DE2361420B2 - METHOD OF CONTROLLING THE TEMPERATURE AND THE CARBON CONTENT OF A MELT STEEL - Google Patents

Description

I T

is calculated, where A '(t ONm ³ Cb) from the calorie content of the batch at the start of blowing and at the time of measurement and the target calorie content of the batch at the end point and the calorie loss between the measurement time and the end point and also the amounts of carbon removed from the melt and iron is determined that then the carbon content Cfcam end point based on decarbonization parameters and the calculated amount of oxygen Δ Q according to the formula

iflOV- \ Q

is determined, where Cl (%) mean the carbon content in the case of critical decarburization, at which the carbon content begins to decrease disproportionately to the amount of inflated oxygen. V (kg ³ ONm ¹ oxygen) is the maximum decarburization rate, Cp (%) a parameter of the decarburization curve, which is the carbon content difference between the critical carbon content G? and the base of the perpendicular on the abscissa of the decarburization diagram from the intersection of a tangent to the decarburization curve at point Q with an abscissa parallel at distance V , Cb (%) the carbon content at the time of measurement and W ^ r (kg) the weight of the molten steel , and that then finally the total amount of oxygen to be injected, the required amount of coolant and / or the required attenuation of the inflation is determined as a function of the difference between the calculated carbon content at the end point and the target content.

2. The method according to claim 1, characterized in that that the raw materials are prepared in such a way that the end point temperature of the steel melt is above the desired target temperature.

The invention relates to a method for controlling the temperature and the carbon content of a steel melt at the end point of refining in a top-blowing oxygen converter, the temperature and the carbon content of the steel melt being measured simultaneously at a point in time after a quantity of oxygen has been blown into the converter, which is calculated in such a way that a predetermined carbon content of the melt is reached and, based on the measured temperature of the carbon content, the amount of oxygen that will probably have to be blown in until the end point, the amount of coolant required and / or the possibly required change in the Blowing conditions is determined, the amount of oxygen to be blown in up to the end point being obtained from a heat balance based on the instantaneous temperature values measured during freshening.

Such a method is for example from the magazine "Stahl und Eisen", 89 (1969), pages 1315 bis 1319, known. This known method assumes it the end. that the remaining blowing time after the carbon content has dropped to below 1.0% by a simple Equation can be determined that as the only variable quantity is the ratio of an initial carbon content contains to a final carbon content. It is necessary to position the lance after the Decrease in carbon content to 1.0% constant or variable according to a predetermined scheme to keep so that only about the blowing time and not too Corrections to the final carbon content can be made via the lance position. Self-

■ 45 can of course, but independently of the control the carbon content, also a control of the bath temperature take place; because by such an independent Control, however, does not record the interaction between bath temperature and carbon content carbon content and bath temperature at the end point of freshening cannot be reliably in narrow limits can be set to the desired setpoints. For example, if the Temperature measurement based heat calculation by means of predetermined, determined over the blowing process Temperature curves show that the blowing time must be shortened in order to achieve the desired target temperature is, this inevitably also changes the carbon content, since a certain blowing time beforehand was determined, with which the desired carbon content is now independent of the bath temperature Endpoint can be achieved.

Similarly, in a method known from DT-AS 15 33 937, only the desired one is initially used

<\ - carbon content at the end point to its setpoint controlled, after which the bath temperature resulting from the carbon burn-off that has taken place up to that point calculated at the end point and, if necessary, included

wire corrects known measures. ΑικΓ. here therefore, the measures for temperature correction cannot have a retroactive effect on the carbon content Taken into account so that the temperature correction either can only be done so carefully that no significant change in the carbon content occurs, but the bath temperature at the end point in fluctuates within a wide range or, on the other hand, the desired target temperature has been reached well at the end point will, however, due to the explained repercussions the carbon content fluctuates within comparatively western limits.

Finally, it is known from DT-AS 15 08 199. to determine the decarburization speed of the bath by means of measurements from a comparison of an exhaust gas analysis with empirical empirical values of the system and to derive the amount of oxygen still required to set the predetermined final carbon content of the bath from a further empirically created family of curves. In addition, the temperature of the bath can be measured at a point in time during the freshening process and the temperature rise can be calculated, which is to be expected due to the addition of the amount of oxygen that is still required to achieve the final carbon content and the resulting final temperature can be used to calculate the amount of coolant to be used and / or the height setting of the oxygen supply lance can be calculated. Again, the disadvantage arises. that - apart from the inaccuracy and time delay of the exhaust gas analysis - a height adjustment of the oxygen supply lance required to achieve the desired final temperature, in turn, has repercussions on the empirically estimated final carbon content, ^etc. .ndi temperature of the hdac can be set with sufficient accuracy.

The object of the invention is to provide a method of To create the genus mentioned at the beginning, with which both the final temperature during tapping and the Final carbon content can also be set very precisely to predetermined target values.

According to the invention, this object is achieved by the characterizing features of claim 1.

Thus, according to the invention, the measured values for the bath temperature and the carbon content obtained at the same time are used immediately and simultaneously as input values for a control calculation in each fresh process. The carbon content at the end point is extrapolated as a function of the relationship between the decarburization parameters and a pre-calculated amount of oxygen still to be injected AQ , compared with the target value and then adjusted to the target value. The setting of the carbon content at the end point and the bath temperature at the end point takes into account the interaction between the grading measures required for this, so that both values can be set very precisely as a result. Since, in particular, the accuracy of the setting of the carbon content is of considerable importance for the steel obtained, this value is set as the last one and is thus preserved unadulterated. In contrast to the known sieving process, the final carbon content is not set first and then a possible correction of the bath temperature is considered, but rather the final bath temperature is set and initially set using the heat calculation, taking into account the measured values of temperature and carbon content via the amount of oxygen still to be blown only then is it determined what the resulting final carbon content is to be expected, after which it is first determined what total amount of oxygen is required to achieve this carbon content at the end point and what amount of coolant and what change in the blowing conditions is required

ίο is. in order to get exactly the at the preset temperature to achieve the desired carbon content at the end point.

In a preferred embodiment of the invention, the raw materials are prepared in such a way that the The end point temperature of the molten steel is above the desired target temperature. This is also in In extreme cases, the use of almost any amount of coolant to fine-tune the carbon content possible without the bath temperature falling the intended setpoint decreases

The invention is explained in more detail below in an exemplary embodiment with reference to the drawing
F i g. 1 three different types of control for setting the temperature and the carbon content of the steel melt at the end point in individual representations (a), (b) and (c) ,

F i g. 2 schetiatisch the workflow of a das Process computer controlling the process,

F i g. 3 is a graph showing the rate of decarburization above the carbon content and

F i g. 4 in individual representations (A) and (B) representations the accuracies of the enate temperature and of the process according to the invention that can be achieved Final carbon content in successive freshening processes of the same converter.

The designations according to Fig. 1 have the following meaning:

AQ - the calculated amount of oxygen to be injected to increase the bath temperature to the target temperature at the end point without changing the blowing conditions after simultaneous measurement of the temperature and the carbon content of the bath;

Qu = the amount of oxygen actually blown in to the end point after correcting the amount of oxygen AQ;

Tb = the bath temperature at the time of measurement; Tea - the set temperature at the end point;

Cb = the carbon content at the time of measurement;

Cu = the projected carbon content at the end point;

CtA = the target carbon content at the end point;

A '= location of the coolant supply.

Curves I and II show the course of the bath temperature and the carbon content when the oxygen concentration AQ is blown in, without any change in the bath and bath conditions following the measurement;

the curves Γ and ΙΓ show the through the Tax influence modified courses of curves I and II.

According to the present embodiment,

\ J I TC * \ J

Λ = / (E ₀ ,
where means
A 'E ₀

Eb

Eea

El

AWc

AW _Fe

when freshening in an oxygen top-up converter, the procedure is such that (a) the raw materials required for a given temperature are prepared in such a way that the bath temperature at the end point is slightly higher than the target temperature at the end point, (b) the amount of oxygen after the start of inflation a static model is calculated and displayed so that the carbon content of the melt is a predetermined value within the range from 0.50 to 1.00%, depending on the desired carbon content of the steel to be produced (e.g. 0 , 50% for low- and medium-carbon steels), (c) after this amount of oxygen has been inflated, a measuring lance is inserted into the molten steel so that the molten steel temperature and the liquidus temperature are measured simultaneously by a probe and then the temperature and the Carbon content of the molten steel can be read off according to an automatic display program and (d) unmitt elbar after the measurement, a predetermined heating factor and decarburization parameters can be calculated in order to determine the amount of oxygen required to bring the final temperature to the target temperature at the end point if the inflation process is continued under the conditions prevailing at the time of the measurement, whereupon a calculated Carbon content at the end point is determined on the basis of the amount of oxygen determined in this way and the decarbonization parameters.

At this point it must be determined whether by the end of inflation this calculated amount of oxygen after the measurement (1) either the calculated carbon content at the end point is within that of the desired steel grade depending on the permissible range [control scheme according to individual illustration (a) in 35 F i g. Ij, furthermore, (2) whether the calculated carbon content is predicted to be excessively high at the end point [control scheme according to individual illustration (b) in Fig. IJ so that the introduction of a coolant is required, or whether (3) the calculated carbon 40 salary at the end point is predicted to be excessively low [control scheme according to individual illustration (c) in Fig. Ij where a decrease in inflation, where means thus an increase in the height setting of the oxygen lance and / or a lowering of the feed 45 oxygen pressure with the consequence of a reduction in the decarburization rate and an increase in the Bath temperature is required. The control then takes place in accordance with one of those indicated in FIG. 1 Schemes. 50

The heating factor A used in the method according to the invention with the dimension tons ⁰ CZNm ³ Oz is generally defined by

Target end temperature, determined using the following equation:

b, E _ea , E _l , iW _c , \ W _Fe

= the extrapolated heating factor for the special case (in tons ° C / Nm ³ O ₂ ),

= the calorie content of the batch at the start of blowing (in kcal),

= the calorie content of the batch at the time of measurement (in kcal),

= the target calorie content of the batch at the end point (in kcal),

= the calorie loss between the measurement and the end point (in kcal),

= Amount of carbon removed from the melt (in t),

= Amount of iron removed from the melt (in t).

The amount of oxygen blown in to increase the temperature to the value calculated after Measurement is thus calculated using the following equation:

IQ =

Assuming that there is a relationship between the rate of decarburization and the carbon content according to Figure 3, there is the decarburization rate from the following equation:

\ oo

= V \ l - exp (- - ^ 2

Q c

Cp

= the speed of decarburization

kgC / Nm ³ O ₂ ),

r = the weight of the molten steel (kg),
= the total amount of oxygen (in No. ³ ),
= the carbon content (in%),
= the maximum decarburization speed (in

kgC / Nm3O ₂ ),

= a curve parameter (in%),
= the carbon content in the case of critical decarburization

HnQdV

A =

W _T - AT

55

where means:

■■ the amount of oxygen blown in to increase the temperature to an extrapolated value after the measurement in Nm ³ ),

g (4 AT τ = the temperature rise after the measurement ("C).

The extrapolated heating factor is, as well as the

The expressions V, Cp and C ₀ are referred to here as decarburizing parameters

The carbon content Q, in the case of critical decarburization ^ £ *** if ⁶¹ * ⁵ "^ Carbon content at which the carbon content begins to decrease disproportionately to the amount of inflated oxygen which decarburization oxygen escapes, so that did of this "bags carbon content Q from any Propotueti & ~ between the amount of oxygen anfgeblasenea the Abfafl of Kohlenstoffgehafts ond more results I> he KJOTrenparameter Cp results from the Entkohhmgs-

5951

oil 420

curve that changes depending on the bias conditions changes. If in the manner shown in FIG from the intersection of the tangent to the decoction curve with an abscissa parailel through the point Vdas Plumb down on the abscissa; then O results from the difference in carbon content on this

Abscissa intersection of the perpendicular and the critical carbon content Co.

Furthermore, with C «as the carbon content at the time of measurement (: n%) and G., as the target carbon content at the end point (in '''·,) using equation (3), the following equation is obtained:

ι ρ =

H w C ₁ . UOl

" ^p (v, j

Hence uili.

C ₁ , - C. · C ₁ . In ^; I.

exp ■ C,

where Ch is the calculated carbon content (; r ° 'o) at the end point. Of the decarburization parameters, C- is a constant based on the determination of actual results from previous freshening operations, while Kund Cp can be determined experimentally as a function of the conditions. Therefore, if the carbon content C _{H is} measured during the BL process, the calculated carbon content Ci / can be determined at the end point. The control is determined according to the difference between the calculated carbon content at the end point and the intended soil carbon content at the end point.

The raw materials are prepared such that the temperature ate molten steel at the end point is somewhat higher ais the target temperature at the end point, as when the measurement results of the measuring probe, the measured from a solidification temperature, by a silicon tube protected thermocouple, in one of the MeßTanze attached, sample vessel is arranged, as well as an attached to the bottom of the sample vessel, the steel melt temperature measuring TTierrnoiremerit and at the same time measures the temperature and the carbon content of the steel melt, indicate the need for a change in the gas conditions, the time span from the measurement with the dtr measuring probe to the end point two up to three minutes which naturally limits the effects of lower pressure inflation? will. This grande becomes the melt temperature at the beginning of the initial inflation "; kept slightly higher, and the raw materials are prepared in such a way that at the end a slightly higher temperature than the target temperature is achieved at the end point, so that the correct t eraser * «« · tüwi the "afetige fUateaettafgehait am Eaapttakt and" asm erzkk will ", whom is blown at low pressure . In addition, the temperature and the Kotterwtoffeefcrt * the place SG & raeize te ^ ßeeafi ^ mg As Airfbteset »the« Horder Bc & en SaaeftColfeKiKg zar & ztefeeig eetes past ^ «wepreefoead deat given the showing the» desfwfc. "Rael ims" dk if the measurements are not carried out at virtually the same Stahischmelzenzusammensetzungen, and secondly because eir.e period of two to three minutes is required for the effective lance effect in changing the bias conditions The coolant used can be of übiic.her to such . B. scrap

Based on the explanations above, the Individual representations according to F1 g. 1 largely by itself understand yourself out.

Ir. Fig. 1 (a) illustrates a graph. which according to the invention occurs when the bath temperature and the carbon content at the end point when inflating the calculated. The amount of oxygen AQ is within a permissible tolerance range of the specified target values, so that no further controlling influence on the process of the frying foreground is required. The amount of oxygen Δ0 calculated after the measurement corresponds to the actual amount up to End point of injected oxygen quantity Qs.

in the example according to F: g. i (b) has resulted. da3 the resultant without taking place subsequent to the measurement of additional controlling effect actual Kohienstoffgehait C = C higher than the SoUgehak C ^ a: st After gieichzenigen .Vfessung the Badtempera air and Kohienstoffgehaites is at the Steise X a refrigerant in such an amount added, which corresponds to the determined difference between the values Csc and C = * , in order to avoid an excessive increase in the bath temperature, and oxygen is also absorbed in such an amount. soft results from asm difference between the values Cec and Cc. ₄ Through the Kühimitteiznschfag a larger one for the additional tr rrijcohteaig enorüeraeae e ¹ ^ iKtCgV ΊΛλ- sea, otae dted aaameb em aäi 4er

Dwi «Soe Äefc

595J

Decarburization rate is reduced and the temperature rise is increased, thereby compensating for the temperature drop as a result of the actual oxygen rings Qr, which is reduced compared to the calculated amount of oxygen AQ.

As can be seen from the individual representations according to FIG. I, the end values for the The bath temperature and the carbon content are set to the desired setpoints within permissible tolerance limits will.

In Fig. 2 is the timing of the program of the the process controlling process computer illustrated. The oval boxes mean entries from Data or commands in the process computer, the rectangular boxes a processing of the data through the calculator and the oval tapered box outputs of the calculator, which are in a suitable form for Display. With 1 to 3 there is a program for calculating the thermal equilibrium before the Inflate illustrates which indicates the aggregates required. 1 means entering the Final cast iron temperature, 2 the heat compensation calculation and 3 the raw material display.

With 4 to 8 a program of the computer is referred to, which eight minutes after the start of inflation begins. 4 means the control command for an eight-minute interruption after the onset of the Blowing, 5 a data check, 6 a data error display, 7 an oxygen quantity calculation for the Probe insertion and 8 an oxygen quantity display

The actual core of the computer program is designated with steps 9 to 16 'St. 9 means entering the bath temperature and 10 means entering the liquidus temperature. The liquidus temperature is used to calculate the carbon content, with the bath temperature and liquidus temperature being measured simultaneously using a probe and the carbon content being derived immediately and immediately from the liquidus temperature, 11 means the calculation of the carbon content according to the calibration curve, 12 the display of bath temperature and carbon content, 13 the Calculation of the heating factor | and the decarburization parameters. and using these values to calculate the carbon content at the end point 14 to determine the required correction to (a), (b) or (c) in Fig. 1, 15 to calculate the amount of oxygen, the coolant Inenge and Leichtblasschemas at the end point and 16 the display of the amount of oxygen, the amount of coolant and the change in the blowing conditions at the end point.

With 17 to 19 a program for displaying the results of the inflation is illustrated, which are always recalculated when an oxygen quantity of 40 Nm ³ is injected. 17 denotes the control command for the program run after 40 Nm ^{3 of} oxygen blown in, 18 denotes the calculation of the temperature rise and decarburization, and 19 denotes the display of the calculated temperature and the calculated carbon content.

With the program runs illustrated at 20 and 21 as well as 22 and 23, values keep them as empirical values for the next frfechVörgang are used, so that based on this Values the accuracy of the sequence of the following fresh process can be set even better.

With 20 the temperature input at the end point is designated, with 21 the calculation of a correction value for the heating factor, with 22 the input of the carbon content at the end point and with 23 a correction calculation for the decarburization parameters.

The measuring times of the bath temperature and the liquidus temperature are automatically shown by the usual display device displayed. The correction values for the heating factor and the decarburization parameters can be changed

ίο Setting tables or set on a control panel or can be entered.

In the following example, the application of the method according to the invention is explained in more detail. A converter was charged with a charge of 82.8 hot ^{metal melt at a temperature of 1280 °} C. and with 18.7 t of scrap. Since the steel to be produced was a medium-carbon steel, the total amount of oxygen was 4060 Nm ^! inflated after calculation according to a static model, wherein

jo the temperature and the carbon content of the steel melt at this point were measured by means of a probe. The measured values for melt temperature and carbon contents were 1584 ° C and 0.46%, respectively.

These values were determined in the process computer according to FIG. 2 in accordance with the equations given above processed with the necessary control performed. In this operation, the entered amount of coolant (scrap) 320 kg that

After the measurement, the amount of oxygen blown in was 660 Nm ³ , so that the total oxygen rings inflated to the end point was 4720 Nm ³ , the temperature at the end point 1651 ° C. and the carbon content at the end point 0.09%.

In this example, the target temperature and the

Target carbon content at the end point at 1660 ⁰ C or

0.10%. so that both the temperature and the

Carbon content almost corresponded to the target values.

The results achieved are exemplified in FIG

illustrates when simultaneous control of temperature and carbon content in accordance with the method of the present invention has been applied to a number of freshening operations in succession. With X as the average value of the accuracy and σ as the normal

The deviation in accuracy resulted in values of F = 0.4 ° C and a = 8.5 ° C for the temperature and F = 0.001% and σ = 0.0175% for the carbon content. The accuracy was therefore 81% with regard to the temperature and with regard to the carbon

substance content 73%, the simultaneous accuracy 63%; the Simultaneous accuracy refers to the case in which both the temperature and the Carbon content in the same batch, the target values within the specified tolerance limits

was enough. With regard to the temperature, an accuracy of ± 10 ^° C. and with regard to the carbon content an accuracy of ± 0.02% were considered as the permissible tolerance limit. The temperature range at the end point was 1600 to 1690 ^° C .; the carbon

The hold range at the end point was 0.08 to 0.18%.

Very considerable advantages can thus be achieved with the method according to the invention. So can he Carbon content of the molten steel can be adjusted to the correct value and there is no risk for

an abnormally high increase in oxygen content hn Stole; in addition, a reduction in non-metallic inclusions is ensured, while also a constant output on ferro-alloys

595,

is ensured. By simultaneously controlling the bath temperature and the carbon content, a reduction in postblowing and the addition of coolant after the end point ensured what to leads to an improvement in the efficiency and production output of steelmaking.

For this 3 sheets of ZcidiiHmuun

Claims (1)

Claims 1. A method of controlling the temperature and carbon content of a steel melt at the end point of refining in a top-blowing oxygen converter, wherein the temperature and carbon content of the steel melt are measured simultaneously at a point in time after oxygen has been blown into the converter in an amount, which is calculated so that a predetermined carbon content of the melt is achieved, and on the basis of the measured temperature and the carbon content the amount of oxygen which must be expected to be blown to the end point, further the amount is about required of coolant and / or any necessary change in the Blowing conditions is determined, characterized by the fact that initially the oxygen quantities AQ (Nm ^J ). who are egg-blown C ₁ , --- C ₀ - C, in \ ! - fevr must, in order to set the desired temperature, from the weight of the total batch Wt (t) and the difference between measurement and final temperature .47 "( ⁰ C) and an extrapolated heating factor A 'according to the equation