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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
First Claim
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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×

    .

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