3. Answer the following

iii. What are the differences between cast iron, wrought iron and steel ?


Cast iron, wrought iron, and steel are three different forms of iron alloys, each with distinct properties and applications. Here are the main differences between them:

  1. Composition:

    • Cast Iron: Cast iron is primarily composed of iron, carbon (typically 2% to 4%), and silicon. It also contains small amounts of impurities like sulfur and phosphorus.
    • Wrought Iron: Wrought iron contains very low carbon content (typically less than 0.1%) and is primarily iron with small amounts of slag inclusions.
    • Steel: Steel is primarily composed of iron and carbon, with carbon content typically ranging from 0.2% to 2.1%. It can also contain other alloying elements like manganese, chromium, nickel, and others.
  2. Production Process:

    • Cast Iron: Cast iron is produced by melting the iron and adding carbon and other elements to the molten metal. It is then cast into molds to create various shapes.
    • Wrought Iron: Wrought iron is produced through a labor-intensive process called “puddling,” where impurities are removed from cast iron, and the resulting pure iron is worked (wrought) into shape.
    • Steel: Steel is typically produced by refining iron ore in a blast furnace and then adjusting the carbon content and alloying elements through various processes like basic oxygen furnace (BOF), electric arc furnace (EAF), or other methods.
  3. Strength and Hardness:

    • Cast Iron: Cast iron is brittle and has low tensile strength but high compressive strength. It is known for its hardness and wear resistance.
    • Wrought Iron: Wrought iron is relatively soft and ductile, making it easy to forge and shape. It has low tensile strength compared to steel.
    • Steel: Steel has a wide range of mechanical properties, depending on its composition and heat treatment. It can have high tensile strength and hardness or be more ductile and malleable, depending on its intended use.
  4. Uses:

    • Cast Iron: Cast iron is often used for products where its hardness and resistance to wear are advantageous, such as in engine blocks, cookware, pipes, and architectural elements.
    • Wrought Iron: Wrought iron is used for decorative and ornamental purposes, as well as in historical architectural features like gates, railings, and fencing.
    • Steel: Steel is incredibly versatile and is used in a wide range of applications, including construction, manufacturing, automotive, aerospace, and many other industries.
  5. Appearance:

    • Cast Iron: Cast iron often has a rough, grainy surface texture and is usually dark gray in color.
    • Wrought Iron: Wrought iron has a fibrous appearance due to its slag inclusions and is often dark gray to black in color.
    • Steel: Steel can have a smooth and shiny surface when polished or a rougher texture depending on the finishing and treatment.

In summary, cast iron, wrought iron, and steel differ in terms of composition, production methods, mechanical properties, and applications. The choice between them depends on the specific requirements of a given application.