Rolling bearing steel heat treatment methods
Heat Treatment generally includes heating, heat preservation, cooling three processes, sometimes only two processes of heating and cooling. The process is convergence with each other and can not be interrupted.
Heating is an important step of heat treatment. There are many ways for rolling steel heat heating process, the first is the use of charcoal and coal as a heat source, and then the application of liquid and gaseous fuels. Application of electric heating is easy to control, and no environmental pollution. With these heat source may be directly heated, can also molten salt or rolling bearing steel, as well as the floating particles indirect heating.
When the rolling bearing steel is heated, the work piece is exposed to the air, often oxidation, decarbonization (ie, reduce the carbon content of the steel parts of the surface), which parts of the surface properties after heat treatment have a very negative impact. Thus the rolling bearing steel should normally be in a controlled atmosphere or protective atmosphere, molten salt and vacuum heating, paint or packaging methods can also be used to protect heating.
The heating temperature is one of the important parameters of the heat treatment process to select and control the heating temperature, the heat treatment is to ensure the quality of the main issues. The heating temperature to be treated with the purpose of rolling bearing steel material and heat treatment vary, but are generally heated to a temperature above the phase transition, in order to obtain tissue needed. Further change will take some time, so when the rolling bearing steel surface to reach the required heating temperature, must at this temperature for a certain time, so that the temperature inside and outside the same, so the micro structure of the transition is completed, this time called the incubation period. When using high energy-density heating and surface heat treatment, heating fast, generally no holding time or the holding time is very short, and the holding time of chemical treatment is often longer.
Also a lack of cooling heat treatment process step is not available, because the process of cooling methods differ, mainly for controlling the cooling rate. General annealing cooling slowest cooling faster normalizing, quenching cooling faster. But also because of different grades have different requirements, such as empty hard steel can be used as cooling rate normalizing hardened.
Rolling steel heat treatment process can be divided into the overall heat treatment, surface heat treatment, local heat treatment and chemical heat treatment. Depending on the heating medium, heating temperature and cooling methods, each category can be divided into a number of different heat treatment process. The same kind of rolling bearing steel with different heat treatment process, available in different organizations, so as to have different properties. Steel is the most widely used industrial rolling bearing steel, and the steel micro structure is also the most complex, and therefore a wide range of steel heat treatment process.
Overall heat treatment of the work piece as a whole is heated and then cooled at a rate appropriate to change the rolling bearing steel heat treatment process its overall mechanical properties. Roughly the overall heat treatment ofsteel annealing, normalizing, quenching and tempering four basic processes.