| Title |
A Study on the Cavitation at Grain Boundary under Creep - Fatigue Interaction in Type 304L and Nitrogen alloyed - 304NG Stainless Steels |
| Authors |
홍현욱(Hyun Uk Hong) ; 노병섭(Byung Sup Rho) ; 남수우(Soo Woo Nam) ; 이용득(Yong Deuk Lee) ; 이수찬(Soo Chan Lee) |
| Abstract |
The influence of nitrogen on the low cycle fatigue and creep-fatigue properties for Type 304L stainless steel was investigated with a strain rate of 4×10³/sec at 600℃ in air atmosphere. Under low cycle fatigue test, 304NG(i.e. N-alloyed steel) had shorter fatigue lives than 304L, which can be explained by lower ductility in 304NG due to the addition of nitrogen. When the creep deformation was introduced by imposing tensile hold time(20 min), result was completely reversed compared with the result of continuous fatigue. From the result of microstructural observation and Yoon-Nam`s life prediction model, the major damaging mechanism can be said to be the cavitation at grain boundary for two alloys during creep-fatigue test. And the reason why 304NG has longer creep-fatigue lives than 304L can be explained that 304NG has lower density of carbide that provides beneficial site for the cavity nucleation, which results in lowering cavity nucleation, because 304NG has a smaller content of carbon than 304L, which is compensated with the addition of nitrogen to maintain strength and the nitrogen is believed to retard carbide nucleation at grain boundary by inhibiting the diffusion of Cr to grain boundary. |