• Journal of the Korean institute of surface engineering
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• v.36 no.6
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• pp.475-479
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, tests are conducted on spring steel and shot peened specimens. Various tests are accomplished to evaluate mechanical properties influenced by shot peening process, and fatigue tests are also performed to evaluate the improvement of fatigue strength. And then the residual stresses are examined. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength of notched specimen remarkably increased. In the case of 1-step shot peening, fatigue strength increased by about 20％ than unpeened specimen. Especially, in the case of 2-step shot peening, fatigue strength increased by about 40％, because the residual compressive stress at surface was higher than that of 1-step shot peened specimen. The fatigue strength and life are closely related to the value and position of maximum compressive residual stress by shot peening.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.336-341
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• 2004

The effect of shot peening conditions on the fatigue properties of heat-treated spring steel has been investigated by using residual stress measurement and metallography. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength and fatigue life increased about 20% to 40% by 1-step and 2-step shot peening process. The fatigue strength and life were closely related to the value and position of maximum compressive residual stress by shot peening process. In the case of warm shot peening, compressive residual stress of specimens shot peening processed at $200^{\circ}C$ was higher than those of specimens shot peening processed at room temperature, $100^{\circ}C$ and $300^{\circ}C$.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.67-72
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.