Method for reducing aggregation of Al2O3 inclusions in ultra-low carbon steel

Abstract

The invention relates to a method for reducing aggregation of Al2O3 inclusions in ultra-low carbon steel, and belongs to the technical field of refining. The method comprises the steps that in the converter tapping process, aluminum slag balls and small-particle lime are added into molten steel so as to carry out slag modification on the molten steel, and RH refining in-station molten steel is obtained; carrying out decarburization treatment on the RH refining incoming molten steel so as to reduce the carbon content in the RH refining incoming molten steel; carrying out deoxidation treatment on the decarburized RH refining incoming molten steel by using a magnesium-aluminum-iron alloy; and the deoxidized RH refining in-station molten steel is continuously subjected to RH vacuum circulation, so that Al2O3 inclusions in the RH refining in-station molten steel are reduced. In the RH refining process, magnesium-aluminum-iron alloy is adopted for deoxidation treatment, stable MgO.Al2O3 inclusions are generated, the inclusions float upwards more easily than independent Al2O3 inclusions and are removed, gathering of pure Al2O3 inclusions at a water gap can be obviously reduced, and therefore water gap blocking of the Al2O3 inclusions in the casting process is reduced.

Description

Technical Field

[0001] The present application relates to the field of refining technology, and in particular to a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel. Background Art

[0002] When casting ultra-low carbon steel (C < 0.0030%), aluminum particles are often used in the RH refining process to deoxidize the steel. Aluminum particles react with oxygen in the molten steel to form Al2O3 inclusions, which may affect the plasticity and toughness of the steel. Ultra-low carbon steel is an important automotive steel material. Titanium is usually added to the steel after deoxidation to form precipitates to improve the deep drawing properties of the steel. However, as an element with strong deoxidation ability, titanium enters the molten steel and forms Al-Ti type composite inclusions with Al2O3, which increases the wettability of the molten steel and is more difficult to remove and float. In the later calming and casting process, some of these composite inclusions still exist in the molten steel, and they are easy to gather at the outlet of the submerged water nozzle of the crystallizer, causing water nozzle blockage. Water nozzle blockage can cause the molten steel to flow asymmetric in the flow field of the crystallizer, thereby affecting the liquid level fluctuation, causing slag roll defects, and further affecting the quality of the ingot.

[0003] One method to improve the cleanliness of low-carbon steel is to add carbon structural alloy balls, ferromanganese and silicon-manganese alloy into the ladle when the converter is 1 / 8 to 1 / 6 of the steel to deoxidize and alloy the molten steel, so as to control the carbon, manganese and silicon elements in the steel and the types of inclusions in the steel. The RH process controls the processing parameters to promote the floating removal of inclusions in the steel, thereby improving the cleanliness of the molten steel. However, the addition is carried out during the converter steel-making process, which is different from the RH refining method introduced in this article. The preparation method of the micro-carbon aluminum-magnesium-iron alloy used for final deoxidation and alloying of molten steel is also provided, but the industrial application process is not introduced in detail. Summary of the invention

[0004] The present application provides a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel to solve the following technical problem: how to reduce the aggregation of Al2O3 inclusions in carbon steel at a nozzle.

[0005] The present application provides a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel, the method comprising:

[0006] In the process of steel tapping from the converter, aluminum slag balls and small-grained lime are added to the molten steel to modify the molten steel to obtain RH refined steel.

[0007] Decarburizing the RH refined incoming steel to reduce the carbon content in the RH refined incoming steel;

[0008] Using magnesium-aluminum-iron alloy, deoxidizing the RH refined incoming steel liquid after decarburization treatment;

[0009] The RH refined incoming steel liquid after deoxidation treatment continues to be subjected to RH vacuum circulation to reduce Al2O3 inclusions in the RH refined incoming steel liquid.

[0010] Optionally, the composition of the magnesium-aluminum-iron alloy includes, by mass fraction: Mg: 10% to 12%, Al: 65% to 75%, Fe: 15% to 25%.

[0011] Optionally, the particle size of the magnesium-aluminum-iron alloy is 10 mm to 50 mm.

[0012] Optionally, the oxygen content of the molten steel produced from the converter is 500ppm to 700ppm.

[0013] Optionally, the temperature of the molten steel tapped from the converter is 1670°C to 1685°C.

[0014] Optionally, the amount of the aluminum slag balls is 1.4kg / t steel to 1.7kg / t.

[0015] Optionally, the usage of the small-grain lime is 2.7kg / t to 4.0kg / t steel.

[0016] Optionally, the temperature of the decarburization treatment is 1610° C. to 1620° C., and the time of the decarburization treatment is 14 min to 16 min.

[0017] Optionally, the vacuum degree of the RH vacuum cycle is 70Pa to 100Pa, and the time for continuing the RH vacuum cycle is 7 minutes to 9 minutes.

[0018] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0019] The present application provides a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel, the method comprising: adding aluminum slag balls and small particles of white ash to molten steel during the process of steel tapping from a converter to perform slag modification on the molten steel to obtain RH refined incoming steel; decarburizing the RH refined incoming steel to reduce the carbon content in the RH refined incoming steel; using a magnesium-aluminum-iron alloy to deoxidize the RH refined incoming steel after the decarburization treatment; continuing to perform an RH vacuum cycle on the RH refined incoming steel after the deoxidation treatment to reduce the Al2O3 inclusions in the RH refined incoming steel. In the RH refining process, after the RH refined incoming steel is decarburized, a magnesium-aluminum-iron alloy is used to perform deoxidation treatment.

[0020] Mg and Al in magnesium-aluminum-iron alloy have strong oxygen affinity and can react with oxygen in molten steel to form stable MgO·Al2O3 inclusions. These inclusions are easier to float and be removed than single Al2O3 inclusions, which can significantly reduce the aggregation of pure Al2O3 inclusions in the nozzle, thereby reducing the nozzle blockage caused by Al2O3 inclusions during the casting process. 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 reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel according to some embodiments 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, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has 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 applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0026] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" 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. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. 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.

[0027] Figure 1 A schematic flow chart of a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel provided in an embodiment of the present application.

[0028] See also Figure 1 The present application provides a method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel, the method comprising:

[0029] S1. During the process of steel tapping from a converter, aluminum slag balls and small-grained lime are added to the molten steel to perform slag modification on the molten steel to obtain RH refined steel entering the station;

[0030] In some embodiments, the oxygen content of the molten steel tapped from the converter is 500ppm to 700ppm.

[0031] The positive effect of controlling the oxygen content of the molten steel from the converter to 500ppm to 700ppm: When the oxygen content of the molten steel from the converter is high, the number of inclusions in the steel will increase. Too much oxygen is dissolved in the molten steel, and deoxidation treatment is required during steel tapping, which will generate more primary and secondary deoxidation products, which become inclusions in the steel. When the oxygen content of the molten steel from the converter is too low, it may not be possible to form dispersed fine inclusions that meet the content requirements. Exemplarily, the endpoint oxygen content can be 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, etc.

[0032] In some embodiments, the temperature of the molten steel tapped from the converter is 1670°C to 1685°C.

[0033] The positive effects of controlling the temperature of the molten steel from the converter to 1670℃~1685℃: The appropriate temperature of the molten steel from the converter is conducive to the floating removal of inclusions in the molten steel, providing a good basic condition for subsequent refining operations, ensuring the smooth progress of the refining process and achieving the expected refining effect. Too high a temperature may lead to uneven composition of the ingot during the casting process, affecting the quality and performance of the steel, and too low a temperature may affect the fluidity of the molten steel. Exemplarily, the terminal temperature of the converter smelting can be 1670℃, 1672℃, 1678℃, 1680℃, 1685℃, etc.

[0034] In some embodiments, the amount of the aluminum slag balls is 1.4 kg / t steel to 1.7 kg / t.

[0035] In some embodiments, the amount of the small-grain lime used is 2.7 kg / t to 4.0 kg / t steel.

[0036] The positive effect of adding aluminum slag balls and small-grained lime: Modify the slag to optimize the desulfurization, deoxidation and fluidity of the slag. If too much aluminum slag balls and small-grained lime are added during steelmaking, on the one hand, the amount of slag is too large, which increases the total amount of slag and may increase the difficulty of subsequent processing steps, such as slag transportation and treatment. On the other hand, it will lead to an increase in raw material costs. If too little aluminum slag balls and small-grained lime are added during steelmaking, on the one hand, the slag performance is not improved enough, the fluidity of the slag cannot be fully optimized, and it is not conducive to the floating removal of inclusions, which reduces the purity of the molten steel. On the other hand, the desulfurization and deoxidation effects are not good, and the sulfur and oxygen content in the molten steel cannot be effectively reduced, affecting the quality of the steel. Exemplarily, the dosage of aluminum slag balls can be 1.4kg / t steel, 1.42kg / t steel, 1.5kg / t steel, 1.6kg / t steel, 1.7kg / t, etc.; the dosage of small-grain lime can be 2.7kg / t, 2.8kg / t, 3.0kg / t, 3.5kg / t, 4.0kg / t steel, etc.

[0037] S2, decarburizing the RH refined incoming molten steel to reduce the carbon content in the RH refined incoming molten steel;

[0038] The mode of decarburization treatment mainly depends on the conditions of the molten steel when it enters the station, including the C content in the molten steel, temperature and other conditions. The decarburization mode can be forced decarburization or natural decarburization.

[0039] In some embodiments, the temperature of the decarburization treatment is 1610° C. to 1620° C., and the time of the decarburization treatment is 14 min to 16 min.

[0040] Decarburization can reduce the carbon content in steel, thereby improving the mechanical properties and processing properties of steel. Carrying out decarburization at the right temperature can optimize the use of energy. Too low a temperature may result in a slow decarburization reaction rate, while too high a temperature may increase energy consumption and may cause the molten steel to overheat.

[0041] The positive effect of the decarburization treatment temperature being 1610°C to 1620°C: within this temperature range, the fluidity of the molten steel is good, which is conducive to the diffusion and dissolution of the gas in the molten steel, thereby promoting the decarburization reaction. Exemplarily, the decarburization treatment temperature can be 1610°C, 1612°C, 1614°C, 1618°C, 1620°C, etc.

[0042] The positive effect of decarburization treatment time of 14 minutes to 16 minutes: Control of decarburization time is crucial. Too long decarburization time may lead to excessive oxidation of molten steel and increase the formation of inclusions; while too short decarburization time may make the molten steel unable to reach the expected carbon content. Therefore, when smelting ultra-low carbon steel, the decarburization time is controlled between 14 and 16 minutes to ensure that the carbon content in the molten steel is stable and reaches the target value. Exemplarily, the decarburization time can be 14 minutes, 15 minutes, 16 minutes, etc.

[0043] S3, using magnesium-aluminum-iron alloy to deoxidize the RH refined incoming molten steel after decarburization treatment;

[0044] In some embodiments, the magnesium-aluminum-iron alloy comprises, by mass fraction, Mg: 10% to 12%, Al: 65% to 75%, and Fe: 15% to 25%.

[0045] The magnesium-aluminum-iron alloy is a purchased product.

[0046] If the Mg content in the magnesium-aluminum-iron alloy is too high, it will lead to the formation of too many inclusions, affecting the purity of the molten steel and increasing the cost. If the Mg content is too low, the deoxidation effect is not significant, and it cannot form MgO-Al2O3 type composite inclusions with Al2O3 type inclusions, and it is difficult to play its role in improving the fluidity of the molten steel. For example, the Mg content can be 10%, 10.5%, 11%, 11.5%, 12%, etc.

[0047] If the Al content in the magnesium-aluminum-iron alloy is too high, a large amount of Al2O3 inclusions will be generated, which may cause the pouring performance of the molten steel to deteriorate. If the Al content is too low, deoxidation is insufficient and the goal of reducing the oxygen content cannot be achieved. For example, the Al content can be 65%, 67%, 69%, 73%, 75%, etc.

[0048] Magnesium, aluminum and iron can play a synergistic role in the deoxidation process. Magnesium and aluminum are both strong deoxidizers that can quickly combine with oxygen in molten steel to form stable oxides. The appropriate amount of iron content helps to adjust the density and melting point of the alloy, allowing it to be better dispersed and dissolved in molten steel, thereby improving the deoxidation efficiency. In addition, the addition of iron can reduce the activity of the alloy, reduce the burning loss of magnesium and aluminum at high temperatures, and retain more deoxidizing elements in the molten steel to play a deoxidizing role. Exemplarily, the Fe content can be 15%, 17%, 19%, 23%, 25%, etc.

[0049] In some embodiments, the particle size of the magnesium-aluminum-iron alloy is 10 mm to 50 mm.

[0050] The positive effect of controlling the particle size of the magnesium-aluminum-iron alloy to 10 mm to 50 mm is that the moderate particle size helps the alloy to dissolve and disperse rapidly in the molten steel and accelerates the deoxidation reaction. For example, the particle size of the magnesium-aluminum-iron alloy can be 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc.

[0051] In some embodiments, Ti—Fe and Mn—Fe alloys may be added after 2 to 5 minutes of deoxidation.

[0052] The addition of Ti-Fe and Mn-Fe alloying elements aims to adjust the titanium and manganese content in the steel and further improve the performance of the steel.

[0053] S4. The RH refined incoming steel liquid after deoxidation treatment is further subjected to RH vacuum circulation to reduce Al2O3 inclusions in the RH refined incoming steel liquid.

[0054] In some embodiments, the vacuum degree of the RH vacuum cycle is 70 Pa to 100 Pa, and the duration of the RH vacuum cycle is 7 minutes to 9 minutes.

[0055] The positive effect of the vacuum degree of the RH vacuum cycle being 70Pa to 100Pa: within this vacuum degree range, the insoluble gas in the molten steel can be effectively released in a vacuum environment, significantly reducing the gas content in the molten steel, thereby improving the purity of the molten steel. Exemplarily, the vacuum degree of the RH vacuum cycle can be 70Pa, 75Pa, 80Pa, 90Pa, 100Pa, etc.

[0056] The positive effect of the RH vacuum cycle time of 7 minutes to 9 minutes: If the cycle time is too long, it will increase production costs, including energy consumption and equipment operation time costs. At the same time, it will cause the molten steel temperature to drop too much, affecting the subsequent casting operation. Therefore, in the RH refining link, strictly controlling the cycle time to 7 minutes to 9 minutes is a reasonable choice that comprehensively considers cost and process requirements while ensuring the refining effect and molten steel quality. Exemplarily, the RH vacuum cycle time can be 7 minutes, 8 minutes, 9 minutes, etc.

[0057] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples that do not specify specific conditions are usually measured according to industry standards; if there are no corresponding industry standards, they are carried out according to common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0058] Example 1

[0059] In a certain batch of ultra-low carbon SDC04 steel, the terminal temperature of converter smelting is 1679℃, the terminal oxygen content is 527ppm, aluminum slag balls and small white ash are added for slag modification during steel tapping, RH refining is carried out for natural decarburization, the decarburization time is 15min, magnesium-aluminum-iron alloy is used for complete deoxidation, and the Alt content in the steel is adjusted to 0.042% according to the target after deoxidation. At the same time, Fe-Ti and manganese-iron alloy are added, and RH pure circulation is 8min to break the air. By using magnesium-aluminum-iron alloy RH deoxidation for ultra-low carbon SDC04, the oxygen content of the tundish is detected to be 12ppm, and the inclusions of the ingot are mostly Al2O3-MgO composite inclusions. The average size of the inclusions is 4.3μm. The position of the plug rod does not change much during the entire casting process. The replacement of the water nozzle is observed, and it can be observed that the submerged nozzle is not significantly blocked. Through long-term tracking of this method, it is found that the water nozzle blockage rate has been reduced from the original 2.1% to 0.8%, and the effect is significant.

[0060] Comparative Example 1

[0061] In a certain batch of ultra-low carbon SDC04 steel, the end temperature of converter smelting was 1679℃, the end oxygen content was 561ppm, aluminum slag balls and small-grained lime were added for slag modification during steel tapping, RH refining was used for natural decarburization, the decarburization time was 14min, Al particles were used for complete deoxidation, and the Alt content in the steel was adjusted to 0.044% according to the target after deoxidation. At the same time, Fe-Ti and ferromanganese alloy were added, and the RH pure cycle was 7min. By using Al particles RH deoxidation for ultra-low carbon SDC04, the oxygen content in the tundish was detected to be 16.6ppm, and the inclusions in the ingot were mostly Al2O3 inclusions, with an average particle size of 6.8μm. The position of the plug rod increased greatly during the entire casting process, and the replacement of the water inlet was observed, and it was observed that one side of the submerged water inlet was obviously blocked.

[0062] It can be seen from Example 1 and Comparative Example 1 that after RH refining and decarburization, Example 1 uses magnesium-aluminum-iron alloy instead of Al particles for deoxidation, and the oxygen content in the tundish is significantly lower than the oxygen content in the tundish when Al is used for deoxidation during RH refining, and the deoxidation effect is better. After RH refining and decarburization, Example 1 uses magnesium-aluminum-iron alloy instead of Al particles for deoxidation, and it can be observed that the submerged water nozzle does not have obvious blockage. The blockage caused by the accumulation of Al2O3-type inclusions at the water nozzle is improved. After RH refining and decarburization, Example 1 uses magnesium-aluminum-iron alloy instead of Al particles for deoxidation. The types of inclusions detected and analyzed in the ingot inclusions are mostly Al2O3-MgO composite inclusions, and the average size of the inclusion particle size is lower than the average size of the inclusion particle size of the ingot inclusions after RH refining and deoxidation of Al particles. Deoxidation of aluminum-magnesium-iron alloy can make the inclusions in the steel smaller, which helps to improve the overall performance of the steel.

[0063] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0064] The method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel provided in an embodiment of the present invention generates deoxidation products mainly of Al-Mg-O, the particle size of these products is finer, the proportion of inclusions <5μm is increased by about 10%, and the distribution is more dispersed. Compared with Al particle deoxidation, the aggregation degree of inclusions is significantly reduced, thereby significantly improving the cleanliness of the molten steel.

[0065] 2. Deoxidation of magnesium-aluminum-iron alloy can improve the morphology of alumina inclusions. The generated inclusions are mainly MgO·Al2O3. This fine and dispersed inclusion has little effect on the fatigue properties of steel. At the same time, the magnesium dissolved in the steel plays the role of spheroidizing carbides, which helps to improve the performance of the steel.

[0066] 3. The inclusion scrap rate of IF steel deoxidized by magnesium-aluminum-iron alloy in cold-rolled plate production is significantly reduced by about 1.0%, which shows that deoxidation of magnesium-aluminum-iron alloy can improve the cleanliness of molten steel and improve product quality.

[0067] 4. Deoxidation of magnesium-aluminum-iron alloy can reduce the formation of Al2O3 inclusions, thereby reducing aluminum consumption and improving production efficiency. The number of continuous casting furnaces can be increased by one furnace on average, and the number of water outlets used can be reduced.

[0068] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application 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 these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features applied for by the present application.

Claims

1. A method for reducing the aggregation of Al2O3 inclusions in ultra-low carbon steel, characterized in that: The method comprises: In the process of steel tapping from the converter, aluminum slag balls and small-grained lime are added to the molten steel to modify the molten steel to obtain RH refined steel. Decarburizing the RH refined incoming steel to reduce the carbon content in the RH refined incoming steel; Using magnesium-aluminum-iron alloy, deoxidizing the RH refined incoming steel liquid after decarburization treatment; The RH refined incoming steel liquid after deoxidation treatment continues to be subjected to RH vacuum circulation to reduce Al2O3 inclusions in the RH refined incoming steel liquid.

2. The method according to claim 1, characterized in that: In terms of mass fraction, the components of the magnesium-aluminum-iron alloy include: Mg: 10% to 12%, Al: 65% to 75%, and Fe: 15% to 25%.

3. The method according to claim 1, characterized in that The particle size of the magnesium-aluminum-iron alloy is 10 mm to 50 mm.

4. The method according to claim 1, characterized in that: The oxygen content of the molten steel tapped from the converter is 500ppm to 700ppm.

5. The method according to claim 1, characterized in that The temperature of the molten steel tapped from the converter is 1670°C to 1685°C.

6. The method according to claim 1, characterized in that The usage of the aluminum slag balls is 1.4kg / t steel to 1.7kg / t.

7. The method according to claim 1, characterized in that The usage of the small-grain lime is 2.7kg / t to 4.0kg / t steel.

8. The method according to claim 1, characterized in that The temperature of the decarburization treatment is 1610° C. to 1620° C., and the time of the decarburization treatment is 14 min to 16 min.

9. The method according to claim 1, characterized in that: The vacuum degree of the RH vacuum cycle is 70Pa to 100Pa, and the time for continuing the RH vacuum cycle is 7 minutes to 9 minutes.

Images