JP2013049908A - Method for producing high-purity steel by electroslag remelting method - Google Patents

Abstract

The present invention proposes a method for producing high-purity steel capable of simultaneously achieving ultra-low sulfidation and ultra-low phosphatization.
In a method of melting a steel produced by a continuous casting method or an ingot-making method into a high-purity steel by remelting by an electroslag remelting method, the flux added at the time of remelting the electroslag and the slag at the time of melting Composition
_{CaO: 20~60mass%, Al 2 O} 3: 10~40mass%,
CaF _2: 20~60mass%, T. Fe (iron oxide): 1 to 10 mass%,
CaO / Al ₂ O ₃ : 1.0 to 6.0,
Adjust to.
[Selection figure] None

Description

  The present invention relates to a method for producing high-purity steel by applying an electroslag remelting method.

  High-purity steel has a low content of impurity elements such as carbon, silicon, manganese, phosphorus, and sulfur, and is widely used as an iron source for materials for special alloys that are materials for electrical and electronic parts.

  Among them, high-purity iron produced through a blast furnace using iron ore as a starting material-hot metal pretreatment-primary and secondary steel refining-continuous casting (ingoting) process is produced by electrolysis in an iron salt aqueous solution. Although the purity is lower than that produced, it can be produced at a low cost and in large quantities.

As a conventional technique for producing high-purity iron using iron ore, for example, Patent Document 1 discloses that, at the end of the deoxidation step, CaO is 44 to 62% by weight, Al ₂ O ₃ is 27 to 46% by weight, A CaO—Al ₂ O ₃ —SiO ₂ ternary flux containing SiO ₂ in the range of ₂ to 20% by weight is added onto the molten steel, and (T. A method is disclosed in which melting is completed while keeping Fe + MnO) at 3% by weight or less.

  Moreover, in patent document 2, the flux which added iron ore, calcium oxide, or many solvents was added in the molten iron which passed through the ironmaking and steelmaking processes, and it hold | maintains at the temperature of 1550-1680 degreeC by gas stirring, A method of subsequent refinement is disclosed.

JP-A-9-235611 JP-A-6-147567

  By the way, although the methods disclosed in Patent Document 1 and Patent Document 2 described above all have a certain reduction effect with respect to carbon, sulfur, and manganese, desulfurization requires refining, while desulfurization is required. Since phosphorus needs to be subjected to oxidative refining, in particular, phosphorus is only reduced to about 0.002 mass%, and it has been difficult to achieve both extremely low sulfidation and extremely low phosphatization.

  Therefore, an object of the present invention is to propose a method for producing high-purity steel capable of realizing ultra-low sulfidation and ultra-low phosphatization at the same time without adding extra steps.

The present invention, which was developed to overcome the above-mentioned problems of the prior art and achieve the above-mentioned object, is a high-purity steel that was produced by continuous casting or ingot-making by remelting by electroslag remelting. In the method of melting in steel, the composition of the flux added at the time of remelting the electroslag and the slag at the time of melting,
_{CaO: 20~60mass%, Al 2 O} 3: 10~40mass%,
CaF _2: 20~60mass%,
T.A. Fe: 1 to 10 mass%,
CaO / Al ₂ O ₃ : 1.0 to 6.0,
It is a method for melting high-purity steel by an electroslag remelting method, characterized in that it is adjusted.

In the high-purity and high-melting method having the above-described configuration,
1) The steel produced by the continuous casting or ingot-making method is subjected to hot metal pretreatment of one or more of desiliconization, demanganese, dephosphorization, and desulfurization for hot metal discharged from a blast furnace, and then a converter Decarburization, dephosphorization, and further vacuum degassing to decarburize until it becomes ultra-low carbon steel,
2) Steel obtained by remelting by the electroslag remelting method is
P: 0.0010 mass% or less, S: 0.0010 mass% or less,
Being
3) Remelting of steel produced by the continuous casting or ingot forming method is performed when the surface scale thickness is 0.5 mm or less,
4) adding 2.0 kg / ton or less of Al during the re-dissolution;
further,
5) The flux or slag contains 1.0 to 15.0 mass% SiO ₂ and CaO / SiO ₂ is 4.0 or more.
Is preferable as a specific means for solving the problem.

According to the present invention having the above configuration, the composition of the flux added at the time of remelting the electroslag and the slag at the time of melting is set to CaO.
_{: 20~60mass%, Al 2 O 3} : 10~40mass%,
CaF _2: 20~60mass%, T. Fe (iron oxide): 1 to 10 mass%, CaO / Al ₂ O ₃ : adjusted to 1.0 to 6.0 and redissolved, so both P and S concentrations are 0.0010 mass% or less Can be reduced.

  Further, according to the method for melting high-purity steel by electroslag remelting method according to the present invention, as the steel produced by continuous casting or ingot-making method, hot metal discharged from the blast furnace is desiliconized, demanganese, At least one of hot metal pretreatment of dephosphorization and desulfurization was performed, followed by decarburization and dephosphorization refining in a converter, and further decarburization treatment by vacuum degassing treatment to become ultra-low carbon steel Since steel is used, ultra-low sulfurization and ultra-low phosphorus can be simultaneously achieved without adding extra steps, and high-purity steel can be produced in large quantities at low cost.

  According to the present invention, it is possible to achieve extremely low phosphatization and extremely low sulfidation in which both the P concentration and the S concentration are 0.0010 mass% or less only by remelting by the electroslag remelting method.

  Further, according to the method for melting high-purity steel according to the electroslag remelting method of the present invention, the remelting of the steel produced by continuous casting or the ingot-making method is performed when the surface scale thickness is 0.5 mm or less. Therefore, the T.W. A significant increase in Fe can be avoided.

  Furthermore, according to the melting method of high purity steel by the electroslag remelting method according to the present invention, iron oxide in the slag can be reduced by adding 2.0 kg / ton or less of Al during remelting. In the slag. A significant increase in Fe can be prevented.

Further, according to the present invention, by a CaO / SiO ₂ of 4.0 or more by using a flux or slag containing SiO ₂ of 1.0～15.0Mass%, to increase the electrical resistance of the slag The steel ingot (electrode) can be efficiently remelted. This also reduces the melting point of the slag and stabilizes the dissolution rate of the electrode.

  In the present invention, as the steel used as an electrode in remelting by the electroslag remelting method, the hot metal discharged from the blast furnace is subjected to at least one hot metal pretreatment of desiliconization, demanganese, dephosphorization, and desulfurization. Then, decarburization and dephosphorization refining in a converter, and further, vacuum degassing treatment and decarburization treatment until becoming ultra low carbon steel (C: ≦ 0.0030 mass%, Si: ≦ 0) 0.02 mass%, Mn: ≦ 0.04 mass%, P: ≦ 0.0030 mass%, S: ≦ 0.0030 mass%, Al: ≦ 0.030 mass%, Cr: ≦ 0.02 mass%, Ni: ≦ 0.02 mass %, Cu: ≦ 0.02 mass%, Ti: ≦ 0.002 mass%, balance Fe and inevitable impurities).

  The above steel is made into a slab (steel ingot) by continuous casting or ingot forming method, then processed into an electrode and remelted by electroslag remelting method. The composition of the slag needs to be adjusted to an appropriate range.

In the present invention, in order to make the S concentration 0.0010 mass% or less, the concentration of CaO in the slag is 20 mass% or more, and CaO / Al ₂ O ₃ is 1.0 or more.

This is because when the concentration of CaO in the flux and slag is 20% or more and CaO / Al ₂ O ₃ is 1.0 or more, as shown in the reaction of the following formulas (1) and (2), This is because desulfurization with CaO proceeds and the S concentration in the steel can be lowered to an extremely low sulfur concentration of 0.0010 mass% or less.

[S] + (CaO) = (CaS) + [O] (1)
[S] + (O ²⁻ ) = (S ²⁻ ) + [O] (2)

Incidentally, for the above CaO, when the concentration is too high, the concentration of relatively CaF ₂ is reduced, the melting point of the slag is increased. As a result, the meltability of the slag is lowered and the fluidity is deteriorated, so that there is a concern that the cast surface of the steel ingot becomes worse (occurrence of uneven ripple marks). For this reason, in this invention, the density | concentration of CaO was made into the range of 20-60 mass%.

For Al ₂ O ₃ , the electrical resistance (ρ) necessary for causing the slag to generate Joule heat is secured, the melting point of the slag is lowered, the electrode dissolution rate is stabilized (stabilization of operation), and the desulfurization reaction is performed. It is an element useful for progressing, and for that purpose, its concentration needs to be 10 mass% or more.

On the other hand, when the concentration of Al ₂ O ₃ exceeds 40 mass%, the concentration of CaO is relatively decreased, the desulfurization reaction is decreased, and the melting point of slag is increased due to the decrease in the concentration of CaF ₂ , thereby reducing the meltability. As a result, the fluidity deteriorates, and the casting surface of the steel ingot is inevitably deteriorated (occurrence of uneven ripple marks).

Therefore, in the present invention, it was in the range of concentration of _Al 2 _{O 3} of 10~40mass%.

The CaF _2, reduction of the slag melting point, melt resistance, (uneven prevention of ripple marks due to the steel ingot casting surface is deteriorated) for improving the fluidity and the concentration of 20 mass% or more.

However, when the concentration exceeds 60 mass%, the desulfurization reaction is inhibited due to a relatively low CaO concentration, and the electrical resistance (ρ) decreases due to a decrease in Al ₂ O ₃ concentration and a decrease in CaO concentration. In addition, the amount of heat generated by the slag is insufficient and the dissolution rate becomes unstable (stable operation becomes difficult).

Therefore, in the present invention, the range of concentration of CaF ₂ of 20~60mass%.

T.A. Fe (iron oxide) is particularly important in reducing the phosphorus concentration in the steel. T.A. By containing Fe (iron oxide) in an amount of 1 mass% or more, a dephosphorization reaction as shown in the following formula (3) proceeds, and the P concentration can be reduced to an extremely low phosphorus concentration of 0.0010 mass% or less, Due to the presence of CaO in the slag, phosphorus oxide ions are stabilized as CaP ₂ O ₅ , and an increase in P concentration can be suppressed.

2 [P] +5 [O] +3 (O ²⁻ ) = 2 (PO ₄ ³ ) (3)

  In particular, T.W. By setting the content of Fe (iron oxide) to 3 mass% or more, the P concentration can be lowered to 0.0008 mass% or less.

The reduction effect is particularly remarkable when CaO / Al ₂ O _{3 is set} to 1.0 to 6.0, as in the case of extremely low sulfidation.

In the present invention, CaO / Al ₂ O ₃ was set to 6.0 or less because the flowability deteriorates due to the decrease in meltability of slag when the concentration of CaO increases, and the cast skin of the steel ingot On the other hand, if the concentration of Al ₂ O ₃ is too low, the required electric resistance (ρ) cannot be secured. Therefore, in the present invention, CaO / Al ₂ O ₃ was set to 6.0 or less.

  T. When Fe (iron oxide) is present in 1% by mass or more in the slag, vaporization desulfurization from the slag proceeds as shown in the following formula (4), so the S concentration in the slag decreases, This is the direction in which sulfur moves to the slag, which is advantageous in extremely low sulfidation.

_{^{(S 2-) + 3 / 2O}} 2 (g) = SO 2 (g) + (O 2-) ‥‥‥ (4)

In view of the above, blast furnace-hot metal pretreatment of one or more of desiliconization, demanganese, dephosphorization and desulfurization-decarburization and dephosphorization by converter-ultra-low carbon concentration by vacuum degassing-casting (continuous casting, obtained by Zokatamariho) per steel having the above _{composition, CaO: 20~60mass%, Al 2} O 3: 10~40mass% ,: 10~40mass%, CaF 2: 20~60mass% T. Fe (iron _{oxide): 1~10mass%, CaO / Al} 2 O 3: 1.0~6.0 flux is adjusted to a range of uses slag by remelting by electroslag remelting method, Ultra-low sulfur and ultra-low phosphorus high-purity steel in which the concentrations of sulfur and phosphorus are both 0.0010 mass% or less can be produced.

  In the present invention, the T.I. In order to prevent a significant increase in Fe (iron oxide), the surface scale should be removed from the steel (electrode) before remelting when performing electroslag remelting.

  In particular, when the scale thickness on the surface of the steel ingot (electrode) is 0.5 mm or less, the T.I. Fe (iron oxide) can be made 10 mass% or less.

  In addition, when redissolving, the iron oxide in the slag is reduced and T.P. From the viewpoint of preventing a significant increase in Fe (iron oxide), Al can be added.

When Al is added in excess of 2.0 kg / t, the casting surface of the steel ingot is poor due to the temperature drop of the molten steel pool, the increase in Al ₂ O _{3 in} the slag (Al ₂ O ₃ concentration is 40 mass) It is feared that this leads to an increase in Al in the steel ingot (the Al content exceeds 0.030 mass%). Therefore, the upper limit is preferably 2.0 kg / t, more preferably 1.0 kg / t or less.

Furthermore, in the present invention, in order to increase the electric resistance of the slag when the steel ingot is remelted, and to improve the fluidity (stabilization of the dissolution rate of the electrode) by lowering the melting point of the slag, The above flux and slag can contain SiO ₂ .

However, by incorporating SiO _2, because desulfurization reaction with CaO / SiO ₂ is less than 4.0 is lowered, the order to contain SiO _2, in the range of 1.0 to 15.0 It is important to add CaO / SiO ₂ to 4.0 or more.

  The hot metal discharged from the blast furnace is subjected to desiliconization, dephosphorization, and desulfurization by hot metal pretreatment, Si concentration is 0.020 to 0.040 mass%, Mn concentration is 0.05 to 0.15 mass%, and P concentration is 0. 0.020 to 0.040 mass%, S concentration to 0.0010 to 0.0030 mass%, decarburization and dephosphorization in converter, C concentration to 0.015 to 0.045 mass%, Si concentration to 0 A molten steel having a Mn concentration of 0.02 to 0.04 mass%, a P concentration of 0.0010 to 0.0030 mass%, and an S concentration of 0.0015 to 0.0030 mass% was melted by 200 t.

  And after taking out the obtained molten steel to a ladle, about some molten steel, after adding CaO containing flux for anti-phosphorus and anti-sulfur prevention, it is extremely low carbon by RH type vacuum degassing treatment. Decarburization treatment was carried out to a concentration, so that the C concentration was 0.0015 mass% or less and the N concentration was 0.0030 mass% or less.

  And after that, about some of the said molten steel, Al was added in 0.030 mass% or less in order to reduce oxygen concentration to 0.0200 mass% or less.

  In addition, for some of the molten steel produced from the converter, slag removal, CaO-containing flux, addition of Al, anti-reversion and desulfurization treatment by molten steel heat treatment (LF), Decarburization treatment is performed to an extremely low carbon concentration by RH vacuum degassing treatment and oxygen supply treatment into the vacuum chamber, C concentration is 0.0030 mass% or less, S concentration is 0.0030 mass% or less, and N concentration is 0. .0030 mass% or less, and in some of them, Al was reduced in a range of 0.030 mass% or less in order to reduce the oxygen concentration to 0.0100 mass% or less.

  Next, using each molten steel processed through the above steps, a size of 300 × 400 mm (continuous casting) with the component composition shown in Table 1-1 and Table 1-2 by continuous casting and ingot forming methods. Method), and a steel piece (steel ingot) having a diameter of 450 mm (ingot making method) was produced.

Table 1-1

Table 1-2

  Next, the obtained steel slab (steel ingot) is processed into an electrode for electroslag remelting (for melting 6 ton) (including one having a surface scale thickness of 0.5 mm or less), and then a voltage of 60 to 90 V. Under the conditions of current of 10 to 15A, remelting treatment was performed using fluxes (slag before remelting, slag before remelting) as shown in Table 1-1 and Table 1-2 with various compositions changed, and the diameter was 610 mm. A steel ingot was produced.

  During remelting, Ar gas was introduced into the mold. Moreover, about some steel ingots, Al was added in the mold during remelting.

The analysis results of the components in the bottom part (center part of the length direction 10% from the lower end) and top part (center part of the length direction 10% from the upper end) of the obtained steel ingot (steel ingot after remelting) Tables 2-1 and 2-2 together with the presence / absence of electrode scale removal, the unit rate of addition of Al during remelting (kg / ton), and the steel ingot cast surface state are also shown.

Table 2-1

Table 2-2

  As is clear from Tables 2-1 and 2-2, the steels manufactured according to the present invention (Example Nos. 1 to 16) have an S concentration of 0.0010 mass% or less and a P concentration of It was 0.0010 mass% or less.

  On the other hand, in the steel (Comparative Examples Nos. 17 to 26) remelted using a flux that does not satisfy the composition defined in the present invention, and slag at the time of melting (slag before remelting, slag after remelting) It was confirmed that the effects as expected were not achieved.

  Moreover, in the remelting of the steel of the comparative example, it was recognized that the operation was unstable and the casting surface of the steel ingot deteriorated.

  According to the present invention, it has become possible to simultaneously achieve extremely low sulfuration and extremely low phosphorus by adjusting the composition of flux and slag used in remelting steel to which the electroslag remelting method is applied. .

  According to the present invention, a blast furnace—a hot metal pretreatment of one or more of desiliconization, demanganese, dephosphorization, and desulfurization—decarburization by a converter, dephosphorization—extremely low carbon concentration by vacuum degassing—casting ( High-purity steel with both P and S being 0.0010 mass% or less can be manufactured in large quantities at low cost simply by remelting the steel obtained by the continuous casting method and the ingot-making method by the electroslag remelting method. .

Claims (6)

In the method of melting the steel produced by the continuous casting method or the ingot-making method into the high purity steel by remelting by the electroslag remelting method,
The composition of the flux added at the time of remelting the electroslag and the slag at the time of melting,
_{CaO: 20~60mass%, Al 2 O} 3: 10~40mass%,
CaF _2: 20~60mass%, T. Fe (iron oxide): 1 to 10 mass%,
CaO / Al ₂ O ₃ : 1.0 to 6.0,
A method for producing high-purity steel by electroslag remelting, characterized by adjusting to the above.   The steel produced by the continuous casting or ingot-making method is subjected to hot metal pretreatment of one or more of desiliconization, demanganese, dephosphorization, and desulfurization for the hot metal discharged from the blast furnace, and then degassed in the converter. The high-purity steel by electroslag remelting according to claim 1, characterized in that the steel is decarburized through charcoal and dephosphorization and further decarburized by vacuum degassing. Method of melting. Steel obtained by remelting by the electroslag remelting method is
P: 0.0010 mass% or less, S: 0.0010 mass% or less,
The method for producing high-purity steel by electro-remelting method according to claim 1 or 2, wherein:   4. The electroslag remelting method according to claim 1, wherein remelting of the steel produced by the continuous casting or ingot forming method is performed when the surface scale thickness is 0.5 mm or less. 5. A method for melting high-purity steel.   5. The method for melting high-purity steel by electroslag remelting according to claim 1, wherein 2.0 kg / ton or less of Al is added during the remelting. The flux or slag, containing SiO ₂ of 1.0～15.0Mass%, to any one of claims 1 to 5 CaO / SiO ₂ is equal to or is made to 4.0 or higher A method for producing high-purity steel by the electroslag remelting method described.