High-strength wear-resistant backing bearing steel and heat treatment process thereof

Abstract

The invention provides high-strength wear-resistant backing bearing steel and a heat treatment process thereof, and belongs to the technical field of bearings. According to the process, under the vacuum condition, high-density aluminum oxide is converted into low-density stable dodecacalcium heptaaluminate by utilizing interface diffusion and a phase change mechanism of calcium, and meanwhile, CaF2-CaO-based slag is adopted to optimize the sulfur adsorption capacity and promote floating of inclusions. And by controlling the deoxidation temperature and the reaction time, calcium ions are guaranteed to be fully diffused, and the high-stability inclusion conversion rate is achieved. Harmful inclusions and sulfur and oxygen impurities are effectively reduced, the impact toughness of the material is improved, the fatigue life of the material is prolonged, the anisotropy of the material is improved, and finally the high-quality bearing steel with high strength, high toughness and excellent isotropy is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of bearings, and particularly relates to a high-strength wear-resistant backing bearing steel and its heat treatment process. Background Art

[0002] High-strength wear-resistant bearing steel is a key material for high-end equipment such as aerospace and precision machine tools, and its performance directly affects the reliability and service life of the equipment. Especially under harsh working conditions such as high load and high speed, higher requirements are put forward for the strength, toughness and wear resistance of bearing steel.

[0003] Although the traditional bearing steel smelting process can meet certain performance requirements, there are still some defects. For example, the deoxidation means used are often difficult to effectively control the oxygen content in the steel, and it is easy to form large-sized alumina inclusions. These inclusions will become stress concentration points, reducing the fatigue life and impact toughness of the steel. In addition, the traditional process may also lead to uneven microstructure of the steel and obvious anisotropy, thus affecting its mechanical properties.

[0004] Therefore, developing a heat treatment process that can effectively improve the purity of steel and the uniformity of microstructure is an important challenge faced by the current bearing steel field. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a high-strength wear-resistant backing bearing steel and its heat treatment process.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a heat treatment process for high-strength wear-resistant backing bearing steel, comprising the following steps:

[0007] S1. Melting iron-based raw materials and alloying elements to form molten steel, and carrying out preliminary deoxidation and deep deoxidation in sequence; ferromanganese and ferrosilicon are used as deoxidants for preliminary deoxidation, controlling the temperature of the molten steel at 1500 - 1600 °C, and the preliminary deoxidation time is 15 - 30 min; deep deoxidation includes adding aluminum and calcium under vacuum conditions, controlling the temperature of the molten steel at 1300 - 1660 °C, and the deep deoxidation time is 30 - 90 min;

[0008] S2. Casting the molten steel in step S1 into electrodes and remelting with CaF2-CaO-based slag as the medium; the composition of the CaF2-CaO-based slag includes 75 - 85% CaF2 and 15 - 25% CaO by mass percentage;

[0009] S3. Heating the remelted steel ingot and then hot rolling it, and carrying out spheroidizing annealing on the rolled steel.

[0010] In a preferred embodiment of the present invention, in step S1, the addition amount of ferromanganese is 0.4-0.6% of the total mass of the molten steel, and the addition amount of ferrosilicon is 0.2-0.4% of the total mass of the molten steel.

[0011] In a preferred embodiment of the present invention, in step S1, the iron-based raw materials include industrial pure iron accounting for 85-90% and scrap steel accounting for 10-15%; the alloying elements include ferrochrome with Cr≥60%, and the addition amount is 2.4-2.6%; ferrovanadium with V≥50%, and the addition amount is 0.3-0.5%; nickel plate with Ni≥99.9%, and the addition amount is 0.25-0.35%; ferromolybdenum with Mo≥55%, and the addition amount is 0.15-0.22%; ferro-titanium with Ti≥30%, and the addition amount is 0.027-0.040%; electrolytic copper with Cu≥99.95%, and the addition amount is 0.08-0.12%; graphite carburizer with C≥98%, and the final C content is adjusted to 0.80-0.90%.

[0012] In a preferred embodiment of the present invention, in step S1, the deep deoxidation includes the following steps:

[0013] A1. Add 0.0027%-0.00495% of the total mass of the molten steel to the molten steel to ensure that aluminum is evenly dispersed in the molten steel;

[0014] A2. Control the temperature of the molten steel at 1580-1660°C and let it stand for reaction for 10-30 minutes to make aluminum fully react with the oxygen in the molten steel to form alumina inclusions;

[0015] A3. Add 0.0080%-0.0147% of the total mass of the molten steel of calcium to the molten steel;

[0016] A4. Control the temperature of the molten steel at 1300-1500°C and let it stand for reaction for 20-60 minutes to make calcium fully react with the residual oxygen and alumina inclusions in the molten steel to form dodecacalcium heptaaluminate inclusions.

[0017] In a preferred embodiment of the present invention, in step S1, calcium is fed in the form of cored wire, the wire feeding speed is 2-4 m / s, and the wire feeding depth is 1 / 3-2 / 3 of the total height of the molten steel.

[0018] In a preferred embodiment of the present invention, in step S2, the basicity of the CaF2-CaO-based slag is 1.8-2.2.

[0019] In a preferred embodiment of the present invention, in step S2, the remelted ingot is slowly cooled to room temperature at a rate of ≤10°C / h.

[0020] In a preferred embodiment of the present invention, in step S3, the final rolling temperature of hot rolling is 850-900°C, the total reduction ratio is ≥70%, and the rolled steel is water-cooled to 300-400°C at a rate of 20-30°C / s.

[0021] In a preferred embodiment of the present invention, the spheroidizing annealing in step S3 includes the following stages:

[0022] In the first stage, it is heated to 760 - 780°C at a rate of 50 - 100°C / h and held for 2 - 4 h;

[0023] In the second stage, it is cooled to 500°C at a rate of ≤20°C / h and then air-cooled to room temperature.

[0024] Another technical solution provided by the present invention: Based on the above heat treatment process, it contains Fe and inevitable impurities, and also contains the following chemical elements in mass percentages:

[0025] C: 0.80 - 0.90%; Si: 0.20 - 0.30%; Mn: 0.25 - 0.35%; Cr: 1.45 - 1.55%; V: 0.15 - 0.25%; S: ≤0.015%; P: ≤0.025%; Ni: 0.25 - 0.35%; Ti: 0.008 - 0.012%; Mo: 0.08 - 0.12%; Cu: 0.08 - 0.12%.

[0026] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0027] (1) A high-strength wear-resistant back-up bearing steel and its heat treatment process provided by the present invention realize the controllable transformation of the inclusion morphology and the efficient removal of sulfur and oxygen impurities through the temperature control, calcium addition amount control, and slag basicity adjustment in the deep deoxidation stage, and overall improve the fatigue life, impact toughness, and isotropy of the bearing steel.

[0028] (2) By precisely controlling the deep deoxidation temperature and utilizing the interfacial reaction between calcium ions and alumina, the present invention converts high-density alumina into low-density stable dodecacalcium heptaaluminate. Compared with the traditional process, the present invention significantly reduces the residual amount of alumina, eliminates the stress concentration source, directly improves the fatigue life of the material, and reduces the crack initiation points. At the same time, the low-density inclusions are easier to float, further improving the purity of the steel.

[0029] (3) Through the coordinated optimization of calcium treatment and slag basicity, the present invention realizes the efficient removal of sulfur and oxygen impurities in the molten steel. The synergistic effect of calcium and slag significantly reduces the activity coefficient of sulfur, making sulfur preferentially adsorbed on the slag phase, effectively reducing grain boundary oxidation. Compared with the traditional process, the present invention effectively improves the impact toughness of the steel and solves the performance defects caused by high sulfur and oxygen contents.

[0030] (4) On the one hand, the present invention ensures the complete reaction of calcium ions with alumina by controlling the temperature of deep deoxidation to form stable heptaaluminate dodecacalcium and avoid the generation of harmful sulfides; on the other hand, by controlling the basicity of the slag, it promotes the floating and removal of inclusions and enhances the sulfur adsorption capacity, achieving ultra-low residuals of sulfur and oxygen, ensuring the high strength, high toughness and long life of bearing steel. The present invention solves the performance defects of traditional bearing steel caused by residual inclusions and high sulfur and oxygen contents, realizes a bearing steel material with high strength, high toughness and long life, and is applicable to high-load and high-speed scenarios such as aero-engine bearings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0032] Figure 1 is a flowchart of a heat treatment process for a high-strength wear-resistant backing bearing steel;

[0033] Figure 2 is a flowchart of deep deoxidation in step S1;

[0034] Figure 3 is a flowchart of spheroidizing annealing in step S3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Unless otherwise specified below, all raw materials are obtained through commercial purchase or prepared by conventional methods in the art.

[0036] Application Overview:

[0037] Traditional deep deoxidation processes usually add aluminum and calcium and control the temperature of the molten steel at about 1600°C. However, the residual alumina inclusions in this process become stress concentration points, reducing the fatigue life and impact toughness of the steel. It was unexpectedly found that when the temperature of the molten steel in the deep deoxidation stage was reduced to about 1400°C, the deoxidation effect was better than the traditional 1600°C process.

[0038] Under the condition that other conditions are controlled to be the same, experiments were carried out at deoxidation temperatures of 1300 °C, 1400 °C, and 1500 °C respectively. The results show that at 1400 °C, the proportion of stable dodecacalcium heptaaluminate (12CaO·7Al2O3) formed in the molten steel is as high as 98%, and the residual amount of undeformed alumina is only 0.5%. At 1300 °C, the proportion of stable inclusions is only 82%, and the residual amount of undeformed alumina is as high as 12%; at 1500 °C, the proportion of stable inclusions drops sharply to 75%. Further analysis shows that 1400 °C is the optimal activation temperature for the reaction of calcium with alumina. Calcium ions can fully diffuse into the interior of alumina, destroy its crystal structure, form low-density stable dodecacalcium heptaaluminate, and are easy to float and remove. Other temperatures are not conducive to the progress of this reaction.

[0039] Exemplary process:

[0040] As Figure 1 shown, a heat treatment process for high-strength wear-resistant back-up bearing steel includes the following steps:

[0041] S1. Melting iron-based raw materials and alloying elements to form molten steel, and successively carrying out preliminary deoxidation and deep deoxidation; using ferromanganese and ferrosilicon as deoxidizers for preliminary deoxidation, the preliminary deoxidation time is 15 - 30 min, and the temperature of the molten steel is controlled at 1500 - 1600 °C; deep deoxidation includes adding aluminum and calcium under vacuum conditions, controlling the temperature of the molten steel at 1300 - 1660 °C, and the deep deoxidation time is 30 - 90 min;

[0042] S2. Casting the molten steel in step S1 into an electrode and remelting it with a CaF2-CaO-based slag as the medium; the composition of the CaF2-CaO-based slag includes 75 - 85% CaF2 and 15 - 25% CaO by mass percentage;

[0043] S3. Heating the remelted steel ingot and then hot rolling it, and carrying out spheroidizing annealing on the rolled steel.

[0044] This process is applicable to manufacturing bearing steels for high-load and high-speed scenarios such as aeroengine bearings and precision machine tool spindle bearings, which need to serve for a long time under high temperatures of 300 °C, high-frequency impacts of 10 4 times / min, and high contact stresses of 2.5 GPa. Traditional bearing steels suffer from stress concentration caused by large-sized Al2O3 inclusions and insufficient fatigue life; due to excessive oxygen content, grain boundary oxidation brittleness occurs, and the impact toughness decreases significantly.

[0045] This process reduces the oxygen content to 30 - 50 ppm through preliminary deoxidation and further reduces it to 3 - 6 ppm through vacuum deep deoxidation; converts Al2O3 into low-density dodecacalcium heptaaluminate through calcium treatment, with the size refined to 1 - 5 μm, which is easy to float and remove; and removes sulfur and phosphorus impurities through CaF2-CaO slag.

[0046] Further, in step S1, the melting temperature is 1580 - 1650 °C, which is the critical temperature for complete melting of the iron-based raw materials, and at the same time, overheating leading to grain coarsening is avoided. The iron-based raw materials include industrial pure iron and scrap steel. Among them, the purity of industrial pure iron is ≥99.8%, accounting for about 85 - 90% as the matrix material, and the total amount of residual elements is ≤0.15%; the proportion of scrap steel is 10 - 15%, which is used to adjust the carbon content and for recycling. The alloying elements include ferrochrome with Cr ≥ 60%, the addition amount is 2.4 - 2.6%, providing a Cr content of 1.45 - 1.55%; ferrovanadium with V ≥ 50%, the addition amount is 0.3 - 0.5%, providing a V content of 0.15 - 0.25%; nickel plate with Ni ≥ 99.9%, the addition amount is 0.25 - 0.35%, directly providing the Ni content; ferromolybdenum with Mo ≥ 55%, the addition amount is 0.15 - 0.22%, providing a Mo content of 0.08 - 0.12%; ferrotitanium with Ti ≥ 30%, the addition amount is 0.027 - 0.040%, providing a Ti content of 0.008 - 0.012%; electrolytic copper with Cu ≥ 99.95%, the addition amount is 0.08 - 0.12%, directly providing the Cu content; graphite carburizer with C ≥ 98%, added as needed to adjust the final C content to 0.80 - 0.90%.

[0047] Further, in step S1, ferromanganese and ferrosilicon are used as deoxidizers for preliminary deoxidation. The addition amount of ferromanganese is 0.4 - 0.6% of the total mass of the molten steel, ensuring the formation of MnO inclusions, which effectively float up and are removed; the addition amount of ferrosilicon is 0.2 - 0.4% of the total mass of the molten steel, generating SiO2 to improve the fluidity of the molten steel. Among them, the particle size of ferromanganese is controlled at 10 - 30 mm, and the particle size of ferrosilicon is 5 - 15 mm, ensuring uniform melting, and the oxygen content of the molten steel is monitored in real time, and the feeding rate of the deoxidizer is dynamically adjusted.

[0048] Further, as Figure 2 shown, the deep deoxidation in step S1 is carried out under a vacuum condition, and the vacuum degree is controlled at 10 - 100 Pa, including the following steps:

[0049] A1. Add 0.0027% - 0.00495% of the total mass of the molten steel to the molten steel to ensure that aluminum can be evenly dispersed in the molten steel.

[0050] A2. Control the temperature of the molten steel at 1580 - 1660 °C, and let it stand and react for 10 - 30 min to make aluminum fully react with the oxygen in the molten steel to generate alumina inclusions.

[0051] A3. Add 0.0080% - 0.0147% of the total mass of the molten steel of calcium to the molten steel.

[0052] A4. Control the temperature of the molten steel at 1300 - 1500 °C, and let it stand for reaction for 20 - 60 min to fully react calcium with the residual oxygen and alumina inclusions in the molten steel, generating dodecacalcium heptaaluminate inclusions.

[0053] Further, in step S1, calcium is fed in the form of cored wire, the wire feeding speed is 2 - 4 m / s, and the wire feeding depth is 1 / 3 - 2 / 3 of the total height of the molten steel, using the static pressure of the molten steel to prevent calcium from floating and oxidizing. In a specific embodiment, the cored wire with a calcium core diameter of 8 mm and a steel strip thickness of 0.3 mm is added through a wire feeder, and argon is blown and stirred at the bottom of the ladle with a flow rate of 10 L / min.

[0054] Further, in step S2, the basicity (CaO / SiO2) of the CaF2 - CaO - based slag is 1.8 - 2.2, and the SiO2 content in the slag is ≤1.5% through raw material pretreatment (waste steel SiO2 ≤ 1.2%) and low - silicon iron (SiO2 ≤ 0.5%).

[0055] Further, in step S2, the remelted ingot is slowly cooled to room temperature at a rate of ≤10 °C / h, the resistance heating furnace is temperature - controlled in zones, and the temperature difference between the core and the surface of the ingot is ≤5 °C. During the slow cooling process, argon protection is adopted with a flow rate of 20 L / min and an oxygen content of ≤5 ppm. Specifically, the ingot is placed in a closed slow - cooling box, and argon is uniformly introduced from the bottom porous bricks.

[0056] Further, in step S3, the final rolling temperature of hot rolling is 850 - 900 °C, using dynamic recrystallization to refine the grains to 5 - 8 μm; the total reduction ratio is ≥70%, and the rolled steel is water - cooled to 300 - 400 °C at a rate of 20 - 30 °C / s. Among them, the pH value of the cooling water is 6.5 - 7.5, and the pressure is 15 MPa.

[0057] Further, as Figure 3 shown, the spheroidizing annealing in step S3 includes the following stages:

[0058] The first stage: Heat up to 760 - 780 °C at a rate of 50 - 100 °C / h and hold for 2 - 4 h for austenitization and dissolution of coarse carbides;

[0059] The second stage: Cool down to 500 °C at a rate of ≤20 °C / h and air - cool to room temperature to promote the uniform precipitation of spherical carbides.

[0060] Exemplary product:

[0061] A high - strength wear - resistant back - up bearing steel, based on the above - mentioned exemplary process, contains Fe and inevitable impurities, and also contains the following chemical elements in the following mass percentages:

[0062] C: 0.80 - 0.90%; Si: 0.20 - 0.30%; Mn: 0.25 - 0.35%; Cr: 1.45 - 1.55%; V: 0.15 - 0.25%; S: ≤0.015%; P: ≤0.025%; Ni: 0.25 - 0.35%; Ti: 0.008 - 0.012%; Mo: 0.08 - 0.12%; Cu: 0.08 - 0.12%; Total amount of residual elements ≤0.10%.

[0063] In this product, the design principles of each element are as follows:

[0064] Carbon (C) is the main strengthening element in steel, forming cementite and alloy carbides with iron, providing matrix hardness and wear resistance. When the carbon content is less than 0.80%, the matrix hardness after quenching is <58HRC, and the contact fatigue life decreases by 30%; when it is higher than 0.90%, the carbides coarsen and the impact toughness decreases significantly. When the carbon content >0.95%, it is difficult to control the carbide morphology during spheroidizing annealing, and the spheroidization rate <70%. Therefore, spheroidizing annealing is required to ensure uniform spheroidization of carbides.

[0065] Silicon (Si), as a deoxidizer, reacts with oxygen to form low-melting-point SiO2, improving the fluidity of molten steel and reducing casting defects. Silicon dissolved in ferrite can increase the yield strength. When the silicon content is less than 0.20%, incomplete deoxidation leads to oxygen residue >10ppm, increasing the risk of intergranular oxidation brittleness; when it is higher than 0.30%, the viscosity of molten steel is too high, and the tundish nozzle is prone to blockage during continuous casting. Excessive silicon will form a hard shell of SiO2 on the surface during hot working, causing rolling cracks. Its content range needs to be coordinated with vacuum deoxidation to ensure that the oxygen content ≤6ppm.

[0066] Manganese (Mn) improves hardenability by expanding the γ-phase region, ensuring that the core hardness of large-section bearings ≥55HRC. At the same time, it fixes sulfur to form MnS, avoiding the hot brittleness of FeS. When the manganese content is less than 0.25%, sulfur cannot be completely fixed, and "red brittleness" occurs during hot rolling; when it is higher than 0.35%, the content of retained austenite >15%, and the dimensional stability decreases. Manganese needs to be controlled in matching with sulfur to ensure that the aspect ratio of MnS ≤3, and it is modified into spherical CaS-MnS composite inclusions through calcium treatment.

[0067] Chromium (Cr) forms (Fe,Cr)7C3-type carbides, significantly improving wear resistance, and forming a Cr2O3 passivation film on the surface, making the rusting rate ≤0.005mm / year. When the chromium content is less than 1.45%, the carbide hardness is insufficient and the wear resistance decreases by 20%; when it is higher than 1.55%, the risk of carbide segregation increases and the fatigue life decreases by 25%. Chromium needs to be coordinated with high carbon to ensure that the carbide volume fraction is 8 - 10%, and the distribution uniformity is optimized through electroslag remelting.

[0068] Vanadium (V) refines grains by generating nanoscale VC carbides and inhibits the growth of austenite grains. When the vanadium content is less than 0.15%, the grains coarsen and the impact toughness is < 18 J / cm 2 ; when it is higher than 0.25%, the aggregation of carbides causes the grinding surface to be rough. The secondary hardening effect of vanadium requires low-temperature tempering to avoid excessive coarsening of VC, and at the same time depends on the water-cooling process to fix the fine-grained structure.

[0069] Sulfur (S) exists in the form of sulfides. In traditional processes, MnS is in a long strip shape, which induces fatigue cracks. In the present invention, MnS is modified into spherical CaS-MnS composite inclusions through calcium treatment. When the sulfur content exceeds 0.015%, even with calcium treatment, it is difficult to be completely modified, and the fatigue life decreases by 30%; when it is lower than 0.005%, the easy-cutting effect disappears and the processing efficiency is reduced by 20%. Sulfur control needs to be matched with the calcium addition amount to ensure the optimization of the inclusion morphology.

[0070] Phosphorus (P) is prone to segregate at grain boundaries to form brittle Fe3P phases, and its content needs to be strictly restricted. When the phosphorus exceeds 0.025%, the impact toughness at -20 °C drops from 25 J / cm 2 sharply to 10 J / cm 2 ; when it is lower than 0.005%, the extremely high smelting cost is required. Through vacuum degassing and the adsorption of molten slag in electroslag remelting, the dephosphorization rate is ≥ 90%, ensuring that the phosphorus content ≤ 0.025%.

[0071] Nickel (Ni) reduces the ductile-brittle transition temperature, enabling the material to still maintain a Charpy impact value ≥ 20 J / cm at -50 °C 2 , and forms a NiO·Fe2O3 oxide film to enhance the salt spray corrosion resistance. When the nickel is lower than 0.25%, the impact toughness at -40 °C is < 15 J / cm 2 ; when it is higher than 0.35%, the cost increases significantly, and the retained austenite > 10% affects the dimensional stability. The uniform distribution of nickel depends on the slow cooling process of electroslag remelting to avoid segregation.

[0072] Titanium (Ti) generates high-melting-point TiN to refine grains and fixes nitrogen to prevent the formation of brittle AlN phases. When the titanium is lower than 0.008%, the amount of TiN is insufficient and the grains coarsen; when it is higher than 0.012%, the size of TiN > 5 μm becomes a crack source. Titanium needs to cooperate with a high cleanliness process to avoid Al2O3-TiN composite inclusions.

[0073] Molybdenum (Mo) forms Mo2C carbides, improves the high-temperature strength and inhibits temper embrittlement. When the molybdenum is lower than 0.08%, the high-temperature strength is insufficient; when it is higher than 0.12%, the spheroidizing annealing time needs to be extended to 6 h. Molybdenum needs to cooperate with spheroidizing annealing to ensure the uniform distribution of carbides.

[0074] Copper (Cu) controls the salt spray corrosion rate within ≤0.01 mm / year through the surface CuO·Fe3O4 oxide film, and the aging precipitation of ε-Cu phase enhances the strength. When the copper content is below 0.08%, the corrosion resistance does not increase significantly; when it is above 0.12%, hot rolling is likely to cause surface thermal cracking. Its distribution uniformity depends on the slow solidification process of electroslag remelting.

[0075] For residual elements such as W, Pb, and Sn, the total amount should be ≤0.10% to avoid damage to performance caused by low melting point phases or brittle phases.

[0076] Example 1

[0077] A heat treatment process for high-strength wear-resistant backing bearing steel includes the following steps:

[0078] S1. 85% industrial pure iron and 15% scrap steel are used as iron-based raw materials, and 2.5% ferrochrome, 0.4% ferroniobium, 0.3% nickel plate, 0.18% ferromolybdenum, 0.034% ferrotitanium, 0.1% electrolytic copper, and graphite carburant are added to adjust C to 0.85%. After mixing, they are melted in an electric arc furnace at 1600 °C to form molten steel. 0.5% ferromanganese with a particle size of 20 mm and 0.3% ferrosilicon with a particle size of 10 mm are added to the molten steel, the temperature of the molten steel is controlled at 1550 °C, and preliminary deoxidation is carried out for 15 min. The preliminarily deoxidized molten steel is transferred to a vacuum degassing tank for deep deoxidation, the vacuum pressure is adjusted to 10 Pa, 0.004% aluminum block is added, and the reaction is carried out for 20 min; 0.0080% calcium cored wire is fed, the wire feeding speed is 3 m / s, the bottom argon blowing flow rate is 10 L / min, the temperature of the molten steel is controlled at 1400 °C, and the reaction is carried out for 40 min.

[0079] S2. The molten steel processed in step S1 is cast into an electrode and subjected to electroslag remelting with pre-melted CaF2-CaO slag as the medium, where CaF2 accounts for 80% and CaO accounts for 20%, the basicity CaO / SiO2 = 2.0, the melting rate is 50 kg / h, the molten pool temperature is 1720 °C, and the remelting time is 5 h; after remelting, the ingot is slowly cooled to room temperature at a rate of 10 °C / h, argon is introduced during the slow cooling process, the argon flow rate is 20 L / min, and the total slow cooling time is 24 h.

[0080] S3. The remelted ingot is heated to 1230 °C and held for 2 h, followed by hot rolling. The final rolling temperature is 875 °C, the total reduction ratio is 70%, and the rolling deformation rate is 1.0 s -1 , and the rolled steel is water-cooled to 350 °C at a rate of 25 °C / s. The pH value of the cooling water is 7.0, and the pressure is 15 MPa; the rolled steel is spheroidized annealed. In the first stage, it is heated to 770 °C at a rate of 75 °C / h and held for 3 h. In the second stage, it is cooled to 500 °C at a rate of 15 °C / h, and then air-cooled to room temperature. The total annealing time is 18 h.

[0081] Example 2

[0082] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, in step S1, deep deoxidation includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, and reacting for 20 min; feeding 0.0110% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1400 °C, and reacting for 40 min.

[0083] Example 3

[0084] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, in step S1, deep deoxidation includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, and reacting for 20 min; feeding 0.0147% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1400 °C, and reacting for 40 min.

[0085] Example 4

[0086] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, step S2 includes casting the molten steel treated in step S1 into an electrode and performing electroslag remelting with a pre-melted CaF2-CaO slag as the medium, where CaF2 accounts for 80%, CaO accounts for 20%, the basicity CaO / SiO2 = 1.8, the melting rate is 50 kg / h, the molten pool temperature is 1720 °C, and the remelting time is 5 h; after the remelting is completed, the ingot is slowly cooled to room temperature at a rate of 10 °C / h, argon is introduced during the slow cooling process, the argon flow rate is 20 L / min, and the total slow cooling time is 24 h.

[0087] Example 5

[0088] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, step S2 includes casting the molten steel treated in step S1 into an electrode and performing electroslag remelting with a pre-melted CaF2-CaO slag as the medium, where CaF2 accounts for 80%, CaO accounts for 20%, the basicity CaO / SiO2 = 2.2, the melting rate is 50 kg / h, the molten pool temperature is 1720 °C, and the remelting time is 5 h; after the remelting is completed, the ingot is slowly cooled to room temperature at a rate of 10 °C / h, argon is introduced during the slow cooling process, the argon flow rate is 20 L / min, and the total slow cooling time is 24 h.

[0089] Example 6

[0090] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, the deep deoxidation in step S1 includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, reacting for 20 min; feeding 0.0110% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1300 °C, and reacting for 40 min.

[0091] Example 7

[0092] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, the deep deoxidation in step S1 includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, reacting for 20 min; feeding 0.0110% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1500 °C, and reacting for 40 min.

[0093] Example 8

[0094] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, the deep deoxidation in step S1 includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, reacting for 20 min; feeding 0.0110% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1400 °C, and reacting for 20 min.

[0095] Example 9

[0096] Different from Example 1, in a heat treatment process of a high-strength wear-resistant back-up bearing steel provided in this example, the deep deoxidation in step S1 includes transferring the preliminarily deoxidized molten steel to a vacuum degassing tank for deep deoxidation, adjusting the vacuum pressure to 10 Pa, adding 0.004% aluminum blocks, reacting for 20 min; feeding 0.0110% calcium cored wire at a wire feeding speed of 3 m / s, with an argon blowing flow rate at the bottom of 10 L / min, controlling the temperature of the molten steel at 1400 °C, and reacting for 60 min.

[0097] Experimental Example 1

[0098] Experimental process:

[0099] (i) Use 85% industrial pure iron and 15% scrap steel as the iron-based raw materials, add 2.5% ferrochrome, 0.4% ferroniobium, 0.3% nickel plate, 0.18% ferromolybdenum, 0.034% ferrotitanium, 0.1% electrolytic copper, and adjust C to 0.85% with a graphite carburizer. After mixing, melt in an electric arc furnace at 1600 °C to form molten steel. Add 0.5% ferromanganese with a particle size of 20 mm and 0.3% ferrosilicon with a particle size of 10 mm to the molten steel, control the molten steel temperature at 1550 °C, and react for 15 min. Conduct deep deoxidation on the preliminarily deoxidized molten steel, including adding 0.004% aluminum block, controlling the molten steel temperature at 1550 °C, standing and reacting for 15 min, then feeding 0.0080%-0.0147% calcium cored wire (adjusted according to the group), with a wire feeding speed of 3 m / s, controlling the molten steel temperature at 1400 °C, and standing and reacting for 40 min.

[0100] (ii) Cast the molten steel in step S1 into electrodes and remelt it with a CaF2-CaO based slag as the medium. The slag ratio is CaF2:CaO = 80:20, the basicity is 1.8 - 2.2 (adjusted according to the group), the melting rate is 50 kg / h, the molten pool temperature is 1720 °C, and the slow cooling rate is 10 °C / h.

[0101] (iii) Heat and hot roll the remelted steel ingot, with a final rolling temperature of 875 °C, a reduction ratio of 70%, and a water cooling rate of 25 °C / s. Conduct spheroidizing annealing on the rolled steel, with spheroidizing annealing at 770 °C for 3 h and air cooling at 500 °C.

[0102] Prepare bearing steel samples according to the groups in (i)-(iii) as shown in the following table:

[0103] Table 1 Sample groups

[0104] Group Calcium addition amount (%) <![CDATA[Basicity of slag (CaO / SiO2)]]> Group 1 0.0080 2.0 Group 2 0.0110 2.0 Group 3 0.0147 2.0 Group 4 0.0110 1.8 Group 5 0.0110 2.2

[0105] Refer to GB / T20123 to detect the sulfur content in the samples; refer to GB / T11261 to detect the oxygen content in the samples; refer to ASTM E23 to detect the Charpy impact toughness of the samples; refer to GB / T4337 to detect the fatigue life of the samples; refer to ASTM E23 to detect the transverse / longitudinal impact ratio of the samples, and the results are shown in the following table:

[0106] Table 2 Key performance parameter table

[0107]

[0108] Among them, the sulfur content is directly related to the morphology and distribution of sulfide inclusions. When the excessive sulfur exceeds 15 ppm, the long-strip MnS inclusions will become the crack initiation source, significantly shortening the fatigue life; the oxygen content reflects the cleanliness of the molten steel. When the oxygen residue exceeds 6 ppm, alumina inclusions will aggregate, forming stress concentration points and weakening the material toughness; the impact toughness characterizes the ability of the material to resist impact loads. The higher the value, the less likely the material is to brittle fracture under dynamic loads; the fatigue life reflects the durability of the material under cyclic loads. The higher the value, the more suitable it is for high-load scenarios; the transverse-to-longitudinal impact ratio approaching 1 indicates excellent material isotropy, reducing performance fluctuations caused by grain orientation differences.

[0109] The data in Table 2 show that as the calcium addition amount increases from 0.008% to 0.011%, the sulfur content decreases from 12 ppm to 5 ppm, the oxygen content decreases from 5 ppm to 3 ppm, and the impact toughness increases from 28.5 J / cm 2 to 32.0 J / cm 2 , and the fatigue life increases from 1.5×10 7 cycles to 2.2×10 7 cycles. The transverse-to-longitudinal impact ratio is optimized from 0.92 to 0.98. However, when the calcium addition amount further increases to 0.0147%, the sulfur content rises back to 18 ppm, and the impact toughness and fatigue life decrease significantly to 25.8 J / cm 2 and 1.0×10 7 cycles. When the slag basicity increases from 1.8 to 2.2, the sulfur content decreases from 15 ppm to 8 ppm, and the impact toughness increases from 29.2 J / cm 2 to 30.5 J / cm 2 .

[0110] In Group 2, both the sulfur content of 5 ppm and the oxygen content of 3 ppm are at ultra-low levels. The impact toughness of 32.0 J / cm 2 and the fatigue life of 2.2×10 7 cycles reach the peak, and the transverse-to-longitudinal impact ratio of 0.98 is close to complete isotropy. This is because when the calcium addition amount is 0.011%, the molar ratio of calcium to alumina is close to the theoretical value. Through the diffusion of calcium ions into the alumina lattice, its hexagonal close-packed structure is destroyed and transformed into dodecacalcium heptaaluminate of the cubic crystal system. Using the buoyancy difference caused by density, it is more likely to float to the slag phase, and the size is refined to 1-5 μm, significantly reducing the risk of stress concentration. When the basicity is 2.0, the activity of calcium oxide in the slag and the affinity for sulfur reach the peak, and sulfur ions are efficiently adsorbed to the slag phase through the interfacial exchange reaction. At the same time, the slag fluidity is moderate, neither hindering the floating of inclusions due to excessive viscosity nor causing a decrease in sulfur removal efficiency due to too low basicity. Calcium treatment not only promotes the denaturation of alumina but also inhibits the formation of manganese sulfide, and the optimization of the slag basicity further adsorbs the residual sulfur and oxygen, ultimately achieving the dual control of grain boundary oxidation brittleness and inclusion residue.

[0111] The sulfur content of group 3 is 18ppm and the oxygen content is 6ppm, which is high. The impact toughness is 25.8J / cm 2 and fatigue life 1.0×10 7 The ratio of transverse to longitudinal impact is 0.85, indicating significant anisotropy. This is because the excessive addition of 0.0147% calcium causes the free calcium ions that do not participate in the denaturation of alumina to combine with sulfur to form hard calcium sulfide inclusions with a size of more than 10μm, which becomes the preferred crack propagation path and directly reduces fatigue life. When calcium is excessive, the interface reaction rate is unbalanced, and the adsorption layer of calcium ions on the surface of alumina is too thick, which hinders subsequent diffusion, resulting in part of the alumina not being completely converted into dodeca-heptaluminate, forming a high-density stress concentration source. Excessive calcium increases the free Ca in the slag. 2+ The concentration leads to an increase in slag viscosity, a decrease in the floating rate of inclusions, and difficulty in removing sulfur and oxygen impurities, further aggravating performance degradation.

[0112] Experimental Example 2

[0113] Based on Group 1 of Experimental Example 1, in this experimental example, the experimental process (i) controls the deep deoxidation temperature after adding calcium to 1300-1500°C (adjusted according to the group) and the reaction time to 20-60min (adjusted according to the group). The composition of calcium dodecaaluminate and the residual alumina in the inclusions are identified by SEM-EDS, and the results are shown in the following table:

[0114] Table 3 Effect of deoxidation temperature and reaction time on inclusions of dodecalcium heptaaluminate and alumina

[0115]

[0116]

[0117] Among them, the proportion of stable inclusions reflects the conversion efficiency of alumina to dodeca-heptaluminate. The higher the proportion, the less harm the inclusions will cause to the material properties. Too much residual unmodified alumina will form a hard and brittle phase, which will become the origin of fatigue cracks. The inclusion density is lower than 3.0 g / cm 3 It is easier to separate from the molten steel through buoyancy and reduce residue.

[0118] Table 3 shows that when the deoxidation temperature increases from 1300℃ to 1400℃, the proportion of stable inclusions increases from 82% to 98%, and the amount of unmodified alumina residue decreases from 12% to 0.5%; but when the temperature rises to 1500℃, the proportion of stable inclusions drops sharply to 75%. When the reaction time is extended from 20 minutes to 40 minutes, the proportion of stable inclusions increases from 88% to 98%; when the time increases to 60 minutes, the proportion drops to 95%. Group 1 with 1400℃ combined with 40 minutes of reaction time has the best effect, with only 0.5% unmodified alumina.

[0119] The optimal values of the proportion of stable inclusions in Group 1 are 98% and the unmodified alumina is 0.5%. The inclusion density is 2.7 g / cm 3 . This is because 1400 °C is located in the stable phase region of dodecacalcium heptaaluminate in the calcium aluminate phase diagram. The diffusion rate of calcium ions matches the activation energy required for the destruction of the alumina lattice, ensuring that the reaction proceeds in the direction of forming low-density products. The 40-minute reaction time allows calcium ions to fully penetrate into the alumina grain boundaries, completely destroying its crystal structure, while avoiding the sinking of inclusions caused by changes in the slag state due to too long reaction time. The adsorption and diffusion rates of calcium on the alumina surface reach equilibrium, neither causing local calcium depletion due to too fast reaction nor leaving unmodified regions due to too slow reaction.

[0120] The proportion of stable inclusions in Group 7 is 75% and the unmodified alumina is 18%, showing the worst performance. The inclusion density increases to 3.0 g / cm 3 . This is because 1500 °C exceeds the stable phase region of dodecacalcium heptaaluminate. Thermal disturbance leads to the formation of high-density calcium aluminate in the orthorhombic system, whose density is close to 3.0 g / cm 3 , which is difficult to remove by buoyancy. High temperature accelerates the volatilization of calcium, resulting in insufficient calcium concentration at the reaction interface. Only partial conversion of alumina occurs, and residual unmodified regions form preferential propagation paths for microcracks. High temperature enhances the convection of the molten steel, causing some high-density inclusions to sink to the bottom of the ingot, resulting in local segregation and further deteriorating the material uniformity.

[0121] Based on the ideal embodiments of the present invention as inspiration, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A heat treatment process for high-strength wear-resistant backing bearing steel, characterized in that: The following steps are involved: S1, smelting iron-based raw materials and alloy elements to form molten steel, and sequentially performing preliminary deoxidation and deep deoxidation; the preliminary deoxidation uses ferromanganese and ferrosilicon as deoxidizers, controls the temperature of the molten steel to 1500-1600° C., and the preliminary deoxidation time is 15-30 min; the deep deoxidation includes adding aluminum and calcium under vacuum conditions, controlling the temperature of the molten steel to 1300-1660° C., and the deep deoxidation time is 30-90 min; S2, casting the molten steel in step S1 into an electrode, and remelting it with a CaF2-CaO-based slag as a medium; the composition of the CaF2-CaO-based slag includes 75-85% CaF2 and 15-25% CaO by mass percentage; S3, heating the remelted steel ingot and then hot rolling it, and performing spheroidizing annealing on the rolled steel.

2. The heat treatment process according to claim 1, characterized in that: In step S1, the amount of ferromanganese added is 0.4-0.6% of the total mass of the molten steel, and the amount of ferrosilicon added is 0.2-0.4% of the total mass of the molten steel.

3. The heat treatment process according to claim 1, characterized in that: The iron-based raw materials in step S1 include 85-90% industrial pure iron and 10-15% scrap steel; the alloy elements include ferrochrome with Cr≥60% and an addition amount of 2.4-2.6%; ferrovanadium with V≥50% and an addition amount of 0.3-0.5%; nickel plate with Ni≥99.9% and an addition amount of 0.25-0.35%; ferromolybdenum with Mo≥55% and an addition amount of 0.15-0.22%; ferrotitanium with Ti≥30% and an addition amount of 0.027-0.040%; electrolytic copper with Cu≥99.95% and an addition amount of 0.08-0.12%; and graphite recarburizer with C≥98%, and the final C content is adjusted to 0.80-0.90%.

4. The heat treatment process according to claim 1, characterized in that: The deep deoxidation in step S1 comprises the following steps: A1. Add 0.0027%-0.00495% of the total mass of the molten steel to ensure that aluminum is evenly dispersed in the molten steel; A2. Control the temperature of the molten steel to 1580-1660℃, and let it stand for 10-30 minutes to allow the aluminum to fully react with the oxygen in the molten steel to form alumina inclusions; A3, adding 0.0080%-0.0147% of calcium to the molten steel; A4. Control the temperature of the molten steel to 1300-1500℃ and let it stand for 20-60 minutes to allow calcium to fully react with residual oxygen and alumina inclusions in the molten steel to form dodecacalcium heptaaluminate inclusions.

5. The heat treatment process according to claim 4, characterized in that: In step S1, the calcium is fed in the form of cored wire, the wire feeding speed is 2-4 m / s, and the wire feeding depth is 1 / 3-2 / 3 of the total height of the molten steel.

6. The heat treatment process according to claim 1, characterized in that: The basicity of the CaF2-CaO-based slag in step S2 is 1.8-2.

2.

7. The heat treatment process according to claim 1, characterized in that: In step S2, the remelted steel ingot is slowly cooled to room temperature at a rate of ≤10°C / h.

8. The heat treatment process according to claim 1, characterized in that: The final rolling temperature of the hot rolling in step S3 is 850-900°C, the total reduction ratio is ≥70%, and the rolled steel is water-cooled to 300-400°C at a rate of 20-30°C / s.

9. The heat treatment process according to claim 1, characterized in that: The spheroidizing annealing in step S3 includes the following stages: In the first stage, the temperature is raised to 760-780℃ at 50-100℃ / h and kept at this temperature for 2-4h; In the second stage, the temperature is lowered to 500°C at ≤20°C / h and then air-cooled to room temperature.

10. A high-strength wear-resistant backing bearing steel, based on the heat treatment process described in any one of claims 1 to 9, containing Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.80-0.90%; Si: 0.20-0.30%; Mn: 0.25-0.35%; Cr: 1.45-1.55%; V: 0.15-0.25%; S: ≤0.015%; P: ≤0.025%; Ni: 0.25-0.35%; Ti: 0.008-0.012%; Mo: 0.08-0.12%; Cu: 0.08-0.12%.

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