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전위차법 (電位差法) 에 의한 35wt% MgCl2 수용액중에서의 304 계 스테인레스강의 응력부식균열의 생성 및 전파거동에 관한 연구
변수일,최종교,이우봉 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.11
The behaviour of stress corrosion(SC) crack initiation and propagation of Type 304 stainless steel in 35 wt% MgCl₂ has been studied as a function of temperature and applied stress at the applied electrochemical potential of-106mV_(SHE) by using electrical potential method. In the present study. the electrical potential method allows to differentiate the incubation period from the propagation period for SC crack. The optical microscopy revealed that the pit is a primary source of SC crack initiation under the applied stress lower than yield strength. SC crack initiation stage is composed of three steps, 1) pit initiation, 2) pit growth to critical size, and 3) crack propagation in the lateral and the through-thickness directions. The portion if anodic dissolution trenches to pits as sites of SC crack initiation increased with applied stress higher than yield strength. The activation energy of the electrochemical reaction contribution to the SC crack initiation and the energy of the stress contribution to the SC crack initiation under 212MPa are evaluated to be 30.5 kJ/㏖ and 14.0 kJ/㏖ respectively. The fractography of SC crack propagation showed the transition of fracture mode from fully transgranular mode to the mixed zone with intergranular mode in the interior of the specimen. The intergranular portion is nearly independent of temperature, however it increases with the applied stress.
압흔 주위 변형 양상 분석을 통한 구조용 강의 Luders strain 평가
최열,최종교,주웅용,권동일,안정훈 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
The continuous indentation test was used to evaluate Lu¨ders strain of various steels such as ultra-fine grained steels and AISI 1020 steels. Inhomogeneous pile-up deformation in the indentation test could be related to Lu¨ders strain in tensile test. The pile-up deformation could be characterized as a localized flow phenomena. We analyzed the pile-up area as the parameter of Lu¨ders strain, and described the pile-up amount more quantitatively by considering the relation between plastic-zone size and pile-up radius. Finally, we derived the master curve for some steels, which included the ratio of elastic modulus to hardness as plastic-zone size. For various steels in this study, the values of Lu¨ders strain obtained from the master curve are consistent with those measured from the tensile test.