Title of Invention: High-strength 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 an austenitic stainless steel capable of exhibiting high strength while having non-magnetic properties 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.
[4]
In addition, 300 series stainless steel is subjected to work hardening to increase strength, and at this time, the austenite phase is transformed into the martensitic phase. The martensitic phase that appears during work hardening is called a processing induced martensitic phase, and the processing induced martensitic phase sharply increases the strength of the material. In order to increase the strength of 300 series stainless steel, the processing-induced martensitic phase is widely used. However, since the martensite phase exhibits magnetism, there is a problem in that it cannot satisfy the non-magnetic properties required by electronic devices.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[5]
The present invention optimizes the ferrite fraction formed during solidification of austenitic stainless steel, prevents the generation of magnetism by suppressing the formation of the processing-induced martensite phase formed during high strength, and secures high strength by utilizing the fine secondary phase. An object of the present invention is to provide a non-magnetic austenitic stainless steel and a method for manufacturing the same.
means of solving the problem
[6]
High-strength non-magnetic austenitic stainless hot-rolled steel sheet according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0% , Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, remaining Fe and unavoidable impurities, and satisfies the following formula (1).
[7]
(1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0
[8]
Here, Cr, Mo, Si, Ni, C, N, and Mn refer to the content (wt%) of each element, and the cooling rate refers to the cooling rate (°C/s) of the slab solidified from the molten steel.
[9]
In addition, according to an embodiment of the present invention, the hot-rolled annealed steel sheet may have a magnetic permeability (μ) of 1.01 or less.
[10]
In addition, according to an embodiment of the present invention, the hot-rolled annealed steel sheet may satisfy C + N: 0.25% or more.
[11]
High-strength non-magnetic austenitic stainless cold-rolled steel sheet according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, remaining Fe and unavoidable impurities, C + N: 0.25% or more, and satisfy the following formulas (1) and (2) do.
[12]
(1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0
[13]
(2) 551 - 462*(C+N) - 9.2*Si - 8.1*Mn - 13.7*Cr - 29*Ni - 18.5*Mo ≤ -200
[14]
In addition, according to an embodiment of the present invention, the cold-rolled steel sheet is a cold-rolled material having a reduction ratio of 80% or more, the magnetic permeability (μ) may be 1.02 or less and the yield strength 1,280 MPa or more.
[15]
In addition, according to an embodiment of the present invention, the number of carbonitride precipitates having an average diameter of 20 to 200 nm in the cold-rolled steel sheet may be 40 pieces/㎛ 2 or more.
[16]
The method of manufacturing high-strength non-magnetic austenitic stainless steel according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0% , Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, C + N: 0.25% or more, hot rolling and annealing heat treatment of a slab containing the remaining Fe and unavoidable impurities to manufacture a hot-rolled annealed steel sheet step; and cold-rolling the hot-rolled annealed steel sheet at a reduction ratio of 80% or more to produce a cold-rolled steel sheet, wherein the slab satisfies the following formulas (1) and (2), and the magnetic permeability (μ) of the cold-rolled steel sheet is 1.02 is below.
[17]
(1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0
[18]
(2) 551 - 462*(C+N) - 9.2*Si - 8.1*Mn - 13.7*Cr - 29*Ni - 18.5*Mo ≤ -200
[19]
In addition, according to an embodiment of the present invention, the magnetic permeability (μ) of the hot-rolled annealed steel sheet may be 1.01 or less, and the increase in magnetic permeability by cold rolling may be 0.01 or less.
[20]
In addition, according to an embodiment of the present invention, the cold-rolled steel sheet may have a yield strength of 1,280 MPa or more, and the number of carbonitride precipitates having an average diameter of 20 to 200 nm may be 40 pieces/㎛ 2 or more.
Effects of the Invention
[21]
The austenitic stainless steel according to an embodiment of the present invention can secure nonmagnetic properties by optimizing the fraction of ferrite formed during solidification and suppressing processing-induced martensite transformation. Suppression of magnetism can have the effect of preventing communication errors and increasing power efficiency in smart devices.
[22]
In addition, instead of improving strength through the existing processing-induced martensitic transformation, it is possible to exhibit the characteristics of strength improvement by using an alloy component. The improvement in strength can contribute to the weight reduction of parts, which can reduce the weight of smart devices.
Brief description of the drawing
[23]
1 is an optical micrograph showing a fine carbonitride secondary phase formed according to an embodiment of the present invention.
[24]
2 is a diagram showing the analysis of constituent elements of the fine carbonitride secondary phase formed according to an embodiment of the present invention.

Best mode for carrying out the invention
[25]
High-strength non-magnetic austenitic stainless hot-rolled steel sheet according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0% , Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, remaining Fe and unavoidable impurities, and satisfies the following formula (1).
[26]
(1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0
[27]
Here, Cr, Mo, Si, Ni, C, N, and Mn refer to the content (wt%) of each element, and the cooling rate refers to the cooling rate (°C/s) of the slab solidified from the molten steel.
Modes for carrying out the invention
[28]
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.
[29]
In the present invention, the fraction of the ferrite phase formed during solidification of the austenitic stainless steel was optimized, and in particular, an optimal condition for preventing magnetic formation was derived in consideration of the increase of the remaining ferrite phase even in the case of rapid cooling. In addition, the degree of stabilization of the austenite phase was increased in order to suppress the formation of the processing-induced martensite phase formed during high strength. Through this, while preventing the occurrence of magnetism, high strength was secured through solid solution strengthening by addition of interstitial elements such as C and N and precipitation hardening using fine carbonitride secondary phase to increase strength.
[30]
High-strength non-magnetic austenitic stainless steel according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni : 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, remaining Fe and unavoidable impurities.
[31]
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.
[32]
The content of C is 0.02 to 0.12%.
[33]
C is a strong austenite phase stabilizing element, and is an effective element for increasing material strength by solid solution strengthening. It contributes to stabilizing the austenite phase in order to exhibit non-magnetic properties, and in particular, in the present invention, it contributes to increasing the strength by forming a fine precipitated phase of 200 nm or less. In order to secure the stability of the austenite phase, 0.02% or more is required to be added, and since excessive addition causes coarsening of the precipitated phase and a corresponding decrease in corrosion resistance, it is preferable to limit it to 0.12% or less.
[34]
The content of Si is 1.2% or less.
[35]
Si is effective in improving corrosion resistance, but there is a problem of increasing the magnetic permeability as a ferrite phase stabilizing element. In addition, if it is excessive, it is preferable to limit it to 1.2% or less because it promotes the precipitation of intermetallic compounds such as σ phase and deteriorates mechanical properties and corrosion resistance.
[36]
The content of Mn is 0.5 to 2.0%.
[37]
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 undesirable when corrosion resistance is required due to the formation of inclusions such as MnS, it is preferable to limit the Mn content to 0.5 to 2.0%.
[38]
The content of Cr is 17.0 to 22.0%.
[39]
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. When the Cr content increases, the ferrite phase fraction increases, so that a large amount of Ni content must be included to obtain non-magnetic properties, so the cost increases, and the formation of σ phase is promoted, which causes deterioration of mechanical properties and corrosion resistance. Therefore, it is preferable to limit the Cr content to 22.0% or less.
[40]
The content of Ni is 11.0 to 15.0%.
[41]
Ni is the most powerful element among the austenite phase stabilizing elements, and should be contained in an amount of 11.0% 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 15.0% or less.
[42]
The content of Mo is 3.0% or less.
[43]
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 3.0% or less because the formation of the σ phase is promoted, which causes deterioration of mechanical properties and corrosion resistance.
[44]
The content of N is 0.25% or less.
[45]
N is a useful element for stabilizing the austenite phase and is an essential element for securing non-magnetic properties. However, when a large amount is added, it is preferable to limit it to 0.25% or less, since it reduces the hot workability and lowers the yield rate of steel.
[46]
The remainder of the stainless steel except for the above-mentioned alloying elements consists of Fe and other unavoidable impurities.
[47]
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. The austenite phase existing in the structure of 300 series stainless steel has a face-centered cubic structure and does not exhibit magnetism, but the ferrite phase becomes magnetic due to the characteristics of the structure having a body-centered cubic structure. Some residual ferrite phases are ferrite formed during solidification, and magnetic properties of a desired size can be obtained by controlling the content of the remaining ferrite phases. In particular, in the case of non-magnetic steel, it is essential to reduce or eliminate the fraction of the ferrite phase as low as possible.
[48]
The content of the ferrite phase remaining during solidification is greatly affected by the alloy composition. In addition, with the recent development of various manufacturing technologies, it is possible to apply various cooling rates during manufacturing, and in this case, the content of the residual ferrite phase may be changed according to the cooling rate.
[49]
The content of ferrite remaining during solidification in 300 series stainless steel is affected by the ratio of the component elements that stabilize the austenite phase such as Ni, C, and N, and the component elements that stabilize the ferrite phase, such as Cr, Si, and Mo. In general, the remaining ferrite fraction is predicted through empirical formulas such as [Relational Expression] below, and it is known that there is a tendency to be proportional thereto.
[50]
[Relational Expression]
[51]
[{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161
[52]
However, when the cooling rate of the slab is fast, it is difficult to have sufficient time for ferrite to be decomposed in the austenite single phase region that passes during the temperature decrease due to solidification, so a relatively high fraction of ferrite remains. For this reason, in the present invention, Equation (1) was derived considering the cooling rate (℃/s) of the cast steel solidified from the molten steel, and when the value of Equation (1) has a negative value for various 300 series stainless steels, smart devices It can represent a magnetic value of 1.02 or less of the required permeability (μ), etc.
[53]
(1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0
[54]
In order for the final cold rolled material to secure nonmagnetic properties of permeability of 1.02 or less, it is preferable that the magnetic permeability of the hot-rolled annealed steel sheet is 1.01 or less. When the value of Equation (1) is 0 or more, residual ferrite is formed and the magnetic permeability of the hot-rolled annealed steel sheet exceeds 1.01.
[55]
On the other hand, 300 series stainless steel improves strength through work hardening. The strength increases as the martensite phase is formed according to the amount of deformation. However, since the martensite phase shows magnetism in the material for smart devices, it cannot be used as a suitable part. In the present invention, a range of components that do not cause an increase in magnetism during work hardening was derived by suppressing martensite transformation through Equation (2).
[56]
(2) 551 - 462*(C+N) - 9.2*Si - 8.1*Mn - 13.7*Cr - 29*Ni - 18.5*Mo ≤ -200
[57]
When the range of formula (2) is satisfied, only a slight increase in magnetic permeability of 0.01 or less, more preferably 0.005 or less, appears. In particular, when equations (1) and (2) are simultaneously satisfied, the final cold-rolled material can suppress the formation of processing-induced martensite phase even when cold-rolled by 60% or more. can represent
[58]
On the other hand, inhibition of martensitic transformation results in failure to obtain an increase in strength that occurs during work hardening of 300 series stainless steel. In the present invention, in order to prevent such a decrease in strength, high strength properties were secured by utilizing solid solution strengthening and fine secondary phase precipitation by addition of interstitial elements such as C and N.
[59]
According to an embodiment of the present invention, C + N: containing 0.25% or more, the number of carbonitride precipitates having an average diameter of 20 to 200 nm may be 40 pieces/㎛ 2 or more.
[60]
In general, excessive addition of C and N causes deterioration of corrosion resistance due to carbonitride formation. When the content of C and N, which has excellent bonding strength with Cr, is excessive, Cr effective for corrosion resistance is formed as carbonitride at the ferrite-austenite phase boundary, and corrosion resistance is lowered due to a decrease in the Cr content around the grain boundary. The content is limited to 0.05% or less, respectively. In the present invention, considering the case of solidification at a fast cooling rate of 100° C./sec or more, at this time, when the sum of the C content and the N content has a value of 2500 ppm or more, a yield strength of 1,280 MPa or more may be exhibited. The added C and N are distributed in the form of fine carbonitride precipitates, and it can be confirmed that 10 or more fine carbonitrides of 200 nm or less are formed within 0.5 x 0.5 μm 2 as shown in FIG. 1 through microstructure analysis .
[61]
Next, a method for manufacturing high-strength non-magnetic austenitic stainless steel according to an embodiment of the present invention will be described.
[62]
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.
[63]
The method of manufacturing high-strength non-magnetic austenitic stainless steel according to an embodiment of the present invention, by weight, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0% , Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, C + N: 0.25% or more, hot rolling and annealing heat treatment of a slab containing the remaining Fe and unavoidable impurities to manufacture a hot-rolled annealed steel sheet step; and cold-rolling the hot-rolled annealed steel sheet at a reduction ratio of 80% or more to manufacture a cold-rolled steel sheet.
[64]
The hot-rolled annealed steel sheet can exhibit a magnetic permeability (μ) of 1.01 or less by satisfying Equation (1). In addition, by satisfying Equation (2), the increase in magnetic permeability by cold rolling may be 0.01 or less, and further, an increase in magnetic permeability of 0.005 or less is also possible. Accordingly, the cold-rolled steel sheet may exhibit a magnetic permeability of 1.02 or less.
[65]
[66]
Hereinafter, it will be described in more detail through preferred embodiments of the present invention.
[67]
Example
[68]
Steel having the alloy composition shown in Table 1 was prepared by applying three cooling rates.
[69]
In the continuous casting method, after casting into a 200 mm thick slab at an average cooling rate of 10 °C/s, hot annealing steel sheets were manufactured through hot rolling and annealing heat treatment processes. After heating at 1,250°C for 2 hours, hot rolling was performed to a thickness of 2 mm to prepare a hot-rolled coil, and the permeability was measured after annealing at 1,150°C.
[70]
Then, an ingot material was manufactured by applying an average cooling rate of 50 °C/s, and a 2mm hot rolled coil was manufactured by performing hot rolling and annealing heat treatment under the same conditions as the continuous casting method.
[71]
Finally, a 2mm hot-rolled coil was manufactured at an average cooling rate of 100 °C/s using the thin plate casting method, and the permeability was measured after annealing at 1,150 °C.
[72]
After 80% cold-rolling of 2mm hot-rolled coils of each steel type, the magnetic permeability of the cold-rolled steel sheet was measured, and the permeability was measured using a contact ferrometer.
[73]
[Table 1]
Kang type No. C Si Mn Cr Ni Mo N Cooling rate (℃/sec)
One 0.109 0.95 1.10 20.6 12.0 0.07 0.205 100
2 0.056 1.02 0.95 21.4 12.1 0 0.240 100
3 0.097 0.85 1.03 20.2 11.8 0 0.210 100
4 0.120 0.91 0.90 20.9 12.1 0 0.230 100
5 0.026 0.99 0.99 20.6 12.1 0.06 0.236 100
6 0.034 1.01 1.10 20.4 12.2 0 0.218 100
7 0.022 0.43 1.32 17.4 14.7 2.63 0.054 50
8 0.022 0.52 1.31 17.3 14.7 2.52 0.036 10
9 0.021 0.66 1.00 20.3 11.9 0 0.188 100
10 0.031 1.00 1.00 20.3 12.1 0 0.177 50
11 0.023 0.97 1.00 21.0 10.0 0.52 0.150 10
12 0.022 1.01 0.97 21.2 9.8 0.48 0.161 10
13 0.020 0.95 1.10 21.5 10.2 0.52 0.157 10
14 0.041 0.97 0.83 20.6 10.9 0.54 0.164 10
15 0.019 0.47 1.06 16.1 10.1 2.04 0.014 10
16 0.024 0.67 0.67 17.7 12.1 2.04 0.020 10
17 0.032 1.01 2.88 20.7 10.0 0 0.172 50
18 0.031 0.97 3.07 20.7 10.9 0 0.133 50
19 0.030 1.00 1.95 21.6 13.7 0 0.125 50
20 0.055 0.44 1.03 18.2 8.1 0.14 0.046 10
21 0.046 0.44 1.06 18.3 8.1 0.13 0.039 100
[74]
[Table 2]
division Kang type No. Formula (1) Permeability (μ) of hot annealed steel sheet Equation (2) Cold-rolled steel sheet magnetic permeability (μ) increase in permeability
invention example One -5.6 1.000 -244 1.004 0.004
2 -2.1 1.002 -247 1.005 0.003
3 -6.3 1.001 -226 1.002 0.001
4 -7.0 1.002 -264 1.002 0
5 -2.3 1.002 -220 1.005 0.003
6 -2.7 1.002 -217 1.006 0.004
7 -1.0 1.002 -212 1.005 0.003
8 -0.6 1.002 -200 1.005 0.003
comparative example 9 -1.1 1.001 -183 1.061 0.06
10 -0.3 1.002 -191 1.025 0.023
11 9.9 1.361 -133 1.473 0.112
12 10.5 1.062 -134 1.351 0.289
13 10.5 1.013 -148 1.076 0.063
14 4.4 1.016 -167 1.031 0.015
15 6.9 1.046 -28 2.000 0.954
16 7.7 1.034 -111 1.360 0.326
17 3.8 1.015 -149 1.104 0.089
18 4.0 1.038 -158 1.097 0.059
19 2.5 1.021 -239 1.021 0
20 7.2 1.055 6 2.000 0.945
21 9.9 1.316 12 2.000 0.684
[75]
As shown in Table 2, when the value of Equation (1) shows a negative value less than 0, the magnetic permeability of the hot-rolled annealed steel sheet was 1.01 or less, and specifically, it was very small as 1.002 or less in 1 to 10 steel grades. .
[76]
Looking at Tables 1 and 2 together, 1 to 80,000 of the alloy composition systems of the present invention and 1 to 10 steel types satisfying Equation (1) satisfy Equation (2) at the same time. For steel grades 1 to 8, Equation (2) was also satisfied at the same time, so that even during cold rolling with a reduction ratio of 80%, the formation of process-induced martensite phase was suppressed, and the magnetic permeability of the final cold-rolled steel sheet did not increase and satisfies 1.02 or less. It actually showed an increase in permeability of less than 0.004. However, in spite of satisfying the alloy composition system for steel types 9 and 10, the value of Equation (2) was higher than -200, so the magnetic permeability was increased, and accordingly, the magnetic permeability exceeded 1.02.
[77]
For steel types 11 to 18, both equations (1) and (2) were not satisfied, so the permeability of the hot-rolled annealed steel sheet exceeded 1.01, and the increase in magnetic permeability was also high, so that the magnetic permeability of the final cold-rolled steel sheet also exceeded 1.02. In particular, in the case of 19 steel types that correspond to the alloy composition system of the present invention and satisfy Equation (2), the increase in magnetic permeability is 0, but Equation (1) is unsatisfactory, so that the permeability of the hot-rolled annealed steel sheet already exceeds 1.02. From this, it was confirmed that it is important to control the magnetic permeability of the hot-rolled annealed steel sheet to 1.01 or less through the satisfaction of Equation (1).
[78]
For steel grades 15, 20, and 21 whose value of formula (2) is relatively higher than -200, which is the upper limit of the present invention, the increase in magnetic permeability was higher than 0.5, indicating that a large amount of processing-induced martensite phase was generated by cold rolling. can
[79]
[80]
Table 3 shows the results of measuring the yield strength of 80% cold rolled material according to the C+N content.
[81]
[Table 3]
division Steel grade No. C+N Yield strength (MPa)
invention example One 0.3134 1,360
2 0.2960 1,312
3 0.3070 1,355
4 0.3500 1,410
5 0.2619 1,289
6 0.2520 1,283
comparative example 7 0.0760 1,229
8 0.0584 1,119
9 0.2090 1,249
10 0.2080 1,241
11 0.1730 1,194
12 0.1825 1,204
13 0.1767 1,253
14 0.2053 1,222
15 0.0337 1,235
16 0.0434 1,175
17 0.2040 1,262
18 0.1640 1,219
19 0.1550 1,212
20 0.1007 1,180
21 0.0848 1,120
[82]
As shown in Table 3, when the C + N content is 0.25% or more, it was possible to achieve a yield strength of 1,280 MPa or more without generating a processing-induced martensite phase. Steel grades 7 and 8 in Table 2 satisfy Equation (1) and Equation (2), and the magnetic permeability, but the C+N content is less than 0.25%, so the yield strength of the final cold rolled steel is 1,230 MPa or less. The increase in yield strength when high content of C and N was added was confirmed by precipitation of fine carbonitride secondary phase as shown in FIGS. 1 and 2 .
[83]
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
[84]
The austenitic stainless steel according to the present invention can implement non-magnetic and high-strength 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: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, A high-strength non-magnetic austenitic stainless hot-rolled annealed steel sheet that contains the remaining Fe and unavoidable impurities, and satisfies the following formula (1). (1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0 (where , Cr, Mo, Si, Ni, C, N, Mn means the content (wt%) of each element, and the cooling rate means the cooling rate (℃/s) of the cast steel solidified from the molten steel)
[Claim 2]
The high-strength non-magnetic austenitic stainless hot-annealed steel sheet according to claim 1, wherein the magnetic permeability (μ) is 1.01 or less.
[Claim 3]
The high-strength non-magnetic austenitic stainless hot-rolled annealed steel sheet according to claim 1, wherein C+N: 0.25% or more.
[Claim 4]
By weight%, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, A high-strength non-magnetic austenitic stainless steel cold-rolled steel sheet containing the remaining Fe and unavoidable impurities, C + N: 0.25% or more, and satisfying the following formulas (1) and (2). (1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0 (2 ) 551 - 462*(C+N) - 9.2*Si - 8.1*Mn - 13.7*Cr - 29*Ni - 18.5*Mo ≤ -200 (where Cr, Mo, Si, Ni, C, N, Mn are means the content (wt%) of each element, and the cooling rate refers to the cooling rate (°C/s) of the slab solidified from the molten steel)
[Claim 5]
The high-strength 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 80% or more and a magnetic permeability (μ) of 1.02 or less.
[Claim 6]
The high-strength 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 80% or more, and a yield strength of 1,280 MPa or more.
[Claim 7]
The high-strength nonmagnetic austenitic stainless steel cold-rolled steel sheet according to claim 4, wherein the number of carbonitride precipitates having an average diameter of 20 to 200 nm is 40 pieces/μm 2 or more.
[Claim 8]
By weight%, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, C + N: at least 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 cold-rolling the hot-rolled annealed steel sheet at a reduction ratio of 80% or more to produce a cold-rolled steel sheet, wherein the slab satisfies the following formulas (1) and (2), and the magnetic permeability (μ) of the cold-rolled steel sheet A method for producing high-strength non-magnetic austenitic stainless steel having a silver of 1.02 or less. (1) [{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161 - 161 -log(cooling rate) < 0 (2 ) 551 - 462*(C+N) - 9.2*Si - 8.1*Mn - 13.7*Cr - 29*Ni - 18.5*Mo ≤ -200 (where Cr, Mo, Si, Ni, C, N, Mn are means the content (wt%) of each element, and the cooling rate refers to the cooling rate (°C/s) of the slab solidified from the molten steel)
[Claim 9]
The method of claim 8, wherein the magnetic permeability (μ) of the hot-rolled annealed steel sheet is 1.01 or less, and the increase in magnetic permeability by the cold rolling is 0.01 or less.
[Claim 10]
The method of claim 8, wherein the cold-rolled steel sheet has a yield strength of 1,280 MPa or more, and the number of carbonitride precipitates having an average diameter of 20 to 200 nm is 40 pieces/㎛ 2 or more.