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Hot-rolled steel sheet for high-strength electric-resistance welded pipe having sour-gas resistance and exellent weld toughness, and method for manufacturing the same

  • US 20050183798A1
  • Filed: 02/03/2005
  • Published: 08/25/2005
  • Est. Priority Date: 02/24/2004
  • Status: Active Grant
First Claim
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1. A hot-rolled steel sheet for a high-strength electric-resistance welded pipe having sour-gas resistance and excellent weld toughness, comprising:

  • about 0.02% to about 0.06% C;

    about 0.05% to about 0.50% Si;

    about 0.5% to about 1.5% Mn;

    about 0.010% or less P;

    about 0.0010% or less S;

    about 0.01% to about 0.10% Al;

    about 0.01% to about 0.10% Nb;

    about 0.001% to about 0.025% Ti;

    about 0.001% to about 0.005% Ca;

    about 0.003% or less O;

    about 0.005% or less N, and at least one element selected from the group consisting of about 0.01% to about 0.10% V;

    about 0.01% to about 0.50% Cu;

    about 0.01% to about 0.50% Ni; and

    about 0.01% to about 0.50% Mo on the basis of mass, wherein C, Si, Mn, Cu, Ni, Mo, and V satisfy Px given by Relationship 1;


    Px=(C)+(Si)/30+((Mn)+(Cu))/20+(Ni)/60+(Mo)/7+(V)/10≦

    0.17 



    (1)where (M) indicates the content by mass percent of an element M;

    Ca, O, and S satisfy Py given by Relationship 2;


    Py={(Ca)−

    (130×

    (Ca)+0.18)×

    (O)}/(1.25×

    (S)) 1.2

    Py


    3.6 



    (2)where (M) indicates the content by mass percent of an element M;

    the balance is Fe and incidental impurities; and

    the microstructure of the steel sheet is composed of about 95% by volume or more bainitic ferrite.

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