Art
[1]
The present invention relates to a ferritic stainless steel and that, more specifically, the strength and acid resistance are excellent ferritic stainless steel and a method for the preparation thereof.
BACKGROUND
[2]
Particularly ferritic stainless steel of the stainless steel is widely used in building materials, kitchen containers, appliances, automotive exhaust system components.
[3]
Ferritic stainless steels recently has been some application of automotive battery cell,, Vehicles Inc. There are demands for higher strength and corrosion resistance than conventional ferritic stainless steel to ensure long-term battery performance, lower in order to lower the price of batteries material prices and demand.
[4]
High strength How ferritic stainless steels to meet this car's requirements and the work hardening, there are methods such as solid-solution strengthening, precipitation hardening, the ferritic stainless steel, the nature of work hardening during workability with no phase change rapidly falling issues, employment, strengthen effect is excellent Mo, Nb, etc. are difficult to utilize as an expensive element.
[5]
Traditionally, C is not a particular use as the element harm formability ferritic stainless steel was low in most administration than 0.02wt%. But contrary When adding a large amount of C carbide can (carbide) increase due to precipitation of a ferritic stainless steel, the strength of the can, it is possible to secure when the development of the recent process technology secured only to some extent flexible in the strength and workability at the same time.
[6]
However, even if a large amount insert the C when the hot-rolled at a high temperature or a high coiling temperature is low reduction ratio, the carbide becomes coarse to not being finely precipitated in the tissue deformation it is difficult to grain refinement also to ensure a desired strength difficult.
[7]
(Patent Document 0001) Japanese Laid-open Patent Document No. 2006-183081
Detailed Description of the Invention
SUMMARY
[8]
Embodiments of the present invention to provide a ferritic stainless steel superior to improve the strength of ferritic stainless steel and acid-resistant stainless steel through a closed light-based precipitates and grain control Steels Steel alloy by controlling the components.
[9]
In addition, embodiments of the present invention to provide a method of manufacturing a ferritic stainless steel to improve the strength and acid resistance by the precipitates and the crystal grains controlled by controlling the slab reheating temperature during hot rolling, the reduction rate and the coiling temperature.
Problem solving means
[10]
Strength and acid resistance are excellent ferritic stainless steel according to one embodiment of the present invention is, by weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): 0.3 to 1.5%, remainder iron (Fe) and other unavoidable includes impurity and a diameter of more than 100nm: 12.0 to 19.0%, nickel (Ni): 0.01 to 0.5%, copper (Cu) the number per unit area of the carbide having 50 to 200ea / 100㎛ 2 a.
[11]
Further, according to one embodiment of the present invention, the number of days that 10㎛ than average crystal grain diameter.
[12]
Further, according to one embodiment of the present invention, the tensile strength may be at least 520MPa.
[13]
Further, according to one embodiment of the present invention, it may be more than 20% elongation.
[14]
Further, according to one embodiment of the invention, the critical current density (I in a 5% sulfuric acid atmosphere crit ) that may be below 10mA.
[15]
Preparation strength and acid resistance are excellent ferritic stainless steel according to one embodiment of the present invention is, by weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): 12.0 to 19.0%, nickel (Ni): 0.01 to 0.5%, copper (Cu): 0.3 to 1.5%, remainder iron (Fe) and other ferritic stainless steel containing incidental impurities the method comprising hot rolling a steel slab and a step of cold rolling, and the value of to during hot rolling formula (1) satisfies 1000 or less.
[16]
15 * RHT / R4 + CT ------ Eq. (1)
[17]
Here, RHT (℃) means the slab reheating temperature and R4 (%) means a reduction ratio of R4 stand of rough rolling and, a CT (℃) means the coiling temperature.
[18]
Further, according to one embodiment of the invention, the value of the formula (1) can be satisfied, 800 to 1,000.
[19]
Further, according to one embodiment of the present invention, RHT is less than 1,250 ℃, R4 is at least 40%, CT may be less than 650 ℃.
[20]
Further, according to one embodiment of the invention, the cold-rolled plate is the number per unit area of the carbide having a diameter of more than 100nm to 50 200ea / 100㎛ 2 may be, and the average crystal grain diameter 10㎛ below.
Effects of the Invention
[21]
Embodiments of the present invention can improve the strength of ferritic stainless steels and acid resistance by the precipitates and grain control to control a ferritic alloy of stainless steel component and hot rolling condition.
Brief Description of the Drawings
[22]
1 is a graph illustrating the correlation between the number of carbides in a ferritic stainless steel hot-rolling conditions and cold rolled steel.
[23]
Figure 2 is a picture taken through a transmission electron microscope (TEM) the precipitate distribution of a ferritic stainless cold-rolled steel sheet according to one embodiment of the present invention.
[24]
Figure 3 is a picture taken through a transmission electron microscope (TEM) the precipitate distribution of a ferritic stainless cold-rolled steel sheet according to a comparative example of the present invention.
[25]
Figure 4 is a graph illustrating the correlation between the number of carbides and the tensile strength of the ferritic stainless steel, cold-rolled steel sheet.
Best Mode for Carrying Out the Invention
[26]
Strength and acid resistance are excellent ferritic stainless steel according to one embodiment of the present invention is, by weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): 0.3 to 1.5%, remainder iron (Fe) and other unavoidable includes impurity and a diameter of more than 100nm: 12.0 to 19.0%, nickel (Ni): 0.01 to 0.5%, copper (Cu) the number per unit area of the carbide having 50 to 200ea / 100㎛ 2 a.
Mode for the Invention
[27]
Hereinafter will be described in detail with reference to the accompanying drawings, an embodiment of the present invention. The following examples will be presented to fully convey the scope of the invention to those of ordinary skill in the art. The present invention is not limited to the embodiments described herein may be embodied in different forms. Figures may be somewhat exaggerated to express the size of the components, for clarity, not shown, and a portion not related to the description in order to clarify the invention.
[28]
Strength and acid resistance are excellent ferritic stainless steel according to one embodiment of the present invention is, by weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): includes 0.3 to 1.5%, remainder iron (Fe) and other inevitable impurities: 12.0 to 19.0%, nickel (Ni): 0.01 to 0.50%, copper (Cu).
[29]
Carbon (C): 0.1 to 0.2%
[30]
The amount of carbon (C) is 0.1 to 0.2%. When the amount of carbon (C) less than 0.1%, reducing the amount of austenite produced in the hot rolling is the residual ferrite band tissue is not destroyed, and the problem that the size of crystal grains increases, so that the tensile strength of the final cold rolled product there is a problem that the strength is lowered to less than 500MPa. In addition, when the amount of carbon (C) exceeds 0.2%, the carbide of the material increase so much poor in the elongation of the final product, there is a problem to be eliminated in the surface quality and corrosion resistance deterioration of the carbide.
[31]
Nitrogen (N): 0.005 to 0.05%
[32]
The amount of nitrogen (N) 0.005 to 0.05%. When the amount of nitrogen (N) less than 0.005%, refining time is increased and the cost is raised made of refractory life shortened, and also the amount of is a lower isometric jeongyul slab is sub-cooled also in casting low, and nitrogen (N) 0.05 If the% excess, it is probable cause pinholes in a nitrogen during slab casting, a final Cr in the cold rolled product 2. the number per unit area of the N precipitates increased Cr 2 by N precipitate around the chromium depletion region formed in the (Cr depleted zone) final the surface quality is exfoliated by forming a number of pits (pit) on the surface of cold-rolled products.
[33]
Manganese (Mn): 0.01 to 0.5%
[34]
The amount of manganese (Mn) 0.01 to 0.5%. When the amount of manganese (Mn) is less than 0.01%, and a problem that the polishing rates pricey, When the amount of manganese (Mn) greater than 0.5%, there is a poor elongation and corrosion resistance issues.
[35]
Chromium (Cr): 12.0 to 19.0%
[36]
The amount of chromium (Cr) is 12.0 to 19.0%. When the amount of chromium (Cr) less than 12%, there is a problem that corrosion resistance deteriorates, when the amount of chromium (Cr) more than 19%, poor elongation, there is a problem that the sticking (sticking) hot rolling defect occurs.
[37]
Nickel (Ni): 0.01 to 0.50%
[38]
The amount of nickel (Ni) 0.01 to 0.50%. When the amount of nickel (Ni) is less than 0.01%, and a problem that the polishing rates pricey, if the amount of nickel (Ni) exceeds 0.5%, there is a poor elongation problem by increasing the impurity of the material.
[39]
Copper (Cu): 0.3 to 1.5%
[40]
The amount of copper (Cu) is 0.3 to 1.5%. When the amount of the copper (Cu) less than 0.3%, 5% sulfuric acid atmosphere, the critical current density (I crit not) is to ensure sufficient acid resistance in excess of 10mA, if the amount of copper (Cu) exceeds 1.5% of raw material as well as the price rises too much, resulting in a decline in the elongation of the hot workability declines and the final product.
[41]
In order to obtain the desired tensile strength in the final cold-rolled ferritic stainless steels products it is necessary to secure a large number of fine carbides, the miniaturization of the crystal grains is desired.
[42]
One strength, ferritic stainless steel having excellent acid resistance in accordance with an embodiment of the present invention, the number per unit area of the carbide having a diameter of more than 100nm 50ea / 100㎛ 2 or higher.
[43]
For example, the carbide M 23 C 6 can be a type carbide-based metal precipitates.
[44]
In order to increase the number per unit area of ​​the carbide should form a sufficient deformation to the hot-rolled tissue material during the hot rolling step. If the tissue deformation is not sufficiently formed carbide precipitation sites (site) it is not enough, it is difficult to increase the amount of carbide.
[45]
In order to form sufficient tissue strain in the hot-rolled material is controlled to be the slab reheating temperature, rolling reduction rough rolling, hot-rolled coil take-up temperature in the hot rolling step and is to be described later for details thereof.
[46]
In other words, through the control of the hot rolling process conditions the number per unit area of the carbide having a diameter of more than 100nm 50ea / 100㎛ 2 to achieve the above, and by securing thereto a number of fine carbides it can be secured a tensile strength of at least 520MPa. If the process conditions outside the carbide can not be sufficiently obtained the amount of coarse carbides becomes.
[47]
For example, the number per unit area of the carbide having a diameter of more than 100nm 50ea / 100㎛ 2 is less than the tensile strength is lowered, the amount of the carbide to less coarsening of crystal grains occurs.
[48]
For example, the ferritic stainless steel may be less than the average grain diameter 10㎛.
[49]
For example, ferritic stainless steel according to one embodiment of the present invention has the tensile strength may be at least 520MPa.
[50]
For example, ferritic stainless steel according to one embodiment of the present invention may be in the elongation of 20% or more.
[51]
For example, ferritic stainless steel according to one embodiment of the present invention the critical current density (I in a 5% sulfuric acid atmosphere crit A) may be a less than 10mA.
[52]
The ferritic for the production of stainless steel, according to the production method of ferritic stainless steel in accordance with one embodiment of the present invention, by weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05% , manganese (Mn): 0.01 to 0.5%, chromium (Cr): 12.0 to 19.0%, nickel (Ni): 0.01 to 0.5%, copper (Cu): 0.3 to 1.5%, remainder iron (Fe) and other unavoidable impurities a ferritic stainless steel slab comprising the steps of cold rolling the hot rolling, including, and the value of to during hot rolling formula (1) satisfies 1000 or less.
[53]
15 * RHT / R4 + CT ------ Eq. (1)
[54]
Here, RHT (℃) means the slab reheating temperature and R4 (%) means a reduction ratio of R4 stand of rough rolling and, a CT (℃) means the coiling temperature.
[55]
The molten steel containing the above components to produce a ferritic stainless steel slab through a continuous casting. Then, hot rolling, and the slab to produce a hot-rolled coil 2 to 10mm thick by hot rolling.
[56]
For example, the slab reheating temperature (RHT) is less than 1,250 ℃, a reduction ratio (R4) of R4 stand of rough rolling is 40% or more, to the coiling temperature (CT) is performed at less than 650 ℃, At this time, the hot rolling condition is the value of the formula (1) is performed to satisfy more than 1,000.
[57]
1 is a graph illustrating the correlation between the number of carbides in a ferritic stainless steel hot-rolling conditions and cold rolled steel.
[58]
1, the above equation (1) If the value is not more than 1,000 according to, the number per unit area of the carbide having a diameter of more than 100nm 50ea / 100㎛ 2 it can be seen that more than.
[59]
Even if the carbon content is sufficient, if not formed out of the hot rolling conditions of the formula (1) do not have sufficient strain tissue is formed on the hot-rolled material is sufficiently carbide precipitation sites.
[60]
In particular, it is not the coiling temperature to obtain a carbonized material to generate the desired number is high, coarsening of precipitates more than 650 ℃, this crude crystal grains becomes about along can not be obtained and the tensile strength desired in the finished product.
[61]
For example, the value of the formula (1) can be satisfied, 800 to 1,000.
[62]
Is less than the value of the expression (1) 800, the hot rolling when the temperature is too low can result in poor plate-shaped.
[63]
Hot rolled steel causes a sufficient precipitation of carbides through an annealing heat treatment at a temperature of 700 to 900 ℃ in the annealing step go through the annealing process. For example, the annealing heat treatment can be carried out in a BAF annealing step. Since the annealing heat treatment, it is possible to manufacture a cold-rolled sheet is less than 2mm thick and the final heat treatment is carried out through a heat treatment at a temperature of 800 to 900 ℃ through the cold rolling.
[64]
For example, the cold-rolled plate is the number per unit area of the carbide having a diameter of more than 100nm 50ea / 100㎛ 2 is over, the average crystal grain diameter can 10㎛ less.
[65]
[66]
It will be described in detail of the present invention through the following examples.
[67]
Example
[68]
To via the continuous casting Table inventive steels 1 to satisfying the component 4, and to thereby prepare a slab of the comparative steels 1 to 9, according to the hot rolling conditions shown in Table 2, the re-heating after hot rolling of 5mmt through the hot-rolled coil It was prepared. Then, the annealing heat treatment was carried out in 900 ℃ in BAF annealing step. Then, the cold-rolled sheet was prepared in 1mmt through cold rolling and performing a heat treatment at 900 ℃, by pickling with acid including the tax syotbol surface treatment and sulfuric acid and hydrogen peroxide to prepare a final product.
[69]
TABLE 1
C N Mn Cr Ni With
Invention steel 1 0.103 0.014 0.13 14.3 0.11 0.67
Invention steel 2 0.171 0.016 0.11 17.2 0.09 0.45
Invention steel 3 0.122 0.006 0.24 16.7 0.13 1.21
Invention steel 4 0.125 0.008 0.19 16.5 0.12 1.05
Comparative Steel 1 0.133 0.012 0.23 17.5 0.15 1.79
Comparative Steel 2 0.147 0.015 0.24 16.9 0.17 0.14
Comparative Steel 3 0.227 0.022 0.15 17.1 0.21 0.84
Comparative Steel 4 0.232 0.017 0.14 17.6 0.11 0.66
Comparative Steel 5 0.042 0.046 0.21 16.2 0.11 0.12
Comparative Steel 6 0.051 0.042 0.15 15.2 0.13 0.23
Comparative Steel 7 0.047 0.041 0.17 16.9 0.14 0.77
Comparative Steel 8 0.062 0.015 0.16 17.3 0.13 0.81
Comparative Steel 9 0.085 0.015 0.25 18.1 0.15 0.67

[70]
TABLE 2
Grades RHT(℃) CT(℃) R4(%) 15*RHT/R4+CT
Example 1 Invention steel 1 1,130 550 45 927
Example 2 Invention steel 2 1,130 550 45 927
Example 3 Invention steel 3 1,180 550 45 943
Example 4 Invention steel 4 1,180 580 45 973
Comparative Example 1 Invention steel 1 1,250 550 30 1,175
Comparative Example 2 Invention steel 2 1,180 650 30 1,240
Comparative Example 3 Invention steel 3 1,180 580 30 1,170
Comparative Example 4 Invention steel 4 1,250 550 40 1,019
Comparative Example 5 Comparative Steel 1 1,130 550 45 927
Comparative Example 6 Comparative Steel 2 1,130 580 45 957
Comparative Example 7 Comparative Steel 3 1,180 550 45 943
Comparative Example 8 Comparative Steel 4 1,180 580 45 973
Comparative Example 9 Comparative Steel 5 1,180 650 30 1,240
Comparative Example 10 Comparative Steel 6 1,130 550 45 927
Comparative Example 11 Comparative Steel 7 1,180 550 45 943
Comparative Example 12 Comparative Steel 8 1,180 650 45 1,043
Comparative Example 13 Comparative Steel 9 1,250 650 30 1,275

[71]
In the end to produce a measurement of the critical current density in a unit of carbide having a diameter of 100nm or more per area count, and the average crystal grain diameter, tensile strength, elongation, 5% sulfuric acid in accordance with the atmosphere of the cold-rolled steel sheet it is shown in Table 3 below.
[72]
With respect to the final cold-rolled sheet produced per make TEM Replica unit (100㎛ 2 ) to measure the number of carbide precipitates.
[73]
TABLE 3
Number of Carbides (ea / 100㎛ 2 ) The average grain diameter (㎛) Elongation (%) Tensile Strength (MPa) The critical current density in an atmosphere of 5% sulfuric acid (mA)
Example 1 91 6.8 25.7 529 5.6
Example 2 124 5.9 23.9 531 7.2
Example 3 72 7.4 25.3 542 3.7
Example 4 75 8.1 26.7 537 3.5
Comparative Example 1 32 10.8 27.6 498 8.5
Comparative Example 2 45 11.6 25.3 508 5.9
Comparative Example 3 37 10.5 26.7 515 4.2
Comparative Example 4 41 12.1 27.2 498 4.5
Comparative Example 5 81 6.5 18.8 554 3.1
Comparative Example 6 107 5.4 25.7 527 14.5
Comparative Example 7 227 4.8 18.5 567 6.9
Comparative Example 8 305 5.3 19.2 572 7.5
Comparative Example 9 13 18.1 30.1 457 15.6
Comparative Example 10 19 17.3 29.8 453 13.8
Comparative Example 11 28 20.6 28.9 476 6.3
Comparative Example 12 21 14.1 27.7 481 5.4
Comparative Example 13 26 12.0 26.3 491 4.2

[74]
Figure 2 is a picture taken through a transmission electron microscope (TEM) the precipitate distribution of a ferritic stainless cold-rolled steel sheet according to one embodiment of the present invention. Figure 3 is a picture taken through a transmission electron microscope (TEM) the precipitate distribution of a ferritic stainless cold-rolled steel sheet according to a comparative example of the present invention.
[75]
2 is a picture taking a cold-rolled steel sheet according to the second embodiment, Figure 3 is a picture taking a cold-rolled steel sheet according to the Comparative Example 2.
[76]
2 and 3, the comparative examples 1 to during hot rolling as in the fourth slab reheating temperature, R4 reduction ratio, the carbon content to a value of 15 * RHT / R4 + CT exceeds 1,000 according to the relational expressions relating to the coiling temperature even if not enough is enough variations in the tissue-rolled material not forming carbide precipitation site is not enough.
[77]
In addition, the coiling temperature as in Comparative Example 2, it can be seen that there is no possible to obtain a desired number of carbides and coarsening occurs, in the high precipitate.
[78]
Comparative Example When the content of copper excessive, as in 5, and the elongation of the final product can take the elongation to know degraded to 18.8%, when the content of copper less as in Comparative Example 6, the critical current in the 5% sulfuric acid atmosphere, density (I crit ) is represented by the 14.5mA can not ensure sufficient acid resistance.
[79]
Comparative Examples 7 and when the content of excess carbon as in 8, the elongation and the number of carbides increases to determine an Off. When Comparative Examples 9 to lower the content of carbon, such as 13, becomes larger, the size of crystal grains, and the tensile strength to determine the strength deteriorated to less than 500MPa.
[80]
Figure 4 is a graph illustrating the correlation between the number of carbides and the tensile strength of the ferritic stainless steel, cold-rolled steel sheet.
[81]
4, showing the tensile strength and will be carbonized in the cold-rolled steel sheet according to the above embodiments and comparative example in the graph, the number of carbides increases it can be seen that the tensile strength tends to increase too.
[82]
In the above-described bar, although the description has been made to exemplary embodiments of the present invention, in the present invention is not limited to those skilled in the art without departing from the spirit and scope of the claims set forth in the following it will be appreciated from the various changes and modifications are possible.
Industrial Applicability
[83]
Strength and excellent in the acid resistance of ferritic stainless steel and a method according to embodiments of the present invention is also applicable to building materials, kitchen container, household appliances, automotive exhaust system components, automobile battery.

Claims
[Claim 1]
By weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): 12.0 to 19.0%, nickel (Ni): 0.01 0.3 to 1.5%, remainder iron (Fe) and other unavoidable impurities and including, the number per unit area of the carbide having a diameter of more than 100nm to 50 200ea / 100㎛: to 0.5%, copper (Cu) 2 is the strength and acid resistance excellent ferritic stainless steel.
[Claim 2]
According to claim 1, wherein the average grain diameter of not more than 10㎛ strength and is excellent in the acid resistance of ferritic stainless steel.
[Claim 3]
According to claim 1, wherein the ferritic stainless steel excellent strength and acid resistance greater than a tensile strength of 520MPa to.
[Claim 4]
According to claim 1, wherein the ferritic stainless steel excellent strength and acid resistance than an elongation of 20% to.
[Claim 5]
According to claim 1, wherein the critical current density (I in a 5% sulfuric acid in the atmosphere crit ) is a ferritic stainless steel excellent strength and acid resistance less than or equal to 10mA.
[Claim 6]
By weight%, carbon (C): 0.1 to 0.2%, nitrogen (N): 0.005 to 0.05%, manganese (Mn): 0.01 to 0.5%, chromium (Cr): 12.0 to 19.0%, nickel (Ni): 0.01 to 0.5%, copper (Cu): 0.3 to 1.5%, remainder iron to when (Fe) and other inevitable, and the ferritic stainless steel slab containing the impurities comprises the step and the step of cold rolling the hot-rolling, hot-rolled formula (1) strength and acid resistance are excellent manufacturing method of ferritic stainless steels satisfying the value of 1000 or less. 15 * RHT / R4 + CT ------ Eq. (1) Here, RHT (℃) means the slab reheating temperature and, R4 (%) means a reduction ratio of R4 stand of rough rolling and, CT ( ℃); it means the coiling temperature.
[Claim 7]
Claim 6, wherein the formula (1) is the intensity value and the acid resistance is excellent ferritic stainless steel producing method that satisfies the 800 to 1000 of the.
[Claim 8]
7. The method of claim 6, RHT is less than 1,250 ℃, R4 is at least 40%, CT is less than 650 ℃ strength and acid resistance are excellent method of producing a ferritic stainless steel.
[Claim 9]
According, cold-rolled plate is the number per unit area of the carbide having a diameter of more than 100nm to 50 200ea / 100㎛ to claim 6, wherein 2 , the mean grain diameter of not more than 10㎛ strength and acid resistance are excellent method of producing a ferritic stainless steel.