JPS61166910A - Production of chromium-containing alloy - Google Patents

Abstract

PURPOSE:To produce inexpensively a high Cr alloy by allowing a free carbonaceous material to remain and adjusting slag compsn. so as to satisfy respective specific formulas then discharging part of the formed slag and decarburizing the molten alloy in the melting and reducing of Cr oxide in a reaction vessel. CONSTITUTION:The raw material contg. the Cr oxide is charged together with the carbonaceous material such as coke into a top and bottom blown converter type reaction vessel to which a gas contg. oxygen is supplied and the oxide is melted and reduced to manufacture the Cr-contg. alloy. The free carbonaceous material is allowed to remain always in the furnace to progress the reaction so that the components of the molten alloy satisfy formula I. The flux is added to the alloy to adjust the slag compsn. so as to satisfy formula II during the melting and reducing of the Cr oxide. Part of the formed slag is discharged and thereafter the molten alloy is decarburized. The Cr-contg. alloy is thus produced inexpensively at a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing chromium-containing alloys (eg stainless steel) in a mass production process.

(Prior art) High chromium steel such as stainless steel has traditionally been produced by melting a chromium alloy agent such as ferrochrome made by an electric furnace process together with hot metal rock or scrap as a chromium source, and then decarburizing it. It has been manufactured through refining processes such as

As a stainless steel making furnace, a top-bottom blowing converter furnace used for melting ordinary steel is sometimes used, but in most cases, the chromium source is 7ER chromium produced in an electric furnace.

The problem in that case is that chromium ore is reduced in an electric furnace.
The disadvantage of using Erochrome is that the reduction energy cost is high, which ultimately increases the cost of stainless steel molten steel.

One way to solve this problem is to add part of the chromium source to chromium ore or a semi-reduced product obtained by prereducing chromium ore outside the furnace during the converter M steel process, for example, into molten steel. Attempts are being made to replace it by reducing it with the carbon it contains. However, the methods known so far are not optimal for the reduction of chromium oxides, resulting in the problem of high oxide content in the slag after reduction with carbon (e.g. Iron and Steel '82- 8843). In order to reduce its content, it is necessary to increase the blowing temperature to 1700°C or higher, or to add a reducing agent such as ferrosilicon to reduce and recover the chromium oxide in the slag. was necessary. In other words, with the aim of reducing costs by converting the reduction energy of chromium ore from electricity to the combustion heat of carbon, a system was developed in which a large amount of ferrosilicon, which was actually produced using a large amount of electricity, was used for finishing and reduction. Or, it has caused a contradiction in that it places a significant load on refractories.

On the other hand, in recent years, a so-called smelting-reduction method has been announced that uses a top-bottom blowing converter method to produce ferrochrome from the conventional electric furnace method (Japanese patent application No. 58-117824, etc.), indicating the possibility of reducing electricity consumption in the production of ferrochrome. has been done.

However, applying this principle directly to stainless steel manufacturing does not result in an optimal manufacturing method. That is, the normal 7
Since the liquidus temperature of Erochrome is about 1570°C, in the bottom blowing method, the molten metal temperature must naturally be higher than 1570°C to perform bottom blowing operation. Under these temperature conditions, the slag composition required to dissolve the reduction-melting chromium spinel, which is characteristic of chromium ore reduction, has been determined ("iron and steel").
84-8117). On the other hand, stainless crude molten steel (Fe/C
The r ratio is almost close to that of molten stainless steel, but if 0% is high, the liquidus temperature will be lower than that of ferrochrome, so from the perspective of bottom blowing, the blowing temperature should be adjusted. It is possible to lower the temperature to below 1550°C, for example to 1500°C. Lowering the blowing temperature is an advantageous condition, such as lowering the refractory initialization and increasing thermal efficiency. However, in general, the slag conditions for dissolving the refractory chromium spinel, which is a prerequisite for promoting the reduction of chromium ore, have not been clarified, and it has not been possible to utilize the drop in the liquidus line. Therefore, there is no example in which the chromium content in cis-slag has been sufficiently reduced by carbon reduction at such low temperatures as described above.

As mentioned above, chromium ore or its semi-reduced product is used as the main raw material for chromium, and a top-bottom blowing converter type reaction vessel is used to promote the reduction of chromium oxide, which requires ultra-high temperature refining and ferrosilicon. It does not rely on finishing reduction, and also takes advantage of the low liquidus temperature of molten metal for ferrochrome to proceed with reduction efficiently, and ultimately connects it to molten stainless steel to produce stainless steel at low cost. It can be said that no method has been disclosed for producing high chromium alloys such as .

(Problems to be Solved by the Invention) The present invention uses chromium ore or its semi-reduced product as the main chromium source, and uses a top-bottom blowing converter type reaction vessel to perform ultra-high temperature refining and
It does not rely on conventional finishing reduction methods that require erosilicon, etc., and takes advantage of the lower liquidus temperature of the molten metal compared to ferrochrome smelting reduction smelting to efficiently reduce chromium oxide. The present invention provides a method for mass-producing high chromium alloys such as stainless steel at low cost by proceeding with the process and finally linking it to molten stainless steel.

Means for Solving Problem C) In order to solve the above problem, the present invention charges a raw material containing chromium oxide and a carbonaceous material such as coke into a top-bottom blowing converter type reaction vessel. In the method of manufacturing a chromium-containing alloy by melting and reducing oxides by supplying oxygen-containing gas, the composition of the molten alloy is determined by the formula (1) due to the fact that free carbonaceous materials remain in the furnace. A first step of melting and reducing chromium oxide by adjusting the slag composition at the end of the first step so as to satisfy the conditions of equation (2); The method is characterized in that it combines a second step of discharging a portion of the molten slag and a third step of decarburizing the molten alloy.

(C(%))≧0.07[Cr(%):] +4.
3 (1) (Function) In the present invention, reduction of chromium ore, such as ferrochrome, is used as the main chromium source (meaning 30% or more of the amount of chromium contained in the product) for the production of chromium-containing alloys. It is not the chromium ore that has undergone slag separation, but the chromium ore itself or the chromium ore that has been pretreated and pre-reduced.In other words, 30% or more of the chromium content exists as an oxide and is not contained in the chromium ore. MgO, m2o3,
Use one that contains gangue containing 5to2 etc. as its main component without being substantially separated. One example of pretreatment/prereduction is to mix chromium ore powder and carbonaceous powder such as coke, granulate or agglomerate it like R-let or turikerat, and heat it in a rotary kiln or shaft furnace. There is a way to do it. The reduction rate is determined by the heating temperature and the degree of reoxidation during heating, but under proper conditions, it is possible to reduce the chromium content to about 30 to 65 chrome.

The raw material containing chromium oxide is charged into a top-bottom blown converter type reaction vessel, and carbonaceous materials such as coke and gas containing oxygen are supplied to melt and reduce the oxide. conduct. The reason why a top-bottom blown converter type reaction vessel is used is to efficiently reduce slag containing hard-to-reducible chromium oxides by the strong stirring effect of the molten material by the bottom-blowing gas. For bottom blowing, for example, a double pipe tuyere is used to cool the tuyere to suppress wear and tear, while using oxygen gas or inert gas such as argon or nitrogen. For ℃・ru.

Carbon materials such as coke interact with gas containing oxygen. ,c+! -o2-+ c.

or, C+02-CO2,.

It generates heat by the reaction of , and supplies the heat necessary for the reaction and the caloric heat of the contents in the furnace;
and acts to carburize the molten alloy. When lump coke is used, it is charged from above the furnace, and when coke powder is used, at least 50% of the coke is either blown from above the slag or lumped and charged from above the furnace. Adding most of the carbonaceous material to the molten metal from above, rather than by blowing from the bottom, is a desirable condition in order to control the slag condition and stabilize operations (Figure 2). Note that it is also possible to directly use coal as a substitute for coke, although the calorific value decreases.

To begin operation, a source of molten iron, such as hot metal, is charged to the furnace. On the other hand, when the raw material containing chromium oxide is in the form of lumps, it is charged from above the furnace, whereas when it is in the form of powder, it is sprayed from above the slag through, for example, a top blowing lance.

In this process, the following two conditions are necessary. Since chromium is more easily oxidized than iron, when molten metal containing a large amount of chromium is exposed to a blown acid atmosphere, the chromium content will be reoxidized. As a result, it is difficult to reduce the chromium content in the slag to the required level. In order to prevent this, a predetermined amount or more of slag is allowed to coexist in the furnace. The amount of slag for this purpose is as shown in Figure 3, and the chromium content of 30 or more is added with the gangue content present in the chromium ore, and the slag content satisfies the following conditions. This can be achieved by adding a flux containing CaO or 5to2, or by leaving a part of the slag from the previous heat.

Experiments have shown that the slag component satisfies the following two conditions and is necessary to smoothly melt the hardly soluble chromium spinel and promote chromium reduction (Figure 4).

This is because the Az2o5 solubility in the silicate molten slag is the number of curves of temperature, and the At2o5 solubility of the silicate slag is
This is because if 5 minutes exceeds the solubility, magnesia spinel with a high melting point will precipitate around the chromium ore to prevent dissolution of the chromium spinel in the chromium ore.

Next, in order to stably control a large amount of slag without causing 7 ohms compared to normal converter operation, which is necessary to prevent the metal from being exposed to the atmosphere under the above-mentioned strong stirring state, it is necessary to It was found that it is necessary to add carbonaceous materials so that free carbonaceous materials always remain in the molten metal, and as a result, the molten metal must satisfy the component condition of formula (2) (Figure 5).

(C (%)) ≧0.07 [Cr (%)] +4゜3 (1
) By operating while satisfying these conditions, (T, Cr) in the slag can be reduced at relatively low temperatures and at
without relying on reduction using erotic silicon, etc.
(T, Cr) in the slag can be stably reduced to 2 inches or less.

Following the above first step, a portion of the generated large amount of slag is removed. This process involves the first step of stably sealing the strongly stirred molten metal with slag to prevent re-oxidation, and reducing the (T, Cr) of the slag with carbon. This process is for consistently linking the third step of oxidation treatment to reduce the carbon content, and it is desirable that the proportion of slag removed is high. Must be at least 50 inches, preferably 70-9
Preferably, 0% is removed. This is because the remaining slag contains the chromium reoxidized in the third step at least up to the saturation value of chromium oxide, so the amount of chromium reoxidized increases as the amount of slag remaining increases.

In the third step, top and bottom blowing acid is performed again to decarburize the molten metal. In addition, before or during the acid blowing,
Add stainless steel scrap and high carbon 7 erochrome. The amount of addition is determined by the amount of molten metal required, chromium chloride,
And the molten metal temperatures before and after the third step are determined so as to satisfy predetermined conditions.

One of the auxiliary means for adjusting the temperature and composition during the third step of decarburization is to blow powder containing iron oxide, such as iron oxide powder such as iron ore, or chromium ore powder from a top blowing lance together with oxygen. It is spraying.

In this case, the iron oxide in the supplied powder reacts with C in the molten metal to cause an endothermic reaction and decarburize. As mentioned above,
Depending on the combination of the type of chromium source to be added and the type of oxygen source for decarburization, predetermined composition and temperature conditions can be satisfied.

The carbon content of the molten metal after the third step may be as required for a stainless steel product, for example, [C]≦0.05%, but it is also possible to tap the molten metal at an intermediate level of 0% and perform vacuum acid blowing, for example. good. It is better to use equipment that is more suitable for decarburizing high-chromium molten steel in terms of the purpose of the present invention, which is ultra-high-temperature refining and decarburization from finish reduction using ferrosilicon or the like.

In either process, after decarburization is performed to a predetermined value, degassing and adjustment of trace components are performed as necessary, and then casting is performed.

(Example) Using a top-bottom blowing converter with a rated capacity of 150 tons, using outside-furnace phosphorus hot metal as the molten iron source and semi-reduced chromium cladding as the main chromium source, 18% Cr- 0
,9%C stainless steel 11 f884
0.05% C stainless steel was manufactured and continuously cast.

The ingredients of the raw materials used are as follows.

Figure 1 shows the changes in additives, components, and temperature in each step.

The components of the molten steel slag at the end of the first step are as follows.

In the second step, 75% of the produced slag is discharged, leaving molten metal and coke.

In the third step, 18% Cr-0.05% C stainless steel scrap No. 18 was added to this and top and bottom acid blowing was performed to obtain a molten metal with the following components.

(Effects of the Invention) As described above, the present invention utilizes an inexpensive ROM source and improves yield without relying on ultra-high temperature refining and finishing reduction using ferrosilicon, etc., which increase the cost of high chromium alloy smelting. It has made it possible to manufacture chromium-containing alloys such as stainless steel at a high cost and has great economic effects.

[Brief explanation of drawings]

Figure 1 shows the changes in components and temperature in the example, and Figure 2 shows the influence of the ratio of the added carbonaceous material added from above the slag, which is less than about 7 o'clock in the slag. Figure 3 shows the relationship between the degree of chromium reoxidation and the amount of slag, and Figure 4 shows the slag component conditions necessary to smoothly dissolve the hardly soluble chromium spinel and promote chromium reduction. Diagram showing the relationship between and temperature (for each melting temperature, the area on the lower right of the line indicates the necessary slag conditions to smoothly melt the refractory spinel and promote chromium reduction)
, FIG. 5 is a diagram showing the molten metal component conditions necessary to stably control a large amount of slag without causing forming. Fig. 2 02θ 40 10 210
/θθ Addition of Surino Sonotsu 5 Slag 〇 (ratio of (?/,) Figure 3 0 10D , l'θo 3θθ 4
00, fθ0 slab amount (k metal/l metal) Fig. 4 OS y6 /S 20 z
19AIbOs in 5.30 slag (%): (AI
Js (%)) Figure 5 Ccrt%)]

Claims (1)

[Claims] A raw material containing chromium oxide is charged into a top-bottom blown converter type reactor together with carbonaceous material such as coke, and a gas containing oxygen is supplied to melt and reduce the oxide. In the method of manufacturing a chromium-containing alloy by leaving free carbonaceous material in the furnace, the composition of the molten alloy changes to satisfy the formula (1), and the slag composition at the end of the first step satisfies the formula (1). 2
), the first step is to melt and reduce the chromium oxide, the second step is to discharge part of the generated slag, and the third step is to decarburize the molten alloy. A method for producing a chromium-containing alloy, characterized in that it consists of a combination. [C(%)]≧0.07[Cr(%)]+4.3 (1
)1/2(MgO(%))+(Al_2O_3(%))
≦0.09 [Molten metal temperature (℃)] (2)