Composite structure sheet steel with excellent elongation and stretch flange formability

• US 20060130937A1
• Filed: 12/01/2005
• Published: 06/22/2006
• Est. Priority Date: 12/21/2004
• Status: Active Grant

• Current Assignee: Klaus Schmidt
• Original Assignee: Klaus Schmidt, Shinshu Tlo Co., Ltd.
• Inventors: Mukai, Yoichi, Akamizu, Hiroshi, Sugimoto, Koichi, Ikeda, Shushi
• Granted Patent: US 7,413,617 B2
• Time in Patent Office: Days
• US Class Current: 148/320
• CPC Class Codes: C21D 8/02 during manufacturing of plates or strips C21D8/12 takes precedence
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 1/06 with the use of special agents for refining or deoxidising
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese

Abstract

The present invention provide a TRIP-type composite structure steel plate of the TPF steel type in which elongation and stretch flange formability at room temperature are improved by controlling the morphology of the second-phase structure. In a composite structure sheet steel comprising 0.02 to 0.12% C, 0.5 to 2.0% Si+Al and 1.0 to 2.0% Mn, with the remainder being Fe and unavoidable impurities, and comprising 80% or more polygonal ferrite (steel structure space factor) and 1 to 7% retained austenite, with the remainder being bainite and/or martensite, wherein the elongation and stretch flange formability of the composite sheet steel are improved by reducing the number of bulky, massive second phases with an aspect ratio of 1:3 or less and a mean grain size of 0.5 μm or more in the second phase of this composite structure, which comprises retained austenite and martensite.

Claims

1. A composite structure sheet steel with excellent elongation and stretch flange formability comprising 0.02 to 0. 12% C, 0.5 to 2.0% Si+Al and 1.0 to 2.0% Mn by mass percentage, with the remainder being Fe and unavoidable impurities, and comprising 80% or more polygonal ferrite (steel structure space factor) and 1 to 7% retained austenite (volume fraction measured by the saturation magnetization method), with the remainder being bainite and/or martensite, wherein a second-phase structure in the composite structure comprises martensite and retained austenite, and within the second-phase structure not more than 15 massive second-phase structures with an aspect ratio of 1:

3 or less and a mean grain size of 0.5 μ

m or more are contained per 750 μ

m² as observed under a scanning electron microscope at 4000×

.

2. The composite structure sheet steel with excellent elongation and stretch flange formability according to claim 1, containing one or two or more of 0.1% or less (not including 0%) Ti, 0.1% or less (not including 0%) Nb, and 0.1% or less (not including 0%) V by mass percentage.

3. The composite structure sheet steel with excellent elongation and stretch flange formability according to claim 1 or 2, containing one or two or more of 1.0% or less (not including 0%) Mo, 0.5% or less (not including 0%) Ni, and 0.5% or less (not including 0%) Cu by mass percentage.

4. The composite structure sheet steel with excellent elongation and stretch flange formability according to any one of claims 1 through 3, containing one or two of 0.003% or less (not including 0%) Ca and 0.003% or less (not including 0%) REM by mass percentage.