No steel pipes

Abstract

To provide a seamless steel pipe that ensures both weight reduction and weld strength.SOLUTION: A seamless steel pipe has a chemical composition including, in mass%, C: 0.10-0.20%, Si: 0.05-1.00%, Mn: 0.05-1.20%, P≤0.025%, S≤0.005%, Cu≤0.20%, N≤0.007%, Ni: 0.20-0.50%, Cr: 0.30-0.50% (including 0.30% and excluding 0.50%), Mo: 0.30-0.50%, Nb: 0.01-0.05%, Al: 0.001-0.100%, B: 0.0005-0.0020%, Ti: 0.003-0.050%, V: 0.01-0.20%, and the total of one or more selected from the group consisting of Ca, Mg and REM: 0-0.0250%, with the balance being Fe and impurities, satisfying Pcm(=C+(Si / 30)+(Mn / 20)+(Cu / 20)+(Ni / 60)+(Cr / 20)+(Mo / 15)+(V / 10)+5B)≤0.30 and tensile strength≥980 MPa.SELECTED DRAWING: Figure 1

Claims

1. A seamless steel pipe extending in the longitudinal direction and having a pair of pipe ends, The chemical composition is expressed in mass percent. C: 0.10-0.20%, Si: 0.05-1.00%, Mn: 0.05-1.20%, P: 0.025% or less, S: 0.005% or less, Cu: 0.20% or less, N: 0.007% or less, Ni: 0.20-0.50%, Cr: 0.30% or more and less than 0.50% Mo: 0.30-0.50%, Nb: 0.01-0.05%, Al: 0.001-0.100%, B: 0.0005-0.0020%, Ti: 0.003 to 0.050%, V: 0.01-0.20%, Total amount of one or more of Ca, Mg, and REM: 0-0.0250%, The remainder consists of Fe and impurities. The value of Pcm expressed by the following formula [A] is 0.30 or less, The tensile strength is 980 MPa or more. The wall thickness T at the central position in the longitudinal direction of the seamless steel pipe. Ｍ It is 10 mm or less, The pair of pipe ends have a thickened portion on at least one end, The thickness T of the thickened portion at one end. Ｅ１ However, the wall thickness T at the central position in the longitudinal direction of the seamless steel pipe. Ｍ In relation to the above, the following equation (i) is satisfied, Length L in the longitudinal direction of the thickened portion at one end Ｅ１ However, the outer diameter OD at the central position in the longitudinal direction of the seamless steel pipe Ｍ In relation to the above, the following equation (ii) is satisfied, The outer diameter OD E1 of the thickened portion at one end satisfies the following equation (iii) in relation to the outer diameter OD M at the central position in the longitudinal direction of the seamless steel pipe: Seamless steel pipe. Pcm=C+(Si / 30)+(Mn / 20)+(Cu / 20)+(Ni / 60)+(Cr / 20)+(Mo / 15)+(V / 10)+5B...[A] However, the element symbols in formula [A] represent the mass percentage content of each element in the steel, and zero is used if an element is not present. 1.20×T Ｍ ≦T Ｅ１ ・・・(i) 1.50×OD Ｍ ≦L Ｅ１ ・・・(ii) 0.99×OD M ≦OD E1 ≦1.01×OD M ... (iii)

2. The other end of the pair of pipe ends has a thickened section, The thickness T of the thickened portion on the other end side. Ｅ２ However, the wall thickness T at the central position in the longitudinal direction of the seamless steel pipe. Ｍ In relation to the above, the following equation (iv) is satisfied, and Length L in the longitudinal direction of the thickened portion on the other end Ｅ２ However, the outer diameter OD at the central position in the longitudinal direction of the seamless steel pipe Ｍ In relation to the above, the following equation (v) is satisfied, A seamless steel pipe as described in claim 1. 1.20×T Ｍ ≦T Ｅ２ ・・・(iv) 1.50×OD Ｍ ≦L Ｅ２ ・・・(v)

3. Outer diameter OD of the thickened portion on the other end Ｅ２ However, the outer diameter OD at the central position in the longitudinal direction of the seamless steel pipe Ｍ In relation to the above, the following equation (vi) is satisfied: The seamless steel pipe according to claim 2. 0.99×OD Ｍ ≦OD Ｅ２ ≦1.01×OD Ｍ ···(we)

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