JPS62124238A - Method for hot topping operation in vacuum arc melting method - Google Patents

Abstract

PURPOSE:To shorten hot topping time and to improve yield by performing hot topping according to the prescribed electrifying pattern in a vacuum arc melting method (VAR) for metallic material. CONSTITUTION:In VAR, the great portion of the material is melted by means of an electric current capable of giving the desired melting rate, and then the electric current value is lowered and hot topping operation is performed. The current value is regulated from the one giving a pool height (Hs) at the time of hot topping initiation to the one giving the final pool height (Hf) corresponding to the top-end croppage amount at th conclusion of hot topping. Then the above current value is maintained for a period necessary to solidify the difference (Hs-Sf) between above-mentioned pool heights. After a prescribed time, electrification is stopped, so that shrinkage cavities which easily occur at the head end of a steel ingot are removed and the defective parts at the head end of the steel ingot are minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a hot top operation method in a vacuum arc melting method for metal materials, and in particular, the present invention relates to a hot top operation method in a vacuum arc melting method for metal materials. The present invention relates to a hot top operating technology that solidifies while melting the top of the pool after entering the top.

[Conventional technology l Vacuum Arc Melting method (Vacuum ArcRemel)
ting (hereinafter referred to as VAR) is the 6th principle.
As shown in the figure, the material to be melted (consumable electrode) 2 is melted in a water-cooled crucible 1, and the molten steel is solidified in the crucible 1. In other words, the method involves sequentially performing melting and solidification. Since these processes are carried out under vacuum, quality is improved through vacuum refining, flotation separation of inclusions, and layered solidification, and they are used for melting steel and alloys that require a high level of quality.

In addition, in FIG. 6, 3 is a jacket, 4 is a furnace body, 5 is a stinger rod, 6 is a consumable electrode lifting mechanism, 7 is a power source,
8 is a control board, 9 is a direct-view monitoring device, 10 is an exhaust system, 11
12 is a cooling water, 12 is a stub holder, 13 is a stub, and 14 is a steel ingot.

VAR operation operations - Examples are electrode melting, electrode care, electrode welding, melting, hot top, cooling.

It is carried out sequentially through the main process of die cutting.

In VAR, a hot-top operation is performed after initial melting and steady-state melting (a period in which most of the material is melted at a current that provides the desired dissolution rate).

This hot top is an operation that eliminates shrinkage holes (pipes) that tend to occur in the head of steel ingots, and is performed with the aim of reducing the size of defective parts at the top of steel ingots. How high the position is placed has a great effect on improving yield. In other words, since parts including defective parts such as the pipe are discarded after melting, if there is a large amount of discarded parts.

This means that the yield is also poor.

the law of nature An example of conventional hot top operation is shown in Figure.

The graph shown in FIG. 8 has current value (KA) on the vertical axis and time (minutes) on the horizontal axis, and the numbers other than the current value represent the energization pattern indicating time. This graph (
As shown in the pattern diagram), in conventional hot top operation, after entering the hot top, the
The current value was lowered and the hot top was performed for a long time. As an example is shown in this pattern diagram, constant energization was carried out at a low current (2 KA) for a long time (20 minutes). This long-time energization at a low current merely heats the pool surface (solidification) in the crucible.

In this way, in the conventional example, the current value is gradually lowered and hot top is performed for a long time, but this takes too much time for hot top and takes too much time that does not contribute to melting, reducing production efficiency. There were many unnecessary operations.

In the present invention, in order to study an efficient hot top operation method in VAR, we shortened the hot top low current range time (5 minutes) as shown in Figure 9. I learned that the pipe position was lowered and the yield was poor.

(Problems to be Solved by the Invention) The present invention solves the drawbacks of the prior art and aims to shorten the hot top time.

The purpose is to improve production efficiency and yield in hot-top operations.

Other objects and novel features of the present invention will become apparent from the entire description of this specification and the accompanying drawings.

Means for Solving Problem 1 The present invention is based on the current value which becomes the pool depth (Hs) after entering the hot top in the hot top operation method in the vacuum arc melting method of metal materials. Reduce the current value to the current value to obtain the final pool depth (Hf) commensurate with the top section cutoff amount at the end of the hot top, and then solidify the difference in pool depth (Hs - Hf). A hot top operation method in a vacuum arc melting method is characterized in that the operation is carried out using a current pattern in which the current value is held for a necessary time and the current is stopped after the elapse of the time.

Next, the configuration of the present invention will be supplemented by the present inventors, incorporating the knowledge that the present inventors found when considering an efficient hot-top operation method in VAR.

An example of the energization (current) pattern according to the present invention discovered by the present inventors is shown in FIG.

The present invention will be described in detail based on FIG. 1 and FIG. 2 which is an explanatory view of the main parts of the present invention.
As shown in Figure 1.

After passing through the steady phase, the pool depth H
The current value is lowered using a curve connecting the current for s and the current for obtaining Hf.1 Next, the current value for obtaining the Hf is held constant for the time necessary to solidify Hs-Hf. . According to the energization pattern according to the present invention, it is possible to solidify the H8-Hf portion 16 while constantly dissolving the standard cutting portion 15, as shown in FIG. In this case, if you do not do the above and stop the power supply immediately after entering the hot top, the pipe will cool down from above and form a pipe downward, which is the problem in the present invention. The feature of this is that it follows the above-mentioned energization pattern and performs hot-top operation while constantly melting the upper part of the pool.In this way, even if the current value drops on a sharp curve, the pipe position can be raised. The inventors of the present invention have found through intensive studies that there is no problem in the above.

When implementing the energization pattern according to the present invention, the current to obtain the pool depth Hs, the current to ensure the final pool depth (Hs) commensurate with the top truncation amount, and the current to change the pool depth from Hs to Hf. I need to know the time.

In other words, by determining these conditions, the current pattern in the hot top can be determined.

Next, one of the inventors will explain his findings regarding these matters.

As a basic operating condition for a hot top, it is important to minimize the depth of the molten metal at the end of melting, but in order to determine the melting current value, the current value -
It is necessary to clarify the relationship between the pool depth and the two.

In this regard, the dissolution rate is determined by the type (
Crucible), the variation depending on the steel type was small, but it was found that the variation was large regarding the pool depth. This is presumed to be due to the large influence of not only the difference in melting temperature of each steel type but also the difference in thermal conductivity. Therefore, the relationship between current value and pool depth needs to be quantified by type, steel type, etc. Regarding the quantification of pool depth calculation for this melting current, the molten metal pool depth of VAR is generally determined by the diameter of the melting mold, one pole, and the melting current, and can be expressed by the following equation (1).

aJ+ H=A@ (I-a)・φ・ (1) However, 〇; Melting current (KA) A; Coefficient by type and steel type a; Minimum meltable current (KA) H; Pool depth m /m) Note that the minimum melting current a is determined by the mold diameter and steel type. Empirical results may be used.

Table 1 shows an example of the pool depth calculation formula for each type and steel type based on this formula (1) and the conditions investigated using the steel ingot macro, and an example of the graph is shown in Figure 3. show.

Reprint of specification (no change in content) Example of formula for calculating pool depth by WJ1 table type and steel type From the above, it is also possible to calculate the melting current value to ensure the required final solidification pool depth.

The melting current value calculated from the above relationship is the current value that can be melted, so the melting current to ensure a pool depth at the end of melting that corresponds to a certain cutoff amount is a condition that allows the melting to proceed sufficiently. I understand that there is something.

In this way, the depth of the pool just before entering the hot top (Ha
), and determine the final pool depth Hr corresponding to the top cutoff amount.
), calculate the current value (K) to ensure H
Calculate the time ('I') for changing the pool depth from s to Hf'.

Next, the setting of the hot top time (the time required to solidify Hs-Hf) will be described.

This time can be expressed by the relational expression of the following parameters: (no change in content).

HotTo p time (coagulation time); Assuming that the shape of the pool is conical, the # same speed of the pool increases as the surface area becomes larger. Here, Hr can be expressed as P which corresponds to the set HotTop current value. .

Rearranging the above equation (2) results in equation (31).

λ: Thermal conductivity (ca!!/cm -5ec) D: Mold diameter β: Type, #4 type coefficient (steel-containing ingot diameter, thermal conductivity) In this way, for a certain steel type, the mold diameter (D) When is constant, if the dissolution conditions (Hs, Hf) are determined, the above formula (
Pool depth (Hf) at the end of melting from the setting formula shown in 3)
It becomes possible to set a hot top time to ensure

[Example 1 Next, examples of the present invention will be shown.

Example 1 Hot top was performed on jE type A (φ460) based on the pattern shown in FIG.

The relational expression [formula (1)] between the pool depth and melting current for this steel type (mold diameter φ460) was as follows.

6 H = 95 (I -4,5) If 5KA is selected as the current value, the coagulation time is calculated by formula (3)
After 25 minutes, we were able to carry out the hot top according to the pattern shown in Figure 4.

The position of the vibrator was also compared with Comparative Example 1 below.
There were no problems, and no macroscopic abnormalities were observed.

Comparative Example 1 When hot top was performed on the same steel type as in Example 1 based on pattern f shown in FIG. 5, as shown in the same figure, 37 minutes were required for hot top.

[Effect of the invention 1] By performing hot top according to the energization pattern of the present invention, the standard truncated portion is always melted, while the Hs-Hf portion below it is solidified, and as shown in the examples. In addition, we succeeded in reducing the overall hot top time, improving production efficiency, and increasing yield.

According to the present invention, hot top operation is performed while melting is constantly progressing, and even if the current value at the time of entering the hot top suddenly drops, the melting continues, and the melting process is continued by simply heating the molten metal surface as in the conventional method. This invention has great industrial significance in that it has established a very innovative operating method in hot top operation in VAR, which can eliminate wasteful use of low current for a long time.

[Brief explanation of drawings]

Fig. 1 is a diagram of the energization pattern of the present invention, Fig. 2 is an explanatory diagram of the main parts of the present invention, Fig. 3 is a graph showing the relationship between pool depth and melting current, and Fig. 4 is an example of an embodiment of the present invention. 5 is a pattern diagram of a comparative example, FIG. 6 is a principle diagram of an example of VAR, FIG. 7 is a diagram of an energization pattern of a conventional example, and FIG. 8 is a diagram of an energization pattern of a conventional example. ■ Number Crucible? ...Electrode patent applicant Daido Steel Co., Ltd. Representative Patent Attorney Yoshihiro Sato Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Procedural Amendment (Method) % Formula % 1. Indication of the case 1985 Patent Application No. 263537 2. Name of the invention Hot top operation method in vacuum arc melting method 3. Person making the amendment Patent Applicant (371) Daido Steel Co., Ltd. 4. Agent Person 5. Date of amendment order: February 25, 1985 (shipping date) 6. Detailed description of the invention in the specification subject to amendment (!3 Description on pages 10 to 11, written in clear) 7. Submit pages 10 and 11 of the specification, clearly written with details of the amendment. , -1111

Claims (1)

[Claims] In a hot top operation method in a vacuum arc melting method for metal materials, after entering the hot top, the top section cutting at the end of the hot top is determined from the current value that becomes the pool depth (Hs) at the time of entering the hot top. Reduce the current value to the current value to obtain the final pool depth (Hf) commensurate with the amount of waste, and then reduce the current value for the time necessary to solidify these pool depth differences (Hs - Hf). A hot top operation method in a vacuum arc melting method, characterized in that the operation is carried out using a current pattern in which the current is held and then the current is stopped after the elapse of the time period.