JPH0461054B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention improves yield by omitting surface grinding by preventing ingot surface defects when manufacturing ingots by melting and refining titanium using an electron beam remelting furnace (EBR). It is related to the technology that makes it possible. [Prior Art] Currently, the mainstream method for producing titanium ingots is a vacuum arc melting furnace (VAR). Since VAR uses an arc as a heat source, its stability must be ensured and it is only possible to produce ingots with a round cross section. On the other hand, in EBR, since the deflection of the electron beam (EB) can be easily controlled, ingots with various cross-sectional shapes such as not only round but also rectangular shapes can be manufactured. EBR operations are carried out as follows. EB is used to irradiate the molten material fed into the melting chamber to melt the material, and at the same time irradiates the surface of the molten pool in the mold to form and maintain the boule. Solidification progresses as heat is removed from the mold, and the ingot is pulled downward by the solidified amount. Traditionally, Siegfried is the EBR melting condition.
Written by Schiller, Ullrich Heisig, and Siegfied Panzer
ELECTRON BEAM TECHNOLOGY (JOHN
WILEY & SONSI Inc.1982) has some descriptions. That is, Table 4.1 on page 262 of the same book shows that the specific power consumption, which is the total amount of power required to melt 1 kg of titanium, is 2 to 5 KWHr/Kg. Also, Figure 4.12 on page 269 shows the ingot diameter and EB.
Output relationships are shown. However, these conditions only provide a guideline for performing titanium melting work, and do not provide conditions for preventing ingot surface defects, and the ingot has various cross-sectional shapes, which is the most distinctive feature of EBR. The conditions for producing ingots and obtaining beautiful surface skin are not presented. [Problems to be Solved by the Invention] The present invention has been made with attention to such circumstances. In other words, when manufacturing ingots with various cross-sectional shapes using EBR, surface defects occur frequently unless the ingot cross-sectional shape, casting speed, EB output, and EB irradiation pattern are optimized. Surface grinding is required, which reduces yield. The purpose of the present invention is to prevent the occurrence of surface defects in ingots, reduce the amount of surface grinding, and establish an EBR melting technology with a high yield. [Means and effects for solving the problem] The method of the present invention is applicable to the electron beam melting of titanium by reducing the electron beam power E (KW) and mold cross-sectional area S.
(cm ² ), casting speed V (Kg/Hr), 0.1×S≦V≦
The conditions were set to 0.4 x S and 0.06 x S + 0.5 x V + 40 < E < 0.06 x S + 1.0 x V + 110, and the irradiation center of the electron beam in the mold was placed within 40 mm from the mold wall to melt while irradiating. It is characterized by doing. Figure 1 shows the surface defects of ingots produced using EBR under conventional conditions. FIG. 1 shows the cross-sectional shapes of various defects, and the defects include unfilled skin in the mold, double skin, and transverse cracks. The causes of these defects will be described below. If the EB heat input is lower than the amount of heat removed depending on the shape of the ingot, such as conductive heat transfer through the mold or radiation heat transfer from the surface of the molten pool in the mold, and the cooling rate is fast, the molten titanium (molten titanium) This occurs because solidification is completed before the mold is completely filled. There are two causes of double skin. First, if hot water enters the gap formed between the solidified shell and the inner wall of the mold due to solidification shrinkage of the shell or vibration during pulling out of the ingot, and if the strength of the shell is low, the shell will be deformed inward toward the molten pool. is caused, and hot water overflows into the gap, resulting in double skin. Furthermore, when the casting speed is high, the molten pool surface vibrates violently, promoting overflow. Second, when the shell strength is low, double skin occurs due to the so-called bleeding phenomenon in which the shell breaks due to the frictional force between the inner wall of the mold and the shell, and hot water flows out from the broken part. In any case, double skin occurs when the shell strength is low. Since the tensile strength of titanium is low just below its melting point, it is necessary to form a thick shell to reduce stress. Figure 2 shows the results of evaluating the inclination of the solidified shell and double skin by surface roughness, which were determined by observing the ingot cross section, using a 305 x 61 mm mold and adding nickel as a tracer to the molten pool during melting. . It can be seen that the greater the inclination of the shell, that is, the thicker the shell is from the initial stage of solidification, the more the surface roughness decreases, and the occurrence of double skin is reduced due to the aforementioned stress relaxation acting on the shell. The shell shape is controlled by the total EB heat input to the molten pool or the local heating of the pool by the EB irradiation pattern. If the EB irradiation center in the mold is irradiated away from the mold wall, the inclination of the shell will decrease and double skin will occur frequently. If the distance between the center of EB irradiation and the inner wall of the mold exceeds 40 mm, double skin will occur extremely, and the amount of ingot surface grinding will be 3 mm or more.
Yield decreases. Note that double skin occurs frequently as EB output increases. Figure 3 is a diagram showing the EB output and the length at which horizontal cracks occur when a 157 mm square billet is melted.
Lateral cracking increases when the EB output is reduced. this is,
This is thought to be because the surface temperature of the ingot in the mold drops to near the transformation temperature, at which the ductility of titanium decreases, and transverse cracking occurs due to tensile and bending stress caused by frictional force or vibrations associated with drawing. The state in which such transverse cracks occur is controlled by heat removal and casting speed, which depend on EB output, mold shape, etc. In order to investigate the influence of mold shape, we used molds with rounded corners and rectangular cross sections, and investigated the EB output that can form and maintain a molten pool inside the mold. This is thought to be due to the large effect of heat removal due to radiation, but it was found that EB output is proportional to the cross-sectional area of the mold, and that the influence of mold shape can be evaluated by the mold area. The present invention was made based on this knowledge, and is intended to prevent the occurrence of defects by optimizing the EB output, mold shape, casting speed, and EB irradiation method that affect the occurrence of surface defects as described above. . Conditions that can prevent surface defects are as follows. In electron beam melting of titanium, electron beam power E (KW), mold cross-sectional area S (cm ² ), casting speed V
(Kg/Hr) is set to the following conditions: 0.1×S≦V≦0.4×S and 0.06×S+0.5×V+40<E<0.06×S +1.0×V+110, and the irradiation center of the electron beam inside the mold Place it within 40mm from the mold wall and melt while irradiating it. FIG. 4 is a diagram showing the relationship between the conditions of the present invention and the amount of surface grinding of the billet when a square billet is manufactured using a mold with a cross-sectional area of 250 cm ² . The irradiation center in the EB mold was placed 20 mm from the inner wall of the mold. Below the straight line of E = 0.06 x S + 0.5 x V + 40, horizontal cracks and unfilled skin within the mold occur, and E = 0.06
Double skin occurs frequently above the straight line ×S+1.0×V+110, and a grinding amount of more than 1 mm is required to eliminate surface defects. On the other hand, when V is larger than 0.4×S, double skin occurs and the amount of grinding increases. V is
If it is smaller than 0.1×S, it is not only impractical in terms of production efficiency, but also causes frequent horizontal cracks. In addition,
If the EB irradiation center is irradiated at a position more than 40mm from the mold inner wall, surface grinding amount of more than 1mm is required. [Example] Table 1 shows examples. Table 1 Nos. 1 to 4 are examples of the present invention, and Nos. 5 to 8 are comparative examples.
In the table, the optimum condition limits of the present invention are also shown for reference. In No. 1 to No. 4, despite the various mold shapes, the amount of surface grinding was significantly smaller than that of the comparative example as long as the conditions of the present invention were within the range. Nos. 5 and 6 are examples in which melting was performed by setting the electron beam output higher and lower than the optimal condition limit of the present invention, respectively, but in both cases the amount of surface grinding to remove surface defects was large. No. 7 is an example in which casting was performed at a speed higher than the casting speed specified by the cross-sectional area of the mold, but there were many double skins and a large amount of surface grinding. No. 8 is an example in which the electron beam irradiation position was deviated from the conditions of the present invention and melted, but even if the other conditions were appropriate, the amount of surface grinding was large.

〔Effect of the invention〕

The present invention is configured as described above, and when performing EBR melting of titanium, it is possible to perform EBR melting with a high yield by preventing surface defects of ingots with various cross-sectional shapes and reducing the amount of surface grinding. That is.

[Brief explanation of the drawing]

Figure 1 shows the surface defects of EBR melted ingots, Figure 2 shows the relationship between the inclination of the solidified shell and the ingot surface roughness, and Figure 3 shows the relationship between the EB output and the length at which transverse cracks occur. , FIG. 4 is a diagram showing the relationship between the condition range of the present invention and the amount of surface grinding when EBR melting is performed using a mold with a cross-sectional area of 250 cm ² .

Claims (1)

[Claims] 1. In electron beam melting of titanium, electron beam power E (KW), mold cross-sectional area S (cm ² ), casting speed V
(Kg/Hr) is set to the following conditions: 0.1×S≦V≦0.4×S and 0.06×S+0.5×V+40<E<0.06×S +1.0×V+110, and the irradiation center of the electron beam inside the mold A titanium electron beam melting method characterized by placing titanium within 40 mm from the mold wall and melting while irradiating it.