Steel for large-scale rolling mill bearing rolling element and method for producing the same

Abstract

The present application relates to a kind of large-scale rolling mill bearing rolling body steel and its production method, the chemical composition of steel is as follows according to mass percentage: C:0.2~0.25%, Si:0.4~0.6%, Mn:0.6~0.9%, Cr:0.7~0.9%, Ni:0.8~1.1%, Mo:0.15~0.25%, S≤0.008%, P≤0.020%, Cu≤0.25%, Al≤0.05%, Ti≤0.002%, O≤0.0009%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, the balance is Fe and inevitable impurities.Using high-efficiency, large-capacity, low-cost process route of vacuum degassing, continuous casting, rolling, through unique chemical composition design, special smelting process and rolling process, a new steel material with high purity, high organizational uniformity and high mechanical properties is obtained, and the requirements of large-scale rolling mill bearing rolling body steel are met.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and more specifically relates to bearing steel and the corresponding production process. Background Technology

[0002] Rolling mill bearings are a crucial component of the rolling mill stand and a major wear part. Their function is to support the rotating rolls, withstand the multi-directional rolling forces transmitted from the rolls, and maintain the rolls' correct position within the stand. The quality of their assembly, adjustment, and maintenance directly impacts bearing life, product dimensional accuracy, and mill operating rate. Among these bearings, the rolling elements are key rotating components, primarily including cylindrical rolling bearings, deep groove ball bearings, angular contact bearings, and tapered rolling bearings. Due to the harsh working conditions of rolling mill bearings—high temperatures and high dust levels—the rolling elements must possess high strength, high wear resistance, and long service life. Their quality and service life directly affect the mill's production efficiency, product quality, and production costs. Therefore, higher requirements are placed on the materials used for rolling mill bearings. Especially for large-size, high-load rolling mill bearings, which need to withstand greater impact forces during use, the materials used to manufacture the rolling elements of such large-size rolling mill bearings must possess high purity, high structural uniformity, and high mechanical properties.

[0003] Currently, most large-size rolling mill bearings in China use high-carbon chromium bearing steel GCrl5SiMn for their rolling elements. While the smelting and heat treatment processes for this type of high-carbon steel are relatively mature, resulting in rolling elements with good overall hardenability and wear resistance, their overall mechanical properties are poor, particularly in the core. This makes them prone to internal cracking, especially when subjected to large impacts during operation, eventually leading to premature bearing failure and significantly reduced service life. Therefore, large-size rolling mill bearings require not only high wear resistance but also high mechanical properties. Summary of the Invention

[0004] Based on the usage conditions of rolling elements in large-size rolling mill bearings, this application proposes a new type of steel for rolling elements in large-size rolling mill bearings. Through unique composition design and the adoption of a vacuum degassing continuous casting process with high cleanliness, high structural uniformity, and high mechanical properties, it produces a steel with high wear resistance, high mechanical properties, and long service life. This new steel meets the requirements of rolling elements in large-size rolling mill bearings.

[0005] In order to meet the performance requirements of high wear resistance, high strength and high mechanical properties of steel for rolling elements of large-size rolling mill bearings, this invention has invented a new type of steel for rolling elements of large-size rolling mill bearings by rationally designing the chemical composition of the steel.

[0006] The chemical composition of the steel for the rolling elements of large-size rolling mill bearings of this invention is designed as follows:

[0007] The composition by mass percentage is as follows: C: 0.2–0.25%, Si: 0.4–0.6%, Mn: 0.6–0.9%, Cr: 0.7–0.9%, Ni: 0.8–1.1%, Mo: 0.15–0.25%, S≤0.008%, P≤0.020%, Cu≤0.25%, Al≤0.05%, Ti≤0.002%, O≤0.0009%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, with the balance being Fe and unavoidable impurities.

[0008] 1) Determination of C content

[0009] Carbon (C) is an essential element for ensuring the wear resistance of steel. Increasing the carbon content in steel will increase its martensitic transformation ability, thereby improving its hardness and strength, and thus its wear resistance. However, excessively high C content is detrimental to the toughness of steel. In this invention, the C content is determined to be in the range of 0.2% to 0.25%.

[0010] 2) Determination of Si content

[0011] Si dissolved in the ferrite phase has a strong solid solution strengthening effect, which can improve strength, elastic limit, and hardenability, but at the same time reduces the plasticity and toughness of ferrite. The Si content of the steel of this invention is determined to be in the range of 0.4% to 0.6%.

[0012] 3) Determination of Mn content

[0013] Mn, as a deoxidizing element in the steelmaking process, can improve the hardenability of steel. Mn can also fix the form of sulfur in steel and form MnS and (Fe,Mn)S, which are less harmful to steel properties, reducing or inhibiting the formation of FeS. Therefore, the presence of manganese in steel can improve its purity and properties. Simultaneously, manganese plays a role in solid solution strengthening and grain refinement in steel, thereby increasing strength and significantly improving hardenability; however, excessive manganese content has the disadvantage of promoting austenitizing grain growth. In this invention, the Mn content is determined to be in the range of 0.6% to 0.9%.

[0014] 4) Determination of Cr content

[0015] Cr is a carbide-forming element that can improve the hardenability, wear resistance, and corrosion resistance of steel. However, if the Cr content is too high, the steel will be too hard, which is not conducive to customer processing and use. Therefore, the Cr content range of this invention is determined to be 0.7% to 0.9%.

[0016] 5) Determination of Ni content

[0017] Ni is an element that improves the hardenability of steel and is also the most commonly used element to effectively improve the wear resistance of steel. The combined effect of Ni with Cr and residual P in steel helps to improve the corrosion resistance and wear resistance of steel. In this invention, the Ni content is determined to be in the range of 0.8% to 1.1%.

[0018] 6) Determination of Mo content

[0019] Molybdenum can refine the grain size of steel, improve hardenability and hot strength, and maintain sufficient strength and creep resistance at high temperatures. However, molybdenum is a ferrite-forming element, and when the molybdenum content is high, ferrite δ phase or other brittle phases are prone to form, which reduces toughness. In this invention, the Mo content is determined to be in the range of 0.15% to 0.25%.

[0020] 7) Determination of Al content

[0021] Al, added as a deoxidizing element in steel, not only reduces dissolved oxygen in molten steel, but also forms finely dispersed aluminum nitride with nitrogen, which refines the grain size. However, excessive Al content can easily lead to the formation of large-particle brittle inclusions such as Al2O3 during the steelmaking process, reducing the purity of the steel and affecting its service life. In this invention, the Al content is defined as ≤0.05%.

[0022] 8) Determination of Ti content

[0023] Ti forms titanium carbonitride inclusions in steel. These inclusions are hard and angular, which seriously affect the fatigue life of the material. The Ti content range is determined to be ≤0.002% in this invention.

[0024] 9) Determination of O content

[0025] Oxygen naturally enters the steel during the steelmaking process. The oxygen remaining in the steel later mainly exists as inclusions such as FeO, MnO, SiO2, and Al2O3. In particular, Al2O3 inclusions affect the service life of the steel. Numerous experiments have shown that reducing the oxygen content is significantly beneficial for improving the purity of the steel, especially reducing the content of brittle oxide inclusions (mainly Al2O3 inclusions). In this invention, the oxygen content is defined as ≤0.0009%.

[0026] 10) Determination of P and S content

[0027] Phosphorus (P) severely causes segregation during solidification in steel. P dissolves in ferrite, causing grain distortion and coarsening, and increasing cold brittleness. In this invention, the P content is defined as ≤0.020%. Sulfur (S) causes hot brittleness in steel, reducing its ductility and toughness. In this invention, the S content is defined as ≤0.008%.

[0028] 11) Determination of the contents of As, Sn, Sb and Pb

[0029] Trace elements such as As, Sn, Sb, and Pb are all low-melting-point non-ferrous metals. Their presence in steel can cause soft spots and uneven hardness on the surface of parts. Therefore, they are considered harmful elements in steel. In this invention, the content range of these elements is determined as As≤0.04%, Sn≤0.03%, Sb≤0.005%, and Pb≤0.002%.

[0030] In order to obtain rolling element steel for rolling mill bearings with high wear resistance, high mechanical properties and long service life, this invention also explicitly defines the following main technical indicators for the steel:

[0031] The non-metallic inclusions in the steel of this invention are tested according to the GB / T 10561A method, and the levels of various inclusions do not exceed the requirements in Table 1.

[0032] Table 1

[0033]

[0034] The macroscopic defects of the steel of this invention are inspected according to the water immersion high-frequency flaw detection method of SEP 1927 (method for determining the purity of forged and rolled steel bars by ultrasonic immersion testing). The length of a single inclusion shall not exceed 2 mm, and the defect index shall not exceed 10 mm / dm. 3 .

[0035] The low-magnification microstructure of the steel in this invention is graded according to GB / T1979, requiring that general porosity, central porosity, ingot segregation and central segregation do not exceed grade 1.0, and shrinkage cavities, cracks and subcutaneous bubbles are not allowed.

[0036] The grain size of the steel in this invention is tested and rated according to GB / T6394 using the carburizing method, requiring a grain size ≥ 7.

[0037] The end hardenability of the steel of this invention is tested in accordance with GB / T225, requiring J1.5≥50HRC and J9≥40HRC.

[0038] The mechanical properties of the steel used in this invention are tested in accordance with GB / T228, and the specific requirements are shown in Table 2 below.

[0039] Table 2

[0040]

[0041] This invention relates to a method for producing steel for rolling elements of large-size rolling mill bearings. The process flow is as follows: primary refining in a converter or electric furnace → refining in a ladle refining furnace (LF furnace) → vacuum degassing in a vacuum circulating degassing furnace (RH or VD furnace) → continuous casting CCM (large cross section) → heated rolling into finished products → finishing → surface and internal flaw detection → packaging.

[0042] The main steps are as follows:

[0043] (1) Steel smelting:

[0044] Converter or electric arc furnace primary smelting: High-quality molten iron and high-nickel scrap steel (Ni accounts for more than 50% of the mass of the scrap steel) are added together to a converter or electric arc furnace for primary smelting, and 4000-5000m³ of hot metal is blown in. 3 Oxygen and 1000-2000m 3 Argon gas is used, along with activated limestone (CaCO3), to react with harmful elements in the steel, removing harmful elements such as phosphorus (P≤0.020%) and titanium (Ti≤0.002%). The final carbon content at the tapping point of the primary smelting furnace is 0.15%–0.20%, and the tapping temperature is ≥1650℃. Slag is blocked during tapping, and some alloys are added during tapping (initial composition adjustment). Slag removal is performed immediately after tapping, and the steel is quickly hoisted to the refining LF furnace for smelting.

[0045] Steel ladle refining furnace refining: The entire refining process utilizes an argon-protected atmosphere. During the process, SiC and a CaO-SiO2-MgO composite slagging agent are used to deoxidize the molten steel and remove harmful non-metallic inclusions. SiC is added to the molten steel for diffusion and precipitation deoxidation. The high-performance CaO-SiO2-MgO composite slagging agent further diffuses and deoxidizes on the surface of the molten steel, adsorbing and removing harmful non-metallic inclusions. During the smelting process, power is interrupted every 15 minutes, and SiC (30-50 kg) and CaO-SiO2-MgO composite slagging agent (100-150 kg) are added to the molten steel. Temperature measurement and sampling analysis of the molten steel are performed, and the required main elements are added according to the target requirements. The number of temperature measurements and sampling in the refining furnace is controlled at 2-3 times until the composition meets the product requirements. The refining time is controlled at over 45 minutes, and the soft blowing time of the molten steel is 15-20 minutes.

[0046] Vacuum degassing: During RH or VD vacuum degassing, the highest vacuum degree in the vacuum furnace is ≤1.33mbar. The vacuum circulation treatment time of molten steel is maintained at ≥30min to ensure that harmful gases in the steel are effectively removed. After the vacuum treatment, argon gas is blown into the bottom of the ladle. The argon gas flow rate is controlled so that the molten steel is not exposed to the air. The soft blowing time of molten steel is 15-20min. At the same time, 30-50m of silicon-calcium wire is fed in to modify the Al2O3 inclusions in the molten steel, transforming Al2O3 or MgO·Al2O3 into calcium aluminates and composite inclusions with lower melting points to ensure smooth subsequent casting.

[0047] (2) Continuous casting: Argon gas is used for protection during the entire casting process to prevent secondary contamination and oxidation of the molten steel. Preferably, continuous casting uses a large cross-section of 300mm×300mm or larger, and electromagnetic stirring, induction heating in the tundish, and light reduction are used to reduce the superheat of the molten steel and improve the segregation of the billet. Argon-blown stoppers are used in the tundish during continuous casting, and the sealing of the stopper head must be ensured. The superheat of the casting ΔT ≤ 18℃, the light reduction is 12mm~15mm, the casting speed is 0.65~0.85m / min, the steel flow ratio is 0.4~0.6L / kg, and the remaining steel in the ladle is not less than 6 tons. Through the above control technologies, the center segregation of the steel is further improved, and the uniformity of the steel structure is enhanced.

[0048] (3) Heating and rolling: The continuously cast billet is conveyed to a heating furnace with a neutral or weakly oxidizing atmosphere via roller conveyor and then heated and rolled into round bars. The specific rolling process is as follows: The continuously cast billet enters the walking beam heating furnace via conveyor roller conveyor. The air-to-coal ratio of the gas in the furnace is controlled at 0.85 to 0.95 to reduce the residual oxygen content. The steel is heated to 1080℃ to 1180℃ in the heating furnace and held for 2 to 3 hours. The initial rolling temperature of the continuously cast billet is controlled at 960℃ to 1030℃. A three-pass reciprocating large reduction technology is adopted (the steel is rotated 90° after each reduction). The reduction amounts of the three passes are 30% to 35%, 20% to 30%, and 30% to 40%, respectively. This allows the core structure of the billet to undergo deformation and recrystallization preferentially during the deformation process, thereby making the core structure of the steel more uniform and dense under the action of large reduction. The product is then rolled alternately by eight horizontal and vertical rolling mills, and finally rolled into round bars with a specification of φ60mm~φ100mm.

[0049] (4) Finishing: including straightening, chamfering and other finishing processes to ensure that the dimensions, curvature and other indicators meet the requirements.

[0050] (5) 100% non-destructive testing is carried out on the surface and inside. Only products that pass the inspection can be considered qualified products.

[0051] The advantages of this invention are:

[0052] 1. This invention is a high mechanical property carburizing steel with a new chemical composition. It not only has the high wear resistance and high microstructure uniformity of GCrl5SiMn steel used in traditional large-size rolling mill bearings, but also has high mechanical properties that traditional rolling mill bearing rolling element steel does not have, thus obtaining long-life large-size rolling mill bearing rolling elements.

[0053] 2. Special smelting process:

[0054] (1) Converter or electric furnace: Add high-quality molten iron and high-nickel scrap steel (Ni accounts for 50% of the scrap steel) for primary refining, and blow 4000-5000m³ of hot metal into the furnace. 3 Oxygen and 1000-2000m 3Argon gas is used, along with activated limestone (CaCO3), to react with harmful elements in the steel, removing harmful elements such as phosphorus (P≤0.020%) and titanium (Ti≤0.002%).

[0055] (2) Refining furnace and vacuum degassing furnace: In the LF refining furnace, SiC and CaO-SiO2-MgO high-performance composite slag-forming agent are used for deoxidation and removal of harmful non-metallic inclusions. In the RH or VD vacuum degassing furnace, non-metallic inclusions and harmful gases in the steel are further removed in a vacuum environment, and the non-metallic inclusions and O content in the steel are reduced to extremely low levels. The number and size of inclusions reach the world's advanced level.

[0056] (3) Continuous casting adopts argon protection throughout the casting process to protect the molten steel from secondary oxidation and contamination; large cross-sections of 300mm×300mm and above are adopted, and electromagnetic stirring, tundish induction heating and light reduction are used. The casting superheat ΔT≤18℃, the light reduction amount is 12mm~15mm, and the casting speed is 0.65~0.85m / min; the steel flow ratio is 0.4~0.6L / kg, and the remaining steel in the ladle is not less than 6 tons to ensure that the steel has good surface and internal quality.

[0057] 3. Special rolling process:

[0058] A three-pass reciprocating large reduction technique is employed (the steel is flipped 90° after each reduction pass), with reductions of 30%–35%, 20%–30%, and 30%–40% respectively. This allows the core structure of the cast billet to preferentially deform and recrystallize during the deformation process, resulting in a more uniform and dense core structure under the large reduction. The billet is then rolled alternately on eight horizontal and vertical rolling mills, ultimately producing round bars with a diameter of φ60mm–φ100mm. Detailed Implementation

[0059] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0060] The chemical composition (wt%) of the steel used for heavy truck engine bearings in various embodiments of the present invention is shown in Tables 3 and 4.

[0061] Table 3

[0062] C Si Mn P S Cr Cu Ni Al Embodiment 1 of the present invention 0.22 0.50 0.75 0.009 0.003 0.81 0.02 1.01 0.010 Embodiment 2 of the present invention 0.22 0.51 0.76 0.008 0.003 0.82 0.02 1.02 0.012 Embodiment 3 of the present invention 0.23 0.50 0.75 0.008 0.004 0.81 0.03 1.01 0.011

[0063] Table 4

[0064] Mo As Sn Sb Pb Ti O Embodiment 1 of the present invention 0.20 0.0057 0.0021 0.0012 0.001 0.0010 0.00061 Embodiment 2 of the present invention 0.20 0.0052 0.0018 0.0013 0.001 0.0011 0.00062 Embodiment 3 of the present invention 0.19 0.0051 0.0017 0.0014 0.001 0.0010 0.00059

[0065] Table 5 Inclusions in the steel of each embodiment

[0066]

[0067] Table 6 Low-magnification data of steel in each embodiment

[0068]

[0069]

[0070] Table 7 Grain size data of steel samples

[0071]

[0072] Table 8. Water immersion high-frequency flaw detection data of steel in each embodiment.

[0073]

[0074] Table 9 Mechanical property data of steel in each embodiment

[0075]

[0076] Table 10 End-hardenability data of steels from various embodiments

[0077]

[0078] This invention relates to a method for producing steel for rolling elements of large-size rolling mill bearings. The process flow is as follows: converter or electric furnace → ladle refining furnace (LF furnace) → vacuum circulating degassing furnace (RH or VD furnace) → continuous casting CCM (large cross section) → heated rolling into finished products → finishing → surface and internal flaw detection → packaging.

[0079] Specifically, high-quality molten iron and 2 tons of high-nickel scrap steel (Ni accounts for 50% of the scrap steel) are added together to a converter or electric furnace for primary refining, and then blown into a 4000-5000m³ inlet. 3 Oxygen and 1000-2000m 3Argon gas was used, and 4-5 tons of active limestone (CaCO3) were added for smelting. The final carbon content at tapping was controlled at 0.15%-0.20%, phosphorus at ≤0.020%, and titanium at ≤0.002%. The tapping temperature was controlled at 1652℃-1660℃. A slag-blocking system was used for tapping. Some alloying agents were added during tapping (initial composition adjustment). After all the molten steel had been tapped, the slag was removed, and the steel was quickly hoisted to the refining LF furnace. First, a ladle cover is placed over the molten steel, and argon gas is introduced into the ladle cover for steel protection. During the smelting process, the power is stopped every 15 minutes, and SiC (30-50 kg) and CaO-SiO2-MgO high-performance composite slagging agent (100-150 kg) are added to the molten steel. The temperature of the molten steel is measured and samples are taken for analysis. The required main elements are added according to the target requirements. The number of temperature measurements and sampling in the refining furnace is controlled at 2-3 times until the composition meets the product requirements. The refining time is 45–50 min, and the soft blowing time of molten steel is 15–20 min. During RH or VD vacuum degassing, the highest vacuum level in the vacuum furnace is ≤1.33 mbar. The vacuum circulation treatment time of molten steel is 30–35 min, and the soft blowing time of molten steel is 15–20 min, while simultaneously feeding in 30–50 m of silicon-calcium wire. Continuous casting uses large cross-sections of 300 mm × 300 mm or larger, employing electromagnetic stirring, induction heating in the tundish, and light pressure reduction to decrease the superheat of the molten steel and improve billet segregation. Argon-blown stoppers are used in the tundish during continuous casting, and the sealing of the stopper head must be ensured. The casting superheat ΔT ≤ 18℃, the light pressing reduction is 12mm~15mm, and the casting speed is 0.65~0.85m / min; the steel flow ratio and water volume are 0.4~0.6L / kg, and the remaining steel in the ladle is not less than 6 tons; the continuously cast billet enters the walking beam furnace with a neutral or weakly oxidizing atmosphere via a conveyor roller, and the air-to-coal ratio of the furnace gas is controlled at 0.85~0.95 to reduce residual oxygen. The steel is heated in the furnace to 1080℃~1180℃ and held for 2 hours. The continuous casting billet is rolled at a temperature of 960-1030℃ for 3 hours. A three-pass reciprocating large reduction technique is adopted (the steel is rotated 90° after each reduction). The reduction amounts for the three passes are 30%-35%, 20%-30%, and 30%-40%, respectively. The billet is then rolled alternately by eight horizontal and vertical rolling mills. Finally, round bars with a specification of φ60mm-φ100mm are rolled out and slowly cooled to room temperature. The bars are then subjected to subsequent flaw detection and finishing.

[0080] As can be seen from Tables 3, 4, 5, 6, 7, 8, 9, and 10, the steel for rolling elements of large-size rolling mill bearings in the various embodiments of the present invention has achieved the international advanced level in the control of harmful elements such as phosphorus, sulfur, oxygen, titanium, and non-metallic inclusions. From the results of low magnification, mechanical properties, end hardenability, and microstructure grain size, the low magnification quality, hardenability, microstructure uniformity, and mechanical properties of the present invention all meet the requirements for steel for rolling elements of large-size rolling mill bearings.

[0081] Meanwhile, each embodiment was subjected to water immersion high-frequency flaw detection according to the SEP 1927 method, and the macroscopic inclusions achieved zero defects.

[0082] In summary, the steel for rolling elements of large-size rolling mill bearings in various embodiments of the present invention adopts a high-efficiency, high-capacity, and low-cost process route of vacuum degassing, continuous casting, and rolling. Through unique chemical composition design, special smelting and rolling processes, high-purity steel with high microstructure uniformity and high mechanical properties are obtained, resulting in a new type of steel with a high-efficiency, high-capacity, low-cost, and high-quality production mode.

[0083] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A steel for rolling elements of large-size rolling mill bearings, characterized in that: the chemical composition of the steel, by mass percentage, is: C: 0.2-0.25%, Si: 0.5-0.6%, Mn: 0.6-0.9%, Cr: 0.7-0.9%, Ni: 0.8-1.1%, Mo: 0.15-0.2%, S≤0.008%, P≤0.020%, Cu≤0.25%, Al≤0.05%, Ti≤0.002%, O≤0.0009%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, with the balance being Fe and unavoidable impurities; the production method of the steel includes... I. Steel smelting: 1.1 Converter or electric furnace: High-quality molten iron and high-nickel scrap steel are added together to the converter or electric furnace for primary refining. Oxygen and argon are blown in, and active limestone is added to react with harmful elements in the steel to remove harmful elements such as phosphorus and titanium, so that P≤0.020% and Ti≤0.002%. The final carbon content at the end of the primary refining furnace is 0.15%~0.20%, and the tapping temperature is ≥1650℃. Slag is blocked during tapping. Some alloy is added to adjust the composition during tapping. Slag is removed immediately after tapping. After slag removal, the steel is quickly hoisted to the ladle refining furnace for smelting. 1.2 Steel Ladle Refining Furnace: The entire refining process adopts an argon protective atmosphere for smelting. During the process, SiC and CaO-SiO2-MgO composite slag-forming agent are used for deoxidation and removal of harmful non-metallic inclusions. SiC is added to the molten steel for diffusion and precipitation deoxidation. The CaO-SiO2-MgO composite slag-forming agent further diffuses and deoxidizes on the surface of the molten steel and adsorbs and removes harmful non-metallic inclusions. During the smelting process, SiC and CaO-SiO2-MgO composite slag-forming agent are added to the molten steel at intervals during power outages. The temperature of the molten steel is measured and sampled for analysis. The required main elements are added according to the target requirements. The number of temperature measurements and sampling in the refining furnace is controlled at 2 to 3 times until the composition meets the product requirements. The refining time is controlled at more than 45 minutes, and the soft blowing time of molten steel is 15 to 20 minutes. 1.3 Vacuum degassing: During vacuum degassing, the highest vacuum degree in the vacuum furnace is ≤1.33mbar, and the vacuum circulation treatment time of molten steel is maintained at ≥30min to ensure that harmful gases in the steel are effectively removed. After the vacuum treatment is completed, argon gas is blown into the bottom of the ladle, and the argon gas flow rate is controlled so that the molten steel is not exposed to the air. At the same time, silicon-calcium wire is fed in. II. Continuous casting: Argon gas is used for the entire casting process to prevent secondary contamination and oxidation of the molten steel; III. Heating and Rolling: The continuously cast billet enters the walking beam furnace via a conveyor roller conveyor. The air-to-coal ratio of the gas in the furnace is controlled at 0.85 to 0.

95. The steel is heated to 1080℃ to 1180℃ in the furnace and held for 2 to 3 hours. The initial rolling temperature of the continuously cast billet is controlled at 960℃ to 1030℃. A three-pass reciprocating large reduction rolling method is adopted. After each reduction, the steel is rotated 90°. The reduction amounts for the three passes are 30% to 35%, 20% to 30%, and 30% to 40%, respectively. Then, it is rolled alternately by 8 horizontal and vertical rolling mills. Finally, round bars with a specification of φ60mm to φ100mm are rolled.

2. The steel for rolling elements of large-size rolling mill bearings according to claim 1, characterized in that: Non-metallic inclusions in the structure shall be inspected according to GB / T 10561 Method A, and the levels of various inclusions shall not exceed the requirements in Table 1. Table 1 ； Macroscopic defects in the structure shall be inspected according to the water immersion high-frequency flaw detection method in SEP 1927 Method for Determining the Purity of Forged and Rolled Steel Bars. The length of a single inclusion shall not exceed 2 mm, and the defect index shall not exceed 10 mm / dm. 3 ; The low-magnification structure is graded according to GB / T1979, and the general porosity, central porosity, ingot segregation and central segregation shall not exceed grade 1.0, and shrinkage cavities, cracks and subcutaneous bubbles are not allowed. Grain size is tested and graded according to GB / T6394 using the carburizing method, and the grain size must meet grade ≥7.

3. The steel for rolling elements of large-size rolling mill bearings according to claim 1, characterized in that: The mechanical properties of the steel were tested according to GB / T228 and met the requirements of Table 2. Table 2 ； The end hardenability of steel shall be tested in accordance with GB / T225, and shall meet the requirements of J1.5≥50HRC and J9≥40HRC.

4. A method for producing steel for rolling elements of large-size rolling mill bearings as described in claim 1, 2, or 3, characterized in that: include I. Steel smelting: 1.1 Converter or electric furnace: High-quality molten iron and high-nickel scrap steel are added together to the converter or electric furnace for primary refining. Oxygen and argon are blown in, and active limestone is added to react with harmful elements in the steel to remove harmful elements such as phosphorus and titanium, so that P≤0.020% and Ti≤0.002%. The final carbon content at the end of the primary refining furnace is 0.15%~0.20%, and the tapping temperature is ≥1650℃. Slag is blocked during tapping. Some alloy is added to adjust the composition during tapping. Slag is removed immediately after tapping. After slag removal, the steel is quickly hoisted to the ladle refining furnace for smelting. 1.2 Steel Ladle Refining Furnace: The entire refining process adopts an argon protective atmosphere for smelting. During the process, SiC and CaO-SiO2-MgO composite slag-forming agent are used for deoxidation and removal of harmful non-metallic inclusions. SiC is added to the molten steel for diffusion and precipitation deoxidation. The CaO-SiO2-MgO composite slag-forming agent further diffuses and deoxidizes on the surface of the molten steel and adsorbs and removes harmful non-metallic inclusions. During the smelting process, SiC and CaO-SiO2-MgO composite slag-forming agent are added to the molten steel at intervals during power outages. The temperature of the molten steel is measured and sampled for analysis. The required main elements are added according to the target requirements. The number of temperature measurements and sampling in the refining furnace is controlled at 2 to 3 times until the composition meets the product requirements. The refining time is controlled at more than 45 minutes, and the soft blowing time of molten steel is 15 to 20 minutes. 1.3 Vacuum degassing: During vacuum degassing, the highest vacuum degree in the vacuum furnace is ≤1.33mbar, and the vacuum circulation treatment time of molten steel is maintained at ≥30min to ensure that harmful gases in the steel are effectively removed. After the vacuum treatment is completed, argon gas is blown into the bottom of the ladle, and the argon gas flow rate is controlled so that the molten steel is not exposed to the air. At the same time, silicon-calcium wire is fed in. II. Continuous casting: Argon gas is used for the entire casting process to prevent secondary contamination and oxidation of the molten steel; III. Heating and Rolling: The continuously cast billet enters the walking beam furnace via a conveyor roller conveyor. The air-to-coal ratio of the gas in the furnace is controlled at 0.85 to 0.

95. The steel is heated to 1080℃ to 1180℃ in the furnace and held for 2 to 3 hours. The initial rolling temperature of the continuously cast billet is controlled at 960℃ to 1030℃. A three-pass reciprocating large reduction rolling method is adopted. After each reduction, the steel is rotated 90°. The reduction amounts for the three passes are 30% to 35%, 20% to 30%, and 30% to 40%, respectively. Then, it is rolled alternately by 8 horizontal and vertical rolling mills. Finally, round bars with a specification of φ60mm to φ100mm are rolled.

5. The method according to claim 4, characterized in that: In step 1.1, high-nickel scrap steel is used, with Ni accounting for more than 50% of the scrap steel by mass; during smelting, 4000-5000 mg / L of nickel is blown in. 3 Oxygen and 1000-2000 m 3 Argon gas; addition of activated limestone (CaCO3) to remove P and S from steel.

6. The method according to claim 4, characterized in that: During the refining process in the ladle refining furnace, power is cut off every 15 minutes, and SiC: 30-50 kg and CaO-SiO2-MgO high-performance composite slagging agent: 100-150 kg are added to the molten steel.

7. The method according to claim 4, characterized in that: In step 1.3, the soft blowing time of argon blowing in molten steel is 15-20 minutes, while 30-50m of silicon-calcium wire is fed in at the same time.

8. The method according to claim 4, characterized in that: In step two, continuous casting uses a large cross-section of 300mm×300mm or larger, employing electromagnetic stirring, induction heating in the tundish, and light reduction to reduce the superheat of the molten steel and improve billet segregation. Argon-blown stoppers are used in the tundish during continuous casting, with a pouring superheat ΔT ≤ 18℃, a light reduction of 12mm~15mm, and a pouring speed of 0.65~0.85m / min. The steel flow rate is 0.4-0.6 L / kg, and the remaining steel in the ladle is not less than 6 tons.

9. The method according to claim 4, characterized in that: The rolled round steel bars undergo finishing processes, including straightening and chamfering.

Images