PROCESS FOR PRODUCING SEAMLESS STEEL PIPE

摘要

This invention provides a process for producing a seamless steel pipe that can produce a seamless steel pipe while effectively suppressing a failure of a mandrel bar to be withdrawn after stretch-rolling of a rolling material formed of a high alloy steel containing not less than 5% of Cr. In the production process, a seamless steel pipe comprising a high alloy steel containing not less than 5% of Cr is produced by stretch-rolling a rolling material (3) using a retained mandrel mill (1) for maintaining the speed of a mandrel bar (2) in an axial direction at a constant value while regulating the movement speed of the mandrel bar (2) by the retained mandrel mill (1) so as to satisfy a requirement represented by formula 0.15 = Vb/{(Vi + Ve)/2} = 0.70 wherein Vb represents the movement speed of the mandrel bar (2); Vi represents the speed of the rolling material (3) on the inlet side of the retained mandrel mill (1); and Ve represents the speed of the rolling material (3) on the outlet side of the retained mandrel mill (1).