WO2016105092A1 - Ferrite-based stainless steel and method for manufacturing same - Google Patents

Abstract

The present invention relates to a ferrite-based stainless steel and a method for manufacturing the same, wherein the ferrite-based stainless steel has excellent moldability by controlling the contents of ingredients constituting molten steel and the size of crystal grains. The ferrite-based stainless steel according to an embodiment of the present invention contains C (0.0005-0.01 wt%), N (0.005-0.015 wt%), Si ( 0.01-0.20 wt%), Mn ( 0.01-0.20 wt%), P (0.001-0.03 wt%), S (0.0001-0.005 wt%), Cr (10-20 wt%), Ni (0.001-0.15 wt%), Al (0.05-0.30 wt%), the balance Fe, and other inevitable impurities, the ratio of Nb/Ti being 0.1-0.6, and satisfies expression (1) below. 0.1 < 400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ----------- (1), wherein in expression (1), C, N, P, Si, and Nb mean contents (wt%) of respective ingredients.

Description

Ferritic stainless steel 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 and a method for producing excellent moldability by adjusting the content of the constituting the molten steel and the size of the crystal grains.

Generally, stainless steel is classified according to chemical composition or metal structure. According to the metal structure, stainless steel is classified into austenite series (300 series), ferrite series (400 series), martensite series, and ideal system.

Among these stainless steels, ferritic stainless steel (400 series) is excellent in high temperature characteristics such as thermal expansion rate and thermal fatigue, and is excellent in stress corrosion cracking and high temperature strength. Based on such characteristics, it is applied to automobile exhaust systems, household appliances, structures, home appliances, elevators, and the like.

However, in order to use ferritic stainless steel sheets for applications requiring high corrosion resistance, such as kitchen utensils, gas stoves, dishwashers, etc., the corrosion resistance and workability must be satisfied at the same time. There was a problem.

In addition, high corrosion-resistant ferritic stainless steels have a high Cr content, which causes hot sticking defects, and thus, an element that contributes to improvement of corrosion resistance while appropriately adjusting Cr content should be added to secure desired level of corrosion resistance.

On the other hand, many researchers have been proposed a variety of manufacturing methods for improving the workability of ferritic stainless steel.

For example, there is a method of improving the processability by adjusting the process variable during the manufacturing process, among the methods of controlling the R value through cold rolling and heat treatment "the ferritic stainless steel excellent in workability and its manufacturing method ( It is specifically known in Unexamined-Japanese-Patent 10-2012-0073644; patent document 1).

However, the same technique as that of Patent Document 1 improves the workability through the improvement of the manufacturing process, and the applicant has derived a method of improving the workability and corrosion resistance by controlling the content of the alloy component forming the molten steel without improving the manufacturing process. .

In particular, research on ferritic stainless steels, which have high corrosion resistance and excellent workability while suppressing sticking defects, has been conducted by various researchers in various ways, but has been difficult or expensive to apply in the field. .

The present invention provides a ferritic stainless steel excellent in formability of the final product produced by optimizing the size of the alloying component and crystal grains affecting the elongation decrease, and a manufacturing method thereof.

Ferritic stainless steel according to an embodiment of the present invention, C: 0.0005 ~ 0.01 wt%, N: 0.005 ~ 0.015 wt%, Si: 0.01 ~ 0.20 wt%, Mn: 0.01 ~ 0.20 wt%, P: 0.001 ~ 0.03 wt%, S: 0.0001 to 0.005 wt%, Cr: 10 to 20 wt%, Ni: 0.001 to 0.15 wt%, Al: 0.05 to 0.30 wt%, Ti: 0.1 to 0.3 wt%, Nb: 0.01 to 0.18 wt %, The balance Fe and other unavoidable impurities, the ratio of Nb / Ti is 0.1 ~ 0.6, characterized by satisfying the following formula (1).

0.1 <400C + 85.7N + 55.6P + 7.7Si + 7.3Nb <5 ----------- (1)

In the formula (1), C, N, P, Si and Nb means the content (wt%) of each component.

Preferably, the ferritic stainless steel according to an embodiment of the present invention may be characterized by satisfying the following Equation (2).

0 <60.4C + 7.8P + 0.7Si + 1.2Nb-GS / 100 <0.2 ---------- (2)

In the formula (2), C, N, P, Si and Nb means the content (wt%) of each component, GS means the average diameter of the grain (㎛).

At this time, it is preferable that the average diameter GS of the said crystal grain is 15-40 micrometers.

In addition, the ferritic stainless steel according to an embodiment of the present invention, the elongation is more than 35%, the yield strength is 250MPa or less, when the stress is 5 to 10% it is preferable that the work hardening index (n) is 0.25 or more. .

On the other hand, the ferritic stainless steel manufacturing method according to an embodiment of the present invention, C: 0.0005 ~ 0.01 wt%, N: 0.005 ~ 0.015 wt%, Si: 0.01 ~ 0.20 wt%, Mn: 0.01 ~ 0.20 wt%, P: 0.001 to 0.03 wt%, S: 0.0001 to 0.005 wt%, Cr: 10 to 20 wt%, Ni: 0.01 to 0.20 wt%, Al: 0.05 to 0.30 wt%, Ti: 0.1 to 0.3 wt%, Nb: 0.01 to 0.18 wt%, and a slab containing the balance Fe and other unavoidable impurities is produced, and the slab is hot rolled, hot rolled, cold rolled, and cold rolled annealed at a temperature in the range of 800 to 900 ° C.

According to an embodiment of the present invention, by adjusting the content of the alloying component that affects the elongation decrease optimally, the elongation is maintained at 35% or more, the yield strength 250MPa or less, the work hardening index (n) is 0.25 or more to maintain the formability There is an effect that can be improved.

1 is a graph showing the relationship between the elongation and the relationship between the alloying components affecting the elongation reduction,

2 is a graph showing the relationship between the alloying components and the grain size and the yield strength affecting the yield strength,

Figure 3 is a graph showing the relationship between the alloying components and the particle size relationship and the work hardening index (n) affecting the yield strength.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art to the fullest extent. It is provided to inform you.

Ferritic stainless steel according to an embodiment of the present invention, C: 0.0005 to 0.01 wt%, N: 0.005 to 0.015 wt%, Si: 0.01 to 0.20 wt%, Mn: 0.01 to 0.20 wt%, P: 0.001 ~ 0.03 wt%, S: 0.0001-0.005 wt%, Cr: 10-20 wt%, Ni: 0.001-0.15 wt%, Al: 0.05-0.30 wt%, consisting of balance Fe and other unavoidable impurities, Nb / It is preferable that the ratio of Ti satisfy | fills 0.1-0.6.

Hereinafter, the reason for numerical limitation of the component content in the embodiment according to the present invention will be described. Unless otherwise specified, the units are in weight percent.

The amount of carbon (C) is preferably 0.0005 wt% or more and 0.01 wt% or less.

When the amount of carbon (C) is increased, the strength is improved, but the workability is lowered. When it is added in excess of 0.01wt%, the impurities of the material are increased, the elongation and work hardening index (n) are lowered, and the yield strength is increased. The moldability is reduced, there is a problem that the training cost for making a high-purity product is increased when added to less than 0.0005wt%.

The amount of nitrogen (N) is preferably 0.005 wt% or more and 0.015 wt% or less.

Nitrogen (N) has the effect of raising the strength of the material like carbon (C).

If the amount of nitrogen (N) is less than 0.005wt% TiN crystallization is lowered, the isotropic crystallization rate of the slab is lowered, if it exceeds 0.015wt% there is a problem that the elongation is lowered by increasing the impurities of the material.

The amount of silicon (Si) is preferably 0.01 wt% or more and 0.20 wt% or less.

Silicon (Si) is a useful element for deoxidation, and when added to less than 0.01wt%, the refining cost is increased, and when it exceeds 0.20wt%, impurities of the material increase, so that the elongation is lowered.

The amount of manganese (Mn) is preferably 0.01 wt% or more and 0.20 wt% or less.

Manganese (Mn) has the effect of increasing the strength of the steel, the effect can be obtained by containing 0.01wt% or more, but when excessively contained, MnS, which causes corrosion, deteriorates the corrosion resistance, elongation due to the increase of impurities in the material It contains less than 0.20wt% since it reduces.

The content of phosphorus (P) is preferably 0.001 wt% or more and 0.03 wt% or less.

Phosphorus (P) is an element that is inevitably included in the steel, the amount of refining is less than 0.001wt%, there is a problem that the refining cost is increased, 0.03wt% or less because it is easy to degrade the weldability and cause grain boundary corrosion when excessively Limited to

The content of sulfur (S) is preferably 0.0001wt% or more and 0.005wt% or less.

When sulfur (S) is added less than 0.0001wt%, the refining cost is increased, if it exceeds 0.005wt% it is limited to 0.0001 ~ 0.005wt% because it lowers the corrosion resistance and workability.

The content of chromium (Cr) is preferably 10 wt% or more and 20 wt% or less.

Chromium (Cr) is the most important element added to ensure the corrosion resistance of stainless steel. If it is added below 10wt%, the corrosion resistance is lowered. If it is added above 20wt%, the cause of hot-rolling sticking defects Therefore, the content is 20 wt% or less.

The content of nickel (Ni) is preferably 0.01wt% or more and 0.2wt% or less.

If the nickel (Ni) is less than 0.01wt%, the refining cost is increased, if it exceeds 0.2wt%, impurities in the material are increased to reduce the elongation, so it is limited to 0.01 ~ 0.2wt%.

The amount of aluminum (Al) is preferably 0.01 wt% or more and 0.10 wt% or less.

If the amount of aluminum (Al) is less than 0.01wt%, there is a problem that the refining price is expensive, and if the amount of aluminum (Al) exceeds 0.10wt%, impurities of the material increase and the elongation is lowered.

The amount of titanium (Ti) is preferably 0.10 wt% or more and 0.30 wt% or less.

If the amount of titanium (Ti) is less than 0.10wt%, the amount of TiN crystallization is reduced, so that the isotropic crystallinity of slabs is lowered, and the elongation is reduced due to the increase of the dissolved C and N elements. There is a problem that workability is lowered due to increase.

The amount of niobium (Nb) is preferably 0.01 wt% or more and 0.18 wt% or less.

Niobium (Nb) preferentially combines with carbon (C) and nitrogen (N) to form precipitates that suppress the deterioration of corrosion resistance, but when excessively added, it causes poor appearance and toughness due to inclusions and increases raw material costs. The content is limited to 0.01 wt% or more and 0.18 wt% or less.

At this time, titanium (Ti) and niobium (Nb) is preferably added so that the ratio of Nb / Ti satisfies 0.1 ~ 0.6.

If the ratio of Nb / Ti is less than 0.1, the grains are coarsened, resulting in ridging defects caused by orange peels in the final product, and if it exceeds 0.6, the raw material cost is increased and elongation due to fine niobium (Nb) precipitates is increased. This is because the work hardening index (n) is decreased, and the yield strength is increased, thereby degrading the formability.

Ferritic stainless steel according to an embodiment of the present invention is produced by performing molten steel having the above composition to produce a slab and then reheating it to perform hot rolling, hot annealing cold rolling and final annealing.

As described above, the final elongation of the ferritic stainless steel according to an embodiment of the present invention is more limited to the amount of C, N, P, Si and Nb that are elements that affect the reduction in elongation in order to satisfy 35% or more. It is preferable to limit to.

For example, it is preferable to satisfy following formula (1).

0.1 <400C + 85.7N + 55.6P + 7.7Si + 7.3Nb <5 ----------- (1)

Hereinafter, in formula (1), "400C + 85.7N + 55.6P + 7.7Si + 7.3Nb" is defined as "A" for convenience of description, wherein C, N, P, Si, and Nb of each component Content (wt%).

On the other hand, the ferritic stainless steel according to an embodiment of the present invention, C, which is an element affecting the yield strength and the work hardening index (n) to satisfy the yield strength of 250MPa or more, work hardening index (n) 0.25 or more, It is preferable to limit the content of P, Si, and Nb and the average grain size (GS; Grain Size) to satisfy the following formula (2).

0 <60.4C + 7.8P + 0.7Si + 1.2Nb-GS / 100 <0.2 ---------- (2)

Hereinafter, in the formula (2), "60.4C + 7.8P + 0.7Si + 1.2Nb-GS / 100" is defined as "B" for convenience of description, wherein C, N, P, Si, and Nb are each Mean content of the component (wt%), GS means the average diameter of the grain (㎛).

Hereinafter, the present invention will be described using various embodiments.

No. C N Si Mn P Cr Al Ni Ti Nb Remarks One 0.00109 0.0008 0.11 0.13 0.016 16.49 0.06 0.07 0.22 0.07 Comparative example 2 0.00029 0.0009 0.1 0.14 0.042 16.49 0.07 0.11 0.18 0.06 3 0.0003 0.0009 0.38 0.12 0.017 16.47 0.05 0.09 0.19 0.05 4 0.00047 0.0011 0.15 0.15 0.018 16.49 0.05 0.09 0.19 0.08 5 0.00029 0.0008 0.11 0.14 0.017 16.48 0.06 0.08 0.00 0.30 6 0.00027 0.0008 0.09 0.11 0.015 16.42 0.06 0.12 0.19 0.14 7 0.00022 0.0009 0.07 0.08 0.017 16.51 0.07 0.10 0.20 0.16 8 0.00028 0.0007 0.09 0.12 0.011 17.20 0.07 0.08 0.21 0.06 9 0.00021 0.0008 0.08 0.12 0.016 16.49 0.05 0.10 0.22 0.08 10 0.00033 0.0010 0.12 0.11 0.011 17.20 0.07 0.13 0.24 0.04 11 0.00026 0.0008 0.07 0.12 0.018 16.47 0.05 0.09 0.19 0.06 Example 12 0.00024 0.0009 0.09 0.10 0.017 16.51 0.07 0.08 0.20 0.05 13 0.00022 0.0009 0.06 0.08 0.011 13.21 0.07 0.10 0.18 0.07 14 0.00041 0.0007 0.08 0.09 0.011 19.42 0.07 0.12 0.22 0.06

Table 1 shows the composition range for each component of the various examples and comparative examples of the present invention.

Ferritic stainless steel according to an embodiment of the present invention after producing a slab by playing a molten steel having a composition as shown in Table 1 in a conventional method, it is subjected to hot rolling at a temperature of 800 ~ 1250 ℃, hot rolled annealing And after performing cold rolling, it is manufactured by performing final cold-rolling annealing in the temperature range of 800-900 degreeC.

As described above, various characteristic values such as elongation and yield strength of the ferritic stainless steels were measured and shown in Table 2.

In this case, the elongation was evaluated by measuring the elongation at break after tensile strength in the rolling direction after processing with JIS13B specimens, and the work hardening index (n) at the yield strength and strain of 5 to 10% according to the 0.2% offset method. Measured and evaluated.

No. A B CA (℃) GS (μm) OP occurrence El (%) YS (MPa) n value (5-10%) Remarks One 7.3 0.61 880 33 X 31.2 275 0.234 Comparative example 2 5.5 0.36 860 28 X 33.5 267 0.225 3 6.2 0.22 920 42 O 32.1 268 0.219 4 5.5 0.41 860 22 X 32.8 252 0.247 5 5.8 0.60 780 14 X 31.9 269 0.218 6 4.3 0.23 860 28 X 35.6 256 0.238 7 4.3 0.26 860 25 X 35.2 245 0.245 8 3.5 0.27 780 12 X 35.3 258 0.252 9 3.6 0.29 760 11 X 35.1 264 0.256 10 4.0 -0.06 920 48 O 37.8 229 0.261 11 3.7 0.11 860 31 X 37.3 240 0.278 Example 12 3.7 0.14 840 26 X 37.8 219 0.269 13 3.3 0.08 860 26 X 39.2 226 0.281 14 3.9 0.16 860 30 X 36.8 240 0.257

In Table 2, CA means final cold annealing temperature, OP is Orange Peel, GS is the average diameter of the grain, n means the work hardening index value.

As shown in Table 2, when the content of each component exceeds the above-mentioned preferred range, it can be seen that the elongation, yield strength and work hardening index (n) do not reach the reference value, the moldability is lowered.

1 is a graph showing the relationship between the elongation and the relationship between the alloy components affecting the elongation decrease.

Even if the content of each component is controlled within the above-mentioned preferred range, when the A value does not satisfy the condition of Equation (1), the elongation is less than 35%, which is the reference value as shown in No. 4, and the moldability is deteriorated, whereas the alloy When the content of the component and the A value satisfy the above formula (1) at the same time, the elongation is 35% or more, it can be seen that the moldability is improved.

Therefore, in order to satisfy the required elongation of 35% or more to improve moldability, it is preferable to control the contents of C, N, P, Si, and Nb so that the A value satisfies the formula (1).

2 is a graph showing the relationship between the alloying formula and the particle size relationship and the yield strength affecting the yield strength, Figure 3 is a relationship between the alloying component and the particle size affecting the yield strength and the work hardening index ( n) is a graph showing the relationship between.

As shown in Table 1, Table 2, Fig. 2 and Fig. 3, even though the value of each component is controlled within the above-mentioned preferred range and the A value satisfies the condition of the formula (1), the B value is the condition of the formula (2). If it is not satisfied, the yield strength exceeds 250 MPa as shown in Nos. 6, 8 and 9, or the work hardening index (n) is less than 0.25 as shown in Nos. 6 and 7. Can be.

On the other hand, when the final annealing temperature is less than 800 ℃, elongation, yield strength and work hardening index (n) does not meet the target value, the moldability is reduced, and the final annealing temperature is 900 ℃ like No. 3 and No. 10 When it exceeds the average diameter (GS) of the grain becomes larger than 40㎛, it can be seen that the orange peel occurs.

therefore. Final annealing temperature is controlled to 800 ~ 900 ℃ by controlling the average grain size of 15 ~ 40㎛ can prevent the generation of orange peel.

Although the invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the invention is not limited thereto, but is defined by the claims that follow. Accordingly, one of ordinary skill in the art may variously modify and modify the present invention without departing from the spirit of the following claims.

Claims (6)

C: 0.0005 to 0.01 wt%, N: 0.005 to 0.015 wt%, Si: 0.01 to 0.20 wt%, Mn: 0.01 to 0.20 wt%, P: 0.001 to 0.03 wt%, S: 0.0001 to 0.005 wt%, Cr: 10 to 20 wt%, Ni: 0.001 to 0.15 wt%, Al: 0.05 to 0.30 wt%, Ti: 0.1 to 0.3 wt%, Nb: 0.01 to 0.18 wt%, including residual Fe and other unavoidable impurities, including Nb A ferritic stainless steel, wherein the ratio of / Ti is 0.1 to 0.6, and the following formula (1) is satisfied. 0.1 <400C + 85.7N + 55.6P + 7.7Si + 7.3Nb <5 ----------- (1) In the formula (1), C, N, P, Si and Nb means the content (wt%) of each component. The method according to claim 1, A ferritic stainless steel, characterized by satisfying the following formula (2). 0 <60.4C + 7.8P + 0.7Si + 1.2Nb-GS / 100 <0.2 ---------- (2) In the formula (2), C, N, P, Si and Nb means the content (wt%) of each component, GS means the average diameter of the grain (㎛). The method according to claim 2, The average diameter GS of a grain is 15-40 micrometers, Ferritic stainless steel. The method according to claim 1, Yield strength is 250 MPa or less, ferritic stainless steel, characterized in that the work hardening index (n) is 0.25 or more when the stress is 5 to 10%. The method according to claim 1, Ferritic stainless steel characterized by an elongation of 35% or more. C: 0.0005 to 0.01 wt%, N: 0.005 to 0.015 wt%, Si: 0.01 to 0.20 wt%, Mn: 0.01 to 0.20 wt%, P: 0.001 to 0.03 wt%, S: 0.0001 to 0.005 wt%, Cr: 10 to 20 wt%, Ni: 0.01 to 0.20 wt%, Al: 0.05 to 0.30 wt%, Ti: 0.1 to 0.3 wt%, Nb: 0.01 to 0.18 wt%, producing a slab containing the balance Fe and other unavoidable impurities The slab is hot rolled, hot rolled annealed, cold rolled, A method for producing ferritic stainless steel, characterized in that the cold rolling annealing at a temperature range of 800 ~ 900 ℃.

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