Abstract
The effects of vacuum environment on fatigue fracture surfaces of high strength steel were investigated quantitatively. Uni-axial fatigue tests were carried out on SNCM439 in vacuum and air environments. 3D-fractography was then performed using 3D-SEM to determine the fracture surface roughness and to clarify the effects of environments on fracture surface. These analyses targeted on three typical fracture surfaces as follows: (a)surface fracture in air environment, (b)surface fracture in vacuum environment and (c)subsurface fracture. As a result, fracture surface roughness of surface fracture in air environment was large compared to that in vacuum environment. On the other hand, fracture surface roughness of subsurface fracture agreed quite well with that of surface fracture in vacuum environment. These results show that the effects of vacuum environment and environment inside subsurface crack on fatigue crack propagation are exactly similar. Therefore the behavior of subsurface crack propagation can probably be estimated from surface crack propagation in vacuum environment.
