PRODUCTION OF ELECTRIC WELDED OIL WELL STEEL PIPE HAVING HIGH STRENGTH AND EXCELLENT RESISTANCE TO SOURING AND CRUSHING

摘要

PURPOSE:To obtain an electric welded oil well steel pipe having high strength and excellent resistance to souring and crushing by hot-rolling a steel sheet at a low temp. then cooling quickly the sheet, coiling the same at a low temp. to increase plastic strain, forming the sheet into a pipe and subjecting the pipe to a heat treatment at a low temp. for short time. CONSTITUTION:Hot rolling is accomplished at a low temp. of 740-830 deg.C to form finer crystal grains. The hot rolled sheet is quickly cooled at an average cooling rate of 15 deg.C/sec and is coiled at <=500 deg.C to preserve stably solid soln. carbon and solid soln. nitrogen. An electric welded steel pipe is formed under strong rolling down to attain >=3% longitudinal strain so that a large number of dislocation is introduced. The pipe is thereafter heated to 100-450 deg.C and is held for 30sec- 30min to fix the solid soln. nitrogen and solid soln. carbon to the introduced dislocation. The electric welded oil well steel pipe having high crushing strength and excellent resistance to souring is obtd. by the above-mentioned method.