JPS63105915A - Method for producing steel containing low phosphorous and chromium - Google Patents

Abstract

PURPOSE:To omit dephosphorizing treating process, to enable Cr addition within the ordinary degassing treating time and to easily, surely and efficiently produce the titled molten steel by injecting Cr oxide into the molten steel containing the specific composition of low P and Cr by inert gas. CONSTITUTION:In the molten steel 2 containing <=0.30% C, <=100ppm P, >=0.050% Al, an uptake tube 4 and a downtake tube 3 of a vacuum degassing apparatus is immersed and the pressure in a vacuum vessel 5 is reduced and by blowing circulating gas, that is, the inert gas, such as Ar gas, etc., from a tuyere 6, the molten gas 2 is introduced into the vessel 5 to execute the degassing. Then, the chromium oxide having <=5mm diameter is injected from a tuyere 7 arranged at the vessel 5 bottom part by the inert gas, and by the soluble Al in the molten steel 2, the chromium oxide is reduced to produce the above molten steel.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for melting copper containing low phosphorous and chromium.

(Prior Art) In recent years, from the viewpoint of improving corrosion resistance and hardenability, there has been a tendency for the production of chromium-containing molten steel to increase more and more. or,
From the perspective of improving low-temperature toughness, phosphorous reduction treatment of molten steel is becoming necessary. In addition to adding metallic chromium or ferrochrome to molten steel, methods for producing chromium-containing molten steel include injecting finely powdered chromium ore into the iron bath in a converter-type refining vessel from the bottom of the furnace. There is a method of reduction with carbonaceous material (Japanese Unexamined Patent Publication No. 153223/1983), but this method is not preferable for melting copper containing low phosphorus and chromium because phosphorus enters from the carbonaceous material. In addition, there are two methods for dephosphorizing molten steel: oxidative dephosphorization and reductive dephosphorization.The general oxidative dephosphorization treatment method uses quicklime when tapping molten steel from a converter. , a method of dephosphorizing by adding a dephosphorizing agent consisting of iron oxide and fluorite to molten steel (Japanese Unexamined Patent Publication No. 59-490310), a method of dephosphorizing by adding a dephosphorizing agent consisting of iron oxide and fluorite to molten steel (JP-A-59-490310); A method of adding a dephosphorizing agent and dephosphorizing while controlling the temperature (Japanese Patent Application Laid-Open No. 60-92416) has been disclosed. These treatment methods are very effective in reducing phosphorus in molten steel.If metal chromium, etc., which has a low phosphorus content, is added to molten steel that has undergone low phosphorus treatment, it can be used to reduce phosphorus in molten steel. It is now possible to manufacture However, metals such as chromium with low phosphorus content are very expensive, so it is difficult to melt copper with low phosphorus content! ! ! There are problems such as increased costs. Therefore, a chromium-containing ferroalloy such as ferrochrome, which is relatively cheaper than pot metal chromium, is used. Dephosphorization is required. Therefore, when chromium-containing molten steel with a phosphorous content is treated by the above-mentioned dephosphorization method, the chromium in the molten steel is oxidized (by the dephosphorizing agent), causing problems such as a decrease in chromium yield. Therefore, as another method for dephosphorizing high-chromium molten steel, a reductive dephosphorization method using metallic calcium, etc. is being considered, but in the reductive dephosphorization method, calcium phosphide is present in the slag after the dephosphorization treatment. This calcium phosphide reacts with moisture in the atmosphere and generates toxic phosphine, which poses a problem in slag treatment after dephosphorization.

(Problems to be Solved by the Invention) The present invention was developed to solve the above-mentioned problems and to produce low-phosphorus-chromium containing molten steel at low cost and efficiently.

(Means to solve the problem) Its characteristics include less than 0.30% carbon and 1% phosphorus.
Diameter in molten steel containing 0.00 ppm or less and 0.50% or more of soluble aluminum! l)l! This is a method for melting copper containing low phosphorus and chromium, which is characterized by blowing in chromium oxide of II+ or less using an inert gas and reducing the chromium oxide with soluble aluminum.

In general, chromium-containing copper is required to have low phosphorous properties, as well as low sulfidation, low oxygen, and low hydrogen levels due to its required material properties. Therefore, desulfurization of the molten steel is usually performed after adding chromium alloy such as ferrochrome to low-phosphorus molten steel. However, in order to increase the desulfurization efficiency, strong deoxidation using aluminum, silicon, etc. is used to lower the oxygen in the molten steel. Desulfurization is often carried out in the same condition.

In this way, after adjusting the alloy components required for steel materials,
Vacuum degassing treatment removes hydrogen gas from the molten steel and produces the desired molten steel.

The present invention makes it possible to produce low-phosphorus-chromium molten steel even if, for example, the dephosphorization step is omitted in the above-mentioned normal production method. The reason why the dephosphorization step is necessary in the above-mentioned normal melting method is to remove phosphorus brought in from ferrochrome.

The present invention attempts to produce low-phosphorus chromium steel at low cost by using chromium oxide with low phosphorus content as a chromium source, for example, by omitting the dephosphorization process. Generally, simply adding chromium oxide to molten steel does not reduce the chromium platen, so it does not exist as an oxide in the molten steel, and the necessary metallic chromium is not produced, or rather, This will impair the cleanliness of the molten steel and reduce the material properties.

However, as in the present invention, if chromium oxide with a diameter of 5 or less is blown into molten steel containing 0.30% or less carbon, 100 ppm or less phosphorus, and 50% or more soluble aluminum using an inert gas, Chromium oxide reacts with soluble aluminum in molten steel in a manner similar to the fIJ formula, producing chromium and alumina.

Cr203 +2 Aj =2 (! r + A)z
ol... (■) In this case, the higher the carbon content in the molten steel, the better the reaction efficiency, but the usual low phosphorus chromium content copper is 0.30% or less. Therefore, increasing the carbon concentration,
If the reaction efficiency is reduced, a treatment step for re-treating the molten steel with carbon metal becomes necessary9, which is unfavorable from the viewpoint of productivity, cost, etc. Therefore, industrially, the carbon content in molten steel is 0.
In order to reduce the amount to 30% or less and increase the reaction efficiency, the daughter degree of soluble aluminum is specified to be in the total passability range.

In the present invention, it is necessary to contain soluble aluminum i in a ratio of 0.050 or more in the molten steel. The present inventors conducted various studies on the influence of the content of soluble aluminum in molten steel on the reduction of chromium oxide. The results are shown in FIG. This figure shows molten steel (C: 0.10%, Si: 0.25
%, Mn: 0.95%, P: 0.0015%, S: O,
0O15%, Fe: Soluble aluminum in the remaining cavity'
It can be seen that by containing ji0.050% or more, an industrially viable reduction rate of 70% can be ensured. From this, the content of soluble aluminum is 0.050%
It is necessary to do more than that. Furthermore, although increasing the soluble aluminum content increases the reduction rate of chromium oxides, increasing the soluble aluminum content results in problems such as a large amount of aluminum used) and an increase in melting costs. Therefore, industrially, soluble aluminum is 0.05% or more, 0.
．． It is desirable to keep it within a range of 20% or less.

The present inventors also conducted various studies regarding the shape of the chromium string. The results are shown in FIG. When the carbon content and the soluble aluminum content are held constant, the reduction rate of chromium oxide in a time period increases significantly when the diameter of the chromium oxide is less than 5 mm. Therefore, from the viewpoint of productivity, the diameter of the chromium oxide needs to be 5 mm or less. Furthermore, when the diameter of the chromium oxide is made smaller, the reduction rate gradually increases, but the crushing cost of the chromium oxide increases exponentially, so the effect of improving the reduction rate is outweighed by the crushing cost. It will be more expensive. According to the studies conducted by the present inventors, the diameter of chromium oxide is industrially 0.1 m1 or more, 5 m1 or more.
It is desirable to use it below W+. Incidentally, argon gas or nitrogen gas is used as the blowing gas, but since nitrogen gas has problems such as increasing nitrogen in the molten steel, it is generally better to use argon gas.

Next, the implementation method will be explained. Carbon smelted in converter 0
．． While tapping the molten steel containing 30% or less phosphorus and 30 ppm or less, ferrosilicon, ferromanganese, aluminum, etc. are added to adjust the combined elements other than chromium to the target composition. In this case, by removing the converter slag and preventing rephosphorization from the converter slag, it is possible to reduce the phosphorus content of the molten steel.

Next, sulfur is removed to 20 ppm or less using a desulfurization device such as a ladle furnace.The molten steel that has become low in phosphorus and has a low value is then subjected to chromium addition treatment and dehydration using a vacuum degassing device. Perform elementary treatment. Dehydrogenation treatment is the same as the normal vacuum degassing treatment method, but in order to add chromium, the following operations are performed at the same time: 1. Adjust soluble aluminum to a ratio of 0.050 or higher An additional operation is added to the molten steel in which chromium oxide with a concentration of 5 or less is injected into the molten steel using argon gas.In this way, the chromium oxide is reduced with soluble aluminum, making it possible to add metallic chromium to the molten steel. becomes.

As shown in FIG. 3(a), the method for injecting intensified chromium into molten steel is to immerse the riser pipe 4 and downfall pipe 3 of the vacuum degasser into the molten steel 2 placed in the ladle 1. . Thereafter, the vacuum chamber 5 is depressurized and argon gas is blown into the reflux gas blowing tuyere 6 to guide the molten steel 2 into the vacuum chamber 5 and degas it. At this time, the chromium oxide may be blown in with argon gas from a chromium oxide blowing vane provided at the bottom of the vacuum chamber. In addition, as shown in FIG. 3 ('bj), the rising pipe 4 and the descending pipe 3 of the vacuum degassing device are immersed in the molten steel 2 placed in the ladle 1, and then the vacuum chamber 5 is depressurized. The molten steel 2 is introduced into the vacuum chamber 5 and degassed by injecting argon gas all through the reflux gas blowing tuyeres 6. At this time, the chromium oxide blowing lance 8 immersed in the molten steel 2 in the ladle 1 Alternatively, as shown in FIG. 3(C), a chromium oxide injection lance 9 is immersed in a ladle 1 containing molten steel 2. Chromium oxide may be blown in with an argon gas.If all of the above treatments are carried out, copper with low phosphorous and chromium content can be melted.

(Example) In Example 1, the molten steel temperature was 1650°C, carbon was 0.1%, and SiI
J Core 0.25%, Mangani 10.95%, Phosphorus 0.
150 tons of molten steel with 0.0015% sulfur, 0.0015% sulfur, and 0.055 to 0.065% soluble aluminum are degassed using a vacuum degassing device at a vacuum level of 1 torr or less, and chromium oxide 1000% with a purity of 98% is extracted. This is the case where argon gas was blown into the lower tank of the Makabe degassing device for 10 minutes. Chromium in the molten steel increased by 0.45%, and the yield was 82%. Also, no increase in phosphorus was observed.

Incidentally, aluminum was added to the molten steel in the upper part of the vacuum degasser to ensure a soluble aluminum content of 11wc.

Example 2 has a molten steel temperature of 1650°C, carbon 0.10%, silicon 0.25%, manganese 0.95%, and phosphorus 0.0015%.
%, sulfur 0.0015%, soluble aluminum 0.05
While degassing the molten vs150t with a concentration of 5% to 0.065% at a vacuum level of 1 torr or less using a vacuum degassing device, chromium oxide with a purity of 98% is removed from the bottom of the vacuum degassing device using 4500/19J-argon gas. This is the case where the water was blown into the tank for 10 minutes. Chromium in the molten steel increased by 2.0%, and the yield was 81%. Also, no increase in phosphorus was observed. Note that aluminum was added to the molten steel from the top of the vacuum degasser to ensure the soluble aluminum content.

Comparative example is molten steel temperature 1680℃, carbon 0.10%, silicon 0.25%, manganese 0.959F; phosphorus 0.001
5%, sulfur 0.0015%, soluble aluminum 0.0
While degassing 150 tons of molten steel of No. 552 using a vacuum degassing device, 1 tons of ferrochrome 4200 with a chromium content of 75% was processed.
It was added from the top inside the Kyk vacuum hinoki. The chromium in the molten steel increased by 2-Oy, and the yield was 95%. Also, phosphorus
It increased significantly to 05%.゛As above,
By using the method of the present invention for processing molten steel, it has become possible to easily produce chromium steel with low phosphorus content.

(Effects of the Invention) According to the present invention, compared to the conventional melting method for low phosphorus-containing chromium steel, the dephosphorization process can be omitted, and chromium can be added within the normal degassing time of 10 minutes. As a result, the overall molten steel processing time is shortened, the temperature drop of the molten steel is reduced, and there is less erosion of refractories in the take-off or degassing equipment, so there are no operational hindrances. It is now possible to prevent this.Also, it can be prevented without using expensive fluorescent chromium.
For example, it has become possible to melt copper with low phosphorus and chromium content even by using purified chromium ore. As described above, according to the present invention, copper containing low phosphorous and chromium can be melted easily and reliably compared to conventional methods. Figure 2 is a diagram showing the effect of chromium oxide diameter on the reduction of chromium oxide, Figure 3 (a), Figure 3+1) l is a diagram showing the effect of chromium oxide diameter on the reduction of chromium oxide, Figure 3(c) is a schematic diagram of the method of adding chromium oxide using a top blowing powder blowing device.

1... Ladle 2... Molten steel 3... Descending pipe 4... Rising pipe 5... Vacuum chamber 6...・Recirculation gas blowing vane lower・・・Chromium oxide blowing tuyere 8.9・・・
...Chromium is a chemical injection lance Applicant: Nippon Steel Corporation Figure 1 0. 0,05 0. to O,+
5 02゜呵juse L7 Ivmi;tsu4 (7',) 2nd evil

Claims (1)

[Claims] Low phosphorus chromium content characterized by blowing chromium oxide with a diameter of 5 mm or less into molten steel containing 0.30% or less carbon, 100 ppm or less phosphorus, and 0.050% or more soluble aluminum using an inert gas. Copper melting method.