MANDREL BAR FOR HOT MANUFACTURING SEAMLESS TUBE AND HOT MANUFACTURING METHOD OF SEAMLESS TUBE

摘要

PROBLEM TO BE SOLVED: To obtain a mandrel bar having longer life without generating burning even when the bar is used for rolling high alloy steel containing chromium by forming a chromium plating film in the range of the specific thickness on the mandrel bar.;SOLUTION: The chromium plating film of 60-200 μm thick is formed on the surface of a base metal of the mandrel bar. The major cause of generation of burning is peeling of the chromium plating by heat cracks and a lot of burnings are generated in parts where the base metal of the bar is exposed by the elimination of the chromium plating film by wear, so it is necessary to thicken the chromium plating film and, when the thickness is 60-200 μm, the life is rapidly improved. The surface roughness Ra in the direction of the axial length of the base metal is defined as ≥0.1 to 4 μm. Tool steel for hot working is preferable as the base stock of the mandrel bar. Even when the bar is used 100 passes or more in rolling the high alloy steel containing ≥2 wt.% Cr in rolling with a mandrel mill, burning is not generated.;COPYRIGHT: (C)2001,JPO