The Maintenance of Bearing
2018-07-23 by zysbearing
1 high carbon chromium bearing steel ball annealing Isothermal annealing
Carbon chromium bearing steel ball annealing is to obtain ferrite matrix uniformly distributed fine, small, uniform, round carbide particles organization for the future and the ultimate cold quenching and tempering for tissue preparation.
The traditional ball annealing process is performed at a temperature slightly above the Ac1 (eg GCr15 of 780 ~ 810 ℃) after incubation with the furnace slow cooling (25 ℃ / h) to 650 ℃, cooled baked. The process heat for a long time (20h or more), and after annealing carbide particles unevenly affect subsequent cold working and final quenching and tempering organization and performance. Then, according to the characteristics of supercooled austenite transformation, development isothermal spheroidization annealing process: rapid cooling after heating to a temperature range of less Ar1 (690 ~ 720 ℃) isothermal, isothermal austenite to complete the process ferrite and carbides of transition and change can be directly cooled baked finish. The heat treatment process has the advantage of saving time (the overall process about 12 ~ 18h), after treatment of carbide fine and uniform. Another time-saving ball annealing process is repeated: the first heated to 810 ℃ and then cooled to 650 ℃, and then heated to 790 ℃ to 650 ℃ and then cooled baked cooled. Although this process can save some time, but the process operation is relatively complex.
(2) high carbon chromium bearing steel martensitic quenching and tempering
Conventional quenching and tempering of martensite microstructure and properties
Organization: martensite, residual austenite, undissolved (residual) carbides.
Martensite forms: under the microscope (magnification generally less than 1000 times)
Can be divided into martensite lath martensite and plate martensite two typical organization, usually after quenching martensite lath and flake hybrid organization
Or called in between intermediate form - pit-like martensite - bearing industry on the so-called hidden martensite, martensite crystals
In the high-powered electron microscope: its sub-structures can be divided into dislocation tangles and twinning. The specific morphology depends mainly on the carbon content of the matrix
Austenitic higher the temperature, the more unstable the original organization, the austenitic matrix carbon content is higher, the organization retained austenite after quenching the more the more the plate martensite, the larger the size of sub-structure The greater the proportion of twins, and easy to form microcracks quenching.
The matrix carbon content less than 0.3%, the martensite structure is mainly based dislocation lath martensite; matrix carbon content higher than 0.6%, martensite is mixed dislocations and twinning film substructure shaped martensite; matrix carbon content of 0.75%, the obvious ridge appears with a large surface plate martensite and plate martensite growth at each other when hit with microcracks.
With the austenitizing temperature, the quenched hardness, toughness decreased, but due to high temperature austenite retained austenite after quenching caused by excessive decrease in hardness.
Conventional martensite after quenching organization retained austenite content is generally 6 to 15%.
Soft residual austenite metastable phase, under certain conditions (such as tempering, or part of the natural aging process of using), which instability occurs decomposition of martensite or bainite. Decomposition is part consequences hardness, toughness decreases, dimensional changes affect the dimensional accuracy of parts or work.
Requiring high dimensional accuracy bearing parts, the general hope of retained austenite as possible, such as water or supplement after quenching cryogenic treatment, the use of higher temperature tempering.
Residual austenite can increase the toughness and crack propagation resistance, under certain conditions, the residual austenite workpiece surface can reduce the contact stress concentration, improve the bearing contact fatigue life, in this case the composition of materials in the process and to take certain measures to retain a certain amount of residual austenite and to improve its stability, austenite stabilizing elements such as adding Si, Mn, for stabilization treatment.
Conventional martensitic quenching and tempering process
Heated to 830 ~ 860 ℃ heat after oil quenching, tempering
GCr15 Steel Bearing: 150 ~ 180 ℃
Steel bearing member GCr15SiMn: 170 ~ 190 ℃
-50 ~ -78 ℃ cold treatment
Quenching martensite obtained in a stable retained austenite high dimensional stability and high toughness.
Quenched and tempered martensite deformation and dimensional stability
Part shape and size uniformity of the original organization, the rough state before quenching, quenching speed and the heating temperature of the workpiece layouts, into the oil, quenching the cycle characteristics of the medium mode, medium temperature etc. affected part of the deformation.
Deformation control measures: use of rotating hardened, die quenching, control parts into the oil, etc.
The vapor phase to the membrane phase transition boiling temperature is too high, a large cooling speed and produce a large thermal stress of the low yield point which causes deformation of austenite part distortion.
Deformation between the individual parts or components caused by oil-soaked uniform, especially the introduction of new oil is easier to be the case.
Ms point in the cooling rate on the deformation plays a decisive role in the Ms point and below the low temperature cooling rate can be reduced distortion.
