Learning Objectives:

• To understand where metals come from and how they are prepared for use.

• To look at examples of ferrous metals and to know the properties of different ferrous metals.

• Mild Steel - Carbon content of 0.1 to 0.3% and Iron content of 99.7 -99.9%. Used for engineering purposes and in general, none specialised metal products.

• Carbon steel -Carbon content of 0.6 to 1.4% and Iron content of 98.6 to 99.4%. Used to make cutting tools such as drill bits.

• Stainless Steel - Made up of Iron, nickel and chromium. Resists staining and corrosion and is therefore used for the likes of cutlery and surgical instrumentation.

• Cast Iron - Carbon 2 - 6% and Iron at 94 to 98%. Very strong but brittle. Used to manufacture items such as engine blocks and manhole covers. Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. The alloy constituents affect its colour when fractured:

  1. White cast iron has carbide impurities which allow cracks to pass straight through.

  2. Grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks.

  3. Malleable iron is cast as white iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form.

• Wrought Iron -Composed of almost 100% iron. Used to make items such as ornamental gates and fencing.

Plain Carbon Steel: These steel contain carbon as their primary alloying element. Low carbon(upto 0.2% C) and medium carbon (0.2 to 0.6% C) are used for piping, plant fabrication and other applications. High carbon steel (above 0.6% C) are subjected to heat treatment.

Solved Example: 52-1-01

A ferrous metal or alloy contains: (SSC JE ME Sep 2019)

A. Copper

B. Iron

C. Tin

D. Zinc

Ferrous Metals mostly contain Iron. They have small amounts of other metals or elements added, to give the required properties. Non-Ferrous Metals do not contain Iron, are not magnetic and are usually more resistant to corrosion than ferrous metals.

Correct Answer: B

Solved Example: 52-1-02

A reversible change in the atomic structure of steel with corresponding change in the properties is known as:

A. Molecular change

B. Physical change

C. Allotropic change

D. Solidus change

Correct Answer: C

Solved Example: 52-1-03

The metallic structure of mild steel is:

A. Body centered cubic

B. Face centered cubic

C. Hexagonal close packed

D. Cubic structure

Correct Answer: A

Solved Example: 52-1-04

For the allotropic forms of iron, the points of arrest are:

A. The points where no further change occurs

B. Constant for all metals

C. The points where there is no further flow of metal

D. The points of discontinuity

Correct Answer: D

Solved Example: 52-1-05

The percentage of carbon in pig iron varies from: (NRL GET Mech Sep 2021- Shift I)

A. 0.1 to 1.2%

B. 1.5 to 2.5%

C. 2.5 to 4%

D. 4 to 4.5%

Correct Answer: D

Solved Example: 52-1-06

Mild steel belongs to the following category:

A. Low carbon steel

B. Medium carbon steel

C. High carbon steel

D. Alloy steel

Mild steel (steel containing a small percentage of carbon, strong and tough but not readily tempered), also known as plain-carbon steel and Low carbon steel. It is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications. Mild steel contains approximately 0.05 - 0.25% carbon making it malleable and ductile.

Correct Answer: A