Product Description
Strictly speaking, only tangent method is used to compare the principle of bearing science, because the deviation from pure thermal expansion is caused by the volume effect caused by the change of bearing shape, but this method is easy to produce subjective visual error, so it is necessary to use high-precision thermal expansion instrument to reduce the experimental error. The critical point determined by the value method deviates from the true value, but it is easy to judge the value point, so this method is often used to compare and analyze the influencing factors of the phase transition temperature of bearing materials.
2.5.2 study the heating transition of bearings.
Austenitizing is a necessary process in the heat treatment of bearing steel materials. However, compared with the research on austenite decomposition, the research on austenitizing process is still less, and the mechanical properties of bearing steel materials are mainly determined by the cooling products after austenitizing, so austenitizing conditions have a great influence on the final microstructure and mechanical properties of steel materials. It also has a great influence on the finished products of bearings.
Heat conduction of bearing materials.
3.1 Overview
When there is a temperature difference between the two ends of the bearing material, the phenomenon that heat is automatically transferred from the hot end to the cold end is called heat conduction. Heat conduction is a form of heat transfer, and the heat transfer ability of matter can be characterized by thermal conductivity.
The carriers of heat conduction in bearing solids are electrons, bearing vibration waves and electromagnetic radiation, and the total heat conduction is the superposition of each carrier. There are a lot of free electrons in the bearing and its weight is light, which can quickly realize heat transfer.
Measuring the cooling transition curve of bearing steel.
The decomposition characteristics of undercooled austenite with temperature and time can be described by isothermal transformation curve (TTT diagram) and continuous cooling transformation curve (CCT diagram), which are very important for the industrial application of bearing steel in new steel. Magnetic method and expansion method are often used in TTT curve, while expansion method is mainly used in CCT curve. Compared with the classical metallographic methods, these physical methods greatly reduce the workload and have high data accuracy.
According to the expansion characteristics and phase transformation process of bearing steel, volume expansion will occur when undercooled austenite is transformed into pearlite, bainite or martensite, and the more the transformation amount, the greater the volume effect, so it is easy to calculate the decomposition degree of undercooled austenite by expansion method. In detail, TTT curve represents the time-varying curve of expansion amount of samples measured by dilatometer during isothermal process at different temperatures. CCT curve represents the relationship between the microstructure transformation and time in the continuous cooling process of steel, and the transformation amount of each microstructure can be obtained by using the lever rule. Since the austenite transformation amount is linearly related to its expansion amount, the expansion curve can be directly regarded as the relationship between transformation amount and time, that is, the isothermal transformation kinetic curve.
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