A method for controlling surface quality defects in thin strip continuously cast stainless steel

Abstract

This invention relates to the field of stainless steel thin strip continuous casting technology, and provides a method for controlling surface quality defects in stainless steel thin strip continuous casting. The method comprises three main measures: molten steel composition control, crystallizing roll treatment, and molten pool fluctuation control during continuous casting. Molten steel composition control limits the content of Se, S, and N, and ensures that Se / S ≥ 3. The crystallizing roll undergoes unique treatment, employing a micro-pit embedded coating. Three levels of molten pool fluctuation control are achieved during continuous casting: first-level control involves adding a porous Si3N4 baffle to the flow distribution system to mechanically disperse the molten steel flow; second-level control involves adding an electromagnetic eddy current damper to suppress surface waves, reducing amplitude by 60%; and third-level control involves combining laser ranging with PID liquid level control to suppress molten pool fluctuations. This combination of three measures synergistically eliminates the chain reaction of defects, effectively controlling three types of defects in stainless steel strips: transverse cracks, vibration marks, and micro-shrinkage cavities.

Description

Technical Field

[0001] This invention relates to the field of stainless steel strip continuous casting technology, and specifically to a method for controlling surface quality defects in stainless steel strip continuous casting. Background Technology

[0002] Thin strip continuous casting integrates continuous casting, rolling, and heat treatment processes, allowing the produced thin strip billets to be formed into industrial finished products in one go after only a short subsequent rolling process. This simplifies the production process of aluminum alloy thin strips, shortens the production cycle, and makes the aluminum alloy thin strip production process more compact, continuous, efficient, and environmentally friendly. At the same time, production costs are significantly reduced, and the quality and performance of the produced thin strip products are no less than or even better than those produced by traditional processes.

[0003] The existing vertical twin-roll thin strip continuous casting process for stainless steel strip has the following problems: the three types of defects, namely surface transverse cracks, vibration marks and depressions, and micro-shrinkage cavities, cannot be controlled in a coordinated manner. In particular, the defect coupling effect caused by thermal stress concentration, molten pool fluctuation and uneven heat transfer at the crystallizing roll interface under sub-rapid solidification conditions (cooling rate ≥10³K / s) is particularly problematic.

[0004] In summary, there is an urgent need for a method that is easy to operate and can simultaneously control three types of defects: surface transverse cracks, vibration marks, and micropores, in order to solve the problems existing in the prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling surface quality defects in thin-strip continuously cast stainless steel that is easy to operate and can simultaneously control three types of defects: transverse cracks, vibration marks, and micro-shrinkage cavities. The specific technical solution is as follows:

[0006] A method for controlling surface quality defects in thin-strip continuously cast stainless steel includes the following steps:

[0007] Steel molten composition control: Se 0.005%~0.01%; S≤0.003%; N 0.15%~0.22%; Se / S≥3;

[0008] The crystallization roller processing includes: machining the surface of a copper roller to obtain a copper alloy substrate; processing a micro-pit array on the surface of the copper alloy substrate, wherein the micro-pit array has a diameter of 50±5μm, a depth of 20±2μm, and a density of 200 pits / cm²; and spraying Al₂O₃-13%TiO₂ to form an Al₂O₃-TiO₂ coating with a thickness of 2.0±0.3μm, a thermal conductivity of 5.8W / m·K, and a bonding strength ≥45MPa.

[0009] The control of molten pool fluctuations during continuous casting includes: improving equipment, specifically: adding a porous Si3N4 baffle wall to the flow distribution system and setting an electromagnetic eddy current damper; starting continuous casting; detecting molten pool fluctuations and outputting molten pool fluctuation result data; and starting PID liquid level control based on the molten pool fluctuation result data.

[0010] Preferably, the parameters of the porous Si3N4 barrier wall include: pore diameter Φ3mm, porosity 30%, and inclination angle 15°;

[0011] Parameters of the electromagnetic eddy current damper: frequency 50Hz, magnetic field strength 0.15T, and operating depth 50mm;

[0012] In PID liquid level control: laser ranging accuracy ±0.1mm, response time <0.5s.

[0013] Preferably, the parameters of the copper alloy matrix are: material CuCrZr, thermal conductivity of 320W / m·K.

[0014] Preferably, the control of molten steel composition specifically includes: EAF initial smelting; LF furnace desulphurization to S≤0.003%; VD furnace vacuum treatment; addition of Se to make Se / S≥3; and nitrogen blowing alloying.

[0015] Preferably, during the detection of molten pool fluctuations, the PID stopper rod adjustment is activated when the molten pool fluctuation change ΔH > ±1.5mm.

[0016] Preferably, after forming the Al2O3-TiO2 coating during the crystallization roller treatment, the temperature is preheated to 250°C under argon protection.

[0017] The method for controlling surface quality defects in thin-strip continuously cast stainless steel using this invention includes three major measures: molten steel composition control, crystallizing roll treatment, and molten pool fluctuation control during continuous casting. The molten steel composition control, by limiting the content of Se, S, and N and ensuring Se / S ≥ 3, effectively purifies grain boundaries and improves crack resistance. The unique treatment of the crystallizing roll, employing a micro-pit embedded coating, enhances heat flow uniformity and suppresses oscillation marks. The molten pool fluctuation control during continuous casting achieves three levels of molten pool fluctuation control (specifically: adding a porous Si3N4 baffle to the molten pool fluctuation control distribution system to mechanically disperse the molten steel flow, achieving first-level molten pool fluctuation control; adding an electromagnetic eddy current damper to suppress surface waves, reducing amplitude by 60%, achieving second-level molten pool fluctuation control; and combining laser ranging with PID liquid level control to suppress molten pool fluctuations, achieving third-level molten pool fluctuation control), stabilizing the solidification front and reducing shrinkage cavities. Based on the combination of these three measures, a synergistic elimination of defect chain reactions is ultimately achieved, effectively controlling three types of defects in stainless steel strips: surface transverse cracks, oscillation marks, and micro-shrinkage cavities.

[0018] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 This is a schematic diagram of the method for controlling surface quality defects in thin-strip continuously cast stainless steel in this invention.

[0021] Figure 2 This is a schematic diagram illustrating the method for controlling surface quality defects in thin-strip continuously cast stainless steel in this invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0023] A method for controlling surface quality defects in thin strip continuous casting stainless steel mainly involves controlling the composition of molten steel, the crystallizing roll, and the fluctuation of the molten pool during the continuous casting process. Other processes refer to existing thin strip continuous casting processes.

[0024] See details Figure 1 The surface quality defect control method for thin-strip continuously cast stainless steel in this embodiment includes three dimensions: molten steel composition design, innovative crystallizing roll structure, and multi-stage melt pool fluctuation suppression. Based on these three dimensions, synergistic defect control is achieved, resulting in the suppression of transverse cracks, homogenization of oscillation marks and depressions, and elimination of micropores. Specifically, it includes the following steps:

[0025] First, control of molten steel composition: Se 0.005%~0.01%; S≤0.003%; N 0.15%~0.22%; Se / S≥3. Controlling Se at 0.005%~0.01% allows for the formation of SeS compounds to replace MnS, eliminating crack initiation sites and improving grain boundary bonding strength; S≤0.003% reduces sulfide inclusions and avoids competition with Se for consumption; N controlled at 0.15%~0.22% expands the austenite phase region and inhibits δ-ferrite precipitation (target content <5%); Se / S≥3 ensures complete fixation of S. Specific molten steel composition control includes: EAF initial smelting; LF furnace desulphurization to S≤0.003%; VD furnace vacuum treatment; adding Se to achieve Se / S≥3; and nitrogen blowing alloying.

[0026] The second step is the crystallization roller treatment, which includes: machining the surface of the copper roller to obtain a copper alloy substrate; processing a micro-pit array on the surface of the copper alloy substrate, wherein the micro-pit array has a diameter of 50±5μm, a depth of 20±2μm, and a density of 200 pits / cm²; spraying Al₂O₃-13%TiO₂ to form an Al₂O₃-TiO₂ coating with a thickness of 2.0±0.3μm, a thermal conductivity of 5.8W / m·K, and a bonding strength ≥45MPa. The parameters of the copper alloy substrate are: material CuCrZr, thermal conductivity of 320W / m·K. The processing of the copper alloy substrate can be carried out by centrifugal casting combined with age hardening to ensure basic heat transfer efficiency; the processing of the micro-pit array is carried out by fiber laser processing, with a wavelength of 1064nm, a pulse width of 100ns, and an energy density of 8J / cm², which can store liquid protective slag and buffer solidification shrinkage stress. The Al2O3-TiO2 coating was applied using atmospheric plasma spraying (APS) with parameters of 500A current and 40L / min argon flow rate to achieve localized thermal resistance adjustment, stabilizing the oscillation mark depth at 15±3μm. After the Al2O3-TiO2 coating was formed during the crystallization roller treatment, it was preheated to 250℃ under argon protection.

[0027] Third, molten pool fluctuation control during continuous casting (i.e., multi-stage molten pool fluctuation suppression) includes: improving equipment, specifically: adding porous Si3N4 baffles to the flow distribution system and setting up electromagnetic eddy current dampers; starting continuous casting; detecting molten pool fluctuations and outputting molten pool fluctuation result data; and starting PID liquid level control based on the molten pool fluctuation result data.

[0028] This embodiment specifically employs a three-level melt pool fluctuation suppression mechanism, which includes:

[0029] Primary molten pool fluctuation control: Adding a porous Si3N4 baffle to the flow distribution system can mechanically disperse the molten steel flow fluctuation. The parameters of the porous Si3N4 baffle include: pore diameter Φ3mm, porosity 30%, and inclination angle 15°.

[0030] Secondary molten pool fluctuation control: The addition of an electromagnetic eddy current damper can suppress surface waves, reducing the amplitude by 60%. The parameters of the electromagnetic eddy current damper are: frequency 50Hz, magnetic field strength 0.15T, and operating depth 50mm.

[0031] Three-stage molten pool fluctuation control: PID liquid level control combined with laser ranging suppresses molten pool fluctuations, stabilizes the solidification front, and reduces shrinkage porosity. In PID liquid level control: laser ranging accuracy ±0.1mm, response time <0.5s. During molten pool fluctuation detection, PID stopper rod adjustment is activated when the molten pool fluctuation change ΔH > ±1.5mm.

[0032] The combination of these three measures will ultimately achieve the synergistic elimination of the chain reaction of defects. See details below. Figure 2The molten steel with a Se / S ratio ≥3 can purify the grain boundaries and improve crack resistance. The micro-pit embedded coating roller improves heat flow uniformity and suppresses vibration marks. Multi-stage molten pool control can stabilize the solidification front and reduce shrinkage cavities. Through the control of molten steel with a Se / S ratio ≥3, the design of the micro-pit embedded coating roller, and the multi-stage molten pool control, the three types of defects of stainless steel strip—surface transverse cracks, vibration mark depressions, and micro-shrinkage cavities—are effectively controlled in a coordinated manner. At the thermodynamic level, Se / S ≥ 3 ensures grain boundary purification, but this reaction requires time during sub-rapid solidification. This necessitates a stable molten pool (fluctuation ≤ ±1.5 mm) to provide continuous reaction conditions. The micro-pitted roller surface reduces temperature disturbances through heat flow homogenization, creating an environment conducive to the reaction. Secondly, at the stress transfer level, calculations show that when the oscillation mark depth > 20 μm, the stress concentration factor at the bottom of the pit reaches 3.2, sufficient to tear the Se-strengthened grain boundaries. This explains why it is necessary to simultaneously control the oscillation marks (micro-pitted embedded coating roller design) and grain boundaries (steel composition design). Finally, at the engineering implementation level, if only the steel composition design and the micro-pitted embedded coating roller design are used without controlling the molten pool, the impact of the steel flow in actual production will cause excessive fluctuations, rendering the first two measures ineffective. Pilot-scale data from a steel plant shows that when the fluctuation increases from ±1.5 mm to ±2.5 mm, the crack density surges from 3 cracks / m to 11 cracks / m.

[0033] Examples 1-3:

[0034] The specific parameters of the technical solution adopted in this invention are detailed in Table 1.

[0035] Comparative Examples 1-4:

[0036] The differences between Comparative Examples 1-4 and Example 1 are detailed in Table 1.

[0037] Table 1. Comparison of technical solutions, key parameters, and defect control effects between Example 1 and Comparative Examples 1-4

[0038]

[0039] As can be seen from Examples 1-3 and Comparative Examples 1-4, by adopting the technical solution of the present invention, and combining the three major measures of steel composition control, crystallizing roll treatment, and molten pool fluctuation control during continuous casting, it is possible to ensure that: transverse crack density ≤3 cracks / m, vibration mark depth fluctuation ±2μm, micro-shrinkage cavity ratio within 0.035%, and crystallizing roll surface life 500 heats, with significant effects.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling surface quality defects in thin-strip continuously cast stainless steel, characterized in that, Includes the following steps: Steel molten composition control: Se is 0.005%~0.01%; S≤0.003%; N is 0.15%~0.22%; Se / S≥3; The crystallization roller processing includes: machining the surface of a copper roller to obtain a copper alloy substrate; processing a micro-pit array on the surface of the copper alloy substrate, wherein the micro-pit array has a diameter of 50±5μm, a depth of 20±2μm, and a density of 200 pits / cm²; and spraying Al₂O₃-13%TiO₂ to form an Al₂O₃-TiO₂ coating with a thickness of 2.0±0.3μm, a thermal conductivity of 5.8W / m·K, and a bonding strength ≥45MPa. The control of molten pool fluctuations during continuous casting includes: improving equipment, specifically: adding a porous Si3N4 baffle wall to the flow distribution system and setting up an electromagnetic eddy current damper; starting continuous casting; detecting molten pool fluctuations and outputting molten pool fluctuation result data; and starting PID liquid level control based on the molten pool fluctuation result data. The parameters of the porous Si3N4 barrier wall include: pore diameter Φ3mm, porosity 30%, and inclination angle 15°; Parameters of the electromagnetic eddy current damper: frequency 50Hz, magnetic field strength 0.15T, and operating depth 50mm; In PID liquid level control: laser ranging accuracy ±0.1mm, response time <0.5s.

2. The method for controlling surface quality defects in thin-strip continuously cast stainless steel according to claim 1, characterized in that, The parameters of the copper alloy matrix are as follows: the material is CuCrZr, and the thermal conductivity is 320W / m·K.

3. The method for controlling surface quality defects in thin-strip continuously cast stainless steel according to claim 2, characterized in that, The specific control of molten steel composition includes: EAF initial smelting; LF furnace desaturation to S≤0.003%; VD furnace vacuum treatment; addition of Se to make Se / S≥3; and nitrogen blowing alloying.

4. The method for controlling surface quality defects in thin-strip continuously cast stainless steel according to claim 1, characterized in that, During the detection of molten pool fluctuations, the PID stopper rod adjustment is activated when the molten pool fluctuation change ΔH > ±1.5mm.

5. The method for controlling surface quality defects in thin-strip continuously cast stainless steel according to claim 1, characterized in that, After forming an Al2O3-TiO2 coating during the crystallization roller treatment, the coating is preheated to 250°C under argon protection.

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