[K] - CAST IRONS (CAST IRON)

Cast irons are Fe-C-Si alloys, approximately 2-4.5%C. Carbon in cast irons very often has the form of graphite. Depending on the carbon and silicon content, they are classified into:

K 15-16 - Grey Cast Irons

(2.5-4.0%C , 1.0-3.0%Si)

• Microstructure:
• Carbon is found mainly in the form of graphite flakes within the metallic matrix (martensitic, ferritic, or pearlitic).
• Applications:
• Engine housings, machine tool bases, cylinder blocks, brakes, pumps, and valves.
• Machinability:
• Chips: Short and brittle (due to the graphite flakes)
• Tool wear: Low
• Cutting type: High cutting speeds, low feed
• Surface quality: Good
• Details:
• Due to the high content of graphite flakes, grey cast iron has natural lubricating characteristics, reducing friction and wear on tools.
• The chips are brittle (powder), which makes their removal easy.

K 17-18 - Ductile Cast Irons with Spheroidal Graphite

(2.0-2.6%C , 1.1-1.6%Si)

• Microstructure:
• Carbon forms compact spheroidal graphite instead of flakes. This microstructure improves ductility and increases the toughness of the cast iron.
• Applications:
• Pipes for hydraulic networks, gears, crankshafts, gearboxes, vehicle suspension.
• Machinability
• Chips: Continuous and long
• Tool wear: Moderate to high
• Cutting type: Moderate speeds, higher feed than grey cast iron
• Surface quality: Moderate to good
• Details:
• Spheroidal graphite does not act as a lubricant, resulting in higher wear on cutting tools.
• The chips are continuous and difficult to remove
• Due to its higher strength, greater cutting force is required.
• Higher stresses on the tools lead to higher temperature and possible fatigue.

K 19-20 - Malleable Cast Irons

(3.0-4.0%C , 1.8-2.8%Si)

• Microstructure:
• Carbon is initially in the form of carbides (white cast iron) and then, through heat treatment, is converted into graphite in the form of nodules.
• Applications:
• Components that require impact resistance, such as pipe fittings, automotive components, moving parts in mechanisms.
• Machinability
• Chips: Short and broken (better than ductile)
• Tool wear: Moderate
• Cutting type: Moderate speeds, similar feed to ductile
• Surface quality: Good
• Details:
• Graphite nodules help reduce friction, but not as much as in grey cast iron.
• It has medium compressive and tensile strength, therefore it is easier to machine than ductile
• It can be machined with HSS tools