Preparation method of low-gas high-purity chromium

Abstract

The invention discloses a preparation method of low-gas high-purity chromium. The preparation method comprises the following steps: S1, preparing part of metal chromium by adopting an aluminothermic method, and crushing the metal chromium into powder with the particle size of 60-200 meshes; preparing the other part of metal chromium by adopting an electrolytic method, and crushing the metal chromium into powder with the particle size of 60-200 meshes; s2, the two parts of metal chromium powder and graphite powder are mixed and pressed into a round ingot of 30 mm * (18 + / -2) mm, the round ingot is loaded into a graphite crucible, and the graphite powder accounts for 0.5%-2% of the total mass of the round ingot; s3, the graphite crucible containing the round ingot is put into a vacuum furnace to be smelted; heating is started when the vacuum degree in the vacuum furnace is smaller than or equal to 5 Mpa, the temperature is increased to 1400-1600 DEG C and kept for 10-15 h, then cooling is conducted, when the temperature is reduced to 1200-1100 DEG C, hydrogen is charged into the vacuum furnace to 15-20 Pa, and pressure is kept for 1 h; and S4, after pressure maintaining is finished, the temperature is increased to 1400-1600 DEG C, heat preservation is carried out for 2 h, then cooling is carried out, and when the temperature is reduced to the room temperature, discharging is carried out.

Description

Technical Field

[0001] The invention relates to the technical field of metal smelting, and in particular to a method for preparing low-gas high-purity chromium. Background Art

[0002] High-purity chromium is mainly used in high-temperature alloys. Since high-temperature alloys are mainly used in high-end fields such as aerospace, ships, etc., with the rapid development of my country's aerospace industry, the demand for high-purity metallic chromium dedicated to high-temperature alloys and target materials is increasing. However, due to the strict requirements on the impurity content of such high-purity metallic chromium, high purity and low impurity content are required, especially oxygen, sulfur, nitrogen and carbon. Therefore, most products still need to be imported.

[0003] At present, the general method for preparing metallic chromium is to use chromium oxide as raw material and carbonaceous reducing agent for vacuum furnace reduction, or to reduce it under high temperature and high vacuum conditions. Using carbon as a reducing agent easily leads to a high carbon content in metallic chromium.

[0004] CN1102872C discloses a method for removing non-metallic impurities. In this method, the raw material is ground into powder, the chromium powder is pressed into blocks by a high-pressure machine, and then hydrogen is introduced to remove non-metallic impurities such as C, O, S and N under high temperature conditions. The C and O contents of this method are both low, but the reaction time of this method is long, the amount of hydrogen used is large, and the production cost is very high. Summary of the invention

[0005] In view of this, it is necessary to provide a method for preparing low-gas high-purity chromium with relatively low non-metallic impurity content.

[0006] A method for preparing low-gas high-purity chromium comprises the following steps:

[0007] Step S1: preparing part of the metal chromium by aluminothermic method and crushing it into powder with a particle size of 60 mesh to 200 mesh; preparing another part of the metal chromium by electrolysis method and crushing it into powder with a particle size of 60 mesh to 200 mesh;

[0008] Step S2: mixing the two parts of metal chromium powder with graphite powder, pressing them into a 30 mm×(18±2) mm round ingot, and placing them into a graphite crucible, wherein the graphite powder accounts for 0.5% to 2% of the total mass of the round ingot;

[0009] Step S3: placing the graphite crucible containing the round ingot into a vacuum furnace for smelting; when the vacuum degree in the vacuum furnace is ≤5Mpa, heating is started to rise to 1400°C-1600°C, and the temperature is lowered after maintaining for 10-15h. When the temperature drops to 1200-1100°C, hydrogen is filled into the vacuum furnace to 15-20Pa, and the pressure is maintained for 1h;

[0010] Step S4: After the pressure holding is completed, the temperature is raised to 1400°C to 1600°C, and the temperature is lowered after being kept for 2 hours. When the temperature drops to room temperature, the furnace is taken out.

[0011] Beneficial effects: The present invention utilizes the characteristics of chromium prepared by the aluminothermic method with high carbon and oxygen content and low sulfur content, and chromium prepared by the electrolytic method with low carbon, oxygen content and high sulfur content, and compound the chromium prepared by the two methods to reduce gas impurities while meeting the sulfur content requirement of the product. At the same time, the phenomenon of air absorption during the cooling process after high-temperature reduction of metallic chromium is utilized. During the cooling process, when the temperature reaches 1100°C, hydrogen is charged during the air absorption. After the hydrogen is fully adsorbed by the metallic chromium, the temperature is raised for dehydrogenation. During the dehydrogenation process, hydrogen and oxygen in the product react, thereby reducing the oxygen content of the product, thereby achieving the purpose of reducing carbon and oxygen in the final product. DETAILED DESCRIPTION

[0012] In order to more clearly illustrate the technical solution of the embodiment of the present invention, it will be described below in conjunction with the embodiment.

[0013] A method for preparing low-gas high-purity chromium comprises the following steps:

[0014] Step S1: preparing part of the metal chromium by aluminothermic method and crushing it into powder with a particle size of 60 mesh to 200 mesh; preparing another part of the metal chromium by electrolysis method and crushing it into powder with a particle size of 60 mesh to 200 mesh;

[0015] Step S2: mixing the two parts of metal chromium powder with graphite powder, pressing them into a 30 mm×(18±2) mm round ingot, and placing them into a graphite crucible, wherein the graphite powder accounts for 0.5% to 2% of the total mass of the round ingot;

[0016] Mixing chromium prepared by two methods has two effects. The first effect is that as shown in Table 1, the impurity content in the metal chromium obtained by the two preparation methods is different and biased. After mixing, the carbon, oxygen, and sulfur contents are relatively balanced, and the impurity removal time is relatively short. The second effect is that the chromium metal obtained by the two preparation methods has different expansion degrees after heating. When the two different powders are reduced by hydrogen at high temperature, hydrogen can better penetrate into the interior of the chromium metal, thereby achieving a better impurity removal effect.

[0017] Table 1: Content of some components of metallic chromium prepared by aluminothermic method and electrolytic method.

[0018]

[0019]

[0020] Graphite powder can also be replaced by activated carbon with a carbon content of ≥99.9% and a particle size of less than -325 mesh.

[0021] Step S3: placing the graphite crucible containing the round ingot into a vacuum furnace for smelting; when the vacuum degree in the vacuum furnace is ≤5Mpa, heating is started to rise to 1400°C-1600°C, and the temperature is lowered after maintaining for 10-15h. When the temperature drops to 1200-1100°C, hydrogen is filled into the vacuum furnace to 15-20Pa, and the pressure is maintained for 1h;

[0022] The present invention first heats the metal chromium to 1400-1600°C in a vacuum furnace and keeps the temperature for 10-15 hours, removes part of the oxygen in the metal chromium by utilizing the reducing property of carbon, and then cools the temperature to 1200-1100°C. During the cooling process, the chromium metal has an air absorption phenomenon. By utilizing this phenomenon, hydrogen is filled in the vacuum furnace so that the hydrogen is fully absorbed by the chromium.

[0023] Step S4: After the pressure holding is completed, the temperature is raised to 1400°C to 1600°C, and the temperature is lowered after being kept for 2 hours. When the temperature drops to room temperature, the furnace is taken out.

[0024] When the chromium is heated again, the hydrogen reacts with the remaining oxygen and sulfur to produce gas, thereby further removing oxygen from the metallic chromium.

[0025] By removing impurities with carbon and hydrogen together, and taking advantage of the fact that chromium can absorb hydrogen during the cooling process, not only is the carbon content reduced, so that the carbon content in the final metal chromium is less, but also the oxygen content in the metal chromium is less, and high-purity chromium with low carbon and low oxygen is obtained. In addition, the time used for removing impurities with carbon and hydrogen together is relatively short, only 13 to 18 hours. Compared with the composite degasser used in the production method for preparing high-purity metal chromium for high-temperature alloys and targets with application number 201711071630.8 and the name of a composite degasser, which needs to be kept warm in a vacuum furnace for 29 hours to 35 hours, the time used by the present invention is shorter, which improves production efficiency and reduces production costs.

[0026] In a preferred embodiment, the mass ratio of chromium powder prepared by aluminothermic method to chromium powder prepared by electrolytic method is (4-6): (6-4).

[0027] In a preferred embodiment, the ratio of chromium metal powder prepared by aluminothermic method and chromium metal powder ≤ 200 mesh prepared by electrolysis method does not exceed 5%.

[0028] The effects of the present invention will be verified below in conjunction with the embodiments.

[0029] Embodiment 1

[0030] The method of the invention is adopted to prepare high-purity metallic chromium. That is, step S1: prepare 1000kg of metal chromium by aluminothermic method and crush it into powder with a particle size of 60-200 mesh; prepare 1000kg of metal chromium by electrolysis method and crush it into powder with a particle size of 60-200 mesh; mix the two parts of metal chromium powder with graphite powder, press them into round ingots, and put them into a graphite crucible, wherein the graphite powder accounts for 0.5%-2% of the total mass of the round ingot; put the graphite crucible with the round ingot into a vacuum furnace for smelting; start heating when the vacuum degree in the vacuum furnace is ≤5Mpa, the temperature rises to 1400℃-1600℃, keeps for 10-15h and then cools down, when the temperature drops to 1200-1100℃, fill the vacuum furnace with hydrogen to 15-20Pa, and keep the pressure for 1h; after the pressure is maintained, start heating to 1400℃-1600℃, keep the temperature for 2h and then cool down, and take out of the furnace when the temperature drops to room temperature.

[0031] Embodiment 2

[0032] The other steps are the same as those in the first embodiment, but in step S3, the metal chromium is heated to 1400° C. to 1600° C. in the vacuum furnace and kept at this temperature for 10 to 15 hours. There is no need to cool it down, and hydrogen is directly introduced for impurity removal.

[0033] Embodiment 3

[0034] The other aspects are the same as those of Example 1, but without carbon addition, and only using hydrogen to remove impurities.

[0035] Embodiment 4

[0036] Other aspects are the same, except that carbon is used for oxygen removal and hydrogen is not used for impurity removal.

[0037] The carbon and oxygen components of the metallic chromium obtained in the three examples are shown in Table 2.

[0038] Table 2 Content of some components of metallic chromium

[0039] C(％) O(％) Embodiment 1 0.16 0.015 Embodiment 2 0.17 0.074 Embodiment 3 0.008 0.396 Embodiment 4 0.45 0.12

[0040] Embodiment 1 The method of the present invention is used to prepare metallic chromium with relatively low carbon content and oxygen content.

[0041] In the second embodiment, the metal chromium is not cooled and then filled with hydrogen, thus eliminating the step of chromium absorbing hydrogen. After the same impurity removal time, the carbon content in the metal chromium is similar, but the oxygen content is significantly higher.

[0042] After sufficient time, the deoxygenation effect of Example 3 will be better. However, after the same deoxidation time as Example 3, the oxygen content in the metal chromium will be much higher, which does not meet the use requirements of high-purity metal chromium. At the same time, since no carbon deoxidation is used, the carbon content in the metal chromium is relatively low.

[0043] Example 4 adopts conventional carbon impurity removal. Compared with Example 1, the carbon content and oxygen content after impurity removal are relatively high.

[0044] The above experimental results show that, within the same impurity removal time, the present invention can obtain metal chromium with lower carbon and oxygen contents and has a better impurity removal effect.

[0045] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for preparing low-gas high-purity chromium, characterized in that: The following steps are involved: Step S1: preparing part of the metal chromium by aluminothermic method and crushing it into powder with a particle size of 60 mesh to 200 mesh; preparing another part of the metal chromium by electrolysis method and crushing it into powder with a particle size of 60 mesh to 200 mesh; Step S2: Mix the two parts of metal chromium powder and graphite powder, press them into a 30 mm×(18±2) mm round ingot, and put them into a graphite crucible, wherein the graphite powder accounts for 0.5% to 2% of the total mass of the round ingot; Step S3: placing the graphite crucible containing the round ingot into a vacuum furnace for smelting; when the vacuum degree in the vacuum furnace is ≤5Mpa, heating is started to rise to 1400°C-1600°C, and the temperature is lowered after maintaining for 10-15h. When the temperature drops to 1200-1100°C, hydrogen is filled into the vacuum furnace to 15-20Pa, and the pressure is maintained for 1h; Step S4: After the pressure holding is completed, the temperature is raised to 1400°C~1600°C, and the temperature is lowered after being kept for 2 hours. When the temperature drops to room temperature, the product is taken out of the furnace.

2. The method for preparing low-gas high-purity chromium according to claim 1, characterized in that: In step S1, the mass ratio of chromium powder prepared by aluminothermic method to chromium powder prepared by electrolytic method is (4-6): (6-4).

3. The method for preparing low-gas high-purity chromium according to claim 1, characterized in that: The proportion of chromium metal powder prepared by the aluminothermic method and chromium metal powder ≤200 mesh prepared by electrolysis shall not exceed 5%.

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