Heat Treatment of Steel
Heat treatment of steel refers to the following: through heating, insulation, cooling methods of steel, it will improve its inside structure and get the desired performance.
The common heat treatment of steel includes two kinds: general heat treatment of steel and surface heat treatment of steel. For further detailed classification, the general heat treatment of steel can be divided into the following technologies: annealing, normalizing, quenching and tempering. The surface heat treatment of steel includes: surface quenching and chemical heat treatment of steel.
Annealing is such a technology: it will process the metal or the alloy into some certain temperature and keep a period of time, and then it will be cool slowly. It is a kind of technologies of heat treatment.
The main purpose of annealing is to classify the structure, improve its performance and reduce hardness. It will be convenient for cutting production and eliminate the inner power, improve the toughness and stable the size.
It will heat the steel parts to the stagnation temperature: over 30-50 temperature. After keeping it for some time and it will in the still air to be cooling. Its purpose is to fining the structure, improve the steel performance and get the near balance state structure. The difference between annealing and normalizing is the cooling speed of normalizing is faster.
Heating the steel part into the temperature critical point and keeping it for a period of time and then you can get the steel part cool with certain speed. The martensitic structure is got after quenching and it is a kind of unbalance structure. It has high hardness and poor toughness.
After quenching, the steel will be hard. After heating again and keeping for a period of time, the material will be cool to the indoor temperature. This is tempering technology. After tempering, the steel cannot be used directly and it must have the tempering for further application. The quenching steel has high hardness and large fragile. When you directly use it, it is easy to break. Through tempering, it will eliminate or reduce the inner power and reduce the fragility and improve the toughness. On the other side, it will adjust the quenching steel power performance and make reach the application performance of steel.
Only having the surface quenching technology of steel is called as surface quenching.
Chemical Heat Treatment:
Put the metal or alloy in some active medium with certain temperature to keep. It will make one or several elements into its surface and change the surface chemical composition, structure and performance.