Answer to Home work #4

1) Discuss how temperature could affect the fatigue limit of steel.

2) Two groups of samples made of the same steel experienced fatigue

tests in air and in H2 gas, respectively. Which curve represents result
of tests in H2 gas? Why?
1) Increasing T may activate more slip systems in BCC,
thus reducing the barrier to plastic deformation and
consequently lowering the fatigue limit.
a
2) Hydrogen can result hydrogen embrittlement of
steel. Thus, the dashed curve should be the result
Stress amplitude

of testing in H2 environment.

Air

H2
Hydrogen reduces the
No. of cycles to failure, Nf surface energy of iron,
facilitating cracking.
III. Wear of Engineering
Materials

Metallic materials
Ceramics
Polymers
III. Wear of Engineering Materials

A material may perform differently under different wear

conditions or in different wear modes

e.g., WC/NiCrBSi hardfacing overlay shows excellent wear

resistance under low-stress abrasion condition but may perform less
impressively under impact wear and corrosive wear conditions.
Discontinued bucket wheel excavators in the oil sands mining industry

Bucket wheel excavators were, at one time,

used for mining operation at Fort McMurray
where the large oil sand deposits are found
in Northern Alberta.

Broken and missing teeth on the front of

the buckets. (The bright spots are
hardened buttons to reduce side wear
on the buckets as they cut through the
abrasive sand.)
General guidelines for material selection and design
Wear Mode Material requirement
Abrasive wear Harder than the abrasive, good strain-hardening
capability

Adhesive wear Low solubility/compatibility, resistant to thermal

softening, high melting temperature

Erosion High hardness for low-angle impact

High toughness for high-angle impact

Fatigue wear Hard and tough, no non-metallic inclusions, no

surface micro-cracks, high Young’s modulus

Corrosive wear High electrode potential, or high passivation

capability with good passive film, resistant to wear

High-T wear High-T strength, protective oxide scale, high thermal

conductivity

High-speed sliding wear High thermal conductivity, resistant to thermal shock,

low thermal expansion, high melting temperature

Cost is also a factor for material selection

 III – 1 Metallic Materials

III – 1.1 Steel

1) Microstructure and properties

Because of low cost and high availability, steels are widely used for
tribological applications.

e.g.,
Shafting or bearing journals
Gears
Ball and roller bearings
Tools and dies
Wheels and rails
Fasteners
Pumps and compressors
Knives
Thrust bearings Surface is often modified.
Drill bits
 Time-Temperature-Transformation (TTT ) Diagram

Mechanical and tribological properties of steels are

strongly affected by their microstructures, which
could be controlled or modified by heat treatment
based on phase diagram and TTT diagram of Fe-C
system.

Fe-C Phase diagram

Fe-C TTT diagram

 Martensite versus Bainite

Martensite
Bainite

Martensite: body- Bainite forms by the

centered tetragonal decomposition of austenite
(BCT) structure at a temperature which is
(single phase). above MS but below that at
which fine pearlite forms.

Coarse pearlite Fine pearlite

 When %C is in the range of 0.76%, the steel
Pearlite
has pearlitic microstructure (lamellar
%C ~ 0.76%
ferrite+Fe3C)

Pearlite is about 5 times harder than austenite

Pearlite
+
Primary ferrite Fine P H Wear resistance
%C < 0.76% (to abrasion and adhesive
wear; metal-metal contact is
reduced)

Pearlite Wear
%C Primary Fe3C +P
+ resistance
Primary Fe3C
%C > 0.76% However, H toughness

There is a critical hardness value, beyond which

the wear resistance decreases.
Wear resistance

Effect of toughness on
Usually,
wear resistance Ductility H
Fracture toughness, KIC
 (2)

(4)

(1), (3)

Q37: Why? This material may have a larger toughness but

its strength is low so that it cannot withstand
larger stress and its fluctuations, leading to
 (1)
lowered wear resistance.
(2)
S - Toughness
(4)
S
(3)


(1) Has low resistance to stress fluctuation; (3) has low resistance to wearing stress. (2) has
a good combination of strength and ductility, consuming more energy before failure.
– Martensitic steel
Martensite is the hardest (but brittle) and the most resistant to wear, especially to
low-stress wear.

In order to reduce the brittleness, high-carbon martensite is usually tempered at

230C for stress relief and phase transformation.

A small amount of retained/residual austenite is beneficial to the toughness (you

may stabilize austenite using, e.g., Mn)
Martensite is metastable, not recommended for
high-T applications (> 200C). At higher
temperatures, martensite will decompose into

Ferrite + Fe3C Hardness

(Tempered martensite)
 – Austenitic steel (FCC)

Mn can stabilize austenite at room temperature

Toughness high resistance to impact

high work-hardening capability

Higher resistance to impact wear and high-stress wear

e.g., solid-particle erosion

High work-hardening may be attributed to A M under impact force

or stress. This was confirmed by analyzing wear debris using TEM
Martensite was observed in wear debris

Induced M Hardness , compressive stress wear resistance

Austensitic manganese steels is widely used in mining industry, dirt moving

machinery, pump parts, ore handling, mining facilities.
In general, we have the following relation between wear and microstructure

Ferrite Pearlite Austenitic Mn steel Bainite Martensite

Wear Resistance Q38: is this order good for
selecting steels to resist
impact wear and high-speed
Pearlitic steels
Austenitic steels
solid particle erosion
Bainitic steels resistance?
Quenched and
tempered steels
Relative wear resistance

No.

Hardness
 The slurry-erosion mass loss of
X70 pipeline steel (~0.07%C) is
71% higher than that of another
steel (~0.25wt%C).
Slurry speed: 3.5 m/s.
The steel with 0.25%C is slightly
harder than X70 with higher
toughness

2) Modification of carbon steel for improved performance

Q39: can we add
Mn, Si, Cr, Mo, Ni, V, W are often used to modify more carbon to
increase hardness
carbon steels for enhanced wear resistance for higher slurry
erosion resistance

A: It may reduce
a) Improvement in hardenability weldability and
toughness; tests
are needed.
When added elements are less than 5% (in total), they are mainly used to
improve the hardenability of steels containing more than 0.4%C (less than 0.4%,
steels are not hardenable).

DI – ideal critical
diameter

e.g., a carbon steel of 0.4%C has its grain size number = 7 and contains 1%Mn, 0.35%Si,
0.7%Ni, 0.6%Cr and 0.25%Mo, its DI = 0.213(“)x4.333x1.245x1.255x2.296x1.75=5.79(“)
b) Solid solution strengthening

Cr, V, Mo, W, Cu, Ni, B, N are also used for solid solution strengthening
(austenite) when their content is less than 5%.

Interstitial or substitutional solute atoms can pin dislocations H

 * Solid solution hardening
Two parameters/mechanisms for solution hardening:

(1) Metallic bond strength ~ valence electron density:

E  0 (  > 0 ) Strengthening
E  0 (  < 0 ) Weakening

(2) Difference in atomic size:

d Strengthening, H  0

JACM, 737 (2018) 323-329.

17
c) Second phase strengthening

When more than 5%, the above-mentioned elements may form second
phases to strengthen the steel
e.g., Cr, V, Mo, W, Nb, Ti can form hard carbides (C: 0.7 ~ 1.5%)

Ni, Mo can reduce network of carbides and pearlite

A tool steel.
Its structure
consists of
carbide particles,
martensite,
residual
austenite

Carbides in a steel
d) Stabilize austenite
Mn (11% ~ 14%) can stabilize austenite at room temperature

Toughness

Heat treatment reduces carbide formation at grain boundaries

Toughness

Quench from T > 1000C; quench medium: water

1.38%Cr-12.2%Mn-Fe
Austenite+carbide network After quenching
c) Improving passivation capability

Cr and Ni are used to improve passivation capability of steels

for applications in corrosive environments

0.08%C-18%Cr-8%Ni-2%Mn-1%Si-Fe
scratching
Application of rare-earth
elements (e.g., Y, Ce) to
improve the passive film

Corrosive wear resistance

Wear-resistant steels used for slurry handling and transport in oil sands
mineral processing applications (e.g., Trip steel pipes and plates)

Shovels (excavators)
Trucks
Crushers
Outlet Hopper, Chutes (Storage Silo)
Rotating Drum (Screen)

shovels

crushers TRIP steels - a triple-phase

bucket of dragline microstructure consisting of ferrite,
bainite and retained austenite.
Retained austenite is metastable at
bed of a truck room temperature and transforms to
martensite during straining.
 Some Examples of the Equipment Used in Oil sands and Oil/Gas Industries and Materials

Equipment Applications Conditions Materials Surface Engineering

Blade cutting edges Roadways and material Abrasive wear High-grade steel PTAW WC/Ni overlays
collection
Crusher tooth Break up mined material High-stress abrasion CrC overlays, cast iron PTAW WC/Ni overlays
indentation, gouging

Hydro-transport screens Separate and remove big Corrosion, erosion– CrC overlays PTAW WC/Ni overlays
rocks corrosion
Tailings pipelines Transportation of tailings Corrosion, erosion– Hardened carbon steel, Martensitic stainless steel
corrosion CWIs
Oil sands slurry pipelines Transportation of diluted Erosion, erosion- Carbon steel, stainless
bitumen to refineries corrosion steel
Centrifugal pumps Pumping of slurry and Low-stress abrasion CWIs, CrC WC-based sprayed
tailings erosion–corrosion coatings

Elbows, joints, valves Transportation of slurry Corrosion, erosion– Hardened carbon steel, Martensitic stainless steel;
and tailings corrosion CWIs application of WC/Ni,
WC/stainless steel PTAW
overlays

Drill pipes, drill bits, and SAGD drilling, Abrasion, corrosive wear Alloy steel, hard inserts in
related equipment. Oil and gas well drilling steel

CrC = chromium carbide; CWIs = chromium white irons; Ni = nickel; PTAW = plasma transfer arc welding; WC = tungsten
carbide.
A large amount of steel
pipelines are needed for
refining plants in Canada
and US to turn Alberta’s
bitumen into gasoline,
diesel, heating oil and jet
fuel.
Some steels used for slurry handling and transport in mineral processing applications
Pipeline steel: e.g., X56, X60, X65, X70 This pipeline from the oil
sands of northern Albert is
used to transport diluted
X70:
bitumen -- a slurry of tarry
C Si Mn P S Cr Ni Al Cu Mo Nb V Ti N hydrocarbons, solvent,
0.07 0.30 1.71 0.012 0.001 0.07 0.05 0.05 0.04 0.02 0.05 0.01 0.02 0.005 water and sand -- to
refineries some 300 miles
south.
Relationships between slurry erosion (silica and water) and properties of
steels at low dissolved oxygen level

Q40: Explain the relationships between erosion and these properties.

 Performances of carbon steel (harder than SS) and stainless (SS)
pipeline steel during sand-containing slurry erosion test

Average weight loss eroded in open air; Slurry Average weight loss eroded in open air; Slurry
speed = 3.5 m/s speed = 5.5 m/s

At lower velocities, stainless steel performs better (suppresses the

erosion-corrosion synergy) while harder carbon steels perform better at
higher velocities due to the fact that the passive film on the stainless steel
is damaged when the erosion velocity is high enough.
Stainless steels are used selectively in areas where
low erosive and higher corrosive environments are
expected to predominate. Typical applications include
tailings lines, pump boxes, primary separation vessels,
and sections near the inlet of oil sands slurry pipelines.
e.g., Duplex Stainless Steels (approximately 50/50 austenite and ferrite)
Chemistry of Duplex SS There are two parts to SAGD, the injector
Name C Cr Ni
system
Mo
which
N
consists
Cu
of steam piping to
inject steam into the ground and soften the
2304 .03 23 4 0.5
bitumen so.12
it can be produced. The other
2205 .03 21.8 5 2.8 is the producer
part .12 which consists of steel
2205 .03 22.5 5 3.2 .16
2507 .03 25 7
piping
4.0
to collect
.28
the oil
.5
and recover it to the
255 .03 25.5 5.5 surface.
3.4 .20 2.0

Duplex Stainless Steels have roughly

twice the yield strength of their
counterpart austenitic grades. Higher
resistance to the various corrosive media
found in onshore/offshore environments,
e.g. CO2, H2S, chlorides, low pH etc.
Steam assisted gravity drainage (SAGD)
Grinding Rods and Balls for Mineral Processing

e.g., 1090 steel

Some commonly used steels
Select materials
based on the
wear mode
 III-1.2 Cast Iron

Cast iron contains %C>1.8% with Si, Mn, S, P, Cr, ….. Inexpensive, with
many applications, e.g.,

Automotive crankshafts and connecting rods

Piston rings
Brakes and clutches
Gears
Die blocks
Grinding balls
Machine ways and slides
Crushers
Cams and tappets
Valves
Pumps
Crane wheels
Wheels and rollers for heat treatment furnaces
Chromium white irons (CWI) are widely used in the oil sands industry for
components such as pump impellers and casings, cyclofeeders, cyclones and
nozzles. Used to remove fine solids and
Pump materials (Weir) water from bitumen emulsions

Alloy Description/nominal composition

A05 High Cr white iron to ASTM A532 111A (27% Cr, 3% C), heat-treated
A07 CrMo white iron to ASTM A532 11B (15% Cr, 3% Mo, 3% C), heat-treated
A12 Proprietary first generation hypereutectic Cr white iron (30% Cr, 4.5% C), as-cast
A14 Lower C, improved toughness hypoeutectic Cr white iron (27% Cr, 2% C)
A25 NiCrMo steel with high toughness
A49
White iron (30% Cr, 1.5% C) with high corr. and moderate wear resistance, as-cast
A51
White iron (40% Cr, 1.5% C) with increased corrosion resistance, as-cast
A61
A217
Hypereutectic, similar composition to A12, carbides refined by inoculation, heat-treated
C26 Higher chrome (35%) and carbon (5%) hypereutectic white iron, refined primary carbides, heat-treated
C55 Duplex stainless steel (CD-4MCu)
Super duplex stainless steel (Ferralium 255)
1) Typical cast irons

- Grey cast iron (contains 1~3%Si, 0.25~1%Mn, 0.02~0.25%S,

0.05~1%P, and 2.5 ~ 4%C

Microstructure: Flake graphite + matrix (ferrite, pearlite, bainite or

martensite, depending on the casting process and
composition)

If cooling rate is low, austenite transforms to pearlite and graphite; if the

cooling rate is sufficiently rapid, carbon forms carbides rather than
graphitizing. Ti helps form graphite.

Flake graphite can be changed to nodular or spheroidal forms by

addition of Mg and/or Ce.
 Grey iron Nodular iron

Wear behavior: Good sliding resistance with low friction

(graphite is a solid lubricant), exceptionally
Q41: which has a higher
wear resistance? High damping capability (resistant to fretting
With low noise and stick-slip), High thermal
Nodular one is better with
lower stress concentration. Conductivity

Nodular graphite higher toughness

Applications: e.g., cylinder liners, piston rings, machine

tool, slide ways, combustion engine components.
Flake cast iron has higher thermal conductivity than nodular cast iron

- White iron (%C= 1.8 ~ 3.6%)

White irons contain low fractions of Si and are made with

large cooling rates. Other elements may also be alloyed,
e.g., Mn, S, P, Cr, Mo, ….
Microstructure: Carbides (e.g., Fe3C, Cr3C, ….) + pearlitic matrix
 In 1930’s, high-Cr white iron was developed.

%Cr M3C changes to M7C3 (Hv 1300 ~ 1800)

hardness , corrosion resistance (passivation)

High Cr white iron has very high

resistance to sliding wear but performs
less Impressively during high-speed
erosion due to breakup or fracture of
large primary carbide particles (can be
modified, discussed later)
Gray Nodular White

Wear resistance
 2) Effects of composition
Quenching
Cr – suppresses graphite formation and stabilize carbides
results in a very
brittle product High %Cr M3C changes to M7C3 (harder)
(partially due to
larger residual If no or small impact, high-Cr iron with martensitic matrix performs the best. If
stress); Cr may impact is large, choose low Cr irons (%Cr < 5%). Cheaper and wear resistant
also promote
Cheaper and wear resistant.
the formation of
Cu, Ni - help form graphite
martensite at
lower cooling
rates. Si – improves resistance to corrosion, especially to corrosion in hydrochloric
acid and sulfuric acid (Si carburizing , stabilizer for ferrite)

P (~ 0.2%) - forms steadite phase (very hard) wear resistance

V – promotes the formation of carbide (VC)

Ni (4 ~ 5%) – promotes the formation of austenite matrix. However, Ni

also helps form graphite. Therefore, Cr is needed to form carbides.

Mg, Ce – Spherodizing agents nodular microstructure

Mn (8% ~ 9%) - Stabilize austenite toughness

 3) Microstructure effects

M7C3 Cracks

M7C3

Oil sands slurry pumps

Q42: 1) for sliding wear,

Hypo-eutectic; which one do you select?
Tougher but Eutectic Hyper-eutectic;
softer Hard but less 2) If larger stress
toughness fluctuation is involved,
which one do you
select?

1) Hypereutectic

2) Eutectic

Eutectic structure often performs the best.

 Adding Ti to consume carbon in
the matrix of a hypereutectic cast
iron, generating an eutectic micro-
structure with fine TiC carbides in
addition to Cr carbides.

R. J. Chung, X. Tang, D.Y. Li, Hinckley, K. Dolman, Effects of titanium

Ingots with different amounts of titanium addition: addition on microstructure and wear resistance of hypereutectic high
(a) 0 wt.% Ti; (b) 1 wt.% Ti; (c) 2 wt.% Ti; (d) 6 wt.% Ti. chromium cast iron Fe-25wt.%Cr-4wt.%C, Wear, 267 (2009) 356-361.
Sample applications of cast irons for
slurry handling

Visited Suncor in Fort

McMurray, Alberta, 2011.
III – 1.3 Non-ferrous wear resistant materials

1) Cu – based alloys

Copper base alloys have found many applications due to their unique
mechanical, physical and chemical properties.

e.g., High electrical conductivity Non sparking contacts

High thermal conductivity e.g., electric motor shaft
bushing.
High corrosion resistance (high
electrochemical potential;
particularly for marine environment)

Examples of application:
- Beryllium copper

It has a strength comparable to that of steel with high intrinsic

corrosion resistance (good for marine and industrial environments),
non-magnetic, conductive (prevent sparks). It can be used
effectively at temperature up to 315C.

Widely used for underground mines, for hydroelectric facilities,

dies, bearings, and components under high loads.
 The solubility of Be in Cu is about 1% at 200C. So Cu
alloy containing 2%Be can be hardened by precipitation.

Be – rich Beta phase

Note: Inhalation of dust from processing beryllium copper is a

serious health hazard.
- Aluminium Bronze (cast)
Bronze (Cu-Sn) containing 5 ~ 11%Al exhibits good corrosion
resistance and strength up to 260C/

5 ~ 8%Al solid solution strengthening

> 8%Al precipitation
Al strengthening (Beta phase – AlCu3)

Al bronze
Containing
3%Fe

Beta phase
(dark)

Iron precipitates
(grey)
- Tin Bronzes

Bronze containing 5 ~ 15 wt%Tin and a small amount of

zinc is often used for gears and heavily loaded bushings
(e.g., 88%Cu-10%Sn-2%Zn)

The large dark dendritic phase is the

low tin content cored zone.

The delta phase can be seen as

smaller and dispersed light grey
domains

88%Cu-10%Sn-2%Zn
 - Lead Tin Bronze Up to 30%Pb
Lead is insoluble in copper. Lead is added to bronze to
provide intrinsic solid lubrication (forming low shear-strength
coating that reduces friction and overheating during loss of oil
or grease lubrication.

 phase strengthens the material

Pb phase reduces friction

Good bearing materials

- Porous Bronze
Porous sintered bronzes which hold liquid lubricant are used in many
“lubricated for life” applications such as electric motors, machine tools,
and aircraft accessories.

Wear Properties of Bearing Bronzes

 2) Al-Si alloys (light, corrosion resistant)

Excellent castability, low density, high corrosion resistance, good thermal

conductivity combined with good mechanical properties render Al-Si
alloys to have wide-range applications.
Examples of applications:
Engine crankcase Compressor pistons Transmission pump Cylinder liner
Piston rings
Aircraft engine components Video cassette recorders Video tape recorders

Si is used to strengthen aluminum. Si phase is very hard but brittle. Al protects it

when subjected to impact. They mutually support each other.
 Hypereutectic Al-Si alloy

Hypoeutectic Al-Si alloys

Other elements are also added to strengthen the
alloy by introducing second phases.
Q43: 1) It seems precipitation strengthening 2) The strengthening effectiveness decreases as the
(by second-phase) is more effective precipitates are sufficiently large, due to the loss of
than solid solution strengthening. interfacial coherency (defected zone), larger spacing
Why? between precipitates, and reduced number of
2) Aging help precipitates to grow. Are larger obstacles.
precipitates more effectively strengthen
Precipitate growth by aging leads to loss of interfacial coherency.
materials than small ones?
1) Precipitate hardening is more effective,
since dislocations have to move across
by cutting it (Mode I: through a different
lattice) or leave dislocation loops (Mode II).

Al-4 wt.%Cu

Hardness of Al-Cu, Al-Si-Cu or Al-Si-Mg alloys as a

function of aging temperature and duration.
3) Superalloys (for applications at elevated temperatures and also R.T.)

Superalloys include Ni, Co and Fe base alloys capable for service above
650C. High-T strength and oxidation resistance are required.

Examples of applications:

Gas turbine parts

Exhaust valves in internal combustion engines Rock drilling bits

High speed tools

Nuclear reactors (e.g., heat exchange tubes, fuel rods, separators)

Tubes in the high-T erosion tester

are made of a superalloy.
 - Ni base superalloys
e.g., A Ni alloys such as IC-50: 11.3%Al + 0.6%Zr + 0.02%B + Ni
The Ni base superalloys contain ordered intermetallic phase such as Ni3Al
(gamma’) in Ni-Al matrix (Gamma), which is stable up to high T and thus keeps
the alloys strong at elevated T.

Strengthening mechanism:
 ' Phase can pin dislocations;
(a)

 '(Ni3 Al): : an ordered fcc phase (a)The anti-phase boundary (APB) with high  APB

a  3.57 A increases the energy barrier to dislocation
movement;
(c)  '/ interface is coherent, which reduces interfacial cracking.

Comment: You may use carbides that have high-T

strength. However, possibly weak carbide/metal
interfaces could be an issue.

Other elements may be added (e.g., Cr, Ti, Nb, B,

Si) to result in the following phases to strengthen
the alloy:
Ni3Al, Ni3Nb, Ni3Si, Ni3B, Co3Al, Ni3Ti, CrB,
Cr3B, Cr3B2, Cr5B3, M23C6, M7C3, …
Ni base alloys are oxidation resistant. When T is high enough,
oxidation of Ni alloys reduction of adhesion during
sliding. Such reduction is
significant when T > 540C.
 Another ordered hard phase, known as Laves phase, may exist to
strengthen the alloy (e.g., MgNi2, ……)

Cu

MgCu2 is a Laves phase

Better interfacial bonding than

that of ceramic/metal interfaces.
Mg

Q44: Why is C/M interfacial bonding generally

not as strong as that of M/M interfaces?

Discussion: Electrons in ceramics are

localized (e.g., covalent bonds) and have weak
interactions with metals.
Sample alloys: e.g., Inconel 718 – a nickel-
based superalloy

0.1%C-0.75%Si-0.5%Mn-0.75%Cu-50%Ni-
18%Cr-5%Co-3%Mn-8%Al-1%Ti – Fe

Tribaloy T – 700
50%Ni-32%Mo-15%Cr-3%Si-0.08%C
- Co base superalloys

Excellent high-T oxidation resistance; their high-T strength may not be

mayNi
as good as notbase
be superalloys; high resistance to impact and thermal
shock; corrosion resistant. Co transforms from hcp to fcc at about 430C.

Predominant strengthening phases: M7C3, M23C6

A compacted layer of mixed debris of

oxide and wear debris at elevated
temperatures, which is protective

ERCoCr-A Oxide glaze forms

Some high-T alloys
Abrasive wear of some high-T alloys