JPS58197209A - Production of low nitrogen and low hydrogen steel - Google Patents

Abstract

PURPOSE:To enable the easy production of low nitrogen and low hydrogen steel by decarburizing and refining molten iron which is subjected to preliminary desiliconization, dephosphorization and desulfurization treatments with the samll amt. of the lime to be used in a converter then shielding the same from the atmospheric air with a device for tapping the steel isolatedly from the atmospheric air and tapping the steel into a ladle. CONSTITUTION:The molten iron which is beforehand subjected to preliminary desiliconization, desulfurization and dephosphorization treatments by using NaCO3, etc. is charged into a converter 1, and mainly the decarburization, as well as desiliconization, desulfurization and dephosphorization are perfected by oxygen top blowing refining or the like, whereby the molten iron is refined to steel. Since the molten iron is refined preliminarily in this case, the required amt. of basic slag can be as small as 5-50kg for each 1 tone of the molten steel, and the amt. of the lime to be charged can be correspondingly smaller, so that the moisture to be carried from the lime into the molten steel is reduced considerably. A gas such as argon, CO2 or the like contg. moisture and nitrogen in an extremely small amt. is blown into the converter from the tuyere at the bottom thereof and the steel is tapped isolatedly from the atmospheric air through a communicating pipe 3 into a ladle 5 kept in an atmosphere of Ar or the like, whereby the absorption of nitrogen from the atmospheric air is reduced and the steel contg. nitrogen and hydrogen slightly is produced stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing low nitrogen and low hydrogen steel.

Generally, the content of nitrogen and hydrogen during steel melting is greatly influenced by the melting conditions in the key converter and the amount of pick-up of the above-mentioned components during steel tapping. For example, the hydrogen content in molten steel at the end of blowing in a converter is largely influenced by the water content in the auxiliary material that has been subjected to blowing. Therefore, the inventor has always experienced that there is a seasonal response depending on the humidity in the atmosphere.

On the other hand, it has recently been discovered that it is possible to melt steel with a low nitrogen content by blowing argon, carbon dioxide, and other gases such as oxygen from the bottom of the furnace during melting. It's being served.

However, molten steel with low nitrogen or hydrogen content at the end of blowing has a particularly large amount of nitrogen or hydrogen when tapped, and therefore it is difficult to fully utilize the nitrogen and hydrogen reduction effect at the end of blowing into the final product. It's difficult.

On the other hand, from the viewpoint of improving material quality and saving resources by saving valuable elements such as Mn and T11B, there is a need to improve the manufacturing method of low-hydrogen and low-nitrogen steel.

Generally speaking, DH is a method for reducing the hydrogen content in steel.
Vacuum degassation methods such as the RH method and the RH method are well known.

In order to make the hydrogen level after the process sufficiently low in this vacuum degassing process, it is necessary to ensure a sufficiently long degassing process time, but to set the hydrogen content before the process to a low value in advance. In particular, in order to rationally perform continuous casting of steel by combining continuous casting equipment with continuous casting equipment (usually referred to as continuous casting), it is necessary to perform so-called casting work and the vacuum degassing process that is the pre-process. Therefore, the degassing time in the vacuum degassing process is limited, and a shorter time is desirable. Therefore, in order to reduce the hydrogen content in molten steel as much as possible under such limited conditions, it is necessary to establish a technique for reducing the hydrogen content in molten steel before vacuum degassing treatment.

Unlike hydrogen, nitrogen in molten steel does not change much even when vacuum treatment is performed, so it is necessary to keep the content low before vacuum treatment.

In conventional converter blowing, as a method to reduce the hydrogen content in molten steel during blow-stopping, materials with low moisture content are used as auxiliary materials such as quicklime and iron ore that are charged into the converter. In addition, as a means to reduce the amount of molten metal used, operation is carried out at a low hot metal ratio to reduce the amount of molten metal charged.Furthermore, these auxiliary materials are charged completely at the beginning of blowing, and the decarburization reaction is weak. It has been suggested that it is better to avoid using it in the final stages of blowing.

Furthermore, a method is known in which steel is tapped without being deoxidized in order to suppress pick-up during tapping, but this method results in a large temperature drop during tapping, resulting in a high blow-off temperature). It is disadvantageous to phosphorus and its effectiveness is therefore limited by the large amount of lime that must be used in the converter for dephosphorization.

Recently, St, P, and S in the hot metal have been removed in advance and then decarburized in the converter, and blowing has been carried out in the converter using almost no auxiliary materials such as quicklime or ore. It is also known that the hydrogen content at the end of blowing can be brought below the level in normal converter operation.

However, since the above-mentioned method results in blowing with virtually no slag, a large amount of FeO foam is generated, which increases iron loss. A sudden decarburization reaction may occur during the refining process, which can cause problems such as molten steel blowing out, and this has the disadvantage of affecting operational stability.

Furthermore, this method has virtually no slag, so
Because it is no longer possible to carry out the so-called slag coating operation, which is highly effective for protecting large objects lining the furnace, there are drawbacks such as significant melting of large objects lining the furnace. Even if the hydrogen and nitrogen content is low at the time of blow-stopping, there will be big errors in the tapping process! However, there are defects that prevent this effect from being fully utilized in products (5).

The present invention has been made to solve the above-mentioned drawbacks, and uses hot metal that has been previously desiliconized, dephosphorized, and desulfurized as a starting material, and decarburizes and dephosphorizes part of it in a converter at a rate of 5 to 50 kg/Ton.
A small amount of slag of -8 te·l is used, and the use of auxiliary materials such as quicklime is limited to an extremely small amount. By forming this small amount of slag, it is possible to suppress the increase in fume generation and also to enable slab coating of the refractory lining. Furthermore, by injecting 0.2 Nm3/Ton-Min or less of high-purity argon or carbon dioxide gas containing less nitrogen and hydrogen from the bottom of the furnace during blowing, sudden decarburization reactions can be suppressed, and the final stage of blowing can be suppressed. The object of the present invention is to provide a method for producing low-nitrogen, low-hydrogen steel, which is characterized by supplementing the decarburization reaction that weakens in the process.

The present invention will be explained in detail below. First, in the present invention, phosphorus and sulfur in hot metal are reduced to P<0.040 using a CILO-based or Na2CO3-based refining agent.
%, S <0.020%, the hot metal is charged into a converter together with a small amount of sflag. , .

The phosphorus content of hot metal, per ton of molten steel) is 5 to 50 (6) )! Lime (quicklime, limestone, calcium ferrite, etc.) is charged to form a considerable amount of slag, and the V
) 0.2 Nm /Ton=Min preferably 0.0
Acid is blown using a top blowing lance while blowing high purity argon or carbon dioxide gas at 3 to 0.1 ONm3/Ton-Min.

If the amount of slag is too small, the generation of fumes will increase, and furthermore, it will become difficult to coat the slag, which is essential for furnace body management. On the other hand, if it is too large, the purpose of reducing moisture entering the converter cannot be sufficiently achieved, so the maximum amount is 50 kg/Ton.
- Limited to 8 tesl.

At this time, if the phosphorus content of the hot metal is high, the amount of lime charged will be large, so reduce the amount of sflag used, and add sintered ore with a low moisture content during blowing to activate the decarburization reaction. It is desirable to promote the release of hydrogen to the outside of the system.

Furthermore, a converter with a tap hole opening/closing device slidably installed in the tap hole and a ladle with a lid installed through the molten steel communication pipe are used in combination to perform sealed steel tapping where the atmosphere is shut off. This is desirable.

Further, it is desirable that the hydrogen and nitrogen content in the alloy used as an additive component be as low as possible.

Next, an example of the present invention will be shown.

Prior to charging hot metal, scrap equivalent to 5 tons of the charging amount was charged into the converter 1, and then treated with a CaO-based refiner to desiliconize, dephosphorize, and desulfurize P = 0.020%. S=0.
0.15% low silicon, low phosphorus, and low sulfur pig iron was charged into the converter. The molten steel was blown using D7 kg of quicklime per ton of molten steel, and the amount of slag was about 15 kg/Ton-8 teal. Addition of auxiliary materials such as quicklime and sintered ore was completed during the first half of the blowing process.

In addition, high-purity argon gas was supplied from the bottom of the converter at a rate of 0.03 Nm3/Ton-Mln during the first half of blowing, and at a rate of 0.03 Nm3/Ton-Mln during the second half.
It was blown into the molten metal at a rate of 1 ONm3/Ton-Min. For molten steel after blow-stopping, a converter 1 is provided with a tap hole opening/closing device 2 in the tap hole, and a lid 4 is installed through the molten steel communication pipe 3.
Sealed steel tapping was carried out in combination with a ladle 5 having a ladle 5.

That is, after finishing blowing and before tapping the steel in the converter, the tapping hole is closed and the furnace body 1 is tilted to a substantially horizontal position.

The inside of the ladle 5 is replaced with a gas having low nitrogen or hydrogen content, such as argon, and further argon is blown into the ladle 5. Align the molten steel communication pipe 3 with the tapping hole and ladle lifting device (not shown)
After the steel is crimped onto the lower surface of the opening/closing device 2 using the tapping hole opening/closing device 2, the tapping hole opening/closing device 2 is opened to tap the tap in a state where contact between the tapping flow and the atmosphere is almost completely cut off. At the final stage of steel tapping, alloy was added through the alloy chute 6 whose interior had been previously replaced with argon to adjust the composition.

The nitrogen and hydrogen contents and refining costs in the ladle self-molten steel according to the present invention were determined by using the conventional converter blowing method (A method) using ordinary hot metal and the ordinary hot metal. Blowing method (
The effect was shown in comparison with Method B).

Sealed tapping is particularly effective for medium and high carbon steels where the oxygen content in the molten steel is low; however, in the case of low carbon steel, when the oxygen content in the molten steel is high, it can be used instead of sealed tapping. Even if the steel is tapped in an undecarburized state, the pickup of hydrogen and nitrogen will not be as large as in the case of medium- to high-carbon steel.

Figure 2 shows the evaluation of N and H values after component adjustment in the conventional methods (methods A and B) and the present invention based on the method A (9). ) compared to the law
This shows that the value decreased by 25% and the H value decreased by 20%, indicating that both the nitrogen and hydrogen values decreased significantly. In addition, Figure 3 shows a comparison of the refining costs of the conventional (methods A and B) and the method of the present invention. It was able to bring about great effects, such as making it possible.

The present invention is constructed as described above, and the amount of slag produced when charging the refining auxiliary material is suppressed to a small amount to the extent that it is possible to prevent the generation of fumes and coat the furnace lining with slag. By performing metallurgical operations such as suppressing the sudden decarburization reaction by injecting low-nitrogen, low-hydrogen stirring gas from the steel, it is now possible to produce low-nitrogen, low-hydrogen steel at low cost and efficiency, which was extremely difficult in the past. The resulting effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic overall configuration diagram used for carrying out the present invention, and FIG.
The figure is a comparison diagram of N and H after adjusting the composition (10) of the conventional method (method A, method B) and the present invention.
Fig. 3 is a relative comparison diagram of the refining costs of the present invention. Patent Applicant Nippon Steel Corporation Agent Ozeki Kazuyuki Wainu (11) Law 1 Ha and Ougi 2 Koku 3

Claims (2)

[Claims] (1) When blowing hot metal that has been previously dephosphorized and desiliconized in an oxygen-blown converter, the amount of lime added is determined according to the phosphorus content in the hot metal, and is 5 to 50 kg/unit weight of molten steel.
While generating slag of Ton 5 Teel,
A method for producing low nitrogen, low hydrogen steel, which comprises blowing a low nitrogen, low hydrogen, high purity gas or a high purity mixed gas such as argon or carbon dioxide at a rate of 0.2 Nm3/'ron-Min or less from the bottom of the furnace. (2) When blowing hot metal that has been dephosphorized and desiliconized in advance in an oxygen-blown converter, the amount of lime added is determined according to the phosphorus content in the hot metal, and the amount of lime added is 5 to 50 kg per unit weight of molten steel.
At the same time as generating slag of 1.5 ton, 5 steel, low nitrogen, low hydrogen, high purity gas such as argon or carbon dioxide or high purity mixed gas of 0.2 Nm3/'I'on -Min or less is blown from the bottom of the furnace. 1. A method for producing low nitrogen and low hydrogen steel, which is characterized in that the steel is tapped using an air cut-off device between the tap hole of the converter and the ladle.