Patent ID: 8585837

Claim:
A manufacturing method of a high-manganese spheroidal graphite cast iron having a composition which contains 2.5 to 4.0 wt. % of C, 1.5 to 6.0 wt. % of Si, 7.0 to 18.0 wt. % of Mn, and 0.015 to 0.1 wt. % of Mg, and contains Ni in an amount of 0 to 10.0 wt. % when the Mn content falls within the range of 7.0 to 10.0 wt. %, or in an amount satisfying the relationship of formula (I) below when the Mn content falls within the range of 10.0 to 18.0 wt. %, with the balance being Fe and impurities: which comprises (a) heating the cast iron to a temperature of 1273 to 1373K to decompose carbides and to solidify in austenite, (b) holding the cast iron for 30-60 minutes at a temperature of 1073 to 1273K, wherein the heating temperature of (a) and the holding temperature of (b) are different, and then (c) quenching from 1073 to 1273K the resulting cast iron to form a metastable austenite matrix structure that contains no carbide or a reduced amount of carbides, Mn wt. %>Ni wt. %≧0 (1).