What is Niobium:
Niobium is a bright, white metal that, when exposed to air, usually develops a layer on its surface and changes color to various colors of blue, green, or yellow. It can be used for a variety of things, including superconducting magnets, engines, and hypoallergenic jewelry. Niobium (Nb), with an atomic weight of 92.91 and an atomic number of 41, has a density of 8.57 gm/cc. The substance is also referred to as columbium (Cb). Nb has a melting point of 2467°C and a boiling point of 4740°C.
In the manufacture of tool steel, niobium (Nb) took the place of tungsten (W). Nb was employed to stop corrosion in stainless steel by the 1930s. Since the 1940s, it has been known that Nb can sustain fine grain sizes in steels at higher temperatures, and steels that benefit from this property have been developed for many years in the industrial sector. Nb is now primarily recognized in recent years as one of the most crucial elements for microalloying.
It performs a crucial function in (high strength low alloy) steels. Moreover, tool steels, wear and abrasion-resistant steels, steels for high-temperature service, stainless steels, and super alloys all have significant uses for it. Due to its high affinity for carbon and nitrogen, many of these uses are dependent on it.
About 80% of the niobium that is produced is used as a microalloying component in steels for the transportation sector, for pipelines carrying oil and gas, and for construction. The manufacture of stainless steel for use in exhaust systems for vehicles is another key application for niobium. Superalloys containing niobium are used in various superconducting materials, jet and rocket parts, and other applications. Functional ceramics and catalysts for the optical and electrical sectors also employ niobium.
Addition agents and practice of Niobium:
Nb can be found as a ferroalloy. Niobium makes up about 60% of ferro-niobium (Fe-Nb) standard grade. Additionally, Fe-Nb may have a maximum of 2.0% titanium, 3.0% silicon, and 3.5% aluminum (Al) (Ti). Tantalum (Ta) content is less than 0.50%, and Carbon content is restricted to 0.30%. supreme purity Fe-Nb has a minimum of 62–68% Nb, a maximum of 1.0% Al, a maximum of 0.2% Si, a maximum of 0.1% C, and a maximum of 0.30% Ta.
After the additions of silicon, aluminum, and/or manganese, Fe-Nb is added to the steel teeming ladle, either concurrently with or right after manganese. Fe-Nb addition should start when the ladle is approximately one-quarter full and should be finished before the ladle is halfway full. Due to Ferro-relatively Nb’s high melting range (1400°C to 1580°C), adding it early in the operation helps ensure thorough dissolving and appropriate dispersion. This enhances recuperation as well. Fe-Nb has a chill effect, which causes a 0.7-degree C/kg/ton decrease in bath temperature at 1600 degrees Celcius. Although alloy recoveries are often relatively high and Nb recovery when remelting scrap in an oxidizing atmosphere is only in the 10% to 20% range, It is not known for being an extraordinarily strong deoxidizer. Recoveries in totally dead steels are at least 80% and, under carefully regulated conditions, can easily reach 90%. Despite being a grain refiner, Nb does not cause nozzle obstructions during continuous casting.
The molten steel utilized along with other molten steels containing silicon does not significantly benefit from the deoxidizing power of niobium. However, it is significantly higher than manganese, so it is hypothesized that niobium may combine with oxygen, which becomes super-saturated with a decrease in temperature during the solidification of steel, to precipitate nonmetallic inclusions made up of different niobium oxides. However, due to their minuscule size and low concentration, these oxides have little impact on the cleanliness value of steel material as measured by the JIS method. Niobium has such a high affinity for carbon and nitrogen that it may easily interact with these substances to create carbides and nitrides.
Rolling and Hot Working of Niobium in Steel:
Through the precipitation of a hard and stable carbide, nitride, or carbo-nitride, Nb significantly strengthens rolled steels. Nb has a better tendency to generate carbides than vanadium (V) but is less effective at generating nitrides than titanium (Ti). At lower rolling temperature ranges, the carbo-nitrides of Nb are stable. The controlled thermo-mechanical rolling of steels is based on the presence of carbo-nitrides at these rolling temperatures and their capacity to precipitate throughout the hot rolling process.
For the rolled steels to have the appropriate qualities, thermo-mechanical rolling aims to develop extremely small grain sizes in the steels.
Starting with a finer existing grain structure, hot rolling of steels alloyed with Nb is performed. The expansion of the deformed and recrystallized austenite grains is slowed down as the hot rolling process continues due to the persistent NbC(N) precipitation. Eventually, these austenite grains are transformed into exceedingly fine-grained ferrite-pearlite or acicular structures.
The advantageous impact of Nb begins to take effect as steel is being reheated during the hot rolling of steel. At this high temperature, Nb is partially in solid solution and partially as still-precipitated fine carbo-nitrides. Before rolling, the residual precipitates maintain a fine austenitic grain size. To obtain their intended strength levels, steels with high toughness requirements must rely comparatively more on grain refining than precipitation strengthening. To make use of this effect, these steels should be warmed between 1095 and 1150 degrees Celsius. Precipitation strengthening can be more advantageous for steels with less strict toughness requirements. To optimize the possibility of precipitation strengthening subsequently, these steels are therefore warmed to slightly higher temperatures to dissolve all Nb carbo-nitrides before rolling commences.
A crucial technique for improving strength and toughness while retaining low carbon equivalent values (CEV) for optimal weldability is accelerated cooling (AC), which comes after controlled rolling. Nb is particularly advantageous to AC steels because, while producing small-grained austenite, it stimulates the formation of ferrite-bainite microstructures, and yield strengths of the order of 600 MPa are being achieved in the as-rolled and AC state at a CEV 0.35.
Nb functions as a ferrite stabilizer, gradually completing the gamma loop when present in sufficient amounts. Maintaining a fine grain size is the primary role of Nb in micro-alloyed forging steels. High toughness, a crucial factor in safety-related applications like steering- and suspension system components, is influenced by fine grain size. To attain high strength levels, low to medium carbon Nb-V steels combine precipitation hardening with grain size. The mechanical characteristics of low-carbon Nb-Mo micro-alloyed forging steels are derived from a fine-grained bainitic structure.
These forging steels’ properties are dependent on cooling rate, with the best strength and toughness obtained by quenching immediately after forging. NbC can segregate and reduce the ductility in the center of big forgings in very large Nb-treated stainless steel ingots.
Niobium Influence on Steel:
Additionally, Nb lowers the temperature at which the g-d transformation occurs, which aids in the development of extremely small, acicular ferrite or bainite grains with high dislocation densities. Steels with these microstructures have exceptional strength and top-notch toughness. Weldability is typically quite high in these high-strength steels since the Carbon concentration in these steels can be fairly low. The ferrite in micro-alloyed steels can be further reinforced by precipitation of extremely small Nb carbo-nitride particles during transformation.
Steels that have been normalized or austenitized make use of Nb’s ability to prevent grain development during quenching and tempering. The Nb additions lead to finer grains that either increase strength and toughness at constant CEV levels or allow for the maintenance of constant strength and toughness levels at lower CEV levels. The creation of favorable crystallographic textures, the removal of strain aging, and better formability are other advantages of Nb additions. The degree to which Carbon and N (nitrogen) are joined to form Nb carbo-nitrides determines this. Steels that are (interstitial-free) are created when Carbon and Nitrogen are sufficiently removed from the solid solution in ferrite.
Nb contributes to a finer grain structure and decreases the transition temperature in low Carbon alloy steels. Because it produces extremely stable carbides, nb slows down tempering and may reduce steel’s capacity to be hardened. This could result in less Carbon being dissolved during heat treatment of the austenite.
Heat treatment of Niobium:
Due to its potent capacity to pull Carbon out of the solution, Nb has a detrimental effect on the hardenability of martensite. Therefore, Nb is not a defined component of the constructional alloy steels that can be heat treated. Nb is sometimes combined with Mn (manganese), Mo (molybdenum), Ni (nickel), Cu (copper), and Cr (chromium) in certain grades of structural, pressure vessel, and abrasion-resistant steels (chromium).
Commercial direct quenching of micro-alloyed Nb forging steels is a common procedure. Roller quenched and tempered steels are used in many Nb-bearing sheets/plates of steel. The auto tempered martensitic structure of one heat treatable, low C micro alloyed Nb forging steel demands regulated quenching after forging. Cu-Ni-Nb steels are heat treated at 550 degrees Celsius using rapid cooling and a straightforward aging process.
Applications of Niobium In The Steel Industry:
Niobium steel is used in a wide range of industries, including drilling equipment, big boilers, heavy machinery, ships, railroads, autos, tractors, bridges, construction, heavy machinery, heavy machinery, tools, and molds.
More than 80% of the niobium used in the steel industry is used to make low-alloy high-strength steel, which typically includes 0.02-0.05% niobium. Niobium can be used to refine crystal grains, create stable carbides and carbo-nitrides, and precipitate niobium carbide to increase steel’s strength and resistance to creep.
Metal niobium bars or ferroniobium with 50–70% niobium are typically used as high alloy steel with niobium additions. Stainless steel, heat-resistant steel, and corrosion-resistant steel are among the high-alloy steels that contain niobium. In recent years, the use of stainless steel electrodes containing niobium has increased.
In Cast Iron Niobium can be used to greatly increase the toughness and strength of cast iron by promoting graphitization, reducing casting cracks, and improving casting wear resistance. Niobium-containing cast iron (containing roughly 0.3% Nb) can increase the wear resistance and service life of cylinder liners and piston rings.
Steel producers employ a wide variety of different approaches to obtain the necessary balance of attributes. Steel properties like strength and toughness depend on both the chemical composition and processing techniques. Although adding more carbon to steel is the simplest approach to increase strength, this affects other crucial qualities including weldability, toughness, and formability. A cost-effective way to achieve a well-balanced mix of characteristics is through microalloying with elements like niobium, vanadium, or titanium in levels below 0.1wt% (1000 grams/tonne).
As it is common that Niobium additions are found in the majority of structural steels with strengths of 355 MPa and higher. Niobium content may rise as steel strength surpasses 355 MPa, depending on the specific steel manufacturing strategy used by the mill, to guarantee the steel has the proper balance of strength, toughness, and weldability.
Large diameter line pipes for the transfer of gas and oil, shipbuilding, offshore platforms, bridges, and energy generation structures like wind turbines are just a few of the uses for niobium micro-alloyed high strength steel plates. Plates with a thickness greater than 50 mm are typical.
Steels consisting of Niobium may be more cost-effective in some grades since they require just about half as much Nb to achieve the same gain in strength as Vandanium additions. The most significant use of Niobium is as an alloying element to fortify high strength low alloy (HSLA) steels used in the construction of vehicles and high-pressure gas transmission pipes.
The choice of steel composition is influenced by a variety of factors. Nb is a more efficient strengthening element in low carbon HSLA steels (C less than 0.1%) than V or Ti, and the majority of contemporary HSLA steels fall into this low C group.
To maximize synergistic benefits and get the greatest results, micro alloys are typically added in combination. In IF steel vehicle parts, where the improved surface quality that arises from this combined addition is essential, one example of this is the usage of Nb and Ti together. The ability to produce large integrated sheet panels and complex parts using IF steel with Nb and Ti microalloying has helped to reduce the number of welds, the number of parts created, and the weight of the parts.
When Nb and Ti are functioning together, synergy is far more significant than when Nb and V are both present in the steel.
Another significant use of Nb microalloying is in steels for shipbuilding and offshore platforms. A steel plate with a thickness greater than 50 mm is typical for this purpose.
Adding to that a typical application of it is civil construction. They are employed in the construction of high-rise structures, viaducts, bridges, etc.
Nb can be used to manufacture long items in higher strength grades. In civil construction, railroad wagons, transmission towers, and other applications, structural sections (such as angles and I beam) are frequently employed. In this application, Nb and V have been battling it out.
The primary raw material utilized to create nuts & bolts, fasteners, springs, etc. is wire rods. In several high-strength fasteners used in the automotive industry, Nb and V have found employment. The use of microalloying technology here enables the elimination of intermediate processing (spheroid annealing), quenching, and tempering of the final product. Nb with a V is now a typical addition to spring steels. Weight reduction in the completed product is made possible by the increased strength obtained via Nb microalloying.
High-strength and wear-resistant rails for train tracks that operate under heavy axle loads have found some use for niobium.
About 10% of the world’s total consumption of Nickel is consumed from stainless steel, particularly the ferritic grades (nickel free). About 25% of the Nb demand in Japan is for stainless steel. In car exhaust systems, ferritic grades containing Nb are primarily used. Steels used in power plants and the petrochemical industry that is heat resistant employ nb.
For the manufacturing of seamless pipe used in oil and gas well drilling operations, high-strength Nb micro alloyed grades are used (drill pipe and well casing).
In essence, tool steels are robust matrix-embedded hard metal carbides. The inclusion of niobium to create hard niobium carbides is one of the new metallurgical techniques being used to improve the performance of tool steels.
Other applications of Niobium:
Superconducting materials industry: A superconducting generator, high-power accelerator magnets, superconducting magnetic energy storage, magnetic resonance imaging equipment, etc. are only a few examples of industrial superconductors that are made using niobium compounds and alloys with high superconducting transition temperatures. NB Ti and Nb Sn are now the most significant superconductor materials, and they are widely employed 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 primarily utilized in the aerospace industry for the production of engines and heat-resistant parts for rockets and spacecraft. Hot alloys based on NB and Ta have frequently been used in gas turbine blades and aircraft parts because of their outstanding thermal and thermal resistance and processability.
Atomic energy industry: Niobium has a high melting point, strong thermal conductivity, superior corrosion resistance, and a small cross-section for neutron capture. It is a substance that works well in atomic reactors. The incorporation of nuclear fuel, nuclear fuel alloys, and the structural components of heat exchangers in nuclear reactors are among the primary uses of niobium in the atomic energy sector.
Electronic industry: Capacitor manufacturing can make use of niobate ceramics. With good crystal, piezoelectric, pyroelectric, and optical capabilities, single crystals like lithium and potassium niobate compounds are a new form of optoelectronics and electronics that have been extensively used in the infrared, laser, and electronic industries. Niobium also has a high melting point, a strong electron emission capacity, and the capacity to draw air. It can be utilized to create vacuum-based electrical devices like electron tubes.
Medical field: Niobium is frequently used in the production of bone plates, skull plate screws, plant roots, surgical instruments, etc. because of its anti-corrosive physiological properties and good biological compatibility, which prevents various liquid substances from harming biological tissues in the human body.
Chemical Industry: Niobium is a high-quality, corrosion-resistant material that can be utilized in culinary appliances, refrigerators, and heaters in the chemical sector. Niobium acid is a significant catalyst as well.
The major function of niobium in the foundry industry is to generate a hard carbide and alter the morphology and size of graphite, which are frequently used in the production of automotive cylinder heads, piston rings, and brakes, among other things. Niobium is additionally occasionally used with gold and silver in commemorative coins.
Pipingmart is B2B portal specializes in industrial, metal and piping products. Also, share latest information and news related to products, materials and different types grades to help business dealing in this industry.
