JPS56148053A - Flaw detection for eddy flow in hot steel - Google Patents

Abstract

PURPOSE:To obtain a stable flaw detection means by a method inwhich corner section of a test material and the area around there is heated nearly up to the Cury point of the material and the corner section is magnetically saturated. CONSTITUTION:An exciting coil 3 is wound on a core 4, on which a test sample is put and is magnetized with D.C. source. There is, then, arranged a probe coil 2 for flaw detection around the intermediate point between the both magnetic poles of the core 4. By means of using such a device, it is conducted comparison between two cases: one is the sample being magnetized and the other is the same is being nonmagnetized. In the case of being magnetized, the phase angle induced from flaw signal varies nearly only within 5 deg.-10 deg. for the temperature variation range of 500- 900 deg.C and the variation of output level of flaw signal remains only within 5%. Against such a degree, however, in the other case of nonmagnetized, the both of phase angle and output vary in large scale nonlinearly at discontinuous boundary point being nearly close to 750 deg.C. There is found also the variation of phase angle of about 60 deg. for the temperature difference between less than or equal to 750 deg.C and more than or equal to 800 deg.C and still further the output level for about 750 deg.C or more than that is remarkably unstable.