Journal
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS
Volume 16, Issue 5, Pages 1015-1019Publisher
UNIV FED SAO CARLOS, DEPT ENGENHARIA MATERIALS
DOI: 10.1590/S1516-14392013005000095
Keywords
case depth; SAE 1020 steel; Barkhausen noise; frequency spectrum
Categories
Funding
- SCIT/RS
- FAPERGS
- CNPq
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The most widely used thermochemical process for surface hardening of steels is case hardening. Using several different heat treatments, martensitic surface layers were formed on SAE 1020 steel into which carbon had been diffused. Case depths were measured by traditional destructive techniques. Barkhausen noise measurements were made and both the RMS Barkhausen pulse envelope and the fast Fourier transform (FFT) were obtained from numerical calculation. The FFT amplitudes, functions of frequency, were associated with distance from the sample surface using the skin depth equation delta = 1/(pi f sigma mu)(1/2), where f is the frequency of the electromagnetic wave, sigma is the electrical conductivity, and mu is the magnetic permeability. We define a normalized power index (NPI) which can be used to estimate case depths. The NPI is discussed in relation to the sample microstructure and it is shown that the case depth is most easily determined when the magnetic properties of the surface layer and core are substantially different.
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