Focusing on the characteristics of rolling bearings, the types of bearing steels, and the gap between bearing steels at home and abroad, this paper summarizes the art of the status of the requirement of the bearing steel of the high-end equipment, the types of the bearing steels, the processing equipment and metallurgical quality of the bearing steels, the heat treatment technologies, and the evaluation technologies for both metallurgical quality and performance. It is put forward that the important role to improve the rolling contact life of the bearing steel by ultra-purification technologies among different melting routes, the new heat treatment technologies and the new bearing steel developments. This paper pointed out that it needs to be done in the future through the refinement, the homogenization and the stabilization of the inclusions, carbides and the matrix of the bearing steel to improve the quality and performance of existing bearing steels, to develop the high performance heat treatment technologies, to innovate the high performance bearing steel and to strengthen the basic research on the mechanism of the fatigue-resistance of the bearing steels, which would finally enhances the rolling contact fatigue life of the bearing steel significantly.

The following process is used to produce wheel medium carbon bearing steel S55C: 120 t BOF smelting—► LF refining—► RH vacuum treatment —► 240 mm x 240 mm continuous casting billet—►Φ55 mm and Φ60 mm bar rolling. Catch carbon practice is used in BOF smelting to control end [C] \0. 10% , and the slagging-off detection system is e- quipped. The basicity of slag is controlled within 4.0 ~ 6.5 during LF refining. The cyclic degassing in RH is carried out under the condition of high vacuum degree ≤66. 7 Pa, and die soft blowing time after degassing is not less than 40 min. Protective casting is carried out in the whole casting process, and M-EMS and F-EMS as well as light reduction technology is applied, the control rolling and control cooling technology are adopted in the rolling process to control finishing rolling at 880 -950 ℃. The measuring results show that the oxygen content in product is ≤ 0.001 0% , and the titanium content is ≤ 0.001 5%. The internal quality of the bars meets the ultrasonic grade A； and there are no macro defects and large inclusions； and the longitudinal material fatigue life exceeds 10 ⁷ times.

The production flowsheet of 300 mm x400 mm casting bloom of bearing steel GCrl5(/% ： 0.95 ~ 1.05C, 0.20 ~0. 30Si, 0. 30 ~0.40Mn, 1.40 ~ 1.50Cr) is 120 t BOF-LF-RH-CC-continuous rolling to Φ60 mm products. The effect of high-temperature diffusion time 4. 5 ~ 24 h of casting bloom at 1180 ~ 1260°C on carbide banded structure of Φ60 mm hot-rolled products has been tested. Results show that with increasing holding time the rating of banded structure of hot-rolled products decreases, and with holding time 4.5 ~6.5 h, 6.5 ~ 10 h and ≥13 h the rating of banded structure of Φ60 mm products is respectively 2.5, 2. 0 and 1. 5. It is available based on the requirement on different rating of banded structure to define the corresponding holding time.

For bearing steel in the cold and hot charging heating for laboratory thermal simulation, analyzed the level of casting billet grain size of hot charging by different heating temperature, and compared the grain size under the condition of cold charging, find the reasonable hot charging heating temperature. The results show that： when the hot charging temperature over 700℃, compared with cold charging, its casting billet organization of grain become bulky, grain size level between grade 1 ~ 2； According to the work site ,the before phase change cooling rate of casting billet as an average of 0.41 ℃/s, the hot charging temperature of GCrl5 bearing steel casting billet should be controlled less than 670 ℃.

The effect of consumable electrode on ESR ingot cleanliness was investigated during electroslag remelting (ESR) of G20CrNi2Mo bearing steel. The results show that the ingot cleanliness is much correlated with that of electrode. The ingot oxygen content presents a rising trend with increasing electrode oxygen content. The SEM-EDS analysis reveals that the number density of low-melting-point CaO-MgO-Al ₂O ₃ inclusions in high oxygen-containing electrode is much larger than that in low oxygen-containing electrode. The low interfacial energy between low-melting-point inclusions and steel significantly limits the efficiency of inclusions removal, thus resulting in relatively high ingot oxygen content. With increasing carbon content before EAF tapping, the number of ingots less than 0.002 0% oxygen occupies total more than 90%.

Based on electromagnetic stirring (EMS) in the electroslag process fbr bearing steel GCrl5,the effects of EMS on the superalloy solidification structure and chemical composition are analyzed. The result is as follows: Electromagnetic electroslag can signiHcantly improve the heat transfer condition of ingot solidification process, reduce the formation of network carbide in steel GCrl5 ingot. At the same time, because of the effect of electromagnetic stirring, the segregation index of main elements such as C and Cr in the ingot is stable less than 1.03. When the stirring current is 50 A to 2(X) A, the frequency is 6Hz. , there is no net carbide in the center of the ingot, and the carbon segregation index is 1.02.

Nail-shooting technique is applied to measure shell thickness of typical high-carbon chromium bearing steel GCrl5 240 mm x240 mm casting bloom, and the electromagnetic stirring position at different casting speed is calculated by the solidification law which can determine the length of the liquid core and the solidification coefficient according to the solidification rate 0. 65 and 0.75. Meanwhile, compared with the calculation results of the secondary model of the casting machine, the influence of the casting speed on the quality of the continuous casting bloom is discussed without changing the position of final electromagnetic stirring (9.4 m). And the magnetic stirring strength of the final electromagnetic stirring is measured by using the tesla meter HT201 to determine the optimal process parameters of final electromagnetic stirring. The results show that increased pulling speed from 0. 68 m/min to 0. 75 m/min has better effect； the optimized electric stirring parameters are current 450 A and frequency 8 Hz ； after process improved, the qualified rate of central segregation is increased from original 75% to 92%.

Cleanliness in GCrl5 bearing steel produced by 120 t BOF-LF-RH-CC process investigated results show that the inclusions dominated in steel are Al ₂ 0 ₃ . MgO spinel and Al ₂ 0 ₃ -MgO-CaO type after LF refining and the Al ₂ O ₃ • MgO spinel is almost disappeared and the inclusions in steel are mainly liquid calcium aluminate after RH treatment. T. 0 content decreases to 5. 3 X 10 ^-6 after RH treatment and Al ₂O ₃ • MgO spinel regenerates in tundish liquid during casting, and the ≥20um calcium aluminate inclusions are not found in liquid at end RH and tundish, and in casting bloom.

Low secondary dendrite arm spacing (SDAS) and large center equiaxed crystal ratio (ECR) are beneficial to reduce center segregation of high-carbon steel casting bloom with M + F-EMS. A Cellular Automaton-Finite Element (CAFE) coupling model and secondary dendrite arm spacing (SDAS) model of 220 mm x 260 mm casting bloom of steel GCrl5 are established to study the effects of M-EMS, superheat and casting speed on central equiaxed crystal ratio (ESR) and SDAS. It is found that ECR in the center of bloom increases with decreasing superheat and increase intensifying M- EMS, while SDAS decreases with the decrease of superheat and with the increase of M-EMS. The results reveal that M- EMS and superheat has a significant effect on center ECR compared with casting speed. Casting speed has the obvious in fluence on solidification end and central solid fraction in strand. Industrial test results as compared supeheat 35 ℃ and casting speed 0. 75 m/min less than superheat 25 ℃ and casting speed 0.8 m/min and with M + F-EMS, the ECR in the center of bearing steel GCrl5 bloom increases from original 27% to 38% and the SDAS is effectively refined, center carbon segregation index decreases from original 1.06 ～ 1.39 to 0.93 ～ 1.13.

When producing GCr15 bearing steel ϕ50 ~75 mm bar,there is center porosity in rolled bar. A numerical simulation is carried out to study the penetration of effective strain in the core of bar and optimize the rough rolling pass technology, increase the reduction of the first two passes from original 21 mm and 58 mm to 51 mm and 85 mm respectively, and reduce the third pass from 60 mm to 34 mm. Through the effective strain value gradually increases with the increase of the pass,the tensile stress in the bar becomes compressive stress after the optimized process,and the uniformity of deformation is also obtained to promote the deformation of core of casting slab be available to the closure of the center porosity. After the process optimization,the qualified rate by ultrasonic detection of bearing steel increases from original 93.25% to 96.06%.

The formation mechanism of CaO-MgO-Al ₂O ₃ inclusions in GCr15 bearing steel at LF refining end point is studied by ASPEX automatic scanning electron microscope combined with thermodynamic theory analysis. The results show that Al ₂O ₃ is the main type inclusion in molten steel when the LF refining started to reach stability, and then evolves into an approximately spherical Al-Mg-Ca-( S) type composite inclusion at LF refining end. The stable phase diagram of MgO • Al ₂O ₃/CaO • A1 ₂O ₃/A1 ₂O ₃ shows that MgO •Al ₂O ₃ can be transformed into CaO-MgO-Al ₂O ₃ inclusions when [ Ca] is greater than 1.2 x 10 ^-6 in molten steel. The MgO • A1 ₂O ₃ inclusion would be formed firstly in the refining process, afterwards ,the Ca would react with MgO • A1 ₂O ₃ inclusion to form CaO-MgO-A1 ₂O ₃ composite inclusion. As a result of the precipitation of CaS inclusion in the solidification, therefor the CaO-MgO-Al ₂O ₃ -(CaS) composite oxide inclusion is detected in the final steel sample.

By established a model of inclusions dynamic at the steel-slag interface the refining slag absorbing inclusions phenomenon is studied. Results show that certain parameters, i. e. particle size, interfacial tension and slag viscosity ,determine the inclusions transfer behavior. Paiticle size and interfacial tension determine definitely large size inclusions transfer behavior, while interfacial tension only determines definitely micro size inclusions rating ≤20 ㎛ transfer behavior. Macro-sizes affects the inclusions displacement more than the Micro-sizes. For the removal of Micro-inclusions, by inclusions mathematical dynamic model coupled by steel and slag surface tension models, the effect of interfacial tension on obsorbing process has been studied. It is obvious that the particles blow 122.9 ㎛  size could be rebounded into steel when they are flowed to steel-slag interface layer. It is obtained that there is no way by re-designing refining slags to effectively remove ≤ 122. 9 ㎛ micro-inclusions from steel to slag layer and further to get the aim to decrease the oxygen content in steel.

The tested bearing steel 9Cr18Mo (/% ： 0.98C, 0.21 Si, 0.32Mn, 0.005P, ＜0. 001S, 16.95Cr, 0.51Mo) is melted by 500 kg vacuum induction melting furnace (VIM) -electroslag remelting unit (ESR) -vacuum arc remelting unit (VAR) triplex process, forged breakdown and rolled to Φ30 mm bar products. The gas content, deleterious elements content and non-metallic inclusions in steel 9Crl8Mo are examined and analyzed. Results show that the triplex process is available to increase the cleanliness of bearing steel, the oxygen content in tested steel 9Cr18Mo is 0.0008% , nitrogen content is 0.0038% and the S content is ＜0. 001 % , and with controlling the Ti content and pentad-deleterious elements content in raw materials, in finished products the Ti content is ＜0.002% , the Sn, As and Sb content are respectively ＜0.002% and the Pb and Bi content are respectively ＜0.0001 % ； by triplex process the nonmetallic inclusions in steel is a little, and the inclusions with size less than 3μm amount are more than 90% of total inclusions up to quite high cleanliness level.Material Index Bearing Steel 9Cr18Mo, Cleanliness, VIM-KSR-VAR Triplex Melting Process, Inclusions.

With the deoxidation by adding ferroaluminium and ferrosilicon in EAF tapping and the LF initial refining slag (/%:27.39~37.34 Al ₂O ₃，38.42~38.68 CaO，14.20~18.38 SiO ₂，8.50~10.72 MgO，0.82~0.89 FeO，0.27~0.33 MnO，0.69~0.74 S，0.66~0.75TiO ₂，（CaO）/（SiO ₂）=2.09~2.72,（CaO）/（Al ₂O ₃）=1.04~1.40) _, at LF end point the T[O] is 0.0012% ~0.001 _{9% , the T[N] is 0.0043% ~0.0050% , and the [Ti] and [Ca] are respectively 0.002% and 0.006% ~ 0.009%. The analysis on oxide inclusions in bearing steel GCr15 at LF refining end show that the main oxide inclusions in steel are magnesia-alumina spinel (} MgO·Al₂O_{3 ) and calcium oxide-niagnesium-alumina spinel (} CaO·MgO·Al₂O_{3 ) ； the average size of magnesia-alumina spinel is less than 0. 5μm, and as MnS, TiN etc precipitated on them the average size increases； the average size of calcium oxide-inagnesia-alumina is normally more than 2μm and in refining temperature this inclusions are liquid state and easily aggregate and grow up, their size ( 1.39 〜2.12μm) is more than solid status calcium oxide-magnesia-alumina-MnS, so easily removed by floating up and absorbed by refining slag. With decreasing sulfur content in liquid during refining process, the average size of bearing MnS compound inclusions with core of magnesium-alumina and calcium oxide-magnesium-alumina spinel decreases. With suitable decrease of MgO content in refining end slag, optical basicity and viscosity of end slag the amount and average size of inclusions in steel shall be decreased.}

The critical point measurement and continuous cooling transformation test with cooling rate 0.02 ~40 °C/s of high temperature bearing steel M50 (/% ：0. 82C,4. 25Cr,4. 17Mo, 1. 03V) are carried out by expansion method in DIL805A quenching dilatometer, and the static CCT curve is drawn. Combined with the microstructure and Vickers hardness analysis at room temperature, the effects of cooling rate and austenitizing temperature ( 1 000 °C and 1 120 °C)on the microstructure transformation as well as the static CCT curve of high temperature bearing steel M50 are systematically studied. The results show that the critical point of high temperature bearing steel M50 is not influenced by austenitizing temperature. The temperatures of A _c1 and Accm are 808 °C and 852 °C respectively ； the critical cooling rate of pearlite transformation is 0. 05 °C/s. The increase of austenitizing temperature promotes the decrease of the initial temperature of martensite transformation and the right shift of bainite transformation interval on the static CCT curve, and significantly improves the room temperature hardness of high temperature bearing steel M50 at lower cooling rate.

A micro segregation model of solute elements in the mushy zone in continuously cast bloom of bearing steel GCrl5 is established in consideration of δ/γ phase transformation, which is applied in the solidification heat transfer of 220 mm x 260 mm continuous casting bloom. The results show that accurate solidus and liquidus temperature and relationship between temperature and solid fraction during the solidification process of high carbon steel can been acquired by the model only y phase precipitates out from liquid steel directly during the solidification process of bearing steel GCrl5 ；the segregation ratio of S,P and C is bigger at the final solidification stage, as solid fraction increases, the effect of cooling rate on segregation is more remaritable, the content of S,P and cooling rate have a bigger effect on ZDT. After the continuous casting process parameters optimized based on the solidification heat transfer model, the center carbon segregation ratio is 0.96 to 1. 05 and the internal cracks don't appear.

For the 55SiCr valve spring steel with strict service condition,its deoxidation,desulfurization and inclusion change are studied by laboratory experiments under a low oxygen condition by adding SiCaBa alloy into the molten steel. The results show that SiCaBa alloy has the effect of deep deoxidation and desulfurization, as well as refining the inclusion size. By adding 0.48 kg/t steel of SiCaBa alloy with 49. 8% Si-25. 6% Ca-11. 1% Ba and a proper amount of refining slag with Fe ₂0 ₃ content less than 1% ,the T[0] and [S] can respectively decrease to 11 x 10 ^-6 and 8 x 10 ^-6.

The process flowsheet for steel 20CrMnTiH is 100 t BOF-LF-VD-bloom casting-rolling. By improving converter tapping [C] ≥08% , optimizing refining slag system, controlling the CaO/Al ₂O ₃ in slag 1. 5 to 1. 7 ,using feeding SiCa wire to replace feeding Ca wire and preventing secondary oxidation of molten steel in casting, the oxygen content in gear steel 20CrMnTiH is 0.0015% ~0. 0019% and rating of inclusions in steel is ≤0.5.

The thermodynamics and kinetics theoretical basis of modification of inclusions by calcium treatment is expounded. Through the test by LF-VD flowsheet,at calcium-free treatment conditions,except low carbon steel,the castability of medium and high carbon steel is good, the Ca content in the steel can be controlled by ≤0.001% ,and the hit rate of non-metallic inclusions of rating D and Ds W1,0 is obviously improved. By optimizing ingredient of refining slag and using a method of later sulfur-alloying for sulfur-containing aluminum killed steel, it can improve the morphology of inclusions, resulting in fine,diffuse distribution of ( Ca / Mn) • S inclusions to improve the cutting performance of steel.