KR800000617B1 - Method of manufacturing for stainless steel - Google Patents

Abstract

Semireduced Cr ore pellets, reduced Fe ore pellets and SUS 430 scraps in a vacuum electric furnace, were melted at 180-130v, 1000A and 230-280torr for 120 minutes and decarburized with charging ferroalloy, quicklime and fluorite at 130v, 1050A and 230-280 torr for 35minutes to give a stainless steel.

Description

Manufacturing method of stainless steel

1 is a process diagram of the present invention.

2 is an example of a hermetic arc suitable for the method of the present invention.

3 is a partial cross-sectional view of FIG.

4 is a vertical cross-sectional detail view of the engaging portion of the furnace body and the furnace lid of the present arc.

5 is a sealing device for the telescopic sliding material provided in the electrode through portion of the furnace lid of the present arc.

6 shows the applied arc voltage and vacuum ranges.

The present invention relates to a method for producing stainless steel which is melted, decarburized and refined under reduced pressure in an airtight acro of vacuum decompression materials as a main raw material of return pellet of chromium ore as an inexpensive chromium source and iron reducing pellet as an iron source. It is about.

Conventionally, as the manufacturing method of stainless steel, various methods as shown next are known and it is performed.

(A) The most commonly used method is charging stainless steel or snow with an alloy furnace such as FeCr and FeMn into an electric furnace, and melting: decarburizing molten steel containing 1.0 to 2.5% of carbon. V) Introduce gaseous oxygen to oxidize and decarburize carbon to 0.04 ~ 0.08%, and then use metal reducing agents such as chromium, manganese and iron produced by deoxidation using reducing agents such as silicon chromium or ferro silicon. A method of operating the solvent in the same furnace (electric furnace) by roughly four steps of reducing and recovering and then refining.

B) Using the raw materials described above, dissolve in an electric furnace or a melting furnace such as cupola to charge the melt into a converter and use gaseous oxygen until the chromium in the molten metal is not oxidized. Decarburization, and the metal is finally vacuum decarburized and refined by a vacuum degassing apparatus to produce stainless steel.

C) Until the melt is made, the same as (B), but charge the used melt into the converter (gas oxygen + other gas) and blow the degassed by blowing the mixture gas from the air vent installed at the bottom of the furnace. A method for producing stainless steel, in which the metal oxide to be produced is reduced and recovered by using a reducing agent such as silicon chromium and ferrosilicon.

D) The following converters are the same as the above (B), but instead of the melting furnace of (B), using a combustion type furnace such as blast furnace, and using a reducing agent such as coke in chromium ore or iron ore as a raw material and containing high carbon A method for producing stainless steel by producing chrome molten iron and combining blast furnace → converter or blast furnace → converter → degassing.

By the way, in each of the above-described methods, it is preferable to use low-carbon alloy iron for the purpose of reducing carbon in stainless steel as the raw material for manufacturing stainless steel. However, since the low-carbon alloy iron is manufactured from ore through a complicated process, the price is low. Inevitably, the manufacturing cost of stainless steel also increases.

In addition, relatively inexpensive ferroalloy is used. Since all of these ferroalloys contain a large amount of carbon, more than the specified carbon exists in the stainless steel, and in order to lower the amount of carbon in the molten steel, gaseous oxygen must be removed and decarburized in the stainless capacity by any stainless steelmaking method. With this gaseous oxygen bleeding, losses due to oxidation of metal powders are inevitable, and furthermore, they require a lot of extensive equipment, complicated processes, difficult operation and large expenses. In stainless steels, dry refining was carried out in an electric furnace together with chromium ore, reducing agent, and refining agent, which had been pretreated with only high-carbon ferrochrome, which is the main raw material and relatively low-cost ferrochrome. It is expensive and takes up a large portion of stainless steel manufacturing costs. On the other hand, in the case of snowfall, which is another main raw material, the use of stainless steel is generally expensive, and since the fluctuation of the market is extremely large, it is a great cause of fluctuation of the manufacturing cost of stainless steel.

An object of the present invention is to solve the above-mentioned problems at first, and first replaces high-carbon waste chromium, which is the main raw material of the Slenres steel, with a cheap chromium returning pellet, and inexpensive snowfall and stable iron. It is possible to manufacture stainless steel of low carbon sufficiently by replacing with reduced pellet of carbon steel and by injecting gaseous oxygen from the outside in the molten stainless steel with extremely low carbon decarburization, especially the loss of chromium. It is to provide a steelmaking method which can improve the work efficiency and productivity and also prevent the generation of pollution such as NOx dust.

According to the manufacturing method of the stainless steel of the present invention, in advance, a known type of airtight electric furnace of vacuum pressure-reducing material with a return source pellet of chromium and a reducing pellet of iron together with an appropriate amount of stainless steel snow and a preparation agent (hereinafter hermetic electric furnace) And decarburization under reduced pressure, and decarburization and refining, or in an airtight electric furnace, decarburization of arc dissolution tank under reduced pressure only, and final decarburization and refinement using a known vacuum degassing apparatus without refining. Since the stainless steel of can be obtained, the objective can be achieved.

The manufacturing method of this invention is demonstrated by the process diagram of FIG.

The Fe reduction pellet, Cr return pellet, stainless snow and the crude agent are charged into an arc of vacuum pressure reducing material, melted under reduced pressure, and refined after receiving molten steel in the injection section (2). For example, a method (A) for casting slab by casting with a continuous casting machine (5) and pollution and coarse decarburization in the above-mentioned arc furnace, the molten steel is accommodated in the degassing unit (3), and vacuum degassing is carried out. The production method of the present invention can be roughly divided into two method embodiments of the method (B) of casting (for example) by casting with a continuous casting machine (5) after the treatment in the apparatus (4), and the methods (A) and (B). This will be described later in detail.

[A law]

The chromium and iron source are mainly air-tight electric furnaces having an arc heating electrode with chromic semi-reduced pellets, iron-reduced pellets and other necessary stainless steel raw materials prepared by known techniques such as stainless steel and quicklime. Charged into an electric furnace), dissolved under reduced pressure, and decarburized together with almost no gaseous oxygen.

In this method, since this electric furnace alone dissolves and decarburizes together under reduced pressure, the amount of the metal oxide in the charged material, that is, mainly the unreduced content in the reduced pellet, for example, Cr ₂ O ₃ minutes and FeO content (these metals) Oxygen of the oxide becomes an oxygen source for decarburization) and the total amount of carbon in the charged raw material must be balanced. At this time, when the amount of metal oxide in the raw material is insufficient as an oxygen source, a small amount of gaseous oxygen may be introduced to contribute to decarburization. Melting is carried out in the same manner as in normal air melting, but when dissolving under high pressure, it glows. Therefore, in order to avoid this glow discharge, the vacuum degree needs to be about 250torr.

As described above, after melting, decarburizing and refining with an airtight electric furnace, the molten steel is discharged to the injection section 2 and slabed by the continuous casting machine 2.

[B Act]

The raw material is the same as the [A] method, but the amount of total carbon in the raw material is slightly increased, these are charged into an electric furnace and dissolved using the same means as the [A] method. At the same time as melting, the metal oxide in the raw material reacts with the carbon in the raw material to start decarburization, but unlike the [A] method, decarburization is not carried out to the final target carbon value.

That is, decarburization stops at the carbon value (C: 0.6% or less) decarburizable with the vacuum degassing apparatus 4 of a post process, and it goes out to the degassing section 3 as long as it does not refine | purify.

The degassing section 3 is conveyed to the vacuum degassing apparatus 4 where the final decarburization is carried out under a fairly high vacuum (preferably below 50 torr). When the final refining is completed, the slab is manufactured by the continuous casting machine (5) after the components and temperature control.

According to this [B] method, productivity is significantly improved compared to the [A] method by performing final decarburization and refining by using a vacuum degassing device which has a greater decarburization and refining capacity than a gas-tight electric furnace for vacuum decompression materials in a post process. In particular, it is possible to advantageously perform a solvent of ultra low carbon stainless steel.

Next, an example of the airtight arc of a pressure sensitive material which can be used suitably in the manufacturing method of this invention is demonstrated. As shown in FIG. 2 and FIG. 3, the ratio between the inner diameter of the furnace and the length of the furnace section of the furnace body 1 and the furnace refractories, that is, the furnace inner core, has a shape of 0.5 to 2.0, and the furnace body 1 Refractories are attached to the inside of the furnace angle. Usually, the innermost layer of the refractory uses magnesia-based basic refractory. As shown in FIG. 3 and FIG. 4, the uppermost part of the furnace shell is provided with a recess 3 on a thick steel plate 2, and a water cooling box 4 is provided below this.

The hemispherical furnace lid 5 is covered on the furnace part of the furnace body 1. The outside of the furnace lid is made of steel sheet, and the inside thereof is attached with a refractory material. The part where the furnace lid 5 engages with the furnace part of the furnace main body 1 is made into the water cooling box 7 which has the thick steel plate which installed the downward recessed part 6 as the bottom face, and the upward recessed part 3 and the downward recessed part. In the case of contacting (6) facing each other, a hollow annular space sphere is formed. The hollow annular space sphere formed by the recesses 3 and 6 is fitted with a synthetic rubber circular ring 8 having strong temperature resistance to block the atmosphere inside the furnace from outside air.

The double water-cooled stainless steel cylinder 10 (refer to FIG. 3, FIG. 5) is fixed to the inner surface of the furnace cover through-hole at the part through which the furnace cover 5 penetrates. On the other hand, the double water-cooled stainless steel cylinder 11 surrounding the electrode intermediate surface and having an outer diameter slightly smaller than the inner diameter of the cylinder 1, has an outer diameter slightly smaller than the inner diameter of the cylinder 11, and is also extremely small than the outer diameter of the electrode. A double water-cooled stainless steel cylinder 12 having a large inner diameter was sequentially inserted into the cylinder 10 by sliding the cylinder 11 into the cylinder 10 and the cylinder 12 by sliding upward and downward. To the electrode surface. In order to keep the gap between the slide surfaces of the cylinders 10 and 11 and the cylinders 11 and 12 sealed, as shown in FIG. Install on. Therefore, when the electrode moves up and down during operation, the barrel (10), (11), (i2) of the barrel (11) slides the inner surface of the calibration cylinder (10) and moves to Shanghai, the cylinder (12) is the inner surface of the cylinder (11) You can slide up and down. That is, the sliding of the telescope can be performed. The electrode support arm 15 and the rod cover hanger frame 16 are installed on a support 14 that can support, lift and pivot the electrode 9 and the furnace lid 5 together. The arm 15 and the frame 16 can be raised and lowered individually (in the second and third degrees, the case where the lifting positions of the arm 15 and the frame 16 are the same height is indicated).

The furnace lid 5 is provided with an exhaust hole 17, and the furnace gas can be discharged through the water-cooled double exhaust cylinder 18 engaged with the hole.

The alloy can be charged into the furnace from the alloy bath 19 provided on the furnace cover 5.

The furnace is tilted by the trunnion 20 provided in the furnace angle 1.

The roche is fixed and the tapping hole is provided at the bottom of the ladle, or the roche of the blowing type is used. The furnace format to be used can be used in the method of the present invention.

Next, an Example is described.

Example 1

The reduced iron pellet as an iron source or the return pellet as a chromium source used what was manufactured by a well-known technique. In addition, when used in the present Example, although it was an air-cooled pellet, respectively, it is preferable to use the pellet of the extreme high temperature state as it is in terms of energy saving. The component quality of a reduced iron pellet and a return one chromium pellet is shown next.

Reduced iron pellets

Next, the specification of hermetic electric furnace is shown.

Nominal Dissolution 150kg

Transformer capacity 250KVA

Roche diameter 950 mm

3 inches (76 mm) electrode diameter

1. Raw material formulation

The type of solvent steel was SUS 430.

2. Operational situation

What was improved according to the above raw material mixture was manually charged into the government by electricity. After charging was complete | finished, the furnace lid was received and the inside of a furnace was made into the fully sealed state.

Thereafter, energization was started and a vacuum pump was started to reduce the pressure in the airtight furnace. Particularly, if the pressure is too high, a glow discharge is generated as shown in Fig. 6, and the pressure reduction degree is 250 tor. The input power condition was controlled by adjusting the secondary voltage to 150V and the secondary current to about 1000A.

Since it became 250 torr about 5 minutes after power supply, after that, the vacuum pump was adjusted and the pressure reduction degree was the range of 230-280 torr. After 120 minutes of energization, the power consumption became approximately 380 kWH. Therefore, the energization was stopped and the pressure was released to measure and sample the temperature.

Temperature measurement and sampling results were as follows.

Temperature 1550 ° C

Chemical composition

According to the analysis results, 1.2 kg of FeSi, 0.3 kg of low coal FeMn, 6 kg of low coal FeCr were added, and 3 kg of CaO and ₁ kg of CaF ₂ were added. After the addition of crude steel and alloy steel, the electric furnace was sealed again and energization was started to reduce the pressure. The input power was set at a secondary voltage of 180 V and a secondary current of 1050 A, and the degree of decompression was adjusted to the same degree as that of the dissolver.

The time required for such refining was 35 minutes, after which the energization was stopped and the reduced pressure was opened to measure the temperature. As a result, the temperature was 1630 占 폚.

The molten steel thus obtained was poured into the blown and cast again into the mold.

The chemical composition of the obtained steel mass, the amount of non-metallic inclusions, and the like, were able to fully counter each other in comparison with other steelmaking methods.

At this time, the same result was obtained even when decarburization in the gas-tight electric furnace of the vacuum decompression material in the above step was stopped halfway, and the molten steel which was tapped was charged into a vacuum degassing apparatus to carry out final decarburization refining.

As is clear from the above examples, according to the alignment furnace of the present invention, using a cheap returning chromium pellet as a chromium source and a cheap reducing iron pellet as an iron source, decarburization and refining can be performed under reduced pressure with almost no gaseous oxygen. The generation of arc and NOx can be prevented, and the surface oxidation of the electrode can be prevented and the pre-process [A] method of dissolution and refining or most of the process [B] method can be applied to a single vacuum refining furnace. In this case, the thermal efficiency becomes extremely good, and has many advantages as follows, compared to the refining by a conventional melting furnace and a refining furnace.

1. The raw material cost is very cheap because chrome semi-reducing pellets and iron-reducing pellets can be used in large quantities.

2. The manufacturing process is simplified from the ore to the slab, thus reducing the equipment cost.

3. Since decarburization by gaseous oxygen is hardly performed, there is almost no oxidation of chromium. Therefore, since chromium is not recovered by a reducing agent such as ferrosilicon, damage to the refractory agent is small.

4. Because the furnace is sealed

i) No dust collector is needed.

ii) Thermal efficiency is good because it does not suck cold air (atmosphere).

iii) Less noise.

iv) The generation of nitrogen oxides is extremely low.

v) Low oxidation of electrode.

Claims (1)

A process for producing stainless steel, characterized by melting and decarburizing a source pellet of chromium ore and reducing pellets of iron ore as main raw materials under reduced pressure in an airtight arc.

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