JPS59222511A - Production of high chromium steel by composite blowing converter - Google Patents

Abstract

PURPOSE:To suppress erosion of furnace refractories and to produce economically a high chromium steel by performing blowing in such a way that the flow rate Qb of the bottom blowing gas to be blown into a molten iron through tuyeres and the height H of a lance to top blowing oxygen satisfy a specific relation. CONSTITUTION:A molten high chromium iron 5 is produced by subjecting a molten chromium-contg. iron to oxygen top blowing under gaseous stirring by using a top and bottom blown composite blowing converter 3. The blowing is accomplished in such a way that the flow rate Qb (Nm<3>/min.ton) of the inert gas or neutral gas to be blown from the tuyeres 1 and the height H of a lance 2 for top blowing oxygen (the distance between the bottom end of the lance and the molten metal surface; m), as control factors, satisfy the equation. Then, the concn. of Cr2O3 in the slag at the end point of blowing is 30-40wt% and the erosion of the refractories in the furnace is suppressed by the self-coating effect by Cr2O3 in the slag. At the same time, the excess oxidation of Cr in the steel is prevented and the high Cr steel is obtainable economically advantageously.

Description

Detailed Description of the Invention The present invention (1. The bottom of the furnace is equipped with a tuyere for blowing inert gas or neutral gas and is equipped with a top blowing lance for oxygen blowing.)
It relates to a method for producing high chromium steel using a bottom-blown combined blowing converter, and more specifically, all chromium-containing hot metal in this converter is top-blown with oxygen under gas agitation with a blade of 1 m f at the bottom of the furnace. The self-coding effect of chromium oxide (% Cr2O3) in the slag suppresses the G loss of the refractories in the furnace, while at the same time preventing excessive oxidation of the glue in the steel. Concerning a method for producing high chromium steel using a combined blowing converter.

When high chromium steel is heated,
As it is well known that in the AOD method, argon gas, nitrogen gas, etc. This is achieved by impregnating the Co component with an inert gas.

On the other hand, strong stirring of the hot metal is ensured. Even with oxygen blowing, the hot metal bath as a whole approaches the metallurgical equilibrium between carbon and chromium = oxygen, so decarburization can be achieved while preventing excessive oxidation of chromium. The reaction can proceed. In order to produce high chromium steel using gold, it is preferable to use, for example, a top-bottom blowing composite blowing converter, the outline of which is shown in FIG. This method (top-bottom blowing combined blowing converter method)
In addition, even if the gas injected from the bottom tuyeres is also an inert gas, the FI
'J? ': It requires less oxygen than the EΔOD method, and since oxygen is not supplied from the hearth bottom, it has advantages in terms of the structure of the hearth bottom tuyere and its damage. As long as the stirring is guaranteed, the stirring (companion gas is 1.l [1
Another advantage is that it is not limited to inert gases.

The present invention relates to the further improvement of the manufacturing method of high chromium steel using the double-bottom blowing combined blowing converter method.
The object of the present invention is to suppress the erosion of furnace refractories through the self-coating action of R203) and at the same time prevent excessive oxidation of chromium in the steel, thereby producing high chromium steel economically. As a method to effectively achieve this purpose, the present invention includes a top-bottom blowing combined blowing converter method with a furnace bottom blade of 1 m, J:! :1 Gas flow rate Qb (Nm/min・ton l) for stirring gas blown into the hot metal, lance height I (lower end of the lance
distance at; yn, ) and all control factors, 00104 (■1-0.4)2≧Qb≧0.010
4 By blowing so that the relationship of (H-1,8)2 is satisfied, the (Cr) in the slag at the end of blowing
203) Provides a method for producing high chromium steel using a top-bottom blowing composite blowing converter, characterized in that the control factor is set to the open side 1 so that the concentration is 30 to 40% by weight. The present invention will now be described in detail.

FIG. 1 is a schematic diagram of a two-bottom blown composite blowing converter in which the method of the present invention is carried out, and is equipped with a tuyere 1 for blowing inert gas and neutral gas at the bottom of the furnace, and for oxygen blowing. 1 shows a top-bottom blowing combined blowing converter 6 equipped with a top-blowing lance 2. Gas 4 for stirring the chromium-containing pig iron 5 in the converter 3 is injected into the bottom of the furnace 1 to 6, and pure oxygen is completely top-blown from the top blowing lance 2 while sufficiently stirring the τ chromium hot metal 5. Despite this, the decarburization reaction can proceed.

[F] Figure 2 shows the top-bottom blowing combined blowing converter (hereinafter referred to as
When blowing chromium-containing hot metal using a converter (simply referred to as a combined blowing converter), the flow rate Qb of the blown gas from the bottom tuyere 1 was varied. The end point of
This is in a converter (an old blowing converter that does not perform bottom blowing). As shown in Fig. 2, when the bottom blowing gas I#i and the amount Qbf and y increase (accordingly, as the stirring is strengthened, the same end point [%C]'<A:) is obtained. Possible 1
, it is clear that the acidity of Cr decreases by 6 or more points at the end point (Cr, 0.) in the slag. In particular, the bottom blowing gas flow rate Ql) is [J06 Nm”/mj,n
-ton's implementation results (red stamp data) show that the conventional 1.
■] It was possible to obtain it using the converter method 7, about H17'1,
End point (%Cr203) u decrease. This (1,
In a combined blowing converter, if strong agitation by the bottom blowing gas is guaranteed, the metallurgical equilibrium that exists between carbon, chromium, and oxygen will be reached as a whole in the steel bath, and at the same time the excess acid of chromium will be removed. This shows that it is possible to prevent the decarburization reaction and promote the decarburization reaction.

Although it is possible to melt the desired high chromium steel using this composite blowing converter alone, in combination with this composite blowing converter, it is possible to melt the desired high chromium steel. The desired high chromium steel can also be produced by performing the known finishing smelting process. However, in any case, after carrying out double-bottom blowing in this composite blowing converter, it is possible to recover metal Or by performing chromium oxide (% Cr2O,) in the slag. In this case, the chromium oxide concentration in the end point slag of the top and bottom blowing should be increased to a certain degree rather than simply lowering the Cr203 and damaging the furnace wall arranging material by t/-. By adopting blowing conditions that maintain the (Cr2O:) in this slag within a range of
) is advantageous in utilizing the self-coating knob effect on the furnace wall refractories.

3rd light, the rate of wear of the refractory on the furnace wall when the concentration of chromium oxide (% Or', 0.l) in the end point slag was varied by varying the blowing conditions of the combined blowing converter. Investigation/ζ
This shows the results. From the results shown in Figure 3, it can be seen that when the end point (%Cr2O,,J is less than 6owt%),
As the concentration decreases, the wear and tear becomes more severe,
When the end point (%Cr203) is more than 30% by weight, the melting point and viscosity of the slag increase, and the melting point and viscosity of the slag (%Cr203) are uniformly increased due to the aggressive action of coach 1 on the refractories in the furnace. It would be great if the level of JJJ wear and tear would be reduced.

Therefore, from the viewpoint of wear and tear on the furnace wall refractories of a combined blowing converter, it is preferable to set all blowing conditions so that slag having an end point (%Cr2o3) of 50% by weight or more is formed. However, the higher the end point (%0r203) is, the more burden will be placed on the reduction of (%cr2o3) to metal Or in the next process, and, unfortunately, the self-coating will become excessive. The higher the end point (%CR203) concentration, the better. From this comprehensive perspective, the final point (%Cr203) Fj is 4 at most.
The upper limit should be around 0 weight factor.

In other words, in complex converter blowing, (%
Or203) Adjust the concentration to 30-40% by weight,
It can be said that setting all the blowing conditions is the most preferable from both the viewpoint of maintaining the furnace wall strength and economic refinement.

The inventors have proposed that the chromium oxide (% C
In order to obtain the above-mentioned effect by setting the concentration of r2O3) to 30 to 40%, one of the blowing control factors of top-bottom blowing using this combined converter is to The bottom-blown gas flow rate Qb (Nm″/m1n-ton
) and the lance height H (distance between the lower end of the lance and the hot water surface 1; m) of the top-blown oxygen lance as control factors, and between these two control factors, 0.0104 (H-0, 4)2
≧Qb≧0.0104 (1ζ.

Figure 4 shows the bottom blowing gas flow rate Qb, keeping other conditions constant.
By changing only the lance height H, high chrono steel (18-
The end point (%Cr,
, 03) are different from the results of the present invention, in which changes in From this Figure 4, if all of these are properly controlled using Qb and TI as control factors, then lS, +1, BL')
'iJl-a Seki's % and TCG points (%cr203)
It is clear that it is possible to control the above-mentioned range of 60 to 4 degrees. This (% Cr203) is 60
In order to control and maintain it at ~40% by weight, as the amount of bottom blowing gas is increased, the rough inside (%Cr203) shown in Figure 2 decreases, so to compensate for this, Ic Using the relationship shown in Figure 4, the lance height at of 1 synth for top-blown oxygen is increased, and due to the so-called soft blow effect (%
It is important to perform an operation that slightly increases cr203).

Figure 5] a. Behind the arrangement of the above relationships, 60
This shows the correlation between Q'b and 11 to reach the end point (% Cr20:+) of ~40 fold h1%, and falls within the shaded area between curves F1 and b in Figure 5. YoT
This shows that it is only necessary to control CQb and H. Here, the curve ai, Qb = 0.0104 (H-0,4
12 curve bi, Qb = 0.0104 (H-1
,812, therefore, 0.0104 (H-0,4)2≧Qb≧0.0104
(The relationship of 1-1-1,812 is satisfied, but Qb
(It is good to fully control the blowing.

In implementing the present invention, as shown in FIG. C% C') F0.10 Less than M amount% Door S: f
7J: Vs, J: It is better to blow the sea urchin. Further, it is preferable to fully control the lance height H within the range of 1 to 5177. Within 1 m, the molten steel is physically blown away due to the pure oxygen dienotoxicity of the top-blown oxygen lance, causing a splash problem that causes a decrease in metal yield. It is difficult to obtain a practically sufficient decarburization rate because the steel bath does not freeze sufficiently [7Z] and becomes uneconomical. In addition to inert gases such as a1 argon and helium, nitrogen (
Neutral gases), carbon dioxide, carbon oxide, hydrogen, ammonia, and other gases can be produced.

Example Table 1 shows the bottom blowing gas flow rate (Ql) and lance height H as variable factors using the combined blowing converter shown in Figure 1, and with other conditions constant, the 18-8 system height was The end point [C] and the end point (%Cr201.1) show the wear rate of the furnace wall refractories when chromium 1A is blown.

Example 1 (01 work 2, Qb and H in the table is an example within the scope of the present invention, and in this case, the wear rate of the furnace wall refractory is 0.5 to 0.6 m@/mm/ There was a particular problem with heat:) There was no wear rate.

This is a comparative example outside the scope of the present invention in which Qb and H deviate from the relationship defined in the present invention, and in this case a
In a, the end point (Cr,, o3) is low, but the furnace wall, p
The wear rate of surface J large items is 1.6 to 1.8T.
n1. / It became as high as the heat.

Implementation NfL 5 is also a comparative example outside the scope of the present invention in which Qb and H are outside the relationship specified by the present invention, and in this case, the wear rate of the furnace wall refractory is as low as 0.4 mm/heat. However, the end point (% Cr,,03) is 71i'! l
It was too much.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of a top-bottom blowing combined blowing converter in which the method of the present invention is carried out. Figure 3 shows the relationship between flow rate and end point [%C] and finishing point (% Cr203). Fig. 4 (bottom blowing gas flow rate, lance height and end point (t) when high chromium steel is melted in a C complex blowing converter)
l) Relationship diagram with Cr203), end point (% Cr2
0a l'l: This is a correlation diagram between the bottom blowing gas flow rate controlled to 0 to 40 hY% and the top blowing oxygen month 1 rank lance Takaba. 2. Oxygen” Yu blowing lance,
3... Combined blowing converter, 4... Bottom blowing scum, 5...
・・High chromium hot metal Qb-bottom blowing gas flow Q (Nm3/mj, n-ton
)H...Is the lance height of the top-blown oxygen lance +? j
Figure 4: Height of the lance for double-blown oxygen H (m) Figure 5: Height of the lance for top-blown oxygen H (m)

Claims (1)

[Claims] Using a double-bottom blowing composite blowing converter equipped with a tuyere metal for blowing an inert gas and a neutral gas into the bottom of the furnace and a 21st order lance for oxygen blowing. In a high chronograph steel production method in which chromium-containing 8 pig iron is top blown with oxygen under stirring of slag in Category 1, Category 1'l, 11: The flow rate of the blown gas Qb ( Nml/mi, n・i, on l, and the −”
The lance l',';sa I+ (distance between the lower end of the lance and the top of the hot water surface; 1?1) of the lance for double-blown oxygen is the controlling factor, and U, U2O5 (old -o, i)2; -T; Qbl? 4 0
．． 0+04 (11-1,8) 2nd night, ) Attendant: , Uel; J・11 plus fL FC, J 2, blowing end point (・C''?) slag (% Cr20
3) Control the control factor so that the concentration is 50 to 40%.
4-Manufacture of 1゛...'''' τ1-no steel using a bottom-blown combined blowing converter.