A non-magnetic stainless steel substrate with high magnetic shielding effectiveness and a preparation method thereof

Abstract

The application relates to the technical field of stainless steel, in particular to a high-magnetic-shielding-performance non-magnetic stainless steel base material and a preparation method thereof, which comprises the following components: 0.07%-0.12% of C, 15.0%-18.3% of Mn, 16.1%-16.5% of Cr, 4.3%-5.1% of Ni, 0.15%-0.20% of N, 0.6%-0.8% of Cu, and the balance of Fe and other impurity elements; Cr eq / Ni eq =(Cr+Mo+1.5Si) / (Ni+0.5Mn+30C+30N+0.5Cu), and Cr eq / Ni eq =1.02-1.05, the high-magnetic-shielding-performance non-magnetic stainless steel base material realizes the balance and unification of full austenite structure, high bulk conductivity, high magnetic shielding performance, small relative magnetic permeability fluctuation and stable magnetism, and solves the problems of limited magnetic shielding performance improvement, large relative magnetic permeability fluctuation and unstable magnetic shielding performance.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology, and in particular to a non-magnetic stainless steel substrate with high magnetic shielding effectiveness and its preparation method. Background Technology

[0002] Non-magnetic stainless steel is an austenitic stainless steel with good magnetic shielding performance. It can be used as a high-end shielding material to isolate external magnetic fields, reduce magnetic field penetration, prevent signal distortion, protect sensitive components from magnetization, and block electromagnetic interference to ensure the stable operation of communication systems. It plays an irreplaceable role in many high-end fields such as electronic communication, energy engineering, national defense and aviation, medical care, and marine engineering.

[0003] The magnetic shielding effectiveness of non-magnetic stainless steel is mainly related to the material's relative permeability and bulk conductivity. The higher the bulk conductivity, the greater the reflection loss, and the better the shielding effect against high-frequency electromagnetic waves. On the other hand, the higher the relative permeability, the greater the absorption loss, and the better the shielding effect against low-frequency magnetic fields. However, the parameters of relative permeability and bulk conductivity of traditional non-magnetic stainless steel are relatively low, which results in very limited improvement in the magnetic shielding effectiveness of non-magnetic stainless steel.

[0004] In existing technologies, the magnetic shielding effectiveness of non-magnetic stainless steel is mainly improved by increasing the relative permeability (which provides magnetic shielding by absorbing electromagnetic waves). However, a higher relative permeability can easily lead to magnetic saturation, and the magnetic shielding effect of stainless steel will deteriorate after magnetic saturation. Relying solely on increasing the relative permeability has limited effect on improving the magnetic shielding effectiveness of non-magnetic stainless steel. In addition, existing non-magnetic stainless steel also suffers from large fluctuations in relative permeability, resulting in unstable magnetism and unstable magnetic shielding effectiveness.

[0005] The improvement of the bulk conductivity of non-magnetic stainless steel mainly relies on increasing the amount of highly conductive elements such as nickel and copper. However, nickel and copper are both expensive, which will lead to a significant increase in cost and may also lead to the deterioration of the mechanical properties of non-magnetic stainless steel. For example, excessive copper content will increase the risk of hot brittleness, which may cause the stainless steel material to crack during hot rolling during processing. It will also increase the risk of fluctuation in the relative magnetic permeability of non-magnetic stainless steel, which may lead to problems such as unstable magnetic properties and unstable magnetic shielding effectiveness.

[0006] There is no existing research that can simultaneously address the limited improvement in magnetic shielding effectiveness of non-magnetic stainless steel, as well as the large fluctuations in relative permeability and the instability of magnetic shielding effectiveness. Summary of the Invention

[0007] In response to the problems raised in the background art, the purpose of this invention is to propose a non-magnetic stainless steel substrate with high magnetic shielding effectiveness. By increasing the Mn content to dominate the bulk conductivity improvement mechanism of non-magnetic stainless steel, reducing the dependence on Cu content, and reducing the amount of Ni, a balance and unity is achieved in non-magnetic stainless steel with a full austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, small relative permeability fluctuation, and stable magnetism. This solves the problems of limited improvement in magnetic shielding effectiveness and large relative permeability fluctuation and unstable magnetic shielding effectiveness of existing non-magnetic stainless steel.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned non-magnetic stainless steel substrate with high magnetic shielding effectiveness. The prepared non-magnetic stainless steel substrate with high magnetic shielding effectiveness has high bulk conductivity, small relative permeability fluctuation, and high and stable magnetic shielding effectiveness, thus solving the problems of limited improvement in magnetic shielding effectiveness and large relative permeability fluctuation and unstable magnetic shielding effectiveness of existing non-magnetic stainless steel.

[0009] To achieve the above objectives, this invention proposes a non-magnetic stainless steel substrate with high magnetic shielding effectiveness, comprising the following components by mass percentage: C: 0.07%~0.12%, Mn: 15.0%~18.3%, Cr: 16.1%~16.5%, Ni: 4.3%~5.1%, N: 0.15%~0.20%, Cu: 0.6%~0.8%, with the balance being Fe and other impurity elements; wherein, Cr... eq / Ni eq Calculate using the following formula:

[0010] Cr eq / Ni eq =(Cr+Mo+1.5Si) / (Ni+0.5Mn+30C+30N+0.5Cu), where Cr, Mo, Si, Ni, Mn, C, N, and Cu are all expressed as mass percentages, and satisfy Cr eq / Ni eq =1.02~1.05.

[0011] Optionally, the non-magnetic stainless steel substrate with high magnetic shielding efficiency comprises the following components by mass percentage: C: 0.08%~0.10%, Mn: 16.5%~17.5%, Cr: 16.2%~16.4%, Ni: 4.6%~4.9%, N: 0.16%~0.18%, Cu: 0.65%~0.75%, with the balance being Fe and other impurity elements.

[0012] This invention also proposes a method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness, used to prepare a non-magnetic stainless steel substrate with high magnetic shielding effectiveness as described in any of the above-mentioned methods, comprising the following steps: Step S1, preparing raw materials according to the composition and amount of the non-magnetic stainless steel substrate with high magnetic shielding effectiveness, and sequentially passing the raw materials through electric furnace melting, AOD refining and LF refining to obtain molten steel with the target composition; wherein, in the AOD refining step: during the decarburization period, an Ar / O2 mixed gas is blown in, wherein the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (2:1)~(4:1); decarburization is carried out to C≤0.05% by mass percentage; during the reduction period, Ar is blown in from the bottom for stirring, and the composition of the molten steel is analyzed in real time using a laser-induced breakdown spectrometer and the Cr is calculated. eq / Ni eq According to Cr eq / Ni eq Fine-tuning is achieved by adding iron-chromium alloy or iron-nickel alloy to dynamically control Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation value is within ±0.010; Step S2, continuous casting process: the molten steel is continuously cast to obtain a billet; Step S3, hot rolling process: the billet is hot rolled to obtain a rough product; Step S4, pickling process: the rough product is pickled to obtain a non-magnetic stainless steel substrate.

[0013] Optionally, in step S1, the flow rate of the bottom-blown Ar is controlled at 0.10~0.15 Nm. 3 / t·min.

[0014] Optionally, in the LF refining step, Ni cored wire is fed at a feeding speed of 15 m / min to 25 m / min; chromium nitride is added to fine-tune the N content in order to dynamically control the Cr content. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010; LF refining is terminated when S≤0.003% by mass percentage.

[0015] Optionally, in step S2, the molten steel is injected into a crystallizer for continuous casting, an electromagnetic brake is used for stirring in the crystallizer, and dynamic light pressure is applied at the end of the solidification of the molten steel; the current of the electromagnetic brake is 350A~450A and the frequency is 2.5Hz~3.5Hz; the reduction amount of the dynamic light pressure is 7mm~9mm.

[0016] Optionally, in step S3, the billet is subjected to five passes of rough rolling and eight passes of finish rolling to obtain a rough product; during the rough rolling, the single-pass reduction rate in the first four passes is 23%~38%, while the reduction rate in the fifth pass is set to 39%~45%.

[0017] Optionally, during the finishing rolling, the rolling temperature T is set using the following formula during the fifth finishing rolling pass: T = 865 - 10 × (Mn content × 100 - 16), where the Mn content is expressed as a mass percentage.

[0018] Optionally, in step S4, the crude product is sequentially subjected to acid washing with nitric acid solution and acid washing with a composite acid solution, wherein the composite acid solution is a mixture of citric acid and tartaric acid; wherein the molar ratio of citric acid and tartaric acid is (2:1) to (4:1); the temperature for acid washing with the composite acid solution is 55℃ to 65℃, and the acid washing time is 20s to 30s.

[0019] Optionally, in step S4, after the crude product is pickled with the composite acid solution, the crude product is further passivated with a passivating solution.

[0020] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0021] The high magnetic shielding effectiveness non-magnetic stainless steel substrate of the present invention improves the magnetic shielding effectiveness of non-magnetic stainless steel by increasing the Mn content, which dominates the bulk conductivity enhancement mechanism of non-magnetic stainless steel. This reduces the dependence of existing non-magnetic stainless steels on high Cu content when improving their bulk conductivity, and can reduce the amount of expensive Ni element used while ensuring the basic performance of non-magnetic stainless steel. Simultaneously, by increasing the Cr content... eq / Ni eq The Cr content was precisely controlled within the range of 1.02 to 1.05 during the preparation process through precise dynamic control. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010, resulting in small fluctuations in the relative permeability of the non-magnetic stainless steel substrate, stable magnetism, and stable magnetic shielding performance. Ultimately, this invention achieves this through high Mn content, low Cu content, low Ni content, and precise control of Cr... eq / Ni eq The synergistic approach achieves a balance and unity between the all-austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, and small fluctuations in relative permeability and stable magnetic properties of non-magnetic stainless steel. This solves the problem that existing technologies cannot simultaneously address the limited improvement in magnetic shielding effectiveness and the large fluctuations in relative permeability and unstable magnetic shielding effectiveness of non-magnetic stainless steel. Attached Figure Description

[0022] Figure 1 Macroscopic images of center segregation in cast billets from embodiments and comparative examples of the non-magnetic stainless steel substrate of the present invention are shown; wherein, Figure 1 (a) is a macroscopic image of the center segregation of the billet in Example 1. Figure 1 (b) is a macroscopic image of the center segregation of the billet in Comparative Example 8;

[0023] Figure 2 This is a surface quality sample image of the non-magnetic stainless steel substrate of the present invention; wherein, Figure 2 (a) is a surface quality sample diagram of Example 1. Figure 2 (b) is a surface quality sample diagram of Comparative Example 9. Detailed Implementation

[0024] This invention proposes a non-magnetic stainless steel substrate with high magnetic shielding efficiency, comprising the following components by mass percentage: C (carbon): 0.07%~0.12%, Mn (manganese): 15.0%~18.3%, Cr (chromium): 16.1%~16.5%, Ni (nickel): 4.3%~5.1%, N (nitrogen): 0.15%~0.20%, Cu (copper): 0.6%~0.8%, with the balance being Fe (iron) and other impurity elements;

[0025] Among them, Cr eq / Ni eq The ratio of Cr equivalent to Ni equivalent is calculated using the following formula:

[0026] Cr eq / Ni eq =(Cr+Mo+1.5Si) / (Ni+0.5Mn+30C+30N+0.5Cu), where Cr, Mo (molybdenum), Si (silicon), Ni, Mn, C, N, and Cu are all expressed as mass percentages, and Cr satisfies... eq / Ni eq =1.02~1.05.

[0027] This invention, by increasing the Mn content and designing it between 15.0% and 18.3%, can effectively improve the bulk conductivity of non-magnetic stainless steel substrates, thereby enhancing their magnetic shielding effectiveness. Furthermore, it reduces the amount of expensive Ni element used while maintaining the basic properties of non-magnetic stainless steel, effectively lowering production costs. Typically, at low concentrations (Mn content less than 5%), Mn atoms, as a solute, scatter electrons, thus reducing bulk conductivity. However, the inventors' research has shown that when the Mn content exceeds the critical value of 15%, its mechanism of action undergoes a fundamental change, including electron donor effects and lattice ordering effects. On the one hand, the 3d... 5High-spin states provide a large number of delocalized electrons in the austenite lattice, significantly increasing the free electron concentration and forming an "electron gas," which directly improves bulk conductivity. On the other hand, high concentrations of Mn cause the solid solution to shift from short-range order to long-range order, reducing lattice distortion and grain boundary scattering, increasing the mean free path of electrons, thereby improving bulk conductivity. Experiments by the inventors have demonstrated that the bulk conductivity of the non-magnetic stainless steel substrate with high magnetic shielding effectiveness described in this invention is increased to 8.3% IACS (International Annealed Copper Standard), while the bulk conductivity of traditional 304 stainless steel is only 2.5% IACS (International Annealed Copper Standard).

[0028] By designing the Cu content between 0.6% and 0.8%, the corrosion resistance of non-magnetic stainless steel can be improved to a certain extent, and the bulk conductivity can be enhanced, thereby improving the magnetic shielding effectiveness of non-magnetic stainless steel. At the same time, it can avoid the increased risk of hot brittleness caused by excessive Cu content (when the Cu content is ≥1%, a low-melting-point Cu-rich phase is easily formed at the hot working temperature, which can easily lead to hot rolling cracking of the non-magnetic stainless steel base) and the increased risk of relative magnetic permeability fluctuation (Cu is not a strongly magnetic element, but when the Cu content is ≥1%, it can easily induce local segregation, which indirectly affects the uniformity of the microstructure of non-magnetic stainless steel, thereby increasing the risk of relative magnetic permeability fluctuation).

[0029] Non-magnetic stainless steel is an austenitic stainless steel, while δ-ferrite (which is magnetic) is a solid solution formed by dissolving other elements in δ-ferrite. It has a body-centered cubic structure and is magnetic. The stability of δ-ferrite or austenite at high temperatures depends on the Gibbs free energy of the system. Cr eq (Cr equivalent) and Ni eq (Ni equivalent) is essentially a quantification of the contribution of each alloying element to the free energy of austenite / δ-ferrite, achieved through precise control of Cr. eq and Ni eq The ratio can suppress the precipitation of δ-ferrite and keep the content of δ-ferrite in a relatively stable state (when Cr eq / Ni eq When δ ferrite is less than 1.02, insufficient δ ferrite leads to poor thermoplasticity, thus increasing the tendency for hot rolling cracking. Conversely, when Cr... eq / Ni eq When the ferrite content is greater than 1.05, the ability to form ferrite is enhanced, leading to insufficient austenite stability, increased δ-ferrite content, and easier precipitation of the highly magnetic δ-phase, thus resulting in increased fluctuations in relative permeability. This invention utilizes Cr... eq and Ni eqBy precisely controlling the ratio between 1.02 and 1.05, the content of δ-ferrite and austenite in the non-magnetic stainless steel substrate can achieve an optimal balance. This ensures processing stability while maintaining the non-magnetic requirement of non-magnetic stainless steel, avoiding increased fluctuations in relative permeability, and providing stable magnetic shielding performance. Furthermore, it ensures that non-magnetic stainless steel substrates prepared in different batches also possess stable magnetic shielding performance. Experiments conducted by the inventors have demonstrated that the relative permeability of the high magnetic shielding performance non-magnetic stainless steel substrate described in this invention is ≤1.003, with a fluctuation range within ±0.0002. In contrast, traditional stainless steel materials, due to the lack of Cr... eq / Ni eq Precise control is difficult to achieve, as it is difficult to precisely control the stability of the δ-ferrite content. This results in the relative permeability fluctuation range generally being controlled within ±0.002, leading to magnetic instability and an unstable magnetic shielding effect.

[0030] This invention improves the magnetic shielding effectiveness of non-magnetic stainless steel by increasing the Mn content, which is the dominant mechanism for enhancing the bulk conductivity. It reduces the dependence of existing non-magnetic stainless steels on high Cu content when improving their bulk conductivity, and can reduce the use of expensive Ni elements while maintaining the basic properties of non-magnetic stainless steel. Simultaneously, it increases the Cr content... eq and Ni eq The ratio is precisely controlled between 1.02 and 1.05, resulting in minimal fluctuations in the relative permeability of the non-magnetic stainless steel substrate and stable magnetism, thus providing stable magnetic shielding performance. Ultimately, this invention achieves this through high Mn content, low Cu content, low Ni content, and precise control of Cr... eq and Ni eq The synergistic effect of this invention achieves a balance and unity between the all-austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, and small fluctuations in relative permeability and stable magnetism of non-magnetic stainless steel. This solves the problem that existing technologies cannot simultaneously address the limited improvement in magnetic shielding effectiveness of non-magnetic stainless steel and the large fluctuations in relative permeability and unstable magnetic shielding effectiveness. Experiments conducted by the inventors have demonstrated that the magnetic shielding effectiveness of the non-magnetic stainless steel substrate of this invention reaches over 60dB (1MHz), while the magnetic shielding effectiveness of traditional stainless steel is less than 45dB (1MHz).

[0031] It should be noted that Mo and Si elements are produced during the steelmaking process of stainless steel substrates. The Si content is generally between 0.3% and 0.5%, while the Mo content is relatively small. In actual calculations of Cr... eq / Ni eq Generally, the Mo content can be considered as 0% or calculated based on the actual measurement results. The other impurity elements include any one or more of the trace elements such as molybdenum (Mo), silicon (Si), sulfur (S), phosphorus (P), lead (Pb), and tin (Sn).

[0032] Preferably, the non-magnetic stainless steel substrate with high magnetic shielding efficiency comprises the following components by mass percentage: C: 0.08%~0.10%, Mn: 16.5%~17.5%, Cr: 16.2%~16.4%, Ni: 4.6%~4.9%, N: 0.16%~0.18%, Cu: 0.65%~0.75%, with the balance being Fe and other impurity elements.

[0033] Mn is a strong austenitic stabilizer. When the Mn content is too low (e.g., below 15%), the mechanism of action of Mn is not fundamentally changed, making it difficult to improve the bulk conductivity of non-magnetic stainless steel substrates. When the Mn content is between 15.0% and 18.3%, the bulk conductivity of non-magnetic stainless steel substrates can be effectively improved through electron donor effect and lattice ordering effect. However, when the Mn content is too high (greater than 18.3%), firstly, it will cause a sharp increase in the deformation resistance of the non-magnetic stainless steel substrate: Excessive Mn content significantly increases the material's high-temperature strength and deformation resistance, making hot rolling difficult, increasing roller load, and resulting in a thicker hot-rolled finished product (i.e., the non-magnetic stainless steel substrate), which is unfavorable for manufacturing thinner non-magnetic stainless steel substrates. Secondly, it will increase the hot brittleness tendency of the non-magnetic stainless steel substrate: at hot rolling temperatures, excessively high Mn content will significantly reduce the material's high-temperature plasticity, making it extremely easy to generate hot cracks at austenite grain boundaries, leading to a surge in the risk of rolling cracking and a significant reduction in yield. Thirdly, it will lead to... The stability of the surface passivation film on the substrate decreases: the stability of Mn oxides (MnO, Mn2O3) is much lower than that of Cr oxides (Cr2O3). Excessive Mn content leads to an increased proportion of Mn oxides in the surface passivation film, thus reducing its stability and decreasing the pitting corrosion resistance of the non-magnetic stainless steel. Fourthly, excessive Mn content also exacerbates Mn segregation, easily reducing the uniformity of the non-magnetic stainless steel material. The higher the Mn content, the more severe the Mn concentration difference (i.e., segregation) between the center and edge of the billet during solidification, resulting in greater fluctuations in the relative magnetic permeability between the center and edge of the stainless steel billet, leading to magnetic instability of the non-magnetic stainless steel substrate. Therefore, this invention preferably uses an Mn content of 16.5%~17.5%, which helps to improve the bulk conductivity of the non-magnetic stainless steel substrate while ensuring good processing performance and material properties.

[0034] This invention also proposes a method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness, used to prepare a non-magnetic stainless steel substrate with high magnetic shielding effectiveness as described in any one of the above claims, comprising the following steps and procedures:

[0035] Step S1: Prepare raw materials according to the composition and amount of the non-magnetic stainless steel substrate with high magnetic shielding efficiency, and sequentially process the raw materials through electric furnace melting, AOD refining (argon-oxygen furnace refining) and LF refining (ladle refining furnace refining) to obtain molten steel with the target composition.

[0036] In the AOD refining step:

[0037] During the decarbonization period, an Ar / O2 mixed gas is blown in, wherein the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (2:1) to (4:1); preferably, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 3:1.

[0038] By mass percentage, decarbonization is carried out to C ≤ 0.05%;

[0039] During the reduction period, Ar was blown from the bottom and stirred. The composition of the molten steel was analyzed in real time using laser-induced breakdown spectroscopy (LIBS), and the Cr content was calculated. eq / Ni eq According to Cr eq / Ni eq Fine-tuning is achieved by adding iron-chromium alloy or iron-nickel alloy to dynamically control Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010;

[0040] Step S2, continuous casting process: The molten steel is continuously cast to obtain a billet;

[0041] Step S3, hot rolling process: The cast billet is hot rolled to obtain a rough product;

[0042] Step S4, pickling process: The crude product is pickled to obtain a non-magnetic stainless steel substrate.

[0043] This invention utilizes laser-induced breakdown spectrometry to perform real-time analysis and calculation of the Cr content of the molten steel during the reduction phase of the AOD refining process. eq / Ni eq According to Cr eq / Ni eq Fine-tuning can be achieved by adding iron-chromium alloy or iron-nickel alloy, thereby realizing dynamic control of Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010, Cr eq / Ni eqThe fluctuation is small, which can achieve a stable relative permeability of the non-magnetic stainless steel substrate and avoid increased fluctuations in relative permeability. The prepared non-magnetic stainless steel substrate meets the requirements of Cr. eq / Ni eq =1.02~1.05, and has stable magnetic shielding performance. Moreover, the non-magnetic stainless steel substrates prepared in different batches can also have stable magnetic shielding performance.

[0044] Among them, laser-induced breakdown spectrometry (LIBS) enables online, real-time, and multi-element synchronous analysis (hundreds of analyses per second, with a component analysis speed ≤15 seconds). Traditional spectrometers are slow (minutes on the order of minutes) and cannot provide real-time feedback. LIBS provides the basis for data analysis (it should be noted that Mo and Si can also be measured in real-time using LIBS to calculate Cr). eq / Ni eq ), thereby enabling the control of Cr eq / Ni eq Precise control. It has been proven that real-time online analysis of the composition of the molten steel using laser-induced breakdown spectrometry, and based on Cr... eq / Ni eq Fine-tuning is achieved by adding iron-chromium alloy or iron-nickel alloy to dynamically control Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010, achieved through precise adjustment of Cr. eq / Ni eq This allows for a 100% pass rate in the preparation of non-magnetic stainless steel substrate components, whereas traditional processes involve manual sampling and analysis, as well as manual adjustment of the content of each component, such as Cr. eq / Ni eq The fluctuation value can generally only be controlled within ±0.05, and the qualified rate of the non-magnetic stainless steel substrate is ≤85% (wherein, the qualified rate of the component refers to the proportion of samples that meet the designed content range of the components of the final non-magnetic stainless steel substrate after sampling and testing. For example, if 100 non-magnetic stainless steel substrate samples are sampled and tested, and 85 samples are qualified in all components, then the qualified rate of the component is 85%).

[0045] This invention designs the composition of non-magnetic stainless steel substrate to enhance the bulk conductivity of non-magnetic stainless steel by increasing the Mn content, thereby improving its magnetic shielding effectiveness. It also reduces the dependence of existing non-magnetic stainless steels on high Cu content to improve their bulk conductivity, and reduces the use of expensive Ni elements while maintaining the basic properties of the non-magnetic stainless steel. Ultimately, this invention achieves this through high Mn content, low Cu content, low Ni content, and precise control of Cr content. eq and Ni eq The ratio of synergistic properties achieves a balance and unity between the all-austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, and small fluctuations in relative magnetic permeability and stable magnetism of non-magnetic stainless steel.

[0046] It should be noted that during the decarburization period of the AOD refining, the Ar / O2 mixed gas is blown in to decarburize to C ≤ 0.05% (by mass percentage), which provides a basis for subsequent component content adjustment. During the reduction period of the AOD refining and the LF refining, the C content is finely adjusted again by adding iron-chromium alloy or iron-nickel alloy (which generally contain carbon elements), so that the C content in the final molten steel reaches 0.07%~0.12% (by mass percentage).

[0047] To further explain, in step S1, the flow rate of the bottom-blown Ar is controlled at 0.10 Nm. 3 / t·min~0.15Nm 3 / t·min;

[0048] This invention employs bottom-blown Ar to perform strong stirring of the molten steel during real-time analysis, wherein the flow rate of the bottom-blown Ar is increased to 0.10 Nm³. 3 / t·min~0.15Nm 3 / t·min (the preferred flow rate of the bottom-blown Ar is 0.12 Nm³) 3 / t·min), ensuring the mixing time of the molten steel is <2min, guaranteeing the homogeneity of each component in the molten steel, eliminating local representativeness errors at LIBS analysis points, and ensuring that the real-time LIBS analysis results of the molten steel composition during the reduction period can represent the entire molten pool, thereby achieving the control of Cr during the preparation process. eq / Ni eq Precise control. The inventors' experiments have proven that the uniformity of the content of each component in the molten steel is within ±0.05% (that is, the fluctuation range of the content of each component in the molten steel, expressed as a percentage by mass, is within ±0.05%).

[0049] Furthermore, the other process parameters in the AOD refining step can be designed with reference to existing technologies or according to actual needs.

[0050] To further explain, in the LF refining step, Ni cored wire is fed at a feed rate of 15 m / min to 25 m / min; chromium nitride is added to fine-tune the N content in order to dynamically control the Cr content. eq / Ni eq Between 1.03±0.01; by mass percentage, LF refining is terminated when S≤0.003%.

[0051] In the LF refining step, Ni cored wire is fed at a feed rate of 15 m / min to 25 m / min to precisely replenish Ni, controlling the Ni content to be between 4.7 ± 0.1% by mass. Furthermore, the N content is fine-tuned by adding chromium nitride to control the N content to be between 0.17 ± 0.005% by mass, achieving high-precision control of Ni and N content, and dynamically controlling Cr content. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010, thus achieving precise control of Cr. eq / Ni eq The results were between 1.02 and 1.05. To stabilize the relative permeability of the non-magnetic stainless steel substrate and avoid increasing fluctuations in relative permeability, the prepared non-magnetic stainless steel substrate can have stable magnetic shielding performance. Moreover, the non-magnetic stainless steel substrates prepared in different batches can also have stable magnetic shielding performance.

[0052] Preferably, in the LF refining step, Ni cored wire is fed at a feeding speed of 20 m / min.

[0053] By setting the feeding speed of the Ni-core wire to a low speed (15m / min~25m / min, preferably 20m / min), mechanical transmission fluctuations can be effectively suppressed (traditional methods use high-speed feeding speeds >30m / min, which easily leads to slippage or vibration due to inertia, affecting feeding stability), ensuring that the Ni-core wire is fed into the molten steel at a uniform speed, thereby reducing Ni content fluctuations. Experiments by the inventors have proven that this invention, preferably using a feeding speed of 20m / min for the Ni-core wire, can reduce Ni content (by mass percentage) fluctuations to ±0.05% (in traditional high-speed feeding processes, Ni content fluctuations range from ±15%), achieving precise Ni replenishment and further enabling precise dynamic control of Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010, thus precisely controlling Cr. eq / Ni eq Between 1.02 and 1.05, Cr eq / Ni eq Control precision is improved by at least 3 times.

[0054] Furthermore, since the high magnetic shielding efficiency of the non-magnetic stainless steel substrate described in this invention has a high Mn content, based on the diffusion kinetics of high manganese steel, a high Mn content (e.g., around 17%) will reduce the Ni diffusion coefficient. By setting the Ni cored wire feeding speed to 20 m / min, the melting time of the Ni alloy can be extended, the alloy diffusion optimized, and splash loss reduced. Low-speed feeding can extend the residence time of the Ni cored wire in the molten steel, allowing the Ni element to diffuse fully. The inventors' research has proven that 20 m / min... The optimal feeding speed (n) allows the Ni cored wire to have the best melting and diffusion time in the molten steel, approximately 12 minutes. This improves the melting uniformity of the Ni alloy in the molten steel by 40%, preventing local enrichment or depletion of Ni. Traditional high-speed feeding (>30 m / min) easily causes molten steel splashing, leading to alloy oxidation loss. This invention uses a low feeding speed of 20 m / min, and can be used in conjunction with a vertical guide tube (inclination angle <1.5°) to accurately inject the Ni cored wire into the molten steel vortex. The splash loss rate can be reduced from 15% in the traditional process to less than 5%.

[0055] This invention ensures Ni homogenization by setting the feeding speed of the Ni cored wire to a low speed (20m / min), thus avoiding localized enrichment or depletion of Ni and the resulting Cr degradation. eq / Ni eq Out of control, thus causing Cr eq / Ni eq The result was precisely controlled between 1.02 and 1.05, effectively solving the problem of homogenization of alloying elements in high-manganese environments in existing technologies.

[0056] Specifically, in the LF refining step, laser-induced breakdown spectroscopy (LIBS) is used to analyze the composition of the molten steel in real time and calculate Cr. eq / Ni eq To dynamically control Cr eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010.

[0057] Furthermore, other process parameters in the LF refining step can be designed with reference to existing technologies or according to actual needs.

[0058] To further explain, in step S2, the molten steel is injected into a crystallizer for continuous casting, an electromagnetic brake is used for stirring in the crystallizer, and dynamic light pressure is applied at the end of the solidification of the molten steel; the current of the electromagnetic brake is 350A~450A and the frequency is 2.5Hz~3.5Hz; the reduction amount of the dynamic light pressure is 7mm~9mm.

[0059] Because the high magnetic shielding efficiency of the non-magnetic stainless steel substrate described in this invention has a high Mn content, based on the solidification characteristics of high manganese steel, when the Mn content is high, the tendency of Mn segregation is aggravated, the solidification range is widened, and the solidification shrinkage is aggravated (the root cause of segregation is that when the molten steel is injected into the crystallizer at high speed from the nozzle, a strong impact stream is generated, which will wash away the solidification front (between dendrites), and carry the molten steel rich in solutes such as Mn and P towards the center of the billet, resulting in solute enrichment in the final solidification area and the formation of central segregation). This will reduce the uniformity of the non-magnetic stainless steel material, which will easily lead to an increase in the relative magnetic permeability fluctuation between the center and the edge of the billet.

[0060] This invention employs an electromagnetic brake for stirring, applying a low-frequency strong magnetic field within the crystallizer. When conductive molten steel flows through this magnetic field, an electromagnetic force opposite to the flow direction is induced, effectively weakening the kinetic energy of the flow stream and smoothing the injection flow of the molten steel, thereby suppressing Mn convection segregation. Combined with a dynamic light-pressure process, the liquid core can be squeezed to compensate for solidification shrinkage. By using an electromagnetic brake with a current intensity of 350A~450A and a frequency of 2.5Hz~3.5Hz for stirring, the Mn segregation index of the cast billet can be ≤1.03 (the segregation index of traditional high-manganese steel is ≥1.25), and the central porosity of the cast billet can be reduced by 90%.

[0061] Preferably, the electromagnetic brake has a current of 400A and a frequency of 3Hz, and the dynamic light pressure is applied with a deflection of 8mm. The 400A current determines the strength of the magnetic field applied by the electromagnetic brake, ensuring sufficient braking force: if the current is too small, the magnetic field is too weak, resulting in insufficient braking effect; if the current is too large, it can easily lead to abnormal solidification of the molten steel surface. By setting the frequency of the electromagnetic brake to 3Hz, new unstable flows in the molten steel can be avoided, and the magnetic field penetration depth can be prevented from being too shallow, ensuring effective braking throughout the entire flow depth.

[0062] Furthermore, other process parameters in the continuous casting process can be designed with reference to existing technologies or according to actual needs.

[0063] To further explain, in step S3, the billet is subjected to five passes of rough rolling and eight passes of finish rolling to obtain a rough product; during the rough rolling, the single-pass reduction rate in the first four passes is 23%~38%, while the reduction rate in the fifth pass is set to 39%~45%. Preferably, the reduction rate in the fifth pass is set to 40%.

[0064] This invention achieves effective fragmentation of the δ phase through a large deformation roughing step, thereby improving the non-magnetic nature of the non-magnetic stainless steel substrate: In the first four roughing passes, the single-pass reduction rate is 23%~38%, causing microcracks and interfacial debonding in the δ phase. In the fifth roughing pass, the reduction rate reaches 39%~45% (preferably 40%), providing a critical shear strain (ε≥2.0), which generates ultra-high shear stress (≥250MPa), far exceeding the strength limit of the δ phase (i.e., δ ferrite) (approximately 150MPa). This causes the pre-damaged δ phase to undergo relatively complete brittle fracture under strong shear (the δ phase is a hard and brittle phase). The δ phase (hardness reaches HV350) is absorbed and melted by the austenitic matrix phase (γ phase). Furthermore, the δ phase and γ phase exhibit significant differences in plasticity (δ phase elongation <10%, γ phase >40%). Under large deformation, strain concentration occurs at the interface between the two, causing the δ phase to debond from the matrix and fragment into dispersed fragments ≤1μm. This allows control over the grain size of non-magnetic stainless steel, preventing increased fluctuations in relative permeability due to coarse grains (coarse grains mean fewer grain boundaries and larger magnetic domains; grain boundaries are important barriers hindering electromagnetic waves and magnetic domain movement; fewer grain boundaries result in lower magnetic loss, and large magnetic domains are difficult to flip at high frequencies, leading to an insensitive magnetic loss mechanism). Experiments by the inventors have demonstrated that the residual δ phase after large deformation rough rolling is ≤0.2% (compared to ≥3% under traditional rough rolling processes), effectively improving the non-magnetic nature of the non-magnetic stainless steel substrate.

[0065] To further explain, the reduction rate of the five roughing passes gradually increases. That is, the reduction rate of the first roughing pass is relatively low, and the reduction rates of the second to fifth roughing passes are all higher than those of the previous roughing pass. This can prevent the center of the billet from delamination. In addition, the relatively low reduction rate is preferentially used in roughing, which can reduce the amount of heat generated and make the temperature drop controllable. The reduction rate is gradually increased in subsequent roughing passes, so that a large amount of deformation heat can be generated by large deformation, which can effectively make up for the heat loss in the subsequent roughing process.

[0066] To further explain, the entire process of five rough rolling passes is carried out under high pressure of 28 MPa for descaling, which helps to remove oxide scale.

[0067] To further explain, during the finishing rolling process, the rolling temperature T is set using the following formula during the fifth finishing rolling pass: T = 865 - 10 × (Mn content × 100 - 16), where the Mn content is expressed as a mass percentage.

[0068] Because the high magnetic shielding efficiency non-magnetic stainless steel substrate of this invention has a high Mn content, the recrystallization temperature of austenite decreases by 15°C for every 1% increase in Mn content. Through extensive research, the inventors derived the formula T = 865 - 10 × (Mn content × 100 - 16), which enables dynamic matching of the rolling temperature window. This formula can dynamically adjust the rolling temperature of the fifth finishing pass according to the Mn content, ensuring that austenite remains in the recrystallization region and avoiding stress concentration caused by low-temperature rolling. Experiments have shown that the high magnetic shielding efficiency non-magnetic stainless steel substrate of this invention can achieve crack-free rolling (while traditional finishing processes result in a crack rate ≥10% for high-manganese steel).

[0069] Furthermore, during the finishing rolling process, the initial rolling temperature is 1050℃±10℃, and the final rolling temperature is 840±5℃. Further, during the finishing rolling process, the reduction rate per pass is 35%~52%. Further, in the eight-pass finishing rolling process, the reduction rate of the first five passes is greater than the reduction rate of the sixth to eighth passes. Specifically, due to the high reduction rate of the first four finishing rolling passes, the allowable rolling temperature is relatively high (rolling temperature > 865 - 10 × (Mn content × 100 - 16) is sufficient) to ensure processing safety and thorough recrystallization. After the large deformation rolling of the first four finishing rolling passes, the original coarse cast austenite grains have been fully broken up and dynamic recrystallization has occurred, forming fine new grains. Therefore, if the rolling temperature of the fifth finishing rolling pass is too high, these newly formed fine grains will rapidly merge and grow (leading to abnormal grain growth). If the rolling temperature is too low, it will cause insufficient recrystallization, severe work hardening, and may lead to excessive rolling force or even cracks. Therefore, this invention uses the formula T = 865 - 10 × (Mn content × 100 - 16) to accurately set the rolling temperature during the fifth finishing rolling pass. Based on the Mn content (the Mn content significantly affects the recrystallization temperature), the optimal temperature window that can suppress grain growth while ensuring smooth recrystallization can be calculated, thus "locking" the already obtained fine-grained structure and preventing it from coarsening. After the "crystallization" of the fifth finishing rolling pass, the main task of the subsequent sixth to eighth finishing rolling passes is to continue to apply deformation and control the plate shape. The precision requirements for rolling temperature are relatively low, and the reduction rate is low, making it less prone to cracking. The rolling temperature can be ≤865-10×(Mn content×100-16).

[0070] Furthermore, other process parameters in the hot rolling process can be designed with reference to existing technologies or according to actual needs.

[0071] To further explain, in step S3, after the billet undergoes five passes of rough rolling and eight passes of finish rolling, a layer-cooling coiling step is required to obtain the rough product. During the layer-cooling coiling step, the cooling rate is controlled: when the rough product is to be a thin plate, the coiling rate is 25°C / s, and the coiling temperature is 360°C; when the rough product is to be a thick plate, the layer-cooling coiling rate is 15°C / s, and the layer-cooling coiling temperature is 375°C.

[0072] To further explain, in step S4, the crude product is sequentially pickled with nitric acid solution and then with a composite acid solution, wherein the composite acid solution is a mixture of citric acid and tartaric acid; wherein the molar ratio of citric acid to tartaric acid is (2:1) to (4:1); the temperature for pickling with the composite acid solution is 55℃ to 65℃, and the pickling time is 20s to 30s.

[0073] Preferably, the molar ratio of citric acid to tartaric acid is 3:1, the temperature for pickling with the composite acid solution is 60°C, and the pickling time is 25 seconds.

[0074] This invention first uses nitric acid solution for pickling to dissolve the relatively loose outer layer of iron oxides (FeO, Fe2O3) in the oxide scale of the crude product, thereby reducing the time required for the composite acid solution to penetrate into the inner layer of the oxide scale to dissolve the stubborn chromium oxide (Cr2O3) and improving the efficiency of the composite acid solution in cleaning chromium oxide.

[0075] The dense chromium oxide in the oxide scale of stainless steel surfaces is a challenge in the pickling process, as chromium oxide is insoluble in most acids. This invention, however, effectively improves the pickling process by using a combination of environmentally friendly citric acid (C6H8O7) and tartaric acid (C4H6O6) to address the insoluble chromium oxide in metal ions such as chromium oxide. 3+ Fe 3+ The complexing ability of the compound can dissolve the stubborn chromium oxide in the oxide scale of the crude product, and can completely replace the hydrofluoric acid (HF) used in traditional pickling, achieving zero fluorine emissions in the pickling process, reducing the safety risks of using HF and protecting the environment.

[0076] Furthermore, this invention, through a fluorine-free pickling process using a composite pickling of citric acid and tartaric acid, can also solve the problems of residual fluoride ions and micro-corrosion on the stainless steel surface caused by traditional HF pickling. Fluoride ions are paramagnetic and can locally change the electromagnetic properties of the material, introducing interference. Moreover, if HF pickling is not properly controlled, it can cause micro-defects such as intergranular corrosion. These micro-defects can scatter electromagnetic waves, reduce surface conductivity, and thus weaken the magnetic shielding effectiveness of non-magnetic stainless steel.

[0077] To be more specific, citric acid and tartaric acid are both organic polycarboxylic acids that can bind to metal ions (such as Cr) by providing multiple coordination sites.3+ Fe 3+ To form stable complexes, citric acid and tartaric acid are used in combination, producing a synergistic effect that results in more stable and structurally complex mixed ligand complexes. Citric acid, a tribasic acid with three carboxyl groups and one hydroxyl group, provides multiple coordination sites and can form stable cyclic chelates with metal ions. Tartaric acid, a dibasic acid with two hydroxyl groups and two carboxyl groups, has two carboxyl groups in its molecular structure that can be esterified by the carboxyl groups of citric acid to obtain a polycarboxylic acid, enhancing the cross-linking effect. When citric acid and tartaric acid are used in combination, they can simultaneously react with the same metal ion (such as Cr). 3+ Fe 3+ The metal ions are coordinated to form mixed complexes with higher stability constants. These mixed complexes have larger ring structures or more stable spatial configurations, which can more tightly "lock" the metal ions, making it difficult for them to reprecipitate or participate in other reactions.

[0078] To further explain, this is achieved through the reaction Cr₂O₃ + 2C₄H₆O₆ → 2[Cr(C₄H₄O₆)₂]. 2- The +3H2O reaction clearly demonstrates the mechanism by which tartaric acid dissolves chromium oxide scale. Tartaric acid converts insoluble Cr2O3 into soluble chromium tartrate complex anions. Simultaneously, the addition of citric acid further stabilizes the entire complex system, preventing its decomposition. Furthermore, citric acid can strongly complex Fe... 3+ Ni 2+ Plasma, in conjunction with other metal oxides, can dissolve them, thus enabling fluoride-free pickling.

[0079] The composite acid solution used in this invention can also remove silicon-containing impurities to a certain extent: under high temperature and high concentration conditions, the combined use of organic acids such as citric acid and tartaric acid can provide a strongly acidic environment, which itself has a partial dissolving effect on SiO2. Citric acid and other organic acids also have a certain removal capacity for certain silicides (such as ferric silicate, composite silicate scale containing Ca and Mg, and free silica particles coexisting with metal oxides). Among these, citric acid and tartaric acid are effective against iron ions (Fe... 3+ ) and calcium ions (Ca 2+ ), magnesium ions (Mg 2+Metal ions such as Mg and Ca have good complexing ability. When the composite acid solution penetrates into the oxide scale or scale layer, it can combine with the iron ions in ferric silicate to form soluble ferric citrate or ferric tartrate complexes. By removing key cations, it disrupts the overall stability of ferric silicate, causing the insoluble ferric silicate structure to become loose and porous, greatly reducing its adhesion. The loose silicate residue is more easily peeled off from the metal substrate in particulate form (not directly dissolved) under the subsequent flow, flushing, or physical stirring of the acid solution, achieving a physical removal effect. For composite silicate scale containing Ca and Mg, the composite acid solution preferentially attacks and complexes Ca. 2+ and Mg 2+ The complex acid solution forms a complex with relatively active metal ions, thereby disintegrating the network structure of the complex silicate scale by removing key cations. This loosens the structure, making it easier for the scale to be peeled off from the metal matrix in particle form under the action of subsequent acid flow, rinsing, or physical stirring, thus achieving physical removal. For free silica particles coexisting with metal oxides, the complex acid solution can efficiently dissolve metal oxides such as Cr2O3 and Fe2O3 surrounding the silica particles, exposing and releasing the bound silica particles. The acidic environment provided by the complex acid solution can cause slight hydration or change the surface charge of the silica particles, thereby reducing the tendency of silica particles to re-attach and helping them to be discharged with the waste liquid.

[0080] In addition, after the complex acid solution dissolves the metal oxides (such as chromium oxide, iron oxide, etc.), the remaining silicides may also become loose, which helps to physically remove them in the subsequent rinsing and washing.

[0081] To further clarify, in the composite acid solution, the concentration of citric acid is 120 g / L and the concentration of tartaric acid is 40 g / L;

[0082] To further clarify, the concentration of the nitric acid solution is 150 g / L to 250 g / L, the temperature during pickling is 45°C, and the pickling time is 35 seconds; the preferred concentration of the nitric acid solution is 200 g / L.

[0083] To further explain, in step S4, after the crude product is pickled with the composite acid solution, the crude product is also passivated with a passivating solution.

[0084] To further clarify, the passivation solution comprises sodium titanate (Na2TiO3, CAS No. 12034-36-5) and hydrogen peroxide (H2O2). The passivation solution is a mixed aqueous solution of sodium titanate and hydrogen peroxide, wherein the concentration of Na2TiO3 is 50 g / L and the concentration of H2O2 is 5 mL / L.

[0085] By passivating the rough product, a self-healing film is generated on the surface of the rough product, so that the scratch repair rate of the non-magnetic stainless steel substrate with high magnetic shielding efficiency prepared by the present invention is >90%.

[0086] In terms of composition design, this invention improves the magnetic shielding effectiveness of non-magnetic stainless steel by increasing the Mn content, which dominates the bulk conductivity enhancement mechanism. This reduces the dependence of existing non-magnetic stainless steels on high Cu content when improving their bulk conductivity, and also reduces the amount of expensive Ni used while maintaining the basic properties of non-magnetic stainless steel. Simultaneously, by increasing the Cr content... eq / Ni eq By precisely controlling the relative permeability between 1.02 and 1.05, the non-magnetic stainless steel substrate exhibits minimal fluctuations in relative permeability and stable magnetism, resulting in stable magnetic shielding effectiveness. This achieves a balance and unity between the all-austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, and minimal fluctuations in relative permeability and stable magnetism of the non-magnetic stainless steel. Since the high-magnetic-shielding-effective non-magnetic stainless steel substrate of this invention has a high Mn content, classifying it as high-manganese non-magnetic steel, this invention incorporates novel and systematic parameter integration and precise control in the manufacturing process, addressing the limitations of existing technologies in simultaneously improving the magnetic shielding effectiveness of non-magnetic stainless steel and the problems of large fluctuations in relative permeability and unstable magnetic shielding effectiveness. The high-magnetic-shielding-effective non-magnetic stainless steel substrate prepared by this invention can meet the high-magnetic-shielding-effectiveness material requirements of advanced manufacturing technologies such as 6G communication shielding covers and nuclear magnetic resonance chambers.

[0087] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0088] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0089] (a) Examples 1-5 and Comparative Examples 1-6:

[0090] 1. Example 1:

[0091] A non-magnetic stainless steel substrate with high magnetic shielding effectiveness comprises the following components by weight percentage:

[0092] C: 0.08%, Mn: 16.8%, Cr: 16.3%, Ni: 4.7%, N: 0.17%, Cu: 0.65%, with the balance being Fe and other impurity elements;

[0093] Among them, Cr eq / Ni eq Calculate using the following formula:

[0094] Cr eq / Ni eq =(Cr+Mo+1.5Si) / (Ni+0.5Mn+30C+30N+0.5Cu), where Cr, Mo, Si, Ni, Mn, C, N, and Cu are all expressed as mass percentages, and satisfy Cr eq / Ni eq =1.02~1.05.

[0095] The preparation method of Example 1 is as follows:

[0096] Step S1: Prepare raw materials according to the composition and dosage of the non-magnetic stainless steel substrate with high magnetic shielding efficiency. Sequentially process the raw materials through electric furnace smelting, AOD refining, and LF refining to obtain molten steel with the target composition. Specifically, in the AOD refining step: during the decarburization period, an Ar / O2 mixed gas is blown in, wherein the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 3:1; decarburization is carried out to C ≤ 0.05% by mass percentage; during the reduction period, bottom-blown Ar is stirred, and the flow rate of bottom-blown Ar is controlled at 0.12 Nm³. 3 / t·min; The composition of molten steel was analyzed in real time using laser-induced breakdown spectroscopy, and the Cr was calculated. eq / Ni eq As a result, according to Cr eq / Ni eq As a result, fine-tuning was performed by adding iron-chromium alloy or iron-nickel alloy to dynamically control Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010; in the LF refining step, Ni cored wire is fed at a feeding speed of 20 m / min, and the Ni content is controlled between 4.7 ± 0.1% by mass; chromium nitride is added to fine-tune the N content, controlling the N content between 0.17 ± 0.005% by mass, and the Cr content is dynamically controlled. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010; LF refining is terminated when S ≤ 0.003% by mass percentage, thereby obtaining molten steel with the target composition;

[0097] Step S2, Continuous casting process: The molten steel is continuously cast to obtain a billet; the molten steel is injected into a crystallizer for continuous casting, and an electromagnetic brake is used to stir the molten steel. Dynamic light pressure is applied at the end of the solidification of the molten steel; the current of the electromagnetic brake is 400A and the frequency is 3Hz; the reduction amount of the dynamic light pressure is 8mm.

[0098] Step S3, Hot Rolling Process: The billet undergoes five passes of rough rolling, eight passes of finish rolling, and layer-cooling coiling to obtain a rough product. The entire five-pass rough rolling process is performed under high-pressure descaling at 28 MPa. The reduction rates for the five rough rolling passes are 23%, 29%, 33%, 38%, and 40%, respectively. The reduction rates for the eight finish rolling passes are 35%, 38%, 40%, 42%, 45%, 48%, 50%, and 52%, respectively. The initial rolling temperature is 1050℃±10℃, and the final rolling temperature is 840±5℃. During the fifth finish rolling pass, the rolling temperature T is set using the following formula: T = 865 - 10 × (Mn content × 100 - 16), where the Mn content is expressed as a mass percentage. Then, layer-cooling coiling is performed at 25℃ / s, with a coiling temperature of 360℃.

[0099] Step S4, Pickling Process: The crude product is sequentially pickled with nitric acid solution, pickled with a composite acid solution, and passivated with a passivating solution to obtain a non-magnetic stainless steel substrate; wherein, the concentration of the nitric acid solution is 200 g / L, the temperature of the nitric acid pickling is 45℃, and the pickling time is 35 s; the composite acid solution is a combination of citric acid and tartaric acid; wherein the concentration of citric acid is 120 g / L, the concentration of tartaric acid is 40 g / L, and the molar ratio of citric acid to tartaric acid is 3:1; the temperature of the composite acid pickling is 60℃, and the pickling time is 25 s; the passivating solution is a mixed aqueous solution of sodium titanate and hydrogen peroxide, wherein the concentration of sodium titanate is 50 g / L, and the concentration of hydrogen peroxide is 5 mL / L.

[0100] 2. Examples 2-5 and Comparative Examples 1-6:

[0101] The difference between Examples 2-5 and Comparative Examples 1-6 and Example 1 lies in the composition content of the non-magnetic stainless steel substrate. The parameters in the preparation methods of Comparative Examples 1-6 are the same as those in Example 1, but the Cr content in Comparative Examples 1-6 is not strictly controlled. eq / Ni eq Between 1.02 and 1.05 and Cr eq / Ni eq The fluctuation range is within ±0.010, and the specific component content design is carried out according to Table 1:

[0102] Table 1. Component content design of Examples 1-5 and Comparative Examples 1-6 (unit: by mass percentage)

[0103] .

[0104] 3. Testing and Result Analysis:

[0105] The bulk conductivity, relative permeability and their fluctuation values, and Cr of the non-magnetic stainless steel substrates prepared in Examples 1-5 and Comparative Examples 1-6 were measured or calculated. eq / Ni eq The fluctuation value, magnetic shielding effectiveness, hot-rolled edge crack rate, and Mn segregation index are shown in Tables 2 and 3 below:

[0106] Among them, the bulk conductivity was measured according to the international standard for annealed copper;

[0107] The relative permeability and its fluctuation values ​​were obtained by repeatedly measuring the same sample at different locations, resulting in a relative permeability sequence μ1, μ2, ..., μ... n The relative permeability fluctuation value is calculated by statistically analyzing the relationship between the standard deviation and the mean of multiple measurements (where N=10 times in Examples 1-5 and Comparative Examples 1-5).

[0108] Cr eq / Ni eq The fluctuation value refers to the value obtained during the preparation process by real-time analysis and calculation of the steel liquid composition using a laser-induced breakdown spectrometer. It can be understood that this value is related to Cr. eq / Ni eq Multiple measurements and calculations were performed, and Cr was finally calculated by statistically analyzing the relationship between the standard deviation and the mean of the multiple measurement results. eq / Ni eq and fluctuation values;

[0109] Cr eq / Ni eq This refers to determining the composition of the final non-magnetic stainless steel product and calculating the Cr content. eq / Ni eq Result value.

[0110] Magnetic shielding effectiveness: The results were obtained by performing N repeated measurements at different locations of the same sample (where N = 10 times in Examples 1-5 and Comparative Examples 1-5).

[0111] Hot-rolled edge crack rate: The percentage of samples with edge cracks out of the total number of samples is calculated by visual inspection. In each embodiment and comparative example of the present invention, the total number of samples is 100.

[0112] Method for determining Mn segregation index: Samples are taken from the center of the cross-section of the billet, ground and polished to a mirror finish, and analyzed by electron probe microanalysis (EPMA). Line scan measurement is used to collect and process the data, and the segregation index result is calculated and determined.

[0113] Table 2 Test results of Examples 1-5

[0114] .

[0115] Table 3 Test results of Comparative Examples 1-6

[0116] .

[0117] As can be seen from the data in Tables 1, 2, and 3, the Mn content in Examples 1-5 is increased to between 15.0% and 18.3%, resulting in higher bulk conductivity and magnetic shielding effectiveness. This reduces the dependence of existing non-magnetic stainless steels on Cu or Ni content when improving their bulk conductivity, reduces the amount of expensive Ni element used, and also reduces Cr content. eq / Ni eq The fluctuation is relatively small, Cr eq / Ni eq Precisely controlled within the range of 1.02 to 1.05, the processing performance is stable, the relative permeability fluctuation is small, and it possesses stable magnetic shielding effectiveness, with a magnetic shielding effectiveness > 66 dB (1 MHz). Specifically, the Mn content in Examples 1, 3, and 4 falls within the optimal window of 16.5% to 17.5% (by mass percentage), and the Cr content... eq / Ni eq With precise control, the non-magnetic stainless steel substrate exhibits the best overall performance (high bulk conductivity, small fluctuation in relative permeability, high magnetic shielding effectiveness, and no processing defects). The Mn content (15.0%) in Example 2 is slightly lower, resulting in slightly inferior bulk conductivity and magnetic shielding effectiveness of the non-magnetic stainless steel substrate. The Mn content (18.3%) in Example 5 is close to the upper limit, and the non-magnetic stainless steel substrate begins to show slight hot working problems (increased hot rolling edge crack rate) and increased Mn segregation tendency.

[0118] The Mn content in Comparative Example 1 is too low, so the bulk conductivity cannot be improved by solid solution with high Mn content, resulting in a serious deficiency in its bulk conductivity and magnetic shielding effectiveness.

[0119] The Mn content in Comparative Example 2 is too low. Although the Cu content in Comparative Example 2 is increased to 1.0%, which can improve the bulk conductivity and magnetic shielding effectiveness to a certain extent, the improvement is low compared to Comparative Example 1. Furthermore, the high Cu content also leads to increased fluctuations in relative permeability, causing hot brittleness, resulting in a significant increase in hot rolling edge crack rate and a significant decrease in processing performance.

[0120] Comparative Example 3 increased the Mn content to 13.6%, but did not reach the effective threshold of 15%. The mechanism of action of Mn was not fundamentally changed, and the improvement in the bulk conductivity and magnetic shielding effectiveness of the non-magnetic stainless steel was not significant. Furthermore, Cr... eq / Ni eq Excessive levels of magnetic permeability lead to the precipitation of the delta phase, which in turn causes a deterioration in the relative permeability and its fluctuations.

[0121] Comparative Example 4 increased the Mn content to 19%. The excessively high Mn content led to severe Mn segregation, with an Mn segregation index ≥1.25. Although the bulk conductivity was slightly higher than that of Example 1, the improvement was not significant. Furthermore, Comparative Example 4 was difficult to hot roll, resulting in large fluctuations in relative permeability and an extremely high hot rolling edge crack rate, further reducing processing performance. This would lead to unstable magnetic shielding effectiveness of the non-magnetic stainless steel.

[0122] Comparative Example 5 increased the Ni content to 8.0% based on Comparative Example 2. While simultaneously increasing the Ni and Cu content aimed to improve bulk conductivity and magnetic shielding effectiveness, the improvement was not significant, and Cr... eq / Ni eq Too low a Cu content or too high a Cu content increases the tendency to crack, significantly reduces processing performance, greatly increases preparation costs, and has a poor effect on improving the performance of non-magnetic stainless steel.

[0123] Comparative Example 6 has an Mn content of 16.8% by mass percentage and increases the Cu content to 1.0%. The bulk conductivity is close to that of Example 1. However, the high Cu content leads to increased fluctuations in relative permeability, causing hot brittleness, resulting in increased hot rolling edge cracking rate and decreased processing performance. This leads to unstable magnetic shielding effectiveness of non-magnetic stainless steel.

[0124] (II) Examples 1 and Comparative Examples 7-9: Comparative Examples 7-9 have the same component content as Example 1, but some process parameters in the preparation steps are different (Note: the remaining process parameters not mentioned are the same as in Example 1), as shown below:

[0125] 1. The difference between Comparative Example 7 and Example 1 lies in step S1. Step S1 of Comparative Example 7 is as follows: Step S1: Prepare raw materials according to the composition and amount of the non-magnetic stainless steel substrate with high magnetic shielding efficiency. The raw materials are sequentially subjected to electric furnace melting, AOD refining, and LF refining to obtain molten steel with the target composition. In the AOD refining step: during the decarburization period, an Ar / O2 mixed gas is blown in, wherein the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 3:1, and the decarburization is carried out to C≤0.05% by mass percentage. During the reduction period, Ar is blown in the bottom for stirring, and the flow rate of the bottom-blown Ar is controlled at 0.10 Nm. 3 / t·min; Samples of molten steel are taken and measured using a conventional spectrometer (Thermo Fisher Scientific ARL series direct-reading spectrometer). Based on the test results of each component, iron-chromium alloy or iron-nickel alloy is added for fine-tuning. In the LF refining step, Ni cored wire is fed in at a feeding speed of 30m / min, and chromium nitride is added to fine-tune the N content. The LF refining is terminated when S≤0.003% by mass percentage.

[0126] Results and analysis:

[0127] Example 1 uses laser-induced breakdown spectrometry to perform real-time analysis of the composition of the molten steel and dynamically control the Cr content. eq / Ni eq Combined with increasing the flow rate of bottom-blown Ar to 0.12 Nm 3 The strong stirring operation at / t·min ensures the homogeneity of the components in the molten steel. In LF refining, Ni-core wire is fed at a low speed of 20m / min for precise Ni replenishment, controlling the Ni content within 4.7% ± 0.1%. Furthermore, the N content is fine-tuned by adding chromium nitride to control it within 0.17% ± 0.005%, achieving high-precision control of both Ni and N content. Dynamic control of Cr during the preparation process... eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range was within ±0.010. Samples of the molten steel were taken from the upper, middle, and lower positions of the ladle for testing. The fluctuation range of the content of each component in the molten steel, expressed as a percentage by mass, was within ±0.05%. The Cr content of the non-magnetic stainless steel substrate... eq / Ni eq It is 1.034, and the fluctuation of relative permeability is also small.

[0128] The traditional spectrometer used in Comparative Example 7 could not perform real-time online analysis and had a slow analysis speed, failing to provide timely feedback on the content of each component. Furthermore, the high-speed Ni wire feeding at 30 m / min during LF refining resulted in uneven Ni diffusion due to the high Mn content, leading to molten steel splashing and alloy oxidation loss. Ultimately, the Ni content fluctuated within ±15% of the target Ni content (by mass percentage). During the preparation process, Cr... eq / Ni eq It can only be controlled within 1.03±0.05, with large fluctuations. The relative permeability also fluctuates greatly. The relative permeability and its fluctuation value of Comparative Example 7 are ≤1.003 (±0.002).

[0129] 2. The difference between Comparative Example 8 and Example 1 is that step S2 is different. In step S2 of Comparative Example 8, the molten steel is injected into the crystallizer for continuous casting, without the use of electromagnetic brake stirring and without the combination of dynamic light reduction technology.

[0130] Results and analysis:

[0131] Because the Mn content in Examples 1 and 8 is relatively high, the tendency for Mn segregation is increased. Example 1, by employing the electromagnetic brake for stirring and combining it with dynamic light reduction technology, effectively suppresses the convective segregation of Mn and squeezes the liquid core to compensate for solidification shrinkage; the Mn segregation index of the cast billet is ≤1.03. Comparative Example 8, however, did not use an electromagnetic brake for stirring and did not combine it with dynamic light reduction technology. (See reference...) Figure 1 Compared with the example 8, the Mn segregation was severe, and the central porosity and shrinkage cavities inside the billet were serious, with the Mn segregation index ≥1.25.

[0132] 3. The difference between Comparative Example 9 and Example 1 is that step S3 is different. Comparative Example 9 uses a traditional and relatively rough hot rolling process (the initial rolling temperature range is 920℃~1100℃, and the final rolling temperature range is 800℃~900℃): the reduction rate of each rough rolling pass of Comparative Example 9 is between 8% and 10%; and the rolling temperature of the fifth finishing rolling pass is not dynamically adjusted according to the Mn content.

[0133] Results and analysis:

[0134] In Example 1, the single-pass reduction rate in the first four roughing passes reached 23%~38%, and in the fifth roughing pass, the reduction rate even reached 40%. This large deformation roughing step effectively broke down the δ phase, causing it to debond from the matrix and break into dispersed fragments ≤1μm. This controlled the grain size of the non-magnetic stainless steel, preventing large grains from increasing the fluctuation of relative magnetic permeability. After large deformation roughing, the residual δ phase was ≤0.2% (the residual δ phase was tested using a ferrite analyzer), and the magnetic shielding effectiveness was >68dB (1MHz), effectively improving the non-magnetic properties of the non-magnetic stainless steel. Simultaneously, Example 1 dynamically matched the rolling temperature window according to the Mn content, achieving a crack-free rolling effect on the prepared non-magnetic stainless steel substrate.

[0135] In Comparative Example 9, the reduction rate in each of the five roughing passes was between 8% and 10%, resulting in coarse grains, poor microstructure uniformity, and a residual δ phase content ≥3%. Furthermore, the relative permeability and its fluctuation value in Comparative Example 9 were ≤1.004 (±0.002), and the magnetic shielding effectiveness was ≤45dB (1MHz). This indicates a large fluctuation in relative permeability and low magnetic shielding effectiveness. (See also...) Figure 2 The non-magnetic stainless steel substrate prepared in Example 1 has no processing defects on its surface, while the non-magnetic stainless steel substrate prepared in Comparative Example 9 has more cracks on its surface.

[0136] Based on the above experimental results, it can be seen that, in terms of composition design, this invention improves the magnetic shielding effectiveness of non-magnetic stainless steel by increasing the Mn content, which dominates the bulk conductivity enhancement mechanism. This reduces the dependence of existing non-magnetic stainless steels on high Cu content when improving their bulk conductivity, and also reduces the amount of expensive Ni element used while ensuring the basic performance of non-magnetic stainless steel. Simultaneously, by increasing the Cr content... eq and Ni eq The ratio is precisely controlled between 1.02 and 1.05, resulting in minimal fluctuations in the relative permeability and stable magnetism of the non-magnetic stainless steel substrate, thus achieving stable magnetic shielding effectiveness. This balance and unification of the all-austenitic structure, high bulk conductivity, high magnetic shielding effectiveness, and minimal fluctuations in relative permeability and stable magnetism in non-magnetic stainless steel are realized. Since the high-magnetic-shielding-effective non-magnetic stainless steel substrate of this invention has a high Mn content, belonging to high-manganese non-magnetic steel, this invention incorporates novel and systematic parameter integration and precise control in the manufacturing process, addressing the limitations of existing technologies in simultaneously improving the magnetic shielding effectiveness of non-magnetic stainless steel and the problems of large fluctuations in relative permeability and unstable magnetic shielding effectiveness. The high-magnetic-shielding-effective non-magnetic stainless steel substrate prepared by this invention can meet the high-magnetic-shielding-effectiveness material requirements of advanced manufacturing technologies such as 6G communication shielding covers and nuclear magnetic resonance chambers.

[0137] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness, characterized in that, A non-magnetic stainless steel substrate for preparing high magnetic shielding effectiveness, the non-magnetic stainless steel substrate comprising the following components by mass percentage: C: 0.07%~0.12%, Mn: 15.0%~18.3%, Cr: 16.1%~16.5%, Ni: 4.3%~5.1%, N: 0.15%~0.20%, Cu: 0.6%~0.8%, with the balance being Fe and other impurity elements; Among them, Cr eq / Ni eq Calculate using the following formula: Cr eq / Ni eq =(Cr+Mo+1.5Si) / (Ni+0.5Mn+30C+30N+0.5Cu), where Cr, Mo, Si, Ni, Mn, C, N, and Cu are all expressed as mass percentages, and satisfy Cr eq / Ni eq =1.02~1.05; The preparation method includes the following steps and procedures: Step S1: Prepare raw materials according to the composition and amount of the non-magnetic stainless steel substrate with high magnetic shielding efficiency, and sequentially process the raw materials through electric furnace melting, AOD refining and LF refining to obtain molten steel with the target composition. In the AOD refining step: During the decarbonization period, an Ar / O2 mixed gas is blown in, wherein the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (2:1) to (4:1); By mass percentage, decarbonization is carried out to C ≤ 0.05%; During the reduction period, Ar was blown from the bottom and stirred. The composition of the molten steel was analyzed in real time using laser-induced breakdown spectroscopy, and the Cr content was calculated. eq / Ni eq According to Cr eq / Ni eq Fine-tuning is achieved by adding iron-chromium alloy or iron-nickel alloy to dynamically control Cr. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010; Step S2, continuous casting process: The molten steel is continuously cast to obtain a billet; Step S3, hot rolling process: The cast billet is hot rolled to obtain a rough product; Step S4, pickling process: The crude product is pickled to obtain a non-magnetic stainless steel substrate; In step S1, the flow rate of the bottom-blown Ar is controlled at 0.10~0.15 Nm. 3 / t·min; In the LF refining step, Ni cored wire is fed at a feed rate of 15 m / min to 25 m / min; chromium nitride is added to fine-tune the N content in order to dynamically control the Cr content. eq / Ni eq Between 1.02 and 1.05, and Cr eq / Ni eq The fluctuation range is within ±0.010; The refining of LF is terminated when S ≤ 0.003% by mass percentage; In step S2, the molten steel is injected into a crystallizer for continuous casting, an electromagnetic brake is used for stirring in the crystallizer, and dynamic light pressure is applied at the end of the solidification of the molten steel. The electromagnetic brake has a current of 350A~450A and a frequency of 2.5Hz~3.5Hz; The compression amount under dynamic light pressure is 7mm~9mm; In step S3, the billet is subjected to five rough rolling passes and eight finish rolling passes to obtain a rough product; During the roughing process, the single-pass reduction rate in the first four passes is 23% to 38%, while the reduction rate in the fifth pass is set to 39% to 45%.

2. The method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness according to claim 1, characterized in that, The high magnetic shielding effectiveness non-magnetic stainless steel substrate comprises the following components by weight percentage: C: 0.08%~0.10%, Mn: 16.5%~17.5%, Cr: 16.2%~16.4%, Ni: 4.6%~4.9%, N: 0.16%~0.18%, Cu: 0.65%~0.75%, with the balance being Fe and other impurity elements.

3. The method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness according to claim 1, characterized in that: During the finishing rolling process, the rolling temperature T is set using the following formula during the fifth finishing rolling pass: T = 865 - 10 × (Mn content × 100 - 16), where the Mn content is expressed as a mass percentage.

4. The method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness according to claim 1, characterized in that: In step S4, the crude product is sequentially acid-washed with nitric acid solution and then acid-washed with a composite acid solution, wherein the composite acid solution is a mixture of citric acid and tartaric acid; wherein the molar ratio of citric acid to tartaric acid is (2:1) to (4:1); The temperature for pickling with the compound acid solution is 55℃~65℃, and the pickling time is 20s~30s.

5. The method for preparing a non-magnetic stainless steel substrate with high magnetic shielding effectiveness according to claim 4, characterized in that: In step S4, after the crude product is pickled with the composite acid solution, the crude product is also passivated with a passivation solution.

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