UIC CODE
3rd edition, January 2015
Original
Recommendations for the use of rail steel grades
Recommandations pour l’emploi de différentes nuances d’aciers à rails
Empfehlungen für die Verwendung unterschiedlicher Schienenstahlsorten
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Leaflet to be classified in volume:
VII - Way and Works
Application :
With effect from 1 January 2015
All members of the International Union of Railway
Record of updates
1st edition, January 1980
First issue
2nd edition, March 2005
Overhaul of leaflet for conformity with CEN standards
3rd edition, January 2015
Overhaul of leaflet with new knowledge from e.g. EU-project
INNOTRACK
The person responsible for this leaflet is indicated in the UIC Code
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Contents
Summary ..............................................................................................................................1
1-
Introduction .................................................................................................................2
2-
Rail defects influencing steel grade selection .........................................................3
2.1 - Wear (UIC-defect code 220)..................................................................................3
2.2 - Plastic deformation (UIC-defect code 223 and 224)..............................................3
2.3 - Rolling Contact Fatigue (RCF)...............................................................................4
3-
Criteria for determining steel grade selection ..........................................................6
3.1 - Economic criteria ...................................................................................................6
3.2 - Technical criteria....................................................................................................6
3.3 - Rail maintenance ...................................................................................................8
4-
Recommendation for the use of steel grades ........................................................10
5-
Outlook .......................................................................................................................12
List of abbreviations ..........................................................................................................13
Bibliography .......................................................................................................................14
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Summary
During recent years significant research and development aimed at RCF of rails has been conducted,
motivated by the more frequent occurrence of RCF experienced by railways.
Further, the way in which the UIC Leaflet 721, 2nd edition has been employed varies between
Infrastructure Managers across Europe.
This new knowledge also included a systematic approach to combine the experience from the current
operational situation and respective degradation models.
Due to the new findings steels with a hardness  350 HBW may be installed also in curves with larger
radii than previously recommended.
This leaflet gives an overview on the topic of rail grade selection. For more detailed information on
specific topics, please refer to the bibliography.
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1 - Introduction
Increases in railway traffic, heavier axle loads, higher speeds and the introduction of new generations
of rolling stock have increased loads and degradation rates of rails. In particular, the occurrence of
rolling contact fatigue in many larger radii curves has increased.
In the EU-project INNOTRACK the influence of the steel grades on the degradation behaviour of the
rails was a main research topic. The knowledge generated in INNOTRACK Concluding Technical
Report, gave some important impulse for the current revision of the UIC Leaflet 721 (see Bibliography
- page 14). This leaflet reflects a common understanding between UIC and UNIFE experts.
One conclusion of the INNOTRACK project which is considered in this leaflet is that steels with a
hardness  350 HBW (see List of abbreviations - page 13) may be installed also in curves with larger
radii than previously recommended.
The aim of the current UIC Leaflet 721 is to provide assistance in the selection of rail steel grades so
that the most suitable rail is chosen based on the specific railway operating conditions in a case-bycase analysis.
The presented recommendations do not apply for heavy haul conditions (over 25 tons/axle). Further, rail
grades under trial are excluded, in particular bainitic grades are only referred to in a future perspective.
Timely execution of maintenance measures (tamping, grinding/milling, and lubrication of the railwheel-interface) has a decisive impact on the service life of rails in curves.
Often, a combination of the two measures - a proper choice of rail steel grade and related maintenance
procedures - is necessary in order to achieve a cost-effective service life for rails.
The decision to select the appropriate rail grade can only be taken considering the historical
occurrence of the specific rail defects as well as prevailing specific operating conditions (speed, traffic
type, track geometry and permanent-way design, lubrication, weather conditions etc.).
In addition to the issue of rail grade selection, the UIC Leaflet 721 also covers recommendations to
assure quality when installing and maintaining rails.
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2 - Rail defects influencing steel grade selection
There are several potential defects that influence the steel grade selection. These defects may arise
on the head, web and foot of the rail, or can be limited to the rail ends or welds. Different alloys and
heat treatments influence the mechanical properties of the rails - such as the residual stresses and
not least the weldability of rail steels - and thus the degradation under traffic. Improvements in steel
production, the increasing hardness of standard rail grades and the changes in traffic have led to a
change in the occurrence of the most relevant rail defects.
In recent years the dominating rail defects leading to the highest maintenance costs arise on the rail
head and will be summarized in the following.
The numbering follows the classification in UIC Leaflet 712 (see Bibliography - page 14).
2.1 -
Wear (UIC-defect code 220)
The wear mechanism depends on the relationship between (dynamic) contact stresses, slip conditions
and material properties.
2.1.1 - Lateral wear (UIC-defect code 2203)
In tight curves with (unlubricated) wheel flange contact the highest contact stresses occur on the gage
face of the rail head. The highest wear rates occur due to the adhesive wear mechanism and is commonly accompanied by plastic deformation.
From today's perspective high strength pearlitic steels withstand these operational demands best.
An increase in hardness from 260 HBW to 350 HBW reduces the wear rate approximately by a factor
of three.
2.1.2 - Corrugation (UIC-defect code 2201 and 2202)
Corrugation is a periodic type of wear. Usually there is a division into short pitch and long pitch corrugation depending on the peak-to-peak distance.
The degradation rate (depths of the troughs) can be reduced by a choice of high strength pearlitic
steels. Occurrence cannot usually be prevented, however the amplitude and the wavelength will be
reduced by such a choice (see Testing of hsh rails Report in high-speed tracks to minimise rail
damage in Bibliography).
2.2 -
Plastic deformation (UIC-defect code 223 and 224)
Defect 223 crushing and/or 224 local batter of the running surface may occur if the plastic limit of the
rail steel is repeatedly reached not only at the surface but also at depths of a few millimetres.
A harder rail grade (i.e. a rail material with a higher yield limit) is beneficial to prevent plastic deformation.
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2.3 -
Rolling Contact Fatigue (RCF)
RCF is one of the major cost drivers on rail infrastructure.
There are basically two major types of RCF:
-
Head checking and
-
Squats.
Occurence of spalling of the running surface of low rails in sharp curves is also to be considered.
NB:
2.3.1 -
Lateral wear (see point 2.1.1 - page 3) is the dominant degradation mechanism in tight curves
and RCF becomes more and more relevant with increasing radii. Artificial wear removes (at
least reduces) RCF damage (see point 2.3) and both artificial and natural wear influence the
contact stresses and thus RCF formation.
Head-checking (UIC-defect code 2223)
Surface cracks at the rail head - head-checking - are a dominant defect in curves within the range of
approximately 300 m to 3 000 m (depending on operational conditions). Further influencing
parameters are speed, cant, gradient, vehicle properties, the acceleration/braking situation,
lubrication, rail head and wheel tread profiles, and maintenance strategy (e.g. preventive grinding).
Similar to wear, crack propagation in head check affected rails can be reduced by the use of pearlitic
steels with higher hardness. An increase in hardness from 260 HBW to 350 HBW reduces the crack
propagation rate approximately by a factor of two.
2.3.2 -
Squats (UIC-defect code 227)
A typical singular defect originating from surface fatigue is the so-called squat. Squats originate from
imprints or other local irregularities in the rail surface. On corrugated rails (UIC-defect code 212) this
defect can occur periodically. Most squats arise at tangent track or wide curves with less lateral wear.
It has been observed on some networks that softer pearlitic rail grades behave less susceptible
regarding squat formation.
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2.3.3 -
Spalling of the running surface of the low rail
On the running surface of low rails in curves, especially with cant excess, a network of fine cracks
(sometimes called "snake skin") develops and some small pieces of metal flake off between these
cracks (similar to UIC rail defect code 2221).
Fig. 1 - Spalling of the running surface of the low rail (courtesy of Tata Steel Inc.)
The choice for harder pearlitic rails as well as preventive grinding is beneficial in this case.
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3 - Criteria for determining steel grade selection
The present edition of UIC Leaflet 721 refers to steel grades specified in the European Standard
EN 13674-1 (see Bibliography - page 14).
The manufacture and acceptance of rails is dealt with in UIC Leaflet 860 and EN 13674-1 (see
Bibliography).
Most railways use the steel grade R 260 (see List of abbreviations - page 13) , and to a very limited
degree, the R 260 Mn (see List of abbreviations), as standard rail grade for their track.
In tight curves and/or rails subjected to high loads, many railways achieve a longer service life by
installing rails made from steel grades with a minimum hardness of 350 HBW.
The corresponding hardness of these rails is obtained either through heat treatment or by the addition
of alloys like chromium.
3.1 -
Economic criteria
Technical considerations and economic factors must be taken into account when selecting a rail
grade. It is recommended to use LCC-calculations (see List of abbreviations) to achieve the best
economic solutions for each railway.
Life Cycle Cost analyses include:
-
Material and installation costs,
-
Maintenance costs,
-
Costs for removal.
The annual costs of the rails are the sum of the core maintenance costs, the costs for operational
hindrances and the depreciation costs (material, installation and removal costs divided by the life span
of the rail). In most cases the depreciation costs are larger than the maintenance costs. If the
infrastructure manager wants to reduce the annual costs for the rails it is thus often efficient to do so
by a reduction of the depreciation costs. Normally a long life-span of the rail is therefore valuable.
When selecting the rail grades the infrastructure manager's goal is to install rails with the lowest LCC.
Normally this is the rail with the largest life span.
3.2 -
Technical criteria
Selection of rail grade can set out from a general, network wide guideline based on the combination
of traffic (MGT - see List of abbreviations) and curve radius (see Fig. 3 - page 10). To aid in this, a
network wide investigation of the curve radii above which head checks and excessive wear do not
occur is useful (see point 4 - page 10).
This general guideline for the network can then be improved locally by adopting knowledge on the
local operational characteristics and damage characteristics as described below.
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3.2.1 -
Experience / local rail history
Many aspects and parameters influence the rail grade selection. It is important that the rail grade
selection is also based on the experience of the local track and traffic conditions and not just to the
general recommendation of this leaflet.
This may result in a more specific rail grade selection than the general recommendation in Fig. 3 page 10.
3.2.2 -
Local parameters
The following local parameters influence the development of wear and rolling contact fatigue defects.
3.2.2.1 -
Curve radius
The most important track parameter for rail grade selection is the curve radius.
Natural lateral wear tends to evolve inversely to the curve radius. Therefore in tight curves the lateral
wear is the predominant phenomenon.
In addition to lateral wear corrugation may occur, in particular on the low rail in curves.
Head-checks may occur on curved rails and cause serious problems. The formation and evolution of
these defects may be delayed, under specific conditions, by natural wear since this will remove small
RCF defects. The dominating damage mechanism will then shift from RCF to wear.
Due to the large variety of track and traffic parameters a specific radius range for head checking and
natural wear cannot be given. For first evaluation on some networks a radius of 3 000 m is the upper
limit for the appearance of head checking. For high speed lines this limit may be shifted to 5 000 m.
3.2.2.2 -
Annual traffic load
Due to LCC-aspects the annual traffic load affects the selection of the rail grades as indicated in Fig. 3.
3.2.2.3 -
The impact of falling and rising gradients
Assuming operation with constant speed:
-
On steep rising gradients, of approximately 15 ‰ and more, head checking and squats appear
more severe than on flat tracks.
-
On steep falling gradients, of approximately 15 ‰ and more, head checking and crack
propagation is normally reduced to some degree if not stopped at all.
3.2.2.4 -
Acceleration and braking
In general terms acceleration increases the risk of head-check and squat formation on tangent rails,
whereas braking mainly promotes RCF on wheels. The effect of braking on tangent rails typically
results in wear and plastic deformation. Sometimes, squats can also be observed.
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3.2.2.5 -
Speed and cant on curves
Given the different traffic requirements, a compromise must be established when prescribing cant in
curves. In practice the result of that compromise is that some trains run on a cant deficiency and others
on cant excess.
Cant deficiency contributes to lateral wear on the high rail and to propagation of head checks whereas
cant excess causes plastic deformation on the low rail.
3.2.2.6 -
Axle load
A higher axle load will result in a higher normal load between the wheel and rail and often also in higher
tangential contact stresses. Wear, plastic deformation and head-checking are therefore more
pronounced under higher axle loads.
3.2.2.7 -
Type of rolling stock
Certain properties of the (traction) units e.g. primary yaw stiffness, vehicle suspension (lateral stiffness), high slip and the applied operative tractive efforts are potential causes to an increase in rail
degradation.
Smaller wheel radii may also contribute to an increase in rail damage.
3.3 -
Rail maintenance
Maintenance methods such as lubrication, grinding and milling help to reduce or eliminate wear and
rolling contact fatigue if applied appropriately. In establishing maintenance routines, it has to be
considered that different maintenance approaches, in particular grinding strategies, are needed for
harder rail steels.
3.3.1 -
Lubrication on the gauge corner of the high rail
The most common lubrication measures are fixed automatic lubricators, or lubrication by rolling stock
and in exceptional circumstances manual lubrication. Irrespective of the application method,
lubrication remains the most reliable means of delaying lateral wear on high rail in curves.
Regarding rolling contact fatigue, lubrication has the effect of decreasing lateral stresses, which
generally decreases RCF formation. However, excessive lubrication may contribute to the generation
of shelling-like defects (see Fig. 2 - page 9) at the gauge corner. Moreover, lubrication in presence of
head-checks may cause accelerated crack growth and spalling. To obtain an accurate balance it is
important to tune the amount, friction characteristics and application strategies of lubrication. Further,
it is important to assure continuous lubrication. Account must also be taken for the influence of weather
conditions (e.g. temperature, humidity).
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Fig. 2 - Shelling-like defects at the gauge corner (courtesy of Tata Steel Inc.)
As mentioned above harder steel grades generally decreases lateral rail wear. A correct friction
management further promotes this effect.
3.3.2 -
Rail grinding / milling
This track maintenance measure prolongs rail service life by preventing the emergence of defects or
by delaying their development, and by maintaining a proper rail profile. There are in principle two types
of rail grinding: preventive grinding and corrective grinding.
Preventive grinding is designed to control surface fatigue cracks before, or shortly after initiation by a
regular and slight material removal. When applied systematically as a maintenance measure, it preempts the emergence of certain rail-surface defects. Preventive grinding is up to now the only way to
prevent the formation of squats.
Corrective grinding is designed to remove rail defects that have already developed (corrugation, head
checking, ballast marks etc.) and to re-profile the rail to improve the wheel/rail contact conditions.
Rail grinding / milling has to be carried out carefully to ensure the complete removal of the damaged
(cracked) layer. Furthermore low tolerances on transverse and longitudinal profile are necessary to
extend the time till surface fatigue or periodic defects like corrugations will recur again.
Note that harder rail grades do not remain free of head-checks and thus these grades need a suitable
grinding strategy although the degradation rate is more delayed compared to softer rails. The strategy
aimed at removing incipient cracks should be established based on the local operational conditions individual railways may have their own experience on the necessary grinding effort.
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4 - Recommendation for the use of steel grades
As mentioned above, rail grade selection should be a process where network strategies are derived
based on the general guidelines in this Leaflet and the operational experiences from the concerned
network. Such a strategy should also account for logistics constraints in that too many rail grades
cannot be employed in a network. Further, it should be considered that the chosen strategy will
influence the maintenance needs.
A suitable starting point is Fig. 3, which gives general recommendations of steel grades as a function
of curve radius and annual traffic load. There is a coloured transition area between the
recommendation for use of rails with 260 HBW and rails with a hardness 350 HBW. In this context
it should be noted that rails made of R 260 or R 350 HT (see List of abbreviations - page 13) steel
grades are by far the most common today.
To further adapt the selection strategy for the considered network, an analysis of occurring damage
patterns should be carried out. From this analysis it is possible to derive the curve radii above which
no extensive wear or head checking is found for the existing rail grades. With this knowledge the
limiting curves of the coloured region in Fig. 3 may be adjusted.
Fig. 3 - Recommendation for the use of pearlitic rail grades
Once general guidelines for the network are established, local selection criteria may be employed to
specific stretches of the track. These may be based on the damage characteristics at the location in
noting that occurrence of severe wear and head checks imply that a shift towards harder rails may be
in order. In this process it should be noted that operational characteristics influences the response in
terms of wear and RCF. More explicitly, the influencing parameters discussed in point 3 - page 6 will
shift the upper limit of where rails with lower hardness are suitable to the right or to the left.
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Parameters which generally move the limit towards the right:
-
Increase of speed,
-
Higher axle loads,
-
Higher gradients,
-
Aggressive rolling stock,
-
Bogies with bad steering capabilities.
These parameters are all increasing the propensity for RCF formation and lateral wear.
Parameters which generally move the limit towards the left:
-
Lubrication,
-
Wide-spread squat formation,
-
Preventative grinding, eg. High Speed Grinding with a minimum material removal can also shift
the limit to the left (experience might be different from railway to railway).
Lubrication decreases the propensity for RCF and the amount of lateral wear.
According to the experience of some European networks, softer perlitic steel grades behave less
susceptible to squat formation.
Preventive grinding (except High Speed Grinding) removes small cracks and maintains the transverse
profile, which decreases the risk of RCF formation.
For logistic reasons, it is recommended to equip the two rails with the same steel grade.
Both technical and economic criteria must be considered when making a rail grade selection, (see e.g.
INNOTRACK - Concluding Technical Report in Bibliography - page 14). As mentioned above,
maintenance policy (rail lubrication, grinding and milling) has a significant impact on the service life of
rails, be they of normal or hard steel type. As service life is a key factor in any economic analysis, the
maintenance policy adopted must be taken into account when choosing the steel grade for rails.
Due to the lack of small curve radii on high-speed lines, a choice of R 260 is commonly made.
Given the substantial loads and small radii encountered, hard steel is frequently used for suburban
traffic, in line with the general rules set out in this Leaflet.
The present recommendation accounts for logistics constraints and refers only to two steel grades. A
different strategy of rail grade selection with the recommendation of a broader variety of steel grades
is described in INNOTRACK: Deliverable report D4.1.5GL (see Bibliography).
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5 - Outlook
Various railways are currently carrying out tests on particular steel grades, such as bainitic rail steels,
in order to remedy or attenuate problems, notably those resulting from rolling contact fatigue (e.g.
head checking).
Welding procedures such as flash butt welding or aluminothermic welding (see EN 14730-1:2010,
EN 14587-1:2007 and EN 14587-2:2009, Bibliography - page 14) play an increasingly important role
in these tests. New welding procedures might need to be developed to incorporate the desired rail
steel properties into the weld. Depending on the scope of the track tests it is advisable to carry out
evaluations of both the technical/economical features of new rail grades and also their welding
properties.
Bainitic microstructures show different behaviour and may remain free of head checking. However
bainitic steels typically shows an increased wear compared with a pearlitic grade of the same
hardness. Detailed behaviour of the variety of non-standard bainitic steels regarding these issues can
however not be described at present.
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List of abbreviations
CEN
European Committee for Standardization
Cr
Chromium
EN
European Norm
HBW
Hardness Brinell Wolfram (Tungsten)
HT
Heat Treated
LCC
Life Cycle Costs
LHT
Low Alloyed Heat Treated
MGT
Million Gross Tons
Mn
Manganese
R
Rail (grade, e.g. R 260)
R
Recommended (e.g. UIC 721 R)
RCF
Rolling Contact Fatigue
UIC
International Union for Railways
(Union Internationale des Chemins de fer)
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Bibliography
1. UIC Leaflets
International Union of Railways (UIC)
UIC Leaflet 712: Rail defects, 4th edition, January 2002
UIC Leaflet 860: Technical specification for the supply of rails, 9th edition, January 2008
2. European Standards
European Committee for Standardization (CEN)
EN 13674-1:2011: Railway applications - Track - Rail - Part 1: Vignole railway rails 46 kg/m and above,
2011
EN 14587-1:2007: Railway applications - Track - Flash butt welding of rails - Part 1 : new R220, R260,
R260Mn and R350HT grade rails in a fixed plant, 2007
EN 14587-2:2009: Railway applications - Track - Flash butt welding of rails - Part 2 : new R220, R260,
R260Mn and R350HT grade rails by mobile welding machines at sites other than a fixed plant, 2009
EN 14730-1:2010: Railway applications - Track - Aluminothermic welding of rails - Part 1 : approval of
welding processes, 2010
3. Miscellanous
Deutsche Bahn AG
Testing of hsh rails in high-speed tracks to minimise rail damage. Wear, 258:1014-1021, Heyder, R.
and G. Girsch, 2005
INNOTRACK
Concluding Technical Report, Anders Ekberg & Björn Paulsson, 2010
Deliverable report D4.1.5GL: Definitive guidelines on the use of different rail grades, Peter Pointern,
Albert Joerg, Jay Jaiswal, 2009
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Warning
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Railways (UIC). The same applies for translation, adaptation or transformation, arrangement or reproduction by
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"analyses and brief quotations justified by the critical, argumentative, educational, scientific or informative nature
of the publication into which they are incorporated".
(Articles L 122-4 and L122-5 of the French Intellectual Property Code).
 International Union of Railways (UIC) - Paris, 2015
Printed by the International Union of Railways (UIC)
16, rue Jean Rey 75015 Paris - France, January 2015
Dépôt Légal January 2015
ISBN 978-2-7461-2326-7 (French version)
ISBN 978-2-7461-2327-4 (German version)
ISBN 978-2-7461-2328-1 (English version)
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