Corrosion-resistant soft non-magnetic stainless steel

Abstract

The invention discloses corrosion-resistant soft non-magnetic stainless steel which comprises the following chemical components in percentage by weight: 0.01%-0.08% of C, 0.10%-1.00% of Si, 7.0%-12.0% of Mn, less than or equal to 0.06% of P, less than or equal to 0.015% of S, 15.0%-17.0% of Cr, 5.0%-9.0% of Ni, 0.01%-0.50% of Mo, 0.50%-2.50% of Cu, 0.01%-0.10% of N and the balance of Fe and inevitable impurities. Meanwhile, the strain-induced martensite phase transformation temperature point Md30 / 50 meets the condition that Md30 / 50 is larger than or equal to-150 DEG C and smaller than or equal to-50 DEG C, and the calculation formula of the martensite phase transformation temperature point is Md30 / 50 = 580%-520% of C, 2% of Si, 16% of Mn, 16% of Cr, 23% of Ni, 300% of N, 26% of Cu and 10% of Mo; pREN meets the condition that Cr% + 3.3 Mo% + 20 C% + 20 N%-0.5 Mn%-0.25 Ni% is larger than or equal to 10.0. The product obtained through component design is better than 305 stainless steel in nonmagnetic performance and economical efficiency.

Description

Technical Field

[0001] This invention relates to steel smelting processes, and more particularly to a corrosion-resistant, soft, non-magnetic stainless steel. Background Technology

[0002] 305 (UNS S30500) is an austenitic stainless steel with excellent corrosion resistance, corresponding to the Chinese grade 10Cr18Ni12. To ensure its good non-magnetic properties, the nickel content usually needs to be controlled above 12%. Chinese patent publication CN111218623A, through a high nickel content design, controls the material's magnetic permeability below 1.005, possessing non-magnetic and low work hardening characteristics, suitable for deep stamping and spinning, and widely used in the manufacture of non-magnetic electronic components. However, the high nickel content design of this scheme leads to higher material costs. To reduce alloy costs, Chinese patent publication CN101691644B provides a method for manufacturing non-magnetic soft stainless steel wire rods and plates. By controlling lower carbon and nitrogen content and adding copper, the material achieves both low hardness and good cold workability; however, this scheme has a low PREN value and Md... 30 / 50 The high temperature (>-25℃) resulted in poor corrosion resistance and a magnetic permeability greater than 1.005 after forming, leading to suboptimal non-magnetic properties. Chinese invention patent publication number CN104662189A, however, increases the total content of manganese, nickel, and copper alloys while controlling the total carbon and nitrogen content, thereby reducing Md... 30 / 50 Temperature control achieves a balance between excellent formability and super non-magnetic properties, but this solution does not consider the negative impact of excessively high manganese content on the material's corrosion resistance, and the total nickel-copper content in the composition design of the preferred embodiment is too high, lacking significant economic advantages.

[0003] In summary, in the field of non-magnetic stainless steel, there is still considerable room for research and development in controlling material costs while ensuring the necessary properties such as magnetic permeability and corrosion resistance. Summary of the Invention

[0004] The purpose of this invention is to provide a corrosion-resistant, soft, non-magnetic stainless steel.

[0005] The technical solution to achieve the objective of this invention is: a corrosion-resistant soft non-magnetic stainless steel, the weight percentage of its chemical composition being as follows: C 0.01%~0.08%, Si 0.10%~1.00%, Mn 7.0%~12.0%, P≤0.06%, S≤0.015%, Cr 15.0%~17.0%, Ni 5.0%~9.0%, Mo 0.01%~0.50%, Cu 0.50%~2.50%, N 0.01%~0.10%, with the balance being Fe and unavoidable impurities; simultaneously, the martensitic phase transformation temperature point Md 30 / 50 Satisfies: -150℃≤Md30 / 50 The formula for calculating the martensitic phase transformation temperature point ≤-50℃ is as follows: Md 30 / 50 =580-520C%-2Si%-16Mn%-16Cr%-23Ni%-300N%-26Cu%-10Mo%; PREN satisfies Cr%+3.3Mo%+20C%+20N%-0.5Mn%-0.25Ni%≥10.0.

[0006] Preferably, its chemical composition by weight percentage is as follows: C 0.04%, Si 0.4%, Mn 10.3%, P 0.001%, S 0.001%, Cr 16.2%, Ni 7.1%, Mo 0.01%, Cu 1.60%, N 0.05%, with the balance being Fe and unavoidable impurities. This cost system offers high performance-to-price ratio.

[0007] In the technical solution described in this invention, the design principles of each chemical element in the non-magnetic stainless steel are as follows: Carbon is an element that strongly forms, stabilizes, and expands the austenite region. To some extent, it can replace nickel, promoting austenite formation, stabilizing the austenite structure, and significantly reducing Md. 30 / 50 Temperature inhibits the formation of magnetic martensite phase during straining. However, excessively high carbon content increases material strength and hardness, hindering forming and negatively impacting the corrosion resistance of stainless steel. Conversely, excessively low carbon content increases the difficulty and cost of the preparation process. Therefore, the carbon content in the steel of this invention is designed to be 0.01%–0.08%.

[0008] Silicon is a common element in steelmaking. It is a ferrite-forming and stabilizing element. Silicon is used for deoxidation during smelting, but excessive silicon content increases the brittleness of the material. Therefore, the silicon content in the steel of this invention is designed to be 0.10% to 1.00%.

[0009] Manganese, while a relatively weak austenite-forming element, is a strong austenite-stabilizing element in stainless steel. In low-nickel austenitic stainless steel, manganese interacts with elements such as carbon and nitrogen to partially replace nickel, ensuring an austenitic structure at room temperature. It also significantly reduces the molecular weight (M) of the stainless steel. d30 / 50 The temperature value. However, excessive manganese will affect the corrosion resistance of stainless steel, therefore, the Mn content in the steel of this invention is controlled at 7.0% to 12.0%.

[0010] Chromium is the most important element for steel to achieve corrosion resistance. Generally, the minimum chromium content for obtaining corrosion resistance is 12%. Since chromium significantly enhances corrosion resistance, the chromium content in the steel of this invention is controlled at 15.0% or higher to ensure good corrosion resistance. However, chromium is a major ferrite-forming element; excessively high chromium levels will lead to the formation of a ferrite phase in the material, failing to guarantee the acquisition of completely non-magnetic austenite at room temperature. Therefore, a correspondingly higher nickel equivalent is required to ensure a room-temperature austenitic structure. Thus, the chromium content in the steel of this invention is controlled between 15.0% and 17.0%.

[0011] Nickel is a strong austenite-forming and stabilizing element, but it is expensive. Therefore, the Ni content is controlled between 5.0% and 9.0% to ensure good economic efficiency of the material. This also ensures the austenitic structure of the steel at room temperature.

[0012] Molybdenum plays a crucial role in stainless steel by significantly enhancing corrosion resistance and improving strength and hardness through solid solution strengthening. However, excessive molybdenum content can increase the tendency for intermetallic phase precipitation, making processing more difficult and reducing the material's economic viability. Therefore, the molybdenum content in the steel of this invention is controlled between 0.01% and 0.50%.

[0013] Copper, an austenite-forming element, can partially substitute for nickel. It also reduces the cold work hardening tendency of stainless steel, improves its plasticity and cold formability, making the material easier to process and shape. However, excessive copper content may lead to difficulties in hot working and the phenomenon of "copper brittleness." The copper content in the steel of this invention is controlled between 0.50% and 2.50%.

[0014] Nitrogen is a strong austenite-forming element. It is a key factor in the formation and stabilization of the austenitic phase in nitrogen-containing nickel-saving austenitic stainless steel, effectively suppressing the formation of magnetic martensite phase during strain. Its effect on reducing martensite formation during strain is similar to that of carbon. More advantageously, nitrogen has a high solid solubility in austenite, and unlike carbon, which readily forms carbides, nitrides generally do not precipitate in the austenitic phase. However, excessively high nitrogen content can lead to a significant increase in the material's yield strength, affecting its formability. Therefore, the nitrogen content in the steel of this invention is controlled at 0.01%–0.10%.

[0015] Phosphorus: ≤0.06%. Phosphorus is considered a harmful element in stainless steel and should be kept as low as possible.

[0016] Sulfur: S≤0.015%. Sulfur is also considered a harmful element in stainless steel. Especially in this invention, the steel has a high manganese content, so the sulfur content needs to be strictly controlled, and the lower the better.

[0017] Currently, the main approach to achieving low magnetic permeability in non-magnetic stainless steel is through high alloy content design to minimize Md. 30 / 50This leads to higher material costs. This invention breaks with the design convention of "high alloy content" by precisely controlling austenite stability through compositional design, constructing a Cr-Mn-Ni-Cu medium-low alloy system. Furthermore, by utilizing the synergistic effect of multiple alloys in this system, it can achieve medium-low alloy content while also reducing Md content. 30 / 50 Maintaining ultra-low magnetic permeability within a low range represents an innovative direction in composition design. This invention yields a corrosion-resistant, soft, non-magnetic stainless steel with a fully austenitic microstructure in its solid solution state and a yield strength Rp. 0.2 With a strength of ≤330 MPa, microhardness HV≤190, and relative permeability μ≤1.005, this product does not produce a magnetic martensitic phase after cold working, making it superior to 305 in terms of non-magnetic properties and economy. Furthermore, after a 240-hour neutral salt spray corrosion test, no rust was observed on the surface, demonstrating excellent corrosion resistance. Attached Figure Description

[0018] Figure 1 The microstructure of the longitudinal section of the hot-rolled solid solution state is shown in Example 1. Detailed Implementation

[0019] The preferred embodiment of the preparation process of a corrosion-resistant soft non-magnetic stainless steel according to the present invention is described in detail below: Example 1

[0020] This invention uses an alloy melting furnace (IF) – converter (AOD) – LF smelting production process as an example: High-nickel pig iron and chromium pig iron are melted in the alloy melting furnace. After melting, the molten steel is poured into the AOD furnace, where alloys are further added for carbon removal, sulfur removal, and nitrogen control through blowing. When the smelting composition meets the requirements, the LF furnace is finely adjusted, gently stirred, and stabilized. The molten steel is then poured into a tundish and cast on a vertical bending continuous casting machine. The superheat of the continuous casting is 30–80°C, and the slab drawing speed is 0.6–2 m / min. The continuously cast slab is placed in a roller hearth furnace and heated to 1200–1280°C. After rolling to the required thickness on a hot continuous rolling mill, it is coiled. Then, continuous solution pickling is performed, controlling the solution temperature at 1050°C–1150°C. It is then cooled to room temperature at an average cooling rate of ≥20°C / s to obtain a hot-rolled solution-treated product. Subsequently, cold rolling, cold annealing, and solution pickling are performed. The solution treatment temperature is 1040℃~1120℃, and the product is cooled to room temperature at an average cooling rate of ≥20℃ / s to obtain a cold-rolled solution-treated product. The above process is a conventional technical method and will not be described in detail here.

[0021] The chemical compositions of Examples 1-11, Comparative Examples 1-3, and 305 stainless steel of the present invention are shown in Table 1.

[0022] Table 1 Chemical composition (wt.%) of the examples and comparative examples

[0023] Table 2 shows the Md of the steel grades in the embodiments of the present invention. 30 / 50 Table 2 provides the relevant parameters and properties of the standard 305 austenitic stainless steel, including temperature, pitting corrosion equivalent (PREN), mechanical properties, neutral salt spray corrosion test results, and relative magnetic permeability. The stainless steel in this embodiment belongs to the Cr-Mn-N series nickel-saving austenitic stainless steel, and its pitting corrosion equivalent is calculated using the formula PREN = Cr% + 3.3Mo% + 20C% + 20N% - 0.5Mn% - 0.25Ni%. 305 belongs to the Cr-Ni series austenitic stainless steel, and its pitting corrosion equivalent is calculated using the formula PREN = Cr% + 3.3Mo% + 16N%. The mechanical properties of the materials were tested according to GB / T228.1 "Metallic Materials - Tensile Testing - Part 1: Tests at Room Temperature," and the corrosion performance was tested according to the neutral salt spray test in GB / T 10125-2021 "Artificial Atmosphere Corrosion Tests - Salt Spray Tests," with a test temperature of 35±1 ℃ and a test period of 240 hours. The relative permeability was tested using the FERROMASTER instrument.

[0024] Table 2 Manufacturing process and performance of the examples and comparative examples

[0025] As can be seen from the performance test results in Table 2, the non-magnetic properties and microhardness of the embodiments of the present invention are comparable to those of 305 stainless steel, and the corrosion resistance is excellent. All of them can pass the 240-hour neutral salt spray corrosion performance test.

[0026] Figure 1 The microstructure of the longitudinal section of the hot-rolled solid solution state of Example 1 was obtained by electrolytic corrosion of the sample with saturated oxalic acid solution. It was a complete austenitic stainless steel structure with typical step grain boundary morphology and no carbide or nitride precipitation was observed.

[0027] As can be seen from the process parameters and test results of the embodiments, the products obtained by the present invention through the control of low and medium alloy content still have excellent corrosion resistance and maintain good non-magnetic properties, namely, no rust in the 240-hour neutral salt spray test and relative magnetic permeability μ≤1.005; the relatively low C and N content, the strength of the solid solution material is comparable to that of 305, and the formability is good. It can be used in industries such as electronics, instruments, and high-end textile products that require materials with corrosion resistance, non-magnetic properties, and easy formability; and the current alloy cost of the embodiments of the invention is about 14,000 RMB / ton, while that of 305 is 18,000 RMB / ton, which reduces the cost of the alloy by about 20%, showing obvious economic benefits.

[0028] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent process transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A corrosion resistant soft non-magnetic stainless steel, characterized by: The weight percentage of its chemical composition is as follows: C 0.01%-0.08%, Si 0.10%-1.00%, Mn 7.0%-12.0%, P≤0.06%, S≤0.015%, Cr 15.0%-17.0%, Ni 5.0%-9.0%, Mo 0.01%-0.50%, Cu 0.50%-2.50%, N 0.01%-0.10%, the balance being Fe and inevitable impurities; meanwhile, the martensite phase transformation temperature point Md 30 / 50 satisfies: -150℃≤Md 30 / 50 ≤-50℃, the calculation formula of the martensite phase transformation temperature point is Md 30 / 50 =580-520C%-2Si%-16Mn%-16Cr%-23Ni%-300N%-26Cu%-10Mo%; PREN satisfies Cr%+3.3Mo%+20C%+20N%-0.5Mn%-0.25Ni%≥10.

0.

2. The corrosion resistant, soft, non-magnetic stainless steel according to claim 1, characterized in that: The weight percentage of the chemical components are as follows: C 0.04%, Si 0.4%, Mn 10.3%, P 0.001%, S 0.001%, Cr 16.2%, Ni 7.1%, Mo 0.01%, Cu 1.60%, N 0.05%, the balance being Fe and unavoidable impurities.

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