JP3626445B2 - Fe-Ni alloy for low thermal expansion and high rigidity shadow mask excellent in surface property and etching processability and method for producing the same - Google Patents

Description

【００３４】
【表２】

【００３５】
【発明の効果】
以上説明したとおり、本発明に係るＦｅ−Ｎｉ系合金は、合金中に含まれる非金属介在物が、ＭｎＯ−ＦｅＯ−ＳｉＯ_２−Ｎｂ_２Ｏ_５−ＭｇＯ−Ａｌ_２Ｏ_３−ＣａＯ系複合酸化物、シリカ、スピネルおよびニオブ酸化物のうちの一種又は二種以上に制御されており、かつ一部のＭｎＯ−ＦｅＯ−ＳｉＯ_２−Ｎｂ_２Ｏ_５−ＭｇＯ−Ａｌ_２Ｏ_３−ＣａＯ系非金属介在物は、Ａｌ_２Ｏ_３：４０ｗｔ％以下、ＣａＯ：４０ｗｔ％以下、ＭｇＯ：４０ｗｔ％以下、ＦｅＯ：３０ｗｔ％以下に制御されているために、表面性状およびエッチング加工性が良好である。しかも、この合金は、低熱膨張高剛性を示してシャドウマスク材料として有用である。また、本発明方法によれば、こうした合金を確実に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an Fe-Ni alloy suitable as an electronic component material, and in particular, proposes an Fe-Ni alloy for shadow masks with low thermal expansion and high rigidity excellent in surface properties and etching processability, and an advantageous manufacturing method thereof. To do.
[0002]
[Prior art]
Fe-Ni alloys containing 30 to 45 wt% of Ni are often used as electronic component materials because of their low thermal expansion characteristics. In particular, an Fe—Ni alloy containing 35 to 37 wt% of Ni is awarded as a shadow mask material for TV or computer monitors because of its extremely low coefficient of thermal expansion. However, these shadow mask materials are also demanded to have further lower thermal expansion and higher rigidity in recent years as TVs and monitors are enlarged. The low thermal expansion is dealt with by a further decrease in trace elements such as Mn, Cr, Si, and the high rigidity is dealt with by a method of adding Nb (Japanese Patent No. 2781336).
However, in the Fe—Ni alloy containing Nb, the inclusion morphology changes due to the addition of Nb, and alumina clusters are more likely to be generated than in the conventional Fe-36 wt% Ni alloy, which causes surface defects on the cold-rolled sheet. There was a problem.
[0003]
Conventionally, in the case of an Fe-36 wt% Ni alloy, Japanese Patent Application Laid-Open No. 6-41687 discloses that Mn: 0.1 to 0.4 wt%, Si: 0.05 to 0.2 wt%, acid-soluble Al : Proposing a method of melting 0.001 to 0.003 wt% of Nb-free Fe—Ni alloy or the like and controlling the composition of nonmetallic inclusions to MnO—SiO ₂ —Al ₂ O ₃ system Yes. Japanese Patent Application Laid-Open No. 8-225881 discloses a method for controlling the composition of non-metallic inclusions to Mn-silicate based on Al: 0.003 wt% or less and Si (wt%) / Al (wt%) ≧ 10. is suggesting. However, these techniques are examples of alloys that do not contain Nb, and there is a problem that they cannot be applied to inclusion control of an Fe-36 wt% Ni alloy when so-called Nb is added.
[0004]
By the way, the Fe—Ni-based alloy is generally made into a cold-rolled sheet having a product plate thickness of about 0.05 to 1.0 mm, and thereafter, it is usually commercialized by etching using a ferric chloride aqueous solution. Yes. During this etching process, the presence of non-metallic inclusions is a factor that greatly affects the etching processability. As for the etching workability of Fe—Ni alloys, many inventions have been made from the viewpoints of surface properties (JP-A-4-99152, etc.), surface orientation (JP-A-1-247558, etc.) and the like. . Further, examples studied by paying attention to non-metallic inclusions in the alloy include those disclosed in JP-A Nos. 61-84356 and 7-268558. However, they all aim only at reducing the amount of non-metallic inclusions. However, even if the amount of non-metallic inclusions is reduced, pore shape defects may occur depending on the chemical composition of the non-metallic inclusions. In particular, in the case of an Fe-36 wt% Ni alloy containing Nb, there is a problem that these techniques cannot be applied because the inclusion form is different from that of the conventional Fe-36 wt% Ni alloy.
[0005]
[Problems to be solved by the invention]
As described above, the above prior art has proposed an Fe—Ni-based alloy plate with good etching processability, but all of them are Nb-free alloy types. However, recent shadow mask materials are required to have high rigidity as described above, and the addition of Nb is indispensable. On the other hand, the addition of Nb leads to a change in the form of inclusions dispersed in the alloy. Therefore, alumina clusters are more easily generated than conventional Fe-36 wt% Ni alloys, and surface defects are generated in the cold-rolled sheet. It can also be a cause. Further, when Nb is added, there is a problem that acid-soluble inclusions are also generated, and thus severe etching defects are caused.
[0006]
Therefore, the present invention aims to develop a technique that can solve the above-mentioned problems of the prior art, and particularly Fe- for low thermal expansion and high rigidity shadow mask having excellent surface properties and etching processability. The object is to provide a Ni-based alloy.
[0007]
[Means for Solving the Problems]
The inventors have conducted various studies on the above-described problems with respect to alloys that do not cause deterioration of surface properties and etching hole shapes, particularly the composition of non-metallic inclusions contained in this alloy. That was dissolved Fe-36 wt% Ni with magnesia crucible in the laboratory, then after addition of _{CaO-SiO 2 -Al 2 O 3} -MgO-F slag, Si, Mn, Al, Mg, Ca After deoxidizing with a deoxidizing agent such as Nd, Nb was added and a steel ingot was produced. The steel ingot was forged and then hot rolled, and then cold rolled to a product plate thickness of 0.25 mm. And the evaluation test of the surface property of a cold-rolled board and the etching workability was done.
[0008]
As a result, the inventors have found that Nb added to the Fe-36 wt% Ni alloy is not as strong as Si, Al, Mg, and Ca, but has a strong affinity for oxygen and has a strong influence on deoxidation. As shown in the formula (1), it has been found that there is an action of easily reacting with alumina in the slag to dissolve Al in the molten steel.
6 Nb +5 (Al ₂ O ₃ ) _slag = 3 (Nb ₂ O ₅ ) _slag +10 Al (1)
() ... Slag component, underline ... Molten steel component [0009]
That is, it was confirmed that when Nb is added to a conventional Fe-36 wt% Ni alloy, alumina clusters are easily formed, and as a result, surface flaws are easily caused. Further, Fe—Nb, which is an Nb raw material used industrially, contains about 0.1 to several wt% of Al, and this Al is also dissolved in the molten steel. It turned out to be disadvantageous. As a result of further research, one of the conditions for preventing alumina clusters is to control the Al concentration in molten steel to 0.005 wt% or less. It was also found that in order to keep the Al concentration in molten steel containing 0.01 to 1.0 wt% Nb at this level, the alumina concentration in the slag needs to be 5 wt% or less.
[0010]
On the other hand, since an Fe-36 wt% Ni alloy is usually used after being etched, it must have excellent etching processability. Therefore, the inventors have continuously conducted research on the influence of the inclusion composition on the etching processability. As a result, it was found that when acid-soluble MgO simple inclusions and CaO simple inclusions were generated, the shape of the etching hole was disturbed. In addition, it has been found that the above-described alumina clusters also disturb the shape of the etching holes. Furthermore, when the formation of alumina inclusions is prevented, MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO formed in the Nb-containing Fe-36 wt% Ni alloy.
It was found that when CaO or MgO was contained in the —Al ₂ O ₃ —CaO-based composite oxide in excess of 40 wt%, the shape of the etching hole was disturbed. CaO and CaO-containing inclusions are produced when Ca is added as a deoxidizer, but MgO is not only added when Mg is added, but also when the basicity of slag is higher than 4. Generated.
[0011]
In addition, regarding the alloy composition, if the concentration of Si and Mn is too low as less than 0.001 wt%, deoxidation failure occurs, the oxygen concentration becomes as high as 0.02 wt% or more, and the cleanliness exceeds 0.05. Oops. As a result, etching failure occurred due to a large amount of inclusions.
[0012]
The present invention has been developed on the basis of the above knowledge, and Si: 0.001 to 0.1 wt%, Mn: 0.001 to 0.1 wt%, Nb: 0.01 to 1.0 wt%, Ni : 35-37 wt%, Cr: 0.1 wt% or less, O: 0.0005-0.02 wt%, S: 0.002 wt% or less, Al: 0.005 wt% or less, Mg: 0.001 wt% or less, Ca : includes the following 0.001 wt%, and at the same time having the component composition and the balance being Fe and unavoidable _impurities, the _{MnO-FeO-SiO 2 -Nb 2} O 5 -MgO-Al 2 O 3 -CaO based composite oxide In addition, it is characterized by containing a non-metallic inclusion consisting of one or more of silica (SiO ₂ ), spinel (MgO.Al ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ). Surface It is Jo and etching excellent in low thermal expansion and high rigidity shadow Fe-Ni alloy mask.
[0013]
In the present invention, the MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO-based non-metallic inclusions are Al ₂ O ₃ : 40 wt% or less, FeO: 30 wt% or less, CaO : 40 wt% or less, MgO: 40 wt% or less, and the balance is MnO, SiO ₂ and Nb ₂ O ₅ , and the shape of the nonmetallic inclusions in the cross section parallel to the rolling direction of the Fe—Ni alloy sheet is JIS It is preferably controlled to B system and C system classified by G 0555, and the cleanliness according to JIS G 0555 is controlled to 0.05 or less.
[0014]
In the present invention, the raw material of the Fe—Ni alloy composed mainly of Fe and Ni and composed of the above components is oxidized and refined, deoxidized by adding Si or Si alloy iron, and then Nb is added. When adjusting the finishing ingredients, one or more of limestone, aragonite, and quartz sand are added together, and the basicity (C / S) of the slag produced at this time is 1.5 to 4.0. , And refined by controlling the alumina concentration in the slag to 5 wt% or less, then cast by continuous casting method or ordinary ingot method, and in the case of ordinary ingot method, hot forging was performed, and then obtained A method for producing a Fe-Ni alloy for a low thermal expansion and high rigidity shadow mask excellent in surface properties and etching processability, characterized by subjecting a slab to hot rolling according to a conventional method and further cold rolling is proposed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason why the content of the Fe—Ni-based alloy according to the present invention is limited with regard to its component composition will be described.
Si: 0.001 to 0.1 wt%
Si is an element that contributes to deoxidation and is useful, but is also an element that increases the coefficient of thermal expansion. If the Si content exceeds 0.1 wt%, the coefficient of thermal expansion becomes too large and it is not suitable as a shadow mask material. On the other hand, if this amount is less than 0.001 wt%, the deoxidizing power becomes weak and the numerical value of cleanliness becomes high. Therefore, the Si content is determined to be 0.001 to 0.1 wt%. Within this range, 0.005 to 0.09 wt% is preferable, and 0.01 to 0.08 wt% is more preferable.
[0016]
Mn: 0.001 to 0.1 wt%
Mn is an element that contributes to deoxidation in the same manner as Si, and is an element that is useful but increases the coefficient of thermal expansion. If this Mn exceeds 0.1 wt%, the coefficient of thermal expansion becomes too large and it is not suitable as a shadow mask material. On the other hand, if this amount is less than 0.001 wt%, the deoxidizing power becomes weak and the numerical value of cleanliness becomes high. Therefore, the Mn content is determined to be 0.001 to 0.1 wt%. Within this range, 0.005 to 0.09 wt% is preferable, and 0.01 to 0.08 wt% is more preferable.
[0017]
Nb: 0.01 to 1.0 wt%
Nb is an element necessary for increasing the rigidity of the shadow mask to obtain a Fe-Ni alloy for a high-rigidity shadow mask. However, if this Nb exceeds 1.0 wt%, the coefficient of thermal expansion becomes too large to be suitable for a shadow mask. On the other hand, if this amount is less than 0.01 wt%, sufficient rigidity cannot be obtained. Therefore, the Nb content is determined to be 0.01 to 1.0 wt%. Within this range, 0.02 to 0.8 wt% is preferable, and 0.04 to 0.6 wt% is more preferable.
[0018]
Ni: 35-37 wt%
Ni is an element that greatly affects the coefficient of thermal expansion, and it is known that the coefficient of thermal expansion becomes minimum at around 36 wt% at 200 ° C. If it is less than 35 wt% and exceeds 37 wt%, the coefficient of thermal expansion becomes inappropriate as a shadow mask. Therefore, the Ni content is determined to be 35 to 37 wt%.
[0019]
Cr: 0.1 wt% or less Cr is an element that increases the coefficient of thermal expansion, and is preferably as low as possible. Therefore, considering the influence on the coefficient of thermal expansion, the Cr content was determined to be 0.1 wt% or less. Within this range, it is preferably 0.08 wt% or less.
[0020]
O: 0.0005 to 0.02 wt%
When the concentration of O is high, the cleanliness is deteriorated, and FeO in the inclusions exceeds 30 wt%, which adversely affects the etching processability. On the other hand, when the concentration of O is low, the inclusions are likely to become acid-soluble MgO and CaO inclusions, and the etching processability is deteriorated. In addition, depending on the slag composition, Al ₂ O ₃ inclusions are mainly used to form hard alumina clusters and deteriorate the surface properties. Therefore, the O content is determined to be 0005 to 0.02 wt%. Within this range, 0.001 to 0.015 wt% is preferable, and 0.002 to 0.01 wt% is more preferable.
[0021]
S: 0.002 wt% or less If S exceeds 0.002 wt%, the hot workability is deteriorated, ear cracking is likely to occur during rolling, the yield is lowered, and rust is easily generated on the product surface. Become. Therefore, S is determined to be 0.002 wt% or less. Within this range, it is preferably 0.0018 wt% or less, more preferably 0.0015 wt% or less.
[0022]
Al: 0.005 wt% or less Since Al is an element that forms alumina clusters, it is a harmful element and desirably has a low concentration. As described above, when Al exceeds 0.005 wt%, Al ₂ O ₃ clusters harmful to the surface properties are generated. Therefore, in the present invention, Al contained as an inevitable impurity is limited to 0.005 wt% or less. Within this range, it is preferably 0.0045 wt% or less, and more preferably 0.004 wt% or less.
[0023]
As will be described later, in order to make this Al concentration as low as possible, it is necessary to control the alumina concentration in the slag to 5 wt% or less. Furthermore, although it is not necessary to limit in particular, since a trace amount of Al is also contained as an impurity in the auxiliary material such as FeSi and FeNb, it is preferable to use a low Al content product as the auxiliary material.
[0024]
Mg: 0.001 wt% or less Mg is a MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO based composite oxide or spinel MgO. It is an element useful for controlling to Al ₂ O ₃ . However, when Mg exceeds 0.001 wt%, the MgO concentration in the MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO based composite inclusion increases to exceed 40 wt%. In addition, MgO alone is generated as an inclusion species, which adversely affects etching processability. Therefore, Mg is determined to be 0.001 wt% or less. Within this range, 0.0008 wt% or less is preferable.
[0025]
Ca: 0.001 wt% or less Ca is a MnO—FeO— that is harmless to the quality of the shadow mask for non-metallic inclusions.
It is an element useful for controlling the SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO-based composite oxide. However, when this Ca exceeds 0.001 wt%, the CaO concentration in the MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO composite inclusion exceeds 40 wt%. At the same time, CaO alone is also generated as an inclusion species, which adversely affects etching processability. Therefore, Ca is determined to be 0.001 wt% or less. Within this range, 0.0008 wt% or less is preferable.
[0026]
Furthermore, in the present invention, in order to obtain an inclusion that does not adversely affect the surface properties and does not impair the etching processability, the composition is changed to MnO—FeO—SiO ₂ —Nb ₂ O ₅ —.
In addition to MgO—Al ₂ O ₃ —CaO-based composite oxide, one or _{two of} silica (SiO ₂ ), spinel (MgO · Al ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ) Control to non-metallic inclusions composed of the above. In the present invention, the reason for precipitating such non-metallic inclusions is that they do not form clusters like alumina, and further, because they are not acid-soluble, they do not adversely affect etching processability. is there. However, MnO—FeO—SiO ₂ —
Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO-based non-metallic inclusions become acid-soluble when CaO exceeds 40 wt% and MgO exceeds 40 wt%, and adversely affects etching processability. On the other hand, if FeO exceeds 30 wt%, the oxygen concentration increases, the cleanliness deteriorates beyond 0.05, and the etching processability is adversely affected. Furthermore, when Al ₂ O ₃ exceeds 40 wt%, it becomes easy to generate alumina simple inclusions rapidly, which causes a cluster.
[0027]
_{Therefore, MnO-FeO-SiO 2 -Nb} 2 O 5 -MgO-Al 2 O 3 -CaO based nonmetallic _inclusions, Al ₂ O 3: 40wt% or less, FeO: 30 wt% or less, CaO: 40 wt% or less, MgO: 40 wt% or less, with the balance being made of MnO, SiO ₂ and Nb ₂ O ₅ . Further, such inclusions are defined as described above because they are B-type and C-type classified by JIS G 0555 in the thin plate.
[0028]
Next, the manufacturing method of the Fe-Ni type alloy which concerns on this invention is demonstrated. The production method of the present invention is characterized by deoxidizing the Fe—Ni alloy material having the above component composition by adding Si or Si alloy iron, and then adding the required amount of Nb to refine the finish. In the process. That is, in this finishing refining treatment, the composition of the slag in the ladle is adjusted as follows.
a. Basicity of slag (C / S): 1.5 to 4.0
Slag basicity is an indispensable factor for refining molten steel such as deoxidation and desulfurization of molten steel. Similarly, it is an important control factor for controlling the composition of inclusions in the alloy. In this invention, the basicity of the slag in the ladle after this deoxidation refining shall be 1.5-4.0. This is because, when the basicity is less than 1.5, the deoxidation reaction of the molten steel is difficult to proceed, and the cleanliness exceeds 0.05, resulting in poor etching processability. At the same time, the desulfurization reaction does not proceed easily, S exceeds 0.002 wt%, and hot workability is deteriorated, and rust is easily generated. On the other hand, when the basicity exceeds 4.0, the activity coefficient of MgO in the slag increases, so that MgO is reduced by Si and Nb by the reaction of the following formulas (2) and (3), It will mix in molten steel as dissolved Mg.
2 (MgO) _slag + Si = 2 Mg + (SiO ₂ ) _slag (2)
5 (MgO) _slag + 2 Nb = 5 Mg + (Nb ₂ O ₅ ) _slag (3)
As a result of the above reaction, Mg becomes higher than 0.001 wt%, and MgO alone is generated as an inclusion, or MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO-based non- MgO in the metal inclusion becomes higher than 40 wt%. As a result, a defective shape of the etching hole is caused. Therefore, the basicity of the slag was determined as 1.5 to 4.0.
[0029]
Note that MgO in the slag is mixed into an electric furnace, AOD furnace or ladle from a refractory such as commonly used dolomite, magnesia carbon, alumina magnesia carbon, etc. by melting into the slag. Moreover, in order to protect magnesia-based refractories, it may be actively put into slag.
[0030]
b. Alumina concentration in slag: 5 wt% or less Alumina in slag is a harmful element that reacts with Nb in molten steel to dissolve Al in the molten steel according to the above formula (1), and is preferably as low as possible.
In order to prevent the formation of alumina clusters in the case of Fe-36 wt% Ni molten steel obtained by adding 0.01 to 1.0 wt% Nb to obtain a high-rigidity shadow mask material as in the present invention, The alumina concentration in the slag needs to be 5 wt% or less. Therefore, the alumina concentration in the slag was limited to 5 wt% or less. Alumina is often added as a hazing agent, but in the present invention, it is necessary to keep the alumina concentration as low as possible, and it is preferable not to add it. Although there is no particular limitation, since auxiliary materials such as CaO and CaF ₂ contain a very small amount of Al ₂ O _3, it is preferable to use alumina having a low concentration as much as possible.
[0031]
【Example】
In an electric furnace, an Fe-36 wt% Ni alloy was melted, and then oxidative refining was performed by AOD. After desoldering, the Fe-Si alloy was added, and limestone, meteorite, and in some charges, silica sand was added for deoxidation. Dolomite was used for the AOD refractory, and magnesia carbon and alumina magnesia carbon refractories were used for the ladle. After sufficient deoxidation, Nb was added and a finishing treatment for adjusting the components was performed. Subsequently, casting was performed by a continuous casting machine, the continuous cast slab was hot-rolled, and then cold-rolled to a product plate thickness of 0.25 mm. Thus, the sample was cut out from the obtained thin plate, and the following evaluation was performed.
(1) Chemical component: A sample cut from a slab was analyzed using a fluorescent X-ray analyzer.
(2) Slag composition: Slag samples collected during operation were analyzed using a fluorescent X-ray analyzer.
(3) Nonmetallic inclusion composition: 20 inclusions were randomly analyzed using EDS.
(4) Form of inclusions and cleanliness: According to “JIS G 0555”, a cross section parallel to the rolling direction was measured with an optical microscope under the condition of 400 × / 60 field of view.
(5) Surface properties: The number of surface defects caused by inclusions present in an arbitrary 20 m ² portion of the surface was counted visually.
{Circle around (6)} Etching workability: A 200 mm × 400 mm test piece was cut out from the obtained thin plate sample and etched with a ferric chloride aqueous solution (45 Baume, temperature 60 ° C.). Thereafter, 100 etching holes were randomly observed with an electron microscope, and holes having poor shapes were counted.
[0032]
Tables 1 and 2 show the evaluation results. In the present invention, both the chemical component and the slag composition are included in the scope of the present invention, so that the inclusion composition of all charges is MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O _3. It is controlled to be one or more of —CaO-based composite oxide and SiO ₂ , MgO.Al ₂ O ₃ and Nb ₂ O ₅ , and MnO—FeO—SiO ₂ —Nb ₂ The O ₅ —MgO—Al ₂ O ₃ —CaO-based nonmetallic inclusions are controlled to be Al ₂ O ₃ : 40 wt% or less, CaO: 40 wt% or less, MgO: 40 wt% or less, and FeO: 30 wt% or less. Therefore, it was found that there was no problem in the inclusion form and cleanliness, and as a result, the surface properties and etching processability were also excellent. On the other hand, in the comparative example, the chemical component and the slag composition deviated from the specified range in at least one point, and therefore, the specified range of the inclusion composition, form, and cleanliness could not be satisfied. As a result, generation of surface defects or etching defects occurred, and the required quality could not be satisfied.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
【The invention's effect】
As described above, in the Fe—Ni alloy according to the present invention, the nonmetallic inclusions contained in the alloy are MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO based composite oxidation. things, silica, spinel and one or are controlled in two or more, and part of _{MnO-FeO-SiO 2 -Nb 2} O 5 -MgO-Al 2 O 3 -CaO based nonmetallic of niobium oxide Since the inclusions are controlled to be Al ₂ O ₃ : 40 wt% or less, CaO: 40 wt% or less, MgO: 40 wt% or less, and FeO: 30 wt% or less, the surface properties and etching processability are good. Moreover, this alloy exhibits low thermal expansion and high rigidity and is useful as a shadow mask material. Further, according to the method of the present invention, such an alloy can be produced reliably.

Claims (5)

Si: 0.001-0.1 wt%, Mn: 0.001-0.1 wt%, Nb: 0.01-1.0 wt%, Ni: 35-37 wt%, Cr: 0.1 wt% or less, O: 0.0005 to 0.02 wt%, S: 0.002 wt% or less, Al: 0.005 wt% or less, Mg: 0.001 wt% or less, Ca: 0.001 wt% or less, with the balance being Fe and inevitable impurities In addition to MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO based composite oxide, silica (SiO ₂ ), spinel (MgO · Al ₂ O ₃₎ and niobium oxide (one or a low thermal expansion and high rigidity with excellent surface quality and the etching workability, characterized by containing the non-metallic inclusions of two or more of Nb 2 _{O 5)} shea Fe-Ni-based alloy for Doumasuku. The MnO—FeO—SiO ₂ —Nb ₂ O ₅ —MgO—Al ₂ O ₃ —CaO-based composite oxide is Al ₂ O ₃ : 40 wt% or less, FeO: 30 wt% or less, CaO: 40 wt% or less, MgO: or less 40 wt%, the balance being MnO, Fe-Ni based alloy for a shadow mask according to claim 1, characterized in that it is made of SiO ₂ and _Nb 2 _{O 5.} The shape of the non-metallic inclusions in the cross section parallel to the rolling direction of the Fe-Ni alloy sheet is controlled to the B system and the C system classified in JIS G 0555. The Fe-Ni type alloy for shadow masks as described. The degree of cleanliness according to JIS G 0555 in a cross section parallel to the rolling direction of the Fe-Ni alloy thin plate is 0.05 or less, for a shadow mask according to any one of claims 1 to 3 Fe-Ni alloy. When the raw material of Fe-Ni based alloy containing Fe and Ni as a main component is oxidized and refined, Si or Si alloy iron is added and deoxidized, and then Nb is added to adjust the finishing components, Add one or more of meteorite and quartz sand, and control the basicity (C / S) of the slag produced at this time to 1.5-4.0 and the alumina concentration in the slag to 5 wt% Then, after casting into a slab, performing the hot rolling and cold rolling according to a conventional method, the production of the Fe—Ni-based alloy according to any one of claims 1 to 4 is performed. A method for producing a Fe—Ni alloy for a low thermal expansion and high rigidity shadow mask, which is characterized.