Method for controlling surface quality defects of thin-strip continuous casting stainless steel

Abstract

The invention relates to the technical field of stainless steel thin-strip continuous casting, and provides a thin-strip continuous casting stainless steel surface quality defect control method which comprises the three measures of molten steel component control, crystallization roller treatment and molten pool fluctuation control in the continuous casting process, the content of Se, S and N is limited in the molten steel component control, and Se / S is larger than or equal to 3; through unique treatment of a crystallization roller, the crystallization roller with a coating embedded in a micro-pit is adopted; three-level molten pool fluctuation control is achieved through molten pool fluctuation control in the continuous casting process, specifically, a porous Si3N4 retaining wall is additionally arranged on a flow distribution system, molten steel flow movement can be mechanically dispersed, and first-level molten pool fluctuation control is achieved; an electromagnetic eddy current damper is additionally arranged to inhibit surface waves, so that the amplitude is reduced by 60%, and secondary molten pool fluctuation control is realized; molten pool fluctuation is restrained through PID liquid level control combined with laser ranging, and three-level molten pool fluctuation control is achieved. Based on the combination of the three measures, the defect chain reaction is synergistically eliminated, and the three defects of surface transverse cracks, vibration mark recesses and micro shrinkage cavities of the stainless steel band are effectively and synergistically controlled.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel thin strip continuous casting, and in particular to a method for controlling surface quality defects of thin strip continuous casting stainless steel. Background Art

[0002] Thin strip continuous casting integrates continuous casting, rolling, heat treatment and other processes, so that the thin strip blanks produced can be formed into industrial finished products in one go after a little subsequent rolling. It 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, the production cost is significantly reduced, and the quality and performance of the thin strip products produced are not inferior to or even better than those of traditional processes.

[0003] The existing vertical twin-roll thin strip casting process for stainless steel strip faces the problem of being unable to coordinately control three types of defects: surface transverse cracks, vibration marks and depressions, and micro-pores. This is particularly true for the defect coupling effect caused by thermal stress concentration, melt pool fluctuations, and uneven heat transfer at the crystallization roll interface under sub-rapid solidification conditions (cooling rate ≥ 10³K / s).

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

[0005] The present invention aims to provide a method for controlling surface quality defects of thin strip continuous casting stainless steel, which is easy to operate and can simultaneously control three types of surface defects: transverse cracks, vibration marks and depressions, and micro-shrinkage holes. The specific technical solution is as follows: A method for controlling surface quality defects of thin strip continuous casting stainless steel comprises the following steps: Molten steel composition control: Se is 0.005%~0.01%; S≤0.003%; N is 0.15%~0.22%; Se / S≥3; Crystallization roller processing, including: turning a copper roller surface to obtain a copper alloy substrate; machining a micro-pit array on the surface of the copper alloy substrate, wherein the micro-pit array has a diameter of 50±5 μm, a depth of 20±2 μm, and a density of 200 pits / cm²; spraying Al2O3-13%TiO2 to form an Al2O3-TiO2 coating having a thickness of 2.0±0.3 μm, a thermal conductivity of 5.8 W / m·K, and a bonding strength of ≥45 MPa; Controlling molten pool fluctuation during continuous casting includes: improving equipment, specifically: adding porous Si3N4 retaining walls to the flow distribution system and setting 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.

[0006] Preferably, the parameters of the porous Si3N4 retaining wall include: pore diameter Φ3mm, porosity 30%, inclination angle 15°; Parameters of electromagnetic eddy current damper: frequency 50Hz, magnetic field intensity 0.15T, action depth 50mm; PID liquid level control: laser ranging accuracy ±0.1mm, response time <0.5s.

[0007] Preferably, the parameters of the copper alloy substrate are: material is CuCrZr, and thermal conductivity is 320 W / m·K.

[0008] Preferably, the molten steel composition control specifically includes: EAF primary refining; LF furnace desulfurization to S≤0.003%; VD furnace vacuum treatment; Se addition to make Se / S≥3; and nitrogen blowing alloying.

[0009] Preferably, during the detection of molten pool fluctuation, when the molten pool fluctuation variation ΔH>±1.5mm is satisfied, the PID stopper rod adjustment is activated.

[0010] Preferably, after the Al2O3-TiO2 coating is formed during the crystallization roller treatment, it is preheated to 250°C under argon protection.

[0011] The method for controlling surface quality defects of thin-strip continuous casting stainless steel of the present invention comprises three major measures: molten steel composition control, crystallization roller treatment, and molten pool fluctuation control during continuous casting. In the molten steel composition control, the contents of Se, S, and N are limited, and Se / S ≥ 3, which can effectively purify grain boundaries and improve crack resistance. Through the unique treatment of the crystallization roller and the use of a crystallization roller with a micro-pit embedded coating, heat flow uniformity can be improved and vibration marks can be suppressed. Through the molten pool fluctuation control during continuous casting, three-level molten pool fluctuation control is achieved (specifically: during the continuous casting process, a porous Si3N4 retaining wall is added to the molten pool fluctuation control flow distribution system to mechanically disperse the molten steel flow, thereby achieving first-level molten pool fluctuation control; an electromagnetic eddy current damper is added to suppress surface waves, reducing the amplitude by 60%, thereby achieving second-level molten pool fluctuation control; and PID liquid level control combined with laser ranging suppresses molten pool fluctuation, thereby achieving third-level molten pool fluctuation control), stabilizing the solidification front and reducing shrinkage cavities. Based on the combination of the three major measures, the chain reaction of defects can be synergistically eliminated, and three types of defects, namely, surface transverse cracks, vibration mark depressions, and micro-shrinkage cavities, of the stainless steel strip can be effectively and synergistically controlled.

[0012] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 This is a schematic diagram of the method for controlling surface quality defects of thin strip continuous casting stainless steel in the present invention; Figure 2 It is a schematic diagram of the control method of surface quality defects of thin strip continuous casting stainless steel in the present invention. DETAILED DESCRIPTION

[0014] The embodiments of the present invention are 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.

[0015] A method for controlling surface quality defects of thin strip continuous casting stainless steel is disclosed. The method mainly controls the composition of molten steel, crystallization rollers, and molten pool fluctuations during the thin strip continuous casting stainless steel process. Other processes refer to the existing thin strip continuous casting process.

[0016] See Figure 1 The method for controlling surface quality defects in thin strip continuous casting stainless steel in this embodiment involves three dimensions: molten steel composition design, innovative crystallization roller structure, and multi-stage melt pool fluctuation suppression. This method achieves coordinated defect control, achieving the goals of suppressing transverse cracks, equalizing vibration marks and depressions, and eliminating micro-shrinkage cavities. Specifically, the following steps are included: First, control the molten steel composition: Se is 0.005% to 0.01%; S is ≤ 0.003%; N is 0.15% to 0.22%; and Se / S is ≥ 3. Controlling Se to 0.005% to 0.01% allows the formation of SeS compounds to replace MnS, eliminating crack sources and improving grain boundary bonding strength. S is ≤ 0.003% to reduce sulfide inclusions and prevent competition with Se for consumption. N is controlled at 0.15% to 0.22% to expand the austenite phase and inhibit delta ferrite precipitation (target content < 5%). Se / S is ≥ 3 to ensure that Se fully fixes the sulfur element. Molten steel composition control specifically includes: EAF primary refining; LF furnace desulfurization to ≤ 0.003%; VD furnace vacuum treatment; Se addition to achieve a Se / S ratio of ≥ 3; and nitrogen blowing for alloying.

[0017] Second, crystallization roller processing involves turning the copper roller surface to obtain a copper alloy substrate; machining a micro-pit array on the surface of the copper alloy substrate, with 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 of ≥45MPa. The copper alloy substrate parameters are: material: CuCrZr, thermal conductivity: 320W / m·K. The copper alloy substrate can be processed using centrifugal casting combined with aging hardening to ensure basic heat transfer efficiency. The micro-pit array is processed using fiber laser processing with a wavelength of 1064nm, a pulse width of 100ns, and an energy density of 8J / cm², capable of storing liquid mold slag and buffering solidification shrinkage stress. The Al2O3-TiO2 coating was applied using atmospheric plasma spraying (APS) with a current of 500A and an argon flow rate of 40L / min. This achieved local thermal resistance regulation, maintaining a stable oscillation mark depth of 15±3μm. After forming the Al2O3-TiO2 coating during the crystallization roller process, the roller was preheated to 250°C under argon protection.

[0018] Third, control of melt pool fluctuations during continuous casting (i.e., multi-stage melt pool fluctuation suppression) includes: improving equipment, specifically: adding porous Si3N4 retaining walls to the flow distribution system and setting up electromagnetic eddy current dampers; starting continuous casting; detecting melt pool fluctuations and outputting melt pool fluctuation result data; and starting PID liquid level control based on the melt pool fluctuation result data.

[0019] In this embodiment, there is a three-stage molten pool fluctuation suppression, specifically: Primary molten pool fluctuation control: Adding a porous Si3N4 retaining wall to the flow distribution system can mechanically disperse the molten steel flow. The parameters of the porous Si3N4 retaining wall include: pore diameter Φ3mm, porosity 30%, and inclination angle 15°; Secondary molten pool fluctuation control: Adding 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 action depth 50mm; Three-level melt pool fluctuation control: PID liquid level control combined with laser ranging suppresses melt pool fluctuations, stabilizes the solidification front, and reduces shrinkage cavities. During PID liquid level control, laser ranging accuracy is ±0.1mm, and response time is <0.5s. During melt pool fluctuation detection, PID stopper adjustment is activated when the melt pool fluctuation variation, ΔH, exceeds ±1.5mm.

[0020] Based on the combination of the three major measures, a chain reaction of collaborative defect elimination is finally achieved. Figure 2, molten steel Se / S≥3 can purify grain boundaries and improve crack resistance, micro-pit embedded coating roller improves heat flow uniformity and suppresses vibration marks, and multi-stage molten pool control can stabilize the solidification front and reduce shrinkage holes. Through molten steel Se / S≥3 control, micro-pit embedded coating roller design and multi-stage molten pool control, the three types of surface defects of stainless steel strip, namely surface transverse cracks, vibration mark depressions and micro-shrinkage holes, can be effectively and synergistically controlled. From a thermodynamic perspective, a Se / S ratio of ≥3 ensures grain boundary purification. However, this reaction takes time during sub-rapid solidification, requiring a stable melt pool (fluctuation ≤ ±1.5 mm) to provide sustained reaction conditions. Micro-pitted roller surfaces reduce temperature disturbances through heat flow homogenization, creating a favorable environment for the reaction. Secondly, regarding stress transfer, calculations show that when the vibration mark depth exceeds 20 μm, the stress concentration factor at the bottom of the depression reaches 3.2, sufficient to tear the Se-strengthened grain boundaries. This explains the need for simultaneous control of vibration marks (micro-pit embedded coating roller design) and grain boundaries (molten steel composition design). Finally, from an engineering perspective, if only molten steel composition design and micro-pit embedded coating roller design are employed without controlling the melt pool, the impact of the steel flow in actual production will cause fluctuations to exceed the specified limits, rendering the first two measures ineffective. Pilot data from a steel plant showed that when the fluctuation increased from ±1.5 mm to ±2.5 mm, the crack density soared from 3 to 11 cracks / m.

[0021] Example 1-Example 3: The technical solution of the present invention is adopted, and the specific parameters are shown in Table 1.

[0022] Comparative Examples 1-4: The differences between Comparative Examples 1-4 and Example 1 are detailed in Table 1.

[0023] Table 1 Comparison of technical solutions, key parameters and defect control effects of Example 1 and Comparative Examples 1-4

[0024] In combination with Examples 1-3 and Comparative Examples 1-4, it can be seen that the technical solution of the present invention, combined with the three major measures of molten steel composition control, crystallization roller treatment and molten pool fluctuation control during continuous casting, can ensure: the density of transverse cracks ≤ 3 lines / m, the fluctuation of vibration mark depth ±2μm, the proportion of microshrinkage holes within 0.035%, and the life of the crystallization roller surface 500 furnaces, with significant effects.

[0025] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for controlling surface quality defects of thin strip continuous casting stainless steel, characterized in that: The following steps are involved: Molten steel composition control: Se is 0.005%~0.01%; S≤0.003%; N 0.15%~0.22%; Se / S≥3; Crystallization roller processing, including: turning a copper roller surface to obtain a copper alloy substrate; machining a micro-pit array on the surface of the copper alloy substrate, wherein the micro-pit array has a diameter of 50±5 μm, a depth of 20±2 μm, and a density of 200 pits / cm²; spraying Al2O3-13%TiO2 to form an Al2O3-TiO2 coating having a thickness of 2.0±0.3 μm, a thermal conductivity of 5.8 W / m·K, and a bonding strength of ≥45 MPa; Controlling molten pool fluctuation during continuous casting includes: improving equipment, specifically: adding porous Si3N4 retaining walls to the flow distribution system and setting 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.

2. The method for controlling surface quality defects of thin strip continuous casting stainless steel according to claim 1, characterized in that: The parameters of the porous Si3N4 retaining wall include: pore diameter Φ3mm, porosity 30%, and inclination angle 15°; Parameters of electromagnetic eddy current damper: frequency 50Hz, magnetic field intensity 0.15T, action depth 50mm; PID liquid level control: laser ranging accuracy ±0.1mm, response time <0.5s.

3. The method for controlling surface quality defects of thin strip continuous casting stainless steel according to claim 1 or 2, characterized in that: The parameters of the copper alloy substrate are: material is CuCrZr, and thermal conductivity is 320 W / m·K.

4. The method for controlling surface quality defects of thin strip continuous casting stainless steel according to claim 3, characterized in that: The composition control of molten steel specifically includes: EAF primary refining; LF furnace desulfurization to S≤0.003%; VD furnace vacuum treatment; Se addition to make Se / S≥3; nitrogen blowing alloying.

5. The method for controlling surface quality defects of thin strip continuous casting stainless steel according to claim 1, characterized in that: During the detection of molten pool fluctuation, when the molten pool fluctuation change △H>±1.5mm is satisfied, the PID stopper rod adjustment is activated.

6. The method for controlling surface quality defects of thin strip continuous casting stainless steel according to claim 1, characterized in that: After the Al2O3-TiO2 coating is formed during the crystallization roller treatment, it is preheated to 250°C under argon protection.

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