Direct Quenching Process in Seamless Tube Manufacturing

Abstract

Direct quenching in a seamless tube production mill contributes to a considerable amount of energy saving because a high proportion of the seamless tubes is heat treated. Moreover, it contributes to an improvement of mechanical properties of tubes due to a high hardenability of direct quenching. For its application to a production mill, the most important point is to secure enough temperature of tubes at the quenching zone and to develop a suitable cooling method for on-line quenching. This report refers to temperature evaluation of tubes throughout the rolling process by a theoretical model and also refers to the development of new quenching facilities installed in a new mill. In order to secure high temperature at the end of the rolling train, special rolling processes, such as bar retract operation system in 3-roll transval mill and tandem arrangement of retained mandrel mill with sizing mill, are adopted for the new mill. Those special processes enable the direct quenching even without any reheating furnace. In the processes the uniform and non-deformation cooling system of a long tube up to 29m is accomplished by the rotation of the tube with rapid longitudinal jet flow inside and the curtain wall laminar flow along the outer surface of the tube.