JPS5831023A - Melt-manufacturing method of very low carbon steel - Google Patents

Abstract

PURPOSE:To refine very low carbon steel by a VAD furnace only, by heating molten steel in a pressure-reduced state, and blowing oxygen toward the surface of the molten steel in a ladle through an oxygen lance which has been made to pass through the side wall of a vacuum vessel. CONSTITUTION:The inside of a vacuum vessel 1 is held in a pressure-reduced state, the inside of molten steel 5 is bubbled by blowing in inert gas 7 such as Ar or N2, etc. from the lower part of a ladle 2, and an arc is generated through an electrode 3, by which the molten steel 5 is heated. On the orther hand, decarburization is executed by blowing oxygen toward the surface of the molten steel 5 from an oxygen lance 8 inclined through the side wall of the vessel 1. When blowing of oxygen is unnecessary, for instance, at the time of heating, the lance 8 is moved backward. The lance 8 is burned out when it is used for a long period of time, therefore, it is advanced by that portion. Also, according to this method, it is also possible to execute a dephosphorization treatment. In this case, a slag for dephosphorization is thrown into the molten steel 5 through a slag throw-in hopper 6, and oxygen blow-refining is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of melting steel using a VAD furnace.

VAD furnaces were initially developed for the purpose of dehydrogenation, but their scope of application has expanded to include denitrification, decarburization, deoxidation, and dephosphorization, and they now play an important role as one of the manufacturing methods for high-grade steel. occupies .

By the way, when trying to manufacture ultra-low carbon steel with a C content of 0.02% or less, if you try to refine it in a converter or electric furnace,
Despite the problems of low tapping yield and severe melting damage of large furnace bodies, it has been difficult to obtain a stable carbon content. I am getting . One example is a method in which vacuum decarburization is performed while supplying oxygen gas to the upper surface of molten steel in a VOD furnace. However, since the VOD furnace itself does not have heating equipment, in order to compensate for the temperature drop during refining, steel must be tapped at a high temperature from the mother molten steel melting furnace (for example, a converter), and decarburization due to the temperature drop is required. There are also time constraints. As another example, a VAD-VOD process is known in which a VAD furnace and a VOD furnace are combined in order to compensate for the temperature drop. It has the disadvantage that it takes a long time and the heat loss during that time is also large.

On the other hand, since VAD furnaces have heating equipment, there are no problems in temperature control of molten steel, and therefore they are originally suitable for melting ultra-low carbon steel. However, in decarburization in a VAD furnace,
The necessary oxygen depends on the dissolved oxygen in the mother molten steel and the oxygen in the slag added from the outside, so if the amount of carbon in the mother molten steel is high, oxygen deficiency will occur, making it difficult to produce stable ultra-low carbon steel. In addition, if a lack of oxygen is expected, it is necessary to blow down the carbon content in the mother molten steel melting furnace in advance, but blowing down will reduce the tapping yield of the mother molten steel. There is also the problem that the refractories of the base molten steel melting furnace become more susceptible to erosion.

The present invention solves the above-mentioned conventional problems all at once.
The purpose is to provide a melting method that does not require special blowing down of carbon in a base molten steel melting furnace and can melt steel of a desired quality using a VAD furnace alone.

To achieve this object, the present invention provides a method for melting steel in the ladle by installing a ladle in a vacuum container having a heating device and heating it under reduced pressure. The present invention differs from the prior art in that oxygen is blown into the surface of the molten steel in the ladle through an oxygen lance that is In this case, the oxygen lance is passed through the side wall of the vacuum container instead of being lowered from the top.Next, the present invention will be explained based on FIG.
This figure shows an outline of an AD furnace. 1 is a vacuum container, and a ladle 2 is installed inside the vacuum container. The inside of the vacuum container 1 is maintained at a reduced pressure state by a vacuum pump (not shown). A three-phase arc electrode 3 is arranged in the upper part of the furnace, and a slag charging hopper 06, which can freely move up and down through the ladle lid 4 toward the surface of the molten steel 5, is also connected from the bottom of the ladle 2. In the present invention, an inert gas 7 such as Ar or nitrogen is blown into the container to perform bubbling. In the present invention, an oxygen lance 8 is provided through the side wall of the vacuum container 1 at an angle toward the surface of the molten steel 5. Ru. The gap between the oxygen lance 8 and the side wall of the vacuum vessel 1 is sealed with an O-ring 9 made of heat-resistant rubber, and the oxygen lance 8 is allowed to move forward and backward.

During melting, the inside of the vacuum vessel 1 is maintained in a reduced pressure state, the molten steel 5 in the ladle 2 is bubbled, and the electrode 3 is
An arc is generated through the molten steel 5 to heat the molten steel 5. In this way, oxygen is blown from the oxygen lance 8 toward the surface of the molten steel 5 to achieve decarburization.Also, when oxygen injection is unnecessary, for example during heating, the oxygen lance 8 is moved back.
) If used for a long period of time, it will melt and damage, so it is better to extend it accordingly.

According to such a melting method, decarburization can be reliably achieved.
To explain this in Figure 2, line A in the figure relies only on dissolved oxygen in the mother molten steel, line B relies on dissolved oxygen in the mother molten steel and the oxygen contained in it by adding slag, and line C It can be seen that ultra-low carbon steel can be easily obtained when oxygen is blown according to the method of the present invention.

By the way, in the present invention, the reason why the oxygen lance 8 is inserted from the side wall is mainly for the sake of equipment. In other words, if you try to point the oxygen lance downward from above, there are electrodes etc. at the top of the furnace and you cannot take up space.Next, the amount of oxygen blown from the oxygen lance 8 is 20ON<
/Il (~70oNrn/H is preferable.The reason is that below 20ONm//H, the oxygen supply is not sufficient, and when it exceeds 70ONm//H, there will be a lot of splash.) Undesirable.

The oxygen supply time is usually preferably 10 minutes to 30 minutes. The present invention is not limited to decarburization, but can also be applied to dephosphorization treatment. In this case, dephosphorization slag is charged into the molten steel 5 through the slag charging hopper 6, and oxygen blowing is performed over 0 or more times. Since the tapping temperature in the mother molten steel melting furnace does not need to be particularly raised, it is possible to prevent melting of the refractories in the mother molten steel smelting furnace, and also to reduce the temperature of the molten steel from the mother molten steel smelting furnace. You don't have to pay special attention to the descent.

In this respect, it is particularly suitable when handling small amounts of molten steel. In addition, since oxygen is supplied during melting, oxygen shortages can be prevented and ultra-low carbon steel can be produced in a stable manner.Also, there is no need to blow down the carbon content more than necessary in the mother molten steel melting furnace. , a decrease in the tapping yield 9 can be prevented. Furthermore, since the oxygen lance for oxygen blowing passes through the side wall of the vacuum container, oxygen can be supplied without interfering with the lifting and lowering operations of the heating electrode.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a VAD furnace for carrying out the method of the present invention;
Figure 2 shows a comparison of decarburization behavior between the method of the present invention and the conventional method.
It is a -0 amount correlation diagram. 1. Vacuum container 2. Ladle 3. Electrode 5. Molten steel 6. Dephosphorization slag input ho, bar

Claims (1)

[Claims] (1) In a method in which a ladle is installed in a vacuum container equipped with a heating device and the steel in the ladle is melted without being heated under reduced pressure, the ladle is heated through an oxygen lance that passes through the side wall of the vacuum container. A method for producing ultra-low carbon steel characterized by blowing oxygen toward the surface of the molten steel.