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Measurement of Induction-Hardening Depth

  • Masahiko Hirao
  • Hirotsugu Ogi

Abstract

Induction hardening is one of the classical surface-modification methods for steel products such as shafts and gears. The surface is heated using a high-frequency AC current up to the austenitic phase (fcc) and then quenched. Phase transformation (fcc to bct) produces a case of hardened metal and compressive residual stress, both of which enhance tolerance for fatigue, wear, and corrosion during service. There are currently two techniques for case-depth testing. One is direct measurement of hardness on the cross-section, but it is destructive. The other detects the ultrasonic-backscattering signals from the grain-structure change in the steel parts, which is less laborious and nondestructive (Good, 1984; Fujisawa and Nakanishi, 1989). Because the core metal has larger grains, the core-to-case interface produces a backscattering echo, whose arrival time relative to the front-surface echo gives the case thickness in an A-scope display. It, however, requires the parts to be immersed in a water tank for acoustic coupling, making on-line inspection inapplicable. Another shortcoming is that the dominant front echo masks the signal from a shallow interface and this technique fails for a thin surface layer.

Keywords

Rayleigh Wave Compressive Residual Stress Thin Surface Layer Case Depth Acoustic Coupling 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 2003

Authors and Affiliations

  • Masahiko Hirao
    • 1
  • Hirotsugu Ogi
    • 1
  1. 1.Osaka UniversityJapan

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