Patent ID: 6589369
Filing Date: 2003-07-08
Classification: C21D,C22C

Abstract:
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.