Review

Michael R. Pendley, MSc.Lone Star College

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metals and their mixtures (alloys).

It also covers the technology of metals: the way in which science is applied to their practical use.

Metals are elements with metallic bonding (positive ions surrounded by a “sea” of free electrons).

Metals generally have high electrical and thermal conductivity, luster and density.

Metals occupy the bulk of the periodic table.

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Metals are composed of crystals. A crystal is homogenous solid formed by a

repeating, three-dimensional pattern of atoms with long range order.

A Bravais lattice is one of the 14 possible arrangements of lattice points in space such that the arrangement of points about any chosen point is identical with that about any other point.

There are 14 Braviais lattices in 7 basic groups.

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Phases are present in all alloys. A phase is a homogenous, physically distinct

and mechanically separable portion of the material with a given chemical composition and structure.

The number and type of phases present at a given temperature and composition can be represented on a phase diagram.

Must be homogeneous in crystal structure and atomic arrangement.

Must have the same chemical and physical properties throughout.

Must have a definite interface. Must be able to be mechanically separated

from its surroundings.

State Phase Interaction Example

Solids Phases are chemically and structurally distinct

Carbide particles in a steel matrix.

Liquids Miscibility determines if phases will be soluble in each other

Oil and water are immiscible.Liquid silver is miscible in liquid zinc.

Gases Only one phase The atmosphere consist of several gases (nitrogen, oxygen, CO2, etc.)

Pure metal phases are composed mostly of one metal with minor additions of another element.

Solid solutions are formed when the solvent metal incorporates atoms of another (solute) metal into its crystal structure.

The type of solid solution formed depends upon the relative sizes of the two atoms.

The two types are substitutional and interstitial.

Interstitial compounds are formed between metals and non-metals (such as hydrogen, oxygen, and carbon).

Intermetallic compounds are formed between metals but are non-metallic in behavior.

Electron compounds are formed between certain metals including copper /aluminum and silver/cadmium.

Atomic Size Atomic size of the two components must be within 15% to get complete solubility.

Electrochemistry Must be similar. The more electropositive one element and the more electronegative the other, the greater the tendency to form an intermetallic compound instead of a solid solution.

Valency The higher the valency of one component, the more likely will it tend to dissolve in the other component.

Crystal Structure Must have the same crystal structure for complete solubility

Phase diagrams show the phases present at a given temperature and composition.

Percentages of the chemical elements are usually shown in weight percent.

For simplicity, impurity elements are ignored. For binary phase diagrams, temperature is

plotted on the vertical axis. Composition is plotted on the horizontal axis.

Liquid/Solid

Eutectic Isothermal

Peritectic Isothermal

Monotectic Isothermal

Solid State

Eutectoid Isothermal

Peritectoid Isothermal

L

L

21 LL

When a sufficient load is applied to a metal or other structural material, it will cause the material to change shape.

This change in shape is called deformation. Elastic deformation is self-reversing, as the

material returns to its original shape. Plastic deformation creates a permanent

change in the shape of a material.

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Slip is the shear displacement of part of a crystal.

Occurs when the critical resolved shear stress is exceeded.

Ease of slip depends upon the number of slip systems.

FCC metals have 12 slip systems and are ductile.

CPH metals have only 3 slip systems and are brittle.

FCC BCC CPHSlipSystems

12 12 (48) 3

CRSS (psi) 50-100 5000-10000 50-100

Behavior Ductile Strong Brittle

Examples AluminumCopperSilver

IronMolybdenum

Tungsten

MagnesiumCobalt

Titanium

The critical resolved shear stress is the resolved shear stress required to cause slip in given slip system.

It is a threshold value, therefore “critical.” Slip occurs when the critical resolved shear

stress of a metal is exceeded. CRSS is a material property - each metal has

its own critical resolved shear stress.

Dislocations are imperfections in crystals that allow slip to occur one atom at a time.

Account for the weakness of metals compared to theoretical values.

Instead of slip taking place with entire planes of atoms moving simultaneously, it takes place one atom at a time.

Two types of dislocations are edge and screw.

Cold working is plastic deformation performed below the recrystallization temperature for the purpose of shaping a product.

Cold working increases the strength of a material but reduces the ductility.

Cold working processes include rolling, drawing, extruding, stamping, and bending.

Strain hardening is the increase in strength and hardness (and corresponding loss in ductility) due to plastic deformation by cold working.

Grains elongate in the direction of working. Dislocations become tangled up, making

further plastic deformation difficult.

Annealing consists of heating a material to a given temperature, holding it, and then cooling at an appropriate rate.

Annealing of cold worked material restores ductility while reducing strength and hardness.

Recovery (or stress relieving) is the reduction of residual stresses.

Recrystallization involves the formation of new stress-free grains.

Grain growth occurs if the material is heated beyond the time needed for complete recrystallization.

Hot working is deformation conducted above the recrystallization temperature.

Hot working does not produce strain hardening.

Hot working improves cast structure, breaks up impurities, heals porosity, refines grain structure, and improves mechanical properties.

Mechanical properties are characteristics of a metal they describe how the metal will react to an applied stress.

Important mechanical properties include tensile and yield strength, hardness, toughness, and ductility.

Mechanical testing encompasses a wide variety of tests designed to determine the mechanical properties of a material.

Various standardized tests have been developed to establish uniform testing procedures.

Tension Compression Shear Torsion Flexure

Elastic Region Strain is directly proportional to stress, no permanent deformation.

Proportional Limit The maximum stress at which stress is directly proportional to strain.

Elastic Limit The stress at which the specimen takes on permanent plastic deformation.

Yield Point Strain increases without an increase in stress.

Hardness is the ability of a material to resist penetration of the surface.

Hardness testing is one of the most widely used mechanical test methods.

Method Principle Examples

ScratchCompares hardness of various materials

Mohs scaleFile testing

IndentationMeasures depth or area of an indentation

Brinell TesterRockwell Tester

ReboundMeasures the rebound of a dropped object

Scleroscope TesterEquotip Tester

Type Method Scale Measures

Scratch File test Macro Resistance to scratching

Indenter

Brinell Macro Area of indentation

Vickers Macro or Micro Area of indentation

Rockwell Macro and Superficial Depth of indentation

Knoop Micro Area of indentation

Rebound Scleroscope Macro Rebound height

Equotip Macro Rebound height

Toughness is the ability of a material to absorb energy and deform plastically before fracturing.

A tough metal is ductile and deforms plastically before fracturing.

A brittle metal breaks with little or no plastic deformation.

Toughness is commonly evaluated by impact testing.

A notched bar impact test measures the amount of energy needed to break a small specimen containing a machined notch.

In a common test method, a free-swinging pendulum is raised to a fixed height and released, striking the specimen.

The swing of the pendulum after striking the specimen indicates the absorbed energy.

Test results are measured in ft-lbs or joules.

Fatigue is the failure of a material under alternating (cyclic) stress.

Fatigue is a common failure mode for moving parts.

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Fatigue testing is an example of a dynamic test.

In a fatigue test, a specimen is subjected to alternating stress (tension to compression) for a large number of cycles.

The fatigue limit is the stress corresponding to certain number of cycles, usually 10 million.

Fracture toughness is an indication of the amount of stress required to propagate a preexisting flaw.

Stress raisers include notches, cracks, and internal flaws.

Fracture toughness is a method of characterizing fracture behavior in terms of material toughness, flaw size, and stress level.

Bend tests are a measure of a metals ductility.

In a guided-bend test, a rectangular test plate is bent around a U-shaped die.

The specimen is bent 180°, revealing any flaws.

Commonly used to test welds.

Torsion is a measure of the ability of a material to withstand a twisting load (shear).

Torsion tests measure the maximum torsional stress that a material sustains before rupture.

Shear strength can be estimated from tensile strength.

Metallography is the study of the microstructure of a metal.

Metallography is conducted on a microscopic scale.

Metallographic specimens must be carefully prepared in order to reveal the microstructural features.

A metallographer is a person who prepares and evaluates the specimen.

Metallography is conducted for a variety of reasons, including:

Quality control. Process control and verification. Materials identification. Research and development. Failure analysis. Historical studies.

Before a specimen can be examined, it must be prepared by:

Cutting to an appropriate size.

Mounting in a hard plastic medium.

Grinding to a rough finish.

Polishing to a mirror-like finish.

Etching with an acid solution.

Metallographic examination requires the use of a special microscope called a metallograph.

Metallographs are optical microscopes and generally have a range of 100 – 1000x.

The image is obtained from light reflected from the specimen surface.

A camera attachment allows microstructures to be photographed.

Quantitative metallography is the use of metallography to measure specific features such as:

Grain size.

Porosity rating.

Inclusion rating.

Most metals are polycrystalline, they consist of many small grains.

Grain size affects the mechanical properties of steels and other metals.

Fine-grained steels produce better properties.

Steel specifications often specify a maximum grain size based on ASTM standards.

A fracture occurs when a metal separates into two or more pieces.

Fractures occur when a material is stressed beyond its load-bearing capacity.

Fractures normally begin with crack formation followed by crack propagation.

Fractography is the study of fracture surfaces.

The features observed on a fracture surface can provide important clues about the nature and cause of the fracture.

Various fracture features can provide clues about the nature of the fracture including:

Fracture Orientation (shape/direction).

Fracture Morphology (texture/appearance).

Ductile fractures exhibit material tearing and large scale plastic deformation.

Brittle fractures display little or no plastic deformation.

Fatigue fractures advance in discrete steps separated by periods of no growth creating “arrest lines” or “beach marks” which mark the temporary positions of the advancing crack front.

Brittle materials often fracture along crystal planes creating a “cleavage” fracture.

Brittle fractures can be intergranular (between metal grains) or transgranular(breaking grains in half).

Brittle fractures occur without warning and are often catastrophic.

Normally ductile metals can become brittle due to various causes including H2S and low temperature.

A fracture surface may exhibit more than one morphology.

The driving force for fracture propagation often changes as the fracture grows.

This can cause a change in the fracture orientation and morphology.

Many fractures exhibit three distinct fracture zones.

Zone Description

Initiation Region where the fracture starts

Propagation Main (intermediate) area of fracture

Final Fracture Last area to fail

In fractography, one of the most important things is to determine the fracture origin.

The fracture origin can help to determine the cause of the failure.

Several macroscopic features can be used to determine the fracture origin:

Radial lines

Chevron patterns

Arrest lines

Ratchet marks

A failure analysis is conducted to determine the cause of a failure.

The four steps of a failure analysis are field investigation, fractographic examination, destructive examination, and writing of a failure report.

It is vital that metals be properly identified prior to use.

Material mix-ups can have catastrophic consequences.

Like luggage, many metals look alike. It is difficult, if not impossible, to identify a

metal by sight.

Metal products are identified by various means including stamping, stenciling, and color coding.

Unknown metals can be identified by color, magnetism, density, sparking, chemical spot testing, and metallography.

Chemical composition can be checked by XRF or OES.

Nondestructive testing refers to various methods used to inspect a metal without causing damage.

Called “NDT” or “NDE” for short. NDT methods use various physical

phenomena (sound waves, magnetism, etc.) to detect flaws.

NDT is used for quality control, purchase inspection, process monitoring, and failure analysis.

Also called liquid penetrant. Used for detecting cracks and porosity on the

surface of non-porous materials. Based upon capillary action. A low surface tension fluid penetrates into

cracks and other surface discontinuities. Used to detect cracks and surface flaws in

forgings, castings, and welds.

In MT, the part being is tested is magnetized using AC or DC current.

Magnetic field leakage occurs at cracks, voids, and other flaws.

The magnetic field leaks attract iron powder which is applied to the part to indicate the flaw locations.

Ultrasonic testing uses high-frequency sound waves to penetrate solids and detect interior flaws.

Ultrasonic waves travel in a straight line at constant speed until they encounter a surface.

When a flaw is encountered, some of the wave energy is reflected back and some is transmitted.

Radiographic testing uses electromagnetic radiation to determine the interior soundness of metal parts.

X-rays and gamma rays are used. X-rays and gamma rays penetrate matter but

are partially absorbed. The amount of radiation that gets through

depends upon the type and thickness of the metal.

Eddy-Current Testing is an electrical NDT method which can be used to detect surface or near surface flaws in electrically-conducting materials.

In ET, a magnetic coil is placed near the part creating swirling electric currents (eddy currents).

Flaws will cause a change in eddy current flow indicated by a change in the phase and amplitude of the measured current.

AE detects the energy released by a structure under stress.

AE equipment detects the propagating elastic waves using sensors mounted on the structure's surface.

Method Principle Coverage Comments

LiquidPenetrant

Capillary Action

Surface Quick and easy.Portable.

Magnetic Particle

Magnetism Surface and Near-surface

Only works on ferromagnetic metals.

Ultrasonic SoundWaves

Volumetric Works on all metals.Requires skill and experience.

Radiography Radiation Volumetric Works on all metals.Expensive and slow.

Eddy-Current

InducedCurrents

Near-surface Requires skill and experience.

Acoustic Emission

ElasticEnergy

Volumetric Must be supplemented by other NDT.Can provide continuous monitoring.

A material standard is a written document that establishes the procedures and requirements for a given material, process, or test.

Material specifications list the technical and commercial requirements that a material must meet.

Test methods give instructions for measuring the properties of a material.

A recommended practice gives instructions for operations which do not involve identifying or evaluating a material.

Codes are a set of standards or regulations that have been given the force of law.

Trade associations are organizations that represent the producers of metals or other products.

Technical societies are composed of groups of engineers and scientists with a common professional interest.

National and international standards organizations develop and administer standards in conjunction with government agencies.

Private corporations issue their own proprietary standards.

ASTM is the largest standards organization in the world.

ISO publishes international standards.

Supply Chain orders materials using drawings, bills of material, and specifications.

The receiving department checks incoming material to make sure it meets applicable requirements.

Materials must be properly stored to prevent deterioration.

Ferrous alloys are metals based on iron.

Various alloying elements are added to the iron to produce a wide array of properties.

Ferrous metals are the most important metal products in terms of worldwide production and engineering application.

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Iron ore is turned into impure pig iron in a blast furnace.

Three basic ingredients are:

Iron Ore

Coke

Limestone Pig iron is refined into steel by removing

impurities.

3 types of steelmaking furnaces:

Basic Oxygen

Open Hearth

Electric Arc

Steel is deoxidized to remove excess oxygen from the melt.

Killed Steel (complete deoxidation)

Semikilled Steel (moderate deoxidation)

Rimmed Steel (no deoxidation)

Capped Steel (limited deoxidation)

Molten steel can be refined in the ladle to remove dissolved gases and nonmetallics and control inclusion shape.

Steel is produced in semifinished forms –blooms, billets, rounds, and slabs.

Semifinished forms are turned into finished products by hot working or cold working.

Ferrous metals are grouped into several broad classes, based on the amount and type of alloying elements.

There are 4 basic groups of ferrous metals:

Carbon and Alloy Steels

Tool Steels

Stainless Steels

Cast Irons

Carbon steel is the most important metal ever developed by mankind.

Carbon steel is an alloy of iron and a limited amount of carbon.

Pure iron is weak but the addition of a small amount of carbon greatly increases its strength.

When the carbon gets above 2%, we move from carbon steel to cast iron.

Iron is polymorphic (or allotropic) – it changes crystal structure at certain temperatures.

An allotrope is a specific crystal structure. Iron has 3 different allotropes:

Delta Iron

Gamma Iron

Alpha Iron

The Fe-C phase diagram is the foundation of ferrous metallurgy.

It is vital to an understanding of the phases that we encounter in carbon steels.

It is an equilibrium diagram (slow cooling or heating).

The main area of interest is the part of the diagram between pure iron (0% C) and cementite (6.67%C).

Phase Symbol Description

Liquid L Liquid solution of carbon in iron

Delta Ferrite d Interstitial carbon in BCC iron.

Austenite Interstitial carbon in FCC iron.

Ferrite Interstitial carbon in BCC iron.

Cementite Fe3C Hard and brittle interstitial compound.

Pearlite Fe3C Aggregate of ferrite and cementite.

A1 Austenite to Pearlite Boundary (Eutectic Temperature)

A3 Austenite to Ferrite + Austenite Boundary

Acm Austenite to Cementite Boundary

In the eutectoid reaction, a solid isothermally transforms to form two new solid phases when cooling at the eutectoid temperature.

The eutectoid reaction is the most important part of the iron-carbon phase diagram.

In carbon steel, the eutectoid composition is 0.83%C.

The eutectoid temperature is 1333°F.

There are 3 types of carbon steel, depending upon the carbon content:

Eutectoid (0.83% C).

Hypoeutectoid (<0.83%C).

Hypereutectoid (>0.83%C). Each has a different transformation behavior

upon cooling below the eutectoid temperature.

Mechanical properties of carbon steel are determined by:

Carbon content

Manganese content

Grain size

Heat treatment

Increasing the carbon content increases the amount of pearlite or cementite.

Increasing the carbon content leads to:

Increase in strength and hardness.

Decrease in ductility and toughness.

Number Class Description

10XX Plain Carbon No more than 1.0% Manganese

11XXResulfurized (Free Machining)

Contains added sulfur for improved machinability

12XXResulfurized and Rephosphorized(Free Machining)

Contains added sulfur and phosphorus for improved machinability

15XX Plain Carbon Contains extra Mn – 1.0 to 1.65%

In AISI carbon steel grades, the carbon level (in hundredths of a percent) is designated by the last two digits of the grade.

For example, 1020 steel contains 0.20% C.

Alloy steels contain additions of various elements (such as Cr, Ni, Mo, etc.) in order to improve the properties.

Low alloy steels contain between 1-5% of a given alloying element.

High alloy steels contain higher levels of alloying elements.

Wide range of properties. Can be heat treated to high strength levels. High hardenability. High toughness levels at low temperatures. Corrosion resistance. Inexpensive compared to stainless steel and

nickel/cobalt superalloys.

Costlier than carbon steel due to cost of alloying elements.

May require special heat treating and welding procedures.

The AISI system classifies alloy steels using a similar system as for carbon steels.

Mechanical properties, heat treat condition, product form, etc. are not specified.

Classification consists of a two-digit class code followed by a two-digit grade code.

As with carbon steel, the final two digits denote carbon content.

For example, a 4130 steel has 0.30% carbon.

Element Effect

Chromium Increases hardenability

Nickel Improves toughness

Molybdenum Improves strength and wear resistance

Manganese Increases strength

Tungsten Improves high-temperature strength

Copper Improves corrosion resistance

Silicon Increases strength but lowers ductility

Aluminum Deoxidizer

Tool steels are specialty steels that are intended to be made into cutting and shaping tools.

Required properties for tool steels include red hardness, toughness, wear resistance, and dimension stability.

Tool steels must be heat treated to attain the desired properties.

There are 7 groups of tool steels:

Water Hardening (W)

Cold Work (A, O and D)

Shock Resisting (S)

Special Purpose (L and F)

Plastic Mold (P)

High Speed (T and M)

Hot Work (H)

CLASS AISI ALLOYING CHARACTERISTICS

Water-hardening W High Carbon steel. Hard surface, tough core.

Cold-working

O Low alloy.Oil-hardening.

Wear resistance to moderate temperatures.

A Medium alloyAir-hardening.

Minimum distortion and cracking on quenching.

D High carbon, high Chromium High hardness and excellent wear resistance.

Shock resisting S Tungsten Excellent toughness and low strength.

High speedT Tungsten High hardenability, high hardness.

M Molybdenum High hardenability, high hardness.

Hot-working H

H1–H19: Chromium

Good resistance to softening at high temperature.

Good toughness.H20–H39: Tungsten

H40–H59: Molybdenum

Plastic mold P Low carbonLow hardness.

Low resistance to work hardening.

Special purpose

L Low alloy High toughness and good strength.

F Carbon and tungstenTough core and hard surface.

Good galling resistance.

Element Effect

Chromium Increases abrasion and wear resistance

Cobalt Increases cutting ability, improves red hardness

Molybdenum Improves red hardness

Nickel Improves toughness

Tungsten Increases wear resistance by forming carbides

Stainless steels contain at least 12% chromium plus other alloying elements.

Stainless steels owe their corrosion resistance to the formation of a protective layer of chromium oxide.

The type and amount of alloying elements determines the structure and properties of a given stainless steel grade.

Six families of stainless steels are:

Ferritic

Martensitic

Austenitic

Duplex

Precipitation hardening

Cast

Element Effect

Chromium Forms protective layer. Minimum of 10.5% needed. Stabilizes ferrite.

Nickel Austenite stabilizer, increases oxidation resistance

Molybdenum Resistance to pitting and crevice corrosion

Carbon Increases susceptibility to intergranular corrosion by “stealing” chromium to form chromium carbides

TitaniumColumbium

Improve resistance to intergranular corrosion by combining with carbon, preventing the formation of chromium carbides

Have an austenitic microstructure at room temperature.

Cannot be strengthened by heat treatment. Can be strengthened by cold work. Excellent weldability. Good low temperature toughness. Good resistance to high temperature

oxidation and scaling.

Cheapest stainless due to low alloy content. Plain chromium stainless (12-18% Cr). Have a ferritic microstructure. Low strength - cannot be strengthened by

heat treatment or by cold work. Good corrosion resistance. Poor weldabilty. Toughness can be improved by reducing

interstitial elements (C and N) to very low levels.

Have a martensitic microstructure. Can be heat treated (quenched and

tempered) to high strength levels. Strongly magnetic. Base alloy is 410. 410 is widely used in the oilfield. Poor weldability. Allowed for sour service up to 22 HRC.

Duplex stainless steels have a “duplex” (mixed) structure of austenite and ferrite.

High chromium content (18-28%). Can develop high strengths. Excellent corrosion resistance. Good weldability. The most widely-used grade is 2205. Sigma phase embrittlement is a danger if

improperly heat treated.

Can be martensitic, semi-austenitic or austenitic.

Can develop very high tensile strengths while maintaining a fair amount of ductility.

17-4PH is the most common grade with 17% chromium, 4% nickel, 4% copper.

Moderate corrosion resistance. Good weldability.

Similar composition to wrought grades except silicon is added for castability.

Stainless steel castings are classified as either corrosion-resistant or heat-resistant.

May be austenitic, ferritic, martensitic, or duplex.

Cast structure yields inferior properties compared to wrought stainless.

Cast iron is defined as an iron alloy with more than 2% carbon as the main alloying element.

Cast irons also contain from 1 to 3% silicon which give them excellent castability.

Cast iron has a much lower melting temperature than steel.

Cast iron is an important engineering material.

Cast irons contain more than 2% carbon. Cast irons are an economical way to produce

complex shapes. Disadvantages of cast irons include low

strength, poor toughness, low ductility, and poor weldability.

Cast irons go through the eutectic reaction on solidification.

Liquid + Fe3C/graphite The cooling rate has an important effect on

solidification and the type of cast iron that forms.

The six types of cast iron are:

Gray iron

White iron

Malleable iron

Ductile iron

Compacted graphite iron

Alloy iron

Gray iron is the most widely used cast iron. Gray iron is named after the gray color of the

fracture it forms, which is due to the presence of graphite.

Gray iron forms when solidification proceeds slowly so that the carbon precipitates out as graphite flakes.

Depending upon the cooling rate, the matrix is either pearlite or ferrite.

White iron forms during fast cooling, which doesn’t allow time for graphite formation.

Instead, the carbon precipitates out as cementite (Fe3C).

White iron contains massive amounts of Fe3C in a pearlitic matrix.

It is very hard and brittle.

Malleable iron is formed by the heat treatment of white iron.

During heat treatment, the cementite decomposes into rounded clumps of graphite resembling popcorn.

These clumps or nodules are called “temper carbon.”

The rounded shape of the nodules provides a good combination of strength and ductility.

Ductile Iron is produced by adding magnesium just before casting.

The magnesium is an inoculant that suppresses graphite flake formation and causes the graphite to form spheres or nodules.

Ductile iron consists of graphite spheroids in a matrix of ferrite and/or pearlite.

The graphite spheroids provide improved mechanical properties.

Compacted graphite iron is produced by adding an inoculant before solidification to prevent the formation of flake graphite.

The structure consists of elongated graphite particles mixed with spherical graphite particles.

The graphite structure is called quasiflake, aggregated flake, seminodular and vermicular graphite.

Alloy iron contains one or more alloying elements (up to 30% total) to enhance specific properties.

Graphitizers (Si, Ni, Al) promote graphite formation.

Carbide stabilizers (Cr, Mo, V) form carbides.

Light metals have low density. The three most important light metals are

aluminum, titanium, and magnesium. After steel, aluminum and titanium are the

two most important structural metals.

Light metals are reactive and are never found in nature in the metallic state.

Aluminum is produced from bauxite ore using electrolysis.

Magnesium is produced from sea water using electrolysis.

Titanium is produced from rutile ore using a chemical process.

Aluminum has a FCC structure. Magnesium has a CPH structure. Titanium has 2 allotropes:

Alpha (CPH) below 1620°F.

Beta (BCC) above 1620°F.

In general, the light metals have:

High strength-to-weight ratio.

Good corrosion resistance.

Good electrical and thermal conductivity.

Good weldability.

Ability to be strengthened by precipitation hardening or cold working.

3 types of titanium alloys are alpha, beta, and alpha-beta.

Some titanium alloys can be heat treated to yield strengths up to 200 ksi.

Copper is man's oldest metal, dating back more than 10,000 years.

Copper is one of the few metal to occur in uncombined form in nature.

Yellowish red color (one of a few metals that is not silver or gray).

Non-magnetic.

Good thermal and electrical conductivity (highest electrical conductivity of any metal except silver).

Easy to fabricate. Weldable. Tough, ductile and malleable. Germicidal properties. Non-sparking. Wear and galling resistance.

There are 6 families of copper alloys:

Coppers

Modified copper alloys

Brasses

Bronzes

Copper nickels

Nickel silvers

BrassAn alloy with copper and zinc as the

primary alloying elements

BronzeAn alloy of copper and some other

element (e.g. aluminum, tin, silicon).

Nickel Silver

An alloy of copper, nickel and zinc.

Has a silvery appearance but contains no

elemental silver.

Because electrical applications require a very low level of impurities, commercially pure copper is used extensively for cables and wires, electrical contacts, and other electrical components.

Excellent thermal and electrical conductivity.

Soft, weak and ductile.

The primary bronze families are:

Tin Bronze

Aluminum Bronze

Silicon Bronze Manganese bronze is actually a brass

containing manganese.

Nickel and cobalt alloys have high strengths and excellent corrosion and oxidation resistance.

Nickel and cobalt superalloys are used in high temperature applications such as in jet engines.

Three types of superalloys are iron based, nickel based, and cobalt based.

Cobalt-based alloys, such as Stellite, are used for wear-resistant hardfacing materials.

Stellite 6 is the most widely-used cobalt alloy.

Lead is a soft, ductile, heavy metal. Lead is used in batteries, radiation shielding,

and as a solid lubricant.

Tin is a soft, malleable metal with a low melting point.

Tin is used as a protective coating for steel. Tin alloys are used for solders, pewter, and

babbitt (bearing) alloys. Tin is an important alloying element in

bronzes. Tin has two allotropes – metallic beta tin and

powdery alpha tin.

Zinc is a hard, brittle metal. Zinc is used as a protective coating for steel

(galvanizing). Zinc die castings are cheap and have good

structural strength.

Precious metals have high economic value.

Gold, Silver, and Platinum metals. Refractory metals have high melting points.

Tantalum, Niobium, Molybdenum, Tungsten. Special metals have unique uses.

Beryllium and Zirconium.

The cooling rate from the austenitizing temperature determines what products will form.

Slow cooling rates produce pearlitic products (ferrite, pearlite, and cementite).

Intermediate cooling rates produce bainite. Fast cooling rates produce martensite.

Three types of transformation diagrams are used:

Fe-C Phase Diagram

Equilibrium cooling only.

Isothermal Transformation

Non-equilibrium cooling at a constant temperature.

Continuous Cooling Transformation

Non-equilibrium cooling at a specific cooling rate.

Hardenability is the ability of the steel to be hardened in depth by quenching.

Hardenability depends on the chemical composition of the steel and other factors including grain size.

Hardenability should not be confused with hardness or hardening power.

Carbon has the greatest effect on hardenability.

Other elements also influence hardenability including:

Macroalloying elements (Cr, Mo, Mn, Si, Ni)

Microalloying elements (Ti, V, and Cb)

Boron

The ideal critical diameter is the largest diameter bar of a particular steel that will be hardened to 50% martensite by an perfect (or ideal) quench.

The higher the ideal critical diameter, the greater the hardenability of the steel.

The Jominy end-quench test is the standard method for measuring the hardenability of steels.

A standard test piece is heated to a pre-determined temperature and quenched by a jet of water sprayed onto one end.

When the specimen is cold, hardness measurements are made at intervals along the test piece from the quenched end.

The results are plotted on a standard chart from which is derived a hardenability curve.

The hardening response of a steel depends upon the media it is cooled in.

Brine cools very rapidly (severe quench) while air cools very slowly (mild quench).

Quench media are ranked in severity using the Grossman scale.

When selecting material for a given application, use the cheapest steel (the steel with the least amount of alloying additions) that will provide the desired hardenability and meet other requirements.

High hardenability steels can encounter problems with higher cost, quench cracking, poor weldability, and decreased toughness and other properties.

Heat treating is process of heating and cooling metals in order to obtain the desired properties.

Heat treating allows us to vary the properties (mechanical, physical, metallurgical) of a given material to optimize its performance.

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The three primary types of heat treatment are:

Hardening (quench-and-temper).

Annealing

Case Hardening

Hardening heat treatments involve 3 steps:

Austenitizing

Quenching

Tempering Heat treat results are affected by the severity

of the quench.

If the quench is too severe, quench cracking may occur.

When austenite transforms to martensite during the quenching of a steel part, the volume of the metal expands slightly (4%) creating stress.

These stresses can cause quench cracking.

Martensite is hard and brittle. During quenching, severe internal stresses

are created in the part. Tempering softens the martensite and adds

ductility and toughness, but reduces strength.

Tempering also relieves residual stresses and helps to prevent distortion.

Annealing heat treatments produce pearlitic microstructures (ferrite, pearlite, cementite).

Various types of annealing include:

Full Annealing

Normalizing

Spheroidizing

Process Annealing

Stress Relieving

Reduction of residual stresses. Homogenization of microstructure. Improved ductility. Improved machinability. Refined grain size.

Case hardening treatments produce a thin, hard layer on the surface of a steel part.

Case hardening methods include:

Carburizing.

Carbonitriding.

Nitriding.

Nitrocarburizing.

Induction hardening.

Flame hardening.

Casting is the process of pouring molten metal into a prepared mold cavity of a desired shape and allowing the metal to solidify.

A mold is a hollow shape into which a molten metal is poured, allowed to solidify, and removed.

Molds can be permanent or expendable.

Melting stock comes virgin materials, foundry returns, and scrap metal.

The top half of a sand cast mold is the cope, the bottom half is the drag.

The freezing range is the difference between the liquidus and the solidus.

A short freezing range produces a columnar structure, while a long freezing range yields an equiaxed structure.

The primary casting methods include:

Sand Casting

Centrifugal Casting

Investment Casting

Permanent Mold Casting

Die Casting

Casting defects include porosity, solidification shrinkage, flash, incomplete casting, inclusions, and hot tears.

Metal joining is required when the desired component cannot be made by simple fabrication methods such as casting or forging.

Metal joining is essential to modern industry and construction.

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Three joining methods are:

Welding

Brazing

Soldering Welding involves fusion of the metals being

joined. Brazing and soldering rely on adhesion.

Types of Welding Processes include:

Arc Welding

Gas Welding

Resistance Welding

Specialty Welding

Solid State Welding

There are a number of different arc welding processes including:

Shielded Metal Arc Welding (SMAW)

Gas Metal Arc Welding (GMAW)

Gas Tungsten Arc Welding (GTAW)

Flux Cored Arc Welding (FCAW)

Submerged Arc Welding (SAW)

Plasma Arc Welding (PAW)

The three weld zones are:

Weld metal – Melted and resolidified base metal and filler metal.

Heat Affected Zone – Region adjacent to weld that has been metallurgically changed by heat of welding.

Base Metal – Material unaffected by heat of welding.

Welds cool rapidly due to the heat sink effect of the surrounding metal.

The rapid cooling rate from the welding temperature is similar to quenching in heat treatment.

This can create hard, brittle martensite in the HAZ, leading to cracking.

Preheat and postheat are used to help prevent cracking.

PREHEATING is the application of heat to the base metal before welding.

Preheating can be done by oxyacetylene torch, induction heating, electrical resistance heating or by placing the part in a furnace.

Typical preheat temperature range for low alloy steels is 300°-400°F.

PWHT (stress relieving) is the application of heat after welding.

PWHT is usually conducted at a temperature below the critical range.

The PWHT temperature will depend upon the type of material being welded and the desired hardness.

PHWT can be done in a furnace or locally using a torch or other device.

Welding specifications include:

Filler metal specifications

Welding codes

Welding Procedure Specification (WPS)

Procedure Qualification Record (PQR)

Welder Performance Qualification (WPQ)

Weldability is the capacity of a material to be welded and to perform satisfactorily in the intended service.

Welds are susceptible to certain types of defects.

Weld cracking is not acceptable.

Powder metallurgy is a forming technique for producing solid objects from metal powders by compaction and sintering.

The three steps in powder metallurgy are mixing, compacting, and sintering.

Mixing

Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients.

Compaction

Powder is fed into a precision die and is compacted at pressures usually between 30 and 50 tons per square inch producing a "green compact.”

SinteringThe green compact is heated to a temperature BELOW the melting point until the particles bond to each other by solid state diffusion.

Forging is the process of working metal into a desired shape by the application of impact or pressure.

Other forming techniques include rolling, extrusion, bending, and stamping.

Machining is the removal of metal from a workpiece using machine tools.

Machining processes include turning, milling, and drilling.

TurningWorkpiece is rotated against the cutting tool. Lathes are the principal machine tool used in turning.

MillingCutting tool rotates to bring cutting edges to bear against the workpiece. Milling machines are the principal machine tool used in milling.

Drilling

Holes are produced by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece. Drilling operations are done primarily in drill presses.

Hardfacing is the application of a coating to prevent surface damage including adhesive wear, galling, gouging, erosion, and fatigue.

Hardfacing can be applied by welding or by thermal spray.

Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface.

Thermal spray processes include:

Detonation Gun

Flame Spray (wire or powder)

High Velocity Oxyfuel

Plasma Spray

Conversion coatings are coatings for metals where the part surface is converted into the coating with a chemical or electro-chemical process.

Conversion coatings include black oxide, phosphating, and chromate.

Electroplating is the deposition of a thin protective layer of metal using electrochemical processes.

A wide variety of metals can be applied to steel using electroplating.

Electroless nickel applies a layer of nickel using a chemical reaction instead of electroplating.

Temperature can have a big effect on the properties and behavior of metals.

High temperatures can cause:

Creep - A time-dependent increase in length.

Loss of strength.

Unique forms of corrosion including carburization, oxidation, sulfidation, and hydrogen attack.

Low temperatures can cause metals to become brittle.

The Nil Ductility Temperature (NDT) is the temperature at which a given metal exhibits a steep drop in impact toughness.

FCC metals (such as austenitic stainless) do not exhibit a NDT and can be used for cryogenic applications.

Corrosion is the decaying or destruction of a material caused by the environment.

The process of corrosion requires four elements:

An anode

A cathode

An electrolyte

A metallic path.

Corrosion occurs at a rate determined by an equilibrium between two opposing electrochemical reactions.

The anodic reaction releases metal ions and electrons (the metal is dissolved).

The cathodic reaction consumes electrons.

Various environmental factors affect the corrosion rate of a given metal.

The most important are:

pH

Aggressive Species

Oxidizing Species

Temperature

Aeration

Corrosion takes 3 basic forms: General or Uniform Corrosion

Localized Corrosion

Galvanic Corrosion. Localized corrosion takes several forms: Erosion-corrosion

Crevice Corrosion

Pitting

Stress Corrosion Cracking

Methods for corrosion prevention include:

Material Selection and Design.

Barrier Coatings.

Cathodic Protection.

Modifying the Environment.

Your journey through the wonderful world of metals is now complete.

Good luck on the Final!

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