JP5368843B2 - Manufacturing method of high cleanliness steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease oxide-based inclusions while keeping a specification range for a component of a steel material as much as possible. <P>SOLUTION: In a process of manufacturing a high-cleanliness steel by melting a steel material 5 with an electron beam 2, this manufacturing method includes controlling the [C] in the steel material 5 to 0.03 mass% or more, an electric power supplied to the electron beam 2 to 4-10 kWh/kg by an electric power consumption rate, a degree of vacuum in melting to 1&times;10<SP>-3</SP>Torr or less, and the value of the electric power consumption rate/surface area of molten steel to 0.015 kWh/kg&times;cm<SP>2</SP>or more, when melting the steel material 5 with the electron beam 2. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for producing high cleanliness steel.

Conventionally, it is desirable that high cleanliness steel used for bearing steels and spring steels contain as little inclusions as possible, mainly oxide inclusions (for example, Al ₂ O ₃ ). Therefore, in the secondary refining, the oxide inclusions contained in the steel are reduced by reducing and decomposing the oxide inclusions contained in the molten steel or by flotation separation.
In this way, high purity steel required by users is manufactured by reducing oxide inclusions in secondary refining, but in recent years, more oxide inclusions than in the past have been produced. Less high cleanliness steel has been sought. Therefore, various methods for producing high cleanliness steel with very few oxide inclusions have been developed in response to such user demands (Patent Documents 1 and 2).

Patent document 1 is a method of reducing oxide inclusions by melting a steel material cast by a casting process performed after secondary refining with an electron beam, and is obtained from an electron beam output and a melting rate. The composition of the melting material to be used for electron beam melting is that the energy is 1.0 × 10 ³ kcal / kg or more, the dissolution vacuum is 1 × 10 ⁻³ Torr or less, the dissolution pool surface area is 200 cm ² or more, and C] ≧ 0.03%, [Al] ≦ 0.005%, and [S] ≦ 0.01%.
Patent Document 2 discloses that a rod-shaped melted base material that advances horizontally from the rear of the rectangular dish-shaped copper water-cooled refining vessel is continuously melted by irradiating it with an electron beam from above. Of the type that is passed through the tunnel type cough provided in front of the smelting vessel and flows out from the outflow hole at the front end of the smelting vessel to the vertical water-cooled copper mold provided below the smelting vessel. In the electron beam melting method, bearing steel that does not contain Mn in excess of 0.20% is used as a base material, and the relationship between the dimensions of the refining vessel, the position of the cough, and the melting rate satisfies a predetermined condition. ing.

JP 2006-233254 A JP 2003-171714 A

When the techniques of Patent Document 1 and Patent Document 2 are used, oxide inclusions can be reduced, but in most steel materials, for example, there is a problem that Mn deviates from a required standard value.
Then, an object of this invention is to provide the manufacturing method of the high cleanliness steel which can reduce an oxide type inclusion, without removing the specification range of the component of steel materials as much as possible.

In order to achieve the above object, the present invention has taken the following measures.
That is, the present invention provides a method for producing a high cleanliness steel by melting a steel material with an electron beam. When the steel material with [C] of 0.03% by mass or more is melted with an electron beam, the electron beam The electric power supplied to the electric power unit is 4 to 10 kWh / kg in terms of electric power unit, the degree of melting vacuum is 1 × 10 ⁻³ Torr or less, and the relationship between the electric power basic unit and the molten steel surface area in the molten meniscus is expressed by the formula (1) The point is to satisfy.

  According to the present invention, oxide inclusions can be reduced without removing the standard range of the components of steel materials as much as possible.

It is the schematic of an electron beam melting apparatus.

The manufacturing method of the high cleanliness steel of this invention is demonstrated.
In the method for producing a high cleanliness steel according to the present invention, first, decarburization refining (primary refining) of molten steel is performed in a converter, and then molten steel is secondarily refined by a secondary refining apparatus such as an LF apparatus, a CAS apparatus, or an RH apparatus. Remove oxide inclusions and adjust components (secondary refining). And in the manufacturing method of high cleanliness steel, the molten steel after secondary refining is cast with a continuous casting device (continuous casting), the cast steel material is melted with an electron beam melting device, and the oxide in the steel material System inclusions are removed.
FIG. 1 shows a schematic diagram of an electron beam melting apparatus.

As shown in FIG. 1, an electron beam melting apparatus 1 includes a cathode chamber 3 that irradiates an electron beam 2, an intermediate chamber 4 that is connected to the cathode chamber 3 and through which the irradiated electron beam 2 passes, and this intermediate chamber. 4 is provided with a melting chamber 6 in which the electron beam 2 irradiated through 4 enters and melts the steel material 5. Although not shown, an irradiation device for irradiating the electron beam 2 toward the melting chamber 6 is installed in the cathode chamber 3. The cathode chamber 3 and the intermediate chamber 4 may be integrated.
The intermediate chamber 4 and the melting chamber 6 are formed with an exhaust port 7 for evacuating and the like, and evacuating through the exhaust port 7 communicates with the intermediate chamber 4, the melting chamber 6 and the intermediate chamber 4. The cathode chamber 3 is also at a predetermined degree of vacuum.

The melting chamber 6 is provided with a supply device 8 for supplying a melting steel material (sometimes referred to as a melting base material) 5 a, and the melting base material 5 a supplied from the supply device 8 into the melting chamber 6 is provided. On the other hand, by irradiating the electron beam 2, the base material 5a for melting is melted.
Further, the melting chamber 6 is provided with a mold 9 made of water-cooled copper to make the steel 5b from which the oxide inclusions have been removed by cooling again the molten steel 11 when the melting base material 5a is melted. The steel material (ingot) 5 b cooled by 9 is drawn out at a predetermined speed by the drawing device 10.

In order to melt the melting base material 5a by the electron beam melting apparatus 1 and remove the oxide inclusions in the steel material 5, first, the cathode chamber 3, the intermediate chamber 4 and the melting chamber 6 are evacuated. Thus, a predetermined degree of vacuum is obtained. Further, the melting base material 5a is supplied to the melting chamber 6 by the supply device 8, and the electron beam 2 is irradiated to the melting base material 5a.
Then, the molten solution (molten steel 11) is received by the mold 9 and cooled to form an ingot 5b. At this time, the solution (molten steel 11) contained in the mold 9 is also irradiated with the electron beam 2 separately from the melting base material 5a to bring the molten steel 11 on the upper surface side of the mold 9 into a molten state. In other words, the electron beam melting apparatus 1 can perform the drip melt method in the electron beam melting method, and the steel material 5 is melted and solidified by the apparatus, whereby the oxide inclusions in the steel material 5 are obtained. Can be removed. Note that the present invention is not limited to the electron beam melting apparatus 1 shown in FIG.

Hereafter, the manufacturing method which manufactures the high cleanliness steel of this invention is demonstrated in detail.
The target steel in the manufacturing method of high cleanliness steel of this invention is steel for bearings, steel for springs, etc.
Specifically, C: 0.03-1.1 mass%, Si: 0.15-0.70 mass%, Mn: 1.2 mass% or less (excluding 0%), Cr: 0.9 It is intended for the steel material 5 containing ˜1.6 mass%, N: 0.002 to 0.02 mass%, and the balance containing Fe and inevitable impurities.
Here, considering the mechanism for removing the oxide inclusions of the steel material 5 by melting the melting base material 5a with an electron beam, oxide inclusions (Al ₂ O ₃ , SiO ₂ , MnO, MgO [O] generated by reduction of an oxide such as Al ₂ O ₃ , SiO ₂ , MnO, MgO, etc.) is combined with [C] in the molten steel 11 to produce CO gas. There is a reductive decomposition reaction of removing out of the system.

  This reductive decomposition reaction is represented by the formula (a), and the reaction equilibrium constant is represented by the formula (b).

As shown in the formulas (a) and (b), the higher the [C] of the steel material (dissolving base material) 5a before melting, the more the reductive decomposition reaction is promoted, and the [O] in the molten steel 11 after melting is increased. Since it can be reduced, the concentration of [C] in the steel material (melting base material) 5a before melting needs to be increased to some extent.
Therefore, according to the present invention, when the melting base material 5a is melted by the electron beam 2, the [C] of the melting base material 5a is set to 0.03% by mass or more.
As a result of various experiments, when [C] of the dissolving base material 5a is 0.03% by mass or more, the reductive decomposition reaction can be promoted, and oxide inclusions can be sufficiently removed. On the other hand, when [C] of the base material 5a for melting is less than 0.03% by mass, the reductive decomposition reaction does not proceed sufficiently, and many oxide inclusions remain in the steel material 5b after melting. become.

  In the present invention, as a result of various experiments, the power (supply power) supplied to the electron beam 2 is 4 to 10 kWh / kg in terms of the power unit. This electric power consumption is the supplied electric power (input electric power) per hour converted to 1 kg of the melting steel material (dissolving base material) 5a, and is calculated by the equation (c).

In the formula (c), E represents the power consumption unit (kWh / kg), P represents the supplied power (kW), and V represents the melting rate (kg / h) of the steel material (base material for melting) 5a. The supplied power is power supplied to the electron beam 2 irradiation device. In other words, the supplied power is a combination of the power of the first electron beam 2 irradiated to melt the melting base material 5a and the power of the second beam irradiated to the molten steel 11 dropped on the mold 9. .
If the supply power supplied to the electron beam 2 is less than 4 kWh / kg in terms of power unit, the power is too weak, and the molten steel temperature of the molten steel 11 in the mold 9 is low. Thus, when the molten steel temperature is low, oxide inclusions exist stably, so that the reductive decomposition reaction is not sufficiently promoted, and many oxide inclusions remain in the steel material 5b after melting. become.

On the other hand, when the supply power supplied to the electron beam 2 is 4 kWh / kg or more in terms of the power unit, the power is strong and the molten steel temperature is high. Therefore, the decomposition reaction of the oxide inclusions is promoted, and the oxide inclusions can be sufficiently removed.
However, if the supply power supplied to the electron beam 2 exceeds 10 kWh / kg in terms of power unit, the amount of evaporation of components such as Mn, Cr, and N contained in the molten steel 11 is too large and the amount of evaporation is saturated. The relationship between the supplied power and the evaporation amount deviates from the predetermined relationship.
Further, when the power supply exceeds 10 kWh / kg in terms of the power unit, the energy supplied to the molten steel 11 is localized and the concentration segregation inside the mold 9 increases, and there is a direct proportional relationship between the power supply and the evaporation amount. It will come off. As a result, after removing oxide inclusions, the component value contained in the steel material 5b after melting changes significantly, and the hit ratio of the component decreases.

Therefore, in order to sufficiently remove the oxide inclusions by promoting the reductive decomposition reaction while keeping the components in the steel material 5b after melting within the range of the standard component values, the power supplied to the electron beam 2 is It is necessary to set it to 4-10 kWh / kg in an electric power basic unit.
Further, in the present invention, as a result of various experiments, the degree of dissolution vacuum is set to 1 × 10 ⁻³ Torr or less. The melting degree of vacuum is the degree of vacuum in the cathode chamber 3, the intermediate chamber 4 and the melting chamber 6.
If the degree of dissolution vacuum is larger than 1 × 10 ⁻³ Torr and the degree of vacuum is small, as shown in the formula (b), the partial pressure of CO becomes high and the reductive decomposition reaction becomes difficult. Will remain.

On the other hand, if the degree of dissolution vacuum is 1 × 10 ⁻³ Torr or less, the partial pressure of CO becomes very low, the reductive decomposition reaction easily proceeds, and oxide inclusions can be sufficiently removed.
Furthermore, in the present invention, the power supplied to the electron beam 2 is set in the above-described range, and the relationship between the power unit and the molten steel surface area in the molten meniscus in the molten steel material 5 satisfies the formula (1). Yes. That is, the molten steel surface area is the surface area of the molten metal surface on the upper surface side of the mold 9.

The removal of oxide inclusions in the steel material 5 by the electron beam 2 is a floating removal (levitation) in which the oxide inclusions in the molten molten steel 11 are levitated and removed in addition to the above-described reductive decomposition reaction. There is also separation). The floating separation of the oxide inclusions irradiates the molten steel 11 in the mold 9 with the electron beam 2 and delays the solidification of the molten steel 11 in the mold 9 to form a molten pool (molten steel pool). By doing that.
When the relationship between the power consumption rate and the molten steel surface area does not satisfy the formula (1), and the value obtained by dividing the power consumption rate by the molten steel surface area (power consumption rate per unit area) is smaller than 0.015 kWh / kg · cm ² The depth of the molten steel pool in the mold 9 becomes shallow. In other words, when the relationship between the power intensity and the molten steel surface area does not satisfy the formula (1), when the steel material 5 is melted and dipped in the mold 9, the molten steel 11 dripped in the mold 9 immediately solidifies, It becomes a state where the floating time of the oxide inclusions by the molten steel pool cannot be obtained sufficiently.

Therefore, when the relationship between the power unit and the molten steel surface area does not satisfy the formula (1), the molten steel 11 is solidified before the oxide inclusions in the molten steel 11 float in the mold 9. As a result, oxide inclusions remain.
On the other hand, when the relationship between the power unit and the molten steel surface area satisfies the formula (1), solidification of the molten steel 11 drip into the mold 9 can be delayed to ensure the floating time of the oxide inclusions. Therefore, the oxide inclusions in the molten steel 11 can be sufficiently raised.
As described above, according to the present invention, when the steel material 5 is melted by the electron beam 2, the [C] of the steel material 5 is set to 0.03% by mass or more, and the power supplied to the electron beam 2 is 4 in terms of the power unit. 10 kWh / kg, the degree of dissolution vacuum is 1 × 10 ⁻³ Torr or less, and the relationship between the electric power consumption and the molten steel surface area of the molten steel material 5 satisfies the formula (1), and the oxide in the steel material 5 System inclusions are sufficiently removed.

  Table 1 summarizes the examples produced by the production method for producing the high cleanliness steel of the present invention and the comparative examples produced by a method different from the present invention.

  In Examples 1 to 4 and Comparative Examples 5 to 8, the melting base material 5a subjected to electron beam melting was C: 1.0% by mass, Si: 0.26% by mass, Mn: 0.35% by mass. , Cr: 1.4% by mass, N: 0.006% by mass, and the same dissolving base material composed of the remaining Fe and inevitable impurities was used. In Comparative Example 9, the melting base material 5a subjected to electron beam melting was C: 0.02 mass%, Si: 0.26 mass%, Mn: 0.35 mass%, Cr: 1.4 mass%, N: A melting base material containing 0.006% by mass and comprising the balance Fe and inevitable impurities was used.

Before carrying out the examples and comparative examples, in order to know the evaporation status of various components, the evaporation rate coefficient K _X of each component was evaluated. The evaporation rate coefficient K _X was obtained under the conditions shown in Table 2.

Here, the base material 5a for dissolution in determining the evaporation rate coefficient K _X is C: 1.0 mass%, Si: 0.26 mass%, Mn: 0.35 mass%, Cr: 1.4 mass%. , N: 0.006% by mass and the balance including Fe and unavoidable impurities. In the component analysis of the melting base material 5a before melting and the steel material 5b after electron beam melting, the C amount is determined by the “combustion infrared absorption method”, and the Si amount, Mn amount, and Cr amount are determined by “ICP emission spectroscopy analysis”. The amount of N was measured by the “inert gas melting thermal conductivity method”.
When obtaining the evaporation rate coefficient K _X of various components, the concentration of the component X (X = C, Si, Mn, Cr, N) of the melting base material 5a before melting is C _Xb0, and the steel material 5b after melting is melted. When the concentration of the component X (X = C, Si, Mn, Cr, N) is C _Xa0 , it is obtained by the equation (2).

When the evaporation rate coefficient K _X was obtained, it was as shown in Table 3.

In Examples and Comparative Examples, the hit ratio of each component was determined using the evaporation rate coefficient K _x of each component. Specifically, in Examples and Comparative Examples, the concentration of the component X (X = C, Si, Mn, Cr, N) of the melting base material 5a before melting is C _Xb, and the components of the steel material 5b after melting With the concentration of X (X = C, Si, Mn, Cr, N) as C _Xa , the hit ratios of various components were determined by Equation (3).

In the examples and comparative examples, evaluations were made with the hit ratios of various components determined by the above-described method being 90% or more as good “◯” and those with less than 90% as bad “×”. went. In addition, in the Example and comparative example which were shown in Table 1, the thing with the lowest hit ratio of a component is shown among various components. Further, in the evaluation of the hit ratio of various components, since the hit ratio is generally 90%, it can be used industrially, so that value was used as a reference value.
In Examples and Comparative Examples, “JXA-8500F” manufactured by JEOL Ltd. was used, and all oxides contained in an arbitrary measurement region (100 mm ² ) of the steel material 5b after melting were converted to EPMA (Electron Probe Micro -Analysis) was performed by elemental analysis. In the examples and comparative examples, in the measurement region (100 mm ² ), the case where there are no oxide inclusions of 15 μm or more is evaluated as “good”, and the case where there is one or more is evaluated as “bad”. did. Here, in the evaluation of oxide inclusions, the size of oxide inclusions was set to 15 μm in consideration of the general industrial applicability.

As shown in Example 1 to Example 4, when the steel material (dissolving base material) 5a is melted by the electron beam 2, the [C] of the steel material (dissolving base material) 5a is 0.03% by mass or more, The electric power supplied to the electron beam 2 is 4 to 10 kWh / kg in terms of power unit, the degree of melting vacuum is 1 × 10 ⁻³ Torr or less, and the relationship between the power unit and the molten steel surface area of the molten steel 5 is expressed by the formula (1 ), The steel material 5b after melting has no oxide inclusions with a size of 15 μm or more, and a component median ratio of 90% or more can be secured. That is, in Examples 1 to 4, the oxide inclusions can be reduced without removing the standard range of the components of the steel material 5 as much as possible.

On the other hand, in Comparative Example 5, the supply power supplied to the electron beam 2 exceeded 10 kWh / kg in terms of the electric power unit, so that the oxide inclusions having a size of 15 μm or more could be eliminated in the steel material 5b after melting. Although it was made, the component middle ratio could not be made 90% or more.
In Comparative Example 6, since the supply power supplied to the electron beam 2 was less than 4 kWh / kg in terms of the power unit, the component median ratio could be 90% or more, but the oxide having a size of 15 μm or more System inclusions could not be eliminated.
In Comparative Example 7, since the degree of dissolution vacuum was higher than 1 × 10 ⁻³ Torr, the component median ratio could be increased to 90% or more, but the oxide inclusions having a size of 15 μm or more were eliminated. I couldn't.

In Comparative Example 8, the value of power intensity / molten steel surface area was smaller than 0.015 kWh / kg · cm ² and did not satisfy the formula (1). The oxide inclusions having a size of 15 μm or more could not be eliminated.
In Comparative Example 9, [C] of the steel material (dissolving base material) 5a was less than 0.03% by mass, so that the component middle ratio could be 90% or more, but the size was 15 μm or more. The oxide inclusions could not be eliminated.
Comparative Example 10 shows the number of oxide inclusions in SUJ2 (mass production steel) shown in JIS standards. The steel material 5 of SUJ2 is said to have the smallest oxide inclusions in the JIS standard. Even if compared with this steel material 5, the steel material 5 manufactured according to the present invention is an oxide inclusion. It can be seen that the number of is very small.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Electron beam melting apparatus 2 Electron beam 3 Cathode chamber 4 Intermediate chamber 5 Steel material 5a Steel material before melting (base material for melting)
5b Steel material 6 after melting 6 Melting chamber 7 Exhaust port 8 Feeder 9 Mold 10 Pulling device 11 Molten steel

Claims (1)

In a manufacturing method for manufacturing a high cleanliness steel by melting a steel material by an electron beam,
When a steel material having [C] of 0.03% by mass or more is melted by an electron beam, the electric power supplied to the electron beam is 4 to 10 kWh / kg in terms of the power unit, and the melting vacuum is 1 × 10 ⁻³ Torr. A method for producing a high cleanliness steel, characterized in that the relationship between the power unit and the molten steel surface area in the molten meniscus satisfies the formula (1).

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