Cast Irons

Question 1

Common properties of cast irons

Answer 1

• low impact resistance and ductility
• mechanical properties depend on structure and distribution of microstructural constituents
• physical properties are strongly influenced by microstructure
• distribution of free graphite in the microstructure (most important)

Question 2

What are Gray irons made of

Answer 2

Between 2.5 and 4.0 wt.% carbon
Between 1.0 and 3.0 wt.% Si

Question 3

Features of grey irons

Answer 3

Graphite exists as flakes which are surrounded by a ferrite and pearlite matrix

Question 4

Mechanical behaviour of grey irons

Answer 4

Relatively weak and brittle in tensions due to the graphite tips acting as stress concentrators
Strength and ductility are good in compression

Question 5

What are grey irons used for

Answer 5

Damping vibrations so used in base structures for machines
High resistance to wear
Low shrinkage when cooling in moulds
Least expensive

Question 6

What is ductile (nodular) iron made of

Answer 6

Small amounts of Mg and/or Ce are added to the grey iron before casting

Question 7

Features of ductile iron

Answer 7

Graphite forms as nodules instead of flakes
Matrix is either pearlite or ferrite (most of the time pearlite)

Question 8

Mechanical properties of ductile irons

Answer 8

Stronger and more ductile than grey iron

Question 9

Applications of ductile iron

Answer 9

Crank shafts and gear, machine components

Question 10

What are white irons made of and features

Answer 10

Less an 1wt.% Si
Carbon exists as cementite instead if graphite
Fracture surface is white

Question 11

Mechanical properties of white iron

Answer 11

Due to a large amount of cementite, it’s extremely hard but also very brittle

Question 12

Applications of white irons

Answer 12

Rollers for rolling mills
Due to very low ductility

Question 13

How are malleable irons formed and features

Answer 13

By heating whit iron between 800 degrees and 900 degrees for a prolonged period of time in a neutral atmosphere in order to prevent oxidation of the material
Cementite decomposes into ferrite and graphite
Graphite exists in clusters surrounded by a ferrite or pearlite matrix

Question 14

Mechanical properties of malleable iron

Answer 14

Similar to nodular iron, relatively high strength and ductility

Question 15

Applications of malleable iron

Answer 15

Transmission gears, connecting rods