IRON & ITS PROPERTIES

IRON

Pure iron is a metal It oxidizes readily in the presence of

oxygen and moisture. In order to obtain metallic iron, oxygen must be removed from naturally occurring ores by chemical reduction.

The properties of iron can be modified by alloying it with various other metals (and some non-metals, notably carbon and silicon) to form steels.

Engineering Applications

The Construction Of Machinery And Machine Tools,

Automobiles, The Hulls Of Large Ships, And Structural Components For Buildings Rail Transportation Oil And Gas Industries Electrical Equipment Appliances And Utensils

Commercial Iron

Since pure iron is quite soft, it is most commonly used in the form of steel. Some of the forms in which iron is produced commercially include:

Pig iron has 3.5–4.5% carbon Cast iron contains 2–4% carbon, 1–6%

silicon, and small amounts of manganese

Wrought iron contains less than 0.25% carbon.

Wrought Iron

An iron alloy with a very low carbon content.

has fibrous inclusions, known as slag. is tough, malleable, ductile and easily

welded. A modest amount of wrought iron was

used as a raw material for manufacturing of steel, which was mainly to produce swords, cutlery and other blades.

Wrought Iron

Wrought iron lacks the carbon content necessary for hardening through heat treatment.

An advantage of its low carbon content is its excellent weldability

sheet wrought iron cannot bend as much as steel sheet metal

Wrought iron can be cast, but no engineering advantage in that.

Cast Irons

White cast iron is named after its white surface when fractured, due to its carbide impurities which allow cracks to pass straight through.

Grey cast iron is named after its grey fractured surface, which occurs because the graphitic flakes deflect a passing crack and initiate countless new cracks as the material breaks.

Cast Irons

Cast iron tends to be brittle. low melting point, good fluidity, castability, excellent machinability, resistance to deformation, and wear

resistance

Cast Irons

Chemical composition

Material Fe C Mn S P Si

Pig iron 91–94 3.5–4.5 0.5–2.5 0.018–0.1 0.03–0.1 0.25–3.5

Carbon steel

98.1–99.5 0.07–1.3 0.3–1.0 0.02–

0.060.002–0.1

0.005–0.5

Wrought iron 99–99.8 0.05–

0.25 0.01–0.1 0.02–0.1 0.05–0.2 0.02–0.2

Grey Cast Iron

remainder 2.5-3.4 0.5-0.8 0.06-

0.12 0.1-0.9 1.8-2.5

Malleable Iron

remainder 2.2-2.8 0.25-0.6 0.05 <0.18 0.8-1.5

Effect of chemical composition %C: Carbon is often added to increase its hardness.

However, the increased hardness comes with a disadvantage -it is much less ductile. Careful control of the heat treatment allows one to control hardness and ductility.

%P: Phosphorus can have beneficial as well as harmful effects. The addition of only 0.17% phosphorus increases both the yield and tensile strength of low-carbon sheet steel. cold-forming applications. deep drawability. improve machining characteristics and atmospheric corrosion resistance.

Detrimental effects of phosphorus include various forms of embrittlement which reduce the toughness and ductility

Effect of chemical composition %S: it increases machinability. The amount

generally used for this purpose is from 0.06 to 0.30%. Sulphur is detrimental to the hot forming properties.

%Mn: It is normally present in all steel and functions both as a deoxidizer and also to impart strength and responsiveness to heat treatment. Usually present in quantities from 0.5% to 2%, but certain special steels are made in the range of 10% to 15%.

Effect of chemical composition %Si: Silicon is one of the common

deoxidizers used during the process of manufacture. has a beneficial effect on certain properties such as tensile strength. In higher percentages, silicon is added as an alloy to produce certain electrical characteristics.

Physical properties

Material

Densitykg/m3

*10³

Melting Point 0 C

Specific Heat J/kg0 K

Thermal Cond. W/m0

K

Electric resistivity Ohm*m

Coefficient of thermal expansion10-6/C at 20 °C

Carbon steel

7.872 1425-1540

481 64.9 1.40*10-

7

10.8

Wrought iron

7.5–7.8 1540 500 59 11.1

Grey Cast Iron

7.06-7.34

1175-1290

460 46-79 1.1*10-7 10.8

Malleable Iron

7.2- 7.45

1300 461 36 3.9*10-7 11.5

Physical Properties

Density: important with respect to strength:weight

Specific heat capacity: the measure of the heat energy required to increase the temperature of a unit quantity of a substance by unit degree. lower this value, higher is the temperature rise in the material.

Thermal Conductivity: the property of a material that indicates its ability to conduct heat.

Physical Properties

Electric Resistivity: a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge.

Coefficient of Thermal Expansion: is a thermodynamic property of a substance. It relates the change in temperature to the change in a material's linear dimensions. It is the fractional change in length per degree of temperature change.

Mechanical Properties

Material

Tensile Strength(MPa)

Elongation%

Hardness(HB)

Yield strength (MPa)

Poisson’s Ratio

Young’s Modulus(GPa)

Carbon steel

295 30 49 (RB) 165 0.303 200

Wrought iron

234–372 159–221

0.278 193

Grey Cast Iron

276 1 180-302 0.211 60,000 psi

Malleable Iron

586 20 217-269 483 0.271 172

Mechanical Properties

Tensile Strength: maximum load that a material can support without fracture when being stretched, divided by the original cross-sectional area of the material.

Yield Point: stress at which material yields & begins to deform plastically.

Poisson’s Ratio: The absolute value of the ratio of the lateral to longitudinal strains

Poisson’s Ratio

Mechanical Properties

Ductility: The ability of a material to undergo plastic deformation without fracture.

Brittleness: Material behaviour where fracture takes place with little or no plastic deformation.

Elongation: Increase in length in tensile testing, usually expressed as a %age of the original gage length.

Young’s Modulus: The ratio of stress to strain in the elastic range in tension or compression.

Other properties

Material properties that influence their castability include their pouring temperature, fluidity, shrinkage, and slag/dross formation tendencies.

Alloys of Iron

Carbon steel contains 2.0% carbon or less, with small amounts of Mn, S, P, and Si.

Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they can usually only be justified for specialist uses.

Disadvantages of Iron

Advantages: Tough and durable Available in various types i.e. cast iron, wrought

iron etc. Provides high security Resistant to termite

attack Disadvantages: Rust and corrode easily when

exposed to water and air. Need high finish (paint etc.) to prevent rusting. Iron is good conductor of heat, It become very

hot to touch in hot days.

Properties of Iron

forges as if it were clay it takes on texture, chisels Highly plastic, spreads and draws out

with ease. Cleaned easily to give a bright silvery finish.

With continuous hot bending the material showed no sign of cracking that would have occurred with mild steel had it been subjected to the same treatment

Magnets

Soft magnets have high permeability. Used in generators, electromagnets, transformers.

Pure iron used in elctrotransformers. Permeability is prop to MS

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