History of stainless steel: who invented it and when
A hundred years ago, the world heard about a wonderful material that is extremely widely used in various areas of our lives - stainless steel.
The public often learns about technological innovations from the media, but such reports are usually not based on diplomatic sources. On January 31, 1915, this rule was broken. The New York Times published a short article entitled A Non-Rusting Steel.
The newspaper report said that a company in the British city of Sheffield had launched a new type of steel "that does not corrode, tarnish or stain." The manufacturer claimed that it is extremely suitable for making cutlery, since products made from it are easy to wash and do not lose their shine when in contact with even the most acidic foods.
The American consul in Sheffield, John Savage, was named as the source of the information. This is how, without much fuss and with considerable delay, the world learned about the invention of stainless steel.
Types of stainless steel Stainless steels differ in properties, composition and purpose, but in general they can be divided into several main groups based on 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, ductile, relatively easy to process and at the same time cheap, but cannot be heat treated (hardening). Martensitic stainless steels are chromium (10−17% chromium) steels containing up to 1% carbon. They lend themselves well to heat treatment (hardening and tempering), which gives products made from such steels high hardness (knives, bearings, and cutting tools are made from them).
Martensitic steels are more difficult to process and, due to their lower chromium content, are less resistant to corrosion than ferritic steels. Austenitic stainless steels - chromium-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 (hardening); during heat treatment (hardening), their hardness decreases. Dual-phase steels combine various properties of ferritic and austenitic steels.
Ancestors of stainless steel
In fact, such steel was produced in Europe and the USA even before the Sheffield metallurgists. Ordinary steel, an alloy of iron and carbon, is easily coated with a film of iron oxide - that is, it rusts. By the way, this very circumstance was one of the reasons for the brilliant commercial success of the American entrepreneur King Kemp Gillette, 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 were made from unalloyed steel from Bessemer converters, quickly rusted and became dull and therefore required frequent replacement. It is curious that the recipe for combating this disease of the main metal of the then industry was found long ago. In 1821, French geologist and mining engineer Pierre Berthier noticed that iron-chromium alloys had good acid resistance, and proposed making kitchen and table knives, forks and spoons from them.
However, this idea remained a wish for a long time, since the first alloys of iron and chromium were very brittle. It was only at the beginning of the 20th century that iron alloy formulations were invented that could claim the title of stainless steel. Among their authors was one of the pioneers of the American automobile industry, Elwood Haynes, who intended to use his alloy to make metal-cutting tools.
In 1912, he applied for a corresponding patent, which was granted only seven years later after lengthy disputes with the US Patent Office.
Blades for Gillette machines were made of hard carbon steel. They were not very durable, as they rusted easily from constant exposure to moisture.
Chance find
But the official parent of the well-known stainless steel was a man who did not look for it at all and created it only thanks to a happy accident. This lot fell to the self-taught English metallurgist Harry Brearley, who in 1908 headed a small laboratory established by two Sheffield steel companies.
In 1913, he conducted research on steel alloys that were supposed to be used to make gun barrels. Scientific metallurgy was then in its infancy, so Brearley acted by trial and error, testing alloys with different additives for strength and heat resistance.
He simply put the unsuccessful pieces in the corner, and they quietly rusted there. He once noticed that a casting taken out of an electric furnace a month ago did not look rusty at all, but shined 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 that steel, which was later reported by the New York Times. It was smelted in August 1913.
And table knives made by a company 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 discovered that it resisted nitric acid well. Although the new alloy was not successful as a weapon steel, Brearley realized that this material would have many other uses.
Sheffield has been famous for its metal products such as knives and cutlery since the 16th century, so Brearley decided to try out his alloy for this purpose. However, two local manufacturers to whom he sent the castings were skeptical of his proposal.
They found that knives made from the new steel required more labor to manufacture and harden. Metallurgical companies, including the one for which Brearley worked, were also not enthusiastic.
It is clear that both cutlers and metal manufacturers feared that stainless steel products would be so durable that the market would quickly become saturated and demand for them would fall. Therefore, until the summer of 1914, all Brierley’s attempts to convince industrialists of the promise of the new alloy did not lead to anything worthwhile.
But then he got lucky. In the middle of summer, fate brought him into contact with his school friend Ernest Stewart. Stewart, an employee of the cutlery company RF Mosley & Co, at first did not believe in the reality of the existence of steel, which is not subject to rust, but agreed to make several cheese knives from it as an experiment.
The products turned out to be excellent, but Stuart considered this venture a failure, since his tools quickly became dull when making these knives. But in the end, Stewart and Brearley finally found a heating mode at which the steel could be processed and did not become brittle after cooling.
In September, Stewart made a small batch of kitchen knives, which he distributed to friends for testing with one condition: he asked to return them if stains or rust appeared on the blades of the knives. But not a single knife ever returned to his workshop, and soon Sheffield manufacturers recognized the new steel.
Heavenly Iron Quite often you can come across the statement that meteorite iron does not rust. In fact, this is pure myth. Iron-nickel meteorites contain about 10% nickel, but do not contain chromium, and therefore do not have corrosion resistance. You can verify this by visiting the mineralogical section of a natural history museum.
Taking a closer look at samples of iron-nickel meteorites (say, the Sikhote-Alin meteorite, which is often found in such exhibitions), you can see numerous traces of rust. But a sample of an iron-nickel meteorite purchased at a mineralogical souvenir store most likely will not really rust. The reason is “pre-sale preparation”, which consists of coating the sample with a thick protective lubricant.
It is necessary to wash off this grease 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 USA, and then in several European countries. Strictly speaking, he did not even patent the alloy itself, but only the knives, forks, spoons and other cutlery made from it.
Haynes challenged Brearley's American patent on the grounds of priority, but the parties eventually reached an agreement. This made possible the establishment in Pittsburgh of a joint Anglo-American corporation, The American Stainless Steel Company. But that's a completely different story.
It is worth noting that Haynes stainless steel contained much more carbon than Brearley steel, and therefore had a different crystalline structure. This is understandable: carbon provides hardness during hardening, and Haynes sought to create an alloy for the manufacture of machine cutters and milling cutters.
Nowadays, Haynes-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).
Indian miracle Iron (Kutubov) column is one of the main attractions of Delhi. Erected in 415, it has suffered almost no corrosion for 1,600 years - only small spots of rust are visible on the surface, while ordinary steel products of a similar size during this time are almost completely oxidized and crumble into dust.
Many hypotheses have been put forward in attempts to explain this phenomenon: the use of very pure or meteorite iron, natural nitriding of the surface, bluing, constant oil treatment, and even natural radioactive irradiation, which turned the top layer into amorphous iron. There were attempts to explain the preservation of the column by external factors - in particular, a very dry climate.
Analyzes showed 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 FePO4·H3PO4·4H2O phosphates less than 0.1 mm thick is formed on the surface, and, unlike rust, which crumbles and does not prevent further oxidation, this layer forms a durable 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 stains.”
According to the standard explanation, 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 term “stainless steel”. By the way, the title of the article in the New York Times announced the appearance of stainless steel (not low-rust!) steel.
Her secret is simple. With a sufficient concentration of chromium (at least 10.5% and up to 26% for particularly aggressive environments), a solid transparent film of chromium oxide Cr2O3 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 valuable quality - it self-heals in damaged areas, so it is not afraid of scratches.
Stainless steel cutlery has gained immense popularity also because it allows us to get rid of the specific taste characteristic of inexpensive metal utensils.
The chromium oxide layer allows you to enjoy the natural taste of food, since it prevents direct contact of the taste buds of the tongue with the metal. In general, stainless steel, which the modern industry produces in many varieties, is truly a remarkable accidental invention.
The article “Steel without stains” was published in the magazine “Popular Mechanics” (No. 3, March 2015).
Source: https://www.PopMech.ru/technologies/56589-istoriya-nerzhaveyushchey-stali-kto-i-kogda-ee-izobrel/
Stainless steels: ferrite, martensite, austenite
Stainless steels are prized for their high corrosion resistance. All truly stainless steels contain at least 11% chromium. This chromium content ensures the formation of a thin protective surface layer of chromium carbide when steel interacts with oxygen.
The effect of chromium on the corrosion resistance of steel
It is chromium that makes steel stainless. In addition, chromium is an element that increases the stability of ferrite. Figure 1 illustrates the effect of chromium on the iron-carbon phase diagram. Chromium causes the austenitic region to shrink while the ferritic region expands in size. At high chromium content and low carbon content, ferrite is the only phase up to the liquidus temperature.
Figure 1 - Effect of 17% chromium on the iron-carbon phase diagram. With a low carbon content, ferrite is stable at all temperatures. The letter "M" stands for "metal", such as chromium or iron, as well as other alloying elements.
There are several types of stainless steels based on differences in crystal structure and strengthening mechanisms.
Ferritic stainless steels
Ferritic stainless steels contain up to 30% chromium and no more than 0.12% carbon.
Due to their body-centered crystal structure (BCC), ferritic steels have good strength and decent ductility, which are achieved through solid solution strengthening and strain hardening.
Ferritic steels are ferromagnetic or, in simple terms, “magnetic”. They are not amenable to heat treatment. Ferritic steels have excellent corrosion resistance, moderate workability, and are relatively inexpensive.
Ferritic stainless steels include steels 08Х13, 12Х17, 08Х17Т, 15Х25Т, 15Х28 according to GOST 5632-72.
Martensitic stainless steels
From Figure 1 it can be seen that steel with 17% chromium and 0.5% carbon when heated to 1200 ºC forms 100% austenite, which turns into martensite when steel is quenched in oil. The martensite is then tempered to produce high strength and hardness of the steel (Figure 2).
Figure 2 – Martensitic stainless steel. Contains large primary carbides and small carbides that were formed during tempering.
chromium in martensitic steels is usually no more than 17%, since otherwise the austenitic region on the phase diagram becomes too small. This leads to the fact that it becomes technologically difficult to get into: strict control of the carbon content and austenitization temperature is required.
The lower chromium content allows the carbon content to be expanded from 0.1 to 1.0%, which makes it possible to obtain martensite of various hardnesses.
The combination of high hardness, strength and corrosion resistance makes these steels suitable for the manufacture of products such as high-quality knives and ball bearings.
Martensitic stainless steels include steels 20Х13, 30Х13, 40Х13, 14Х17Н2 according to GOST 5632-72.
Austenitic stainless steels
Nickel is an element that increases the stability of austenite. The presence of nickel in steel increases the size of the austenitic region, while ferrite almost completely disappears from iron-chromium-carbon alloys (Figure 3).
Figure 3 – Cross-section of the iron-chromium-nickel-carbon phase diagram at 18% chromium and 8% nickel. At low carbon content, austenite is stable at room temperature.
If the carbon content drops below 0.03%, then carbides are not formed in the steel at all and the steel is completely austenitic at room temperature (Figure 4).
Figure 4 – Austenitic stainless steel
Austenitic stainless steels have high ductility, pressure machinability, and corrosion resistance.
Heat treatment of austenitic stainless steels involves quenching in water from a temperature of 1050-1100 °C. Such heating causes the dissolution of chromium carbides, and rapid cooling fixes the state of a saturated solid solution. It is very important to note that as a result of hardening, the hardness of these steels does not increase, but decreases. Therefore, for austenitic stainless steels, hardening is a softening thermal operation.
Austenitic stainless steel gains its strength through cold hardening. Austenitic steels can be strain hardened to significantly higher values than ferritic stainless steels. At deformations of the order of 80-90%, the yield strength reaches 980-1170 MPa, and the tensile strength reaches 1170-1370 MPa. It is clear that such hardening can only be achieved in the manufacture of such types of products as thin sheets, tape, and wire.
Austenitic stainless steels are non-magnetic, which gives them an advantage in many applications.
Representatives of austenitic stainless steels are steels 12Х18Н9 and 17Х18Н9, 12Х18Н10Т and 12Х18Н9Т, 08Х18Н10Т, 08Х18Н12Б, 03Х18Н11 according to GOST 5632-72.
Precipitation hardening stainless steels
These steels are also called high-strength stainless steels.
Precipitation hardening stainless steels contain aluminum, niobium or tantalum and obtain their properties through quenching, strain hardening, age hardening and martensitic transformation.
The steel is first heated and hardened to transform austenite into martensite. Reheating causes the precipitation of strengthening particles such as NiAl3 from the martensite. The high strength of these steels is achieved even with low carbon content.
Dispersion-hardening steels include steels 07Х16Н6, 09Х15Н8У, 08Х17Н5М3, 04Х25Н5М2, ХН40МДТУ according to GOST 5632-72.
Dual phase stainless steels
In some cases, a mixture of different phases is deliberately obtained in the structure of stainless steels. With appropriate control of the chemical composition and heat treatment conditions, steel is obtained containing, for example, 50% ferrite and 50% austenite.
This combination of phases in the structure of the steel gives it a unique combination of mechanical properties, corrosion resistance, workability and weldability that cannot be achieved in any other stainless steels.
Sometimes they are called in foreign languages - duplex steels.
Two-phase stainless steels include steels 08Х22Н6Т, 03Х23Н6, 08Х21Н6М2Т, 03Х22Н6М2, 08Х18Г8Н2Т, 03Х24Н6М3 according to GOST 5632-72.
Source: https://steel-guide.ru/klassifikaciya/nerzhaveyushhie-stali/nerzhaveyushhie-stali-ferrit-martensit-austenit.html
Stainless steel - grades, types and characteristics
Stainless (corrosion-resistant) steels are alloys based on iron and carbon, containing, in addition to the main components and standard impurities, alloying elements.
The main additive is chromium (Cr), which in a corrosion-resistant alloy must be at least 10.5%. At this level, Cr has a significant effect on the iron-carbon phase diagram.
Chromium and nickel, also in most cases present in stainless steels, increase not only the metal’s resistance to corrosion, but also other technical characteristics.
Rules for marking corrosion-resistant steels
The designation consists of numbers and letters. The two-digit number at the beginning of the marking is the amount of carbon in hundredths of a percent. The following are letters characterizing certain alloying elements.
After them are placed numbers equal to the percentage of alloying elements, rounded to the nearest whole number. If the percentage of the additive is in the range of 1-1.5, then the number is not placed after the letter.
To symbolize alloying components in Russian regulatory documentation, the Russian alphabet is used:
- X – chromium;
- N – nickel;
- T – titanium;
- B – tungsten;
- G – manganese;
- D – copper;
- M – molybdenum.
Groups of corrosion-resistant steels by structure
The structure of corrosion-resistant steels, their properties and areas of application are determined by the percentage of carbon, the list and amount of alloying additives. Based on its structure, stainless steel is divided into several types. Main: ferritic, martensitic, austenitic. There are intermediate options.
Ferritic
This group refers to low-carbon alloys - C up to 0.15%. chromium – up to 30%. The bulk crystalline structure provides a combination of fairly high strength and ductility. Stainless steels of ferritic grades are classified as ferromagnetic.
Main characteristics:
- ability to cold deformation;
- the main type of heat treatment is annealing, which removes hardening;
- good corrosion resistance;
- relatively low cost.
The main reason for the loss of performance characteristics of ferritic steels is intergranular corrosion (ICC), as a result of which destruction occurs along grain boundaries. To eliminate this negative phenomenon, sharp cooling of the metal from +800°C is avoided, stabilizing annealing is carried out, and an optimal balance is found between the carbon and chromium content. The introduction of carbide-forming elements—titanium and niobium—can completely eliminate the tendency to MCC.
According to the AISI standard, ferritic steels belong to the 400 series:
- 403-420 – chromium content 11-14%, no nickel;
- 430 and 440 – 15-18% C, no nickel;
- 630 – contains 3-5% nickel. It is well processed, resistant to corrosion in various environments, similar in properties to 08Х18Н10.
These materials are used in the production of a wide range of pipes, sheets, and profiles.
Table of grades of ferritic stainless steel according to GOST and AISI, main areas of use
| Brand according to GOST 5632 | AISI brand | Areas of use |
| 08Х13 | 409 | Cutlery |
| 12Х13 | 410 | Containers for liquid alcohol-containing products |
| 12Х17 | 430 | Containers for high-temperature processing of food products |
Martensitic
This group includes metals with a chromium content of up to 17%, carbon - up to 0.5% (in some cases - higher). Martensite is a structure obtained by hardening a workpiece and then tempering it. It is characterized by a combination of high hardness, strength, elasticity and corrosion resistance.
Alloys are used in the production of critical metal products intended for use in aggressive environments. These are springs, shafts, knives, flanges. As the C content increases, a carbide phase appears in the structure, providing high hardness and wear resistance.
Carrying out low tempering after hardening (+200+300°C) provides high hardness - 50-52 HRC, high tempering (+500+600°C) - lower hardness (28-30HRC) and higher viscosity. Hardening is carried out at temperatures +950+1050°C.
Table of martensitic steel grades according to GOST and AISI, their main areas of application
| Brand according to GOST 5632 | AISI brand | Areas of use |
| 20Х13 | 420 | Kitchen equipment |
| 30Х13 | ||
| 40Х13 | ||
| 14Х17Н2 (martensitic-ferritic) | 431 | Compressor unit parts, equipment operated in aggressive environments and at low temperatures |
Austenitic class
This broad class of corrosion-resistant steels (according to AISI - class 300 and a representative of class 200 - AISI 201) has high corrosion resistance, ductility in cold and hot states, strength, good weldability, and the ability to contact without destruction with nitric acid.
Non-magneticity significantly expands the range of applications of the material. A combination of 18% Cr and 8% Ni is economically advantageous. If it is necessary to obtain a stable state of austenite, the amount of nickel is increased to 9%. Such steels can be unstabilized and stabilized.
The stabilized group is alloyed with titanium and niobium, which reduce the susceptibility of austenitic grades to intergranular corrosion.
Hardening is carried out at temperatures of +1050+1100°C with rapid cooling, which fixes the state of the saturated solid solution. The peculiarity of this group is the absence of hardening during hardening. In this case, this type of maintenance is a mitigating operation aimed at relieving the effects of hardening. Annealing can be used for the same purpose. Small parts are subjected to hardening, massive ones are annealed.
Table of austenitic steel grades according to GOST and AISI, their main areas of application
| Brand according to GOST 5632 | AISI brand | Areas of use |
| 12Х18Н10Т | 321 | Technological lines of the chemical industry and oil refining enterprises |
| 08Х18Н10 | 304 | Technological piping systems in the chemical and food industries, limited range of cookware, not including products for hot food processing |
| 08Х17Н13М2 | 316 | Technological equipment for the chemical industry, use as a “food” material |
| 12X15G9ND | 201 | Tanks and pipelines in contact with organic acids and moderately aggressive media |
Brief characteristics of some types of austenitic stainless steels:
- 304 is a common representative of this class. It lends itself perfectly to deep drawing, so it is used for the manufacture of three-dimensional products. Susceptible to crevice corrosion in warm environments with high chlorine content, therefore not recommended for use in seawater or in industries that use chlorine cleaning compounds.
- 321 and 347 are improved versions of grade 304, differing in the addition of niobium or titanium.
- 316 – exhibits maximum corrosion resistance among commonly used corrosion-resistant steels.
- 201 is a relatively inexpensive analogue of steels 304 and 321. It shows good performance in medium-aggressive environments, thanks to its balanced chemical composition and new manufacturing technologies.
Source: https://TreydMetall.ru/info/nerzhaveyushchaya-stal-marki-vidy-i-harakteristiki
Ferritic steels
Ferritic steels owe their name to ferrite. This is the name of the phase component of iron alloys. Upon closer examination, this turns out to be a solid solution of alloying elements and carbon located in α-iron. One of its features is the presence of a cubic body-centered lattice. Ferrite often acts as a component of other structures.
Modern ferritic stainless steels stand out for their resistance to corrosion. They perform best when used in environments that do not contain chlorine ions. When used in such environments, they remain of high quality and are in many ways not inferior to their chromium-nickel counterparts. There are a number of environments in which this type of steel is superior to the described analogues and shows better resistance, including corrosion cracking.
This type of product lends itself well to additional alloying. This helps improve the characteristics of the composition and expand the boundaries of its use.
The table below shows the chemical properties of steels of this type depending on the use of various alloying elements:
Table 1. Chromium ferritic steels: chemical composition.
| steel grade | C | Si | Mn | Cr | Mo | S | P | other elements |
| 08X13 | ≤0,08 | ≤0,8 | ≤0,8 | 12,0..14,0 | — | ≤0,025 | ≤0,030 | ≥6(C+N) Ti |
| 08Х17Т | 16,018,0 | ≤0,035 | 0.500.80 Ti | |||||
| 08Х23С2У | 1,5 1,8 | 0,40,7 | 22,024,0 | ≤0,015 | ≤0,030 | Not regulated | ||
| 04Х14Т3Р1Ф (ChS-82) | 0,020,06 | ≤0,6 | ≤0,5 | 13,016,00 | 0,020 | 0,025 | 2.3 3.5 Ti, 1.1 1.8 V | |
| EP 882-VI | ≤0,015 | ≤0,5 | 16,518,5 | 1,52,0 | ≤0,020 | ≤0,025 | 0.150.35 Nb | |
| EP 904-VI | ≤0,012 | ≤0,3 | 18 | — | 0.1 0.4 Nb, 2.2 3.5 A1 | |||
| 15Х25Т | ≤0,08 | ≤0,8 | ≤0,8 | 29,027,0 | ≤0,025 | ≤0,035 | 0.5 0.9 Ti |
Central properties and features of the use of the material
When using this type of product, you will need to take into account a number of significant features that impose restrictions or expand the possibilities of application. Among these features are:
- High resistance to corrosion. As already noted, this resistance is especially evident under conditions when chlorine ions are not present in the medium. Another indicator is the ability to maintain stable performance characteristics when exposed to nitric acid. This type of material resists pitting corrosion well, as well as cracking and high stress corrosion damage. Experts call the optimal corrosion resistance of steel after slow cooling and after annealing at elevated temperatures.
- Steel can withstand fairly high heat because it is hardened at elevated temperatures.
- When processed, it forms quite vulnerable welds. Therefore, cooking will need to be approached with caution (this will be discussed further below).
- The material is highly durable and withstands mechanical stress well.
Central applications
The possibilities described above explained the wide range of applications of ferritic steels. Depending on the specific grade of steel, it can be used to create parts for high-temperature equipment and internal elements of chemical apparatus. An equally significant area of use is the creation of pyrolysis coils, as well as various types of containers and containers.
Usage is determined by analyzing the technical characteristics of a particular brand. To give the reader a better understanding of these mechanical properties, we have collected them in a separate table below:
Table 2. Chromium ferritic steels: mechanical properties, no less.
| steel grade | σв, MPa | σ0.2,MPa | δ5, % | ψ,% | KCU, J/cm2 | Examples of using |
| 08Х13 | 590 | 410 | 20 | 60 | 10 | Internal devices of chemical apparatus |
| 08Х17Т | 372 | — | 17 | — | — | |
| 08Х23С2У | 490 | 10 | 60 | Pyrolysis coils | ||
| 04Х14Т3Р1Ф | 500 | 320 | 15 | 20 | 10 | Nuclear fuel racks, containers |
| EP 882-VI | 372 | 245 | 22 | — | 60 | Substitute for Cr-Ni austenitic steels |
| EP 904-VI | 440 | 323 | 24 | High temperature equipment parts | ||
| 15Х25Т | — | 14 | 20 | Internal devices of chemical apparatus |
Welding Features
There is a lot of conflicting information about whether it is possible to weld ferritic steels, what the end result is, and what characteristics the resulting seams have.
The weldability of these types of steel directly depends on their composition. By limiting the composition of C and N, it is possible to achieve good weldability. Also, the parameters differ in many ways depending on the level of carbon content.
For example, if carbon and nitrogen are ~0.020%, the material acquires good ductility and high impact resistance, and does not become brittle when welded.
The fragility index of welded joints of chromium ferritic steels is related to the content of interstitial impurities in the solid solution.
It is also worth paying attention to the fact that with the right choice of material, welded joints of chromium ferritic steels will be resistant to corrosion. This is also true when used in aggressive environments. One of the possibilities for improving the quality of the weld is alloying using titanium or niobium. This further increases resistance to intercrystalline corrosion. Moreover, this resistance remains unchanged even after heat treatment.
The table below contains basic recommendations for the thermal conditions for welding this type of steel. Compliance with them ensures that the material will remain durable and receive a high level of resistance to various types of external influences.
Table 3. Recommendations for thermal conditions for welding chromium ferritic steels.
| steel grade | Heating temperature, оС | Storage duration before heat treatment, h | Heat treatment |
| 08Х13 | 150250 | Not limited | Holiday at 680700oC |
| 08Х13 (bimetal cladding layer) | without heating | Not regulated | |
| 08Х17Т, 15Х25Т | 150200 | ||
| 08Х17Т, 15Х25Т (bimetal cladding layer) | without heating | ||
| 08Х23С2У | 200 250 | Not allowed | Annealing at 900°C |
| EP 882-VI, EP 904-VI | without heating | Not regulated |
In addition, when working with ferritic steels, specialists are required to use the correct equipment and the correct welding method. It is possible to weld using manual arc, electron beam and laser methods. The question of choice depends on what grade of steel you are currently using.
Details of the choice of a specific type of impact depending on the steel grade are given in the table below:
Table 4. Welding methods, welding materials and mechanical properties of welded joints of chromium ferritic steels.
| steel grade | Welding method, welding materials | Mechanical properties of welded joints | |
| σв, MPa | KCU, J/cm2 | ||
| 08Х13 | Manual arc welding: - electrodes E-10H25N13G2 OZL-6, TsL-25, E-10H25N13G2B TsL-9, E-08H20N15FB ANV-9, E-10H20N15B ANV-10 | 540 | 5 |
| — electrodes E-2X13 UONI-13NZH, ANV-1, TsL-51 | 590 | ||
| ADS: wire Sv-07Х25Н12Г2Т, Sv-06Х25Н12ТУ, Sv-06Х25Н12БТУ, flux AN-26s, ANF-14, OF-6, AN-18 | 540 | ||
| ArDS: wire CB-06X25N12T, Sv-06X25N12BTYu, Sv-07X25N12G2T, argon | |||
| 08Х17Т | RDS: electrodes E-10X25N13G2B TsL-9, UONI-10X17T. ADS: wire Sv-10XI7T, fluxes ANF-6, OF-6 | 440 | |
| 08Х23С2У | RDS: electrodes TsT-33, TsT-38 | 500 | |
| 04Х14Т3Р1Ф | Electron beam and laser welding | ||
| EP 882-VI | RDS: electrodes E-10Х25Нl3G2 TsL-25, TsT-45, EA-400/10T.ArDS: wire Sv-02ХI8М2Б-VI, argon | 372 | |
| EP 904-VI | RDS:electrodes TsT-52 | 390 | — |
| ArDS: wire Sv-02Х19У3Б-VI, argon | 372 | 5 | |
| 15Х25Т | RDS: electrodes 3iO-7, EA-48M/22, ANV-9, AN9-10. ArDS: wire Sv-07Kh25N 13, argonADS: wire Sv-07Kh25N13, fluxes AN-26s, ANF-14, OF-6, AN -16 | 440 | 5 |
Correct use of welding, as well as accurate calculation of the area of application depending on the grade, can ensure long-term use of ferritic steels.
Today, this variety has become widespread in industry and is often found in various areas of materials production. When using the material and working with it, we recommend focusing on the tables given in the text. They will help you avoid common mistakes, change the properties of steel and maintain high quality of the final product when welding, heating or cooling.
Source: http://profnastil-perm.ru/ferritnye-stali/
Classification of stainless steels - austenitic, ferritic, duplex, martensitic
Austenitic stainless steel contains a significant amount of chromium and a sufficient amount of nickel and manganese to form an “austenitic” microstructure, which give these grades of steel good formability, ductility and corrosion resistance (and also make the steel non-magnetic).
The typical composition of austenitic steel contains 18% chromium and 8% nickel, which corresponds to the popular "zero" ("0") grade as defined by the American Iron and Steel Institute (AISI). This brand is known in Russia as AISI 304, DIN 1.4301 and corresponds to the Russian analogue 08Х18Н9.
Austenitic steel grades are distinguished by high strength, have corrosion resistance in a wide range of aggressive environments and are characterized by good processability and weldability.
Ferritic stainless steel
Ferritic grades of stainless steel are similar in properties to low-carbon steel, but have higher corrosion resistance. The most common grades of ferritic steel contain an average of 11% and 17% chromium. The former are usually used in the production of automobile exhaust systems, and the latter in the production of kitchen appliances, washing machines, and architectural interior decoration.
AUSTENITIC-FERRITIC Stainless Steel (DUPLEX)
Austenitic-ferritic steels are characterized by a high chromium content (18-22%) and a low (economical) nickel content (4-6%, in some cases up to 2%). Additional alloying elements - molybdenum, copper, titanium, niobium. The chemical composition of these steels is such that the ratio of austenite to ferrite after optimal heat treatment is approximately 1:1.
This class of steels has a number of advantages compared to austenitic steels: higher (1.5-2 times) strength with satisfactory ductility and resistance to impact loads, greater resistance to intergranular corrosion and stress-corrosion cracking.
They are mainly used in the manufacturing industry, construction and in products in contact with seawater.
Martensitic stainless steel
Martensitic, like ferritic grades, contain on average from 12% to 17% chromium, but have a higher carbon content. These steels are used primarily in a heat-treated state, often with a carefully ground and sometimes polished surface. They are used in the production of turbine blades, cutlery and razor blades.
Table of mutual conformity of austenitic stainless steels specified according to JIS, W.-nr., DIN, BS, EN, AFNOR, UNI, UNE, SS, AISI/SAE (ANSI/ASTM), GB standards. Correspondence table for stainless ferritic and martensitic steels specified according to JIS standards, W.-nr.
, DIN, BS, EN, AFNOR, UNI, UNE, SS, AISI/SAE (ANSI/ASTM), GB. Table of mutual conformity of alloy steels specified according to the standards JIS, W.-nr., DIN, BS, EN, AFNOR, UNI, UNE, SS, AISI/SAE (ANSI/ASTM), GB.
Table of mutual correspondence of heat-resistant steels specified according to JIS standards, W.-nr.
, DIN, BS, EN, AFNOR, UNI, UNE, SS, AISI/SAE (ANSI/ASTM), GB.
Source: https://dpva.ru/guide/guidematherials/metalls/steelsandsteelalloys/stainlesssteels/ssclassification/
Stainless chromium (ferritic and martensitic) steels
Stainless (corrosion-resistant) and heat-resistant steels and alloys based on iron and nickel are the most important category of special structural materials, which are used in many industries. Increased resistance to uniform corrosion in a wide range of corrosive environments of varying degrees of aggressiveness is a distinctive feature of stainless and heat-resistant steels and alloys.
https://www.youtube.com/watch?v=Wj3yX7R9dE4
Many stainless steels are also resistant to special types of corrosion such as intergranular corrosion, pitting corrosion, crevice corrosion and corrosion cracking.
The main alloying element that gives steel corrosion resistance in oxidizing environments is Cr - chromium. Chromium promotes the formation of a protective dense passive film of Cr2O3 oxide on the surface of stainless steel. A film thickness sufficient to impart corrosion resistance to stainless steel is formed by adding at least 12.5% chromium to the alloy. Chromium and iron form a solid solution in the alloy.
The cost of chromium is relatively low; it is not a scarce component. Therefore, chromium stainless steels are relatively inexpensive and, having a fairly good set of technological properties, are widely used in industry. Elements of equipment operating at high pressure and temperature under conditions of exposure to aggressive environments are made from chromium stainless steels.
Chromium, which is alloyed with stainless steels, provides not only the corrosion resistance of steels in oxidizing environments, but also forms their structure, mechanical and technological properties and heat resistance. The continuous series of solid solutions formed by chromium and iron at concentrations starting from 12.5% and higher contributes to the formation of different structures in chromium stainless steels, providing a variety of their properties.
Carbon in chromium stainless steels
In addition to chromium, the carbon content has a significant influence on the formation of the physical and mechanical properties of chromium steels. The structure of stainless steel, depending on the carbon content, is divided into three main classes: martensitic, martensitic-ferritic and ferritic. This is reflected in the classification of stainless steels according to the previously valid GOST 5632-72 “High-alloy steels and corrosion-resistant, heat-resistant and heat-resistant alloys.”
The carbon contained in stainless steel, including chromium steel, is an undesirable element. Carbon is too active a component, binding chromium into carbides, it depletes the solid solution, thereby reducing the corrosion resistance of stainless steel. In addition, the increased carbon content requires an increase in the quenching temperature to 975-1050 ° C, for a more complete dissolution of chromium carbides.
As an example of the serious influence of carbon on the structure and properties of stainless steel, consider steel containing 18% Cr. For example, steel 95X18, which contains 0.9-1.0% C and has a martensite structure, has high hardness (>55HRC), but its corrosion resistance is moderate. And stainless steels 12Х17, 08Х17Т, 08Х18Т1, with a ferrite structure, have, on the contrary, low hardness and high corrosion properties.
Martensitic-ferritic stainless steels
This class includes steels with partial γ→α transformation. The thermokinetic diagram of these steels consists of two transformation regions. At temperatures >600°C at low cooling rates, the formation of a ferrite component of the structure is possible. At high cooling rates
Source: http://www.mpoltd.ru/poleznoe/206-nerzhaveyushchie-khromistye-ferritnye-i-martensitnye-stali.html
High alloy creep resistant steels and heat resistant steels
Chromium is the main alloying element for producing corrosion-resistant, heat-resistant and heat-resistant steels. When its content is more than 12.6%, the electrochemical potential sharply increases and the steel becomes corrosion-resistant (stainless).
Chromium promotes the formation of a dense oxide film on the metal surface, protecting the metal from oxidation at high temperatures, and gives the steel heat resistance (scale resistance). The higher the chromium content in steel, the higher the heat resistance. Therefore, in heat-resistant ferritic steels its content is increased to 13 - 27%.
Steel 08Х13 is used under conditions of exposure to sulfur dioxide at temperatures up to 500°C, steel 08Х17Т, 12Х17 are heat-resistant up to 900°С, steel 15Х25Т - up to 1100°С. Heat resistance is also increased by aluminum and silicon (steel 15Х18СУ).
Chrome has a body-centered cube lattice isomorphic to α-iron. In this regard, it is the main stabilizer of the ferrite structure. When heated and cooled, ferritic steels do not undergo phase transformations and when cooled in air they retain their ferritic structure.
To obtain heat-resistant properties, chromium steels are alloyed with carbide-forming elements tungsten, molybdenum, vanadium and niobium with a slight reduction in chromium content to 11 - 12% (martensitic-ferritic steels 14Х12В2МФ, 18Х11МНФБ).
These elements increase the dispersion of the carbide phase and its resistance to coagulation and thereby increase the effect of hardening and maintaining strength when heated. In addition, in the presence of these elements in steel, an intermetallic phase Fe2(W,Mo) is formed in a highly dispersed form.
Ferritic steels are used in the manufacture of household appliances, chemical equipment, parts of gas turbines and boiler plants.
Austenitic steels
In austenitic steels, along with chromium, the main alloying element is nickel. Nickel has a close-packed face-centered crystal lattice, isomorphic to γ-iron. Therefore, nickel, as well as manganese, carbon and nitrogen, are austenizers.
Alloying steels with nickel in an amount of more than 8% stabilizes the austenitic structure. Austenitic steels have high heat resistance up to 1150°C, which, like ferritic steels, depends on the alloying level of Cr, Si and Al (10X23h28, 08Х20Н14С2, 20Х25Н20С2).
High heat resistance in austenitic steels is achieved due to:
1) using austenite instead of ferrite as a base; 2) strengthening of the Fe-Cr-Ni austenite solid solution with Mo and W elements; 3) dispersion strengthening of the grain body with finely dispersed carbides, intermetallic compounds such as Ni3(Ti, Al); 4) strengthening of grain boundaries by microalloying with surface active elements (boron, rare earth metals Ce, Nd, La, etc.);
5) limiting the content of fusible impurities of lead, tin, antimony, sulfur, phosphorus, etc., neutralizing their harmful effects.
Ferritic steels
Main problems:
1) grain growth in the HAZ and embrittlement; subsequent heat treatment does not refine the grain and does not eliminate brittleness; 2) development of intergranular corrosion (ICC) during rapid cooling from a temperature of T 900°C; MCC can be eliminated by tempering at T = 650 – 900°C or by bonding carbon into niobium or titanium carbides;
3) embrittlement in the HAZ at elevated temperatures is caused by the formation of the σ-phase (Fe-Cr intermetallic compound) in the temperature range T = 650 - 850°C and the development of 475°C brittleness in the range T = 450 - 525°C.
These phenomena intensify with increasing chromium content in steel; 475°С - brittleness is eliminated by hardening from T = 700 - 800°C, and brittleness from the σ - phase is eliminated by annealing at T > 900°C.
Welding methods and welding materials
The presence of active alloying elements Cr, Ti, AI in steels determines the use of welding methods and welding materials that limit the loss of alloying elements: electrodes with a basic or fluoride type of coating, inert Ar and He or weakly oxidizing mixtures of inert and active gases Ar + 1 - 3% O2 and Ar + 2 - 4% CO2, passive fluoride and basic fluoride, low-active and active low-silicon fluxes, depending on alloying.
Chromium ferritic steel, austenitic ferritic steel, martensitic ferritic steel
"Ferrite" comes from the Latin ferrum - iron. It is an alloy that consists of carbon and an alloying element that has a body-centered cubic crystal lattice and is part of various structures.
Ferritic steel consists of alloyed ferrite and carbide. This is a low-carbon steel with a high content of alloyed elements (vanadium, molybdenum, silicon and others). Depending on the ratio of the latter to iron and carbon, alloyed ferrite, austenite and cementite are formed.
The ferritic structure of steel is obtained thanks to the following ferrite-forming elements: Cr, Zr, Si, Nb, Al, W, Ti. Chromium (Cr) creates a protective layer on the surface, which is why ferritic steels are called chromium steels. They belong to stainless steels. Steel classification.
Types of ferritic steels
There are several types of ferritic steels:
- Austenitic-ferritic;
- Martensitic-ferritic.
Austenitic-ferritic - duplex high-alloy steels, which consist of two phases: austenite and ferrite. These are substitutes for chromium-nickel steels of the austenitic class. They have a great advantage - high corrosion resistance even in the most aggressive environments, since they contain at least 20% chromium.
They also have high strength, resistance to crack corrosion, pitting, and stress-corrosion cracking. Abroad, austenitic-ferritic steels are used as a material from which structures for heat exchange equipment are made, which is almost impossible to make from chromium-nickel steel.
Martensitic-ferritic steels are produced by two-phase thermokinetic transformation. Depending on the cooling rate and temperature, on the one hand, a ferrite component is created, on the other, austenite transforms into martensite. These steels contain approximately 14% chromium and have ideal corrosion resistance. They are used in petrochemical and other industries.
industries. In particular, energy and petrochemical equipment and various equipment are made from martensitic-ferritic steel.
Disadvantages and advantages of ferritic steels
The cost of producing chromium ferritic steel can vary from low to high, depending on the ferrite-forming elements used and their quantity in the ferritic structure.
Inexpensive steels have their disadvantages:
- fragility of welded joints;
- predisposition to grain growth;
- tendency to intergranular corrosion;
- it has magnetic properties (this is a disadvantage of steels that belong to the ferritic class)
But, due to low manufacturing costs, this steel is well suited for the production of light-duty metal products, accessories, and consumer goods.
These disadvantages are eliminated through the use of more expensive alloying elements and other methods. For example, alloying a weld with titanium or niobium makes the joint resistant to intergranular corrosion.
Chrome ferritic steel can be used in various aggressive environments, as it is highly resistant to corrosion. Multifunctionality and a wide range of applications give this metal many advantages. It does not contain nickel, which guarantees price stability. In accordance with the goals, objectives, and purpose, the manufacturer himself determines which grade of ferritic steel to use.
Source: https://vikant.com.ua/news/ferritnie_stali
Welding of austenitic-ferritic stainless steels
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The most common steels of the austenitic-ferritic class include steel types 08Х22Н6Т, 12Х21Н5Т, 03Х23Н6, 08Х18Г8Н2Т, 08Х21Н6М2Т, 03Х22Н6М2. The microstructure of chromium-nickel steel 08Х22Н6Т and chromium-nickel-molybdenum steel 08Х21Н6М2Т is shown in Fig. 18.1. The amount of austenant and ferritic phases in steels of this class usually ranges from 40-60%. The chemical composition of austenant-ferritic steels is given in Table 18.1, mechanical properties - in Table. 18.2.
Austenitic-ferritic steels have relatively high yield and strength limits and satisfactory ductility and impact toughness, as well as high corrosion resistance and good weldability. This makes it possible to reduce the specific metal consumption in the manufacture of chemical equipment designed for strength, due to a decrease in sheet thickness. According to the state diagram Fe-Cr-Ni alloys have some characteristic features; the region of existence of a two-phase austenitic-ferritic structure in them is in the temperature range 20-1350 ° C; when steel is heated above a temperature of 1100 ° C, austenite transforms into ferrite and the more intensely, the higher the temperature and duration of heating , at temperatures above 1200 °C, a complete γ→α transformation occurs; upon subsequent cooling, the reverse transformation of ferrite into austenite occurs. The final ratio of the number of structural components depends on the cooling rate of the steel. During isothermal exposure in the temperature range of 700–800 °C, the formation of a brittle component of the σ phase is possible in steel. Austenitic-ferritic steels are supplied in a hardened state at temperatures of 950–1050 °C. The difference in Cr and Ni content between the austenite and ferrite phases is 2–5%. Austenitic-ferritic steels lose toughness when heated in the temperature range 450-650 ° C. This is due to the fact that the brittleness caused by the precipitation of carbides is enhanced by the action of the so-called 475 ° brittleness.
The approximate purpose and operating temperature of austenitic-ferritic steels are shown in Table 18.3.
Weldability of steels
Austenitic-ferritic steels are characterized by an increased tendency to grain growth in the heat-affected zone when exposed to the welding thermal cycle. Along with the growth of ferrite grains, the total amount of ferrite increases. Subsequent rapid cooling fixes the resulting structure.
The grain size and amount of ferrite, as well as the width of the overheating zone, depend on the heat input of welding, the ratio of structural components in the initial state and the sensitivity of the steel to overheating. The ratio of the number of structural components (γ- and α-phases) in the initial state largely depends on the Ti content in the steel.
The amount of titanium in the steel also determines the stability of the austenite phase against the γ→δ transformation during welding heating. The higher the Ti content, the more sensitive the steel is to overheating (Fig. 18.2).
Due to grain growth and a decrease in the amount of austenite, a decrease in the impact toughness of the metal in the heat-affected zone and the bending angle of welded joints of austenitic-ferritic steels are observed. Steels that do not contain Ti are less sensitive to welding heating—these are steels 03Х23Н6 and 03Х22Н6М2.
Welding technology and joint properties
Austenitic-ferritic steels can be welded using both manual and mechanized electric arc welding, as well as other welding methods (electron beam, electroslag), plasma arc, etc.). Welding methods with low heat input are preferable. The welding technique and modes of austenitic-ferritic steels do not differ from those generally accepted for the entire class of stainless steels.
When choosing types of seams for welded joints, it is recommended to be guided by GOST 5264-69, GOST 8713-70, GOST 14771-69, OST 26-291-71 and enterprise standards. Preparation of edges for all types of welding is carried out mechanically in order to eliminate the occurrence of heat-affected zones (HAZs), which reduce the regulated properties of welded joints.
Welding materials used for welding austenitic-ferritic steels are given in table. 18.4 and 18.5. The joint seams made with the specified welding materials have an austenitic-ferritic structure. The amount of ferrite phase in welds is 15–60% and depends not only on the welding materials used, but also on the share of the metal being welded in the weld metal, and on fluctuations in the chemical composition within the grade.
The highest percentage of ferrite phase in the seams is observed during automatic submerged arc butt welding without cutting edges using Sv-06Kh21N7BT wire. Due to the high ferrite content, the seams are sufficiently resistant to the formation of hot cracks. Changing the content of the ferrite phase in the weld due to alloying or heat treatment leads to a significant change in its mechanical properties.
The yield and strength limits with sufficiently high ductility and toughness of the weld reach a maximum when the percentage of austenite and ferrite phases in it is equal.
Mechanical properties of welded joints
Mechanical properties of seams and joints made with welding materials specified in table. 18.4 and 18.5 are given in table. 18.6. Analysis of the mechanical properties shows that the highest strength of welds during automatic submerged arc welding of chromium-nickel austenitic-ferritic steels can be obtained by using Sv-06Kh21N7BT (EP500) wire, and for chromium-nickel-molybdenum steels - using Sv-06Kh20N11MZTB (EP89) wire.
The combination of sufficiently high strength and ductility is achieved when using Sv-03Kh21N10AG5 (EK-91) wire for automatic submerged arc welding of chromium-nickel austenitic-ferritic steels, and Sv-03Kh19N15G6M2AV2 (ChS-39) wire for chromium-nickel-molybdenum steels. It is preferable to use these wires when welding steel of significant thickness (>10 mm) end-to-end, without cutting edges.
To improve the ductility of welded joints of austenitic-ferritic steels, if the dimensions of the products allow, heat treatment can be carried out - hardening from 1000 °C with cooling in water.
Corrosion resistance of welded joints
When welding products whose welds are required to be resistant to intergranular corrosion, the weld layer facing the aggressive environment must be made last. Due to the fact that austenitic-ferritic steels are susceptible to embrittlement in the temperature range of 450–500 and 650–800 °C, when welding them, special attention must be paid to strict adherence to the welding and cooling conditions of the products.
When welding metal products with a thickness of 16–20 mm, it is recommended to use the processing of the boundaries of seams with the base metal by argon arc welding. The resulting local heating with low heat input (q=4200 J/cm2) of a section of a large HAZ grain until melting leads, upon cooling, to the formation of a fine-grained ferritic structure with austenitic layers along the grain boundaries.
A metal with such a structure is more ductile than coarse-grained ferrite formed during HAZ welding and is more corrosion resistant.
With a ratio of austenite and ferrite phases close to unity, the welds are resistant to both intergranular and structural selective corrosion.
This dependence of corrosion resistance on the ratio of structural components is explained by the fact that at 40-60% of the α-phase, the grain sizes of ferrite and austenite are approximately the same, and the chemical heterogeneity in Cr and Ni between the phases is minimal (Fig. 18.3).
When the amount of austenite phase in a weld or heat-affected zone decreases to 20% or less, the metal exhibits a tendency to intergranular corrosion. Tempering of welded joints at 850 °C prevents intergranular corrosion of welded joints.
Structurally, selective corrosion can be explained by the difference in the electrode potentials of austenite and ferrite in a two-phase metal, as well as by the difference in the surfaces of structural components in places of contact with an aggressive environment.
Electrode potentials between structural components in an aggressive environment may differ with different contents of alloying elements in them, which determine the corrosion resistance of the metal in this environment.
In oxidizing environments (nitric acid), the passivating ability and, consequently, the corrosion resistance of the austenitic and ferritic phases of the metal depend mainly on the Cr content, and in non-oxidizing environments (sulfuric acid solutions) on the Ni and Mo content. The austenite phase is always responsible for the deterioration of the corrosion resistance of an austenitic-ferritic metal.
In addition, in joints of austenitic-ferritic steels there are always areas that differ in their electrode potential. This is the weld, the HAZ, the base metal. Such a connection in the electrolyte is a multielectrode system with several cathodes and anodes. The part of the system that will have the most negative electrode potential in a given electrolyte, i.e., will be the cathode, will undergo preferential dissolution in the electrolyte.
The negative influence of silicon and vanadium in the weld on the corrosion resistance in oxidizing environments of welded joints made of austenitic-ferritic steels has been established.
Thus, when choosing a filler material, it is necessary to strive to ensure equality not only of the mechanical properties of the weld and the base metal and the resistance of the weld against intergranular corrosion, but also equality of the overall corrosion resistance of the metal of all zones of the welded joint.
It is necessary to take into account the influence of carbide-forming elements (Ti and Nb) on the properties of welds in joints of austenitic-ferritic steels, since stabilizers (carbide-forming elements) are necessary to ensure resistance to intergranular corrosion with a carbon content of >0.07%.
Steel 08Х22Н6Т is resistant to nitric acid: 65% concentration up to a temperature of 50 °C, 56% up to a temperature of 70 °C, 30% up to the boiling point. Steel 08Х21Н6М2Т is resistant in formic acid, regardless of concentration, at temperatures up to 60 ° C, in 30% boiling acid and in 85% phosphoric acid at T≤80 ° C, in 10% sulfuric acid.
Volchenko V.N. "Welding and weldable materials."
Source: https://www.autowelding.ru/publ/1/1/svarka_austenitno_ferritnykh_nerzhavejushhikh_stalej/2-1-0-294
Difference Between Austenitic and Martensitic Stainless Steel
The key difference between austenitic and martensitic stainless steel is that the crystal structure of austenitic stainless steel is a face-centered cubic structure, whereas the crystal structure of martensitic stainless steel is a body-centered cubic structure.
There are four main groups of stainless steel depending on the crystalline structure of the steel: austenitic, ferritic, martensitic and two-phase. The microstructure of these alloys depends on the alloying elements present in them. Thus, these alloys also have different alloying elements.
- Overview and main differences
- What is Austenitic Stainless Steel
- What is Martensitic Stainless Steel
- What is the difference between austenitic and martensitic stainless steel
- Conclusion
What is Austenitic Stainless Steel?
Austenitic stainless steel is a form of stainless steel alloy that has exceptional corrosion resistance and impressive mechanical properties. The primary crystal structure of this alloy is a face-centered cubic structure containing "austenite" (a metallic and non-magnetic allotrope of iron or a solid solution of iron with an alloying element).
Structure of austenitic stainless steel
In addition, this material has better strength, toughness, formability and ductility. Austenitic stainless steel is used in cryogenic (low) and high temperature applications.
This steel has a face-centered cubic structure in which there is one atom at each corner of the cube, and there is one atom at each face (at the center of the face). The austenitic structure is formed when enough nickel is mixed with iron and chromium.
Typically this material contains about 15% chromium and 8 to 10% nickel.
What is martensitic stainless steel?
Martensitic stainless steel is an alloy that contains more chromium and usually no nickel. And this material can be either high carbon or low carbon steel. In addition, it contains 12% iron, 17% chromium and 0.10% carbon. The notable properties of this material are its high mechanical properties and wear resistance.
Martensitic stainless steel tweezers
The crystal structure of martensitic stainless steel is a body-centered cubic structure. Here, each corner of the cube contains atoms, and at the center of the cube there is one atom. This steel contains no nickel. In addition, this material is ferromagnetic, heat-curable, less corrosion resistant, etc.
Structure of martensitic stainless steel
What is the difference between austenitic and martensitic stainless steel?
Austenitic stainless steel is a form of stainless steel alloy that has exceptional corrosion resistance and impressive mechanical properties, while martensitic stainless steels are an alloy that has more chromium and usually no nickel.
The key difference between austenitic and martensitic stainless steel is that the crystal structure of austenitic stainless steel is a face-centered cubic structure, whereas for martensitic stainless steel it is a body-centered cubic structure.
Additionally, another difference between austenitic and martensitic stainless steel is that austenitic stainless steel contains nickel while martensitic stainless steel does not. Nickel in austenitic stainless steel ranges from 8 to 10%. Additionally, austenitic stainless steel is diamagnetic, while the martensitic form is ferromagnetic.
Austenitic stainless steel is a type of stainless steel alloy that has exceptional corrosion resistance and impressive mechanical properties, while martensitic stainless steels are an alloy that has more chromium and usually no nickel.
The key difference between austenitic and martensitic stainless steel is that the crystal structure of austenitic stainless steel is a face-centered cubic structure, whereas the crystal structure of martensitic stainless steel is a body-centered cubic structure.
Source: https://raznisa.ru/raznica-mezhdu-austenitnoj-i-martensitnoj-nerzhavejushhej-stalju/
