Long-life bearing steel and preparation method therefor, and electroslag remelting mold powder

Abstract

Disclosed in the present invention are long-life bearing steel and a preparation method therefor, and electroslag remelting mold powder. The bearing steel is prepared by electric furnace or converter smelting, LF refining, vacuum degassing, continuous casting or die casting pouring, electroslag remelting and rolling, and rare-earth alloys, lanthanum and cerium, are added into molten steel before continuous casting or die casting pouring. According to the present invention, new electroslag remelting mold powder is used, so as to solve the problem that inclusions and carbide precipitation in bearing steel affect the contact fatigue life of the bearing steel, the contact fatigue life L10 value of the bearing steel under 4.5 GPa can be stably increased to 5×107 turns or more, and the use requirements of bearing steel in high-end fields such as high-speed rail bearings, aviation bearings, and wind turbine bearings can be met.

Description

Long-life bearing steel, preparation method thereof, and electroslag remelting protective slag Technical Field

[0001] The present invention relates to the technical field of steelmaking, and more particularly to a long-life bearing steel and a preparation method thereof, and an electroslag remelting protective slag. Background Art

[0002] Bearings are core components of advanced manufacturing, with large quantities and wide applications, and play an important supporting role in the manufacturing industry. Their development trend is higher reliability, longer life and better environmental adaptability. The most widely used bearing steel is high carbon chromium GCr15 bearing steel. The contact fatigue life (L10 value) of ordinary bearing steel under 4.5GPa is less than 10 7 The application of ordinary bearing steel in ordinary automobile or mechanical parts can meet the relevant fatigue life requirements. However, for EMU high-speed rail or aerospace fields, ordinary bearing steel cannot meet their reliability and long life requirements. It is necessary to develop long-life bearing steel to meet the relevant requirements. The contact fatigue life (L10 value) must be higher than 2*10 7 Two factors primarily affect the contact fatigue life of bearing steel: inclusions and carbide precipitation. Developing long-life bearing steel requires addressing key issues such as the complete detoxification of inclusions and the miniaturization of carbides. Smelting and casting are crucial for controlling inclusion and carbide precipitation.

[0003] Recent studies have shown that rare earth treatment can improve the fatigue life of bearing steel. However, even if rare earth treatment forms a large number of fine rare earth inclusions less than 15 μm, it is still inevitable that large rare earth inclusions greater than 50 μm will form and cannot be eliminated, which will seriously damage the stability of the bearing steel.

[0004] In order to solve the problem of large rare earth inclusions, the existing technology proposes the idea of ​​rare earth treatment followed by electroslag treatment.

[0005] For example, Chinese patent application 201210105658.X discloses a rare earth-doped bearing steel and its preparation method, comprising the following steps: a) weighing the components by weight percentage; b) vacuum induction melting; c) pouring a remelting electrode rod; d) electroslag remelting to obtain a steel ingot; e) homogenization heat treatment; f) forging a bar for bearing processing; and g) spheroidizing heat treatment. However, this preparation method fails to understand how the rare earth content affects the contact fatigue life of the bearing steel, nor does it address how to stably control the rare earth content to ensure that the contact fatigue life meets the required longevity.

[0006] Chinese patent application No. 202210290982 proposes a new material and preparation method for rare earth railway carburized bearing steel. This method involves controlling the range of the rare earth element Ce and performing electroslag treatment. However, the slag system used in the electroslag treatment is a conventional electroslag slag system, with the electroslag remelting mold slag composition consisting of: CaF2: 30%, Al2O3: 45%, CaO: 30%, and MgO: 5%. With this slag system, rare earth inclusions in the electrode rod react with the steel slag during the electroslag treatment process to form alumina inclusions or calcium aluminate (Ds) inclusions. Furthermore, it is difficult to control the rare earth element content in the steel within the ideal range.

[0007] In view of the above situation, it is urgent to study a process method for smelting long-life bearing steel. On the basis of sufficient research on the effect of rare earth content on contact fatigue life, the influence of rare earth treatment on the precipitation of inclusions and carbides should be comprehensively considered to improve the fatigue life of bearing steel.

[0008] Summary of the Invention

[0009] In view of the problem that inclusions and carbide precipitation in the prior art affect the contact fatigue life of bearing steel, the purpose of the present invention is to provide a long-life bearing steel and its preparation method and electroslag remelting protective slag, which can extend the contact fatigue life of bearing steel at 4.5GPa to L 10 The value is steadily increased to 5×10 7 The above can meet the requirements of bearing steel in high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A first aspect of the present invention provides a method for preparing bearing steel, comprising the following steps:

[0012] S1, molten steel is subjected to the following steps: electric furnace / converter smelting, LF refining, vacuum degassing, and continuous casting / mold casting to produce an ingot, wherein rare earth alloys lanthanum and cerium are added to the molten steel before continuous casting / mold casting;

[0013] S2, cleaning the surface of the ingot and making the ingot into an electrode rod for electroslag remelting;

[0014] S3, using the electrode rod as a raw material, performing electroslag remelting in an electroslag furnace to obtain an electroslag ingot; the protective slag used in the electroslag remelting process includes the following components in weight percentage: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%;

[0015] S4, the electroslag ingot is diffused in a soaking furnace at 1200-1250° C. and then rolled into bearing steel.

[0016] Preferably, the protective slag in step S3 consists of the following components in weight percentage: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%.

[0017] Preferably, in step S1, rare earth alloys lanthanum and cerium are added by a dropping method, wherein before the rare earth alloy is added, argon gas is blown into the bottom of the ladle containing molten steel to blow open the slag surface to expose the molten steel, and then the rare earth alloy is added into the molten steel; after the rare earth alloy is added, the weight percentage of the rare earth elements in the molten steel is controlled to be Ce: 0.006~0.011%, La: 0.003~0.006%.

[0018] Preferably, the rare earth alloy is added so that the yield of the rare earth elements in the final bearing steel product is 50-60%.

[0019] Preferably, in step S1, when continuous casting is adopted, the superheat of the molten steel is controlled at 30-40°C, and a stopper rod is used to control the flow in the casting crystallizer, and argon is blown into the stopper rod with a flow rate range of 2-5NL / min.

[0020] Preferably, in step S1, the mass of the ingot is 1.5 to 3 tons. When the ingot is a square billet, the side length of the ingot is 0.33 to 0.38 m and the length is 2 to 4 m; when the ingot is a round ingot, the diameter is 0.35 to 0.4 m and the length is 2 to 3 m.

[0021] Preferably, in step S3, the electroslag remelting process is carried out under a protective atmosphere, using a constant melting rate, and the melting rate of the electrode rod during the electroslag remelting process is 5-8 kg / min.

[0022] Preferably, in step S3, the amount of mold slag added is 40-60 kg / t 钢 .

[0023] Preferably, the bearing steel includes the following chemical components in weight percentage: C: 0.9-1.1%, Cr: 1.4-1.6%, Mn: 0.3-0.6%, Si: 0.2-0.3%, Al: 0.008-0.03%, Ce: 0.004-0.01%, La: 0.002-0.006%, Ti<0.0015%, N<0.005%, S<0.01%, P<0.015%, and the remainder is iron and other inevitable impurities.

[0024] Preferably, the bearing steel includes inclusions, more than 95% of which are fine inclusions with a rare earth oxide content exceeding 60% and a size less than 10 μm, and the rest are composite inclusions of rare earth oxide-aluminum oxide-calcium oxide-silicon oxide, and the size of the composite inclusions is less than 15 μm.

[0025] Preferably, the contact fatigue life L of the bearing steel at 4.5 GPa is 10 5×10 7 Turn above.

[0026] The second aspect of the present invention provides a bearing steel prepared by the above-mentioned preparation method, wherein the bearing steel includes the following chemical components in weight percentage: C: 0.9~1.1%, Cr: 1.4~1.6%, Mn: 0.3~0.6%, Si: 0.2~0.3%, Al: 0.008~0.03%, Ce: 0.004~0.01%, La: 0.002~0.006%, Ti<0.0015%, N<0.005%, S<0.01%, P<0.015%, and the remainder is iron and other inevitable impurities.

[0027] The third aspect of the present invention provides an electroslag remelting protective slag used in the above-mentioned preparation method, wherein the protective slag includes the following components in weight percentage: CaF2: 40~65%, Al2O3: 5~10%, ZrO2: 10~15%, CaO: 5~10%, MgO: 2~5%, SiO2: 3~5%, Ce2O3+La2O3: 10~15%.

[0028] Preferably, the protective slag is composed of the following components by weight: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%.

[0029] Unless otherwise specified, the contents of molten steel, steel ingots, mold slag and other components in the present invention are all expressed in weight percentages.

[0030] The present invention has the following beneficial effects:

[0031] The contact fatigue life L of the bearing steel of the present invention under 4.5GPa is 10 The value (contact fatigue life that meets the failure probability of less than 10%) is stable at 5×10 7 This performance is significantly higher than that of ordinary high-carbon chromium bearing steel GCr15, and can be widely used in high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings. Furthermore, the long-life bearing steel produced by this invention can replace carburized bearing steel, which is more expensive to manufacture, in industrial applications. DETAILED DESCRIPTION

[0032] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0033] The present invention provides a method for preparing long-life bearing steel, the process of which is electric furnace (or converter) smelting - LF refining - VD (or RH) vacuum degassing - continuous casting (or die casting) pouring - electroslag remelting - rolling. The key to the process design is to stably control the content of rare earth elements and the size of rare earth inclusions during the preparation process, so as to ultimately completely eliminate the hazards of inclusions, and to use rare earth elements to inhibit the precipitation of carbides at grain boundaries without affecting the performance of the bearing steel, thereby significantly improving the life of the bearing steel. The contact fatigue life of the prepared high-carbon chromium bearing steel exceeds that of conventional carburized bearing steel, and can replace the more expensive carburized bearing steel in industrial applications.

[0034] In an embodiment of the present invention, a method for preparing bearing steel comprises the following steps:

[0035] S1, molten steel is subjected to electric furnace / converter smelting, LF refining, vacuum degassing, continuous casting / mold casting to obtain an ingot, and rare earth alloys lanthanum and cerium are added to the molten steel before continuous casting / mold casting.

[0036] Specifically, the large-scale production process involves electric furnace / converter smelting—LF refining—VD (or RH) vacuum degassing—bloom continuous casting (or round billet continuous casting or mold casting) to produce square or round ingots. Rare earth alloys lanthanum and cerium are added to the molten steel before continuous casting / molding. The resulting ingot weighs 1.5 to 3 tons. If the final ingot is a square billet, its side length is 0.33 to 0.38 meters and its length is 2 to 4 meters. If the final ingot is a round ingot, its diameter is 0.35 to 0.4 meters and its length is 2 to 3 meters. These ingot designs are selected to meet the size requirements of the subsequent electroslag electrode rods.

[0037] In the above-mentioned large-scale production process, the throughput of the electric furnace or converter is 60 to 150 tons. If the ingot size of the square billet or round billet is larger than the size described above, the round billet can be prepared by initial rolling and opening as an electrode rod for electroslag remelting, with a diameter of 0.35 to 0.4 meters and a length of 2 to 3 meters. During the smelting process, the capacity of the electric furnace or converter is 60 to 150 tons, which can ensure the smooth production of electrode rods for electroslag in the subsequent production. If the capacity of the primary refining furnace is too low, the production cost of bearing steel will be relatively high. If the capacity of the primary refining furnace is too large, it will make it difficult to cast stably during the continuous casting process. At the same time, considering that the ingot shape of the continuous casting billet or the molded ingot shape may not meet the size requirements of the electrode rod, the required electrode rod size can be achieved during the initial rolling and opening process.

[0038] The electrode rods required for subsequent electroslag smelting are produced using a large-scale production process, similar to conventional bearing steel production processes. This choice aims to reduce production costs. Unlike conventional bearing steel production, rare earth alloys are added before pouring to provide the rare earth elements needed for stable control of the rare earth composition of the final long-life bearing steel. The rare earth alloys, lanthanum and cerium, are added using a drop-in method. Before adding the rare earth alloys, argon is blown into the bottom of the ladle containing the molten steel to open the slag surface and expose the molten steel. The rare earth alloys are then added to the molten steel, with the yield of the rare earth alloys being 50-60% in the final bearing steel. After the rare earth alloys are added, their concentrations are controlled to 0.006-0.011% for Ce and 0.003-0.006% for La. This drop-in method offers high rare earth yields, is easy to operate, and allows for control over the final form of the rare earth elements in the bearing steel. After the rare earth alloy is added to the molten steel, the rare earth element content in the molten steel is required to be controlled at Ce: 0.006-0.011%, and La: 0.003-0.006%. This content is slightly higher than the rare earth content required in the steel after the final electroslag remelting, mainly considering the slight loss of rare earth elements during the electroslag remelting process.

[0039] When the above-mentioned ingot is cast by continuous casting, the superheat of the molten steel is controlled at 30-40°C. At the same time, a stopper rod is used to control the flow in the casting crystallizer, and argon is blown into the stopper rod to prevent nozzle blockage during the casting process. Among them, the casting superheat of 30-40°C is selected mainly because the castability of the molten steel will be slightly reduced after the addition of rare earths, so a slightly higher superheat of the molten steel is set. At the same time, argon is blown into the casting nozzle of the crystallizer to avoid nozzle blockage. Because step S1 is only used to prepare the electrode rod for subsequent electroslag, the segregation problem caused by high superheat and the bubble problem caused by argon blowing that need to be considered in the conventional bearing steel billet production process do not exist in the present invention because the subsequent electroslag remelting process is required.

[0040] The method for preparing bearing steel of the present invention further includes the following steps after step S1:

[0041] S2, cleaning the surface of the ingot and making the ingot into an electrode rod for electroslag remelting;

[0042] S3, using electrode rods as raw materials, and performing electroslag remelting in an electroslag furnace to obtain electroslag ingots; the protective slag used in the electroslag remelting process includes the following components in weight percentage: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%.

[0043] The addition amount of the above-mentioned mold slag is 40~60kg / t 钢 , where t 钢Refers to tons of steel. The electroslag ingot obtained by electroslag remelting is a cylindrical electroslag ingot with a diameter of 0.4 to 0.6m.

[0044] Electroslag remelting (ESR) is a key step in producing long-life bearing steel. This is primarily due to the fact that bearing steel produced through large-scale production processes inevitably contains a large number of inclusions with particle sizes greater than 15μm. In particular, the high density of these large rare earth inclusions generated after the rare earth treatment in step S1 inevitably reduces the contact fatigue life of the bearing steel. Therefore, ESR is required for bearing steel treated with rare earth elements to consistently improve its contact fatigue life.

[0045] During electroslag remelting (ESR), an energized circuit connects the electrode rod, slag, and molten steel in the mold. Under low-voltage, high-current conditions, localized heating of the slag causes the tip of the electrode rod, where it contacts the slag, to gradually dissolve into droplets. A large number of these droplets then pass through the slag layer and fall into the mold's molten steel pool. The portion of the molten steel pool that contacts the mold solidifies again, purifying the molten steel. ESR filters the molten steel through mold slag, completely removing large inclusions.

[0046] The present invention utilizes a novel electroslag remelting mold slag system that not only removes large inclusions from molten steel but also stabilizes the rare earth element content in the finished bearing steel. Neither excessively high nor excessively low rare earth element content in bearing steel improves the contact fatigue life and bending fatigue life of the bearing steel. The inventors discovered that when the rare earth element Ce and La content in the bearing steel meets the following criteria: Ce: 0.004-0.010%, La: 0.002-0.006%, the contact fatigue life can be significantly improved. This is because, in addition to reducing the risk of inclusions and improving the contact fatigue life of the bearing steel, rare earth elements also limit carbon diffusion in the steel and inhibit carbon precipitation at grain boundaries. However, if the rare earth element content is too high, since all rare earth elements are large atoms, they can affect the overall plasticity of the bearing steel, thereby reducing its contact fatigue life. If the rare earth element content is too low, the steel will not produce rare earth element oxide inclusions, but instead will produce traditional aluminum-calcium oxide inclusions. However, aluminum-calcium oxide inclusions are highly harmful and can deteriorate the contact fatigue life of bearing steel. Therefore, the rare earth element content must be controlled within the above range during electroslag remelting. Because rare earth elements are active, they are particularly susceptible to reaction with mold slag during electroslag remelting, leading to rare earth element loss.

[0047] The inventors have discovered that using the following ESR mold slag system: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, and Ce2O3 + La2O3: 10-15% ensures that the rare earth element content during the ESR process is stably controlled within the desired range. Furthermore, after ESR, rare earth element inclusions are essentially limited to fine inclusions of rare earth oxides, which are not only harmless but also improve the solidification structure of bearing steel by serving as nucleation sites.

[0048] The protective slag system of the present invention uses ZrO2, mainly considering that ZrO2 has too strong a neutral property and is not easy to react with rare earth elements. It is also not easy to absorb water relative to MgO and CaO, and can well adjust the performance of the electroslag. At the same time, the MgO and CaO contents are controlled in a relatively low range to prevent the protective slag from absorbing water and avoid hydrogen-induced cracks in the bearing steel. Compared with ordinary bearing steel electroslag slag systems, the Al2O3 content in the protective slag system designed in the present invention is greatly reduced, mainly considering avoiding the generation of a large amount of Al2O3 brittle inclusions during the electroslag remelting process. Because the hardness of Al2O3 brittle inclusions is high, it has a great impact on the contact fatigue life of the bearing steel.

[0049] In the above-mentioned electroslag remelting process, argon needs to be blown into the crystallizer for more than 20 minutes before power is turned on to replace the remaining air in the crystallizer. The electroslag remelting process needs to be carried out under a protective atmosphere (such as pure argon), and constant melting rate electroslag remelting is adopted. The melting rate of the electrode rod during the electroslag remelting process is controlled to 5-8 kg / min. After the electroslag remelting is powered on, the electroslag ingot is obtained, and argon blowing protection must be maintained for more than 15 minutes to prevent secondary oxidation of the ingot. Among them, electroslag remelting under a protective atmosphere is mainly to prevent secondary oxidation of the ingot. If a protective atmosphere is not used, it is easy to cause serious loss of silicon, carbon and rare earth in the molten steel due to oxidation. Control of the melting rate during the electroslag remelting process ensures stable control of the final electroslag ingot structure.

[0050] Unless otherwise specified, the protective atmosphere in the present invention refers to pure argon, wherein the volume fraction of Ar is above 99.6%.

[0051] The diameter of the electroslag ingot obtained by electroslag remelting is required to be 0.4 to 0.6m, mainly to meet the size requirements of the ingot for subsequent initial rolling and high-temperature diffusion process in the soaking furnace.

[0052] The method for preparing bearing steel of the present invention further includes the following steps after step S3:

[0053] S4, the electroslag ingot is diffused in a soaking furnace at 1200-1250°C and then rolled into bearing steel.

[0054] The purpose of selecting high-temperature diffusion of electroslag ingots in a soaking furnace is to further reduce the carbide size, thereby improving the contact fatigue life. The high-temperature diffusion temperature in the soaking furnace is 1200-1250°C.

[0055] The above-mentioned bearing steel includes the following chemical components in weight percentage: C: 0.90~1.1%, Cr: 1.4~1.6%, Mn: 0.30~0.60%, Si: 0.20~0.30%, Al: 0.008~0.030%, Ce: 0.004~0.010%, La: 0.002~0.006%, Ti<0.0015%, N<0.005%, S<0.01%, P<0.015%, and the balance is iron and other inevitable impurities.

[0056] As previously mentioned, controlling the rare earth element content within 0.004-0.010% Ce and 0.002-0.006% La can significantly improve the contact fatigue life of bearing steel. Using appropriate ESR mold slag during electrode rod preparation and ESR can stabilize the rare earth element content in the finished bearing steel within this range. Neither excessively high nor low rare earth element content improves the contact fatigue life and bending fatigue life of bearing steel. The content ranges of other elements in the bearing steel are similar to those of conventional bearing steel.

[0057] Over 95% of the inclusions in the bearing steel are fine inclusions with a rare earth oxide content exceeding 60% and a size less than 10 μm. The remainder are composite inclusions of rare earth oxide, aluminum oxide, calcium oxide, and silicon oxide, with sizes less than 15 μm. In the present invention, inclusion sizes are determined by automated analysis of SEM images of steel cross-sections using Oxford Instruments' AZtecFeature SEM particle analysis system.

[0058] In the above-mentioned production method, inclusion control in bearing steel requires not only size control but also composition control. This process control ensures that the majority of inclusions are harmless, fine-particle rare earth oxides. These inclusions deform similarly to the steel matrix during subsequent rolling and are therefore generally harmless. Furthermore, this inclusion control process reduces the amount of conventional aluminum oxide-calcium oxide-silicon oxide inclusions, extending the life of the bearing steel.

[0059] The contact fatigue life L of the above bearing steel under 4.5GPa 10 (Contact fatigue life that meets the failure probability of less than 10%) is stable at 5×10 7The contact fatigue life is tested by a contact fatigue testing machine (TRF-1000) produced by Tokyo Hengji Co., Ltd., Japan.

[0060] The bearing steel and its preparation method and the electroslag remelting protective slag of the present invention are further introduced below with reference to specific examples.

[0061] Example 1

[0062] This embodiment adopts a 150t electric furnace smelting-LF-VD vacuum degassing-bloom continuous casting-electroslag remelting-rolling process, which mainly includes the following steps:

[0063] 1) The molten steel is subjected to 150t electric furnace smelting, LF refining, and VD vacuum degassing in sequence. The molten steel is smelted and refined according to conventional bearing steel production methods. After the VD vacuum degassing treatment, the composition of the molten steel is [C]: 0.98%, [Cr]: 1.48%, [Mn]: 0.41%, [Si]: 0.25%, [Al]: 0.015%, [Ti]: 0.0011%, [N]: 0.0045%, [S]: 0.0045%, [P]: 0.013%, and the balance is Fe and other inevitable impurities. The above composition meets the conventional standard for GCr15 bearing steel. After the composition test is qualified, the ladle bottom blowing argon flow rate is increased to 300-500 NL / min to ensure the slag surface is blown open. 15 kg of rare earth alloy containing La and Ce (based on a 55% yield) is manually added. The bottom blowing flow rate is then slightly reduced to 100-200 NL / min to ensure the slag surface is closed. After a slightly increased blowing (300-500 NL / min) and stirring for 2 minutes, the bottom blowing argon flow rate is adjusted to 50-100 NL / min, the required low-pressure stirring rate. The rare earth element content of the molten steel is subsequently measured to be 0.0065% for Ce and 0.0034% for La. After soft blowing and stirring in the ladle, the molten steel is transferred to the continuous casting process for casting into 0.35 m square billets, which are then cut into 3.8 m long ingots. During the continuous casting process, the molten steel superheat is controlled at 35°C. A stopper rod is used to control the flow of the molten steel. Argon is blown into the stopper rod to prevent nozzle blockage during the pouring process. The argon flow rate is 2NL / min. Since the continuous casting process can continuously pour multiple heats of steel, the ingots from one heat can be selected and cut into ingots for subsequent electroslag treatment. Multiple ingots can be produced from a single heat.

[0064] 2) Cleaning the surface of the ingot obtained in step 1, grinding away the iron oxide scale on the surface of the ingot, and making an electrode rod that can be used for slag smelting.

[0065] 3) Electrode rods are loaded into an electroslag furnace as raw material for electroslag remelting. The electroslag furnace performs electroslag remelting under an Ar gas protective atmosphere. Before power is applied to the electroslag, argon is blown into the crystallizer for at least 20 minutes to displace any remaining air. A 0.6-meter diameter crystallizer is used, and the electroslag remelting protective slag composition is 45% CaF2, 8% Al2O3, 15% ZrO2, 8% CaO, 5% MgO, 4% SiO2, and 15% Ce2O3 + La2O3. A total of 160 kg of electroslag remelting protective slag is added. Power is then applied to begin the electroslag remelting process. Electroslag ingots with a diameter of 0.6 m and a length of 1.6 m are produced. The entire electroslag remelting process must be performed under a protective atmosphere. A constant melting rate is used for electroslag remelting, and the melting rate of the electrode rods is controlled at 6 kg / min. After the electroslag is powered on, the electroslag ingot is obtained, and argon blowing protection must be maintained for 15 minutes to prevent secondary oxidation of the ingot.

[0066] 4) The electroslag ingot is transported to a soaking furnace at 1220°C for 16 hours of high-temperature diffusion, and then initially rolled into a square billet with a side length of 140 mm. It is then finish-rolled into bearing steel with a diameter of less than 60 mm according to user requirements. Its composition is: [C]: 0.97%, [Cr]: 1.45%, [Mn]: 0.40%, [Si]: 0.24%, [Al]: 0.014%, [Ce]: 0.005%, [La]: 0.0032%, [Ti]: 0.0012%, [N]: 0.0048%, [S]: 0.003%, [P]: 0.012%, and the balance is Fe and other inevitable impurities. The inclusions in the steel were automatically scanned and analyzed by electron microscope (SEM) combined with the AZtecFeature system of Oxford spectrometer. 98% of them were fine inclusions with rare earth oxide content exceeding 60%, and their sizes were all less than 10μm. 2% were rare earth oxide-aluminum oxide-calcium oxide-silicon oxide composite inclusions, and their sizes were less than 15μm. At the same time, the contact fatigue life of the bearing steel was tested under 4.5GPa. A total of 12 samples were tested, and the results were L 10 The value is 5.7×10 7 change.

[0067] The prepared bearing steel has stable performance and long contact fatigue life, and is suitable for high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0068] Example 2

[0069] This embodiment adopts a 150t converter smelting - LF refining - RH vacuum degassing - round billet continuous casting - electroslag remelting - rolling process, which includes the following steps:

[0070] 1) The molten steel is subjected to a 150t converter smelting, LF refining, and RH vacuum degassing process in sequence. The molten steel is smelted and refined according to conventional bearing steel production methods. After the RH vacuum degassing process, the composition of the molten steel is [C]: 1.05%, [Cr]: 1.58%, [Mn]: 0.59%, [Si]: 0.28%, [Al]: 0.029%, [Ti]: 0.0014%, [N]: 0.0035%, [S]: 0.0065%, [P]: 0.014%, and the balance is Fe and other unavoidable impurities. The above composition meets the conventional standard for GCr15 bearing steel. After passing the composition test, the ladle bottom blowing argon flow rate is increased to 300-500 NL / min to ensure the slag surface is blown open. 15 kg of rare earth alloy containing La and Ce (based on a 55% yield) is manually added. The bottom blowing flow rate is then slightly reduced to 100-200 NL / min to ensure the slag surface is closed. After a slightly higher blowing (300-500 NL / min) and stirring for 2 minutes, the bottom blowing argon flow rate is adjusted to 50-100 NL / min, required for normal weak stirring. The rare earth element content of the molten steel is subsequently measured and found to be 0.009% for Ce and 0.0045% for La. After soft blowing and stirring in the ladle, the molten steel is transferred to the continuous casting process for casting into 0.38m diameter round billets, which are then cut into 2.9m long ingots. During the continuous casting process, the molten steel superheat is controlled at 39°C. A stopper rod is used to control the flow of the molten steel. Argon is blown into the stopper rod to prevent nozzle blockage during the pouring process. The argon flow rate is 3NL / min. Since the continuous casting process can continuously pour multiple heats of steel, the ingots from one heat can be selected and cut into ingots for subsequent electroslag treatment. Multiple ingots can be produced from a single heat.

[0071] 2) Cleaning the surface of the round ingot obtained in step 1, grinding away the iron oxide scale on the surface of the ingot, and making an electrode rod that can be used for slag smelting.

[0072] 3) The electrode rods are loaded into an electroslag furnace for electroslag remelting under an Ar gas protective atmosphere. Before the electroslag is powered on, argon is blown into the mold for at least 25 minutes to displace any remaining air. A 0.48-meter-diameter mold is used, and the electroslag remelting mold slag composition is 64% CaF2, 5% Al2O3, 10% ZrO2, 5% CaO, 3% MgO, 3% SiO2, and 10% Ce2O3 + La2O3. The total amount of mold slag added is 100 kg. Subsequently, power is applied to initiate electroslag treatment, producing an electroslag ingot with a diameter of 0.48 m and a length of 1.9 m. The entire electroslag remelting process is conducted under a protective atmosphere. A constant melting rate is used for electroslag remelting, with the melting rate controlled at 5 kg / min. After the electroslag is powered on, the resulting ingot is subjected to argon blowing for another 20 minutes to prevent secondary oxidation of the ingot.

[0073] 4) The electroslag ingot is transferred to a soaking furnace at 1200°C for 14 hours of high-temperature diffusion. It is then initially rolled into square billets with a side length of 140 mm. Then, according to user requirements, it is finish-rolled into bearing steel with a diameter of up to 60 mm. The final bearing steel composition is: [C]: 1.01%, [Cr]: 1.53%, [Mn]: 0.56%, [Si]: 0.25%, [Al]: 0.023%, [Ce]: 0.006%, [La]: 0.004%, [Ti]: 0.0009%, [N]: 0.0038%, [S]: 0.007%, [P]: 0.012%, with the balance being Fe and other unavoidable impurities. The inclusions in the steel were automatically scanned and analyzed by electron microscope (SEM) combined with the AZtecFeature system of Oxford spectrometer. 99% of them were fine inclusions with rare earth oxide content exceeding 60%, and their sizes were all less than 10μm. 1% were rare earth oxide-aluminum oxide-calcium oxide-silicon oxide composite inclusions, and their sizes were less than 15μm. At the same time, the contact fatigue life of the bearing steel was tested under 4.5GPa. A total of 12 samples were tested and the L 10 The value is 5.2×10 7 change.

[0074] The prepared bearing steel has stable performance and long contact fatigue life, and is suitable for high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0075] Example 3

[0076] This embodiment adopts a 150t electric furnace smelting-LF-RH vacuum degassing-die casting-blowing-electroslag remelting-rolling process, which includes the following steps:

[0077] 1) The molten steel is subjected to 150t electric furnace smelting, LF refining, and RH vacuum degassing. The molten steel is smelted and refined according to conventional bearing steel production methods. After the RH vacuum degassing treatment, the composition of the molten steel is [C]: 0.98%, [Cr]: 1.42%, [Mn]: 0.38%, [Si]: 0.25%, [Al]: 0.01%, [Ti]: 0.001%, [N]: 0.0045%, [S]: 0.0055%, [P]: 0.013%, and the balance is Fe and other inevitable impurities. The above composition meets the conventional standard for GCr15 bearing steel. After the composition is tested and qualified, the ladle bottom argon flow rate is increased to 300-500 NL / min to ensure the slag surface is blown open. 15 kg of rare earth alloy containing La and Ce (based on a 55% yield) is manually added. The bottom blowing rate is then slightly reduced to 100-200 NL / min to ensure the slag surface is closed. After a slightly higher blowing rate (300-500 NL / min) and stirring for 2 minutes, the bottom blowing argon flow rate is adjusted to the 50-100 NL / min required for normal weak stirring. The rare earth element content of the molten steel is subsequently measured and found to be 0.010% for Ce and 0.005% for La. After soft blowing and stirring in the ladle, the molten steel is transferred to the mold for casting into ingots with a diameter of 0.6 m and a weight of 6 tons.

[0078] 2) The above-mentioned ingots are opened by initial rolling, rolled and cut into ingots with a diameter of 0.34m and a length of 3.5m.

[0079] 3) The surface of the round ingot obtained in step 2 is cleaned, and the iron oxide scale on the surface of the ingot is polished clean to make an electrode rod that can be used for slag smelting.

[0080] 4) The electrode rods are loaded into an electroslag furnace for electroslag remelting under an Ar gas protective atmosphere. Argon is blown into the mold for at least 15 minutes before the electroslag is powered on to displace any remaining air. A 0.42m diameter mold is used, and the electroslag remelting mold slag composition is 45% CaF2, 9% Al2O3, 14% ZrO2, 9% CaO, 5% MgO, 5% SiO2, and 13% Ce2O3 + La2O3. The total amount of remelting mold slag added is 94kg. Subsequently, power is applied to initiate electroslag treatment, producing an electroslag ingot with a diameter of 0.42m and a length of 2.2m. The entire electroslag remelting process is conducted under a protective atmosphere. A constant melting rate is used for electroslag remelting, with a melting rate controlled at 4.5kg / min. After the electroslag is powered on, the ingot is obtained and argon blowing is maintained for 20 minutes to prevent secondary oxidation of the ingot.

[0081] 5) The electroslag ingot is transferred to a soaking furnace at 1200°C for 14 hours of high-temperature diffusion. It is then initially rolled into square billets with a side length of 140 mm. Then, according to user requirements, it is finish-rolled into bearing steel with a diameter of up to 60 mm. The final bearing steel composition is: [C]: 1.01%, [Cr]: 1.53%, [Mn]: 0.56%, [Si]: 0.25%, [Al]: 0.023%, [Ce]: 0.006%, [La]: 0.004%, [Ti]: 0.0009%, [N]: 0.0038%, [S]: 0.007%, [P]: 0.012%, with the balance being Fe and other unavoidable impurities. The inclusions in the steel were automatically scanned and analyzed by electron microscope (SEM) combined with the AZtecFeature system of Oxford spectrometer. 99% of them were fine inclusions with rare earth oxide content exceeding 60%, and their sizes were all less than 10μm. 1% were rare earth oxide-aluminum oxide-calcium oxide-silicon oxide composite inclusions, and their sizes were less than 15μm. At the same time, the contact fatigue life of the bearing steel was tested under 4.5GPa. A total of 12 samples were tested and the L 10 The value is 5.8×10 7 change.

[0082] The prepared bearing steel has stable performance and long contact fatigue life, and is suitable for high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0083] Example 4

[0084] This embodiment adopts a 150t converter smelting - LF refining - RH vacuum degassing - round billet continuous casting - electroslag remelting - rolling process, which includes the following steps:

[0085] 1) The molten steel is subjected to 150t converter smelting, LF refining, and RH vacuum degassing. The molten steel is smelted and refined according to conventional bearing steel production methods. After the RH vacuum degassing treatment, the composition of the molten steel is [C]: 1.05%, [Cr]: 1.58%, [Mn]: 0.59%, [Si]: 0.28%, [Al]: 0.029%, [Ti]: 0.0014%, [N]: 0.0035%, [S]: 0.0065%, [P]: 0.014%, and the balance is Fe and other inevitable impurities. The above composition meets the conventional standard for GCr15 bearing steel. After passing the composition test, the ladle bottom blowing argon flow rate is increased to 300-500 NL / min to ensure the slag surface is blown open. 15 kg of rare earth alloy containing La and Ce (based on a 55% yield) is manually added. The bottom blowing flow rate is then slightly reduced to 100-200 NL / min to ensure the slag surface is closed. After a slightly higher blowing (300-500 NL / min) and stirring for 2 minutes, the bottom blowing argon flow rate is adjusted to 50-100 NL / min, required for normal weak stirring. The rare earth element content of the molten steel is subsequently measured and found to be 0.009% for Ce and 0.0045% for La. After soft blowing and stirring in the ladle, the molten steel is transferred to the continuous casting process for casting into 0.38m diameter round billets, which are then cut into 2.9m long ingots.

[0086] During the continuous casting process, the molten steel superheat is controlled at 39°C. A stopper rod is used to control the flow of the molten steel. Argon is blown into the stopper rod to prevent nozzle blockage during the pouring process. Because the continuous casting process can continuously pour multiple heats of steel, the ingots from one heat can be selected and cut into ingots for subsequent electroslag treatment. Multiple ingots can be produced from a single heat.

[0087] 2) Clean the surface of the round ingot and polish away the iron oxide scale on the surface of the ingot to make an electrode rod that can be used for slag smelting.

[0088] 3) Electrode rods are loaded into an electroslag furnace as raw material for electroslag remelting. The electroslag furnace performs electroslag remelting under an Ar gas protective atmosphere. Before power is applied to the electroslag, argon is blown into the crystallizer for at least 25 minutes to displace any remaining air. A 0.48m diameter crystallizer is used, and the electroslag remelting protective slag composition is 40% CaF2, 10% Al2O3, 15% ZrO2, 10% CaO, 5% MgO, 5% SiO2, and 15% Ce2O3 + La2O3. The total amount of remelting protective slag added is 105kg. Subsequently, power is applied to initiate electroslag treatment, producing an electroslag ingot with a diameter of 0.48m and a length of 1.9m. The electroslag remelting process must be conducted under a protective atmosphere, using a constant melting rate. The melting rate of the electrode rods during the electroslag remelting process is controlled at 5kg / min. After the electroslag is powered on, the electroslag ingot is obtained, and argon blowing protection must be maintained for 20 minutes to prevent secondary oxidation of the ingot.

[0089] 4) The electroslag ingot is transferred to a soaking furnace at 1230°C for 14 hours of high-temperature diffusion. It is then initially rolled into square billets with a side length of 140 mm. Then, according to user requirements, it is finish-rolled into bearing steel with a diameter of up to 60 mm. The final bearing steel composition is: [C]: 1.01%, [Cr]: 1.53%, [Mn]: 0.56%, [Si]: 0.25%, [Al]: 0.023%, [Ce]: 0.006%, [La]: 0.004%, [Ti]: 0.0009%, [N]: 0.0038%, [S]: 0.007%, [P]: 0.012%, with the balance being Fe and other unavoidable impurities. The inclusions in the steel were automatically scanned and analyzed by electron microscope (SEM) combined with the AZtecFeature system of Oxford spectrometer. 99% of them were fine inclusions with rare earth oxide content exceeding 60%, and their sizes were all less than 10μm. 1% were rare earth oxide-aluminum oxide-calcium oxide-silicon oxide composite inclusions, and their sizes were less than 15μm. At the same time, the contact fatigue life of the bearing steel was tested under 4.5GPa. A total of 12 samples were tested and the L 10 The value is 5.2×10 7 change.

[0090] The prepared bearing steel has stable performance and long contact fatigue life, and is suitable for high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0091] Example 5

[0092] This embodiment adopts a 150t electric furnace smelting-LF-RH vacuum degassing-round billet continuous casting-electroslag remelting-rolling process, which includes the following steps:

[0093] 1) The molten steel is subjected to 150t electric furnace smelting, LF refining, and RH vacuum degassing. The molten steel is smelted and refined according to conventional bearing steel production methods. After the RH vacuum degassing treatment, the composition of the molten steel is [C]: 1.05%, [Cr]: 1.58%, [Mn]: 0.59%, [Si]: 0.28%, [Al]: 0.029%, [Ti]: 0.0014%, [N]: 0.0035%, [S]: 0.0065%, [P]: 0.014%, and the balance is Fe and other inevitable impurities. The above composition meets the conventional standard for GCr15 bearing steel. After passing the composition test, the ladle bottom blowing argon flow rate is increased to 300-500 NL / min to ensure the slag surface is blown open. 15 kg of rare earth alloy containing La and Ce (based on a 55% yield) is manually added. The bottom blowing flow rate is then slightly reduced to 100-200 NL / min to ensure the slag surface is closed. After a slightly higher blowing (300-500 NL / min) and stirring for 2 minutes, the bottom blowing argon flow rate is adjusted to 50-100 NL / min, required for normal weak stirring. The rare earth element content of the molten steel is subsequently measured and found to be 0.009% for Ce and 0.0045% for La. After soft blowing and stirring in the ladle, the molten steel is transferred to the continuous casting process for casting into 0.38m diameter round billets, which are then cut into 2.9m long ingots.

[0094] During the continuous casting process, the molten steel superheat is controlled at 39°C. A stopper rod is used to control the flow of the molten steel. Argon is blown into the stopper rod to prevent nozzle blockage during the pouring process. Because the continuous casting process can continuously pour multiple heats of steel, the ingots from one heat can be selected and cut into ingots for subsequent electroslag treatment. Multiple ingots can be produced from a single heat.

[0095] 2) Clean the surface of the round ingot and polish away the iron oxide scale on the surface of the ingot to make an electrode rod that can be used for slag smelting.

[0096] 3) The electrode rods are loaded into an electroslag furnace for electroslag remelting under an Ar gas protective atmosphere. Argon is blown into the mold for at least 25 minutes before the electroslag is powered on to displace any remaining air. A 0.48m diameter mold is used. The electroslag remelting mold slag composition is 65% CaF2, 5% Al2O3, 10% ZrO2, 5% CaO, 2% MgO, 3% SiO2, and 10% Ce2O3 + La2O3. The total amount of mold slag added is 105kg. Subsequently, power is applied to initiate electroslag treatment, producing an electroslag ingot with a diameter of 0.48m and a length of 1.9m. The entire electroslag remelting process is conducted under a protective atmosphere. A constant melting rate is used for electroslag remelting, with a controlled melting rate of 5kg / min. After the electroslag is powered on, the resulting ingot is subjected to argon blowing for another 20 minutes to prevent secondary oxidation of the ingot.

[0097] 4) The electroslag ingot is transferred to a soaking furnace at 1230°C for 14 hours of high-temperature diffusion. It is then initially rolled into square billets with a side length of 140 mm. Then, according to user requirements, it is finish-rolled into bearing steel with a diameter of up to 60 mm. The final bearing steel composition is: [C]: 1.01%, [Cr]: 1.53%, [Mn]: 0.56%, [Si]: 0.25%, [Al]: 0.023%, [Ce]: 0.006%, [La]: 0.004%, [Ti]: 0.0009%, [N]: 0.0038%, [S]: 0.007%, [P]: 0.012%, with the balance being Fe and other unavoidable impurities. The inclusions in the steel were automatically scanned and analyzed by electron microscope (SEM) combined with the AZtecFeature system of Oxford spectrometer. 99% of them were fine inclusions with rare earth oxide content exceeding 60%, and their sizes were all less than 10μm. 1% were rare earth oxide-aluminum oxide-calcium oxide-silicon oxide composite inclusions, and their sizes were less than 15μm. At the same time, the contact fatigue life of the bearing steel was tested under 4.5GPa. A total of 12 samples were tested and the L 10 The value is 5.2×10 7 change.

[0098] The prepared bearing steel has stable performance and long contact fatigue life, and is suitable for high-end fields such as high-speed rail bearings, aviation bearings, and wind power bearings.

[0099] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for preparing bearing steel, characterized in that: The following steps are involved: S1, molten steel is subjected to electric furnace / converter smelting, LF refining, vacuum degassing, continuous casting / mold casting, to obtain an ingot, wherein rare earth alloys lanthanum and cerium are added to the molten steel before continuous casting / mold casting; S2, cleaning the surface of the ingot and making the ingot into an electrode rod for electroslag remelting; S3, using the electrode rod as a raw material, and performing electroslag remelting and smelting in an electroslag furnace to obtain an electroslag ingot; the protective slag used in the electroslag remelting process includes the following components in weight percentage: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%; S4, the electroslag ingot is diffused in a soaking furnace at 1200-1250° C. and then rolled into bearing steel.

2. The method for preparing bearing steel according to claim 1, characterized in that: In step S1, rare earth alloys lanthanum and cerium are added by a throwing method, wherein before the rare earth alloy is thrown in, argon gas is blown into the bottom of the ladle containing molten steel to blow open the slag surface to expose the molten steel, and then the rare earth alloy is thrown into the molten steel; after the rare earth alloy is thrown in, the weight percentage of rare earth elements in the molten steel is Ce: 0.006~0.011%, La: 0.003~0.006%.

3. The method for preparing bearing steel according to claim 1, characterized in that: The rare earth alloy is added according to the yield of the rare earth element in the final finished bearing steel being 50-60%.

4. The method for preparing bearing steel according to claim 1, characterized in that: In the step S1, when continuous casting is adopted, the superheat of the molten steel is controlled at 30-40°C, and a stopper rod is used to control the flow in the casting crystallizer, and argon is blown into the stopper rod, and the flow range of argon is 2-5NL / min.

5. The method for preparing bearing steel according to claim 1, characterized in that: In step S1, the mass of the ingot is 1.5-3 tons. When the ingot is a square billet, the side length of the ingot is 0.33-0.38 m and the length is 2-4 m. When the ingot is a round ingot, the diameter is 0.35-0.4 m and the length is 2-3 m.

6. The method for preparing bearing steel according to claim 1, characterized in that: In the step S3, the electroslag remelting smelting process is carried out in a protective atmosphere, using a constant melting rate smelting process, and the melting rate of the electrode rod during the electroslag remelting smelting process is 5-8 kg / min.

7. The method for preparing bearing steel according to claim 1, characterized in that: In step S3, the amount of mold slag added is 40-60 kg / t 钢 , where t 钢 Refers to tons of steel.

8. The method for preparing bearing steel according to claim 1, characterized in that: The bearing steel includes the following chemical components in weight percentage: C: 0.90-1.1%, Cr: 1.4-1.6%, Mn: 0.30-0.60%, Si: 0.20-0.30%, Al: 0.008-0.030%, Ce: 0.004-0.010%, La: 0.002-0.006%, Ti<0.0015%, N<0.005%, S<0.010%, P<0.015%, and the remainder is iron and other inevitable impurities.

9. The method for preparing bearing steel according to claim 1, characterized in that: The bearing steel contains inclusions, more than 95% of which are fine inclusions with a rare earth oxide content exceeding 60% and a size less than 10 μm, and the rest are composite inclusions of rare earth oxide-aluminum oxide-calcium oxide-silicon oxide, and the size of the composite inclusions is less than 15 μm.

10. The method for preparing bearing steel according to claim 1, characterized in that: The contact fatigue life L of the bearing steel at 4.5 GPa 10 5×10 7 Turn above.

11. A bearing steel prepared by the method for preparing bearing steel as described in any one of claims 1 to 10, comprising the following chemical components in weight percentage: C: 0.9-1.1%, Cr: 1.4-1.6%, Mn: 0.3-0.6%, Si: 0.2-0.3%, Al: 0.008-0.03%, Ce: 0.004-0.01%, La: 0.002-0.006%, Ti<0.0015%, N<0.005%, S<0.01%, P<0.015%, and the remainder is iron and other inevitable impurities.

12. A protective slag used in the method for preparing bearing steel as described in any one of claims 1-10, comprising the following components in weight percentage: CaF2: 40-65%, Al2O3: 5-10%, ZrO2: 10-15%, CaO: 5-10%, MgO: 2-5%, SiO2: 3-5%, Ce2O3+La2O3: 10-15%.

13. A protective slag used in the method for preparing bearing steel according to any one of claims 1 to 10, which is composed of the following by weight percentage: CaF2: 40~65%, Al2O3: 5~10%, ZrO2: 10~15%, CaO: 5~10%, MgO: 2~5%, SiO2: 3~5%, Ce2O3+La2O3: 10~15%.