How Chromium Alloys are Produced

Abstract

The present invention provides a method for producing a chromium alloy containing extremely little impurities, said method using chromium ore as a starting material. This method for producing a chromium alloy comprises: a first step (S1) wherein chromium ore and calcined lime are melted; a second step (S2) wherein, to the molten starting materials (hereinafter referred to as a primary slag) melted in the first step, a reducing agent is added in an amount of from 20% by mass to 70% by mass of the theoretical reduction amount that reduces chromium oxide and iron oxide in the primary slag, and the resulting mixture is stirred, thereby producing a secondary slag and a by-product metal; and a third step (S3) wherein a reducing agent is added to the secondary slag, which has been separated from the by-product metal, and the resulting mixture is stirred, thereby producing a tertiary slag and a chromium alloy.

Description

[Technical field]

[0001] The present invention relates to a method for producing a chromium alloy containing chromium and iron, and to a method for producing a chromium alloy with few impurities. [Background technology]

[0002] Low-carbon ferrochrome is known as a chromium alloy containing chromium and iron. Low-carbon ferrochrome is generally produced by reducing chromium ore with a silicon-based reducing agent (see Patent Document 1). The so-called Perrin process is adopted as a specific production method. The basic process of the Perrin process includes a first process in which chromium ore and quicklime are melted, and a second process in which a reducing agent is added to the melted raw material (hereinafter referred to as primary slag) melted in the first process, and the mixture is stirred to cause a reduction reaction to produce low-carbon ferrochrome and secondary slag. The stirring in the second process is usually performed by relay rings in which two ladles are prepared and the molten primary slag containing a silicon-based reducing agent is repeatedly transferred between them.

[0003] In the conventional manufacturing method of low carbon ferrochrome, when reducing the primary slag, impurities such as P and S, which have a lower oxygen affinity than chromium, are preferentially reduced. This causes the problem that the amount of impurities such as P and S contained in the finished low carbon ferrochrome is high.

[0004] On the other hand, the applicant has proposed a method for producing metallic chromium with extremely low impurities (see Patent Document 2). This metallic chromium contains 99% by mass or more of chromium. The method for producing metallic chromium includes a first step of dissolving chromium oxide, quicklime, and a reducing agent and carrying out a reduction reaction to produce a chromium-containing metal and a primary slag, and a second step of adding quicklime and fluorite to the chromium-containing metal from which the primary slag has been separated, thereby refining the chromium-containing metal. According to this method for producing metallic chromium, the produced chromium-containing metal is refined in the second step, so that the impurities contained in the metallic chromium product can be extremely reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 1-225743 [Patent Document 2] Patent No. 3338701 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional method for producing metallic chromium, the starting material is not chromium ore but chromium oxide obtained by roasting chromium ore with soda and extracting it with sulfuric acid, and therefore the cost of the starting material is high. Some applications of chromium alloys do not require a high chromium content as in metallic chromium, and a small amount of iron is allowed.

[0007] The present invention has been made in consideration of the above problems, and has an object to provide a method for producing a chromium alloy with extremely low impurity content using chromium ore as a starting material. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention includes a first step of dissolving chromium ore and quicklime, a second step of adding a reducing agent to the dissolved raw material (hereinafter referred to as primary slag) dissolved in the first step in an amount of 20% by mass to 70% by mass of a theoretical reduction amount for reducing chromium oxide and iron oxide in the primary slag and stirring the mixture to generate secondary slag and by-product metals, and a third step of adding a reducing agent to the secondary slag separated from the by-product metals and stirring the mixture to generate tertiary slag and a chromium alloy. The chromium alloy contains 80% by mass or more and 95% by mass or less of Cr and 5% by mass or more and 20% by mass or less of Fe. A method for producing chromium alloys. Another aspect of the present invention is a method for producing a chromium alloy, comprising: a first step of dissolving chromium ore and quicklime; a second step of adding a reducing agent to the dissolved raw material (hereinafter referred to as primary slag) dissolved in the first step, in an amount of 20% by mass or more and 70% by mass or less of a theoretical reduction amount for reducing the chromium oxide and iron oxide in the primary slag, and stirring the mixture to produce secondary slag and by-product metals; a third step of adding a reducing agent to the secondary slag separated from the by-product metals, and stirring the mixture to produce tertiary slag and a chromium alloy; and a fourth step of adding a silicon-based reducing agent to the tertiary slag separated from the chromium alloy, and stirring the mixture to produce quaternary slag and silicochromium, in which the silicochromium separated and recovered from the quaternary slag is used as a main reducing agent in the third step. Effect of the Invention

[0009] According to one aspect of the present invention, a chromium alloy containing very few impurities such as P, S, and Co can be produced by using chromium ore as a starting material. According to another aspect of the present invention, a chromium alloy containing very little impurities such as P, S, and Co can be produced by using chromium ore as a starting material. In addition, a chromium alloy containing little carbon as an impurity can be produced by using the recovered silicochromium with reduced carbon content as a main reducing agent in the third step. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a process diagram of a method for producing a chromium alloy according to an embodiment of the present invention. [Diagram 2] 1 is a graph showing the standard free energy of formation of oxides. [Diagram 3] 1 is a graph showing the relationship between the basicity of secondary slag and (P) / (Cr). [Figure 4] FIG. 2 is a vertical cross-sectional view of a reaction vessel. [Diagram 5] 1 is a graph showing the relationship between [Si]% and [C]% of recovered silicochrome. [Figure 6] 1 is a graph showing the relationship between the (Cr)% of the quaternary slag and the [Si]% of the recovered silicochrome. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a method for producing a chromium alloy according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the method for producing a chromium alloy according to the present invention can be embodied in various forms and is not limited to the embodiments described in the present specification. The present embodiment is provided with the intention of enabling a person skilled in the art to fully understand the invention by fully disclosing the specification.

[0012] FIG. 1 is a process diagram of a method for producing a chromium alloy according to one embodiment of the present invention.

[0013] As shown in FIG. 1, first, a mixture of chromium ore and quicklime as a flux is melted in an electric furnace to generate a molten raw material (hereinafter referred to as primary slag) (first step (S1)).

[0014] A fixed type electric furnace is used, which has a tapping port located higher than the bottom of the furnace and forms a basin. The basin is formed in order to maintain a stable amount of heat even after the primary slag is tapped. The primary slag is tapped into a reaction vessel from the tapping port. The tapping temperature of the primary slag is high, between 1800°C and 2000°C.

[0015] Next, a reducing agent is added to the reaction vessel into which the primary slag has been poured and stirred to produce secondary slag and by-product metals (second step (S2)). The reducing agent is a silicon-based reducing agent such as silicochrome, ferrochrome, or metallic chromium. The amount of the reducing agent is adjusted to 20% by mass or more and 70% by mass or less, preferably 40% by mass or more and 50% by mass or less, of the theoretical reduction amount for reducing the chromium oxide and iron oxide in the primary slag according to the following formula: Cr2O3+3 / 2Si→2Cr+3 / 2SiO2 FeO+1 / 2Si→Fe+1 / 2SiO2

[0016] By weakly reducing chromium oxide and iron oxide, impurities such as Cu and Co, which have a lower oxygen affinity than these, can be preferentially reduced and transferred to by-product metals. Figure 2 shows the standard free energy of formation of oxides. As shown in Figure 2, Cu and Co have a lower oxygen affinity than Cr and Fe. For this reason, Cu, Co, etc. are preferentially reduced and transferred to by-product metals. This makes it possible to reduce impurities such as Cu and Co in the secondary slag.

[0017] In addition, as shown in Figure 2, the oxygen affinity of Fe is lower than that of Cr. Therefore, when chromium oxide and iron oxide are weakly reduced, Fe is preferentially reduced and converted to by-product metals. This allows the Cr / Fe ratio of the secondary slag to be increased.

[0018] If the amount of reducing agent is less than 20 mass% of the theoretical reduction amount, it becomes difficult to transfer impurities such as Cu and Co to the by-product metals. If the amount of reducing agent exceeds 70 mass% of the theoretical reduction amount, the chromium oxide in the secondary slag is reduced, and the Cr / Fe ratio of the secondary slag becomes small.

[0019] The basicity of the secondary slag is adjusted to 1.5 or more and 3.5 or less. Figure 3 shows the relationship between the basicity of the secondary slag and the (P) / (Cr) of the secondary slag. As shown in Figure 3, lowering the basicity makes it possible to lower the (P) / (Cr), i.e., to reduce the P in the secondary slag. On the other hand, lowering the basicity increases the S in the secondary slag. To reduce both P and S, the basicity is adjusted to 1.5 or more and 3.5 or less, preferably 1.5 or more and 3 or less. The basicity can be adjusted by the amount of quicklime charged into the electric furnace, or by the silica stone added to the reaction vessel.

[0020] The second process is carried out in a reaction vessel equipped with a bottom gas blowing device. The use of a bottom gas blowing device allows for sufficient stirring to transfer impurities to the by-product metal, and also prevents the temperature of the molten metal from dropping. Because the reduction reaction between chromium oxide and iron oxide is an exothermic reaction, the temperature of the molten metal (secondary slag) after the reaction is completed is high, between 1800°C and 2000°C. If the temperature of the secondary slag is raised to a high temperature, the S in the secondary slag volatilizes, and the amount of S as an impurity decreases. If the temperature of the molten metal in the second process is less than 1800°C, it may solidify in the subsequent third and fourth processes, making it impossible to cast the metal.

[0021] Figure 4 shows a vertical cross-sectional view of the reaction vessel. A refractory material 4 is provided at the bottom of the steel shell 3 of the reaction vessel 1. A slit-type plug 2 is inserted into the central through-hole of the refractory material 4 as a bottom gas blowing device. By introducing an inert gas into the pipe part 2a of the slit-type plug 2 and blowing the inert gas into the reaction vessel 1 through the slits of the slit-type plug 2, the secondary slag 5a and by-product metal 5b in the reaction vessel 1 can be agitated.

[0022] Next, as shown in Fig. 1, the secondary slag is tapped into another reaction vessel equipped with a bottom gas blowing device, and the recovered silicochrome is added as a reducing agent to the reaction vessel and stirred (third process (S3)). In the third process, the chromium oxide and iron oxide in the secondary slag react with the recovered silicochrome to produce tertiary slag and a chromium alloy. The recovered silicochrome is the silicochrome recovered in the third process described below.

[0023] As mentioned above, the secondary slag contains very little impurities such as P, S, Cu, and Co. By reducing this secondary slag with low impurities using recovered silicochrome, it is possible to produce a chromium alloy with low impurities. In addition, as described below, by using recovered silicochrome with low C as a reducing agent, it is possible to produce a chromium alloy with low C as an impurity.

[0024] The molten chromium alloy is poured into a mold to produce a product. The chromium alloy of the product contains 80% to 95% by mass of Cr and 5% to 20% by mass of Fe. The chromium alloy also contains 0.007% by mass or less of P, 0.003% by mass or less of S, 0.01% by mass or less of C, and 0.01% by mass or less of Co. Since Al is not used as a reducing agent, the Al content is 0.01% by mass or less.

[0025] The reaction vessel used in the third step is a reaction vessel having a bottom gas blowing device similar to that used in the second step. The reaction vessel used in the third step has substantially the same configuration as the reaction vessel used in the second step, and therefore the same reference numerals are used and the description thereof is omitted. By using the bottom gas blowing device in the third step, it is possible to achieve sufficient stirring to transfer chromium and iron to metal, and it is possible to prevent the temperature of the molten metal from decreasing. Since the reduction reaction of chromium oxide and iron oxide is an exothermic reaction, the temperature of the molten metal (tertiary slag) after the reaction is completed is a high temperature of 1800°C or more and 2000°C or less.

[0026] Next, as shown in Figure 1, the tertiary slag produced is separated from the chromium alloy, poured into a ladle, and metallic silicon is added as a silicon-based reducing agent and stirred (fourth step (S4)). This causes the chromium oxide remaining in the tertiary slag to react with metallic silicon, producing quaternary slag and silicochrome. The silicochrome is separated and recovered from the quaternary slag, and used as the main reducing agent in the third step.

[0027] Figure 5 shows the relationship between [Si]% and [C]% of recovered silicochrome. There is a correlation between the silicon content and the carbon content of recovered silicochrome, in that as the silicon content increases, the carbon content decreases. By utilizing this correlation and increasing the silicon content to, for example, 40 mass% or more, the carbon content can be reduced. By using recovered silicochrome with reduced carbon content as the main reducing agent in the third step, a chromium alloy with reduced carbon impurities can be produced.

[0028] Here, in order to reduce the carbon in the chromium alloy, it is desirable to use only recovered silicochrome as the reducing agent in the third step. However, another reducing agent (metallic silicon) may be added to adjust the amount of reducing agent. "Using recovered silicochrome as the main reducing agent" means that the mass of recovered silicochrome is 1 / 2 or more of the total mass of the reducing agents.

[0029] The quaternary slag separated from the recovered silicochrome is used as roadbed material or fertilizer. The chromium content of the quaternary slag is adjusted to 1.0 mass% or less, and the basicity is adjusted to 1.3 or less, preferably 1.2 or less. Silica may be charged into the ladle to adjust the basicity.

[0030] Figure 6 is a graph showing the relationship between the (Cr)% of the quaternary slag and the [Si]% of the recovered silicochrome. As shown in Figure 6, if the silicon content of the recovered silicochrome is set to 30 mass% or more, the chromium content of the quaternary slag can be set to 1.0 mass% or less.

[0031] By reducing the basicity of the quaternary slag to 1.3 or less, the harmful hexavalent chromium compounds in the quaternary slag can be converted to harmless trivalent chromium compounds. This is because, as shown in the following formula, CaO is removed from the hexavalent chromium compounds (CaO CrO3) that bond with CaO, and the harmful hexavalent chromium compounds are converted to harmless trivalent chromium compounds (Cr2O3). 2(CaO·CrO3)+2SiO2→2(CaO·SiO2)+Cr2O3+3 / 2O2 EXAMPLES

[0032] Chromium alloys were manufactured according to the manufacturing process diagram in Figure 1. 7,700 kg of chromium ore and 4,000 kg of quicklime were charged as raw materials into an electric furnace and melted to produce primary slag.

[0033] The primary slag was discharged into a reaction vessel, and 1,080 kg of silicochrome (40 mass% of the theoretical reduction amount) was added to the primary slag and stirred, producing 8,440 kg of secondary slag and 1,610 kg of by-product metals.

[0034] The composition of the secondary slag is shown in Table 1. The basicity of the secondary slag was 2.75. The Cr / Fe ratio of the secondary slag was 10 or more, and the P, Co, and S contents of the secondary slag were extremely small.

[0035] [Table 1] The composition of the by-product metals is shown in Table 2. The by-product metals included P, Co, and S.

[0036] [Table 2]

[0037] 490 kg of recovered silicochrome was added to 4,020 kg of secondary slag and stirred to produce 1,000 kg of chrome alloy and 3,440 kg of tertiary slag. The chrome alloy was separated from the tertiary slag and cast into a mold.

[0038] The composition of the chromium alloy is shown in Table 3. The secondary slag, which contains few impurities, is reduced with recovered silicochrome, so the chromium alloy contains very little Al, P, Co, C, or S.

[0039] [Table 3] Table 4 shows the composition of the tertiary slag.

[0040] [Table 4]

[0041] 410 kg of metallic silicon was added to 3,440 kg of tertiary slag and stirred to produce 480 kg of recovered silicochrome and 3,290 kg of quaternary slag.

[0042] Table 5 shows the composition of the recovered silicochrome. The carbon content of the recovered silicochrome was 0.001% by mass.

[0043] [Table 5] The total chromium yield, including chromium alloy, by-product metal, and recovered silicochromium, was over 95%.

[0044] The composition of the quaternary slag is shown in Table 6. The Cr2O3 content of the quaternary slag was 0.5 mass%, and the basicity was 1.0. No harmful hexavalent chromium was detected in the quaternary slag.

[0045] [Table 6]

[0046] This specification is based on Japanese Patent Application No. 2020-016909, filed on February 4, 2020, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0047] S1…1st process S2…Second process S3…3rd process S4…4th process

Claims

1. A first step of dissolving chromium ore and quicklime; A second step of adding a reducing agent to the melted raw material (hereinafter referred to as primary slag) melted in the first step in an amount of 20% by mass to 70% by mass of a theoretical reduction amount for reducing chromium oxide and iron oxide in the primary slag and stirring the mixture to generate secondary slag and by-product metals; and a third step of adding a reducing agent to the secondary slag separated from the by-product metal and stirring the resulting mixture to produce a tertiary slag and a chromium alloy. A method for producing a chromium alloy, the chromium alloy containing 80% by mass or more and 95% by mass or less of Cr and 5% by mass or more and 20% by mass or less of Fe.

2. The basicity (CaO / SiO ２ 2. The method for producing a chromium alloy according to claim 1, wherein the ratio of the chromium content to the total content of the chromium alloy is adjusted to 1.5 or more and 3.5 or less.

3. A method for producing a process ... A second step of adding a reducing agent to the melted raw material (hereinafter referred to as primary slag) melted in the first step in an amount of 20% by mass to 70% by mass of a theoretical reduction amount for reducing chromium oxide and iron oxide in the primary slag and stirring the mixture to generate secondary slag and by-product metals; a third step of adding a reducing agent to the secondary slag separated from the by-product metal and stirring the mixture to produce a tertiary slag and a chromium alloy; A fourth step of adding a silicon-based reducing agent to the tertiary slag separated from the chromium alloy and stirring the mixture to produce a fourth slag and a silicochrome; A method for producing a chromium alloy, in which the silicochromium separated and recovered from the quaternary slag is used as a main reducing agent in the third step.

4. The chromium content of the fourth slag is set to 1.0 mass% or less, and the basicity (CaO / SiO ２ 4. The method for producing a chromium alloy according to claim 3, wherein the ratio of Cr to H is adjusted to 1.3 or less.

5. The second step is carried out in a reaction vessel having a bottom gas blowing device, 5. The method for producing a chromium alloy according to claim 1, wherein the third step is carried out in a separate reaction vessel having a bottom gas blowing device.

6. The temperature of the secondary slag at the end of the reaction in the second step is 1800°C to 2000°C; 6. The method for producing a chromium alloy according to claim 1, wherein the temperature of the tertiary slag at the end of the reaction in the third step is 1800°C to 2000°C.

7. 7. The method for producing a chromium alloy according to claim 1, wherein the chromium alloy contains 0.01% by mass or less of P, 0.01% by mass or less of S, and 0.02% by mass or less of C.

8. The method for producing a chromium alloy according to claim 7, characterized in that the chromium alloy contains 0.007% by mass or less of P, 0.003% by mass or less of S, 0.01% by mass or less of C, 0.01% by mass or less of Co, and 0.01% by mass or less of Al.

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