A method for smelting alloy steel

Abstract

The present invention provides a smelting method for alloy steel, belonging to the technical field of steelmaking. The smelting method comprises: obtaining a pre-refined molten steel; in the pre-refined molten steel, the mass fraction of Si is 0.3-0.5%, and the mass fraction of Al is 0.035-0.045%; and performing VD vacuum refining on the pre-refined molten steel to obtain the alloy steel molten steel. Using the smelting method provided by the present invention, the Al loss during the VD smelting process is 2.38-5.41%, which is low Al loss. The smelting time is 53-54 minutes, the production efficiency is high, the Si yield is 90.91-92.86%, which is high, the finished product sulfur mass fraction is 0.0048-0.0050%, which is low sulfur content, and the inclusion density is 20-30 per mm. 2 , the cleanliness of steel is high.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to a method for smelting alloy steel. Background Art

[0002] Alloy steel is typically produced by adding an Al-containing alloy during the converter tapping process for deoxidation and alloying. The Al alloy composition after alloying is higher than the target Al alloy composition to compensate for Al losses during the VD vacuum refining process. This alloy steel production method results in Al losses exceeding 40% during VD vacuum refining, reducing the cleanliness of the molten steel and increasing smelting costs. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a smelting method of alloy steel, which reduces the Al loss in the VD vacuum refining process.

[0004] The present invention provides a smelting method for alloy steel, which comprises:

[0005] Obtaining a pre-refined molten steel; in the pre-refined molten steel, the mass fraction of Si is 0.3-0.5%, and the mass fraction of Al is 0.035-0.045%;

[0006] The pre-refined molten steel is subjected to VD vacuum refining to obtain alloy steel molten steel.

[0007] Furthermore, the mass fraction of Si is 0.35-0.45%.

[0008] Furthermore, the mass fraction of Si is 0.4-0.45%.

[0009] Furthermore, the smelting method further comprises:

[0010] The molten iron and scrap steel are loaded into a converter for smelting to obtain converter end-point molten steel;

[0011] tapping the final molten steel from the converter and adding a silicon-containing alloy and an aluminum-containing alloy to perform alloying to obtain alloyed molten steel;

[0012] Slag is added to the alloyed molten steel for pre-refining to obtain the pre-refined molten steel.

[0013] Furthermore, the temperature of the molten steel at the converter endpoint is 1680-1700°C.

[0014] Furthermore, when the converter smelting end temperature is 1690-1700°C, the effective addition amount of Al in the aluminum-containing alloy is 1.2-1.6 kg / ton of steel; when the converter end temperature is 1680-1690°C, the effective addition amount of Al in the aluminum-containing alloy is 1.5-2.0 kg / ton of steel.

[0015] Furthermore, the mass fraction of SiO2 in the slag of the pre-refining process is 8-10%.

[0016] Furthermore, the amount of slag is 10-12 kg per ton of steel.

[0017] Furthermore, the basicity of the slag is 4.5-5.5.

[0018] Furthermore, the ratio of CaO to Al2O3 in the slag is 1.5-1.7.

[0019] Furthermore, the slag includes the following components in mass fractions: CaO: 48-52%, SiO2: 8-10%, Al2O3: 28-32%, MgO: 7-10%, and CaF2: 0-5%.

[0020] Furthermore, in the VD vacuum refining, the holding time is 11-13 minutes and the holding pressure is 67 Pa.

[0021] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0022] The present invention provides a smelting method for alloy steel, comprising: obtaining a pre-refined molten steel; wherein the mass fraction of Si in the pre-refined molten steel is 0.3-0.5% and the mass fraction of Al is 0.035-0.045%; and subjecting the pre-refined molten steel to VD vacuum refining to obtain molten alloy steel. The Si and Al contents in the molten steel before VD vacuum refining are controlled to suppress the leftward reaction of 2(Al2O3)+3[Si]=4[Al]+3(SiO2), thereby suppressing the chemical reaction and consumption of Al in the molten steel with SiO2 in the slag during the VD vacuum refining process. This improves the Al yield during the VD vacuum refining process, reduces Al loss, and saves production costs. By adopting the smelting method provided by the present invention, the Al loss in the VD smelting process is 2.38-5.41%, the Al loss is low, the smelting time is 53-54 minutes, the production efficiency is high, the Si yield is 90.91-92.86%, the sulfur mass fraction of the finished product is 0.0048-0.0050%, the sulfur content is low, and the inclusion density is 20-30 pieces / mm 2 , the cleanliness of steel is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A process step diagram of a method for smelting alloy steel provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments and examples are for illustrating the present invention, rather than for limiting the present invention.

[0026] Throughout this specification, unless otherwise specified, the terms used herein should be understood as having the same meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of any conflict, the present specification shall take precedence.

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

[0028] It should be noted that, in this document, relational terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0029] The technical solution provided by the embodiments of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0030] Figure 1 The process steps of the alloy steel smelting method provided by the embodiment of the present invention are combined with Figure 1 , an embodiment of the present invention provides a method for smelting alloy steel, the method comprising:

[0031] S1, molten iron and scrap steel are charged into a converter for smelting to obtain converter terminal molten steel;

[0032] Furthermore, in this embodiment, the temperature of the molten steel at the converter endpoint is 1680-1700°C.

[0033] Because pre-refining replaces the LF furnace in the alloy steel smelting process, and the VD furnace is a pure temperature drop process, the converter endpoint temperature is controlled relatively high to meet the continuous casting temperature requirements. Excessively high converter endpoint molten steel temperature will result in high oxygen activity in the molten steel, increasing deoxidation pressure and deoxidizer consumption. Excessively low converter endpoint molten steel temperature will not guarantee the VD holding time, and the molten steel temperature may be too low to keep up with continuous casting.

[0034] S2, tapping the final molten steel from the converter and adding a silicon-containing alloy and an aluminum-containing alloy to alloy the molten steel to obtain an alloyed molten steel;

[0035] Silicon alloying can be performed here to control the mass fraction of silicon in the alloyed steel to 0.3-0.5%, preferably 0.35-0.45%, and more preferably 0.4-0.45%; the mass fraction of aluminum is 0.035-0.0045%. Adding silicon alloy to perform silicon alloying during the tapping process, and controlling the silicon content within the range of 0.3-0.5%, can suppress the reaction 2(Al2O3)+3[Si]=4[Al]+3(SiO2) from proceeding to the left under conditions such as VD vacuum refining, and even promote the reaction to proceed to the right, thereby suppressing the chemical reaction and consumption of Al in the molten steel with SiO2 in the slag. If the silicon content is too high, the aluminum oxide in the slag reacts with the silicon in the molten steel to the right, resulting in a low Si yield in the VD process. If the silicon content is too low, Al will chemically react with SiO2 in the slag, reducing the Al yield in the VD smelting process. Aluminum is added during the tapping process to remove oxygen and sulfur from the molten steel, ensuring that the mass fraction of aluminum in the molten steel is 0.02-0.04% to reduce aluminum loss during the VD smelting process. If the mass fraction of Al alloying during the tapping process is too high, the Al in the molten steel will react with SiO2 in the slag to produce Si and Al2O3, increasing Al loss during the VD smelting process. If the mass fraction of Al alloying during the tapping process is too low, the Si in the molten steel will react with Al2O3 in the slag to produce Al and SiO2, increasing Si loss during the VD smelting process. Therefore, the Si and Al contents after the tapping alloying should be matched so that the reaction 2(Al2O3)+3[Si]=4[Al]+3(SiO2) neither proceeds to the left nor to the right, but reaches an equilibrium state, thus neither causing Al loss nor Si loss.

[0036] It should be noted that during the LF refining process, the chemical reaction 2(Al2O3)+3[Si]=4[Al]+3(SiO2) cannot occur. Only when the molten steel and slag are mixed under vacuum conditions can the equilibrium reaction 2(Al2O3)+3[Si]=4[Al]+3(SiO2) occur.

[0037] Specifically, in this embodiment, when the converter end temperature is 1690-1700°C, the effective addition amount of Al in the aluminum-containing alloy is 1.2-1.6 kg / ton of steel; when the converter end temperature is 1680-1690°C, the effective addition amount of Al in the aluminum-containing alloy is 1.5-2.0 kg / ton of steel.

[0038] When the converter end temperature is low, the oxygen activity in the molten steel is lower than when the converter end temperature is high. Therefore, the amount of Al heated at low temperature is lower than the amount of Al added at high temperature.

[0039] S3, adding slag to the alloyed molten steel for pre-refining to obtain pre-refined molten steel;

[0040] Sulfur and oxygen can be removed from the molten steel through pre-refining, and there is basically no loss of Al and Si elements during the pre-refining process.

[0041] Furthermore, the mass fraction of SiO2 in the slag of the pre-refining process is 8-10%.

[0042] Too much SiO2 in the slag will reduce the slag basicity, thereby weakening the desulfurization effect. At the same time, the increase in SiO2 content will also increase the Al burn-off in the molten steel during the VD vacuum refining process; too little SiO2 in the slag will increase the basicity of the slag, reduce the slag fluidity, and reduce the slag reaction efficiency.

[0043] Furthermore, the amount of slag is 10-12 kg per ton of steel.

[0044] The slag volume is smaller than that of the traditional LF+VD process. The smaller the slag volume, the less SiO2 is available to react with Al in the molten steel during the VD vacuum refining process. This inhibits the reaction between Al and SiO2, thereby reducing aluminum loss during the VD vacuum refining process. Excessive slag can lead to slag overflow during the VD vacuum refining process, impacting production safety and increasing costs. Too little slag reduces the efficiency of S and O removal, failing to meet steel grade cleanliness control requirements.

[0045] Furthermore, the basicity of the slag is 4.5-5.5.

[0046] A high slag basicity can improve slag desulfurization effectiveness. If the slag basicity is too low, the SiO2 mass fraction in the slag is too high, which promotes the reaction between Al in the molten steel and SiO2 in the slag, increasing Al burn-off during the VD vacuum refining process. If the slag basicity is too high, the SiO2 mass fraction in the slag is low, reducing the slag's fluidity and the slag's efficiency in participating in desulfurization and deoxidation reactions. Basicity here refers to the ratio of the mass fraction of CaO to the mass fraction of SiO2.

[0047] Furthermore, the ratio of CaO to Al2O3 in the slag is 1.5-1.7.

[0048] The ratio of CaO to Al2O3 affects the slag's ability to absorb oxides, especially the deoxidized product Al2O3. When the C / A (the ratio of the mass fraction of CaO to the mass fraction of Al2O3) is between 1.5 and 1.7, the slag has the best effect in adsorbing inclusions. If this ratio exceeds 1.7, during the actual smelting process, it is very easy for the slag to have a high CaO content in some areas, resulting in poor slag fluidity and poor inclusion adsorption. If this ratio is less than 1.5, during the actual smelting process, the viscosity of some parts of the slag is too low, reducing the efficiency of Al2O3 adsorption by the slag.

[0049] Furthermore, the slag includes the following components in mass fractions: CaO: 48-52%, SiO2: 8-10%, Al2O3: 28-32%, MgO: 8-10%, and CaF2: 5%.

[0050] S4, performing VD vacuum refining on the pre-refined molten steel to obtain alloy steel molten steel.

[0051] Furthermore, in this embodiment, the VD vacuum refining process has a holding time of 11-13 minutes and a holding pressure of 67 Pa. During the VD vacuum refining process, the slag and molten steel mix and tumble, and under vacuum conditions, the following equilibrium reaction occurs: 2(Al2O3) + 3[Si] = 4[Al] + 3(SiO2). Although the molten steel comes into contact with the slag during the pre-refining process, this equilibrium reaction does not exist and can only occur under vacuum conditions.

[0052] The above alloy steel liquid can be further alloyed with silicon-containing alloy, B-containing alloy and titanium-containing alloy according to the target composition requirements to achieve the target alloy composition requirements.

[0053] For steel grades with a target Si content exceeding 0.5%, a process of adding silicon-containing alloys twice can be adopted. The first addition of silicon-containing alloys during the converter tapping process can remove oxygen from the molten steel and ensure that the Si mass fraction in the molten steel is in the range of 0.3-0.5%, and is combined with an Al content of 0.035-0.0045% to avoid silicon and aluminum loss during VD vacuum refining. The second addition of silicon-containing alloys after the VD breaks the air can achieve the target composition.

[0054] The present invention controls the Si and Al contents before VD vacuum refining and adopts a converter-pre-refining-VD smelting mode to achieve alloying of Si and Al elements while reducing Al and Si losses. Pre-refining replaces the LF furnace while shortening the VD smelting time, improving production efficiency, and at the same time reducing the S content to 0.0050%.

[0055] The following is a detailed description of the alloy steel smelting method of the present invention in combination with embodiments, comparative examples and experimental data.

[0056] Example 1 to Example 5

[0057] Examples 1 to 4 provide an Al-deoxidized low-carbon clean steel, the finished product composition of which is shown in Table 1, and the smelting method thereof includes:

[0058] Step 1: The final temperature is controlled at 1680-1700°C through converter smelting. Ferrosilicon and ferroaluminum are added during the converter tapping process to control the silicon content and aluminum content in the molten steel, as shown in Table 2.

[0059] Step 2: After tapping the converter, slag is added to the ladle for pre-refining to remove sulfur from the molten steel. The composition of the slag is shown in Table 2.

[0060] Step 3: The molten steel treated in step 2 is vacuumed for VD vacuum refining. The holding pressure and holding time are shown in Table 3.

[0061] Step 4: After the molten steel obtained from the VD vacuum refining in step 3 is degased, SiFe alloy is added to the molten steel for alloying, and the molten steel is sent to a casting machine for casting to obtain a billet of alloy steel.

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a smelting method for Al-deoxidized low-carbon clean steel. Taking Example 1 as a reference, the difference between Comparative Example 1 and Example 1 is that the silicon content and aluminum content in the molten steel after the converter is tapped are lower than those in Example 1, as shown in Table 2.

[0064] Comparative Example 2

[0065] Comparative Example 2 provides a smelting method for Al-deoxidized low-carbon clean steel. Taking Example 1 as a reference, the difference between Comparative Example 1 and Example 1 is that the silicon content and aluminum content in the molten steel after the converter is tapped are higher than those in Example 1, as shown in Table 2.

[0066] Comparative Example 3

[0067] Comparative Example 3 provides a smelting method for Al-deoxidized low-carbon clean steel, whose target composition is the same as that of Example 1. The smelting method is converter-LF furnace-VD vacuum refining, and ferrosilicon and ferroaluminum are added during the converter tapping process.

[0068] Table 1

[0069] serial number C / ％ Si / % Mn / % P / ％ S / ％ Al / ％ T.[O],ppm Example 1 0.08 0.78 1.50 0.012 0.0050 0.038 15 Example 2 0.07 0.82 1.51 0.013 0.0048 0.041 16 Example 3 0.10 0.77 1.49 0.012 0.0051 0.036 15 Example 4 0.06 0.75 1.51 0.011 0.0050 0.035 12 Example 5 0.09 0.79 1.49 0.012 0.0050 0.037 13 Comparative Example 1 0.08 0.80 1.50 0.011 0.0050 0.025 17 Comparative Example 2 0.08 0.80 1.50 0.013 0.0050 0.042 12 Comparative Example 3 0.08 0.78 1.50 0.012 0.0050 0.038 15

[0070] Table 2

[0071]

[0072] Table 3

[0073]

[0074] Table 4

[0075]

[0076] After VD was completed, bucket samples were taken from the molten steel of Examples 1 to 5 and Comparative Examples 1 to 3, and the 5 mm 2 The density of inclusions is statistically analyzed in the field of view, as shown in Table 4.

[0077] From the data in Table 4, it can be seen that the smelting methods provided by Examples 1 to 5 of the present invention have a VD smelting process in which the Al loss is 2.38-5.41%, the Al loss is low, the smelting time is 53-54 min, the production efficiency is high, the Si yield is 90.91-92.86%, the yield is high, the sulfur mass fraction of the finished product is 0.0048-0.0050%, the sulfur content is low, and the inclusion density is 20-30 pieces / mm 2 , the cleanliness of steel is high.

[0078] In the smelting methods provided in Comparative Examples 1 and 2, the Al loss in the VD smelting process is 12.50-28.57%, which is higher than that in Examples 1 to 5 of the present invention. The smelting time is 54-55 min, which is equivalent to that in Examples 1 to 5 of the present invention. The sulfur mass fraction of the finished product is 0.0050%, and the inclusion density is 38-42 pieces / mm 2 The cleanliness of the steel is lower than that of Examples 1 to 5 of the present invention. This is because the Al loss is high and the lost Al reacts with oxygen to form inclusions.

[0079] In the smelting method provided in Comparative Example 3, the Al loss in the VD smelting process is 45.71%, which is higher than that in Examples 1 to 5 of the present invention. The Si yield is 85.95%, which is lower than that in Examples 1 to 5 of the present invention. The smelting time is 73 min, which is longer than that in Examples 1 to 5 of the present invention, and the production efficiency is low. The sulfur mass fraction of the finished product is 0.0050%, and the inclusion density is 49 pieces / mm 2 The cleanliness of the steel is lower than that of Examples 1 to 5 of the present invention. This is because the Al loss is high and the lost Al reacts with oxygen to form inclusions.

[0080] It should be noted that the mass fraction of Si in the SiFe used in Examples 1 to 5 and Comparative Examples 1 to 3 is 75%; the mass fraction of Al in the AlFe is 40%. The present invention controls the content of Si and Al before VD vacuum refining and cooperates with the smelting mode of converter-pre-refining-VD to achieve the alloying of Si and Al elements while reducing the loss of Al and Si. Pre-refining replaces the LF furnace while shortening the VD smelting time, improving production efficiency, and also reducing the S content to 0.0050%. Using the smelting method provided by the present invention, the Al loss in the VD smelting process is 2.38-5.41%, the Al loss is low, the smelting time is 53-54min, the production efficiency is high, the Si yield is 90.91-92.86%, the yield is high, the sulfur mass fraction of the finished product is 0.0048-0.0050%, the sulfur content is low, and the inclusion density is 20-30 pieces / mm 2 , the cleanliness of steel is high.

[0081] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0082] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0083] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for smelting alloy steel, characterized in that: The smelting method comprises: The molten iron and scrap steel are loaded into a converter for smelting to obtain converter end-point molten steel; tapping the final molten steel from the converter and adding a silicon-containing alloy and an aluminum-containing alloy to perform alloying to obtain alloyed molten steel; The alloyed steel liquid is pre-refined by adding slag to obtain a pre-refined steel liquid; in the pre-refined steel liquid, the mass fraction of Si is 0.35-0.5%, and the mass fraction of Al is 0.035-0.045%, so as to avoid Al loss and Si loss; the mass fraction of SiO2 in the slag during the pre-refining process is 8.8-10%, the basicity of the slag is 4.5-5.5, and the amount of the slag is 10-12 kg / ton of steel; The pre-refined molten steel is subjected to VD vacuum refining to obtain alloy steel molten steel.

2. The alloy steel smelting method according to claim 1, characterized in that: The mass fraction of Si is 0.4-0.45%.

3. The alloy steel smelting method according to claim 1, characterized in that: The temperature of the molten steel at the converter endpoint is 1680-1700°C.

4. The alloy steel smelting method according to claim 1, characterized in that: The ratio of CaO to Al2O3 in the slag is 1.5-1.

7.

5. The alloy steel smelting method according to claim 1, characterized in that: The slag includes the following components in mass fractions: CaO: 48-52%, Al2O3: 28-32%, MgO: 7-10%, and CaF2: 0-5%.

6. The alloy steel smelting method according to claim 1, characterized in that: In the VD vacuum refining, the holding time is 11-13 minutes and the holding pressure is 67 Pa.

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