A method for improving control of edge defects in s32101 duplex stainless steel cast slab

Abstract

This invention discloses a method for controlling edge defects in S32101 duplex stainless steel billets, comprising the following steps: S1, selection of mold flux for the crystallizer; S2, control of the usage parameters of the mold flux; S3, control of the cooling water flow rate at each section of the secondary cooling zone in continuous casting; S4, control of the continuous casting speed. In S1, the physicochemical properties of the mold flux are controlled to meet the following requirements: basicity: 1.35-1.50, melting point: 1030-1080℃, viscosity at 1300℃: 0.10~0.18 Pa·s, carbon content ≤2.0%, volatile matter ≤6.0%. This invention effectively eliminates edge defects in S32101 billets through the integrated synergistic control of mold flux, cooling water, and casting speed.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production and processing technology, and specifically relates to a method for controlling edge defects of S32101 duplex stainless steel billets. Background Technology

[0002] S32101 duplex stainless steel, as a nickel-saving and economical duplex steel, possesses both ferritic and austenitic dual-phase microstructures, exhibiting excellent corrosion resistance, high strength, and good formability. It is widely used in chemical equipment, shipbuilding, and municipal water supply and drainage. Continuous casting, as the core forming process for this steel grade, directly determines the yield and surface quality of the subsequent hot-rolled and cold-rolled finished products due to the quality of the cast billet's edge.

[0003] In the current S32101 continuous casting production process, defects frequently occur at the edge of the billet, mainly manifested as longitudinal cracks at the edge, transverse cracks at the corner, porosity, and looseness. The defects mainly stem from the following shortcomings in process control: (1) Poor compatibility of protective slag. The melting point and viscosity of conventional stainless steel protective slag do not match the solidification characteristics of S32101 steel liquid. The thickness of the liquid slag layer fluctuates greatly and the slag film is unevenly distributed, resulting in insufficient lubrication of the billet shell at the edge of the crystallizer and heat transfer imbalance, which induces initial cracks. (2) The cooling water in the second cooling zone adopts a uniform water distribution mode throughout the entire area. Differentiated flow control is not implemented for the wide face, narrow face, and corner of the billet. The cooling intensity at the edge is too large or too small, resulting in uneven temperature drop of the billet shell, concentration of phase transformation stress, and further expansion of cracks. (3) The casting speed and cooling and protective slag conditions are not coordinated. If the casting speed is too fast, the billet shell thickness will be insufficient. If the casting speed is too slow, the temperature drop and stress accumulation at the edge will be aggravated, further amplifying the risk of defects.

[0004] Therefore, existing technologies mostly optimize a single process parameter without forming a synergistic control system integrating protective slag, cooling water, and casting speed. This makes it difficult to eliminate edge defects of S32101 billets at their source and needs improvement. Summary of the Invention

[0005] In order to solve all or part of the above problems, the purpose of this invention is to provide a method for controlling edge defects of S32101 duplex stainless steel billets. By controlling the protective slag, cooling water and casting speed in a three-in-one coordinated manner, the edge defect problem of S32101 billets can be effectively eliminated.

[0006] This invention provides a method for controlling edge defects in S32101 duplex stainless steel billets, comprising the following steps: S1, Selection of protective slag for crystallizer; S2 controls the operating parameters of the protective slag; S3 controls the cooling water flow rate of each section of the secondary cooling zone in continuous casting; S4 controls the continuous casting speed; In S1, the physicochemical properties of the control flux must meet the following requirements: Basicity: 1.35-1.50, melting point: 1030-1080℃, viscosity at 1300℃: 0.10~0.18 Pa·s, carbon content ≤2.0%, volatile matter ≤6.0%.

[0007] Optionally, in S2, the parameters for controlling the use of the protective slag include: The batch quantitative slag addition mode is adopted, with a single slag addition amount of 0.5-1.0 kg and a slag addition interval of 3-5 min, maintaining the liquid slag layer thickness in the crystallizer at 8-12 mm, and the slag layer thickness fluctuation ≤ ±2 mm.

[0008] Optionally, in S3, differentiated flow distribution is performed based on the middle, edge, narrow, and corner portions of the billet's wide face, and the foot roll area, zone one, zone two, and zone three of the secondary cooling zone are graded and controlled to eliminate thermal stress.

[0009] Optionally, in S3, the water content in the middle of the wide face is controlled at 0.35-0.45 L / kg, and the water content at the edge of the wide face is controlled at 0.26-0.38 L / kg.

[0010] Optionally, in S3, the water volume in the narrow section is controlled at 0.30-0.40 L / kg, and the water volume in the corner section is controlled at 0.21-0.32 L / kg.

[0011] Optionally, in S3, the cooling water flow fluctuation in each zone is controlled to be ≤±3%, the nozzle pressure is controlled to be 0.35-0.50MPa, and the cooling intensity of the foot roller zone is controlled to account for 30%-35% of the total water volume of the second cooling zone, the cooling intensity of the first zone accounts for 25%-30% of the total water volume of the second cooling zone, the cooling intensity of the second zone accounts for 20%-25% of the total water volume of the second cooling zone, and the cooling intensity of the third zone accounts for 15%-20% of the total water volume of the second cooling zone.

[0012] Optionally, in S4, a linkage mechanism is established between the casting speed and the protective slag condition and cooling water flow rate. The casting speed is set according to the billet cross-sectional specifications and the superheat of the molten steel to ensure that the billet shell thickness matches the cooling rhythm.

[0013] Optionally, in S4, the reference drawing speed is set to 0.8-1.1m / min based on the slab cross-sectional dimensions of 150-220mm×1000-1500mm.

[0014] Optionally, in S4, if the superheat of the molten steel is higher than 45°C, the casting speed is reduced by 0.05-0.10 m / min; if the superheat of the molten steel is lower than 25°C, the casting speed is increased by 0.03-0.05 m / min, and the fluctuation of the casting speed adjustment is controlled within ±0.02 m / min.

[0015] Optionally, in S4, when the thickness of the liquid slag layer deviates from 8-12mm, the pulling speed is simultaneously fine-tuned by ±0.02-0.03m / min. If the cooling water flow is abnormal, the pulling speed adjustment is paused and resumed after the water flow stabilizes.

[0016] As can be seen from the above technical solution, the method for controlling edge defects of S32101 duplex stainless steel billets provided by the present invention has the following advantages: This control method effectively eliminates edge defects in S32101 billets through the integrated control of protective slag, cooling water, and casting speed. Porosity and looseness are completely eliminated, and the edge quality compliance rate is increased to over 99%. Simultaneously, differentiated cooling water control eliminates edge thermal stress, resulting in a more uniform microstructure at low magnification and an increased equiaxed crystal content. Furthermore, this control method requires no modification to existing continuous casting equipment; it can be implemented simply through process parameter optimization, making it suitable for the mass industrial production of S32101 duplex stainless steel.

[0017] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0018] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0019] Figure 1 This is a flowchart illustrating an embodiment of the present invention; Figure 2 This is a comparison diagram of the billet before and after the improvement in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0021] like Figure 1 , Figure 2 The illustration shows an embodiment of the present invention, which discloses a method for controlling edge defects in S32101 duplex stainless steel billets, comprising the following steps: S1, Selection of protective slag for crystallizer; S2 controls the operating parameters of the protective slag; S3 controls the cooling water flow rate of each section of the secondary cooling zone in continuous casting; S4 controls the continuous casting speed.

[0022] Considering the low-nickel, high-nitrogen solidification characteristics of S32101 duplex stainless steel, a special low-carbon, high-basicity protective slag is selected. Therefore, in S1, the physicochemical properties of the protective slag are controlled to meet the following requirements: Basicity: 1.35-1.50, melting point: 1030-1080℃, viscosity at 1300℃: 0.10~0.18Pa·s, carbon content ≤2.0%, volatile matter ≤6.0%, ensuring moderate slag film fluidity and appropriate crystalline phase ratio, avoiding slag ring accumulation and slag entanglement at the edges.

[0023] Strict control of the protective slag usage parameters is essential to ensure uniform lubrication and heat transfer within the crystallizer shell. Therefore, in S2, the parameters for controlling the protective slag usage include: The batch quantitative slag addition mode is adopted, with a single slag addition amount of 0.5-1.0 kg and an interval of 3-5 min. The thickness of the liquid slag layer in the crystallizer is maintained at 8-12 mm, and the slag layer thickness fluctuation is ≤±2 mm. This eliminates the phenomenon of local slag deficiency and slag accumulation at the edge, ensures uniform coverage of the slag film on the meniscus, and reduces the frictional stress and uneven heat transfer between the edge of the billet shell and the crystallizer wall.

[0024] In S3, differentiated flow distribution is performed based on the middle, edge, narrow, and corner of the billet's wide face. The foot roll area, zone one, zone two, and zone three of the secondary cooling zone are graded and controlled to eliminate thermal stress.

[0025] In S3, the water content in the middle of the wide face is controlled at 0.35-0.45 L / kg, and the water content in the edge of the wide face (the area 50-100 mm from the edge) is controlled at 0.26-0.38 L / kg. This means the water content in the edge of the wide face is reduced by 15%-25% compared to the middle, to prevent overcooling of the edges and subsequent embrittlement of the billet shell. The water content in the narrow face is controlled at 0.30-0.40 L / kg, and the water content in the corner is controlled at 0.21-0.32 L / kg. This means the water content in the corner is reduced by 20%-30% compared to the narrow face.

[0026] In S3, the cooling water flow fluctuation in each zone is controlled to ≤±3%, and the nozzle pressure is 0.35-0.50MPa to ensure uniform water flow coverage, no off-center spraying, and no clogging. Simultaneously, the cooling intensity of the foot roller zone is controlled to account for 30%-35% of the total water volume in the secondary cooling zone, the first zone for 25%-30%, the second zone for 20%-25%, and the third zone for 15%-20% of the total water volume in the secondary cooling zone. This ensures uniform solidification of the billet shell from the surface inwards and inhibits the initiation of edge cracks.

[0027] In S4, a linkage mechanism is established between casting speed and protective slag conditions and cooling water flow. The casting speed is set according to the billet cross-sectional specifications and molten steel superheat to ensure that the billet shell thickness matches the cooling rhythm and avoid edge defects induced by casting speed fluctuations.

[0028] In S4, based on the slab cross-sectional dimensions of 150-220mm × 1000-1500mm, the baseline casting speed is set to 0.8-1.1m / min. If the superheat of the molten steel is higher than 45℃, the casting speed is reduced by 0.05-0.10m / min; if the superheat of the molten steel is lower than 25℃, the casting speed is increased by 0.03-0.05m / min. The fluctuation of the casting speed adjustment is controlled within ±0.02m / min, avoiding sudden increases or decreases. When the slag layer thickness deviates by 8-12mm, the casting speed is simultaneously fine-tuned by ±0.02-0.03m / min. If the cooling water flow is abnormal, the casting speed adjustment is paused and resumed after the water flow stabilizes, thus achieving coordinated adaptation of the three major process parameters.

[0029] The control method in this embodiment achieves uniform lubrication and heat transfer in the crystallizer by selecting a suitable protective slag and precisely controlling the thickness of the liquid slag layer; it also implements differentiated secondary cooling water flow distribution for the wide face, narrow face, and corners of the billet to eliminate edge temperature stress; and it establishes a coordinated control mechanism for casting speed, protective slag, and cooling water to stabilize the solidification rhythm of the billet shell and significantly reduce the incidence of edge defects in the billet. To more clearly illustrate this application, specific embodiments are listed below: Example 1 S1, Selection of protective slag: Basicity 1.42, melting point 1050℃, viscosity 0.14 Pa·s at 1300℃; S2, controls the parameters for using protective slag: The liquid slag layer thickness is 10 mm, and 0.8 kg of slag is added at a time with an interval of 4 min. S3 controls the cooling water flow rate: The water content in the middle of the wide face is 0.40 L / kg, the water content at the edge of the wide face is 0.32 L / kg, the water content in the narrow face is 0.35 L / kg, the water content at the corner is 0.28 L / kg, and the water content in the foot roller area accounts for 32%.

[0030] S4 controls the continuous casting speed to be 0.95 m / min.

[0031] Upon inspection, the edges of the cast billet showed no cracks, porosity, or looseness.

[0032] Example 2 S1, Selection of protective slag: Basicity 1.45, melting point 1060℃, viscosity at 1300℃ 0.16 Pa·s; S2, controls the parameters for using protective slag: The liquid slag layer thickness is 11 mm, and 0.8 kg of slag is added at a time with an interval of 4 min. S3 controls the cooling water flow rate: The water content in the middle of the wide face is 0.42 L / kg, the water content at the edge of the wide face is 0.34 L / kg, the water content in the narrow face is 0.35 L / kg, the water content at the corner is 0.29 L / kg, and the water content in the foot roller area accounts for 32%.

[0033] S4 controls the continuous casting speed to be 0.90 m / min.

[0034] Upon inspection, the edges of the cast billet showed no cracks, porosity, or looseness.

[0035] As can be seen from the above process, this control method reduces the generation of billet defects from the source by optimizing the compatibility of the protective slag, the differentiated flow control of the continuous casting cooling water, and the continuous casting speed. It forms a three-in-one synergistic control system of mold protective slag, secondary cooling zone cooling water, and continuous casting speed, thereby eliminating edge defects of S32101 billet from the root and improving the product quality and yield of S32101.

[0036] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0037] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for improving the control of edge defects in a S32101 duplex stainless steel cast slab, characterized in that, Includes the following steps: S1, Selection of protective slag for crystallizer; S2 controls the operating parameters of the protective slag; S3 controls the cooling water flow rate of each section of the secondary cooling zone in continuous casting; S4 controls the continuous casting speed; In S1, the physicochemical properties of the control flux must meet the following requirements: Basicity: 1.35-1.50, melting point: 1030-1080℃, viscosity at 1300℃: 0.10~0.18 Pa·s, carbon content ≤2.0%, volatile matter ≤6.0%.

2. The control method according to claim 1, characterized by, In S2, the parameters for controlling the use of the protective slag include: The batch quantitative slag addition mode is adopted, with a single slag addition amount of 0.5-1.0 kg and a slag addition interval of 3-5 min, maintaining the liquid slag layer thickness in the crystallizer at 8-12 mm, and the slag layer thickness fluctuation ≤ ±2 mm.

3. The control method according to claim 1, characterized by, In S3, differentiated flow distribution is performed based on the middle, edge, narrow, and corner of the billet's wide face. The foot roll area, zone one, zone two, and zone three of the secondary cooling zone are controlled in stages to eliminate thermal stress.

4. The control method according to claim 3, characterized by, In S3, the water content in the middle of the wide face is controlled at 0.35-0.45 L / kg, and the water content at the edge of the wide face is controlled at 0.26-0.38 L / kg.

5. The control method according to claim 3, characterized by, In S3, the water volume in the narrow section is controlled at 0.30-0.40 L / kg, and the water volume in the corner section is controlled at 0.21-0.32 L / kg.

6. The control method according to claim 3, characterized by In S3, the cooling water flow fluctuation in each zone is controlled to be ≤±3%, the nozzle pressure is 0.35-0.50MPa, and the cooling intensity of the foot roller zone is controlled to account for 30%-35% of the total water volume of the second cooling zone, the cooling intensity of the first zone accounts for 25%-30% of the total water volume of the second cooling zone, the cooling intensity of the second zone accounts for 20%-25% of the total water volume of the second cooling zone, and the cooling intensity of the third zone accounts for 15%-20% of the total water volume of the second cooling zone.

7. The control method according to claim 1, characterized by, In S4, a linkage mechanism is established between casting speed and protective slag conditions and cooling water flow rate. The casting speed is set according to the billet cross-sectional specifications and the superheat of molten steel to ensure that the billet shell thickness matches the cooling rhythm.

8. The control method according to claim 7, characterized by In S4, based on the slab cross-sectional dimensions of 150-220mm×1000-1500mm, the reference drawing speed is set to 0.8-1.1m / min.

9. The control method according to claim 7, characterized by, In S4, if the superheat of the molten steel is higher than 45℃, the casting speed is reduced by 0.05-0.10 m / min; if the superheat of the molten steel is lower than 25℃, the casting speed is increased by 0.03-0.05 m / min, and the fluctuation of the casting speed adjustment is controlled within ±0.02 m / min.

10. The control method according to claim 7, characterized by, In S4, when the thickness of the liquid slag layer deviates from 8-12mm, the pulling speed is simultaneously fine-tuned by ±0.02-0.03m / min. If the cooling water flow is abnormal, the pulling speed adjustment is paused and resumed after the water flow stabilizes.

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