A method for producing a chromium-aluminum-iron alloy

Abstract

This invention provides a method for producing a chromium-aluminum-iron alloy, including steps such as raw material mixing. The raw materials used in the mixing process are chromium oxide, aluminum powder, lime, and sodium chlorate. The process employs a two-step smelting method: first, an aluminothermic reduction reaction is used, and second, an electric heating method is employed in a refining furnace. This process homogenizes the molten iron, chromium, and aluminum alloys with different specific gravities, preventing heavier iron and chromium from sinking and lighter aluminum from floating, thus avoiding alloy segregation. The chromium oxide yield produced by this method reaches 93.97%, which is 5-6 percentage points higher than the yield of metallic chromium produced by the conventional aluminothermic method. The metallic aluminum yield reaches 98%-99%, with low aluminum burn-off.

Description

Technical Field

[0001] This invention relates to the field of chromium-aluminum-iron alloy preparation technology, and in particular to a method for producing chromium-aluminum-iron alloy. Background Technology

[0002] Iron-chromium-aluminum alloys are used in the preparation of electric furnace wires. They have high resistivity, light weight, strong resistance to oxidation and carburization, and are inexpensive. They can be used at higher temperatures than nickel-chromium electric furnace wires, but they become brittle after repeated high-temperature use, which leads to a decrease in resistivity.

[0003] Currently, the main domestic production method for chromium-aluminum-iron alloys is the electric furnace smelting of elemental chromium, elemental aluminum, and elemental iron to form the alloy. This process uses electric heating for the reaction, which results in a slow heating rate and significant heat dissipation, leading to severe aluminum powder loss. Furthermore, the reaction process involves contact with air, introducing oxygen and resulting in a high oxygen content in the alloy. Summary of the Invention

[0004] Based on the above description, the present invention provides a method for producing a chromium-aluminum-iron alloy, comprising the following steps:

[0005] S1: Mix the following raw materials according to the following mass percentage ratio: chromium oxide: iron oxide: aluminum powder: lime: potassium chlorate / sodium chlorate = 0.8: 0.5: 0.5~1: 0.1~0.2: 0.01-0.03, and then mix them to obtain a mixture;

[0006] S2: Pretreatment of the mixture: drying chromium oxide and iron oxide, high-temperature roasting and decarburization of lime; drying of the exothermic agent;

[0007] S3: First, lay aluminum powder at the bottom of the reactor body, then lay a layer of iron powder on top of the aluminum powder layer, and then load the pretreated mixture into the reactor body.

[0008] S4: Spread ignition agent on the mixture to carry out the aluminothermic reaction;

[0009] S5: Place the furnace body after the above aluminothermic reaction under the refining furnace for electric heating. The electrode heating voltage is 110~130V and the duration is 8-10 minutes.

[0010] S6: Power off, aluminum powder spraying begins;

[0011] S7: Immediately after the spraying is finished, start electric heating and adjust the heating voltage to 130~160V for 8-10 minutes;

[0012] S8: After refining, disconnect the power and cool for more than 60 hours until it is taken out of the furnace.

[0013] This invention employs a two-step smelting process. First, an aluminothermic reduction reaction is used. This reaction is ignition-based, resulting in rapid ignition and combustion, thus a fast reaction rate. Furthermore, as a reduction reaction, even contact with air does not cause oxidation, thus avoiding any impact on reaction quality. The second step utilizes an electrically heated refining furnace, employing a two-stage refining process. Before the injection, a lower voltage and longer smelting time are used. In the first stage, the electrode 40 is positioned at a higher position, contacting the slag layer surface, for example, 0-1 / 4H of the slag layer 30 thickness. The purpose of heating the slag layer is to raise its temperature by heating it with a low voltage and high current, so that the slag melts as much as possible and the effective metals in it melt and settle into the alloy liquid 20. After blowing, a higher voltage and a shorter time are used for smelting, which is the second stage. The electrode 40 is inserted into a deeper position inside the slag layer, such as 3 / 4-1H of the slag layer thickness, and the temperature can reach 2800-3000℃. The high temperature homogenizes the chromium, iron and aluminum alloy liquids with different specific gravities, and avoids the heavier iron and chromium sinking and the lighter aluminum floating, which would cause alloy segregation.

[0014] Existing technologies use elemental chromium, elemental iron, and elemental aluminum in a reaction process that involves contact with air, resulting in high oxygen and carbon content in the products. Another method uses an electric furnace for heating, reacting aluminum powder and chromium oxide as reducing agents; however, electric furnaces are slow, have low reaction efficiency, and require excessively long heating times. Attached Figure Description

[0015] Figure 1 , 2 This is a schematic diagram illustrating the principle of the refining steps in this invention. Figure 1 This is a period of refinement. Figure 2 It is in the second stage of refining.

[0016] In the diagram, there is a reactor 10, a liquid alloy 20, a slag layer 30, and an electrode 40. Implementation

[0017] See Figure 1 , 2 The present invention provides a method for producing a chromium-aluminum-iron alloy, comprising the following steps:

[0018] S1: Mix the following raw materials according to the following mass percentage ratio: chromium oxide: iron oxide: aluminum powder: lime: sodium chlorate = 0.8: 0.5: 0.5~1: 0.1~0.2: 0.01-0.03, and then mix them to obtain a mixture;

[0019] S2: Pretreatment of the mixture: drying chromium oxide and iron oxide, high-temperature roasting and decarburization of lime; drying of the exothermic agent;

[0020] S3: First, lay aluminum powder at the bottom of the reactor body, then lay a layer of iron powder on top of the aluminum powder layer, and then load the pretreated mixture into the reactor body.

[0021] S4: Spread ignition agent on the mixture to carry out the aluminothermic reaction;

[0022] S5: Place the furnace body after the above aluminothermic reaction under the refining furnace for electric heating. The electrode heating voltage is 110~130V and the duration is 8-10 minutes.

[0023] S6: Power off, aluminum powder spraying begins;

[0024] S7: Immediately after the spraying is finished, start electric heating and adjust the heating voltage to 130~160V for 8-10 minutes;

[0025] S8: After refining, disconnect the power and cool for more than 60 hours until it is taken out of the furnace.

[0026] In this design, the total amount of aluminum powder is divided into three parts: the first part is added as a reducing agent in the raw materials, the second part is used as a base layer of aluminum powder, and the third part is used as sprayed aluminum powder. In this invention, iron possesses ductility and flexibility. By adjusting the ratio of chromium, iron, and aluminum content and optimizing the process, performance is improved, and brittleness after repeated use at high temperatures is reduced.

[0027] Further, in step S2, chromium oxide is granulated to a particle size of about 3 mm and then dried; iron oxide is granulated to a particle size of about 3 mm and then dried; lime is ball-milled and sieved to control its particle size range of 0-3 mm, and then calcined at a high temperature of 1000℃ to remove carbon; the exothermic agent potassium chlorate / sodium chlorate is dried to remove moisture in order to increase the temperature.

[0028] Furthermore, the high-temperature roasting and decarburization temperature of lime is 1000-1200℃.

[0029] Furthermore, in step S3, the amount of aluminum powder used in the bottom layer of the reactor body is 10-20% of the total amount of aluminum powder.

[0030] Furthermore, in step S4, the igniter is magnesium powder.

[0031] Furthermore, in step S6, during the aluminum powder blowing process, the amount of aluminum powder used is 10-20% of the total amount of aluminum powder.

[0032] Furthermore, in step S3, the amount of iron powder laid on top of the aluminum powder layer is 5-10% of the iron oxide. In this scheme, the elemental iron powder is sprinkled on top of the aluminum powder layer and does not participate in the reaction. After the reduction reaction is complete, it is melted into the alloy liquid along with the aluminum powder. However, because the specific gravity of iron powder is greater than that of aluminum and chromium, the iron powder is sprinkled on the upper layer. As the molten aluminum powder floats up, it carries the iron powder to the surface and into the alloy liquid. In this scheme, the aluminum and iron powder only undergo a phase change from solid to liquid without undergoing a chemical reaction. The difference from the reaction of elemental chromium, elemental iron, and elemental aluminum is that the heat released by the reduction reaction provides heat for the reduction of iron oxide and chromium oxide in advance, avoiding the heat consumption of melting aluminum and iron powder, thereby improving the oxide conversion rate. Moreover, the reduction of iron oxide is also an exothermic reaction, and the heat is used to supply the reduction reaction. Therefore, the addition of iron oxide not only provides some elemental iron to the alloy but also supplements some of the heat of the reduction reaction, thereby reducing the amount of potassium chlorate / sodium chlorate added and thus reducing the impurity content. Example 1

[0033] S1: Granulate chromium oxide to a particle size of about 3mm and then dry it at a drying temperature of 300℃; granulate iron oxide to a particle size of about 3mm and then dry it; ball mill and sieve lime to control its particle size range of 0-3mm, and then calcine it at a high temperature of 1000℃ to remove carbon; dry sodium chlorate to remove moisture at a drying temperature of 100~200℃; the purpose of decarburization is to remove carbon from calcium carbonate and prevent it from entering the alloy liquid.

[0034] S2: Calculate the following raw materials according to the weight ratio: chromium oxide, iron oxide, aluminum powder, lime, and sodium chlorate 960kg, 600kg, 820kg, 10kg, and 160kg respectively, and mix them. Sodium chlorate acts as an exothermic agent, releasing a large amount of heat upon combustion to supplement the heat of the alloy liquid. Since chromium is a refractory metal with a melting point as high as 3000℃, the heat released by the reduction reaction of aluminum powder is insufficient to supply the reaction, so an exothermic agent is used to supplement the heat.

[0035] S3: The above mixture is loaded into the furnace bottom of a reactor body containing 225 kg of aluminum powder, and then a layer of 50 kg of iron powder is laid on top of the aluminum powder layer and compacted. In this scheme, the smelted product is a chromium-aluminum-iron alloy. The role of aluminum powder is partly as a raw material entering the alloy liquid to be converted into part of the alloy product, and partly as a reducing agent to reduce chromium oxide and provide heat. For the first part of aluminum powder, entering the alloy liquid simply involves melting the cold aluminum powder into a liquid state and entering the alloy liquid. This phase change process requires the absorption of the alloy liquid temperature. Since chromium oxide is difficult to melt and has a large heat requirement, in order to ensure sufficient heat for the reduction reaction in advance, part of the aluminum powder in this raw material ratio participates in the reaction as a reducing agent (approximately 55%), and the other part enters the alloy liquid. It is mixed evenly with chromium oxide in advance, and after ignition, the two undergo a reduction reaction. The aluminum powder in the first part is spread evenly on the bottom of the furnace beforehand. Since it does not come into contact with chromium oxide, it does not participate in the reduction reaction beforehand and will not absorb the heat of the reaction. This ensures that the reduction reaction proceeds first. After the reduction reaction is completed, the preheating temperature in the alloy liquid is as high as 2000℃, which is sufficient to melt this part of aluminum powder into aluminum liquid and enter the alloy liquid to form the aluminum element in the chromium-aluminum-iron alloy.

[0036] Although this method prevents the molten aluminum powder from fully mixing with the alloy liquid, the subsequent refining step involves adjusting the voltage and current to stir and churn the alloy liquid. Furthermore, since the specific gravity of molten aluminum is much lower than that of chromium, it naturally floats to the surface. Therefore, the aluminum powder layer spread at the bottom of the furnace not only does not participate in the reduction reaction, absorb reaction heat, or lower the temperature of the alloy liquid, but also enters the alloy liquid in elemental form, greatly saving heat and reducing energy consumption in the reduction reaction.

[0037] S4: Spread ignition agent on the compacted reaction material and ignite it to carry out the aluminothermic reaction.

[0038] S5: Place the furnace body after the above aluminothermic reaction under the refining furnace and heat it electrically for 10 minutes;

[0039] S6: Power off, perform aluminum powder spraying of 200kg;

[0040] S7: Immediately after the blowing is completed, perform electric heating for 8 minutes;

[0041] S8: After refining, disconnect the power and cool for 60 hours or more until room temperature before removing from the furnace.

[0042] The aluminothermic reduction reaction is as follows:

[0043] Cr₂O₃ + 2Al = 2Cr + Al₂O₃

[0044] NaClO3 + 2Al = NaCl + Al2O3

[0045] The sampled composition of the chromium-aluminum-iron alloy prepared in this embodiment is as follows: chromium (Cr) 50.53%, C 0.015%, S 0.009%, O 0.053%, N <0.001%, with the balance being aluminum, and the alloy weight is 1462 kg. Example 2

[0046] S2: Calculate and mix the following raw materials according to the weight ratio: chromium oxide, iron oxide, aluminum powder, lime, sodium chlorate = 940kg, 600kg, 800kg, 12kg, 180kg, and mix them together.

[0047] S3: Load the above mixture into the bottom of the reactor body which is covered with 100kg of aluminum powder, and then lay a layer of 60kg of iron powder on top of the aluminum powder layer and compact it.

[0048] S6: Power off, perform aluminum powder spraying of 200kg;

[0049] The other process steps are the same as in Example 1.

[0050] The sampled composition of the chromium-aluminum-iron alloy prepared in this embodiment is as follows: chromium (Cr) 35.21%, Fe 31.04%, C 0.015%, S 0.001%, O 0.062%, N <0.001%, with the balance being aluminum. The alloy weight is 1387 kg, and the yield of metallic chromium is 94.07%.

[0051] In the two embodiments described above, the yield of chromium oxide reached 93.83%, which is 5-6 percentage points higher than the yield of metallic chromium produced by the conventional aluminothermic process. The yield of metallic aluminum reached 98%~99%, and the aluminum burn-off was low.

[0052] In the above embodiments: the composition of the raw material chromium oxide is: Cr2O3: 98.93%, C: 0.073%, S: 0.02%. The iron oxide content is 99%. The aluminum powder composition is: Al: 99.32%, Fe: 0.06%, Cu: 0.0041%, Si: 0.038%. The lime contains more than 88% CaO and more than 98% sodium chlorate (NaClO3).

Claims

1. A method for producing a chromium-aluminum-iron alloy, characterized in that... Includes the following steps: S1: Mix the following raw materials according to the following mass percentage ratio: chromium oxide: iron oxide: aluminum powder: lime: potassium chlorate / sodium chlorate = 0.8: 0.5: 0.5-1: 0.1-0.2: 0.01-0.03, and then mix them to obtain a mixture; S2: Pretreatment of the mixture: drying chromium oxide and iron oxide, high-temperature roasting and decarburization of lime; drying of the exothermic agent; S3: First, lay aluminum powder at the bottom of the reactor body, then lay a layer of iron powder on top of the aluminum powder layer, and then load the pretreated mixture into the reactor body. S4: Spread ignition agent on the mixture to carry out the aluminothermic reaction; S5: The furnace body after the above aluminothermic reaction is placed under the refining furnace for electric heating. The electrodes of the refining furnace are brought into contact with the surface of the slag layer. The thickness of the slag layer is H, and the depth of the electrodes is 0-1 / 4H. The slag layer is heated by the electrodes. The electrode heating voltage is 110-130V, and the duration is 8-10 minutes. S6: Power off, aluminum powder spraying begins; S7: Immediately after the blowing is completed, electric heating is performed. The depth of the electrode is 3 / 4-1H, and the heating voltage is adjusted to 130-160V for 8-10 minutes. S8: After refining, disconnect the power and cool for more than 60 hours until it is taken out of the furnace.

2. The method for producing chromium-aluminum-iron alloy as described in claim 1, characterized in that: In step S2, chromium oxide is granulated to a particle size of about 3 mm and then dried, and iron oxide is granulated to a particle size of about 3 mm and then dried. Lime is ball-milled and sieved to control its particle size range of 0-3 mm, and then calcined at a high temperature of 1000℃ to remove carbon. The exothermic agent potassium chlorate / sodium chlorate is dried to remove moisture in order to increase the temperature.

3. The method for producing chromium-aluminum-iron alloy as described in claim 2, characterized in that: The temperature for decarburization of lime by high-temperature roasting is 1000-1200℃.

4. The method for producing chromium-aluminum-iron alloy as described in claim 1, characterized in that: In step S3, the amount of aluminum powder used in the bottom layer of the reactor body is 10-20% of the total amount of aluminum powder in step S1.

5. The method for producing chromium-aluminum-iron alloy as described in claim 1, characterized in that: In step S4, the igniter is magnesium powder.

6. The method for producing chromium-aluminum-iron alloy as described in claim 1, characterized in that: In step S6, the amount of aluminum powder used during the aluminum powder blowing process is 10-20% of the total amount of aluminum powder in step S1.

7. The method for producing chromium-aluminum-iron alloy as described in claim 1, characterized in that: In step S3, the amount of iron powder laid on top of the aluminum powder layer is 5-10% of the amount of iron oxide in step S1.

Images