SUP10, which has surface defects, was subjected to a fatigue test and the effects of fine particle peening were analyzed. Moreover, a comparison with shot peening was performed.

The surface defect was made with a twist drill （0.2, 0.4, 0.6 mm）. The defect depth is half the diameter of the twist drill bit. High-speed steel balls were used for fine particle and shot peening.

When each processing was performed after introducing a surface defect in the sample, it was found that fine particle peening suppresses fatigue strength reduction more than shot peening. The reason for this is considered to be an improvement in the hardness of the drill bottom and the influence of residual stress.

HA188 cobalt-base superalloy is generally used under the high temperature environment. The mechanical properties of the alloy decrease under creep fatigue condition in high temperature as gas turbine components. In this study, the recovery of deteriorated properties was tried using heat treatment, and the condition for recovery was found. Concretely the elongation and the reduction of area at room temperature of Alloy 188 was decreased after creep fatigue applied the tensile stress 80 MPa at 1000°C, and the degenerate properties were recovered after heat treatment at 1100°C/1 h/fan cooled.

The auto-tempering, which occurs during quenching, is an important issue in martensitic steels with carbon because it affects the mechanical properties of products. Therefore, from an engineering view point, it is required to evaluate quantitatively the degree of auto-tempering. In this study, the degree of auto-tempering was evaluated by the diffusion area of carbon which is calculated by the diffusion coefficient of carbon in bcc iron. As a result, it is found that the auto-tempering of martensite occurs markedly in the temperature range of 500-350°C during cooling, the rapid cooling more than 40°C/s is enough to suppress the auto-tempering as is same as the 200°C − 1 h tempering or less, and so on.

It has been widely known that high compressive residual stress on a peened surface can be obtained by using micro shot peening media with high hardness. However, in the case of using media with high hardness not enough to plastically deform during collision with a test piece, Young's modulus of media is expected to be dominant factor of surface modification on a peened surface.

In this work, in order to clarify the effect of Young's modulus of media on surface modification, carburized JIS-SCM420 test pieces peened by 2 kinds of micro shot peening media were examined. These media showed comparable hardness, density, particle size and shape, but different Young's modulus.

As a result, on the peened surface, the maximum compressive residual stress and the thickness of nano crystal layer increased by using media with high Young's modulus. In the discussion from the view point of kinetic energy, it was cleared that the residual stress and the thickness were caused by the increase of kinetic energy loss of media by collision with test piece.

The kinetic energy loss was caused by coefficient of restitution. In the case of using media with high Young's modulus, the amount of elastic strain energy in media during collision was small. Also, the amount of released elastic strain energy at unloading after collision was small. Therefore, it was suggested that because collision of media with high Young's modulus showed low coefficient of restitution, kinetic energy loss by the media was large.

A low temperature plasma carburizing process can produce an expanded-austenite layer (generally called the S phase), which has high hardness and corrosion resistance at the surface of austenitic stainless steels. We have investigated S phase formation behaviors by using a combined process of active screen and DC plasma carburizing for austenitic stainless steels such as JIS SUS304 and 316 with the aim of developing a highly effective and efficient production technique. The influence of carburizing parameters (processing temperature, time, gas atmosphere, etc.) on the formation of the S phase was studied in terms of thickness, hardness, carbon concentration, lattice constant, and residual stress. The mechanical properties and corrosion resistances of the obtained S phases were also evaluated by using a ball-on-disk test and a salt spray test (SST). The results show that S-phases produced efficiently by the combined process under a condition of 733 K and a 10.5 vol% of CH₄ gas ratio have both excellent wear and corrosion resistances.