| Title |
A Study on the Behaviour of Stress - Corrosion Crack Initiation and Propagation of Type 304 Stainless Steel in Aqueous 35 wt % MgCl2 solution by electrical Potential Method |
| Authors |
최종교(Jong Kyo Choi); 변수일(Su Il Pyun); 이우봉(Woo Bong Rhee) |
| Abstract |
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. |