Title of Invention: High-strength ferritic stainless steel for clamp and manufacturing method thereof
technical field
[One]
The present invention relates to high-strength ferritic stainless steel, and more particularly, to high-strength ferritic stainless steel having a yield strength of 350 MPa or more, which can be applied to clamps of automobiles or general hoses, and a method for manufacturing the same.
background
[2]
Ferritic stainless steel is cheaper than austenitic stainless steel, has a low coefficient of thermal expansion, and has good surface gloss, formability and oxidation resistance, so it is widely used in heat-resistant appliances, sink tops, exterior materials, home appliances, and electronic parts. In the case of a ferritic stainless steel cold-rolled sheet, it is manufactured through a hot rolling process, an annealing and pickling process that removes scale from the surface of the hot rolled coil, and annealing and pickling process, cold rolling and annealing process.
[3]
1 shows a clamp for an automobile or general hose. Clamps require high strength because they serve to fasten plastic hoses or pipes, and excellent ductility is also required because there should be no cracks during bending. In addition, since corrosion resistance is required as it is used in the outdoor environment of automobiles as well as indoors, the demand for stainless steel for clamps is increasing recently.
[4]
Utility ferrite such as 410UF, which is generally manufactured, has poor corrosion resistance with a Cr content of 12%, and cannot be used for clamps due to its low elongation. Therefore, an attempt is made to use 16%Cr 430 series (general 430, 430LX) having a relatively high Cr content, but it is difficult to satisfy the market demand with low tensile strength. Tensile strength (TS) of 510 MPa or more in all three directions of 0˚, 45˚ and 90˚, yield strength (YS) of 350 MPa or more, and elongation (El) of 20% or more based on the market requirements (SPEC.) In order to be satisfied, the development of ingredient systems and optimization of the manufacturing process should be preceded.
[5]
The main quality issues in ferritic stainless steel represented by STS430 are the improvement of ridge, improvement of orange peel, and improvement of in-plane anisotropy during molding. There are few studies on the review of components satisfying high strength and optimization of manufacturing technology so that they can be applied for clamp applications.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[6]
The present invention relates to STS430 ferritic stainless steel capable of realizing high-strength content of Si, Al, V, C, N, etc. in the component system, control of the size and amount of precipitates by hot rolling non-annealing, and yield strength of 350 MPa or more through temper rolling, and manufacturing thereof We want to provide a way
means of solving the problem
[7]
The method for manufacturing high-strength ferritic stainless steel for clamps according to an embodiment of the present invention, by weight, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0% , Al: 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, including the remaining Fe and unavoidable impurities, the slab satisfying the following formulas (1) and (2) to 1,000 to 1,200 ℃ hot rolling by reheating; winding the hot-rolled steel sheet at 700° C. or higher; omitting the annealing heat treatment of the wound hot-rolled steel sheet, and cold rolling at a reduction ratio of 60% or more; annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less; and temper-rolling the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%.
[8]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[9]
(2) 0.09% ≤ C+N ≤ 0.12%
[10]
Here, Si, Al, V, C, and N mean the content (% by weight) of each element.
[11]
In addition, according to an embodiment of the present invention, in the cold rolled annealed steel sheet, the number of (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less may be 2.5×10 6 pieces/mm 2 or more.
[12]
In addition, according to an embodiment of the present invention, the slab may further include any one or more selected from the group consisting of Ni: 0.001 to 0.5%, P: 0.05% or less, and S: 0.005% or less.
[13]
In addition, according to an embodiment of the present invention, the cold rolled annealed steel sheet may have a yield strength of 320 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more.
[14]
Further, according to an embodiment of the present invention, the temper-rolled cold-rolled annealed steel sheet may have a yield strength of 350 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more.
[15]
High-strength ferritic stainless steel for clamp according to an embodiment of the present invention, by weight, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0%, Al : 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, including the remaining Fe and unavoidable impurities, and satisfies the following formulas (1) and (2), and has a yield strength of 350 MPa or more.
[16]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[17]
(2) 0.09% ≤ C+N ≤ 0.12%
[18]
Further, according to an embodiment of the present invention, Ni: 0.001 to 0.5%, P: 0.05% or less, and S: any one or more selected from the group consisting of 0.005% or less may be further included.
[19]
In addition, according to an embodiment of the present invention, (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less may be distributed over 2.5×10 6 pieces/mm 2 .
[20]
In addition, according to an embodiment of the present invention, the tensile strength may be 510 MPa or more and the elongation may be 20% or more.
Effects of the Invention
[21]
The high-strength ferritic stainless steel according to an embodiment of the present invention satisfies a yield strength of 350 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more, so that it can be used for clamping applications such as automobiles.
Brief description of the drawing
[22]
1 is a diagram showing the shape of a general clamp (Clamp).
[23]
Figure 2 is a graph showing the yield strength (YS) according to the value of Equation (1) before performing the temper rolling of the present invention.
[24]
3 is a graph showing the tensile strength (TS) according to the value of Equation (2) before performing the temper rolling of the present invention.
[25]
4 is a photograph taken with a scanning electron microscope (SEM) and a transmission electron microscope (TEM) of the precipitates of the invention example and the comparative example according to an embodiment of the present invention.
Best mode for carrying out the invention
[26]
The method for manufacturing high-strength ferritic stainless steel for clamps according to an embodiment of the present invention, by weight, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0% , Al: 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, including the remaining Fe and unavoidable impurities, the slab satisfying the following formulas (1) and (2) to 1,000 to 1,200 ℃ hot rolling by reheating; winding the hot-rolled steel sheet at 700° C. or higher; omitting the annealing heat treatment of the wound hot-rolled steel sheet, and cold rolling at a reduction ratio of 60% or more; annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less; and temper-rolling the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%.
[27]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[28]
(2) 0.09% ≤ C+N ≤ 0.12%
[29]
Here, Si, Al, V, C, and N mean the content (% by weight) of each element.
Modes for carrying out the invention
[30]
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.
[31]
High-strength ferritic stainless steel for clamp according to an embodiment of the present invention, by weight, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0%, Al : 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, remaining Fe and unavoidable impurities.
[32]
Hereinafter, the reason for numerical limitation of the alloy element content of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.
[33]
The content of C is 0.04 to 0.1%.
[34]
C in steel is an impurity that is unavoidably included in ferritic stainless steel, and is precipitated as (Cr,Fe) 23 C 6 , (Cr,Fe) 7 C 3 carbide to improve strength, so it contains 0.04% or more. However, when excessively contained in the base material, the elongation is lowered and the workability of the product is significantly reduced, so it is limited to 0.1% or less.
[35]
The content of Si is 0.2 to 0.6%.
[36]
Although Si is an unavoidable impurity contained in steel, it is an element added as a deoxidizer during steel making and is a ferrite stabilizing element. If it is contained in a large amount in steel, it causes hardening of the material and reduces ductility, so it is usually managed at 0.4% or less. However, in order to manufacture high-strength ferritic stainless steel for clamps, it is necessary to optimally use Si. Accordingly, in the present invention, the Si content is controlled to 0.2 to 0.6% to improve tensile strength and yield strength by a solid solution strengthening effect, and the Si content is limited to 0.6% or less to maintain elongation.
[37]
The content of Mn is 0.01 to 1.5%.
[38]
Mn is an impurity that is unavoidably included in steel, but since it is an austenite stabilizing element, it serves to suppress roping and ridging. However, when it is included in a large amount, manganese-based fume is generated during welding and causes MnS phase precipitation to decrease elongation, so the content is limited to 0.01 to 1.5%.
[39]
The content of Cr is 14.0 to 18.0%.
[40]
Cr is an alloying element added to improve the corrosion resistance of steel, and its critical content is 12%. However, ferritic stainless steel containing C and N may cause intergranular corrosion, and its content is limited to 14.0 to 18.0% in consideration of the possibility of intergranular corrosion and increase in manufacturing cost.
[41]
The content of Al is 0.005 to 0.2%.
[42]
Al plays a role in lowering the oxygen content in molten steel as a strong deoxidizer, and in the present invention, 0.005% or more is added. However, when the content is excessive, the sleeve defect of the cold-rolled strip occurs due to the increase of non-metallic inclusions and at the same time deteriorates weldability, it may be limited to 0.2% or less, and more preferably to 0.1% or less.
[43]
The content of V is 0.005 to 0.2%.
[44]
V serves to form carbonitrides by fixing C and N, and is an element effective for inhibiting and refining the growth of carbonitrides. In the present invention, 0.005% or more is added, and more preferably 0.03% or more is added. However, when the content is excessive, the manufacturing cost rapidly increases, so it may be limited to 0.2% or less, and more preferably to 0.1% or less.
[45]
The content of N is 0.02 to 0.1%.
[46]
N in steel is present as an impurity element on the same level as C, and it is added by 0.02% or more because it is precipitated as Cr 2 N nitride in the manufacturing process to improve strength. However, since a large amount of addition not only impairs workability but also causes stretcher strain in cold-rolled products, the content is limited to 0.1% or less.
[47]
Further, according to an embodiment of the present invention, Ni: 0.001 to 0.5%, P: 0.05% or less, and S: any one or more selected from the group consisting of 0.005% or less may be further included.
[48]
The content of Ni is 0.001 to 0.5%. Ni is an austenite stabilizing element along with Cu and Mn, and it has an effect of suppressing roping and ridging by increasing the austenite fraction, and serves to improve corrosion resistance by adding a small amount. However, when a large amount is added, the content thereof is limited to the above-mentioned range due to deterioration of processability and an increase in manufacturing cost.
[49]
The content of P is 0.05% or less. P is an unavoidable impurity contained in steel, which causes intergranular corrosion during pickling or inhibits hot workability, so its content is controlled within the above-mentioned range.
[50]
The content of S is 0.005% or less. S is an unavoidable impurity contained in steel and segregates at grain boundaries to impair hot workability, so its content is limited to the above-mentioned range.
[51]
The remainder of the stainless steel except for the above-mentioned alloying elements consists of Fe and other unavoidable impurities.
[52]
In addition, the following formulas (1) and (2) are satisfied at the same time as the composition of the above component system.
[53]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[54]
(2) 0.09% ≤ C+N ≤ 0.12%
[55]
In the present invention, in order to realize high strength, the yield strength (YS) may be increased to 320 MPa or more by a solid solution strengthening effect according to an increase in the content of Si, Al, and V, which are substitutional elements. When the Si+Al+V value is less than 0.35%, it is difficult to realize the desired yield strength, and when it exceeds 0.6%, the elongation is lowered. In addition, as in the manufacturing method to be described later, it is possible to achieve a yield strength of 350 MPa or more by performing temper rolling on the annealed cold-rolled steel sheet. If the yield strength before performing temper rolling does not reach 320 MPa, a high rolling reduction is required during temper rolling, and in this case, the elongation is lowered, which is undesirable. Therefore, it is important to secure a yield strength of 320 MPa or more by satisfying Equation (1) before performing temper rolling.
[56]
Tensile strength (TS) of 510 MPa or more can be realized by increasing the (Fe,Cr) carbonitride precipitation by increasing the C + N content, and by omitting the hot rolling annealing heat treatment to increase the work hardening amount due to the precipitate miniaturization effect. When the C+N value is less than 0.09%, it is difficult to realize the desired tensile strength, and when it exceeds 0.12%, the elongation is lowered.
[57]
The microstructure of the present invention according to the above-described alloy element control may include 2.5×10 6 pieces/mm 2 or more of (Fe,Cr) carbonitride precipitates having an average diameter of 0.5 μm or less . The (Fe,Cr) carbonitride precipitate may be (Cr,Fe) 23 C 6 , (Cr,Fe) 7 C 3 carbide or Cr 2 N nitride according to an increase in C+N content. By precipitating a large amount of fine precipitates of 0.5 μm or less, the amount of work hardening during tension can be increased.
[58]
However, for the precipitation of (Fe, Cr) carbonitride, it is required to omit the hot rolling annealing heat treatment in addition to controlling the alloy elements.
[59]
In the case of clamps for connecting hoses, if the hose diameter is small, a thickness of 1 mm or less is mainly used, and a yield strength (YS) of 320 MPa or more is required, and if the hose diameter is large, a thickness of 1 mm or more is used. More is requested. Although it is possible to obtain 320 MPa or more through the control of the alloy elements and carbonitride precipitates described above, it is difficult to secure more than 350 MPa. Therefore, in order to realize a yield strength of 350 MPa or more, it was necessary to modify the process in the manufacturing method.
[60]
The method for manufacturing high-strength ferritic stainless steel for clamps according to an embodiment of the present invention, by weight, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0% , Al: 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, including the remaining Fe and unavoidable impurities, the slab satisfying the above formulas (1) and (2) to 1,000 to 1,200 ℃ hot rolling by reheating; winding the hot-rolled steel sheet at 700° C. or higher; omitting the annealing heat treatment of the wound hot-rolled steel sheet, and cold rolling at a reduction ratio of 60% or more; annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less; and temper-rolling the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%.
[61]
The hot rolling finishing temperature is preferably 800°C or higher. Fine precipitates are formed in the hot-rolled coil state through finish rolling at a temperature of 800°C or higher and winding at 700°C or higher, and then, the hot-rolling annealing heat treatment is omitted to prevent coarsening of the precipitates.
[62]
In general, ferritic stainless steel used for clamps is subjected to batch annealing in a hot rolling annealing heat treatment after hot rolling, but the present invention is characterized in that the hot rolling annealing heat treatment is omitted. When performing phase annealing (BAF), the fine precipitates deposited in the hot-rolled coil are coarsened and the total number is reduced, making it difficult to secure high strength.
[63]
The yield strength of 350 MPa or more can be secured by cold-rolled temper rolling of the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%. When the reduction ratio is more than 8%, the elongation is lowered.
[64]
Hereinafter, it will be described in more detail through preferred embodiments of the present invention.
[65]
Example
[66]
The ferritic stainless steel of the component system with C, N, Si, Al and V in Table 1 below was tested in Lab. It was prepared as a slab by vacuum dissolution. After reheating the slab at 1,000 to 1,200°C, the hot-rolled sheet was prepared by rolling it to a finish rolling completion temperature of 800°C or higher by a roughing mill and a continuous finishing mill.
[67]
[Table 1]
steel grade alloy composition (wt%) division
C Si Mn Cr Al V N
A 0.0690 0.35 0.50 16.20 0.043 0.06 0.0360 Invention Example 1
B 0.0631 0.30 0.48 16.29 0.083 0.03 0.0329 Invention Example 2
C 0.0680 0.14 0.49 16.17 0.033 0.01 0.0360 Comparative Example 1
D 0.0610 0.12 0.46 16.15 0.031 0.02 0.0310 Comparative Example 2
E 0.0689 0.14 0.46 16.16 0.033 0.01 0.0261 Comparative Example 3
F 0.0631 0.20 0.48 16.25 0.081 0.01 0.0229 Comparative Example 4
G 0.0631 0.20 0.48 16.23 0.081 0.02 0.0229 Comparative Example 5
H 0.0631 0.30 0.47 16.29 0.083 0.03 0.0329 Comparative Example 6
I 0.0590 0.12 0.47 16.14 0.078 0.01 0.0215 Comparative Example 7
[68]
The hot-rolled sheet was manufactured as a final cold-rolled sheet by performing temper rolling on some steel types after cold rolling and annealing heat treatment.
[69]
Table 2 below shows the numerical values ​​of formulas (1) and (2) defined as Si+Al+V and C+N for the steel having the alloy composition of Table 1, and the number of precipitates in hot-rolled annealing conditions and cold-rolled annealing materials was shown. In addition, the yield strength (YS), tensile strength (TS) and elongation (EL) obtained by performing a tensile test at a crosshead speed of 20 mm/min at room temperature in the 0° direction from the rolling direction on the plate surface of the cold-rolled annealed material were shown. .
[70]
[Table 2]
division steel grade Formula (1)
(wt%) Formula (2)
(weight)
Number of precipitates under 0.5㎛
(10 6 pieces/㎟) hot- rolled
annealing temper
rolling
reduction YS
(MPa) TS
(MPa) EL
(%)
Invention Example 1 A 0.453 0.105 3.6 skip 7% 361.6 573.0 23.7
Invention Example 2 B 0.414 0.096 3.2 skip 4% 352.8 547.4 23.1
Comparative Example 1 C 0.183 0.104 3.0 skip - 303.0 546.0 23.0
Comparative Example 2 D 0.171 0.092 2.8 skip - 304.0 538.0 25.0
Comparative Example 3 E 0.183 0.095 2.7 skip - 297.0 513.0 27.0
Comparative Example 4 F 0.292 0.086 2.6 skip 6% 326.2 511.7 22.4
Comparative Example 5 G 0.312 0.086 2.4 skip 5% 329.6 509.2 23.9
Comparative Example 6 H 0.414 0.096 0.2 BAF - 304.5 494.1 28.0
Comparative Example 7 I 0.208 0.081 0.2 BAF - 277.9 486.1 30.1
[71]
Invention Examples 1 and 2
[72]
A and B steel types are vacuum melted by controlling C, N, Si, Al and V of ferritic stainless steel. A hot-rolled sheet was prepared by rolling to the completion temperature, and then pickling was performed without hot-rolling annealing, followed by cold-rolling, cold-rolling annealing and temper rolling.
[73]
It can be seen that the A and B steel grades satisfy Si+Al+V ≥ 0.35%, and yield strength (YS) ≥ 350 MPa by performing temper rolling. In addition, it can be seen that the A and B steel grades satisfy the tensile strength (TS) ≥ 510 MPa as C+N ≥ 0.09%.
[74]
Comparative Examples 1-3
[75]
For steel grades C to E, the C+N value is 0.09% or more, which satisfies the formula (1) of the present invention, but the Si+Al+V value is 0.35% or less and the yield strength (YS) value is 300 MPa. It was confirmed that a low value that did not even reach 320 MPa before appeared.
[76]
Comparative Examples 4 and 5
[77]
For steel grades F and G, Si+Al+V values ​​were 0.35% or less and C+N values ​​were 0.09% or less, and both yield strength (YS) and tensile strength (TS) satisfies the target strength level of the present invention despite temper rolling. You can see that it can't be done.
[78]
Comparative Examples 6 and 7
[79]
H steel grade satisfies Si+Al+V values ​​of 0.35% or more and C+N values ​​of 0.09% or more, but yield strength (YS) ≥ 320 MPa and tensile strength (TS) ≥ 510 MPa due to hot-rolled BAF annealing It can be seen that it does not satisfy
[80]
In addition, in the case of I steel, the Si+Al+V value does not satisfy 0.35 or more and the C+N value does not satisfy 0.09% or more. and the tensile strength (TS) was also low at 490 MPa or less, indicating that the target strength of the present invention was not satisfied.
[81]
2 is a graph showing the yield strength (YS) according to the value of Equation (1) before performing the temper rolling of the present invention, and FIG. 3 is the tensile strength according to the value of Equation (2) before performing the temper rolling of the present invention. It is a graph showing (TS).
[82]
2 and 3, in order to realize high strength in the present invention, the yield strength due to the solid solution strengthening effect of the base material by controlling the value of Equation (1) defined as the sum of substitutional elements Si+Al+V to 0.35% or more was increased to 320 MPa or more. By performing the temper rolling here, it was possible to secure the required yield strength of 350 MPa or more. In addition, by controlling the value of Equation (2) defined as C + N to 0.09% or more, (Fe,Cr)-carbonitride precipitation amount is increased and the work hardening amount is increased due to the precipitate miniaturization effect by omitting the hot rolling annealing process. The tensile strength could be realized over 510 MPa.
[83]
4 is a photograph taken with a scanning electron microscope (SEM) and a transmission electron microscope (TEM) of the precipitates of Inventive Examples and Comparative Examples according to an embodiment of the present invention. The no-annealing column is a photograph of steel grade A of Inventive Example 1, and the BAF column is a photograph of steel grade I of Comparative Example 7.
[84]
In the case of steel type A of Invention Example 1, it can be confirmed that a large amount of precipitates having an average diameter of 0.5 μm or less are formed, whereas in the case of steel type I of Comparative Example 7, it can be confirmed that precipitates having a size of 0.5 to 2.0 μm are formed. could That is, it can be seen that the problem of the present invention can be achieved only when hot rolling non-annealing is satisfied together with alloy component control.
[85]
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
[86]
The ferritic stainless steel according to the present invention can secure a yield strength of 350 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more, and thus can be applied to clamps of automobiles or general hoses.
Claims
[Claim 1]
By weight%, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0%, Al: 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to 0.1%, comprising the remaining Fe and unavoidable impurities, and reheating the slab satisfying the following formulas (1) and (2) to 1,000 to 1,200 ° C. and hot rolling; winding the hot-rolled steel sheet at 700° C. or higher; omitting the annealing heat treatment of the wound hot-rolled steel sheet, and cold rolling at a reduction ratio of 60% or more; annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less; and temper-rolling the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%. (1) 0.35% ≤ Si+Al+V ≤ 0.6% (2) 0.09% ≤ C+N ≤ 0.12% (here, Si, Al, V, C, N mean the content (wt%) of each element )
[Claim 2]
The method of claim 1, wherein the number of (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less in the cold-rolled annealed steel sheet is 2.5×10 6 pieces/mm 2 or more.
[Claim 3]
The method of claim 1, wherein the slab further comprises at least one selected from the group consisting of Ni: 0.001 to 0.5%, P: 0.05% or less, and S: 0.005% or less. .
[Claim 4]
The method of claim 1, wherein the cold-rolled annealed steel sheet has a yield strength of 320 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more.
[Claim 5]
The method of claim 1, wherein the temper-rolled cold-rolled annealed steel sheet has a yield strength of 350 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more.
[Claim 6]
By weight%, C: 0.04 to 0.1%, Si: 0.2 to 0.6%, Mn: 0.01 to 1.5%, Cr: 14.0 to 18.0%, Al: 0.005 to 0.2%, V: 0.005 to 0.2%, N: 0.02 to High-strength ferritic stainless steel for clamps containing 0.1%, remaining Fe and unavoidable impurities, satisfying the following formulas (1) and (2), and having a yield strength of 350 MPa or more. (1) 0.35% ≤ Si+Al+V ≤ 0.6% (2) 0.09% ≤ C+N ≤ 0.12% (here, Si, Al, V, C, N mean the content (wt%) of each element )
[Claim 7]
The high-strength ferritic stainless steel for clamps according to claim 6, further comprising at least one selected from the group consisting of Ni: 0.001 to 0.5%, P: 0.05% or less, and S: 0.005% or less.
[Claim 8]
The high-strength ferrite for clamp according to claim 6, wherein (Cr,Fe)-carbonitride precipitates are included, and (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less are distributed at 2.5×10 6 pieces/mm2 or more. series stainless steel.
[Claim 9]
The high-strength ferritic stainless steel for clamps according to claim 6, wherein the tensile strength is 510 MPa or more and the elongation is 20% or more.