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ELECTROMAGNETIC INSPECTION OF HARDENED STEEL.
FRANKFORD ARSENAL PHILADELPHIA PA FIRE CONTROL DEVELOPMENT AND ENGINEERING LABS
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A program was undertaken to investigate the use of eddy current test techniques for 1 The measurement of case depth on steel parts processed by heat treat methods no carbon added to the surface, and 2 The determination of through hardness or tempering temperature history of Stentor tool steel and 4340 steel parts. Eddy current tests showed that the relationship of case depth to eddy current output had insignificant correlation. The effects of case depth variation appeared to be obscured by the effects of other material variations such as hardness and grain structure. The effectiveness of phase sensitive and harmonic eddy current test methods for determining tempering temperature history of 4340 and Stentor tool steels was evaluated by performing numerous tests on specially prepared specimens. Eddy current tests utilizing third harmonics of the probe energizing frequency showed that tempering temperature history of 4340 and Stentor steel can be determined for all temperatures 265 F to 820 F used for specimen preparation on this program.
APPROVED FOR PUBLIC RELEASE