JP7260400B2 - Method for Suppressing Blackening of Ferronickel Cast Piece, and Method for Producing Ferronickel Cast Piece - Google Patents

Description

In the production of ferronickel cast pieces obtained by casting ferronickel, which is an iron-nickel alloy made from nickel oxide ore, into shots, the blackening of the surface of the ferronickel cast pieces is suppressed. "Method" and "Method for producing ferronickel cast pieces" involving the implementation of the method.

Ferronickel is an alloy composed mainly of iron and nickel, and is used as a raw material for stainless steel and special steel. Ferronickel is generally produced by a pyrometallurgical method in which nickel oxide ore is reduced and melted in an electric furnace or the like (see Patent Document 1).

In the production of ferronickel by the above-mentioned pyrometallurgy, the reduced-melted ferronickel is, if necessary, further subjected to a desulfurization step or the like, and then cast in a casting step in many cases into a shot-like (flake-like) shape. Shipped as ferronickel cast pieces.

Conventionally, in the production of ferronickel cast slabs as described above, there has been a problem of blackening of the surface due to surface deposition of chromium oxide or the like. As a conventional technique intended to suppress such discoloration of an iron-based alloy, a technique of applying a water-based derusting paint to the surface of a metal material to form a coating is known (see Patent Document 2). .

For example, when applying the technology described in Patent Document 2 to the production of ferronickel cast pieces, it is necessary to newly add a step of applying a water-based derusting paint as a step to be performed after casting. However, most of the blackening of the surface of the ferronickel cast piece occurs during the process of solidifying the ferronickel melt during the casting process. Since the cast slab that has turned black in this way cannot be practically commercialized, the technique described in Patent Document 2 is not suitable as means for suppressing the blackening of the ferronickel cast slab. Further, even if the effect of suppressing the progress of blackening of ferronickel cast pieces after casting can be expected to some extent, it is difficult to evenly apply paint to shot products with uneven surfaces. , the drug cost will be enormous. In addition, there is a risk that the application of the same paint will deviate from the product standard of ferronickel cast pieces in terms of composition.

JP 2019-39045 A JP 2015-74743 A

The present invention is a novel process developed in view of the above situation, and includes a "method for suppressing blackening of ferronickel cast slabs" that suppresses blackening of the surface of ferronickel cast slabs in the production of ferronickel cast slabs, and the method. It is an object of the present invention to provide a "method for manufacturing a ferronickel cast piece" capable of manufacturing a ferronickel cast piece in which blackening is suppressed by implementing the above.

The present inventors have studied the entire manufacturing process of ferronickel cast pieces in detail, and focused on the ratio of silicon (Si) to chromium (Cr) in the ferronickel melt discharged from a melting furnace such as an electric furnace. , and found that the above problem can be solved by optimizing this, and have completed the present invention. The present invention specifically provides the following.

(1) A melting reduction step of reducing a nickel oxide ore in a melting furnace to obtain a ferronickel molten body, and a casting step of casting the ferronickel molten body to obtain a shot-shaped ferronickel cast piece. A Si/Cr quality measuring step of measuring the Si/Cr quality, which is the ratio of silicon (Si) to chromium (Cr) in the ferronickel melt, and the Si/Cr quality Si/Cr that maintains the Si/Cr quality of the ferronickel melt at a predetermined value or more by adding a necessary amount of silicon (Si)-containing agent to the ferronickel melt, which is determined according to the measured value of A method for suppressing blackening of a ferronickel cast piece by performing a grade adjustment step.

According to the invention (1), that is, the "method for suppressing blackening of ferronickel cast pieces," the "Si/Cr quality of the ferronickel melt, which has not been noted in the past, has not been noticed in the production of ferronickel cast pieces. is optimized at a stage before the casting process, blackening of the surface of the ferronickel cast piece obtained after the casting process can be suppressed or prevented. In the production of conventional ferronickel cast slabs, it was no longer possible to adjust the composition at the stage of the ferronickel melt. Therefore, in order to prevent the surface of the ferronickel cast piece from turning black, it was necessary to control the reaction conditions of the melting reduction process, which is the upstream process. However, it is extremely difficult to optimize the reaction conditions because the reaction inside the electric furnace or the like in which the same process is performed is affected by the raw material composition and operating conditions. On the other hand, the blackening suppression method of the present invention is a method of adding additives according to the composition of the ferronickel molten body after being discharged from an electric furnace or the like, so that the quality control of the product can be performed at a high level. can be easily done.

(2) The method for suppressing blackening of ferronickel cast pieces according to (1), wherein the predetermined value is 0.2.

According to the invention of (2), the above effect of the invention of (1) is obtained under general manufacturing conditions for ferronickel cast slabs, and blackening of ferronickel cast slabs is prevented with higher accuracy. can do.

(3) A method for producing a cast piece of ferronickel in which the method for suppressing blackening according to (1) or (2) is performed, comprising the melting reduction step, the Si/Cr quality measurement step, and the Si/Cr quality A ferronickel cast piece comprising an adjusting step and the casting step, wherein the ferronickel molten body subjected to the blackening suppression method is cast in the casting step to obtain shot-like ferronickel. manufacturing method.

(3) "Manufacturing method of ferronickel cast piece" does not require condition change in the upstream process, and only by addition treatment of additives at the stage just before the casting process, (1) or ( It is a manufacturing method which can enjoy the said effect which the blackening suppression method of 2) shows. Conventionally, in the production of ferronickel cast slabs, there was no way to deal with defective products with blackened surfaces other than repeating them in the upstream process of the system. , to respond flexibly to sudden fluctuations in the "Si/Cr quality" in the ferronickel molten body during the production of ferronickel cast pieces, and to prevent the occurrence of defective products due to blackening of the surface of ferronickel cast pieces. can be minimized.

(4) Add the necessary amount of the silicon (Si)-containing agent to the ladle into which the ferronickel molten body discharged from the melting furnace is divided into several times and transported to the next step, and the ferronickel molten body The method for producing a ferronickel cast piece according to (3), wherein the ferronickel cast piece is charged in advance before charging.

According to the invention of (4), it is possible to further improve the productivity of manufacturing ferronickel cast pieces by the "method for manufacturing ferronickel cast pieces" of (3).

According to the present invention, in the production of a ferronickel cast piece, a "method for suppressing blackening of a ferronickel cast piece" that suppresses blackening of the surface thereof, and a ferronickel cast piece whose blackening is suppressed by implementing the method. It is possible to provide a "method for producing a ferronickel cast piece" capable of producing a nickel cast piece.

BRIEF DESCRIPTION OF THE DRAWINGS It is process drawing which shows an example of the flow of the manufacturing method of a nickel oxide ore.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In addition, the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

<Manufacturing method of ferronickel cast piece>
The ferronickel cast pieces are manufactured by a manufacturing method comprising a melting reduction step of reducing nickel oxide ore in a melting furnace and a casting step of casting the reduced ferronickel melt into shots. is common. The ``method for producing a ferronickel cast slab'' of the present invention is characterized in that the ``method for suppressing blackening of a ferronickel cast slab'' of the present invention is further performed as an essential treatment step in such a conventional manufacturing process. It is a manufacturing method that

The basic flow of the "method for producing a ferronickel cast piece" of the present invention is as shown in FIG. Further, in the "method for suppressing blackening of ferronickel cast pieces" of the present invention, the two steps of "Si/Cr quality measurement step S2" and "Si/Cr quality adjustment step S3" shown in Fig. 1 are performed as a series of processes. process. That is, in the "method for manufacturing a ferronickel cast piece" of the present invention, the melting reduction step S1 and the casting step S5 are performed as essential steps, and after performing the melting reduction step S1, before performing the casting step S5 In the stage of , the above-mentioned "method for suppressing blackening of ferronickel cast pieces", that is, the two steps of "Si/Cr quality measurement step S2" and "Si/Cr quality adjustment step S3" are performed as essential steps. .

In the case of producing cast pieces of ferronickel by the production method of the present invention, as in the conventional general production method, nickel oxide ore as a raw material is prepared in advance before being introduced into the melting reduction step S1. Preliminary treatments (not shown) such as drying, calcination and partial reduction are preferred. Moreover, it is preferable to carry out a desulfurization step S4 in which the ferronickel molten body obtained in the melting reduction step S1 is desulfurized in accordance with the required product specifications, before being subjected to the casting step S5.

[Melting Reduction Step]
The melting reduction step S1 is a step of melting and reducing the raw material ore in a reducing furnace such as an electric furnace to produce ferronickel (metal) and slag. The ferronickel molten body produced in this process is mainly composed of iron and contains nickel at a grade of about 16% by weight to 25% by weight depending on the set amount of the carbonaceous reducing agent. In addition, the slag produced separately from the ferronickel melt contains most of the iron oxide in the raw material ore, silicon dioxide and magnesium oxide, and is used as a magnesia flux for component adjustment in the sintering process of steel, and as a concrete It is used as fine aggregate for construction, materials for civil engineering work, etc.

[Si/Cr quality measurement step]
The Si/Cr quality measurement step S2, which is one of the essential steps of the "method for suppressing blackening of ferronickel cast pieces" of the present invention, is performed by measuring the "Si/Cr quality ” is a step of measuring "Si/Cr grade" as used herein is the ratio (weight ratio) of silicon (Si) to chromium (Cr). The method for measuring the Si/Cr quality is not particularly limited, and conventionally known various methods can be used. For example, this step can be performed by subjecting molten ferronickel to a fluorescent X-ray analysis method.

[Si/Cr grade adjustment step]
The Si/Cr quality adjustment step S3 is a step of adding a silicon (Si)-containing agent to the ferronickel melt. The amount of the silicon (Si)-containing agent to be added is determined according to the measured value of the "Si/Cr quality" of the ferronickel melt measured in the Si/Cr quality measurement step S2. The addition amount of the silicon (Si)-containing agent added to the ferronickel molten body in the Si/Cr quality adjustment step S3 is, in detail, such that the "Si/Cr quality" of the ferronickel molten body after addition of the agent is "a predetermined value. ” is determined to be greater than or equal to Ferrosilicon, for example, can be preferably used as the silicon (Si)-containing agent.

The above-mentioned "predetermined value" as an index for determining the amount of silicon (Si)-containing agent to be added in the Si/Cr quality adjustment step S3, that is, the ferronickel molten body to be maintained in the Si/Cr quality adjustment step S3 The Si/Cr grade of is 0.2 as a general criterion. When the Si/Cr quality of the ferronickel molten body introduced into the casting step S5 is less than 0.2, a silicon (Si)-containing agent is added to maintain the Si/Cr quality after addition at 0.2 or more. It has been elucidated by the studies of the present inventors that blackening of the surface of the ferronickel cast body can be sufficiently suppressed by doing so.

The timing of performing the Si/Cr quality adjustment step S3, that is, the timing of adding the silicon (Si)-containing agent to the ferronickel molten body is immediately after the ferronickel molten body is discharged from the electric furnace or the like in the melting reduction step S1. Any timing between the stage after the stage and the stage immediately before performing the next step may be used. For example, if the desulfurization step S4 is performed prior to the casting step S5, it can be performed at any timing after the melting reduction step S1 is completed and before the desulfurization step S4 is started.

Here, the ferronickel molten material discharged from an electric furnace or the like is usually divided into multiple batches and transferred to the next step in a ladle. For example, in the first ladle in which the first transfer is performed, even if it is difficult to grasp the Si/Cr grade in advance, the Si and Cr grades of the ferronickel melt first discharged from the electric furnace are Measure to grasp the Si/Cr grade, calculate the necessary amount of silicon (Si) containing agent to be added, and add the required amount to the ladle that receives the ferronickel molten body discharged from the electric furnace after this calculation. An embodiment in which the silicon (Si)-containing agent is added in advance can be exemplified as a more preferable embodiment of the Si/Cr quality adjustment step S3. As a result, as described above, the working time for adding the silicon (Si)-containing agent can be shortened, and the productivity of the ferronickel cast pieces can be further improved.

[Casting process]
The casting step S5 is a step of casting the ferronickel molten body into shot-shaped (flake-shaped) ferronickel cast bodies. A shot-shaped ferronickel casting is produced, for example, by pouring molten ferronickel into a disc provided at a position higher than the water surface in the center of a water tank containing cooling water, and rotating the disc to produce ferronickel. It can be obtained by scattering the molten material in the form of shots, dropping them into cooling water in a water tank, and cooling them.

[Other processes]
As described above, in the case of producing a ferronickel cast piece by the production method of the present invention, as in the case of the conventional general production method, as a step preceding the melting reduction step S1, the "drying step , and the calcination and partial reduction step, the desulfurization step S4 is preferably performed prior to the casting step S5.

(Drying process)
In the drying process, after blending the raw ore so that it has a predetermined mixing ratio, it is dried using a heating furnace such as a rotary kiln to remove a part of the attached moisture (35% to 45% by mass) contained in the raw ore. remove the part. For example, the amount of adhering moisture contained in the raw material ore is set to about 25% by mass to 35% by mass.

(Baking and partial reduction process)
A carbonaceous reducing agent (coal) and, if necessary, a melting agent are added to the raw material ore dried in the drying process, put into a heating furnace such as a rotary kiln, and fired at a firing temperature of about 800 ° C to 900 ° C. By doing so, the moisture remaining in the ore (attached water, crystal moisture) is completely removed, and partially reduced calcined ore is produced. When these steps are performed prior to the "melting reduction step S1", the calcined ore thus produced is put into the "melting reduction step S1".

(Desulfurization process)
The ferronickel molten body obtained in the "melting reduction step S1" is transferred to the desulfurization step S4 if desulfurization treatment is required according to the product specifications, and a mechanical stirrer using a ladle or the like or an electric Desulfurization is performed by an induction agitator. Specifically, in the desulfurization step S4, a desulfurizing agent such as calcium carbide is added to the ferronickel molten body and stirred to convert sulfur in the ferronickel molten body into calcium sulfide (CaS) in the slag. to separate and remove.

<Method for Suppressing Blackening of Ferronickel Cast Piece>
The "method for suppressing blackening of a ferronickel cast piece" of the present invention is a method for producing a ferronickel cast piece that includes at least a melting reduction step S1 and a casting step S5, and further performs this method in the flow of the method. , is a method that can significantly suppress or prevent the blackening of ferronickel cast pieces.

Specifically, this "method for suppressing blackening of ferronickel cast slabs" is an intermediate treatment process consisting of a Si/Cr quality measurement step S2 and a Si/Cr quality adjustment step S3, and is a method for producing a ferronickel cast slab. is performed before the start of the casting step S5 after the completion of the melting reduction step S1.

Here, in the conventional general production of ferronickel cast pieces, the Si content in the ferronickel melt that has undergone the melting reduction step S1 is controlled to about 1 to 3%. This Si grade fluctuates due to changes in the operating conditions of the furnace, etc., and may be 1% or less. It has been conventionally known that blackening of ferronickel cast pieces tends to occur when the Si grade is lowered in this way. However, this blackening does not always occur when the Si quality is low (about 1% or less as a guideline). The inventors of the present invention have repeatedly studied and newly focused on the "relationship between the Cr quality and the Si quality" instead of the "Si quality" in ferronickel, and as a result, the fluctuation of the "Si/Cr quality" and the above found that there is a strong correlation between the blackening of the clarified.

When manufacturing a ferronickel cast piece, after performing the melting reduction step S1 and before performing the casting step S5, the Si/Cr quality measurement step S2 and the Si/Cr quality adjustment step S3 are performed. "Method" is a novel process developed based on the above new findings.

EXAMPLES The present invention will be described in more detail below with reference to examples of test operations, but the present invention is not limited to the following examples.

(Conditions for conducting test operation)
As a test operation, an operation was performed in which the melting reduction process was performed in an electric furnace, the ferronickel molten body was received in a ladle and separated, followed by the casting process of casting the ferronickel molten body into shots. The amount of ferronickel molten material that can be discharged from the electric furnace is 18 times the amount that can be transferred with the ladle, and the number of transfer times with the ladle to extract all the ferronickel molten material from the electric furnace is 18 times. . After that, the ferronickel molten material was retained in the electric furnace again, and the same operation was repeated twice, for a total of three times. The total number of transfers in the ladle was 54 times (=54 lots).
In each of the first to third operations, the ferronickel melt of the first lot was analyzed to determine the Si/Cr quality. The analysis method is a fluorescent X-ray analysis method, and the measurement results and Si/Cr I was able to figure out the quality.

(First operation: Comparative example)
In the first run, the Si/Cr grades of all 18 lots were stable between 0.18 and 0.20.
No silicon (Si) containing agent was added to 18 lots of the first run.
As a result, in 11 out of 18 lots, blackening of the surface of the ferronickel cast piece occurred.

(Second operation: Reference example)
In the second run, the Si/Cr grades of all 18 lots were stable between 0.22 and 0.24.
No silicon (Si)-containing agent was added to lot 18 of the second run.
As a result, blackening of the surface of the ferronickel cast piece did not occur in any of the 18 lots.

(Third operation (first lot to second lot): Example 1)
In the third run, the Si/Cr grades of all 18 lots were stable between 0.16 and 0.18.
For the first lot and the second lot of the third operation, when the ferronickel molten material was discharged from the electric furnace into the ladle (capacity 30t), ferro-silicon (Si grade 75%) was placed in the ladle. was added to the ferronickel melt. The added amount was adjusted between 8 and 10 kg so that the Si/Cr grade of the ferronickel melt was 0.20.
As a result, in the first lot and the second lot of this third run, no blackening of the surface of the ferronickel cast piece occurred. However, due to the working time required to add the silicon (Si)-containing agent, there was a two minute delay in the normal flow.

(Third operation (3rd lot to 18th lot): Example 2)
For the 3rd lot to the 18th lot of the 3rd operation, a predetermined amount of silicon (Si) containing agent (ferro-silicon ) was added to the ferronickel melt by the method of charging the silicon (Si) containing agent. The amount of the silicon (Si)-containing agent to be added was determined by calculating the amount so that the ferronickel melt had a Si/Cr grade of 0.21.
As a result, in the 3rd lot to the 18th lot of this 3rd operation, no blackening of the surface of the ferronickel cast piece occurred. No blackening of the cast piece surface occurred. In addition, the work for adding the silicon (Si)-containing agent was completed during preparation of the ladle, and the normal flow was not stagnated.

From the comparison of the results of the reference example and the comparative example, it can be seen that when the Si/Cr grade in the ferronickel molten body is less than 0.2, the surface of the ferronickel cast piece is likely to be blackened. From the results of Examples 1 and 2, it can be seen that the blackening of ferronickel cast pieces can be significantly suppressed by applying the present invention.

S1 Melting reduction process S2 Si/Cr quality measurement process S3 Si/Cr quality adjustment process S4 Desulfurization process S5 Casting process

Claims (4)

a melting reduction step of reducing a nickel oxide ore in a melting furnace to obtain a ferronickel melt;
a casting step of casting the ferronickel molten body to obtain a shot-shaped ferronickel cast piece;
In the production of a ferronickel cast piece comprising
a Si/Cr quality measuring step of measuring the Si/Cr quality, which is the ratio of silicon (Si) to chromium (Cr) in the ferronickel melt;
A necessary amount of silicon (Si)-containing agent determined according to the Si/Cr quality measurement is added to the ferronickel melt to maintain the Si/Cr quality of the ferronickel melt at a predetermined value or higher. and a Si/Cr quality adjustment step, and a method for suppressing blackening of a ferronickel cast piece. 2. The method for suppressing blackening of ferronickel cast pieces according to claim 1, wherein said predetermined value is 0.2. A method for producing a ferronickel cast piece by performing the method for suppressing blackening according to claim 1 or 2,
the melting reduction step;
the Si/Cr quality measurement step;
the Si/Cr quality adjustment step;
said casting step;
In the casting step, the ferronickel molten body subjected to the blackening suppression method is cast to obtain shot-like ferronickel,
A method for producing a ferronickel cast piece. Before charging the ferronickel molten body, a necessary amount of the silicon (Si)-containing agent is added to a ladle in which the ferronickel molten body discharged from the melting furnace is charged in multiple times and transported to the next step. 4. The method for producing a ferronickel cast piece according to claim 3, wherein the ferronickel cast piece is charged in advance.

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