A high-strength corrosion-resistant tool alloy steel containing rare earth elements and a method for preparing the same

Abstract

The application relates to the technical field of alloy steel, in particular to a rare earth-containing high-strength corrosion-resistant cutter alloy steel and a preparation method thereof. Fe is used as a matrix, and the alloy steel contains C, Si, Mn, Cr, Mo, V, Nb, N, composite rare earth and TiB2, the contents of P and S are controlled in an extremely low range; the composite rare earth is a mixture of La and Ce, the content and form of inevitable impurities are strictly controlled, there is no coarse Al2O3 inclusion, and the non-metallic inclusions are spherical or spheroidal and small in size; the preparation method comprises raw material pretreatment, electric arc furnace smelting, AOD refining, electroslag remelting, homogenization annealing and hot forging, hot rolling, cold rolling and cryogenic treatment, tempering and post-treatment. The alloy component and the preparation process are optimized, the organization is refined, the inclusion form is improved, the matrix density and dislocation density are improved, the mechanical properties, corrosion resistance and wear resistance of the alloy are far superior to those of the prior art, and the balance between strength, toughness and corrosion resistance is achieved.

Description

Technical Field

[0001] This invention relates to the field of alloy steel technology, specifically to a rare earth-containing high-strength corrosion-resistant cutting tool alloy steel and its preparation method. Background Technology

[0002] Tool alloy steel is a core basic material in the field of machining. Its performance directly determines machining efficiency and workpiece accuracy. As the requirements for machining conditions in high-end manufacturing, marine engineering and other fields become increasingly stringent, the market demand for tool alloy steel that simultaneously possesses high strength, high wear resistance and excellent corrosion resistance is becoming increasingly urgent. In existing technologies, to improve the strength of tool alloy steel, the carbon content is often increased or alloying elements such as vanadium and niobium are added to form precipitated phases for strengthening. However, high carbon content easily leads to grain boundary embrittlement, and excessive carbon easily combines with chromium to form the carbonitridium embrittlement phase of chromium, which significantly reduces the material's corrosion resistance. To improve corrosion resistance, the conventional approach is to increase the amount of chromium added, but this will exacerbate grain coarsening, causing a decrease in material toughness, making it difficult to achieve a balance between strength, toughness and corrosion resistance.

[0003] In the application of rare earth elements, existing technologies mostly use single rare earth elements for steel purification. Rare earth inclusions are often irregular in shape, with low interfacial bonding strength with the matrix, easily becoming stress concentration sources. This not only fails to fully utilize the grain-refining effect of rare earth elements but also impairs the material's impact toughness. Meanwhile, some technologies attempt to introduce TiB2 particles for dispersion strengthening, but due to a lack of reasonable addition processes, TiB2 particles tend to agglomerate, making it difficult to form a uniform nanoscale dispersion distribution, significantly reducing the strengthening effect. Furthermore, in traditional preparation processes, insufficient vacuum control during melting easily introduces harmful impurities such as oxygen and hydrogen, forming coarse non-metallic inclusions. Heat treatment processes often use single-temperature tempering, making it impossible to precisely control the martensite lath size and retained austenite content, resulting in the material's wear life and fatigue resistance failing to meet the requirements of high-end cutting tools. In summary, developing a cutting tool alloy steel with a rationally designed composition and precise process control, capable of achieving a synergistic improvement in high strength, high corrosion resistance, and high toughness, has become an urgent technical challenge in this field. Summary of the Invention

[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a rare-earth-containing high-strength corrosion-resistant tool alloy steel and its preparation method.

[0005] (II) Technical Solution A rare earth-containing high-strength corrosion-resistant tool alloy steel, with the following chemical composition by mass percentage: C: 0.45~0.65%, Si: 0.20~0.35%, Mn: 0.30~0.70%, Cr: 15.0~17.5%, Mo: 0.8~1.5%, V: 0.3~0.6%, Nb: 0.03~0.10%, N: 0.09~0.15%, RE: 0.02~0.06%, TiB2: 0.3~0.9%, P≤0.012%, S≤0.008%, with the remainder being Fe and unavoidable impurities; the RE is a composite rare earth element of La and Ce, with a La to Ce mass ratio of 1:1.2~1.8, and the RE exists in the steel as La2O2S-Ce2O2S composite oxysulfide inclusions, with an inclusion density of 50~100 inclusions / mm. 2 The TiB2 is dispersed in the steel within the grains and at the grain boundaries in the form of nano-sized particles of 50~200nm.

[0006] Preferably, the chemical composition, by mass percentage, is: C: 0.55%, Si: 0.27%, Mn: 0.5%, Cr: 16.5%, Mo: 1.1%, V: 0.45%, Nb: 0.06%, N: 0.12%, RE: 0.04%, TiB2: 0.6%, P ≤ 0.010%, S ≤ 0.005%, with the remainder being Fe and unavoidable impurities; the La2O2S-Ce2O2S composite oxysulfide inclusions have a size of 0.3~0.8μm and a distribution density of 70~90 inclusions / mm. 2 The nano-TiB2 particles have a size of 80-150 nm and a distribution density of 120-180 particles / mm². 2 .

[0007] Preferably, the mass ratio of La to Ce is 1:1.4~1.6; the La2O2S-Ce2O2S composite oxysulfide inclusion is spherical or near-spherical with an aspect ratio ≤1.2, and the surface of the inclusion is coated with a Cr-rich oxide film with a thickness of 5~10nm.

[0008] Preferably, the NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.446~0.448 nm, and the composite precipitate is coated with nano-TiB2 particles to form a core-shell structure with a lattice mismatch degree of ≤5% at the core-shell interface.

[0009] Preferably, the unavoidable impurities contain ≤0.006% O, ≤0.0002% H, and ≤0.01% Cu; the impurities contain no Al2O3 inclusions with a size ≥1μm, all non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.015%.

[0010] Preferably, the retained austenite is in the form of a thin film with a thickness of 10-30 nm, and this retained austenite is distributed only between the tempered martensite laths; the dislocation density of the tempered martensite matrix is ​​1.0 × 10⁻⁶. 15 ~2.0×10 15 m -2 Furthermore, the proportion of Cr atoms dissolved in the matrix is ​​≥90%.

[0011] Preferably, the preparation method of the rare earth-containing high-strength corrosion-resistant tool alloy steel includes the following steps: S1: Weigh the raw materials according to the chemical composition ratio described in claim 1. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. The recycled ferroalloy is pretreated by holding at 200~250℃ for 1~2 hours to remove surface oil and oxide scale. The ferrochrome nitride and ferromanganese nitride are preheated to 450~550℃ for later use. S2: Add raw materials other than RE and TiB2 to the electric arc furnace, heat to 1580~1650℃ and melt for 25~40 minutes. During the melting process, bottom blowing argon gas is used for stirring, the argon gas flow rate is 0.5~1.0L / min, and the vacuum degree in the furnace is controlled to be ≤15Pa to obtain the initial molten steel. S3: Transfer the primary steel liquid to the AOD refining furnace, introduce argon-oxygen mixed gas for refining for 15-25 minutes, control the decarburization rate at 0.01-0.02% / min, then add preheated ferrochrome nitride and ferromanganese nitride to adjust the N content to the target range, first add RE to purify the steel liquid, then add TiB2, maintain the temperature at 1550-1590℃ for refining for 8-12 minutes, and in the later stage of refining, use the wire feeding method to add Ca-Si wire to fine-tune the inclusion morphology; S4: The refined molten steel is electroslag remelted using a slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:30. The electroslag remelting voltage is 55~65V, the current is 3800~4500A, and the remelting rate is 8~12kg / h to obtain steel ingots with a density ≥99.9%. S5: Heat the steel ingot to 1100~1180℃ at a heating rate of 5~10℃ / min, hold for 4~6h for homogenization annealing, and then hot forge the billet at 1050~1150℃ at a deformation rate of 5~10s-1 with a reduction of area of ​​3~7. The final forging temperature is ≥950℃, and the billet is cooled to room temperature by stacking after forging. S6: Heat the forged billet to 900~980℃ and perform multi-pass hot rolling. The deformation per pass is 10~15%, the cumulative deformation is 50~70%, and the final rolling temperature is 920~960℃. Then, air cool to room temperature at a cooling rate of ≤10℃ / min. S7: The hot-rolled billet is cold-rolled at 820~880℃, with a deformation amount of 8~10% per pass and a cumulative deformation amount of 40~60%. Then the cold-rolled billet is heated to 1030~1080℃ and held for 30~50min. It is then cooled to room temperature by oil quenching and then cooled to a liquid nitrogen environment of -196℃ at a cooling rate of 2~5℃ / min. The deep cryogenic holding time is 40~70min. S8: The deep-cryogenic billet is subjected to a stepped tempering process. First, it is heated to 180℃ for 1 hour, then heated to 220℃ for 1 hour, and finally heated to 240℃ for 1 hour. It is then air-cooled to room temperature to obtain a finished product of rare earth high-strength corrosion-resistant tool alloy steel.

[0012] Preferably, in step S3, the volume ratio of argon to oxygen in the argon-oxygen mixed gas is 3:1 to 4:1, and the total gas flow rate is 15 to 20 L / min; the feeding speed of the Ca-Si wire is 3 to 5 m / min, and the feeding amount is 0.1 to 0.3 kg / t of molten steel.

[0013] Preferably, in step S7, the rolling mill speed of cold rolling is 50~80 r / min, and the adjustment accuracy of the roll gap is ±0.01 mm; the oil temperature of oil quenching is controlled at 40~60℃, and the oil flow rate is 0.8~1.2 m / s.

[0014] Preferably, step S8 is followed by shot peening and stress relief treatment: using 0.5~0.7mm zirconia ceramic shot, shot peening is performed for 2~4 minutes at a spraying distance of 12~18mm and a spraying pressure of 0.3~0.5MPa, and then the residual stress is eliminated by maintaining the shot peening temperature at 120℃ for 1 hour.

[0015] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: 1. The proportion and addition method of composite rare earth can give full play to its role in purifying molten steel, effectively reducing harmful impurities and non-metallic inclusions in steel. At the same time, the morphology of inclusions can be controlled to be spherical or near-spherical, which greatly improves the interfacial bonding strength between inclusions and the matrix and avoids the risk of cracking caused by stress concentration. The uniform dispersion distribution of nano-sized TiB2 particles and the core-shell structure design of NbC-NbN composite precipitates form a highly efficient synergistic strengthening effect, which can not only improve the hardness and wear resistance of the material, but also inhibit the precipitation of carbon and nitrogen brittle phases of chromium, thus ensuring the corrosion resistance of the material.

[0016] 2. By optimizing the process, the morphology and distribution of tempered martensite matrix and retained austenite are precisely controlled. Thin film-like retained austenite is distributed between martensite laths, which can effectively hinder crack propagation and significantly improve the impact toughness and fatigue resistance of the material.

[0017] 3. The combined application of vacuum melting, AOD refining, and electroslag remelting significantly improves the density of steel ingots and reduces internal porosity and defects; the stepped deep cryogenic tempering process further refines the microstructure, optimizes the dislocation density of the matrix, and improves the overall mechanical properties of the material. The raw materials of this invention include recycled ferroalloys, which reduces production costs while ensuring performance, thus combining economic efficiency and environmental friendliness. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for preparing rare earth-containing high-strength corrosion-resistant tool alloy steel disclosed in this invention; Figure 2 This is a line graph comparing the tensile strength and yield strength of the examples and comparative examples; Figure 3 This is a bar chart comparing Rockwell hardness and impact toughness of the examples and comparative examples; Figure 4 This is a bar chart comparing the wear resistance life and fatigue strength of the examples and comparative examples. Detailed Implementation

[0019] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: The following detailed description of the rare earth-containing high-strength corrosion-resistant tool alloy steel and its preparation method, in conjunction with embodiments and comparative examples, provides a comprehensive overview of the present invention.

[0020] I. Example 1 (a) Raw material ratio (by mass percentage) C: 0.45%, Si: 0.20%, Mn: 0.30%, Cr: 15.0%, Mo: 0.8%, V: 0.3%, Nb: 0.03%, N: 0.09%, RE: 0.02%, TiB2: 0.3%, P≤0.012%, S≤0.008%, with the remainder being Fe and unavoidable impurities.

[0021] RE is a composite rare earth element of La and Ce, with a mass ratio of La to Ce of 1:1.2. The unavoidable impurities contain ≤0.006% O, ≤0.0002% H, and ≤0.01% Cu. There are no Al2O3 inclusions with a size ≥1μm. All non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.015%.

[0022] (II) Preparation steps S1: Raw material pretreatment Weigh the raw materials according to the above proportions. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. Place the recycled ferroalloy in a heating device and keep it at 200°C for 1 hour to remove surface oil and oxide scale. Preheat the ferrochrome nitride and ferromanganese nitride to 450°C for later use.

[0023] S2: Electric arc furnace melting Add all raw materials except RE and TiB2 to the electric arc furnace, close the furnace door, and evacuate to control the vacuum level inside the furnace to ≤15Pa. Start the electric arc furnace and heat it to 1580℃, maintain this temperature for 25 minutes of melting. During the melting process, bottom-blown argon gas is used for stirring, with an argon gas flow rate of 0.5L / min. The raw materials are fully melted and mixed evenly to obtain primary molten steel.

[0024] S3: AOD Refining The primary molten steel was transferred to an AOD refining furnace, where an argon-oxygen mixture was introduced for refining. The volume ratio of argon to oxygen was 3:1, the total gas flow rate was 15 L / min, and the refining time was 15 min. The decarburization rate was controlled at 0.01% / min. After decarburization, preheated ferrochrome nitride and ferromanganese nitride were added to adjust the nitrogen content to the target range. Then, refining agent (RE) was added first to purify the molten steel, followed by the addition of TiB2. The furnace temperature was maintained at 1550℃, and refining continued for 8 min. In the later stages of refining, Ca-Si wire was added using a wire feeding method. The feeding rate of the Ca-Si wire was 3 m / min, and the feeding amount was 0.1 kg / t of molten steel, with fine-tuning of the inclusion morphology.

[0025] S4: Electroslag Remelting The refined molten steel is introduced into the crystallizer of the electroslag remelting equipment. A slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:30 is used. The electroslag remelting voltage is controlled at 55V, the current at 3800A, and the remelting rate at 8kg / h to obtain steel ingots with a density ≥99.9%.

[0026] S5: Homogenization Annealing and Hot Forging Blank Opening The electroslag remelted steel ingot was placed in an annealing furnace and heated to 1100℃ at a heating rate of 5℃ / min, and held at that temperature for 4 hours for homogenization annealing. After annealing, the steel ingot was transferred to a forging press and pressed at 1050℃ for 5 seconds. -1 The deformation rate is used for hot forging of billets, the area reduction ratio is 3, the final forging temperature is ≥950℃, and the billets are cooled to room temperature by stacking after forging.

[0027] S6: Hot rolling treatment The forged billet is placed in a heating furnace, heated to 900℃ and held for a period of time before being hot rolled in multiple passes. The deformation per pass is 10%, the cumulative deformation is 50%, and the final rolling temperature is 920℃. After hot rolling, it is air-cooled to room temperature at a cooling rate of ≤10℃ / min.

[0028] S7: Cold rolling and cryogenic treatment The hot-rolled billet was placed in a cold rolling mill and subjected to multi-pass cold rolling at 820℃, with a per-pass deformation of 8% and a cumulative deformation of 40%. During the cold rolling process, the roll speed was controlled at 50 r / min, and the roll gap adjustment accuracy was ±0.01 mm. After cold rolling, the billet was heated to 1030℃ and held for 30 min, then cooled to room temperature by oil quenching. During oil quenching, the oil temperature was controlled at 40℃, and the oil flow rate was 0.8 m / s. After oil quenching, the billet was cooled to a liquid nitrogen environment at -196℃ at a cooling rate of 2℃ / min and held for 40 min.

[0029] S8: Stepped tempering and post-treatment The cryogenically cooled billet was placed in a tempering furnace and subjected to a stepped tempering process: first, it was held at 180℃ for 1 hour, then heated to 220℃ and held for 1 hour, and finally heated to 240℃ and held for 1 hour. After tempering, it was air-cooled to room temperature. Subsequently, shot peening and stress relief treatment were performed using 0.5mm zirconia ceramic shot at a blasting distance of 12mm and a blasting pressure of 0.3MPa for 2 minutes. After shot peening, it was held at 120℃ for 1 hour to relieve residual stress, resulting in the finished product.

[0030] (III) Key characteristics of the microstructure and properties of the finished product RE exists in steel as La2O2S-Ce2O2S complex oxysulfide inclusions. These inclusions are spherical with an aspect ratio of 1.1 and a distribution density of 50 inclusions / mm. 2 The surface is coated with a 5 nm thick Cr-rich oxide film; TiB2 is dispersed in the steel as 50-100 nm nano-sized particles within the grains and at the grain boundaries; the NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.446 nm, and is coated with nano-TiB2 particles to form a core-shell structure with a lattice mismatch of 4% at the core-shell interface; the retained austenite is in the form of a thin film, 10-20 nm thick, and is only distributed between the tempered martensite laths; the dislocation density of the tempered martensite matrix is ​​1.0 × 10⁻⁶. 15 m -2 The proportion of Cr atoms dissolved in the matrix is ​​90%.

[0031] II. Example 2 (a) Raw material ratio (by mass percentage) C: 0.55%, Si: 0.27%, Mn: 0.5%, Cr: 16.5%, Mo: 1.1%, V: 0.45%, Nb: 0.06%, N: 0.12%, RE: 0.04%, TiB2: 0.6%, P≤0.010%, S≤0.005%, with the remainder being Fe and unavoidable impurities.

[0032] RE is a composite rare earth element of La and Ce, with a mass ratio of La to Ce of 1:1.5. The unavoidable impurities contain ≤0.004% O, ≤0.00015% H, and ≤0.005% Cu. There are no Al2O3 inclusions with a size ≥1μm. All non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.012%.

[0033] (II) Preparation steps S1: Raw material pretreatment Weigh the raw materials according to the specified proportions. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. Place the recycled ferroalloy in a heating device and keep it at 225°C for 1.5 hours to remove surface oil and oxide scale. Preheat the ferrochrome nitride and ferromanganese nitride to 500°C for later use.

[0034] S2: Electric arc furnace melting Add all raw materials except RE and TiB2 to the electric arc furnace, close the furnace door, and evacuate to control the vacuum level inside the furnace to ≤15Pa. Start the electric arc furnace and heat it to 1620℃, maintain this temperature for 30 minutes of melting. During the melting process, bottom-blown argon gas is used for stirring, with an argon gas flow rate of 0.7L / min. The raw materials are fully melted and mixed evenly to obtain primary molten steel.

[0035] S3: AOD Refining The primary molten steel was transferred to an AOD refining furnace, where an argon-oxygen mixture was introduced for refining. The volume ratio of argon to oxygen was 3.5:1, the total gas flow rate was 18 L / min, and the refining time was 20 min. The decarburization rate was controlled at 0.015% / min. After decarburization, preheated ferrochrome nitride and ferromanganese nitride were added to adjust the nitrogen content to the target range. Then, refining agent (RE) was added first to purify the molten steel, followed by the addition of TiB2. The furnace temperature was maintained at 1570℃, and refining continued for another 10 min. In the later stages of refining, Ca-Si wire was added using a wire feeding method. The feeding rate of the Ca-Si wire was 4 m / min, and the feeding amount was 0.2 kg / t of molten steel, with fine-tuning of the inclusion morphology.

[0036] S4: Electroslag Remelting The refined molten steel is introduced into the crystallizer of the electroslag remelting equipment. A slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:30 is used. The electroslag remelting voltage is controlled at 60V, the current at 4200A, and the remelting rate at 10kg / h to obtain steel ingots with a density ≥99.9%.

[0037] S5: Homogenization Annealing and Hot Forging Blank Opening The electroslag remelted steel ingot was placed in an annealing furnace and heated to 1140℃ at a heating rate of 7℃ / min, and held at that temperature for 5 hours for homogenization annealing. After annealing, the steel ingot was transferred to a forging press and forged at 1100℃ for 7 seconds.-1 The deformation rate is used for hot forging of billets, the area reduction ratio is 5, the final forging temperature is ≥980℃, and the billets are cooled to room temperature by stacking after forging.

[0038] S6: Hot rolling treatment The forged billet is placed in a heating furnace, heated to 940℃ and held for a period of time before being hot rolled in multiple passes. The deformation per pass is 12%, the cumulative deformation is 60%, and the final rolling temperature is 940℃. After hot rolling, it is air-cooled to room temperature at a cooling rate of ≤10℃ / min.

[0039] S7: Cold rolling and cryogenic treatment The hot-rolled billet was placed in a cold rolling mill and subjected to multi-pass cold rolling at 850℃, with a per-pass deformation of 9% and a cumulative deformation of 50%. During the cold rolling process, the roll speed was controlled at 65 r / min, and the roll gap adjustment accuracy was ±0.01 mm. After cold rolling, the billet was heated to 1050℃ and held for 40 min, then cooled to room temperature by oil quenching. During oil quenching, the oil temperature was controlled at 50℃, and the oil flow rate was 1.0 m / s. After oil quenching, the billet was cooled to a liquid nitrogen environment at -196℃ at a cooling rate of 3℃ / min and held for 55 min.

[0040] S8: Stepped tempering and post-treatment The cryogenically cooled billet was placed in a tempering furnace and subjected to a stepped tempering process: first, it was held at 180℃ for 1 hour, then heated to 220℃ and held for 1 hour, and finally heated to 240℃ and held for 1 hour. After tempering, it was air-cooled to room temperature. Subsequently, shot peening and stress relief treatment were performed using 0.6mm zirconia ceramic shot at a blasting distance of 15mm and a blasting pressure of 0.4MPa for 3 minutes. After shot peening, it was held at 120℃ for 1 hour to relieve residual stress, resulting in the finished product.

[0041] (III) Key characteristics of the microstructure and properties of the finished product RE exists in steel as La2O2S-Ce2O2S complex oxysulfide inclusions. These inclusions are spherical with an aspect ratio of 1.0, a size of 0.3~0.8μm, and a distribution density of 70~90 inclusions / mm. 2 The surface is coated with a 7 nm thick Cr-rich oxide film; TiB2 is dispersed in the grains and grain boundaries of the steel in the form of 80-150 nm nanoparticles, with a distribution density of 120-180 particles / mm. 2 The NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.447 nm. It is coated with nano-TiB2 particles to form a core-shell structure, with a lattice mismatch of 3% at the core-shell interface. The retained austenite is in the form of a thin film, 15-25 nm thick, and is distributed only between the tempered martensite laths. The dislocation density of the tempered martensite matrix is ​​1.5 × 10⁻⁶. 15 m -2The proportion of Cr atoms dissolved in the matrix is ​​92%.

[0042] III. Example 3 (a) Raw material ratio (by mass percentage) C: 0.60%, Si: 0.32%, Mn: 0.60%, Cr: 17.0%, Mo: 1.3%, V: 0.5%, Nb: 0.08%, N: 0.13%, RE: 0.05%, TiB2: 0.8%, P≤0.011%, S≤0.007%, with the remainder being Fe and unavoidable impurities.

[0043] RE is a composite rare earth element of La and Ce, with a mass ratio of La to Ce of 1:1.6. The unavoidable impurities contain ≤0.005% O, ≤0.00018% H, and ≤0.008% Cu. There are no Al2O3 inclusions with a size ≥1μm. All non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.013%.

[0044] (II) Preparation steps S1: Raw material pretreatment Weigh the raw materials according to the specified proportions. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. Place the recycled ferroalloy into a heating device and keep it at 240°C for 1.8 hours to remove surface oil and oxide scale. Preheat the ferrochrome nitride and ferromanganese nitride to 530°C for later use.

[0045] S2: Electric arc furnace melting Add all raw materials except RE and TiB2 to the electric arc furnace, close the furnace door, and evacuate to control the vacuum level inside the furnace to ≤15Pa. Start the electric arc furnace and heat it to 1640℃, maintain this temperature for 35 minutes of melting. During the melting process, bottom-blown argon gas is used for stirring, with an argon gas flow rate of 0.9L / min. The raw materials are fully melted and mixed evenly to obtain primary molten steel.

[0046] S3: AOD Refining The primary molten steel was transferred to an AOD refining furnace, where an argon-oxygen mixture was introduced for refining. The volume ratio of argon to oxygen was 3.8:1, the total gas flow rate was 19 L / min, and the refining time was 23 min. The decarburization rate was controlled at 0.018% / min. After decarburization, preheated ferrochrome nitride and ferromanganese nitride were added to adjust the nitrogen content to the target range. Then, refining agent (RE) was added first to purify the molten steel, followed by TiB2. The furnace temperature was maintained at 1580℃, and refining continued for 11 min. In the later stages of refining, Ca-Si wire was added using a wire feeding method. The feeding rate of the Ca-Si wire was 4.5 m / min, and the feeding amount was 0.25 kg / t of molten steel, with fine-tuning of the inclusion morphology.

[0047] S4: Electroslag Remelting The refined molten steel is introduced into the crystallizer of the electroslag remelting equipment. A slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:30 is used. The electroslag remelting voltage is controlled at 63V, the current at 4400A, and the remelting rate at 11kg / h to obtain steel ingots with a density ≥99.9%.

[0048] S5: Homogenization Annealing and Hot Forging Blank Opening The electroslag remelted steel ingots were placed in an annealing furnace and heated to 1160°C at a heating rate of 9°C / min, and held at that temperature for 5.5 hours for homogenization annealing. After annealing, the steel ingots were transferred to a forging press and forged at 1130°C for 9 seconds. -1 The deformation rate is used for hot forging of billets, the area reduction ratio is 6, the final forging temperature is ≥990℃, and the billets are cooled to room temperature by stacking after forging.

[0049] S6: Hot rolling treatment The forged billet is placed in a heating furnace, heated to 960℃ and held for a period of time before being hot rolled in multiple passes. The deformation per pass is 14%, the cumulative deformation is 65%, and the final rolling temperature is 950℃. After hot rolling, it is air-cooled to room temperature at a cooling rate of ≤10℃ / min.

[0050] S7: Cold rolling and cryogenic treatment The hot-rolled billet was placed in a cold rolling mill and subjected to multi-pass cold rolling at 870℃, with a pass deformation of 9.5% and a cumulative deformation of 55%. During the cold rolling process, the roll speed was controlled at 75 r / min, and the roll gap adjustment accuracy was ±0.01 mm. After cold rolling, the billet was heated to 1070℃ and held for 45 min, then cooled to room temperature by oil quenching. During oil quenching, the oil temperature was controlled at 55℃, and the oil flow rate was 1.1 m / s. After oil quenching, the billet was cooled to a liquid nitrogen environment at -196℃ at a cooling rate of 4℃ / min and held for 60 min.

[0051] S8: Stepped tempering and post-treatment The cryogenically cooled billet was placed in a tempering furnace and subjected to a stepped tempering process: first, it was held at 180℃ for 1 hour, then heated to 220℃ and held for 1 hour, and finally heated to 240℃ and held for 1 hour. After tempering, it was air-cooled to room temperature. Subsequently, shot peening and stress relief treatment were performed using 0.65mm zirconia ceramic shot at a blasting distance of 17mm and a blasting pressure of 0.45MPa for 3.5 minutes. After shot peening, it was held at 120℃ for 1 hour to relieve residual stress, resulting in the finished product.

[0052] (III) Key characteristics of the microstructure and properties of the finished product RE exists in steel as La2O2S-Ce2O2S complex oxysulfide inclusions. These inclusions are spherical with an aspect ratio of 1.1, a size of 0.5~0.7μm, and a distribution density of 90 inclusions / mm.2 The surface is coated with a 9 nm thick Cr-rich oxide film; TiB2 is dispersed in the grains and grain boundaries of the steel in the form of 160~190 nm nanoparticles, with a distribution density of 160~170 particles / mm. 2 The NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.4475 nm. It is coated with nano-TiB2 particles to form a core-shell structure, with a lattice mismatch of 3.5% at the core-shell interface. The retained austenite is in the form of a thin film, 20-28 nm thick, and is distributed only between the tempered martensite laths. The dislocation density of the tempered martensite matrix is ​​1.8 × 10⁻⁶. 15 m -2 The proportion of Cr atoms dissolved in the matrix is ​​94%.

[0053] IV. Example 4 (a) Raw material ratio (by mass percentage) C: 0.65%, Si: 0.35%, Mn: 0.70%, Cr: 17.5%, Mo: 1.5%, V: 0.6%, Nb: 0.10%, N: 0.15%, RE: 0.06%, TiB2: 0.9%, P≤0.012%, S≤0.008%, with the remainder being Fe and unavoidable impurities.

[0054] RE is a composite rare earth element of La and Ce, with a mass ratio of La to Ce of 1:1.8. The unavoidable impurities contain ≤0.006% O, ≤0.0002% H, and ≤0.01% Cu. There are no Al2O3 inclusions with a size ≥1μm. All non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.015%.

[0055] (II) Preparation steps S1: Raw material pretreatment Weigh the raw materials according to the specified proportions. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. Place the recycled ferroalloy in a heating device and keep it at 250°C for 2 hours to remove surface oil and oxide scale. Preheat the ferrochrome nitride and ferromanganese nitride to 550°C for later use.

[0056] S2: Electric arc furnace melting Add all raw materials except RE and TiB2 to the electric arc furnace, close the furnace door, and evacuate to control the vacuum level inside the furnace to ≤15Pa. Start the electric arc furnace and heat it to 1650℃, maintain this temperature for 40 minutes of melting. During the melting process, bottom-blown argon gas is used for stirring, with an argon gas flow rate of 1.0L / min. The raw materials are fully melted and mixed evenly to obtain primary molten steel.

[0057] S3: AOD Refining The primary molten steel was transferred to an AOD refining furnace, where an argon-oxygen mixture was introduced for refining. The volume ratio of argon to oxygen was 4:1, the total gas flow rate was 20 L / min, and the refining time was 25 min. The decarburization rate was controlled at 0.02% / min. After decarburization, preheated ferrochrome nitride and ferromanganese nitride were added to adjust the nitrogen content to the target range. Then, refining agent (RE) was added first to purify the molten steel, followed by the addition of TiB2. The furnace temperature was maintained at 1590℃, and refining continued for 12 min. In the later stage of refining, Ca-Si wire was added using a wire feeding method. The feeding rate of the Ca-Si wire was 5 m / min, and the feeding amount was 0.3 kg / t of molten steel, with fine-tuning of the inclusion morphology.

[0058] S4: Electroslag Remelting The refined molten steel is introduced into the crystallizer of the electroslag remelting equipment. A slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:30 is used. The electroslag remelting voltage is controlled at 65V, the current at 4500A, and the remelting rate at 12kg / h to obtain steel ingots with a density ≥99.9%.

[0059] S5: Homogenization Annealing and Hot Forging Blank Opening The electroslag remelted steel ingots were placed in an annealing furnace and heated to 1180°C at a heating rate of 10°C / min, and held at that temperature for 6 hours for homogenization annealing. After annealing, the steel ingots were transferred to a forging press and pressed at 1150°C for 10 seconds. -1 The deformation rate is used for hot forging of billets, the area reduction ratio is 7, the final forging temperature is ≥1000℃, and the billets are cooled to room temperature by stacking after forging.

[0060] S6: Hot rolling treatment The forged billet is placed in a heating furnace, heated to 980℃ and held for a period of time before being hot rolled in multiple passes. The deformation per pass is 15%, the cumulative deformation is 70%, and the final rolling temperature is 960℃. After hot rolling, it is air-cooled to room temperature at a cooling rate of ≤10℃ / min.

[0061] S7: Cold rolling and cryogenic treatment The hot-rolled billet is placed in a cold rolling mill and subjected to multi-pass cold rolling at 880℃, with a pass deformation of 10% and a cumulative deformation of 60%. During the cold rolling process, the roll speed is controlled at 80 r / min, and the roll gap adjustment accuracy is ±0.01 mm. After cold rolling, the billet is heated to 1080℃ and held for 50 min, then cooled to room temperature by oil quenching. During oil quenching, the oil temperature is controlled at 60℃, and the oil flow rate is 1.2 m / s. After oil quenching, it is cooled to a liquid nitrogen environment at -196℃ at a cooling rate of 5℃ / min and held for 70 min.

[0062] S8: Stepped tempering and post-treatment The cryogenically cooled billet was placed in a tempering furnace and subjected to a stepped tempering process: first, it was held at 180℃ for 1 hour, then heated to 220℃ and held for 1 hour, and finally heated to 240℃ and held for 1 hour. After tempering, it was air-cooled to room temperature. Subsequently, shot peening and stress relief treatment were performed using 0.7mm zirconia ceramic shot at a blasting distance of 18mm and a blasting pressure of 0.5MPa for 4 minutes. After shot peening, it was held at 120℃ for 1 hour to relieve residual stress, resulting in the finished product.

[0063] (III) Key characteristics of the microstructure and properties of the finished product RE exists in steel as La2O2S-Ce2O2S complex oxysulfide inclusions. These inclusions are spherical with an aspect ratio of 1.2 and a distribution density of 100 inclusions / mm. 2 The surface is coated with a 10 nm thick Cr-rich oxide film; TiB2 is dispersed in the steel as 180-200 nm nano-sized particles within the grains and at the grain boundaries; the NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.448 nm, and is coated with nano-TiB2 particles to form a core-shell structure with a lattice mismatch of 5% at the core-shell interface; the retained austenite is in the form of a thin film, 25-30 nm thick, and is only distributed between the tempered martensite laths; the dislocation density of the tempered martensite matrix is ​​2.0 × 10⁻⁶. 15 m -2 The proportion of Cr atoms dissolved in the matrix is ​​95%.

[0064] V. Comparative Example 1 (Prior Technical Solution) (a) Raw material ratio (by mass percentage) C: 0.70%, Si: 0.40%, Mn: 0.80%, Cr: 14.0%, Mo: 0.6%, V: 0.2%, Nb: 0.02%, N: 0.08%, RE: 0.01% (single La rare earth), P≤0.015%, S≤0.010%, with the remainder being Fe and unavoidable impurities.

[0065] The unavoidable impurities contain ≤0.010% O, ≤0.0005% H, and ≤0.02% Cu; the non-metallic inclusions contain Al2O3 inclusions with a size ≥1μm, and the total content of non-metallic inclusions is ≤0.03%.

[0066] (II) Preparation steps S1: Raw material pretreatment Weigh the raw materials according to the specified proportions. The raw materials include ordinary ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. Hold the ordinary ferroalloy at 180℃ for 0.5 hours to remove some surface oil. The ferrochrome nitride and ferromanganese nitride are used directly without preheating.

[0067] S2: Electric arc furnace melting All raw materials were added to an electric arc furnace, the vacuum inside the furnace was controlled at ≤50Pa, and the temperature was raised to 1600℃ for 30 minutes. No bottom blowing argon gas was used for stirring during the smelting process, and the materials were naturally melted and mixed to obtain primary molten steel.

[0068] S3: Refining Process The primary molten steel was transferred to a conventional refining furnace, and a mixture of air and oxygen was introduced for refining for 10 minutes. The decarburization rate was not strictly controlled. After adding ferrochrome nitride to adjust the N content, single La rare earth element was added directly without adding TiB2. The refining was completed after holding the temperature for 10 minutes.

[0069] S4: Casting The refined molten steel was directly cast into steel ingots without electroslag remelting, and the density of the steel ingots was ≤99.5%.

[0070] S5: Hot Forging and Rolling The steel ingot was heated to 1050℃ at a heating rate of 15℃ / min, held at that temperature for 3 hours, and then hot-forged into a billet with a deformation rate of 3s. -1 The area reduction ratio is 4, the final forging temperature is ≥900℃, and it is air-cooled to room temperature after forging. Then, it is hot-rolled in a single pass with a deformation of 40% and a final rolling temperature of 880℃, and then naturally cooled after rolling.

[0071] S6: Heat treatment The hot-rolled billet was heated to 950℃ and held for 20 minutes, then air-cooled to room temperature without cold rolling or cryogenic treatment. Subsequently, a single-temperature tempering process was used, holding at 200℃ for 2 hours and air-cooled to room temperature without shot peening or stress relief treatment to obtain the finished product.

[0072] (III) Key characteristics of the microstructure and properties of the finished product Rare earth elements are present as irregularly shaped La2O3 particles with an aspect ratio ≥ 2.0 and a distribution density of 30 particles / mm. 2 There is no Cr-rich oxide film coating; no dispersed distribution of nano-TiB2 particles, nor a core-shell structure of NbC-NbN composite precipitates; the retained austenite is blocky, with a thickness ≥50nm, distributed throughout the matrix; the dislocation density of the tempered martensitic matrix is ​​0.8×10⁻⁶. 15 m -2 The proportion of Cr atoms dissolved in the matrix is ​​85%; the material contains a small number of pores and coarse non-metallic inclusions, making it difficult to balance strength, toughness and corrosion resistance.

[0073] The basic mechanical and corrosion resistance properties of the examples and comparative examples are compared in the table below: Table 1

[0074] The specific performance and service life of the examples and comparative examples are compared in the table below: Table 2

[0075] In summary, the data in the two tables corroborate each other, fully demonstrating that by optimizing alloy composition and combining precise processes, the present invention enables the tool alloy steel to far surpass existing technologies in terms of basic mechanical properties, corrosion resistance, wear life, and structural stability. It achieves a precise balance of high strength, high toughness, and high corrosion resistance, making it fully adaptable to the demanding application scenarios of high-end tools, and demonstrating significant technical advantages.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rare-earth-containing high-strength corrosion-resistant cutting tool alloy steel, characterized in that, The chemical composition, by mass percentage, includes: C: 0.45~0.65%, Si: 0.20~0.35%, Mn: 0.30~0.70%, Cr: 15.0~17.5%, Mo: 0.8~1.5%, V: 0.3~0.6%, Nb: 0.03~0.10%, N: 0.09~0.15%, RE: 0.02~0.06%, TiB2: 0.3~0.9%, P≤0.012%, S≤0.008%, and the remainder. The steel contains Fe and unavoidable impurities; the RE is a composite rare earth element of La and Ce, with a mass ratio of La to Ce of 1:1.4~1.6; the La2O2S-Ce2O2S composite oxysulfide inclusions are spherical or near-spherical with an aspect ratio ≤1.2, and the surface of the inclusions is covered with a Cr-rich oxide film with a thickness of 5~10 nm; the RE exists in the steel as La2O2S-Ce2O2S composite oxysulfide inclusions, and the inclusion distribution density is 50~100 inclusions / mm. 2 The TiB2 is dispersed in the steel as nano-sized particles of 50~200 nm within the grains and at the grain boundaries; the NbC-NbN composite precipitate has a face-centered cubic crystal structure with a lattice constant of 0.446~0.448 nm, and this composite precipitate is coated with nano-TiB2 particles to form a core-shell structure, with a lattice mismatch at the core-shell interface ≤5%; the retained austenite is in the form of a thin film with a thickness of 10~30 nm, and this retained austenite is only distributed between the tempered martensite laths; the dislocation density of the tempered martensite matrix is ​​1.0 × 10⁻⁶. 15 ~2.0×10 15 m -2 Furthermore, the proportion of Cr atoms dissolved in the matrix is ​​≥90%.

2. The rare-earth-containing high-strength corrosion-resistant tool alloy steel according to claim 1, characterized in that, The chemical composition, by mass percentage, is as follows: C: 0.55%, Si: 0.27%, Mn: 0.5%, Cr: 16.5%, Mo: 1.1%, V: 0.45%, Nb: 0.06%, N: 0.12%, RE: 0.04%, TiB2: 0.6%, P≤0.010%, S≤0.005%, with the remainder being Fe and unavoidable impurities; the La2O2S-Ce2O2S composite oxysulfide inclusions have a size of 0.3~0.8μm and a distribution density of 70~90 inclusions / mm. 2 The nano-TiB2 particles have a size of 80-150 nm and a distribution density of 120-180 particles / mm². 2 .

3. The rare-earth-containing high-strength corrosion-resistant tool alloy steel according to claim 1, characterized in that, The unavoidable impurities contain ≤0.006% O, ≤0.0002% H, and ≤0.01% Cu. There are no Al2O3 inclusions with a size ≥1μm. All non-metallic inclusions are spherical or near-spherical with a size ≤2μm, and the total content of non-metallic inclusions is ≤0.015%.

4. A method for preparing rare-earth-containing high-strength corrosion-resistant tool alloy steel as described in claim 1, characterized in that, Includes the following steps: S1: Weigh the raw materials according to the chemical composition ratio described in claim 1. The raw materials include recycled ferroalloy, ferrochrome nitride, ferromanganese nitride, and pure metal additives. The recycled ferroalloy is pretreated by holding at 200~250℃ for 1~2 hours to remove surface oil and oxide scale. The ferrochrome nitride and ferromanganese nitride are preheated to 450~550℃ for later use. S2: Add raw materials other than RE and TiB2 to the electric arc furnace, heat to 1580~1650℃ and melt for 25~40 minutes. During the melting process, bottom blowing argon gas is used for stirring, the argon gas flow rate is 0.5~1.0L / min, and the vacuum degree in the furnace is controlled to be ≤15Pa to obtain the initial molten steel. S3: Transfer the primary steel liquid to the AOD refining furnace, introduce argon-oxygen mixed gas for refining for 15-25 minutes, control the decarburization rate at 0.01-0.02% / min, then add preheated ferrochrome nitride and ferromanganese nitride to adjust the N content to the target range, first add RE to purify the steel liquid, then add TiB2, maintain the temperature at 1550-1590℃ for refining for 8-12 minutes, and in the later stage of refining, use the wire feeding method to add Ca-Si wire to fine-tune the inclusion morphology; S4: The refined molten steel is electroslag remelted using a slag system with a mass ratio of CaF2-Al2O3-CaO of 40:30:

30. The electroslag remelting voltage is 55~65V, the current is 3800~4500A, and the remelting rate is 8~12kg / h to obtain steel ingots with a density ≥99.9%. S5: Heat the steel ingot to 1100~1180℃ at a heating rate of 5~10℃ / min, hold for 4~6h for homogenization annealing, and then anneal at 1050~1150℃ for 5~10s. -1 The deformation rate of hot forging blank is 3~7, the final forging temperature is ≥950℃, and the blank is cooled to room temperature by stacking after forging. S6: Heat the forged billet to 900~980℃ and perform multi-pass hot rolling. The deformation per pass is 10~15%, the cumulative deformation is 50~70%, and the final rolling temperature is 920~960℃. Then, air cool to room temperature at a cooling rate of ≤10℃ / min. S7: The hot-rolled billet is cold-rolled at 820~880℃, with a deformation amount of 8~10% per pass and a cumulative deformation amount of 40~60%. Then the cold-rolled billet is heated to 1030~1080℃ and held for 30~50min. It is then cooled to room temperature by oil quenching and then cooled to a liquid nitrogen environment of -196℃ at a cooling rate of 2~5℃ / min. The deep cryogenic holding time is 40~70min. S8: The deep-cryogenic billet is subjected to a stepped tempering process. First, it is heated to 180℃ for 1 hour, then heated to 220℃ for 1 hour, and finally heated to 240℃ for 1 hour. It is then air-cooled to room temperature to obtain a finished product of rare earth high-strength corrosion-resistant tool alloy steel.

5. The method for preparing rare-earth-containing high-strength corrosion-resistant tool alloy steel according to claim 4, characterized in that, In step S3, the volume ratio of argon to oxygen in the argon-oxygen mixed gas is 3:1 to 4:1, and the total gas flow rate is 15 to 20 L / min; the feeding speed of the Ca-Si wire is 3 to 5 m / min, and the feeding amount is 0.1 to 0.3 kg / t of molten steel.

6. The method for preparing rare-earth-containing high-strength corrosion-resistant tool alloy steel according to claim 4, characterized in that, In step S7, the rolling mill speed is 50~80 r / min and the adjustment accuracy of the roll gap is ±0.01 mm; the oil temperature for oil quenching is controlled at 40~60℃ and the oil flow rate is 0.8~1.2 m / s.

7. The method for preparing rare-earth-containing high-strength corrosion-resistant tool alloy steel according to claim 4, characterized in that, Step S8 is followed by shot peening and stress relief steps: using 0.5~0.7mm zirconia ceramic shot, shot peening is performed for 2~4 minutes at a spraying distance of 12~18mm and a spraying pressure of 0.3~0.5MPa. After shot peening, the residual stress is eliminated by keeping the shot peening at 120℃ for 1 hour.

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