ferrous metals (Ch 07 Edition 11th) - uses and applications.pptx

Chapter 07: Ferrous Metals
and Alloys
DeGarmo’s Materials and Processing in
Manufacturing

Classification of Common Ferrous Metals
and Alloys
Note:
Figure 6-1 Classification of common ferrous metals andalloys.
%Carbon > 2.11 - cast irons; %Carbon < 2.11 - steels

7.3 Iron
 Iron is the most important of the engineering metals
 Four most plentiful element in the earth’s crust
 Occurs in a variety of mineral compounds known as ores
 Metallic iron is made from processing the ore
 Breaks the iron-oxygen bonds (chemical reduction
reaction)
 Ore, limestone, coke (carbon), and air are continuously
inputted into a furnace and molten metal is extracted
 Results in pig iron
 C 3.0-4.5%, Mn 0.15-2.5%, P 0.1-2.0%, Si 1.0-3.0%, S 0.05-0.1%
 A small portion of pig iron is cast directly; classified as
cast iron

Pig iron
• The product of smelting iron ore with a high-carbon
fuel such as coke, usually with limestone as a flux in
blast furnace.
• Pig iron has a very high carbon content, typically 3.5–
4.5%, along with silica and other impurities.
• This makes it very brittle and not useful directly as a
material.
• The traditional shape of the molds used for these
ingots was a branching structure at right angles to a
central channel or runner.
• Pig iron is intended for remelting, and converted to
steel and cast iron.

Pig iron
The product of smelting iron ore with a high-carbon fuel such as coke, usually
with limestone as a flux in blast furnace.
Pig iron has a very high carbon content, typically 3.5–4.5%, along with silica and
other impurities,
This makes it very brittle and not useful directly as a material .
The traditional shape of the molds used for these ingots was a branching
structure at right angles to a central channel or runner.
Pig iron is intended for re melting, and converted to steel and cast iron.

• Manganese is added because it converts sulpher into manganese
sulfide instead of iron sulfide.
• The manganese sulfide is lighter than the melt so it tends to float out
of the melt and into the slag.
• Nickel is one of the most common alloying elements because it
improves toughness.

Cast Iron
• Cast irons are called so, because, they are usually
manufactured through casting techniques, owing to their
brittle nature due to presence of iron carbide.
• A hard, brittle, nonmalleable iron-carbon alloy and is cast
into shape.
• Contains 2 to 4.5 percent carbon, 0.5 to 3 percent silicon,
lesser amounts of sulfur, manganese, and phosphorus.
• Carbon (C) and silicon (Si) are the main alloying elements.
• This technically makes these base alloys ternary Fe–C–Si
alloys.
• The principle of cast iron solidification can be understand
from the binary iron–carbon phase diagram.

Iron-carbon alloys with more than 2.11% carbon are
known as cast irons
Relatively inexpensive with good fluidity and low
liquidus temperatures make them ideal for casting
Contain significant amounts of silicon,
manganese, and sulfur
High silicon content enhances oxidation and
corrosion resistance of cast irons

• The compositions of most cast irons are around the
eutectic point of the iron–carbon system.
• The melting temperatures ranges from 1150 to 1200 °C,
which is about 300 °C lower than the melting point of
pure iron.
• With its relatively low melting point, good fluidity,
castability, excellent machinability, resistance to
deformation and wear resistance cast irons have become
an engineering material with a wide range of applications.
• Cast irons mostly serve as structural components,
e.g. automobile motor castings, lathe bed, sliding
guides‘ in machinery.
• Used in pipes, machines and automotive industry
parts, cylinder heads (declining usage), cylinder blocks
and gearbox cases (declining usage).

Production of Cast Iron
• Cast iron is made by re-melting pig iron, often along with
substantial quantities of scrap iron, scrap steel, lime stone, carbon
(coke) .
• Taking various steps to remove undesirable contaminants.
Phosphorus and sulfur may be burnt out of the molten iron.
• This also burns out the carbon, which must be replaced.
• Depending on the applications, carbon and silicon content are
adjusted to the desired levels.
• Other elements are then added to the melt before the final form is
produced by casting.
• Iron is sometimes melted in a special type of furnace known as a
cupola furnaces.
• After melting is complete, the molten iron is poured into a
holding furnace or ladle

Types of Cast Iron
 Cast iron (> 2% Carbon)
 Grey cast iron
 White cast iron
 Malleable cast iron
 Ductile or nodular cast iron
 Austempered ductile iron
 Compacted graphite cast iron
 High-alloy cast iron

Gray Cast Iron
 Least expensive and most common variety
 Promotes the formation of graphite
 Most cast irons have a chemical composition of 2.5–4.0%
carbon, 1–3% silicon.
 Gray cast iron is characterized by its graphitic microstructure.
Carbon (free) is present in the form of graphite flakes.
Figure 6-9 Photomicrograph showing the distribution
of graphite flakes in gray castiron

Gray Cast Iron
 Reduced shrinkage makes it easier to make intricate and more complex
parts
 Size and shape of the graphite flakes are significant on the overall
properties of gray cast iron
 Offer excellent compressive strength, good machinability and good
resistance to adhesive wear
 Outstanding sound and vibration damping characteristics (graphite
flakes absorb transmitted energy)
 High silicon contents promote good corrosion resistance, the enhanced
fluidity for casting
 High thermal conductivity, low rate of thermal expansion, good stiffness,
resistance to thermal fatique
 Gray cast iron has less tensile strength and shock resistance than steel
 100% recyclability
 Used: in automotive engine blocks, heads, and cylinders; transmission
housing; machine tool bars, and large equipment parts that are
subjected to compressive loads and vibration

Damping capacity is the ability of a material to absorb energy by converting mechanical energy intoheat

White Cast Irons
 Excess carbon is in the form of iron carbide (cementite)
 White surface appears when the material is fractured
 Composition range of 1.8-3.6% C, 0.5-1.9%Si, 0.25-0.8%Mnand
rapid cooling
 Very hard and brittle, high abrasive resistance application
 It is common to pursue hard, wear-resistant martensite structure

White Cast Irons
• Carbon in the form of cementite
• Formed by rapid cooling of the molten metal after pouring,
thus causing the carbon to remain chemically combined
with iron in the form of cementite.
• When fractured, the surface has a white crystalline
appearance that gives the iron its name.
• Hard, brittle, excellent wear resistant, good strength
• Application: Railway brake shoes

Malleable Cast Iron
• Malleable iron starts as a white iron casting.
• Then heat treated at about 900 °C .
• So that surface tension has time to form graphite flakes into spheroidal
particles.
• They have blunt boundaries, as opposed to flakes.
• This alleviates the stress concentration problems faced by gray cast iron.
• In general, the properties of malleable cast iron are more like mild steel.
 Greater ductility than gray cast iron
 Favorable graphite shape removes the internal notches
 Ferritic malleable cast iron
 Structure of irregular graphite in a ferrite
matrix
 Excellent impact strength, corrosion
resistance, and machinability
 Pearlitic malleable cast iron
 Higher strength and lower ductility than
ferritic malleable cast iron
 Reduced machinability

Malleable Cast Iron
• Carbon in the form of irregular graphite nodules
• Obtained by heat treating white cast iron,
separating carbon out of solution and form
graphite aggregates.
• Up-to 20 % elongation
• Applications: Pipe fittings, flanges, certain
machine components, railroad equipment parts.

Ductile Cast Iron
 A more recent development is nodular or ductile cast iron.
 Tiny amounts of magnesium or cerium along with careful control of other
elements and timing allows the carbon to separate as spheroidal particles as
the material solidifies.
 The properties are similar to malleable iron, but parts can be cast with
larger sections.
 Combination of good ductility, high
strength, toughness, wear
resistance, machinability, low
melting point castability and up to a
10% weight reduction
 Most expensive cast iron due to
the cost of nodulizer
Figure 6-11 Ductile cast iron with a ferritematrix

Austempered Ductile Cast Irons
 Austempered ductile iron (ADI)
 Ductile iron that has undergone a special austempering heat
treatment
 Ability to cast intricate shapes with strength, fatigue, and
wear resistance properties those are similar to heat treated
steel
 8 to 10% reduction in density (strength-to-weight is excellent)
 Enhanced damping capacity (due to graphite nodules)
 Poorer machinability
 High stiffness
Austempering
In steel it produces a bainite microstructure.
In cast irons it produces a mixture structure of acicular ferrite (needle-shaped
structure) and high carbon, stabilized austenite known as ausferrite.

Mechanical Properties of Cast Irons

Compacted Graphite Cast Iron (CGI)
 Compacted graphite cast iron (CGI)
 Ductile iron with the addition of Mg-Ce-Ti
 Compacted graphite is intermediate to flake graphite of gray
cast iron and nodular graphite of ductile iron
 Strength, stiffness, and ductility are greater than gray iron
 Castability, machinability, thermal conductivity, and damping
capacity exceed those of ductile iron
 Good impact and fatigue properties
 Graphite in form of worms (vermicular).* Microstructure is in between
gray and ductile cast iron
 A relative recent addition to the family of cast irons.

Usages of cast irons
Gray cast iron
• Engine cylinder blocks, flywheels, gearbox cases,
machine-tool bases.
White cast iron
• Bearing surfaces
Malleable iron
• Axle bearings, track wheels, automotive
crankshafts
Ductile or nodular iron
• Gears, camshafts, crankshafts

The Role of Alloys in Cast Irons
Cast iron product are used in the as-cast condition with only heat treatment being
a stress relief or annealing
Alloy elements are selected by
Affecting the formation of graphite or cementite
Modifying the morphology of the carbon-rich phase
Strengthening the matrix material
Enhancing wear resistance through the formation of alloy carbides
Nickel promotes finer graphite structures
Chromium retards graphite formation and stabilize cementite
0.5-10% Molybdenum is added to gray cast iron to improve strength, form alloy
carbide and control size of graphite
High-alloy cast iron is to enhance corrosion resistance and/or good elevated
temperature service

Steel
• Steels are serving major part of present engineering applications.
• Steels are classified based on their C content/ alloying additions, which in turn
dictates their applications.
• In steels, carbon atoms occupies interstitial sites of Fe
• Offers strength, rigidity, durability
 Construction and the automotive industries consume the most
steel
 Steel is manufactured by an oxidation process that decreases the amount
of carbon, silicon, manganese, phosphorous, and sulfur in pig iron or steel
scrap
 Kelly-Bessemer process
 Open-hearth process
 Current commercial steels are produced by oxygen and electric
arc furnaces
 air or oxygen passes over or through the molten metal
 Carbon oxidizes to form gases CO, CO2
 Other elements, such as Silicon, phosphorus are oxidized and rise to be
collected in a removable slag

Solidification Concerns
 Steel must undergo a change from liquid to solid
regardless of how it is processed
 Molten metal is poured into ladles
 Ladle metallurgy
 Processes designed to provide final purification
 Alloy additions can be made
 Dissolved gases can be reduced or removed
 Grain size can be refined
 Processed liquid is often poured into a continuous
caster
 Continuous casting produces the feedstock
material that is used in forging or rolling operations

Steel Processing
Figure 6-3 a) Schematic representation of the
continuous casting process for producingbillets,
slabs, and bars. (Courtesy of Materials
Engineering, Penton Publishing, New York, NY.)

Deoxidation and Degasification
 Steel may have large amounts of oxygen
dissolved in the molten metal
 Solubility decreases during subsequent cooling
and solidification
 Oxygen and other gases are rejected
 May become trapped and form bubbles
Figure 6-4 Solubility of gas in a metal as a
function pf temperature showing significant
decrease upon solidification

Deoxidation
 Defects may be in the final product
 Porosity problems can be avoided if the
oxygen is removed prior to solidification
 The oxygen can also be reacted with other
materials that have a higher affinity for oxygen
than steel
 Called deoxidizers
 Oxygen reacts with deoxidizers and produce
solid metal oxide that are removed from the
molten metal or become dispersed throughout
the structure

Degassification
 Hydrogen and Nitrogen gases
 Having deleterious effects on the performance
of steel
 For alloy steels, H2 and N2 solubility tends to
be increased by alloying additions, such as
vanadium, niobium and chromium
 Cause to embrittlement

Degassification
 In vacuum degassing, a
stream of molten metal
passes through a vacuum
chamber into a mold
Method of degassing steel bypouring
through a vacuum.

Degassification
 Consumable-electrode
remelting process
 Solidified metal electrode
replaces the ladle of molten
metal
 As the electrode is remelted,
molten droplets pass through a
vacuum
 High surface area of molten
droplets allows for degassing
 Vacuum arc remelting (VAR)
 Vacuum induction melting (VIM)
 Fails to remove nonmetal
impurities
Vacuum arc melting (VAR) process

Degassification
 Electroslag remelting
(ESR)
 Used to produce
extremely clean, gas-
free metal
 The entire remelting is
conducted under a
blanket of molten flux
 Nonmetallic impurities
float and are collected
in the flux
Production of an ingot by the electroslag
remelting process

1) Plain Carbon Steel
• Plain Carbon Steels: Steels that contain only residual concentrations of
impurities other than carbon and a little manganese
• Carbon steel is by far the most widely used kind of steel. The properties of
carbon steel depend primarily on the amount of carbon it contains.
• Most carbon steel has a carbon content of less than 1%.
• Indeed, it is good to precise that plain carbon steel is a type of steel having a
maximum carbon content of 1.5% along with small percentages of silicon,
sulphur, phosphorus and manganese.
• Theoretically, steel is an alloy of only iron and carbon, but steel contains
other elements (Mn, P, S, Si) in detectable amounts
• Plain carbon steel is when these elements are present, but not in any
specified amount
• Strength is primarily a function of carbon content
Strength is a function of carbon content,
Carbon increases, strength increases
BUT ductility, toughness, weldability
decrease

Types of Carbon Steels
 Low-carbon steels (< 0.20% carbon)
 Structure: ferrite and pearlite
 good formability and weldability
 Relatively soft and weak, but without standing ductility and toughness,
machine-able, weld-able and least expensive to produce.
 Medium-carbon steels (0.20 - 0.50% carbon)
 Can be quenched to form martensite and bainite
 Best balance of properties
 High toughness and ductility are good with respect to the levels
of strength and hardness
 High carbon steels (> 0.50% carbon)
 Toughness and formability are low, but hardness and wear
resistance are high
 Severe quenches can form martensite, but hardenability is poor
 Quench cracking is often a problem
 Carbon steels have high strength, high stiffness, and
reasonable toughness
 Rust easily and require surface protection

2) Alloy Steels
• Alloy steels are the types of steels in which elements
other than carbon and iron are present in sufficient
amount to modify the properties of the materials.
• Alloy Steel: More alloying elements are intentionally
added in specific concentration
• The utility of alloy steels permit a much wider range of
physical and mechanical properties that is not possible
in plain carbon steels.
• The different alloying elements in steel are: (i) Carbon (ii)
Magnesium (iii) Silicon (iv) Copper (v) Chromium (vi)
Molybdenum (vii) Vanadium (viii) Nickel (ix) Aluminium (x)
Boron (xi) Titanium (xii) Zirconium (xiii) Calcium (xiv) Lead
(xv) Nitrogen (xvi) Tungsten
 Low alloy steels contain less than 8% alloy additions
 High alloy steels contain more than 8% alloy additions

Alloy steels
Alloy steels containing alloys in specifiable
amounts
• 1.65% or more manganese
• 0.60% silicon
• 0.60% copper
Most common alloying elements are chromium,
nickel, molybdenum, vanadium, tungsten, cobalt,
boron and copper

Purpose of Alloying:
1- increase hardenbility
2-improve strength at ordinary temperature
3-Improve mechanical properties at higher and
lower temperatures
4-improve toughness
5-increase wear resistance
6-increase corrosion resistance
7-improve magnetic properties

Effects of alloying element
 In general, small amount (less than 5%) of alloying element is added to improve strength
or hardenability
 Large amount (up to 20%) is added to produce special properties, such as corrosion or
stability at high temperature
 Manganese, silicon, aluminum are added during steelmaking process to remove
dissolved oxygen from the melt
 Manganese, silicon, nickel, copper increase strength by forming solid solution in ferrite
 Chromium, vanadium, molybdenum, tungsten, and other elements increase strength by
forming dispersed second-phase carbides
 Nickel and copper are added in small amount to improve corrosion resistance
 Nickel increase toughness and impact resistance
 Molybdenum helps resist embrittlement
 Zirconium, cerium, and calcium increase toughness by controlling the shape of inclusion
 Lead, bismuth, selenium, tellurium increase machinability
 Manganese, molybdenum, chromium, silicon, nickel improve hardenability
 Boron is powerful hardenability

AISI-SAE Classification System
 Historically, many methods for identifying alloys by their
composition have been developed.
 Classifies the alloys by chemistry
 Society of Automotive Engineers (SAE) and the American
Iron and Steel Institute (AISI) have developed systems for
classifying steel
 Incorporated into the Universal Numbering System
 Identified by a four-digit number
 First number indicates the major alloying elements
 Second number designates a subgrouping within the major alloy
system
 Last two digits indicate the carbon percentage expressed as
“points”
 i.e. AISI1080 – plain carbon steel with 0.80% carbon
AISI 4340 – Mo-Cr-Ni alloy with 0.40% carbon

i.e. AISI1080 – plain carbon steel with 0.80% carbon
AISI4340 – Mo-Cr-Ni alloy with 0.40% carbon

Other Designations
 Letters may be used in the AISI-SAE
systems
 B- addition of boron
 L- lead addition
 E- electric furnace process
 American Society for Testing Materials
(ASTM) and the U.S. government have
specifications based on the application

Selecting Alloy Steels
 Two or more alloying elements can produce similar
effects
 Typically, the least expensive alloy is selected
 Important to consider both use and fabrication
 Define required properties
 Determine the best microstructure
 Determine method of product or part (casting, machining,
metal forming, etc.)
 Select the steel with the best carbon content and
hardenability

Types of Alloy Steels
General categories of alloy steels are:
Constructional alloys
the desired properties are developed a heat treatment and the specific alloy
elements tend to be selected for their effect on hardenability (AISI-SAE
identification)
Conventional high-strength steels
steels rely largely on the chemical composition to develop the desired
properties in a single-phase ferritic microstructure, usually in the as-rolled or
normalized condition.
Advanced high-strength steels (AHSS)
primarily multiphase steels (ferritic, martensite, bainite, and/or retained
austenite) that provide high strength with unique mechanical properties

High-Strength Steels (HSLA,
Microalloyed, and Bake-Hardenable)
The conventional high-strength steels
Provide increased strength-to-weight, good weldability, and
acceptable corrosion resistance
A modest increase in cost (compared to low carbon, plain
carbon steels)
Available in sheet, strip, plate, structural shapes, and bars
Ductility and hardenability are limited
The conventional high-strength steels are used in
automobiles, trains, bridges and building because of its
higher yield strength and weight saving 20-30%

High-Strength Low Alloy (HSLA) or
Microalloyed Steels
HSLA or Microalloyed steels are between carbon steels and alloy grades with
respect to cost and performance
being used as substitutes for heat treatment steels
Low- and medium- carbon steels contain solid-solution strengthening alloys
(such as Mn and Si) with small amounts (0.05-0.15%) of alloying elements (Nb,
V, Ti, Mo, Zr, B, rare earths or combinations)
These steels offer maximum strength with minimum carbon, while preserves
weldability, machinability, and formability
Energy savings can be substantial
no need of straightening or stress relieving after heat treatment
Quench cracking is not a problem

Bake-Hardenable Steel
Low carbon steels that are
resistant to aging during normal storage, and
begin to age during sheet metal forming, and
continue to age while exposed to heat during the paint baking operation
(finishing operation in automotive manufacture)
Increase in strength occurs after the forming operations
Material offers good formability
Improved dent resistance
Significant in automotive sheet application
Spot weldability, good crash energy absorption, low cost and full recyclability

Typical Compositions and Properties of
HSLA

Advanced High-Strength Steels (AHSS)
AHSS replaces low carbon and HSLA steels in automotive applications
AHSS is primarily ferrite-phase, soft steels with varying amount of martensite,
bainite or retained austenite – which offer high strength with enhanced ductility
Improved formability
Enable the stamping or hydroforming of complex parts
Higher strength provides improved fatigue resistance
Possibility of weight reduction

Types of Advanced High-Strength Steels
(AHSS)
Dual-phase (DP) steels
microstructure of Ferrite and martensite
Improved forming characteristics and no loss in weldability (compared with
HSLA)
High strain-rate sensitivity
The faster the steel is crushed, the more energy it absorbs
A feature to enhance crash resistance in automotive applications
Transformation-induced plasticity (TRIP) steels
Microstructure of Ferrite , hard martensite or bainite and at least 5 vol% of
retained austenite
At higher strains, the retain austenite transforms progressively to martensite,
enabling high work-hardening to persist to greater levels of deformation
Excellent energy absorption during crash deformation

Types of Advanced High-Strength Steels
(AHSS)
Complex-phase (CP) steels and martensitic (Mart) steels
high strength with capacity for deformation and energy absorption
CP steels – microstructure of ferrite and bainite with small amount of
martensite, retained austenite and pearlite
Strengthened by grain refinement created by a fine precipitate of Niobium,
titanium or vanadium carbides or nitrides
Mart steels – almost entirely martensite
Other types
Ferritic-bainite (FB) steels
Twinning-induced plasticity (TWIP) steels - (17-24% Mn)
Nano steels - (replace hard phase with nano-size precipitates)

Low Alloy Steels
Iron - carbon alloys that contain additional alloying
elements in amounts totaling less than  10 % by
weight.
• Mechanical properties superior to plain carbon steels
for given applications.
• Higher strength, hardness, hot hardness, wear
resistance, toughness, and more desirable
combinations of these properties.
• Heat treatment is often required to achieve these
improved properties.

High-strength low-alloy steel (HSLA)
• Type of alloy steel that provides better mechanical properties or
greater resistance to corrosion than carbon steels.
• HSLA steels are not made to meet a specific chemical composition
but rather to specific mechanical properties.
• They have a carbon content between 0.05–0.2% to retain formability
and weldability.
• These steels were developed for the automotive industry to reduce
weight without losing strength.
• High-strength, low alloy (HSLA) steels: Low-carbon steels
containing maximum of 10% other alloying elements (e.g.:coppoer,
vandium, nickel, and molybdenum
• Applications: automobile body parts, structural shapes (I-beam,
channels etc), and sheets for pipes, buildings and tin cans.
• Examples of uses include door-intrusion beams, chassis members,
reinforcing and mounting brackets, steering and suspension parts,
bumpers, and wheels.

Special Steels
Maraging Steels
• The term maraging is derived from the strengthening
mechanism, which is transforming the alloy to
martensite with subsequent age hardening.
• Carbon free iron-nickel alloys with additions of
cobalt, molybdenum, titanium and aluminium.
• The common, non-stainless grades contain 17–19
wt.% nickel, 8–12 wt.% cobalt, 3–5 wt.%
molybdenum, and 0.2–1.6 wt.% titanium.

• Air cooling the alloy to room temperature from 820 °C
creates a soft iron nickel martensite, which contains
molybdenum and cobalt in supersaturated solid
solution.
• Tempering at 480 to 500 °C results in strong hardening
due to the precipitation of a number of intermetallic
phases, including, nickel-molybdenum, iron-
molybdenum and iron-nickel varieties.
• With yield strength between 1400 and 2400 MPa
maraging steels belong to the category of ultra-high-
strength materials.
• The high strength is combined with excellent toughness
properties and weldability.

Applications
• Maraging steel's strength and malleability in the
pre-aged stage allows it to be formed into thinner
rocket and missile skins than other steels, reducing
weight for a given strength.
• Aerospace, e.g. undercarriage parts and wing
fittings.
• Tooling & machinery, e.g. extrusion press rams
and mandrels in tube production, gears.
• Ordnance components and fasteners.

Long products for the aircraft industry (Courtesy of Boehler AG, Austria)

• Maraging steel production, import, and export
by certain states, such as the United States, is
monitored.
• It is particularly suited for use in gas
centrifuges for uranium enrichment
• Lack of maraging steel significantly hampers
this process. Older centrifuges used aluminum
tubes; modern ones, carbon fiber composite.

Free-Machining Steels
 Steels machine readily and form small chips when cut
 The smaller the chips reduce friction on the cutting tool which
reduces the amount of energy required
 Reduces tool wear
 Free-machining steels carry a cost of 15-20% over conventional
steels
 Carbon steel with addition of S, Pb, Bi, Se, Te or P
 Enhance machinability
 Additions provide built-in lubrications
 sulfur combines with manganese to form soft manganese sulfide inclusions
 Lead – as insoluble particle
 Bismuth - more environmentally friendly than lead
 Ductility and impact properties are reduced

Precoated Steel Sheet
 Typical sheet metal processes shape bare steel
followed by finishing (or coating)
 Expensive and time-consuming stages of manufacture
 Precoated steel sheets can also be formed
 Eliminates the post processing finishing operations
 Dipped, plated, vinyls, paints, primers and
polymer coatings can be used
 These coating are specially formulated to
endure the subsequent forming and bending

Steels for Electrical and Magnetic
Applications
 Soft magnetic materials can be magnetized by low-
strength magnetic fields
 Lose almost all of their magnetism when the field is removed
 Products such as solenoids, transformers, generators, and
motors
 Materials such as high-purity iron, low-carbon steel, iron-silicon
electrical steels, amorphous ferromagnetic alloys, iron-nickel
alloys and soft ferrite (ceramic material)
 Amorphous metals
 No crystal structure, grains, or grain boundaries
 Magnetic domains can move freely
 Properties are the same in all directions
 Corrosion resistance is improved

Special Steels
Maraging steels
Used when extremely high strength is required
Typically also have high toughness
Very-low-carbon steel with 15-20% Nickel and significant amount of Co, Mo, Ti
Steels for High-Temperature Service
Plain-carbon steels should not be used for temperatures in excess of 250°C
Tend to be low-carbon materials (< 0.1% carbon)

Stainless Steels
• In 1913, English metallurgist Harry Brearly, accidentally discovered that
adding chromium to low carbon steel gives it stain resistance.
• In addition to iron, carbon, and chromium, modern stainless steel may also
contain other elements, such as nickel, niobium, molybdenum, and titanium.
• Nickel, molybdenum, niobium, and chromium enhance the corrosion
resistance of stainless steel.
• It is the addition of a minimum of 12% chromium to the steel that makes it
resist rust, or stain 'less' than other types of steel
• Excellent corrosion resistance
• Contain at least 11% Chromium Cr oxidizes easily and forms a thin
continuous layer of oxide that prevents further oxidation of the metal
• Stainless steels are divided in following major classes on the basis of
predominant phase constituent.

Stainless Steels
• Stainless steel is low-carbon steel with the addition of 4-6%
Chromium
• Chromium additions provide
• Improved corrosion resistance
• Outstanding appearance
• Tough, corrosion-resistant oxide layer can heal itself if oxygen is
present
• Materials that have this corrosion resistant layer are said to be true
stainless steels
• Designations for stainless steels are based on their microstructures

• The chromium in the steel combines with oxygen in the
atmosphere to form a thin, invisible layer of chrome-
oxide, called the passive film.
• The sizes of chromium atoms and their oxides are
similar, so they pack together on the surface of the
metal, forming a stable layer only a few atoms thick.
• If the metal is cut or scratched and the passive film is
disrupted, more oxide will quickly form and recover the
exposed surface, protecting it from oxidative corrosion.
• Iron, on the other hand, rusts quickly because atomic
iron is much smaller than its oxide, so the oxide forms a
loose rather than tightly-packed layer and flakes away.

• The passive film requires oxygen to self-repair, so
stainless steels have poor corrosion resistance in
low-oxygen and poor circulation environments.
• In sea water, chlorides from the salt will attack and
destroy the passive film more quickly than it can be
repaired in a low oxygen environment.
 Tough, corrosion-resistant oxide layer can heal
itself if oxygen is present
 Materials that have this corrosion resistant layer are
said to be true stainless steels
 Designations for stainless steels are based on
• their microstructures

Types of Stainless Steels:
The three main types of stainless steels are:
• Ferritic
• Austenitic, and
• Martensitic.
• These three types of steels are identified by their
microstructure or predominant crystal phase.

Microstructures for Stainless Steel
 Ferritic stainless steel
• Above 13 %Cr in Iron, this binary alloys are ferritic over the whole
temperature range.
• This ferrite is called delta ferrite, because it exist from the melting point to
room temperature.
• Stainless Steel containing 0.04%C and 18% Cr is fully ferritic.
• Ferritic steels have ferrite (body centered cubic crystal) as their main phase.
• Ferritic steel is less ductile than austenitic steel and is not hardenable by heat
treatment.
• Readily weldable
• Cheapest

 Martensitic stainless steels
• The characteristic orthorhombic martensite microstructure was
first observed by German microscopist Adolf Martens around
1890.
• Martensitic steels are low carbon steels built around the Type
410 composition of iron, 12% chromium, and 0.12% carbon
• They may be tempered and hardened.
• Martensite gives steel great hardness, but it also reduces its
toughness and makes it brittle, so few steels are fully hardened.
 Increased strength
 More carbon content, less chromium
 Less corrosion resistant than ferritic
 More expensive than ferritic
Used in cutlery

 Austenitic stainless steels
 If a Ni is added to low carbon 18 % Cr steel Gama phase field
expanded.
 At about 8% Ni Gama phase field exist at room temperature.
 8% Ni is the minimum amount which makes Gama stable at room
temperature.
 Austenitic steels have austenite as their primary phase (face
centered cubic crystal).
 These are the ferrous alloys containing 18% chromium, and 8%
nickel in low carbon
 Costs two to three times as much as the ferritic alloys
 Nonmagnetic structure
 High corrosion resistance (except hydrochloric acid and other
halide acids and salts
 May be polished to a mirror finish)
 Increased strength
 Best combination of corrosion resistance and toughness
 Be easily welded and do not embrittle at low temperature

 Precipitation-hardening variety
 Martensite or austenite modified by the addition of Cu, Al,Ti
 These additions permit the precipitation of hard intermetallic alloys
 Addition of alloying elements to increase strength
 Duplex stainless steels
 Alpha forming element Mo, Ti, Nb, Si, Al.
 Gama forming elements Ni, Mn, C and N.
 Duplex structure (Alpha+Gama) can be produced by adding
correct balance of elements for Alpha and Gama stabilizer.
 Good toughness and high yield strength
 Resistance to both stress corrosion cracking and pittingcorrosion
 Free-machining stainless steels
 Addition of sulfur, phosphorous, selenium
 Designated by letter F or Se following the three-digit alloy code

Designations for Stainless Steels

Stainless steels
“Ferritic stainless steel”
UNS letter S indicates stainless steel

Stainless steels: “Austenitic stainless
steel”

Stainless steels: “Martensitic stainless
steel

Popular Stainless Steels
Figure 7-10 Popular alloys and key properties for different types of stainless
steels.

7.7 Tool Steels
 High carbon, high strength, ferrous alloys that have a
balance of strength, toughness , and wear resistance
 Tool Steels are a class of highly alloyed steels designed for use
as industrial cutting tools, dies and molds. They posses high
strength, hardness, hot hardness, wear resistance, and
toughness under impact.
 Types of tool steels
 Water-hardening tool steels (W)
 Least expensive method for small parts that are not subjected
to extreme temperatures
 Cold-work steels (O,A)
 Larger parts that must be hardened
 Oil or air quenched grades

Types of Tool Steels
 Shock resisting tool steels (S)
 Offers high toughness for impact applications
 High speed tool steels
 Used for cutting tools where strength and hardness are
needed at high temperatures
 Hot-work steels (H)
 Provide strength and hardness during high temperature
applications
 Plastic mold steels (P)
 Meets requirements of zinc die and plastic injection
molding
 Special purpose tool steels (L,F)
 Extreme toughness, extreme wear resistance

Cast Steels
 Ferrous casting alloy can classified by carbon contents:
 Cast steels - less than 2% carbon
 Cast iron – more than 2% carbon
 Cast steels are used whenever a cast iron is not
adequate
 Cast steels are stiffer, tougher, and more ductile over a
wider temperature range than cast iron
 Cast steels are easily welded, but have a higher melting
point, less fluidity, and increased shrinkage

The Role of Processing on Cast
Properties
Properties of metals are influenced by how they are
processed
For cast products, how they are solidified will
impact properties
Alloy cast irons and cast steels are specified by
ASTM designation
SAE has specification for cast steels used in
automotive industry

Summary
The processing of steels determines the final
material properties
Steel’s typically have high strength, rigidity, and
durability
Steel is recyclable
Different alloying elements may be added to
produce known effects to the material
Stainless steels are a commonly used steel that
have good corrosion resistance

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