HISTORY OF STEEL

Evidence of the use of iron alloys of meteoric origin dates back to at least 2000 BC in regions near the current periphery of Arab nations (ancient Sumeria), India, and China. Ancient civilizations lacked the technology to achieve the required temperature or the technique to reduce ferrous minerals to obtain the metal at an acceptable degree of purity. However, they were able to melt native Iron-Nickel metal alloys found in meteorites. The oldest objects made of iron alloys that have survived to this day prove that the metal was known more for its meteoric origin (containing small doses of Nickel) than as a constituent of minerals like Hematite or Magnetite. This "metal from the sky," probably Taenite or Kamacite (depending on the amount of Nickel), was prized above other previously known metals (Copper, Lead, Silver, and Gold) due to its extraordinary toughness and hardness in comparison.

The oldest "Iron" weapons and tools are therefore objects forged from meteorites that contained some Nickel, a metal that provides slight corrosion resistance, sufficient for some objects from prehistoric civilizations to have survived to our days. Obtaining metallic Iron through methods traditionally used for Bronze or precious metals (Silver and Gold) in a typical ancient furnace was simply impossible for several reasons. Among these was the partial (or total) ignorance of how to produce quality "Steel" from typical iron minerals, which, by the way, have always been abundant throughout history. Suffice it to say that elemental Iron is, by weight, the most abundant transition metal in the Earth's crust and the most abundant chemical element, by weight, on the entire Planet (including the mantle and the double-layer of the core). Yet, even at the zenith of the Egyptian Empire's splendor, Iron/Steel objects were so scarce that their price was comparable to that of gold. This value has been attributed to two fundamental factors: the fact that "Iron" literally fell from the sky in the form of meteorites gave it a "mystical" cache superior to other metals (including gold – the "tears of the Sun"), and it was simultaneously much stronger, stiffer, and more durable than the best Bronzes produced by Egypt and other subsequent civilizations, such as the Persian, Babylonian, and a long etcetera up to the times of Ancient Rome, where owning a mere poor-quality Steel sword was, believe it or not, a rare privilege only within reach of the military elites.

Another more important and easily understandable problem was the technology of the time. Today we have the capacity to melt Tungsten through rapid electron beam fusion, but at that time, things were radically different. It has been said that Steel was not known during the Roman era, for example; this is a lie. Of course, the metal was known, and even more so in eastern regions like ancient Persia and other empires/nations currently located on the Arab periphery. The problem was that large-scale production of the metal was very complicated and costly. For metallurgists of the time, it was much easier to produce Bronze than Steel or Cast Iron, among other things because Bronze did not (and does not) have a specific composition: a typical Bronze of 12% Tin with a Copper base does not differ much from one with 10% Tin, do you understand? But in the case of Iron, it is completely different, as even small quantities of Phosphorus, Sulfur, and of course, Carbon, greatly affect its properties. Today, the production of quality Steel is massive. Specific grades have been established (usually governed by the AISI) that formulate not only the chemical composition of each grade of Steel but also how to produce and heat-treat them, if possible. Of course, it was not always like this. In fact, in a historical context, modern Steel is relatively young compared to metals known to men in antiquity, such as Copper, Tin, precious metals, and their respective combinations.

In antiquity, when a blacksmith was able to forge tougher swords than another, he gained a great reputation. It was said, for example: "So-and-so's steel is of a quality that only Hephaestus (the Greek god of blacksmiths) could match." This man would then gain fame over his guild mates because, "for some reason," his objects were mechanically superior to those produced by others. People then spoke of "so-and-so's Steel," "such-and-such's Steel"; all blacksmiths and artisans wanted to develop the highest quality alloy possible. All kinds of tests were carried out, just as today: flexibility, toughness, hardness, strength... What changes between those heroes and the average metallurgist of today is that they achieved great things blindly, with very rustic, poorly crafted furnaces compared to the colossal ones we have today. This is interesting when one thinks about it in detail, because when it comes to metals, there is no possible deception. If you go to Extremadura and order a pata negra Iberian ham, I assure you that you will not find anything similar in (probably) any other region of Europe. Why? For many factors: the breeding of the animal, what it eats, the climate, etc. However, when you buy an AISI 440 grade knife whether in China, Uzbekistan, Russia, Colombia, or Malaysia, you will be sure that beyond appearances, the quality is practically the same. This is because, regardless of the manufacturer, the Steel remains the same. There is no difference between a "piece of Iron" from Chile and one from Alaska: they are exactly the same, as long as the "recipe" (chemical composition) is the same. That is why it does not matter where you buy or from whom you buy a hammer, a knife... if the manufacturer is serious and does not cheat you, you have exactly the same thing that I or anyone else has in their home, I don't know if I make myself clear. 

There is no possible deception with metals today; they are either good or they are not. But in the past, things were not so easy. There were no clear rules, manuals, or encyclopedias, and everyone made Steel as best they could to earn a living. In Japan, for example, a country where absolute devotion was paid to katanas in the feudal era (for a Samurai, his katana was part of his body – it was more than material, it was spiritual), the artisan's reputation was everything. If "Mr. Kokoto" (to give a fictional example) had a reputation for forging good katanas, then it was normal for his prices and clientele to be higher, reaching the nobility. Emperors, for example, had their own artisans, and they were surely the best in the entire nation; even if the sword never entered combat, it was simply "there," but he (or she) felt special because they knew it was of great quality.

Today it is difficult to find handmade Steel objects for various reasons. Most Steel objects are manufactured on a large scale in massive production lines that reduce the price of each unit, and all have the same quality, and this quality is, by logical rule, superior to that obtainable by a medieval artisan, no matter how much effort he put into it. But, as I have said, we did not always have large furnaces, we did not always have the opportunity to buy thirteen meters of chain to build a well for less than five hundred euros. One does not have to go back very far to realize that reality was very different from today; Steel was a luxury material good, within the reach of very few. Producing it on a large scale was virtually impossible, and whoever had an axe or a sword would care for it with such meticulousness that it would acquire a certain spiritual value that, with the passage of generations, would become cultural. I bet the famous Excalibur, had it truly existed, was made of high-quality Steel.

The mass production of steel is one of the fundamental pillars of modern industrial development. This alloy, composed primarily of iron (Fe) and carbon (C), has been instrumental in the evolution of infrastructure, transportation, machinery, and military technology from the 19th century to the present.

Steel has superior mechanical properties to pure iron, such as greater tensile strength, hardness, and toughness, as well as remarkable versatility in forming and welding processes. These characteristics make it an ideal material for structural applications, tools, vehicles, and defense systems. Its large-scale production was made possible by technological advances such as the Bessemer converter, the open-hearth furnace, and later the basic oxygen process, which reduced costs, increased efficiency, and improved the quality of the final product.

During the Industrial Revolution, the mastery of steelmaking technology was a decisive factor in the economic growth of powerhouses such as the United Kingdom, Germany, and the United States. The ability to manufacture steel in large volumes facilitated the construction of railways, bridges, factories, ships, and weapons, consolidating the infrastructure necessary for territorial expansion, global trade, and military supremacy.

In the civil sphere, steel has been essential in the development of transportation systems such as railways, whose structure depends on rails, locomotives, and components made from this alloy. Likewise, modern architecture relies on steel for the construction of high-rise buildings, stadiums, and other structures subject to high mechanical demands.

Despite the emergence of alternative materials such as aluminum (Al), titanium (Ti), and carbon fiber composites, steel remains the most widely used material in terms of volume and cost-effectiveness. Its relative abundance in the Earth's crust, along with the efficiency of its recycling processes, reinforce its position as a strategic resource in global industry.

In conclusion, the mass production of steel has not only transformed the economy and modern technology, but also continues to be a key element in the sustainability and competitiveness of contemporary societies.

Steel is a metallic alloy composed primarily of iron (Fe) and carbon (C), whose structure and mechanical properties vary significantly depending on the carbon content and the heat treatment applied. Elemental iron, classified as a transition metal, exhibits a space-centered cubic crystal structure (Ferrite, α-Fe) at room temperature, giving it moderate hardness, good ductility, and malleability. However, these properties can be drastically modified by the controlled incorporation of carbon, which acts as a hardening element.

During the melting process, liquid iron can dissolve carbon into its metallic matrix, generating a series of structural transformations. At temperatures above 910°C, iron adopts a face-centered cubic structure (Austenite, γ-Fe), which allows for greater carbon solubility due to its more open atomic configuration. This phase is stable until approximately 1400°C, at which point the system returns to the ferrite phase, expelling some of the carbon in the form of gas (CO, CO₂), while another fraction remains trapped in the matrix without forming a chemical bond (graphite), and the remainder combines to form cementite (Fe₃C), a ceramic intermetallic compound.

Cast iron, an intermediate product with a carbon content close to 2%, is characterized by its high hardness and brittleness. Although it has historically been used in applications with low mechanical demands, such as household utensils, its structural usefulness is limited. To obtain quality steel, the carbon content must be reduced through thermal and mechanical refining processes. In ancient times, this adjustment was achieved by beating the cast iron at red heat, promoting the expulsion of excess carbon and favoring the phase transition between ferrite and austenite. This procedure achieved a balance between hardness and malleability, suitable for the manufacture of tools and weapons. Iron's ability to form solid solutions with carbon is limited to a maximum of approximately 2.1% by mass, depending on the temperature and the state of the crystalline phase. The transition between ferrite and austenite is determined not only by temperature but also by carbon concentration, which complicates precise control of the final steel composition. Furthermore, the presence of graphite and cementite in the microstructure directly influences the material's mechanical properties, such as toughness, wear resistance, and brittleness.

Mass production of steel was historically limited by the lack of efficient refining technologies. The development of processes such as the Bessemer converter, the Siemens-Martin furnace, and Krupp techniques made it possible to overcome these barriers, facilitating the large-scale industrial manufacture of steel with controlled properties. These technological advances gave the nations that adopted them a strategic advantage in both the economic and military spheres, enabling the construction of infrastructure, heavy machinery, and defense systems with high-performance materials. In short, steel is an alloy whose complexity lies in the interaction between iron and carbon, as well as in the phase transformations that occur during its thermal processing. Its versatility and strength make it an essential material for modern engineering, and its controlled production has been key to the industrial development of contemporary societies.

Steel is an alloy quite different from those known to metallurgists of the past. It involves many stages, which I will describe little by little in this chapter, starting now. To obtain the alloy, we need iron and carbon, but also other elements, which are always relegated to a very discreet role in steel literature, when in reality they are indispensable for generating an alloy with good mechanical properties. The process for obtaining quality steel in mass production is due to several factors, not only the chemical control of the ingredients, but also the adjustment of the temperature of the refractory furnace in which the reaction takes place and finally, the heat treatment employed in its final manufacturing, if possible. And I say "if possible" because not all steels can be heat-treated. But for now, let's focus. Step by step. 

Steel production begins with the preparation of iron-containing raw materials, with oxidized ores being the primary sources. Among them, hematite (Fe₂O₃) and magnetite (Fe₃O₄) stand out, both widely used in the steel industry due to their high iron concentration and favorable behavior in reduction processes. Other sources are also used, such as siderite (FeCO₃), an iron carbonate, and steel scrap, which represents an efficient path for recycling and energy utilization. Although there are other iron-containing minerals, such as pyrite (FeS₂), their use is limited due to the presence of sulfur, an undesirable element in steel manufacturing because of its negative effect on the mechanical properties of the final product.

Before being introduced into the blast furnace, the ores undergo a crushing process to reduce their size and facilitate thermal distribution during smelting. This fragmentation improves process efficiency by allowing more homogeneous heat transfer and simpler material handling in automated transport systems.

Once prepared, the ores are loaded into the blast furnace along with a carbon source, generally coke, which serves a dual function. Firstly, it acts as a reducing agent, promoting the conversion of iron oxides into metallic iron through reaction with the oxygen present in the minerals. Secondly, carbon is partially incorporated into the molten iron, initiating the formation of the basic alloy that will become steel. This process generates gases such as carbon monoxide (CO) and carbon dioxide (CO₂), which are expelled from the system, while the impure iron obtained—known as pig iron—constitutes the precursor to steel after subsequent refining.

The roasting and reduction of ferrous ores therefore represent the initial and essential stage in the steel production chain, determining the energy efficiency, product quality, and economic viability of the steelmaking process.

Based on the fact that iron (whether pure or in mineral form in the reaction) will absorb up to a maximum of 2.1% by mass of carbon, we aim to reduce this quantity to the desired point. For this, the inclusion of third chemical elements is necessary, which will help control the excess carbon, either by aiding its release or simply by facilitating its inclusion in the metallic matrix so that it does not have a detrimental effect on it. 

Iron, whether in its pure state or in mineral form during the reduction process, has the capacity to absorb up to 2.1% carbon by mass. This limit defines the boundary between steel and pig iron, with precise control of this content being a critical aspect in obtaining alloys with specific mechanical properties. The regulation of carbon not only determines the hardness, toughness, and ductility of steel but also influences its behavior towards heat treatments and mechanical stresses.

To adjust the carbon percentage to desired levels, additional chemical elements are incorporated that act as microstructure modifiers. Some of these elements promote the expulsion of excess carbon during smelting, while others facilitate its integration into the metallic matrix without compromising the material's structural stability. The goal is to prevent the excessive formation of compounds like cementite (Fe₃C) or the precipitation of free graphite, which can induce brittleness or reduce the formability of steel.

The selection of these elements depends on the type of steel to be obtained and the specific conditions of the manufacturing process. In high-strength alloys, for example, elements such as manganese (Mn), silicon (Si), or chromium (Cr) are used, which stabilize certain crystalline phases and modify carbon solubility. In other cases, aluminum (Al) or oxygen (O) can act as deoxidizing agents, indirectly contributing to carbon content regulation.

This approach allows for the design of steels with optimized properties for structural applications, cutting tools, automotive components, or pressure systems, ensuring a balance between mechanical strength, workability, and durability. The precise management of carbon, along with the strategic use of alloying elements, therefore constitutes an essential stage in modern metallurgical engineering.

During the steelmaking process, oxygen plays an ambivalent role. Although it can facilitate certain necessary oxidation reactions in previous stages, its residual presence in the metallic matrix represents a considerable risk to the structural integrity of the alloy. Oxygen, by reacting with molten iron, can generate internal oxides that compromise the toughness of steel, induce intergranular brittleness, and reduce its mechanical strength. To avoid these adverse effects, deoxidizing elements are incorporated that have a greater chemical affinity for oxygen than iron itself, allowing for its controlled elimination during smelting.

These elements do not interact directly with carbon but do interact with oxygen and, in some cases, with iron, forming stable compounds that separate from the metallic phase. They are added in small proportions, sufficient to neutralize oxygen without significantly altering the overall composition of the alloy. Among the most used elements are manganese, silicon, and phosphorus, while aluminum, although chemically effective, is used less frequently due to its low solubility in molten steel and the formation of undesired inclusions.

Manganese stands out for its triple function: it acts as a deoxidizer, a grain refiner, and a sulfur fixer, preventing the formation of brittle sulfides that can weaken the steel structure. Silicon, for its part, contributes to microstructure homogenization and grain size reduction, in addition to effectively fulfilling its role as a deoxidizer. Phosphorus, although historically present in certain steel grades, is currently avoided due to its detrimental effect on ductility and impact resistance. Aluminum, despite being more economical than other deoxidizers, is rarely used in significant proportions, as its benefits do not outweigh those obtained with silicon or manganese.

The precise incorporation of these elements allows for control of oxygen reactivity during smelting, ensuring a stable internal structure free of defects. This control is essential for obtaining high-quality steels, especially in applications where mechanical strength, toughness, and durability are fundamental requirements. Once the balance between carbon and oxygen is resolved, the next step is to address the presence of additional impurities that can compromise the final quality of the alloy.

Almost anyone living in a first or second-world country can go to a hardware store and buy a hammer, a pair of pliers, or any such tool, knowing that in any case, it will be of great quality. This, however, was not always the case, as I have repeatedly stated throughout this chapter. Just a few moments ago, I mentioned the case of the Titanic and why the poor quality of its Steel could, to a lesser extent, have further contributed to its resounding end.

What happens with elemental Iron is that it “contaminates” very easily. It is a base metal, very reactive, forming compounds with almost all non-metals and also with some metalloids, although that is not really its problem. The real problem is that, even in doses as low as 0.1%, “undesirable” elements completely alter the properties from one alloy to another. Let's take a practical example.

On one side, we have Carbon Steel with a carbon content of 0.5%, and on the other, Steel with exactly the same amount of Carbon, but with 0.1% Sulfur. Do you think they will be mechanically identical? The most obvious answer is no, of course, but... to what extent are they different? That is the real question. What I am trying to explain is that in the case of Steels, even such a discreet amount as 0.1% already greatly affects the properties of the final alloy. This is why Steel must be generated with great caution and precision; otherwise, the quality between one manufacturer and another will be affected. It is not enough simply to add the exact chemical ingredients; we must take many factors into account. For example, when you visit a Steel refinery, you cannot see Sulfur. Neither can I. It is not present in sufficient quantity to be detected, but it is present. How? In the form of gases or in small solid doses not appreciable to the naked eye. 

Do you remember when I mentioned the Iron Pillar of Delhi? We haven't talked about it yet, but if you recall correctly, I previously said that Indian metallurgists, either deliberately (consciously) or semi-unconsciously, used woods rich in Phosphorus which, once burned, released this non-metal into the atmosphere, with the detail that -part- of that Phosphorus released was “trapped” (dissolved) by the Iron that was in a liquid state. Well, the same thing happens with Sulfur. It's not that the raw materials are of poor quality: even with the best starting materials, the presence of Sulfur will be inevitable, as it is a very, very abundant element not only in all living beings (remember that when we burn wood, we are basically burning something that was once alive) but also in all large factories and industries, rarely in its elemental state, frequently in a gaseous or liquid state. Since Iron (metal) can dissolve a considerable amount of Sulfur (just as it does with Carbon), the in-situ formation of Iron Sulfates/Sulfides must be avoided during casting. For this, the transition metal that precedes Iron itself in the periodic table, Manganese, is the most used, as it is more reactive and forms volatile sulfates that “fix” the excess Sulfur, freeing the Iron from this additional “burden.” As you can see, many of the chemical elements added to Steel play a fundamental role. Everyone says, “Steel is every Iron-Carbon alloy...” but they rarely take into account the presence of Silicon, Manganese, and the so-called unwanted impurities such as excess Carbon, Phosphorus, and Sulfur. The latter, particularly, because its effects on the king alloy are very detrimental.

In steel manufacturing, no chemical element can match the functionality of Manganese as a deoxidizer and as a sulfur neutralizing agent, especially when considering its cost-effectiveness. Although it is not a metal particularly noted for its aesthetic or commercial properties, its role in metallurgy is absolutely essential. Without Manganese, the production of high-quality steel would be practically unfeasible.

One of the reasons Manganese is so effective is its chemical affinity with sulfur. By reacting with this element, it forms stable compounds that prevent the formation of iron sulfides, which weaken the structure of steel and reduce its mechanical resistance. Additionally, Manganese contributes to the deoxidation of the molten metal bath and improves the toughness of the final product.

Unlike Copper or Tungsten, Manganese offers multiple advantages. Copper, although useful in other alloys, does not possess desulfurizing capacity and can cause hot shortness if its proportion is exceeded. Tungsten, on the other hand, is a high-cost element used in special steels to increase hardness, but it does not perform chemical refinement or impurity neutralization functions.

Steel, the culminating product of a technical and historical process that has evolved over centuries, represents much more than a simple chemical transformation. From the extraction of minerals like hematite—a stone that, although known for its ornamental value, holds the potential to become one of humanity's most versatile alloys—to its conversion into bars ready for industrial use, the journey is extensive and demanding.

Hematite, rich in iron oxides, begins its journey deep within the earth. After extraction, it undergoes smelting processes that generate crude, impure, and brittle iron. This iron, far from being the final product, goes through successive stages of refining, deoxidation, desulfurization, and composition adjustment, until it reaches the precise proportions that define steel. Each phase requires not only energy—in the form of fuels, furnaces, and heavy machinery—but also accumulated knowledge, technical precision, and impeccable coordination among operators, engineers, and metallurgists.

Although summarized here in a few lines, this process can extend for weeks or even months, depending on the type of steel, the required degree of purity, and the intended final use. Behind every steel bar is a story of human effort, constant innovation, and respect for a tradition that has enabled the construction of bridges, tools, vehicles, buildings, and even spacecraft.

Recognizing the value of steel is not just appreciating its strength or malleability, but understanding that every gram encapsulates the work of generations. Therefore, beyond the technique, it deserves recognition: not only for what it is, but for all that it has cost to achieve it.