Difference between iron-based and nickel-based high-temperature alloys

Nickel-based high-temperature alloys can withstand higher operating temperatures compared to iron-based high-temperature alloys.

Nickel-based high-temperature alloys are nickel-based (content generally greater than 50%) high-temperature alloys with high strength and good resistance to oxidation and gas corrosion in the range of 650 to 1000 ℃.
Nickel-based alloys are the most widely used high-temperature alloys, high-temperature strength of the highest class of alloys. The main reason, one is that nickel-based alloys can dissolve more alloying elements, and can maintain good organizational stability; second, the formation of co-lattice ordered A3B-type intermetallic compound γ'[Ni3(Al, Ti)] phase as a strengthening phase, so that the alloy is effectively strengthened to obtain higher high-temperature strength than iron-based high-temperature alloys and cobalt-based high-temperature alloys; third, nickel-based alloys containing chromium have a better resistance to oxidation and gas corrosion than iron-based high-temperature alloys Alloys have better oxidation resistance and gas corrosion resistance. Nickel-based alloys contain more than ten elements, of which Cr mainly plays the role of oxidation resistance and corrosion resistance, while other elements mainly play the role of strengthening. According to their strengthening effect can be divided into: solid solution strengthening elements, such as tungsten, molybdenum, cobalt, chromium and vanadium; precipitation strengthening elements, such as aluminum, titanium, niobium and tantalum; grain boundary strengthening elements, such as boron, zirconium, magnesium and rare earth elements.

Iron-based high-temperature alloy is a material with certain strength and resistance to oxidation and gas corrosion at 600~800 degrees Celsius. Mainly iron-based austenitic alloys containing a certain amount of chromium and nickel.

Nickel in iron-based high-temperature alloys is the main element to form and stabilize austenite, and in the aging process to form Ni3 (Ti, Al) precipitation strengthening phase. Chromium is mainly used to improve oxidation resistance, gas corrosion resistance. Molybdenum and tungsten are used to strengthen the solid solution. Aluminum, titanium and niobium are used for precipitation strengthening. Carbon, boron, zirconium and other elements are used to strengthen grain boundaries. Iron-based high-temperature alloys can be divided into deformed and cast high-temperature alloys according to the manufacturing process, and into process-hardened, solution-reinforced and precipitation-reinforced high-temperature alloys according to the strengthening method (see Strengthening of Metals). The composition and properties of some typical iron-based high-temperature alloys are shown in the table. Organization The matrix of iron-based high-temperature alloys is austenite, and the main precipitation-reinforced phases are γ' [Ni3 (Ti, Al)] and γ" (Ni3Nb) phases. In addition, there are trace carbides, borides, Laves (such as Fe2Mo) phase and δ phase. Compared with the organization of nickel-based high-temperature alloys, the phase organization in iron-based alloys is more complex and less stable, and it is easy to precipitate η (such as Ni3Ti), σ (such as FexCry), G (such as Fe6Ni16Si7), μ (such as Fe7Mo6) and Laves and other harmful phases (see alloy phases).