SUNSPEED Bearing shares the causes of several forms and elimination methods of the uneven forms of carbides. These defects are easy to appear in high-carbon steel and mold steel, and should be avoided as much as possible. We are engaged in offering the market with high quality bearings and giving our customers practical support. To get more about us,please click here.
Carbides in high-carbon steel and high-carbon alloy steel often show unevenness. This unevenness is mainly manifested as carbide liquid analysis, carbide band-shaped and carbide mesh.
1 carbide solution analysis
Carbonized liquid analysis is a sub-stabilized Crystal Lailin in the liquid-phase carbon and alloy elements. During the heat processing, the carbide liquid analysis is broken into irregular pieces, and it is distributed in a chain or strip in the direction of the pressure delay, as shown in Figure 1.
Carbonized liquid analysis is due to the comprehensive result of steel fluid overheating, high pouring temperature, too slow steel cooler cooling, and chromium reduction in the maximum solid solution of carbon. It is generally believed that the carbide liquid analysis belongs to the carbide of the triangular crystal, and its hardness is extremely high. Its existence will cause the bearing to produce quenching cracks during thermal treatment. During the use process The liquid analysis of carbides can cause fatigue cracks and reduce fatigue life.
2 carbides
The carbide zone is the crystallization bias (bias analysis) formed by the steel liquid in the solidification process, causing the carbon high and low concentration of different analytical bands.
After the rolling extension, a large amount of excess overcover secondary carbides are prevented from high concentrations during the cooling process, thereby forming a carbide band tissue of black and white (high and low carbon), as shown in Figure 2.
The final solidification zone of the steel ingot or casting is rich in a large amount of alloying elements, namely sulfur, phosphorus and other impurities. It is the most gathering area for non -metal miscellaneous materials and carbides. The total amount and distribution status of carbides during the cooling process depends mainly on the degree of primitive analysis. With the intensification of carbonized band analysis, the sensitivity of the cracking of thermal treatment increases, and the microscopic hardness difference between high and low carbon belt increases, affecting the fatigue life of contact. Band-shaped carbides can be evaluated based on GB/T 1299 "Alloy Tool Steel".
3 carbide mesh
The carbide mesh is an excess carbide distributed in the network-shaped distribution of the cyber-shaped distribution of the borders of the co-analyzed steel. It is related to the chemical composition and bias of the steel. The uneven band is also a factor that affects the service life of the part. The carbide mesh can be evaluated based on GB/T 1298 "Carbon Tool Steel".
Figure 3 shows the microstrip tissue completely annealing the T12 steel. The dark sheet layer in the figure is pearly body, and the white mesh around it is a secondary carbon hypacette.
In summary, the uneven carbides in high-carbon steel and high-carbon high-alloy steel are essentially the result of the macro and micro -analysis of the steel liquid during the cooling process. Among the three, carbide solution is the most harmful. Although carbide liquid analysis is completely different from non -metallic mixed objects in essence, as far as its harmfulness is concerned, carbide liquid analysis can be combined into the scope of the tests of miscellaneous objects. To eliminate carbide solution, in essence, it is necessary to reduce the degree of analysis of branches in the steel, so that the most serious areas in the steel can not form common crystal -lilars.
4 Bearing steel mesh carbide formation and harm
The mesh carbide was formed in the Austrian body crystal world during the high-end rolling temperature and slow cold after rolling. Once the mesh carbides are formed, especially when the carbide is completely surrounded by the crystal world and is wide, it will have bad consequences during future processing and use. First of all, the severe carbonized mesh in the bearing steel cannot be completely eliminated in the future ballization annealing. In this way, grinding cracks can be easily produced during the grinding process of bearing processing, also known as cracking; second, if carbides The mesh is serious, not only the ballization annealing cannot be eliminated, but even in the future quenching organization. In this case, it is easy to cause quenching cracks. The mesh will also easily cause fatigue cracks.
When there is a carbide mesh tissue in the bearing steel, the brittleness of the steel will be increased and the fatigue life of the bearing parts will be reduced. Therefore, no serious carbide mesh tissue is allowed in the bearing steel tissue in the use state.
5 How to eliminate carbonized mesh
High-carbon chromium bearing steel has a high carbon content, and contains a certain amount of carbides to form elements. During the solidification process, these elements are prone to bias, resulting in uneven distribution of carbides in steel.
The measures taken to eliminate carbide mesh during the production process are as follows:
1) When smelting high -carbon chromium bearing steel, the content of carbon and chromium is strictly controlled to meet the requirements.
2) During the coagulation process of the steel ingot, the branches of the steel in the steel should be reduced and the level of the carbide should be reduced.
3) Control the low-rolling temperature and speed up the cooling speed after rolling to reduce the carbide level of bearing steel.
With the continuous development of rolling technology, the method of cooling after rolling has gradually been widely used, that is, on the basis of reducing the final rolling temperature, wind-cooling, water spraying, or cooling the steel through the water sink after rolling. Practice has proved that when the final rolling temperature is less than 850 ° C, the Austrian body crystal is small, and it is cooled after rolling, which prevents the precipitation of internet-shaped carbides in the Aorer crystal world. It is better to eliminate mesh carbides?