JP2002285220A - Dephosphorizing method from molten cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate a dephosphorizing work and also, to shorten the treating time by reducing additional frequencies of oxidizing agent added while dividing into a plurality of times and further, to perform the dephosphorizing treatment without becoming high cost by reducing the additional quantity of the oxidizing agent. SOLUTION: Iron sulfide (FeS) as a sulfur additive containing at least either one side of the sulfur and the sulfur compound, is added into molten spheroidal graphite cast iron, and after adding the sulfur additive, ferrous oxide (FeO) as oxidizer and shell as lime base flux, are added to perform the dephosphorization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing phosphorus from molten cast iron, and more particularly to a method for removing phosphorus from molten cast iron by adding an oxidizing agent and a lime-based flux to the molten cast iron.

[0002]

2. Description of the Related Art Generally, pig iron for casting, steel scrap, cast iron return material, and the like are used as iron sources for cast iron.
Steel scrap accounts for about 60% of the iron source, and the quality of the steel scrap has a great influence on the quality of the cast iron. In recent years, various types of surface treatment, alloying, and compounding have been used due to the diversification of machines and parts of steel and castings, and a large amount of iron-based scrap containing elements harmful to cast iron has been produced. Is spinning. One of the harmful elements is phosphorus. Phosphorus is useful when imparting wear resistance to a casting, but when spheroidal graphite cast iron has a phosphorus content of 0.05% by mass or more, it has a hard and pointy structure on the base of the cast iron. (Eutectoid structure of iron phosphide and γ-iron) is crystallized, resulting in poor machinability, poor finish of the cut surface, easy occurrence of shrinkage porosity, and fragility due to being hard and poor elongation and impact value become. For this reason, in order to produce a spheroidal graphite cast iron having a good cut surface finish, hardly causing shrinkage cavity defects and being resistant to elongation and impact, it is necessary to remove phosphorus from the cast iron.

Conventionally, as a dephosphorization method, there is a method developed as a hot metal pretreatment technique before steel making in an iron making process. But since this is all oxidizing refining,
Since it removes not only phosphorus but also carbon and silicon, which are important elements necessary for cast iron, there is a problem in application to molten cast iron. As a dephosphorization technique for removing phosphorus while suppressing the reduction of carbon, as shown in FIG. 3, an oxidizing agent (oxidizing oxidizing agent) is used which oxidizes phosphorus after adding a lime-based flux (shell) to molten cast iron and stirring. Ferrous iron, rolled oxide scale) in several portions to prevent phosphorus return
There is a method in which phosphorus is removed by stirring to convert phosphorus into phosphorus pentoxide, crystallized, and then floated together with lime as phosphorus-containing slag.

[0004]

However, when the content of phosphorus is high in the molten cast iron, the addition of the oxidizing agent after adding the lime-based flux to the molten cast iron is divided into a plurality of times and repeated. Must be performed, the work is complicated,
In addition, there is a problem that the processing time becomes longer. Further, there is a problem that it is difficult to obtain ferrous oxide or a rolled oxide scale as an oxidizing agent. This is available only in areas where ferrous oxide and rolled oxide scales are limited.Delivery costs are high in remote areas depending on the amount of supply, and dephosphorization of a large amount of cast iron that requires a large amount of oxidizing agent. It is difficult to do.

Under these circumstances, the inventors of the present invention have proposed a dephosphorization that is easy to operate without increasing the cost when producing a casting using steel scrap as an iron source of cast iron from the viewpoint of recycling of metal materials. The method was studied, and a method for removing phosphorus by promoting the oxidation of phosphorus in the molten metal was studied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made to reduce the number of times of adding an oxidizing agent to be added in a plurality of times to facilitate the work and shorten the processing time. It is another object of the present invention to provide a method for dephosphorizing cast iron from which molten phosphorus can be dephosphorized without increasing the cost by reducing the amount of an oxidizing agent.

[0007]

The technical means of the present invention for solving such problems is to remove phosphorus from cast iron melt by adding an oxidizing agent and a lime-based flux to the cast iron melt to remove phosphorus. In the method, a configuration was employed in which a sulfur additive containing at least one of sulfur and a sulfur compound was added. As a result, the sulfur contained in the sulfur additive promotes the oxidation reaction of phosphorus in the molten cast iron, so that the number of additions of the oxidizing agent to be added in a plurality of portions is reduced so that the work is facilitated and the treatment is simplified. Since the time is shortened and the addition amount of the oxidizing agent is reduced, the dephosphorization treatment can be performed without increasing the cost.

[0008] If necessary, the sulfur additive is added before the oxidizing agent is added. Since phosphorus is not reacted with the oxidizing agent, the sulfur additive is not wasted and the function of the oxidation reaction can be sufficiently exhibited. Further, if necessary, the sulfur additive is added so that the sulfur content in the molten metal is 0.05% by mass to 0.5% by mass. Sulfur content in molten cast iron is 0.05% by mass
If the amount is less than this, the effect of accelerating the oxidation reaction does not appear remarkably, and if the sulfur content in the molten cast iron is more than 0.5% by mass, sulfur must be removed later, which is not preferable. Further, if necessary, the sulfur additive is added so that the sulfur content in the molten metal becomes 0.4% by mass to 0.5% by mass. The oxidation reaction can be efficiently promoted.

Further, if necessary, the oxidizing agent may be replaced with Fe.
O was adopted. By using an oxidizing agent having iron, it is easily available and easy to handle. And, if necessary, the sulfur additive was configured to be FeS.
By using an oxidizing agent having iron, it is easily available and easy to handle. In addition, if necessary, the sulfur additive was formed of Dalai powder which is a cutting chip and contains a sulfur compound. The production cost can be reduced by adding easily available and inexpensive Dalai powder. Further, if necessary, the above cast iron was configured to be spheroidal graphite cast iron. Spheroidal graphite cast iron is used for automotive parts such as crankshafts, rolls for metal rolling, large gears, cast iron tubes, exteriors such as street lights, etc. Good damping ability and good machinability. The chemical components of the spheroidal graphite cast iron are, for example, 3.0 to 4.5% by mass of carbon and 1.0 to 3.0% by mass of silicon.
0 mass%, manganese 0.4 mass% or less, phosphorus 0.08 mass% or less (preferably 0.05 mass% or less), sulfur 0.
The content of manganese and phosphorus in the matrix is one of the main factors affecting the material.
Therefore, in the production of spheroidal graphite cast iron, it is necessary to adjust the contents of manganese and phosphorus. However, the phosphorus removal method according to the present invention easily removes phosphorus to reduce the phosphorus content to 0.0%.
It can be reduced to 8% by mass or less (preferably 0.05% by mass or less), and a high-quality spheroidal graphite cast iron having elongation, toughness and strength can be produced.

Further, a desulfurizing agent is added to the molten metal at a required time after the addition of the sulfur additive, if necessary. When the sulfur content in the molten metal is small and the added sulfur remains, the sulfur can be easily removed. And, if necessary, the lime-based flux was composed of a shell. As a result, a large amount of discarded shells, which are currently a problem in the coastal areas of Hokkaido and Tohoku, can be used as lime-based flux. Further, when the sulfur content in the molten metal increases, it reacts with sulfur to form calcium sulfide and is contained in the slag, so that the removal of sulfur can be facilitated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for removing phosphorus from a molten cast iron according to an embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the method for dephosphorizing molten cast iron of the present invention comprises adding a sulfur additive containing at least one of sulfur and a sulfur compound to a molten cast iron and then adding an oxidizing agent and a lime-based flux. This is a method for dephosphorization. Here, iron-based scrap is used as the iron source, and the cast iron is spheroidal graphite cast iron.

As the sulfur additive, iron sulfide (FeS) was used. This iron sulfide is added and stirred so that the sulfur content in the molten metal becomes 0.05% by mass to 0.5% by mass. In this case, it is desirable to add so that the sulfur content in the molten metal is 0.4% by mass to 0.5% by mass. Ferrous oxide (FeO) was used as the oxidizing agent. Ferrous oxide is added a plurality of times (2 to 3 times) after the addition of the sulfur additive and stirred. Next, waste shells are added as lime-based flux. In this case, a large amount of discarded shells is a problem in the coastal areas of Hokkaido and Tohoku, but this can be used as a new use for discarded shells. Then, phosphorus is removed by crystallizing the phosphorus into phosphorus pentoxide and floating, and removing it as phosphorus-containing slag together with lime. At this time, when the sulfur content in the molten metal becomes high, a desulfurizing agent and a shell are added after dephosphorization. Thereafter, the molten metal is cast into a mold and demolded to produce a cast iron product.

According to such a dephosphorization method, by adding sulfur (iron sulfide) to the molten metal, the oxidation reaction of phosphorus can be promoted to generate phosphorus pentoxide, thereby promoting the dephosphorization reaction. Therefore, the number of times of adding the oxidizing agent to be added in a plurality of times can be reduced. Therefore, the dephosphorization operation can be facilitated and the processing time can be shortened. Further, since the amount of the oxidizing agent can be reduced, the cost does not increase. And by such a dephosphorization method, the spread of the technology of the dephosphorization treatment from the cast iron melt becomes easier.

Next, Examples 1 and 2 and a comparative example relating to a method for removing phosphorus from molten cast iron will be described. Example 1 In a high-frequency melting furnace, 0.125% by mass
First, FeS, a sulfur additive, is added to 3 kg of a molten cast iron containing phosphorus so that the sulfur content in the molten metal becomes 0.45% by mass, followed by stirring. Thereafter, 240 g of a shell is added as a lime-based flux. Next, ferrous oxide (FeO) is added in two portions as an oxidizing agent. The oxidizing agent is added by adding 30 g of FeO 10 minutes after the addition of the shell and stirring. Ten minutes after that, 30 g of FeO is added and stirred in the same manner as the first time, and a total of 60 g of the oxidizing agent is added. FIG. 2 shows the results of measuring the phosphorus content in the molten metal when an oxidizing agent was added to the molten metal containing sulfur. Then, phosphorus is removed by crystallizing the phosphorus into phosphorus pentoxide and floating, and removing it as phosphorus-containing slag together with lime. Here, the temperature in the molten metal is 135
The temperature was 0 ° C. (1623 K), and the molten cast iron contained 1% by mass of silicon. Thereafter, the molten metal is cast into a mold and demolded to produce a cast iron product.

[Example 2] In a high frequency melting furnace, 0.
First, FeS, a sulfur additive, is added to 3 kg of a cast iron molten metal containing 135% by mass of phosphorus so as to have a sulfur content of 0.1% by mass, followed by stirring. Thereafter, 240 g of a shell is added as a lime-based flux. Next, ferrous oxide (FeO) is added as an oxidizing agent in three portions.
The oxidizing agent was added by adding FeO 3 minutes after the addition of the shell.
Add 0 g and stir. After 10 minutes, 30 g of FeO is added and stirred in the same manner as in the first time, and further, after 10 minutes, 30 g of FeO is added and stirred in the same manner as in the first time, and a total of 90 g of the oxidizing agent is added. FIG. 2 shows the result of measuring the phosphorus content in the molten metal when the oxidizing agent was added to the molten metal containing sulfur. Then, phosphorus dephosphorization is performed by removing phosphorus that has crystallized from phosphorus pentoxide and floated and is removed together with lime as phosphorus-containing slag. here,
The temperature in the molten metal is 1350 ° C. (1623 K), and the molten cast iron contains 1% by mass of silicon. Thereafter, the molten metal is cast into a mold and demolded to produce a cast iron product.

Comparative Example 1 As a comparative example, a dephosphorization method according to a conventional method without adding a sulfur additive was performed. In a high-frequency melting furnace, 240 g of a shell as a lime-based flux is added to 3 kg of a cast iron melt containing 0.125% by mass of phosphorus. Next, ferrous oxide (FeO) is added as an oxidizing agent in three portions. The oxidizing agent is added by adding 30 g of FeO 10 minutes after the addition of the shell and stirring. 10 minutes later, 30 FeO was added as in the first time.
g and stirred, and 5 minutes later, 15 g of FeO was added.
Add and stir to add a total of 75 g of oxidant. FIG. 2 shows the results of measuring the phosphorus content in the molten metal when an oxidizing agent was added to the molten metal containing sulfur. And
Dephosphorization is performed by removing phosphorus that has crystallized from phosphorus pentoxide and crystallized and floated together with lime as phosphorus-containing slag. Here, the temperature in the molten metal is 1350 ° C.
(1623K) and 1% by mass in the molten cast iron.
Contains silicon. As a comparative example, no sulfur additive was added, but the molten metal contained 0.02% by mass of sulfur. Thereafter, the molten metal is cast into a mold and demolded to produce a cast iron product.

As shown in FIG. 2, when the oxidizing agent was added to the sulfur-containing molten metal, the phosphorus content in the molten metal was measured, and the results were shown in Example 1 (sulfur content 0.45% by mass).
Comparative Example 1 (sulfur content 0.02%) in Example 2 (sulfur content 0.10% by mass) and the phosphorus content in the molten metal
% By mass), and by adding the sulfur additive, the oxidation reaction of phosphorus in the molten metal is accelerated and easily removed.

In the method for removing phosphorus from molten cast iron according to the above embodiment, FeS is used as a sulfur additive. However, the present invention is not limited to this. However, it may be composed of Dalai powder containing a sulfur compound. According to this, since the Dalai powder contains a sulfur compound, it works not only as a sulfur additive but also as an oxidizing agent having an oxidizing action. Therefore, if a high sulfur content of Dalai powder is added, the oxidation reaction of phosphorus can be promoted to generate phosphorus pentoxide, and the dephosphorization reaction can be promoted. The number of additions can be reduced. The use of Dalai powder not only enables the production of high quality pig iron castings from inexpensive raw materials, but also promotes the reuse of waste.

[0019]

As described above, according to the method for removing phosphorus from molten cast iron of the present invention, a method for removing phosphorus from molten cast iron by adding an oxidizing agent and a lime-based flux to the molten cast iron to remove phosphorus. In the configuration, a sulfur additive containing at least one of sulfur and a sulfur compound is added, so that the sulfur contained in the sulfur additive promotes the oxidation reaction of phosphorus in the molten cast iron, so that the The number of additions of the oxidizing agent to be separately added is reduced to facilitate the work and shorten the processing time. Can do it.

When the sulfur additive is added before the oxidizing agent is added, the phosphorus additive is not reacted with the oxidizing agent, so that the sulfur additive is not wasted and the function of the oxidation reaction can be sufficiently exhibited. it can. Further, when the sulfur additive is added so that the sulfur content in the molten metal is 0.05% by mass to 0.5% by mass, the sulfur additive in the molten cast iron has an effect of accelerating the oxidation reaction. The content increases and does not need to be removed later. In this case, it is effective to add the sulfur additive so that the sulfur content in the molten metal becomes 0.4% by mass to 0.5% by mass.

Furthermore, when the oxidizing agent is made of FeO, it can be easily obtained and handled easily. If the sulfur additive is made of FeS, it can be easily obtained and handled easily. Also, the sulfur additive
In the case where the cutting chips are made of Dalai powder containing a sulfur compound, the production cost can be reduced by adding easily available and inexpensive Dalai powder. Furthermore,
When cast iron is used as spheroidal graphite cast iron, the main factor affecting the material of spheroidal graphite cast iron is the content of manganese and phosphorus in the base structure. However, dephosphorization is easily performed by the dephosphorization method of the present invention to reduce the phosphorus content to 0.1.
08 mass% or less, and a high-quality spheroidal graphite cast iron having elongation, toughness, and strength can be produced.

Further, when the desulfurizing agent is added to the molten metal at a required time after the addition of the sulfur additive, if the sulfur content in the molten metal is small and the added sulfur remains, the sulfur can be easily removed. Can be removed. When the lime-based flux is composed of shells, a large amount of waste shells, which are problematic, can be used as the flux. Further, when the sulfur content in the molten metal increases, it reacts with sulfur to form calcium sulfide and is contained in the slag, so that the removal of sulfur can be facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for dephosphorizing molten cast iron according to an embodiment of the present invention.

FIG. 2 is a table showing the effect of the initial sulfur content on dephosphorization in the method for dephosphorizing cast iron melt according to the embodiment of the present invention.

FIG. 3 is a view showing a conventional method for dephosphorizing molten cast iron.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 33/08 C22C 33/08 // C22C 37/04 37/04 Z (72) Inventor Akira Ibarjima Iwate 35-2, Iiooka-Shinda, 35-2, Iwate Prefectural Industrial Technology Center (72) Inventor Hiroyuki Ike 35-2, Iioka-Shinta, 35-2, Iwate Prefectural Industrial Technology Center F term (reference) 4K014 AA03 AB00 AB04 AC03 AC08 BA01 BB03 BC01 BC04 BD00 BD02

Claims (10)

[Claims] 1. A method for removing phosphorus from a cast iron melt by adding an oxidizing agent and a lime-based flux to the cast iron melt, wherein a sulfur additive containing at least one of sulfur and a sulfur compound is added. A method for dephosphorization from molten cast iron, characterized in that: 2. The method for removing phosphorus from molten cast iron according to claim 1, wherein the sulfur additive is added before the oxidizing agent is added. 3. The cast iron melt according to claim 1, wherein the sulfur additive is added so that the sulfur content in the molten metal is 0.05% by mass to 0.5% by mass. Dephosphorization method. 4. The dephosphorization from a molten cast iron according to claim 3, wherein the sulfur additive is added so that the sulfur content in the molten metal is 0.4% by mass to 0.5% by mass. Method. 5. The method for removing phosphorus from molten cast iron according to claim 1, wherein the oxidizing agent is FeO. 6. The method for removing phosphorus from molten cast iron according to claim 1, wherein said sulfur additive is FeS. 7. The dephosphorization from molten cast iron according to claim 1, wherein said sulfur additive is made of Dalai powder which is a cutting chip and contains a sulfur compound. Method. 8. The method for removing phosphorus from molten cast iron according to claim 1, wherein the cast iron is spheroidal graphite cast iron. 9. A desulfurizing agent is added to the molten metal at a required time after the addition of the sulfur additive.
3. The method for removing phosphorus from molten cast iron according to 3, 4, 5, 6, 7 or 8. 10. The method according to claim 1, wherein the lime-based flux is composed of a shell.
The method for removing phosphorus from molten cast iron according to 7, 8, or 9.