JP2018035404A - Method of refining cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method in which impurities in a cast iron including manganese, phosphorous and boron can be efficiently and economically removed.SOLUTION: The method of refining cast iron according to the present invention is a method of refining cast iron in which refining is performed by making the inside of a furnace into an oxygen atmosphere and stirring the cast iron molten iron in the furnace, and maintaining the carbon component in the cast iron molten iron substantially constant, and in which the manganese component in the cast iron molten iron is first removed, and the produced slag is then discharged, and after that, the phosphorus component is removed while adding quicklime to the cast iron molten iron.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for refining cast iron according to removal of manganese, phosphorus and boron in a cast iron melt.

  Cast iron castings are used for automobile parts and machine parts. About half of cast iron castings are produced for automobiles, and about 10% of the total weight of automobiles is cast iron castings. Cast iron is used as a raw material for the cast iron casting. Cast iron is manufactured in the same way as hot metal for steelmaking manufactured in a blast furnace, and suitable components are adjusted after pretreatment such as desiliconization, dephosphorization, and desulfurization is performed on the hot metal discharged from the blast furnace. Is cooled and manufactured as a casting mold having a predetermined shape. The dephosphorization and desulfurization of hot metal is performed by, for example, blowing dehydrated lime and the like together with air in a molten iron pan, kneading car, etc., and blowing or adding lime and sodium carbonate together with nitrogen. Desulfurization is performed.

  Cast iron obtained by desiliconizing, dephosphorizing or desulfurizing the hot metal discharged from this blast furnace has a significant temperature drop in the process of dephosphorizing and desulfurizing the hot metal. There was a problem that it was easy to produce. In order to solve this problem, Patent Document 1 discloses that high-purity cast pig iron cast after dephosphorization and desulfurization of hot metal discharged from a blast furnace is blown up with oxygen-enriched air at least during dephosphorization, and carbon is added. A method of producing pig iron for high-purity castings has been proposed in which Si is added during casting and the amount of Si added is increased in accordance with the temperature drop in the casting.

In addition, regarding the dephosphorization of hot metal, in Patent Document 2, when the hot metal is dephosphorized by performing flux addition, oxygen top blowing and bottom blowing stirring, the bottom blowing stirring power is 1.0 kW / t or more, and the slag after treatment Proposed a converter steelmaking method in which dephosphorization refining is performed by adjusting the amount of flux input and / or bottom blowing gas so that the CaO / SiO2 content is 0.6 to 2.5 and the end point temperature is 1250 ° C to 1400 ° C. Has been.

  On the other hand, as steel materials have been improved in performance, weight, and functionality, the price of rare metals has been rising recently, and relatively inexpensive Mn has been added to reduce costs. Therefore, Patent Document 3 proposes a method for removing impurities in a cast iron melt using the scrap as a raw material for cast iron castings. That is, a method for removing impurities including manganese (Mn) while suppressing the depletion of carbon (C) and silicon (Si) contained in a previously melted cast iron melt, the temperature of the cast iron melt being Is maintained at 1250 ° C. or higher and lower than 1500 ° C., while the molten metal and the acidic slag layer are in contact with each other, the theoretical combustion ratio of fuel and oxygen (oxygen amount (volume) × 5 / fuel (volume) amount) is 1 to There has been proposed a method for removing impurities in a cast iron melt by directly exposing an oxygen-excess flame of 1.5 to the surface of the cast iron melt and heating the surface. In this impurity removal method, an oxygen-excess flame directly exposes the molten metal surface to the flame and removes impurities without increasing the temperature of the entire molten metal while contacting the remaining molten metal surface with acidic slag. It is said that de-Mn treatment can be performed at 1500 ° C. while suppressing depletion of C and Si after hot water supply.

  In addition, in Patent Document 4, a sulfur additive containing at least one of sulfur and a sulfur compound is added in a dephosphorization method from a cast iron melt that removes phosphorus by adding an oxidizing agent and a lime-based flux to the cast iron melt. A dephosphorization method from molten cast iron has been proposed. According to this dephosphorization method, the phosphorus content can be reduced to 0.08% by mass or less, and high-quality spheroidal graphite cast iron having elongation, viscosity, and strength can be produced.

Japanese Patent Laid-Open No. 05-33028 Japanese Unexamined Patent Publication No. 07-70626 JP 2011-153359 A JP 2002-285220 A

  Various methods have been proposed for the desiliconization, dephosphorization, or desulfurization treatment of hot metal discharged from the blast furnace. Phosphorus or desulfurization treatment is required. In particular, the problem of increasing the Mn content of steel sheet scraps is that the amount of steel sheets containing a large amount of manganese is increasing along with the demand for reducing the weight of automobiles, and recycling of the scraps has become a problem. For this reason, a method more efficient and economical than the method for removing manganese from cast iron described in Patent Document 3 is required.

  On the other hand, the iron removal method for cast iron will take into account the fact that there are already casting irons from which phosphorus has been removed in Japan, and that iron ore used for ironmaking in Japan does not have a high phosphorus content. There are few proposals. However, due to the progress of overseas expansion by domestic companies and the adoption of parts and materials related to local production overseas or production by local companies, removal of impurities in cast iron casting materials including phosphorus has recently been required. Yes. Recently, high-strength steel sheets for automobiles, in which phosphorus is added to suppress the manganese content for cost reduction, are commercially available, and the removal of impurities from cast iron casting raw materials containing manganese and phosphorus is required. However, there are no proposals for removing cast iron containing manganese and phosphorus.

  An object of the present invention is to provide a refining method capable of efficiently and economically removing impurities of cast iron containing manganese, phosphorus and boron in view of the problems and requirements of the prior art.

The refining method for cast iron according to the present invention is a refining method for 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 refining is performed while maintaining the carbon component in the molten cast iron substantially constant. And
First, the manganese component of the cast iron melt is removed, and then the produced slag is discharged, and then the phosphorus component is removed while adding quicklime to the cast iron melt.

  In the above invention, quicklime is preferably added so that the basicity of the molten slag is 1 or more.

  Further, refining is preferably performed so as to suppress a decrease in the silicon component, and refining is preferably performed while maintaining the temperature of the cast iron melt almost constant in the range of 1400 ° C. to 1200 ° C.

  Further, the refining method for cast iron according to the present invention is a refining method for cast iron in which the inside of the furnace is made an oxygen atmosphere, the molten cast iron in the furnace is stirred, and the carbon component in the molten cast iron is kept almost constant. Then, the manganese component and the phosphorus component are removed while adding quicklime so that the molten slag has a basicity of less than 1 in the cast iron melt. Further, it is carried out by removing the boron component while adding quick lime.

  Further, the method for refining cast iron according to the present invention is a method in which sulfur (S) is poured into a ladle with a cast iron melt of S: 0.01 or less by an electroslag melting method using an electric arc furnace using Dalai powder. Inside the oxygen atmosphere, stirring the cast iron melt, a refining method of cast iron that performs refining while maintaining the carbon component in the cast iron melt almost constant, first removing the manganese component of the cast iron melt, Next, after discharging | emitting the produced | generated slag, it implements by removing a phosphorus component, adding quicklime to the cast iron molten metal.

  According to the refining method of the present invention, it is possible to efficiently and economically remove these components as impurities in cast iron containing manganese, phosphorus or boron with substantially constant carbon components.

It is explanatory drawing of the furnace used for implementation of this invention. It is a graph which shows an example of the impurity removal test of cast iron molten metal. It is a graph which shows the relationship between the phosphorus residual rate and processing time in an impurity removal test. It is a graph which shows the relationship between manganese residual rate and processing time in an impurity removal test. It is a graph which shows the relationship between the silicon residual rate and processing time in an impurity removal test. It is a graph which shows the relationship between the boron residual rate and processing time in an impurity removal test. It is a graph which shows the relationship between the molten metal temperature and processing time in an impurity removal test.

  Hereinafter, modes for carrying out the present invention will be described. The refining method for cast iron according to the present invention is a refining method for cast iron in which the inside of the furnace is made 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. . In this refining method, first, the manganese component of the cast iron melt is removed, and then the generated slag is discharged, and then the phosphorus component is removed while adding quicklime to the cast iron melt. That is, in the present invention, first, manganese removal for removing the manganese component is performed, and then, after the generated slag is discharged, phosphorus removal is performed while adding the quick lime to the molten cast iron.

  In the present invention, making the inside of the furnace in an oxygen atmosphere means that oxygen is blown into the furnace space on the upper surface of the poured cast iron melt to make an oxygen atmosphere. Stirring of the cast iron melt may be a method in which the cast iron melt flows and is stirred, and may be a mechanical stirring method or an electromagnetic stirring method. Such a stirring method has an advantage that the control is relatively easier than a method of stirring the cast iron melt by bubbling of gas such as air or inert gas.

  In the present invention, the furnace for treating the cast iron melt can be used even if it is a ladle that does not have any heating means. What is necessary is just to be able to make a predetermined oxygen atmosphere in the furnace and to stir the cast iron melt with a predetermined stirring force. For example, the present invention can be implemented using a ladle shown in FIG. In FIG. 1, a furnace 10 has a furnace body 11, a furnace lid 12, an oxygen supply means 16 that can make the interior of the furnace 10 an oxygen atmosphere, and a paddle 17 that can stir the molten cast iron 20. . 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.

FIG. 2 shows the result of an impurity removal test for removing phosphorus and manganese as impurities using the furnace shown in FIG. In this test, 500 kg of cast iron melt was poured into a ladle and pure oxygen was supplied into the furnace at 20 Nm ³ / hr, and the cast iron melt was stirred with a paddle (200 rpm, about 55 Hz, 5 A). As for quicklime, 10 kg of granular quicklime was added to the cast iron melt after 10 minutes of treatment time, and then powdered quicklime was continuously added at 500 g / 30 sec until the treatment time of 15 minutes. 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.

  In FIG. 2, the horizontal axis is the processing time after pouring of the cast iron melt, and the vertical axis is the residual content of phosphorus (P), carbon (C), silicon (Si) and manganese (Mn) with respect to the initial content of each component. The ratio of the amount (residual rate = (initial content−residual content) / initial content) and the standardized temperature of the molten cast iron (melt temperature = cast iron melt temperature ° C./1000) are shown. As shown in FIG. 2, the carbon component is kept substantially constant (1.02 to 0.97) in this test. Also, the molten metal temperature is almost constant (1.30 to 1.22). Manganese components are rapidly decreasing up to a treatment time of 10 minutes. However, after 10 minutes of treatment, when quick lime is added, the manganese component starts to increase, and recovered manganese is generated. This indicates that after the demanganese process in which demanganese is performed, it is necessary to dephosphorize after the generated slag is discharged.

  On the other hand, the phosphorus component is almost constant in the demanganese process up to a treatment time of 0 to 10 minutes without the addition of quicklime. And when quick lime is thrown in after 10 minutes of processing time, a phosphorus component will begin to reduce and the dephosphorization process will begin. In addition, the phosphorus component is decreasing at a substantially constant rate (dephosphorization rate: 0.08 / 10 min) from the processing time of 10 to 20 minutes, and is also decreasing after 15 minutes of the processing time when the addition of quicklime is stopped. The decrease in phosphorus component stopped after 20 minutes of treatment time.

In dephosphorization, slag basicity (CaO / SiO ₂ ) is important. For example, the slag basicity should be 0.6 to 2.5. For this reason, in an impurity removal test for removing phosphorus, manganese or boron as impurities, a test was conducted to examine the effect of the timing and amount of quicklime introduced into the furnace. Table 1 shows the timing and amount of quicklime. As shown in Table 1, in Test 1, Test 2 and Test 4, quick lime was continuously added from the beginning of the test, and in Test 3, quick lime was continuously added from the middle. The basicity indicates an average basicity obtained from the amount of quicklime added and the amount of SiO ₂ component in the furnace. Test 3 is the test shown in FIG. 2, and the basicity of Test 3 is the average basicity when quicklime is added. Moreover, in Test 2, since the blowout occurred when quicklime was added, there is a possibility that the predetermined slag basicity is not achieved.

  The cast iron melt used in this test was prepared by melting the casting raw material by an electroslag melting method using an electric arc furnace using Dalai powder, and the test was started at a molten metal temperature of 1400-1300 ° C. As shown in FIG. 1, the molten metal temperature gradually decreases at first, but then turns to a substantially constant value or increases. This impurity removal test was performed in the range of 1200 to 1400 ° C. for molten cast iron.

  The test results are shown in FIGS. 3 shows the phosphorus (P) residual rate, FIG. 4 shows the manganese (Mn) residual rate, FIG. 5 shows the silicon (Si) residual rate, and FIG. 6 shows the boron (B) residual rate. 3 to 6, the horizontal axis represents the processing time, and the vertical axis represents the residual ratio of each component of P, Mn, Si, or B. For example, the parameter P1 in FIG. 3 indicates the residual rate of phosphorus in Test 1, and the numbers indicate the test numbers shown in Table 1. P2 is the residual rate of phosphorus in test 2, P3 is the residual rate of phosphorus in test 3, and P4 is the residual rate of phosphorus in test 4. The same applies to each parameter of the Mn residual rate, Si residual rate or B residual rate shown in FIGS. FIG. 7 shows the melt temperature during the test. In FIG. 7, the horizontal axis indicates the processing time, and the vertical axis indicates the temperature.

  According to FIG. 3, the dephosphorization is most advanced in Test 1, with the dephosphorization rate for the first 5 minutes of treatment time being 0.09 / 5 min and the dephosphorization rate for 10 minutes of the next treatment time being 0.08 / 10 min. In the case of Test 3, dephosphorization does not proceed at all for a treatment time of 0 to 10 minutes when quicklime is not added, but dephosphorization proceeds rapidly (0.08 / 10min) after 10 minutes of treatment time when quicklime is added. It is out. In the case of Test 2, dephosphorization does not proceed at all for a treatment time of 0 to 5 minutes, but progresses rapidly (0.06 / 10 min) during a treatment time of 5 to 10 minutes. In the case of Test 4, the dephosphorization rate at the treatment time of 0 to 10 minutes is the lowest at 0.03 / 10 min, and the phosphorus component increases after the treatment time of 10 minutes has elapsed. In addition, in the case of Test 4, the amount of quicklime added is twice that in Test 1, the basicity in Test 4 is 1.6, and the basicity in Test 1 is 0.8.

  According to FIG. 4, the Mn residual rate in tests 1, 2, and 4 decreased in proportion to the treatment time, the demanganese rate in test 1 was 0.26 / 10 min, the demanganese rate in test 2 was 0.15 / 10 min, The demanganese rate in Test 4 is 0.09 / 10 min. The Mn survival rate curve of Test 3 almost overlaps with the survival rate curve of Test 2 during the treatment time of 0 to 5 minutes, and approaches the Mn survival rate curve of Test 1 rapidly after 5 minutes of treatment time. It is presumed that after the lapse of minutes, if there was no quick lime input, it would have shifted so that demanganese progressed more than Test 1.

  According to FIG. 5, the desiliconization rate of Test 1 is 0.26 / 10 min for the processing time of 0 to 5 minutes, but 0.15 / 10 min for the processing time of 5 to 15 minutes. And it is estimated that the silicon residual rate of Test 1 changes so as to follow the Si residual rate curve of Test 2 after the processing time of 15 minutes elapses. The silicon removal rate in Test 2 is 0.18 / 10 min. The desiliconization rate in Test 4 is 0.1 / 10 min. The Si residual rate curve of Test 3 overlaps with the Si residual rate curve of Test 4 at the treatment time of 0 to 5 minutes, and then rapidly approaches the Si residual rate curve of Test 2 and is closest when the treatment time of 15 minutes elapses. In the case of Test 3, it can be said that desiliconization is considerably suppressed as compared with Test 1. Note that after the treatment time of 15 minutes has elapsed, the inclination angle of the test 3 Si residual rate curve changes away from the test 2 Si residual rate curve.

  According to FIG. 6, it is shown that boron can be removed in this test regardless of whether or not quicklime is added. In the case of Test 1, the boron removal rate is the highest. In addition, the boron content increased abnormally in the treatment time of 5 minutes in test 3, and boron increased slightly in test 2, but the reason is unknown.

  According to FIG. 7, the melt temperature during the test is the highest in test 4 and the lowest in test 1. In general, the temperature of the molten metal drops rapidly during the treatment time of 0 to 5 minutes, and then becomes a substantially constant temperature (stabilization temperature). However, in the case of Test 4, the molten metal temperature suddenly changes after about 10 minutes of treatment time. Yes. The molten metal temperature curves of tests 1, 2 and 4 are generally the same from the start of the test to the treatment time of 5 minutes, and the temperatures at the start of the test are test 4: 1450 ° C, test 2: 1340 ° C, test 4: 1300 ° C. ing. The slope of the molten metal temperature curve of Test 3 is about half that of the molten metal temperature curve of Test 1. The stabilization temperature of Test 1 is 1225 ° C, the stabilization temperature of Test 2 is 1280 ° C, and the stabilization temperature of Test 3 is 1250 ° C.

<Dephosphorization and demanganese>
As shown in FIGS. 3 and 4, the condition of Test 1 is preferable for performing dephosphorization and demanganese simultaneously. Although the basicity (average basicity) in Test 1 was 0.8, according to FIG. 5, the decrease in the silicon component was the largest in Test 1 and the generation of silicon oxide was the largest. Considering this point, it is understood that the basicity can be less than 1 (less than 1 and 0.5 or more).

On the other hand, when performing the dephosphorization and demanganese treatment, first, the demanganese process is performed, and then, when the dephosphorization process is performed, it is necessary to carry out the waste after the demanganese process. In the dephosphorization step, the basicity is preferably about 1.6 from the example of Test 3, but considering the effect of blowing in Test ₂ , the formation of SiO ₂ during the test, etc., 1 or more (1 or more 2 It is understood that the following can be made. Moreover, according to FIGS. 3, 4 and 7, the test start temperature and the stabilization temperature of the molten metal are related to the slope of the phosphorus residual rate curve, and the test temperature can be 1400-1200 ° C, but the lower one Is preferable, and 1300-1200 degreeC or 1250-1200 degreeC is preferable.

  According to FIGS. 3, 4 and 7, the molten metal temperature has an influence on the phosphorus residual rate and the manganese residual rate, and it is understood that the lower molten metal temperature is preferable for dephosphorization or demanganese in this test range. Is done. The influence of the molten metal temperature is remarkable when the cases of Test 1 and Test 4 are compared. In particular, in response to the fact that the molten metal temperature changed suddenly after the treatment time of 10 minutes in the case of Test 4, it was judged from the fact that the phosphorus residual ratio was reversed from decrease to increase. It is understood that temperature control is more important when dephosphorizing the cast iron melt.

  In this impurity removal test, as described above, a cast iron melt obtained by melting a casting raw material by an electroslag melting method using an arc electric furnace using Dalai powder was used. According to this electroslag melting method, the sulfur component in the cast iron melt can be lowered. For example, the sulfur (S) components of the cast iron melts used in tests 1 to 4 were S1: 0.002%, S2: 0.002%, S3: 0.001%, and S4: 0.002%, respectively. That is, if a cast iron melt obtained by the present electroslag melting method is used, desulfurization may not be performed.

10 furnace
11 Furnace body
12 hearth
16 Oxygen supply means
17 paddle
20 Cast iron melt

Claims (7)

A refining method for cast iron that stirs molten iron in the furnace with an oxygen atmosphere inside the furnace, refining while maintaining the carbon component in the molten cast iron substantially constant,
A method for refining cast iron in which first the manganese component of the molten cast iron is removed, and then the generated slag is discharged, and then the phosphorus component is removed while adding quicklime to the molten cast iron.   2. The method for refining cast iron according to claim 1, wherein the quicklime is added so that the basicity of the molten slag becomes 1 or more.   The method for refining cast iron according to claim 1 or 2, wherein refining is performed so as to suppress a decrease in silicon component.   The method for refining cast iron according to any one of claims 1 to 3, wherein the refining is performed while maintaining the temperature of the cast iron melt almost constant in the range of 1400 ° C to 1200 ° C. . A refining method for cast iron that stirs molten iron in the furnace with an oxygen atmosphere inside the furnace, refining while maintaining the carbon component in the molten cast iron substantially constant,
A method for refining cast iron, wherein quick lime is added to the molten cast iron so that the basicity of the molten slag is less than 1, while removing manganese and phosphorus components.   The method for refining cast iron according to claim 5, further comprising removing a boron component. Sulfur (S) is melted by an electroslag melting method using an electric arc furnace using Dalai powder, and a cast iron melt with S: 0.01 or less is poured into a ladle to bring the inside of the furnace into an oxygen atmosphere, and the cast iron melt is stirred. Meanwhile, a refining method of cast iron that performs refining while maintaining the carbon component in the cast iron melt almost constant,
A method for refining cast iron in which first the manganese component of the molten cast iron is removed, and then the generated slag is discharged, and then the phosphorus component is removed while adding quicklime to the molten cast iron.

Images