Chemical heat treatment of steel

Chemical heat treatment is to place the steel workpiece in a certain medium, through heating and heat preservation, make some elements in the chemical medium penetrate into the surface of the workpiece, so as to change the chemical composition of the surface, so that the core and the surface have different structures and mechanical properties.

Characteristics: compared with other heat treatment, not only its structure has changed, but also its chemical composition has changed.

(I) role of chemical heat treatment

1. Strengthen the surface: improve some mechanical properties of the workpiece, such as: hardness, wear resistance, fatigue limit.

2. Protect the working surface: improve the physical and chemical properties of the workpiece, such as high temperature resistance and corrosion resistance.

(II) types of chemical heat treatment

1. Diffusion elements enable non-metallic elements to form interstitial solid solution with iron, such as carburizing, nitriding and boronizing, which will obviously increase the surface hardness and wear resistance of steel.

2. Diffusion elements enable metal elements to form replacement solid solution with iron, such as chromizing, lead infiltrating and silicon infiltrating. Chromizing can improve wear resistance and corrosion resistance, lead can increase high temperature oxidation resistance and silicon can improve acid resistance. All in all, improve the physical and chemical properties of the surface.

(III) chemical heat treatment process

1. Decomposition: the chemical medium should first decompose the active atoms;

2. Absorption: the workpiece surface absorbs the active atoms to form solid solution or compound;

3. Diffusion: the active atoms absorbed by the workpiece diffuse from the surface to the inside to form a certain thickness of diffusion layer.