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two. New technology for thermal processing of bearing data The current specification for aero-engine bearings is high-speed steel with good fatigue strength at temperatures up to 300 ° C. However, when the bearings are operated at high speed or super high speed, the crack resistance of this data, Hardness and resistance to cracking and expansion are not satisfactory. In order to improve data arrangement; improve data function; satisfied with the demand for bearing development of aircraft engine skills; SKF has studied three different bearing materials; Tests have shown the interrelationship between the data scheduling functions. These three types of information are: a cast hot rolled steel (M2); a powder metallurgical data (ASP23) and a carbon content of 0.65 (percent by weight), High-speed steel derived materials with low alloying elements. /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
1. Cracking resistance is in aircraft engines; because the bearing speed is extremely high; and thus strong centrifugal force occurs; therefore, the cracking resistance of the bearing data is particularly important.
In hardened high-speed steel; the cracking process involves the appearance of cracks caused by the opening carbide cracks; or the depolymerization force formed by the martensite matrix arrangement in the elastic region at the end of the crack. SKF has examined these three kinds of data; Follow the progress of data tolerance; the hardness of the data is reduced; and the quenching temperature is lowered. This is mainly due to the lower martensite content and the improvement of the elasticity of the half-base matrix arrangement. Some of the carbides in the steel are hardened by lower temperatures; They choose the impact of cracking resistance to helium. In the case of low hardness; because of the reduction of data yield strength; the difference between the low hardness steel cracking depends on the detailed dispersion of carbide; in the case of high hardness; The volume occupied by carbides is reduced; the voids between carbides are about the same as the size of elasticity; at this moment; cracking resistance is no longer primarily dependent on the dispersion of carbides; and the matrix arrangement is also minimally elastic. Therefore, the cracking of these three kinds of data The resistance value is set at 750 HV and higher hardness. Under conditions of low hardness and large elastic area; after advanced carbide diameter or constant hardness Save carbide ratio can improve the crack resistance and;. When the hardness progress; crack resistance value change rate will be reduced when the elastic region and the small gap between the large carbides; The base arranged on the greatest impact crack resistance.
In general, the cracking resistance of high-speed steel depends mainly on the elasticity of the matrix arrangement; and the elasticity of the matrix arrangement is largely influenced by the martensite arrangement and its carbon content. SKF researchers pointed out that it is of course impossible to eliminate the beginning. The influence of other factors such as carbide, residual stress, retained austenite and carbides separated from martensite in tempering on cracking resistance.
2. Weary crack development process
SKF researchers divided the development of the crack into the following periods:
During the first period; the crack opening is enlarged. Although the critical stress intensity of high speed steel can be modified by heat treatment, the absolute value of the change is not large; between 3~5MPa/m2.
The second period; crack enlargement. The crack propagation speed of high-speed steel is similar; as in the case of 10Mpa/m2; about 5×10-6mm/cycle. However, the steel with higher resistance can slow the crack expansion.
During the third period; the crack is agile. When the crack reaches this period; the bearing will immediately fail.
3. The external surface treatment process is based on the analysis of cracking resistance and other links and the development of data cracks; we can see that the high dn value and the presence of circumferential stress; the surface treatment of high speed steel and the hardening of high carbon steel with low carbon content The change of appearance depth has important meaning. To this end, SKF has developed a data surface treatment process; it can enhance the appearance hardness; and compressive stress occurs. The data processed by the appearance has the following characteristics: better fatigue crack resistance; second During the period; the crack propagation rate is lower and the crack resistance value of the core data is higher than that of the lack of quenching or low carbon content.
The external treatment method developed by SKF includes:
(1) Partial heat treatment of quenching general high-speed steel by laser, electron beam or induction quenching; to obtain the outer hardened layer. The demand here indicates that the lack of quenching is to improve the cracking resistance.
(2) Using a chemical heat treatment method to obtain a hardened outer layer. This method involves infiltrating carbon or nitrogen into the general high-speed steel micro-arrangement; or slightly changing the carbon content.
In general, SKF believes that when formulating new steel analysis methods or improving heat treatment processes for the next generation of aero engines, it can obtain appropriate benefits from the effects of external disposal. It can be said; if it is developed by heat treatment Micro-arrangement and related mechanical properties are thoroughly understood by everyone; quenched steel and high-speed steel will be fully utilized in aerospace engine bearings.
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SKF aviation rolling bearing skills (2)
Source: China Bearing Network Time: 2017-11-04