Sherardizing is a chemical heat treatment in the ferrite state. It uses zinc powder as the raw material, and the heated steel infiltrated parts are in contact with zinc powder under vacuum conditions. After a very complicated physical and chemical reaction process, the zinc atoms evenly diffuse and penetrate into the surface of the steel parts, thus changing The composition, organization and structure of the surface layer form a dense and uniform intermetallic compound with different zinc-iron ratios on the surface of the substrate-zinc-iron alloy infiltrated layer (referred to as sherardized layer).
Sherardizing is mainly used to improve the corrosion resistance of steel materials in the atmosphere and natural water environment. The process method is similar to that of aluminizing, and it is divided into two types: dip plating type and diffusion type. The surface structure obtained by hot-dip galvanizing (also called hot-dip galvanizing, liquid zinc infiltration, etc.) is composed of a diffusion layer and a zinc coating, which belongs to the dip galvanizing type. The diffusion type sherardizing layer is completely composed of the diffusion layer and is obtained by powder sherardizing and vacuum sherardizing processes.
Hot-dip galvanizing is a chemical heat treatment process for immersing clean surface steel into molten zinc or zinc alloy melt towel to obtain the sherardizing layer. Continuous hot-dip galvanizing is used for steel strips and steel wires. Steel parts (such as section steel, fasteners and other mechanical parts) are hot-dip galvanized in batches. Here, only the process and performance of batch hot-dip galvanizing are introduced.
The powder sherardizing layer is formed by the zinc-iron diffusion reaction, and its main component is the δ phase (FeZn17). The δ phase contains 7% to 11% (mass fraction) Fe, with good compactness and toughness, corrosion resistance not lower than that of the hot-dip galvanized layer, hardness of about 250HV, and good wear resistance.
Vacuum sherardizing is also a sherardizing layer formed by the zinc-iron diffusion reaction, so the structure, performance and application range of the vacuum sherardizing layer are basically the same as powder sherardizing.