JPH0819460B2 - Manufacturing method of metal material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing a metal material by heating the metal material by a direct current heating method.

(Prior Art) A direct electric heating method is used for heating a metal sintered body such as a refractory metal. This direct current heating method (also called direct resistance heating method, hereinafter referred to as current heating method) is the third method.
As shown in the figure, while holding both ends of the metal material 1, for example, a sintered body of a high melting point metal by the electrodes 2 and 2 and the gripping bodies 3 and 3, respectively,
Connect each electrode 2, 2 to AC power supply G,
This is a method in which a current is directly applied between both ends of the metal material 1 via 2 and 2 and the resistance heat generated in the metal material 1 is used to heat the metal material 1 itself.

Therefore, in this electric heating method, it is required to heat the metal material with a uniform temperature distribution. For metal materials that are required to have particularly severe temperature conditions (there is little variation in allowable temperature conditions), the uniformity of the heating temperature is more severely required than the heating time during electric heating.

(Problems to be solved by the invention) Then, looking at the relationship between the heating temperature of the metal material in the electric heating method and the current flowing through the metal material, the resistivity of the metal material and the cross-sectional dimension of the metal material From this, the material saturation temperature at each current value of the current flowing through the metal material is determined. Therefore, the metal material can be heated to a predetermined heating target temperature by passing a current in which a standard current value corresponding to the heating target temperature is set.

Therefore, when prioritizing the uniformity of the temperature distribution of the metal material in the conventional energization heating method, heating is performed by flowing a current having a standard current value corresponding to the heating target temperature to the metal material over the entire heating time.

However, in this case, there are the following problems. That is, in FIG. 3, the temperature of the portions B, B adjacent to the inside of the gripping portions A, A gripped by the gripping bodies 3, 3 of the metal material 1 and the electrodes 2, 2 is different from that of the other portions of the metal material 1. The temperature will be higher than the target temperature and will exceed the heating target temperature. This is due to the following reasons. The grippers 3, 3 and the electrodes 2, 2 have a water-cooling structure in which cooling water is passed through to cool the grippers A,
A and its adjacent portions B and B are cooled. However, the temperature of the portions B, B of the metal material 1 exceeds the cooling effect due to the contact resistance due to the contact between the electrodes 2, 2 and the grippers 3, 3 and rises in temperature. The temperature distribution of the metal material 1 in this case is shown in the diagram of FIG.

In order to deal with this, a current having a current value smaller than the standard current value corresponding to the heating target temperature is flown through the metal material for the entire heating time to heat to the heating target temperature. In this case, the heating time becomes longer than in the former case.

However, in this case, the temperatures of the portions B, B of the metal material 1 reach the heating target temperature as in the central portion, but the following problems occur. As is clear from the diagram showing the temperature distribution in the metal material 1 of FIG. 5, the temperature of the gripping portions A, A of the metal material 1 becomes lower than the temperature of the other parts of the metal material 1 and lower than the heating target temperature. become. This is because the influence of the cooling effect on the grips A, A of the metal material 1 is large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a metal material, which can electrically heat the metal material with a uniform temperature distribution.

[Structure of Invention]

(Means and Actions for Solving Problems) In order to achieve the above-mentioned object, the method for producing a metal material according to the present invention is such that the metal material itself is heated by the resistance heat generated in the metal material by passing an electric current directly through the metal material. In doing so, when the current value corresponding to the heating target temperature of the metal material is the standard current value, from the heating start time to the time close to the heating end time, a current having a current value smaller than the standard current value is applied. The metal material is heated by flowing, and from the time point close to the heating end time point to the heating end time point, the metal material is heated by flowing a current having a current value equal to or higher than the standard current value. To do.

 The present invention will be described below.

In this description, as shown in FIG. 3, the case where a sintered body of a high melting point metal is electrically heated as the metal material 1 is taken as an example. First
The figure is a diagram showing the energized state of the metal material, and FIG. 2 is a diagram showing the temperature distribution of the metal material.

As shown in FIG. 3, the energization heating of the metal material 1 causes a current to flow directly from the AC power supply G to the metal material 1 via the electrodes 2 and 2, and the metal material 1 itself is heated by the resistance heat generated in the metal material 1. .

First, as shown in FIG. 1, the time from the heating start time S1 to the time S2 close to the heating end time S3, that is, most of the heating time, is a current smaller than the standard current value I corresponding to the heating target temperature T. A current of a value I1 (small current) is passed through the metal material 1. As a result, the metal material 1 is heated to a temperature T'which is lower than the heating target temperature T. That is, as shown by the broken line X in FIG. 2, the central portion of the metal material 1 and the portions B, B adjacent to the gripping portions A, A are uniformly heated to the temperature T ', and the portion connecting these portions has a temperature distribution. Be uniform. However, the grip of the metal material 1
The temperatures A and A rise only to a lower temperature due to the temperature T '.

After the heating time of the metal material 1 elapses up to the time point S2, the time from the time point S2 to the heating end time point S3 is a current having a current value I2 larger than the standard current value I corresponding to the heating target temperature T (large Current) to the metal material 1. As a result, the metal material 1 is heated to the heating target temperature T. That is, as shown by the solid line Y in FIG.
The temperature of the portions B, B adjacent to A rises to the heating target temperature T. Further, the grips A, A of the metal material 1 are also heated and the temperature rises to the heating target temperature T. Since the time for which the current value I2 is larger than the standard current value I is short, the parts B, B of the metal material 1
Does not rise above the heating target temperature T.

In this way, the metal material 1 is electrically heated to the heating target temperature T with a uniform temperature distribution throughout. Therefore, the metal material 1 can be satisfactorily processed even when severe temperature conditions are required in the processing after the electric heating, for example, hot rolling.

The current flowing from the time point S2 to the heating end time point S3 may have the standard current value I.

(Example) A tungsten sintered body having a diameter of 13 mm and a length of 700 mm was heated by a direct current heating method. The heating target temperature is 1400 ° C, and the standard current value of the current flowing through the sintered body is 2600A.

As an example of the present invention, a current value was divided into two stages of 2400A and 3500A and a current was passed through the sintered body. As a result, the entire sintered body
It was possible to heat with a uniform temperature distribution of 1400 ° C.

As a conventional example, only a current having a current value of 2400 A was passed through the sintered body. As a result, the temperature distribution of the sintered body is 480 for the grips A and A.
℃, 1400 ℃ in other parts, the temperature of the grip part decreased.

〔The invention's effect〕

As described above, according to the method for manufacturing a metal material of the present invention, the whole metal material is electrically heated with a uniform temperature distribution by the direct current heating method in which a small current and a large current are combined to perform two-step current application. It is suitable for electric heating of metal materials that require severe temperature conditions during processing.

[Brief description of drawings]

FIGS. 1 and 2 show the method of the present invention, FIG. 1 is a diagram showing the energized state of a metal material, FIG. 2 is a diagram showing the heating temperature distribution of the metal material, and FIG. 4 and 5 are diagrams showing a heating temperature distribution of a conventional metal material. 1 ... Sintered body, 2 ... Electrode, 3 ... Gripping body.

Claims (2)

[Claims] 1. When heating a metal material itself by resistance heat generated in the metal material by passing an electric current directly through the metal material, when the current value corresponding to the heating target temperature of the metal material is set to a standard current value, heating is performed. From the start time to the time close to the heating end time, the metal material is heated by passing a current having a current value smaller than the standard current value, and from the time close to the heating end time to the heating end time. Is a method for manufacturing a metal material, wherein the metal material is heated by passing a current having a current value equal to or higher than the standard current value. 2. The metal material according to claim 1, wherein a current having a current value exceeding the standard current value is passed from a time point close to a heating end time point to a heating end time point. Production method.