Write short notes on the following i. Normalizing ii. Annealing iii. Tempering iv. hardening – NABTEB QUESTION

i. NORMALIZING

Normalizing is a heat treatment process in which the steel heated to 3°C-500°C above the upper critical point and cooled freely in air. To bring to normal the internal structure.

ii. ANNEALING

The purpose of annealing is to make the metal softer and more ductile. It can then
be cold worked without any danger of it breaking. The steel is heated to 30°C – 50°C above the upper critical point and held at this temperature for a time depending on the thickness of the meal. It is then cooled very slowly, usually in the furnace.

iii. TEMPERING

A steel which has been harden is very brittle and it is likely to crack in service it can be tempered by heating it to a temperature below the lower critical temperature and then quenching. This treatment takes away some of the brittleness and make the metal tougher and more ductile but less hard and strong.

iv. HARDENING

In the hardening process the steel is heated to 30°C – 50°C above the upper critical point and cooled rapidly by quenching in which water, brine or oil, water causes the steel to be harder than oil but with some work quenching in water causes it to crack and distort. The hardness produced depends upon the carbon content of the steel.