Ni-Cr-Fe-Mo alloy having excellent surface properties, and method for producing same

Abstract

The Ni-Cr-Fe-Mo alloy comprises, in mass%, 0.03% to 0.30% of C, 0.05% to 1.50% of Si, 0.05% to 2.00% of Mn, 0.05% or less of P, 0.005% or less of S, 18.0% to 28.0% of Cr, 6.0% to 15.0% of Mo, 1.0% or less of Cu, 0.01% to 0.50% of Al, 0.01% to 0.40% of Ti, 0.02% to 0.60% of Nb, 15.0% to 22.0% of Fe, 0.5% to 4.0% of Co, 0.10% to 2.00% of W, 0.0001% to 0.0100% of B, 0.005% to 0.100% of N, 0.0001% to 0.0060% of O, 0.0001% to 0.0300% of Mg, 0.0001% to 0.0080% of Ca, and the balance being Ni and unavoidable

Description

Technical Field

[0001] The present invention relates to a Ni-Cr-Fe-Mo alloy having excellent surface properties and a method for manufacturing the same, and more particularly, to a Ni-Cr-Fe-Mo alloy having excellent surface properties and a method for manufacturing the same, in which non-metallic inclusions in a melt are controlled to a harmless composition by controlling the slag composition and Si, Al, Mg, Ca, and O in the melt, and further the number of inclusions on the surface is reduced. The present invention relates to a Ni-Cr-Fe-Mo alloy having high creep properties, which can be used for a combustion tower component for a gas turbine through which a high-temperature gas of more than 1000 °C flows and can withstand a harsh environment. Background Art

[0002] A burner for a gas turbine is a component that functions to burn fuel to generate a high-temperature and high-pressure combustion gas for turbine drive and guide the combustion gas to the turbine inlet. Generally, the temperature of the combustion gas used in a gas turbine is 1100 °C to 1300 °C, and at this time, the temperature of the burner is about 550 °C to 650 °C. However, in recent years, in order to improve power generation efficiency, the temperature of the combustion gas has been increasing year by year, and products with a temperature exceeding 1500 °C have also been developed. It is considered that a gas turbine with a combustion gas temperature of about 1600 °C can be realized in the future, and accordingly, it can be expected that the temperature of the burner will also reach about 1000 °C. Therefore, heretofore, for Ni-based alloys used as burner materials, Ni-based alloys that exhibit creep properties at higher temperatures have also been required to be developed.

[0003] Among Ni-based alloys having excellent high-temperature strength and corrosion resistance, in addition to Ni as the main component, Cr, Mo, Nb, and Ti are also contained, and these metals are extremely expensive compared to iron. Therefore, it is very important to improve the yield rate and suppress the manufacturing cost. Here, if surface defects such as linear flaws are generated on the surface of a Ni-Cr-Fe-Mo alloy, they need to be removed by grinding or cutting, and the yield rate is greatly reduced. Therefore, a Ni-Cr-Fe-Mo alloy having excellent surface properties is required.

[0004] In Patent Document 1, a technique for a Ni-based alloy material having excellent strength, workability, and creep properties at room temperature by precipitating carbides and nitrides through heat treatment is disclosed. However, carbides or nitrides are not the cause of surface flaws in products, and the invention of Patent Document 1 cannot address the problem of surface properties caused by oxide-based non-metallic inclusions generated in the refining process targeted by the present invention, and the problem of surface defects caused by oxide-based non-metallic inclusions still exists.

[0005] In Patent Document 2, the following technology is disclosed: In the production method of a high-Ni alloy for high temperatures containing Al and Ti and a high-Ni alloy, by making the mass ratio of Ca / Al in oxide-based inclusions in the range of 1.0 to 1.5, the composition of the oxide-based inclusions is controlled to CaO-Al with a low melting point. 2 O 3 system, clogging of the submerged nozzle of the continuous casting machine is prevented, thereby preventing surface defects of the product.

[0006] However, Patent Document 2 targets high-Ni alloys with Mo of 5% or less. In contrast, the present application is an invention related to a Ni-Cr-Fe-Mo alloy containing 6.0 to 15.0% of Mo. Mo is a component that greatly increases the activity of Si as a deoxidizing material. Even if trace components such as Ca, Mg, Al, Si, and O are the same, the composition of the oxide-based non-metallic inclusions is very different, and different technologies are required for controlling the inclusion composition of alloys with different Mo concentrations. In addition, Patent Document 2 controls the inclusion composition by adding a Ca alloy to the molten steel. Ca is a stronger deoxidizing material than Al, Si, Ti, etc., and has the ability to change the composition of the already formed inclusions to CaO-Al 2 O 3 system, but at the same time generates a large amount of inclusions. That is, if a strong deoxidizing material such as Ca is added at the end of refining, the cleanliness deteriorates and the surface quality of the product deteriorates. That is, the technology disclosed in Patent Document 2 cannot be said to be a technology that sufficiently improves the surface properties of the Ni-Cr-Fe-Mo alloy of the present invention.

[0007] In Patent Document 3, the following technology is disclosed: In a high-Ni alloy, the composition of non-metallic inclusions in the alloy is controlled to form low-melting-point inclusions with good tensile-truncation properties during hot rolling or cold rolling, thereby reducing surface defects. However, the high-Ni alloy in Patent Document 3 targets alloys containing 0.5% or less or 3 to 10% of Cr, which is different from the Ni-Cr-Fe-Mo alloy of the present invention containing 18.0 to 28.0% of Cr. The Cr content has a great influence on the control of the inclusion composition. Even if trace components such as Ca, Mg, Al, Si, and O are the same, the composition of the oxide-based non-metallic inclusions is very different. That is, the method for controlling the composition of non-metallic inclusions described in Patent Document 3 cannot be said to be a technology that sufficiently improves the surface properties of the Ni-Cr-Fe-Mo alloy of the present invention.

[0008] In Patent Document 4, it is reported that by controlling the inclusions in the stainless steel sheet to harmless MgO, CaO-Al 2 O 3-Technique for reducing surface defects using MgO-based oxides. In the Ni-Cr-Fe-Mo alloy of the present invention, Nb contained in an amount of 0.02 to 0.60% has an oxidation ability comparable to that of Si and Mn. However, the stainless steel sheet described in Patent Document 4 does not contain Nb. In addition, the stainless steel sheet of Patent Document 4 also does not contain Ti contained in the Ni-Cr-Fe-Mo alloy of the present invention in an amount of 0.01 to 0.40%. Similar to Nb, Ti is also a component that has a great influence on the composition of non-metallic inclusions, and the technique disclosed in Patent Document 4 cannot improve the surface properties of the Ni-Cr-Fe-Mo alloy of the present invention.

[0009] In Patent Document 5, a technique for adding Nb to an Fe-Ni-Cr alloy with a high yield was reported. However, the Mo content of the target Fe-Ni-Cr alloy is 1 to 5%, and as described above, the present application is an invention related to a Ni-Cr-Fe-Mo alloy with Mo of 6.0 to 15.0%. Mo is a component that greatly increases the activity of Si as a deoxidizing material. Even if trace components such as Ca, Mg, Al, Si, and O are the same, the composition of oxide-based non-metallic inclusions is very different, and different techniques are required for controlling the inclusion composition of alloys with different Mo concentrations. In addition, Patent Document 6 does not contain Ti. Ti is a component that has a great influence on the composition of non-metallic inclusions, which is very different from the control of non-metallic inclusions of the Ni-Cr-Fe-Mo alloy of the present application containing Ti: 0.01 to 0.40%. That is, the technique of Patent Document 5 cannot be used for the surface defects of the Fe-Ni-Cr alloy targeted by the present application.

[0010] In Patent Document 6, the following technique was disclosed: by controlling the non-metallic inclusions of a Ni-Cr-Mo-Nb alloy to separate MgO and a composite oxynitride of MgO and (Ti, Nb)N to suppress large clusters, in the products of thin sheets, good quality without surface defects was obtained. The target Ni-Cr-Mo-Nb alloy of Patent Document 6 is a technique for a Ni-Cr-Mo-Nb alloy containing 2.5 to 5% of Nb, which is very different from the Ni-Cr-Fe-Mo alloy of the present patent containing Nb: 0.02 to 0.60%. Nb is a component that has a great influence on the composition of non-metallic inclusions, which is very different from the control of necessary non-metallic inclusions. That is, the technique of Patent Document 6 cannot be used for the surface defects of the Fe-Ni-Cr alloy targeted by the present patent.

[0011] Prior art documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-185352,

[0014] Patent Document 2: Japanese Patent Application Laid-Open No. 2021-70838

[0015] Patent Document 3: Japanese Patent Application Laid-Open No. 11-315354

[0016] Patent Document 4: Japanese Patent Application Laid-Open No. 2019-35124

[0017] Patent Document 5: Japanese Patent Application Laid-Open No. 2014-105341

[0018] Patent Document 6: Japanese Patent Application Laid-Open No. 2017-159449. Summary of the Invention

[0019] Problems to be Solved by the Invention

[0020] In view of the above problems, an object of the invention of the present application is to control the composition of non-metallic inclusions that affect the surface properties and provide a Ni-Cr-Fe-Mo alloy having excellent surface properties. In addition, a method for manufacturing a Ni-Cr-Fe-Mo alloy for achieving the above object is also provided.

[0021] Means for Solving the Problems

[0022] The inventors repeatedly conducted in-depth research and investigation to solve the above problems, and by using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS) to analyze in detail the surface defects of a Ni-Cr-Fe-Mo alloy and a plate that had surface defects, it was found that the cause of the surface defects was non-metallic inclusions of MgO-CaO-TiO 2 oxide system. Figure 1 , Figure 2 shows the mechanism of generating such surface defects in continuous casting. In Figure 1 , reference numeral 1 is a ladle that holds the melt 2. The melt 2 moves to the tundish 3 and is injected into the mold 5 through the submerged nozzle 4. The melt 2 in the mold 5 is drawn downward and solidifies to form a solidified shell 6, and at the same time is cooled in the spray cooling zone 7, and a slab is obtained on the downstream side. In this process, as Figure 2As shown, the non-metallic inclusions 8a contained in the melt 2 flow, and part of them adhere to the inner wall of the submerged nozzle 4 to form a block like 8b. Such non-metallic inclusions adhere to the inner wall of the submerged nozzle used for casting from the tundish to the mold in the continuous casting machine and are easily enlarged. The inclusions that fall off, such as 8c, flow into the mold 5 and are captured by the solidified shell 6 and easily become the starting point of surface defects, thereby becoming the starting point of surface defects of the Ni-Cr-Fe-Mo alloy plate. It should be noted that although the tundish and the submerged nozzle are not used in ordinary block making (ingot casting), since the same refractory flow path for introducing the melt into the mold is used, there is a problem of non-metallic inclusions adhering to the inner wall of the flow path, which is the same as continuous casting.

[0023] The inventors further conducted an in-depth study on the relationship between the composition of inclusions and metal components in Ni-Cr-Fe-Mo alloys. Specifically, in the manufacturing process of Ni-Cr-Fe-Mo alloys, metal samples of Ni-Cr-Fe-Mo alloys were collected from the tundish of the continuous casting machine, and 20 inclusions larger than 5 μm were randomly selected from the samples, and the inclusion composition was measured using SEM / EDS. In addition, the immersion nozzle used to supply the melt from the tundish to the mold of the continuous casting machine was collected, and the inclusion composition was determined by SEM / EDS. Figure 2 The attachments on the inner wall of the nozzle shown in the figure were analyzed by SEM / EDS. Based on the above, the relationship between the composition of inclusions, metal composition and the attachments on the inner wall of the submerged nozzle was studied in depth.

[0024] The results show that if the non-metallic inclusions contain MgO, CaO, MgO-CaO oxides, MgO-CaO-NbO-TiO 2 One or more of the oxides of MgO-CaO-NbO-TiO 2 The oxide contains 0.1 to 5.0% NbO and 20% or less TiO by mass%. 2 , then non-metallic inclusions are difficult to adhere to and accumulate on the inner wall of the immersion nozzle, that is, it is difficult to enlarge and become the cause of surface defects.

[0025] In addition, it is also clarified that MgO, CaO, and MgO-CaO series oxide inclusions are fine non-metallic inclusions that will not adhere to the inner wall of the submerged nozzle of the continuous casting machine tundish, will not affect the surface quality of the Ni-Cr-Fe-Mo series alloy plate invented in the present application, and should be controlled to MgO, CaO, and MgO-CaO series oxide inclusions, which are one of the preferred non-metallic inclusion compositions.

[0026] In order to control such non-metallic inclusions, refining is required to control trace components such as Si, Al, Ca, Mg, O, etc. and the slag composition within an appropriate range. In addition, it has been found that the composition of the melt when adding Nb and Ti is important.

[0027] Therefore, the Ni-Cr-Fe-Mo alloy of the present invention is completed based on the above insights. It is a Ni-Cr-Fe-Mo alloy composed of, by mass%, C: 0.03 to 0.30%, Si: 0.05 to 1.50%, Mn: 0.05 to 2.00%, P: 0.05% or less, S: 0.005% or less, Cr: 18.0 to 28.0%, Mo: 6.0 to 15.0%, Cu: 1.0% or less, Al: 0.01 to 0.50%, Ti: 0.01 to 0.40%, Nb: 0.02 to 0.60%, Fe: 15.0 to 22.0%, Co: 0.5 to 4.0%, W: 0.10 to 2.00%, B: 0.0001 to 0.0100%, N: 0.005 to 0.100%, O: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0300%, Ca: 0.0001 to 0.0080%, with the balance being Ni and unavoidable impurities. It is characterized in that the non-metallic inclusions contain one or more of MgO, CaO, MgO-CaO-based oxides, and MgO-CaO-NbO-TiO 2 -based oxides, and in the case of containing MgO-CaO-NbO-TiO 2 -based oxides, the MgO-CaO-NbO-TiO 2 -based oxides contain 0.1 to 5.0% of NbO and 20% or less of TiO 2 .

[0028] In addition, the number ratio of the MgO-CaO-NbO-TiO 2 -based oxides in the non-metallic inclusions is preferably 50% or less.

[0029] Furthermore, the present invention also provides a manufacturing method. That is, a manufacturing method of a Ni-Cr-Fe-Mo alloy with excellent surface properties, characterized in that raw materials are melted in an electric furnace, and then, after decarburization by AOD and / or VOD, lime and fluorite are added. Then, one or two of ferrosilicon alloy and pure silicon and Al are added as primary deoxidizers. Nb is added at the moment when the O concentration reaches 0.0070 to 0.0120%. Then, a CaO-SiO composed of CaO: 50 to 70%, SiO 2 : 1 to 8%, Al 2 O 3 : 10 to 30%, MgO: 5 to 15%, F: 2 to 8% is used.2 -MgO-Al 2 O 3 -F-based slag, add one or two of ferrosilicon alloy and pure silicon and Al for Cr reduction, secondary deoxidation, and desulfurization, then add Ti when the O concentration reaches below 0.0060%, and produce slabs or ingots through continuous casting machine or ordinary briquetting. In the case of ingots, perform hot forging, and then perform hot rolling or hot rolling and cold rolling. Description of the Drawings

[0030] Figure 1 Schematic cross-sectional view of a continuous casting machine in casting.

[0031] Figure 2 Schematic cross-sectional view of an immersion nozzle.

[0032] Figure 3 Schematic diagram of non-metallic inclusions.

[0033] Figure 4 Schematic diagram of non-metallic inclusions with low melting point.

[0034] Figure 5 Schematic diagram of non-metallic inclusions with high melting point.

[0035] Figure 6 Schematic diagram of non-metallic inclusions with high melting point. Detailed Description of the Invention

[0036] First, the reasons for limiting the chemical composition of the Ni-Cr-Fe-Mo alloy of the present invention are shown. It should be noted that in the following description, "%" refers to "mass%".

[0037] (C: 0.03 - 0.30%)

[0038] C forms M6C-type carbides. In addition, at high temperatures, new M6C-type carbides and M23C-type carbides are formed during use, which are elements that strengthen the grain boundaries and the interior of the grains, thereby improving the creep properties. To obtain this effect, at least 0.03% needs to be added. However, if more than 0.30% is added, coarse undissolved carbides will be generated and remain, deteriorating the workability and creep properties. Therefore, C is set in the range of 0.03 - 0.30%. It is preferably set in the range of 0.04 - 0.20%, and more preferably 0.05 - 0.10%.

[0039] (Si: 0.05 - 1.50%)

[0040] ​​​​​​Si is an element effective in improving oxidation resistance and is also effective in deoxidation. Therefore, it is an important element in the present invention. To control the oxygen concentration within the range of 0.0001 to 0.0060%, 0.05% of Si is required. In addition, it also has the effect of reducing CaO - SiO 2 -MgO - Al 2 O 3 -F - based slag, where CaO and MgO respectively adjust Mg in the melt to 0.0001 to 0.0300% and Ca to 0.0001 to 0.0080%. Therefore, it has the effect of controlling the composition of non - metallic inclusions. From this perspective, 0.05% of Si is also required. On the other hand, if the Si content exceeds 1.50%, CaO and MgO in the slag will be overly reduced, resulting in the supply of Mg and Ca to the melt with Mg exceeding 0.0300% and Ca also exceeding 0.0080%. If the alloy contains excessive amounts of Mg and Ca, the hot workability will decrease, and cracks will occur during hot rolling, leading to surface defects. Therefore, the Si content is specified to be 0.05 to 1.50%. Preferably, it is 0.10 to 1.00%. More preferably, it is 0.20 to 0.60%.

[0041] (Mn: 0.05 - 2.00%)

[0042] Mn is an austenite phase stabilizing element and also contributes to deoxidation. Therefore, it is necessary to add more than 0.05%. However, if a large amount is added, the oxidation resistance will be impaired. Therefore, the upper limit is 2.00%. Preferably, it is 0.10 to 1.50%. More preferably, it is 0.30 to 1.00%.

[0043] (P: 0.05% or less)

[0044] P is a harmful element that segregates at grain boundaries and causes cracks during hot working. Therefore, it is desirable to minimize it, and it is limited to 0.05% or less. Preferably, it is 0.04% or less. More preferably, it is 0.03% or less.

[0045] (S: 0.005% or less)

[0046] S is a harmful element that segregates at grain boundaries to form low - melting - point compounds, thus hindering hot workability. Therefore, it is desirable to minimize it, and it is limited to 0.005% or less. To achieve this, the lower limit of the Al content is set to 0.01%, and deoxidation is carried out to control the O concentration within the range of 0.0001 to 0.0060% to desulfurize. Preferably, it is 0.003% or less. More preferably, it is 0.001% or less.

[0047] (Cr: 18.0 - 28.0%)

[0048] Cr is one of the main elements of the Ni-Cr-Fe-Mo alloy of the present invention. The Cr component forms a good protective film, thereby improving the oxidation resistance of the alloy. In addition, M23C6 type carbides are formed during use at high temperatures, which has the effect of increasing the strength of the grain boundaries. It is an important element. However, if the Cr content is less than 18.0%, sufficient oxidation resistance cannot be obtained. On the contrary, if the content exceeds 28.0%, σ phase is formed, resulting in embrittlement. For the above reasons, the Cr content is specified to be 18.0 to 28.0%. Preferably, it is 19.0 to 26.0%. More preferably, it is 20.0 to 24.0%.

[0049] (Mo: 6.0 to 15.0%)

[0050] Mo is one of the main elements constituting the Ni-based alloy material of the present invention. It has the effect of dissolving in the matrix phase to improve the creep characteristics. In addition, it forms M6C type carbides with C to strengthen. Furthermore, M6C type carbides are formed and precipitated in the grains during use at high temperatures, which has the effect of improving the creep characteristics. If its content is less than 6.0%, sufficient creep characteristics cannot be obtained. On the other hand, if the Mo content exceeds 15.0%, the oxidation resistance deteriorates. Therefore, the range of the Mo content is specified to be 6.0 to 15.0%. Preferably, it is 7.0 to 12.5%. More preferably, it is 8.0 to 10.0%.

[0051] In addition, Mo has the effect of increasing the activity coefficient of Si, which is the main deoxidizing component, and enhancing the deoxidizing ability. Therefore, in order to control the inclusion composition, it is necessary to consider the Mo component range of the present application and study the addition amount and addition timing of Al and Si as deoxidizing materials.

[0052] (Cu: 1.0% or less)

[0053] Cu is an element contained due to waste materials as raw materials. If the content exceeds 1.0%, the oxidation resistance decreases. Therefore, the content of Cu is set to 1.0% or less. Preferably, it is 0.5% or less. More preferably, it is 0.3% or less.

[0054] (Al: 0.01 to 0.50%)

[0055] Al is an element that is very effective for deoxidation and is a particularly important element in the present invention. Al can control the oxygen concentration in the range of 0.0001 to 0.0060%, and at the same time reduce CaO-SiO 2 -MgO-Al 2 O 3 -F series slag of MgO and CaO, respectively supply Mg of more than 0.0001% and Ca of more than 0.0001% to the melt, and have the effect of controlling non-metallic inclusions to a harmless composition. These effects are obtained through the following reactions.

[0056] 3(MgO) + 2 Al = 3 Mg +(Al 2 O 3 )…(1)

[0057] 3(CaO) + 2 Al = 3 Ca +(Al 2 O 3 )…(2)

[0058] The components in the slag are shown in parentheses, and the components in the melt are underlined.

[0059] If the Al concentration is lower than 0.01%, deoxidation cannot be sufficiently carried out, and the oxygen concentration will increase to more than 0.0060%. In addition, since deoxidation is not carried out, desulfurization is hindered, and the S concentration will increase to more than 0.005%. On the other hand, if the Al concentration is higher than 0.50%, the Mg concentration will increase to more than 0.0300% through the reaction of the above formula (1), and the Ca concentration will also increase to more than 0.0080% through the reaction of the above formula (2). Therefore, the range of the Al content is specified as 0.01 - 0.50%. Preferably 0.03 - 0.40%. More preferably 0.05 - 0.30%.

[0060] (Ti: 0.01 - 0.40%)

[0061] Ti forms TiN nitride that remains even after annealing, inhibits the growth of grains during annealing, and the grains become fine, thereby improving the strength at room temperature. In addition, during use at high temperatures, extremely fine TiN nitride precipitates in the grains, and M6C-type carbide precipitates uniformly and finely with it as the nucleus, so it has the effect of improving creep characteristics. To improve strength and creep characteristics, Ti of 0.01% or more is required. However, if it is added in excess to more than 0.40%, in addition to the increase in the thermal expansion coefficient, the welding crack sensitivity will also increase. Therefore, the Ti content is specified as 0.01 - 0.40%. Preferably 0.02 - 0.30%. More preferably 0.03 - 0.20%.

[0062] (Nb: 0.02 - 0.60%)

[0063] Nb is an important element in the invention of this application. It forms NbN nitride that remains even after annealing, inhibits the growth of grains during annealing, makes the grains finer, and thus improves the strength at room temperature. In addition, during use at high temperatures, extremely fine NbN nitride precipitates within the grains, and M6C-type carbides are uniformly and finely formed with it as the core, so it has the effect of improving creep properties. To improve strength and creep properties, it needs to be 0.02% or more. However, if added in excess to exceed 0.60%, in addition to the increase in the coefficient of thermal expansion, the welding crack sensitivity will also increase. Therefore, the Nb content is specified to be 0.02 - 0.60%. Preferably, it is 0.05 - 0.50%. More preferably, it is 0.10 - 0.30%.

[0064] (Fe: 15.0 - 22.0%)

[0065] Fe is one of the main elements contained due to the waste used as raw materials. If its content exceeds 22.0%, the content of Ni will relatively decrease, resulting in a reduction in oxidation resistance. On the other hand, if it is reduced to less than 15.0%, the content of Ni will relatively increase, which will not only increase the raw material cost but also reduce the hot workability. Therefore, the Fe content is set to 15.0 - 22.0%. Preferably, it is 16.0 - 21.0%. More preferably, it is 17.0 - 20.0%.

[0066] (Co: 0.5 - 4.0%)

[0067] Co is an element that improves creep properties through solid solution strengthening. However, Co is an expensive element. In addition, if it exceeds 4.0%, the above effect will saturate, and an effect commensurate with the addition amount cannot be obtained. Therefore, the Co content is specified to be 0.5 - 4.0%. Preferably, it is 0.6 - 3.0%. More preferably, it is 0.7 - 2.0%.

[0068] (W: 0.10 - 2.00%)

[0069] W is an element that improves creep properties through solid solution strengthening. In addition, it forms M6C-type carbides with C to strengthen. Moreover, even during use at high temperatures, M6C-type carbides are formed and precipitate within the grains, having the effect of improving creep properties. However, W is an expensive element. In addition, if it exceeds 2.00%, the above effect will saturate, and an effect commensurate with the addition amount cannot be obtained. Therefore, the W content is set to 0.10 - 2.00%. Preferably, it is 0.18 - 1.80%. More preferably, it is 0.20 - 1.50%.

[0070] (B: 0.0001 - 0.0100%)

[0071] B is an element that improves creep characteristics by enhancing the strength of grain boundaries. However, if the addition of B exceeds 0.0100%, low-melting-point compounds will precipitate, reducing hot workability. Therefore, the content of B is set to 0.0001 - 0.0100%. Preferably, it is 0.0005 - 0.0080%. More preferably, it is 0.0010 - 0.0050%.

[0072] (N: 0.005 - 0.100%)

[0073] N has the effect of dissolving in the matrix phase to increase strength at room temperature and high temperature, and is considered a useful element that should be actively added. Moreover, it forms fine MN-type nitrides with Ti and Nb, inhibits the growth of grains during annealing, makes the grains fine, and thus leads to an increase in strength at room temperature. In addition, during use at high temperature, extremely fine MN-type nitrides precipitate in the grains, and M6C-type carbides precipitate uniformly and finely with these nitrides as nuclei, having the effect of improving creep characteristics. Such effects become apparent when the addition of N is 0.005% or more. However, if the addition of N exceeds 0.100%, the workability at room temperature will deteriorate due to solidification of the matrix phase or coarsening of the nitrides. Therefore, in the present invention, the content of N is set to 0.005 - 0.100%. Preferably, it is 0.010 - 0.080%, and more preferably, it is 0.015 - 0.060%.

[0074] In addition, N also affects the characteristics of non-metallic inclusions generated during the refining process, so it is a component that should be precisely controlled. In the control of N, N is added by blowing nitrogen gas into the melt in AOD or VOD. In cases where it is necessary to reduce N, Ar gas is blown into AOD or VOD or LF to reduce the N concentration, thereby precisely controlling the N content of the melt.

[0075] (O: 0.0001 - 0.0060%)

[0076] The oxygen concentration is very important in the present invention because it is closely related to inclusions. If the O content in the alloy exceeds 0.0060%, the number of inclusions will increase, leading to the occurrence of surface defects and at the same time hindering desulfurization and increasing the S concentration. However, if it is less than 0.0001%, the ability of Al to reduce CaO and MgO in the slag will be excessively increased, causing the Mg concentration to exceed the upper limit of 0.0300% and the Ca concentration to exceed the upper limit of 0.0080% respectively. Therefore, the O content is specified as 0.0001 - 0.0060%. Preferably, it is 0.0003 - 0.0050%. More preferably, it is 0.0005 - 0.0040%.

[0077] (Mg: 0.0001 - 0.0300%)

[0078] Mg is an effective element for controlling the composition of non-metallic inclusions in the melt to MgO and MgO-CaO-based oxides that have no adverse effect on the surface properties. If the content is less than 0.0001%, this effect cannot be achieved. Conversely, if the Mg content exceeds 0.0300%, the hot workability decreases, and thus cracks are likely to occur in the hot rolling process, resulting in surface defects in the final product. Therefore, the Mg content is specified to be 0.0001 to 0.0300%. Preferably, it is 0.0005 to 0.0200%. More preferably, it is 0.0010 to 0.0100%.

[0079] To effectively add Mg to the melt, it is preferable to utilize the reaction represented by formula (1). To control Mg within the above range, it is only necessary to control the slag composition to CaO: 50 to 70%, SiO 2 : 1 to 8%, Al 2 O 3 : 10 to 30%, MgO: 5 to 15%, F: 2 to 8%.

[0080] (Ca: 0.0001 to 0.0080%)

[0081] Ca is an effective element for controlling the composition of non-metallic inclusions in the melt to CaO and MgO-CaO-based oxides that do not form clusters and have no adverse effect on the surface quality. If the content is less than 0.0001%, this effect cannot be achieved. Conversely, if the Ca content exceeds 0.0080%, the hot workability decreases, and thus cracks are likely to occur in the hot rolling process, resulting in surface defects in the final product. Therefore, the Ca content is specified to be 0.0001 to 0.0080%. Preferably, it is 0.0002 to 0.0050%. More preferably, it is 0.0003 to 0.0030%.

[0082] To effectively supply Ca to the melt, it is preferable to utilize the reaction represented by formula (2). To control Ca within the above range, it is only necessary to control the slag composition to CaO: 50 to 70%, SiO 2 : 1 to 8%, Al 2 O 3 : 10 to 30%, MgO: 5 to 15%, F: 2 to 8%.

[0083] (Ni: balance)

[0084] The target alloy of the present invention contains the components described above, and the balance is Ni.

[0085] (Non-metallic inclusions)

[0086] In the invention of the present application, the following is taken as a preferred solution: the non-metallic inclusions include one or more of MgO, CaO, MgO-CaO-based oxides, and MgO-CaO-NbO-TiO 2 -based oxides, and the MgO-CaO-NbO-TiO 2 -based oxides contain 0.1 to 5.0% of NbO and 20% or less of TiO by mass%. 2 .

[0087] Furthermore, the number ratio of the MgO-CaO-NbO-TiO 2 -based oxides is preferably 50% or less.

[0088] The basis for limiting the composition and number ratio of the non-metallic inclusions is shown below.

[0089] (including one or more of MgO, CaO, MgO-CaO-based oxides, and MgO-CaO-NbO-TiO 2 -based oxides)

[0090] In the Ni-Cr-Fe-Mo-based alloy related to the invention of the present application, according to the contents of Si, Al, Mg, Ca, and O in the Ni-Cr-Fe-Mo-based alloy and the addition amounts and addition times of Nb and Ti, it contains one or more of MgO, CaO, MgO-CaO-based oxides, and MgO-CaO-NbO-TiO 2 -based oxides.

[0091] MgO, CaO, and MgO-CaO-based oxides are high-melting-point solid non-metallic inclusions, so they will not adhere to the inner wall of the submerged nozzle of the tundish of the continuous casting machine. They are fine non-metallic inclusions and will not affect the surface quality of the Ni-Cr-Fe-Mo-based alloy plate of the present application. MgO, CaO, and MgO-CaO-based oxide inclusions are preferred non-metallic inclusion compositions that should be controlled. In addition, for CaO and MgO-CaO-based oxide inclusions, during the solidification process of the Ni-Cr-Fe-Mo-based alloy using a continuous casting machine, a part of CaO reacts with S in the melt to form CaS. S segregates at the grain boundaries during the solidification process of the Ni-Cr-Fe-Mo-based alloy, deteriorating the hot workability and causing surface cracks and edge cracks. CaO and MgO-CaO-based oxide inclusions have the effect of keeping the surface quality clean by fixing S in the melt that deteriorates the hot workability with CaS.

[0092] In addition, the CaO inclusions present on the surface become Ca(OH) through a hydration reaction in a humid environment 2And it falls off, forming small pits, resulting in deterioration of corrosion resistance. However, the Ni-Cr-Fe-Mo alloy targeted in this application is used for combustion tower components for gas turbines through which high-temperature gases above 1000 °C flow, and there is no problem of deterioration of corrosion resistance in a humid environment caused by CaO inclusions.

[0093] (MgO-CaO-NbO-TiO 2 The system oxide contains 0.1 to 5.0% of NbO and 20% or less of TiO by mass%. 2 )

[0094] MgO-CaO-NbO-TiO 2 The system oxide of MgO-CaO-NbO-TiO becomes a liquid-phase MgO-CaO-TiO around inclusions of MgO, CaO, and MgO-CaO system oxides at the refining temperature of 1600 °C of the Ni-Cr-Fe-Mo alloy, as Figure 3 shown, in the form of a liquid-phase MgO-CaO-TiO system oxide. If a liquid-phase MgO-CaO-TiO system oxide is formed around inclusions of MgO, CaO, and MgO-CaO system oxides, the liquid-phase inclusions act like an adhesive, and in addition, the solid-phase MgO, CaO, and MgO-CaO system oxides act as aggregates, promoting the adhesion of non-metallic inclusions to the refractories on the inner wall of the submerged nozzle, as 2 shown. After the non-metallic inclusions coarsen and fall off, they are transported into the mold together with the melt and are captured by the solidification shell, which can thus cause surface defects. 2 Therefore, the inventors repeatedly conducted a large number of investigations on the deposits on the inner wall of the submerged nozzle and the non-metallic inclusions inside the surface defects of the Ni-Cr-Fe-Mo alloy and the plate, and found that by making the MgO-CaO-TiO Figure 2 system oxide contain 0.1 to 5.0% of NbO by mass%, the adhesion to the inner wall of the submerged nozzle can be prevented, and the deterioration of the surface properties can be prevented. The effect of NbO will be described.

[0095] As 2 shown, NbO in the MgO-CaO-TiO system oxide exists in the liquid phase part, and NbO has the effect of lowering the melting point of the MgO-CaO-TiO system oxide in the liquid phase part. That is, the adhesive-like effect of the liquid-phase MgO-CaO-TiO system oxide is reduced by NbO, and it has the effect of preventing the MgO-CaO-TiO

[0096] As Figure 4 shown, MgO-CaO-TiO 2 In the system oxide, NbO exists in the liquid phase part, and NbO has the effect of lowering the melting point of the MgO-CaO-TiO system oxide in the liquid phase part. That is, the adhesive-like effect of the liquid-phase MgO-CaO-TiO system oxide is reduced by NbO, and it has the effect of preventing the MgO-CaO-TiO 2 system oxide from having an adhesive-like effect, and has the effect of preventing the MgO-CaO-TiO 2 system oxide from adhering to the inner wall of the submerged nozzle and preventing the reduction of surface properties. 2Effect of the series of oxides on the adhesion to the inner wall of the immersion nozzle. However, MgO-CaO-NbO-TiO containing more than 5.0% of NbO by mass% 2 In the series of oxides, through the reaction shown in formula (3), part of NbO becomes NbN and is included in the non-metallic inclusions.

[0097] [NbO] + N = O + [NbN]…(3)

[0098] [] The components in the brackets show the components of the non-metallic inclusions, and the underlines show the components in the melt.

[0099] NbN is a nitride with a melting point of 2573 °C. As Figure 5 shown, around the MgO, CaO, and MgO-CaO series oxide inclusions, a high-melting-point liquid-phase MgO-CaO-TiO 2 series oxide + NbO (-NbN) is regenerated. The high-melting-point liquid-phase inclusions act as an adhesive again, promoting the adhesion of non-metallic inclusions to the inner wall of the immersion nozzle. The non-metallic inclusions adhere and accumulate on the inner wall, and after coarsening, they fall off, resulting in the deterioration of cleanliness. For the above reasons, MgO-CaO-NbO-TiO 2 series oxide preferably contains 0.1 - 5.0% of NbO by mass%.

[0100] However, MgO-CaO-NbO-TiO containing more than 20% of TiO 2 by mass% 2 In the series of oxides, through the reaction shown in formula (4), part of TiO 2 becomes TiN and is included in the non-metallic inclusions.

[0101] [TiO 2 + N = 2O + [TiN]…(4)

[0102] [] The components in the brackets show the components in the metal inclusions, and the underlines show the components in the melt.

[0103] TiN is a nitride with a melting point of 2950 °C. As Figure 6 shown, around the MgO, CaO, and MgO-CaO series oxide inclusions, a high-melting-point liquid-phase MgO-CaO-NbO-TiO 2 (-TiN) series oxide is formed. In MgO-CaO-NbO-TiO containing more than 20% of TiO 2 by mass% 2In the case of the oxide system, even if it contains 0.1 to 5.0% of NbO by mass%, there is no effect of lowering the melting point of liquid inclusions, resulting in deterioration of cleanliness. For the above reasons, in the MgO-CaO-NbO-TiO 2 oxide system, it contains 0.1 to 5.0% of NbO by mass%, and TiO 2 is specified to be 20% or less.

[0104] Even in the MgO-CaO-NbO-TiO 2 oxide system, if it contains SiO 2 : 2% or less, Al 2 O 3 : 2% or less, it will not change the effects of the above NbO and TiO 2 .

[0105] In order to make the MgO-CaO-NbO-TiO 2 oxide system contain 0.1 to 5.0% of NbO, it is important to add Nb at the right time during melt refining. Add one or two of ferrosilicon alloy, pure silicon and Al as primary deoxidation, and add Nb when the O concentration reaches 0.0070 to 0.0120%, whereby the NbO concentration in non-metallic inclusions can be precisely controlled.

[0106] In addition, in order to make TiO 2 in the MgO-CaO-NbO-TiO 2 oxide system be 20% or less, it is important to add Ti at the right time during melt refining. Add Nb after primary deoxidation, and then use a CaO-SiO 2 : 1 to 8%, Al 2 O 3 : 10 to 30%, MgO: 5 to 15%, F: 2 to 8% composed of CaO-SiO 2 -MgO-Al 2 O 3 -F slag system, add one or two of ferrosilicon alloy and pure silicon and Al for Cr reduction, secondary deoxidation and desulfurization, and then add Ti when the O concentration reaches 0.0060% or less, which is important to control the TiO 2 concentration in non-metallic inclusions to 20% or less.

[0107] In addition, in the control of N content, add N by blowing nitrogen into the melt in AOD or VOD, and in the case of needing to reduce N, blow Ar gas through AOD or VOD or LF to reduce the N concentration, whereby the N content of the melt can be precisely controlled.

[0108] In this application, for Figures 3 to 6The composition of non-metallic inclusions composed of oxides of two or more phases as shown represents the concentration (mass %) of each component of the non-metallic inclusions in terms of the overall average composition.

[0109] (MgO - CaO - NbO - TiO 2 The number ratio of the oxides in the system is 50% or less)

[0110] As described above, MgO - CaO - NbO - TiO 2 The oxides in the system are one of the non-metallic inclusions that adhere to the inner wall of the immersion nozzle, fall off after coarsening, and thus cause deterioration of cleanliness. However, if the number ratio of the MgO - CaO - NbO - TiO 2 oxides in the system is 50% or less, the adhesion tendency is mild, and it is judged that the number of surface defects generated is suppressed. Therefore, the number ratio of the MgO - CaO - NbO - TiO 2 oxides in the system is specified to be 50% or less.

[0111] (Manufacturing method)

[0112] In the present invention, a manufacturing method of a Ni - Cr - Fe - Mo alloy is also proposed. First, melt the raw materials in an electric furnace to melt a Ni - Cr - Fe - Mo melt with a specified composition. Then, after decarburization using AOD (Argon Oxygen Decarburization) or using VOD (Vacuum Oxygen Decarburization) after AOD, add lime and fluorite, add one or two of ferrosilicon alloy and pure silicon and Al as primary deoxidation, add Nb when the O concentration reaches 0.0070 - 0.0120%, and then use a CaO - SiO 2 : 1 - 8%, Al 2 O 3 : 10 - 30%, MgO: 5 - 15%, F: 2 - 8% - composed CaO - SiO 2 - MgO - Al 2 O 3 - F - based slag, add one or two of ferrosilicon alloy and pure silicon and Al for Cr reduction, secondary deoxidation, and desulfurization, then add Ti when the O concentration reaches 0.0060% or less, and then tap the steel into the ladle, adjust the temperature and composition through LF (Ladle Furnace), and manufacture slabs or ingots using a continuous casting machine or ordinary ingot casting. Subject the ingot to hot forging to manufacture slabs. Thus, the non-metallic inclusions include MgO, CaO, MgO - CaO - based oxides, MgO - CaO - NbO - TiO 2One or more of the following oxides, MgO - CaO - NbO - TiO 2 The oxide system contains 0.1 to 5.0% of NbO and TiO by mass%. 2 When it is 20% or less, a Ni - Cr - Fe - Mo alloy with excellent surface properties can be obtained. This method is to grind the surface of the manufactured slab, perform hot rolling after heating or cold rolling after hot rolling, perform annealing and pickling to remove the scale on the surface, and finally manufacture the plate.

[0113] In the manufacturing method of the Ni - Cr - Fe - Mo alloy according to the present invention, as described above, the composition of the slag has characteristics. Hereinafter, the basis for the slag composition specified in the present invention will be described.

[0114] (CaO: 50 - 70%)

[0115] The CaO concentration and SiO in the slag 2 The concentration is an element for effectively deoxidizing and desulfurizing and controlling inclusions. If the CaO concentration exceeds 70%, the activity of CaO in the slag increases, and the reaction of formula (2) proceeds excessively. Thus, if the reduced Ca concentration in the melt increases to exceed 0.0080%, the hot workability decreases, and thus cracks are likely to occur in the hot rolling process, bringing surface defects to the final product. Therefore, the upper limit is specified as 70%. On the other hand, if the CaO concentration is lower than 50%, deoxidation and desulfurization cannot be carried out, and the S concentration and O concentration in the present invention cannot be controlled within the specified range. Therefore, the lower limit is specified as 50%. It is preferably 53 - 67%. More preferably 55 - 65%.

[0116] (SiO 2 : 1 - 8%)

[0117] SiO in the slag 2 is an element necessary to ensure the appropriate fluidity of the slag, so it needs to be at least 1%. However, if it increases to exceed 8%, the Al concentration, Mg concentration, and Ca concentration in the melt decrease to below the specified range, so the upper limit is specified as 8%. It is preferably 2 - 7%. More preferably 3 - 6%.

[0118] (Al 2 O 3 : 10 - 30%)

[0119] If the Al 2 O 3 in the slag is too high, exceeding 30%, sufficient deoxidation cannot be carried out, and the O concentration cannot be controlled within the specified range. As non - metallic inclusions, the number ratio of MgO - CaO - NbO - TiO generated exceeds 50%. 2is an oxide. On the other hand, if the Al in the slag 2 O 3 is less than 10%, the fluidity of the slag cannot be ensured, desulfurization cannot be carried out, and the S concentration will exceed the established range. It is preferably 12 - 28%. More preferably, it is 15 - 25%.

[0120] (MgO: 5 - 15%)

[0121] MgO in the slag is an important element for controlling the Mg concentration in the melt within the concentration range described in the claims, and at the same time is an important element for controlling the non-metallic inclusions to the preferred composition of the present invention. Therefore, MgO in the slag needs to be at least 5% or more. On the other hand, if the MgO concentration exceeds 15%, the reaction of formula (1) will proceed excessively, the Mg concentration in the melt will increase, and the hot workability will decrease, thus bringing surface defects to the final product. Therefore, the upper limit of the MgO concentration is specified as 15%. MgO in the slag becomes the specified range by being dissolved into the slag from the dolomite brick or magnesia-chrome brick used during AOD refining or VOD refining. Or, in order to control it within the specified range, one or both of the waste bricks of dolomite brick and magnesia-chrome brick can also be added. It is preferably 7 - 14%. More preferably, it is 9 - 13%.

[0122] (F: 2 - 8%)

[0123] F is contained in the fluorite added during slag refining and has the function of finely adjusting the melting state of the slag and needs to be added at least 2% or more. If the F concentration is less than 2%, the slag will not melt and the fluidity will decrease. On the other hand, if the F concentration rises above 8%, the fluidity of the slag will increase significantly, and thus the melting loss of the brick will become significant. Therefore, it is specified as 2 - 8%.

[0124] Examples

[0125] Examples are shown below to further clarify the effects of the present invention. However, the present invention is not limited to the following examples. Using an electric furnace with a capacity of 60 tons, nickel-iron alloy, pure nickel, ferrochrome alloy, iron filings, stainless steel filings, Fe-Ni-based alloy filings, Fe-Mo, etc. are melted as raw materials. Then, oxygen blowing refining for removing C, that is, oxidative refining, is carried out by AOD or after AOD by VOD, and limestone and fluorite are added to generate CaO-SiO 2 -Al 2 O 3-MgO-F based molten slag, one or two of FeSi alloy and pure Si and Al are added, Cr reduction is carried out, and then deoxidation is carried out. Then, Ar stirring is further carried out for desulfurization. After deoxidation, Nb and Ti are appropriately added. The furnace body in AOD and VOD is lined with magnesia-chrome bricks. Then, the molten steel is tapped into a ladle, and the temperature and composition are adjusted through LF (Ladle Furnace), and slabs or ingots are manufactured through continuous casting or ordinary ingot making. The ingots are hot forged to manufacture slabs.

[0126] The surface of the manufactured slab is ground, heated at 1200 °C, and hot rolled to manufacture hot rolled coils. Then, annealing and pickling are carried out. After removing the scale on the surface, cold rolling is carried out to a specified thickness to manufacture cold rolled coils. The chemical composition of the obtained Ni-Cr-Fe-Mo alloy system, the slag composition at the end of AOD or VOD refining, the manufacturing process, the non-metallic inclusion composition, the morphology of inclusions, and the quality evaluation are shown in Tables 1 and 2. In the table, the values in parentheses indicate outside the scope of the claims. It should be noted that there are examples in parentheses in the invention examples. Although they do not meet the scope of the dependent claims, they meet the scope of the independent claims.

[0127] [Table 1]

[0128]

[0129] [Table 2]

[0130]

[0131] (1) Chemical composition of the alloy and slag composition: Quantitative analysis is carried out using a fluorescent X-ray analyzer, and the oxygen concentration of the alloy is quantitatively analyzed by the inert gas pulse melting infrared absorption method.

[0132] (2) Non-metallic inclusion composition: The sample collected in the tundish immediately after the start of casting is mirror polished, and SEM / EDS is used to randomly measure 20 inclusions with a size of 5 μm or more.

[0133] (3) Number ratio of non-metallic inclusions: Based on the measurement results in (2) above, the number ratio of MgO-CaO-NbO-TiO 2 system oxides to the total number of non-metallic inclusions is evaluated.

[0134] (4) Surface defect evaluation: Visually observe the surface of the 1 mm thick Ni-Cr-Fe-Mo alloy plate after pickling and annealing to remove the surface scale, and count the number of surface defects caused by non-metallic inclusions and hot workability in a width of 1 m and a length of 10 m. When conducting quality evaluation, if within 10 m 2If the number of surface defects is less than 2, the evaluation is ◎; if it is 3 - 5, the evaluation is ○; if it is 6 - 10, the evaluation is △; if it is 11 or more, the evaluation is ×.

[0135] Examples 1 to 13 of the invention fall within the scope of the invention of the present application. Therefore, the surface defects in the plate are few, and good surface properties can be obtained.

[0136] In Invention Example 12, the Si concentration is 0.11% and the Al concentration is 0.03%. Although both are within the established range, they are relatively low, the deoxidation is slightly weak, and the O concentration is as high as 0.0045%. The supply of Mg and Ca from the slag is also small, with Mg as low as 0.0008% and Ca as low as 0.0002%. As a result, the number ratio of MgO - CaO - NbO - TiO 2 series oxides is as high as 65%, several coarse inclusions are generated, the number of surface defects is 7, and the judgment is △.

[0137] In Invention Example 13, the Si concentration is 0.09% and the Al concentration is 0.02%. Although both are within the established range, they are relatively low, the deoxidation is slightly weak, and the O concentration is as high as 0.0048%. The supply of Mg and Ca from the slag is also small, with Mg as low as 0.0007% and Ca as low as 0.0002%. As a result, non - metallic inclusions of only MgO - CaO - NbO - TiO 2 series oxides are formed, several coarse inclusions are generated, the number of surface defects is 9, and the judgment is △.

[0138] On the other hand, Comparative Examples 14 - 20 deviate from the scope of the invention of the present application. Therefore, many surface defects are generated and the surface properties deteriorate. Each example is described below.

[0139] In Comparative Example 14, the O concentration before adding Nb after primary deoxidation is as high as 0.0142%, and NbO in the MgO - CaO - NbO - TiO 2 series oxides is as high as 5.5%. In the liquid phase part of the MgO - CaO - NbO - TiO 2 series oxides, a part of NbN is also generated, becoming a high melting point. There is also a lot of adhesion on the submerged nozzle, and many exfoliated coarse non - metallic inclusions are generated, and many surface defects are also generated, with 14. The judgment is ×.

[0140] In Comparative Example 15, the O concentration before adding Ti after secondary deoxidation is as high as 0.0075%, and TiO in the MgO - CaO - NbO - TiO 2 series oxides 2 is as high as 21.1%. In the MgO - CaO - NbO - TiO 2A part of the liquid phase of the system oxide also forms a part of TiN, becoming a high melting point. There is also a lot of adhesion of the immersion nozzle, and many large non-metallic inclusions that fall off are generated, and many surface defects are also generated, which are 16. Judged as ×.

[0141] In Comparative Example 16, the O concentration before adding Nb after primary deoxidation was as low as 0.0060%, and the NbO in the MgO-CaO-NbO-TiO 2 system oxide was as high as 0.02%. When NbO is 0.02%, the MgO-CaO-NbO-TiO 2 system oxide has a small effect of lowering the melting point of the liquid phase and becomes a high melting point. There is also a lot of adhesion of the immersion nozzle, and many large non-metallic inclusions that fall off are generated, and many surface defects are also generated, which are 12. Judged as ×.

[0142] In Comparative Example 17, the O concentration before adding Nb after primary deoxidation was as low as 0.0058%, and the NbO in the MgO-CaO-NbO-TiO 2 system oxide was as low as 0.03%. In addition, Al was as low as 0.008%, the O concentration was high, Mg was as low as 0.0002%, and Ca was as low as 0.0001%, forming only non-metallic inclusions of MgO-CaO-NbO-TiO 2 system oxide. When NbO is 0.03%, the MgO-CaO-NbO-TiO 2 system oxide has a small effect of lowering the melting point of the liquid phase and becomes a high melting point. There is also a lot of adhesion of the immersion nozzle, and many large non-metallic inclusions that fall off are generated, and many surface defects are also generated, which are 18. Judged as ×.

[0143] In Comparative Example 18, Si was as high as 1.55%, Al was as high as 0.52%, the O concentration was as low as 0.00003%, the supply of Mg from the slag increased, and Mg was as high as 0.0310%. As a result, non-metallic inclusions formed only non-metallic inclusions of MgO and CaO, and there was no adhesion of the immersion nozzle. However, the Mg concentration was high and the hot workability decreased, so cracks were generated in the hot rolling process, and many surface defects were also generated, which are 20. Judged as ×.

[0144] In Comparative Example 19, Al was slightly higher, being 0.45%, the O concentration was as low as 0.00003%, and in addition, since a Ca alloy was added at the end of refining, the Ca concentration was as high as 0.0092%. As a result, non-metallic inclusions formed only non-metallic inclusions of CaO and MgO, and there was no adhesion of the immersion nozzle. However, the Ca concentration was high and the hot workability decreased, so cracks were generated in the hot rolling process. In addition, since a Ca alloy was added at the end of refining, the non-metallic inclusions in the melt could not float up and separate sufficiently and flowed into the mold, resulting in deterioration of cleanliness. Many surface defects were generated, which are 22. Judged as ×.

[0145] In Comparative Example 20, Si was as low as 0.04%, Al was as low as 0.003%, the O concentration was as low as 0.0078%, deoxidation and desulfurization were ineffective, the S concentration was as high as 0.0060%, the Mg concentration was 0.00003%, and the Ca concentration was 0.00003%. Non-metallic inclusions were not counted in Table 2, but MgO·Al 2 O 3 and Al 2 O 3 -SiO 2 -MnO-Cr 2 O 3 series oxides were detected. MgO·Al 2 O 3 tends to adhere to the inside of the immersion nozzle and is one of the non-metallic inclusions that should be avoided. Al 2 O 3 -SiO 2 -MnO-Cr 2 O 3 series oxides are low-grade oxides formed in a melt with insufficient deoxidation. Due to poor deoxidation, a large amount of non-metallic inclusions flow into the mold in the state of being formed in the melt, so they are one of the non-metallic inclusions that should be avoided. Many surface defects were generated, and the number was 27. It was judged as ×.

[0146] Industrial Applicability

[0147] By controlling the morphology of non-metallic inclusions, the technology of the present invention can provide a Ni-Cr-Fe-Mo series alloy with high creep characteristics, suitable for use as a combustion tower component for gas turbines, and excellent surface properties.

[0148] Symbol Explanation

[0149] 1: Ladle, 2: Melt, 3: Tundish, 4: Immersion nozzle, 5: Mold, 6: Solidified shell, 7: Spray cooling zone, 8a: Non-metallic inclusion, 8b: Attached non-metallic inclusion, 8c: Detached coarse non-metallic inclusion.

Claims

1. A Ni-Cr-Fe-Mo alloy, by mass percentage, consists of C: 0.03 - 0.30%, Si: 0.05 - 1.50%, Mn: 0.05 - 2.00%, P: below 0.05%, S: below 0.005%, Cr: 18.0 - 28.0%, Mo: 6.0 - 15.0%, Cu: below 1.0%, Al: 0.01 - 0.50%, Ti: 0.01 - 0.40%, Nb: 0.02 - 0.60%, Fe: 15.0 - 22.0%, Co: 0.5 - 4.0%, W: 0.10 - 2.00%, B: 0.0001 - 0.0100%, N: 0.005 - 0.100%, O: 0.0001 - 0.0060%, Mg: 0.0001 - 0.0300%, Ca: 0.0001 - 0.0080%, and the balance being Ni and inevitable impurities, forming a Ni-Cr-Fe-Mo alloy, characterized in that, The non-metallic inclusions include one or more of MgO, CaO, MgO-CaO-based oxides, and MgO-CaO-NbO-TiO 2 -based oxides, and in the case of including the MgO-CaO-NbO-TiO 2 -based oxides, the MgO-CaO-NbO-TiO 2 -based oxides contain 0.1 to 5.0% of NbO and 20% or less of TiO by mass 2 .

2. The Ni-Cr-Fe-Mo alloy according to claim 1, characterized in that, The number ratio of the MgO-CaO-NbO-TiO 2 system oxides is 50% or less with respect to all non-metallic inclusions in the Ni-Cr-Fe-Mo alloy system.

3. A manufacturing method of the Ni-Cr-Fe-Mo alloy, which is the manufacturing method of the Ni-Cr-Fe-Mo alloy according to claim 1 or 2, characterized in that, The raw materials are melted in an electric furnace. Then, after decarburization by AOD and / or VOD, lime and fluorite are added. Next, one or two of ferrosilicon alloy, pure silicon, and Al are added as primary deoxidizers, and Nb is added when the O concentration reaches 0.0070 - 0.0120%. Then, a CaO - SiO 2 : 1 - 8%, Al 2 O 3 : 10 - 30%, MgO: 5 - 15%, F: 2 - 8% composed CaO - SiO 2 -MgO - Al 2 O 3 -F - based slag is added, and one or two of ferrosilicon alloy and pure silicon and Al are added for Cr reduction, secondary deoxidation, and desulfurization. Then, Ti is added when the O concentration reaches 0.0060% or less, and a slab or ingot is produced by a continuous caster or ordinary ingot making. In the case of an ingot, hot forging is carried out, and then hot rolling or hot rolling and cold rolling are carried out.

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