JPS6191311A - Refining method of molten steel - Google Patents

Abstract

PURPOSE:To produce a steel contg. N2 at a lower rate at a good yield of a deoxidizing agent by putting the molten steel tapped from a converter without deoxidation into a ladle refining furnace and adding the deoxidizing agent such as Al to the molten steel after removing molten slag therefrom. CONSTITUTION:The pickup of N2 from the inside of the air increases if the content of O2 in the molten steel is low. The molten steel tapped from the converter is therefore tapped together with the molten slag into the ladle refining furnace without subjecting the same to the deoxidizing treatment. Al as the deoxidizing agent is added to the molten steel after the molten slag is removed in the ladle refining furnace. The Al is used for the deoxidation of the molten steel at a high yield without oxidation loss by the molten slag as molten slag does not exist in the molten steel. The pickup of N2 is eliminated as the molten steel is not deoxidized in the stage of tapping from the converter. The deoxidation with high yield of the Al which is the reducing agent is thus made possible and the low nitrogen steel is produced stably at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing molten steel using a ladle refining furnace, particularly a method for producing low nitrogen steel.

[Conventional technology]

Generally, molten steel is produced by blowing it in a converter and then tapping it into a ladle, but at the time of tapping, the temperature is set at around 1630 to 40° C. and temperature compensation is performed.

Furthermore, deoxidized steel is produced by adding deoxidizer 1 ferroalloy at the time of steel tapping. The slag remains in the ladle and is bubbled.

[Problem that the invention seeks to solve]

In general, the adsorption capacity of N varies depending on the O3 content in molten steel, and 0. It is known that the adsorption capacity increases as the amount of . In the conventional method, N2 is used to deoxidize during tapping.
This causes the N in the molten steel to become entangled or to be picked up.
, the content will increase.

Moreover, even if Al, which is a deoxidizing agent, is added, a part of it reacts with the slag and does not contribute to deoxidizing.A! The amount added is larger than necessary. Furthermore, there is a large variation in Alt reacting with slag, and even if a certain amount of Al is added, the amount of deoxidation varies, making it difficult to perform desired deoxidation.

The present invention has been made in view of the above circumstances, and its purpose is to be able to stably obtain low-nitrogen steel, and moreover! This is an advantageous method for producing molten steel in which the amount of addition is small and is stable.

[Structure of the invention]

In the present invention, after extracting undeoxidized steel from a converter and preventing the entrainment and pickup of N, the slag is removed in a ladle refining furnace and then a deoxidizing agent is added. Able to stably deoxidize in small quantities without being affected and with a narrow range of S.
. This is a molten steel refining method that enables A-Al control (0.0151 width).

The present invention will be explained in detail below.

In the first stage of production, undeoxidized steel is tapped from the converter.

If deoxidized at the time of tapping as in the past, nitrogen tends to be drawn in and pick-up occurs, but if the steel is tapped without being deoxidized as in the present invention, the entrainment and pickup of nitrogen is prevented, and as a result, the nitrogen content in the molten steel is reduced. The amount can be reduced.

The slag is then removed in a ladle refining furnace and a deoxidizing agent is added. Since the slag is removed, the deoxidizing agent AA does not react with the slag, and A! The amount added can be kept to the minimum necessary. See you again! Since it is not affected by slag, deoxidation can be performed stably, desired deoxidation can be performed with a predetermined amount of AI added, and narrow range 5ob-AA control (0,015chi) is possible. . in this case,
The slag is preferably removed by a conventional method, for example, by vacuum suction treatment (VSC).

〔Example〕

After removing the slag from undeoxidized ordinary pig (extraction temperature +63o'C) and vacuum adsorption treatment, 1 AA was added to the ladle refining furnace.
．． 20 Klton was added to deoxidize.

The nitrogen content of the obtained raw steel was 15 to 20 pI)m.

On the other hand, in the conventional method, AA is 1.55Kp/
) The nitrogen content of the raw steel was 20 to ao p'pm.

From this, the nitrogen content of the example can be reduced,
Also %A! It can be seen that the amount of AA can also be reduced. Furthermore, it can be seen that the variations in oxygen content in the examples are smaller than in the conventional method.

〔Effect of the invention〕

As explained above, according to the present invention, the nitrogen content is reduced by tapping undeoxidized steel, and deoxidation is performed in a ladle after removing slag, thereby reducing the amount of At deoxidizer per prefecture and increasing the deoxidation rate. Stability can be increased.

Claims (1)

[Claims] A molten steel refining method in which undeoxidized steel is extracted from a converter, slag is removed in a ladle refining furnace, and then a deoxidizing agent is added.