| 摘要 |
PROBLEM TO BE SOLVED: To obtain a medium carbon steel with dispersed fine spheroidal graphite structure, in which fine ZrC is allowed to function as a nucleation site of graphite, having high strength and excellent workability and machinability. SOLUTION: The medium carbon steel with dispersed fine spheroidal graphite structure has a composition containing 0.1-1.5% Si, <=1.0% C, and 0.01-0.5% Zr. A stock (ingot) of this composition is subjected, after hot rolling, or after heat treatment (solution heat treatment) at 750-1,300 deg.C for 0.5-10 hr after the hot rolling, or after the precipitation of fine ZrC in a matrix by further applying water quenching, to graphitization treatment where heat treatment is performed at <=740 deg.C for 0.5-100 hr to grow graphite by using ZrC as a nucleation site. By this method the medium carbon steel having dispersed fine spheroidal graphite structure can be manufactured.
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