×

Heavy wall quenched and tempered seamless steel pipes and related method for manufacturing said steel pipes

  • US 9,644,248 B2
  • Filed: 04/08/2014
  • Issued: 05/09/2017
  • Est. Priority Date: 04/08/2013
  • Status: Active Grant
First Claim
Patent Images

1. A seamless quenched and tempered steel pipe comprising:

  • a yield strength from 415 MPa to 635 MPa and a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm;

    wherein the steel pipe has a chemical composition consisting of;

    0.050-0.085 wt % C;

    0.80-1.65 wt % Mn;

    0.10-0.45 wt % Si;

    0.10-0.70 wt % Cr;

    0.08-0.45wt % Ni;

    0.08-0.40 wt % Mo;

    0.015-0.040 wt % Al;

    0.0008-0.0050 wt % Ca;

    0.0030-0.0090 wt % N;

    0.000-0.040 wt % Nb;

    0.000-.020 wt % Ti;

    0.000-0.030 wt % Zr;

    0.000-0.030 wt % Ta;

    0.000-0.010 wt % V;

    0.000-0.25 wt % Cu;

    0.000-0.003 wt % S;

    0.000-0.015 wt % P; and

    0.000-0.0005 wt % B;

    the remainder being Fe;

    wherein CEIIW=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15) is in the range of 0.36% to 0.43%;

    wherein, defining a first parameter P1=50×

    C+Cr+10×

    Mo+70×

    V, the chemical composition satisfies a first condition 4.2<

    P1<

    8.0;

    wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 50% and ferrite (VF) lower than or equal to 50%,wherein the quenched and tempered steel pipe has, at a distance up to 2 mm starting from outer and inner surfaces of the steel pipe, a microstructure comprising, in volume percentage, tempered martensite lower than 70% and tempered bainite higher than 30%;

    wherein the microstructure of the quenched and tempered steel pipe has an average prior austenite grain size, measured by ASTM Standard E112, smaller than 25 μ

    m;

    and wherein the maximum hardness values, measured at 1.5-2.0 mm depth from the outer and inner surfaces, are not higher than 235 HV10.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×