To obtain a bifurcate tube having high dimensional precision without developing cavity defect in a short manufacturing term by executing a hot hydrostatic pressing after casting a cast steel material by a lost wax precision casting method.
The hot hydrostatic pressing treatment for giving the hydrostatic pressing at 1100-1200°C and 1000-1500 atm. pressure for 2-5 hr with argon gas, etc., is executed and the cavity defect existing in the inner part of the precision cast steel product is pressed and eliminated. By this method, the bifurcate tube 1 having sound quality and material characteristic, is obtd. In the bifurcate tube 1, a boiler characteristic is improved by improving the dimensional precision and the balance of steam distribution, etc., and also, the reliability is improved by improving the uniformity of the thickness. Further, the manufacturing cost can be reduced and machining finish is scarcely necessary and the manufacturing term can be shortened. To flattening test, expanding test, creep-rupture strength, low cycle fatigue strength and flaw detecting test, etc., this bifurcate tube is used without causing any trouble.
KOGA KATSUHIRO
HAGIWARA SHIKAO
WATANABE KIYOSHI
FUJIMOTO SHIGEHISA
KAYUKAWA YOSHIHITO
