Views: 0 Author: Site Editor Publish Time: 2024-07-24 Origin: Site
The term "stainless steel" is an abbreviation of "stainless and acid-resistant steel." This particular alloy is resistant to corrosion by air, steam, water, and other weak corrosive media. When this steel is used in a particular context, it is referred to as "stainless steel." It will be resistant to chemical corrosive media, such as acids, alkalis, salts, and other chemical impregnation. In contrast, corrosion of the steel is called "acid-resistant steel."
The disparity in chemical composition between the two and their respective corrosion resistance profiles result in ordinary stainless steel typically exhibiting limited resistance to chemical media corrosion, whereas acid-resistant steel is generally characterised by enhanced corrosion resistance. The term "stainless steel" does not simply refer to a single type of stainless steel, but rather encompasses over a hundred distinct industrial stainless steel varieties, each of which has been developed to exhibit optimal performance within its respective application domain. The initial step in achieving success is to identify the intended application, followed by the selection of the appropriate grade. In the context of building construction, there are typically only six steel grades that are of relevance. All of the aforementioned varieties contain between 17 and 22% chromium, with the superior grades additionally incorporating nickel. The incorporation of molybdenum enhances the atmospheric corrosion resistance, particularly in the presence of chlorinated atmospheres.
The term "stainless steel" is used to describe the corrosion resistance of steel in various environments, including air, steam, water, and other weak corrosive media, as well as acids, alkalis, salts, and other chemical impregnating media. In practice, the term "stainless steel" is often used to describe steel that is resistant to weak corrosive media, whereas "acid-resistant steel" is used to describe steel that is resistant to chemical media. However, due to the differences in the chemical composition of the two types of steel, it is not necessarily the case that stainless steel is resistant to chemical media corrosion, whereas acid-resistant steel is generally stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.
The classification of stainless steel is often based on the state of organisation, which can be broadly categorised as follows: martensitic steel, ferrite steel, austenitic steel, austenitic-ferrite (duplex) stainless steel and precipitation-hardening stainless steel. Additionally, the composition of stainless steel can be further subdivided into the following categories: chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel.
Ferritic stainless steel contains between 15 and 30 per cent chromium. As the chromium content is increased, the corrosion resistance, toughness and weldability of this steel type improve. Furthermore, chloride stress corrosion resistance is superior to that of other types of stainless steel. The Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti and Cr28 variants are examples of this category. The corrosion resistance and oxidation resistance of ferritic stainless steel are relatively good due to its high chromium content. However, the mechanical properties and process performance are poor, limiting its applications to acid-resistant structures of low strength and oxidation-resistant steel. This type of steel exhibits resistance to corrosion in various environments, including the presence of nitric acid and brine solutions. Additionally, it demonstrates excellent high-temperature oxidation resistance and a low coefficient of thermal expansion. Its applications include equipment used in nitric acid and food factories, as well as high-temperature components such as gas turbine parts.
Austenitic stainless steel is characterised by the presence of over 18% chromium, in addition to approximately 8% nickel and a trace amount of molybdenum, titanium, nitrogen and other elements. The comprehensive performance of the material is satisfactory, and it is capable of resisting corrosion in a variety of media. Austenitic stainless steel is most commonly used in grades such as 1Cr18Ni9 and 0Cr19Ni9. The steel number "0" is marked on the 0Cr19Ni9 steel, which has a WC of less than 0.08%. This type of steel contains a substantial quantity of Ni and Cr, which enables the steel to exist in an austenitic state at room temperature. This type of steel exhibits favourable characteristics including good plasticity, toughness, weldability and corrosion resistance. It displays low or negligible magnetic properties, particularly in oxidising and reducing media. Its corrosion resistance is enhanced in such environments, making it an ideal material for use in acid-resistant equipment such as corrosion-resistant containers and equipment linings, conveying pipelines, and parts resistant to nitric acid. Additionally, it can be employed as the primary material for watch ornaments. The austenitic stainless steel is typically subjected to a solid solution treatment, whereby the steel is heated to a temperature range of 1050 to 1150°C and subsequently cooled using either water or air to achieve a single-phase austenitic structure.
Austenitic-ferritic duplex stainless steels represent a synthesis of the advantageous properties of austenitic and ferritic stainless steels, coupled with the additional benefit of superplasticity. Approximately half of all stainless steel is comprised of austenitic and ferritic organisations. In the case of low carbon content, the chromium content is in the range of 18% to 28%, while the nickel content is in the range of 3% to 10%. Additionally, some steels contain Mo, Cu, Si, Nb, Ti, N and other alloying elements. This type of steel exhibits characteristics of both austenitic and ferritic stainless steels. In comparison to ferritic stainless steel, it displays enhanced plasticity and toughness, an absence of room-temperature brittleness, and significantly improved resistance to intergranular corrosion and welding performance. It also exhibits the brittleness typical of ferritic stainless steel at 475 ℃, high thermal conductivity, and other distinctive characteristics. In comparison to austenitic stainless steel, there has been a notable enhancement in both strength and resilience to intergranular corrosion and chloride stress corrosion. Duplex stainless steel exhibits excellent resistance to pore corrosion and is also a nickel-saving stainless steel.
The matrix is of the austenitic or martensitic variety. The precipitation hardening of stainless steel is commonly employed in the production of grades such as 04Cr13Ni8Mo2Al. Precipitation hardening (also known as age hardening) is a treatment that renders stainless steel harder and stronger.
Martensitic stainless steel exhibits high tensile strength but displays poor ductility and weldability. The most commonly utilised grades of martensitic stainless steel include 1Cr13 and 3Cr13, amongst others. Due to its elevated carbon content, the material exhibits high strength, hardness, and wear resistance. However, its corrosion resistance is somewhat limited. This material is employed in applications where mechanical properties are of paramount importance and corrosion resistance is a secondary consideration. Examples of such applications include springs, turbine blades, hydraulic valves, and other similar components. This particular steel is employed following a quenching and tempering process. Subsequent to forging and stamping, an annealing process is necessary.
The necessity for welding performance varies according to the intended use of the product. While a particular class of tableware may not require welding performance, including some pots and pans, the majority of products necessitate a high level of welding performance in their raw materials. This encompasses two types of tableware, insulation cups, steel pipes, water heaters, water dispensers, and other similar items.
The majority of stainless steel products require good corrosion resistance, as evidenced by their use in a variety of applications, including tableware, kitchen utensils, water heaters, drinking fountains, and other similar items. Some foreign businessmen have also conducted corrosion resistance tests on the product. A NACL aqueous solution is heated to boiling point and left to stand for a period of time. The solution is then poured off, the product is washed and dried, and the loss of corrosion is determined by weighing. This method allows the degree of corrosion to be quantified. However, it should be noted that the product is polished, which may result in the presence of Fe content in the sandcloth or sandpaper used. This may lead to the formation of rust spots on the surface of the product.
The polishing performance of stainless steel products in the context of general production is a process that is only undertaken for a limited range of items, such as water heaters and water dispensers. It is therefore essential that the raw materials exhibit an optimal polishing performance. The factors that affect the polishing performance can be broadly classified into the following categories:
1. Defects in the surface of the raw materials. These include scratches, pockmarks and overpickling.
2. Issues with the raw material. The material in question displays insufficient hardness, rendering polishing an arduous process. Furthermore, the material's inherent lack of hardness renders it susceptible to the orange peel phenomenon, which in turn affects the BQ. Conversely, a material displaying high hardness exhibits relatively favourable BQ characteristics.
The term "heat resistance" is used to describe the ability of stainless steel to maintain its superior physical and mechanical properties even when exposed to high temperatures.
The influence of carbon on austenitic stainless steel is significant, with the carbon atoms forming and stabilising the structure. The objective is to stabilise the austenite phase and expand the austenite zone elements. The capacity of carbon to form austenite is approximately 30 times that of nickel. As an interstitial element, carbon can significantly enhance the strength of austenitic stainless steel through solid solution strengthening. Furthermore, the incorporation of carbon into austenitic stainless steel can enhance its resistance to stress corrosion in highly concentrated chloride solutions, such as a boiling solution of 42% MgCl2.
Nevertheless, in austenitic stainless steel, carbon is frequently regarded as a detrimental element. This is primarily due to the formation of high-chromium Cr23C6-type carbon compounds, which occurs when carbon and chromium in the steel combine at temperatures between 450 and 850°C. This depletion of chromium results in a decline in the steel's corrosion resistance, particularly in terms of intergranular corrosion. Consequently, since the 1960s, the latest developments in chromium-nickel austenitic stainless steel have focused on ultra-low carbon types with a carbon content of less than 0.03% or 0.02%. It can be observed that as the carbon content decreases, the steel's intergranular corrosion sensitivity also decreases. However, the most significant effect is seen when the carbon content is less than 0.02%. Additionally, some experiments have indicated that carbon can also enhance the corrosion resistance of chromium austenitic stainless steel. Given the detrimental effects of carbon, it is imperative to maintain the lowest possible carbon content during the austenitic stainless steel smelting process. This is to be followed by rigorous control during subsequent hot, cold and heat treatment processes, with the aim of preventing an increase in carbon content at the surface of the stainless steel. This is to avoid the precipitation of chromium carbide.
When the atomic number of chromium present in steel is not less than 12.5%, it can precipitate a sudden alteration in the electrode potential of steel, from a negative potential to a positive electrode potential. The objective is to cease electrochemical corrosion.
The corrosion resistance of stainless steel is inversely proportional to the carbon content, with the majority of stainless steels exhibiting a carbon content of less than 1.2%. Some steels, such as 00Cr12, have an even lower carbon content, with a maximum of 0.03%. The primary alloying element in stainless steel is chromium (Cr). The corrosion resistance of the steel is only achieved when the Cr content reaches a specific threshold. It can be concluded, therefore, that the general chromium content of stainless steel is at least 10.5%. In addition to the aforementioned elements, stainless steel also contains Ni, Ti, Mn, N, Nb, Mo, Si, Cu and other elements.
The diversity of products, their processing technology and the requisite quality of raw materials result in a multitude of variations. In general, the requirements for raw material thickness tolerance of different stainless steel products vary. For instance, the thickness tolerance for two types of tableware and insulation cups is typically higher, at -3 to 5%. In contrast, the tolerance for tableware is generally -5%, while the steel tube class requires -10% and hotels with freezer materials require -8%. Distributors typically have a tolerance range of -4 to 6%. Consequently, the disparate internal and external sales of products will also result in varying customer requirements regarding the thickness tolerance of raw materials. In general, the thickness tolerance requirements for export products are higher than those for domestic sales. The latter are typically lower, often due to cost considerations. Some customers even require a thickness tolerance of -15%.
1.The term "DDQ (deep drawing quality)" is used to describe a specific type of material that is employed in the context of deep drawing (punching) operations. This material is often referred to as a "soft material," and its primary characteristics include a high degree of elongation (greater than 53%), a relatively low level of hardness (less than 170%), and an internal grain level that falls within the range of 7.0 to 8.0. The material's deep drawing performance is particularly noteworthy. The enterprise's production of thermos flasks, pots and pans typically exhibits a higher processing ratio (BLANKING SIZE/product diameter) than the industry average. This ratio ranges from 3.0 to 1.96 to 2.13 to 1.98, respectively. The SUS304DDQ material is primarily employed in the production of products with a higher processing ratio. However, for products with a processing ratio exceeding 2.0, the material must undergo several tensile processes. If the raw material extension is insufficient, deep drawing products are prone to cracking and pull-through, which negatively impacts the quality of the finished product and increases manufacturing costs.
2.The general material is employed in conjunction with the DDQ use of materials. It is distinguished by a relatively low elongation (≧ 45%) and a relatively high hardness (≦ 180HB), with an internal grain size grade between 8.0 and 9. In comparison to DDQ materials, this material exhibits somewhat inferior deep-drawing performance. It is primarily utilised in products that do not require stretching, such as tableware spoons, forks, electrical appliances, and steel pipes. However, it has the advantage over DDQ material of exhibiting relatively good BQ properties, which can be attributed to its slightly higher hardness.
Stainless steel sheet is a relatively inexpensive material, yet customers have exceedingly high expectations regarding the quality of its surface. It is inevitable that stainless steel sheet will manifest a variety of defects during the production process, including scratches, pitting, sand holes, dark lines, creases, and contamination. Therefore, the quality of the surface of the material, including the presence of scratches, creases, and other defects, must be strictly monitored. The occurrence of pitting and sand holes in the production of spoons and forks is also unacceptable, as these defects are difficult to remove during polishing. It is essential to ascertain the grade of surface quality, and thus the grade of the product, in accordance with the degree and frequency of the occurrence of diverse defects on the surface.
1. Density : Carbon steel is slightly denser than ferritic and martensitic stainless steels and slightly less dense than austenitic stainless steels;
2. Resistivity：The electrical resistivity increases in the order of carbon, ferritic, martensitic and austenitic stainless steels;
3, the size of the coefficient of linear expansion in a similar order, austenitic stainless steel is the highest and carbon steel is the smallest;
4, carbon steel, ferritic and martensitic stainless steel is magnetic, austenitic stainless steel is non-magnetic, but its cold work hardening generates a martensitic phase transition will produce magnetic, available heat treatment methods to eliminate this martensitic organization and restore its non-magnetic.
1. High resistivity, about 5 times that of carbon steel.
2. Large coefficient of linear expansion, 40% larger than carbon steel, and as the temperature rises, the value of the coefficient of linear expansion increases accordingly.
3. Low thermal conductivity, about 1/3 of carbon steel.
The majority of applications necessitate the preservation of the original architectural character of the building over time. In selecting the appropriate grade of stainless steel, the primary considerations are the desired aesthetic standard, the corrosive nature of the surrounding environment, and the cleaning regimen to be employed. Nevertheless, an increasing number of applications are seeking only structural integrity or impermeability. Such applications include roofs and side walls of industrial buildings. In such applications, the financial outlay incurred by the proprietor may be of greater consequence than the visual appeal of the structure, and it is permissible for the surface to be of a less than pristine condition. The utilisation of 304 stainless steel is an effective solution for dry interior environments.
However, in order to maintain its visual appeal in both rural and urban settings, it is necessary to perform regular cleaning. In areas with high levels of industrial and coastal pollution, the surface may become severely contaminated, even exhibiting signs of corrosion. Nevertheless, in order to achieve the desired aesthetic effect in an outdoor setting, it is necessary to utilise a nickel-containing stainless steel. Consequently, 304 stainless steel is frequently employed in the construction of curtain walls, sidewalls, roofs, and other architectural elements. However, 316 stainless steel is the preferred option in environments with high levels of aggression, such as industrial or marine settings. A number of design guidelines encompass both 304 and 316 stainless steel.
Duplex stainless steel 2205 is also included in the European guidelines due to its combination of good atmospheric corrosion resistance with high tensile and flexural strength. Indeed, stainless steel is manufactured in all standard metal shapes and sizes, as well as numerous specialty shapes. The most commonly utilised products are manufactured from sheet and strip, however, medium and thick plates are also employed in the production of bespoke items, such as hot-rolled and extruded structural sections. Additionally, steel tubes are available in a variety of shapes, including round, oval, square, rectangular, and hexagonal. These tubes can be welded or seamless, and they are produced in a range of forms, such as profiles, bars, wires, and castings. A diverse array of commercial surface finishes has been developed to satisfy the aesthetic demands of architects.
The field of 3D printing
Stainless steel is inherently resistant to corrosion, and at elevated temperatures, it can retain its superior physical and mechanical properties and other characteristics. It is a widely utilized material in the domain of 3D printing.
The efficacy of antimicrobial stainless steel in killing Escherichia coli and Staphylococcus aureus has been tested by authoritative units and found to be above 99%. Furthermore, it has been demonstrated to have a significant killing effect on other bacteria, including Candida albicans and Kukuroi. This evidence supports the conclusion that antimicrobial stainless steel has excellent broad-spectrum antimicrobial and antimicrobial durability. The National Institute for Drug and Biological Products Inspection has demonstrated that the antibacterial stainless steel is fully compliant with national technical standards in terms of toxicity and human safety. The antibacterial properties of stainless steel are not at the expense of the material's other properties, which remain comparable to those of the original stainless steel in terms of mechanics, corrosion resistance, hot and cold processing, welding and other characteristics.
The successful development of antibacterial stainless steel provides a significant opportunity for the advancement of antibacterial products. The potential for the development of antibacterial stainless steel products is considerable, with a broad market outlook. In the present era, a number of domestic manufacturers of antibacterial stainless steel have expressed a keen interest in this subject. They are actively seeking support for pilot testing and endeavour to expeditiously transform the results into commodities.
Precipitation hardening stainless steel is a material with excellent moulding properties and good weldability, making it an ideal choice for use in the nuclear, aviation and aerospace industries, where ultra-high strength is required.
The classification of stainless steel is dependent on its chemical composition. The most common types are the Cr system (400 series), the Cr-Ni system (300 series), the Cr-Mn-Ni system (200 series), heat-resistant chromium alloy steel (500 series) and precipitation hardening system (600 series).
201, 202, etc.: Manganese is present in place of nickel, resulting in reduced corrosion resistance. These materials are widely utilised as a cost-effective alternative to the 300 series.
301: This grade exhibits good ductility, making it suitable for use in molded products. Additionally, the material can be rapidly hardened through machining. The material exhibits good weldability. The material exhibits superior wear resistance and fatigue strength in comparison to 304 stainless steel.
302: Corrosion resistance comparable to that of 304 is achieved due to the relatively high carbon content, which results in enhanced strength.
303: The addition of a modest quantity of sulfur and phosphorus renders it more amenable to cutting and processing than 304.
304: 304 is a general-purpose type of stainless steel, also known as 18/8 stainless steel. The product range includes items such as corrosion-resistant containers, cutlery, furniture, railings and medical equipment. The standard composition is 18% chromium and 8% nickel. This non-magnetic stainless steel cannot be altered by heat treatment to change its metallurgical structure. Its GB grade is 0Cr18Ni9.
304 L: This variant exhibits the same characteristics as 304, but with a lower carbon content, thereby conferring enhanced corrosion resistance. It is also more amenable to heat treatment, although its mechanical properties are somewhat compromised. However, welding and heat treatment of the product are not recommended.
304 N: This variant of the 304 stainless steel contains nitrogen, which is added during the manufacturing process to enhance the material's strength.
309: The 309 alloy exhibits superior temperature resistance compared to the 304 alloy, with a temperature resistance of up to 980 ℃.
309S: The high chromium and nickel content provides excellent heat and oxidation resistance, making it suitable for use in a range of applications, including heat exchangers, boiler components, and injection engines.
310: This material exhibits excellent high-temperature oxidation resistance, with a maximum service temperature of 1200°C.
316: Subsequently 304 is the second most prevalent grade, predominantly utilised in the food industry, watch and jewellery manufacturing, the pharmaceutical sector and surgical apparatus. The incorporation of molybdenum endows it with a distinctive structure that exhibits resistance to corrosion. Additionally, it is employed as a "marine steel" due to its superior resilience to chloride corrosion in comparison to 304. SS316 is frequently utilised in nuclear fuel recovery units. Furthermore, 18/10 grade stainless steel is frequently employed in this particular application.
316L: 316 L is a low-carbon variant that exhibits enhanced corrosion resistance and is amenable to heat treatment. Its applications include chemical processing equipment, nuclear power generators, and refrigerant storage tanks.
321: The properties of this grade are similar to those of 304, with the exception that the risk of corrosion of the material's welds is reduced by the addition of titanium.
347: The addition of the stabilising element niobium renders it suitable for welding parts of aeronautical appliances and chemical equipment.
408: The 408 alloy exhibits good heat resistance but displays weak corrosion resistance. Its composition includes 11% Cr and 8% Ni.
