Fe-Ni ALLOY HAVING SUPERIOR SURFACE PROPERTIES

Abstract

To provide an Fe-Ni alloy having sound surface properties and a method for producing the same.SOLUTION: An Fe-Ni alloy having superior surface properties is provided, the Fe-Ni alloy comprising, in mass%, C: 0.001 to 0.1%, Si: 0.01 to 0.5%, Mn: 0.01 to 1%, P: 0.01% or less, S: 0.005% or less, Ni: 30 to 50%, Cr: 0.01 to 0.5%, Mo: 0.1% or less, Cu: 0.2% or less, Al: 0.001 to 0.02%, Ti: 0.001 to 0.005%, Co: 1% or less, W: 0.1% or less, Sn: 0.001 to 0.01%, Ca: 0.0001 to 0.005%, Mg: 0.0001 to 0.005%, N: 0.01% or less, and O: 0.02% or less, the balance being Fe and inevitable impurities, where the average composition of non-metallic inclusions consists of MnO: 0.5 to 30%, CaO: 2 to 30%, SiO2: 5 to 50%, Al2O3: 10 to 60%, MgO: 5 to 50%, and TiO2: 5% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an Fe-Ni alloy having a controlled morphology of non-metallic inclusions and excellent surface properties, and a method for producing the same.

Background Art

[0002] Fe-Ni alloys have the characteristic of having a low coefficient of thermal expansion near room temperature among metals. Fe-36Ni alloy has been used in precision instruments, precision measuring instruments, watches, experimental devices, and tanks of LNG tankers by taking advantage of the small dimensional change with temperature. In recent years, carbon fiber reinforced plastic (CFRP) has been widely used. This material has both high strength and light weight. It is a material used in a wide range of fields from sports applications such as golf clubs to the automotive and aerospace industries. In particular, when used in the aircraft and automotive industries, very high dimensional accuracy is required, so an Invar alloy (Fe-36%Ni) with a small coefficient of thermal expansion is widely used as a mold (see, for example, Patent Documents 1 and 2).

[0003] In the fields of semiconductor lead frames, soft magnetic materials, electronic components for glass sealing, and terminals for crystal oscillators, Fe-42%Ni alloy is used. When processing these electronic components, punching is applied, which is suitable for forming fine lead patterns. Oxide-based non-metallic inclusions have been cited as factors that inhibit this workability (see, for example, Patent Documents 3 to 8).

[0004] Non-metallic inclusions pose a problem when applied to these uses. Especially in electronic components, even the slightest surface defect is not allowed. So far, as described above, techniques for controlling non-metallic inclusions have been disclosed, but depending on the morphology, defects occur on the surface of the product. As such, the morphology has not been controlled.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-269613 [Patent Document 2] Patent No. 7007510 [Patent Document 3] JP 2008-115466 A [Patent Document 4] JP 2002-004006 A [Patent Document 5] JP 2002-266017 A [Patent Document 6] JP 2002-206144 A [Patent Document 7] JP 2002-167650 A [Patent Document 8] JP 2000-017398 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, the main aim of the present invention is to prevent the clustering of nonmetallic inclusions, which become coarse surface defects, by controlling not only the composition of the nonmetallic inclusions but also their structure. Furthermore, the steel must have good mechanical properties. At the same time, the inclusions such as CaO and Al 2 O 3 Inclusions have a tendency to cluster, so their formation must be prevented. 2 O 3 When it comes to inclusions in the system, they must be prevented because they are formed in an environment with a high oxygen concentration, so the total number of inclusions is large and they are prone to clustering.

[0007] That is, an object of the present invention is to comprehensively consider the above and to provide an Fe-Ni alloy having a defect-free and good surface quality, and a method for producing the same. [Means for solving the problem]

[0008] In order to solve the problems of the above prior art, the inventors repeatedly conducted intensive experiments as follows. First, in the laboratory, 20 kg of Fe-42%Ni alloy was melted using a magnesia crucible. At that time, a high-frequency induction furnace was used as the melting device, and argon gas was blown from above the crucible to cut off the atmosphere. The raw materials used were pure Ni, electrolytic iron, ferrochrome, Mo, copper wire, Ti, ferrochrome nitride, Co, W, etc. Finally, either Si or Al or both were added for deoxidation, and 1 kg of CaO-SiO 2 -Al 2 O 3 -MgO-F-based slag was added, and sampling was carried out to intensively observe the composition of non-metallic inclusions. The observation was carried out using SEM. The analysis was performed by EDS. In particular, elemental mapping was carefully carried out, and attention was paid to the tissue morphology for observation. It was found that at least 10 points of analysis of inclusions were required to find compositional characteristics, 20 points were better, and 30 points or more were sufficient.

[0009] In addition, the alloy block cast into the mold was forged to 20 mmt, then the surface was ground and cold-rolled. The final plate thickness was 0.5 mm, and the surface was carefully observed to determine the presence or absence of defects.

[0010] As a result, the occurrence of defects was strongly related to the tissue morphology of non-metallic inclusions. It was found that the tissue morphology of MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides containing MgO or MgO·Al 2 O 3 has a high ability to suppress clustering. The schematic diagram thereof is shown in FIG. 1. FIG. 1(a) shows that the MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxide completely contains MgO or MgO·Al 2 O 3 within its approximate spherical surface, which is a good form that can suppress clustering. On the other hand, as shown in FIG. 1(b), a part of the outer edge is MnO-CaO-SiO 2 -Al 2 O3 - It is an MgO-based system, and most of the interior is high-melting-point MgO or MgO·Al 2 O 3 oxide, and it has been clarified that when it protrudes from within the approximate spherical surface of the inclusion, it promotes clustering. Although there are many unclear points in its mechanism, MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based melt is presumed to play the role of a sintering aid at the so-called steelmaking temperature (1400 - 1550 °C) and sinter by adhering to each other. The main sintering location is estimated from experience to be the inner wall of the immersion nozzle of the continuous caster in the actual machine.

[0011] On the other hand, it has also been confirmed that when MgO·Al 2 O 3 in its single form, and the combined form of both MgO·Al 2 O 3 and MgO in its single form, no sintering behavior occurs. It has been clarified that the morphological structure of the surrounding MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxide melt has a great influence on the final quality.

[0012] Based on this, for some steel grades, the raw materials were melted in a 70-ton electric furnace, decarburized, dechromed, and dephosphorized in AOD, slag was removed once, quicklime was added from above again, and at the same time FeSi and / or Al were added, and refining was carried out by promoting deoxidation and desulfurization. Then, slabs were produced by a continuous caster, and after surface grinding, hot rolling and cold rolling were carried out, and finally passed through an annealing and pickling line to produce 0.5-mm-thick thin plates.

[0013] That is, the present invention started from the above laboratory study and was developed by conducting actual machine tests for confirmation. The chemical components are all in mass% as follows. C: 0.001 to 0.1%, Si: 0.01 to 0.5%, Mn: 0.01 to 1%, P: less than 0.01%, S: less than 0.005%, Ni: 30 to 50%, Cr: 0.01 to 0.5%, Mo: less than 0.1%, Cu: less than 0.2%, Al: 0.001 to 0.02%, Ti: 0.001 to 0.005%, Co: less than 1%, W: less than 0.1%, Sn: 0.001 to 0.01%, Ca: 0.0001 to 0.005%, Mg: 0.0001 to 0.005%, N: less than 0.01%, O: less than 0.02%, containing the balance Fe and unavoidable impurities, and the average composition of non-metallic inclusions is MnO: 0.5 to 30%, CaO: 2 to 30%, SiO 2 : 5 to 50%, Al 2 O 3 : 10 to 60%, MgO: 5 to 50%, TiO 2 : 5% or less, which is an Fe-Ni alloy.

[0014] Furthermore, it is more preferable that the morphological form of the non-metallic inclusions is such that 70% or more of the non-metallic inclusions in terms of the number ratio with respect to all non-metallic inclusions are any one or two or more of the following seven types a to g. a: MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides are in a form that completely encloses MgO·Al 2 O 3 inside a substantially spherical surface b: MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides are in a form that completely encloses MgO·Al 2 O 3 and MgO inside a substantially spherical surface c: MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides d: MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides are in a form that completely encloses MgO inside a substantially spherical surface e: MgO single crystal f: MgO·Al 2 O 3 single crystal g: MgO and MgO·Al 2 O 3 The combined form of both simple substances

[0015] The above-mentioned MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides contain MnO: 1 to 40%, CaO: 0.1 to 40%, SiO 2 : 10 to 50%, Al 2 O 3 : 5 to 60%, MgO: 5 to 50%, TiO 2 : 5% or less is better.

[0016] The above-mentioned MgO·Al 2 O 3 may contain 0.5% or less of MnO.

[0017] The above-mentioned simple substance of MgO may contain Al 2 O 3 : 3% or less, SiO 2 : 1% or less, CaO: 10% or less, MnO: 1% or less.

[0018] This application also provides a manufacturing method. That is, raw materials such as Fe-Ni alloy scraps, ferronickel alloys, Ni, and iron scraps are melted in an electric furnace, and then oxygen blowing refining is carried out in AOD for decarburization, dechroming, and dephosphorization refining, followed by slag removal. Furthermore, quicklime, fluorite, and a magnesia source are added to form a CaO-SiO 2 -Al 2 O 3 -MgO-F-based slag, and at the same time ferrosilicon alloy and / or Al are added for deoxidation and desulfurization, and then a slab is manufactured by a continuous casting machine. After grinding the surface, it undergoes a hot rolling process and then cold rolling. This is a manufacturing method of Fe-Ni alloy.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0020] The reasons for the numerical limitations of the present invention and the scientific viewpoints will be explained below. The following units are in mass%. C: 0.001 to 0.1% C is an important element for maintaining the strength of the Fe-Ni alloy. Therefore, 0.001% is necessary. On the other hand, when added in excess of 0.1%, there are also drawbacks such as the formation of carbides such as Ti and embrittlement. Therefore, it is defined as 0.001 to 0.1%. The addition is controlled by introducing a carbon source after desulfurization in AOD. Preferably, it is 0.002 to 0.08%, more preferably 0.003 to 0.07%.

[0021] Si: 0.01 to 0.5% Si is an element effective for deoxidation and is very important in the present invention. Deoxidation can be carried out according to the following formula. That is, it is carried out by introducing an FeSi alloy or pure Si during deoxidation in AOD. Si +2 O =(SiO 2 ) …(1) Here, the underlines are the components in the molten steel, and the parentheses are the components in the slag. As will be described later, by reducing the activity coefficient of SiO 2 in the slag, deoxidation can be effectively advanced and the oxygen concentration of the present invention can be controlled. Furthermore, desulfurization can also be carried out simultaneously. 0.01% is necessary to exert its effect. When it exceeds 0.5%, the Ca and Mg concentrations become too high and exceed the upper limit of the scope of the present invention. As a result, harmful inclusions of the CaO system are formed, or low-melting-point compounds such as Ni 2 Mg are formed, reducing the hot workability. Therefore, it is defined as 0.01 to 0.5%. Preferably, it is 0.012 to 0.45%, more preferably 0.013 to 0.42%.

[0022] Mn: 0.01 to 1% Mn is an element useful for deoxidation and is important for controlling the morphology of inclusions to MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides. If it is too high, the amount of MnS will be too large, reducing corrosion resistance. Therefore, it is specified to be 0.01 to 1%. Preferably, it is 0.02 to 0.9%, and more preferably, it is 0.03 to 0.8%.

[0023] P: 0.01% or less P not only segregates at grain boundaries and reduces corrosion resistance, but is also a harmful element that causes red-hot brittleness during welding and leads to cracking. In AOD, P in the slag can be removed by performing oxygen blowing. Therefore, it is set to 0.01% or less. Preferably, it is 0.009% or less, and more preferably, it is 0.006% or less. 2 O 5 As a result, it is set to 0.01% or less. Preferably, it is 0.009% or less, and more preferably, it is 0.006% or less.

[0024] S: 0.005% or less If S is in an appropriate amount, it forms fine MnS and improves punching properties. Conversely, if it is too high, it reduces hot workability and causes ear cracking. Therefore, it is specified to be 0.005% or less. As will be described in detail later, desulfurization can proceed according to the following reaction formula. 3(CaO) + 2 Al + 3 S =(Al 2 O 3 ) + 3(CaS) …(2) 2(CaO) + Si + 2 S =(SiO 2 ) + 2(CaS) …(3) Reducing the activity coefficients of alumina and silica in the slag can promote the desulfurization reaction efficiently. Since appropriate properties can be obtained at 0.005% or less, it is specified within this range. Preferably, it is 0.004% or less, and more preferably, it is 0.003% or less. Although not limited, it is desirable to contain 0.0001% or more to ensure punching properties.

[0025] Ni: 30 to 50% Ni is a major element of the present invention and is an important element for maintaining the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 30 to 50%. Preferably, it is 33 to 49%, and more preferably, it is 35 to 48.8%.

[0026] Cr: 0.01 to 0.5% Cr is an important element for maintaining strength by solid solution strengthening in the present invention. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Furthermore, there is a risk of forming MnO-Cr 2 O 3 system inclusions. Therefore, it is specified to be 0.01 to 0.5%. Preferably, it is 0.02 to 0.4%, and more preferably, it is 0.03 to 0.3% or less.

[0027] Mo: 0.1% or less Mo is an important element for maintaining strength by solid solution strengthening in the same way as Cr. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 0.1% or less. Preferably, it is 0.08% or less. More preferably, it is 0.06% or less.

[0028] Cu: 0.2% or less Cu is an important element for maintaining strength by solid solution strengthening in the same way as Cr and Mo. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 0.2% or less. Preferably, it is 0.17% or less, and more preferably, it is 0.15% or less.

[0029] Al: 0.001 to 0.02% Al is an element useful for deoxidation. On the other hand, if it is too high, it will form AlN and impair hot workability, or the Ca and Mg concentrations will become too high and exceed the upper limit of the scope of the present invention. As a result, it will form harmful CaO-based inclusions or form a low-melting-point compound of Ni 2 Mg and reduce hot workability. The deoxidation reaction proceeds as follows. 2 Al +3 O =(Al 2 O3 ) …(4) As will be described in detail later, deoxidation proceeds efficiently by reducing the activity of alumina in the slag. Further, desulfurization can be carried out simultaneously. Therefore, it is specified to be 0.001 to 0.02%. Preferably, it is 0.0013 to 0.018%, more preferably 0.0019 to 0.015%, and still more preferably 0.002 to 0.013%.

[0030] Ti: 0.001 to 0.005% Ti fixes N to form TiN, thereby preventing the formation of blowholes exceeding the solubility of nitrogen during solidification. Therefore, it is specified to be 0.001 to 0.005%. Preferably, it is 0.001 to 0.003%. More preferably, it is 0.001 to 0.002%.

[0031] Co: 1% or less Co is an important element for maintaining strength by solid solution strengthening, similar to Cr and Mo. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 1% or less. Preferably, it is 0.8% or less, and more preferably 0.5% or less.

[0032] W: 0.1% or less W is an important element for maintaining strength by solid solution strengthening, similar to Cr, Mo, and Co. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 0.1% or less. Preferably, it is 0.09% or less, and still more preferably 0.06% or less.

[0033] Sn: 0.001 to 0.01% Sn is an important element for maintaining strength by solid solution strengthening, similar to Cr, Mo, Co, and W. However, if it is too high, it will deteriorate properties such as the coefficient of thermal expansion and soft magnetic properties. Therefore, it is specified to be 0.001 to 0.01%. Preferably, it is 0.0015 to 0.008%, and still more preferably 0.002 to 0.005%.

[0034] Ca: 0.0001 to 0.005% Ca is an important element for controlling the morphological form of non-metallic inclusions into favorable MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides. Controlling to this form can produce a sound product without forming surface defects without clustering. Ca is effectively added by utilizing the following reactions. 3(CaO) + 2 Al =(Al 2 O 3 ) + 3 Ca …(5) 2(CaO) + Si =(SiO 2 ) + 2 Ca …(6) To control this reaction, the activities of alumina and silica in the slag may be controlled within an appropriate range. This will be described in detail in the manufacturing method. Conversely, if it is too high, harmful CaO inclusions will be formed, promoting clustering and forming defects. Therefore, it is specified to be 0.0001~0.005%. Preferably, it is 0.0002~0.004%, and more preferably, it is 0.0002~0.003%.

[0035] Mg: 0.0001~0.005% Mg is an important element for controlling the morphological form of non-metallic inclusions into favorable MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides, MgO, MgO·Al 2 O 3 To control to this form can produce a sound product without forming surface defects without clustering. Mg is effectively added by utilizing the following reactions. 3(MgO) + 2 Al =(Al 2 O 3 ) + 3 Mg …(7) 2(MgO) + Si =(SiO 2 ) + 2 Mg …(8) To control this reaction, it is only necessary to control the activities of alumina and silica in the slag within an appropriate range. This will be described in detail in the manufacturing method. Conversely, if it is too high, a low melting point compound Ni2Mg will be formed, reducing the hot workability. Therefore, it is specified to be 0.0001 to 0.005%. Preferably, it is 0.0002 to 0.0045%, and more preferably, it is 0.0003 to 0.004%.

[0036] N: 0.01% or less N is an important element for maintaining strength by solid solution strengthening. However, if it is too high, TiN clusters will be formed, causing surface defects. Therefore, it is specified to be 0.01% or less. Preferably, it is 0.008% or less, and more preferably, it is 0.006% or less.

[0037] O: 0.02% or less When oxygen is too high, it is easy to form clustered MnO-Cr 2 O 3 -type inclusions. Furthermore, it is necessary to lower it to increase the number of non-metallic inclusions and form surface defects. Therefore, it is set to 0.02% or less. Preferably, it is 0.016% or less, more preferably, it is 0.014% or less, and even more preferably, it is 0.01% or less.

[0038] The Fe-Ni alloy of the present invention has the balance being iron and inevitable impurities. Also, as inevitable impurities, for example, it may contain extremely trace amounts of Pb, Ta, Ag, Na, K, Zr. All of them are mixed in from raw materials such as Fe-Ni alloy scraps, iron scraps, and other ferroalloys.

[0039] Subsequently, the average composition of non-metallic inclusions will be described. The average composition of non-metallic inclusions is as follows. MnO: 0.5 to 30% MnO is effective for forming harmless MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides. However, if it is too high, harmful MnO-Cr 2 O 3Defects are formed by forming oxides. Therefore, it is defined as 0.5 to 30%. Preferably, it is 0.6 to 29%.

[0040] CaO: 2 to 30% CaO is harmless MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides, but if it is too high, it will form harmful CaO inclusions and cause defects. Therefore, it is defined as 2 to 30%. Preferably, it is 3 to 29%. More preferably, it is 4 to 28%.

[0041] SiO 2 : 5 to 50% SiO 2 is a compound present in MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides, and it is effective because it lowers the melting point. Therefore, it is defined as 5 to 50%. Preferably, it is 5 to 45%.

[0042] Al 2 O 3 : 10 to 60% Al 2 O 3 is harmless MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides, and in addition, it is extremely effective in forming MgO·Al 2 O 3 However, if it is too high, it will form harmful Al 2 O 3 monomer and cause defects. Therefore, it is defined as 10 to 60%. Preferably, it is 15 to 50%.

[0043] MgO: 5 to 50% MgO is harmless MnO-CaO-SiO 2 -Al 2 O 3-In addition to being effective in forming MgO-based oxides, MgO alone and MgO·Al 2 O 3 alone are also extremely effective in forming. Therefore, it is specified to be 5 to 50%. Preferably, it is 10 to 45%.

[0044] TiO 2 : 5% or less TiO 2 is harmless MnO-CaO-SiO 2 -Al 2 O 3 -It is effective in lowering the melting point of MgO-based oxides. However, when the concentration is high, the melting point becomes high, so it is specified to be 5% or less. Preferably, it is 4% or less.

[0045] Cr 2 O 3 : 2% or less Although not particularly limited, when Cr 2 O 3 is high, it is easy to form MnO-Cr 2 O 3 -based inclusions. Furthermore, the oxygen concentration in the molten steel also increases, and the number of non-metallic inclusions increases, causing defects. Therefore, 2% or less is desirable. More preferably, it is 1.8% or less. Even more preferably, it is 1% or less.

[0046] Here, there are several methods to obtain the average composition. It becomes clear by randomly analyzing 10 points with SEM / EDS. At this time, it is necessary to analyze 2 points at the center and the outer peripheral part, and the average can be obtained by taking mapping and measuring the area ratio by image analysis. Preferably, analysis of 20 points or more, more preferably 30 points or more is preferred. Another one is the so-called electrolysis method, widely known as the Speed method. That is, an appropriate potential is applied in an appropriate solution to dissolve the metal part. Then, the non-metallic inclusions remaining as residues are filtered and collected. When this is subjected to chemical analysis, the average composition is immediately obtained. The analysis method is not limited.

[0047] Furthermore, an explanation will be added regarding the morphological form of non-metallic inclusions. It is a more preferable embodiment that 70% or more of the non-metallic inclusions in terms of the number ratio for all non-metallic inclusions are any one or two or more of the following seven types a to g. Note that the morphological forms corresponding to a to g are shown together in FIGS. 2(a) to (g). a: MnO - CaO - SiO 2 - Al 2 O 3 - The morphological form in which the MgO - based oxide completely encloses MgO·Al within a substantially spherical surface 2 O 3 b: MnO - CaO - SiO 2 - Al 2 O 3 - The morphological form in which the MgO - based oxide completely encloses MgO·Al and MgO within a substantially spherical surface 2 O 3 c: MnO - CaO - SiO 2 - Al 2 O 3 - MgO - based oxide d: MnO - CaO - SiO 2 - Al 2 O 3 - The morphological form in which the MgO - based oxide completely encloses MgO within a substantially spherical surface e: MgO single body f: MgO·Al 2 O 3 single body g: The morphological form in which both single bodies of MgO and MgO·Al 2 O 3 are combined Here, being completely enclosed within a substantially spherical surface means the state where the internal substance is completely encapsulated by the outer - edge substance as shown in FIG. 1(a), and those in which the internal substance protrudes partially outside as shown in FIG. 1(b) are not included.

[0048] ​​Although it has also been described in the means for solving the problems, the form in Fig. 1(b) does not appear in the following operations. To control these organizational forms, among the chemical components, Si, Al, Ca, Mg, O, and Mn should be controlled within the scope of the present invention, but it does not stop there. The organizational forms in Figs. 2(a), (b), and (d) are also characteristic in the present application. To achieve this organizational form, there are key points in the deoxidation treatment in AOD. Note that dolomite is preferred for the AOD bricks. During the deoxidation period, first, quicklime is added, and at the same time, fluorite and further waste bricks containing MgO are added. The MgO waste bricks can be added as needed. Then, when ferrosilicon alloy or pure Si and Al are added, Si and Al are added to the molten slag that has already been formed. Deoxidation is possible with only Si. This directly reacts with CaO and MgO in the slag and can effectively add Ca and Mg.

[0049] Mg is supplied into the molten steel in advance according to the reactions of the above-mentioned formulas (7) and (8). Although there are many points that are unclear about the cause, Ca is delayed. This dissolved Mg reacts with silica and alumina, which are the original non-metallic inclusions, as follows. 2 Mg +SiO 2 (Inclusion) = 2MgO (Inclusion) + 2 Si …(9) 3 Mg +Al 2 O 3 (Inclusion) = 3MgO (Inclusion) + 2 Al …(10) 2 Mg +4 Al +4SiO 2 (Inclusion) = 2MgO·Al 2 O 3 (Inclusion) + 4 Si …(11) 3 Mg +4Al 2 O 3 (Inclusion) = MgO·Al 2 O 3 (Inclusion) + 2 Al …(12) As shown in the above formulas (9) to (12), simple MgO, MgO·Al 2 O 3It can be initially formed as a single entity. Subsequently, Ca is supplied from the slag. By the reaction of Mn, Si, and Ca in the molten steel with the above inclusions, MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides are vigorously formed. And this molten oxide covers the MgO single entity and MgO·Al 2 O 3 single entity to render it harmless. That is, it acts as a harmless MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based inclusion. Therefore, since the non-metallic inclusion behaves as described above when it is spherical, it becomes harmless.

[0050] Furthermore, the composition range of the above MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxide will be described. MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxide has MnO: 1 to 40%, CaO: 0.1 to 40%, SiO 2 : 10 to 50%, Al 2 O 3 : 5 to 60%, MgO: 5 to 50%, TiO 2 : 5% or less When it is within the above range, it can maintain a molten state at the steelmaking temperature, that is, near 1500°C, so the above range is set. If MnO is too high, harmful MnO-Cr 2 O 3 -based oxides are formed, so it is specified as 1 to 40%. If CaO is too high, harmful CaO single entity inclusions are formed, so CaO: 0.1 to 40% is specified. If Al 2 O 3 is too high, Al 2 O 3 single entity is formed, so Al 2 O 3 : 5 to 60% is set. SiO 2 is effective in lowering the melting point, but if it is too high, harmful MnO-Cr 2 O 3 inclusions are formed, so it is set as 10 to 50%. TiO2 If it is too high, it raises the melting point, so it was set to 5% or less. MgO has the effect of lowering the melting point when it is 5% or more, but conversely, if it exceeds 50%, the melting point becomes high and the molten state cannot be maintained. Therefore, MgO was specified as 5 to 50%.

[0051] MgO·Al 2 O 3 MnO concentration in it: 0.5% or less MgO·Al 2 O 3 Since MnO is dissolved in the MgO site of MgO·AlO, it was specified as 0.5% or less.

[0052] Al in MgO single inclusions 2 O 3 : 3% or less, SiO 2 : 1% or less, CaO: 10% or less, MnO: 1% or less Since MgO single inclusions are harmless, it is desirable to dissolve to a certain extent in this inclusion. Considering the solid solubility limit, Al 2 O 3 : 3% or less, SiO 2 : Containing 1% or less, CaO: 10% or less, MnO: 1% or less.

[0053] The present invention also provides a manufacturing method. That is, the raw materials are melted in an electric furnace, and then oxygen is blown and refined in an AOD to carry out decarburization, dechroming, and dephosphorization treatments. The raw materials are blended according to the target components such as Fe-Ni alloy scraps, iron scraps, pure Ni, ferrosilicon alloys, etc. After the decarburization, dechroming, and dephosphorization processes in the AOD are completed, the slag is removed once. Further, after adding quicklime, magnesia source, and fluorite, either or both of ferrosilicon alloy and Al are added to form a CaO-SiO 2 -Al 2 O 3 -MgO-F-based slag to carry out deoxidation and desulfurization. Then, the chemical components are adjusted and the temperature is adjusted by ladle refining, a slab is manufactured by a continuous casting machine, and after the surface is ground, hot rolling is carried out followed by cold rolling. At this time, it is necessary to control the slag composition within an appropriate range in order to control the morphological form of non-metallic inclusions into a preferable form.

[0054] CaO - SiO 2 - Al 2 O 3 The CaO - SiO 2 - Al 2 O 3 - MgO - F - based slag preferably has the following range. CaO: 45 - 74% The CaO concentration can be adjusted by adding quicklime. CaO has a great effect on deoxidation and desulfurization. That is, as shown in formulas (2) - (3), the sulfur concentration can be adjusted to the range of the present invention by stably existing as CaS in the slag. However, if it exceeds 74%, CaO inclusions will be formed. Therefore, 45 - 74% is good. Preferably, it is 46 - 73%. More preferably, it is 47 - 72%.

[0055] Al 2 O 3 : 8% or less Al 2 O 3 is effective for melting the CaO - SiO 2 - Al 2 O 3 - MgO - F - based slag. On the other hand, if it exceeds 8%, Al 2 O 3 single inclusions will be formed and clustering will proceed. Therefore, 8% or less is desirable. Preferably, it is 7% or less. More preferably, it is 6% or less.

[0056] MgO: 3 - 18% MgO is effective for melting the CaO - SiO 2 - Al 2 O 3 - MgO - F - based slag. On the other hand, if the MgO concentration is high, the Mg concentration in the molten steel will be high and Ni 2 Mg will be formed, reducing the hot workability. Therefore, 3 - 18% is desirable. More desirably, it is 3.1 - 16%, and even more desirably, it is 3.5 - 15.5%.

[0057] SiO 2 : 5 - 35% SiO 2 is for the CaO - SiO 2 - Al 2 O 3 2 - Al 2 O 3 ​​​​​​​​​​​​​​​​​​-MgO-F-based slag is effective for melting. On the other hand, when the SiO 2 concentration is high, the oxygen concentration in the molten steel becomes high, and the non-metallic inclusion composition also becomes the MnO-Cr 2 O 3 system, resulting in surface defects. Therefore, 35% or less is desirable. More desirably, it is 33% or less. Even more desirably, it is 30% or less.

[0058] F: 1 to 10% F is added as fluorite. F is CaO-SiO 2 -Al 2 O 3 -MgO-F-based slag is effective for melting. On the other hand, when the F concentration is high, it corrodes the bricks of the AOD furnace and the ladle, shortening the life. Therefore, 1 to 10% is good. More desirably, it is 1.5 to 9%.

[0059] Furthermore, it is desirable that the concentrations of MnO, Cr 2 O 3 , and FeO are low. MnO: 2% or less When MnO is at a high concentration, the oxygen concentration becomes high, forming MnO-Cr 2 O 3 system inclusions. Therefore, 2% or less is good. Desirably, it is 1.8% or less, and more desirably, it is 1.5% or less.

[0060] Cr 2 O 3 : 1% or less Cr 2 O 3 When it is at a high concentration, the oxygen concentration becomes high, forming MnO-Cr 2 O 3 system inclusions. Therefore, 1% or less is good. Desirably, it is 0.7% or less. More desirably, it is 0.6% or less.

[0061] FeO: 1% or less When FeO is at a high concentration, the oxygen concentration becomes high, forming MnO-Cr 2 O 3An intermediate is formed. Therefore, it is preferably 1% or less. Desirably, it is 0.9% or less. More desirably, it is 0.8% or less.

[0062] Furthermore, a higher S concentration is desirable. The reason is to indicate that desulfurization has proceeded normally. It is preferably 0.01% or more, more desirably 0.02% or more.

Examples

[0063] Examples are shown below to clarify the effectiveness of the present invention. The raw materials were melted in a 70-ton electric furnace, and then oxygen was blown in an AOD for decarburization, dechroming, and dephosphorization refining. The raw materials were blended according to the target composition with Fe-Ni alloy scraps as the center, including iron scraps, stainless steel scraps, ferro-nickel alloys, ferrosilicon alloys, etc.

[0064] After the decarburization, dechroming, and dephosphorization processes in the AOD were completed, the slag was removed to the slag pot to discharge Cr and P out of the system. Then, the deoxidation process was advanced in the AOD. That is, quicklime, magnesia-containing waste bricks, and further fluorite were added, and then ferrosilicon alloy or pure Si was added. Al was added in some charges. Finally, CaO-SiO 2 -Al 2 O 3 -MgO-F-based slag was formed. Even when Al was not added, alumina was supplied by the oxidation of Al, which is an impurity in the FeSi alloy or pure Si.

[0065] After deoxidation, alloying elements such as C, Mo, Co, Cr, and Ni were added in the ladle refining to finely adjust the chemical composition. In this way, after deoxidation and desulfurization, a slab with a thickness of 200 mmt × width of 1200 mmw × length of 7 m was produced by a continuous casting machine. After grinding the oscillation marks on the surface, it was heated to 1000 - 1250 °C according to the steel type, and then passed through a hot rolling process, and finally cold rolling was carried out and passed through an annealing and pickling line. As a result, cold-rolled coils with a thickness of 1 mmt were produced for all steel types.

[0066] At this time, the evaluation was conducted by the following method. 1) Chemical composition: The surface of a φ30 mm × 10 mm height suction sample collected from the tundish of the continuous casting machine was ground with a grinder. The main elements were analyzed by fluorescent X-ray analysis. Part of C and S were analyzed by the combustion method. Also, N and O were analyzed by the infrared absorption method. 2) Slag composition: The slag was collected with an iron rod and crushed. A sample obtained by pressing this into a cylindrical shape was prepared. The value of this sample was determined using the fluorescent X-ray analysis method. F was determined by chemical analysis. 3) Average composition of non-metallic inclusions: The above-mentioned suction sample was cut out, embedded in resin, and mirror-polished. This was put into an SEM for observation and quantitative analysis. 30 inclusions of 5 μm or more were randomly selected, and the center and outer periphery were analyzed. For each inclusion, the elemental distribution was determined by mapping, the ratio of each phase was calculated by image analysis, and considering the weighted average, the representative analysis value of each inclusion particle was obtained. The average value of these 30 points was calculated and obtained. 4) Microstructure morphology of non-metallic inclusions: When observed and analyzed as described above, the morphology was classified. Note that the morphology corresponding to Fig. 1(b) was not confirmed. 5) Composition of each oxide: It was obtained from the composition of each oxide phase described above. 6) Comprehensive evaluation: When a 1 mmt Fe-Ni alloy plate was passed through, the inspector evaluated it with the naked eye. The evaluation results were determined as follows. In the following, the allowable range without cutting means that there are up to 3 linear defects with a length of 1 mm or more per 10 m of the steel plate surface. 2 This means that there are up to 3 linear defects with a length of 1 mm or more per 10 m of the steel plate surface. Qualified: ◎ No surface defects occurred (good product rate at the time of shipment: 100%) Qualified: 〇 Some surface defects occurred, but within the allowable range of the required quality (same good product rate: 95%) Qualified: △ Some surface defects occurred, but it can be shipped by partial cutting (same good product rate: 80%) Unqualified: × Surface defects occurred throughout the entire length of the coil and were subjected to chip treatment (same good product rate: 0%)

[0067]

Table 1

[0068]

Table 2

[0069] Examples are shown below to clarify the effectiveness of the invention of the present application. The organizational forms of the inventive examples are shown in FIGS. 2(a) to (g), and the organizational forms of the comparative examples are shown in FIGS. 2(h) to (j). The reason why the chemical components do not total 100% is due to inevitable impurities. For Nos. 1 to 14 of the inventive examples, the chemical analysis was within the range, and the slag composition also satisfied the desirable range. As a result, the organizational form of the non-metallic inclusions also satisfied the range of a to g. Finally, all the products passed the inspection.

[0070] However, in No. 5, the MgO concentration of the MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based inclusions was low, the Cr 2 O 3 concentration was high, the Al 2 O 3 concentration in simple MgO was high and out of range, and the Al 2 O 3 in the form of combined MgO·Al 2 O 3 and MgO, as well as the SiO 2 , MnO became high. Furthermore, one alumina inclusion and one MnO-Cr 2 O 3 -based inclusion were confirmed. In No. 8, two simple CaO inclusions were observed. Therefore, the evaluation was ○.

[0071] Furthermore, in No. 10, the Cr 2 -Al 2 O 3 -MgO-based inclusion had a high Cr 2 O 3 concentration, the MnO concentration in MgO·Al 2 O 3 was high, and the SiO 2 , Al 2 O 3 and MnO in the MgO inclusion were high. MgO·Al 2 O3 MgO·Al in a form combined with MgO 2 O 3 The MnO concentration in it became high and the CaO concentration in MgO increased. At the same time, CaO single inclusions, Al 2 O 3 single inclusions and MnO-Cr 2 O 3 system inclusions were confirmed. As a result, the evaluation was Δ.

[0072] Subsequently, the comparative examples will be described. In No.15, Si and Al deviated significantly, and the Ca and Mg concentrations increased. The CaO concentration in the slag also exceeded the desirable range, and Al 2 O 3 , SiO 2 also deviated. As a result, among the average compositions of the inclusions, MgO, Al 2 O 3 , SiO 2 , CaO deviated. The tissue morphology also had more h·CaO single bodies, and the MnO, CaO, SiO in MnO-CaO-SiO 2 -Al 2 O 3 -MgO-based oxides deviated in terms of MnO, CaO, SiO 2 , Al 2 O 3 , MgO concentrations. In addition, the CaO concentration in MgO single bodies was high, and the SiO in the form combined with MgO·Al 2 O 3 and the CaO concentration increased. The CaO single inclusions became the center and defects occurred, resulting in chipping. 2

[0073] In No.16, since the Si concentration deviated significantly, the Ca and Mg concentrations also deviated significantly. The CaO and Al 2 O 3 concentrations in the slag were high, and the SiO 2 concentration was low. In the average composition of the inclusions, MgO, Al 2 O 3 , SiO 2 , CaO deviated from the range. The MnO-CaO-SiO 2 -Al 2 O 3 ​- CaO and SiO in the -MgO based oxide 2 、Al 2 O 3 、the MgO concentration was out of range. Since the Ti and N concentrations were also extremely high, TiN clusters were also formed. Furthermore, due to the formation of a large number of h·CaO single inclusions in the microstructure, surface defects occurred frequently, and the coil became fragmented.

[0074] In No.17, since Si and Al were extremely low, Ca and Mg did not enter the molten steel. Moreover, because the Mn, sulfur, and oxygen concentrations were high, the number of non-metallic inclusions also increased. Also, the slag composition deviated from the range, such as high silica, low CaO, high MnO and FeO, which also had an adverse effect on the inclusion composition. In addition, the F concentration was low, and the deterioration of the slag fluidity also inhibited desulfurization. The average composition of the inclusions deviated from the range for all oxides except TiO 2 . The microstructure also had a large number of j·MnO-Cr 2 O 3 -type inclusions formed. As a result of the confirmation of MnO-CaO-SiO 2 -Al 2 O 3 -MgO based oxides, all except TiO 2 were out of range. Also, the Cr concentration was extremely high and the alloy properties deviated. As a result of the confirmation of MnO-Cr 2 O 3 -type inclusions, surface defects occurred throughout the entire length, and finally the coil became fragmented.

[0075] In No.18, the Al concentration was high, the alumina concentration in the slag was high, while the CaO concentration was low and out of range. The average composition of the non-metallic inclusions was 100% alumina, and the microstructure also consisted only of i·Al 2 O 3 single inclusions. As a result, surface defects occurred throughout the entire length and it became fragmented.

[0076] In No.19, since the Si and Al concentrations were low, the Ca and Mg concentrations were low, and the oxygen concentration was extremely high and out of range. MnO and Cr 2 O 3, the FeO concentration is high, and in the average composition of non-metallic inclusions, Al 2 O 3 and Cr 2 O 3 are high, and three types of tissue forms, h, i, and j, are formed. In particular, many i·Al 2 O 3 inclusions were observed. Furthermore, the components dissolved in the simple inclusions of MgO·Al 2 O 3 , the simple inclusions of MgO, and the form in which MgO·Al 2 O 3 and MgO are combined also deviated. In addition, the Mo, Cu, and Sn concentrations are high and the alloy properties deviated. Finally, surface defects occurred throughout the length and it became chipping.

[0077] No. 20 has low Al, and high oxygen and sulfur deviated. In the slag, MnO and Cr 2 O 3 , the FeO concentration is high, and F is low. The deterioration of the slag fluidity also contributed to inhibiting desulfurization. As a result, the tissue form is mainly the j·MnO-Cr 2 O 3 system, and flaws occurred throughout the length and it became chipping. Also, Cr and Co are high and the alloy properties deviated.

Claims

1. By mass percentage: C: 0.001 - 0.1%, Si: 0.01 - 0.5%, Mn: 0.01 - 1%, P: 0.01% or less, S: 0.005% or less, Ni: 30 - 50%, Cr: 0.01 - 0.5%, Mo: 0.1% or less, Cu: 0.2% or less, Al: 0.001 - 0.02%, Ti: 0.001 - 0.005%, Co: 1% or less, W: 0.1% or less, Sn: 0.001 - 0.01%, Ca: 0.0001 - 0.005%, Mg: 0.0001 - 0.005%, N: 0.01% or less, O: 0.02% or less, the balance being Fe and unavoidable impurities, and the average composition of non-metallic inclusions being MnO: 0.5 - 30%, CaO: 2 - 30%, SiO ２ : 5 - 50%, Al ２ O ３ : 10 - 60%, MgO: 5 - 50%, TiO ２ : 5% or less, characterized by an excellent surface property Fe-Ni alloy.

2. The morphological form of the non-metallic inclusions is such that 70% or more of the non-metallic inclusions, in terms of the number ratio with respect to all non-metallic inclusions, are any one or two or more of the following seven types a to g. The Fe-Ni alloy excellent in surface properties according to Claim 1, characterized in that. a: MnO - CaO - SiO ２ -Al ２ O ３ -MgO-based oxide has a form that completely encloses MgO·Al ２ O ３ within a substantially spherical surface b: MnO - CaO - SiO ２ - Al ２ O ３ - MgO-based oxides in a form that completely encloses MgO·Al ２ O ３ and MgO within a substantially spherical surface c: MnO - CaO - SiO ２ - Al ２ O ３ - MgO-based oxide d: MnO - CaO - SiO ２ -Al ２ O ３ -MgO-based oxide in a form that completely encloses MgO within a substantially spherical surface e: MgO single crystal f: MgO·Al ２ O ３ monomer g: The combined form of both simple substances of MgO and MgO·Al ２ O ３ in which the two simple substances are combined

3. The aforesaid MnO-CaO-SiO ２ -Al ２ O ３ -MgO-based oxide is characterized in that it contains MnO: 1 to 40%, CaO: 0.1 to 40%, SiO ２ : 10 to 50%, Al ２ O ３ : 5 to 60%, MgO: 5 to 50%, TiO ２ : 5% or less, and is the Fe-Ni alloy excellent in surface properties according to claim 2.

4. The above-mentioned MgO·Al ２ O ３ is an Fe-Ni alloy excellent in surface properties according to claim 2, characterized by containing 0.5% or less of MnO.

5. The MgO single crystal is Al ２ O ３ : 3% or less, SiO ２ : 1% or less, CaO: 10% or less, MnO: 1% or less, and the Fe-Ni alloy excellent in surface properties according to claim 2 is characterized by containing the same.

6. A method for manufacturing an Fe-Ni alloy excellent in surface properties according to any one of claims 1 to 5, comprising melting raw materials such as Fe-Ni alloy chips, ferronickel alloy, Ni, and iron chips in an electric furnace, then performing oxygen blowing refining in an AOD to carry out decarburization, dechroming, and dephosphorization refining, followed by slag removal. Further, adding quicklime, fluorite, and a magnesia source to form a CaO-SiO ２ -Al ２ O ３ -MgO-F-based slag, and at the same time adding ferrosilicon alloy and / or Al to carry out deoxidation and desulfurization, then manufacturing a slab with a continuous casting machine, grinding the surface, and performing cold rolling through a hot rolling process. A method for manufacturing an Fe-Ni alloy excellent in surface properties, characterized by the above steps.

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