Ingot manufacturing method

Abstract

To provide an ingot production method utilizing an ESR method which solves the problem that slag intrudes into an ingot by securing the heat value and fluidity of slag to obtain an ingot having high cleanliness.SOLUTION: Provided is an ingot production method of executing electroslag remelting using slag comprising, by mass%, 5.0%≤CaO≤25.0%, 2.0%≤SiO2≤10.0%, 10.0%≤Al2O3≤30.0%, and the balance CaF2 with inevitable impurities.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an ingot using an electroslag remelting method.

Background Art

[0002] When manufacturing ingots of alloy materials that require high cleanliness, such as super heat-resistant alloys and austenitic stainless steels, a vacuum arc melting method (VAR) or an electroslag remelting method (ESR) is used. In particular, in ESR, it has sometimes been difficult to grasp the reaction equilibrium between the slag and the alloy material. Specifically, there has been a problem that the oxidation-reduction reaction between CaO and Al2O3 in the slag and the alloy material progresses, and the Al concentration in the obtained ingot fluctuates with respect to the ESR consumable electrode.

[0003] In order to control the reaction equilibrium between the slag and the alloy material for such problems, for example, a slag as in Patent Document 1 has been proposed. In Patent Document 1, it is proposed to supply a slag that satisfies (%CaO) + (%SiO2) + (%MgO) ≥ 90, 1.0 < (%CaO) / (%SiO2) < 1.3, 1 ≤ (%MgO) ≤ 20, and (%Al2O3) ≤ 2 in mass%. This Patent Document 1 is excellent in that it can avoid Al pickup into the molten steel and exhibit a high desulfurization ability by applying the above slag.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The slag disclosed in Patent Document 1 mentioned above is advantageous in that it has high desulfurization capacity while suppressing the Al concentration due to Al pickup from exceeding the upper limit of the target range. However, when attempting to apply the slag with the component composition disclosed in Patent Document 1 to the ESR method, there are problems such as difficulty in securing the heat generation of the slag due to its low electrical resistance, and difficulty in securing the fluidity of the slag due to its high melting point. The problem of reduced calorific value and fluidity of slag is that some of the slag that did not melt completely mixes into the molten steel and remains in the ingot, causing a decrease in mechanical properties and cracking. Therefore, it is necessary to remove this portion, which leads to a decrease in yield. Furthermore, when attempting to apply the slag disclosed in Patent Document 1 to austenitic stainless steel, it becomes difficult to sufficiently reduce the oxygen concentration in the molten steel, which leads to the problem of a decrease in the position of nonmetallic intermediaries in the ingot.

[0006] The objective of the present invention is to provide a method for manufacturing ingots using the ESR method that solves the problem of slag contamination in the ingot by ensuring the calorific value and fluidity of the slag, thereby enabling the production of ingots with high cleanliness. [Means for solving the problem]

[0007] The present invention is a method for producing an ingot by remelting electroslag using slag consisting of, by mass%, 5.0%≦CaO≦25.0%, 2.0%≦SiO2≦10.0%, 10.0%≦Al2O3≦30.0%, with the remainder being CaF2 and unavoidable impurities. Furthermore, the method for producing the ingot of the present invention preferably uses a slag consisting of, by mass%, 7.0%≦CaO≦20.0%, 3.0%≦SiO2≦7.0%, 15.0%≦Al2O3≦25.0%, with the remainder being CaF2 and unavoidable impurities.

[0008] The method for manufacturing ingots of the present invention is suitable for alloy materials containing Al ≤ 0.015% by mass. Furthermore, the method for manufacturing the ingot of the present invention is more preferable for alloy materials containing, by mass%, C≦0.03%, Si≦1.00%, Mn≦2.00%, P≦0.045%, S≦0.03%, 12.00%≦Ni≦15.00%, 16.00%≦Cr≦18.00%, and 2.00%≦Mo≦3.00%, with the remainder being Fe and unavoidable impurities. [Effects of the Invention]

[0009] The present invention's method for manufacturing ingots is a useful technique because it solves the problem of slag contamination in ingots when using the ESR method, and allows for the production of ingots with high purity. [Brief explanation of the drawing]

[0010] [Figure 1] An example of a scanning electron microscope image of an area identified as a defect in ultrasonic testing. [Modes for carrying out the invention]

[0011] The present invention is characterized by the use of a slag consisting of 5.0% ≤ CaO ≤ 25.0%, 2.0% ≤ SiO2 ≤ 10.0%, 10.0% ≤ Al2O3 ≤ 30.0%, with the remainder being CaF2 and unavoidable impurities, when applying the electroslag remelting method to the production of ingots such as austenitic stainless steel. The reasons for limiting each component (mass%) will be explained in detail below.

[0012] "5.0% ≤ CaO ≤ 25.0%" CaO is useful for smoothing the surface of the ingot. In this invention, by keeping the CaO content at 25.0% or less, a good balance of CaO / Al2O3 can be maintained, ensuring sufficient heat generation. This suppresses the unevenness of the slag skin on the ingot surface, resulting in a smooth surface. For the same reasons as above, it is preferable to keep the CaO content at 20.0% or less. Furthermore, CaO is useful in promoting the deoxidation and desulfurization effects in ESR, reducing the amount of nonmetallic inclusions and contributing to improved cleanliness. For this reason, the present invention contains 5.0% or more CaO.

[0013] "2.0 ≤ SiO2 ≤ 10.0%" SiO2 is useful for adjusting the fluidity of the slag. In this invention, the SiO2 content is set to 10.0% or less. This suppresses the slag from becoming incorporated into the ingot. Also, for the same reasons as above, it is preferable to set the SiO2 content to 7.0% or less. Furthermore, SiO2 has a higher standard reaction energy for oxides at molten steel temperatures than Al2O3, which will be discussed later. When SiO2 and Al2O3 coexist in a molten state, the reduction reaction of SiO2 proceeds, suppressing the reduction reaction of Al2O3 and reducing the amount of Al picked up. For this reason, in order to control the Al concentration to a low level, for example, to obtain an ingot of alloy material containing Al ≤ 0.015%, SiO2 should be included at a concentration of 2.0% or more. Also, for the same reasons as above, it is preferable to have SiO2 at a concentration of 3.0% or more.

[0014] "10.0% ≤ Al2O3 ≤ 30.0%" Al2O3 is useful for adjusting the calorific value of slag. In this invention, by increasing the Al2O3 content to 10.0% or more, the electrical resistance of the slag is increased, ensuring sufficient calorific value of the slag in ESR, suppressing the formation of unmelted slag, preventing it from mixing into the ingot, and contributing to improved cleanliness. For the same reasons as above, it is preferable to increase the Al2O3 content to 15.0% or more. On the one hand, if Al2O3 is excessively contained in the slag, the melting point of the slag will rise too much, promoting the formation of unmelted slag. Therefore, in the present invention, the content of Al2O3 is made 30.0% or less. Also, for the same reason as above, it is preferable that the content of Al2O3 is 25.0% or less.

[0015] "CaF2" The slag used in the present invention is composed of CaF2 and inevitable impurities as the remainder other than CaO, SiO2, and Al2O3 described above. CaF2 is useful for lowering the melting point of the slag. By making the content of CaF2 50.0% or more, it is preferable in that the problem of the decrease in the fluidity of the slag due to the rise in the melting point of the slag can be suppressed. As a result, in addition to suppressing the unevenness of the slag skin on the surface of the ingot and making the surface texture of the ingot smooth, it is possible to suppress the slag from mixing into the ingot, and it has the effect of contributing to the improvement of cleanliness. On the other hand, by making the content of CaF2 70.0% or less, it is preferable in that the increase in the electrical conductivity of the slag can be suppressed, the calorific value of the slag can be ensured, and the formation of unmelted slag can be suppressed. As a result, it is possible to suppress the unmelted slag from mixing into the ingot, and it has the effect of contributing to the improvement of cleanliness.

[0016] In order to suppress the increase in the oxygen concentration and the component variation in the ingot, it is preferable to perform ESR in an inert gas atmosphere in the method for manufacturing an ingot of the present invention. The inert gas referred to in the present invention means a noble gas such as argon. Moreover, the method for manufacturing an ingot of the present invention is applicable to ingots of all sizes regardless of the size of the ingot. The manufacturing method of the present invention is useful for alloy materials such as austenitic stainless steels generally defined in JIS G 4303 and alloy tool steels equivalent to SKD61 defined in JIS G 4404.

Examples

[0017] First, a consumable electrode for ESR was produced using a vacuum induction melting furnace. The component systems of the alloy materials were all equivalent to SUS316L specified in JIS G 4303.

[0018] Next, using the consumable electrode for ESR obtained above, with the slag having the components shown in Table 1, Ar gas was supplied to the molten steel and above the slag, and ESR was carried out under an Ar atmosphere. Then, samples were taken from the positions corresponding to the top and bottom parts of each obtained ingot, and component analysis of Al and oxygen was performed. The results are shown in Table 1. After subjecting each of the ingots obtained above to hot working, they were subjected to an ultrasonic flaw detection test. If unmelted slag mixed into the molten steel during ESR and remained in the ingot, defects would be detected by the ultrasonic flaw detection test. Here, cases where defects caused by slag were not detected were evaluated as ○, and cases where they were detected were evaluated as ×. The results are shown in Table 1.

[0019]

Table 1

[0020] In Comparative Examples 3 and 4, defects were detected by the ultrasonic flaw detection test. When the defective part was cut out on the cross-section, slag as shown in Fig. 1 was detected on the cross-section. In contrast, in Invention Examples 1 to 5 where the slag components were within the scope of the present invention, no defective parts were detected by the ultrasonic flaw detection test. That is, it was confirmed that unmelted slag was not formed during ESR and did not remain in the ingot.

[0021] It was confirmed that for the ingots obtained in Comparative Example 5, the oxygen concentration exceeded 35 mass ppm in both the top and bottom parts. In contrast, in Invention Examples 1 to 5 where the slag components were within the scope of the present invention, it was confirmed that the oxygen concentration in the ingots was 35 mass ppm or less.

[0022] According to the ingot manufacturing method of the present invention, by keeping the slag component within the range of the present invention, it was possible to control the Al concentration to 0.015 mass% or less in both the top and bottom portions of the ingot for use with ESR consumable electrodes. On the other hand, in Comparative Examples 1 and 2, which used slag that was not part of the slag components of the present invention, the Al concentration in the ingot exceeded 0.015% by mass, and it was confirmed that the pickup of Al by the reduction of Al2O3 could not be suppressed.

Claims

【Request Item 1】 In mass percent, 5.0% ≤ CaO ≤ 25.0%, 2.0% ≤ SiO ２ ≤10.0%, 10.0% ≤Al ２ O ３ ≤30.0%, the remainder is CaF ２ A method for producing an ingot by electroslag remelting an alloy material containing, by mass%, C ≤ 0.03%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.03%, 12.00% ≤ Ni ≤ 15.00%, 16.00% ≤ Cr ≤ 18.00%, 2.00% ≤ Mo ≤ 3.00%, Al ≤ 0.015%, with the remainder being Fe and unavoidable impurities, using slag consisting of these and unavoidable impurities. 【Request Item 2】 In mass percent, 7.0% ≤ CaO ≤ 20.0%, 3.0% ≤ SiO ２ ≤7.0%, 15.0% ≤Al ２ O ３ ≤25.0%, the remainder is CaF ２ A method for producing an ingot according to claim 1, comprising remelting electroslag using slag consisting of and unavoidable impurities.

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