CN113084113B - Different steel type mixed casting method suitable for slab caster - Google Patents

Different steel type mixed casting method suitable for slab caster Download PDF

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CN113084113B
CN113084113B CN202110249387.4A CN202110249387A CN113084113B CN 113084113 B CN113084113 B CN 113084113B CN 202110249387 A CN202110249387 A CN 202110249387A CN 113084113 B CN113084113 B CN 113084113B
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steel
molten steel
tundish
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ladle
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CN113084113A (en
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李广艳
张海波
王利
张庆峰
刘洪银
亓伟伟
孙建卫
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Shandong Iron and Steel Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/18—Controlling or regulating processes or operations for pouring
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/007—Continuous casting of metals, i.e. casting in indefinite lengths of composite ingots, i.e. two or more molten metals of different compositions being used to integrally cast the ingots

Abstract

The invention discloses a different steel type mixed casting method suitable for a slab caster, which utilizes a calculus equation to accurately calculate a law equation of the change of the components of mixed molten steel in a tundish along with time under various variable process conditions, calculates the time of the components of the mixed molten steel in the tundish reaching the requirement of a high-grade steel type, takes the time as a node, and judges the produced casting blank as a high-grade casting blank.

Description

Different steel type mixed casting method suitable for slab caster
Technical Field
The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a different steel type mixed casting method suitable for a slab caster.
Background
In the continuous casting process in the steelmaking production, in order to improve the continuous casting production speed and save the replacement time and the replacement cost of a tundish, the continuous casting process generally adopts a mixed casting method for producing steel grades with similar components and performances, and molten steel of different steel grades are mixed in the mixed casting process. Because the components of the part of mixed molten steel cannot be accurately calculated, the mixed casting judging process of the continuous casting billets in most steel mills at present judges the whole furnace high-grade mixed casting molten steel into low-grade molten steel, and wastes of chemical component cost are caused.
With the progress of steel smelting equipment, the capacity of a steel ladle in a domestic steel mill is generally more than 100 tons at present, the capacity of a tundish is about 30-60 tons, according to analysis, after a new steel ladle is poured, the content of molten steel components in the tundish is rapidly changed along with the pouring time, the molten steel components in the tundish can be close to the same as the molten steel components in the new steel ladle in the middle and later period of the casting of the steel ladle of the furnace, and a continuous casting billet produced in the middle and later period of the casting of the new steel ladle can be completely free of judgment so as to reduce the waste of high-grade molten steel.
Disclosure of Invention
Aiming at the problems, the invention provides a different steel type mixed casting method suitable for a slab caster, which utilizes a calculus equation to accurately calculate a regular equation of the change of the components of the mixed molten steel in a tundish along with time under various variable process conditions, calculates the time for the components of the mixed molten steel in the tundish to meet the requirement of a high-grade steel type, and takes the time as a node, and then the produced casting blank is judged to be a high-grade casting blank.
In order to achieve the purpose, the invention adopts the following technical scheme:
a mixed casting method of dissimilar steel suitable for a slab caster comprises the following steps:
firstly, in continuous casting production, firstly producing low-grade steel, then producing high-grade steel, and keeping the casting blank casting speed of a continuous casting machine unchanged when producing low-grade steel, high-grade steel and mixed casting of the two types of steel;
step two, after the heat casting of the low-grade steel is finished, when the liquid level in the tundish is reduced to 400-500 mm, the ladle of the high-grade steel starts to be cast; after the ladle is poured, the opening degree of a steel ladle sliding gate valve is set to be 100%, the liquid level of the molten steel in the tundish quickly rises, and when the liquid level of the molten steel in the tundish rises to the maximum, the opening degree of the steel ladle sliding gate valve is reduced, the injection speed of the molten steel in the ladle into the tundish is reduced, and the liquid level of the molten steel in the tundish is controlled to be in a stable state without rising or falling;
step three, mixing chemical components omega of molten steel in the tundish after the high-grade steel is pouredInThe change rule along with the time t is calculated according to the following formula：
1) Mixing the chemical components omega of the molten steel in the tundish in the process of pouring the ladle to the full ladle of the molten steel in the tundishInThe law equation of change with time t is calculated according to the following formula (1):
Figure BDA0002965356300000021
wherein, VSteelThe injection speed of the steel ladle molten steel to the tundish is ton/min; omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time of the molten steel of the high grade steel after casting in minutes; vInThe pouring speed of the tundish molten steel to the crystallizer is ton/min; omegaInThe chemical component concentration in the tundish molten steel; q0The mass of molten steel in the tundish before the molten steel of high grade steel is poured is ton; omegaLow gradeThe chemical component concentration in the low-grade molten steel;
2) after the tundish molten steel is fully filled, the molten steel liquid level of the tundish does not change, namely the molten steel weight of the tundish does not change, and the chemical component omega of the mixed molten steel in the tundishInThe change law with time t is calculated according to the following formula (2):
Figure BDA0002965356300000022
in the formula (2), VSteelThe injection speed of the steel ladle molten steel to the tundish is ton/min; omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time of the molten steel of the high grade steel after casting in minutes; vIn (1)The pouring speed of the molten steel in the tundish into the crystallizer is VSteel＝VInTon/min; omegaInThe chemical component concentration in the tundish molten steel; qInThe mass of the molten steel in the tundish is ton; c is a constant;
wherein, the calculation process of C is as follows, firstly, t and omega when the tundish is full are calculated by the formula (1)In (1)Then, t and ω are addedInSubstituted into formula (2)Calculating C;
step four, inputting the following data in the formula (1) or the formula (2): the method comprises the steps of calculating the chemical component concentration of the steel ladle molten steel in the tundish, the chemical component concentration of the steel ladle molten steel, the time after the high-grade steel molten steel is poured, the injection speed of the steel ladle molten steel in the crystallizer, the quality of the molten steel in the tundish before the high-grade steel molten steel is poured, the chemical component concentration of the low-grade steel molten steel and the quality of the steel ladle in the tundish to obtain the chemical component concentration of the steel ladle in the tundish, taking the time t of finally reaching a certain component of the high-grade steel as a time node for judging that a casting blank is a high-grade casting blank, taking the casting blank behind the time node as the high-grade casting blank, and taking the casting blank before the time node as the low-grade casting blank.
In the invention, the chemical composition in the molten steel is one of C, Si, Mn, P, S, Nb, V and Ti. In the specific implementation process, because of different steel types, the chemical components in the molten steel can be other chemical components besides the above chemical components, which are different according to different steel types.
In combination with the reality, the concrete measures of the mixed pouring method of the invention are as follows:
firstly, in the continuous casting production, a low-grade steel grade is produced, and a high-grade steel grade is produced.
The physical properties of the low-grade steel grade and the high-grade steel grade have an overlapping interval.
The low-grade steel is a steel with lower requirements on chemical component content and physical and mechanical properties;
the high-grade steel is a steel grade with higher requirements on chemical component content and physical and mechanical properties.
And step two, after the heat casting of the low-grade steel is finished, when the liquid level in the tundish is reduced to 400-500 mm, the ladle of the high-grade steel starts to be cast.
The casting blank pulling speed of the continuous casting machine is kept unchanged when producing low-grade steel, high-grade steel and mixed casting of the two steel.
After the ladle is poured, the opening degree of the steel ladle sliding gate valve is set to be 100%, the liquid level of the molten steel in the tundish quickly rises, and when the liquid level of the molten steel in the tundish rises to the maximum, the opening degree of the steel ladle sliding gate valve is reduced, the injection speed of the molten steel in the ladle into the tundish is reduced, and the liquid level of the molten steel in the tundish is controlled to be in a stable state without rising or falling.
The large ladle is a ladle for injecting molten steel into the tundish in the continuous casting process.
The tundish is a refractory container used in the continuous casting process, firstly receives molten steel poured from a ladle, and then is distributed into each crystallizer through a tundish nozzle.
The liquid level of the molten steel in the tundish is the depth of the molten steel in the tundish.
Step three, mixing chemical components omega in molten steel in a tundish after casting high-grade steelInThe law equation of variation with time t is calculated according to the following formula:
1) when the ladle is opened and poured to the process that the tundish molten steel is full of the ladle, the tundish is mixed with the chemical components omega in the molten steelInThe law equation of change with time t is calculated according to the following formula (1):
Figure BDA0002965356300000041
wherein, VSteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the high-grade molten steel is poured; vInThe speed of the molten steel in the tundish leaving the tundish, namely the injection speed of the molten steel in the tundish into the crystallizer, (ton/min); omegaInThe chemical component concentration in the tundish molten steel; q0The mass (ton) of molten steel in the tundish before the high-grade molten steel is poured; omegaLow gradeThe chemical component concentration in the low-grade molten steel;
the derivation process of the calculation formula (1) in the invention is as follows:
according to the following steps: (the mass of the chemical components injected into the molten steel of the tundish) - (the mass of the chemical components leaving the molten steel of the tundish) is the variable quantity of the mass of the chemical components in the molten steel in the tundish, and a formula is obtained;
the variable quantity of the mass of the chemical components in the molten steel in the tundish is (the mass of the chemical components in the molten steel in the tundish at the moment t + delta t) - (the mass of the chemical components in the molten steel in the tundish at the moment t), and a formula II is obtained;
the variation of the chemical component concentration in the molten steel in the tundish (the chemical component concentration in the molten steel in the tundish at the moment t + delta t) - (the chemical component concentration in the molten steel in the tundish at the moment t) is obtained, and the formula (c) is obtained;
Vsteel*ωSteel*Δt-VIn*ωIn*Δt＝ΔWCombination of Chinese herbs ①
ΔWCombination of Chinese herbs＝ω(t+Δt)*[Q0+(VSteel-VIn)*(t+Δt)]-ωt*[Q0+(VSteel-VIn)*Δt] ②
ω(t+Δt)-ωt＝ΔωIn ③
(III) VSteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the high-grade molten steel is poured; vInThe speed of the molten steel in the tundish leaving the tundish, namely the injection speed of the molten steel in the tundish into the crystallizer, (ton/min); omegaInThe chemical component concentration in the tundish molten steel; wIn (1)The mass of chemical components in the tundish molten steel is (ton); omega(t+Δt)The chemical component concentration in the tundish molten steel at the t + delta t moment; omegatChemical component concentration in the tundish molten steel at the time t; q0The mass (ton) of molten steel in the tundish before the high-grade molten steel is poured; omegaLow gradeThe chemical component concentration in the low-grade molten steel;
(iii) obtaining a formula (iv) in a united vertical type (v):
Vsteel*ωSteel*Δt-VIn*ωIn*Δt＝ΔωIn*[Q0+(VSteel-VIn)*t]+ω(t+Δt)*(VSteel-VIn)*Δt ④
When delta t approaches 0, the chemical component concentration in the tundish molten steel at the time t + delta t is equal to the chemical component concentration in the tundish molten steel at the time t, and a formula is obtained;
Figure BDA0002965356300000051
when the delta t approaches to 0, the vertical connection type ((C) to get):
Vsteel*ωSteel*Δt-VSteel*ωIn*Δt＝ΔωIn*[Q0+(VSteel-VIn)*t] ⑥
In the condition of definite mixed casting process and continuous casting equipment, VSteel、VIn (1)、ωSteel、Q0Is a constant value, t and ωInAs a variable, the formula (c) is transformed into the formula (c);
Figure BDA0002965356300000052
the formula (c) is transformed into the following formula (b);
Figure BDA0002965356300000053
is provided with [ Q0+(VSteel-VIn)*t]Is a variable, (V)Steel*ωSteel-VSteel*ωIn) For another variable, the two sides of the pair of the above formula are integrated respectively to obtain:
Figure BDA0002965356300000054
using the integral equation:
Figure BDA0002965356300000055
integrating the two sides of the formula ninthly respectively:
Figure BDA0002965356300000056
according to the mixed casting operation process, at the moment t is 0, the chemical component concentration omega in the molten steel of the tundishInIs the concentration omega of chemical components in low-grade molten steelIs low inSubstituting these two data into formula (R), solving C, and converting formula (R) into formula (R)
Figure BDA0002965356300000057
Namely, calculating formula (1);
Figure BDA0002965356300000058
2) after the tundish molten steel is fully filled, the molten steel liquid level of the tundish does not change, namely the molten steel weight of the tundish does not change, and the chemical component omega of the mixed molten steel in the tundishInThe law of change with time t equation is calculated by the following equation (2):
Figure BDA0002965356300000061
v in the formula (2)SteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the high-grade molten steel is poured; vIn (1)The pouring speed of the molten steel in the tundish into the crystallizer is VSteel＝VIn(ton/min); omegaInThe chemical component concentration in the tundish molten steel; qInThe mass of the tundish molten steel (ton); c is a constant;
the derivation process of equation (2) is:
according to the following steps: (the mass of chemical component injected into molten steel in tundish) - (the mass of chemical component leaving molten steel in tundish) ═ the amount of change in the mass of chemical component in molten steel in tundish, equation
Figure BDA0002965356300000062
Figure BDA0002965356300000063
Formula (II)
Figure BDA0002965356300000064
V inSteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the high-grade molten steel is poured; omegaInThe chemical component concentration in the tundish molten steel; vInThe pouring speed of the molten steel in the tundish into the crystallizer is VSteel＝VIn(ton/min); qInThe mass of molten steel in the tundish molten steel (ton);
in the case of defined mixed casting processes and continuous casting installations, VIn、VSteel、ωSteel、QInIs a constant value, t and ωInIs a variable, therefore the formula
Figure BDA00029653563000000610
Is converted into the following formula
Figure BDA00029653563000000611
Figure BDA0002965356300000065
General formula
Figure BDA00029653563000000612
Is converted into the following formula
Figure BDA00029653563000000613
Figure BDA0002965356300000066
Let t be a variable, (V)Steel*ωSteel-VIn*ωIn) For another variable, the two sides of the pair of the above formula are integrated respectively to obtain:
Figure BDA0002965356300000067
the following two integration equations are utilized: : ═ k × dx ═ kx + c and:
Figure BDA0002965356300000068
right and left sides of the above formula are respectively integrated to obtain formula
Figure BDA0002965356300000069
I.e., equation (2):
Figure BDA0002965356300000071
according to the mixed casting operation process, at t when the tundish is just filled with molten steelIs full ofAt that time, the chemical component concentration in the tundish molten steel is ωIs full ofCan be calculated by equation (1) and t isIs full of、ωIs full ofThese two data are substituted into
Figure BDA0002965356300000072
Can solve the constant C and can be further simplified
Figure BDA0002965356300000073
And fourthly, according to the calculation formula (1) and the calculation formula (2) in the third step, a computer is utilized to work out a chemical component concentration change model in the mixed casting molten steel, the model automatically reads the components of the high-grade molten steel and the last low-grade molten steel in the steel ladle from the steel-making system, reads the casting time of the high-grade molten steel in the continuous casting system, the molten steel quality in the tundish when the high-grade molten steel is cast, the molten steel speed of the steel ladle injected into the tundish, the molten steel speed flowing into the tundish from the tundish, the full-ladle molten steel quality of the crystallizer of the tundish and other parameters, and automatically calculates a change equation of the percentage content of elements such as C, Si, Mn, P, S, Nb, V, Ti and the like in the molten steel along with the casting time of the high-grade steel according to the parameters. And calculating the time for the mixed molten steel components in the tundish to meet the requirement of the high-grade steel grade, and judging the casting blank produced thereafter to be the high-grade casting blank and the casting blank produced heretofore to be the low-grade casting blank by taking the time as a node.
And step five, because the casting blank produced by the furnace high-grade molten steel belongs to a mixed casting blank, the components in the casting blank have a gradual change process, and each casting blank produced by the furnace high-grade molten steel is marked independently and is used for rolling rolled materials with different thicknesses.
Because the chemical composition range of the low-grade casting blank produced by the furnace molten steel early-stage mixed casting process is between the composition of the low-grade molten steel and the lower limit of the internal control composition of the high-grade molten steel, the chemical composition content is slightly higher than the middle limit chemical composition content of the low-grade steel produced by the non-mixed casting process, and the low-grade casting blank produced by the furnace molten steel is used for rolling the low-grade rolled material with the thickness of more than 12mm in order to reduce the strength of the rolled material.
Because the chemical components in the high-grade casting blank generated by the later mixed casting process of the furnace molten steel are between the lower limit of the internal control components of the high-grade molten steel and the normal components of the high-grade molten steel, the chemical component content is slightly lower than the middle limit chemical components of the high-grade casting blank produced by the non-mixed casting process, and the generated high-grade casting blank is used for rolling the high-grade rolled material with the thickness less than 5mm in order to improve the strength of the rolled material.
Compared with the prior art, the invention has the following advantages:
1) the letter variables contained in the rule equation of change of the components of the mixed molten steel in the tundish along with the time comprise independent variables corresponding to the conditions of continuous casting process equipment, such as the speed of injecting molten steel into the tundish, the speed of flowing molten steel out of the tundish, the casting time of high-grade molten steel, the weight of molten steel in the tundish and the like, and the partial variables can correspond to the changed continuous casting process working conditions.
2) The method accurately calculates the change rule of the mixed molten steel components in the tundish along with the time by using the equation, thereby accurately determining the time node of the molten steel components in the tundish meeting the standard requirement of high-grade steel grades, and determining the billet judging process according to the time node, so that the chemical component loss caused by incorrect judgment can be reduced.
3) Because the components of the mixed casting blank are different compared with the components of the non-mixed casting blank, the chemical components of the mixed casting blank judged to be of the high-grade steel are slightly lower than those of the normal non-mixed casting high-grade casting blank, so that the mixed casting blank of the part of the high-grade steel is used for producing a high-grade thin rolled material with the thickness of less than 5mm, the thin rolled material is used for rolling with high reduction rate, the strength and toughness of the steel can be increased along with the increase of the reduction rate, the performance qualification rate of the steel can be improved, and the phenomenon that the performance is lower than the lower limit can be reduced.
The chemical components of the mixed casting blank judged as the low-grade steel grade are slightly higher than the components of the normal non-mixed casting low-grade casting blank, so that the mixed casting blank of part of the low-grade steel grade is used for producing a low-grade thick rolling material with the thickness of more than 12mm, the strength and the toughness of the thick rolling material are reduced along with the reduction of the reduction rate due to the small rolling reduction rate, the phenomenon that the physical performance of the low-grade rolling material exceeds the upper limit is reduced, and the performance qualified rate of the steel material can be improved.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments.
Example 1:
a mixed casting method of dissimilar steel suitable for a slab caster comprises the following steps:
step one, in the continuous casting production, mixed casting is carried out by adopting Q355B and Q235B, in the continuous casting production, a low-grade steel grade Q235B is produced firstly, and a high-grade steel grade Q355B is produced secondly.
The physical properties of the low-grade steel Q235B and the high-grade steel Q355B have an overlap interval.
The low-grade steel grade Q235B is a steel grade with lower requirements on chemical component content and physical and mechanical properties;
the high-grade steel grade Q355B is a steel grade with higher requirements on chemical component content and physical and mechanical properties.
And step two, after the heat casting of the low-grade steel Q235B is finished, when the liquid level in the tundish is reduced to 400mm, the ladle with the high-grade steel Q355B heat is started to be cast.
The casting blank pulling speed of the continuous casting machine is kept unchanged when the low-grade steel Q235B, the high-grade steel Q355B and the two steel grades are produced and mixed for casting.
After the ladle is poured, the opening degree of the steel ladle sliding gate valve is set to be 100%, the liquid level of the molten steel in the tundish quickly rises, and when the liquid level of the molten steel in the tundish rises to the maximum (727mm), the opening degree of the steel ladle sliding gate valve is reduced, the injection speed of the molten steel in the ladle into the tundish is reduced, and the liquid level of the molten steel in the tundish is controlled to be in a stable state of not rising and not falling.
The large ladle is a ladle for injecting molten steel into the tundish in the continuous casting process.
The tundish is a refractory container used in the continuous casting process, firstly receives molten steel poured from a ladle, and then is distributed into each crystallizer through a tundish nozzle.
The liquid level of the molten steel in the tundish is the depth of the molten steel in the tundish.
Step three, mixing the chemical components omega of the molten steel in the tundish after the high-grade steel is pouredInThe law equation of variation with time t is calculated according to the following formula:
1) when the ladle is cast to the tundish molten steel full ladle process, the chemical composition omega of the molten steel is mixed in the tundishInThe law equation of change with time t is calculated according to the following formula (1):
Figure BDA0002965356300000091
VsteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the molten steel is poured under the high mark Q355B; vInIs tundish steelThe speed at which the water leaves the tundish, i.e. the speed at which the molten steel of the tundish is poured into the mould, (tons/min); omegaInThe chemical component concentration in the tundish molten steel; q0The mass (ton) of molten steel in the tundish before the high-grade Q355B molten steel is poured; omegaLow gradeThe chemical component concentration in the low-grade Q235B molten steel;
2) after the molten steel in the tundish is fully filled, the liquid level of the molten steel in the tundish is not changed, namely the weight of the molten steel in the tundish is not changed, and the component omega of the mixed molten steel in the tundish is not changedInThe law of change with time t equation is calculated by the following equation (2):
Figure BDA0002965356300000092
v in the formula (2)SteelThe pouring speed of molten steel in a steel ladle into a tundish is (ton/minute); omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time (minutes) after the molten steel is poured under the high mark Q355B; omegaInThe chemical component concentration in the tundish molten steel; vInThe pouring speed of the molten steel in the tundish into the crystallizer is VSteel＝VIn (1)(ton/min); qInThe mass of the tundish molten steel (ton); c is a constant;
and step four, according to the calculation formula (1) and the calculation formula (2) in the step three, a computer is utilized to compile a chemical component concentration change model in the mixed casting molten steel, the model automatically reads the components of the high-grade molten steel Q355B and the last low-grade molten steel Q235B in the ladle from the steelmaking system, reads the casting time of the high-grade molten steel Q355B in the continuous casting system, the molten steel quality in the tundish when the high-grade molten steel Q355B is cast, the molten steel speed when the ladle is injected into the tundish, the molten steel speed when the tundish flows into the crystallizer, the molten steel quality of the full tundish and other parameters, and automatically calculates a change equation of the percentage content of elements such as C, Si, Mn, P, S, Nb, V, Ti and the like in the molten steel along with the casting time of the high-grade steel according to the parameters. And calculating the time for the mixed molten steel components in the tundish to meet the requirement of the high-grade steel grade, and judging the casting blank produced thereafter to be the high-grade casting blank and the casting blank produced heretofore to be the low-grade casting blank by taking the time as a node.
In this example, after the high grade steel is poured, the molten steel velocity V of the ladle is poured into the tundishSteel: 9 tons/min; speed V of molten steel flowing out of tundishIn: 4 ton/min; weight Q of molten steel in tundish when high grade steel is poured0: 22 tons; the weight of molten steel in the full tundish is as follows: 40 tons; after the tundish is full, the molten steel velocity V of the tundish is injected into the ladleSteel: 4 tons/min. The controlled range of the chemical components and the actual components of Q235B and Q355B are shown in the following table 1:
the chemical composition internal control range and actual composition of the materials in tables 1, Q235B and Q355B
Figure BDA0002965356300000101
According to the parameters, the tundish is fully packed 3.6min after the high-grade steel is poured, and the chemical components C, Si, Mn, P and Ti in the tundish are calculated by adopting the formula (1) when the tundish is fully packedInThe components are taken as an example, the invention takes the continuous casting parameters, the carbon content in high-grade molten steel and the carbon content in low-grade molten steel into the formula (1), and calculates the carbon content in the tundish molten steel at the full ladle time, as shown in the following formula
Figure BDA0002965356300000102
As shown.
Figure BDA0002965356300000103
At the moment when the tundish is full, the calculation processes of the contents of other elements Si, Mn, P and Ti are not shown in a column, and only the calculation results are filled in the table 2.
After the ladle is fully filled, the change rule of the ingredients in the molten steel of the tundish is calculated by the formula (2);
Figure BDA0002965356300000111
first, the tundish in Table 2 below was filled with molten steel tIs full ofTime value, chemical component concentration in tundish molten steel omegaIs full ofThe constant C in equation (2) can be solved by substituting the value in equation (1). As an example, the invention takes the above continuous casting parameters, the carbon content in the high-grade molten steel and the carbon content in the low-grade molten steel into formula (2), and calculates the constant C value in the equation (2) for calculating the change of the carbon content in the chemical composition, as shown in the following formula
Figure BDA0002965356300000112
As shown, the other calculation processes of "calculating the constant C value in the content change equation (2) of Si, Mn, P, and Ti" are not shown in a list, and only the calculation results are filled in table 2.
Figure BDA0002965356300000113
Figure BDA0002965356300000114
Then substituting the C value into a formula (2), then obtaining a formula by using the formula (2), and calculating the time t when the carbon content reaches the lower limit of the internal control of 0.16 percent, wherein the formula is shown as follows;
here, if the chemical component concentration at the full ladle time is greater than the high-grade molten steel internal control lower limit, the time t required for the chemical component concentration to reach the internal control lower limit is calculated by equation (1), and if the chemical component concentration at the full ladle time is less than the high-grade molten steel internal control lower limit, the time t required for the chemical component concentration to reach the internal control lower limit is calculated by equation (2).
For example, the present invention substitutes the above continuous casting parameters, the carbon content in the high-grade molten steel, and the carbon content in the low-grade molten steel into equation (2), calculates the time that the carbon content in the tundish molten steel reaches the lower control limit of Q355B, and the other calculation processes of "calculating the time that the contents of Si, Mn, P, and Ti reach the lower control limit of Q355B" after the high-grade Q355B molten steel is poured, and only fills the calculation results in table 2.
Figure BDA0002965356300000115
t＝8.9min
As can be seen from the following table 2, after the high-grade molten steel ladle is poured, the contents of C, Si, Mn, P, S and Ti in the tundish reach the lower internal control limit of the element component of the high-grade steel type Q355B within 8.9min, 0.9min, 15.84min, 0min and 15.92mm respectively, so that after the high-grade molten steel Q355B is poured for 15.92min, the mixed molten steel component in the tundish reaches the internal control range of the high-grade steel type Q355B, the casting blank produced after the high-grade Q355B is poured for 15.92min is judged to be the high-grade Q355B casting blank, and the casting blank produced before is judged to be the low-grade Q235B casting blank.
TABLE 2 data of chemical component concentration change of molten steel in tundish calculated according to equations (1) and (2)
Figure BDA0002965356300000121
And step five, because the casting blank produced by the furnace high-grade molten steel Q355B belongs to a mixed casting blank, the components in the casting blank have a gradual change process, and each casting blank produced by the furnace high-grade molten steel Q355B is marked independently and is used for rolling rolled products with different thicknesses.
Because the chemical composition range of the low-grade casting blank produced by the furnace Q355B molten steel early-stage mixed casting process is between the composition of the low-grade Q235B molten steel and the lower limit of the internal control composition of the high-grade Q355B molten steel, the chemical composition content is slightly higher than the middle limit chemical composition content of the low-grade Q235B steel produced by the non-mixed casting process, and in order to reduce the strength of the rolled material, the Q235B low-grade casting blank produced by the furnace Q355B early-stage casting is used for rolling the low-grade Q235B rolled material with the thickness larger than 12 mm.
Because the chemical components in the high-grade casting blank generated by the late mixed casting process of the molten steel in the furnace Q355B are between the lower limit of the internal control components of the high-grade molten steel Q355B and the normal components of the high-grade molten steel Q355B, the chemical component content is slightly lower than the middle limit chemical components of the high-grade casting blank Q355B produced by the non-mixed casting process, and in order to improve the strength of a rolled material, the generated high-grade casting blank is used for rolling the high-grade rolled material Q355B with the thickness less than 5 mm.
The effect is as follows:
the law equation of the change of the composition of the mixed molten steel in the tundish with time in the embodiment can correspond to the molten steel injection speed V from different steel ladles to the tundishSteelIn the different molten steel flow-out speed V of the tundish and in the different molten steel weight Q of the tundishIn (1)The method can adapt to complex and variable continuous casting process working conditions, and has wide equation applicability and good external expansibility.
In the embodiment, the weight of molten steel in the furnace is 130 tons, the casting blank produced after the molten steel with the high grade Q355B is cast for 15.92min is judged to be a casting blank with the high grade Q355B, 46 tons of molten steel are remained in a ladle with the high grade Q355B, 40 tons of molten steel are remained in a tundish, namely, the mixed casting blank produced by the remained molten steel with the high grade of 46+40 tons is judged to be a casting blank with the high grade of Q355B, the mixed casting blank produced by the molten steel with the high grade of 130-86 tons is judged to be a casting blank with the low grade, the mixed casting rate of the molten steel in the furnace is only 100% 42/130% 32%, the mixed casting rate is low, and the waste of chemical elements in the steel with the high grade is reduced.
According to production experience, casting blanks with the same chemical component content have obvious change of physical and mechanical properties of rolled materials along with different rolling reduction rates, the strength of the rolled materials can be improved by 15Mpa and the toughness of the rolled materials can be improved by 10J when the thickness of the rolled materials is reduced by 2mm, so that the casting blank judged as the low-grade Q235B in the mixed casting blank of the furnace is used for producing the low-grade Q235B rolled materials with the thickness of more than 12mm, the casting blank judged as the high-grade Q355B is used for producing the high-grade Q355B rolled materials with the thickness of less than 5mm, the mechanical property qualification rate of the rolled materials can be improved, and statistics shows that the mixed casting blanks in 2 months to 8 months in 2019 and Q235B and Q355B produced by a total 80-furnace mixed casting process, and the qualification rate of the physical and mechanical properties of the rolled materials is 100 percent after the rolling process is adopted
The method can be realized by upper and lower limit values and interval values of intervals of process parameters (such as temperature, time and the like), and embodiments are not listed.
Conventional technical knowledge in the art can be used for the details which are not described in the present invention.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (4)

1. A mixed casting method of dissimilar steel suitable for a slab caster comprises the following steps:
firstly, in continuous casting production, firstly producing low-grade steel, then producing high-grade steel, and keeping the casting blank pulling speed of a continuous casting machine unchanged when producing the low-grade steel, the high-grade steel and mixed casting of the two steel;
step two, after the heat casting of the low-grade steel is finished, when the liquid level in the tundish is reduced to 400-500 mm, the ladle of the high-grade steel starts to be cast; after the ladle is poured, the opening degree of a steel ladle sliding gate valve is set to be 100%, the liquid level of the molten steel in the tundish quickly rises, and when the liquid level of the molten steel in the tundish rises to the maximum, the opening degree of the steel ladle sliding gate valve is reduced, the injection speed of the molten steel in the ladle into the tundish is reduced, and the liquid level of the molten steel in the tundish is controlled to be in a stable state without rising or falling;
step three, mixing chemical components omega of molten steel in the tundish after the high-grade steel is pouredInThe change rule along with the time t is calculated according to the following formula:
1) mixing the chemical components omega of the molten steel in the tundish in the process of pouring the ladle to the full ladle of the molten steel in the tundishIn (1)The law equation of change with time t is calculated according to the following formula (1):
Figure FDA0002965356290000011
wherein, VSteelThe injection speed of the steel ladle molten steel to the tundish is ton/min; omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time of the molten steel of the high grade steel after casting in minutes; vInThe pouring speed of the tundish molten steel to the crystallizer is ton/min; omegaIn (1)The chemical component concentration in the tundish molten steel; q0The mass of molten steel in the tundish before the molten steel of high grade steel is poured is ton; omegaLow gradeThe chemical component concentration in the low-grade molten steel;
2) after the tundish molten steel is fully filled, the molten steel liquid level of the tundish does not change, namely the molten steel weight of the tundish does not change, and the chemical component omega of the mixed molten steel in the tundishInThe change law with time t is calculated according to the following formula (2):
Figure FDA0002965356290000012
in the formula (2), VSteelThe injection speed of the steel ladle molten steel to the tundish is ton/min; omegaSteelThe chemical component concentration in the steel ladle molten steel; t is the time of the molten steel of the high grade steel after casting in minutes; vInThe pouring speed of the molten steel in the tundish into the crystallizer is VSteel＝VInTon/min; omegaIn (1)The chemical component concentration in the tundish molten steel; qInThe mass of the tundish molten steel is ton; c is a constant;
wherein, the calculation process of C is as follows, firstly, t and omega when the tundish is full are calculated by the formula (1)InThen, t and ω are addedInSubstituting the formula (2) into the formula (2) to calculate C;
step four, inputting the following data in the formula (1) or the formula (2): the method comprises the steps of calculating the concentration of chemical components in molten steel of a steel ladle to a tundish, the concentration of the chemical components in the molten steel of a steel ladle, the time after the molten steel of a high grade is poured, the injection speed of the molten steel of a tundish to a crystallizer, the mass of the molten steel in the tundish before the molten steel of the high grade is poured, the concentration of the chemical components in the molten steel of a low grade and the mass of the molten steel of the tundish, and taking the time t of finally reaching a certain component of the composition standard of the high grade as a time node for judging that a casting blank is a casting blank of a high grade, the casting blank after the time node is a casting blank of a high grade, and the casting blank before the time node is a casting blank of a low grade.
2. The mixed casting method of dissimilar steel suitable for a slab caster according to claim 1, wherein the chemical composition in the molten steel is one of C, Si, Mn, P, S, Nb, V and Ti.
3. The mixed casting method of different steel grades suitable for a slab caster as claimed in claim 1, wherein the low-grade billet is used for rolling a low-grade rolled product with a thickness of more than 12mm, and the high-grade billet is used for rolling a high-grade rolled product with a thickness of less than 5 mm.
4. The mixed casting method of dissimilar steel grades suitable for a slab caster as claimed in claim 1, wherein there is an overlap interval of physical properties of the low-grade steel grade and the high-grade steel grade.
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