Stress-Free heat treated rail for outstanding wear resistance TATA

SlideTata Steel 1Stress-Free heat treated rail

Stress-Free heat treated rail for outstanding wear resistance

18 March 2015


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


Summary


2 Heat Treated Rail



5 Summary

6 Questions


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


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?


How will GCC conditions impact on rail degradationWear

Rail head wear drives rail replacement:

• Tight curves – all networks

• Heavy haul


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.


Subkah’s present a major corrosion challenge

even on relatively new rail


Summary


2 Heat Treated Rail



5 Summary

6 Questions


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


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


Summary


2 Heat Treated Rail



5 Summary

6 Questions


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


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


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.


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


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


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



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

http://www.fra.dot.gov/Elib/Document/2099



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


Summary


2 Heat Treated Rail



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


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



Summary


2 Heat Treated Rail



5 Summary

6 Questions


How will GCC conditions impact on rail degradationWear

Rail head wear drives rail replacement:

• Tight curves – all networks

• Heavy haul


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.


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


Any questions?

Engineering

Stress-Free heat treated rail for outstanding wear resistance TATA