To provide a manufacturing method of a seamless steel tube by a mandrel mill tube-making line by which the generation of carburized layer on the inside surface is prevented even when a mandrel bar to which graphite is stuck is used and seamless alloy steel tube excellent in corrosion resistance which is manufactured by this method.
At the time of manufacturing the seamless steel tube of alloy steel containing, by weight, ≤0.10% C and 4-30% Cr using a non-graphitic lubricant by the mandrel mill tube-making line, the amount of adherence of graphite on the surface of the mandrel bar is controlled to ≤100 mg/m2. In this way, the product tube in which the amount ΔC of carburization in the position 100 μm apart in the thickness direction from the inside surface of the tube is not more than 3 times the carbon content of a base material and which is excellent in corrosion resistance is obtained.
ABE TOSHIHARU
IIDA SUMIO
