Investigation of slide mechanism of tread during operation of railway wheel

Abstract

Causes of reasons and explanation of mechanism forming damages
of railway wheels tread were investigated. At slipping on contact surfaces wheelrail a between by simultaneous development of processes of work-hardening and softening metal determines the terms of origin damages of railway wheels tread were fixed.

Full text

Scientific Journal of Silesian University of Technology. Series Transport
Zeszyty Naukowe Politechniki Śląskiej. Seria Transport
Volume 90 2016
p-ISSN: 0209-3324
e-ISSN: 2450-1549
DOI: 10.20858/sjsutst.2016.90.16
Journal homepage: http://sjsutst.polsl.pl
Article citation info:
Vakulenko, I., Proidak, S., Perkov, O. Investigation of slide mechanism of tread during
operation of railway wheel. Scientific Journal of Silesian University of Technology. Series
Transport. 2016, 90, 187-193. ISSN: 0209-3324. DOI: 10.20858/sjsutst.2016.90.16.
Igor VAKULENKO
1
, Svetlana PROIDAK
2
, Oleg PERKOV
3
INVESTIGATION OF SLIDE MECHANISM OF TREAD DURING
OPERATION OF RAILWAY WHEEL
Summary. Causes of reasons and explanation of mechanism forming damages
of railway wheels tread were investigated. At slipping on contact surfaces wheel-
rail a between by simultaneous development of processes of work-hardening and
softening metal determines the terms of origin damages of railway wheels tread
were fixed.
Keywords: damage, railway wheel tread, hardness, slipping, work-hardening,
softening, energy of activation
1. INTRODUCTION
During operation of railway wheels different level of strength, the forming damages of
metal railway wheels tread are conditioned the simultaneous action forces of friction and
cyclic change of stresses [1]. Supposing that forming damages of surface tread is mainly
determined the internal structure in volumes of metall near the tread of realway wheel [2], it is
necessary to expect different of character development of processes structural changes in
a metal with the different level of strength.
1
Dnipropetrovsk National University of Railway Transport after Academican V. Lazaryаn, 2 Lazaryana str.,
49010, Dnipropetrovsk, Ukraine. E-mail: dnuzt_texmat@ukr.net
2
Dnipropetrovsk National University of Railway Transport after Academican V. Lazaryаn, 2 Lazaryana str.,
49010, Dnipropetrovsk, Ukraine. E-mail: dnuzt_texmat@ukr.net
3
Iron and Steel Institute after Academican Z. Necrasov, AS Ukraine, Starodubov sq., 49050, Dnipropetrovsk,
Ukraine. E-mail: dnuzt_texmat@ukr.net

186 I. Vakulenko, S. Proidak, O. Perkov
Taking into account the tendency of produce railway wheels with the high level strength as
a result of microalloying, change of content carbon in steel and use hardened heat treatments,
the internal structure of metal near by the surface of railway wheels tread in majority of cases
corresponds quenching and follow tempering in the middle interval of temperatures. It ensues
from experience of exploitation of railway wheels, that at the identical level of strength and
high-quality different structural state of metal, the processes of wear can substantially
differ [2].
On the basis of analysis reasons of premature withdrawal of railway wheels it is discovered
from exploitation, that except for the unrationed amount of nonmetallic inclutions of different
morphology and nature of origin at arrangement near-by with railway wheels tread [3],
substantial value, arising up acquire additional moving of wheelpair in relation to the frame of
light cart [4]. The indicated displacements of wheelpair during exploitation are reason of
origin shear component of deformation to the constituent of metal on a contact surface wheel-
rail. As a result on-the-railway wheel tread areas are formed with the different degree of wear
and complicated internal structure of metal from simultaneous influence of a few factors [5].
Forming of such areas is a break by homogeneity of distributing of internal stresses in the
metal of wheel and results of bring nonhomogeneous strain hardening metal on the railway
wheels tread.
On the basis of it the estimation terms of forming of the local slipping presents certain
interest in the process of exploitation of railway wheels with the different level of strength, as
one of the stages of complicated process of formation damage on the railway wheels tread.
2. PURPOSE OF WORK
The purpose of this work was investigation of mechanism of slipping on the railway
wheels tread during operation.
3. MATERIAL AND RESEARCH METHOD
For research carbon steel of railway wheel served as material with contain of carbon 0,6%.
Heat treatment was reach at the different state of structure of metal. As a result of quenching
from the normal temperatures of heating the structure of martensite was formed with hardness
65 HRC, and after subsequent tempering at temperatures 450 − 470°C is a structure of
the tempered martensite with hardness 39 HRC. Heat higher than temperature
3
Ac
,
the required self-control for homogenization of аustenite and cooling with a furnace allowed
to get lamellar pearlitic structure in steel with hardness 13 HRC.
The analysis of behaviour speciment of the probed steel in conditions of the normal contact
rolling was carried out use the proof-of-concept machine of SMC-2 for the normal load 18 kg
on the speciment. At tests, the change of kinematics chart of machine become possibility of
receive of different sizes of slipping on the contact surfaces of speciments, due to the change
of their angulator speed of rotation. Speed of turns spindle of proof-of-concept machine was
300 and 500 min
1
, at the temperatures of test 20 and 120°C (293 and 393°K). As a result of
test determined the beginning moment of forces in the area of contact surfaces speciments.
For explanation the character development processes changes of structure for tests
descriptions, analysis parameters the thin crystalline structure of metal, were used. Estimation
degree of tetragonality crystalline lattice of ferrite, size of areas coherent dispersion (
L
),

Investigation of slide mechanism of tread during operation of railway wheel 187.
density of dislocations (

) and distortions of the second-type (

) carry out, through
the methods of x-rays analysis [6].
4. DISCUSSION OF THE GOT RESULTS
The analysis of known experimental of facts [1, 3, 7] bear witness that to the formation of
extrusions and intrusions (Fig. 1) on the railway wheels tread which become the turn into of
superficial damages in future, local changes are preceded in the area of contact wheel-rail.
Taking into account high-rate of heating at the local slipping, the temperature of beginning of
phase transformations in steel of wheel can be arrived in thin of layer near railway wheels
tread. After completion of the stage of slipping a sharp cooling from the heated metal in more
remote volumes of rim of wheel is able to provide development of phase transformations on
intermediate or even to diffusionless transformation [2, 5].
On that was transformation railway wheels tread with the practically homogeneous strain
hardening of metal, transform into alternating areas with different hardness and capacity for
the deformation work-hardening. During subsequent exploitation of wheel on the indicated
areas with different hardness and internal structure (cold work state and structures after
quenching) it is necessary to expect further growth of distinctions in character of the local
slipping and proper changes in the level of strength properties.
The make use of disk brake systems far of the wheel light carts the estimation of
localization plastic flow of metal on a contact surface a wheel-rail is presented by certain
practical interest.
а b
Fig. 1. Chart of forming extrusion (a) and their real kind on the profile of railway wheels tread
(b) Magnification 100
4.1. Estimation of beginning slide on a contact surface wheel-rail
At certain correlations of strain hardening of metal on the railway wheel tread (degree and
distributing of plastic deformation) and temperature of warming-up during exploitation, there
must be a change of balance between the indicated effects. Above all things the process of
slipping will be determined in size tripping of metal of wheel with a rail. The indicated
characteristic can be estimated on the origin moment of forces in the area of contact surfaces.
From other side, the size of tripping of wheel with a rail must change with the temperature of

188 I. Vakulenko, S. Proidak, O. Perkov
warming-up of metal near-by with the railway wheel tread. On the basis of it, as description
for the estimation of the looked after phenomenon it is necessary to avail in size of energy,
which must be expended for achievement effect of slipping.
Taking into account that a process of slipping is thermally activated, will take advantage of
equalization of Arrhenius for energy activation of process of plastic deformation. In a general
view equalization can be written [8]:
m
M
RT
Q
A)exp(


, (1)
where


− speed of deformation,
A
− value of constant,
Q
− energy of activation process,
R
− universal gas constant,
T
− temperature (°K),
M
− moment of forces at slipping,
m
−
index of degree. After taking the logarithm of correlation (1) get:
Mm
RT
Q
Alnlnln 


(2)
For a condition of constant temperature, after differentiation (2),
m
determined as
a tangent angle of slope from a graphic construction
)(lnln Mf


:
Md
d
mln
ln



(3)
There is a size of relation at unchanging speed of deformation
m
Q
determined as an angular
coefficient from dependence
)
1
(ln T
fM 
:
mmRT
Q
M


ln
ln 
, (4)
and take into account (3) get a numeral value
Q
[8].
Estimation of size energy activation of process slipping, carried out from experimental
data, on speciments of railway wheel steel became able after quenching from the normal
temperatures of heating (Fig. 2). The resulted structure is largely similar to the structure of
metal railway wheel after forming of slide-block onthe tread [2, 7].
a b
Fig. 2. Structure quenching railway wheel steel. Magnification (a) − 1000, (b) – 13000

Investigation of slide mechanism of tread during operation of railway wheel 189.
As speed of deformation the number turns of spindle of proof-of-concept machine was
accepted (

). As show in [7] a calculation of energy activation carried out on tests at no less
as two speeds of deformation and two temperatures of loading. Size

made values 300 and
500 mines
1
, at temperatures +20 and +120°C and the moment of forces in the area of contact
surfaces was arrived at the size of slipping 10%.
Beginning from the first cycles loadings at rolling, from the diagrams change of size
M
it
was found out high instability of values. In area of first hundred cycles of loading decrease of
size of moment of forces on contact surfaces arrived at a few times. As far as the increase of
number of cycles at rolling of unmonotony in character change of the indicated description
went down and only after set in relation to the stable mode, determined the moment of forces.
For the estimation of size
Q
used values
M
at reject 3 − 5% in relation to the average set
level.
From a correlation
Mlnln 

(Fig. 3) values were certain
m
, which were 0,83 and 0,2
for temperatures 293 and 393°K (20 and 120°C) accordingly. Size
Q
estimated rewritting
correlation (4) with preliminary replacement


on

and by the substitution of numeral
values proper descriptions:
)lnln(

 MmRTQ
(5)
It was discovered from the analysis of the got results, that in the interval of the use speeds
(300, 500 мин
1
) decrease of temperature from 120 to 20°C accompanied decrease of the
required energy for development of process slipping approximately in 1,3 of time (from 20,6
to 15,3
mol
kJ
).
Thus, at permanent level of loading and speed of rotation, the indicated decrease of
temperature on the tread metal is accompanied decrease size of tripping with speciments
approximately on 25%. In the isothermal terms of loading the increase of speed of rotation in
the use range of values practically does not change the size energy of activating process of
slipping.

ln

ln
Mln
Mln
a b
Fig. 3. Correlation between

and
M
at the temperatures of test (a) − 20, (b) − 120°C

190 I. Vakulenko, S. Proidak, O. Perkov
At the change of the structural state of metal, depending on the terms of rolling it is
necessary to expect other character of dependence of tripping in the area of contact surfaces
high-quality. So, as compared to tempering on a martensite, metal of railway wheel after the
homogenizing annealing with the level of hardness 13 HRC, at the temperature of test +20°C,
with the increase of speed of rotation in the use range (300 to 500 mines
1
) a show growth in
1,5 of time moment of forces in the area of contact surfaces. Moreover, confirmation was
predictably got high-quality other character of change of tripping of metal at slipping. As
compared to a quenching metal on a martensite, for speciments after annealing there was
absence of area with the unmonotonous change of size
M
on the initial stages of increase of
cycles of loading.
It was found out the analogical character of behaviour carbon steel and able after
quenching with subsequent tempering in the middle interval of temperatures, for example at
the level of hardness 39 HRC. In both cases, since the first cycles of loading there was
a monotonous increase of hardness on-the tread of the tested speciments.
Thus, forming of structures on a diffusionless transformation mechanism on the tread of
railway wheels results in appearance of neighbour areas with a high-quality different conduct
at a loading.
4.2. Research mechanism of soften steel after quenching at rolling
After quenching (Fig. 2) the level hardness of carbon steel (65 HRC) is provided
the beginning certain degree of tetragonality crystalline lattice, which in same queue is
conditioned the concentration atoms of carbon, dissolve in austenite. With the increase
concentration of carbon in steel growth of degree of tetragonality of crystalline lattice of
ferrite (
a
c
) as a result of quenching estimated on correlation [9]:
1 0,045
cp
a
, (6)
where
p
− gravimetric % carbon in steel,
a
− a parameter of crystalline lattice of ferrite,
c
−
size of rib of lattice ferrite after forming crystal of martensite [9]. After a substitution in (6)
for the probed steel of size
p
and the experimentally got values
a
and
c
, there was
a calculated degree of tetragonality of crystalline lattice of ferrite after quenching, which
made
1,027
c
a
. Comparative analysis with the known experimental dates for steel with
analogical concentration of carbon after quenching on a martensite [9] show a good enough
coincidence. It is necessary to examine the got result as a confirmation of absence of
disintegration of super soturation solid solution at cooling.
After 1200 cycles of rolling of specimens slip-free, to the discover decrease of hardness
from 5 to 7% diminish of degree of tetragonality of crystalline lattice of ferrite of quenching
steel corresponded from 1,027 to 1,0255 (on 0,15%). The decrease of the indicated parameter
testifies to development of processes of softened of quenching steel in the process of
the contact phenomena at rolling. Analogical results on influence of insignificant plastic
deformation on the strength middle carbon steel after quenching is got in [10]. For
explanation of mechanism of looked after softened, will take advantage of correlation (6).

Investigation of slide mechanism of tread during operation of railway wheel 191.
After a substitution in (6) values
c
a
=1,0255 it was discovered that size
p
corresponds
concentration of carbon 0,56%.
It is thus necessary to suppose that way out atoms of carbon from martensite of crystals in
the process of rolling, is principal reason of decrease of hardness steel after quenching.
However, if looked after soften at heating to the temperatures higher 500 − 550°C the work-
hardened carbon steel accompanied the increase sizes of areas of coherent dispersion,
reducing the accumulated dislocations and decrease level of distortions of the second-type
[11], after rolling was found out an increase

on 19% (from
210
105,96 
cm
to
210
105,118 
cm
),

(from
4
1,98 10

to
3
1,66 10

) and diminishing
L
на 30% (from 618 to
445
A
). Resulted character of change parameters thinly crystalline structure are show on
the presence effect of the deformation work-hardening of martensite crystals in the process of
rolling. Moreover, the looked correlation between by the processes of work-hardening and
softened at rolling of metal must continuously change depending on the total size of plastic
deformation. If on the initial stages of loading, when the effects increase amount of defects
crystalline structure are insignificant, a total result is a softened effect. At growth of amount
of cycles of loading at rolling, when the role of processes of the deformation work-hardening
will continuously increase, and soften from disintegration of super saturated solid solution
will go down, after the certain number of cycles it is necessary to expect began exceedings
effect of work-hardening.
Research of parameters of thinly crystalline structure of metal at rolling with a 10%
slipping did not result in the high-quality changes character of soften of quenching metal.
Already after 600 cycles of l0ading with slipping, hardness was 62 HRC (before a test
65 HRC), here
L
504 made
A
,

and

attained values
3
2,6 10

and
211
1015 
см
accordingly.
On the basis of the known experimental results [1-3] and results of the conducted
researches there are the looked after cases of forming on the railway wheels tread areas of
«white layer», in actual fact by the appear result of development structural transformations in
a metal on a diffusionless mechanism at slipping in the places of contact wheel-rail.
Development of processes of softening on these areas will be accompanied the inevitable
deformation work-hardening on near by areas without the local slipping. As a result there will
be growth of gradient of hardness on the boundary of section between them. Even in the case
of absence damage surface of rolling on the area of slipping, a growth of strength properties
rate on the indicated near by areas during exploitation of wheel will not be identical.
Taking into account the high enough degree of heterogeneity of distributing size of plastic
deformation on the railway wheels tread, an important practical value has a between by
development of the indicated processes, especially on the stages of braking of railway
carriage. In fact insignificant in size areas with slipping after a roll-up in the process of
exploitation of wheel will result in the origin of high gradients of internal tensions in
the volumes of metal near by with the tread. The indicated areas during further exploitation of
railway wheels become the potential places of forming damages of railway wheels tread.

192 I. Vakulenko, S. Proidak, O. Perkov
5. CONCLUSIONS
1. Forming damages of railway wheels tread is conditioned correlation of the developed
processes of work-hardening and softening in the area of contact a wheel − rail.
2. The found out the decrease hardness of quenching steel at rolling is accompanied the
increase of density dislocations, reduce of areas coherent dispersion and growth of
distortions of the second-type.
3. Regardless of the structural state of carbon steel, the decrease of temperature during
exploitation of railway wheel is promote in development of the local slipping on
the railway wheels tread.
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Received 11.08.2015; accepted in revised form 21.09.2015
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