evaluation of material deterioration of rails subjected to .../menu/general/co… · evaluation of...

3-4.Oct. 2012, Nordic Seminar

Evaluation of material deterioration of rails subjected to rolling contact fatiguesubjected to rolling contact fatigue

using x-ray diffraction

Motohide Matsui

1) Department of Applied Mechanics, Chalmers University of TechnologySE-412 96 Gothenburg, Sweden

2) Materials Technology Division Railway Technical Research Institute2) Materials Technology Division, Railway Technical Research Institute2-8-38 Hikari Kokubunji Tokyo 185-8540, [email protected], [email protected]

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute

OverviewOverview

1) Background

2) Purpose of this work

3) Experimental

4) Results of x-ray examinations4) Results of x ray examinations5) Conclusions


Appearance of rail RCF damageFC← TD: Train direction

Head check

Squat

GC

As-rolled (tangent) Head-hardened (curve)Flaking Side wear

As rolled (tangent)

Squat(GCC) Other problem:pside wearcorrugation

Head-hardened (curve)

Side wear corrosion fatigue(bottom side) etc..


( )

Chemical compositionChemical composition of of rail in Japanrail in Japan

(mass%)(mass%)

C Si Mn P S CrA 0 63 0 15 0 70As-

rolled0.63-0.75

0.15-0.30

0.70-1.10 0.030 0.025 -

H dHead hardened(HH340)

0.72-0.82

0.10-0.55

0.70-1.10 0.030 0.020 0.20(HH340)

:JIS (Japanese Industrial Standard)As-rolled : tangent rail

Head hardened : only curve rail (usually less than R800m)


y ( y )

Mechanical strength of rail in JapanMechanical strength of rail in Japan

Tensile strength (MPa)

Total elongation(%)( ) (%)

As-rolled 800 10

Head hardened(HH340) 1080 8

:JIS (Japanese Industrial Standard)


Portion of RCF damage for rail replacement

Others(joint

Over 50% of rail replacementsOver 50% of rail replacements

S t 26%

(joint, etc..), 9%

Squat, 26%Corrosion,

30%Head

check, 35%

2008-2009 in Tokyo districty

Reduction in reliability and operational life of rails


Mitigating action (Rail grinding by grinding stones)

レール削正車

SPENO grinding car for Shinkansen line

Rail grinding operations are periodically performed to remove

Grinding operation

Rail grinding operations are periodically performed to remove the RCF layers.

i di d h d i l l i i ll d id dGrinding depth and interval are almost empirically decided.

Quantitative microstructural analyses on RCF layersRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute

Quantitative microstructural analyses on RCF layers

Purpose of this workPurpose of this work

Clarify how the RCF layer forms from a material aspect aiming at the effectivematerial aspect, aiming at the effective mitigating actions for RCF damage

Estimate the crystallite size and dislocation density of RCF layer using x-ray diffraction


What is crystallite ?What is crystallite ?

Grain size from x-ray measurement

Crystal grain with nearly the same crystal orientation

What is dislocation ?What is dislocation ?

Irregularity of alignment of atoms

When a material is plastically deformed, dislocations are induced d i

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteand increase.

Principle of xPrinciple of x--ray diffraction ray diffraction

Incident x-rayBragg’s law

Diffracted x-ray

θdλn sin2= ･

dθdd

Wavelength : λL tti i : dLattice spacing: dangle: θ

Texture formation, crystallite size, nonuniform distortion(lattice strain) and dislocation densit etc

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteand dislocation density etc..

Microstructural evolution due to RCF(grain subdivision)

Initial Dislocation induced

Dislocation cell, subgrain

High angle grain boundaryMicrostructural refinement,

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteHigh angle grain boundary metallic flow, texture …..

Effect of strain on xEffect of strain on x--ray diffraction peak ray diffraction peak d

lattice

d’

d

lattice

d’elastic strain

d

undistorted elastically distorted

d1 d２ d3d1

d２d3plastically 1 ２ 3

deformed

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itutenonuniformly distorted

How to estimate crystallite size and dislocation How to estimate crystallite size and dislocation densitydensity

β：integral peak widthθ: diffraction angle

density density Williamson-Hall equation

ε

1

λ

sinθ2η

λ

cosθβ +=

θ: diffraction angleη：nonuniform distortionε： crystallite size (nm)λ i idελλ λ：incident x-ray wave length

22/1

Modified Williamson-Hall equationC di l ti t t f t d fi d)O(KC'K 22/1 ++=Δ KCβα

'1

'α =λ

θsin2=K

C: dislocation contrast factor definedby Warren

'εModified Warrren-Averbach equation

λL: Fourier lengthA(L): real part of Fourier

222 )())(()(ln CKPCKLXLA +−= γ

)ln()(22 RLbLX eρπ

coefficient of (hkl) diffraction

ρ: dislocation density (1/m2)

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute)ln(

2)(

LLX eρ= ρ y ( )

RCF test equipment10510

0φ5

φ50

Overview

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteTest sample

Sample subjected to RCF test Contact pressure : 1.2GPaSlip ratio : 0%100 000 cycles

0.0

1 0τmax

0 1E16

100,000 cyclesDryRarely worn after test

1.0

2.0

3 0

Z/a

τxz_range

20

0

1E15

1E16

Crystallite size Dislocation density 1/

m2

Surface roughness < 30μm3.0

4.0

5 0

40

1E14

1E15

te si

ze, n

m

n de

nsity

, 1

(111) texture formation

5.0 0 200 400 600 800

Stress, MPa

80

60

1E13

Cry

stalli

t

Disl

ocat

ion ( )

0.6

0.7

111

sity

0 100 200 300 400 500 600100

80

1E12

D

0 3

0.4

0.5

inte

gral

inte

ns

Depth from surface, μm

It is significant to consider the effect of 0.10.2

0.3

Nor

mal

ized

i

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itutesurface roughness on the contact patch

0 100 200 300 400 500 6000.0


Serviced tangent rail without rail grinding(500MGT passenger & freight mixed)(500MGT, passenger & freight mixed)

0

1E16

WEL

40

20

1E15

1E16 Crystallite size

e, n

m Dislocation density

sity,

1/m

2Metallic flowSurface roughness

60

40

1E14

talli

te si

ze

atio

n de

ns

(111) texture formation

80 1E13C

ryst

Disl

oc

0 500 1000 1500 2000100 1E12

Depth from surface μm

100μm


・Similar tendency to the test sample.Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute

y p・It is possible to investigate how the RCF evolves even in the case of serviced rail.

Hardness (500MGT)Hardness (500MGT)

340

320H

V

280

300

Har

dnes

s, H

260

280H

0 100 200 300 400 500 600 700

Depth from surface μmDepth from surface, μm

Vickers hardness distribution (0.3HV)

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute・Total RCF layer is not evaluable.・Measurement beneath the surface is difficult.

Serviced tangent rail without rail grinding(50MGT passenger & freight mixed)(50MGT, passenger & freight mixed)

0 1E16

201E15

Crystallite size

m

Dislocation density

y, 1

/m2

Metallic flowSurface roughness < 20μm

40

1E14 ite si

ze, n

m

on d

ensit

y

Texture will be formed

80

60

1E13Crys

talli

Disl

ocat

io

100μm0 100 200 300

100

80

1E12

D

0 100 200 300


X i f ibl f thi RCF lRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute

X-ray is feasible even for a thin RCF layer.We can quantify the degree of RCF layer formation for each condition.

ConclusionsConclusions

1. This x-ray measurement makes it possible to quantify the RCF layer f h f d i h i l i h d E i ll ifrom the surface and into the material in one method. Especially it is feasible even for a quite thin layer.

2 On the other hand it is hard to carry out hardness measurement just2. On the other hand, it is hard to carry out hardness measurement just on the surface. The hardness measurement could not cover the total RCF layer.y

3. Both crystallite size and dislocation density largely change in RCF layers. The surface layer was in all cases more damaged by RCF th th b f l (111) t t i f d i d ththan the subsurface layer. (111) texture is formed in some depths. (111) texture can be highly enhanced after a while serviced as a tangent railtangent rail.

4. It is significant to consider the surface roughness in the contact patch in the evaluation of RCF layer.


Thank you for your kind attentionThank you for your kind attention


0 7

0.83

Williamson-Hall Modified Williamson-Hall

0 4

0.5

0.6

0.7

K1 5

2

2.5

K

0.1

0.2

0.3

0.4Δ

0.5

1

1.5Δ

00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

KC1/2

00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

K

-4

-2

0

Modified Warrren-Averbach

-8

-6

4ln

(A)

-12

-10

0 5 10 15 20 25 30

Railway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteK2C

111 texture formation(500MGT, serviced tangent rail)111 texture formation(500MGT, serviced tangent rail)

12 (110)

10 (100) (211)

nten

sity

6

8 (310) (111)

nteg

ral i

n

4

6

aliz

ed in

2

Nor

ma

0 500 1000 1500 2000 25000

Depth from surface mRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst ituteRailway Technical Research Inst itute


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