Title of Invention: Non-magnetic austenitic stainless steel
technical field
[One]
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.
background
[2]
Recently, as smart devices with various functions are used, there is an increasing demand for steel materials with reduced magnetism to reduce power loss and prevent malfunctions. 300 series stainless steel has an austenite phase as a main structure and has a non-magnetic characteristic, so it is widely used as a material for electronic devices.
[3]
However, in normal STS304 or STS316 austenitic stainless steel, δ-ferrite is formed in a fraction of 1 to 5% during steel making/casting. The formed δ-ferrite is a structure that induces magnetism, and there is a problem in that the final product exhibits magnetism. Therefore, conventional STS304 and STS316 austenitic stainless steels have a problem in that they cannot secure non-magnetic properties due to δ-ferrite.
[4]
δ-ferrite can be decomposed by heat treatment in a temperature range of 1,300 to 1,400 °C. However, δ-ferrite may remain in the structure without being completely removed even in the rolling and annealing processes, and there is a problem in that non-magnetic properties cannot be secured due to increased magnetism by the remaining ferrite.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[5]
In order to solve the above problems, the present invention is to provide a non-magnetic austenitic stainless steel that can be applied as a material for various electronic devices.
means of solving the problem
[6]
As a means for achieving the above object, the present specification, in 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%, the remaining Fe and other unavoidable impurities, and the value of the following formula (1) is a negative value.
[7]
(1) 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 28
[8]
In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each alloy element.
[9]
In each non-magnetic austenitic stainless steel of the present invention, by weight%, Cu: 2.5% or less may be further included.
[10]
In addition, as another means for achieving the above object, the present specification is, 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%, the remaining Fe and other unavoidable impurities, and the value of the following formula (2) is 70 or more Disclosed is a non-magnetic austenitic stainless steel. .
[11]
(2) ΣA 5 /ΣA x 100
[12]
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.
[13]
In each non-magnetic austenitic stainless steel of the present invention, by weight%, Cu: 2.5% or less may be further included.
[14]
In each nonmagnetic austenitic stainless steel of the present invention, at a thickness of 1 mm or less, the magnetic permeability may be 1.02 or less.
Effects of the Invention
[15]
According to the present invention, it is possible to provide a non-magnetic austenitic stainless steel that is applied to various electronic devices by controlling the fraction of the ferrite phase causing magnetism to be low.
[16]
According to the present invention, the fraction of the ferrite phase can be lowered by controlling the alloy components to suppress the formation of ferrite, or by accelerating the decomposition of ferrite through the control of the microstructure.
Brief description of the drawing
[17]
1 is a graph showing the change in the ferrite fraction according to the value of Equation (1) in Table 1.
[18]
2 is a graph showing a change in magnetic permeability according to the value of Equation (2) in Table 2.
Best mode for carrying out the invention
[19]
Non-magnetic austenitic stainless steel according to an embodiment of the present invention is, 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%, remaining Fe and other unavoidable impurities, and the value of the following formula (1) is a negative value.
[20]
(1) 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 28
[21]
In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each alloy element.
Modes for carrying out the invention
[22]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes preferred embodiments of the present invention. However, the embodiment of the present invention may be modified in various other forms, and the technical idea of ​​the present invention is not limited to the embodiment described below. In addition, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.
[23]
The terms used in this application are only used to describe specific examples. Therefore, for example, a singular expression includes a plural expression unless the context clearly requires it to be singular. In addition, the terms "comprises" or "includes" as used in the present application are used to clearly indicate that the features, steps, functions, components, or combinations thereof described in the specification exist, and other features It should be noted that it is not intended to be used to preliminarily exclude the existence of elements, steps, functions, components, or combinations thereof.
[24]
Meanwhile, unless otherwise defined, all terms used herein should be regarded as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Accordingly, unless explicitly defined herein, certain terms should not be construed in an unduly idealistic or formal sense. For example, a singular expression herein includes a plural expression unless the context clearly dictates otherwise.
[25]
In addition, in this specification, "about", "substantially", etc. are used in or close to the numerical value when manufacturing and material tolerances inherent in the stated meaning are presented, and are used in a precise sense to aid the understanding of the present invention. or absolute figures are used to prevent unreasonable use of the mentioned disclosure by an unconscionable infringer.
[26]
Non-magnetic austenitic stainless steel according to an embodiment of the present invention is, 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%, the remaining Fe and other unavoidable impurities may be included. In addition, Cu: 2.5% or less may be further included.
[27]
Hereinafter, the reason for limiting the alloy composition will be described in detail. All of the following component compositions refer to weight % unless otherwise specified.
[28]
Carbon (C): 0.01 to 0.1% by weight
[29]
C is a strong austenite phase stabilizing element, and is an element that suppresses the increase in magnetism during solidification. In the present invention, C may be added in an amount of 0.01 wt % or more for austenite phase stabilization effect. However, if the C content is excessive, it combines with Cr to form carbides at the grain boundaries, and there is a risk of lowering the Cr content around the grain boundaries locally to reduce corrosion. Therefore, in order to ensure sufficient corrosion resistance, the upper limit of the C content in the present invention is preferably limited to 0.1% by weight.
[30]
Silicon (Si): 1.5 wt% or less (excluding 0)
[31]
Si is an element that improves corrosion resistance. However, Si is a ferrite phase stabilizing element that induces magnetism, and if the Si content is excessive, it promotes precipitation of intermetallic compounds such as sigma phase, which may reduce mechanical properties and corrosion resistance. Accordingly, the upper limit of the Si content in the present invention is preferably limited to 1.5% by weight.
[32]
Manganese (Mn): 0.5 to 3.5 wt%
[33]
Mn is an austenite phase stabilizing element such as C and Ni, and is effective for non-magnetic strengthening. Accordingly, in the present invention, Mn may be added in an amount of 0.5 wt% or more. However, when the Mn content is excessive, there is a problem of forming inclusions such as MnS to reduce corrosion resistance and reduce surface gloss. Accordingly, the upper limit of the Mn content in the present invention is preferably limited to 3.5% by weight.
[34]
Chromium (Cr): 16 to 22 wt%
[35]
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 induces magnetism. In addition, if the Cr content is excessive, the cost increases because a large amount of Ni must be included in order to obtain non-magnetic properties, and the formation of σ phase is promoted, thereby reducing mechanical properties and corrosion resistance. Accordingly, the Cr content is preferably limited to 22% by weight.
[36]
Nickel (Ni): 7 to 15 wt%
[37]
Ni is the strongest austenite phase stabilizing element, and in the present invention, Ni may be added in an amount of 7 wt% or more to obtain nonmagnetic properties. However, since the raw material price increases when the Ni content is increased, it is preferable that the upper limit of the Ni content is limited to 15% by weight.
[38]
Molybdenum (Mo): 3% by weight or less
[39]
Mo is an element that improves corrosion resistance. However, Mo is a ferrite phase stabilizing element, and if the Mo content is excessive, the formation of the σ phase is promoted and there is a risk of lowering mechanical properties and corrosion resistance. Accordingly, the upper limit of the Mo content in the present invention is preferably limited to 3% by weight,
[40]
Nitrogen (N): 0.01 to 0.3 wt%
[41]
N is an austenite phase stabilizing element, and in the present invention, N may be added in an amount of 0.01 wt % or more to obtain non-magnetic properties. However, if the N content is excessive, the hot workability of the steel is reduced and the surface quality is deteriorated, so the upper limit of the N content is preferably limited to 0.3% by weight.
[42]
The non-magnetic austenitic stainless steel according to an embodiment of the present invention may optionally further include Cu: 2.5 wt% or less. Hereinafter, the reason for limiting the Cu component will be described in detail.
[43]
Copper (Cu): 2.5 wt% or less
[44]
Cu is an austenite phase stabilizing element and can be used instead of expensive Ni. However, when the Cu content is excessive, a low-melting-point phase is formed, which lowers the hot workability and deteriorates 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.
[45]
The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since the impurities are known to any person skilled in the art of a conventional manufacturing process, all details thereof are not specifically mentioned in the present specification.
[46]
In general, STS 304 or 316 stainless steel is composed of an austenite phase as a main structure, and has a microstructure in which a ferrite phase formed during steelmaking/casting 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 nonmagnetic properties desired by the present invention depending on the fraction of the remaining ferrite phase. Accordingly, in order to secure the non-magnetic properties, it is necessary to control the fraction of the ferrite phase that induces magnetism as low as possible. Hereinafter, specific technical means for securing the desired non-magnetic properties of the present invention will be described in detail.
[47]
alloy composition control
[48]
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 decrease the fraction of the ferrite phase when added, and component elements such as Cr and Mo increase the fraction of the ferrite phase. In consideration of this, the present inventors derived the following Equation (1) that can control the fraction of the ferrite phase.
[49]
(1) 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 28
[50]
In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each alloy element.
[51]
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%.
[52]
microstructure control
[53]
Meanwhile, the ferrite phase remaining during steelmaking/casting may be decomposed according to a heat treatment process performed later. The present inventors found that the decomposition of the ferrite phase in the heat treatment process can be accelerated through the control of the microstructure even when the value of Equation (1) has a positive value so that the ferrite phase remains, and accordingly, the steel becomes magnetic. did. The acceleration of 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.
[54]
(2) ΣA 5 /ΣA x 100
[55]
In 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 compared to the sum of the areas of all ferrite particles.
[56]
According to an example of the present invention, the value of Equation (2) above may be controlled 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 to be high as described above. As a result, the permeability after heat treatment may be 1.02 or less, and in particular, the magnetic permeability may be 1.02 or less at a thickness of 1 mm or less.
[57]
It is sufficient if the size distribution of the ferrite phase is controlled so that the value of Equation (2) becomes 70, and can be controlled by various processes. For example, it may be controlled through a forging or rolling process, and the like, and may be controlled by variously adjusting the reduction ratio, the number of rolling, and the like. However, it is necessary to note that the above examples only list examples to help the understanding of the present invention, and do not specifically limit the technical spirit of the present invention.
[58]
According to the present invention, as described above, by controlling the alloy component, controlling the microstructure, or controlling both the alloy component and the microstructure, it is possible to control the magnetic ferrite phase fraction as low as possible. Accordingly, the present invention can provide a non-magnetic austenitic stainless steel applied as a material for various electronic devices.
[59]
Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.
[60]
{Example}
[61]
Steel having the chemical composition shown in Table 1 below was cast into a 200mm 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 annealed at a temperature of 1,150°C.
[62]
The value of Equation (1) in Table 1 is a value derived by substituting the weight% of each alloy element in Table 1 into Equation (1) below.
[63]
(1) 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 28
[64]
In Formula (1), Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each alloy element.
[65]
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 ferrite scope. When no value appears upon contact, the fraction of the ferrite phase was determined to be 0%.
[66]
[Table 1]
steel grade Alloy composition (wt%) Formula (1) Ferrite fraction (%)
C Mn Cr Ni Si Mo Cu N
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
[67]
According to Table 1, steel types 17 to 30 satisfy the alloy composition range limited by the present invention, and since the value of Equation (1) has a negative value, the ferrite fraction was 0%. On the other hand, in steel types 1 to 16, each alloy component is within the composition range limited by the present invention, but since the value of Equation (1) has a positive value, ferrite remained even after heat treatment.
[68]
1 is a graph showing the change in 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 tends to increase at the 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, it can be visually confirmed from FIG. 1 that the ferrite fraction tends to be 0%.
[69]
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, it is possible to secure the desired non-magnetic properties. .
[70]
On the other hand, it is possible to control the magnetic permeability to be low by accelerating the decomposition of ferrite through the control of the microstructure of grades 1 to 16 of steel having a ferrite fraction exceeding 0.0%. The evaluation results in Table 2 below were for steel types 1 to 16 in which the ferrite fraction exceeded 0.0% in Table 1, and the ferrite phase remained. Hot-rolled coils having a thickness of 6 mm according to steel grades 1 to 16 were cold-rolled to a thickness of 1 mm or less, followed by annealing heat treatment.
[71]
The value of Equation (2) in Table 2 was derived through image analysis using an optical microscope after cold rolling.
[72]
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 ferrite scope. When no value appears upon contact, the fraction of the ferrite phase was determined to be 0%.
[73]
Permeability μ in Table 2 was measured using a ferromaster, which is a contact type magnetic permeability meter. Steel grades 1 to 16 were cold-rolled to a thickness of 1 mm or less by applying various reduction ratios.
[74]
[Table 2]
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
[75]
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, so that the ferrite fraction is 0.0%, and as a result, permeability of 1.02 or less can be secured it can be seen 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 magnetic permeability value exceeded 1.02.
[76]
2 is a graph showing the change in permeability according to the value of Equation (2) in Table 2. Referring to FIG. 2 , it can be seen that the permeability decreases from 1.02 at the point where the value of Equation (2) changes from 70 to more. That is, as a result of controlling the value of Equation (2) to be 70 or more in the present invention, it can be visually confirmed from FIG. 2 that the permeability of 1.02 or less is secured.
[77]
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 residual ferrite after hot rolling and annealing heat treatment to accelerate the decomposition of the desired non-ferrite It can be seen that the sexual characteristics can be secured.
[78]
In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art will not depart from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.
Industrial Applicability
[79]
The non-magnetic austenitic stainless steel according to the present invention can be applied as a material for various electronic devices.
Claims
[Claim 1]
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: Non-magnetic austenitic stainless steel containing 0.01 to 0.3%, remaining Fe and other unavoidable impurities, and having a negative value of 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, Mn mean the content (wt%) of each alloying element ).
[Claim 2]
The non-magnetic austenitic stainless steel according to claim 1, further comprising, by weight %, Cu: 2.5% or less.
[Claim 3]
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: Non-magnetic austenitic stainless steel containing 0.01 to 0.3%, the remaining Fe and other unavoidable impurities, and having a value of the following formula (2) of 70 or more: (2) ΣA 5 /ΣA x 100 (in the 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).
[Claim 4]
The non-magnetic austenitic stainless steel according to claim 3, further comprising, by weight %, Cu: 2.5% or less.
[Claim 5]
4. The non-magnetic austenitic stainless steel according to claim 3, wherein, at a thickness of 1 mm or less, the magnetic permeability is 1.02 or less.