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Bearing steel training skills
Source: Bearing network time: 2018-05-10
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L10 (relative life) = 372 [O] - 1. 6
Where [O] is the oxygen content in the steel; 10-6.
One of the most significant effects of the selection of leading exercise skills is the decrease in oxygen content in steel; from 30×10-6 in the early 1960s to today’s (3~5)×10 -6; L10 is more than 30 times before vacuum degassing.
1 vacuum degassing and outstanding skills outside the furnace
In 1964, the ladle degassing method was used; that is, the ladle was placed in a vacuum chamber; the inert gas was used for mixing; the pressure was lowered to 66. 5 Pa (0.5 Torr), and the oxygen content in the steel was changed from (25). ~35)×10-6 drops to (15~20)×10-6. The disadvantage of this method is that the alkaline slag is also the same; the purity of the steel is difficult to maximize the limit. To solve this problem In 1968, the introduction of the promotion degassing method (RH method) under the high vacuum of 13. 3 Pa (0.1 Torr); the hydrogen and oxygen in the steel were removed; the inclusions were lowered; and the slag was not wounded. 60t The application of high-power electric furnace plus RH degassing; the oxygen content in steel is reduced from (15~20)×10-6 to (8.3~15)×10-6.1974; in order to cooperate with ultra-high power electric furnace Application; introduction of ladle quintessence skills (LF method); that is, ladle with heating, mixing and vacuum degassing equipment; completion of recovery period in ladle; formation of restorative slag; and deoxidation, desulfurization, dehydrogenation; Temperature, composition accuracy of molten steel and pouring time. At this time, UHP furnace is combined with +LF+RH method; the oxygen content in steel is reduced to (5~10)×10-6; It is indispensable to match with successive castings. In addition, in order to further improve the effect of vacuum degassing, a vacuum degassing method and a circulating vacuum degassing method (known as DH method) are also developed and selected to produce vacuum degassing bearings. steel.
2 Vacuum exercise in the bearing steel exercise; apply vacuum; not only can prevent the oxidation of molten steel, but also deoxidize the molten steel; achieve higher purity than vacuum degassing. The specific methods are as follows [2]:
2.1 vacuum induction method (VIM method)
In the vacuum induction exercise, select the scrap that is not free of impurities, chemical composition and exercise alloy steel grade into the small electric induction furnace; the furnace is placed in a large vacuum chamber; the vacuum chamber contains a sealing hopper to increase the required alloy The degassing of the molten steel is started at the moment of rapid melting and quintessence; after the end of the exercise; the furnace is skewed and the molten steel is written into the steel mold. In the vacuum sealed chamber; the steel mold actively enters and exits the casting orientation. This vacuum induction The exercise furnace process is one of the earliest vacuum training methods for making high quality aerospace bearing steel. Today, one of its primary effects is to supply electrodes for the production of ultra-high purity vacuum arc remelted steel.
2. 2 vacuum arc remelting method (VAR method)
In this process, an electrode with an aspirational chemical composition is placed in a copper mold that is cooled by water and internally vacuumed. The arc is generated between the bottom surface of the electrode and the substrate of the same alloy composition. When the electrode is depleted under extremely high vacuum Time; it will actively fall; and control the voltage to maintain a stable exercise parameters. Because the coagulation method is manipulated; so the remelted steel has no intermediate pores and pouring bonds. The remelted steel improves the mechanical properties, uniquely Mechanical properties in the transverse direction.
2. 3 other vacuum exercise skills in order to get higher purity steel; sometimes combined with two vacuum exercise skills or a vacuum exercise skills.
VIM+VAR: The steel produced by VIM method is used as the electrode of VAR; the purity of the electrode is improved again after self-consumption and remelting; the internal arrangement is improved to make it more uniform. The oxygen content is less than 8×10-6; Compared with the degassing steel; its data density is high; the grain is fine and uniform; the mechanical properties are greatly improved. The military aviation engine bearing steel in Europe and America is used to exercise.
Repeated VAR: The bearing steel rod produced by the VAR method is used as a consumable electrode from the beginning; it is treated twice or even three times. The Boeing aircraft engine bearing rule uses this steel.
VIM+ESR: The high-speed steel MSRR6015 used in the world-renowned British Speyer Engine Company Rules must be produced using the VIM+ESR method.
3 other exercise skills
3.1 The large-scale smelting equipment since 1965; gradually introduced UHP (Ultra High Power) and ultra-UHP (Super UHP); its biggest feature is that the electricity introduced into the furnace is the traditional method 2 ~3 times; even higher; the capacity of the transformer and the furnace are also increased together; the exercise time is shortened; the yield is improved; the capacity of the furnace is from 30t to 150t; the yield is improved from 15t/h to 125t/h.
Choose giant ladle (70~150t), giant steel drum (70~150t); large continuous casting billet (370mm×470mm×2000mm); large steel ingot (weight 7~10t; big head 450mm×450mm); large billet, rolling Equipment; large 1300C heavy oil high temperature smashing furnace, normalizing furnace, large continuous gas spheroidizing annealing furnace; then ensure the bearing steel carbide non-uniformity and appearance decarburization layer is excellently controlled.
3.2 Introduction of successive castings
In the 1950s, the top casting method was used; in the 1950s, the bottom casting method was selected; the anti-oxidation masking agent was successively selected; the inert gas was ensured; the raw material of the floor brick was improved; and the purity of the steel ingot cast by the bottom casting method was also greatly improved. From the beginning of 1982, the introduction of large-section (370mm × 470 mm billet) straight continuous casting skills has brought the bearing steel production skill to a new level. In the process of successive casting slabs, it has adopted a useful method to block the molten steel and air touch; Strictly control the quality of refractory materials; make the oxygen content of the billet be well controlled; reach (3~8)×10-6. Because the high-power electromagnetic mixing equipment is used for the setting moment, the crystallization arrangement can be greatly improved.
3. 3 partial pain steel outlet (EBT)
Generally, the tapping is a skewed furnace body. After the steel tapping trough, the molten steel is poured into the ladle. In 1986, the tapping of the bottom of the furnace is selected; that is, the steel port is opened below the side of the electric shock of the arc furnace bottom; Before the steel, the slag on the molten steel surface is discharged from the bottom; the molten steel is separated from the acid slag; the LF ladle is convenient; the high-purity steel can be more stably produced; the production power is improved together. The test is marked; the EBT is selected. The oxygen content can be further reduced (evenly decreased by 0.4×10-6). The most outstanding strength is to improve the shape of the inclusions; the B-type coarse series and the D-type coarse series inclusions which have the worst influence on the touch fatigue life are obtained. Significant improvement.
3. 4 Electroslag Remelting (ESR)
The electroslag remelting process is very similar to the consumable electrode vacuum training process except that the slag liquid pool located at the bottom of the electrode constitutes the resistance required for melting. It can not only feed the slag pool of the molten state into the furnace but also supply the powder slag; When the arc is triggered between the bottom plate and the electrode, the powder slag melts rapidly. When the steel water droplets pass through the slag pool; the molten steel finishes the essence. The components of the controlled slag can remove sulfur, oxygen and other harmful impurities. The method reduces the pores; reduces the segregation to the lowest limit; and improves the physical properties of the steel bond in the lateral and longitudinal directions. As a method of producing high-quality steel; it will continue to be used or cooperated with other exercise methods.
Others; finished steel ingots, billet surface quality online finishing, together with strict online non-destructive testing equipment; four methods (eddy current, magnetic powder, leaky magnetic flux and ultrasonic flaw detection method) for 4 to 7 times of flaw detection, sufficient to ensure steel No cracks factory.
4 Exercise skills in developed countries Japan introduced vacuum degassing equipment in the 1960s [3; 5]. In the 1970s, the skills of LF and CC introduced were improved. In the 1980s, the so-called longevity and longevity numbers were always developed. Bearing steel; Z steel developed by NSK is one of its latest effects [6]. This steel is a high-quality steel grade that has been declared low cost based on many experiments and improved steelmaking equipment and exercise conditions. Titanium content <0.004%; oxygen content <9×10-6; sulfur content <0.0008% (for falling bearing noise). Compared with general vacuum degassing steel (MGH); bearing life (L10) Doubled on the basis of this; improved the electric furnace bottom blowing method, LF slag layout, deoxidation method, temperature control and mixing in LF and RH; established a set of Sanyang new steelmaking method SNRP (SANYO New Refining) Process) [7]; control the oxygen content of the steel at around 5×10-6; and use a new set of inclusion identification methods (NSK ISD2 method); control the size, shape and distribution of inclusions; Uniform together; eliminate large inclusions; developed a high longevity number Steel for bearings - EP steel (Extremely Purified Steel). Its L10 is 5 times that of Z steel; 10 times for general vacuum degassing steel; 80 times of calculated life (the calculation of bearing steel bearing with atmospheric exercise) The number L10 is 1); the fatigue limit is 700~900MPa higher than Z steel; reaching 1030MPa. It is uniquely suitable for bearings with smooth grease and clean oil smooth operation, high demand and long life; such as automobile wheel parts and related electrical appliances , railway vehicles and high-speed motor bearings.
Sweden developed the essence of ASEA-SKF ladle in 1964; used the double-shell electric furnace in cooperation with this quintessential skill; it is called SKF-MR method; it has been continuously improved and improved; it has been used until now. In addition to the SKF-ASEA ladle essence equipment Also used is a double arc exercise furnace. The double furnace has two furnace tanks with two oxyfuel burners and two furnace lids; one with graphite electrodes; the other without electrodes. One furnace is used; the other furnace is installed Material and preheating. In the exercise furnace; carbon and sulfur content is adjusted below the maximum limit of the end. Then; the ladle steel is sent to the ASEA ladle furnace with independent electrode cover. This equipment can supply many metallurgy Process; including vacuum degassing, desulfurization, deoxidation and adjustment of the chemical composition of molten steel. Others; under the conditions of severe temperature control; induction mixing can also use aluminum for deposition deoxidation; then make the steel oxygen content and non-metallic inclusion content Very low.
The United States developed the Finkl-VAD ladle essence method in 1967 and continued to make progress; it has been used so far. Its bearing steel quality level is also very good; and it is secure and reliable; it reaches the level of the world-recognized ASTM A 295 specification. This method is steel The exercise is carried out in a ladle furnace; this furnace overcomes the general constraints of starting an arc melting furnace. It is equipped with an independent electrode for controlling the temperature of the molten steel; and is equipped with an electromagnetic mixer that circulates the molten steel. Thus; no need to be as previously described Various specifications of the ladle degassing process need to overheat the molten steel in the electric arc furnace to compensate for this future temperature drop. The spray gun can make the powdered alloy enter the inside of the ladle. Hydrogen is used as the gas carrier of these powder alloys; the generated bubbles help The alloy powder is evenly distributed in the ladle. The combination of the spray gun and the added wire can control the shape of the inclusion, reduce the sulfur content and improve the fluidity, chemical uniformity and overall micro cleanliness. The ladle furnace skill can make the scrap in the electric arc furnace Agile melting; improving the quintessence of this future ladle furnace operation. The equipment is improving the economic benefits of steelmaking together Also improve the quality of steel.
The United States in the future in 1986; the use of a special air smelting method combining high efficiency and appropriate messy casting system; producing a new steel grade called Parapromium [8]. The magnetic particle limit of the steel fits AMS2300 Specification (in 1986; this specification is only applicable to vacuum remelted steel); its oxygen content and vacuum remelting steel. The ultrasonic observation method is used to check the inclusion content; the total length of inclusions is less than that of sedimentary deoxidation + protective jet casting. E. F. Q. B2 type bearing steel. This steel has the ability to replace vacuum remelted steel or E. F. Q. B2 steel is used in applications where the quality of steel is high.
In recent years, Germany FAG developed a new method of bearing steel to produce so-called "aluminum-free steel" [9]; that is, it is generally deoxidized with A1 to be deoxidized with Si; although it is slightly worse than Al with deoxidation [in steel] High oxygen content (2~3)×10-6]; but the deoxidation with Si can reduce the content of inclusions such as brittle calcium aluminate and alumina in steel; and the inclusions become finely dispersed; the harmful effect is greatly reduced. Introduction; FAG's current continuous casting bearing steels are all de-oxygenated by this method; because the shape of the inclusions becomes fine and scattered; it is not customary to check the inclusions with traditional gauge images; then develop a high-power ultrasonic inclusion Measuring instrument; capable of 100% continuous inspection of steel; together with this instrument can also see steel cracks.
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