Heat Treatment of Steel
There are three types of steel heat treatment. Such as overall heat treatment, surface heat treatment, and chemical heat treatment. According to the mediator, temperature and the way of cooling of heat treatment, every classification can be divided into several different heat treatment process.
Overall Steel Heat Treatment
Heat treat the hole steel, then cooling it at the right temperature. It can change the whole mechanical property. It includes annealing, normalizing, quenching, tempering. And the quenching and tempering are closely related. People always used together. Each part of them is indispensable.
Heat the material to make it get the appropriate temperature. According to the size and material of it to choose the right time of heat preservation. Then make it cool slowly. The purpose is to make the material get ready for quenching. Make the material internal structure get equilibrium state. Then it will get great technological properties.
The steel sample is heated to a suitable temperature and then cooling it in the air. Its influence on the material is the same as annealing. But the resulting tissue is finer. People usually use it to improve the free cutting performance of mild steel. And sometimes use it to do finally heat treatment for the material of lower request.
Heat the steel material to get the right temperature and keep it. Then make it fast cooling in the transmitter substance of water, oil, inorganic salts and etc. After quenching, steel material will become harder. But at the same time, it becomes brittle.
In order to make steel get lower brittleness. The steel after quenching is kept warm for a long time at a suitable temperature above room temperature and below 650 ° C and then cooled.
These four steps will evolve different heat treatment according to the different temperature and the way of cooling. In order to get great strength and toughness, need to do the processing of combining quenching and high-temperature tempering. Some alloy steel would form a supersaturated solid solution after quenching. Put it at the room temperature for a long time. Then its hardness, strength, electrical magnetic and etc will get improved. People call this heat treatment as aging treatment.
The way of thermomechanical treatment needs pressure processing deformation and heat treatment effectively combining. It will make the steel material get good hardness and toughness. The heat treatment performed in a vacuum atmosphere or in a vacuum is referred to as a vacuum heat treatment. It not only can prevent the steel material from being deoxidized and does not decarburize. Stay the surface of the steel smooth after treatment. Improving the performance of steel.
Surface Heat Treatment
It is the way of just only heat treats the steel surface, to change its mechanical properties of the surface. In order to just processing its surface without excessive heat being involved in the steel inside. Need to use the heat source with high energy density. It can give more heat energy to steel material per unit area. Make the surface of steel quickly get high temperature. The main methods of surface heat treat are flame quenching and induction heat treatment. The oxyacetylene, ethylene oxide and etc are the most useful heat sources.
Chemical Heat Treatment
It is to change the chemical composition, structure, properties of steel material surface. It can change the chemical composition of the surface layer of the steel material. It is a big difference between chemical heat treatment and surface heat treatment. The way of chemical heat treatment is to heat the material in a medium (gas, liquid, solid) containing carbon, nitrogen or other alloying elements for a long time. To make the carbon, nitrogen, boron and chromium elements get into its surface layer. After that, also need other heat treatments sometimes, such as quenching and tempering. Carburizing, nitriding are the main methods of chemical heat treatment.
Heat treatment is one of the most important processing for the production of machine fittings and mold base. It can control all kinds of properties of steel material. Such as wear resistance, corrosion resistance, magnetic properties and so on. Use the right heat treatment processing to the gear wheel, its useful life would longer than the general ones. By the way, adding some alloy elements to low-quality carbon steel would make it improve the properties. Then it can use to instead of some heat-resistant steel and stainless steel. And almost all of the tool steel needs to be through heat treatment before the use.
Heat treatment is one of the most effective technological skill to maximizing the potential properties of steel. The purpose of make steel been through heat treatment is to get the desired structure and properties. Truly understand the influence of heat treatment on the properties of steel. Then make an effective and right heat treatment way is really important.