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Vol. 9. Issue 1.
Pages 291-300 (January - February 2020)
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Vol. 9. Issue 1.
Pages 291-300 (January - February 2020)
Original Article
DOI: 10.1016/j.jmrt.2019.10.057
Open Access
Effect of the PEN/C surface layer modification on the microstructure, mechanical and tribological properties of the 30CrMnSiA mild-carbon steel
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L.G. Zhurerovaa, B.K. Rakhadilovb, N.A. Popovac, M.K. Kylyshkanovd, V.V. Buraniche,
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hunters325@gmail.com

Corresponding author.
, A.D. Pogrebnjaka,e
a D. Serikbaev East Kazakhstan State Technical University, Ust-Kamenogorsk, Kazakhstan
b Sarsen Amanzholov East-Kazakhstan State University, Ust-Kamenogorsk, Kazakhstan
c Tomsk State Architecture and Construction University, Tomsk, Russia
d Ulba Metallurgical Plant VSC, Ust-Kamenogorsk, Kazakhstan
e Sumy State University, 2, Rimsky Korsakov Str., 40007 Sumy, Ukraine
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Tables (4)
Table 1. Results of elemental composition measurement defined by cross-sectional EDS from 3 different regions of nitrocarburized 30CrMnSiA steel surface.
Table 2. Morphological components of α-phase in 30CrMnSiA steel after nitrocarburizing and quantitative share of γ-phase there (Electron microscopy data).
Table 3. Morphological components of α-phase in 30CrMnSiA steel after nitrocarburizing and quantitative characteristics of dislocation structure (Electron microscopy data).
Table 4. Results of tribological testing.
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Abstract

As result of plasma-electrolytic nitrocarburizing 30CrMnSiA carbon steel (ferrite-perlite grade), there was a change in the elemental and phase composition, as well as the surface layer microstructure (40 ÷ 45 microns thick from the surface). A formation of Me23(CN)6 carbonitrides, FeN nitrides, Fe3C - (Fe,Cr)3C carbides and an increase in dislocation density within α–phase (tempered martensite crystallites), high-temperature lamellar martensite were observed. As a result of PEN / C exposure for 7min. at 750°C there is a reduction of friction coefficient and wear rate, what is connected with finely dispersed secondary phases FeN, (Fe, Cr)3C, Me23(C, N)6 formation. Thus there is an 2,5 ÷ 3,3 times increase in hardness of 30CrMnSiA carbon steel samples.

Keywords:
Carbonitrides
Microstructure
Electrolytic plasma processing
Wear rate
Hardness
Mild-Carbon steel
Full Text
1Introduction

Electrolyte-plasma processing of metals and alloys is widely used in a semi-industrial scale [1–12]. However, the widespread introduction of all processing types such as electrolyte-plasma oxidation of Ti, Zr, Mg, Al alloys, nitrogen / carbon saturation, thermal quenching and cooling, etc. [13–16], gets difficult due to low repeatability (normally around 95 ÷ 97,8%) whereas the customer requires all 99.99% reproducible processes [17].

Due to its simplicity, plasma electrolytic deposition (PED) processes successfully compete in cost with PVD coatings and electro-galvanizing methods [18–20]. PED can be used to fabricate oxide layers with enhanced mechanical properties during plasma electrolytic oxidation (PEO) or to saturate materials with various alloying elements during plasma electrolytic saturation (PES). PES processes strongly depends on mean current value (which determines the deposition rate), voltage amplitude of cathode or anode (accordingly to process), working electrolyte temperature and composition. There are also some practical difficulties mentioned precisely in the literature [22–24]. Therefore, mainly the scope of electrolytic plasma treatment (EPT) limited to technologies with reproducibility up to 100%.

EPT processing is one of the most promising and economically feasible techniques. Distinctive features of this method is controllability of the process, wide range of hardening (from several microns to mm), possibility of processing samples, products and working sites of any geometry [14,15]. Treatment of metal samples and products occurs in arc discharge plasma, burning in the active environment of chemical compounds, in particular the chemical-thermal method of the material surface treatment in electrolyte-plasma cathode regime [25–27].

High-energy impact, to which we can add electrolyte-plasma hardening can also be attributed, consists in high-speed heating to temperatures above critical ones by the plasma flow in the local portion of the sample surface layer and its rapid cooling, mainly due to heat conduction to internal volumes of the material, as well as heat transfer from the surface [21].

Thus, the purpose of this work is to study the elemental, phase composition of the surface layers and their microstructure of carbon steel ferrite-perlite class (CrMnSiCFe) and their effect on hardness, wear rate and friction properties as a result of electrolytic plasma treated samples (in solid).

2Materials and methods

The EPP-processed 30CrMnSiA high strength low alloy (HSLA) steel samples in the as-delivered conditions were used as the material of study (hardened at 880°C and tempered at 540°C). Chemical composition of the steel is: C: 0.28-0.35%; Cг: 0.8–1.1%; Mn: 0.8–1.1%; Si: 0.9–1%; P: 0.025%; S: 0.025%, and Fe ˜96% (30CrMnSiA).

Fig. 1 illustrates a system used for PEN/C processing. A 30CrMnSiA steel specimen to be processed was mounted and clamped on the clamping mechanism. The supply of electrolyte in the dielectric reservoir (15 liters) was provided by a pump designed to work in aggressive environments. As power supply a powerful rectifier was used, giving a maximum output of 360V / 60A. The main energy parameters of the plasma jet and movement dynamics of the workpiece were controlled by computer.

Fig. 1.

Principal scheme (а) and overview (b) of electrolytic plasma treatment (EPT) system:1– computer; 2–power supply; 3– plasma torch; 4– working bath; 5– sample installation part; 6 – stepper motor; 7– electrolyte reservoir; 8 – pump.

(0.31MB).

PES processing (nitriding, boriding and nitrocarburizing) of 30CrMnSiA structural steel carried by means of the classical technological parameters of plasma-electrolytic modification in two regimes: the temperature was T=750–950°C (depending on the type of processing), and the processing duration: 3, 5, 7min. In the first regime 1:10% of ammonium chloride (NH4Cl) and 10% of glycerine (C3H5(OH)3) electrolyte solution was used and under regime 2: 10% of sodium chloride (NaCl) and 15% of urea ((NH2)2CO) electrolyte accordingly.

Structural-phase examination of 30CrMnSiA steel samples was conducted by the Otto von Guerke University (Magdeburg, Germany). Samples were examined by X-Ray structural analysis using XPertPRO diffractometer at monochromated CuKα-radiation, optical microscopy at NEOPHOT 21 and AXIOPHOT-2 machines, transmission electron diffraction microscopy on thin sheet sat JEOL-2100 electron microscope using goniometric devices at raising voltage 100kV (TGASU, Tomsk, RF).

The microscope column working magnification was 100,000 times. To conduct research with spark cutting, the samples (size 30×30×8 mm3) were cut into thin sheets (foils) 0.2–0.3mm thick. Cutted sheets were thinned chemically in the electrolyte of 90% hydrofluoric acid and 10% perhydrol, then by electrolyte in supersaturated solution of phosphoric acid, chrome anhydride at room temperature, operating voltage 20V and 2–4A/cm2 current density.

The volume fractions of the phases were determined by images confirmed by micro-diffraction patterns and dark-field images taken in the reflexes of corresponding phases. To identify phases there were used the schemes of microdiffraction images calculated from the tabular values of lattice grids.

Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) using multifunctional general-purpose scanning electron microscope JEOL JSM-6010/A. In touch scope operated at 20kV.

Mechanical microhardness tests were carried on the PMT-3M microhardness tester (St. Petersburg, Russia) after the nitrocarburizing process. A high-temperature tribometer (TNT, CSM Instruments, Switzerland) was used to determine the tribological characteristics. The wear test (wear rate, weight loss) was performed by using pin-on-disk test instrument.

According to the conducted metallographic studies of the 30CrMnSiA steel in the as-delivered conditions [28], it was found that α-phase of varying degrees of doping is the main phase component (matrix) of 30CrMnSiA steel regardless on the sample processing and the place of the study. In its initial state the 30CrMnSiA steel belongs to the ferrite-perlite class containing ˜ 65% of perlite grain and 35% of ferrite grain (20% of them are non-fragmented and 15% of fragmented ferrite). It has been established that morphologically α-phase presents in the form of non-fragmented and fragmented ferrite at the boundaries (with an average particle size of 32nm, volume fraction in the material is ˜1%) and inside (average particle size 4nm, volume fraction in the material is ˜0,5%) containing carbide particles M23C6; lamellar perlite in the form of interchanging parallel plates of ferrite (α-phase) and doped cementite (Cr up to 20%); tempered martensite in the form of mixed structure of lath martensite, low-and high-temperature lamellar martensite.

3Results and discussion3.1Structure and morphology

X-ray diffraction structure investigations of 30CrMnSiA steel carried out after nitrocarburizing has shown at Fig. 2. After modifying in the surface layer nitride FeN, carbide FeC, (Fe,Cr)3C and carbonitride M23(C,N)6 phases are formed. Martensitic transformations are also noted along the boundaries of which residual austenite is present. Complex carbonitride phases were not detected. Perhaps their volume fraction does not exceed the detection limit of X-ray phase analysis. It is clearly seen how with increasing processing time (3, 5 and 7min) carbides and nitrides of iron and alloying elements are formed.

Fig. 2.

XRD patterns of 30CrMnSiA steel sample after high-temperature (T=750°C) plasma-electrolyte nitrocarburizing: a) 7min, b) 5min, c) 3min.

(0.41MB).

Scanning electron microscopy analysis of fragments (Fig. 3) showed that after 30CrMnSiA steel samples electrolytic nitrocarburizing, there is a significant change in the morphology of the surface layer. Enrichment of ferrite with atomic carbon and nitrogen is observed, which contributes to the growth of carbide and nitride particles, as well as martensitic structures in the near-surface modified layer.

Fig. 3.

SEM microstructures of the modified 30CrMnSiA steel after PEN/C treatment: regime 1 – a) 3min., b) 5min., c) 7min., regime 2 – d) 3min., e) 5min., f) 7min.

(0.97MB).

Steel nitrocarburizing, as noted above, led to substantial qualitative and quantitative changes in the structure. As the distance from the treated surface changes, such parameters as defect density, organization, size and type, as well as the concentration of alloying elements and impurities. All this eventually led to a change in the phase composition and to the phases formation which inherent in this structural type, as well as their morphology [29,30].

α-phase structure has undergone significant changes. Unlike the initial state, it is a mixture of three morphological components: batch (or rack) tempered low-temperature martensite and high-temperature lamella tempered martensite. Ferrite and perlite grains on nitrocarburized sample surface were not detected by primary analyzes, but they still were observed with TEM studies of thin section (see below).

As we see from the Fig. 3a–c (Regime 1) during plasma electrolytic nitrocarburizing with an increase of the process duration, the dispersion of ferritic particle grains decreases. After 7min a coarse-grained structure is observed, which is characterized by stability of carbide and nitride particles with diffusion of implanted atoms, which in turn are responsible for increasing surface hardness and wear resistance.

Sample surface microstructure under 2nd regime (Fig. 3d–f) markedly different from the obtained fragments microstructure obtained under regime 1 conditions. Here, the formation of martensitic phases is visually seen. The layer structure varies with changing the distance from the sample surface.

Fig. 4a, b shows SEM image of surface layer cross-section, obtained with a relatively small magnification. The surface layer is quite clearly divided into two separate zones (I and II), with carbides and carbonitrides distribution. The image shows a well-marked nitrocarburized surface layer, ˜30μm thick. Further, deep into the sample, the transition (intermediate) layer follows, then - the base metal layer (zone). The difference in the structure of the nitrocarburized layer and the changes in its structure with distance from the surface into the sample becomes even more noticeable with a larger magnification (Fig. 4b).

Fig. 4.

Cross-sectional SEM images of nitrocarburized 30CrMnSiA steel structure a) in depth with indexed layer distribution, b) with higher magnification (EDS analysis carried in 3 marked regions).

(0.49MB).

Since the phase composition of the upper-surface is the principal factor that determine mechanical and tribological properties of the modified sample, for its study was carried out Energy-dispersive X-ray spectroscopy (EDS) analysis of the 3 marked regions (Table 1). The increased diffusion of carbon and nitrogen along the grain boundaries in I and II zones due the surface activation by the discharge electric field influence, but this stimulation decreases with increasing depth of analysis.

Table 1.

Results of elemental composition measurement defined by cross-sectional EDS from 3 different regions of nitrocarburized 30CrMnSiA steel surface.

ElementEDS 1EDS 2EDS 3
Wt %  At %  Wt %  At %  Wt %  At % 
22.2  56.6  4.2  16.7  3.9  12.3 
0.0  0.0  0.0  0.0  10.9  26.0 
0.6  0.3  0.9  0.8  0.9  1.6 
Si  1.2  1.3  1.4  2.4  3.4  4.7 
Cr  1.1  0.7  1.3  1.2  2.3  1.7 
Fe  74.9  41.2  92.1  78.9  77.4  52.9 
Mn  0.0  0.0  0.0  0.0  1.1  0.8 

In the first zone, a weak etching of the grain boundaries is observed, the internal structure of the grains is not clearly expressed. In 2nd zone, the grain boundaries are clearly identified, and a rather well-defined structure inside the grain is present. This is especially clearly seen on thin sections, where the etching was carried out to identify not only the grain boundaries, but also to reveal the internal structure of the grains (Fig. 4a). At transition zone, which follows the nitrocarburized layer, the clearly identified grain boundaries, there is also a fairly well-defined structure inside the grains (Fig. 4b).

Grain size increases as the material moves deeper into the material: the average grain size is minimal on the surface of the processed sample, then it quickly increases to a depth of ˜200μm (at large distances from the surface the study was not conducted). Note that different grain sizes from 10nm to μm increases the strength characteristics (properties) of 30CrMnSiA structural steel [23,24].

Fig. 5 illustrates examples of non-fragmented ferrite 5a and its schemes 5b; fragmented ferrite 5c and its schemes 5d in the initial state in 30CrMnSiA steel.

Fig. 5.

Non-fragmented and fragmented ferrite in the initial state of 30CrMnSiA steel.

(0.52MB).

Fig. 6 illustrates electron-microscopy image of 30CrMnSiA structure in its initial state: a – bright field image (F – ferrite grain, P – lamellar perlite grain); b – microdiffraction image and its indicated diagram taken from the ferrite grain. There are some reflexes related to (111)α flat area; c - microdiffraction image and d- it is indicated diagram, taken from the grains of perlite, there are also reflexes related to flat area (120) and (137) α-phase and (221) of cementite Fe3C. The arrow points coinciding directions of α-phase [001] and cementite [01¯2], i.e. [001]αII [01¯2] Fe3C, the relation: 120αII221Fe3C (Bagaryatsky ratio).

Fig. 6.

TEM image of 30CrMnSiA steel microstructure in its initial state.

(0.48MB).

Fig. 7 illustrates Electron-microscopy image of tempered lath martensite. It is a process of separating of γ-phase along the boundaries of the laths and presenting of M23(C,N)6 carbonitride particles on the dislocations inside of the laths. 30CrMnSiA steel is shown after nitrocarburizing. Surface of the sample is as follows: а―bright field image; b—dark field image; c—microdiffraction image; d—its indicated scheme. There are also reflexes belonging to the flat areas (113) and (133) α- phase, (123) γ- phase and (150) of M23(C,N)6, carbonitride marked as “C” at scheme.

Fig. 7.

TEM image of tempered lath martensite. Separating of γ-phase along the boundaries of the laths and M23(C,N)6 carbonitride particles on the dislocations inside the laths. 30CrMnSiA steel is after nitrocarburizing. Surface of the sample: а ― bright field image; b – dark field image; c ―microdiffraction image; d –identified scheme.

(0.4MB).

The α-phase structure was significantly changed. In contrast to its initial state, it presents a mixture of three morphological components: lath tempered martensite (Fig. 7), lamellar tempered low-temperature martensite (Fig. 8c) and lamellar tempered high-temperature martensite (Fig. 8b). There are no ferrite and perlite grains on the EPP-processed sample surface. As it was mentioned above, lath martensite is a structural formation, which featured with joined equally oriented crystals of martensite - laths which form individual packages. The volume fraction of the martensite in steel matrix is ˜30% of the volume of steel matrix, Table 2. Lamellar martensite is like single martensite crystals (LLM), which are not grouped into packages [31]. This is a morphological component of the steel matrix and makes ˜20% of the volume of the steel matrix, Table 2. Lamellar high-temperature martensite (LHM) is some structurless regions without clearly defined boundaries. This is the main morphological component of the steel matrix which makes about 50% of the volume of steel matrix, Table 2.

Fig. 8.

Microstructure of the 30CrMnSiA steel sample surface after nitrocarburizing. LLM – lamellar low-temperature martensite; LHM – high-temperature martensite. Retained austenite (γ) at the boundaries of the lamellar (а) as twin-type colonies (b) and small regions (c). Cementite particles (c) indicated by arrows.

(0.32MB).
Table 2.

Morphological components of α-phase in 30CrMnSiA steel after nitrocarburizing and quantitative share of γ-phase there (Electron microscopy data).

Morphological components of steel matrixVolume share in steel matrixPV, (%)  Share of retained austenite in crystals α-phase, δ,(%) 
Sample surface
Tempered martensiteLath martensite  30%  1.5 
Lamellar low-temperature martensite  20%  1.7 
Lamellar high-temperature martensite  50%  4.0 
Inside of material100%  2.6 
50μm from the sample surface
Tempered martensiteLath martensite  55%  1.3 
Lamellar low-temperature martensite  20%  4.7 
Lamellar high-temperature martensite  25%  6.0 
Inside of material100%  3.2 

The γ-phase presents in the form of retained austenite and it is located either as interlayers along the boundaries of martensite laths (Fig. 7) and lamellars (Fig. 8a) or inside of the martensite lamellars in the form of twin-type colonies (Fig. 8b), or small regions (Fig. 8c). Table 2 provides data on volume fraction of γ - phase in various morphological components of α - phase.

Nitrocarburizing resulted in carbide subsystem changes of steel-cementite that presents inside the crystals of tempered martensite (Fig. 6c). The particles are acicular form with different size and distribution density in any morphological components of α-phase. However, the volume fraction of cementite in each morphological component of the α-phase does not exceed 0.4-0.5% from total volume of material.

Such carbonitrides as M2C0.61N0.39, M4(C,N), M7(C,N)3 and M23(C,N)6 are generated on the sample surface in all morphological components of α-phase after nitrocarburizing.

Steel nitrocarburizing caused a formation of two more carbonitride types: M4(C, N) and M7(C, N)3 on the sample surface as it was noted above. It was found that some nanoparticles (˜5-8nm) of carbonitride M4(C,N) are formed on the interfacial surfaces “Carbonitride M7(C,N)3 - α-phase” with average size of ˜ 0.2μm.

A decrease of dislocations density along the sample surface (Table 3) responds to indicate the manifestation of diffuse shear deformation during saturation process that also affects hardening of the material.

Table 3.

Morphological components of α-phase in 30CrMnSiA steel after nitrocarburizing and quantitative characteristics of dislocation structure (Electron microscopy data).

Morphological components of steel matrixVolume share in steel matrixPV, (%)  Dislocation density,ρ×10−10, (сm-2Excess of dislocation density,ρ×10−10, (сm-2
Sample surface
Tempered martensiteLath martensite  30%  4.4 
Lamellar low-temperature martensite  20%  3.9 
Lamellar high-temperature martensite  50%  3.5 
Inside of material  3.9 
50μm from the sample surface
Tempered martensiteLath martensite  55%  7.6  2.9 
Lamellar low-temperature martensite  20%  4.1  4.1 
Lamellar high-temperature martensite  25%  3.2  1.2 
Inside of material  5.8  2.7 
3.2Tribological and mechanical properties

At Figs. 9–11 (Table 4) the experimental data from tribological tests on modified 30CrMnSiA steel samples by different types of electrolytic treatment and dependences of the wear rate (mm3/N×mm), coefficient of friction (COF) are presented.

Fig. 9.

Coefficient of Friction (COF) against Sliding time dependence of the 30CrMnSiA steel samples: a) Initial, b) Nitriding, c) Nitrocarburizing.

(0.29MB).
Fig. 10.

Wear rate behavior (diagram) of 30CrMnSiA steel samples under different plasma electrolytic treatment.

(0.08MB).
Fig. 11.

Friction coefficient behavior (diagram) of 30CrMnSiA steel samples under different plasma electrolytic treatment.

(0.12MB).
Table 4.

Results of tribological testing.

№  Type of electrolytic treatment  Wear rate[(mm2/N)/mm],  Coefficient of friction, μ 
Initial state  0,00071  0,9 
Nitriding 750°C, 7minutes  0,000164  1,4 
Boriding 900°C, 7minutes  0,0001  0,6 
Nitrocarburizing 750°C, 6minutes  0,00008106  0,8 

According to the Table 4 wear rate of the 30CrMnSiA steel samples compared to the initial state varies with different dynamics. A noticeable decrease in the wear rate can be seen for samples obtained after nitrocarburizing at T=750°C for 6min at 8.7 times, nitriding at T=850°C for 7min at 4.3 times, boriding at T=950°C during 7min at 7.1 times accordingly. According to Table 4, we plotted the experimental data on wear resistance (Fig. 10) and the friction coefficient (Fig. 11) of all treated 30CrMnSiA steel samples. Fig. 12 shows micrographs of the 30CrMnSiA steel upper-surface after the tribological tests. Based on the nature of the surface damage trace, it can be concluded that samples obtained during nitrocarburizing treatment acquire a higher wear resistance.

Fig. 12.

Micrographs of the 30CrMnSiA steel surface after the tribological tests.

(0.75MB).

The results of experimental work on the modified surface microhardness determination carried on the microsection of 30CrMnSiA steel, after the PEN/C process has shown at Figs. 13 and 14.

Fig. 13.

Diagram of the surface microhardness after nitrocarburizing process in electrolyte plasma against time and working solution type (green – Initial state, blue – Regime 1, T =750°C (10% NH4Cl + 10% C3H5(OH)3), red – Regime 2T =750°C (10% NaCl + 15% (NH2)2CO) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

(0.13MB).
Fig. 14.

The microhardness distribution along the cross-section depth of 30CrMnSiA steel after nitrocarburizing T=750°C, 1–3min, 2–5min, 3–7min, a –α-Fe+FeC + (Fe, Cr)3C+M23(C, N)6; b – M + γ-Fe; b – α-Fe.

(0.43MB).

From the obtained experimental data about the modified surface layers microhardness determination, an already established regularity can be observed: with increasing hardness of surface, the degree of doping of the material also increases [32], on the basis of which lies the choice of the optimal mode. However, in world practice [33–35] the opposite concept also exists: not all wear-resistant materials have a high surface hardness [36,37]. Nevertheless, according to our research on the microhardness and wear resistance determination, the following regularities were established: with an increase in the wear resistance of the 30CrMnSiA steel samples surface during plasma electrolytic saturation (PES): nitriding, boriding and nitrocarburizing a significant increase in microhardness has been observed. Samples processed in nitrogen-containing electrolytes showed increase in microhardness by an order of magnitude, which is most likely due to the formation of finely dispersed nitrides on modified layers. The maximum microhardness value is a nitrocarburized 30CrMnSiA steel sample at regime 1 which is equal to 8.9GPa, and the surface microhardness after processing at regime 2 is 3.2GPa (Figs. 13 and 14), which corresponds to the minimum microhardness value.

Analyzing the experimental data, it can be seen that with hardness increase (Fig. 13), the resistance to wear (Fig. 10) also increases, however, this pattern does not appear in all cases during the nitrocarburizing process [30].

All changes in mechanical (hardness) and tribological (friction coefficient, wear rate) properties are associated within the formation of the secondary phases: nitrides, carbides, carbonitrides, iron borides and alloying elements. On the other hand, changing the temperature, electrolyte composition, current and potential (actual processing parameters) can also affect the microstructure, uniformity and degree of alloying of the material, which consequently contributes to the steel samples modification.

4Conclusion

  • 1)

    Samples obtained during plasma-electrolytic processing of 30CrMnSiA mild-carbon steel surface demonstrate 2.5 times increase in microhardness and 4 times increase in wear resistance;

  • 2)

    Found out that the ferrite-pearlite structure of the steel matrix is modified according to the method of electrolytic saturation (PES):

  • 3)

    Upon nitrogen, boron and carbon saturation for 3, 5, 7min and working temperature T=750–950°C followed by quenching in electrolyte, a modified layer (average thickness 30μm) is formed, that includes nitride FeN, carbide FeC, (Fe, Cr)3C and complex carbonitride phases.

  • 4)

    Revealed, that hardening of 30CrMnSiA structural steel occurs in low-temperature plasma conditions, due to the formation of carbides, carbonitrides, and alloying elements, that enhance performance at effective surface modification until the heat affected zone (hardening depth ˜ 45μm).

  • 5)

    Upon nitrocarburizing (regime 1) at 750°C, 3–7minutes followed by quenching in the electrolyte containing an aqueous solution of 10% (NH4Cl) +10% (NaCl) and 15% ((NH2)2CO), surface microhardness increases by 3,3 times, wear resistance increases by 8.7 times depending on the processing type of the initial sample.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgments

This work supported by Ministry of Education and Science of Ukraine with the state budget programs entitled “Multilayer and multicomponent coatings with adaptive behaviour and wear (No. 0118U003579).

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