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High temperature wear mechanism maps Sinuhe Hernandez Supervisors: - - PowerPoint PPT Presentation

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Tribodays 2013 Lule University of Technology 26 th -27 th September High temperature wear mechanism maps Sinuhe Hernandez Supervisors: Braham Prakash Jens Hardell 1 Tribology at high temperatures A challenge Need of applications

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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

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0,2 0,4 0,6 0,8 1 1,2 1,4 100 200 300 400

Coefficient of friction 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

  • xidised 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

COF SWR

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Specific wear rate and friction map

Temperature (°C) Contact Pressure (MPa) Specific Wear Rate (mm3*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
  • n 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)