Nickel alloy excellent in internal quality, alloy sheet, and production method therefor

Abstract

To provide a nickel alloy excellent in internal quality by detoxifying a void defect affected to the internal quality.SOLUTION: The present invention relates to a nickel alloy excellent in internal quality and comprising, in terms of mass%, 99.00% or more Ni, 0.001 to 0.020% C, 0.01 to 0.30% Si, 0.01 to 0.30% Mn, 0.001 to 0.015% P, 0.0001 to 0.0030% S, 0.001 to 0.130% Al, 0.40% or less Fe, 0.0003 to 0.0050% O, 0.003 to 0.030% Mg, 0.0001 to 0.0050% B, 0.0030% or less H, and the balance of inevitable impurities. It is preferable that either one or both of a Formula 1 and a Formula 2 calculated from mass% of H, P, S, and Mg in the alloy is satisfied. Formula 1 is (20×H)×(2×P+10×S+3×Mg)×104≤15.0 and Formula 2 is (25×S+3×Mg)÷H≥28.0.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a nickel alloy containing 99.00 mass% or more of nickel and a nickel alloy plate using the same, and precisely controls trace components such as P, Mg, S, and H in the nickel alloy, and reduces the porosity amount in the cross-section of a nickel alloy slab cast by continuous casting. The present invention relates to a nickel alloy, a nickel alloy plate, and a method for manufacturing the same, which have excellent internal quality.

Background Art

[0002] A nickel alloy containing 99.00 mass% or more of Ni has excellent corrosion resistance and heat resistance, and thus is an alloy used in a wide range of fields such as the chemical industry, electronic component materials, and the aerospace industry. Here, nickel, which occupies the main component of the nickel alloy, is a very expensive metal compared to iron. Therefore, improving the yield is very important for suppressing the manufacturing cost. In the continuous casting process, void defects caused by unavoidably generated center porosity may have a great influence on the final product quality and yield, such as becoming the starting point of cracks during punching, cutting, welding, etc.

[0003] Here, several manufacturing methods of nickel alloys having a high yield are disclosed. Patent Document 1 describes a technique for obtaining a nickel cold-rolled coil having high productivity and yield by containing 4 to 100 ppm of boron and further controlling the average pressure of each pass by cold rolling.

[0004] Further, Patent Document 2 discloses a technique for manufacturing a nickel alloy plate having excellent surface quality by controlling the non-metallic inclusion composition and suppressing the number of MgO·Al2O3 inclusions.

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

[0006] In addition, technologies for improving internal quality, particularly void defects, are also disclosed. In Patent Document 3, when continuously casting molten steel with C ≤ 0.18%, a portion of the solid fraction at the center of the slab where the solid fraction is 90 - 98% is subjected to one-pass rolling reduction with a rolling reduction rate of 2 - 5% using a rolling reduction roll, thereby disclosing a method for manufacturing a continuously cast slab with excellent internal quality.

[0007] Patent Document 4 is a technology for manufacturing a molten steel chromium-containing molten steel with excellent internal quality by determining the position to start rolling reduction of the slab based on the surface temperature and roll reaction force of the slab and performing appropriate rolling reduction when continuously casting chromium-containing molten steel.

[0008] However, since the above technologies relate to Fe-based alloys with Fe as the main component, they cannot be applied to nickel alloys containing 99.00 mass% or more of Ni, which is the subject of the present application. In addition, while these Fe-based alloys contain many other components in addition to Fe, in nickel alloys containing 99.00 mass% or more of Ni, the behavior of solidification and segregation is significantly different, which has a great influence on the generation of void defects caused by center porosity and the rolling behavior. That is, the problems regarding the internal quality in nickel alloys still remained.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0011] In order to solve the above problems, the inventors of the present application have conducted intensive research. First, the inventors of the present application evaluated the internal quality of nickel alloy slabs and nickel alloy plates containing 99.00 mass% or more of Ni. As shown in FIG. 1, the inventors of the present application cut a 200 mm t-thick nickel alloy slab 1 ingot-cast and collected samples, and mirror-polished samples of the slab cross-section (internal quality inspection surface 2) perpendicular to the casting direction. The equivalent circle diameter, number, and area of the porosity present on the entire mirror-polished surface of the sample were measured at a magnification of 200 times using a SEM (scanning electron microscope) having a particle analysis function. At the same time, elemental analysis by EDS (energy dispersive X-ray spectroscopy) was performed to distinguish non-metallic inclusions from porosity. Here, the equivalent circle diameter is the diameter of a circle having the same area calculated from the area of the irregular porosity.

[0012] Furthermore, these nickel alloy slabs were subjected to hot rolling and cold rolling to produce a 1 mm t-thick nickel alloy plate, and an ultrasonic flaw detection test (UT) was performed to investigate the amount of internal defects generated. Then, samples of the internal defect parts were collected, and the shape of the internal defects and the presence or absence of foreign substances were investigated by SEM and EDS. Furthermore, using a SIMS (secondary ion mass spectrometer), it was investigated whether light elements such as hydrogen were present around the internal defects. Also, a hole was drilled with a 1 mm φ diameter drill from the surface of the sample of the internal defect part, and the gas released from the internal defect was collected, and the gas component analysis was also performed.

[0013] As a result of the investigation, porosity exists in the range of 1 / 5 of the thickness from the center of the slab cross-section. All the internal defects detected by the ultrasonic flaw detection test of the nickel alloy plate with a thickness of 1 mm t were defects caused by porosity, and it was revealed that a gas mainly composed of hydrogen exists in the voids. An example of this defect is shown in Fig. 2. As shown in Fig. 2, the porosity of the nickel alloy plate has a gap of about 1 μm in thickness, and in the region very close to the porosity, it was observed that Mg, P, S, and H were concentrated. Here, although non-metallic inclusions of the CaO-SiO2-Al2O3-MgO-MnO system, CaO-Al2O3 system, MgO system, and CaO system were also detected in the nickel alloy plate, since they are about several μm in size and small in number, they do not affect the punching, cutting, welding, etc. of the nickel alloy plate. As will be described later, Al2O3, that is, alumina-based inclusions, cluster and become coarse, causing Hegel defects on the coil surface, so they are oxide-based inclusions to be avoided.

[0014] Based on the above results, the generation mechanism of the internal defects of the nickel alloy plate detected by the ultrasonic flaw detection test was considered as follows. As shown in Figs. 3 and 4, the shrinkage cavity (porosity) 4 generated at the final solidification position 3 near the center of the thickness of the slab 1 during the casting of the nickel melt by the continuous casting machine is in a negative pressure state due to solidification shrinkage, and H, which is an impurity component dissolved in the nickel alloy immediately after solidification, becomes a gas and is released and filled inside the shrinkage cavity (porosity) 4. Here, Mg, P, and S, which have a high vapor pressure at about 1450 °C, the liquidus temperature of the nickel melt, are released as gases into the porosity 4 from the state of being dissolved in the nickel alloy immediately after solidification (in the figure, the underscore of the element represents the dissolved state), just like H. Furthermore, when the slab is cooled to room temperature (Fig. 4(b)), since Mg, P, and S are in a state where the solid phase is stable, they will adhere to the inner surface of the porosity.

[0015] After that, as shown in FIGS. 5 and 6, during hot rolling, the porosity 4 inside the slab is compressed in the thickness direction together with the nickel alloy. When there are no segregation elements of Mg, P, and S on the inner surface of the porosity as shown in FIG. 5, as the internal pressure of the porosity increases, hydrogen gas diffuses into the nickel alloy, and finally the nickel alloys are completely bonded and the porosity disappears. However, when there are segregation elements of Mg, P, and S on the inner surface of the porosity as shown in FIG. 6, since Mg, P, and S are elements with larger atomic radii than H, they are less likely to diffuse into the nickel alloy and become a barrier to the diffusion of hydrogen gas into the nickel alloy. As a result, a porosity 4 of hydrogen gas with a thickness of about 1 μm remains in the Ni alloy plate, and segregation 5 of Mg, P, and S is detected around the porosity 4.

[0016] Furthermore, the inventors of the present application have also discovered that a small amount of Mg forms a fine compound with H in the form of MgH2 or Mg2NiH4 in the nickel alloy and has the effect of reducing the H segregated near the center of the slab thickness by fixing H.

[0017] Furthermore, as shown in FIG. 7, the inventors of the present application have discovered that a small amount of S has the effect of suppressing the coarsening of shrinkage cavities (porosities) 4 generated 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 side to the liquid phase side during the solidification process of the nickel melt (about 1450 °C in semi-molten state), concentrates at the dendrite trunk and grain boundaries, and deteriorates the hot workability. The final solidification position 3 near the center of the slab thickness generates shrinkage cavities (porosities) 4 due to the negative pressure caused by solidification shrinkage. However, S has the effect of reducing the surface tension of the nickel melt, increasing the fluidity of the semi-molten nickel melt that has started to solidify, and flowing into the shrinkage cavities, thereby discovering that it has the effect of suppressing the coarsening of the shrinkage cavities (porosities) 4. As a result, the number of fine shrinkage cavities (porosities) increases, but there is an effect of suppressing the coarsening of the porosities. This phenomenon occurs before gas components such as H described above are released and filled inside the shrinkage cavities (porosities).

[0018] The inventors of the present application investigated the internal quality of nickel alloy slabs and nickel alloy plates manufactured under various components and various operating conditions, analyzed a large amount of data, and discovered the relationship between each component and various operating conditions for obtaining a nickel alloy plate with excellent internal quality in which internal defects are not detected by ultrasonic flaw detection tests, that is, a nickel alloy plate with a reduced porosity amount. Taking into account the findings obtained from the above-mentioned intensive research, the present invention was completed.

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

[0020] In the nickel alloy of the present invention, it is a preferred embodiment that at least one of the following relational expressions represented by Formula 1 and Formula 2 calculated from the chemical components (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)

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

[0022] The nickel alloy plate with excellent internal quality of the present invention is a nickel alloy plate made of the above nickel alloy. In the cross-section perpendicular to the casting direction of the slab of the nickel alloy cast by a continuous casting machine, the size of the porosity existing in the range of 1 / 5 thickness from the thickness center is 5.0 mm or less in terms of the equivalent diameter of a circle, and the total area ratio of the 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. A slab characterized by this is manufactured, and subsequently, it is obtained by performing hot rolling or hot rolling and cold rolling.

[0023] In the nickel alloy plate of the present invention, it is a preferred embodiment that the reduction ratio (= (slab thickness - nickel alloy plate thickness) / slab thickness × 100) calculated from the thickness of the slab cast by a continuous casting machine and the thickness of the nickel alloy plate after hot rolling the slab is 97.0% or more.

[0024] Also, the manufacturing method of the nickel alloy with excellent internal quality of the present invention described above is to melt the raw materials in an electric furnace, then decarburize in the electric furnace and / or AOD and / or VOD, charge lime and fluorite dried to a moisture content of 0.20 mass% or less, produce a CaO - SiO2 - Al2O3 - MgO - F - based slag, further charge Si and / or Al, perform deoxidation and desulfurization, adjust the temperature and components while promoting the floating of inclusions by Ar stirring in LF, and then manufacture a slab by continuous casting using a continuous casting mold powder with a moisture content of 0.20 mass% or less.

[0025] Moreover, the method for manufacturing a nickel alloy sheet excellent in internal quality of the present invention described above includes melting raw materials in an electric furnace, then decarburizing in the electric furnace and / or AOD and / or VOD, charging lime and fluorite dried to a moisture content of 0.20 mass% or less, producing a CaO-SiO2-Al2O3-MgO-F-based slag, further charging Si and / or Al, performing deoxidation and desulfurization, adjusting the temperature and components while promoting inclusion floating by Ar stirring in LF, then producing a slab by continuous casting using a continuous casting mold powder with a moisture content of 0.20 mass% or less, and subsequently performing hot rolling or hot rolling and cold rolling.

[0026] In the method for manufacturing a nickel alloy sheet of the present invention, it is a preferred embodiment that the reduction ratio (= (thickness of slab - thickness of nickel alloy sheet) / thickness of slab × 100) calculated from the thickness of the slab cast by a continuous casting machine and the thickness of the nickel alloy sheet after hot rolling the slab is 97.0% or more.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0028] First, the reasons for limiting the chemical composition of the nickel alloy plate of the present invention are shown. Ni: 99.00 mass% or more It is a main component of the nickel alloy and is essential for exhibiting seawater resistance, alkali resistance, especially corrosion resistance against caustic soda and chlorine gas. Therefore, in the present invention, it is set to 99.00 mass% or more. Preferably it is 99.10 mass% or more, and more preferably 99.20 mass% or more.

[0029] C: 0.001 - 0.020 mass% If C is present in excess, it precipitates as graphite at the grain boundaries in the temperature range of 430 to 650 °C, which causes embrittlement. Therefore, it is necessary to control it to 0.020 mass% or less. On the contrary, C has the effect of improving strength, and in order to ensure the tensile strength and yield strength as a nickel alloy plate, 0.001 mass% or more is required. Therefore, in the present invention, the content of C is set to 0.001 to 0.020 mass%. Preferably, it is 0.003 to 0.018 mass%, and more preferably 0.005 to 0.015 mass%.

[0030] Si: 0.01 - 0.30 mass% Si is an element effective for deoxidation. When Si is contained in an amount of 0.01 mass% or more, a deoxidation effect can be obtained. On the other hand, when the content of Si exceeds 0.30 mass%, it becomes difficult to ensure Ni: 99.00% or more. Therefore, in the present invention, the content of Si is set to 0.01 to 0.30 mass%. Within this range, preferably, it is 0.03 to 0.25 mass%. More preferably, it is 0.05 to 0.20 mass%.

[0031] Mn: 0.01 - 0.30 mass% Mn is an element effective for deoxidation, similar to Si. When the amount of Mn is 0.01 mass% or more, a deoxidation effect can be obtained. On the other hand, if it exceeds 0.30 mass%, it becomes difficult to ensure Ni: 99.00% or more. Therefore, in the present invention, the content of Mn is defined as 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%.

[0032] P: 0.001 - 0.015 mass% P is an element that tends to segregate during the solidification of nickel molten metal. When it exceeds 0.015 mass%, the P concentrated in the center of the slab thickness becomes a barrier to the diffusion of hydrogen gas, inhibits the bonding of porosity, and further deteriorates the hot workability. Here, the nickel alloy containing 99.00 mass% or more of Ni targeted by the present application is an alloy excellent in ductility at high temperatures. Conversely, it is also an alloy with poor shear workability at high temperatures. Therefore, during the finish rolling of hot rolling, when cutting the front and rear ends of the crop with a shearing machine before rolling, residues are generated, making it difficult to continue hot rolling. The inventors of the present application have found that by containing 0.001 mass% or more of P, the shear workability during hot rolling can be ensured even in a nickel alloy containing 99.00 mass% or more. For this reason, the content of P is set to 0.001 to 0.015 mass%. Preferably, it is 0.002 to 0.012 mass%, and more preferably 0.003 to 0.010 mass%.

[0033] S: 0.0001 - 0.0030 mass% Since S segregates at grain boundaries, deteriorates hot workability, and causes cracking during hot rolling, it is necessary to control it to 0.0030 mass% or less. Furthermore, S is an element that easily segregates during the solidification of nickel molten metal. When it exceeds 0.0030 mass%, S concentrated in the center of the plate thickness becomes a barrier to the diffusion of hydrogen gas, inhibiting the bonding of porosity. Also, as described above, S has the effect of preventing the coarsening of porosity. To obtain this effect, it is necessary for S to be 0.0001 mass% or more. Therefore, the content of S was determined to be 0.0001 - 0.0030 mass%. Preferably it is 0.0002 - 0.0020 mass%, and more preferably 0.0003 - 0.0010 mass%.

[0034] Al: 0.001 - 0.130 mass% Al is a deoxidizing element. When the content of Al is less than 0.001 mass%, deoxidation does not work sufficiently, the O concentration becomes higher than 0.0050 mass%, the number of oxide-based inclusions increases, and it causes surface defects. On the other hand, when it exceeds 0.130 mass%, it becomes difficult to secure Ni: 99.00% or more, and the oxide-based inclusions become coarse alumina clusters, causing surface defects. Therefore, the Al content was determined to be 0.001 - 0.130 mass%. Preferably, it is 0.005 - 0.100 mass%, and more preferably 0.010 - 0.080 mass%.

[0035] Fe: 0.40 mass% or less Fe is an unavoidably mixed component and is an impurity in nickel alloys, and it is desirable to be as low as possible. Therefore, it was determined to be 0.40 mass% or less. Preferably it is 0.35 mass% or less, and more preferably 0.30 mass% or less.

[0036] Mg: 0.003 - 0.030 mass% Mg forms a compound with H in the form of MgH2 or Mg2NiH4 in the nickel alloy and fixes H, thereby reducing the H segregating near the center of the slab thickness. If it is 0.003 mass% or more, these effects will be manifested. On the other hand, as described above, Mg is an element that is prone to segregation during the solidification of the nickel melt. When it exceeds 0.030 mass%, the Mg concentrated in the center of the plate thickness becomes a barrier to the diffusion of hydrogen gas and inhibits the bonding of porosity near the center of the slab thickness. Therefore, the Mg content is defined as 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%.

[0037] O: 0.0003 - 0.0050 mass% When O exists in the nickel alloy exceeding 0.0050 mass%, the amount of oxide-based inclusions increases, which not only has an adverse effect on the surface properties but also becomes the starting point of cracks during the processing of the nickel alloy plate. Furthermore, it inhibits desulfurization and the S concentration in the nickel melt exceeds 0.0030 mass%. Conversely, when it is lower than 0.0003%, the deoxidizing element Al is controlled to exceed 0.130 mass%, and the oxide-based inclusions become coarse alumina clusters, causing surface defects. Therefore, the O content is defined as 0.0003 to 0.0050 mass%. Preferably, it is 0.0004 to 0.0040 mass%, and more preferably, it is 0.0005 to 0.0030 mass%.

[0038] B: 0.0001 - 0.0050 mass% B is a component that improves hot workability. If it is less than 0.0001 mass%, the effect is not exerted. Conversely, if it exceeds 0.0050 mass%, boron compounds (borides) are formed, causing deterioration of corrosion resistance and workability. Therefore, it is set to 0.0001 to 0.0050 mass%. Preferably, it is 0.0003 to 0.0040 mass%, and more preferably, it is 0.0005 to 0.0030 mass%.

[0039] H: 0.0030 mass% or less H is a gas component present inside the porosity of a nickel alloy plate, and it is mixed in from the moisture in auxiliary materials such as lime used in the steelmaking process and the moisture in the atmosphere. As described above, when casting nickel molten metal with a continuous casting machine, the shrinkage cavity (porosity) generated at the final solidification position near the center of the slab thickness is in a negative pressure state due to solidification shrinkage. Hydrogen dissolved in the nickel molten metal becomes a gas and is released and fills the inside of the shrinkage cavity (porosity). When H exceeds 0.0030 mass%, large porosities are likely to be generated, and furthermore, the number of porosities also increases, and porosities remain inside the nickel alloy plate produced by hot rolling or hot rolling and cold rolling. Therefore, in the present invention, it is set to 0.0030 mass% or less. Preferably it is 0.0020 mass%, and more preferably 0.0010 mass% or less. How to achieve H: 0.0030 mass% or less is described below. It is preferable to use lime and fluorite used in the refining process with a moisture content of 0.2 mass% or less. Furthermore, reduce H to 0.0010 mass% or less in the vacuum degassing process. Furthermore, the tundish during continuous casting is sealed with Ar or N2 gas with a moisture concentration of 1 vol.ppm or less to prevent contact between the atmosphere and the molten nickel alloy. Furthermore, it is preferable to use a mold powder with a moisture content of 0.2 mass% or less used in continuous casting to prevent an increase in H of the molten nickel alloy.

[0040] (20×H)×(2×P + 10×S + 3×Mg)×10 4 ≦15.0 …(Equation 1) (25×S + 3×Mg)÷H ≧ 28.0 …(Equation 2) As described above, H is a gas component present inside the porosity of the nickel alloy plate and is the component that most affects the internal quality of the nickel alloy plate. Also, P, S, and Mg act as barriers to the diffusion of hydrogen gas present inside the porosity. However, trace amounts of S and Mg have the effect of preventing the coarsening of the porosity and fixing H, thereby reducing the segregation of H to the vicinity of the center of the slab thickness. The inventors of the present application considered the degree of influence of H, P, S, and Mg in the Ni alloy on the internal quality as coefficients and compared them with the internal quality of a large number of nickel alloy plates. As a result, within the chemical composition range of the nickel alloy plate of the present invention, it was derived that it is a preferable range for the internal quality of the nickel alloy plate that the left sides of Formula 1 and Formula 2 calculated from the chemical compositions (mass%) of H, P, S, and Mg in the Ni alloy satisfy the conditions on the right sides of Formula 1 or / and Formula 2. (20×H)×(2×P + 10×S + 3×Mg)×10 4 ≦15.0 …(Formula 1) (25×S + 3×Mg)÷H ≧ 28.0 …(Formula 2)

[0041] Porosity in slab cross-section In the present invention, in a cross-section perpendicular to the casting direction of the slab cast by a continuous casting machine, the size of the porosity present in the range from the center of the thickness to 1 / 5 of the thickness is 5.0 mm or less in terms of the equivalent circle diameter, and the total area ratio of the porosity with an equivalent circle diameter of 0.5 mm or more (= total porosity area / inspection area × 100) is 0.60% or less. It is a preferred embodiment to manufacture a slab having these characteristics and then perform hot rolling or hot rolling and cold rolling. The basis for the reasons for the limitations is shown below.

[0042] The size of the porosity existing in the range of 1 / 5 thickness from the center of the slab thickness is 5.0 mm or less in terms of equivalent circle diameter Porosity that inevitably occurs at the final solidification position of continuous casting will cause internal defects in the final product if it remains as it is. As the nickel alloy is rolled in the hot rolling process, the thickness of the porosity decreases and the bonding progresses. However, if the porosity at the slab stage is coarse, it cannot be completely bonded and remains as a defect in the final product. The inventors of the present application found from the investigation of the internal defects by ultrasonic flaw detection of the porosity existing in the cross-sections of a large number of slabs and the nickel alloy plates subjected to hot rolling or hot rolling and cold rolling that, at the slab stage, those with a size of the detected porosity equivalent to a circle diameter larger than 5.0 mm cannot be bonded by hot rolling and will become defects in the final product. Therefore, in the present application, the size of the defects detected at the slab stage is set to 5.0 mm or less in terms of the equivalent circle diameter. More preferably, it is 3.0 mm or less, and even more preferably, it is 1.0 mm or less. Here, the reason for limiting it to 1 / 5 from the center of the slab thickness is that the porosity is generated near the final solidification position, that is, near the center of the slab thickness.

[0043] The total area ratio of the porosity with a size of 0.5 mm or more in terms of equivalent circle diameter existing in the range of 1 / 5 thickness from the center of the slab thickness (= total porosity area / inspection area × 100) is 0.60% or less As described above, porosity that inevitably occurs at the final solidification position in continuous casting will cause internal defects in the final product if left as it is. However, for small porosity, as the nickel alloy is rolled in the hot rolling process, the porosity thickness becomes smaller and crimping easily progresses, becoming harmless in the final product. However, when the size of the porosity at the slab stage is 0.5 mm or more in terms of the equivalent diameter of a circle and the total area ratio of the porosity (= total porosity area / inspection area × 100) exceeds 0.60%, the inventors of the present application have found that some of the porosity remains as a defect in the final product without being crimped. During hot rolling, as the internal pressure of the porosity increases, hydrogen gas diffuses into the nickel alloy, and finally the nickel alloy is completely crimped and the porosity disappears. However, when the porosity area ratio in the range of 1 / 5 of the slab thickness from the center of the slab thickness exceeds 0.60% and the porosity area is large, the dissolved H concentration at the center of the nickel alloy thickness increases during hot rolling, and the hydrogen gas inside the porosity is inhibited from diffusing into the nickel alloy. Therefore, in the present application, it is defined that the total area ratio of the porosity is 0.60% or less. Preferably it is 0.50% or less, and more preferably 0.40% or less. Here, the reason for limiting it to 1 / 5 from the center of the slab thickness is that the porosity is generated near the final solidification position, that is, near the center of the slab thickness.

[0044] Reduction ratio during hot rolling When performing rolling on a nickel alloy slab manufactured by a continuous casting machine after heating it at 1000°C to 1100°C with a hot rolling mill, it is a preferred mode that the 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 is 97.0% or more.

[0045] This is because if the rolling reduction rate is 97.0% or more, the porosity existing in the nickel alloy slab is crimped, and by eliminating the porosity, a nickel alloy plate with excellent internal quality can be manufactured. Here, the reason for not specifying the rolling reduction rate of cold rolling is that in the rolling reduction of cold rolling performed at normal temperature, diffusion of hydrogen inside the porosity into the nickel alloy cannot be expected. That is, since there is no effect of crimping the porosity, only the rolling reduction rate of hot rolling performed at 1000°C to 1100°C is specified in the present application.

[0046] Method for manufacturing slab First, the raw materials are melted in an electric furnace, then decarburized in the electric furnace and / or AOD and / or VOD, and lime and fluorite dried to a moisture content of 0.20 mass% or less are added to produce a CaO-SiO2-Al2O3-MgO-F-based slag. Further, Si and / or Al are added for deoxidation and desulfurization. After adjusting the temperature and components while promoting the floating of inclusions by Ar stirring in LF, a nickel alloy slab is produced by continuous casting using a mold powder for continuous casting with a moisture content of 0.20 mass% or less. The manufacturing method of a nickel alloy with excellent internal quality and the manufacturing method of a nickel alloy using the nickel alloy will be described in detail.

[0047] The moisture content of lime and fluorite is 0.20 mass% or less The inventors of the present application have determined from a number of operating conditions and the moisture content of lime and fluorite that the main cause of H dissolving in the nickel melt during the refining process is from the moisture in the lime and fluorite. In order to achieve H: 0.0030 mass% or less, it is necessary to use lime and fluorite dried to a moisture content of 0.20 mass% or less.

[0048] The moisture content of the mold powder for continuous casting is 0.20 mass% or less During continuous casting, the mold powder is a powdery oxide that serves to keep the molten metal surface warm in the mold, lubricate the mold and the slab, and absorb non-metallic inclusions. However, the inventors of the present application have determined that in order to reduce the generation of porosity in the slab cross-section, it is preferable to use a powder with a moisture content of 0.20 mass% or less as the mold powder.

Example

[0049] Next, examples are presented to more clearly illustrate the configuration, working effects of the invention of the present application. However, the invention of the present application is not limited only to the following examples.

[0050] Using an electric furnace with a capacity of 30 tons or 60 tons, pure nickel, pure nickel scraps, etc. were used as raw materials and melted. Then, oxygen blowing refining (oxidation refining) for removing C was carried out in the electric furnace and / or AOD and / or VOD, limestone and fluorite were added to generate a CaO-SiO2-Al2O3-MgO-F-based slag, and further, pure Si and / or Al were added to reduce NiO, and then deoxidation was carried out. After that, further Ar stirring was carried out to promote desulfurization. In AOD and VOD, magnesite bricks were used for lining. Then, it was poured into a ladle, and the temperature and composition were adjusted in LF, and a slab with a thickness of 200 mm was manufactured by a continuous casting machine.

[0051] From the manufactured slab, a cross-sectional sample perpendicular to the casting direction was taken. For this cross-sectional sample, a nickel alloy slab with a thickness of 200 mm was cut to take a sample, and the sample of the slab cross-section perpendicular to the casting direction was mirror-polished. Using a SEM (scanning electron microscope) with particle analysis function, the equivalent circle diameter, number, and area of porosity existing at 1 / 5 from the center of the mirror-polished slab thickness of the sample were measured at a magnification of 200 times. At the same time, elemental analysis by EDS (energy dispersive X-ray spectroscopy) was carried out to distinguish non-metallic inclusions and porosity. Also, the surface of the manufactured slab was ground, heated at 1050 °C, and hot-rolled to manufacture a hot strip with a thickness of 3.0 - 6.8 mm. Then, annealing and pickling were carried out to remove the scale on the surface. Finally, cold rolling was carried out to manufacture a nickel alloy thin sheet with a width of 1000 mm and a thickness of 1 mm.

[0052] Table 1 shows the chemical composition of the nickel alloy obtained, the values of the left sides of Formula 1 and Formula 2 calculated from the chemical compositions of H, P, S, and Mg in the Ni alloy (mass%), the maximum equivalent circle diameter of the porosity existing in the range of 1 / 5 thickness from the thickness center of the cross-section perpendicular to the casting direction of the slab, the total area ratio of the porosity with an equivalent circle diameter of 0.5 mm or more, the moisture content, the reduction ratio during hot rolling, and the results of the internal quality evaluation by ultrasonic flaw detection test of the 1 mm thick nickel thin plate. These measurement methods and evaluation methods are as follows.

[0053] 1) Chemical composition of nickel alloy Samples were taken from the nickel alloy plate and quantitatively analyzed using a fluorescent X-ray analyzer. The oxygen concentration and hydrogen concentration were quantitatively analyzed by the 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 inevitable impurities such as Cr, Mo, Cu, Ti, W, Co, Pb, Sn, N, Se, and V are present.

[0054] 2) Maximum equivalent circle diameter of porosity and porosity area ratio with an equivalent circle diameter of 0.5 mm or more The sample of the slab cross-section perpendicular to the casting direction was mirror-polished, and the equivalent circle diameter, number, and area of the porosity existing at 1 / 5 from the thickness center of the mirror-polished slab of the sample were measured at a magnification of 200 times using a SEM (scanning electron microscope) with a particle analysis function, and calculated from those values.

[0055] 3) Reduction ratio during hot rolling It was calculated by 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 ratio = (thickness of slab - thickness of nickel alloy plate) / thickness of slab × 100

[0056] 4) Moisture content The moisture content of lime, fluorite used in the refining process, and mold powder used during continuous casting was measured by the drying loss method in which a sample for measurement was taken before use, heated at 105 °C for 5 hours, and the weight loss before and after drying was quantified as the moisture content.

[0057] 5) Internal quality evaluation An ultrasonic flaw detection test was carried out on a 1 mm thick coil with a width of 1000 mm rolled to the product thickness. The flaw detection was carried out with a sensitivity capable of detecting a porosity (void) with a minimum width of 50 μm × length of 100 μm × thickness of 1 μm. The flaw detection area was 100 m 2 If the number of detected defects is 0.10 or less per 100 m, the evaluation is ⊙; if it is 0.11 to 0.20, the evaluation is ○; if it is 0.21 to 0.30, the evaluation is □; if it is 0.31 to 0.40, the evaluation is △; if it is 0.41 or more, the evaluation is ×. Also, when there are many hedge defects on the surface and it becomes a shaving process and the internal quality cannot be evaluated, and when there is a residue due to crop cutting during hot rolling and it becomes a shaving process and the internal quality cannot be evaluated, the evaluation is also ×.

[0058] Here, before the ultrasonic flaw detection test of the 1 mm thick nickel thin plate, which is the final internal quality evaluation, for a coil with many hedge defects on the surface and becoming a shaving process, and for a coil with a residue generated when cutting the crop at the front and rear ends with a charring machine before the finish rolling of hot rolling and becoming a shaving process, the internal quality cannot be evaluated and the evaluation is ×.

[0059]

Table 1

[0060]

Table 2

[0061] Inventions 1 to 16 of the invention examples satisfied the scope of the present invention, so the number of defects detected by the ultrasonic flaw detection test at the product thickness was small and good quality could be obtained.

[0062] In invention example 8, since the thickness after hot rolling was thick, the rolling reduction rate during hot rolling was as low as 96.6%, the porosity near the center of the slab thickness could not be completely pressed, and the number of defects detected by the ultrasonic flaw detection test at the product thickness was 0.12 pieces / 100 m 2 and the internal quality evaluation was ○.

[0063] In Invention Examples 9 to 12, since the left sides of Formula 1 and Formula 2 calculated from the chemical component (mass%) of H, P, S, and Mg in the Ni alloy do not satisfy any of the conditions on the right side of Formula 1 or Formula 2, the internal quality evaluation was ○.

[0064] In Invention Examples 13 to 14, since the left sides of Formula 1 and Formula 2 calculated from the chemical component (mass%) of H, P, S, and Mg in the Ni alloy do not satisfy both of the conditions on the right sides of Formula 1 and Formula 2, the internal quality evaluation was □.

[0065] In Invention Example 15, the moisture content of lime and fluorite used in the refining process was as high as 0.24 mass%, the H concentration was also increased within the range of 0.0029 mass%, the equivalent diameter of the maximum porosity circle in the slab cross-section was also large at 4.4 mm within the range, the area ratio of porosity was also high at 0.61%, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.37 pieces / 100 m 2 and the internal quality evaluation was △.

[0066] In Invention Example 16, the moisture content of the mold powder used during continuous casting was as high as 0.22 mass%, H was mixed into the nickel melt during continuous casting, the equivalent diameter of the maximum porosity circle in the slab cross-section was also large at 5.2 mm, the area ratio of porosity was also increased within the range of 0.58%, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.31 pieces / 100 m 2 and the internal quality evaluation was △.

[0067] On the other hand, Comparative Examples 17 to 26 deviate from the scope of the present invention. Each example will be described below.

[0068] Since Comparative Examples 17 to 26 deviate from the chemical component range of the nickel alloy plate of the present invention, the numerical values on the left sides of Formula 1 and Formula 2 calculated from the chemical components (mass%) of H, P, S, and Mg in the Ni alloy are described in parentheses in Table 1.

[0069] In Comparative Example 17, since high moisture contents of 0.36 mass% of lime and fluorite used in the refining process were used, H became as high as 0.0036 mass%, the equivalent diameter of the maximum porosity circle in the slab cross-section was as large as 5.3 mm, the area ratio of porosity was also as high as 0.76%, a large number of porosities remained even at the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.71 pieces / 100 m 2 As a result, the internal quality evaluation was ×.

[0070] In Comparative Example 18, Mg that should be added in LF was not added, Mg was as low as 0.001 mass%, the effect of fixing H by Mg could not be obtained, the equivalent diameter of the maximum porosity circle in the slab cross-section was as large as 5.1 mm, the area ratio of porosity was also relatively high within the range of 0.51%, porosities remained even at the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.45 pieces / 100 m 2 As a result, the internal quality evaluation was ×.

[0071] In Comparative Example 19, S that should be added in LF was not added, S was as low as 0.00003 mass%, the effect of preventing coarsening of porosity by S could not be obtained, the equivalent diameter of the maximum porosity circle in the slab cross-section was as large as 5.2 mm, porosities remained even at the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.43 pieces / 100 m 2 As a result, the internal quality evaluation was ×.

[0072] In Comparative Example 20, P from impurities in the raw materials charged into the electric furnace was mixed in, P became as high as 0.018 mass%, P concentrated in the center of the plate thickness became a barrier to the diffusion of hydrogen gas, inhibited the crimping of porosity, the equivalent diameter of the maximum porosity circle in the slab cross-section was relatively large within the range of 4.5 mm, the area ratio of porosity was also relatively high within the range of 0.52%, a large number of porosities remained even at the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.58 pieces / 100 m 2 As a result, the internal quality evaluation was ×. Furthermore, the hot workability also deteriorated, and ear cracks occurred on both sides of the coil after hot rolling.

[0073] In Comparative Example 21, the addition amount of Al in the refining process was small, with Al as low as 0.0003 mass%, deoxidation and desulfurization were not sufficiently carried out, S was as high as 0.0039 mass%, and the concentrated S in the center of the slab thickness became a barrier to the diffusion of hydrogen gas, inhibiting the crimping of porosity. The equivalent diameter of the maximum porosity circle in the slab cross-section was relatively large within the range of 4.4 mm, and the area ratio of porosity was also relatively high within the range of 0.50%. A large number of porosities remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.56 pieces / 100 m 2 As a result, the internal quality evaluation was ×. Furthermore, the hot workability also deteriorated, ear cracks occurred on both sides of the coil after hot rolling, there were also many oxide inclusions, and Heg defects were observed on the coil surface.

[0074] In Comparative Example 22, an excessive amount of Mg to be added in LF was added, with Mg as high as 0.033 mass%. The concentrated Mg in the center of the slab thickness became a barrier to the diffusion of hydrogen gas, inhibiting the crimping of porosity. The equivalent diameter of the maximum porosity circle in the slab cross-section was relatively large within the range of 4.8 mm, and the area ratio of porosity was also relatively high within the range of 0.53%. A large number of porosities remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.65 pieces / 100 m2, resulting in an internal quality evaluation of ×.

[0075] In Comparative Example 23, P was as high as 0.018 mass%, S was as high as 0.0034 mass%, and Mg was as high as 0.035 mass%. The concentrated P, S, and Mg in the center of the slab thickness became barriers to the diffusion of hydrogen gas, inhibiting the crimping of porosity. A large number of porosities remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 0.77 pieces / 100 m 2 As a result, the internal quality evaluation was ×.

[0076] In Comparative Example 24, H was as high as 0.0033 mass%, further, P was as high as 0.017 mass%, S was as high as 0.0033 mass%, and Mg was as high as 0.034 mass%. The concentrated P, S, and Mg at the center of the slab thickness became barriers to the diffusion of hydrogen gas, inhibiting the crimping of porosity. The equivalent diameter of the maximum porosity circle in the slab cross-section was as large as 7.2 mm, and the area ratio of porosity was also as high as 0.88%. A large number of porosities remained even in the product thickness, and the number of defects detected by ultrasonic flaw detection test at the product thickness was 1.13 pieces / 100 m. 2 As a result, the internal quality evaluation was ×.

[0077] In Comparative Example 25, the addition amount of Al in LF was large, and Al was as high as 0.152 mass%. Aluminum inclusions were generated in the nickel melt and further became coarse alumina clusters. As a result, a large number of Hegel flaw defects occurred on the surface of the coil. Before the ultrasonic flaw detection test of the 1 mm thick nickel thin plate, which is the final internal quality evaluation, there were a large number of Hegel flaws on the surface and it became scrap treatment, so the internal quality could not be evaluated and was rated as ×.

[0078] In Comparative Example 26, P that should be added in LF was not added, and P was as low as 0.0003 mass%. When cutting the crop at the front and rear ends with a shurring machine before finish rolling in hot rolling, residues occurred and it became scrap treatment. The evaluation of the ultrasonic flaw detection test of the 1 mm thick nickel thin plate, which is the final internal quality evaluation, could not be performed and was rated as ×.

Industrial Applicability

[0079] The technology of the present invention can supply a nickel alloy plate with excellent internal quality that precisely controls trace components such as P, Mg, S, and H in the nickel alloy and reduces the amount of porosity in the cross-section of the nickel alloy slab cast by continuous casting.

Explanation of Signs

[0080] 1: Nickel alloy slab, 2: Internal quality inspection surface, 3: Final solidification position, 4: Shrinkage cavity (porosity), 5: Mg, P, S segregation part on the surface of the shrinkage cavity, 6: Ni molten metal with a small amount of S segregated, EF: Electric furnace, AOD: Argon Oxygen Decarburization, VOD: Vacuum Oxygen Decarburization, LF: Ladle Furnace, CC: Continuous casting

Claims

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

2. The nickel alloy with excellent internal quality according to Claim 1, characterized in that it satisfies at least one of the following relational expressions represented by Formula 1 and Formula 2 calculated from the chemical component (mass%) of H, P, S, and Mg in the nickel alloy. (20 × H) × (2 × P + 10 × S + 3 × Mg) × 10 ４ ≤ 15.0 …(Equation 1) (25 × S + 3 × Mg) ÷ H ≥ 28.0 … (Formula 2)

3. The nickel alloy with excellent internal quality according to Claim 2, characterized in that it satisfies both of the above Formula 1 and Formula 2 among the relational expressions.

4. A nickel alloy plate with excellent internal quality made of the nickel alloy according to any one of Claims 1 to 3, 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 thickness is all 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. A slab is manufactured, and then hot rolling or hot rolling and cold rolling are continuously carried out to obtain a nickel alloy plate with excellent internal quality.

5. The reduction ratio (= (thickness of slab - thickness of nickel alloy plate) / thickness of slab × 100) calculated from the thickness of the slab cast by a continuous casting machine and the thickness of the nickel alloy plate after hot rolling of the slab is 97.0% or more. The nickel alloy plate with excellent internal quality according to Claim 4.

6. 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, charging lime and fluorite dried to a water content of 0.20 mass% or less, and CaO-SiO ２ -Al ２ O ３ -MgO-F-based slag is prepared, further, Si and / or Al are added, deoxidation and desulfurization are performed, after adjusting the temperature and components while promoting inclusion floating 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. A method for producing a nickel alloy having excellent internal quality, characterized in that

7. A method for manufacturing a nickel alloy plate according to claim 4, wherein raw materials are melted in an electric furnace, then decarburized in the electric furnace and / or AOD and / or VOD, and lime and fluorite dried to 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, and further, Si and / or Al are charged to perform deoxidation and desulfurization. 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 excellent in internal quality, characterized by the above steps.

8. A method for manufacturing a nickel alloy plate according to claim 5, wherein raw materials are melted in an electric furnace, then decarburized in the electric furnace and / or AOD and / or VOD, and lime and fluorite dried to a moisture content of 0.20 mass% or less are added, and CaO-Si ２ -Al ２ O ３ -MgO-F-based slag is produced, further Si and / or Al are added, deoxidation and desulfurization are performed, and after adjusting the temperature and components while promoting inclusion floating by Ar stirring in LF, 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 carried out. A method for manufacturing a nickel alloy plate having excellent internal quality, characterized by this.

9. The reduction ratio (= (thickness of slab - thickness of nickel alloy plate after hot rolling) / thickness of slab × 100) calculated from the thickness of the slab cast by a continuous casting machine and the thickness of the nickel alloy plate after hot rolling the slab is 97.0% or more. A method for manufacturing a nickel alloy plate with excellent internal quality according to claim 7, characterized by this.

10. The reduction ratio (= (thickness of slab - thickness of nickel alloy plate after hot rolling) / thickness of slab × 100) calculated from the thickness of the slab cast by a continuous casting machine and the thickness of the nickel alloy plate after hot rolling the slab is 97.0% or more. A method for manufacturing a nickel alloy plate with excellent internal quality according to claim 8, characterized by this.

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