High-temperature alloys-nickel-based alloys
High-temperature alloys refer to a type of metal material based on iron, nickel, and cobalt that can work at high temperatures above 600°C and under certain stress for a long time, and has high high-temperature strength, good oxidation resistance, and hot corrosion resistance. , good fatigue performance and fracture toughness and other comprehensive properties, it is called superalloy in Europe and the United States. It is usually used for components that work under high temperature (600~1200℃) and complex stress conditions for a long time.
Nickel-based alloy is currently the most widely used high-temperature alloy and is mainly used in working environments such as high temperature, strong acid or alkali, and strong oxidation. Its development and use began in the late 1930s against the background that the emergence of jet aircraft placed higher requirements on the performance of high-temperature alloys. This article will introduce nickel-based alloys from the following aspects.
type
Divided according to performance:
Nickel-based corrosion-resistant alloy: The main alloy elements are copper, chromium, and molybdenum. It has good comprehensive performance and can resist various acid corrosion and stress corrosion. Mainly include nickel-copper (Ni-Cu) alloy (Monel alloy), nickel-chromium (Ni-Cr) alloy (nickel-based heat-resistant alloy, Incoloy, Inconel series), nickel-molybdenum (Ni-Mo) alloy (Hastelloy B series), nickel-chromium-molybdenum (Ni-Cr-Mo) alloy (mainly Hastelloy C series), etc. At the same time, pure nickel is also a typical representative of nickel-based corrosion-resistant alloys.
Nickel-based wear-resistant alloy: The main alloy elements are chromium, molybdenum, and tungsten, and also contain small amounts of niobium, tantalum, and indium. In addition to its wear resistance, it also has good anti-oxidation, corrosion resistance and welding properties.
Nickel-based precision alloys: including nickel-based soft magnetic alloys, nickel-based precision resistance alloys and nickel-based electrothermal alloys, etc. The most commonly used soft magnetic alloy is Permalloy, which contains about 80% nickel. It has high maximum magnetic permeability and initial magnetic permeability and low coercive force. It is an important iron core material in the electronics industry. The main alloying elements of nickel-based precision resistance alloy are chromium, aluminum, and copper. This alloy has high resistivity, low temperature coefficient of resistivity and good corrosion resistance, and is used to make resistors. Nickel-based electric heating alloy is a nickel alloy containing 20% chromium. It has good anti-oxidation and anti-corrosion properties and can be used for a long time at temperatures of 1000 to 1100°C.
Nickel-based memory alloy: a nickel alloy containing 50 (at)% titanium. Its recovery temperature is 70°C and its shape memory effect is good. A small change in the proportion of nickel-titanium components can change the recovery temperature within the range of 30 to 100°C.
Common nickel-based alloy properties
Inconel 600: It has good high temperature corrosion resistance and oxidation resistance, excellent hot and cold processing and welding properties, and has satisfactory thermal strength and high plasticity below 700°C;
Inconel 625: Excellent resistance to pitting, crevice corrosion, intergranular corrosion and erosion in chloride media; acid resistant and good weldability; low-cycle fatigue versions of Inconel 625 are commonly used Bellows.
Inconel 690: The cobalt content is low, suitable for nuclear energy-related applications, and the resistivity is low. For example, the heat transfer tubes of steam generators in pressurized water reactor nuclear power plants are all made of 690 material.
Inconel 713C: Precipitation hardened nickel-chromium based casting alloy.
Inconel 718: With γ" phase strengthening phase, good welding performance.
Inconel 751: Adding more aluminum content gives it better breaking strength in the high temperature range near 870°C.
Inconel 792: Adding more aluminum content makes it more corrosion-resistant at high temperatures, making it suitable for manufacturing gas turbines.
Inconel 939: γ' phase strengthening to increase welding performance.
Incoloy 020: Demonstrates excellent corrosion resistance in chemical environments containing sulfuric acid, chloride, phosphoric acid and nitric acid.
Incoloy 028: Resistant to both acids and salts, the copper content makes it resistant to sulfuric acid.
Incoloy 330: Exhibits good strength at high temperatures and good resistance to oxidizing and reducing environments.
Incoloy 800: It has excellent resistance to stress corrosion cracking in chloride, low-concentration NaOH aqueous solutions and high-temperature and high-pressure water. It can remain stable and maintain its austenitic structure even after long-term exposure to high temperatures.
Incoloy 803: Designed for use in sulfur-rich environments.
Incoloy 825: It has good corrosion resistance in reducing and oxidizing acids, resistance to stress corrosion cracking, pitting corrosion and crevice corrosion, excellent corrosion resistance to sulfuric acid and phosphoric acid and good hot and cold processing properties. , easy to cold form and weld.
Incoloy 908: has high tensile strength, resistance to fatigue crack growth, good weldability, metallurgical stability and ductility, high fracture and impact toughness, low thermal expansion coefficient, resistance to oxygen embrittlement, and no cracking during hot processing characteristic.
Incoloy 907: High strength and low thermal expansion coefficient at high temperatures.
Incoloy 945X: Designed for chlorine-rich environments, molybdenum increases its resistance to crevice corrosion and pitting corrosion.
Incoloy MA956: Made through mechanical alloying rather than an integral melting process, it is difficult to weld and needs to be heated to 200C to form.
Monel 400: It has high strength and excellent corrosion resistance in acidic and alkaline environments, especially suitable for reducing conditions. It also has good ductility and thermal conductivity. Commonly used in marine engineering, chemical and hydrocarbon processing, heat exchangers, valves and pumps.
Monel 401: It has the characteristics of easy tungsten inert gas shielded welding, resistance welding and brazing. For specialized electrical and electronic applications.
Monel 404: Can be used for welding and forging using common welding techniques, but cannot be hot processed. It has low temperature, low permeability and good brazing properties. Generally used for transistors and metal seals.
Monel 405: easy to cut, mainly used as raw material for automatic screw machines, and is generally not recommended for other applications.
Monel 450: Has good fatigue strength and high thermal conductivity. Generally used in condensers, distillers, evaporators and heat exchanger tubes as well as brine pipes.
Monel K-500: It has basically the same performance as Monel 400 and is commonly used in pump shafts, impellers, scrapers, oil well drill collars, instruments and electronic components.
Monel 502: has good creep resistance and oxidation resistance, and can also be processed like austenitic stainless steel.
Hastelloy B-2: Excellent corrosion resistance in reducing environments.
Hastelloy B-3: an upgraded version of B2, has excellent corrosion resistance to hydrochloric acid at any temperature and concentration;
Hastelloy C-4: Good thermal stability, good toughness and corrosion resistance at 650~1040℃;
Hastelloy C-22: Its resistance to uniform corrosion in oxidizing media is better than that of C-4 and C-276, and its resistance to localized corrosion is excellent;
Hastelloy C-276: has good resistance to oxidative and moderate reduction corrosion, and excellent resistance to stress corrosion;
Hastelloy C-2000: The most comprehensive corrosion-resistant alloy with excellent uniform corrosion resistance in both oxidizing and reducing environments;
Hastelloy G-30: Nickel-based alloy with high chromium content, excellent performance in phosphoric acid and other strongly oxidizing mixed acid media;
Hastelloy X: Combined high strength, antioxidant and easy processing.
Comparison of characteristics of commonly used brands
The chemical composition of N5 is similar to that of N02201, and the chemical composition of N6 and N7 is similar to that of N02200. Since N02200 has a carbon content of ≤0.15%, graphitization at 315°C makes the material brittle, so the maximum temperature used is 315°C.
800, 800H, and 800HT have the same chemical element composition in the ASME standard. 800 has the lowest carbon content, the annealing temperature is 982-1038°C, and the use temperature is below 600°C; 800H has a limited Al+Ti content, and after special solid solution treatment (1121-1177°C), the crystal grains are coarse, and the grains are ASTM- 5.0, the creep rupture resistance above 600℃ is significantly improved; 800HT increases the Al+Ti content. After special solid solution treatment (1121-1177℃), the crystal grains are coarse and the grains are ASTM-5.0 , which has the highest creep rupture resistance above 700℃ and has a significant improvement. If the heat treatment temperature is too high, the material grains will expand, have higher creep limit and lasting strength limit, and reduce the toughness. Higher heat treatment temperatures result in faster nucleation and an increased number of crystals. At this time, the grains are relatively fine. When the holding time is lengthened, the grains will grow. When the cooling rate is slow, the grains will also become larger. Generally speaking, the higher the temperature (smaller gradient), the larger the grain size. The smaller the grains, the higher the strength and hardness, and the better the plasticity and toughness. However, in a high-temperature working environment, the grains become coarser and the total length of the grain boundaries is reduced. The deformation or damage caused by sliding along the grain boundaries or the creep performance is improved.
The main chemical composition of N06600: 72Ni-15Cr-8Fe, the main chemical composition of N08800: 33Ni-42Fe-21Cr, which is equivalent to dividing the 72Ni content in N06600 into 33Ni+45Fe, and reducing costs by replacing part of the nickel.
The main chemical composition of N10675 is 65Ni-29.5Mo-2Fe-2Cr, and the chemical composition of N10276 is 54Ni-16Mo-15Cr. It can be approximately regarded as dividing 29.5Mo in N10675 into 16Mo+15Cr. Due to the increase in Cr content, the material is resistant to oxidizing media corrosion. Ability.
