PhD lecture
1 like212 views
The document discusses the development of application-oriented wear testing methods for assessing wear-resistant steels in the mining industry, addressing the inadequacies of traditional low-stress wear testing. It highlights the need for testing under high-stress erosive conditions, where wear mechanisms differ significantly, necessitating new material solutions. The research underscores that the material response in high-stress scenarios is more critical for performance than hardness alone.
![…made more complex in high-stress
conditions
[Lindroos, 2016]](https://image.slidesharecdn.com/lectionikoojala-170502093941/85/PhD-lecture-9-320.jpg)
PhD lecture
- 1. Lectio Praecursoria Application oriented wear testing of wear resistant steels in mining industry Niko Ojala 28.4.2017 Tampere University of Technology Laboratory of Materials Science Tampere Wear Center
- 2. Wear environment in mining industry
- 3. The problem • Vast amount of wear related publications have been done over last 40- 50 years • Consensus is:
- 4. The industrial standpoint? • An internet query for 42 companies, globally, was performed • Response rate was 62 %, of them: 60% 66% 82% 96% 79% Needs test method with better correlation Has some own test equipment Were conducting tests at the time Had done wear testing Recognize term 'Application oriented'
- 5. Motivation for this research • Previously mostly low-stress wear conditions have been utilized – Particle size typically around 0.3 mm – Particles often rounded – Typical particle speeds around 5-10 m/s
- 6. Motivation for this research • High-stress erosive conditions have not been studied extensively (erosion by large particles) • Change in wear environment (e.g. from low-stress to high-stress wear) requires new material solutions and research In mining applications: Particle speeds can range from 2 to 30 m/s and size can vary from micrometers to several centimeters
- 7. Stress states in wear Change in the wear environment → Different material response = deformations, work hardening, embedment, tribolayer formation… Shear band High-stress wear Abrasives are crushed & target material deformed (for steels) Low-stress wear Abrasives are not crushed & target material not deformed (for steels) 400 HB steel 500 HB steelCross-sections of:
- 8. WearWear of materials: a complex process…
- 9. …made more complex in high-stress conditions [Lindroos, 2016]
- 10. New wear tester developed An application oriented approach for mining applications: • Sample speeds 5 – 20 m/s • Abrasive particles up to 10 mm size – Possible to use natural gravels and minerals! • Versatile test environments: wet or dry 10
- 11. Possible to have correlation? A field test was compared to an application oriented dry-pot and a conventional abrasion tests.
- 12. Field test Application oriented test Conventional test Conventional test
- 13. Replicating wear of mining applications • Reproducing the environment: testing parameters and conditions – Particle size and speed, angle of incidence etc. • Imitate the shape of the component: sample shape and edge wear – Component shape, edge effect • Wear mechanisms and deformations: stress state and material response – Low- or high-stress conditions – Wear surface features and deformations
- 14. Material response in low- and high- stress wear • High-stress wear – Embedment of abrasives – Tribolayer and/or composite layer formation – Extensive deformation -> work hardening, white layers – (In general role of corrosion decreasing) • Low-stress wear – Minimal embedment and tribolayer formation – Limited deformation and work hardening – (In general role of corrosion higher)
- 15. High-stress wear mechanisms • Strain hardening is a natural defense mechanism of metals • However, it leads to less ductile behavior on wear surface Cross-section of a quenched steel sample tested with 8/10 mm granite slurry at 45° sample angle. A) SEM BSE image of the plastically deformed surface layer and B) SEM SE image of a stepwise formed scratch that has cut through the deformed surface layer.
- 16. Impact of the work • Application oriented wear testing offers tools for successful simulation of demanding mining applications in laboratory scale • Without correct material response, it is impossible to have a good correlation in laboratory tests – Low-stress vs. high-stress conditions E.g. exhaustion of ductility on wear surfaces observed in high-stress wear, and effect of abrasive embedment higher in high-stress – Hardness alone doesn’t dictate the wear performance of wear resistant steels in high-stress conditions Instead material response of steel dominates the performance