Surface Hardening of 18CrNi3MoA-SH Steel with Heating in
Electrolytic Plasma
Mazhyn Skakov1,a and Lyaila Bayatanova1,b, Michael Sheffler 2
1
D. Serikbaev East Kazakhstan State Technical University, Ust-Kamenogorsk, Kazakhstan,
2
Institute of materials and connecting technologies, Otto-von-Guericke University,
Magdeburg, Germany
a
skakovmk@mail.ru, bleila_1809@mail.ru
Keywords: electrolyte-plasma processing; microhardness; wear resistance; microstructure.
Abstract. We investigated 18CrNi3MoA-Sh steel hardened by electrolyte-plasma processing
method. The comparative analysis of microstructure, microhardness and wear-resistance of the
samples in initial state and after electrolyte-plasma treatment is presented. It was found out that
18CrNi3MoA-Sh steel microstructure has fine-grained martensite-bainite structure after the
treatment. It was set that 18CrNi3MoA-Sh steel possesses high wear-resistance after electrolyteplasma treatment so that technology is characterized by low power consumption and cost price.
Scanning analysis of transient surface demonstrated that in the course of details’ electrolyte-plasma
heating chemical surface modification takes place along with tempering. Microhardness increases
2-2.5 times more before treatment that indicates the technology efficiency. This method advantages
are minor energy expenditure in the time of tempering high speeds, possibility of local surface
processing especially of large size details with complicated shape.
Introduction
As it is known [1] increased requirements to quality of details of cars are stimulated with creation of
new methods of purposeful change of phase structure and structure of their blankets. In particular,
the wide circulation was received by influence methods on a surface of details the concentrated
streams of energy. In our opinion, the most perspective, energysaving and ecologically safe
technology is electrolyte-plasma treatment method [2]. The structure and material properties change
in thin surface coatings due to physical exposure by ions of high-temperature plasma and electric
discharge.
The basic advantage of electrolyte-plasma processing method is possibility difficulty of profile
hardening, internal surfaces and cavities; absence of surfaces special preparation before hardening;
ecological safety (utilizing of special treatment facilities is not required). The analysis of existing
technologies of low-carbon alloyed steel products tests has allowed to suppose that electrolyteplasma hardening can be proper thermal hardening technology for production of details.
At processing in electrolyte to plasma there is change of structurally-phase conditions and
properties of material in thin blankets owing to physical influence of high-temperature ions plasma
and electric category. Therefore researches of changes of structure, properties of 18CrNi3MoA-Sh
steel after electrolyte-plasma processing are represented by big scientific and practical interest [6].
In connection with above-stated purpose of influence electrolyte-plasma processing on structure,
phase structure and mechanical properties of 18CrNi3MoA-Sh steel is present work research.
Material and Experiment Technique
For research 18CrNi3МoА-Sh steel (0,16-0,18%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) State standard 4543-71 was
selected. The 18CrNi3МoА-Sh steel is usually applied to details manufacturing of drill chisels and
rolling cutter. Appointment - in cemented and the improved condition is applied to responsible
details to which high durability demands are made, viscosity and wear resistance, and also for the
details which are exposed to high vibrating and dynamic loadings. Low-carbon alloyed
temperature-resistant steel of electroslag remelting may be applied at temperature from – 700С up to
+4500С [4]. Alloying elements - carbon, chrome, molybdenum, manganese, silicon raise durability.
Nickel provides durability at good impact elasticity, molybdenum provides durability and hightemperature properties of steel [5].
For research samples of 18CrNi3MoA-Sh steel 30x30x10 mm3 in size were cut from roller cone
in the initial position with diamond disk 1 mm thick. It was immersed into cooling liquid. The
cutting speed n = 350 revolutions per minute, loading m=250 g (at such mode the sample does not
test significant deformations and thermal influence). For metallographic microanalysis
metallographic section after polishing with application of chrome dioxide paste were etched by 5 %
of nitric acid spirit solution. Experimental researches and mechanical tests were carried out in
Regional engineering profile laboratory «IRGETAS» at D.Serikbaev EKSTU and in scientific
laboratory of sub-department «Technical Physics». Metallographic analysis was made on
microscope for metallographic studies (MIM 7) with a digital camera «Fujifilm». The qualitative
and quantitative samples structure phase analysis of steel was made on X-ray diffractometer
«X′Pert PRO» of "PANanalytical" firm with application of Cu-Kα radiations. The element samples
structure processed in electrolyte plasma was investigated on scanning electronic microscope JSM6390LV - JEOL firm (Japan) with installation of energy dispersed microanalysis INCA Energy
«OXFORD Instruments» firm. Microhardness measurements were made on instrument device
PMT-3 with diamond pyramidion, at loading on indentor 1 N according to State standard 9450-76.
Wear resistance of samples was estimated on weight loss in time unit as a result of tested sample
abrasion on abrasive disk at sliding friction without lubricant according to State standard 23.208-79.
For measurement of samples weight electronic scales VL-120 with 0.1 mg precision were used.
Electrolyte-plasma processing represents electrochemical process of thermal processing and
masstransaction (covering drawings) on a surface of a detail (product) by means of a plasma stream
[2]. The plasma stream is partially or completely ionized gas, a combination to the electrodigit
phenomena on border of a working electrode - a water solution of electrolyte at high potentials to
1000 V. The category is lighted from a source of a direct current 1, with thyristor adjustment
connected to an industrial network (380 V, 50 Hz), with target parameters: pressure U=0÷350 V,
force of current I=0÷60A. All process of processing copes are managed through the personal
computer.
Experimental Results and Discussion
Cementation was carried out in cathodic mode with two-level electrolytic heating in electrolytes
of following structure: 15 % sodium carbonate water solution Na2CO3 and 15 % a sodium carbonate
water solution Na2CO3 + 10 % of glycerine С3Н8О3. Voltage at heating to cementation temperature
is 320 V, exposure interval at temperature of cementation 180 V. Heating temperature at
cementation is 850-860°С. After heating to the set temperature the endurance during 1.5; 2; 2.5; 3.5
min. was made. The subsequent hardening was made in stream of cooled electrolyte.
After cathode warming with short time of endurance and the subsequent hardening steel surface
has fine-grain structure due martensite (А→М) transformation is not proceeded till the end and
there are disintegration products in steel [7]. Increase of time endurance up to 3.5 minutes leads to
increase of grains sizes.
It is set that electrolyte-plasma processing allows to receive the strengthened layer with thickness
1000 … 1700 microns. Microhardness of initial condition is 2700 МPа. After processing with
endurance during 1.5 minutes microhardness increases to 5000 MPа. With increase in processing
duration microhardness decreases. It is connected with the fact that at long endurance size of grain
increases [6].
Scanning element analyses of the processed surface have shown that at electrolyte-plasma details
heating along with hardening there is chemical modification of surface metal layers (Figure 1). The
qualitative and quantitative analysis of sample structure was defined in one point. Defined elements
were from boron to uranium. In water solution Na2CO3 (electrolytes) ions Na+, CO-, ОН-, Н+ are
formed. The ions having negative charge, give excess electrons while passing through anode orifice
- 12Cr18Ni10Тi stainless steel, cations are dragged by electrolyte hydrodynamic stream and
recombine on cathode-surface of processed detail of boring head. Transformation of electric power
to heat is, basically, in plasma layer on heated surface of product-cathode [4].
Figure 1. Scanning element analysis of surface electrolyte-plasma
processed 18CrNi3MoA-Sh steel.
In a plasma layer power is transferred to a product in the form of the specific type of
nonequilibrium electric discharges. Processed surfaces are cemented by carbon ions and are
hardened in electrolyte for considerably short time. The increase in carbon percentage (Table 1)
relatively to initial state is explained by the fact that in plasma layer - the electric gaseous discharge
from water sodium carbonate solution Na2CO3 and glycerin С3Н8О3 while at electric current
charged carbon ions [5] are formed and they carbonize sample surface.
Table 1. Qualitative and quantitative analysis electrolyte-plasma processing of sample [weight %].
Spectrum
Spectrum 1
C
0.86
O
3.14
Si
0.30
Cr
0.74
Mn
0.75
Fe
94.21
result
100.00
Scanning element analyses of the processed surface have shown that at electrolyte-plasma
heating of details along with hardening there is chemical modification of metal surface layer.
Wear of processed steel sample by electrolyte plasma in comparison with initial state is much
less. The best wear resistance has the sample after electrolyte – plasma processing which increases
steel resistance to abrasion.
In presence of fine-grained martensite strong surface structure is formed. It is does not collapse
even at heaviest forms of abrasion wear. Prevent formation of big centers of destruction. The
greatest wear is observed on initial - raw sample of steel. Ferrite-perlite structure is easily used by
abrasive. That is confirms fact about low wear resistance of thermally not processed steel. Wear of
sample electrolyte plasma processed steel in comparison with initial is much less.
Summary
1. Influence of EPT modes on structure and phase compound of steel is investigated. It is
established that in plasma layer of the electric gas category, at course of electric current ions of
carbon which carbonize the surface of sample and leads to formation carbides phases are formed in
water solution soda ash Na2CO3 and glycerin.
2. Influence of surface hardness and depth of the tempered layer on modes of electrolyte-plasma
treatment is investigated. It is established that after processing of steel 18CrNi3MoA-SH
microhardness more than 2 times concerning of irrespective initial condition. Abrasive wear
resistance of steel exceeds wear resistance of sample of the electrolyte-plasma hardening processed
on technology, not less than 2 times.
Thus, on the basis of analysis done it is established that the most effective way of surface
strengthening for bearing unit track of the boring tool is electrolyte-plasma processing. Advantages
of such approach are: low power inputs at fair speed of autohardening, possibility of local processing
of details surface with complex configurations operating under intensive loadings, simplicity of
process realization.
The present research work was done on the basis of the Cooperation Agreement between D.
Serikbaev East Kazakhstan State Technical University 2008 in accordance with the contract of JointStock Company “Science Fund of the Republic Kazakhstan” on theme «Working out and innovative
technology introduction of electrolyte-plasma hardening for chisel tool material » since December
10, 2010.
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