CAST IRON	DUCTILE IRON
Microstructure consists of graphite in the form of flakes which act as stress raisers.	Microstructure consists of graphite in the form of spheroids acts like crack arrestors.
Impact resistance is poor. Under severe impact it will break.	Strong impact resistance. Under sevre impact it will bend.
Tensile strength is low No elongation or Ductility ISO 185 : 1985 Grade : 350 (Grey Cast Iron). Tensile Strength: 350 N / mm2 Min. Elongation : Nil.	Tensile strength is high Almost twice than cast iron Moderate elongation & ductility ISO 1083 : 1987 Grde : 500/7 Tensile Strength : 500 N / mm2 Min. Elongation : 7% Min.
Due to lower strength, weight of the manhole covers will be more for a specfic duty.	Due to high strength, weight of the manhole covers will be less (Min. 2/3rd) by weight.
Due to higher weight handling will be difficult.	Dut to low weight transportation, handling, installation and inspection is easy.
Poor capability of vibration absorption.	High capability of vibration absorption.

Group	Place of Installation	Minimum Class	Application
1	The area where pedestrian & pedal cyclists only be used	A 10
2	Suitable for use in car parks, footways, areas accessible to normal light vehicle traffic	B 125
3	Can be used only in areas of kerb side channel of roads extending up to 500mm in to the carriageway.	C 250
4	Suitable for hard shoulders, road carrying heavy traffic, pedestrian areas and all types of road vehicles.	D 400
5	Can be used for areas for fast moving and specially very heavy traffic such as docks. and aircraft pavement.	E 600
6	Suitable for use at areas particularly involving high wheel load like aircraft pavements.	F 900