METHOD TO TEMPER STEEL PIPE Russian patent published in 2015 - IPC C21D9/08 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of thermal treatment. To prevent the formation of tempering cracks in a steel pipe, a pipe (1) from medium- or high-carbon steel or from martensite stainless steel is tempered, including heating of the steel pipe material to a temperature above A_c3, cooling by means of water cooling from the external surface of the steel pipe, besides, end sections of the steel pipe are exposed to air cooling, and at least a part of the main body, which is not an end section of the pipe, is exposed to water cooling, providing for the martensite content in the steel pipe material, excluding the end sections, in the amount of 80 vol. % or higher. In the axial direction at least in the part of the main body that differs from the end sections of the pipe there is an area or areas, which are not exposed to direct water cooling along their entire perimeter, start and stop of water cooling are periodically repeated at least in a part of the tempering process. Intensified water cooling of the external pipe surface is carried out to a temperature above the Ms point, afterwards moderate water cooling or air cooling of the external surface is carried out by means of switching, and then intense cooling of the steel pipe external surface is carried out down to a temperature of Ms point or below.

EFFECT: prevention of tempering cracks.

10 cl, 11 dwg, 3 tbl