A long-life steel for automobile water pump shaft bearing and a production method thereof

Abstract

The present application relates to a kind of long-life automobile water pump shaft bearing steel and its production method, belong to the field of iron-based alloy, the element composition weight percentage of steel is as follows:C:0.80~0.90%, Si:0.65~0.85%, Mn:0.20~0.40%, P:≤0.020%, S:≤0.010%, Cr:1.60~1.70%, Ni:0.40~0.50%, Mo:0.30~0.40%, Al:≤0.050%, rare earth La:0.0010%~0.0020%, Ti:≤0.0020%, Ca≤0.0010%, O:≤0.0010%, the balance is Fe and unavoidable impurities.The production process of steel is as follows:electric furnace or converter initial smelting-external refining-VD or RH vacuum degassing-continuous casting-continuous rolling-normalizing-finishing-punching into warehouse.The metallographic structure of steel surface layer is ferrite+pearlite structure, and the metallographic structure of core is cementite+pearlite.The rolling contact fatigue rated life of steel under 4.5GPa contact stress is more than 5*10 7 ​

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automobile steel and its smelting technology, in particular to a kind of automobile water pump shaft bearing steel and its production method. BACKGROUND

[0002] The cooling system of automobile engine is an important component of automobile. Its stability, reliability and the compactness of its structure directly affect the mechanical properties of automobile, and also affect the overall appearance of automobile. Therefore, the cooling system of automobile engine produced by industrial development countries generally uses cooling water pump shaft bearing. The function of automobile water pump is to circulate cooling water between engine water jacket and radiator to ensure that engine works normally within a certain temperature range. Automobile water pump shaft bearing has been widely used in domestic automobiles and imported vehicles. The water pump is composed of water pump shell, shaft bearing, water seal, impeller, fan and transmission parts, and the shaft bearing is an important component of water pump.

[0003] The steel material commonly used for automobile water pump shaft bearing is high-carbon chromium bearing steel (GCr15), which is smelted by vacuum deoxidization and electromagnetic stirring, and has less oxide content. It can withstand large contact stress and large high tensile stress, and the hardness is above 60HRC after heat treatment.

[0004] Since the rotating speed of water pump is high, the rotating speed of general water pump reaches 6000r / min, and the rotating speed of high-speed water pump reaches 9000r / min. Therefore, the shaft bearing should have high carrying capacity to meet the life requirements of water pump at a certain rotating speed. At the same time, due to the limited space position of water pump, small heat dissipation area and poor working conditions, the shaft bearing should be able to meet the requirements of normal operation at high temperature while not reducing the carrying capacity of the bearing. The high-carbon chromium bearing steel GCr15 produced by the conventional process is prone to failure under high speed and high temperature conditions, which eventually leads to early failure of water pump shaft bearing. SUMMARY

[0005] In view of the problems existing in the prior art, based on the conventional bearing steel GCr15, the steel element composition is reasonably optimized, and the steel production process is improved, a new type of automobile water pump shaft bearing steel and its production method are proposed. The produced water pump shaft bearing has the characteristics of high temperature resistance, high stability and long service life.

[0006] The main technical indexes of the steel material are as follows: the metallographic structure of the steel material (round steel) after hot rolling is bainite structure, and the core structure is cementite + pearlite structure; the surface layer of the steel material is ferrite + pearlite structure after normalizing treatment, and the core is cementite + pearlite structure. After normalizing treatment, the decarburization layer depth of the steel material is ≤0.6%D (D is the diameter of the steel material).

[0007] The macro-defects of the finished steel after normalizing are tested by SEP 1927 method for water immersion high-frequency flaw detection, and the total ultrasonic flaw index is not more than 5 mm / dm 3 , and the maximum length of a single ultrasonic flaw is not more than 5 mm; the macrostructure is required to be rated according to GB / T 1979, the center porosity is ≤1.0 level, the general porosity is ≤1.0 level, the ingot type segregation is ≤1.0 level, the center segregation is ≤1.0 level, and there is no shrinkage hole, crack and subsurface bubble; the steel is tested for carbide network, carbide band, liquid precipitation and micro-pore according to GB / T 18254-2016, the carbide network is ≤1.5 level, the carbide band is ≤2.0 level, and there is no carbide liquid precipitation and micro-pore. The non-metallic inclusions of the steel are tested according to GB / T 10561A method, wherein the brittle and non-deformable inclusions B-fine is ≤1.0 level, B-coarse is ≤1.0 level, D-fine is ≤1.0 level, D-coarse is ≤0.5 level, and Ds is ≤1.0 level. The rated service life of the steel under a contact stress of 4.5 GPa is more than 5*10 7 .

[0008] The element composition of the steel according to the present application is as follows: C: 0.80-0.90%, Si: 0.65-0.85%, Mn: 0.20-0.40%, P: ≤0.020%, S: ≤0.010%, Cr: 1.60-1.70%, Ni: 0.40-0.50%, Mo: 0.30-0.40%, Al: ≤0.050%, rare earth La: 0.0010%-0.0020%, Ti: ≤0.0020%, Ca: ≤0.0010%, O: ≤0.0010%, and the balance is Fe and inevitable impurities.

[0009] The setting of the element composition of the steel according to the present application is as follows:

[0010] 1) Determination of C content

[0011] C is an essential element for ensuring the wear resistance of the steel, and increasing the C content in the steel will increase its martensite transformation capacity, thereby improving its hardness and strength, and further improving the wear resistance. However, too high C content is not conducive to the toughness of the steel. In addition, too high C content will also cause serious center C segregation, thereby affecting the core toughness of the steel. The C content in the present application is controlled to be 0.80-0.90%. The steel according to the present application belongs to the category of high-carbon steel.

[0012] 2) Determination of Si content

[0013] The addition of Si in the steel can strengthen the ferrite, improve the strength, elastic limit and hardenability, but Si increases the overheating sensitivity, cracking and decarburization tendency of the steel. The Si content in the present application is determined to be 0.65-0.85%.

[0014] 3) Determination of Mn content

[0015] Mn as a deoxidizing element in the steelmaking process is an effective element for strengthening steel, which plays a role of solid solution strengthening. Moreover, Mn can improve the hardenability of steel and improve the hot working performance of steel. Mn can eliminate the influence of S (sulfur): Mn can form high-melting-point MnS with S in steel smelting, thereby weakening and eliminating the adverse effects of S. However, high Mn content can reduce the toughness of steel. The Mn content of the present application is controlled at 0.20-0.40%.

[0016] 4) Determination of Al content

[0017] Al is added as a deoxidizing element in steel, in addition to reducing the dissolved oxygen in molten steel, Al forms fine aluminum nitride inclusions with N, which can refine the grains. However, when the Al content is too high, large-particle Al2O3 and other brittle inclusions are easily formed during the molten steel smelting process, which reduces the purity of the molten steel and affects the service life of the finished product. The Al content range of the present application is determined to be ≤0.05%.

[0018] 5) Determination of Cr content

[0019] Cr is a carbide-forming element, which can improve the hardenability, wear resistance and corrosion resistance of steel. However, when the Cr content is too high, it is easy to form large blocks of carbides combined with carbon in steel. This insoluble carbide reduces the toughness of the steel and reduces the service life of the bearing. The Cr content range of the present application is designed to be 1.60-1.70%.

[0020] 6) Determination of Ni content

[0021] Nickel can reduce the ability of surface atoms to absorb carbon atoms, accelerate the diffusion of carbon atoms in austenite, and reduce the concentration of carbon in the carburized layer, so nickel can slow down the carburizing speed; at the same time, the addition of nickel can improve the toughness of steel. The Ni content range of the present application is determined to be 0.40%-0.50%.

[0022] 7) Determination of Mo content

[0023] Molybdenum can refine the grains of steel, improve the hardenability and thermal 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 easily formed, which reduces the toughness. The Mo content range of the present application is determined to be 0.30-0.40%.

[0024] 8) Determination of rare earth La content

[0025] The rare earth element is added in the steel, can refine the modification inclusions, purify the molten steel, and can improve the plasticity, heat resistance and wear resistance of the steel. But the rare earth element is not added properly, causes the continuous casting nozzle to be blocked, and the performance is poor. Therefore, the content of the rare earth element La is determined as 0.0010-0.0020%.

[0026] 9) The determination of Ca content

[0027] The Ca content can increase the number and size of the pointy oxides in the steel, and because the pointy oxides have high hardness and poor plasticity, they do not deform when the steel deforms, and are easy to form voids at the interface, so that the performance of the steel is poor. The content of Ca in the present application is determined to be ≤0.001%.

[0028] 10) The determination of O content

[0029] The oxygen content represents the amount of oxide inclusions, and the brittle inclusions of the oxides limit the service life of the finished product. A large number of tests show that the reduction of oxygen content is beneficial to improving the purity of the steel, especially reducing the content of brittle inclusions of the oxides in the steel. The oxygen content in the present application is determined to be ≤0.0010%.

[0030] 11) The determination of P and S content

[0031] P seriously causes segregation during solidification in the steel, P dissolves in ferrite to make the grain distorted and coarse, and increases the cold brittleness. The content of P in the present application is determined to be ≤0.020%. S makes the steel produce thermal brittleness, reduces the ductility and toughness of the steel, and the content of S in the present application is determined to be ≤0.010%.

[0032] The production process of the steel for the shaft bearing of the automobile water pump shaft is as follows: electric furnace or converter preliminary smelting-external refining-VD or RH vacuum degassing-continuous casting-continuous rolling-normalizing-finishing-packing into warehouse.

[0033] The main production steps are as follows:

[0034] Converter or electric furnace preliminary smelting: high-quality molten iron and scrap steel are added into the converter or electric furnace for preliminary smelting, 4000-5000 m 3 of oxygen and 1000-2000 m 3 of argon are blown in, and active limestone (CaCO3) is added to react with harmful elements in the steel to remove harmful elements phosphorus (P≤0.020%) and titanium (Ti≤0.002%), the end point carbon of the preliminary smelting furnace is 0.15%-0.20%, the tapping temperature is ≥1650℃, and the slag is blocked during tapping, and part of the alloy is added during tapping (initial composition adjustment), and immediately after the end of tapping, the slag is removed, and after the slag removal treatment, it is quickly lifted to the refining LF furnace for smelting.

[0035] Refining furnace: The whole refining process is carried out in argon protective atmosphere, and SiC and CaO-SiO2-MgO high-performance composite slagging agent are used for deoxidation and removal of harmful non-metallic inclusions. SiC is added to the molten steel for diffusion and precipitation deoxidation, and CaO-SiO2-MgO high-performance composite slagging agent further diffuses and removes harmful non-metallic inclusions on the surface of the molten steel. During the smelting process, every 15 minutes, the power is cut off, SiC (30-50 Kg / 100 tons of molten steel) and CaO-SiO2-MgO high-performance composite slagging agent (100-150 Kg / 100 tons of molten steel) are added to the molten steel, and the molten steel is temperature measured and sampled for analysis, and alloying elements are added according to the target requirements. The number of temperature measurement and sampling of the refining furnace is controlled at 2-3 times, until the element composition meets the design requirements. The refining time is controlled at more than 45 minutes, and the molten steel soft blowing time is 15-20 minutes.

[0036] Vacuum degassing: During RH or VD vacuum degassing, the maximum vacuum degree in the vacuum furnace is ≤1.33 mbar, and the molten steel vacuum circulation treatment time is ≥30 min to ensure that harmful gases in the steel are effectively removed. After vacuum treatment, argon is blown into the ladle bottom to stir the molten steel, and the argon flow is controlled so that the molten steel is not exposed to the air. The molten steel soft blowing time is 15-20 min. After vacuum treatment and breaking, La-Fe alloy is added to the molten steel for rare earth treatment. Because the density of La-Fe is lower than that of the molten steel, direct addition cannot sink into the molten steel. If the alloy is stirred into the molten steel after addition, the molten steel will be contaminated, affecting the purity. The specific addition method is as follows: 10-15 kg / 100 tons of La-Fe is loaded into a special sleeve (iron-based alloy), and covered with soft cotton cloth. The sleeve is bound with a slag rod and inserted into the molten steel for 1 minute, then the sleeve is melted and the rare earth alloy enters the molten steel. The purpose of adding rare earth is to modify the inclusions in the steel into fine particulate inclusions, and to purify the molten steel, improve the plasticity, heat resistance and wear resistance of the material.

[0037] Step 4 continuous casting: long nozzle argon blowing protection is used in the process of ladle to tundish, argon flow is ≤250L / min; and ladle slag detection technology is used to prevent the remaining metallurgical slag from pouring into the tundish to contaminate the pure molten steel. Double-layer protection of tundish covering agent and carbonized rice husk is used to isolate air, prevent secondary oxidation of molten steel, reduce tundish temperature drop, and control the superheat of molten steel at 10-30℃. A slag dam is arranged in the tundish to filter and block some harmful impurities. The opening degree of stopper is accurately controlled by computer system, and the molten steel flows into the submerged entry nozzle and then into the mold through the opening of stopper. The mold level fluctuation is controlled within the range of -5mm to +5mm. Special mold powder is added into the mold to form a shell under the condition of mold cooling water. The molten steel in the mold is subjected to electromagnetic stirring by external mold electromagnetic stirring equipment. The casting speed is ≤0.8m / min. The continuous casting billet is cooled by segmenting the cooling capacity according to the different time required in the solidification process of the casting billet. The cooling end electromagnetic stirrer is provided to stir the liquid core of the continuous casting billet, break the coarse columnar crystal, form more equiaxed crystals, and reduce the positive segregation at 1 / 2R. The continuous casting billet is cut into a fixed size in the vertical direction by a flame cutting machine with a speed synchronized with the casting speed, and then is transferred to the horizontal roller and heated in the heating furnace.

[0038] Step 5 heating and high-temperature diffusion: the continuous casting billet is heated in the furnace at a temperature of 1200-1250℃, and the temperature is maintained for more than 6 hours. The air-coal ratio of the gas is controlled at 1.01-1.05 to reduce the residual oxygen content and prevent the steel from decarburization.

[0039] Step 6 rolling: the opening rolling temperature is controlled at 1100-1150℃ after high-pressure water descaling, so that the steel starts to be rolled in the austenite single-phase zone, and then is rolled by multiple horizontal rolling mills alternately. Since the alloy content of the product is high, water cooling is not allowed during rolling to prevent the whole steel from cracking due to the large organizational stress caused by organizational transformation. The final rolling temperature is controlled at 950-1050℃, so that the whole rolling process is carried out in the austenite single-phase zone. Then the steel is normally cooled on the cooling bed and is offline. Since the steel is rolled in the high-temperature single-phase zone, the grain of the steel is coarse. At this time, the metallographic structure of the surface layer of the hot-rolled steel is bainite, and the core structure is cementite+pearlite. At the same time, the steel does not use controlled rolling and controlled cooling process during rolling, and the carbide network is serious in the hot-rolled state, which is above 3.0. In order to ensure the performance of the steel, normalizing heat treatment is needed.

[0040] Step 7 normalizing: first, the rolled steel is austenitized at 880℃±(0-10℃) for 3 hours or more, and then air-cooled to room temperature. After normalizing, the bainite structure on the surface of the original steel is transformed into ferrite+pearlite structure, and the carbide network of the steel is significantly improved after normalizing, and the carbide network is ≤1.5 level.

[0041] Compared with the prior art, the advantages of the present application are that:

[0042] 1) In the element component design of the present application, Ni, Mo and other alloys are added, and a small amount of rare earth La is added, which significantly improves the contact fatigue life of the product and can meet the use requirements of the long-life automobile water pump shaft bearing.

[0043] 2) The present application uses special steelmaking, rolling and normalizing process to ensure that the steel reaches the required metallographic structure and performance, and meets the use requirements. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The typical metallographic structure diagram of the water pump shaft bearing steel after hot rolling according to the embodiment of the present application is shown in the figure, and the metallographic structure on the surface of the steel after hot rolling is bainite structure, and the core structure is cementite+pearlite structure.

[0045] Figure 2 The typical metallographic structure diagram of the bearing steel after controlled rolling and controlled cooling according to the comparative example is shown in the figure, and the metallographic structure on the surface of the steel after hot rolling is sorbite structure, and the core structure is cementite+pearlite structure.

[0046] Figure 3 The typical metallographic structure diagram of the water pump shaft bearing steel after normalizing according to the embodiment of the present application is shown in the figure, and the surface of the steel after normalizing is ferrite+pearlite structure, and the core is cementite+pearlite structure. DETAILED DESCRIPTION

[0047] The present application will be further described in detail below in combination with the embodiments, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[0048] The chemical composition (wt%) of the automobile water pump shaft bearing steel corresponding to the embodiments 1-3 and the GCr15 steel of the comparative example is shown in Tables 1 and 2, and the non-metallic inclusion detection condition is shown in Table 3.

[0049] Table 1

[0050] Examples C Si Mn P S Cr Cu Ni Al The present invention 1 0.86 0.65 0.23 0.018 0.002 1.62 0.01 0.42 0.015 The present invention 2 0.81 0.72 0.32 0.016 0.002 1.65 0.01 0.46 0.023 The present invention 3 0.88 0.75 0.38 0.015 0.001 1.67 0.02 0.49 0.020 Comparative example GCr15 0.95 0.23 0.36 0.018 0.003 1.45 0.03 0.03 0.025

[0051] Table 2

[0052] Examples Mo La Ca Ti O The present invention 1 0.32 0.0012 0.0002 0.0009 0.00048 The present invention 2 0.35 0.0015 0.0002 0.0011 0.00053 The present invention 3 0.38 0.0019 0.0001 0.0008 0.00052 Comparative example GCr15 0.02 ＜0.0002 0.0005 0.0012 0.00058

[0053] Table 3 Non-metallic inclusion detection of each example and comparative steel

[0054]

[0055] The typical microstructure of the hot-rolled and normalized steel material of the embodiment of the present application is shown in Figure 1. Figure 1 and Figure 3 The microstructure of the hot-rolled steel material of the comparative example is shown in Figure 2. Figure 2 .

[0056] The carbide banding, netting and liquation of the steel material of the embodiment of the present application and the rolling contact fatigue life rating results under a contact stress of 4.5 GPa are shown in Table 4.

[0057] Table 4 Carbide and contact fatigue life detection of each example and comparative steel

[0058] Examples Carbide banding Carbide network Carbide liquation Contact fatigue life The present invention 1 1.5 1.0 0 6.3 x 10 7 ]] The present invention 2 1.0 1.0 0 5.7 x 10 7 ]]> The present invention 3 1.5 1.0 0 7.8 x 10 7 ]] Comparative steel 2.0 2.5 0 2.8 x 10 7 ]]>

[0059] The manufacturing process of the long-life automobile water pump shaft bearing steel of Examples 1-3 is electric furnace or converter - secondary refining - VD or RH vacuum degassing - continuous casting - continuous rolling - normalizing - finishing - piece making and warehousing.

[0060] The tapping end C of the three examples is controlled at 0.15-0.25%, the end P is required to be ≤0.020%, the electric furnace / converter, refining furnace, vacuum degassing and continuous casting processes are performed according to the requirements of the aforementioned smelting production steps, the continuous casting superheat is controlled within 10-30℃, and the withdrawal speed is 0.40-0.70 m / min. The specific rolling process of the continuous casting billet of each example is: the continuous casting billet is heated into a walking beam furnace, the heating temperature is 1200-1250℃, the temperature is maintained for more than 6 hours, the air-coal ratio of the coal gas is controlled at 1.01-1.05 to reduce the residual oxygen content and prevent the steel material from exceeding the decarburization standard; the opening rolling temperature is set to 1100-1150℃, and the finish rolling temperature is 950-1050℃, so that the entire rolling process is carried out in the austenite single-phase region, and then the steel material is normally cooled on the cooling bed and discharged. After being discharged, the surface layer of the steel material has bainite microstructure, and the core has cementite + pearlite microstructure.

[0061] Then the steel material is normalized, specifically at 880℃±(0-10℃) for heat preservation, so as to be austenitized, and the temperature is maintained for 4 hours, then the steel material is air-cooled, and the steel material is cooled to room temperature and discharged. After normalizing, the bainite microstructure of the surface layer of the steel material is transformed into ferrite + pearlite microstructure, and the core is cementite + pearlite microstructure. At the same time, after normalizing, the carbide netting of the steel material is obviously improved, and the carbide netting is ≤1.5 level.

[0062] As can be seen from the data in Tables 1-3, compared with the traditional GCr15, the automobile water pump shaft connecting bearing steel in the above examples is designed in the composition, the performance of the material is improved by adding alloy elements such as Ni and Mo, and the contact fatigue life is more than twice that of the traditional bearing steel GCr15. In addition, after normalizing treatment, the steel of the application significantly improves the carbide network, and the network is less than or equal to 1.5 levels. At the same time, the metallographic structure of the surface layer of the hot-rolled steel is transformed from the original bainite structure to ferrite + pearlite structure, which avoids the easy generation of internal stress and internal cracking due to different structures in the subsequent use. In summary, the steel of the application is significantly better than the comparative steel in performance, and has better competitiveness.

Claims

1. A method for producing a long-life automotive water pump shaft bearing steel, characterized by: The element content of the steel is as follows: C: 0.80-0.90%, Si: 0.65-0.85%, Mn: 0.20-0.40%, P: ≤0.020%, S: ≤0.010%, Cr: 1.60-1.70%, Ni: 0.40-0.50%, Mo: 0.30-0.40%, Al: ≤0.050%, rare earth La: 0.0010%-0.0020%, Ti: ≤0.0020%, Ca: ≤0.0010%, O: ≤0.0010%, and the balance of Fe and inevitable impurities; the metallographic structure of the surface layer of the steel is ferrite+pearlite, and the metallographic structure of the core is cementite+pearlite; the non-metallic inclusions of the steel are tested according to GB / T 10561 A, wherein the brittle non-deformable inclusions Bfine≤1.0, Bcoarse≤1.0, Dfine≤1.0, Dcoarse≤0.5, and Ds≤1.0 have an influence on the service life of the bearing; and the rated service life of the steel under a rolling contact fatigue stress of 4.5 GPa is 5×10 7 or more. The production method involves molten steel smelting, continuous casting, heating, continuous rolling, normalizing process, and specifically as follows: The molten steel smelting involves preliminary smelting, refining and vacuum degassing, dephosphorization and de-titanium of the molten steel in the preliminary smelting stage, the end-point carbon of 0.15% to 0.20% in the tapping of the preliminary smelting, the tapping temperature of ≥1650℃, the initial adjustment of the composition by adding part of the alloy in the tapping, the argon gas protection atmosphere smelting in the whole refining process, the deoxidation and the removal of harmful non-metallic inclusions by using SiC and CaO-SiO2-MgO high-performance composite slagging agent in the process, the diffusion and precipitation deoxidation by adding SiC into the molten steel, the further diffusion deoxidation and the adsorption and removal of harmful non-metallic inclusions by CaO-SiO2-MgO high-performance composite slagging agent on the surface of the molten steel, the removal of the gas components in the molten steel by vacuum degassing, the blowing of argon gas into the bottom of the ladle after the vacuum treatment, the control of the argon gas flow so that the molten steel is not exposed to the air, the soft blowing time of 15 to 20 minutes, the addition of La-Fe alloy into the molten steel for rare earth treatment after the end of the vacuum treatment and the breaking of the vacuum. The continuous casting: the continuous casting billet is cut into a fixed size casting billet and is heated in the furnace. The heating: the continuous casting billet is heated in the furnace to realize high-temperature diffusion, the heating temperature is 1200-1250℃, the temperature is kept for 6 hours, and the air-coal ratio of the coal gas is controlled to be 1.01-1.

05. The continuous rolling: the continuous casting billet is subjected to continuous rolling after the descaling by high-pressure water, the opening rolling temperature is 1100-1150℃, the rolling is started in the austenite single-phase zone, and then the rolling is alternately performed through multiple horizontal vertical rolling mills, the final rolling temperature is 950℃-1050℃, the whole rolling process is performed in the austenite single-phase zone, the steel material is cooled offline on the cooling bed after rolling, the metallographic structure of the surface layer of the hot-rolled steel material is bainite structure after the hot-rolled steel material is offline from the cooling bed, the core structure is cementite+pearlite structure, and the carbide network in the hot-rolled state is above 3.0 level. The normalizing: the steel material is kept at 880℃±(0-10℃) to make the structure austenitized, and the temperature is kept for more than 3 hours, then the steel material is air-cooled to room temperature, and the furnace is discharged, the bainite structure of the surface layer is transformed into ferrite+pearlite structure, and the carbide network is ≤1.5 level.

2. The production method of the long-life automotive water pump shaft bearing steel according to claim 1, characterized in that: Macroscopic defects of steel are tested by SEP 1927 method, the total ultrasonic defect index is not more than 5mm / dm 3 , the maximum length of single ultrasonic defect is not more than 5mm; the macrostructure is tested by GB / T 1979, the center porosity is ≤1.0 level, the general porosity is ≤1.0 level, the ingot type segregation is ≤1.0 level, the center segregation is ≤1.0 level, there is no shrinkage, crack and subsurface bubble; the carbide network, band, liquidation and micro-pore are tested according to GB / T 18254-2016, the carbide network is ≤1.5 level, the carbide band is ≤2.0 level, there is no carbide liquidation and micro-pore.

3. The method of producing a long-life automotive water pump shaft bearing steel according to claim 1, characterized by: In the initial smelting stage of molten steel, high-quality molten iron and scrap steel are added to the converter or electric furnace for initial smelting, 4000-5000 m 3 Oxygen and 1000-2000 m 3 Argon is blown in, and active limestone is added to react with harmful elements in the steel to achieve dephosphorization and detitanium, with phosphorus P≤0.020% and titanium Ti≤0.002%. The initial smelting molten steel is blocked, and immediately after the tapping is finished, the slag is handled.

4. The method of producing a long-life automotive water pump shaft bearing steel according to claim 1, characterized by: In the refining stage of the molten steel smelting, the power is cut off every 15 minutes, SiC: 30-50Kg and CaO-SiO2-MgO high-performance composite slagging agent: 100-150kg are added into the molten steel, the temperature of the molten steel is measured and the sample is analyzed, the alloy elements are added according to the target requirements, the number of temperature measurement and sampling of the refining furnace is controlled to be 2-3 times, and the composition content reaches the design range; the refining time is controlled to be more than 45 minutes, and the soft blowing time of the molten steel is 15-20 minutes.

5. The method of producing a long-life automotive water pump shaft bearing steel according to claim 1, characterized by: In the vacuum degassing stage of the molten steel smelting, the maximum vacuum degree in the vacuum furnace is ≤1.33mbar, the vacuum circulation treatment time of the molten steel is ≥30 minutes; 10-15kg of La-Fe alloy is loaded into the iron-based alloy sleeve and covered with soft linen cloth, the sleeve is bound and deeply inserted into the molten steel by using the slag rod for 1 minute, then the sleeve is melted, and the rare earth alloy is melted into the molten steel.

6. The method of producing a long-life automotive water pump shaft bearing steel according to claim 1, characterized by: The long nozzle is used for argon blowing protection from the ladle to the tundish, the argon flow is ≤250L / min; the ladle slag detection technology is used to control the slag; the double-layer protection of the tundish covering agent and carbonized rice husk is used to isolate air and control the superheat of the molten steel in the tundish to be 10-30℃; the slag wall is arranged in the tundish to filter and block some harmful impurities; the opening degree of the stopper is accurately controlled by the computer system, the molten steel flows into the submerged nozzle through the stopper opening and then is injected into the mold; the mold level fluctuation is controlled to be in the range of-5mm to +5mm; the mold powder is added into the mold, the molten steel forms the shell under the condition of the mold cooling water; the electromagnetic stirring device is used to stir the molten steel in the mold; the withdrawal machine withdraws the billet at a speed of ≤0.8m / min; the secondary cooling zone is used to cool the continuous casting billet according to the solidification process of the billet; the electromagnetic stirring device is arranged at the end of the cooling zone to stir the liquid core of the continuous casting billet, break the coarse columnar crystal, form more equiaxed crystal and reduce the positive segregation at 1 / 2R; the flame cutting machine is used to cut the billet into the fixed-size billet in the vertical direction, the billet is transferred to the horizontal roller and then is heated in the heating furnace.

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