RU2262541C1 - Method of control of annealing metal in bell-type furnace - Google Patents

Abstract

FIELD: control of heating process at heat treatment of ferrous metals.

SUBSTANCE: control of heating the metal in bell-type furnace consists in regulation of temperature by bell-type furnace thermocouple and stand thermocouple at preset holding at heat. Heating is performed at stages: at first heating stage temperature of holding at heat is set by stand thermocouple which is equal to temperature of beginning of re-crystallization and temperature by bell-type furnace thermocouple is above point A₁ of metal being heated by 80-90°C. Heating is continued till required temperature has been attained by stand thermocouple and temperature specified by bell-type furnace thermocouple is increased by 30-40°C. Heating is continued till temperature by stand thermocouple is above temperature of beginning of re-crystallization of metal being heated by 90-110°C.

EFFECT: increased output of furnace; reduced consumption of energy carrier; improved quality of metal; profitableness of process.

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Description

The invention relates to metallurgy, in particular to the heat treatment of cold rolled steel in bell-type furnaces, and in particular to processes for controlling annealing of metal, and can be used in the production of broadband steel intended for cold deformation.

A known method of controlling the heating of metal in a bell furnace, including setting the task on the bell and bench thermocouple and heating the metal to a temperature set on the bench thermocouple, while the task on the bell thermocouple is set at 40-70 ° C above the point Ac _{1 of the} heated metal, carry out heating and when the set temperature is reached, the hood thermocouple task is reduced by 80-100 ° C and the hood thermocouple is held at a temperature until the bench thermocouple reaches a temperature of 30-70 ° C higher than the river start temperature crystallization of the heated metal (RF patent No. 21545466).

The disadvantage of this method is the inability to provide high uniformity of the mechanical properties and microstructure of the heated metal of 08Y grade steel in broadband rolls weighing 25 tons or more, as it is intended for annealing rolls of tin weighing no more than 14 tons.

The closest analogue is a control method for heating rolled steel sheet for particularly complex drawing (WWS), which includes controlling the temperature in the bell furnace by the bell (zone) and bench thermocouples in accordance with the set shutter temperatures for step heating. In this case, the temperature in the zone thermocouple is set no higher than 820 ° C, and its specific values are set at 100-140 ° C higher than the set shutter temperature for the bench thermocouple (AS USSR No. 1406186).

The disadvantages of the closest analogue are the low productivity of the furnace, increased energy consumption, welding of coil turns, increased metal sorting by the “kink” defect, welding spots, and reduced yield. This is due to the irrational choice of shutter temperature for zonal and bench thermocouples.

The objective of the invention is to increase the productivity of the furnace, reducing energy consumption, reducing sorting by defect "kink", increasing the metal yield of exhaust ability of WWS and group I surface finishes, increasing the profitability of production.

The problem is achieved in that in the method of controlling metal annealing in a bell furnace, including stepwise temperature control in accordance with the set shutter temperatures for the bell and bench thermocouples, in contrast to the closest analogue, the set shutter temperature for the bench thermocouple is set at the first control stage equal to the temperature of the onset of recrystallization of the metal, and over a bell-shaped thermocouple — at 80-90 ° C above the point Ac _{1 of the} annealed metal, and heating is carried out until the specified temperature is reached temperatures according to the bench thermocouple, at the second stage of regulation, the set temperature for the bell thermocouple is raised not 30-40 ° C, and for the bench thermocouple is set 90-110 ° C above the temperature of the onset of recrystallization of the heated metal and is heated until the specified holding temperature for the bench thermocouple .

The selected method of controlling the heating of metal in a bell furnace of cold rolled broadband steel is optimal. Changing the conditions of the proposed method leads to a change in thermal conditions, which leads to cost overruns and a deterioration in the quality of the metal with an increase in sorting by defects in the microstructure and surface of the strip or to delay the annealing process.

An increase in the tasks at the first stage of regulation by a bench thermocouple is higher than the temperature of the onset of recrystallization, and by a bell thermocouple more than 80-90 ° C above the Ac ₁ point _{of the} heated metal, they lead separately and together to overheat the outer coils of the rolls, which leads to a decrease in the metal yield WWS, increase the yield of metal with a defect "kink", to excessive consumption of fuel. A decrease in the task for the bench thermocouple below the proposed one, as well as a decrease in the task for the bell thermocouple, lead separately and together to delay the annealing process.

At the second stage of regulation, increasing the task by less than 30 ° C leads to underheating of the metal and a decrease in the metal yield of the ability to extract WWS, a deterioration in the complex of mechanical properties of the annealed metal, and a decrease in the performance of the bell furnace.

An increase in the task of a bell-type thermocouple at the second stage of regulation by more than 40 ° C leads to overheating of the outer coil turns, an increase in sorting by defect “kink” due to sticking and welding of the coil turns, to an excessive consumption of fuel.

An example of a specific implementation of the method

Rolls of cold rolled broadband steel 08Y, OCB grade inner roll diameter 610 mm, outer 2100 mm, strip width 1250 mm, roll weight 25 tons are formed on the stand of the bell furnace in the cage, the number of rolls in the cage 4, convector gaskets are installed between the coils for circulation of the protective medium when heating and cooling. The cage is covered with a muffle, a heating hood is installed and heating is carried out through the hood and bench thermocouples.

At the first stage of regulation, the task for the bench thermocouple was set equal to 600 ° С (the temperature of the onset of recrystallization of steel grade 08Yu), for the bell-shaped thermocouple equal to 810 ° С (temperature of the point Ас ₁ , which is ≈730 ° С + 80 ° С), upon reaching the heating process using a bench thermocouple at a temperature of 600 ° C and completion of the shutter speed of 6 hours, the task for a bell thermocouple was set to 840 ° C (810 ° C + 30 ° C) and further heating was carried out until the bench thermocouple reached a temperature of 690 ° C (at 90 ° C above the onset temperature of recrystallization nations steel grade 08Yu) and carried out aging for 22 hours. The heating time was 48 hours; upon completion of the annealing process, the cage was cooled in a protective medium under the muffle to a temperature of 120 ° C using a bench thermocouple, then the muffle was removed, the coils were cooled in the warehouse to the tempering temperature, i.e. up to 40 ° C.

In the process of training, the quality of the strip surface was assessed for the presence or absence of a “kink” defect, the location of this defect along the strip width, and its length along the strip length. The quality of the annealed metal was evaluated by the output volume of group I of the surface finish and sorting it into a lower surface finish group (into group III according to GOST 9045-93 or grade II according to the “kink” defect).

As a result of using the proposed method for controlling metal annealing in a bell furnace, a metal with higher consumer characteristics was obtained, while saving energy and increasing the efficiency of the bell furnace (see table).

As can be seen from the table, the proposed method allows to increase the yield of metal with high surface finish (group I according to GOST 9045-93), significantly reduce the sorting by defect "kink" in the lower surface finish group while saving energy and increasing the performance of the bell furnace.

Table. No. Indicators According to the proposed method According to the closest analogue Norm in accordance with GOST 9045-93 1. Yield strength, σ _t , n / mm ² 183 190 195 2. Tensile strength, σ _in , n / mm ² 298 315 250-350 3. Elongation, δ ₄ ,% 42 39 36 4. The output of metal ability to extract OSV,% 98.5 95.0 not standardized 5. The output of the metal is particularly high surface finish (I group according to GOST 9045-93),% 85 fifty not standardized 6. Sorting of metal in the Ш group of surface finish by defect "kink",% 0.20 2,5 not standardized 7. Sorting of metal in grade S by defect "kink",% 0,07 0.5 not standardized 8. Energy saving 8% no saving not standardized 9. The capacity of the bell furnace, t / h 1.8 1.3 not standardized

Claims (1)

A method of controlling metal annealing in a bell furnace, including stepwise temperature control in accordance with the set shutter temperature for the bell and bench thermocouples, characterized in that at the first control stage, the set shutter temperature is set for the bench thermocouple equal to the temperature of the recrystallization of the heated metal and the bell temperature thermocouple - at 80-90 ° C above the Ac ₁ point of the heated metal, and heating is performed until reaching a predetermined temperature by the thermocouple metal on WTO second control stage at a predetermined temperature thermocouple bell raised to 30-40 ° C and for Metal thermocouple set at 90-110 ° C above the recrystallization onset temperature of the heated metal, and heating is performed until a predetermined holding temperature of Metal thermocouple.