TW201529866A - Ferritic stainless steel and method for producing same - Google Patents

Abstract

Provided are: a ferritic stainless steel which has sufficient corrosion resistance and excellent formability; and a method for producing this ferritic stainless steel. A ferritic stainless steel according to the present invention contains, in mass%, 0.005-0.05% of C, 0.02-0.50% of Si, 0.05-1.0% of Mn, 0.04% or less of P, 0.01% or less of S, 15.5-18.0% of Cr, 0.001-0.10% of Al and 0.01-0.06% of N, with the balance made up of Fe and unavoidable impurities. This ferritic stainless steel is configured to satisfy El ≥ 25%, (average r value) ≥ 0.70 and |[increment]r| ≤ 0.20.

Description

Fertilizer iron-based stainless steel and manufacturing method thereof

The present invention relates to a ferrite-based iron-based stainless steel excellent in formability and a method for producing the same.

Among the ferrite-based stainless steels, SUS430 (16 to 18 mass% Cr), which is defined by Japanese Industrial Standard JIS G 4305, is used in building materials, transportation equipment, home electric appliances, kitchen appliances, and the like because it is inexpensive and excellent in corrosion resistance. Various uses such as automobile parts, and the scope of application in recent years has been further expanded. In order to be suitable for such applications, it is required to have not only corrosion resistance but also sufficient formability to be processed into a predetermined shape (large stretchability (hereinafter referred to as "ductile property"), and average Langford The value ((Lankford value)) (hereinafter referred to as "average r value") is large, and the absolute value of the in-plane anisotropy of the r value (hereinafter referred to as "Δr|) is small).

In view of the above, the ferrite-based iron-based stainless steel disclosed in Patent Document 1 is excellent in moldability and wrinkle resistance, and contains, in terms of % by mass, C: 0.02 to 0.06%, Si: 1.0% or less, and Mn: 1.0% or less. P: 0.05% or less, S: 0.01% or less, Al: 0.005% or less, Ti: 0.005% or less, Cr: 11 to 30%, Ni: 0.7% or less, and satisfying 0.06 ≦ (C + N) ≦ 0.12, 1 ≦N/C and 1.5×10 ^-3 ≦(V×N)≦1.5×10 ^-2 (C, N, and V represent the mass % of each element, respectively). However, the anisotropy in Patent Document 1 is not mentioned at all. Further, after hot rolling, it is necessary to perform so-called box annealing (for example, annealing at 860 ° C for 8 hours). Since such a box annealing process involves heating and cooling processes, it takes about one week, and there is a problem of low productivity.

On the other hand, the ferrite-based iron-based stainless steel disclosed in Patent Document 2 is excellent in both workability and surface properties, and is characterized in that it contains, by mass%, C: 0.01 to 0.10%, Si: 0.05. ~0.50%, Mn: 0.05~1.00%, Ni: 0.01~0.50%, Cr: 10~20%, Mo: 0.005~0.50%, Cu: 0.01~0.50%, V: 0.001~0.50%, Ti: 0.001~ 0.50%, Al: 0.01~0.20%, Nb: 0.001~0.50%, N: 0.005~0.050%, and B: 0.00010~0.00500% steel are hot rolled, and then box furnace or AP processing line is used. (annealing and pickling line, annealing and pickling line) continuous furnace, according to the ferrite iron single-phase temperature region to perform hot-rolled sheet annealing, more cold rolling and refined annealing. However, when a box type furnace is used, the productivity is low as in the case of Patent Document 1 described above. Further, Patent Document 2 does not mention at all about the stretchability. When the hot-rolled sheet is annealed in a single-phase temperature region of a continuous annealing furnace, the recrystallization is insufficient because the annealing temperature is low. In the case of box annealing in the single-phase temperature region of the ferrite-grained iron, the stretchability is lowered. Further, in general, the ferrite-based iron-based stainless steel shown in Patent Document 2 generates a crystal grain group (group, colony) having a crystal orientation similar to that at the time of casting or hot rolling, resulting in a problem that |Δr| becomes large.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent No. 3,584,881 (Reissue No. WO00/60134)

Patent Document 2: Japanese Patent No. 3581801 (JP-2001-3134)

The present invention has been made in view of the above problems, and an object thereof is to provide a ferrite-based iron-based stainless steel having sufficient corrosion resistance and excellent formability and a method for producing the same.

In the present invention, the term "sufficient corrosion resistance" refers to a steel plate which is subjected to a polishing process using a #600 rigid sandpaper and then seals the end surface portion, and performs a salt spray cycle test as specified in JIS H 8502. Spray (35 ° C, 5 mass % NaCl, spray 2 h) → dry (60 ° C, relative humidity 40%, 4 h) → wet (50 ° C, relative humidity ≧ 95%, 2 h)) 1 cycle test] At the time of circulation, the rust area ratio (=rust area/total steel plate area × 100 [%]) on the surface of the steel sheet was 25% or less.

In the tensile test according to JIS Z 2241, the tensile elongation at break (El) is 25% or more, and in the tensile test according to JIS Z 2241, the strain is applied at 15% strain. The average Ranke value (hereinafter referred to as "average r value") calculated by the following formula (1) is 0.70 or more, and the in-plane anisotropy of the r value calculated by the following formula (2) ( Hereinafter, the "Δr") absolute value (|Δr|) is 0.20 or less.

Average r value = (r _L + 2 × r _D + r _C ) / 4 (1)

Δr=(r _L -2×r _D +r _C )/2 (2)

Wherein a direction parallel to the direction of the line _L and rolling toward the purposes of the r value r tensile test; r _D r value based implementation of the tensile test at 45 ° toward the direction and rolling direction; r _C toward the line and rolling direction at right angles The r value at the time of the tensile test.

After intensive research to solve the problem, it was found that the steel sheet after hot rolling of the ferrite-based stainless steel for the appropriate composition was used as the two-phase of the ferrite phase and the Worthite iron phase before the cold rolling. When the temperature region is annealed, a ferrite-based iron-based stainless steel having sufficient corrosion resistance and excellent formability can be obtained.

The present invention has been completed based on the above findings, and the gist thereof is as follows.

[1] A ferrite-based iron-based stainless steel containing C: 0.005 to 0.05%, Si: 0.02 to 0.50%, Mn: 0.05 to 1.0%, P: 0.04% or less, and S: 0.01% or less, in terms of mass%. , Cr: 15.5 to 18.0%, Al: 0.001 to 0.10%, N: 0.01 to 0.06%, and the rest are composed of Fe and unavoidable impurities, and El ≧ 25%, average r value ≧ 0.70, and | Δr | ≦ 0.20.

[2] A ferrite-based iron-based stainless steel containing, by mass%, C: 0.01 to 0.05%, Si: 0.02 to 0.50%, Mn: 0.2 to 1.0%, P: 0.04% or less, and S: 0.01% or less Cr: 16.0~18.0%, Al: 0.001~0.10%, N: 0.01~0.06%, and the rest are composed of Fe and unavoidable impurities, El≧25%, average r value ≧0.70 and |Δr|≦0.20.

[3] The ferrite-based stainless steel according to the above [1] or [2], which further contains, in terms of % by mass, from 0.1 to 1.0% of Cu, from 0.1 to 1.0% of Ni, and from 0.1 to 1.0% of Mo. One or two or more of 0.5% and Co: 0.01 to 0.5% are selected.

[4] The ferrite-based iron-based stainless steel according to any one of [1] to [3], further comprising, in terms of % by mass, from V: 0.01 to 0.25%, Ti: 0.001 to 0.10%, Nb: 0.001 to 0.10%, Mg: 0.0002 to 0.0050%, B: 0.0002 to 0.0050%, REM: 0.01 to 0.10%, and Ca: 0.0002 to 0.0020%, one or two or more selected.

[5] A method for producing a ferrite-based iron-based stainless steel, which comprises subjecting a steel preform having the composition described in any one of the above [1] to [4] to hot rolling, and then performing the temperature range of 900 to 1000 ° C. Annealing is performed for 5 seconds to 15 minutes to form a hot rolled annealed sheet, followed by cold rolling, followed by annealing of a cold rolled sheet maintained at a temperature of 800 to 950 ° C for 5 seconds to 5 minutes.

In addition, in this specification, "%" of a steel component all mean "mass %."

According to the present invention, a ferrite-based iron-based stainless steel having sufficient corrosion resistance and excellent formability can be obtained.

Hereinafter, the present invention will be described in detail.

The purpose of the ferrite-grained stainless steel of the present invention is that it can be used for various purposes such as building materials parts, home appliance parts, kitchen appliances, and automobile parts by press working. In order to be suitable for such applications, sufficient formability (stretchability and average r value is large, |Δr| is small) is required.

For example, when a spherical exhaust mask is produced by press-molding, if the stretchability is insufficient, necking or fracture may occur in the direction of the worst stretchability during molding, resulting in failure to form. Further, the thickness of the pressed portion after the forming is greatly different depending on the direction of the steel sheet before forming, and the appearance of the product is deteriorated. Or a large-scale pot manufactured by deep-drawing processing or the like may cause necking and fracture when the average r value is low, and it may not be formed into a predetermined product shape. The thickness of the pan portion of the pan will vary greatly depending on the position, resulting in a poor thermal conductivity. Or when forming by deep drawing, if |Δr| is too large, the edge after molding becomes large, the manufacturing cost increases due to the additional trimming step after forming, and the amount of the steel sheet to be cut is changed. Large, resulting in lower product yield. Accordingly, the stretchability and the average r value are expected to be large, and |Δr| is small. However, generally, if the average r value becomes large, |Δr| also becomes large. Therefore, the inventors conducted in-depth investigations on press-formed products used for various purposes such as building materials, conveyors, home appliances, kitchen appliances, and automobile parts, and found that if both ≧25%, average r value ≧0.70, and | Δr|≦0.20 can be press-formed into a variety of processed products.

Among the ferrite-based stainless steels, SUS430LX (16 mass% Cr-0.15 mass% Ti or 16 mass% Cr-0.4 mass% Nb) and SUS436L (18 mass% Cr-1.0 mass%) according to Japanese Industrial Standard JIS G 4305 Mo-0.25 mass% Ti) or the like contains a large amount of Ti and Nb, and has excellent moldability of both stretchability (El) and average r value, and is used in various applications. However, since these steel types contain a large amount of Ti and Nb, there is a problem that the raw material cost and the manufacturing cost are high and the price is expensive. On the other hand, the production of fat iron-based stainless steel is the most Since SUS430 (16 mass%) is not contained in a large amount of Ti and Nb, it is cheaper than SUS430LX and SUS436L, but its formability is inferior to SUS430LX and SUS436L. Therefore, the demand has been improved by the formability of SUS430.

In the method of obtaining a SUS430 (16 mass%)-based component which does not contain a large amount of Ti and Nb, and the method of the inventors, etc., which satisfies the ferrite-based stainless steel of El≧25%, average r value ≧0.70, |Δr|≦0.20, Conduct in-depth research. Moreover, the method of annealing (hereinafter referred to as "hot-rolled sheet annealing") is performed on the hot-rolled iron-based stainless steel sheet after hot rolling, and is subjected to box annealing (batch annealing) and continuous annealing. In view of not using a box type annealing which requires a long time and low productivity, a high productivity continuous annealing is used to obtain a predetermined formability for review.

A problem with the conventional technique of using a continuous annealing furnace is that since the hot-rolled sheet annealing is carried out in accordance with the single-phase temperature region of the ferrite iron, sufficient recrystallization does not occur, sufficient stretchability cannot be obtained, and the population remains until After the cold rolled sheet is annealed, |Δr| is excessively large. The reason is that the inventor proposed to perform hot-rolled sheet annealing in the two-phase region of the ferrite phase and the Worthfield iron phase, and then perform cold rolling and cold-rolled sheet annealing according to the usual method, and finally become the ferrite iron sheet again. Organization. That is, the annealing of the hot-rolled sheet is carried out according to the two-phase region of the ferrite-rich iron phase which is higher in the single-phase temperature region of the ferrite-rich iron, and promotes the recrystallization of the iron phase of the ferrite, thereby avoiding the cause The ferrite-grained iron crystal grains which are introduced into the processing strain by hot rolling remain until the cold-rolled sheet is annealed, and the stretchability after annealing of the cold-rolled sheet is improved. Moreover, when the Wolster iron phase is formed from the ferrite grain iron phase by the hot-rolled sheet annealing, since the Worthfield iron phase is formed to have a crystal orientation different from that of the ferrite grain before annealing, the ferrite iron can be effectively destroyed. The group of the phase. Therefore, in the cold-rolled annealed sheet metal structure after cold rolling and cold-rolled sheet annealing, the γ-fiber aggregate structure which raises the r value is prosperous, and the group is cut off, and the anisotropy of the metal structure is alleviated, and the obtained |Δr| is excellent in characteristics.

Furthermore, if the hot-rolled annealed sheet containing the granulated iron phase is cold-rolled, since the granulated iron phase is relatively harder than the ferrite-iron phase, the ferrite-phase iron phase near the granulated iron phase preferentially deforms. This leads to the concentration of the rolling strain and increases the recrystallization position when the cold rolled sheet is annealed. Thereby, recrystallization at the time of annealing of the cold-rolled sheet is further promoted, and metal anisotropy after annealing of the cold-rolled sheet is further alleviated.

Furthermore, in detail, the effect of annealing the hot-rolled sheet in the two-phase region was examined in detail for each component, and it was found that even if a large amount of Ti and Nb were not contained, the stretchability (El) was 25% by using an appropriate component. The above, the average r value is 0.70 or more, and the excellent formability of |Δr| is 0.20 or less.

Next, the composition of the ferrite-based iron-based stainless steel of the present invention will be described. Hereinafter, "%" means "% by mass" unless otherwise stated.

C: 0.005~0.05%

The C system has the effect of promoting the formation of the iron phase of the Worthfield and expanding the two-phase temperature region of the ferrite phase and the Worthite iron phase during annealing of the hot rolled sheet. In order to obtain this effect, it must be more than 0.005%. However, when the amount of C exceeds 0.05%, the steel sheet is hardened to cause a decrease in ductility. Therefore, the amount of C is set to be in the range of 0.005 to 0.05%. The lower limit is preferably 0.01%, more preferably 0.015%. The upper limit is preferably 0.035%, more preferably 0.03%, and particularly preferably 0.025%.

Si: 0.02~0.50%

The Si system functions as a deoxidizer when the steel is melted. In order to obtain this effect, it must be more than 0.02%. However, when the amount of Si exceeds 0.50%, the steel sheet is hardened and the rolling load during hot rolling is increased. Moreover, the ductility after annealing of the cold rolled sheet is lowered. Therefore, the amount of Si is set to be in the range of 0.02 to 0.50%. It is preferably in the range of 0.10 to 0.50%. Better 0.25~0.35% range.

Mn: 0.05~1.0%

Similarly to C, the Mn system promotes the formation of the iron phase of the Worthfield, and expands the effect of the two-phase temperature region of the ferrite phase and the Worthite iron phase during the annealing of the hot rolled sheet. In order to obtain this effect, it must be more than 0.05%. However, when the amount of Mn exceeds 1.0%, the amount of MnS produced increases, and the corrosion resistance decreases. Therefore, the amount of Mn is set to be in the range of 0.05 to 1.0%. The lower limit is preferably 0.1%, more preferably 0.2%. The upper limit is preferably 0.8%, more preferably 0.35%, and particularly preferably 0.3%.

P: 0.04% or less

The P system is an element that contributes to the destruction of the grain boundary due to segregation at the grain boundary, so the smaller the better, the upper limit is set to 0.04%. Preferably, it is 0.03% or less. More preferably, it is 0.01% or less.

S: 0.01% or less

The S system is an element that causes a decrease in ductility, corrosion resistance, and the like due to a sulfide system such as MnS. In particular, when the content exceeds 0.01%, such adverse effects may occur remarkably. Therefore, the amount of S is preferably as small as possible, and the upper limit of the amount of S in the present invention is set to 0.01%. More preferably, it is 0.007% or less. Very good is 0.005% or less.

Cr: 15.5~18.0%

The Cr system is an element having a passivation film formed on the surface of the steel sheet to enhance the corrosion resistance effect. In order to obtain this effect, the amount of Cr must be set to 15.5% or more. However, if the amount of Cr exceeds 18.0%, the formation of the Worthite iron phase during the annealing of the hot rolled sheet is insufficient, resulting in no The method obtains the established material properties. Therefore, the amount of Cr is set to be in the range of 15.5 to 18.0%. Preferably, it is in the range of 16.0 to 18.0%. More preferably in the range of 16.0 to 17.25%.

Al: 0.001~0.10%

The Al system belongs to an element having a function as a deoxidizer similarly to Si. In order to obtain this effect, it must be more than 0.001%. However, when the amount of Al exceeds 0.10%, Al-based inclusions such as Al ₂ O ₃ increase, and surface properties are liable to lower. Therefore, the amount of Al is set to be in the range of 0.001 to 0.10%. It is preferably in the range of 0.001 to 0.05%. More preferably in the range of 0.001 to 0.03%.

N: 0.01~0.06%

Similarly to C and Mn, the N system has an effect of promoting the formation of the iron phase of the Worthfield, and expanding the two-phase temperature region of the ferrite phase and the Worthite iron phase when the hot rolled sheet is annealed. In order to obtain this effect, the amount of N must be set to 0.01% or more. However, if the amount of N exceeds 0.06%, the ductility is remarkably lowered, and the corrosion resistance is lowered by the precipitation of the nitride which promotes chromium. Therefore, the amount of N is set to be in the range of 0.01 to 0.06%. It is preferably in the range of 0.01 to 0.05%. More preferably in the range of 0.02 to 0.04%.

The rest are Fe and inevitable impurities.

The effects of the present invention can be obtained by the above composition, and the following elements can be contained for the purpose of improving manufacturability or material properties.

One or two or more selected from the group consisting of Cu: 0.1 to 1.0%, Ni: 0.1 to 1.0%, Mo: 0.1 to 0.5%, and Co: 0.01 to 0.5%.

Both Cu and Ni are elements that enhance corrosion resistance, especially when high corrosion resistance is required. The situation is valid. Further, both Cu and Ni have the effect of promoting the formation of the iron phase of the Worthfield, and expanding the two-phase temperature region of the ferrite phase and the Worthite iron phase when the hot rolled sheet is annealed. These effects are only apparent if they contain more than 0.1%. However, when the Cu content exceeds 1.0%, the hot workability is lowered, which is not preferable. Therefore, when Cu is contained, it is set to 0.1 to 1.0%. It is preferably in the range of 0.2 to 0.8%. More preferably in the range of 0.3 to 0.5%. When the Ni content exceeds 1.0%, the workability is lowered, which is not preferable. Therefore, when Ni is contained, it is set to 0.1 to 1.0%. It is preferably in the range of 0.1 to 0.6%. More preferably in the range of 0.1 to 0.3%.

Mo is an element that enhances corrosion resistance, and is particularly effective when it is required to have high corrosion resistance. This effect is more than 0.1%. However, when the Mo content exceeds 0.5%, the formation of the Worthite iron phase during the annealing of the hot rolled sheet is insufficient, and the predetermined material properties cannot be obtained, which is not preferable. Therefore, when Mo is contained, it is set to 0.1 to 0.5% or less. It is preferably in the range of 0.1 to 0.3%.

Co is an element that enhances toughness. This effect can be obtained by containing more than 0.01%. On the other hand, if the content exceeds 0.5%, the manufacturability is lowered. Therefore, when Co is contained, the content is set to be in the range of 0.01 to 0.5%.

From V: 0.01 to 0.25%, Ti: 0.001 to 0.10%, Nb: 0.001 to 0.10%, Mg: 0.0002 to 0.0050%, B: 0.0002 to 0.0050%, REM: 0.01 to 0.10%, Ca: 0.0002 to 0.0020% Choose one or more of them

V: 0.01~0.25%

V will combine with C and N in steel to reduce solid solution C and N. Thereby increasing the average r value. Further, the precipitation behavior of the nitrogen carbides in the hot rolled sheet is controlled, and the occurrence of linear defects due to hot rolling/annealing is suppressed, and the surface properties are improved. In order to obtain this effect, the amount of V must be 0.01% or more. However, if the amount of V exceeds 0.25%, the workability is lowered and the manufacturing cost is increased. Therefore, the amount of V is set to be in the range of 0.01 to 0.25%. It is preferably in the range of 0.03 to 0.20%. More preferably in the range of 0.05 to 0.15%.

Ti: 0.001 to 0.10%, Nb: 0.001 to 0.10%

Like the V, Ti and Nb are elements having a high affinity with C and N, and are precipitated in the form of carbides or nitrides during hot rolling to lower the solid solution C and N in the parent phase. The workability effect after annealing the cold rolled sheet. In order to obtain such effects, it is necessary to contain 0.001% or more of Ti and 0.001% or more of Nb. However, when the amount of Ti exceeds 0.10% or the amount of Nb exceeds 0.10%, excessive TiN and NbC are precipitated, and good surface properties cannot be obtained. Therefore, when Ti is contained, it is set to a range of 0.001 to 0.10%, and when Nb is contained, it is set to a range of 0.001 to 0.10%. The amount of Ti is preferably in the range of 0.001 to 0.015%. More preferably in the range of 0.003 to 0.010%. The amount of Nb is preferably in the range of 0.001 to 0.025%. More preferably in the range of 0.005 to 0.020%.

Mg: 0.0002~0.0050%

The Mg system is an element having an effect of improving hot workability. In order to obtain this effect, it must be more than 0.0002%. However, if the amount of Mg exceeds 0.0050%, the surface quality is lowered. Therefore, when Mg is contained, it is set in the range of 0.0002 to 0.0050%. Preferably, it is in the range of 0.0005 to 0.0035%. More preferably in the range of 0.0005 to 0.0020%.

B: 0.0002~0.0050%

B is an effective element to prevent embrittlement in low temperature secondary processing. In order to obtain this effect, it must be more than 0.0002%. However, if the amount of B exceeds 0.0050%, hot workability will reduce. Therefore, when B is included, it is set to the range of 0.0002 to 0.0050%. Preferably, it is in the range of 0.0005 to 0.0035%. More preferably in the range of 0.0005 to 0.0020%.

REM: 0.01~0.10%

REM is an element which enhances oxidation resistance, and particularly has an effect of suppressing formation of an oxide film in a welded portion and improving corrosion resistance of a welded portion. In order to obtain this effect, it must be more than 0.01%. However, when the content is more than 0.10%, the manufacturability such as pickling property during annealing of the cold-rolled sheet is lowered. Further, since REM is a high monovalent element, excessive inclusion may cause an increase in manufacturing cost, which is not preferable. Therefore, when REM is included, it is set to the range of 0.01 to 0.10%.

Ca: 0.0002~0.0020%

The Ca system is an effective component for preventing the clogging of the Ti-based inclusions which are likely to occur during continuous casting, resulting in nozzle clogging. In order to obtain this effect, it must be more than 0.0002%. However, when the amount of Ca exceeds 0.0020%, CaS is generated to cause a decrease in corrosion resistance. Therefore, when Ca is contained, it is set in the range of 0.0002 to 0.0020%. Preferably, it is in the range of 0.0005 to 0.0015%. More preferably in the range of 0.0005 to 0.0010%.

Next, a method of producing the ferrite-based iron-based stainless steel of the present invention will be described.

The ferrite-based stainless steel of the present invention is subjected to hot rolling of a steel slab having the above composition, and then subjected to hot-rolled sheet annealing at a temperature ranging from 900 to 1000 ° C for 5 seconds to 15 minutes to form a hot rolled annealed sheet, and then After cold rolling, it can be obtained by annealing the cold rolled sheet at a temperature range of 800 to 950 ° C for 5 seconds to 5 minutes.

First, it is melted by a known method such as a converter, an electric furnace, or a vacuum melting furnace. The molten steel composed of the above components is formed into a steel material (steel blank) by a continuous casting method or an ingot-block method. The steel preform is heated at 1100 to 1250 ° C for 1 to 24 hours, or directly subjected to hot rolling while being left unheated to form a hot rolled sheet.

Second, hot rolling is performed. It is preferable to set the coiling temperature to 500 ° C or more and 850 ° C or less at the time of coiling. If it is less than 500 ° C, the insufficient recrystallization after coiling may cause a decrease in ductility after annealing of the cold rolled sheet, which is not preferable. When the coiling is performed at a temperature exceeding 850 ° C, the particle diameter becomes large, and the skin may be rough during press working. Therefore, the coiling temperature is preferably in the range of 500 to 850 °C.

Then, the hot-rolled sheet is annealed at a temperature of 900 to 1000 ° C which is a two-phase temperature of the iron phase of the ferrite grain and the iron phase of the Vostian, and is maintained for 5 seconds to 15 minutes.

Secondly, pickling is carried out as needed, and cold rolling and cold rolled sheet annealing are performed. Further, as needed, pickling becomes a product.

From the viewpoints of stretchability, bendability, press formability, and shape correction, cold rolling is preferably carried out at a rolling reduction ratio of 50% or more. Further, in the present invention, the cold rolling-annealing may be repeated twice or more.

In order to obtain good formability, the annealing of the cold-rolled sheet is maintained at a temperature of 800 to 950 ° C for 5 seconds to 5 minutes. Further, in order to obtain a more luster, BA annealing (gloss annealing) can be performed.

In addition, in order to further improve the surface properties, grinding, polishing, and the like may be performed.

The reasons for the better limitation of the relevant manufacturing conditions are as follows.

Hot-rolled sheet annealing at 900~1000 °C for 5 seconds to 15 minutes

Hot Rolled Sheet Annealing The present invention is an extremely important step for obtaining excellent formability. If the annealing temperature of the hot rolled sheet is less than 900 ° C, sufficient recrystallization will not be formed and it will become a single phase region of the ferrite iron, and thus the effect of the present invention which is exhibited by the annealing of the two-phase region cannot be obtained. but, If the annealing temperature of the hot rolled sheet exceeds 1000 ° C, the amount of formation of the Worth iron phase is lowered. Therefore, the amount of granules of the granulated iron produced by the annealing of the hot rolled sheet is reduced, and the cold rolling of the metal structure containing the ferrite phase and the granulated iron phase is not sufficiently obtained, and the strain is concentrated due to the rolling strain. The iron phase of the ferrite in the vicinity of the iron phase of the Ma Tian caused the anisotropy of the metal structure, resulting in the inability to obtain the established |Δr|. If the annealing time is less than 5 seconds, even if annealing is performed at a predetermined temperature, the formation of the iron phase of the Worth and the recrystallization of the iron phase of the ferrite are not sufficiently obtained, and the desired formability cannot be obtained. On the other hand, if the annealing time exceeds 15 minutes, a part of the chromium carbide will be solid solution, which will promote the concentration of C in the iron phase of the Vostian, resulting in the transformation of the iron phase by the Worthfield after the annealing of the hot rolled sheet. Excessive C concentration in the generated granulated iron phase. When the cold-rolled sheet is annealed, the granulated iron phase decomposes into a carbide-fat iron phase, causing a change to a ferrite-rich iron phase containing a large amount of carbide. Thereby, the metal structure after annealing of the cold-rolled sheet becomes a ferrite-grained iron grain which is a ferrite-grain-phase factor in the annealing of the hot-rolled sheet, and has less carbides in the grain and the grain boundary, and because When the hot-rolled sheet is annealed, it belongs to the iron phase of the Vostian, and thus the mixed structure of the ferrite-rich iron particles in the grains and on the grain boundaries is excessive. If it is such a metal structure, since the crystal grains with less carbides and the more crystal grains may have a hardness difference, deformation strain concentration occurs at the interface between the crystal grains at the time of forming, resulting in easy grain boundary The carbides act as a starting point to promote pore formation, resulting in reduced ductility. Therefore, the hot-rolled sheet annealing is maintained at a temperature of 900 to 1000 ° C for 5 seconds to 15 minutes. It is preferably maintained at a temperature of 910 to 960 ° C for 15 seconds to 3 minutes.

Cold rolled sheet annealing at 800~950 °C for 5 seconds to 5 minutes

Cold-rolled sheet annealing belongs to the two-phase structure of the ferrite-iron phase formed by annealing the hot-rolled sheet and the granulated iron phase, forming an important step of the ferrite-iron single-phase structure. If the annealing temperature of the cold-rolled sheet is less than 800 ° C, recrystallization does not occur sufficiently, and the predetermined ductility and the average r value cannot be obtained. On the other hand, when the annealing temperature of the cold rolled sheet exceeds 950 ° C, if the temperature is The steel composition of the two-phase temperature region of the ferrite phase and the Worthite iron phase is formed by the annealing of the cold-rolled sheet, which results in the hardening of the steel sheet and the inability to obtain the desired ductility. Further, since this temperature becomes a steel component in the single-phase temperature region of the ferrite-rich iron, the crystal grain is remarkably coarsened, and the gloss of the steel sheet is lowered, so that the surface quality is not preferable. When the annealing time is less than 5 seconds, even if the annealing is performed at a predetermined temperature, the recrystallization of the ferrite iron phase does not sufficiently occur, and thus the predetermined ductility and the average r value cannot be obtained. When the annealing time exceeds 5 minutes, the crystal grains are significantly coarsened, and the gloss of the steel sheet is lowered, so that the viewpoint of surface quality is not preferable. Therefore, the cold rolled sheet annealing is maintained in the range of 800 to 950 ° C for 5 seconds to 5 minutes. Preferably, it is maintained at 850 ° C ~ 900 ° C for 15 seconds ~ 3 minutes.

[Example 1]

Hereinafter, the present invention will be described in detail using an embodiment.

A stainless steel pot having the chemical composition shown in Table 1 was melted using a 50 kg small vacuum melting furnace. These steel blocks were heated at 1150 ° C for 1 hour, and then hot rolled to form a hot rolled sheet having a thickness of 3.5 mm. Next, the hot-rolled sheets were annealed by hot-rolled sheets according to the conditions described in Table 2, and then the surface was subjected to bead blasting treatment and derusting by pickling. Further, after cold rolling was performed until the thickness of the sheet was 0.7 mm, the cold-rolled sheet was annealed according to the conditions described in Table 2, and then subjected to descaling treatment by pickling to obtain a cold-rolled pickling-annealed sheet.

The following evaluation was performed on the cold-rolled pickling annealed sheet obtained in this manner.

(1) Ductility evaluation

The JIS 13B tensile test piece was taken from the cold-rolled pickling-annealed sheet in the L direction (parallel direction in the rolling direction), the D direction (45° direction in the rolling direction), and the C direction (the direction perpendicular to the rolling direction). Then, according to JIS Z2241, a tensile test was carried out, and the tensile elongation was measured. When the tensile elongation in each direction was 25% or more, it was evaluated as "qualified (○)", as long as one of the directions was not If it is 25%, it will be rated as "failed (×)".

(2) Evaluation of average r value and |Δr|

JIS 13B tensile test piece was taken from the cold-rolled pickling annealed sheet in the parallel (L direction), 45° (D direction) and right angle (C direction) directions of the rolling direction, and the tensile test was performed according to JIS Z2241 until strain 15% is interrupted, the r value in each direction is measured, and the average r value [=(r _L +2r _D +r _C )/4] and the plane anisotropy of the r value are calculated [Δr=(r _L -2r _D +r _C )/2] absolute value (|Δr|). Here, r _L , r _D , and r _C are r values in the L direction, the D direction, and the C direction, respectively. If the average r value is 0.70 or more, it is rated as "qualified (○)", and if it is less than 0.70, it is rated as "failed (×)". If |Δr| is less than 0.20, it is rated as "acceptable (○)", and if it exceeds 0.20, it is rated as "failed (x)".

(3) Evaluation of corrosion resistance

A 60 mm × 100 mm test piece was taken from the cold-rolled pickling annealed sheet, and the surface was subjected to a polishing process using #600 emery paper, and a test piece having a sealed end portion was prepared to provide a salt spray cycle test prescribed in JIS H 8502. The salt spray cycle test was carried out with salt spray (5 mass% NaCl, 35 ° C, spray 2 h) → dry (60 ° C, 4 h, relative humidity 40%) → wet (50 ° C, 2 h, relative humidity ≧ 95%) for 1 cycle , the implementation of 8 cycles.

The photograph was taken on the surface of the test piece after 8 cycles of the salt spray test, and the rust area on the surface of the test piece was measured by image analysis, and the rust area ratio was calculated from the ratio of the total area of the test piece ((in the test piece) Rust area / total area of test piece) × 100 [%]). The rust area ratio of 10% or less is particularly excellent in corrosion resistance, and it is rated as "eligible (?)". More than 10% and 25% or less are rated as "qualified (○)", and more than 25% are rated as "unqualified ( ×)".

The evaluation results of the combined hot-rolled sheet annealing and cold-rolling annealing conditions are shown in Table 2.

In the steel composition and the production method, No. 1 to 14, 20 to 30, and 40 to 52 which satisfy the scope of the present invention, it was confirmed that the tensile elongation at break was 25% or more, the average r value was 0.70 or more, and |Δr| was 0.20 or less. Formability. Further, the relevant corrosion resistance is also a good characteristic in which the rust area ratio of the surface of the test piece is 25% or less after 8 cycles of the salt spray test.

In particular, Ni contains 0.4% of steel D and AC, Cu contains 0.3% of steel F, Cu contains 0.4% of steel AR, Mo contains 0.3% of steel G, and No. 4 and No. 22 corresponding to steel AI. No. 6, No. 50, No. 7, and No. 41, the rust area ratio after the salt spray circulation test was 10% or less, or the corrosion resistance was further improved.

On the other hand, in No. 15 in which the Cr content is lower than the range of the present invention, a predetermined ductility, an average r value, and |Δr| can be obtained, but since the Cr content is insufficient, a predetermined corrosion resistance cannot be obtained.

No. 16 having a Cr content higher than the range of the present invention can obtain sufficient corrosion resistance. However, since Cr is excessively contained, the Worstian iron phase is not formed during annealing of the hot rolled sheet, resulting in failure to obtain a predetermined average r. Value and |Δr|.

No. 17 having a C amount higher than the range of the present invention can obtain a predetermined average r value and |Δr|, but since the amount of solid solution C is increased, the strength of the steel sheet is remarkably improved, resulting in failure to obtain a predetermined ductility.

On the other hand, the amount of C is lower than No. 18 in the range of the present invention, because the iron phase stability of the Worth field caused by C is insufficient, so that a sufficient amount of the Worthfield iron phase is not generated in the hot-rolled sheet annealing, resulting in The given average r value and |Δr| cannot be obtained.

The hot-rolled sheet annealing temperature is 875 ° C or 871 ° C low temperature No. 19 or No. 35, because the hot-rolled sheet annealing temperature becomes the ferrite-iron single-phase temperature, resulting in the Worstian iron phase, thus the heat After the annealing of the rolled sheet, no granulated iron phase will be formed, resulting in failure to obtain The steel sheet containing the granulated iron is subjected to cold rolling to obtain an anisotropic effect of a predetermined metal structure, so that a predetermined |Δr| cannot be obtained. The hot-rolled sheet annealing temperature is 1014 ° C or 1011 ° C, the high temperature of No. 31 or No. 36, the amount of Worstian iron phase generated in the annealing temperature is reduced, the hot field is annealed after the hot rolled sheet The amount of loose iron phasor is reduced, so that the effect of mitigating the anisotropy of a predetermined metal structure caused by subsequent cold rolling cannot be obtained, resulting in failure to obtain a predetermined |Δr|. The hot-rolled sheet annealing time is No. 32 and No. 37 of the short time of 1 second, because the formation of the iron phase of Vostian does not generate sufficient recrystallization, and thus the obtained ductility, average r value, and |Δr cannot be obtained. |. No. 33 and No. 38, which have a cold-rolled sheet annealing temperature of 780 ° C, are not sufficiently recrystallized, and the processed structure due to cold rolling remains, and as a result, a predetermined ductility and an average r value cannot be obtained. No.34 and No.39, which have a cold-rolled sheet annealing temperature of 960 °C, will regenerate the Worthfield iron phase when the cold-rolled sheet is annealed. After the cold-rolled sheet is annealed, the Worthite iron phase will be transformed into The iron phase of Ma Tian, resulting in the apparent hardening of the steel plate, led to the inability to obtain the established ductility. Further, since the microstructure after annealing of the cold-rolled sheet contains the granulated iron phase, the r value is lowered, and a predetermined average r value cannot be obtained.

From the above, it is known that both the steel component and the production method are required to satisfy the scope of the present invention in order to obtain the desired formability provided by the present invention.

(industrial availability)

The ferrite-based iron-based stainless steel obtained by the present invention is particularly suitable for a press-formed product mainly composed of deep drawing, and is required for high corrosion resistance (for example, building materials, conveying equipment, and automobile parts).

Claims (5)

A ferrite-based iron-based stainless steel containing C: 0.005 to 0.05%, Si: 0.02 to 0.50%, Mn: 0.05 to 1.0%, P: 0.04% or less, S: 0.01% or less, and Cr: 15.5~18.0%, Al: 0.001~0.10%, N: 0.01~0.06%, the rest are composed of Fe and unavoidable impurities, El≧25%, average r value ≧0.70 and |Δr|≦0.20. A ferrite-based iron-based stainless steel containing C: 0.01 to 0.05%, Si: 0.02 to 0.50%, Mn: 0.2 to 1.0%, P: 0.04% or less, S: 0.01% or less, and Cr: 16.0~18.0%, Al: 0.001~0.10%, N: 0.01~0.06%, the rest are Fe and unavoidable impurities, El≧25%, average r value ≧0.70 and |Δr|≦0.20. The ferrite-based iron-based stainless steel according to the first or second aspect of the patent application, wherein, in terms of % by mass, further contains from 0.1 to 1.0% of Cu, 0.1 to 1.0% of Ni, 0.1 to 1.0% of Mo, and 0.1 to 0.5% of Mo: One or two or more of 0.01 to 0.5% are selected. The ferrite-based iron-based stainless steel according to any one of claims 1 to 3, wherein, in terms of % by mass, further comprises from V: 0.01 to 0.25%, Ti: 0.001 to 0.10%, and Nb: 0.001 to 0.10. %, Mg: 0.0002 to 0.0050%, B: 0.0002 to 0.0050%, REM: 0.01 to 0.10%, and Ca: 0.0002 to 0.0020%, one or two or more selected. A method for producing a ferrite-based iron-based stainless steel, which comprises subjecting a steel preform having the composition of any one of claims 1 to 4 to hot rolling, and then performing a temperature range of 900 to 1000 ° C for 5 seconds to 15 seconds. Annealing is performed for a minute to form a hot rolled annealed sheet, and then cold rolling is performed, followed by annealing of a cold rolled sheet maintained at a temperature of 800 to 950 ° C for 5 seconds to 5 minutes.