Iron-based cast high-temperature alloys

Cast high-temperature alloy with iron as the main component. It is a class of austenitic alloys that can be applied at temperatures from 600 to 850°C, under certain stresses and conditions of oxidation and corrosion. Because it contains more nickel, it is also called iron-nickel-based cast high-temperature alloy. Most of the iron-based cast high-temperature alloys evolved from iron-based deformed high-temperature alloys. Because of the iron-based casting high-temperature alloy is long in the medium temperature applications, simple process and economic reasons, many countries have developed such alloys.

Features Casting high-temperature alloys have the following characteristics.
(1) high degree of alloying. γ' strengthening phase (see high-temperature alloy materials, metal ask compound phase) formation elements such as aluminum, titanium, niobium, tantalum up to 16%, but also add a certain amount of solid solution strengthening elements tungsten, molybdenum.
(2) Chromium content is low, most are below 10%.
(3) grain boundary strengthening elements boron content are in the O.01% or more.
(4) Most of the carbon content is more than O.1%, some of the carbon content of cobalt-based cast high-temperature alloys up to 1%. (5) Some casting high-temperature alloys are added 1% to 2% hafnium, to improve mid-temperature plasticity, and improve creep strength.
Microstructure characteristics Casting high temperature alloy microstructure (see high temperature alloy material microstructure), in addition to γ' phase, there are γ- γ' eutectic phase, primary carbide phase is also more, along the dendritic intergranular distribution, some alloys and M3B2 boride precipitation. Casting high temperature alloy heat treatment process is relatively simple, and some even do not need to heat treatment can be used.
Casting high-temperature alloys are generally smelted in a large vacuum induction furnace to produce the master alloy, and then remelted and cast into parts in a small vacuum induction furnace using the lost wax precision molding method.
Defects and elimination Casting parts will inevitably produce some microscopic sparse, can be used to reduce or eliminate the hot isostatic treatment, increasing the reliability of the parts. Casting high-temperature alloy parts have a relatively large grain size, which is detrimental to fatigue performance. The surface grain refinement method is usually used to obtain a fine crystal of the surface layer of the part.