RU2374015C1 - Method and device for continuous manufacturing of steel thick sheet - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method and corresponding device are provided for reduction of production expenditures at manufacturing of plate steel of thickness less than 100 mm and width up to 4000 mm or less from flat blank received from the stage of continuous casting. Hydrostatic pressure at rolling, providing welding of inner pores of metal at less number of passes is achieved ensured by that method includes stage of clamping with liquid core up to thickness more or equal to 55 mm by continuous method up to completion of stage of finishing rolling with high reduction rate at least in one mill. Average temperature at inlet of stage is more or equal to 1250°C but it can be reduced considerably for unalloyed or low-alloy steel. Device contains corresponding equipment.

EFFECT: reduction of production expenditures at manufacturing of plate steel.

11 cl, 2 dwg

Description

The invention relates to a method and a corresponding device for manufacturing a steel plate in a continuous manner from a continuous casting unit to the last rolling stand.

It is known that, in this industry, rolling mill stands are usually used for rolling through several longitudinal and transverse passages in order to increase the length and width of the product each time, moreover, the ingot, preferably with a rectangular cross-section or slab, is preheated to the required temperature in a heating furnace with temperature equalization, and get a thick sheet with the desired thickness and width. The dimensions of the ingot or slab, of which the second can be made by continuous casting, are in the range from 120 to 400 mm in thickness and in the range from 1000 to 2000 mm in width, depending on the type of steel and the technology used for the manufacture.

It is also known that when processing this kind of ratio of the thickness of the starting material, that is, the ingot or slab, and the thickness of the desired final thick sheet should be at least 1: 4, to ensure brewing pores, possibly present in the Central part or in the middle region, which is typical for ingots / slabs of large thickness. This means that for a sheet with a final thickness of 50 mm, the minimum thickness of the initial flat billet is 200 mm.

With the subsequent development of the technology for producing thin slabs, devices were developed by means of which thin slabs were cast with a thickness of 150 mm or less and a width of 3600 mm or less. These thin slabs were then cut and, after passing through a heating furnace with temperature equalization, sent in line to a reversing rolling mill, which, however, was adapted only for longitudinal rolling.

When using these devices, the ratio of the thickness of the flat billet and the final thick sheet can be as low as 1: 3, whereby a thin slab with a minimum thickness of 150 mm is required for a sheet 50 mm thick. Naturally, using such devices, it is also possible to produce not only thick sheets, but also strips wound into rolls, using the same reversible rolling stand for working with two guides in the furnace (“Thick Plate Technology / Stekkel Rolling Mill”). It is clear that with a reduced ratio of the thicknesses of the thin slab and the final sheet of 1: 3, to obtain the thickness of the final sheet of 40-50 mm, it is necessary that the slabs with a size of 120-150 mm are cast at a maximum speed of about 2 m / min, which is insufficient for continuous rolling process in a line, requiring, in contrast, a minimum speed of 3.5 m / min.

These factors impeded the use for the manufacture of plate material according to the scheme "casting-rolling", already known in the field of tape manufacturing. On the basis of experiments, which, however, did not make it possible to reduce sizes by more than 35%, due to the reduced torque value of such stands of the rolling mill, mathematical simulation models were developed. From these models it follows that results with similar quality can be achieved with a compression ratio of even more than 50% and up to 60% or less, which provides the possibility of reducing the dimensions of the device, as well as reducing production costs and investments.

Therefore, the purpose of this invention is the provision of a method and an appropriate device for the manufacture of thick sheets with a thickness of 100 mm or less and a width of 4000 mm or less with little investment and production costs.

When adapting the technology used for manufacturing in accordance with the patents EP 0925132, EP 0946316 and EP 1011896 (in the name of the present applicant), it was found that, starting from the product thickness at the mold exit 75 mm and at the exit from the continuous casting machine with the product thickness 55 mm, after crimping with a liquid central part (soft reduction), an average temperature of more than 1200 ° C was set at a speed of 5 m / min. The rolling in the line was performed by two stands providing a high degree of reduction (33% for the first stand and 30% for the second stand) to obtain final thick sheets with a thickness of 25 mm and, accordingly, the ratio of the thickness of the slab / sheet is approximately 1: 2. The quality of the product was comparable to the quality of thick sheets made in accordance with the prototype, in particular, there were no pores and a homogeneous microstructure throughout the thickness was ensured.

The purpose of the present invention is thus achieved by the method and the corresponding device defined in paragraphs 1, 7 of the claims, respectively.

These and other objectives, advantages and features of the present invention will be more apparent from the following detailed description of two options for its implementation, presented in the form of a non-limiting example with reference to the accompanying drawings, in which:

Figure 1 is a diagram of a device in accordance with this invention for the manufacture of thick sheets of stainless steel;

Figure 2 is a diagram of a device in accordance with this invention for the manufacture of thick sheets of unalloyed or low alloy steel.

Figure 1 shows a device in which the corresponding distances between the various components of the device form a total distance between the continuous casting machine 1 and the end of the rolling step of approximately 60 m. Thickness values are also indicated, which differ from the values mentioned in the example above, however in any case, falling within the declared range of values. With an initial thickness of 70 mm, slab 10 fed from continuous casting machine 1 at a speed of 3.5 m / min and an average temperature of 1200 ° C was passed through descaling machine 2 and then, without stopping, through rolling mill 3 installed in line with machine 1 for continuous casting, without disrupting the continuity of the process until the output sheet is 8 mm thick or less. In accordance with the type of steel and the desired sheet thickness, the number of stands of the rolling mill indicated by three numbers (M1-M3) could be reduced by one or two. Due to the implementation of the stated temperature conditions, it was possible to obtain the final thick sheet even when using one rolling stand and a suitable degree of reduction, located between 1: 1.5 and 1: 2.5 and preferably approximately 1: 2.

It should be noted that a favorable temperature profile for a thin slab, in which the temperature in the central part or in the middle region is quite high and close to 1350 ° C, increases the average temperature of rolling and provides a high degree of reduction in thickness, respectively, ensuring the welding of internal pores with fewer passes when rolling compared to a conventional plate mill. In fact, when a certain predetermined reduction ratio or deformation factor is exceeded at a constant width, the hydrostatic stress or the specific pressure in the central part of a thin flat billet reaches values that are high enough to brew any existing pores. In addition, high deformation temperatures increase recrystallization, i.e., the process by which crystalline grains are deformed and then completely recrystallize due to the high temperature, thereby supporting the formation of uniform microstructures, as opposed to what happens when rolling at lower temperatures, for example from 1050 to 900 ° C, as described in EP 0580062. Such low temperatures usually lead ultimately to mixed structures that are not completely recrystallized.

High rolling temperatures also increase the solubility of chromium carbides in stainless steel, respectively eliminating their accumulation without the possibility of a process inverse to the specified specific dissolution.

As can be seen in FIG. 1, this is followed by an accelerated cooling step, indicated by the number 4, which provides an additional improvement in the microstructure and profile characteristics of the thick sheet.

In conclusion, after the cutter 5, a dressing step 6 may be provided for cutting the sheet into segments of the desired length. As can be seen in FIG. 2, another embodiment of the device according to the invention is shown, which is particularly suitable for thick sheets of unalloyed or low alloy steel. In this case, an intermediate cooling unit 4 'is provided as an intermediate link between stands M2 and M3, capable of lowering the high rolling temperature by 50-100 ° C, as is required for these types of steel. In these cases, thermomechanical processing is required in combination with rolling, including mechanical deformation and cooling.

The distance between M2 and M3 is increased due to the placement of an additional cooling system 4 'between the two stands. It may also be provided, taking into account in a similar manner the above thermomechanical treatment, which is required for unalloyed or low alloy steel, a reduced distance between the first stand M1 and the intensive cooling unit 4 at the exit of the rolling mill.

Claims (11)

1. A method of manufacturing plate steel with a thickness of less than 100 mm and a width of up to 4000 mm or less from a slab coming from a continuous casting step, characterized in that it includes the step of crimping a slab with a liquid core to a thickness of more than or equal to 55 mm and at an average temperature of the slab more than or equal to 1200 ° C during the continuous process until the end of the finish rolling stage with high degrees of reduction by means of one or more stands, after which the cooling and cutting to thick sheets of a given length are carried out. 2. The method according to claim 1, characterized in that it includes a stage of final editing. 3. The method according to claim 1, characterized in that the ratio of the thickness of the flat workpiece after its manufacture by continuous casting and the final thickness of the thick sheet after rolling is in the range from 1: 1.5 to 1: 2.5. 4. The method according to claim 1, characterized in that before the specified rolling step includes a step of descaling. 5. The method according to any one of claims 1 to 4, characterized in that at the beginning of the rolling phase, the temperature of the Central part of the material to be rolled is approximately 1350 ° C. 6. The method according to claim 1, characterized in that for unalloyed or low alloy steel requiring thermomechanical processing, an additional intermediate cooling step is carried out between the stands of the rolling mill to reduce the rolling temperature by 50-100 ° C. 7. A device for manufacturing plate steel with a thickness of less than 100 mm and a width of up to 4000 mm or less from a slab made by continuous casting, characterized in that it contains means for crimping with a liquid core located after the mold (1) of the continuous casting device to obtain an output thickness greater than or equal to 55 mm at an average temperature greater than or equal to 1200 ° C, which operates continuously until the last stand of the finishing rolling mill (3) with one or more stands (M1, M2, ...) located in one the first line with said continuous casting apparatus, and ensures a high degree of compression, and followed by cooling means (4) and the cutter (5) for cutting the sheet into a predetermined length. 8. The device according to claim 7, characterized in that it contains a machine (6) for final editing. 9. The device according to claim 7, characterized in that it contains a descaling tool (2) located immediately in front of the rolling mill (3) in the direction of movement of the material. 10. The device according to claim 7, characterized in that the total length of the section from the mold (1) of the continuous casting device to the final cooling means (4) does not exceed 60 m. 11. The device according to claim 7 or 8, characterized in that for the manufacture of unalloyed or low alloy steel, requiring significant thermomechanical processing, it has additional cooling means (4 ') in intermediate positions between the stands (M1, M2, ...) of the rolling mill for decrease in rolling temperature by 50-100 ° C.

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