| 摘要 |
PROBLEM TO BE SOLVED: To refine carbide and to improve both workability and hardenability by regulating carbon content in a high carbon steel, grain size of carbide, and grain size of ferrite, to values in specific ranges, respectively. SOLUTION: The content of C in a high carbon steel is regulated to >=0.2wt.%, and the grain size of ferrite as principal constituent and the grain size of carbide are regulated to >1-4μm and <=1.3μm, respectively. Other components are not particularly limited. In the composition, C causes the distribution of strain to the ferrite grain boundaries having a function of forming carbide in the steel and to the inner part of ferrite grains or to the interface between ferrite and carbide and also provides the steel with hardenability. It is preferable to refine carbide in order to allow the carbide to enter into solid solution quickly in austenite. By finely precipitating the carbide in the steel, the entering of the carbide into solid solution can be accelerated during heating and holding. Ferrite grain size is a parameter improving elongation under the condition of specific grain size.
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