電磁超音波による熱間鋼材内部欠陥探傷の可能性検討

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This paper reports the results of feasibility test on detection of inner defects of hot steel using electro-magnetic ultrasonic transducer.Experimental electro-magnetic ultrasonic transducer has been manufactured and basic characteristics were investigated. The transmission ability of transmitter which consists of transmission coil, high voltage power supply and discharge gap, was about equal to piezoelectric transducer, and the receiving ability of receiver, which consists of magnetic circuit, receiving coil and receiving circuit, was 46dB less than piezo-electric transducer.Artificial defect detection test in hot condition (1, 000°C) was done by this transducer and experimental furnace. Consequently, defect echo of flat bottom hole with 5.6mm diameter and 90mm depth was obtained in the case of SUS 304 steel, but even bottom echo was not obtained in the case of S 25 C steel.By these results and study of relation between grain size of steel and ultrasonic attenuation, the conclusion was drawn out that even in hot condition, the defects corresponding to horizontal hole with 2mm diameter can be detected, if the tested steel is rolled and has average grain size less than about 0.12mm.
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