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Data elements affecting bearing life
Source: Bearing network time: 2017-11-11
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Early failure modes of rolling bearings; primary cracking, plastic deformation, wear, corrosion and fatigue; under normal conditions, the first is fatigue. The failure of bearing parts is in addition to the conditions of service; the hardness, strength, durability and resistance of steel are the primary. Grinding, corrosion resistance and internal stress conditions are constrained. The main connotation factors affecting these functions and conditions are as follows.
1.1 The martensite high carbon chromium steel in the quenched steel is originally arranged as granular pearlite; in the quenching low temperature tempering condition; the carbon content of the quenched martensite; significantly affects the mechanical function of the steel. The strength and the resistance are at 0. 5% or so; touch fatigue life is about 0.55%; anti-crush can be around 0.44%; when GCr15 steel quenching martensite carbon content is 0.5% to 0.56%; Obtaining the best resistance to failure can be the most inductive mechanical function.
It should be noted that the martensite obtained in this case is cryptocrystalline martensite; the measured carbon content is the uniform carbon content. In practice, the carbon content in the martensite is uneven in the microdomain. The concentration of carbon around the carbides is higher than that of the original ferrites away from the carbides; therefore, the temperature at which they start martensite transformation is different; then the growth of the martensite grains and the appearance of the microscopic shape are followed. It becomes cryptocrystalline martensite. It can prevent microcracks which are easy to appear when quenching high carbon steel; and its sub-layout is dislocation-type lath martensite with high strength and resistance. Therefore; only when high carbon steel When the medium carbon cryptocrystalline martensite is obtained during quenching, the bearing parts can achieve the best resistance to failure.
1.2 Retained austenitic high carbon chromium steel in quenched steel after normal quenching; can be rich in 8% to 20% Ar (residual austenite). Ar in bearing parts has advantages and disadvantages; It should be appropriate. Because the amount of Ar is mainly related to the austenitizing condition of quenching heating; how much it affects the carbon content of quenched martensite and the amount of undissolved carbide; it is difficult to correctly reflect the influence of Ar amount on mechanical function. For this purpose; fixed austenitic conditions; using austenite thermal stabilization treatment process; to obtain different amounts of Ar; here we studied the effect of Ar content on the hardness and touch fatigue life of GCr15 steel after quenching low temperature tempering Following the increase in austenite content; hardness and touch fatigue life are added; after reaching the peak, it decreases; but the peak Ar content is different; the hardness peak is around 17% Ar; The peak value of fatigue life is around 9%. When the experimental load is reduced, the effect of the increase in the amount of Ar on the fatigue life of the touch is reduced. This is because when the amount of Ar is small, the effect on the strength is small; The effect is more significant. The reason is the load Hours; a few deformations of Ar; both reduced the stress peak; and strengthened the deformed Ar processing and the stress-strain-induced martensitic transformation. However, if the load is large, the larger plastic deformation of Ar and the basic understanding part The stress is gathered and cracked; then the life is reduced. It should be pointed out that the beneficial effect of Ar is necessary to be stable under Ar; if it is spontaneously transformed into martensite; the resistance of steel will be drastically reduced and embrittled.
1.3 Undissolved carbides in quenched steel The quantity, trace, size and dispersion of undissolved carbides in hardened steel; affected by the chemical composition of steel and the original arrangement before quenching; and subjected to austenitizing conditions Influence; less influence on the bearing life of undissolved carbides. Carbides are hard and brittle phases; in addition to the good wear resistance; the load will cause stress (especially carbide is non-spherical) and the matrix causes stress Cracking occurs; then the resistance and fatigue resistance are reduced. The quenching of the undissolved carbide in addition to its own effect on the function of the steel; also affects the carbon content and Ar content of the quenched martensite and the dispersion; Additional effects of function. In order to remind the effect of undissolved carbides on the function; choose steel with different carbon content; after quenching, make the martensite carbon content the same as the Ar content and the undissolved carbide content is different; After tempering at 150 Â° C; because martensite contains the same amount of carbon; and the hardness is higher; therefore, a small increase in undissolved carbides has little increase in hardness; the crush load reflecting strength and resistance decreases; Gathering spirit The fatigue life of touch is significantly reduced. Therefore, excessive quenching of undissolved carbide is harmful to the inductive mechanical function and failure resistance of steel. Properly reducing the carbon content of bearing steel is one of the ways to improve the service life of the workpiece. .
Quenching of undissolved carbides has an effect on the data function; scale, tracing, and dispersion also affect the data function. In order to prevent damage to undissolved carbides in the bearing steel; less undissolved carbides are required (less quantity) Ç”å½ç¼§.(16)é¾‹Ã¹ç¬®â€èˆœèˆœå—–è©ˆå—–è©ˆ. æ›³ é¾‹ é¾‹ (16) çŽ» è“Ÿé”çŒ¿ Lè“Ÿé”çŒ¿ is endangered. It should be noted that there is a small amount of undissolved carbide after bearing steel quenching is necessary; Adhere to the wear resistance of the meet; and is also a necessary condition for obtaining fine-grained cryptocrystalline martensite.
1.4 After quenching and tempering residual stress bearing parts after quenching and low temperature tempering; still have large internal stress. Residual internal stress in parts has advantages and disadvantages. After heat treatment of steel parts; followed by residual residual compressive stress The increase of steel fatigue strength; the residual internal stress is the tensile stress; then the steel fatigue strength is reduced. This is because the fatigue failure of the part is presented in the time of receiving excessive tensile stress; When the large compressive stress remains, it will offset the tensile stress of the equal value; and the practice of the steel accepts the tensile stress value minus è›Š@é¢“æ…·ç‡ƒæ‹—ç¿Ÿé¾ˆæ’¸,ç »å¬—åŒ—ç »å¬—è–ªæ´—ç½„Î±Î£å†™åª¸ä¿åµŠæ°¤æƒºè‰¿ç¦Î±Ï… testis silly jewel value æ°–Guide food æƒºè‰¿ç¦Î±Î³é£¨ é¾ƒèž… é¾ƒèž… è›Š é¢“æ…· é¢“æ…· é¢“æ…· é¢“æ…· é¢“æ…· é¢“æ…· é¢“æ…· å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ å› è€Œ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿ è½´æ‰¿One of the methods of life (of course, excessive residual stress can lead to deformation or even cracking of parts; should be given satisfaction).
1.5 Impurity content of steel Impurities in steel contain non-metallic impurities and harmful elements (acid-soluble) content; their damage to steel function often grows with each other; for example, the higher the oxygen content; the more oxide impurities The influence of impurities in steel on mechanical function and the resistance to failure of the workpiece is related to the type, nature, quantity, size and shape of the impurities; however, it generally has the effect of reducing the tolerance, plasticity and fatigue life.
With the increase of the scale of the impurities; the fatigue strength decreases accordingly; and the tensile strength of the steel is higher; the downward trend is increased. The oxygen content in the steel is increased (the oxide noisy is increased); the tortuous fatigue and the fatigue of the touch fatigue are Under the high stress effect, it also decreases. Therefore, regarding the bearing parts operating under high stress; it is necessary to reduce the oxygen content of the steel for production. Some studies indicate that the MnS impurities in the steel; due to the shape of the ellipsoid, And it can wrap large oxides and noisy, so it has little effect on the decline of fatigue life and can also be beneficial, so it can be manipulated from wide.
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