stress-free heat treated rail for outstanding wear resistance tata
TRANSCRIPT
SlideTata Steel 1Stress-Free heat treated rail
Stress-Free heat treated rail for outstanding wear resistance
18 March 2015
SlideTata Steel 2Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel 3Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel 4Stress-Free heat treated rail
What do Railways want from their rail solution?
Lowest initial cost
Rail
Logistics
Welding
Installation
Longest possible asset life
Least level of maintenance intervention
Grinding, tamping, inspection frequency, emergency repairs
Lowest whole life cost
All of the above
Predictable and safe rail
Absolute priority for all networks
SlideTata Steel 5Stress-Free heat treated rail
Wear
Rail head wear drives rail replacement
in:• Tight curves – all networks
• Heavy haul
• Intense traffic – metros
Rolling Contact Fatigue (RCF)
Fatigue cracks form on the gauge
corner and grow across and into the rail
– leading to brittle fracture:• Intermediate curves
• Gradients
• S&C
• Stations
Welds
Welds can degrade quicker than the
parent rail :• Weld hardness variations causes
differential wear leading to cupping
• Differential stresses in the weld can
result in dipped welds
• Cupping and dipping increase dynamic
loading and can lead to RCF / foot fatigue
Corrosion / Foot Fatigue
Corrosion pits can lead to the onset of
foot fatigue, followed by brittle failure
Detection of foot defects is not usually
possible before failure occurs
Foot fatigue failures are found in:• New rail in extremely corrosive
conditions: Coastal, level crossings, wet
tunnels.
• Old rail in any environment
How do rails degrade and what will define their life?
SlideTata Steel 6Stress-Free heat treated rail
How will GCC conditions impact on rail degradationWear
Rail head wear drives rail replacement:
• Tight curves – all networks
• Heavy haul
• Intense traffic – metros
Sand at the rail wheel interface will increase
wear
Rolling Contact Fatigue (RCF)
Fatigue cracks form on the gauge corner and
grow across and into the rail – leading to
brittle fracture:
• Intermediate curves
• Gradients
• S&C
• Stations
Sand will increases wear and help to reduce
RCF but loss of rail profile may increase RCF.
Welds
Welds often degrade quicker than the parent
rail :
• Weld hardness variations causes
differential wear leading to cupping
• Differential stresses in the weld results in
dipping
• Cupping and dipping increase dynamic
loading and can lead to RCF / foot fatigue
Supply chain economics dictate the use of
short rail so there will be more welds and
higher risk of deterioration
Corrosion / Foot Fatigue
Corrosion pits can lead to the onset of foot
fatigue, followed by brittle failure
Detection of foot defects is not usually
possible before failure occurs
Foot fatigue failures are found in:
• New rail in extremely corrosive
conditions: Coastal, level crossings, wet
tunnels.
• Old rail in any environment
Subkah’s present a major corrosion challenge
even on relatively new rail
SlideTata Steel 7Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel 8Stress-Free heat treated rail
What are the benefits of heat treated rail?
Widespread industry recognition that heat treatment of rails can deliver
Increased levels of wear resistance
Better retention of crown profile
Reduced maintenance costs
Several technologies for heat treatment are available
Water cooling
Polymer quench
Air cooling
Tata Steel’s patented accelerated air cooling method provides unique
rail performance benefits
SlideTata Steel 9Stress-Free heat treated rail
Heat treatment for improved wear resistance
Twin-disc testing
R260 350HT MHH
We
ar
Re
sis
tan
ce
(m o
f s
lip
/ma
ss
lo
ss
)
Wear resistance of Tata Steel’s rail grades
Many sites monitored across Europe
over many years
Summary of track observations
350HT is typically 3x more
resistant to wear than R260
MHH is typically 3x more wear
resistant than 350HT
Independent Track trials consistently
confirm that MHH rail is the most
wear resistant rail.
Track measurements
MHH delivers exceptional resistance to wear
SlideTata Steel 10Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel 11Stress-Free heat treated rail
The Importance of residual stress
Rails are rolled at high temperatures
As rails cool the thermal and microstructural changes occur
These changes introduce residual stresses to the rail
Typically a naturally cooled rail without any straightening process has a tensile residual stress in the base of the foot between 50-100MPa
Residual stresses of on-line heat treated rails can be significantly higher
Straightening operations after cooling alter residual stress distributions (to change the rail shape),
Increasing the tensile residual stress in the rail foot and head
Higher yield strengths give bigger increases in residual stress, so heat treated rail generally has higher residual stress than standard grade rail
European specification maximum is 250MPa tensile in rail foot
Tensile foot stresses after straightening remain for the service life of the rail
Why do residual stresses occur
SlideTata Steel 12Stress-Free heat treated rail
The effect of residual stress on critical defect size to initiate fatigue
0
4
8
12
16
20
24
0 50 100 150 200 250 300
Applied Stress Range, MPa
Critical defe
ct
siz
e
for
fatigue,
mm
0 MPa 50 MPa 150 MPa 250 MPa
Typical
17t axle load
Foot fatigue life is transformed by lowering
tensile residual foot stresses in a rail
SlideTata Steel 13Stress-Free heat treated rail
Stress-Free rail products
Tata Steel Stress-Free rails are heat treated after straightening
Relieves residual stresses present from rolling, cooling and straightening
Unbeatably low residual stresses are guaranteed
• <50MPa in rail foot (EN specification)
• Web saw cut closes (AREMA specification)
Provides higher resistance to fatigue than all other current processes
Heat treatment process imparts excellent mechanical properties
High wear resistance
High ductility
Low residual stress
Unique process – Unique product
SlideTata Steel
Heat Treatment Investment at Tata Steel
New Capacity
• New 70kt rail heat treatment plant,
commissioned in October 2013.
• Produces rail up to 108m long and more than
doubles capacity for heat treated rail.
• Demand has exceeded capacity for heat
treated rail over recent years
• The new plant allows for growth into key
target markets, including GCC Countries.
Performance review
• Safety : project was delivered with no injuries
• The plant was installed / commissioned on
plan & budget.
• Delivery destination include France, Holland,
Germany, South Africa and India.
SlideTata Steel 15Stress-Free heat treated rail
Fatigue performance effects of residual stress
0
50
100
150
200
250
300
350
400
10,000 100,000 1,000,000 10,000,000
Life, cycles
Str
ess R
ange,
MP
a
Standard stress Notched Low residual stress Notched
Standard stress notched run-out Low residual stress notched run-out Proving the benefit of low stressed rail
A rail was heat treated rail at Hayange
It was then cut in half
One half was fatigue tested
The other half was roller straightened and
then fatigue tested
Results
The blue line (unstraightened rail) takes
double the number of cycles to failure
than the straightened rail (green line)
The first test pass (5million cycles without
failure) was 150MPa loading for the
straightened rail and 250MPa for the
unstraightened rail
Foot fatigue life is doubled by heat treating rail after roller straightening
SlideTata Steel 16Stress-Free heat treated rail
Fatigue performance effects of residual stress
Tata Steel optimised process
Low residual stress
4 point bend testing
Foot in tension
Stress range - 350MPa
Standard heat treatment
SlideTata Steel 17Stress-Free heat treated rail
MHH – The highest performing heat treated rail
Exceptional wear resistance
Resists plastic flow
Resists corrugation
Retains profile
The most wear resistant rail available
Uniquely low residual stress
Improved foot fatigue performance
Greater resistance to initiate fatigue
Greater fatigue crack size required to
initiate failure
The lowest residual stress rail available
Longer life : Less maintenance
SlideTata Steel 18Stress-Free heat treated rail
MHH – The highest performing heat treated rail
Ta
ta S
teel
(MH
H)
Independently monitored (TTCI) Test site – Tehachapi (CA – USA) [1]
[1] - U.S. Department of transportation - federal railroad administration report - http://www.fra.dot.gov/Elib/Document/2099
Other rails supplied by NSC,NKK, VA, RMSM, PST
SlideTata Steel 19Stress-Free heat treated rail
MHH – The highest performing heat treated rail
Independently monitored (TTCI) Test site – Tehachapi (CA – USA)
Ta
ta S
teel
(MH
H)
Tata Steel MHH is the most wear resistant rail tested
Other rails supplied by NSC,NKK, VA, RMSM, PST
SlideTata Steel 20Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel
The need for protection against corrosion
Typical corrosive environments
Coastal routes Stray current
Level crossingsTunnels
Photograph courtesy of BBC
21Premium rail for more life with less maintenance
SlideTata Steel
Protection against rail corrosion
Foot failures induced by corrosion
make up a significant proportion
of rail breaks.
The foot area is nearly impossible
to inspect in service.
Existing/historic corrosion
prevention systems:
Not universal in application
Often unsuitable for third rail
areas
Not damage tolerant in an
aggressive environment
•Tata Steel developed Railcote to address these needs
This rail was removed after three
months’ service at a level crossing
suffering stray current corrosion
22Premium rail for more life with less maintenance
SlideTata Steel
Railcote case study
Above:Railcote rail installed
at the level crossing during
Oct 2009.
Below:
The same rail after 3 months
in service
No signs of corrosion
These rails are performing
well and remain in track 65
months after installation
Already achieved a 20 times
life extension over previous
standard rail
23Premium rail for more life with less maintenance
SlideTata Steel 24Stress-Free heat treated rail
Summary
1 What Railways need from their rail solution?
2 Heat Treated Rail
3 Tata Steel’s “Stress-Free” rail
4 Railcote corrosion protection systems
5 Summary
6 Questions
SlideTata Steel 25Stress-Free heat treated rail
How will GCC conditions impact on rail degradationWear
Rail head wear drives rail replacement:
• Tight curves – all networks
• Heavy haul
• Intense traffic – metros
Sand at the rail wheel interface will increase wear
Heat treated rail will reduce wear by a factor
of 3 and Tata Steel’s MHH will reduce wear by
a factor of 9 compared to 260 grade rail
Rolling Contact Fatigue (RCF)Fatigue cracks form on the gauge corner and grow
across and into the rail – leading to brittle fracture:
• Intermediate curves
• Gradients
• S&C
• Stations
Sand will increases wear and help to reduce RCF but
loss of rail profile may increase RCF.
Heat treated rail will help to reduce RCF by
maintaining crown profile for longer
WeldsWelds often degrade quicker than the parent rail :
• Weld hardness variations causes differential
wear leading to cupping
• Differential stresses in the weld results in
dipping
• Cupping and dipping increase dynamic loading
and can lead to RCF / foot fatigue
Supply chain economics dictate the use of short rail
so there will be more welds and higher risk of
deterioration
Tata Steel can help to find the optimum
welding and heat treatment solutions to
minimse risk of weld deterioration
Corrosion / Foot FatigueCorrosion pits can lead to the onset of foot fatigue,
followed by brittle failure
Detection of foot defects is not usually possible
before failure occurs
Foot fatigue failures are found in:
• New rail in extremely corrosive conditions:
Coastal, level crossings, wet tunnels.
• Old rail in any environment
Subkah’s present a major corrosion challenge even
on relatively new rail
Railcote systems will address extreme
environments to extend rail life by at least 3X
Guaranteed low stress in Stress free heat
treated rail will double foot fatigue life in all
conditions
SlideTata Steel 26Stress-Free heat treated rail
Any questions?