Basic Civil Engineering

Ferrous Metals

A ferrous material is the one in which iron is a main constituent. Iron ore is first converted into pig iron and then pig iron is subjected to various metallurgical processes to mix different percentage of carbon and to get the following three useful ferrous materials:
1. Cast iron—carbon content 1.7% to 4.5%
2. Wrought iron—carbon content 0.05% to 0.15%
3. Steel—carbon content 0.25% to 0.25%.
All ferrous materials contain about 0.5 to 3% silica, less than 2% manganese, 0.15% sulphur and 0.6% phosphorous.
1. Cast Iron:

Important properties of cast iron are:
(a) Compression strength is 700 N/mm2 and tensile strength is 150 N/mm2.
(b) It is brittle and does not absorb shocks
(c) Its specific gravity is 7.5.
(d) Its structure is coarse, crystalline and fibrous.
(e) It cannot be magnetised.
(f) It does not rust-easily.
(g) It has low melting point of about 1200°C.

Uses of Cast Iron:
(a) 1. It is used for making rain water and sanitary pipes, sanitary fittings and manhole covers.
2. It is used for making railings and spiral stair cases.
3. Fire gratings, cover for pumps and motors and brackets are made with cast irons.

2. Wrought Iron: It is almost pure iron. It contains less than 0.15% carbon. Attempts are made
to reduce the other impurities during the process of manufacturing.

Properties of Wrought Iron:
1. Its ultimate compressive strength is 200 N/mm2 and ultimate tensile strength is 375 N/mm2.
2. It is ductile and brittle.
3. Its unit weight is 77 kN/m3.
4. It melts at about 1500°C. It becomes so soft at 900°C that two pieces can be joined by hammering.
5. It can absorb shocks very well.
6. It forms temporary magnets but it cannot be magnetised permanently.
7. It rusts more easily.

Uses of Wrought Iron:
1. It is used for making nails nuts and botts, wires and chains.
2. It is used for making roofing sheets, grills, fences, window gaurds etc.
3. Steel: It is extensively used building material. The following three varieties of steel are extensively used:
(a) Mild steel
(b) High carbon steel and
(c) High tensile steel.
(a) Mild Steel: It contains a maximum of 0.25% carbon, 0.055% of sulphur and 0.55% of phosphorus.

Properties of Mild Steel:
(i) It is malleable and ductile
(ii) It is more elastic
(iii) It can be magnetized permanently.
(iv) Its specific gravity is 7.8.
(v) Its Young’s modulus is 2.1 × 105 N/mm2.
(vi) It can be welded easily.
(vii) It is equally strong in tension and in compression.

Uses of Mild Steel:
(i) Round bars are extensively used as reinforcement in R.C.C. works.
(ii) Rolled sections like I, T, L, C, plates etc. are used to build steel columns, beams, trusses etc.
(iii) Tubular sections are used as poles and members of trusses.
(iv) Plain and corrugated mild steel are used as roofing materials.
(v) Mild steel sections are used in making parts of many machineries.

(b) High Carbon Steel: The carbon containts in this steel is 0.7% to 1.5%.
Properties of Carbon Steel:
(i) It is more tough and elastic compared to mild steel.
(ii) Welding is difficult.
(iii) It can be magnetized permanently.
(iv) It is stronger in compression than in tension.
(v) It withstands shocks and vibrations better.
Uses of High Carbon Steel:
(i) It is used for making tools such as drills, files, chisels.
(ii) Many machine parts are made with high carbon steel since it is capable of withstanding
shocks and vibrations.
(c) High Tensile Steel: It contains 0.8% carbon and 0.6% manganese. The strength of this steel
is quite high. High tensile steel wires are used in prestressed concrete works.

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