JP2009084631A - Electroslag remelting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform nitrogen removal without affecting the cleaning of ingots during electroslag remelting. <P>SOLUTION: When melting an ingot 3 by an electroslag remelting method, a sulfur compound 7a is added together with a deoxidizing material 6a under a nonoxidizing atmosphere to remove nitrogen. By this method, sulfur as a surface-active element can be positively utilized and nitrogen removal can be quickened and, even during a time until a droplet melted and separated from an electrode falls into a metal pool or even during a short reaction time between molten metal and slag in the metal pool, an excellent nitrogen removing effect can be obtained. Moreover, the sulfur contributed to the nitrogen removal is captured by the slag and does not move to the metal pool and hereby does not deteriorate the cleanliness of the ingot. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electroslag remelting method in which a predetermined material is used as an electrode to remelt and clean the material.

  In general, elements such as S, O, and N are known to deteriorate the corrosion resistance of metal materials, particularly the stress corrosion cracking sensitivity. In addition, in an alloy to which B is added, N is combined with B to become BN, which deteriorates mechanical properties. Therefore, it is said that the N content is preferably as low as possible. The ESR (electroslag remelting) process is superior in desulfurization capability due to the high basicity of the slag used, and O can be suppressed to a low level by dissolving with slag with a low oxygen potential, and oxide-based nonmetals Inclusions also have an excellent feature that most of the inclusions can be removed by allowing the metal to be dissolved to pass through the slag as droplets to be efficiently absorbed by the slag. For this reason, the ESR method is widely used in the production of high-grade tool steel and Ni-base superalloy that require high cleanliness. However, it has been said that it is almost impossible to perform denitrification during ESR. Therefore, when producing ESR electrodes, vacuum degassing is performed during ladle refining, or vacuum casting is used under vacuum. A method of producing a low nitrogen electrode by degassing or melting under reduced pressure by a vacuum induction melting furnace (VIM) is generally used. In addition, even if such a process is adopted, when the amount of nitrogen in the electrode is high, degassing is performed by remelting the ingot manufactured by ESR as an electrode in a vacuum arc melting furnace. .

On the other hand, as a method for performing denitrification in ESR, a method called Metal bearing Solution Refining (MSR) has been reported in Patent Document 1, Non-Patent Documents 1 and 2, and the like. This MSR method enables denitrification in ESR by using Ca—CaF ₂ slag instead of CaO—CaF ₂ slag generally used in ESR.
However, the MSR method has a problem that the Ca content in the ingot is increased by picking up Ca in the slag. The Ca content in the ingot produced by MSR depends on the Ca concentration in the CaF ₂ melt and the Ni and Si concentrations in the steel. For example, in the case of 18Cr-13Ni steel, the Ca concentration in the ingot is 0.1. 01 to 0.02% (see Non-Patent Document 3). Moreover, since Ca-CaF ₂ slag has high electrical conductivity, the power consumption rate is poor, and the manufacturing cost is higher than that of normal ESR.
Japanese Patent Laid-Open No. 51-59002 Transactions ISIJ vol. 16 (1976), pp. 623-627 Steelmaking Research No. 289 (1976), pp. 85-90 Journal of the Japan Institute of Metals, Vol. 15, No. 6, 1976, pp. 387-391

  As described above, in the conventional ESR method, denitrification due to slag is usually not observed because the slag nitride capacity is small, and the molten metal surface is covered with slag. However, denitrification during melting as in the vacuum arc melting method is impossible. The MSR method, which is the only report of denitrification in ESR, has the problem of an increase in Ca content in the ingot and a deterioration in power consumption during operation.

  The present invention has been made to solve the above-described problems of the prior art, and aims to make it possible to perform denitrification during electroslag remelting with almost no influence on the ingot. Yes.

  That is, among the electroslag remelting methods of the present invention, the first present invention adds a sulfur compound together with a deoxidizing material in a non-oxidizing atmosphere when melting an ingot by the electroslag remelting method. It is characterized by performing denitrification.

  The electroslag remelting method of the second aspect of the present invention is the method of the first aspect of the present invention, wherein the deoxidizing material is composed of one or more components of Ca, Al, Mg, La, Y, and REM. It is characterized by being.

  In the electroslag remelting method of the third aspect of the present invention, in the first or second aspect of the present invention, the sulfur oxide is composed of one or more of Fe-S, Mo-S, and Ni-S. It is characterized by.

  The electroslag remelting method of the fourth invention is characterized in that, in any of the first to third inventions, the non-oxidizing atmosphere is an inert gas atmosphere or a vacuum atmosphere. To do.

That is, according to the electroslag remelting method of the present invention, the deoxidizing material to be added is prevented from being oxidized by the atmosphere by performing the deoxidation with the deoxidizing agent in the non-oxidizing atmosphere. The amount of residual oxygen in the atmosphere is desirably 0.1% by volume or less.
The atmosphere can be obtained by an inert gas atmosphere such as argon or a vacuum atmosphere. As the inert gas, nitrogen is excluded because it interferes with denitrification.
In that case, a lid can be provided on the mold being melted to maintain the atmosphere in the mold, and a slag deoxidizing element can be added during melting, and a sulfur compound can be further added.

  The slag deoxidizing element has the effect of keeping the oxygen potential of the slag low and keeping the oxygen in the molten metal low. Moreover, denitrification is enabled by entering the slag in the form of a metal element. The sulfur compound has an effect of promoting denitrification by imparting sulfur, which is a surface active element, to the molten metal and slag. By combining these, denitrification during electroslag remelting can be performed quickly.

In addition, a known thing can be used as slag used for the electroslag remelting method of this invention. Ca-CaF ₂ slag is not preferable because it causes Ca uptake into the ingot as described above and power consumption at the time of operation deteriorates. However, there may be circumstances such as high denitrification. The use of Ca—CaF ₂ slag is not excluded as the present invention.

  In addition, as a deoxidation material used by this invention, what is comprised by the component of 1 or 2 or more of Ca, Al, Mg, La, Y, and REM can be illustrated. In the present invention, the type of the deoxidizing material is not limited to a specific type, and a known material having a deoxidizing action can be appropriately used. In addition, the quantity of a deoxidizer is not specifically limited, What is necessary is just to use a normal quantity.

  Moreover, the sulfur compound used with the said deoxidation material should just become a supply source of sulfur, and can use a material suitably, for example, 1 type or 2 types of Fe-S, Mo-S, Ni-S What consists of the above can be used. Sulfur in the sulfur compound serves to transfer the nitrogen of the molten metal to the slag during electroslag remelting as described above, and effectively reduces the nitrogen content in the molten metal. Sulfur that acts on denitrification is not taken into the ESR ingot, but is effectively transferred to slag by the action of the deoxidizing material, and the cleanliness of the ESR ingot is not impaired.

As other elements constituting the sulfur compound, elements that are the main components of the ESR ingot (Fe for steel, Ni for Ni-based alloy, etc.) can be used without considering adverse effects on the ingot. Further, other components can also be adopted as constituent elements of the sulfur compound even when migration into ESR is allowed. It is also possible to select a constituent element other than sulfur of the sulfur compound for the purpose of intentionally taking it into the ESR ingot.
In addition, although the quantity of a sulfur compound is not limited to a specific range, For example, it can be set as the range of 0.01-1.0 mass% with respect to ingot mass.

  The electroslag remelting method of the present invention is intended to effectively perform denitrification, and is suitable for high-grade tool steel and Ni-base superalloy that require high cleanliness. However, the present invention is not limited to a specific material to be re-dissolved, and various materials can be targeted.

  As described above, according to the present invention, when the ingot is melted by the electroslag remelting method, the sulfur compound is added together with the deoxidizing material in a non-oxidizing atmosphere to perform denitrification. Sulfur can be actively used to promote denitrification, and excellent denitrification effect is achieved even when droplets that have melted and separated from the electrode fall into the metal pool or even when the molten metal and slag in the metal pool have a short reaction time. In addition, sulfur that contributes to denitrification is not trapped by the slag and transferred to the metal pool, and the cleanliness of the ingot is not impaired.

An embodiment of the present invention will be described below with reference to FIG.
A water-cooled mold 4 for re-dissolving the electroslag of the consumable electrode 1 prepared to a predetermined component is prepared, and the water-cooled mold 4 is provided with a seal lid 8 that covers the upper portion except for the insertion portion of the electrode 1. Yes. The water-cooled mold 4 is connected to an inert gas introduction pipe 5 for adjusting the inside of the mold to an inert gas atmosphere. Further, a deoxidizer is added to introduce a deoxidizer 6 a into the water-cooled mold 4. The apparatus 6 and the sulfur compound addition apparatus 7 for supplying the sulfur compound 7a are provided.

In a normal electroslag remelting method, the consumable electrode 1 is melted by Joule heat generated by a current flowing through the slag 2 in the water-cooled mold 4, and the ingot 3 is sequentially solidified from below in the water-cooled mold 4.
In the present invention, the surface of the slag 2 is inactivated by introducing an inert gas from the inert gas introduction pipe 5 into the water-cooled mold 4 while preventing the atmosphere from entering the water-cooled mold 4 by the seal lid 8 at this time. Dissolve as a gas atmosphere. At that time, the dissolution is performed while simultaneously adding the deoxidizer 6a from the deoxidizer addition device 6 and the sulfur compound 7a from the sulfur compound adder 7. As a result, a deoxidation reaction and a denitrogenation reaction are caused in the slag 2, and a low nitrogen ingot 3 is produced.
In the above description, the deoxidizing material and the sulfur compound are added at the same time. However, the present invention does not specify the addition timing of these materials, but adds them at different times. May be.

Next, examples of the present invention will be described below in comparison with comparative examples.
An Fe—Ni alloy ingot having a mass of 8 tons of the components (remaining Fe and inevitable impurities) shown in Table 1 was selected as an electrode, and ESR was performed using this ingot as a consumable electrode and a mold having a diameter of 750 mm. The atmosphere was an argon atmosphere, and the residual oxygen amount at that time was <1.0% by volume. At this time, Ca was added as a deoxidizing material, and Fe-S was added as a sulfur compound. The addition amount of Ca was 1.0 wt% with respect to the ingot mass, and the addition amount of Fe-S was 0.5 wt% with respect to the ingot mass. The melted ingot was forged, samples were taken from each part (bottom (B) to top (T)), and component analysis (remainder Fe and inevitable impurities) was performed.

  Table 1 shows the amount of nitrogen in the electrode and the amount of nitrogen in the ingot before dissolution. The nitrogen contained in the electrode at 34 mass ppm was reduced to 12 to 20 mass ppm by the electroslag remelting method of the present invention. Moreover, although Fe-S was added during electroslag remelting, the added S was desulfurized and hardly remained in the ingot.

  Next, in the same manner as described above, an Fe-Ni alloy ingot having a mass of 8 ton of the components shown in Table 2 (remainder Fe and unavoidable impurities) was selected as an electrode, and electrolysis was performed in the same manner as above except that Fe-S was not added. Slag remelting was performed. The melted ingot was forged, samples were taken from each part (bottom (B) to top (T)), and component analysis (remainder Fe and inevitable impurities) was performed.

  Table 2 shows the amount of nitrogen in the electrode before dissolution and the amount of nitrogen in the ingot. In this example, the amount of nitrogen in the ingot was only slightly reduced compared to the electrode, and almost no denitrification effect was obtained. Therefore, it can be seen that N is hardly reduced only by the electroslag remelting method unless Fe-S is added.

  The present invention has been described based on the above-described embodiments and examples. However, the present invention is not limited to the contents of these embodiments and examples, and is naturally within the scope of the present invention. Appropriate changes can be made.

FIG. 1 is a sectional side view showing an ESR device according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Consumable electrode 2 Slag 3 Ingot 4 Water cooling mold 5 Gas inlet 6 Deoxidation material addition apparatus 6a Deoxidation material 7 Sulfur compound addition apparatus 7a Sulfur compound 8 Seal lid

Claims (4)

  An electroslag remelting method characterized by adding a sulfur compound together with a deoxidizing material in a non-oxidizing atmosphere to perform denitrification when melting an ingot by an electroslag remelting method.   2. The electroslag remelting method according to claim 1, wherein the deoxidizer is composed of one or more components of Ca, Al, Mg, La, Y, and REM.   The electroslag remelting method according to claim 1 or 2, wherein the sulfur oxide is composed of one or more of Fe-S, Mo-S, and Ni-S.   The electroslag remelting method according to claim 1, wherein the non-oxidizing atmosphere is an inert gas atmosphere or a vacuum atmosphere.

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