Metal working – Method of mechanical manufacture – Combined manufacture including applying or shaping of fluent...
Patent
1993-01-08
1994-07-19
Vo, Peter D.
Metal working
Method of mechanical manufacture
Combined manufacture including applying or shaping of fluent...
29 8103, 29DIG5, 29DIG32, 72201, 723662, 164442, B21B 146, B22D 1112
Patent
active
053296885
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and relevant plant for producing coils of steel strips, having characteristics of a cold-rolled product and directly obtained in a hot-rolling line from a continuous casting with arc-shaped path and horizontal outlet.
It is known that for obtaining hot-rolled steel strip coils, the following operations are provided, successively: mm, and possibly storing the same; again to a rolling temperature of at least 1050.degree. C.; hot-rolled strips having a minimum thickness of 2 mm; a reconstruction of the grain which has been deformed and become dishomogeneous during the preceding operations, in particular hot-rolling step; the oxides previously formed, especially during annealing; and mounting the coil onto an unwinding reel to bring again the strip onto a plane, causing the strip to pass through at least one cold-rolling stand until obtaining thicknesses of less than 1 mm, down to 0.5-0.2 mm and finally winding the strip on a reel to obtain the final coil.
It will be noted that the number of passes in the stands for cold-rolling depends on the desired final thickness and the reduction percentage which is to be obtained, in other words the ratio between thickness of the hot-rolled strip and thickness of the final product. For high values of such a percentage reduction it is not enough to increase the number of said passes, but it will be necessary to subject the strip to another annealing operation and the consequent pickling, otherwise the material hardens and the final product results to be of low quality.
Although it is possible to obtain by hot-rolling strips having a thickness of less than 2 mm, hot-rolling is usually avoided to reach these values, as this type of processing is considered anti-economical, above all due to the reduced productivity that would be obtained in this case with a conventional rolling mill. The costs relating to the reduction of strip thickness are however extremely high in any case. Assuming 100 the cost of hot-rolling, starting from liquid steel, the cost of cold-rolling step alone is of at least 80.
Attempts have been described as to making plants for obtaining thin strips by means of more compact operating cycles with respect to the above-mentioned conventional cycle, in order to reduce complexity and duration of the latter. For example EP-A-226446 describes a number of hot-rolling examples, all in line and at a very high speed (not less than 1500 mm/min) but the final product not only has a thickness of 2-6 mm, falling thereby in the range of hot-rolling, but also certainly does not show the structural features of a cold-rolled product. The main purpose of this published application is in fact restricted to a high productivity while obtaining at the same time a product of good processability, but not of high quality.
In EP-370 575 there is described a method for the manufacture of a steel strip having a final thickness of between 0.5 and 1.5 mm, comprising the steps of hot-rolling a steel slab of less than 100 mm thickness, at a temperature of between 300.degree. C. and a temperature at which at least 75% of the material is converted into ferrite, with a thickness reduction of over 30% in at least one reduction stage, and an exit speed after hot-rolling of less than 1000 m/min, with final coiling of the strip after recrystallization. This was an attempt to avoid the two successive cycles of hot- and cold-rolling, with intermediate stages of annealing and pickling, but also this attempt has been unsuccessful, and it could not find success indeed, apart from the proposed solution, as in any case the inner structure of the material, when subjected to cold-rolling, is unsuitable to undergo this treatment for obtaining a final product of acceptable quality. This occurs owing to the fact that the inner structure, if not recrystallized before cold-rolling, results to be dishomogenous under a dimensional aspect and with insufficiently fine grains, in comparison with the grain size which would be required by the conventional cold-rolling techn
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T. Okamoto et al.: "Manufacturing of deep.varies.drawing sheet by warm rolling", Sheet Metal Industries, vol. 50, No. 5, May 1973, (Redhill, GB), pp. 297-302.
Steel Times International: "Thin end of wedge for minimill in Italy", Incorporating Iron & Steel International, vol. 14, No. 5, Sep. 1990, (Redhill, Surrey, GB), pp. 38-39.
Arvedi Giovanni
Gosio Giovanni
Arvedi Giovanni
Hoogovens Groep BV
Vo Peter D.
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