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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


  1. Tribodays 2013 Luleå University of Technology 26 th -27 th September High temperature wear mechanism maps Sinuhe Hernandez Supervisors: Braham Prakash Jens Hardell 1

  2. Tribology at high temperatures – A challenge • Need of applications working under harsh conditions • Limited use of conventional lubrication methods F N Heat Abrasion conduction Adhesion Oxidation Vslide Microstructural Diffusion changes Thermal Reduction of fatigue hardness 2

  3. Significance of the materials investigated • 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 3

  4. Wear mechanisms maps- earlier work Childs, T. H. C., The sliding wear mechanisms of metals, mainly steels. Tribol. Int., 1980, 13, 285–293. Lim, C. Y. H., Surface coatings for cutting tools. Ph.D. thesis. Singapore: National University of Singapore, 1996. 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 4

  5. 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 5

  6. Experimental setup • High-temperature pin-on-disc machine (Phoenix Tribology TE67) Chimney F N Force transducer Air blower Pyrometer 6

  7. 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 0.2- 0.2- 1- max max 0.14- 0.005 - - - 234 steel 0.25 0.35 1.3 0.03 0.01 0.26 0.6- max max 0.8 0.14 max Tool steel 0.32 0.8 1.35 - 460 1.1 0.010 0.003 1 7

  8. Test Matrix • Influence of load and temperature Disc Sliding Velocity (ms -1 ) Pin Specimen Temperature (°C) Pressure (MPa) specimen 2 (25N) 25 4 (50N) 6 (75N) 2 100 4 6 2 0.2 Boron steel Tool steel 200 4 6 2 300 4 6 2 400 4 6 8

  9. Friction coefficient 1,4 25 N 50 N 75 N 1,2 Coefficient of friction 1 0,8 0,6 0,4 0,2 0 100 200 300 400 Temperature (°C) 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 9

  10. Glaze layer formation Agglomeration, Generation of wear Wear debris compaction and particles retention formation of compact layers T • Reduce metal-to-metal contact Glaze Layer Sintering • Load bearing areas formation • Easy to shear 10

  11. Glaze layer constituents 11

  12. Wear behavior Strong adhesion Transfer particle Wear particles Strong adhesion Sliding direction Tool steel disc at 25N and 25 °C 25N 25 ° C • Metal-to-metal contact Transfer particle Grooves made by ploughing effect of transfer particles acting as two-body abrasive Sliding direction Sliding direction particles 12

  13. Wear behavior Strong adhesion Transfer particle Strong adhesion Sliding direction 75N 25 ° C • Bigger grooves made by the transfer particles Formation of cracks at the grooves Sliding direction 13

  14. Wear behavior 25N 100 ° C • Formation of isolated patches of an oxidised protective layer 14

  15. Wear behavior 50N 300 ° C • Smooth and continuous glaze layer 15

  16. Wear behavior 75N 300 ° C • Detachment/breaking of the wear protective layers 16

  17. Wear behavior 25N 25 ° C • Grooves made by two- body transfer particles Transfer particle Sliding direction 17

  18. Wear behavior 75N 25 ° C • More and bigger grooves made by two- body transfer particles 18

  19. Wear behavior 75N 300 ° C • Formation of more continuous isolated wear protective patches. 19

  20. Wear behavior 75N 400 ° C • The increased applied load (50N and 75N) led to the development of wear protective layers 20

  21. Development of a wear and friction map SWR COF 21

  22. Specific wear rate and friction map Specific Wear Rate (mm 3 *Nm -1 ) Contact Pressure (MPa) Temperature ( ° C) 22

  23. Friction and wear mechanisms map 23

  24. 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. 24

  25. 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) 25

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