WO2016093093A1

WO2016093093A1 - Methods for manganese removal for cast iron

Info

Publication number: WO2016093093A1
Application number: PCT/JP2015/083567
Authority: WO
Inventors: 潔木下; 博敏村田
Original assignee: 株式会社木下製作所; 株式会社ナニワ炉機研究所
Priority date: 2014-12-12
Filing date: 2015-11-30
Publication date: 2016-06-16
Also published as: CN107406898A; JPWO2016093093A1; JP6110018B2; US20170342515A1

Abstract

The present invention needs neither a manganese-removing agent, e.g., a sulfide, nor a combustible gas in manganese removal for cast iron, yields little slag, attains a high manganese removal efficiency, and renders a safe operation possible. One of the methods for manganese removal for cast iron according to the present invention is practiced by making the interior of a furnace an oxygen atmosphere and blowing air into a melt for cast iron within the furnace, thereby keeping the carbon content in the melt for cast iron approximately constant to remove the manganese components. Another method for manganese removal for cast iron according to the present invention is practiced by making the interior of a furnace an oxygen atmosphere and stirring a melt for cast iron within the furnace, thereby keeping the carbon content in the melt for cast iron approximately constant to remove the manganese components.

Description

Method for removing manganese from cast iron

The present invention relates to a method for removing manganese from a raw material having a high manganese content, which is used for producing cast iron parts.

Cast iron castings are used for automobile parts and machine parts. About half of the production of cast iron castings is produced for automobiles, and cast iron castings account for about 10% of the total weight of automobiles. The raw material used for the production of this cast iron casting uses steel scraps of automotive steel sheets. Due to the recent demand for weight reduction, the manganese content of automotive steel sheets has increased, and manganese is a pearlite-promoting element. Therefore, it is a problem because toughness is lowered and internal defects are easily generated.

The following proposals have been made for the problem of increasing the manganese content of the raw material used for the production of cast iron parts. For example, Patent Document 1 proposes a demanganese treatment method for cast iron, in which a demanganese treatment agent containing sulfur is added to a molten cast iron containing manganese and floated as manganese sulfide to remove manganese from the molten metal. And about the removal of a manganese component, MnS produced | generated in the molten metal floats and is removed in the slag of the molten metal surface. In order to promote this floating removal, it is effective to stir the molten metal, for example, by blowing gas from a porous plug at the bottom of the ladle containing the molten metal. In the case of gas stirring, compressed air and nitrogen gas are inexpensive and easy to use as the blowing gas. However, an inert gas such as Ar is preferred in order to suppress an increase in the amount of oxygen and nitrogen in the molten metal.

Patent Document 2 discloses a method for removing manganese in a cast iron melt by reducing the manganese content in the production of cast iron and adding only sodium sulfate as an additive to the cast iron melt at a temperature of 1400-1500 ° C. Proposed. In this method of removing manganese, if the temperature of the molten cast iron is less than 1300 ° C., the generation of SiO ₂ is severe and the wear of Si, which is the main component of cast iron, is not preferable. In a cast iron melt at 1300 ° C. or higher, MnS is not formed unless the Mn or S content (%) is in a very high region. And this invention can make Mn removal rate 70% or more, even if Mn content of a cast iron molten metal is 1.5 mass% or more. The Mn removal rate is said to increase according to the amount of Na ₂ SO ₄ added until the amount of Na ₂ SO ₄ added is approximately 10% by mass.

In Patent Document 3, in melting by a rotary furnace using natural gas, liquefied petroleum gas, kerosene or the like as a heat source and pure oxygen, only steel scraps and return scraps or steel scraps are used as charging materials, and an oxidative combustion period In addition, there has been proposed a method for producing spheroidal graphite cast iron obtained by hot water means obtained by combining raw metal obtained by performing de-Mn melting and molten metal previously melted in another furnace and adjusted in components. In the embodiment of the method for producing the spheroidal graphite cast iron, a material bar having a mixing ratio of steel scrap 60% and return scrap 40% is charged into the rotary furnace through the material inlet, and the upper portion thereof is used as a slagging agent 1.62% quartz sand and 0.30% limestone were sprayed. It is said that it was dissolved while adjusting the volume ratio of pure oxygen to natural gas (CH ₄ ) in the range of 1.95 to 2.10.

Patent Document 4 discloses a method for removing impurities including manganese (Mn) while suppressing the depletion of carbon (C) and silicon (Si) contained in a molten cast iron melted in advance. The temperature of the molten metal is maintained at 1250 ° C or higher and lower than 1500 ° C, and the molten metal and the acidic slag layer are brought into contact with each other, while the theoretical combustion ratio of fuel and oxygen (oxygen amount (volume) x 5 / fuel (volume) amount) There has been proposed a method for removing impurities in a cast iron melt by directly exposing an oxygen-excess flame having a 1 to 1.5 to the surface of the cast iron melt and superheating the surface. The temperature of the molten cast iron at the time of hot water supply is preferably less than 1500 ° C, more preferably 1250 ° C or more and less than 1500 ° C. When the temperature is within this temperature range, it is easy to remove Mn while suppressing the depletion of C and Si after hot water supply. In addition, it is preferable that an oxygen-excess flame is burned using LPG gas or LNG gas while supplying an excess amount of oxygen more than that required for combustion. The oxygen-excess flame exposes the molten metal surface directly to the flame and removes impurities without increasing the temperature of the entire molten metal while bringing the remaining molten metal surface into contact with acidic slag. However, it is said that the wear of C and Si can be reduced.

JP 2003-105420 A Japanese Patent No. 4210603 JP-A-7-268432 JP 2011-153359 A

The method for removing manganese described in Patent Document 1 or 2 has a problem that a sulfide is used as a manganese removal agent, and an amount of several percent is required by mass%, and a large amount of slag containing sulfur is generated. In addition, according to the method described in Patent Document 2, the increase in sulfur in the cast iron melt is said to be small, but since the sulfur content increases to 0.02 to 0.03%, desulfurization is necessary for use in spheroidal graphite cast iron parts. There is a problem of becoming.

On the other hand, the method for removing manganese described in Patent Document 3 or 4 has an advantage that the amount of generated slag can be reduced because manganese contained in cast iron is oxidized and removed as slag. In particular, unlike the method described in Patent Document 3, the method described in Patent Document 4 can reduce the amount of generated slag because no ironmaking material is used. However, the manganese treatment method described in Patent Document 3 or 4 requires a flammable gas and is not preferable in the field where high-temperature work is performed.

As a method for removing manganese from cast iron, a method in which a large amount of slag is produced and a slag containing sulfur is generated is not preferable in a society where environmental conservation is important. And the manganese removal method of cast iron has a preferable method which does not require a combustible gas from a viewpoint of handleability and work efficiency. Moreover, it is preferable from a viewpoint of energy saving that the processing temperature of manganese removal of cast iron is as low as possible.

In view of such conventional problems and demands, the present invention does not require a manganese removal agent such as sulfide or a flammable gas in removing manganese from cast iron, produces less slag, has high manganese removal efficiency, and is safe. It aims at providing the manganese removal method of cast iron which can be operated.

The method for removing manganese from cast iron according to the present invention is to remove the manganese component by making the inside of the furnace an oxygen atmosphere and blowing air into the molten cast iron in the furnace to keep the carbon component in the molten cast iron substantially constant. Implemented by doing.

Further, the method for removing manganese from cast iron according to the present invention removes the manganese component by setting the furnace interior to an oxygen atmosphere, stirring the cast iron melt in the furnace, and maintaining the carbon component in the cast iron melt almost constant. Is implemented.

In the above invention, the manganese component can be removed while maintaining the carbon component in the cast iron melt almost constant while adjusting the amount of oxygen supplied to the furnace and / or the stirring speed of the cast iron melt in the furnace. .

In the above invention, the manganese component can be removed while maintaining the ratio between the removal rate of the silicon component and the removal rate of the manganese component substantially constant, and the removal of the manganese component is suppressed while suppressing the decrease in the silicon component. Can do.

In the above invention, the manganese component can be removed while maintaining the temperature of the cast iron melt almost constant, and the temperature of the cast iron melt can be set to 1400 ° C. to 1200 ° C.

The method for removing manganese from cast iron according to the present invention is a method for removing manganese that does not require a manganese removal agent such as sulfide or a flammable gas and generates less slag, and can remove manganese with high efficiency.

It is explanatory drawing of the furnace used for the test A of this invention. It is explanatory drawing of the furnace used for the test B of this invention. 6 is a graph showing the test results of Example 1 in Test A. 4 is a graph showing the Mn residual rate of test A. 4 is a graph showing the C residual ratio of test A. 6 is a graph showing the Si residual rate in Test A. 3 is a graph showing a cast iron melt temperature in Test A. 4 is a graph showing the Mn residual rate of test B. 4 is a graph showing the C residual ratio of test B. 4 is a graph showing the Si residual rate in Test B. 3 is a graph showing a cast iron melt temperature in Test B. 4 is a graph showing the relationship between the stirring speed and the Mn removal speed in Test B. It is a graph which shows Si / Mn reduction | decrease ratio.

Hereinafter, modes for carrying out the present invention will be described. The method for removing manganese according to the present invention is a method for removing manganese from cast iron, wherein the inside of the furnace is in an oxygen atmosphere and air is blown into the molten cast iron to remove the manganese component contained in the molten cast iron, the carbon in the molten cast iron. It is carried out by removing the manganese component while keeping the component substantially constant. That is, the present manganese removal method belongs to the oxygen treatment method because the manganese removal treatment is performed by blowing air into the cast iron melt in a furnace in an oxygen atmosphere. And this manganese removal process is implemented by removing a manganese component, keeping a carbon component constant.

In the present invention, it is important for the supply of oxygen that the furnace is in an oxygen atmosphere. Although oxygen can also be supplied by bubbling with air, it is preferable to supply oxygen by providing a dedicated supply means that can supply oxygen on the surface of the molten metal in the furnace. In the present invention, the supply method and supply amount of oxygen influence the effect of manganese removal treatment. In the present invention, the removal rate of the manganese component in the molten cast iron or the molten metal temperature can be adjusted by adjusting the supply amount of oxygen.

Blowing air into the cast iron melt increases the area of the reaction interface between oxygen in the air blown by the flow and stirring of the cast iron melt and oxygen supplied into the furnace, and promotes oxidation of manganese. For this reason, an inert gas is not preferable. Also, a mixed gas of air and oxygen is not preferable because it involves oxidation and combustion. The amount of air blown into the cast iron melt does not require an amount or strength to scatter the melt or slag. That is, the blowing of air into the cast iron melt does not require intense bubbling.

The temperature of the molten metal when performing the manganese removal treatment is preferably 1400 ° C. or lower and 1350 ° C. to 1175 ° C. in order to suppress carbon consumption in the cast iron molten metal. The temperature of the cast iron melt is preferably low from the viewpoint of energy saving, but is preferably 1350 ° C. to 1200 ° C. in view of energy saving including the next step. That is, the cast iron melt from which Mn has been removed is heated to 1400-1550 ° C. and then used for casting or the like.

In the present invention, the furnace for treating the molten cast iron may be a furnace that does not have its own heating means, such as a ladle. What is necessary is just to have the air supply means which can blow in. For example, a ladle as shown in FIG. 1 can be used. In FIG. 1, a furnace 10 includes an air supply means 15 that can blow air into a furnace body 11, a furnace lid 12, a cast iron melt 20, and an oxygen supply means 16 that can make the interior of the furnace 10 an oxygen atmosphere. Have. The furnace 10 has an operation port 12a for taking out a sample and an exhaust port 12b for exhausting gas generated during the processing operation.

As described above, the manganese removal method for cast iron according to the present invention blows air into the cast iron melt in an oxygen atmosphere to flow and agitate the cast iron melt, thereby increasing the area of the reaction interface between the cast iron melt and oxygen. It promotes oxidation. Such a method of flowing and stirring the cast iron melt may be a method of directly stirring the cast iron melt. That is, it is possible to remove the manganese component while maintaining the carbon component in the cast iron melt almost constant by stirring the cast iron melt in the furnace with an oxygen atmosphere in the furnace. Such a method of directly stirring the cast iron melt has an advantage that control is relatively easy.

This method of directly stirring the cast iron melt can remove the manganese component while keeping the carbon component in the cast iron melt almost constant at a substantially constant temperature with little temperature drop of the cast iron melt. Moreover, the method of stirring this cast iron molten metal directly can adjust the removal rate of the manganese component in a cast iron molten metal by adjusting the stirring speed or stirring force which stirs a cast iron molten metal. Furthermore, by adjusting the stirring speed or stirring force for stirring the cast iron melt, it is possible to keep the cast iron melt at a substantially constant temperature or to raise the temperature.

As described above, the present invention efficiently removes the manganese component in the cast iron melt by adjusting the oxygen amount to be supplied to the furnace and / or the stirring speed or stirring force for stirring the cast iron melt. Can do. A method of removing the manganese component in the molten cast iron by setting the interior of the furnace in an oxygen atmosphere and stirring the molten cast iron in the furnace can be performed by the furnace 10 shown in FIG. The furnace 10 includes a furnace body 11, a furnace lid 12, a stirring means 17 for stirring the cast iron melt 20, and an oxygen supply means 16 that can make the interior of the furnace 10 an oxygen atmosphere. The furnace 10 has an operation port 12a for taking out a sample and an exhaust port 12b for exhausting gas generated during the processing operation. The furnace 10 of this example mechanically agitates the cast iron melt 20 by the agitating means 17 having a drive source such as a motor, but has an agitating means capable of agitating the cast iron melt by an electromagnetic method such as high frequency. It may be a thing.

Using the furnace shown in FIG. 1, a manganese removal test (test A) of cast iron was performed. The components of the cast iron melt during the test were measured using an emission spectroscopic analyzer (PDA-7020 manufactured by Shimadzu Corporation) for a sample taken from a furnace in a timely manner. The temperature of the cast iron melt was measured with an immersion type thermocouple. The cast iron pouring amount was 500 kg or 300 kg (Example 2 only). As the oxygen supply means for supplying oxygen, a burner capable of supplying only oxygen or a mixture of oxygen and propane gas (LPG) or a sonic nozzle capable of supplying oxygen at supersonic speed was used. When only oxygen was supplied by the burner, the oxygen flow rate was 5 Nm ³ / h. When supplying oxygen with a sonic nozzle, the oxygen flow rate was ³ Nm ³ / h. The inner diameter of the air inlet of the burner was about 15 mm, and the inner diameter of the air inlet of the sonic nozzle was about 2 mm.

Test conditions for Test A are shown in Table 1. In Table 1, the treatment time indicates the elapsed time after pouring molten cast iron melted in the cast iron melting furnace into a preheated furnace and starting the manganese removal test. In Example 1, air was blown into the molten cast iron at a flow rate of 200 L / min, and oxygen was supplied first by a burner for 15 minutes and then by a sonic nozzle until 34 minutes. In Example 2, only air blowing (400 L / min) was performed. In Example 3, air was blown (200 L / min) and oxygen was supplied. In Comparative Example 1, a mixed gas of oxygen and LPG was supplied by a burner, and air was first blown at a flow rate of 200 L / min for 21 minutes, and then the flow rate was increased to 400 L / min for 41 minutes. In Comparative Example 2, air was blown (200 L / min) and oxygen was supplied. Then, 10-20 kg of charcoal was introduced intermittently for 15 minutes from the beginning of the test. When charcoal was charged, a thriving flame was observed from the sample inlet. In Comparative Example 1, the mixed gas of oxygen and LPG is an oxygen-excess gas with respect to the theoretical combustion gas. When a sonic nozzle is used, oxygen can be supplied at an extremely high speed (sound speed or higher). Vigorous bubbling occurred when the air was blown at a flow rate of 400 L / min, but this was not the case at a flow rate of 200 L / min.

Table 2 shows the test results of Example 1 of Test A. In Table 2, the component content is mass%, and the balance other than the components shown in Table 2 is iron and inevitable impurities. According to Table 2, except for the above manganese (Mn), carbon (C) and silicon (Si), the content of titanium (Ti) was initially 0.017% but became 0.008% after 34 minutes of treatment time. The content is almost halved. In addition, the aluminum (Al) content decreased by about 20% after the treatment time of 34 minutes, and the chromium (Cr), boron (B), and zinc (Zn) contents also decreased somewhat. .

The result of Example 1 is shown in FIG. In FIG. 3, the horizontal axis represents the treatment time, and the vertical axis represents the residual ratio of Mn, Si or C, and the molten metal temperature. The residual ratio is the ratio of the residual content to the initial content of the Mn, C, or Si content. According to FIG. 3, the C residual ratio is in the range of 1.00 to 1.02, and the C amount is maintained at a substantially constant value within a fluctuation range within 2% of the initial content. In contrast, the Mn residual rate curve is a steep descending curve, and after 34 minutes of processing time, the Mn residual rate is 0.6 (60% of the initial content), and the Mn content decreases rapidly. It shows that. On the other hand, the Si residual rate curve falls smoothly, and the residual rate after 34 minutes of processing time is 0.84 (84% of the initial content). That is, in this example, Mn is removed at a rate twice or more that of Si. The molten metal temperature gradually decreased from the initial 1257 ° C. to 1152 ° C., then gradually increased after the processing time of 20 minutes, and reached 1181 ° C. after the processing time of 34 minutes. It is understood that the effect of the sonic nozzle appears.

The graphs shown in FIGS. 4 to 7 show the relationship between the Mn residual rate, C residual rate, Si residual rate, or molten metal temperature and treatment time in Test A, respectively. 4 to 6, the horizontal axis represents the processing time, and the vertical axis represents the residual ratio of Mn, C or Si. In FIG. 7, the horizontal axis represents the processing time, and the vertical axis represents the molten metal temperature. In the Mn residual rate curve or Si residual rate curve, the gradient or removal rate is the ratio of the amount of components removed per unit processing time to the initial content ((residual rate a-residual rate b) / (processing time b-processing Time a)).

<Blowing of combustion gas>
Comparative Example 1 (□ mark) is a case where a manganese removal test was performed by spraying LPG combustion gas onto the molten cast iron surface in an oxygen-excess furnace. This Comparative Example 1 is an example in which the oxygen amount and LPG gas amount are increased after 10 minutes of processing time, and the air blowing into the cast iron melt is increased from 200 L / min to 400 L / min after 26 minutes of processing time. According to FIG. 4, the slope of the Mn residual rate curve of Comparative Example 1 is smaller than the slope of the Mn residual rate curves of Examples 1 to 3, and the Mn removal rate of Comparative Example 1 is the Mn removal rate of Examples 1 to 3. About 80%. According to FIG. 5, C removal is about 4% after about 40 minutes of processing time even if the amount of air is increased, and C removal (carbon consumption) is suppressed. The slope of the Si residual rate curve shown in FIG. 6 is the smallest until the processing time is 20 minutes, and Si removal is also suppressed.

The effect of increasing the amount of oxygen and the amount of LPG gas does not appear in the Mn residual rate curve (FIG. 4), and hardly appears in the C residual rate curve (FIG. 5) and the Si residual rate curve (FIG. 6). However, the molten metal temperature rises after 10 minutes of treatment time, and corresponds well to increases in the oxygen content and LPG gas content. On the other hand, the effect of increasing the air amount appears in the Mn residual rate curve and clearly in the C residual rate curve and the Si residual rate curve.

<Atmosphere in furnace>
In Comparative Example 2 (circle mark), the supply of oxygen to the cast iron melt and the blowing of air were the same as in Example 1 or 3, but the charcoal was introduced into the furnace and the environment in the furnace was changed to that in Example 1 or 3. This is a case where the manganese removal test was conducted in a different state. As shown in FIG. 4, the slope of the Mn residual rate curve is the slowest, and the Mn removal rate of Comparative Example 2 is about 40% of the Mn removal rate of Example 1 or 3. According to the C residual rate curve shown in FIG. 5, the effect of carburizing with charcoal is observed, but the C residual amount is within a 4% variation range of the initial content. According to the Si residual rate curve shown in FIG. 6, the residual rate of Si is the highest, and the residual rate is 0.93 even after 30 minutes of processing time. That is, it is understood that the inside of the furnace is difficult to oxidize and is an environment where oxidation of Si is suppressed. According to the molten metal temperature curve shown in FIG. 7, an increase in the molten metal temperature due to charcoal combustion is not observed and overlaps with the molten metal temperature curve of Example 3. The index a straight line shown in FIG. 4 and the index a straight line shown in FIG. 6 are straight lines having the same gradient. That is, it is shown that the Mn removal rate of Comparative Example 2 shown in FIG. 4 is substantially equal to the Si removal rate of Examples 1 to 3 shown in FIG.

The furnace shown in FIG. 2 was used to conduct a cast iron manganese removal test (Test B). As shown in Table 3, the test was performed by changing the oxygen supply conditions or the cast iron molten metal stirring conditions. In Examples 4 to 6, air was blown in at 200 L / min along with the supply of oxygen. This air blowing was performed in the same manner as in Example 1 or 3 of Test A above. In Examples 7 to 9, oxygen was supplied at 20 N ³ / h from the start to the end of the test, and the stirring speed of the stirring means 17 was variously changed. For example, the stirring speed of the stirring means 17 was started at 200 rpm from the start to the end of the test in Example 7, and started at 100 rpm in Example 8, and increased to 200 rpm after 11 minutes of the processing time. The component measurement or temperature measurement of the molten cast iron during this test was performed using the same emission spectroscopic analyzer or immersion thermocouple as in test A. The amount of molten iron poured into the cast iron furnace was 500 kg.

The results of Test B are shown in Figs. 8 shows the Mn residual rate, FIG. 9 shows the C residual rate, FIG. 10 shows the Si residual rate, the horizontal axis shows the processing time, and the vertical axis shows the residual rate of Mn, C, or Si. In FIG. 11, the horizontal axis indicates the processing time, and the vertical axis indicates the molten metal temperature. The Mn removal rate shown in FIG. 8 shows the results of Examples 1 and 3 of Test A together with the results of Test B. Further, the index a straight line and the index b straight line in FIG. 8 indicate straight lines having the same gradient as the index a straight line and the index b straight line shown in FIG. The slopes of the index a straight line, the index b straight line, and the index c straight line are 1: 3.2: 6.1 based on the index a straight line.

According to FIG. 8, the Mn residual rate decreases substantially along the index b straight line or the index c straight line from the start of the processing to the processing time of 10 to 20 minutes. The Mn residual ratios of Example 1, Example 3, Example 5, and Example 8 decrease along the index b straight line. The Mn residual ratios of Example 4, Example 6, Example 7, and Example 9 decrease along the index c straight line. The Mn residual rate curves of Example 5 and Example 8 are bent downward at a processing time of 11 minutes, and have a different shape from the other Mn residual rate curves.

Referring to FIG. 9, the C residual ratio is in the range of approximately 1.02 to 0.96, which is a substantially constant value. That is, C removal (decarburization) is suppressed. According to FIG. 10, the Si residual ratio in each example decreases substantially along the straight line b. The residual ratio of Si in Example 5 initially decreased along the straight line a, but rapidly decreased after 16 minutes of processing time, and decreased along the straight line b after 25 minutes of processing time. In the case of Example 9, the removal of Si is most advanced. According to FIG. 11, the treatment proceeds at a molten metal temperature of 1410 to 1270 ° C., and the molten metal temperature curve generally shows that the molten metal has risen during the treatment and the molten metal has been heated.

<Oxygen supply>
In Examples 1, 3, 4 to 6 shown in FIG. 8, the air blowing rate is the same at 200 L / min, but the oxygen supply amount or the supply method is different. Observing these Mn residual rate curves, it can be seen that the removal rate of Mn can be adjusted by the supply amount of oxygen. That is, according to the Mn residual rate curve of Example 4, the gradient up to the treatment time of 7 minutes when a large amount of oxygen (50 Nm ³ / h) was supplied was the largest, and 30% of the initial Mn content was removed in the treatment time of 12 minutes. Has been. It is understood that supplying sufficient oxygen first was effective. The bending, in the case of Example 5, due to the increased supply of oxygen from the beginning of 15 Nm ³ / h after the lapse processing time 11 minutes to 20 Nm ³ / h, Mn residual ratio curve in the processing time 11 minutes It is observed that the removal of Mn is promoted.

According to FIGS. 5 and 9, the C residual amount of Examples 1, 3, 4 to 6 is in a range of 1.02 to 0.97, and is almost constant. The residual ratio of C hardly depends on the supply amount of oxygen and the supply method. On the other hand, it is shown in FIGS. 6 and 10 that the Si residual rate is affected by the supply amount and supply method of oxygen. In general, when the supply amount of oxygen is small, the Si residual rate decreases along the index a line, and when the oxygen supply amount is large, the Si residual rate decreases along the index b line. The effect of changing the supply amount of oxygen appears well in the case of Example 5. That, Si residual rate, the supply of oxygen is reduced along the index a straight line when the 15 Nm ³ / h, the supply of oxygen is rapidly reduced with increasing the 20 Nm ³ / h. The Si residual rate decreases along the index b straight line after 25 minutes of processing time. On the other hand, in Example 4 in which a large amount of oxygen (50 Nm ³ / h) was initially supplied and the supply amount of oxygen was rapidly reduced to a treatment time of 7 minutes (20 Nm ³ / h) and 15 minutes (10 Nm ³ / h). Almost no effect appears in the Si residual rate curve, the C residual rate curve, and the molten metal temperature curve (FIGS. 9 to 11).

When FIG. 7 and FIG. 11 are compared, the molten metal temperature of Example 1 or 3 decreases by about 100 ° C. during the treatment. On the other hand, the temperature drop in Examples 4 to 6 is small, and the temperature drop in Example 4 is 55 ° C. at the maximum. It is understood that when the supply amount of oxygen becomes a certain amount (for example, 15 Nm ³ / h) or more, a decrease in the melt temperature due to the blowing of air into the melt can be suppressed. Moreover, according to FIG. 11, it turns out that there exists a tendency for molten metal temperature to rise, if oxygen amount is increased. That is, the molten metal temperature can be adjusted by adjusting the oxygen supply amount.

<Agitation of molten metal>
As shown in Table 3, Examples 7, 8 and 9 are tests conducted by changing the stirring conditions of the cast iron melt while supplying oxygen at 20 Nm ³ / h. Example 7 is a case where the test was conducted at a stirring speed of 200 rpm. According to Example 7, Mn can be efficiently removed (FIG. 8), decarburization is small (FIG. 9), and the decrease in molten metal temperature is about 20 ° C. and Mn removal is performed at a substantially constant molten metal temperature. It can be done (FIG. 11). In the case of Example 8, due to the fact that the stirring speed was increased from the initial 100 rpm to 200 rpm after 11 minutes from the processing time, the Mn residual rate decreased rapidly along the index b straight line, and the processing speed decreased. It decreases along the index c straight line after 18 minutes. That is, it is shown that the degree of Mn removal can be adjusted by adjusting the stirring speed of the molten metal. According to FIG. 8, the Mn residual ratio of Examples 7 to 9 decreases linearly until the processing time of 10. FIG. 12 shows the relationship between the slope of the Mn residual rate curve (Mn removal rate) and the stirring speed. According to FIG. 12, a certain relationship is observed between the Mn removal speed and the stirring speed. For this reason, the degree of Mn removal can be adjusted by adjusting the stirring speed of the molten metal based on FIG.

According to FIG. 11, in Example 8, the molten metal temperature increased after 15 minutes of processing time, which corresponds well to increasing the stirring speed from 100 rpm to 200 rpm after 11 minutes of processing time. Further, Example 9 is an example in which the treatment was started at a stirring speed of 150 rpm and the stirring speed was increased to 250 rpm after 20 minutes of processing time, but the molten metal temperature was increased after 20 minutes of processing time, and the stirring speed was changed. The effect is clearly shown. In the case of Example 9, as shown in FIGS. 8 to 10, the effect of changing the stirring speed hardly appears in the Mn residual rate, the C residual rate, and the Si residual rate.

<Mn removal and Si removal>
According to FIG. 8, the Mn residual rate decreases along each of the index b straight line and the index c straight line. Moreover, according to FIG.6 and FIG.10, Si residual ratio is reducing along each of the parameter | index b straight line and the parameter | index c straight line. The ratio of the slope of the index b straight line to the slope of the index c straight line is 32/61, which is about 1/2. That is, the reduction rate ratio is about 1/2.

FIG. 13 is a graph showing the relationship between the Si / Mn reduction ratio ((1.00-Si residual rate a) / (1.00-Mn residual rate a)) and the processing time at the processing time a. According to FIG. 13, the Si / Mn reduction ratio of Example 7 is approximately 0.5 and constant. That is, the decrease rate of Si is 1/2 of the decrease rate of Mn. Further, according to FIG. 13, the Si / Mn reduction ratio of Example 9 is constant at about 0.8, but Example 4 vibrates in the range of Si / Mn reduction ratio of 0.1 to 0.7. The Si / Mn reduction ratio of Example 6 increases almost linearly in the range of 0.62 to 0.9. The Si / Mn reduction ratio of Example 8 increases almost linearly in the range of 0.01 to 0.5, and the removal (consumption) of Si is suppressed. In the method for removing manganese from molten cast iron, it is preferable that the degree of removal of Si can be predicted as compared with the removal of Mn. From this viewpoint, the method of Example 7 or Example 9 is preferable.

<Cr, Ti, Al, B, Zn>
The present invention can remove metal components such as Cr, Ti, Al, B, and Zn. Table 4 shows the results of Example 5, and Table 5 shows the results of Example 7. In this table, time indicates the processing time, and temperature indicates the molten metal temperature. Content of each component shows the mass%. Comparing Table 4 and Table 5, B can be efficiently removed in both cases of Example 5 and Example 7. However, Zn is difficult to remove in the case of Example 5 by air blowing, and it is difficult to remove Cr and Al in the case of Example 7 by molten metal stirring. According to Example 5, Cr, Ti, or Al can be removed by 40 to 50% in about 30 minutes. According to Example 7, 50 to 60% of Ti or Zn can be removed in 15 minutes.

10 Furnace 11 Furnace body 12 Furnace lid 15 Air supply means 16 Oxygen supply means 20 Cast iron melt

Claims

A method for removing manganese from cast iron, in which the inside of the furnace is in an oxygen atmosphere and air is blown into the molten cast iron in the furnace to keep the carbon component in the molten cast iron almost constant.
A method for removing manganese from cast iron, in which the inside of the furnace is placed in an oxygen atmosphere, the molten cast iron in the furnace is agitated, and the carbon component in the molten cast iron is kept almost constant to remove the manganese component.
The method for removing manganese from cast iron according to claim 2, wherein the manganese component is removed while adjusting the amount of oxygen supplied into the furnace and / or the stirring speed of the molten cast iron in the furnace.
The method for removing manganese from cast iron according to any one of claims 1 to 3, wherein the ratio between the removal rate of the silicon component and the removal rate of the manganese component is maintained substantially constant.
The method for removing manganese from cast iron according to any one of claims 1 to 3, wherein the manganese component is removed while suppressing a decrease in the silicon component.
The method for removing manganese from cast iron according to any one of claims 1 to 3, wherein the molten iron temperature of the cast iron melt is kept substantially constant.
The method for removing manganese from cast iron according to any one of claims 1 to 6, wherein the temperature of the molten cast iron is 1400 ° C to 1200 ° C.
Bring the furnace atmosphere to oxygen and blow the air into the cast iron melt in the furnace or stir the cast iron melt in the furnace to keep the carbon component in the cast iron melt almost constant. A method for removing a metal component of cast iron, wherein the metal component of chromium, titanium, aluminum, boron or zinc is removed together with the manganese component.