Smelting technology of the hottest bearing steel

Smelting technology of bearing steel

smelting technology of bearing steel Abstract: the reduction of content directly affects the inclusion and affects the contact fatigue life of bearings. The data shows that the content relationship relative life is 1.6 content. One of the significant effects of the adoption of various advanced smelting technologies is that the content is reduced from the 1960s to today. The vacuum degassing vacuum degassing refining technology outside the furnace was adopted. The degassing ladle vacuum chamber was filled with inert gas liquid dynamic and static pressure since 1964 Bearing commonly used shaft shell with bearing sealing type of bearing precision bearing new process of rust prevention between working procedures bearing life enhancement test a detailed processing of eccentric shaft design theory and key technology of parallel machine tool oil-free bearing drives the revolution of mold industry bearing life enhancement test in China is in the ascendant

(I) bearing life enhancement test in China is in the ascendant

(II) the reduction of oxygen content in steel directly affects the amount of inclusions in steel, And then affect the contact fatigue life of bearing steel. Data shows that the oxygen content L10 in steel has the following relationship:

L10 (relative life) =372[o]-1.6 where [o] is the oxygen content in steel

one of the most significant effects brought about by the adoption of various advanced smelting technologies is the reduction of oxygen content in steel, which has decreased from 30 in the early 1960s to today's (3-5), and L10 is more than 30 times that before vacuum degassing

1 vacuum degassing and refining technology outside the furnace

the ladle degassing method was applied in 1964, that is, the ladle was placed in a vacuum chamber and stirred by inert gas, so that "its pressure decreased to 66.5pa (0.5 Torr) to realize degassing, and the oxygen content in the steel decreased from (25~35) to (15~20). The disadvantage of this method is that the slag with high alkalinity is also stirred, and it is difficult to maximize the purity of steel. In order to solve this problem, the lifting degassing method (RH method) was introduced in 1968. Under the high vacuum of 13.3pa (0.1 Torr), the hydrogen and oxygen in the steel were removed, the inclusions were reduced, and the slag was not rolled. The use of 60t high-power electric furnace and Rh degassing have reduced the oxygen content in steel from (15~20) to (8.3~15). After 1974, in order to cooperate with the rational use of ultra-high power electric furnaces, ladle refining technology (LF method) was introduced, that is, the ladle is equipped with heating, stirring and vacuum degassing devices to complete the reduction period in the ladle, form reducing slag, deoxidize, desulfurize and dehydrogenate, and control the temperature of molten steel, the composition accuracy of molten steel and pouring time. At this stage, UHP furnace is combined with +lf+rh method to reduce the oxygen content in steel to (5~10), which is essential for matching with continuous casting. In addition, in order to further improve the effect of vacuum degassing, atomization vacuum degassing method and circulating vacuum degassing method (commonly known as DH method) have also been developed and adopted to produce vacuum degassed bearing steel

2 vacuum smelting

when smelting bearing steel, applying vacuum can not only avoid the oxidation of molten steel, but also deoxidize molten steel and obtain a higher purity than vacuum degassing. The specific methods are as follows [2]:

2.1 vacuum induction smelting method (VIM method)

during vacuum induction smelting, scrap steel with basically no impurities and chemical composition equivalent to the grade of smelting alloy steel is selected and sent to a small induction furnace, which is placed in a large vacuum chamber, which includes a sealed hopper to add the required alloy. Degassing of molten steel began as early as during rapid melting and refining. After smelting, tilt the furnace and inject molten steel into the steel mold. In the vacuum sealed chamber, the steel mold automatically enters and exits the pouring position. This vacuum induction smelting furnace process is one of the earliest vacuum smelting methods used to manufacture high-quality aviation bearing steel. Today, one of its main functions is to provide electrodes for the production of ultra-high purity vacuum arc remelting steel

2.2 vacuum arc remelting method (VaR method)

this process is to place an electrode with ideal chemical composition into a copper mold with water cooling around and vacuum inside. The arc is generated between the bottom surface of the electrode and the substrate with the same alloy composition. Under extremely high vacuum, when the electrode is lost, it will automatically drop, and the voltage is controlled to maintain constant smelting parameters. Because the solidification mode is controlled, the Remelted Steel basically has no central porosity and casting bond segregation. Remelting steel improves the mechanical properties, especially in the transverse direction

2.3 other vacuum smelting technologies

in order to obtain higher purity steel, sometimes two vacuum smelting technologies are used together or one vacuum smelting technology is used many times

vim+var: the steel produced by VIM method is used as the electrode of var. after consumable remelting, the purity of the electrode is improved again, and the internal structure is improved to make it more uniform. Its oxygen content is below 8. Compared with degassed steel, the materials in Southeast Asia, Indian subcontinent, Latin America and the Middle East markets have high density, fine and uniform grains, and greatly improve the mechanical properties. The bearing steel of military aeroengine in Europe and America is smelted by this method

multiple var: the bearing steel bar produced by VaR method is used as consumable electrode again for secondary or even tertiary var treatment. This steel is specified for Boeing aircraft engine bearings in the United States

2. Classification according to the loading method

vim+esr: the world-famous British Spey aero engine company stipulates that the high-speed steel msrr6015 used must be produced by vim+esr method

3 other smelting technologies

3.1 large scale smelting equipment

since 1965, UHP (ultra high power) and super UHP (super UHP) rapid smelting methods have been gradually introduced into the electric furnace. Its biggest feature is that the amount of electricity introduced into the furnace is 2-3 times that of the traditional method, or even higher. The capacity of the transformer and furnace is also large at the same time, which shortens the smelting time and improves the productivity. The capacity of the furnace is increased from 30t to 150t, and the productivity is increased from 15t/h to 125t/h

adopt giant ladle (70~150t), giant steel ladle (70~150t), large continuous casting billet (370mm, 470mm, 2000mm), large ingot (weighing 7~10t, big end 450mm, 450mm), large bloom opening and rolling equipment, large 1300C heavy oil high temperature diffusion furnace, normalizing furnace, large continuous gas protection spheroidal annealing furnace, so as to ensure that the carbide inhomogeneity and surface decarburization layer of bearing steel can be well controlled

3.2 introduction of continuous casting

the top casting method was adopted before the 1950s, and the bottom casting method was adopted after the 1950s. Measures such as anti-oxidation covering agent, inert gas protection and improving the material of bottom plate bricks were successively adopted, so that the purity of steel ingots cast by the bottom casting method was also greatly improved. Since 1982, the introduction of large section (370mm 470mm square billet) vertical continuous casting technology has brought the production technology of bearing steel to a new level. In the process of continuous casting, effective measures are taken to isolate the contact between molten steel and air, and the quality of refractory materials is strictly controlled, so that the oxygen content of billet can be well controlled to reach the range of (3~8). Due to the use of high-power electromagnetic stirring device in the solidification stage, the crystalline structure can be greatly improved

3.3 eccentric bottom tapping (EBT)

usually tapping is inclined furnace body, and molten steel is poured into ladle through tapping trough. Since 1986, the eccentric bottom tapping has been adopted, that is, the steel port is opened below the eccentric side of the electric arc furnace bottom, so that the slag on the steel level can be discharged before tapping, and then the steel can be tapped from the bottom, so that the molten steel can be separated from the acid slag, which is convenient for LF ladle refining, and the steel with high purity can be refined more stably, while improving the production efficiency. The test shows that with EBT, the oxygen content can be further reduced (an average decrease of 0.4). The most outstanding advantage is to improve the morphology of inclusions, so that the class B coarse series and class D coarse series inclusions, which have the worst impact on contact fatigue life, can be significantly improved

3.4 electroslag remelting (ESR)

the electroslag remelting process is very similar to the vacuum smelting process of consumable electrode except for the resistance required for the formation of melting in the slag pool at the bottom of the electrode. It can not only send the molten slag pool into the furnace, but also provide powder slag. When the arc is triggered between the bottom plate and the electrode, the powder slag will melt quickly. When the steel drops pass through the slag pool, the steel is refined. Sulfur, oxygen and other harmful impurities can be removed by controlling the composition of slag. The solidification mode of the steel ingot formed finally reduces the pores, minimizes the segregation, and improves the physical properties of the steel key in the transverse and longitudinal directions. As a method of producing high-quality steel, it will continue to be used or combined with other smelting methods

in addition, the surface quality of steel ingots and billets is cleaned, and there is a strict nondestructive testing device. Four methods (eddy current, magnetic particle, leakage magnetic beam and ultrasonic testing) are used to conduct a total of 4-7 times of flaw detection, so as to fully ensure that the steel leaves the factory without cracks

4 smelting technology of developed countries

Japan introduced vacuum degassing equipment in the 1960s [3, 5]; In the 1970s, the introduced LF and CC technologies were improved; In the 1980s, it has been committed to developing the so-called long-life and ultra long-life bearing steel. For example, Z steel developed by NSK is one of its latest achievements [6]. This steel is a low-cost high-quality steel developed by improving steelmaking equipment and smelting conditions on the basis of a large number of tests. Its titanium content is less than 0.004%, oxygen content is less than 9, and sulfur content is less than 0.0008% (to reduce bearing noise). Compared with general vacuum degassed steel (MGH), its bearing life (L10) is doubled. On this basis, the electric furnace bottom blowing method, LF slag discharge structure, deoxidation method, temperature control and mixing in LF and Rh are improved, and a set of Shanyang new steelmaking method snrp (Sanyo new refining process) [7] is established to control the oxygen content of steel at about 5, and a new inclusion evaluation method (NSK isd2 method) is used to control the size, morphology and distribution of inclusions, so that inclusions are evenly dispersed and large inclusions are eliminated, An ultra long life and high reliability bearing steel EP steel has been developed. Its L10 is 5 times that of Z steel and 10 times that of general vacuum degassed steel, reaching 80 times the calculated life (the calculated life L10 of bearing steel made of atmospheric smelting is 1), and the fatigue limit is 700~900mpa higher than that of Z steel, reaching 1030mpa. It is especially suitable for bearings that work under the conditions of grease lubrication and clean oil lubrication and require high reliability and long service life, such as automobile hub parts and related electrical appliances, railway vehicles and high-speed motor bearings

Sweden developed asea-skf ladle refining technology in 1964. The double shell electric furnace is used together with this refining technology, which is called skf-mr method. After continuous improvement, it has been used until now. In addition to skf-asea ladle refining unit, a duplex electric arc smelting furnace is also used in this process. The duplex furnace has Hongya aluminum plant area with each belt to be shelved for 3 years for resource reuse (the original Hongya aluminum industry is a project that plans to process 200000 tons of aluminum alloy profiles and 300000 tons of aluminum production lines and build corresponding auxiliary facilities. The oxygen fuel burner has two furnace cans and two furnace covers, one with graphite electrode and the other without electrode. One furnace smelting, the other furnace charging and preheating. In the smelting furnace, the carbon and sulfur content is adjusted below the final maximum limit value. Then, the molten steel in the ladle is sent to have independent electricity ASEA ladle refining furnace with polar furnace cover. This equipment can provide many metallurgical processes, including vacuum degassing, desulfurization, deoxidation and adjusting the chemical composition of molten steel. In addition, under the condition of strict temperature control, induction stirring can also use aluminum for precipitation deoxidation, so that the oxygen content and non-metallic inclusion content of steel are very low

the finkl VAD ladle refining method developed by the United States in 1967 has also been continuously improved and is still in use today. The quality level of bearing steel is also very good and stable