DE1508229B1 - Use of non-pyrophoric, powdery sponge iron as a metallurgical additive to liquid cast iron or steel - Google Patents

Description

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The invention relates to the use of non-iron ore and 77 to 99% free or pyrophoric, powdery)! Sponge iron as containing iron bound in the form of the oxide FeO, metallurgical additive to liquid cast iron or steels. indicates a content solely in the form of It is about solidifying under the same FeO-bound oxygen of 22 to 0%. early improvement of the structure, degassing and rice 5 Powdered iron sponge, which is sunbathing of liquid cast iron and steels, e.g. B. in the case of the nucleation of pig iron and steels the production of blocks in molds, suitable by addition according to the invention, shows properties, certain and controlled quantities of a pure, powdery which with sufficient accuracy within right shaped, non-pyrophoric sponge iron can be varied by narrow limits and its output Composition, crystalline structure and choice essentially a function of the nature of the Grain size in the ladle or in the casting molds of the starting material and the self-contained during its manufacture. applied procedures. Such a product,

Numerous attempts have been made with the which advantageously by the method of The aim is to crystallize the cast iron produced in the course of the direct reduction of iron ore Modifying solidification by adding Ferro- 15 corresponds to the following key figures: silicon, Silico-Calcium, Silico-Manganese-Zirconium.

etc. in the ladle. One observes on this chemical analysis:

Way a multiplication and refinement of the total iron 77.0 to 99.0 »/ 0

Graphite particles, austenitic grains and fl ^e ~. · J? ^{until lüü} ' ^ü ' »

eutectic cells. However, from the nature of the 20 5 ^ ³ ν ''"'" \ ","

added seed particles even this method always Jn, Zn, Cu, As ™ "} $ Άϊ * ^SpUre "

the origin of heterogeneous inclusions. ^. ⁿ · · · · · - "> _o y '°

The iron and steel industry, for its part, has analogous ver ς- ς ρ <r η m ο /

search carried out with the aim of performing the operation of c «'/ ·" c

Cooling and crystallization of the mold in molds 25 ^ AuerstolUin form

cast steels and in particular the unquenched steels. ^{v <} ? ^{n b} ^ ■: " ^{υ to I2} '°' °

Steels by adding various powdered Mickstoft and water

Means, such as metal shavings or iron ore, to the bath to ς · η Äin MT ^- O ^ "io?

modify. The results leave no clear ² ~ * ~ ^Α1 2 ^υ 3 ~ r ¹¹ O ₂ · ■ <Wo

Conclusions, be it because the supplementary material is not 30 Physical Analysis

incorporated into the bath, be it because the steel obtained has a grain size of 40 to 2000 microns

after its solidification as of undesired inputs (preferably 40 to

Is found to be contaminated. 400 microns)

It appears that these failures are mainly due to bulk density 2.3 to 3.0 g / cm ³

with the composition of the vaccines used 35 effective density 6 ^ 0 to 7.2 g / cm ³

and are related to the macroscopic scale of their particle dimensions, which is located above the baths of molten cast iron or steel half that of the elementary crystals of the resulting added amount of vaccine may vary depending on its Structure is located. Content of FeO range up to 5 percent by weight, whereby the object of the invention is therefore to find an additive that has the desired properties of the end product can be iert for the treatment of liquid cast iron.

and steels that do not cause undesirable inclusions The condition of the fine distribution of the iron

leads into the structure, but at the same time a cleaning sponge gives the bound in the form of FeO and degassing of the melt and a refinement of oxygen as well as the air that is in the mikrodes Structure causes. 45 scopic cavities enclosed by the granules

According to the invention it was found that one is extremely responsive to substitution the earlier used vaccines by iron over oxidizable elements and unbound, floated of great purity and suitably solidly dissolved gases in the liquid cast iron or steel layers Properties surprising results and baths. Furthermore, the very high porosity and the Extraordinary quality products due to the small grain size of the vaccine due to the fine 50 profound modification of the cooling and the distribution in a very even form the cooling-crystallization the treated cast iron and steels treatment speed and the crystallization of the receives. To influence the melt in its entirety.

The invention relates to the use of finally have the porous granules which, 55 99 ° / consist of non-pyrophoric, powdered sponge iron a network of atoms according to the cubic Zender ₀ free iron or iron (II) oxide or a-centered crystal system, given Their struk-mixture of free iron and iron (II) -oxide and as turellen analogy with the main constituent the rest contains impurities and a bulk density melt a nucleating effect once through the epitaxy from 2.3 to 3.0 with a size of the porous grains (regularly oriented crystal intergrowth from 40 to 2000 microns, as metallurgical 60 gene) in the course of the solidification as well as through the changes-addition in the ladle or in the casting mold when the concentration of the melt in the neighboring cast iron or steel for cleaning and degassing is liquid each inoculation granule.

of the melt and to refine the solidification. Among the special effects which the result

structure, with the proviso that such a treatment is necessary for the treatment of nis, one must adhere to Steels with carbon contents below 0.05 of the melt 65 first and foremost the degassing of the cast iron and the together with the sponge iron of finely divided carbon steels. It is known that cast iron and the fuel is added. According to the invention, the majority of steels contain a certain proportion of gas turned iron sponge, which contained by reducing solution, in particular hydrogen and nitrogen

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material. At the moment of supplying certain menitride and achieving a less contaminated one The sponge iron in the liquid bath contributes to the disintegration of the surface.

porous granules spontaneously given the extremely The technique of inoculation for nucleation allows-

violent expansion of the air which they enclose. light the casting of ingots from unquieted The strong particle division that results from it, 5 steel from a height which is considered to be inevitable allows the immediate implementation of FeO particles exceeding the considered value of 1.8 to 2 meters, Powder with the carbon of the bath according to the as well as continuous casting into strands Reaction or slabs.

■ Pen _i_ r ν * _i_ rη 57 η w _Q i The characteristics corresponding to the above

ίο Vaccination shows as a further effect that in a very

The endothermic character of the reaction advantageously cleans the cast iron or steel melts, combined with the bulk cooling, which of the inoculants to which it is applied. Causes a noticeable reduction in the presence of non-metallic components, the solubility of the dissolved gases, and the carbon, which they contain in a very low concentration, take on oxide vesicles as they rise to the surface 15, such as. B. SiO ₂ and Al ₂ O ₃ , in the medium in statu by the turbulence a significant proportion of the nascendi and extremely finely divided. Since they are using gas. ^Λ infusible under the conditions of treatment

In the case of very low carbon steels, they rise very quickly because of the heaviness material content one must effect the degassing by the surface, whereby it is a substantial proportion of the with the inoculation product finely divided carbon 20 impurities which are in the melt are added, to initiate the reactions. If you can, get carried away.

However, the treatment according to the invention on half The influence of inoculation on the degassing and the

Applying soft steels, just like the unskilled steels, has depletion of the baths in carbon and silicon for deep drawing, the steels with high magnetic in the same way a fundamental change in the Permeability or certain alloy steels of the auste- 25 hardness and their depth in the case of chilled cast iron and meliernitic Nickel-chromium type 18/8, in which it results in tem casting when pouring into the mold. Man With regard to the dangers of overoxidation, for example, a slight depth of the rig is to reduce the carbon content to values below the hardened layer with an addition of 1.5 weight-0.05% lower, it allows the extraordinary percentage of sponge iron of special particle size, Reactivity of the iron powder towards the 30 which are between 40 and 400 microns and Carbon under excellent conditions - the content of FeO is 24%, to get to degassing and decarburization in good time, Among the special modes of action of the invented

Without the other constituents of the melt, proper use must ultimately be the except in particular the silicon and the manganese, influences quite significant influence of the inoculation on that will. 35 Crystalline structure of cast iron and steels themselves

As shown above, doing this each gets mentioned.

porous vaccine granules, which are separated by the

Development of the powdery aggregates set free formation of the cast iron or the partial transformation will induce crystallization by moving from austenite to ferrite in steels, the effect of the mass cooling, the change 40 especially in the gradations with low coherence Iron concentration in the vicinity of the partial fuel content and high silicon content, which lead to Chens and an orderly production of magnetic sheets proceeding from the latter are intended, whose Crystal growth. The finely divided state of iron - hot brittleness and internal tension in considerable powder thus has a positive effect on the nucleation-like way and its magnetic one Speeds and germ growth, which significantly improves 45 permeability, it gives the end product a finer structure in the black The ferrite-forming effect of the sponge iron

cast iron is the consequence of the deposition of a certain corresponding to the lack of microporosity. th amount of nitrogen and hydrogen as these gases The process of crystallization in the form of dendrites stabilizers of the carbon compounds of iron is found fundamentally through the shortening of the 50 in the form of cementite or perlite. Modified crystallization zone; The end product is thus effected in the case of eutectic cast iron with lamollarem is more uniform and less internal stresses graphite and pearlitic matrix an inoculation with subject. 1.5 percent by weight of pure iron sponge with 24%

When using the inventive FeO the immediate formation of 12 to more than When driving on unskilled steels one finds that the 55 20% ferrite depending on the working temperature. The treatment turbulence — more violent, however, of a much shorter duration is much more effective when one is on better peripheral cooling and faster ductile iron, since in this case the Release of the dissolved gases allowed. For example, ferrite formation has been facilitated to such an extent In the course of the casting of 5 ton ingots, that is in many cases a heat treatment a reduction in the duration of turbulence from a 60 to ferrite formation with its risk of deformation Third to a quarter observed, thanks to which the addition is no longer necessary.

of 1.5 percent by weight vaccine, which contains 28% FeO In contrast, the vaccination of black-

and contained 71.5% metallic iron, and a verzem malleable cast iron and in particular of cast iron with No reduction of half to two thirds with additions of spheroidal graphite, the thermal ferrite formation 2%. In addition, the use of the 65 allows the treatment to be omitted; however, it shortens theirs Add the amount of aluminum by a third or half thanks to the storage cabinets, what to reduce the brittleness lent improvement of the tendency to ferrite formation, causing aluminum content of the metal - which the treatment gives to these products.

In general, pieces of cast iron treated with sponge iron show a more homogeneous structure, too the risk of cracks, gas bubbles and undesired inclusions occurring is reduced.

Among the numerous results that have been achieved in the foundry, it should be mentioned, for example: Improving the quality of rolling mill rolls made of hardened, ordinary or alloyed cast iron, of rollers and wheels made of ordinary hardened cast iron, as well as semi-hard and three-quarter hard Rollers. For the molding of these products, cast iron was used, which is according to the invention with 3 percent by weight sponge iron with 24% FeO content, the mean grain size of which is between 40 and 600 microns were vaccinated. Regardless of the analytical composition of the cast iron used there was a significant reduction in cracks and pinholes, as well as one Increasing the hardness of the work surface and the flexural strength.

Another advantageous application of the present invention relates to the reduction of excretions in the head part of large blocks of unkilled steel.

Untilled steel billets have interesting deep-drawing and wire-drawing properties, however undesired excretion of certain elements, such as carbon, manganese and sulfur, the latter becoming more important as the mass is increased. By adding This phenomenon is significantly limited by aluminum or with mechanical cover, but you only get reduced qualities, especially with regard to weldability and Deep drawability.

According to the invention it has been found that the advantages of the unkilled steel are preserved and its disadvantages This can be avoided by adding a special amount of sponge iron to the ingot as it solidifies incorporated in powder form of given FeO content.

The delayed addition of the pure sponge iron to the mass has a resurgence of the turbulence to the Consequence, since the reaction of the oxygen available in the form of the oxide FeO with the excreted oxygen Elements in which the still liquid part of the block is enriched occurs. Simultaneously the convection current is accelerated, with the zone of columnar crystallization and the secondary Blowing bubbles against the center of the block will. It extends to a fairly large depth of the block thanks to the thermosiphon effect that is created from the endothermic character of the reactions and the absorption of heat by the bath supplied, cold sponge iron results, with gas washing and possibly inclusions in the direction be taken to the headboard. The developed from the given structure of the sponge iron The reaction proceeds at great speed, and the pure Eiseakörnchen then act as homogeneous Seed, so that the accelerated solidification takes place without enlarging the austenitic grains and no precipitation occurs as the material solidifies in its given state.

The amount of sponge iron used can be up to 5 percent by weight of the ingot, according to the FeO content, range. However, excellent results are obtained with much lower amounts in the Of the order of 0.2 to 0.7% If, for example, 0.5% by weight of a sponge, which contains 36.3% iron oxide, added to a steel ingot of 5 tons 8 minutes after casting, you put in the head part of the ingot a reduction of 0.02% carbon, 0.1% manganese and 0.01% sulfur and consequently an improved homogeneity of the mass solid. The total time it took to freeze is reduced by a quarter to a third.

Claims (6)

Patent claims: 1. Use of non-pyrophoric, powdery sponge iron, which is 99% free iron ( or iron (II) oxide or a mixture of free iron and iron (II) oxide and the remainder impurities and a bulk density of 2.3 to 3.0 with a porous grain size of 40 to 2000 microns, as a metallurgical additive in the ladle or in the mold volatile cast iron or steels for cleaning and degassing the melt and for refining of the solidification structure with the proviso that for the treatment of steels with carbon contents less than 0.05% of the melt was added together with the sponge iron, finely divided carbon will. 2. Use according to claim 1, characterized in that the grain size is between 40 and is 400 microns. 3. Use according to claim 1 or 2, characterized in that the sponge iron as a function its FeO content in an amount of at most 5 percent by weight of the melt will. 4. Use according to one of claims 1 to 3, characterized in that the sponge iron the cast iron and steel melts in the case of continuous casting, continuous in the case of of the standing casting is added all at once. 5. Use according to any one of claims 1 to 4, characterized in that when adding the Sponge iron to non-killed steels have a reduced amount of regulator aluminum Melt clogs. 6. Use according to one of claims 1 to 3, characterized in that the sponge iron for the production of ingots from unskilled steel is added in the course of solidification.