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SPOT WELDED JOINT AND SPOT WELDING METHOD

  • US 20120141829A1
  • Filed: 08/30/2010
  • Published: 06/07/2012
  • Est. Priority Date: 08/31/2009
  • Status: Active Grant
First Claim
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1. A spot welded joint of a high-strength steel plate, comprising:

  • two or more thin steel plates which are spot welded to each other; and

    a nugget formed in a joint surface of the thin steel plates,wherein at least one of the two or more thin steel plates is a high-strength steel plate whose tensile strength is 750 MPa to 1850 MPa and whose carbon equivalent Ceq represented by formula (1) below is 0.22 mass % to 0.55 mass %, andwherein, in a nugget outer layer zone being a zone except a similar figure zone which is 90% as large as an outer shape of the nugget in the nugget,a microstructure consists of a dendrite structure in which an average value of arm intervals is equal to or less than 12 pm,an average grain diameter of carbides contained in the microstructure is 5 nm to 100 nm, and a number density of the carbides is equal to or more than 2×

    106/mm2,
    Ceq=[C]+[Si]/30+[Mn]/20+2[P]+4[S] 



    (1)([C], [Si], [Mn], [P], and [S] each represent respective contents (mass %) of C, Si, Mn, P and S).

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