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High temperature wear mechanism maps

Sinuhe Hernandez

Supervisors: Braham Prakash

Jens Hardell

Tribodays 2013 Luleå University of Technology

26th -27th September

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Tribology at high temperatures – A challenge

• Need of applications working under harsh conditions

• Limited use of conventional lubrication methods

Vslide

FN

Abrasion

Microstructural changes

Reduction of hardness

Adhesion

Diffusion

Heat conduction

Oxidation

Thermal fatigue

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• Boron steel is increasingly used in many applications such as structural components in the automotive industry

• These parts are processed through hot metal forming operations

• Toolox 44 is often chosen as tool material in view of its good mechanical properties even at elevated temperatures

Significance of the materials investigated

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Wear mechanisms maps- earlier work

Lim, S. C. and Ashby, M. F., Wear-mechanism maps. Acta Metall., 1987, 35, 1–24.

I.A. Inman et al. / Wear 260 (2006) 919–932

Lim, C. Y. H., Surface coatings for cutting tools. Ph.D. thesis.

Singapore: National University of Singapore, 1996.

Childs, T. H. C., The sliding wear mechanisms of metals, mainly steels.

Tribol. Int., 1980, 13, 285–293.

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Objectives

• To understand wear mechanisms of tool steel-boron steel pairs at different temperatures

• To develop a simplified high-temperature wear map for that material pair

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Experimental setup

• High-temperature pin-on-disc machine (Phoenix Tribology TE67)

FN

Pyrometer

Air blower

Chimney

Force transducer

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Experimental work • Materials

– Prehardened (quenched and tempered) tool steel • Flat discs (ø75mm x 7.9mm thick) (lower disc specimen)

– Boron steel • Cylindrical pins (ø4mm x 4mm high) (upper pin specimen)

Material Chemical Composition (wt%) HV C Si Mn P S Cr B Mo V Ni

Boron steel

0.2-0.25

0.2-0.35

1-1.3

max 0.03

max 0.01

0.14-0.26 0.005 - - - 234

Tool steel 0.32 0.6-1.1 0.8 max

0.010 max

0.003 1.35 - 0.8 0.14 max 1 460

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Test Matrix

• Influence of load and temperature

Pin Specimen Disc

specimen Temperature (°C) Pressure (MPa) Sliding Velocity (ms-1)

Boron steel Tool steel

25

2 (25N)

0.2

4 (50N)

6 (75N)

100

2

4

6

200

2

4

6

300

2

4

6

400

2

4

6

9

0,2

0,4

0,6

0,8

1

1,2

1,4

0 100 200 300 400

Coef

ficie

nt o

f fric

tion

Temperature (°C)

25 N 50 N 75 N

Friction coefficient

Average CoF at the steady state region • For a given load, the CoF decreases as the temperature is

increased • In general, for a given temperature, the CoF decreases as

the load is increased

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Glaze layer formation

Generation of wear particles

Wear debris retention

Agglomeration, compaction and

formation of compact layers

Sintering Glaze Layer formation

T • Reduce metal-to-metal

contact • Load bearing areas • Easy to shear

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Glaze layer constituents

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Wear behavior

• 25N 25 °C Metal-to-metal contact Grooves made by ploughing effect of transfer particles acting as two-body abrasive particles Sliding direction

Wear particles

Strong adhesion

Strong adhesion

Sliding direction

Transfer particle

Sliding direction

Transfer particle

Tool steel disc at 25N and 25 °C

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Wear behavior

• 75N 25 °C Bigger grooves made by the transfer particles Formation of cracks at the grooves

Strong adhesion

Strong adhesion

Sliding direction

Transfer particle

Sliding direction

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Wear behavior

• 25N 100 °C Formation of isolated patches of an oxidised protective layer

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Wear behavior

• 50N 300 °C Smooth and continuous glaze layer

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Wear behavior

• 75N 300 °C Detachment/breaking of the wear protective layers

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Wear behavior

• 25N 25 °C Grooves made by two-body transfer particles

Sliding direction

Transfer particle

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Wear behavior

• 75N 25 °C More and bigger grooves made by two-body transfer particles

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Wear behavior

• 75N 300 °C Formation of more continuous isolated wear protective patches.

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Wear behavior

• 75N 400 °C The increased applied load (50N and 75N) led to the development of wear protective layers

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Development of a wear and friction map C

OF

SW

R

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Specific wear rate and friction map

Temperature (°C)

Con

tact

Pre

ssur

e (M

Pa)

Spe

cific

Wea

r Rat

e (m

m3 *

Nm

-1)

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Friction and wear mechanisms map

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Conclusions • The frictional behaviour is both, load and temperature

dependant. In general the friction coefficient decreases as both, temperature and load are increased

• Above 100 °C, development of wear protective layers on the boron steel pin surface was observed

• An increase in load resulted in breaking-up of the layers thus increasing the wear rate

• The formation of stable protective wear layers on the tool steel surface was noticed at temperatures above 200°C.

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Acknowledgments • Austrian Comet-Program (governmental funding

program for pre-competitive research) via the Austrian Research Promotion Agency (FFG) and the TecNet Capital GmbH (Province of Niederöserreich)