LU83476A1 - IMPROVEMENTS IN CONTINUOUS CASTING PROCESSES FOR METALS, AND LINGOTIERE FOR THE IMPLEMENTATION OF THESE PROCESSES - Google Patents

Description

i i -ΙΟ 2150 / 8107- METALLÜGIC RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Improvements to continuous metal casting processes, and ingot mold for the implementation of these processes.

The present invention relates to improvements concerning processes for the continuous casting of metals, and especially for the continuous casting of steels, mainly those having a carbon content of between 0.1% and 0.2%.

During the process of extracting the ingot from a continuous casting ingot mold, supplied with metal (for example steel) continuously at its upper orifice, the friction forces between the ingot mold and the ingot undergo significant variations due notably to the oscillatory movement ^^^ imposed on the mold.

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It is known that during a phase of the ingot mold oscillation cycle, the speed of descent of the latter is greater than that of the ingot, and it has been found that during this phase, the upper part of the ingot, particularly thin at the place where its solidification begins, was subject to a bending stress towards the inside of the ingot mold, which causes its curving towards this inside.

This phenomenon causes, by contraction of the steel, the formation of an oscillation wrinkle which can serve as a primer for the cracking of the skin of the ingot at a level lower than that where solidification begins, because in this place, the skin of the steel strand is thinner and is therefore more affected by * the thermal and mechanical stresses which stress the steel strand during its solidification, as moreover during its cooling in the continuous casting machine. repetitive, the outer surface of the ingot presents a series of successive wrinkles affecting the quality of sound. aspect.

To make the ingot look satisfactory, one is, during packaging, currently forced to lose by chalu-meautage or grinding, a certain amount of metal, which constitutes a significant drawback.

. The subject of the present invention is a method by which this drawback can be remedied.

The process, object of the present invention, during which liquid metal is poured into a continuous casting mold, is essentially characterized in that the wall of the upper part of the mold faces the metal zone where solidification begins. and where the oscillation wrinkle is formed, is less cooled than the lower part of the so-called ingot mold.

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In this way, the tendency to flex towards the inside of the ingot part where solidification begins, and consequently the formation of the wrinkle, is reduced.

According to a first operational modality of this method, this differential cooling is carried out by constituting the said upper face of an insert of appropriate dimensions and whose thermal conductivity is lower than that of copper.

This insert reduces heat transfer in the upper part of the ingot, at the level of the formation of oscillation wrinkles.

According to a variant of this modality, one can make use of an insert whose dimensions have been calculated to obtain the desired differential cooling, by giving it at its upper part a thickness greater than that of its lower part, which attenuates the 'cooling effect at the said upper part.

It is also possible to provide the ingot mold for continuous casting with two distinct water cooling circuits, or conveying cooling fluids with different thermal conductivities or to modify (reinforce) the thickness thereof at its upper part, in such a way that the re-cooling of said upper part is less than that of the lower part, the temperature of the internal wall of the upper part of the mold cannot, however, in the case of copper or low alloy copper, exceed temperatures between 200 ° C and 350 ° C depending on the nature and content of the elements alloyed with copper (for example Ag, P, Te, Zr, Cr, Be, Ni, Si, ...).

According to the invention, a stainless steel or any other refractory metallic material can be used as insert, preferably with the lowest possible wettability with respect to steel and slag of powder, electrofused material, cermet, boron nitride. These materials can even have a certain porosity, thanks to which one can blow through, towards the metal, a gas for example of argon or nitrogen, possibly preheated.

I According to a second advantageous variant of the process of the invention! tion, the upper part of the mold has on its side facing the metal being solidified, a vibrating plate or a material, for example of the kind mentioned, vibrated, which in particular has the effect of destroying any tendency for sticking of the ingot skin on the ingot mold.

„It is not outside the scope of the invention to constitute the ingot mold ea, two superimposed parts, each part having its own cooling system, and the lower part being moreover subjected to a vibratory movement.

It is also advantageous, according to the invention, to carry out this differential cooling, by increasing in the region of the edges of the mold, the thickness of the layer of covering powder usually deposited on the liquid metal and intended to serve as a lubricant. The most interesting results have been obtained with lubricants in non-pulverulent form, for example agglomerates, in platelets or ribbons.

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One can also make use of one or the other heating means (preferably non-oxidizing), focused against the internal upper edge of the ingot mold facing the metal zone during the beginning of solidification.

By way of nonlimiting example, focusing by optical means, such as a laser, electric or inductive transmitter, I can be used.

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5.- Experience has shown that such a method makes it possible to obtain an ingot whose external face no longer or almost no longer bears the aforementioned wrinkles.

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Claims (11)

1. Process for the continuous casting of metals, and in particular of steel, characterized in that during the casting of the metal in the continuous casting ingot mold, the wall of the upper part of the ingot mold, which faces the metal area where solidification begins, is less cooled than the lower part of the mold (differential cooling). 2. Method according to claim 1, characterized in that this lower cooling is achieved by making use, in the mold, of two separate water cooling circuits, or conveying cooling fluids of different thermal conductivities, in such a way that the cooling of said upper part is less than that of the lower part, the temperature of the internal wall cannot however, in the case of a copper or low alloy copper ingot mold, exceed temperatures between 200 ° C and 350 ° C (depending on the nature and content of the alloying elements). 3. Method according to claim 1, characterized in that this differential cooling is achieved by increasing in the region of the edges of the mold, the thickness of powder or covering material usually deposited on the liquid metal and intended to serve as a lubricant. 1 Method according to claim 1, characterized in that,. to obtain differential cooling, use is made of a heating means (preferably non-oxidizing) directed 4 against the internal upper edge of the ingot mold facing the metal zone in the process of solidification beginning, for example electrical means (inductive or other), focusing by optical means, for example a laser transmitter ... 4 V I 7 · - j 5. Ingot mold for implementing the processes listed in one or other of Claims 1 to 4, characterized in that its internal upper face comprises an insert of appropriate dimensions and whose thermal conductivity is lower than that of copper . 6. Ingot mold according to claim 5, characterized in that the thickness of the insert at its upper part is greater than its thickness at its lower part. 7. Ingot mold according to either of Claims 5 and 6, characterized in that the insert comprises one or more of the following components: stainless steel, electro-molten material, cermet, boron nitride, etc., or any other metallic or refractory material having only a very low wettability with respect to the cast metal and the slag coming from the covering powder, which components may have a certain porosity. 8. Ingot mold according to either of claims 5 to 7, characterized in that the insert can be accompanied or constituted by a vibrating plate, the whole provided with means for placing the plate and / or the insert in state of vibration. , 9. Ingot mold for implementing the processes set out in claims 1 to 4, characterized in that it consists of two superposed parts, each of the two parts being provided with its own cooling device, the upper part being in addition provided with means to make it vibrate. JL * ♦ 8.- 10. A method for implementing the ingot mold listed in claims 7 or 8, characterized in that one blows through the insert towards the metal inside the ingot mold, a gas such as for example argon or nitrogen, possibly preheated. 11. Processes and molds as described and claimed above. ^ ^ *