Question

The addition of alloying element nickel to cast iron will primarily improve
1. Wear resistance
2. Toughness
3. Carbide formation
4. Machinability

Answer 1

Correct Answer - Option 4 : Machinability

Explanation:

Effect of addition of nickel in cast iron:

The addition of Nickel as an alloying agent in the engineering cast irons is to control the structure formation by retarding austenite transformation, stabilizing pearlite and maintaining combined carbon at the eutectoid quantity.

Nickel lowers the critical temperature so pearlite is formed at lower temperature.

As a result pearlite is finer and tougher. Nickel also reduces the carbon content. These factor increases toughness, plasticity and fatigue resistance.

The addition of Nickel in cast iron has following effects mainly:

1. It increases impact strength, machinability, toughness.
2. Increases hardenability, but is least effective among hardenability agents.
3. It helps in reducing distortion and cracks in quenching phase of heat treatment.

Effect of various elements on Cast Iron is shown in table below:

ELEMENT	EFFECT ON CAST IRON
Sulphur	Makes cast iron hard and brittle.
Manganese	Makes cast iron white and hard.
Phosphorus	It increases the flowability of grey cast iron.
Silicon	It makes cast iron soft and easily machinable.
Nickel	It is used to refine grain structure, increase strength, machinability, toughness, and increase resistance to corrosion.