| 摘要 |
PURPOSE:To produce a normalized type steel plate of API, K-55 class for oil wells by not rolling a specifically composed steel material contg. a slight amt. of Ti to a plate material, forming the plate material to a pipe shape, welding the edges to a steel pipe and further normalizing the steel pipe. CONSTITUTION:A steel slab contg. 0.29-0.33% C, 0.20-0.30% Si, 1.40-1.60% Mn, <0.025% P, <0.010% S, 0.010-0.035% T.Al, 0.10-0.30% Cr, 0.0007- 0.0020% B, 0.010-0.030% Ti and <0.0060% N is hot rolled to a steel plate at 850-920 deg.C finish temp. and 700-800 deg.C coiling temp. The steel plate is formed to a tubular shape and the edges are heated and welded to manufacture a steel pipe. The electric welded steel pipe is normalized by heating for 5-10min at 750-950 deg.C. Ti having higher affinity to N than B is incorporated into the steel to prevent slab cracking by N and the normalized type steel pipe of API, K-55 class for oil wells is produced. |
