Steel tube excellent in exfoliation resistance of scale on inner surface

摘要

A steel tube excellent in exfoliation resistance of scale on its inner surface is provided. The steel tube includes 9 to 28% by mass of Cr and has a maximum height of profile (Rz) on the inner surface after cold working of 15 mum or more. Preferably DeltaHv of the tube is 100 or more, wherein DeltaHv is the difference in Vickers hardness between an inner surface layer and a thickness center part of the tube. The steel may desirably have a microstructure of ASTM austenite grain size No. 7 . or more.