JPS63186815A - Method for melting high chromium alloy steel - Google Patents

Abstract

PURPOSE:To execute decarbonizing refining under restraining oxidation of Cr in a top-bottom blowing refining furnace, by specifying uniform mixing time for molten steel of high chromium alloy steel and quantifying relative relation between oxygen supplying velocity and transition of C and Cr. CONSTITUTION:At the time of refining as decarbonizing the high Cr alloy steel having 1,600-1,800 deg.C molten temp. in the refining furnace, the uniform mixing time of the molten steel is made to <=40sec. Further, the top-bottom blowing total oxygen supplying velocity K02 (Nm<3>/min/ton of molten steel) is controlled, so that value of RIDAS shown by the equation becomes to <=30. In the equation, %Cr and %C are respectively concn. (weight%) in the molten steel. In this way, the decarbonization is executed without Cr loss. Further, in order to control of the oxygen supplying velocity, the oxygen supplying velocity related to sum up of stirring energy of the bottom blowing and the top blowing or the uniform mixing time is continuously or step by step controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing high chromium alloy steel.

[Conventional technology]

When decarburizing stainless steel, due to the strong oxidizing power of chromium, there is a problem that chromium, which is expensive, turns into chromium oxide, so it is desirable to suppress the oxidation loss of chromium and preferentially oxidize (C). Chromium oxidation is particularly noticeable when the carbon concentration decreases, so after decarburizing to a predetermined carbon concentration, a large amount of expensive ferro-alloys such as ferrosilicon and aluminum are added to reduce the chromium oxide. Or use a large amount of expensive Ar! By injecting carbon monoxide at the flame point, or decarburizing to a very low carbon concentration (R1 for the final decarburization later), or von
Methods such as vacuum refining furnaces are used. Therefore, I? The load on II'PVOD will be quite large. Therefore, a blowing method is required that suppresses the oxidation loss of chromium and preferentially oxidizes (C).

As a conventional technology, (C
) as a theoretical formula showing /l' pre-oxidation, l5CO= (
20oz/(2(1oz+Qd)) (Qoz/(1
'l/l) 1 However, there is a reported example (Tetsu to Hagane 78-5169) of the variable l5CO defined as Gloz is the oxygen flow rate, Qd is the dilution gas flow rate, W is the amount of molten steel, and t is the uniform mixing time. However, this does not quantitatively indicate the preferential oxidation of (C) over (Cr), and it is also disclosed in JP-A No. 6
No. 1-3815, Boc
-oat/ ((w/l)x Cc) )However, Q. t
There is a description of a manufacturing method in which the BOC value, where is the amount of blown acid, W is the ton of molten steel, and t is the uniform mixing time, is controlled to 30 or less. However, in the above BOC, (Cr) is not considered as a necessary element for determining the amount of blown acid. According to the knowledge of the present inventors (
The higher the chromium oxidation amount is, the higher the oxidation amount of chromium is. Therefore, it is better to lower the amount of blown acid. In other words, when selecting blown M1), it is better to consider (Cr) as well. It is more suitable for decarburizing molten steel.

In addition, in JP-A-55-1) 5914, in the blowing of high chromium steel under combined blowing, tNAr is the number of moles of inert gas, M is the atomic weight of carbon, W
is the weight of molten steel, and K is calculated from the equilibrium constant i. There is a description of a method of supplying 1.2 to 1.5 times as much oxygen as the oxygen (1). However, the above method shows a decarburization method in which the steel bath carbon concentration is in a low carbon region where chromium oxidation takes precedence over carbon oxidation, mainly in molten steel [%C] of 0.40% or less. It is inappropriate to prevent oxidation of chromium in the medium to high coal range where the molten steel [%C] is 0.40 or more.

According to the knowledge of the present inventors, even in the medium to high coal range, if the time between oxygen supply and stirring is too large, the amount of chromium oxidized increases. That is, when selecting the oxygen supply amount, it is more appropriate to consider the stirring, oxygen supply rate, and [%C] over a wide range.

Therefore, the present inventors have developed a broader range of (Cr) and (C)
Researched the method of blowing acid that could be applied to
A patent application was filed under No. 90. Namely, the patent application No. 60-2452
No. 90 uses a top-bottom blowing converter with a bottom-blowing gas flow rate of 0.06 Nm3/min or more per ton of molten steel, and blows acid from the top ff.
i K oz (Nn+3/min/ton) is calculated from RIDAS (RI
DAS=(Cr)/(1,73(C)”+0.31
((:) ) However, subsequent research has shown that oxygen and inert gas are injected through tuyeres below the bath surface, such as AO.
Even in the case of smelting furnaces like D, or when oxygen and inert gas are blown from the top and from below the bath surface as in JP-A-58-130216, chromium can be By suppressing oxidation loss of (C
) was found to be oxidized to (,!).

Furthermore, it has been found that by increasing the stirring power, it is possible to increase the amount of oxygen supplied that can preferentially oxidize (C) while suppressing chromium liquefaction loss.

[Problem that the invention seeks to solve]

Based on the above knowledge, the present invention suppresses chromium oxidation in top-bottom blowing and bottom-blowing smelting furnaces by quantifying the interrelationship between oxygen supply rate, stirring intensity, and changes in (C) and (Cr). The aim is to make it possible to decarbonize while at the same time.

More specifically, it is an acid blowing method that preferentially removes (C) while suppressing the oxidation of chromium in a relatively low temperature region, and can deal with a wide range of combinations of (C) and (Cr). It concerns the blowing acid method.

As a result, it is possible to blow a wide range of ROM-level stainless steels with a high chromium yield, reduce the amount of expensive ferro-alloys such as ferrosilicon and aluminum necessary to reduce chromium oxide, and reduce the amount of expensive ferro-alloys such as argon. The purpose is to reduce the amount of inert gas and the load on the furnace refractories, and also to make it possible to significantly reduce or omit the load on the finishing decarburization process (R1), VOD, etc.) It is an object.

[Means for solving problems]

The present invention provides (1) a temperature of molten steel in the refining furnace of 1600 to 180;
When decarburizing high chromium alloy steel at 0°C, the uniform mixing time τ of molten steel is set to 40 seconds or less, and the total oxygen supply rate of top blowing and bottom blowing to the molten steel is 0z (Nm'/min/ton of molten steel).
This method is based on a high chromium alloy steel melting method in which decarburization is controlled and refined so that the RIDAS value expressed by the following formula is 30 or less.

However, KoZ is the total oxygen supply rate of top blowing and bottom blowing to molten steel (Nm'/min/ton of molten steel) [%Cr] is the chromium concentration in the steel bath (weight percent) [%C] is the Carbon concentration in the bath (ffl amount percent) More specifically, K so that the RIDAS value is within the range of 30 or less for the carbon/chromium concentration depending on the blowing process.

All you have to do is cover it up.

In this case, the uniform mixing time τ, which can be calculated as 2 below, is 4
It is necessary to set the time to 0 seconds or less.

τ= 800A-01・Nl/3 = 800(t tNt-'1'' + A IINM
-'-83ff)-0.'Here, 67, t, is defined as follows.

U(0,0) xlJt' NM.

US ” Jco・g-R-T2/M Tz=T+・(Pt/Pυ(7-1/r)Ay, AIl
: 'fA stirring energy of top blowing and bottom blowing (Wat t/
t) NA, N,: Number of nozzles for top blowing and bottom blowing (pieces) G,,Q
, I: Top blowing, bottom blowing gas flow ffl(Nm'/lll1n
) K: Volume increase rate due to gas decomposition W: Molten @ rat (ton) χ: Lance height (m) d: Lance nozzle diameter (m) θ: Lance nozzle rounding angle (°) γ: Specific heat ratio (0□ is 1. 4) p,, p, : Lance nozzle population, outlet pressure (kg/
c++I) TI+'h: Lance nozzle inlet and outlet temperature (・K) T: Molten steel temperature (・K) Lo: Steel bath depth (m) M: Gas molecules m (kir/kg-not) g: Gravitational acceleration 9. 8 m/sec”R: Gas constant 848.
4 kg -ra/° to -kg-mol uniform mixing time τ
The reason why chromium oxide is set to 40 seconds or less is to ensure the stirring necessary for once generated chromium oxide to be stirred into the steel bath and reduced again by the molten steel [%C].

The molten steel temperature of 1,600 to 1,800°C indicates the usual case when high chromium steel is decarburized, but from the viewpoint of protecting the furnace refractories, it is desirable to set it to 1,740°C or less. The reason why we set the upper limit of RIDAS to 30 is because (Cr) tends to oxidize when blowing is performed at 30 or more, and it is necessary to add a large amount of expensive ferro-alloys such as ferrosilicon or aluminum to reduce oxides. Or high (C)
The reason for this is that the operational load on the secondary refining furnace such as R1)-OR becomes excessive in order to stop blowing at a certain level.

Based on this technology, we further investigated and discovered the following method that focuses on stirring energy.

(2) When decarburizing high chromium alloy steel with a molten steel temperature of 1,600 to 1,800°C using a refining furnace with top and bottom blowing functions, the total oxygen supply rate of top and bottom blowing to the molten steel Kaz ( A method for producing high chromium alloy steel in which decarburization is carried out by continuously or stepwise controlling the RIDAS (A It is.

However, Ko2 is the total oxygen supply rate of top blowing and bottom blowing (
(Nm3/min/ton of molten steel) [%Cr] is the degree of chromium in the steel bath (weight percent) [%C] is the carbon concentration in the steel bath (weight percent) AV is the bottom blowing and top blowing agitation It is the sum of energy, kv =' v, s +0.1 A V, t (Wa
tt/l).

Here, 'V+fi is the bottom blowing stirring energy and 92. is the top blowing stirring energy (3) When decarburizing high chromium alloy steel with a molten steel temperature of 1600 to 1800°C using a refining furnace with top and bottom blowing functions, the total amount of top blowing and bottom blowing to the molten steel is A high chromium alloy that undergoes decarburization refining by controlling the oxygen supply rate Koz (Nm'/min/ton of molten metal) continuously or stepwise so that the value of RIDAS (τ) expressed by the following formula is 1200 or less. It is a method of melting steel.

However, K, 2 is the total oxygen supply rate of top blowing and bottom blowing (N1/min/ton of molten steel) [%Cr) is the chromium concentration in the steel bath (weight percent) [%C] is the oxygen supply rate of the top blowing and bottom blowing (N1/min/ton of molten steel) The carbon concentration (weight percent) in τ is 540 (jv, a + 0.IAv, yLo, 5%l t
nz・ds,
x In the above inventions (2) and (3), each symbol is as follows.

Q6 is the bottom blowing gas amount (Nm'/min), TL is the steel bath temperature (K), and is the bath volume (N1), ρ. is the density of the steel bath (kg/Nmff) R2 is the atmospheric pressure (10330 kg/rd) (is the bath depth (m) T7 is the gas temperature (K) η is the opening angle of the top blow lance hole) M is the molecular weight of the top-blown gas, QA is the amount of top-blown gas (N1/min), n is the number of holes in the top-blowing lance, d is the diameter of the top-blowing lance outlet (m), and χ is the lance height (m). Regarding inventions (2) and (3), [
0/l5(A) upper limit is 1.0 or less or RID
T(oz''ll) may be injected so as to control it continuously or stepwise so that the upper limit of AS(τ) is 1200 or less.

The molten steel temperature of 1,600 to 1,800°C indicates the usual case of decarburizing high chromium steel, but from the viewpoint of protecting the large parts of the furnace body, it is desirable to set the temperature to 1,740°C or less.

In decarburization refining of stainless steel, it has been known that the oxygen supply rate is lower in the low carbon region than in the high carbon region.

However, the conventional method is based only on the empirical knowledge that oxidation of chromium is suppressed by lowering the oxygen supply rate in the low carbon region, and it is also clear which region is the low carbon region. It has not become. For this reason, the oxygen supply rate is excessively reduced, resulting in an extension of the blowing time and a drop in the steel bath temperature.Also, the oxygen supply rate is too high, which increases the oxidation of chromium. The current situation is that this is not the case.

However, by decarburizing and refining by controlling the oxygen supply rate continuously or stepwise based on the method of the present invention, it becomes possible to efficiently decarburize while suppressing the oxidation of chromium, thereby increasing the chromium yield of stainless steel. Perform a good blowing,
In addition, it is possible to reduce the use of expensive ferro-alloys such as ferrosilicon and aluminum necessary to reduce chromium oxide, reduce the use of expensive inert gases such as argon, and reduce the load on large furnace bodies. , and further a final decarburization process (R1
), VOD, etc.) can be significantly reduced or omitted.

Next, the concept of the present invention will be explained.

In general, in the decarburization refining of stainless steel, it is explained that the decarburization reaction is rate-determined by the oxygen supply, since the higher the oxygen supply rate in the high carbon region, the higher the decarburization rate. However, in the low carbon region, the decarburization reaction is not simple and is thought to proceed in a complex manner involving various factors, but since the decarburization rate depends on the carbon concentration, the idea that it is rate-limiting by carbon diffusion is dominant. However, conventional knowledge is only a qualitative classification such as a high carbon region and a low carbon region, and the decarburization reaction itself has not been clarified, so there is no way to decarburize while suppressing chromium oxidation. had not been fundamentally elucidated.

Therefore, the inventors of the present invention conducted and analyzed a number of experiments in which the oxygen supply rate was varied under the same stirring intensity (constant amount of bottom-blowing gas), and as a result, the decarburization reaction increased as the oxygen supply rate increased. It is divided into a region (1st period), a region where the decarburization rate depends on the carbon concentration (■ period), and a region where the decarburization rate does not depend on the carbon concentration and reaches the decarburization limit (■), and from the 1st period to ■ It was discovered that the transition (C) to the first stage (critical [C]) and the transition (C) from the first stage to the second stage (C) shift to the lower odor side as the oxygen supply rate is reduced.

In addition, chromium oxidation hardly occurs in the first stage, and l F
It has been found that this phenomenon starts to occur from JT to upJ1 henotransition (C) (critical [C]), and becomes more pronounced as the carbon becomes lower.

Therefore, if the oxygen supply rate, the 5p field (C), and the chromium oxidation behavior can be quantified, conditions that enable decarburization while suppressing chromium oxidation can be derived.

In addition, the high chromium alloy w4 according to the present invention is shown in the Examples column to be described later.
An example of melting has been shown, but by changing the top blowing oxygen supply pattern in a similar manner, the RIDAS value and -Δ[%Cr
) /−Δ[%C] was investigated.

In addition, using a 2.5 tAOD furnace and varying the oxygen supply rate and Ar dilution pattern, the RIDAS value and -Δ[
The relationship of %Crl/-Δ[%C] was investigated.

As a result, as shown in Figure 1, -Δ[%Cr)/-Δ[
%C] is organized by RIDAS value, top-bottom blowing converter, AO
If the RIDAS value is controlled to 30 or less, preferably 20 or less in Furnace D, -Δ[%Cr]/-Δ[%C] is approximately 2 or less, which means that decarburization is possible with almost no chromium loss. Understood.

A test was also conducted in which oxygen and Ar were simultaneously blown into the furnace from the top and bottom blowing, and the results were similar to those of the top and bottom blown converter furnace and the AOD furnace.

As a result of research focusing on stirring energy based on this technology, the transition from I to ■ (C) (critical [C])
and n %The transition from J1 to m phase (C) shifts to the low coal side as the stirring intensity increases, so the oxygen supply rate that can preferentially oxidize (C) while suppressing chromium oxidation loss is They found that it is possible to increase the

Therefore, by variously changing the oxygen supply pattern and stirring intensity (bottom blowing gas amount), RIDAS(A), RIDAS(τ
) and -Δ[%Cr)/-Δ[%C] was investigated.

As a result, as shown in Figures 2 and 3, -Δ[%Cr]
/-Δ[%C] is RIDAS(A), RIDAS(
τ), and the upper limit of the RIDAS(&) value is 1.
．． 0 or less, preferably 0.7 or less, or RIDAS (
It has been found that if the oxygen supply rate is controlled continuously or stepwise so that the upper limit of the τ) value is 1200 or less, preferably 700 or less, it is possible to decarburize while minimizing chromium oxidation loss. .

When the entire amount of oxygen is blown from the bottom, such as in AOD, oxidation of chromium is likely to occur at the flame point, so it is necessary to set the RIDASCA (A) value to be smaller than the RIDAS(τ) mentioned above. It is necessary that the upper limit of the RIDAS(τ) value be 0.7 or less and the upper limit of the RIDAS(τ) value be 700 or less.

The same applies to top-bottom blown combined refining furnaces, and if the bottom-blown oxygen ratio in the total oxygen supply is high, RIDAS(&)
, It is desirable to set the upper limit of RIDAS(τ) to a small value.

[Example 1] 1? It was decided to carry out acid blowing to keep the IDASO value in the range of 30 or less. 0 shown in the figure
In the tables and figures, A is an example of the present invention in which acid was blown at RIDAS = 20, and B is a comparative example. The bottom blowing gas was 0.15 Nm3/min/ton of molten steel for both charges. The uniform mixing time for both charges is 28 to 32 seconds.

As shown in Table 1, in case A, the amount of blown acid decreases as decarburization progresses. B is an example in which the amount of blown acid is not changed, and when (C) decreases, the RIDAS value becomes 26o. Therefore, as shown in Table 2, (C) is increased from 1.0% to 0.17%.
The blowing acid time for B is 1). Although it is early at 0 minutes,
The (%Cr) at the end of acid blowing is about 4% lower than that of io, a and A.

In the case of B, the steel bath temperature rose rapidly due to oxidation of (Cr).

Figure 5 shows the ratio of the oxidation amount of (Cr) during decarburization of the unit (C) during blowing, as values indicating the degree of preferential oxidation of (C);
In other words, (-Δ[%Cr) /-Δ[%C))] In B, the amount of chromium oxidation increases rapidly when (C) becomes 0.8% or less, but in A, [C] However, up to 0.3%, the loss of chromium due to oxidation is small.

[Example 2] Next, a top-bottom blown converter with 5 tons of top-blown oxygen, bottom-blown inert gas, and a top-bottom blown converter with 5 tons of top-blown oxygen, bottom-blown oxygen, and inert gas simultaneously injected. The blowing examples are shown in Tables 3 and 4.
In the table, both C and D are of the present invention, which were blown at RIDAS = 20. Here, C is a top-bottom blown converter that supplies oxygen from the top and inert gas from the bottom, and D is a top-bottom blown converter that simultaneously supplies top-blown oxygen, bottom-blown oxygen, and inert gas. It is a furnace. As shown in Table 3, the oxygen supply methods for C and D are different, but the oxygen supply rates to molten steel [%C] are the same.

As shown in Table 4, ΔCr for both C and D is 0.3°0.
This shows a good agreement of 4%.

Although there are differences in oxygen supply methods, RIDAS'
Align the values, that is, t8 steel [%C], [%Cr
) It was found that it was possible to equalize the amount of chromium oxidation by adjusting the oxygen supply rate to the two.

[Example 3] 1) A blowing example in which the present invention was implemented in a 0 ton top and bottom blowing converter was as follows:
The results are shown in Tables 5 and 6 and Figures 6 and 7 together with comparative examples. In the tables and figures, E is an example of the present invention that was blown with RIDAS (RI-0.7), and F is a comparative example.The bottom blowing gas was 0.16 Nm'/min/ton of molten steel for both charges. C.O.
□ was used. Further, A1'3 of both charges is about 29.

As shown in Table 5, in the case of E, the amount of blown acid decreases as decarburization progresses. F is an example in which the amount of blown acid is not changed, but when (C) decreases, the value of RIDAS (A) becomes 5.2. Therefore, as shown in Table 6, (C) is increased from 1.03% to 0.3%.
The blowing time for blowing down the acid to 0% is fast at 4.0 minutes in the case of F, but the [%Cr) at the end of blowing is 13.8%, which is approximately 2% lower than in the case of E. .

In the case of F, the steel bath temperature rapidly rose due to the oxidation of (Cr), reaching 1818° C. at the end of acid blowing.

Figure 7 shows the ratio of the oxidation amount of (Cr) during decarburization of the unit (C) during blowing, as values indicating the degree of preferential oxidation of (C);
In other words, it shows (-Δ[%Cr) /-Δ[%C)]. In F, the amount of oxidation of chromium increases rapidly when (C) becomes 0.6% or less, but in E, the amount of chromium oxidation increases rapidly. Oxidation losses are negligible.

[Example 4] Next, the effect of the bottom blowing gas amount will be explained.

1) In a 0 ton top and bottom blowing converter, the G method shown in Table 7 has a constant bottom blowing gas of 0.8 Nm3/min/ton of molten steel, and the H method has a molten steel [%C] of 1.2%. The temperature is 0.1 Nm'/min/ton of molten steel, and then O until the molten steel [%C] is 0.04%.
16Nm'/min/ton of molten steel, then 0.40Nm
A pattern was adopted in which the bottom blowing gas amount was gradually increased as the molten steel tons/min/molten steel [%C] decreased. A meter was used for bottom blowing gas. Also, the RID^sB) value of both charges is 1.
．． Same as 0. The blowing conditions and blowing examples at that time are summarized in Tables 7 and 8, and the oxygen bottom blowing pattern is shown in FIG.

The main results are shown below.

As shown in Table 7 and Figure 8, the G method can increase the oxygen delivery rate compared to the H method, and the blowing time can be approximately 3 to 30 minutes.
It can save 5 minutes. Also, as shown in Table 8, G
Since blowing was performed to achieve the same RIDAS (A) value as in the , H method, the amount of chromium oxidation was almost the same as 0, 6%, and 0.7%, taking into account the carbon/chromium concentration, stirring power, and oxygen delivery rate. It can be seen that the amount of chromium oxidation can be controlled by the RIDAS(A) value.

Further, in the case of the G method, the tuyere elution rate is 5 to 7 u/ch, but in the II method, it is 1 to 2+u/ch, which seems to be influenced by the flow rate of the bottom blowing gas. Further, the chromium yield was 91 to 93% in the case of the G method, but 95 to 97% in the case of the H method.

In this way, the decarburization refining time can be shortened by increasing the amount of bottom blown gas, but from the viewpoint of protecting the furnace refractories and tuyeres and preventing dust loss, the amount of bottom blown gas is
~0.40 Nra3/min/ton of molten steel is desirable. The above range is also desirable in terms of reducing the use of expensive inert gas such as Ar gas.

[Example 5] ■An example of blowing in which the present invention was implemented in a 10-ton top-bottom blowing converter.
The results are shown in Tables 9 and 10 and Figures 9 and 10 together with comparative examples.

In the tables and figures, I is an example of the present invention that was blown at RIDAS (τ) = 750, and J is a comparative example. Note that CO□ was used as the bottom blowing gas at a rate of 0 and 16 Nm3/min/ton of molten steel for both charges. The co-balanced mixing time for both charges was approximately 37 seconds.

As shown in Table 9, in the case of 1, the amount of blown acid decreases as decarburization progresses. J is an example in which the amount of blown acid is not changed, but when (C) decreases, the value of RIDAS (τ) reaches 5700. Therefore, as shown in Table 10, (C) is increased from 1.2% to 0.2%.
The blowing time for blowing down the acid to 5% is fast at 4.6 minutes in the case of J, but the 0% Cr) at the end of blowing acid is 13.7%, which is about 2% lower than in the case of 1. .

In the case of J, the steel bath temperature rose rapidly due to the oxidation of (Cr), reaching 1815° C. at the end of acid blowing.

Figure 10 shows the ratio of the oxidation amount of (Cr) during decarburization of the unit (C) during blowing, that is, (-Δ[%Cr)/-] as a value indicating the degree of preferential oxidation of (C). Δ[%G)) In J, the amount of oxidation of chromium increases rapidly when [C] becomes 0.6% or less, but in ■, the oxidation loss of chromium is negligible.

[Example 6] 1) A comparative example of the blowing method in which the present invention was carried out in a 0-ton top-bottom blowing converter, as well as Tables 1) to 12 and Table 0 shown in Figure 1) And in the figure, the K method is 1? IDAs(τ)=
This is an example of the present invention in which the steel was blown at a temperature of 740, and the L method is a comparative example in which the steel was blown at a BOC≦30 as shown in the example of the conventional method. The bottom blowing gas amount was 0.16 Nm3/min/ton of molten steel for both charges, and CO□ was used.

The joint equalization-mixing time τ of both charges is about 37 seconds.

As shown in Table 1) and Figure 1), compared to the L method, the oxygen delivery rate of the method is considerably larger in the high coal region ([%C]≧0.6%), and becomes lower order. This is a method in which the value decreases as the value increases.

Compared to the L method, the K method has a higher oxygen delivery rate in the high coal region, so the blowing time is significantly shortened. In addition, the amount of chromium oxidation is Δ[
%Cr) -0, 4, 0, 3%. In this way, the method is capable of decarburizing at a high speed while suppressing bechrome oxidation compared to the L method.

[Example 7] 1) In a 0 ton top and bottom blown converter, the M method uses bottom blown gas of 0.8N+
a! /min/ton of molten steel is constant, and in the N method, molten steel [%C] is 1
．． 0.1 Nm'/min/ton of molten steel until it reaches 2%, and then 0,16 Nm'/ton until molten steel [%C] reaches 0.6%.
Min/? 8 tons of steel, and then a pattern was adopted in which the amount of bottom blowing gas was gradually increased to 0.40 h'/min/ton of molten steel as the molten steel [%C] decreased.

Ar was used as the bottom blowing gas. Also, both charges are RID
The AS(τ) value was set similarly to 600.

A summary of the blowing conditions and blowing examples at that time is shown in Tables 13 and 14, and a top blowing oxygen pattern and a bottom blowing pattern are shown in FIG.

The main results are shown below.

As shown in Table 13 and FIG. 12, the M method can increase the oxygen delivery rate and shorten the blowing time by about 4 to 8 minutes compared to the N method.

Also, as shown in Table 14, both the M and N methods use the same RIDAS.
(τ) value, the amount of chromium oxidation is 0.
．． 4% and 0.5%, which shows that it is possible to control the amount of chromium oxidation by the RIDAS (τ) value that takes into consideration the carbon/lime concentration, stirring power, and oxygen delivery rate.

Further, in the case of the M method, the tuyere erosion rate is 5 to 7 m@/ch, but that in the N method is 1 to 2 mm/ch, which is thought to be influenced by the bottom blowing gas flow rate. Furthermore, the chromium yield was 91 to 93% in the case of the M method, but 95 to 97% in the case of the N method.

In this way, the decarburization refining time can be shortened by increasing the amount of bottom blown gas, but from the viewpoint of protecting the furnace refractories and siding and preventing dust loss, the amount of bottom blown gas is 0.10.
~0.40 Nm3/min/ton of molten steel is desirable. The above range is also desirable in terms of reducing the use of expensive inert gas such as gauge gas.

〔Effect of the invention〕

The present invention is based on research into a quantified acid blowing method that preferentially oxidizes and removes (C) while suppressing the oxidation of (Cr) in a top-bottom blowing converter. By blowing molten steel with a wide range of Cr levels, such as stainless steel, in a top-bottom blowing converter with a good chromium yield, or using expensive ferroalloys such as ferrosilicon and aluminum necessary to reduce chromium oxides. It has also become possible to reduce the use of expensive inert gases such as argon, and to reduce the load on the furnace refractories.

In addition, it becomes possible to significantly reduce or omit the load on the final decarburization process (R1), VOD, etc.), and the effect of improving the stainless steel 12I melting cost is significant.

[Brief explanation of the drawing]

Figure 1 shows RIDAS and -Δ[%Cr) /-Δ[%C]
Figure 2 shows RIDAS(j) and -Δ[%C
Figure 3 shows RIDAS (r)/-Δ[%C].
τ) and -Δ[%Cr) /-Δ[%C], Figure 4 is a diagram showing the oxygen supply pattern of A charge and B charge, and Figure 5 is the unit for each molten steel [%C]. A diagram showing the ratio of the oxidation amount of (Cr) during decarburization of (C), Figure 6 is a diagram showing the oxygen supply pattern of E charge and F charge, and Figure 7 is a diagram showing the ratio of oxidation amount of (Cr) during decarburization of (C). (C) while decarburizing unit (C)
Figure 8 is a diagram showing the oxygen supply pattern and bottom blow pattern of G method and H method, Figure 9 is a diagram showing the oxygen supply pattern of I charge and J charge, Figure 10 shows the unit (C) in each molten steel [%C] during decarburization (
Figure 1) is a diagram showing the ratio of the oxidation amount of Cr3, Figure 1) is a diagram showing the oxygen supply pattern of the Ni method and L method, and Figure 12 is a diagram showing the oxygen supply pattern and bottom blowing pattern of the M method and N method. be. RIDAS O: 13Cr, △: 16Cr []:
AOD (2,5t) Fig. 1 Fig. 3 Molten steel (%C) Fig. 4 0 0.2 0.4 0.6 0.
8 1.0 Molten steel [%C] Molten steel (%C) Molten steel [%C] Fig. 7 Fig. 8 0 0.2 0.4 0.6 0.8
1.0 1.2f6 Steel (XCI Molten Steel [XCI 1st) Figure 12

Claims (3)

[Claims] (1) When decarburizing high chromium alloy steel with a molten steel temperature of 1,600°C to 1,800°C in a refining furnace, the uniform mixing time τ of the molten steel is set to 40 seconds or less, and the top-blowing total oxygen supply rate to the molten steel Kο_2 (Nm^3/min/ton of molten steel) is controlled so that the RIDAS value expressed by the following formula is 30 or less. RIDAS={[%Cr]/(1.73[%C]^2+
0.31 [%C])}×K_o_2 However, K_o_2 is the total top-blowing oxygen supply rate to the molten steel (Nm^3/min/
molten steel tons) [%Cr] is the chromium concentration in the steel bath (weight percent) [%C] is the carbon concentration in the steel bath (weight percent) (2) A refining furnace with top and bottom blowing function allows the molten steel temperature to reach 1
When decarburizing high chromium alloy steel at 600 to 1800℃, the total oxygen supply rate of top blowing and bottom blowing to molten steel is K_
o_2 (NM^3/min/ton of molten steel) is R expressed by the following formula
A method for producing high chromium alloy steel, characterized by continuously or stepwise controlling the IDAS (ε) value to be 1.0 or less. RIDAS(ε)=[[%Cr]/{ε_ν^1^/^
3×(1.73[%C]^2+0.31[%C])]・
K_o_2 However, K_o_2 is the total oxygen supply rate of top blowing and bottom blowing to molten steel (NM^3/min/ton of molten steel) [%Cr] is the concentration of chromium in the steel bath (weight percent) [%C] is: Carbon concentration (weight percent) in the steel bath ε_ν is the sum of the stirring energy of bottom blowing and top blowing. (3) The molten steel temperature is 1
When decarburizing high chromium alloy steel at 600 to 1800℃, the total oxygen supply rate of top blowing and bottom blowing to molten steel is K_
o_2 (Nm^3/min/ton of molten steel) is R expressed by the following formula
A method for producing high chromium alloy steel, characterized by continuously or stepwise controlling the IDAS (τ) value to be 1200 or less. RIDAS(τ) = {([%Cr]・τ)/(1.73
[%C]^2+0.31[%C])}・K_o_2 However, K_o_2 is the total oxygen supply rate for top blowing and bottom blowing to molten steel (Nm^3/min/ton of molten steel) [%Cr] is Chromium concentration in the bath (weight percent) [%C] is carbon concentration in the steel bath (weight percent) τ is uniform mixing time (seconds)