SU1252350A1 - Method of controlling steel melting in converter - Google Patents

Description

where iC is the difference between the current value of carbon content in steel and the given residual value.

This invention relates to black steel, in particular to steel processes.

The purpose of the invention is to increase the durability of the refractory lining and reduce the loss of alloying elements by controlling the temperature of the melt.

FIG. 1 shows a block diagram of a device implementing the method; and FIG. 2 - curves characterizing the proposed method.

The lined steelmaking gregat 1 is equipped with pipelines 2 VI b to supply respectively Oj and neutral gas (for example, argon Ar). Flow sensors 4 and 5 O and Ar are connected to the corresponding inputs of the ratio control 6, the output of which is connected to control valves 7 and 8 on the supply lines of argon and oxygen, respectively, and the third input of the ratio control 6 is connected to the output of the temperature controller 9 . Moreover, the valve 8 has, in relation to the valve 7, a response characteristic.

The inputs of the controller 9 are connected to the setting device 10 and the signal generation unit 11 proportional to the derivative of the steel temperature in time (dT / d). The temperature sensor 12 (T) is connected both to the input I1 of the unit and to one of the inputs or control unit, block 13, which is intended to form the achievement of the critical value of the temperature of the metal () by lining conditions, calculate the values of tg, LT and G, and issue an appropriate reference effect on the dispenser 14, where 6 time} s. carbon burnout to a given residual content in steel; 4T - temperature increase; G - the dose of the cooler.

aa coefficients determined according to the previous heat.

Information about the amount of carbon in steel comes from the output of block 15, which contains a sensor for controlling the flow of flue gases associated with diaphragm 16, sensors for determining their composition and elements for calculating the carbon content in steel by the formulas

, 0333-U, 00128 -;

Oh oh

, 00536 V dc

og / co ,, ,,

where vso

og

- waste gas flow rate; - CO content in waste

gases; - COg content in waste

gases.

The output of the temperature sensor 12 and the control output of the unit 13 are connected to the inputs of the coolant supply controller 17.

A variant of the method is continuous introduction of a cooler after it has been reached, this operation being used as a regulating effect to stabilize

steel temperatures at

The ratio of oxygen consumption and

"R

natural gas is maintained at the level at which it was at the time it reached

The TCr value is chosen in the range of 1680-1760 ° C and is determined by the operating tolerances of the applied lining of the steelmaking unit.

The optimal value of the steel temperature rise rate is determined on the basis of the following relationships.

The oxidation process of iron-chromium-carbon melt follows the laws resulting from the equilibrium conditions of the total reaction.

-i-Cr, 05- -C - | -Cr + CO

(one)

The equilibrium constant of this reaction, depending only on temperature, can be written as follows: 1 /

|,

1M

 (T) - + V,

(2)

Crgo,

but

with.

where, C; for practical purposes a

Thus, each level of temperature and / or partial pressure of CO corresponds to well-defined equilibrium ratios of carbon and chromium contents. In the case when this value is lower than its actual value, preferably the direction of development of the reaction (1) to the right, while carbon undergoes oxidation, and the ratio of chromium and carbon contents increases to reach an equilibrium level at a given temperature. A higher ratio of chromium to carbon in comparison with the equilibrium leads to preferential oxidation of chromium, which continues until an equilibrium of these conditions is reached between the chromium and carbon ratios.

From expression (2), it follows that, ceteris paribus, the preferred oxidation of carbon (high equilibrium ratio / Ls) can be achieved by a corresponding decrease in the CO partial pressure in the resulting gaseous reaction products. With regard to the conditions of argon-oxygen refining, this is ensured by an increase in the fraction of argon in the blast

with

mixes. At a given value of P, the equilibrium ratio of chromium and carbon is determined by the value of the equilibrium constant, which in turn is inversely dependent on temperature, and the lower the value of Kp (or the higher the temperature), the more equal

the weight ratio of chromium and carbon, i.e. the more likely the predominant oxidation of carbon at

; minimal chromium loss.

Thus, the decarburization process should be characterized by a lower R. or increased argon fraction in the blast and the highest possible temperature level.

,:

t5

-Yu

20

25

s

 ,

However, maintaining a low oxidation potential by blowing unacceptably reduces the performance of the steelmaking unit, and excessive overheating of the metal, preferably Fibiii from the standpoint of thermodynamics, is unacceptable, since it leads to the destruction of the lining and, as a consequence, to low ctoi fKOCTH and even crashes.

Therefore, the optimization task is to select and maintain the necessary oxidizing potential to blow and carry out the process in temperature wards, guaranteeing a minimum chromium carbon loss and satisfactory 1) resistance of the refractory lining. A simple restriction of the upper limit of heating of the steel bath-ifti is not enough, since the rate of temperature exit I is also an optimal region. The excessively high rate of temperature rise, is a consequence of the excessive oxidation of chromium, which occurs with B1 1 releasing large amounts of heat (the oxidation of chromium is very thermal, especially at low temperatures).

Fg1 assessing the importance of the heating rate parameter of a chromium-containing melt during its purging with argon-oxygen mixtures. Experiments were carried out in laboratory conditions, the results of which are summarized in FIG. 2

According to the data presented, the rate of temperature rise that is found to be optimal for a given chromium content is such that chromium is minimized. The left side of the curve is due to the process being delayed over time, which (apart from loss of productivity) leads to preferential oxidation of chromium at lower temperatures.

5 initial stage of the process. Excessive chromium waste is observed at an increased rate of temperature rise, which is a consequence of the excessive oxidation of chromium.

50 For melts containing 16-18% chromium, the optimum rate of temperature rise is S-IA C / MMH, for those containing 13-15% 10-1b sec / min.

Heating the bath should be carried out with

55 with the optimal speed to achieve the maximum permissible (critical) level of temperature in terms of lining preservation, such as

35

40

The tanks are 1680-1760 ° C (depending on the chromium content),

Thus, maintaining a predetermined heating rate of the metal and limiting the 1 {Having scrubbed the upper limit of the temperature rise by optimally controlling the composition of the blown supply and the additives of the coolers, it is possible to ensure minimal chromium waste even at high initial concentrations

The values of the coefficients a (, aj, a, a) are determined from the data of the previous heat as the values that allow the results of the calculation to be reconciled with the actual results of the previous heat.

So, it is defined as the inverse of the carbon burnout rate at temperatures close to the critical one, and the periods associated with the temperature drop due to the introduction of a cooler are excluded from consideration, where V is the actual carbon burnout rate,

dc is equal to. Coefficient a. to define

and L is defined as the rate at which the temperature of the steel rises and is equal to dT / dt in areas not associated with a temperature drop due to the introduction of a coolant. The coefficient is determined by

according to the formula, where G is the dose of the coolant introduced once; dT - the actual temperature change as a result of the dose G G

The implementation of the method is as follows.

Under the action of a mixture of 0 and Ar blown through the molten steel, carbon burns out in the steel (mainly), due to which its temperature is high. The value of the derivative of the temperature change, calculated by block 11, is maintained at the optimum level set at the setting unit 10 by the temperature controller 9, generating the command action of the regulator 6 of the ratio of oxygen and argon in the blast. Upon reaching the critical steel temperature in block 13, the dose of the cooler (ore) and

On this signal, the automatic metering unit 14 weights the calculated amount of the cooler and puts it into the unit. The maximum refrigerant dose level, corresponding to a steel temperature lowering of 60 ° C, was chosen based on the fact that when the temperature decreases by an amount greater than 60 ° C, there is a noticeable increase in the carbon loss of alloying elements, and smaller doses of the refrigerant lead to more frequent switching of the metering device 14, which negatively affects the dynamics of temperature regulation

ry

When implementing the method with the continuous introduction of a cooler when the value of T is reached, the output of the regulator 17 is connected to the input of the automated dispenser 14, through which the task for analog dosing of the material is transmitted. At the regulating input of the regulator 17, the signal from the sensor 12 is received.

the input, and the input of the task is a signal proportional from block 13.

Thus, taking into account the temperature of melting, the introduction of certain doses of the cooler to the unit for

bringing the carbon value to a predetermined value by varying the flow rates of oxygen and neutral gas in accordance with a given rate of temperature change allows increasing the resistance of the refractory lining and reducing the loss of alloying elements.

r

Oi

Charcoal Cr, a5c.%

f

I I I I I I I M I And I I I I I I I And H

5Yu152025

Speed of temperature rise, ° С / min

FIG. 2

Compiled by A. Abrosimov Editor A. Shishkina Tehred L. SerdyukovE; Proofreader T. Kolb

Order 4589/27 Circulation 552Subscription

VNIIPN USSR State Committee on Inventions and Discoveries 4/5, Moscow, Zh-35, Raushsk nab. 113035

Production and printing company, Uzhgorod, st. Project, 4

Claims (2)

1. METHOD OF CONTROL OF MELT OF STEEL IN THE CONVERTER, including control of the flow of oxygen and neutral gas during the purging of liquid steel, as well as the composition of the exhaust gases and changing the ratio of the flow rates of oxygen and neutral gas, characterized in that, in order to increase the resistance of the refractory lining and reduce losses alloying elements by regulating the temperature regime of melting, in addition, during the heating of the bath, the temperature (T) of the metal is measured, its first time derivative is calculated, and it is compared with a predetermined by the beginning of the rate of temperature change and they work out the excess of the value of the first derivative in time over a given value by a decrease in oxygen consumption, and in the case of a decrease in the value of the first derivative compared to a set value, its deviation is worked out by an increase in oxygen consumption while maintaining the total gas flow in the blast constant, calculate the carbon content in steel flow from the measured values and the composition of the exhaust gases when the _tem-: perature conditions critical to the metal lining Conway torus tem- 'perature T _X p, the difference between the target residual carbon content and its current value is determined during carbon burnout to a predetermined residual content of it in steel calculated possible gain for this time temperature dT steel corresponding to this calculated temperature increase in the dose of G cooler and introduce it into the unit to reduce the temperature, and during the period of temperature decrease caused by the introduced dose of the cooler, the ratio of oxygen to neutral gas flow is maintained its value at the moment of reaching T _cr, and then continue to become purge oxygen and neutral gas mixture at a predetermined temperature change rate to a predetermined value in the carbon steel and at the next _to achieve T p and input the calculation procedure is repeated cooler. 2. Method., Πο π, 1, with the fact that the time, temperature increase dT and the dose G of the cooler are determined by the formulas ^ = a, ° C) lT = a (· ΐ _β J G = a, λΤ G = a <60 ° at at at dT jjr = cons t; ? Ti60 ° C; dT> 60 ° С, where iC is the difference between the current value of the carbon content a ₍ , a, a and _e are the coefficients determined according to the data of the previous steel alloy and the given residual. ki.