What is niobium:
Niobium is a bright white metal that, when exposed to air, often forms a layer on its surface and changes color to various colors, including blue, green, or yellow. It can be used in a variety of applications, including superconducting magnets, motors, and hypoallergenic jewelry. Niobium (Nb) has an atomic weight of 92.91, an atomic number of 41, and a density of 8.57 g/cm3. This substance is also known as columbium (Cb). The melting point of Nb is 2467°C and the boiling point is 4740°C.
In the manufacture of tool steel, niobium (Nb) replaces tungsten (W). By the 1930s, niobium was being used to stop corrosion in stainless steel. Niobium has been known to maintain fine grain sizes in steels at higher temperatures since the 1940s, and steels that benefit from this property have been developed in industry for many years. In recent years, niobium has been considered one of the most important elements for microalloying.
It plays a vital role in (high strength low alloy) steel. In addition, tool steels, wear-resistant steels, high-temperature steels, stainless steels and superalloys all have important uses. Many of these uses rely on it due to its high affinity for carbon and nitrogen.
About 80% of the niobium produced is used as a microalloying component in steel used in the transportation industry, oil and gas pipelines, and construction. The manufacture of stainless steel for use in vehicle exhaust systems is another important application for niobium. Niobium-containing superalloys are used in a variety of superconducting materials, jet and rocket components, and other applications. Functional ceramics and catalysts in the optical and electrical fields also use niobium.
Niobium additives and methods:
Niobium can exist as an iron alloy. Niobium makes up approximately 60% of the standard grade of ferroniobium (Fe-Nb). Additionally, Fe-Nb can contain up to 2.0% titanium, 3.0% silicon, and 3.5% aluminum (Al) (Ti). Tantalum (Ta) content is less than 0.50%, and carbon content is limited to 0.30%. The highest purity Fe-Nb has a minimum Nb content of 62-68%, a maximum Al content of 1.0%, a maximum Si content of 0.2%, a maximum C content of 0.1%, and a maximum Ta content of 0.30%.
Fe-Nb is added to the molten steel ladle after the addition of silicon, aluminum and/or manganese, simultaneously with or immediately following the addition of manganese. Fe-Nb addition should be started when the ladle is approximately one quarter full and should be completed before the ladle is half full. Due to the higher melting range of ferroniobium relative to niobium (1400°C to 1580°C), addition early in the operation helps ensure complete dissolution and proper dispersion. This also enhances recovery capabilities. Fe-Nb has a chilling effect. At 1600°C, the molten pool temperature will decrease by 0.7°C/kg/ton. Although alloy recovery is generally relatively high, and Nb recovery is only in the 10 to 20 percent range when scrap is remelted in an oxidizing atmosphere, it is not a very strong deoxidizer. The recovery rate of completely dead steel is at least 80% and under carefully regulated conditions can easily reach 90%. Although niobium is a grain refiner, it does not cause nozzle clogging during continuous casting.
Molten steels used with other silicon-containing molten steels do not benefit significantly from niobium’s deoxidizing capabilities. However, its content is significantly higher than that of manganese, so it is speculated that niobium may combine with oxygen and become supersaturated with decreasing temperature during the solidification of the steel, thus precipitating non-metallic inclusions composed of different niobium oxides. However, due to their tiny size and low concentration, these oxides have little impact on steel cleanliness values measured by the JIS method. Niobium has a high affinity for carbon and nitrogen and therefore readily interacts with these species to form carbides and nitrides.
Rolling and hot working of niobium in steel:
Niobium significantly increases the strength of rolled steel by precipitating hard and stable carbides, nitrides or carbonitrides. Niobium forms carbides more readily than vanadium (V), but forms nitrides less effectively than titanium (Ti). Nb carbonitrides are stable in the lower rolling temperature range. Controlled thermomechanical rolling of steel is based on the presence of carbonitrides at these rolling temperatures and their ability to precipitate throughout the hot rolling process.
In order to achieve the appropriate quality of rolled steel, the purpose of thermomechanical rolling is to create extremely small grain sizes in the steel.
Niobium-containing alloy steel is hot rolled starting from the existing finer grain structure. As the hot rolling process continues, deformation and expansion of recrystallized austenite grains slow down due to continued NbC(N) precipitation. Eventually, these austenite grains transform into an extremely fine-grained ferrite-pearlite or needle-like structure.
The beneficial effects of Nb come into play when the steel is reheated during hot rolling. At such high temperatures, the niobium is partly in solid solution and partly as fine carbonitrides that are still precipitated. Before rolling, the residual precipitates maintain a small austenite grain size. To achieve the desired strength levels, steels with high toughness requirements must rely more on grain refinement than precipitation strengthening. To exploit this effect, these steels should be heated to between 1095 and 1150 degrees Celsius. For steels with less stringent toughness requirements, precipitation strengthening is more beneficial. To optimize the possibility of subsequent precipitation strengthening, these steels are therefore heated to a slightly higher temperature to dissolve any niobium carbonitride before rolling begins.
A key technique for improving strength and toughness while maintaining low carbon equivalent value (CEV) for optimal weldability is accelerated cooling (AC), which is performed after controlled rolling. Nb is particularly beneficial for AC steel because it stimulates the formation of a ferrite-bainite microstructure when producing small-grained austenite, and achieves levels of 600 MPa in the rolled and AC conditions at CEV 0.35 yield strength.
Niobium acts as a ferrite stabilizer, gradually completing the gamma ring when present in sufficient amounts. Maintaining fine grain size is the primary role of niobium in microalloyed forged steels. High toughness, a key factor in safety-related applications such as steering and suspension system components, is affected by fine grain size. To achieve high strength levels, low to medium carbon niobium vanadium steels combine precipitation hardening with grain size. The mechanical properties of low-carbon Nb-Mo microalloy forged steel originate from the fine-grained bainite structure.
The properties of these forged steels depend on the rate of cooling, with optimum strength and toughness obtained by quenching immediately after forging. NbC segregates and reduces the ductility in the center of large forgings in large Nb-treated stainless steel ingots.
Effect of niobium on steel:
Furthermore, Nb lowers the temperature at which gd transformation occurs, which contributes to the formation of extremely small acicular ferrite or bainite grains with high dislocation density. Steels with these microstructures have exceptional strength and best-in-class toughness. The weldability of these high-strength steels is usually quite high because the carbon concentration in these steels can be quite low. The ferrite in microalloyed steels can be further strengthened by the precipitation of extremely small niobium carbonitride particles during the transformation process.
Steels that have been normalized or austenitized take advantage of niobium’s ability to prevent grain development during quenching and tempering. The addition of niobium creates finer grains that increase strength and toughness at a constant CEV level, or maintain constant strength and toughness levels at a lower CEV level. Other advantages of adding niobium include the creation of favorable crystal structures, strain relief and better formability. This is determined by the extent to which carbon and N (nitrogen) combine to form Nb carbonitride. When carbon and nitrogen are sufficiently removed from the ferrite solid solution, (interstitial-free) steel results.
Nb helps form a finer grain structure and lowers the transformation temperature of low carbon alloy steels. Because niobium produces extremely stable carbides, it slows tempering and may reduce the steel’s ability to harden. This may result in less carbon being dissolved during austenitic heat treatment.
Heat treatment of niobium:
Niobium has a detrimental effect on the hardenability of martensite due to its strong ability to separate carbon from solution. Therefore, Nb is not a limiting component of heat-treatable structural alloy steels. In certain grades of structural steel, pressure vessel steel, and wear-resistant steel (chromium), Nb is sometimes combined with Mn (manganese), Mo (molybdenum), Ni (nickel), Cu (copper), and Cr (chromium).
Commercial direct quenching of microalloyed niobium forged steels is a common procedure. Many niobium containing steel sheets/plates are roller hardened and tempered steels. The self-tempering martensitic structure of a heat-treatable low-C microalloyed niobium forged steel requires conditioning quenching after forging. Cu-Ni-Nb steel is heat treated at 550 degrees Celsius using rapid cooling and a simple aging process.
Applications of niobium in the steel industry:
Niobium steel has a wide range of applications, including drilling equipment, large boilers, heavy machinery, ships, railways, automobiles, tractors, bridges, construction, heavy machinery, heavy machinery, tools, molds, etc.
More than 80% of the niobium used in the steel industry is used to make low-alloy high-strength steel, which usually contains 0.02-0.05% niobium. Niobium can be used to refine grains, produce stable carbides and carbonitrides, and precipitate niobium carbide to improve the strength and creep resistance of steel.
Metallic niobium rods or ferroniobium with a niobium content of 50-70% are commonly used as high alloy steels with added niobium. Stainless steel, heat-resistant steel and corrosion-resistant steel are high-alloy steels containing niobium. In recent years, the use of niobium-containing stainless steel electrodes has increased.
In cast iron, niobium can greatly improve the toughness and strength of cast iron by promoting graphitization, reducing casting cracks, and improving casting wear resistance. Niobium-containing cast iron (containing about 0.3% niobium) can improve the wear resistance and service life of cylinder liners and piston rings.
Steel producers use a variety of different methods to obtain the necessary balance of properties. Steel properties such as strength and toughness depend on chemical composition and processing techniques. While adding more carbon to steel is the simplest way to increase strength, this affects other key qualities including weldability, toughness and formability. A cost-effective way to achieve a balanced combination of properties is microalloying with elements such as niobium, vanadium or titanium at levels below 0.1wt% (1000g/ton).
Niobium is commonly added to most structural steels with strengths of 355 MPa and higher. When the steel strength exceeds 355 MPa, the niobium content may be increased, depending on the specific steel fabrication strategy adopted by the factory to ensure that the steel has the right balance of strength, toughness and weldability.
Large-diameter line pipes for natural gas and oil transportation, shipbuilding, offshore platforms, bridges and energy generation structures such as wind turbines are just a few of the uses for niobium microalloyed high-strength steel sheets. Sheets thicker than 50 mm are typical.
In some grades, steels containing niobium may be more cost-effective because they only require about half the niobium to achieve the same strength gain as adding vanadium. The most important use of niobium is as an alloying element to strengthen high-strength low-alloy (HSLA) steel used in the manufacture of vehicles and high-pressure gas transmission pipelines.
The choice of steel composition is influenced by a variety of factors. In low carbon HSLA steels (C less than 0.1%), Nb is a more effective strengthening element than V or Ti, and most contemporary HSLA steels fall into this low C group.
To maximize synergistic benefits and obtain the best results, microalloys are often added in combination. In IF steel vehicle parts, the improvement in surface quality brought about by this combination of additions is crucial, one example of which is the simultaneous use of Nb and Ti. The ability to produce large integrated plates and complex parts using IF steel microalloyed with Nb and Ti helps reduce the number of welds, the number of parts manufactured, and the weight of the parts.
When Nb and Ti work together, the synergistic effect is more significant than when Nb and V are present in the steel.
Another important use for niobium microalloying is in steels for shipbuilding and offshore platforms. Steel plates thicker than 50 mm are often used for this purpose.
Apart from this, one of its typical applications is civil construction. They are used in the construction of high-rise buildings, viaducts, bridges, etc.
Niobium can be used to make longer parts with higher strength levels. Structural profiles (such as angles and I-beams) are often used in civil construction, railway wagons, transmission towers, and other applications. In this application, Nb and V are constantly competing.
The main raw material used for manufacturing nuts and bolts, fasteners, springs, etc. is wire rod. Among several high-strength fasteners used in the automotive industry, niobium and vanadium are used. The use of microalloying technology here eliminates intermediate processing (spheroidizing annealing), quenching and tempering of the final product. Nb with V is now a typical addition to spring steel. Increased strength through niobium microalloying can reduce the weight of the finished product.
Some uses for niobium have been found in high-strength, wear-resistant steel rails for train tracks operating under heavy axle loads.
About 10% of the world’s total nickel consumption comes from stainless steels, especially ferritic stainless steels (nickel-free). About 25% of Japan’s niobium requirements are for stainless steel. In automobile exhaust systems, ferritic steel grades containing niobium are mainly used. Niobium is used in heat-resistant steel used in power plants and the petrochemical industry.
To manufacture seamless pipes for oil and gas drilling operations, high-strength niobium microalloyed steels (drill pipe and casing) are used.
Essentially, tool steel is a solid matrix embedded with hard metal carbides. The addition of niobium to form hard niobium carbides is one of the new metallurgical techniques used to improve the properties of tool steels.
Other applications of niobium:
Superconducting materials industry: Superconducting generators, high-power accelerator magnets, superconducting magnetic energy storage, magnetic resonance imaging equipment, etc. are just a few examples of industrial superconductors made using niobium compounds and alloys with high superconducting transition temperatures. NB Ti and Nb Sn are currently the most important superconducting materials and are widely used in medical diagnostic equipment such as nuclear magnetic resonance spectrometers and magnetic resonance imaging machines for spectral line analysis.
Aerospace industry: High-purity niobium is mainly used in the aerospace industry for the production of engines and heat-resistant components for rockets and spacecraft. Thermal alloys based on NB and Ta are often used in gas turbine blades and aircraft parts due to their excellent heat resistance and processability.
Atomic energy industry: Niobium has a high melting point, strong thermal conductivity, excellent corrosion resistance, and small cross-section, which is beneficial to neutron capture. It is a substance that works well in atomic reactors. Nuclear fuel, nuclear fuel alloys and structural components of nuclear reactor heat exchangers are the main uses of niobium in the atomic energy field.
Electronics industry: Capacitor manufacturing can use niobate ceramics. Single crystals such as lithium niobate and potassium niobate compounds have good crystal, piezoelectric, thermoelectric and optical properties. They are a new form of optoelectronics and electronics and have been widely used in infrared, laser and electronic industries. Niobium also has a high melting point, strong electron emission, and the ability to absorb air. It can be used to make vacuum-based electrical devices such as electron tubes.
Medical field: Because of its anti-corrosion physiological properties and good biocompatibility, niobium can prevent various liquid substances from harming biological tissues in the body. It is often used in the production of bone plates, skull plate screws, plant roots, surgical instruments, etc. human body.
Chemical Industry: Niobium is a high-quality, corrosion-resistant material used in the chemical industry for cooking utensils, refrigerators, and heaters. Niobic acid is also an important catalyst.
The main function of niobium in the foundry industry is to generate hard carbides and change the shape and size of graphite. Graphite is often used in the production of automobile cylinder heads, piston rings and brakes. Niobium is also sometimes used in commemorative coins along with gold and silver.
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 1989 with a registered capital of 10.0 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
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Post time: Jan-10-2024
