Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551 Received for review: 2022-04-05
© 2022 The Authors. CC BY 4.0 Int. Licensee: SV-JME Received revised form: 2022-08-02
DOI:10.5545/sv-jme.2022.147 Original Scientific Paper Accepted for publication: 2022-08-10
*Corr. Author’s Address: Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland, tadeusz.lesniewski@pwr.edu.pl 542
Functional Surface Layer Strengthening  
and Wear Resistance Increasing of a Low Carbon Steel  
by Electrolytic-Plasma Processing
Kombayev, K. – Muzdybayev, M. – Muzdybayeva, A. – Myrzabekova, D. – Wieleba, W. – Leśniewski, T.
Kuat Kombayev
1
 – Murat Muzdybayev
1
 – Alfiya Muzdybayeva
1
 –  
Dinara Myrzabekova
1
 – Wojciech Wieleba
2
 – Tadeusz Leśniewski
2,*
1 
East Kazakhstan State Technical University, Technological Machines and Transport Department, Republic of Kazakhstan 
2 
Wrocław University of Science and Technology, Faculty of Mechanical Engineering, Poland
The modified technology for strengthening the surface layer of low-carbon steel for machine components by electroplasma processing is 
proposed. This technology is to be used as an alternative carburizing method with subsequent hardening. The developed technology of 
strengthening by the proposed method is based on the author’s invention. The parameters of this process are given, resulting in a thickness 
of the reinforced surface layer of 1000 µm to 1700 µm. An increase in microhardness of 1.5 to 2 times (compared to the initial state) was 
observed. With hardening, chemical modification of the material’s surface layer occurs. The microstructure of the treated surface of the steel 
samples is characterised by a dark modified surface layer: a fine needle-like structure of martensitic origin under the dark layer transforms 
into an initial perlite-ferritic structure. The advantage of strengthening based on the electrolytic plasma processing consists of low energy 
consumption at high hardening speeds and the possibility of local processing of surface areas, especially large parts of complex shapes. In 
addition, the proposed surface treatment method using electrolytic plasma processing (EPP) not only achieves a smooth surface but also 
improves the service qualities of the components, specifically wear resistance.
Keywords: low-carbon compound steel, strengthening, electrolytic plasma processing
Highlights
• 	 The author’s technology of strengthening the surface layer of low-carbon compound steel for details of machines by electrolytic 
plasma processing is developed. 
• 	 This technology is proposed as an alternative method of carburizing with subsequent hardening; the total thickness of the 
strengthened surface layer is 1000 µm to 1700 µm, and the microhardness of the strengthened area of a martensitic 
structure is 6500 MPa to 7200 MPa.
• 	 The microstructure of the processed surface of steel samples is characterized by a dark modified surface layer. A fine needle-
like structure of martensitic origin under the dark layer changes into the initial pearlite-ferritic structure. 
• 	 It is stated that in the structure of 18CrNi3Mo-Sh steel sample after electrolytic plasma processing, particles of residual 
cementite Fe3C, a-phase based on Fe, Cr0.6 Fe1.4 - phase and Fe2.7 Mo0.8 Ni0.1 - phase appear, which confirms availability 
of martensite hardening. 
• 	 The advantage of strengthening based on the electrolytic plasma processing consists of low energy consumption at high 
hardening speeds and the possibility of local processing of surface areas, especially large parts of complex shapes.
0  INTRODUCTION
Mechanical engineering development is largely 
related to solving the tasks of increasing machines’ 
reliability. To increase the operational reliability of 
machines, it is necessary to increase the endurance 
and durability of their parts [1] and [2] and reduce 
the risk of their failures [3] and [4]. This is achieved 
by various methods, including strengthening the 
operating surfaces of component parts and creating 
new technological processes of highly wear-resistant 
materials manufacturing [5] to [7]. Toughening 
the requirements concerning the microstructure 
and properties of the surface layers of machines’ 
component parts requires new methods for their 
modification and strengthening [8]. Techniques 
involving the influence of concentrated energy flows 
on the surface of component parts appeared to be 
widely used [9]. The most promising technology 
for surface strengthening of component parts is 
electrolytic plasma processing (EPP) [10]. EPP is 
an electrochemical heat treatment process and mass 
transfer (coating) on a component part (product) 
surface using a plasma jet. A plasma jet is a partially 
or fully ionized gas in combination with electric 
discharged phenomena at the boundary of the main 
electrode-water electrolyte solution at high capacities 
up to 1000 V [11].
With a gradual increase in the applied constant 
voltage, salt electrolysis occurs. According to Ohm’s 
law, the current increases (section from 0 to A, Fig. 
1). This area is characterized by scaling up the current 
with voltage increasing. Doing this, the electrolyte 
temperature also increases. This is a consequence of 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
543 Functional Surface Layer Strengthening and Wear Resistance Increasing of a Low Carbon Steel by Electrolytic-Plasma Processing  
the current passing through the electrolyte. When a 
certain voltage value is reached (from 100 V to 176 
V), the electrolyte starts boiling on the surface of the 
cathode, and an active release of bubbles near the 
surface occurs (bubble boiling). At bubble boiling, 
the temperature of the component part is close to 
the steam point. When bubble boiling occurs around 
the active electrode, large current pulsations can be 
observed. Their amplitude is significantly reduced 
when the component part is heated above 470 °C. 
Fig. 1.  Volt-ampere characteristic of electrolyte plasma processing
Over a further increase in rectified voltage, 
film boiling appears (point A, Fig. 1), which is 
characterized by the disappearance of bubble boiling 
and a sharp drop in current because the resulting gas-
steam jacket has a higher electrical resistance than a 
liquid electrolyte (section from A to B, Fig. 1). Since 
the gas-steam jacket is less electrically conductive, the 
main voltage drop occurs precisely where more heat is 
generated. The low-temperature plasma of a specific 
blue glow around the component part is formed due 
to a gas-steam jacket forming an electric current 
passing through it. The brighter the blue colour of 
plasma burning, the more ions it contains, including 
ion modifiers. An abnormal discharge is observed 
when increasing the voltage [12]. The principle of 
the technological process of strengthening based 
on the method of EPP is as follows. The cathode is 
made of 18CrNi3Mo-Sh steel (which corresponds 
to the standard 18HN3MA-Ш TU 3-850-80) for 
manufacturing roller cones. It is immersed in the 
electrolyte (10 % water solution Na2CO3) to 4 mm 
to 6 mm depth. The anode is stainless X10 CrNiTi 
18-10 (corresponding to the standard 12X18H10T 
GOST 5949-75 Steel). It is in the form of a disk with 
a diameter of 50 mm and a thickness of 2 mm; 4 mm 
holes are drilled in the disk. Plasma arises between 
the cathode and liquid electrolyte. Negative ions ease 
excess electrons when passing through the holes of 
the anode of stainless X10 CrNiTi 18-10 steel. The 
cations are entrained by the hydrodynamic flow of 
electrolyte and recombine at the cathode (the surface 
of the sample material of the drill bit). The conversion 
of electrical energy into heat occurs mainly in the 
plasma layer on the heated cathode surface. When 
being processed, cathode surfaces are cemented with 
carbon ions and hardened in an electrolyte in a short 
time.
The modification of the surfaces of machines’ 
component parts with the EPP method contributes 
to the compositional restructuring of a surface 
layer that increases strengthening properties and 
wear resistance due to physical input (ions of high-
temperature plasma, electrical discharge). The EPP 
method is currently used when modifying the surfaces 
of component parts of bent shafts, iron cylinders 
of diesel engines, circular saws [13], and others. 
The main advantages of the EPP method are the 
following: a complex profile strengthening, internal 
surfaces and cavities; no need for special preparation 
of surfaces before strengthening; ecological safety 
(use of special treatment facilities is not required). 
Analysis of existing technologies for low-carbon 
compound steel products hardening suggested that 
electrolytic plasma strengthening could be the most 
appropriate technology for the thermal hardening 
of component parts. The aim of this research is to 
identify experimentally the values of parameters 
for the technological process of electrolyte-plasma 
hardening of 18CrNi3Mo-Sh steel. The article 
presents the research methodology description, the 
obtained results, their discussion, conclusions, and 
acknowledgements.
1  METHODS AND EXPERIMENTAL APPROACH
A multiple-factor experiment has been fully 
implemented to select optimal electrolyte plasma 
processing conditions. Experiments of this type can 
localize the area necessary and present all possible 
independent variables’ values. Heating a sample 
of a component part in depth is associated with 
an inhomogeneous temperature distribution in the 
volume of the material of a component part [14].
A drill bit (Fig. 2) provided by JSC 
V ostokmashzavod (VKMZ JSC) was selected to study 
the effectiveness of various methods of strengthening. 
Contact durability, abrasive and shock-abrasive 
wear resistance of the drill bit’s component parts are 
provided by gas carburizing followed by hardening. 
Deformation, low carbon steel cracking, and high 
labour and energy intensity are the disadvantages 
of that heat processing. In order to eliminate the 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
544 K o mba y e v ,	K .	–	Muzdyba y e v ,	M.	–	Muzd yb a y e v a,	A .	–	Myr zabek o v a,	D.	–	Wieleba,	W .	–	Leśnie wski,	T .
disadvantages of the above treatment method, for 
EPP, the following samples from drill bit’s component 
parts were used: 18CrNi3Mo-Sh (0.16 % to 0.18 
% С; 3.3 % Ni; 0.9 % Cr; 0.51 % Mo; 0.44 % Mn; 
0.34 % Si; 0.05 % Al; 0.008 % S; 0.012 % P; 0.015 
% N; 0.01 % O; 0.01 % H) NSS 4543-71 [13]. Low-
carbon, compound, heat-resistant steel of electroslag 
remelting can be used at –70 ºС to +450 ºС. Carbon, 
chromium, molybdenum, manganese, and silicon 
are alloying constituents, increasing strengthening 
properties. Nickel provides strength and good 
toughness; molybdenum provides heat resistance to 
steel. Samples of 10 mm × 10 mm × 20 mm were 
cut out of roller cones with a diamond blade with a 
thickness of 1 mm, which was immersed in cooling 
fluid. The samples were made from roller cones 
in the initial condition and compared after thermal 
processing on the JSC “VKMZ” base. Two series of 
samples (3 repetitions in each) hardened according 
to the method given by JSC “VKMZ” and processed 
using the EPP method were examined.
Fig. 2.  Roller cone
At low cutting speeds (n = 350 rpm) and low 
load (m = 250 g), the sample does not experience 
significant deformations and thermal effects. The 
samples were first polished with chromium dioxide 
cement and then etched with 5 % alcoholic nitric acid 
solution to do a metallographic microanalysis.
Application investigations and mechanical 
testing were carried out in the Regional University 
Engineering Laboratory Irgetas and the research 
and manufacturing complex Machine industry of 
D. Serikbayev East Kazakhstan State Technical 
University [15]. Metallographic analysis was 
carried out using an Axioscop-2MAT microscope 
equipped with a Sony digital camera. Qualitative 
and quantitative phase analysis of the steel samples’ 
structure was carried out using an X’Pert PRO X-ray 
diffractometer of the PAN analytical firm, applying 
Cu-K a radiation. The electron images were made with 
the following equipment: a raster electron microscope 
JSM-6390LV “JEOL Ltd.” (Japan) with an energy 
dispersive microanalysis system INCA Energy Penta 
FET X3 “OXFORD Instruments Analytical Limited”. 
Microhardness measurements were carried out using 
a PMT-3 device, equipped with a diamond pyramid, 
with a load on the 2H indenter by 9450-76 GOST. The 
wear resistance of the samples was estimated by the 
loss of mass per unit time when the sample was being 
tested by attrition on the abrasive disc when sliding 
rubbing without lubricant [16]. To measure the mass 
of the samples, an electronic weighing unit of the VL-
120 model with an accuracy of 0.1 mg was used.
2  RESULTS
The influence of technological and electrical parameter 
changes during electrolyte (10 % water solution of 
Na
2
CO
3
 calcined soda) on the strengthening quality 
was studied. It was experimentally proved that the 
considered factors of EPP modes affect the quality of 
the steel surface, which is strengthened. It should be 
noted that the main technological parameters, such 
as the thickness of strengthening, microhardness, and 
wear resistance of steel depend on the heating time, 
hardening time, the number of strengthening cycles 
by the EPP method and the electric current voltage 
[14]. Fig. 3 shows the initial microstructure of the 
material of the sample of a strengthened component 
part of 18CrNi3Mo-Sh steel. It is seen that a coarse-
grained pearlite-ferritic microstructure characterizes 
the material of the sample. 
Fig. 3.  The initial structure of the sample material of a component 
part of 18CrNi3Mo-Sh steel

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
545 Functional Surface Layer Strengthening and Wear Resistance Increasing of a Low Carbon Steel by Electrolytic-Plasma Processing  
at mode A, the influence of high-temperature plasma 
is observed (Fig. 4a, the dark area from left to right). 
The layer of coarse needle-like martensite smoothly 
transfers into the initial structure as it deepens into 
the material. When processing at mode B, there is 
also an area of high-temperature plasma exposure. 
Its depth is comparatively larger than at mode A and 
is approximately 200 μm deep (Fig. 4b, dark area 
from left to right). The availability of fine needle-
like martensite with a smooth transition to the initial 
structure of the sample material is noted. 
a) 
b) 
c) 
Fig. 4.  Micro sections of the cross-section (to the depth of 
material) of electrolytic plasma processed steel
After 15 s of EPP processing (at mode C), a 
deposited layer of anode material (steel X10 CrNiTi 
In the course of the study, a series of searching 
experiments were carried out, involving EPP testing 
for sample processing to identify the logical modes of 
the process. The ranges of the numerical values of the 
parameters studied are presented in Table 1.
Table 1.  Technological parameters for hardening of 18CrNi3Mo-Sh 
steel by the EPP method
Terms in the program 
of the experiment
Physical factors
Factor levels
min max
X1
The heating time of a work 
piece from the plasma 
temperature [s]
1 15
X2
The hardening time in the flow 
of electrolyte [s]
1 10
X3 DC voltage [V] 180 260
X4 Number of cycles [-] 20 40
It was decided to switch to a three-factor 
experiment model and settle the number of processing 
cycles at 30 to conduct a comparative analysis of 
technological modes’ influence on the material of 
the component part strengthening. To systematize 
the assessment of the EPP modes’ effect on the 
quality indicators of steel of drill bits strengthening, 
depending on such main parameters as heating time 
T
heating
 from ionized plasma and hardening time 
T
hardening
 in the electrolyte flow, taking into account the 
direct current (DC) voltage U between the electrodes, 
we converted micrographs of material microstructure 
into a tabular form (Table 2). In one case, the images 
located along the edges lack the modes for optimal 
hardening of the material of a sample (left). In another 
case, the sample matrix burns out (right), transforming 
the hardening process in EPP into the process of ion 
transfer of metal from the anode to the strengthened 
cathode.
Table 2.  EPP modes while steel drill bit strengthening
Parameters
Modes EPP processing
A B C
Heating time t
heating
 [s] 2 4 15
Hardening time t
hardening
 [s] 2
4
15
DC voltage U [V] 190 200 250
Fig. 4 shows the microsections of electrolyte-
plasma processed steel to the depth of the hardened 
layer (cross-section). A comparison of microsections 
(cross-sectional cuts to the deep from left to right), 
presented in Fig. 4, makes it possible to note the 
features of the microstructure of the material obtained 
at different modes of EPP processing: when processing 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
546 K o mba y e v ,	K .	–	Muzdyba y e v ,	M.	–	Muzd yb a y e v a,	A .	–	Myr zabek o v a,	D.	–	Wieleba,	W .	–	Leśnie wski,	T .
18-10) on the microsection occurs. The sample 
substrate’s border and martensitic transformation are 
clearly visible (Fig. 4c, to the depth from left to right). 
Thus, images of microsections reveal:
• mode A lacks parameter values of EPP processing 
for the optimal hardening of the sample material 
(Fig. 4a),
• mode B burns out the material of a sample while 
EPP processing (Fig. 4b), transforming the 
hardening process into the process of ion transfer 
of metal from the anode to the strengthened 
cathode.
It is stated that electrolyte-plasma processing 
requires low power (within 3 kWh) when rapid motion 
occurs. The obtained data are used in [17].
In actual practice, a thermal exchange is 
a complex process. To facilitate its study and 
simplify the correlations obtained, the concept of 
elementary types of thermal exchange is introduced: 
experimentally determined thermocouples made by 
a natusral thermal junction. Two thermocouples are 
installed in two layers of the sample workpiece at a 
depth of h1 and h2 from the heated surface (Fig. 5). 
Thermocouples are installed to control the temperature 
mode of the process to prevent the material’s melting 
from being strengthened.
Fig. 5.  The layout of thermal junctions in the surface layer of 
the sample when measuring the temperature in the process of 
electrolytic plasma heating
A 10 mm × 10 mm × 20 mm steel sample acts 
as a cathode. The temperature is measured by a 
thermocouple mounted in the cathode body. The 
thermocouple is a thermoelectric converter of the 
ТХА type, conditional designation ХА (К) according 
to GOST 3044-84. The measurement range is from 
minus 200 ºС to plus 1000 ºС. Admission class 1. The 
limits of permissible deviations are ±0,004× Т when a 
measurement is in the range above plus 375 ºС to plus 
1350 ºС. The sensitivity of the thermocouple is 40 μV/
ºС. The range of measured temperatures corresponds 
to the temperature of phase transformations from plus 
840 ºС to plus 860 ºС.
Heating temperature is the main parameter 
of phase transformations for 18CrNi3Mo-Sh steel 
and is 860 °C [18]. At EPP, the bulk temperature 
increases to the hardening temperature of 860 °C, 
and the temperature of the ionized plasma overheats 
the surface. Its temperature exceeds 1100 °C. When 
ionized plasma is excited (plasma temperature 
ranging from 6000 K to 30000 K), a gas-vapor layer 
appears on the sample surface due to electrolyte 
dissociation [19]. The gas-vapor layer prevents the 
ingress of electrolyte on the overheated surface. It 
reduces the cooling rate, eliminating the formation of 
thermal (hardening) cracks. As a result, the operating 
durability of steel increases. Thus, the main factors 
determining the quality of steel strengthening at EPP 
have been experimentally stated. They are heating 
time, hardening time, and electric current voltage. 
A mathematical model is developed to describe 
the change in the key parameter of the technological 
process of steel strengthening at the EPP method: 
the heating temperature T. The following regression 
equation expresses the logarithmic dependence of the 
temperature T on the main factors:
 
ln() ln() ln()
ln() ,
TC at Db U
Ed t
heating
cooling
  
 (1)
where Т is steel heating time [s], t
heating
 heating time 
[s], t
cooling
 cooling time in the electrolyte flow [s], U 
voltage [V], and C = 4.5, D = 4.8, E = 18, a = 2, b = 1, 
c = 1 the coefficients for Eq. (1) were found by using 
logarithm in the Deductor Studio Academic software.
Then Eq. (1), which describes the dependence of 
the heating temperature on the heating time, cooling 
time and voltage, was transformed to Eq. (2):
 Tt Ut
heatingc ooling
   45 48 18
2
.. , (2)
where Т is steel heating time [s], t
heating
 heating time 
[s], t
cooling
 cooling time in the electrolyte flow [s], and 
U voltage [V] [20]. 
Experimentally determined optimal modes of 
steel hardening by the EPP method (t
heating
 = 4 s, 
t
cooling
 = 4 s, U = 200 V) have a good correlation with 
the established dependence, see Eq. (2).
A raster elemental analysis of the processed 
surface (Fig. 6) revealed chemical modification of 
the surface layer of the metal happening along with 
hardening during the electrolytic plasma heating of 
the sample [21].

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
547 Functional Surface Layer Strengthening and Wear Resistance Increasing of a Low Carbon Steel by Electrolytic-Plasma Processing  
Fig. 6.  Raster elemental analysis of the 18CrNi3Mo-Sh steel 
surface after EPP strengthening
Table 3.  Qualitative and quantitative analysis of the sample 
processed [23]
No. of spectrum Spectrum 1 Spectrum 2 Spectrum 3
C 0.56 0.69 0.71
Na – 0.38 –
Si – – 0.31
Cr 0.66 0.66 0.54
Mn 0.48 – 0.54
Fe 95.73 95.75 95.48
Ni 2.57 2.52 2.42
Total 100.00 100.00 100.00
Temper increasing (Table 3), relative to the initial 
state, is because charged carbon ions [22], saturating 
the surface of the sample, are generated in the plasma 
layer of electrical gas discharge from the water 
solution of soda ash Na
2
CO
3
 when electric current 
flows. In water solution Na
2
CO
3
, such ions as 2Na
+
, 
CO
3
2-
, ОН
-
, Н
+
 occur. When passing through the holes 
in the anode, anions ease away excess electrons. The 
cations are entrained by the hydrodynamic electrolyte 
flow and recombine on the cathode (the product’s 
surface).
All the results in Table 3 are presented in weight 
fractions and expressed in percentage terms. X-ray 
structural analysis of 18CrNi3Mo-Sh steel samples 
in the state, as received (Fig. 7a), and after EPP 
strengthening according to mode B (Fig. 7b) revealed 
the a phase line, based on Fe, line Cr
0.6
 Fe
1.4
 phase, 
and also the line Fe
2.7
 Mo
0.8
 Ni
0.1
 phases.
a) 
b) 
Fig. 7.  X-ray diffraction pattern of 18CrNi3Mo-Sh steel;  
а)	in	the	initial	s tat e,	b)	af t er	EPP	s trengthening
Table 4.  The phase composition of 18CrNi3Mo-Sh steel samples
Processing type Phase composition 2Theta [deg] d [A] h k l l [%]
After 
EPP
Initial
a-phase
44.677 2.0267 1 1 0 100
65.028 1.4331 2 0 0 11.5
82.344 1.1701 2 1 1 17.4
Cr
0.6
 Fe
1.4
 
63.845 1.456730 3 0 2 17
67.048 1.3947 2 0 5 13
61.739 1.5013 2 1 3 21
Fe
2.7
 Mo
0.8
 Ni
0.1
96.981 1.0286 4 0 0 6
98.149 1.0195 4 0 1 1
99.472 1.0094 2 2 4 20
Fe
3
C
44.750 2.0235 1 1 0 10.8
65.108 1.4315 2 0 0 10
82.444 1.1689 2 1 1 37
99.064 1.0125 2 2 0 14

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
548 K o mba y e v ,	K .	–	Muzdyba y e v ,	M.	–	Muzd yb a y e v a,	A .	–	Myr zabek o v a,	D.	–	Wieleba,	W .	–	Leśnie wski,	T .
3  DISCUSSION
After EPP, an expansion of intensity acceleration and 
diffraction lines can be observed (Fig. 7b) relative to 
the initial state (Fig. 7a). This indicates a stress state 
due to thermal exposure. The phase composition of 
samples of 18CrNi3Mo steel is presented in Table 4.
As is known from [24], while hardening, the 
martensitic (A → M) transformation is not fully 
completed, and the decay products are left in steel. 
Lines after EPP, a phase of Fe
3
C residual cementite 
and a-phase based on Fe, line Cr
0.6
 Fe
1.4
 phase, line 
Fe
2.7
 Mo
0.8
 Ni
0.1
 phase indicate martensitic hardening. 
According to the Kurdjumow-Sachs theory [25], 
a martensitic crystal appears on the forming shear 
area. Stresses play a very important role. Sources of 
stress are heat gradients along the cross-section, the 
heterogeneity of chemical composition, structural 
imperfections, different spatial crystal orientations, 
the specific volumes of austenite and martensite, 
and various coefficients of phase linear extension. 
There is a fine-grained lamellar structure of a fine 
needle-like martensitic class on the cross-section cut 
of the electrolytic plasma-processed sample (Fig. 8). 
The microstructure to the processed surface (left) is 
characterized by a dark layer, which is the structural 
phase transformation formed under the influence of 
an ionized high plasma temperature [23]. The methods 
and methodology relating to Fig. 8 are mentioned in 
the patent specification [24].
 
Fig. 8.  The microstructure of the cross section of 18CrNi3Mo-Sh 
steel after EPP strengthening (100 times increase)
 It is established that electrolytic plasma 
processing makes it possible to obtain a strengthened 
layer of thickness from 1000 μm to 1700 μm (Fig. 9). 
Microhardness at the cross-section of the strengthened 
area (martensitic structure) ranged from 6500 MPa to 
7200 MPa.
The results of microhardness measurements on 
the surface of a heat-treated sample in a plant (VKMZ 
JSC) averaged 7000 MPa (Fig. 9). Microhardness 
decreases to the initial state and averages 3000 MPa 
when moving away from the processed surface [26]. 
The microrelief on the worn EPP surface of the steel 
sample after wear testing (Fig. 10a) indicates the least 
abrasive wear. With fine-grained martensite, a strong 
surface structure is formed that cannot be broken even 
when worn (during the experiment) by severe forms 
of abrasive wear, thereby preventing large areas of 
destruction.
Fig. 9.  The value of the microhardness of 18CrNi3Mo-Sh steel 
after EPP strengthening
The worst wear can be observed on the initial 
untreated steel sample (Fig. 10c). The pearlite-ferritic 
structure is easily abraded by abrasion, confirming 
the low wear resistance of thermally unprocessed 
steel. A steel sample that was thermally treated at 
JSC “VKMZ” wears out less than the initial sample 
(Fig. 10b). However, in terms of wear resistance, it is 
significantly inferior to the sample strengthened with 
the EPP method.
A sample after EPP strengthening has better wear 
resistance. As can be seen from Table 5, the steel 
resistance to abrasion increased significantly after 
EPP strengthening.
Table 5.  Value of wear of 18CrNi3Mo-Sh steel samples
Processing type Hv [MPa] Wear [mg/h]
EPP strengthening 6817 54.4
Thermo processed at JSC “VKMZ” 6298 100.4
State as received 3271 150.0

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
549 Functional Surface Layer Strengthening and Wear Resistance Increasing of a Low Carbon Steel by Electrolytic-Plasma Processing  
The practical significance of the obtained 
results of scientific research in the field of working 
surface hardening by the EPP method means that 
the developed technology applies to a wider range 
of parts. In particular, they include the vast majority 
of the articulated elements of machines that work as 
friction pairs. A special feature of the operating modes 
of articulated joints is the intense relative movement 
of the mated working surfaces, high contact load, 
unsatisfactory lubrication conditions of the friction 
surfaces due to the extrusion of the lubricant, the 
ingress of corrosive media into the mating zone, as 
well as abrasive particles. Such conditions are typical 
for loading and delivering vehicles when working in 
underground mines and open pit mining.
The experimental research was conducted to 
ensure the operability of parts on the example of the 
rotary mechanism hinge assembly of the underground 
loader Caterpillar R1300G confirmed the possibility 
of effective use of the developed technology to 
strengthen the surface parts based on the EPP method.
Thus, it has been stated by experiments that 
controlling EPP modes makes it possible to affect 
the quality of steel strengthening and obtain wear-
resistant surfaces and significantly improve EPP 
productivity. This fact suggests the controllability of 
the EPP technological process and the possibility of 
practical implementation of the developed technology 
in the production
4  CONCLUSIONS
The effect of electrolytic plasma processing on 
phase transformations and structural changes and 
the properties of low-carbon and compound steels 
has been theoretically and experimentally studied. 
The microstructure of the processed surface of steel 
samples is characterized by a dark modified surface 
layer. A fine needle-like structure of martensitic 
origin under the dark layer changes into the initial 
pearlite-ferritic structure. The total thickness of the 
strengthened surface layer is 1000 μm to 1700 μm. 
The microhardness of the strengthened area of a 
martensitic structure is 6500 MPa to 7200 MPa. The 
structure of 18CrNi3Mo-Sh steel sample in the initial 
state is composed of particles of a–phase based on Fe, 
Cr
0.6
 Fe
1.4
 phase, as well as Fe
2.7
 Mo
0.8
 Ni
0.1
 phase 
after electrolytic plasma processing in the structure of 
18CrNi3Mo-Sh steel samples there appear particles 
of residual cementite Fe
3
C, a-phase based on Fe, 
Cr
0.6
 Fe
1.4
 phase, Fe
2.7
 Mo
0.8
 Ni
0.1
 phase, that testifies 
availability of martensite hardening. The most 
effective surface strengthening method of drill bit 
Fig. 10.  Microrelief of 18CrNi3Mo-Sh steel samples after testing 
f o r	abrasiv e	w ear	resis tance,	1 00	times	increase;	а)	af t er	EPP	
strengthening, b) thermo processed at VKMZ JSC, and c) initial 
state
Based on the data obtained, it can be concluded 
that electrolytic plasma processing significantly 
increases the wear resistance of drill bit component 
parts at low labour intensity, which reduces the cost of 
the product as a whole [27].

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
550 K o mba y e v ,	K .	–	Muzdyba y e v ,	M.	–	Muzd yb a y e v a,	A .	–	Myr zabek o v a,	D.	–	Wieleba,	W .	–	Leśnie wski,	T .
parts is electrolytic plasma processing. The advantages 
of this method are low energy consumption at high 
speeds of hardening, the possibility of local surface 
processing of parts of complex shapes operating under 
conditions of intense loads and the simplicity of the 
process.
5  ACKNOWLEDGEMENTS
This research was funded by the Science Committee 
of the Ministry of Education and Science of the 
Republic of Kazakhstan within the framework of the 
grant project IRN AR09058518.
6  REFERENCES
[1] Rembeza, A.I. (ed.) (1986). Reliability and Efficiency in 
Technology. Methodology. Organization. Terminology. 
Maszynostroienie, Moscow. (in Russian)
[2] Sokolski, P., Smolnicki, T. (2021). A method for monitoring the 
technical condition of large-scale bearing nodes in the bodies 
of machines operating for extended periods of time. Energies, 
vol. 14, no. 20, art. ID 6637, DOI:10.3390/en14206637.
[3] Henli, A.J., Kumamoto, H. (1984). Reliability of Technical 
Systems and Risk Assessment. Translated from English. 
Syromjatnikova, V.S., Demina, G.S. (eds.): Machine Industry, 
Moscow. (in Russian)
[4] Gui, W., Lin, J., Hao, G., Qu, Y., Liang, Y., Zhang, H. (2017). 
Electrolytic plasma processing-an innovative treatment for 
surface modification of 304 stainless steel. Scientific Reports, 
vol. 7, art. ID 308, DOI:10.1038/s41598-017-00204-w.
[5] Davis, J.R. (ed.) (2002). Surface Hardening of Steels: 
Understanding the Basics. ASM International, Materials Park.
[6] Nestler, K., Böttger-Hiller, F., Adamitzki, W., Glowa, G., Zeidler, 
H., Schubert, A. (2016). Plasma electrolytic polishing - an 
overview of applied technologies and current challenges to 
extend the polishable material range. Procedia CIRP, vol. 42, 
p. 503-507, DOI:10.1016/j.procir.2016.02.240.
[7] Jumbad, V.R., Chel, A., Verma, U., Kaushik, G. (2020). 
Application of electrolytic plasma process in surface 
improvement of metals: a review. Letters in Applied 
NanoBioScience, vol. 9, no. 3, p. 1249-1262, DOI:10.33263/
LIANBS93.12491262.
[8] Lachowicz, M., Leśniewski, T., & Lachowicz, M. (2022). Effect 
of Dual-stage Ageing and RRA Treatment on the Three-body 
Abrasive Wear of the AW7075 Alloy. Strojniški vestnik - Journal 
of Mechanical Engineering, vol. 68, no. 7-8, p. 493-505, 
DOI:10.5545/sv-jme.2022.142.
[9] Janicki, D., Musztyfaga, M. (2016). Direct Diode Laser 
Cladding of Inconel 625/WC Composite Coatings. Strojniški 
vestnik - Journal of Mechanical Engineering, vol. 62, no. 6, p. 
363-372, DOI:10.5545/sv-jme.2015.3194.
[10] Rakhadilov, B.K., Kozhanova, R.S., Popova, N.A., Nugumanova, 
A.B., Kassymov, A.B. (2020). Structural-phase transformations 
in 0.34C-1Cr-1Ni-1Mo-Fe steel during plasma electrolytic 
hardening. Material Science - Poland, vol. 38, no. 4, p. 699-
706, DOI:10.2478/msp-2020-0073.
[11] Kulikov, I.S., Vashhenko, S.V., Kamenev, A.J. (2010). 
Electrolyte-Plasma Processing of Materials. Biełaruskaja 
Navuka, Minsk. (in Russian)
[12] Pogrebnjak, A.D., Kul’ment’eva, O.P., Kobzev, A.P., Tyurin, 
Yu.N., Golovenko, S.I., Bojko, A.G. (2003). Mass transfer and 
alloying processes during electrolytic plasma processing of 
cast iron. Letters to Technical Physics Journal, vol. 29, no. 8, p. 
8-15, DOI:10.1134/1.1573301.
[13] Rakhadilov, B., Zhurerova, L., Pavlov, A. (2016). Method of 
electrolyte-plasma surface hardening of 65G and 20GL low-
alloy steels samples. IOP Conference Series: Materials Science 
and Engineering, vol. 142, art. ID 012028, DOI:10.1088/1757-
899X/142/1/012028.
[14] Rakhadilov, B.K., Kurbanbekov, Sh.R., Kylyshkhanov, M.K., 
Kenesbekov, A.B. (2018). Changing the structure and phase 
states and the microhardness of the R6M5 steel surface 
layer after electrolytic plasma nitriding. Eurasian Journal of 
Physics and Functional Materials, vol. 2, no. 3, p. 259-266, 
DOI:10.29317/EJPFM.2018020307.
[15] Gorelik, S.S., Skakov, J.A., Rastorguev, L.N. (2002). X-ray and 
electron-optical analysis, (edition 4, updated and revised). 
Moscow Institute of Steel and Alloys, Moscow. (in Russian)
[16] Geller, J.A., Rahshtat, A.G. (1989). Materials Sciences, (edition 
6, updated and revised). Metallurgy, Moscow. (in Russian)
[17] Skakov, M., Zhurerova. L., Scheffler, М. (2012). Way of 
hardening surface coating of details from steel 30CrMnSi 
in electrolytic plasma. Key Engineering Materials, vol. 531-
532, p. 178-181, DOI:10.4028/www.scientific.net/KEM.531-
532.178. 
[18] Skakov, М.K., Uazyrkhanova, G.K., Popova, N.A., Sсheffler, M. 
(2012). Influence of heat treatment and deformation on the 
phase-structural state of steel 30CrMnSiA. Key Engineering 
Materials, vol. 531-532, p.13-17, DOI:10.4028/www.scientific.
net/KEM.531-532.13.
[19] Skakov, M., Rakhadilov, B., Scheffler, M., Batyrbekov, 
E. (2015). Microstructure and tribological properties of 
electrolyte plasma nitrided high-speed steel. Materials Testing, 
vol. 4, no. 57, p. 360-364, DOI:10.3139/120.110709.
[20] Kombaev, K.K., Kylyshkanov, M.K., Lopuhov, J. (2009). 
Influence of electrolytic plasma processing of 18CN3МА-ShSh 
steel on the surface microstructure and hardness. Journal of 
the Siberian Federal University, Engineering and Technology, 
vol. 2, no. 4, p. 394-399, handle/2311/1562, accessed on 
2022-08-29. (in Russian)
[21] Kozha, E., Smagulov, D.U., Ahmetova, G.E., Kombaev, 
K.K. (2017). Laboratory installation for electrolytic-plasma 
treatment of steel. News of the National Academy of Science 
of the Republic of Kazakhstan, vol. 4, no. 424, p. 219-224.
[22] Tjulenin, A.N., Tjurin, Ju.N., Gradnev, A.I. (1988). Hysteresis 
of current-voltage characteristic of power supplies. MITOM. 
Мoscow, no. 1, p. 9-12.
[23] Kombaev, K.K., Kozha, E., Smagulov, D.U., Sadeh, B. (2016). 
Structural phase transitions of low-carbon alloy steels 
during electrolytic-plasma processing. Proceedings of the 
2nd International Conference on Artificial and Industrial 
Engineering, p. 491-495, DOI:10.2991/aiie-16.2016.114.
[24] Kombaev, K.K., Skakov, M.K., Putrenko, N.F. (2010). Patent 
#649, Republic of Kazakhstan. Test Stand for Testing 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)9, 542-551
551 Functional Surface Layer Strengthening and Wear Resistance Increasing of a Low Carbon Steel by Electrolytic-Plasma Processing  
Materials for Friction and Wear. Patent of the State Treasury 
Enterprise “Eastern Kazakhstan State Technical University 
named after D. Serikbayev “Ministry of Education and Science 
of the Republic of Kazakhstan” No. 2010 / 016.2. Kazakhstan, 
Nur-Sultan.
[25] Kylyshkanov, M.K., Kombaev, K.K., Pogrebnyak, A.D. (2009). 
Patent #23178, of Republic of Kazahstan. Method of 
Electrolytic Plasma Strengthening of Drill Bit Component 
Parts, Nur-Sultan.
[26] Kozha, E., Smagulov, D.U., Akhmetova, G.E., Kombaev, 
K.K. (2017). Laboratory installation for electrolytic plasma 
treatment of steel. News of National Academy of Sciences of 
the Republic of Kazakhstan, Almaty, vol. 4, no. 424, p. 219-
225.
[27] Rahadilov, B.K., Satbayeva Z., Baizhan, D. (2019). Effect of 
electrolytic-plasma surface strengthening on the structure 
and properties of steel 40KHN. Proceedings 28
th
 International 
Conference on Mettallurgy and Materials, p. 950-955, 
DOI:10.37904/metal.2019.739.