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High fatigue strength steel sheet excellent in burring workability and method for producing the same

  • US 6,589,369 B2
  • Filed: 07/25/2001
  • Issued: 07/08/2003
  • Est. Priority Date: 04/21/2000
  • Status: Active Grant
First Claim
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1. A high fatigue strength steel sheet excellent in burring workability characterized in that:

  • the steel sheet is made of a steel containing, by mass, 0.01 to 0.3% of C, 0.01 to 2% of Si, 0.05 to 3% of Mn, 0.1% or less of P, 0.01% or less of S, and 0.005 to 1% or Al, and the balance consisting of Fe and unavoidable impurities;

    the microstructure is a compound structure having ferrite as the main phase and martensite as the second phase;

    the quotient of the volume percentage of the second phase divided by its average grain size is 3 or more and 12 or less; and

    the quotient of the average hardness of the second phase divided by the average hardness of the ferrite is 1.5 or more and 7 or less.

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