JPS60106911A - Arc furnace steel making method of chromium steel - Google Patents

Abstract

PURPOSE:To enable stirring by inexpensive and simple means in the stage of melting the raw material for a chromium steel in an arc furnace then performing refining operation in succession thereto by blowing air to the molten steel to stir the molten steel in the reduction period thereof. CONSTITUTION:The raw material for a chromium steel such as a stainless steel is melted by using an arc furnace. The molten steel in the reduction period of the refining operation is stirred by blowing of air thereto in the stage of subjecting the molten chromium steel formed in the arc furnace to the refining operation. The dry air removed of moisture as far as possible (for example, about <=10 deg.C dew point) is used for the air to be blown. The grade of the molten steel is thus satisfactorily maintained and the variance in the grade of the molten steel occurring in the change of weather, season, etc. is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing chromium-containing steel such as stainless steel, and particularly to an arc furnace steel manufacturing method in which melting and refining are performed only in an arc furnace.

As a steel manufacturing method for chromium-containing steel such as stainless steel, scraps of chromium-containing steel raw materials are melted in an arc furnace, and then the molten steel is transferred to an outside furnace refining facility where it is oxidized and decarburized (oxidation stage). Next, a method has been used in which oxides such as chromium oxide are reduced and returned to the molten steel (reduction stage), but conventionally, arc furnace steelmaking involves a series of melting and refining processes performed only in an arc furnace. There are many places where the law is being implemented.

When carrying out such an arc furnace steelmaking method, in the reduction period, after adding a reducing agent such as Fe-8i, 8i→i, etc., the interfacial reaction between the molten steel and puffer fish is promoted and the molten steel is homogenized. In order to achieve this, it is desirable to stir the molten steel, and this is usually done by stirring with electromagnetic stirring equipment, stirring with a pletsuki (stirring rod), or by blowing oxygen gas or the like into the molten steel.

However, electromagnetic stirring equipment is very expensive, and stirring using a platter is not only laborious but also requires a long time to obtain a sufficient stirring effect. Furthermore, when oxygen is blown in, there is a drawback that the reduction reaction is inhibited and the yield of Or and other alloying elements such as 8i and Kn is reduced.

The present invention has been made against the background of the above-mentioned circumstances, and its purpose is to produce chromium-containing steel in an electric arc furnace by stirring molten steel during the reduction period by an inexpensive and simple means. It is about providing law.

In order to achieve this object, the present invention provides a method for melting a chromium-containing steel raw material using an arc furnace, and subsequently performing a refining operation on the formed chromium-containing molten steel in the arc furnace. The molten steel was stirred during the reduction stage of the refining operation by blowing air into the molten steel.

In this way, molten steel can be stirred extremely simply and effectively in the same way as conventional oxygen stirring, and the negative effects on the reduction reaction are alleviated compared to oxygen stirring, and the yield of alloying elements such as Cr is reduced. It is both improved and economical.

In addition, in the case of oxygen stirring, F added as a reducing agent
Since e-8i, 81-Mn, etc. partially react with the blown oxygen, a large amount of reducing agent was required, but since the amount of oxygen supplied was reduced by using air, the amount of reducing agent consumed was reduced. It can be reduced.

Here, it has been conventionally believed that using air to stir molten steel causes nitrogen gas, hydrogen gas, etc. in the air to enter the molten steel and deteriorate the quality. However, as shown in the examples below, the nitrogen and hydrogen concentrations in the molten steel do not change much compared to oxygen agitation, and instead tend to decrease. It is noteworthy that this was even recognized. The theoretical analysis of this phenomenon will be left to future research.

In addition, by using air in this way, the calorific value is lower than when oxygen is used, but by adjusting the cold material used or the input power, etc., the molten steel temperature can be lowered. can be maintained properly.

Here, the chromium-containing steel raw materials to which the present invention can be applied include special steel characterized by stainless steel, alloy steel, etc.
Any material containing chromium may be used, and they generally have a Cr content of about 12% to 25%.

After melting these chromium-containing steel raw materials in an arc furnace, oxygen is blown into the molten steel in the arc furnace to oxidize impurities such as carbon and lead and (H) (N) gases. It will be removed. At this time, alloy components such as chromium are also oxidized and melted into the slag, so a reducing agent is then added to return the necessary alloy components to the molten steel. Kono reducing agent and t, -C are Fe-8i, Fe
-Mn.

81-Mn, A1, etc. can be used, but they may be appropriately adopted in consideration of their reducing power, the type of oxide to be reduced, etc.

Here, in order to promote the reaction between the reducing agent and oxides and the interfacial reaction between the slag and the molten steel, air is blown into the molten steel to stir it. Although it is convenient to take in air from the existing industrial air piping installed in the interior, a new compression pump or the like may be installed to blow in air from the atmosphere. Note that the air pressure at this time varies depending on the degree of agitation of the molten steel, but it is sufficient that it is at least at a level that causes the interface between the molten steel and slag to flow. May be used.

In addition, before blowing such air into the molten steel, it is passed through a drying device such as an air dryer to dry it to the extent that water vapor components in the air will not enter the molten steel and affect the quality of the molten steel. Dry air, e.g.
By using dry air at about 0° C. or lower, the quality of molten steel can be maintained well, and variations in the quality of molten steel due to changes in weather, seasons, etc. can be prevented. Note that the use of dry air is based on the consideration that the water vapor component in the air does not affect the molten steel, and it is not necessarily necessary to use dry air when carrying out the present invention.

When blowing air as described above, an air inlet may be provided at the bottom or side wall of the arc furnace and the air may be blown directly into the molten steel, or a blowing pipe may be inserted from the top of the arc furnace lid or side wall. Alternatively, the blowing pipe may be inserted and blown from above the molten steel, or the tip of the blowing pipe may be inserted into the molten steel and blown into the molten steel. An example of this is shown in FIG.

In the figure, an arc is generated between an electrode 12 and a chromium-containing molten steel 14 in an arc furnace 10, and a slag 1 containing oxides such as chromium oxide is placed above the molten steel 14.
6 is floating. Further, a lance pipe 20 is inserted into the upper part of the furnace wall 18 of the arc furnace 10, and is used to blow oxygen during the oxidation period and to blow air for stirring the molten steel during the reduction period. Note that the position of the tip of the lance pipe 20 can be moved up and down as appropriate depending on the stage of refining during oxidation and reduction. The figure shows the stirring state due to air blowing during the reduction period, and shows the case where the tip i of the lance pipe 2 (1) is inserted into the molten steel.

Next, one embodiment of the present invention will be described in order to clarify the present invention more specifically. It goes without saying that the present invention is not limited in any way by the description of the embodiments.

Example 1 Stainless steel flow material was used as a raw material for chromium-containing steel, and it was melted in an arc furnace, and then oxygen was continuously blown in to adjust the components of carbon, etc. in the molten steel, and remove harmful gases and impurities. (During the oxidation period, 51-Mn, a lower element, is used as a reducing agent to reduce chromium oxide etc. in the slag.

Fe-8i was introduced (reduction period).

At this time, in order to promote the interfacial reaction between the slag and molten steel, a commercially available air dryer was used to dry the slag at a dew point of approximately 5°C.
Blowing amount of industrial air that has been dried to a certain degree is 8.
The molten steel was stirred by blowing into the molten steel twice for 2 minutes each at Nm/min.

In addition, in order to investigate the temperature change of the molten steel accompanying this stirring, the molten steel temperature before and after stirring was measured.

Thereafter, the alloy was adjusted and the steel was tapped into steel, and the chromium and silicon contents were measured, as well as the oxygen, nitrogen, and hydrogen concentrations in the molten steel.

For comparison, a case was also conducted in which argon stirring and oxygen stirring were performed instead of air stirring.

First, FIG. 2 shows the results of calculating the yield from the chromium content. Taking the average values of these results, the chromium yield is approximately 89.0% in the case of oxygen stirring, approximately 90.9% in the case of air stirring, and approximately 91.1% in the case of argon stirring.
%, and air agitation according to the present invention is about 0.2% inferior to argon agitation, but about 1% inferior to oxygen agitation.
．． This represents an improvement of 9%.

Next, regarding oxygen stirring and air stirring, the results of measuring the oxygen concentration, nitrogen concentration, and hydrogen concentration in the molten steel tapped into the ladle are shown in FIGS. 3 to 5.

Then, taking the average value of each of these results, the oxygen concentration in the case of oxygen stirring is approximately 107 pp
m, and in the case of air agitation, it is about 105 ppm, which shows that there is almost no change. Furthermore, the nitrogen concentration was approximately 450 ppm in the case of oxygen agitation and approximately 495 ppm in the case of air agitation, which was an unexpected result in that air agitation was actually lower.

Regarding the hydrogen concentration, in the case of oxygen stirring, it is about 5.3cc/
Approximately 8.5cc/100 for 100g 1 air agitation
g, and the latter air agitation has a lower result.

Table 1 also shows the results of calculating the yield of silicon introduced as a reducing agent, comparing oxygen agitation and air agitation. In addition, the silicon yield values in this table are
This is the average value of 80 times of oxygen stirring and 20 times of air stirring. In addition, the results of measuring changes in temperature, nitrogen concentration, and hydrogen concentration of molten steel due to stirring will also be shown.

As is clear from Table 1, air agitation improved the silicon yield by about 6.2% compared to oxygen agitation.

As a result, the amount of silicon added as a reducing agent is reduced, and when silicon is included as an alloying element, the amount of silicon added at the time of alloy adjustment is reduced.

In addition, the temperature change in molten steel due to stirring increases in the case of oxygen stirring, but slightly decreases in the case of air stirring, but this level of humidity change does not interfere with temperature adjustment. It does not occur. In addition, it can be seen that there is almost no difference in the amount of change in nitrogen concentration and hydrogen concentration between oxygen agitation and air agitation.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an arc furnace for explaining air agitation according to the method of the present invention. FIG. 2 is a histogram showing a comparison of the chromium yield when the method of the present invention is implemented and when the conventional method is implemented. Figures 8 to 5
The figure shows the element concentration of molten steel tapped during rad μ, and
Use the method of the present invention for nitrogen concentration and hydrogen concentration! ! This is a histogram showing a comparison between a case where the conventional method is applied and a case where the conventional method is applied. 10: Arc furnace 14: Molten steel (chromium-containing molten steel) 20: Applicant Hunsbaig Daido Special Steel Co., Ltd. Figure 2 Chromium 11 ('mu) Figure 3 51! 1 NeJ Shakyam U (cc/1009)

Claims (2)

[Claims] (1) After melting a chromium-containing steel raw material using an arc furnace, when subsequently performing a refining operation on the formed chromium-containing molten steel in the arc furnace, stirring of the molten steel during the reduction period of the refining operation An arc furnace steelmaking method for chromium-containing steel, characterized in that the steps are performed by blowing air into the molten steel. (2) The arc furnace steelmaking method for chromium-containing steel according to claim 1, wherein the blown air is dry air from which moisture has been removed as much as possible.