Effect of Ultrasonic Shot Peening on High Cycle Fatigue Behavior in Type 304 Stainless Steel at Elevated Temperature

Abstract

Ultrasonic shot peening was applied to type 304 austenitic stainless steel and four-point rotating bending fatigue tests were performed at room temperature (R.T.) and 573K up to 10 8 cycles. The fatigue strengths at 573K were much lower than those at R.T. irrelevant to shot peening process. The shot-peened specimens exhibited higher fatigue strengths than untreated ones at both R.T. and 573K, indicating that shot peening had beneficial effect even at the elevated temperature of 573K. Clear fatigue limits were recognized in both shot-peened and untreated specimens at R.T. On the contrary, at 573K, fatigue failure occurred at high cycle fatigue (HCF) region (N > 2×10 6 cycles) in the shot-peened specimens, while not in the untreated ones. Fatigue crack initiated at the specimen surface due to cyclic slip deformation in the untreated specimens at R.T. and 573K and in the shot-peened ones at R.T. However the shot-peened specimens showed sub-surface crack initiation with a typical fish-eye pattern in the HCF failures at 573K. Inclusions were not recognized at the center of the fish-eye. The transition of crack initiation mechanism at 573K of shot-peened specimens could be attributed to the combined effects of the surface hardening by shot peening and the softening of material at the elevated temperature.

On the Influence of Ultrasonic Surface Mechanical Attrition Treatment (SMAT) on the Fatigue Behavior of the 304L Austenitic Stainless Steel

“…Consistently with the results from the literature [13,15,23], the use of SMAT was found to be an efficient way to increase the fatigue resistance of the 304L stainless steel. Enhancements of 28% and 17% were observed in rotating-bending and tension-compression, respectively.…”

“…Indeed, the surface strain-hardening generated by SMAT pushed the onset of the plasticity at the surface to a higher stress range and delayed the generation of significant self-heating. Regarding the thermal exposure during the tests, the work of Kakuichi et al [23] showed that the exposure to 300 • C during rotating-bending fatigue at high and low stress amplitudes does not relax the surface residual stresses of a 304L sample ultrasonic shot-peened at room temperature. This would mean that the observed self-heating mainly behaves as a mechanical property reducer and that the key factor governing the residual stress relaxation is the introduction of supplementary plastic strains.…”

“…The effect of SMAT treatments on the fatigue behavior of the 304L was investigated at room temperature (RT), as well as elevated temperature, by Kakiuchi et al [23]; the shot-peened specimens exhibited higher fatigue strengths than the untreated ones at both RT and 300 • C. By decreasing or removing the surface topology induced by severe shot peening through a repeening or grinding process, the fatigue life of a shot peened low-alloyed steel can be further improved as shown in the work of Bagherifard et al [20].…”

On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: Effect of load ratio and associated residual stress modification

“…For the RTC conditions, the maximum applied loads are just a few tens of MPa above the material elastic limit, causing only moderate and localized plastic strain. As confirmed by the surface analysis in stainless steel treated by SMAT and then loaded at R = -1 under rotating bending [72], it should be noticed that their fatigue tests were conducted at a temperature of 300 °C. It is possible that this elevated temperature can facilitate the use of these particles as stress raisers because it enhances the differences in mechanical properties between the austenitic matrix and the hard inclusion.…”

Modeling of the fatigue behavior of functionally graded materials: Study of the residual stresses induced by surface severe plastic deformation

“…[1][2][3][4][5][6][7][8] Among them, austenitic stainless steels have been widely studied. [9][10][11][12][13][14][15][16][17] However, conflicting results concerning the efficiency of these surface treatments to improve the fatigue life were observed and reported when specific treatment conditions were employed, [18][19][20][21] thus showing that the treatment parameters are sometimes critical and need to be wisely chosen in order to provide the desired enhancement in fatigue properties. Due to the importance of fatigue crack initiation in the fatigue life, such reduction of the fatigue limit is often attributed to the surface roughness and characteristic surface damage induced by the treatment.…”