Steel Production and Ferrous Metals: Processes and Types

Posted on Dec 11, 2024 in Chemistry

Blast Furnace Operation

  1. The raw material, consisting of iron ore (60%), coking coal (30%), and flux (10%), is introduced into the blast furnace.
  2. The furnace operates continuously.
  3. As the load descends from the top, its temperature increases until it reaches the bosh. Here, the temperature reaches 1650°C, and liquid iron is deposited in the crucible.
  4. The flux reacts with the ore to form slag, which floats on the molten iron. Slag is removed through a hole called the slag runner. This slag is used to manufacture cement or insulation.
  5. Periodically, the tap hole is opened, and liquid pig iron is extracted from the crucible. This iron, called pig iron, contains impurities.
  6. Almost all the iron is converted into steel in a converter. Sometimes, it is formed into ingots.
  7. Surrounding the furnace is a ring that introduces hot air into the furnace through nozzles.

Electric Arc Furnace Operation

It is the only furnace that turns scrap metal into steel.

  1. The lid is removed, and scrap metal and flux are introduced.
  2. The oven is closed, and the electrodes are brought close to the scrap, initiating the melting process.
  3. When the scrap is melted, oxygen is injected.
  4. The oven is tilted to remove the slag. Then, carbon and ferro-alloys are added, and the mixture is heated.
  5. The oven is tilted again to pour the steel into a ladle, which is then taken to the molding area.

Casting of Steel

The liquid steel obtained from the electric furnace is solidified using one of these casting methods:

  • Conventional Casting: Liquid steel is poured into molds shaped like the desired piece, left to cool, and then the piece is removed.
  • Continuous Casting: A more modern and economical process, where liquid steel is poured into a bottomless mold with a curved cross-section and the geometric shape of the product. The steel moves as it cools.
  • Casting in Molds: When product demand is low, steel is discharged into molds and allowed to cool. The mold is then removed, and the ingots are stored until demand increases.

Rolling Mill

Rolling consists of passing the material between two rollers to reduce its cross-section and increase its length.

There are two types:

  • Hot Rolling: The material’s temperature is usually around 1000°C.
  • Cold Rolling: This is done at room temperature.

Ferrous Metals

  • Iron: Ferrous products with a carbon percentage between 0.01% and 0.03% are soft, difficult to obtain, and therefore have limited commercial applications.
  • Steels: Iron-carbon alloys with a carbon percentage between 0.03% and 1.76%.
  • Cast Irons: Iron-carbon alloys with a carbon percentage between 1.76% and 6.67%.
  • Graphite is obtained when the carbon percentage exceeds 6.67%. It has no applications because it is very fragile.

Steel Grades

They are classified into:

  • Non-alloy Steels: When the percentage of chemical elements involved in the alloy is less than 0.10%. They are further classified based on carbon content:
    • Extra Mild Steel: 0.1% to 0.2% C
    • Mild Steel: 0.2% to 0.3% C
    • Medium Carbon Steel: 0.3% to 0.4% C
    • Carbon Steel: 0.4% to 0.5% C
    • Hard Steel: 0.5% to 0.6% C
    • Extra Hard Steel: 0.6% to 0.7% C
  • Alloy Steels: These contain iron and carbon, along with other elements at rates higher than 0.10%.

Commercial Presentations of Steel

The most common forms of steel used in mechanical engineering and metalworking are:

  • Plates: Rolled plates measuring from 1×2 m to 3×3 m.
  • Bars: These parts are longer than they are wide, solid, and have variable sections. If the bar’s section is round and its diameter is less than 5 mm, it is called wire. When the plates have a very small thickness and a large length, they are called strips.
  • Profiles: Hollow pieces with variable sections whose length can vary between 5 and 12 m.

Cast Irons

These are iron-carbon alloys that may also contain other elements. The carbon percentage is between 1.76% and 6.67%.

Cast irons are classified based on their fracture properties and composition:

  • Regular:
    1. White Cast Iron (very hard and brittle, used as raw material to produce malleable alloys).
    2. Gray Cast Iron (gray because the carbon is in the form of graphite, used in malleable foundries).
    3. Mottled Cast Iron (has properties intermediate between the other two).
  • Alloyed: Contains carbon, iron, and other chemicals to improve its properties.
  • Special:
    1. White Heart Malleable: The piece is molded in white cast iron, coated with iron ore, placed in an oven at 1000°C, and slowly cooled to room temperature.
    2. Pearlitic Malleable: The piece is molded in white cast iron, covered with sand, placed in an oven at 900°C, and slowly cooled to room temperature.
    3. Spheroidal Graphite or Nodular Cast Iron: Cerium and magnesium are added to the cast iron, which is then poured into a mold and cooled.