Heat resistant alloy
Heat-resistant alloy alloys, also known as high-temperature alloys, are of great significance to the industrial sector and application technology in high temperature conditions.
In general, the higher the melting point of a metallic material, the higher the temperature limit that can be used. This is because as the temperature rises, the mechanical properties of the metal material decrease significantly, and the tendency of oxidation corrosion increases accordingly. Therefore, the general metal materials can only work for a long time at 500°C-600°C. Metals that can operate at high temperatures above 700 °C are called heat-resistant alloys. "Heat-resistant" means that it maintains sufficient strength and good oxidation resistance at high temperatures.glenflange
There are two ways to improve the oxidation resistance of steel: First, alloy elements such as Cr, Si, and Al are added to the steel, or Cr, Si, and Al are alloyed on the surface of the steel. They can quickly generate a dense oxide film in an oxidizing atmosphere and adhere firmly to the surface of the steel, effectively preventing oxidation from proceeding. The second is the use of various methods to form high melting point oxides, carbides, nitrides, and other high temperature resistant coatings on the surface of steel.
There are many ways to improve the high temperature strength of steel. From the chemical point of view of structure and nature, there are roughly two main methods:glenflange
One is to increase the binding force between atoms in steel at high temperatures. Studies have shown that the binding force in metals, ie the strength of metal bonds, is mainly related to the number of unpaired electrons in the atom. From the periodic table, the VIB element metal bonds are the strongest in the same cycle. Therefore, adding Cr, Mo, W, etc. to the steel has the best effect.glenflange
The second is to add elements that can form various carbides or intermetallic compounds to strengthen the steel matrix. The carbides formed by a number of transition metals and carbon atoms belong to interstitial compounds, which, on the basis of metal bonds, again increase the composition of covalent bonds, and therefore have extremely high hardness and a high melting point. For example, adding W, Mo, V, and Nb can produce carbides such as WC, W2C, MoC, Mo2C, VC, and NbC, thereby increasing the high-temperature strength of steel.glenflange
By using the alloy method, in addition to the iron-based heat-resistant alloy, nickel-based, molybdenum-based, niobium-based, and tungsten-based heat-resistant alloys can also be obtained, which have good mechanical properties and chemical stability at high temperatures. Nickel-base alloy is the best super-heat-resistant metal material. The matrix in the structure is Ni?Cr?Co solid solution and Ni3Al metal compound. After treatment, the temperature can reach 1 000 °C to 1 100 °C.