Patent ID: 9102992
Filing Date: 2015-08-11
Classification: B24C,C21D,C22C,C23C

Abstract:
1. A method for improving a fatigue strength of a spherical graphite cast iron, the spherical graphite cast iron having a cast iron material which contains 2.0 to 4.0% C, 1.5 to 4.5% Si, at most 2.0% or Mn, at most 0.08% P, at most 0.03% S, 0.02 to 0.1% Mg, and 1.8 to 4.0% Cu, by weight ratio, and has applied thereto tempering heat treatment so as to be made with a tensile strength of at least 800 MPa, the method comprising the steps of: performing a first shot peening treatment with shots having the hardness of at least 600 Hv and a particle size (φ) of 0.5 to 0.8 mm; performing a second shot peening treatment with shots having the hardness of at least 600 Hv 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 at least 600 Hv and a particle size (φ) of at most 0.1 mm.