RU2458153C1 - Method of annealing coils of cold-rolled mild steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method of annealing coils of cold-rolled mild steel includes coils heating up to the temperature of recrystallisation annealing set by the test bed thermal couple, holding at this temperature, holding under the bell with blown out burners and cooling, note that annealing temperature under the furnace bell is set to 820°C by zone thermo couple, the temperature after heating is 670°C by test bed thermal couple, the temperature of coil core is 650°C, coils cooling to the temperature 600°C by test bed thermal couple is done at a speed 16°/hour, then the coils are held under the bell with blown out burners for 5 hours, then final cooling by water is carried out from the temperature 280°C by test bed thermal couple.

EFFECT: increase of strip surface quality, uniformity of physical-mechanical properties of metal and increase of application properties.

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Description

The invention relates to rolling production and can be used in the technology of heat treatment of cold rolled strips of low carbon steels used in the automotive industry.

There is a method of annealing strips, mainly of steel sheet, including two-stage annealing with heating to a temperature of 550-590 ° C, then below the start of recrystallization, while metal is heated to a temperature of 550-590 ° C in two stages: in the first - up to 330- 370 ° C with an unregulated speed, at the second - with a controlled speed, then at a temperature below the onset of recrystallization, exposure and final cooling are carried out (SU No. 1475942, C21D 9/46).

The surface of the strip obtained in a known manner has a low surface quality.

The closest analogue to the claimed method is a method of annealing rolls of cold rolled strips rolled on rough work rolls in bell-type furnaces, including heating the rolls to a temperature of recrystallization annealing, holding at this temperature, and after the end of holding at the final temperature, the gas supply to the burners is stopped and the rolls are kept for four hours under the hood with the burners extinguished, and after removing the hood, the rolls are naturally cooled under the muffle to a temperature of 140 ° C along the walls thermocouple for metal of the second group of surface finishes and 110 ° C for metal of the first group of surface finishes (I.V. Franzenyuk, A.I. Franzenyuk. Modern metallurgical production, M., 2000, p. 187, 515).

However, this method does not provide high-quality cold-rolled automotive sheet. After rolling the metal on rough rolls on the strip surface, various deposits can be present - emulsion residues, oxide layers, iron dust, a means to prevent coalescing of the coils. Such deposits usually reduce the tendency to weld. As a result, high contamination is observed in the resulting strip, which does not meet modern requirements for metal for the automotive industry, especially for the manufacture of front parts for cars and trucks.

The technical task of the present invention is to obtain uniform physical and mechanical properties of the metal, improving the quality of the strip surface in the absence of defects of the "strip-slip line", "kink" due to the reduction of contamination of the strip during rolling on textured rolls and by preventing coalescing during annealing without reducing the performance of the bell furnace.

To solve this problem, in the proposed method of annealing coils of cold-rolled low-carbon steel, which includes heating the coils to the temperature of recrystallization annealing given by a bench thermocouple, holding at this temperature, holding it under a hood with extinguished burners and cooling, in contrast to the closest analogue, the annealing temperature under a furnace hood 820 ° С is set for the zonal thermocouple, while the temperature upon completion of heating is 670 ° C for the bench thermocouple at a core temperature of 650 ° C, and the coils are cooled about a temperature of 600 ° C through a bench thermocouple lead at a speed of 16 ° C / hour, then rolls are kept under a hood with an extinguished burner for 5 hours, then from a temperature of 280 ° C through a bench thermocouple they are finally cooled with water.

The given process parameters are obtained empirically and are empirical.

The essence of the proposed technical solution is to optimize the annealing modes of coils of cold-rolled low-carbon steel with the ability to extract “VG” and “G”, rolled on textured rolls, in bell furnaces, and is illustrated by the drawing, where the annealing schedule is given.

The task temperature for a zone thermocouple of 820 ° C for steel coils with the ability to extract “VG” and “G” is required to prevent overheating of the outer coils of the coils.

When setting the temperature of the zonal thermocouple below 820 ° C, the performance of the bell furnace decreases due to the increase in the duration of heating to the first exposure and then to subsequent exposures. The temperature of the task for the zonal thermocouple above 820 ° C leads to overheating of the outer layers of the rolls, which leads to uneven physical and mechanical properties of the metal.

The welding of individual coil turns takes place in a bell furnace. It depends mainly on the radial stress field and the process displayed on the temperature-time graph. This process affects the welding of coils both directly - through temperature and time, and indirectly - through thermal loads caused by the temperature field in the roll.

During the heating period, the outer coils of the coil, due to the radial component of the heat transfer, are hotter than the inner coils, due to which, under the action of thermal expansion, some roll fading occurs. Upon cooling, the reverse phenomena are observed. Immediately after the start of cooling, the temperatures of the colder outer coils and the hotter inner coils vary significantly. The outer turns are pressed against the inner ones, as a result of which the pressure of one turn on the other significantly increases. The occurrence of such compressive stresses acting at relatively high temperatures for several hours can be considered the main reason for the cohesion of the turns.

Cooling the coils from the final aging temperature for steel with the ability to draw “VG” and “G” - 670 ° С (according to a bench thermocouple) to a temperature of 600 ° С at a speed of 16 ° С / hour prevents the coiling of the coils from sticking together and, accordingly, the formation of “strip” defects slip lines ”,“ kink ”. An increase in the cooling rate from the temperature of final soaking of 670 ° С along the bench thermocouple to 600 ° С leads to the formation of “strip-slip line”, “kink” defects on the surface of the cold-rolled sheet.

Water cooling from temperatures above 280 ° C using a bench thermocouple causes excessive vaporization, lowering the temperature below 280 ° C using a bench thermocouple leads to a decrease in the performance of a bell furnace.

Feasibility studies have shown that the use of the present invention at MMK for steel with the ability to extract “VG” and “G” will increase the yield of rolled products with improved consumer properties, which will increase the profit from its sale by at least 15%.

Concrete example

Cold rolled steel rolls of “VG” drawing ability, rolled on textured rolls, with a strip thickness of 0.8 mm, are subjected to recrystallization annealing in bell-type furnaces with 100% hydrogen atmosphere. During recrystallization annealing of steel, the ability of the “VG” to be drawn, the temperature under the hood for the zonal thermocouple is 820 ° С, under the muffle for the bench thermocouple 670 ° С, the core temperature is 650 ° С. Adjustable cooling to 600 ° C by bench thermocouple at a speed of 16 ° C / hour, then stand for five hours under a hood with extinguished burners, water cooling starts from a temperature of 280 ° C by bench thermocouple.

The yield of sheets with a quality surface was 100%.

Claims (1)

A method of annealing coils of cold-rolled low-carbon steel, including heating the coils to a recrystallization annealing temperature set by a bench thermocouple, holding at this temperature, holding it under a hood with extinguished burners and cooling, characterized in that the temperature of the recrystallization annealing under the hood of the furnace is set at 820 ° C thermocouple, while the temperature at the end of coil heating by bench thermocouple is 670 ° C at a core temperature of coil 650 ° C, and the coils are cooled to temperatures 600 ° C by the thermocouple lead Metal at 16 ° C / h, then kept under surveillance rolls with burners extinguished within 5 hours, then the temperature of 280 ° C by the thermocouple Metal produce final cooling water.

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