JPH03104813A - Production of low nitrogen steel - Google Patents

Abstract

PURPOSE:To rapidly produce a low nitrogen steel at a low cost by adding a deoxidizer to a molten steel after the conclusion of blowing in a converter, tapping the molten steel while protecting it by means of a CO2 gas, etc., and directly delivering the molten steel to continuous casting equipment. CONSTITUTION:Prescribed amounts of metallic Al are thrown and added into a molten steel after the conclusion of blowing in a converter to carry out the deoxidation of the molten steel. An atmosphere in the region through which the tapping stream of the above molten steel is allowed to pass is previously substituted by Ar gas, He gas, CO2 gas, CO gas, etc., and then, the molten steel is tapped while being protected by means of the substituted gas and is directly delivered to continuous casting equipment to undergo continuous casting. By this method, [N] picking up can be effectively prevented though the molten steel is oxidized, and the low nitrogen steel can be rapidly obtained at a low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a low-nitrogen steel that reduces [N] in molten steel, and particularly relates to a method for producing molten steel for continuous casting of thin plate slabs. This article relates to a wide range of manufacturing methods for low nitrogen steel.

[Prior Art] In recent years, low-nitrogen steel has come to be used for surface-treated steel sheets such as tin plates and outer panels of automobile bodies, and there is a demand for technology for rapidly and stably manufacturing this type of steel sheet. In order to continuously cast thin slabs for low-nitrogen steel sheets, from the converter process to the casting process, contamination of the molten steel by nitrogen gas in the atmosphere, that is, preventing [N] pick-up, is necessary to reduce the nitrogen content of the molten steel. It is necessary to control the amount.

The conventional method for manufacturing low nitrogen steel involves tapping molten steel in a converter furnace in an undeoxidized state, and deoxidizing it in a ladle refining process (processing such as LF method, RH degassing refining method, etc.). After adjustment, continuous casting is performed. The reason why converter molten steel must be tapped without being deoxidized is because when the tapped molten steel is deoxidized, the amount of dissolved oxygen decreases, and the tapped flow easily comes into contact with [N] pickup. It is.

[Problems to be solved by the invention] However, in the conventional manufacturing method of low nitrogen steel,
Between the converter process and the casting process, a stop is made at a ladle refining facility to deoxidize the molten steel, so the lead time required for melting is long. It is also disadvantageous from the viewpoint of temperature compensation of molten steel. Therefore, there is a drawback that the manufacturing cost increases as a whole.

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 manufacturing low-nitrogen steel that can manufacture thin plate slabs for continuous casting of low-nitrogen steel at low cost.

[Means for solving the problem] In order to prevent re-oxidation of molten steel extracted from a converter, the inventors
Developed and commercialized oxidation-free steel tapping equipment.

Special application Hei 1. According to the non-oxidation steel tapping apparatus described in No. 96320, the area through which the tapping flow passes is shielded, and molten steel can be tapped while being shielded from the atmosphere.

The inventors focused on the functions of such an oxidation-free steel tapping device and used this device to effectively prevent [N] big-up.
I: We have conducted various studies on the inexpensive production of thin plate slabs for continuous casting of low nitrogen steel by deoxidized steel extraction, and have found that considerable effects can be expected.

In the method for manufacturing low nitrogen steel according to the present invention, when a deoxidizing agent is added to molten steel in a converter to produce deoxidized steel, the atmosphere in the region through which the tapped steel flows is changed to an inert gas, carbon dioxide gas, or The method is characterized in that carbon monoxide gas is replaced with one or more types of gas, the molten steel is tapped while being protected by the replacement gas, and the tapped molten steel is directly sent to continuous casting equipment for continuous casting. . In this case, it is preferable to use an inert gas such as argon gas or helium gas, or CO2 gas or CO gas alone, or a mixture of two or more of these gases as the replacement gas, and use CO2 gas alone. is most preferable.

[Function] In the method for manufacturing low nitrogen steel according to the present invention, since the molten steel has already been deoxidized when it is tapped from the converter, it is possible to continuously cast the tapped molten steel as it is. At this time, the deoxidized tapped steel stream is sealed with a replacement gas such as CO2 gas to prevent [N] surprise during tapping, so that low nitrogen steel with the desired composition can be obtained.

[Example] Hereinafter, with reference to the attached drawings, examples of the present invention will be described. Examples will be explained in detail.

A large molten steel ladle is placed in front of the converter to receive the molten steel being tapped. The converter is equipped with a non-oxidation steel tapping device. The non-oxidized steel tapping device has a shielding member that allows airtight communication between the tapping port of the converter and the receiving port of the molten steel ladle. The upper end portion of the shielding member is formed to slide against the tapping port. A gas pipe penetrates a part of this shielding member and opens into the tapping flow passage area. The proximal end of the gas pipe is connected to a CO2 gas supply source equipped with a flow rate control valve.

The molten steel ladle is mounted on a traveling trolley. The rails of the running bogie extend from the converter plant to the foundry. A continuous casting machine is installed in the foundry, and the molten steel ladle is lifted above the casting machine by a crane.

Next, with reference to FIG. 1, a case will be described in which a thin plate slab for continuous casting of low nitrogen steel is manufactured.

At the end of blowing, the carbon concentration of the molten steel is measured using a sublance, and the end point is determined based on the measured value.

At the end point time, the blowing of oxygen gas from the main lance is stopped and the blowing is completed. The molten steel at the end of blowing is [
C] The amount is about 400 ppm, [○] The amount is about 600 p
pm, [N amount is about 10 to 15 ppll1, and the temperature is about 1610°C (Step 11).

A predetermined amount of aluminum metal is added to the molten steel in the converter.
to deoxidize the molten steel. Through this aluminum deoxidation treatment, the molten steel temperature rises to approximately 1650°C and [0
] amount decreases to about 1 ppm (Wang Cheng) 2).

A shielding member of the non-oxidation tapping equipment is attached to the molten steel ladle, and the equipment is kept waiting at a predetermined position in front of the converter. The converter is tilted, and the tapping port is communicated with the opening at the upper end of the shielding member.

CO2 gas is supplied from the gas pipe to the inside of the shielding member, and the atmosphere in the tapping flow passage area is replaced with CO2 gas.

Next, the tap hole is opened to start tapping the steel. At this time, since the output fI4 flow passage area is filled with CO2 gas,
Even though the molten steel has been deoxidized, [N] pickup is effectively prevented (step 13).

When tapping is stopped, the converter is returned to its upright position and the molten steel ladle is removed from the converter factory. The molten steel ladle is delivered to the foundry, lifted above the continuous casting machine by a crane, and loaded onto the ladle truck. A molten steel pot is placed directly above the tundish, and molten steel is cast into the mold through the tundish. The [N] fA of the molten steel during casting is approximately 15 ppIi. This produces a thin slab of low nitrogen steel.

According to the above embodiment, since intermediate RH degassing treatment, LF refining treatment, etc. can be omitted, low nitrogen steel can be manufactured quickly and at low cost.

It also becomes possible to lower the converter tapping temperature than before.

In addition, in the above embodiment, a case was explained in which a deoxidizing agent is added to the molten steel before the start of tapping, but the present invention is not limited to this, and it is possible to add a deoxidizing agent to the molten steel flow. It may be added directly to deoxidize.

In addition, in the above embodiment, CO2 is used as the replacement gas for shielding.
Although gas is used, the present invention is not limited to this, and other gases such as argon gas, helium gas, and CO gas may be used alone or in combination.

[Effects of the Invention] According to the present invention, deoxidized steel is tapped using a non-oxidation tapping device, thereby making it possible to omit the deoxidation treatment in the conventional ladle refining process. Since the ladle refining process exists between the converter process and the casting process, the overall manufacturing time can be shortened, and low nitrogen steel can be manufactured quickly and at low cost. Additionally, it is possible to simplify logistics within the steel factory. As a result, it is expected that significant cost reductions will be realized in the integrated production system for low nitrogen steel.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method for manufacturing low nitrogen steel according to an embodiment of the present invention.

Claims (1)

[Claims] When deoxidized steel is tapped by adding a deoxidizing agent to the molten steel in the converter, the atmosphere in the area through which the tapped steel flows is filled with one or more of inert gas, carbon dioxide gas, or carbon monoxide gas. A method for producing low-nitrogen steel, which is characterized in that the molten steel is discharged in a state in which the molten steel is protected by the purge gas, and the tapped molten steel is directly sent to a continuous casting facility for continuous casting.