JPH0429722B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a vacuum arc melting method for obtaining an ingot with excellent homogeneity, surface quality and productivity in vacuum arc melting of high melting point active metals such as Ti and Zr and their alloys. Conventional technology High melting point active metals are usually melted by vacuum arc melting, but this method involves constant melting with a constant electric current.
In the latter stage of melting, the melting current is reduced within a relatively short period of about 20 to 60 minutes, a so-called hot-top process. However, in such a method, the influence of the deep molten metal pool during steady melting remains, and the melting ends in a considerably deep state. As a result, component segregation and shrinkage pores may occur in the center of the ingot top, and in order to prevent the formation of these defects, it is important to adjust the depth of the molten metal pool at the end of melting. is an important element. Therefore, various efforts have been made in the past,
As a method for reducing the occurrence of shrinkage pores, for example, there is a method of gradually lowering the dissolution current, as described in Japanese Patent Publication No. 41-8321, and as a method for reducing component segregation, for example, as described in Japanese Patent Publication No. 40-4445, there is a method of gradually lowering the dissolution current. Component Mn
There is a way to side charge when hot-topping. Problems to be Solved by the Invention The above method for reducing the occurrence of shrinkage pores gradually reduces the depth of the molten metal pool while preventing solidification from the upper surface of the molten metal pool, thereby preventing the occurrence of shrinkage pores and reducing component segregation. This is what I am trying to do. However, in this case, it is clear that because the hot-top time is increased, the dissolution rate decreases and productivity deteriorates. Furthermore, the surface condition at the top of the ingot is inferior to that during high current melting. In order to solve this problem, if the hot-top time is shortened, component segregation will increase and large shrinkage pores will be generated. In addition, when adding Mn fine powder, the above method of reducing component segregation may cause it to scatter due to the arc and adhere to the mold, or conversely cause surface solidification, forming undissolved areas and promoting component segregation. There is sex. In view of the current situation, this invention proposes a vacuum arc melting method for high melting point active metals and their alloys in order to shorten hot-top time and obtain ingots with excellent homogeneity, surface quality, and productivity. . Means for Solving the Problems This invention provides a method for vacuum arc melting of active metals with high melting points and their alloys, when primary melting is performed by consumable electrode type arc melting. Parts of Fe, Ni, Cr, Al, Sn,
By adjusting components with significant segregation such as O and Mo, the hot-top time can be shortened. When primary melting is performed by non-consumable electrode type arc melting, Fe, Ni, Cr,
Hot-top time can be shortened by adjusting components with significant segregation such as Al, Sn, O, and Mo. The gist is that. In this invention, in order to prevent component segregation, components that are likely to be segregated are adjusted in advance. On this occasion,
Component segregation is caused by solidification, and elements with equilibrium distribution coefficient k < 1 (Fe, Ni, Cr, Al, Sn, etc. in the case of Ti and Zr)
has positive segregation, so it is adjusted to be lower by that amount, and k
Elements with >1 (O, Mo, etc. in the case of Ti and Zr) have negative segregation, so adjust to a high value. Through this adjustment, a uniform ingot without component segregation can be obtained. To adjust these easily segregated components, if primary melting is performed by consumable electrode type vacuum arc melting, the components of the primary electrode part must be adjusted, and if primary melting is performed by non-consumable electrode type arc melting, the components of the primary melting mixture should be adjusted. Adjust the ingredients. Examples Example 1 Using a compact molded by a hydraulic press, a primary electrode of 788 mm in diameter, 6300 mm in length, and 7200 kg in weight was produced by plasma beam welding, and this was then melted into a secondary electrode using a consumable electrode type vacuum arc melting furnace. A pure titanium ingot with a diameter of 980 mm, a length of 2100 mm, and a weight of 7150 kg was produced by heavy melting. At this time, all primary melting was performed under the same conditions,
By changing the hot top conditions of the secondary dissolution, we investigated two types: a conventional method, which was relatively short at 30 minutes, and a comparatively long one at 150 minutes. In addition, in carrying out this invention, when producing the primary electrode, Fe is 0.010% lower and O (oxygen) is 0.020% higher than the target value for the 15% portion corresponding to the top part of the secondary ingot. However, the hot-top time for secondary lysis was 30 minutes. The secondary melting current patterns of these ingots are shown in FIG. Line A in the figure shows the conventional method with a short hot-top time, line B shows the deceleration melting method with a long hot-top time, and line C shows an embodiment of the present invention. At the same time, each ingot was longitudinally cut into two, and the component distribution of Fe and O, which were significantly segregated, was investigated, and productivity and surface quality were observed. The results are shown in Table 1.

【table】

[Table] Maximum segregation value = Maximum analysis value / Target value Also, based on the above results, calculate the maximum variation from the target value (Figure a), the ingot surface quality index (Figure b), and the production efficiency (Figure c). Shown in Figure 2. From the above results, it can be seen that the inventive method C has significantly improved component segregation compared to the conventional method A in which no component adjustment was performed, and the same homogeneity as B, which was hot-topped for a long time, was obtained. It can be seen that an ingot with excellent productivity and surface quality can be obtained. Example 2 Using a non-consumable electrode type vacuum arc melting furnace,
A titanium ingot with a diameter of 800 mm, a length of 3200 mm, and a weight of 7200 kg is melted, and a diameter of 980 mm, a length of 2100 mm,
A pure Ti ingot weighing 7150Kg was produced. At this time, in the primary melting, sponge titanium 55 is used as a raw material.
%, using 45% titanium scrap, Fe is 0.010% lower than the target value and O is 0.020 in the 15% portion corresponding to the top of the secondary ingot when mixing raw materials.
Adjusted to be higher. The thickness of the above ingot is reduced by rough forging and blooming.
The slab is 200mm wide, 1100mm wide, 7200mm long, and weighs 7115kg, then hot-rolled and cold-rolled to a thickness of 0.7mm.
A cold-rolled coil with a width of 1050mm, a length of 1810m, and a weight of 5970Kg was manufactured. Then, Fe and O, which are significantly segregated, were investigated at five points on the surface of the ingot and at 100 mm intervals at the center of the width of the cold-rolled coil, and as for surface quality, the ingot and slab maintenance yields were investigated. The above test results are shown in Table 2. Regarding the melting conditions, all primary melting conditions were the same, and the hot top conditions for the secondary melting were changed: A for 30 minutes in the conventional method, B for the relatively long 150 minutes,
We investigated these three conditions with 30 minutes of this invention method as C.

【table】

[Table] However, the maximum variation from the target value and the maximum degree of segregation are the same as the notes in Table 1.
Furthermore, based on the above results, the maximum variation amount from the target value (Figure a), the ingot surface quality index (Figure b), and the production efficiency (Figure c) are shown in Figure 3. From the above results, this invention method C has significantly improved component segregation compared to conventional method A in which no component adjustment is performed, and can obtain homogeneity equivalent to method B, which uses hot top for a long time. ,Productivity,
It can be seen that an ingot with excellent surface quality can be obtained. Effects of the Invention This invention reduces the hot-top time by adjusting components that are significantly segregated in the electrode or the melted compound raw materials in the latter half of the final melting process when high melting point active metals and their alloys are vacuum arc melted. It is possible to obtain ingots with excellent homogeneity, surface quality, and productivity.

[Brief explanation of drawings]

Figure 1 is a diagram showing the secondary melting current pattern in consumable electrode type vacuum arc melting, Figure 2 is a diagram showing the ingot homogeneity, surface quality, and production in Example 1, and Figure 3 is in Example 2. 1 is a chart showing the influence of dissolution patterns on properties. A...Conventional method, B...Long time hot top method, C...
Inventive method, _Ip ...steady melting current, _TA ...total hot-top time in A pattern, T _B ...total hot-top time in B pattern, T _C ...total hot-top time in C pattern.

Claims (1)

[Claims] 1. In vacuum arc melting of high melting point active metals and their alloys, when double melting is performed by consumable electrode type arc melting, Fe, Ni, Cr, Al, Sn,
A vacuum for high melting point active metals and their alloys, which is characterized by shortening hot-top time and obtaining ingots with excellent homogeneity, surface quality, and productivity by adjusting components with significant segregation such as O and Mo. Arc melting method. 2. In vacuum arc melting of high melting point active metals and their alloys, when primary melting is performed by non-consumable electrode type arc melting, Fe, Ni,
A high-melting-point active product characterized by shortening hot-top time and obtaining ingots with excellent homogeneity, surface quality, and productivity by adjusting components with significant segregation such as Cr, Al, Sn, O, and Mo. Vacuum arc melting method for metals and their alloys.