CN112207246A - Method for measuring solidification end point of square billet - Google Patents

Method for measuring solidification end point of square billet Download PDF

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CN112207246A
CN112207246A CN202011149365.2A CN202011149365A CN112207246A CN 112207246 A CN112207246 A CN 112207246A CN 202011149365 A CN202011149365 A CN 202011149365A CN 112207246 A CN112207246 A CN 112207246A
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tracer
lead
casting
billet
end point
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张炯明
马海涛
尹延斌
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University of Science and Technology Beijing USTB
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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
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B22D2/005—Arrangement of indicating or measuring devices, e.g. for temperature or viscosity of the fused mass for the thickness of a frozen shell
    • G—PHYSICS
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Abstract

A method for measuring the solidification end point of a square billet belongs to the technical field of steelmaking and continuous casting. The technical scheme is as follows: establishing a mathematical model according to the actual production conditions of the on-site casting machine to calculate the time from the tracer material lead liquid flowing to the permeation end point; at the last stage of continuous casting and pouring, continuously and uniformly adding molten lead into a crystallizer, simultaneously starting to record time and marking at a specific position, and finishing recording the time when the marking position reaches the position of a flame cutting machine; after the tail billet is pulled out, the experimental casting billet is numbered at the position of the casting billet mark, the processed sample is subjected to X-ray scanning, the shell thicknesses of the samples with different numbers are measured, and the shell thicknesses of the casting billet at different positions are subjected to multi-point correction calculation through a casting billet solidification heat transfer model to obtain the casting billet solidification end point position. The invention provides important parameters for implementing technologies such as tail end electromagnetic stirring, tail end pressing and the like, and has good popularization and use values.

Description

Method for measuring solidification end point of square billet
Technical Field
The invention relates to a method for measuring a square billet solidification end point, and belongs to the technical field of steelmaking and continuous casting.
Background
With the progress and development of society, the requirements of various industries on steel products are higher and higher, and the internal structure defects of central loosening shrinkage, central segregation and the like of continuous casting slabs cannot meet the requirements of high-quality steel products. The internal defects of the casting blank can seriously affect the non-uniformity of the internal structure of the casting blank, so that the casting blank is broken by drawing, and meanwhile, the segregation can reduce the welding performance of the product, so that the product is not easy to weld and even cracks. In order to improve the quality of a casting blank, the technology of electromagnetic stirring at the tail end of the casting blank, the technology of light pressing at the tail end of the casting blank and the like are developed in recent years, in order to match with the advanced technologies, the key problem is that the position of the solidification end point of the casting blank is accurately grasped, most of casting machines adopt a nail shooting method to predict the solidification end point of the casting blank, and the method belongs to single-point correction and is easy to generate errors. In addition, the method for detecting the liquid core of the continuous casting billet, which is disclosed by the patent publication CN105436452A, does not consider the settling time of the lead liquid, and has certain experimental errors. Therefore, designing a method for determining the solidification end point of the billet becomes a key problem.
Disclosure of Invention
The invention aims to provide a method for measuring a billet solidification end point, which can accurately measure the billet solidification end point and provide reference for the implementation of technologies such as electromagnetic stirring at the tail end of a continuous casting machine, light pressing at the tail end and the like.
The technical scheme for implementing the method is as follows:
a method for measuring the solidification end point of a square billet is characterized in that,
the method comprises the following steps: firstly, determining a tracer material;
step two: establishing a convection diffusion model of the tracer in the molten steel according to the tracer filling time, the casting machine parameters, the tracer and the physical parameters of the steel, and calculating to obtain the time t required by the molten lead to fall to the permeation end point1；
Step three: melting the tracer agent at the last stage of casting, heating to a liquid temperature, and keeping the molten state to prevent condensation; filling a container with a self-made tracer, uniformly and continuously adding the tracer into a crystallizer, and keeping the pulling speed unchanged; at the beginning of tracer infusion, begin recordingRecording time and marking at a specific position, finishing recording the time when the marking position of the casting blank reaches the position of the flame cutting machine, and obtaining the time t from the beginning of filling the tracer to the cutting of the casting blank2Calculating the distance S between the mark position and the meniscus;
step four: after pulling out the tail billet, sawing and numbering the casting blanks at the marked positions at intervals of Amm; machining each sample by a machine tool according to the standard size to find the central surface of the casting blank;
step five: and carrying out X-ray scanning on the processed sample, obtaining the distribution of the tracer in the casting blank according to the X-ray scanning result, measuring the shell thicknesses of the samples with different numbers, and carrying out multi-point correction calculation on the shell thicknesses of different positions of the casting blank through a casting blank solidification heat transfer model to obtain a casting blank solidification end point.
Furthermore, the lead liquid is used as a tracer, has higher density and lower melting point than the molten steel, is not mixed with the molten steel, and can effectively carry out experiments.
Further, the convection diffusion model of the tracer lead liquid in the molten steel established in the step two is as follows:
equation of continuity
Figure BDA0002740708700000021
Equation of conservation of momentum
Figure BDA0002740708700000022
③ Source terms in the conservation of momentum equation
Figure BDA0002740708700000023
In the formula, ρbThe density of the molten lead is shown, and rho is the density of the molten steel;
heat transfer equation of casting blank
Figure BDA0002740708700000024
Where enthalpy H can be expressed as a function of temperature;
solute diffusion equation
Figure BDA0002740708700000031
Further, the distance S between the mark position and the meniscus is calculated according to a calculation formula (6), the calculation process is shown in the schematic diagram 1, the distance between the sample with any number and the meniscus can be calculated according to the distance S between the mark position and the meniscus, the distribution of lead can be displayed on an X-ray film according to the difference of the transmission capacity of the X-ray to steel and lead, and the thickness of the blank shell of the sample with different numbers is measured;
Figure BDA0002740708700000032
in the formula: l is the distance of the meniscus from the flame cutting position, m; s is the distance m between the mark position and the meniscus; v-casting blank pulling speed, m/min; t is t1-the time(s) from the start of lead pouring to the end of lead sinking penetration. t is t2-the time(s) taken for the lead filling to start and for the slab to remain.
And further, machining each sample by a machine tool according to a standard size, before machining by the machine tool, finding a geometric center line of the sample in a casting blank drawing direction, sawing the left side and the right side by Cmm and Dmm respectively, and then milling the thickness of the Cmm on the left side by a milling machine to find a central plane.
The invention has the beneficial effects that:
the X-ray detection method provided by the invention can be used for carrying out X-ray detection on the taken sample, can visually display the liquid core change of the continuous casting billet according to different physical characteristics of lead and steel, has an obvious visual effect, can be used for carrying out multi-point correction on the solidified shell of the casting billet, greatly reduces the experimental error, improves the experimental accuracy, provides accurate and reliable experimental data for a field reduction experiment, optimizes the production conditions, improves the quality of the continuous casting billet, and has a very high popularization value.
Drawings
FIG. 1 is a schematic view of a calculated lead trace
1-meniscus; 2-end of solidification; 3-marking the position; 4-flame cutting position;
FIG. 2 calculation results of molten steel flow of molten lead
FIG. 3 is a schematic view of lead solution pouring
5-tundish; 6-filling a lead pot; 7-a continuous casting platform; 8-submerged entry nozzle;
FIG. 4 schematic drawing of casting blank reference numerals
FIG. 5 is a schematic view of the preparation of a sample
9-center line, 10-direction of withdrawal;
FIG. 6 calibration of the calculated solidified shell by measuring the solidified shell;
FIG. 7 shows the liquid core distribution of a casting blank and the liquid core calculation of a casting blank solidification heat transfer model in a lead-filling tracer experiment,
11-calculating the liquid core distribution of the casting blank by a casting blank solidification heat transfer model; 12-pouring lead tracer experiment casting blank liquid core distribution.
Detailed Description
The method for determining the solidification end point of a square billet with the size of 150mm multiplied by 150mm comprises the following specific steps:
the method comprises the following steps: determining experimental materials, adopting lead liquid as a tracer, wherein the lead liquid has higher density and lower melting point than the molten steel, is not mixed with the molten steel, and can effectively perform experiments;
step two: establishing a mathematical model of the flow diffusion of the molten lead in the molten steel according to the actual production conditions on site,
equation of continuity
Figure BDA0002740708700000041
Equation of conservation of momentum
Figure BDA0002740708700000042
③ Source terms in the conservation of momentum equation
Figure BDA0002740708700000043
In the formula, ρbIs the density of lead, rho is the density of the molten steel;
heat transfer equation of casting blank
Figure BDA0002740708700000044
Where enthalpy H can be expressed as a function of temperature;
solute diffusion equation
Figure BDA0002740708700000045
Calculating the time t required by the molten lead to fall to the solidification end point1As in fig. 2.
Step three: melting 30kg of lead half an hour before stopping pouring, heating to 350 ℃, and keeping the molten state to prevent condensation; a self-made lead pouring kettle is utilized to uniformly and continuously add a lead liquid tracer into a crystallizer, and the drawing speed is kept unchanged at 2.3m/min in a drawing 3; recording time when molten lead pouring starts and marking at a specific position; ending the recording of the time when the mark position of the casting blank reaches the position of the flame cutting machine to obtain the time t from the beginning of lead pouring to the cutting of the casting blank2；
Step four: after the tail blank is pulled out, according to the formula:
Figure BDA0002740708700000051
calculating the distance S between the marking position and the meniscus, and sawing and numbering samples at the marking position every 0.5m of the casting blank, as shown in FIG. 4; machining each sample by a machine tool according to a standard size, before machining by the machine tool, finding a geometric center line of the sample in a casting blank drawing direction, respectively sawing 5mm and 25mm on the left side and the right side, and then milling the left side by the thickness of 5mm by a milling machine to find a center plane, wherein the central plane is shown in figure 5;
step five: 13084mm is obtained by calculation according to the distance between the mark position and the meniscus, the distance between different sample numbers and the meniscus can be calculated, the processed sample is scanned by X-ray, the distribution of lead in the casting blank can be obtained according to the scanning result of the X-ray, the shell thicknesses of the samples with different numbers are measured, figure 6 is that the shell thicknesses of the casting blank at different positions are corrected by multiple points, and the solidification end point of the casting blank is 13291mm by calculation of a solidification heat transfer model of the casting blank, figure 7.

Claims (5)

1. A method for measuring the solidification end point of a square billet is characterized in that,
the method comprises the following steps: firstly, determining a tracer material;
step two: establishing a convection diffusion model of the tracer in the molten steel according to the tracer filling time, the casting machine parameters, the tracer and the physical parameters of the steel, and calculating to obtain the time t required by the tracer to fall to the permeation end point1；
Step three: melting the tracer agent at the last stage of casting, heating to a liquid temperature, and keeping the molten state to prevent condensation; filling a container with a self-made tracer, uniformly and continuously adding the tracer into a crystallizer, and keeping the pulling speed unchanged; when the tracer agent is filled, starting to record time and marking at a specific position, and ending to record time when the casting blank marking position reaches the position of the flame cutting machine to obtain the time t from the start of filling the tracer agent to the cutting of the casting blank2Calculating the distance S between the mark position and the meniscus;
step four: after pulling out the tail billet, sawing and numbering the casting blanks at the marked positions at intervals of Amm; machining each sample by a machine tool according to the standard size to find the central surface of the casting blank;
step five: and carrying out X-ray scanning on the processed sample, obtaining the distribution of the tracer in the casting blank according to the X-ray scanning result, measuring the shell thicknesses of the samples with different numbers, and carrying out multi-point correction calculation on the shell thicknesses of different positions of the casting blank through a casting blank solidification heat transfer model to obtain a casting blank solidification end point.
2. The method of claim 1, wherein the end point of solidification of the billet is determined by using a molten lead as a tracer, wherein the molten lead has a density higher than that of the molten steel and a melting point lower than that of the molten steel, and is not mixed with the molten steel, thereby enabling efficient experiments.
3. The method for determining the solidification end point of a billet according to claim 1, wherein in the second step, a convection diffusion model of molten lead in molten steel is established;
equation of continuity
Figure FDA0002740708690000011
Equation of conservation of momentum
Figure FDA0002740708690000012
③ Source terms in the conservation of momentum equation
Figure FDA0002740708690000021
In the formula, ρbThe density of the molten lead is shown, and rho is the density of the molten steel;
heat transfer equation of casting blank
Figure FDA0002740708690000022
Where enthalpy H can be expressed as a function of temperature;
solute diffusion equation
Figure FDA0002740708690000023
Calculating to obtain the tracer lead liquid falling to solidificationTime t required for endpoint1。
4. The method of claim 1, wherein the distance S between the mark position and the meniscus is calculated according to the calculation formula (6), and the distance S between the mark position and the meniscus is calculated according to the distance S between the mark position and the meniscus, thereby calculating the distance between the sample of any number and the meniscus; according to the difference of the transmission capacity of X-ray to steel and lead, the X-ray film can display the distribution of lead, and the thickness of the blank shell of the test sample with different numbers is measured;
Figure FDA0002740708690000024
in the formula: l is the distance of the meniscus from the flame cutting position, m; s is the distance m between the mark position and the meniscus; v-casting blank pulling speed, m/min; t is t1-the time(s) from the start of the lead pouring to the end of the lead sinking penetration; t is t2-the time(s) taken for the lead filling to start and for the slab to remain.
5. The method for determining the solidification end point of a square billet according to claim 1, wherein each sample is machined by a machine tool according to standard sizes, before machining, a geometric center line of the billet blank drawing direction of the sample is found, the left side and the right side of the geometric center line are respectively sawed by Cmm and Dmm, and then the left side of the Cmm is milled by a milling machine to find a central plane.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS469551Y1 (en) * 1967-06-26 1971-04-05
CN101367115A (en) * 2008-08-22 2009-02-18 武汉钢铁(集团)公司 Casting blank liquid core length measuring method
CN105436452A (en) * 2015-11-22 2016-03-30 河北钢铁股份有限公司承德分公司 Method for detecting continuously-cast small-square-billet liquid core
CN110802207A (en) * 2019-11-12 2020-02-18 苏州大学 Combined pressing method for continuous casting billet

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS469551Y1 (en) * 1967-06-26 1971-04-05
CN101367115A (en) * 2008-08-22 2009-02-18 武汉钢铁(集团)公司 Casting blank liquid core length measuring method
CN105436452A (en) * 2015-11-22 2016-03-30 河北钢铁股份有限公司承德分公司 Method for detecting continuously-cast small-square-billet liquid core
CN110802207A (en) * 2019-11-12 2020-02-18 苏州大学 Combined pressing method for continuous casting billet

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
伍兵等: "攀钢连铸机结晶器冷却能力的研究 ", 《钢铁钒钛》 *
程常桂等: "轻压下技术在连铸中的应用", 《炼钢》 *

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