Patent ID: 8784581

Claim:
A method for manufacturing an Fe—Ni alloy pipe stock, comprising piercing and rolling a billet by use of a Mannesmann piercing and rolling mill, wherein the billet comprises, 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: 20 to 30%, Ni: 30 to 45%, Mo: 0 to 10%, W: 0 to 20%, with Mo(%)+0.5W(%): more than 1.5% to not more than 10%, Cu: 0.01 to 1.5%, Al: not more than 0.10% and N: 0.0005 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 less than 1300, not more than 120 and not less than 0, respectively, wherein: T GBm =1440−6000P−100S−2000C (1), P sr =Ni+10(Mo+0.5W)+100N (2), P σ =(Ni−35)+10(N−0.1)−2(Cr−25)−5(Mo+0.5W−3)+8 (3), and further wherein each element symbol in the equations (1) to (3) represents the content by mass % of the element concerned, 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 1: 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.