Ferrous metals

Iron ore

Iron ore  (IO) is very abundant, (around 5% or 50 000 ppm of the earth's crust). Iron ores are rocks and minerals from which metallic iron can be economically extracted. Most are rich in iron oxides (hematite, magnetite). Mining iron ore is a high volume low margin business, concentrated in a few large mining corporations.

Mined ore is of varying chemical composition. The characteristics paid attention to are detailed hereunder. In trading terms, those are materialized by escalators or de-escalators which apply for each characteristic, reflecting the premium or discount paid per gradient point above a given threshold.

• Iron: (Fe) varies between 55 and 65 %.
• Moisture: is expected not to exceed 10%.
• Alumina: (Al₂O₃) varies between 0.5 and 4%. Increases viscosity of the slag when smelting, with adverse effects on furnace operations.
• Silica: (SiO₂) varies between 2 and 7%. Produces 'grey iron' which is less brittle.
• Phosphorus: (P) varies between 0.05 and 0.10 %. Makes slag more fluid and increases iron hardness. On the other hand, at high concentration, it makes iron 'cold short' and produces steel which tends to be more brittle.
• Sulfur: (S) is expected to be below 0.05 %. Sulfur produces 'hot short' iron, which brittles when heating, and should be avoided.

Iron ore is made available in following forms, all of which are designed (in conjunction with coke) to maintain a porous feed bed in the blast furnace and thus facilitate rapid and uniform reduction of the iron ore (iron oxide) to iron metal.

• Direct Shipping Ore (DSO): ore that is mined, crushed and screened only, before being sold.
• Fines: is the natural smaller (<6mm) fraction of DSO.
• Lump: is the natural larger (>6mm, <30mm) fraction of DSO. Lump is sold at a premium, because it can be fed as such to a blast furnace, whereas fines have first to be transformed to sinter or pellets.
• Sinter: is made from fines, often beneficiated with concentrates, ignited with coke to produce a fused biscuit which is crunched and screened to appropriate sizes.
• Pellets: are made by taking very fine iron ore and/or concentrates and agglomerating them with moisture and a binder (clay) in drums, to form balls approximately 16mm in diameter. These are then baked and fused to form very strong agglomerates for charging to the blast furnace. Pellets are essentially artificial lump.

Quality differentials are mainly motivated by the iron (Fe) content, whereby form (fines, lump) or origin are considered as well. The global benchmarks are hooked on deliveries in Northern and Eastern China, corresponding to the world's major consumption area. Quotes usually adopted are those published by Argus , Fastmarkets (Metal Bulletin)  or Platt's  (which merged with TSI).

Quality gradients to the normalized, standard specifications are also published. This covers composition, but form as well, buyers paying a premium to have lump or pellets delivered rather than fines.

Iron

Ore is first smelted in blast furnaces by adding coke as reducing agent, carbon binding the oxygen contained in the iron oxides. Depending on the process, distinct iron (Fe)  products are obtained. Those iron-rich ingredients are further reprocessed to reduce carbon and then add other elements to produce different grades of steel.

• Pig iron  is obtained by smelting iron ore in a blast furnace and casting the molt into ingots. It has still a high carbon content (3.8 - 4.7 %), which makes it very brittle.
• Direct reduction iron (DRI) , also called sponge iron, is obtained by a reducing gas, which transforms iron oxides to metallic iron at temperatures below melting point. It may be further compacted to Hot Briquetted Iron (HBI).

Steel

Steel (ST)  of which iron is the key ingredient represents 95% of all metals consumed worldwide. Steel is used primarily in structural engineering applications, in maritime purposes, automobiles, and general industrial applications (machinery). Carbon steel is an alloy that consists mostly of iron (carbon content: 0.2% - 2.1% by weight). Steel being a manufactured product, has approximately up to 3500 different grades , which characteristics are normed by international or national Standards development organizations (SDO).

The principal characteristics are:

• Chemical composition
• Yield strength : compressive stress at which a material begins to deform plastically.
• Tensile stength : tension stress at which a material begins to elongate (if ductile) or brittle.

Steel products are also categorized by their forms ans shapes and purposed application. In the foundry the smelt liquid is continuously cast into ingots or slabs, which are further hot rolled into blooms or billets. Those intermediate products  are often referred to as semi-finished steel.

• Ingot: tapered, rectangular bars of reduced length, to facilitate handling and storage.
• Slab: length of metal with a rectangular cross-section, usually further rolled into sheets.
• Bloom: length of metal with a circular or square cross-section, which area is greater than 230 cm² (36 in²). To be transformed further into structural shapes, rails or pipes.
• Billet: length of metal with a circular or square cross-section, which area is smaller than 230 cm² (36 in²). Will be transformed further into bars, rods or wires.

The steel products, prior to further manufacturing to finished products are usually categorized as follows:

• Flat steel
  • Hot rolled coil (HRC): Rolling  happens on a metal which is above recrystallization temperature. Used mainly to produce sheet metal.
  • Cold rolled coil (CRC): Rolling on a metal which is below recrystallization temperature. It improves strength and surface finish. Will further be casted in upper grade finished products.
  • Hot dipped galvanized coil (HDG): Galvanization  is applying a coating to prevent rusting, usually by immersing the metal in molten Zinc. It offers good corrosion resistance at a lower cost than stainless steel. Used for outdoor appliances.
  • Pre-painted galvanized iron (PPGI): Galvanization is followed by a continuous paint line  where the steel is coated (paints, vinyls) before forming.
  • Plate: steel plates of various dimensions and thickness.
• Long steel
  • Rebar: Reinforcing bars  is a bar or mesh of steel wires used mainly to reinforce concrete.
  • Wire rod: steel ropes of different diameters. Of mesh quality (lower carbon content) means that it can be used to fabricate reinforcing mesh.
  • Beam, Section, Merchant bar, Rail: Various types and dimesions of I-beams , Sections of varying profiles, Bars (circle or rectangle) and Rails.

Very instructive explanations on their industry are provided by the World Steel Association  as well as by some of the major players, such as Arcelor Mittal  or Outokumpu .

Stainless steel

Stainless steel (SL)  is obtained by alloying iron with chromium (between 10-20%) to prevent corrosion. Depending on the type and percentage of metal alloyed, over 150 different grades  of stainless steel exist, of which 15 are most commonly used. As for steel, the way stainless is produced will give the material specific characteristics:

• Hot rolled (HR): Occurs above recrystallization temperature. Also named 'quarto milled' (QM).
• Cold rolled (CR): Carried in cluster mills, to the desired thickness (also called gauge).
• Bars: Rolling produces coils or plates, bars are straigth length of varying geometry.

After shaping, further treatments (annealing, pickling, coating) are applied to recrystalize, alter the microstructure or change properties and polish for particular applications. Typical surface finish are 2B, 2R, BA (Bright annealing) or CMP (Chemical mechanical polishing).

Ferro alloys

Several alloys are obtained by alloying other materials with the iron/carbon mixture to produce ferro-alloys with desired properties (e.g. Nickel for strength, Titanium for lightness).

Steel scrap

Metals recycling  is of increasing importance and amounts for some metals between 30 to 40% of the total raw material availability. It has thus grown into the biggest mine worldwide. It represents important savings in energy and raw materials and reduces overall pollution (air, water, waste).

As for steel, steel scrap (SS) is categorized in different grades, in terms of recycling ratio, but as well of treatment needed to process sometimes hazardous materials. The standards are set by the major industry associations of the recycling business.

Coking coal, Coke

Coking coal is the major energy source in the metallurgical industry, the more so that coke, which is produced of coal, is used as reducing agent in blast furnaces, as part of the iron ore smelting process.
Those products are detailed in the Coal pages 🔎 of this site.