New methods of obtaining steel were invented. Steel: steel making, process and methods. Steel production technology. Cutters and knives
BC. in Europe, wrought iron was already being produced everywhere. Many splendid Greek and Roman buildings were constructed of stone with butterfly-shaped iron tools plated with lead. In 500 BC. NS. the Etruscans who lived on the western coast of Italy produced more than 4.5 thousand kilograms of iron per year. Iron was forged in a smithy, and charcoal was used to maintain the fire. The fire was fanned with the help of special furs sewn from animal skins. Later, the small stone furnaces were dismantled and the massive smelting of iron began. Ore was delivered to the furnaces on sailing ships. Due to the fact that the method of processing ore, which was used by the Etruscans, was ineffective, its reserves were quickly depleted. In addition, the production of charcoal has sharply reduced the amount of forests in western Italy.
The first steel was created by the Celts around AD 200. NS. They cut wrought iron into thin strips and put them in a container with charred bones and charcoal, after which they heated it all in an oven for 10-12 hours over very high heat. As a result, the metal surface was enriched with carbon. Then they welded these strips together by forging and thus created knives. These knives are the forerunners of what we mistakenly call Damascus blades. The Celtic steelmaking process in 1050 was copied by the Vikings and the Germans. Since then, steel blades have been produced in these countries, the manufacturing method of which was strictly classified. Damascus steel was produced in Pakistan and sent to Syria in the form of damask blanks, where the famous Damascus blades were made. The production process of Damascus steel is very complicated, as it had to be heated to a very high temperature, and if the temperature was exceeded, the material could collapse.
Over time, the melting temperature of iron in the furnaces became higher and higher, so the resulting iron contained 3-4% carbon. It was fragile and suitable only for casting. It was impossible to make knives and parts for transport from it. In addition, by this time, a huge part of the forests in Europe had been cut down for construction purposes and the production of charcoal. Then the king of England issued a decree that forests can no longer be cut down, and steel producers had to come up with a way to convert coal into coke. In England, they developed a method for tinning steel, whereby they mixed molten iron with iron silicate and iron oxide. Iron silicate is one of the components of wrought iron.
Coal-fired stoves were called a blast furnace. One worker had to stir the resulting mixture, resulting in the formation of carbon dioxide, so the melting point of iron became higher and the tinning process began. Large pieces weighing from 90 kg to 130 kg were placed inside. Another worker, using a pair of large forceps, took these pieces and placed them under a press to squeeze the iron silicate out of them. After the press, the pieces were placed in a rolling mill, where strips of blast iron were formed from them. These strips were cut into short pieces and connected together, after which they were placed in a cavity filled with carbon and heated to the welding temperature. After that, the strips of blooming iron were sent back to the rolling mill and bar-iron was obtained. This method was used not only in Europe, but in the eastern United States.
To obtain steel, the thin bars were placed in a cavity filled with carbon from bone burning and heated at a high temperature for several days. The carbon was absorbed by the iron and the result was bubble steel. Bubble steel was called cement steel or stew. This concept appeared thanks to outward appearance strips extracted from a carbon pit that were covered in bubbles. After that, the strips were folded together and forged, then folded and forged again, in this way, high quality steel was obtained.
England needed high quality steel to build a fleet that could cross the ocean. One enterprising Englishman noticed that glass blowers can get very high temperatures in their furnaces. He took strips of bubble steel and placed them in a ceramic crucible, after which he placed the container in the glass blowers' furnace. As a result, the steel melted, the iron silicate evaporated, and the carbon remained, and a very high quality steel was obtained. At that time, many people watched the process, and he could not keep it a secret. In this way, cast steel was obtained, from which a large number of old tools were made in the USA, marked "cast steel". Many people mistakenly consider them cast, as the name implies.
Steel production received a new impetus when the Bessemer steelmaking process was invented. This steel was used for the construction of large objects, such as the Grand Coulee Dam, because it is not subject to corrosion. At the beginning of the 20th century, the production of various alloys began. Then, in gas open-hearth furnaces, manganese, chromium, nickel and other elements began to be added to iron. During the Second World War, when the demand for metal increased, the production of alloys received a new powerful impetus. Since then, a huge step has been taken in the production and improvement of various steels.
Steel has higher physical and mechanical properties compared to cast iron: it can be forged, rolled, it has high strength and significant ductility, and is well processed by cutting. In the molten state, steel has sufficient fluidity to produce castings.
Mild steel with a carbon content of less than 0.25% has high ductility, ability to weld well, and is easily forged and rolled in hot and cold conditions. Therefore, such steel is the main material for modern mechanical engineering, transport and other sectors of the country's national economy.
In ancient times, mild steel (technical iron) was obtained directly from ores in a pasty state. Later they learned how to make steel from cast iron in a brick forge, also in a doughy state. In 1740, England began to use the method of producing liquid steel in crucibles, which had been known long before in the East. Since 1784, they began to use puddling - the production of steel in a doughy state from cast iron by oxidizing its impurities on the hearth of a combustion furnace. All these methods were of low productivity and required a lot of fuel and labor.
The rapid growth of industry and railway transport in the second half of the 19th century. demanded an enormous amount of steel, and the old methods of obtaining it could not satisfy this need. New, more productive methods of melting steel were created. In 1856, the Bessemer method appeared (named after its inventor G. Bessemer), and in 1878, the Thomas method (proposed by S. Thomas) for producing cast steel from liquid iron in converters. In 1857, a major Russian metallurgist P.M. PM Obukhov's gun steel was superior in quality to the best foreign steels. Since 1864, the open-hearth method of steel production in flame furnaces (named after its inventor P. Martin) has been used, and since 1899 - the method of steel production in electric furnaces, based on the application of the phenomenon of an electric arc, discovered in 1802 by Acad. V.V. Petrov.
The task of converting cast iron into steel is to remove excess carbon, silicon, manganese and other impurities. It is especially important to remove harmful impurities. sulfur and phosphorus... Cast iron carbon, combining with oxygen, turns into gas (carbon monoxide CO), which volatilizes. Other impurities are converted into oxides and other compounds, insoluble or slightly soluble in the metal; these compounds, together with fluxes, form a slag on the metal surface. During combustion, manganese and silicon form oxides MnO and SiO 2 insoluble in the metal. When phosphorus is burned, its oxide P 2 O 5 is formed, which dissolves well in the metal. To remove phosphorus from the metal, slag is added with an excess of lime (consisting mainly of CaO), which binds P2O5 into a strong compound (CaO) 4 P2O5, insoluble in the metal.
Sulfur is dissolved in cast iron as part of the FeS compound; it is removed from the metal with the help of manganese or lime, which form with it either the MnS compound, which is poorly soluble in the metal, or the CaS insoluble compound.
At present, the following methods of steel production are used in the country's metallurgy: converter, open-hearth and electric smelting.
Electric melting is mainly used for the production of high-quality steel and for last years is developing intensively.
Technical progress in steelmaking is characterized by an intensive increase in the capacity of smelting units, widespread use of the oxygen-converter process and continuous casting of steel, and an improvement in the quality of the metal.
When they say "steel character", they mean firmness and determination, reliability and masculinity. The alloy of iron with carbon today serves as a symbol of the best qualities that are attributed not only to things, but also to people. There are two types:
- alloyed;
- carbonaceous.
A quality classification has also been adopted. There are ordinary and high-quality alloys as well as of higher quality and the best high-quality alloys.
What is made from the most durable material
The original steel was first produced by the Celts. It happened around 200 BC. The technology of the then production consisted of the following: forged iron was cut into thin strips, which were placed in a container, which already contained burnt bones and coal. The container, along with all its contents, was heated and remained in the oven, in which a strong fire was maintained, for about 10-12 hours. As a result of this long and laborious process, the metal surface was enriched with carbon.
The first tools that were made from steel were knives. The sheets were joined together and processed to obtain a specific shape. For a very long time, the recipe for making a durable alloy was classified and passed from mouth to mouth only to initiates. Since then, steel has gone far in its improvement. Steel products can be found in every home.
The invention of stainless steel in the 20th century was a big breakthrough. This product of production has found application in many areas of industry and in everyday life. It is easier to say where it is not used. The most common and demanded types of steel products are:
- rolled metal products;
- decorations;
- instruments;
- dishes;
- parts for machine tools and transport, etc.
The high demand for the material is based on its amazing properties. This is strength, and corrosion resistance, and thermal conductivity, and electrical conductivity, etc. Different kinds alloy can be characterized by different qualities.
Where to buy high quality steel products
As mentioned above, there are various classifications of the alloy, one of which is based on its quality. It must correspond to the purpose of what is being manufactured. A wide range of steel products is offered by the All.biz business portal. The resource contains spare parts, tools, rolling and much more. Here http://www.kz.all.biz/ has everything that is produced in our country and abroad. The search engine is configured so that you can find everything you need. The prices are especially attractive.
The durability and reliability of mechanisms depend on the material from which they were made, that is, on the totality of all its properties and features, which determine the operational characteristics. Today, most of the units and parts of machines are made from various grades of steel. Let's consider this material in more detail.
What is steel
Steel is an alloy of two chemical elements: iron (Fe) and carbon (C), and the content of the latter should not exceed 2%. If there is more carbon, then this alloy belongs to cast irons.
But steel is not only a chemically pure compound of two elements, it contains both harmful impurities, such as sulfur and phosphorus, and special additives that give the required properties to the material - increase strength, improve workability, plasticity, etc.
If the carbon alloy is less than 0.025% and contains a small amount of impurities, then it is considered technical iron. This material differs from steels in all respects, it has high magnetic characteristics, and it is used as for the manufacture of electrical elements. Pure iron does not exist in nature; it is very difficult to obtain it even under laboratory conditions.
Despite the fact that there is very little carbon in percentage terms, it has a significant effect on the mechanical and technical properties of the material. An increase in this substance leads to an increase in hardness, strength increases, but plasticity sharply decreases. And, as a consequence, technological characteristics change: with an increase in carbon, casting properties decrease, and machinability deteriorates. At the same time, low-carbon steels are also poorly machined.
Getting steel. Metallurgy
Steel is the most abundant alloy on the planet. It is obtained industrially from cast iron, from which excess carbon and other impurities are burned out under the influence of high temperatures. Steels are mainly obtained in two ways: melting in open-hearth furnaces and melting in electric furnaces. The material made in an electric furnace is called electric steel. It turns out to be cleaner in composition. In addition, there are many special processes for producing alloys with special properties, such as vacuum arc melting or electron beam melting.
More details about steels and other alloys can be found in the study of such a science as metal science. It is considered one of the branches of physics and covers not only information about steel grades and their composition, but also contains information about the structure and properties of materials at the atomic and structural level.
Students of specialized universities take a special course "Industrial steels", where they analyze in detail alloys for special purposes: construction, improved, case-hardened, for cutting and measuring tools, magnetic, spring-spring, heat-resistant, steel for structures in cold climates, etc.
Classification of steels by quality
All steels are subdivided by quality into:
Common quality steel;
High quality;
High quality steel;
High quality.
The quality of steel directly depends on the percentage of harmful impurities (composition) and compliance with the declared mechanical and technological characteristics. All types of steel are used in industry, but in different directions: ordinary quality steel - for irrelevant parts, high quality steel and high quality - in structures to which special requirements are imposed.
Steel according to GOST: classification
Steel. Properties: tables for the most common grades with basic mechanical and technological characteristics
steel grade | Mechanical properties | Technological properties |
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Machinability by cutting | Weldability | Cold forming ductility |
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hot rolled | ||||||
H - low;
Y - satisfactory;
B - high;
σт - physical yield strength, MPa;
σw - ultimate tensile strength, MPa;
δ - relative elongation,%.
Steel Is an iron-carbon alloy that contains about 1.5% carbon, if its content increases, then the brittleness and hardness of steel increases significantly. The main source material for steel production- steel scrap and pig iron.
Iron is primarily oxidized by the interaction of oxygen and cast iron in steel furnaces. Together with iron, phosphorus, silicon, carbon and manganese are oxidized. Iron oxide, which is formed at high temperature conditions, gives up its oxygen in cast iron to more active impurities, while oxidizing them.
Steel production is carried out in three stages.
The first stage of steel production - rock melting
The charge melts and the liquid metal bath is heated. The temperature of the metal is low, iron is vigorously oxidized, iron oxide is formed and impurities are oxidized: manganese, silicon and phosphorus.The most important task of this stage steel production Is the removal of phosphorus. To do this, it is necessary to melt in the main furnace, where the slag will contain calcium oxide (CaO). Phosphoric anhydride - P2O5 will form a fragile compound (FeO) 3 x P2O5 with iron oxide. Calcium oxide is a stronger base than iron oxide, and at not very high temperatures binds P2O5 and turns it into slag.
In order to remove phosphorus, a not very high temperature is needed, baths of slag and metal, a sufficient content of FeO in the slag. In order to increase the FeO content in the slag and accelerate the oxidation of impurities, scale and iron ore are added to the furnace, inducing iron slag. Gradually, as phosphorus is removed from the metal into the slag, the phosphorus content in the slag increases. So you need to remove this slag from the mirror of the metal, and then replace it with a new one with fresh additions of calcium oxide.
The second stage of steelmaking is boiling
The metal bath is boiling. It starts gradually as it heats up to high temperatures. With an increase in temperature, the oxidation reaction of carbon occurs more intensively, proceeding with the absorption of heat:In order to oxidize carbon, it is introduced into the metal a small amount of scale, ore or oxygen blown. When carbon reacts with iron oxide, bubbles of carbon monoxide are removed from the liquid metal, and a "boiling bath" occurs. During "boiling" the carbon content in the metal is reduced to the required amount, the temperature is equalized throughout the volume of the bath, non-metallic inclusions are slightly removed, which adhere to the floating CO bubbles and gases that penetrate the CO bubbles. All this leads to an increase in the quality of the metal. This means that this stage is the main one in the steel production process.
Conditions are created to remove sulfur. In steel, sulfur is in the form of sulfide - FeS, which is dissolved in the main slag. The higher the temperature regime, the more iron sulfide will dissolve in the slag and will interact with calcium oxide CaO:
The compound that is formed - CaS, dissolves in the slag, but does not dissolve in the iron, so that the sulfur is removed into the slag.
The third stage of production is steel deoxidation
The reduction of iron oxide, which is dissolved in the liquid metal, occurs. An increase in the oxygen content in the metal during melting is necessary for the oxidation of impurities, but in the finished steel oxygen is a harmful impurity, because it lowers the mechanical properties of the steel.Steel deoxidation is carried out by two methods: diffusion and precipitation.
Diffusive deoxidation occurs due to slag deoxidation. In crushed form, ferrosilicon, ferromanganese and aluminum are transferred to the surface of the slag. These deoxidizers reduce iron oxide, and at the same time reduce its content in the slag. This means that iron oxide, which is dissolved in steel, goes into this slag. The oxides that are formed during this process remain in the slag, and the iron, already in reduced form, goes into steel, and the content of non-metallic inclusions in it decreases and its quality increases.
Precipitating deoxidation occurs due to the introduction of soluble deoxidizers (ferrosilicon, ferromanganese, aluminum) into liquid steel, which contain elements with a higher affinity for oxygen in comparison with iron. In the end, after deoxidation, iron is reduced and oxides are created: SiO2, MnO, Al2O5, which have a lower density in comparison with steel, and are removed into the slag.
Depending on the level of deoxidation, the following types of steel can be smelted: - boiling - not completely deoxidized in the furnace. The deoxidation of such steel continues in the mold during the solidification of the ingot, due to the interaction of carbon and iron oxide: FeO + C = Fe + CO.
Carbon monoxide, which is formed, is removed from the steel, ensuring the removal of hydrogen and nitrogen from the steel, gases are removed in the form of bubbles, leading it to boiling. Boiling steel has no non-metallic inclusions, therefore it has a high degree of ductility.
- calm - obtained with absolute deoxidation in a ladle and in a furnace.
- semi-calm - they are distinguished by intermediate deoxidation between boiling and calm steels. Partly deoxidized in a ladle and in a furnace, and partly in a mold, due to the interaction of carbon and iron oxide, which are contained in steel.
Equipment for the production and smelting of steel
For steel production steel mills must have special equipment:Oxygen converters
- argon economy;
- parts of converters (vessels and carrier rings of the converter);
- dust filtration;
- suction of converter gas;
Electric ovens
- (manufacturing of peripherals);
- (manufacturing of power supports, steel parts for furnaces, cooling of electrodes);
- loading buckets;
- scrap department;
- frequency converters for induction heating;
Secondary metallurgy
- desulfurization of steel;
- homogenization of steel;
- electroslag remelting;
- creating a vacuum;
Bucket technology
- LF type equipment;
- SL type equipment;
Bucket farm
- casting and casting ladle covers;
- foundry and casting ladles;
- slide gates;
Continuous casting equipment
- casting swing bed for handling tundishes and ladles;
- segments of continuous casting equipment;
- trolley trolleys;
- emergency trays and vessels;
- tundish and folding stands;
- plug mechanism;
- movable cast iron stirrers;
- cooling equipment;
- outlet sections of continuous casting;
- metallurgical rail vehicles.
The public often learns about technological innovations from the media, but such reports usually do not rely on diplomatic sources. On January 31, 1915, this rule was broken. The New York Times published a short article entitled A Non-Rusting Steel. A newspaper report said the Sheffield-based company had launched a new type of steel "that resists corrosion, tarnishes, and stains." The manufacturer claimed that it is extremely suitable for making cutlery, since products made from it are easy to clean and do not lose their luster when in contact with even the most acidic foods. John Savage, the American consul in Sheffield, was named as a source of information. So, without much ado and with a fair delay, the world learned about the invention of stainless steel.
Stainless steels differ in properties, composition and purpose, but in general they can be divided into several main groups according to their crystal structure: ferritic, austenitic, martensitic and two-phase (ferritic-austenitic). Ferritic stainless steels are chromium (10-30% chromium) and low-carbon (less than 0.1%) steels. They are quite strong, plastic, relatively easy to process and at the same time cheap, but not amenable to heat treatment (hardening). Martensitic stainless steels are chromium (10-17% chromium) containing up to 1% carbon. They lend themselves well to heat treatment (quenching and tempering), which gives products from such steels high hardness (knives, bearings, cutting tools are made of them). Martensitic steels are more difficult to work with and, due to their lower chromium content, are less resistant to corrosion than ferritic ones. Austenitic stainless steels - chrome-nickel. They contain 16-26% chromium and 6-12% nickel, as well as carbon and molybdenum. They are superior to ferritic and martensitic steels in corrosion resistance and are non-magnetic. High strength is obtained by cold working (work-hardening), while heat treatment (hardening), their hardness decreases. Duplex steels combine the different properties of ferritic and austenitic steels.
Ancestors of stainless steel
In fact, such steel was produced in Europe and the United States even before the Sheffield metallurgists. Ordinary steel, an alloy of iron and carbon, is easily covered with a film of iron oxide - that is, it rusts. By the way, it was this circumstance that was one of the reasons for the brilliant commercial success of the American entrepreneur King Kemp Gillett, who invented the safety razor. In 1903, his company sold only 51 blades, in 1904 - almost 91,000, and by 1915 total sales exceeded 70 million. Gillette blades, which used unalloyed steel from Bessemer converters, quickly rusted and became dull and therefore required frequent replacement. It is curious that a recipe for combating this disease of the main metal of the then industry was found long ago. In 1821, the French geologist and mining engineer Pierre Berthier noticed that iron-chromium alloys have good acid resistance, and suggested making them kitchen and table knives, forks and spoons. However, this idea remained a good wish for a long time, since the first alloys of iron and chromium were very fragile. Only at the beginning of the 20th century were formulations of iron alloys invented, capable of claiming the title of stainless steel. Among their authors was one of the pioneers of the American automotive industry, Elwood Haynes, who was going to use his alloy to make metal-cutting tools. In 1912, he applied for a corresponding patent, which was obtained only seven years later after lengthy disputes with the US Patent Office.
Blades for Gillette machines were made of solid carbon steel. They were not very durable, as they easily corroded from constant exposure to moisture.
Accidental find
But the official parent of the well-known stainless steel was a man who did not look for it at all and created only thanks to a lucky chance. The lot fell to the British self-taught metallurgist Harry Brearley, who in 1908 headed a small laboratory established by two Sheffield steel companies. In 1913, he conducted research on steel alloys, which were supposed to be used for the manufacture of gun barrels. Scientific metal science was then in its infancy, so Brearley acted by trial and error, testing the strength and heat resistance of alloys with different additives. He simply folded the unsuccessful blanks in the corner, and they quietly rusted there. Once he noticed that the casting, taken out of the electric furnace a month ago, does not look rusty at all, but shines like new. This alloy contained 85.3% iron, 0.2% silicon, 0.44% manganese, 0.24% carbon and 12.8% chromium. It was he who became the world's first example of the steel, which was later reported by the New York Times. It was melted in August 1913.
And the cutlery knives from one of the companies in Sheffield may not have been as sharp, but they resisted corrosion well.
Failure and success
Brearley became interested in the unusual casting and soon found out that it resisted the action of nitric acid well. Although the new alloy was not successful as a weapon steel, Brearley realized that the material would find many other uses. Sheffield has been known for metalwork such as knives and cutlery since the 16th century, so Brearley decided to try his alloy in this capacity. However, two local manufacturers to whom he sent the castings were skeptical about his proposal. They found that the new steel knives were labor intensive to make and harden. The metallurgical companies, including the one for which Brearley worked, were also not enthusiastic. Understandably, both cutters and metal producers feared that stainless steel products would prove so durable that the market would quickly become saturated and demand for them would fall. Therefore, until the summer of 1914, all Brearley's attempts to convince industrialists of the promise of a new alloy did not lead to anything worthwhile.
But then he got lucky. In the middle of summer, fate pushed him against his school friend Ernest Stewart. Stewart of R.F. Mosley & Co, which produced cutlery, at first did not believe at all in the reality of the existence of steel, which is not subject to rust, but agreed to experimentally make several knives for cheese from it. The products turned out to be excellent, but Stuart considered this venture unsuccessful, since his tools in the manufacture of these knives quickly became dull. But in the end, Stewart and Brearley did choose a heating mode in which the steel was workable and did not become brittle after cooling. In September, Stewart made a small batch of kitchen knives, which he gave to friends for testing on one condition: he asked them to return them in case of stains or rust on the blades of the knives. But not a single knife ever returned to his workshop, and soon the Sheffield manufacturers recognized the new steel.
Quite often you can find the statement that meteoric iron does not rust. In fact it is pure water myth. Iron-nickel meteorites contain about 10% nickel, but do not contain chromium, therefore they do not have corrosion resistance. This can be seen by visiting the mineralogical section of a natural history museum. Looking closely at the samples of iron-nickel meteorites (say, the Sikhote-Alin meteorite, which is often found in such exhibitions), one can see numerous traces of rust. But a sample of an iron-nickel meteorite bought in a mineralogical souvenir shop, most likely, will not really rust. The reason is in "pre-sale preparation", which consists in covering the sample with a thick protective grease. It is worth washing off this lubricant with a solvent - and then the moisture and oxygen of the atmosphere will take revenge.
Cutters and knives
In August 1915, Brearley received a patent for his invention in Canada, in September 1916 - in the United States, then in several European countries. Strictly speaking, he patented not even the alloy itself, but only knives, forks, spoons and other cutlery made from it. Haynes challenged Brearley's US patent, citing his priority, but the parties eventually came to an agreement. This made possible the establishment in Pittsburgh of the joint Anglo-American corporation The American Stainless Steel Company. But that's a completely different story. It is worth noting that Haynes's stainless steel contained much more carbon than Brearley's and therefore had a different crystal structure. This is understandable: carbon provides hardness during hardening, and Haynes sought to create precisely the alloy for the manufacture of machine tools and milling cutters. Now the Heins-type steels are called martensitic, and steels that historically go back to the Brearley alloy are called ferritic (there are other types of stainless steels).
The Iron (Kutubova) Column is one of the main attractions of Delhi. Erected in 415, it has hardly suffered from corrosion for 1600 years - only small specks of rust are visible on the surface, while ordinary steel products of this size are almost completely oxidized and crumbled into dust during this time. In attempts to explain this phenomenon, many hypotheses have been put forward: the use of very pure or meteoric iron, natural nitriding of the surface, bluing, constant oil treatment, and even natural radiation exposure, which turned the top layer into amorphous iron. There were attempts to explain the safety of the column by external factors - in particular, by a very dry climate. Analyzes have shown that the column consists of 99.7% iron and does not contain chromium, that is, it is not stainless in the modern sense of the word. The main impurity in the column material is phosphorus, and this, according to scientists, is the main reason for corrosion resistance. A layer of phosphates FePO4 · H3PO4 · 4H2O with a thickness of less than 0.1 mm is formed on the surface, and, unlike rust, which crumbles and does not prevent further oxidation, this layer forms a strong protective film that prevents rusting of iron.
Natural taste
Stewart not only opened the way to the use of new steel, but also found for it the now generally accepted English-language name stainless steel, "steel without spots". If the standard explanation is to be believed, it occurred to him when he dipped a polished steel plate in vinegar and, looking at the result, said in surprise: “This steel stains less,” that is, “There are few stains on this steel.” Brearley called his brainchild a little differently - rustless steel, which corresponds to the Russian-language term "stainless steel". By the way, the title of the article in the New York Times heralded the appearance of stainless (and not weak-rusting!) Steel.
Its secret is simple. With a sufficient concentration of chromium (at least 10.5% and up to 26% for especially aggressive environments), a hard transparent film of chromium oxide Cr 2 O 3 is formed on the surface of stainless steel products, firmly adhered to the metal. It forms a protective layer invisible to the eye, which does not dissolve in water and prevents the oxidation of iron, and therefore does not allow it to rust. This film has another most valuable quality - it heals itself in damaged areas, so it is not afraid of scratches. Stainless steel cutlery has gained immense popularity also because it allowed to get rid of the specific taste inherent in inexpensive metal dishes. The chromium oxide layer makes it possible to enjoy the natural taste of food, since it prevents the taste buds of the tongue from coming into direct contact with the metal. All in all, the stainless steel that the modern industry produces in many varieties is a truly remarkable accidental invention.
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