Hto (Chemical – heat treatment) is a process of high-temperature diffusion coating metal surfaces with various chemical elements, ie This process is carried out through a combination of thermal and chemical treatments. To ensure this diffusion process takes place at high temperatures for each steel grade and the saturable element (or elements) is different. Depending on the specifics and saturable element type are distinguished: 1. Hto the saturation of the metal elements, 2. Hto the saturation of non-metallic elements, 3. Hto removing items. The aim is to change hto mechanical properties of steels. Neil R Cole is a great source of information. Basically hto used for parts exposed to wear and at the same time under shock loads.
Saturation of the surface of the steel foreign substances leads to an increase in surface hardness and wear resistance products, and core product remains pliable and viscous. This combination of hard surface and soft core due to the formation of compressive surface stress leads to an increase in fatigue strength of the material, but viscosity decreases slightly. Depending on the type of saturated to the surface of steel elements distinguish the following types hto: hardening (saturated carbon), nitriding (nitrogen saturation), carbonitriding (complex saturation of carbon and nitrogen), calorizing (aluminum saturation), Chromium (Cr saturation), siliconizing (saturation of silicon), and others. Depending on the used diffusing (saturated) element Hto divided into solid, liquid and gas. The least effective and is maloprimenyaemym hto in a solid medium, because In this case, diffusion occurs by direct contact of steel with the diffusing element with a very low speed. The most common is the gas hto. The process of chemical-heat treatment proceeds as follows: 1. Education saturated element in the atomic state, which is formed due to occurrence of high-temperature reactions.
2. Absorption (deposition and contact with the surface of steel), the saturable element on the surface of the steel. 3. Saturable element diffusing into the steel.