Properties of Cast Iron

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.