Patent ID: 9267186
Filing Date: 2016-02-23
CPC Classification: C21D

Claim Text:
1. A method for quenching a steel pipe, in which a heated steel pipe is immersed in a water bath with an axis thereof being kept in parallel with water surface to primarily cool an outer surface of the steel pipe, and a water flow from one end of the steel pipe to the other end thereof is generated in an axial portion of the steel pipe by injecting cooling water from an axial center nozzle to primarily cool an inner surface of the steel pipe, so that an entire surface of the steel pipe is rapidly cooled, the method for quenching a steel pipe comprising: moving the axial center nozzle following the motion of the axis of the steel pipe, and when the injection of cooling water is started from the axial center nozzle while the steel pipe is being immersed in the water bath, starting the injection of cooling water such that the cooling water injected into one end of the steel pipe at the start of the injection arrives at the other end just at the time that an entire circumference of the outer surface of the steel pipe is immersed.