Differences between malleable iron and cast iron
Cast iron vs. malleable iron. This guide explains the differences between these irons and what they have in common. What are the uses of cast iron? What is malleable cast iron used for? Cast iron vs. malleable iron fittings – which is easier to remove? The answers are here. We cover the following topics:
What is cast iron?
Cast iron is a group of iron alloys that typically contain between 2% and 4% carbon. Depending on the type of cast iron, it can even reach as high as 5%. It’s formed by smelting iron ore or pig iron and mixing it with various scrap metals and other alloys. The molten material is then poured into a mold, or cast. It solidifies into the mold’s shape without compromising its strength. Cast iron’s high-carbon content gives it outstanding wear resistance and strength.
What is malleable cast iron?
Malleable cast iron is created through an annealing heat treatment of cast iron. This process reduces carbon content and improves workability and ductility. Initially, white cast iron – another type of cast iron with high carbon content – is cast. It’s then heated just below its melting point for an extended period, causing carbon to transform into graphite. This results in the formation of nodules or spheres, creating malleable cast iron. The annealing process reduces brittleness, enhancing resistance to fractures and enabling bending and shaping without cracking.
Cast-iron properties
What are the properties of cast iron? That depends on the type of cast iron, which we’ve listed below. The higher the carbon content, the more brittle the cast iron, making it vulnerable to cracking and breaking under stress. With high thermal mass, cast iron also has excellent heat retention.
| Type of cast iron | Properties of cast iron |
|---|---|
| Gray cast iron | Lower tensile strength and not as ductile as other cast irons; corrosion resistant; highly brittle – difficult of create a smooth surface; excellent thermal conductor and high level of vibration damping. |
| White cast iron | Not weldable; high compressive strength and good wear resistance; excellent properties for low-impact applications. |
| Ductile cast iron | Nodular graphite in its microstructure through the addition of magnesium, provides higher strength, toughness and ductility than gray iron. |
| Compacted graphite iron | Graphite structure, associated properties are a blend of gray and white iron, higher tensile strength and improved ductility than gray iron. |
What is cast iron used for?
Cast-iron uses depend on the cast-iron type. You’ll see some overlap below. We’ve also included uses of malleable cast iron.
| Cast iron used | Uses for cast iron |
|---|---|
| Gray cast iron | Pipes, valve bodies, valve parts, machine tool housings, brake drums |
| White cast iron | Applications where there’s sliding friction between two surfaces, i.e. wear plates & liners for mining equipment, cement mixers, ball mills and some drawing dies & extrusion nozzles |
| Ductile cast iron | Water & sewer pipes, tractor & implement parts, automotive and diesel crankshafts, pistons & cylinder heads; electrical fittings, switch boxes, motor frames & circuit breaker parts; mining equipment: hoist drums, drive pulleys, flywheels and elevator buckets; & steel mill: furnace doors & table rolls |
| Compacted graphite iron | Diesel engine blocks, turbo housings, exhaust manifolds |
| Malleable cast iron | Automotive drive train & axle components, agricultural and railroad equipment; also, expansion joints and railing castings on bridges, chain-hoist assemblies, industrial casters, pipe fittings, & connecting rods |
Cast iron vs malleable iron
The properties of malleable cast iron include exceptional machinability, toughness and ductility. Shock resistant, it has an excellent ability to withstand high levels of stress.
Malleable iron is easier to work with than cast irons. For example, malleable iron railings or malleable pipe fittings are possible in intricate designs. It typically has a higher melting point than cast irons at 2300°F – again, this depends on the alloys in the cast iron, such as the amount of carbon it contains. But cast iron’s usually lower melting point gives it better castability, so that it easily pours into molds without cooling too fast.
Another comparison: malleable iron vs. cast iron fittings. Malleable iron cannot be broken apart for easy removal, like cast iron fittings can.
Advantages of malleable cast iron
When does the use of malleable cast iron make sense? When you need these benefits:
- Ductility – ideal for applications that will need extensive machining during finishing. Compared to ductile iron, it lacks the same level of tensile strength, elasticity and impact resistance, but it still easily enables machining without breaking.
- Can be flattened and hammered, compared to some cast irons that would break or fracture.
- Nearly as strong as gray cast iron.
- Good impact resistance at extremely low temperatures.
Disadvantages of malleable cast iron
The physical properties of malleable cast iron has disadvantages, Always take note of a material’s downside:
- Shrinks when cooled, as it loses volume. All cast irons – or any material – does this to some degree, but it’s more pronounced with malleable cast iron.
- Low corrosion resistance.
- Not as strong as ductile cast iron or steel. For applications needing high tensile or compressive strength, choose another cast iron.
- Can also become brittle at high temperatures, making it vulnerable to cracking.
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You might find it helpful to check out What are the Differences Between Iron and Steel?
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