Rare earth steel additive, rare earth steel, production method and use

Abstract

The invention discloses a rare earth steel additive, rare earth steel, a production method and a use thereof. The rare earth steel additive comprises the following components: 4-15wt% La, 8-28wt% Ce, 30-65wt% Si, 0.5-3.5wt% Al, 0.5-15wt% Ca and 5-30wt% Fe. The additive of the invention is beneficial to improving the castability in the continuous casting production of molten steel.

Description

Technical Field

[0001] The invention relates to a rare earth steel additive, rare earth steel, a production method and application. Background Art

[0002] Rare earth steel is a special type of steel containing a certain amount of rare earth. Compared with non-rare earth steel, rare earth steel has unique physical, chemical and mechanical properties, and is a high-quality new steel material. The expansion of rare earth steel production is also conducive to the large-scale consumption of high-abundance rare earth elements, achieving balanced utilization of rare earth resources, and promoting the sustainable and healthy development of the rare earth industry.

[0003] In recent years, the smelting technology of rare earth steel has made some progress, but the production process of rare earth steel still has the problem of poor castability, for example, there is a problem of nozzle nodules during continuous casting. In the steelmaking process, the problem of molten steel castability directly affects the continuous production and product quality of steel.

[0004] CN101550475A discloses a method for producing ultra-low carbon steel, the process route of which is: hot metal desulfurization pretreatment - converter smelting - ladle furnace treatment - RH vacuum treatment - slab continuous casting. In the RH vacuum treatment step, Al2O3 impurities in the steel are removed after vacuum deoxidation, avoiding clogging of the water inlet and achieving smooth casting of molten steel. However, this method is not suitable for the production of rare earth steel.

[0005] CN113088791A discloses a method for preparing rare earth steel by reducing rare earth oxides in steps during the refining process. The method first adds the prepared slag containing rare earth oxides at the beginning of LF refining or before LF refining and when the converter is tapped, and uses the aluminum in the steel to reduce the cerium oxide in the refined slag; after the LF refining treatment is completed, the calcium wire is fed, and the slag containing rare earth oxides is added again while feeding the calcium wire, and the slag containing rare earth oxides is stirred by bottom blowing of the ladle to achieve the reduction of rare earth lanthanum and cerium and direct alloying. The method still has the problem of nozzle nodules. In addition, the method adds rare earth oxides twice to the slag, which is costly, has low smelting efficiency, and is difficult to reduce.

[0006] CN116219261A discloses a method for preparing rare earth steel, which uses rare earth manganese alloy as a rare earth source to improve the actual rare earth yield in rare earth steel. This method still has the problem of outlet blockage. In addition, this method is only applicable to steel grades that do not require manganese. The rare earth used in the embodiment of this method is relatively expensive yttrium, not relatively cheap lanthanum cerium.

[0007] CN116274905A discloses a method for producing rare earth steel. The method uses a rare earth wire cored wire to feed the rare earth into the molten steel through a crystallizer. The castability of the method still needs to be improved, and the cost of the method is relatively high.

[0008] CN118460927A discloses a method for producing rare earth steel. The method includes: 1. component design; 2. blowing; 3. ladle deoxidation, alloying and slag making; 4. temperature control, power supply, argon blowing, adding silicon-barium alloy 3 minutes before steel tapping, adding rare earth alloy when refining and power off steel tapping; 5. blowing argon, adding carbonized rice husks to obtain clean molten steel; 6. pouring the clean molten steel. Although this method can alleviate the problem of nozzle nodules, it still needs to be further improved. In addition, the rare earth alloy added in the refining step is ferrosilicon-cerium alloy, and the cost is still high. Summary of the invention

[0009] In view of this, an object of the present invention is to provide a rare earth steel additive, which is beneficial to improving the castability in the continuous casting production of molten steel and continuously producing rare earth steel.

[0010] Another object of the present invention is to provide use of the rare earth steel additive.

[0011] Another object of the present invention is to provide a method for producing rare earth steel.

[0012] Another object of the present invention is to provide rare earth steel produced according to the production method as described above.

[0013] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0014] In one aspect, the present invention provides a rare earth steel additive, comprising the following components:

[0015] La 4~15wt%

[0016] Ce 8~28wt%

[0017] Si 30~65wt%

[0018] Al 0.5~3.5wt%

[0019] Ca 0.5~15wt%, and

[0020] Fe 5~30wt%.

[0021] The present invention also provides a rare earth steel additive, which consists of the following components:

[0022] La 4~15wt%

[0023] Ce 8~28wt%

[0024] Si 30~65wt%

[0025] Al 0.5~3.5wt%

[0026] Ca 0.5~15wt%, and

[0027] The balance is iron and inevitable impurities.

[0028] The rare earth steel additive according to the present invention is preferably composed of the following components:

[0029] La 8~15wt%

[0030] Ce 10~28wt%

[0031] Si 35~48wt%

[0032] Al 0.8~3.0wt%

[0033] Ca 0.5~5.0wt%, and

[0034] The balance is iron and inevitable impurities.

[0035] The rare earth steel additive according to the present invention is preferably composed of the following components:

[0036] La 9~13wt%

[0037] Ce 14~25wt%

[0038] Si 38~46wt%

[0039] Al 0.9~2.5wt%

[0040] Ca 0.6~2.0wt%, and

[0041] The balance is iron and inevitable impurities.

[0042] On the other hand, the present invention also provides a use of the rare earth steel additive as described above in improving the castability in the production process of rare earth steel, wherein the rare earth steel additive is added to molten steel in a ladle during steel tapping from a converter.

[0043] In another aspect, the present invention further provides a method for producing rare earth steel, comprising the following steps:

[0044] 1) When the converter smelting is finished, steel is tapped. When the tapping amount is 1 / 4 to 1 / 3, lime, silicon-manganese alloy, the rare earth steel additive and coke powder are added to the ladle, and the molten steel in the converter is continuously transferred to the ladle; during the process, inert gas is blown into the molten steel in the ladle for stirring; wherein, based on 1 t of molten steel, the amount of the rare earth steel additive is 0.3 to 3.5 kg;

[0045] 2) Place the ladle in the LF refining furnace and insert the electrode for heating; detect the oxygen content, silicon content and manganese content in the molten steel, as well as the basicity of the slag and the rare earth content in the slag;

[0046] 3) According to the test results of step 2), lime, fluorite, aluminum-iron alloy, and silicon-manganese alloy are added to the LF refining furnace, and stirred for reaction, and calcium wire is fed for reaction to complete refining; after the refining is completed, the off-site oxygen content and rare earth content of the molten steel are detected; wherein the rare earth content in the molten steel is controlled to be greater than or equal to 10ppm, and the off-site oxygen content of the molten steel is controlled to be less than or equal to 10ppm;

[0047] 4) After the molten steel passes the quality inspection, it is moved into the casting position, left to stand, and then casting begins to obtain rare earth steel; wherein, there is no liquid level fluctuation and no nozzle nodule during casting.

[0048] According to the production method of the present invention, preferably:

[0049] In step 1), the tapping temperature is 1600-1650° C., and the inert gas is argon;

[0050] In step 1), based on 1 t of molten steel, the amount of lime used is 1.7-2.1 kg, the amount of silicon-manganese alloy used is 4-8 kg, and the amount of coke powder used is 0.8-1.9 kg.

[0051] According to the production method of the present invention, preferably, in step 2), the in-situ temperature of the molten steel is controlled to be 1555-1665°C; the in-situ oxygen content of the molten steel is less than or equal to 50 ppm; and the basicity of the slag is 1-3.

[0052] According to the production method of the present invention, preferably:

[0053] In step 3), the temperature of the molten steel is controlled to be 1665-1680°C; the basicity of the slag is controlled to be 1.1-3.5;

[0054] In step 3), the length of the calcium feeding line is 130 to 200 m.

[0055] In yet another aspect, the present invention further provides a rare earth steel produced according to the production method as described above.

[0056] The rare earth steel additive of the present invention can improve the castability in the continuous casting production of molten steel, eliminate the phenomenon of nozzle nodules, and continuously produce rare earth steel. The rare earth steel additive of the present invention is added to the molten steel in the ladle when the molten steel is transferred out, rather than being added in the refining process, which is more conducive to improving the castability. In addition, the rare earth steel additive of the present invention can also reduce the off-site oxygen content of the obtained molten steel. In addition, the cost can also be reduced. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0058] At present, there are still problems of nozzle nodules and poor castability in the production of rare earth steel, which affect the continuity of continuous casting production. In addition, the cost is relatively high. These are the important reasons why rare earth steel has not been produced on a large scale.

[0059] The present invention has found that the rare earth steel additive of the specific composition of the present invention is added before refining and during the steel tapping process of the converter, rather than during refining, which can significantly improve the castability of the rare earth steel continuous casting production process, and can also make the oxygen content in the rare earth steel lower. In addition, the present invention uses a small amount of rare earth steel additive of a specific composition to reduce the addition amount of the traditional deoxidizer aluminum iron alloy, can reduce the addition amount of silicon manganese alloy, can replace the rare earth alloy (such as lanthanum cerium iron alloy, silicon iron cerium alloy) used in the prior art, and reduce costs. The present invention adds a rare earth steel additive of a specific composition at a specific stage, which not only solves the problems of nozzle nodules and poor castability in the continuous casting production of rare earth steel, but also reduces costs and has very good application prospects. This is not a conventional choice.

[0060] <Rare Earth Steel Additives>

[0061] The rare earth steel additive of the present invention is an alloy material containing rare earth metals. The rare earth steel additive of the present invention can be used in the production of rare earth steel, especially for improving the castability in continuous casting production. The rare earth steel additive can be added in the form of blocks, particles or powders.

[0062] The rare earth steel additive of the present invention comprises the following components: La 4-15wt%, Ce 8-28wt%, Si 30-65wt%, Al 0.5-3.5wt%, Ca 0.5-15wt% and Fe 5-30wt%. In certain embodiments, the rare earth steel additive of the present invention consists of the following components: La 4-15wt%, Ce 8-28wt%, Si 30-65wt%, Al 0.5-3.5wt%, Ca 0.5-15wt%, and the balance is iron and unavoidable impurities. The rare earth steel additive with such a ratio is conducive to improving castability and at the same time is conducive to lowering the oxygen content of molten steel when it leaves the situ.

[0063] In the rare earth steel additive of the present invention, La is lanthanum, and the amount of La can be 4-15wt%, preferably 6-15wt%, more preferably 8-15wt%, and further preferably 9-13wt%. Ce is cerium, and the amount of Ce can be 8-28wt%, preferably 10-28wt%, more preferably 14-25wt%, and further preferably 16-25wt%. The amount of La and Ce within such a range is conducive to improving castability while reducing the oxygen content in molten steel.

[0064] In the rare earth steel additive of the present invention, Si is silicon element, and the amount of Si can be 30-65wt%, preferably 35-55wt%, more preferably 38-50wt%, and more preferably 38-48wt%. If the amount of Si is not within the scope of the present invention, the castability cannot be improved more effectively.

[0065] In the rare earth steel additive of the present invention, Al is an aluminum element, and the amount of Al can be 0.5-3.5wt%, preferably 0.8-3.0wt%, and more preferably 0.9-2.5wt%. Ca is a calcium element, and the amount of Ca can be 0.5-15wt%, preferably 0.5-10wt%, more preferably 0.5-5wt%, and more preferably 0.6-2.0wt%. Such an amount of Al and Ca is more conducive to improving the castability in the continuous casting production of molten steel.

[0066] In the rare earth steel additive of the present invention, Fe is an iron element, and the amount of Fe can be 5-30wt%, preferably 9-28wt%, more preferably 12-26wt%, and further preferably 15-25wt%. Such an amount of Fe is more conducive to improving the castability in the continuous casting production of molten steel.

[0067] According to one aspect of the present invention, the rare earth steel additive comprises the following components but does not contain Mg, Ti and K:

[0068] La 4~15wt%

[0069] Ce 8~28wt%

[0070] Si 30~65wt%

[0071] Al 0.5~3.5wt%

[0072] Ca 0.5~15wt%, and

[0073] Fe 5~30wt%.

[0074] According to another aspect of the present invention, the rare earth steel additive consists of the following components and inevitable impurities:

[0075] La 4~15wt%

[0076] Ce 8~28wt%

[0077] Si 30~65wt%

[0078] Al 0.5~3.5wt%

[0079] Ca 0.5~15wt%, and

[0080] Fe 5~30wt%.

[0081] According to a specific embodiment of the present invention, the rare earth steel additive of the present invention is composed of the following components:

[0082] La 8~15wt%

[0083] Ce 10~28wt%

[0084] Si 35~55wt%

[0085] Al 0.8~3.0wt%

[0086] Ca 0.5~5.0wt%, and

[0087] The balance is iron and inevitable impurities.

[0088] According to another specific embodiment of the present invention, the rare earth steel additive consists of the following components and inevitable impurities:

[0089] La 9~13wt%

[0090] Ce 15~27wt%

[0091] Si 38~48wt%

[0092] Al 0.8~2.5wt%

[0093] Ca 0.5~2.0wt%, and

[0094] Fe 12~25wt%.

[0095] The rare earth steel additive of the present invention can be obtained by the following steps:

[0096] According to the element composition of the rare earth steel additive, powdered rare earth oxides (lanthanum oxide and cerium oxide), silicon oxide, iron filings, aluminum oxide and calcium oxide of corresponding proportions are added to the submerged arc furnace, and alloy liquid is generated under the reduction effect of coke, wherein the furnace mouth temperature of the submerged arc furnace is 500-600°C, and the arc zone temperature is greater than or equal to 2000°C. The obtained alloy liquid is put into a ladle, then ingotized and crushed to obtain the rare earth steel additive as described above.

[0097] <Purpose>

[0098] The present invention also provides the use of the rare earth steel additive. Specifically, the present invention provides the use of the rare earth steel additive in improving the castability in the rare earth steel production process, wherein the rare earth steel additive is added to the molten steel in the ladle when the converter is tapped (i.e., the molten steel is transferred from the converter to the ladle). The rare earth steel additive is as described above. The molten steel can be those known in the art, which will not be repeated here.

[0099] The present invention finds that adding the rare earth steel additive in the tapping stage of the steelmaking process, rather than in the refining stage, is more helpful in improving the castability of the molten steel and reducing the oxygen content of the molten steel. In addition, this can also save costs.

[0100] <Rare earth steel and its production method>

[0101] The present invention also provides a method for producing rare earth steel, comprising the following steps: 1) tapping and adding rare earth steel additives; 2) ladle placement and detection steps; 3) refining and detection steps; 4) casting steps. The prior art usually adds aluminum-iron alloy, lime, silicon-manganese alloy, and coke powder during tapping, and adds rare earth alloy, lime, fluorite, carburizer, aluminum-iron alloy, and silicon-manganese alloy during refining to prepare rare earth steel, but it is prone to problems such as nozzle nodules and poor castability. In addition, this method of the prior art is also relatively costly. The production method of the present invention has good castability in continuous casting production and no nozzle nodules.

[0102] A detailed description is given below.

[0103] Steps for tapping steel and adding rare earth steel additives

[0104] At the end of converter smelting, steel is tapped (i.e., at the end of converter smelting, the molten steel in the converter is transferred into a ladle). When the transferred amount is 1 / 4 to 1 / 3, lime, silicon-manganese alloy, the rare earth steel additive as described above and coke powder are added into the ladle, and the molten steel in the converter is continuously transferred into the ladle. During the process, inert gas is blown into the molten steel in the ladle for stirring. Specifically, the amount of the rare earth steel additive used is 0.3 to 3.5 kg based on 1 t of molten steel.

[0105] The type of molten steel in the converter is not particularly limited, and may be, for example, molten steel for forming ordinary carbon steel, low alloy steel or silicon steel. According to a specific embodiment of the present invention, the molten steel in the converter is HRB400 molten steel, and the quality is controlled according to Q235B.

[0106] The molten steel in the converter can be obtained by pre-treating the molten iron. The pre-treatment can adopt a process known in the art, which will not be described in detail here.

[0107] The tapping temperature is 1600-1650° C., preferably 1605-1645° C., and more preferably 1605-1640° C. The inert gas may be helium or argon, preferably argon. The oxygen content of the molten steel during tapping is 400-780 ppm, for example, 600-780 ppm.

[0108] Based on 1t of molten steel, the dosage of the rare earth steel additive can be 0.3-3.5kg, preferably 0.4-2.5kg, more preferably 0.5-2.0kg, more preferably 0.6-1.5kg, and further preferably 0.7-1.2kg. The dosage of the rare earth steel additive can be, for example, 0.7kg, 0.8kg, 0.9kg, 0.95kg, 1.0kg, 1.1kg, 1.2kg. The dosage of the rare earth steel additive within this range can not only improve the castability of the molten steel in the continuous casting production process, but also reduce the oxygen content to the target range. In addition, this can also save costs.

[0109] Based on 1 t of molten steel, the amount of lime used may be 1.7 to 2.1 kg, preferably 1.75 to 2.0 kg, and more preferably 1.8 to 1.9 kg.

[0110] Based on 1 t of molten steel, the amount of silicon-manganese alloy used may be 4-8 kg, preferably 5-7.5 kg, and more preferably 5.5-7 kg.

[0111] Based on 1 t of molten steel, the amount of coke powder used may be 0.8 to 1.9 kg, preferably 0.9 to 1.7 kg, and more preferably 1.0 to 1.5 kg. Coke powder is the undersize of coke.

[0112] 1t of molten steel refers to 1 ton of molten steel.

[0113] During the steel tapping and charging process, an inert gas is blown into the molten steel in the ladle, for example, argon is blown for stirring. When blowing argon, the argon flow rate is greater than 50 L / min and less than 800 L / min, preferably 80 to 500 L / min, for example, 300 L / min. The argon blowing time is not less than 20 minutes.

[0114] Ladle placement and inspection steps

[0115] Place the ladle in the LF refining furnace, insert the electrode for heating, test the oxygen content, silicon content and manganese content in the molten steel, and test the basicity of the slag and the rare earth content in the slag. This is beneficial to the refining process.

[0116] Specifically, the ladle is transferred from the converter and placed in the LF refining furnace. During the placement process, argon is blown and stirred throughout the process, and the argon flow rate can be 100-300L / min. Insert the electrode for heating, heat in place for 8-12 minutes, preferably 10-11 minutes, and then blow argon and stir for 1-2 minutes. Here, large argon can be blown. Large argon means increasing the flow rate of argon, which can be greater than 300L / min, for example, 400-800L / min.

[0117] The situ temperature of the molten steel is controlled to be 1555-1665°C, preferably 1580-1660°C, more preferably 1600-1660°C, and more preferably 1650-1660°C. Take molten steel samples and dip slag samples for testing. The situ oxygen content of the molten steel is less than or equal to 50ppm, meeting the set requirements. The basicity of the slag is 1-3, preferably 1-2, more preferably 1-1.5, and more preferably 1-1.1.

[0118] In the present invention, the definition of basicity is: the ratio of basic oxides to acidic oxides in slag is called basicity, usually expressed as CaO / SiO2.

[0119] Refining and testing steps

[0120] According to the test results of the above test steps, lime, fluorite, aluminum-iron alloy, and silicon-manganese alloy are added to the LF refining furnace, stirred for reaction, and calcium wire is fed for reaction to complete the refining; after the refining is completed, the off-site oxygen content and rare earth content of the molten steel are tested; and the basicity of the slag is tested. In the refining step of the present invention, there is no need to add rare earth alloy.

[0121] Before refining, most of the rare earth metal elements in the rare earth steel additive react fully with oxygen and sulfur in the molten steel under argon blowing and stirring, forming compounds that enter the slag, forming slag containing rare earth oxides, and some rare earth elements remain in the molten steel. In the refining stage of the present invention, it is not necessary to add rare earth alloys (metals) to the molten steel, and it is also not necessary to add rare earth oxides to the refined slag. The present invention utilizes the reducing atmosphere formed by the aluminum-iron alloy (metal aluminum) and calcium wire (metal calcium) added during refining, and by adjusting the basicity of the refined slag, the rare earth metals in the steel are inhibited from continuing to oxidize, and at the same time, some of the rare earth elements in the slag can be reduced and enter the steel, thereby adjusting the rare earth content in the steel to form rare earth steel. That is, in the refining step of the present invention, the basicity of the slag can be adjusted by adjusting the amount of white ash, which can inhibit the rare earth elements in the molten steel from continuing to oxidize, and the reducing atmosphere of the aluminum-iron alloy and calcium wire can be used to reduce the rare earth oxides in the slag to rare earth elements and enter the molten steel, thereby controlling the La and Ce rare earth contents in the molten steel.

[0122] The present invention does not adopt the process of adding rare earth alloy in the refining stage in the prior art, which is more conducive to improving the castability of molten steel and simplifying the process. The method of the present invention is more conducive to achieving uniform distribution of rare earth in molten steel, grain refinement, etc., thereby effectively improving castability and avoiding the problem of nozzle nodules.

[0123] Based on 1 t of molten steel, the amount of lime used is 2.5 to 3.5 kg, preferably 2.8 to 3.3 kg, and more preferably 2.9 to 3.2 kg.

[0124] Based on 1 t of molten steel, the amount of fluorite used is 0.8 to 1.8 kg, preferably 0.9 to 1.6 kg, and more preferably 1.0 to 1.4 kg.

[0125] Based on 1 t of molten steel, the amount of aluminum-iron alloy used is 0.1-1.1 kg, preferably 0.2-0.8 kg, and more preferably 0.2-0.5 kg.

[0126] In step 3), a recarburizer may be added after adding fluorite and before adding aluminum-iron alloy. Carbon-containing substances added to make up for the low carbon content in the steel smelting process are called recarburizers. Recarburizers may be those known in the art. According to a specific embodiment of the present invention, the present invention uses a carbon powder recarburizer. Based on 1 t of molten steel, the amount of the recarburizer is 1.2 to 2.5 kg, preferably 1.4 to 2.2 kg, and more preferably 1.5 to 2.0 kg.

[0127] After adding lime, fluorite, recarburizer and aluminum-iron alloy, the stirring time is 8 to 15 minutes, preferably 10 to 15 minutes, and more preferably 10 to 12 minutes.

[0128] Based on 1 t of molten steel, the amount of silicon manganese alloy used is 5 to 7.5 kg, preferably 5.5 to 7.0 kg, and more preferably 5.8 to 6.5 kg.

[0129] After adding the silicon-manganese alloy, the stirring reaction time is 2 to 6 minutes, preferably 3 to 5 minutes, and more preferably 3 to 4 minutes.

[0130] The length of the calcium feeding line is 130 to 200 m, preferably 140 to 180 m, more preferably 145 to 165 m. The reaction time is 2 to 5 min, preferably 2 to 4 min, more preferably 2 to 3 min.

[0131] After refining, the temperature of the molten steel is controlled to be 1665-1680°C, preferably 1670-1680°C, and more preferably 1675-1680°C.

[0132] The oxygen content of molten steel is controlled to be less than or equal to 10 ppm.

[0133] The ex-situ rare earth (La, Ce) content of the molten steel is controlled to be greater than 10ppm, for example, 15-22ppm. In the molten steel, the La content can be 5-15ppm, preferably 6-10ppm, and more preferably 6.5-9ppm. The Ce content can be 10-25ppm, preferably 11-20ppm, and more preferably 13-16ppm. The weight ratio of La to Ce can be 1:1.5-2. This is conducive to improving the castability of the molten steel.

[0134] The ex-situ aluminum content of the molten steel is less than or equal to 0.02wt%, preferably less than or equal to 0.01wt%, and more preferably less than or equal to 0.008wt%.

[0135] The basicity of the slag is controlled to be 1.1 to 3.5, preferably 1.3 to 2.5, more preferably 1.5 to 2.0, more preferably 1.65 to 1.85, and further preferably 1.75 to 1.85. According to a specific embodiment of the present invention, the basicity of the slag in step 3) is controlled to be greater than the basicity of the slag in step 2). In this way, by adjusting the basicity of the slag, the rare earth elements in the molten steel can be inhibited from continuing to oxidize, and the reducing atmosphere of the aluminum-iron alloy and the calcium wire can be used to reduce the rare earth oxides in the slag to rare earth elements and enter the molten steel, thereby controlling the La and Ce rare earth contents in the molten steel.

[0136] Casting steps

[0137] After the molten steel passes the quality inspection, it is moved into the casting position, left to stand, and then casting begins to obtain rare earth steel.

[0138] The ladle is allowed to stand for 9 to 11 minutes, preferably 10 to 11 minutes, before pouring. Comprehensive protective casting measures are adopted in the continuous casting process, and those known in the art can be used. Start pouring, billet, eight-strand casting, and the billet pulling speed is 1.5 to 2.6 m / min, preferably 2.0 to 2.6 m / min, and more preferably 2.2 to 2.6 m / min. Billet and eight-strand casting are both known in the art. Continue to observe whether the liquid level fluctuates. No liquid level fluctuations are found until the end of casting, no nozzle nodule phenomenon, and good castability. Nodule nodule phenomenon generally refers to the high melting point compound solidifying and precipitating at the nozzle and adhering to the nozzle wall to form nozzle nodules.

[0139] The present invention also provides a rare earth steel produced by the production method of the present invention. In the rare earth steel, the oxygen content is less than or equal to 50ppm, preferably less than or equal to 20ppm, more preferably less than or equal to 15ppm, and more preferably less than or equal to 10ppm. In the rare earth steel, the Al content is less than or equal to 0.01wt%, preferably less than or equal to 0.008wt%, and more preferably less than or equal to 0.0075wt%. In the rare earth steel, the rare earth content (the sum of La and Ce content) is greater than or equal to 10ppm, and more preferably less than or equal to 15ppm. The La content can be 5 to 15ppm, preferably 6 to 10ppm, and more preferably 6.5 to 9ppm. The Ce content can be 10 to 25ppm, preferably 11 to 20ppm, and more preferably 13 to 16ppm. The weight ratio of La to Ce can be 1:1.5 to 2. According to one embodiment of the present invention, in the rare earth steel, the oxygen content is less than or equal to 10 ppm, the Al content is less than or equal to 0.008 wt%, the rare earth content (the sum of La and Ce contents) is greater than or equal to 20 ppm; the La content is 6.5-10 ppm, and the Ce content is 10-25 ppm.

[0140] <Analysis Method>

[0141] A fast oxygen sensor is used to detect the oxygen content in molten steel.

[0142] The content of La, Ce, Al and other elements in molten steel was determined by spectrometer analysis.

[0143] Determination of slag basicity: The mass percentage of CaO and SiO2 is measured respectively by chemical analysis method, and the ratio of the two is the basicity, expressed as CaO / SiO2.

[0144] The raw materials used in the embodiments are described below:

[0145] Silicon manganese alloy is Mn 65 Si 17 .

[0146] The aluminum-iron alloy is 39 aluminum-iron.

[0147] HRB400: A type of hot-rolled ribbed steel bar with a strength grade of 400MPa.

[0148] Q235B: Carbon structural steel consists of Q+number+quality grade symbol. Its steel number is prefixed with "Q", which represents the yield point of the steel, and the number behind it represents the yield point value in MPa; if necessary, the steel number can be followed by symbols indicating the quality grade and deoxidation method. The quality grade symbols are A, B, C, and D.

[0149] Preparation Example 1

[0150] The rare earth steel additive of the present invention is composed of the following components:

[0151] Ca 0.75wt%, Si 44.76wt%, Al 1.32wt%, La 11.29wt%, Ce 21.76wt%, and the balance is Fe and inevitable impurities.

[0152] According to the element composition of the rare earth steel additive, powdered rare earth oxides (lanthanum oxide, cerium oxide), silicon oxide, iron filings, aluminum oxide, and calcium oxide of corresponding proportions are added to the submerged arc furnace, and alloy liquid is generated under the reduction effect of coke. Among them, the temperature of the submerged arc furnace is 600°C, and the temperature of the arc zone is 2000°C. The obtained alloy liquid is put into a ladle, then ingot is cast, and crushed to obtain the rare earth steel additive as described above.

[0153] Example 1

[0154] In this embodiment, the molten steel in the converter is HRB400 molten steel. The quality of the molten steel in the converter is controlled according to Q235B.

[0155] The amount of molten steel in the converter is 162.8t. Oxygen is fixed and the temperature is measured at the end of blowing. The oxygen content is 732ppm, the tapping temperature is 1609℃, and argon is blown from the bottom of the ladle before tapping. Tapping begins when the argon flow rate is 800L / min. The molten steel in the converter is transferred to the ladle. When the tapping amount is about 1 / 3, the tapping is stopped. 300kg of lime, 1000kg of silicon-manganese alloy, 150kg of the rare earth steel additive of Preparation Example 1 and 200kg of coke powder are added to the ladle in sequence from the material pipe. Tap again, that is, continue to transfer the molten steel in the converter to the ladle. During the tapping and feeding process, the molten steel in the ladle is stirred by blowing argon. When blowing argon, the argon flow rate is 300L / min, and the argon blowing time is not less than 20min.

[0156] Place the ladle in the LF refining furnace, and keep blowing argon gas for stirring during the whole process, with an argon gas flow rate of 300L / min. Then, insert the electrode for heating, heat in place for 10 minutes, and then blow argon gas for stirring for 1 minute.

[0157] The in-situ temperature was detected to be 1656°C, the oxygen content in the molten steel was detected to be 36.8ppm, the silicon content was 0.09wt% and the manganese content was 0.51wt%. The basicity of the slag was detected to be 1.07, the La content in the slag was 26ppm, and the Ce content in the slag was 65ppm.

[0158] According to the above test results, 500kg lime, 200kg fluorite, 300kg carbon powder recarburizer, and 50kg aluminum-iron alloy were added to the LF refining furnace in turn and stirred for 10 minutes. Then 1000kg silicon-manganese alloy was added to react for 3 minutes, 150m calcium wire was fed to react for 2 minutes, and then soft blowing was continued for 10 minutes to complete the refining.

[0159] After refining, the off-site temperature of the molten steel was 1680°C, the off-site oxygen content of the molten steel was 9.8ppm, the aluminum content was 0.0074%, the La content was 7.7ppm, and the Ce content was 14.3ppm. The basicity of the slag was 1.75.

[0160] After the molten steel is qualified in the quality inspection, it is moved to the casting position and the ladle is left to stand for 10 minutes before pouring. Comprehensive protective casting measures are adopted in the continuous casting process. Start pouring, small square billet, eight-stream casting, and the billet pulling speed is 2.6m / min. Continue to observe whether the liquid level fluctuates until the casting is completed. In this embodiment, no liquid level fluctuation is found, no nozzle nodule phenomenon, and the castability is good.

[0161] The method of Example 1 was used to continuously produce 6 batches of rare earth steel, all of which had good castability. See Table 1.

[0162] Table 1

[0163] serial number Is castability good? Example 1 (1st furnace) + Example 1 (second furnace) + Example 1 (3rd furnace) + Example 1 (4th furnace) + Example 1 (Fifth furnace) + Example 1 (6th furnace) + Comparative Example 1 - Comparative Example 2 -

[0164] Note: In Table 1, “+” indicates good castability, and “-” indicates poor castability with nozzle nodules.

[0165] Before refining, the test results of the average in-situ oxygen content of molten steel in five consecutive heats except Example 1 (the first heat) are shown in Table 2 below.

[0166] Table 2

[0167] serial number In-situ oxygen content of molten steel / ppm Average value of 5 furnaces 28.98 In the prior art, aluminum-iron alloy deoxidation is used when steel is produced. 106.4

[0168] After refining, the test results of the off-site oxygen content, aluminum content, lanthanum content, cerium content of the molten steel and the basicity of the slag are shown in Table 3 below.

[0169] Table 3

[0170]

[0171] The present invention adopts a rare earth steel additive with a specific composition, which is added during the steel tapping process and before refining, which can not only improve castability, but also deoxidize well, significantly reduce the oxygen content in the rare earth steel, and reduce costs. The cost list is shown in Table 4.

[0172] Table 4

[0173]

[0174] Comparative Example 1

[0175] In this comparative example, the rare earth source used is a rare earth alloy, which is composed of: La 10.26wt%, Ce 19.74wt%, and the balance is Fe and inevitable impurities. The addition method is to add the steel in the form of blocks in the later stage of refining, and the addition amount is 0.5kg / t steel. In the whole deoxidation refining process, the rare earth steel additive used in the present invention is not used, and the other processes and parameters are the same as those in Example 1.

[0176] Comparative Example 2

[0177] In this comparative example, the composition of the rare earth steel additive used is: Ca 8.75wt%, Si 16.76wt%, Al 1.32wt%, La 11.29wt%, Ce 21.76wt%, and the balance is Fe and unavoidable impurities. The remaining processes and parameters are the same as those in Example 1.

[0178] In summary, the use of the rare earth steel additive with a specific composition of the present invention can make the castability in the continuous casting process good and without the phenomenon of sprue nodules. The sum of the rare earth (La, Ce) content in the off-site molten steel of the present invention is greater than 10ppm. The oxygen content in the off-site molten steel of the present invention is low and can be less than or equal to 10ppm. In addition, the method of the present invention has low cost, is suitable for industrialization and marketization, and has great application prospects.

[0179] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A rare earth steel additive, characterized in that: Includes the following ingredients: La 4~15wt% Ce 8~28wt% Si 30~65wt% Al 0.5~3.5wt% Ca 0.5~15wt%, and Fe 5~30wt%.

2. A rare earth steel additive, characterized in that: The following ingredients composition: La 4~15wt% Ce 8~28wt% Si 30~65wt% Al 0.5~3.5wt% Ca 0.5~15wt%, and The balance is iron and inevitable impurities.

3. The rare earth steel additive according to claim 1 or 2, characterized in that: The following ingredients composition: La 8~15wt% Ce 10~28wt% Si 35~48wt% Al 0.8~3.0wt% Ca 0.5~5.0wt%, and The balance is iron and inevitable impurities.

4. The rare earth steel additive according to claim 1 or 2, characterized in that: It is composed of the following ingredients: La 9~13wt% Ce 14~25wt% Si 38~46wt% Al 0.9~2.5wt% Ca 0.6~2.0wt%, and The balance is iron and inevitable impurities.

5. Use of the rare earth steel additive according to any one of claims 1 to 4 in improving the castability of rare earth steel in the production process, characterized in that: The rare earth steel additive is added into the molten steel in the ladle when the converter is tapping the steel.

6. A method for producing rare earth steel, characterized in that: The steps include: 1) When the converter smelting is finished, steel is tapped. When the tapping amount is 1 / 4 to 1 / 3, lime, silicon-manganese alloy, the rare earth steel additive according to any one of claims 1 to 4 and coke powder are added to the ladle, and the molten steel in the converter is continuously transferred to the ladle; during the process, inert gas is blown into the molten steel in the ladle for stirring; wherein, based on 1 t of molten steel, the amount of the rare earth steel additive is 0.3 to 3.5 kg; 2) Place the ladle in the LF refining furnace and insert the electrode for heating; detect the oxygen content, silicon content and manganese content in the molten steel, as well as the basicity of the slag and the rare earth content in the slag; 3) According to the test results of step 2), lime, fluorite, aluminum-iron alloy, and silicon-manganese alloy are added to the LF refining furnace, and stirred for reaction, and calcium wire is fed for reaction to complete refining; after the refining is completed, the off-site oxygen content and rare earth content of the molten steel are detected; wherein the rare earth content in the molten steel is controlled to be greater than or equal to 10ppm, and the off-site oxygen content of the molten steel is controlled to be less than or equal to 10ppm; 4) After the molten steel passes the quality inspection, it is moved into the casting position, left to stand, and then casting begins to obtain rare earth steel; wherein, there is no liquid level fluctuation and no nozzle nodule during casting.

7. The production method according to claim 6, characterized in that: In step 1), the tapping temperature is 1600-1650° C., and the inert gas is argon; In step 1), based on 1 t of molten steel, the amount of lime used is 1.7-2.1 kg, the amount of silicon-manganese alloy used is 4-8 kg, and the amount of coke powder used is 0.8-1.9 kg.

8. The production method according to claim 7, characterized in that: In step 2), the situ temperature of the molten steel is controlled to be 1555-1665°C; the situ oxygen content of the molten steel is less than or equal to 50 ppm; and the basicity of the slag is 1-3.

9. The preparation method according to claim 7, characterized in that: In step 3), the temperature of the molten steel is controlled to be 1665-1680°C; the basicity of the slag is controlled to be 1.1-3.5; In step 3), the length of the calcium feeding line is 130 to 200 m.

10. A rare earth steel produced by the production method according to any one of claims 7 to 9.

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