Improvement of the Fatigue Strength of Stainless Steel SUS316L by a Cavitating Jet with an Associated Water Jet in Water

Abstract

Cavitation impact induced by a cavitating jet can be utilized to improve fatigue strength in the same way as shot peening. The peening method using cavitation impact is known as "cavitation shotless peening", as shot are not required. For practical purposes, enhancement of the cavitation impact is required in order to get a better peening effect and to shorten the processing time. In the present paper, intensification of the cavitation impact was successfully realized by injecting a low-speed water jet around a cavitating jet in water, and an improvement in the fatigue strength of stainless steel was demonstrated by subjecting treated materials to a fatigue test. The fatigue strength of stainless steel was improved by about 28 % by cavitation shotless peening compared with a non-peened specimen. In order to clarify the mechanism for surface enhancement by cavitation shotless peening, the residual stress on the surface was measured using an X-ray diffraction method. It was shown that cavitation shotless peening using a cavitating jet with an associated low-speed water jet in water introduced compressive residual stress on the surface of the steel. Interestingly, it was also found that the full width at half maximum of the X-ray diffraction profile from the surface decreased, even though compressive residual stress of about 500 MPa had been introduced by the cavitation shotless peening.

Optimum Injection Pressure of a Cavitating Jet for Introducing Compressive Residual Stress into Stainless Steel

“…The peening method is called "cavitation shotless peening", as shot are not required, or simply called "cavitation peening". The introduction of compressive residual stress into various steels using a cavitating jet has been reported (1)(2) (7)(8)(9)(10)(11)(12)(13)(14) . The improvement in the fatigue strength of metallic materials treated by a cavitating jet has also been reported (15)(16)(17)(18)(19)(20) .…”

Cavitation shotless peening effects on fatigue crack growth behaviour under bending loads

“…An innovative approach to surface modification was presented, which utilised a cavitation jet process, notably controlled by various parameters, including nozzle size and upstream pressure [9] [10]. The process centres on creating a compressive residual stress field in the treated surface; this is then recognised as cavitation shotless peening.…”

“…An innovative approach to surface modification was presented, which utilised a cavitation jet process, notably controlled by various parameters, including nozzle size and upstream pressure. 9,10 The process centres on creating a compressive residual stress field in the treated surface; this is then recognised as cavitation shotless peening. A rationale underpinning the process being referred to as shotless is owing to the fact that peening is carried out by the cavitating jet without any shots required (see Figure 1A).…”

“…The effects of cavitation shotless peening was examined with various materials, including Titanium [7], Carbonised steel [8], Stainless steel [9] and Aluminium [10], with the researchers establishing that a material's fatigue strength can be reinforced through shotless peening [11] [7]. In addition, it was also determined that micro-strains could also be relieved as a result of cavitation shotless peening, notably through introducing macro-strain in the case of a polycrystalline metal surface [12].…”

“…5 Moreover, the influences of initial residual stresses in regards scratch/dent-type surface anomalies were examined by Doremus et al in specific consideration to fatigue crack initiation and propagation in the case of Direct Aged (DA) Inconel 718 alloy, with the study establishing that the residual stress fields are of notable impact on crack shape evolution, which subsequently results in the creation of ear-shaped cracks. 6 The effects of cavitation shotless peening were examined with various materials, including titanium, 7 carbonised steel, 8 stainless steel, 9 and aluminium, 10 with the researchers establishing that a material's fatigue strength can be reinforced through shotless peening. 7,11 In addition, it was also determined that micro-strains could also be relieved as a result of cavitation shotless peening, notably through introducing macro-strain in the case of a polycrystalline metal surface.…”