Recently, the improvement of the high strength of fine grain steels has been investigated actively. Fine grained steels have high yield stress, as expected by the Hall-Petch relationship. Therefore, these materials are considered for use as structural material. Welding is one of the most effective methods for connecting structural components. Nevertheless, the negative influence of tensile residual stresses and coarse grains due to the welding process must be taken into consideration. It has been proved that the shot peening process can effectively overcome these problems. In this study, samples prepared with various mean grain sizes were processed by shot peening. The triaxial residual stress distribution after shot peening was measured by X-ray diffraction. Moreover, the distribution of the hardening effect and nanocrystalline layer near the shot peened surface was observed. In this paper, the relationships between the effects of triaxial residual stress, structure, fatigue and hardness are discussed. As a result, thin nanocrystalline layer was formed on the surface layer of over 90 percent of surface area. Therefore, hardness of the surface, fatigue limit and fatigue life improved. The surface of plastic flow layer became the starting point of the crack initiation. Moreover, compressive residual stress by shot peening processing was confirmed and the depth of the nanocrystalline layer and the plastic flow layer correlated with depth of changing point of the triaxial residual stress distribution.

Recently, the study of fine grain steels aimed at achieving into high strength has become active. Welding is one of the most effective methods for connecting the structural components. For those cases, the negative influence of any residual tensile stress induced during the welding process must be considered. It has been proved that shot-peening can effectively solve this problem. However, the influence of the Shot-Peening process on fine grain steels after welding has only been briefly reported up to now. In this study, fine grain steels were used, and specimens were obtained after heat treatment. Residual stress distributions near the surface of the fine grain steel after shot-peening were measured by X-ray diffraction technology. Moreover, the effect of hardness on distributions near the shot-peened surface was also estimated.

Recently, fine grain steel has been actively researched. However, as we know, the influence concerning the shot peening processing to fine grain steels has been few reported up to now. Therefore residual stress distribution near the surface of fine grain steel after shot-peening was measured by X-ray diffraction technology. Moreover, the hardening effect the distributed near the shot-peened surface was also estimated. The relationships between the effects of shot-peening and the grain size of material were discussed.

A shot peening process is generally utilized as one of the surface treatment processes to improve the fatigue life and the fatigue strength of cyclically loaded components. This improvement is achieved by inducing compressive residual stresses and work hardening effects in areas close to the surface. But the influence of the shot peening process on fatigue strength is not clarified enough. It's significant technologically and industrially to clarify the influence factor of shot peening on the fatigue strength. Former study of author confirmed that main effect on the fatigue strength of the SUS304 steel hitted by controlled steel ball is the hardening of austenite structure itself due to the shot peening. In this study, the SUS329J1 steel having both austenite and ferrite phases was also investigated from the viewpoint of the work hardening of both structures. An effect of the residual stress on fatigue limit is not observed at all. As a result, we found that the work hardening of the SUS329J1 steel by shot peening was attributed to both the strain-induced martensitic transformation and the hardening of austenite and ferrite phase themselves. Especially, the ferrite phase influences the Vickers hardness distribution of shot-peened material, and the hardness increment of the austenite phase is larger than other phase and mainly due to the fine structure.

It is well known that the shot peening process is often used industrially for the purpose of improvement of the fatigue strength of many kinds of steels. Generally the surface of these steels subjected to this process is hardened and addition to it, the compressive residual stress is also induced on the surface layer. In this study, the fatigue tests of shot-peened steel SUS 304 were conducted using the rotating-bending fatigue test machine, and residual stresses were detected by X-ray stress measurement. And surface characteristics related to residual stress σR, hardness and microstructure are also investigated to clarify the influential factors on the bending fatigue strength of stainless steel SUS 304 by shot peening. As a result, the surface layer was hardened by the shot peening process and the strain-induced transformation was ascertained by X-ray analysis. And residual stresses were almost released at the initial time during fatigue cycles. Concerned about work hardening, it is also studied precisely. We found that the increments of hardness was attributed to both martensitic transformation and hardness of austenite itself, and then the bending fatigue strength of austenitic stainless steel with shot peening process was improved by twenty percents. Consequently, it is found that the increments of hardness by the shot peening are mainly due to hardness of austenite structure itself, and it affects the improvement of the fatigue strength of the shot peened austenite stainless steel.

Since recently a speed changer in a motor vehicle or a gear reducer in a generalized industrial equipment have been demanded to transmit high torque or to be compact, an improvement of a load carrying capacity of gears used in it will properly be required. Their current gears are almost case-carburized and hardened steels. However, it is often said that these materials have already gotten the limit of endurance. Then, a shot peening process may be expected to improve the fatigue strength of case-carburized and hardened steel. It is very difficult to make the surface roughness of the roller or gear tooth finished smaller than the oil film thickness by a grinding machine. Even if possible, grinding time of the surface will be very long, and it is not economical from the viewpoint of manufacturing process. However, it is thought that the both processes of shot peening and barrelling, which can easily be applied to the gear with complex configuration, are an advantageous for processing time. In the present paper, outlines of pitting strength of rollers finished by these processes are indicated and machining precisions and tooth surface characteristics of gears finished by these ones are discussed. The authors would like to recommend to employ the processes of shot peening and barrelling after grinding the gear tooth of case-carburized and hardened steel from both viewpoints of the improvement of fatigue strength and the economy of attaining a high quality gear.

In the previous report, effects of surface characteristics of case-carburized and hardened steel rollers finished by many surface machining processes upon the surface durability were examined under rolling/sliding conditions using a two rollers contact fatigue testing machine. Consequently, it was clarified that the surface durability of rollers whose surfaces are subjected to processes of shot peening and barrelling after grinding is improved as compared with other processes. The shot peening process induces a compressive residual stress and the barrelling process improves a surface roughness. If the processes of shot peening and barrelling would be applied to a gear with complex configurations, it may be obtained a high quality gear with the highly load carrying capacity. In the present report, it is actually investigated, in addition to the roller test so as to reconfirm the effects of many processes on the surface durability, whether the processes of shot peening and barrelling can be applied to the tooth surface of the gear like the same as the roller, or not.

A surface durability of case-carburized and hardened steel rollers is examined by a highly loaded two rollers contact fatigue testing machine. The surfaces of test rollers are finished to a surface roughness of about 3μmRmax by a cylindrical grinding machine. Thereafter, in order to improve the ground surface, the processes of shot peening, barrelling and hydraulic horning are employed. These processes can be applied to surfaces with complex configuration, such as gears. Each surface roughness of rollers finished by above machining processes is measured before/after running test, and residual stress in the vicinity of the surface of test pieces is also detected by an X-ray diffraction method. It is confirmed that the surface durability of rollers whose surfaces are subjected to the barrelling process after the shot-peening process is appreciably improved.

In the present investigation, using a rolling contact fatigue testing machine, the surface durability (pitting limit) of steel rollers which are case-carburized and hardened to 750 Hv is examined under rolling/sliding conditions. Four kinds of rollers which are finished to a surface roughness of about O.2μm Rmax or about 3μm Rmax by a cylindrical grinding machine are used. To improve the ground surface the shot peening and barrelling processes are employed and they are compared to the non-treated surface. The processes of shot peening and barrelling can be applied to surfaces with complex configurations, such as gears. It is shown that the surface durability of rollers whose surfaces are subjected to a barrelling process after a shot-peening process is improved.

Generally, a shot-peening process is utilized in order to improve the bending fatigue strength of a tooth root of a gear. In this investigation, surface durability of austempered ductile cast iron (ADI) rollers is examined using a two-rolling-contact fatigue testing machine, and it is elucidated whether or not the surface durability is improved when an ADI roller finished by a cylindrical grinding machine is subjected to an additional shot-peening process on its surface. The pitting strength of shot-peened ADI rollers is just slightly improved. Furthermore, it is shown that austempered ductile cast iron rollers are more easily worn in comparison with steel rollers which are case-carburized and hardened. In particular, shot-peened ADI rollers show large amount of wear compared with non-shot-peened ones.

This paper presents the results of a study on the effects of the shot-peening process on the fatigue characteristics of austempered ductile iron (ADI). Experiments mainly involve surface durability tests using cylindrical roller specimens and bending fatigue tests, as well as X-ray stress measurements. The elasto-hydrodynamic lubrication (EHL) theory was used in the determination of surface durability. It was found that the surface durability of the shot-peened ADI was slightly lower than the of the non-shot-peened ADI, and this difference was attributed to the difference in surface roughness. Moreover, it was found that residual stress does not affect the surface durability of the shot-peened ADI. Results also showed that the shot-peening of the ADI is useful for improving the bending fatigue strength. Consequently, from the viewpoint of fatigue strength of ADI, surface roughness, especially as related to the surface durability, should be strongly considered in the case of application of shot-peened ADI to machine elements subjected to bending and/or sliding abrasion.

This paper presents the study of the effect of surface hardening treatment on the wear characteristics of the hardened steel for rolling contact problem. The surface hardened steels have been studied in many papers, but the analysis that treated rolling-sliding contact with FEM is scarcely found. The wear characteristics of the contact surfaces during rolling and sliding should be predicted precisely. We have calculated the deformation, equivalent plastic strain, residual stress, and shear stress-strain curve at the treated area of the steel. It is found that the deformation of treated steel is smaller than that of not-treated steel. And it is the same as in the case where the friction force exists.

The purpose of this study is to investigate the fatigue strength of carburized gear steel chemically vapor deposited with titanium carbide, and to clarify the main effect of carburized gear steel coated with titanium carbide on fatigue strength, including comparison with noncoated steel. Case depth of carburized gear deff is 1.3 mm. Quenching and tempering heat treatment after coating was also introduced. Smooth specimen, that is, flat plates and spur gear, module 4 with number of teeth 55, were supplied to fatigue test. Residual stress in TiC surface layer and substrate was detected by X-ray diffraction method. It is concluded that main effect on fatigue strength of chemically coated steel on carburized steel is substrate hardness near surface layer, and residual stress in titanium carbide layer doesn't effect prominently on fatigue strength. And finally it is found that the residual stress in both TiC layer and substrate near interface indicates possibility of a micro crack initiation at the interface between titanium carbide and substrate.

In the present study, the effects of TiC coating with or without post heat treatment on fatigue strength and wear characteristics of coated steel specimen were investigated. And also the conspicuous factors of fatigue strength and wear characteristics were studied by detecting residual stresses and hardness. For the specimen, two kinds of steels which were coated with TiC by the chemical vapor deposition (CVD) method, were used. The fatigue property was tested by a bending fatigue test machine.It was found that quench-tempering heat treatment was very important from the point of view of strength of fatigue and wear, and also found that fatigue strength and wear of TiC coated steels depended on substrate hardness and residual stress of TiC layer and the substrate region adjacent to the interface.

In the previous study, it was found that heat treatments of quenching and tempering after TiC coating improved the fatigue strength, and also the fatigue life of TiC coated steels depended on the hardness of substrate.In this study, the authors investigated in detail the effect of condition of quenching and tempering after TiC coating on the fatigue strength of tool steel. Four kinds of quenching and tempering conditions after TiC coating were selected, but TiC coating condition was all the same. Fatigue tests were conducted using the smooth specimens of a flat plate. The residual stresses were measured by an X-ray diffraction method. As the results, it was found that the condition of heat treatment of quenching and tempering influenced the hardness of substrate and consequently the fatigue strength which was not necessarily dominated by the hardness of substrate, and there existed an optimal hardness of substrate in relation to the fatigue strength. And it was reconfirmed that tensile stress existing in the top part of substrate, which was balanced by the compressive stress in TiC layer, was not only the main factor controlling the fatigue strength, and the secondary tempering condition played some role.

The aim of the present study was to clarify the residual stress of TiC coated steels by the X-ray diffraction measurements and to make clear the effect of TiC coating on fatigue strength. TiC layers were coated on three kinds of steels by a chemical vapor deposition method (CVD) under several coating conditions. Fatigue tests were conducted by using the plain specimens (flat plate type) and stress concentration type specimens (cantilever flat plate type). As the results, it was confirmed that a large compressive stress was observed in the CVD layer of TiC, whereas tensile stress or smaller compressive stress occurred in the substrate region adjacent to the interface. It was also found that the fatigue strength of TiC coated steels become lower than that of the specimens without TiC coating, but the quenching and tempering treatment after TiC coating improved the fatigue strength. It was concluded that the hardness of substrate and the residual stress in the top part of substrate and the TiC layer were the main factors affecting fatigue strength of TiC coated steels.