Abstract
The effects of carbide particle sizes and amounts of undissolved carbides in martensite matrix on the fatigue life and other properties have been investigated by using the SUJ 2 kind (JIS) of bearing steel having coarse particle carbides and fine particle ones, respectively, and low chromium steels with different carbon contents.
The specimens were previously quenched from various austenitizing temperatures in order that the carbon content in the martensite matrix was made constant, and accordingly the amounts of undissolved carbide in the low chromium steels were changed variously.
The results obtained are summarized as follows:
(1) The bearing steel with fine particle carbides are superior in fatigue life, hardness and compressive breaking strength to that with coarse partile carbides.
(2) In the neighbourhood of the fatigue flaking surface caused by the fatigue life test, cracks do not take place in carbides themselves but proceed along the boundary between carbide and matrix.
(3) When the carbon content in the martensite matrix is constant, the hardness rises slightly with the increase in undissolved carbides, but the fatigue life shortens and the compressive breaking strength decreases.
(4) The presence of some amount of the undissolved carbide is desirable in view of the wear resistance and the control of heat treatment.
