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 applicable to clamps of automobiles or general hoses, and a method for manufacturing the same.
background
[2]
Ferritic stainless steel has a lower price 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, countertops for sinks, 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 the surface scale of the hot-rolled coil and removes the internal stress of the material, 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]
In the case of utility ferrite such as 410UF, which is generally manufactured, the Cr content is 12%, so the corrosion resistance is inferior, and the elongation is low, so it cannot be used for clamps. 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. Based on the market requirements (SPEC.), tensile strength (TS) of 510 MPa or more in all three directions of 0˚, 45˚, 90˚, yield strength (YS) of 320 MPa or more, and elongation (El) of 20% or more In order to be satisfied, the development of ingredient systems and optimization of the manufacturing process should be preceded.
[5]
The major quality issues in ferritic stainless steel represented by STS430 are 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]
An object of the present invention is to provide a ferritic stainless steel capable of realizing high strength by controlling the content of Si, Al, V, C, N, etc. in the component system, and the size and amount of precipitates by hot rolling non-annealing, and a method for manufacturing the same.
means of solving the problem
[7]
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, satisfying the following formulas (1) and (2), and of precipitates having an average diameter of 0.5 μm or less The number is 2.5×10 6 pieces/mm 2 or more.
[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 (wt%) of each element.
[11]
In addition, 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.
[12]
In addition, according to an embodiment of the present invention, the precipitate may include Cr carbonitride.
[13]
In addition, according to an embodiment of the present invention, the yield strength may be 320 MPa or more, the tensile strength 510 MPa or more, and the elongation may be 20% or more.
[14]
In a 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) at 1,000 to 1,200 ° C. hot rolling by reheating; winding the hot-rolled steel sheet at 700° C. or higher; cold rolling the wound hot-rolled steel sheet at a reduction ratio of 60% or more; and annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less, and omitting the annealing heat treatment of the wound hot-rolled steel sheet.
[15]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[16]
(2) 0.09% ≤ C+N ≤ 0.12%
[17]
In addition, according to an embodiment of the present invention, in the cold-rolled steel sheet subjected to annealing heat treatment, the number of precipitates having an average diameter of 0.5 μm or less may be 2.5×10 6 pieces/mm 2 or more.
[18]
In addition, according to an embodiment of the present invention, the precipitate may include Cr carbonitride.
[19]
In addition, according to an embodiment of the present invention, the annealed cold-rolled 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.
Effects of the Invention
[20]
The high-strength ferritic stainless steel according to an embodiment of the present invention satisfies a yield strength of 320 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
[21]
1 is a diagram showing the shape of a general clamp (Clamp).
[22]
Figure 2 is a graph showing the yield strength (YS) according to the value of the formula (1) of the present invention.
[23]
3 is a graph showing the tensile strength (TS) according to the value of Equation (2) of the present invention.
[24]
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.
Best mode for carrying out the invention
[25]
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, satisfying the following formulas (1) and (2), and of precipitates having an average diameter of 0.5 μm or less The number is 2.5×10 6 pieces/mm 2 or more.
[26]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[27]
(2) 0.09% ≤ C+N ≤ 0.12%
[28]
Here, Si, Al, V, C, and N mean the content (wt%) of each element.
Modes for carrying out the invention
[29]
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.
[30]
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.
[31]
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.
[32]
The content of C is 0.04 to 0.1%.
[33]
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.
[34]
The content of Si is 0.2 to 0.6%.
[35]
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. When 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 through a solid solution strengthening effect, and the Si content is limited to 0.6% or less to maintain elongation.
[36]
The content of Mn is 0.01 to 1.5%.
[37]
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 a large amount is included, 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%.
[38]
The content of Cr is 14.0 to 18.0%.
[39]
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.
[40]
The content of Al is 0.005 to 0.2%.
[41]
Al as a strong deoxidizer serves to lower the oxygen content in the molten steel, and is added by 0.005% or more in the present invention. 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.
[42]
The content of V is 0.005 to 0.2%.
[43]
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.
[44]
The content of N is 0.02 to 0.1%.
[45]
N in steel exists as an impurity element on the same basis as C, and it is added by 0.02% or more because it is precipitated as Cr 2 N nitride during 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.
[46]
In addition, 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.
[47]
The content of Ni is 0.001 to 0.5%. Ni is an austenite stabilizing element along with Cu and Mn, which increases the austenite fraction to suppress roping and ridging, and serves to improve corrosion resistance by adding a small amount. However, when a large amount is added, the content is limited to the above-mentioned range due to deterioration of processability and an increase in manufacturing cost.
[48]
The content of P is 0.05% or less. P is an unavoidable impurity contained in steel that causes intergranular corrosion during pickling or inhibits hot workability, so its content is controlled within the above-mentioned range.
[49]
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.
[50]
The remainder of the stainless steel except for the above-mentioned alloying elements consists of Fe and other unavoidable impurities.
[51]
In addition, the following formulas (1) and (2) are satisfied simultaneously with the composition of the above component system.
[52]
(1) 0.35% ≤ Si+Al+V ≤ 0.6%
[53]
(2) 0.09% ≤ C+N ≤ 0.12%
[54]
In the present invention, in order to realize high strength, the yield strength (YS) may be increased to 320 MPa or more due to a solid solution strengthening effect according to an increase in the contents 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.
[55]
In addition, by increasing the amount of 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 effect of refining the precipitates, the tensile strength (TS) can be implemented to 510 MPa or more. If the C+N value is less than 0.09%, it is difficult to realize the desired tensile strength, and if it exceeds 0.12%, the elongation is lowered.
[56]
The microstructure of the present invention according to the control of the alloy elements described above may include 2.5 × 10 6 pieces/mm 2 or more of precipitates having an average diameter of 0.5 μm or less . The precipitate may be (Cr,Fe) 23 C 6 , (Cr,Fe) 7 C 3 carbide or Cr 2 N nitride, that is, Cr-carbonitride according to the 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.
[57]
However, for the precipitation of Cr-carbonitride, it is required to omit the hot rolling annealing heat treatment in addition to controlling the alloy elements.
[58]
In a 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%, containing the remaining Fe and unavoidable impurities, and reheating the slab satisfying formulas (1) and (2) to 1,000 to 1,200 ° C. to hot-rolling; winding the hot-rolled steel sheet at 700° C. or higher; cold rolling the wound hot-rolled steel sheet at a reduction ratio of 60% or more; and annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less.
[59]
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.
[60]
In general, ferritic stainless steel used for clamps is subjected to batch annealing in a hot rolling annealing heat treatment after hot rolling, but in the present invention, 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.
[61]
[62]
Hereinafter, it will be described in more detail through preferred embodiments of the present invention.
[63]
Example
[64]
In the 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.
[65]
[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
[66]
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 room temperature at a crosshead speed of 20 mm/min in the 0° direction from the rolling direction on the plate surface of the cold-rolled annealed material were shown. .
[67]
[Table 2]
division steel grade Formula (1) (wt%) Formula (2) (wt%) Number of precipitates less than 0.5㎛ (10 6 pieces/㎟) hot-rolled annealing YS(MPa) TS(MPa) EL(%)
Invention Example 1 A 0.453 0.105 3.6 skip 335.0 568.0 25.0
Invention Example 2 B 0.414 0.096 3.2 skip 321.2 533.9 24.3
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 307.7 509.2 24.2
Comparative Example 5 G 0.312 0.086 2.4 skip 317.8 504.8 25.0
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
[68]
Invention Examples 1 and 2
[69]
A and B steel types are vacuum melted by adjusting C, N, Si, Al and V of ferritic stainless steel. After reheating the above steel in a temperature range of 1,000 to 1,200 ° C, it is heated to 800 ° C or higher by a rough rolling mill and a continuous finishing mill. 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 and cold-rolling annealing.
[70]
It can be seen that the A and B steel grades satisfy the yield strength (YS) ≥ 320 MPa as Si+Al+V ≥ 0.35%. In addition, it can be seen that the A and B steel types satisfy the tensile strength (TS) ≥ 510 MPa as C+N ≥ 0.09%.
[71]
Comparative Examples 1-3
[72]
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 it is confirmed that the Si+Al+V value is 0.35% or less and the yield strength (YS) value is as low as 300 MPa. could
[73]
Comparative Examples 4 and 5
[74]
For steel grades F and G, the Si+Al+V value is 0.35% or less and the C+N value is 0.09% or less, and neither the yield strength (YS) nor the tensile strength (TS) meets the target strength level of the present invention. Able to know.
[75]
Comparative Examples 6 and 7
[76]
H steel grade satisfies Si+Al+V value of 0.35% or more and C+N value of 0.09% or more. It can be seen that it does not satisfy
[77]
In addition, as for steel type I, the Si+Al+V value does not satisfy 0.355 or more and the C+N value does not satisfy 0.09% or more, and as the hot-rolled BAF annealing is performed, the yield strength (YS) is as low as 280 MPa or less. 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.
[78]
[79]
Figure 2 is a graph showing the yield strength (YS) according to the value of the formula (1) of the present invention, Figure 3 is a graph showing the tensile strength (TS) according to the value of the formula (2) of the present invention.
[80]
2 and 3, in order to realize high strength in the present invention, by controlling the value of Equation (1) defined as the sum of substitutional elements Si+Al+V to 0.35% or more, yield strength due to the solid solution strengthening effect of the base material was increased to 320 MPa or more. In addition, by controlling the value of Equation (2) defined as C+N to be 0.09% or more, the amount of Cr-carbonitride precipitation is increased and the amount of work hardening is increased due to the effect of refinement of precipitates by omitting the hot rolling annealing process to increase the tensile strength to 510 MPa could be implemented above.
[81]
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 Invention Example 1, and the BAF column is a photograph of steel grade I of Comparative Example 7.
[82]
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.
[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 may not depart from the concept and scope of the claims described below. It will be appreciated that various modifications and variations are possible.
Industrial Applicability
[84]
The high-strength ferritic stainless steel according to the present invention satisfies a yield strength of 320 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.
Claims
[Claim 1]
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%, the remaining Fe and unavoidable impurities, satisfying the following formulas (1) and (2), and having an average diameter of 0.5 μm or less of precipitates of 2.5×10 6 pieces/mm 2 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 2]
The high-strength ferritic stainless steel for clamps according to claim 1, 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 3]
The high-strength ferritic stainless steel for clamps according to claim 1, wherein the precipitates contain Cr carbonitride.
[Claim 4]
The high-strength ferritic stainless steel for clamps according to claim 1, wherein the yield strength is 320 MPa or more, the tensile strength is 510 MPa or more, and the elongation is 20% or more.
[Claim 5]
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 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; cold rolling the wound hot-rolled steel sheet at a reduction ratio of 60% or more; and annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less. (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 6]
The method for manufacturing high-strength ferritic stainless steel for clamps according to claim 5, wherein the number of precipitates having an average diameter of 0.5 μm or less is 2.5×10 6 pieces/mm 2 or more in the annealed cold-rolled steel sheet .
[Claim 7]
[Claim 7] The method of claim 6, wherein the precipitate contains Cr carbonitride.
[Claim 8]
The method of claim 5, wherein the cold-rolled steel sheet subjected to annealing heat treatment has a yield strength of 320 MPa or more, a tensile strength of 510 MPa or more, and an elongation of 20% or more.