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Analysis of Bearing Heat Disposal Methods in Foreign Mechanical Occupations
Source: China Bearing Network Time: 2014-01-10
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.1): Heat treatment: Wastewater, waste gas, waste salt, dust, noise and electromagnetic radiation formed during the heat treatment process will pollute the environment. Disposal of environmental pollution problems of heat treatment; implementation of sanitary heat treatment (or Green environmental heat treatment) is one of the directions for the development of heat treatment skills in developed countries. In order to reduce the emissions of SO2, CO, CO2, dust and cinders, coal has been used as a fuel; the use of heavy oil is also becoming less and less; Most of the light oil is used; natural gas is still the most ideal fuel. The waste heat application of the incinerator has reached a high level; the optimization of the layout of the incinerator and the strict control of the air-fuel ratio ensure the rational incineration; the NOX and CO Drop to the lowest 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; 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, based on 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 required function or 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 elements for the useful use of power; establishing a professional heat treatment plant to ensure full-load production and abundant development of equipment can be a scientific management choice. In terms of layout, 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 process with long cycle and high energy consumption.
.4): no oxidation heat treatment: heating by controlled atmosphere heating instead of 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. Significant 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 be significantly improved Quality, reduction of distortion, and forward 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 . Annealing of high carbon chromium bearing steel: The spheroidizing annealing 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 Tempering arrangement preparation. The traditional spheroidizing annealing process is performed at a temperature slightly higher than Ac1 (such as GCr15 of 780~810 °C) and then cooled slowly (25 °C / h) to below 650 ° C. The heat treatment time is longer (more than 20h); and the particles of the carbide are not uniform after annealing; affecting the future cold working and the end quenching and tempering arrangement and function. After that; according to the transformation characteristics of supercooled austenite; developing isothermal spheroidizing 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 cooled. The advantage of this process is that it saves heat treatment time (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: after the first heating to 810 °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 Arrangement and function of conventional martensite quenching and tempering. In the past 20 years, the development of the conventional martensitic quenching and tempering process of high carbon chromium bearing steel has been divided into two aspects: on the one hand, the influence of the quenching and tempering process parameters on the arrangement and function; Arrange the transformation, the differentiation of the remaining austenite, the tolerance and fatigue function after quenching and tempering, and the process function of quenching and tempering on the other hand; such as the influence of quenching conditions on scale and deformation, the stability of scale, etc. The arrangement after quenching is composed of martensite, retained austenite and undissolved (residual) carbide. In the meantime, the arrangement of martensite can be divided into two categories: under a metallographic microscope (the expansion factor is usually lower than 1000 times); martensite can be divided into two types of slab martensite and flaky martensite; usually after quenching is a mixed arrangement of slats and flaky martensite; or between The central shape of the 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 The shape of the arrangement depends primarily on the carbon content of the substrate; the higher the austenite temperature The more unstable the original arrangement is; the higher the carbon content of the austenitic matrix; the more retained austenite in the post-quenching arrangement; the more flaky martensite; the larger the scale; the greater the share of twins in the sub-layout And easy to form quenching microcracks. Usually; when the matrix carbon content is less than 0.3%; martensite is mainly the lath martensite with dislocation sub-layout, and the matrix carbon content is higher than 0.6%. Martensite is a sheet-like martensite of a dislocation and twin mixed sub-layout with a matrix carbon content of 0.75%; a large sheet of martensite with a pronounced mid-ridge; and a flaky horse When the body grows, it strikes with microcracks at the same time; together with the advancement of austenitizing temperature; the hardness after quenching advances; the resistance decreases; but the austenitizing temperature is too high due to the remaining austenite after quenching Excessive body and hardness decrease. The content of retained austenite in the arrangement after conventional martensite quenching is usually 6~15%; the remaining austenite is soft sub-stable phase; under certain conditions (such as tempering) , natural aging or the use of parts in the process; its instability occurs into martensite or bainite. The result of differentiation is the part Degree advancement; resistance to decline; scale changes affect the dimensional accuracy of the part and even normal operation. Bearing parts with higher requirements on scale accuracy; usually the less retained austenite is better; for example, after quenching, make up for water cooling or cryogenic treatment Use higher temperature tempering, etc., but 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 touch stress gathering; the touch bearing fatigue life of the forward bearing In this case, a certain method is adopted in the composition of the process and materials to preserve the necessary austenite and advance its stability; for example, to participate in the austenite stabilization element Si, Mn, for stability and disposal.
2. 2 Conventional martensite quenching and tempering process practice High carbon chromium bearing steel Martensite quenching and tempering: heating the bearing parts to 830~860 °C after heat preservation; quenching in oil; then low temperature tempering. Quenching 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; such as the composition of austenite, the recrystallization of austenite, the dispersion of residual carbides and the use of non-spherical arrangements as the original arrangement. G. Lowisch and other two austenitized quenched bearing steel 100Cr6 mechanical functions were studied: first; austenitizing at 1050 ° C and cooling to 550 ° C after air cooling; obtain a uniform fine-leaf pearlite; Performing secondary austenitization and quenching at 850 °C; fine-grained martensite and carbide scale, high carbon content of martensite matrix and high retained austenite content after quenching; Fire makes austenite differentiation; many fine carbides are separated in martensite; reduced quenching stress; forward hardness, strong tolerance and bearing capacity of bearing. Under the effect of touch stress; its function; further research is needed However, it can be estimated that its touch fatigue function should be better than the conventional quenching. Sakai Yuyu et al [7] studied the micro-arrangement and mechanical function of SUJ2 bearing steel after cyclic heat treatment: first heat to 1000 °C to maintain 0. 5h to make the spheroidal carbide solid solution; then; pre-cooled to 850 ° C to quench oil. Then repeat 1 to 10 times from the rapid heating to 750 ° C, 1 min after heat preservation, oil cooling to room temperature thermal cycle; the final rapid heating to 680 ° C Insulation for 5 minutes, oil cooling. At this moment, it is arranged as Fine ferrite plus fine carbide (ferrite grain size less than 2μm, carbide less than 0.2μm); superplasticity at 710 °C (crack elongation can reach 500%); Characteristics: Warm processing of bearing parts. Finally; heating to 800 ° C to maintain the quenching oil and tempering at 160 ° C. After this treatment; the touch fatigue life L10 is greatly advanced than the conventional treatment; its failure method is handled by the conventional The early failure type 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; then tempering at 180 ° C; the carbon concentration in the quenched martensite can be more dispersed. Uniform; impact resistance doubles than conventional quenching and tempering. Thus; Ð’. Ð’. БÐЛОЗЕРОВ et al. proposed that the carbon concentration of martensite can be used as a quality standard for heat treatment parts.
2.3 The deformation and scale stability of martensite quenching and tempering. Martensite quenching and tempering; because of the uneven cooling of parts of the part; inevitably exhibiting thermal stress and arranging stress and causing deformation of the part. The deformation of the part after quenching and tempering (including scale change and shape change) is affected by many Factor influence; is a suitable messy problem, such as the shape and scale of the part, the uniformity of the original arrangement, the roughing condition before quenching (the size of the feed amount during turning, the residual stress of machining, etc.), the heating during quenching Speed ​​and temperature, 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. Many studies have been carried out at home and abroad; many methods for manipulating deformation have been proposed; Such as the use of rotary quenching, die quenching, oil control methods for controlling parts, etc. Beck et al.'s research indicates that the transition temperature from the vapor film to the jubilation period is too high; the large cold speed and the large thermal stress are low. The deformation of the austenite at the yield point causes distortion of the part. Lübben et al. think that the deformation is a non-uniform immersion between individual parts or parts; especially The new oil is more likely to present this kind of scene. Tensi et al. believe that the cooling rate at the Ms point has a decisive effect on the deformation; the low cooling rate can be used to reduce the deformation at the Ms point and below. The Volkmuth et al. system studies the quenching medium ( Contains 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. The results indicate: because the cooling method is not the same; the diameter of the ferrule will have a different degree of "increased"; and with the temperature of the medium Advance; the diameter of the ferrules at the end of the diameter tends to be common; that is, the "horn" deformation is reduced. The 惶 Φ Φ è€ è€ neck 湫 ǖヒ痪 ǖヒ痪 èš± èš± 婺诘 婺诘 ä¾—æ¶ ä¾—æ¶ d d d d d d d d d d d d谌σ蚋斩冉 Washing èž… 浔湫 ∮谕馊 ∮谕馊. After the martensite quenching and tempering, the dimensional stability of the part is mainly affected by three different transformations: carbon is removed from the martensite lattice to form ε-carbide, Remaining austenite differentiation and composition of Fe3C; three transformations superimposed on each other. 50~120 °C; because the deposition of ε-carbide is separated; the volume of the part is reduced. 懔慵 After 150 ° C tempering, this is completed. Transformation; its impact on the dimensional stability of the future use of parts can be neglected 10 Between 0 and 250 ° C; residual austenite differentiation; transformation to martensite or bainite; will accompany the volume increase, above 200 ° C; ε-carbide conversion to cementite; incur volume reduction. It is indicated 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 a change in the size of the part. Therefore, in practical use, the tempering temperature of all bearing parts should be higher than Use a temperature of 50 ° C; parts with higher requirements for dimensional stability should try to reduce the content of retained austenite; and choose a higher tempering temperature.
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