Method for controlling quality of casting blank with high residual element content

Abstract

The invention provides a method for controlling the quality of a casting blank with high residual element content, and belongs to the field of steel preparation. The method comprises the steps that a raw material structure with the large scrap steel ratio is adopted for smelting, and primary smelting molten steel with the high residual element content is obtained; refining the primary molten steel to obtain refined molten steel; according to the relation between the crack sensitive equivalent Weq and the critical crack sensitive equivalent W0eq of the refined molten steel, the secondary cooling comprehensive specific water flow of continuous casting and the surface temperature of a casting blank entering a straightening section are adjusted; and under the conditions of secondary cooling comprehensive specific water flow and the surface temperature of the casting blank entering the straightening section, the refined molten steel is subjected to continuous casting, and the casting blank is obtained. By adjusting the secondary cooling comprehensive specific water flow of continuous casting and the surface temperature of the casting blank entering the straightening section, the surface temperature of the casting blank in the straightening process is higher than the brittleness temperature range, the thermal stress and mechanical stress of the casting blank in the straightening process are reduced, and the crack sensitivity of the casting blank is effectively controlled.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to a method for controlling the quality of continuous casting billets with high residual element content. Background Art

[0002] Common residual elements in steel can be divided into three categories according to their oxidation potential. The first category of elements includes Cu, Ni, Mo, Co, As, W, Sn, Sb. Since their oxidation potential is less than that of iron, they do not participate in the oxidation reaction during the steelmaking process and ultimately almost all accumulate in steel products and are completely retained. The second category of elements includes S, P, Mn, Cr, C, H, N. Their oxidation potential is close to that of iron. During the steelmaking process, only a part of them is oxidized and removed, and the degree of removal is related to the characteristics of the elements themselves, so they will be partially retained. The third category of elements includes Pb, Zn, V, Ti, Al, Ti, Si, Mg, Ca, Nb, Zr. Their oxidation potential is greater than that of iron, and most of them will be oxidized and removed during the steelmaking process, and only a very small part remains in the steel. Therefore, controlling the residual elements in steel is actually controlling the elements contained in the first and second categories.

[0003] The long-process smelting technology based on a large scrap ratio and the electric furnace smelting process with all scrap or a high scrap ratio are the most important carbon reduction process routes for steel enterprises in China. Scrap has the characteristics of wide sources and complex compositions. After a large amount of scrap is used, the first-category residual elements such as Cu, Ni, Sn, etc. that are not easily removed will continue to accumulate, resulting in excessive content, which will inevitably affect the subsequent production process and the quality of steel. The existence of these residual elements will significantly affect the phase transformation temperature of steel grades and the precipitates at grain boundaries. Research shows that due to the low melting point of Cu (1083 °C), at high temperatures, Fe in the continuous casting billet is preferentially oxidized to FeO, and Cu will be enriched under the FeO skin and easily form a low-melting phase; or after Cu melts, its content exceeds the solubility in the molten steel and precipitates along the grain boundaries, becoming a weak link at the grain boundaries. In addition, residual elements such as Sn, Sb, As are all prone to segregate at the austenite grain boundaries to form low-melting eutectic phases, reducing the grain boundary surface energy and promoting the formation and growth of grain boundary pores; during the high-temperature oxidation process, these elements accumulate together to form a lower-melting phase under the iron oxide skin of the continuous casting billet, all of which will become the origin of surface cracks in the continuous casting billet. During the continuous casting process, if the temperature of the continuous casting billet in the straightening section is within the third brittle zone temperature of the steel grade, the risk of surface cracks due to the surface being subjected to tensile stress is very high. The existence of residual elements such as Cu, Sn, Sb, As will greatly reduce the temperature range and the minimum value of the third brittle zone of the steel grade. Therefore, while promoting the carbon reduction process route of current steel enterprises, it is particularly urgent and important to develop a continuous casting process for controlling the quality of continuous casting billets with high residual element content. Summary of the Invention

[0004] The present application provides a method for controlling the quality of a continuous casting billet with a high residual element content, so as to solve the technical problem of surface cracks in the continuous casting billet caused by a high residual element content in the steel.

[0005] An embodiment of the present application provides a method for controlling the quality of a continuous casting billet with a high residual element content, the method comprising:

[0006] Smelting with a raw material structure having a large scrap ratio to obtain an initial molten steel with a high residual element content;

[0007] Refining the initial molten steel to obtain refined molten steel;

[0008] According to the crack sensitivity equivalent W eq of the refined molten steel and the critical crack sensitivity equivalent W 0 eq therebetween, adjusting the total secondary cooling water ratio of the continuous casting and the surface temperature of the continuous casting billet when entering the straightening section; and

[0009] Under the conditions of the total secondary cooling water ratio and the surface temperature of the continuous casting billet when entering the straightening section, continuously casting the refined molten steel to obtain a continuous casting billet.

[0010] Optionally, when the crack sensitivity equivalent W eq > the critical crack sensitivity equivalent W 0 eq , the total secondary cooling water ratio is 0.15 L / kg to 0.5 L / kg, and the surface temperature of the continuous casting billet when entering the straightening section > 1000 °C.

[0011] Optionally, when the crack sensitivity equivalent W eq ≤ the critical crack sensitivity equivalent W 0 eq , the total secondary cooling water ratio is 0.6 L / kg to 1.2 L / kg, and the surface temperature of the continuous casting billet when entering the straightening section is 850 °C to 950 °C.

[0012] Optionally, the crack sensitivity equivalent W eq satisfies the following relational expression:

[0013] W eq = [Cu] + 7[Sn] + 4[Sb] + 2[As] + [Pb] + [N] + [S] - [Ni] - 0.2([Cr] + [Mo])

[0014] Wherein, [Cu] represents the mass fraction of Cu in the refined molten steel, [Sn] represents the mass fraction of Sn in the refined molten steel, [Sb] represents the mass fraction of Sb in the refined molten steel, [As] represents the mass fraction of As in the refined molten steel, [Pb] represents the mass fraction of Pb in the refined molten steel, [N] represents the mass fraction of N in the refined molten steel, [S] represents the mass fraction of S in the refined molten steel, [Ni] represents the mass fraction of Ni in the refined molten steel, [Cr] represents the mass fraction of Cr in the refined molten steel, and [Mo] represents the mass fraction of Mo in the refined molten steel.

[0015] Optionally, the critical crack sensitivity equivalent W 0 eq satisfies the following relationship:

[0016] When [C] < 0.03%, W 0 eq is 0.28;

[0017] When 0.03% ≤ [C] ≤ 0.2%, W 0 eq is 0.11;

[0018] When [C] > 0.2%, W 0 eq is 0.16;

[0019] Wherein, [C] represents the mass fraction of C in the continuous casting billet.

[0020] Optionally, the raw material structure with a large scrap ratio is all scrap or a burden structure with a scrap ratio ≥ 50%, and the types of scrap are not limited.

[0021] Optionally, the refining adopts single LF, single RH, single VD, double LF+RH or double LF+VD.

[0022] Optionally, the smelting adopts electric furnace smelting or induction furnace + converter smelting.

[0023] Optionally, the residual elements include one or more of Cu, Sn, Sb, As, Pb, Ni, Mo and Cr.

[0024] Optionally, the incidence rate of surface cracks of the continuous casting billet ≤ 0.2%.

[0025] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0026] The embodiments of the present application provide a method for controlling the quality of continuous casting billets with high residual element content. By the crack sensitivity equivalent W eq and the critical crack sensitivity equivalent W0 eq The size relationship can be used to adjust the comprehensive secondary cooling water volume of continuous casting and the surface temperature of the billet entering the straightening section, so that the surface temperature of the billet during the straightening process is higher than the brittle temperature range, reduce the thermal stress and mechanical stress of the billet during the straightening process, thereby avoiding cracking when bending and being stressed, and further effectively controlling the crack sensitivity of the billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic flowchart of a method for controlling the quality of billets with high residual element content provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0031] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0032] In addition, in the description of the specification of the present application, terms such as "include" and "comprise" mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as weight parts and mass parts represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0033] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0034] Figure 1 It is a schematic flow chart of a method for controlling the quality of a continuous casting billet with a high residual element content provided for the embodiments of the present application.

[0035] As Figure 1 shown, the present application provides a method for controlling the quality of a continuous casting billet with a high residual element content, and the method includes:

[0036] S1. Smelting with a raw material structure having a large scrap ratio to obtain an initial molten steel with a high residual element content;

[0037] In some embodiments, the residual elements include one or more of Cu, Sn, Sb, As, Pb, Ni, Mo, and Cr.

[0038] It should be noted that a high residual element content means that the content of any one residual element exceeds the control range of the residual elements required for a certain steel grade.

[0039] In some embodiments, the raw material structure with a large scrap ratio is a full scrap or a charge structure with a scrap ratio ≥ 50%, and the types of scrap are not limited.

[0040] The grade of the scrap raw material is not limited. After the electric furnace or converter smelting is completed, one or several of the residual elements Cu, Sn, Sb, As, Pb, Ni, Mo, and Cr in the molten steel will have a content exceeding the required range of the smelted steel grade.

[0041] In some embodiments, the smelting is carried out by electric furnace smelting or induction furnace + converter smelting.

[0042] In the "induction furnace → converter" process, the induction furnace is responsible for heating up or melting the scrap or other raw materials charged into the furnace (direct reduced iron, hot briquetted iron), and then pouring it into the converter for smelting into the primary molten steel.

[0043] S2. Refine the primary molten steel to obtain refined molten steel;

[0044] In some embodiments, the refining is carried out by LF single connection, RH single connection, VD single connection, LF + RH double connection, or LF + VD double connection.

[0045] The refining process is carried out for normal refining according to the requirements of the steel grade.

[0046] S3. According to the relationship between the crack sensitivity equivalent W eq and the critical crack sensitivity equivalent W 0 eq adjust the secondary cooling comprehensive water ratio of the continuous casting and the surface temperature of the billet when entering the straightening section; and

[0047] In some embodiments, the crack sensitivity equivalent W eq satisfies the following relational expression:

[0048] W eq = [Cu] + 7[Sn] + 4[Sb] + 2[As] + [Pb] + [N] + [S] - [Ni] - 0.2([Cr] + [Mo])

[0049] In the formula, [Cu] represents the mass fraction of Cu in the refined molten steel, [Sn] represents the mass fraction of Sn in the refined molten steel, [Sb] represents the mass fraction of Sb in the refined molten steel, [As] represents the mass fraction of As in the refined molten steel, [Pb] represents the mass fraction of Pb in the refined molten steel, [N] represents the mass fraction of N in the refined molten steel, [S] represents the mass fraction of S in the refined molten steel, [Ni] represents the mass fraction of Ni in the refined molten steel, [Cr] represents the mass fraction of Cr in the refined molten steel, and [Mo] represents the mass fraction of Mo in the refined molten steel.

[0050] Among them, the residual elements Cu, Sn, Sb, As, and Pb are all prone to segregate at the austenite grain boundaries, reducing the grain boundary energy, weakening the cohesion between grains, and reducing the plasticity of the slab. Moreover, the Sn element can further promote the segregation of other elements such as Cu at the grain boundaries, thus having a greater impact on Weq. In the electric furnace process, the N content in the steel is relatively high, increasing the precipitation amount of nitrides at the grain boundaries. The precipitation of sulfides in the steel at the grain boundaries will also reduce the high-temperature plasticity. Ni can increase the melting temperature of Cu and the solubility of Cu in austenite, inhibiting the cracking of the slab. Mo and Cr have the characteristic of refining the slab structure, but the effect is relatively small.

[0051] In some embodiments, the critical crack sensitivity equivalent W 0 eq satisfies the following relationship:

[0052] When [C] < 0.03%, W 0 eq is 0.28;

[0053] When 0.03% ≤ [C] ≤ 0.2%, W 0 eq is 0.11;

[0054] When [C] > 0.2%, W 0 eq is 0.16;

[0055] Among them, [C] represents the mass fraction of C in the slab.

[0056] W 0 eq is determined according to the steel grade characteristics and production experience, representing the critical value at which the molten steel does not crack under certain conditions. The carbon content of the molten steel plays a decisive role in the solidification structure and phase composition of the slab and overall affects the crack sensitivity. Therefore, the critical crack sensitivity equivalent W 0 eq is distinguished according to the carbon content of the steel grade.

[0057] In some embodiments, when the crack sensitivity equivalent Weq > the critical crack sensitivity equivalent W 0 eq When it is, the comprehensive secondary cooling water ratio is 0.15 L / kg to 0.5 L / kg, and the surface temperature of the continuous casting billet entering the straightening section > 1000 °C.

[0058] When smelting with a raw material structure of all scrap steel or a high scrap ratio, the types and contents of residual elements brought by the scrap steel are increasing day by day. On the one hand, these residual elements have a segregation phenomenon at the metal grain boundaries themselves. On the other hand, they exacerbate the segregation of easily segregated elements such as Cu to the austenite grain boundaries, and at the same time reduce the melting temperature of the composite phase, which has a great impact on the crack sensitivity of the steel grade. The larger the crack sensitivity equivalent value, the worse the high-temperature hot plasticity of the steel grade, the wider the hot brittleness zone, and at the same time the lower the low plasticity value becomes. If the continuous casting process does not respond to changes, serious surface cracks of the continuous casting billet will occur.

[0059] The crack sensitivity equivalent W eq is an index of the influence of residual elements on the crack sensitivity of the steel grade. When W eq is low, the high-temperature plasticity of the continuous casting billet is good, the control window of the continuous casting process is relatively wide, and the quality of the continuous casting billet is easy to control; when W eq is high, the high-temperature plasticity of the continuous casting billet is poor, and the continuous casting process needs to be strictly controlled.

[0060] If the W of the molten steel is calculated after refining eq > W 0 eq When it is, the brittle temperature range of the continuous casting billet becomes wider. To avoid the surface temperature of the continuous casting billet during straightening being within the brittle temperature range and cracks occurring when bending and straightening under stress, the comprehensive secondary cooling water ratio in the continuous casting process is reduced to 0.15 L / kg to 0.5 L / kg, and the surface temperature of the continuous casting billet entering the straightening section is increased > 1000 °C, which can avoid cracking of the continuous casting billet. If the water ratio is too low, the surface temperature of the continuous casting billet is too high, Fe oxidation is serious, which aggravates the enrichment of residual elements at the grain boundaries and reduces the hot plasticity, and cracks are likely to occur; if the water ratio is too high, the surface temperature of the continuous casting billet is too low, and it will be subjected to greater stress during straightening, affecting the quality of the continuous casting billet. Exemplarily, when the crack sensitivity equivalent W eq > the critical crack sensitivity equivalent W 0 eq When it is, the comprehensive secondary cooling water ratio can be 0.15 L / kg, 0.20 L / kg, 0.25 L / kg, 0.30 L / kg, 0.35 L / kg, 0.45 L / kg, 0.5 L / kg, etc., and the surface temperature of the continuous casting billet entering the straightening section can be 1005 °C, 1020 °C, 1040 °C, 1060 °C, 1080 °C, 1100 °C, 1130 °C, 1150 °C, etc.

[0061] In some embodiments, when the crack sensitivity equivalent W eq≤ the critical crack sensitivity equivalent W 0 eq When it is in this range, the comprehensive secondary cooling water ratio is 0.6 L / kg to 1.2 L / kg, and the surface temperature of the continuous casting billet entering the straightening section is 850°C to 950°C.

[0062] If the W of the molten steel is calculated after refining eq ≤W 0 eq at this time, the continuous casting of the refined molten steel can be carried out according to the existing continuous casting process.

[0063] In some embodiments, the comprehensive secondary cooling water ratio of continuous casting is the most direct parameter for controlling the cooling effect of the continuous casting billet during production, characterizing the cooling capacity of applying a unit weight of high-temperature metal, determining the temperature change history of the billet during continuous casting, and is an important process parameter in the continuous casting process. The comprehensive water ratio N 比 is closely related to the total secondary cooling water volume, steel grade, continuous casting drawing speed, and section specification. The comprehensive water ratio N 比 satisfies the following relational expression:

[0064] N 比 = Q / (V×L×H×ρ)

[0065] In the formula, N 比 represents the comprehensive water ratio, with the unit of L / kg; Q represents the total secondary cooling water volume, with the unit of L; V represents the continuous casting billet drawing speed, with the unit of m / min; L represents the width of the continuous casting billet, with the unit of mm; H represents the thickness of the continuous casting billet, with the unit of mm; ρ represents the high-temperature density of the steel grade, with the unit of kg / m 3 .

[0066] On the premise that the comprehensive secondary cooling water ratio of continuous casting is known, the water distribution for continuous casting can be carried out according to the formula of the comprehensive water ratio N 比 . Thus, this application does not add additional production processes, nor does it increase the burden on the steelmaking furnace, such as an electric furnace or a converter, for the strict and refined requirements of the furnace charge, and solves the problem of the quality of the continuous casting billet caused by high residual element content.

[0067] S4. Under the conditions of the comprehensive secondary cooling water ratio and the surface temperature of the continuous casting billet entering the straightening section, carry out continuous casting of the refined molten steel to obtain a continuous casting billet.

[0068] In some embodiments, the surface crack incidence rate of the continuous casting billet ≤ 0.2%.

[0069] This application involves two process routes: ① Electric furnace → Refining furnace → Continuous casting, ② Induction furnace → Converter → Refining furnace → Continuous casting. It includes the following steps: The electric furnace conducts all-steel scrap smelting, or the induction furnace first melts the steel scrap and then pours it into the converter for smelting. Due to the instability of the quality of the steel scrap, the content of residual elements in the molten steel after the initial smelting is much higher than the normal range required by the steel grade, and these elements cannot be removed during the subsequent refining process; the refining process is smelted normally according to the requirements of the steel grade. After the refining is completed, the composition of the molten steel is analyzed, and the crack sensitivity equivalent W eq is calculated according to the formula in this application. When W eq is greater than the critical crack sensitivity equivalent W 0 eq of this steel grade, during the continuous casting process, the comprehensive secondary cooling water ratio is reduced to 0.15 - 0.5 L / kg, and the surface temperature of the slab when it reaches the secondary cooling bending and straightening section is greater than 1000 °C, which is higher than the brittle temperature range of this steel grade, avoiding cracking of the slab when it is bent and stressed. The smelting method provided by this application can control the surface crack incidence rate of the continuous casting billet with high residual element content below 0.2%, and the quality of the billet is good. Exemplarily, the surface crack incidence rate of the billet can be 0.05%, 0.07%, 0.10%, 0.12%, 0.15%, 0.18%, 0.2%, etc.

[0070] In summary, a method for controlling the quality of continuous casting billets with high residual element content provided by the embodiments of this application has the following advantages:

[0071] (1) Raw material flexibility: This method adopts a raw material structure with a large steel scrap ratio. The types and grades of steel scrap are not restricted, which greatly reduces the raw material cost and improves the resource utilization efficiency at the same time, making the smelting process more flexible and economical.

[0072] (2) Diversified refining processes: Multiple refining methods can be adopted during the refining process, such as single-stage LF, single-stage RH, single-stage VD, and their combinations, which ensures that the requirements of different steel grades can be met and improves the adaptability and market competitiveness of the products.

[0073] (3) Precise control of crack sensitivity: By calculating the crack sensitivity equivalent W eq and comparing it with the critical crack sensitivity equivalent W 0 eq , the comprehensive secondary cooling water ratio of continuous casting and the surface temperature of the billet when it enters the straightening section can be precisely adjusted, thereby effectively controlling the crack sensitivity of the billet. This precise control method greatly improves the quality of the billet and reduces the incidence rate of surface cracks.

[0074] (4) Easy adjustment of process parameters: The comprehensive secondary cooling water ratio in continuous casting, as a key parameter for controlling the cooling effect of the casting billet, can be calculated and adjusted through formulas without adding additional production processes or having strict and refined requirements for the furnace charge. This makes the production process more flexible and efficient.

[0075] (5) Improvement of the quality of the casting billet: Since this method precisely controls the crack sensitivity and optimizes the continuous casting process parameters, the incidence of surface cracks in the casting billet can be significantly reduced, improving the overall quality of the casting billet. This is of great significance for improving the reliability and service life of the product.

[0076] (6) Reduction of production costs: By increasing the utilization rate of scrap steel and optimizing the continuous casting process, this method helps to reduce resource waste and environmental pollution, while reducing production costs. This has a positive effect on improving the economic efficiency and sustainable development ability of the enterprise.

[0077] The following will further elaborate on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0078] Example 1

[0079] Steel grade: Medium carbon steel, and the process routes adopted are: "Electric furnace - LF refining - VD refining - Continuous casting" or "Electric furnace - LF refining - Continuous casting" or "Electric furnace - LF refining - Continuous casting".

[0080] The electric furnace uses all scrap steel for smelting.

[0081] Refining uses the "LF single connection" process or the "LF - VD" double connection process to smelt the primary molten steel. The chemical composition of the refined molten steel after refining is shown in Table 1.

[0082] Table 1 Chemical composition (wt.%) of the refined molten steel in Example 1, with the balance being Fe and unavoidable impurities

[0083] Component C Si Mn P S Al Nb Ti N Content, % 0.09 0.1 1.65 0.01 0.003 0.035 0.055 0.02 0.005 Component Ni Mo Cu Sn As Sb Cr Pb Content, % 0.06 0.012 0.19 0.038 0.008 0.003 0.01 0.0014

[0084] Among them: Ni, Mo, Cu, Sn, As, Sb, Cr are all residual elements brought in by the scrap steel.

[0085] Calculated according to the composition of the molten steel after refining, the crack sensitivity equivalent W eq of this steel grade is 0.429, which is much greater than the critical crack sensitivity equivalent W 0 eq (0.11), indicating that the residual elements increase the crack sensitivity of the casting billet.

[0086] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 0.26 L / kg. The surface temperature of the billet when entering the straightening section of the continuous caster is 1109 °C, and the incidence rate of surface cracks of the billet is 0.15%. (Incidence rate of cracks = number of billets with surface cracks / total number of billets produced; Method for measuring crack defects: visible cracks observed by quality inspection personnel with the naked eye, which is also the common method in iron and steel enterprises; the same below.)

[0087] Comparative Example 1

[0088] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0089] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 0.65 L / kg. The surface temperature of the billet when entering the straightening section of the continuous caster is 920 °C, and the incidence rate of surface cracks of the billet is 3.5%.

[0090] Example 2:

[0091] Steel grade: ultra-low carbon steel. The process route adopted is: "induction furnace - converter - LF refining - RH refining - continuous casting" or "induction furnace - converter - RH refining - continuous casting".

[0092] Smelting is carried out with a scrap ratio of 80%. First, the scrap is melted in the induction furnace and then poured into the converter to smelt the primary molten steel.

[0093] Refining is carried out on the primary molten steel by using the "LF - RH" double - refining process or "RH refining". The chemical composition of the refined molten steel after refining is shown in Table 2.

[0094] Table 2 Chemical composition (wt.%) of the refined molten steel in Example 2, with the balance being Fe and unavoidable impurities

[0095] Component C Si Mn P S Al Nb Ti N Content, % 0.0015 1.0 0.25 0.006 0.002 0.25 - - 0.003 Component Ni Mo Cu Sn As Sb Cr Pb Content, % 0.03 0.013 0.17 0.033 0.007 0.002 0.01 0.0011

[0096] Among them: Ni, Mo, Cu, Sn, As, Sb, Cr are all residual elements brought in by the scrap.

[0097] Calculated that the W of the composition of the molten steel after refining eq is 0.3965, which is greater than the W of this steel grade 0 eq (0.28), indicating that the residual elements increase the crack sensitivity of the billet.

[0098] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 0.49 L / kg. The surface temperature of the billet when entering the straightening section of the continuous caster is 1073 °C, and the incidence rate of surface cracks of the billet is 0.2%.

[0099] Comparative Example 2

[0100] On the basis of what is disclosed in Example 2, this comparative example is modified as follows:

[0101] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 1.0 L / kg. The surface temperature of the slab when entering the straightening section of the continuous caster is 868 °C, and the incidence rate of surface cracks of the slab is 1.6%.

[0102] Example 3

[0103] Steel grade: high carbon steel. The process routes adopted are: "electric furnace - LF refining - VD refining - continuous casting", "induction furnace - converter - LF refining - RH refining - continuous casting" or "induction furnace - converter - LF refining - continuous casting".

[0104] All use all scrap steel for smelting.

[0105] Refining uses the "LF - VD double - process", "LF - RH double - process" or "LF single - process" to smelt and process the primary molten steel. The chemical composition of the refined molten steel after refining is shown in Table 3.

[0106] Table 3 Chemical composition (wt.%) of the refined molten steel in Example 3, the balance is Fe and unavoidable impurities

[0107] Component C Si Mn P S Al Nb Ti N Content, % 0.42 0.27 0.66 0.017 0.006 0.025 - - 0.004 Component Ni Mo Cu Sn As Sb Cr Pb Content, % 0.15 0.012 0.21 0.041 0.007 0.002 0.01 0.0011

[0108] Among them: Ni, Mo, Cu, Sn, As, Sb, Cr are all residual elements brought in by scrap steel.

[0109] Calculated according to the composition of the molten steel after refining, the crack sensitivity equivalent W of this steel grade eq is 0.3757, which is greater than the critical crack sensitivity equivalent W 0 eq (0.16), indicating that the residual elements increase the crack sensitivity of the slab.

[0110] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 0.34 L / kg. The surface temperature of the slab when entering the straightening section of the continuous caster is 1111 °C, and the incidence rate of surface cracks of the slab is 0.12%.

[0111] Comparative Example 3

[0112] On the basis of what is disclosed in Example 3, this comparative example is modified as follows:

[0113] The refined molten steel is subjected to continuous casting. The comprehensive secondary cooling water ratio for continuous casting is 0.7 L / kg. The surface temperature of the slab when entering the straightening section of the continuous caster is 906 °C, and the incidence rate of surface cracks of the slab is 1.3%.

[0114] In addition, one or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0115] In the embodiment of the present application, the incidence rate of surface cracks of the continuous casting billet is controlled below 0.2%, and the quality of the continuous casting billet is good.

[0116] In the embodiment of the present application, the influence equivalent W of various composite residual elements in steel on the crack sensitivity of the continuous casting billet is developed. eq Calculation formula: W eq = [Cu] + 7[Sn] + 4[Sb] + 2[As] + [Pb] + [N] + [S] - [Ni] - 0.2([Cr] + [Mo]), and the sensitivity threshold of W for different steel grades is proposed. eq And the corresponding secondary cooling control process is developed according to W. eq The present application quantitatively studies for the first time the influence of residual elements in steel grades on the surface quality of continuous casting billets and develops corresponding innovative control strategies.

[0117] The above are only specific embodiments of the present application, which enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for controlling the quality of a casting with a high residual element content, the method comprising: The raw material structure with a large scrap ratio is used for smelting to obtain a primary molten steel with a high residual element content; Refining the primary molten steel to obtain refined molten steel; According to the crack sensitivity equivalent W of the refined steel liquid eq and critical crack sensitivity equivalent W 0 eq The relationship between the two cooling water ratios of the continuous casting and the surface temperature of the slab entering the straightening section are adjusted; as well as Under the conditions of the comprehensive water ratio of the secondary cooling and the surface temperature of the ingot entering the straightening section, the refined molten steel is continuously cast to obtain the ingot.

2. The method according to claim 1, characterized in that: When the crack sensitivity equivalent W eq >The critical crack sensitivity equivalent W 0 eq When the secondary cooling comprehensive water volume is 0.15L / kg to 0.5L / kg, the surface temperature of the ingot entering the straightening section is greater than 1000°C.

3. The method according to claim 1, characterized in that: When the crack sensitivity equivalent W eq ≤ the critical crack sensitivity equivalent W 0 eq When the secondary cooling comprehensive water volume is 0.6L / kg~1.2L / kg, the surface temperature of the ingot entering the straightening section is 850℃~950℃.

4. The method according to claim 2 or 3, characterized in that: The crack sensitivity equivalent W eq Satisfies the following relationship: W eq =[Cu]+7[Sn]+4[Sb]+2[As]+[Pb]+[N]+[S]-[Ni]-0.2([Cr]+[Mo]) In the formula, [Cu] represents the mass fraction of Cu in the refined steel liquid, [Sn] represents the mass fraction of Sn in the refined steel liquid, [Sb] represents the mass fraction of Sb in the refined steel liquid, [As] represents the mass fraction of As in the refined steel liquid, [Pb] represents the mass fraction of Pb in the refined steel liquid, [N] represents the mass fraction of N in the refined steel liquid, [S] represents the mass fraction of S in the refined steel liquid, [Ni] represents the mass fraction of Ni in the refined steel liquid, [Cr] represents the mass fraction of Cr in the refined steel liquid, and [Mo] represents the mass fraction of Mo in the refined steel liquid.

5. The method according to claim 2 or 3, characterized in that: The critical crack sensitivity equivalent W 0 eq Satisfies the following relationship: When [C]<0.03%, W 0 eq is 0.28; When 0.03%≤[C]≤0.2%, W 0 eq is 0.11; When [C]>0.2%, W 0 eq is 0.16; Wherein, [C] represents the mass fraction of C in the ingot.

6. The method according to claim 1, characterized in that The raw material structure with a large scrap steel ratio is a charge structure of all scrap steel or a scrap steel ratio ≥ 50%, and the type of scrap steel is not limited.

7. The method according to claim 1, characterized in that The refining adopts LF single refining, RH single refining, VD single refining, LF+RH double refining or LF+VD double refining.

8. The method according to claim 1, characterized in that: The smelting adopts electric furnace smelting or induction furnace + converter smelting.

9. The method according to claim 1, characterized in that: The residual elements include one or more of Cu, Sn, Sb, As, Pb, Ni, Mo and Cr.

10. The method according to claim 1, characterized in that The occurrence rate of cracks on the surface of the casting is ≤0.2%.

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