| 摘要 |
PURPOSE:To improve the ultrasonic flaw detectability of a cast steel product and to make possible the inspection of the material for defect during use by casting the tubular end of said product to a projecting polygonal shape, elliptical shape, etc., and pressurizing the projecting part to deform plastically said part to a circular shape having a prescribed size then subjecting the product to a heat treatment for recrystallization. CONSTITUTION:A valve part 1 is cast of an austenitic stainless steel of a 2-phase type having a ferite phase. The end 6 to be welded to the other part is preliminarily cast to a square shape. Such part is grasped by a pair of dies 7 and 7 and is subjected repeatedly to pressurization with a press so that the part is bent and deformed over the entire circumference by the force 8 in the diametral direction to deform plastically the part to the circular section having the prescribed size. The par is thereafter subjected to heating to >=1,000 deg.C recrystallization temp. which serves also as a soln. heat treatment. The heated part is quickly cooled. The finer crystal grains of the structure are formed and the ultrasonic flaw detectability is improved.
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