DD233809A5 - POWDER-FORMAL CALCIUM-ALUMINATE AGENT AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The invention relates to a pulverulent calcium aluminate active ingredient, in particular for the refining of molten steel, and to a process for the preparation of the active substance, and furthermore to a molten steel refining process using the active substance according to the invention. According to the invention, a metallic aluminum core is contained inside the calcium aluminate particles. The active ingredient is prepared by preparing a syrupy lime containing slaked lime and adding to it aluminum powder with constant mixing, with 40-50 parts by weight of hydrated lime containing 60-55% by weight of aluminum, whereupon the mixture is heated at a temperature of 600C is being dewormed. If the active substance is to be used for refining molten steel, it is fed to the melt in an amount of 0.5-3 kg / ton steel.

Description

Explanation of the essence of the invention

The stated object is achieved by a powdered calcium-Aiuminat active ingredient, wherein in the interior of the calcium aluminate Kömchen a metallic aluminum core is included.

The aforesaid active ingredient is prepared by preparing a syrupy-type slaked lime and supplying thereto under stirring aluminum powder so that 40-45% by weight of hydrated lime accounts for 60-65% by weight of aluminum, whereupon the mixture is heated at a temperature is dehydrated to a maximum of 600 ° C. The grain size of the aluminum powder used for the preparation of the active ingredient is suitably between 0.1 and 1 mm. Experience has shown that the average grain size of the active ingredient produced falls between 1, 5 times and 1.28 times the average grain size of the aluminum powder used.

The dehydration is advantageously carried out in a temperature range between 350 and 600 ° C within a period of 1 to 3 hours.

The active ingredient according to the invention in an amount of 0.5-3 kg / ton of steel alone or together with other active ingredients fed to the melt. At least part of the active ingredient is expediently fed to the melt by powder blowing with the aid of a carrier gas.

The inventive method is based on the finding that in the course of both the metallic calcium-containing agents as well as by means of synthetic lime-clay slag and refining made by lime-aluminum mixtures desulfurization and the elimination of inclusions in particular by the calcium aluminates , In the treatment with synthetic slag, the calcium aluminates are finished fed to the steel, in the other two processes, however, they are produced by the reactions of the precipitation reduction (deoxidation) and then cause the fusion-deoxidation processes. This knowledge can already be found in the literature, although it has not yet been generally accepted. A greater agreement is that the conditions for binding the sulfur dissolved in the molten steel through the nonmetallic phases in contact with the melt improve as the activity of the oxygen in the melt decreases. In all of this, it should be noted that the deoxidation, desulfurization and entrapment assimilation processes occur within a finite time.

As has now been discovered, the free aluminum containing powdered calcium aluminate active ingredient melts very rapidly at the tapping and casting temperatures of the steels and therefore acts as a short-acting deoxidizer and desulphuriser. The original calcium aluminate shell also provides assurance that none is present Steel floating pure AI ₂ O ₃ inclusions arise. As a result of the original free aluminum content of the active ingredient, however, reduces the developing from the powder granules of the drug structure on the one hand oxygen binding on the one hand, the activity of the various oxides, so the MnO, SiO 2 activity in the molten steel, when this structure floats in the molten steel, and the FeO-MonO and SiO ₂ activities in the slag in the case of debris penetrated into the top slag. On the other hand, the calcium aluminates formed in the course of the application of the process - since they are not saturated in CaO - assimilate extremely effectively and, in the accompaniment of exothermic reactions, the various oxides, in particular the SiO ₂ . The melting point, and thus the viscosity of the complex oxides arising from the active substance in this way, gradually diminish in the course of the increase in the weight ratio of the oxides entering into them to a very great extent. At the same time, the sulfur solubility of the complex oxides resulting in this way generally increases, especially in the case of incorporation of SiO ₂ , to the 25% weight ratio of the latter progressively.

The process according to the invention was successfully used in production tests of various steel grades, wherein the active substance was fed to the molten steel in quantities of 0.5-3 kg / t by injection of powder or in some other way. The steels treated in this way exhibited low oxygen and sulfur contents, and virtually in the finished steel, the silicate and corundum inclusions did not exceed 10 microns, the latter fact being advantageous also with regard to the steels' continuous castability.

In the case of powder blistering using the drug, the degree of desulfurization of the steel further increases when ground water glass (Na ₂ SiO ₃ ) is added to the active ingredient up to 5-20% by weight. Furthermore, in the case of desulfurization carried out by powder blowing, an advantage can be achieved if the active ingredient is mixed with ground ferrosilicon. Instead, a simultaneous or previous addition of lumpy ferrosilicon can take place. Particularly advantageous is the treatment with the active ingredient in steel grades with a lower carbon content in which the final silicon content or end aluminum content is limited upwards.

For steels to be produced having a prescribed minimum aluminum content (e.g., above 0.02%), it is desirable to add lime powder in a 60-75% weight ratio in addition to the required amount of aluminum and the powdered calcium aluminate active ingredient containing the free aluminum.

The active ingredient can be used in continuous casting. As a ceiling component, it can be placed in the stub pan, also in place of the calcium silicon component in the flux used in the crystallizer ζ. B. mixed with ground water glass and the usual oxidants (saltpetre, scale).

The adoring invention has in addition to the listed advantages, d. H. Gene favorable metallurgical influences, also the advantage that it is less expensive than the known methods in terms of specific operating costs, and that its application requires no investment in complicated grinding and classifying, because the grinding or pulverization of aluminum a completely safe operation whereas grinding of calcium silicon is associated with an explosion hazard. Further, no use of melting furnaces is required, as in the treatment with synthetic lime-clay slag. Finally, a powder bladder device of average power is quite sufficient, while in the case of lime-aluminum-fluorspar injection is not the case

 Further details of the invention can be seen from the exemplary embodiments.

-3- 645

Exemplary embodiments Example 1

A medium carbon steel having a chromium content of 1% (quality BC3) was produced. From this alloyed chrome steel rods were rolled with diameters of 34-42mm. In the conventional technology used in the electric arc furnace, aluminum end deoxidation was used to maintain the prescribed mechanical properties with 0.04-0.05% total aluminum content, whereupon the finished steel was cast into bars. The object to be achieved by the method according to the invention is a final deoxidation which ensures the pourability of the steel on a continuous casting machine, which means that a residual aluminum content of max. 0.02% required.

The calcium aluminate active ingredient of the present invention was prepared by quenching one-third parts by weight of quick lime and mixing 2/3 parts by weight of aluminum grit having an average grain size of 1 mm into the slaked lime having a syrupy density.

The active ingredient as a result of running during and after mixing, chemical reactions produced in air-dry condition was then placed on a Metalltablettin the preheating furnace is in operation in addition to the furnace and held there for two hours at a temperature of 500-600 ⁰ C. Then, the metal tray was taken out of the preheating oven, the active ingredient was cooled for 10 minutes, whereupon the required amount of active ingredient was weighed and filled into a paper bag. The weighed drug was then dropped into the ladle at a feed rate of 0.6kg / ton along with the paper bag prior to tapping. After tapping, the steel was poured on the continuous caster with good surface finish. ;

The residual aluminum content of the steel was 0.014%, and during the tapping, the sulfur content of the steel decreased from 0.025% to 0.018%. The cast and rolled steel proved to be cleaner in terms of inclusions than the steels made using conventional technology.

Example 2!

The steel to be produced was an unalloyed heat-treatable steel (grade C45). According to the conventional technology, this steel is produced in a basic electric arc furnace by keeping it under the reducing slag for a corresponding period of time during the abrading and then adding pieces of aluminum for end deoxidation prior to oven tapping or during pan leaving. The goal to be achieved by the method according to the invention was a shortening of the Abgarzeit and a reduction of the oxide and sulfide inclusions of the steel. As described in Example 1, an active ingredient was prepared by mixing slaked lime and aluminum powder having a grain size of 0.3 mm. The mixture contained 45% by weight of hydrated lime and 55% by weight of aluminum. The average grain size of the produced mixture was 0.35 mm. The dehydration was carried out for one hour at a temperature of 500-550 ⁰ C. The dried active ingredient was sieved through a sieve with a mesh size of 4 mm and filled into bags.

From the active ingredient, a quantity corresponding to a dosage of 1 kg / t was placed in a paper sack together with lumpy ferrosilicon having a silicon content of 75% in an amount of 1.5 kg / t before tapping into the pan.

During the tapping, an amount of active ingredient of 0.75 kg / tin was blown into the melt with the aid of argon as the carrier gas.

In this complex treatment, the oxygen content of the steel decreased from 0.0117% to 0.0054% and its sulfur content from 0.022 to 0.012%. With regard to inclusions, the steel proved more favorable than a steel batch having a similar final composition but produced by conventional technology.

Example 3

Welding electrodes were made of low carbon unalloyed steel (quality ESAB Z). The specification of the composition of the steel includes Al, Ti and Si contents of max. 0.02%, whereby the observance of the prescribed max. 150 ppM O ₂ content at the prescribed C content of 0.06-010% can be ensured by applying a vacuum to the conventional technology. The invention now makes it possible to produce the electrodes in a Martin oven in which no vacuum system is available. By mixing 40 parts by weight of hydrated lime and 60 parts by weight of aluminum powder having a grain size of 0.7 mm, an active ingredient having an average grain size of 0.8 mm was prepared. The active ingredient was then dried in an oven at a temperature of 550-600 ° C for about 3 hours and then during tapping through a chute (along with a manganese carrier necessary to secure an Mn content of 0.40-0.60% ) is added in portions to the molten steel.

The steel thus produced conformed to all the requirements of the composition.

From the foregoing, it can be seen that extremely innovative refining can be achieved in a very simple manner with the aid of the novel active ingredient prepared according to the invention. However, the use of this agent reduces the manufacturing cost of the steels and simplifies the technology required to do so.

Claims (4)

claims: Powdered calcium aluminate active ingredient, in particular for refining (refining) molten steel, characterized in that a metallic aluminum core is contained inside the calcium aluminate grain. 2. A process for the preparation of the active ingredient according to claim!, Characterized in that one produces a syrupy-like slaked lime and this is mixed with continuous mixing aluminum powder by adding to 40-50 wt. Parts of lime hydrate 60-55% wt. Parts of aluminum powder mixed, whereupon the mixture is dewatered at a temperature of 600 ⁰ C. 3. The method according to claim 2, characterized in that aluminum powder is used with a particle size of 0.1-1.0 mm and an active ingredient having a grain size exceeding the above 15-28% grain size is produced. 4. The method according to claim 2 or 3, characterized in that the dehydration is carried out at a temperature of 350-600 ° C. Field of application of the invention The invention relates to a powdered calcium aluminate active ingredient, in particular for refining (refining) of molten steel and a process for the preparation of the active substance. Characteristic of the known technical solutions Methods are known for refining steel melts using metallic calcium containing agents. The use of these active ingredients in powder form is also widespread, these being introduced into carrier gas in the melt by means of a powder blowing device. The steel treated with metallic calcium has favorable mechanical properties due to the degree of deoxidation and desulfurization of the steels and the favorable morphology of the remaining non-metallic inclusions. The calcium is also supplied in elemental or alloyed form to improve the castability of continuous cast steels. In addition to all these advantages, the use of metallic calcium-containing agents such. As the calcium-silicon, calcium carbide, etc. the disadvantage that their production is costly and cumbersome, resulting from the energy costs or installation costs required for the reduction process and in particular for the grinding and Klassierungsvorgänge. Also well known is molten steel refining with synthetic lime-clay slags. For the composition of the synthetic lime-clay slags, contents of 52-53% CaO, 44-45% Al ₂ O ₃ and less than 1% FeO are characteristic. The process is realized by discharging the steel onto the synthetic slag after previously melting it in an oven used for this purpose. The disadvantage of using this method is the need for tempered melting of the synthetic slag fed in% by weight of 4-6 and the fact that the beneficial effects of the process (deoxidation, desulphurisation and elimination of the delays) do not take effect when the condition the synthetic slag contained in the steel ladle at the time of discharging the steel does not meet the requirements. Also known is a steel refining process in which powdered quick lime and aluminum powder are blown into the melt together with calcium fluoride in appropriate weight ratios. The application of the method gives good results in terms of reducing the oxygen and sulfur content of the steel as well as the morphology of the remaining non-metallic inclusions. The disadvantages of this method are on the one hand the considerable material costs for the required amount of flux and on the other hand the extension of the duration of treatment. The three mentioned steel refining processes accordingly give comparable results in their metallurgical effect. The distribution of the amounts of active substance required in the process can be illustrated by the following example: Desulphurization of a 0.15% carbon steel from 0.035 to 0.040% sulfur to about 0.010% sulfur can be achieved by blowing about 2 kg to 30% Ca-containing powdered calcium-silicon in the ladle (at 0.05% Al addition), or by discharging the steel to a liquid synthetic lime-clay slag amount of 10 kg / ton steel or by blowing CaO + Al + CaF ₂ powder in turn in amounts of 2; 0.5; 3kg / to steel can be achieved. Object of the invention The aim of the present invention is therefore the development of an active substance for the economic refining of steel melts, which at the same time also reduces the specific operating costs and capital expenditure compared to the conventional solutions, the metallurgical effect being at least equivalent to the conventional solutions.