JPS61157617A - Production of alloy steel containing cr - Google Patents

Abstract

PURPOSE:To enable the replacing operation by N2 instead of Ar, the omitting of the sampling and the shortening of the whole operation hours by refining Cr-contg. alloy steel while blowing gaseous O2 and N2 into the molten steel of Cr-contg. alloy steel after the primary melting and thereafter performing the submerged arc refining in vacuum. CONSTITUTION:While blowing O2 and gaseous N2 instead of Ar into molten steel 2 of alloy steel contg. >=2wt% Cr after the primary melting from a tuyere 3 of a furnace 1, the decarburization is performed. Then the reduction of Cr is performed under the violent stirring of slag 4 and molten steel 2 by using gaseous N2. Furthermore the molten steel 2 is transferred into a ladle 6 provided with a vacuum installation (degassing function) and the electrodes 5 and the slag off is performed and the degassing and the heating by the submerged arc refining in vacuum is performed and the fine regulation of the component is performed while heating it. The one part of the refining process which is performed while blowing gaseous N2 is desirably performed by the blowing of gaseous Ar. As the above-mentioned Cr-contg. alloy steel, stainless is preferable.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing Cr-containing alloy steel, and more particularly, to a method for producing stainless steel in which refining (melting) is performed by combining the so-called AOD method and the '/LF method. Technology] AOD (Argon) is used for melting (refining) stainless steel.
Oxygen Dacarburization) method is being used. This method generally involves injecting Ar gas and 02 under stirring into molten steel 2 melted (primary melting) in an electric furnace or the like through a tuyere 5 in an AOD furnace 1 shown in FIG. It is determined by the uj method for stainless steel, which performs decarburization and finishing. In Figure 5, 4 in the middle is slag. As is well known, stainless steel generally has a Cir of 10%.
For the purpose of reducing costs with alloys containing the above, decarburization as described above is performed starting from molten steel containing a high content of G (this process is generally referred to as the decarburization stage), and then,
0□ Refining is carried out through a finishing stage such as so-called Cr reduction, in which chromium oxide oxidized by suction is reduced to chromium. By the way, Ar gas is expensive, and most of the AOD operating cost is accounted for by the Ar gas cost, and it is said that the AOD operating cost is greatly influenced by the price of this gas. Therefore, using water vapor instead of Ar gas, so-called a
The Lu method has also been proposed. Furthermore, in the above AOD method, inexpensive N2 is used in the carbon removal period, and Ar gas is not used in the Cr reduction. However, in any case, in these conventional examples, Ar gas must be used. The objective is to establish AODAr-less operation, which can be performed using cheap N2 gas without using AODAr. Another object of the present invention is that in the AOD method, N2
When using Cr, the amount of N increases in molten steel, so in order to reduce the amount of N (bringing the H content to the standard value), a large amount of Ar gas was injected for Cr reduction. The object of the present invention is to provide a method for manufacturing a Cr-containing alloy steel that can be refined without blowing gas, that is, even with an increased amount of N. Still another object of the present invention is that the AOD method always requires sampling at least once after Cr reduction, which causes problems such as cooling of the molten steel.
An object of the present invention is to provide a method for producing Cr-containing alloy steel that can be refined without the need for sampling after AOD. Still another object of the present invention is to provide a method for producing Cr-containing alloy steel, which allows easy fine adjustment of the components and allows strict control of the molten steel components. Other objects of the present invention will become apparent from the entire description of the present specification and the accompanying drawings. [Means for Solving the Problems] and [Operation] The present inventors performed AOD by using a method of blowing N2 gas instead of Ar gas, that is, without using Ar gas at all. However, N2 gas, for example, at
The amount of N when using some Ar gas for reduction is 1760
Although it rarely reached ppm+1, it rose to about 2,500 ppm, but this molten steel was transferred to I, F, which has vacuum equipment.
(Ladleyurnace) or the so-called V
l, F (When the method was further applied to the molten steel, it was discovered that the excess N in the molten steel was degassed and could be reduced to a predetermined level. Furthermore, by the multi-process of the above AOD method and the vr, y method, , the ingredients can be adjusted freely by heating with VLF, so conventional

[There is no need to perform sampling after AOD, and therefore the CAOD furnace can be made completely tilt-free, and the molten steel can be refined without being cooled. Also, by heating with VLF,
I learned that it is possible to fine-tune the composition and to precisely control the composition of molten steel. The present invention was completed based on the discovery of a method for manufacturing a Cr-containing alloy steel that is inexpensive and has excellent refining capabilities. In the present invention, steel is manufactured by blowing oxygen and nitrogen gas in place of argon gas after primary melting, and then subjected to submerged arc refining under vacuum.
A method for manufacturing an alloy steel containing 2% by weight or more of In the following explanation, in the present invention, N gas is used instead of Ar gas.
Since it uses two gases, it is called the NOD method rather than the AOD method. The VLF (method) performed following the NOD method of the present invention is L
This is F (method) with vacuum equipment (degassing function) added.
For example, as shown in FIG. 6, the LF method is a method of performing so-called submerged arc refining in which an arc from an electrode 5 is generated in the slag 8 above the molten steel 7 in the ladle 6. is added, Ar is blown into the bottom 9 of the ladle 6, and the process can be carried out while maintaining the interior of the ladle 6 in a strongly reducing atmosphere without stirring by the Ar. In FIG. 6, 10 is a furnace lid. An outline of the method for manufacturing CRR-containing alloy steel according to the present invention will be explained based on a few examples. Melting and refining in the atmosphere using electric furnaces, converters, etc. (primary melting)
The molten steel subjected to this process is subjected to out-of-furnace refining using a combination of the NOD method and the VLF method. The above-mentioned primary melting is preferably carried out using an electric furnace steelmaking method, particularly an arc furnace. As is well known in the art, an arc furnace (AF) generates an arc within the furnace and utilizes the radiant heat generated by the arc and the electrical resistance heat flowing through the molten steel. The molten steel received in the ladle after melting in such an electric furnace is AOD
Transfer to the furnace and start the NOD pigeon. The Cr-containing alloy steel is decarbonized while blowing in N 2 gas and 02 gas. Subsequently, using N2 gas, Cr reduction is performed while vigorously stirring the slag and molten steel. Conventionally, sampling was performed after CRR, and it took time to wait for analysis, but the sampling was omitted and the system was then moved to VI and F, which have a vacuum device, to perform slag-off (SO).
, fine adjustment of ingredients, degassing, heating, fine adjustment of ingredients, etc. At this time, Ar gas is blown in, but even if the N content in the solution is, for example, 2400 pIP■ when SO, it has decreased to about so ppm due to degassing by VI and F. 8 N ms/T, the Ar gas used can be blown to a level of, for example, Q, lNm5/. By the way, the inventors' studies have revealed that the de[N] behavior during VLF vacuum degassing can be simulated using the following equation (1), for example. After Nf-hypothetical gas (N amount Ha-hypothetical gas before [N) K-hypothetical (N) constant - Hypothetical gas time As shown in the examples below, there was an extremely good agreement between theory and actual results. The manufacturing method according to the present invention is advantageously applied to alloy steels containing Cr, which require Ar gas injection for Cr reduction, such as alloy steels containing 2% by weight or more of Cr, such as 18-
Applicable to 8 stainless steel, etc. There is no particular upper limit to the amount of crr, but it can be applied up to about 26% by weight. In addition, Mn non-magnetic steel made of 18%Mn-15%Cr steel and 25
It can also be applied to %0r-0.7%T1 steel. [Example] Next, an example of the present invention will be shown. Example 1 NOD for 150r (steel type 5US410) alloy steel
and VLF treatment. Molten steel (20 tons) tapped from the arc furnace was placed in an AOD furnace as shown in Figure 5, and decarbonized for 41 minutes while vigorously stirring the slag and molten steel and blowing in N gas and 0° gas.
Then, CR reduction was carried out for 4 minutes while blowing in horse gas. The amount of N in molten steel before Cr reduction is 1750 m) p! 11
Ashi, cr The amount of N in the molten steel after reduction is 2400 ppm
Met. The molten steel was subjected to SO for 4 minutes to finely adjust its composition, and then degassed for 8 minutes and heated for 14 minutes. Fine adjustments were made to the ingredients during heating. In addition, the blowing of Ar gas into the VLF was 0, I
It was N11l/t. The amount of N in the molten steel before VLF was 2400 ppm+, but after degassing it was 800 ppm, and after VLF the amount was 820 ppm, which passed the N standard. FIG. 1 shows the above process flow and the amount of N 70-. Comparative Example 1 The same alloy as in Example 1 was subjected to AOD treatment. Decarbonization was carried out for 41 minutes while blowing in N2 gas and 02 gas. The amount of N in the molten steel at the C-free edge was 1760 DI)m. After removing carbon, Cr reduction was performed for 7 minutes while blowing Ar gas. The amount of N in the Cr reduction was 900 ppm. It took 16 minutes to sample and wait for analysis. After fine-tuning the ingredients, I spent a minute making final adjustments to him. After adjusting the components, Ar gas was blown. Ar gas required a total of 5.8 sq. FIG. 2 illustrates the process flow and the amount of N at 70-. Example 2 Ni-Cr alloy steel type 574304, N standard 0.
03/0.08), NOD and 'l/LP treatments were performed in the same manner as in Example 1. However, Cr
Reduction for 4 minutes, VLF degassing x (v) for 10 minutes, heating (
H) was set to 3 minutes. Figure 3 shows the process flow and the N content in molten steel.
Illustrated. The amount of N in the ladle is as described above (according to formula 11, o, o
(S O (600 ppm).Actually 720
There was a good agreement in ppm. Example 3 Ni-Crr5US (steel type 91.88-II 504
, N amount 0,06/o,t o ), NOD and VLF treatments were performed in the same manner as in Example 2. However, V was set to 8 minutes and H was set to 4 minutes. The amount of N in the ladle is (1,080 according to formula 11.Actual 1 it is 72
0 ppm and l'A were almost identical. Example 4 In the combination of NOD and l/LF of the present invention, Cr reduction was performed by blowing Ar gas. NOD and VLF treatments were carried out in the same manner as in Example 2 for 15 cr stainless steel containing 10% coo. However, the Cr reduction was carried out by blowing Ar gas, and V was set for 15 minutes and H was set for 21 minutes. The amount of Ar gas was 110 MAIL/l. The amount of N after SO is 7BOppm, the amount of N after V is 350 E) pl
The amount of N after a-H was 540 ppm. Comparative Example 2 AOD was performed on one of the same samples as in Example 3. Ar gas was blown through the C removal and Cr reduction [6 minutes]. The amount of Ar gas required was 12.4 N m5/. Example 5 For various steel types, the agreement between the theoretical value and the actual value based on equation (1) was investigated. The results are shown in FIG. 4 in terms of the relationship between the degassing time [minutes] and the amount of N. Each plot in FIG. 4 shows a solid line value, and each curve shows a theoretical value according to equation (1). As shown in FIG. 4, an extremely good agreement is seen, and [N] control of stainless steel by descaling can be achieved with high precision using equation 11). [Effects of the Invention] fil According to the present invention, in the conventional AOD, it was possible to perform the operation using inexpensive N2 gas (about -10% of the cost of Ar gas) without using expensive Ar gas. (2) According to the present invention, even if the N amount remained increased after NOD, the N amount could be reduced by the subsequent VLIF and brought to the N standard value. (3) In the present invention, sampling after NOD for component adjustment can be omitted. As a result, it is possible to achieve non-tilting of the AOD reactor.
Well, it eliminates the analysis waiting time for sampling, and there is no need to cool the molten steel. (4) According to the present invention, component adjustment can be performed by heating with VLF, so not only can sampling be omitted, but also component adjustment with AOD, which was conventionally done, is not necessary, and VI, While heating at F, the ingredients can be adjusted as appropriate, and it is also possible to precisely control the ingredients. (5) According to the present invention, the overall working time is shortened;
For example, as shown in the comparison between Example 1 and Comparative Example 1, in the conventional example, AOD treatment required 65 minutes, but in the present invention, N
It is sufficient that the OD treatment takes 45 minutes. (6) In the present invention, part of the melting process (NOD) performed while blowing nitrogen gas (Cr reduction gold argon gas may be blown in. This also allows only a small amount of Ar gas to be used, The combination of this and '/LF has the advantage that the above-mentioned sampling can be omitted, the components can be finely adjusted, and the components can be precisely controlled.

[Brief explanation of drawings]

Figure 1 is a flowchart in Example 1, where a) is the process flow (DJ is the flow of refining gas, Pl is the flow of N amount,
Figure 2 A] (B) 1 is a flow diagram of Comparative Example 1, (A) is the process flow, (B) is the flow of the refining gas, ←1 is the N
Figure 5 is the N flow diagram of Example 2, Figure 4 is a graph showing the VLF vacuum mega 1 hour [N] behavior in the present invention, Figure 5 is an explanatory diagram of the AOD furnace, Figure 6 is VL
It is an explanatory view of F furnace. 1... AOD furnace 6... Ladle 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. Cr steel is produced by melting the steel after primary melting while blowing oxygen and nitrogen gas in place of argon gas, and then performing submerged arc refining under vacuum.
A method for producing alloy steel containing at least % by weight. 2. The manufacturing method according to claim 1, wherein part of the melting step performed while blowing nitrogen gas is performed by blowing argon gas. 3. The manufacturing method according to claim 1, wherein the alloy steel containing 2% by weight or more of Cr is stainless steel. 4. The manufacturing method according to claim 1, wherein the primary melting is performed by a so-called electric furnace steelmaking method. 5. The manufacturing method according to claim 4, wherein the electric furnace is an arc furnace.