Title of Invention: Non-magnetic austenitic stainless steel and manufacturing method thereof
technical field
[One]
The present invention relates to a non-magnetic austenitic stainless steel, and more particularly, to a non-magnetic austenitic stainless steel having excellent hot workability and low magnetic permeability during manufacturing, and a method for manufacturing the same.
background
[2]
Recently, with the advent of smart devices having various functions, new demands for factors that can affect the functions of devices are being strengthened even for materials used in electronic devices. In particular, there is an increasing demand for magnetic reduction to improve electrical efficiency and prevent malfunction. Since 300 series stainless steel usually exhibits non-magnetic properties due to the non-magnetic properties of the austenite phase, it is widely used as a material for such electronic devices.
[3]
On the other hand, 300 series stainless steel forms delta-ferrite upon solidification. Delta-ferrite formed during solidification has the effect of suppressing grain growth and improving hot workability. In general, delta-ferrite can be stably decomposed in the temperature range of 1,300 to 1,450 ° C through heat treatment. However, the delta-ferrite may remain without being completely removed even in the rolling and annealing processes, and the remaining delta-ferrite has a problem in that it cannot be used as a material for electronic devices due to increased magnetism.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[4]
The present invention controls the content of delta-ferrite formed during solidification in order to prevent magnetic formation and deterioration of hot workability of austenitic stainless steel, and non-magnetic austenite that can suppress the increase in magnetism due to martensite transformation even in the work hardening process An object of the present invention is to provide a nitrite-based stainless steel and a method for manufacturing the same.
means of solving the problem
[5]
Non-magnetic austenitic stainless steel hot annealed steel sheet according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, remaining Fe and unavoidable impurities, and the following formula (1) is satisfied.
[6]
(1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5
[7]
Here, Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each element.
[8]
In addition, according to an embodiment of the present invention, the hot-rolled annealed steel sheet may have a magnetic permeability of 1.05 or less and a hardness of 170 Hv or more.
[9]
In addition, according to an embodiment of the present invention, the number of surface cracks of the hot-rolled annealed steel sheet may be 0.3 or less per unit meter (m).
[10]
Non-magnetic austenitic stainless steel cold rolled steel sheet according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni : 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, remaining Fe and unavoidable impurities, and satisfies the following formulas (1) and (2).
[11]
(1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5
[12]
(2) 660 - 500*(C+N) - 10*Cr - 30*(Ni+Si+Mo+Cu) ≤ 0
[13]
Here, Cr, Mo, Si, C, N, Ni, Mn, and Cu mean the content (% by weight) of each element.
[14]
In addition, according to an embodiment of the present invention, the cold-rolled steel sheet may be a cold-rolled material having a reduction ratio of 60% or more, and a magnetic permeability of 1.05 or less and a hardness of 350 Hv or more.
[15]
The method for manufacturing a non-magnetic austenitic stainless steel according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, hot rolling and annealing a slab containing the remaining Fe and unavoidable impurities to prepare a hot rolled annealed steel sheet ; and manufacturing a cold rolled steel sheet by cold rolling the hot-rolled annealed steel sheet at a reduction ratio of 60% or more, wherein the slab satisfies the following formulas (1) and (2), and the hot-rolled annealed steel sheet and the cold-rolled steel sheet The permeability of is less than 1.05.
[16]
(1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5
[17]
(2) 660 - 500*(C+N) - 10*Cr - 30*(Ni+Si+Mo+Cu) ≤ 0
[18]
In addition, according to an embodiment of the present invention, the hardness of the hot-rolled annealed steel sheet is 170 Hv or more, and the hardness may be increased by 150 Hv or more by the cold rolling.
Effects of the Invention
[19]
The non-magnetic austenitic stainless steel according to an embodiment of the present invention can secure non-magnetic properties by suppressing delta-ferrite formation without deterioration of hot workability. In addition, it is possible to prevent the formation of magnetism during work hardening to improve strength by suppressing the formation of process-induced martensite.
[20]
Suppression of magnetism can have the effect of preventing communication errors and increasing power efficiency in smart devices, and improving strength through work hardening can contribute to weight reduction of parts, thereby reducing the weight of smart devices.
Brief description of the drawing
[21]
1 is a graph showing the distribution of the number of surface cracks of a hot-rolled annealed steel sheet according to Equation (1) of an embodiment of the present invention.
[22]
2 is a graph showing the magnetic permeability distribution of the cold-rolled steel sheet according to Equation (2) of the embodiment of the present invention.
Best mode for carrying out the invention
[23]
Non-magnetic austenitic stainless steel hot annealed steel sheet according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, remaining Fe and unavoidable impurities, and the following formula (1) is satisfied.
[24]
(1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5
[25]
Here, Cr, Mo, Si, C, N, Ni, and Mn mean the content (wt%) of each element.
Modes for carrying out the invention
[26]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein and may be embodied in other forms. The drawings may omit the illustration of parts irrelevant to the description in order to clarify the present invention, and may slightly exaggerate the size of the components to help understanding.
[27]
Non-magnetic austenitic stainless steel according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, remaining Fe and unavoidable impurities.
[28]
Hereinafter, the reason for numerical limitation of the alloy element content in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.
[29]
The content of C is 0.01 to 0.05%.
[30]
C is a strong austenite phase stabilizing element, and is an effective element for suppressing increase in magnetism not only during solidification but also during work hardening. For the stabilizing effect of the austenite phase, it is necessary to add 0.01% or more. However, when the content is excessive, there is a problem of reducing the corrosion resistance by lowering the Cr content around the grain boundary because it forms carbides by combining with Cr effective for corrosion resistance at the grain boundary. Therefore, in order to secure sufficient corrosion resistance, it is necessary to limit the C content to 0.05% or less.
[31]
The content of Si is 1.5% or less.
[32]
Si is effective in improving corrosion resistance, but there is a problem of generating magnetism as a ferrite phase stabilizing element. In addition, if it is excessive, it is preferable to limit it to 1.5% or less because it promotes the precipitation of intermetallic compounds such as σ phase and deteriorates mechanical properties and corrosion resistance.
[33]
The content of Mn is 0.5 to 3.5%.
[34]
Mn is an austenite phase stabilizing element such as C and Ni, and is effective for non-magnetic strengthening. However, since the increase of the Mn content is involved in the formation of inclusions such as MnS, and there is a problem of lowering corrosion resistance and lowering the surface gloss, it is preferable to limit the Mn content to 0.5 to 3.5%.
[35]
The content of Cr is 17.0 to 22.0%.
[36]
Cr is the most important element for improving the corrosion resistance of stainless steel. In order to ensure sufficient corrosion resistance, it is preferable to contain 17.0% or more, but since Cr is a ferrite phase stabilizing element, it is necessary to limit the addition in non-magnetic steel. As the Cr content increases, the ferrite phase fraction increases, which increases the cost because a large amount of Ni must be included in order to obtain non-magnetic properties, and promotes the formation of σ phase, which causes deterioration of mechanical properties and corrosion resistance. Therefore, it is preferable to limit the Cr content to 22.0% or less.
[37]
The content of Ni is 9.0 to 14.0%.
[38]
Ni is the strongest element among the austenite phase stabilizing elements, and should be contained in an amount of 9.0% or more in order to obtain non-magnetic properties. However, since an increase in the Ni content is directly related to an increase in the raw material price, it is preferable to limit it to 14.0% or less.
[39]
The content of Mo is 1.0% or less.
[40]
Mo is a useful element for improving corrosion resistance, but as a ferrite phase stabilizing element, when a large amount is added, the ferrite phase fraction is increased, so that it is difficult to obtain non-magnetic properties. In addition, it is preferable to limit the amount to 1.0% or less because the formation of the σ phase is promoted, which causes deterioration of mechanical properties and corrosion resistance.
[41]
The content of Cu is 0.2 to 2.5%.
[42]
Cu is a useful element for stabilizing the austenite phase, and may be used by substituting for expensive Ni. 0.2% or more is required to secure non-magnetic properties and reduce cost. However, when a large amount is added, a low melting point phase is formed, which reduces hot workability and deteriorates the surface quality. Therefore, it is preferable to limit it to 2.5% or less.
[43]
The content of N is 0.05 to 0.25%.
[44]
N is a useful element for stabilizing the austenite phase and is an essential element for securing non-magnetic properties. Therefore, it is necessary to add at least 0.05%. However, when a large amount is added, the hot workability is reduced and the surface quality of the steel is deteriorated, so it is preferable to limit it to 0.25% or less.
[45]
The remainder of the stainless steel except for the above-mentioned alloying elements consists of Fe and other unavoidable impurities.
[46]
In general, 300 series stainless steel is mostly composed of an austenite phase and appears as a microstructure in which some ferrite phases formed during solidification remain. In 300 series stainless steel, the ferrite phase is effective in improving hot workability by preventing grain boundary segregation during solidification and suppressing grain growth during reheating. Therefore, in the case of normal 304 and 316 steel grades, a ferrite phase is formed during solidification, and some ferrite phases are also contained in the product.
[47]
On the other hand, the austenite phase existing in the structure of the 300 series stainless steel does not show magnetism in the face-centered cubic structure, but the ferrite phase becomes magnetic due to the characteristics of the structure having the body-centered cubic structure. Therefore, it may exhibit magnetism depending on the content of the remaining ferrite phase, so that its application to electronic products may be limited. For this reason, in the case of non-magnetic steel, it is essential to make the fraction of ferrite phase as low as possible or to eliminate it.
[48]
The content of the remaining ferrite phase is greatly affected by alloying components and annealing heat treatment. The content of ferrite formed during solidification in 300 series stainless steel is affected by the content of constituent elements such as Ni, Mn, C, and N that stabilize the austenite phase and Cr and Mo that stabilize the ferrite phase. Since the ferrite phase generated during solidification is unstable at high temperature, it can be reduced through hot rolling and annealing heat treatment, which is a subsequent process. As a result of evaluating the residual ferrite fraction considering the degree of decomposition by subsequent processes after continuous casting and hot rolling for various components, an expression for the residual ferrite content as in Equation (1) was derived.
[49]
(1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5
[50]
When Equation (1) has a negative value less than 0, cracks occur on the surface due to deterioration of hot workability. 1 is a graph showing the distribution of the number of surface cracks per unit meter (pieces/m) of a hot-rolled annealed steel sheet according to Equation (1). Referring to FIG. 1 , when the value of Equation (1) is less than 0, it can be seen that the number of cracks frequently occurs at 0.3 cracks/m or more.
[51]
On the other hand, the residual ferrite fraction of the hot-rolled annealed steel sheet is limited to 1% or less in order to secure the non-magnetic properties of the magnetic permeability of 1.05 or less. When the value of Equation (1) exceeds 5, the residual ferrite fraction becomes 1% or more. Through this, in the present invention, when the value of Equation (1) has a range of 0 to 5, it is possible to manufacture an austenitic stainless steel that satisfies the non-magnetic properties without deterioration in hot workability.
[52]
On the other hand, austenitic stainless steel generates magnetism due to the formation of a martensitic phase during work hardening. Work hardening occurs not only in the process applied to increase the strength of the material, but also during molding to make the product shape. When the magnetism is increased, it is necessary to suppress the increase in the magnetism because the use for home appliances is limited.
[53]
In order to prevent an increase in magnetism due to work hardening, the austenitic stainless steel of the present invention may satisfy Equation (2).
[54]
(2) 660 - 500*(C+N) - 10*Cr - 30*(Ni+Si+Mo+Cu) ≤ 0
[55]
When the value of Equation (2) represents a positive value greater than 0, martensitic transformation occurs during cold working. When the nonmagnetic austenitic stainless steel cold rolled steel sheet according to the present invention satisfies Equation (2), it is possible to suppress the process-induced martensitic phase formation even during cold rolling of 60% or more, thereby providing a final cold rolled material having a magnetic permeability of 1.05 or less. have.
[56]
Next, a method for manufacturing a non-magnetic austenitic stainless steel according to an embodiment of the present invention will be described.
[57]
The method for manufacturing non-magnetic austenitic stainless steel according to the present invention may be manufactured through a general process of austenitic stainless steel. It is important to control the composition of alloy elements to prevent the residual ferrite fraction after hot rolling annealing heat treatment and the formation of work-induced martensite phase during cold rolling.
[58]
In the method of manufacturing a non-magnetic austenitic stainless steel according to an embodiment of the present invention, C: 0.01 to 0.05% by weight, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni : 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5%, N: 0.05 to 0.25%, hot rolling and annealing a slab containing the remaining Fe and unavoidable impurities to prepare a hot rolled annealed steel sheet; and cold-rolling the hot-rolled annealed steel sheet at a reduction ratio of 60% or more to manufacture a cold-rolled steel sheet.
[59]
By satisfying Equation (1), the hot-rolled annealed steel sheet may exhibit a magnetic permeability of 1.05 or less, and by satisfying Equation (2), the cold-rolled steel sheet may exhibit a magnetic permeability of 1.05 or less.
[60]
According to an embodiment of the present invention, the hardness of the hot-rolled annealed steel sheet may be 170 Hv or more, and it is possible to suppress the processing-induced martensite phase formation during cold rolling, so that it is possible to secure an increase in hardness of 150 Hv or more under 60% cold rolling conditions.
[61]
The increase in hardness of hot-rolled and cold-rolled steel sheets is due to the addition of interstitial elements such as C and N. Typical 300 series stainless steel shows an increase in strength through martensitic transformation, but in the present invention, this transformation phenomenon is limited in order to suppress the increase in magnetism and the effect of solid solution strengthening by the addition of interstitial elements is maximized. Through this, it is possible to increase the hardness of the hot-rolled annealed material, and to secure an increase in strength through a dislocation pinning phenomenon during cold working.
[62]
[63]
Hereinafter, it will be described in more detail through preferred embodiments of the present invention.
[64]
Example
[65]
1. Hot workability and non-magnetic evaluation
[66]
Steel having the alloy composition shown in Table 1 was cast into a 200 mm thick slab through a continuous casting process, and then hot annealed steel sheets were manufactured through hot rolling and annealing heat treatment processes. Hot rolling was carried out to a thickness of 6mm after heating at 1,250°C for 2 hours, and characteristic evaluation was performed after annealing the hot-rolled steel sheet at 1,150°C.
[67]
[Table 1]
Steel grade No. C Si Mn Cr Ni Mo Cu N
One 0.029 0.37 0.97 21.2 9.5 0.51 0.76 0.209
2 0.041 0.97 0.83 20.6 10.9 0.54 0.21 0.164
3 0.022 0.39 0.80 21.3 10.1 0.60 0.81 0.200
4 0.030 1.00 1.95 21.6 13.7 0.00 0.99 0.125
5 0.030 0.40 0.80 21.3 10.3 0.60 0.80 0.220
6 0.027 0.39 0.92 21.4 9.4 0.54 0.82 0.207
7 0.029 0.33 0.95 21.2 9.5 0.55 0.75 0.218
8 0.032 1.01 2.88 20.7 10.0 0.00 2.00 0.172
9 0.031 0.97 3.07 20.7 10.9 0.00 2.03 0.133
10 0.029 1.48 2.06 17.0 10.0 0.76 2.00 0.104
11 0.026 0.40 0.78 21.2 9.3 0.58 0.84 0.240
12 0.027 0.39 0.86 21.4 10.2 0.58 0.72 0.238
13 0.032 1.01 1.96 19.9 9.0 0.00 2.01 0.209
14 0.030 1.00 1.00 20.7 11.1 0.00 2.00 0.178
15 0.030 1.49 2.05 17.1 10.0 0.50 1.99 0.096
16 0.031 0.96 2.03 18.8 10.0 0.00 2.01 0.114
17 0.025 0.99 2.00 18.0 8.0 0.00 1.98 0.156
18 0.020 1.48 2.02 17.0 9.1 0.50 1.99 0.140
19 0.022 0.97 1.00 21.2 10.0 0.52 0.21 0.157
20 0.015 0.61 0.66 17.7 12.1 2.07 0.27 0.013
21 0.024 0.67 0.67 17.7 12.1 2.04 0.28 0.020
22 0.019 0.47 1.06 16.1 10.1 2.04 0.29 0.014
23 0.030 0.40 0.80 21.3 9.3 0.60 0.80 0.200
24 0.031 0.99 2.00 20.3 10.9 0.00 0.99 0.180
25 0.025 0.42 0.86 21.2 9.4 0.54 0.79 0.280
26 0.025 0.97 0.96 20.4 12.4 0.20 0.30 0.179
27 0.024 0.47 1.31 17.3 14.6 2.54 0.20 0.049
28 0.050 0.93 1.02 20.3 12.1 0.00 0.00 0.200
29 0.023 0.45 1.27 17.3 14.4 2.55 0.00 0.048
30 0.097 0.98 0.98 20.5 12.2 0.00 0.00 0.210
31 0.033 1.01 1.98 17.9 7.8 0.00 2.00 0.197
[68]
Table 2 shows the results of evaluation of the number of surface cracks and permeability of a 6mm hot rolled coil, and the magnetic permeability of a cold rolled steel sheet after 60% cold rolling to a thickness of 2.4mm. The number of surface cracks is obtained by dividing the total number of surface cracks by the coil length in a 6mm thick coil to obtain the number of cracks per unit meter. Usually, when the number is 0.3 or less, it is judged as an excellent surface quality material. The permeability was measured using a contact ferrometer, and a value of 1.05 or less is required to be used for electronic products.
[69]
[Table 2]
division Kang type No. Formula (1) Number of cracks (pieces/m) Permeability (μ) of hot annealed steel sheet Equation (2) Cold-rolled steel sheet magnetic permeability (μ)
invention example One 3.50 0.00 1.040 -4.4 1.046
2 4.43 0.00 1.024 -26.3 1.036
3 4.42 0.00 1.010 -21.0 1.020
4 1.43 0.00 1.004 -104.2 1.003
5 2.25 0.00 1.020 -41.0 1.022
6 4.92 0.00 1.008 -5.5 1.024
7 2.89 0.03 1.046 -8.4 1.045
8 1.13 0.03 1.030 -39.3 1.031
9 1.35 0.07 1.039 -46.0 1.039
10 0.91 0.07 1.005 -3.7 1.038
11 2.89 0.12 1.027 -18.6 1.042
12 1.39 0.13 1.037 -44.1 1.036
13 0.16 0.15 1.005 -20.1 1.008
14 2.38 0.21 1.007 -74.0 1.007
comparative example 15 0.96 0.12 1.007 6.6 1.067
16 0.72 0.14 1.002 10.4 1.051
17 0.19 0.19 1.014 60.4 1.096
18 0.26 0.24 1.012 17.9 1.084
19 9.47 0.00 1.673 7.5 1.702
20 8.00 0.00 1.131 18.5 1.247
21 7.33 0.00 1.058 9.6 1.150
22 5.43 0.00 1.080 96.0 2.000
23 5.55 0.00 1.062 -1.0 1.076
24 -0.66 0.34 1.003 -34.9 1.003
25 -0.03 0.43 1.002 -39.0 1.017
26 -0.12 0.45 1.002 -60.9 1.002
27 -1.54 0.46 1.002 -84.3 1.003
28 -3.94 0.62 1.003 -58.9 1.004
29 -1.16 0.71 1.002 -70.5 1.003
30 -6.91 0.83 1.002 -93.9 1.003
31 -2.76 0.65 1.004 41.7 1.081
[70]
Looking at Tables 1 and 2 together, the hot-rolled annealed steel sheets of steel grades 1 to 18 showed good surface quality with the number of surface cracks being 0.24 pieces/m or less when the value of Equation (1) had a positive value of 0 or more. On the other hand, in steel grades 24-31, the number of cracks increased because the value of Equation (1) had a negative value.
[71]
The magnetic permeability was also measured to be 1.05 or less when the value of Equation (1) was 5 or less, and when it was more than 5, the magnetic permeability was more than 1.05 due to an excess of the residual ferrite fraction.
[72]
Through this, it was confirmed that the range of Equation (1) should have a range of 0 to 5 in order to obtain a level of permeability suitable for use in electronic products without a problem of hot workability, and the distribution of the number of cracks according to Equation (1) was confirmed. 1 is shown.
[73]
Of the 1 to 18 steel types that satisfy Formula (1), 1 to 140,000 are simultaneously satisfied with Formula (2). For steel grades 1 to 14, Eq. (2) was also satisfied, so that even during cold rolling with a reduction ratio of 60%, the formation of a process-induced martensite phase was suppressed, so that the magnetic permeability of the final cold rolled steel sheet did not increase and satisfies 1.05 or less. However, for steel grades 15 to 18, the permeability of the hot-rolled annealed steel sheet was 1.05 or less by satisfying Equation (1), but the value of Equation (2) showed a positive value, and the permeability increased after cold rolling. From this, it was found that a process-induced martensite phase was formed during cold rolling.
[74]
For steel grades 19 to 23, the value of formula (1) exceeds 5, and permeability corresponds to 1.05 or more. Among them, steel types 19 to 22 had a positive value in Equation (2), indicating a large increase in magnetic permeability, and from this, it was possible to infer the formation of a processing-induced martensite phase. 23 The alloy composition of the steel type satisfies the range of the present invention, but the permeability of the hot-rolled annealed steel sheet was high due to the dissatisfaction of Equation (1), and the increase in permeability was not large due to the satisfaction of Equation (2).
[75]
For steel grades 24 to 31, the value of Equation (1) shows a negative value, showing a case where the hot workability is poor. As a result of the cold rolling process in spite of the high number of surface cracks due to the inferiority of the hot workability for steel grades 24 to 30, Equation (2) was satisfied and the increase in magnetic permeability was very small. However, although the number of surface cracks in steel type 31 was high, the magnetic permeability of the hot-rolled annealed steel sheet was very low at 1.004, but it was confirmed that the permeability was significantly increased to 1.081 due to the high value of Equation (2).
[76]
As such, it was confirmed that when the value of Equation (2) satisfies 0 or less, the non-magnetic properties can be maintained by suppressing the generation of the processing-induced martensite phase in the cold rolling process by 60% or more, and As a graph, the permeability distribution according to Equation (2) is shown.
[77]
[78]
2. Hardness evaluation
[79]
Table 3 shows the results of evaluating the hardness of each of the cold-rolled steel sheets after 60% cold-rolling to 6 mm hot-rolled coils of the 1 to 14 steel types and 2.4 mm.
[80]
[Table 3]
Steel grade No. Hardness of hot annealed steel sheet (Hv) Cold-rolled steel sheet hardness (Hv) Hardness increase (Hv)
One 187 392 205
2 175 389 214
3 198 387 189
4 195 356 161
5 201 395 194
6 194 372 178
7 192 433 241
8 207 371 164
9 198 353 155
10 207 365 158
11 206 380 174
12 199 382 183
13 208 385 177
14 200 366 166
[81]
The hardness of the hot-rolled annealed steel sheets of grades 1 to 14 satisfying the alloy composition of the present invention was 170 Hv or more, and after 60% cold rolling, the hardness increased at least 150 Hv or more. The final cold rolled material exhibited excellent hardness of 350 Hv or more without the formation of a processing-induced martensite phase, and it was confirmed that sufficient hardness could be secured when used for electronic products.
[82]
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
[83]
The austenitic stainless steel according to the present invention can implement non-magnetic and high hardness characteristics, and thus can be applied to various fields requiring non-magnetic properties, such as smart devices, which are becoming increasingly diversified.
Claims
[Claim 1]
By weight%, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5% , N: 0.05 to 0.25%, including the remaining Fe and unavoidable impurities, and non-magnetic austenitic stainless steel hot-rolled annealed steel sheet satisfying the following formula (1). (1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5 (where Cr, Mo, Si, C, N, Ni , Mn means the content (wt%) of each element)
[Claim 2]
The non-magnetic austenitic stainless hot annealed steel sheet according to claim 1, wherein the magnetic permeability is 1.05 or less and the hardness is 170 Hv or more.
[Claim 3]
The non-magnetic austenitic stainless hot annealed steel sheet according to claim 1, wherein the number of surface cracks is 0.3 or less per unit meter (m).
[Claim 4]
By weight%, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5% , N: 0.05 to 0.25%, including the remaining Fe and unavoidable impurities, the non-magnetic austenitic stainless steel cold-rolled steel sheet satisfying the following formulas (1) and (2). (1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5 (2) 660 - 500*(C+N) - 10 *Cr - 30*(Ni+Si+Mo+Cu) ≤ 0 (here, Cr, Mo, Si, C, N, Ni, Mn, Cu mean the content (wt%) of each element)
[Claim 5]
The non-magnetic austenitic stainless steel cold-rolled steel sheet according to claim 4, wherein the cold-rolled steel sheet is a cold-rolled material having a rolling reduction ratio of 60% or more, a magnetic permeability of 1.05 or less and a hardness of 350 Hv or more.
[Claim 6]
By weight%, C: 0.01 to 0.05%, Si: 1.5% or less, Mn: 0.5 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 1.0% or less, Cu: 0.2 to 2.5% , N: 0.05 to 0.25%, hot rolling and annealing heat treatment of the slab containing the remaining Fe and unavoidable impurities to prepare a hot rolled annealed steel sheet; and manufacturing a cold rolled steel sheet by cold rolling the hot-rolled annealed steel sheet at a reduction ratio of 60% or more, wherein the slab satisfies the following formulas (1) and (2), and the hot-rolled annealed steel sheet and the cold-rolled steel sheet A method of manufacturing a non-magnetic austenitic stainless steel having a magnetic permeability of 1.05 or less. (1) 0 ≤ 3*(Cr+Mo) + 5*Si - 65*(C+N) - 2*(Ni+Mn) - 27 ≤ 5 (2) 660 - 500*(C+N) - 10 *Cr - 30*(Ni+Si+Mo+Cu) ≤ 0 (here, Cr, Mo, Si, C, N, Ni, Mn, Cu mean the content (wt%) of each element)
[Claim 7]
The method of claim 6, wherein the hardness of the hot-rolled annealed steel sheet is 170 Hv or more, and the hardness is increased by 150 Hv or more by the cold rolling.