Article
citation information:
Askerov, H., Vakulenko, I.,
Grischenko, N. Insights into factors of damage of surface rolling of railway
wheels during operation. Scientific Journal of Silesian
University of Technology. Series Transport. 2019, 105, 27-33. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2019.105.3.
Hangardas ASKEROV[1], Igor
VAKULENKO[2], Nikolaji GRISCHENKO[3]
INSIGHTS
INTO FACTORS OF DAMAGE OF SURFACE ROLLING OF RAILWAY WHEELS DURING OPERATION
Summary. The systematization results of microstructure
studies of carbon steel has made it possible to explain the mechanism of
formation of certain damages to the rolling surface of railway wheels during
operation. The evaluation ability of metal to strain hardening was used to
explain the nature of the influence compactly located non-deformable dispersed
particles on the strength properties steel during cold plastic deformation. In
the process of the interaction of a railway wheel with a rail, successively
occurring heterogeneities in the distribution of the plastic flow metal are one
of the main reasons for the formation of defects on the rolling surface of the
wheel.
Keywords: carbon steel,
microhardness, strain hardening, rolling surface of a railway wheel,
non-metallic particles
1. INTRODUCTION
The process of damage
formation on the rolling surface of railway wheels is determined not only by
the rate accumulation of defects in the crystalline structure but also by the
uniformity of their distribution in the metal [1-4]. A high degree localisation
of the plastic deformation carbon steel on the rolling surface of the wheel
leads to a corresponding increase in the heterogeneity of the strength
properties in adjacent micro volumes of the metal [5]. In addition, the very
nature of loading introduces certain difficulties in the development processes
of strain hardening of carbon steel. Indeed, when compared with simple
deformation schemes, a change in the magnitude and even the sign of the
deformation is accompanied by qualitative structural changes, which greatly
complicates the assessment of the service life of cyclically loaded metal
structures [6]. Additional strengthening of the negative effect of
inhomogeneous metal hardening should be expected from the presence of
non-deformable particles of non-metallic inclusions of various nature of origin
and their location [7]. Based on this, the formation of defects in the rolling
surface of railway wheels is the result of the gradual accumulation of metal
damage with a rather complex interaction with the rail.
2. MATERIALS AND METHODS
The material for the
study was a part of a rim railway wheel, which was withdrawn after completion
of its service life. The carbon steel of wheel with a carbon content of 0.59%,
silicon 0.31%, manganese 0.75% and other chemical elements fully met the
regulatory and technical documentation requirements for railway wheels [8]. The
microstructure was examined under a light microscope. To identify the structure
of the steel under study, the standard reagent “nital” was used.
The size of the structural elements was estimated using quantitative
metallographic techniques [9].
Microhardness (Hμ) was used as a characteristic of
the strength of micro volumes of metal. The ability of the metal to strain
hardening in micro volumes was evaluated by a technique similar to the construction
of a tensile curve [10]. In the Hμ
magnitude, for a certain load on the indenter, the current stress value (σᵢ) was determined (the
maxima load on indenter 0,098 N). The true deformation (εᵢ,) was determined by the ratio: εᵢ = ln(dᵢ/d̥ₐ), where dᵢ - is the current value
diagonal of the imprint, and d̥ₐ
- is the initial value (of minimum). The diagonal d̥ₐ of print was taken with a minimum load on the
indenter. Analysis of the obtained ratio
σᵢ - εᵢ,
allows us to judge the nature of the development strain hardening processes in
micro volumes of metal [11].
3. RESULTS AND DISCUSSION
The cyclic nature of the change in stress on the rolling surface causes
the development of fatigue processes in the metal of wheel rim [5]. These
phenomena in metallic materials are irreversible, and traces of their presence
are detected even at stresses significantly lower than when the first signs of
plastic deformation appear [12]. A detailed analysis [5] indicates that in the absence
of negative influence from nonmetallic particles of various nature origin, one
of the main signs of fatigue damage to be considered are the formation of
extrusions (extruded) and intrusions (absent) of metal volumes on the rolling
surface [13].
Studies of the rolling surface profile railway wheel after operation
confirms the above positions (Fig. 1a). According to external signs, the
observed anomalies on the surface of rolling should be considered as a certain
alternation of extruded and concave volumes of metal. The study of the
microhardness distribution of the metal matrix near the contour of the rolling
surface (Fig. 1a) showed the existence of a certain pattern in the change of Hμ (Fig. 1b).
From the analysis of the given distribution of microhardness, it follows
that in the vast majority of cases, convex volumes of metal correspond to
higher values, and concave volumes correspond to lower values. Indeed, in the
conduct of a joint analysis location of indenter prints and the corresponding
value of the microhardness of the metal (Fig. 1), we can find that regardless
of the size (depth) of the intrusion, the minimum values of the hardness metal
remain almost unchanged. Furthermore, as it moves along the banks of the
recess, towards the surface of the skating, the absolute values of
microhardness begin to increase gradually, reaching certain extreme values
around the middle of the convex part. Based on the presented character of the
distribution microhardness, it can be assumed that the convex sections should,
in fact, correspond to the extrusion or that part of them that remained on the
surface of the wheel. The fact is that after extrusion is formed, the extruded
part of the metal is partially carried away from the interaction with the rail
and only a certain part of it remains, as evidenced by the absolute values of
microhardness (Fig. 1b).
On the other hand, the sites of formation of future intrusions can be
unambiguously determined by the nature Hμ of the change. This is due to the fact that during the propagation of
plastic flow, the development of processes strain hardening of the metal leads
to an increase in the strength characteristics [12]. Based on this, in places
of current maximum stresses, in the direction of the likely localisation of plastic
deformation, a certain increase in microhardness should be expected. The given
position was confirmed by the data of microhardness measurements on places with
numbers from 19 to 22 and designation “A”
(Fig. 1a). Subsequently, considering that the values of Hμ qualitatively reflect the level of residual stresses in the micro
volumes of metal [12], traces of the increased solubility of metal in the
etchant should indicate the most probable direction of the local propagation
plastic deformation (from N = 19 to N = 22). After the metal has exhausted
the resource of accumulation defects of crystal structure and, in the first
place, dislocations, an intrusion was formed with an inevitable relaxation of
internal stresses. Thus, micro volumes with local plastic flow become places of
origin of future damage rolling surface of railway wheels during operation.
Compared to the mechanism influence
of a non-deformable non-metallic inclusion considered in detail on the
formation system of internal stresses in carbon steel [14], the compact
arrangement dispersed particles can have a qualitatively different effect. This
was confirmed by the results
of a study in which a site with a local arrangement of dispersed carbide
particles in ferrite during plastic deformation was able to behave as a whole
[15].
Figure 2 shows such
volume metal of the wheel rim in which, next to insulated particles
(designation B), a section with
compactly dispersed non-metallic inclusions was observed. In accordance with
the methodology [11], microhardness was measured at various levels of loading
on the indenter and the corresponding curves were constructed to evaluate the
ability of the metal to strain hardening (Fig. 3). Considering that the
accuracy of microhardness determination is inversely proportional to the load
on indenter [16], the section curve with values εᵢ, < 0.4 is most likely due to a large error in the
determination of Hμ.
Subsequently, the indicated section curves (Fig. 3) was excluded from the
analysis of nature strain hardening of the metal. At initial loads on indenter (εᵢ,> 0.4), a metal with dispersed non-metallic
inclusions (Fig. 3a) has almost the same resistance to plastic flow (of the
order 1 GPa) compared to the volume without particles (Fig. 3b). As the load on
indenter increases, the degree of plastic deformation increases in proportion to
its introduction into the metal. A comparative analysis of the constructed
curves under loading volumes of metal with and without particles indicates the
existence of certain differences in the shape of the curves.
a
b
Fig. 1. The profile surface rolling of wheel's (a) and the nature of
change microhardness (load on the indenter is 0,196 N) in accordance with
the numbers (N) of
measurement sites (b). Magnification 350 x 1.2
Visually, the stress growth rate for a place with inclusions (Fig. 3a)
significantly exceeds the similar characteristic for a metal without inclusions
(Fig. 3b), thereby ensuring a higher hardness level at the same values of
εᵢ. The above increase in microhardness does not contradict the
well-known effect of dispersion hardening metal matrix from the presence of
particles second phase [17]. Based on this, it can be
assumed that the indicated differences in curves can be explained to a certain
extent by the nature of accumulation defects crystal structure during the
plastic flow of the metal. Hence, according to [12, 18], the estimation of the
rate accumulation dislocations by the value of angular coefficient of tangent
in the region of uniform strain hardening was fairly well confirmed by the
analysis of density dislocations by the expansion of X-ray interference [15].
Considering that, the strain hardening characteristics quite unambiguously
estimate the growth rate of defects in the crystal structure during plastic
deformation of carbon steels [17, 18], this technique can be used to analyse
the loading curves under study (Fig. 3). As a characteristic of strain
hardening, the angular coefficient of the tangent, constructed at points with
the same value of εᵢ,, was
adopted. Numerically, the coefficient of tangents corresponded to the magnitude
of the increase in microhardness at a unit change of εᵢ, (ΔΗμ/Δεᵢ), when the Δεᵢ → 0. The values of the angular
coefficient were determined in the range of εᵢ,
0.4 - 0.6. The analysis of ΔΗμ/Δεᵢ
values indicates that for a volume of metal with non-metallic inclusions, this
characteristic is approximately an order of magnitude higher than the value for
a metal matrix without inclusions (7.5 versus 0.6 GPa, respectively). The
observed difference in the parameters of strain hardening is in fair agreement
with the estimate of the ductility margin for carbon steels [19]. From the
results of the studies [20], it is obvious that the lower characteristics
strain hardening, the higher the plastic properties of medium- and high-carbon
steels.
В
Fig. 2. The
volume of metal with compactly located disperse non-metallic inclusions after
measuring microhardness. Magnification 350 x 1.6
Thus, one of the reasons
formation damage railway wheels along the rolling surface should be considered
is an increase of density defects of crystalline structure and, firstly,
dislocations, in areas with a local arrangement non-metallic dispersed
particles. Based on this, during the operation of railway wheels, regardless of
the strength level and structural state of the steel, the location of metal
volumes with such non-metallic dispersed inclusions near the rolling surface
will lead to the rapid exhaustion of the resource of accumulation defects of crystal
structure and cause the formation of surface damage.
Based on this,
assessment nature of the accumulation defects of crystalline structure in a
metal near the rolling surface should be considered as a tool for studying the
processes of structure formation and developing measures to increase the
service life of railway wheels.
4. FINDINGS
1. The formation of extrusions on
rolling surface of a railway wheel was accompanied by an increase in
microhardness carbon steel and intrusions by its decrease.
2. Regardless of the intrusion
depth, the microhardness carbon steel remained practically unchanged.
3. The local arrangement of
non-metallic particles contributed to an increase in the strain hardening
characteristics in micro volumes carbon steel.
4. The formation of damage rolling
surface due to accelerated growth density defects of crystalline structure from
the presence of non-metallic dispersed particles.
а
b
Fig. 3. The ratio of σᵢ - εᵢ for volumes of metal
with dispersed particles of non-metallic inclusions (a) and without them (b)
Acknowledgements
The authors are grateful to Dr.
V.G. Anofriev for providing material for research. Thanks to Drs. O.N. Perkov
and O.A. Tchaikovsky for their valuable advice on research results and paper
design.
References
1.
Knott J.F. 1973. Fundamentals of
fracture mechanics. London: Butterworths.
2.
Koymatcik H., T. Tozlu, H. Cug, Y. Sun, H. Ahlatci. 2013.
“Hardening of the head portions of the pearlitic rails by accelerated
cooling”. JESTECH. 16: 53-58.
3.
Sysyn Mykola, Ulf Gerber, Dimitri Gruen, Olga Nabochenko, Vitalii
Kovalchuk. 2019. “Modelling and vehicle based measurements of ballast
settlements under the common crossing”. European Transport \ Trasporti Europei 71(5). ISSN: 1825-3997.
4.
Vasauskas V., Ž. Bazaras, V. Čapas. 2005. “Strength
anisotropy of railway wheels under contact load”. Mechanika 1(51): 31-38. ISSN: 1392-1207.
5.
Jahanmir S., N.P. Suh. 1977. “Surface topography and integrity
effects on sliding wear”. Wear. 44:
87-99.
6.
Walther F., D. Eifler. 2004. “Fatigue behaviour of railway wheels
at different temperatures” Mater.
Test. 46: 158-162.
7.
Gubenko S., Y. Proidak. 2012. “Investigation of wear mechanism of
tread during operation of railway wheels” Transport problems 7: 111- 125.
8.
En N.F. 2009 “European standard for Wheels – EN 12262
Product requirements”.
9.
Boljshakov V.I., G.D. Sukhomlin, N.Eh. Pogrebnaya. 2001. “Atlas
struktur metallov I splavov” [In Russian: „Atlas of metal and alloy structures”]. Dnepropetrovs, Ukraine: Gaudeamus.
10. Hollomon J.H. 1945.
“Tensile deformation”. Trans.
A.I.M.E 162: 268-290.
11. Patent UA 418818 G01N
3/40. Спосіб
оцінки
деформаційного
зміцнення
мікрооб’ємів
зерен
полікристалів.
Київ, UA. Бюл. №11, Публ.
10.06.2009, 4с. [In Ukrainian: A method of
estimating the strain hardening of the micro-volumes of polycrystalline grains.
Kiev, UA. Bul. No 11, Publ. 10.06.2009, 4s].
12. Trefilov V.I.,
V.F.Moiseev. 1978. “Dispersnihe
chasticih v tugoplavkikh metallakh” [In Russian: “Dispersed particles in refractory metals”]
Kiev, Ukraine: Naukova dumka.
13. Cahn R.W. (Ed.). 1965.
“Physical Metallurgy”.
Amsterdam: North-Holland publishing company.
14. Gubenko S., Y. Proidak, A.
Kozlovsky, et. al. 2008. “Influence of nonmetallic inclusions on micro breaks formation in
wheel steel and railway wheels”. Transport
Problems 3: 77-81.
15. Babich V.K., Yu.P. Gulj, I.E. Dolzhenkov. 1972. “Deformacionnoe starenie stali”. [In Russian: „Deformation
aging of steel”]. Moscow: Metallurgiya.
16. Grigorovich V.K. 1976. “Tverdostj i mikrotverdostj metallov” [In Russian: „Hardness
and microhardness of metals ”]. Moscow: Metallurgiya. Moskva: Nauka.
17. Pickering F.B. 1978.
“Physical metallurgy and the design
of steels”. Applied science publishers LTD.
18. Bergstrom J., B.
Aronson. 1971. “The application of a dislocation model to the strain and
temperature dependence of the strain hardening exponent n in Ludwik’s
relation between stress and strain in mild steels”. Inst. Metallforsk 753: 27-39.
19. Morrison W.B. 1966.
“The effect of grain size on the stress-strain relationship in low carbon
steel”. Trans. Am. Soc. Metals.
59: 824-846.
20. Fetisov V.P., V.K.
Babich, V.A. Pirogov. 1983. “Opredelenie
deformiruemosti katanki iz nizkouglerodistoyj stali pri volochenii”. [In Russian: „Determination deformability of a low
carbon steel wire rod during drawing”]. Chernaya metallurgiya. Byul. NTI 17: 58-59.
Received 03.10.2019; accepted in revised form 21.11.2019
Scientific
Journal of Silesian University of Technology. Series Transport is licensed
under a Creative Commons Attribution 4.0 International License