Carburizing bearing steel for turntable bearing of large-size petroleum drilling machine and production method of carburizing bearing steel

Abstract

The invention relates to carburized bearing steel for a turntable bearing of a large-size petroleum drilling machine and a production method of the carburized bearing steel. The carburized bearing steel comprises the following chemical components: 0.19-0.23% of C, 0.15-0.40% of Si, 0.30-0.55% of Mn, 1.25-1.75% of Cr, less than or equal to 0.08% of Mo, 3.25-3.75% of Ni, 0.01-0.03% of Al, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 0.25% of Cu, less than or equal to 0.0005% of Ca, less than or equal to 0.0015% of Ti, less than or equal to 0.0010% of O, 0.005-0.010% of La and the balance of Fe and inevitable impurities. The production process comprises the steps of molten iron pretreatment, converter or electric arc furnace smelting, LF refining, RH or VD furnace refining, large-section CCM continuous casting of a large round billet, continuous casting of the large round billet, slow cooling of the continuous casting of the large round billet, heating, rolling, slow cooling of a rolled material, annealing and finishing. And the requirements of the steel for the turntable bearing of the large-size petroleum drilling machine are met.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and in particular relates to carburized bearing steel for large-size oil drilling rig turntable bearings and a production method thereof. Background Art

[0002] As one of the world's major energy resources, oil is a non-renewable fossil energy with important economic, energy and strategic significance. It is widely used in transportation, industrial production, agriculture, electricity and other fields, and plays a pivotal role in the economic development and industrial operation of modern society. Today's world is still in the industrial society stage, and the world economy is generally in a period of rapid development. Therefore, the demand for oil is bound to be great, and oil extraction technology is particularly important. As one of the most important equipment in the oil extraction process, oil drilling rigs have very high requirements for the quality of raw materials.

[0003] At present, the conventional drilling rigs commonly used in countries around the world are a large-scale comprehensive unit. The entire drilling rig is composed of several systems such as power system, transmission system, working system and auxiliary system. Among them, the turntable is the key equipment of the oil drilling rig and one of the three major working machines of the oil drilling rig. The turntable is essentially a high-power bevel gear reducer. During the drilling process, the function of the turntable is to transmit the power of the engine to the square drill rod, drill rod, drill collar and drill bit through the square tile, drive the drill bit to rotate, thereby achieving footage and drilling out the wellbore. With the harsh working conditions of the oil drilling rig, the bearings in the turntable need to withstand greater impact force during use. Therefore, in addition to high strength and high wear resistance, the requirements for such bearing materials must also have sufficient impact resistance.

[0004] Traditional oil rig turntable bearings are generally large in structure and require large-size steel as their manufacturing materials. In combination with the service environment and required performance requirements of oil rig turntable bearings, the present invention selects carburized bearing steel as the manufacturing material of oil rig turntable bearings. Among them, after carburizing quenching and low-temperature tempering treatment, the surface of the carburized bearing steel G20Cr2Ni4 has high hardness, wear resistance and contact fatigue strength, while the carbon content in the core is low, with good toughness, and can withstand the impact of large loads. It is very suitable for manufacturing large oil rig turntable bearings. At present, carburized bearing steel G20Cr2Ni4 is mostly produced by electroslag remelting process. Since the steel produced by electroslag remelting process has many quality advantages such as high uniformity of organization and high density, its quality stability has always been good. However, the electroslag remelting production process also has obvious disadvantages such as very low production efficiency and production capacity, and very high energy consumption and production cost. Therefore, the market competitiveness of electroslag remelting steel is very low. Compared with the electroslag remelting process, the vacuum degassing plus continuous casting process can greatly improve production efficiency and capacity, significantly reduce energy consumption and production costs, and thus has more competitive advantages.

[0005] The steel of the present invention is based on the technical standard requirements of high-quality steel G20Cr2Ni4A specified in the existing national standard GB / T 3203. On the one hand, the chemical composition is fine-tuned and optimized, and on the other hand, a high-efficiency, high-capacity, low-cost process route of vacuum degassing, continuous casting, and rolling is adopted. While improving the purity of molten steel, continuous casting adopts a specific continuous casting large round billet and rolling adopts a specific large-reduction rolling process to produce large-size raw steel. The raw steel has the characteristics of high purity, high structural uniformity and high density, which fully meets the use requirements of large-size oil rig turntable bearings and can replace the current electroslag remelting production process. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a carburized bearing steel for large-size oil rig turntable bearings and a preparation method thereof in response to the above-mentioned prior art, so that the carburized bearing steel for oil rig turntable bearings can meet the quality requirements, and at the same time, the product has strong market competitiveness through optimization and adjustment of the production process.

[0007] The technical solution adopted by the present invention to solve the above problems is: a carburized bearing steel for a large-size oil drilling rig turntable bearing, the chemical composition of the steel and its mass percentage are: C: 0.19-0.23, Si: 0.15-0.40, Mn: 0.30-0.55, Cr: 1.25-1.75, Mo: ≤0.08, Ni: 3.25-3.75, Al: 0.01-0.03, P≤0.020, S≤0.010, Cu≤0.25, Ca≤0.0005, Ti≤0.0015, O≤0.0010, La: 0.005-0.010, and the balance is Fe and unavoidable impurities.

[0008] The main elements C, Si, Mn, Cr, Ni, Mo, Al, and Ni are all within the range of G20Cr2Ni4 specified in the current national standard GB / T 3203-2016 carburized bearing steel, and the rare earth element La (lanthanum) is added on this basis. The rare earth element La (lanthanum) is added because La can react with oxygen and sulfur in manganese sulfide, aluminum oxide and aluminosilicate inclusions that may be generated in the steel to generate non-metallic compounds with higher melting points. These compounds float to the slag layer, reducing the content of inclusion elements in the steel, thereby achieving the purification of the molten steel. With the increase of rare earth elements, large particle inclusions in the steel are significantly reduced and the size is also significantly reduced. In addition, rare earth elements can strengthen grain boundaries, inhibit segregation at grain boundaries and aggregation of low-melting-point harmful elements, and hinder the expansion of intergranular cracks to improve plasticity and high-temperature performance. Therefore, the addition of rare earth elements can significantly increase the service life of oil rig turntable bearings that work under high temperature, high impact and harsh operating environment. In addition, since the present invention adopts the vacuum degassing + continuous casting large round billet process, the harmful elements O and Ti can be significantly reduced compared with the electroslag remelting process, O can be controlled at ≤0.0010%, and Ti can be controlled at ≤0.0015%.

[0009] Determination of the main inspection items and indicators of the present invention:

[0010] The present invention puts forward strict requirements on both microscopic inclusions and macroscopic inclusions. Microscopic inclusions include plastic inclusions of types A and C and brittle inclusions of types B and D. Brittle inclusions are hard particles in steel, which produce stress concentration when the bearing is running. At the same time, they are easy to separate from the matrix and produce cracks during the deformation of the steel, which further aggravates the stress concentration and easily causes cracking. The larger the inclusion particles and the longer the length, the greater the harm. Plastic inclusions are soft particles in steel, which are not easy to separate from the matrix during the deformation of the steel, so their harm is relatively small.

[0011] In order to meet the requirement of a long service life of the oil drilling rig turntable bearing, the steel is required to have a high purity. The present invention requires that the microscopic brittle inclusions be small: B fine series ≤1.5 level, B coarse series ≤0.5 level, D fine series ≤1.0 level, D coarse series ≤0.5 level, DS series ≤1.0 level. The specific requirements are shown in Table 1 below. Macroscopic inclusions significantly reduce the wear resistance of the steel, causing serious stress concentration and easily causing early failure of the bearing during use. Macroscopic inclusions are tested according to the GB / T15711 tower-type hairline acid leaching method, and hairlines are not allowed.

[0012] Table 1

[0013]

[0014] The uniformity and density of the macrostructure of steel have an impact on the life of the bearing. The present invention requires that the macrostructure adopts GB / T 1979 for grading the macrostructure of steel, requiring central porosity ≤1.0 level, general porosity ≤1.0 level, ingot segregation ≤1.0 level, central segregation ≤1.0 level, and shrinkage cavities, cracks and subcutaneous bubbles are not allowed to appear.

[0015] In order to ensure the strength, toughness and impact resistance of the steel, the present invention requires the metallographic structure to be a uniform and fine bainite structure. At the same time, the present invention has requirements on the grain size, requiring the grain size to be ≥ level 5.

[0016] Secondly, according to the use requirements of oil rig turntable bearings, the steel is required to have higher strength, certain toughness and impact resistance after quenching and low-temperature tempering. The specific mechanical property requirements are shown in Table 2.

[0017] Table 2

[0018]

[0019] At the same time, in order to ensure the cold processing performance of steel, the hardness is required to be ≤241HBW.

[0020] Another purpose of this application is to provide a method for producing carburized bearing steel for large-size oil rig turntable bearings to meet customer To meet the above requirements for large-size raw steel bars, the present invention adopts continuous casting of large round billets with a diameter of 700 mm or more instead of electroslag remelting to smelt billets. The main steps are as follows:

[0021] (1) Molten steel smelting: The smelting raw materials must be pre-treated with KR molten iron to reduce the content of harmful elements P and obtain clean molten iron; primary smelting is carried out in a converter or electric furnace to reduce the content of C and P elements in the molten iron, and clean scrap steel is added to strictly control the quality of scrap steel to reduce the content of residual harmful elements in the molten steel. The final carbon of the steel is controlled at 0.06-0.12%, the final phosphorus is controlled at ≤0.20%, and the steel tapping temperature is between 1650-1700℃; low Ti, low Ca alloys and high-quality refractory materials are selected in the LF refining furnace, and deoxidation is carried out by Slag surface diffusion deoxidation method, and use high-performance refined synthetic slag, maintain a long refining and slagging process, the entire LF smelting time ≥ 50 minutes, so that non-metallic inclusions can be fully floated; vacuum degassing in RH or VD furnace, the furnace reaches a sufficient vacuum degree, the vacuum degree is 1.0-1.45mbar, ensure high vacuum time ≥ 35min, and maintain sufficient circulation treatment time, circulation time ≥ 40min, after the vacuum degassing is completed, add rare earth lanthanum iron alloy to further improve the non-metallic inclusions in the molten steel, and obtain high-purity molten steel;

[0022] (2) Large-section continuous casting CCM continuous casting large round billet: The size of the continuous casting round billet is greater than φ700mm, ensuring a large compression ratio of the steel, thereby ensuring the density of the material; protective casting is adopted throughout the process to protect the molten steel from secondary oxidation contamination; the tundish induction heating, light pressure reduction, and electromagnetic stirring technology are adopted to effectively improve low-magnification defects such as central porosity and shrinkage, and can reduce the spacing between secondary dendrite arms, inhibit the growth of columnar crystal areas, expand the central equiaxed crystal area, and refine the grains; low superheat casting is adopted, and the superheat is controlled at ≤30℃, which effectively reduces the component segregation of the continuous casting billet and significantly improves the quality of the continuous casting billet;

[0023] (3) Slow cooling of continuous casting large round billets: The continuous casting large round billets are slowly cooled, the pit temperature is greater than 650°C, the pit slow cooling time is greater than 48 hours, and the pit exit temperature is less than 200°C;

[0024] (4) Heating and rolling: Heating in a heating furnace with a neutral or weakly oxidizing atmosphere, the preheating section temperature is controlled at 650-900℃, the heating section temperature is controlled at 1120-1200℃, the soaking section temperature is controlled at 1220-1250℃, and the heating and holding time is ≥14h, so that the steel can fully diffuse at high temperature. The continuous casting billet after leaving the furnace is first dephosphorized by high-pressure water before rolling, and then rolled after dephosphorization by high-pressure water. The initial rolling temperature is controlled at 1050-1100℃, the finishing rolling temperature is controlled at above 950℃, and the final rolling temperature is controlled at above 850℃. In the initial rolling process, a special large reduction process is used for rolling, and the total reduction of the initial rolling is controlled at above 110mm. Through a total of 11 back and forth rolling, the matrix structure in the steel can be greatly refined and homogenized, and the structure can be made denser. Subsequently, it passes through a continuous rolling mill and is finally rolled to a target size of more than φ250mm.

[0025] (5) Slow cooling and annealing of rolled products: The rolled bars are put into the pit for slow cooling again. The slow cooling temperature is required to be ≥450℃, the pit opening temperature is ≤200℃, and the slow cooling time is ≥60 hours. The bars are subjected to stress relief annealing within 48 hours after pit opening. The stress relief annealing temperature is 650-700℃, and the holding time is ≥4h. Then, the bars are cooled to 400℃ in the furnace and then air-cooled to room temperature after being taken out of the furnace.

[0026] (6) Finishing: The steel is subjected to finishing processes such as straightening, chamfering and flaw detection. All products must undergo 100% non-destructive testing to ensure the surface and internal quality of the products.

[0027] The carburized bearing steel for large-size oil drilling rig turntable bearing produced by the present invention meets the following index requirements:

[0028] 1. Micro inclusions are tested according to GB / T 10561A method: Class A fine system ≤1.5, Class A coarse system ≤1.0, Class B fine system ≤1.5, Class B coarse system ≤0.5, Class C fine system = 0, Class C coarse system = 0, Class D fine system ≤1.0, Class D coarse system ≤0.5, DS class ≤1.0; Macro inclusions are tested according to GB / T 15711 tower-type hairline acid leaching method, and hairlines are not allowed.

[0029] 2. Macrostructure requirements GB / T 1979 shall be adopted for macrostructure rating of steel, requiring central porosity ≤1.0, general porosity ≤1.0, ingot segregation ≤1.0, central segregation ≤1.0, and shrinkage cavities, cracks and subcutaneous bubbles are not allowed.

[0030] 3. The invention steel requires a grain size ≥ grade 5.

[0031] 4. Mechanical property requirements of invention steel: tensile strength requirement ≥1200MPa, elongation after fracture ≥12%, section shrinkage ≥45%, impact performance AKU requirement ≥65J.

[0032] 5. To ensure the cold processing performance of steel, the final rolled product annealing hardness is ≤241HBW.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] 1. The production process of vacuum degassing and continuous casting of large round billets is adopted. Compared with the electroslag remelting technology, it improves the production efficiency, effectively reduces the manufacturing cost and improves the economic benefits.

[0035] 2. The deoxidation and vacuum degassing technology is used to significantly reduce the O and H content in the steel. At the same time, rare earth lanthanum iron alloy is added after vacuum degassing to further improve inclusions and improve the purity of molten steel.

[0036] 3. The continuous casting process adopts low superheat pouring to effectively reduce the component segregation of the continuous casting billet. At the same time, it also adopts the induction heating of the tundish, light pressure reduction and electromagnetic stirring technology, which can effectively improve the low-magnification defects such as central looseness and shrinkage holes of the continuous casting round billet as a whole.

[0037] 4. The continuous casting of large round billets adopts a special initial rolling and large reduction production technology to greatly refine and homogenize the matrix structure in the steel.

[0038] 5. Slowly cool the continuously cast round billets and rolled products in the pit to avoid cracking of the steel due to changes in surface and internal thermal stress and structural stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope image of non-metallic inclusions in the product of Example 1 of the present invention.

[0040] Figure 2 This is a scanning electron microscope image of non-metallic inclusions in the product of Example 2 of the present invention.

[0041] Figure 3 This is a scanning electron microscope image of non-metallic inclusions in the product of Example 3 of the present invention.

[0042] Figure 4 The following is a scanning electron microscope image of non-metallic inclusions in the comparison product. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0044] The manufacturing process of carburized bearing steel for large-size oil drilling rig turntable bearings in the embodiment of the present invention is to produce steel by adopting a molding process of molten iron pretreatment + top and bottom blowing converter BOF (high-power electric arc furnace EAF) - ladle refining furnace LF - vacuum circulation degassing furnace RH (VD furnace) - large-section continuous casting CCM continuous casting large round billet - slow cooling - heating and rolling into products - slow cooling, annealing - finishing.

[0045] Specifically, the molten iron is first subjected to KR molten iron pretreatment to obtain high-quality molten iron, and high-quality scrap steel and raw and auxiliary materials are added to the converter or electric furnace for smelting, and high-quality deoxidizers and refractory materials are selected. In the electric furnace / converter production process, the steel tapping end point C of the three embodiments is respectively controlled at 0.06-0.12%, the end point P is controlled at ≤0.020%, and the steel tapping temperature is 1650-1700°C. In the LF refining furnace, low Ti, low Ca alloy and high-quality refractory materials are selected, and high-performance refining synthetic slag is used to maintain a long refining and slag-making process. The entire LF smelting time is ≥50 minutes. Vacuum degassing is carried out in the RH or VD furnace, and sufficient vacuum is achieved in the furnace, and sufficient circulation treatment time is maintained. After the vacuum degassing is completed, rare earth lanthanum iron alloy is added. The entire continuous casting process adopts protected pouring, and uses induction heating of the tundish, light pressure and electromagnetic stirring technology. The superheat is controlled at 10-30°C, and the produced continuous casting large round billets are slowly cooled in the pit. The pit temperature is greater than 650°C, the slow cooling time is more than 48 hours, and the pit exit temperature is less than 200°C to prevent the continuous casting large round billets from cracking.

[0046] The chemical compositions (wt %) of the embodiments of the present invention and (for comparison) the electroslag remelted G20Cr2Ni4A currently used in the market are shown in Table 3 and Table 3.

[0047] Table 3

[0048]

[0049] Table 3

[0050]

[0051] From the composition point of view, the main difference between the present invention and electroslag steel is that the present invention adds the rare earth alloy element La; in addition, LF refining adopts low Ti alloy, high-performance synthetic slag slag deoxidation technology, RH vacuum cycle degassing and continuous casting full-process protective pouring technology, so the Ti content and O content of the present invention are significantly better than those of electroslag material.

[0052] Subsequently, the continuously cast large round billet, which has been slowly cooled for more than 48 hours, is sent to a heating furnace in a neutral or weakly oxidizing atmosphere for heating and rolling. The temperature of the preheating section is controlled at 650-900°C, the temperature of the heating section is controlled at 1120-1200°C, the temperature of the soaking section is controlled at 1220-1250°C, and the heating and holding time is ≥14h to allow the steel to undergo sufficient high-temperature diffusion. The start rolling temperature is controlled at 1050-1100°C. During the initial rolling process, a special large-reduction process is used for rolling. Through a total of 11 back-and-forth rolling, the matrix structure in the steel can be greatly refined and homogenized, and the structure is made denser. After the continuous rolling mill, it is finally rolled to a target size of more than φ250mm. After rolling, the bar is slowly cooled in the pit. The slow cooling temperature in the pit is required to be ≥450℃, and the slow cooling time is ≥60 hours. The bar is subjected to stress relief annealing within 24 hours after the pit is removed. The stress relief annealing temperature is 650-700℃, and the holding time is ≥4h. Then it is cooled to 400℃ with the furnace and then air-cooled to room temperature after being taken out of the furnace. Finally, the bar is subjected to subsequent flaw detection and finishing.

[0053] Table 4 Non-metallic inclusion detection of each embodiment and electroslag comparison steel

[0054] Example A thin A thick B thin B thick C Thin C thick D Thin D thick Ds The present invention 1 0.5 0 0～0.5 0 0 0 0.5 0～0.5 0～0.5 The present invention 2 0.5 0 0～0 0 0 0 0.5 0 0 The present invention 3 0.5 0 0～0.5 0 0 0 0～0.5 0 0～0.5 Contrast steel 0.5 0 0～1.0 0～0.5 0 0 0～0.5 0～0.5 0～1.5

[0055] From the detection of non-metallic inclusions, since the present invention adopts high-performance synthetic slag slag making and deoxidation technology, RH (or VD) vacuum cycle degassing and continuous casting full-process protective pouring technology in LF refining, and adds rare earth lanthanum iron alloy after the vacuum degassing, the non-metallic inclusions in the molten steel are further improved to obtain high-purity molten steel. In terms of the indicators of B fine, B coarse and DS brittle inclusions that may cause premature failure of the turntable bearing material of the oil drilling rig, the control level is slightly better than that of electroslag steel.

[0056] See the SEM image of non-metallic inclusions of the product of Example 1 of the present invention. Figure 1 , SEM image of non-metallic inclusions of product in Example 2 is shown in Figure 2 , SEM images of non-metallic inclusions of product in Example 3 are shown in Figure 3 , see the SEM images of non-metallic inclusions in the comparative products Figure 4 .

[0057] Table 5 Grain size, hardness and mechanical properties data of each embodiment

[0058]

[0059]

[0060] From the perspective of mechanical properties, since the continuous casting process of the present invention adopts light pressure reduction and electromagnetic stirring technology and the continuous rolling process adopts high-temperature heating technology, both of which can effectively uniformly organize and refine the grains, and the present invention improves plasticity by adding rare earth lanthanum iron alloy, the grain size and impact toughness indicators of the present invention are better than those of electroslag steel.

[0061] Table 6 Macro data of steel materials in various examples and tower-shaped crack inspection of macroscopic inclusions

[0062]

[0063] From the inspection of tower-shaped cracks of macro and macro inclusions, the present invention has the same index as that of electroslag steel.

[0064] In summary, the present invention relates to a carburized bearing steel for large-scale oil drilling rig turntable bearings and a production method thereof. By adding rare earth lanthanum iron alloy elements to the steel, a high-efficiency, high-capacity, low-cost process route of vacuum degassing, continuous casting, and rolling is adopted, and key processes are optimized, studied, and controlled, so that the steel is comparable to the electroslag remelting process in terms of non-metallic inclusion control, organizational uniformity, and mechanical properties, or even better than the electroslag remelting process. Therefore, the present invention is more competitive in terms of production efficiency, production cost, and product quality stability.

[0065] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carburized bearing steel for large-size oil drilling rig turntable bearings, characterized in that The chemical composition of the steel is, by mass percentage, C: 0.19-0.23, Si: 0.15-0.40, Mn: 0.30-0.55, Cr: 1.25-1.75, Mo: ≤0.08, Ni: 3.25-3.75, Al: 0.01-0.03, P≤0.020, S≤0.010, Cu≤0.25, Ca≤0.0005, Ti≤0.0015, O≤0.0010, La: 0.005-0.010, and the balance is Fe and unavoidable impurities.

2. The carburized bearing steel for large-size oil drilling rig turntable bearing according to claim 1 is characterized in that: The grain size of the bearing steel is ≥ Grade 5; the microscopic inclusions are tested according to GB / T 10561A method, Class A fine system ≤1.5, Class A coarse system ≤1.0, Class B fine system ≤1.5, Class B coarse system ≤0.5, Class C fine system = 0, Class C coarse system = 0, Class D fine system ≤1.0, Class D coarse system ≤0.5, DS class ≤1.0; the macroscopic inclusions are tested according to GB / T 15711 tower-shaped hairline acid leaching method test, no hairline; GB / T1979 is used to grade the macrostructure of steel, central porosity ≤1.0, general porosity ≤1.0, ingot-shaped segregation ≤1.0, central segregation ≤1.0, and shrinkage cavities, cracks and subcutaneous bubbles are not allowed; tensile strength requirements ≥1200MPa, elongation after fracture ≥12%, cross-sectional shrinkage ≥45%, impact performance AKU requirements ≥65J; annealing hardness ≤241HBW. .

3. A method for producing carburized bearing steel for large-size oil drilling rig turntable bearings as claimed in claim 1, characterized in that: The method adopts continuous casting instead of electroslag remelting to smelt the blank, and comprises the following steps: (1) Molten steel smelting: The smelting raw materials are pretreated with KR molten iron to reduce the content of harmful elements P and obtain clean molten iron; primary smelting is carried out in a converter or electric furnace to reduce the content of C and P elements in the molten iron; low Ti, low Ca alloys and high-quality refractory materials are selected in the LF refining furnace, and deoxidation is carried out by slag surface diffusion deoxidation, and high-performance refined synthetic slag is used. The entire LF smelting time is ≥50 minutes; vacuum degassing is carried out in the RH or VD furnace, and rare earth lanthanum iron alloy is added after the vacuum degassing is completed to further improve the non-metallic inclusions in the molten steel and obtain high-purity molten steel; (2) Large-section continuous casting CCM continuous casting large round billet: The continuous casting billet size is greater than φ700mm to ensure a large compression ratio of steel; (3) Slow cooling of continuous casting large round billets: The continuous casting large round billets are slowly cooled, the pit temperature is greater than 650°C, the pit slow cooling time is greater than 48 hours, and the pit exit temperature is less than 200°C; (4) Heating and rolling into products: heating in a heating furnace with a neutral or weakly oxidizing atmosphere, the continuous casting billet after being taken out of the furnace is first dephosphorized by high-pressure water before rolling, and then rolled after dephosphorization by high-pressure water. The initial rolling temperature is controlled at 1050-1100°C, the finishing rolling temperature is controlled at above 950°C, and the final rolling temperature is controlled at above 850°C. Subsequently, it is passed through a continuous rolling mill and finally rolled into a target size of φ250 mm or more; (5) Slow cooling and annealing of rolled products: The rolled bars are put into the pit for slow cooling again. The slow cooling temperature is required to be ≥450°C, the pit opening temperature is ≤200°C, and the slow cooling time is ≥60 hours. The bars are subjected to stress relief annealing within 48 hours after pit opening. (6) Finishing: The steel is subjected to finishing process and all products are 100% non-destructively tested to ensure the surface and internal quality of the products.

4. The method for producing carburized bearing steel for large-size oil drilling rig turntable bearings according to claim 3 is characterized in that: In step (1), the final carbon content of the primary steelmaking is controlled at 0.06-0.12%, the final phosphorus content is controlled at ≤0.20%, and the steelmaking temperature is between 1650-1700° C.; vacuum degassing is performed in an RH or VD furnace to achieve a sufficient vacuum degree in the furnace, the vacuum degree is 1.0-1.45 mbar, and the high vacuum time is ensured to be ≥35 min, while maintaining sufficient circulation processing time, and the circulation time is ≥40 min.

5. The method for producing carburized bearing steel for large-size oil drilling rig turntable bearings according to claim 3, characterized in that: In step (2), the entire continuous casting process adopts protective pouring to protect the molten steel from being contaminated by secondary oxidation; the tundish induction heating, light pressure reduction and electromagnetic stirring technology are adopted to effectively improve the central low-magnification defects, reduce the secondary dendrite arm spacing, inhibit the growth of the columnar crystal zone, expand the central equiaxed crystal zone, and refine the grains; low superheat pouring is adopted, and the superheat is controlled at ≤30°C, which effectively reduces the component segregation of the continuous casting billet and significantly improves the quality of the continuous casting billet. The final continuous casting round billet size is greater than φ700mm.

6. The method for producing carburized bearing steel for large-size oil drilling rig turntable bearings according to claim 3, characterized in that: In step (4), the temperature of the preheating section is controlled at 650-900°C, the temperature of the heating section is controlled at 1120-1200°C, the temperature of the soaking section is controlled at 1220-1250°C, and the heating and heat preservation time is ≥14h to allow the steel to undergo sufficient high-temperature diffusion.

7. The method for producing carburized bearing steel for large-size oil drilling rig turntable bearings according to claim 3, characterized in that: In step (4), during the initial rolling process, a large reduction process is adopted for rolling, and the total reduction of the initial rolling is controlled to be above 110 mm. Through a total of 11 back-and-forth rolling, the matrix structure in the steel is greatly refined and homogenized, and the structure is made denser.

8. The method for producing carburized bearing steel for large-size oil drilling rig turntable bearings according to claim 3, characterized in that: In step (5), the stress relief annealing temperature is 650-700°C, and the holding time is ≥4h. The steel is then cooled to 400°C in the furnace and then air-cooled to room temperature.

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