A high-strength wear-resistant backing bearing steel and its heat treatment process

Abstract

The present invention provides a high-strength, wear-resistant backing bearing steel and a heat treatment process thereof, belonging to the field of bearing technology. The process converts high-density alumina into a low-density, stable type dodecacalcium heptaaluminate by utilizing the interface diffusion and phase change mechanism of calcium under vacuum conditions, while using CaF2-CaO-based slag to optimize sulfur adsorption capacity and promote the floating of inclusions. By controlling the deoxidation temperature and reaction time, the calcium ions are fully diffused and a high-stable inclusion conversion rate is achieved. The present invention effectively reduces harmful inclusions and sulfur and oxygen impurities, improves the impact toughness and fatigue life of the material, improves the anisotropy of the material, and ultimately obtains high-quality bearing steel with high strength, high toughness and excellent isotropy.

Description

Technical Field

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

[0002] High-strength, wear-resistant bearing steel is a key material for high-end equipment such as aerospace and precision machine tools. Its performance directly impacts the reliability and lifespan of these equipment. Harsh operating conditions, such as high loads and high speeds, place even higher demands on the strength, toughness, and wear resistance of bearing steel.

[0003] While traditional bearing steel smelting processes can meet certain performance requirements, they still have some drawbacks. For example, deoxidation methods often fail to effectively control the oxygen content in the steel, leading to the formation of large alumina inclusions. These inclusions act as stress concentration points, reducing the steel's fatigue life and impact toughness. Furthermore, traditional processes can lead to uneven microstructure and significant anisotropy, which in turn affects its mechanical properties.

[0004] Therefore, developing a heat treatment process that can effectively improve the purity of steel and improve the uniformity of its structure is an important challenge currently facing the 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 a heat treatment process thereof.

[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 sequentially performing preliminary deoxidation and deep deoxidation; the preliminary deoxidation uses ferromanganese and ferrosilicon as deoxidizers, controls the molten steel temperature at 1500-1600° C., and the preliminary deoxidation time is 15-30 minutes; the deep deoxidation includes adding aluminum and calcium under vacuum conditions, controls the molten steel temperature at 1300-1660° C., and the deep deoxidation time is 30-90 minutes;

[0008] S2, casting the molten steel from step S1 into an electrode, and remelting the electrode with a CaF2-CaO-based slag as a medium; the CaF2-CaO-based slag comprises 75-85% CaF2 and 15-25% CaO by mass percentage;

[0009] S3. The remelted steel ingot is heated and then hot rolled, and the rolled steel is subjected to spheroidizing annealing.

[0010] In a preferred embodiment of the present invention, 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.

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

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

[0013] 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;

[0014] 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.

[0015] A3, adding 0.0080%-0.0147% of the total mass of the molten steel to the molten steel;

[0016] A4. Control the temperature of the molten steel to 1300-1500℃ and let it stand for 20-60 minutes to allow the calcium to 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, the basicity of the CaF2-CaO based slag in step S2 is 1.8-2.2.

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

[0020] In a preferred embodiment of the present invention, 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.

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

[0022] In the first stage, the temperature is raised to 760-780°C at 50-100°C / h and kept at this temperature for 2-4 hours;

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

[0024] Another technical solution provided by the present invention is based on the above-mentioned heat treatment process, containing Fe and inevitable impurities, and further containing the following chemical elements in the following 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) The present invention provides a high-strength, wear-resistant backing bearing steel and its heat treatment process, which achieves controllable transformation of inclusion morphology and efficient removal of sulfur and oxygen impurities through temperature control, calcium addition control, and slag alkalinity adjustment in the deep deoxidation stage, thereby improving the fatigue life, impact toughness, and isotropy of the bearing steel as a whole.

[0028] (2) The present invention precisely controls the deep deoxidation temperature and utilizes the interfacial reaction between calcium ions and alumina to convert high-density alumina into a low-density, stable dodecacalcium heptaaluminate. Compared with conventional processes, the present invention significantly reduces alumina residue, eliminates stress concentration sources, directly improves the fatigue life of the material, and reduces crack initiation points. Furthermore, low-density inclusions are more likely to float, further improving the purity of the steel.

[0029] (3) The present invention achieves efficient removal of sulfur and oxygen impurities from molten steel through the synergistic optimization of calcium treatment and slag basicity. The synergistic effect of calcium and slag significantly reduces the activity coefficient of sulfur, allowing sulfur to preferentially adsorb in the slag phase, effectively reducing grain boundary oxidation. Compared with traditional processes, the present invention effectively improves the impact toughness of steel and resolves performance defects caused by high sulfur and oxygen content.

[0030] (4) On the one hand, the present invention ensures that calcium ions react completely with alumina through temperature control during deep deoxidation, forming stable dodecacalcium heptaaluminate and avoiding the formation of harmful sulfides. On the other hand, by controlling the alkalinity of the slag, it promotes the removal of inclusions and enhances the sulfur adsorption capacity, achieving ultra-low residual sulfur and oxygen, ensuring the high strength, high toughness and long life of the bearing steel. The present invention solves the performance defects of traditional bearing steel caused by residual inclusions and high sulfur and oxygen content, and realizes a high-strength, high-toughness and long-life bearing steel material, which is suitable for high-load, high-speed scenarios such as aircraft engine bearings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0032] Figure 1 This is a flow chart of the heat treatment process for high-strength, wear-resistant backing bearing steel;

[0033] Figure 2 is a flow chart of deep deoxygenation in step S1;

[0034] Figure 3 This is a flow chart of the spheroidizing annealing in step S3. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise specified below, all raw materials are purchased from commercial sources or prepared by conventional methods in the art.

[0036] Application Overview:

[0037] Traditional deep deoxidation processes typically add aluminum and calcium and keep the molten steel temperature at around 1600°C. However, the residual alumina inclusions in this process act as stress concentration points, reducing the fatigue life and impact toughness of the steel. An unexpected discovery was that lowering the molten steel temperature during the deep deoxidation stage to around 1400°C actually resulted in even better deoxidation than the traditional 1600°C process.

[0038] Experiments were conducted at deoxidation temperatures of 1300°C, 1400°C, and 1500°C, keeping all other conditions constant. The results showed that at 1400°C, the proportion of stable dodecacalcium heptaaluminate (12CaO·7Al2O3) formed in the molten steel reached 98%, with only 0.5% remaining unmodified alumina. At 1300°C, however, the proportion of stable inclusions dropped to only 82%, with a high 12% remaining unmodified alumina. At 1500°C, the proportion of stable inclusions plummeted to 75%. Further analysis revealed that 1400°C is the optimal activation temperature for the calcium-alumina reaction, allowing calcium ions to fully diffuse into the alumina, disrupting its crystal structure and forming low-density stable dodecacalcium heptaaluminate, which is easily floated and removed. Other temperatures, however, are not conducive to this reaction.

[0039] Exemplary process:

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

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

[0042] S2, casting the molten steel from step S1 into an electrode, and remelting the electrode with a CaF2-CaO-based slag as a medium; the CaF2-CaO-based slag comprises 75-85% CaF2 and 15-25% CaO by mass percentage;

[0043] S3. The remelted steel ingot is heated and then hot rolled, and the rolled steel is subjected to spheroidizing annealing.

[0044] This process is suitable for manufacturing bearing steel in high load and high speed scenes such as aircraft engine bearings and precision machine tool spindle bearings. 4 Long-term service under high-frequency impacts of 2.5 GPa and high contact stresses of 2.5 times / min. Conventional bearing steels experience stress concentration due to large Al2O3 inclusions, resulting in insufficient fatigue life. Excessive oxygen content leads to grain boundary oxidation brittleness, significantly reducing impact toughness.

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

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

[0047] Furthermore, in step S1, ferromanganese and ferrosilicon are used as deoxidizers for the initial deoxidation process. The ferromanganese is added at a rate of 0.4-0.6% of the total mass of the molten steel to ensure the formation of MnO inclusions, which are effectively floated and removed. The ferrosilicon is added at a rate of 0.2-0.4% of the total mass of the molten steel to generate SiO2 and improve the fluidity of the molten steel. The ferromanganese particle size is controlled to 10-30mm, and the ferrosilicon particle size is 5-15mm to ensure uniform melting. The oxygen content of the molten steel is monitored in real time, allowing for dynamic adjustment of the deoxidizer feed rate.

[0048] Furthermore, if Figure 2 As shown, the deep deoxidation in step S1 is carried out under vacuum conditions, with the vacuum degree controlled at 10-100 Pa, and includes the following steps:

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

[0050] 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.

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

[0052] A4. Control the temperature of the molten steel to 1300-1500℃ and let it stand for 20-60 minutes to allow the calcium to fully react with the residual oxygen and alumina inclusions in the molten steel to form dodecacalcium heptaaluminate inclusions.

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

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

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

[0056] Furthermore, in step S3, the finishing temperature of the hot rolling is 850-900°C, and dynamic recrystallization is used 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, wherein the pH value of the cooling water is 6.5-7.5 and the pressure is 15 MPa.

[0057] Furthermore, if Figure 3 As shown, the spheroidizing annealing in step S3 includes the following stages:

[0058] The first stage: heating to 760-780℃ at 50-100℃ / h, keeping warm for 2-4h, austenitizing and dissolving coarse carbides;

[0059] The second stage: cooling to 500℃ at ≤20℃ / h and air cooling to room temperature to promote the uniform precipitation of spherical carbides.

[0060] Example products:

[0061] A high-strength, wear-resistant backing bearing steel, based on the exemplary process described above, contains Fe and unavoidable impurities, and further 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%; the total amount of residual elements is ≤0.10%.

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

[0064] Carbon (C) is the primary strengthening element in steel, forming cementite and alloy carbides with iron, contributing to matrix hardness and wear resistance. When the carbon content is below 0.80%, the matrix hardness after quenching is less than 58 HRC, and contact fatigue life decreases by 30%. Above 0.90%, carbides coarsen and impact toughness decreases significantly. When the carbon content exceeds 0.95%, spheroidizing annealing becomes difficult to control carbide morphology, resulting in a spheroidization rate of less than 70%. Therefore, spheroidizing annealing is necessary to ensure uniform spheroidization of the carbides.

[0065] Silicon (Si) acts as a deoxidizer, reacting with oxygen to form low-melting-point SiO2, which improves the fluidity of molten steel and reduces casting defects. Silicon dissolved in ferrite can increase yield strength. When the silicon content is less than 0.20%, incomplete deoxidation results in oxygen residues >10ppm, increasing the risk of grain boundary oxidation brittleness. When the silicon content is higher than 0.30%, the viscosity of the molten steel is too high, and the water nozzle is easily blocked during the continuous casting process. Excessive silicon will form a surface SiO2 crust during hot working, causing rolling cracks. Its content range must be coordinated with vacuum deoxidation to ensure that the oxygen content is ≤6ppm.

[0066] Manganese (Mn) improves hardenability by expanding the γ phase, ensuring a core hardness of large-section bearings ≥55 HRC. It also fixes sulfur to form MnS, preventing hot brittleness of FeS. When the Mn content is below 0.25%, sulfur cannot be fully fixed, resulting in "red brittleness" during hot rolling. When the Mn content is above 0.35%, the retained austenite content exceeds 15%, reducing dimensional stability. Manganese and sulfur must be carefully matched to ensure an aspect ratio of MnS of ≤3. Calcium treatment is then used to modify the inclusions into spherical CaS-MnS composite inclusions.

[0067] Chromium (Cr) forms (Fe,Cr)7C3 carbides, significantly improving wear resistance and forming a Cr2O3 passivation film on the surface, reducing the corrosion rate to ≤0.005mm / year. Below 1.45% chromium, the carbides lack sufficient hardness, reducing wear resistance by 20%. Above 1.55%, the risk of carbide segregation increases, reducing fatigue life by 25%. Chromium must be combined with high carbon to ensure a carbide volume fraction of 8-10%, and electroslag remelting is used to optimize the distribution of these carbides.

[0068] Vanadium (V) refines the grains by generating nano-scale VC carbides and inhibits the growth of austenite grains. When the vanadium content is less than 0.15%, the grains are coarsened and the impact toughness is <18J / cm 2 Above 0.25%, carbides aggregate, resulting in a rough ground surface. The secondary hardening effect of vanadium requires low-temperature tempering to prevent excessive coarsening of VC, while also relying on water cooling to maintain a fine-grained structure.

[0069] Sulfur (S) exists as sulfides. In conventional processes, MnS forms long strips, causing fatigue cracks. This invention modifies MnS into spherical CaS-MnS composite inclusions through calcium treatment. When the sulfur content exceeds 0.015%, even calcium treatment is difficult to fully modify, resulting in a 30% decrease in fatigue life. Below 0.005%, the free-machining effect disappears, reducing machining efficiency by 20%. Sulfur control must be coordinated with calcium addition to ensure optimal inclusion morphology.

[0070] Phosphorus (P) easily segregates at grain boundaries to form Fe3P brittle phase, so its content must be strictly limited. When phosphorus exceeds 0.025%, the impact toughness at -20℃ decreases from 25J / cm 2 Dropped to 10J / cm 2 Lower than 0.005% requires extremely high smelting costs. Through vacuum degassing and slag adsorption from electroslag remelting, the dephosphorization rate is ≥ 90%, ensuring the phosphorus content is ≤ 0.025%.

[0071] Nickel (Ni) reduces the ductile-brittle transition temperature, allowing the material to maintain a Charpy impact value of ≥20J / cm at -50°C 2 , and form NiO·Fe2O3 oxide film to improve salt spray corrosion resistance. When nickel is less than 0.25%, the impact toughness at -40℃ is less than 15J / cm 2 Above 0.35%, the cost increases significantly, and retained austenite >10% affects dimensional stability. Uniform nickel distribution relies on the electroslag remelting and slow cooling process to avoid segregation.

[0072] Titanium (Ti) forms high-melting-point TiN, which refines grains and fixes nitrogen to prevent AlN brittleness. When Ti content is below 0.008%, the TiN content is insufficient, resulting in grain coarsening. When Ti content is above 0.012%, TiN >5μm in size becomes a crack source. Titanium must be used in conjunction with high-cleanliness processes to avoid Al2O3-TiN composite inclusions.

[0073] Molybdenum (Mo) forms Mo2C carbides, improving high-temperature strength and suppressing temper brittleness. Molybdenum content below 0.08% results in insufficient high-temperature strength; above 0.12%, the spheroidizing annealing time must be extended to 6 hours. Molybdenum must be incorporated into the spheroidizing annealing to ensure uniform distribution of carbides.

[0074] Copper (Cu) maintains a salt spray corrosion rate of ≤0.01 mm / year through the CuO·Fe₃O₄ oxide film on its surface, and precipitates the ε-Cu phase over time to enhance strength. Corrosion resistance is not significantly improved below 0.08% Cu, while hot rolling can easily induce surface thermal cracking above 0.12%. The uniformity of Cu distribution depends on the slow solidification process during electroslag remelting.

[0075] The total amount of residual elements, such as W, Pb, and Sn, must be ≤0.10% to avoid low melting point phases or brittle phases that damage performance.

[0076] Example 1

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

[0078] S1, 85% industrial pure iron, and 15% scrap steel are used as iron-based raw materials. 2.5% ferrochromium, 0.4% ferrovanadium, 0.3% nickel plate, 0.18% ferromolybdenum, 0.034% ferrotitanium, 0.1% electrolytic copper, and a graphite recarburizer are added to adjust the carbon content to 0.85%. After mixing, the steel is smelted 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 steel is initially deoxidized for 15 minutes at a controlled temperature of 1550°C. After the initial deoxidation, the molten steel is transferred to a vacuum degassing tank for deep deoxidation. The vacuum pressure is adjusted to 10 Pa, 0.004% aluminum blocks are added, and the reaction is continued for 20 minutes. 0.0080% calcium cored wire is fed at a feed speed of 3 m / s, with a bottom argon purge flow of 10 L / min. The steel temperature is controlled at 1400°C and the reaction is continued for 40 minutes.

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

[0080] S3. The remelted steel ingot is heated to 1230°C and kept at this temperature for 2 hours, and then hot rolled. The final rolling temperature is 875°C, the total reduction is 70%, and the rolling deformation rate is 1.0s. -1 The rolled steel was water-cooled to 350°C at a rate of 25°C / s, the pH value of the cooling water was 7.0, and the pressure was 15MPa; the rolled steel was subjected to spheroidizing annealing, with the first stage heating to 770°C at 75°C / h and keeping warm for 3h, and the second stage cooling to 500°C at 15°C / h, and then air-cooled to room temperature. The total annealing time was 18h.

[0081] Example 2

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

[0083] Example 3

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

[0085] Example 4

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

[0087] Example 5

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

[0089] Example 6

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

[0091] Example 7

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

[0093] Example 8

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

[0095] Example 9

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

[0097] Experimental Example 1

[0098] Experimental process:

[0099] (i) 85% commercial pure iron and 15% scrap steel were used as iron-based raw materials. 2.5% ferrochrome, 0.4% ferrovanadium, 0.3% nickel plate, 0.18% ferromolybdenum, 0.034% ferrotitanium, 0.1% electrolytic copper, and a graphite recarburizer were added to adjust the carbon content to 0.85%. After mixing, the mixture was 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 were added to the molten steel. The molten steel temperature was controlled at 1550°C and the reaction was carried out for 15 minutes. The molten steel after preliminary deoxidation is deeply deoxidized, including adding 0.004% aluminum blocks, controlling the molten steel temperature at 1550°C, allowing it to react for 15 minutes, and then feeding 0.0080%-0.0147% calcium cored wire (adjusted according to the group) at a feeding speed of 3m / s, controlling the molten steel temperature at 1400°C, and allowing it to react for 40 minutes.

[0100] (ii) The molten steel from step S1 was cast into electrodes and remelted using a CaF2-CaO-based slag with a slag ratio of CaF2:CaO = 80:20, a basicity of 1.8-2.2 (adjusted according to the group), a melting rate of 50 kg / h, a molten pool temperature of 1720°C, and a slow cooling rate of 10°C / h.

[0101] (iii) The remelted steel ingot was heated and then hot rolled to a final rolling temperature of 875°C, a reduction of 70%, and a water cooling rate of 25°C / s. The rolled steel was then spheroidized annealed at 770°C for 3 h and then air-cooled at 500°C.

[0102] Bearing steel samples were prepared according to grouping (i)-(iii), as shown in the following table:

[0103] Table 1 Sample groups

[0104] Group Calcium addition amount (%) <![CDATA[slag basicity (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] The sulfur content in the sample was tested with reference to GB / T20123; the oxygen content in the sample was tested with reference to GB / T11261; the Charpy impact toughness of the sample was tested with reference to ASTME23; the fatigue life of the sample was tested with reference to GB / T4337; and the transverse / longitudinal impact ratio of the sample was tested with reference to ASTME23. The results are shown in the following table:

[0106] Table 2 Key performance parameters

[0107]

[0108] Among them, the sulfur content is directly related to the morphology and distribution of sulfide inclusions. When the excess sulfur exceeds 15ppm, long strips of MnS inclusions will become the source of crack initiation, significantly shortening the fatigue life; the oxygen content reflects the cleanliness of the molten steel. Oxygen residue exceeding 6ppm will cause alumina inclusions to aggregate, forming stress concentration points and weakening the toughness of the material; impact toughness characterizes the ability of the material to resist impact loads. The higher the value, the less likely the material is to fracture under dynamic loads; 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 close to 1 indicates that the material is excellently isotropic, reducing performance fluctuations caused by differences in grain orientation.

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

[0110] The sulfur content of group 2 is 5ppm and the oxygen content is 3ppm, both of which are at ultra-low levels, and the impact toughness is 32.0J / cm 2 and fatigue life 2.2×10 7 The peak value was reached at a transverse to longitudinal impact ratio of 0.98, approaching complete isotropy. This is due to the fact that at a calcium addition of 0.011%, the molar ratio of calcium to alumina approaches the theoretical value. Calcium ions diffuse into the alumina lattice, disrupting its hexagonal close-packed structure and transforming it into an equiaxed dodecacalcium heptaaluminate. This density-induced buoyancy difference facilitates its buoyancy to the slag phase, where it is refined to a size of 1-5 μm, significantly reducing the risk of stress concentration. At a basicity of 2.0, the activity of calcium oxide in the slag and its affinity for sulfur reach a peak, allowing sulfur ions to be efficiently adsorbed into the slag phase through interfacial exchange reactions. Simultaneously, the slag exhibits moderate fluidity, neither hindering inclusion buoyancy due to excessive viscosity nor reducing sulfur removal efficiency due to low basicity. Calcium treatment not only promotes alumina denaturation but also inhibits the formation of manganese sulfide. Optimizing the slag basicity further adsorbs residual sulfur and oxygen, ultimately achieving dual control over grain boundary oxidation brittleness and inclusion retention.

[0111] Group 3 has a high sulfur content of 18ppm and an oxygen content of 6ppm, and an impact toughness of 25.8J / cm 2 and fatigue life 1.0×10 7 The transverse to longitudinal impact ratio of 0.85 indicates 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 dodecacalcium heptaaluminate, forming a high-density stress concentration source. Excessive calcium increases the free Ca in the slag. 2+ The concentration increases the slag viscosity, reduces the floating rate of inclusions, and makes it difficult to remove 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 20-60 minutes (adjusted according to the group). The composition of dodecacalcium heptaaluminate in the inclusions and the amount of residual alumina are identified by SEM-EDS. 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 dodecacalcium heptaaluminate. The higher the proportion, the less harmful the inclusions are to the material properties. Excessive residual unmodified alumina will form a hard and brittle phase, which will become the origin of fatigue cracks. The inclusion density is lower than 3.0g / 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°C to 1400°C, the proportion of stable inclusions increases from 82% to 98%, while the amount of unmodified alumina decreases from 12% to 0.5%. However, at 1500°C, the proportion of stable inclusions drops sharply to 75%. When the reaction time increases from 20 minutes to 40 minutes, the proportion of stable inclusions increases from 88% to 98%, but at 60 minutes, the proportion drops to 95%. Group 1, combining a 1400°C reaction time with a 40-minute reaction time, achieves the best results, with only 0.5% of unmodified alumina remaining.

[0119] The stable inclusion ratio of group 1 is 98% and the unmodified alumina ratio is 0.5%, both of which are the optimal values. The inclusion density is 2.7g / cm 3 This is because 1400°C is located in the stable phase region of dodeca-calcium heptaaluminate in the calcium aluminate phase diagram, and the calcium ion diffusion rate matches the activation energy required for the destruction of the alumina lattice, ensuring that the reaction proceeds in the direction of generating low-density products. The 40-minute reaction time allows the calcium ions to fully penetrate the alumina grain boundaries, completely destroying its crystal structure, while avoiding the sinking of inclusions caused by changes in the slag state due to excessive time. The adsorption and diffusion rate of calcium on the alumina surface are balanced, and neither local calcium depletion due to excessively rapid reaction nor unmodified areas are left behind due to excessively slow reaction.

[0120] Group 7, with 75% stable inclusions and 18% unmodified alumina, performed the worst, with inclusion density rising to 3.0 g / cm 3 This is because 1500℃ exceeds the stable phase region of dodeca-heptaluminate, and thermal disturbance leads to the formation of high-density calcium aluminate of orthorhombic system, with a density close to 3.0g / cm 3 , making it difficult to remove by buoyancy. High temperatures accelerate calcium volatilization, resulting in insufficient calcium concentration at the reaction interface, only partial conversion of alumina, and the remaining unmodified areas forming preferential microcrack propagation paths. High temperatures enhance convection in the molten steel, causing some high-density inclusions to sink to the bottom of the ingot, resulting in localized segregation and further deteriorating material uniformity.

[0121] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and 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. Melting iron-based raw materials and alloying elements to form molten steel, and sequentially performing preliminary deoxidation and deep deoxidation; the preliminary deoxidation uses ferromanganese and ferrosilicon as deoxidizers, controls the molten steel temperature at 1500-1600° C., and the preliminary deoxidation time is 15-30 minutes; the deep deoxidation includes adding aluminum and calcium under vacuum conditions, and comprises the following steps: A1. Add 0.0027%-0.00495% of aluminum to the molten steel to ensure that the 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 the total mass of the molten steel to the molten steel; A4. Control the temperature of the molten steel to 1300-1500°C and allow it to react for 20-60 minutes to allow the calcium to fully react with the residual oxygen and alumina inclusions in the molten steel to form dodecacalcium heptaaluminate inclusions. S2, casting the molten steel from step S1 into electrodes, and remelting the electrodes with a CaF2-CaO-based slag as a medium; the CaF2-CaO-based slag comprises 75-85% CaF2 and 15-25% CaO by mass; and the basicity of the CaF2-CaO-based slag is 1.8-2.2; S3. The remelted steel ingot is heated and then hot rolled, and the rolled steel is subjected to spheroidizing annealing.

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 alloying elements include ferrochrome with Cr ≥ 60%, added in an amount of 2.4-2.6%; ferrovanadium with V ≥ 50%, added in an amount of 0.3-0.5%; nickel plate with Ni ≥ 99.9% with an addition amount of 0.25-0.35%; ferromolybdenum with Mo ≥ 55%, added in an amount of 0.15-0.22%; ferrotitanium with Ti ≥ 30%, added in an amount of 0.027-0.040%; electrolytic copper with Cu ≥ 99.95%, added in an amount of 0.08-0.12%; and graphite recarburizer with C ≥ 98%, adjusting the final C content to 0.80-0.90%.

4. The heat treatment process according to claim 1, 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.

5. 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.

6. 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.

7. 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°C at 50-100°C / h and kept at this temperature for 2-4 hours; In the second stage, the temperature is lowered to 500°C at ≤20°C / h and then air-cooled to room temperature.

8. A high-strength, wear-resistant backing bearing steel, prepared by the heat treatment process according to any one of claims 1 to 7, containing Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in percentage by mass: 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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