Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2000-08-15
2003-03-04
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S602000
Reexamination Certificate
active
06527882
ABSTRACT:
PRIORITY CLAIM
This is a U.S. national stage of application No. PCT/DE98/03259, filed on Nov. 3, 1998. Priority is claimed on that application and on the following application:
Country: Germany, Application No.: 197 58 108.0, Filed: Dec. 17, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an installation for the endless production of hot-rolled, thin flat products from thin cast strip, comprising a single-stand roughing train, a multi-stand finishing train, a delivery roller table with devices for cooling the hot-rolled strip and coiling machines arranged upstream and downstream of the cooling devices for coiling up the hot-rolled strip.
2. Discussion of the Prior Art
For producing hot-rolled strips, slabs with a thickness greater than 120 mm or thin slabs with thicknesses between 40 and 120 mm are used as the starting material. In the case of individual slabs, the rolling installations generally comprise a single- or multi-stand roughing train in which the slabs are reduced in a number of rolling passes in reversing operation, as well as a multi-stand finishing train or a Steckel stand. The approximately uniform temperature over the length of the hot-rolled strip is achieved either by means of a coil box between the roughing train and the finishing train, by speeding up in the finishing train or by coiling furnaces upstream and downstream of the Steckel stand. In these cases, a discontinuous process is concerned, i.e. the roughing train and finishing train generally operate and roll the individual slabs in isolation from each other.
In the case of an installation known from European Reference EP 753 359 A1, the roughed strips of two slabs rolled in the roughing train are welded at the head and foot with the aid of a heating and pressing apparatus between the roughing train and the finishing train. The seam between the two roughed strips is subsequently machined before the roughed strip runs into the finishing train. In the finishing train, it is then endlessly rolled, while the roughing train operates discontinuously. The problems entailed by a seam, of process stability and the quality of the hot-rolled strip in the region of the rolled-out piece of the seam, are disadvantageous. Ferritic or combined austenitic-ferritic rolling are possible only with the micro-structural transformation in the finishing train, with the disadvantages already mentioned.
In the case of thin slabs, a distinction must be drawn between rolling installations which use thin slabs with a thickness of 40 to 65 mm or greater than 65 mm as the starting material.
The former comprise a multi-stand finishing train, a delivery roller table with devices for cooling the hot-rolled strip to coiling temperature and coiling machines for coiling up the hot-rolled strip.
On account of the greater deformation work necessary for the same final thickness, installations for thin slabs>65 mm comprise a single- or multi-stand roughing train with more than one rolling pass and a multi-stand finishing train as well as a delivery roller table with devices for cooling the hot-rolled strip to coiling temperature and coiling machines for coiling up the hot-rolled strip. Between the roughing train and the finishing train there are devices for heating and/or coiling the roughed strip, which ensure the necessary temperature of the hot-rolled strip on entering the finishing train over the length of the hot-rolled strip.
The rolling installations are generally designed and operated in such a way that the deforming in the individual passes takes place in a fully austenitic or else combined austenitic-ferritic process.
In the case of austenitic rolling, the rolling temperature in all the passes is above the GOS line of the iron-carbon diagram, it being intended for the final rolling temperature in the last stands of the finishing train to lie just above the GOS line in order to achieve a fine-grained structure.
In the case of combined austenitic-ferritic rolling of steels with a carbon content of greater than 0.015%, the rolling temperature in the last stands of the finishing train lies below the GOS line in the range of approximately 810 to 890° C. This can be achieved with the same final thickness by lowering the temperature of the slabs on leaving the furnace, as a result of which the proportion of micro-alloying elements in solution is reduced and the quality of the rolled strip is impaired. Lowering the rolling rate without lowering the temperature of the slabs on leaving the furnace is also possible, as a result of which the rolled stock is subjected to more intensive cooling. However, this leads to the disadvantage of reduced production. A combination of the two measures is also possible, with the disadvantages already mentioned.
In the case of ferritic rolling, the lowering of the final rolling temperature to a minimum of 720° C. takes place by means of the measures already mentioned with respect to combined austenitic-ferritic rolling, including their disadvantages. The ferritic range is only reached in the last two or three rolling passes, as a result of which the reduction in this range is small. The transformation point lies (centrally) within the finishing train and is shifted by temperature influences between the stands, which leads to drops in rolling force owing to the lower deformation resistance of the material in the ferritic temperature range. This is disadvantageous for the roll-bending and adjusting systems for ensuring the thickness, profile and contour as well as flatness of the rolled strip, since these systems use the measured rolling force as an output signal.
In German reference DS 196 00 990 A1 it is proposed to cool the rolled strip between the stands of the finishing train at a cooling rate of over 30 K/s for ferritic transformation. Since the micro-structural transformation and the temperature equalization between the core and the surface take time, an equalizing zone of several meters is required after the cooling zone to the next stand. However, this is disadvantageous for austenitic rolling with a final rolling temperature of greater than 890° C.; this is because increasing the distances between the stands increases the temperature losses of the hot-rolled strip.
In European reference EP 0 761 325 A1 there is proposed a second downstream single- or multi-stand rolling train for the ferritic rolling of rolled strip after a multi-stand rolling train with a delivery roller table, devices for cooling the hot-rolled strip and downstream coiling machines for coiling up the austenitically rolled hot-rolled strip. The hot-rolled strip initially austenitically deformed in the first multi-stand rolling train is cooled with the aid of the devices arranged between the two rolling trains for cooling to the ferritic temperature range. The downstream single- or multi-stand rolling train serves exclusively for the ferritic rolling, virtually necessitating two rolling trains, which represents a high level of expenditure on technical equipment.
In European reference EP 0 761 326 A1 there is proposed a production installation comprising a multi-stand rolling train, a delivery roller table with devices for cooling the hot-rolled strip, and downstream coiling machines, in which installation at least the first stand is designed as a reversing stand with at least one coiling furnace arranged upstream and downstream of it. A controllable cooling device is provided between the upstream coiling furnace and the following reversing stand. After the rolling of the hot-rolled strip in the austenitic temperature range, the hot-rolled strip is cooled by means of the controllable cooling device into the ferritic temperature range and is coiled up in the coiling furnace. The micro-structural transformation takes place in the coiling furnace. The rolling is subsequently performed in reversing mode through the rolling train downstream of the coiling furnace, in the ferritic temperature range. During the austenitic rolling, cooling is not carried out. The hot-rolled strip may be hea
Jacobi Horst
Skoda-Dopp Ulrich
Wehage Harald
Cohen & Pontani, Lieberman & Pavane
Kastler Scott
SMS Demag AG
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