International audienceThis paper deals with the non-destructive evaluation of surface oxidation of gear steel using magnetic Barkhausen noise profiles analysis. Martensitic specimens are subjected to tempering at various temperatures in a muffle furnace. Tempering induced changes result in Barkhausen profile height increase and peak centers shift to lower fields. Single peak profiles are associated with specimens tempered up to 500 °C. Double peak profiles are seen with specimens tempered at 600 °C and 700 °C. Single peak profiles are observed after removing the oxide layer. The utilization of MBN method for this purpose is based on the difference in the inherent magnetic properties between the degraded surface layer and the sub-surface unaffected bulk. The observations are discussed in the light of established models of Barkhausen noise

Blaow, M. M.

M. M. , Sawalem

English

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Detection of Iron Oxide Layer in Quenched and
Tempered Gear Steel Using Magnetic Barkhausen Noise
M. M. Blaow, Sawalem M. M.
To cite this version:
M. M. Blaow, Sawalem M. M.. Detection of Iron Oxide Layer in Quenched and Tempered Gear Steel
Using Magnetic Barkhausen Noise. Mechanics, Materials Science & Engineering Journal, Magnolithe,
2016, ￿10.13140/RG.2.1.1027.5444￿. ￿hal-01336854￿
Mechanics, Materials Science & Engineering, July 2016 – ISSN 2412-5954 
 
MMSE Journal. Open Access www.mmse.xyz 
Detection of Iron Oxide Layer in Quenched and Tempered Gear Steel Using 
Magnetic Barkhausen Noise 
 
M. M. Blaow 1, a and M. M. Sawalem 2, b 
 
1 – Department of Materials Science and Engineering, Faculty of Engineering, University of Misurata, Aljazera Street, 
Misurata, Libya 
2 – Department of Mechanical Engineering, Faculty of Engineering, University of Misurata, The Coase Road, Misurata, 
Libya 
a – mblaow@yahoo.co.uk 
b – ferretti355@gmail.com 
 DOI 10.13140/RG.2.1.1027.5444 
 
Keywods: magnetic Barkhausen noise profile, tempering, oxidation, hysteresis. 
 
ABSTRACT. This paper deals with the non-destructive evaluation of surface oxidation of gear steel using magnetic 
Barkhausen noise profiles analysis. Martensitic specimens are subjected to tempering at various temperatures in a 
muffle furnace. Tempering induced changes result in Barkhausen profile height increase and peak centers shift to lower 
fields. Single peak profiles are associated with specimens tempered up to 500 °C.  Double peak profiles are seen with 
specimens tempered at 600 °C and 700 °C.  Single peak profiles are observed after removing the oxide layer.  The 
utilization of MBN method for this purpose is based on the difference in the inherent magnetic properties between the 
degraded surface layer and the sub-surface unaffected bulk.  The observations are discussed in the light of established 
models of Barkhausen noise. 
 
Introduction. The manufacturing processes for gear components include heat treatment operations 
to achieve surface characteristics for components to increase wear resistance. Heat treatments 
include carburizing and induction hardening which introduce a hard layer at the surface and 
maintain a soft interior.  Recently Ovako 667 steel was developed for low cost manufacture of 
wear-resistant elements. This type of steel could be fully hardened by air-cooling from the austenite 
region. Another feature is that the material is resistant to over-tempering.  
When a ferromagnetic material is magnetized by a varying magnetic field, the local changes in the 
magnetization induces voltage pulses in a search coil placed on the surface which are known as 
magnetic Barkhausen noise [1]. Magnetic Barkhausen noise (MBN) is mainly associated with the 
irreversible domain wall movement and refers to the abrupt discontinues changes in the 
magnetization rate that result from domain walls overcoming various types of obstacles in their 
path. Obstacles include grain boundaries, voids and precipitates [2]. The sensitivity of MBN to 
microstructural inhomogeneities makes it potentially useful as a non-destructive testing technique.  
Also, the assessment of microstructure and mechanical properties after initial heat treatment as a 
quality control measurement and their subsequent degradation during service such as exposure to 
high temperature [3].  In steels, microstructural defects like grain boundaries, inclusions and 
dislocations promote both mechanical and magnetic hardening, increasing the area of hysteresis 
curve and reducing permeability.  This happens because the same defects which pin dislocations 
also may “pin” domain walls while moving under the effect of a time varying excitation field [4].   
In case carburized and decarburized steels a hardness gradient is present [5-9]. This can cause two 
MBN intensity peaks to appear at different field strengths. The reason is that each peak originates in 
a material layer of different hardness. The variation in ferromagnetic material properties can be 
correlated to different parameters derived from the MBN signal profile generated during the 
Mechanics, Materials Science & Engineering, July 2016 – ISSN 2412-5954 
 
MMSE Journal. Open Access www.mmse.xyz 
magnetization cycle [10].  The aim of the study is to investigate the magnetic Barkhausen noise 
response from iron oxide layer formed at the surface of martensite tempered at elevated 
temperatures as a function of weeping magnetic field. 
Materials and Method. The composition of the stock material is shown in Table 1.  In the present 
work, bars (10×10×120 mm) machined from the stock were austenitized in vacuum to prevent 
surface oxidation and decarburization of the specimens.  Martensitic specimens were tempered in a 
muffle furnace at 500, 600 and 700o C for 1 hour to produce different degrees of oxidation.  The 
details of the MBN apparatus is shown elsewhere [13].  In this experiment, the magnetizing 
frequency used was 1 Hz to enhance the MBN signal to noise ration and maintain a low 
magnetization rate. 
 
Table 1. Composition of Ovako 677 steel 
Element C Mn Ni Cr Mo Si S P 
Wt % 0.67 1.48 0.11 1.03 0.25 1.46 0.007 0.016 
 
Results. Figure 1 shows half-cycles MBN profiles of a quenched specimen and quenched and 
tempered at 500°C specimen.   
0
10
20
30
40
50
60
-0.25 0 0.25 0.5 0.75 1
M
B
N
 
(
 
(
A
r
b
i
t
r
a
r
y
 
u
n
i
t
s
)
Magnetizing current, A
Martensite 
tempered at 
500oC
Air cooled
 
Fig. 1. Half-magnetizing cycle Barkhausen profile from specimen tempered at 500 o C. 
Mechanics, Materials Science & Engineering, July 2016 – ISSN 2412-5954 
 
MMSE Journal. Open Access www.mmse.xyz 
0
10
20
30
40
50
60
70
80
90
-0.25 0.25 0.75
M
B
N
 
(
A
r
b
i
t
r
a
r
y
 
u
n
i
t
s
)
Magnetizing current, A
Martensite 
tempered at 
600oC
Oxidized 
surface
Clean 
surface
 
Fig. 2. Half-magnetizing Barkhausen profile from the specimen tempered at 600 o C. 
 
The specimens oxidized at 600 and 700 °C show MBN profiles appear to consist of two overlapping 
peaks (Figs. 2 and 3). It seems reasonable to assume that the MBN profiles reflect the composition 
gradient at the skin depth of the specimens, which are the iron oxide at the surface and the steel at 
the subsurface. Figure 4 shows that the second peak at higher field from the oxidized specimen fits 
with MBN profile of the cleaned specimen which implies that the oxide layer is thin and does not 
attenuate the Barkhausen emission from the bulk material.  After removal of the oxide layer, the 
specimen tempered at 700 °C shows a remarkable increase in the MBN emission (Fig. 3) compared 
to that from the oxidized surface.   
0
50
100
150
200
250
300
350
-0.25 0.25 0.75
M
B
N
 
(
A
r
b
i
t
r
a
r
y
 
u
n
i
t
s
)
Magnetizing current, A
Oxidized 
surface
Clean 
surface
Martensite 
tempered at 700oC
 
Fig. 3.  Half-magnetizing Barkhausen profile from the specimen tempered at 700°C. 
 
Mechanics, Materials Science & Engineering, July 2016 – ISSN 2412-5954 
 
MMSE Journal. Open Access www.mmse.xyz 
This indicates that the oxide layer is able to attenuate the MBN signals from the bulk material.  
Barkhausen profiles of the quenched and tempered specimens without oxides are shown in Fig. 4. 
 
0
50
100
150
200
250
300
-0.25 0.25 0.75
M
B
N
 
(
A
r
b
i
t
r
a
r
y
 
u
n
i
t
s
)
Magnetizing current, A
            
Quenche
Quenced and 
tempered at 
600oC
Quenced and 
tempered at 
700oC
 
Fig. 4. MBN profiles showing tempering induced changes. 
 
Discussion. Although MBN has been attributed to a number of mechanisms, most current thinking 
associates it with the irreversible movement of domain walls. Theoretical models highlighting the 
connection MBN and the irreversible component of magnetisation Mirr have been reviewed by Jiles 
14. A basic assumption is that the intensity of emission is proportional to the differential 
susceptibility χirr= dMirr/dH, where H is the magnetic field. This is illustrated schematically in Fig. 
5, where the Mirr–H hysteresis loop is shown in relation to MBN emission for a complete 
magnetisation cycle. The amplitude of emission is greatest when the slope of the Mirr–H curve is a 
maximum, and smallest at points approaching saturation.  The MBN characteristics observed for the 
different microstructures (Fig. 4) are consistent with the theory. If the hysteresis loop becomes 
narrower, with steeper sides, the peak intensity of emission will increase and the position of the 
peak will shift towards zero field. The converse will occur if the hysteresis loop becomes broader 
with a smaller maximum slope. In the experiments, peak position (Fig. 4) shifted to lower values as 
the microstructure changes from martensite to ferrite-cementite microstructure.  
 
 
Fig. 5. Magnetic hysteresis loops and the corresponding MBN signals [14]. 
Mechanics, Materials Science & Engineering, July 2016 – ISSN 2412-5954 
 
MMSE Journal. Open Access www.mmse.xyz 
It is widely accepted that the Barkhausen noise signal is strongly dependent on the number of 
pinning obstacles met by domain walls during the magnetization process. The peak amplitude is 
thus strongly sensitive to the phase proportion, whereas the position of the peak is usually linked to 
the nature and the strength of the obstacles. The discontinuous jumps of Bloch walls are due to their 
local pinning by different obstacles such as inclusions, precipitates, grain boundaries, and 
dislocation tangles. The MBN increases with the number of these pinning obstacles. A shift of the 
peak to the high value of the magnetic field is also observed when the influence of these obstacles 
on Bloch walls increases. Because the magnetic structure is directly linked to the nature of 
metallurgical state and hence its differential susceptibility, each phase has its inherent magnetisation 
saturation and hence a distinctive MBN response [15, 16].  This is consistent with the present 
observations on the oxidized and non oxidized specimens. The differential susceptibility of iron 
oxide layer is different from that of ferrite and cementite structure and hence this results in two 
magnetization responses (MBN) relative to the applied sweeping field .   
Summary 
1. Iron oxide layer results in a split of the profile into two peak’s profiles revealing the iron oxide 
and the bulk material. 
2. Iron oxide layer at the surface of the specimens attenuates the MBN signals. 
3. Magnetic Barkhausen noise technique is very sensitive to microstructural gradient at the surface 
and the subsurface bulk. 
References 
[1] E. Gorknov, Yu. Dragoshanskii, and M. Mikhovki. Barkhausen noise and its utilization in 
structural analysis of ferromagnetic materials (review article v) 5. Effects of volume and surface 
thermal processing, Russian Russian Journal of Nondestructive Testing, 36 (6) 389 (2000). 
[2] D.C. Jiles, The influence size and morphology of eutectoid carbides on the magnetic properties 
of carbon steels, Journal of Applied Physics, 63, 2980, 1988. 
[3] D. D'Amato, C. Verdu, X. Kleber, G. Regheere, and A. Vicent, Characterization of 
Austempered Ductile Iron Through Barkhausen Noise Measurements Journal of Nondestructive 
Evaluation, Vol 22 (4), pp 127-139, 2004, doi: 10.1023/B:JONE.0000022032.66648.c5. 
[4] D. C. Jiles, "Dynamics of domain magnetization and the Barkhausen effect, Czechoslovak 
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MMSE Journal. Open Access www.mmse.xyz 
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Detection of Iron Oxide Layer in Quenched and Tempered Gear Steel Using Magnetic Barkhausen Noise

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Detection of Iron Oxide Layer in Quenched and Tempered Gear Steel Using Magnetic Barkhausen Noise

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