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The development direction of bearing data and heat treatment in China
Source: Bearing network time: 2013-06-28
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Compared with industrial developed countries; although the oxygen content of bearing steel in China is close to the leading level in foreign countries; the uniformity of uniformity and composition uniformity of inclusions and carbides according to the bearing scale is still far away from foreign countries; There are many inclusions and carbides in the scale, and the basic components are uneven, which constitutes the black and white area. The quality of the bearing parts is congenitally insufficient; the bearing life, reliability and consistency of the bearing are severely affected. In addition, the large-scale inclusions on the touch surface are rolled over. There is still a serious decline in appearance accuracy; adding bearing noise. To this end; bearing occupation should negotiate with metallurgical occupation; promote metallurgical occupation on the basis of further reducing oxygen content; develop pouring condensation skills, rolling skills, inclusion control and detection skills Such as the study; such as improving the electromagnetic mixing during continuous casting, adding the scale of Dalian casting billet, strengthening high-temperature dispersion annealing, etc.; to improve the scale and uniformity of inclusions and carbides.
Second, the development and implementation of new steel varieties are not satisfied with the needs of bearings:
With the miniaturization, light weight and high speed of the main engine; the operating environment of the bearing is more and more diversified; the demand for bearings is becoming more and more stringent; at present, the existing steel grades in China are not satisfactory or can not be satisfied with the bearing. Demand; for this purpose; development and implementation of new materials should be actively pursued. For example, high-hardenability steel for large-scale bearings, heavy-duty and clean-smooth conditions, or steel for bearing applications under small and lightweight conditions, in pollution Bearings used under high carbon steel and carburized steel, quasi-high temperature (operating temperature below 200 °C) bearing steel and special conditions for bearing steel (stainless steel, high temperature steel).
3. Discussion and implementation of new heat treatment technologies:
1. Bainite quenching;
The bainite austempering bearing has good impact toughness and external compressive stress; whether it is cracking during installation, it is still the tendency of the casing to sag and the inner sleeve to be broken during the operation. The gears are convex and arrogant. Therefore, the average life and reliability of the bearing after isothermal quenching is significantly improved compared with the conventional quenching. The process is widely used in railway bearings, rolling mill bearings and bearings used under special working conditions. The process is compared with other life extension methods; the process is simple; the cost is low. In these years; China has developed a new steel grade GCr18Mo bainite quenching special steel; to promote the application of bainite quenching on large-scale bearing parts. Many advantages; advocated in the use of harsh conditions (large impact load, poor smoothness, etc.) or demand for high reliability of the bearings; and further study the wear resistance and fatigue life after bainite treatment.
2. Appearance carbonitriding;
The Luoyang Bearing Research Institute started the martensitic stress quenching of bearing steel in the 1980s; after special carbonitriding and quenching of high carbon chromium bearing steel parts; improving the residual austenite content; Appearance stress condition; greatly improved the carbonitriding of the gearbox; improve the residual austenite content on the surface without reducing the appearance hardness; to improve the fatigue life and reliability of the bearing under the condition of smooth pollution.
Fourth, the appearance of modification skills;
Appropriate appearance treatment to improve the appearance of the function; to meet the functional requirements of the bearing under special conditions. For example, using the vapor deposition technique to coat the bearing raceway with the diamond coating can achieve the effect of friction reduction and wear resistance; greatly improve the wear of the bearing. Lifespan and precision adhere to the function; can be used in household appliances bearings, computer hard drive bearings, using thermal coating skills to coat alumina ceramic material on the outer cylinder surface of the bearing; can improve the electrical insulation function of the bearing; avoid electric shock Injury; improve the life and reliability of the motor bearing, in the bearing parts surface sulfur or accumulation of MoS2 can reach the anti-friction smoothing effect.
5. Heat treatment equipment and related skills:
1. Atmosphere and control;
It is heated by a controlled atmosphere to control the carbon potential and nitrogen potential in a controlled atmosphere; the function of the parts after heat treatment is improved; the disadvantages of heat treatment such as decarburization and cracking are greatly reduced. Contact heat treatment and quenching deformation control skills; Finishing allowance after heat treatment; improving the utilization rate of the data and machining power; improving the appearance of the bearing parts after finishing; such as the carbon content, arrangement, hardness and stress status of the surface.
2. Automation and intelligence:
On the one hand, it is based on the application requirements, data and layout scale of the parts; using physical metallurgy common sense and leading computer simulation and testing skills; optimizing process parameters; reaching the required functions or maximizing the potential of data, on the other hand, progress The degree of automation and stability of heat treatment; sufficient to ensure the stability of the optimized process; the quality of the finished product is very disproportionate. è¾ è¾ è¾ è¾ è¾ è¾ è¾ è¤‚ 褂 褂 褂 褂 褂 骰 骰 骰 骰 骰The hospital is fading.
Sixth, deformation and scale stability:
Martensite quenching process; uneven cooling of parts of parts; inevitably exhibiting thermal stress and arranging stress and causing deformation of parts. The deformation of parts after quenching and tempering (including scale change and shape change) is affected by many factors; Is a proper 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 amount of feed during turning, 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, the temperature of the medium, etc. all affect the deformation of the part. The deformation should be studied in connection with the detailed equipment and products; the method of controlling the deformation is proposed; Quenching, die hardening, control parts oiling methods, etc.; reduce heat treatment deformation; improve processing power and parts functions.
After martensite quenching; the dimensional stability of the part is mainly affected by the following three different transformations: carbon migration from the martensite lattice constitutes ε-carbide, residual austenite differentiation and composition of Fe3C. Superimposed on each other. Between 50 and 120 ° C; because of the deposition of ε-carbide; incurs the volume shrinkage of the part. 懔慵 After 150 ° C tempering, this transformation has been completed; its scale in the future use of parts The effect of stability can be neglected, between 100 and 250 ° C; residual austenite differentiation; transformation to martensite or bainite; will accompany the volume increase, above 200 ° C; ε-carbide carburization Body transformation; incurs a reduction in the volume of parts. The study indicates that the remaining austenite is also differentiated at the external load effect or at a lower tempering temperature (even at room temperature); it causes a change in the size of the part. Therefore; in practical use; The heating temperature of the 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 the dimensional stability, accuracy and life of the storage and operation should be improved. Number and reliability.
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