Size Estimation of Sulfide Inclusions in Hot Rolled Steels Detected by Ultrasonic Testing

Abstract

It is feared that non-metallic inclusion will impair ductility and toughness in through thickness direction of rolled steels. In beam-column joints of steel frame of building, the stress occurs in through thickness direction of steel plate. Therefore, the size estimation of inclusion in rolled steels used in actual structure is necessary to maintain the performance of joints.
This paper describes ultrasonic inspection methods for estimating the size of non-metallic inclusion.
The two kinds of ultrasonic inspection methods were examined and the abilities for measurement were discussed.
The following results were obtained.
(1) The "C-scope method" with an immersion focusing type probe is effective for inspecting the shape and size of flat form defects such as leaf type inclusion around focusing point. But, this method is difficult to apply in actual structure.
(2) The "Acrylic resin delayed method" with AVG diagram is applicable to inspection of rolled steel in actual structure. This method, however, tends to underestimate the area of defects comprised of non-metallic inclusion. This paper proposes equations for estimating the size of inclusion based on the sound field of the probe and the reflection loss on the interface between inclusion and steel matrix.