BAKE-HARDENING HOT-ROLLED STEEL SHEET WITH EXCELLENT WORKABILITY AND PROCESS FOR PRODUCING THE SAME

Title:

BAKE-HARDENING HOT-ROLLED STEEL SHEET WITH EXCELLENT WORKABILITY AND PROCESS FOR PRODUCING THE SAME

Document Type and Number:

WIPO Patent Application WO/2006/077760

Kind Code:

A1

Abstract:

A bake-hardening hot-rolled steel sheet which contains 0.01-0.2 mass% carbon, 0.01-2 mass% silicon, 0.1-2 mass% manganese, up to 0.1 mass% phosphorus, up to 0.03 mass% sulfur, 0.001-0.1 mass% aluminum, up to 0.01 mass% nitrogen, and 0.005-0.05 mass% niobium, the remainder comprising iron and unavoidable impurities. The microstructure of the sheet is a polygonal ferrite having an average particle diameter of 2-8 µm and/or a continuous cooling transformation texture. The proportion of a solid solution of carbon and/or a solid solution of nitrogen present at the grain boundaries in the sheet is 0.28 or lower. Also provided is a process for producing the hot-rolled steel sheet which comprises heating a steel billet comprising those ingredients to at least a temperature satisfying the equation SRT (°C) = 6670/&lcub 2.26-log(%Nb)(%C)&rcub -273 (A) rough-rolling the steel billet heated, finish-rolling the sheet under such conditions that the final temperature is in the range of from the Ar₃ transformation point to (Ar₃ transformation point + 100°C), cooling it at a cooling rate of 80°C/sec or higher for cooling from cooling initiation to 500°C or lower, and winding it up.

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Inventors:

YOKOI TATSUO (JP)
YAMADA TETSUYA (JP)
TASAKI FUMINORI (JP)

Application Number:

PCT/JP2006/300263

Publication Date:

July 27, 2006

Filing Date:

January 12, 2006

Export Citation:

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Assignee:

NIPPON STEEL CORP (JP)
YOKOI TATSUO (JP)
YAMADA TETSUYA (JP)
TASAKI FUMINORI (JP)

International Classes:

C22C38/00; B21B1/26; B21B3/00; C21D9/46; C22C38/12; C22C38/58; C23C2/06

Foreign References:

JP2002030385A	2002-01-31
JP2001152254A	2001-06-05
JP2000239791A	2000-09-05
JPH1192859A	1999-04-06

Other References: