1.There are many kinds of rolling bearings, but the structure is usually composed of coat, inner sleeve, rolling body (ball, roller, needle) and cage.Most of the rolling bearings are concentrated, high loads, bearing alternating stresses, and service under high speed.The main forms of failure are fatigue and wear.The bearing rings and rolling elements of rolling bearings are generally made of high purity special chromium alloy steel, mainly GCr15 steel and GCr15SiMn steel, with the maximum amount of GCr15 steel.Heat treatment plays an important role in improving the inner quality of rolling bearing and extending service life. In this case, the heat treatment technology application of GCr15 steel is used to communicate with your colleagues.
2. Production process
The main production processes of such bearings as the specification model: TM6305, TM6205, TM6206 and TM6207 are as follows:
(1) outer ring processing.
Raw materials (bearing steel bar) blanking to spheroidizing annealing, forging, hot forging or high speed forging to ultra refined processing, rough turning machining to finish turning to strengthening heat treatment, shot to double coarse grinding, centerless grinding coarse grinding, coarse grinding groove outside to supplement the tempering, cryogenic treatment to double fine grinding, centerless grinding fine grinding and fine grinding groove outside to outside groove lapping, parts and final inspection identification, parts cleaning.
(2) inner ring machining
Raw materials (bearing steel bar) blanking to spheroidizing annealing, forging, hot forging or high speed forging to ultra refined processing, rough turning machining to finish turning to strengthening heat treatment, shot to double coarse grinding, centerless grinding and fine grinding of coarse grinding groove, coarse grinding inner hole to supplement the tempering, cryogenic treatment to double fine grinding, fine grinding inside groove - fine grinding inner hole - lapping inside groove - parts cleaning.
(3) assembly (inner circle, outer ring, steel ball, cage)
Complete detection of vibration value, full size, appearance inspection, anti-rust packaging.
3. Prepare heat treatment process.
In view of the high chromium carbide forming elements in GCr15 steel, the carbon content and chromium content are high, and the following preheating treatment technology is set up:
(1) the isothermal spherification annealing process is carried out before forging.With the model of GKT -50 roll-bottom vacuum lock continuous annealing production line, after spherification, the tissue is point and ball pearlite, hardness: 185 ~ 207HBW.The goal of refining carbide after spheroidizing annealing.
(2) superfine processing technology for the carbide after forging.In order to reduce energy consumption, the use of forging heat, to guarantee the bearing blank finish forging workpiece temperature at 850 ~ 900 ℃, and then heated to 1050 ℃ solution and make the carbide dissolution, and make composition homogenization, and then quenching into the constant temperature trough under 310 ℃ isothermal transformation to obtain bainite organization, then after the completion of the isothermal transformation of isothermal spheroidizing artifacts for a short time.After this treatment, the workpiece has superfine carbide, the shape of carbides is relatively round, and the distribution is more uniform, which also helps to eliminate or reduce the defects such as banded segregation.
4. Carburizing process of carbon and nitrogen.
In view of the characteristics of GCr15 steel and the service conditions of rolling bearing, considering the characteristics of heavy load of such automobile bearings, carbon and nitrogen co-infiltration technology is adopted in the inner and outer rings:
In order to reduce the cost of heat treatment, we have developed a suit of carbonitriding continuous mesh belt furnace carbonitriding processing, specific parameters is: heating temperature: 835 ℃ + / - 5 ℃, the last part temperature to 825 ℃ + / - 5 ℃;Carbon potential: 1.3%C, and 1.2%C in the last area;Total time from furnace to heating: 420min;CH3OH: 2000 ml/min.NH3:2 l/min.Use graded quenching heat the carbonitriding process, the oil temperature: 110 ℃ + / - 5 ℃;To clean: 60 ~ 80 ℃;Cooling off: 5 ~ 15 ℃;Return fire: 190 + + 5 (outer ring: 210 + + 5), temper time: 180 min.The test results of the workpiece after the above mentioned carbonitrification treatment were: surface hardness: benchmark (61 ~ 65HRC), with a performance of 63HRC;Depth of penetration: base (greater than 0.25mm), with an actual performance of 0.4mm;Metallographic structure: carbide 1, martensite 1.According to the characteristics of the rolling element we also developed a new equipment of carbonitriding, can make a deep roller is evener, use and inner ring similar carbonitriding process, to achieve the effect of the reinforcement.In order to eliminate the stress caused by the machining process before the finishing process, a supplementary tempering of 180 and 4h was added.In order to reduce quench tissue, the content of retained austenite in and make the rest of the retained austenite tends to be stable, thus increasing the dimensional stability - 50 ℃ cryogenic treatment, 1.5 h.
5. Use effect
After the application of the heat treatment process of rolling bearing and strengthened the same model of the rolling bearing, bearing wear resistance after strengthened obviously, increase the service life of engine bearing.
6. Conclusion
By using isothermal spheroidizing annealing, refining and homogenizing treatment of pretreatment ultrafine carbide, very good to improve the zonal segregation, again through the inner ring and outer ring, rolling body of carbonitriding strengthening heat treatment, as well as the process to reduce the stress in the process of machining supplement improve the dimension stability of cryogenic tempering and make motor rolling bearing has the extremely high wear resistance and durable service life high characteristic, improved the safety of the user.
