White cast iron

cast iron

Cast iron is an iron-carbon alloy with carbon content > 2%(typically 2.5–3.8%), with silicon (1–3%) as a key graphitizing element; its classification is mainly based on the form of carbon (graphite or cementite, Fe₃C) and graphite morphology. Here are the major commercial types, with their microstructures, properties, and typical applications:

Types of cast iron

1.      White cast iron

White Cast Iron is a type of ferrous alloy where carbon exists almost entirely as cementite (Fe₃C)rather than graphite, giving it a bright white crystalline fracture surface, from which its name derives. It is formed by high-carbon, low-silicon composition and rapid cooling to suppress graphitization.

  Classification

·         Ordinary white cast iron: No alloy additions, cost-effective for low-severity wear.

·         Alloy white cast iron(low/medium/high alloy): Cr, Mo, V, W added to form M₇C₃, MC carbides, enhancing wear/corrosion resistance 

(e.g., high-chromium white iron for mining/cement machinery).

2. Gray Cast Iron

 Grey Cast Iron (also called laminated graphite,Flake graphite cast iron,gray cast iron)

Gray cast iron is defined as a type of cast iron in which most of the carbon is present in the form of graphite flakes, making it softer, more machinable, and less brittle than white cast iron. It is characterized by its fluidity when molten, allowing for the manufacture of intricate castings.

3.  Ductile (Nodular) Cast Iron

Ductile (Nodular) Cast Iron (also called Spheroidal Graphite Iron, SG Iron) is a high-performance cast iron alloy, defined by its spherical graphite nodules (instead of the sharp flakes in gray cast iron), which delivers an exceptional balance of castability, strength, ductility and toughness.

Microstructure & Grades

The matrix around graphite nodules determines properties:

3.1.      Ferritic  Ductile Iron (QT400-18, EN-GJS-400-18): high ductility, good machinability, lower strength.

3.2.      Pearlitic  Ductile Iron (QT700-2, EN-GJS-700-2): higher strength and wear resistance, lower ductility.

3.3.      Austempered Ductile Iron (ADI): heat-treated to bainitic matrix, excellent strength+ductility, often replaces forged steel.

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