Foreign mechanical occupation bearing heat disposal method
2024-01-17 02:07:07
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Foreign mechanical occupation bearing heat disposal method
Source: China Bearing Network Time: 2018-01-27
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(1) Sanitary heat treatment Wastewater, waste gas, waste salt, dust, noise and electromagnetic radiation, which are produced by heat treatment, will pollute the environment. Disposal of environmental pollution problems of heat treatment; implementation of sanitary heat treatment (or green heat treatment) Disposal) is one of the directions for the development of heat treatment skills in developed countries. In order to reduce emissions of SO2, CO, CO2, dust and cinders, coal has been used as a fuel; the use of heavy oil is also less and less; Natural gas is still the most ideal fuel. The waste heat application of the incinerator has reached a high level; the optimization of the incinerator layout and the strict control of the air-fuel ratio ensure the rational incineration; the NOx and CO are minimized. Limit, use gas carburizing, carbonitriding and vacuum heat treatment skills instead of salt bath disposal to reduce the pollution of waste water and CN-toxic substances to water sources, use water-soluble quenching oil instead of some quenching oil; use biodegradable Vegetable oil replaces some mineral oil to reduce oil pollution.
(2) Fine heat treatment Fine heat treatment has two aspects: on the one hand, according to the application requirements of the parts, data, layout scale; using physical metallurgy common sense and leading computer simulation and detection skills; optimizing process parameters; The function or the maximum limit to carry forward the potential of the data, on the other hand is to ensure the stability of the optimization process; the quality of the finished product is very disproportionate.
(3) Energy-saving heat treatment Scientific production and power management are the most promising factors for the useful use of power; establishing a professional heat treatment plant to ensure full-load production and abundant development of equipment can be the selection of scientific management. Priority is given to selecting a power, using waste heat and waste heat, and selecting a process with low energy consumption and short cycle to replace the long cycle and high energy consumption process.
(4) Less oxidation-free heat treatment is heated by a controlled atmosphere heating instead of an oxidizing atmosphere to control the carbon potential and nitrogen potential in a controlled atmosphere; the function of the parts after heat treatment is advanced; the disadvantages of heat treatment such as decarburization, cracking, etc. Reduction; reduction of finishing allowance after heat treatment; advancement of data utilization rate and machining power. Vacuum heating gas quenching, vacuum or low pressure carburizing, nitriding, nitrocarburizing and boronizing can significantly improve quality Reduce distortion and advance life.
The thermal handling quality of bearing parts is the most severe in the entire mechanical profession. The thermal treatment of bearings has made great progress in the past 20 years; the first table is now the following aspects: the discussion of the basic theory of heat treatment, heat treatment Research on process and application skills, development of new heat treatment equipment and related skills.
1. The spheroidizing annealing of the annealed high carbon chromium bearing steel of high carbon chromium bearing steel is to obtain the arrangement of fine, small, uniform and round carbide particles evenly distributed on the ferrite matrix; for the future cold working and the end quenching Preparation of fire arrangement. The traditional spheroidizing annealing process is carried out at a temperature slightly higher than Ac1 (such as GCr15 of 780~810 °C) and then slowly cooled (25 °C / h) to 650 ° C below the furnace air cooling. Long treatment time (20h or more) [1]; and the carbide particles are not uniform after annealing; affect the future cold processing and the end quenching and tempering arrangement and function. After; according to the transformation characteristics of supercooled austenite; develop isothermal ball Annealing process: after heating, it is cooled to a temperature range below Ar1 (690~720 °C) for isothermal; in the isothermal process, the transformation of austenite to ferrite and carbide is completed; after the completion of the transformation, it can be directly discharged. Air cooling. The strength of the process is the time to save heat (the whole process is about 12~18h), and the carbides are finely uniform in the arrangement after disposal. Another time-saving process is repeated spheroidizing annealing: the first heating to 810 After °C, cool to 650 ° C After heated to 790 deg.] C and then cooled to 650 ℃ cooled baked in time, although the process can save the bound; but the process operation is more complex.
2. Martensitic quenching and tempering of high carbon chromium bearing steel
2.1 Conventional martensite quenching and tempering arrangement and function for nearly 20 years; the conventional high carbon chromium bearing steel martensite quenching and tempering process is mainly divided into two aspects: one is the quenching and tempering process parameters Influence on arrangement and function; such as arrangement change during quenching and tempering, differentiation of retained austenite, tolerance and fatigue after quenching and tempering [2~10], on the other hand, process function of quenching and tempering Such as the influence of quenching conditions on scale and deformation, dimensional stability, etc. [11~13]. The arrangement after conventional martensite quenching is martensite, residual austenite and undissolved (residual) carbide composition. The shape of martensite can be divided into two categories: under a metallographic microscope (expansion multiple is usually less than 1000 times); martensite can be divided into two types: lath martensite and flaky martensite. Usually, after quenching, it is a mixed arrangement of slats and flake martensite; or a central shape between the two, jujube nucleus martensite (bearing occupational so-called cryptocrystalline martensite, crystalline martensite) ), under high power electron microscope; its sub-layout can be divided into dislocation entanglement and twinning. Its detailed arrangement The shape depends mainly on the carbon content of the matrix; the higher the austenite temperature; the less stable the original arrangement; the higher the carbon content of the austenite matrix; the more retained austenite in the post-quench arrangement; the more flaky martensite More; the larger the scale; the greater the proportion of twins in the sub-layout; and it is easy to form quenching microcracks. Usually; the carbon content of the matrix is ​​less than 0.3%; the martensite is the main board of dislocation sub-layout. Martensite, the carbon content of the matrix is ​​higher than 0.6%; martensite is a sheet of martensite with dislocation and twin mixed sub-layout, the matrix carbon content is 0.75%; Large flake martensite in the middle ridge; and the lamellar martensite grows with microcracks at the impact of each other [8]. Together with this; advance with austenitizing temperature; hardness after quenching advances; The resistance is decreased; however, if the austenitizing temperature is too high, the hardness decreases due to the excess austenite remaining after quenching. The content of retained austenite in the arrangement after the conventional martensite quenching is usually 6~15%; The body is a soft sub-solid phase; under certain conditions (such as tempering, natural aging or the use of parts); its instability The result is differentiation of martensite or bainite. The result of the differentiation is the hardness of the part; the resistance is reduced; the scale change affects the dimensional accuracy of the part and even the normal operation. The bearing parts with higher requirements on the scale accuracy; The less austenite, the better; if quenching, make up for water cooling or cryogenic treatment; use higher temperature tempering [12~14]. However, the retained austenite can advance resistance and crack expansion resistance; under certain conditions The remaining austenite on the surface of the workpiece can also reduce the concentration of touch stress; the fatigue life of the forward bearing; in this case, the necessary method is adopted in the process and the composition of the data to preserve the necessary amount of retained austenite and advance Its stability; such as the participation of austenite stability elements Si, Mn, for stability and disposal [15,16].
2.2 Conventional martensite quenching and tempering process practice High carbon chromium bearing steel Martensitic quenching and tempering: heating the bearing parts to 830~860 °C; quenching in oil; then low temperature tempering. The mechanical function after tempering is related to the original arrangement and quenching process before quenching; it also depends largely on the tempering temperature and time. With the increase of tempering temperature and the extension of holding time; the hardness decreases; the strength and the resistance advance The suitable tempering process can be selected according to the operation requirements of the parts: GCr15 steel bearing parts: 150~180°C, GCr15SiMn steel bearing parts: 170~190°C. For parts with special requirements or before tempering with higher temperature The operating temperature of the inlet bearing; or the cold treatment of -50 to -78 °C between quenching and tempering to achieve dimensional stability of the forward bearing; or martensitic quenching to stabilize the remaining austenite to achieve high dimensional stability Sexuality and high tolerance. Many experts have studied the transformation in the heating process [2; 7~9, 17]; such as the composition of austenite, the recrystallization of austenite, the dispersion and application of residual carbides. The non-spheroidal arrangement is used as the original arrangement. Lowisch et al [3;8] studied the mechanical function of the bearing steel 100Cr6 after austenitizing twice: first; austenitizing at 1050 °C and cooling to 550 °C for air cooling; obtaining uniform fines Pearlite; followed by secondary austenitization and quenching at 850 ° C; after quenching, the scale of martensite and carbide is fine, the carbon content of martensite matrix and residual austenite content are higher; Higher temperature tempering causes austenite to differentiate; many fine carbides are separated in martensite; reduced quenching stress; advancing hardness, strong tolerance and bearing bearing capacity. Under the effect of touch stress; Further research is needed; however, it can be estimated that the touch fatigue function should be better than the conventional quenching. Sakai Jiuyu et al [7] studied the microstructure and mechanical function of SUJ2 bearing steel after cyclic heat treatment: first heated to 1000 ° C heat preservation 0. 5h to make the spheroidal carbide solid solution; then; pre-cooled to 850 ° C quenching oil. Then repeat 1 to 10 times from the rapid heating to 750 ° C, 1 minute heat preservation, oil cooling to room temperature thermal cycle; Speed ​​heating to 680 ° C for 5 min oil cooling. At this moment Add fine carbides to ultrafine ferrite (ferrite grain size less than 2μm, carbide less than 0.2μm); superplasticity at 710°C (crack elongation can reach 500%); This feature is used for the warm processing of bearing parts. Finally, heating to 800 ° C to maintain the quenching oil and tempering at 160 ° C. After this treatment; touch fatigue life L10 is much larger than the conventional treatment; its failure method is by convention The early failure type of the treatment becomes the wear failure type. The bearing steel is austenitized at 820 °C and then subjected to short-time grading isothermal air cooling at 250 ° C; followed by tempering at 180 ° C; the carbon concentration in the martensite after quenching can be dispersed. More uniform; impact resistance doubles than conventional quenching and tempering. Thus; Ð’. Ð’. БÐЛОЗЕРОВ et al. proposed that the uniformity of carbon concentration of martensite can be used as a quality standard for heat treatment parts [6].
2.3. Martensite quenching and tempering deformation and dimensional stability Martensite quenching and tempering; because of the uneven cooling of parts of the parts; inevitably presenting thermal stress and arranging stress and causing deformation of the part. Quenching back The deformation of the part after fire (including scale changes and shape changes) is affected by many factors; it is a proper messy problem, such as the shape and scale of the part, the uniformity of the original arrangement, and the roughing condition before quenching (the amount of feed during turning) The size of the machine, the residual stress of machining, etc.), the heating rate and temperature during quenching, the placement method of the workpiece, the oil inlet method, the characteristics of the quenching medium and the circulation method, and the temperature of the medium all affect the deformation of the part. This has been studied a lot; many methods for manipulating deformation have been proposed; such as rotary quenching, die quenching, oil handling methods for controlling parts, etc. [11,13;18]. The study by Beck et al. When the transition temperature to the jubilant period is too high; the large cold speed and the large thermal stress cause the austenite attack at the low yield point to deform and cause distortion of the part. Lübben et al. The oil immersion between the parts or parts is uneven; especially when new oil is used, it is easier to present this scene. Tensi et al. think that the cooling rate at the Ms point is decisive for the deformation; the low temperature is selected at the Ms point and below. Speed ​​can reduce deformation. Volkmuth et al. [13] systematically studied the quenching medium (including oil and salt. â”’ 沧 沧 鲎 鲎 鲎 谕馊 慊鸨湫 慊鸨湫 慊鸨湫 慊鸨湫 慊鸨湫 慊鸨湫 慊鸨湫. The results indicate: because the cooling method is not the same; ferrule The diameter will have a different degree of "increasing"; and with the advancement of the medium temperature; the diameter of the ferrule at the end of the diameter tends to be common; that is, the "horn" deformation is reduced. The 惶 Φ Φ è€ è€ è€ è€ç—ª èš± èš± èš± ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ d d d d ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ ä¾—æ¶ âˆ®è°•é¦Š ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊 ∮谕馊Effect [12,14]: carbon migration from martensite lattice constitutes ε-carbide, residual austenite differentiation and composition of Fe3C; three transformations are superimposed on each other. Between 50 and 120 °C; because of ε-carbide Sedimentation and separation; incurring the volume shrinkage of the parts. This change has been completed after tempering at 150 °C; The influence on the dimensional stability of the parts in the future application process can be neglected between 100~250 °C; the remaining austenite differentiation; the transformation to martensite or bainite; the accompanying volume increases, above 200 °C; ε- Carbide transformation to cementite; incurs volume reduction. The study also indicates that the remaining austenite can also differentiate under the effect of external load or at a lower temperature (or even at room temperature); it causes changes in the scale of the part. Thus; In use; the tempering temperature of all bearing parts should be higher than the operating temperature of 50 ° C; the parts with higher requirements for dimensional stability should be reduced as much as possible of the retained austenite; and a higher tempering temperature is selected.
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