Patent ID: 9340846
Filing Date: 2016-05-17
CPC Classification: B24C,C21D,C22C

Claim Text:
1. A method for improving a fatigue strength of a cast iron material, the cast iron material being a spheroidal graphite cast iron containing 2.0 to 4.0% C, 1.5 to 4.5% Si, 2.0% or less Mn, 0.08% or less P, 0.03% or less S, 0.02 to 0.1% Mg, and 1.8 to 4.0% Cu, by weight ratio, and is applied normalizing heat treatment so as to impart the tensile strength of 850 MPa or more, the method comprising the steps of: performing a first shot peening treatment with shots having the hardness of 600 Hv or more and a particle size (φ) of 0.5 to 0.8 mm; performing a second shot peening treatment with shots having the hardness of 600 Hv or more and a particle size (φ) of 0.1 to 0.3 mm; and performing a third shot peening treatment with shots having the hardness of 600 Hv or more and a particle size (φ) of 0.1 mm or less.