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Factors affecting bearing life
Source: China Bearing Network Time: 2013-01-01
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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 obtain the best matrix resistance against 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, the effect of Ar content on the hardness and touch fatigue life of GCr15 steel after quenching low temperature tempering is studied. 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 attack stress gathers and breaks; 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 Gathering cracks; then reducing patience and fatigue resistance. Quenching of undissolved carbides in addition to their own effects on the function of steel; also affecting the carbon content and Ar content and dispersion of quenched martensite; Additional effects of functional seizures. In order to remind the effect of undissolved carbides on the function; choose steels with different carbon content; after quenching, the martensite carbon content is the same as the Ar content and the undissolved carbide content is different; After tempering at 150 ° 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 function of the data; scale, tracing, and scattering also affect the function of the data function. In order to prevent the damage of undissolved carbides in the bearing steel; the demand for undissolved carbides is small (less quantity), Ç”å½ç¼§.(16)龋ù笮â€èˆœ 嗖詈 .. 曳 龋 龋 (16) 玻 è“Ÿé”猿 è“Ÿé”猿 è“Ÿé”猿 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 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 pressure The increase of the stress; the fatigue strength of the steel increases accordingly; when the residual internal stress is the tensile stress; the fatigue strength of the steel is decreased. This is because the fatigue failure of the part is exhibited when the excessive tensile stress is received; When there is a large compressive stress remaining; it will offset the tensile stress of the equality value; and the practice of the steel accepts the tensile stress value minus. 蛊@颓慷燃拗翟龈撸,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 惺艿ç¦Î±Î³é£¨ 龃螅 龃螅 蛊 颓慷 颓慷 颓慷 颓慷 颓慷 颓慷 颓慷 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 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承 轴承One of the ways to use the number of life (of course, excessive residual stress can lead to deformation or even cracking of the part; 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 even can be beneficial, so it can be manipulated from wide.
2 The manipulation of the data elements affecting the bearing life is in order to make the above-mentioned data elements affecting the bearing life in the best condition; the primary requirement is to control the original arrangement of the steel before quenching; the technical methods that can be adopted are: high temperature (1050 ° C) austenite Isothermal normalizing to 630 ° C isothermal normalizing to obtain pseudo-eutectoid fine pearlite arrangement; perhaps cold to 420 ° C isothermal treatment; obtaining bainite arrangement. Can also use wrought waste heat blast annealing; obtain fine-grained pearlite arrangement; Ensure that the carbides in the steel are finely and evenly distributed. The original arrangement of this condition is in the austenitization of quenching heating; in addition to the carbides dissolved in the austenite; the undissolved carbides will be aggregated into fine particles.
When the original arrangement in the steel is punctual; the carbon content of the quenched martensite (ie the austenite carbon content after quenching heating), the amount of retained austenite and the amount of undissolved carbide depend primarily on the quenching heating temperature and persistence. Time; followed by quenching heating temperature increase (time must be); steel in the amount of undissolved carbide reduction (hardened martensite carbon content increased), the amount of retained austenite increased; hardness is first added with the increase of quenching temperature; arrival The peak value then decreases with the increase of temperature. When the quenching heating temperature is punctual; the extension of the austenitizing moment; the reduction of the amount of undissolved carbide; the increase of the amount of retained austenite; the increase of hardness; This trend slows down. When the carbides in the original arrangement are fine; because the carbides are easily dissolved into austenite; the hardness peak after quenching is shifted to a lower temperature and appears at a shorter austenitizing moment.
In summary, the undissolved carbides of GCrl5 steel after quenching are about 7%; the retained austenite is about 9% (the uniform carbon content of cryptocrystalline martensite is about 0.55%) is the best arrangement. And; when the original arrangement of fine carbides. Zhi Ji Ren Bao Hui Kang Kang fresh éŠ å— South halo (19) 橹槌墒 挥 诨竦 诨竦 诨竦 诨竦 诨竦 Ï Ï Ï åŸ½ 埽 埽 埽 埽 埽 埽 埽 埽倜. It should be pointed out; the original arrangement with finely dispersed carbides; the quenching heating and heat preservation; the undissolved fine carbides will gather and grow; roughen them. Thus; the quenching heating moment of the bearing parts with such original arrangement Should not be too long; use the rapid heating austenitizing quenching process; will achieve higher inductive mechanical function.
In order to quench the bearing parts after quenching and tempering, the surface has a large compressive stress; the carburizing or nitriding atmosphere can be introduced during the quenching heating; the external carburizing or nitriding is performed in a short time. The practice of carbon is not high; it is much lower than the equilibrium concentration shown on the phase diagram; thus it can absorb carbon (or nitrogen). When austenite is rich in higher carbon or nitrogen; its Ms decreases; when quenching The surface layer has a martensite transformation after the inner layer and the core; a large residual compressive stress is exerted. The GCrl5 steel is heated and quenched in a carburizing atmosphere and a non-carburizing atmosphere (all subjected to low temperature tempering), and the touch fatigue test is performed. It can be seen that the life of external carburizing is 1.5 times higher than that of non-carburizing. The reason is that the surface of carburized parts has large residual compressive stress.
3 The main data elements and the degree of control that affect the service life of high carbon chromium steel rolling bearing parts are:
.1) The carbide requirements in the original arrangement of steel before quenching are fine and diffuse. High temperature austenitizing 630 ° C, or 420 ° C high temperature can also be used, which can also be completed by wrought waste heat blast annealing process.
.2) After quenching of GCr15 steel; microscopic arrangement of undissolved carbides with a uniform carbon content of about 0.55% cryptocrystalline martensite, about 9% Ar and about 7% in a uniform and round state This microscopic arrangement can be manipulated using quenching heating temperatures and timing.
.3) After the quenching of the parts, the residual surface has a large compressive stress after the tempering; this will contribute to the progress of the fatigue resistance. The treatment process of carburizing or nitriding in a short time at the time of quenching heating may be selected; There is a large compressive stress.
.4) Making steel for bearing parts; demand has high purity; the first is to reduce the content of O2, N2, P, oxide and phosphide. Optional electroslag remelting; vacuum training and other technical methods to make data oxygen The quantity ≤ 15PPM is suitable.
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