Patent Application
20170342515
The present invention relates to a method for removing manganese in a feedstock having a high manganese content to be used for the production of cast iron members.
Cast iron castings have been used for vehicle components or machine components, approximately half of the amount of cast iron castings produced is for vehicles, and cast iron castings account for approximately 10% of the gross vehicle weight. The feedstock used for the production of cast iron castings utilizes steel scraps of automobile steel plates; the recent request for weight reduction has increased the manganese content in automobile steel plates; manganese is a pearlitization accelerating element, and accordingly causes a problem which is that the toughness is degraded and internal defects tend to be caused.
For the problem of the increase of the manganese content in the feedstock used for the production of cast iron members, the following proposals have been made. For example, Patent Literature 1 proposes a demanganese treatment method of cast iron in which manganese is removed from the molten metal by adding a sulfur-containing demanganese treatment agent to the molten cast iron containing manganese, to float manganese as manganese sulfide. In the removal of the manganese component, the MnS produced in the molten metal is floated, and removed into the slag on the surface of the molten metal. In order to promote the flotation removal, it is effective to stir the molten metal by, for example, blowing a gas from the porous plug in the bottom of the ladle containing the molten metal. In the case of the gas stirring, as the blowing-in gas, compressed air or compressed nitrogen gas is low in price and easy to use. In this regard, it is regarded as preferable to use an inert gas such as Ar in order to suppress the increase of the amount of oxygen or the amount of nitrogen in the molten metal.
Patent Literature 2 proposes a method for decreasing the manganese content in the production of a cast iron, wherein the method is a method for removing manganese in the molten cast iron by adding and mixing only sodium nitrate as an additive in the molten cast iron at a temperature of 1400 to 1500° C. In the method for removing manganese, when the temperature of the molten cast iron is lower than 1300° C., SiO2 is produced in large amounts, and Si, a main component of the cast iron, is unpreferably depleted significantly. In addition, in the molten cast iron at 1300° C. or higher, MnS is regarded to be formed only in a region having an extremely high Mn or S content (%). According to this invention, it is possible to achieve a Mn removal rate of 70% or more even when the Mn content of the molten cast iron is 1.5% by mass or more. The Mn removal rate is described to be improved according to the amount of Na2SO4 added, when the amount of Na2SO4 added is approximately 10% by mass or less.
Patent Literature 3 proposes a method for producing a spheroidal graphite cast iron, wherein in the melting by using a rotary furnace by utilizing a heat source such as a natural gas, a liquefied petroleum gas or kerosene and pure oxygen, as a charge material raw metal, steel scraps and return scraps or only steel scraps are used, and an original molten metal obtained by performing a Mn-removal melting in an oxidative combustion period, and a molten metal preliminarily melted in another furnace and regulated in components are combined by a molten-metal combining device to produce the spheroidal graphite cast iron. In Example of the method for producing the spheroidal graphite cast iron, a material raw metal having mixing proportions of 60% of steel scraps and 40% of return scraps was charged from a material charge inlet into a rotary furnace, and 1.62% of silica sand and 0.30% of limestone were sparged as a forming agent on the material raw metal. It has been reported that the melting was performed while the volume ratio of pure oxygen and natural (CH4) gas was being regulated in a range from 1.95 to 2.10.
Patent Literature 4 proposes a method for removing impurities in a molten cast iron, wherein the method is a method for removing impurities containing manganese (Mn) while the depletion of carbon (C) and silicon (Si) contained in a molten cast iron preliminary melted is being suppressed; under the condition that the temperature of the molten cast iron is maintained at 1250° C. or higher and lower than 1500° C., while the aforementioned molten metal and an acidic slag layer are being allowed to contact with each other, an excessive oxygen flame having a theoretical combustion ratio of fuel and oxygen (amount (volume) of oxygen×5/amount (volume) of fuel) of 1 to 1.5 is directly exposed to the surface of the molten cast iron to overheat the surface of the molten cast iron. The temperature of the molten cast iron at the time of feeding the molten cast iron is preferably lower than 1500° C., and more preferably 1250° C. or higher and lower than 1500° C. In such a temperature range, the Mn removal treatment after the feeding of the molten cast iron is made easy while the depletion of C or Si is being suppressed. The excessive oxygen flame is considered to be preferably a flame of a burner obtained by combusting LPG gas or LNG gas while feeding oxygen in an amount excessive than the amount of oxygen necessary for combustion. The excessive oxygen flame removes impurities while directly exposing the molten metal surface to the flame and allowing the rest of the molten metal surface to contact with the acidic slag, without increasing the temperature of the whole molten metal; thus, it is considered that the depletion of C or Si can be made small while the oxidation removal of Mn is proceeding.
The method for removing manganese described in Patent Literature 1 or 2 uses a sulfide as a demanganese agent, requires the amount of the sulfide to be a few percent in terms of percent by mass, and suffers from a problem which is that a large amount of a sulfur-containing slag is produced. The method described in Patent Literature 2 gives a small increase of sulfur in the molten cast iron; however, the sulfur content is increased to 0.02 to 0.03%, and hence the method concerned suffers from a problem which is that desulfurization is required when the cast iron is used for spheroidal graphite cast iron members.
On the other hand, the method for removing manganese described in Patent Literature 3 or 4 is a method in which the manganese contained in the cast iron is oxidized and removed as slag, and accordingly has an advantage that the amount of the produced slag is small. In particular, the method described in Patent Literature 4, in contrast to the method described in Patent Literature 3, uses no slag forming flux, and accordingly the amount of the produced slag can be made small. However, the method for treating manganese described in Patent Literature 3 or 4 requires a combustible gas, and suffers from a problem that the method concerned is not preferable at a site of work in hot environment.
As a method for removing manganese of cast iron, in a society emphasizing environmental conservation, a method producing a large amount of slag and a sulfur-containing slag is not preferable. In addition, the method for removing manganese of cast iron is preferably a method requiring no combustible gas from the viewpoints of handleability and work efficiency. The treatment temperature in the removal of manganese of cast iron is preferably as low as possible from the viewpoint of energy saving.
In view of such conventional problems and requirements, an object of the present invention is to provide a method for removing manganese of cast iron, not requiring a demanganese agent such as a sulfide or a combustible gas in the removal of manganese of cast iron, being small in the amount of the produced slag, being high in the manganese removal efficiency, and allowing the work to be performed safely.
The method for removing manganese of cast iron according to the present invention is implemented by performing the removal of a manganese component by allowing a furnace to be in an oxygen atmosphere, and by blowing air into a molten cast iron in the furnace, while a carbon component in the molten cast iron is being maintained at an approximately constant amount.
Alternatively, the method for removing manganese of cast iron according to the present invention is implemented by performing the removal of the manganese component by allowing the furnace to be in an oxygen atmosphere, and by stirring the molten cast iron in the furnace, while the carbon component in the molten cast iron is being maintained at an approximately constant amount.
In the foregoing invention, the removal of the manganese component can be performed while the amount of oxygen fed into the furnace or/and the stirring speed of the molten cast iron in the furnace are being regulated, and the carbon component in the molten cast iron is being maintained at an approximately constant amount.
In the foregoing invention, the removal of the manganese component can also be performed while the ratio between the removal rate of the silicon component and the removal rate of the manganese component is being maintained at an approximately constant value, and the removal of the manganese component can be performed while the decrease of the silicon component is being suppressed.
In the foregoing invention, the removal of the manganese component can also be performed while the temperature of the molten cast iron is being maintained at an approximately constant value, and the temperature of the molten cast iron can be set at 1400° C. to 1200° C.
The method for removing manganese of cast iron of the present invention provides a method for removing manganese, not requiring a demanganese agent such as a sulfide or a combustible gas, and being small in the amount of the produced slag, and can remove manganese in a high efficiency.
Hereinafter, the embodiments of the present invention are described. The method for removing manganese according to the present invention is a method for removing manganese of cast iron by allowing a furnace to be in an oxygen atmosphere, and by blowing air into the molten cast iron to remove the manganese component contained in the molten cast iron, wherein the method concerned is implemented by performing the removal of the manganese component while the carbon component in the molten cast iron is being maintained at an approximately constant amount. In other words, the present method for removing manganese performs the manganese removal treatment by blowing air into the molten cast iron in the furnace allowed to be in an oxygen atmosphere, and accordingly belongs to an oxygen treatment method. In addition, the manganese removal treatment is implemented by performing the removal of the manganese component while the carbon component is maintained at a constant amount.
In the present invention, for the feeding of oxygen, it is important to allow the furnace to be in an oxygen atmosphere. Although oxygen can be fed by bubbling with air, it is preferable to feed oxygen by providing a dedicated unit capable of feeding oxygen onto the surface of the molten cast iron in the furnace. In the present invention, the method for feeding oxygen and the amount of oxygen fed affects the effect of the manganese removal treatment. In the present invention, by regulating the amount of oxygen fed, the removal rate of the manganese component in the molten cast iron, the temperature of the molten metal or the like can be regulated.
The blowing of air into the molten cast iron expands the reaction interface between the oxygen in the air blown into the molten cast iron by the fluidization/stirring of the molten cast iron and the oxygen fed into the furnace, and thus promotes the oxidation of manganese. Accordingly, an inert gas is not preferable. A mixed gas of air and oxygen is not preferable because such a mixed gas causes oxidation/combustion. The degree of the blowing of air into the molten cast iron is not required to have an amount or strength to scatter the molten metal or the slag. In other words, the blowing of air into the molten cast iron is not required to be an intense bubbling.
The temperature of the molten metal in performing the manganese removal treatment is favorably 1400° C. or lower for the purpose of suppressing the consumption of carbon in the molten cast iron, and can be regulated to be 1350° C. to 1175° C. The temperature of the molten cast iron is preferably as low as possible from the viewpoint of energy saving; however, in consideration of the energy saving inclusive of the successive steps, the temperature of the molten cast iron is preferably 1350° C. to 1200° C. Specifically, this is because the molten cast iron having been subjected to the removal of Mn is increased in temperature to 1400 to 1550° C., and then used for casting or the like.
The furnace for treating the molten cast iron in the present invention may be a tool having no heating unit by itself such as a ladle, or alternatively, may be a furnace being capable of allowing the furnace to be in an oxygen atmosphere and having an air feeding unit capable of blowing air into the molten cast iron. For example, such a ladle as shown in
As described above, in the method for removing manganese of cast iron according to the present invention, by blowing air into the molten cast iron in an oxygen atmosphere to subject the molten cast iron to fluidization/stirring, the area of the reaction interface between the molten cast iron and oxygen is expanded to promote the oxidation of Mn. Such a method of subjecting the molten cast iron to fluidization/stirring may be a method of directly stirring the molten cast iron. Specifically, the furnace is allowed to be in an oxygen atmosphere, then the molten cast iron in the furnace is stirred, and thus the removal of the manganese component can be performed while the carbon component in the molten cast iron is being maintained at an approximately constant amount. Such a method of directly stirring the molten cast iron has an advantage of being relatively simple to control.
The method of directly stirring the molten cast iron is small in the temperature decrease of the molten cast iron, and allows the manganese component to be removed at an approximately constant temperature while the carbon component in the molten cast iron is being maintained at an approximately constant amount. In addition, the method of directly stirring the molten cast iron can regulate the removal rate of the manganese component in the molten cast iron by regulating the stirring speed or the stirring force in the stirring of the molten cast iron. Moreover, by regulating the stirring speed or the stirring force in the stirring of the molten cast iron, the molten cast iron can be maintained at an approximately constant temperature, or can be increased in temperature.
As described above, the present invention can perform an efficient removal of the manganese component in the molten cast iron, by allowing the furnace to be in an oxygen atmosphere, and by regulating the amount of oxygen fed or/and the stirring speed or the stirring force in the stirring of the molten cast iron. The furnace 10 shown in
By using the furnace shown in
The test conditions of the test A are shown in Table 1. In Table 1, the treatment time means the elapsed time after the start of the manganese removal test in which the molten cast iron melted in a cast iron melting furnace was poured into a preheated furnace. In Example 1, the blowing of air into the molten cast iron was performed at a flow rate of 200 L/min, and the feeding of oxygen was first performed with a burner for 15 minutes, and then successively performed with a sonic nozzle to an elapsed time of 34 minutes. In Example 2, only the blowing of air (400 L/min) was performed. In Example 3, the blowing of air (200 L/min) and the feeding of oxygen were performed. In Comparative Example 1, a mixed gas of oxygen and LPG was fed with a burner, and the blowing of air was first performed at a flow rate of 200 L/min for 21 minutes and then successively performed at an increased flow rate of 400 L/min to an elapsed time of 41 minutes. In Comparative Example 2, the blowing of air (200 L/min) and the feeding of oxygen were performed. In addition, for 15 minutes from the start of the test, 10 to 20 kg of charcoal was intermittently input in the furnace. When charcoal was input, active flame was observed from the sample input opening. It is to be noted that in Comparative Example 1, the mixed gas of oxygen and LPG was an excessive oxygen gas in relation to the theoretical combustion gas. When a sonic nozzle is used, oxygen can be fed at an ultrafast speed (equal to or faster than sonic speed). When the blowing of air was performed at a flow rate of 400 L/min, fierce bubbling occurred, but when the blowing of air was performed at a flow rate of 200 L/min, such fierce bubbling did not occur.
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The results of the test A of Example 1 are shown in Table 2. In Table 2, the contents of the components are given in percent by mass, the residual components other than the components shown in Table 2 are iron and inevitable impurities. For the components other than foregoing manganese (Mn), carbon (C) and silicon (Si), according to Table 2, the content of titanium (Ti) was 0.017% at the beginning, was reduced to 0.008% after a treatment time of 34 minutes, and thus was reduced nearly by half. The content of aluminum (Al) was reduced by approximately 20% after a treatment time of 34 minutes, and the contents of chromium (Cr), boron (B) and zinc (Zn) are seen to be reduced to some extents.
The results of Example 1 are shown in
The graphs in
<Blowing of Combustion Gas>
Comparative Example 1 (symbol: □) is a case where a manganese removal test was performed in an excessive oxygen furnace, by blowing LPG combustion gas to the surface of the molten cast iron. Comparative Example 1 is an example of the case where the amount of oxygen and the amount of LPG gas were increased after an elapsed treatment time of 10 minutes, and the blowing of air into the molten cast iron was also increased from 200 L/min to 400 L/min after an elapsed treatment time of 26 minutes. According to
The effects of the increase of the amount of oxygen and the increase of the amount of LPG gas are not manifested in the Mn residual rate curves (
<Furnace Atmosphere>
Comparative Example 2 (symbol: ◯) is a case where the feeding of oxygen to the molten cast iron and the blowing of air into the molten cast iron were the same as in Example 1 or 3, but the manganese removal test was performed under the condition that charcoal was input in the furnace to alter the environment in the furnace from the case of Example 1 or 3. As shown in
By using the furnace shown in
The results of the test B are shown in
According to
According to
<Feeding of Oxygen>
Examples 1, 3 and 4 to 6 shown in
The amounts of residual C of Examples 1, 3 and 4 to 6 fall within a range from 1.02 to 0.97 according to
From a comparison of
<Stirring of Molten Metal>
As shown in Table 3, Examples 7, 8 and 9 are the tests in which the oxygen feeding was performed at 20 Nm3/h, and the stirring conditions of the molten cast iron were varied. Example 7 is the case where the test was performed at a stirring speed of 200 rpm. According to Example 7, Mn can be removed efficiently (
According to
<Removal of Mn and Removal of Si>
According to
In the method for removing manganese of molten cast iron, preferably the degree of the removal of Si can be predicted in relation to the removal of Mn. From such a viewpoint, the method of Example 7 or 9 is preferable.
<Cr, Ti, Al, B and Zn>
The present invention can remove the metal components such as Cr, Ti, Al, B and Zn. Table 4 shows the results obtained in Example 5, and Table 5 shows the results obtained in Example 7. In each of these tables, the time means the treatment time, and the temperature means the temperature of the molten metal. The contents of the respective components are given in percent by mass. From a comparison between Table 4 and Table 5, B can be efficiently removed in both of the case of Example 5 and the case of Example 7. However, the removal of Zn is difficult in the case of Example 5 based on the blowing of air, and the removal of Cr and Al is difficult in the case of Example 7 based on the stirring of the molten metal. According to Example 5, a treatment of approximately 30 minutes can remove 40 to 50% of Cr, Ti or Al. According to Example 7, a treatment of 15 minutes can remove 50 to 60% of Ti or Zn.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-252462 | Dec 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/083567 | 11/30/2015 | WO | 00 |
