Ni-based alloy with excellent surface properties

Abstract

Provided are an Ni-based alloy having no defects on the surface and having sound surface properties and a method for producing the Ni-based alloy. The Ni-based alloy contains, in terms of mass%, 0.001-0.1% of C, 0.01-0.4% of Si, 0.1-1% of Mn, up to 0.03% of P, up to 0.002% of S, 13-35% of Cr, up to 18% of Mo, up to 5% of W, up to 1% of Cu, 0.001-0.35% of Al, 0.001-0.2% of Ti, 0.0001-0.02% of Ca, 0.0001-0.02% of Mg, 0.001-0.03% of N, 2-11% of Fe, up to 0.005% of O, and up to 4% of one or more of Co, Nb, and B, with the remainder being Ni and unavoidable impurities, the average composition of non-metallic inclusions comprising, in terms of mass%, 30-70% of MgO, 15-40% of Al2O3, up to 30% of SiO2, 10-40% of CaO, and up to 1% of MnO.

Description

Ni-based alloy with excellent surface quality

[0001] The present invention relates to a Ni-Cr-Mo-W-Fe based Ni-based alloy having excellent surface properties and a method for producing the same.

[0002] Ni-based alloys, which have excellent corrosion resistance and acid resistance, contain Cr, Mo, and W in addition to Ni as the main component. Since these metals are extremely expensive compared to iron, it is extremely important to improve yield and reduce manufacturing costs. However, if surface defects such as linear scratches occur on the surface of a Ni-based alloy, the required corrosion resistance will not be exhibited and many other issues will arise, such as impaired weldability. Furthermore, since the defective areas significantly reduce yield, a Ni-based alloy with excellent surface properties has been desired.

[0003] Patent Document 1 discloses a technique for improving surface properties by carefully controlling the composition of non-metallic inclusions in a Ni-based alloy. However, depending on the structure of the non-metallic inclusions, defects are not necessarily eliminated, posing a technical problem.

[0004] Patent Document 2 discloses a method for refining a Ni-based alloy. However, the method does not examine the structure of non-metallic inclusions.

[0005] Patent Document 3 discloses a technique for surface treatment of Ni-based alloys. It explains that corrosion resistance can be improved by properly forming a passive film. However, no technical development has been done regarding surface defects.

[0006] In fact, Ni-based alloys containing large amounts of Ni, Cr, Mo, W, etc., and having improved corrosion resistance and acid resistance, are widely used in flue gas desulfurization equipment used on ships and thermal power plants, which are operated in harsh sulfuric acid environments. In recent years, the demand for Ni-based alloys has been expanding as environmental regulations regarding ship exhaust gases have become stricter. Furthermore, the importance of nuclear power generation has been highlighted from the perspective of carbon neutrality, and it is expected that their uses will continue to expand in the future.

[0007] Patent Document 4 discloses a technology for improving stainless steel for use in nuclear power plants. In recent years, in harsh operating environments, Ni-based alloys are required for the inside of nuclear power plant pressure vessels, although this depends on the location.

[0008] Patent Documents 5 and 6 present techniques relating to Ni-based alloy products intended for use as structural components of nuclear reactors that are used for long periods in high-temperature water environments. However, the problem of surface defects remains unresolved.

[0009] Japanese Patent No. 6990337 Japanese Patent Laid-Open No. 2009-114544 Japanese Patent Laid-Open No. 2015-183290 Japanese Patent Publication No. 35-16661 Japanese Patent No. 4340899 Japanese Patent No. 4433230

[0010] As mentioned above, the main aim of the present invention is to prevent the clustering of nonmetallic inclusions, which can cause large surface defects, by controlling not only the composition of the nonmetallic inclusions but also their structure. 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 are formed in an environment with a high oxygen concentration, so the total number is large and they are prone to clustering, so they must be prevented.

[0011] That is, an object of the present invention is to comprehensively consider the above and to provide a Ni-based alloy having a sound surface quality without surface defects, and a method for producing the same.

[0012] In order to solve the problems of the above-mentioned conventional techniques, the inventors have repeatedly conducted extensive experiments as described below.

[0013] First, 20 kg of Ni-16%Cr-16%Mo-3%W-6%Fe alloy was melted in a magnesia crucible in the laboratory. A high-frequency induction furnace was used as the melting equipment, and argon gas was blown into the crucible from above to isolate it from the atmosphere. The raw materials used were electrolytic iron, ferrochrome, Mo, copper wire, and W. Finally, Si and Al were added to deoxidize the alloy, and an artificial slag, CaO-Al, was obtained. ２ O ３-MgO-SiO ２ One kilogram of -F slag was charged, and samples were taken to closely observe the composition of the nonmetallic inclusions. Observations were performed using a SEM. Analysis was performed using EDS. Elemental mapping was performed carefully, and the structural morphology was carefully observed. It was found that to identify compositional characteristics, analysis of at least 10 inclusions is necessary, 20 is better, and 30 or more is sufficient.

[0014] The Ni-based alloy ingot cast into the mold was forged to a thickness of 20 mm, after which the surface was ground and cold rolled to a final thickness of 0.5 mm. The surface was carefully observed to determine whether or not there were any defects.

[0015] As a result, the occurrence of defects is strongly related to the morphology of nonmetallic inclusions, and CaO-Al ２ O ３ -MgO-based oxide is MgO or MgO.Al ２ O ３ We found that the structure containing CaO-Al has a high ability to suppress clustering. A schematic diagram of this is shown in Figure 1. Figure 1(a) shows the structure of CaO-Al ２ O ３ -MgO-based oxide has MgO or MgO.Al within its approximately spherical surface. ２ O ３ On the other hand, as shown in Figure 1(b), part of the outer edge is CaO-Al. ２ O ３ -MgO system, with the majority of the interior being high-melting point MgO or MgO.Al ２ O ３ It has been revealed that when the oxides are in the form of protruding from the approximately spherical surface of the inclusions, clustering is promoted. ２ O ３ It is presumed that the MgO-based melt acts as a sintering aid at the so-called refining temperature (1400-1550°C), adhering to each other and sintering. Based on experience, it was speculated that the main sintering location in an actual machine is the inner wall of the submerged nozzle of the continuous casting machine.

[0016] On the other hand, MgO·Al ２ O ３It was also confirmed that sintering behavior did not occur when MgO was used alone. ２ O ３ It has become clear that the structural morphology of the MgO-based oxide melt has a significant effect on the final quality.

[0017] Using this, for some alloy types, raw materials were melted in a 70-ton electric furnace, decarburized using an AOD, and quicklime was added from above while FeSi was added at the same time, Cr reduction was performed, and then Al was added to proceed with deoxidation and desulfurization, thereby refining. Slabs were then produced using a continuous casting machine, and after surface grinding, they were hot rolled, cold rolled, and finally passed through an annealing and pickling line to produce 0.5 mm thick thin plates. The surfaces were observed with the naked eye to study the presence or absence of surface defects.

[0018] That is, the present invention was developed by starting from the above laboratory studies and then conducting actual machine tests to confirm the results, as described below.

[0019] The chemical compositions are all in mass % below: C: 0.001-0.1%, Si: 0.01-0.4%, Mn: 0.1-1%, P: 0.03% or less, S: 0.002% or less, Cr: 13-35%, Mo: 18% or less, W: 5% or less, Cu: 1% or less, Al: 0.001-0.35%, Ti: 0.001-0.2%, Ca: 0.0001-0.02%, Mg: 0.0001-0.02%, N: 0.001-0.03%, Fe: 2-11%, O: 0.005% or less, and one or more of Co, Nb, and B in an amount of 4% or less, with the balance being Ni and unavoidable impurities. The average composition of non-metallic inclusions is MgO: 30-70%, Al: 1.5%-1.5%, and MgO: 0.01-0.4%. ２ O ３ :15~40%, SiO ２ It is a Ni-based alloy composed of: SiO 30% or less, CaO 10-40%, and MnO 1% or less.

[0020] In the Ni-based alloy of the present invention, the structural form of the non-metallic inclusions is more preferably one or more of the following five types of non-metallic inclusions, a to e, in which the non-metallic inclusions account for 70% or more of the total number of non-metallic inclusions: a: CaO—Al ２ O ３ -MgO-based oxide is MgO.Al within the approximately spherical surface ２O ３ Form b: CaO-Al ２ O ３ -MgO-based oxide c: CaO-Al ２ O ３ - A form in which MgO is completely enclosed within an approximately spherical surface of an MgO-based oxide d: MgO alone e: MgO·Al ２ O ３ Single unit

[0021] In addition, the CaO-Al ２ O ３ -MgO-based oxides are included, and CaO-Al ２ O ３ -MgO-based oxides are CaO: 20 to 60%, Al ２ O ３ :30~60%, MgO:1~30%, SiO ２ :20% or less, TiO ２ : 0.5% or less is a preferred embodiment.

[0022] Here, the above-described MgO.Al ２ O ３ It contains MgO.Al ２ O ３ It is preferable that the content of MnO is 0.5% or less.

[0023] Furthermore, the above-mentioned simple MgO is contained, and the simple MgO contains Al ２ O ３ :3% or less, SiO ２ It is preferable that the content of the SiO2 is 1% or less, CaO is 10% or less, and MnO is 1% or less.

[0024] The present invention also provides a manufacturing method, namely, melting raw materials in an electric furnace, then decarburizing and refining them in an AOD, adding quicklime, magnesia-containing waste bricks, fluorite, ferrosilicon alloy, and one or more of Si and Al to carry out Cr reduction, and then adding Al to form CaO-Al ２ O ３ -MgO-SiO ２ This is a method for producing a Ni-based alloy, in which F-based slag is formed, deoxidized, and desulfurized, and then a slab is produced using a continuous casting machine, the surface is ground, and then the slab is subjected to a hot rolling process and then cold rolling.

[0025] 1 is a comparative diagram of the structural morphology of non-metallic inclusions of the present invention and those of other non-metallic inclusions, and FIG. 2 is a schematic diagram showing the classification of the structural morphology of non-metallic inclusions of the present invention and those of other non-metallic inclusions.

[0026] The reasons for the numerical limitations of the present invention and their scientific viewpoints are also explained below. The units used below are mass %. C: 0.001-0.1% C is an important element for maintaining the strength of Ni-based alloys and for improving wear resistance by forming carbides with Cr. Therefore, 0.001% is necessary. On the other hand, adding more than 0.1% also has the disadvantage of forming carbides of Ti, Nb, etc., which can lead to embrittlement. Therefore, the limit is specified as 0.001-0.1%. Addition is controlled by adding pig iron after desulfurization in the AOD. Preferably, it is 0.002-0.09%, more preferably 0.005-0.07%.

[0027] Si: 0.01 to 0.4% Si is an element that is effective in deoxidation and also improves heat resistance, making it very important in the present invention. Deoxidation can be achieved by the following formula. In other words, it is achieved by adding an FeSi alloy to the Cr reduction in the AOD. Si + 2O = (SiO ２ ) ... (1) Here, the underlined parts are the components in the molten alloy, and the parentheses are the components in the slag. As will be described later, SiO ２ By lowering the activity coefficient of , deoxidation can be effectively promoted and the oxygen concentration can be controlled to the level specified in the present invention. Furthermore, desulfurization can also be achieved at the same time. To achieve this effect, 0.01% is necessary, and if it exceeds 0.4%, it not only forms a σ phase, reducing corrosion resistance, but also causing embrittlement. Therefore, the range is specified as 0.01 to 0.4%. Preferably, it is 0.02 to 0.38%, and more preferably, it is 0.02 to 0.37%.

[0028] Mn: 0.1 to 1% Mn is an effective element because it is useful for deoxidation. Therefore, the content is specified as 0.1 to 1%. The content is preferably 0.2 to 0.9%, and more preferably 0.3 to 0.8%.

[0029] P: 0.03% or less P is a harmful element that not only segregates at grain boundaries and reduces corrosion resistance, but also causes red shortness during welding, leading to cracking. Therefore, the content is set to 0.03% or less. Preferably, it is 0.028% or less, and more preferably, it is 0.025% or less.

[0030] S: 0.002% or less S is a harmful element because it segregates at grain boundaries and forms MnS, which becomes the starting point for pitting corrosion. It also reduces hot workability and causes edge cracking. Therefore, the content is set to 0.002% or less. As will be described in detail later, desulfurization can be promoted by the following reaction formula: 3(CaO) + 2Al + 3S = (Al ２ O ３ )+3(CaS)...(2) 2(CaO)+Si+2S=(SiO ２ ) + 2(CaS) ... (3) Reducing the activity coefficients of alumina and silica in the slag allows the desulfurization reaction to proceed efficiently. If the content is 0.002% or less, the above problems can be avoided, so this range is specified. Preferably, it is 0.0018% or less, more preferably, it is 0.0017% or less, and even more preferably, it is 0.0015% or less.

[0031] Cr: 13 to 35% Cr is a major element in the present invention, and is essential for forming a dense passive film on the surface of the Ni-based alloy and maintaining corrosion resistance. For this reason, the content is specified as 13 to 35%. Preferably, it is 14 to 34%, more preferably, 14.5 to 33%, and even more preferably, 15 to 32.5%.

[0032] Mo: 18% or less Mo is an important element in the present invention. It plays a role in slowing the progression of pitting corrosion and improving corrosion resistance. However, if the content is too high, it forms intermetallic compounds and causes embrittlement. Therefore, the content is specified as 18% or less. Preferably, it is 17% or less, and more preferably, it is 16% or less. Furthermore, a content of 0.5% or more is desirable. Furthermore, a content of 2% or more is even more desirable.

[0033] W: 5% or less W is an important element in the present invention. It plays a role in slowing the progression of pitting corrosion and improving corrosion resistance. However, if the content is too high, it forms intermetallic compounds and causes embrittlement. Therefore, the content is specified as 5% or less. Preferably, it is 4.5% or less, and more preferably, it is 4.2% or less. Furthermore, a content of 0.5% or more is desirable. Furthermore, a content of 2% or more is even more desirable.

[0034] Cu: 1% or less Cu is an important element for improving acid resistance and sulfuric acid resistance, thereby maintaining corrosion resistance. It also has the effect of softening in cold working, making it an extremely important element for deep drawing applications. However, if the Cu content is too high, the Ni-based alloy will soften. Therefore, the Cu content is specified as 1% or less. Preferably, it is 0.9% or less, and more preferably, it is 0.6% or less. Furthermore, a Cu content of 0.01% or more is desirable.

[0035] Al: 0.001-0.35% Al is a useful element for deoxidation. It also improves high-temperature oxidation resistance. On the other hand, if the content is too high, AlN is formed, impairing hot workability, and the Ca and Mg concentrations become too high, exceeding the upper limit of the range of the present invention. As a result, harmful CaO-based inclusions are formed, and NiMg ２ The deoxidation reaction proceeds as follows: 2Al + 3O = (Al ２ O ３ ) ... (4) As will be described in detail later, by reducing the alumina activity in the slag, deoxidation proceeds efficiently. Furthermore, desulfurization also becomes possible at the same time. Therefore, the content is specified as 0.001 to 0.35%. Preferably, it is 0.005 to 0.3%, more preferably, 0.007 to 0.28%, and even more preferably, 0.01 to 0.25%.

[0036] Ti: 0.001 to 0.2% Ti has the effect of fixing N in the form of TiN, preventing blowholes caused by nitrogen gas release during solidification. However, if the content is too high, not only will there be too much TiN, but the formation of TiC can also cause surface defects. Therefore, the content is specified to be in the range of 0.001 to 0.2%. Preferably, it is 0.002 to 0.1%. More preferably, it is 0.002 to 0.05%.

[0037] Ca: 0.0001 to 0.02% Ca favorably regulates the structure of nonmetallic inclusions to CaO-Al ２ O ３ Ca is an important element for controlling the alloy to be an MgO-based oxide. By controlling the alloy to this form, it is possible to manufacture a sound product without forming clusters or surface defects. Ca is effectively added by utilizing the following reaction: 3(CaO) + 2Al = (Al ２ O ３ )+3Ca...(5) 2(CaO)+Si=(SiO ２ ) + 2Ca ... (6) To control this reaction, the activity of alumina and silica in the slag can be controlled within an appropriate range. This will be explained in detail in the manufacturing method section. Conversely, if it is too high, harmful CaO inclusions will form, promoting clustering and forming defects. Therefore, the Ca content is specified to be 0.0001 to 0.02%. Preferably, it is 0.0003 to 0.018%, and more preferably, it is 0.0005 to 0.015%. Furthermore, it is preferably 0.0006 to 0.01%.

[0038] Mg: 0.0001 to 0.02% Mg is a component that favors the structure of nonmetallic inclusions. ２ O ３ - MgO-based oxides, MgO, MgO.Al ２ O ３ By controlling the morphology in this way, it is possible to produce a sound product without clustering or forming surface defects. Mg is effectively added by utilizing the following reaction: 3(MgO) + 2Al = (Al ２ O ３ )+3Mg...(7) 2(MgO)+Si=(SiO ２ ) + 2Mg ... (8) To control this reaction, the activity of alumina and silica in the slag should be controlled within an appropriate range. This will be explained in detail in the manufacturing method section. On the other hand, if the content is too high, Mg will vaporize during solidification and form blowholes, which will cause surface defects. Therefore, the content is specified to be 0.0001 to 0.02%. Preferably, it is 0.0005 to 0.018%, and more preferably, it is 0.001 to 0.015%.

[0039] Fe: 2 to 11%. Fe is an important element for maintaining strength by dissolving in Ni-based alloys. It also reduces costs by allowing the use of ferroalloys as raw materials. However, if the content is too high, it reduces corrosion resistance. Therefore, the content is specified as 2 to 11%. Preferably, it is 3 to 10.5%, and more preferably, it is 4 to 10%.

[0040] N: 0.001 to 0.03% N is effective in maintaining strength by dissolving in Ni-based alloys. It also prevents pitting corrosion. ４ It plays a role in preventing pitting corrosion by providing Cl. Therefore, the range is specified as 0.001 to 0.03%, preferably 0.002 to 0.028%, and more preferably 0.008 to 0.025%.

[0041] O: 0.005% or less The oxygen content must be reduced because it increases the number of nonmetallic inclusions and forms surface defects. Therefore, the oxygen content is set to 0.005% or less. Preferably, the oxygen content is 0.003% or less, more preferably, 0.002% or less, and even more preferably, 0.001% or less.

[0042] One or more of Co, Nb, and B, 4% or less. Co is an effective element because it behaves in the same way as Ni. It is also sometimes contained in pure Ni raw materials, and plays an important role in terms of utilizing inexpensive raw materials. Nb is useful for maintaining strength through solid solution. B improves hot workability. It is more preferable to contain one or more of these elements in an amount of 4% or less. In other words, they may be added as needed.

[0043] The balance of the Ni-based alloy of the present invention is Ni. In addition, it may contain trace amounts of unavoidable impurities, such as Pb, Sn, Ta, Ag, Na, K, and Zr. All of these are mixed in from the scrap raw material.

[0044] Next, the average composition of the nonmetallic inclusions will be explained. The average composition of the nonmetallic inclusions is as follows: MgO: 30-70% MgO is a harmless CaO-Al ２ O ３ - MgO alone and MgO.Al, which are effective in forming MgO-based oxides and are also harmless. ２ O３ It is extremely effective for forming a monomer. Therefore, the range is specified as 30 to 70%, and preferably 35 to 65%.

[0045] Al ２ O ３ : 15 to 40% Al ２ O ３ is a harmless CaO-Al ２ O ３ - MgO.Al, which is effective in forming MgO-based oxides and is also harmless. ２ O ３ However, if it is higher than 40%, it can cause harmful Al ２ O ３ Since it forms a single element, it causes defects. Therefore, the content is specified to be 15 to 40%, and preferably 18 to 39%.

[0046] SiO ２ :30% or less SiO ２ is CaO-Al ２ O ３ - It is a compound present in MgO-based oxides, and is effective in lowering the melting point. However, if it exceeds 30%, it acts in the direction of increasing the oxygen concentration, which increases the number of non-metallic inclusions and also increases the number of harmful MnO-Cr ２ O ３ The formation of a base oxide results in the formation of defects. Therefore, the content is specified to be 30% or less, and preferably 28% or less.

[0047] CaO: 10-40% CaO is harmless CaO-Al ２ O ３ Although it is effective for forming MgO-based oxides, if it is too high, harmful CaO inclusions are formed, causing defects. Therefore, the range is specified as 10 to 40%. Preferably, it is 12 to 39%. More preferably, it is 13 to 38%.

[0048] MnO: 1% or less MnO is MgO alone, MgO.Al ２ O ３ It is harmless because it dissolves in the MgO site of the simple inclusion. However, if it is too high, it can become harmful. ２ O ３The formation of a base oxide results in the formation of defects. Therefore, the content is specified to be 1% or less. Preferably, it is 0.9% or less. More preferably, it is 0.8% or less.

[0049] Cr ２ O ３ : 1.5% or less Although not particularly limited, Cr ２ O ３ When the value is high, MnO-Cr ２ O ３ This makes it easier for non-metallic inclusions to form. Furthermore, the oxygen concentration in the molten alloy increases, increasing the number of non-metallic inclusions and causing defects. Therefore, the oxygen content is preferably 1.5% or less, more preferably 1.3% or less, and even more preferably 0.6% or less.

[0050] There are several methods for determining the average composition. This can be determined by randomly analyzing 10 points using SEM / EDS. In this case, it is necessary to analyze two points on the periphery of the center, and the average can be determined by taking a mapping image and measuring the area ratio using image analysis. Preferably, 20 or more points are analyzed, and more preferably, 30 or more points are analyzed. The other method is the so-called electrolytic method, widely known as the Speed ​​method. In other words, an appropriate potential is applied in an appropriate solution to dissolve the metal parts. The non-metallic inclusions that remain as residue are then collected by filtration. This can be subjected to chemical analysis to determine the average composition all at once. There are no limitations on the analytical method.

[0051] Furthermore, we will explain the structural form of nonmetallic inclusions. It is more preferable that nonmetallic inclusions account for 70% or more of the total number of nonmetallic inclusions and are one or more of the following five types a to e. The structural forms corresponding to a to e are also shown in Figures 2(a) to (e). a: CaO-Al ２ O ３ -MgO-based oxide is MgO.Al within the approximately spherical surface ２ O ３ Form b: CaO-Al ２ O ３ -MgO-based oxide c: CaO-Al ２ O ３- A form in which MgO is completely enclosed within an approximately spherical surface of an MgO-based oxide d: MgO alone e: MgO·Al ２ O ３ Here, "completely enclosed within a substantially spherical surface" refers to a state in which the inner material is completely enclosed within the outer peripheral material as shown in FIG. 1(a), and does not include a state in which the inner material partially protrudes to the outside as shown in FIG. 1(b).

[0052] As explained in the Summary of the Invention section, the structure shown in Figure 1(b) does not appear in the following procedure. To achieve these structural morphologies, it is sufficient to control the chemical components of Si, Al, Ca, Mg, O, and Mn within the ranges of the present invention, but this is not all. A and c are also characteristic of the present invention. To achieve these structural morphologies, the key point lies after the decarburization process in the AOD. During the Cr reduction period, quicklime is first added, followed by fluorite and waste bricks containing MgO. Then, when ferrosilicon alloy and Al are added, Si and Al are added to the already formed molten slag. This reacts directly with the CaO and MgO in the slag, effectively adding Ca and Mg.

[0053] Mg is supplied to the molten alloy in advance according to the reactions of equations (7) and (8). The reason for this is largely unknown, but the reaction of Ca is delayed. This dissolved Mg reacts first with the original non-metallic inclusions, silica and alumina, as follows: 2Mg + SiO ２ (Inclusions) = 2MgO (Inclusions) + 2Si...(9) 3Mg+Al ２ O ３ (Inclusions) = 3MgO (Inclusions) + 2Al ... (10) 2Mg + 4Al + 4SiO ２ (Inclusions) = 2MgO・Al ２ O ３ (Inclusions) + 4Si ... (11) 3Mg + 4Al ２ O ３ (Inclusions)=MgO・Al ２ O ３ (inclusions) + 2Al ... (12) As shown in the above formulas (9) to (12), MgO alone, MgO·Al ２ O ３Then, Ca is supplied from the slag, and the Ca in the molten alloy reacts with the above inclusions, forming CaO-Al on the surface. ２ O ３ -MgO-based oxides are formed vigorously. Then, the molten oxides are MgO alone, MgO.Al ２ O ３ In other words, the harmless CaO-Al melt is covered with the element. ２ O ３ - They behave as MgO-based inclusions. Therefore, if the non-metallic inclusions are spherical, they behave as described above and are harmless.

[0054] Furthermore, the above CaO—Al ２ O ３ The composition range of MgO-based oxides is explained below: CaO: 20-60%, Al ２ O ３ :30~60%, MgO:1~30%, SiO ２ :20% or less, TiO ２ : 0.5% or less Within the above range, CaO-Al is ２ O ３ The above range was set to maintain the molten state of the MgO-based oxides. If the CaO content is too high, harmful simple CaO inclusions are formed, so the CaO content is set to 20-60%. ２ O ３ If too high, Al ２ O ３ Al to form a single unit ２ O ３ The content of MgO was set to 1-30% in order to maintain the molten state. ２ If the value is too high, harmful MnO-Cr ２ O ３ The content was set to 20% or less to prevent the formation of inclusions. ２ This is specified because the molten state can be maintained if the content is 0.5% or less.

[0055] MgO.Al ２ O ３ MnO concentration in: 0.5% or less MgO.Al ２ O ３Since MnO dissolves in the MgO site, MgO can be made harmless. Therefore, the content is specified to be 0.5% or less.

[0056] Al in MgO simple inclusions ２ O ３ :3% or less, SiO ２ : 1% or less, CaO: 10% or less, MnO: 1% or less. MgO inclusions are harmless, so it is desirable for some solid solution to occur in these inclusions. Taking into account the solid solubility limit, Al ２ O ３ :3% or less, SiO ２ : 1% or less, CaO: 10% or less, MnO: 1% or less.

[0057] The present invention also provides a manufacturing method. Specifically, raw materials are melted in an electric furnace and then decarburized and refined using an AOD. The raw materials can be stainless steel scrap, Ni, ferronickel alloy, ferrosilicon alloy, iron scrap, Mo, Mo trioxide, ferromolybdenum alloy, ferroniobium alloy, ferrochromium alloy, copper wire, or other alloys blended according to the desired alloy type.

[0058] After the decarburization process is complete, the Cr in the molten alloy is oxidized to Cr ２ O ３ Therefore, quicklime and FeSi are added to carry out Cr reduction according to the following reaction: 2 (Cr ２ O ３ )+3Si=3(SiO ２ )+4Cr...(13)

[0059] Further adding Al, CaO-Al ２ O ３ -MgO-SiO ２ After forming the -F slag and deoxidizing and desulfurizing it, a slab is produced in a continuous casting machine, the surface is ground, and then the slab is subjected to a hot rolling process and then cold rolling. At this time, in order to control the structural form of the nonmetallic inclusions to a desirable form, it is necessary to control the slag composition within an appropriate range.

[0060] CaO-Al ２ O ３ -MgO-SiO ２The following range is desirable for -F-based slag: CaO: 35-70%. The CaO concentration can be adjusted by adding quicklime. CaO is extremely effective in deoxidation and desulfurization. In other words, as shown in equations (2) and (3), desulfurization is possible by stably preserving CaS in the slag. However, if the content exceeds 70%, CaO inclusions will form. Therefore, 35-70% is best. 40-65% is preferable. 50-63% is even more preferable.

[0061] Al ２ O ３ :30% or less Al ２ O ３ is CaO-Al ２ O ３ -MgO-SiO ２ On the other hand, if it exceeds 30%, the Al content will be too high. ２ O ３ This creates simple inclusions and promotes clustering. Therefore, it is desirable that the content be 30% or less. Preferably, it is 25% or less. More preferably, it is 22% or less.

[0062] MgO: 3 to 25% MgO is CaO-Al ２ O ３ -MgO-SiO ２ This is effective for molten -F-based slag. On the other hand, if the MgO concentration is high, the Mg concentration in the molten alloy will increase, which will release Mg gas during solidification and cause blowholes. Therefore, a content of 3 to 25% is desirable. A content of 5 to 20% is more desirable, and a content of 7 to 15% is even more desirable.

[0063] SiO ２ : 3 to 32% SiO ２ is CaO-Al ２ O ３ -MgO-SiO ２ -F-based slag is effective in molten state. ２ When the concentration is high, the oxygen concentration in the molten alloy becomes high, and the composition of the nonmetallic inclusions becomes MnO-Cr. ２ O ３ As a result, surface defects occur. Therefore, 3 to 32% is desirable. 5 to 30% is more desirable. 5 to 20% is even more desirable.

[0064] F: 0.5-10% F is added as fluorite. F is CaO-Al ２ O ３ -MgO-SiO ２ -F is effective in molten F-based slag. On the other hand, if the F concentration is high, it will corrode the AOD bricks and ladle bricks, shortening their lifespan. Therefore, a concentration of 0.5 to 10% is preferable, and 1 to 9% is more preferable.

[0065] Furthermore, Cr ２ O ３ , the FeO concentration is preferably low. ２ O ３ :1% or less Cr ２ O ３ When the concentration is high, the oxygen concentration becomes high and MnO-Cr ２ O ３ This causes the formation of system inclusions. Therefore, it is best to keep it at 1% or less. It is preferably 0.7% or less, and more preferably 0.6% or less.

[0066] FeO: 1% or less If the FeO concentration is high, the oxygen concentration will increase and MnO-Cr ２ O ３ This causes the formation of system inclusions. Therefore, it is best to keep it at 1% or less. It is preferably 0.9% or less, and more preferably 0.8% or less.

[0067] Furthermore, a high S concentration is desirable because it indicates that desulfurization has progressed normally. A concentration of 0.3% or more is desirable, and a concentration of 0.4% or more is more desirable.

[0068] The effectiveness of the present invention will be clarified by the following examples. A 70-ton electric furnace was used to melt raw materials, which were then decarburized and refined using an AOD. The raw materials included special steel scrap, stainless steel scrap, pure Ni, ferrosilicon alloy, ferrosilicon alloy, iron scrap, Mo, Mo trioxide, ferromolybdenum alloy, ferroniobium alloy, ferrochrome alloy, tungsten, Ti, copper wire, and other materials blended according to the target alloy type.

[0069] After the decarburization process is completed, the Cr that has been transferred to the slag ２ O ３In other words, quicklime and magnesia-containing waste bricks were added, followed by fluorite, and then Al was added. This reduced the Cr oxide in the slag, completing the Cr reduction process, which returns the valuable metal Cr to the molten alloy.

[0070] Furthermore, some alloys contain ferrosilicon alloys, resulting in CaO-Al ２ O ３ -MgO-SiO ２ Even when Al was not added, the Al impurity in the FeSi alloy was oxidized to provide alumina.

[0071] For some alloy types, alloying elements such as Nb, Mo, C, Co, W, Cr, B, and Ni were added to precisely adjust the chemical composition. After deoxidation and desulfurization in this manner, slabs measuring 200 mm thick x 1200 mm wide x 7 m long were produced using a continuous casting machine. After the surface oscillation marks were ground, the slabs were heated to 1100 to 1250°C depending on the alloy type, and then subjected to a hot rolling process. Finally, cold rolling was performed and the slabs were passed through an annealing and pickling line. In this way, 1 mm cold-rolled coils were produced for all alloy types.

[0072] The evaluation was carried out using the following methods. 1) Chemical composition: The surface of a 30 mm diameter x 10 mm high suction sample taken from the tundish of the continuous casting machine was ground with a grinder. Major elements were analyzed using X-ray fluorescence analysis. Some C and S were analyzed using the combustion method. N and O were analyzed using the infrared absorption method. In some cases, H values ​​were obtained using a hydrogen analyzer. 2) Slag composition: Slag was taken with an iron rod and crushed. This was compressed into a cylindrical powder sample. Values ​​for this sample were determined using X-ray fluorescence analysis. F was determined by chemical analysis. 3) Average composition of non-metallic inclusions: The above suction sample was cut out, embedded in resin, and mirror-polished. This was placed in an SEM for observation and quantitative analysis. 30 inclusions of 5 μm or larger were randomly selected, and the center and periphery were analyzed. The element distribution of each inclusion was determined by mapping, the ratio of each phase was calculated by image analysis, and a representative analysis value for each inclusion particle was obtained by taking into account a weighted average. This was determined by calculating the average value of 30 points. 4) Morphology of non-metallic inclusions: Morphology was classified when observed and analyzed as described above. Note that no morphology corresponding to Figure 1(b) was confirmed. 5) Composition of each oxide: Determined from the composition of each oxide phase described above. 6) Overall evaluation: An inspector evaluated with the naked eye when a 1 mmt Ni-based alloy plate was threaded. The evaluation results were determined as follows. In the following, the acceptable range in which defects are not cut is the range within 10 mm of the steel plate surface. ２ This means that there are up to three linear defects of 1 mm or more in length per coil. Pass: ◎ No surface defects (100% good product rate at time of shipping) Pass: 〇 Surface defects have occurred in some areas but are within the required quality tolerance range (95% good product rate) Pass: △ Surface defects have occurred in some areas but can be shipped by cutting partially (80% good product rate) Fail: × Surface defects have occurred along the entire length of the coil and the coil is discarded (0% good product rate)

[0073]

[0074]

[0075] The structural morphologies of the examples are shown in Figures 2(a) to (e), and those of the comparative examples are shown in Figures 2(f) to (h). The total chemical composition of the examples is less than 100% due to unavoidable impurities. Inventive examples Nos. 1 to 14 had chemical analysis results within the range, and the slag composition also met the desired range. As a result, the structural morphology of non-metallic inclusions also met the ranges a to e. Ultimately, all products were judged to be acceptable.

[0076] However, in No. 5, there was one alumina inclusion and MnO-Cr ２ O ３ In No. 8, one simple CaO inclusion was observed, so the evaluation was rated as good. In No. 10, there was a small amount of MnO and Cr in the slag. ２ O ３ The concentration was high and the reduction was poor, so Al ２ O ３ Simple inclusions and MnO-Cr ２ O ３ In addition, in No. 11, MgO.Al inclusions were confirmed. Therefore, the evaluation was rated as good. ２ O ３ The MnO concentration is high in the MgO inclusions, and the SiO ２ At the same time, the content of MnO increased, and simple CaO inclusions and Al ２ O ３ Simple inclusions and MnO-Cr ２ O ３ Inclusions were confirmed. As a result, the evaluation was △.

[0077] Next, we will explain the comparative examples. In No. 15, the Si content was low. Conversely, the Al content was high and the CaO concentration in the slag exceeded the desired range, resulting in high Ca and Mg concentrations. As a result, MgO and CaO were not included in the average composition of the inclusions. The structure also contained more f-CaO alone, resulting in a CaO-Al ２ O ３ - CaO in the MgO-based oxides was high. In other words, the CaO simple substance inclusion became the center, causing defects and resulting in scrap.

[0078] No. 16 was out of the range because the Si concentration was high, and so the Ca and Mg concentrations were also high. The high Si concentration resulted in the SiO ２ The concentration was also too high. The F concentration was also low, resulting in poor slag fluidity. The Ti concentration was also too high, resulting in the formation of TiN clusters. In the average composition of the inclusions, MgO and CaO were out of range, resulting in the CaO-Al ２ O ３ -Alumina, MgO, SiO in MgO-based oxides ２ The thickness was outside the range, and many f-CaO simple inclusions were formed in the structure. The formation of many TiN and CaO simple inclusions caused many surface defects, and the coil became scrap.

[0079] In No. 17, the Si content was low and Al was not included, which resulted in low Ca and Mg concentrations, and the oxygen concentration was high, resulting in a large number of non-metallic inclusions. In addition, the slag composition was also out of range, with high silica and low CaO, which adversely affected the inclusion composition. The average composition of the inclusions was out of range for all oxides, and the structure was h.MnO-Cr. ２ O ３ Many CaO-Al inclusions were formed. ２ O ３ -Alumina and silica are also removed from MgO-based oxides, and MnO-Cr ２ O ３ As a result, surface defects occurred along the entire length, resulting in scrapping.

[0080] No. 18 was out of the range because the Al concentration was too high, and the alumina concentration in the slag was high, while the CaO concentration was too low. The average composition of the non-metallic inclusions was 100% alumina, and the structure was also g.Al. ２ O ３ Only single inclusions remained, resulting in surface defects along the entire length, causing scrapping.

[0081] No. 19 had a low Al concentration, which resulted in low Ca and Mg concentrations, and a high oxygen concentration, which was out of the range. ２ O ３The strength was high, and three types of structure were formed: f, g, and h. ２ O ３ Many MgO and Al inclusions were observed. ２ O ３ The simple inclusions and the components dissolved in the MgO simple inclusions were also removed. In addition, the Ti and N concentrations were high, and TiN clusters were also observed. As a result, surface defects occurred along the entire length, resulting in scrapping.

[0082] In No. 20, the Ti and N contents were too high, which resulted in the formation of many TiN clusters and surface defects, resulting in scrapping.In Table 2, all of the inclusion types are a and b, which at first glance appears to be good, but this is because TiN is not counted as an inclusion.

Claims

1. The following is a mass percentage: C: 0.001-0.1%, Si: 0.01-0.4%, Mn: 0.1-1%, P: 0.03% or less, S: 0.002% or less, Cr: 13-35%, Mo: 18% or less, W: 5% or less, Cu: 1% or less, Al: 0.001-0.35%, Ti: 0.001-0.2%, Ca: 0.0001-0.02%, Mg: 0.0001-0.02%, N: 0.001-0.03%, Fe: 2-11%, O: 0.005% or less, and one or more of Co, Nb, and B are 4% or less, with the balance being Ni and unavoidable impurities. The average composition of non-metallic inclusions is MgO: 30-70%, Al: 0.001-0.35%, Ti: 0.001-0.2%, Ca: 0.0001-0.02%, Mg: 0.0001-0.02%, N: 0.001-0.03%, Fe: 2-11%, O: 0.005% or less. ２ O ３ :15~40%, SiO ２ : 30% or less, CaO: 10 to 40%, MnO: 1% or less.

2. The Ni-based alloy with excellent surface properties according to claim 1, characterized in that the structural form of the nonmetallic inclusions is such that 70% or more of the nonmetallic inclusions in terms of number ratio to the total nonmetallic inclusions are one or more of the following five types a to e. a: CaO-Al ２ O ３ -MgO-based oxide is MgO.Al within the approximately spherical surface ２ O ３ Completely containing CaO-Al ２ O ３ -MgO-based oxide c: CaO-Al ２ O ３ - MgO-based oxide completely contains MgO within the approximately spherical surface. d: MgO alone e: MgO.Al ２ O ３ Single 3. The CaO-Al ２ O ３ -MgO-based oxide is included, and the CaO-Al ２ O ３ -MgO-based oxides are CaO: 20-60%, Al ２ O ３ :30~60%, MgO:1~30%, SiO ２ 3. The Ni-based alloy having excellent surface properties according to claim 2, characterized in that: C: 20% or less, and TiO2: 0.5% or less.

4. The MgO.Al ２ O ３ The MgO.Al ２ O ３ The Ni-based alloy having excellent surface properties according to claim 2, characterized in that it contains 0.5% or less of MnO.

5. The MgO element is contained, and the MgO element is Al ２ O ３ : 3% or less, SiO ２ 3. The Ni-based alloy having excellent surface properties according to claim 2, characterized in that it contains: 1% or less of Mo, 10% or less of CaO, and 1% or less of MnO.

6. A method for producing a Ni-based alloy according to any one of claims 1 to 5, comprising the steps of melting the raw materials in an electric furnace, then decarburizing and refining the raw materials in an AOD, adding one or more of quicklime, magnesia-containing waste bricks, fluorite and ferrosilicon alloy, Si and Al to carry out Cr reduction, and then adding Al to produce a CaO-Al alloy. ２ O ３ -MgO-SiO ２ A method for producing a Ni-based alloy with excellent surface properties, comprising forming an F-based slag, deoxidizing and desulfurizing the slab, producing a slab using a continuous casting machine, grinding the surface, subjecting the slab to a hot rolling process, and then performing cold rolling.

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