Ferrous and non ferrous alloys by Hari Prasad

FERROUS AND

NON-FERROUS ALLOYS

Unit – 7

Alloys

Ferrous(Iron based )

Non-ferrous(No-iron content)

Engineering Materials

Metals

Ferrous

Iron

Steel

Pig iron

Cast iron

Wrought iron

Non-Ferrous

Copper & Alloys

Aluminium

Zinc

Tin

Lead

Non-Metals

Rubber

Plastics

Resin

FERROUS METALS AND ALLOYS

What is a ‘ferrous metal’ or ‘ferrous alloy’?

It is simply a metal or alloy that contains Iron (the element ferrous) as the base (starting) metal.

26th element Iron or Ferrous 55.85 Atomic Mass

http://www.radiochemistry.org/periodictable/elements/images/26.gif

GENERAL CATEGORIES OF FERROUS METALS AND ALLOYS

Carbon and alloy steels Stainless steel Tool and Die steel Cast Irons Cast Steels

**Ferrous tools first appear about 4000 to 3000 BC, made from meteoritic iron.

Real ironworking started in about 1100 BC in Asia Minor, and started the Iron Age.

PRODUCTION OF IRON AND STEEL

RAW MATERIALS FOR PRODUCTION

Iron Ore

Limestone ----------

Coke

IRON ORE

Abundant, makes up 5% of earth’s crust Is not found in ‘free state’, must be found

in rocks and oxides, hence Iron ore. After mining, the ore is crushed and the

iron is separated, then made into pellets, balls or briquettes using binders, such as water.

The pellets are typically 65% iron, and about 1” in diameter.

COKE

Coke is formed by heating coal to 2100*F (1150 C), then cooling it in quenching towers.

You need more than Iron? Why coke is used…

1. Generates high heat, needed in order for chemical reactions in iron making to take place.

2. Produces CO (carbon monoxide) which reduces

iron-oxide to Iron.

LASTLY, LIMESTONE

Limestone (calcium carbonate) is used to remove impurities.

When the metal is melted, limestone combines with impurities and floats to the top of the metal, forming slag.

The slag can then be removed, purifying the iron.

Ferrous alloys

Steels (C% is <2.1)

Cast irons (C% is >2.1)

Ferrous alloys can be broadly classified into 2 groups:

1. Steels (C% is <2.1)

2. Cast iron (C% is >2.1-6.67)Steels have carbon in the combined

form (austenite, cementite etc.)Cast irons have carbon in the free form

as graphiteThese ferrous alloys are not only iron

and carbon alloys, few other alloying elements are also added for special properties

STEELS

Steels can be classified in many ways, the basic classification of steel according to:

Types of steel based upon deoxidization process

Carbon content Grade Method of manufacture Applications Standard institutions

KILLED – SEMI-KILLED – RIMMED STEEL

Killed Steel – This is a fully deoxidized steel, and thus, has no porosity. This is accomplished by using elements

like aluminum to de-oxidize the metal. The impurities rise and mix with the slag.

It is called killed because when the metal is poured it has no bubbles, it is quiet.

Because it is so solid, not porous, the ingot shrinks considerably when it cools, and a “pipe” or “shrinkage cavity” forms. This must be cut off and scrapped.


Semi-Killed Steel: This is practically the same as killed steel, with some minor differences. It is only partially de-oxidized, and

therefore, is a little more porous than killed steel.

Semi-Killed does not shrink as much as it cools, so the pipe is much smaller and scrap is reduced.

It is much more economical and efficient to produce.


Rimmed Steel: This is produced by adding elements like aluminum to the molten metal to remove unwanted gases. The gasses then form blowholes around the rim. Results in little or no piping. HOWEVER, impurities also tend to

collect in the center of the ingot, so products or rimmed steel need to be inspected and tested.

CARBON STEELSLow alloy

Low carbon High carbon

High alloy

Tool Stainless

Medium carbon

LOW CARBON STEEL

These steels contain less than about 0.25 wt% C These unresponsive to heat treatment because of

very less amount of martensite Can be strengthened by cold work Microstructures consist of ferrite and pearlite

constituents these alloys are relatively soft and weak but have outstanding ductility and toughness; in addition, they are machinable, weldable, and, of all steels, are the least expensive to produce

Applications

Bridges, towers, support columns in high-rise buildings, and pressure vessels

MEDIUM CARBON STEEL These steels have 0-25 – 0.6 wt% C It is stronger than low carbon steel but

less tougher than it These alloys may be heat-treated by

austenizing, quenching, and then tempering to improve their mechanical properties

These steels are often called machinery steels

Applications These are used for making camshafts,

connecting rods, gears, piston rods, etc.

HIGH CARBON STEELS These steels have 0.6 – 2.1 wt% C These are mainly tool steels They have very good hardness and wear

resistance values The tool and die steels are high-carbon

alloys, usually containing chromium, vanadium, tungsten, and molybdenum.

These alloying elements combine with carbon to form very hard and wear resistant carbide compounds (e.g., Cr23C6, V4C3, and WC

These steels are utilized as cutting tools and dies for forming and shaping materials, as well as in knives, razors, hacksaw blades, springs, and high-strength wire

High Carbon Steel Nails

HIGH ALLOY STEELS Alloying elements are added to steel for

many purposes:

i. To improve strength

ii. To increase the hardenability

iii. To improve wear and abrasion resistance

iv. To improve oxidation and corrosion resistance

v. To increase high temperature resistance

vi. To increasing the toughness with retaining strength

ALLOYING ELEMENTS USED IN STEEL

Manganese (Mn) combines with sulfur to prevent

brittleness >1%

increases hardenability

11% to 14% increases hardness good ductility high strain hardening capacity excellent wear resistance

Ideal for impact resisting tools


Sulfur (S)

Imparts brittleness Improves machinability Okay if combined with Mn Some free-machining steels

contain 0.08% to 0.15% S Examples of S alloys:

11xx – sulfurized (free-cutting)


Nickel (Ni)

Provides strength, stability and toughness, Examples of Ni alloys: 30xx – Nickel (0.70%), chromium (0.70%) 31xx – Nickel (1.25%), chromium (0.60%) 32xx – Nickel (1.75%), chromium (1.00%) 33XX – Nickel (3.50%), chromium

(1.50%)

ALLOYING ELEMENTS USED IN STEELChromium (Cr)

Usually < 2% increase hardenability and strength Offers corrosion resistance by forming stable oxide

surface typically used in combination with Ni and Mo

30XX – Nickel (0.70%), chromium (0.70%) 5xxx – chromium alloys 6xxx – chromium-vanadium alloys 41xxx – chromium-molybdenum alloys

Molybdenum (Mo) Usually < 0.3% increase hardenability and strength Mo-carbides help increase creep resistance at elevated

temps typical application is hot working tools


Vanadium (V) Usually 0.03% to 0.25% increase strength

without loss of ductility

Tungsten (W) helps to form stable carbides increases hot hardness

used in tool steels


Copper (Cu) 0.10% to 0.50% increase corrosion resistance Reduced surface quality and hot-working

ability used in low carbon sheet steel and structural

steels

Silicon (Si) About 2% increase strength without loss of ductility enhances magnetic properties


Boron (B) for low carbon steels, can

drastically increase hardenability improves machinability and cold

forming capacity

Aluminum (Al) deoxidizer 0.95% to 1.30% produce Al-nitrides during Nitriding

Alloying elements

Carbide forming

elements

Graphitizing elements

Austenite stabilizers

ferrite stabilizers

Cr, W, Ti, V, Mo,

Mn

Si, Co, Al, Ni

Mn, Ni, Co, Cu

Cr, W, Mo, Si

EFFECT OF ALLOYING ELEMENTS ON STEEL

Elements which tend to form carbides: Chromium, Tungsten, Titanium, Vanadium, Molybdenum, Manganese etc.

Elements which tend to graphitize carbon: these elements are added to oppose the formation of carbides and they stabilize the carbon to occur in its free form as graphite. E.g.: Si, Co, Al, Ni etc.

Austenite stabilizers: these elements raise the peritectic point, increase the austenite range, and stabilize the austenite. E.g. Mn, Ni, Co, Cu

EFFECTS OF ELEMENTS ON STEELS Boron: Improves hardenability without the loss of (or

even with some improvement in) machinability and formability.

Calcium: Deoxidizes steels, improves toughness, and may improve formability and machinability.

Carbon: improves hardenability, strength, hardness, and wear resistance; it reduces ductility, weldability, and toughness.

Cerium: controls the shape of inclusions and improves toughness in high-strength low alloy steels; it deoxidizes steels.

Chromium: improves toughness, hardenability wear and corrosion resistance, and high-temperature strength; it increases the depth of the hardness penetration resulting from heat treatment by promoting carburization.

Cobalt: improves strength and hardness at elevated temperatures.

EFFECTS OF ELEMENTS ON STEELS

Copper: improves resistance to atmospheric corrosion and, to a lesser extent, increases strength with little loss in ductility; it adversely affects the hot-working characteristics and surface quality.

Lead: improves machinability; it causes liquid-metal embrittlement.

Magnesium: has the same effects as cerium. Manganese: improves hardenability, strength,

abrasion resistance, and machinability; it deoxidizes the molten steel, reduce shot shortness, and decreases weldability.

Molybdenum: improves hardenability, wear resistance, toughness, elevated-temperature strength, creep resistance, and hardness; it minimizes temper embrittlement.

EFFECTS OF ELEMENTS ON STEELS

Nickel: improves strength, toughness, and corrosion resistance; it improves hardenability.

Niobium (columbium): imparts fineness of grain size and improves strength and impact toughness; it lowers transition temperature and may decrease hardenability.

Phosphorus: improves strength, hardenability, corrosion resistance, and machinability; it severely reduces ductility and toughness.

Selenium: improves machinability. Silicon: improves strength, hardness, corrosion

resistance, and electrical conductivity; it decreases magnetic-hysteresis loss, machinability, and cold formability.

Sulphur: Improves machinability when combined with manganese; it lowers impact strength and ductility and impairs surface quality and weldability. But decreases the high temperature strength.

Tantalum: has effects similar to those of niobium. Tellurium: improves machinability, formability, and

toughness. Titanium: improves hardenability; it deoxidizes

steels. Tungsten: has the same effects as cobalt. Vanadium: improves strength, toughness, abrasion

resistance, and hardness at elevated temperatures; it inhibits grain growth during heat treatment.

Zirconium: has the same effects as cerium

HIGH ALLOYED STEELS

Tool steels Stainless steels

Tool and die steels are alloyed steels design for high strength, impact toughness, and wear resistance at normal and elevated temperatures.

High-speed steels Maintain their hardness and strength at elevated operating temperatures.

There are two basic types the M-series and T-series

TOOL AND DIE STEELS

M-series contain 10 % molybdenum and have higher abrasion resistance than T- series

T- Series contain 12 % to 18 % tungsten. They undergo less distortion in heat treatment and are less expensive than the M-series.

M- series steel drill bits coated with titanium

Dies are tools used for drawing wire, and for blanking, bending, cutting, machine forging, and embossing. . H-series (Hot-working steels) for use at

elevated temperatures. They have high toughness and high resistance to wear and cracking.

S-series (shock resisting steels) designed for impact toughness.

Defining property AISI-SAE grade Significant characteristics

Water-hardening W

Cold-working

O Oil-hardening

A Air-hardening; medium alloy

D High carbon; high chromium

Shock resisting S

High speedT Tungsten base

M Molybdenum base

Hot-working H

H1–H19: chromium baseH20–H39: tungsten baseH40–H59: molybdenum base

Plastic mold P

Special purposeL Low alloyF Carbon tungsten

STEEL SPECIFICATIONS

The steels are sold with standard specifications and associated notations

Some knowledge of the specifications is essential

These specifications and notations may vary from country to country

In India not only the knowledge the of the Indian standard specifications is essential, but the familiarity with American, British , etc. standards is essential

INDIAN STANDARD SPECIFICATIONS

The steels have been classified on the basis of properties, and the chemical compositions

Code designation based on Mechanical properties E.g.

Fe E 210 – steel with minimum yield strength = 210N/mm2

St E 250 – steel with minimum yield strength = 250 kg/mm2

Code designation based on chemical composition

E.g. C15 – C=0.15% 30C5 – C=0.30; Mn=0.5% 37Mn2 – C=0.37%; Mn=2.0%

AISI/SAE SPECIFICATIONS The American Iron and Steel Institute and

Society of Automotive Engineers have cooperated together and have similar specifications based on chemical compositions of the steel.

The specifications normally have four numerical digits (sometimes 5 digits)

A=Alloy steel, basic open - hearth B=carbon steel, acid bessemer C=carbon steel, basic open-hearth D=carbon steel, acid open-hearth E= electric furnace steel

AISI CXXXX: is the basic open hearth carbon steel due to the letter prefix ‘C’. The first digit of the numerical represents the following types of steels

1= Carbon steel 2= Ni steel 3= Ni-Cr Steel 4= Mo steel 5= Cr steel 6= Cr-V steel 7= W steel 8= Ni-Cr-Mo(Low)- Triple alloy steel 9= Si-Mn Steel

AISI A X X XX

Indicates the method of steel making Type of steel

% of main alloying element

Indicate Carbon points

STAINLESS STEELS Excellent corrosion resistance Contain 12 to 30% Chromium

Cr oxidizes easily and forms a thin continuous layer of oxide that prevents further oxidation of the metal

Cr is a ferrite stabilizer

Austenite is restricted to a small region of the phase diagram

•Ferritic Stainless Steels are essentially Fe-Cr Alloys• Ferrite phase (bcc structure)•Inexpensive, high strength

Austenitic Stainless Steels Nickel is an austenite stabilizer. The addition of both Cr and Ni

results in the austenite (g, fcc) phase being retained to room temperature

The austenite phase is very formable (fcc structure)

Ni makes these alloys expensive

Martensitic Stainless Steels Have both Cr and C There is more Cr than in ferritic SS

since Cr tends to form Cr23C6, which removes available Cr for corrosion protection

Can be heat treated to high strength

STAINLESS STEELS

The reason for the name stainless is due to the fact that in the presence of oxygen, the steel develops a thin, hard, adherent film of chromium. Even if the surface is scratched, the protective

film is rebuilt through passivation. For passivation to occur there needs to be a minimum

chromium content of 10% to 12% by weight.

MAGNETIC ALLOYS Magnetic alloys are the combination of Iron, Nickel, and Cobalt

They are classified into:

Soft magnetic materials: where the hysteresis loop is very thin and these alloys posses high permeability (used in transformer cores).E.g. Permalloy (45%Ni)

Hard magnetic materials: are those whose hysteresis loop gives a large area under the B-H Curve. These all are used for permanent magnetic materials and used for magnetic poles for alternators and motors

E.g. Alnico= Ferrous alloy with

Al, Ni, Co

It has high magnetic coercivity (resistance

to loss magnetism)

CAST IRONS Fe-C alloys with 2-4%C 1-3% Si is added to improve castability Phase diagram shows graphite rather than Fe3C

since C may be present in the form of both graphite and cementite

Temperatures and compositions are different from the Fe-Fe3C diagram

Features: Low melting temperature (1153ºC to 1400ºC) Low shrinkage Easily machinable Low impact resistance Low ductility

GRAY CAST IRON

Gray iron 2.5-4% Carbon graphite flakes weak & brittle under

tension stronger under

compression excellent vibrational

dampening wear resistant High fluidity Used for pressure

vessels, clutch plates, base structure for machines

DUCTILE IRON (SG)

Ductile iron (SG) add Mg or Ce graphite in nodules not

flakes matrix often pearlite -

better ductility

White iron <1wt% Si so harder but brittle 1.8-3.2% Carbon more cementite

Fe3C-light phase, Pearlite dark phase

Fracture surface – whitish surface

Malleable iron heat treat at 800-900ºC graphite in rosettes more ductile

NONFERROUS ALLOYS

Non Ferrous Alloys

• Al Alloys

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

aircraft parts & packaging)

• Mg Alloys

-very low r : 1.7g/cm3 -ignites easily

- aircraft, missiles

• Refractory metals

-high melting T -Nb, Mo, W, Ta

• Noble metals

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

• Ti Alloys

-lower r: 4.5g/cm3

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

• Cu Alloys

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

OVER VIEW OF NON-FERROUS ALLOYS

NON-FERROUS ALLOYS

Among the above Al, Mg, and Ti alloys are called “Light Alloys”

COPPER AND ITS ALLOYS

PROPERTIES OF COPPER

Excellent electrical conductivity: next to silver

Excellent thermal conductivity: used in heat exchangers, boiler tubes and parts

Good ductility and malleability: can be drawn into wires easily

Good corrosion resistance: used in fuel and oil lines in aircrafts

Copper is non magnetic

CLASSIFICATION OF CU-ALLOYS

1. Brasses (Cu + Zn)

2. Bronzes (Cu + Sn, Al, Si, Be)

3. Cupronickels (Cu + Ni)

4. Nickel silver (Cu + Ni, Zn)

Recording Brass trumpetBronze Coin

Cupronickel piping system

Nickel Silver is also known as German Silver, Argentan, New Silver, and Nickel Brass

Nickel Silver is used in saxophones and cutlery

A German Silverhair comb

BRASS

Copper and zinc form solid solution up to ~ 39% zinc at 456oC, giving a wide rage of properties.

Sn, Al, Si, Mg, Ni, and Pb are added elements, called ‘alloy brasses’.

Commercially used brasses can be divided into two important groups:

1) α brasses (hypo-peritectic) with α structure containing up to ~35% Zn.

2) α+β brasses (hyperperitectic) with α+β two phase structure, based on 60:40 ratio of Cu and Zn

α phase – FCC structure β phase – BCC structure (disordered) β’ phase – BCC structure (ordered) γ phase – complex structure (brittle)

Alpha Brasses are classified as:

i. Yellow alpha brass

ii. Red brass

ALPHA-BRASSES

Alpha – brasses having up to 20% Zn are reddish in colour, and are often called red – brasses

When the Zn is between 20% to 36% and are called yellow brasses

Season cracking occurs in alpha – brasses when intergranular corrosion occurs specially in ammonia atmosphere

As high residual stresses are responsible for season cracking, the defect can be avoided if alpha brasses are stress annealed at 7500C

Α+Β BRASSES

40% Zn addition provides a complex structure of α and β phases.

60%Cu-40%Zn (Muntz metal) is the most widely used.

These brasses are stronger and have very good wear resistance

They have low ductility at room temperature

Can’t be cold worked that easily

BRONZE

It is an alloy of Copper and Tin (Cu + Sn)

The addition of tin increases the strength significantly but ductility drops

There are different kinds of bronzes:

i. Tin Bronzes (Phosphor Bronzes)

ii. Silicon Bronzes

iii. Aluminum Bronzes

iv. Beryllium Bronzes

TIN BRONZES Wrought Cu-Sn bronzes contain about

1-10% Cu,

1.25-10% Sn

with up to 0.1% P; hence usually called phosphor bronzes. ‘P’ is added as deoxidizing agent to

improve castability. The wrought tin bronzes possess

higher strength than brasses, especially in the cold-worked condition and has better corrosion resistance.

TYPES OF TIN BRONZES 1. Admiralty gun metal: Cu = 88%, Sn =

10%, Zn 2% (Used for steam pipe fittings and bearings)

2. Bell metal: Cu = 70%, Sn = 30%

Gun metal products

Ferrous and non ferrous alloys by Hari Prasad

Engineering

Transcript of Ferrous and non ferrous alloys by Hari Prasad