Metal treatment – Stock – Ferrous
Reexamination Certificate
2002-05-23
2009-02-03
Yee, Deborah (Department: 1793)
Metal treatment
Stock
Ferrous
C148S331000, C148S334000
Reexamination Certificate
active
07485194
ABSTRACT:
This disclosure proposes a high-strength hot rolled steel sheet having excellent anti-die-galling property and anti-fatigue property, in which the steel sheet has a composition including C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.2 mass % but not more than 1.2 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Mo: not less than 0.1 mass % but not more than 1.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, P: not more than 0.03 mass % S: not more than 0.01 mass % and the remainder being substantially Fe and inevitable impurities, and has a steel microstructure containing not less than 55 vol % of ferrite and not less than 10 vol % but not more than 40 vol % of martensite provided that a total of both is not less than 95 vol %, and a ratio ds/dc of an average crystal grain size ds of the ferrite in a surface layer portion of the steel sheet to an average crystal grain size dc of the ferrite in a center portion of the steel sheet is 0.3<ds/dc≦1.0 and a surface roughness is not more than 1.5 μm as an arithmetic mean roughness Ra, as well as a method of producing the same.
REFERENCES:
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Computer-generated English translation of Japanese patent 11-100641, Takagi Shusaku et al, Apr. 13, 1999.
Mega Tetsuya
Sakata Kei
DLA Piper (LLP) US
JFE Steel Corporation
Yee Deborah
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