Handouts PrinciplesOfMetallurgy

8/12/2019 Handouts PrinciplesOfMetallurgy

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Principles of Metallurgy

Industrial Metallurgists, LLC

Northbrook, IL 60062

847.528.3467

www.imetllc.com

Copyright 2012 Industrial Metallurgists, LLC

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Introduction

Overall goal: understand how manufacturing processes enable us to modify

mechanical properties of metals.

Cover fundamental metallurgical concepts

Explain methods for strengthening metals

Course Learning Objectives

1. Explain the relationship between a metals properties and its composition,microscopic structure, and the manufacturing processes used to fabricate the

metal.

2. Describe three types of microscopic structures present in metals.

3. Explain how cold working, alloying, and heat treating are used to strengthen ametal.

4. Explain the microstructure and property changes that occur in cold worked

metals, steels, and precipitation hardened alloys when they are heat treated.

5. Relate the heat treatment time and temperature to the microscopic structures

and properties of precipitation hardened alloys, steels, and cold worked metals.

Continue


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Course Content

1. Material properties

2. Composition

3. Microscopic structures

a. Crystal structureb. Grains and grain boundaries

c. Metallurgical phasesd. Crystal structure defects

4. Diffusion

5. Examplesa. Cold working

b. Annealing cold-worked metalsc. Solution hardening

d. Steel heat treating

e. Precipitation hardening

Concepts applicable to components


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Concepts applicable to Non-Mechanical Joints

Solder and braze joint

Weld joints

Materials Properties


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Module learning objective

Explain the relationship between properties, composition, microscopic structures, and

processing.

Properties

Composition

Microscopic

structure

Manufacturing

defects

Continue


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Materials Properties

PhysicalDensity

MechanicalHardnessYield strength

Tensile strength

Modulus of elasticityFatigue strength

Fracture toughnessCreep strength

ThermalMelting point

ConductivitySpecific heat

Coefficient of thermal expansion

Thermal coefficient of resistance

ElectricalConductivity

Coercive force

Magnetic hysteresisMagnetic permeability

ElectrochemicalElectrochemical potentialCorrosion resistance

ManufacturingFormability

WeldabilityMachinability

Composition refers to elements that make up a metal

Steel - iron, carbon, manganese, and silicon

Brass - copper and zinc


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Microscopic structures

10 mm

0.0004

Phases

(Courtesy of Aston Metallurgical Services)Courtesy of Aston Metallurgical Services

Grains

Arrangement of atoms

Manufacturing defects

Alter metal properties

Try to minimize defects

What manufacturing defects can be tolerated?

How can the level of defects be controlled?

No more discussion of manufacturing defects in this course

Forging lap

0.125 mm

Gas porosity in die casting

0.5 mm


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Properties

Composition

Microscopic

structure

Can process an alloy different ways

Obtain different microscopic structures

Obtain different properties

Properties

Composition

Microscopic

structure

Manufacturing

Processes


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Courtesy of Aston Metallurgical Services Courtesy of Aston Metallurgical Services

Can process a metal different ways

Obtain different microscopic structures

Obtain different properties

Critical concept

Alloy and process selectionControl variation

Harder and stronger

For any particular design, want to

Select materials that have the desired properties

Use manufacturing processes capable of transforming a material into desired

shape with desired properties.

Properties

Composition

Microscopic

structure

Manufacturing

Processes


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Questions for further thought

1. What metals are used in your products?

2. What are the desired properties of the metals?

3. What manufacturing processes are used to obtain the desired properties in themetals?

Continue

Composition


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Learning objectives

At the end of this module learners will be able to do the following:

1. Explain how the composition of a metal is expressed

2. Explain the difference between an alloying element and impurity3. Describe the effects of composition changes on the properties of two alloys

4. Explain why there are a large number of different alloys

Continue

Metal Composition

Elemental make up


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Metals can be single element or alloys

Examples of single element

Copper

Aluminum

Gold

Alloys

Intentional mixtures of various elements

Carbon Steel (iron + carbon + manganese)

Brass (copper + zinc)

Die cast aluminum (aluminum + silicon + copper + iron)

Impurities

Unintentionaladdition of elements

Steel: sulfur and phosphorous are often impurities

Eliminating all impurities impossible

Some level of impurities tolerable

What amount of impurities is tolerable?

Keep impurities below maximum allowable amounts


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Alloy composition usually in weight percent

Al 10.5 wt.% Si 2.5 wt.% Cu

100 gram sample

10.5 grams Si2.5 grams Cu

87 grams Al

Steel Alloys

Plain carbon steels

Alloy steels

Stainless steels

Continue


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Plain carbon steel

These alloys contain iron, carbon, and manganese. The amount of carbon

and manganese added depends on the desired mechanical properties.

Sulfur and phosphorous might be present as impurities that should not

exceed a specified amount. In free-machining alloys phosphorous and

sulfur are added intentionally to improve the ease of machining

components.

Continue

Alloy steels

This class of steels contain iron, carbon, and manganese. Additionally theyalso contain nickel, chromium, and/or molybdenum. These elements are

added to improve mechanical and corrosion properties, and improve the

ease of obtaining certain mechanical properties during heat treatment.

Continue


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Stainless steels

Stainless steels contain at least 12 percent chromium in addition to iron,

manganese, and carbon. The addition of the chromium gives greatly

enhanced corrosion properties compared to the other steels. Other elements

like nickel and molybdenum are added in a wide variety of amounts to modifystrength, corrosion resistance, formability, and weldability.

Continue

Carbon (Wt. %) Maximum hardness

(Rockwell C)

0.1 37

0.2 46

0.3 53

0.4 58

0.5 62

Effect of carbon content on steel maximum hardness


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Aluminum alloysAluminum alloys are categorized according to the major alloying

element present. Copper, manganese, silicon, magnesium, or zinc are

added as major alloying elements. In addition, other elements are

added in smaller quantities. The designations for wrought alloys are

shown in the table. The first digit indicates the group, with the alloysbeing grouped by the major alloying element.

In the 1xxxgroup, the series 10xxdesignates unalloyed compositions

that have natural impurity limits. The last two of the four digits indicate

the minimum aluminum percentage. Designations having second digits

other than zero indicate special control of one or more individual

impurities.

In the 2xxxthrough 8xxxalloy groups, the second digit in the

designation indicates alloy modification. If the second digit is zero, it

indicates the original alloy. Integers 1 through 9 indicate modifications

of the original alloy. The last two digi ts have no special significance, butserve only to identify the different aluminum alloys in the group.

In all cases the specific alloying elements present and their quantities

are meant to provide specific performance and reliability properties. In

addition, alloying elements are added to modify processing properties.

Continue

Aluminum, 99.00% 1xxx

Copper 2xxx

Manganese 3xxx

Silicon 4xxx

Magnesium 5xxx

Magnes ium and silicon 6xxx

Zinc 7xxx

Other elements 8xxx

Copper Alloys

This list shows some of the different categories of copper alloys.

Coppers: >99% copper

High copper alloys: >96% copper + alloying elements

Brasses: Copper-zinc alloys

Leaded brasses: Copper-zinc-lead alloys

Phosphor bronzes: Copper-tin-phosphorous alloys

Nickel silvers: Copper-nickel-zinc alloys

Continue


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Weightpercent zinc

Yield strength(OS025 temper),

MPa (ksi)

Electricalconductivity

(relative to purecopper)

0 76 (11) 100%

10 97 (14) 44%

15 110 (16) 37%

30 130 (19) 28%

Brass alloys (Copper zinc)

Cost decreases as the amount of zinc increases

Huge variety of alloys

Modify properties of an alloy by altering composition

Properties of materials within a product

Properties as they relate to ease of manufacturing

Small changes in composition can alter properties substantially

Costs are different for different alloys

Select materials that optimize

Cost

Ease of manufacturing

Product performance and reliability

Variety of alloys increases likelihood of finding optimum choice


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Module review

1. Single elements, alloys, and impurities

2. Composition usually in weight percent

3. There are different classes of alloys for different metals based uponthe alloying elements to the main element.

4. Composition modifications can have a large influence on the

properties of an alloy.


1. What are some of the alloys used at your company?

2. What are their compositions?

3. Why were those compositions selected?

4. Have there ever been problems where an alloys composition was not

what it was supposed to be? What problems arose from this?

Continue


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Microscopic Structures

Learning objectives

At the end of this module learners will be able to:

1. Describe three microscopic structures present in metals

2. Explain why there are many grains in metals

3. List three examples of metal phases

4. List three characteristics of phases that influence the properties of ametal.

Overall outcome: Recognize metal objects as being an assembly of

microscopic structures. Not just an abstract slab of material.

Continue


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Practical importance of microscopic structures

1. They are present inside every metal component and joint

2. They directly influence the properties of a material

3. Manufacturing processes affect microscopic structures, which causes

changes in the metal's properties.

Will discuss how manufacturing processes are used to modify microscopicstructures

Produce desired mechanical properties


Need a microscope to see these structures

Dimensions typically less than 0.1 millimeters (0.004 inches)

Crystal structure

Arrangement of

atoms within a metal

20 mm

Phases

Materials

within a metal

0.005

Grains

Individual crystalswithin a metal


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Consider 1 mm (0.040 inch) thick sheet metal

Each grain about 0.020 mm (0.0008 in.) diameter

About 50 grains across the sheet thickness

0.625 mm (0.025 )

0.005

Atoms about 0.3 nm (0.0000003 mm) diameter

Over 3 million atoms across the sheet thickness


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Crystal Structure

Refers to the specific arrangement of atoms within a metal

Metals are typically crystalline materials

Atoms are arranged in a periodic manner

Periodic arrangement of atoms in metals

Crystal lattice structure specific arrangement of atoms within a crystal

Unit cell

Repeated in all three directions throughout a metal crystal

Lattice sites


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ActualModel

A crystal lattice continues unbroken throughout a crystal

Metals comprised of many crystals called grains

Within a crystal lattice there is a position where each atom belongs


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Body centered cubic

ChromiumIron

Tungsten

Face centered cubic

CopperAluminum

GoldSilver

Hexagonal

TitaniumZinc

Magnesium

Total of 14 possible lattice structures

Most pure metals body centered cubic, face-centered cubic, or hexagonal

There are metal compounds and alloys that have one of the other 14 lattice

structuresCrystal structure constant for a pure metal, metal alloy, or metal compound

Grains

Most metals polycrystallineComprised of many grains

Each grain a crystal

Each grain (crystal) forms independently

Crystal lattices are tilted in different directions from grain to grain

Courtesy of Aston Metallurgical Services


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Grain boundaries

Regions between grains where atoms try to accommodate crystal latticemisalignment

(Reprinted with permission of ASM International. All rights reserved.)

Grain boundaries


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Practical significance of grains and grain boundaries

1. Grain size affects mechanical properties

Metal strength increases as grain size decreases

Influences creep strength, fatigue strength, and forming properties

2. Grain size affects magnetic and electrical properties

Grain boundaries interfere with current flow if grains very small

Grain boundaries can degrade magnetic permeability

Grain size can be modified using one or more of the following methods

Thermal treatment Mechanical treatment

Alloying


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Orange Peel

Surface roughness in areas that have undergone significant deformation

Deep drawn metal

Surface has appearance of the peel of an orange

Occurs in sheet metal with large grains

Individual grains tend to deform independently of each other

Grains stand out in relief on surface

Can be corrected by using finer grain metal

Individual grains difficult to distinguish by eye


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125 mm

125 mm

Metallurgical Phases

Physically distinct material

Within an alloy more than one phase can be present at one time

Depends on composition and how alloy was processed

Each phase is a mixture or compound formed from alloying elements

Phase 1

Phase 2


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Phase 1 Phase 2

1060 steel

Ferrite a mixture of iron and carbon

Cementite (iron carbide) is Fe3C


20 m

0.0008

Ferrite(light color)

Cementite(dark color)


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Nickel + 20 weight percent vanadium

An alloy can be heat treated to obtain different size and shape of the phases

Long time at 980o CShort time at 980o C

2 mm

Ni3V (dark)

mixture of nickel andvanadium (light)

20 mm

Tin-Lead Solder Joint

Tin + 37% lead

Tin-LeadSolder

Componentlead

Circuit board

Light phase = tin with lead atoms mixed in

Dark phase = lead with tin atoms mixed in


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Phases present and their amounts, shape, size, and location depend on

Alloy composition

How the alloy was processed (i.e. thermal and/or mechanicaltreatment)

Possible to process a particular alloy in different ways

Obtain different amounts, size, and shape of the phases

Obtain different phases

Phase 1

Phase 2


10 mm

0.0004

CementiteFerriteFerrite

Harder and stronger


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The phases within a metal affect its properties

1. Different phases have different properties

In steels, cementite is hard and brittle and ferrite is soft

2. Properties of an alloy depend on

Phases present

Relative amount of the phases

Size and shape of the phases

Location of the phases

3. Can modify phases present and their amounts, size, shape, and location

Alloy composition

Thermal treatment

Thermal + mechanical treatment

Microstructure

Microstructure a description of grains and phases present in a metal

Grain size and shape

Phases present

Shape, size, location, and relative amounts of different phases

Uniform distribution of lead

particles in a tin matrixFine grains of ferrite



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Module review

1. Microscopic structures present in metals

Crystal lattice structure

Grains

Phases

2. Grains and phases can be modified to obtain desired properties

3. Metals are an assembly of microscopic structures


1. What is the desired grain size in the metal components used in yourcompany s products?

2. What phases are supposed to be present in the alloys used in your

company s products?

3. What properties do the phases give to the components in which thealloys are used?

Continue


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Crystal Defects

Learning objectives

At the end of this module learners will be able to:

1. Describe four types of crystal defects present in metals

2. Explain why crystal defects are important for metal properties

Continue


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Crystal lattice defects

Not the same as manufacturing defects such as voids, cracks, and pits

Enable materials to be modified and manipulated

Add alloying elements

Heat treating to soften and harden metals

Shape metals using processes like stamping and forging

Vacancy

Vacancy

Number of vacancies increases as temperature increases

25 C: About one vacancy per trillion atoms

Just below melting point: one vacancy per 1000 atoms


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Substitution

Atom of a different element that occupies a lattice site of the parent metal

Intentionally added or an impurity

Substitution

Substitutions enable us to form alloys

Zinc in copper (Brass)

Manganese in iron (Steel)

Copper in aluminum


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Substitution solid solution

An alloy that has alloying elements present as substitutions

Alloying elements dissolved into crystal lattice of another element

Analogous to salt (solute) dissolved in water (solvent)

Solvent atom

Solute atom

Amount of an element that can be dissolved in another element depends on

Solvent and solute elements involved

Metal temperature


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Interstitial

Atoms must be small enough to fit in interstitial sites

Hydrogen, carbon, nitrogen, boron, oxygen

Carbon in iron (steel)

Interstitial

Interstitialsite

Interstitial solid solution

An alloy that has alloying elements present as interstitials

Amount of an element that can be dissolved in another element depends on

Solvent metal and solute element

Metal temperature

Solvent atom

Solute atom


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Vacancies, substitutions, and interstitials enable property modifications

Interstitials and substitutions enable alloying

Carbon interstitials in iron enables steel to be hardened

Chromium and nickel substitutions improve steel corrosion resistanceZinc substitutions improves brass strength

Copper substitutions enables aluminum to be hardened

Vacancies and interstitial sites enable atoms to move through a metal

Annealing after cold working

Metal hardening

Dislocation

Screw dislocations

Present in all metals

Edge Dislocation

A.G. Guy, The Essentials of Materials Science, McGraw-Hill, 1976.(Courtesy of Irene Guy)

1 2 3 4 5

1 2 3 4 5 6


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Electron microscope micrograph of dislocations in a metal

0.00004

Influence of dislocations on metal strength

Metal strength depends on ease of dislocation movement through a metal

Easier for dislocations to move in annealed copper or aluminum compared to

hardened steel

Therefore, the steel is stronger than the copper and aluminum


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Modify metal strength by controlling ability of dislocations to move

Heat treating Mechanical treatment

Alloying

Ease of dislocation motion depends on

Alloy composition

Grain size

Phases present

Number of dislocations present

Size and shape of the phases


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Dislocations in a metal with second phase particles

dislocation

matrix

particle

0.00025 mm (0.25 mm)0.00001 inch

Practical Considerations

1. Dislocations enable metals to be deformed

Metals can be bent, compressed, and stretched to the desired shape

2. Can intentionally modify stresses required for dislocations to move

Modify a metal to obtain the desired strength

Annealing brass

Heat treating steel


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Module review

Crystal lattice defects present in metals

Vacancies, substitutions, interstitials, and dislocations

Enables us to modify the properties of a metal

Diffusion


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Learning objectives

By the end of this module learners will be able to:

1. Explain the two mechanisms by which diffusion occurs

2. Relate heat treating time and temperature to the extent of changes in metalmicrostructure and properties

Continue

Diffusion

Vacancies and interstitial sites allows atoms to move through a solid metal

Diffusion is movement of atoms through crystal lattice of a solid metal

See changes in microstructure and properties

VacancyInterstitial sites


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Diffusion important for many processes

Heat treatment for alloy hardening

Annealing to increase metal ductility

Soldering and brazing

Steel surface treatments (e.g., carburizing and nitriding)

Thermally activated process

Metal must be heated for atoms to have the energy to move

Required temperature depends on metal and heat treatment objectives

Low melting point metals do not have be heated up as much as metals with

high melting points.

Practical reasons for understanding diffusion

Improve ability to select and control manufacturing process conditions

Process development

Supplier evaluation and selection

Root cause analysis

Poor control of atom motion within a metal will result in not obtaining the desired

properties in the item being fabricated


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Diffusion processes Vacancy Diffusion

(b)(a)

Diffusion processes Interstitial Diffusion

(a) (b)


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Vacancy Diffusion: Self Diffusion

Start Finish

Atoms vibrate because of their thermal energy

T1 T2 T3

Increasing temperature

Vacancy Diffusion: Substitution

Start Finish


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Interstitial Diffusion

Start Finish

For metallurgical process that involves diffusion

Concerned with speed and extent of atom motion through a metal

Speed with which atoms move depends on

Energy required for atoms to jump from site to site

Metal temperature

Extent of atom motion depends on

Speed of atom motion

Time at temperature

Cannot influence energy required for atoms to jump from site to site

Can control the temperature and time

2 equations to help understand effects of temperature and time


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Temperature

Diffusivity

D = Diffusion coefficient or diffusivity

Do= Frequency factor

Q = Activation energy

k = Boltzmans constantT = Temperature

Diffusivity increases exponentially with temperature

x = diffusion distance

D = diffusivityt = time

As time increases

Diffusion distance increases

Increase in extent of metallurgical changes

Increase in extent of changes in properties


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Example: Annealing a cold rolled metal

The larger the grains the softer and more ductile the metal

As diffusion distance increases

Grain size increasesMetal hardness decreases and ductility increases

Temperature

Time


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Temperature too low or time too short

Diffusion based process will not proceed far enough

Temperature is too high or time too long

Diffusion based process will go too far

Selection and control of the temperature and time is critical

Diffusion to proceed as needed

Obtain desired microstructure and properties

Problem 2: Carburized steel blade

Steel heated in a furnace along with a gas that contains carbon atomsCarbon atoms diffuse into the surface of the steel

Additional carbon enables surface layers to be hardened

Hardened surface layer forms when the steel is cooled

(Courtesy of Aston Metallurgical Services)

0.010

Hardened layer

Steel core


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Module review

1. Diffusion involves the motion of atoms through crystal lattice

2. Vacancy and interstitial diffusion

3. Diffusion requires thermal energy

4. Diffusion rate increases exponentially with temperature

5. Diffusion distance generally proportional to square root of time

6. Control diffusion to obtain the desired microstructure and properties


1. What heat treating processes are used at your company or by suppliers to yourcompany?

2. What are the purposes of the heat treatments?

3. What changes occur in the metal as a result of the heat treatment?

Continue


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Applications of Metallurgy Principles

Learning objectives

By the end of the next 5 modules learners will be able to:

1. Explain why cold working strengthens metals

2. Relate the effects of annealing a cold worked metal on its grain size and strength.

3. Explain how alloy composition is used to strengthen a metal.

4. Relate the effects of aging time and temperature to the strength and hardness of

a precipitation strengthened alloy.

5. List the different metallurgical phases that can be present in steel and their effects

on steel strength.

6. Explain the effects of carbon content on steel strength.

7. Explain the effects of tempering time and temperature on quenched hardened

steel.

Continue


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Phases


Diffusion

Temperature

Time


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Examples of common approaches used to modify properties of metals

Alloying, mechanical treatments, and heat treatments

Used to modify metal properties by modifying microscopic structures

Each example is in its own module

Cold working

Annealing

Solid solution strengthening

Precipitation

Steel quenching and tempering

Quiz will be given after all examples have been covered

Define three properties

Hardness

Yield strength

Tensile strength


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Hardness

Resistance to deformation due to an indenter pushing against metal

For a test load, indentation depth decreases as hardness increases

Resistance to deformation directly related to metal yield strength

Depends on ease of dislocation motion

Annealed aluminum vs. hardened steel

Aluminum has a lower strength

For the same test load, indentation in aluminum will be larger

Aluminum hardness reading will be lower

Aluminum Steel


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Yield Strength

Stress required for permanent deformation to begin

radius

Area = x radius2

width

thickness

Area = width x thickness

Tensile strength

Maximum stress that a metal can support


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Example 1: Cold Working

Learning objectives


1. Explain how cold working strengthens metals

Continue


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Cold Working

Plastic deformation of a metal at low temperatures

Less than about one-third melting point temperature

Cold rolling Sheet metal forming

Wire drawing

Most of the energy expended in cold work appears in the form of heat

A portion of the energy goes into the creation of more dislocations

Increase number of dislocations 10,000 to 1,000,000 times

Soft, annealed metal: 106 to 108 dislocations per cm2

Heavily cold worked metal: 1012 dislocations per cm2


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As metal deforms, number of dislocations increases

Dislocations generate new dislocations

Dislocations interfere with each other and become entangled

Increased stress to move dislocations through the metal

Increase in yield strength, tensile strength, and hardness

Dislocations in a metal


(amount of cold work)


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Temper

Minimum

tensile strength

Minimum

yield strength

MPa ksi MPa ksi

Annealed 515 75 205 30

hard 860 125 515 75

hard 1035 150 760 110

hard 1205 175 930 135

Full hard 1275 185 965 140

Cold-Rolled Tempers for 301 Stainless Steel

Temper refers to the amount of cold working

Temper

Minimum

tensile strength

Minimum

yield strength

MPa ksi MPa ksi

Annealed 515 75 205 30

hard 860 125 515 75

hard 1035 150 760 110

Full hard 1275 185 965 140

Cold-Rolled Tempers for301 Stainless Steel

Different metals with same temper designation have different strengths

Temper

Minimum

tensile strength

Minimum

yield strength

MPa ksi MPa ksi

Annealed 300 44 75 11

hard 370 54 275 40

hard 425 62 360 52

Full hard 525 76 435 63

Cold-Rolled Tempersfor Cu-30Zn Brass


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Effects of cold working applies to all metals

Degree to which a metal can be cold worked depends on the metal

Ductile metals like aluminum and copper alloys can withstand a significant

amount of cold working.

High strength steels cannot withstand much cold working.


1. What cold-formed tempers are specified for the metals used in your companysproducts?

2. What are the reasons for specifying those tempers?

3. What cold-formed tempers are specified for the metal products your company

supplies to its customers? Why?

Continue


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Example 2: Annealing Cold Worked Metals

Learning objectives


1. Relate a metal s strength to its grain size

2. Describe the processes used to modify metal grain size

3. Relate recrystallization annealing temperature and time to grain size

Continue


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Recrystallization anneal

Heat treatment used with cold worked metals

Improve metal ductility

Reduce metal strength and hardness

Purpose

Enable further cold working

Meet specific mechanical property specifications

Metallurgical effects

1. Eliminate dislocations and crystal lattice damage from cold working

2. New grains form and grow

Healing of microscopic structures is a diffusion based process

Cu-30 Zn brass cold-rolled and annealed

50% reduction550 C anneal75 MPa yield strength

50% reduction650 C anneal60 MPa yield strength

B CA50% reduction

550 MPa yield strength


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50% reduction

550 C anneal75 MPa yield strength

50% reduction


50% reduction550 MPa yield strength

Decrease in strength during anneal

Recovery and recrystallization processes occur inside metal

Recovery: Reduction in number of dislocations formed by cold working

Recrystallization: Form new grains

Diffusion based processes

50% reduction


50% reduction


50% reduction

550 MPa yield strength

Difference in strength between 550 C and 650 C samples

Due to difference in grain sizeAfter recrystallization, continued annealing results in grain growth

Larger grains grow at the expense of smaller grains


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Grain size and metal strength

Grain boundaries influence motion of dislocations in a way that makes areas neargrain boundaries stronger.

Yield strength and hardness increases as grain size decreases

Ductility decreases as grain size decreases

Strengthened area

Grain boundary

550 C anneal 650 C anneal

B CA

Difference in grain size between annealed samples makes sense

Diffusion rate and diffusion distance greater at higher temperatureMore grain growth at higher annealing temperature


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Applications and annealing temperature

Recrystallization annealing can be used with any cold worked metal

Specific annealing temperature depends on particular metal

Temperature increases as melting point temperature increases

AnnealingTemperature

Melting PointTemperature

Aluminum About 260 to 440 C(500 to 825 F)

About 630 to 660 C

(1166 to 1220 F)

1010 steel About 700 C(1292 F)

1535 C

(2792 F)


1. Are there specifications for the grain size of the metals used in your products orfor the metals your company supplies to its customers?

2. How is the grain size verified? Who does the analysis?

3. What happens if the grain size does not meets the specifications? On

manufacturing processes? On component performance? How is the problem

fixed?

Continue


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Example 3

Solid Solution Strengthening

Learning objectives


1. Explain how alloying elements as substitutions and interstitials can strengthen

an alloy.

Continue


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Solid Solution Hardening

Increase in metal strength due to presence of substitution or interstitial atoms.

Alloying elements (solute) dissolved in the crystal lattice of a solvent metal.

The solute atoms distort the crystal lattice.

Strain

Strain energy is associated with the lattice distortion


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Strain energy associated with a dislocation

Edge Dislocation

A.G. Guy, The Essentials of Materials Science, McGraw-Hill, 1976.

(Courtesy of Irene Guy)

Solute atom strain energy interacts with dislocation strain energy

Increased force to move dislocation past solute atoms compared to solute

free metal

Force increases as number of solute atoms increases

Stress to deform an alloy increases compared to a solute free metal

dislocation


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Effect of magnesium content on yield strength of aluminum alloys

% Magnesium

YieldStrength(MPa)

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6

1050

5005

5050

5052

5086

5083 5056

Weight percent

zinc

Yield strength,

MPa (ksi)

0 76 (11)

10 97 (14)

15 110 (16)

30 130 (19)

Cu alloys, OS025 temper

Effects of zinc added to copper in brass alloys


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Example 4

Steel Heat Treating

Learning objectives


1. Describe the metallurgical phases that can be present in steel and their effects

on steel strength.

2. Describe the process steps for through hardening a steel alloy.

3. Explain the effects of quench temperature on martensite formation.

4. Relate steel strength and hardness to steel carbon content and tempering

temperature and time.

Continue


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Steel metallurgy and heat treatment

Focus on plain carbon, low alloy, and tool steels

Not stainless steels

Variety of steel microstructures can be created

Possible to heat treat a steel alloy to obtain different microstructures

Resulting strength and hardness are different

Phases of interest

Austenite

Ferrite

Cementite (Fe3C)

Martensite


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Austenite

Iron solid solution

Substitutions: manganese, chromium, or nickel

Iron atom

Carbon interstitial

Substitutions

Austenite normally a high temperature phase

Circumstances when austenite exists at room temperature

For strengthening, steel first heated to form austenite

When steel is cooled it transforms to one or more of the other phases

Approximate austenite formation temperatures

Austeniteregion


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Ferrite

Soft, low strength phase

Iron solid solution

Very li ttle carbon can dissolve in ferrite

About 0.02% at 727 C

Less than 0.005% at room temperature

Iron atom

Carbon interstitial

Substitutions (e.g. Mn, Cr, Ni)

Grains of ferrite in a low carbon steel

0.005 inches


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Cementite

Hard, brittle phase

Fe3C

Three iron atoms for every carbon atomAlso called iron carbide


Cementite can be present in one of three different shapes

Cementite shape depends on how steel was heat treated

Pearlite (lamellae) Spheroidized cementite

Cementite

Ferrite

Cementite

1060 Steel (0.60% carbon)

HARDER AND STRONGER

10 mm

0.0004


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1. Heated to 860 C (1580 F)2. Air cooled

1. Heated to 860 C (1580 F)

2. Air cooled3. Heated to 650 C (1202 F) for

several hours

Possible to take an alloy and process it in different ways to obtain different

microstructures and properties.


10 mm

0.0004

Ferrite-Pearlite

Alloys with less than 0.78% carbon

Heat to form austenite

Slow cool

1050 Steel


Ferrite

Pearlite

0.002


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Solid solution of carbon interstitials in iron

Martensite strength and hardness

Crystal lattice contains more carbon in solid solution than steel wants

Excess carbon atoms in solid solution strains the crystal lattice

Iron

Carbon

Lattice strain impedes dislocation motion

Increase in steel strength and hardnessAmount of strain increases as carbon content increases

Iron

Carbon


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Forming martensite

1. Heat steel to form austenite

About 775 to about 950 C (1427 to 1742 F)

2. Rapidly cool (quench)

Reason for quenching

Prevent formation of ferrite, cementite, or pearlite.

Not enough time at elevated temperatures for atoms to diffuse through steelto form ferrite, cementite, or pearlite.

Instead, groups of iron atoms shift slightly at once to form martensite

Austenite to martensite transformation

Non-equilibrium processProcess does not allow atoms to move to where they want to move

Extent of transformation depends only on temperature, not time

Martensite formation does not depend on diffusion

As temperature decreases more martensite forms

Transformation stops if cooling stops

Continued transformation if cooled to lower temperatures

For some alloys, cooling below room temperature required to obtain 100%martensite


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Martensite hardness governed primarily by carbon content

As-quenched martensite hardness

Tempering

Martensitehas poor toughness in the as-formed condition

Increase toughness by heating between 125 and 705 C (257 and 1292 F)

Martensitedecomposes

Carbon diffuses out of martensite

Forms iron carbide particles

Hardness and strength decreases while toughness increases

Temperature and time selected to obtain desired microstructure and properties


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(Reprinted with permission of ASM International. All rights reserv ed.)

Hardness(RockwellC)

Tempering time (seconds)

%

CarbonMicrostructure

Hardness,

Rockwell C

Hardness,

Brinell

Yield

Strength,

MPa (ksi)

Tensile

Strength,

MPa (ksi)

0.20

Spheroidized --- 111 295 (43) 395 (57)

Ferrite-pearlite --- 131 345 (50) 440 (64)

Martensite* 30 286 552 (80) 724 (105)

0.40

Spheroidized --- 149 350 (51) 520 (75)

Ferrite-pearlite --- 170 370 (54) 595 (86)

Martensite* 50 481 676 (98) 910 (132)

0.60

Spheroidized --- 179 370 (54) 625 (91)

Ferrite-pearlite 21 229 420 (61) 775 (113)

Martensite* 60 654 814 (118) 1104 (160)

Typical plain carbon steel properties

*As-quenched martensite


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1. What steel alloys does your company use, process, or produce?

2. What are the required properties of the steel alloys?

3. What manufacturing processes are used to achieve those properties?

4. What happens if the metal stock or components do not have the required

properties?

Continue

Example 5: Precipitation Strengthening


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Learning objectives


1. Describe the heat treating process for precipitation strengthening.

2. Explain why precipitation strengthens a metal.3. Relate metal strength to precipitation aging temperature and time.

Continue

Precipitation Strengthening

Also referred to as aging

Particles of a different phase form within a matrix phase

Particles often less than 1 mm (0.00004 )

Particles are referred to as precipitates


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Aluminum 5 weight % copper alloy with precipitates

Solution treated at 545 C for 1 week

Fast cooled to 20 C

Aged at 300 C for 12 hours

DoITPoMS Micrograph Library, University of Cambridge.

Precipitates obstacles to dislocation motion

Greater stress required to move dislocations through metalStrength and hardness increases

dislocation

precipitate

0.00025 mm

0.00001 inch


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Alloys for Precipitation Strengthening

Aluminum alloys: Al-Cu, Al-Mg-Si, Al-Mg-Zn, Al-Mg-Zn-Cu

2xxx, 6xxx, 7xxx wrought Al alloys

Some 2xx, 3xx, 5xx, 7xx, and 8xx cast Al alloys

Copper alloys: Cu-Be, Cu-Zr, Cu-Cr

Some stainless steel alloys: 13-8 PH, 15-5 PH, 17-4 PH and 17-7 PH

Some nickel alloys

Some magnesium alloys

2) Fast cool

Form supersaturatedsolid solution

Microstructure

1) Solution heat treatA (solvent)

B (solute)

Precipitation strengthening process


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3) Reheat alloy

Intermediate temperature

Excess solute atoms form precipitates with solvent atoms

Aging

Size and number of precipitates depends on aging time and temperature

Microstructure

after aging

Onset of coarsening

Large precipitates grow at expense of small precipitates

Maximum

strength and

hardness

Aging a supersaturated solid solution

a b c

d e f


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2014 Aluminum: Al 4.4Cu 0.8Si 0.8Mn

Maximum yield strength increases as aging temperature decreases

Number of precipitates increases as aging temperature decreases

Greater number of precipitates presents more obstacles to dislocations


Time to reach maximum strength increases as aging temperature decreases

Diffusion rate decreases as temperature decreasesTime required for precipitate formation and growth increases



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1. What precipitation strengthened alloys does your company use, process, or

produce?

2. What are the required properties of the alloys?

3. What happens if the metal stock or components do not have the requiredproperties?

Continue

Course Review


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Properties, composition, microstructure, and processing


Modified by alloying and mechanical and thermal processes

Effects of modification on mechanical properties

Properties

Composition

Microscopic

structure

Manufacturing

Processes

Discussed microscopic structures

Crystal lattice Grains Phases



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Discussed crystal defects

Vacancy, Substitution, Interstitial

A.G. Guy, The Essentials of MaterialsScience, McGraw-Hill, 1 976. (Courtesy of

Irene Guy)

1 2 3 4 5

1 2 3 4 5 6

Dislocations

Diffusion temperature and time dependence

Temperature

Time


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Presented examples

Common approaches to modify properties of metals

Cold-work metal

Increase number of dislocations

Increase metal strength and hardness

Decrease metal ductility

(amount of cold work)(Reprinted with permission of ASM International. All rights reserved.)


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Anneal cold-worked metal

Eliminate many dislocations

New grains form and grow

Increase ductility and reduce strength

Solid solution hardening

Impede dislocation motion


dislocation


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Through hardening and tempering steel

Form martensitein steel

Increase strength and hardness

Temper to reduce lattice strainImprove toughness

Martensite in 1040 steel

20 mm0.0008Courtesy of Aston Metallurgical Services

Precipitation hardening

Precipitates interfere with dislocation motion


0.010 mm0.0004

DoITPoMS Micrograph Library, University of Cambridge.


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Many other things that we can do to alter other properties

Electrical conductivity

Corrosion behavior

Fatigue behavior

Many more

Further Information

1. ASM Handbook Volume 1, Properties and Selection: Irons, Steels, and High-Performance Alloys

2. ASM Handbook Volume 2, Properties and Selection: Non-Ferrous Alloys andSpecial Purpose Materials

3. ASM Handbook Volume 4, Heat Treating, ASM International

4. Introduction to Materials Science for Engineers, J.F. Shackelford

5. Physical Metallurgy Principles, R. Abbaschian, L. Abbaschian, R. E. Reed-Hill

6 Annual Book of ASTM Standards ASTM

Handouts PrinciplesOfMetallurgy

Documents

Transcript of Handouts PrinciplesOfMetallurgy