Method for reducing nitrogen content in molten iron and application thereof

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a method for reducing the nitrogen content in molten iron and application thereof. Comprising the following steps: carrying out KR treatment on molten iron, and then carrying out converter steelmaking; in the molten iron, the content of silicon ranges from 0.5% to 0.6%, the content of titanium ranges from 0.05% to 0.06%, and the content of nitrogen ranges from 0.007% to 0.008%. According to the method, separation of TiN is improved by increasing the content of titanium in the molten iron, so that nitrogen in the molten iron is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and particularly relates to a method for reducing nitrogen content in molten iron and application thereof. Background Art

[0002] The nitrogen content in steel has a direct impact on the structure and properties of steel: as the nitrogen content in steel increases, the plasticity and toughness of the steel decrease significantly, the weldability and cold bending properties deteriorate, and the cold brittleness and hot brittleness increase. Excessive nitrogen content causes harmful intermetallic phases (such as martensite, ferrite, nitride, etc.) to appear in the steel, thereby reducing the corrosion resistance and stability of the steel. Therefore, reducing the nitrogen content in steel is one of the important ways to improve the quality of steel.

[0003] At present, the nitrogen content in steel is reduced by precipitating TiN from molten iron. However, the nitrogen content of molten steel at the end of converter production is ≤0.0025%, and the iron-to-water ratio must be above 80%, which results in high costs. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for reducing the nitrogen content in molten iron and its application. The method increases the titanium content in the molten iron to increase the precipitation of TiN, thereby reducing the nitrogen in the molten iron.

[0005] The present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for reducing nitrogen content in molten iron, comprising the following steps:

[0007] The molten iron is KR treated and then enters the converter for steelmaking;

[0008] In the molten iron, the content of silicon is 0.5% to 0.6%, the content of titanium is 0.05% to 0.06%, and the content of nitrogen is 0.007% to 0.008%.

[0009] The method for reducing the nitrogen content in molten iron provided by the present invention, since the empirical content ratio of silicon content to titanium content in molten iron is 9-10, the silicon content in molten iron can be controlled by raw materials, that is, the titanium content can be controlled. The titanium content can be increased by increasing the silicon content in molten iron, and a higher titanium content can promote the precipitation of TiN. According to the relationship between the nitrogen content in molten iron and the precipitation temperature of TiN, when the nitrogen content is 0.007%-0.008%, the precipitation temperature of TiN is above 1400°C. With a higher TiN precipitation temperature, as the temperature of molten iron decreases during desulfurization and converter steelmaking, TiN gradually precipitates out of the molten iron, that is, a higher TiN precipitation temperature can promote the precipitation of TiN in the molten iron, thereby reducing the nitrogen content in the molten iron.

[0010] In some possible implementations, the molten iron consists of the following components in mass fractions:

[0011] Carbon 4.3% to 4.4%, silicon 0.50% to 0.60%, titanium 0.05% to 0.06%, nitrogen 0.007% to 0.008%, sulfur 0.025% to 0.040%, and the balance is iron and unavoidable impurities.

[0012] In some possible implementations, during the KR treatment, the temperature of the molten iron at the KR inlet is 1340° C. to 1360° C., and the nitrogen content in the molten iron at the inlet is ≤0.0065%.

[0013] In some possible implementations, in the KR treatment, the amount of desulfurizer added is 15kg / t to 20kg / t, the stirring speed is 110rpm to 130rpm, the insertion depth of the stirring head is 0.6m to 1m, the treatment time is 25min to 30min, and the desulfurization end point temperature is 1300° C. to 1330° C. In this case, deep desulfurization of molten iron can be achieved, and nitrogen in the molten iron can be further removed.

[0014] In some possible implementations, in the KR treatment, the amount of nitrogen removal is 0.0010% to 0.0015%.

[0015] In some possible implementations, after the KR treatment, the nitrogen content in the molten iron is less than 0.0050%.

[0016] In some possible implementations, the desulfurizer is composed of the following components in mass fractions: 12% to 16% CaF2, 80% to 85% CaO, and 2% to 3% SiO2; preferably, it is composed of the following components in mass fractions: 12% CaF2, 85% CaO, and 3% SiO2.

[0017] In some possible implementations, in the converter steelmaking, the molten iron ratio is 72% to 80%.

[0018] In some possible implementations, the final nitrogen content of the molten iron obtained after converter steelmaking is ≤0.0025%.

[0019] In a second aspect, the present invention provides an application of the method for reducing nitrogen content in molten iron provided by the present invention in the field of production of low-nitrogen steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present drawings 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, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0021] Figure 1 The present invention is a schematic flow chart of a method for reducing nitrogen content in molten iron according to an embodiment of the present invention.

[0022] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described and illustrated in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0024] Obviously, the following descriptions are only some examples or embodiments of the present invention, and for those of ordinary skill in the art, the present invention can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the contents disclosed in the present invention, some changes in design, manufacturing or production based on the technical contents disclosed in the present invention are just conventional technical means, and should not be understood as the contents disclosed in the present invention being insufficient.

[0025] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present invention and is not intended to limit the subject matter described in the claims.

[0026] If not otherwise specified, all embodiments and optional embodiments of the present invention may be combined with each other to form a new technical solution, and all technical features and optional technical features of the present invention may be combined with each other to form a new technical solution.

[0027] The term "content" refers to mass fraction.

[0028] The term "molten iron ratio" refers to: molten iron volume / (molten iron volume + scrap steel) × 100%. For example, if the molten iron volume is 160t and the scrap steel is 60t, the molten iron ratio is 160 / (160+60) × 100% ≈ 73%.

[0029] The precipitation temperature of TiN in molten iron is different under different nitrogen contents. It is well known that within the range of 0.002% to 0.008% nitrogen content, the higher the nitrogen content, the higher the precipitation temperature of TiN. When the temperature of molten iron entering the converter from the blast furnace decreases, TiN is easier to precipitate and the nitrogen content in the molten iron is lower; conversely, the nitrogen content in the molten iron is higher. In addition, in order for TiN to precipitate out of molten iron, the titanium content in the molten iron must also be relatively high so that it can combine with nitrogen for precipitation.

[0030] When molten iron enters the converter for steelmaking, controlling the nitrogen content in the molten iron to below 0.0025% can reduce the converter iron-to-water ratio, thereby reducing production costs.

[0031] It can be seen that in order to reduce the nitrogen content in molten iron, an embodiment of the present invention proposes a method for reducing the nitrogen content in molten iron. The method controls the titanium content in the molten iron by controlling the silicon content in the molten iron, thereby reducing the nitrogen content in the molten iron.

[0032] The following is a detailed description of a method for reducing nitrogen content in molten iron and its application in an embodiment of the present invention.

[0033] A first aspect of the present invention provides a method for reducing the nitrogen content in molten iron, such as Figure 1 As shown, the following steps are included:

[0034] S10. The molten iron is KR treated and then enters the converter for steelmaking;

[0035] In the molten iron, the silicon content is 0.5% to 0.6%, the titanium content is 0.05% to 0.06%, and the nitrogen content is 0.007% to 0.008%.

[0036] The method for reducing the nitrogen content in molten iron provided by the embodiment of the present invention, since the empirical content ratio of silicon content to titanium content in molten iron is 9 to 10, the content of silicon in molten iron can be controlled by raw materials, that is, the content of titanium can be controlled. The content of titanium can be increased by increasing the content of silicon in molten iron, and a higher titanium content can promote the precipitation of TiN. According to the empirical relationship between the nitrogen content in molten iron and the precipitation temperature of TiN, when the nitrogen content is 0.007% to 0.008%, the precipitation temperature of TiN is above 1400°C. With a higher TiN precipitation temperature, as the temperature of molten iron decreases during desulfurization and converter steelmaking, TiN is gradually precipitated from molten iron, that is, a higher TiN precipitation temperature can promote the precipitation of TiN from molten iron, thereby reducing the nitrogen content in molten iron. In addition, during KR treatment, partial carbon oxidation will inevitably occur in molten iron, and CO will overflow from the liquid surface after carbon oxidation, which is also the reason for the generation of foamy slag during the desulfurization process. The generated CO bubbles act as a small vacuum chamber for the dissolved nitrogen in the molten iron, where the nitrogen partial pressure P(N2)≈0, so the nitrogen dissolved in the molten iron can diffuse into the small vacuum chamber and be taken out, further reducing the nitrogen in the molten iron. The lower the degree of desulfurization, the more serious the carbon oxidation, the greater the rate of CO bubble generation, and the greater the degassing rate.

[0037] In some embodiments, in the above step S10, the molten iron is composed of the following components in mass fractions:

[0038] Carbon 4.3% to 4.4%, silicon 0.5% to 0.6%, titanium 0.05% to 0.06%, nitrogen 0.007% to 0.008%, sulfur 0.025% to 0.040%, phosphorus 0.090% to 0.110%, and the balance is iron and unavoidable impurities. In this case, in the high-carbon, high-silicon and high-titanium molten iron, carbon oxidation produces CO bubbles to promote the escape of nitrogen, and the high silicon content makes the titanium content correspondingly higher, which promotes the precipitation of TiN.

[0039] In some specific embodiments, the molten iron consists of the following components in mass fractions:

[0040] Carbon 4.3%, silicon 0.50%, titanium 0.052%, nitrogen 0.0072%, sulfur 0.03%, phosphorus 0.100%, and the balance is iron and inevitable impurities.

[0041] In some specific embodiments, the molten iron consists of the following components in mass fractions:

[0042] Carbon 4.4%, silicon 0.60%, titanium 0.059%, nitrogen 0.008%, sulfur 0.040%, phosphorus 0.09%, and the balance is iron and inevitable impurities.

[0043] In some specific embodiments, the molten iron consists of the following components in mass fractions:

[0044] Carbon 4.3%, silicon 0.55%, titanium 0.057%, nitrogen 0.0075%, sulfur 0.025%, phosphorus 0.110%, and the balance is iron and inevitable impurities.

[0045] In some embodiments, in the above step S10, during the KR treatment, the temperature of the molten iron at the KR inlet is 1340° C. to 1360° C., and the nitrogen content in the molten iron at the inlet is ≤0.0065%.

[0046] KR treatment includes conventional KR desulfurization and further removal of nitrogen using CO gas generated during the KR desulfurization process.

[0047] In some embodiments, in the above step S10, during the KR treatment, the amount of desulfurizer added is 15kg / t to 20kg / t, the stirring speed is 110rpm to 130rpm, the insertion depth of the stirring head is 0.6m to 1m, the treatment time is 25min to 30min, and the desulfurization end point temperature is 1300° C. to 1330° C. In this case, deep desulfurization of molten iron can be achieved, and nitrogen in the molten iron can be further removed.

[0048] In the KR treatment, calcium oxide in the desulfurizer reacts with sulfur to produce carbon monoxide. The chemical reaction formula is as follows:

[0049] CaO(s)+[S]+[C]=CaS(s)+CO.

[0050] The CO generated during the desulfurization process overflows from the surface of the molten iron, acting as a small vacuum chamber for the dissolved nitrogen in the molten iron. The gas dissolved in the molten iron can diffuse into it and be carried away by the CO bubbles, thereby reducing the nitrogen content in the molten iron.

[0051] In some embodiments, in the above step S10, the denitrification amount in the KR treatment is 0.0010% to 0.0012%.

[0052] In some embodiments, in the above step S10, after KR treatment, the nitrogen content in the molten iron is less than 0.0050%. In this case, the converter iron ratio can be reduced to 72% to 80%, thereby reducing production costs.

[0053] In some embodiments, in the above step S10, the desulfurizing agent is composed of the following components by mass fraction: 12% to 16% CaF2, 80% to 85% CaO, and 2% to 3% SiO2; preferably, it is composed of the following components by mass fraction: 12% CaF2, 85% CaO, and 3% SiO2. In this case, the oxygen in the desulfurizing agent is oxidized with the carbon in the molten iron to generate CO and take out the nitrogen in the molten iron, thereby achieving the purpose of reducing the nitrogen content in the molten iron.

[0054] In some embodiments, in the above step S10, in converter steelmaking, the molten iron ratio is 72% to 80%.

[0055] In some embodiments, in the above step S10, the final nitrogen content of the molten iron obtained after converter steelmaking is ≤0.0025%.

[0056] In some embodiments, a method for reducing nitrogen content in molten iron is provided, comprising the following steps:

[0057] S11. The molten iron is subjected to KR treatment: the stirring speed is 110rpm~130rpm, the insertion depth of the stirring head is 0.6m~1m, the treatment time is 25min~30min, and the desulfurization end point temperature is 1300℃~1330℃.

[0058] S21. The molten iron after KR treatment is subjected to converter steelmaking, the molten iron ratio during steelmaking is 72% to 80%, and the final nitrogen content of the molten iron obtained after steelmaking is ≤0.0025%.

[0059] A second aspect of an embodiment of the present invention provides an application of the method for reducing nitrogen content in molten iron provided by an embodiment of the present invention in the field of production of low-nitrogen steel.

[0060] The following is further described in conjunction with specific embodiments.

[0061] Example 1

[0062] Example 1 provides a method for reducing the nitrogen content in molten iron, the steps are as follows:

[0063] (1) 210 tons of molten iron is smelted in a blast furnace. The composition of the molten iron is controlled by adding raw materials: 4.3% carbon, 0.50% silicon, 0.052% titanium, 0.0072% nitrogen, 0.03% sulfur, and the remainder is iron and inevitable impurities; the molten iron tapping temperature is 1499°C, and the precipitation temperature of TiN is 1406°C.

[0064] (2) KR treatment of molten iron: TiN is precipitated as the temperature of the molten iron decreases before the molten iron enters the KR treatment from the blast furnace, so that the molten iron temperature at the KR inlet is 1350° C. and the nitrogen content in the molten iron is 0.0058%;

[0065] The desulfurizer is composed of the following components in mass fraction: 12% CaF2, 85% CaO and 3% SiO2, the amount of desulfurizer added is 18kg / t, the stirring speed is 120rpm, the insertion depth of the stirring head is 0.8m, the processing time is 28min, and the desulfurization endpoint temperature is 1322℃; the nitrogen content in the molten iron after desulfurization is 0.0043%.

[0066] (3) The molten iron after KR treatment is subjected to converter steelmaking, the molten iron ratio during steelmaking is 73%, and the nitrogen content of the molten steel obtained after steelmaking is 0.0021%.

[0067] Example 2

[0068] Embodiment 2 provides a method for reducing the nitrogen content in molten iron, the steps are as follows:

[0069] (1) 210 tons of molten iron is smelted in a blast furnace. The composition of the molten iron is controlled by adding raw materials: carbon 4.4%, silicon 0.60%, titanium 0.059%, nitrogen 0.008%, sulfur 0.040%, phosphorus 0.09%, and the remainder is iron and inevitable impurities; the molten iron tapping temperature is 1499°C, and the precipitation temperature of TiN is 1425°C.

[0070] (2) KR treatment of molten iron: TiN is precipitated as the temperature of the molten iron decreases before it enters the KR treatment from the blast furnace, so that the temperature of the molten iron at the KR inlet is 1360°C and the nitrogen content in the molten iron is 0.0063%. The desulfurizer is composed of the following components by mass fraction: 12% CaF2, 85% CaO and 3% SiO2. The amount of desulfurizer added is 20kg / t, the stirring speed is 110rpm, the insertion depth of the stirring head is 0.6m, the treatment time is 30min, and the desulfurization end point temperature is 1321°C; the nitrogen content in the molten iron after desulfurization is 0.0048%.

[0071] (3) The molten iron after KR treatment is subjected to converter steelmaking, the molten iron ratio during steelmaking is 80%, and the nitrogen content of the molten steel obtained after steelmaking is 0.0017%.

[0072] Example 3

[0073] Example 3 provides a method for reducing the nitrogen content in molten iron, the steps are as follows:

[0074] (1) 210 tons of molten iron is smelted in a blast furnace. The composition of the molten iron is controlled by adding raw materials: 4.3% carbon, 0.55% silicon, 0.057% titanium, 0.0075% nitrogen, 0.025% sulfur, 0.110% phosphorus, and the remainder is iron and inevitable impurities; the molten iron tapping temperature is 1499°C, and the precipitation temperature of TiN is 1420°C.

[0075] (2) KR treatment of molten iron: TiN is precipitated as the temperature of the molten iron decreases before it enters the KR treatment from the blast furnace, so that the temperature of the molten iron at the KR inlet is 1340°C and the nitrogen content in the molten iron is 0.0062%. The desulfurizer is composed of the following components by mass fraction: 12% CaF2, 85% CaO and 3% SiO2. The amount of desulfurizer added is 15kg / t, the stirring speed is 130rpm, the insertion depth of the stirring head is 1m, the treatment time is 30min, and the desulfurization end temperature is 1322°C; the nitrogen content in the molten iron after desulfurization is 0.0049%.

[0076] (3) The molten iron after KR treatment is subjected to converter steelmaking, the molten iron ratio during steelmaking is 72%, and the nitrogen content of the molten steel obtained after steelmaking is 0.0018%.

[0077] Comparative Example 1

[0078] Comparative Example 1 provides a method for reducing the nitrogen content in molten iron, the steps are as follows:

[0079] (1) 210 tons of molten iron was selected, the silicon content was 0.15%, the titanium content was 0.0142%, and the nitrogen content was 0.0074%; the molten iron tapping temperature was 1502°C, and the precipitation temperature of TiN was 1309°C.

[0080] (2) The molten iron is subjected to converter steelmaking. The molten iron temperature at the converter inlet is 1375° C., the nitrogen content in the molten iron is 0.0068%, the molten iron ratio during steelmaking is 75%, and the nitrogen content of the molten steel obtained after steelmaking is 0.0028%.

[0081] From the above examples and comparative examples, the final nitrogen content of molten iron can be obtained:

[0082] (1) The method for reducing the nitrogen content in molten iron in the embodiment of the present invention can increase the precipitation temperature of TiN and promote the precipitation of TiN by controlling the silicon content, titanium content and nitrogen content in the molten iron to be maintained within a relatively high range.

[0083] (2) The method for reducing the nitrogen content in molten iron according to the embodiment of the present invention can significantly reduce the nitrogen content in molten iron by controlling the silicon content, titanium content and nitrogen content in molten iron and combining with KR treatment, so that the nitrogen content in molten iron is ≤0.0025%.

[0084] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A method for reducing nitrogen content in molten iron, characterized in that: The steps include: The molten iron is KR treated and then enters the converter for steelmaking; In the molten iron, the content of silicon is 0.5% to 0.6%, the content of titanium is 0.05% to 0.06%, and the content of nitrogen is 0.007% to 0.008%.

2. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: The molten iron is composed of the following components by mass fraction: Carbon 4.3% to 4.4%, silicon 0.5% to 0.6%, titanium 0.05% to 0.06%, nitrogen 0.007% to 0.008%, sulfur 0.025% to 0.040%, and the balance is iron and unavoidable impurities.

3. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: In the KR treatment, the temperature of the molten iron at the KR inlet is 1340° C. to 1360° C., and the nitrogen content in the molten iron at the inlet is ≤0.0065%.

4. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: In the KR treatment, the amount of desulfurizer added is 15kg / t to 20kg / t, the stirring speed is 110rpm to 130rpm, the insertion depth of the stirring head is 0.6m to 1m, the treatment time is 25min to 30min, and the desulfurization end point temperature is 1300°C to 1330°C.

5. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: In the KR treatment, the amount of nitrogen removal is 0.0010% to 0.0015%.

6. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: After the KR treatment, the nitrogen content in the molten iron is less than 0.0050%.

7. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: The desulfurizer is composed of the following components by mass fraction: 12% ~ 16% CaF2, 80% ~ 85% CaO, 2% ~ 3% SiO2.

8. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: In the converter steelmaking, the molten iron ratio is 72% to 80%.

9. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that: The final nitrogen content of the molten iron obtained after converter steelmaking is ≤0.0025%.

10. Use of the method for reducing nitrogen content in molten iron as claimed in any one of claims 1 to 9 in the production of low-nitrogen steel.

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