Rail metallurgy and inservice performance

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Rail metallurgyand in-service performance
International Union of RailwaysTehran - December
2003

• Daniel Boulanger, Corus Rail

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Rail functions

• Wheel support and guidance

SAFETY
QUALITY
SAVING
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Traffic effects

• Static loads
• Vehicle weight
• Quasi-static loads
• Centrifugal force, centering force, cross winds
• Dynamic loads
• Track irregularities geometry, stiffness,
  discontinuities (welds, joints), rail running
  surface (corrugation, ballast prints), vehicle
  defects (wheel flats, vibrations, hunting)
• Contact stresses
• Acceleration and braking areas
• Thermal stresses

RAIL
Internal Fatigue Wear Plastic Flow Rolling
Contact Fatigue
BREAKS
Risks
DERAILMENTS
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Corus Rail500 000 tons of rails per year
80 profiles and 25 steel grades
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Track specificities
80 profiles and 25 steel grades
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Rail characteristics

• Qualifying tests
• Fracture toughness
• Fatigue crack growth rate
• Fatigue test
• Residual stress
• Variation of centre line running surface hardness
  of HT rails
• Tensile strength and elongation
• Segregation

• Acceptance tests
• Chemical composition
• Microstructure
• Decarburisation
• Oxide cleanness
• Sulfur prints
• Hardness
• Tensile tests
• Dimension tolerances
• Straightness, surface flatness and twist
• Internal quality
• Surface quality

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Rail abilities
1960
1980
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Internal fatigue
RAIL PRODUCTION
Basic Oxygen Converter Low aluminium killing
process Vacuum degassing Continuous
casting Ultrasonic inspection
Gauge corner shelling
Tache ovale
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Corus Rail steel production
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Ultrasonic inspection

• European project
• ³70 Head
• ³ 60 Web
• Foot
• Calibration
• Holes Æ 2 mm

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Wear and plastic flow
RAIL PRODUCTION

Heat treatment
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Wear vs. hardness for perlitics
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Rail failure evolution
RAIL PRODUCTION
INTERNAL FATIGUE
Basic Oxygen Converter Low aluminium killing
process Vacuum degassing Continuous
casting Ultrasonic inspection Heat treatment
NEW GRADES
RAIL CONTACT FATIGUE
NEW MAINTENANCE
WEAR

1980 / 1990
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Rolling Contact Fatigue

• Surface damage is caused by high tangential loads
  or / and high local friction coefficient
• Squat and head check are initiated on the running
  surface of the rail in shear mode then develop in
  a sublayer according to the local stress field
• The material of the rail running surface presents
  a high degree of cold hardening, together with
  plastic flow

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Squat
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Head check
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Steel grades vs. wear
721R Draft
350LHT
350HT
260
260Mn
320Cr
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Main Corus Rail steel grades
Bainitics
Tramway
Arema
UIC
Euronorm
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Steel grades vs. RCF?
?
MHH
B320
B360
350LHT
ROLLING CONTACT FATIGUE
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RCF test areas

• Squat
• SNCF, Reims region (Oeilly), tangent track,
  references 700 900A, 1993
• Studied parameters steel hardness,
  decarburisation, grinding
• Head checking
• SNCF, Bordeaux region (Saint Benoit), radius 985
  m, reference 900A, 1997
• Studied parameters steel hardness, wear
• SNCF, Montauban region (Dieupentale), radius 1140
  m , reference 900A, 1998
• Studied parameters steel structure (perlitic vs
  bainitic)
• SBB, Basel region (Frick), radius 449 m,
  reference 350LHT, 1999
• Studied parameters steel structure (perlitic vs
  bainitic)
• ProRail, Utrecht region (Bunnik), radius 2275 m,
  reference 260Mn, 2000
• Studied parameters steel hardness, wear

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SNCF - Oeilly
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White layer on standard grades
900A / 9

• The white layer causes the cracking
• The cracks sink into the base metal as soon as
  the critical thickness of the white layer is
  reached

900A / 9
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 Development of white layer
DISSOLUTION OF THE CEMENTITE LAMELLA
900A
No differentiation between 700, 900A and 900A
highly decarburised rails
DEVELOPMENT OF A STRUCTURE WITH NIDDLES
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White layer on HH grades
900A HH / 56

• In spite of a fatigue limit that is higher than
  that of the grade 900A, the treated grades react
  far less well on the track
• After the cracking of the hard white layer, the
  base metal is stressed on severe cuts to which it
  is less resistant than the grades with a lower
  yield strength

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SNCF - Saint Benoit
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"Hairy" head checking for MHH
Initial hardness

• MHH
• Immediate slight cracks
• No development afterwards
• Very low cold hardening

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Profile evolution
800
900A
900X
Profile vs. position
MHH
Plastic flow
Profile vs. grade
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No magic natural wear
Deep penetrant tests
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ProRail - Bunnik
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Head checkingaspect and dimensions
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Corus Rail MHHUltra fine pearlite
No transition zone
x8000

• Accurate heating of the whole section by
  induction
• Air cooling of the whole head

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High hardness and ductilityOptimised residual
stresses
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The Corus Rail bainitic grades

• Low Carbon base, more ductile and readily
  weldable steel
• Radically different microstructure embrittling
  carbide phase replaced with soft and ductile
  austenite
• As-rolled, i.e. no heat treatment required

B 320 bainite residual austenite
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SNCF - Dieupentale
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Hardness and wear evolution
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Head checking on 900A
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Good weldability of the bainitics

• Expansion coefficient
• 11,8.10-6 m/mC at 20C
• 12,2.10-6 m/mC at 60C
• Resistivity
• 39 µW.cm (25 for 900A)

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SBB - Frick
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Head checking on 350LHT
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No more wear for bainitic
Mixed welds
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Conclusion

• Changes in the steel manufacturing process and in
  the rail inspections have eliminated
  manufacturing defects as a major cause of
  replacement
• Heat treated rails are available to address the
  wear issue
• RCF is now the principal cause of rail failure
• In alignment,
• limited hardness grades and smooth grinding can
  prevent the white layer formation and avoid the
  crack propagation in the base material
• In curve,
• the low carbon bainitic steels show very
  encouraging results, but adjustments are
  essential to carry the experiment further
• MHH gives the best results against wear and RCF.
  The stress distribution limits the crack
  propagation and makes it possible to grind less
  often