1. Morphology of step‐wise S – N curves depending on work‐hardened layer and humidity in a high‐strength steel
- Author
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Masaki Nakajima, H.-N. Ko, Keiro Tokaji, and H. Itoga
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Humidity ,Work hardening ,humanities ,eye diseases ,Stress (mechanics) ,Dew point ,Mechanics of Materials ,Residual stress ,Vickers hardness test ,General Materials Science ,Layer (electronics) ,Surface finishing - Abstract
The present paper describes the effects of work-hardened layer and humidity on the fatigue response of high strength steel, JIS SNCM439 (AISI4340). Tests were conducted in laboratory air and in dry air using cantilever-type rotating bending fatigue testing machines. The dew point of dry air was -60 °C. Specimens with two different surface conditions were prepared, i.e., buff-finished and electro-polished specimens. In the buff-finished specimens, a stepwise S-N curve was seen in both environments, but the transition stress below which subsurface crack initiation occurred shifted to a higher stress level in dry air than in laboratory air. In the electro-polished specimens, stepwise S-N curve was not observed in laboratory air, but seen in dry air. At stress levels where cracks initiated at the surface, the fatigue lives of the electro-polished specimens were shorter than those of the buff-finished specimens. At stress levels where subsurface cracks initiated, the fatigue lives of both specimens were the same, irrespective of surface finishing condition and humidity.
- Published
- 2003
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