PURPOSE: To restrain the development of scale, to prevent the deterioration of mechanical property and to improve the quality by controlling speed to prevent the absorption of hydrogen and the precipitation of σ phase, at the time of executing heat treatment in hydrogen atmosphere.

CONSTITUTION: A two-phase stainless steel pipe 5 is carried from the neighborhood of outlet of a heating zone 1 in connecting type hydrogen atmospheric furnace to a part coming to a connecting part 2 for connecting the heating zone 1 to a cooling zone 3. Then, the carrying speed is raised so that the cooling speed of the two-phase stainless steel pipe following advancing to the atmosphere of a phase precipitating temp. zone (500-950°C) exceeds the σ phase precipitating cooling speed zone. Successively, after the steel pipe 5 advances to the cooling zone 3, the steel pipe is rapidly cooled to the end of the σ phase precipitating temp. zone by the speed exceeding the σ phase precipitating cooling speed zone. Further, by keeping in a zone of 200°C to a phase precipitation temp. for ≥5min, hydrogen absorbed in the steel pipe 5 is moved.