Continuous casting production method for reducing center defects of small square billets made of 165 mm plain carbon steel

Abstract

The invention discloses a continuous casting production method for reducing center defects of a small square billet made of 165 mm plain carbon steel, and relates to the technical field of continuous casting of ferrous metallurgy. The continuous casting production method specifically comprises the steps that molten steel is injected into a crystallizer for pouring, meanwhile, continuous casting covering slag is added to the surface of the molten steel in the crystallizer, and a casting blank with an initial blank shell is obtained through cooling of the crystallizer; in the secondary cooling area, a subarea all-water cooling mode is adopted, and a dynamic calculation model is constructed according to the relation of the pulling speed of each cooling area, the superheat degree of molten steel and the water amount of each cooling area; carrying out secondary cooling on the casting blank with the primary blank shell by adopting the constructed relationship among the pulling speed of each cooling area, the superheat degree of molten steel and the water quantity of each cooling area, and then carrying out withdrawal and straightening to obtain a small square billet of the plain carbon steel of 165 mm; the invention discloses a continuous casting production method for performing integrated synergistic effect on the superheat degree, the pulling speed and a secondary cooling area so as to realize accurate control on the solidification process, reduce the center defect of a casting blank and stably produce a high-quality small square blank.

Description

Technical Field

[0001] This invention relates to a continuous casting production method for reducing center defects in 165mm plain carbon steel billets, belonging to the field of continuous casting technology in iron and steel metallurgy. Background Technology

[0002] In the continuous casting production of 165mm×165mm cross-section small square billets of ordinary carbon steel, the low-magnification quality of the billet (such as central porosity, shrinkage cavities, and central segregation) is a key indicator for measuring its internal quality. The superheat of molten steel, continuous casting speed, and secondary cooling are three core process parameters that determine the solidification process and the final microstructure, and these three are coupled with each other and have a significant impact.

[0003] Currently, most manufacturing enterprises have the following systemic flaws when controlling these three key parameters: (1) Static control of secondary cooling zone: The static model with a single correlation between "casting speed and water volume" is generally adopted, which cannot dynamically respond to casting speed fluctuations, resulting in billet reheating or overcooling, causing thermal stress cracks and disrupting the solidification end morphology.

[0004] (2) Imbalance between casting speed and thermodynamics: Casting speed is often set with the pursuit of output as the guide, without effective coordination with the thermodynamic balance of the casting machine; when high casting speed is matched with high superheat, the depth of the liquid phase cavity is extended. If the secondary cooling zone system remains unchanged, it will lead to poor feeding at the end of solidification and deterioration of the center quality.

[0005] (3) Isolation of superheat control: Superheat is usually controlled as an independent variable within a range (e.g., 20~30℃) without coordination with pulling speed and secondary cooling zone. High superheat promotes columnar crystal growth, but if the secondary cooling zone is not adjusted in conjunction, it will aggravate central defects.

[0006] (4) Lack of multi-parameter collaborative model: The relevant technology lacks an adaptive dynamic secondary cooling zone model that can simultaneously respond to changes in pulling speed and superheat, and cannot achieve intelligent matching and optimization decision-making of parameters.

[0007] Therefore, there is an urgent need in this field for a continuous casting production method that can integrate superheat, casting speed and secondary cooling zone to achieve precise control of the solidification process, reduce central defects such as central cracks, central shrinkage cavities and central segregation in the billet, and stably produce high-quality small billets. Summary of the Invention

[0008] To address the shortcomings of related technologies, this invention provides a continuous casting production method for reducing center defects in 165mm plain carbon steel billets. By constructing a dynamic cooling model with coordinated response of casting speed, superheat, and water volume, the method achieves real-time, adaptive, and precise matching of secondary cooling intensity to production conditions. This significantly stabilizes the solidification process of the billet, fundamentally improves the quality of the microstructure under low magnification, and solves the problems of unstable solidification paths and severe central porosity and segregation in the billet caused by the isolated and static control of casting speed, superheat, and secondary cooling water volume in the continuous casting production of 165mm small billets.

[0009] The purpose of this invention is to provide a continuous casting production method for reducing center defects in 165mm plain carbon steel billets, specifically including the following steps: (1) The molten steel is poured into the crystallizer for casting, and at the same time, continuous casting protective slag is added to the surface of the molten steel in the crystallizer. The molten steel is cooled by the crystallizer to obtain a billet with a primary billet shell.

[0010] (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. A dynamic calculation model is constructed based on the relationship between the drawing speed (V), the superheat of molten steel (ΔT), and the water volume (Q) of each cooling zone, as follows: Water volume in Zone 1: Q1 = S × (-0.44V) 2 +9.12V-2.66), and Q1≥8.8m 3 / h; Water volume in Zone 2: Q2 = S × (0.55V) 2 +7.64V-2.20), and Q2≥9.5m 3 / h; Water volume in Zone 3: Q3 = S × (0.92V) 2 +2.01V-0.38), and Q3≥6.2m 3 / h; Water volume in Zone 4: Q4 = S × (0.48V) 2 +0.58V-0.03), and Q4≥1.7m 3 / h; The superheat coefficient S is determined based on the real-time ΔT. Specifically, when ΔT > 30℃, S = 1.1; when ΔT < 20℃, S = 0.9; and when 20℃ ≤ ΔT ≤ 30℃, S = 1.0. The unit of casting speed is m / min, the unit of steel superheat is ℃, and the unit of water volume in each cooling zone is m³ / min. 3 / h.

[0011] (3) Using the relationship between the drawing speed, molten steel superheat and water volume of each cooling zone constructed in step (2), the billet with the initial shell is subjected to secondary cooling, and then drawn straightened to obtain a 165mm plain carbon steel square billet.

[0012] Preferably, the molten steel in step (1) is ordinary carbon steel, and the composition of the molten steel by mass percentage includes C≤0.025%, Si≤0.035%, Mn≤0.070%, P≤0.045%, S≤0.045%, with the balance being Fe and unavoidable impurities.

[0013] Preferably, in step (1), the pouring is done using an immersion nozzle with an insertion depth of 100~120mm.

[0014] Preferably, in step (1), the thickness of the slag layer in the continuous casting protective slag liquid is 8~13mm, the slag consumption is 0.3~0.4kg / t, and the composition of the continuous casting protective slag, by mass percentage, includes: 22~35% SiO2, 20~33% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the basicity of the continuous casting protective slag is 1.0±0.15; the content of fixed C in the continuous casting protective slag, by mass percentage, is 7~16%, the content of F, by mass percentage, is ≤4%; the moisture content of the continuous casting protective slag, by mass percentage, is ≤0.50%, the melting point is 1160±50℃, and the bulk density is 0.50~1.1g / cm³. 3 Melting rate ≤60s / 1350℃, viscosity 0.20~0.85Pa·s / 1300℃, and particle size of 0.15~1mm accounting for ≥95% by mass percentage.

[0015] Preferably, the cooling conditions for the crystallizer in step (1) are: the water volume in the crystallizer is 120~130m³. 3 The crystallizer is cooled by water flow at a pressure of 1.2~1.6MPa and a temperature difference of 6~9℃.

[0016] Preferably, the nozzle configurations for each cooling zone in step (2) are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles; Zone 2: 10 rows × 4 nozzles = 40 nozzles; Zone 3: 8 rows × 4 nozzles = 32 nozzles; Zone 4: 6 rows × 4 nozzles = 24 nozzles.

[0017] More preferably, in step (2), the nozzle model of zone one is 3 / 8PZ11167QZ5, the upper 5 rows of the nozzle model of zone two is 3 / 8PZ11067QZ5, the lower 5 rows of the nozzle model is 1 / 4PZ7065QZ5, the nozzle model of zone three is 1 / 4PZ4865QZ5, and the nozzle model of zone four is 1 / 4PZ4865QZ5.

[0018] Preferably, the drawing speed in step (2) is 2.0~2.7m / min; and the superheat of the molten steel is 15~40℃.

[0019] Preferably, the cooling water pressure for the secondary cooling in step (3) is 1.2~1.5MPa.

[0020] Preferably, the conditions for the straightening in step (3) are: hot billet pressure 2.5~4.0MPa, the gap between the rollers after pressing is 140±5mm, and the straightening temperature is 1050±30℃.

[0021] Mechanism of the invention: The key to suppressing center defects in this invention lies in setting a macroscopic solidification path by adjusting the casting speed and superheat, then using dynamically optimized secondary cooling to control the temperature and stress fields along this path, and finally completing the feeding process at the solidification end through precise mechanical pressing. The process flow diagram is shown below. Figure 1 As shown in the figure. The number and type of nozzles configured in this invention, combined with changes in casting speed and superheat, can calculate the secondary cooling flow rate in real time, thereby jointly controlling the solidification process, temperature distribution, and stress state of the cast billet. This creates a favorable solidification environment for the target steel grade and working conditions. A physical image of the small carbon steel billet obtained from continuous casting is shown in the figure. Figure 2 As shown, the specific mechanism of this invention is as follows: (1) Synergistic suppression of internal cracks: Internal cracks are mainly caused by thermal or mechanical stress at the solidification front. This invention controls the cooling curve of the secondary cooling zone and the surface temperature of the billet by the synergistic effect of the casting speed and the over-coupling of molten steel. The cooling curve of this invention achieves the combination of "high casting speed" and "optimized secondary cooling", as well as the synergy of "superheat" and "optimized secondary cooling".

[0022] (2) Synergistic improvement of central shrinkage cavity and porosity: central shrinkage cavity and porosity are caused by insufficient feeding at the end of solidification. This invention maintains an efficient feeding channel through the synergistic effect of coupling the casting speed and the superheat of the molten steel, and implements pressing down in a timely manner. The water distribution data of each zone calculated by this invention can ensure the strength of the billet shell in the early stage of secondary cooling, and slow down the cooling, extend the feeding time, and homogenize the stress in the later stage, thereby reducing central porosity and shrinkage cavity.

[0023] The beneficial effects of this invention are: (1) Synergistic response to superheat: This invention introduces a superheat coefficient S, which quantifies the influence of molten steel superheat ΔT on solidification structure (columnar / equiaxed crystal ratio) into an adjustment command for secondary cooling strength. Its design follows the following metallurgical principles: When ΔT>30℃ (high superheat), S=1.1, appropriately increasing the secondary cooling strength to suppress excessive growth of columnar crystals and promote the formation of equiaxed crystals, thereby reducing center segregation and porosity; when ΔT<20℃ (low superheat), S=0.9, appropriately reducing the secondary cooling strength to avoid overcooling of the billet surface, mitigate the temperature gradient at the solidification front, and optimize feeding conditions; when 20℃≤ΔT≤30℃, S=1.0.

[0024] (2) Significant improvement in quality at low magnification: This invention effectively suppresses the excessive growth of columnar crystals by synergistically coupling the pulling speed and the superheat of molten steel in real time and dynamically. It achieves the secondary cooling in the early stage to ensure the strength of the billet shell, and the heat preservation in the later stage slows down the cooling, prolongs the feeding time, and homogenizes the stress, thereby reducing the central porosity and shrinkage cavities.

[0025] (3) Achieving synergy and fault tolerance: Through the formula Q=S×f(V), the model converts the coupling effect of casting speed (kinetics) and superheat (thermodynamics) into the optimal water volume setting of the four cooling zones in real time and automatically, and ensures process safety through minimum water volume limit; This enables the system to automatically optimize and stabilize the solidification path and end morphology of the billet within a wide range of superheat (15~40℃) and casting speed (2.0~2.7m / min). Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention.

[0027] Figure 2 This is a photograph of a small carbon steel billet produced by continuous casting according to the present invention. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments and comparative examples of this invention are commercially available analytical grade. The continuous casting equipment for producing small square billets in this invention embodiment is a 165mm×165mm cross-section 7-machine 7-strand 9m arc small square billet continuous casting machine; in the zoned full water cooling mode, a four-zone full water cooling system is adopted, with a horizontal tolerance of ±2mm / m for the support rollers in the secondary cooling zone, a tolerance of ±2mm for the arc alignment in the secondary cooling zone, and a tolerance of ±2mm for the arc alignment of the spray pipes; the wear of both the upper and lower straightening rollers during the straightening process is <4mm.

[0029] Example 1 A continuous casting production method for reducing center defects in 165mm plain carbon steel billets specifically includes the following steps: (1) Molten carbon Q235 steel is poured into the crystallizer for casting. The casting uses an immersion nozzle with an insertion depth of 110 mm. At the same time, a continuous casting protective slag with an alkalinity of 1.13 is added to the surface of the molten steel in the crystallizer. (The composition of the continuous casting protective slag by mass percentage includes: 22% SiO2, 33% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the fixed C content in the continuous casting protective slag by mass percentage is 15.24%, the F content by mass percentage is ≤4%, the moisture content by mass percentage is ≤0.50%, the melting point is 1160±50℃, and the bulk density is 0.74 g / cm³.) 3Melting rate ≤ 60s / 1350℃, viscosity 0.467Pa·s / 1300℃, particle size 0.15~1mm (≥95% by mass percentage), forming a 10mm thick liquid slag layer, slag consumption 0.35kg / t, passing through a crystallizer with a water flow of 120m³. 3 Under the conditions of / h and cooling water pressure of 1.4MPa, a casting with a primary shell is obtained by cooling, and the temperature difference of the crystallizer water is 7~8℃; (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. The nozzle configurations for each cooling zone are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles (model 3 / 8PZ11167QZ5), Zone 2: 10 rows × 4 nozzles = 40 nozzles (the upper 5 rows are model 3 / 8PZ11067QZ5, and the lower 5 rows are model 1 / 4PZ7065QZ5), Zone 3: 8 rows × 4 nozzles = 32 nozzles (model 1 / 4PZ4865QZ5), Zone 4: 6 rows × 4 nozzles = 24 nozzles (model 1 / 4PZ4865QZ5). At a drawing speed of 2.6 m / min (high drawing speed) and a steel superheat (ΔT) of 35℃ (high superheat scenario), since ΔT = 35℃ > 30℃, S = 1.1 is taken, and a dynamic calculation model is constructed as follows: Water volume in Zone 1: Q1 = 1.1 × (-0.44 × 2.6) 2 +9.12×2.6-2.66)=19.89m 3 / h>8.8m 3 / h; Water volume in Zone 2: Q2 = 1.1 × (0.55 × 2.6) 2 +7.64×2.6-2.20)=23.52m 3 / h>9.5m 3 / h; Water volume in the third zone: Q3=1.1×(0.92×2.6 2 +2.01×2.6-0.38)=12.17m 3 / h>6.2m 3 / h; Water volume in Zone 4: Q4 = 1.1 × (0.48 × 2.6) 2 +0.58×2.6-0.03)=5.19m 3 / h>1.7m 3 / h; The unit for casting speed is m / min, the unit for steel superheat is °C, and the unit for water volume in each cooling zone is m³ / min. 3 / h; (3) Using the relationship between the drawing speed, superheat of molten steel and water volume of each cooling zone constructed in step (2), the billet with the initial shell is subjected to secondary cooling. The cooling water pressure of the secondary cooling is 1.2 MPa, the roller spacing after pressing is 140±5 mm, the straightening temperature is 1050±30℃, and the straightening pressure is 3 MPa, to obtain a 165 mm plain carbon steel square billet.

[0030] This embodiment achieves the production of 165mm plain carbon steel billets with qualified microstructure (compliant with Table 1) under high superheat and high casting speed conditions through the synergistic effect of real-time and dynamic coupling between casting speed and molten steel superheat.

[0031] Example 2 A continuous casting production method for reducing center defects in 165mm plain carbon steel billets specifically includes the following steps: (1) Molten carbon Q195 steel is poured into the crystallizer for casting. The casting uses an immersion nozzle with an insertion depth of 110 mm. At the same time, a continuous casting protective slag with an alkalinity of 1.15 is added to the surface of the molten steel in the crystallizer. (The composition of the continuous casting protective slag by mass percentage includes: 32.86% SiO2, 26.48% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the fixed C content in the continuous casting protective slag by mass percentage is 15.35%, the F content by mass percentage is ≤4%, the moisture content by mass percentage is ≤0.50%, the melting point is 1160±50℃, and the bulk density is 0.80 g / cm³.) 3 Melting rate ≤ 60s / 1350℃, viscosity 0.791Pa·s / 1300℃, particle size 0.15~1mm (≥95% by mass percentage), forming a 10mm thick liquid slag layer, slag consumption 0.35kg / t, through a crystallizer with a water flow of 130m³ 3 Under the conditions of / h and cooling water pressure of 1.4MPa, a casting with a primary shell is obtained by cooling, and the temperature difference of the crystallizer water is 6~8℃; (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. The nozzle configurations for each cooling zone are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles (model 3 / 8PZ11167QZ5), Zone 2: 10 rows × 4 nozzles = 40 nozzles (the upper 5 rows are model 3 / 8PZ11067QZ5, and the lower 5 rows are model 1 / 4PZ7065QZ5), Zone 3: 8 rows × 4 nozzles = 32 nozzles (model 1 / 4PZ4865QZ5), Zone 4: 6 rows × 4 nozzles = 24 nozzles (model 1 / 4PZ4865QZ5). At a drawing speed of 2.2 m / min and a steel superheat (ΔT) of 18℃ (low superheat scenario), since ΔT = 18℃ < 20℃, S = 0.9 is taken, and a dynamic calculation model is constructed as follows: Water volume in Zone 1: Q1 = 0.9 × (-0.44 × 2.2)2 +9.12×2.2-2.66)=13.75m 3 / h>8.8m 3 / h; Water volume in Zone 2: Q2 = 0.9 × (0.55 × 2.2) 2 +7.64×2.2-2.20)=15.54m 3 / h>9.5m 3 / h; Water volume in the third zone: Q3=0.9×(0.92×2.2 2 +2.01×2.2-0.38)=7.65m 3 / h>6.2m 3 / h; Water volume in Zone 4: Q4 = 0.9 × (0.48 × 2.2) 2 +0.58×2.2-0.03)=3.21m 3 / h>1.7m 3 / h; The unit for casting speed is m / min, the unit for steel superheat is °C, and the unit for water volume in each cooling zone is m³ / min. 3 / h; (3) Using the relationship between the drawing speed, superheat of molten steel and water volume of each cooling zone constructed in step (2), the billet with the initial billet shell is subjected to secondary cooling. The cooling water pressure of the secondary cooling is 1.2 MPa, the roller spacing after pressing is 140±5 mm, the straightening temperature is 1050±30℃, and the hot billet pressure is 4 MPa, to obtain a 165 mm plain carbon steel square billet.

[0032] This embodiment achieves the production of 165mm plain carbon steel billets with qualified microstructure (compliant with Table 1) under low superheat conditions by synergistically coupling the casting speed with the real-time dynamic superheat of the molten steel. This avoids undercooling of the billet and ensures stable quality under low superheat conditions.

[0033] Example 3 A continuous casting production method for reducing center defects in 165mm plain carbon steel billets specifically includes the following steps: (1) Molten carbon Q195 steel is poured into the crystallizer for casting. The casting uses an immersion nozzle with an insertion depth of 100 mm. At the same time, a continuous casting protective slag with an alkalinity of 1 is added to the surface of the molten steel in the crystallizer. (The composition of the continuous casting protective slag, by mass percentage, includes: 30.15% SiO2, 26.33% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the fixed C content in the continuous casting protective slag is 7% by mass percentage, the F content is ≤4% by mass percentage, the moisture content of the continuous casting protective slag is ≤0.50% by mass percentage, the melting point is 1160±50℃, and the bulk density is 0.5 g / cm³.) 3 Melting rate ≤ 60s / 1350℃, viscosity 0.85Pa·s / 1300℃, particle size 0.15~1mm (≥95% by mass percentage), forming a 13mm thick liquid slag layer, slag consumption 0.3kg / t, through a crystallizer with a water flow of 120m³ 3 Under the conditions of / h and cooling water pressure of 1.2MPa, a casting with a primary shell is obtained by cooling, and the temperature difference of the crystallizer water is 8~9℃; (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. The nozzle configurations for each cooling zone are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles (model 3 / 8PZ11167QZ5), Zone 2: 10 rows × 4 nozzles = 40 nozzles (the upper 5 rows are model 3 / 8PZ11067QZ5, and the lower 5 rows are model 1 / 4PZ7065QZ5), Zone 3: 8 rows × 4 nozzles = 32 nozzles (model 1 / 4PZ4865QZ5), Zone 4: 6 rows × 4 nozzles = 24 nozzles (model 1 / 4PZ4865QZ5). At a drawing speed of 2.0 m / min and a steel superheat (ΔT) of 15℃ (low superheat scenario), since ΔT = 15℃ < 20℃, S = 0.9 is taken, and a dynamic calculation model is constructed as follows: Water volume in Zone 1: Q1 = 0.9 × (-0.44 × 2.0) 2 +9.12×2.0-2.66)=12.44m 3 / h>8.8m 3 / h; Water volume in Zone 2: Q2 = 0.9 × (0.55 × 2.0) 2 +7.64×2.0-2.20)=13.75m 3 / h>9.5m 3 / h; Water volume in the third zone: Q3=0.9×(0.92×2.0 2 +2.01×2.0-0.38)=6.59m 3 / h>6.2m 3 / h; Water volume in Zone 4: Q4 = 0.9 × (0.48 × 2.0)2 +0.58×2.0-0.03)=2.75m 3 / h>1.7m 3 / h; The unit for casting speed is m / min, the unit for steel superheat is °C, and the unit for water volume in each cooling zone is m³ / min. 3 / h; (3) Using the relationship between the drawing speed, superheat of molten steel and water volume of each cooling zone constructed in step (2), the billet with the initial shell is subjected to secondary cooling. The cooling water pressure of the secondary cooling is 1.3MPa, the roller spacing after pressing is 140±5mm, the straightening temperature is 1050±30℃, and the hot billet pressure is 2.5MPa, to obtain a 165mm plain carbon steel square billet.

[0034] This embodiment achieves the production of 165mm plain carbon steel billets with qualified microstructure (compliant with Table 1) under low superheat conditions by synergistically coupling the casting speed with the real-time dynamic superheat of the molten steel. This avoids undercooling of the billet and ensures stable quality under low superheat conditions.

[0035] Example 4 A continuous casting production method for reducing center defects in 165mm plain carbon steel billets specifically includes the following steps: (1) Molten carbon Q195 steel is poured into the crystallizer for casting. The casting uses an immersion nozzle with an insertion depth of 120 mm. At the same time, a continuous casting protective slag with an alkalinity of 0.85 is added to the surface of the molten steel in the crystallizer. (The composition of the continuous casting protective slag by mass percentage includes: 35% SiO2, 20% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the fixed C content in the continuous casting protective slag by mass percentage is 16%, the F content by mass percentage is ≤4%, the moisture content by mass percentage is ≤0.50%, the melting point is 1160±50℃, and the bulk density is 1.1 g / cm³.) 3 Melting rate ≤ 60s / 1350℃, viscosity 0.20Pa·s / 1300℃, particle size 0.15~1mm (≥95% by mass percentage), forming an 8mm thick liquid slag layer, slag consumption 0.4kg / t, through a crystallizer with a water flow of 125m 3 Under the conditions of / h and cooling water pressure of 1.6MPa, a casting with a primary shell is obtained by cooling, and the temperature difference of the crystallizer water is 6~7℃; (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. The nozzle configurations for each cooling zone are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles (model 3 / 8PZ11167QZ5), Zone 2: 10 rows × 4 nozzles = 40 nozzles (the upper 5 rows are model 3 / 8PZ11067QZ5, and the lower 5 rows are model 1 / 4PZ7065QZ5), Zone 3: 8 rows × 4 nozzles = 32 nozzles (model 1 / 4PZ4865QZ5), Zone 4: 6 rows × 4 nozzles = 24 nozzles (model 1 / 4PZ4865QZ5). At a drawing speed of 2.7 m / min and a steel superheat (ΔT) of 40℃ (high superheat scenario), since ΔT = 40℃ > 30℃, S = 1.1 is taken, and a dynamic calculation model is constructed as follows: Water volume in Zone 1: Q1 = 1.1 × (-0.44 × 2.7) 2 +9.12×2.7-2.66)=20.63m 3 / h>8.8m 3 / h; Water volume in Zone 2: Q2 = 1.1 × (0.55 × 2.7) 2 +7.64×2.7-2.20)=24.68m 3 / h>9.5m 3 / h; Water volume in the third zone: Q3=1.1×(0.92×2.7 2 +2.01×2.7-0.38)=12.93m 3 / h>6.2m 3 / h; Water volume in Zone 4: Q4 = 1.1 × (0.48 × 2.7) 2 +0.58×2.7-0.03)=5.54m 3 / h>1.7m 3 / h; The unit for casting speed is m / min, the unit for steel superheat is °C, and the unit for water volume in each cooling zone is m³ / min. 3 / h; (3) Using the relationship between the drawing speed, molten steel superheat and water volume of each cooling zone constructed in step (2), the billet with the initial billet shell is subjected to secondary cooling. The cooling water pressure of the secondary cooling is 1.5MPa, the roller spacing after pressing is 140±5mm, the straightening temperature is 1050±30℃, and the hot billet pressure is 4MPa, to obtain a 165mm plain carbon steel square billet.

[0036] This embodiment achieves the production of 165mm plain carbon steel billets with qualified microstructure (compliant with Table 1) under low superheat conditions by synergistically coupling the casting speed with the real-time dynamic superheat of the molten steel. This avoids undercooling of the billet and ensures stable quality under low superheat conditions.

[0037] Table 1 Comparative Example 1 A method for producing 165mm plain carbon steel billets using the original static water distribution model through continuous casting specifically includes the following steps: (1) Molten carbon Q195 steel is poured into the crystallizer for casting. The casting uses an immersion nozzle with an insertion depth of 120 mm. At the same time, a continuous casting protective slag with an alkalinity of 0.85 is added to the surface of the molten steel in the crystallizer. (The composition of the continuous casting protective slag, by mass percentage, includes: 34.86% SiO2, 28.48% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the fixed C content in the continuous casting protective slag is 16% by mass percentage, the F content is ≤4% by mass percentage, the moisture content of the continuous casting protective slag is ≤0.50% by mass percentage, the melting point is 1160±50℃, and the bulk density is 0.5 g / cm³.) 3 Melting rate ≤60s / 1350℃, viscosity 0.20Pa·s / 1300℃, particle size 0.15~1mm (≥95% by mass percentage), crystallized in a crystallizer with a water flow of 140m³. 3 Under the conditions of / h and cooling water pressure of 1.2MPa, a casting with a primary shell is obtained by cooling, and the temperature difference of the crystallizer water is 5~6℃; (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. The nozzle configurations for each cooling zone are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles (model 3 / 8PZ11167QZ5), Zone 2: 11 rows × 4 nozzles = 40 nozzles (the upper 5 rows are model 3 / 8PZ7065QZ5, and the lower 6 rows are model 1 / 4PZ4865QZ5), Zone 3: 8 rows × 4 nozzles = 32 nozzles (model 1 / 4PZ4865QZ5), Zone 4: 6 rows × 4 nozzles = 24 nozzles (model 1 / 4PZ4865QZ5). A static water distribution model is used, and the water distribution parameters are shown in Table 2. Table 2 The water distribution model uses a fixed distribution ratio and a fixed specific water volume method for water distribution; that is, the specific water volume remains unchanged, and the specific water volume is set manually according to the pulling speed V≤2.2m / min to 1.2 and V≥2.3m / min to 1.4; the water volume ratio of each zone is fixed at 30:36:26:8.

[0038] (4) The relationship between the casting speed and the water volume of each cooling zone constructed in step (2) is used to perform secondary cooling on the billet with the initial shell. The cooling water pressure of the secondary cooling is 1.2MPa, and the roller spacing after pressing is 140±5mm, resulting in a 165mm plain carbon steel square billet. The cooling water volume of the water distribution method in this comparative example is only related to the casting speed, ignoring other variables. The fixed cooling logic adopted cannot adapt to the dynamic changes in the solidification process, resulting in an unreasonable temperature field and stress field. Under the condition of changes in casting speed and superheat, the low magnification can only meet the index of the static model control method in Table 1.

[0039] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A continuous casting production method for reducing center defects of 165 mm square billets of plain carbon steel, characterized by, Specifically, the following steps are included: (1) The molten steel is poured into the crystallizer for casting, and at the same time, continuous casting protective slag is added to the surface of the molten steel in the crystallizer. The molten steel is cooled by the crystallizer to obtain a billet with a primary billet shell. (2) In the secondary cooling zone, a zoned full-water cooling mode is adopted. A dynamic calculation model is constructed based on the relationship between the drawing speed V, the superheat of molten steel ΔT, and the water volume Q in each cooling zone, as follows: Zone water quantity: Q1 = S x (-0.44V 2 + 9.12V - 2.66), and Q1 ≥ 8.8 m 3 / h; Two-zone water quantity: Q2 = S x (0.55V 2 + 7.64V - 2.20), and Q2≥9.5m 3 / h; Three-zone water quantity: Q3 = S x (0.92V 2 + 2.01V - 0.38), and Q3≥6.2m 3 / h; Water volume in Zone 4: Q4 = S × (0.48V) 2 +0.58V-0.03), and Q4≥1.7m 3 / h; The superheat coefficient S is determined based on the real-time superheat of the molten steel. Specifically, when the superheat of the molten steel > 30℃, S = 1.1; when the superheat of the molten steel < 20℃, S = 0.9; and when 20℃ ≤ superheat of the molten steel ≤ 30℃, S = 1.

0. The unit of casting speed is m / min, the unit of molten steel superheat is ℃, and the unit of water volume in each cooling zone is m³. 3 / h; (3) Using the relationship between the drawing speed, molten steel superheat and water volume of each cooling zone constructed in step (2), the billet with the initial shell is subjected to secondary cooling, and then drawn straightened to obtain a 165mm plain carbon steel square billet.

2. The continuous casting production method for reducing center defects of 165 mm square billets of plain carbon steel according to claim 1, characterized by, In step (1), the molten steel is ordinary carbon steel, and the composition of the molten steel by mass percentage includes C≤0.025%, Si≤0.035%, Mn≤0.070%, P≤0.045%, S≤0.045%, with the balance being Fe and unavoidable impurities.

3. The continuous casting production method for reducing center defects in 165mm plain carbon steel billets according to claim 1, characterized in that, In step (1), the pouring is done using an immersion nozzle with an insertion depth of 100~120mm.

4. The continuous casting production method for reducing center defects in 165mm plain carbon steel billets according to claim 1, characterized in that, In step (1), the thickness of the slag layer in the continuous casting protective slag liquid is 8~13mm, the slag consumption is 0.3~0.4kg / t, and the composition of the continuous casting protective slag by mass percentage includes: 22~35% SiO2, 20~33% CaO, MgO≤6%, Al2O3≤8%, Fe2O3≤5%; the basicity of the continuous casting protective slag is 1.00±0.15; the content of fixed C in the continuous casting protective slag by mass percentage is 7~16%, the content of F by mass percentage is ≤4%; the moisture content of the continuous casting protective slag by mass percentage is ≤0.50%, the melting point is 1160±50℃, and the bulk density is 0.50~1.1g / cm³. 3 Melting rate ≤60s / 1350℃, viscosity 0.20~0.85Pa·s / 1300℃, particle size 0.15~1mm, percentage by mass ≥95%.

5. The method of claim 1, wherein the method is characterized by: The cooling conditions for the crystallizer in step (1) are as follows: the water volume in the crystallizer is 120~130m³. 3 The crystallizer is cooled by water flow at a pressure of 1.2~1.6MPa and a temperature difference of 6~9℃.

6. The continuous casting production method of reducing center defects of 165 mm square billets of plain carbon steel according to claim 1, characterized by, The nozzle configurations for each cooling zone in step (2) are as follows: Zone 1: 3 rows × 8 nozzles = 24 nozzles; Zone 2: 10 rows × 4 nozzles = 40 nozzles; Zone 3: 8 rows × 4 nozzles = 32 nozzles; Zone 4: 6 rows × 4 nozzles = 24 nozzles.

7. The method of claim 1, wherein the method is a method of reducing centerline defects in a 165 mm square billet of plain carbon steel produced by continuous casting, characterized in that, The drawing speed in step (2) is 2.0~2.7m / min; the superheat of the molten steel is 15~40℃.

8. The continuous casting production method of reducing center defects of 165 mm square billets of plain carbon steel according to claim 1, characterized by, The cooling water pressure for the secondary cooling in step (3) is 1.2~1.5MPa.

9. The continuous casting production method for reducing center defects in 165mm plain carbon steel billets according to claim 1, characterized in that, The conditions for the straightening in step (3) are: hot billet pressure 2.5~4.0MPa, roll gap after pressing 140±5mm, and straightening temperature 1050±30℃.

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