Hierro. Materiales y materias primas.

The Importance of Iron in Human History

The Discovery and Utilization of Iron

• Since ancient times, humans have known and utilized seven different metallic elements, with iron being a crucial raw material that named one of the prehistoric stages.

• The development of iron led to significant advancements, including the production of various items from pins to monumental structures like the Eiffel Tower and essential components for industries such as railways.

The Rise of Iron Metallurgy

• Around 1900 BC, civilizations in Asia Minor effectively challenged the powers of Egypt, Babylon, and Assyria due to their mastery over iron.

• Not all cultures extracted iron from the earth; some received it from meteorites. This marked the beginning of the Iron Age as iron began replacing bronze in tools and weapons.

Advancements by Civilizations

• By 1500 BC, Hittites extensively used iron with advanced metallurgical techniques to create fast chariots and powerful weaponry that expanded their empire.

• The culture spread from the Middle East to Europe, with evidence found in Switzerland marking the onset of the Iron Age on that continent.

Unique Properties of Damascus Steel

• Eight centuries separate the Third Crusade from modern nanotechnology; connections exist between Damascus swords and carbon nanotubes.

• In 1991, research revealed that authentic Damascus steel contained carbon nanotubes, explaining its legendary strength and sharpness—an achievement realized long before modern science understood these structures.

Innovations in Indian Metallurgy

• Archaeological findings indicate India had advanced metallurgy practices producing "Wootz" steel traded as disks through a specific smelting process involving charcoal.

• A unique method involved using bellows to introduce air into stone furnaces which created sponge iron through reactions between carbon monoxide and iron oxide.

Forging Techniques: A Key Differentiator

• The skillful forging techniques employed by Syrian blacksmiths at temperatures between 650°C - 850°C resulted in extraordinary ductility and super-elasticity not seen in European methods.

• European smithing often failed because they forged at much higher temperatures (around 1000°C), leading to disintegration rather than effective shaping.

Evolution Through Medieval Practices

• During medieval times, previously considered useless materials became foundational for modern steel production. Catalan forges produced sponge iron but lost significant amounts due to slag.

Iron Ore and Steel Production Process

Types of Iron Ores

• The main types of iron ores discussed are magnetite, hematite, limonite, siderite, and pyrite. The "law" refers to the percentage of metal contained in the mineral necessary for use in the steel industry.

• For industrial use, materials must contain a minimum of 40% iron; magnetite contains 72%, hematite 70%, while pyrite has only 47%.

• China ranks as the third-largest producer of iron ore globally after Brazil and Australia and is also the leading producer of crude steel.

Locations of Iron Ore Deposits

• In Argentina, significant deposits are found in regions such as Jujuy, Salta, Catamarca, La Rioja, Mendoza, San Juan, San Luis, and parts of Patagonia like Sierra Grande in Río Negro.

Differences Between Steel Types

• The primary raw material for both steel types is iron; however, one type is referred to as "steel" while the other is called "foundry." This distinction hinges on a small percentage of carbon content.

• Pure iron is not used in industry; instead it’s alloyed with elements like carbon. Alloys with less than 1.76% carbon are classified as steels; those with higher percentages are considered cast irons.

Steel Production Methods

Direct Reduction Method

• The direct reduction method produces steel with up to 1.7% carbon from raw materials in a single stage.

Indirect Reduction Method

• In indirect methods, pig iron (with 3–4.5% carbon) is first produced before refining it to obtain desired steel composition below 1.7% carbon.

Initial Processing Steps

• Iron ore arrives at steel mills via ships as pellets or lumps (55–65 tons), which are then transported by conveyor belts to storage areas.

Transformation into Steel

• The first transformation stage occurs at direct reduction plants using high-grade iron oxide pellets/lumps and natural gas.

Reduction Process Details

• In reduction furnaces:

• Upper circuit preheats and reduces iron oxide using hydrogen and carbon monoxide at around 960°C.

• Gases react with iron oxide to produce nearly pure sponge iron discharged from the furnace's bottom.

Sponge Iron Production Insights

• Producing 5,000 tons daily requires about one million cubic meters of gas—equivalent to residential consumption in Rosario over that period.

Electric Arc Furnace Operations

• Electric arc furnaces utilize a mix comprising 35% scrap metal and 65% sponge iron for melting processes.

Furnace Specifications

• These furnaces can hold up to 270 tons of molten material and reach temperatures up to 3600°C using vertical electrodes creating an electric arc.

Final Refining Processes

Liquid Steel Collection

• Liquid steel obtained from electric arc furnaces undergoes further refining in ladle furnaces where ferroalloys/additives create various steels based on strict specifications.

Energy Consumption Comparison

• To melt a load of 110 tons takes energy equivalent to what an average household consumes over thirty years.

Overview of Indirect Method Stages

High Furnace Operation

• The indirect method involves two stages:

• First stage: Reducing iron ore in blast furnaces producing pig iron (arrabio).

• Second stage: Converting pig iron into crude steel using special converters with enriched air inputs.

Blast Furnace Structure

Steel Production Process

Overview of the Steelmaking Process

• The interior of the furnace is lined with refractory bricks designed to withstand high temperatures and erosion caused by descending loads and chemical reactions.

• Material enters the furnace at approximately 150°C, where oxygen-enriched air is injected through tuyeres, raising the temperature to around 2000°C. This process generates carbon monoxide that reduces iron ore by removing oxygen.

• High temperatures facilitate the reduction of manganese oxide, sulfur removal, and melting of iron ore into pig iron—a metal alloy with high carbon content and impurities collected at the bottom of the furnace.

• Pig iron is extracted by breaking a clay plug (piquera), flowing into ladles; this process is known as casting. The pig iron typically contains 91% to 94% iron along with small amounts of carbon, manganese, sulfur, phosphorus, and silicon.

Transition from Pig Iron to Steel

• The transformation from pig iron to steel occurs in special converters; this refining process is crucial for producing various products like tea spoons.

• The history of steel metallurgy links back to Sheffield, England—renowned since the 14th century for its quality knives and swords. Henry Bessemer invented the first converter in 1855.

• Bessemer's converter was a tilting furnace lined with silica that allowed for efficient steel production while reducing costs significantly over three decades.

Phases of Steel Refining

• The refining process consists of three phases: filling (tilting for loading pig iron), blowing (injecting hot air vertically), and emptying (tilting again to pour out steel).

• Each cycle lasts about 20 minutes, capable of refining between 10 to 25 tons but lacks precise control over steel composition due to refractory lining limitations.

Innovations in Steelmaking

• In 1875, Sydney Thomas improved upon Bessemer's design by using dolomite lining which enabled phosphorus removal as calcium phosphate slag—this innovation had agricultural benefits as well.

• Evolving technologies led to Siemens-Martin furnaces and electric furnaces post-WWII; experiments began using pure oxygen instead of air during refining processes.

Modern Steel Refining Techniques

• In Austria in 1948, basic oxygen processes were developed where liquid pig iron was treated in a vessel called a ladle before adding fluxes like lime for impurity capture.

• Oxygen agitation oxidizes carbon and silicon from molten metal reaching temperatures above 1500°C transforming it into steel; after blowing ends, slag is removed followed by pouring refined steel into ladles for further processing.

Continuous Casting Process

Laminación en Caliente y Tipos de Aceros

Proceso de Laminación en Caliente

• La laminación en caliente es un proceso donde se pasa la palanquilla entre dos rodillos que giran a la misma velocidad y en sentidos opuestos, reduciendo su sección transversal mediante presión.

• Este proceso permite obtener productos como flejes para tubos, perfiles, barras de diferentes secciones para construcción, alambrones y alambres industriales.

Laminado en Frío y Productos Derivados

• Las chapas laminadas en caliente son sometidas a un laminado en frío, lo que reduce el espesor y mejora el aspecto superficial para diversas aplicaciones comerciales.

• La industria también produce aceros revestidos con materiales como zinc o cromo para aumentar la resistencia a la corrosión.

Clases de Acero

• Existen cinco clases principales de acero: al carbono, aleados de baja aleación ultrarresistentes, inoxidables y para herramientas.

• Más del 90% de los aceros son al carbono, utilizados principalmente en estructuras de construcción y objetos comunes.

Propiedades del Acero Aleado e Inoxidable

• Los aceros aleados contienen elementos como molibdeno y manganeso; se utilizan para fabricar engranajes y cuchillos.

• Los aceros inoxidables poseen alta resistencia mecánica y a la corrosión; son reciclables y se usan en tuberías, tanques refinerías, fuselajes de aviones e instrumentos quirúrgicos.

Impacto Ambiental de la Siderurgia

• La siderurgia contribuye significativamente al efecto invernadero debido a las emisiones de CO2 y otros gases contaminantes.

• A pesar del impacto ambiental negativo, las empresas siderúrgicas invierten en mejorar procesos para minimizar contaminación.