Method for manufacturing Ni base alloy pipe stock

1. A method for manufacturing an Ni base alloy pipe stock, comprising piercing and rolling a billet, by use of a Mannesmann piercing and rolling mill, which satisfies the chemical compositions consisting of, by mass %, C: not more than 0.04%, Si: not more than 0.50%, Mn: 0.01 to 6.0%, P: not more than 0.03%, S: not more than 0.01%, Cr: 15 to 30%, Ni: more than 45% to not more than 60%, Mo: 0 to 18%, W: 0 to 36%, with Mo (%)+0.5W (%): more than 1.5% to not more than 18%, Cu: 0.01 to 1.5%, Al: not more than 0.10% and N: 0.005 to 0.20%, and the balance being substantially Fe, with values of T GBm , P sr and P σ represented by the following equations (1) to (3) being not more than 1300, not more than 200 and not less than 0, respectively, and moreover being subjected to piercing and rolling by a Mannesmann piercing and rolling mill:

T GBm =1380−5000P−100S−4400C  (1),

P sr Ni+10(Mo+0.5W)+100N  (2),

P σ =(Ni−50)+10(N−0.1)−2(Cr−25)−5(Mo+0.5W−6)+12  (3),

wherein each element symbol in the equations (1) to (3) represents the content by mass % of the element concerned.

2. The method for manufacturing an Ni base alloy pipe stock according to claim 1 , wherein the piercing and rolling by the Mannesmann piercing and rolling mill is performed in a condition where the value of fn represented by the following equation (4) is not more than 0.3:

fn ={P/(0.025H−0.01)} 2 +{S/(0.015H−0.01)} 2   (4),

wherein P and S represent contents, by mass %, of P and S in the pipe stock, respectively, and H represents the pipe expansion ratio represented by the ratio of the outer diameter of the pipe stock to the diameter of the steel stock billet.

3. A method for manufacturing an Ni base alloy pipe stock, comprising piercing and rolling a billet, by use of a Mannesmann piercing and rolling mill, which satisfies the chemical compositions consisting essentially of, by mass %, C: not more than 0.04%, Si: not more than 0.50%, Mn: 0.01 to 6.0%, P: not more than 0.03%, S: not more than 0.01%, Cr: 15 to 30%, Ni: more than 45% to not more than 60%, Mo: 0 to 18%, W: 0 to 36%, with Mo (%)+0.5W (%): more than 1.5% to not more than 18%, Cu: 0.01 to 1.5%, Al: not more than 0.10% and N: 0.005 to 0.20%, and the balance being substantially Fe, with values of T GBm , P sr and P σ represented by the following equations (1) to (3) being not more than 1300, not more than 200 and not less than 0, respectively, and moreover being subjected to piercing and rolling by a Mannesmann piercing and rolling mill:

T GBm =1380−5000P−100S−4400C  (1),

P sr Ni+10(Mo+0.5W)+100N  (2),

P σ =(Ni−50)+10(N−0.1)−2(Cr−25)−5(Mo+0.5W−6)+12  (3),

wherein each element symbol in the equations (1) to (3) represents the content by mass % of the element concerned, and

which further consists essentially of an element or elements of one or more groups selected from the groups (a) to (d) listed below in lieu of part of Fe:

(a): one or more selected from among V: 0.001 to 0.3%, Nb: 0.001 to 0.3%, Ta: 0.001 to 1.0%, Ti: 0.001 to 1.0%, Zr: 0.001 to 1.0% and Hf: 0.001 to 1.0% by mass %;

(b): B: 0.0001 to 0.015% by mass %;

(c): Co: 0.3 to 5.0% by mass %;

(d): one or more selected from among Mg: 0.0001 to 0.010%, Ca: 0.0001 to 0.010%, La: 0.0001 to 0.20%, Ce: 0.0001 to 0.20%, Y: 0.0001 to 0.40%, Sm: 0.0001 to 0.40%, Pr: 0.0001 to 0.40% and Nd: 0.0001 to 0.50% by mass %.

4. The method for manufacturing an Ni base alloy pipe stock according to claim 3 , wherein the piercing and rolling by the Mannesmann piercing and rolling mill is performed in a condition where the value of fn represented by the following equation (4) is not more than 0.3:

fn ={P/(0.025H−0.01)} 2 +{S/(0.015H−0.01)} 2   (4),

wherein P and S represent contents, by mass %, of P and S in the pipe stock, respectively, and H represents the pipe expansion ratio represented by the ratio of the outer diameter of the pipe stock to the diameter of the steel stock billet.