Fatigue properties of high-strength steel in diesel oil

AbstractThis paper describes the fatigue properties of chromium-molybdenum steel in air and diesel oil. 4-point bending fatigue tests were conducted at a stress ratio of R=0.05. The corrosion mark was not confirmed on the specimens tested in diesel oil, and the fatigue strength at Nf < 3×104 improved and that at Nf > 3×104 declined compared to in air. The fatigue crack initiation life accounted for about 90 % of the fatigue life Nf. The results of the elemental analysis of the specimen surface tested in diesel oil which were broken at Nf > 3×104, O, Si, and C had been concentrated. The reduction of fatigue strength at Nf > 3×104 is considered to be caused by some influence of deterioration of the diesel oil winhich progress with the fatigue test. On the other hand, the fatigue test at Nf < 3×104 is usually finished within one day, so diesel oil does not have the time to deteriorate. Then, a few fatigue tests were conducted in the deteriorated diesel oil at a relatively high stress range, in order to break the specimen at Nf < 3×104. As a result, fatigue life tends to shorten. Therefore, it was found that the diesel oil deterioration should be considered as one of the important factors to explain the decrease of fatigue strength