Nickel alloy excellent in internal quality, alloy plate and method for producing same

Abstract

Provided is a nickel alloy detoxified of void defects affecting the internal quality thereof and having excellent internal quality, and comprising, in mass%, no less than 99.00% Ni, 0.001-0.020% C, 0.01-0.30% Si, 0.01-0.30% Mn, 0.001-0.015% P, 0.0001-0.0030% S, 0.001-0.130% Al, no more than 0.40% Fe, 0.0003-0.0050% O, 0.003-0.030% Mg, 0.0001-0.0050% B, and no more than 0.0030% H, the remainder comprising unavoidable impurities, and the nickel alloy preferably satisfying one or both of formula 1 and formula 2 calculated from the mass% of H, P, S, and Mg in the alloy.　(Formula 1): (20 × H) × (2 × P + 10 × S + 3 × Mg) × 104 ≤ 15.0, and (Formula 2): (25 × S + 3 × Mg) ÷ H ≥ 28.0

Description

Nickel alloy with excellent internal quality, alloy plate and manufacturing method thereof

[0001] The present invention relates to a nickel alloy containing 99.00 mass% or more of Ni and a nickel alloy plate using the same, and also to a nickel alloy and nickel alloy plate with excellent internal quality in which trace components of the nickel alloy, such as P, Mg, S, and H, are precisely controlled and the amount of porosity in the cross section of a nickel alloy slab cast by continuous casting is reduced, and a method for producing the same.

[0002] Nickel alloys containing 99.00 mass% or more of Ni have excellent corrosion resistance and heat resistance, and are therefore used in a wide range of fields, including the chemical industry, electronic component materials, and the aerospace industry. Nickel, which is the main component of nickel alloys, is a very expensive metal compared to iron, so improving yield is extremely important for reducing production costs. Void defects caused by center porosity, which inevitably occur in continuous casting processes, can become the starting point for cracks during punching, cutting, welding, and other processes, and can have a significant impact on final product quality and yield.

[0003] Here, several methods for producing nickel alloys with high yields have been disclosed. Patent Document 1 describes a technique for obtaining nickel cold-rolled coils with high productivity and yields by adding 4 to 100 ppm of boron and further controlling the average pressure of each pass in cold rolling.

[0004] In addition, in Patent Document 2, the composition of nonmetallic inclusions is controlled, and MgO.Al ２ O ３ A technique has been disclosed for producing nickel alloy sheets with excellent surface quality by suppressing the number of inclusions.

[0005] However, all of the above techniques focus on surface quality and are not suitable for applications where internal quality is particularly important.

[0006] Furthermore, a technique for improving internal quality, particularly void defects, has also been disclosed. Patent Document 3 discloses a method for producing a continuously cast slab with excellent internal quality, in which, when continuously casting molten steel with a C content of 0.18% or less, a portion of the slab in which the solid phase fraction is 90 to 98% is reduced once with a reduction roll at a reduction ratio of 2 to 5%.

[0007] Patent Document 4 describes a technology for producing chromium-containing molten steel with excellent internal quality by determining the position at which to start reducing the slab based on the surface temperature of the slab and the roll reaction force when continuously casting the chromium-containing molten steel and by appropriately reducing the slab.

[0008] However, since the above technology relates to Fe-based alloys containing Fe as the main component, it cannot be applied to nickel alloys containing 99.00 mass% or more of Ni, which is the subject of the present application. Furthermore, while these Fe-based alloys contain many other components in addition to Fe, the behavior of solidification and segregation in nickel alloys containing 99.00 mass% or more of Ni is significantly different, which significantly affects the generation of void defects caused by center porosity and the crimping behavior. In other words, the problem of internal quality in nickel alloys remains.

[0009] Patent No. 5246547 Patent No. 7015410 Japanese Patent Application Publication No. 7-80615 Publication No. 11-123517

[0010] In view of the above problems, the present invention proposes a method for producing a nickel alloy with excellent internal quality by neutralizing porosity, i.e., void defects that affect internal quality.

[0011] The present inventors conducted extensive research to solve the above-mentioned problems. First, the inventors evaluated the internal quality of nickel alloy slabs and nickel alloy plates containing 99.00 mass% or more of Ni. As shown in Figure 1, the inventors cut a 200 mm thick nickel alloy slab 1 produced by continuous casting to obtain samples, and mirror-polished the slab cross section (internal quality inspection surface 2) perpendicular to the casting direction. Using a scanning electron microscope (SEM) with particle analysis capabilities, the circle-equivalent diameter, number, and area of ​​porosity present on the entire mirror-polished surface of the sample were measured at 200x magnification. At the same time, elemental analysis was performed using energy dispersive X-ray spectroscopy (EDS) to distinguish between nonmetallic inclusions and porosity. Here, the circle-equivalent diameter refers to the diameter of a circle with the same area calculated from the area of ​​amorphous porosity.

[0012] Furthermore, these nickel alloy slabs were hot-rolled and cold-rolled to produce nickel alloy plates with a thickness of 1 mm, and ultrasonic testing (UT) was performed to investigate the amount of internal defects. Samples of the internal defects were then taken, and the cross sections were examined using SEM and EDS to investigate the shape of the internal defects and the presence or absence of foreign matter. SIMS (secondary ion mass spectrometry) was also used to investigate the presence or absence of light elements such as hydrogen around the internal defects. Furthermore, a hole with a diameter of 1 mm was drilled from the surface of the sample of the internal defect, and gas released from the internal defect was collected and analyzed for its components.

[0013] As a result of the investigation, it was found that porosity was present within a range of 1 / 5 of the thickness from the center of the slab cross section, and that all of the internal defects detected in the ultrasonic flaw detection test of the nickel alloy plate with a thickness of 1 mmt were defects caused by porosity, and that gas, mainly hydrogen, was present in the voids. An example of this defect is shown in Figure 2. As shown in Figure 2, the porosity of the nickel alloy plate had gaps about 1 μm thick, and it was observed that Mg, P, S, and H were concentrated in the area very close to the porosity. Here, the nickel alloy plate contained CaO-SiO ２ -Al ２ O ３ -MgO-MnO system, CaO-Al ２ O ３Non-metallic inclusions based on Al, MgO and CaO were also detected, but they were very small in size (several micrometers) and in small numbers, so they do not affect the punching, cutting, welding, etc. of the nickel alloy plate. ２ O ３ That is, alumina-based inclusions are oxide-based inclusions that should be avoided because they cluster and become coarse, causing scabs on the coil surface.

[0014] Based on the above results, the mechanism of formation of internal defects in nickel alloy plates detected by ultrasonic testing was considered as follows. As shown in Figures 3 and 4, shrinkage cavities 4, which occur at the final solidification position 3 near the center of the thickness of a slab 1 when molten nickel is cast using a continuous casting machine, are under negative pressure due to solidification shrinkage. H, an impurity element dissolved in the nickel alloy immediately after solidification, turns into gas and is released into the interior of the shrinkage cavities 4, filling the interior. Mg, P, and S, which have high vapor pressures at the liquidus temperature of the nickel alloy (approximately 1450°C), are released as gas into the interior of the porosity 4 from their dissolved state in the nickel alloy immediately after solidification (Figure 4(a)). In addition, when the slab is cooled to room temperature (Figure 4(b)), Mg, P, and S become stable solids and adhere to the inner surfaces of the porosity.

[0015] Then, as shown in Figures 5 and 6, the porosity 4 inside the slab is crushed in the thickness direction along with the nickel alloy during hot rolling. As shown in Figure 5, if segregated elements such as Mg, P, and S are not present on the inner surface of the porosity, hydrogen gas diffuses into the nickel alloy as the internal pressure of the porosity increases, eventually resulting in the nickel alloy being completely compressed and the porosity disappearing. However, as shown in Figure 6, if segregated elements such as Mg, P, and S are present on the inner surface of the porosity, Mg, P, and S have a larger atomic radius than H, and therefore are less likely to diffuse into the nickel alloy, acting as a barrier to the diffusion of hydrogen gas into the nickel alloy. As a result, hydrogen gas porosity 4 about 1 μm thick remains in the Ni alloy plate, and segregations 5 of Mg, P, and S are detected around the porosity 4.

[0016] Furthermore, the inventors of the present invention have found that a small amount of Mg can be converted into MgH in a nickel alloy. ２ or Mg ２ NiH ４ It was also discovered that this has the effect of reducing H segregation near the center of the slab thickness by forming fine compounds with H in the form of H and fixing the H.

[0017] Furthermore, the inventors of the present invention discovered that, as shown in Figure 7, trace amounts of S suppress the coarsening of shrinkage cavities (porosity) 4 that occur at the final solidification position 3 near the center of the slab thickness. S is an element that is easily released from the solid phase to the liquid phase during the solidification process of molten nickel (semi-molten at approximately 1,450 °C), where it concentrates at dendrite trunks and grain boundaries, impairing hot workability. At the final solidification position 3 near the center of the slab thickness, shrinkage cavities 4 form due to negative pressure caused by solidification shrinkage. S has the effect of reducing the surface tension of the molten nickel, increasing the fluidity of the semi-molten nickel molten metal that is beginning to solidify and flowing into the shrinkage cavities, thereby suppressing the coarsening of the shrinkage cavities 4. As a result, although the number of fine shrinkage cavities increases, the effect of suppressing porosity coarsening is also observed. This phenomenon occurs before the aforementioned gas components such as H are released into and fill the shrinkage cavities.

[0018] The present inventors investigated the internal quality of nickel alloy slabs and nickel alloy plates produced with various compositions and various operating conditions, analyzed a large amount of data, and discovered the relationship between each composition and various operating conditions for obtaining nickel alloy plates in which internal defects are not detected by ultrasonic flaw detection tests, i.e., nickel alloy plates with reduced porosity and excellent internal quality, and by taking into account the knowledge obtained from the above-mentioned intensive research, they have completed the present invention.

[0019] That is, the nickel alloy of the present invention having excellent internal quality is characterized by having Ni: 99.00 mass% or more, C: 0.001 to 0.020 mass%, Si: 0.01 to 0.30 mass%, Mn: 0.01 to 0.30 mass%, P: 0.001 to 0.015 mass%, S: 0.0001 to 0.0030 mass%, Al: 0.001 to 0.130 mass%, Fe: 0.40 mass% or less, O: 0.0003 to 0.0050 mass%, Mg: 0.003 to 0.030 mass%, B: 0.0001 to 0.0050 mass%, H: 0.0030 mass% or less, with the balance being unavoidable impurities.

[0020] In a preferred embodiment, the nickel alloy of the present invention satisfies at least one of the following relational expressions, represented by Equation 1 and Equation 2, calculated from the chemical components (mass%) of H, P, S, and Mg in the nickel alloy: (20×H)×(2×P+10×S+3×Mg)×10 ４ ≦15.0…(Formula 1) (25×S+3×Mg)÷H≧28.0…(Formula 2)

[0021] In the nickel alloy of the present invention, it is a preferred embodiment that both of the above-mentioned formulas 1 and 2 are satisfied.

[0022] The method for producing a nickel alloy plate having excellent internal quality of the present invention is a method for producing a nickel alloy plate made of the nickel alloy, comprising: producing a slab in which, in a cross section perpendicular to the casting direction of a nickel alloy slab cast by a continuous casting machine, the porosity sizes present within a range of 1 / 5 of the thickness from the center of the thickness are all 5.0 mm or less in equivalent circle diameter, and the total area ratio of porosity with a circle equivalent diameter of 0.5 mm or more (=total porosity area / inspection area×100) is 0.60% or less; and subsequently performing hot rolling or hot rolling and cold rolling; and calculating a reduction ratio (=(slab thickness−nickel alloy plate thickness) / slab thickness×100) calculated from the thickness of the slab cast by the continuous casting machine and the thickness of the nickel alloy plate after hot rolling the slab, of 97.0% or more.

[0023] The method for producing a nickel alloy having excellent internal quality according to the present invention includes melting raw materials in an electric furnace, decarburizing the raw materials in an electric furnace and / or an AOD and / or a VOD, adding lime and fluorite dried to a moisture content of 0.20 mass% or less, and then melting the raw materials into a mixture of CaO-SiO ２ -Al ２ O ３ The method is characterized in that a -MgO-F based slag is prepared, and then Si and / or Al are added to perform deoxidation and desulfurization. The temperature and composition are adjusted while promoting the floating of inclusions by Ar stirring in an LF, and then a slab is produced by continuous casting using a mold powder for continuous casting with a moisture content of 0.20 mass% or less.

[0024] In addition, the method for producing a nickel alloy sheet having excellent internal quality according to the present invention includes melting raw materials in an electric furnace, decarburizing the raw materials in an electric furnace and / or an AOD and / or a VOD, adding lime and fluorite dried to a moisture content of 0.20 mass% or less, and then melting the raw materials into a mixture of CaO-SiO ２ -Al ２ O ３ The method is characterized in that a -MgO-F based slag is produced, Si and / or Al are added, deoxidation and desulfurization are performed, the temperature and composition are adjusted while promoting the floating of inclusions by Ar stirring in an LF, and then a slab is produced by continuous casting using a mold powder for continuous casting with a moisture content of 0.20 mass% or less, and subsequently hot rolling or hot rolling and cold rolling are performed.

[0025] FIG. 1 is a schematic cross-sectional view showing an internal quality inspection surface of a nickel alloy slab of the present invention. FIG. 2 is an image of an internal defect detected by ultrasonic flaw detection of a nickel alloy plate. FIG. 3 is a schematic cross-sectional view showing a final solidification position in a nickel alloy slab of the present invention. FIG. 4 is a schematic cross-sectional view of shrinkage cavities (porosity) at the final solidification position, (a) showing immediately after solidification and (b) showing after cooling. FIG. 5 is a schematic cross-sectional view showing a mechanism (porosity compression) accompanying rolling of shrinkage cavities (porosity) in the absence of segregation of Mg, P, and S. FIG. 6 is a schematic cross-sectional view showing a mechanism (porosity residual) accompanying rolling of shrinkage cavities (porosity) in the presence of segregation of Mg, P, and S. FIG. 7 is a schematic cross-sectional view showing a mechanism of suppressing coarsening of shrinkage cavities (porosity) due to segregation of S.

[0026] First, the reasons for limiting the chemical composition of the nickel alloy sheet of the present invention will be explained. Ni: 99.00 mass% or more This is the main component of nickel alloys and is essential for achieving seawater resistance and alkali resistance, particularly corrosion resistance against caustic soda and chlorine gas. Therefore, in the present invention, Ni is set to 99.00 mass% or more. Preferably, it is 99.10 mass% or more, and more preferably, it is 99.20 mass% or more.

[0027] C: 0.001 to 0.020 mass% If present in excess, C precipitates as graphite at grain boundaries in the temperature range of 430 to 650°C, causing embrittlement, so it must be controlled to 0.020 mass% or less. Conversely, C has the effect of improving strength, and 0.001 mass% or more is required to ensure the tensile strength and yield strength of a nickel alloy sheet. Therefore, in the present invention, the C content is set to 0.001 to 0.020 mass%. Preferably, it is 0.003 to 0.018 mass%, and more preferably, it is 0.005 to 0.015 mass%.

[0028] Si: 0.01 to 0.30 mass% Si is an effective element for deoxidation, and a Si content of 0.01 mass% or more can provide a deoxidizing effect. On the other hand, if the Si content exceeds 0.30 mass%, it becomes difficult to ensure a Ni content of 99.00% or more. Therefore, in the present invention, the Si content is set to 0.01 to 0.30 mass%. Within this range, the Si content is preferably 0.03 to 0.25 mass%. More preferably, it is 0.05 to 0.20 mass%.

[0029] Mn: 0.01 to 0.30 mass% Like Si, Mn is an effective element for deoxidation, and a Mn content of 0.01 mass% or more can provide a deoxidizing effect. On the other hand, if the Mn content exceeds 0.30 mass%, it becomes difficult to ensure a Ni content of 99.00% or more. Therefore, in the present invention, the Mn content is set to 0.01 to 0.30 mass%. Preferably, it is 0.02 to 0.28 mass%. More preferably, it is 0.03 to 0.25 mass%.

[0030] P: 0.001 to 0.015 mass% P is an element that easily segregates during solidification of molten nickel. At a P content exceeding 0.015 mass%, concentrated P at the center of the slab thickness acts as a barrier to hydrogen gas diffusion, inhibiting porosity crimping and further degrading hot workability. Nickel alloys containing 99.00 mass% or more of Ni are alloys with excellent ductility at high temperatures. Conversely, they also have poor shear workability at high temperatures. Therefore, when cutting off the crops at the leading and trailing ends with a shearing machine before the finish rolling of hot rolling, uncut portions are generated, making it difficult to continue hot rolling. The inventors of the present application have discovered that by including 0.001 mass% or more of P, shear workability during hot rolling can be ensured even in nickel alloys containing 99.00 mass% or more. For this reason, the P content is set to 0.001 to 0.015 mass%, preferably 0.002 to 0.012 mass%, and more preferably 0.003 to 0.010 mass%.

[0031] S: 0.0001 to 0.0030 mass% S segregates at grain boundaries, impairs hot workability, and causes cracking during hot rolling, so it must be controlled to 0.0030 mass% or less. Furthermore, S is an element that easily segregates during solidification of molten nickel. If the S content exceeds 0.0030 mass%, concentrated S at the center of the plate thickness acts as a barrier to hydrogen gas diffusion and inhibits porosity compression. Furthermore, as described above, S has the effect of preventing porosity coarsening, and to achieve this effect, S must be 0.0001 mass% or more. For this reason, the S content is set to 0.0001 to 0.0030 mass%. It is preferably 0.0002 to 0.0020 mass%, and more preferably 0.0003 to 0.0010 mass%.

[0032] Al: 0.001 to 0.130 mass% Al is a deoxidizing element. If the Al content is less than 0.001 mass%, the deoxidizing effect is insufficient, the O concentration exceeds 0.0050 mass%, and the number of oxide-based inclusions increases, causing surface defects. On the other hand, if the Al content exceeds 0.130 mass%, not only does it become difficult to ensure Ni: 99.00% or more, but the oxide-based inclusions become coarse alumina clusters, causing surface defects. For this reason, the Al content is set to 0.001 to 0.130 mass%. Preferably, it is 0.005 to 0.100 mass%, more preferably 0.010 to 0.080 mass%.

[0033] Fe: 0.40 mass% or less Fe is an unavoidable component and an impurity in nickel alloys, and it is desirable that its content be as low as possible. Therefore, the content is set to 0.40 mass% or less. It is preferably 0.35 mass% or less, and more preferably 0.30 mass% or less.

[0034] Mg: 0.003 to 0.030 mass% Mg is MgH in nickel alloys ２ or Mg ２ NiH ４ By forming a compound with H in the form of Mg and fixing the H, it has the effect of reducing H segregation near the center of the slab thickness. These effects are realized if the Mg content is 0.003 mass% or more. On the other hand, as mentioned above, Mg is an element that easily segregates when molten nickel solidifies. If the Mg content exceeds 0.030 mass%, the Mg concentrated in the center of the plate thickness acts as a barrier to hydrogen gas diffusion and inhibits the bonding of porosity near the center of the slab thickness. For this reason, the Mg content is specified to be 0.003 to 0.030 mass%. Preferably, it is 0.005 to 0.025 mass%. More preferably, it is 0.007 to 0.020 mass%.

[0035] O: 0.0003 to 0.0050 mass%. If O is present in a nickel alloy at more than 0.0050 mass%, the amount of oxide-based inclusions increases, adversely affecting surface properties and also serving as the starting point for cracks during processing of the nickel alloy sheet. Furthermore, it inhibits desulfurization, causing the S concentration in the molten nickel to exceed 0.0030 mass%. Conversely, if the O content is less than 0.0003%, the deoxidizing element Al exceeds 0.130 mass%, causing oxide-based inclusions to form coarse alumina clusters and resulting in surface defects. Therefore, the O content is specified as 0.0003 to 0.0050 mass%. It is preferably 0.0004 to 0.0040 mass%, and more preferably 0.0005 to 0.0030 mass%.

[0036] B: 0.0001 to 0.0050 mass% B is a component that improves hot workability. If it is less than 0.0001 mass%, it will not be effective, and if it exceeds 0.0050 mass%, it will form boron compounds (borides), which will cause deterioration in corrosion resistance and workability. Therefore, the B content is set to 0.0001 to 0.0050 mass%. The B content is preferably 0.0003 to 0.0040 mass%, and more preferably 0.0005 to 0.0030 mass%.

[0037] H: 0.0030 mass% or less. H is a gas component present within the porosity of nickel alloy sheet. It is mixed in through moisture in auxiliary materials such as lime used in the steelmaking process and moisture in the atmosphere. As described above, when molten nickel is cast in a continuous casting machine, shrinkage cavities that occur at the final solidification position near the center of the slab thickness are under negative pressure due to solidification shrinkage. Hydrogen dissolved in the molten nickel becomes gas and is released into the shrinkage cavities, filling them. If H exceeds 0.0030 mass%, large porosity is likely to be formed, and the number of porosity increases, resulting in porosity remaining within the nickel alloy sheet produced by hot rolling or hot rolling and cold rolling. Therefore, in the present invention, the H content is set to 0.0030 mass% or less. Preferably, it is 0.0020 mass%, and more preferably, it is 0.0010 mass% or less. The method for achieving H: 0.0030 mass% or less is described below. It is preferable to use lime and fluorite with a moisture content of 0.2 mass% or less in the refining process. Furthermore, the H is reduced to 0.0010 mass% or less in the vacuum degassing process, and further, the tundish during continuous casting is filled with Ar or N with a moisture concentration of 1 vol. ppm or less. ２ It is preferable to seal with gas to prevent the molten nickel alloy from coming into contact with the atmosphere, and further to use a mold powder with a moisture content of 0.2 mass % or less for continuous casting to prevent an increase in H in the molten nickel alloy.

[0038] (20 x H) x (2 x P + 10 x S + 3 x Mg) x 10 ４ ≦15.0 ... (Equation 1) (25 × S + 3 × Mg) ÷ H ≧ 28.0 ... (Equation 2) As mentioned above, H is a gas component present within the porosity of nickel alloy sheet and is the component that most affects the internal quality of the nickel alloy sheet. Furthermore, P, S, and Mg act as barriers to the diffusion of hydrogen gas present within the porosity. However, trace amounts of S and Mg have the effect of preventing porosity coarsening and fixing H, thereby reducing H segregation near the center of the slab thickness. The present inventors considered the degree of influence of H, P, S, and Mg in the Ni alloy on the internal quality using coefficients and compared it with the internal quality of numerous nickel alloy sheets. They concluded that within the chemical composition range of the nickel alloy sheet of the present invention, the left side of Equation 1 and Equation 2, calculated from the chemical components (mass%) of H, P, S, and Mg in the Ni alloy, satisfies the condition of the right side of Equation 1 and / or Equation 2, which is a preferable range for the internal quality of the nickel alloy sheet. (20 x H) x (2 x P + 10 x S + 3 x Mg) x 10 ４ ≦15.0…(Formula 1) (25×S+3×Mg)÷H≧28.0…(Formula 2)

[0039] In the present invention, a preferred embodiment involves producing a slab in which, in a cross section perpendicular to the casting direction of a slab cast by a continuous casting machine, the size of the porosity present within 1 / 5 of the thickness from the center of the thickness is 5.0 mm or less in equivalent circle diameter, and the total area ratio of porosity with a circle equivalent diameter of 0.5 mm or more (=total porosity area / inspection area x 100) is 0.60% or less, and subsequently carrying out hot rolling or hot rolling and cold rolling. The grounds for these limitations are explained below.

[0040] The size of porosity present within one-fifth of the thickness from the center of the slab thickness is 5.0 mm or less in equivalent circle diameter. Porosity inevitably occurs at the final solidification position of continuous casting, and if it remains, it can cause internal defects in the final product. As the nickel alloy is rolled in the hot rolling process, the porosity thickness decreases and compression progresses, but if the porosity is large at the slab stage, it cannot be completely compressed and remains as a defect in the final product. The inventors of the present application investigated the porosity present in the cross sections of many slabs and internal defects using ultrasonic flaw detection in nickel alloy sheets that had been hot rolled or hot rolled and cold rolled, and found that porosity detected at the slab stage with a size of more than 5.0 mm in equivalent circle diameter was not compressed during hot rolling and became a defect in the final product. Therefore, in this application, the size of defects detected at the slab stage was set to 5.0 mm or less in equivalent circle diameter. More preferably, it is 3.0 mm or less, and more preferably, it is 1.0 mm or less. The reason why the distance is limited to 1 / 5 from the center of the slab thickness is that porosity occurs near the final solidification position, that is, near the center of the slab thickness.

[0041] The total area ratio (= total porosity area / inspection area × 100) of porosity with a circle equivalent diameter of 0.5 mm or more present within one-fifth of the slab thickness center is 0.60% or less. As mentioned above, porosity that inevitably occurs at the final solidification position in continuous casting can cause internal defects in the final product if it remains as is. However, as the nickel alloy is rolled in the hot rolling process, the porosity thickness of small porosity decreases and they are easily compressed, becoming harmless in the final product. However, the inventors have found that when the total area ratio (= total porosity area / inspection area × 100) of porosity with a circle equivalent diameter of 0.5 mm or more at the time of slab formation exceeds 0.60%, some porosity remains uncompressed and remains as a defect in the final product. During hot rolling, as the internal pressure of the porosity increases, hydrogen gas diffuses into the nickel alloy, eventually completely compressing the nickel alloy and eliminating the porosity. However, if the porosity area ratio within 1 / 5 of the slab thickness from the center exceeds 0.60%, resulting in a large porosity area, the dissolved H concentration at the center of the nickel alloy thickness increases during hot rolling, inhibiting the diffusion of hydrogen gas within the porosity into the nickel alloy. Therefore, in this application, the total porosity area ratio is specified as 0.60% or less. Preferably, it is 0.50% or less, and more preferably, it is 0.40% or less. The reason for limiting the porosity to 1 / 5 of the slab thickness from the center is that porosity occurs near the final solidification position, i.e., near the center of the slab thickness.

[0042] Reduction ratio during hot rolling When a nickel alloy slab produced by a continuous casting machine is heated at 1000°C to 1100°C and then rolled by a hot rolling mill, it is preferable that the reduction ratio calculated from the thickness of the slab cast by the continuous casting machine and the thickness of the nickel alloy plate after hot rolling (= (thickness of slab - thickness of nickel alloy plate) / thickness of slab × 100) is 97.0% or more.

[0043] This is because, if the reduction ratio is 97.0% or more, the porosity present in the nickel alloy slab is compressed and disappears, thereby making it possible to produce a nickel alloy plate with excellent internal quality. Here, the reason why the reduction ratio of cold rolling is not specified is that, in cold rolling performed at room temperature, it is not expected that hydrogen inside the porosity will diffuse into the nickel alloy, that is, there is no effect of compressing the porosity. Therefore, in this application, only the reduction ratio of hot rolling performed at 1000°C to 1100°C is specified.

[0044] First, raw materials are melted in an electric furnace, and then decarburized in an electric furnace and / or AOD and / or VOD. Lime and fluorite are then added, dried to a moisture content of 0.20 mass% or less, and CaO-SiO ２ -Al ２ O ３ This paper describes in detail a method for producing a nickel alloy with excellent internal quality, characterized by producing a -MgO-F system slag, adding Si and / or Al, deoxidizing and desulfurizing it, adjusting the temperature and composition while promoting the floating of inclusions by Ar stirring in an LF, and then producing a slab by continuous casting using a continuous casting mold powder with a moisture content of 0.20 mass% or less. It also describes a method for producing a nickel alloy using this nickel alloy.

[0045] The moisture content of lime and fluorite is 0.20 mass% or less. The present inventors have determined from a number of operating conditions and the moisture content of lime and fluorite that the main cause of H dissolving in molten nickel during the refining process is the moisture in lime and fluorite. In order to achieve H: 0.0030 mass% or less, it is necessary to use dried lime and fluorite with a moisture content of 0.20 mass% or less.

[0046] Moisture content of mold powder for continuous casting: 0.20 mass% or less Mold powder used in continuous casting is a powdered oxide that serves to keep the molten metal surface warm in the mold, lubricate the mold and slab, and absorb non-metallic inclusions. However, the inventors of the present application have discovered that in order to reduce the occurrence of porosity in the cross section of the slab, it is preferable to use mold powder with a moisture content of 0.20 mass% or less.

[0047] Next, examples will be presented to clarify the configuration and effects of the present invention, but the present invention is not limited to the following examples.

[0048] Pure nickel and pure nickel scraps were melted in a 30-ton or 60-ton electric furnace. Then, oxygen refining (oxidation refining) was carried out in the electric furnace and / or AOD and / or VOD to remove carbon, and limestone and fluorite were added to form CaO-SiO ２ -Al ２ O ３ A -MgO-F slag was generated, and pure Si and / or Al were added to reduce NiO, followed by deoxidation. Ar stirring was then used to further desulfurize the slag. Magnesium-chrome bricks were used for the AOD and VOD processes. The slag was then poured into a ladle, and the temperature and composition were adjusted in the LF. A 200 mm thick slab was then produced in a continuous casting machine.

[0049] A cross-sectional sample perpendicular to the casting direction was taken from the produced slab. A 200 mm thick nickel alloy slab was cut from this cross-sectional sample to obtain a sample. The slab cross-section perpendicular to the casting direction was mirror-polished. Using a scanning electron microscope (SEM) with particle analysis capabilities, the circle-equivalent diameter, number, and area of ​​porosity present in the mirror-polished slab at 1 / 5 of the slab's thickness center were measured at 200x magnification. At the same time, elemental analysis was performed using energy dispersive X-ray spectroscopy (EDS) to distinguish between nonmetallic inclusions and porosity. The surfaces of the produced slabs were ground, heated at 1050°C, and hot-rolled to produce 3.0-6.8 mm thick strips. The strips were then annealed and pickled to remove surface scale. Finally, cold rolling was performed to produce nickel alloy sheets 1000 mm wide and 1 mm thick.

[0050] Table 1 shows the values ​​of the left sides of Equation 1 and Equation 2 calculated from the chemical components of the obtained nickel alloy and the chemical components (mass%) of H, P, S, and Mg in the Ni alloy, the maximum circle-equivalent diameter of the porosity present within 1 / 5 of the thickness from the center of the thickness of the cross section perpendicular to the casting direction of the slab, the total area ratio of porosity with a circle-equivalent diameter of 0.5 mm or more, the moisture content, the reduction rate during hot rolling, and the results of internal quality evaluation by ultrasonic flaw detection testing of a 1 mmt nickel thin plate. The measurement and evaluation methods for these are as follows.

[0051] 1) Chemical composition of nickel alloy Samples were taken from the nickel alloy plate and quantitatively analyzed using an X-ray fluorescence analyzer, and the oxygen and hydrogen concentrations were quantitatively analyzed using an inert gas fusion-non-dispersive infrared absorption method. The total of the chemical compositions of each example shown in Table 1 is less than 100 mass% because of the presence of unavoidable impurities such as Cr, Mo, Cu, Ti, W, Co, Pb, Sn, N, Se, and V.

[0052] 2) Maximum circle equivalent diameter of porosity and porosity area ratio with a circle equivalent diameter of 0.5 mm or more A sample of the slab cross section perpendicular to the pouring direction was mirror-polished, and the circle equivalent diameter, number, and area of ​​porosity present in 1 / 5 of the mirror-polished slab thickness from the center of the sample were measured at 200x magnification using a scanning electron microscope (SEM) with particle analysis function, and calculations were made from these values.

[0053] 3) Reduction rate during hot rolling The reduction rate was calculated using the following formula from the thickness of the slab cast by the continuous casting machine and the thickness of the nickel alloy plate after hot rolling: Reduction rate = (thickness of slab - thickness of nickel alloy plate) / thickness of slab x 100

[0054] 4) Moisture content The moisture content of lime and fluorite used in the refining process and mold powder used in continuous casting was measured by collecting a sample for measurement before use, heating it at 105°C for 5 hours, and then measuring the moisture content by the loss on drying method, in which the weight loss before and after drying is determined as the moisture content.

[0055] 5) Internal quality evaluation Ultrasonic flaw detection tests were carried out on coils of 1000 mm width and 1 mm thickness that had been rolled to the product thickness. The flaw detection was carried out with a sensitivity that could detect a minimum porosity (void) of 50 μm width × 100 μm length × 1 μm thickness. The flaw detection area was 100 m ２ If the number of detected defects per piece was 0.10 or less, it was rated A (best), if it was 0.11 to 0.20, it was B (excellent), if it was 0.21 to 0.30, it was C (good), if it was 0.31 to 0.40, it was D (passable), and if it was 0.41 or more, it was E (unacceptable). In addition, if there were many scabs on the surface and the piece was scrapped, and it was not possible to evaluate the internal quality, or if there was an uncut portion generated during crop cutting during hot rolling and it was scrapped, and it was not possible to evaluate the internal quality, it was also rated E.

[0056] Here, coils that had numerous scabs on the surface and were discarded as scrap before the ultrasonic flaw detection test on the 1 mmt nickel thin plate, which was the final internal quality evaluation, and coils that had uncut parts when cutting off the crops at the front and rear ends with a shearing machine before finish rolling in hot rolling, were unable to be evaluated for internal quality and were given a rating of E.

[0057]

[0058]

[0059] Inventive Examples 1 to 16 satisfied the range of the present invention, and therefore the number of defects detected in the product thickness by ultrasonic flaw detection testing was small, and good quality was achieved.

[0060] In Example 8, the thickness after hot rolling was thick, so the reduction rate during hot rolling was low at 96.6%, and the porosity near the center of the slab thickness was not completely compressed, and the number of defects detected by ultrasonic testing in the product thickness was 0.12 / 100m. ２ The internal quality rating was B.

[0061] Inventive Examples 9 to 12, the left sides of Equation 1 and Equation 2 calculated from the chemical components (mass%) of H, P, S, and Mg in the Ni alloy did not satisfy either of the conditions on the right sides of Equation 1 or Equation 2, and therefore the internal quality evaluation was B.

[0062] Inventive Examples 13 and 14, the left sides of Equation 1 and Equation 2 calculated from the chemical components (mass%) of H, P, S, and Mg in the Ni alloy did not satisfy the conditions on the right sides of Equation 1 and Equation 2, and therefore the internal quality evaluation was C.

[0063] Inventive Example 15, the moisture content of the lime and fluorite used in the refining process was 0.24 mass%, which was high, and the H concentration was also 0.0029 mass%, which was high within the range. The maximum porosity circle equivalent diameter of the slab cross section was 4.4 mm, which was also high within the range, and the porosity area ratio was also high at 0.61%. The number of defects detected by ultrasonic flaw detection testing in the product thickness was 0.37 / 100m. ２ The internal quality rating was D.

[0064] Inventive Example 16, the moisture content of the mold powder used during continuous casting was as high as 0.22 mass%, and H was mixed into the molten nickel during continuous casting. The maximum porosity circle equivalent diameter of the slab cross section was as large as 5.2 mm, and the porosity area ratio was also high within the range at 0.58%. The number of defects detected by ultrasonic flaw detection testing in the product thickness was 0.31 / 100m. ２ The internal quality rating was D.

[0065] On the other hand, Comparative Examples 17 to 26 are outside the scope of the present invention. Each example will be explained below.

[0066] Since Comparative Examples 17 to 26 are outside the chemical composition range of the nickel alloy sheet of the present invention, the values ​​on the left side of Equation 1 and Equation 2 calculated from the chemical components (mass%) of H, P, S, and Mg in the Ni alloy are shown in parentheses in Table 1.

[0067] In Comparative Example 17, lime and fluorite used in the refining process had a high moisture content of 0.36 mass%, resulting in a high H of 0.0036 mass%, a large maximum porosity circle equivalent diameter of the slab cross section of 5.3 mm, a high porosity area ratio of 0.76%, and many porosities remaining even in the product thickness. The number of defects detected in the product thickness by ultrasonic flaw detection was 0.71 / 100 m. ２ The internal quality rating was E.

[0068] In Comparative Example 18, Mg, which should have been added in LF, was not added, and the Mg content was low at 0.001 mass%, so the H fixing effect of Mg could not be obtained. The maximum porosity circle equivalent diameter of the slab cross section was large at 5.1 mm, and the porosity area ratio was also high within the range at 0.51%. Porosity remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection testing in the product thickness was 0.45 / 100m. ２ The internal quality rating was E.

[0069] In Comparative Example 19, S, which should be added in LF, was not added, and the S content was low at 0.00003 mass%, so the effect of preventing porosity coarsening by S was not obtained. The maximum porosity circle equivalent diameter of the slab cross section was large at 5.2 mm, and porosity remained even in the product thickness. The number of defects detected in the product thickness by ultrasonic flaw detection was 0.43 / 100 m. ２ The internal quality rating was E.

[0070] In Comparative Example 20, P was mixed in as an impurity in the raw materials charged into the electric furnace, resulting in a high P content of 0.018 mass%. The P that was concentrated in the center of the plate thickness acted as a barrier to the diffusion of hydrogen gas and inhibited the bonding of porosity. The maximum porosity circle equivalent diameter of the slab cross section was 4.5 mm, which was large within the range, and the porosity area ratio was also 0.52%, which was high within the range. Many porosities remained even in the product thickness, and the number of defects detected in the product thickness by ultrasonic flaw detection was 0.58 / 100m. ２ The internal quality rating was E. Furthermore, the hot workability was also deteriorated, and edge cracks occurred on both sides of the coil after hot rolling.

[0071] In Comparative Example 21, the amount of Al added in the refining process was small, with Al being low at 0.0003 mass%, and deoxidation and desulfurization were not sufficiently performed. As a result, S was high by 0.0039 mass%, and S concentrated in the center of the plate thickness acted as a barrier to hydrogen gas diffusion and inhibited porosity bonding. The maximum porosity circle equivalent diameter in the slab cross section was 4.4 mm, which was large within the range, and the porosity area ratio was also high within the range at 0.50%, and many porosities remained even in the product thickness. The number of defects detected in the product thickness by ultrasonic flaw detection was 0.56 / 100m. ２The internal quality rating was E. Furthermore, the hot workability was also deteriorated, edge cracks occurred on both sides of the coil after hot rolling, there were many oxide-based inclusions, and scabs were also observed on the coil surface.

[0072] In Comparative Example 22, excess Mg was added in excess of what should have been added in LF, resulting in a high Mg content of 0.033 mass%. The Mg concentrated in the center of the plate thickness acted as a barrier to the diffusion of hydrogen gas and inhibited the porosity from being compressed. The maximum porosity circle equivalent diameter of the slab cross section was 4.8 mm, which was large within the range, and the porosity area ratio was 0.53%, which was also high within the range. Many porosities remained even in the product thickness, and the number of defects detected in the product thickness by ultrasonic testing was 0.65 / 100 m, resulting in an internal quality rating of E.

[0073] In Comparative Example 23, P was high at 0.018 mass%, S was high at 0.0034 mass%, and Mg was high at 0.035 mass%. The P, S, and Mg concentrated in the center of the plate thickness acted as a barrier to the diffusion of hydrogen gas, inhibiting the bonding of porosity. Many porosity remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection in the product thickness was 0.77 / 100m. ２ The internal quality rating was E.

[0074] In Comparative Example 24, H was high at 0.0033 mass%, P was also high at 0.017 mass%, S was high at 0.0033 mass%, and Mg was high at 0.034 mass%. The P, S, and Mg concentrated in the center of the plate thickness acted as a barrier to the diffusion of hydrogen gas and inhibited the bonding of porosity. The maximum porosity circle equivalent diameter in the slab cross section was large at 7.2 mm, and the porosity area ratio was also high at 0.88%. Many porosity remained even in the product thickness, and the number of defects detected in the product thickness by ultrasonic flaw detection was 1.13 / 100m. ２ The internal quality rating was E.

[0075] In Comparative Example 25, the amount of Al added in the LF was large, with Al being as high as 0.152 mass%, and aluminum inclusions were generated in the molten nickel, which in turn became coarse alumina clusters. As a result, many scab defects occurred on the surface of the coil, and before the ultrasonic flaw detection test of the 1 mmt nickel thin plate, which is the final internal quality evaluation, there were many scab defects on the surface and the coil was treated as scrap, so internal quality could not be evaluated and it was given an E rating.

[0076] In Comparative Example 26, P that should have been added in LF was not added, and the P content was low at 0.0003 mass%, and when the crops at the front and rear ends were cut off with a shearing machine before the finish rolling of the hot rolling, uncut portions were generated and turned into scrap. As a result, the ultrasonic flaw detection test of the 1 mmt nickel thin plate, which is the final internal quality evaluation, could not be performed and the steel was given a rating of E.

[0077] The technology of the present invention precisely controls trace elements of nickel alloys, such as P, Mg, S, and H, and can provide nickel alloy plates with excellent internal quality by reducing the amount of porosity in the cross section of nickel alloy slabs cast by continuous casting.

[0078] 1: Nickel alloy slab, 2: Internal quality inspection surface, 3: Final solidification position, 4: Shrinkage cavity (porosity), 5: Mg, P, S segregation area on the shrinkage cavity surface, 6: Ni molten metal with trace amounts of S segregated, EF: Electric furnace, AOD: Argon oxygen decarburization (argon oxygen decarburization equipment), VOD: Vacuum oxygen decarburization (vacuum oxygen decarburization equipment), LF: Ladle furnace (ladle refining equipment), CC: Continuous casting

Claims

1. A nickel alloy having excellent internal quality, characterized in that it contains Ni: 99.00 mass% or more, C: 0.001 to 0.020 mass%, Si: 0.01 to 0.30 mass%, Mn: 0.01 to 0.30 mass%, P: 0.001 to 0.015 mass%, S: 0.0001 to 0.0030 mass%, Al: 0.001 to 0.130 mass%, Fe: 0.40 mass% or less, O: 0.0003 to 0.0050 mass%, Mg: 0.003 to 0.030 mass%, B: 0.0001 to 0.0050 mass%, H: 0.0030 mass% or less, and the balance consists of inevitable impurities.

2. The nickel alloy excellent in internal quality according to claim 1, wherein at least one of the following relational expressions represented by Formula 1 and Formula 2 calculated from the chemical component contents (mass%) of H, P, S, and Mg in the nickel alloy is satisfied. (20 × H) × (2 × P + 10 × S + 3 × Mg) × 10 ４ ≤ 15.0 … (Formula 1) (25 × S + 3 × Mg) ÷ H ≥ 28.0 … (Formula 2) 3. The nickel alloy having excellent internal quality according to claim 2, characterized in that both of the formula 1 and the formula 2 among the above relationships are satisfied.

4. A method for manufacturing a nickel alloy plate having excellent internal quality, comprising a nickel alloy according to any one of claims 1 to 3, wherein in a cross-section perpendicular to the casting direction of a slab of the nickel alloy cast by a continuous casting machine, the size of porosity existing in the range of 1 / 5 thickness from the center of the thickness is 5.0 mm or less in terms of the equivalent diameter of a circle, and the total area ratio of porosity with an equivalent diameter of a circle of 0.5 mm or more (= total porosity area / inspection area × 100) is 0.60% or less, to produce a slab, and then hot rolling or hot rolling and cold rolling are continuously performed, and the reduction ratio (= (thickness of the slab - thickness of the nickel alloy plate) / thickness of the slab × 100) calculated from the thickness of the slab cast by the continuous casting machine and the thickness of the nickel alloy plate after hot rolling of the slab is 97.0% or more. A method for manufacturing a nickel alloy plate having excellent internal quality.

5. A method for producing a nickel alloy according to any one of claims 1 to 3, comprising melting raw materials in an electric furnace, then decarburizing in the electric furnace and / or AOD and / or VOD, adding lime and fluorite dried to a moisture content of 0.20 mass% or less, and producing a CaO-SiO ２ -Al ２ O ３ -MgO-F-based slag, further adding Si and / or Al, performing deoxidation and desulfurization, adjusting the temperature and components while promoting the floating of inclusions by Ar stirring in LF, and then producing a slab by continuous casting using a mold powder for continuous casting with a moisture content of 0.20 mass% or less. A method for producing a nickel alloy with excellent internal quality, characterized by this.

6. The raw materials are melted in an electric furnace, then decarburized in the electric furnace and / or AOD and / or VOD, lime and fluorite with a water content of 0.20 mass% or less are charged, and CaO - SiO ２ -Al ２ O ３ -MgO - F-based slag is produced. Further, Si and / or Al are charged, deoxidation and desulfurization are carried out, and after adjusting the temperature and components while promoting the floating of inclusions by Ar stirring in LF, a slab is produced by continuous casting using a mold powder for continuous casting with a water content of 0.20 mass% or less, and subsequently hot rolling or hot rolling and cold rolling are carried out. A method for manufacturing a nickel alloy plate having excellent internal quality according to claim 4, characterized in that.

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