Ferrous Metals: Production, Treatments, and Material Properties

Ferrous Metals: Production, Treatments, and Properties

Mechanical Treatments for Metals

Mechanical treatments improve the characteristics of metals through controlled mechanical deformation.

Types of Mechanical Treatments:

• Hot Mechanical Treatment: Involves heating the metal followed by stretching or deformation.
• Cold Mechanical Treatments: Deformation performed at room temperature.

Related Surface Treatments:

Examples include metallization and chrome plating.

Ferrous Metals: Definition and Classification

Ferrous metals are those containing technically pure Iron (Fe) as their basis. Fe is a magnetic, blue-white metal material, known for being ductile and malleable. Its melting point is 1535 °C.

Classification of Ferrous Metals by Carbon Content

• Industrial Iron: When carbon content is less than 0.03%.
• Steel: When carbon content is comprised between 0.03% and 1.67%.
• Cast Iron (Casting): The percentage of carbon is between 1.67% and 6.67%.

Steel Characteristics

The more carbon steel contains, the greater its strength and tensile resistance will be, but this also increases its fragility (brittleness). Steel's melting point ranges between 1300 °C and 1400 °C.

Properties of Steel

• Steel is ductile and malleable.
• Its strength, hardness, and brittleness increase with carbon content.
• Weldability decreases as the percentage of carbon increases.
• Steel oxidizes easily.

Cast Iron (Castings)

Cast iron is an alloy of iron and carbon, typically produced in a furnace, containing between 1.67% and 6.67% carbon.

Types of Castings

• Ordinary Castings: Those containing only iron, carbon, and small amounts of silicon, manganese, sulfur, and phosphorus.
• White Castings: Carbon is combined with iron, forming cementite (iron carbide).
• Gray Castings: Most of the carbon is arranged in the form of graphite. These are generally softer than white castings.
• Mottled Castings: Castings that are intermediate between white and gray.

Obtaining Coke for Metallurgy

Coke acts as both a fuel and a reducing agent for iron oxides in the smelting process. It is obtained from coal with low sulfur (less than 1%) and low ash content (below 8%).

Pig Iron Production (Reduction Reaction)

The primary chemical reaction in the blast furnace:

Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂

Secondary Metallurgy (Steel Refining)

Key processes in secondary metallurgy include:

• Adjusting the composition
• Desulfurization
• Degassing
• Heating

Protective Coatings for Steel

1. Dip Coating (Hot-Dip Galvanizing)

The steel strip is passed through a tank containing the molten coating material (e.g., zinc). The heat is controlled to ensure proper adhesion.

2. Coating by Electrolysis (Electroplating)

The steel strip is coated with a protective metal by passing it through an electrolytic cell (or bath) containing a solution of a metal salt intended for deposition on the steel surface.