KR20140080353A - Ferritic stainless steel sheet with excellent ridging resistance and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a ferritic stainless steel sheet with a superior anti-ridging property and a method of manufacturing the same, and more particularly, to a ferritic stainless steel sheet with a superior anti-ridging property and a method of manufacturing the same, capable of improving elongation and ridging properties by adjusting the content of components constituting molten steel for manufacturing stainless steel. The ferritic stainless steel sheet with a superior anti-ridging property according to an embodiment of the present invention, comprises 0.0005-0.01wt% of C, 0.005-0.015 wt% of N, 0.01-0.20 wt% of Si, 0.01-0.20 wt% of Mn, 0.001-0.03 wt% of P, 0.0001-0.005 wt% of S, 15.0-17.0 wt% of Cr, 0.01-0.20wt% of Ni, 0.001-0.10 wt% of Al, 0.10-0.30 wt% of Ti, Nb having a content satisfying the ratio Nb/Ti being 0.1-0.6, and the remainder consisting of Fe and other inevitable impurities inevitably. The components satisfy equation 1: 400C + 85.7N + 55.6P + 7.7Si + 7.3Nb<5.

Description

FIELD OF THE INVENTION The present invention relates to a ferritic stainless steel having excellent ridging resistance and a ferritic stainless steel sheet with excellent ridging resistance and manufacturing method thereof,

The present invention relates to a ferritic stainless steel excellent in anti-ridging property and a manufacturing method thereof, and more particularly to a ferritic stainless steel having excellent anti-ridging property capable of improving the elongation and ridging properties by controlling the content of components constituting the molten steel for producing stainless steel Excellent ferritic stainless steel and a manufacturing method thereof.

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, household appliances, etc. Since the parts are manufactured by deep drawing, It is one of quality characteristics. It is also important to reduce defects formed on the surface after molding.

However, ferritic stainless steels have a problem that ridging defects, which are stripe-like surface defects, are generated parallel to the rolling direction in a forming process such as deep drawing.

Such ridging defects not only deteriorate the appearance of the product but also cause a problem in that when the ridging is severe, a polishing process is added after molding, resulting in an increase in manufacturing cost.

The cause of ridging has not yet been clarified, but it has generally been known as: Unevenness appears on the surface due to the plastic anisotropy of the region having different texture in the final cold-rolled and annealed sheet. Particularly, coarse grains having {001} // ND crystal orientation existing in the hot- And the like. Since these coarse grains are densely packed as they are after cold rolling, they cause ridging. Therefore, it is necessary to effectively reduce the number of coarse grains and to remove colony tissues throughout the manufacturing process, that is, from performance to cold- A steel sheet without ridging can be obtained.

Various manufacturing methods have been proposed by many researchers to improve the ridging properties of ferritic stainless steels. For example, there is a method of improving the ridging property by improving the equilibrium constant and decreasing the fraction of the main phase.

Further, there is a method of improving the ridging property by controlling the process parameters during the manufacturing process. For example, there is a method of controlling the rolling temperature, the rolling reduction rate, and the annealing temperature during annealing after cold rolling. In particular, the method of controlling the annealing temperature in the annealing treatment after cold rolling is specifically known in "Ti-added ferritic stainless steel excellent in anti-ridging property and its manufacturing method (Patent Publication 10-2012-0066476) ".

On the other hand, the conventional ferritic stainless steels have STS 430 as a steel grade with reduced ridging. The STS 430 has a C + N of 600 ppm or more and a maximum austenite phase content of 30% or more, thereby effectively destroying the band structure during hot rolling Thereby reducing ridging.

However, such a technology is not only deteriorated in workability due to a large number of C and N, but also causes a defect in the steel due to a defect such as a golden dust due to intergranular erosion when the material is exposed to austenite phase transformation temperature (Ac1) There has been a problem that the surface quality is deteriorated.

In order to solve these problems, annealing may be performed at a low temperature for a long time, but this is one of the main causes of deteriorating the productivity of the product.

Unlike austenitic stainless steels, ferritic stainless steels have no phase transformation during deformation, and contain a large amount of Cr, making it difficult to obtain an elongation of 35% or more.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-0066476 (June 22, 2012)

The present invention relates to a ferritic stainless steel which is capable of suppressing the occurrence of ridging defects by controlling the content of internal tissue recrystallization and the grain size of hot rolled rolled material by optimally adjusting the content of components constituting the molten steel for producing stainless steel Based stainless steel and a method of manufacturing the same.

Also, the present invention provides a ferritic stainless steel excellent in anti-ridging property and capable of improving elongation by optimally adjusting the content of components constituting molten steel for producing stainless steel, and a process for producing the ferritic stainless steel.

The ferritic stainless steel excellent in anti-ridging properties according to one embodiment of the present invention is characterized in that it contains 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, 0.01 to 0.20 wt% of Mn, 0.001 to 0.03 wt% of S, 0.0001 to 0.005 wt% of S, 15.0 to 17.0 wt% of Cr, 0.01 to 0.20 wt% of Ni, 0.001 to 0.10 wt% of Al, 0.10 to 0.30 wt% of Ti, Is characterized in that the ratio of Nb / Ti is 0.1 to 0.6, and the balance of Fe and other unavoidable impurities, satisfies the following formula (1).

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

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

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

The stainless steel has a ridging height of 10 탆 or less.

Meanwhile, a method for producing a ferritic stainless steel excellent in anti-ridging property according to an embodiment of the present invention comprises: 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, 15.0 to 17.0 wt% of Cr, 0.01 to 0.20 wt% of Ni, 0.001 to 0.10 wt% of Al, 0.10 to 0.30 wt% of Ti, , The content of Nb is in the range of 0.1 to 0.6 in Nb / Ti ratio, and a slab composed of the remaining Fe and other unavoidable impurities is prepared, and the slab is subjected to hot rolling, hot rolling, hot rolling, cold rolling, The components constituting the molten steel for producing the slab are characterized in that the content of each component is adjusted so as to satisfy the following formula 1.

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

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

The rolled material after hot rough rolling is characterized in that the recrystallization fraction (RF) of the internal structure is 80% or more and the grain size (GS) is 300 탆 or less.

After the cold-annealing, the stainless steel has an elongation of 35% or more and a ridging height of 10 占 퐉 or less.

According to the embodiment of the present invention, by optimally adjusting the content of the components constituting the molten steel for producing stainless steel, it is possible to improve the recrystallization fraction of the internal structure after the hot rolling and prevent the crystal grains from coarsening. Accordingly, occurrence of ridging due to crystal grain coarsening can be lowered, and occurrence of ridging defects on the product surface can be suppressed.

The ferritic stainless steel has an effect of maintaining the elongation percentage of the final product at 35% or more by restricting the content of components that lower the elongation.

Thus, according to the embodiment of the present invention, it is possible to improve the quality of the ferritic stainless steel and to reduce the number of processes due to defect resolution, thereby improving the productivity of the final product.

1A to 1C are photographs showing the internal structure of a bar (BAR) after hot rough rolling of a comparative material and an inventive material according to the present invention,
Fig. 2 is a graph showing the relationship between the elongation and the numerical formula shown in [Equation 1] of the present invention. Fig.

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. Wherein like reference numerals refer to like elements throughout.

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. When the amount of carbon (C) is less than 0.0005 wt%, the refining price for producing a high-purity product is expensive. When the amount of carbon (C) is more than 0.01 wt%, the impurities of the material are increased to deteriorate the elongation.

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 rate decreases.

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. When the ratio of Nb / Ti is less than 0.1, crystal grains become coarse and ridging occurs due to orange peel in the final product. When the ratio of Nb / Ti is 0.6 or more, the raw material cost rises and fine Nb precipitates inhibit recrystallization of the internal structure of bar, The band structure is not sufficiently destroyed, resulting in ridging in the final product.

Figs. 1A to 1C are photographs showing the internal structure of a bar (BAR) after hot rough rolling of a comparative material and an inventive material according to the present invention, and the reasons for limiting the content ratio of Nb / Ti are as described above.

FIG. 1A is a photograph of a comparative material obtained by hot-rolling a slab made of molten steel having a Nb / Ti ratio of 0.8, wherein internal recrystallization fraction (RF) was 47.4% Can not be sufficiently destroyed.

Fig. 1B is a photograph of the inventive material of the present invention obtained by hot rough rolling a slab made of molten steel having a ratio of Nb / Ti of 0.32, wherein the inner structure was recrystallized appropriately to confirm that the grain size (GS) was 207 mu m .

Fig. 1C is a photograph of the structure of a comparative material obtained by subjecting a slab made of molten steel having a Nb / Ti ratio of 0 to hot rough rolling. It can be confirmed that the grain size GS is too large as 431 탆.

Meanwhile, in order to produce a stainless steel having excellent elongation and excellent anti-ridging property, the present invention is characterized in that a molten steel having the above-described composition is produced by a conventional method to produce a slab and then subjected to hot rolling, hot rolling, hot- 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 &lt; 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. 2 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 the formula 1. FIG. As can be seen from FIG. 2, 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, %. &Lt; / RTI &gt; Therefore, in order to maintain 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 the formula 1 does not exceed 5. [

On the other hand, when the slab is produced using the molten steel whose total content of the components lowering the elongation is controlled as described above, and the produced slab is hot rolled under the normal hot rolling condition, the rolling The internal tissue recrystallization fraction (RF) of the re-bar becomes at least 80%, and thus the band structure formed during hot rough rolling is removed, so that the grain size GS is less than 300 탆. As the recrystallization fraction of the internal structure and the size of the crystal grains are controlled, the coarsening of the crystal grains is suppressed, whereby the occurrence of ridging is suppressed, and the ridging height of the final product is controlled to 10 탆 or less.

[Example]

The following examples illustrate the present invention.

Experiments were conducted to produce final products according to the production conditions of commercially produced ferritic stainless steels. As shown in Table 1, hot rolled and hot finish rolled from continuously cast slabs using molten steel produced while varying the content of each component A hot rolled sheet having a thickness of 4 to 5 mm was subjected to hot rolling annealing, cold rolling and cold annealing.

No. I.I Nb / Ti C N Si Mn P Cr Al Ti Nb Remarks One 7.3 0.32 109 83 0.1 0.1 0.016 16.49 0.06 0.22 0.07

Comparative Example


2 5.5 0.33 29 91 0.1 0.1 0.042 16.49 0.07 0.18 0.06 3 6.2 0.26 30 88 0.4 0.1 0.017 19.47 0.05 0.19 0.05 4 5.5 0.42 47 108 0.2 0.2 0.018 16.49 0.05 0.19 0.08 5 5.8 - 29 80 0.1 0.1 0.017 16.48 0.06 0.00 0.3 6 3.7 0.00 26 84 0.1 0.1 0.019 16.44 0.08 0.21 0 7 4.3 0.74 27 83 0.1 0.1 0.015 16.42 0.06 0.19 0.14 8 4.3 0.80 22 87 0.1 0.1 0.017 16.51 0.07 0.20 0.16 9 3.6 0.36 21 82 0.1 0.1 0.016 16.49 0.05 0.22 0.08
Honor 10 3.7 0.32 26 84 0.1 0.1 0.018 16.47 0.05 0.19 0.06 11 3.7 0.25 24 85 0.1 0.1 0.017 16.51 0.07 0.20 0.05

Here, the I.I (Impurity index) means (400C + 85.7N + 55.6P + 7.7Si + 7.3Nb) in Equation (1). In addition, the content units of C and N are ppm, and the content units of other components except C and N are wt%.

The internal tissue recrystallization fraction (RF), grain size (GS), elongation and ridging height of the final product are shown in Table 2.

No RF (%) GS (占 퐉) Elongation (%) Rising height (탆) Remarks One 84.3 181 31.2 8.7


Comparative Example



2 88.1 223 33.5 7.6 3 90.7 194 32.1 9.3 4 87.6 179 32.8 7.1 5 33.2 107 31.9 12.8 6 97.2 431 37.7 12.4 7 55.3 137 35.6 11.8 8 47.4 133 35.2 12.0 9 92.4 196 36.9 8.2
Honor
10 95.6 207 37.3 7.5 11 89.4 224 37.8 7.7

As can be seen from Table 2, when the content of each component is controlled within the preferable range as described above, the internal tissue recrystallization fraction (RF) after the hot rolling is maintained at 80% or more, and the grain size (GS) It was confirmed that the ridging height of the final product was controlled to be 10 mu m or less.

In addition, it was confirmed that the elongation of the final product was maintained at 35% or more by controlling II to be less than 5.

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)

0.001 to 0.005 wt% of Cr, 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% 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 the balance of Fe and other elements is 0.1 to 0.6 wt% A ferritic stainless steel comprising an inevitable impurity and excellent in anti-ridging property satisfying the following formula (1).
400C + 85.7N + 55.6P + 7.7Si + 7.3Nb &lt; 5 ... ... ... ... ... ... [Formula 1]
In Equation 1, C, N, P, Si and Nb mean the content (wt%) of each component.
The method according to claim 1,
Wherein the stainless steel has an elongation of 35% or more and is excellent in anti-ridging properties.
The method according to claim 1,
Wherein the stainless steel is a ferritic stainless steel having a ridging height of 10 占 퐉 or less and excellent anti-ridging property.
0.001 to 0.005 wt% of Cr, 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% 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 the balance of Fe and other elements is 0.1 to 0.6 wt% A slab made of unavoidable impurities is produced, and the slab is subjected to hot rolling, hot rolling, hot rolling, cold rolling and cold rolling annealing,
Wherein the component constituting the molten steel for producing the slab is controlled in the content of each component so as to satisfy the following [formula 1].
400C + 85.7N + 55.6P + 7.7Si + 7.3Nb &lt; 5 ... ... ... ... ... ... [Formula 1]
In Equation 1, C, N, P, Si and Nb mean the content (wt%) of each component.
The method of claim 4,
The method of manufacturing a ferritic stainless steel according to claim 1, wherein the rolled material after the hot rolling has a recrystallization fraction (RF) of 80% or more of internal structure and a grain size (GS) of 300 탆 or less.
The method of claim 4,
Wherein the stainless steel after the cold-annealing has an elongation of 35% or more and a ridging height of 10 占 퐉 or less.

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