STRUCTURAL STUDIES OF BEARING STEEL UNDERGOING CYCLIC STRESSING
Summary rept. no. 3
SKF INDUSTRIES INC KING OF PRUSSIA PA RESEARCH LAB
Pagination or Media Count:
The microstructural changes seen in bearing steels after prolonged cyclic stressing are reviewed. It is shown that these changes arise from both plastic flow and the diffusion of carbon. The regions of plastic flow appear under the electron transmission microscope, as cell structures and under the light microscope as light etching bands, designated deformation bands. Carbon diffusion is shown by the development of large carbides which grow during cycling. These are designated lenticular carbides. Microstructural alterations are seen as a bulk material phenomenon where the calculated shear stress exceeds an estimated threshold value of 120,000 psi. They also develop locally around stress raisers. It is shown that stress raisers severe enough to cause the growth of deformation bands are also frequently involved in the nucleation of fatigue failures. Sequences of photographs are shown which illustrate various stages of failure initiation at four types of microscopic defects Debris dents, grinding furrows, surface pits of unknown origin, and non-metallic inclusions.
- Properties of Metals and Alloys
- Machinery and Tools