A method for preparing rare earth steel

Abstract

The invention provides a method for preparing rare earth steel. A rare earth manganese alloy is used as a rare earth source. Compared with the common rare earth oxide, the rare earth manganese alloy has a relatively low melting point and is more easily soluble in molten steel than the rare earth oxide. Compared with the common rare earth iron alloy, the rare earth manganese alloy has fewer impurity elements and is purer, which is conducive to preparing rare earth steel with high purity and high quality. Moreover, the binding force between the rare earth and manganese is greater than the binding force between the rare earth and iron. Therefore, compared with the rare earth iron alloy, the rare earth and manganese in the rare earth manganese alloy are relatively difficult to separate, thereby achieving the goal of avoiding the loss of rare earth elements caused by the rare earth combining with elements such as oxygen, sulfur and nitrogen after the rare earth and manganese in the rare earth manganese alloy are separated under high temperature conditions. The rare earth in the rare earth manganese alloy will be melted in the molten steel together with the manganese element, thereby improving the rare earth recovery rate. The actual rare earth recovery rate in the prepared rare earth steel can reach 65% to 80%.

Description

Technical Field

[0001] The invention relates to the field of steel materials, and in particular to a method for preparing rare earth steel. Background Art

[0002] Rare earth elements are known as "industrial vitamins" and have a purifying effect. Due to their strong chemical activity, rare earth elements can interact violently with harmful impurities such as oxygen, sulfur, phosphorus, and low-melting-point metals such as lead, antimony, tin, bismuth, and arsenic in steel, thereby reducing or even eliminating the harm of the above trace impurities. Among them, when the content of impurities such as oxygen and sulfur is low and the amount of rare earth added is large, it is possible to interact with the alloying elements in the steel to a certain extent, that is, to play a micro-alloying role. In addition, adding rare earth to steel can not only play a deoxidation, desulfurization and micro-alloying role, but also change the deformation ability of rare earth inclusions, thereby improving the comprehensive performance of steel.

[0003] There are 17 rare earth elements discovered so far, with similar elemental properties, low melting points, active chemical properties, and easy to combine with oxygen, sulfur, nitrogen and other elements. In the smelting process, rare earths are often added in the late stage of steel smelting, when the temperature of the molten steel is above 1600℃. When added in the form of pure rare earth, according to thermodynamic calculations, the Gibbs free energy of the reaction between rare earth and oxygen is the lowest. Therefore, in theory, rare earth and oxygen react most easily and first to form rare earth oxides, followed by sulfur, nitrogen and other elements. Most of the rare earth compounds generated become steel slag floating on the surface of the molten steel, and a small part remains in the steel as inclusions in the steel. When added in the form of rare earth iron alloy, the affinity of rare earth elements with oxygen, sulfur and nitrogen is greater than that with iron. At high temperatures, the rare earth in the rare earth iron alloy has a stronger binding force with oxygen, sulfur and nitrogen than the binding force between rare earth and iron, so it will cause the loss of rare earth elements as mentioned above. Therefore, the recovery rate of rare earth in rare earth steel is not high. Especially when high-quality steel is smelted in a vacuum smelting furnace, whether pure rare earth or rare earth iron alloy is added, the rare earth recovery rate is often less than 50%, the rare earth resource loss is serious, and the amount of rare earth added is difficult to control. Therefore, providing a method for preparing rare earth steel with high rare earth recovery rate is a technical problem that needs to be solved in the prior art. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing rare earth steel. The method for preparing rare earth steel provided by the present invention has a high rare earth yield.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing rare earth steel, comprising the following steps:

[0007] (1) using a rare earth manganese alloy as a rare earth source, and subjecting the remaining alloy elements to a first smelting according to the chemical composition and mass percentage of the target rare earth steel, to obtain a precursor melt;

[0008] adding a rare earth manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt;

[0009] (2) performing a first casting on the alloyed melt obtained in step (1) to obtain an alloy ingot;

[0010] (3) Annealing the alloy ingot obtained in step (2) to obtain rare earth steel.

[0011] Preferably, the method for preparing the rare earth manganese alloy in step (1) comprises the following steps:

[0012] ① Remelting manganese to obtain manganese metal liquid;

[0013] ② adding rare earth to the manganese metal liquid obtained in step ① for mixed melting to obtain rare earth manganese metal liquid;

[0014] ③ Perform a second casting on the rare earth manganese metal liquid obtained in step ② to obtain a rare earth manganese alloy;

[0015] In the step ③, the mass ratio of rare earth to manganese in the rare earth manganese alloy is (3-7): (3-7).

[0016] Preferably, the vacuum degree of remelting in step ① is controlled by first evacuating the vacuum to a value of 0.8×10 -4 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa; the remelting temperature is 1250-1330°C.

[0017] Preferably, the melting temperature in step ② is 1240-1330° C., the melting time is 10-20 min, and the melting vacuum is 4×10 -3 ~1.5×10 -2 Pa.

[0018] Preferably, the amount of the rare earth manganese alloy in step (1) is calculated by formula 1:

[0019] The amount of rare earth manganese alloy is: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)) formula 1;

[0020] In the formula 1, the target rare earth yield is 65% to 80%, κ is the yield correction coefficient, also known as the batching error value, and κ is 0.0082 to 0.0087.

[0021] Preferably, the vacuum degree control method of the first smelting in step (1) is to first evacuate the vacuum to a vacuum degree of 0.8×10 -3 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa; the temperature of the first smelting is 1610-1680°C.

[0022] Preferably, the temperature of the second smelting in step (1) is 1610-1680°C, the time of the second smelting is 7-12 min, and the vacuum degree of the second smelting is 4×10 -3 ~1.5×10 -2 Pa.

[0023] Preferably, the temperature of the first casting in step (2) is 1620-1660°C.

[0024] Preferably, the vacuum degree of the annealing treatment in step (3) is

[0025] Preferably, the heating method of the annealing treatment in step (3) is as follows: in the first stage, the temperature is increased from room temperature to 280-320°C at a rate of 4-8°C / min and kept warm for 2-7min; in the second stage, the temperature is increased from 280-320°C to 780-820°C at a rate of 9-15°C / min and kept warm for 4-9min; in the third stage, the temperature is increased from 780-820°C to 1020-1060°C at a rate of 5-11°C / min and kept warm for 11h-16h; in the fourth stage, the temperature is naturally cooled with the furnace.

[0026] The invention provides a method for preparing rare earth steel. A rare earth manganese alloy is used as a rare earth source. Compared with commonly used rare earth oxides, the rare earth manganese alloy has a lower melting point and is more easily soluble in molten steel. Compared with commonly used rare earth iron alloys, the rare earth manganese alloy has fewer impurity elements and is purer, which is conducive to preparing rare earth steel with high purity and high quality. The binding force between the rare earth and manganese is greater than the binding force between the rare earth and iron. Therefore, compared with the rare earth iron alloy, the rare earth and manganese in the rare earth manganese alloy are relatively difficult to separate, thereby achieving the goal of avoiding the rare earth from oxygen, sulfur and nitrogen in the rare earth manganese alloy after the rare earth and manganese are separated under high temperature conditions. The rare earth elements in the rare earth manganese alloy will be melted in the steel liquid together with the manganese elements, thereby increasing the rare earth yield. According to the chemical composition and mass percentage of the rare earth steel, the remaining alloying elements are first smelted to obtain a precursor melt, and then the rare earth manganese alloy is added to the precursor melt for a second smelting to obtain an alloyed melt, and then the first casting and annealing treatment are performed in sequence. The annealing treatment is used to make the components more uniform, which is conducive to further melting of the rare earth elements in the rare earth steel, and finally a rare earth steel with a high rare earth yield is prepared. The results of the embodiment show that the rare earth steel prepared by the method provided by the present invention has an actual rare earth yield of 65% to 80%, reaching a relatively high rare earth yield. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing rare earth steel, comprising the following steps:

[0028] (1) using a rare earth manganese alloy as a rare earth source, and subjecting the remaining alloy elements to a first smelting according to the chemical composition and mass percentage of the target rare earth steel, to obtain a precursor melt;

[0029] adding a rare earth manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt;

[0030] (2) performing a first casting on the alloyed melt obtained in step (1) to obtain an alloy ingot;

[0031] (3) Annealing the alloy ingot obtained in step (2) to obtain rare earth steel.

[0032] The present invention adopts rare earth manganese alloy as rare earth source, performs first smelting on the remaining alloy elements according to the chemical composition and mass percentage of target rare earth steel, and obtains a precursor melt.

[0033] In the present invention, unless otherwise specified, the raw materials used are conventional commercial products in the art.

[0034] In the present invention, the method for preparing the rare earth manganese alloy preferably comprises the following steps:

[0035] ① Remelting manganese to obtain manganese metal liquid;

[0036] ② adding rare earth to the manganese metal liquid obtained in step ① for mixed melting to obtain rare earth manganese metal liquid;

[0037] ③ Perform a second casting on the rare earth manganese metal liquid obtained in step ② to obtain a rare earth manganese alloy;

[0038] In the step ③, the mass ratio of rare earth to manganese in the rare earth manganese alloy is (3-7): (3-7).

[0039] In the present invention, manganese is preferably remelted to obtain molten manganese.

[0040] In the present invention, the manganese is preferably pure manganese metal.

[0041] In the present invention, the remelting equipment is preferably a vacuum medium frequency induction melting furnace.

[0042] In the present invention, the remelting vacuum degree control method is preferably to first evacuate the vacuum to a vacuum degree of 0.8×10 -4 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa, preferably, first evacuate the vacuum to a degree of 1×10 -4 ~1×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 5×10 -3 ~1×10 -2 Pa. The present invention adopts a vacuum control method, which is conducive to removing oxygen in the furnace as much as possible, reducing the oxygen content in the furnace, reducing the rare earth burnout, so as to prepare a rare earth manganese alloy with high purity, and at the same time it is conducive to reducing the subsequent oxygen introduced into the rare earth steel, reducing the burnout of rare earth elements, and maintaining a low cost. In the present invention, the inert gas is preferably one or both of nitrogen and helium; the introduction rate of the inert gas is preferably 10 to 12 L / min.

[0043] In the present invention, the remelting temperature is preferably 1250-1330° C., more preferably 1250-1320° C. The present invention controls the remelting temperature within the above range to ensure that each component is fully melted and to avoid excessively high remelting temperature that may cause element burnout and increase costs.

[0044] The present invention has no particular limitation on the remelting time, as long as the purpose of melting all the materials into liquid is achieved.

[0045] After obtaining the manganese metal liquid, the present invention preferably adds rare earth to the manganese metal liquid for mixed melting to obtain rare earth manganese metal liquid.

[0046] In the present invention, the rare earth is preferably pure rare earth.

[0047] In the present invention, the temperature of the mixed melting is preferably 1240-1330°C, more preferably 1250-1320°C. In the present invention, the time of the mixed melting is preferably 10-20 minutes, more preferably 12-18 minutes. The present invention controls the time and temperature of the mixed melting within the above range, so that the rare earth metal is completely melted and the rare earth and manganese metals are melted evenly. In the present invention, the vacuum degree of the mixed melting is preferably 4×10 -3 ~1.5×10 -2 Pa, more preferably 5×10 -3 ~1×10 -2 Pa. The present invention controls the vacuum degree of the mixed melt within the above range to reduce the oxygen content in the furnace and prepare a rare earth manganese alloy with high purity.

[0048] After obtaining the rare earth manganese molten metal, the present invention preferably performs a second casting on the rare earth manganese molten metal to obtain a rare earth manganese alloy.

[0049] In the present invention, the temperature of the second casting is preferably 1210-1310°C, more preferably 1220-1300°C. The present invention controls the temperature of the second casting within the above range to avoid the temperature being too low and the metal fluidity being poor, and to avoid the temperature being too high and causing the elements to burn out. In the present invention, the casting equipment is preferably a molybdenum crucible. In the present invention, the casting method is preferably to filter the rare earth manganese molten metal through a sieve plate placed on the top of the molybdenum crucible and then flow it into the molybdenum crucible, let it stand for 30min-60min, and gradually increase the vacuum degree after the rare earth manganese molten metal solidifies, and continue to introduce inert gas protection until the molten metal solidifies. The present invention has no characteristic limitation on the vacuum degree, and the purpose of removing the air in the molybdenum crucible can be achieved.

[0050] After the casting is completed, the present invention preferably demolds the cast product to obtain a rare earth manganese alloy.

[0051] The present invention has no special limitation on the demoulding method, and conventional technical solutions in the art can be used.

[0052] In the present invention, the mass ratio of rare earth to manganese in the rare earth manganese alloy is preferably (3-7): (3-7). The present invention controls the mass ratio of rare earth to manganese in the rare earth manganese alloy within the above range, which is conducive to preparing rare earth steel with high rare earth yield.

[0053] After obtaining the rare earth manganese alloy, the present invention uses the rare earth manganese alloy as a rare earth source, performs a first smelting on the remaining alloy elements according to the chemical composition and mass percentage of the rare earth steel to obtain a precursor melt; and adds the rare earth manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt.

[0054] In the present invention, the amount of the rare earth manganese alloy is preferably calculated by Formula 1:

[0055] The amount of rare earth manganese alloy is preferably: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)) formula 1;

[0056] In the present invention, the target rare earth yield in Formula 1 is preferably 65% ​​to 80%; the κ is a yield correction coefficient, also known as a batching error value, and the κ is preferably 0.0082 to 0.0087.

[0057] In the present invention, the dosage range of the rare earth manganese alloy can be calculated by formula 1, and then a value is preferably taken within the dosage range of the rare earth manganese alloy as the actual dosage of the rare earth manganese alloy, and rare earth steel is subsequently prepared.

[0058] In the present invention, the rare earth manganese alloy is sequentially surface cleaned and mechanically crushed before use.

[0059] The present invention has no special restrictions on the surface cleaning method, as long as the purpose of keeping the rare earth manganese alloy pure is achieved. The present invention has no special restrictions on the mechanical crushing method, as long as the prepared rare earth manganese alloy block is conducive to the subsequent melting into the precursor melt.

[0060] In the present invention, in the first smelting process, the order of adding the remaining alloy elements is preferably to first add the metal that is difficult to burn out, and then add the metal that is easy to burn out.

[0061] In the present invention, the first smelting equipment is preferably a vacuum medium frequency induction melting furnace.

[0062] In the present invention, the vacuum degree control method of the first smelting is preferably to first evacuate the vacuum to a degree of 0.8×10 -3 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa, preferably, first evacuate the vacuum to a degree of vacuum of 0.9×10 -3 ~1×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 5×10 -3 ~1×10 -2Pa. The present invention is conducive to removing oxygen in the furnace as much as possible and reducing the oxygen content in the furnace through the vacuum control method of the first smelting, thereby reducing the burnout of rare earth elements and preparing rare earth steel with high purity while maintaining low cost. In the present invention, the inert gas is preferably one or both of nitrogen and helium; the introduction rate of the inert gas is preferably 10 to 12 L / min.

[0063] In the present invention, the temperature of the first smelting is preferably 1610-1680°C, more preferably 1620-1670°C. The present invention controls the temperature of the first smelting within the above range to ensure that each component is fully melted and to avoid excessively high remelting temperature that may cause element burnout and increase costs. The present invention has no special restrictions on the time of the first smelting, as long as each component is fully melted into liquid.

[0064] In the present invention, the temperature of the second smelting is preferably 1610-1680°C, more preferably 1620-1670°C. In the present invention, the time of the second smelting is preferably 7-12 minutes, more preferably 8-10 minutes. The present invention controls the time and temperature of the second smelting within the above ranges to completely melt the rare earth manganese alloy and evenly melt various metals. In the present invention, the vacuum degree of the second smelting is preferably 4×10 -3 ~1.5×10 -2 Pa, more preferably 5×10 -3 ~1×10 -2 Pa. The present invention controls the vacuum degree of the second smelting within the above range to reduce the oxygen content in the furnace and prepare rare earth steel with high purity.

[0065] After obtaining the alloyed melt, the present invention performs a first casting on the alloyed melt to obtain an alloy ingot.

[0066] In the present invention, the temperature of the first casting is preferably 1620-1660° C., more preferably 1630-1650° C. The present invention controls the temperature of the first casting within the above range, which is beneficial to the casting sequence.

[0067] After the casting is completed, the present invention preferably demolds the cast product to obtain an alloy ingot.

[0068] The present invention has no special limitation on the demoulding method, and conventional technical solutions in the art can be used.

[0069] After obtaining the alloy ingot, the present invention performs annealing treatment on the alloy ingot to obtain rare earth steel.

[0070] In the present invention, the annealing treatment equipment is preferably a vacuum heat treatment furnace. In the present invention, the vacuum degree of the annealing treatment is preferably 0.8×10-2 ~1.5Pa, more preferably 1×10 -2 The present invention controls the vacuum degree of annealing treatment within the above range, which is conducive to removing oxygen in the furnace as much as possible, reducing the oxygen content in the furnace, thereby reducing the burnout of rare earth elements, and preparing rare earth steel with high purity.

[0071] In the present invention, the heating method of the annealing treatment is preferably: in the first stage, the temperature is increased from room temperature to 280-320°C at a rate of 4-8°C / min and kept for 2-7min; in the second stage, the temperature is increased from 280-320°C to 780-820°C at a rate of 9-15°C / min and kept for 4-9min; in the third stage, the temperature is increased from 780-820°C to 1020-1060°C at a rate of 5-11°C / min and kept for 11h-16h; in the fourth stage, the temperature is increased from 780-820°C to 1020-1060°C at a rate of 5-11°C / min and kept for 11h-16h. The first stage is to heat the furnace naturally, more preferably the first stage, from room temperature to 290-310°C at a rate of 5-8°C / min, and keep warm for 3-6min; the second stage is to heat the furnace from 290-310°C to 790-810°C at a rate of 9-14°C / min, and keep warm for 5-8min; the third stage is to heat the furnace from 790-810°C to 1030-1050°C at a rate of 6-10°C / min, and keep warm for 12h-15h; the fourth stage is to cool the furnace naturally.

[0072] After obtaining the rare earth steel, the present invention preferably performs "trimming" on the rare earth steel to remove defective parts existing due to the first casting, performs rare earth content component analysis, and measures the mass percentage of actual rare earth in the rare earth steel.

[0073] After obtaining the mass percentage of the actual rare earth in the rare earth steel, the present invention preferably substitutes the mass percentage of the actual rare earth in the rare earth steel into (mass percentage of the actual rare earth in the rare earth steel × mass of the target rare earth steel) / (actual amount of rare earth manganese alloy × mass percentage of rare earth in the rare earth manganese alloy) formula 2 to calculate the actual rare earth yield in the rare earth steel.

[0074] After obtaining the actual rare earth yield in the rare earth steel, the present invention preferably substitutes the actual rare earth yield in the rare earth steel into (target rare earth yield-actual rare earth yield in rare earth steel) / target rare earth yield formula 3 to calculate the verification correction coefficient κ'.

[0075] In the present invention, if the verification correction coefficient κ' is between 0.0082 and 0.0087, the amount of the rare earth manganese alloy is within the batching error range.

[0076] The method for preparing rare earth steel provided by the invention has a high rare earth yield.

[0077] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0078] Example 1

[0079] 1. Preparation method of yttrium manganese alloy:

[0080] ① Use a 50Kg vacuum medium frequency induction melting furnace to remelt 15Kg of pure manganese metal. When the metal manganese is completely melted, manganese metal liquid is obtained;

[0081] The vacuum degree of the remelting is controlled by evacuating the vacuum to a value of 1×10 -3 Pa, nitrogen was introduced to further ensure the purity of the metal, and the vacuum degree was maintained at 5×10 -3 Pa, stop introducing nitrogen; the remelting temperature is 1290°C;

[0082] ② Add 35 kg of pure yttrium to the manganese metal liquid obtained in step ①, and mix and melt to ensure that all the pure yttrium is melted to obtain yttrium manganese metal liquid;

[0083] The melting temperature in step ② is 1290°C, the melting time is 12 min, and the vacuum degree of the melting is 5×10 -3 Pa

[0084] ③ The yttrium manganese metal liquid obtained in step ② is subjected to a second casting, and then demolded to obtain a yttrium manganese alloy;

[0085] The second casting equipment in step ③ is a molybdenum crucible with a sieve plate placed on the top. The yttrium manganese liquid is filtered through the sieve plate and then flows into the molybdenum crucible. It is left to stand for 40 minutes. After the yttrium manganese liquid solidifies, the vacuum degree is gradually increased and inert gas protection is continuously introduced. The temperature of the second casting is 1250°C.

[0086] In the step ③, the mass ratio of yttrium to manganese in the yttrium-manganese alloy is 7:3, and the mass percentage of yttrium in the yttrium-manganese alloy is calculated to be 70%.

[0087] 2. Preparation method of rare earth steel:

[0088] (1) Using the yttrium manganese alloy prepared by the above preparation method as a rare earth source, according to the chemical composition and mass percentage of the target rare earth steel, the remaining alloy elements are first smelted in a 100 kg vacuum medium frequency induction melting furnace to obtain a precursor melt;

[0089] The weight of the target rare earth steel is 100 kg, and the target mass percentage of rare earth in the target rare earth steel is 0.080%;

[0090] Adding yttrium manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt;

[0091] According to the dosage of the yttrium manganese alloy: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)), formula 1;

[0092] In the formula 1, κ is 0.0082-0.0087; the rare earth content in the rare earth manganese alloy corresponds to an empirical value of a target rare earth yield of 80%.

[0093] The dosage range of the yttrium manganese alloy is calculated by formula 1 as (0.080%×100Kg) / (70%×80%×(1-κ))=0.1440Kg to 0.1441Kg, and 0.1440Kg is taken as the actual dosage of the yttrium manganese alloy within the dosage range of the yttrium manganese alloy;

[0094] The yttrium manganese alloy is surface cleaned and mechanically crushed into blocks before use;

[0095] The vacuum degree control method of the first smelting is to first evacuate the vacuum to a vacuum degree of 1×10 -3 Pa, and then the inert gas nitrogen was introduced to keep the vacuum degree at 5×10 -3 Pa; the temperature of the first smelting is 1620°C; during the first smelting process, the order of adding the remaining alloy elements is preferably to first add the metal that is difficult to burn, and then add the metal that is easy to burn;

[0096] The temperature of the second smelting is 1620°C; the time of the second smelting is 8 minutes; the vacuum degree of the second smelting is 5×10 -3 Pa;

[0097] (2) performing a first casting on the alloyed melt obtained in step (1), and then demolding the melt to obtain an alloy ingot;

[0098] The temperature of the first casting is 1630°C;

[0099] (3) Annealing the alloy ingot obtained in step (2) to obtain rare earth steel.

[0100] The vacuum degree of the annealing treatment is 1×10 -2Pa; the heating method of the annealing treatment is: in the first stage, the temperature is increased from room temperature to 300°C at a rate of 5°C / min and kept for 3 minutes; in the second stage, the temperature is increased from 300°C to 800°C at a rate of 9°C / min and kept for 5 minutes; in the third stage, the temperature is increased from 800°C to 1030°C at a rate of 6°C / min and kept for 12 hours; in the fourth stage, the furnace is naturally cooled;

[0101] The rare earth steel is subjected to “cutting off” to remove defective parts existing due to the first casting, and rare earth content composition analysis is performed, and the actual mass percentage of rare earth in the rare earth steel is measured to be 0.07995%;

[0102] Substituting the actual rare earth mass percentage in the rare earth steel, i.e., 0.07995%, into the formula (actual rare earth mass percentage in rare earth steel × mass of target rare earth steel) / (actual amount of rare earth manganese alloy × mass percentage of rare earth in rare earth manganese alloy) 2, the actual rare earth recovery rate in the rare earth steel is calculated to be 79.32%.

[0103] The specific calculation process is (0.07995%×100Kg) / (0.1440Kg×70%)=79.32%;

[0104] After obtaining the actual rare earth recovery rate in the rare earth steel, which is 79.32%, the actual rare earth recovery rate in the rare earth steel is substituted into (target rare earth recovery rate - actual rare earth recovery rate in rare earth steel) / target rare earth recovery rate formula 3, and the verification correction coefficient κ' is calculated to be 0.0085.

[0105] The specific technical process is (80%-79.32%) / 80%=0.0085;

[0106] When the verification correction coefficient κ' is between 0.0082 and 0.0087, the weight of the yttrium manganese alloy batch is within the batch error range.

[0107] Example 2

[0108] 1. A method for preparing yttrium manganese alloy comprises the following steps:

[0109] ① Use a 50Kg vacuum medium frequency induction melting furnace to remelt 35Kg of pure manganese metal. When the metal manganese is completely melted, manganese metal liquid is obtained;

[0110] The vacuum degree of the remelting is controlled by evacuating the vacuum to a value of 1×10 -3 Pa, nitrogen was introduced to further ensure the purity of the metal, and the vacuum degree was maintained at 5×10 -3 Pa, stop introducing nitrogen; the remelting temperature is 1250°C;

[0111] ② Add 15 kg of pure yttrium to the manganese metal liquid obtained in step ①, and mix and melt to ensure that all the pure yttrium is melted to obtain yttrium manganese metal liquid;

[0112] The melting temperature in step ② is 1250° C., the melting time is 13 min, and the vacuum degree of the melting is 5×10 -3 Pa

[0113] ③ The yttrium manganese metal liquid obtained in step ② is subjected to a second casting, and then demolded to obtain a yttrium manganese alloy;

[0114] The second casting equipment in step ③ is a molybdenum crucible with a sieve plate placed on the top. The yttrium manganese liquid is filtered through the sieve plate and then flows into the molybdenum crucible. It is left to stand for 40 minutes. After the yttrium manganese liquid solidifies, the vacuum degree is gradually increased and inert gas protection is continuously introduced. The temperature of the second casting is 1250°C.

[0115] In the step ③, the mass ratio of yttrium to manganese in the yttrium-manganese alloy is 3:7, and the mass percentage of yttrium in the yttrium-manganese alloy is calculated to be 30%.

[0116] 2. A method for preparing rare earth steel, comprising the following steps:

[0117] (1) Using the yttrium manganese alloy prepared by the above preparation method as a rare earth source, according to the chemical composition and mass percentage of the target rare earth steel, the remaining alloy elements are first smelted in a 100 kg vacuum medium frequency induction melting furnace to obtain a precursor melt;

[0118] The weight of the target rare earth steel is 100 kg, and the target mass percentage of rare earth in the target rare earth steel is 0.080%;

[0119] Adding yttrium manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt;

[0120] According to the dosage of the yttrium manganese alloy: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)), formula 1;

[0121] In the formula 1, κ is 0.0082-0.0087; the rare earth content in the rare earth manganese alloy corresponds to an empirical value of 66% of the target rare earth recovery rate.

[0122] The dosage range of the yttrium manganese alloy is calculated by formula 1 as (0.080%×100Kg) / (30%×66%×(1-κ))=0.4074Kg to 0.4076Kg, and 0.4074Kg is taken as the actual dosage of the yttrium manganese alloy within the dosage range of the yttrium manganese alloy;

[0123] The yttrium manganese alloy is surface cleaned and mechanically crushed into blocks before use;

[0124] The vacuum degree control method of the first smelting is to first evacuate the vacuum to a vacuum degree of 1×10 -3 Pa, and then the inert gas nitrogen was introduced to keep the vacuum degree at 5×10 -3 Pa; the temperature of the first smelting is 1620°C; during the first smelting process, the order of adding the remaining alloy elements is preferably to first add the metal that is difficult to burn, and then add the metal that is easy to burn;

[0125] The temperature of the second smelting is 1620°C; the time of the second smelting is 8 minutes; the vacuum degree of the second smelting is 5×10 -3 Pa;

[0126] (2) performing a first casting on the alloyed melt obtained in step (1), and then demolding the melt to obtain an alloy ingot;

[0127] The temperature of the first casting is preferably 1630°C;

[0128] (3) Annealing the alloy ingot obtained in step (2) to obtain rare earth steel.

[0129] The vacuum degree of the annealing treatment is preferably 1×10 -2 Pa; the heating method of the annealing treatment is preferably: in the first stage, the temperature is increased from room temperature to 300°C at a rate of 5°C / min and kept for 3 minutes; in the second stage, the temperature is increased from 300°C to 800°C at a rate of 9°C / min and kept for 5 minutes; in the third stage, the temperature is increased from 800°C to 1030°C at a rate of 6°C / min and kept for 12 hours; in the fourth stage, the furnace is naturally cooled;

[0130] The rare earth steel is subjected to “cutting off” to remove defective parts existing due to the first casting, and rare earth content composition analysis is performed, and the actual mass percentage of rare earth in the rare earth steel is measured to be 0.07997%;

[0131] Substituting the actual rare earth mass percentage in the rare earth steel, i.e., 0.07997%, into the formula (actual rare earth mass percentage in rare earth steel × mass of target rare earth steel) / (actual amount of rare earth manganese alloy × mass percentage of rare earth in rare earth manganese alloy) 2, the actual rare earth recovery rate in the rare earth steel is calculated to be 65.43%.

[0132] The specific calculation process is (0.07997%×100Kg) / (0.4074Kg×30%)=65.43%.

[0133] After obtaining the actual rare earth recovery rate in the rare earth steel, which is 71.38%, the actual rare earth recovery rate in the rare earth steel is substituted into (target rare earth recovery rate - actual rare earth recovery rate in rare earth steel) / target rare earth recovery rate formula 3, and the verification correction coefficient κ' is calculated to be 0.0086;

[0134] The specific calculation process is (66%-65.43%) / 66%=0.0086;

[0135] When the verification correction coefficient κ' is between 0.0082 and 0.0087, the weight of the yttrium manganese alloy batch is within the batch error range.

[0136] Example 3

[0137] 1. A method for preparing yttrium manganese alloy comprises the following steps:

[0138] ① Use a 50Kg vacuum medium frequency induction melting furnace to remelt 25Kg of pure manganese metal. When the metal manganese is completely melted, manganese metal liquid is obtained;

[0139] The vacuum degree of the remelting is controlled by evacuating the vacuum to a value of 1×10 -3 Pa, nitrogen was introduced to further ensure the purity of the metal, and the vacuum degree was maintained at 5×10 -3 Pa, stop introducing nitrogen; the remelting temperature is 1290°C;

[0140] ② Add 25 kg of pure yttrium to the manganese metal liquid obtained in step ①, and mix and melt to ensure that all the pure yttrium is melted to obtain yttrium manganese metal liquid;

[0141] The melting temperature in step ② is 1250° C., the melting time is 13 min, and the vacuum degree of the melting is 5×10 -3 Pa

[0142] ③ The yttrium manganese metal liquid obtained in step ② is subjected to a second casting, and then demolded to obtain a yttrium manganese alloy;

[0143] The second casting equipment in step ③ is a molybdenum crucible with a sieve plate placed on the top. The yttrium manganese liquid is filtered through the sieve plate and then flows into the molybdenum crucible. It is left to stand for 40 minutes. After the yttrium manganese liquid solidifies, the vacuum degree is gradually increased and inert gas protection is continuously introduced. The temperature of the second casting is 1250°C.

[0144] In the step ③, the mass ratio of yttrium to manganese in the yttrium-manganese alloy is 1:1, that is, the mass percentage of yttrium in the yttrium-manganese alloy is 50%.

[0145] 2. A method for preparing rare earth steel, comprising the following steps:

[0146] (1) Using the yttrium manganese alloy prepared by the above preparation method as a rare earth source, according to the chemical composition and mass percentage of the target rare earth steel, the remaining alloy elements are first smelted in a 100 kg vacuum medium frequency induction melting furnace to obtain a precursor melt;

[0147] The weight of the target rare earth steel is 100 kg, and the target mass percentage of rare earth in the target rare earth steel is 0.080%;

[0148] Adding yttrium manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt;

[0149] According to the dosage of the yttrium manganese alloy: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)), formula 1;

[0150] In the formula 1, κ is 0.0082-0.0087, and the rare earth content in the rare earth manganese alloy corresponds to an empirical value of a target rare earth yield of 72%;

[0151] The dosage range of the yttrium manganese alloy is calculated by formula 1 to be 0.080%×100Kg / (50%×72%×(1-κ))=0.2240Kg to 0.2242Kg, and 0.2241Kg is taken as the actual dosage of the yttrium manganese alloy within the dosage range of the yttrium manganese alloy;

[0152] The yttrium manganese alloy is surface cleaned and mechanically crushed into blocks before use;

[0153] The vacuum degree control method of the first smelting is to first evacuate the vacuum to a vacuum degree of 1×10 -3 Pa, and then the inert gas nitrogen was introduced to keep the vacuum degree at 5×10 -3 Pa; the temperature of the first smelting is 1630°C; during the first smelting process, the order of adding the remaining alloy elements is preferably to first add the metal that is difficult to burn, and then add the metal that is easy to burn;

[0154] The temperature of the second smelting is 1630°C; the time of the second smelting is 8 minutes; the vacuum degree of the second smelting is 5×10 -3 Pa;

[0155] (2) performing a first casting on the alloyed melt obtained in step (1), and then demolding the melt to obtain an alloy ingot;

[0156] The temperature of the first casting is preferably 1630°C;

[0157] (3) Annealing the alloy ingot obtained in step (2) to obtain rare earth steel.

[0158] The vacuum degree of the annealing treatment is preferably 1×10 -2 Pa; the heating method of the annealing treatment is preferably: in the first stage, the temperature is increased from room temperature to 300°C at a rate of 5°C / min and kept for 3 minutes; in the second stage, the temperature is increased from 300°C to 800°C at a rate of 9°C / min and kept for 5 minutes; in the third stage, the temperature is increased from 800°C to 1030°C at a rate of 6°C / min and kept for 12 hours; in the fourth stage, the furnace is naturally cooled;

[0159] The rare earth steel is subjected to “cutting off” to remove defective parts existing due to the first casting, and rare earth content composition analysis is performed, and the actual mass percentage of rare earth in the rare earth steel is measured to be 0.0800%;

[0160] Substitute the actual rare earth mass percentage in the rare earth steel, i.e. 0.0800%, into (actual rare earth mass percentage in rare earth steel × mass of target rare earth steel) / (actual amount of rare earth manganese alloy × mass percentage of rare earth in rare earth manganese alloy) formula 2, and calculate the actual rare earth yield in the rare earth steel to be 71.40%. The specific calculation process is (0.080% × 100Kg) / (0.2241Kg × 50%) = 71.40%.

[0161] After obtaining the actual rare earth recovery rate in the rare earth steel, which is 71.40%, the actual rare earth recovery rate in the rare earth steel is substituted into (target rare earth recovery rate - actual rare earth recovery rate in rare earth steel) / target rare earth recovery rate formula 3, and the verification correction coefficient κ' is calculated to be 0.0083;

[0162] The specific calculation process is (72%-71.40%) / 72%=0.0083;

[0163] When the verification correction coefficient κ' is between 0.0082 and 0.0087, the weight of the yttrium manganese alloy batch is within the batch error range.

[0164] It can be seen from the above embodiments that the rare earth steel prepared by the method provided by the present invention has an actual rare earth yield of 65% to 80%, achieving a relatively high rare earth yield.

[0165] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing rare earth steel, comprising: (1) using a rare earth manganese alloy as a rare earth source, and subjecting the remaining alloy elements to a first smelting according to the chemical composition and mass percentage of the target rare earth steel, to obtain a precursor melt; adding a rare earth manganese alloy to the precursor melt for a second smelting to obtain an alloyed melt; (2) performing a first casting on the alloyed melt obtained in step (1) to obtain an alloy ingot; (3) annealing the alloy ingot obtained in step (2) to obtain rare earth steel; The vacuum degree control method of the first smelting in step (1) is to first evacuate the vacuum to a vacuum degree of 0.8×10 -3 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa; the temperature of the first smelting is 1610~1680℃; The heating method of the annealing treatment in the step (3) is as follows: in the first stage, the temperature is increased from room temperature to 280-320°C at a rate of 4-8°C / min and kept at that temperature for 2-7 minutes; in the second stage, the temperature is increased from 280-320°C to 780-820°C at a rate of 9-15°C / min and kept at that temperature for 4-9 minutes; in the third stage, the temperature is increased from 780-820°C to 1020-1060°C at a rate of 5-11°C / min and kept at that temperature for 11h-16h; in the fourth stage, the temperature is naturally cooled with the furnace.

2. The preparation method according to claim 1, characterized in that: The method for preparing the rare earth manganese alloy in step (1) comprises the following steps: ① Remelting manganese to obtain manganese metal liquid; ② adding rare earth to the manganese metal liquid obtained in step ① for mixed melting to obtain rare earth manganese metal liquid; ③ Perform a second casting on the rare earth manganese metal liquid obtained in step ② to obtain a rare earth manganese alloy; In the step ③, the mass ratio of rare earth to manganese in the rare earth manganese alloy is (3-7):(3-7).

3. The preparation method according to claim 2, characterized in that: The vacuum degree control method of remelting in step ① is to first evacuate the vacuum to a vacuum degree of 0.8×10 -4 ~1.5×10 -3 Pa, and then the inert gas was introduced to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa; the remelting temperature is 1250~1330℃.

4. The preparation method according to claim 2, characterized in that: The temperature of the melting in step ② is 1240-1330°C, the melting time is 10-20 min, and the vacuum degree of the melting is controlled by introducing an inert gas to keep the vacuum degree at 4×10 -3 ~1.5×10 -2 Pa.

5. The preparation method according to claim 1, characterized in that: The amount of the rare earth manganese alloy in step (1) is calculated by formula 1: The amount of rare earth manganese alloy is: (target mass percentage of rare earth in target rare earth steel × weight of target rare earth steel) / (mass percentage of rare earth in rare earth manganese alloy × target rare earth yield × (1-κ)) formula 1; In the formula 1, the target rare earth yield is 65% to 80%, κ is the yield correction coefficient, also known as the batching error value, and κ is 0.0082 to 0.0087.

6. The preparation method according to claim 1, characterized in that: The temperature of the second smelting in step (1) is 1610-1680°C, the time of the second smelting is 7-12 min, and the vacuum degree of the second smelting is 4×10 -3 ~1.5×10 -2 Pa.

7. The preparation method according to claim 1, characterized in that: The temperature of the first casting in step (2) is 1620-1660°C.

8. The preparation method according to claim 1, characterized in that: The vacuum degree of the annealing treatment in step (3) is 0.8×10 -2 ~1.5Pa.