Process for producing seamless steel pipe

摘要

A process for producing a seamless steel pipe, in which the occurrence of inner surface flaws in the pipe can be reduced through the lowering of the friction coefficient during the elongation rolling by means of a mandrel mill is provided. The reduction of inner surface flaws is accomplished through the use of a lubricant composed mainly of either or both of graphite and mica coated to the surface of a mandrel bar, and another lubricant composed mainly of an alkali metal borate that is applied onto the inner surface of the hollow stock pipe. The temperature of the pipe prior to receiving the lubricant, during lubricant application, and prior to elongation rolling is controlled. The time between descaling or piercing and lubricant application and between lubricant application and elongation rolling is also controlled.