Iron

Position of iron in the periodic table.

Iron.

Iron is a chemical element with symbol Fe and atomic number 26. It is a metal and a very common element in Earth's crust, after only oxygen, silicon, and aluminum. It can be naturally found in small quantities in a nearly-pure form from meteorites and telluric iron. Most iron is extracted from Iron ores which are quite abundant in the Earth's crust, requiring kilns or furnaces to extract usable metal. Humans started to master that process in Eurasia around 3000 BCE with the development of the bloomery furnace. The displacement of copper alloys by iron tools and weapons is considered to mark the transition from the Bronze Age to the Iron Age. In the modern world, iron alloys, such as steel, stainless steel, cast iron and special steels, have been by far the most common industrial metals because of their mechanical properties and low cost.

Uses

See also: Spear

Iron can be used as a crafting material for a spear's head.

Dependencies

• Iron ore
  • Iron

(Weapons and tools)

• Axe
• Hammer
• Knife
• Spear
• Sword
• Shovel

(Other)

• Scrap iron
• Steel

• Bloomery furnace
• Kiln

Types of Iron

I. Raw Materials and Manufacturing Intermediates

• Iron Ore:
  • Achieved: Mined directly from the earth. Common forms include Hematite (Fe₂​O₃​), Magnetite (Fe₃​O₄​), Limonite (FeO(OH)⋅nH₂​O), and Siderite (FeCO₃​). Requires processing (crushing, washing, sometimes concentrating) before smelting.
  • Properties: Varies widely by ore type. Key property is iron content and the nature of impurities (gangue). Not usable as a metal in this state.
  • Uses: The fundamental raw material for all iron and steel production.
• Direct Reduced Iron (DRI) / Sponge Iron:
  • Achieved: Solid-state reduction of iron ore (usually pellets or lump ore) using a reducing gas (like hydrogen, carbon monoxide, or natural gas) or sometimes solid carbon (coal) at temperatures below iron's melting point. Avoids the need for a blast furnace.
  • Properties: Porous ("spongy") solid iron with impurities (gangue) from the original ore. Iron content is typically high (90-97%).
  • Uses: Primarily used as a feedstock for electric arc furnaces (EAFs) in steelmaking. Can be an alternative to scrap metal or pig iron, especially where coking coal for blast furnaces is scarce.
• Pig Iron:
  • Achieved: Smelting iron ore in a blast furnace with coke (fuel and reductant) and limestone (flux to remove impurities). Molten iron is tapped from the furnace and typically cast into ingots called "pigs".
  • Properties: High carbon content (typically 3.8–4.7%), along with silicon and other impurities. Relatively low melting point (1150-1200°C), brittle, not directly useful for structural applications due to brittleness.
  • Uses: Primary intermediate product. Re-melted and refined to produce steel or various types of cast iron.

II. Cast Irons (Generally > 2% Carbon)

• Grey Iron:
  • Achieved: Slow cooling of molten iron with appropriate carbon and silicon content, allowing carbon to precipitate out as graphite flakes within the iron matrix.
  • Properties: Excellent machinability, good wear resistance, excellent damping capacity (absorbs vibrations), relatively low tensile strength and ductility (brittle compared to steel due to graphite flakes acting as stress risers). Good fluidity for casting complex shapes.
  • Uses: Engine blocks, cylinder heads, machine tool bases, manifolds, cookware (e.g., skillets), pipe fittings, decorative castings.
• White Iron:
  • Achieved: Rapid cooling (chilling) of molten iron, often with lower silicon and higher chromium content, preventing carbon from precipitating as graphite. Carbon remains combined with iron as iron carbide (cementite, Fe3​C).
  • Properties: Extremely hard, brittle, excellent abrasion resistance, difficult to machine.
  • Uses: Wear surfaces (e.g., grinding mill liners, slurry pump housings, shot-blasting nozzles), raw material for producing malleable iron.
• Malleable Iron:
  • Achieved: Producing white iron castings and then subjecting them to a prolonged heat treatment (annealing) process. This breaks down the brittle cementite structure and causes the carbon to form irregular nodules (temper carbon) within an iron (ferrite or pearlite) matrix.
  • Properties: Better ductility and toughness than grey or white iron, good machinability, shock resistance. Largely superseded by ductile iron but still has niche uses.
  • Uses: Automotive components (differential housings, steering gear components), pipe fittings, electrical hardware, small machine parts requiring some ductility.
• Ductile Iron (Nodular Iron / Spheroidal Graphite Iron):
  • Achieved: Adding small amounts of specific elements (typically magnesium, sometimes cerium) to molten iron of appropriate composition just before casting. This causes the graphite to precipitate as spheres (nodules) rather than flakes.
  • Properties: Combines the casting advantages of grey iron with mechanical properties approaching those of steel (good strength, toughness, ductility, wear resistance, machinability). More impact resistant than grey iron.
  • Uses: Pressure pipes and fittings, automotive components (crankshafts, gears), heavy machinery parts, wind turbine components, axle housings. A very versatile cast material.
• Compacted Graphite Iron (CGI):
  • Achieved: Similar to ductile iron production but with tighter control over additives (often Mg and Ti) to form graphite particles that are short, thick, and interconnected (worm-like or vermicular), intermediate between flakes (grey) and spheres (ductile).
  • Properties: Intermediate properties between grey and ductile iron. Higher strength and stiffness than grey iron, better thermal conductivity and damping than ductile iron. Good castability and machinability.
  • Uses: High-performance engine blocks and cylinder heads (where higher strength-to-weight ratio and good thermal properties are needed), exhaust manifolds.
• Austempered Ductile Iron (ADI):
  • Achieved: Subjecting ductile iron castings to a specific heat treatment process called austempering (austenitizing followed by quenching in a salt bath at a specific temperature range and holding). This creates a unique microstructure (ausferrite).
  • Properties: Very high strength, good toughness, excellent wear resistance, good fatigue strength. Properties can be tailored by adjusting the heat treatment parameters.
  • Uses: High-strength, wear-resistant applications like gears, crankshafts, suspension components, agricultural and construction equipment parts, military applications. Represents a high-performance grade of cast iron.

III. Wrought Iron (Historically Significant)

• Wrought Iron:
  • Achieved: Historically made in bloomeries or finery forges by heating iron ore with charcoal, creating a spongy mass (bloom) of iron mixed with slag. This bloom was repeatedly heated and hammered (wrought) to expel slag and consolidate the iron.
  • Properties: Very low carbon content (< 0.08%), contains fibrous slag inclusions (silicates). Ductile, malleable, weldable (forge welding), relatively soft, good corrosion resistance compared to simple steels. Has a characteristic "grain" due to slag fibers.
  • Uses: Historically used for decorative ironwork (gates, railings), chains, anchors, nails, tools, early structural applications (beams, bridges like the Eiffel Tower's structure). Largely replaced by mild steel, but important for historical context and restoration. (Modern materials sometimes called "wrought iron" are often actually mild steel).

IV. Steels (Generally < 2.14% Carbon, typically much lower)

A. Carbon Steels (Properties primarily determined by carbon content)

• Low Carbon Steel (Mild Steel):
  • Achieved: Refining processes reduce carbon content to typically 0.05–0.25%.
  • Properties: Relatively soft, ductile, malleable, easily welded, good machinability, relatively low strength compared to higher carbon steels.
  • Uses: Vast range of applications - structural shapes (beams, channels), plates, sheets (car bodies, appliances), pipes, wire, fasteners (nails, screws, bolts). The most common type of steel.
• Medium Carbon Steel:
  • Achieved: Refining processes achieve carbon content typically between 0.25–0.60%. Often requires heat treatment (quenching and tempering) to achieve desired properties.
  • Properties: Higher strength and hardness than mild steel, lower ductility. Good wear resistance after heat treatment.
  • Uses: Machinery parts (gears, axles, shafts, couplings), railway tracks, structural components requiring higher strength.
• High Carbon Steel:
  • Achieved: Refining processes achieve carbon content typically between 0.60–1.25% (sometimes higher for ultra-high carbon steels). Almost always used in a heat-treated condition.
  • Properties: Very hard, strong, excellent wear resistance after heat treatment, but lower ductility (more brittle).
  • Uses: Cutting tools (knives, drills, saws), springs, high-strength wire, punches, dies.

B. Alloy Steels (Contain significant amounts of alloying elements besides carbon to modify properties)

• General Alloy Steels (e.g., Chromium-Molybdenum / Chromoly):
  • Achieved: Adding elements like chromium (Cr), Molybdenum (Mo), Nickel (Ni), Manganese (Mn), Vanadium (V), Tungsten (W) during steelmaking.
  • Properties: Wide range depending on alloy content. Can enhance hardness, strength, toughness, hardenability (ability to harden deeply during heat treatment), corrosion resistance, high-temperature strength, wear resistance.
  • Uses: High-stress structural components, automotive parts (axles, gears), pressure vessels, machine tools, aircraft components.
• Stainless Steel:
  • Achieved: Adding a minimum of 10.5% Chromium (Cr), often with Nickel (Ni), Molybdenum (Mo), and other elements. The chromium forms a passive oxide layer protecting the surface.
  • Properties: Excellent corrosion resistance is the defining characteristic. Various grades offer different levels of strength, toughness, weldability, and resistance to specific environments (e.g., acids, chlorides). Can be austenitic (non-magnetic, formable), ferritic (magnetic, less formable), martensitic (magnetic, hardenable by heat treatment), or duplex (mixed structure).
  • Uses: Cutlery, cookware, surgical instruments, chemical processing equipment, architectural trim, automotive exhaust systems, food processing equipment.
• Tool Steel:
  • Achieved: High-quality carbon or alloy steels specifically designed for making tools. Often contain Tungsten (W), Molybdenum (Mo), Vanadium (V), Chromium (Cr), Cobalt (Co) to enhance hardness, wear resistance, toughness, and heat resistance ('hot hardness'). Require precise heat treatment.
  • Properties: High hardness, abrasion resistance, ability to hold a cutting edge, toughness (to resist chipping), resistance to softening at high temperatures (for cutting tools).
  • Uses: Cutting tools (drills, taps, milling cutters), dies (forging, stamping, extrusion), molds (plastic injection), punches, shear blades.

Production Tree: From Iron Ore to Usable Metal

This section details the potential pathways for transforming raw iron ore into various usable forms of iron and steel. While limited to materials available in a pre-industrial setting (primarily clay, stone, wood, animal products for bellows/mechanisms) and hand-crafted tools, this tree leverages a modern understanding of metallurgy and engineering principles to inform the design and execution of processes.

Raw Material

• Iron Ore
  • Naturally occurring minerals rich in iron (e.g., Hematite (), Magnetite (Fe₃​O₄​), Limonite (FeO(OH)⋅nH₂​O), Pyrite (FeS₂), Siderite (FeCO₃​)).
  • Identification relies on visual cues (color, streak, density, shapes of the crystal forms), magnetic properties (for Magnetite), and location (ore deposits; or in the sand for Pyrite).

Ore Preparation

• Basic Ore Processing
  • Inputs: Iron Ore, Firewood/Fuel, Stone Hammers/Tools, Water (optional).
  • Process:
    • Crushing ore to smaller, relatively uniform size using stone or early metal tools.
    • Washing/Sluicing (optional, for some ore types like iron sands) to concentrate heavier iron minerals and remove lighter impurities (gangue).
    • Roasting (Calcining) the ore in a fire or simple hearth to remove water, break down carbonates, and make it more porous, improving reducibility.
  • Output: Prepared Iron Ore, ready for smelting

Initial Reduction from Ore to Useful Metal

Path A: Bloomery Smelting (Solid-State Reduction)

• Inputs: Prepared Iron Ore, Charcoal, Air Blast (from bellows or blower), Clay/Stone for furnace construction.
• Process: Heating layered ore and charcoal in a relatively low-temperature furnace (typically 1000−1200°C, below the melting point of pure iron) with airflow. Carbon monoxide gas produced from incomplete combustion of charcoal reduces iron oxides to spongy metallic iron. Impurities form molten slag (primarily iron silicates) which is tapped or remains within the iron mass. The iron itself does not melt significantly.
• Output: Direct Reduced Iron (a spongy mass of low-carbon iron and trapped slag - precursor to Wrought Iron).
• Feasibility: Highly accessible as an initial step. Requires achievable temperatures and basic furnace/bellows construction with primitive materials. This is the most likely first method to yield usable iron metal.

Path B: Blast Furnace Smelting (Melting Reduction)

• Inputs: Prepared Iron Ore, Charcoal (requires prior charcoal making), Flux (e.g., limestone or crushed seashells - helps impurities form a fluid slag at lower temperatures), Stronger Air Blast (requires more powerful and consistent bellows than bloomery, potentially water- or windmill-powered wooden/hide designs), Refractory Clay/Stone for taller furnace construction.
• Process: Heating layered ore, fuel, and flux in a taller furnace with a strong air blast. Achieves temperatures high enough to melt iron (typically 1200−1500°C). As molten iron trickles down through the hot, carbon-rich fuel, it readily dissolves significant amounts of carbon. Molten slag separates and floats on the molten iron in the hearth.
• Output: Molten Cast Iron / Pig Iron (High-carbon liquid Iron, typically 3.5-4.5% Carbon).
• Feasibility: More challenging than bloomery as an initial step due to requirements for higher sustained temperatures, a stronger/more reliable air blast over extended periods, and more complex/taller furnace construction with primitive refractories and tapping mechanisms. Modern knowledge aids in designing efficient air supply (e.g., multi-stage bellows, potentially powered by simple windmills or waterwheels) and furnace geometry to maximize heat and reduction, making it potentially achievable earlier than historical timelines but still a significant engineering hurdle compared to a bloomery.

Working with the Initial Metal Forms

From Iron Bloom (Path A Output):

• Bloom Consolidation (Forging)
  • Inputs: Direct Reduced Iron (Sponge Iron), Forge, Charcoal, Air Blast, Heavy Hammers (stone or early forged iron), Anvil (stone or early forged iron).
  • Process: Reheating the bloom to welding temperature and repeatedly hammering it while hot to expel trapped slag and weld the iron particles together into a solid, dense bar or billet.
  • Output: Wrought Iron Bars / Billets (Relatively pure iron with linear slag inclusions, highly malleable and ductile, but soft and not hardenable by simple quenching).
• Carburization (Cementation or Case Hardening)
  • Inputs: Wrought Iron Bars/Objects, Carbon Source (Charcoal, bone, other organic matter), Sealed Clay Box/Crucible, Furnace capable of sustained high heat (typically 850−1000°C, below melting point).
  • Process: Heating wrought iron in a carbon-rich environment for hours/days. Carbon atoms diffuse into the surface or bulk of the iron, increasing its carbon content.
  • Output: Carburized Iron / Blister Steel (Wrought iron with a hardened, higher-carbon surface layer or a bulk increase in carbon content, can be hardened by quenching).
• Crucible Melting (Steel Production)
  • Inputs: Wrought Iron [or mix of Wrought Iron and Cast Iron], Carbon Source (e.g., Charcoal, if starting only with Wrought Iron), Refractory Crucibles (made from suitable high-temperature clay), High-Temperature Furnace (more demanding than bloomery furnace, capable of reaching and sustaining steel melting temperatures, ∼1300−1500°C).
  • Process: Melting the iron and carbon-rich materials in sealed crucibles within a hot furnace. The carbon dissolves uniformly into the molten iron, creating a homogeneous steel alloy.
  • Output: Crucible Steel Ingots (High-quality steel with relatively controlled and uniform carbon content, can be forged and heat treated).
  • Feasibility: Challenging due to requirements for good quality refractory crucibles that can withstand extreme heat and thermal shock, and a furnace capable of reliably reaching and sustaining steel melting temperatures. Modern knowledge of clay composition and furnace design is crucial here.

From Molten Cast Iron (Path B Output):

• Casting
  • Inputs: Molten Cast Iron, Molds (made from sand, clay, or stone).
  • Process: Pouring molten cast iron directly into prepared molds to create objects of desired shape.
  • Output: Cast Iron Objects (Brittle due to high carbon, but useful for shapes that are difficult to forge, like pots, weights, furnace components. Cannot be easily forged).
• Decarburization (e.g., Finery Process)
  • Inputs: Cast Iron (solid or molten), Hearth/Furnace, Strong Air Blast, Fuel, Tools for manipulating semi-molten metal (e.g., early metal rods/paddles).
  • Process: Heating cast iron in an oxidizing environment (with air blown over or through it) to burn out excess carbon and silicon. Historically done in fining hearths or later puddling furnaces. The process is often stopped when the iron becomes pasty ("comes to nature") as carbon content drops and the melting point rises.
  • Output: Wrought Iron (from Cast) (Lower carbon, forgeable iron, similar properties to wrought iron from bloomery. Can loop back to the Wrought Iron processing path).
  • Feasibility: Requires a source of cast iron and a sufficiently hot, oxidizing hearth with robust air supply. Manipulating the hot, pasty metal requires durable tools, likely needing early forged iron for reliability.

Final Shaping and Use

From Wrought Iron Bars/Billets:

• Forging & Shaping
  • Inputs: Wrought Iron, Forge, Charcoal, Air Blast, Hammers, Anvil.
  • Process: Reheating and hammering the wrought iron to shape tools, components, structural elements, etc. Wrought iron's ductility makes it suitable for bending and forming.
  • Output: Wrought Iron Tools/Items (Durable, malleable, resistant to fatigue, but edges won't hold hardness well for cutting tools).

From Carburized Iron / Blister Steel or Crucible Steel Ingots:

• Forging & Heat Treatment (Hardening & Tempering)
  • Inputs: Steel (Carburized or Crucible), Forge, Charcoal, Air Blast, Hammers, Anvil, Quenching Medium (Water, Oil/Fat), Tempering Heat Source (Lower temperature heat, e.g., hot sand, ash, or controlled reheating in the forge).
  • Process: Forging steel to final shape. Then, heating to the critical temperature (austenite phase, judged visually by color, ∼750−900∘C) and rapidly cooling (quenching) in water or oil to form hard, brittle martensite. Followed by reheating to a lower temperature (tempering, judged by oxide colors on the surface, ∼200−600°C) and cooling to reduce brittleness and increase toughness.
  • Output: Hardened and Tempered Steel Tools / Components (Strong, holds a sharp edge, tough - properties vary based on carbon content and specific heat treatment).

From Cast Iron Objects:

• Finishing / Assembly
  • Inputs: Cast Iron Objects, Files, Grinders (simple abrasive stones or early grinding wheels), Assembly tools.
  • Process: Cleaning, smoothing, and assembling cast parts. Cast iron is difficult to work with cutting tools and cannot be forged.
  • Output: Functional Cast Iron Products (e.g., pots, weights, simple machine parts, architectural elements).

See also

• Copper
• Gold
• Lead
• Manganese
• Mercury
• Nickel
• Silver
• Sponge Iron
• Tin
• Titanium
• Wrought Iron
• Zinc
• Tungsten
• Chemical elements

References

This article uses material from the Wikipedia article Iron, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License (view authors).

External links

• Iron Prills - primitivetechnology.wordpress.com, 17 August 2018
• Primitive Technology: Iron prills - Primitive Technology, 17 August 2018, YouTube