specimen.