The term steel comes from the Latin "aciarius", and this from the word "acies", which is what the edge of a knife is called in this language. "Aciarius" would therefore be the appropriate metal, due to its hardness and resistance, to be used in the cutting part of weapons and tools.

The exact date on which the technique to obtain iron from the fusion of minerals was discovered is unknown. However, the first archaeological remains of iron utensils date back to 3000 BC. C. and were discovered in Egypt, although there are vestiges of previous ornaments. Quintus Horacio Flaco points out that steel weapons such as the falcata were used in the Iberian Peninsula as early as the century BC. C., while noric steel (in Latin: chalybs noricus) was used by Roman troops.[5] During the Han dynasty of China, steel was produced by melting wrought iron with cast iron, around the century BC. C.[6][7] They also adopted production methods for creating wootz steel, a process that emerged in India and Sri Lanka from approximately 300 BC. C. and exported to China around the 1st century. This early method used a wind furnace, blown by the monsoons.[8]​[9]​ Also known as Damascus steel, it was an iron alloy with a large number of different materials, including traces of other elements in concentrations less than 1000 parts per million or 0.1% of the rock composition. Studies carried out by Peter Paufler suggested that its structure included carbon nanotubes, which could explain some of the qualities of this steel - such as its durability and ability to maintain an edge - although due to the technology of the time it is possible that they were obtained by chance and not by a premeditated design.[10]​.

Between the centuries and crucible steel was produced in Merv, in which steel was obtained by heating and cooling iron and carbon using different techniques. During the Song dynasty of the century in China, steel production was carried out using two techniques: the first produced low-quality steel because it was not homogeneous - the "Berganesque" method - and the second, a precursor to the Bessemer method, removed the carbon with repeated forgings and subjected the piece to abrupt cooling.[11]​.

Iron for industrial use was discovered around 1500 BC. C., in Metsamor and Mount Ararat, in Armenia.[12] Iron technology was kept secret for a long time, spreading widely around the year 1200 BC. c.

There are no records that hardenability was known until the Middle Ages. The ancient methods for making steel consisted of obtaining soft iron in the furnace, with charcoal and air draft, with a subsequent expulsion of the slags "Slag (metallurgy)") by hammering and carburizing the soft iron to cement it. Then cementation was perfected by melting the cemented steel in clay crucibles and in Sheffield (England) crucible steels were obtained from 1740 onwards.[13] The technique was developed by Benjamin Huntsman.

In 1856, Henry Bessemer developed a method to produce steel in large quantities, but since only iron containing phosphorus and sulfur in small proportions could be used, it was abandoned. The following year, Carl Wilhelm Siemens created another, the Martin-Siemens procedure, in which steel was produced from the decarburization of soft iron casting and iron oxide as a product of heating with oil, coke gas, or a mixture of the latter with blast furnace gas. This method also fell into disuse.

Although in 1878 Siemens was also the first to employ electricity to heat steel furnaces, the use of electric arc furnaces for commercial production began in 1902 by Paul Héroult, who was one of the inventors of the modern method of smelting aluminum. In this method, an electric arc is passed inside the furnace between scrap steel whose composition is known and large carbon electrodes located on the roof of the furnace.

In 1948, the L-D basic oxygen process was invented. After World War II, experiments began in several countries with pure oxygen instead of air for steel refining processes. Success was achieved in Austria in 1948, when a steel factory located near the city of Linz, Donawitz, developed the basic oxygen or L-D process.

In 1950, the continuous casting process was invented, which is used when it is required to produce rolled steel profiles of constant section and in large quantities. The process consists of placing a mold with the required shape under a crucible, which with a valve can dose molten material into the mold. By gravity, the molten material passes through the mold, which is cooled by a water system; as the molten material passes through the cold mold, it becomes pasty and takes on the shape of the mold. Subsequently, the material is shaped. with a series of rollers that at the same time drag it towards the outside of the system. Once the material has been formed into the necessary shape and with the appropriate length, the material is cut and stored.

Currently, some metals and metalloids are used in the form of ferroalloys, which, together with steel, provide excellent qualities of hardness and resistance.[14]​.

Currently, the steel manufacturing process is completed by the so-called secondary metallurgy. At this stage, the desired chemical properties, temperature, gas content, level of inclusions and impurities are given to the liquid steel. The most common unit of secondary metallurgy is the ladle furnace. The steel produced here is ready to be subsequently cast, conventionally or in continuous casting.

The intensive use that steel has and has had for the construction of metallic structures has seen great successes and resounding failures that have at least allowed the advancement of materials science. Thus, on November 7, 1940, the world witnessed the collapse of the Tacoma Narrows Bridge as it entered into resonance "Resonance (mechanical)") with the wind. Already during the first years of the Industrial Revolution, premature failures of railway axles occurred, leading William Rankine to postulate material fatigue, and during World War II there were some unforeseen sinkings of the American Liberty freighters when the steel became brittle due to the mere drop in temperature,[15] a problem initially attributed to welding.

Alloy or special steels contain other elements, in addition to carbon, that modify their properties. These are classified according to their influence:.

Elements that increase hardness: phosphorus, nickel, copper, aluminum. Especially those that retain hardness at high temperatures: titanium, vanadium, molybdenum, tungsten, chromium, manganese and cobalt.

Elements that limit grain size growth: aluminum, titanium and vanadium.

Elements that determine hardenability: increase hardenability: manganese, molybdenum, chromium, nickel and silicon. Decreases hardenability: cobalt.

Elements that modify resistance to corrosion or oxidation: increase resistance to oxidation: molybdenum and tungsten. Promotes resistance to corrosion: chromium.

Elements that modify the critical transformation temperatures: Critical points increase: molybdenum, aluminum, silicon, vanadium, tungsten. Critical temperatures decrease: copper, nickel and manganese. In the particular case of chromium, the critical points rise when the steel has a high percentage of carbon but decreases when the steel has a low carbon content.

Contenido

Los dos componentes principales del acero se encuentran en abundancia en la naturaleza, lo que favorece su producción a gran escala. Esta variedad y disponibilidad[16]​ lo hace apto para numerosos usos como la construcción de maquinaria, herramientas, edificios y obras públicas, contribuyendo al desarrollo tecnológico de las sociedades industrializadas.[13]​ A pesar de su densidad (7850 kg/m³ de densidad en comparación a los 2700 kg/m³ del aluminio, por ejemplo) el acero es utilizado en todos los sectores de la industria, incluso en el aeronáutico, ya que las piezas con mayores solicitaciones (ya sea al impacto o a la fatiga) solo pueden aguantar con un material dúctil y tenaz como es el acero, además de la ventaja de su relativo bajo costo.

Other elements in steel

Standard steel classifications such as AISI, ASTM and UNS establish minimum or maximum values ​​for each type of element. These elements are added to obtain certain characteristics such as hardenability, mechanical resistance, hardness, toughness, wear resistance, weldability") or machinability.[17] Some of the effects of alloying elements on steel are listed below:[18]​

[19]​.

• - Aluminum: it is used in some high-hardness Cr-Al-Mo nitriding steels in concentrations close to 1% and in percentages less than 0.008% as a deoxidizer in high-alloy steels.

• - Boron: in very small quantities (from 0.001 to 0.006%) it increases hardenability without reducing machinability, as it combines with carbon to form carbides, providing a hard coating. It is used in low alloy steels in applications such as plow blades and wires with high ductility and surface hardness. Also used as a nitrogen trap, especially in steels for drawing, to obtain N values ​​less than 80 ppm.

• - Cobalt: very hardening. Decreases hardenability. Improves resistance and hardness when hot. It is an unusual element in steels. Increases the magnetic properties of steels. It is used in high-speed tool steels and refractory steels.

• - Chromium: Forms very hard carbides and gives the steel greater hardness, resistance and toughness at any temperature. Alone or alloyed with other elements, it improves corrosion resistance. Increases the depth of penetration of hardening by thermochemical treatment such as carburizing or nitriding. It is used in stainless steels, tool steels and refractories. It is also used in decorative coatings or hard coatings with high wear resistance, such as pistons, shafts, etc.

• - Molybdenum: it is a common element in steel and greatly increases the depth of hardening of steel, as well as its toughness. Austenitic stainless steels contain molybdenum to improve corrosion resistance.

• - Nitrogen: added to some steels to promote the formation of austenite.

• - Nickel: it is a gammagen element allowing an austenitic structure at room temperature, which increases toughness and impact resistance. Nickel is widely used to produce stainless steel because it increases corrosion resistance.

• - Lead: lead is not combined with steel, it is found in it in the form of very small globules, as if emulsified, which favors easy machining by chip removal (turning, brushing, drilling, etc.) since lead is a good cutting lubricant, the percentage ranges between 0.15% and 0.30% and the carbon content must be limited to values lower than 0.5% because it makes tempering difficult and reduces hot toughness. It is added to some steels to greatly improve machinability.

• - Silicon: moderately increases hardenability. It is used as a deoxidizing element. Increases the resistance of low carbon steels.

• - Titanium: used to stabilize and deoxidize steel, it keeps the properties of steel stable at high temperatures. Its high affinity with carbon is used to prevent the formation of iron carbide when welding steel.

• - Wolfram: also known as tungsten. It forms very complex, stable and very hard carbides with iron, withstanding high temperatures well. In percentages of 14 to 18%, it provides high-speed steels with which it is possible to triple the cutting speed of carbon tool steels.

• - Vanadium: it has an energetic deoxidizing action and forms complex carbides with iron, which provide the steel with good resistance to fatigue, traction and cutting power in tool steels.

• - Niobium: It is used to give hardness, flexibility and elasticity to steel, it is mainly used for structural steel and automotive steel.

All undesirable elements in the composition of steels are called impurities. They are found in steel and also in foundries as a result of being present in minerals or fuels. Efforts are made to eliminate them or reduce their content because they are detrimental to the properties of the alloy. In cases where eliminating them is impossible or too costly, their presence is allowed in minimal quantities.

• - Sulfur: approximate maximum limit: 0.04%. Sulfur with iron forms sulfide, which, together with austenite, gives rise to a eutectic whose melting point is low and which, therefore, appears in grain boundaries. When cast steel ingots must be hot rolled, said eutectic is in a liquid state, which causes the material to break apart.

• - Phosphorus "Phosphorus (element)"): approximate maximum limit: 0.04%. Phosphorus is harmful, either by dissolving in ferrite, as it reduces ductility, or by forming FeP ("iron phosphide"). Iron phosphide"), together with austenite and cementite, forms a ternary eutectic called "essteadite", which is extremely fragile and has a relatively low melting point, which is why it appears in grain boundaries, transmitting its fragility to the material.

Depending on the manufacturing method

• - Electrical steel.

• - Cast steel.

• - Calmed steel.

• - Effervescent steel.

• - Fried steel.

• - Drawn steel.

According to the way of working it

• - Cast steel.

• - Forged steel.

• - Laminated steel.

Depending on the composition and structure

• - Ordinary steels.

• - Alloy or special steels.

Alloy or special steels contain other elements, in addition to carbon, that modify their properties. These are classified according to their influence:.

• - Elements that increase hardness: phosphorus, nickel, copper, aluminum. Especially those that retain hardness at high temperatures: titanium, vanadium, molybdenum, tungsten, chromium, manganese and cobalt.

• - Elements that limit grain size growth: aluminum, titanium and vanadium.

• - Elements that determine hardenability: manganese, molybdenum, chromium, nickel and silicon increase hardenability, while cobalt decreases it.

• - Elements that modify resistance to corrosion or oxidation: increase resistance to oxidation: molybdenum and tungsten. Promotes resistance to corrosion: chromium.

• - Elements that modify the critical transformation temperatures: The critical points increase: molybdenum, aluminum, silicon, vanadium, tungsten. Critical temperatures decrease: copper, nickel and manganese. In the particular case of chromium, the critical points rise when the steel has a high percentage of carbon but decreases when the steel has a low carbon content.

According to the uses

• - Steel for magnets or magnetic.

• - Self-tempered steel.

• - Construction steel.

• - Fast cutting steel.

• - Cutting steel.

• - Cutting steel.

• - Non-deformable steel.

• - Stainless steel.

• - Tool steel.

• - Spring steel.

• - Refractory steel.

• - Bearing steel.

According to your application

• - Construction steels.

• - General purpose steels.

• - Cemented steels.

• - Steels for quenching and tempering.

• - Stainless steel or for special uses.

• - Steels for cutting and machining tools.

Aunque es difícil establecer las propiedades") físicas y mecánicas del acero debido a que estas varían con los ajustes en su composición y los diversos tratamientos térmicos, químicos o mecánicos, con los que pueden conseguirse aceros con combinaciones de características adecuadas para infinidad de aplicaciones, se pueden citar algunas propiedades genéricas:.

• - Su densidad media es de 7850 kg/m³.

• - En función de la temperatura el acero se puede contraer, dilatar o fundir.

• - El punto de fusión del acero depende del tipo de aleación y los porcentajes de elementos aleantes. El de su componente principal, el hierro es de alrededor de 1510 °C en estado puro (sin alear), sin embargo el acero presenta frecuentemente temperaturas de fusión de alrededor de 1375 °C, y en general la temperatura necesaria para la fusión aumenta a medida que se aumenta el porcentaje de carbono y de otros aleantes. (excepto las aleaciones eutécticas que funden de golpe). Por otra parte el acero rápido funde a 1650 °C.[20]​.

• - Su punto de ebullición es de alrededor de 3000 °C.[21]​.

• - Es un material muy tenaz, especialmente en alguna de las aleaciones usadas para fabricar herramientas.

• - Relativamente dúctil. Con él se obtienen hilos delgados llamados alambres.

• - Es maleable. Se pueden obtener láminas delgadas llamadas hojalata. La hojalata es una lámina de acero, de entre 0,5 y 0,12 mm de espesor, recubierta, generalmente de forma electrolítica, por estaño.

• - Permite una buena mecanización en máquinas herramientas antes de recibir un tratamiento térmico.

• - Algunas composiciones y formas del acero mantienen mayor memoria"), y se deforman al sobrepasar su límite elástico.

• - La dureza de los aceros varía entre la del hierro y la que se puede lograr mediante su aleación u otros procedimientos térmicos o químicos entre los cuales quizá el más conocido sea el templado del acero, aplicable a aceros con alto contenido en carbono, que permite, cuando es superficial, conservar un núcleo tenaz en la pieza que evite fracturas frágiles. Aceros típicos con un alto grado de dureza superficial son los que se emplean en las herramientas de mecanizado, denominados aceros rápidos que contienen cantidades significativas de cromo, wolframio, molibdeno y vanadio. Los ensayos tecnológicos para medir la dureza son Brinell, Vickers y Rockwell, entre otros.

• - Se puede soldar con facilidad.

• - La corrosión es la mayor desventaja de los aceros ya que el hierro se oxida con suma facilidad incrementando su volumen y provocando grietas superficiales que posibilitan el progreso de la oxidación hasta que se consume la pieza por completo. Tradicionalmente los aceros se han venido protegiendo mediante tratamientos superficiales diversos. Si bien existen aleaciones con resistencia a la corrosión mejorada como los aceros de construcción «corten» aptos para intemperie (en ciertos ambientes) o los aceros inoxidables.

• - Posee una alta conductividad eléctrica. Aunque depende de su composición es aproximadamente de[22]​ 3 · 10 S "Siemens (unidad)")/m. En las líneas aéreas de alta tensión se utilizan con frecuencia conductores de aluminio con alma de acero proporcionando este último la resistencia mecánica necesaria para incrementar los vanos entre la torres y optimizar el coste de la instalación.

• - Se utiliza para la fabricación de imanes permanentes artificiales "Imán (física)"), ya que una pieza de acero imantada no pierde su imantación si no se la calienta hasta cierta temperatura. La magnetización artificial se hace por contacto, inducción o mediante procedimientos eléctricos. En lo que respecta al acero inoxidable, al acero inoxidable ferrítico") sí se le pega el imán, pero al acero inoxidable austenítico no se le pega el imán ya que la fase del hierro conocida como austenita no es atraída por los imanes. Los aceros inoxidables contienen principalmente níquel y cromo en porcentajes del orden del 10% además de algunos aleantes en menor proporción.

• - Un aumento de la temperatura en un elemento de acero provoca un aumento en la longitud del mismo. Este aumento en la longitud puede valorarse por la expresión: , siendo al coeficiente de dilatación, que para el acero vale aproximadamente 1,2 · 10 (es decir ). Si existe libertad de dilatación no se plantean grandes problemas subsidiarios, pero si esta dilatación está impedida en mayor o menor grado por el resto de los componentes de la estructura, aparecen esfuerzos complementarios que hay que tener en cuenta. El acero se dilata y se contrae según un coeficiente de dilatación similar al coeficiente de dilatación del hormigón, por lo que resulta muy útil su uso simultáneo en la construcción, formando un material compuesto que se denomina hormigón armado.[23]​ El acero da una falsa sensación de seguridad al ser incombustible, pero sus propiedades mecánicas fundamentales se ven gravemente afectadas por las altas temperaturas que pueden alcanzar los perfiles en el transcurso de un incendio.

Wear

It is the physical degradation (loss or gain of material, appearance of cracks, plastic deformation, structural changes such as phase transformation or recrystallization, corrosion phenomena, etc.) due to the movement between the surface of a solid material and one or more contact elements.

To homogenize the different varieties of steel that can be produced, there are systems of standards that regulate the composition of steel and its performance in each country, in each steel manufacturer, and in many cases in the largest consumers of steel.

For example, in Spain they are regulated by the UNE-EN 10020":2001 standard and previously they were regulated by the UNE-36010 standard, both published by AENOR.[24]​.

There are other regulatory standards for steel, such as the AISI classification (of much more widespread use internationally), ASTM, DIN, or ISO 3506.

Surface treatments

Due to the ease with which steel rusts when it comes into contact with the atmosphere or water, it is necessary and convenient to protect the surface of steel components to protect them from oxidation and corrosion. Many surface treatments are closely related to beautifying and decorative aspects of metals.

The most used surface treatments are the following:

• - Zinc plating: antioxidant surface treatment by electrolytic or mechanical process to which different metallic components are subjected.

• - Chrome: surface coating to protect from oxidation and beautify.

• - Galvanized: surface treatment given to the steel sheet.

• - Nickel plating: nickel plating that protects a metal from oxidation.

• - Blueing: surface treatment given to small steel parts, such as screws.

• - Paint: used especially on structures, cars, boats, etc.

Heat treatments

An adequate heat treatment process allows the mechanical properties of hardness, toughness and mechanical resistance of the steel to be significantly increased. Heat treatments change the microstructure of the material, so the macroscopic properties of the steel are also altered.

The heat treatments that can be applied to steel without changing its chemical composition are:

• - Tempered.

• - Tempered.

• - Annealed.

• - Normalized.

They are thermal treatments in which, in addition to changes in the structure of the steel, changes also occur in the chemical composition of the surface layer, adding different chemicals up to a certain depth. These treatments require the use of controlled heating and cooling in special atmospheres. Among the most common objectives of these treatments are to increase the surface hardness of the parts, leaving the core softer and more tenacious, reduce friction by increasing the lubricating power, increase wear resistance, increase fatigue resistance or increase corrosion resistance.

• - Carburizing (C): increases the surface hardness of a mild steel piece, increasing the carbon concentration on the surface. It is achieved by taking into account the medium or atmosphere that surrounds the metal during heating and cooling. The treatment manages to increase the carbon content of the peripheral zone, subsequently obtaining, through quenching and tempering, great surface hardness, wear resistance and good toughness in the core.

• - Nitriding (N): like carburizing, it increases surface hardness, although it does so to a greater extent by incorporating nitrogen into the composition of the surface of the piece. It is achieved by heating the steel to temperatures between 400 and 525 °C, within a stream of ammonia gas, plus nitrogen.

• - Cyanidation (C+N): surface hardening of small pieces of steel. Baths with cyanide, carbonate and sodium cyanate are used. Temperatures between 760 and 950 °C are applied.

• - Carbonitriding (C+N): like cyanidation, it introduces carbon and nitrogen into a surface layer, but with hydrocarbons such as methane, ethane or propane; ammonia (NH) and carbon monoxide (CO). The process requires temperatures of 650 to 850 °C and it is necessary to perform quenching and subsequent tempering.

• - Sulfinization") (S+N+C): increases wear resistance due to the action of sulfur. The sulfur was incorporated into the metal by heating at low temperature (565 °C) in a salt bath.

Among the factors that affect steel heat treatment processes are the temperature and the time during which the material is exposed to these conditions. Another determining factor is the way the steel returns to room temperature. Process cooling may include immersion in oil or the use of air as a coolant.

The method of heat treatment, including cooling, influences whether the steel takes on its commercial properties.

According to this method, in some classification systems, a prefix indicative of the type is assigned. For example, steel O-1, or A2, A6 (or S7) where the letter O is indicative of the use of oil (from English: oil quenched), and A is the initial for air; The prefix S is indicative that the steel has been treated and considered shock resistant*.

rolled steel

The steel used for the construction of metal structures and public works is obtained by rolling steel into a series of standardized profiles.

The rolling process consists of previously heating the molten steel ingots to a temperature that allows the deformation of the ingot through a stretching and grinding process that occurs in a chain of pressure cylinders called a rolling mill. These cylinders form the desired profile until the required measurements are achieved. The dimensions of the sections obtained in this way do not adjust to the required tolerances and that is why laminated products often have to be subjected to machining phases to adjust their dimensions to the required tolerance.

forged steel

Forging is the process that modifies the shape of metals by plastic deformation when the steel is subjected to pressure or a continuous series of impacts. Forging is generally carried out at high temperatures because this improves the metallurgical quality and mechanical properties of the steel.

The meaning of forging steel parts is to reduce as much as possible the amount of material that must be removed from the parts in their machining processes. In stamp forging, the flow of the material is limited to the cavity of the stamp, composed of two matrices that have the shape of the piece to be achieved engraved.

corrugated steel

Corrugated steel is a type of rolled steel used especially in construction, for use in reinforced concrete. These are steel bars that have projections or "corrugations" that improve adhesion with the concrete. It is equipped with great ductility, which allows it to not suffer damage when cutting and bending, and it has great weldability, all of this to make these operations safer and with less energy expenditure.

Corrugated steel bars are standardized. For example, in Spain they are covered by Standards UNE 36068:2011, UNE 36065:2011 and UNE 36811:1998 IN.

Corrugated steel bars are produced in a range of diameters from 6 to 40 mm, in which the section in cm² that each bar has is quoted as well as its weight in kg.

Bars less than or equal to 16 mm in diameter can be supplied in bars or rolls, for diameters greater than 16 they are always supplied in the form of bars.

The corrugated product bars have technical characteristics that must be met to ensure the corresponding calculation of the reinforced concrete structures. Among the technical characteristics, the following stand out, all of them are determined by the tensile test:.

• - elastic limit Re (Mpa).

• - unit breaking load or tensile strength") Rm (MPa).

• - elongation at break A5 (%).

• - elongation under maximum load Agt (%).

• - relationship between loads Rm/Re.

• - Young E's modulus.

Steel stamping

Steel stamping consists of a machining process without chip removal where the steel plate is subjected, by means of appropriate presses, to drawing and stamping processes to obtain certain metal parts. For this, the appropriate molds are placed in the presses.

Steel punching

Steel punching consists of a machining process without chip removal where all types of holes are drilled in the steel plate using impact presses where their respective dies and matrices are placed.

Soft machining

Steel parts can be machined in chip removal processes in machine tools (drill, lathe, milling machine, CNC machining centers, etc.), then hardened by heat treatment and finished with abrasive procedures in the different types of grinding machines that exist.

Rectified

The grinding process allows us to obtain very good surface finish qualities and measurements with very close tolerances, which are very beneficial for the construction of quality machinery and equipment. But the size of the part and the grinding machine's travel capacity can present an obstacle.

Hard machining

On special occasions, the heat treatment of steel can be carried out before machining in chip removal processes, depending on the type of steel and the requirements that must be observed for a given part. With this, it must be taken into account that the tools necessary for such jobs must be very strong as they may suffer rapid wear during their useful life. These peculiar occasions may arise when manufacturing tolerances are so narrow that the induction of heat in treatment is not allowed because it may alter the geometry of the work, or also due to the composition of the batch of material itself (for example, the pieces are shrinking a lot due to being treated). Machining after heat treatment is sometimes preferable, since optimal material stability has been achieved and, depending on the composition and treatment, the machining process itself is not much more difficult.

EDM machining

In some manufacturing processes that rely on electrical discharge with the use of electrodes, the hardness of the steel does not make a noticeable difference.

deep drilling

In many situations, the hardness of the steel is decisive for a successful result, such as in deep drilling when ensuring that a hole maintains its position relative to the axis of rotation of the carbide drill bit. Or for example, if the steel has been hardened by heat treatment and softened by subsequent heat treatment, the consistency may be too soft to benefit the process, since the path of the drill bit will tend to deviate.

Bent

Bending steel that has been heat treated is not highly recommended as the cold bending process of hardened material is more difficult and the material has most likely become too brittle to be bent; The bending process using torches or other methods to apply heat is also not recommended since when heat is reapplied to the hard metal, its integrity changes and may be compromised.

steel profiles

For use in construction, steel is distributed in metal profiles, these having different characteristics depending on their shape and dimensions and must be used specifically for a specific function, whether beams or pillars.

Steel in its different types is overwhelmingly present in our daily lives in the form of tools, utensils, mechanical equipment and as part of household appliances and machinery in general as well as in the structures of the homes we live in and in the vast majority of modern buildings. In this context there is the modern version of steel profiles called Metalcón").

Manufacturers of means of transporting goods (trucks) and agricultural machinery are large consumers of steel.

Railway construction activities are also large consumers of steel, from the construction of road infrastructure as well as the manufacture of all types of rolling stock.

The same can be said of the arms manufacturing industry, especially that dedicated to building heavy weapons, armored vehicles and battleships.

Large shipyards that build ships, especially oil tankers, gas tankers and other tankers, also consume a lot of steel.

Major consumers of steel include automobile manufacturers because many of their significant components are made of steel.

As an example, the following automobile components are made of steel:

• - They are made of forged steel among other components: crankshaft, connecting rods, pinions, gearbox transmission shafts and steering articulation arms.

• - The doors and other body components are made of stamped sheet metal.

• - The profiles that make up the "Frame (machinery)" frame are made of laminated steel.

• - All the springs they incorporate are made of steel, such as; valve springs, seats, clutch presses, shock absorbers "Shock absorber (car)"), etc.

• - All bearings used in automobiles are made of high-quality steel.

• - The wheel rims are made of die-cut sheet metal, except for the high-end ones that are made of aluminum alloys.

• - All screws and nuts are made of steel.

It should be noted that when the car is scrapped due to its age and deterioration, all the steel parts are separated, converted into scrap metal and recycled back into steel using electric furnaces and rolling mills or cast iron parts.

Cuando un técnico proyecta una estructura metálica, diseña una herramienta o una máquina, define las calidades y prestaciones que tienen que tener los materiales constituyentes. Como hay muchos tipos de aceros diferentes y, además, se pueden variar sus prestaciones con tratamientos térmicos, se establecen una serie de ensayos mecánicos para verificar principalmente la dureza superficial, la resistencia a los diferentes esfuerzos que pueda estar sometido, el grado de acabado del mecanizado o la presencia de grietas internas en el material, lo cual afecta directamente al material pues se pueden producir fracturas o roturas.

Hay dos tipos de ensayos, unos que pueden ser destructivos y otros no destructivos.

Todos los aceros tienen estandarizados los valores de referencia de cada tipo de ensayo al que se le somete.[25]​.

Non-destructive testing

The non-destructive tests are as follows:

• - Microscopic testing and surface roughness: microscopes and roughness meters.

• - Ultrasonic tests.

• - Penetrating liquid tests.

• - Magnetic particle tests.

• - Hardness test (Brinell, Rockwell, Vickers); using durometers.

Destructive tests

The destructive tests are as follows:

• - Tensile test with a standardized "Template (mechanical)" specimen.

• - Resilience essay "Resilience (engineering)").

• - Compression test with standardized specimen.

• - Shear test.

• - Bending test.

• - Torsion test.

• - Folding test").

• - Fatigue test.

Evolution of global steel consumption (2021)

Global consumption of finished steel finished products in 2021 reached 1.8 billion tons, an increase of 2.7% compared to 2020. The largest consumer of steel globally is China, which accounts for 52% of the world's steel. However, its consumption compared to previous years has decreased by 5.4%. In contrast, the rest of the world has increased its use and consumption, with the European Union 16%, Central and South America 3%, and the United States, Canada and Mexico 20%.[26]​.

World steel production (2021)

World production of crude steel in 2021 amounted to 1,879 million tons, which represents an increase of 3.8% compared to 2021. This evolution was common across most countries. As one of the few exceptions, China, which decreased its total steel production by 3%. On the other hand, India, Japan and the United States have increased their production by 17%, 16% and 18% respectively. Even so, the majority of world production is in the Asian continent, which generates 72% of all steel.[26]​.

The distribution of steel production in 2021 was as follows according to figures estimated by the World Steel Association in June 2022.[26]​.

Available data on world steel production in 2019, in millions of tons per year:[27]​[28]​.

El acero, al igual que otros metales, puede ser reciclado. Al final de su vida útil, todos los elementos construidos en acero como máquinas, estructuras, barcos, automóviles, trenes, etc., se pueden desguazar, separando los diferentes materiales componentes y originando unos desechos seleccionados llamados comúnmente chatarra. La misma es prensada en bloques que se vuelven a enviar a la acería para ser reutilizados. De esta forma se reduce el gasto en materias primas y en energía que deben desembolsarse en la fabricación del acero. Se estima que la chatarra reciclada cubre el 40% de las necesidades mundiales de acero (cifra de 2006).

El proceso de reciclado se realiza bajo las normas de prevención de riesgos laborales y las medioambientales. El horno en que se funde la chatarra tiene un alto consumo de electricidad, por lo que se enciende generalmente cuando la demanda de electricidad es menor. Además, en distintas etapas del reciclaje se colocan detectores de radiactividad, como por ejemplo en la entrada de los camiones que transportan la chatarra a las industrias de reciclaje.

Be careful when handling scrap

Personnel who handle scrap metal must always be vaccinated against tetanus infection, as they can become infected by suffering an injury from scrap metal. Anyone who suffers a cut with a steel element must go to a medical center and receive said vaccine, or a booster if they received it previously.

• - Wikimedia Commons hosts a multimedia gallery on Steel.

• - Wiktionary has definitions and other information about steel.

• - Steel industry tables.

• - International Iron and Steel Institute.

The term steel comes from the Latin "aciarius", and this from the word "acies", which is what the edge of a knife is called in this language. "Aciarius" would therefore be the appropriate metal, due to its hardness and resistance, to be used in the cutting part of weapons and tools.

The exact date on which the technique to obtain iron from the fusion of minerals was discovered is unknown. However, the first archaeological remains of iron utensils date back to 3000 BC. C. and were discovered in Egypt, although there are vestiges of previous ornaments. Quintus Horacio Flaco points out that steel weapons such as the falcata were used in the Iberian Peninsula as early as the century BC. C., while noric steel (in Latin: chalybs noricus) was used by Roman troops.[5] During the Han dynasty of China, steel was produced by melting wrought iron with cast iron, around the century BC. C.[6][7] They also adopted production methods for creating wootz steel, a process that emerged in India and Sri Lanka from approximately 300 BC. C. and exported to China around the 1st century. This early method used a wind furnace, blown by the monsoons.[8]​[9]​ Also known as Damascus steel, it was an iron alloy with a large number of different materials, including traces of other elements in concentrations less than 1000 parts per million or 0.1% of the rock composition. Studies carried out by Peter Paufler suggested that its structure included carbon nanotubes, which could explain some of the qualities of this steel - such as its durability and ability to maintain an edge - although due to the technology of the time it is possible that they were obtained by chance and not by a premeditated design.[10]​.

Between the centuries and crucible steel was produced in Merv, in which steel was obtained by heating and cooling iron and carbon using different techniques. During the Song dynasty of the century in China, steel production was carried out using two techniques: the first produced low-quality steel because it was not homogeneous - the "Berganesque" method - and the second, a precursor to the Bessemer method, removed the carbon with repeated forgings and subjected the piece to abrupt cooling.[11]​.

Iron for industrial use was discovered around 1500 BC. C., in Metsamor and Mount Ararat, in Armenia.[12] Iron technology was kept secret for a long time, spreading widely around the year 1200 BC. c.

There are no records that hardenability was known until the Middle Ages. The ancient methods for making steel consisted of obtaining soft iron in the furnace, with charcoal and air draft, with a subsequent expulsion of the slags "Slag (metallurgy)") by hammering and carburizing the soft iron to cement it. Then cementation was perfected by melting the cemented steel in clay crucibles and in Sheffield (England) crucible steels were obtained from 1740 onwards.[13] The technique was developed by Benjamin Huntsman.

In 1856, Henry Bessemer developed a method to produce steel in large quantities, but since only iron containing phosphorus and sulfur in small proportions could be used, it was abandoned. The following year, Carl Wilhelm Siemens created another, the Martin-Siemens procedure, in which steel was produced from the decarburization of soft iron casting and iron oxide as a product of heating with oil, coke gas, or a mixture of the latter with blast furnace gas. This method also fell into disuse.

Although in 1878 Siemens was also the first to employ electricity to heat steel furnaces, the use of electric arc furnaces for commercial production began in 1902 by Paul Héroult, who was one of the inventors of the modern method of smelting aluminum. In this method, an electric arc is passed inside the furnace between scrap steel whose composition is known and large carbon electrodes located on the roof of the furnace.

In 1948, the L-D basic oxygen process was invented. After World War II, experiments began in several countries with pure oxygen instead of air for steel refining processes. Success was achieved in Austria in 1948, when a steel factory located near the city of Linz, Donawitz, developed the basic oxygen or L-D process.

In 1950, the continuous casting process was invented, which is used when it is required to produce rolled steel profiles of constant section and in large quantities. The process consists of placing a mold with the required shape under a crucible, which with a valve can dose molten material into the mold. By gravity, the molten material passes through the mold, which is cooled by a water system; as the molten material passes through the cold mold, it becomes pasty and takes on the shape of the mold. Subsequently, the material is shaped. with a series of rollers that at the same time drag it towards the outside of the system. Once the material has been formed into the necessary shape and with the appropriate length, the material is cut and stored.

Currently, some metals and metalloids are used in the form of ferroalloys, which, together with steel, provide excellent qualities of hardness and resistance.[14]​.

Currently, the steel manufacturing process is completed by the so-called secondary metallurgy. At this stage, the desired chemical properties, temperature, gas content, level of inclusions and impurities are given to the liquid steel. The most common unit of secondary metallurgy is the ladle furnace. The steel produced here is ready to be subsequently cast, conventionally or in continuous casting.

The intensive use that steel has and has had for the construction of metallic structures has seen great successes and resounding failures that have at least allowed the advancement of materials science. Thus, on November 7, 1940, the world witnessed the collapse of the Tacoma Narrows Bridge as it entered into resonance "Resonance (mechanical)") with the wind. Already during the first years of the Industrial Revolution, premature failures of railway axles occurred, leading William Rankine to postulate material fatigue, and during World War II there were some unforeseen sinkings of the American Liberty freighters when the steel became brittle due to the mere drop in temperature,[15] a problem initially attributed to welding.

Alloy or special steels contain other elements, in addition to carbon, that modify their properties. These are classified according to their influence:.

Elements that increase hardness: phosphorus, nickel, copper, aluminum. Especially those that retain hardness at high temperatures: titanium, vanadium, molybdenum, tungsten, chromium, manganese and cobalt.

Elements that limit grain size growth: aluminum, titanium and vanadium.

Elements that determine hardenability: increase hardenability: manganese, molybdenum, chromium, nickel and silicon. Decreases hardenability: cobalt.

Elements that modify resistance to corrosion or oxidation: increase resistance to oxidation: molybdenum and tungsten. Promotes resistance to corrosion: chromium.

Elements that modify the critical transformation temperatures: Critical points increase: molybdenum, aluminum, silicon, vanadium, tungsten. Critical temperatures decrease: copper, nickel and manganese. In the particular case of chromium, the critical points rise when the steel has a high percentage of carbon but decreases when the steel has a low carbon content.

Contenido

Los dos componentes principales del acero se encuentran en abundancia en la naturaleza, lo que favorece su producción a gran escala. Esta variedad y disponibilidad[16]​ lo hace apto para numerosos usos como la construcción de maquinaria, herramientas, edificios y obras públicas, contribuyendo al desarrollo tecnológico de las sociedades industrializadas.[13]​ A pesar de su densidad (7850 kg/m³ de densidad en comparación a los 2700 kg/m³ del aluminio, por ejemplo) el acero es utilizado en todos los sectores de la industria, incluso en el aeronáutico, ya que las piezas con mayores solicitaciones (ya sea al impacto o a la fatiga) solo pueden aguantar con un material dúctil y tenaz como es el acero, además de la ventaja de su relativo bajo costo.

Other elements in steel

Standard steel classifications such as AISI, ASTM and UNS establish minimum or maximum values ​​for each type of element. These elements are added to obtain certain characteristics such as hardenability, mechanical resistance, hardness, toughness, wear resistance, weldability") or machinability.[17] Some of the effects of alloying elements on steel are listed below:[18]​

[19]​.

• - Aluminum: it is used in some high-hardness Cr-Al-Mo nitriding steels in concentrations close to 1% and in percentages less than 0.008% as a deoxidizer in high-alloy steels.

• - Boron: in very small quantities (from 0.001 to 0.006%) it increases hardenability without reducing machinability, as it combines with carbon to form carbides, providing a hard coating. It is used in low alloy steels in applications such as plow blades and wires with high ductility and surface hardness. Also used as a nitrogen trap, especially in steels for drawing, to obtain N values ​​less than 80 ppm.

• - Cobalt: very hardening. Decreases hardenability. Improves resistance and hardness when hot. It is an unusual element in steels. Increases the magnetic properties of steels. It is used in high-speed tool steels and refractory steels.

• - Chromium: Forms very hard carbides and gives the steel greater hardness, resistance and toughness at any temperature. Alone or alloyed with other elements, it improves corrosion resistance. Increases the depth of penetration of hardening by thermochemical treatment such as carburizing or nitriding. It is used in stainless steels, tool steels and refractories. It is also used in decorative coatings or hard coatings with high wear resistance, such as pistons, shafts, etc.

• - Molybdenum: it is a common element in steel and greatly increases the depth of hardening of steel, as well as its toughness. Austenitic stainless steels contain molybdenum to improve corrosion resistance.

• - Nitrogen: added to some steels to promote the formation of austenite.

• - Nickel: it is a gammagen element allowing an austenitic structure at room temperature, which increases toughness and impact resistance. Nickel is widely used to produce stainless steel because it increases corrosion resistance.

• - Lead: lead is not combined with steel, it is found in it in the form of very small globules, as if emulsified, which favors easy machining by chip removal (turning, brushing, drilling, etc.) since lead is a good cutting lubricant, the percentage ranges between 0.15% and 0.30% and the carbon content must be limited to values lower than 0.5% because it makes tempering difficult and reduces hot toughness. It is added to some steels to greatly improve machinability.

• - Silicon: moderately increases hardenability. It is used as a deoxidizing element. Increases the resistance of low carbon steels.

• - Titanium: used to stabilize and deoxidize steel, it keeps the properties of steel stable at high temperatures. Its high affinity with carbon is used to prevent the formation of iron carbide when welding steel.

• - Wolfram: also known as tungsten. It forms very complex, stable and very hard carbides with iron, withstanding high temperatures well. In percentages of 14 to 18%, it provides high-speed steels with which it is possible to triple the cutting speed of carbon tool steels.

• - Vanadium: it has an energetic deoxidizing action and forms complex carbides with iron, which provide the steel with good resistance to fatigue, traction and cutting power in tool steels.

• - Niobium: It is used to give hardness, flexibility and elasticity to steel, it is mainly used for structural steel and automotive steel.

All undesirable elements in the composition of steels are called impurities. They are found in steel and also in foundries as a result of being present in minerals or fuels. Efforts are made to eliminate them or reduce their content because they are detrimental to the properties of the alloy. In cases where eliminating them is impossible or too costly, their presence is allowed in minimal quantities.

• - Sulfur: approximate maximum limit: 0.04%. Sulfur with iron forms sulfide, which, together with austenite, gives rise to a eutectic whose melting point is low and which, therefore, appears in grain boundaries. When cast steel ingots must be hot rolled, said eutectic is in a liquid state, which causes the material to break apart.

• - Phosphorus "Phosphorus (element)"): approximate maximum limit: 0.04%. Phosphorus is harmful, either by dissolving in ferrite, as it reduces ductility, or by forming FeP ("iron phosphide"). Iron phosphide"), together with austenite and cementite, forms a ternary eutectic called "essteadite", which is extremely fragile and has a relatively low melting point, which is why it appears in grain boundaries, transmitting its fragility to the material.

Depending on the manufacturing method

• - Electrical steel.

• - Cast steel.

• - Calmed steel.

• - Effervescent steel.

• - Fried steel.

• - Drawn steel.

According to the way of working it

• - Cast steel.

• - Forged steel.

• - Laminated steel.

Depending on the composition and structure

• - Ordinary steels.

• - Alloy or special steels.

Alloy or special steels contain other elements, in addition to carbon, that modify their properties. These are classified according to their influence:.

• - Elements that increase hardness: phosphorus, nickel, copper, aluminum. Especially those that retain hardness at high temperatures: titanium, vanadium, molybdenum, tungsten, chromium, manganese and cobalt.

• - Elements that limit grain size growth: aluminum, titanium and vanadium.

• - Elements that determine hardenability: manganese, molybdenum, chromium, nickel and silicon increase hardenability, while cobalt decreases it.

• - Elements that modify resistance to corrosion or oxidation: increase resistance to oxidation: molybdenum and tungsten. Promotes resistance to corrosion: chromium.

• - Elements that modify the critical transformation temperatures: The critical points increase: molybdenum, aluminum, silicon, vanadium, tungsten. Critical temperatures decrease: copper, nickel and manganese. In the particular case of chromium, the critical points rise when the steel has a high percentage of carbon but decreases when the steel has a low carbon content.

According to the uses

• - Steel for magnets or magnetic.

• - Self-tempered steel.

• - Construction steel.

• - Fast cutting steel.

• - Cutting steel.

• - Cutting steel.

• - Non-deformable steel.

• - Stainless steel.

• - Tool steel.

• - Spring steel.

• - Refractory steel.

• - Bearing steel.

According to your application

• - Construction steels.

• - General purpose steels.

• - Cemented steels.

• - Steels for quenching and tempering.

• - Stainless steel or for special uses.

• - Steels for cutting and machining tools.

Aunque es difícil establecer las propiedades") físicas y mecánicas del acero debido a que estas varían con los ajustes en su composición y los diversos tratamientos térmicos, químicos o mecánicos, con los que pueden conseguirse aceros con combinaciones de características adecuadas para infinidad de aplicaciones, se pueden citar algunas propiedades genéricas:.

• - Su densidad media es de 7850 kg/m³.

• - En función de la temperatura el acero se puede contraer, dilatar o fundir.

• - El punto de fusión del acero depende del tipo de aleación y los porcentajes de elementos aleantes. El de su componente principal, el hierro es de alrededor de 1510 °C en estado puro (sin alear), sin embargo el acero presenta frecuentemente temperaturas de fusión de alrededor de 1375 °C, y en general la temperatura necesaria para la fusión aumenta a medida que se aumenta el porcentaje de carbono y de otros aleantes. (excepto las aleaciones eutécticas que funden de golpe). Por otra parte el acero rápido funde a 1650 °C.[20]​.

• - Su punto de ebullición es de alrededor de 3000 °C.[21]​.

• - Es un material muy tenaz, especialmente en alguna de las aleaciones usadas para fabricar herramientas.

• - Relativamente dúctil. Con él se obtienen hilos delgados llamados alambres.

• - Es maleable. Se pueden obtener láminas delgadas llamadas hojalata. La hojalata es una lámina de acero, de entre 0,5 y 0,12 mm de espesor, recubierta, generalmente de forma electrolítica, por estaño.

• - Permite una buena mecanización en máquinas herramientas antes de recibir un tratamiento térmico.

• - Algunas composiciones y formas del acero mantienen mayor memoria"), y se deforman al sobrepasar su límite elástico.

• - La dureza de los aceros varía entre la del hierro y la que se puede lograr mediante su aleación u otros procedimientos térmicos o químicos entre los cuales quizá el más conocido sea el templado del acero, aplicable a aceros con alto contenido en carbono, que permite, cuando es superficial, conservar un núcleo tenaz en la pieza que evite fracturas frágiles. Aceros típicos con un alto grado de dureza superficial son los que se emplean en las herramientas de mecanizado, denominados aceros rápidos que contienen cantidades significativas de cromo, wolframio, molibdeno y vanadio. Los ensayos tecnológicos para medir la dureza son Brinell, Vickers y Rockwell, entre otros.

• - Se puede soldar con facilidad.

• - La corrosión es la mayor desventaja de los aceros ya que el hierro se oxida con suma facilidad incrementando su volumen y provocando grietas superficiales que posibilitan el progreso de la oxidación hasta que se consume la pieza por completo. Tradicionalmente los aceros se han venido protegiendo mediante tratamientos superficiales diversos. Si bien existen aleaciones con resistencia a la corrosión mejorada como los aceros de construcción «corten» aptos para intemperie (en ciertos ambientes) o los aceros inoxidables.

• - Posee una alta conductividad eléctrica. Aunque depende de su composición es aproximadamente de[22]​ 3 · 10 S "Siemens (unidad)")/m. En las líneas aéreas de alta tensión se utilizan con frecuencia conductores de aluminio con alma de acero proporcionando este último la resistencia mecánica necesaria para incrementar los vanos entre la torres y optimizar el coste de la instalación.

• - Se utiliza para la fabricación de imanes permanentes artificiales "Imán (física)"), ya que una pieza de acero imantada no pierde su imantación si no se la calienta hasta cierta temperatura. La magnetización artificial se hace por contacto, inducción o mediante procedimientos eléctricos. En lo que respecta al acero inoxidable, al acero inoxidable ferrítico") sí se le pega el imán, pero al acero inoxidable austenítico no se le pega el imán ya que la fase del hierro conocida como austenita no es atraída por los imanes. Los aceros inoxidables contienen principalmente níquel y cromo en porcentajes del orden del 10% además de algunos aleantes en menor proporción.

• - Un aumento de la temperatura en un elemento de acero provoca un aumento en la longitud del mismo. Este aumento en la longitud puede valorarse por la expresión: , siendo al coeficiente de dilatación, que para el acero vale aproximadamente 1,2 · 10 (es decir ). Si existe libertad de dilatación no se plantean grandes problemas subsidiarios, pero si esta dilatación está impedida en mayor o menor grado por el resto de los componentes de la estructura, aparecen esfuerzos complementarios que hay que tener en cuenta. El acero se dilata y se contrae según un coeficiente de dilatación similar al coeficiente de dilatación del hormigón, por lo que resulta muy útil su uso simultáneo en la construcción, formando un material compuesto que se denomina hormigón armado.[23]​ El acero da una falsa sensación de seguridad al ser incombustible, pero sus propiedades mecánicas fundamentales se ven gravemente afectadas por las altas temperaturas que pueden alcanzar los perfiles en el transcurso de un incendio.

Wear

It is the physical degradation (loss or gain of material, appearance of cracks, plastic deformation, structural changes such as phase transformation or recrystallization, corrosion phenomena, etc.) due to the movement between the surface of a solid material and one or more contact elements.

To homogenize the different varieties of steel that can be produced, there are systems of standards that regulate the composition of steel and its performance in each country, in each steel manufacturer, and in many cases in the largest consumers of steel.

For example, in Spain they are regulated by the UNE-EN 10020":2001 standard and previously they were regulated by the UNE-36010 standard, both published by AENOR.[24]​.

There are other regulatory standards for steel, such as the AISI classification (of much more widespread use internationally), ASTM, DIN, or ISO 3506.

Surface treatments

Due to the ease with which steel rusts when it comes into contact with the atmosphere or water, it is necessary and convenient to protect the surface of steel components to protect them from oxidation and corrosion. Many surface treatments are closely related to beautifying and decorative aspects of metals.

The most used surface treatments are the following:

• - Zinc plating: antioxidant surface treatment by electrolytic or mechanical process to which different metallic components are subjected.

• - Chrome: surface coating to protect from oxidation and beautify.

• - Galvanized: surface treatment given to the steel sheet.

• - Nickel plating: nickel plating that protects a metal from oxidation.

• - Blueing: surface treatment given to small steel parts, such as screws.

• - Paint: used especially on structures, cars, boats, etc.

Heat treatments

An adequate heat treatment process allows the mechanical properties of hardness, toughness and mechanical resistance of the steel to be significantly increased. Heat treatments change the microstructure of the material, so the macroscopic properties of the steel are also altered.

The heat treatments that can be applied to steel without changing its chemical composition are:

• - Tempered.

• - Tempered.

• - Annealed.

• - Normalized.

They are thermal treatments in which, in addition to changes in the structure of the steel, changes also occur in the chemical composition of the surface layer, adding different chemicals up to a certain depth. These treatments require the use of controlled heating and cooling in special atmospheres. Among the most common objectives of these treatments are to increase the surface hardness of the parts, leaving the core softer and more tenacious, reduce friction by increasing the lubricating power, increase wear resistance, increase fatigue resistance or increase corrosion resistance.

• - Carburizing (C): increases the surface hardness of a mild steel piece, increasing the carbon concentration on the surface. It is achieved by taking into account the medium or atmosphere that surrounds the metal during heating and cooling. The treatment manages to increase the carbon content of the peripheral zone, subsequently obtaining, through quenching and tempering, great surface hardness, wear resistance and good toughness in the core.

• - Nitriding (N): like carburizing, it increases surface hardness, although it does so to a greater extent by incorporating nitrogen into the composition of the surface of the piece. It is achieved by heating the steel to temperatures between 400 and 525 °C, within a stream of ammonia gas, plus nitrogen.

• - Cyanidation (C+N): surface hardening of small pieces of steel. Baths with cyanide, carbonate and sodium cyanate are used. Temperatures between 760 and 950 °C are applied.

• - Carbonitriding (C+N): like cyanidation, it introduces carbon and nitrogen into a surface layer, but with hydrocarbons such as methane, ethane or propane; ammonia (NH) and carbon monoxide (CO). The process requires temperatures of 650 to 850 °C and it is necessary to perform quenching and subsequent tempering.

• - Sulfinization") (S+N+C): increases wear resistance due to the action of sulfur. The sulfur was incorporated into the metal by heating at low temperature (565 °C) in a salt bath.

Among the factors that affect steel heat treatment processes are the temperature and the time during which the material is exposed to these conditions. Another determining factor is the way the steel returns to room temperature. Process cooling may include immersion in oil or the use of air as a coolant.

The method of heat treatment, including cooling, influences whether the steel takes on its commercial properties.

According to this method, in some classification systems, a prefix indicative of the type is assigned. For example, steel O-1, or A2, A6 (or S7) where the letter O is indicative of the use of oil (from English: oil quenched), and A is the initial for air; The prefix S is indicative that the steel has been treated and considered shock resistant*.

rolled steel

The steel used for the construction of metal structures and public works is obtained by rolling steel into a series of standardized profiles.

The rolling process consists of previously heating the molten steel ingots to a temperature that allows the deformation of the ingot through a stretching and grinding process that occurs in a chain of pressure cylinders called a rolling mill. These cylinders form the desired profile until the required measurements are achieved. The dimensions of the sections obtained in this way do not adjust to the required tolerances and that is why laminated products often have to be subjected to machining phases to adjust their dimensions to the required tolerance.

forged steel

Forging is the process that modifies the shape of metals by plastic deformation when the steel is subjected to pressure or a continuous series of impacts. Forging is generally carried out at high temperatures because this improves the metallurgical quality and mechanical properties of the steel.

The meaning of forging steel parts is to reduce as much as possible the amount of material that must be removed from the parts in their machining processes. In stamp forging, the flow of the material is limited to the cavity of the stamp, composed of two matrices that have the shape of the piece to be achieved engraved.

corrugated steel

Corrugated steel is a type of rolled steel used especially in construction, for use in reinforced concrete. These are steel bars that have projections or "corrugations" that improve adhesion with the concrete. It is equipped with great ductility, which allows it to not suffer damage when cutting and bending, and it has great weldability, all of this to make these operations safer and with less energy expenditure.

Corrugated steel bars are standardized. For example, in Spain they are covered by Standards UNE 36068:2011, UNE 36065:2011 and UNE 36811:1998 IN.

Corrugated steel bars are produced in a range of diameters from 6 to 40 mm, in which the section in cm² that each bar has is quoted as well as its weight in kg.

Bars less than or equal to 16 mm in diameter can be supplied in bars or rolls, for diameters greater than 16 they are always supplied in the form of bars.

The corrugated product bars have technical characteristics that must be met to ensure the corresponding calculation of the reinforced concrete structures. Among the technical characteristics, the following stand out, all of them are determined by the tensile test:.

• - elastic limit Re (Mpa).

• - unit breaking load or tensile strength") Rm (MPa).

• - elongation at break A5 (%).

• - elongation under maximum load Agt (%).

• - relationship between loads Rm/Re.

• - Young E's modulus.

Steel stamping

Steel stamping consists of a machining process without chip removal where the steel plate is subjected, by means of appropriate presses, to drawing and stamping processes to obtain certain metal parts. For this, the appropriate molds are placed in the presses.

Steel punching

Steel punching consists of a machining process without chip removal where all types of holes are drilled in the steel plate using impact presses where their respective dies and matrices are placed.

Soft machining

Steel parts can be machined in chip removal processes in machine tools (drill, lathe, milling machine, CNC machining centers, etc.), then hardened by heat treatment and finished with abrasive procedures in the different types of grinding machines that exist.

Rectified

The grinding process allows us to obtain very good surface finish qualities and measurements with very close tolerances, which are very beneficial for the construction of quality machinery and equipment. But the size of the part and the grinding machine's travel capacity can present an obstacle.

Hard machining

On special occasions, the heat treatment of steel can be carried out before machining in chip removal processes, depending on the type of steel and the requirements that must be observed for a given part. With this, it must be taken into account that the tools necessary for such jobs must be very strong as they may suffer rapid wear during their useful life. These peculiar occasions may arise when manufacturing tolerances are so narrow that the induction of heat in treatment is not allowed because it may alter the geometry of the work, or also due to the composition of the batch of material itself (for example, the pieces are shrinking a lot due to being treated). Machining after heat treatment is sometimes preferable, since optimal material stability has been achieved and, depending on the composition and treatment, the machining process itself is not much more difficult.

EDM machining

In some manufacturing processes that rely on electrical discharge with the use of electrodes, the hardness of the steel does not make a noticeable difference.

deep drilling

In many situations, the hardness of the steel is decisive for a successful result, such as in deep drilling when ensuring that a hole maintains its position relative to the axis of rotation of the carbide drill bit. Or for example, if the steel has been hardened by heat treatment and softened by subsequent heat treatment, the consistency may be too soft to benefit the process, since the path of the drill bit will tend to deviate.

Bent

Bending steel that has been heat treated is not highly recommended as the cold bending process of hardened material is more difficult and the material has most likely become too brittle to be bent; The bending process using torches or other methods to apply heat is also not recommended since when heat is reapplied to the hard metal, its integrity changes and may be compromised.

steel profiles

For use in construction, steel is distributed in metal profiles, these having different characteristics depending on their shape and dimensions and must be used specifically for a specific function, whether beams or pillars.

Steel in its different types is overwhelmingly present in our daily lives in the form of tools, utensils, mechanical equipment and as part of household appliances and machinery in general as well as in the structures of the homes we live in and in the vast majority of modern buildings. In this context there is the modern version of steel profiles called Metalcón").

Manufacturers of means of transporting goods (trucks) and agricultural machinery are large consumers of steel.

Railway construction activities are also large consumers of steel, from the construction of road infrastructure as well as the manufacture of all types of rolling stock.

The same can be said of the arms manufacturing industry, especially that dedicated to building heavy weapons, armored vehicles and battleships.

Large shipyards that build ships, especially oil tankers, gas tankers and other tankers, also consume a lot of steel.

Major consumers of steel include automobile manufacturers because many of their significant components are made of steel.

As an example, the following automobile components are made of steel:

• - They are made of forged steel among other components: crankshaft, connecting rods, pinions, gearbox transmission shafts and steering articulation arms.

• - The doors and other body components are made of stamped sheet metal.

• - The profiles that make up the "Frame (machinery)" frame are made of laminated steel.

• - All the springs they incorporate are made of steel, such as; valve springs, seats, clutch presses, shock absorbers "Shock absorber (car)"), etc.

• - All bearings used in automobiles are made of high-quality steel.

• - The wheel rims are made of die-cut sheet metal, except for the high-end ones that are made of aluminum alloys.

• - All screws and nuts are made of steel.

It should be noted that when the car is scrapped due to its age and deterioration, all the steel parts are separated, converted into scrap metal and recycled back into steel using electric furnaces and rolling mills or cast iron parts.

Cuando un técnico proyecta una estructura metálica, diseña una herramienta o una máquina, define las calidades y prestaciones que tienen que tener los materiales constituyentes. Como hay muchos tipos de aceros diferentes y, además, se pueden variar sus prestaciones con tratamientos térmicos, se establecen una serie de ensayos mecánicos para verificar principalmente la dureza superficial, la resistencia a los diferentes esfuerzos que pueda estar sometido, el grado de acabado del mecanizado o la presencia de grietas internas en el material, lo cual afecta directamente al material pues se pueden producir fracturas o roturas.

Hay dos tipos de ensayos, unos que pueden ser destructivos y otros no destructivos.

Todos los aceros tienen estandarizados los valores de referencia de cada tipo de ensayo al que se le somete.[25]​.

Non-destructive testing

The non-destructive tests are as follows:

• - Microscopic testing and surface roughness: microscopes and roughness meters.

• - Ultrasonic tests.

• - Penetrating liquid tests.

• - Magnetic particle tests.

• - Hardness test (Brinell, Rockwell, Vickers); using durometers.

Destructive tests

The destructive tests are as follows:

• - Tensile test with a standardized "Template (mechanical)" specimen.

• - Resilience essay "Resilience (engineering)").

• - Compression test with standardized specimen.

• - Shear test.

• - Bending test.

• - Torsion test.

• - Folding test").

• - Fatigue test.

Evolution of global steel consumption (2021)

Global consumption of finished steel finished products in 2021 reached 1.8 billion tons, an increase of 2.7% compared to 2020. The largest consumer of steel globally is China, which accounts for 52% of the world's steel. However, its consumption compared to previous years has decreased by 5.4%. In contrast, the rest of the world has increased its use and consumption, with the European Union 16%, Central and South America 3%, and the United States, Canada and Mexico 20%.[26]​.

World steel production (2021)

World production of crude steel in 2021 amounted to 1,879 million tons, which represents an increase of 3.8% compared to 2021. This evolution was common across most countries. As one of the few exceptions, China, which decreased its total steel production by 3%. On the other hand, India, Japan and the United States have increased their production by 17%, 16% and 18% respectively. Even so, the majority of world production is in the Asian continent, which generates 72% of all steel.[26]​.

The distribution of steel production in 2021 was as follows according to figures estimated by the World Steel Association in June 2022.[26]​.

Available data on world steel production in 2019, in millions of tons per year:[27]​[28]​.

El acero, al igual que otros metales, puede ser reciclado. Al final de su vida útil, todos los elementos construidos en acero como máquinas, estructuras, barcos, automóviles, trenes, etc., se pueden desguazar, separando los diferentes materiales componentes y originando unos desechos seleccionados llamados comúnmente chatarra. La misma es prensada en bloques que se vuelven a enviar a la acería para ser reutilizados. De esta forma se reduce el gasto en materias primas y en energía que deben desembolsarse en la fabricación del acero. Se estima que la chatarra reciclada cubre el 40% de las necesidades mundiales de acero (cifra de 2006).

El proceso de reciclado se realiza bajo las normas de prevención de riesgos laborales y las medioambientales. El horno en que se funde la chatarra tiene un alto consumo de electricidad, por lo que se enciende generalmente cuando la demanda de electricidad es menor. Además, en distintas etapas del reciclaje se colocan detectores de radiactividad, como por ejemplo en la entrada de los camiones que transportan la chatarra a las industrias de reciclaje.

Be careful when handling scrap

Personnel who handle scrap metal must always be vaccinated against tetanus infection, as they can become infected by suffering an injury from scrap metal. Anyone who suffers a cut with a steel element must go to a medical center and receive said vaccine, or a booster if they received it previously.

• - Wikimedia Commons hosts a multimedia gallery on Steel.

• - Wiktionary has definitions and other information about steel.

• - Steel industry tables.

• - International Iron and Steel Institute.