Properties of Cast Iron

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Questions and Answers

What are the primary elements that cast iron is composed of?

Iron, carbon, and oxygen

Iron, carbon, and silicon (correct)

Iron, manganese, and phosphorus

Iron, sulfur, and chromium

What is a characteristic of cast iron?

It is highly malleable and ductile

It is relatively brittle and non-malleable (correct)

It has low compressive strength

It has high tensile strength

What is a beneficial property of cast iron?

High ductility

Excellent compressive strength (correct)

High tensile strength

Low resistance to corrosion

How many categories of cast iron are based on composition and metallurgical structure?

5 Signup and view all the answers

What is an advantage of alloyed cast irons?

They have enhanced resistance to heat, oxidation, and corrosion Signup and view all the answers

What is the main factor that influences the strength of gray cast iron?

Matrix in which the graphite flakes are embedded Signup and view all the answers

What is the result of preventing graphitization of the carbon dissolved in the iron at high temperatures during cooling?

Formation of a pearlitic matrix Signup and view all the answers

What is the primary difference between gray cast iron and spheroidal graphite cast iron?

The shape of the graphite particles Signup and view all the answers

What is the typical microstructure of white cast iron?

Cementite and pearlite Signup and view all the answers

What is the purpose of adding silicon to the melt when producing spheroidal graphite cast iron?

To ensure the precipitation of carbon as graphite Signup and view all the answers

What is the primary reason for the poor weldability of cast irons?

High carbon content Signup and view all the answers

What is the main advantage of producing iron castings in the as-cast condition?

No need for heat treatment Signup and view all the answers

Why do corrosion rates of buried cast iron pipes decrease over time?

Formation of graphite-containing corrosion products Signup and view all the answers

What is the characteristic of gray cast iron that makes it ideal for producing shrinkage-free, intricate castings?

High fluidity of liquid gray iron Signup and view all the answers

Why does gray iron exhibit poor toughness?

Presence of graphite flakes Signup and view all the answers

What happens when a localized area of a cast iron is cooled very rapidly from the melt?

Carbides are formed Signup and view all the answers

What is the purpose of adding chromium to cast iron?

To control chill depth, increase hardness, and improve abrasion resistance Signup and view all the answers

What is a common application of high chromium containing cast iron?

Crushing of rocks and minerals Signup and view all the answers

What property of brass makes it ideal for applications that require formability?

Malleability Signup and view all the answers

What is a common use of brass due to its high corrosion resistance?

Plumbing pipes and tubing Signup and view all the answers

What is the main reason why white cast iron is considered un-weldable?

Due to its inability to accommodate welding-induced stresses Signup and view all the answers

What is the result of decomposing iron carbide in white cast iron under certain conditions?

Formation of temper carbon nodules in a ferrite matrix Signup and view all the answers

What is the characteristic of compacted graphite irons (CG irons) that sets them apart from gray iron?

Shorter and thicker graphite particles with rounded edges Signup and view all the answers

What is the purpose of adding chromium to chilled cast iron?

To control chill depth and increase hardness Signup and view all the answers

What is the advantage of malleable cast iron over ductile cast iron?

Malleable properties up to the surface of the casting Signup and view all the answers

What is a characteristic of polymer bearings?

Low friction Signup and view all the answers

What is the primary application of bronze bearings?

Applications where self-lubrication is required Signup and view all the answers

What is the main cause of season cracking?

Tensile stress and corrosive environment Signup and view all the answers

What is the purpose of precipitation hardening?

To strengthen certain alloys Signup and view all the answers

What is the result of the precipitation hardening process?

Production of materials with high strength, toughness, and corrosion resistance Signup and view all the answers

What type of bearings are used in applications where traditional lubricants may not be suitable?

Bronze bearings Signup and view all the answers

What is the effect of precipitation hardening on alloying elements?

They are dissolved into the solid solution Signup and view all the answers

What is the primary method of preventing season cracking?

Selecting materials resistant to the specific environment Signup and view all the answers

What is the typical application of precipitation hardened alloys?

All of the above Signup and view all the answers

What is the effect of rapid cooling in the precipitation hardening process?

Allows precipitates to form within the material Signup and view all the answers

What is a characteristic of bronze that makes it suitable for use in marine and fishing applications?

High resistance to corrosion from saltwater Signup and view all the answers

What is a common application of bronze alloys due to their excellent electrical conductivity?

Electrical connectors and springs Signup and view all the answers

What is a characteristic of aluminum-lithium alloys that makes them suitable for aerospace applications?

High strength-to-weight ratio Signup and view all the answers

What is a common application of lead-antimony alloys due to their ability to resist sulfation?

Lead-acid batteries for vehicles Signup and view all the answers

What is a characteristic of ceramic bearings that makes them suitable for high-speed and high-temperature applications?

Reduced weight compared to steel bearings Signup and view all the answers

Study Notes

Cast Irons

Composition: primarily iron (Fe), carbon (C), and silicon (Si), with traces of sulfur (S), manganese (Mn), and phosphorus (P)
Characteristics: brittle, non-malleable, relatively weak in tension, but excellent compressive strength
Classification: 5 groups based on composition and metallurgical structure:
- Gray cast iron
- Ductile cast iron
- White cast iron
- Malleable cast iron
- Compacted graphite iron
- Alloy cast iron

Gray Cast Iron

Composition: 2.5% to 4% carbon, 1% to 3% silicon
Characteristics: oldest and most common form of cast iron, brittle, good machinability, good damping characteristics
Properties: poor toughness, high ratio of performance to cost, ideal for production of shrinkage-free, intricate castings
Applications: engine blocks, valve bodies, machine tool housings, brake drums

Ductile Cast Iron (Spheroidal Graphite Iron)

Composition: similar to gray cast iron, but with addition of magnesium or cerium
Characteristics: higher strength and toughness, spherical graphite particles
Properties: excellent toughness, widely used in crankshafts, pearlitic matrix
Applications: water and sewer pipes, agricultural and automotive parts, electrical fittings, mining machinery

White Cast Iron

Composition: less than 4.3% carbon, low silicon content
Characteristics: hard, brittle, abrasion-resistant, light appearance
Properties: un-weldable, used in applications where abrasion resistance is important
Applications: liners for cement mixers, ball mills, drawing dies, extrusion nozzles

Malleable Cast Iron

Composition: heat-treated white cast iron
Characteristics: intermediate strength, toughness, and machinability between gray and ductile cast iron
Properties: ideal for applications where toughness and machinability are required
Applications: small castings, thin-section castings, automotive and agricultural parts, industrial casters

Compacted Graphite Iron

Composition: between gray and nodular graphite cast iron
Characteristics: useful combination of strength, thermal conductivity, and other properties
Properties: production requires controls similar to those for ductile iron castings
Applications: not specified

Chilled Cast Iron

Composition: localized area of cast iron cooled rapidly from the melt
Characteristics: carbides formed, hardness increases with carbon content
Properties: used in applications where high wear resistance is desirable
Applications: crushing of rocks and minerals

Alloyed Cast Iron

Composition: corrosion-resistant and elevated-temperature service alloys
Characteristics: classified into two types, with high chromium content for high wear resistance
Properties: used in applications where high wear resistance is desirable
Applications: chemical processing plants, petroleum refining, food handling, and marine service

Brass

Composition: primarily copper and zinc, with other metals added
Characteristics: malleable, high corrosion resistance, low melting point
Properties: high thermal conductivity, non-ferromagnetic, susceptible to cracking
Applications: decorative applications, musical instruments, plumbing pipes, electronic applications

Bronze

Composition: primarily copper and 12% tin, with other elements added
Characteristics: hardness, brittleness, high corrosion resistance, low metal-to-metal friction
Properties: used in functional and aesthetic applications
Applications: marine and fishing, sculptures, musical instruments, electrical connectors, bushings, and bearings

Aluminum Alloys

Duralumin (Aluminum-Copper): strong, lightweight, used in aircraft construction, automotive components
Aluminum-Lithium Alloys: high strength-to-weight ratio, used in aerospace applications
Aluminum-Silicon Alloys: excellent casting properties, used in automotive engine components

Lead Alloys

Solder (Lead-Tin): low melting point, good electrical conductivity, used in electronic components
Lead-Antimony Alloys: used in lead-acid batteries for vehicles and UPS
Lead-Calcium Alloys: used in maintenance-free lead-acid batteries

Tin Alloys

Bronze (Copper-Tin): used in art, sculpture, musical instruments, bearings
Pewter (Tin-Alloyed with Copper, Antimony, or Bismuth): used in decorative items, jewelry, small sculptures
Babbitt Metal (Tin-Antimony-Copper): low-friction alloy, used in bearings### Zinc Alloys
Zamak alloys are used in die-casting applications for producing complex shapes with excellent surface finish, making them suitable for automotive parts, electronic housings, and consumer goods.
Brass alloys have a wide range of applications including plumbing fixtures, musical instruments, decorative hardware, and electrical connectors due to their malleability, corrosion resistance, and attractive golden color.
Galvanized Steel is used in construction, automotive manufacturing, and household appliances to protect steel from corrosion.

Bearing Materials

High-carbon chromium bearing steel is commonly used for bearing applications due to its high hardness, wear resistance, and ability to withstand heavy loads and high temperatures.
Ceramic bearings are made from materials like silicon nitride (Si3N4) or zirconia (ZrO2) and offer advantages such as high hardness, corrosion resistance, and reduced weight.
Polymer bearings are made from materials like polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK) and offer advantages such as low friction, corrosion resistance, and self-lubrication.
Bronze bearings are used in applications where self-lubricating properties are required, such as in machinery and equipment.

Season Cracking

Season cracking, also known as stress corrosion cracking (SCC), is a phenomenon where a material fails prematurely under stress in the presence of a specific environment.
It occurs due to the combined effects of tensile stress and a corrosive environment, leading to the initiation and propagation of cracks in the material.
Materials susceptible to season cracking include certain alloys of brass, aluminum, stainless steel, and high-strength steels.
Preventing season cracking involves selecting materials resistant to the specific environment, controlling stress levels through proper design and manufacturing processes, and implementing corrosion control measures.

Precipitation Hardening

Precipitation hardening is a heat treatment process used to strengthen certain alloys, typically aluminum, stainless steel, or some nickel-based alloys.
The process involves heating the material to a specific temperature to dissolve alloying elements into a solid solution, followed by rapid cooling and then aging at a lower temperature to allow precipitates to form within the material.
The precipitates act as obstacles to dislocation movement, effectively increasing the strength and hardness of the alloy.
Precipitation hardening allows for the production of materials with a combination of high strength, toughness, and corrosion resistance, making them suitable for aerospace components, structural parts, and high-performance applications.

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Description

Learn about the composition and properties of cast iron, including its carbon content, brittleness, and behavior under tension.