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MIAT 105 Materials Metals Day 2

Second Lecture on Materials Metals

MIAT 105 WandM

on 7 November 2013

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Transcript of MIAT 105 Materials Metals Day 2

Metals Day 2

Physical and mechanical properties of steel are affected by:

Carbon content
Addition of various alloying metal
Heat treatment
Hardness is the resistance of a material to localized deformation (indentation, scratching, cutting or bending).
In metals, ceramics and most polymers, the deformation considered is plastic deformation of the surface.

It is a measure of the capacity of a metal to resist penetration.

A few of the more common methods used to measure the hardness of a metal are:
- Brinell Hardness Test (HB)
- Rockwell Hardness Test (HRA, HRB, HRC, …)
- Vickers and Knoop Microhardness Tests (HV and HK)
In North America the numerical index system for the classification of carbon and alloying steels is set by:

AISI - American Iron and Steel Institute
SAE - Society of Automotive Engineers
ASME - American Society of Mechanical Engineers
CSA - Canadian Standards Association
Numbering systems for metals
Heat treating is accomplished in three major stages:

Stage l—Heating the metal slowly to ensure a uniform temperature.

Stage 2—Soaking (holding) the metal at a given temperature for a given time and cooling the metal to room temperature.

Stage 3—Cooling the metal to room temperature
Heat treatment (cont.)
The various types of heat-treating processes are similar because they all involve the heating and cooling of metals; they differ in the heating temperatures and the cooling rates used and the final results.

The usual methods of heat-treating ferrous metals (metals with iron) are :
annealing, normalizing, hardening, and tempering.

Most nonferrous metals can be annealed, but never tempered, normalized, or case-hardened.
Heat treatment (cont.)
The process of heat treating is the method by which metals are heated and cooled in a series of specific operations that never allow the metal to reach the molten state.

The purpose of heat treating is to make a metal more useful by changing or restoring its mechanical properties.

Through heat treating, we can make a metal harder, stronger, and more resistant to impact.
Also, heat treating can make a metal softer and more ductile.

The one disadvantage is that no heat-treating procedure can produce all of these characteristics in one operation.
Some properties are improved at the expense of others; for example, hardening a metal may make it brittle.
Heat treatment
Nickel – increases strength and toughness and also increases it’s resistance to impact.

Tungsten – produces dense, fine grain which helps the steel retain hardness and it’s strength at high temperatures.

Vanadium – retards grain growth and improves impact resistance.
How do different alloying elements effect the properties of a steel?
When metal parts are subjected to repeated loading and unloading, they may fail at stresses far below their yield strength with no sign of plastic deformation. This is called fatigue failure.
Aircraft fuselage structure and wings, rotating shafts, wind turbine blades, etc. are subjected to fatigue loading.

Fatigue failure occurs in 3 stages:
- crack initiation
- slow, stable crack growth
- rapid fracture

Fatigue strength of a material is influenced by:
- loading pattern
- number of cycles of cycling loading
- stress concentration
- corrosion
- temperature
- overload
- internal structure residual stresses
Creep is a time-dependent deformation of a material while under an applied load that is below its yield strength.

It is usually associated with high temperature, but some materials creep at room temperature.
Low temperature creep can take months or years to alter machine parts that are habitually left in a stressed condition. As the temperature increases, creep becomes more of a problem.

Creep terminates in rupture if steps are not taken to bring to a halt.

Metals that can be hammered or rolled into sheets are malleable.

Most ductile metals are also malleable, but some very malleable metals such as lead are not very ductile and cannot be easily drawn in wire.

Alloys tend to be less malleable and therefore require a softening heat treatment.
Elasticity is the ability of metal to return to its original size, shape, and dimensions after being deformed, stretched, or pulled out of shape.

The elastic limit is the point at which permanent damage starts.

The yield point is the point at which definite damage occurs with little or no increase in load.

The yield strength is the number of pounds per square inch (or kiloPascals) it takes to produce damage or deformation to the yield point.
The mechanical properties of a material are those properties that involve a reaction to an applied load. 

The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected. 

Mechanical properties are also used to help classify and identify material.
Mechanical properties of steel
The proprieties of a metal, such as steel may be classified in:

- Physical proprieties
color, luster, density, fusibility, thermal dilation and conductibility, electric conductibility, magnetism, corrosion resistance

- Mechanical proprieties
- strength proprieties
- technological (workability) proprieties
Properties of Steel
Steel is defined as iron combined with .03 to 1.7 % of Carbon and usually is called straight carbon steel.

Iron alloyed with various proportions of carbon gives low, mid and high carbon steels, with increasing carbon levels reducing ductility and toughness.

Alloy steel is produced by adding elements, such as nickel, chromium, manganese, molybdenum, vanadium and other elements to steel in controlled amounts.

The addition of chromium, nickel and molybdenum to carbon steels (more than 10%) results in stainless steels.

The addition of silicon to will produce cast irons.
Of all the metallic alloys in use today, the alloys of iron make up the largest proportion both by quantity and commercial value.

The alloys of iron contain:
◙ steel
◙ alloy steel
- stainless steel
- tool steel
- special alloy steel
◙ cast iron
Alloys of iron
An alloy is an intimate mixture of two or more elements in which the major component is a metal.

Most pure metals are either too soft, brittle or chemically reactive for practical use.

The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster.

Any ferrous or nonferrous metal may be alloyed to form an alloy metal with new and desirable characteristics.
What is an Alloy?

- It is applied in thin layers to iron and steel products that need to be protected from rusting. This process is called galvanizing. Galvanizing is done in a number of ways.
Generally, the metal is dipped in molten zinc. It can also be done by electroplating or by painting on a layer of zinc compound.
More than half of the zinc consumed is used for galvanizing.

The second largest use of zinc is as an alloy (other than brass or bronze).

Making brass and bronze accounts for another portion of zinc consumption.

The remaining zinc consumption is for making paint, chemicals, agricultural applications, in the rubber industry, in TV screens, fluorescent lights and for dry cell batteries.
Zinc (cont.)

It is use in the production of stainless steel, a bright, shiny steel that is strong and resistant to oxidation (rust). Stainless steel production consumes most of the chromium produced annually.

Chromium is also used to make heat-resisting steel.
So-called "superalloys" use chromium and have strategic military applications.

Chromium also has some use in the manufacture of certain chemicals.
For example, chromium-bearing chemicals are used in the process of tanning leather.

Chromium compounds are also used in the textiles industries to produce a yellow color.
Chromium (cont.)

- Most titanium is used in its oxide form which is a white pigment used in paint, varnishes and lacquers (49%), plastics (25%), paper (16%), and other products such as fabrics, printing inks, roofing granules, and special coated fabrics.

- It is used in the aerospace industry where it is mostly used to make engines and structural components for airplanes, satellites, and spacecraft.
An estimated 60% of metallic titanium is used in the aerospace industry.

- Since it is very resistant to corrosion by seawater, it is used to make propeller shafts and other ship parts that will be exposed to ocean water.

For medical uses, titanium is considered to be bio-compatible and often is used to make joint replacement parts such as hip joints.

Because of its strength, it is also used to make armor plated vehicles for the military.

- Titanium is also used to produce silvery-white sparks in some fireworks.
Titanium (cont.)
It is very resistant to corrosion.

It is hard, has a high melting temperature, and is lightweight.

Its strength is similar to steel, but is 45% lighter.

Titanium alloys can be twice as strong as aluminum alloys.

Titanium has no known nutritional benefit for animals.

It does, however, have some slight benefits for plant health.

Titanium has been found to be very compatible with the human body and is often used in surgical instruments and medical implants.
Much tin is used to coat so-called “tin” cans. Since tin does not oxidize (rust) in air or water, it is applied to the surface of flat-rolled steel to make tin plate, which is then fabricated to produce “tin” cans. This use accounts for about 1/4 of the tin consumed annually.

Alloys such as bronze and pewter are also a major use of tin. Tin is useful in electrical applications, mainly low-melting-point solders, that account for one-fourth of tin consumption.

It is also used in construction, transportation (mainly in bearings requiring soft metal alloys) and other various industrial applications.

For example, window glass is made by pouring molten glass onto molten tin; this process results in flat sheets of glass.

An alloy of tin and niobium has proven to be a “superconducting” compound at very low temperatures.
In pure form, copper is drawn into wires or cables for power transmission, building wiring, motor and transformer wiring, wiring in commercial and consumer electronics and equipment; telecommunication cables; electronic circuitry
Plumbing, heating and air conditioning tubing

Roofing, flashing and other construction applications

Electroplated coatings and undercoats for nickel, chrome, zinc, etc.

As an alloy with tin, zinc, lead, etc. (brass and bronze), it is used in extruded, rolled or cast forms in plumbing fixtures, commercial tubing, electrical contacts, automotive and machine parts, decorative hardware, coinage, ammunition, and miscellaneous consumer and commercial uses.

Copper is an essential micronutrient used in animal feeds and fertilizers.
Today most copper is obtained by the electrolysis process in which impure copper is refined.

Copper and copper alloys have a number of properties that make them useful, including high electrical and thermal conductivity, high ductility, and good corrosion resistance.

Copper weights about 3x as much as Aluminum and about 1.14x as much as Wrought iron.

It is one of the best conductors of heat an electricity – second only to much costlier Silver.
Low density and strength make it ideal for construction of aircraft, lightweight vehicles, and ladders.

An alloy of aluminum called duralumin is often used instead of pure aluminum because of its improved properties.

Easy shaping and corrosion resistance make it a good material for drink cans and roofing materials.

Corrosion resistance and low density leads to its use for greenhouses and window frames.

Good conduction of heat leads to its use for boilers, cookers and cookware.

Good conduction of electricity leads to its use for overhead power cables hung from pylons (a tall structure erected as a support esp. for electric power cables or boundary or decoration). The low density gives it an advantage over copper.

High reflectivity makes it ideal for mirrors, reflectors and heat resistant clothing for fire fighting.
Aluminum was not commercially used until the 1880’s when the electrical process of refining the ore was developed.
Aluminum was first produced by Christian Oersted in 1825.
However it was not until 20 years later that significant quantities were produced.
Frederich Wohler fused anhydrous aluminum chloride with potassium to set free aluminum. Later Ste Claire Deville in 1854 put together a production process using sodium instead of potassium.
At present, Aluminum is rapidly increasing in use and may replace copper & tin for 2nd place.
Aluminum and its alloys are used because they are easily to form, machine or cast , are readily available, inexpensive, and recyclable.
Aluminum weights about 2.9x less than Steel.
Iron is readily reduced by carbon.
If reduced at temperatures below 700-8000C (ca.1300-15000F) it is not suitable for forging and must be produced at temperatures above 11000C (ca. 20000F).

Wrought iron was the first form of iron known to man.
The product of reaction was a spongy mass of iron intermixed with slag.
This was then reheated and hammered to expel the slag and then forged into the desired shape.

Iron is rarely found in its native state, the only known sources being Greenland where the iron occurs as nodules in basalt that erupted through beds of coal and two very rare nickel-iron alloys.
General Material Classifications
There are thousands of materials available for use in engineering applications.

Most materials fall into one of 3 classes that are based on the atomic bonding forces of a particular material.
These three classifications are metallic, ceramic and polymeric.

Additionally, different materials can be combined to create a composite material.

Within each of these classifications, materials are often further organized into groups based on their chemical composition or certain physical or mechanical properties.

Composite materials are often grouped by the types of materials combined or the way the materials are arranged together.
General Material Classifications
Most steels require rapid cooling (quenching) for hardening but a few can be air-cooled with the same results.

Hardening increases the hardness and strength of the steel, but makes it less ductile.

Case Hardening
Case hardening produces a hard, wear-resistant surface or case over a strong, tough core.
Case hardening may be achieved by carburizing, cyaniding, and nitriding.

The purpose of tempering is to reduce the brittleness imparted by hardening and to produce definite physical properties within the steel.

Tempering always follows, never precedes, the hardening operation.

Besides reducing brittleness, tempering “toughens” the steel
Heat treatment (cont.)
The metals are annealed to relieve internal stresses, soften them, make them more ductile, and refine their grain structures
(for steels -rapid cooling, for copper and aluminum -slow or rapid cooling)

In general, annealing is the opposite of hardening.

The purpose of normalizing is to remove the internal stresses induced by heat treating, welding, casting, forging, forming, or machining.

It differs from annealing in that the metal is heated to a higher temperature and then removed from the furnace for air cooling.
Heat treatment (cont.)
Chromium – increases resistance to corrosion and improves the responsiveness to heat treatment.

Manganese – increases strength and responsiveness to heat treatment.

Molybdenum – increases toughness and improves the strength of steel at high temperatures.
How do different alloying elements effect the properties of a steel?
Commonly, the fatigue strength characteristic of a material is given by the so known S-N curve (stress-S against the number of cycles to failure -N).

In most of the cases the S-N curve is given for an R ratio of 0.1 but families of curves, with each curve at a different R ratio, are also often available.
FATIGUE (cont.)
As the temperature decreases, the strength hardness and elasticity increase for almost all metals.

In which means the effect of temperature drop on ductility there are two categories of metals:
those that become brittle at low temperatures and those that remain ductile.

The metals that are brittle at low temperatures shows a a temperature range (called transition zone) where ductility and, most important, toughness drop rapidly.

The operating temperatures of a mechanical part should be above the transition zone.

Nickel is one of the most effective alloying elements lowering the transition temperature of steels.
Metals at low temperatures
After this metal alloy is poured in to ingots that are later rolled in to billets, slabs or blooms.
Steel production (cont.)
Started with the Bronze Age when ancient man found that by adding tin to copper he would end up with a stronger material which was bronze.

By adding zinc to copper the resulting alloy is brass.

The typical alloying elements in some common metals are:
Alloying of Metal
Although copper can be found free in nature the most important sources are the minerals cuprite, malachite (green friable stone), azurite, chalcopyrite and bornite.

The symbol for copper is Cu and comes from the Latin word “cuprum” meaning from the island of Cyprus.
Copper is found as a natural
occurring metal in nature.
Aluminum (symbolized as Al) is a silvery white metal, which is light, nontoxic, nonmagnetic, non sparkling and stands 2nd among metals in the scale of malleability and 6th in ductility.
Is the most abundant metal found on earth and the third most abundant of all elements in the Earth’s crust

Aluminum is a reactive metal, and does not occur in the metallic state in nature.

The main ore of aluminum is bauxite, the source of over 99% of metallic aluminum.
Iron is the 4th most abundant metal found on earth.
Iron and steel are the most common metals in industrial use.

Steel alloys are used for strength critical applications.
The first iron encountered by man actually came from outer space in the form of meteors.
This native iron is easily distinguishable because it contains 6-8% nickel.
In fact the ancient Egyptians called iron “Metal from heaven”
Metals have useful properties including strength, ductility, high melting points, thermal and electrical conductivity, and toughness.
Refractory materials
(Columbium , Tantalum)
(applications of > 2000° F)
Common Industrial Metals
Grain size is normally quantified by a numbering system.
Coarse 1-5 and fine 5-8.
The number is derived from the formula N=2n-1 where n is the number of grains per square inch at a magnification of 100 diameters.
Grain size has an important effect on physical properties.

For service at ordinary temperatures it is generally considered that fine grained steels give a better combination of strength and toughness, whereas coarse grained steels have better machinability.
Grain Size (cont.)
In brittle materials, the UTS will be at the end of the linear-elastic portion of the stress-strain curve or close to the elastic limit.

In ductile materials, the UTS will be well outside of the elastic portion into the plastic portion of the stress-strain curve.

This mechanical capacity is mainly quantified by :

Yield Tensile Strength = the stress required to produce a small-specified amount of plastic deformation.
The yield strength obtained by an offset method is commonly used for engineering purposes because it avoids the practical difficulties of measuring the elastic limit or proportional limit.

Ultimate Tensile Strength = the maximum engineering stress level reached in a tension test.
Nickel (Ni) is a silvery shiny, tough, ductile and partially magnetic metal belonging to the iron-cobalt family.

Except for Chromium, it is the metal most commonly used in steel alloys.
Vital as an alloying constituent of stainless steel, plays key role in the chemical and aerospace industries.

Nickel alloys are used for higher temperatures (ca.1500-2000°F) applications or when good corrosion resistance is required.
Tin (silvery gray metal) is rarely used on its own and is most commonly alloyed to copper to form bronze.

Tin's symbol is Sn from the Latin word “stannum” and weights about 1.2x less than Copper.

Native Tin is not found in nature. The primary mineral source for tin is cassiterite.

The tin ore is stannic oxide and is generally found with quartz, feldspar or mica.
Grain size can be influenced by:

the control of solidification process

Cold work (i.e. cold rolling and forging)

Heat treatment
Grain Size (cont.)
Each grain is a distinct crystal with its own orientation.

The areas between the grains are known as grain boundaries.
When a metal solidifies from the molten state, millions of tiny crystals start to grow.

Usually, the longer the metal takes to cool the larger the crystals grow.

These crystals form the grains in the solid metal.
Toughness = area under the stress -strain curve from a tensile test.
The key to toughness is a good combination of strength and ductility.

A tough steel, such as cold chisel, is one that can withstand considerable stress, slowly or suddenly applied, and which will deform before failure.
Toughness is the ability of a metal to deform plastically and to absorb energy (to resist shock) in the process before fracture.

It characterizes the ability of a material or metal to resist fracture, plus the ability to resist failure after the damage has begun.
Brittle steel fracture
Ductile steel fracture
Brittleness is the property opposite of plasticity or ductility.
Brittleness is simply the lack of significant ductility and should not be confused as a lack of strength.

A brittle metal is one than cannot be visibly deformed permanently, or one that lacks plasticity.

A brittle steel will fractures easily when bent sharply or struck a sharp blow.
Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance.
The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom.

The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron.

These liquid products are drained from the furnace at regular intervals.

The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions.
Steel production (cont.)
Zinc is a blue-gray, metallic element.

At room temperature, zinc is brittle, but it becomes malleable at ca.1000C (ca. 2100F).

Zinc is a moderately good conductor of electricity. It is relatively resistant to corrosion in air or water.

Zinc is recovered from a number of different zinc minerals such as sphalerite (the most significant), smithsonite and zincite.
Titanium is a silvery gray metal which first entered commercial production in 1948.

Often thought of as the 9th industrial metal.
There are two major ore forms of titanium for the manufacture of titanium metal : rutile (is preferred containing 95% of titanium dioxide, and is relative free of iron) and ilmenite.
The amount of ductility is an important factor when considering forming operations such as rolling and extrusion.

Ductility is also used a quality control measure to assess the level of impurities and proper processing of a material.

Any metal that can be draw into a wire is ductile.
Iron, aluminum, gold, silver, nickel are ductile metals.



The conventional measures of ductility are the strain at fracture (usually called elongation EL% ) and the reduction of area at fracture (AR%).
7. Hardenability
5. Castability
6. Forgeability
4. Machinability
3. Weldability
2. Ductility
1. Malleability
Mechanical properties of steel (cont.)
6. Hardness
2. Elasticity

3. Plasticity

4. Toughness

5. Brittleness
1. Strength (tension, compression, bending, shear, torsion)
Mechanical properties of steel (cont.)
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