JPH0559424A - Method for producing high cleanliness steel - Google Patents

Abstract

PURPOSE:To easily produce a low Cr clean steel by blowing oxygen-containing gas into molten steel in a furnace and also suitably adjusting temp. of the molten steel and T-Fe content in molten slag at the time of producing the low Cr clean steel by using a furnace producing the Cr-containing steel. CONSTITUTION:By using the metal refining furnace contaminated with Cr caused by production of alloy steel containing much Cr content, steel scrap, etc., for raw material is melted and Fe2O3-containing raw material of scale, etc., is added and also, the pure oxygen gas or the oxygen-containing gas is blown into the molten steel for raw material. The Fe2O3 in the molten slag is made to strong oxidizing property of >=30% as the T-Fe and also, C, Si and Cr in the molten steel are refined to the oxidized-removal oxidizing force of the gaseous oxygen. The ratio (Cr)/[Cr] of the Cr content (Cr) as Cr2O3 in the molten slag to the Cr content [Cr] in the molten steel rapidly becomes large when the temp. of molten steel is <=1650 deg.C, and de-Cr reaction is promoted. After preventing restoration of Cr in the molten slag into the molten steel by removing the molten slag containing much (Cr), the molten steel temp. is risen and the high purity molten steel containing <=0.1% [Cr] is stably tapped off from the refining furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-cleanliness steel using a furnace in which chromium-containing steel is produced.

[0002]

2. Description of the Related Art Generally, when melting steels having greatly different components in the same furnace, contamination of molten steel between heats poses a problem. Although measures have been taken to prevent molten steel contamination, it has been difficult to completely remove trace components. Even when using a furnace in which high-chromium steel such as stainless steel is smelted, it is not easy to smelt high-cleanliness steel from which chrome is removed because chromium is inevitably mixed in the molten steel.

[0003]

DISCLOSURE OF THE INVENTION The present invention uses a furnace in which chromium-containing steel, which is difficult to avoid contamination with molten steel due to chromium, is melted, and [Cr] ≦ 0.1% of high cleanliness steel is efficiently produced. The challenge is to provide a refining method for manufacturing.

[0004]

Means and Actions for Solving the Problems Crude molten steel for producing high cleanliness steel is produced by mixing scrap iron or the like with predetermined components and melting it in an arc type electric furnace, for example. Even when a material containing no chromium is used as a compounding raw material, when a furnace in which chromium-containing steel is smelted is used, about 1% of chromium is mixed in the crude molten steel. In the dechromization method of the present invention, crude molten steel is charged into various refining furnaces such as a converter, a slag material is added if necessary, and oxygen or a gas containing oxygen is blown to oxidize C, Si or the like. Chromium is oxidized and removed together with the components that can be removed by the reaction to 0.1% or less.

In the present invention, in order to efficiently carry out the dechromization, the temperature during refining is controlled to 1650 ° C. or lower, and at the same time, T-Fe in the slag is controlled to 30% or higher. Generally, the dechromation reaction is represented by the following formula. 2Cr + 30 = Cr ₂ O _{3 Since} lowering the molten steel temperature acts to accelerate this reaction,
The lower the molten steel temperature, the more advantageous. FIG. 1 shows the relationship between the molten steel temperature at the end of the oxidation step and the dechromization rate (Cr) / [Cr].

As shown in FIG. 1, (Cr) / [Cr] increases with a decrease in molten steel temperature, and the tendency is remarkable especially at 1650 ° C. or lower. Therefore, the molten steel temperature is 16
It is necessary to set the temperature to 50 ° C or lower. Further, since T-Fe in the slag reduces the activity of chromium oxide produced by the dechromization reaction in the slag, (Cr) / [Cr] improves as T-Fe increases. Figure 2 T during slag
The relationship between -Fe and the dechromization rate (Cr) / [Cr] is shown.

As shown in FIG. 2, (Cr) / [Cr] increases with an increase in T-Fe, and the molten steel temperature is 1650 ° C.
In the following cases, the tendency is particularly remarkable when T-Fe is 30% or more, and therefore it is necessary to set T-Fe to 30% or more.

Removal of components such as C, Si and Cr in the oxidation step is a reaction accompanied by exothermic heat of oxidation, and the same applies to the oxidation of iron for increasing T-Fe in slag.
Therefore, the molten steel temperature tends to rise as refining proceeds. Therefore, by supplementing a part of oxygen necessary for the oxidation reaction with a solid oxygen source containing iron oxide, it becomes possible to advance the oxidation reaction while controlling the molten steel temperature by utilizing the cooling effect. In particular, the use of iron oxide such as iron ore as a solid oxygen source not only facilitates molten steel temperature control because the endothermic effect of the dissolution and decomposition reaction of iron oxide can be utilized, but the iron oxide causes T-in the slag. Fe can also be increased.

If the molten steel temperature required in the reduction step after the oxidation step and further in the casting step thereafter is higher than the temperature at the end of the oxidation step, the molten steel temperature is changed to a higher temperature in the oxidation step to carry out the reduction or desulfurization treatment. The means for ensuring the necessary temperature is generally adopted. However, when performing melting of low chromium steel, it is necessary to keep the temperature of molten steel low in the oxidation step because the dechromization reaction is hindered by raising the temperature of molten steel. After carrying out the oxidation process for dechromization, the dechromization reaction is carried out by performing a forced slag to prevent the chromium from returning to the steel and then providing a heating period to raise the temperature to the required molten steel. It is possible to secure the required molten steel temperature without inhibiting the above.

As described above, the Cr removal treatment according to the present invention is applied to the crude molten steel, whereby [Cr] ≤0.1.
% Low chromium steel can be easily manufactured.

[0011]

EXAMPLES Examples of the present invention will be shown below. Crude molten steel is produced in an arc type electric furnace, and 60 tons A are produced using this crude molten steel.
Invar (36% Ni steel) was melted in an OD furnace. The results are shown in Table 1. Tests No. 1 to No. 5 are examples of the present invention, in which oxygen and Ar gas were blown into the molten steel, and at the same time the molten steel temperature was controlled to about 1650 ° C. or lower, while T-Fe ≧ 3.
Oxidation treatment was performed to form 0% slag. Due to this oxidation step, chromium in molten steel is 0.0
It was possible to reduce the amount to 7% or less and the product [Cr] to 0.1% or less.

[0012]

[Table 1]

In Table 1, Test No. 6 and Test No. 7 show comparative examples. As seen in Test No.6, TF in slag
By increasing e to about 59%, chromium in molten steel is 0.08
%, But since the molten steel temperature is high, the smelting time is approximately doubled, resulting in a marked decrease in productivity. Also test N
In o.7, the results of refining with the molten steel temperature at 1610 ° C and T-Fe at 23% are shown.
Since the e is low, dechromization is insufficient even if smelting is performed for a time equivalent to that of test No. 2, and chromium in steel after smelting is 0.13
%, The product Cr was 0.17%, and could not be made 0.1% or less. In addition, the furnace body refractory damage index shows the amount of melting loss in other examples when the amount of refractory melting in Test No. 1 is 1, and the present invention example is a comparative example. It is only 1/5 to 1/25 times the damage to the furnace refractories.

[0014]

By implementing the present invention, [Cr]
High cleanliness steel of ≤0.1% can be efficiently produced using a furnace in which chromium-containing steel is melted. Conventionally, in the melting of low chromium steel, a large amount of oxygen is blown into the molten steel in order to oxidize and remove chromium. For this reason, the dechromization reaction was hindered by the rise in the molten steel temperature, and it took a long time for the melting. Moreover, the damage to the refractory body of the furnace body was also large due to the rise in molten steel temperature and the long-term melting. On the other hand, in the present invention, by controlling the molten steel temperature to the low temperature side, it becomes possible to efficiently carry out the dechromization reaction, so that the melting time can be shortened. As a result, it is possible to prevent damage to the refractory body of the furnace body and also to significantly improve productivity. Further, when inexpensive iron ore is used as the oxygen source, the smelting cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the molten steel temperature and the chromium removal rate (Cr) / [Cr], and FIG. 2 is T-Fe in the slag and the chromium removal rate (C).
It is a figure which shows the relationship of r) / [Cr].

Front page continuation (72) Inventor Yanagi Katshiro 3434 Shimada, Hikari City, Yamaguchi Prefecture Inside the Nippon Steel Corporation, Nippon Steel Corporation (72) Inventor Sumimi Yamada, 3434 Shimada, Hikari City, Yamaguchi Prefecture Shin Nippon Steel Hikari Steel Works Co., Ltd.

Claims (3)

[Claims] 1. When producing a high-cleanliness steel having a weight percentage of [Cr] ≦ 0.1% by using a furnace in which chromium-containing steel is produced, oxygen or a gas containing oxygen is added to the molten steel. In the oxidation step of oxidizing and removing C, Si, Cr, etc. in the steel by blowing, the molten steel temperature is controlled to 1650 ° C. or lower, and the T-Fe in the slag is controlled to 30% or higher. Method of melting cleanliness steel. 2. The melting method according to claim 1, wherein a solid oxygen source containing iron oxide is added in the oxidation step. 3. The refining method according to claim 1, wherein after the oxidation step, a heating step for adjusting the molten steel temperature is provided subsequent to the slag step for discharging the generated slag out of the system. Method for melting high-cleanliness steel.