JP5599253B2 - Steel continuous casting method - Google Patents

Description

  The present invention, in continuous casting of steel, cast mold powder into the mold to generate a molten layer of mold powder, to block the molten steel in the mold from the outside air, and between the mold copper plate and the initial solidified shell In particular, the continuous casting method is performed while ensuring the lubricity between the two, especially when the mold powder as the front powder is put into the mold at the start of continuous casting, and when the continuous casting is in a steady state, the front powder at the start is replaced. The present invention relates to a continuous casting method in which a steady-state mold powder having optimum properties for each steel type (hereinafter, the steady-state mold powder is referred to as “main body powder”).

  In a continuous casting technique in conventional continuous casting of steel, a method is generally used in which a special mold powder having heat generation characteristics is used as a front powder at the start of casting, compared to a mold powder used in a steady state. However, in the method using the front powder having the heat generation characteristic, the composition of the front powder and the mold powder which is the main body powder in the steady state is different from each other (that is, the composition in the molten state). In the progress stage (that is, the transition state) in the middle of switching to the state, a mixed state is formed by powders of two types of compositions. In such a mixed state of two types of powders, since the composition of the main body powder as the running powder determined for each steel type is deviated, the initial solidification in the mold until the transition state ends and becomes a steady state. Becomes non-uniform.

By the way, the mold powder for continuous casting is added into the mold and hatched on the surface of the molten steel. In such mold powder, there is a front powder added particularly at the early stage of casting, and the resulting slab is obtained by preventing the temperature of the molten steel from being lowered and keeping the molten steel warm to prevent the occurrence of deckle. This prevents the generation of surface flaws. Such a front powder contains metal powder such as Ca—Si alloy powder or Al—Mg alloy powder as a heat generating material in a general mold powder for continuous casting (see, for example, Patent Document 1). However, in the case of such exothermic mold powder, the exothermic material reacts abruptly, there is no sustain of the exothermic effect, and the continuous heat insulation effect cannot be obtained, and a dramatic improvement in the slab surface quality can be expected. In addition, it has been pointed out that oxides such as Fe ₂ O ₃ contained in the exothermic mold powder as an oxidation source and oxidation reaction products such as Al ₂ O ₃ and SiO ₂ deteriorate the quality inside the slab. (For example, refer to Patent Document 2).

  Also, instead of using exothermic front powder, a non-woven fabric formed by mixing fibers of metal oxide and metal calcium and metal silicon is stuck around the mold, and lubrication between the mold and the solidified shell of molten steel There has been proposed a method for reducing the wrinkles such as cracks and dents on the surface of the slab from the start of casting by improving the properties (see, for example, Patent Document 3).

  Furthermore, liquid lubricant is dripped into the mold shortly before the start of casting in continuous casting, and during the speed increase, mold powder and liquid lubricant are applied for lubrication between the mold and the slab. A method for suppressing the occurrence of breakout has been developed (see, for example, Patent Document 4).

  Furthermore, there has been proposed a method for obtaining a slab in which vertical cracks on the surface of the slab are prevented by using different mold powders having different solidification temperatures (see, for example, Patent Document 5). This method causes instability due to mixing of different mold powders, and this is one of the causes of the occurrence of slab defects.

JP-A-3-169467 Japanese Patent Laid-Open No. 4-143052 JP-A-8-215795 Japanese Patent No. 3536530 Japanese Patent Laid-Open No. 7-124716

  The problem to be solved by the present invention is to prevent the occurrence of surface flaws in the initial casting material by using a front powder with a specially designed composition as the mold powder used at the start of continuous casting in continuous casting of steel. It is to provide a continuous casting method.

FIG. 2 schematically shows a conventional front powder 6 in which a metal heating material such as a Ca—Si alloy and a lower oxide oxidizing agent 5 such as KMnO ₄ or Fe ₂ O ₃ are added to the powder base 3. The heat generating powder front powder 6 which is a front powder in the prior art has problems such as molten steel contamination. Therefore, in the means of the invention of the present application, the mold powder added with the metal heating material and the lower oxide oxidant 5 as shown in FIG. 2 is not used as a front powder at the start of casting of continuous casting, It shall not be used as mold powder (hereinafter referred to as “main body powder”) at the time of casting in a steady state.

  Furthermore, in the means of the invention of the present application, in order to eliminate the composition fluctuation due to the mixed state of the main powder used in the steady state with the front powder, the powder base material constituting the front powder used at the start of continuous casting is a steady state in the steady state. Although the composition is the same as the powder base material constituting the main body powder, the front powder and the main body powder are the front powder 1 schematically shown in FIG. 1A and the main body powder schematically shown in FIG. As schematically shown as 4, it is used as a mold powder that differs only in the content of free carbon (FC) 2.

  In addition, evaluation of the possibility of using the mold powder which differs only in content of the main body powder 4 and the free carbon 2 as the front powder 1 as mentioned above is performed by a slag conversion rate test. A front powder having an appropriate hatchability as the front powder 1 is designed by evaluating the hatchability by this slag rate test.

  Therefore, the means of the present invention for solving the above-described problems is that, in the invention of claim 1, in the method for continuously casting steel having a carbon content of 0.1 to 1.5% by mass, , Al, Ca, Mg, Na, Li, and a compound having a total F concentration, and a total of the mass of the oxide compound and the total F content of the compound having a total F concentration When the mass of the powder base 3 is 100%, the mass of the free carbon 2 relative to the mass of the powder base 3 is 2 to 8%, preferably 3 to 6%. Continuous by continuous casting of steel, characterized by a method of casting at the start of continuous casting using a front powder 1 made of a mixture and having a viscosity at 1300 ° C. of 0.1 to 5.0 Pa · s. Casting method

  In the above method, if the viscosity at 1300 ° C. is less than 0.1 Pa · s, the viscosity is too low and it is difficult for the molten layer of the front powder 1 to form a lubricating film uniformly between the mold and the solidified layer of the molten steel at the start of casting. The lubricity between the mold and the solidified layer is insufficient. If the viscosity at 1300 ° C. is higher than 5.0 Pa · s, the fluidity of the molten layer of the front powder 1 is low, and the lubricity between the mold and the solidified layer at the start of casting becomes insufficient.

In the invention of claim 2, the method of performing casting at the start of continuous casting using the front powder 1 is a front powder having a viscosity of 0.1 to 5.0 Pa · s when held at 1300 ° C. for 5 minutes. When 1 is put into a mold, it is a method of casting by using a front powder 1 having a slag formation rate of 40% to 90%, desirably 50 to 80% shown in the following formula (1). A continuous casting method by continuous casting of steel according to the means of claim 1.
Slag rate (%) = {(mass of hatched front powder) / (mass of mixture of hatched front powder and unhatched front powder)} × 100 (1)

  In the invention of claim 3, following the method of casting at the start of casting of continuous casting performed using the front powder 1 in the means of claim 1 or 2, the front powder 1 used at the start of casting of continuous casting, The main body powder 4 made of a mixture having the same composition as that of the powder base material 3 of the oxide compound and the compound having the total F concentration, but different only in the ratio of the mass of the free carbon 2 to the mass of the powder base material 3 is used. A continuous casting method using continuous casting of steel, characterized by comprising a method of casting in a steady state of continuous casting.

  Since the present invention is a continuous casting method using the front powder at the start of continuous casting of the above means and the main body powder at the continuous state of continuous casting, it is the same as the slab at the continuous state of continuous casting. Continuous cast initial slabs with excellent surface properties can be obtained, and slabs with excellent surface properties can be obtained even in the subsequent slabs in steady state, and there is no waste from the beginning of continuous casting. The production of the piece was obtained. In addition, the continuous casting initial slab in the present invention means a slab cast from the initial stage of casting until it switches from the front powder to the main body powder until it reaches a steady state through an intermediate stage.

In this invention, it is a schematic diagram which shows the ratio of free carbon (FC) and a powder base material, (a) is front powder, (b) is main body powder. It is a schematic diagram which shows the ratio of the metal heat generating material in a conventional front powder, a lower oxide oxidizing agent, and a powder base material.

  Embodiments of the present invention will be described below. In this embodiment, in the production of various steels having a carbon content of 0.1 to 1.5% by mass% by continuous casting in continuous casting, the initial casting at the start of continuous casting of these molten steels. The front powder 1 was put on the molten steel in the mold to generate a molten layer of the front powder 1 on the molten steel. The molten layer of the generated front powder 1 blocks the molten steel in the mold from the outside air, ensures lubricity between the mold and the solidified shell of the molten steel, and is obtained at the beginning of casting at the start of continuous casting. The surface properties of the cast slabs were prevented from being deteriorated, and the surface properties of the slabs in the steady state of continuous casting were excellent. The used front powder 1 is a mold powder made of a mixture of a powder base material 3 and free carbon 2.

The mixture of the powder base 3 and the free carbon 2 on which the front powder 1 is formed will be described. The powder base 3 is composed of oxide compounds and fluoride compounds of Si, Al, Ca, Mg, Na, Li. (Hereinafter, the fluoride compound is referred to as “F compound”), and when the powder base 3 is 100% by mass, it corresponds to 2 to 8%, preferably 3 to 6% of the powder base 3 The front powder 1 is made of a mixture obtained by adding a mass of free carbon 2 to the powder base 3. The front powder 1 has a viscosity at 1300 ° C. of 0.1 to 5.0 Pa · s. Further, Si ₂ , Al ₂ O ₃ , CaO, MgO, Na ₂ O + Li ₂ O are used as oxide compounds of Si, Al, Ca, Mg, Na, and Li, and slag flux is used as the F compound. A meteorite made of some CaF ₂ or sodium fluoride made of NaF. The compounding ratio of these compounds is not particularly limited, but the compounding ratios of typical compounds are approximately SiO ₂ : 35 to 60%, Al ₂ O ₃ : 2 to 15%, CaO: 25 to 35%, MgO: ≦ 10%, Na ₂ O + Li ₂ O: 2 to 20%, and the F compound is composed of CaF ₂ : 5 to 15% and NaF: ≦ 10%.

  By the way, when the viscosity at 1300 ° C. of the front powder 1 is less than 0.1 Pa · s, the viscosity is too low and the molten powder uniformly forms a lubricating film between the mold and the solidified layer of the molten steel at the start of continuous casting. It is difficult to do so and the lubricity becomes insufficient. On the other hand, when the viscosity at 1300 ° C. is higher than 5.0 Pa · s, the fluidity is too low, and the lubricity at the start of continuous casting cannot be obtained sufficiently.

  Furthermore, in the front powder 1 for continuous casting of this steel, the slag conversion rate shown in the following formula (1) obtained by heating to 1300 ° C., holding for 5 minutes and cooling is 40 to 90%, A desirable slag conversion rate is 50 to 80%.

  Slag rate (%) = {(mass of hatched front powder) / (mass of mixture of hatched front powder and unhatched front powder)} × 100 (1)

  That is, the slag conversion rate (%) shown in the above formula (1) is the mass of the mixture of the hatched front powder and the unhatched front powder obtained by heating to 1300 ° C., holding for 5 minutes and cooling. It is the value which showed the ratio of the mass of the hatched front powder which occupies in the percentage.

  In the test for determining the slag conversion rate, the front powder 1 is heated for hatching. This heating condition is one condition of heating to 1300 ° C. and holding at this temperature for 5 minutes. Further, when the front powder 1 is heated under the above-described conditions, it hatches to become a melt, and this melt becomes a lump after cooling and remains on the sieve. On the other hand, since the particle size of the unhatched powder does not change even after the test, it passes through the sieve. By utilizing this phenomenon, the hatched front powder is screened on the sieve by not separating the hatched front powder and the unhatched front powder with a sieve of nominal size 600 μm of JIS Z 8801. In other words, the slagging rate can be obtained by applying unsettled front powder under the sieve and measuring their masses, and applying these obtained masses to the above formula (1) of the slagging rate. .

  In the case of the front powder 1 having a slag conversion rate of less than 40%, the hatchability as the front powder is insufficient and it is difficult to melt. In the case of the front powder 1 having a slag conversion rate exceeding 90%, the front powder particles are not sufficiently covered with free carbon, which may cause problems such as sintering.

  The test method of the slag conversion rate of the front powder 1 can be performed by the same method as the method described in Japanese Patent Application Laid-Open No. 2008-246500 related to another application of the present applicant.

  First, an iron plate having a thickness of 1 mm is processed to produce an iron container having a width of 80 mm, a length of 150 mm, and a depth of 25 mm. In this iron container, 150 g of the front powder is weighed and charged. A muffle furnace was used as a furnace for flattening and melting this, and the iron container charged with the above-mentioned front powder was charged into a muffle furnace set at 1573K and held for 5 minutes to dissolve the front powder. Then, the whole iron container is taken out and naturally cooled.

  All the front powder is taken out from the cooled iron container and pulverized with a ball mill for 10 minutes in order to separate the hatched portion and the unhatched portion. After pulverization, the mixture of the hatched front powder and the unhatched front powder is sieved with a mesh sieve having a nominal size of 600 μm of JIS Z8801. A sieved front powder is formed on the screen remaining on the mesh by this sieving, and its mass is measured. On the other hand, the sieve under the mesh is used as an unhatched front powder, that is, an unhatched front powder, and its mass is measured.

  Applying the respective masses obtained by these measurements to the following formula (1) of the slag formation rate, the mass of the hatched front powder is the total mass of the hatched front powder and the unhatched front powder. By dividing by, that is, by dividing by the total mass of the original front powder used for heating, the slag conversion rate is calculated.

Slag rate (%) = {(mass of hatched front powder) / (total amount of hatched front powder and unhatched front powder)} × 100 (1)
That is, slag conversion rate (%) = {(mass of hatched front powder) / (total mass of original front powder)} × 100 (1)

Here, the composition of each front powder based on the test results of the above slag rate for Invention Example 1 and Comparative Examples 1 to 4 which are embodiments of the present invention, and when held at 1300 ° C. for 5 minutes viscosity, slag Karitsu, solidification temperature, and the surface properties of the continuous people cast at the start of the cast initial slab are shown in Table 1 in. Further, Table 1 shows the composition of the main body powder 4 which is a mold powder used in the steady state of continuous casting, the viscosity at 1300 ° C., the solidification temperature and the slagging rate as the main body powder. In Table 1, F.R. C. Indicates free carbon, and the surface properties of the cast slabs at the beginning of continuous casting, that is, the initial slabs, ◎ indicates that the surface properties of the slab are excellent without any abnormal operation, and ○ indicates that the surface properties of the slab are good. Being present, Δ and × indicate that defects are generated on the surface of the slab. In this case, in Table 1, the powder base material is shown such that the powder melt composition after hatching is 100%. On the other hand, F. C. Burns away and does not affect the powder melt composition after hatching of the powder substrate. Therefore, when the 100% by mass of powder melt composition after slag formation powder base, mixed with respect to the melt composition powder after the slag formation F. C. The mass of is shown in%. As described in the lower part of Table 1, F in Table 1 is the total F concentration of fluorine contained in F compounds such as CaF ₂ , NaF, and AlF ₃ in the powder base material.

Further, according to Invention Example 2 and Comparative Examples 5 to 8 which are embodiments of the present invention, the composition of the front powder, the viscosity when held at 1300 ° C. for 5 minutes, the slagging rate, the solidification temperature, and the continuous casting Table 2 shows the surface properties of the slab at the beginning of casting. Furthermore, Table 2 shows the composition of the main body powder, which is a mold powder used in the steady state of continuous casting, the viscosity at 1300 ° C., the solidification temperature, and the slagging rate as the main body powder. In Table 2, F.I. C. Indicates free carbon, and the surface properties of the cast slabs at the beginning of continuous casting, that is, the initial slabs, ◎ indicates that the surface properties of the slab are excellent without any abnormal operation, and ○ indicates that the surface properties of the slab are good. Being present, Δ and × indicate that a defect is generated on the surface of the slab. In this case, in Table 2, the powder base material is shown such that the powder melt composition after hatching is 100%. On the other hand, F. C. Burns away and does not affect the powder melt composition after hatching of the powder substrate. Therefore, when the powder melt composition after hatching of the powder base material is 100% by mass, the powder melt composition after mixing is mixed with the powder melt composition after hatching. C. The mass is shown in%. As described in the lower part of Table 2, F in Table 2 represents the total F concentration of fluorine contained in F compounds such as CaF ₂ , NaF, and AlF ₃ in the powder base material.

Further, according to Invention Example 3 and Comparative Examples 9 to 12 which are embodiments of the present invention, the composition of the front powder, the viscosity when held at 1300 ° C. for 5 minutes, the slagging rate, the solidification temperature, and the continuous casting Table 3 shows the surface properties of the slab at the beginning of casting. Furthermore, Table 3 shows the composition of the main body powder, which is a mold powder used in the continuous casting state, the viscosity at 1300 ° C., the solidification temperature, and the slagging rate as the main body powder 3. In Table 3, F.I. C. Indicates free carbon, and the surface properties of the cast slabs at the beginning of continuous casting, that is, the initial slabs, ◎ indicates that the surface properties of the slab are excellent without any abnormal operation, and ○ indicates that the surface properties of the slab are good. Being present, Δ and × indicate that a defect is generated on the surface of the slab. In this case, in Table 3, the powder base material is shown such that the powder melt composition after hatching is 100%. On the other hand, F. C. Burns away and does not affect the powder melt composition after hatching of the powder substrate. Therefore, when the powder melt composition after hatching of the powder base material is 100% by mass, the powder melt composition after mixing is mixed with the powder melt composition after hatching. C. The mass is shown in%. As described in the lower part of Table 3, F in Table 3 is the total F concentration of fluorine contained in F compounds such as CaF ₂ , NaF, and AlF ₃ in the powder base material.

At the beginning of continuous casting of SUJ2 steel specified in JIS, front powder 1 which is a mixture of free carbon 2 and powder base material 3 schematically shown in FIG. 1, that is, the front shown in Invention Example 1 in Table 1 Powder (F compound represented by F: 6.0%, SiO ₂ : 46.4%, Al ₂ O ₃ : 11.2%, CaO: 27.9%, MgO: 5.3%, Na ₂ O + Li ₂ O: Made of a mixture of a powder base material made of 3.1% oxide and FC 2.5% mixed with 100% powder base material by mass%, with a viscosity of 1.1 Pa · s, Casting was started by charging 8 kg of a solidification temperature of 1030 ° C. and a slag formation rate of 60% into the mold. The front powder of Invention Example 1 has a slag conversion rate of 60%, and therefore satisfies the slag conversion rate of 40 to 90%, which is a condition for having the hatchability necessary for the front powder, and is also mass%. To mix with 100% powder base material. C. Is 2.5%, which is a condition for maintaining heat retention due to combustion heat generated by the front powder. C. 2-8% is satisfied, and since the viscosity is 1.1 Pa · s, the viscosity for satisfying the necessary lubricity for the front powder is 0.1 to 5.0 Pa · s. Yes. After the start of continuous casting of Invention Example 1 above, when continuous casting becomes steady, instead of the front powder in the present invention, main body powder 4 (F compound indicated by F) which is a mold powder for SUJ2 steel for steady use : 6.0%, SiO ₂ : 46.4%, Al ₂ O ₃ : 11.2%, CaO: 27.9%, MgO: 5.3%, Na ₂ O + Li ₂ O: 3.1% Mixed with 100% of powder base material by mass% with respect to 100% of powder base material: FC: 5.4%, viscosity 1.1 Pa · s, solidification temperature 1030 ° C., slag conversion rate 33% ) Was used to obtain a slab. These slabs were excellent in surface properties even in the early slabs, and excellent in surface properties that did not change from the slabs obtained after continuous casting became steady. In Table 1, as for the slab surface properties, the degree of slab defects was evaluated by magnetic particle flaw detection and grinder grinding for slabs that were discharged after casting and formed into cold ingots.

At the beginning of continuous casting of S15C steel specified in JIS, front powder 1 that is a mixture of free carbon 2 and powder base material 3 schematically shown in FIG. 1, that is, the front shown in Invention Example 2 in Table 2 Powder (F compound represented by F: 7.8%, SiO ₂ : 42.9%, Al ₂ O ₃ : 6.0%, CaO: 29.3%, MgO: 3.5%, Na ₂ O + Li ₂ O: Made of a mixture of a powder base material composed of 10.4% oxide and FC 3.0% mixed with 100% powder base material by mass%, with a viscosity of 0.4 Pa · s, Casting was started by charging 8 kg of a solidification temperature of 1110 ° C. and a slag conversion rate of 70% into the mold. Since the front powder of Invention Example 2 has a slag conversion rate of 70%, it satisfies the slag conversion rate of 40 to 90%, which is a condition for having the hatchability necessary for the front powder, and is also mass%. To mix with 100% powder base material. C. Is 3.0%, it is a condition for having heat retention due to combustion heat generation required for the front powder. C. 2-8% is satisfied, and furthermore, since the viscosity is 0.4 Pa · s, the viscosity for satisfying the necessary lubricity for the front powder is 0.1 to 5.0 Pa · s. Yes. After the start of continuous casting in Invention Example 2 above, when continuous casting becomes steady, instead of the front powder in the present invention, the main body powder 4 (F compound indicated by F) which is a mold powder for steady use for S15C steel : 7.8%, SiO ₂ : 42.9%, Al ₂ O ₃ : 6.0%, CaO: 29.3%, MgO: 3.5%, Na ₂ O + Li ₂ O: 10.4% (FC mixed with powder base material 100% by mass% with respect to powder base material 100%: 5.0%, viscosity 0.4 Pa · s, solidification temperature 1110 ° C., slag conversion rate 32%) The casting was continued using the slab to obtain a slab. These slabs were excellent in surface properties even in the early slabs, and excellent in surface properties that did not change from the slabs obtained after continuous casting became steady. In Table 2, the surface quality of the slab was evaluated by measuring the degree of slab defects by magnetic particle flaw detection and grinder grinding for a slab released as a cold ingot after casting.

At the beginning of continuous casting of the SCr420 steel specified in JIS, the front powder 1 which is a mixture of the free carbon 2 and the powder base material 3 schematically shown in FIG. 1, that is, the front shown in Invention Example 3 in Table 3 Powder (F compound represented by F: 3.3%, SiO ₂ : 48.6%, Al ₂ O ₃ : 13.2%, CaO: 28.6%, MgO: 1.2%, Na ₂ O + Li ₂ O: Made of a mixture of a powder base material made of 5.1% oxide and FC 3.5% mixed with 100% powder base material by mass%, with a viscosity of 2.3 Pa · s, Casting was started by charging 8 kg of a solidification temperature of 1100 ° C. and a slag conversion rate of 76% into a mold. Since the front powder of Invention Example 3 has a slag conversion rate of 76%, it satisfies the slag conversion rate of 40 to 90%, which is a condition for having the hatchability necessary for the front powder, and is also mass%. To mix with 100% powder base material. C. Is 3.5%, which is a condition for maintaining heat retention due to combustion heat generated by the front powder. C. 2-8% is satisfied, and furthermore, since the viscosity is 2.3 Pa · s, the viscosity 0.1 to 5.0 Pa · s, which is a condition for having the lubricity necessary for the front powder, is satisfied. ing. After the start of continuous casting in Invention Example 3 above, when continuous casting becomes steady, instead of the front powder in the present invention, body powder 4 (an F compound indicated by F) which is a mold powder for steady use for SCr420 steel : 3.3%, SiO ₂ : 48.6%, Al ₂ O ₃ : 13.2%, CaO: 28.0%, MgO: 1.2%, Na ₂ O + Li ₂ O: 5.1% Mixed with 100% of powder base material by mass% with respect to 100% of powder base material: FC: 7.0%, viscosity 2.3 Pa · s, coagulation temperature 1100 ° C., slag formation rate 15% ) Was used to obtain a slab. These slabs were excellent in surface properties even in the early slabs, and excellent in surface properties that did not change from the slabs obtained after continuous casting became steady. In Table 3, the surface property of the slab was evaluated for the degree of slab defects by magnetic particle flaw detection and grinder grinding for a slab discharged as a cold ingot after casting.

DESCRIPTION OF SYMBOLS 1 Front powder 2 Free carbon 3 Powder base material 4 Main body powder 5 Metal heating material and lower oxide oxidizing agent 6 Front powder in conventional technology

Claims (3)

In a method of continuously casting steel having a carbon content of 0.1% to 1.5% by mass, a powder base material comprising an oxide compound of Si, Al, Ca, Mg, Na, Li and an F compound The free carbon is composed of a mixture of free carbon and the mass of the powder base is 100%. When the powder base is 100%, the mass of the free carbon mixed with the powder base is 2 to 8% with respect to 100% of the powder base. A continuous casting of steel characterized by a casting method at the start of continuous casting by using a front powder having a viscosity of 0.1 to 5.0 Pa · s when held at 1300 ° C. for 5 minutes. Casting method. The casting method at the start of continuous casting by using the front powder is as follows when the front powder having a viscosity of 0.1 to 5.0 Pa · s when held at 1300 ° C. for 5 minutes is put into the mold: The continuous casting method by continuous casting of steel according to claim 1, wherein the casting method uses a front powder having a slag conversion rate of 40% to 90% represented by the formula (1).
Slag conversion rate (%) = {(mass of hatched front powder) / ( mass of mixture of hatched front powder and unhatched front powder)} × 100 (1)   The casting method using the front powder having a slag conversion rate of 40% to 90% shown in the formula (1) is different in only the content of the main body powder used in the steady state of continuous casting and the free carbon, and is used in the steady state. Using the main body powder with the same composition as the powder base material of the main body powder, casting at the start of casting continuously, then only the content of the front powder and free carbon is different, the composition of the powder base material is the same The continuous casting method by continuous casting of steel according to claim 2, wherein the casting at a normal time is continued using a certain mold powder.

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