JP6982795B2 - Manufacturing method of boron-containing stainless steel - Google Patents

Description

The present invention _{relates to a method for producing a boron-containing stainless steel by a secondary melting method using slag containing at least Al 2} O ₃ and a consumable electrode, and particularly to improve high-temperature mechanical strength by using fine particles of BN (boron nitride). The present invention relates to a method for producing a possible boron-containing stainless steel.

In the secondary melting method of steel by the ESR (Electro-Slag Remelting) method using slag and consumable electrode, the drops generated at the lower end of the consumable electrode fall in the slag and solidify through the metal pool to form a steel ingot. do. That is, the composition of the ingot can be adjusted by controlling the metal-slag reaction in the slag.

For example, in Patent Document 1, in a method for producing heat-resistant steel containing Ti and Al by the ESR method, in order to suppress fluctuations in the components of Ti and Al by adjusting the component composition of slag and obtain an ingot with less component segregation. The manufacturing method to be carried out is disclosed. The slag is an Al ₂ O _3- CaO (quick lime) -CaF ₂ (fluorite) system, and CaF ₂ is given 5% ≤ Al ₂ O ₃ ≤ 30% and CaO ≤ 15% by mass. Further, it has a composition given 1% ≤ TiO _{2 ≤ 15%.} Thereby, the balance between Ti and Al in the consumable electrode _{and TiO 2} and Al ₂ O _{3 in} the slag can be controlled. The target steel has a component composition containing 0.5% ≤ Ti ≤ 5.0% and 0.1% ≤ Al ≤ 2.0% in mass%.

Similarly, it has been proposed to adjust the component composition of slag in the method for producing B-containing steel by the ESR method.

For example, in Patent Document 2, in the method for producing heat-resistant steel containing B by the ESR method, the components of SiO ₂ and B ₂ O _{3 in} the slag are adjusted according to the components of Si and B of the consumable electrode. Discloses a method for producing a heat-resistant steel that controls the amount of the component B in the component composition of the molten steel. The slag used in such a production method is Al ₂ O _3- CaO-CaF ₂ provided with B ₂ O _{3 together with SiO 2} as a flux. Here, between the molten steel component and the slag component,
3 (SiO ₂ ) + 4B = 2 (B ₂ O ₃ ) + 3Si
In the _{presence of SiO 2} , B is oxidized to cause component segregation and deviation from the target component value. Therefore, _{by adjusting the component amounts of SiO 2} and B ₂ O _{3 in} the slag so as to satisfy a predetermined formula, the balance of both sides of the above reaction formula is controlled and the component amount of B in the molten steel is controlled. There is.

Japanese Unexamined Patent Publication No. 2012-241230 Japanese Unexamined Patent Publication No. 2001-11546

A heat-resistant steel containing B, which is provided with improved high-temperature mechanical strength such as creep by utilizing fine particles of BN, is known. In such heat-resistant steel, metal with Al ₂ O ₃ -CaO-CaF ₂ slag as described above - in the slag reaction, not only the oxide of B, it is also necessary to consider nitride. Here, in particular, since Al also forms a nitride as well as an oxide, it can change the precipitation state of fine particles of BN and affect the high-temperature mechanical strength. Therefore, in particular, heat-resistant steel with a reduced amount of Al has been proposed, and consideration is given to reducing _{Al 2} O _{3 in the slag accordingly.} However, _{by reducing the amount of Al 2} O ₃ in the slag, the specific resistance of the slag becomes small, the power consumption in the secondary melting method increases, and the melting of the consumable electrode may become difficult. This situation can be particularly problematic when trying to obtain large ingots.

The present invention was made in view of such circumstances, it is an object of the boron-containing stainless by secondary dissolved with slag and consumable electrode containing Al ₂ O ₃ in order to suppress the decrease of specific resistance It is an object of the present invention to provide a method for producing a boron-containing stainless steel which can improve the high-temperature mechanical strength in consideration of the slag component which affects the precipitation of BN particles in the method for producing steel.

The method for producing a boron-containing stainless steel according to the present invention contains at least C: 0.08 to 0.40% and Cr: 8 to 14% in mass%, and B: 0. together while containing from 0010 to 0.0300%, secondary dissolution using slag and consumable electrode comprising at least _Al 2 _{O 3} to obtain a boron-containing stainless steel of the chemical composition that suppresses Al below 0.01% a manufacturing method according to the law, the slag, by _{mass%, CaO: 20~40%, Al} 2 O 3: 20~40, SiO 2: with containing 6~15%, _B 2 _{O 3} as an additive Can be contained in an amount of 2% or less, and is characterized by _{having a balance CaF 2 and unavoidable impurities.}

_{According to such an invention, although it is an Al 2} O _3- CaO-CaF ₂ system slag containing a certain amount _{of Al 2} O ₃ so as to suppress a decrease in resistivity, the amount of Al in steel that can compete with BN in nitriding. It provides a boron-containing stainless steel capable of optimizing the amount of B capable of forming BN by suppressing the slag, and precipitating BN fine particles to improve high-temperature mechanical strength.

In the above-mentioned invention, the consumable electrode has C: 0.08 to 0.40%, Cr: 8 to 14%, Ni: 2.5% or less, V: 0.1 to 0.3% in mass%. , Co: 0.5 to 3.5%, Nb: 0.03 to 0.10%, B: 0.0010 to 0.0300%, and N: 0.0100 to 0.0500%. It may be characterized by having a component composition in which the remaining Fe and unavoidable impurities are used, and the contents of Al and Si are suppressed to 0.010% or less and 0.10% or less, respectively. According to such an invention, it is possible to reliably provide a boron-containing stainless steel capable of optimizing the amount of B within the range of the above-mentioned slag component and, as a result, improving the temperature lowering mechanical strength.

In the above invention, the mass% of the component M in the consumable electrode is [% M], the mole fraction of the content Q in the slag is {mfQ}, and the slag is Y = log ([% B]. ⁴ / [% Si] ³ ) If X = log ({mfB ₂ O ₃ } ² / {mfSiO ₂ } ³ ), the component composition within the range of -5.1 ≤ Y-X ≤ -4.6 It may be characterized by having. According to such an invention, a boron-containing stainless steel capable of further optimizing the obtained amount of B and improving the high-temperature mechanical strength is surely provided.

It is a list of the component composition of the steel grade used for the consumable electrode. It is a list of the content of Si and B of the consumable electrode and the composition of slag. It is a table of the value of X, Y, YX, the variation of B in the obtained steel ingot, and the content of Al. It is a graph which plotted X and Y.

A method for producing a boron-containing stainless steel, which is one embodiment of the present invention, will be described in detail with reference to FIG.

In this example, the boron-containing stainless steel to be obtained contains at least C: 0.08 to 0.40% and Cr: 8 to 14% in mass%. Further, by containing B at 0.0010 to 0.0300% and suppressing Al to 0.01% or less, B is distributed in the steel ingot, and BN fine particles are precipitated at the grain boundaries in the subsequent treatment. It is intended to be obtained and to have excellent high temperature mechanical strength such as creep resistance.

Such steel can be produced by a secondary melting method such as ESR (electroslag remelting) using a consumable electrode and slag. The secondary dissolution is preferably carried out in an atmosphere in which argon, nitrogen or the like is adjusted based on an inert gas or vacuum.

Here, as shown in FIG. 1, as the material of the consumable electrode, for example, steel having four kinds of component compositions of steel grades A to D can be used. The composition of steel used as a material for the consumable electrode that can be used in this example is C: 0.08 to 0.40%, Ni: 2.5% or less, Cr: 8 to 14% in mass%. , V: 0.1 to 0.3%, Co: 0.5 to 3.5%, Nb: 0.03 to 0.10%, B: 0.0010 to 0.0300%, N: 0.0100 It is preferably contained as ~ 0.0500%, and the Al content is controlled to 0.01% or less and the Si content is controlled to 0.10% or less. Further, these steels may contain P, S, Cu, Pb, As, Sn, Sb, Ti, O, H and the like as unavoidable impurities.

On the other hand, the slag is a slag _{containing at least Al 2} O _{3 in} order to suppress a decrease in specific resistance, and is CaO: 20 to 40%, Al ₂ O ₃ : 20 to 40%, SiO ₂ : 6 in mass%. 15%, an _{Al 2 O} 3 -CaO-CaF 2 slag having a composition with the remainder CaF _2. By setting such a composition range, the decrease in the electric resistance value in the secondary melting is suppressed, and the metal-slag reaction between the molten metal from the consumable electrode and the slag is balanced, and the amount of Al in the metal pool is suppressed. can. By suppressing the amount of Al, the formation of Al nitride is suppressed in the obtained steel ingot, N remains so as to form a nitride other than Al nitride, and as a result, the formation of BN is promoted. .. As described above, because the lowered specific resistance of slag by reducing the Al ₂ O _3, using a slag containing Al ₂ O ₃ of a predetermined amount so as to suppress a decrease in specific resistance. Such slag is particularly preferable when obtaining a large ingot of 10 tons or more.

Further, the slag may further contain _{B 2} O ₃ as an additive in an amount of 2% by mass or less. Here, the mass% of the component M in the consumable electrode is [% M], and the mole fraction of the content Q in the slag is {mfQ}.
Y = log ([% B] ⁴ / [% Si] ³ ) (Equation 1)
X = log ({mfB ₂ O ₃ } ² / {mfSiO ₂ } ³ ) (Equation 2)
Then, it is preferable that the range is -5.1 ≤ Y-X ≤ -4.6. This makes it easy to suppress the Al content in the obtained ingot.

Such a metal-slag reaction can be controlled by the following equilibrium equation. Here, [] is a component in metal, and {} is a component in slag.
Equilibrium equation a: 4 [Al] +3 {SiO ₂ } ⇔ ₂ {Al 2 O ₃ } + 3 [Si]
Equilibrium equation b: 3 [Si] +2 {B ₂ O ₃ } ⇔ _{3 {SiO 2} } + 4 [B]
Equilibrium equation c: 2 [Al] + {B ₂ O ₃ } ⇔ {Al ₂ O ₃ } + 2 [B]

In these equilibrium equations, in this embodiment, the composition component of the slag is controlled to suppress the Al content in the metal and balance it so as to secure the required B content. For example, _{by increasing the amount of SiO 2} , the equilibrium equation a tends to proceed to the right side, and the Al content in the metal can be suppressed.

By the above-mentioned method for producing boron-containing stainless steel, B can be distributed in the ingot so that fine particles of BN can be deposited, and high-temperature mechanical strength can be improved. That is, the slag composition is adjusted so as to suppress the amount of Al that competes with BN in nitriding.

[Example]
Hereinafter, the results of producing ingots by the method for producing boron-containing stainless steel by the secondary melting method using the consumable electrodes and slag described above will be described with reference to FIGS. 1 to 4.

Here, as shown in FIG. 1, steel grades A to D, which are representative components, were used as the material for the consumable electrode.

As shown in FIG. 2, steel ingots are produced by a secondary melting method according to Examples 1 to 5 and Comparative Examples 1 and 2 using consumable electrodes of each steel type A to D and slag having each slag composition. did.

As a result of manufacturing the ingot, FIG. 3 shows the X value according to the above formula 1, the Y value according to the formula 2, and the YX value regarding the composition of the electrode and the slag used for the production. The variation of B and the content of Al in the ingot are shown. Regarding the variation of B, samples are cut out from the Top side, the center, and the Bottom side of the ingot, the content of B is quantified, the minimum value is subtracted from the maximum value, and this is divided by the average value. Shown as a percentage.

In the steel ingots obtained in Examples 1 to 5, the Al content was as low as 0.002%. That is, by controlling the component composition of the slag, the Al content of the obtained ingot can be suppressed.

On the other hand, in Comparative Examples 1 and 2, _{the content of SiO 2 in} the slag was as low as 0.4%, and the Al content of the obtained ingot was 0.008% by mass and 0, respectively. The amount was increased to 0.011% by mass as compared with Examples 1 to 5. According to the above equilibrium formula a, _{it is easy to increase the Al content in the metal by reducing the content of SiO 2} , and therefore the Al content is also increased in the obtained steel ingot. Conceivable.

Here, referring to FIG. 4 together, (X, Y) are plotted on the graph for each of Examples 1 to 5 and Comparative Examples 1 and 2. In Examples 1 to 5 in which the Al content in the obtained steel ingot was low, the above-mentioned YX value was in the range of −5.1 or more and -4.6 or less. On the other hand, in Comparative Examples 1 and 2 having a high Al content, the value of YX was out of the range. That is, the composition of the alloy of the consumable electrode and the slag is preferably adjusted to be −5.1 ≦ Y−X ≦ -4.6 based on the above formulas 1 and 2, and is obtained thereby. This makes it easy to reduce the Al content in the ingot.

The steel types A to D used for the consumable electrode have different component compositions, but have the same component composition with respect to the Al content in the obtained ingot. For example, the steel grade D is used only in Comparative Example 1, but the value of Y calculated from the component composition of the steel grade of the consumable electrode is the same as that of the other steel grades A to C. That is, it can be said that the main reason for increasing the Al content in Comparative Example 1 is not the component composition of the consumable electrode but the composition of the slag.

By the way, the composition range of slag used in the above-mentioned method for producing boron-containing stainless steel is defined as follows.

The CaO was set to 20% by mass or more in order to secure the refining ability, and 40% by mass or less in order to keep the ingot skin good and prevent deterioration of the yield.

Al ₂ O ₃ is _{20% by mass or more in order to suppress a decrease in specific resistance in Al 2} O _3- CaO-CaF ₂ system slag, and 40% by mass or less in order to maintain good steel ingot skin and prevent deterioration of yield. And said.

SiO ₂ is set to 6% by mass or more in order to suppress nitrogen pickup due to an increase in Al, and 15 mass is used so as to reduce the _{amount of B 2} O ₃ to be added depending on the amount of _{SiO 2 and avoid deterioration of cost.} % Or less.

B ₂ O ₃ may be added in an amount of 2% by mass or less in order to secure the yield of B.

CaF is added to the slag as the remainder of the other components described above, but it is preferably 30% by mass or more in order to avoid an increase in viscosity and ensure operational stability.

Although typical examples according to the present invention and modifications based on the same have been described so far, the present invention is not necessarily limited thereto. One of ordinary skill in the art will be able to find various alternative embodiments without departing from the attached claims.

Claims (3)

By mass%,
C: 0.08 to 0.40%,
Cr: 8-14%,
Ni: 2.5% or less,
V: 0.1 to 0.3%,
Co: 0.5-3.5%,
Nb: 0.03 to 0.10%,
B: 0.0010 to 0.0300% and
N: Containing 0.0100 to 0.0500%, the balance Fe and unavoidable impurities, and having a component composition in which the contents of Al and Si are suppressed to 0.010% or less and 0.10% or less, respectively. A method for producing boron-containing stainless steel by a secondary melting method using consumable electrodes and slag.
The slag, in _{mass%, CaO: 20~40%, Al} 2 O 3: 20~40%, SiO 2: 6 to 15 percent free free, characterized in that the balance CaF ₂ and unavoidable impurities A method for manufacturing stainless steel containing boron. The slag is B as an additive. ₂ O ₃ The method for producing a boron-containing stainless steel according to claim 1, wherein the content is 2% or less. The mass% of the component M in the consumable electrode is [% M], and the mole fraction of the content Q in the slag is {mfQ}.
The slag is
Y = log ([% B] ⁴ / [% Si] ³ )
If X = log ({mfB ₂ O ₃ } ² / {mfSiO ₂ } ³ ),
-5.1 ≤ Y-X ≤ -4.6
The method for producing a boron-containing stainless steel according to claim 1 or 2, which has a component composition within the range of.

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