Fatigue Strength Of Stainless Steel Research Articles

Environmental effect on fatigue strength of stainless steel in PWR primary water: Relation between fatigue life in air and environment

AbstractThe fatigue life of Type 316 stainless steel in the pressurized water reactor (PWR) water environment and its dependency on that in air were investigated. Specimens from two heats of the material were prepared for fatigue tests, and additionally, previous test findings obtained using another heat were applied. The fatigue test results obtained for various strain ranges and strain rates revealed that the fatigue life in the water environment Nf(env) did not depend on that in air Nf(air) when the strain rate was 0.4%/s. The variation in the ratio of Nf(env) to Nf(air) was larger when Nf(air) obtained for each heat of the material was used than that when a general Nf(air) was used. The changes in the penalty factor Fen with applied strain range and strain rate could be predicted by assuming Nf(env) depended not on strain rate but on rise time.

Effect of Microshot Peening on Fatigue Strength of Austenite Stainless Steel

The effects of the peening conditions on the surface characteristics and fatigue strength of stainless steel were investigated by microshot peening (MSP). In recent years, MSP technology has attracted attention. The use of MSP technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. However, the effect of MSP technology on stainless steel has not been much studied. In the present study, an air-type machine was used. The media used was high-carbon cast steel (490 HV) and Fe-Cr-B alloy (1130 HV), with an average diameter of 0.1 mm. The peening time was in the range of 0 - 100 s. Four types of stainless steels, SUS304, SUS304L, SUS316, and SUS316L, were tested. The workpieces were annealed at 1100 K for 1.2 ks in air. In the measurement of fatigue strength, the workpieces were machined in hour-glass shape. As the results, surface roughness of the workpieces treated by MSP was small. Work hardening was evident to the depth of approximately 0.2 mm from the surface. This depth was about twice the diameter of shot media. However, the effect of the peening time on the hardness distribution was not large. The compressive residual stress was added in the surface vicinity. It is assumed that the fatigue limit had increased because the work hardened layer was formed near the workpiece surface.

Effect of compressive residual stress introduced by cavitation peening and shot peening on the improvement of fatigue strength of stainless steel

One of the traditional methods used to improve the fatigue properties of metallic materials is shot peening. More recently, cavitation peening, in which the surface is treated using cavitation impact, has been developed, and the improvements this makes to the fatigue life and the strength of metallic materials have been reported. In order to clarify the difference between these two methods, stainless steel SUS316 L samples were treated by shot peening and cavitation peening, and the fatigue properties of the samples were evaluated utilizing a displacement controlled plane bending fatigue test. The residual stress and hardness before and after the fatigue test were measured, and the surface roughness of each specimen was also measured. It was concluded that the fatigue life of shot peened specimens at bending stress σ a > 450 MPa was longer than that of cavitation peened specimens; however, the fatigue strength of the cavitation peened specimens was slightly larger than that of the shot peened specimens. The compressive residual stress introduced by both peening methods decreased during the fatigue test. The reduction in the compressive residual stress in the shot peened specimens was greater than in the cavitation peened specimens, and after the fatigue test, the compressive residual stress in the shot peened specimens was greater than that in the cavitation peened specimens. It was found that the fatigue strength corresponded well with the yield stress estimated from the Vickers hardness corrected by the residual stress obtained after the fatigue test.

Effect of small defects on the fatigue strength of martensitic stainless steels

The defect tolerance of three different martensitic stainless steels (17-4PH, X20Cr13 and AISI403) under cyclic loading was investigated. Fatigue tests were performed with specimens containing diverse artificial defects (corrosion pits, single and multiple drilled holes, sharp circumferential notches and pre-cracked holes). The measured cyclic strengths are compared to predictions based on the area parameter model proposed by Murakami and Endo. This model is well applicable to small sharp defects if the threshold condition for crack propagation determines the fatigue limit. The transition size from small to large defects, areatrans, – above which the threshold stress intensity factor range, ΔKth, becomes a constant value – is between 80 and 166 µm for the investigated steels. For larger defects, the threshold for long cracks, ΔKth,lc, serves well to predict the fatigue strength under fully reversed loading, i.e. at a load ratio of R = −1. Comprehensive tests were performed to study the influence of mean stress, and threshold conditions were determined that enable to predict the fatigue limit at different load ratios.A simple equation is introduced to estimate the critical defect size, areacritical, which is the size above which defects become detrimental under cyclic loading. It has been found that areacritical increases with increasing load ratio while areatrans is independent of R. Furthermore, higher values of the threshold stress intensity factor range were determined for large defects (with sizes larger than areatrans) compared to long cracks if the load ratio is higher than R = −1. This could be explained by the plane stress condition at the material surface which is prevalent for surface defects, while the condition for long cracks can be assumed as plane strain.It is further demonstrated that the effect of small defects on the fatigue strength of stainless steels is highly sensitive to the notch root radius, ρ. Small holes with diameters of 100 µm (ρ = 50 µm) or larger are less detrimental for the fatigue strength than defects with high stress concentrations – such as corrosion pits.

Comparison between the improvements made to the fatigue strength of stainless steel by cavitation peening, water jet peening, shot peening and laser peening

In order to make a clear comparison between the various peening methods used to improve the fatigue strength of stainless steel 316L, the fatigue strength of specimens treated by cavitation peening, water jet peening, laser peening and shot peening were examined using a plate bending fatigue test. Both cavitation peening and water jet peening were carried out using a submerged water jet system, and these are distinguished by the distance from the nozzle to the specimen. A submerged laser peening system was used for laser peening. The impact with the surface due to laser cavitation was greater than that due to laser ablation. For each peening method, the optimum coverage was examined by measuring the fatigue life at constant bending stress. Then, the fatigue strength of specimens treated with the optimum coverage was examined. The fatigue strength of the non-peened specimen was 279 MPa, whereas it was 348 MPa for cavitation peening, 325 MPa for shot peening, 303 MPa for laser peening and 296 MPa for water jet peening. The fatigue strength of each peening method was affected by the surface roughness and work hardening.

Screw head plugs increase the fatigue strength of stainless steel, but not of titanium, locking plates.

ObjectivesScrew plugs have been reported to increase the fatigue strength of stainless steel locking plates. The objective of this study was to examine and compare this effect between stainless steel and titanium locking plates.MethodsCustom-designed locking plates with identical structures were fabricated from stainless steel and a titanium alloy. Three types of plates were compared: type I unplugged plates; type II plugged plates with a 4 Nm torque; and type III plugged plates with a 12 Nm torque. The stiffness, yield strength, and fatigue strength of the plates were investigated through a four-point bending test. Failure analyses were performed subsequently.ResultsFor stainless steel, type II and type III plates had significantly higher fatigue strength than type I plates. For titanium, there were no significant differences between the fatigue strengths of the three types of plates. Failure analyses showed local plastic deformations at the threads of screw plugs in type II and type III stainless steel plates but not in titanium plates.ConclusionThe screw plugs could increase the fatigue strength of stainless steel plates but not of titanium plates. Therefore, leaving screw holes open around fracture sites is recommended in titanium plates.Cite this article: L-W. Hung, C-K. Chao, J-R. Huang, J. Lin. Screw head plugs increase the fatigue strength of stainless steel, but not of titanium, locking plates. Bone Joint Res 2018;7:629–635. DOI: 10.1302/2046-3758.712.BJR-2018-0083.R1.

Enhancement of Fatigue Strength of Stainless Steel by Submerged Laser Peening Enhancing Bubble Collapse Impact

Enhancement of Fatigue Strength of Stainless Steel by Submerged Laser Peening Enhancing Bubble Collapse Impact

The influence of metallurgical factors on corrosion fatigue strength of stainless steels

Corrosion fatigue strength of stainless steels is controlled by tangled interaction among environmental, mechanical and metallurgical factors. In order to estimate corrosion fatigue strength it is indispensable to understand the role of an each influencing factor. The aim of this paper is to present briefly surveyed results on metallurgical factors on corrosion fatigue strength of stainless steels such as austenitic, martensitic and duplex stainless steels mainly based upon author’s experimental results. The targeted dominant metallurgical factors focussed upon are chemical compositions, heat treatment, manufacturing process and microstructures.The emphasis is placed upon effect of Molybdenum content on corrosion fatigue strength of austenitic stainless steels in 3%NaCl aqueous solution, tempering temperature on corrosion fatigue strength of 13% Chromium stainless steel in 3%NaCl aqueous solution and volume percent ferrite on corrosion fatigue strength of duplex stainless steel in potassium alum aqueous solution. The surface and fracture surface observation by optical and scanning electron microscopy revealed that corrosion pit formed at corrosion fatigue crack initiation area. In light of relatively smaller effect of corrosive environment on corrosion fatigue crack propagation rate it can be surmised that corrosion fatigue strength of stainless steels is governed by crack initiation process. It can be concluded that corrosion fatigue strength of stainless steels is strongly influenced by metallurgical factors such as chemical compositions, heat treatment, manufacturing process and microstructures.The information obtained in this survey directly lead to prevention of corrosion fatigue failure in stainless steels made components, selection of stainless steels in corrosive environments and development of corrosion resistant stainless steels.

超音波ショットピーニングとマイクロショットピーニングによるステンレス鋼の疲労特性

The effects of projection conditions on the surface hardness and fatigue strength of stainless steel was investigated. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot media used were high-carbon cast with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments. The higher effect was found in the ultrasonic peening treatment, because a work-hardened layer was formed deeper in the material.

プラズマ窒化および FPB 処理から構成される複合表面処理によるステンレス鋼のフレッティング疲労強度の改善

プラズマ窒化および FPB 処理から構成される複合表面処理によるステンレス鋼のフレッティング疲労強度の改善

Effect of Hybrid Surface Treatments on Fretting Fatigue Strength of Stainless Steel

Effect of Hybrid Surface Treatments on Fretting Fatigue Strength of Stainless Steel

Mean stress effect on fatigue strength of stainless steel

Influence of mean stress on fatigue life and fatigue limit was investigated for Type 316 stainless steel. The results for prestrained specimens revealed that fatigue life was almost the same in the same strain range regardless of stress amplitude, maximum peak stress and mean strain. The fatigue life was shortened when applying the mean stress for the same strain range, whereas it was increased for the same stress amplitude. It was shown that the reduction in fatigue life was brought about by the change in the effective strain range, which was caused by the increase in minimum peak stress and the ratcheting strain. The fatigue life could be predicted conservatively even if the mean strain was applied by assuming the effective strain range to be equal to the total strain range (by assuming the crack mouth to be never closed). It was concluded that the mean stress correction was not necessary for the load-controlled cyclic loading and for the region where the ratcheting strain was constrained.

Influence of mean stress on fatigue strength of stainless steel

Influence of mean stress on fatigue strength of stainless steel

Environmental effect on fatigue strength of stainless steel in PWR primary water – Role of crack growth acceleration in fatigue life reduction

The influence of the pressurized water reactor (PWR) water environment on fatigue life and fatigue crack growth rate was discussed. The fatigue lives of Type 316 stainless steel in the PWR water environment were investigated using cylindrical hollow specimens. The acceleration in the crack growth due to the environment was quantified by investigating spacing of striations and crack growth tests using compact tension specimens. The growth rates obtained could be represented by the strain intensity factor. It was shown that the fatigue lives estimated by crack growth prediction agreed with those obtained by the tests. Then, it was concluded that the reduction in the fatigue life due to the PWR water environment was brought about not by enhancement of crack initiation but by the acceleration of the crack growth.

Effect of Hybrid Surface Treatment Composed of Plasma Nitriding and DLC Coating on Friction Coefficient and Fatigue Strength of Stainless Steel

This study was conducted to investigate the effect of hybrid surface treatment composed of plasma nitriding and DLC (diamond-like carbon) coating on the friction coefficient and fatigue strength of stainless steel JIS SUS316. The obtained results were compared with the results of the previous study which investigated the effect of hybrid surface treatment composed of plasma carburizing and DLC coating. Plasma nitriding as a pretreatment was more effective to decrease the friction coefficient of DLC-coated stainless steel than plasma carburizing because the hardened layer with greater hardness supported the DLC layer. The mechanical properties were unaffected by both hybrid surface treatments. Plasma nitriding improved the fatigue strength of stainless steel more than plasma carburizing. DLC coating slightly improved the fatigue strength of the plasma-nitrided material; however, its effect was more significant on the plasma-carburized material. [doi:10.2320/matertrans.M2012426]

OS1544 ステンレス銀の疲労強度に及ぼす平均応力の影響

OS1544 ステンレス銀の疲労強度に及ぼす平均応力の影響

Effects of plasma carburizing and DLC coating on friction-wear characteristics, mechanical properties and fatigue strength of stainless steel

This study was conducted to investigate the effects of hybrid surface treatment on the friction-wear characteristics, mechanical properties and fatigue strength of austenitic stainless steel JIS SUS316. In hybrid surface treatment, after plasma carburizing as a pre-treatment had been performed at 773K for 43.2ks (12h), DLC (diamond-like carbon) coating was performed. The formed duplex layer had the DLC layer (thickness 1.6–1.8μm) outermost and the hardened layer (thickness 90μm) below it. The DLC layer was markedly effective in decreasing the friction coefficient and improving wear resistance. At the same time, the durability of the DLC layer was improved by the existence of the hardened layer. Since no marked change in the microstructure of the substrate occurred through hybrid surface treatment, the mechanical properties were almost unchanged. Furthermore, fatigue strength was greatly improved by hybrid surface treatment (improvement rate 53%) because the generation of fatigue cracks from the surface was strongly suppressed by the duplex layer.

OS2124 各種ステンレス鋼のギガサイクル腐食疲労挙動

Giga-cycle corrosion fatigue behavior of 12 Cr martensitic stainless steels in NaCl and NaOH aqueous solution were summarized mainly on the basis of the author's experimental results. Then giga-cycle corrosion fatigue behavior of austenitic stainless steels such as SUS304,SUS304N2, SUS316, 2.5%Cr containing steel and YUS270 super stainless steel are demonstrated on the basis of the author's recent experimental results. Giga-cycle corrosion fatigue behavior of SUS329 duplex stainless steel is touched on briefly. The reduction of giga-cycle corrosion fatigue strength of stainless steels is depending on the kind of stainless steel. It can be concluded that the reduction of corrosion fatigue strength of martensitic, austenitic and duplex stainless steels is due to the corrosion pit formation at corrosion fatigue crack initiation area.

疲労強度に優れる結晶粒微細化ステンレス鋼の開発とシリンダーヘッドガスケットに適した疲労試験方法

High fatigue strength stainless steel was developed for cylinder head gasket. Bead is press formed on the stainless steel gasket to prevent the leak of combustion gases and cooling water. However, fatigue failure is initiated from micro crack on the bead foot induced by press forming. On the developed steel, the micro crack was suppressed by refining the grain size to 1.5∼2.0μm. In addition, suitable fatigue test method for gasket was invented. It was difficult to properly evaluate the fatigue strength of stainless steel for gasket by traditional fatigue test because the test piece had neither bead nor the micro crack on the bead foot. On this invented test, cyclic compressive load is applied to test piece with bead. It was clarified that the developed steel exhibited higher fatigue strength than the conventional steel.

Fatigue properties of 316 stainless steel and its failure due to internal cracks in low-cycle and extremely low-cycle fatigue regimes

Abstract It is important to know residual fatigue strength of materials in the extremely low-cycle fatigue (ELCF) regime in order to assess structural integrity after large cyclic strain caused by an earthquake. In the ELCF regime, it was pointed out that not only surface cracking but also additional bulk damage reduces the fatigue life. In this study, the fatigue strength of stainless steel in the low-cycle and ELCF regimes and the effects of bulk damage on fatigue strength were investigated. Type 316 stainless steel was subjected to axial cyclic strain up to strain amplitude of 6%. Also, the change in fatigue life was investigated when the surface layer of the specimens was removed during the fatigue tests. It was shown that not only the surface cracking but also the bulk damage affected the fatigue life. It was also shown that the bulk damage consisted of two factors: internal cracking and local damage. Internal cracks were observed on the fractured surface when the strain amplitude was more than 1%, and in some cases the specimen was fractured by these internal cracks. Local damage reduced the incubation period before crack initiation and fatigue life decreased as the strain amplitude increased. In all cases, the experiment conducted under the strain amplitude e a = 0.5%, neither the internal cracks nor the local damage affected the fatigue life.