JP2008274347A - Method for refining nickel-based alloy and continuous casting method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce an alloy limited to iron content of a Ni-based alloy by using a large quantity of producing facility having 60 ton scale. <P>SOLUTION: In a process for melting the Ni-based alloy and refining by oxygen-blowing, this refining method is performed as the followings, that is, lime stone is charged into an oxygen blowing furnace and the total of the iron and the Cr content is lowered to ≤3 mass%, and the oxygen-blowing furnace is tilted and slag containing iron and Cr is removed, and deoxidation and desulfurization are performed by using Al and/or Si. And, when the refined molten Ni-based alloy is made to a slab by a continuous casting apparatus, the continuously casted slab is cut off with a torch, wherein this torch is provided with a nozzle for blowing propane and oxygen, 2-4 pieces of nozzles for blowing iron powder and Al powder as a combustion assistant and a powder tank for storing both powders and an ejector, and the Al powder quantity is 20-50 mass% of the total powder quantity and the ejector-shape is vertically directed downward to the powder tank, and the Ni-based alloy slab is cut off by blowing the propane and the oxygen with the torch. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nickel-based alloy refining method and a continuous casting method, and more particularly to a de-ironing technique and a subsequent deoxidation and desulfurization technique for an alloy that requires a low Fe content among nickel-based alloys. Furthermore, a technique is proposed that enables mass production by refining using an oxygen blowing furnace such as AOD (Argon Oxygen Decarburization) and manufacturing a molten alloy slab with a continuous casting machine.

  Nickel-based alloys such as Ni-Cu are excellent in corrosion resistance and have a wide variety of uses such as marine use and eyeglass frames. The production method usually involves melting the raw materials so as to achieve the target composition in a high-frequency induction furnace, obtaining a steel ingot by ordinary ingot making, further forging and hot rolling to produce an alloy plate Yes.

  However, in a high-frequency induction furnace, the maximum melting amount per charge is about 10 tons and batch processing, so that the resulting nickel-based alloy is not only expensive, but also takes time. Therefore, for example, development of a technology that enables mass production of refining a 60-ton scale molten alloy, further obtaining a slab with a continuous casting machine, and hot rolling to obtain an alloy sheet has been desired.

  In order to solve such a problem, a refining method of a nickel base alloy in an arc furnace is disclosed (for example, refer to Patent Document 1). However, in this method, although the iron is certainly removed and the components are satisfactory, the iron furnace is used for iron removal, deoxidation, and finishing. It must be shortened. Moreover, the amount of dissolution is also 20 tons, and it is hard to say that it is mass production. Moreover, the slab is not manufactured by continuous casting, and it is not an efficient production method.

  In order to cut the slab of the alloy after casting, a torch is used to blow and burn fuel gas and oxygen gas, and by blowing a combustion aid such as iron powder to burn a predetermined portion of the slab to perform fusing A technique (hereinafter, sometimes simply referred to as torch cutting or powder cutting) is known (see, for example, Patent Documents 2 and 3).

  However, when this powder cutting is applied to a nickel-based alloy, the cutting becomes difficult as the nickel content in the alloy increases. In this case, even if aluminum powder having a large amount of heat is used in combination with iron powder as a combustion aid, it takes 5 to 10 times as long as stainless steel (for example, SUS304), as will be described in Examples below. With the current equipment, since the cast slab is continuously supplied, cutting is not in time, and one charge must be cast once and then cut after the casting machine is stopped. Cutting was difficult. In particular, this problem occurs in the case of a vertical casting machine.

  The reason why cutting with a torch cannot be performed quickly is that a mixture of slag / molten metal (hereinafter sometimes simply referred to as “cutting noro”) generated by melting part of the slab by the hot air flow from the torch during cutting. If the ability to blow off is low, this cutting blade remains on the cut surface and interferes with cutting. In addition, the higher the nickel content of the slab, the more the cutting blade viscosity increased, making it more difficult to remove it.

  Therefore, when cutting is not performed simultaneously with the progress of casting, a certain amount is cast by limiting the weight of the molten steel so that all slabs can be accommodated in the casting machine, and carefully cutting over 40 to 50 minutes after completion of casting, or Some were cut by a lance with several people. Lance cutting was a heavy work and had a safety problem. In addition, the slab cut surface is inferior in smoothness and requires a recutting process.

JP 7-238330 A JP 59-199170 A Japanese Utility Model Publication No. 57-36368

  As described above, among the nickel-base alloys, an alloy having a particularly limited iron content is in a scale of 60 tons (not particularly limited, but a scale of 45 to 80 tons, preferably 50 to 80 tons). The purpose is to use mass production equipment and to produce by continuous casting. That is, it is only necessary to produce Ni-based alloys in parallel at an ironworks that produces stainless steel or Fe—Ni alloys, but the most serious problem is contamination with iron or Cr. The main raw materials such as Ni and Cu are melted in an electric furnace, and then, in an oxygen blowing furnace such as AOD, oxygen is efficiently blown to remove iron and chrome, thereby oxidizing and removing these elements. Thereafter, the slag containing oxides of iron and Cr is removed to discharge out of the system. Then, it aims at deoxidizing the molten steel which became an oxidation state with Al or Si, and adjusting a component.

  Also, as described above, Ni-based alloys are very difficult to cut by torch cutting, and can only be cast up to about 40 tons unless continuous cutting during casting is realized. Was impossible. Another object of the present invention is to enable continuous casting by realizing rapid cutting of a Ni-based alloy slab.

  That is, the refining method of the nickel-based alloy of the present invention was made as a result of intensive studies in view of the above circumstances, and can be tilted after melting the raw material in the electric furnace and melting the nickel-based alloy. In the process of refining in an oxygen blowing furnace, limestone is put into the oxygen blowing furnace and oxygen is blown to reduce the total content of iron and chromium to 3 mass% or less, and the oxygen blowing furnace is tilted. The present invention is characterized in that slag containing iron and chromium is removed and further deoxidized and desulfurized using at least one of aluminum and silicon.

  The nickel-base alloy continuous casting method of the present invention is manufactured by continuous casting when the refined molten nickel-base alloy is slabed by a continuous casting machine in the nickel-base alloy refining method of the present invention. The slab is cut by a torch, and the torch comprises a nozzle for blowing propane gas and oxygen gas, 2 to 4 nozzles for blowing iron powder and aluminum powder as combustion aids, iron powder and aluminum powder A powder tank and an ejector are provided, the amount of aluminum powder is 20-50 mass% of the total powder amount, the ejector shape is vertically downward with respect to the powder tank, and propane gas and oxygen gas are supplied by a torch. It is characterized by cutting the nickel base alloy slab by blowing.

  Conventionally, Ni-based alloys and Ni-Cu based alloys have been manufactured by melting at several tons in a high-frequency induction furnace or by ingot forming at 10 to 20 tons in an arc furnace. For example, since the ability of deironing and dechroming is improved as compared with the prior art, it is possible to divert an electric furnace in which components remain for use in casting other alloys such as stainless steel. Melting and casting are possible. Therefore, significant cost reduction can be realized. Furthermore, it is not necessary to remove iron and chromium from the electric furnace in advance, and parallel melting and refining is possible while producing stainless steel, so the delivery time is greatly shortened.

  In addition, according to the torch cut of the present invention, the ability to blow off the cutting blade generated when the powder is cut by the torch to the opposite side of the slab is improved, so that the cutting blade does not remain on the cutting surface and the alloy Cutting can be performed quickly while performing continuous casting. Furthermore, even if the nickel content is 35% by mass or more, which is difficult with conventional powder cutting, it is possible to cut the alloy during continuous casting. This makes it possible to cut slabs such as jet lances. Contributes to safety improvement.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
A. Manufacturing Process FIG. 1 is a schematic diagram showing a manufacturing process of a Ni-based alloy in the present invention. Reference symbol A denotes an electric furnace (EF), which melts raw materials such as scrap, nickel alloy, and copper alloy as a melting step.

  Subsequently, the melted raw material is transferred from the electric furnace A to the oxygen blowing furnace B as a refining process. The oxygen blowing furnace B of the present invention is not particularly limited, and may be any furnace provided with an oxygen blowing function and a tilting function for discharging slag, and AOD (Argon-oxygen decarburization) is optimal. However, it may be a converter.

  In an oxygen blowing furnace such as AOD, limestone is charged and oxygen is blown to oxidize iron and Cr in the molten alloy and transfer them to slag. Subsequently, the oxygen blowing furnace is tilted to remove slag, and Al and / or Si are added to perform deoxidation and desulfurization from the molten alloy.

  When the deoxidation and desulfurization of the molten alloy is completed, the molten alloy is put together with the slag into the casting pot of the casting machine for casting. The code | symbol C of FIG. 1 is a schematic diagram of a continuous casting machine (Continuous Casting Machine, CCM). The casting machine shown in FIG. 1 is a vertical casting machine in which a molten alloy is supplied from above and a slab is sent downward. Since many elements are added in high alloys, cracks tend to easily occur when bent when cooled and hardened. However, in a vertical type device, it is difficult to apply an unreasonable force and is suitable for high alloys. Used as However, the continuous casting machine is preferably a vertical type, but is not limited thereto.

  Finally, a molten alloy is cast by the CCM shown in FIG. 1 to produce a slab. In FIG. 1, reference numeral 10 denotes an pouring pan, and the molten steel 20 that has been subjected to the melting step and the refining step is put into the pouring pan 10. Subsequently, the molten steel 20 is supplied to the mold 12 through the tundish 11 provided on the downstream side of the pouring pan 10 and is put into the mold. The molten steel 20 poured into the mold is solidified by passing through a spray cooling zone 13 provided on the downstream side, and is drawn by the pinch roll 14 to obtain a slab 21 having a predetermined thickness. The slab 21 is subjected to the powder cutting of the present invention by the torch 15 at a predetermined position.

  In the vertical CCM, the length of the slab that can be accommodated in the machine is limited, and as a result, the time required for cutting the slab can be limited. In addition, since the cutting direction is perpendicular to the ground axis, it is disadvantageous compared to the curved CCM in that if the ability to blow off the cutting blade generated during cutting is low, the cutting blade remains on the cutting surface and obstructs cutting. I have an important point.

B. Examination of iron removal and Cr removal The present inventors have conducted extensive research in the laboratory on iron removal and Cr removal technology, which is a key point in the refining of Ni-base alloys. It was.

In a high-frequency induction furnace in which an MgO crucible was set, 10 kg of Ni-32 mass% Cu alloy was melted and about 4 mass% of iron was added. Thereafter, 1 kg of CaO—SiO ₂ -based slag (C / S = 3) was added, and after confirming that the slag was sufficiently melted, oxygen gas was blown to start the deironing experiment. The experiment was performed about 30 times in total, changing the amount of oxygen blowing. The result is shown in FIG. As can be seen from the figure, as the NiO concentration in the slag increases, the Fe distribution ratio between the slag metals increases and iron is removed.

A theoretical study of this deironation reaction is as follows.
The oxidation-reduction reaction that occurs between NiO in slag and Fe in the molten Ni alloy is expressed by the following formula (1).
(NiO) + Fe = (FeO) + Ni (l) (1)

  That is, the point is how to form NiO in the slag. In fact, since Ni is a noble metal compared to Fe and Cr, it is hardly oxidized originally. The equilibrium constant of the formula (1) can be expressed by the following formula (2).

Here, it should be noted that since the Ni concentration in the alloy is defined and constant by the steel type, the Fe distribution ratio (a _FeO / a _Fe ) when the activity coefficient is considered is as follows. It is a function of quantity only.

  Simply, it can be assumed that FeO and NiO in the slag and Fe in the molten metal are not so high in concentration and the activity follows Henry's law. Under these assumptions, the fact that when plotted by concentration, a linear approximation as shown in FIG. 2 proves that the deironation reaction follows the equation (1).

  Similarly, an experiment was also performed on Cr removal, and similar analysis results were obtained. That is, the removal of iron and Cr depends on how NiO is formed in the slag. Then, when this slag was removed, the molten Ni-Cu alloy was sampled and the oxygen concentration was measured, it was found that about 1000 to 7000 ppm was dissolved. It was also confirmed by experiment that oxygen can be effectively reduced by adding either or both of Al and Si in order to remove this oxygen. From the above experimental results, it became possible to set basic refining conditions.

C. Examination of Ni-base alloy slab cutting by torch cut In addition, Ni-base alloy shows extremely difficult cutting ability in torch cut cutting with continuous casting machine, so the equipment and torch cut conditions were also optimized from offline cutting experiments . Specifically, the amount of molten alloy that was completely cast in a continuous casting machine was cast by continuous casting, and various Ni-based alloy slabs manufactured by changing the Ni content were cut with a torch for use in experiments. Moreover, the nozzle for blowing propane gas and oxygen gas and the nozzle for blowing iron powder and aluminum powder as combustion aids, the amount of aluminum powder relative to the total amount of powder, and the shape of the ejector were examined.

  A schematic diagram of slab fusing by torch cut by the torch 15 is shown in FIG. As shown in FIG. 1, two torches 15 are provided, and these operate symmetrically. In FIG. 3, one of them is schematically described. In FIG. 3, the direction from the front surface to the back surface is the slab supply direction. That is, it is sectional drawing of the slab in the torch cut part at the time of seeing the downstream from the upstream of a continuous casting apparatus. The slab is cut while moving the torch from the right side toward the left side. Reference numeral 22 denotes an already cut part, reference numeral 23 denotes a combustion part, reference numeral 24 denotes a melting part (cutting nose), and reference numeral 25 denotes an uncut part.

  In this torch cut, fine iron powder or aluminum-containing iron powder is continuously mixed in oxygen gas and supplied. The material to be cut (hereinafter referred to as the base material) is heated to the ignition temperature by the oxidation heat generated by the combustion of the fine iron powder or aluminum-containing iron powder, and when high-purity oxygen is supplied thereto at a high speed, the base material Own combustion occurs. The reaction heat generated by the combustion of the powder and the base material in the combustion section 23 melts the metal and the oxide. Then, the melted portion (cutting nose) 24 is blown off to the opposite side of the slab by the airflow of oxygen, and the cutting groove (the already cut portion 22) is formed. When such a phenomenon occurs continuously, the base material is cut. That is, the properties desired for powder cutting are the following five items.

1) The combustion temperature of the base material is lower than its melting point in order to continuously advance the base material combustion reaction.
2) The oxide or slag has a lower melting point than the base material.
3) Good fluidity of oxide or slag and good peelability from the base material.
4) The amount of incombustible substances and impurities generated by reaction in the base material component is small.
5) The cutting oxygen stream is fast and the melt in the cutting reaction part can be sufficiently eliminated.

  As is clear from the Ellingham diagram, nickel is a precious metal compared to iron and is known to be difficult to burn. Therefore, the combustion of the base material itself in 1) is disadvantageous from the beginning. Furthermore, as for 2) to 5), we thought that the characteristics should be grasped, and investigated and studied cutting noro.

C-1. Observation of cutting blades NW2201 was used as a high nickel alloy, and stainless steel SUS304 was used as a comparative material, and cutting blades generated during torch cutting were investigated. The chemical composition of each base material is as shown in Table 1 below.

  As the combustion aid (powder) used at the time of cutting, only iron powder was used in SUS304. On the other hand, since cutting with NW2201 is difficult, the aluminum-containing iron powder having a larger calorific value was used, and it was collected when cutting over about 45 minutes. For these samples, (i) appearance observation, (ii) X-ray diffraction of oxide portion, (iii) microstructure observation by optical microscope and scanning electron microscope (SEM), and (iv) analysis of oxide by EDS. Carried out.

(I) Appearance Observation Results As shown in FIG. 4, the SUS304 slot is flowing thin, while the NW2201 slot is thickly squirting, so it is estimated that the fluidity was poor. In addition, SUS304 Noro has no luster at all, whereas NW2201 showed almost luster.

(Ii) Results of X-ray diffraction When these samples were ground with a vibration mill (40 seconds), most of the stainless steel 304 was metallic except that a very small amount was powdered. On the other hand, the NW2201 Noro powdered about 50% by weight. The results of X-ray diffraction performed on the powdered sample are shown in FIGS. Both powdered parts were mainly oxides, but the composition was found to be different. That is, as is apparent from FIGS. 5 and 6, SUS304 was an oxide of Fe ₃ O ₄ , Fe ₂ O ₃ and NiO, whereas NW2201 was an oxide consisting only of NiO.

(Iii) Microstructure observation and (iv) Measurement result by EDS FIG. 7 shows a cross-sectional microstructure of the cutting edge of SUS304. Many bubbles were observed in the cutting blade of SUS304, and most of the constituent materials were metals. A high melting point (2275 ° C.) oxide of Cr ₂ O ₃ is seen in the portion that looks like a spot in FIG. 7, but it is a very small amount. In addition, since the oxides of Fe ₃ O ₄ and NiO identified by the above-mentioned X-ray diffraction are not found inside Noro, it is considered that the oxide scale was generated on the surface of the cut Noro.

  On the other hand, the NW2201 slot shown in FIG. 8 has relatively few bubbles, and what appears to be a melt having a metallic luster appears to be folded several times, and NiO oxide is bitten in the gap. This NiO is considered to be an oxide generated during combustion of the base material. Further, when the portion having metallic luster was observed in more detail, it was found that a high melting point (1950 ° C.) oxide of NiO was distributed in a large amount in a dendrite shape. This is presumably that the molten Ni saturated with oxygen became supersaturated during solidification and crystallized as primary crystals.

  From the above results, the reason why the cutting performance is poor in the case of NW2201 can be inferred as follows. In addition to Ni being difficult to burn originally, NiO, which has a very high melting point compared to the melting point of the base material (about 1450 ° C.), is suspended in a large amount in the cutting blade. Furthermore, the apparent viscosity of this mixed melt increases as the temperature decreases. As a result, the mixture is not sufficiently blown away by the oxygen stream and covers the cut surface. Thus, when the mixture covers the surface of the base material, the reaction of oxygen to burn the base material is finally prevented and cutting is inhibited. In addition, since this mixed melt is not sufficiently eliminated, there is a possibility that it remains in the cutting groove and is recombined.

C-2. Oxygen concentration in molten Ni in equilibrium with solid NiO As mentioned above, dendritic NiO scattered in large amounts in the cutting nod of NW2201 is not an oxide generated in situ when the base material is burned by oxygen. It was thought that it was crystallized during solidification from molten Ni in which oxygen reached saturation. Therefore, a thermodynamic study was conducted on the solubility of oxygen in molten pure Ni. The following thermodynamic data was used for the calculation.
2Ni (l) + O ₂ (g) = 2NiO (s)
ΔG ⁰ = −49930 + 185.75T (J) (4)
Equation (4) is the standard free energy change when molten Ni burns.
1 / 2O ₂ (g) = O (in liq. Ni)
ΔG ⁰ = −79700 + 7.15T (J) (5)
Equation (5) is a change in free energy of reaction in which oxygen dissolves in molten Ni. The activity of oxygen in the molten Ni is based on an infinitely dilute solution with mass% as a unit, and the activity of NiO is based on a pure solid. Further, the equation (6) was used as the interaction coefficient between oxygen in molten Ni required for the activity coefficient of oxygen.
e ₀ ⁰ (in liq. Ni) = 0 (6)

By combining the equations (4) to (6), the oxygen concentration in equilibrium with pure solid NiO can be calculated. The calculation results are shown in FIG. The oxygen concentration of pure Ni at 1550 to 1650 ° C. was 4000 to 8000 ppm. This shows a value of about 10 to 20 times the oxygen concentration 300 to 400 ppm at which the Fe-18 mass% Cr molten steel equilibrates with pure solid Cr ₃ O _{4 in the} same temperature range. Furthermore, it can be seen from the Ni-O system phase diagram that there is an oxygen solubility of about 20% at a higher temperature of 2000 ° C. The above results confirm that a large amount of supersaturated oxygen crystallizes as NiO, which is the primary crystal, during solidification from molten Ni in which a large amount of oxygen is dissolved at a high temperature.

C-3. The results of investigating the cause of the time required to cut the slab of the facility improvement NW2201 are summarized below.
1) In addition to Ni being difficult to burn, molten Ni can dissolve a large amount of oxygen at a high temperature, so that a large amount of NiO crystallizes during solidification of the cutting blade.
2) The melting point of NiO is 1950 ° C., which is very high compared to the melting point of 1450 ° C. of the base material of NW2201. Therefore, the molten metal in which a large amount of NiO is suspended has poor fluidity.
3) The oxide produced by the combustion of the base material is also NiO, and when mixed with the molten metal, the fluidity of the cutting blade is further deteriorated despite the molten state.

The above 1) to 3) were compared with the above-described powder cutting mechanism, and the reason why a large amount of time was required for torch cutting of the high nickel alloy was considered as follows.
I. 2) The current cutting oxygen stream is not enough to eliminate the fluid whose fluidity has been extremely deteriorated for the reason of 3).
II. Due to the reason I, noro containing a large amount of high-melting-point oxide (NiO) cannot be eliminated and the cutting surface is covered, the reaction between oxygen and the base material is hindered, and cutting is inhibited.
III. It is rejoined by the melt cutting blade remaining in the cutting groove that cannot be scattered and eliminated by the cutting oxygen stream.

  To solve the above problems, the torch blowing pipe and dispenser were modified. Furthermore, after the installation of the equipment, the amount of Al contained in the cutting powder was optimized.

(I) Improvement of blowing pipe A schematic diagram of a newly introduced blowing pipe is shown in FIG. In FIG. 10, reference numeral 30 denotes a blow pipe main body, and a crater 31 for blowing oxygen gas and fuel gas into the slab is connected to the tip of the blow pipe 30. Further, the blow pipe 30 includes a blow pipe holder 32 and a nozzle holder. A powder nozzle 34 is connected via 33. The powder nozzle 34 is a nozzle for blowing iron powder or aluminum powder. The powder nozzle 34 is connected to a dispenser described later.

  Pipes 35 are connected to the rear of the blow pipe 30, and as shown in the sectional view shown in FIG. 10, for example, cutting oxygen is passed through the central pipe 36, and cooling water (outlet) is supplied to the pipes 37 and 38. ) And cooling water (entering), preheated oxygen can be passed through the pipe 39, preheated gas can be passed through the pipe 40, and the like.

  In the present invention, the amount of heat of cutting is increased by increasing the amount of cutting oxygen and the amount of cutting powder, and the powder nozzle 34 is twined (hereinafter referred to as a twin nozzle) to cut before the cutting blade covers the cutting surface. Went. As a result of this change, the twin nozzles have a higher gas flow rate than the single nozzle, and the cut-off resistance has been improved.

(Ii) Improvement of dispenser The present invention and a conventional dispenser are shown in FIG. In the conventional dispenser of FIG. 11A, an ejector 54 is connected to a tank 50 holding powder, a resistance plate 55 is provided in the tank 50, and a hose 52 connected to a torch (not shown) is further provided. It is connected. Moreover, the direction of the ejector 51 was horizontal (perpendicular to the pressurizing direction in the tank). The conventional dispenser is pressurized by the pressurized gas 53 and the transfer gas 54, and the powder supply amount is adjusted by controlling the pressure difference between them.

  On the other hand, in the conventional dispenser of FIG. 11B, the tank 50, the ejector 51, and the hose 52 are connected downward, that is, arranged in a straight line, and the rotor rotating motor is further interposed between the tank 50 and the ejector 51. 56 and a powder supply amount adjusting unit 57 are provided.

  In the conventional dispenser, the balance between the cutting powder and the cutting oxygen amount is poor, and the problem of incomplete combustion is solved. Therefore, in the dispenser of the present invention, the powder supply method is changed from the pressure difference control between the pressurization and the transfer gas to the rotor control. changed. This made it possible to finely adjust the amount of cutting powder. Furthermore, by changing the shape of the ejector from the conventional horizontal direction to the downward direction, it is possible to optimize various gas pressures and prevent clogging of the cutting powder. Furthermore, with the twin nozzles described above, the number of dispensers has been increased from 2 to 4 in order to stably supply the cutting powder.

C-4. The amount of Al contained in the cutting powder The amount of Al contained in the cutting powder was inadequate, and there was a possibility that combustion was insufficient. Therefore, another experiment was conducted to measure the influence of the ratio of the Al content to the cutting powder (total amount of Al powder and Fe powder) on the cutting time. In this experiment, a high nickel alloy slab having a predetermined size was manufactured, and the Al content was changed as shown in Table 2 below, and torch cutting was performed. The results are shown in the following Table 2 and the graph of FIG.

  From these measurement results, it can be seen that when the Al content is about 25%, the cutting time is shortened, but the Al content tends to be almost constant beyond that. From this experimental result, the Al content was set to 20 to 50%.

C-5. Cutting Time Improvement Effect Table 3 and FIG. 13 show the results of a series of improvement effects as a result of evaluation by cutting time. As the Ni content in the alloy increases, it is clear that the improvement effect appears greatly. In particular, an alloy containing Ni of 50% or more can greatly reduce the slab cutting time compared to the conventional case, and can be reduced to almost half when an alloy containing Ni of 60% or more is used. As a result, even with a high nickel alloy, torch cutting was possible during casting, and the weight limit of casting per time that had been provided so far could be removed. That is, it has become possible to continuously supply molten steel and continue casting without stopping the casting machine. The high nickel alloy referred to here is the evaluation No. shown in Table 3. An alloy of 2, 3, 4, 5, 6, and 7 and the balance other than Ni is one or more of Fe, Cr, Mo, and Cu as main elements, and in some cases, Si, Mn, and Nb , Ti, Al, W, Co, or two or more of them may be appropriately contained.

  As described above, the torch of the present invention includes a nozzle for blowing propane gas and oxygen gas, 2 to 4 nozzles for blowing iron powder and aluminum powder as combustion aids, and a powder for storing powder. When equipped with a tank and an ejector, the amount of aluminum powder is 20-50 mass% of the total powder amount, the ejector shape is vertically downward with respect to the powder tank, and a structure in which propane gas and oxygen gas are blown by this torch, It was found that cutting was completed in 50% of the time.

D. Summary As described above, the present invention has been realized as a result of intensive investigations from the refining conditions to the cutting of the slab, and can be summarized as follows.

  That is, according to the present invention, in the process of melting a raw material in an electric furnace, melting a nickel base alloy and refining in a tiltable oxygen blowing furnace, limestone is introduced into the oxygen blowing furnace and oxygen is blown. Refine the total content of iron and Cr to 3 mass% or less, tilt the oxygen blowing furnace to remove slag containing iron and chromium, and deoxidize using at least one of Al and Si And a nickel-based alloy refining method characterized by desulfurization.

Furthermore, it is effective to add 0.1 to 1 mass% of at least one of C, Si, and Al before performing oxygen blowing in the oxygen blowing furnace. Further, the slag when deoxidizing by blowing oxygen is composed of CaO, SiO ₂ , MgO, and further contains at least one of NiO, FeO, Cr ₂ O ₃ , and slag basicity (mass % CaO / mass% SiO ₂₎ is 2~5, NiO: 5~20%, FeO : 5~40%, Cr 2 O 3: 30% or less.

In addition, at the time of deoxidation and desulfurization, either one or both of Al or Si is set to 0.01 to 0.5 mass% in total, and either or both of limestone and fluorite are added, and CaO, Al ₂ O ₃ , It is composed of SiO ₂ , MgO and F, and the effect is higher when the total of NiO, FeO and Cr ₂ O ₃ is ₃ mass% or less.

  Furthermore, the Ni-based alloy contains 60 mass% or more of Ni, and is effective for an alloy composed of one or more of the balance, Cu, C, Si, Mn, Fe, and Co. It can be applied to an alloy composed of 5 mass% or less, Mn: 3 mass% or less, Fe: 3 mass% or less, Cu: 26 to 36 mass%, the balance being Ni and inevitable impurities.

  Further, in the present invention, when the molten Ni-based alloy refined by the above method is made into a slab with a continuous casting machine, the slab produced by continuous casting is cut with a torch, and the torch is made of propane gas. A nozzle for injecting oxygen gas, 2-4 nozzles for injecting iron powder and aluminum powder as combustion aids, a powder tank and ejector for storing powder, and the amount of aluminum powder is the total powder A continuous casting method is proposed in which the ejector shape is vertically downward with respect to the powder tank and the Ni-based alloy slab is cut by blowing propane gas and oxygen gas with this torch.

E. In order to clarify the contents of the invention more than the input elements and operations , the reasons why the input elements, numerical values, and operation methods are limited will be described.
First, in the process of melting raw materials in an electric furnace and melting a Ni-based alloy and then refining in an oxygen blowing furnace, limestone is introduced and oxygen is blown to make the total of iron and Cr 3 mass% or less To lower. At this time, if iron and Cr are higher than 3 mass%, the required characteristics of the product, particularly corrosion resistance and mechanical properties, are not satisfied, and thus, limited in this way. Preferably it is 2.5 mass% or less, More preferably, it is 2.0 mass% or less, More preferably, it is 1.5 mass% or less.

  Before performing oxygen blowing in the oxygen blowing furnace, at least one of C, Si, and Al is added unless the temperature of the molten Ni-based alloy is increased to 1600 ° C. due to the heat of oxidation caused by oxygen blowing. This is because the process such as deoxidation does not progress.

Slag formed by blowing oxygen is composed of CaO, SiO ₂ , MgO, and further includes one or more of NiO, FeO, Cr ₂ O ₃ , and slag basicity (mass% CaO / mass% SiO ₂₎ is 2~5, NiO: at the time of the 5% to 20%, sufficient de-iron, de-Cr reaction proceeds. A more preferable range of the NiO concentration is 6 to 18%, and further preferably 7 to 15 mass%. Here, CaO is added as limestone. SiO ₂ is obtained by oxidation of Si. Or you may add with silica sand. MgO is added in the form of erosion from the refractory of the oxygen blowing furnace.

Note that the slag after the oxygen吹精, for Fe and Cr is _{oxidized, FeO: 5~40%, Cr 2} O 3: comprise 30% or less.

  Next, the oxygen blowing furnace is tilted to remove the slag because iron and Cr are transferred to the slag as oxides and discharged out of the system.

  This is because either or both of Al and Si are effective as the deoxidizer, and the quality is not impaired. The amount is preferably 0.01 to 0.5 mass% in total of either or both of Al and Si. If it is less than 0.01 mass%, deoxidation does not proceed sufficiently. If it exceeds 0.5 mass%, MgO in the slag is reduced, and Mg is excessively mixed into the molten alloy, reducing hot workability and causing cracks during hot rolling. Therefore, it was specified in this range. Preferably, it is 0.015-0.3 mass%.

Further, limestone as a CaO source and either or both of fluorite as a fluorine source are added to the slag at the time of deoxidation to form a melt composed of CaO, Al ₂ O ₃ , SiO ₂ , MgO, and F. . Al ₂ O ₃ is formed when deoxidizing with Al and becomes a slag constituent material. SiO ₂ is formed when deoxidizing with Si and becomes a slag constituent material. In this slag, deoxidation does not proceed sufficiently unless the total of NiO, FeO, and Cr ₂ O ₃ is ₃ mass% or less. A preferred range is 2 mass% or less, more preferably 1 mass% or less, and still more preferably 0.5 mass%. The reason is that NiO, FeO, and Cr ₂ O ₃ easily react with Si and Al to reduce the deoxidation effect. In order to effectively reduce the total of NiO, FeO, and Cr ₂ O ₃ , it is desirable to add either 0.01 or 0.5 mass% of either Al or Si in total.

Subsequently, the target alloy system will be described.
The Ni-based alloy targeted by the present invention is an alloy containing 60 mass% or more of Ni and comprising the balance, Cu, C, Si, Mn, Fe, or Co. This is because the formula (1) does not occur unless Ni is contained in an amount of 60 mass% or more. The Ni-based alloy in which the present invention is most effective is an alloy composed of C: 0.5 mass% or less, Mn: 3 mass% or less, Fe: 3 mass% or less, Cu: 26 to 36 mass%, the balance being Ni and inevitable impurities That is, NW4400.

  The effect of the present invention will be clarified by showing an example with an actual machine. The analysis of chemical components of slag and metal was obtained with a fluorescent X-ray analyzer. The oxygen concentration was analyzed by an inert gas impulse melting infrared absorption method.

[Invention Example 1]
Prior to this charge, an electric furnace in which a steel type of Fe-36 mass% Ni alloy was melted was used to melt Ni and copper raw materials and Ni-Cu alloy scrap to obtain a Ni-33 mass% molten alloy having a capacity of 57 tons. Due to the influence of the metal component remaining in the previous charge, the initial Fe of the molten alloy of this charge was 4 mass% and Cr was 0.2 mass%. Thereafter, 0.1 mass% of C and 0.1 mass% of Si were added, and oxygen blowing was performed. Table 4 shows the slag composition after oxygen blowing. The total of Table 4 does not reach 100% because of analysis errors and other inevitable impurities such as TiO ₂ and Mo oxide. The oxygen concentration in the molten alloy was 5000 ppm.

  Iron in the molten Ni-33 mass% alloy after oxygen blowing was reduced to 1 mass% and Cr was reduced to 0.02 mass%. Thereafter, the slag in Table 1 was removed, limestone and fluorite were newly added, and deoxidation and desulfurization were further performed using Al and Si. Table 5 shows the slag composition at this time.

  Thereafter, the slab was obtained by casting with a vertical continuous casting machine (total length: 27.5 m). The torch that performs slab cutting was provided with a nozzle for blowing propane gas and oxygen gas and two nozzles for blowing iron powder and aluminum powder as combustion aids. Also, a powder tank for storing powder and an ejector were provided, the amount of aluminum powder was 25 mass% of the total powder amount, and the ejector shape was vertically downward with respect to the powder tank. As a result, continuous cutting was possible during casting. The chemical components of the finally produced slab are as shown in Table 6.

[Invention Example 2]
Prior to this charge, an electric furnace in which SUS304 stainless steel was melted was used to melt Ni and copper raw materials and Ni—Cu alloy scrap to obtain a Ni-31 mass% molten alloy having a capacity of 60 tons. Due to the influence of the metal components remaining in the previous charge, the initial Fe of the molten alloy of this charge was 4 mass% and Cr was 1 mass%. Thereafter, 0.3 mass% of C and 0.1 mass% of Al were added and oxygen blowing was performed. Table 7 shows the slag composition after oxygen blowing. The oxygen concentration in the molten alloy was 3000 ppm.

  Iron in the molten Ni-33 mass% alloy after oxygen blowing was reduced to 1.3 mass% and Cr was reduced to 0.04 mass%. Thereafter, the slag in Table 7 was removed, limestone and fluorite were newly added, and further deoxidized and desulfurized using Al and Si. The slag composition at this time is shown in Table 8.

  Thereafter, the slab was obtained by casting with a vertical continuous casting machine (total length: 27.5 m). The torch that performs slab cutting was provided with four nozzles for blowing propane gas and oxygen gas and for blowing iron powder and aluminum powder as combustion aids. Also, a powder tank for storing powder and an ejector were provided, the amount of aluminum powder was 30 mass% of the total powder amount, and the ejector shape was vertically downward with respect to the powder tank. As a result, continuous cutting was possible during casting. The chemical composition of the finally produced slab is as shown in Table 9.

  A conventional example will be shown below to clarify the effects of the present invention. Basically, it was impossible to remove iron and Cr by AOD, and the torch capacity of the continuous casting machine was insufficient.

[Conventional example 1]
In an electric furnace, Ni, a copper raw material, and Ni—Cu alloy scrap were melted to obtain a Ni-31 mass% molten alloy having a capacity of 40 tons. Since the timing of the electric furnace was immediately after the furnace repair, the initial Fe was 1.4 mass% and Cr was 0.10 mass%. Thereafter, deoxidation and desulfurization treatment was performed using Al and Si in the VOD. Finally, casting was performed by a vertical continuous casting machine (total length: 27.5 m). After casting, the torch was cut for 50 minutes and the slab was discharged out of the machine. The chemical components of the finally produced slab are as shown in Table 10.

[Conventional example 2]
In an electric furnace, Ni, a copper raw material, and Ni—Cu alloy scrap were melted to obtain a Ni-32 mass% molten alloy having a capacity of 21 tons. Since the electric furnace was at the timing after NW2201 (99.5% Ni alloy) was melted, the initial Fe was 0.5 mass% and Cr was 0.14 mass%. Thereafter, deoxidation and desulfurization treatment was performed using Al and Si in the VOD. Finally, a steel ingot was obtained by ordinary ingot making. The final chemical components are as shown in Table 11. Then, the steel ingot was taken out from the mold and the surface was ground. Subsequently, hot forging was performed and the surface was ground again.

上記２つの発明例、従来例から明らかな通り、化学成分は、Ｆｅ、Ｃｒを含めて、同等である。むしろ、発明例では酸素を吹精しているため、Ｃｒが低く、この観点からはより良いと言える。さらに、本発明例の場合、６０トン規模での造塊が可能であることと、なおかつ、造塊タイミングを選ばなくても良いために、納期対応が有利となった。ここで言う納期とは、オーダーインプット後、製品になり出荷されるまでの期間で定義している。

As is clear from the above-described two invention examples and conventional examples, the chemical components are the same including Fe and Cr. Rather, in the inventive example, oxygen is blown away, so Cr is low, which can be said to be better from this point of view. Furthermore, in the case of the present invention example, it is possible to ingotify on a scale of 60 tons, and it is not necessary to select the ingotgating timing. The delivery date referred to here is defined as the period from when an order is input until the product is shipped.

  Table 12 compares the delivery times for each ingot-making method in the case of an order volume of 80 tons. The product weight in the table is the weight of the final product (1.6 mm thin plate), and there are parts that do not become products due to cutting of the front and rear ends of the cold-rolled coil. Become. Obviously, it can be seen that the number of operations is small and the time until completion is shortened. In particular, in the case of Conventional Example 2, since it is not continuous casting, it must be forged, and it is clear that the delivery time is extremely long.

  Realizes large-scale and continuous production of Ni-base alloys and Ni-Cu alloys, contributing to significant cost reductions. In addition, it is possible to melt and refine Ni-base alloys and Ni-Cu alloys in parallel while producing other alloys of stainless steel, so the delivery time is greatly shortened. In addition, slab cutting work such as jet lances is no longer necessary, contributing to safety improvements.

It is a schematic diagram which shows the manufacturing process of the Ni base alloy in this invention. It is a graph which shows the relationship between the NiO density | concentration in slag, and the Fe distribution ratio between slag metals. It is a schematic diagram which shows the mechanism of the powder cutting | disconnection in this invention. It is a photograph which shows the external appearance of a cutting blade. It is a graph which shows the X-ray-diffraction result of the oxide of the cutting noro of NW2201. It is a graph which shows the X-ray-diffraction result of the oxide of the cutting | disconnection noro of SUS304. It is a cross-sectional photograph of the cutting blade of SUS304. It is a cross-sectional photograph of the cutting blade of NW2201. It is a graph which shows the relationship between the oxygen concentration and temperature in molten Ni which equilibrates with solid NiO. It is a schematic diagram which shows the blow pipe for torches in this invention. (A) is a conventional dispenser, (b) is a schematic cross-sectional view showing a dispenser of the present invention. It is a graph which shows the relationship between cutting time and Al content in powder. It is a graph which shows the relationship between cutting time and Ni content in a slab.

Explanation of symbols

A Electric furnace B Oxygen blowing furnace C Continuous casting machine 10 Pouring pan 11 Tundish 12 Mold 13 Spray cooling zone 14 Pinch roll 15 Torch 20 Molten steel 21 Slab 22 Existing cutting part 23 Combustion part 24 Melting part (cutting noro)
25 Uncut part 30 Blow pipe 31 Tinder 32 Blow pipe holder 33 Nozzle holder 34 Powder nozzle 35-40 Pipe 50 Tank 51 Ejector 52 Hose 53 Pressurized gas 54 Transfer gas 55 Resistance plate 56 Motor for rotor rotation 57 Powder supply amount adjustment part

Claims (8)

  In the process of melting the raw material in the electric furnace, melting the nickel base alloy, and refining in the tiltable oxygen blowing furnace, limestone is put into the oxygen blowing furnace and oxygen is blown into the iron and iron Decreasing the total Cr content to 3 mass% or less, tilting the oxygen blowing furnace to remove slag containing iron and chromium, and deoxidizing and desulfurizing using at least one of Al and Si A method for refining a nickel-base alloy characterized by   The nickel-based alloy refining method according to claim 1, wherein at least one of C, Si, and Al is added in an amount of 0.1 to 1 mass% before oxygen blowing in the oxygen blowing furnace. . The slag used to remove iron by blowing oxygen is composed of CaO, SiO ₂ , Al ₂ O ₃ , and MgO, and further includes at least one of NiO, FeO, and Cr ₂ O _3. Item 3. A method for refining a nickel-base alloy according to Item 1 or 2. Slag basicity (mass% CaO / mass% SiO ₂ ) of the slag is 2 to 5, NiO content is 5 to ₂₀ mass%, FeO content is 5 to 40 mass%, and Cr ₂ O ₃ content is 30 mass% or less. The method for refining a nickel-base alloy according to claim 3, wherein: At the time of the deoxidation and desulfurization, at least one of Al or Si is set to 0.01 to 0.5 mass% in total, and at least one of limestone and fluorite is added, and CaO, Al ₂ O ₃ , SiO ₂ , MgO, It consists F, NiO, FeO, refining method of nickel-based alloy according to claim 1, wherein the total content of _Cr 2 _{O 3} is less than 3 mass%.   6. The nickel-based alloy according to claim 1, wherein the nickel-based alloy contains 60 mass% or more of nickel, and the balance is an alloy composed of at least one of Cu, C, Si, Mn, Fe, and Co. Of refining nickel-base alloys.   The nickel-base alloy is characterized in that C is 0.5 mass% or less, Mn is 3 mass% or less, Fe is 3 mass% or less, Cu is 26 to 36 mass%, and the balance is nickel and inevitable impurities. The refining method of the nickel base alloy in any one of -6.   The refining method of the nickel base alloy according to any one of claims 1 to 7, wherein when the refined molten nickel base alloy is made into a slab by a continuous casting machine, the slab produced by continuous casting is used by a torch. The torch is cut into nozzles for blowing propane gas and oxygen gas, 2 to 4 nozzles for blowing iron powder and aluminum powder as combustion aids, and for storing the iron powder and aluminum powder. A powder tank and an ejector are provided, and the amount of the aluminum powder is 20 to 50 mass% of the total powder amount. The ejector shape is vertically downward with respect to the powder tank, and propane gas and oxygen gas are blown by the torch. A method for continuously casting a nickel-base alloy, comprising cutting the nickel-base alloy slab.

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