The primary purpose of annealing (ferritizing) is the production of castings with maximum ductility and toughness, reduced strength and hardness, improved machinability and uniform properties (Table 1). Annealing softens ductile iron by producing a carbide-free, fully ferritic matrix. Annealing practices (Table 2) range from a low-temperature or sub-critical anneal used to ferritize carbide-free castings, to two-stage and high-temperature anneals designed to break down carbides.

Alloy Additions

Different levels of copper and tin can affect annealed properties and result in reduced strength and hardness, increased elongation and generally eliminate the variations in as-cast properties produced by the different alloy levels. Fracture toughness can be affected by the choice of standard and subcritical annealing as well.

Figure 1. Impact properties of 65-45-12 ductile iron as a function of temperature[3]


1. Anchor Bronze & Metals Inc. (
2. Ductile Iron Society (
3. Dura-Bar Expert Tip: Impact v. Fracture (
4. Specialty Casting Inc. (