Patent ID: 9464335
Filing Date: 2016-10-11
CPC Classification: C21D,C22C,C23C

Claim Text:
1. A method for improving a fatigue strength of a cast iron material, comprising the steps of: quenching and subjecting to a tempering or austempering heat treatment a spherical graphite cast iron which contains 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, so as to impart the tensile strength of 1200 MPa or more; then performing on the spherical graphite cast iron 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; then 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 then 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.