Case depth in SAE 1020 steel using barkhausen noise

Abstract

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 equation½ , where f is the frequency of the electromagnetic wave, s is the electrical conductivity, and μ 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.

Use of Time-Frequency Representation of Magnetic Barkhausen Noise for Evaluation of Easy Magnetization Axis of Grain-Oriented Steel

“…Those changes in the magnetic flux can be observed by a coil located at the surface of the material, in the form of voltage noise induced in its turn as a result of rapid changes in the degree of magnetization [ 4 ]. This method is used for various industrial applications for non-destructive condition testing and quality assessment of ferromagnetic materials, e.g., for evaluation of residual stress, active tensile and compressive stress, microstructure and micro hardening [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. In addition to the possible applications mentioned above, the MBN is also used to evaluate the directional properties of ferromagnetic materials.…”

Use of Time-Dependent Multispectral Representation of Magnetic Barkhausen Noise Signals for the Needs of Non-Destructive Evaluation of Steel Materials

“…Consequently, these obstacles arising in the material require additional energy and cause discontinuous changes of the magnetic state. This phenomenon has been studied and gradually used for non-destructive testing (NDT) of materials [4,5,6,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. The stepwise change of the magnetization level during operation of the alternating magnetizing field can be observed by coil placed in the neighbourhood of the material.…”

“…As a result, a voltage U BN called the Barkhausen Noise (BN) is induced in coil. The Magnetic Barkhausen Noise method (MBN) is used mainly for [29]: detection and evaluation of fatigue and stress [4,5,6,11,12,16,17,22,24,26,31,32,34,35,36,37,38,39], material microstructure [19,20,28,37,38,40] and microhardness (i.e., hardening level, case depth) analysis [13,14,23,27].…”

“…Many factors defining material state may affect various properties of BN signals. Mostly the analysis of BN is carried out in time T domain [4,6,11,12,19,20,34,35,36,37,38]; however the frequency F characteristic is also considered, especially for evaluation of material properties [12,13,14,26,27,28,39]. In case of T representation, the BN signal can be analysed by calculating parameters directly from the raw signal.…”

Using Barkhausen noise to measure coating depth of coated high-speed steel

“…It is observed that the ratio of two voltage sweeps with different frequencies produces a good estimation of the case depth. Drehmer et al [34] applied BHN measurement for estimating the case depth of SAE 1020 steel. They used RMS Barkhausen pulse envelope and fast Fourier transforms (FFT) to estimate case depths.…”