JPH02294421A - Production of miscellaneous unalloyed and alloyed steels - Google Patents

Abstract

PURPOSE: To reduce the cost of a gas specific to a refining by performing a treatment in the decarburization, heating and mixing processes in the secondary steel refining of various kinds of non-alloy and alloy steel with perfectly gaseous CO₂.

CONSTITUTION: When various kinds of non-alloy steel and alloy steel containing ≤10% alloy elements is manufactured by temporarily sucking oxygen and/or treatment gas (inert gas N₂ and Ar) as the process gas through a nozzle provided on a bottom of a secondary steel refining converter, the refining is performed by replacing the treatment gas with the gaseous CO₂. The gaseous CO₂ is preferably obtained through evaporation from its liquid phase.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for injecting oxygen and gas as a temporary K process gas through a nozzle located at the bottom of a converter during a process consisting of decarburization, heating and mixing steps. / or in a secondary steel refining converter injected with process gas, various non-alloyed steels and alloying elements 10
The present invention relates to a method for manufacturing alloy steel containing up to

BACKGROUND OF THE INVENTION Post-treatment of various alloy steels in bottom-blown converters is carried out using oxygen as process gas and nitrogen and alponic as process gases. This type of secondary steel refining method is abbreviated as MRP.
(Metal Refining Method), AOD (Alponic Oxygen Decarburization), UB
D (under bottom plowing decarburization) and AS
It is known as M (argon secondary metallurgy). They are useful for refining various low alloy to high platen metal hooks in the converter type of the same name with a bottom nozzle, in which various steels are melted in the electric arc furnace. Generally, non-alloyed steels are not produced in these converters. However, there are manufacturers who smelt non-alloys in these types of converters, even though K is expensive in terms of quality and it is cost-effective to smelt it in arc furnaces.

It is known from German Patent No. 2 430 975 to partially replace nitrogen and argon by mixing with cO2. The specification of Western Patent No. 934772 is as follows:
A process for producing non-alloyed steel in a Petsemer and Thomas converter with a low content of harmful gases is disclosed. At this time, Kco2 is injected into the bath by adding Kco2 as a gas or by adding lime alone or in a mixture with oxygen.

Generally, the steel melt for secondary steel refining is first melted in a melting furnace and then transferred to a new container, ie, a converter. Therefore, the melt is treated by injecting gross gas and coral gas into the melt through the bottom of the converter. For this purpose, a peripheral wall gas nozzle made of general K metal is used, in which process gas is blown through a central nozzle and process gas is blown through a ring nozzle. The process gas blown through the ring nozzle is an inert gas and is particularly useful for cooling the metal nozzle during blowing and for mixing the melt. That is Ar
and N2. By partially replacing these inert gases with CO2, the inherent gas cost can be reduced.

Processing of the melt in the converter takes place in three steps: decarburization, heating and mixing. During heating, it is simultaneously K-desulfurized and alloyed. In the three steps of ζ, sample collection, temperature measurement, and addition of metal and nonmetallic solids are performed, and these three steps are mutually K-branched over time.

Figure 1 K shows alloy steel 4 2CrMO 4 inert gas N
The method steps of treating with 2 and Ar are illustrated.

Decarburization is indicated by range A, heating range B and mixing by range CK. Measurement point I and sampling point y for waterlogging measurement are indicated below a straight line indicating the passage of time in minutes. Below that are shown the changes in concentration of nitrogen and sulfur as well as K carbon (N, 8, C), as well as the change in K temperature T. The lower part of FIG. 1 shows the temporal and quantitative use of the process gas oxygen and the preservation or treatment gases argon and nitrogen.

Problems to be Solved by the Invention The present invention is based on the problem of further reducing the inherent gas cost that occurs during secondary steel refining of alloy steel.

Means for Solving the Problem According to the present invention K, this problem is solved by the features described in the characteristic part K of claim 1 starting from the state of the art considered in the generic concept of claim 1 of the claims. .

Advantageous embodiments of the invention are described in claims 2 to 8.

Can the method of the present invention not only partially but also completely replace inert gases N2 and Ar with CO2? Starting from this amazing observation, the gas cost inherent in K during secondary refining of steel is significantly reduced. The amount of C₂2 injected into the melt per unit time should be such as to provide a sufficiently high mixing energy to the melt. The entire reaction can then proceed under equilibrium conditions. In the method of the present invention, N2 and Ar are completely replaced by CO2 during all three steps of steel processing, including decarburization, heating and mixing.

The progress of the method of the present invention is shown in Fig. 1 for K steel 42CrMo.
4 is illustrated in FIG. From FIG. 2 it is immediately clear that the same basic process result is achieved.

CO2 has different effects in each method step. It is described below.

When starting the treatment method, when raising the converter from the side to a blowing level of 1K, inert gas is blown into the nozzle to prevent the melt from entering. 02 can initially be supplied for safety reasons when the blowing position is reached. When tilting the converter again, corresponding means are required. The amount of gas loaded onto the nozzle while the converter is operating in this manner is said to be a safe amount.

When the melt is decarburized with oxygen, K, and CO, a safe gas amount is supplied while the converter is in the blowing position.

Thereafter, oxygen is blown in through the central nozzle, while cooling is constantly performed with CO2 through the ring nozzle. By charging oxygen and CO2 in combination in this manner, the partial pressures of N2 and H2 are reduced in the decarburization process. This results in off-gassing of the melt. At the same time, loading of the melt with gases N2 and H2 is avoided and therefore N2 and H2
This results in steel with significantly less

From the reaction co2+ C-20o K, additionally c
The O2 is used to decarburize the melt, ie the CO2 is an additional oxygen carrier in the decarburization process.

In the subsequent heating step, the use of CO2 has other effects during desulfurization and alloying. In this case, the melt is heated to the desired temperature by an exothermic reaction of the added aluminum, silicon or aluminum/silicon mixture with oxygen. Traditionally, argon was the only processing gas used in the heating process. This is because nitrogen dissolves in the melt and the melt is undesirably overloaded with nitrogen.

The following reaction should be considered when replacing argon with 002 according to the present invention: ? co2+4 Alto2 A12Cl,, + 3
c (1)3 CO2 +2Al − A120
! 5 + 3 CO (2) or CO2+ 81 - 810 ■ + C (3) CO2+ 8
1 - 810 + CO (4) In the heating step, both reactions take place depending on the aluminum concentration K in the melt. Corresponding to formula (1) or (6), the melt is carbonized in the heating step, the CO2 is completely reduced to K by the aluminum and the carbon atoms are liberated. Simultaneously react (
2) or (4), that is, partial reduction of CO2 proceeds, and these reactions do not cause carbonization of the melt.

As is clear from FIGS. 1 and 2, the melt is carbonized during the heating process. This carbonization can be calculated by the following formula: G [where dC is the carbonization rate Cppm/min and Q is the CO
2 Protective gas flow rate m3/min, Cf is carbonization coefficient 0.6
~0.5, and G is the weight of the melt] Holding gas amount CO22? At F+3/min, carbonization rate is 10t
In the converter, the legging factor Cf − Q. 5 and is as follows: ac - 5 3 6 X 2 X O. 5/1
0 - C 5 6.6 ppm/, min The effects obtained using coz in the decarburization and heating steps according to the present invention are set forth in Tables 1 and 2 below for elm steel. Table 1 showing the nitrogen content measured in the exhaust gas of the melt
describes the results of the operation of conventional methods using nitrogen and argon as well as the results of the method of the present invention.

? Important to the effectiveness of the squares of the present invention during the heating process is the purity of the CO2. Liaoyuan of the melt with aluminum K makes the solubility of 9 elements in steel higher. Therefore, coz
The hydrogen and hydrogen impurities inside are collected in the melt and can no longer be removed. In order to avoid this, the metallurgical treatment of the steel according to the invention requires N2 maximum so o
Industrial K-pure c('12) containing vpm and H20 #high 50 vpm should be used. This purity is obtained by evaporating the CO2 from the liquid phase.

Also in the mixing step, according to the present invention, argon is completely replaced with CO2. Depending on the technical level, the melt should be heated with argon for about 1 minute before tapping.
Mix for ~2 minutes to adjust temperature. At this time, Arco 9
When replacing the gas with CO2, the melt is oxidized by the reaction described in the heating step immediately before the K1 extraction. CO■
A chemical addition of about 1.0 times per fit adjusts for this analytical variation. The concomitant carbonization can be ignored since it amounts to only 50 ppm at most and therefore falls within the analytical tolerance range.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the process of treating alloy steel 4 2 CrMo 4 with inert gas N2 and Ar from the technical water chain K;
Figure t#2 is alloy steel 4 2 from Invention K, similar to Figure 1.
FIG. 3 illustrates a method step for treating CrMO 4 with CO 2 .

Claims (1)

[Claims] 1. During the process steps consisting of decarburization, heating and mixing steps,
Various non-alloyed steels and alloyed steels containing up to 10% of alloying elements are processed in secondary steel refining converters in which oxygen and/or process gases are temporarily injected through a nozzle located at the bottom of the converter. in which the process gas is gaseous CO_2.
and the manufacturing method of alloy steel. 2. Process according to claim 1, characterized in that during times when CO_2 is supplied alone, CO_2 is injected through a ring nozzle and also through a central nozzle, and the oxygen and process gases are injected through a metal peripheral gas nozzle. 3. Process according to claim 1 or 2, characterized in that the CO_2 contains up to 500 vpm of N_2 and up to 50 vpm of H_2O. 4. Process according to claim 1, characterized in that the gaseous CO_2 is obtained by evaporation from a liquid phase. 5. The method according to any one of claims 1 to 4, characterized in that CO_20.2 to 1.0 m^3/min is injected per ton of steel. 6. The method according to any one of claims 1 to 5, characterized in that in the heating step carbonization of the melt is induced by necessary addition of Al or Si. 7. Carbonization rate dC is calculated using the formula: dC = (536 x Q x Cf)/G [In the formula, dC is carbonization rate Cppm/min, and Q is CO_
2 flow rate m^3/min, Cf is a carbonization coefficient of 0.3 to 0.5, and G is the weight of the melt. . 8. Any of claims 1 to 7, characterized in that fluctuations in the analysis due to reoxidation of the melt during the mixing step with pure CO_2 are prevented by the stoichiometric addition of 1.0 kg Al/CO_2 m^3. or the method described in item 1.