Improvement of ultrasonic flaw detectability for austenitic stainless steel casting using local forging technique

In spite of the wide application of stainless steel cast valves in nuclear plants, their metallurgical conditions do not allow ultrasonic examination (UT) to be applied, because of the strong signal attenuation associated with the large grain sizes of the valves. For the enhanced reliability of nuclear power plants, however, UT inspectability of such components is imperative. Thus, the authors have investigated flaw detectability of a cast steel valve body at its inlet/outlet weld connections by means of localized forging on the base metal. It has been found that a localized, plastic, cold working with less than 10% of its original thickness, followed by a solution heat treatment, reduces grain sizes such that; the ultrasonic attenuation coefficient of the base metal is small enough to permit UTs of the welds. This paper reports flaw detection and flaw sizing data obtained by using longitudinal wave angle beam UT detection for fatigue cracks in the weld, at locally forged austenitic casting speciments. (author)