WO2016105080A1 - Ferritic stainless steel having excellent surface quality and ridging resistance - Google Patents

Abstract

The present invention relates to a ferritic stainless steel having excellent ridging resistance, wherein the amounts of components forming molten steel for manufacturing the stainless steel are controlled, thereby improving the ridging resistance. The stainless steel having excellent ridging resistance and formability, according to one embodiment of the present invention, comprises 12.5-18.5 wt% of Cr, 001-0.025 wt% of C, 0.01-0.05 wt% of N, 0.05-0.4 wt% of Ti, 0.01-0.2 wt% of Al, 0.01-0.5 wt% of Si, 0.01-0.5 wt% of Mn, 0.01-0.5 wt% of Cu, 0.001-0.5 wt% of Mo, 0.01-0.5 wt% of Nb, 0.01-0.5 wt% of Ni, and the remainder being Fe and impurities, and satisfies formula (1) below. An amount of precipitated TiN (vol%)>1.1×10^-3 - (1). In formula (1), an amount of precipitated TiN (vol%)=47N+102Ti×N+10C+0.39, and N, Ti and C are defined as the amounts (wt%) of each component.

Description

Ferritic stainless steel with excellent surface quality and leachability

The present invention relates to a ferritic stainless steel, and more particularly to a ferritic stainless steel having excellent surface quality and leachability by controlling the content of the components constituting the molten steel for producing stainless steel to improve the surface quality and leachability It is about.

Stainless steel can be roughly divided into ferritic stainless steel and austenitic stainless steel.

In general, ferritic stainless steels are widely used in kitchen appliances, building exterior materials, home appliances, electronic parts, etc., because they are inexpensive and preferentially have surface gloss, drawing properties, and oxidation resistance, compared to austenitic stainless steels.

In the ferritic stainless steel, the surface defects in the form of wrinkles are formed parallel to the rolling direction during the molding process for application to the components of the above-mentioned applications. This phenomenon is called ridging.

Since such ridging defects deteriorate the appearance of the product, an additional polishing process is required at the portion where the ridging occurs after the molding, which causes a rise in the manufacturing cost of the final product.

STS430 steel, which is one of the ferritic stainless steels, is a steel containing about 16% by weight of chromium (Cr) and is a representative steel of ferritic stainless steel, and is widely used for aquaculture and household appliances.

STS430 steel has excellent leachability among other ferritic stainless steels, but still has ridging defects. Therefore, there is a need for continuous leasing reduction ferritic stainless steels in order to reduce polishing cost or reduce mechanical defects caused by leasing.

The cause of this leasing is inherently due to the coarse cast structure that is undestructed.

That is, when the cast structure remains as a coarse band structure without breaking in the rolling or annealing process, it is expressed as a ridging defect due to the width and thickness deformation behavior different from the surrounding recrystallized structure during tensile processing.

1 is a view for explaining the refinement of the cast structure using TiN in order to improve the leachability.

As shown in FIG. 1, the columnar structure of the slab is subjected to shear deformation during hot rolling so that fracture occurs well in subsequent processes. However, the slab equiaxed structure is subjected to planar deformation during hot rolling, so that the band structure is not destroyed in subsequent processes.

In order to solve this problem, TiN precipitates are generated in the temperature range cast by adding Ti and high N, thereby making the equiaxed crystal structure fine using the TiN pinning effect, thereby fundamentally suppressing coarse band structure formation.

The ferritic stainless steel sheet and the manufacturing method of the conventional steel composition, rolling conditions, annealing conditions by improving the specific texture of the structure by improving the aging resistance, "Ferritic stainless steel sheet with small in-plane anisotropy and excellent ridging resistance and It is known in detail in the manufacturing method (Patent Publication 10-1997-0015775).

However, ferritic stainless steel having an austenite transformation section is required to be subjected to annealing heat treatment for decomposing austenite structure after hot rolling, but for this purpose, the production cost is increased and manufacturing time is increased. As the manufacturing time increases, there is a problem that the productivity is lowered.

In addition, it did not specify the critical range of specific components that can prevent Scab defects and intergranular corrosion.

(Patent Document 0001) Published Patent 10-1997-0015775 (1997. 04. 28.)

The present invention has been made to solve the above problems, by optimizing the content of the alloying components affecting the improvement of the leachability, it is possible to refine the casting structure, and prevent the occurrence of Scab defects and grain boundary corrosion defects Provides ferritic stainless steel with excellent surface quality and leachability.

According to one embodiment of the present invention, the ferritic stainless steel having excellent surface quality and lowering property is in weight%, Cr: 12.5-18.5%, C: 0.001-0.025%, N: 0.01-0.05%, Ti: 0.05- 0.4%, Al: 0.01-0.2%, Si: 0.01-0.5%, Mn: 0.01-0.5%, Cu: 0.01-0.5%, Mo: 0.001-0.5%, Nb: 0.01-0.5%, Ni: 0.01-0.5 %, The remaining Fe and impurities, and characterized by satisfying the following formula (1).

TiN precipitation (Vol%)> 1.1 × 10 ^-3 -------------------------- (1)

In the formula (1), TiN precipitation amount (Vol%) = 47N + 102Ti × N + 10C + 0.39, N, Ti and C means the content (wt%) of each component.

The stainless steel can be characterized by satisfying the following formula (2).

TiN crystallization temperature (℃) ≤ 1,520 ------------------------------ (2)

In formula (2), TiN crystallization temperature (° C.) = [-19,755 / {logN- (7.78 + 0.07Ti-logTi + 0.045Cr)}]-275, and N, Ti and Cr are the contents of each component (wt% ).

It is preferable that N / C ratio is 1.5 or more and 6 or less by mass ratio of the said stainless steel.

The stainless steel can be characterized by satisfying the following formula (3).

Ti / (C + N)> 5.0 ---------------------------------- (3)

In the formula (3), Ti, C and N means the content (wt%) of each component.

The stainless steel may be characterized in that the grain size of the equiaxed crystal structure in the cast state is 2 mm or less.

The stainless steel may be characterized in that the ridging height (Wt) in the cold rolled steel sheet state is less than 11㎛.

According to the embodiment of the present invention, by adjusting the amount of TiN precipitation by optimizing the content of Ti, C and N to improve the lagging properties, there is an effect that can minimize the generation of grain boundary corrosion defects.

In addition, by optimizing the content of N, Ti and Cr to manage the TiN crystallization temperature below 1,520 ℃, there is an effect that can minimize the occurrence of Scab defects to improve the surface quality.

1 is a view for explaining the miniaturization of the cast structure using TiN to improve the leachability;

2 is a view showing a correlation between the threshold value of TiN precipitation amount and the refined equiaxed crystal (2 mm or less) according to an embodiment of the present invention,

FIG. 3 is a graph showing the range of Ti and N amounts in which equiaxed refinement is realized from the threshold value of the minimum TiN derived from FIG.

4 is a view showing a correlation between the threshold value of TiN crystallization temperature and the occurrence of Scab defects according to an embodiment of the present invention,

FIG. 5 is a graph showing a range of Ti and N amounts in which Scab defects do not occur from the threshold value of TiN crystallization temperature derived from FIG. 4;

6 is a view showing the correlation between the threshold value of Ti / (C + N) and grain boundary corrosion defects during HAPL pickling according to an embodiment of the present invention,

FIG. 7 is a graph showing a range of Ti and N amounts in which grain boundary corrosion does not occur from the threshold value of Ti / (C + N) derived from FIG. 6;

8 is a graph showing the relationship between Scab, grain boundary corrosion and equiaxed crystal refinement according to the content of Ti and N.

According to one embodiment of the present invention, the ferritic stainless steel having excellent surface quality and lowering property is in weight%, Cr: 12.5-18.5%, C: 0.001-0.025%, N: 0.01-0.05%, Ti: 0.05- 0.4%, Al: 0.01-0.2%, Si: 0.01-0.5%, Mn: 0.01-0.5%, Cu: 0.01-0.5%, Mo: 0.001-0.5%, Nb: 0.01-0.5%, Ni: 0.01-0.5 %, The remaining Fe and impurities, and characterized by satisfying the following formula (1).

TiN precipitation (Vol%)> 1.1 × 10 ^-3 -------------------------- (1)

In the formula (1), TiN precipitation amount (Vol%) = 47N + 102Ti × N + 10C + 0.39, N, Ti and C means the content (wt%) of each component.

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.

According to one embodiment of the present invention, the ferritic stainless steel having excellent surface quality and lowering property is in weight%, Cr: 12.5-18.5%, C: 0.001-0.025%, N: 0.01-0.05%, Ti: 0.05- 0.4%, Al: 0.01-0.2%, Si: 0.01-0.5%, Mn: 0.01-0.5%, Cu: 0.01-0.5%, Mo: 0.001-0.5%, Nb: 0.01-0.5%, Ni: 0.01-0.5 %, The remaining Fe and impurities.

Hereinafter, the reason for numerical limitation of the component content in the embodiment according to the present invention will be described. In the following, the unit is% by weight unless otherwise specified.

Cr: 12.5-18.5%

The amount of chromium (Cr) is preferably 12.5% by weight to 18.5% by weight.

Because chromium (Cr) is an alloying element added to improve the corrosion resistance of the steel, when chromium (Cr) is contained in less than 12.5% by weight, the corrosion resistance of the ferritic stainless steel is lowered, contained in excess of 18.5% by weight In this case, the manufacturing cost increases unnecessarily.

Therefore, chromium (Cr) in the embodiment according to the present invention is preferably limited to 12.5 ~ 18.5% by weight.

C: 0.001-0.025%

The amount of carbon (C) is preferably 0.001% to 0.025% by weight.

Because carbon (C) is an austenite stabilizing element of steel, it needs to be limited because it acts to maximize the austenite fraction, and carbon (C) is a solid solution strengthening element, which reduces the elongation when the product exceeds 0.025% by weight. This is because the workability of the resin is lowered, the corrosion resistance is reduced, and when the amount is less than 0.001% by weight, additional refining costs are incurred.

In this case, the elongation is a term commonly used as one of quality characteristics indicating the processability of the cold rolled product of ferritic stainless steel, and the amount of elongation until the breakage occurs when the cold rolled product of the ferritic stainless steel is uniaxially tensioned. Calculate from length divided by length.

N: 0.01 ~ 0.05%

The amount of nitrogen (N) is preferably 0.01% by weight to 0.05% by weight.

This is because nitrogen (N) is an important element having the effect of miniaturizing the microstructure of the slab by combining with titanium (Ti) to form titanium nitride (TiN) during casting and solidification. This is because when N) is added in excess of 0.05% by weight, it not only impairs workability but also causes stretcher strain of cold-rolled products.

The more specific range of nitrogen (N) is influenced by the amount of titanium (Ti) and will be described later in detail.

Ti: 0.05-0.40%

The amount of titanium (Ti) is preferably 0.05% to 0.40% by weight.

Because titanium (Ti) is an element that plays an important role in miniaturizing the equiaxed grain size of the cast steel structure, it is added to 0.05% by weight or more since it plays a role of improving workability by fixing carbon (C), nitrogen (N), etc. .

However, when titanium (Ti) is added in excess of 0.40% by weight, the manufacturing cost of stainless steel is increased and Scab defects occur on cast and hot rolled product surfaces and also cause sleeve defects in cold rolled products.

The more specific range of titanium (Ti) is influenced by the content of nitrogen (N) and will be described later in detail.

Al: 0.01 ~ 0.2%

The amount of aluminum (Al) is preferably 0.01% by weight to 0.2% by weight.

Because aluminum (Al) is an element added as a deoxidizer during steelmaking, it is preferably contained at 0.01% by weight or more, but when aluminum (Al) is added in excess of 0.2% by weight, it is present as a non-metallic inclusion and is a cold rolled strip. This is a cause of sleeve defects and causes a decrease in weldability.

Si: 0.01 ~ 0.5%

The amount of silicon (Si) is preferably 0.01% by weight to 0.5% by weight.

Because silicon (Si) is an element added as a deoxidizer during steelmaking, and is a ferrite stabilizing element, it is preferable to be contained in 0.01% by weight or more.

On the other hand, if it contains a large amount in excess of 0.5% by weight, it is preferable to limit the content to 0.5% by weight or less because it causes a problem of hardening of the material and lowering the ductility.

Mn: 0.01 ~ 0.5%

The amount of manganese (Mn) is preferably 0.01% by weight to 0.5% by weight.

This is because manganese (Mn) is an impurity inevitably included in steel, but when it is included in a large amount, manganese fume is generated during welding and causes evaporation of MnS phase, thereby lowering elongation.

Cu: 0.01 ~ 0.5%

The amount of copper (Cu) is preferably 0.01% by weight to 0.5% by weight.

This is because copper (Cu) is an impurity that is inevitably included in steel and has an effect of improving corrosion resistance by adding 0.01% or more, but has a problem of deterioration in workability when added in excess of 0.5%.

Mo: 0.001-0.5%

The amount of molybdenum (Mo) is preferably 0.001% by weight to 0.5% by weight.

Because molybdenum (Mo) is added to 0.001% or more has the effect of improving the corrosion resistance, in particular, corrosion resistance, but when added in excess of 0.5% as an expensive element has a problem of increasing the manufacturing cost, lowering the workability Because there is.

Nb: 0.001-0.5%

The amount of niobium (Nb) is preferably 0.001% by weight to 0.5% by weight.

This is because niobium (Nb) is an expensive element, and 0.001% or more is added to precipitate solid carbon (C) and nitrogen (N) as carbonitrides, thereby improving corrosion resistance and formability, while 0.5% If the amount is added in excess, the appearance defects and toughness due to inclusions are lowered, and the manufacturing cost is increased.

Ni: 0.01 ~ 0.5%

The amount of nickel (Ni) is preferably 0.01% by weight to 0.5% by weight.

Because nickel (Ni) is an impurity that is inevitably included in steel, the addition of 0.01% or more has the effect of improving the corrosion resistance, whereas when added in large amounts, austenite stabilization increases and as an expensive element, This is because there is a problem to raise.

Except for the aforementioned elements, the other elements are made of iron (Fe) and other unavoidable impurities.

In general, the cause of leasing in ferritic stainless steels is that the coarse grains formed during casting are rolled without being removed during hot rolling. According to one embodiment of the present invention, By forming a fine equiaxed crystal by the TiN compound formed, it is possible to manufacture a ferritic stainless steel slab having a fine structure to produce a ferritic stainless steel having excellent dropping properties.

Therefore, in order to satisfy the equiaxed crystal refinement (2 mm or less), the ferritic stainless steel having excellent surface quality and leachability according to an embodiment of the present invention is more limited in the amount of TiN that affects the refinement of the equiaxed crystal. It is desirable to.

For example, it is preferable to cast by the component system which satisfy | fills following formula (1) and (2).

TiN precipitation (Vol%)> 1.1 × 10 ^-3 -------------------------- (1)

At this time, in the formula (1) TiN precipitation amount (Vol%) = 47N + 102Ti × N + 10C + 0.39, N, Ti and C means the content (wt%) of each component.

TiN crystallization temperature (℃)> 1,520 ------------------------------ (2)

At this time, in the formula (2) TiN crystallization temperature (℃) = [-19,755 / {logN- (7.78 + 0.07Ti-logTi + 0.045Cr)}]-275, N, Ti and Cr are the content of each component ( Weight percent).

In addition, in this invention, it is preferable to manage N / C ratio to 1.5 or more and 6 or less.

Because, the relatively high content of N is essential for the formation of TiN, which can make the structure fine during casting, and even if N is added in a certain amount, it is difficult for all N to form TiN compounds because of its natural behavior. This is because Ti must be added according to the range of Ti / N ratio of.

In addition, the ferritic stainless steel according to the embodiment of the present invention is characterized in that it does not include austenite phase transformation until the room temperature after casting.

This is because, if the austenite phase transformation is included, especially if the austenitic phase transformation is included in the hot rolling section, such as in the conventional STS 430 steel, after the hot rolling, the annealing phase for thermal decomposition of the austenite phase decomposition and Cr deficiency layer is essential, And because the production time is increased.

Therefore, the present invention omits the annealing heat treatment process as a complete wastelite component system, and thus performs continuous annealing heat treatment. There is an effect that can reduce the production cost, improve the productivity by shortening the production time.

As described above, the lowering property of the STS 430 steel, which is a representative steel of ferritic stainless steel, is relatively superior to other ferritic stainless steels by removing some of the coarse texture formed during casting by including austenite phase transformation in the hot rolling section. On the other hand, in the present invention, despite being a component system that does not contain austenite phase transformation, it is possible to obtain excellent leachability by casting to the component system to form a fine cast structure.

At this time, whether the austenite phase is formed can be determined by observing the microstructure by heating and etching the material in the range of 900 ℃ ~ 1,100 ℃, and can be determined based on the standard commonly used in materials engineering, so detailed criteria are omitted.

Hereinafter, examples and comparative examples according to the present invention will be described.

However, the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited by the following embodiments.

Remarks	alloy	Alloy component (wt%)
		Cr	Si	Al	Mn	Ni	Cu	P	S	C	N	Ti
Comparison A	#One	16.34	0.174	0.024	0.123	0.08	0.018	0.021	0.001	0.0068	0.0083	0.17
	#2	16.24	0.182	0.043	0.156	0.05	0.015	0.023	0.0009	0.0069	0.0043	0.17
	# 3	16.41	0.181	0.033	0.142	0.06	0.014	0.0223	0.0008	0.0072	0.0084	0.2
	#4	16.52	0.176	0.051	0.136	0.07	0.021	0.021	0.0009	0.0072	0.0073	0.19
	# 5	16.9	0.177	0.03	0.149	0.07	0.011	0.0234	0.001	0.0073	0.0058	0.245
Comparison B	# 6	16.03	0.172	0.089	0.257	0.16	0.071	0.0239	0.0008	0.0083	0.0162	0.237
	# 7	16.22	0.189	0.031	0.101	0.07	0.023	0.0185	0.0013	0.0043	0.0196	0.174
	#8	16.12	0.191	0.077	0.115	0.07	0.021	0.0202	0.0008	0.0042	0.0172	0.239
	# 9	16.2	0.19	0.057	0.098	0.06	0.031	0.0213	0.0008	0.0077	0.0197	0.213
	# 10	16.1	0.174	0.037	0.092	0.07	0.025	0.0217	0.0008	0.0074	0.0187	0.193
	# 11	16.26	0.087	0.048	0.181	0.19	0.092	0.0248	0.0008	0.0096	0.0217	0.169
	# 12	16.36	0.081	0.107	0.222	0.17	0.078	0.0244	0.0013	0.0072	0.0172	0.222
	# 13	16.14	0.106	0.049	0.205	0.18	0.085	0.0257	0.0014	0.0068	0.0208	0.198
	# 14	16.31	0.247	0.02	0.207	0.13	0.069	0.0212	0.0009	0.0065	0.0203	0.182
	# 15	16.02	0.166	0.063	0.177	0.15	0.073	0.0194	0.0008	0.0046	0.0207	0.202
Comparison C	# 16	16.03	0.166	0.044	0.081	0.11	0.027	0.0195	0.001	0.0068	0.0213	0.118
	# 17	16.2	0.2	0.033	0.115	0.11	0.026	0.0163	0.0008	0.0061	0.0194	0.117
	# 18	16.03	0.183	0.038	0.136	0.1	0.028	0.015	0.0006	0.0063	0.0218	0.123
invent	# 19	16.27	0.256	0.027	0.183	0.11	0.024	0.0224	0.0009	0.0067	0.018	0.179
	# 20	16.33	0.24	0.03	0.188	0.12	0.02	0.0206	0.001	0.007	0.0218	0.149
	# 21	16.25	0.297	0.036	0.181	0.12	0.021	0.0186	0.0009	0.0069	0.0196	0.176
	# 22	16.1	0.181	0.048	0.131	0.08	0.013	0.0235	0.0009	0.007	0.0169	0.175
	# 23	16.23	0.171	0.1	0.135	0.08	0.009	0.0231	0.0011	0.0061	0.0191	0.191
	# 24	16.18	0.157	0.033	0.125	0.08	0.007	0.0217	0.001	0.0065	0.0171	0.172
	# 25	16.4	0.176	0.036	0.159	0.09	0.023	0.0182	0.0005	0.0074	0.0146	0.143
	# 26	16.28	0.189	0.041	0.171	0.09	0.021	0.0192	0.0005	0.0071	0.015	0.16
	# 27	16.26	0.176	0.048	0.17	0.09	0.019	0.023	0.0005	0.0073	0.0149	0.182
	# 28	16.2	0.206	0.03	0.167	0.09	0.02	0.0256	0.0005	0.0068	0.0138	0.182
	# 29	16.27	0.179	0.039	0.107	0.07	0.028	0.018	0.0012	0.0055	0.0129	0.172
	# 30	16.08	0.17	0.052	0.107	0.07	0.025	0.0159	0.0012	0.0044	0.0121	0.175
	# 31	16.17	0.172	0.07	0.101	0.07	0.021	0.0165	0.0011	0.0053	0.014	0.171
	# 32	16.47	0.134	0.04	0.127	0.07	0.015	0.0259	0.0011	0.0063	0.0126	0.181
	# 33	16.22	0.178	0.074	0.135	0.16	0.019	0.0241	0.001	0.0062	0.0103	0.18
	# 34	16.32	0.2	0.035	0.155	0.07	0.012	0.0265	0.0011	0.0054	0.0115	0.161

Table 1 is a table showing the alloying components of various embodiments and comparative examples of the ferritic stainless steel having excellent surface quality and leachability produced according to an embodiment of the present invention.

In Table 1, various embodiments of the present invention control the contents of Ti, N, and C. The examples and comparative examples are shown by confirming their components by vacuum dissolving.

In the present invention, by continuously casting the Examples and Comparative Examples according to the composition range of Table 1 to produce a cast, and the produced cast is subjected to rough rolling mill and continuous finish rolling using a rolling mill to produce a ferritic stainless steel hot rolled steel sheet After the continuous annealing and pickling, cold rolling and cold annealing were performed to produce a final ferritic stainless steel.

Remarks	alloy	TiN precipitation (Vol% × 10 3 )	TiN crystallization temperature (℃)	Ti / (C + N)	Isometric is refined?	No Scab	No intergranular corrosion	Leasing Class
Comparison A	#One	0.99	1463	11.3	X	O	O	2
	#2	0.69	1421	15.2	X	O	O	2
	# 3	0.98	1474	12.8	X	O	O	2
	#4	0.95	1461	13.1	X	O	O	2
	# 5	0.86	1459	18.7	X	O	O	2
Comparison B	# 6	1.58	1534	9.7	O	X	O	One
	# 7	1.74	1525	7.3	O	X	O	One
	#8	1.65	1538	11.2	O	X	O	One
	# 9	1.79	1539	7.8	O	X	O	One
	# 10	1.71	1529	7.4	O	X	O	One
	# 11	1.85	1530	5.4	O	X	O	One
	# 12	1.65	1531	9.1	O	X	O	One
	# 13	1.84	1538	7.2	O	X	O	One
	# 14	1.8	1530	6.8	O	X	O	One
	# 15	1.84	1540	8	O	X	O	One
Comparison C	# 16	1.66	1505	4.2	O	O	X	One
	# 17	1.56	1497	4.6	O	O	X	One
	# 18	1.74	1510	4.4	O	O	X	One
invent	# 19	1.64	1510	7.2	O	O	O	One
	# 20	1.81	1511	5.2	O	O	O	One
	# 21	1.74	1516	6.6	O	O	O	One
	# 22	1.57	1515	7.3	O	O	O	One
	# 23	1.73	1519	7.6	O	O	O	One
	# 24	1.58	1515	7.3	O	O	O	One
	# 25	1.37	1490	6.5	O	O	O	One
	# 26	1.43	1500	7.2	O	O	O	One
	# 27	1.45	1508	8.2	O	O	O	One
	# 28	1.38	1503	8.8	O	O	O	One
	# 29	1.31	1494	9.3	O	O	O	One
	# 30	1.26	1492	10.6	O	O	O	One
	# 31	1.38	1500	8.9	O	O	O	One
	# 32	1.3	1495	9.6	O	O	O	One
	# 33	1.15	1482	10.9	O	O	O	One
	# 34	1.2	1482	9.5	O	O	O	One

Table 2 is a table showing the results of confirming the ratio of Ti / N and N / C of the various examples and comparative examples having the composition of Table 1 and the leasing grade for each of the final ferritic stainless steel.

In this case, the ridging grade representing the lowering property is the ridging height grade (Wt basis) measured after 15% tension of the cold rolled steel sheet, and the 1st grade is less than 11㎛, the 2nd grade is 11㎛ ~ 14㎛, and the 3rd grade is 14㎛-18 The micrometer and grade 4 represent 18 micrometers or more, where a grade 1 corresponds to the range aimed by this invention.

2A is a view showing a correlation between the threshold of TiN precipitation amount and the refinement of equiaxed crystals (2 mm or less) according to an embodiment of the present invention, and FIG. 2B illustrates the refinement of equiaxed crystals from the threshold value of the minimum TiN derived from FIG. 2A. Is a graph showing the range of Ti and N amounts to be implemented.

As shown in Table 1, 2 and Figure 2, Comparative A group consisting of Comparative Examples 1 to 5 it can be seen that Ti / N does not satisfy 5 to 20, N / C does not satisfy 1.5 to 6 .

Therefore, TiN precipitation amount was less than 1.1 × 10 ⁻³ (vol%), which did not satisfy Equation (1), and the grain size of the equiaxed crystals exceeded 2 mm, resulting in no refinement of equiaxed crystals. It can be seen that it does not meet the target value of the present invention.

3A is a view showing a correlation between the threshold value of TiN crystallization temperature and the occurrence of Scab defects according to an embodiment of the present invention, and FIG. 3B is a diagram in which a Scab defect does not occur from the threshold value of the TiN crystallization temperature derived from FIG. 3A. Is a graph showing the range of N amounts.

As shown in Table 1, 2 and Figure 3, Comparative B group consisting of Comparative Examples 6 to 15 meets the ratio of Ti / N and N / C according to the embodiment of the present invention, the crystallization temperature (Ti) of TiN It can be seen that the formula (2) does not satisfy above 1520 ℃.

As a result, it may be confirmed that a Scab defect is generated to lower the surface quality.

FIG. 4A illustrates a correlation between a threshold value of Ti / (C + N) and grain boundary corrosion defects during HAPL pickling according to an embodiment of the present invention, and FIG. 4B illustrates Ti / (C + N) derived from FIG. 4A. It is a graph which shows the range of Ti and N amount which grain boundary corrosion does not generate from the threshold value of.

As shown in Table 1, 2 and Figure 3, Comparative C group consisting of Comparative Examples 16-18 is not only the ratio of Ti / N and N / C according to the embodiment of the present invention, but also the crystallization temperature (° C) of TiN Although managed at 1,520 ° C. or less, it can be seen that the Ti / (C + N) value is less than 5.0, which does not satisfy the above formula (3).

Accordingly, it can be seen that grain boundary corrosion occurs and the quality is degraded.

5 is a graph showing the relationship between Scab, grain boundary corrosion and equiaxed crystal refinement according to the content of Ti and N.

As shown in Tables 1, 2 and 5, when satisfying the composition range according to the embodiment of the present invention, while satisfying the above formula (1) to formula (3) at the same time, the grain size of the equiaxed crystal in the cast state is 2 It appears that less than mm, the leaching height (Wt) in the cold-rolled steel sheet state is less than 11㎛ excellent leasing grade, and it is confirmed that the surface quality is improved by preventing defects such as Scab and grain boundary corrosion.

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.

The ferritic stainless steel having excellent surface quality and lowering property according to embodiments of the present invention may be applied to kitchen appliances, building exterior materials, home appliances, electronic components, and the like.

Claims (6)

1. By weight%, Cr: 12.5-18.5%, C: 0.001-0.025%, N: 0.01-0.05%, Ti: 0.05-0.4%, Al: 0.01-0.2%, Si: 0.01-0.5%, Mn: 0.01- 0.5%, Cu: 0.01-0.5%, Mo: 0.001-0.5%, Nb: 0.01-0.5%, Ni: 0.01-0.5%, including the remaining Fe and impurities,

   A ferritic stainless steel having excellent surface quality and lowering property, satisfying the following formula (1).

   TiN precipitation (Vol%)> 1.1 × 10 ^-3 -------------------------- (1)

   In the formula (1), TiN precipitation amount (Vol%) = 47N + 102Ti × N + 10C + 0.39, N, Ti and C means the content (wt%) of each component.
2. The method according to claim 1,

   The stainless steel,

   A ferritic stainless steel excellent in surface quality and dripping property, characterized by satisfying the following formula (2).

   TiN crystallization temperature (℃) ≤ 1,520 ------------------------------ (2)

   In the formula (2), TiN crystallization temperature (° C.) = [-19,755 / {logN- (7.78 + 0.07Ti-logTi + 0.045Cr)}]-275, and N, Ti and Cr are the contents of each component (wt% ).
3. The method according to claim 2,

   The stainless steel,

   A ferritic stainless steel having excellent surface quality and lowering property, wherein the N / C ratio is 1.5 to 6 by mass ratio.
4. The method according to claim 1,

   The stainless steel,

   A ferritic stainless steel excellent in surface quality and leachability, characterized by satisfying the following formula (3).

   Ti / (C + N)> 5.0 ------------------------------------ (3)

   In the formula (3), Ti, C and N means the content (wt%) of each component.
5. The method according to claim 1,

   The stainless steel,

   A ferritic stainless steel having excellent surface quality and lowering property, wherein the grain diameter of the equiaxed crystal structure in the cast state is 2 mm or less.
6. The method according to claim 1,

   The stainless steel

   A ferritic stainless steel having excellent surface quality and lowering property, which has a ridging height Wt of less than 11 µm in a cold rolled steel sheet.

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