High-nitrogen cutting tool steel and preparation method thereof

Abstract

The invention relates to high-nitrogen cutting tool steel and a preparation method thereof. The steel comprises the following chemical components: 0.75%-0.85% of C, 0.10%-0.20% of Si, 1.50%-1.70% of Mn, less than or equal to 0.015% of P, 0.08%-0.10% of S, 0.60%-0.80% of Cr, 0.12%-0.15% of Ti, 0.015%-0.055% of Alt, 0.026%-0.030% of N, 0.0040%-0.0060% of B, 0.0020%-0.0030% of Nd and the balance of Fe and impurities. The problems that existing cutting tool steel is poor in working stability, uneven in performance and prone to fracture and tooth breakage are solved, component segregation of the cutting tool steel is relieved, the surface quality is improved, and the cutting tool steel has high strength, high toughness, long fatigue life and good abrasion resistance, deformation resistance, impact resistance and welding performance.

Description

Technical Field

[0001] The invention relates to the technical field of cutting tool steel production, and in particular to a high nitrogen cutting tool steel and a preparation method thereof. Background Art

[0002] With the rapid development of my country's ore mining, ceramic production, building structure, stone decoration and other industries, the demand for cutting tool steel has increased at an annual rate of 20% to 30%. In order to further improve the yield rate and work efficiency, cutting tools (such as circular saw blades) are gradually developing towards high speed, thinness and large diameter. In harsh working environments, the increase in cutting tool speed increases the impact, friction and vibration it is subjected to during work, resulting in increased stress, reduced working stability, and prone to uneven performance, broken teeth, severe segregation, poor surface quality, reduced abrasion resistance and other problems, which seriously affect the service life of the cutting tool.

[0003] The harsh working environment also puts forward higher requirements on the mechanical properties of cutting tool steel, especially deformation resistance, impact resistance, corrosion resistance and fatigue performance. In order to solve the above problems, the present invention uses N as a precipitation strengthening and fine grain strengthening element to strengthen the performance of cutting tool steel. N in steel has the following three functions: first, it increases the absolute content of solid solution N and combined N in steel; second, it increases the ratio of solid solution N to total N in steel, and promotes the solid solution of N in steel; third, it increases the N content in AlN and BN precipitation phases in steel, as well as the ratio of N content in AlN and BN precipitation phases to total N content, and promotes the precipitation of combined N in steel in the form of AlN and BN phases. By adding N reasonably, it is possible to produce high nitrogen cutting tool steel with good corrosion resistance, high fatigue life, and tensile strength ≥1800MPa, and the thickness of the substrate is reduced to achieve the purpose of lightweighting.

[0004] At present, the methods for increasing nitrogen in steel mainly include nitrogen blowing and alloy nitrogen addition, but there are the following problems: 1) The nitrogen addition method is complex and difficult to implement; 2) The nitrogen recovery rate is low and fluctuates greatly; 3) The nitrogen addition process is accompanied by problems such as an increase in inclusions.

[0005] The Chinese patent application with publication number CN113025780A discloses a "method for producing ultra-high nitrogen tinplate", which includes smelting molten iron to obtain molten steel; refining the molten steel, blowing nitrogen during the refining, and simultaneously evacuating the steel until the vacuum degree is controlled at 2-15KPa, then adding nitrogen-containing alloy for alloying, breaking the air after circulation, and obtaining refined molten steel; quenching the refined molten steel and continuously casting to obtain tinplate ingot with a nitrogen content of ≥150PPm. This production process is relatively complicated and requires precise control during production, which is not conducive to promotion and application.

[0006] The Chinese patent application with publication number CN117467826A discloses "a tin-plated plate for easy-open lids and its manufacturing method". The chemical composition of the tin-plated plate is calculated by weight percentage: C 0.060-0.080%, Si≤0.03%, Mn 0.15-0.25%, P≤0.015%, S≤0.010%, Al 0.04-0.06%, N 0.0060-0.0090%, and the balance is Fe and other inevitable impurities. Its chemical composition design adopts conventional composition design, but the above-mentioned problems still exist.

[0007] The Chinese patent application with publication number CN117587330A discloses "a high nitrogen and high purity tinplate and its production method". The chemical composition of the tinplate is calculated by weight percentage: C 0.06-0.08%, Si≤0.03%, Mn 0.20-0.30%, P≤0.020%, S≤0.010%, Al 0.03-0.06%, N 0.008-0.01%, As≤0.03%, the sum of Cr and Pb≤0.01%, and the balance is Fe and unavoidable impurities. Its C content is high, and the contents of residual elements As, Cr, and Pb in the steel are all high, which is not conducive to the formability and corrosion resistance of the steel plate.

[0008] The Chinese patent application with publication number CN111041153A discloses "a method and system for smelting high nitrogen tinplate molten steel", which measures the nitrogen content of the molten steel in the ladle low blowing furnace to obtain a first nitrogen content; based on the target nitrogen content, the first nitrogen content and the nitrogen blowing rate of the ladle bottom blowing furnace, obtains the bottom blowing nitrogen time t; controls the ladle bottom blowing furnace to switch to bottom blowing nitrogen, and continuously blows nitrogen into the molten steel for t time according to the nitrogen blowing rate and the nitrogen blowing pressure to obtain the first target molten steel. Its production process is complicated, difficult to implement in production, and is not conducive to promotion and application. Summary of the invention

[0009] The present invention provides a high-nitrogen cutting tool steel and a preparation method thereof, which solves the problems of poor working stability, uneven performance, easy fracture and tooth chipping common in existing cutting tool steels, reduces the segregation of cutting tool steel components, and improves the surface quality of cutting tool steel. The prepared high-nitrogen cutting tool steel has high strength, high toughness and high fatigue life, and also has good abrasion resistance, deformation resistance, impact resistance and welding performance.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A high nitrogen cutting tool steel, wherein the chemical composition of the steel is as follows by mass percentage: C 0.75%-0.85%, Si 0.10%-0.20%, Mn 1.50%-1.70%, P≤0.015%, S 0.08%-0.10%, Cr 0.60%-0.80%, Ti 0.12%-0.15%, Alt 0.015%-0.055%, N 0.026%-0.030%, B 0.0040%-0.0060%, Nd 0.0020%-0.0030%, and the balance is Fe and unavoidable impurities.

[0012] Furthermore, the microstructure of the finished steel plate is a tempered bainite structure; the properties of the finished steel plate are: yield strength ≥ 1600 MPa, tensile strength ≥ 1800 MPa, and elongation after fracture A50 ≥ 20%.

[0013] Furthermore, the thickness of the finished steel plate is 1.5 to 20.0 mm.

[0014] A method for preparing high nitrogen cutting tool steel, the process flow includes steelmaking, continuous casting, heating, hot rolling, laminar cooling, coiling, blanking, forming, welding and heat treatment; wherein the following processes are controlled:

[0015] 1) Steelmaking;

[0016] Converter smelting: top and bottom combined blowing converter smelting is adopted, the ratio of molten iron to scrap steel is (80% to 90%): (10% to 20%), and nitrogen is blown at the bottom throughout the whole process; lime and light-burned dolomite are used for slag making, and the oxygen blowing time is 12 to 16 minutes; ferrochrome and ferromanganese are added during the steel tapping process, and the steel tapping temperature is controlled at 1700℃ to 1720℃;

[0017] LF refining: add fluorite to make white slag, add molten steel into LF refining furnace, add deoxidizer to deoxidize, and fine-tune the Mn content in steel to the set range; add ferroboron, ferrochrome and ferrotitanium for alloying, add Nd alloy to modify inclusions, soft argon blowing stirring time ≥10min, calming time ≥14min;

[0018] RH vacuum treatment: After the molten steel is broken, wire feeding and nitrogen addition are carried out. The feeding amount of manganese nitride cored wire is 4.4-5.5m / t steel, and the wire feeding speed is 2.6-3.0m / s. The ladle bottom blowing device is closed during the wire feeding process.

[0019] 2) Continuous casting;

[0020] The continuous casting is carried out using a straight arc continuous casting machine, and the continuous casting superheat is controlled at 10-20℃;

[0021] 3) heating;

[0022] The hot delivery and hot charging process is adopted, the continuous casting billet heating temperature is 1220~1260℃, and the soaking time is 40~50min;

[0023] 4) Hot rolling;

[0024] Rough rolling: 3+3 pass rolling mode is adopted, and the starting rolling temperature of rough rolling is 1140~1180℃;

[0025] Finishing rolling: 7-stand hot rolling is adopted, cooling water is added between stands, and the final rolling temperature is 855~885℃;

[0026] 5) Coiling;

[0027] The coiling temperature is 450-480℃; the coiled steel plate enters the slow cooling pit for slow cooling treatment, and the slow cooling time is not less than 72h;

[0028] 6) Heat treatment;

[0029] The quenching temperature is 820-850°C, and the tempering temperature is 200-260°C.

[0030] Furthermore, during the furnace smelting process, the amount of slag discharged during steel tapping is controlled to be ≤5kg / ton of steel.

[0031] Furthermore, during the LF refining process, the deoxidizer is aluminum-manganese-iron deoxidizer, and the addition amount is 400-600 kg / furnace steel; the thickness of the top slag of the molten steel in the furnace is maintained between 30 mm and 50 mm.

[0032] Furthermore, during the RH vacuum treatment process, the nitrogen content in the manganese nitride cored wire is 7% to 8%, the manganese content is 85% to 90%, and the remainder is impurities.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] It solves the common problems of existing cutting tool steels, such as poor working stability, uneven performance, easy breakage and tooth chipping, reduces the segregation of cutting tool steel components, and improves the surface quality of cutting tool steel. The prepared high-nitrogen cutting tool steel has high strength, high toughness and high fatigue life, as well as good wear resistance, deformation resistance, impact resistance and welding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a metallographic structure photograph of the high nitrogen cutting tool steel produced in Example 1 of the present invention.

[0036] Figure 2 This is an inclusion morphology diagram of the high nitrogen cutting tool steel produced in Example 1 of the present invention.

[0037] Figure 3 This is a metallographic photograph of the cutting tool steel produced in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The invention provides a high nitrogen cutting tool steel with high fatigue life, comprising the following chemical components by mass percentage: C 0.75% to 0.85%, Si 0.10% to 0.20%, Mn 1.50% to 1.70%, P≤0.015%, S 0.08% to 0.10%, Cr 0.60% to 0.80%, Ti 0.12% to 0.15%, Alt 0.015% to 0.055%, N 0.026% to 0.030%, B 0.0040% to 0.0060%, Nd 0.0020% to 0.0030%, and the balance is Fe and unavoidable impurities. After heat treatment, the yield strength of the high nitrogen cutting tool steel plate is ≥1600MPa, the tensile strength is ≥1800MPa, and the elongation after fracture A50 is ≥20%. Compared with ordinary cutting tool steel plates, the fatigue life of high nitrogen cutting tool steel plates is increased by more than 800,000 times, and the corrosion resistance is improved by more than 80%. The microstructure of high nitrogen cutting tool steel is tempered troostite structure with good formability.

[0039] The reasons for selecting the chemical elements in the high nitrogen cutting tool steel of the present invention and their working principles are as follows:

[0040] C: It exists in the form of cementite, TiC and interstitial solid solution in cutting tool steel and is the most important strengthening element in steel. C plays a beneficial role in improving the strength and hardness of cutting tool steel, and nano-sized TiC is beneficial for improving fatigue performance and wear resistance. In addition, a high C content is beneficial to the heat treatment process. The present invention controls the C content to 0.75% to 0.85%.

[0041] Si: It plays a role in calming and deoxidizing in cutting tool steel, but too high Si content will have an adverse effect on the surface quality of cutting tool steel. Therefore, the present invention controls the Si content to 0.10% to 0.20%.

[0042] Mn: It is a commonly used solid solution strengthening element in steel. In order to ensure the strength of the cutting tool steel, the Mn content is controlled to be 1.50% to 1.70% in the present invention.

[0043] P: After P aggregates and grows at the grain boundary, it will reduce the formability and toughness of the cutting tool steel and cause cold brittleness. Therefore, the P content is controlled to be ≤ 0.015% in the present invention.

[0044] S: is a harmful element in steel, and the lower its content, the better. However, in the present invention, S generates a large amount of Mn-SBN-Nd compounds, as well as NdS and Nd2O2S inclusions in the steel, which can effectively improve the cutting performance. Therefore, the present invention controls the S content to 0.08% to 0.10%.

[0045] Ti: It is relatively active in steel and plays a role in precipitation strengthening. On the one hand, Ti combines with C and N to generate TiN, TiC and Ti(C, N), among which TiC and Ti(C, N) are beneficial to the strength of steel. On the other hand, TiC can improve the wear resistance of cutting tool steel and effectively improve the fatigue resistance of cutting tool steel. The present invention controls the Ti content to 0.12% to 0.15%.

[0046] Nd: Its main function is to modify inclusions and play the role of oxide metallurgy, forming spherical and point-shaped Mn-SOBN-Nd inclusions and NdS, NdLa2O3, and Nd2O2S inclusions, thereby improving the fatigue resistance and wear resistance of cutting tool steel. Therefore, the present invention controls the Nd content to 0.0020% to 0.0030%.

[0047] N: A certain amount of N can combine with Ti, B, and C to generate Ti (C, N), BN, etc., which plays a role in precipitation strengthening and grain refinement in steel. N has the following three functions in steel: First, it increases the absolute content of solid solution N and combined N in steel; second, it increases the ratio of solid solution N to total N in steel and promotes the solid solution of N in steel; third, it increases the N content in AlN and BN precipitation phases in steel, as well as the ratio of N to total N in AlN and BN precipitation phases, promotes the precipitation of combined N in steel in the form of AlN and BN phases, and improves the strength of cutting tool steel. In the present invention, the N content is controlled at 0.026% to 0.030%.

[0048] B: Combined with N in cutting tool steel to form BN particles, BN particles have good stability, are not easily dissolved at high temperatures, and have the effect of improving cutting performance. In addition, B segregates at the austenite grain boundary to inhibit the precipitation of proeutectoid ferrite, allowing carbides to disperse and precipitate in the low temperature region. The present invention controls the B content to 0.0040% to 0.0060%.

[0049] Alt: reacts with N to form AlN, which plays a role in refining grains and hindering grain growth. When combined with specific processes, it can effectively improve the strength of cutting tool steel. The present invention controls the Alt content to 0.015% to 0.055%

[0050] It should be pointed out that obtaining high nitrogen cutting tool steel with good strength-toughness matching, cutting tool surface wear resistance, excellent corrosion resistance and forming performance, which is conducive to cutting tool thinning and fatigue life improvement, is not only related to chemical composition design, but also to production technology. Only through reasonable composition design combined with optimized production technology can the expected microstructure be obtained, thereby effectively improving the wear resistance, fatigue resistance and corrosion resistance of cutting tool steel.

[0051] The present invention also provides a method for producing a high nitrogen cutting tool steel plate, the process flow includes: steelmaking → continuous casting → heating → hot rolling → laminar cooling → coiling → blanking → forming → welding → heat treatment, etc. The specific steps are as follows:

[0052] 1. Converter smelting: top and bottom combined blowing converter smelting is adopted, the ratio of molten iron and scrap steel in the converter is (80%~90%):(10%~20%), nitrogen is blown at the bottom throughout the whole process, and lime and light-burned dolomite are used to make slag, the oxygen blowing time is 12~16min, and steel is tapped when the end composition and temperature meet the steel tapping requirements. The tapping port should be round, ferrochrome and ferromanganese are added during the steel tapping process, and the tapping temperature is controlled between 1700℃ and 1720℃; the slag amount is controlled to be ≤5kg / ton steel during steel tapping.

[0053] 2. LF refining: add fluorite to make white slag, add molten steel into LF refining furnace, add deoxidizer to deoxidize, aluminum manganese iron deoxidizer is used as deoxidizer, and the addition amount is 400-600 kg per furnace of steel. Fine-tune the Mn content in the steel to within the set range; add ferroboron, ferrochrome and ferrotitanium for alloying during the refining process, then add Nd alloy to denature the inclusions, the soft argon stirring time is ≥10min, and the calming time is ≥14min. During the refining process, the top slag thickness of the molten steel in the furnace is kept between 30 and 50mm.

[0054] RH vacuum treatment: feeding wire to nitrogen-enrich the molten steel after RH vacuum treatment, feeding manganese nitride cored wire into the molten steel after RH vacuum treatment through a wire feeder, the feeding amount is 4.4-5.5m / t steel, the wire feeding speed is 2.6-3.0m / s, and the ladle bottom blowing device is closed during the wire feeding process. The nitrogen content of the manganese nitride cored wire is 7%-8%, the manganese content is 85%-90%, and the rest is impurities.

[0055] Continuous casting: straight arc continuous casting machine is used for continuous casting, the superheat is controlled between 10 and 20°C, and the fixed length of the continuous casting billet is 10.7m.

[0056] Heating: When heating the continuous casting billet, the hot delivery and hot charging process is adopted. The heating temperature is 1220-1260℃ and the soaking time is 40-50min to fully dissolve the alloy elements in the steel.

[0057] Hot rolling: Rough rolling adopts 3+3 pass rolling mode, and the starting rolling temperature of rough rolling is 1140~1180℃. Finishing rolling adopts 7-stand hot rolling mode, cooling water is added between stands, and the final rolling temperature is 855~885℃.

[0058] Coiling: The coiling temperature is 450-480℃. The steel plate after coiling enters the slow cooling pit for slow cooling treatment. It can be moved only after more than 72 hours of slow cooling.

[0059] Forming: Cutting according to set dimensions, such as cutting into round blanks of different diameters and forming them according to the size of a metal saw to form a saw back.

[0060] Welding: Welding is performed according to the set structure, such as welding the saw back and saw teeth of a certain shape to form the required cutting tool.

[0061] Heat treatment: After quenching (temperature 820-850℃) + tempering (temperature 200-260℃), a high nitrogen cutting tool steel with certain strength and toughness matching and good wear resistance is obtained.

[0062] High nitrogen cutting tool steel undergoes a series of tests and inspections before it becomes a finished product.

[0063] The high nitrogen cutting tool steel prepared according to the method of the present invention has better performance than ordinary cutting tool steel. On the basis of having good strength and toughness matching, it further achieves the goals of cutting tool thinning, improved fatigue life and excellent corrosion resistance.

[0064] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0065] [Example]

[0066] The chemical compositions of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 1.

[0067] Table 1 Chemical composition (mass fraction / %)

[0068]

[0069]

[0070] The steelmaking-coiling production process parameters of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 2.

[0071] Table 2 Steelmaking-coiling production process parameters

[0072]

[0073] The heat treatment process systems of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 3.

[0074] Table 3 Heat treatment process system

[0075]

[0076] The mechanical properties, fatigue resistance and corrosion resistance of the finished products of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 4.

[0077] Table 4 Mechanical properties, fatigue resistance and corrosion resistance of finished products

[0078]

[0079]

[0080] Note: The first parameter of the item "Improvement of fatigue performance" in the table is compared with Comparative Example 1, and the second parameter is compared with Comparative Example 2.

[0081] The continuous casting speeds of Examples 1 to 6 and Comparative Examples 1 to 2 were all 1.1 m / min, and the thickness of the finished steel plates was all 6.0 mm.

[0082] The metallographic structure and inclusion morphology of the high nitrogen cutting tool steel plate prepared in Example 1 are as follows: Figure 1 , Figure 2 As shown, the metallographic structure of the cutting tool steel plate prepared in Comparative Example 1 is as follows Figure 3 As shown. Figure 1 , Figure 3 It can be seen that the metallographic structure of Example 1 is tempered martensite with a grain size of 11 to 11.5, while the metallographic structure of Comparative Example 1 is tempered martensite with a grain size of 9 to 9.5.

[0083] It can be seen from Table 3 that the yield strength of the finished steel plates prepared in Examples 1 to 6 is ≥1600MPa, the tensile strength is ≥1800MPa, and the elongation after fracture is A 50 As the main parameter to measure the performance of cutting tool steel, compared with ordinary cutting tool steel, the fatigue resistance of the finished steel plates prepared in Examples 1 to 6 is improved by more than 800,000 times, the corrosion resistance is improved by more than 80%, and the forming performance is good.

[0084] Conclusion: The high nitrogen cutting tool steel prepared according to the chemical composition and production process of the present invention has excellent wear resistance, fatigue resistance and corrosion resistance after heat treatment, and is particularly suitable for products with high fatigue performance requirements.

[0085] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high nitrogen cutting tool steel, characterized in that: The chemical composition of the steel by mass percentage is: C 0.75%~0.85%, Si 0.10%~0.20%, Mn 1.50%~1.70%, P≤0.015%, S 0.08%~0.10%, Cr0.60%~0.80%, Ti 0.12%~0.15%, Alt 0.015%~0.055%, N 0.026%~0.030%, B0.0040%~0.0060%, Nd0.0020%~0.0030%, and the balance is Fe and unavoidable impurities.

2. A high nitrogen cutting tool steel according to claim 1, characterized in that: The microstructure of the finished steel plate is a tempered bainite structure; the properties of the finished steel plate are: yield strength ≥ 1600MPa, tensile strength ≥ 1800MPa, and elongation after fracture A50 ≥ 20%.

3. The high nitrogen cutting tool steel according to claim 1, characterized in that: The thickness of the finished steel plate is 1.5 to 20.0 mm.

4. A method for preparing a high nitrogen cutting tool steel as claimed in claim 1, 2 or 3, characterized in that: The process includes steelmaking, continuous casting, heating, hot rolling, laminar cooling, coiling, blanking, forming, welding and heat treatment; the following processes are controlled: 1) Steelmaking; Converter smelting: top and bottom combined blowing converter smelting is adopted, the ratio of molten iron to scrap steel is (80% to 90%): (10% to 20%), and nitrogen is blown at the bottom throughout the whole process; lime and light-burned dolomite are used for slag making, and the oxygen blowing time is 12 to 16 minutes; ferrochrome and ferromanganese are added during the steel tapping process, and the steel tapping temperature is controlled at 1700℃ to 1720℃; LF refining: add fluorite to make white slag, add molten steel into LF refining furnace, add deoxidizer to deoxidize, and fine-tune the Mn content in steel to the set range; add ferroboron, ferrochrome and ferrotitanium for alloying, add Nd alloy to modify inclusions, soft argon blowing stirring time ≥10min, calming time ≥14min; RH vacuum treatment: After the molten steel is broken, wire feeding and nitrogen addition are carried out. The feeding amount of manganese nitride cored wire is 4.4-5.5m / t steel, and the wire feeding speed is 2.6-3.0m / s. The ladle bottom blowing device is closed during the wire feeding process. 2) Continuous casting; The continuous casting is carried out using a straight arc continuous casting machine, and the continuous casting superheat is controlled at 10-20℃; 3) heating; The hot delivery and hot charging process is adopted, the continuous casting billet heating temperature is 1220~1260℃, and the soaking time is 40~50min; 4) Hot rolling; Rough rolling: 3+3 pass rolling mode is adopted, and the starting rolling temperature of rough rolling is 1140~1180℃; Finishing rolling: 7-stand hot rolling is adopted, cooling water is added between stands, and the final rolling temperature is 855~885℃; 5) Coiling; The coiling temperature is 450-480℃; the coiled steel plate enters the slow cooling pit for slow cooling treatment, and the slow cooling time is not less than 72h; 6) Heat treatment; The quenching temperature is 820-850°C, and the tempering temperature is 200-260°C.

5. The method for preparing high nitrogen cutting tool steel according to claim 4, characterized in that: During the furnace smelting process, the slag amount during steel tapping is controlled to be ≤5kg / ton of steel.

6. The method for preparing high nitrogen cutting tool steel according to claim 4, characterized in that: In the LF refining process, the deoxidizer is aluminum-manganese-iron deoxidizer, and the addition amount is 400-600 kg / furnace steel; the thickness of the top slag of the molten steel in the furnace is maintained between 30 mm and 50 mm.

7. The method for preparing high nitrogen cutting tool steel according to claim 4, characterized in that: During the RH vacuum treatment, the nitrogen content in the manganese nitride cored wire is 7% to 8%, the manganese content is 85% to 90%, and the remainder is impurities.

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