| 摘要 |
PROBLEM TO BE SOLVED: To manufacture the welded steel tube excellent in corrosion without preheating or postheating by respectively containing C, Si, Mn, Cr, Ni, Al and N in a steel strip by the prescribed quantity. SOLUTION: The steel strip having the composition consisting of, by mass %, <=0.02% C, <=0.5% Si, 0.3-3.0% Mn, 10-14% Cr, 0.1-7.0% Ni, <=0.1% Al, and <=0.03% N, >=10.5 in the value of (%Cr)+0.2(%Ni)-7(%C)-5(%N), <=4.0 in the value of 150(%C)+100(%N), and the balance Fe with inevitable impurities, is formed in an open tubular shape, and end parts opposite to each other are laser beam welded to form a steel tube. In brief the steel strip contains one or more kinds of <=3.0% Mo, <=2.0% Cu, <=0.15% Nb, <=0.15% Ti, <=0.15% Zr, <=0.25% V, <=0.15% Ta, and 0.006% Ca. Welding is preferably performed so that the mean cooling speed of the welded part down to 500 deg.C after welding is >=150 deg.C/second. |
