Ferrous metals

Building Materials - II
Ferrous Metals

Introduction
• Metals are employed for various architectural/engineering purposes;
a) Structural members
b) Roofing materials
c) Damp-proof courses
d) Sanitary fittings, and water tanks
e) Doors and Windows etc.
• Out of all the metals used for architectural/engineering purposes, iron is the most popular metal used for
construction activities.
• It is estimated that it constitutes about 4.60% of the earth’s crust.
27-Apr-18 Ar. Rameez R. Gazi; Dept. of Architecture; NEHU 2

Introduction …
• Metals are grouped as :
a) Ferrous metals
b) Non-ferrous metals
• Iron – Latin – Ferrum (Fe)
• Ferrous metals contain iron as their main constituent.
• There are three important ferrous metals – cast iron, wrought iron and Steel.
• Non-ferrous metals do not contain iron as their main constituent.
• Some of the important non-ferrous metals – Aluminum, Copper, etc. (Have limited use for engineering
purposes.)

Iron ores
• It may be defined as a solid mineral aggregate which occurs naturally
• It is economically important as one or more valuable constituents may be extracted.
• The term gangue is used to indicate substances occurring along with ore.
• Iron ores are thus compounds of iron with non-metallic elements; they contain impurities such as carbon,
manganese, phosphorous, silicon and sulphur.

Selection of iron ore
• Iron ores are taken out or extracted from the earth’s subsurface.
• While selecting the site for such mining activities, following points should be carefully examined:
1) Iron ore should be rich in metallic iron content,
2) Mines should be suitably located – geographically and geologically,
3) Composition of gangue or substances associated with ore should also be carefully studied,
4) The treatment and preparation to be given to the iron ores to make them suitable for blast furnace
should be simple and cheap.

Important varieties of iron ores
• Following are the important commercial varieties of iron ore which are commonly used in the
manufacturing process:
a) Haematite – red oxide of Fe, contains about 65-70% of Fe; Iron black or steel grey in colour.
b) Limonite – Brown haematite, contains 60% of Fe; Brown, yellow brown or yellow in colour.
c) Magnetite – Black oxide of Fe, contains 70-73% of Fe when in pure state; black in colour.
d) Pyrite – Sulphide of Fe, contains 45-47% of Fe (max.); bronze yellow or pale brass yellow, higher
percentage of sulphur makes the resulting iron brittle.
e) Siderite – Carbonate of Fe, contains 40% of Fe (max.); pale yellow, brownish red or brownish black in
colour.

Pig iron
• Crude impure iron which is extracted from iron ores is known as pig-iron.
• It forms the basic material for the manufacture of:
a) Cast iron
b) Wrought iron
c) Steel

Manufacturing process of Pig iron
The following three distinct processes are involved in the manufacturing of Pig iron:
1. Dressing – the ore as obtained from the mines are crushed into pieces of 25mm Ø. This process is
performed in the ordinary rock crushers. The crushing of ores helps in two ways:
i. Particles of uniform size are obtained
ii. Reducing gases can penetrate the ores in a better way.
2. Calcination and roasting – after the iron ores are dressed, they are calcined and roasted. The calcination
consists in heating ores in presence of air so that they are oxidized. Water and CO2 are removed from the
ores by calcination.
3. Smelting – the process of melting in order to separate the metal from the ore is called smelting. It is
carried out in a special type of furnace called a blast furnace.

Blast Furnace

Properties of Pig Iron
Following are the properties of pig-iron:
1. It can be hardened but not tampered
2. It cannot be magnetised
3. It cannot be welded or riveted
4. It does not rust
5. It is difficult to bend
6. It is hard and brittle
7. It is neither ductile or malleable.
8. It melts easily and its fusion temperature is
1200oC
9. It possesses high compression strength.
10. It is weak in shear and in tension.

Cast iron
• cast iron is manufactured by remelting pig-iron with coke and limestone.
• The process of remelting is done in a cupola furnace.
Composition of Cast iron
• Contains about 2-4% of CARBON along with various impurities such as manganese, phosphorus, silicon and sulphur.
• MANGANESE makes cast iron brittle and hard – its amount should therefore be kept low (about 0.75%)
• PHOSPHORUS increases fluidity of cast iron. It also makes the cast iron brittle when the amount is more than 0.30%.
• SULPHUR makes cast iron brittle and hard. Its presence causes rapid solidification of cast iron and it ultimately
results in blow-holes and sand-holes. Its content should be kept below 0.10%.
• SILICON combines with part of iron and forms a solid solution. It also removes combined carbon from graphite form.
If its amount It less than 2.50%, it decreases shrinkage and ensures softer and better castings.

Types of Cast Iron
1. Grey cast iron – Made from grey pig-iron; it has a coarse crystalline structure; it is soft and is weak in strength; it melts
readily. It is extensively used for making castings.
2. White cast iron – It is silvery white in colour; it is hard and it melts with difficulty; it is not easily worked on machine; it
cannot be used for delicate casting.
3. Mottled cast iron – It is an intermediate variety between grey cast iron and white cast iron. This variety is used for small
castings.
4. Chilled cast iron – Chilling consists of making some portion of cast iron hard and other portion soft. It is
hard to a certain depth from the exterior surface and it is indicated by white iron, interior portion of the body of casting is
soft and it is made up of grey iron. It is used to provide wearing surfaces to the castings.
5. Malleable cast iron – A portion of carbon is extracted so that the cast iron becomes malleable. It is used for railway
equipment, automobiles, pipe fittings, agricultural implements, door fastenings, hinges, etc.
6. Toughened cast iron – This variety of cast iron is obtained by melting cast iron with wrought iron scrap. The proportion of
wrought iron scrap is about 1/4th to 1/7th of weight of cast iron.

Properties of cast iron
1. If placed in salt water, it becomes soft.
2. It can be hardened by heating and sudden cooling, but it cannot be tampered.
3. It cannot be magnetized and does not rust easily.
4. It is fusible, hard, but it is brittle as well; it lacks plasticity and hence it is unsuitable for the forging work.
5. It is not ductile and hence it cannot be adopted to absorb shocks and impacts.
6. Its melting temperature is about 1250°C, and shrinks on cooling. This fact is to be considered while making patterns or molds for
foundry work.
7. Its structure is granular and crystalline with whitish or greyish tinge and has a specific gravity is 7.5.
8. It is weak in tension and strong in compression. The tensile and compressive strengths of cast iron of average quality are
respectively 150 N/mm2 and 600 N/mm2.
9. The two pieces of cast iron cannot be connected by the process of riveting or welding. They are to be connected by nuts and bolts
which are fixed to the flanges. The holes for bolts, etc. are either drilled out or cast in the casting.

Uses of Cast Iron
• The use of cast iron is not recommended in horizontal direction either for heavy or variable loads or at places
where there are chances for the slightest shock to exist.
• Cast iron cracks and snaps suddenly when subjected to the shocks, overloading or fire without giving any
warning of approaching failure under such stresses.
• Following are the important uses of cast iron:
a) Making cisterns, water pipes, gas pipes and sewers, manhole covers and sanitary fittings.
b) Making ornamental castings such as brackets, gates, lamp posts, spiral staircases, etc.
c) Making parts of machinery which are not subject to heavy shocks.
d) Manufacturing compression members like columns in buildings, bases of columns, etc.
e) Preparing agricultural implements, rail chairs, carriage wheels, etc.

Wrought iron
• wrought iron is almost pure iron and it hardly contains carbon more than 0.15%.
• Its manufacturing process is very laborious.
• The following operations are involved in its manufacture:
a) Refining
b) Puddling
c) Shingling
d) Rolling

Properties of Wrought iron
1. It becomes soft at white heat and it can be easily forged and welded.
2. It can be used to form temporary magnets, but cannot be magnetized permanently.
3. It fuses with difficulty, therefore it cannot be adopted for making castings.
4. It is tough, ductile, malleable and is moderately elastic.
5. It is not affected by saline water and resists corrosion in a better way.
6. Its fresh fracture shows clear bluish colour with a high silky luster and fibrous appearance.
7. It has a melting point of about 1500°C, and specific gravity of about 7.8.
8. Its ultimate compressive strength is about 200 N/mm2, and ultimate tensile strength is about 400 N/mm2

Uses of Wrought iron
• It is used for rivets, chains, ornamental iron work, railway couplings, water and steam pipes, raw material for
manufacturing steel, bolts and nuts, horse shoe bars, handrails, straps for timber roof trusses, boiler tubes,
roofing sheets, armatures, electro-magnets etc.
• It is being replaced by mild steel to a great extent, thus it is produced to a very small extent at present.
• It is used where tough material is required.
Defects of Wrought iron
• The wrought iron which has become defective may either be cold short or red short.
• The cold short wrought iron is very brittle when it is cold. It cracks, if bent. It may however be worked at high
temperature. This defect occurs when phosphorus is present in excess quantity.
• The red short wrought iron possesses sufficient tenacity when cold. But it cracks when bent or finished at a red
heat. It is therefore useless for welding purpose. This defect occurs when sulphur is present in excess quantity.

Steel
• As far as the carbon content is concerned, the steel forms an intermediate stage between cast iron and wrought iron.
• cast iron contains 2 - 4% carbon; in wrought iron the carbon content does not exceed 0.15%; In steel, the carbon
content varies from anything below 0.25% to a maximum of l.50%.
• Carbon, if in excess of 1.5% does not combine with iron and it is present as free graphite. The dividing line of cast iron
and steel is the presence of free graphite. If there is no free graphite in the composition, it said to be steel whereas, the
presence of free graphite indicates that the material is cast iron.
• Cast iron can take up only compressive stresses and its use is limited to the compression members only. wrought iron is
a fibrous nature and it is suitable to resist tensile stresses.
• Columns of the skeleton of skyscrapers during the 19th century were of cast iron and the beams were of wrought iron.
• Steel was suitable for all constructional purposes in general and hence it has practically replaced cast iron and
wrought iron during late 19th century and is extensively used in present day practice of building construction. It
is equally strong in compression as well as in tension.

Manufacture of steel
Steel is manufactured by the following processes:
1. Bessemer process
2. Cementation process
3. Crucible steel process
4. Duplex process
5. Electric process
6. L.D. process
7. Open-hearth process

Uses of steel
• Depending upon the carbon content, the steel is designated as mild steel or medium carbon steel or high
carbon steel. Various uses of steel are governed by the amount of carbon contained in it.
• The carbon content of mild steel is about 0.10 to 0.25%. When carbon content is less than 0.10%, it is
known as the dead steel or very low carbon steel.
• The carbon content of medium carbon steel is about 0.25 to 0.60%.
• The high carbon steel, also known as hard steel and its carbon content varies from 0.60 to 1.10% or so.

Uses of Steel
Name of Steel Carbon content Application
a) Mild Steel • Upto 0.10% Motor body, sheet metal, tin plate, etc.
b) Medium carbon steel • Upto 0.25% Boiler plates, structural steel, etc.
• Upto 0.45% Rails, etc.
• Upto 0.60% Hammers, large stamping and pressing dies, etc.
c) High carbon steel or
hard steel
• Upto 0.75% Sledge hammers, springs, stamping dies, etc.
• Upto 0.90% Miner’s drills, smith’s tool, stone mason’s tools, etc.
• Upto 1.00% Chisels, hammers, saws, wood working tools, etc.
• Upto 1.10% Axes, cutlery, drills, knives, picks, punches, etc.

Factors affecting physical properties of steel
The physical properties of steel such as ductility, elasticity, strength etc. are greatly influenced by the
following three factors:
1. Carbon content – The variation in carbon percentage produces steel of different grades. Carbon always
assists in increasing the hardness and strength of steel. But at the same time, it decreases the ductility of
steel. Mild steel having carbon content of about 0.10 to 0.25% is widely used for structural work.
2. Heat treatment processes
3. Presence of impurities – Usual impurities in steel are silicon, sulphur, phosphorus and manganese.
a) If silicon content is less than 0.20%, it has no appreciable effect on the physical properties of steel. If
silicon content is raised to about 0.30 to 0.40%, the elasticity and strength of steel are considerably
increased without serious reduction in its ductility.

Factors affecting physical properties of steel …
The physical properties of steel such as ductility, elasticity, strength etc. are greatly influenced by the
following three factors:
3. Presence of impurities – Usual impurities in steel are silicon sulphur, phosphorus and manganese.
b) If sulphur content is between 0.02 to 0.10%, it has appreciable effect on the ductility or strength of
steel. It however decreases malleability and weldability of hot metal. The excess of sulphur decreases
strength and ductility of steel.
c) The phosphorus produces detrimental effects on steel. It is desirable to keep its content below 0.12%.
It reduces shock resistance, ductility and strength of steel.
d) Manganese helps to improve the strength of mild steel. Its desirable content is between 0.30 to 1.00%.
Steel becomes brittle and loses its structural value when the content exceeds bout 1.50%.

Magnetic properties of steel
• The steel is also widely used In electrical machinery, generators, transformers, etc. To make steel suitable for
such use, its magnetic properties are given utmost importance and these properties are obtained by carefully
adjusting its chemical composition.
• Following are the proportions of various elements in steel which helps it to achieve better magnetic properties:
a) Carbon – It is desirable to keep carbon content as low as possible and it should not exceed 0.10%
b) Silicon – Presence of silicon results in considerable increase of electrical losses, hence it is highly undesirable.
c) Sulphur and phosphorus – If combined content of sulphur and phosphorus exceeds about 0.3%, the magnetic
properties of steel are greatly affected.
d) Manganese – If content of manganese exceeds about 0.30% it proves to be injurious to the magnetic properties
of steel.

Defects in steel
Common defects seen in steel are s follows:
a) Cavities or blow holes – These are formed when gas is confined or imprisoned in the molten mass of
metal. Such confined gas produces cavities or blow-holes on solidification of metal.
b) Cold shortness – The steel, having this defect, cracks when it is worked upon in cold state. This defect is
due to the presence or excess amount of phosphorus.
c) Red shortness – The steel, having this defect, cracks when it is worked upon in hot state. This defect is
due to the presence of excess sulphur.
d) Segregation – Some constituents of steel solidify at an early stage and they separate out from the main
mass. This is known as the segregation and it is prominent on the top surface of the ingots or castings.

Market forms of steel
1. Angle sections
2. Channel sections
3. Corrugated steel
4. Expanded metal
5. Flat bars
6. I – Sections
7. Plates
8. Ribbed – torsteel bars
9. Round bars
10. Square bars
11. T - sections

Properties of mild steel
• It can be magnetized permanently.
• It can be readily forged and welded.
• It cannot be easily hardened and tempered.
• It has a fibrous structure.
• It is malleable and ductile.
• It is not easily attacked by salt water.
• It is tougher and more elastic than wrought iron.
• It is used for all types of structural work.
• It rusts easily and rapidly.
• It has a melting point of about 1400°C.
• Its specific gravity is 7.80.
• Its ultimate compressive strength is about 80 to 120
kN/cm2.
• Its ultimate tensile and shear strengths are about 60 to
80 kN/cm2.

Properties of hard steel
• It can be easily hardened and tempered.
• It can be magnetized permanently.
• It cannot be readily forged and welded.
• It has granular structure.
• It is not easily attacked by salt water.
• It is tougher and more elastic than mild steel.
• It is used for finest cutlery, edge tools and for parts
which are to be subjected to shocks and vibrations.
• It rusts easily and rapidly.
• It has a melting point of about 1300°C.
• Its specific gravity is 7.90.
• Its ultimate compressive strength is about 140 to
200 kN/cm2.
• Its ultimate shear strength is about 110 kN/cm2.
• Its ultimate tensile strength is about 80 to 110 kN
/cm2.

Assignments
1) What are the operations involved in the manufacture of Wrought iron?
2) What are the various manufacturing process of steel?
3) What are the various forms in which steel is available in the market?
Note:
• Assignments shall be as a group work.
• It should be presented as a poster comprising of neat sketches, info-graphic charts etc. and the content or
working principle etc. shall be explained to the audience by the group.

Ferrous metals

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