KR20210008732A - Non-magnetic austenitic stainless steel - Google Patents

Abstract

Disclosed is a non-magnetic austenitic stainless steel. According to an embodiment of the present specification, a non-magnetic austenitic stainless steel contains 0.01 to 0.1 wt% of C, 1.5 wt% or less of Si (except for 0%), 0.5 to 3.5 wt% of Mn, 16 to 22 wt% of Cr, 7 to 15 wt% of Ni, 3 wt% or less of Mo, 0.01 to 0.3 wt% of N, the balance Fe, and unavoidable impurities with respect to 100 wt% of the total. As for the non-magnetic austenitic stainless steel, the value of the following formula (1) is a negative value. (1) 3*(Cr + Mo) + 5*Si - 65*(C + N) - 2*(Ni + Mn) - 28, wherein Cr, Mo, Si, C, N, Ni, Mn in the formula (1) means the content (wt%) of each alloy element.

Description

{Non-magnetic austenitic stainless steel}

The present invention relates to a non-magnetic austenitic stainless steel, and more particularly, to a non-magnetic austenitic stainless steel that can be applied as a material for various electronic devices.

Recently, as smart devices having various functions are used, there is an increasing demand for steel materials with reduced magnetism to reduce power loss and prevent malfunction. Since the 300 series stainless steel has an austenite phase as its main structure and generally has non-magnetic properties, it is widely used as a material for electronic devices.

However, in general STS304 or STS316 austenitic stainless steel, δ-ferrite is formed in a fraction of 1 to 5% during steel making/rolling. The formed δ-ferrite is a structure that induces magnetism, and there is a problem in that the final product has magnetism. Therefore, conventional STS304 and STS316 austenitic stainless steels have a problem in that nonmagnetic properties cannot be secured due to δ-ferrite.

δ-ferrite can be decomposed by heat treatment at a temperature range of 1,300 to 1,400°C. However, δ-ferrite may not be completely removed even in the rolling and annealing process and may remain in the structure, and there is a problem in that nonmagnetic properties are not secured due to increased magnetism by the remaining ferrite.

Korean Patent Application Publication No. 10-2018-0068542 (Publication date: June 22, 2018)

In order to solve the above-described problem, the present invention is to provide a nonmagnetic austenitic stainless steel that can be applied as a material for various electronic devices.

As a means for achieving the above object, the present specification is in wt%, C: 0.01 to 0.1%, Si: 1.5% or less (excluding 0), Mn: 0.5 to 3.5%, Cr: 16 to 22%, Ni: 7 To 15%, Mo: 3% or less, N: 0.01 to 0.3%, remaining Fe and other unavoidable impurities, and a nonmagnetic austenitic stainless steel having a negative value in the following formula (1).

(1) 3*(Cr+Mo) + 5*Si-65*(C+N)-2*(Ni+Mn)-28

In the above formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (% by weight) of each alloying element.

In each of the nonmagnetic austenitic stainless steels of the present invention, by weight %, Cu: 2.5% or less may be further included.

In addition, as another means for achieving the above object, the present specification is in wt%, C: 0.01 to 0.1%, Si: 1.5% or less (excluding 0), Mn: 0.5 to 3.5%, Cr: 16 to 22%, Ni: 7 to 15%, Mo: 3% or less, N: 0.01 to 0.3%, remaining Fe and other unavoidable impurities, and discloses a nonmagnetic austenitic stainless steel having a value of 70 or more in the following formula (2). .

(2) ΣA ₅ /ΣA x 100

In the above formula (2), ΣA ₅ is the sum of the areas of ferrite particles having an area of 5 μm ² or less, and ΣA is the sum of the areas of all ferrite particles.

In each of the nonmagnetic austenitic stainless steels of the present invention, by weight %, Cu: 2.5% or less may be further included.

In each of the nonmagnetic austenitic stainless steels of the present invention, at a thickness of 1 mm or less, the permeability may be 1.02 or less.

According to the present invention, it is possible to provide a non-magnetic austenitic stainless steel applied to various electronic device materials by controlling the fraction of the ferrite phase that causes magnetism to be low.

According to the present invention, the fraction of the ferrite phase can be reduced by controlling the alloy component to suppress the formation of ferrite, or by accelerating the decomposition of ferrite through the control of the microstructure.

1 is a graph showing the change of the ferrite fraction according to the value of Equation (1) in Table 1.
2 is a graph showing the change in permeability according to the value of Equation (2) in Table 2.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the technical idea of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided in order to more completely explain the present invention to those with average knowledge in the art.

The terms used in the present application are only used to describe specific examples. So, for example, a singular expression includes a plural expression unless the context clearly has to be singular. In addition, terms such as "include" or "include" used in the present application are used to clearly refer to the existence of features, steps, functions, components or combinations thereof described in the specification, but other features It should be noted that it is not used to preliminarily exclude the presence of elements, steps, functions, components, or combinations thereof.

Meanwhile, unless otherwise defined, all terms used in this specification should be viewed as having the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Therefore, unless clearly defined in the specification, specific terms should not be interpreted in an excessively ideal or formal sense. For example, in the present specification, expressions in the singular include plural expressions unless the context clearly has exceptions.

In addition, "about", "substantially" and the like in the present specification are used at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid understanding of the present invention. Or absolute figures are used to prevent unfair use of the stated disclosure by unconscionable infringers.

The non-magnetic austenitic stainless steel according to an example of the present invention is in wt%, C: 0.01 to 0.1%, Si: 1.5% or less (excluding 0), Mn: 0.5 to 3.5%, Cr: 16 to 22%, Ni: 7 to 15%, Mo: 3% or less, N: 0.01 to 0.3%, the remaining Fe and other inevitable impurities may be included. In addition, Cu: may further contain 2.5% or less.

Hereinafter, the reasons for limiting the alloy composition will be described in detail. All of the following component compositions mean weight percent unless otherwise specified.

Carbon (C): 0.01 to 0.1% by weight

C is a strong austenite phase stabilizing element, and is an element that suppresses an increase in magnetism during solidification. In the present invention, C may be added in an amount of 0.01% by weight or more in order to stabilize the austenite phase. However, if the C content is excessive, it combines with Cr to form carbides at the grain boundaries, and there is a concern that the Cr content around the grain boundaries is locally lowered to lower the corrosiveness. Therefore, in order to secure sufficient corrosion resistance, the upper limit of the C content in the present invention is preferably limited to 0.1% by weight.

Silicon (Si): 1.5% by weight or less (excluding 0)

Si is an element that improves corrosion resistance. However, Si is a ferrite phase stabilizing element that induces magnetism, and when the Si content is excessive, there is a concern that mechanical properties and corrosion resistance may be deteriorated by promoting precipitation of intermetallic compounds such as σ phase. Accordingly, the upper limit of the Si content in the present invention is preferably limited to 1.5% by weight.

Manganese (Mn): 0.5 to 3.5% by weight

Mn is an austenite phase stabilizing element such as C and Ni, and is effective for nonmagnetic enhancement. Accordingly, in the present invention, Mn may be added in an amount of 0.5% by weight or more. However, when the Mn content is excessive, inclusions such as MnS are formed, thereby reducing corrosion resistance and reducing surface gloss. Accordingly, in the present invention, the upper limit of the Mn content is preferably limited to 3.5% by weight.

Chrome (Cr): 16 to 22% by weight

Cr is a typical element for improving corrosion resistance of stainless steel, and in the present invention, Cr may be added in an amount of 16% by weight or more to ensure sufficient corrosion resistance. However, Cr is a ferrite phase stabilizing element that causes magnetism. In addition, when the Cr content is excessive, a large amount of Ni must be included in order to obtain non-magnetic properties, so that the cost increases, and the formation of a sigma phase is promoted, thereby deteriorating mechanical properties and corrosion resistance. Accordingly, the Cr content is preferably limited to 22% by weight.

Nickel (Ni): 7 to 15% by weight

Ni is the most powerful austenite phase stabilizing element, and in the present invention, Ni may be added in an amount of 7% by weight or more to obtain nonmagnetic properties. However, as the Ni content increases, the raw material price increases, so the upper limit of the Ni content is preferably limited to 15% by weight.

Molybdenum (Mo): 3% by weight or less

Mo is an element that improves corrosion resistance. However, Mo is a ferrite phase stabilizing element, and when the Mo content is excessive, formation of a σ phase is promoted, and there is a concern that mechanical properties and corrosion resistance are deteriorated. Accordingly, in the present invention, the upper limit of the Mo content is preferably limited to 3% by weight,

Nitrogen (N): 0.01 to 0.3% by weight

N is an austenite phase stabilizing element, and in the present invention, N may be added in an amount of 0.01% by weight or more to obtain nonmagnetic properties. However, if the N content is excessive, the hot workability of the steel is reduced and the surface quality is deteriorated. Therefore, the upper limit of the N content is preferably limited to 0.3% by weight.

The non-magnetic austenitic stainless steel according to an example of the present invention may optionally further include Cu: 2.5% by weight or less. Hereinafter, the reason for limiting the Cu component will be described in detail.

Copper (Cu): 2.5% by weight or less

Cu is an austenite phase stabilizing element, and can be used in place of expensive Ni. However, when the Cu content is excessive, a phase with a low melting point is formed to reduce hot workability, thereby reducing the surface quality. Therefore, in the present invention, the upper limit of the Cu content is preferably limited to 2.5% by weight or less.

The remaining component of the present invention is iron (Fe). However, in a typical manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed, and this cannot be excluded. Since the impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

Typically, STS 304 or 316 stainless steel is composed of an austenite phase as the main structure, and has a microstructure in which the ferrite phase formed during steelmaking/rolling remains. The austenite phase has a face-centered cubic structure and does not exhibit magnetism, but ferrite has a body-centered cubic structure and thus becomes magnetic. That is, it may be difficult to secure the non-magnetic properties desired by the present invention depending on the proportion of the remaining ferrite phase. Accordingly, in order to secure the non-magnetic properties, the fraction of the ferrite phase that causes magnetism should be controlled as low as possible. Hereinafter, specific technical means for securing the non-magnetic properties desired by the present invention will be described in detail.

Alloy composition control

The composition of the alloy has a significant influence on the fraction of the initially formed ferrite phase. For example, austenite phase stabilizing elements such as Ni, Mn, C, and N reduce the ferrite phase fraction when added, and component elements such as Cr and Mo increase the ferrite phase fraction. In consideration of this, the present inventor derived the following equation (1) that can control the fraction of the ferrite phase.

(1) 3*(Cr+Mo) + 5*Si-65*(C+N)-2*(Ni+Mn)-28

In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (% by weight) of each alloy element.

According to the present invention, when the value of Equation (1) has a negative value, the fraction of the initially generated ferrite phase may be 0%.

Microstructure control

On the other hand, the ferrite phase remaining during steel making/rolling may be decomposed according to a heat treatment process performed later. The present inventors found that even when the ferrite phase remains because the value of equation (1) is positive, and thus the steel becomes magnetic, the decomposition of the ferrite phase in the heat treatment process can be accelerated through the control of the microstructure. I did. The acceleration of the decomposition of the ferrite phase is related to the size distribution of the remaining ferrite phase, and the following equation (2) was derived through analysis.

(2) ΣA ₅ /ΣA x 100

In the above equation (2), ΣA ₅ is the sum of the areas of ferrite particles having an area of 5 μm ² or less, and ΣA is the sum of the areas of all ferrite particles. That is, Equation (2) means the percentage of the sum of the areas of fine ferrite particles of 5 μm ² or less relative to the sum of the areas of all ferrite particles.

According to an example of the present invention, it is possible to control the value of Equation (2) to be 70 or more. The present invention can accelerate the decomposition of the ferrite phase in the heat treatment process by controlling the sum of the areas of the fine ferrite particles high as described above. As a result, the permeability after heat treatment is 1.02 or less, and in particular, the permeability may be 1.02 or less at a thickness of 1 mm or less.

It is sufficient if the size distribution of the ferrite phase is controlled so that the value of Equation (2) is 70, and can be controlled by various processes. For example, it may be controlled through a forging or rolling process, etc., and may be controlled by variously adjusting the reduction rate and the number of rolling. However, it should be noted that the above examples only list examples to aid understanding of the present invention, and do not specifically limit the technical idea of the present invention.

According to the present invention, the ferrite phase fraction exhibiting magnetic properties can be controlled as low as possible by controlling the alloy component, controlling the microstructure, or controlling both the alloy component and the microstructure as described above. Accordingly, the present invention can provide a non-magnetic austenitic stainless steel applied as a material for various electronic devices.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

{Example}

The steel having the chemical composition shown in Table 1 below was cast into a 200 mm thick slab through a continuous casting process. Thereafter, the cast slab was reheated at a temperature of 1,250° C. for 2 hours. Thereafter, the reheated slab was hot-rolled to a thickness of 6 mm, and then annealing heat treatment was performed at a temperature of 1,150°C.

The value of Equation (1) in Table 1 is the value derived by substituting the weight% of each alloy element in Table 1 into Equation (1) below.

(1) 3*(Cr+Mo) + 5*Si-65*(C+N)-2*(Ni+Mn)-28

In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (% by weight) of each alloy element.

The ferrite fraction in Table 1 was derived by measuring the ferrite fraction of the hot-rolled coil subjected to annealing heat treatment with a contact type ferrite scope. When the value did not appear upon contact, the fraction of the ferrite phase was determined as 0%.

Steel grade C Mn Cr Ni Si Mo Cu N Equation (1) Ferrite fraction (%) One 0.022 1.00 21.2 10.0 0.97 0.52 0.21 0.157 8.38 6.3 2 0.015 0.66 17.7 12.1 0.61 2.07 0.27 0.013 7.02 1.9 3 0.024 0.67 17.7 12.1 0.67 2.04 0.28 0.020 6.17 1.3 4 0.030 0.80 21.3 9.3 0.40 0.60 0.80 0.200 4.55 1.2 5 0.019 1.06 16.1 10.1 0.47 2.04 0.29 0.014 4.43 1.6 6 0.027 0.92 21.4 9.4 0.39 0.54 0.82 0.207 3.92 0.1 7 0.041 0.83 20.6 10.9 0.97 0.54 0.21 0.164 3.49 0.4 8 0.022 0.80 21.3 10.1 0.39 0.60 0.81 0.200 3.42 0.2 9 0.029 0.97 21.2 9.5 0.37 0.51 0.76 0.209 2.57 0.7 10 0.026 0.78 21.2 9.3 0.40 0.58 0.84 0.240 1.89 0.3 11 0.029 0.95 21.2 9.5 0.33 0.55 0.75 0.218 1.95 1.0 12 0.030 0.80 21.3 10.3 0.40 0.60 0.80 0.220 1.25 0.1 13 0.030 1.95 21.6 13.7 1.00 0.00 0.99 0.125 0.43 0.2 14 0.027 0.86 21.4 10.2 0.39 0.58 0.72 0.238 0.55 0.8 15 0.031 3.07 20.7 10.9 0.97 0.00 2.03 0.133 0.35 0.7 16 0.032 2.88 20.7 10.0 1.01 0.00 2.00 0.172 0.13 0.4 17 0.030 2.05 17.1 10.0 1.49 0.50 1.99 0.096 -0.04 0.0 18 0.029 2.06 17.0 10.0 1.48 0.76 2.00 0.104 -0.09 0.0 19 0.031 2.03 18.8 10.0 0.96 0.00 2.01 0.114 -0.29 0.0 20 0.020 2.02 17.0 9.1 1.48 0.50 1.99 0.140 -0.74 0.0 21 0.025 2.00 18.0 8.0 0.99 0.00 1.98 0.156 -0.82 0.0 22 0.032 1.96 19.9 9.0 1.01 0.00 2.01 0.209 -0.84 0.0 23 0.025 0.86 21.2 9.4 0.42 0.54 0.79 0.280 -1.03 0.0 24 0.025 0.96 20.4 12.4 0.97 0.20 0.30 0.179 -1.33 0.0 25 0.031 2.00 20.3 10.9 0.99 0.00 0.99 0.180 -1.67 0.0 26 0.023 1.27 17.3 14.4 0.45 2.55 0.00 0.048 -2.16 0.0 27 0.024 1.31 17.3 14.6 0.47 2.54 0.20 0.049 -2.70 0.0 28 0.033 1.98 17.9 7.8 1.01 0.00 2.00 0.197 -3.76 0.0 29 0.050 1.02 20.3 12.1 0.93 0.00 0.00 0.200 -4.94 0.0 30 0.097 0.98 20.5 12.2 0.98 0.00 0.00 0.210 -7.92 0.0

According to Table 1, steel grades 17 to 30 satisfy the alloy composition range defined in the present invention, and since the value of formula (1) has a negative value, the ferrite fraction was 0%. On the other hand, in steel grades 1 to 16, since each alloy component is within the composition range defined by the present invention, the value of formula (1) has a positive value, and thus ferrite remained even after heat treatment.

1 is a graph showing the change of the ferrite fraction according to the value of Equation (1) in Table 1. Referring to FIG. 1, it can be seen that the ferrite fraction increases at a point where the value of Equation (1) changes from 0 to a positive value. That is, as a result of controlling the value of Equation (1) to have a negative value in the present invention, the tendency of the ferrite fraction to be 0% can be visually confirmed from FIG. 1.

From the above results, it can be seen that the present invention can control the ferrite fraction to 0% by controlling the value of Equation (1) to have a negative value, and as a result, the desired nonmagnetic properties can be secured. .

On the other hand, ferrite decomposition can be accelerated by controlling the microstructure of steel grades 1 to 16 degrees having a ferrite fraction exceeding 0.0%, thereby lowering the permeability. The evaluation results in Table 2 below were based on steel grades 1 to 16 in which the ferrite fraction in Table 1 exceeded 0.0%, and the ferrite phase remained. Hot-rolled coils having a thickness of 6 mm according to steel types 1 to 16 were cold-rolled to a thickness of 1 mm or less, and then annealing heat treatment was performed.

The value of Equation (2) in Table 2 was derived through image analysis using an optical microscope after cold rolling.

The ferrite fraction in Table 2 was derived by measuring the ferrite fraction of the cold rolled coil subjected to annealing heat treatment with a contact type ferrite scope. When the value did not appear upon contact, the fraction of the ferrite phase was determined as 0%.

The magnetic permeability μ in Table 2 was measured using a contact-type magnetic permeability meter, Ferromaster. Steel grades 1 to 16 were cold-rolled to a thickness of 1 mm or less by applying various reduction ratios.

Steel grade Thickness (mm) Equation (2) Ferrite fraction (%) Permeability (μ) One 0.5 45.29 2.4 1.247 0.3 59.15 1.0 1.063 2 1.0 60.49 0.8 1.046 0.8 75.28 0.0 1.018 3 1.0 62.48 0.6 1.036 0.8 78.59 0.0 1.016 4 0.5 64.26 0.7 1.041 0.3 71.63 0.0 1.012 5 0.5 62.83 0.7 1.042 0.3 76.13 0.0 1.017 6 0.5 81.55 0.0 1.006 0.2 80.71 0.0 1.004 7 0.5 73.59 0.0 1.008 0.3 83.02 0.0 1.003 8 1.0 75.67 0.0 1.008 0.8 85.56 0.0 1.003 9 1.0 72.85 0.0 1.019 0.8 74.15 0.0 1.009 10 1.0 79.32 0.0 1.010 0.3 81.57 0.0 1.005 11 1.0 56.94 0.3 1.023 0.5 71.10 0.0 1.012 12 0.5 76.37 0.0 1.009 0.3 81.87 0.0 1.005 13 0.5 83.68 0.0 1.004 0.3 84.64 0.0 1.003 14 1.0 66.96 0.3 1.021 0.2 78.91 0.0 1.006 15 1.0 68.01 0.4 1.027 0.2 80.03 0.0 1.006 16 0.5 72.14 0.0 1.012 0.3 79.80 0.0 1.006

According to Table 2, if the microstructure is controlled so that the value of Equation (2) is 70 or more, all residual ferrite is decomposed during annealing heat treatment after rolling, resulting in a ferrite fraction of 0.0%, resulting in a permeability of 1.02 or less. You can see that there is. On the other hand, when the value of Equation (2) was less than 70, the residual ferrite was not completely decomposed during annealing heat treatment after rolling, so that the permeability value exceeded 1.02.

2 is a graph showing the change in permeability according to the value of Equation (2) in Table 2. Referring to FIG. 2, at the point where the value of Equation (2) changes from 70 to more, it can be seen that the permeability decreases from 1.02. That is, as a result of controlling the value of Equation (2) to be 70 or more in the present invention, a tendency to secure a permeability of 1.02 or less can be visually confirmed from FIG. 2.

From the above results, the present invention accelerates the decomposition of residual ferrite during annealing heat treatment after cold rolling by controlling the value of Equation (2) to be 70 or more even when there is ferrite remaining after hot rolling or annealing heat treatment. It can be seen that sex characteristics can be obtained.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and those of ordinary skill in the art are within the scope not departing from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (5)

In% by weight, C: 0.01 to 0.1%, Si: 1.5% or less (excluding 0), Mn: 0.5 to 3.5%, Cr: 16 to 22%, Ni: 7 to 15%, Mo: 3% or less, N: 0.01 to 0.3%, containing the remaining Fe and other inevitable impurities,
Nonmagnetic austenitic stainless steel in which the value of the following formula (1) is negative:
(1) 3*(Cr+Mo) + 5*Si-65*(C+N)-2*(Ni+Mn)-28
(In the formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (% by weight) of each alloy element). The method of claim 1,
By weight %, Cu: non-magnetic austenitic stainless steel further containing 2.5% or less. In% by weight, C: 0.01 to 0.1%, Si: 1.5% or less (excluding 0), Mn: 0.5 to 3.5%, Cr: 16 to 22%, Ni: 7 to 15%, Mo: 3% or less, N: 0.01 to 0.3%, containing the remaining Fe and other inevitable impurities,
Nonmagnetic austenitic stainless steel having a value of 70 or more in the following formula (2):
(2) ΣA ₅ /ΣA x 100
(In the above formula (2), ?A ₅ is the sum of the areas of ferrite particles having an area of 5 μm ² or less, and ?A is the sum of the areas of all ferrite particles). The method of claim 3,
By weight %, Cu: non-magnetic austenitic stainless steel further containing 2.5% or less. The method of claim 3,
Non-magnetic austenitic stainless steel with a permeability of 1.02 or less at a thickness of 1 mm or less.

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