METHOD OF PRODUCING COLD-DRAWN STEEL TUBE

摘要

PROBLEM TO BE SOLVED: To provide a method of producing a cold-drawn steel tube which causes no annealing residual dross even when cold drawing is applied to the tube using lubricating oil, and thereafter, low temperature annealing is performed inside a reducing furnace, and which has excellent surface properties. SOLUTION: The method of producing a cold-drawn steel tube consists of the following stages (1) to (4): (1) a tube stock is dipped into an aqueous solution comprising the alkali metal salt of boric acid or/and the alkali metal salt of phosphoric acid to form a film of the metal salts on the inside and outside faces of the tube stock; (2) the surface of the film is coated with lubricating oil having an S content of≤3 mass% and a viscosity of 4×10-4to 10-3m2/s (400 to 1,000 cSt); (3) cold drawing is performed; and (4) heat treatment is performed at≤650°C while feeding a CO-containing gas of≥0.5 times the furnace volume per hr inside the furnace. COPYRIGHT: (C)2004,JPO