Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengths

Abstract

Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengthes were experimentally studied by rotating bending tests, to investigate the effects of the tensile strength obtained by different heat treatment processes on very high cycle fatigue failure mechanisms. The material with higher tensile strength of 1 710 MPa exhibited typical gigacycle fatigue failure characteristics, whereas one with lower tensile strength of 1 010 MPa showed only traditional fatigue limit during the tests and no gigacycle failure could be found even when the specimen ran up to more than 10 8 cycles. Metallographic and fractographic analysis were carried out by an optical microscope (OM) and scanning electron microscope (SEM). It showed two different crack initiation mechanisms that for the specimen with lower tensile strength the crack prefers surface initiation and for that with higher strength the crack initiates from subsurface inclusions revealed by a fish-eye like microstructure.

A review about the effects of structural and operational factors on the gigacycle fatigue of steels

“…It was pointed out by different studies that in the case of low strength steels (maximum tensile strength ≤1100 MPa), fatigue crack initiation mainly occurs at the specimen surface, and the S‐N curves present a horizontal asymptote . The difference between the fatigue strengths at 10 6 and 10 9 cycles is less than 50 MPa, that is within the typical scatter band of the experimental fatigue data.…”

“…For low strength steels, in VHCF regime, cracks would not initiate at inclusions but at the surface. 6,10,35,36 Further researches show that crack initiation in VHCF regime depends on the loading type. 15 For instance, under cyclic axial loading, the VDSiCr spring steel displays crack initiation at internal inclusion.…”

Experimental study on very high cycle fatigue of martensitic steel of 2Cr13 under corrosive environment

“…It has been reported that the fatigue limit is highly dependent on material strengths. Cracks tend to originate from surfaces for low strength alloys ( σ b < 1200 MPa, is σ b the ultimate strength) with the fatigue limit σ f corresponding to 10 7 cycles in air being estimated by σ f = 0.53 σ b . The fatigue limit of 530 MPa of 2Cr13 just follows the relation.…”

“…Material with same chemical compositions but different microstructures obtained by heat treatment exhibits different responses at very high cycle fatigue, such as AISI4340 in Duan's work. 23 The one with lower strength was observed to have a fatigue limit over 10 8 -10 9 cycles while the other with higher strength showed a continuous decrease over 10 4 -10 9 cycles, indicating no fatigue limit exists. Same observation was reported for bearing steel GCr15 with no fatigue limit in higher strength specimens.…”

A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

“…Very high cycle fatigue (VHCF) behavior of metallic materials has become an important research topic [1][2][3][4][5][6][7][8][9][10][11] due to the fact that modern industries often require metallic components B Youshi Hong hongys@imech.ac.cn 1 The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China to endure exceeding 10 8 loading cycles of safe performance in service. For example, train axles rotate about 10 9 cycles when a high speed train runs at 2.4 × 10 6 km.…”