Apparatus row for seamless steel pipe production and method for producing high-strength stainless steel seamless steel pipe for oil wells using the same

摘要

Provided is an equipment line for manufacturing a seamless steel tube and a method of manufacturing a heavy-walled high-strength stainless seamless steel tube for oil wells having excellent low-temperature toughness using the equipment line. In the equipment line where a heating device, a piercing device and a rolling mill are arranged, a cooling system is further arranged between the heating device and the piercing device or between the piercing device and the rolling mill. A thermostat may be arranged on an exit side of the rolling mill. Using the equipment line, a heated steel having a stainless steel chemical composition or a hollow steel tube formed by piercing the heated steel is cooled by accelerated cooling to a cooling stop temperature of 600°C or above at an average cooling rate of 1.0°C/s or more thus allowing the hollow steel tube to have a phase distribution in a non-equilibrium state and, immediately thereafter, the hollow steel tube is formed into a seamless tube having a predetermined size. Accordingly, the microstructure can become extremely fine even when a hot working amount is small so that the heavy-walled steel tube can ensure excellent low-temperature toughness even at the wall thickness center portion whereby a heavy-walled high-strength stainless seamless steel tube having excellent low-temperature toughness can be manufactured easily at a low cost.