JPS6010087B2 - steel smelting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention discloses the method of blowing gaseous oxygen onto or into the steel melt where the blowing effect is exerted by blowing inert gas and (
or) relates to a method of refining high chromium stainless steel to a low carbon content of 0.03% or less by blowing.

In the past, it was common to melt steel and melt it in smelting furnaces, such as electric arc furnaces.

At the beginning of the VI dynasty it was first considered to use the furnace only for melting, with the smelting and alloying operations carried out in subsequent equipment such as crucibles or converters.

This presented the decisive advantage of allowing the furnace to be loaded higher than the intended purpose and to work economically. The time for one charge was almost halved.

Therefore, it was possible to melt approximately twice the amount in the furnace compared to the previous method. Subsequently, various methods of smelting molten metal in special vessels became known.

The so-called AOD process (argon-oxygen decarburization process), which is known, for example from German Patent Publication No. 150 828 P', consists in blowing a molten steel argon-oxygen mixture transferred from the melting furnace into the converter. In this case, argon gas as inert gas has the purpose of lowering the oxygen partial pressure in the moat and thereby increasing the affinity of oxygen for carbon even more than for chromium. This method also avoids oxidizing or slugging the chromium when blowing or blowing oxygen into the chromium-containing material and requiring replenishment at the end of the L-scouring process. 6
Towards the end of the Iimo era, another scouring method became known, according to which molten steel produced in a melting furnace, such as a hot air cupola, is pre-smelted in an oxygen top-blown converter and then in a pan degasser under vacuum. The final scouring process is carried out by top-blowing gaseous oxygen.
(See pages 196 & 153-159)
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By this known method, it is possible to decarburize the total steel to a carbon content of Q0I% or less with almost no chromium loss. DE 14 58 901 A1 discloses a method for blowing oxygen or an oxygen-argon mixture onto the surface of the molten steel in a rubbo, in which case the oxygen or argon-oxygen mixture is blown through the molten metal.

Instead of argon, steam or methane (see DE 2308469) or oil (see DE 2033975) have also already been used. Proceeding the scouring process under reduced pressure has been proposed for three generations for the production of ferrochrome (see West German Patent Specification No. 676,565), and this proposal has recently been incorporated into US Pat. It was adopted again in No. 3854932.

In both cases, gaseous oxygen is blown onto the bath surface of the molten metal in the converter, and in the case of the US patent gas bubbles of inert gas penetrate the molten metal, exerting a flycatcher effect and promoting scouring. Included as above.

All current or known methods of refining chromium liquid steel aim to avoid oxidation of chromium in the flaws. This was achieved to some extent. However, despite all efforts, it has generally been necessary to replenish the slagged chromium content by addition of chromium in the form of metal or prealloys. A disadvantage of the known method is that the equipment cost is relatively high, and this is because the first method of pre-scouring in the rubbo and finishing scouring under vacuum in the pot degassing device also requires scouring under vacuum. For example, the case according to US Pat. No. 3,854,932 is also the same. In the case of the AOD method, the high argon consumption is economically disadvantageous. The object of the present invention is to obtain a relatively simple process which does not have the above-mentioned disadvantages of the known methods and which makes the scouring process more economical than the known methods.

In order to solve this object, according to the invention, the scouring is carried out in gaseous oxygen in a known manner, initially at atmospheric pressure to a carbon content of about G.

Immediately thereafter, the molten metal was continued to be heated with inert gas in the same container, but the supply of gaseous oxygen was stopped, and the pressure above the port bath was lowered to about 10 torr. A method is proposed in which boiling is carried out under reduction of the metal oxides formed during scouring until the desired final carbon content is reached.

When carrying out the method of the present invention, chromium-containing molten steel is first melted in a furnace according to a known method and transferred to a container such as a converter, and then the carbon is reduced to about 0.0% by top-blowing or blowing oxygen under normal pressure.
Pre-scouring to a value of 2-0.4%.

Next, in the same vessel, the oxygen supply is interrupted and the pressure is continuously lowered to about 10 torr or less while the molten metal is further maintained concentrated by inert gas. The molten steel is boiled at this pressure until it reaches the desired final carbon content. Surprisingly, the chromium oxide and manganese oxide that are unavoidably formed during scouring are reduced during boiling under vacuum and the lacquer is alloyed back to its original chromium and manganese content.

According to the method of the present invention, the addition of these metals to replenish the part that becomes slag during scouring is not necessary to the extent that it is possible with the methods to date, provided that the analysis of the steel before scouring is adjusted to the final amount. Not. The reduction of chromium oxide and manganese oxide that takes place during boiling of molten metal under vacuum is clear from the following table: Steel Chiya composition After scouring, before vacuum application After vacuum treatment C 025 Poly 0.013 grand Mn
0.99 Grandchild 1.11 %Cr
16-34 Grandson 16-73 %02
650ppm 420ppmFe Remainder Remainder temperature 1780C 1724℃
As shown in the table, the chromium content is 16.3 before vacuum treatment.
From 4% to 16.73%, the manganese content increases from 0.99% to 1.11%.

Since chromium and manganese were not added during vacuum processing, this increase is due to the reduction of chromium and manganese oxides from the slag on the steel melt. The oxygen liberated during chromium reduction further reduces the amount of carbon in the flaw.
In order to reduce the carbon content to a value below 0.02%, the advantageous formation of the method of the invention allows the oxide to be added in particular in solid form, for example as scale, or during the boiling under vacuum. extend the time. Reduction of these oxides under vacuum liberates oxygen, which combines with carbon and promotes decarburization. Boiling under vacuum is 17
It is carried out at temperatures above 0.000. The time required for this is approximately 13 minutes and the temperature drop that occurs during this time is 6000 °C. The advantage of the method of the invention over known methods which are carried out in two different containers or devices is that the equipment outlay is low and the time consumption is low.

Compared to known scouring methods which operate under vacuum application, the process according to the invention has the following advantages: Spatter-free scouring is possible.

That is, unlike in the case of scouring under vacuum, flying particles that stick to the converter opening are not generated. Vacuum hoods' can therefore be installed completely airtight. The pump capacity for vacuum generation may be smaller than in the equipment required to carry out known processes which proceed completely under vacuum.

This is because, in the case of vacuum generation at the end of the scouring process, it is not necessary to draw in as much gas as is necessary during oxygen top-blowing scouring. The possibility of reduction of chromium and manganese, which form into slag during scouring, is not as great in the known process as in carrying out the process of the invention.

Claims (1)

[Claims] 1. Making steel, especially high chromium stainless steel, have a low carbon content of 0.03% or less by top-blowing and/or blowing gaseous oxygen into molten steel, which is stirred by blowing inert gas. In the method of scouring, scouring with gaseous oxygen is first carried out at normal pressure until the carbon content is reduced to about 0.2-0.4%, followed immediately by the molten steel being stirred in the same vessel with inert gas, but with gaseous oxygen. The supply of oxygen is discontinued, the pressure above the steel bath is reduced continuously to below about 10 torr, and boiling is allowed to occur under reduction of the metal oxides formed during scouring until the desired final carbon content is reached. A steel refining method characterized by: 2. A process as claimed in claim 1, in which the oxide is added during boiling, preferably in solid form, for example as scale.