Steel components were carburized in an industrial facility. Measurements with four independent electromagnetic test methods
were made at the components in order to test the depth of the carburized layer (case depth). The four methods have different
penetration depth and sensitivity to material properties. Models to predict the case depth were built based on multiple
regression methods. It could be shown that the testing accuracy could be significantly improved by using a combination of
test methods. The reason was that a thin, decarburized layer prevented the accurate measurement by a single method. The distorting
effect of the decarburized layer could be corrected by combining a method with deep penetration depth with a method
that has only a shallow penetration depth.
1. ASM International, ASM Handbook Vol. 4: “Heat Treating” ASM International, Materials Park, Ohio, 1991, p. 461.
2. Sun, H., J.R. Bowler, N. Bowler and M.J. Johnson, “Eddy Current Measurements on Case Hardened Steel,” Review of
Progress in Quantitative Nondestructive Evaluation, Vol 21, D.O. Thompson and D.E. Chimenti, eds., AIP Conference
Proceedings, Vol. 615, 2002, pp. 1561-1568.
3. Lo, C.C.H., E.R. Kinser, Y. Melikhov and D.C. Jiles, “Magnetic Nondestructive Characterization of Case Depth in Surface-
Hardened Steel Components,” Review of Progress in Quantitative Nondestructive Evaluation 25B, D.O. Thompson
and D.E. Chimenti eds., AIP Conference Proceedings, Vol. 820, 2006, pp. 1253–1260.
4. Zhang, C., N. Bowler and C. Lo, “Magnetic Characterization of Surface-Hardened Steel,” Journal of Magnetism and
Magnetic Materials, 321(23), 2009, pp. 3878-3887.
5. Moorthy, V., B.A. Shaw and K. Brimble, “Testing of Case Depth in Case Carburized Gear Steels Using Magnetic
Barkhausen Emission Technique,” Materials Evaluation, 62, 2004, pp. 523–527.
6 Bach, G., K. Goebbels and W.A. Theiner, “Characterization of Hardening Depth by Barkhausen Noise Measurement,”
Materials Evaluation, Volume 46, November 1988, pp. 1576-1580.
7. Wang, C.H. and A. Mandelis, “Case Depth Determination in Heat Treated Steel Products Using Photothermal Radiometric
Interferometric Phase Minima,” NDT&E 40, 2007, pp. 158-167.
8. Chenni, B. and J. Pouliquen, “Non-Destructive Evaluation of Gradient Properties of Hardened Steel by Surface Acoustic
Waves Measurements,” Review of Progress in Quantitative Nondestructive Evaluation, Vol 21, D.O. Thompson and D.E.
Chimenti, eds., AIP Conference Proceedings, Vol. 615, 2002, pp. 1629-1636.
9. http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/depthcurrentdensity.htm.