COOLING METHOD FOR STEEL PIPE

摘要

PURPOSE:To assure desired mechanical properties and metal structure without generating quenching cracks by making combination use of annular outside surface cooling headers and bar-shaped inside surface cooling headers to cool a steel pipe so that the prescribed cooling rate pattern and the max. value of transient thermal stress are assured. CONSTITUTION:The steel pipe 2 emitted from a heating furnace 1 is moved by conveying rollers 4 and is passed between the annular outside surface cooling headers 51-58 and the bar-shaped inside surface cooling headers 15, by which the steel pipe is cooled. The inside surface cooling headers 15 are preliminarily shifted in an adequate moving direction from the outside surface cooling header 51 by a driving device 16. Force cooling nozzles are used for misting nozzles to maintain an air-water ratio at about 5-10. The respective cooling capacities are so set in this constitution as to assure the cooling rate pattern satisfying the temp. history during cooling intrinsic to the kind of the steel to be heated necessary for assuring the mechanical properties and metal structure required for the steel pipe 2 after the cooling over the entire wall thickness direction of the steel pipe and the max. value of the transient thermal stress near the inside and outside surfaces to prevent generation of the quenching cracks during the progression of martensite transformation near the inside and outside surfaces of the steel pipe 2 under cooling.