Fundamentals of metal and steel, heat treatment and material

strengthening

Metallurgy & Metallurgists

• Dictionary– Metallurgy = the science that explains methods of

refining & extracting metals from their ores & preparing them

• Materials Today Magazine– Metallurgy = the science that explains the properties,

behavior & internal structure of metals.

• Metallurgies– Scientists in metallurgy that probe deeply inside the

internal structure of metal to learn what it looks like.

Terms to know !!! Elements = is a pure substance made up of just one kind of materials

Metal = is an element that has metallic properties, i.e. heat & electrical conductor

Compound = is a material that is composed of two or more elements that are chemically joined

Mixture = is a materials composed of 2 or more elements or compounds mixed together, but not chemically joined

Solution = is a special kind of mixture. When 2 materials combine & become a solution, one of two will become the “dictator” & the other one will become quiet & submissive.

Solid solution = is a solution in which both solvent & solute are solids. Both the “dictator” & the dissolved material are solids

Alloy

• Alloy = When 2 or more metals are dissolved together in a solid solution– Steel = alloy of Fe & C– Bronze = alloy of Cu & Sn– Brass + alloy of Cu & Zn

Taxonomy of Metals

Fe3C

cementite

Metal Alloys

Steels

Ferrous Nonferrous

Cast Irons Cu Al Mg Ti<1.4wt%C 3-4.5wt%C

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

austenite

+L

+Fe3C

ferrite+Fe3C

+

L+Fe3C

(Fe) Co, wt% C

Eutectic:

Eutectoid:0.77

4.30

727°C

1148°C

T(°C)

Steels<1.4wt%C

Cast Irons3-4.5wt%C

microstructure: ferrite, graphite cementite

Types of metal alloys

• Groups of metal alloys:– Ferrous alloy (iron is the prime constituent).– Nonferrous alloys.

• Steels: Iron-carbon alloys that may contain appreciable concentrations of other alloying elements. Carbon content is normally less than 1.0 wt%.

• Cast irons: Ferrous alloys with carbon contents above 2.14 wt% (usually 3.0-4.5 wt% C).

Classification for various ferrous alloysMETAL ALLOYS

Ferrous Non-ferrous

Steels Cast iron

Gray iron

Ductile

(nodular) iron

White iron

Malleable ironLow alloy

High alloyLow carbon High carbonMedium carbon

Plain

High strength, low alloy

Plain

Heat treatable

Plain

Tool StainlessTool

Wrought iron

Special alloy cast

iron

STEELS Steel is an alloy or solid solution, dictator = Iron, dissolved

mater. = C

Most widely used materials in the world

High strength, machined & formed easily

Steel are iron-carbon alloys that may contain appreciable concentrations of other alloying elements

Mechanical sensitive to the content of C < 1.0 wt.%

Thousands of alloys that have different compositions and/ or heat treatments.

STEELS Commonly classified according to C concentration

a) Low CSb) Medium CSc) High CS

Subclasses; according to the concentration of other allying elements

a) Plain CS contain only residua; concentrations of impurities other

than C & a little Mn

b) Alloy steels alloying elements are added in specific concentration

Low Alloy High Alloy

low carbon <0.25wt%C

med carbon 0.25-0.6wt%C

high carbon 0.6-1.4wt%C

Uses auto struc. sheet

bridges towers press. vessels

crank shafts bolts hammers blades

pistons gears wear applic.

wear applic.

drills saws dies

high T applic. turbines furnaces V. corros. resistant

Example 1010 4310 1040 4340 1095 4190 304

Additions noneCr,V Ni, Mo

noneCr, Ni Mo

noneCr, V, Mo, W

Cr, Ni, Mo

plain HSLA plainheat

treatableplain tool

austentitic stainless

Name

Hardenability 0 + + ++ ++ +++ 0TS - 0 + ++ + ++ 0EL + + 0 - - -- ++

increasing strength, cost, decreasing ductility

Steels

Composition of Steels

Steel is a mater. Composed primary of iron.

> 90% iron, many steels contain > 99% iron

All steel contain 2nd element = C

% C range just above 0% ~ approx. 2.0%, many steels contain 0.15 ~ 1.0%.

Effect of C in steel

Steel with the least C are more flexible & ductile, not strong.

C content increases, so do strength, hardness & brittleness

In making steel, the iron dissolves the C, when there is too much carbon for the iron to “digest” the alloy is no longer called steel.

Effect of C in steel: Microstructure

In steel, iron dissolves the C

In gray cast iron, the C precipitates out as C flakes

In ductile cast iron, the C precipitates out as a small round nodules

Classification of Steel

• 4 numbers/ digits• 1st 2 digits refer to the

alloy content• Eg;

– 5147 steel, ’51’ = steel has a lot of Cr

– 2517 steel, ’25’ = amount of Ni

– 1040 steel, ’10’ = very little alloy content except C

Steel Numerical Name

Key Alloys

10XX11XX13XX

C onlyC only (free cutting)

Mn

23XX25XX31XX

NiNi

Ni-Cr

33XX303XX40XX

Ni-CrNi-CrMo

41XX43XX44XX

Cr-MoNi-Cr-MoMn-Mo

46XX47XX48XX

Ni-MoNi-Cr-Mo

Ni-Mo

50XX51XX

501XXX

CrCrCr

515XX521XX514XX

CrCrCr

515XX61XX81XX

CrCr-V

Ni-Cr-Mo

86XX87XX88XX

Ni-Cr-MoNi-Cr-MoNi-Cr-Mo

92XX93XX94XX

Si-MnNi-Cr-Mo

Ni-Cr-Mo-Mn

98XXXXBXXXXLXX

Ni-Cr-MoB

Pb

Steel Numbering System

• Last 2 (or 3 in 5 digits case) digits refer to % of C in steel.

• Eg; – 1040 steel, ’40’ =

0.40% C

Steel Name

Appox % C Alloys present in

Larger amount than normal case

1020 0.20 Only C

1118 0.18 Only C

1340 0.40 Mn

2340 0.40 Ni

3140 0.40 Ni & Cr

4024 0.24 Mo

4320 0.20 Ni, Cr & Mo

5135 0.35 Cr

6150 0.50 Cr & V

8622 0. 22 Ni, Cr & Mo

9255 0.55 Si & Mn

Effect of AlloysSteel Alloy Effect on Steel

C Hardness-strength-wear

Cr Corrosion resistance-Hardenability

Pb Machinabiliy

Mn Strength – Hardenability – More response To

Heat TreatAl Deoxidation

Ni Toughness – strength

Si Deoxidation – Hardenability

W High temp. strength – wear

Mo High temp. strength – Hardenability

S Machinabiliy

Ti Elimination of C precipitation

V Fine grain – Toughness

B Hardenability

Cu Corrosion resistance – strength

Columbium Elimination of C precipitation

P Strengt

Tellurium Machinability

Co Hardness-wear

• Greater strength – C, Mn & Ni added

• Corrosion Resistance – Cr or Cu added

• Better machinability – Pb & S added

• Physical properties at high temp. – W or Mo are recommended

STEELS

Low alloy

High alloy

Less expensive

Less alloy content

Few special properties

More expensive

More alloy content

Special properties

Low alloy steel

Low carbon steel

High carbon steel

Medium carbon steel

• 0.05 ~ 0.35% C

• Comparatively less strength

• Comparatively less Hardness

• Easy Machining & Forming

• Least Expensive

• Largest quantity Produced

• 0.35 ~ 0. 50% C

• Hard & strong after heat treating

• More expensive than Low CS

• 0. 50 ~ 1.0% C

• High strength & hardness

• Hard & strong after heat treating

• More expensive than Low & medium CS

OverviewSometimes called plain

carbon steel

Low alloy steel

Low carbon steel

High carbon steel

Medium carbon steel

• Fence wire

• Auto bodies

• Galvanized sheets

• Storage tanks

• Large pipe

• Various parts in building, bridges &

ships

• Wheels

• Axles

• Crankshafts

• Gear

• Tools

• Dies

• Knives

• Railroad wheels

• High strength materials application

Application of Low Alloy Steel

Sometimes called plain carbon steel

High alloy steel

Tool steel Stainless steel

Widely used

Used as cutting tools, mould & dies

Machine parts

Extremely good corrosion resistance

Expensive than CS

Harder to cut & machine

High Cr and/or Ni

Is a grade of steel which one or more alloying elements have been added in larger amounts to give it special properties that ordinary cannot obtained with CS

Category Description

W Water Hardening

O Oil Hardening

A Air Hardening

D Oil or air Hardening

S Shock resistance

H Hot working

M High speed (Mo)

T High speed (W)

L Special purpose

F Special purpose

P Mold making

High Alloy Steel

Stainless steel Tool Steel

Ferritic Martensitic Austenitic Precipitation hardening

Stainless Steel Excellent corrosion resistance in many environment

due to Cr content (>11~ 12% Cr)

Corrosion resistance enhanced by Ni & Mo

Cr forms a surface oxide that protects the underlying Fe-Cr alloy from corroding. To produce the protective oxide, the SS must be exposed to oxidizing agents

SS are divided into 3 classes based on the microstructure phase constituenta) Ferriticb) Martensiticc) Austenitic

Ferritic Stainless Steel

• FSS are essentially Fe-Cr binary alloy containing about 12 ~ 30% Cr

• Called ferritic bcause their structure remains mostly ferritic (BCC, α iron type) at normal heat treatment conditions.

• Relatively low cost

• Mainly used as general construction materials

• The present of the carbides in this steel reduces its corrosion resistance to some extent

• Considered non-heat-treatable because they are all single phase, α iron type alloys whose crystal structure does not change under normal heat-treatment conditions.

• Eg; – 430 SS (general-purpose, non-hardenable uses, range hood, restaurant

equipment)– 446 SS (High-temp. application, heater, combustion chambers)

Type 430 (ferritic) SS strip annealed at 788oC.

The structure consists of a ferrite matrix equiaxed grain & dispersed carbide particles.

Martensitic Stainless Steel

• MSS are essentially Fe-Cr alloys containing 12 ~ 17 % Cr with sufficient C (0.15 ~ 1.0 %).

• Produced from quenching from the austenitic phase region

• Called martensitic because they are capable of developing a martensitic structure from austenitic condition by quenching heat treatment.

• Can be adjusted to optimize strength & hardness but corrosion resistance is relatively poor compared to the ferritic & austenitic steel

• High hardness due to hard martensitic matrix & the presence of a large concentration of primary carbides.

• Considered as heat-treatable because the carbon content is sufficient for the formation of a martensitic structure by austenitizing and quenching processes.

• E.g.;– 410 SS ( General purpose, heat-treatable machine parts, pump shafts, valves)– 440A SS (Cultery, bearing, surgical tools)– 440C SS (Balls bearing, valve parts)

Type 440 (martensitic) SS hardened by autenitizing at 1010oC & air cooled. Structure consists of primary

carbides in martensite matrix.

Austenitic Stainless Steel Austenitic steel are essentially Fe-Cr-Ni ternary alloys containing

about 16~25% Cr & 7~20% Ni.

Called austenitic since their structure remains austenitic (FCC, γ iron type) at all normal heat-treating temperatures.

Better corrosion resistance than ferritic & martensitic SS because the carbides can be retained in solid solution by rapid cooling.

E.g.;– 301 SS (High work hardening rate alloy, structural applications)– 304 SS (Chemical & food processing equipment)– 304L SS (Low carbon for welding, chemical tank)– 321 SS (Stabilized for welding, process equipment, pressure

vessels)– 347 SS (Stabilized for welding, tank cars for chemicals)

Type 340 (austenitic) SS hardened strip annealed 5 min at 1065oC and air cooled. Structure consists of

equiaxed austenite grains.

Example1. What are the 3 basic types of stainless steels? 2. What is the basic composition of ferritic stainless steels

& Why are ferritic stainless steels considered non-heat-treatable?

3. What is the basic composition of martensitic stainless steels and why are these steels heattreatable?

4. What are some applications for ferritic and martensitic stainless steels?

Solution;

Refer your lecture note

ExampleWhat makes it possible for an austenitic stainless steel to have an austenitic structure at room temperature?

Solution;Austenitic stainless steel can retain its FCC structure at room temperature due to the presence of nickel, at 7 to 20 weight percent, which stabilizes the austenitic Fe structure.

What makes austenitic stainless steels that are cooled slowly through the 870 to 600ºC range become susceptible to intergranular corrosion?

Solution;When slowly cooled through 870 to 600ºC, some austenitic stainless steels become susceptible to intergranular corrosion because chromium-containing carbides precipitate at the grain boundaries.

CAST IRON

Gray ironmore common

Ductile

(nodular) ironHigher quality

White ironmost brittle

Malleable ironHigher quality

Special alloy cast iron

Special properties

Cast Irons

Iron-Carbon alloys of 2.0 ~ 6.0%C

Typical composition: 2.0-4.0%C,0.5-3.0% Si, less than 1.0% Mn and less than 0.2% S.

Si-substitutes partially for C and promotes formation of graphite as the carbon rich component instead Fe3C.

Example

Solution:

What are the cast irons? What is their basic range of composition?

Cast irons are a family of ferrous alloys intended to be cast into a desired shape rather than worked in the solid state.

These alloys typically contain 2 to 4 percent C and 1 to 3percent Si.

Additional alloying elements may also be present to control or vary specific properties.

ExampleWhat are some of the properties of cast irons that make them important engineering materials? What are some of their applications?

Cast irons are easily melted and highly fluid and do not form undesirable surface films or shrink excessively; consequently, they make excellent casting irons.

They also possess a wide range of strength and hardness values and can be alloyed to produce superior wear, abrasion, and wear resistance. In general, they are easy to machine.

Their applications include engine cylinder blocks and gear boxes, connecting rods, valve and pump casings, gears, rollers, and pinions.

Gray Cast Iron• Fe-C-Si alloys

• Composes of: 2.5-4.0%C, 1.0-3.0%Si and 0.4-1.0% Mn.

• Gray cast iron contain large amount of C in the form of graphite flakes.

• Microstructure: 3-D graphite flakes formed during eutectic reaction. They have pointed edges to act as voids and crack initiation sites.

Gray Cast Iron• Properties:

– Hard & brittle– Relatively poor TS because graphite flakes in the structure– excellent compressive strength, – excellent machinability, – good resistance to adhesive wear (self lubrication due to graphite

flakes), – outstanding damping capacity ( graphite flakes absorb transmitted

energy), – good corrosion resistance and it has good fluidity needed for casting

operations.– Easy to cast

• It is widely used, especially for large equipment parts subjected to compressive loads and vibrations.

– Eg; brake disc, cylinder blocks, cylinder heads, clutch plates, heavy gear boxes and diesel engine castings

White Cast Iron• Fe-C-Si alloys

• Composes of: 1.8-3.6%C, 0.5-1.9%Si and 0.25-0.8%Mn.

• White cast iron contain large amount of iron carbide that make them hard & brittle

• All of its C is in the form of iron-carbide (Fe3C). It is called white because of distinctive white fracture surface.

• It is very hard and brittle (a lot of Fe3C). More brittle difficult to machine

• It is used where a high wear resistance is dominant requirement (coupled hard martensite matrix and iron-carbide). – Eg; iron mills, stone breaker

Malleable Cast Iron• Fe-C-Si alloys

• 2.0 ~ 2.6% C, 1.1 ~ 1.6% Si

• Malleable cast irons are 1st cast as white cast iron & then are heat-treated at about 940oC & held about 3~20 hrs.

• The iron carbide in the white iron is decomposed into irregularly shaped nodules or graphite.

• Less voids and notches.• Ferritic MCI:

– Ductile, 10% EL,– High TS, 35 ksi yield strength, – 50 ksi tensile strength. – Excellent impact strength, – good corrosion resistance– good machinability.

Malleable Cast Iron• Ductile iron with ferrite matrix (top)

and pearlite matrix (bottom) at 500X.

• Spheroidal shape of the graphite nodule is achieved in each case.

• Advantageous properties of malleable cast irons are toughness, moderate strength, uniformity of structure and ease of machining and casting.

Pearlitic Malleable Cast Iron

• Pearlitic MCI: by rapid cooling through eutectic transformation of austenite to pearlite or martensite matrix.

• Composition: 1-4% EL, 45-85 ksi yield strength, 65-105 ksi tensile strength. Not as machinable as ferritic malleable cast iron.

Ductile Cast Iron• Fe-C-Si alloy• 3.0 ~ 4.0% C, 1.8 ~ 2.8% Si.• Ductile cast iron contain large

amount of C in the form of graphite nodules (spheres).

• Without a heat treatment by addition of ferrosilicon (MgFeSi) formation of smooth spheres (nodules) of graphite is promoted.

• Properties: 2-18% EL, 40-90 ksi yield strength, 60-120 ksi tensile strength.

Ductile Cast Iron

• Attractive engineering material due to: good ductility, high strength, toughness, wear resistance, machinability and low melting point castability.

• Applications for ductile cast irons include valve and pump casings, crankshafts, gears, rollers, pinions and slides.

Example

Why are ductile cast irons in general more ductile than gray cast irons?

SolutionDuctile cast irons are, in general, more ductile than gray cast irons because their spherical graphite nodules are surrounded by relatively ductile matrix regions which allowsignificant deformation without fracture.

In contrast, the gray cast irons consist of an interlacing network of graphite flakes which can be fractured easily.

Example

Why does the graphite form spherical nodules in ductile cast irons instead of graphite flakes as in gray cast irons?

Solution;

Graphite forms spherical nodules in ductile cast irons because the levels of phosphorus and sulfur are reduced significantly compared to those in gray cast irons; these two alloying elements prevent the formation of nodules and thus promote the formation of graphite flakes

Special alloy cast iron Contain High % of Ni, Cu, Cr & other alloys

Ni, Cu & Cr good corrosion & chemical resistance to acids.

Greater strength & better high temperature properties

Used in cylinders, pistons, piston rings & turbine stator vanes

How Steel & Cast Iron Differ ?

Steel Cast Iron

Iron with C still in solution Iron which some of the C has precipitate out & appears as

flakes

C content; 1.6 ~ 2.0% C content; 2.0 ~ 6.0%C

Ductile compare to C. iron Brittle compare to steel

High strength Poor Strength

Hard to machine Easy to machine

Hard to control casting Easy to cast

Low damping capacity Good Damping Capacity

Example

Wrought Iron

Very different from cast iron Almost pure iron, little C

content Low strength & hardness Good corrosion resistance Many fibrous stringers of slag

are distributed throughout wrought iron

Elements Wt.%

Fe balance

C 0.06 ~ 0.08

Si 0.10 ~ 0.16

Mn 0.02 ~ 0.05

S 0.01

P 0.06 ~ 0.07

NonFerrous Alloys

• Cu AlloysBrass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant)Bronze: Sn, Al, Si, Ni are subst. impurity (bushings, landing gear)Cu-Be: precip. hardened for strength

• Al Alloys-lower : 2.7g/cm3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct.

aircraft parts & packaging)

• Mg Alloys-very low : 1.7g/cm3 -ignites easily -aircraft, missles

• Refractory metals-high melting T -Nb, Mo, W, Ta• Noble metals

-Ag, Au, Pt -oxid./corr. resistant

• Ti Alloys-lower : 4.5g/cm3

vs 7.9 for steel -reactive at high T -space applic.

Nonferrous alloys

Cu & its alloys Unalloyed Cu is so soft & ductile; difficult to machine

Highly resistant to corrosion

Unalloyed Cu cannot be hardened or by strengthened by heat heat-treating procedures

Mechanical & corrosion properties can be improved by alloying

Cold working and/or solid-solution alloying must be utilized to improved the mechanical properties

Cu alloys, e.g.; Brass, Bronze, Beryllium Cu, Cartridge brass, Cu-Ni alloy, Tin bronze, Al bronze

Application; Electrical wire, nails, valves, automotive radiator, condenser, heat exchanger components, pistons rings, bearing, gears & so on

Example

What are some of the important properties of unalloyed copper that make it an important industrial metal?

Solution:Properties of unalloyed copper, which are important to industrial applications, include high thermal and electrical conductivity, good corrosion resistance, ease of fabrication,medium tensile strength, controllable annealing properties, and general soldering and joining characteristics.

Al & its alloys Unalloyed Al; low density (2.7 gcm-3), lightweight, high

electrical & conductivity, workability, ductile & low cost. Moderate melting point (660oC)

Resistance to corrosion in most natural environments due to formation oxide film that form on its surface.

Non-toxic, used food container & packaging

Mechanical properties can enhanced by cold work & alloying

Alloying elements; Cu, Mg, Si, Mn & Zn

Al alloy are classified as either cast or wrought

Al & its alloys Chemical composition is designated by 4-digit number indicates

the principle impurities & in some cases, the purity level

Application of Al alloys; aircraft structure parts, beverage cans, Food/chemical handling, storage equipments, bus bodies, automotive parts (engine blocks, pistons & intake manifolds).

To be used as eng. materials for transportation to reduce fuel assumption because its specific strength, which is quantified by the TS-specific gravity ratio. Its TS is inferior to a more dense material (such as steel), on weight basis it will able to sustain a larger load.

A new generation Al-Li alloys applied in aircraft & aerospace industries has low densities (~ 2.5gcm-3), high specific moduli, excellent fatigue, low temp. toughness.

ExampleWhat are some of the properties that make aluminum an extremely useful engineering material?

Solution:Aluminum is an extremely useful engineering material due to its low density (2.70 g/cm3), good corrosion resistance, good strength when alloyed, high thermal & electrical conductivities and low cost.

What are some of the properties that make aluminum to be high prospect for transportation material.

Solution:To be used as eng. materials for transportation to reduce fuel assumption because its specific strength, which is quantified by the TS-specific gravity ratio. Its TS is inferior to a more dense material (such as steel), on weight basis it will able to sustain a larger load.

Mg & its alloys Lightweight metal, low density = 1.74gcm-3. Moderate melting point

(651oC).

Applications requiring a low density metal (aircraft, aerospace & missile)

Soft, low elastic modulus.

Difficult to cast because molten state burn in air

Low strength, poor resistance to creep, fatigue & wear.

At RT, Mg & its alloy are difficult to deform.

Chemically unstable; susceptible to corrosion in marine environments.

Mg alloys are classified as either cast or wrought.

Alloying elements; Al, Zn, Mn & some rare earth elements.

Mg & its alloys Mg alloys have replaced engineering plastic that

have comparable densities inasmuch as the Mg materials are stiffer, more recyclable, & less costly to produce.

Application of Mg alloys; hand held devices (chain saws, power tools, hedge

clippers) Automobile ( steering wheels & columns, seat frames,

transmission case) Audio-video-computer-communications equipment

( laptop computers, camcorders, TV sets, cellular telephones)

ExampleWhat advantages do magnesium alloys have as engineering materials?

Solution:As engineering materials, the primary advantage of magnesium alloys is their lightness; magnesium has the low density value of 1.74 g/cm3.

What are some of the properties that make a Mg can be replaces plastic as an engineering materials ?

Solution:Mg alloys can replaces engineering plastic because it has a comparable densities, stiffer, more recyclable, & less costly to produce.

Ti & its alloys Pure Ti; relatively light metal (density = 4.54 gcm-3), high melting point

(1668oC), high elastic modulus & high strength.

Ti alloys; extremely strong, high TS, spesific strength, highly ductile, easily forged & machined.

Corrosion resistance to many chemical environments.

Limitation; chemical reactivity with other materials at elevated temp.

Expensive because it is difficult to extract to pure state from it compound.

Combine to Al for aircraft structural parts application.

Application; airplane structures, jet engine, space vehicles, gas turbine engine casings, jet engine components (compressor disks, plates & hubs) surgical implants & petroleum & chemical industries.

ExampleWhy are titanium and its alloys of special engineering importance for aerospace applications?

Solution:Titanium and its alloys are of special engineering importance for aerospace applications because of their high strength-to-weight ratios.

Why is titanium metal so expensive?

Solution:Titanium is very expensive because it is difficult to extract in the pure state from its compounds.

Refractory Metals

• metals with exceptionally high melting points; above 2450oC

Metal Melting Point, oC

Density, gcm-3 Cost

RM/ Ib

Niobium (columbium) (Nb)

2468 8.57 192 ~ 210

Tantalum (Ta) 2996 16.6 780 ~ 840

Molybdenum (Mo) 2620 10.22 210 ~ 228

Tungsten 3380 19.3 450

Refractory Metals

Group in periodic Table Group VB Group VIB

Metal Elements Nb, Ta Mo, W

Tensile strength at elevated temperature

Low Low

Elastic moduli Less High

Solid solubility for interstitial elements (C,O,H,N)

High Less

Electronic Configuration Less Stable

Creep Strength Less High

Ductile-to-brittle fraction transition-temperature behaviour (DBTT)

Below room temp

(easy fabricate)

Near OR above room temp

Refractory Metals

DBTT Depends on

a)grain size,

b)impurity content

c) amount of prior cold

work

The Higher Creep Strengths of Mo & W are attributed to theira)Elastic moduli, b)Low diffusivities

Example

Define a refractory metals. Name the metal elements that are considered to be refractory elements?

Solution:

Refractory metals are metals with exceptionally high melting points; above 2450oC.

Refractory elementsi) Niobium (Nb)ii) Tantalum (Ta)iii) Molybdenum (Mo)iv) Tungsten (W)

Superalloys Superalloys have superlative combinations of properties.

Most are used in aircraft turbine components

Must withstand exposure to severely oxidizing environments & high temperature

These materials are classified according to the predominantly metal in alloys;- Co, Ni or Fe.

Other alloying elements; refractory metals (Nb, Mo, W & Ta), Cr & Ti.

Other application; nuclear reactors & petrochemical equipment.

Noble metals The noble metals are a group of 8 elements that have

some physical characteristics in common.

Expensive & superior or notable (noble) in properties.

Examples; Silver (Ag), gold (Au), Platinum (Pt), Palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) & osmium (Os).

Ag, Au & Pt are used as jewelry

Alloys of Ag & Au employed as dental restoration materials & IC electrical contacts.

Pt used for laboratory equipment, catalyst & thermocouples.

Miscellaneous nonferrous alloysNickel & its alloys (eg. Monel) – highly corrosion

resistance.Used in pumps, valves and other components that

are in contact with some acid & petroleum solutions.

Lead (Pb) & Tin (Sn) and its alloys – mechanically soft & weak. Low melting temperature, quite resistance to many

corrosion environment.Many common solders are lead-tin alloys,Application of lead alloys – x-ray shields & storage

batteriesApplication of tin alloys – thin coating on the inside of

plain CS cans (tin cans) used for food containers.

Miscellaneous nonferrous alloysZn – soft & low melting temperature, reactive

with several materials, susceptible to corrosion Zn applications;- thin coating on CS roofingZn alloys applications;- padlocks, plumbing fixtures,

automotive parts (door handles & grilles) & office equipments.

Zirconium & its alloys are ductile, resistance to corrosion in superheated water, transparent to thermal neutronsApplication of Zr alloys – Cladding for uranium fuel in

water-cooled nuclear reactors.Heat exchangers, reactor vessels & piping systems

for the chemical-processing & nuclear industries.