| 摘要 |
PURPOSE:To produce a high strength electric welded steel pipe of a normalizing type having a high yield point and excellent homogeneity for an oil well by producing the electric welded steel pipe of a steel plate consisting of a steel material contg. a specific amt. of V, Al and N in combination and subjecting said pipe to a specific heat treatment. CONSTITUTION:A steel material contg. 0.25-0.40% C, 0.05-0.50% Si, 1.20- 1.80% Mn, 0.0005-0.035% P, 0.0003-0.025% S, 0.010-0.20% V, 0.005-0.074% Al, 0.0050-0.0170% Ni, or further a specific small amt. of Mo, Nb, Ti, B and Ca alone or in combination and having the concn. of solid soln. Al and N in the range enclosed of A'B'C'D shown in the figure 1 at the above-mentioned content of V is hot rolled to a steel plate at a finishing temp. of >=760 deg.C and is coiled at 440-750 deg.C by which a hot coil is produced. An electric welded steel pipe is manufactured of such steel plate and is subjected to normalizing by heating at Ac3-1,050 deg.C and holding for <=30min and is in successively cooled at a cooling rate of air cooling or above and the limit for generating martensite or below. |
