A group of structural steel alloys for heat-chemical treatment, which after carburizing or cyaniding, and heat treatment are expected to obtain a hard and wear-resistant abrasive surface of the product while maintaining sufficiently high core ductility. For this reason, they are most often used and are referred to as steel for gears.

Thermo-chemical treatment of steel for carburizing

The hardness and abrasion-resistant surface is obtained by saturating it with carbon to a depth of 0.8 - 1.5mm and heat treatment, which is followed by hardening and tempering. Steels of this sub-group are characterized by a relatively low carbon content in the chemical composition - up to 0.25% compared to other alloy steel (eg. steel for improvement). ulepszania).

>With respect to other surface hardening methods, such as nitriding, cyanation, or surface hardening, in regard to the carburized surface of the product, the properties and hardness of the material of the core are decreased. However, in order to prevent the formation of an isotactic layer, it is advisable to use mildly effective materials for carburizing the material.

The carburization process depending on the grade of steel is carried out in the temperature range of about 880 - 1050 ℃. Subsequent hardening process for the core is 880-920 ℃, which can be done immediately after carburizing. Hardening of carburized layers takes place in a temperature range of 780-820 ℃. Tempering is carried out at temperatures of about 150-200 ℃.

Chemical composition

The most common alloying additives in carburizing steels are Chromium in the range of 0.7-2.1% of concentration, Manganese - Mn, Molybdenum - Mo, and Nickel - Ni. In addition to chromium, elements that improve and prevent degradation of properties are added, such as Titanium - Ti, Vanadium - V, Tungsten - W, and Boron - B. Chromium, nickel and manganese increase the toughness of the steel and the ductility of the core. Boron added to chromium-manganese steel increases the ductility of the heat-treated material layer. All carburizing steels are produced as killed steels.

Application

For smaller gear wheels and other fine components in quiet working conditions, are used chrome-manganese 14HG, 16HG, 20HG, and 18HGT due to lower core strength properties. Chromium steels such as 15H, 17Cr3, 20H, or 28Cr4 also exhibit the same low parameters. The addition of titanium in 18HGT grade inhibits grain growth in steels with high manganese concentrations, and allows for higher carburizing temperatures and shortens the duration of the first heat treatment step.

Chromium-manganese-molybdenum and chromium-molybdenum steels such as 14HGM, 15HGM, 18HGM, 19HM and 17HGN are used for larger components, sych as gears and shafts, which are characterized by quite high surface strength and large plasticity of the core. Among the aforementioned, in the environment exposed additionally to strong and variable overloads, and strikes, where the highest strength and ductility of the core is required, chromium-nickel grades are additionally supplemented by addition of tungsten or molybdenum as in 15HN, 12HN3A, 12H2N4A , 18H2N2, 20HN3A, 20H2N4A, 18H2N4WA, 26NiCrMo14-6, 1.6958 or 18H2N4MA.

Standards

The above mentioned alloy steels for carburizing are specified in PN-58/H-84029, PN-72/H-84035, PN-89/H-84030, and EN-EN 10084 European Norms.

Cold-rolled stripes for carburizing according to EN 10132-2
Seamless carburizing tubes according to PN-EN 10297-1
Sheets and plates for carburizing according to PN-EN 10051
Forgings and forged bars for carburizing according to PN-79/H-94500, PN-60/H-94010, PN-EN 10250-3
Rolled bars for carburizing according to PN-60/H-93013, PN-EN 10263-3
Bright and drawn bars for carburizing according to PN-EN 10277-4
Wires and wire rod for carburizing according to PN-EN 10263-3