JP2009024241A - Nickel material and refining method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel material excellent in hot workability, and a method for stably producing the nickel material. <P>SOLUTION: The nickel material has a chemical composition including, by mass, 0.0050-0.0150% Mg, 0.0001-0.0010% S, 0.020-0.100% Al, at least one element chosen from the group consisting of ≤0.05% Ti, ≤0.30% Mn, ≤0.40% Fe, ≤0.0030% B and ≤0.02% C and the balance being Ni and impurities, wherein the ΔS parameter (S-0.3×Mg) is within the range of -0.0011% to -0.0030%. The chemical composition can be stably obtained by carrying out ladle refining using a slag, in which the slag basicity (T. CaO/Al<SB>2</SB>O<SB>3</SB>) is ≤2.6 and the MgO concentration is equal to or larger than 4.0 mass% but smaller than 12.0 mass%, provided that the components are adjusted so as to achieve an oxygen activity ao, which is represented by formula (1)(not indicated in a figure), of 0.70-1.30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nickel material and a method for producing the same, and more specifically, a hot material defined by components derived from nickel, in particular, an S concentration and an Mg concentration related to hot workability, and parameters derived from these relationships. The present invention relates to a nickel material excellent in workability, and a nickel refining method capable of controlling the concentration and parameters of these elements with high accuracy.

  Nickel has been used for piping and electrode materials for caustic soda plants because of its extremely excellent alkali resistance. In addition to these, the demand for lithium ion battery members used as batteries for mobile phones and notebook PCs has increased remarkably in recent years.

  Lithium ion battery members are required to have a reduced surface coating thickness for the purpose of improving solderability and a decrease in electrical resistivity to improve power efficiency. In order to satisfy such a requirement, it is necessary to reduce the Si concentration in nickel. However, reducing the concentration of Si, which is also used as a deoxidizing material, results in an increase in S concentration due to a decrease in de-S distribution during refining, thereby reducing hot workability. For this reason, there has been a problem of an increase in the amount of surface defects such as baldness after hot working, and a resulting decrease in yield and efficiency.

  It is well known that S precipitates between grains and remarkably impairs the hot workability of the metal. In particular, nickel, which has a complete austenite structure with high cracking sensitivity, has a great influence. As a method for improving the hot workability of nickel, a method of adding Mg and fixing it as MgS which is a ductile inclusion and making it harmless is widely known. For this reason, in refining the alloy, a metal Mg source such as metal Mg and / or NiMg alloy has been added.

However, since the metal Mg source is a strong deoxidizing material, a large amount of hard inclusions that cause inclusion physical defects such as MgO or Al ₂ O ₃ .MgO spinel are generated when added. In the lithium ion battery member having a thin plate thickness and strict surface quality, there is a problem that the defect occurrence rate is increased by the inclusion.

In addition, since the metal Mg source has a high vapor pressure and easily evaporates during the refining process, the Mg content in the nickel material may fluctuate greatly even if the same amount of the metal Mg source is added. . If the content of Mg in the nickel material is too low, the detoxification effect is insufficient and hot workability is reduced. Conversely, if Mg is excessive, a low melting point Ni—Ni ₂ Mg eutectic alloy is formed. Induces burning to generate. Therefore, it is difficult to obtain a nickel material having suitable hot workability with a high yield by the manufacturing method in which the metal Mg source is added. Moreover, as long as this method is used, it is difficult to reduce the variation in the Mg content in the nickel material, which hinders the improvement of hot workability.

As a technique for improving hot workability, Patent Document 1 discloses a mass ratio of CaO to Al ₂ O ₃ in slag (T. CaO / Al ₂ O ₃ , hereinafter also referred to as “slab basicity”). Is adjusted to 0.2 to 2.0, and the magnesia (MgO) concentration in the slag is adjusted to 1 to 18%, so that the Mg concentration is controlled to 0.005% to 0.04%. A method for obtaining an excellent Al-containing Ni-based alloy is described. However, this technique is intended for Ni-based alloys having a high Al content, and it is unclear whether it can be applied when the Al content is low. Further, even if it is attempted to minimize the generation of Ni—Ni ₂ Mg eutectic alloy, it is difficult to lower the upper limit of the Mg content in the nickel material from 0.04% by the above method. A nickel material having hot workability cannot be obtained stably.

  Patent Document 2 discloses a nickel manufacturing technique for electrical equipment that is excellent in slab defects and hot workability. Since Mg is actively added in this technique, it cannot be said that the controllability of the Mg content in the nickel material is high.

As a technique similar to this, Patent Document 3 discloses a technique for improving the hot workability by defining the relationship between S, Mg, and O. Since this technique is also a technique in which Mg is positively added as in Patent Document 2, it has similar problems such as a decrease in controllability of Mg content and defects due to non-metallic inclusions. In addition, in order to appropriately determine the amount of Mg added, it is necessary to accurately analyze the dissolved oxygen concentration in the molten metal, but the oxygen concentration is affected by non-metallic inclusions in the molten metal or the molten metal temperature. It is difficult to obtain a measured value, and as a result, there is a risk that the Mg concentration becomes excessive or excessive.
JP 2005-23346 A JP-A-8-143996 JP 2002-146458 A

  The present invention is to provide a nickel material excellent in hot workability and to provide a method for stably producing such a nickel material.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have obtained the following new knowledge.

  (A) It is possible to obtain a nickel material with excellent hot workability by setting the chemical composition of the nickel material with particular attention to Mg content and S content and ΔS which is a composite parameter thereof. is there. Here, “ΔS” is S−0.3 × Mg (S: mass% of S, Mg: mass% of Mg).

(B) When performing reductive refining using slag, by controlling the oxygen activity parameter ao of the following formula (1) and the MgO concentration in the slag, a nickel material without adding metal Mg or a metal Mg source It is possible to obtain a nickel material having a suitable Mg content and S content and ΔS which is a composite parameter of these:
ao = 10 ⁴ × 10 ^{(-4.325-0.2355 * (T.CaO / Al2O3) -0.667log (% Al) -0.05% Al)} (1).

Here, “T.CaO / Al ₂ O ₃ ” is a value obtained by converting the total Ca content in slag into CaO content (mass%) (hereinafter referred to as “T.CaO”), and the Al content in slag. the a value obtained by dividing the content of _Al 2 _{O 3-converted} value to the (mass%) (hereinafter referred to as _"Al 2 _{O 3".),} referred to as "slag basicity".

  Based on the above findings, the inventors have completed the following invention.

  (1) By mass%, Mg: 0.0050% or more and 0.0150% or less, S: 0.0001% or more and 0.0010% or less, Al: 0.020% or more and 0.100% or less, Fe: 0.40% or less, Mn: 0.30% or less, Ti: 0.05% or less, B: 0.0030% or less, and C: 0.02% or less The ΔS parameter defined by (S-0.3 × Mg) (S: mass% of S, Mg: mass% of Mg) is −0.0030% or more -Nickel material having a chemical composition of 0.0011% or less.

(2) (T.CaO / Al ₂ O ₃ ) (T.CaO: Total Ca content in slag converted to CaO content (mass%), Al ₂ O ₃ : Al content in slag is Al ₂ The slag basicity defined by the O ₃ content (mass%) is 2.6 or less, and the MgO concentration is 4.0% or more and less than 12.0% by mass%. The above-mentioned (1) is characterized in that the oxygen activity parameter ao represented by the following formula (1) is adjusted to a range of 0.70 to 1.30 and ladle refining is performed. A method for refining a nickel material having the chemical composition described in 1.

ao = 10 ⁴ × 10 ^{(-4.325-0.2355 * (T.CaO / Al2O3) -0.667log (% Al) -0.05% Al)} ...... (1)
Here, in the above formula (1), (T.CaO / Al ₂ O ₃ ) is the slag basicity, and Al is the Al content (unit: mass%) in the molten nickel in the ladle.

  Since the nickel material according to the present invention has ΔS in the range of −0.0030 to −0.0011%, surface defects after hot rolling hardly occur. Therefore, the nickel material according to the present invention is excellent in hot workability, is particularly suitable as a lithium ion battery member that has been in great demand in recent years, and is extremely useful industrially.

  The best mode of the present invention, the range of manufacturing conditions, and the reasons for setting them will be described below. In the present specification, “%” representing the chemical composition is “% by mass” unless otherwise specified.

2. Next, the chemical composition of the nickel material according to the present embodiment will be described.

  S: S is an element contained as an impurity in the raw material, the slagging agent and the like. When S exceeds 0.0010%, the hot workability is lowered, the amount of lashes at the time of hot rolling is increased, and the yield is deteriorated. Therefore, the upper limit of the S content is set to 0.0010%. On the other hand, excessive reduction narrows the optimum range of ΔS and causes a significant increase in refining costs. Therefore, the lower limit is made 0.0001% or more. A desirable S content is 0.0001% or more and 0.0008% or less.

Mg: An element that improves hot workability by fixing S as MgS and O as MgO. When Mg is less than 0.0050%, even if ΔS is satisfied, O fixation becomes insufficient, and hot workability deteriorates. On the other hand, when the Mg content is excessive, a low melting point Ni ₂ Mg—Ni eutectic is formed, and hot workability is significantly impaired. Therefore, the Mg content is 0.0150% or less.

  Al: An element used as a deoxidizer. If the Al content is less than 0.020%, deoxidation is insufficient and hot workability is reduced. On the other hand, when the Al content exceeds 0.100%, the nickel purity is lowered and the molten steel cleanliness is impaired. Therefore, the Al content is set to 0.020% or more and 0.100% or less. It is desirable that the content be 0.020% or more and 0.080% or less.

  In addition to the above elements, the nickel material according to this embodiment includes Ti: 0.05% or less, Fe: 0.40% or less, Mn: 0.30% or less, B: 0.0030% or less, and C: Contains one or more selected from the group consisting of 0.02% or less. The content of each element will be described below.

  Ti: Ti fixes nitrogen mixed as an inevitable impurity during refining as TiN. However, when the Ti content exceeds 0.05%, the effect is saturated, and conversely, the amount of hard Ti-based compound generated increases, which may cause defects. Therefore, the upper limit of the Ti content is set to 0.05%. A preferable content is 0.02% or less.

  Fe: The strength of the nickel material can be increased by containing Fe. However, excessive addition is undesirable because it increases electrical resistivity. Therefore, the upper limit of the Fe content is set to 0.40%. A preferable content is 0.20% or less.

  Similar to Mn: Fe, it can be added to adjust the strength. However, excessive addition is undesirable because it increases electrical resistivity. Therefore, the upper limit of the Mn content is set to 0.30%. A preferable content is 0.20% or less.

  B: Can be added to reduce brittleness. However, excessive addition reduces the high temperature strength, so the upper limit of the B content is 0.0030% or less. A preferable content is 0.0020% or less.

  C: C is an impurity mixed from the raw material or the electrode during melting, and is an element to be removed by refining, but may be added in a small amount to adjust the strength. However, excessive addition increases the hardness remarkably, so that workability as a battery member is impaired, which is not desirable. Therefore, the upper limit of the C content is 0.02% or less.

  The balance is Ni and impurities. Examples of the impurities include Si and N, but are not limited thereto.

2. About ΔS “ΔS” is defined by S−0.3 × Mg (S: mass% of S, Mg: mass% of Mg), and the nickel material according to this embodiment has ΔS of −0.0030% or more. And -0.0011% or less.

(1) Regarding the relationship between ΔS and the grinding amount index When ΔS is in the above range, the grinding amount index is lowered and the productivity is improved. Here, the “grinding index” means that surface defects generated in the hot rolling process of nickel hot coil produced by hot rolling are removed by machining such as grinding before being subjected to cold rolling. In that case, the removal amount is divided by 1/2 of the nickel plate thickness to make it dimensionless.

As described above, this surface defect tends to increase as the S intergranular precipitation increases. However, the addition of Mg renders this S harmless and reduces surface defects. However, excessive addition of Mg produces a Ni—Ni ₂ Mg eutectic alloy having a low melting point, which induces burning and conversely increases surface defects. Therefore, the amount of surface defects generated is evaluated by an index related to the processing amount for removing the generated surface defects, and by defining the relationship between this index and the S content and the Mg content, a suitable nickel material can be obtained. It is possible to objectively grasp the composition range.

  FIG. 1 shows the evaluation result performed based on this idea. FIG. 1 is a diagram showing the relationship between the S content and the Mg content in a nickel material and the coil grinding amount pass / fail, wherein the horizontal axis is the S content and the vertical axis is the Mg content. A nickel material having a grinding amount index of 0.3 or less was indicated as “◯” as a grinding pass, and a nickel material having a grinding amount index exceeding 0.3 was indicated as “x” as a grinding failure.

All grinding passes in the region between S-0.3 × Mg = −0.0030% and S-0.3 × Mg = −0.0011% indicated by two broken lines in FIG. When the nickel material is included and ΔS is in the range of −0.0030 to −0.0011%, S intergranular precipitation is less likely to occur, and low melting point Ni ₂ Mg—Ni is also less likely to occur. Was confirmed.

Further, in order to confirm the effectiveness of this relationship, FIG. 2 is a plot with ΔS as the horizontal axis and the grinding amount index as the vertical axis. As shown in FIG. 2, when ΔS is out of the range of −0.0011% to −0.0030%, the grinding amount is remarkably increased. When ΔS exceeds −0.0011%, S is precipitated between grains, so that hot workability is impaired. On the other hand, if it is less than −0.0030%, Mg becomes excessive, so that a low melting point Ni ₂ Mg—Ni eutectic is precipitated, and the hot workability is significantly impaired.

3. Manufacturing Method The nickel material according to the present embodiment is not particularly limited to the manufacturing method as long as it has the above-described chemical composition characteristics. However, if the following refining method is employed, it is possible to efficiently and stably obtain the nickel material according to the present embodiment.

(1) Outline of Manufacturing Method An outline of one aspect of the manufacturing method of the nickel material according to the present embodiment is as follows.
A raw material containing nickel and other predetermined elements is melted in an electric furnace or the like, and the obtained molten metal is poured into a secondary refining vessel lined with a refractory containing MgO. After removing the slag generated during melting, followed by blowing acid and decarburization refining, one or more of quicklime, fluorite, magnesia, and aluminum are used alone as slag and as needed. Input and implement reduction and desulfurization refining. Thereafter, the chemical components are appropriately adjusted, and then cast by a continuous casting machine to obtain a slab. The slab thus obtained is subjected to surface care as necessary and then hot-rolled by a hot rolling mill to obtain a hot coil. A nickel material can be obtained by appropriately grinding the resulting hot coil to remove surface defects generated by hot rolling.

(2) Outline of the refining method In the refining process of the above manufacturing method, when performing reductive refining using slag, the oxygen activity in the molten nickel and the MgO activity in the slag are adjusted based on the formula (2). By doing so, the Mg concentration can be controlled in principle.

Mg + O = MgO …… (2)
However, since it is difficult to measure thermodynamic data such as the equilibrium constant of the formula (2) in the nickel base, a reliable value is not obtained. For this reason, a realistic control technique based on equation (2) has not been studied so far.

The present inventor has found that the oxygen activity parameter ao described in the equation (1) is effective with respect to the oxygen activity in the equation (2).
ao = 10 ⁴ × 10 ^{(-4.325-0.2355 * (T.CaO / Al2O3) -0.667log (% Al) -0.05% Al)} ...... (1)

Based on this knowledge, the refining process according to the present embodiment is characterized in that the Mg concentration is controlled by controlling the oxygen activity parameter ao and the MgO concentration in the slag. Realization of controlling Mg concentration and S concentration in nickel and ΔS (≡S-0.3Mg), which is a composite parameter, without adding metal Mg or Mg-containing alloy (metal Mg source) that increases the quantity As a result, the hot workability of nickel is improved.

(3) Oxygen activity in the molten nickel Next, the reason why the above formula (1) was derived will be described.
The oxygen activity in the molten nickel follows the equilibrium reaction of equation (3) in the component region shown in this technology.

Al ₂ O ₃ = 2Al + 3O (3)
Here, regarding the formula (3) in the nickel base, the equilibrium constant is the value of Table 1 in F.Ishii, S.Ban-ya and M.Hino, ISIJ Int, 36 (1996) 1, pp. 25, Regarding the interaction coefficient in molten nickel, F.Ishii, S.Ban-ya and M.Hino, ISIJ Int, 36 (1996) 1, pp. 25 and F.Ishii, S.Ban-ya, ISIJ Int , 32 (1992), pp.1091, the values shown in Table 2 are proposed.

On the other hand, with respect to the Al ₂ O ₃ activity in slag, an isoactivity diagram is shown in H.OHTA and H.SUITO, ISIJ Int, 36 (1996) 8, pp. 983. Relationship Al ₂ O ₃ activity by based on the Tokatsu amount diagrams and T.CaO / Al ₂ O ₃ in the slag in the claims is as shown in FIG. 3, shown in (4) It is possible to fit using the approximate expression.
a _Al2O3 = 5.21 × 10 ^{-0.708 (T.CaO / Al2O3)} ...... (4)

Using the values in Tables 1 and 2 and the Al ₂ O ₃ activity derived from the equation (4), the equation for obtaining the oxygen activity parameter ao is derived. In the scope of the present invention,% O is compared with% Al. (1) is obtained at 1600 ° C.

(4) Relationship between MgO concentration and Mg concentration in ao and slag
By changing the MgO concentration in ao and slag, the relationship between ao and Mg concentration and the relationship between ao and ΔS were investigated. In this investigation, since the MgO activity in the slag is difficult to measure, the MgO concentration in the slag was substituted.

  The relationship between ao and Mg concentration obtained as a result is shown in FIG. 4, and the relationship between ao and ΔS is shown in FIG. The negative correlation was obtained between ao and Mg concentration when the MgO concentration in the slag was 4.0% or more, but no clear correlation was observed when it was less than 4.0%. . As for ao and ΔS, a positive correlation was obtained when the MgO concentration in the slag was 4.0% or more (in FIG. 5, the vertical axis is set to be higher as the negative value increases). However, when the ratio is less than 4.0%, no clear correlation is observed.

  Here, it is presumed that the correlation is no longer recognized when the MgO concentration is less than 4.0% for the following reason. The basic process of the refining method according to the present embodiment is the formula (2) as described above, and by reducing the oxygen activity by reducing ao, the reaction leftward in the equilibrium formula shown by the formula (2) Is to make progress. At this time, it has been realized that the Mg concentration capable of detoxifying S is increased to obtain a nickel material having excellent characteristics. However, if the MgO activity in the slag (substituting with the Mg concentration in the slag) is extremely reduced, even if ao is reduced, the reaction in the left direction in the formula (2) does not proceed because the raw material is small in the first place. Since the concentration does not increase, ΔS also deviates from the optimum range. In the refining method according to the present embodiment, the MgO concentration is 4.0% or more from the above viewpoint.

Moreover, about ao, it shall be 0.70-1.30. When ao exceeds 1.30, Mg may be less than 0.0050% as shown in FIG. 4, and there is a concern about deterioration of hot workability. Further, in this case, since S also increases, as shown in FIG. 5, a case where ΔS exceeds −0.0011% may occur. Therefore, ao is preferably 1.30 or less. On the other hand, when ao is less than 0.70, the Mg concentration increases and ΔS is less than −0.0030% (see FIG. 5). In this case, since it is feared that the grinding amount index is abruptly deteriorated due to the formation of Ni ₂ Mg—Ni eutectic, ao is preferably 0.70 or more.

Raw materials including nickel metal, nickel scrap, manganese metal and aluminum were melted in a 40T electric furnace, and the obtained molten metal was put out into a secondary refining vessel lined with a refractory containing MgO. After removing electric furnace slag and performing blowing acid and decarburization refining with VOD, one or more selected from the group consisting of quicklime, fluorite, magnesia and aluminum are added, as shown in Table 3 Reduction and desulfurization refining were carried out as a slag composition. Table 3 shows (T.CaO / Al ₂ O ₃ ) in the slag and the Al concentration and oxygen activity parameter ao during refining.

  Thereafter, the chemical components were appropriately adjusted so as to have the chemical composition shown in Table 3. The ΔS in this chemical composition is shown in Table 3. Subsequently, a 150 mm thick slab was cast by a fully curved continuous casting machine, and the obtained slab was subjected to surface care on the four sides of the front and back sides using a grindstone, and then a tandem or stickel type hot rolling mill. Then, hot rolling was performed as a hot coil having a thickness of 4 mm to 6 mm. The front and back surfaces of the obtained hot coil were ground with a grindstone to remove surface defects generated by hot rolling. The grinding amount index at this time was as shown in Table 3.

  In the nickel materials according to Examples 1 to 4, the slag composition, particularly the MgO concentration, the oxygen activity parameter ao in the molten nickel, and the Mg content, S content, and ΔS in the chemical composition were appropriate. All of the indexes were 0.3 or less, and the nickel material was less likely to cause surface defects.

  On the other hand, since the nickel material according to Comparative Example 1 has an ao parameter of less than 0.70 and an extremely low oxygen activity, an increase in Mg concentration and a decrease in S concentration occur simultaneously, and ΔS is − The amount of grinding was remarkably increased by less than 0.0030%.

  In the nickel material according to Comparative Example 2, Al was less than 0.020%, so ao was 2.20, and the oxygen activity was significantly high. For this reason, an increase in S and a decrease in Mg occurred simultaneously, and ΔS exceeded −0.0011%.

  The nickel material according to Comparative Example 3 satisfied the aO parameter of 0.70 or more and 1.30 or less. However, since the MgO concentration in the slag was less than 4.0%, the Mg concentration was less than 0.0050%, and ΔS However, it exceeded -0.0011%, and the grinding amount increased.

In the nickel material according to Comparative Example 4, although (T.CaO / Al ₂ O ₃ ) and Al concentration were appropriate, the oxygen activity parameter ao exceeded 1.30, so ΔS could not be satisfied. The amount of grinding increased.

It is the figure which showed the relationship between S content and Mg content in a nickel material, and coil grinding amount pass / fail. It is the figure which showed the relation between ΔS and the coil grinding quantity index related to hot workability. It is a diagram showing the relationship derived from Tokatsu amount diagrams and (T.CaO / _Al 2 _{O 3)} and _Al 2 _{O 3} activity. It is the figure which classified and showed the relationship between oxygen activity parameter ao and Mg density | concentration by MgO density | concentration in slag. It is the figure which classified and showed the relationship between oxygen activity parameter ao and (DELTA) S by MgO density | concentration in slag.

Claims (2)

Mg: 0.0050% or more and 0.0150% or less, S: 0.0001% or more and 0.0010% or less, Al: 0.020% or more and 0.100% or less, and Fe: Contains 0.40% or less, Mn: 0.30% or less, Ti: 0.05% or less, B: 0.0030% or less, and C: 0.02% or less. And the balance Ni and impurities,
The ΔS parameter defined by (S-0.3 × Mg) (S: mass% of S, Mg: mass% of Mg) has a chemical composition of −0.0030% or more and −0.0011% or less. Nickel material characterized by that. (T.CaO / Al ₂ O ₃ ) (T.CaO: Value obtained by converting the total Ca content in slag to CaO content (mass%), Al ₂ O ₃ : Al content in slag containing Al ₂ O ₃ The slag basicity defined by the amount (value converted to mass (mass%)) is 2.6 or less, and the MgO concentration is mass%, using 4.0% or more and less than 12.0% slag. ,
The chemical activity according to claim 1, wherein the oxygen activity parameter ao represented by the following formula (1) is adjusted in the range of 0.70 to 1.30 and ladle refining is performed. A method for refining a nickel material having a composition.
ao = 10 ⁴ × 10 ^{(-4.325-0.2355 * (T.CaO / Al2O3) -0.667log (% Al) -0.05% Al)} ...... (1)
Here, in the above formula (1), (T.CaO / Al ₂ O ₃ ) is the slag basicity, and% Al is the Al content (unit: mass%) in the molten nickel in the ladle. .

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