P92 and 15CH2NMFA Steels – A Comparison of Fatigue Characteristics obtained on standard and miniature test specimens

Abstract

In this paper, the results of the fatigue tests of the P92 and 15CH2NMFA steels are presented and discussed. The fatigue S – N curves were obtained by means of both standard and miniature test specimens. The Small Fatigue Test (SFT) specimens were manufactured partially by machining and also by waterjet cutting.The fatigue tests were performed on Amsler 10 HFP 5100 ZWICK//Roell high-frequency pulsator at room temperature and R = 0,1 and R = -1 cycle asymmetries. The results obtained on standard and SFT specimens are compared and in case of P92 steel are also compared the two methods of SFT specimens manufacturing.In case of 15CH2NMFA steel, the results of standard and SFT specimens are in a very good agreement both within the time limit fatigue range and the fatigue limit. After taking the stress concentration of SFT specimens into consideration, the results of traditional fatigue test samples and SFT samples are similar.In case of P92 steel, the leaning branch of S-N curves is much steeper for SFT specimens and the fatigue limits lower than it could be expected after the stress concentration is taken into account. The fatigue limits for equal cycle asymmetry show the same ratio of standard to SFT fatigue limits, for R = 0,1 it is 1,31, for R = 1 it is 1,32. This very good agreement can be used for the evaluation of fatigue behaviour of P92 steel by means of SFT specimens.The comparison of the two ways of SFT samples manufacturing revealed a scatter of fatigue test results, nevertheless the fatigue limits differ by 5 MPa only, so that even the influence of the manufacturing seems to be negligible.