Application oriented wear

testing of wear resistant steels

in mining industry

Niko Ojala

Doctoral student

Tampere Wear Center

Tampere University of Technology

Tampere, FINLAND

8th TWC International Wear Seminar

November 8th, 2016

Tampere, Finland

Motivation

• Demanding abrasive erosion conditions have

not been studied extensively (erosive/abrasive

wear by large particles)

In mining applications:

• The speeds of the particles

can be up to 30 m/s

• The size of the particles

can vary from micrometers

to several centimeters

Motivation

• Change in wear environment/mechanisms

(e.g. from low-stress to high-stress wear)

requires new material solutions and research

Shear band

Low- vs. high-stress

slurry erosion

Contents

• Application oriented wear testing – What? Why?

• Is it possible to simulate industrial wear processes

in laboratory?

• The wear testers

• Replicating wear of mining applications

• Material response in low- and high-stress wear

• Effect of abrasive embedment

• Summary

Application oriented wear

testing

• Laboratory testing where the focus is on

simulating industrial applications

– real conditions, real wear phenomena,

real wear losses

• In short:

Why application oriented?

• Vast amount of wear related publications

have been done over last 40-50 years

• Consensus is:

Is there need?

• An internet query for 42 companies, globally,

was performed

• Response rate was 62%

• About 60% reported a need for wear testing

that would better correlate with real

applicationsResults will be published in the thesis

Is it possible?

Publication:Vuorinen, Ojala, et al., “Erosive and abrasive wear performance of

carbide free bainitic steels – comparison of field and laboratory

experiments”, Tribology international 98 (2016) 108-115

Field test compared to application oriented dry-pot

and conventional (sandpaper) abrasion tests.

Field test

Application oriented test

Conventional test

400

500

600

700

800

900

0 50 100

Hard

nes

s [H

V]

Distance [µm]

CFB270 Dry-pot CFB270 Field

CFB300 Dry-pot CFB300 Field

Dry-pot

Field

Abrasion test

Zero work

hardening

in abrasion

test !!

Similar

material

response

in dry-pot

and field

Dry-pot

closer to

field results

in wear

losses

High speed slurry-pot wear

tester

An application oriented approach for

mining applications:

• Sample speeds 5 – 20 m/s

• Abrasive particles up to 10 mm size

– Natural gravels and ores !!

Ojala, et al., “Wear performance of

quenched wear resistant steels in

abrasive slurry erosion”, Wear, 354-

355 (2016) 21-31

Dry-pot wear tester

• Samples submerged in to a bed of

dry abrasives

• Particle sizes

up to 10 mm

• Speeds

5 – 20 m/s

Vuorinen, Ojala, et al.,

Tribology international

98 (2016) 108-115

Crushing pin-on-disk

Ojala et al.

“Effects of

composition and

microstructure on

the abrasive wear

performance of

quenched wear

resistant steels”,

Wear 317 (2014)

225–232

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

Role of real contact area?

3D profile of large granite

abrasive

Schematic presentations

of a real contact area of

two arbitrary surfaces

[Gagan Srivastava, Carnegie Mellon University]

Material response in low-

and high-stress wear (for steels)

• High-stress wear

– Embedment of abrasives

– Tribolayer and/or composite layer formation

– Deformations -> work hardening, white layers

– Role of corrosion decreasing

• Low-stress wear

– Minimal embedment and tribolayer formation

– Non-existent deformations

– Role of corrosion higher

Two similar commercial steels, but two totally different

mechanical behavior and wear performances in high-stress

abrasion. [Wear 317 (2014) 225–232]

Shear band

8/10 mm granite,

80 minutes

0.1/0.6 mm quartz,

80 minutes

400HB steel 500HB steel

Ojala et al. ”Edge effect in high speed slurry

erosion wear tests of steels and elastomers”,

NORDTRIB 2016, June 2016, Finland.

Two steels with same wear tester, two different abrasives, two

different wear environments: Low- vs high-stress conditions

-> two different material responses

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.

• Strain hardening is a natural defense mechanism of

crystalline materials

• But it eventually leads to exhaustion of ductility on wear

surfaces[Wear 317 (2014) 225–232 , Wear 354-355 (2016) 21-31]

Effect of abrasive

embedment

• Steels and elastomers

were compared in

both low- and high-

stress slurry erosion

• Embedment of

abrasives in

elastomers were

studied by X-ray

tomography

500 µm

[Wear, 354-355 (2016) 21-31]

Volume loss calculated

from mass loss [cm3]

Direct volume loss

measurement [cm3]

Difference

400HB 0.027 0.020 -27 %

NR 0.015 0.025 +66 %

[Submitted to Wear, September 2016]

Results will be published in the thesis and are submitted to the journal

Summary

• Application oriented wear testing have proved to

offer added value to simulating demanding mining

applications in laboratory scale

• Without correct material response it is impossible

to have good correlation in laboratory tests

– Low- vs. high-stress conditions

– Hardness alone doesn’t dictate the wear

performance of wear resistant steels in high-stress

conditions

– Exhaustion of ductility on wear surfaces observed

in high-stress wear

Future work

• More field testing -> improving the correlation

between laboratory and field tests

• Effect of abrasive embedment on wear

performance

– Formation mechanisms still unknown

• More profound understanding of effect of

steels‘ composition and microstructure on

wear performance

Niko Ojala

Research Scientist, Doctoral student

Tampere University of Technology

Department of Materials Science, Tampere Wear Center

P.O.Box 589, FI-33101 Tampere, Finland

phone: +358 50 317 4516

email: niko.ojala@tut.fi

twitter: @Ojala_NJT

www.tut.fi/twc/en