In this study, we have developed new shot materials of tungsten carbide (150 and 100 μm in average diameter) with high hardness and large specific gravity, which is about 1.7 times (HV1400) in hardness and about 1.9 times in specific gravity (specific gravity 14) compared with the conventional one. And we have examined the improvement in the fatigue strength of SM490A welded joint, the outbreak of noise and the use of projection air when this shot material is used.
The following experimental results were obtained :
1) The fatigue strength of welded joint was improved very well even in low projection air pressure 0.2 MPa when the peening was performed with the tungsten carbide shot materials of 150 μm in diameter, which has higher hardness and larger specific gravity than the conventional steel ball shot materials.
2) When the tungsten carbide with 100 μm in diameter or the conventional steel ball with 177 μm in diameter was used as the shot material, the higher projection air pressure above 0.4 MPa was needed in order to obtain the same fatigue strength improvement when the tungsten carbide with 150 μm in diameter was applied.
3) This improvement of the fatigue strength was mainly an effect of hardness increase by peening, but there was an additional effect of the compressive residual stress, too.
4) It was possible to reduce the noise value by approximately 10 dB and also the amount of projection air by more than 50 %, when the shot material with the high hardness and large specific gravity in particle diameter 150 μm was used in order to obtain the similar peening effect of the conventional steel ball shot materials.