Improving the High-Cycle Fatigue Lives of Fe-30Mn-0.9C Twinning-Induced Plasticity Steel Through Pre-straining

Abstract

The tensile properties, high-cycle fatigue properties, and microstructure evolutions during fatigue process of asreceived and pre-strained Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel were investigated. It is found that the fatigue lives of the TWIP steel can be effectively improved through pre-straining, since the deformation twins induced by pre-straining could effectively lead to the improved yield strength and the homogenized deformation. This study may provide possible ways for improving the high-cycle fatigue properties of TWIP steels.In recent years, the advanced high-strength steels have been widely used in automobile industry to satisfy the weight reducing, energy saving, and security principles of new generation cars. [1] Twinning-induced plasticity (TWIP) steels have an excellent combination of high strength and good ductility, so that they are very attractive for automotive industry; therefore, much attention has been paid on the development of TWIP steels. So far, researchers mainly focus on the alloy designing, basic mechanical properties, and the corresponding microstructure evolution during deformation of TWIP steels. [2][3][4][5][6][7][8][9][10] Generally, most automobile parts are under cyclic loading condition during their service, thus, the fatigue resistance is one of the key factors for the practical utilization of TWIP steels. There are many reports about the low-cycle fatigue properties of TWIP steels, [11][12][13][14][15][16] and the pre-strain method was developed to improve their low-cycle fatigue properties. [11,16] As for the high-cycle fatigue, there have been some investigations about the bending fatigue properties of TWIP steels. [17][18][19][20] Hamada et al. [17][18][19] and Karjalainen et al. [20] showed that TWIP steels have quite high bending fatigue strength. However, there are no research findings on the high-cycle fatigue properties of the TWIP steels under axial loading, and the effects of pre-strain on the high-cycle fatigue properties are still not clear so far.In order to improve the fundamental understanding on the axial high-cycle fatigue behaviors of TWIP steels and supplement experimental data, the axial high-cycle fatigue tests of as-received and pre-strained Fe-30Mn-0.9C TWIP steel were performed and the corresponding microstructure evolutions were observed in the current study. The main goal of the current study is to explore further improvement of the high-cycle fatigue properties of TWIP steel via pre-straining.In this study, Fe-30Mn-0.9C (wt pct) TWIP steel was used. The cast ingot was austenized at 1473 K (1200°C) for 4 h, then immediately hot forged into plate with final dimension of 40 9 100 mm 2 at 1223 K to 1473 K (950°C to 1200°C), and finally cooled in air. The plate was annealed at 1323 K (1050°C) for 1 hour and water-quenched, and then dog-bone shaped tensile and fatigue specimens were cut into sectional dimensions of 15 9 3 9 3 and 10 9 5 9 4 mm 3 from the annealed plate, respectively; and the length direction of tensile and fatigue specimen...

A fatigue life prediction method from magnetic pole material to simulation part

“…Considering the dispersion of the fatigue experimental data, the average life is used to fit. The fitted equations are shown as below: where σ a is the stress amplitude; N f is the number of cycles to failure; σf' is fatigue strength coefficient, which is cyclic stress corresponding to N f = 1; b is the fatigue strength exponent, which is the slope of the S–N curve and controlled by the specific damage mechanism (Wang et al., 2015, 2017).…”

“…where a is the stress amplitude; N f is the number of cycles to failure; 0 f is fatigue strength coefficient, which is cyclic stress corresponding to N f ¼ 1; b is the fatigue strength exponent, which is the slope of the S-N curve and controlled by the specific damage mechanism (Wang et al, 2015.…”

Effects of mean strain and tensile pre-strain on torsional fatigue behaviours of duplex stainless steel SAF2205

“…Substantial references have been published focusing on the mechanisms of cold work/pre-straining on the LCF behaviours of ASS, aluminium and magnesium alloy [13][14][15][16][17], among which CL Zhou et al [18,19] investigate the effects of prior tensile plastic deformation on the torsional fatigue properties of a structural steel. As for the DSS, however, the researchers are mainly concerned with the effects of pre-straining/cold-work on the basic mechanical properties, microstructural evolution during monotonic loadings [20][21][22][23][24].…”

Evolution of dislocations and twins in high cycle fatigue of a twinning-induced plasticity steel

“…It was reported that TWIP steels exhibit a fatigue limit (FL) close to the yield stress (YS) [7,8,11,12], which is not superior compared to other steel grades [13,14]. Both prestraining [8,15,16] or grain refinement [12,14] have been proved to be effective strategies to increase the fatigue strength. During cyclic loading, TWIP steels may display cyclic hardening and/or cyclic softening depending on the initial microstructure and applied stress/strain amplitude [8][9][10]16].…”

“…Microstructure evolution during fatigue of TWIP steels has been investigated in only a few studies [8,10,15,16]. The occurrence of deformation twinning under cyclic loading is not yet clarified due to the contradictory experimental evidences reported in the literature.…”