The main purpose of anti-corrosion alloying is to increase resistance precision alloys to the effects of electrochemical corrosion. This is achieved by adding it to the smelted metal chromium, nickel, molybdenum, tungsten, titanium, silicon and other chemical elements. Each of these alloying additives has a certain effect on the physical and mechanical properties of steels and, depending on the mass fraction and combination with other components, changes the structures of the alloys.
Corrosion resistance characterizes the ability of a metal to resist rust when used in aggressive environments. At the same time, the rate of corrosion spread directly depends on the chemical composition of the alloy and its physical and mechanical characteristics, as well as on operating conditions (operating temperature range, mechanical loads, atmospheric factors, etc.).
Ordinary (unalloyed) metals, in the absence of a protective coating, are destroyed fairly quickly by moisture and air. However, with the introduction of alloying additives, it is possible not only to increase the corrosion resistance of the alloy, but to give it new physical and mechanical properties, such as increased strength, hardenability, reduced brittleness, heat resistance, etc.
The main alloying components that are used to increase the corrosion resistance of precision alloys are chromium and nickel. Can also be used aluminum, copper, titanium, niobium etc.
For example, steel grade 12X18H10T It belongs to high-alloyed chromium-nickel alloys and, due to the combination of the chemical elements that make up the composition, has increased resistance to corrosion. However, each of the added components only affects certain anticorrosive qualities of the metal:
In general, anticorrosive alloying can have two goals: increasing corrosion resistance or converting dangerous local corrosion into a less problematic overall one. In the first case, chemical elements such as chromium, nickel, molybdenum, silicon and copper are added; in the second case, titanium, manganese, tantalum, and niobium are added. In addition, some corrosion-resistant alloys, such as the above 12X18H10T steel, as well as 12X18N9 and 12X18H9SMR, have simultaneous protection against both types of destruction of the metal structure. This is achieved by adding several alloying components that affect different anti-corrosion properties of materials.
Metals can be alloyed in one of two ways: volumetric or superficial. In the first case, useful chemical elements are introduced into the entire volume of the alloy being melted, in the second case, only into its surface layer to a depth of no more than 1-2 mm.
The main method volumetric alloying — fusion of base metal with alloying components in crucible, induction, arc, plasma and other furnaces. However, this method may cause large losses of active chemical elements such as titanium, molybdenum, chromium, etc. To reduce the loss of useful additives, ligatures are used — various components that make the metal smelting process more efficient. In nickel alloys, aluminum, manganese are used as ligatures, zirconium or zinc.
Surface alloying provides for the diffusion saturation of the outer layer of the metal during its heat treatment (in the liquid or gas phase). There is also a solid-phase method, which consists in applying alloying components in the form of a layer of the required thickness and then melting it to form a new alloy on the surface of the base metal.
The high degree of resistance of alloy steels to various types of corrosion is due to the interaction of the added chemical elements with external factors. For example, if the alloy contains chromium or nickel, these elements react with the environment, as a result of which an oxide layer forms on the metal surface, which prevents further destruction of steel. Such a surface oxide film acts as a barrier that prevents moisture or oxygen molecules from penetrating deep into the material. At the same time, when scratched or chipped, it recovers very quickly, which prevents rust from appearing at the site of the steel surface defect.
St. Petersburg Precision Alloy Plant produces alloyed metals both in accordance with GOSTs and customer specifications. Contact us, and we will help you find the steel that will be the best solution for your project.