KR101522077B1 - Manufacturing method of ferritic stainless steel sheet with excellent ridging resistance - Google Patents

Abstract

The present invention relates to a ferritic stainless steel excellent in anti-ridging property capable of improving ridging characteristics by controlling the content of carbon and nitrogen to a low level, and a ferritic stainless steel having excellent anti-ridging properties according to an embodiment of the present invention. The method for producing the steel sheet according to claim 1, wherein the steel sheet contains 0.0005 to 0.03 wt% of C, 0.010 to 0.03 wt% of N, 0.01 to 0.50 wt% of Si, 0.01 to 0.70 wt% of Mn, 0.001 to 0.035 wt% of P, By weight, Cr: 15.0 to 17.0% by weight, Ni: 0.001 to 0.50% by weight, the balance Fe and other unavoidable impurities, and the sum of C and N is 0.04% by weight or less. Wherein the maximum austenite phase amount? Max in the internal structure of the slab is less than 10% and the austenite transformation temperature Ac1 is not less than 850 占 폚.

Description

Technical Field [0001] The present invention relates to a ferritic stainless steel sheet having excellent ridging resistance,

The present invention relates to a ferritic stainless steel excellent in anti-ridging property, and more particularly to a ferritic stainless steel excellent in anti-ridging property capable of improving the ridging characteristics by controlling the content of carbon and nitrogen to be low .

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.

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

The present invention relates to a method for producing a steel ingot having a low amount of austenite phase by controlling the amount of carbon (C) and nitrogen (N) to a low level and annealing for a short time at a high temperature, This excellent ferritic stainless steel and its manufacturing method are provided.

The ferritic stainless steel producing method according to one embodiment of the present invention is characterized in that it comprises 0.0005 to 0.03 wt% of C, 0.010 to 0.03 wt% of N, 0.01 to 0.50 wt% of Si, 0.01 to 0.70 wt% of Mn, 0.001 to 0.035 wt% of P, 0.0001 to 0.005 wt% of S, 15.0 to 17.0 wt% of Cr, 0.001 to 0.50 wt% of Ni, balance of Fe and other unavoidable impurities, and the sum of C and N is 0.04 wherein the slab is subjected to hot rolling, primary annealing, cold rolling and secondary annealing, wherein a maximum amount of austenite phase (? max) in the internal structure of the slab is less than 10% and austenite And the transformation temperature Ac1 is 850 DEG C or higher.

And the maximum austenite phase amount? Max is calculated by the following equation.

? 11.5 x [Si] -12.0 (%) = 420 x [C] + 470 x [N] + 23 x [Ni] + 9 x [Cu] + 10 x [Mn] X [Mo] -52.0 x [Al]

The austenite transformation temperature Ac1 is characterized by being calculated by the following equation.

(Mo) + 2.09 x [Si] + 4.86 x Nb + 8.29 x V + 1.77 x Ti + 21.4 x Al + 46 × [B] -7.14 × [C] -8 × [N] -3.28 × [Ni] -1.89 × [Mn] -0.51 × [Cu]

And the annealing temperature during the first annealing after the hot rolling is controlled to be in the range of 920 to 960 占 폚.

The stainless steel subjected to the primary annealing after the hot rolling has a recrystallization ratio of 80% or more.

And the ridging height of the stainless steel subjected to the secondary annealing after the cold rolling is 20 占 퐉 or less.

On the other hand, ferritic stainless steels excellent in anti-ridging properties according to one embodiment of the present invention contain 0.0005 to 0.03 wt% of C, 0.010 to 0.03 wt% of N, 0.01 to 0.50 wt% of Si, 0.01 to 0.70 wt% of Mn, 0.001 to 0.035 wt% of P, 0.0001 to 0.005 wt% of S, 15.0 to 17.0 wt% of Cr, 0.001 to 0.50 wt% of Ni, balance of Fe and other unavoidable impurities, and the sum of C and N is 0.04 wt% or less, and the ridging height is 20 mu m or less.

The stainless steel is characterized in that the maximum amount of austenite phase (? Max) in the internal structure is less than 10% and the austenite transformation temperature (Ac1) is not less than 850 占 폚.

According to the embodiment of the present invention, by controlling the amounts of carbon (C) and nitrogen (N) to be small, the amount of the maximum austenite phase in the internal structure is small and the austenite transformation temperature can be maintained high. Accordingly, since the recrystallization ratio of the internal structure can be increased during annealing after hot rolling, it is possible to prevent the crystal grains from coarsening and to suppress the occurrence of ridging defects on the surface.

Accordingly, according to the embodiment of the present invention, there is no intergranular erosion after pickling, and since the final cold rolling and the ridging height after annealing are low, the effect of improving the quality of the ferritic stainless steel can be expected.

FIG. 1A is an EPMA analysis image of a surface of a comparative example according to a comparative example after annealing at 920 ° C.,
1B is an EPMA analysis image of the surface after annealing at 920 占 폚 according to the inventive example according to the present invention,
2A is a photograph of the surface of the surface after acidic pickling at 920 DEG C of the inventive example according to the present invention photographed by an optical microscope,
FIG. 2B is a photograph of the surface after the acidic pickling at 920 ° C. in the comparative example according to the comparative example, taken by an optical microscope,
3 is a view showing the ridging height according to the annealing temperature in the inventive example according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a steel sheet comprising 0.0005 to 0.03 wt% of C, 0.010 to 0.03 wt% of N, 0.01 to 0.50 wt% of Si, 0.01 to 0.70 wt% of Mn, 0.001 to 0.035 wt% of P, 0.0001 to 0.005 wt% of S, , Cr: 15.0 to 17.0 wt%, Ni: 0.001 to 0.50 wt%, and Fe and other unavoidable impurities.

The content of carbon (C) is preferably 0.0005 wt% or more and 0.03 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 0.03 wt%, the impurities of the material are increased and the elongation is decreased.

The content of nitrogen (N) is preferably 0.010 wt% or more and 0.03 wt% or less. When the amount of nitrogen (N) is less than 0.010 wt%, the equiaxed crystal ratio of the slab is lowered. When the amount of nitrogen (N) is more than 0.03 wt%, impurities of the material increase and the elongation is lowered.

In particular, the sum of the contents of carbon (C) and nitrogen (N) is preferably 0.04 wt% or less. By lowering the amount of carbon (C) and nitrogen (N), it is possible to improve the workability of the product by reducing precipitation of fine carbonitride and to control the amount of maximum austenite phase (γmax) to less than 10% Ac1) Allow the annealing at a high temperature by setting the temperature to 850˚C or higher.

At this time, the maximum amount of the austenite phase (? Max) is calculated by the following formula (1).

[Equation 1]

? 11.5 x [Si] -12.0 (%) = 420 x [C] + 470 x [N] + 23 x [Ni] + 9 x [Cu] + 10 x [Mn] X [Mo] -52.0 x [Al]

The austenite transformation temperature (Ac1) is excellent in anti-ridging property as calculated by the following formula (2).

&Quot; (2) "

(Mo) + 2.09 x [Si] + 4.86 x Nb + 8.29 x V + 1.77 x Ti + 21.4 x Al + 46 × [B] -7.14 × [C] -8 × [N] -3.28 × [Ni] -1.89 × [Mn] -0.51 × [Cu]

The elements not limited in the content among the elements described in the above-mentioned [Mathematical Formulas 1] and [Mathematical Expression 2] are elements which do not need to be limited in their contents, and the range of the content is not limited. Of course, it is a matter of course that for the calculation of the above-mentioned [Equation 1] and [Equation 2], it is necessary to measure up to the content of the elements not limited in the content.

On the other hand, the content of silicon (Si) is preferably 0.01 wt% or more and 0.50 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 0.5 wt%, the impurities of the material increase and the elongation becomes poor.

The content of manganese (Mn) is preferably 0.01 wt% or more and 0.70 wt% or less. When the amount of manganese (Mn) is less than 0.01 wt%, there is a problem that the refining price is expensive. When the amount is more than 0.7 wt%, the impurities of the material increase and the elongation becomes low.

The content of phosphorus (P) is preferably 0.001 wt% or more and 0.035 wt% or less. If the amount of phosphorus (P) is less than 0.001 wt%, there is a problem that the refining price becomes expensive. When the amount of phosphorus (P) is more than 0.035 wt%, the impurities of the material increase and the elongation becomes poor.

The content 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 content 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 content of nickel (Ni) is preferably 0.001 wt% or more and 0.50 wt% or less. If the amount of nickel (Ni) is less than 0.001 wt%, there is a problem that the refining price is expensive. If the amount is more than 0.5 wt%, the impurities of the material increase and the elongation rate decreases.

In order to manufacture a stainless steel excellent in anti-ridging property, molten steel having the above composition is produced by a conventional method to produce a slab, followed by hot rolling, primary annealing, cold rolling and secondary annealing.

[Example]

The following examples illustrate the present invention.

The hot-rolled steel sheets of 4 to 5 mm in thickness, hot-rolled from the continuously cast slabs using molten steel as shown in Table 1 below, were heat-treated while changing the annealing temperature as shown in Table 2 below, Followed by rolling and secondary annealing. The recrystallization ratio (%), grain size (占 퐉), grain boundary erosion and ridging (占 퐉) are shown in Table 2.

[Table 1]

[Table 2]

As can be seen from Tables 1 and 2, when the composition of the alloy component and the annealing temperature are controlled within the preferable range, the grain size is formed to be smaller than 500 μm while the recrystallization ratio is maintained at 80% or more, Mu] m.

On the other hand, in the case of the present invention, the continuous cast slab is heat-treated at 920 캜, which is above the austenite transformation point (Ac 1) temperature, using the molten steel constituted by the alloy component according to the present invention, And the comparative example was heat treated at 920 占 폚, which is higher than the austenite transformation point (Ac1) temperature, using a conventional STS 430 steel, that is, a continuous cast slab using molten steel as an alloy component shown in Table 1 The internal tissues were photographed by EPMA.

FIG. 1A is an EPMA analysis image of a surface after annealing at 920.degree. C. in a comparative example according to a comparative example, FIG. 1B is an EPMA analysis image of a surface after annealing at 920.degree. C. according to the inventive example of the present invention, , FIG. 2A is a photograph of the surface after the 920 ° C. annealing of the inventive example according to the present invention, and FIG. 2B is a photograph of the surface after the 980 ° C. annealing of the comparative example according to the comparative example, It is a photograph taken.

As can be seen from the photograph of FIG. 1A, in the comparative example, when the heat treatment is performed at the Ac1 temperature or more, a chromium deteriorated zone occurs due to the austenite phase transformation during the heat treatment. The Cr depleted zone, as shown in FIG. 2A, causes excessive intergranular erosion at the time of mixed acid picking, and thus it is confirmed that the surface quality is deteriorated.

On the other hand, as can be seen from the photographs of FIGS. 1B and 2B, in the case of the case where the amount of the maximum austenite phase is less than 10%, the Cr depleted zone does not occur even after the heat treatment, I could confirm that I did not.

3 is a view showing the ridging height according to the annealing temperature in the inventive example according to the present invention.

As can be seen from FIG. 3, when the maximum austenite phase is less than 10%, the heat treatment is performed at a temperature of 900 ° C or higher after hot rolling to cause recrystallization of more than 80%, thereby removing the band structure formed during hot rolling, .

However, when annealed at 1000 ℃ or more, it was confirmed that the crystal grain size of the material exceeded 500 袖 m even when recrystallization occurred at 80% or more, and the final cold rolling and lasing after annealing exceeded 20 탆.

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 0.035 wt% of P, 0.0001 to 0.005 wt% of S, 0.0005 to 0.03 wt% of C, 0.010 to 0.03 wt% of N, 0.01 to 0.50 wt% of Si, 0.01 to 0.70 wt% 15.0 to 17.0 wt%, Ni: 0.001 to 0.50 wt%, the balance Fe and other unavoidable impurities, and the sum of C and N is 0.04 wt% or less.
The slab is subjected to hot rolling, primary annealing, cold rolling and secondary annealing, wherein the annealing temperature in the primary annealing is controlled to be in the range of 920 to 960 占 폚,
The maximum austenite phase amount? Max in the internal structure of the slab is less than 10%, the austenite transformation temperature Ac1 is not less than 850 占 폚,
The amount of maximum austenite phase (max) is calculated by the following equation (1), and the austenite transformation temperature Ac1 is calculated from the following formula (2): ferritic stainless steel Gt;
[Equation 1]
? 11.5 x [Si] -12.0 (%) = 420 x [C] + 470 x [N] + 23 x [Ni] + 9 x [Cu] + 10 x [Mn] X [Mo] -52.0 x [Al]
&Quot; (2) "
(Mo) + 2.09 x [Si] + 4.86 x Nb + 8.29 x V + 1.77 x Ti + 21.4 x Al + 46 × [B] -7.14 × [C] -8 × [N] -3.28 × [Ni] -1.89 × [Mn] -0.51 × [Cu]
delete The method according to claim 1,
Wherein the stainless steel subjected to the primary annealing after the hot rolling has an excellent refractory property with a recrystallization ratio of 80% or more.
The method according to claim 1,
Wherein the ridging height of the secondary annealed stainless steel after the cold rolling is 20 占 퐉 or less.
delete delete

Images