Lectio Praecursoria I gaved during my public defense of my Doctoral thesis. You can access the full-text of my thesis via: https://www.researchgate.net/publication/316084414_Application_Oriented_Wear_Testing_of_Wear_Resistant_Steels_in_Mining_Industry

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