Title of the invention: Ferritic stainless steel and ferritic stainless steel pipe with improved mechanical properties of the weld
Technical field
[One]
The present invention relates to a ferritic stainless steel, and in particular, to a ferritic stainless steel and a ferritic stainless steel pipe with improved mechanical properties of a weld.
Background
[2]
Stainless steel refers to steel that has strong corrosion resistance by suppressing corrosion, which is the weak point of carbon steel. In general, stainless steel is classified according to its chemical composition or metal structure. According to the metal structure, stainless steel can be classified into austenite-based, ferrite-based, martensite-based and dual phase-based.
[3]
Among them, ferritic stainless steel is applied to various industrial fields such as home appliances and kitchen appliances because it has excellent corrosion resistance while adding less expensive alloying elements.
[4]
In particular, when used as a material for exhaust pipes, fuel tanks or pipes of automobiles or two-wheeled vehicles, corrosion resistance and heat resistance are required when exposed to exhaust environments and fuel environments, as well as formability during cold working.
[5]
In recent years, as automobile exhaust system parts become lighter and more complex in shape, there is a need to improve mechanical properties and moldability of materials for exhaust system parts. To this end, it has become easy to improve the mechanical properties and formability of the steel itself through the development of technology to improve the microstructure and texture of ferritic stainless steel.
[6]
However, in the welding process that occurs when ferritic stainless steel is used as a material for exhaust pipes, fuel tanks or pipes of automobiles or two-wheeled vehicles, the steel material loses its fine structure and excellent formability texture because it is reheated at high temperature. Very coarse columnar crystal grains are formed.
[7]
This phenomenon is more pronounced in the welded portion including the molten portion and the welded heat-affected portion, which causes the stability of the product to deteriorate. Therefore, finely controlling the grain size of the weld is essential to improve the mechanical properties of products manufactured through welding. As a means for miniaturizing the structure of the welded portion, a technology for controlling grain coarsening using TiN and a technology for generating intragranular ferrite using Ti oxide have been studied and put into practical use. However, the technology for controlling the microstructure of the weld and the texture of the weld has not been developed.
Detailed description of the invention
Technical challenge
[8]
Embodiments of the present invention are intended to provide a ferritic stainless steel and ferritic stainless steel pipe with improved mechanical properties of the weld by controlling the microstructure and texture of the weld.
Means of solving the task
[9]
Ferritic stainless steel having improved weld mechanical properties according to an embodiment of the present invention is, by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3% , Nb: 0.1 to 0.3%, Al: 0.005 to 0.05%, the rest contains Fe and inevitable impurities, and after welding, the maximum strength of the texture in the {001} direction is 30 or less.
[10]
In addition, the ferritic stainless steel may include a secondary phase present at 10 to 100 pieces/mm 2 or less in the welded portion after welding .
[11]
In addition, the secondary phase may include nitride, oxide, and Laves phase precipitates.
[12]
In addition, the ferritic stainless steel may further include one or more of Mo: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less, and B: 0.005% or less.
[13]
Ferritic stainless steel pipe according to another embodiment of the present invention, by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3%, Nb: 0.1 To 0.3%, Al: 0.005 to 0.05%, the rest is a base material containing Fe and inevitable impurities; And a welding portion having a maximum strength of 30 or less of the texture in the {001} direction.
[14]
In addition, the welding portion may include a secondary phase that is 10 to 100 / mm 2 or less.
[15]
In addition, the secondary phase may include nitride, oxide, and Laves phase precipitates.
[16]
In addition, the base material may further include one or more of Mo: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less, and B: 0.005% or less.
[17]
In addition, DBTT (ductile-brittle transition temperature) of the weld may be -50 °C or less.
Effects of the Invention
[18]
According to an embodiment of the present invention, it is possible to provide a ferritic stainless steel and a ferritic stainless steel pipe with improved mechanical properties of a weld.
Brief description of the drawing
[19]
1 is a graph for explaining the relationship between the maximum strength of the welded joint texture and the ductile-brittle transition temperature (DBTT) of a ferritic stainless steel according to an embodiment of the present invention.
[20]
2 is a graph for explaining the relationship between the distribution density of the secondary phase of the welded portion of the ferritic stainless steel and the ductile-brittle transition temperature (DBTT) according to an embodiment of the present invention.
Best mode for carrying out invention
[21]
Ferritic stainless steel having improved weld mechanical properties according to an embodiment of the present invention is, by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3% , Nb: 0.1 to 0.3%, Al: 0.005 to 0.05%, the rest contains Fe and inevitable impurities, and after welding, the maximum strength of the texture in the {001} direction is 30 or less.
Mode for carrying out the invention
[22]
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 exemplary embodiments presented here, and may be embodied in other forms. In the drawings, in order to clarify the present invention, portions not related to the description may be omitted, and the size of components may be slightly exaggerated to aid understanding.
[23]
Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.
[24]
Expressions in the singular number include expressions in the plural unless the context clearly has exceptions.
[25]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[26]
During stainless steel welding, a weak secondary phase is formed by rapid heating/quenching in the weld, which can act as a major factor in the decrease in toughness. The welding part is a concept including a fusion zone and a heat-affected zone (HAZ). In addition, in the present invention, the term "secondary phase" refers to a phase different from the stainless steel base material, and specifically includes a precipitate such as an oxide, nitride, and Laves phase.
[27]
Precipitates that may be formed during welding in ferritic stainless steel include chromium carbide (Cr 3 C 2 ), chromium nitride (CrN), and chromium carbonitride (CrCN). These precipitates consume chromium in the ferritic stainless steel base material, which causes a decrease in the corrosion resistance of the weld. Therefore, it is necessary to suppress the formation of these precipitates by controlling the content of carbon and nitrogen bonded to chromium as low as possible.
[28]
In addition, precipitates such as the Sigma phase and the Laves phase may deteriorate the brittleness and corrosion resistance of the material, and thus formation thereof needs to be suppressed.
[29]
Meanwhile, in the ferritic stainless steel welding process, the molten metal has anisotropy of crystal orientation due to the difference in cooling rate. That is, when the molten metal is solidified, columnar crystal grains are formed in a direction in which cooling preferentially occurs, and at this time, columnar crystals grow in the {001} direction, which has the lowest interfacial energy.
[30]
When crystal grains having similar orientations are clustered as described above, a phenomenon in which stress is concentrated in the clusters where mechanical properties are poor occurs, which deteriorates the mechanical properties of the ferritic stainless steel. Therefore, when considering the mechanical properties of the weld, it is necessary to derive the texture of the weld as disorderly as possible.
[31]
In addition, since crystal grain growth occurs in the weld heat-affected zone, the mechanical properties of the weld zone may be deteriorated. Therefore, it is important to form a micronized equiaxed crystal structure in order to improve the mechanical properties of the weld zone.
[32]
In order to consider both the strength and toughness of the welded portion of ferritic stainless steel, the present inventors found that the distribution density of the secondary phase should be controlled, and at the same time, a disordered texture should be derived. The tissue and aggregate conditions could be derived.
[33]
Ferritic stainless steel with improved mechanical properties of the weld according to an aspect of the present invention is, by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3% , Nb: 0.1 to 0.3%, Al: 0.005 to 0.05%, and the rest contains Fe and unavoidable impurities.
[34]
Hereinafter, the reason for limiting the numerical value of the content of the alloying component in the examples of the present invention will be described. Hereinafter, unless otherwise specified, the unit is% by weight.
[35]
The content of C is 0.005 to 0.02%.
[36]
Carbon (C) is an interstitial solid solution strengthening element and improves the strength of ferritic stainless steel. In addition, since it combines with titanium (Ti) or niobium (Nb) to form carbides to suppress grain growth, it is an essential element to refine grains in the heat-affected zone of welding. Therefore, 0.005% or more can be added in the present invention. However, if the content is excessive, it may cause brittleness by forming a martensite phase during welding, so the upper limit may be limited to 0.02%.
[37]
The content of N is 0.005 to 0.02%.
[38]
Nitrogen (N), like carbon, is an interstitial solid solution strengthening element and improves the strength of ferritic stainless steel, and can suppress crystal grain growth by combining with titanium (Ti) or niobium (Nb) to form nitride. In addition, since such nitride acts as a crystal grain nucleation site during solidification of molten metal during welding, it promotes formation of equiaxed crystal grains having disordered orientations, and thus can be added by 0.005% or more. However, if the content is excessive, the upper limit may be limited to 0.02% because it may cause brittleness by forming a martensite phase during welding.
[39]
The content of Cr is 11.0 to 13.0%.
[40]
Chromium (Cr) is a ferrite stabilizing element and may be added at least 11.0% in order to secure the corrosion resistance required for stainless steel. However, if the content is excessive, there is a problem that the manufacturing cost increases and the moldability is inferior, so the upper limit may be limited to 13.0%.
[41]
The content of Ti is 0.16 to 0.3%.
[42]
Titanium (Ti) is an essential element for grain refinement because it suppresses grain growth by forming carbonitrides by combining with interstitial elements such as carbon (C) and nitrogen (N). In addition, titanium (Ti) combines with nitrogen (N) or oxygen (O) to form nitrides and oxides. These secondary phases act as grain nucleation sites during the solidification of molten metal during welding, resulting in equiaxed crystal grains having disordered orientation. As it promotes formation, 0.16% or more can be added. However, if the content is excessive, it causes an increase in cost, and there is difficulty in manufacturing due to the formation of excessive inclusions, and the upper limit may be limited to 0.3%.
[43]
The content of Nb is 0.1 to 0.3%.
[44]
Niobium (Nb) inhibits grain growth by combining with interstitial elements such as carbon (C) and nitrogen (N) to form carbonitrides, so 0.1% or more can be added for grain refinement. However, if the content is excessive, the upper limit may be limited to 0.3%, since it causes an increase in cost, and increases the brittleness of the weld by forming laves precipitates during the welding process, thereby lowering the mechanical properties.
[45]
The content of Al is 0.005 to 0.05%.
[46]
Aluminum (Al) is an element that is essentially added for deoxidation, and since it is an element that forms an oxide that acts as a nucleation site of a weld zone in the present invention, it can be added by 0.005% or more. However, if the content is excessive, the penetration rate during welding decreases and weldability decreases, so the upper limit may be limited to 0.05%.
[47]
In addition, the ferritic stainless steel having improved mechanical properties of the welding portion according to an embodiment of the present invention is 1 in weight %, Mo: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less, and B: 0.005% or less. It may further include more than a species.
[48]
The content of Mo is 1.0% or less.
[49]
Molybdenum (Mo) may be additionally added to improve corrosion resistance, and if it is added in an excessive amount, the impact property is deteriorated, thereby increasing the risk of fracture during processing and increasing the cost of the material.In the present invention, considering this, the upper limit Is preferably limited to 1.0%.
[50]
The content of Ni is 1.0% or less.
[51]
Nickel (Ni) is an element that improves corrosion resistance, and when a large amount is added, it is hardened and there is a concern that stress corrosion cracking may occur. Therefore, it is preferable to limit the upper limit to 1.0%.
[52]
The content of Cu is 1.0% or less.
[53]
Copper (Cu) may be additionally added to improve corrosion resistance, and if excessively added, there is a problem that the workability is deteriorated, so it is preferable to limit the upper limit to 1.0%.
[54]
The content of B is not more than 0.005%.
[55]
Boron (B) is an effective element in securing good surface quality by suppressing the occurrence of cracks during casting. However, if the content is excessive, nitride (BN) may be formed on the surface of the product during the annealing/pickling process to reduce the surface quality, and the upper limit may be limited to 0.005%.
[56]
The remaining component of the present invention is iron (Fe). However, since unintended impurities from the raw material or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.
[57]
Hereinafter, an assembly structure of a ferritic stainless steel weld with improved mechanical properties of a weld according to an embodiment according to an embodiment of the present invention will be described in detail.
[58]
During welding, the solidification process begins in the partially molten region of the ferritic stainless steel base metal. During the solidification process, columnar microstructures with a specific preferred orientation are formed. Specifically, the columnar crystal structure tends to grow in the {001} direction, which is disadvantageous in formability due to the anisotropy of the interfacial energy. This columnar structure is known to degrade the mechanical properties of the weld, and the formation of the columnar structure during the welding process of most metal materials is a factor that must be controlled.
[59]
Accordingly, in order to improve the mechanical properties of the welded portion, it is necessary to suppress the formation of crystal grains having a {001} plane and increase the volume fraction of crystal grains having a disordered orientation.
[60]
An arrangement with a certain surface and orientation created inside a crystal is called a texture, and the texture can be quantified through the orientation distribution function (ODF).
[61]
In the present invention, the maximum strength of the orientation distribution function was introduced as an aggregate structure index. EBSD (Electron Backscattered Diffraction) was used to measure the grains of the melt and heat affected zone, and the orientation distribution function was calculated from the crystal orientations of the melt and heat affected zone. The strength of the orientation distribution function refers to how many times the orientation is compared to a specimen having a completely disordered texture. That is, the high maximum strength of the orientation distribution function means that there are many grains having a specific orientation, and the maximum strength of the texture of 30 or less means that the preferential development of a specific orientation is suppressed.
[62]
1 is a graph for explaining the relationship between the maximum strength of the welded joint texture and the ductile-brittle transition temperature (DBTT) of a ferritic stainless steel according to an embodiment of the present invention.
[63]
DBTT (Ductile to Brittle Transition Temperature) is a ductile brittle transition temperature, and the fracture behavior changes from ductile fracture to brittle fracture based on the DBTT temperature, which is the main cause of cracking during welding at low temperature conditions. Therefore, it is desirable that the DBTT is low.
[64]
According to an embodiment of the present invention, a maximum strength of a welded structure of a ferritic stainless steel having improved mechanical properties of a welded part satisfying the above-described alloy composition may be 30 or less.
[65]
Referring to FIG. 1, it can be seen that DBTT tends to increase as the maximum strength of the weld texture increases. Specifically, in the case of the embodiments in which the maximum strength of the weld texture is 30 or less, the weld DBTT value satisfies -50 °C or less. That is, it can be seen that the mechanical properties of the welding part are improved compared to the comparative examples.
[66]
In order to disorderly develop the grain structure of ferritic stainless steel, the distribution density of the alloy composition and the secondary phase is important. In general, ferritic stainless steels are completely single-phase steels that do not undergo phase transformation during melting and solidification. If no special measures are taken, a very strong {001} texture develops during melting and solidification. This is because the nucleated crystal grains first grow along the <001> direction, which is the growth direction. Increasing the number of nucleation sites per unit area during solidification can minimize the grain growth during solidification and lower the maximum strength of the texture. .
[67]
During welding, the secondary phase formed in the molten metal can act as a nucleation site during cooling and solidification.
[68]
When the secondary phase is formed in the molten metal, the structure of the weld can be refined by increasing the nucleation site, so studies have been conducted to form the secondary phase in the molten metal through oxide metallurgy and nitride metallurgy.
[69]
TiN nitride and Ti-Al-O oxide may be formed in the liquid phase of the ferritic stainless steel to which Ti and Nb are added in combination according to the disclosed embodiment. As the number of nitrides and oxides formed in the liquid ferritic stainless steel increases, the grain size of the weld zone decreases, and at the same time, the development of disordered texture can be promoted, thereby improving the mechanical properties of the weld zone.
[70]
On the other hand, in order to derive the texture of the weld in a disordered manner, it is necessary to increase the grain nucleation event during solidification. Since uniform nucleation easily occurs as the degree of subcooling increases during solidification, cooling should be performed as quickly as possible during welding, but this has a limitation in the welding process. In order to overcome this limitation, as described above, by forming a secondary phase in the molten metal, disorder of the texture is derived through non-uniform nucleation.
[71]
2 is a graph for explaining the relationship between the distribution density of the secondary phase of the welded portion of the ferritic stainless steel and the ductile-brittle transition temperature (DBTT) according to an embodiment of the present invention.
[72]
Referring to FIG. 2, it can be seen that the DBTT tends to increase as the distribution density of the secondary phase of the welding part increases. Specifically, to obtain a DBTT value of -50 °C or less, a secondary phase distribution density of 100 or less per mm 2 is required.
[73]
As described above, in order to refine the crystal grains of the ferritic stainless steel weld that satisfies the above-described alloy composition and suppress the development of a specific orientation texture, the distribution density of nitrides or oxides present in the weld must be 10 pieces/mm 2 or more.
[74]
However, if there are too many secondary phases in the weld, it causes brittleness, so its distribution density must be limited. In particular, since the secondary phase formed at low temperature, such as the Laves phase, increases brittleness without affecting grain nucleation, formation must be suppressed. Therefore, the distribution density of all secondary phases including nitride, oxide, and Laves precipitates present in the weld can be limited to 100 pieces/mm 2 or less.
[75]
[76]
Hereinafter, the present invention will be described in more detail through examples.
[77]
For various alloy component ranges shown in Table 1 below, a slab having a thickness of 200 mm was prepared by melting an ingot, heated at 1,240° C. for 2 hours, and then hot-rolled to prepare a hot-rolled steel sheet having a thickness of 3 mm.
[78]
Thereafter, in order to evaluate the welding characteristics of the steel sheets manufactured according to the Examples and Comparative Examples, after welding by the GTA process, the crystal grain size of the weld, the texture of the weld, and the impact energy of the weld were investigated. As the main influencing factors, the molten steel component, the number of internal secondary phases, texture, and ductile-brittle transition temperature were investigated and shown in Tables 1 and 2 below.
[79]
[Table 1]
C N Cr Ti Nb Al Mo Ni Cu B
Example 1 0.005 0.009 12.8 0.168 0.146 0.035 0.004 0.06 0.01 0.001
Example 2 0.006 0.007 12.0 0.23 0.145 0.028 0.004 0.07 0.016 0.002
Example 3 0.005 0.009 12.3 0.296 0.165 0.029 0.002 0.13 0.014 0.001
Example 4 0.007 0.009 11.3 0.22 0.123 0.022 0.005 0.07 0.016 0.001
Example 5 0.008 0.009 11.7 0.21 0.22 0.016 0.004 0.06 0.01 0.003
Example 6 0.006 0.009 12.4 0.221 0.29 0.028 0.002 0.05 0.011 0.002
Comparative Example 1 0.006 0.007 11.5 0.105 0.164 0.031 0.004 0.06 0.014 0.001
Comparative Example 2 0.005 0.008 12.2 0.147 0.174 0.022 0.003 0.06 0.01 0.001
Comparative Example 3 0.007 0.009 12.2 0.054 0.031 0.029 0.005 0.1 0.02 0.002
Comparative Example 4 0.006 0.007 11.8 0.112 0.48 0.031 0.002 0.08 0.009 0.001
Comparative Example 5 0.007 0.009 12.1 0.321 0.456 0.026 0.005 0.06 0.011 0.002
Comparative Example 6 0.006 0.009 12.3 0.181 0.35 0.026 0.004 0.07 0.016 0.003
[80]
As for the texture, the area including the total thickness direction of the cross section of the weld including the molten part and the weld heat-affected part was measured using the Electron Backscatter Diffraction (EBSD) method. The texture was quantified by calculating the orientation distribution function from the EBSD data, and the maximum strength of the orientation distribution function was used as the texture index.
[81]
In addition, the mechanical properties of the welding part are ASTM E 23 standard, and the DBTT (Ductile Brittle Transition Temperature, ductile-brittle transition temperature) obtained by measuring the impact energy from -60 to 100℃ at intervals of 20℃ through Charpy impact test is shown in Table 2 below. Shown in.
[82]
[Table 2]
Number of nitrides + oxides (pcs/mm 2 ) Nitride + Oxide + Number of Laves (pcs/mm 2 ) Maximum strength of the collective organization DBTT (°C)
Example 1 13 18 18.2 -68
Example 2 24 21 10.9 -65
Example 3 27 30 5.9 -74
Example 4 15 15 14.1 -70
Example 5 14 46 11.2 -75
Example 6 15 86 9.1 -73
Comparative Example 1 6 22 35.2 -41
Comparative Example 2 8 25 35.4 -43
Comparative Example 3 3 18 41.5 -34
Comparative Example 4 7 188 33.5 -10
Comparative Example 5 32 164 11.3 -19
Comparative Example 6 11 134 13.4 -36
[83]
1 is a graph for explaining the relationship between the maximum strength of the welded joint texture and the ductile-brittle transition temperature (DBTT) of a ferritic stainless steel according to an embodiment of the present invention.
[84]
2 is a graph for explaining the relationship between the distribution density of the secondary phase of the welded portion of the ferritic stainless steel and the ductile-brittle transition temperature (DBTT) according to an embodiment of the present invention.
[85]
As described above, in order to secure the mechanical properties of the weld, the volume fraction of crystal grains having disordered orientation is increased to control the maximum strength of the weld texture to 30 or less, and the distribution density of the secondary phase of the weld is 10 to 100 /mm 2 It must be controlled with.
[86]
1, 2 and Table 2, in the case of the above examples, compared with the comparative examples, it can be confirmed that the DBTT value is -50 °C or less by satisfying the range of the secondary phase distribution density and the maximum strength of the texture of the weld. have.
[87]
In contrast, in Comparative Examples 1 to 3, the Ti content was less than 0.16%, and the number of nitrides and oxides per unit area (mm 2 ) of the weld was less than 10, and the maximum strength of the texture of the weld was 30 or more. First of all, it can be confirmed that the texture with orientation has been strongly developed.
[88]
In Comparative Example 4, as in Comparative Examples 1 to 3, not only the Ti content was less than 0.16%, but also the Laves precipitate was excessively formed by adding an excessive amount of Nb to 0.48%, so that the distribution density of the secondary phase of the weld was increased to the upper limit of the present invention. Exceeded.
[89]
In Comparative Examples 5 and 6, the number of nitrides and oxides per unit area of ​​the weld was 10 or more, and the maximum strength of the texture was 20.0 or less, so that a texture suitable for the mechanical properties of the weld was obtained. However, the content of Nb exceeded 0.3%, which is the upper limit of the present invention, so that the distribution density of the secondary phase of the weld portion exceeded 100 pieces/mm 2 , which means that the Laves precipitate was excessively formed, resulting in a high DBTT value.
[90]
Ferritic stainless steel manufactured according to an embodiment of the present invention can improve mechanical properties by deriving an irregular weld texture by controlling the maximum strength of the weld texture to 30 or less.
[91]
In addition, the ferritic stainless steel manufactured according to an embodiment of the present invention can secure toughness as well as strength by controlling the secondary phase distribution density to 10 to 100 pieces/mm 2 .
[92]
As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and those of ordinary skill in the art are within the scope not departing from the concept and scope of the following claims. It will be appreciated that various changes and modifications are possible in.
[93]
Industrial applicability
[94]
The ferritic stainless steel according to the present invention can be used as a material for exhaust pipes, fuel tanks, or pipes of automobiles or two-wheeled vehicles because the mechanical properties of the welding portion are improved.
Claims
[Claim 1]
In% by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3%, Nb: 0.1 to 0.3%, Al: 0.005 to 0.05%, the remainder is Fe and Ferritic stainless steel with improved mechanical properties of welds containing inevitable impurities and having a texture maximum strength of 30 or less in the {001} direction after welding.
[Claim 2]
According to claim 1, After welding, ferritic stainless steel having improved mechanical properties of a welded portion including a secondary phase present at 10 to 100 pieces/mm 2 or less in the welded portion.
[Claim 3]
The ferritic stainless steel according to claim 2, wherein the secondary phase is a ferritic stainless steel having improved mechanical properties of a weld including nitride, oxide, and Laves phase precipitates.
[Claim 4]
The ferritic stainless steel according to claim 1, further comprising at least one of Mo: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less, and B: 0.005% or less.
[Claim 5]
In% by weight, C: 0.005 to 0.02%, N: 0.005 to 0.02%, Cr: 11.0 to 13.0%, Ti: 0.16 to 0.3%, Nb: 0.1 to 0.3%, Al: 0.005 to 0.05%, the remainder is Fe and A base material containing inevitable impurities; And a welding portion having a texture maximum strength of 30 or less in the {001} direction.
[Claim 6]
The ferritic stainless steel pipe according to claim 5, wherein the welded portion includes a secondary phase present in an amount of 10 to 100 pieces/mm 2 or less.
[Claim 7]
The ferritic stainless steel pipe according to claim 6, wherein the secondary phase contains nitride, oxide, and Laves phase precipitates.
[Claim 8]
The ferritic stainless steel pipe according to claim 5, wherein the base material further comprises at least one of Mo: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less, and B: 0.005% or less.
[Claim 9]
The ferritic stainless steel pipe according to claim 5, wherein the welding portion has a DBTT (ductile-brittle transition temperature) of -50°C or less.