JPS6038220B2 - How to reduce hydrogen in steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing hydrogen in steel, and particularly to a method for reducing hydrogen in steel cast by a bottom pour casting method.

Generally, high-grade killed steel for forging steel or thick plates is cast by a bottom pour casting method (hereinafter referred to as the bottom pour method) after degassing molten steel to deoxidize and dehydrogenate it.

In this case, if the hydrogen content in the cast steel ingot is high, the risk of white spots or internal hair cracks increases, so as a preventive measure, the steel ingot is generally subjected to dehydrogenation annealing treatment after casting. Since this dehydrogenation annealing treatment is extremely expensive, it is desirable to reduce the hydrogen content of the molten steel in the mold as much as possible.
However, in reality, in Minato Steel casting, the molten steel is degassed before casting, so even if the hydrogen content reaches a certain level, in the bottom pouring method, the molten steel passes through the injection port, injection pipe, and runner. Hydrogen is absorbed before it reaches the mold (hereinafter this phenomenon is referred to as hydrogen pickup), and the hydrogen content increases.
That is, although molten steel once reaches a low level of hydrogen content through degassing treatment, it is extremely difficult to produce stable low-hydrogen steel because hydrogen is picked up during subsequent casting. Therefore, in order to prevent white spots or internal hair cracks in steel, the current situation is that steel ingots must be dehydrogenated and hammered, even if it costs a lot of money.
The above has described high-grade killed steel for forged steel or thick plates, but when using the bottom pouring method for other steel types, it is extremely difficult to avoid hydrogen pickup in the molten steel, which can lead to white spots or internal hair cracks. It is the cause.

In other words, it is difficult to produce stable low-hydrogen steel using the conventional bottom pouring method, and if low-hydrogen steel is absolutely necessary, the steel ingot obtained by casting as described above is subjected to dehydrogenation sintering treatment. was. An object of the present invention is to provide a method for reducing hydrogen in steel, which eliminates the drawbacks of the prior art described above and can reduce the hydrogen content of steel core by bottom pouring.

This object of the invention is achieved by the invention which consists of the following summary.

The gist of the present invention is to provide a bottom pour casting method for steel, which includes the step of blowing heated gas into a path through which the molten steel passes, prior to pouring the molten steel. In this hydrogen reduction method, air may be used as the heated gas, but dry nitrogen is particularly effective.
In other words, the inventor investigated the cause of hydrogen pickup in the bottom pouring method of molten steel and found that the cause of hydrogen pickup in molten steel is moisture in the injection pipe, flaws, etc. through which the molten steel passes. It has been found that the hydrogen content of the steel can be significantly reduced by blowing hot gas into the injection pipe and moat to completely remove the moisture therein and prevent hydrogen pickup in the molten steel.

First, hydrogen pickup in steel according to the present invention will be explained with reference to the accompanying drawings.

According to the inventor's research, the amount of hydrogen picked up by molten steel from the time it is degassed to the time it is cast into the mold is 0.2 to 0.3 ppm in winter and 0.3 to 0.3 ppm in summer.
Table 1 shows the results of measuring the hydrogen content of samples taken at the positions shown in FIG. 1 at each point in the molten steel bottom pouring method. FIG. 1 is a sectional view showing an apparatus for performing a steel bottom pouring method and a sample collection position.

In the figure, A shows the sample collection position at the time when molten steel has been injected up to this point, B shows the sample collection position at the time when molten steel has been injected up to this point, and C shows the sample collection position in the injection pipe after the port steel injection is completed. Table 1 shows the difference between the hydrogen content of each sample and the hydrogen content of the molten steel after degassing and before casting, that is, the amount of hydrogen picked up.

Table 1 From Table 1, in A, the amount of hydrogen picked up by the molten steel was as high as 0.8 ppm due to the absorption of water in the injection pipe and the moat, while in B, the hydrogen was gradually diluted and the amount of hydrogen picked up was 0.4 ppm.
ppm, indicating that C has no hydrogen pickup amount.

From the above investigation, it can be said that the cause of hydrogen pickup in the steel bottom pouring method is moisture in the injection pipe and runner through which molten steel passes.

In other words, it was found that the moisture adhering to or contained in the refractory bricks and mortar in the injection pipes and scars was picked up by the molten steel passing through these areas, increasing the hydrogen content of the steel ingot. Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 is a sectional view showing an apparatus for carrying out the invention. Steel bottom pour casting equipment mainly consists of a pouring row, a pouring pipe 2, a runner 3, a pouring nozzle 4, a surface plate 5, a mold 6, and a press sleeve 7.
Consists of etc.

In order to carry out the method of reducing hydrogen in steel according to the present invention, a fan 8, a hot air heater 9, a blower pipe 10, and a
A hot air blowing device consisting of the After that, the molten steel is cast. In this hot air blowing device, the blowing temperature is set at 150 to 50,000, and the temperature of the blowing air at the hot air nozzle 4 becomes almost constant approximately 3 minutes after the start of air blowing, and moisture can be removed sufficiently by drying with air for about 3 hours. can.

FIG. 3 is a cross-sectional view of an apparatus for implementing another embodiment of the present invention. The heating dry nitrogen blowing device consists of a dry nitrogen supply pipe 11, a quick joint 12, a fan 8, a hot air heater 9, and a blower pipe 10. During implementation, the blower pipe 10 is well sealed and connected to the molten steel injection port 1 to achieve the desired effect. dry properly. Since blowing hot air as explained in Figure 2 above may not be sufficient to prevent hydrogen pickup in the summer, heated dry nitrogen is used in place of ordinary hot air, so to speak, intense drying reduces hydrogen almost completely. It is an apparatus for carrying out the method. Table 2 is a table comparing the results of the hydrogen reduction method of the present invention with the conventional method.

As is clear from Table 2, the hot air blowing method of the present invention can significantly reduce the amount of hydrogen picked up, and among these methods, the heated dry nitrogen blowing method is particularly effective. Hydrogen pickup can be completely prevented.

In addition, the steel ingot subjected to the method of the present invention has no occurrence of 8 points or internal hair cracks. The effects of the present invention are
Although it has already been mentioned in the description of the embodiment, it can be summarized as follows.

That is, by carrying out the method for reducing hydrogen in steel according to the present invention, the hydrogen pickup in molten steel that occurs during the steel bottom pouring method is significantly reduced, so that the occurrence of white spots or internal hair cracks in the steel can be prevented. Therefore, the expensive dehydrogenation annealing treatment of the steel ingot can be omitted, and stable low hydrogen steel can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an apparatus for performing a steel bottom pouring method and the position of sample collection, Fig. 2 is a sectional view of an apparatus for carrying out an embodiment of the present invention, and Fig. 3 is a sectional view of another embodiment of the present invention. FIG. 2... Injection pipe, 3... Runway, 4... Hot water nozzle, 6... Mold, 8... Fan, 9... Hot air heater, 10... Air blow pipe, 1 1. ...Dry nitrogen supply pipe. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A method for reducing hydrogen in steel, which comprises a step of blowing heated gas into a path through which the molten steel passes prior to pouring the molten steel, in a bottom pour casting method for steel.