PURPOSE: To obtain an electroseamed steel pipe having composite characteristics excellent in a low yield ratio, low temp. toughness and sour resistance, by heating the whole of the electroseamed steel pipe before hardening.
CONSTITUTION: The electroseamed steel pipe formed by appling electroseaming welding to strip steel molded into a pipe size by roll molding is heated to a temp. ≥800°C to be brought to an austenite state with A3-transformation point or more and, thereafter, the heated steel pipe is hardened so as not to issue the memory of steel to obtain a fine uniform structure. By this method, an electroseamed steel pipe having composite characteristics excellent in a low yield ratio, low temp. toughness and sour resistance is obtained.
CHIYANO ZENSAKU
YAMAMOTO YASUSHI
YAMAMOTO YOUJI
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