Material characterization of cast irons with an EMAT/EC dual probe

Abstract

Mechanical properties of cast irons strongly depend on the graphite morphology and the matrix structure, thus both of them should be evaluated for their characterization. The former can be evaluated by ultrasonic testing (UT), and the latter can be evaluated by eddy current testing (ECT). Considering the background above, this study proposes a novel method for the material characterization of cast irons with an EMAT/EC dual probe. For this purpose, we conducted UT and ECT for cast irons with different graphite morphology and matrix structures with the present probe. As a result, correlations betwe en the nodularity of graphite and ultrasonic velocity, and between one the pearlite ratio and EC signals were obtained. These results imply that the EMAT/EC dual probe is effective for the material characterization of cast irons. Cast iron is an Fe-C base alloy that contains iron as the princ ipal ingredient and carbon more than 2%. It is useful engineering material due to its excellent mecha nical properties, such as strength, ductility, free cutting, and productivity. Accordingly, it is widely used f or the parts of automobiles, industrial machinery and so forth. However, the manufacturing process of casting is complex, and the microstructure control is difficult. Therefore, nondestructive characterization of mechanical properties of cast irons is necessary and one of key issues in the foundry industry. The structure of cast irons consists of graphite and a steel matrix. Mechanical properties of cast irons depend on the graphite morphology and the matrix structure, thus both of them should be evaluated for their characterization. The nodularity of cast irons is estimated by measuring the ultrasonic velocity, and the method is established (1). The matrix structure and hardness of cast iron are estimated by measuring the EC signals of ductile cast irons (2). Therefore, the graphite morphology and matrix structure can be evaluated by ultrasonic testing (UT) and eddy current testing (ECT), respectively. We have proposed an EMAT/EC dual probe (3) that can obtain ultrasonic and EC signals with a single probe structure. This probe was applied to the evaluation of wall thinning of pipes, and the feasibility of the nondestructive evaluation based on the complementarity between ECT and UT was verified. This paper proposes a new method for the material characterization of cast irons with an EMAT/EC dual probe. The material properties of cast irons are not uniform and should be characterized with respect to each point. The dual probe with a single and compact structure can acquire UT and EC signals