Factors affecting the life of rolling mill bearings and their control methods

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Factors affecting the life of rolling mill bearings and their control methods

Source: China Bearing Network Time: 2014-10-17
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Factors affecting the life of rolling mill bearings and their control methods:
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 primary connotation factors and control methods that affect these functions and conditions:
1. Martensite in hardened steel:
When the high carbon chromium 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 around 0.5%; the fatigue life is touched At about 0.55%, the crush resistance can be around 0.44%; when the carbon content of the quenched martensite of GCr15 steel is from 0.5% to 0.56%, the most inductive mechanics can be obtained. Features.
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.
2. Retained austenite in hardened steel:
High carbon chromium steel after normal quenching; can be rich in 8% to 20% Ar (residual austenite). Ar in the bearing parts has advantages and disadvantages; in order to benefit the disadvantages; Ar content should be appropriate. Because the amount of Ar is the first and quenching heating Correlation conditions; how much it affects the carbon content of quenched martensite and the amount of undissolved carbides; it is difficult to correctly reflect the effect of Ar on mechanical function. To this end; fixed austenitic conditions; The thermal stabilization treatment process is used to obtain different amounts of Ar; the effect of Ar content on the hardness and touch fatigue life of GCr15 steel after quenching and low temperature tempering is studied. The increase of austenite content; hardness and The number of touch fatigue life is added; after reaching the peak, it decreases accordingly; but the peak Ar content is different; the hardness peak is around 17% Ar; and the touch fatigue life peak 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 reduction is small; and the toughening effect is more significant. The reason is that the load is small. ;Ar attack a few deformations; both reduction The stress peak is strengthened by the deformation of the Ar processing and the stress-strain-induced martensitic transformation. However, if the load is large, the larger plastic deformation of Ar and the partial stress of the base will occur and break. The number of life drops. 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.
3. Undissolved carbides in hardened steel:
The amount, trace, size and dispersion of undissolved carbide in hardened steel; affected by the chemical composition of steel and the original arrangement before quenching; also affected by austenitizing conditions; the bearing life of undissolved carbide The impact of the study is less. The carbide is a hard and brittle phase; in addition to the good wear resistance; the load will cause cracks (especially the carbide is non-spherical) and the matrix will cause stress to gather; then it will reduce the tolerance and Exhaustive resistance. Quenching of undissolved carbides not only affects the function of steel itself; it also affects the carbon content and Ar content and dispersion of quenched martensite; then it has an additional effect on the function of steel. To remind undissolved carbides The effect on the function; the steel with different carbon content is selected; after the 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 of martensite The carbon content is the same; and the hardness is higher; therefore, the small increase of undissolved carbides has little increase in hardness; the crushing load reflecting strength and resistance is decreased; the sensitivity of touch-sensitive fatigue is significant. under Therefore, excessive quenching of undissolved carbides is detrimental to the inductive mechanical function and failure resistance of steel. Properly reducing the carbon content of bearing steel is one of the methods 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) ǔ叽缧.(16)龋ù笮”舜舜嗖詈嗖詈. 曳 龋 龋 (16) 玻 蓟锝猿 L蓟锝猿 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.
4. Residual stress after quenching and tempering:
The bearing parts are quenched and tempered at low temperature; still have large internal stress. The residual internal stress in the parts has advantages and disadvantages. After the heat treatment of the steel parts; the residual compressive stress increases with the appearance; the fatigue strength of the steel follows Increase; when the internal stress of the external surface is tensile stress; the fatigue strength of the steel is reduced. This is because the fatigue failure of the part is presented when the excessive tensile stress is received; when the external compressive stress remains, it will offset the equality. The value of the tensile stress; and the practice of the steel to accept the tensile stress value minus. 蛊 @颓慷 拗翟龈撸 拗翟龈撸 砻嬗 砻嬗 砻嬗 砻嬗 罄 罄 罄 罄 Σ Σ Σ 嵊氤惺艿睦 嵊氤惺艿睦 嵊氤惺艿睦 υ υ υ υ υ υ υ υ 佣 佣 佣The 惺艿睦αγ飨 龃螅 龃螅 龃螅 颓慷 颓慷 颓慷 颓慷 颓慷 颓慷 颓慷 颓慷 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 因而 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The residual stress can cause deformation or even cracking of the part; it should be given satisfaction).
5. Steel impurity content:
Impurities in steel contain non-metallic inclusions and harmful elements (acid-soluble) content; their damage to steel function tends to grow with each other; for example, the higher the oxygen content; the more oxide impurities; the mechanical properties of impurities in steel The effect of the resistance to failure of the part is related to the type, nature, quantity, size and shape of the impurity; 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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