JPS60106943A - Production of stainless steel - Google Patents

Abstract

PURPOSE:To produce an austenitic stainless steel by producing separately an Ni- Si alloy and molten slag contg. Cr2O3 and CaO by an electric furnace, bringing both into mixing and reaction in a ladle to form an Fe-Cr-Ni alloy then adding a molten steel thereto and subjecting the alloy to vacuum decarburization. CONSTITUTION:An Ni-Si alloy contg. Fe to some extent is manufactured by charging 47-81pts.wt. crude Ni oxide, 70-130pts.wt. silica and 50-70pts.wt. a carbonaceous reducing agent into an mebedded arc furnace and subjecting these materials to melting and reaction. Molten slag consisting principally of Cr2O3 and CaO is manufactured by melting 50-70pts.wt. Cr ore and 30-50pts.wt. quicklime in another electric furnace. An Fe-Cr-Ni alloy is manufactured by bringing 100pts.wt. such molten slag and 18-38pts.wt. said Ni-Si alloy melt into reaction in a ladle and reducing Cr2O3 by Si. An austenitic stainless steel is produced by adding 60-80pts.wt. molten steel to 20-40pts.wt. such alloy and mixing the same then subjecting the steel to a vacuum decarburization and degassing treatment in an RH furnace, DH furnace, etc.

Description

[Detailed Description of the Invention] Conventionally, as shown in Fig. 1, the method for manufacturing austenitic stainless steel is to first prepare a predetermined amount of low carbon ferrochrome or high carbon ferrochrome, which is a chromium-containing material, and ferronine gel, which is a nickel-containing material. The mixture is mixed with scrap and J() in an electric steelmaking furnace, then this molten material is oxygen blown in an electric furnace or converter, decarburized to a predetermined carbon content to obtain crude stainless steel, and finally this is Stainless steel is manufactured by debutyrinizing and refining with ferrosilicon or silicochrome, or refining using a vacuum method.

That is, it is customary to separately produce a chromium-containing material and a nickel-containing material, mix and melt them in separate steps, and then undergo steps such as desulfurization and decarburization.

For prior f7 ferrochromes, the chromium yields for producing high) Further, when high carbon ferrochrome or low carbon ferrochrome is mixed and melted and decarburized by oxygen blowing to produce stainless steel, the chromium yield is 88 to 92%. Therefore, the consistent chromium yield from ore to stainless steel is 78 to 86% even when only the better high carbon ferrochrome is used;
When 0% is used, it becomes 77 to 80%, and in both cases the loss of chromium content is quite large.

Next, regarding ferronickel, high carbon and high sulfur ferronickel is usually obtained by preheating and drying nickel ore and a carbonaceous reducing agent in a rotary kiln, and then refining in an electric furnace. At this time, in order to improve the nickel yield, a large amount of reducing agent is used and when the nickel ore is smelted at a high temperature, a large amount of 5i02 is contained in the nickel ore, so some of it is reduced and enters the ferronickel, which contains silicon. The amount increases. However, when making stainless steel, silicon is disliked and must be reduced as much as possible, but on the other hand, if the silicon content is low, the sulfur content increases, which is an inconvenience.

Furthermore, in conventional steelmaking methods, the amount of high carbon ferrochrome and high carbon ferronickel accounts for 65% or more of the steelmaking raw materials, and most of them are used as cold material raw materials. Therefore, the reality is that a large amount of electrical energy is required to melt these refrigerant raw materials. In recent years, a method has been used in which high-carbon ferrochrome is supplied as a molten metal and the heat generated during the decarburization process in a converter is used to melt high-carbon ferronickel and stainless steel scrap. The nickel content of ferronickel is as low as 23% or less, and therefore, when producing austenitic stainless steel with the target structure, a considerable amount of high carbon ferronickel is required, so it is necessary to melt the entire amount using the heat of reaction. is difficult and the use of electrical energy as a heat source is unavoidable.

The present invention uses high chromium/high nickel alloy iron instead of conventional high carbon ferrochrome or high carbon ferronickel.
The purpose is to use it as a nickel source and add it to molten steel to produce austenitic stainless steel using as little electrical energy as possible.

In the present invention, in order to produce high-chromium, high-nickel ferrochrome nickel, crude nickel oxide is used as a raw material, and it is refined together with silica stone and carbon in a buried arc furnace to produce silicon nickel, which is then melted in a separate process to produce chromium ore. react with synthetic slag containing silicothermite. Next, this high chromium O high nickel ferrochrome nickel is tapped from a blast furnace and desulfurized, then added to high temperature molten steel decarburized in an oxygen-blown converter, mixed and melted to produce austenitic stainless steel. It is something to do.

Next, each process will be explained. A buried arc furnace, which is normally used for producing ferrosilicon, is suitable for producing the silicon nickel alloy of the present invention.

The raw materials for ferrosilicon are silica stone, a carbonaceous reducing agent, and iron scraps, but in the present invention, it is sufficient to use crude nickel oxide, silica stone, and a carbonaceous reducing agent, and the other conditions are exactly the same as for ferrosilicon. good.

That is, silica stone includes lumpy and granular silica stone, as well as silica sand, and petroleum-based or coal-based coke, bituminous coal, anthracite, and the like are used as reducing agents. Nickel oxide is obtained by oxidizing and roasting nickel mud in a rotary kiln or the like. Crude nickel oxide having the composition shown in Table 1 below is usually used, and has the advantage that it has a high nickel content and is granular, making it extremely easy to handle.

Table 1 (wt%) Silicon content in silicon nickel alloy is 30 to 55
% is appropriate. When this alloy is melt-reacted with chromium ore in a later process, 3
Advantageously, it is greater than or equal to 0%. However, if the silicon content is too large, the nickel content becomes relatively low, scouring becomes difficult, the melting point becomes high, and carbon becomes solid solution in the metal in the form of carbide, which is undesirable.

Therefore, it is appropriate that the silicon content in the alloy be 55% or less.

The silicon content in this silicon nickel alloy is 30~
In order to achieve 55%, the raw material mixture should be as follows. Namely, the reaction between nickel oxide and silica stone and the carbonaceous reducing agent is NiO+ C+ Ni + Go (1) Si02 +
Since it is 2C+Si+2CO(2), 47 to 81 parts by weight of nickel oxide, 0 to 130 parts by weight of silicon oxide, and 42 to 80 parts by weight of fixed carbon may be blended. Since the fixed carbon content of the carbonaceous reducing agent is usually 80 to 85%,
The amount of the carbonaceous reducing agent to be blended may be 50 to 70 parts by weight.

The silico-nickel alloy thus obtained has an extremely low content of carbon and sulfur, and has the ability to significantly reduce the burden of the stainless steel refining process. In addition, silicon not only acts as a reducing agent for chromium in the next step, but also acts as a heat source when stainless steel is blown with oxygen, making it possible to obtain stainless steel without using electrical energy.

Next, low carbon ferrochrome nickel is produced by reacting this silicon nickel with a mixture of chromium ore and lime and melting the mixture. The chromium ore and quicklime may be completely melted, or some of them may be added in solid form. In this process, (7)Cr203. Fe
O reacts with Si to become Cr and Fe, and almost all N1 from the silicon nickel alloy is lost due to oxidation etc.
The production transitions to low carbon ferrochrome nickel with a yield close to 0.00%.

Mixing chromium ore and quicklime produces a synthetic slag with a low melting point and good fluidity, and also captures the SiO component produced by the silicothermite reaction in the form of calcium silicate (2CaO/SiO) to accelerate the reaction. It's for a reason. For this reason, the blending ratio of quicklime to chromium ore varies depending on the grade of chromium ore, but usually chromium ore is 50 to 70) I! Quicklime 30~
A suitable amount is 50 parts by weight.

Next, the silicon nickel alloy is added to the synthetic slag obtained by melting chromium ore and quicklime, and the silicon in the silicon nickel alloy and the chromium oxide and iron oxide in the synthetic slag are reduced to C and Fe through a silicothermite reaction. The nickel in the silico-nickel alloy transfers as it is to the produced alloy, so a ferrochrome nickel alloy is produced here.Since this anti-uniform core is an exothermic reaction, the reaction must be promoted by stirring the molten metal in the ladle. If molten silicone nickel alloy is used, the electrical energy for melting chromium ore etc. can be further reduced.

The compounding ratio of synthetic slag and silicone nickel should be such that it matches the ratio of the amount of chromium to the amount of nickel in the target austenitic stainless steel.Normally, 18 to 38 parts by weight of silicone nickel alloy is added to 100 parts by weight of synthetic slag. section is appropriate.

The low carbon ferronickel chromium obtained in this way is of a grade that can be directly applied to the vacuum method without going through processes such as oxygen blowing, so this technical effect is significant. In addition, the yield of chromium in the present invention is 80 to 84% because the chromium ore is used only in one step of the silicothermite reaction with the siliconickel alloy.
%, which is an improvement of 10 to 17% compared to the conventional method.

Next, the final stainless steel refining process will be explained.

Pig iron produced in blast furnaces typically contains 4.5% carbon (C).
, 0.75% silicon (Si), 0.05% sulfur (S), (1.3% phosphorus (P)).This pig iron is first treated by using means such as torpedo car desulfurization treatment. After the hot metal is desulfurized to 0.01% sulfur or less, it is charged into an oxygen-blown smelting converter.In the converter process, flux is added and pure oxygen is blown onto the surface of the molten metal, which is then oxidized and refined to reduce the carbon content to 0.01% or less.
1% or less, silicon 0.5% or less, and phosphorus 0.01% or less. In the converter process, not only top blowing but also bottom blowing and stirring with inert gas may be used in combination.Since oxidation scouring is an exothermic reaction, the molten steel temperature reaches a high temperature of 1700° C. or more. When carbon, silicon, and phosphorus reach a predetermined level, the ejaculation is stopped and the slag is discharged. Next, this high temperature molten steel and the ferrochrome nickel alloy are added to the same converter or to another furnace body. Furthermore, stainless steel scrap for cooling, ferroalloys and nickel oxide for composition adjustment are added to achieve the target structure. Of course, the ferrochrome nickel alloy may be added as a molten metal, but it may also be added as a cold material. Since the nickel content in the alloy is high even when added as cylindrical material, the amount of cylindrical material in the raw material added to molten steel is as low as 20-40%, and it is not possible to melt the molten steel sufficiently using only the heat retained in the molten steel. The greatest advantage of the present invention is that it becomes possible and eliminates the need to use an electrician's key.

Furthermore, according to the present invention, very little carbon or silicon enters from the chromium source or nickel source, so if ferrochrome nickel is added to the refined molten steel and melted, there is no need for oxygen blowing of the molten stainless steel. be.

Of course, the molten steel with various auxiliary materials added is oxygen blown again.
It is possible to finish the molten steel to a desired final composition, and it is naturally possible to heat the molten steel using electrical energy to compensate for the temperature.

However, this final scouring process contains a large amount of chromium, which has a strong affinity for oxygen, so excessive oxygen blasting results in loss of chromium. Therefore, it is necessary to take precautions such as using inert scum in combination to prevent chromium oxidation and ending oxygen blowing slightly before the final target value of carbon content.

After mixed melting, the molten stainless steel is transferred to a vacuum furnace and adjusted to the target carbon content using vapor phase decarburization.

Roughly remove dissolved gases and remove non-metallic inclusions to produce high quality stainless steel. As a vacuum furnace, RH furnace, DH
Commonly used furnaces, ladle smelting furnaces, etc. can be used.

As explained above, according to the present invention, it is possible to improve the yield of chromium and nickel, minimize the use of expensive electrical energy in the stainless steel refining process, and produce austenitic stainless steel extremely economically. becomes possible.

Next, the present invention will be explained with reference to Examples.

Example 1 Crude nickel oxide manufactured by a conventional method and having the following composition was used as nickel oxide.

Table 2 (wt%) 585 parts of this crude nickel oxide, 61,141 parts of silicon with 98% 5i02 content, and 645 parts of breeze coke with 85% fixed carbon were blended and charged into a buried arc electric furnace to produce the following composition: Ferrosilico nickel was obtained. Electricity intensity is 55
It was 00 KWH.

Table 3 (wt%) Separately tffm ore (Cr2O351%, Fe013
%) and 870 parts of quicklime (Ca095%) were mixed, melted in an electric furnace, and placed in a ladle. 360 parts of the above-mentioned ferrosilicon nickel was added to the mixture and mixed and reacted.

This reaction is exothermic and the lining of the ladle is eroded by the hot slag.
70 parts of i8%, Ni 8.5%) were used as the tube material. As a result, ferrochrome nickel was obtained, the composition of which was as follows. The electricity consumption rate was 1800 KWH per ton of ferrochrome nickel.

Table 4 (wt%) Next, carbon 4.5%, silicon 0.78%, phosphorus 0.25
After melting pig iron containing %, sulfur o, and oos% by electricity, it is charged into a converter, flux is added, and then it is blown with oxygen to make it carbon-free.
．． 0.05%, silicon 0.25%, and phosphorus 0.023%. The molten steel temperature was 1780'C.

Next, 657 parts of the molten steel and 204 parts of the molten metal of the ferrosilicochrome alloy were placed in a converter and melted. After melting, the converter body was placed in a vacuum chamber and subjected to vacuum treatment at a pressure of 0.1 atm for 10 minutes. As a result, austenitic stainless steel having the composition shown in Table 5 was obtained.

Table 5 (wt%) Example 2 Crude nickel oxide of the same grade as that used in Example 1 8
Using 12 parts by weight, 13 parts by weight of K-6F, and 500 parts by weight of coke as raw materials, using the same electric furnace as in Example 1, Table 6 was prepared.
The ferrosilico nickel shown in is obtained. Electricity intensity is 36
It was 00 KWII.

Table 6 (wt%) Next, the same synthetic slag as in Example 1 was prepared, and the above ferrosilico nickel solution/! was added to 166 parts by weight of the synthetic slag.
! 577 parts by weight and stainless steel scrap (Cr18%, N
200 parts by weight of i8.3%) were added and a silicothermite reaction was carried out by stirring in a ladle to obtain ferrochrome nickel shown in Table 7. The electric power consumption per ton of ferrochrome nickel was 1800 KW).

Table 7 (-7%) Next, 210 parts by weight of the ferrochrome nickel molten metal in Table 7 was added to 662 parts by weight of the same molten steel as in Example 1.
, ROHM (Cr: 62X, C: 8%, S
(i: 3%) (1) Charge 173 parts of the cold mass into a converter and blow oxygen again to obtain 0.05% carbon and 0.25% silicon.
%, and scouring until the phosphorus content was 0.023%. After oxygen blowing, the molten steel is transferred to a preheated ladle and placed in a direct air tank until the pressure is 0.
Vacuum treatment was performed at 1 atm for 10 minutes. As a result, austenitic stainless steel having the composition shown in Table 8 was obtained.

Table 8 (T%) Example 3 Crude nickel oxide 4 of the same grade as that used in Example 1
77 parts by weight, μ parts by weight, 6130 parts by weight, and coke 703
Using commercially available raw materials as raw materials, the same electric furnace as in Example 1 was used to obtain ferrosiliconnickel shown in Table 9. The electric power intensity was 6,600 KW)I.

Table 9 (t%) Next, the same synthetic slag as in Example 1 was prepared, and 4 parts of the ferrosilico nickel molten metal was added to 1667 parts by weight of the synthetic slag.
77 parts by weight and stainless steel scraps (Cr18%, Ni
8.3%) was added and a silicothermite reaction was carried out by stirring in a ladle to obtain ferrochrome nickel shown in Table IO. The electric power consumption per ton of ferrochrome nickel was 1810 KW).

Table 10 (wt%) Next, 338 parts by weight of the cold ingots of ferrochrome nickel shown in Table 10 and 34 parts by weight of nickel oxide shown in Table 2 were heated in a low frequency vacuum melting furnace to 86 parts by weight of the same molten steel e as in Example 1. Dissolved. After dissolving ferrosilicon (Si 75%)
Part by weight was added to reduce nickel oxide to silicon. Thereafter, the inside of the furnace was maintained at a pressure of 0.1 atm for 20 minutes to perform vacuum scouring. As a result, austenitic stainless steel having the composition shown in Table 11 was obtained.

Table 11 (wt%)

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of stainless steel production by a conventional method, and FIG. 2 is a process diagram of stainless steel production according to the present invention. Patent applicant Showa Denko Co., Ltd. Showa Techno System Co., Ltd. Agent Patent attorney Sei Kikuchi −

Claims (1)

[Claims] A first step of producing a ferrosiliconium alloy by charging 47 to 81 parts by weight of nickel oxide, 0 to 130 parts by weight of silicon oxide, and 50 to 70 parts by weight of a carbonaceous reducing agent into a buried arc electric furnace; 50 to 70 parts by weight of chromium ore and 30 to 50 parts by weight of quicklime are melted in an electric furnace to obtain synthetic slag, and 18 to 38 parts of the ferrosilico-nickel alloy listed in +tl are added in a ladle to 100 parts by weight of the synthetic slag. A second step of obtaining a ferrochrome nickel alloy by reacting with 20 to 40 parts by weight of the ferrochrome nickel alloy and 60 to 8 parts by weight of molten steel.
1. A method for manufacturing stainless steel, comprising a third step of mixing and melting 0 parts by weight and then vacuum treatment.