Fatigue Strength Of Carbon Steel Research Articles

Evaluation of the Influence of Dispersion of Pearlite on the Fatigue of Carbon Steel

It is shown that the slope of a tangent to the fatigue curve can be used to analyze the effect of dispersion of pearlite on the fatigue strength of carbon steel. For a constant thickness of the ferrite-pearlite layer, we established an inversely proportional relationship between the indicated parameter and the density of accumulated dislocations. We also estimated the mechanism of influence of the dispersion of pearlite on the transition from low- to high-cycle fatigue of carbon steel.

401 炭素鋼環状切欠き材のねじり疲労強度に及ぼす静的組合せ負荷の影響(材料力学I)

401 炭素鋼環状切欠き材のねじり疲労強度に及ぼす静的組合せ負荷の影響(材料力学I)

813 ショットピーニング加工熱処理による炭素鋼の疲れ強さ改善(GS-3・4・10 強度向上)

813 ショットピーニング加工熱処理による炭素鋼の疲れ強さ改善(GS-3・4・10 強度向上)

Effect of the morphology and size of iron carbide on the fatigue strength of carbon steels

The effect of the morphology and size of iron carbide in a high-carbon steel on the fatigue strength and critical crack opening is considered. The increase in the fatigue strength induced by a decrease in the pearlite size in medium-and high-carbon steels is caused by the fact that the time of formation of nonuniformities in a uniform dislocation distribution shifts toward high total strains.

Analysis of Cavitation Erosion Resistance of Cast Iron and Nonferrous Metals Based on Database and Comparison with Carbon Steel Data

In our laboratory, cavitation erosion experiments have been carried out on various materials for about 40 years since 1970. The database was constructed and carbon steel data was analyzed in 2004. In this study, erosion resistance of cast irons, aluminum alloys, copper alloys and titanium alloys are compared with the regular carbon steels. The resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 for ductile cast iron as compared with carbon steel of the same hardness. When cast irons are exposed to cavitation, graphite was removed first and the region acts as a stress raiser, and therefore the erosion resistance of cast iron is much lower than that of carbon steel with the same hardness. The resistance is 1/3 to 1/5 for aluminum alloy as compared with carbon steel. Erosion resistance of aluminum alloys are lower than carbon steel, because the fatigue strength of aluminum alloys is as low as one half of the fatigue strength of carbon steel. The resistance of copper alloy and titanium alloy is almost the same as that of carbon steel.

Low Cycle Fatigue Strength of Carbon Steels in Oxygenated High Temperature Water

Surface degradations are induced in components of industrial machineries during long period of operation. The integrity assessment for aging component requires the consideration of actual operating conditions. Among those, surface degradation and low strain rate are the major factors to be considered for fatigue assessment in high temperature water. Fatigue tests using notched specimen in oxygenated high temperature water 300°C were performed to establish the assessment criterion for degraded material. It showed that deeper notch caused more reduction of the fatigue strength at long life region and the lower strain rate resulted in shorter fatigue life. The formation of corrosion groove was also investigated using temperature changing test. The formation of corrosion groove was caused by the rupture of oxidation film at the bottom of groove with the aid of mechanical strain cycling. The oxygen concentration cell assisted the corrosion process. This process was accelerated at relatively low temperature, i.e. 150°C. Fatigue life assessment method was proposed for aging component, which incorporated both effects of surface degradation and strain rate.

ＴｉＮ被覆処理鋼の疲労強度特性に及ぼす切欠きの影響

In order to investigate the effect of notch on the fatigue strength of carbon steel coated with TiN thin hard film, cantilever-type rotating-bending fatigue tests were carried out in air and in 3% saline solution by using U-shaped notch round-bar specimens of 0.35% carbon steel coated with TiN by physical vapor deposition (PVD) method. From the experimental results of the fatigue tests in air, an increase in fatigue strength was observed for the TiN-coating specimens, as compared with those without coating. Improvement in fatigue strength depends on the stress concentration factor, and the maximum improvement of 50% was observed on the sharp notched specimen. The endurance limit was defined as the crack initiation limit for the notched specimen with coating, while it was defined as crack growth limit for the notched specimen without coating. It was clear from an elasto-plastic analysis by FEM and the experimental results that a strain at the notch root for crack initiation limit was increased by the existence of hard thin film. From the corrosion fatigue test results, TiN-coating film effectively protects the substrate from the corrosive environment, and then the improvement of corrosion fatigue strength was about 87% for the dull notched specimen, which was the same as that in the smooth specimen.

Corrosion Resistance and Corrosion Fatigue Strength of Carbon Steel Coated with Chromium Nitride by Multistage PVD Method.

Chromium nitride(CrN) exhibits good corrosion resistance in addition to excellent electrical and mechanical properties. A decrease in the number of defects such as pinholes or voids formed during deposition is required for improvement of corrosion resistance and corrosion fatigue strength of coated materials. A multistage physical vapor deposition(PVD) method was proposed in order to fabricate dense thin-coating films. In an electrochemical anodic polarization test in aerated 2%H2SO4 solution, 0.37 wt%C steel that was coated with CrN thin film using the multistage PVD method showed better corrosion resistance than a specimen coated by a conventional method. This is due to a decrease in the number of small defects in the coating film deposited using the multistage PVD method. Evaluation of the corrosion fatigue strength of multistage-coated steel was performed by means of a cantilever-type rotating-bending fatigue test in 3%NaCl solution. The corrosion fatigue strength of multistage-coated steel was improved compared with that of the uncoated steel;however, the increase in fatigue strength was less in the multistage-coated specimen than in the specimen coated by the conventional method, contrary to the experimental results obtained from the anodic polarization test. It was pointed out that corrosion fatigue strength is dependent on not only the number of defects but also the shape of large defects in the coating film.

Corrosion Resistance and Corrosion Fatigue Strength of Carbon Steel Coated with Chromium Nitride by Multistage PVD Method.

Chromium nitride (CrN) has good corrosion resistance in addition to its good electrical and mechanical properties. A decrease in the number of defects such as pinholes or voids formed during deposition is required for improvement of corrosion resistance and corrosion fatigue strength of coating materials. A multistage physical vapor deposition (PVD) method was proposed in order to fabricate dense thin films. In an anodic polarization test in aerated 2%H2SO4 solution, CrN thin film deposited on 0.37 wt.%C steell using the multistage PVD method showed better corrosion resistance than that of the specimen coated using a conventional method. This is due to a decrease in the number of small defects in coating film by the multistage deposition. Evaluation of corrosion fatigue strength in the multistage coating steel was performed by means of a cantilever-type rotating-bending fatigue test in 3%NaCl solution. Corrosion fatigue strength of the multistage coating steel was improved as compared with that of the uncoated steel, but the increase in fatigue strength was less in the multistage coating method than the conventional method, contrary to the experimental results obtained from the anodic polarization test. It was pointed out that corrosion fatigue resistance is dependent on not only the number of defects but also the shape of large defects in the coating film.

Low-Cycle Fatigue Strength of Carbon Steel Coated with TiN by PVD Method.

Low-Cycle Fatigue Strength of Carbon Steel Coated with TiN by PVD Method.

The Influence of Stress Mode on the Fatigue Strength of TiN-Coated Carbon Steel.

The influence of applied stress ratio on the fatigue strength of carbon steel coated with TiN was studied on the basis of the measurement of crack initiation by the DC potential method. Fatigue tests were performed under the stress ratios of R=0 and -1 in air by using the round notched specimens of 0.37% C steel normalized, JIS S35C, coated with TiN by PVD and CVD. From the experimental results, increase of fatigue strength was observed in TiN-coated specimens under the tests of R=-1, as compared with that of the uncoated specimen. However, the fatigue life of coated specimens by PVD was decreased under the tests of R=0, except for the region of low stress amplitude. Moreover, the fatigue life of specimens coated by CVD under R=0 was smaller than that of the uncoated one. The difference of fatigue life with applied stress ratio is explained by the fracture behavior of coating film on the specimen surface.

Effects of small prestrain on fatigue strength of eutectoid steel with spheroidal pearlite structure.

In order to clarify the effect of small prestrain on the fatigue strength of carbon steel, fatigue behavior of plain specimens of eutectoid steel subjected to tensile prestrains is investigated, and compared with that of annealed or strain-aged specimens. It is found that small prestrain of a few percent does not decrease either the fatigue limit or the crack initiation and propagation lives. Fatigue slip initiation, however, is accelerated by the small prestrain. It is also found that no cyclic strain aging occurs. From these results, it is concluded that dislocations are unpinned by the small prestrain and this causes fatigue slip to occur easily, but the fatigue behavior after the slip initiation is not affected because spheroidal cementite acts as obstacles to further slip deformation and the stage I crack propagation.

Fatigue strength of carbon steel specimens having an extremely shallow notch

In order to elucidate how the principal dimensions of a notch as small as grains affect the fatigue strength of carbon steel, rotating bending fatigue tests were carried out on annealed 0.45% C steel specimens having an extremely small artificial notch whose depth is either 5 or 10μm. The fatigue processes at notched parts were observed successively. In these extremely shallow notches, the parameter controlling fatigue limits for fracture σ w was the notch depth, independently of notch sharpness. On the other hand, the crack initiation limits in the notches σ W1 were determined by a single K t σ W1 — χ relation obtained from the tests on ordinary notches, where K t is the stress concentration factor and χ is the stress gradient at the notch root. These results were studied on the basis of the characteristics of crack initiation process, the stress intensity variations at the crack tip and the stress distribution near the notch root.

高温純水中における炭素鋼の低サイクル疲労特性

An environmental fatigue test machine was developed and axial strain controlled fatigue tests could be conducted in the pressurized high temperature pure water using it. The fatigue life of carbon steel in the environment was investigated.Results obtained are summarized as follows;(1) In 250°C pure water containing 8 ppm dissolved oxygen, the fatigue life of carbon steel degraded markedly with decrease in strain rate in the comparatively large strain amplitude (above 0.25%). However, in the small strain amplitude, there was no degradation in fatigue life.(2) The environmental fatigue degradation was significant in the temperature range of 250°C to 290°C and in the dissolved oxygen contents above 0.2 ppm.(3) It was supposed that the conspicuous environmental fatigue degradation was caused by the combination effects of SCC and dynamic strain aging.(4) The prediction method of fatigue life of carbon steel in high temperature water was proposed with considering strain rate.(5) The environmental correction factor Ken was proposed to correct the design fatigue strength of carbon steel in high temperature water.

０．２％Ｃ炭素鋼レーザ表面焼入切欠き材の疲労特性

Although some case hardening methods, e.g. high frequency induction quenching, cementation and nitriding, are being applied to increase the fatigue strength of carbon steels, these methods require a troublesome treatment. Laser case hardening method has been developed to avoid the trouble and to increase hardness at a small desired area.The present study was planned to investigate the effect of laser case hardening on fatigue strength by using 0.2%C carbon steel specimens with five different types of U and V notches and by applying laser case hardening treatment on the notch part of each specimen. Since it is well known that the fatigue strength in impact fatigue is lower than that in non-impact fatigue, most of the experiments were conducted under impact fatigue load conditions in the wide stress cycles range of 10-107 cycles.The S-N curves under the non-impact load condition and those of the annealed specimens under the impact and non-impact load conditions were also obtained, and the effect of case hardening by laser surface quenching on fatigue strength were discussed by comparing these S-N curves each other, especially from the viewpoint of dependence of strength increase by laser case hardening on the stress concentration factor.The results showed that the laser case hardening method was effective to increase the fatigue strength of notched specimens whose stress concentration factor αis in the range of α<4. In other words, an increase in fatigue life of structual elements can be expected sufficiently by applying this method at locations considered as the initiating part of fatigue failure, because the stress concentration factor scarcely exceeds the value of 4 in service structural elements.

Fatigue strength of carbon steel and alloy steel shafts

Fatigue strength of carbon steel and alloy steel shafts

繰返し応力のもとでひずみ時効した鋼の疲労強度

To investigate the effect of cyclic-strain aging on the fatigue strength of carbon steel, two kinds of cyclic-strain-aged carbon steel were fatigued in rotating bending at room temperature as well as at elevated temperatures. The annealed and surface-rolled specimens were aged at 375°C and 250°C during cyclic stressing above or below the fatigue limits. The strengthening effect due to the aging treatment depends on the aging conditions; the temperature, the cyclic stress amplitude and the number of cycles.The strain-aging treatment at 375°C raises the fatigue strength at room temperature. The strengthening effect at room temperature through the aging treatment in the range of cycles 5.9 ×103∼3.2×106 under the stress just below the fatigue limit at 375°C is independent of the number of cycles at 375°C. In the range of stress 1.15Sw∼0.58Sw for 5.9×103 cycles at 375°C, the higher the stress level at 375°C the more effective the strengthening effects. The strengthening effect through the treatment at 250°C is less than at 375°C and depends on the number of cycles at 250°C.It can be considered that there is not a substantial difference in the strengthening effect through strain aging between annealed and surface-rolled conditions although the surface-rolled specimens have the strongly hardened layers and the residual stress, but that there is a large difference between the treatment at 375°C and 250°C. The strengthening effect seems to be based on dislocation-solute interaction which operates afresh at each cycle at 375°C, and on any cumulative effect of aging at 250°C.

The Effect of Nickel Plating on the Fatigue Strength of Carbon Steel

It is well known that the fatigue strength of machine part is generally reduced when plated with Chromium. But for nickel plating of steel there have yet been but scanty data for ensuring the effective fatigue strength. The author has investigated on that account the effect of nickel plating on the fatigue strength of carbon steel.The fatigue test specimens used in the present experiment were 10mm in diameter, and were made of annealed 0.15%C steel or annealed and quenched-tempered 0.45%C steel. The nickel plating of these fatigue test specimens was carried out in the Watt's type bath, having the composition NiSO4·7H2O 240g/l, NiCl2·6H2O 45g/l, H3BO3·30g/l. Then the current densities were 1.0, 0.7, 0.5A/dm2, and the bath temperature was kept at 25°C.The results obtained can be summarized as follows.1) The higher the fatigue limit is in unplated steel the lower the limit is in nickel plate steel, no matter what the plating condition is.2) The higher the plating current density is the larger the drop of the fatigue limit in nickel plated steel is. It is considered that this is closely connected with the presence of residual tensile stress in the plated layer.3) Moreover, the drop of the fatigue limits in the nickel plated steel is influenced by the plate thickness. The increase of the plate thickness lowers the fatigue limit. This is probably the notch effect due to the rough plate surface and to the crack in the plated metal.

Size Effect on Fatigue Strength of Carbon Steel Machined by a Lathe : X-Ray Detection of Fatigue Damage in Machine Parts

Size Effect on Fatigue Strength of Carbon Steel Machined by a Lathe : X-Ray Detection of Fatigue Damage in Machine Parts

The Effect of Torsional Deformation on the Fatigue Strength of Carbon Steel

Hereunder is presented a report of studies made on the influence of preliminary workings on the fatigue strength of carbon steel. The effects of residual stress and structural change that are produced by cold-workings on the fatigue strength are discussed. For the increase of fatigue strength, in the case of uniaxial deformation like tension or compression, as previously reported, the structural change is considered to be more responsible than residual stress. In the case of biaxial deformation like torsion, however, these fatigue behaviours are not clarified yet.In this paper, the effect of torsional preliminary working on the fatigue strength of S45C steel is discussed in comparison with that of tensile and compressive preliminary workings. The results obtained are summarized as follows:(1) The residual stress produced by torsional deformation assumes a shearing state in the direction counter to the twisting direction that has been previously given.(2) The materials subjected to preliminary workings, in plastic deformation by three kinds of strain, twisting, stretching and compressing, each to equal level of degrees, have shown increase in fatigue strength quantitatively in the descending order as follows;twisting strain>stretching strain>compressing strain(3) The fatigue limit of twisted specimen continues to increase until such a straining as e*=0.400, and then it tends steeply to decrease. Considering the stress strate of twisted specimens, it is concluded that the residual stress due to the preliminary working does not affect the fatigue limit, although the apparent stress amplitude increases with the shearing residual stress. The fractured surface is considered as apt to be preliminary influenced by the shearing residual stress.(4) From the results of the tension test and the compression test of each strained specimen, it is apparent that the yield point for reversal direction of the deformed direction is lower than that of the annealed specimen because of Bauschinger's effect in the case of stretched and compressed specimen. On the other hand, the yield points in both the tensile and the compressive directions in the case of twisted specimen increase over that of the annealed specimen. These anisotropy of work-hardening is considered to contribute to the result that the fatigue strength of twisted specimen is largest among the preliminary strained specimens in the same amount of equivalent plastic strain by the three kinds of straining processes.