KR101623243B1 - Ferritic stainless steel sheet with excellent formability and brightness And Manufacturing method thereof - Google Patents

Abstract

The ferritic stainless steel excellent in moldability and luster according to an embodiment of the present invention is a ferritic stainless steel which is excellent in moldability and gloss and contains ferrites containing C, N, Si, Mn, P, S, Cr, Ni, Al, Ti, Nb, 0.001 to 0.03 wt% of C, 0.005 to 0.015 wt% of N, 0.01 to 0.20 wt% of Si, 0.01 to 0.20 wt% of Mn, 0.001 to 0.03 wt% of P, 15.0 to 17.0 wt% of Cr Ti is 0.10 to 0.30 wt%, the content of Nb is such that the ratio of Nb / Ti is 0.1 to 0.6, and satisfies the following equations (1) and (2) , And the recrystallization temperature is 700 to 900 占 폚.
400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]
(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]
In Equation 1 and 2, C, N, P, Si, Nb and Ti mean the content (wt%) of each component.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel having excellent moldability and gloss and a method of manufacturing the ferritic stainless steel sheet.

The present invention relates to a ferritic stainless steel having excellent moldability and gloss and a method of manufacturing the ferritic stainless steel. More particularly, the present invention relates to a ferritic stainless steel which is excellent in moldability and gloss, And a method for producing the ferritic stainless steel.

Generally, stainless steel is classified according to chemical composition or metal structure. According to the metal structure, the stainless steel is classified into an austenitic system (300 system), a ferrite system (400 system), a martensitic system, and an ideal system.

Among these stainless steels, ferritic stainless steel is excellent in corrosion resistance and is mainly used in various kitchen appliances, automobile exhaust system parts, building materials, home appliances, etc. Since it is manufactured by deep drawing, ) Is one of the important quality characteristics.

On the other hand, unlike austenitic stainless steels, ferritic stainless steels have no phase transformation during deformation and contain a large amount of chromium (Cr), which is relatively easy to process. Therefore, in order to improve the elongation of such a ferritic stainless steel, impurities that are not necessary in manufacturing must be controlled extremely.

In addition, in order to remove trace amounts of solid C and N that are not removed through refining, carbonitride forming elements such as Ti and Nb must be added. Depending on the addition ratio of such carbonitride forming elements, .

Thus, various methods for improving the formability of ferritic stainless steels have been proposed by many researchers. For example, it is possible to derive the elongation rate calculation formula, to set the addition range and the manufacturing condition of the alloy component to an appropriate range by using the derived calculation formula, and to control the manufacturing conditions so as to have the elongation rate higher than a certain level, The improvement is specifically known in, for example, a ferritic stainless steel having excellent elongation and a method of manufacturing the same (Japanese Patent Laid-Open No. 10-2004-0110644).

On the other hand, the recrystallization temperature of the material during the cold rolling annealing is increased due to the precipitation due to addition of the carbonitride forming elements Ti and Nb, and thus the Si scale generated at the high temperature is generated on the surface of the cold- rolled material to form the Si scale layer . Since this Si-scale layer is removed only by mixed acid (hydrofluoric acid + sulfuric acid or hydrofluoric acid + nitric acid) pickling using a strong acidic acid solution, the cold rolled sheet having completed the cold rolling annealing must essentially carry out the pickling process.

However, there is a disadvantage in that when the cold rolled sheet is mixed with acid, the gloss of the surface is lowered.

[Patent document 10] 2004-0110644 (December 31, 2004)

The present invention provides a ferritic stainless steel excellent in moldability and gloss and capable of improving elongation by optimally adjusting the content of components constituting a molten steel for producing stainless steel, and a method for producing the ferritic stainless steel.

In addition, the content of the molten steel for producing stainless steel is optimally adjusted to reduce the recrystallization during cold rolling annealing, thereby preventing the generation of the Si scale layer generated at a high temperature, thereby reducing the glossiness. The present invention also provides a ferritic stainless steel excellent in moldability and gloss and a method for producing the ferritic stainless steel.

The ferritic stainless steel excellent in moldability and luster according to an embodiment of the present invention is a ferritic stainless steel which is excellent in moldability and gloss and contains ferrites containing C, N, Si, Mn, P, S, Cr, Ni, Al, Ti, Nb, 0.001 to 0.03 wt% of C, 0.005 to 0.015 wt% of N, 0.01 to 0.20 wt% of Si, 0.01 to 0.20 wt% of Mn, 0.001 to 0.03 wt% of P, 15.0 to 17.0 wt% of Cr Ti is 0.10 to 0.30 wt%, the content of Nb is such that the ratio of Nb / Ti is 0.1 to 0.6, and satisfies the following equations (1) and (2) , And the recrystallization temperature is 700 to 900 占 폚.

400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]

(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]

In Equation 1 and 2, C, N, P, Si, Nb and Ti mean the content (wt%) of each component.

The stainless steel has a glossiness GS20 of 1000 or more.

The stainless steel has an elongation of 35% or more.

Meanwhile, the ferritic stainless steel producing method according to the embodiment of the present invention is excellent in the formability and the luster of the ferritic stainless steel according to one embodiment of the present invention. A method for producing a ferritic stainless steel comprising the steps of: 0.0005 to 0.01 wt% of C, 0.005 to 0.015 wt% of N, 0.01 to 0.20 wt% of Si, 0.01 to 0.20 wt% of Mn, 0.001 to 0.03 wt% of P, Ti is 0.10 to 0.30 wt%, the content of Nb is in the range of 0.1 to 0.6 in Nb / Ti, Is subjected to hot rolling, hot finishing rolling, hot rolling annealing, cold rolling and cold rolling annealing, and the components constituting the molten steel for producing the slab satisfy the following [Expression 1] and [Expression 2] And the heating temperature of the cold-rolled sheet during the cold-rolling annealing is 900 ° C or lower.

400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]

(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]

In Equation 1 and 2, C, N, P, Si and Nb mean the content (wt%) of each component.

And the recrystallization temperature of the cold-rolled sheet during the cold-rolling annealing is 700 to 900 ° C.

The mixed acid pickling process for removing the Si scale layer is not performed in order to maintain the glossiness (GS20 DEG) of the cold-rolled sheet after the cold-rolling annealing to 1000 or more.

According to the embodiment of the present invention, it is possible to maintain the elongation of the final product at 35% or more as the content of the components for lowering the elongation is limited in the ferritic stainless steel.

By limiting the contents of Ti and Nb, the generation of precipitates of Ti and Nb is suppressed and the reheating temperature of the cold-rolled sheet can be lowered to 900 ° C or less during cold-rolling annealing, It is possible to omit the mixed acid pickling process for removing the Si scale.

As a result, it is possible to improve the productivity by reducing the number of process steps and to prevent the glossiness from being lowered by the mixed acid pickling process and to maintain the glossiness to 1000 or more.

FIG. 1 is a graph showing the relationship between elongation and [Equation 1]
2 is a graph showing the relationship between the glossiness and [Equation 2].

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know.

The present invention relates to a ferritic stainless steel comprising 0.0005 to 0.01 wt% of C, 0.005 to 0.015 wt% of N, 0.01 to 0.20 wt% of Si, 0.01 to 0.20 wt% of Mn, 0.001 to 0.03 wt% of P, 0.0001 to 0.005 wt% of S, Ti: 0.10 to 0.30 wt%; the content of Nb is such that the ratio of Nb / Ti is 0.1 to 0.6; and the balance of Nb / Ti is 0.1 to 0.6. Fe-based stainless steels made of Fe and other unavoidable impurities are targeted.

The amount of carbon (C) is preferably 0.0005 wt% or more and 0.01 wt% or less. If the amount of carbon (C) is less than 0.0005 wt%, the refining price for producing a high-purity product becomes high. If the amount is more than 0.01 wt%, the impurities of the material are increased and the elongation rate is decreased.

The amount of nitrogen (N) is preferably 0.005 wt% or more and 0.015 wt% or less. If the amount of nitrogen (N) is less than 0.005 wt%, the TiN crystallization becomes low and the equiaxed crystal ratio of the slab becomes low. When the amount of nitrogen (N) is more than 0.015 wt%, the impurity of the material increases and the elongation becomes low.

The amount of silicon (Si) is preferably 0.01 wt% or more and 0.20 wt% or less. If the amount of silicon (Si) is less than 0.01 wt%, there is a problem that the refining price is expensive. If the amount is more than 0.2 wt%, the impurities of the material increase and the elongation becomes low.

The amount of manganese (Mn) is preferably 0.01 wt% or more and 0.20 wt% or less. If the amount of manganese (Mn) is less than 0.01 wt%, there is a problem that the refining price is expensive. If the amount is more than 0.2 wt%, the impurities of the material increase and the elongation becomes poor.

The amount of phosphorus (P) is preferably 0.001 wt% or more and 0.03 wt% or less. When the amount of phosphorus (P) is less than 0.001 wt%, there is a problem that the refining price is expensive. When the amount of phosphorus (P) is more than 0.03 wt%, the impurities of the material increase and the elongation becomes poor.

The amount of sulfur (S) is preferably 0.0001 wt% or more and 0.005 wt% or less. If the amount of sulfur (S) is less than 0.0001 wt%, there is a problem that the refining price is expensive. When the amount is more than 0.005 wt%, corrosion resistance and workability deteriorate.

The amount of chromium (Cr) is preferably 15.0 wt% or more and 17.0 wt% or less. When the amount of chromium (Cr) is less than 15.0 wt%, the corrosion resistance and oxidation resistance deteriorate. When the amount of chromium (Cr) is more than 17.0 wt%, the elongation rate decreases and the cost increases.

The amount of nickel (Ni) is preferably 0.01 wt% or more and 0.20 wt% or less. If the amount of nickel (Ni) is less than 0.01 wt%, there is a problem that the refining price is expensive. If the amount is more than 0.2 wt%, the impurities of the material increase and the elongation becomes poor.

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 0.01 wt%, there is a problem that the refining price is expensive. If the amount is more than 0.1 wt%, the impurities of the material increase and the elongation becomes low.

The amount of titanium (Ti) is preferably 0.1 wt% or more and 0.3 wt% or less. If the amount of titanium (Ti) is less than 0.1 wt%, the amount of TiN crystallization is reduced to lower the equiaxed crystal ratio of the slab and increase the number of C and N elements to be solidified. There is a problem that the nozzles are clogged when the performance slab is manufactured.

The amount of niobium (Nb) is preferably added such that the content ratio of Nb / Ti is 0.1 to 0.6. If the content ratio of Nb / Ti is less than 0.1, crystal grains become coarse and ridging due to orange peel occurs in the final product. If the content ratio of Nb / Ti is more than 0.6, the raw material cost rises and the cold annealing temperature rises due to fine Nb precipitates, A Si scale layer is formed. Such a Si scale layer can be removed by a mixed acid pickling process. However, the cold rolled sheet subjected to the pickling process has a disadvantage that its gloss is lower than that of the cold rolled sheet which has not undergone the pickling process.

In order to improve the formability, the present invention relates to a method for producing a ferrite stainless steel excellent in elongation rate and excellent in gloss by producing molten steel having the above composition by a conventional method to produce a slab, Hot rolling, hot rolling, hot rolling, cold rolling and cold rolling annealing.

In particular, when the content of the molten steel component is controlled, it is preferable to limit the total content of the components that lower the elongation to maintain the elongation of the final product at 35% or more. For example, it is preferable to limit the value calculated by applying the content of the corresponding component to [Formula 1] below to be less than 5.

400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]

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

The reason for limiting the total content of the components that lower the elongation is shown in Fig.

FIG. 1 is a graph showing the relationship between the elongation and the formula shown in the formula 1, and shows a change in elongation according to a value calculated by the formula shown in [formula 1].

As can be seen from FIG. 1, when the value calculated by the formula shown in [Formula 1] is smaller than 5, the elongation is maintained at 35% or more, whereas when the value calculated by the formula shown in Formula 1 is larger than 5, Is lower than 35%. Therefore, in order to keep the elongation of the final product at 35% or more, it is preferable to adjust the content of the component so that the value calculated by the formula shown in [Formula 1] does not exceed 5. [ In addition, C, N, P, Si and Nb are each limited to the above-mentioned contents, and the minimum value of the value calculated by the formula shown in the above-mentioned [Formula 1] Particularly, in order to keep the minimum value of the value calculated by the formula shown in the above-mentioned formula 1 smaller than 0.1, the refining price for controlling the content of each component is expensive, and therefore the expected effect is not considerable, It is preferable to limit the minimum value of the value to 0.1.

Further, in order to prevent the generation of the Si scale layer generated when the heating temperature is high in the cold-rolling annealing step, it is preferable to limit the total content of the components generating various precipitates. By regulating the content of the molten steel components, the recrystallization temperature of the cold rolled sheet can be maintained at 900 ° C or less. For example, if the value calculated by applying the content of the component in the following formula 2 is controlled to be less than 2, the recrystallization temperature of the cold-rolled sheet can be maintained at 700 to 900 ° C.

(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]

In the formula 2, C, N, P, Si, Nb and Ti mean the content (wt%) of each component.

The reason for limiting the total content of the components that raise the recrystallization temperature is shown in Fig.

FIG. 2 is a graph showing the relationship between the formula and the glossiness shown in the formula 2, and shows a change in gloss according to a value calculated by the formula shown in [formula 2].

As can be seen from FIG. 2, when the value calculated by the equation shown in [Formula 2] is smaller than 2, the recrystallization temperature during cold rolling annealing is kept low to suppress generation of the Si scale layer, The degree of gloss of the final cold rolled sheet can be made to be 1000 or more through the skin pass process, which is a subsequent process, by avoiding the mixed pickling process which is carried out for removing the scale layer.

On the other hand, when the value calculated by the equation shown in [Equation 2] is larger than 2, the recrystallization temperature in the cold rolling annealing is high and the generation of the Si scale layer can not be suppressed. It is not possible to improve the cohesion of the final cold rolled sheet to 1000 or more even through the subsequent process of the skin pass process.

Therefore, in order to maintain the glossiness of the final cold rolled sheet at 1000 or more, it is preferable to adjust the content of the component so that the value calculated by the formula shown in [Formula 2] does not exceed 2 in the present invention. The minimum value of the value calculated by the formula shown in the above-mentioned [Formula 2] may be a value at least greater than 0.1, since C, N, P, Si, Nb and Ti are limited to the above-mentioned contents. Particularly, in order to keep the minimum value of the value calculated by the formula shown in the above formula 2 smaller than 0.1, the refining price for controlling the content of each component is expensive, and the expected effect is not so great, It is preferable to limit the minimum value of the value to 0.1.

[Example]

The following examples illustrate the present invention.

Experiments were conducted to produce final cold-rolled sheets according to the production conditions of commercially produced ferritic stainless steels. As shown in Table 1, hot rolled and hot finishes were produced from continuously cast slabs using the produced molten steel, The hot rolled sheet having a thickness of 4 to 5 mm rolled was subjected to hot rolling annealing, cold rolling and cold annealing. However, the contents of Fe and other impurities (S, Ni, etc.) in the alloy composition of the present invention are not shown in Table 1.

No. C N Si Mn P Cr Al Ti Nb A B A × B Remarks One 109 83 0.11 0.13 0.016 16.49 0.06 0.22 0.07 7.3 0.32 2.33


Comparative Example


2 29 91 0.1 0.14 0.042 16.49 0.07 0.18 0.06 5.5 0.33 1.83 3 30 88 0.38 0.12 0.017 16.47 0.05 0.19 0.05 6.2 0.26 1.63 4 47 108 0.15 0.15 0.018 16.49 0.05 0.19 0.08 5.5 0.42 2.33 5 29 80 0.11 0.14 0.017 16.48 0.06 0.00 0.3 5.8 - - 6 27 83 0.09 0.11 0.015 16.42 0.06 0.19 0.14 4.3 0.74 3.20 7 22 87 0.07 0.08 0.017 16.51 0.07 0.20 0.16 4.3 0.80 3.42 8 21 82 0.08 0.12 0.016 16.49 0.05 0.22 0.08 3.6 0.36 1.32
Example
9 26 84 0.07 0.12 0.018 16.47 0.05 0.19 0.06 3.7 0.32 1.18 10 24 85 0.09 0.1 0.017 16.51 0.07 0.20 0.05 3.7 0.25 0.92

Here, A means 400C + 85.7N + 55.6P + 7.7Si + 7.3Nb in [Equation 1], and B means a content ratio of Nb / Ti. In addition, the content units of C and N are ppm, and the content units of other components except C and N are wt%.

Table 2 shows the recrystallization temperature and progress of pickling of the cold-rolled annealed products, and elongation (El) and gloss of the final cold-rolled sheet.

No Recrystallization temperature (캜) Mixed mountain sans tax El (%) Glossiness (GS20 °) Remarks One 980 O 31.2 734


Comparative Example


2 920 O 33.5 945 3 880 X 32.1 1023 4 940 O 32.8 917 5 1000 O 31.9 843 6 960 O 35.6 821 7 960 O 35.2 884 8 880 X 36.9 1082
Example
9 880 X 37.3 1019 10 860 X 37.8 1050

Here, in the case of mixed acid pickling, "O" means that mixed acid pickling using a strong acidic acid tax is carried out, and "X" means pickling using a weak acid acid tax without proceeding with mixed acid pickling.

As can be seen from Table 2, when the content of each component is controlled within the preferable range described above, the recrystallization temperature of the cold-rolled sheet is 900 ° C or less, so that the heating temperature can be maintained at 900 ° C or less during cold rolling annealing. As a result, the generation of the Si scale layer on the surface of the cold-rolled sheet can be suppressed and the mixed acid pickling process can be omitted. As a result, the glossiness of the cold-rolled sheet can be improved to 1000 or more by the skin pass process.

Further, by controlling the value calculated by 400C + 85.7N + 55.6P + 7.7Si + 7.3Nb described in [Formula 1] to be less than 5 while controlling the content of each component within the preferable range described above, the elongation of the final cold- And 35% or more.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

Claims (6)

A ferritic stainless steel comprising C, N, Si, Mn, P, Cr, Al, Ti, Nb and the balance Fe and unavoidable impurities,
0.001 to 0.03 wt% of Cr, 15.0 to 17.0 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.0005 to 0.01 wt% of C, 0.005 to 0.015 wt% 0.01 to 0.10 wt%, Ti: 0.10 to 0.30 wt%, and the content of Nb is such that the ratio of Nb / Ti is 0.1 to 0.6,
Satisfy the following [Expression 1] and [Expression 2]
A ferritic stainless steel having a recrystallization temperature of 700 to 900 DEG C and a glossiness (GS20 DEG) of 1000 or more and excellent in moldability and gloss.
400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]
(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]
In Equation 1 and 2, C, N, P, Si, Nb and Ti mean the content (wt%) of each component.
delete The method according to claim 1,
Wherein the stainless steel is a ferritic stainless steel having an elongation of 35% or more and excellent moldability and gloss.
1. A method for producing a ferritic stainless steel comprising C, N, Si, Mn, P, Cr, Al, Ti, Nb and the balance Fe and unavoidable impurities,
0.001 to 0.03 wt% of Cr, 15.0 to 17.0 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.01 to 0.20 wt% of Cr, 0.0005 to 0.01 wt% of C, 0.005 to 0.015 wt% And the Nb content is 0.1 to 0.6, and the slab is hot-rolled, hot-finished, hot-rolled, hot-rolled, cold-rolled, Rolled and cold-rolled annealed,
The components constituting the molten steel for producing the slab are adjusted so that the content of each component satisfies the following [Equation 1] and [Equation 2]
The heating temperature of the cold-rolled sheet during the cold-rolling annealing is 900 DEG C or less,
A method for producing a ferritic stainless steel excellent in moldability and gloss that does not proceed with a pickling process for removal of a Si scale layer in order to maintain the gloss (GS20 DEG) of the cold rolled sheet after the cold rolling annealing to 1000 or more.
400C + 85.7N + 55.6P + 7.7Si + 7.3Nb < 5 ... ... ... ... ... ... ... ... ... ... ... [Formula 1]
(Nb / Ti) x (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) < 2 ... ... ... ... ... [Formula 2]
In Equation 1 and 2, C, N, P, Si and Nb mean the content (wt%) of each component.
The method of claim 4,
Wherein the recrystallization temperature of the cold-rolled sheet during the cold-rolling annealing is 700 to 900 占 폚 and excellent in moldability and gloss.
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