KR20220078166A - Ferritic stainless steel with improved grain boundary erosion and its manufacturing method - Google Patents

Abstract

In the present specification, a ferritic stainless steel with improved intergranular erosion is disclosed.
According to an embodiment of the disclosed ferritic stainless steel with improved intergranular erosion, in wt%, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N : 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% or less, S: 0.005% or less including remaining Fe and impurities,
Ac1 defined by the following formula (1) satisfies 900 or more and 990 or less.
Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)
(Here, C, N, Si, Mn, Cr, Ni, Al, Mn and Mo mean the content (wt%) of each element)

Description

Ferritic stainless steel with improved grain boundary erosion and its manufacturing method

The present invention relates to a ferritic stainless steel and a method for manufacturing the same, and more particularly, to a ferritic stainless steel with improved intergranular erosion and a method for manufacturing the same.

In general, stainless steel is classified according to its chemical composition or metal structure. According to the metal structure, stainless steel is classified into austenitic (300 series), ferritic (400 series), martensitic, and ideal.

Among them, ferritic stainless steel is a steel with high price competitiveness compared to austenitic stainless steel because it contains less expensive alloying elements. Ferritic stainless steel has good surface gloss, drawability and oxidation resistance, and is widely used in kitchenware, building exterior materials, home appliances, and electronic parts.

On the other hand, during hot rolling after reheating a ferritic stainless steel piece, it is formed into two phases of ferrite and austenite. After the hot rolling is performed and then cooled, the austenite is transformed into a martensite phase, which has very high hardness and is not easily deformed.

Accordingly, the ferritic stainless steel is subjected to an annealing process as a subsequent process in order to recrystallize the strain structure formed during hot rolling and decompose the austenite phase generated during hot rolling into a ferrite phase.

In performing the annealing process, in general, a method of continuous annealing by unwinding a coil in which stainless steel on ferrite is wound is adopted. However, 430 ferritic stainless steel undergoes a batch annealing process in which the coil is annealed as it is, instead of the continuous annealing process due to the property of being easily broken when the coil is annealed.

When the annealing temperature rises above the austenite transformation temperature during phase annealing, the austenite phase is regenerated during annealing, which is re-transformed to martensite during cooling, thereby reducing the formability and corrosion resistance.

Therefore, in the phase annealing process, the heat treatment is performed directly under the temperature at which the austenite phase changes to the ferrite phase. Since the austenite phase transformation temperature is usually as low as 800 to 850 °C, the phase annealing process takes a long time (35 to 50 hours) to perform complete annealing.

The phase annealing process not only consumes a lot of energy, but also increases the production cost, thereby lowering productivity. In addition, since the upper annealing process requires a long time, there is a problem such as a delay in delivery due to an increase in manufacturing time.

On the other hand, when 430 ferritic stainless steel is subjected to continuous annealing instead of phase annealing and then pickled by a normal pickling method, intergranular erosion occurs due to grain boundary Cr deficiency due to the formation of Cr carbides deposited during cooling after hot rolling. The steel material in which intergranular erosion has occurred has a problem of causing surface defects during subsequent cold working and poor corrosion resistance.

Korean Patent Publication No. 10-2019-0072279A (published date: June 25, 2019)

SUMMARY OF THE INVENTION An object of the present invention is to provide a stainless steel with improved intergranular erosion and a method for manufacturing the same, in which the phase annealing process is omitted and continuous annealing is possible in order to solve the above-described problems.

Ferritic stainless steel with improved intergranular erosion according to an embodiment of the present invention, by weight, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18% , N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% or less, S: 0.005% or less including the remaining Fe and impurities,

Ac1 defined by the following formula (1) satisfies 900 or more and 990 or less.

Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)

(Here, C, N, Si, Mn, Cr, Ni, Al, Mn, and Mo mean the content (wt%) of each element)

In addition, according to an embodiment of the present invention, the stainless steel may include, by weight%, Mn: 0.4 to 1.0%, Al: 0.1 to 0.15%.

In addition, according to an embodiment of the present invention, the stainless steel may further include Ni: 0.005 to 0.1%, Mo: 0.003% or less by weight%.

According to another embodiment of the present invention, in the method for manufacturing ferritic stainless steel with improved intergranular erosion, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% or less, S: 0.005% or less, including the remaining Fe and impurities, and Ac1 defined by the following formula (1) is 900 or more 990 Below, manufacturing a slab; reheating the slab; finishing rolling after rough rolling of the reheated slab; winding the hot rolled material; Continuous annealing of the wound hot-rolled material in a temperature range of T (A) defined by the following formula (2); and pickling the continuously annealed steel.

Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)

(Here, C, N, Si, Mn, Cr, Ni, Al, Mn, and Mo mean the content (wt%) of each element)

Formula (2): 870 °C ≤ T(A) ≤ (Ac1-10) °C

In addition, according to an embodiment of the present invention, the slab may include, by weight, Mn: 0.4 to 1.0%, Al: 0.1 to 0.15%.

In addition, according to an embodiment of the present invention, the slab may further include, by weight%, Ni: 0.005 to 0.1%, Mo: 0.003% or less.

In addition, according to an embodiment of the present invention, the reheating may be performed at 1,000 to 1,200 ℃.

In addition, according to an embodiment of the present invention, the finishing rolling may be performed at 800 to (Ac1-10) ℃.

In addition, according to an embodiment of the present invention, the winding may be performed at 750 to (Ac1-10) ℃.

In addition, according to an embodiment of the present invention, the continuous annealing may be performed for 3 to 10 minutes.

According to an embodiment of the present invention, continuous annealing is possible by controlling alloy components, so that it is possible to provide a ferritic stainless steel with improved intergranular erosion and a method for manufacturing the same.

1A, 1B, and 1C are photographs taken with an optical microscope to observe the degree of intergranular erosion after pickling of the continuous annealing material of a hot-rolled sheet.
FIG. 1A is a photograph in which intergranular erosion is connected along the grain boundary and has a wide width.
Fig. 1b is a photograph in which intergranular erosion is not connected along the grain boundary and is generated as a line.
1C is a photograph showing grain boundary erosion as a line in some grain boundary traces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes preferred embodiments of the present invention. However, the embodiment of the present invention may be modified in various other forms, and the technical idea of the present invention is not limited to the embodiment described below. In addition, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.

The terms used in this application are only used to describe specific examples. Therefore, for example, a singular expression includes a plural expression unless the context clearly requires it to be singular. In addition, terms such as "comprises" or "including" as used in the present application are used to clearly indicate that the features, steps, functions, components, or combinations thereof described in the specification exist, and other features It should be noted that the use is not intended to preliminarily exclude the existence of elements, steps, functions, components, or combinations thereof.

Meanwhile, unless otherwise defined, all terms used herein should be regarded as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Accordingly, unless explicitly defined herein, specific terms should not be construed in an unduly idealistic or formal sense. For example, a singular expression herein includes a plural expression unless the context clearly dictates otherwise.

In addition, in this specification, "about", "substantially", etc. are used in or close to the numerical value when manufacturing and material tolerances inherent in the stated meaning are presented, and are used in a precise sense to help the understanding of the present invention. or absolute figures are used to prevent unreasonable use by unconscionable infringers of the mentioned disclosure.

The ferritic stainless steel with improved intergranular erosion according to an embodiment of the present invention is, by weight, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% or less, S: 0.005% or less The remaining Fe and impurities are included.

Hereinafter, the reason for limiting the component range of each alloy element will be described below.

The content of carbon (C) is 0.005 to 0.1%.

C is an interstitial solid solution strengthening element that improves the strength of ferritic stainless steel. When the content of C is less than 0.005%, sufficient strength cannot be obtained by reducing the amount of carbide produced. However, when the content is excessive, the temperature at which the ferrite phase is transformed into the austenite phase is lowered, and the upper limit of the continuous annealing temperature is lowered. Therefore, it is preferable to control the content of C to be 0.005% to 0.1%.

The content of silicon (Si) is 0.01 to 1.0%.

Si is an alloying element that is essential for deoxidation of molten steel during steel making, and at the same time improves strength and corrosion resistance, and at the same time stabilizes the ferrite phase, it can be added in an amount of 0.01% or more in the present invention. However, when the content is excessive, there is a problem in that ductility and formability are deteriorated, so the upper limit is to be limited to 1.0%.

The content of manganese (Mn) is 0.01 to 1.5%.

Mn is an effective element to form a uniform scale on the surface layer of ferritic stainless steel during heat treatment and to improve corrosion resistance. However, if the content is excessive, manganese-based fume is generated during welding, which causes MnS phase precipitation and lowers elongation. Therefore, the lower limit of the content of Mn is preferably 0.01%, more preferably 0.4%. The upper limit of the content of Mn is preferably 1.5%, more preferably 1.0%.

The content of chromium (Cr) is 13 to 18%.

Cr is an alloying element added to improve the corrosion resistance of stainless steel. However, when the content is excessive, a sticking defect occurs due to the formation of dense oxide scale during hot rolling, and there is a problem in that the manufacturing cost increases. Therefore, it is preferable to control the content of Cr to 13 to 18%.

The content of nitrogen (N) is 0.005 to 0.1%.

Nitrogen (N), like carbon, is an interstitial solid solution strengthening element and improves the strength of ferritic stainless steel. However, when the content is excessive, the impact toughness and formability of the steel are reduced, and the temperature at which the austenite phase is transformed into the ferrite phase is lowered, thereby lowering the upper limit of the temperature of the continuous annealing of the present invention. Therefore, the content of N is preferably controlled to 0.005 to 0.1%.

The content of aluminum (Al) is 0.005 to 0.2%.

Al is a ferrite phase stabilizing element and serves to lower the oxygen content in molten steel as a strong deoxidizer. However, when the content is excessive, room temperature ductility is reduced, and sliver defects of the cold rolled cold rolled strip occur due to an increase in non-metallic inclusions, and there is a problem of deteriorating weldability at the same time. Therefore, the Al content is preferably controlled to 0.005 to 0.2%. A more preferable lower limit of the content of Al is 0.1%, and a more preferable upper limit is 0.15%.

The content of phosphorus (P) is 0.05% or less.

P is an impurity unavoidably contained in steel, and since it is an element that causes intergranular corrosion during pickling or inhibits hot workability, it is desirable to control its content as low as possible. Therefore, it is preferable to control the content of P to 0.05% or less.

The content of sulfur (S) is 0.005% or less.

S is an impurity unavoidably contained in steel, and is an element that segregates at grain boundaries and is a major cause of inhibiting hot workability. Therefore, it is preferable to control the content of S to 0.005% or less.

In addition, the ferritic stainless steel according to an embodiment of the present invention may further include Ni: 0.005 to 0.1%, Mo: 0.003% or less by weight%.

The content of nickel (Ni) is 0.005 to 0.1%.

Ni is added in an amount of 0.005% or more to have the effect of improving corrosion resistance, whereas when a large amount is added, austenite stabilization is increased, and as an expensive element, the manufacturing cost is increased. Accordingly, the content of Ni may be limited to 0.005 to 0.1%.

The content of molybdenum (Mo) is 0.003% or less.

Mo is an effective element for improving the corrosion resistance of stainless steel. However, as Mo is an expensive element, it causes an increase in raw material cost, and reduces workability when added in a large amount. Therefore, the content of Mo may be limited to 0.003% or less.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since these impurities are known to any person skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

In addition, in the ferritic stainless steel according to an embodiment of the present invention, Ac1 defined by the following formula (1) may satisfy 900 or more and 990 or less.

Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)

(Here, C, N, Si, Mn, Cr, Ni, Al, Mn, and Mo mean the content (wt%) of each element)

Ac1 is the austenite transformation temperature calculated by the alloy composition. When heat treatment is performed at a temperature higher than Ac1, the ferrite phase is transformed into an austenite phase. Conventionally, by adding alloys such as Ti and Nb to increase the austenite transformation temperature, continuous annealing in which heat treatment is performed at high temperature for a short time was possible.

However, Ti has a problem of causing an increase in the manufacturing cost of stainless steel and a defect in a sleeve of a cold-rolled product. In addition, Nb has a problem of lowering appearance and toughness due to inclusions, and increasing the manufacturing cost like Ti.

In the present invention, by controlling the ?t amount of austenite-forming elements such as C and N, and deriving Ac1 to be 900 or more, it is possible to secure an annealing temperature at which recrystallization occurs sufficiently during continuous annealing. In addition, in the present invention, the strength can be improved by controlling Ac1 to 990 or less to form carbides and nitrides.

Ferritic stainless steel according to an embodiment of the present invention is manufactured by the following method.

C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% Hereinafter, S: 0.005% or less The remaining Fe and impurities are included, and Ac1 defined by the following formula (1) is 900 or more and 990 or less, to prepare a slab, reheat the slab, and finish the reheated slab after rough rolling Rolling is performed, the hot-rolled material is wound, the wound hot-rolled material is continuously annealed in the temperature range of T (A) defined by the following formula (2), and the continuously annealed steel material is pickled.

Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)

(Here, C, N, Si, Mn, Cr, Ni, Al, Mn and Mo mean the content (wt%) of each element)

Formula (2): 870 °C ≤ T(A) ≤ (Ac1-10) °C

The reason for limiting the component range of each alloy element is as described above.

Among the stainless steel manufacturing processes, the annealing process is contrasted with continuous annealing and phase annealing. In general, annealing is performed for austenite series by continuous annealing, and for ferritic and martensite series by phase annealing, which is due to the material properties of stainless steel for each type of steel.

의 대기분위기에서 단시간(약 3분) 열처리한다. 이와 달리, 상소둔은 저온(약 750~850

)의 분위기가스(수소 또는 질소+수소 혼합가스)내에서 장시간(약 50시간) 열처리한다. 또한 상소둔은 권취상태에서 행하여지므로, 열연코일의 부위별 소둔온도 편차로 인해, 부위별로 재질의 차이가 발생한다. Comparing the annealing process of hot-rolled coils by stainless steel type, continuous annealing is performed at high temperature (about 900~1150

Heat treatment for a short time (about 3 minutes) in an atmospheric atmosphere of In contrast, phase annealing is performed at low temperature (about 750 to 850

) in an atmosphere gas (hydrogen or nitrogen + hydrogen mixed gas) for a long time (about 50 hours). In addition, since the phase annealing is performed in the winding state, the material difference occurs for each part due to the annealing temperature deviation for each part of the hot-rolled coil.

Meanwhile, in ferritic stainless steel, the austenite phase (martensite phase upon cooling) formed after rolling is re-dissolved into the ferrite phase, and annealing is performed to remove the stress formed during hot rolling to facilitate cold rolling.

In ferritic stainless steel, when the annealing temperature rises above the austenite transformation temperature during annealing, the austenite phase is regenerated during annealing. As the regenerated austenite phase is re-transformed into martensite upon cooling, the formability and corrosion resistance of the steel are reduced. Therefore, ferritic stainless steel is produced through a phase annealing process performed at a low temperature.

As described above, the phase annealing has lower productivity and lower energy efficiency than continuous annealing. In addition, the upper annealing material has a quality deviation due to the difference in the annealing temperature for each part, so the quality is inferior to that of the continuous annealing material. Therefore, in the manufacturing process of ferritic stainless steel, it is necessary to improve the phase annealing process.

According to an embodiment of the present invention, it is possible to provide a method of manufacturing a ferritic stainless steel capable of continuous annealing of a hot-rolled sheet. At this time, the continuous annealing is performed at T(A) of 870 to (Ac1-10)°C.

When the temperature of the annealing is less than 870° C., recrystallization does not occur sufficiently, and when the temperature of the annealing is equal to or higher than the Ac1 value, an austenite phase is formed. Therefore, it is necessary to manage the continuous annealing temperature at 870 to (Ac1-10)°C.

In addition, according to an embodiment of the present invention, the reheating may be performed at 1000 to 1200 ℃.

When the reheating temperature is low, the rolling load of hot rolling may increase, and scratches may occur in the steel piece during hot rolling. In addition, when the reheating temperature is low, it is impossible to re-decompose the coarse precipitates generated during slab casting. Therefore, in the present invention, the lower limit of the slab reheating temperature is 1000 °C.

If the reheating temperature is high, the steel piece may soften and the shape may change, and coarsening of the internal crystal grains cannot be prevented. Therefore, in the present invention, the upper limit of the slab reheating temperature is 1200 °C.

In addition, according to an embodiment of the present invention, the finishing rolling may be performed at 800 to (Ac1-10) ℃.

When the temperature of finishing rolling is less than 800°C, scratches may occur on the steel during rolling, and an uneven structure is formed, thereby reducing toughness and strength. When the temperature of finishing rolling exceeds (Ac1-10)°C, the austenite grains are coarsened and the ferrite grain refinement is not sufficiently achieved after transformation.

In addition, according to an embodiment of the present invention, the winding may be performed at 750 to (Ac1-10) ℃.

The coiling temperature is preferably 750° C. or higher for plate shape and surface quality. When the coiling temperature exceeds (Ac1-10) °C, it may correspond to an austenite phase region, and thus a martensitic phase may be generated during the cooling process.

In addition, according to an embodiment of the present invention, the continuous annealing may be performed for 3 to 10 minutes.

If the annealing time is too short, recrystallization is not sufficient, and if the annealing time is too long, the annealing time is preferably limited to 3 to 10 minutes in consideration of the inferior mechanical properties as the grain size becomes coarse.

On the other hand, an important characteristic of stainless steel is surface gloss, and various manufacturing methods are employed to improve this characteristic. In particular, in the case of a high-gloss product, since a process without annealing and pickling is performed after cold rolling, the surface before cold rolling remains intact even after cold rolling. Therefore, it is important to control the surface shape before cold rolling.

For example, when removing the scale of a hot-rolled annealed sheet, intergranular erosion or scale residues due to excessive pickling make the surface very rough after hot-rolling and pickling, which still deteriorates the surface quality even after cold rolling.

The grain boundary erosion shape on the surface of stainless steel causes the grain boundaries to fold during cold rolling, which can cause surface defects called gold dust defects in the final product.

According to an embodiment of the present invention, in the ferritic stainless steel manufactured according to the control conditions of the present invention, as the continuous annealing temperature is controlled in relation to the austenite phase transformation temperature (Ac1), surface intergranular erosion does not occur after pickling. does not

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

{Example}

For the various alloy component ranges shown in Table 1 below, a slab was prepared by a continuous casting process, and reheated at 1,000 to 1,200 °C. The reheated slab was subjected to rough rolling and then hot rolled to a finishing rolling temperature of 800° C. by a finishing mill, and then wound up at 750° C.

division Alloy component (wt%) Ac1 note C Si Mn Cr Ni Al N river A 0.06 0.20 0.80 16.29 0.1 0.08 0.023 880 comparative steel river B 0.04 0.20 0.50 16.25 0.1 0.10 0.013 940 invention river C 0.03 0.32 0.40 16.20 0.1 0.12 0.010 981 invention

According to the annealing temperature conditions in Table 2, the wound steel was continuously annealed for 10 minutes. Next, the scale of the continuously annealed hot-rolled sheet was removed with a shot blaster, and after primary pickling in a sulfuric acid solution, it was pickled in a mixed acid (nitric acid + hydrofluoric acid) solution.

Table 2 below shows the degree of occurrence of intergranular erosion according to the continuous annealing temperature change after the pickling.

The degree of occurrence of intergranular erosion is, as shown in Fig. 1a, when intergranular erosion is connected along the grain boundary and occurs with a wide width (granular erosion is strong), as shown in Fig. 1b when it is not connected along the grain boundary and occurs as a line (intergranular erosion is normal), As shown in 1c, it was classified as a case where some grain boundary traces appeared as lines (weak grain boundary erosion).

The strength of intergranular erosion is indicated by 'O', normal intergranular erosion is indicated by '-', and weak intergranular erosion is indicated by 'X'.

division steel grade continuous annealing degree of intergranular erosion Annealing temperature (℃) Ac1-10 Example 1 river B 870 930 X Example 2 river B 900 930 X Example 3 river B 930 930 X Example 4 river C 870 971 X Example 5 river C 900 971 X Example 6 river C 930 971 X Example 7 river C 960 971 X Comparative Example 1 river A 810 870 - Comparative Example 2 river A 840 870 - Comparative Example 3 river A 870 870 X Comparative Example 4 river A 900 870 O Comparative Example 5 river A 930 870 O Comparative Example 6 river A 960 870 O Comparative Example 7 river A 990 870 O Comparative Example 8 river B 810 930 - Comparative Example 9 river B 840 930 - Comparative Example 10 river B 960 930 O Comparative Example 11 river B 990 930 O Comparative Example 12 river C 810 971 - Comparative Example 13 river C 840 971 - Comparative Example 14 river C 990 971 -

Referring to Table 2, the value of Ac-10 of the invention steel B is 930 and the value of Ac-10 of the invention steel C is 971. In Examples 1 to 3, the invention steel B was continuously annealed within a temperature range of 870 to 930°C. In Examples 4 to 7, the invention steel C was continuously annealed within a temperature range of 870 to 971 °C. Examples 1 to 7 satisfied the alloy composition, the value of Ac1, and the continuous annealing temperature suggested by the present invention, so that intergranular erosion was weakly generated.

In contrast, Comparative Examples 1 and 2 were subjected to continuous annealing at 810°C and 840°C, which are less than 870°C, respectively, and intergranular erosion occurred to a moderate degree.

In Comparative Example 3, intergranular erosion occurred weakly, but the Ac1 value was as low as 880, which is less than 900, and the austenite phase transformation temperature was low. Therefore, in Comparative Example 3, the temperature range during the process is limited, and recrystallization is difficult to sufficiently occur during continuous annealing.

Comparative Examples 4 to 7 were continuously annealed at a temperature exceeding the Ac1-10 value, and intergranular erosion was strongly generated.

In Comparative Examples 8 and 9, the invention steel B was continuously annealed at a temperature of less than 870°C, and intergranular erosion occurred to a moderate degree.

In Comparative Examples 10 and 11, the invention steel B was continuously annealed at 960°C and 990°C, respectively. In Comparative Examples 10 and 11, the continuous annealing temperature exceeded the Ac1-10 value of 930, and intergranular erosion occurred strongly.

In Comparative Examples 12 and 13, the invention steel B was continuously annealed at a temperature of less than 870°C, and intergranular erosion occurred to a moderate degree.

In Comparative Example 14, invention steel C was continuously annealed at 990°C. In Comparative Example 14, the continuous annealing temperature exceeded 971, which is an Ac1-10 value, and intergranular erosion occurred to a moderate degree.

According to the disclosed embodiment, when the temperature of the continuous annealing was less than 870°C, intergranular erosion occurred to a moderate degree, and as the temperature of the continuous annealing was higher, the intergranular erosion was weakly generated. However, when the continuous annealing temperature exceeded (Ac1-10)°C, intergranular erosion was strongly generated.

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.

Claims (10)

In wt%, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% Below, S: 0.005% or less, including the remaining Fe and impurities,
Ac1 defined by the following formula (1) is 900 or more and 990 or less, ferritic stainless steel with improved intergranular erosion.
Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)
(Here, C, N, Si, Mn, Cr, Ni, Al, Mn and Mo mean the content (wt%) of each element) The method according to claim 1,
The ferritic stainless steel is a ferritic stainless steel with improved intergranular erosion, including, by weight, Mn: 0.4 to 1.0%, Al: 0.1 to 0.15%. The method according to claim 1,
The ferritic stainless steel is a ferritic stainless steel with improved intergranular erosion further comprising, by weight%, Ni: 0.005 to 0.1%, Mo: 0.003% or less. In wt%, C: 0.005 to 0.1%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, Cr: 13 to 18%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, P: 0.05% Below, S: 0.005% or less, including the remaining Fe and impurities,
Ac1 defined by the following formula (1) is 900 or more and 990 or less, manufacturing a slab;
reheating the slab;
finishing rolling after rough rolling of the reheated slab;
winding the hot rolled material;
Continuous annealing of the wound hot-rolled material in a temperature range of T (A) defined by the following formula (2); and
A method of manufacturing ferritic stainless steel with improved intergranular erosion, comprising the step of pickling the continuously annealed steel.
Formula (1): Ac1 = 36Cr+90Si+76Mo+760Al+350-(800C+1300N+150Ni+50Mn)
(Here, C, N, Si, Mn, Cr, Ni, Al, Mn and Mo mean the content (wt%) of each element)
Formula (2): 870 °C ≤ T(A) ≤ (Ac1-10) °C 5. The method according to claim 4,
The slab is, by weight, Mn: 0.4 to 1.0%, Al: containing 0.1 to 0.15%, ferritic stainless steel manufacturing method with improved intergranular erosion. 5. The method according to claim 4,
The slab is, by weight, Ni: 0.005 to 0.1%, Mo: ferritic stainless steel manufacturing method with improved intergranular erosion further comprising 0.003% or less. 5. The method according to claim 4,
The reheating is performed at 1,000 to 1,200 ℃, ferritic stainless steel manufacturing method with improved intergranular erosion. 5. The method according to claim 4,
The finishing rolling is performed at 800 to (Ac1-10) ℃, ferritic stainless steel manufacturing method with improved intergranular erosion. 5. The method according to claim 4,
The winding is performed at 750 to (Ac1-10) ℃, ferritic stainless steel manufacturing method with improved intergranular erosion. 5. The method according to claim 4,
The continuous annealing is performed for 3 to 10 minutes, the grain boundary erosion is improved ferritic stainless steel manufacturing method.

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