JP5326243B2 - How to add lead to molten steel - Google Patents

Description

The present invention, in the course of ladle refining of steel, the addition of lead uniformly in the molten steel are those concerning the addition how a lead that can be uniformly dissolved.

  Lead-containing steel is steel containing lead, which is a free-cutting element. Lead exists in steel alone or as a sulfide, and is an element having an effect of improving machinability without deteriorating the material of the steel. In particular, lead free-cutting steel is in great demand because of its excellent machinability. Lead-containing steel has a high lead content and exhibits excellent machinability as it is uniformly dissolved and dispersed in the molten steel.

  However, it is difficult to increase the lead content in the molten steel and to uniformly dissolve and disperse it in the molten steel for the following reasons.

  (A) The solubility of lead in molten steel is as low as about 0.3 to 0.4% by mass.

  (B) While the specific gravity of molten steel is about 7.1, the specific gravity of lead is as large as about 11.3. Therefore, lead added beyond the solubility unless strength is stirred in the ladle The minute will sink to the bottom of the ladle.

  Therefore, in order to solve this problem, various technical developments related to a method for adding lead to molten steel have been performed. Among them, typical methods for adding lead include the methods shown in the following (1) to (3).

  (1) A method of injecting a lead-containing substance together with an inert gas into molten steel in a ladle using an injection lance (Patent Document 1, Patent Document 2, etc.).

  (2) A method in which a lead-containing substance is freely dropped from above and added to the agitated molten steel surface while blowing the inert gas from the gas bubbling device installed at the bottom of the ladle and stirring the molten steel ( Patent Document 3).

  (3) A method of adding a wire containing a lead-containing substance into the molten steel while stirring the molten steel by blowing an inert gas from a gas bubbling device installed at the bottom of the ladle (Patent Document 3, etc.).

  However, each of the above lead addition methods still has the following problems.

  For example, the addition method using the injection lance described in the above (1) increases the cost of the refractory compared to other methods.

  In addition, the addition method for free-falling the lead-containing material onto the molten steel surface being stirred as described in (2) above can be performed with simple equipment, and addition of alloys other than lead is easy. There is an advantage that can be done. However, as described above, the specific gravity of lead is about 11.3, which is overwhelmingly higher than that of molten steel of about 7.1, and the solubility in molten steel is as small as 0.30 to 0.40 mass%. . Therefore, when adding a large amount of lead exceeding 0.30 mass% with respect to the molten steel, if lead having a large particle size is used, it is very difficult to uniformly dissolve and disperse the molten steel in the molten steel.

  In the method of adding the lead-containing material by free-falling, in order to achieve uniform dissolution and dispersion of lead in the molten steel, it is better to make the particle size of the lead-containing material smaller. If it is too small, lead may melt in the chute due to radiant heat from the molten steel, and the chute outlet may be blocked.

  On the other hand, in the method of adding a wire containing a lead-containing substance described in (3) above, the above-mentioned problem of chute blockage can be avoided. In Patent Document 1 and Patent Document 3 described above, the lead content in the molten steel is 0.30 by reducing the average particle size of the lead-containing material, increasing the stirring force, and lowering the addition rate of the lead-containing material. Even in the case of mass% or more, it is said that lead can be finely and uniformly dispersed without causing undissolved residue of the lead-containing material.

  However, even in the method of adding the wire described in (3), the dissolution of lead in the molten steel and the dispersibility thereof are the fluidity of the molten steel based on the temperature and the C content in the molten steel, and the outer diameter of the wire. It has been found that it varies greatly depending on the wire characteristics such as thickness and thickness and the rate of addition.

JP-A-61-199050 (claims and page 10, lower right column, line 10 to page 3, upper right column, line 12) JP-A-62-60815 (Claims and page 2, lower left column, lines 13 to 19)) JP-A-4-308021 (Claims, paragraphs [0004] and [0008] to [0009]) The Japan Iron and Steel Institute, 3rd edition Handbook of Steel Volume 1 Basics (March 1983): 205 pages

  The present invention has been made in view of the above-mentioned problems, and the problem is that a wire containing a lead-containing substance in the molten steel while stirring the molten steel by blowing an inert gas into the molten steel from the bottom of the ladle. It is an object of the present invention to provide a method for adding lead to molten steel, in which lead can be uniformly dissolved and dispersed in molten steel. In particular, an object of the present invention is to provide a method for melting lead-containing steel for lead free-cutting steel having a lead content of 0.30% by mass or more using the above method.

  The present inventors have researched and developed a method for adding lead to molten steel that solves the above-described problems of the prior art and can uniformly dissolve and disperse lead in the molten steel. And, the method described in Patent Document 3, that is, containing lead into the agitated molten steel while stirring the molten steel by blowing an inert gas into the molten steel from a gas bubbling device installed at the bottom of the ladle Even in the method of adding a wire containing a substance, in order to uniformly dissolve and disperse lead in molten steel, it is necessary to satisfy the following conditions (a) to (c), or The present invention was completed with the knowledge that it was preferable.

  (A) A wire containing a lead-containing substance needs to be charged into a region (hereinafter also referred to as “plume”) in which gas is blown into the molten steel in the ladle from the bottom of the pan and is strongly stirred. This is because immediately after the wire is charged and melted in the molten steel, the lead-containing material is vigorously stirred by the molten steel, mixed with the molten steel, and quickly dissolved and dispersed in the molten steel.

  FIG. 1 is a view for explaining a method of adding lead from the top while blowing an inert gas from the bottom of the pan into molten steel in the ladle.

  The “plume” is a mixture of bubbles 4 of the inert gas 3 blown into the molten steel 2 from the bottom of the pan 1 and the molten steel 2 as shown by reference numeral 5 in the figure, and vigorously stirred and mixed. It means the area that has been. In this region, the molten steel 2 and the gas bubbles 4 are in a violent turbulent mixing state.

  (B) In order to promote uniform dissolution and dispersion of lead in the molten steel, it is necessary to control the C content in the molten steel and the molten steel temperature within an appropriate range. This is because when the C content in the molten steel is lowered, the melting point of the molten steel is increased, so that its fluidity is lowered and the uniform dispersion of lead into the molten steel is inhibited. Therefore, in order to quickly and uniformly disperse the lead added in a larger amount than the solubility in the molten steel, it is effective to increase the temperature before inserting the wire as the C content in the molten steel decreases. is there. Si is a deoxidizing element for steel, and is an element that imparts hardenability to the steel and contributes to strengthening of the steel. In addition, Mn has a deoxidizing action of steel, and at the same time, imparts hardenability to the steel to strengthen the steel, and further forms MnS to improve the machinability of the steel and suppress the formation of FeS. Since it has the effect | action which improves hot workability, it contains in order to acquire these effects.

  (C) In order to increase the dissolution rate of the wire in the plume, it is preferable that the cross-sectional shape of the wire is a square tube and the dimensions and thickness thereof are adjusted appropriately and appropriately. The reason why the cross-sectional shape is a square tube is that it is easy to avoid troubles when inserting the wire into the molten steel.

The present invention has been completed based on the above findings and has as its gist lies in addition how the lead to the molten steel shown in (1) and (2) below.

(1) In molten steel contained in a ladle and containing, by mass%, C: 0.03 to 0.50%, Si: 0.60% or less and Mn: 0.50 to 2.00% Injecting inert gas from the bottom of the pan, and adding lead to molten steel in which iron wire with lead-containing material is inserted into the area where the blown inert gas and molten steel are mixed and vigorously stirred and mixed The temperature of the molten steel before charging the iron wire, the C content in the molten steel, the Si content in the molten steel, and the Mn content in the molten steel are expressed by the following formulas (1) and (3). The temperature of the molten steel is controlled so as to satisfy the relationship, and the outer diameter of the cross section of the iron wire is (15 to 17 mm) × (7.0 to 8.0 mm), and the wall thickness is 0.3. 2 to 10% by mass of calcium carbonate having a particle size of 0.6 mm or less is contained in a square tube of .about.0.5 mm. Using iron wire with a powdery lead-containing substance with a particle size of 0.6 mm or less, 0.4 to 0.7 kg / (min · t-molten steel) of lead is loaded into the molten steel at a lead conversion charging speed. A method for adding lead to molten steel.

V ≧ 1630−90 × X−6.2 × Y−1.7 × Z (1)
V ≦ 1660−90 × X−6.2 × Y−1.7 × Z (3)
Here, V is the temperature (° C.) of the molten steel before charging the iron wire, X is the C content (mass%) in the molten steel, Y is the Si content (mass%) in the molten steel, and Z is in the molten steel. Represents the Mn content (mass%).

(2) adding how the lead to the molten steel according to the the content of lead in the steel, characterized in that a 0.3 to 0.4 wt% (1).

  In the present invention, the “inert gas” means a gas such as argon, helium or neon belonging to the group 18 element of the periodic table, and the use of argon gas is preferable from the viewpoint of economical efficiency.

  “Powdered lead-containing substance” means a mixture of lead and / or a lead compound having a particle size of 0.6 mm or less and a lead content of 89% by mass to 98% by mass, and calcium carbonate It means a mixture.

  “Iron” means carbon steel, high alloy steel, low alloy steel, stainless steel, and the like.

  In the following description, “mass%” indicating the component composition of steel is also simply referred to as “%”.

  According to the present invention, by adding a wire containing lead-containing material into the molten steel while stirring the molten steel by blowing inert gas into the molten steel from the gas bubbling device installed at the bottom of the ladle, Helium can be uniformly dissolved and dispersed. Therefore, by using the method of the present invention, high-quality lead-containing steel in which lead is uniformly dispersed can be melted for lead-free cutting steel having a lead content of 0.30% by mass or more.

  The contents of the present invention and the preferred embodiments of the present invention will be described in more detail below as the invention has been completed.

1. Basic Configuration of the Invention As shown in FIG. 1, the mass accommodated in the ladle 1 is about 70 tons (t), the temperature is 1540 to 1640 ° C., the C content is 0.03 to 0.50%, Into molten steel 2 having a Si content of 0.60% or less and a Mn content of 0.50 to 2.00%, Ar gas 3 is added from the bottom of the ladle to 1.56 to 2.47 Nl / (min · t−. While being blown at a flow rate of molten steel, lead was added into the plume 5 as indicated by the arrow A or into the region other than the plume as indicated by the arrow B by the following method. That is, a powdered lead-containing substance obtained by adding 2 to 10% by mass of calcium carbonate having a particle size of 0.6 mm or less to make a lead mixture has an outer dimension of (15 to 17 mm) × (7.0 to 8). Supply of 0.4 to 0.7 kg / (min · t-molten steel) in terms of the amount of lead of iron wire embedded in a square iron pipe with a wall thickness of 0.3 to 0.5 mm Charged into molten steel at speed. In addition, in order to make the melt | dissolution in molten steel easy as said iron pipe, the pipe | tube made from carbon steel was used.

  As a result, it was found that lead was more uniformly dissolved and dispersed in the molten steel when the wire was charged into the region other than the plume when compared with the case where the wire was charged into the region other than the plume. In the present invention, this evaluation was evaluated by lead yield for confirmation of solubility. However, it was found that even when the wire was put into the plume, the degree of uniform dispersion of lead in the molten steel varied.

  In general, in molten steel processing, the degree of superheat (ΔT) of molten steel (that is, from the molten steel temperature to the liquidus line, taking into account the allowance for an unexpected temperature drop in the molten steel and consideration for the temperature drop in the subsequent process) The value obtained by subtracting the temperature (solidification start temperature) is maintained at a value above a certain level. However, in the melting of lead-containing steel targeted by the present invention, it is necessary to dissolve lead having a solubility in the molten steel of only 0.3 to 0.4% to the vicinity of the limit of the solubility. The solubility of lead increases as the C content in molten steel increases and the molten steel temperature increases. Further, the higher the C content in the molten steel and the higher the molten steel temperature, the higher the fluidity of the molten steel, which is advantageous for uniform stirring of the molten steel. However, when the molten steel temperature becomes high, lead is liable to vaporize, and not only the yield of lead is lowered, but also not preferable in the working environment. Also, it is necessary to avoid raising the temperature of molten steel more than necessary from the viewpoint of refining energy cost.

  Therefore, considering the above points, the superheat degree (ΔT) of the molten steel is high in the region where the C content in the molten steel is low, and the superheat degree (ΔT) of the molten steel is low in the region where the C content in the molten steel is high. I thought of it, and confirmed its effect experimentally.

  According to Non-Patent Document 1, for example, the liquidus temperature of molten steel is represented by the following equation (2).

T _L = 1536− {90 × (% C) + 6.2 × (% Si) + 1.7 × (% Mn) +...} (2)
Here, (% C), (% Si), and (% Mn) represent C, Si, and Mn contents (mass%) in the molten steel, respectively.

According to the above formula (2), for example, when the C content in molten steel is 0.05%, T _L = 1530.7 to 1524.4 ° C., and when the C content in molten steel is 0.45%, T _L = 1494.7 to 1488.4 ° C.

  Therefore, in the research and investigation of the present invention, in the low carbon side where the C content in molten steel is about 0.05%, ΔT = 90 ° C. is near, and the high carbon content in the molten steel is about 0.45%. On the side, assuming that ΔT = 85 ° C. is appropriate, the relationship between molten steel temperature at the start of lead addition and lead yield was investigated.

  FIG. 2 is a diagram showing the relationship between the molten steel temperature at the start of lead addition and the lead yield in the molten steel. From the results shown in the figure, ΔT = 90 ° C. on the low carbon side where the C content in molten steel is about 0.05%, and ΔT = 85 on the high carbon side where the C content in molten steel is about 0.45%. In the vicinity of ℃, the increase in the lead yield due to the high temperature of the molten steel was confirmed.

  FIG. 3 is a diagram showing the influence of the C content in molten steel and the molten steel temperature at the start of lead addition on the lead yield increase. This figure is a rearrangement of the results of FIG.

  From the above results, in the present invention, the C content in molten steel is 0.03 to 0.50%, the Si content in molten steel is 0.60% or less, and the Mn content in molten steel is 0.50 to 2.00. %, The appropriate temperature range of the molten steel before charging the iron wire containing the lead-containing material was defined as the following equation (1).

V ≧ 1630−90 × X−6.2 × Y−1.7 × Z (1)
Here, V is the temperature (° C.) of the molten steel before charging the iron wire, X is the C content (mass%) in the molten steel, Y is the Si content (mass%) in the molten steel, and Z is in the molten steel. Represents the Mn content (mass%).

The adverse effect on lead yield when the molten steel temperature is too high was not clarified in this survey. However, constraints on operations in consideration of such reduction or refractory life of the refining energy loss, temperature V before the molten steel is charged with iron wire, adjust the range represented by the following formula (3) .

V ≦ 1660−90 × X−6.2 × Y−1.7 × Z (3)
Furthermore, as the lead-containing substance-incorporated wire, the inside dimension of the square tube whose outer dimension of the cross section is (15 to 17 mm) × (7.0 to 8.0 mm) and whose wall thickness is 0.3 to 0.5 mm. It was found that it is preferable to use an iron wire containing a powdery lead-containing substance having a particle size of 0.6 mm or less and to insert this into molten steel. This is because the average value of the lead content in the molten steel further increases and the variation in the lead content in the molten steel is reduced.
2. 2. Reasons for defining component requirements and preferred embodiments 2-1. Insertion region of lead-containing material-incorporated wire into molten steel Iron wire with lead-containing material must be inserted into the plume region. In the plume, the molten steel is vigorously stirred by the blown inert gas, and the bubbles and the inert gas are in a turbulent mixed state. Therefore, by inserting the wire into the area inside the plume, the lead-containing substance embedded in the wire is vigorously stirred and mixed in the molten steel, and distributed more uniformly than when the wire is inserted into the area other than the plume. It is because it can be made.

  On the other hand, when the wire was inserted into an area other than the plume, lead was not uniformly dispersed in the molten steel, and the slag was hard in the area other than the plume. There was also a problem that it did not penetrate sufficiently into the molten steel.

2-2. The particle size and content of calcium carbonate and the powdered lead-containing material The particle size of calcium carbonate contained in the powdered lead-containing material is 0.6 mm or less, and the content is 2 to 10% by mass. The reason for containing calcium carbonate is to generate carbon dioxide gas by the decomposition reaction of calcium carbonate and to vigorously perform stirring with bubbles. The reason why the particle diameter is 0.6 mm or less is to rapidly dissolve in molten steel and promote the decomposition reaction of calcium carbonate. If the content of calcium carbonate in the powdery lead-containing material is less than 2%, the above effect cannot be obtained. On the other hand, if the content exceeds 10%, the lead content of the lead-containing material decreases. As a result, the amount of wire charged increases and the wire charging time becomes longer, hindering operation.

  As described above, the powdered lead-containing substance has a particle size of 0.6 mm or less and a lead mixture and / or a lead compound having a lead content of 89% or more and 98% or less, and a mixture of calcium carbonate. It is. When the particle size is larger than 0.6 mm, the dissolution of lead in the molten steel tends to be non-uniform and tends to hinder the uniform dispersion of lead.

2-3. Molten steel temperature before lead-containing substance-incorporated wire charging As described above, the appropriate temperature range of the molten steel before charging the iron wire in which the lead-containing substance is embedded is a range represented by the formula (1). It is because lead can be uniformly dissolved in molten steel and the uniform dispersibility of lead can be improved by charging the wire under the condition satisfying the relationship of the formula (1).

  When the C content in the molten steel is lowered, the melting point of the molten steel is increased, the fluidity of the molten steel is lowered, and lead is not uniformly dispersed in the molten steel. Therefore, in order to quickly and uniformly disperse the lead added above the solubility of the molten steel, it is effective to increase the molten steel temperature before the wire charging with the decrease in the C content in the molten steel. It is.

2-4. Cross-sectional shape and dimensions of lead-containing substance-incorporated wire, and wire charging speed Lead-containing substance-incorporated wire has a cross-sectional outer dimension of (15 to 17 mm) × (7.0 to 8.0 mm), and a wall thickness of 0 using an iron wire was decorated with lead-containing substance of powdery inside of a .3~0.5mm square tube, it charged it in the molten steel. This is because the average value of the lead content in the molten steel is further increased and the variation is reduced. Also, why management of Ru with a tube cross-section square as a wire is because easy to avoid troubles due to habit turns of wire in the instrumentation Nyutoki wire into the molten steel.

  When the outer dimension of the cross section of the lead-containing substance-incorporated wire is less than 15 mm × 7.0 mm, the hot strength of the wire is lowered and it is difficult to deeply penetrate the wire into the molten steel. Therefore, it becomes difficult for lead in the wire to be uniformly dispersed in the molten steel. On the other hand, when the outer dimension of the cross section of the wire becomes larger than 17 mm × 8.0 mm, a relatively large amount of lead-containing substance suddenly contacts the molten steel in a local region in the plume when the wire is melted in the molten steel. For this reason, the molten steel temperature around the lead-containing substance is lowered, and the dispersibility of lead in the molten steel is lowered.

  When the thickness of the lead-containing material-incorporated wire is less than 0.3 mm, the wire dissolves at a relatively upper layer in the plume. Therefore, before the lead is sufficiently stirred and mixed with the molten steel, the lead is removed from the plume. It moves to a relatively fluid region other than the plume, and as a result, the dispersibility of lead in the molten steel decreases. On the other hand, when the thickness of the wire exceeds 0.5 mm, the wire reaches the lower part of the plume, and the wire melts near the boundary between the plume and the relatively slow flow region. It becomes difficult to be sufficiently stirred and mixed in the inside, and as a result, the dispersibility of lead in the molten steel is lowered.

Dumping speed of lead-containing materials interior wire shall be the range of 0.4~0.7kg / (min · t- molten steel) of lead in terms of load velocity. If the charging speed is less than 0.4 kg / (min · t-molten steel), the wire melts in the surface layer portion of the molten steel, lead vapor is likely to be generated, and the yield is lowered, which is not preferable. On the other hand, if the speed exceeds 0.7 kg / (min · t-molten steel), the melting position will be near the bottom of the ladle, lead will easily precipitate, and the yield will decrease, which is not preferable. is there.

2-5. The main component composition of the molten steel chemical composition of molten steel is in the range below.

C: 0.03-0.50%
C is an element having an effect of strengthening steel. If the C content is less than 0.03%, it is difficult to obtain the required strength, which is not preferable. On the other hand, if the C content exceeds 0.50%, the hardness becomes too high and the machinability deteriorates, which is not preferable.

Si: 0.60% or less Si is an element having a function of strengthening steel by imparting hardenability to the steel as well as a deoxidizing action of deoxidizing the steel. If the content exceeds 0.60%, the hardness of the steel increases excessively and the machinability decreases, which is not preferable.

Mn: 0.50 to 2.00%
Mn has a deoxidizing effect on steel, strengthens the steel by imparting hardenability to the steel, and further improves the machinability of the steel by forming MnS, thereby suppressing the formation of FeS and hot working. It is an element having the effect of improving the properties. If the Mn content is less than 0.50%, the required strength is difficult to obtain, and the hot ductility is lowered and the hot workability is deteriorated. On the other hand, if the content exceeds 2.00%, these effects are saturated and the alloy cost increases, which is not preferable.

  In order to confirm the effect of the method of adding lead to the molten steel of the present invention, the following lead-containing steel melting test was conducted and the results were evaluated.

  The mass accommodated in the ladle is about 70 t, the temperature is 1540 to 1640 ° C., the C content is 0.05 to 0.10%, the Si content is 0.01 to 0.02%, and the Mn content is While blowing Ar gas from the bottom of the ladle into the 0.90 to 1.30% molten steel at a flow rate of 1.95 Nl / (min · t-molten steel), into the plume or the area other than the plume by the following method A test for adding lead was conducted.

  That is, a powdery lead-containing substance having a particle size of 0.6 mm or less, which is a lead mixture obtained by adding 2 to 10 mass% of calcium carbonate having a particle size of 0.6 mm or less, has an outer dimension of 16 mm × 7 A steel wire that is housed in a square steel pipe having a thickness of 0.4 mm and a thickness of 0.4 mm, and at a supply rate of 0.4 to 0.7 kg / (min · t-molten steel) in terms of lead amount. The inside was charged for 7 minutes. This lead charge corresponds to 0.30% by mass in terms of the lead content in the molten steel. In some tests, a test in which the cross-sectional shape of the wire was changed was also performed.

  Test conditions and test results are shown in Table 1.

  In the table, “A” at the wire loading position indicates that an iron wire containing lead-containing material was loaded into the area in the plume, and “B” represents that the wire was loaded in an area other than the plume. It represents that it entered (see FIG. 1).

  Moreover, in order to evaluate the dispersibility of lead by uniform solubility, the test result was obtained by obtaining the lead yield calculated by the following equation (4), and evaluated this value. A larger lead yield value means better lead dispersibility.

Lead yield = lead content in product (%) / {(mass of lead-containing material (kg) x lead content (%)) / mass of molten steel (kg)} x 100 (%) (4) )
Test Nos 2-9 and 11-13 are tests for inventive examples satisfying the conditions specified in this onset bright, Test No. 1 and 2, for Comparative examples not satisfying the conditions defined by the present invention It is a test.

  Test number 1, which is a comparative example in which an iron wire containing lead-containing material is inserted into a region other than the plume, and a comparison in which the molten steel temperature before charging the wire is low and does not satisfy the relationship expressed by equation (1) In each of Test No. 10 as an example, the lead yield was relatively low, and the dispersibility of lead in the molten steel was inferior.

On the other hand, Test Nos. 2 to 9 and 11 to 13, which are examples of the present invention, all showed high lead yield and good dispersibility. Especially, the test numbers 3, 4, 7, 8 and 11 to 13, lead yield is obtained a high value of more than 63%, the dispersibility of the very good lead was confirmed.

  According to the method for adding lead to molten steel of the present invention, a wire containing lead-containing material in the molten steel while stirring the molten steel by blowing an inert gas into the molten steel from a gas bubbling device installed at the bottom of the ladle Can be uniformly dissolved and dispersed in molten steel. In particular, the method of the present invention targets lead free-cutting steel having a lead content of 0.30% by mass or more and is suitable for melting high-quality lead-containing steel in which lead is uniformly dispersed. Therefore, the lead addition method of the present invention is a technique that is excellent in machinability and can be widely applied in the field of production technology for lead free-cutting steel, which is in great demand.

It is a figure for demonstrating the method of adding lead from upper part, blowing inactive gas from the bottom part of a ladle into molten steel in a ladle. It is a figure which shows the relationship between the molten steel temperature at the time of a lead addition start, and the yield of lead in molten steel. It is a figure which shows the influence which the C steel content rate in molten steel and the molten steel temperature at the time of a lead addition start exert on a lead yield rise.

Claims (2)

From the bottom of the pan in the molten steel contained in the ladle, in mass%, containing C: 0.03-0.50%, Si: 0.60% or less and Mn: 0.50-2.00% To the area where inert gas is blown and the blown inert gas and molten steel are mixed and vigorously stirred and mixed,
It is a method of adding lead to molten steel that is charged with an iron wire containing a lead-containing substance,
Relationship between the temperature of the molten steel before charging the iron wire, the C content in the molten steel, the Si content in the molten steel, and the Mn content in the molten steel represented by the following formulas (1) and (3) The temperature of the molten steel is controlled to satisfy
As the iron wire, the outer dimension of the cross section is (15 to 17 mm) × (7.0 to 8.0 mm), and the particle diameter is 0.6 mm or less in a square tube having a wall thickness of 0.3 to 0.5 mm. Of iron carbonate containing a powdery lead-containing substance having a particle size of 0.6 mm or less and containing 2 to 10% by mass of calcium carbonate at a lead conversion rate of 0.4 to 0.7 kg / (min · A method for adding lead to molten steel, wherein the lead of (t-molten steel) is charged into the molten steel.
V ≧ 1630−90 × X−6.2 × Y−1.7 × Z (1)
V ≦ 1660−90 × X−6.2 × Y−1.7 × Z (3)
Here, V is the temperature (° C.) of the molten steel before charging the iron wire, X is the C content (mass%) in the molten steel, Y is the Si content (mass%) in the molten steel, and Z is in the molten steel. Represents the Mn content (mass%).   The method for adding lead to molten steel according to claim 1, wherein the lead content in the steel is 0.3 to 0.4 mass%.

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