Preparation method of low-nitrogen steel and low-nitrogen steel

Abstract

The invention provides a preparation method of low-nitrogen steel and the low-nitrogen steel, and belongs to the field of smelting. The method comprises the steps that molten iron is smelted in a converter, CO2 and Ar are blown from the bottom in the whole process, and first molten steel is obtained; the converter smelting mode is a low-nitrogen control mode, and the static slag thickness of converter smelting is larger than or equal to 300 mm; the first molten steel is subjected to converter tapping, a first alloy is added in the converter tapping process, and second molten steel with set chemical components is obtained; the second molten steel is subjected to refining treatment, a second alloy is added into the molten steel in the later stage of refining treatment, and third molten steel is obtained; and the third molten steel is subjected to continuous casting, and the low-nitrogen steel is obtained. Through low-nitrogen control based on the converter and by utilizing the influence of different alloy elements on the nitrogen solubility, the adding sequence of the alloy in the smelting process is optimized, the nitrogen increase of molten steel in the smelting process is reduced, the nitrogen control effect of the low-nitrogen steel is improved, and stable production of the low-nitrogen steel is realized.

Description

Technical Field

[0001] The present application relates to the field of smelting technology, and in particular to a preparation method of low-nitrogen steel and low-nitrogen steel. Background Art

[0002] Nitrogen is generally a residual element in steel. As the nitrogen content in steel increases, the plasticity and toughness of the steel will be significantly reduced, the weldability will deteriorate, the cold brittleness will increase, and the welding performance and cold bending performance of the steel will be damaged. Nitrogen also causes strain aging in low-carbon steel. Therefore, the nitrogen content in steel should be reduced and limited as much as possible. Generally, the nitrogen content should not be higher than 0.008%.

[0003] Elements in molten steel have different degrees of influence on the solubility of nitrogen, which can be divided into four categories: The first category is elements that can form nitrides with nitrogen, such as Ti, Nb, V, etc., which significantly increase the solubility and f of nitrogen in molten steel. N The second category is elements that have a greater affinity for gas elements than Fe, such as Cr, Mn, Mo, etc., which increase the solubility of nitrogen in molten steel and f N ; The third category is elements that can reduce solubility, such as non-metallic elements such as C, Si, P, S, but can increase f N ; The fourth category is elements that have no actual effect on solubility, such as Co, Ni, Cu, etc., and only slightly increase f N . Since the diameter of nitrogen atoms is larger than that of hydrogen atoms, denitrification reactions are more difficult during steelmaking. Therefore, controlling nitrogen addition in molten steel is an indispensable means of smelting low-nitrogen steel, especially for non-vacuum treated steel grades. At present, conventional measures for controlling nitrogen addition are: reducing converter post-blowing, slag foaming, LF micro-positive pressure, appropriate bottom blowing flow and time. Nitrogen control measures mainly focus on process control, and the effect of controlling nitrogen addition is limited. Therefore, how to improve the nitrogen control effect in the preparation process of low-nitrogen steel is a technical problem that urgently needs to be solved. Summary of the invention

[0004] The present application provides a preparation method of low-nitrogen steel and low-nitrogen steel to solve the following technical problem: how to improve the nitrogen control effect during the preparation of low-nitrogen steel.

[0005] In a first aspect, the present application provides a method for preparing low-nitrogen steel, the method comprising:

[0006] The molten iron is subjected to converter smelting and CO2 and Ar are blown from the bottom throughout the whole process to obtain a first molten steel; the converter smelting mode is a low nitrogen control mode, and the static slag thickness of the converter smelting is ≥300 mm;

[0007] tapping the first molten steel into a converter, and adding a first alloy during the tapping process to obtain a second molten steel having a set chemical composition;

[0008] refining the second molten steel, and adding a second alloy to the molten steel at a later stage of the refining process to obtain a third molten steel;

[0009] The third molten steel is continuously cast to obtain low-nitrogen steel.

[0010] Optionally, after the steel is tapped from the converter, the amount of the first alloy added after the refining treatment is ≤1 kg / t steel.

[0011] Optionally, the first alloy includes one or more of carburizer, ferrosilicon, ferrophosphorus, ferrosulphur and sulfide.

[0012] Optionally, the oxygen-carbon ratio of the second molten steel is 0.5-2.0, wherein the oxygen-carbon ratio is the ratio of the carbon content to the oxygen content of the steel grade.

[0013] Optionally, the sulfur content in the second molten steel is greater than 40 ppm in parts per million.

[0014] Optionally, the second alloy includes one or more of ferrotitanium, ferroniobium, ferrovanadium, ferrochromium, ferromanganese, metallic manganese and ferromolybdenum.

[0015] Optionally, the second alloy is not added during the converter smelting and the early and middle stages of the refining treatment.

[0016] Optionally, after adding the second alloy, the circulation time of the molten steel is ≥5 min.

[0017] Optionally, the amount of nitrogen added from the end point of the converter smelting to the end point of the refining treatment is ≤15 ppm, measured in parts per million.

[0018] In a second aspect, the present application provides a low-nitrogen steel prepared by the method described in any one of the embodiments of the first aspect, wherein the nitrogen content of the low-nitrogen steel is ≤35 ppm in parts per million.

[0019] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0020] The present application provides a method for preparing low-nitrogen steel, comprising: subjecting molten iron to converter smelting and bottom blowing CO2 and Ar throughout the process to obtain a first molten steel; the converter smelting mode is a low-nitrogen control mode, and the static slag thickness of the converter smelting is ≥300mm; the first molten steel is tapped from a converter, and a first alloy is added during the converter tapping process to obtain a second molten steel with a set chemical composition; the second molten steel is subjected to a refining treatment, and a second alloy is added to the molten steel in the later stage of the refining treatment to obtain a third molten steel; the third molten steel is continuously cast to obtain low-nitrogen steel. By using the low-nitrogen control based on the converter and utilizing the influence of different alloying elements on nitrogen solubility, the order of adding alloys during the smelting process is optimized, the nitrogen increase of the molten steel during the smelting process is reduced, the nitrogen control effect of the low-nitrogen steel is improved, and the stable production of low-nitrogen steel is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0023] Figure 1 A schematic flow chart of a method for preparing low-nitrogen steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0025] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0026] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0028] The technical solution provided by the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0029] Figure 1 A schematic flow chart of a method for preparing low-nitrogen steel provided in an embodiment of the present application.

[0030] According to a typical implementation of the present invention, see Figure 1 , the present application provides a method for preparing low-nitrogen steel, the method comprising:

[0031] S1, smelting the molten iron in a converter and blowing CO2 and Ar at the bottom throughout the whole process to obtain a first molten steel; the converter smelting mode is a low nitrogen control mode, and the static slag thickness of the converter smelting is ≥300mm;

[0032] As an optional implementation, in the smelting process of step S1, the reason for bottom blowing CO2+Ar throughout the converter smelting process is that the bottom blowing CO2 reacts with [C] to produce more CO bubbles, which greatly increases the stirring kinetic energy;

[0033] As an optional embodiment, in the smelting process of step S1, the reason why the static slag thickness of the converter is ≥300 mm is that a sufficient converter slag thickness reduces the nitrogen content in the air entering the molten steel and causing nitrogen increase. Exemplarily, the static slag thickness of converter smelting can be 300 mm, 320 mm, 350 mm, 370 mm, 400 mm, 450 mm, etc.

[0034] S2, tapping the first molten steel into a converter, and adding a first alloy during the process of tapping the first molten steel into the converter to obtain a second molten steel having a set chemical composition;

[0035] It should be noted that the amount and type of the first alloy added during the process of tapping steel from the converter can be adjusted accordingly according to the type of steel and its chemical composition.

[0036] In some embodiments, after the steel is tapped from the converter, the amount of the first alloy added during the refining process is ≤1 kg / t steel.

[0037] As an optional embodiment, in the smelting process of step S1, the reason why the amount of the first alloy added after the converter steel is tapped is ≤1Kg / t·steel is: to suppress the increase of nitrogen in the molten steel and to leave a certain space for refining and fine-tuning the composition. Exemplarily, the amount of the first alloy added after the converter steel is tapped can be 0, 0.1Kg / t·steel, 0.2Kg / t·steel, 0.3Kg / t·steel, 0.4Kg / t·steel, 0.5Kg / t·steel, 0.6Kg / t·steel, 0.8Kg / t·steel, 1Kg / t·steel, etc.

[0038] In some embodiments, the first alloy includes one or more of a carburizer, ferrosilicon, ferrophosphorus, ferrosulphur, and sulfide.

[0039] As an optional embodiment, in the smelting process of step S1, the first alloy is at least one of materials such as carburizer, ferrosilicon, ferrophosphorus, ferrosulfur, and sulfur wire. The reason is that C, Si, P, and S are elements that can reduce the solubility of nitrogen in steel, and adding them during the converter steelmaking process can inhibit the increase of nitrogen in the molten steel.

[0040] In some embodiments, the oxygen-carbon ratio of the second molten steel is 0.5-2.0, wherein the oxygen-carbon ratio is the ratio of the carbon content to the oxygen content of the steel.

[0041] As an optional embodiment, the reason why the second molten steel contains oxygen during the smelting process of step S2 is that oxygen is a surface active element and can compete with N atoms for active points on the surface of the molten steel. Oxygen is adsorbed preferentially, resulting in a decrease in the area ratio of unadsorbed matter on the surface of the molten steel, thereby reducing nitrogen addition to the molten steel.

[0042] As an optional embodiment, in the smelting process of step S2, the oxygen-carbon ratio of the second steel liquid is 0.5-2.0 because: if the oxygen-carbon ratio is too high, the steel liquid is over-oxidized, resulting in poor quality of the steel liquid; if the oxygen-carbon ratio is too low, the effect of oxygen in the steel on inhibiting nitrogen increase is poor, and the inhibitory effect on nitrogen increase is poor. Exemplarily, the oxygen-carbon ratio of the second steel liquid is 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.8, 2.0, etc.

[0043] In some embodiments, the sulfur content in the second molten steel is greater than 40 ppm, measured in parts per million.

[0044] As an optional embodiment, in the smelting process of step S2, the reason why the sulfur content of the second molten steel is greater than 40ppm is that sulfur is a surface active element and can increase the activity coefficient of N and reduce nitrogen addition in the molten steel. Exemplarily, the sulfur content in the second molten steel can be 41ppm, 42ppm, 43ppm, 45ppm, 47ppm, 48ppm, 50ppm, etc.

[0045] S3, refining the second molten steel, and adding a second alloy to the molten steel at a later stage of the refining process to obtain a third molten steel;

[0046] It should be noted that the amount and type of the second alloy added in the later stage of the refining process can be adjusted accordingly according to the type of steel and its chemical composition.

[0047] In this embodiment, the first alloy and the second alloy are added separately because: the first alloy is an element that can reduce the solubility, and the second alloy is an element that increases the solubility; the first alloy is added during the converter steelmaking process, and the second alloy is added in the later stage of refining, and the element that reduces the solubility of nitrogen in steel is kept at a high content in the early stage of smelting, and the element that increases the solubility of nitrogen in steel is kept at a low content, thereby reducing the amount of nitrogen added in the entire smelting process.

[0048] In some embodiments, the second alloy includes one or more of ferrotitanium, ferroniobium, ferrovanadium, ferrochromium, ferromanganese, metallic manganese, and ferromolybdenum.

[0049] As an optional embodiment, in the smelting process of step S3, the reason why the second alloy includes at least one of materials such as ferrotitanium, ferroniobium, ferrovanadium, ferrochrome, ferromanganese, metallic manganese, and ferromolybdenum is that Ti, Nb, and V are elements that can form nitrides with nitrogen, which significantly improves the solubility of nitrogen in molten steel; Cr, Mn, and Mo are elements that have a greater affinity for gas elements than Fe, which can improve the solubility of nitrogen in molten steel.

[0050] In some embodiments, the second alloy is not added during the converter smelting and the early and middle stages of the refining process.

[0051] As an optional implementation, in the smelting process of step S3, the second alloy is added in the later stage of refining, and the reason for not adding the second alloy at other times is to keep the elements that increase the solubility of nitrogen in steel at a low level and reduce the increase of nitrogen in the molten steel.

[0052] In some embodiments, the circulation time of the molten steel after adding the second alloy is ≥5 min.

[0053] As an optional implementation, in the smelting process of step S3, after the second alloy is added, the circulation time of the molten steel is ≥5 minutes because it is ensured that there is enough time for the components to be mixed after the second alloy is added. Exemplarily, the circulation time of the molten steel after the second alloy is added can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.

[0054] In some embodiments, the amount of nitrogen added from the end point of the converter smelting to the end point of the refining process is ≤15 ppm in parts per million.

[0055] As an optional embodiment, in the smelting process of step S3, based on the low nitrogen control of the converter, the influence of different alloy elements on nitrogen solubility is utilized to optimize the order of adding alloys during the smelting process, thereby reducing the amount of nitrogen added to the molten steel during the smelting process. Exemplarily, the amount of nitrogen added can be 10ppm, 11ppm, 12ppm, 13ppm, 14ppm, 15ppm, etc.

[0056] S4. Continuously casting the third molten steel to obtain low-nitrogen steel.

[0057] Based on a general inventive concept, the present application provides a low-nitrogen steel prepared by the method described in any one of the above embodiments, wherein the nitrogen content of the low-nitrogen steel is ≤35 ppm in parts per million.

[0058] The method for preparing low-nitrogen steel provided in the embodiment of the present invention is based on the low-nitrogen control of the converter, utilizes the influence of different alloy elements on the nitrogen solubility, optimizes the order of adding alloys during the smelting process, and reduces the nitrogen increase of the molten steel during the smelting process. Even without using vacuum denitrification, the N content can be controlled below 35ppm, thereby realizing the stable production of low-nitrogen steel.

[0059] The low nitrogen steel is realized based on the preparation method of the low nitrogen steel mentioned above. The specific steps of the preparation method of the low nitrogen steel can refer to the above embodiment. Since the low nitrogen steel adopts part or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be described one by one here.

[0060] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0061] The following is a detailed description of a method for preparing a low-nitrogen steel of the present application in combination with embodiments, comparative examples and experimental data, comprising the following steps:

[0062] S11, smelting the molten iron in a converter and blowing CO2 and Ar at the bottom throughout the whole process to obtain a first molten steel; the converter smelting mode is a low nitrogen control mode, and the static slag thickness of the converter smelting is ≥300mm;

[0063] S21, tapping the first molten steel into a converter, and adding a first alloy during the process of tapping the first molten steel into the converter to obtain a second molten steel having a set chemical composition;

[0064] S31, refining the second molten steel, and adding a second alloy to the molten steel at a later stage of the refining process to obtain a third molten steel;

[0065] S41, continuously casting the third molten steel to obtain low nitrogen steel. The process parameters of each embodiment and each comparative example are listed in Table 1.

[0066] Table 1 Process parameters of the preparation method of low nitrogen steel

[0067]

[0068]

[0069] From the data in Table 1, we can see that:

[0070] In Comparative Example 1, the converter uses a non-low nitrogen control mode, and the nitrogen content of the molten steel is poorly controlled during the converter smelting process, resulting in high nitrogen content at the converter end point and 57 ppm nitrogen in the final product, indicating a high nitrogen content in the finished product.

[0071] In Comparative Example 2, the oxygen-carbon ratio at the converter end point is low, the oxygen content in the molten steel is low, the molten steel has a strong nitrogen absorption capacity during steel tapping and subsequent treatment, and the nitrogen increase from the converter end point to the end of refining is 25ppm, which is a large amount of nitrogen increase.

[0072] In Comparative Example 3, the oxygen-carbon ratio at the converter end point is low, and the oxygen content in the molten steel is high, which affects the cleanliness of the final molten steel.

[0073] In Comparative Example 4, the first alloy is not added to the converter but is added in the refining process. The first alloy is added late, the effect of suppressing nitrogen increase in the molten steel is poor, and the amount of nitrogen increase in the process is large.

[0074] In Comparative Example 5, 5 kg / t·steel of the first alloy is added after steel tapping is completed. The amount of the first alloy added during converter steel tapping is small, the effect of inhibiting nitrogen increase in molten steel is poor, and the amount of nitrogen increase during the process is large.

[0075] In Comparative Example 6, the second alloy is added late, the circulation time of the molten steel is short, the molten steel is mixed unevenly and the effect is poor, and the composition deviation of the molten steel is large.

[0076] In Comparative Example 7, the static slag thickness of the converter smelting is 50 mm, and the amount of converter slag is small, which is not enough to reduce the nitrogen content in the air entering the molten steel and causing nitrogen increase.

[0077] In Examples 1 to 3, the effect of different alloying elements on nitrogen solubility is utilized to optimize the order of adding alloys during the smelting process, thereby reducing the nitrogen addition in the molten steel during the smelting process. Even without using vacuum denitrification, the N content can be controlled below 35 ppm, thereby achieving stable production of low-nitrogen steel.

[0078] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing low nitrogen steel, characterized in that: The method comprises: The molten iron is subjected to converter smelting and CO2 and Ar are blown from the bottom throughout the whole process to obtain a first molten steel; the converter smelting mode is a low nitrogen control mode, and the static slag thickness of the converter smelting is ≥300 mm; tapping the first molten steel into a converter, and adding a first alloy during the tapping process to obtain a second molten steel having a set chemical composition; refining the second molten steel, and adding a second alloy to the molten steel at a later stage of the refining process to obtain a third molten steel; The third molten steel is continuously cast to obtain low-nitrogen steel.

2. The method according to claim 1, characterized in that After the steel is tapped from the converter, the amount of the first alloy added after the refining treatment is ≤1 kg / t steel.

3. The method according to claim 1 or 2, characterized in that: The first alloy includes one or more of a carburizer, ferrosilicon, ferrophosphorus, ferrosulphur and sulfide.

4. The method according to claim 1, characterized in that: The oxygen-carbon ratio of the second molten steel is 0.5-2.0, wherein the oxygen-carbon ratio is the ratio of the carbon content to the oxygen content of the steel.

5. The method according to claim 4, characterized in that Measured in parts per million, the sulfur content in the second molten steel is greater than 40 ppm.

6. The method according to claim 1, characterized in that The second alloy includes one or more of ferrotitanium, ferroniobium, ferrovanadium, ferrochromium, ferromanganese, metallic manganese and ferromolybdenum.

7. The method according to claim 1, characterized in that The second alloy is not added during the converter smelting and the early and middle stages of the refining treatment.

8. The method according to claim 1, characterized in that: After adding the second alloy, the circulation time of the molten steel is ≥5min.

9. The method according to claim 1, characterized in that: The amount of nitrogen added from the end point of the converter smelting to the end point of the refining treatment is ≤15 ppm in parts per million.

10. A low nitrogen steel prepared by the method according to any one of claims 1 to 9, characterized in that: Measured in parts per million, the nitrogen content of the low nitrogen steel is ≤35 ppm.

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