Unit - 3: Cast Iron
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UNIT - 3
CAST IRON 10 MARKS
CAST IRON o Cast
PG - 455
Irons are basically the alloys of Carbon & Iron in which the carbon varies between 2.0 to 6.67% i.e. more than the solubility limit of carbon in austenite and less than the carbon content of cementite.
CAST IRON o Because
PG - 455
of the poor ductility & malleability, they can not be forged, rolled, drawn or pressed into the desired shape but are formed by melting and casting to the required shape and size and hence the name “cast iron”.
C I - CHARACTERISTICS PG-455 They are cheapest amongst the commercial alloys. o They are easier to melt because of their low melting temperature (1150-1250°c) as compared to steels (1350-1500°c). o They have excellent castability due to high fluidity of melt & low shrinkage during solidification. o
C I - CHARACTERISTICS PG-455 Their corrosion resistance is fairly good. o By proper alloying and suitable heat treatment the properties of any type of CI can be easily adjusted over a wide & useful range. o In general they are brittle and their mechanical properties are o
C I - CLASSIFICATION PG-456 1. On the basis of furnace used in their manufacturing. I. II.
III. IV.
Cupola CI Air furnace CI Electric furnace CI Duplex CI
C I - CLASSIFICATION
PG-456
On the basis of composition & purity.
2. I.
II. III.
Low carbon, low silicon CI High carbon, low sulphur CI Nickel alloy CI
C I - CLASSIFICATION 3.
On the basis of microstructure & appearance of fracture.
White CI ii. Malleable CI iii. Gray CI iv. Nodular CI v. Chilled CI i.
PG-456
WHITE C I •
All the carbon is in the combined form i.e. as cementite & there is no free carbon i.e. Graphite. • The fracture appears white. • All white CI are hypoeutectic. • Composition – C=2.5%, Mn=0.4%, Cr=17%, Si=1.3%, Ni+Cu=1.5%, P=0.15%, S=0.15%, Mo=0.5%.
WHITE C I •
Due to the presence of large amount of cementite it is hard, brittle & difficult to machine. • It is used in ball mills, drawing dies, extrusion nozzles etc. • Microstructure -
MALLEABLE C I •
They contain free carbon i.e. Graphite in the form of irregular spheroids also called as rosettes. • They are produced from White CI by a heat treatment called malleablization. • Composition – C=2-2.65%, Si=0.9-1.4%, Mn=0.250.55%, P=Less than 0.18%,
MALLEABLE C I •
It is used in pipe fittings, chain hoist assembly, railroad equipments etc. • Microstructure –
GRAY C I •
The CI containing graphite in the form of flakes are called Gray CI. • They fracture appears gray in colour. • Properties – • • •
•
Excellent machinability Good compressive strength Good bearing peoperties Fairly good corrosion resistance
GRAY C I •
Composition –
C=3.2-3.7%, Si=2-3.5%, S=0.06-0.1%, P=0.10.2%, Mn=0.5-1.0%. • Microstructure –
White CI
Gray CI
Fracture appears White in Colour.
Fracture appears Gray in Colour.
Melting point is lower than Gray CI.
Melting point is higher than White CI.
It is harder than Gray CI.
It is softer than White CI.
Machining is difficult.
Better machinability than white CI.
Silicon content is between 0.1-0.5 %.
Silicon content is between 0.5-3.5 %.
Widely used in industry.
Has limited applications.
NODULAR C I • • •
These CI contain graphite in the form of nodules or spheroids. This increases tensile strength, ductility & toughness. They are also called as spheroidal graphite cast iron (SGCI) or ductile CI.
NODULAR C I •
They are produced from Gray CI by the addition of small quantity of certain elements called nodulising elements such as magnesium, calcium, barium etc. • The common addition is Mg which is usually added in ladle just prior to pouring into the moulds.
NODULAR C I •
Microstructure –
CHILLED CI •
•
•
This type of CI shows white structure at the surface & gray structure at the centre. Due to this good properties of White CI (hardness & wear resistance) and Gray CI (machinability, damping capacity,) can be coupled together . Generally carbon content varies from 3.3 – 3.5% with silicon content between
CHILLED CI •
The depth of chill i.e. the thickness of white layer can be controlled by controlling the carbon & silicon contents. • Chilled CI are used for crushing rolls, grinding balls, road rollers, hammers, dies etc.
THANK YOU !!!
CAST IRON 10 MARKS
CAST IRON o Cast
PG - 455
Irons are basically the alloys of Carbon & Iron in which the carbon varies between 2.0 to 6.67% i.e. more than the solubility limit of carbon in austenite and less than the carbon content of cementite.
CAST IRON o Because
PG - 455
of the poor ductility & malleability, they can not be forged, rolled, drawn or pressed into the desired shape but are formed by melting and casting to the required shape and size and hence the name “cast iron”.
C I - CHARACTERISTICS PG-455 They are cheapest amongst the commercial alloys. o They are easier to melt because of their low melting temperature (1150-1250°c) as compared to steels (1350-1500°c). o They have excellent castability due to high fluidity of melt & low shrinkage during solidification. o
C I - CHARACTERISTICS PG-455 Their corrosion resistance is fairly good. o By proper alloying and suitable heat treatment the properties of any type of CI can be easily adjusted over a wide & useful range. o In general they are brittle and their mechanical properties are o
C I - CLASSIFICATION PG-456 1. On the basis of furnace used in their manufacturing. I. II.
III. IV.
Cupola CI Air furnace CI Electric furnace CI Duplex CI
C I - CLASSIFICATION
PG-456
On the basis of composition & purity.
2. I.
II. III.
Low carbon, low silicon CI High carbon, low sulphur CI Nickel alloy CI
C I - CLASSIFICATION 3.
On the basis of microstructure & appearance of fracture.
White CI ii. Malleable CI iii. Gray CI iv. Nodular CI v. Chilled CI i.
PG-456
WHITE C I •
All the carbon is in the combined form i.e. as cementite & there is no free carbon i.e. Graphite. • The fracture appears white. • All white CI are hypoeutectic. • Composition – C=2.5%, Mn=0.4%, Cr=17%, Si=1.3%, Ni+Cu=1.5%, P=0.15%, S=0.15%, Mo=0.5%.
WHITE C I •
Due to the presence of large amount of cementite it is hard, brittle & difficult to machine. • It is used in ball mills, drawing dies, extrusion nozzles etc. • Microstructure -
MALLEABLE C I •
They contain free carbon i.e. Graphite in the form of irregular spheroids also called as rosettes. • They are produced from White CI by a heat treatment called malleablization. • Composition – C=2-2.65%, Si=0.9-1.4%, Mn=0.250.55%, P=Less than 0.18%,
MALLEABLE C I •
It is used in pipe fittings, chain hoist assembly, railroad equipments etc. • Microstructure –
GRAY C I •
The CI containing graphite in the form of flakes are called Gray CI. • They fracture appears gray in colour. • Properties – • • •
•
Excellent machinability Good compressive strength Good bearing peoperties Fairly good corrosion resistance
GRAY C I •
Composition –
C=3.2-3.7%, Si=2-3.5%, S=0.06-0.1%, P=0.10.2%, Mn=0.5-1.0%. • Microstructure –
White CI
Gray CI
Fracture appears White in Colour.
Fracture appears Gray in Colour.
Melting point is lower than Gray CI.
Melting point is higher than White CI.
It is harder than Gray CI.
It is softer than White CI.
Machining is difficult.
Better machinability than white CI.
Silicon content is between 0.1-0.5 %.
Silicon content is between 0.5-3.5 %.
Widely used in industry.
Has limited applications.
NODULAR C I • • •
These CI contain graphite in the form of nodules or spheroids. This increases tensile strength, ductility & toughness. They are also called as spheroidal graphite cast iron (SGCI) or ductile CI.
NODULAR C I •
They are produced from Gray CI by the addition of small quantity of certain elements called nodulising elements such as magnesium, calcium, barium etc. • The common addition is Mg which is usually added in ladle just prior to pouring into the moulds.
NODULAR C I •
Microstructure –
CHILLED CI •
•
•
This type of CI shows white structure at the surface & gray structure at the centre. Due to this good properties of White CI (hardness & wear resistance) and Gray CI (machinability, damping capacity,) can be coupled together . Generally carbon content varies from 3.3 – 3.5% with silicon content between
CHILLED CI •
The depth of chill i.e. the thickness of white layer can be controlled by controlling the carbon & silicon contents. • Chilled CI are used for crushing rolls, grinding balls, road rollers, hammers, dies etc.
THANK YOU !!!
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