Steel with excellent nitriding performance, preparation method and nitriding method

Abstract

The present invention discloses a steel with excellent nitriding performance, a preparation method, and a nitriding method. The steel comprises, by mass percentage, 0.001-0.0049% C, 0.01-0.020% Mn, 0.010-0.035% Als, 0.030-0.055% Ti, 0.0010-0.0020% B, and 0.001-0.004% Mo, wherein 0.5≤(Ti-3.4N-3S) / C≤10, and 0≤(S+P+As+Sn+Cu+Sb) / (B+Mo)≤12. By strictly controlling trace elements and combining a small amount of Ti, Mo, and B, the grain boundary performance is improved, the formation of a large number of large-sized AlO, MnS, and Ti inclusions and micropores at the structure and grain boundaries is avoided, and the aggregation of nitrides at these locations during the subsequent nitriding process, which leads to the generation of striation defects, is avoided. At the same time, the nitriding performance is improved, and a nitrided steel with excellent nitriding performance is obtained.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials and gas nitriding technology, and particularly relates to a steel with excellent nitriding performance, a preparation method and a nitriding method. Background Art

[0002] The most frequently used items in the kitchen are cookware. They are repeatedly heated, acidic, and alkaline for long periods of time, which causes corrosion on the surface of the cookware. At the same time, the cookware must be cleaned after use, and some water stains will remain on the surface. In a humid and dark environment, it is extremely easy to corrode and rust, affecting the appearance and even causing the product to be scrapped.

[0003] Currently, cookware is available in a variety of materials on the market, including aluminum alloy, stainless steel, iron, aluminum, enamel, and coatings. However, these materials are expensive to produce, and trace alloying elements migrate during cooking, being absorbed by the body along with the food, seriously impacting human health. While coated pans have a good coating, offering excellent corrosion resistance and non-stick properties, the constant friction between the pan and the spatula can easily cause the coating to crack, making the product unsightly and prone to corrosion. Furthermore, when cooking over high heat, the Teflon coating can degrade and produce toxic substances, potentially impacting human health. Iron, a traditional Chinese cookware material, is also prone to rusting and becoming scrapped during actual use.

[0004] Currently, there is a type of cookware on the market: nitriding pots. Nitriding forms a nitriding layer on the surface of the pot, giving the pot surface excellent corrosion and wear resistance, greatly extending its service life. The low production cost makes this product extremely popular. However, during the nitriding process, the steel plate is prone to forming a nitriding layer structure. This structure is both corrosion-resistant and has high hardness, but it is also brittle and prone to cracking after cooling. Furthermore, if the substrate is not selected correctly and the nitriding process is not properly used, the nitriding layer is prone to cracking, further leading to product failure. Therefore, only by matching the appropriate substrate and nitriding process can an excellent and qualified product be obtained.

[0005] However, the nitriding pot's production process involves blanking steel coils, stamping, cleaning, nitriding, blackening, and finally finishing. However, in actual production, defects such as cracking and streaking are prone to occur. This is significantly influenced by the steel plate's substrate and the nitriding process. Chinese Patent Publication No. CN106222570A, "A Nitriding Steel Substrate with Excellent Corrosion Resistance and Production Method," describes a nitriding steel substrate with excellent corrosion resistance. Its chemical composition (by mass fraction) is as follows: C: 0.01-0.1%, Mn: 0.1-1.0%, Si: 0.01-0.1%, P ≤ 0.02%, S ≤ 0.01%, Als: 0.5-1.5%, N ≤ 0.005%, Cr: 0.1-1.5%, Cu: 0.01-1.0%, Ni: 0.01-1.0%, with the remainder being Fe and unavoidable impurities. After nitriding, a nitriding pot with excellent corrosion resistance is obtained. This patent adopts a low-C, high-Als, and high-Cr composition system, and adds elements such as Cu and Ni to the steel, which will inevitably increase the cost of the product; at the same time, this patent mainly solves the corrosion problem, and high Als under this composition system is very likely to cause stripe defects.

[0006] Chinese patent publication number CN101649441B, "Nitriding Process for Austenitic Stainless Steel Materials," reports a nitriding treatment method for austenitic stainless steel. A two-step process is used: first, pre-treatment with annealing at 810°C for 2 hours, followed by sand blowing, and then nitriding. After holding at 600°C for 10-20 hours, the temperature is raised to 620-650°C and held for 10-20 hours to obtain a nitrided layer of about 20μm. The nitriding process provided in this patent is a stainless steel process. Furthermore, the process requires 20-40 hours of treatment, a long nitriding time, and a complex process. Furthermore, the corrosion resistance of the nitrided sample is not described, and the effectiveness is unknown.

[0007] Chinese Patent Publication No. CN206761522U, "Pots and Cooking Utensils," reports on a pot with multiple coatings formed on the inner surface, a non-stick outer layer, and corrosion and wear resistance. The coating is formed by plasma spraying and is made of metal oxides (Al2O3, TiO2, ZrO2) and metal fluorides (PTFE or PFA), i.e., a coated pot. The presence of these three layers on the inner surface makes the production process complex and the production cost high. The resulting pot is expensive and toxic in high-temperature environments.

[0008] Chinese Patent Publication No. CN110117747A, "A Method for Producing High-Al Nitrided Steel," describes a high-Al nitrided steel with the following chemical composition by mass: C: 0.36-0.40%, Si: 0.22-0.35%, Mn: 0.16-0.22%, P ≤ 0.015%, S ≤ 0.008%, Cr: 1.45-1.55%, Mo: 0.16-0.22%, Al: 0.75-1.0%, Ni ≤ 0.3%, Cu ≤ 0.2%, with the remainder being Fe and unavoidable impurities. This steel belongs to the specialty steel category, with high Cr, Mo, and Al contents. Its products are primarily used in high-fatigue and high-wear-resistant mechanical equipment such as screws, barrels, and cylinders. This patent addresses the challenges of high Al content in steelmaking and rolling processes, resulting in slabs with excellent surface quality and mechanical properties. Summary of the Invention

[0009] The purpose of the present invention is to solve the above technical problems and provide a steel with excellent nitriding performance, a preparation method and a nitriding method, which effectively solve the technical defects of nitriding surface cracking and the appearance of stripe defects on the surface after nitriding.

[0010] To achieve the above object, the present invention provides a steel with excellent nitriding performance, wherein the chemical composition of the steel comprises, by mass percentage, C: 0.001-0.0049%, Si: ≤0.03%, Mn: 0.01-0.020%, P: ≤0.015%, S: ≤0.012%, Als: 0.010-0.035%, N: ≤0.005%, Ti: 0.030-0.055%, As <0.005, Sn <0.005, Cu ≤0.010, Sb ≤0.005, B: 0.0010-0.0020, Mo: 0.001-0.004, and the remainder is Fe and unavoidable impurities;

[0011] 0.5≤(Ti-3.4N-3S) / C≤10, 0≤(S+P+As+Sn+Cu+Sb) / (B+Mo)≤12.

[0012] Furthermore, the (Ti-3.4N-3S) / C is preferably 2-7.

[0013] Furthermore, the (S+P+As+Sn+Cu+Sb) / (B+Mo) is preferably 5-12.

[0014] To ensure that the nitrided steel of the present invention has excellent nitriding performance and can effectively solve the problems of cracking and striping defects under the subsequent specific nitriding process, it is mainly based on the following principles:

[0015] 1) Carbon (C): It is an economical strengthening element in steel grades and affects the strength of steel plates. Generally, increasing its content increases strength, but excessively high carbon content can deteriorate formability. Furthermore, the presence of carbon easily forms carbides and pearlite in the structure. These structures can easily act as defects during the nitriding process, leading to nitrogen segregation in the steel and causing problems such as streaking. The carbon content in this patent is controlled at 0.001-0.0049%. This composition system is distinct from a low-carbon composition system, as its carbon content affects the Fe-N phase transition temperature during nitriding, particularly around 580°C. Furthermore, in an ultra-low-carbon composition system, the structure is primarily pure ferrite, devoid of carbides and pearlite, thus avoiding defects caused by these locations during nitriding.

[0016] 2) Silicon (Si): It plays a role in solid solution strengthening in steel and can be added to steel as a reducing agent and deoxidizer during the smelting process. At the same time, silicon can improve the hardenability and tempering resistance of steel. However, if the Si content is too high, the structure will be brittle and hard. Therefore, it is not recommended to control the Si content to ≤0.03%.

[0017] 3) Manganese (Mn): As a commonly used desulfurization and deoxidation element, it can be infinitely dissolved in ferrite and austenite, improving the strength and wear resistance of the steel plate, and has little effect on the material's formability. Therefore, the Mn content in the present invention is controlled at 0.1-0.3%.

[0018] 4) Phosphorus P: P is prone to segregation, thereby reducing the plasticity, low-temperature toughness and welding performance of steel. At the same time, the P element is prone to segregation at the grain boundaries of the structure, causing the location of grain boundary defects to be lost. During subsequent nitriding, nitrogen atoms preferentially segregate at the grain boundaries, and after nitrogen atoms segregate to a certain extent, they will cause deformation of the structure and lead to the formation of cracks.

[0019] 5) Sulfur S: It is easy to combine with Mn in steel to form MnS and other large-scale precipitates, which are not conducive to nitriding. At the same time, it makes the steel hot brittle, reduces the ductility and toughness of the steel, and causes cracks during rolling.

[0020] 6) Titanium Ti: It has a strong affinity with C and N. It is very easy to combine with N during the nitriding process, promoting nitriding. At the same time, Ti is easy to form TiN and Ti (C, N) during the preparation process. However, the Ti content should not be too high. If the Ti content is too high, large-sized precipitates formed in the structure will cause crystal distortion, and these positions will easily become nitriding defect points. At the same time, the general nitriding temperature is between 500 and 650 ° C. At this temperature, TiC particles are easy to precipitate and grow, causing structural distortion, which in turn leads to defects. Therefore, the Ti content is required to be: 0.5≤(Ti-3.4N-3S) / C≤10

[0021] 7) Aluminum Al: It is a deoxidizer that can avoid the generation of other oxides and prevent porosity defects in molten steel. Al has a strong affinity for N, which can play a nitrogen hardening role and promote the nitriding process. However, if Al is too high, it will form large-sized alumina inclusions with oxygen in the steel. If the nitriding process is not appropriate during the nitriding process, it is very easy for N atoms to combine with aluminum atoms in the alumina, resulting in the generation of stripe defects.

[0022] 8) Arsenic (As) and tin (Sn) are two elements that need to be strictly controlled. They are toxic to the human body and are usually residual elements retained in steel. The content of arsenic (As) and tin (Sn) in some steels is 0.01-0.005%. Therefore, this patent requires control during steelmaking to avoid being absorbed by the human body and causing cancer in the subsequent preparation of cookware.

[0023] 9) On the one hand, the B element is easy to combine with the N element to form BN precipitates. At the same time, the addition of the B element can effectively improve the performance of the grain boundary in the organization, avoid the generation of a large number of defects, and improve the diffusion of the N element in the organization during the nitriding process.

[0024] 10) Cu is a hot brittle element and is easily liquefied during high temperature processes, especially during hot rolling. When liquefied, Cu tends to be enriched at the grain boundaries, which causes N to segregate easily. Therefore, the Cu content needs to be controlled to ≤0.010%.

[0025] 11) Sb is a residual element, and currently a large amount of scrap steel is easily added during the smelting process of molten steel. At the same time, for cost considerations, the residual elements in the scrap steel are not controlled. In addition, Sb is also easy to segregate at the grain boundaries during the hot rolling process, resulting in the segregation of N elements during the nitriding process, leading to the generation of stripe defects.

[0026] 12) Mo is usually used as a corrosion resistance element and a heat resistance element, and the effect of Mo in nitriding steel is similar to that of B. It can effectively improve the defects at the grain boundaries and improve the nitriding efficiency. At the same time, Mo is a thermal stability element, which can effectively improve the nitriding process. Due to the structural changes in the ferrite structure, some nitrogen elements are concentrated in local positions, resulting in nitriding defects.

[0027] S, P, A S Elements such as Sn, Sb, and Cu are easily segregated. In the actual production process, they will segregate at the grain boundaries at different temperatures, resulting in the formation of hard and brittle items and defects such as dislocations and holes at the grain boundaries. In the subsequent nitriding process, N atoms will preferentially gather here, resulting in Fe xNitrogen forms, causing bulges and cracks in the material. Because these elements inevitably remain in the actual steelmaking process, adding a small amount of Mo and B to the steel can effectively improve grain boundary segregation and also contribute to the precipitation of Ti in the steel. Therefore, it is important to control the content within a reasonable range to avoid excessive amounts of harmful elements, which can lead to defects in the subsequent nitriding process.

[0028] Also provided is a method for preparing the steel as described above, comprising molten iron pretreatment - converter smelting - RH process - continuous casting - hot rolling process - cold rolling - annealing process - leveling;

[0029] During the hot rolling process, the furnace temperature is 1200±20° C. and the furnace time is 120 to 150 minutes.

[0030] Furthermore, during the hot rolling process, the dephosphorization water in the rough rolling and finishing rolling is fully opened, and the water pressure is 170-190 Bar, and the final rolling temperature is 890±20°C.

[0031] During the hot rolling process, the furnace temperature and time should not be too high, which will easily lead to the burning of the effective element Ti in the steel. At the same time, the TiN precipitated particles formed are very easy to grow, which is called an obvious defect in the steel and causes the formation of strips during the subsequent nitriding process. The dephosphorization water is fully opened in the rough rolling and finishing rolling, and the water pressure is 170-190 Bar. In order to avoid some iron oxide scale being pressed into the matrix during the hot rolling process, resulting in unclean subsequent pickling and strip defects during the nitriding process, the final rolling temperature is 890±20℃. Because the dephosphorization water is opened in the rough rolling and finishing rolling processes, it will inevitably affect the final rolling temperature. A low final rolling temperature will affect the surface grains of the organization, resulting in the easy appearance of orange peel in the subsequent process, coarse surface grains, and smaller core grains. During the nitriding process, the diffusion of nitrogen is unfavorable, affecting the nitriding efficiency and the formation of nitrides.

[0032] Furthermore, in the annealing process, the continuous annealing temperature is 800±10°C and the soaking time is 55-90 seconds. To ensure that the material has certain formability, the soaking time should not be too long. Excessive soaking time will lead to the large-scale generation of TiN and TiC precipitation particles in the structure, affecting the role of effective Ti in the nitriding process.

[0033] Furthermore, the furnace temperature is 1210-1220°C.

[0034] Furthermore, the water pressure is 180-190 Bar, and the final rolling temperature is 890-910°C.

[0035] Furthermore, the continuous annealing temperature is 800-810°C.

[0036] Furthermore, the flattening elongation is 0.6% to 2.0% to eliminate the yield platform and ensure the plate shape.

[0037] Finally, a method for producing nitrided steel using the aforementioned steel is provided, comprising the following steps: heating the steel to a nitriding temperature of 550-600°C in a furnace, passing ammonia gas, and maintaining the temperature for 1-4 hours; decomposing the ammonia gas into nitrogen atoms, which diffuse into the surface of the steel plate. At this temperature, the nitrogen atoms can effectively form a nitrided layer on the surface of the steel plate, because the presence of a small amount of effective titanium in the steel effectively promotes the diffusion of nitrogen in the substrate. The temperature should not be too high. If the temperature is too high, the amount of ammonia decomposed is too high, the nitrogen content is high, and the nitrogen potential on the steel plate surface is high, forming a nitrogen-containing austenite structure. At the same time, the nitrogen-containing austenite will subsequently transform to form Fe2-3N, which is hard and brittle, causing cracking in the surface of the steel plate. At the same time, the temperature should not be too low, as it will result in a small amount of ammonia decomposition and slow nitrogen diffusion, affecting efficiency. On the other hand, at 550-600°C, TiC and MnS structures in steel are very easy to precipitate, which occurs simultaneously with the diffusion of N elements. Therefore, aggregation will occur around some precipitated particles, leading to the generation and growth of nitrides, which will lead to the generation of stripe defects. Therefore, the temperature needs to be controlled.

[0038] Cooling with the furnace, the cooling rate is 20 ~ 60 ℃ / min. To improve production efficiency, the cooling rate should be as fast as possible, but not too fast, because the nitriding process relies on the diffusion of nitrogen atoms, but the surface nitrogen content of the steel plate is relatively high. If the cooling rate is too fast, the surface nitrided layer will not have time to diffuse, resulting in micro cracks, which will affect the subsequent perforation and corrosion resistance.

[0039] Cookware made from nitrided steel of the present invention has excellent corrosion resistance and can effectively solve the problems of surface cracking and surface streaking defects after nitriding. The prepared nitrided cookware has a simple nitriding process, a short nitriding cycle, high work efficiency, low manufacturing cost, and is economical and practical.

[0040] For the composition system described in the present invention, during actual hot rolling, the hot rolling temperature is controlled at 1200±20°C, and the holding time is 120-150 minutes. Excessively high heating temperatures and prolonged holding times will cause residual segregated star elements to aggregate at grain boundaries, leading to the easy precipitation of TiN in the steel, forming large-sized inclusions. The amount of effective Ti in the steel will also be significantly reduced, which is detrimental to the subsequent nitridability of the steel plate. At the same time, at nitriding temperatures of 550-600°C, the microstructure will not change, and the diffused nitrogen atoms will aggregate there, resulting in the appearance of bulges during the nitriding process. Furthermore, the hot rolling finish temperature is controlled at 890-910°C, and the annealing temperature is controlled at 800-810°C. This, on the one hand, controls the presence of effective Ti in the steel, improves the nitridability of the material, and prevents the large-sized precipitation of TiN and TiC in the steel, which become inclusions, and causes the burning of elements such as Ti, B, and Mo. On the other hand, it can effectively improve the recovery and recrystallization of the structure to obtain a single ferrite, and promote the uniform diffusion of nitrogen atoms in the steel, avoiding the accumulation of local defects and the formation of abnormal nitrides. Therefore, an excellent defect-free nitrided layer can be obtained.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention improves grain boundary properties by strictly controlling trace elements such as Al, S, As, and Cu, while adding a small amount of elements such as Ti, Mo, and B. This prevents the formation of a large number of large-sized inclusions and micropores of AlO, MnS, and Ti (C, N) at the structure and grain boundaries, thereby preventing the accumulation of nitrides at these locations during the subsequent nitriding process, which would lead to the generation of streak defects. At the same time, the nitriding performance is improved, thereby obtaining nitrided steel with excellent nitriding properties.

[0043] The cookware prepared with the nitrided steel of the present invention has good corrosion resistance and can effectively solve the problems of cracking on the nitrided surface and stripe defects on the surface after nitriding; the prepared cookware has the effects of low price, economy and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a physical diagram of Example 2-A;

[0045] Figure 2 This is the poor nitriding diagram of Example 4-B;

[0046] Figure 3 This is the bar graph of nitriding in comparative example 2;

[0047] Figure 4 This is the nitriding cracking diagram of comparative example 5. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] In order to realize the defect-free nitrided steel plate mentioned in the present invention, the following examples are provided: the chemical compositions used in the examples and comparative samples are shown in Table 1.

[0050] C Si Mn P S Als N Ti As Sn Cu Sb B Mo Formula 1 Formula 2 Example 1 0.002 0.02 0.015 0.008 0.008 0.012 0.005 0.045 0.001 0.003 0.008 0.002 0.0012 0.0025 2.0 8.1 Example 2 0.004 0.01 0.02 0.01 0.005 0.018 0.001 0.03 0.002 0.002 0.01 0.003 0.002 0.001 2.9 10.7 Example 3 0.002 0.02 0.02 0.009 0.005 0.03 0.002 0.035 0.001 0.004 0.005 0.002 0.0015 0.003 6.6 5.8 Example 4 0.002 0.03 0.018 0.012 0.012 0.028 0.005 0.055 0.005 0.001 0.004 0.002 0.002 0.0035 1.0 6.5 Example 5 0.002 0.02 0.01 0.01 0.008 0.03 0.002 0.042 0.002 0.005 0.005 0.003 0.0018 0.004 5.6 5.7 Example 6 0.0049 0.02 0.015 0.015 0.006 0.026 0.002 0.05 0.002 0.004 0.01 0.002 0.002 0.0028 5.0 8.1 Example 7 0.002 0.01 0.012 0.012 0.008 0.035 0.002 0.035 0.001 0.005 0.005 0.005 0.0015 0.0015 2.1 12.0 Comparative Example 1 0.004 0.02 0.03 0.32 0.02 0.02 0.005 0.04 0.002 0.005 0.008 0.005 0.0018 0.003 -9.2 75 Comparative Example 2 0.002 0.02 0.02 0.015 0.008 0.055 0.01 0.05 0.002 0.004 0.01 0.005 0.002 0.0018 -4 11.5 Comparative Example 3 0.002 0.03 0.015 0.005 0.001 0.025 0.01 0.075 0.002 0.004 0.008 0.005 0.0018 0.0025 19 5.8 Comparative Example 4 0.005 0.01 0.02 0.005 0.008 0.03 0.005 0.02 0.005 0.004 0.008 0.006 0.0015 0.003 -4.2 8.0 Comparative Example 5 0.005 0.02 0.015 0.008 0.001 0.025 0.005 0.045 0.01 0.012 0.015 0.008 0.0005 0.0005 5 54.0 Comparative Example 6 0.021 0.02 0.02 0.008 0.01 0.04 0.012 0.03 0.005 0.01 0.01 0.005 0.001 0.002 -1.9 16.0

[0051] After continuous casting, the molten steel undergoes hot rolling, pickling, cold rolling and continuous annealing. The main process parameters are shown in Table 2.

[0052] Table 2 Production process parameters

[0053]

[0054]

[0055] The performance of each example and comparative example is shown in Table 3.

[0056] Table 3 Effects after implementation of each embodiment

[0057] Serial number serial number Defects such as stripes and cracks 1 Example 1-A qualified 2 Example 2-A Qualified (see Figure 1 ) 3 Example 2-B Violence 4 Example 3-A qualified 5 Example 4-A qualified 6 Example 4-B Poor nitriding (see Figure 2 ) 7 Example 5-A qualified 8 Example 5-B Poor nitriding 9 Example 6-A qualified 10 Example 6-B Cracking 11 Example 7-A qualified 12 Example 7-B Violence 13 Comparative Example 1 Poor nitriding 14 Comparative Example 2 Violence (see Figure 3 ) 15 Comparative Example 3 Violence 16 Comparative Example 4 Violence 17 Comparative Example 5 Cracking (see Figure 4 ) 18 Comparative Example 6 Violence

[0058] As can be seen from the above examples, cookware made from the nitrided steel of the present invention exhibits excellent corrosion resistance and effectively addresses surface cracking and post-nitriding surface streaking defects. The resulting nitrided cookware features a simple nitriding process, a short nitriding cycle, high efficiency, and low manufacturing costs, making it economical and practical.

[0059] The above description only provides a specific exemplary description of the present invention. It should be noted that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the technical concept and technical solution of the present invention, or the technical concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A steel with excellent nitriding performance, characterized by: The chemical composition of the steel includes, by mass percentage, C: 0.001-0.0049%, Si: ≤0.03%, Mn: 0.01-0.020%, P: ≤0.015%, S: ≤0.012%, Als: 0.010-0.035%, N: ≤0.005%, Ti: 0.030-0.055%, As<0.005, Sn<0.005, Cu≤0.010, Sb≤0.005, B: 0.0010-0.0020, Mo: 0.001-0.004, and the remainder is Fe and unavoidable impurities; 2≤(Ti-3.4N-3S) / C≤7, 5≤(S+P+As+Sn+Cu+Sb) / (B+Mo)≤12.

2. A method for preparing the steel according to claim 1, characterized in that: The preparation method comprises: molten iron pretreatment - converter smelting - RH process - continuous casting - hot rolling process - cold rolling - annealing process - leveling; During the hot rolling process, the furnace temperature is 1200±20° C. and the furnace time is 120 to 150 minutes.

3. The method for preparing steel according to claim 2, characterized in that: During the hot rolling process, the dephosphorization water in the rough rolling and finishing rolling is fully opened, and the water pressure is 170-190 Bar, and the final rolling temperature is 890±20°C.

4. The method for preparing steel according to claim 2, wherein: In the annealing process, the continuous annealing temperature is 800±10° C. and the soaking time is 55 to 90 seconds.

5. The method for preparing steel according to claim 2, wherein: The furnace temperature is 1210-1220°C.

6. The method for preparing steel according to claim 3, characterized in that: The water pressure is 180-190 Bar, and the final rolling temperature is 890-910°C.

7. The method for preparing steel according to claim 4, characterized in that: The continuous annealing temperature is 800-810°C.

8. A method for producing nitrided steel using the steel according to claim 1, characterized in that: The following steps are involved: Heat with the furnace to the nitriding temperature of 550-600℃, pass ammonia gas, and keep warm for 1-4 hours; cool with the furnace at a cooling rate of 20-60℃ / min.

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