Effect of pre-strain on the fatigue behavior of SAPH440 steel

Abstract

The present research envisages the effects of different uniaxial tensile pre-strain levels on the fatigue properties of the SAPH440 steel. The S-N curves of different pre-strain levels (0%, 6%, 12%, 18%) were drawn using different load levels, with a stress ratio R = –1. The test results show that the fatigue strength of the SAPH440 steel increased with an increasement in the uniaxial tensile pre-strain levels. The static tensile test was carried out on different uniaxial tensile and different pre-strain levels specimens. The results show that with an increase in the uniaxial tensile pre-strain levels, the degree of work hardening of the SAPH440 steel and the static strength increased. Additionally, the hardening index and the elongation at break reduced, while the tensile strength and yield strength increased. TEM (Transmission Electron Microscopy) observation of the test samples with different pre-strain levels showed that the dislocation density of different pre-strain levels specimens increased with an increasement in the pre-strain levels. This resulted in an increasement in the fatigue strength of the SAPH440 steel, the degree of work hardening, and the static strength. However, compared with fatigue strength, the increase of dislocation density has a more significant effect on static strength.