A method for determining the soft reduction position of a bloom

Abstract

The present invention discloses a method for determining the soft reduction position of a square billet, including: taking a billet with a predetermined length in the casting direction, intercepting a first specimen at the width center of the billet, intercepting a second specimen at the thickness center of the billet, and preprocessing the first specimen and the second specimen; equally spacing k positions along the length direction of the first specimen to measure the thickness of the shrinkage porosity zone of the specimen, and measuring the width of the shrinkage porosity zone of the second specimen at the k positions; determining the shrinkage porosity zone width-thickness product S based on the measured thickness and width of the shrinkage porosity zone of the specimen; based on the square billet continuous casting process parameters, establishing a two-dimensional solidification heat transfer numerical calculation model of the square billet cross-section, determining the width and thickness of the two-phase zone of the billet cross-section at different casting positions during continuous casting, and calculating the two-phase zone width-thickness product S c ; based on the determined shrinkage porosity zone width-thickness product S and two-phase zone width-thickness product S c determining the position where soft reduction needs to be applied in square billet continuous casting. This method can improve the accuracy of the determined reduction position.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and more particularly to a method for determining the soft reduction position of a square billet. Background Art

[0002] Soft reduction at the solidification end of a continuous casting billet is an effective technical means to improve the central macrosegregation, shrinkage cavity, and porosity of the casting billet. In a suitable casting stream area near the solidification end of the casting stream, by applying a reduction deformation in the thickness direction of the casting billet, it promotes the flow of the concentrated molten steel rich in solute elements in the two-phase region towards the upstream area of the casting stream, and remixes evenly with the molten steel with a lower concentration of segregated solute elements in the upstream area, which can reduce the central segregation. At the same time, the reduction deformation in the thickness direction can effectively compensate for the volume shrinkage of the molten steel in the core of the casting billet during the cooling and solidification process, thereby reducing the central shrinkage cavity and porosity defects of the casting billet.

[0003] The soft reduction position is the core process parameter of the soft reduction technology, which characterizes the casting stream position where the soft reduction is applied and determines the soft reduction process effect. A reasonable soft reduction position can effectively improve the central segregation, shrinkage cavity, and porosity defects of the casting billet, while an unreasonable soft reduction position is not only difficult to effectively improve the above quality defects, but may also cause internal cracks at the solidification front of the casting billet and damage the reduction equipment of the casting machine. Currently, there are some existing technologies for determining the soft reduction position, and their technical methods can be generally classified into four categories. The first category of methods uses a solidification heat transfer model to calculate the solidification heat transfer law of the continuous casting billet, and determines the reduction interval based on the calculated solidification morphology, temperature distribution, solid fraction, etc. of the casting billet, such as the technologies disclosed in patents CN113000804A, CN103447493A, CN112475251A, etc. The second category of methods determines a reasonable reduction interval by calculating the central segregation law of each solute element when reducing at different positions, such as the technology disclosed in patent CN101695747B. The third category of methods uses the sudden change position of the feedback compaction force during reduction as the solidification end position, and accordingly determines the reduction interval, such as the technology disclosed in patent CN101912952B. The fourth category of methods combines experience and on-site tests to formulate a suitable reduction interval for a certain steel grade, such as the technology disclosed in patent CN100417461C.

[0004] Although the above four categories of methods play a guiding role in determining the soft reduction position, they also have certain deficiencies. These four categories of methods do not fully consider the actual defect morphology distribution characteristics such as shrinkage cavity and porosity in the core of the casting billet, resulting in the need to improve the accuracy of the determined reduction position. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the soft reduction position of a square billet to solve at least one of the above problems existing in the prior art.

[0006] To achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a method for determining the soft reduction position of a bloom is provided, including the following steps:

[0008] Step 1: When the casting is stable, take a billet with a predetermined length in the casting direction, intercept a first specimen at the width center of the billet, intercept a second specimen at the thickness center of the billet, and perform pretreatment on the first specimen and the second specimen;

[0009] Step 2: Select k positions at equal intervals along the length direction of the first specimen to measure the thickness of the shrinkage cavity and porosity zone of the specimen, denoted as t1, t2, t3... t k , measure the width of the shrinkage cavity and porosity zone of the second specimen at the k positions, denoted as w1, w2, w3,... w k ;

[0010] Step 3: Determine the product S of the width and thickness of the shrinkage cavity and porosity zone based on the thickness of the shrinkage cavity and porosity zone of the specimen and the width of the shrinkage cavity and porosity zone of the specimen measured in Step 2;

[0011] Step 4: Based on the bloom continuous casting process parameters, establish a two-dimensional solidification heat transfer numerical calculation model for the bloom cross-section, and determine the width W c and thickness T c of the two-phase zone of the billet cross-section at different casting positions during the continuous casting process, and calculate the product S of the width and thickness of the two-phase zone c ;

[0012] Step 5: Determine the position where soft reduction needs to be applied for bloom continuous casting based on the product S of the width and thickness of the shrinkage cavity and porosity zone determined in Step 3 and the product S of the width and thickness of the two-phase zone determined in Step 4 c .

[0013] According to an embodiment of the present invention, in Step 1, the predetermined length is 400 - 600 mm.

[0014] According to an embodiment of the present invention, in Step 1, the specimen is a longitudinal section macrostructure specimen.

[0015] According to an embodiment of the present invention, in Step 1, the pretreatment includes performing macro-etching on the longitudinal section macrostructure specimen using the hot acid method.

[0016] According to an embodiment of the present invention, in Step 2, the measurement position interval is 80 - 120 mm.

[0017] According to an embodiment of the present invention, in Step 2, k is an integer selected from 4 - 10.

[0018] According to an embodiment of the present invention, in Step 3, the product S of the width and thickness of the shrinkage cavity and porosity zone is calculated using the following formula (1):

[0019]

[0020] According to an embodiment of the present invention, in step 4, the product of width and thickness S in the two-phase region is calculated using the following formula (2) c :

[0021] S c =W c ·T c (2).

[0022] According to an embodiment of the present invention, in step 4, the two-dimensional solidification heat transfer numerical calculation model of the bloom cross-section is a two-dimensional solidification heat transfer finite element model established by finite element analysis.

[0023] According to an embodiment of the present invention, in step 5, the casting stream position when S c =S is used as the position where soft reduction needs to be applied in bloom continuous casting.

[0024] Due to the adoption of the above technical solutions, the method for determining the soft reduction position of the bloom provided by the present invention has the following beneficial effects compared with the prior art: By detecting the macrostructure of the pickled bloom with a certain length in the casting direction, the distribution of shrinkage cavities and porosity zones in the width and thickness directions is determined, and further combined with the change law of the two-phase region appearance in the center of the bloom during continuous casting calculated by the two-dimensional solidification heat transfer model, the reduction interval is determined. This method can be applied to different continuous casting steels with different bloom cross-sectional dimensions and steel grades, and its applicability is wider. Moreover, when determining the reduction position, the distribution characteristics of actual defects such as shrinkage cavities and porosity in the center of the casting billet are fully considered, which helps to formulate the soft reduction process of continuous casting blooms efficiently and accurately, and effectively improve the internal quality defects such as center segregation, shrinkage cavities, and porosity of the blooms. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0026] Figure 1 is a flowchart of the method for determining the soft reduction position of a bloom according to an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the sampling position of the longitudinal macro sample;

[0028] Figure 3 is a schematic diagram of the thickness and width of the shrinkage cavity and porosity zones of the pickled macro sample;

[0029] Figure 4 is a schematic diagram of the two-phase region morphology in the cross-section of the casting billet;

[0030] Figure 5 It is a test diagram of the acid pickling macrostructure test according to the test example;

[0031] Figure 6 It is a schematic diagram of the two-dimensional solidification heat transfer finite element model according to the test example;

[0032] Figure 7 It is a schematic diagram of the thickness and width of the two-phase region at different casting stream positions according to the test example;

[0033] Figure 8 It is a schematic diagram of the product of the thickness and width of the two-phase region at different casting stream positions according to the test example;

[0034] Figure 9 It is based on the product of the thickness and width S of the shrinkage cavity and porosity band according to the test example c and the product of the thickness and width S of the two-phase region to determine the schematic diagram of the reduction position. Detailed implementation manners

[0035] The following will describe the detailed implementation manners of the present disclosure with reference to the accompanying drawings. It should be understood that the detailed implementation manners described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0036] In addition, referring to "embodiment" herein means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of the present invention. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0037] Figure 1 The flowchart of the method for determining the soft reduction position of a bloom according to an embodiment of the present invention is shown. The method of the present invention will be introduced in detail below with reference to this figure.

[0038] The method for determining the soft reduction position of a bloom according to the present invention generally includes the following steps:

[0039] Step 1: When the casting is stable, take a billet of a predetermined length in the casting direction, intercept a first sample at the width center of the billet, intercept a second sample at the thickness center of the billet, and perform pretreatment on the first sample and the second sample;

[0040] Step 2: Select k positions at equal intervals along the length direction of the first sample to measure the thickness of the shrinkage cavity and porosity band of the sample, which are respectively denoted as t1, t2, t3... t k , measure the width of the shrinkage cavity and porosity band of the second sample at k positions, which are respectively denoted as w1, w2, w3,... w k ;

[0041] Step 3: Determine the shrinkage porosity width-thickness product S based on the thickness of the shrinkage porosity zone of the specimen measured in Step 2 and the width of the shrinkage porosity zone of the specimen.

[0042] Step 4: Based on the bloom continuous casting process parameters, establish a two-dimensional solidification heat transfer numerical calculation model for the bloom cross-section, determine the width W of the two-phase zone of the bloom cross-section at different casting positions during continuous casting c and the thickness T c , and calculate the width-thickness product S of the two-phase zone c ;

[0043] Step 5: Based on the shrinkage porosity width-thickness product S determined in Step 3 and the width-thickness product S of the two-phase zone determined in Step 4 c determine the positions where soft reduction needs to be applied in bloom continuous casting.

[0044] The specific operations of each step are introduced in detail below.

[0045] In Step 1, when casting is stable, a bloom of a predetermined length in the withdrawal direction is taken. A first specimen (denoted as Specimen 1) is intercepted at the width center of the bloom, and a second specimen (denoted as Specimen 2) is intercepted at the thickness center of the bloom, and the first specimen and the second specimen are pre-treated. In some embodiments, the predetermined length is 400 - 600 mm. In some embodiments, the specimen is a longitudinal section macro specimen. Optionally, the pre-treatment includes performing macro pickling on the longitudinal section macro specimen using the hot acid method, and the processing and pickling methods of the macro specimen comply with GB / T 226 - 2015. The longitudinal section macro sampling positions are as shown in the appendix Figure 2 . At the width center (i.e., at 1 / 2W), the entire specimen is intercepted with a plane parallel to the plane defined by the length L and the thickness T, that is, this cross-section includes the complete thickness T and length L dimensions. Similarly, at the thickness T center of the bloom (i.e., at 1 / 2T), the entire specimen is intercepted with a plane parallel to the plane defined by the length L and the width W, that is, this cross-section includes the complete width W and length L dimensions.

[0046] In Step 2, k positions are selected at equal intervals along the length direction L of the first specimen to measure the thickness of the shrinkage porosity zone of the specimen, denoted as t1, t2, t3... t k , and the width of the shrinkage porosity zone of the second specimen at the k positions is measured, denoted as w1, w2, w3,... w k . As shown in Figure 3 , the measurement positions of the thickness and width of the shrinkage porosity zone of the specimen are at the same length position. That is to say, the plane formed by the measured thickness t i of the shrinkage porosity zone of the specimen and the measured width w i of the shrinkage porosity zone of the specimen is a cross-section perpendicular to the length direction L. The measurement position spacing l can be 80 - 120 mm, and the number of measurement points k can be 4 - 10, and further can be 4 - 6.

[0047] In step 3, based on the thickness of the shrinkage cavity and porosity zone of the specimen at different positions in the length direction measured in step 2 and the width of the shrinkage cavity and porosity zone of the specimen at different positions in the length direction, the shrinkage cavity and porosity zone width-thickness product S is determined. Specifically, the shrinkage cavity and porosity zone width-thickness product S is calculated using the following formula (1):

[0048]

[0049] In step 4, based on the continuous casting process parameters of the billet, a two-dimensional solidification heat transfer numerical calculation model of the billet cross-section is established to determine the width W of the two-phase zone of the billet cross-section at different casting positions during continuous casting c and the thickness T c , as Figure 4 shown, and the two-phase zone width-thickness product S is calculated c . Specifically, the continuous casting process parameters of the billet may include but are not limited to the steel type, steel composition, liquidus temperature, solidus temperature, cross-sectional dimensions, drawing speed, effective height of the mold, cooling intensity of the mold, length of the secondary cooling zone, and specific water volume of the secondary cooling zone. A two-dimensional solidification heat transfer finite element model established by finite element analysis can be used. In some embodiments, the two-phase zone width-thickness product S can be calculated using the following formula (2) c :

[0050] S c =W c ·T c (2).

[0051] In step 5, based on the shrinkage cavity and porosity zone width-thickness product S determined in step 3 and the two-phase zone width-thickness product S determined in step 4 c the position where soft reduction needs to be applied for continuous casting of the billet is determined. Specifically, the casting position when S c =S can be used as the position where soft reduction needs to be applied for continuous casting of the billet.

[0052] The following is a specific test example of the method for determining the soft reduction position of the billet according to the present invention. Unless otherwise specified, the raw materials, equipment, consumables, etc. used in the following examples can be obtained through conventional commercial means.

[0053] When the casting condition is stable, a section of the casting billet with a length L = 500 mm in the casting direction is taken, and two longitudinal low-magnification specimens are intercepted at the center of the width and thickness of the casting billet specimen, and the longitudinal low-magnification specimens are pickled with hot acid. The longitudinal low-magnification sampling positions are as shown in the appendix Figure 2 , and the processing and pickling methods of the longitudinal low-magnification specimens are carried out in accordance with the national standard GB / T 226-2015. The pickled low-magnification specimens are as shown in Figure 5 .

[0054] For the macroetching specimens 1 and 2 after pickling, five positions (i = 1 - 5) were equally spaced along the length direction to measure the thickness of the shrinkage cavity and porosity zone of the pickled macroetching specimen 1 and the width of the shrinkage cavity and porosity zone of the pickled macroetching specimen 2. The measurement position interval l = 100 mm. The measurement results of the thickness and width of the shrinkage cavity and porosity zone at each position are as Figure 5 shown. The thicknesses of the shrinkage cavity and porosity zone at the five measurement points are t1 = 122 mm, t2 = 134 mm, t3 = 137 mm, t4 = 138 mm, t5 = 139 mm, and the widths are w1 = 167 mm, w2 = 178 mm, w3 = 182 mm, w4 = 175 mm, w5 = 172 mm.

[0055] Based on the thickness of the shrinkage cavity and porosity zone at five positions in the length direction of the pickled macroetching specimen 1 and the width of the shrinkage cavity and porosity zone at five positions in the length direction of the pickled macroetching specimen 2 measured, the shrinkage cavity and porosity zone width - thickness product S = 23423.2 mm was calculated and determined using the above formula (1) 2 .

[0056] Based on the continuous casting process parameters of billets, a two - dimensional solidification heat transfer numerical calculation model of the billet cross - section was established to calculate the width W c and thickness T c of the two - phase zone of the billet cross - section at different casting stream positions D, and the two - phase zone width - thickness product S at different casting stream positions was calculated using the above formula (2) c .

[0057] Among them, the continuous casting working conditions of billets are as follows:

[0058] Steel grade: GCr15;

[0059] Steel grade composition (wt%): C - 1.00, Si - 0.25, Mn - 0.30, P - 0.01, S - 0.01, Cr - 1.45;

[0060] Liquidus temperature: 1367 °C;

[0061] Solidus temperature: 1447 °C;

[0062] Cross - section size: 320 mm × 425 mm;

[0063] Casting speed: 0.62 m / min;

[0064] Effective height of the mold: 0.78 m;

[0065] Cooling intensity of the mold: 0.85 MW / m 2 ;

[0066] Length of the secondary cooling zone: 25.72 m;

[0067] Secondary cooling water ratio: 0.22 L / kg;

[0068] Establish a two-dimensional solidification heat transfer model for the cross-section of the bloom:

[0069] Taking the cross-section of the bloom as the object, use MSC.Marc finite element software to establish a two-dimensional solidification heat transfer finite element model as shown in Figure 6 Figure. The model uses quadrilateral elements to divide the mesh, with an element side length of 5 mm, and the above working condition parameters are input as the model calculation parameters.

[0070] Based on the established two-dimensional solidification heat transfer model, calculate the width W of the two-phase zone of the bloom cross-section at different casting stream positions D during continuous casting c and thickness T c , and use the above formula (2) to calculate the product S of the width and thickness of the two-phase zone c . Figure 7 W is the width of the two-phase zone at different casting stream positions D obtained by calculation c and thickness T c , Figure 8 S is the product of the width and thickness of the two-phase zone at different casting stream positions obtained by using formula (2) c .

[0071] Compare the product S = 2342.3 mm of the width and thickness of the shrinkage cavity and porosity zone determined above 2 with the product S of the width and thickness of the two-phase zone at different casting stream positions D determined c . As shown in Figure 9 Figure, when S c = S = 2342.3 mm 2 , the casting stream position D0 = 17.9 m, that is, the reduction position of the example is D0 = 17.9 m.

[0072] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0073] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0074] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for determining the soft reduction position of a bloom, characterized in that It includes the following steps: Step 1: When the casting is stable, take a billet with a predetermined length in the casting direction, intercept a first specimen at the width center of the billet, intercept a second specimen at the thickness center of the billet, and perform pretreatment on the first specimen and the second specimen; Step 2: Select k positions at equal intervals along the length direction of the first specimen to measure the thickness of the shrinkage cavity and porosity zone of the specimen, denoted as t1, t2, t3... tk respectively k , measure the width of the shrinkage cavity and porosity zone of the specimen at the k positions of the second specimen, denoted as w1, w2, w3,... wk respectively k ; Step 3: Determine the shrinkage porosity bandwidth-thickness product S based on the thickness and width of the shrinkage porosity band of the specimen measured in Step 2, where the shrinkage porosity bandwidth-thickness product S is calculated using the following formula (1): ； Step 4: Based on the bloom continuous casting process parameters, establish a two-dimensional solidification heat transfer numerical calculation model for the bloom cross-section, and determine the width W of the two-phase zone of the bloom cross-section at different casting positions during continuous casting c and the thickness T c , and calculate the product S of the width and thickness of the two-phase zone c , where the product S of the width and thickness of the two-phase zone is calculated using the following formula (2) c : ； Step 5: Based on the thick-width product S of the shrinkage and porosity zone determined in Step 3 and the thick-width product S of the two-phase zone determined in Step 4 c Determine the position where soft reduction needs to be applied for bloom continuous casting, and take the casting stream position when S c = S as the position where soft reduction needs to be applied for bloom continuous casting.

2. The method according to claim 1, wherein In Step 1, the predetermined length is 400 - 600 mm.

3. The method according to claim 1, wherein In Step 1, the specimen is a longitudinal section macrostructure specimen.

4. The method according to claim 1, characterized in that In Step 1, the pretreatment includes performing macro-etching on the longitudinal section macrostructure specimen using the hot acid method.

5. The method according to claim 1, characterized in that, In Step 2, the measurement position spacing is 80 - 120 mm.

6. The method according to claim 1, characterized in that In Step 2, k is an integer selected from 4 to 10.

7. The method according to claim 1, characterized in that In Step 4, the two-dimensional solidification heat transfer numerical calculation model for the square billet cross-section is a two-dimensional solidification heat transfer finite element model established using finite element analysis.

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