Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1986-11-25
1986-11-25
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164455, B22D 11124
Patent
active
046242988
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method of cooling strands in the continuous casting of steel.
In a number of steel products, such as high-carbon steel wires, their technological properties are perceptibly impaired by segregations. In the patenting of such wires from the rolling temperature, such segregations can result in the formation, at the point of segregation, of brittle phases, often referred to as "martensite", which greatly diminish the ductility of the wire.
While in the casting of ingots, the segregations are found in the upper third of the ingot and can be removed by cutting off the top, in continuous casting they become distributed over the entire length of the strand and cannot be removed by cutting. Their negative effects are greater in so-called "small-size" strand casting--dimensions from 100 to 140 mm on a side--is greater than in large-size strand casting, i.e., pre-billet sizes of 200 to 300 mm on a side, since the small sizes require less reduction in rolling to the final product. Considerable efforts have already been devoted by people skilled in the art to reduce the segregations in continuous casting or diminish their negative effects on the rolled product. In the course of such developments, the impression has developed that a so-called globulitic structure is associated with low segregation, but a dendritic structure is associated with heavy segregation. By the term, "globulitic structure," as used herein, a structure is to be understood in which the crystals do not have a preferred direction of growth, but are distributed randomly over the cross section. FIG. 1 shows the structure of a continuous-cast billet having a large proportion of such a globulitic structure. By a dendritic structure, on the other hand, a structure is meant in which the predominant direction of growth of the crystals runs into the metal, perpendicular to the strand surface.
On account of the impression that dendritic structure would promote segregations and reduce globulitic structure, the efforts of the art field have concentrated on increasing the proportion of the globulitic structure. A variety of approaches have been taken for this purpose.
One approach is to stir the molten steel in the solidifying strand to prevent the formation of a dendritic structure and thus reduce segregations (see, for example, DE-C-No. 17 83 060). The stirring action is generally brought about by electromagnetic stirring apparatus. In any case, complex apparatus are necessary.
Another approach to achieving globulitic structure is based on keeping the casting temperature very low. In this case, difficulties are caused by the fact that the casting nozzles tend to clog up.
Extensive studies with the aim of reducing segregations by casting at low temperatures or by electromagnetic stirring in steels of 0.3 to 1.0% carbon yielded the finding that a slight reduction of segregations is achievable, but that this reduction is not sufficient to achieve a marked improvement of the technical properties of such steels in the production of rolled wire. In fact, in the application of electromagnetic stirring a more frequent occurrence of "martensite" was observed.
In a continuous steel casting process for steels having a carbon content of 0.05 to 1.1% by weight, especially those having a carbon content of 0.3 to 1.0% by weight, it is the object of the invention to produce billets of reduced segregations, from which rolled wire, preferably, can be produced having improved mechanical and technological properties. In particular, an improvement is to be achieved in small-size continuous casting, i.e., in the case of dimensions up to 140 mm on a side. Also, when the wire rolled from a billet is heat-treated, the development of "martensite" at segregations is to be prevented.
It has been found that, contrary to prevalent opinion, particularly in the case of a steel with a carbon content of 0.3 to 1%, the segregations can be considerably reduced if the steel is cooled very intensively within the stated limits. This effect is also to be observed at high cas
REFERENCES:
patent: 3771584 (1973-11-01), Wojcik
Forster Eckehard F. O.
Rudolph Gunter W.
Stercken Karl
Hamburger Stahlwerke GmbH
Lin Kuang Y.
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