KR101712333B1 - Ferritic stainless steel sheet with excellent blanking workability and process for manufacturing same - Google Patents

Abstract

One form of the ferritic stainless steel sheet is a ferritic stainless steel sheet which contains 0.016% or less of C, 1.0% or less of Si, 1.0% or less of Mn, 0.010 to 0.035% of P, 0.005% or less of S, , N: not more than 0.018%, Cr: 15.6 to 17.5%, Cu: 0.10 to 0.50%, Sn: 0.01 to 0.3%, Ti: 0.05 to 0.30%, Nb: 0.05 to 0.40%, Mo: And Ni: 0.05 to 0.50%, the balance being Fe and inevitable impurities, the Cu concentration of the surface of the steel sheet being 15% or more in terms of the cation fraction, and the ferrite grain size being 30 탆 or less.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a ferritic stainless steel sheet excellent in punching workability and a method of manufacturing the ferritic stainless steel sheet.

The present invention relates to a ferritic stainless steel sheet excellent in punching workability, which is used for kitchen appliances, domestic appliances, coins, containers, and the like, and a manufacturing method thereof.

The present application claims priority based on Japanese Patent Application No. 2013-062077 filed on March 25, 2013, and Japanese Patent Application No. 2013-067972 filed on March 28, 2013 , Its contents are used here.

The ferritic stainless steel sheet is excellent in design and corrosion resistance, and is used for various purposes such as buildings, transportation equipment, household electric appliances, and kitchen utensils. This product (structure) is usually manufactured by cutting, forming, and joining a steel sheet. In the cutting, usually the shearing is performed due to the high productivity, but at this time, so-called " burrs " In the case where the burr is large, even if the "burr" part is caught inside the apparatus when the cut article is automatically charged into the press apparatus, and if the load can be inserted or inserted, a gap due to "burr" There is a possibility that a problem such as the occurrence of a lock may occur. Particularly, the ferritic stainless steel sheet tends to be large in this "burr", which has been an obstacle in terms of expanding the use of the ferritic stainless steel sheet.

For example, Patent Document 1 discloses a technique of eliminating recrystallization of a hot-rolled sheet, which is a cause of roving (also called ridging), which is a surface irregular defect, by properly combining chemical components and hot-rolled coiling temperature. This technique suppresses the content of C, P and S forming FeTiP, Ti ₄ C ₂ S _{2 and} TiC as precipitates in steel, and cools the precipitates by winding the steel sheet after hot rolling at a high temperature . However, the steel sheet obtained by this technique has a problem that the formability and rust-proofing property are improved, but the amount of precipitate to be a starting point of fracture at the time of shearing is small, so that the burr at the time of shearing is large.

Patent Document 2 discloses a ferritic stainless steel excellent in stretch formability by regulating the amount of the employed elements and coarsening of precipitates and coarsening of crystal grains, and a method for producing the ferritic stainless steel. However, the steel sheet obtained by this technique has a problem that the burr is large because the ferrite particles are large and the deformed ferrite particles directly form burrs on the front end face.

Patent Document 3 discloses a ferritic stainless steel sheet having excellent workability and corrosion resistance by addition of a sufficient amount of Ti while reducing the amount of TiO _{2 and} Al ₂ O ₃ which cause surface flaws and further having less surface scratches . However, the steel sheet obtained by this technique also has a problem that the ferrite grain size is large and the amount of intervening material which is a starting point of fracture is small, so that a large burr is generated due to shearing.

Patent Document 4 discloses that FeTiP is appropriately dispersed in steel to cause cracking at the time of shearing with FeTiP as a starting point and to reduce the ferrite grain size to 30 μm or less to suppress deformation of the soft fracture portion at the time of shearing And the yield ratio is set to 0.65 or more, the work hardening is suppressed to a small extent and the deformation of the ferrite particles to the fracture is suppressed. However, there is a problem in this technology that existing FeTiP accelerates the wear of shear tools and shortens tool life.

Japanese Patent Application Laid-Open No. 10-204588 Japanese Patent Application Laid-Open No. 2002-249857 Japanese Patent Application Laid-Open No. 2002-012955 Japanese Patent Application Laid-Open No. 2008-308705

An object of the present invention is to provide a ferritic stainless steel sheet excellent in corrosion resistance and also excellent in punching workability which could not be sufficiently improved in the prior art, and a method for producing the ferritic stainless steel sheet.

With regard to the first aspect of the present invention, the inventors conducted a punching test using various ferritic stainless steel sheets, investigated the occurrence status of burrs generated during machining and the surface of a tool used for punching in detail.

As a result, the following points were found.

(a) The surface of the steel sheet is to be thickened with an appropriate amount of Cu.

(b) The burr height should be kept small only when the mean ferrite grain size of the steel sheet is 30 탆 or less.

Namely, the present inventors have found the following facts, thereby completing the present invention.

(a ') By appropriately thickening Cu on the surface of the steel sheet, the lubrication effect at the time of contact with the punching tool at the time of shearing is expressed, and the starting point crack is stably generated.

(b ') By reducing the ferrite grain size to 30 μm or less, deformation of the soft fracture portion at the time of shearing is suppressed. This is effective in reducing the burr size and also in extending the tool life.

The gist of the first aspect of the present invention is as follows.

(1) A steel comprising (1) 0.016 mass% or less of C, 1.0 mass% or less of Si, 1.0 mass% or less of Mn, 0.010 to 0.035 mass% of P, 0.005 mass% or less of S, 0.50 mass% or less of Al, Ti: 0.05 to 0.30 mass% or less, Nb: 0.05 to 0.40 mass%, Mo: 0.1 to 0.5 mass%, Cr: 15.6 to 17.5 mass%, Cu: 0.10 to 0.50 mass%, and Sn: 0.01 to 0.3 mass% 0.05 to 0.50 mass% and Ni: 0.05 to 0.50 mass%, the balance being Fe and inevitable impurities, the Cu concentration on the surface of the steel sheet being 15% or more in terms of cation fraction, A ferritic stainless steel sheet excellent in punching workability with a grain size of 30 탆 or less.

(2) The steel according to any one of (1) to (3), further comprising, by mass%, 0.001 mass% or less of B, 0.50 mass% or less of V, 0.50 mass% or less of W, 0.50 mass% or less of Co, 0.01 mass% or less of Mg, At least one selected from the group consisting of 0.30 mass% or less of Zr, 0.02 mass% or less of REM (rare earth metal), 0.50 mass% or less of Ta, 0.001 to 0.3 mass% of Sb and 0.0002 to 0.1 mass% of Ga 1]. ≪ / RTI >

(3) A slab of a steel having the composition described in the item (1) or (2) is heated to 1100 占 폚 or higher, followed by hot rolling at a finishing rolling finish temperature of 900 占 폚 or higher, Annealing the hot rolled sheet at 800 to 950 占 폚, acid washing, cold rolling, and finally annealing at a temperature of 820 占 폚 to 950 占 폚 and at an oxygen concentration of 1% or more, And cooling at a cooling rate of 30 占 폚 / s or higher in a temperature range of up to 600 占 폚 is carried out, is excellent in punching workability.

With regard to the second aspect of the present invention, the inventors conducted a punching test using various types of ferritic stainless steel sheets, investigated the occurrence of burrs occurring at the time of machining and the surface of a tool used for punching in detail.

As a result, the following points were found.

(c) Cu is concentrated on the surface of the steel sheet in an appropriate amount.

(d) The burr height shall be kept small only when the mean ferrite grain size of the steel sheet is 30 탆 or less and the surface hardness HV1 satisfies 140 to 180.

Namely, the present inventors have found the following and completed the present invention.

(c ') By appropriately thickening Cu on the surface of the steel sheet, the lubrication effect at the time of contact with the punching tool at the time of shearing is expressed, and the starting point crack is stably generated.

(d ') By reducing the ferrite grain size to 30 占 퐉 or less and setting the surface hardness HV1 to 140 to 180, the viscous deformation of the soft fracture portion at the time of shearing is suppressed. This is effective in reducing the burr size and also in extending the tool life by suppressing the abrasion.

The gist of the second aspect of the present invention is as follows.

(4) A steel comprising: 0.020 mass% or less of C, 0.80 mass% or less of Si, 1.0 mass% or less of Mn, 0.010 to 0.035 mass% of P, 0.005 mass% or less of S, 0.50 mass% or less of Al, Ti: 0.05 to 0.30 mass% or less, Nb: 0.05 to 0.40 mass%, and Ni: 0.005 to 0.5 mass%, Cr: 15.6 to 17.5 mass%, Cu: 0.50 to 2.00 mass%, and Sn: 0.001 to 0.1 mass% 0.05 to 0.50 mass%, the balance being Fe and inevitable impurities, the Cu concentration of the surface of the steel sheet being 15% or more as a cationic fraction, the ferrite grain size being 30 탆 or less, the surface hardness Of 140 to 180. The ferritic stainless steel sheet according to claim 1,

(5) The steel according to any one of (1) to (5), further comprising, by mass%, Mo: 0.01 to 0.50 mass%, B: 0.001 mass% or less, V: 0.50 mass% or less, W: 0.50 mass% 0.003 mass% or less of Ca, 0.30 mass% or less of Zr, 0.02 mass% or less of REM (rare earth metal) and 0.50 mass% or less of Ta, 0.001 to 0.3 mass% of Sb and 0.0002 to 0.1 mass% of Ga Wherein the ferrite-based stainless steel sheet has excellent punching workability as set forth in (4).

(6) A slab of a steel having the composition described in (4) or (5) above is heated to a temperature of 1100 占 폚 or higher, followed by hot rolling at a finish rolling temperature of 80 to 90% The hot-rolled sheet is annealed, pickled, cold-rolled, and then heat-treated at a temperature of from 850 캜 to 950 캜 and at an oxygen concentration of 1% or more And then cooling is performed at a cooling rate of 50 占 폚 / s or more in a temperature range of up to 500 占 폚. The method of producing a ferritic stainless steel sheet excellent in punching workability.

According to the first and second aspects of the present invention, it is possible to provide a ferritic stainless steel sheet excellent in corrosion resistance and also excellent in punching workability and a method of manufacturing the ferritic stainless steel sheet. Therefore, according to the present invention, the use of the ferritic stainless steel sheet can be expanded.

1 is a graph showing the relationship between the surface layer Cu concentration and the burr height of the ferritic stainless steel sheet of the first embodiment.
2 is a graph showing the relation between the ferrite grain size and the burr height at the 20th time of the ferritic stainless steel sheet of the first embodiment.
Fig. 3 is a graph showing an example of measurement of the surface layer Cu concentration of the ferritic stainless steel sheet of the first embodiment, and is a graph showing the relationship between the Cu concentration and the distance from the outermost layer. Fig.
4 is a diagram showing the relationship between the surface layer Cu concentration and the burr height at the 20th time of the ferritic stainless steel sheet of the second embodiment.
5 is a diagram showing the relationship between the ferrite grain size and the burr height at the 20th time of the ferritic stainless steel sheet of the second embodiment.
Fig. 6 is a graph showing an example of measurement of the surface layer Cu concentration of the ferritic stainless steel sheet of the second embodiment, and is a graph showing the relationship between the Cu concentration and the distance from the outermost layer. Fig.

(First Embodiment)

The composition of the ferritic stainless steel sheet according to the first embodiment will be described. The unit% representing the content of the element means% by mass.

(C: 0.016 mass% or less)

C forms Cr carbide and causes sensitization. Therefore, in the present embodiment, Ti or Nb is added and C is fixed by forming a carbide. TiC has a function of promoting work hardening by precipitation strengthening of steel finely. However, if the content of C exceeds 0.016 mass%, it is necessary to add a large amount of Ti, so the content of C is 0.016 mass% or less. It is preferably 0.012 mass% or less. From the viewpoint of avoiding deterioration such as corrosion resistance by C, the content is preferably as small as possible, but excessive reduction of C amount leads to increase of refining cost, so that it is preferable to be 0.001% by mass or more. In consideration of the production cost and the like, the content is preferably 0.002 mass% to 0.009 mass%.

(Si: 1.0 mass% or less)

Si is a solid solution strengthening element, hardens the steel and lowers the ductility. If the ductility is lowered, the deformation capability at the time of punching failure is lowered. As a result, the area of the punching condition which is stable at the position where the burr height is low is narrow, and the burr height becomes remarkably large as the number of times of punching increases. Further, since Si has characteristics that are easily oxidized, Si is concentrated in the oxide scale depending on the heat treatment conditions, and the descaling property is lowered. As a result, it is necessary to increase the amount of lapping at the final descale. Excessive scraping results in the sputtering of the thickened Cu layer in the surface layer, which is unsuitable in this embodiment. Therefore, in this embodiment, it is necessary to make the Si content 1.0 mass% or less. The amount of Si is preferably 0.50% by mass or less, and more preferably 0.25% by mass or less. In addition, Si is an element which may be added as a deoxidizing element. In view of production costs and the like, the amount of Si is preferably set to 0.01 mass% or more.

(Mn: 1.0 mass% or less)

Mn is an element which deteriorates corrosion resistance and is also an element constituting MnS. A large amount of MnS is precipitated, or MnS is coarsened, and punching workability is deteriorated. MnS is precipitated in a ferrite grain boundaries to form ferrite grains as expansion grains, thereby increasing burrs during punching processing. Therefore, in the present embodiment, it is necessary to make the Mn content 1.0 mass% or less. The Mn content is preferably 0.50 mass% or less, and more preferably 0.30 mass% or less. Further, Mn is an element which may be added as a deoxidizing element, and it is preferable to set it to 0.01% by mass or more in view of production cost and the like.

(P: 0.010 to 0.035% by mass)

P has an action of forming FeTiP to promote the occurrence of cracks and progress in punching, and to reduce the height of burrs. This effect is exhibited by containing P in an amount of 0.010 mass% or more.

However, if it is added in an amount exceeding 0.035 mass%, it will lead to embrittlement of the material, so the amount of P will be 0.035 mass% or less. And preferably 0.020 to 0.025 mass%.

(S: 0.005 mass% or less)

S forms MnS or TiS so as to suppress the ferrite particles from being equalized, and promotes new telephone calls, thereby promoting occurrence of burrs. In order to prevent this phenomenon, the S content is required to be 0.005 mass% or less. It is preferably 0.003 mass% or less. However, an excessive reduction leads to an increase in refining costs, so it is preferable to set the S content to 0.0001 mass% or more.

(Al: 0.50 mass% or less)

Al is a component to be added as a deoxidizer, and in order to improve the cleanliness of steel, it is preferable to add Al in an amount of 0.02 mass% or more. However, when Al is added in a large amount, AlN is precipitated to promote softening of the ferrite particles, which causes the ferrite particles to expand in the rolling direction. Therefore, in the present embodiment, the Al content is 0.50 mass% or less. It is preferably 0.10 mass% or less. In addition, Al may be added as a deoxidizing element in some cases, and the high-temperature strength and oxidation resistance are improved. Since the action is expressed from 0.01 mass%, the amount of Al is preferably 0.01 mass% or more.

(N: 0.018 mass% or less)

N is an element that tends to form TiN by binding with Ti. Particularly, when the N content exceeds 0.018 mass%, a large amount of coarse rectangular TiN precipitates in the steel to cause surface scratches on the steel sheet. Therefore, the N content is 0.018 mass% or less. It is preferably 0.008 to 0.014 mass% or less.

(Cr: 15.6 to 17.5% by mass)

Cr is an important element for forming a passive film on the surface of stainless steel and improving the corrosion resistance. In order to maintain the corrosion resistance of the end face, it is necessary to contain not less than 15.6 mass%. However, if it exceeds 17.5 mass%, the hardening by Cr becomes remarkable, the work hardening coefficient is lowered, and the ferrite particles are liable to elongate in the punching direction, so that the burr becomes larger. Therefore, the Cr content is set to 17.5 mass% or less. Preferably, it is in the range of 16.0 to 17.3 mass%.

(Cu: 0.10 to 0.50% by mass)

Cu acts to reduce the friction with the punching tool by concentrating on the surface of the steel sheet, and thus plays an important role in this embodiment. By adding Sn at 0.10 mass% or more, Cu concentration on the surface of the steel sheet is stabilized, burr is reduced, and tool wear is suppressed. On the other hand, if it is added in an amount exceeding 0.50% by mass, hardness is increased due to solid solution strengthening, and Cu is precipitated by intergranular precipitation to easily embrittle the ferrite particles. Therefore, the amount of Cu is 0.50 mass% or less. It is preferably 0.10 to 0.30 mass% or less.

(Sn: 0.01 to 0.30% by mass)

Sn is an important element in this embodiment because it exerts an effect of accelerating the concentration of Cu on the surface of the steel sheet when it coexists with Cu. The effect of accelerating surface enrichment of Cu by the coexistence of Sn and Cu is exhibited by adding Sn in an amount of 0.01 mass% or more. However, Sn is also an element for solid solution strengthening, and when it is added in excess, the work hardening constant increases, so that the amount of Sn is 0.3 mass% or less. Sn is also an element that improves corrosion resistance. The effect of improving the corrosion resistance is exhibited at 0.03 mass% or more. Therefore, it is preferable that Sn is in the range of 0.03 to 0.25 mass%. More preferably, it is in the range of 0.10 to 0.20 mass%.

The steel sheet of the present embodiment further contains at least one selected from Ti: 0.05 to 0.30 mass% or less, Nb: 0.05 to 0.40 mass%, Mo: 0.05 to 0.50 mass% or less and Ni: 0.05 to 0.50 mass% .

(Ti: 0.05 to 0.30 mass%)

Ti combines with C, N, and S to form carbides, nitrides, and sulfides. When the amount of Ti is 0.05 mass% or more, the effect of fixing these elements is exhibited. Therefore, it is necessary to add Ti at 0.05 mass% or more. On the other hand, if the amount of Ti exceeds 0.30 mass%, a large amount of TiN precipitates and scratches the surface of the steel sheet. Therefore, the amount of Ti is set to 0.30 mass% or less.

Preferably, the amount of Ti is in the range of 0.08 to 0.20 mass%. More preferably, the amount of Ti is 0.08 to 0.15 mass%.

(Nb: 0.05 to 0.40 mass%)

Nb is an element improving moldability and corrosion resistance. Moldability and corrosion resistance are improved by adding 0.05 mass% or more of Nb. On the other hand, excessive addition of Nb causes problems such as surface scratches and gloss unevenness, and deterioration of ductility. Therefore, Nb is set in the range of 0.05 to 0.40 mass%. Further, considering the preparation and ductility, the amount of Nb is preferably in the range of 0.10 to 0.30 mass%.

(Mo: 0.05 to 0.50% by mass)

Mo is an element for improving the corrosion resistance and is preferably added in applications where corrosion resistance is required. By adding Mo at 0.05 mass% or more, an effect of improving the corrosion resistance is developed. On the other hand, an excessive amount of Mo causes deterioration of moldability, particularly ductility. Therefore, it is preferable that the content is in the range of 0.05 to 0.50 mass%. Further, it is more preferably in the range of 0.05 to 0.20 mass% in consideration of the composition of the steel sheet and the strength of the steel sheet. The Mo content is more preferably in the range of 0.05 to 0.10 mass%.

(Ni: 0.05 mass% or more and 0.5 mass% or less)

Ni is an element that improves corrosion resistance, but adding Ni in a large amount causes hardening of steel and deterioration of ductility. therefore. The Ni content is 0.5% by mass or less. It is preferably 0.25 mass% or less. When Ni is added, 0.05 mass% or more of Ni is preferably added in order to sufficiently exhibit the effect of improving the corrosion resistance. More preferably, it is 0.10% by mass or more.

In the present embodiment, if necessary, the following elements may be contained.

(B: 0.001 mass% or less)

B is an element segregating at grain boundaries to increase the grain boundary strength, and stabilizes the end face property at the time of punching. However, an excessive amount of B is added to form a low melting point boride, and the hot workability is remarkably lowered. Therefore, when B is added, it is added in a range of 0.001 mass% or less. In order to stably obtain the effect of B, the amount of B is preferably 0.0002 mass% or more, and more preferably 0.0003 mass% or more.

(Co: 0.50 mass% or less)

Co, like Ni, is an element that improves corrosion resistance, but when added in a large amount, it hardens the steel and causes deterioration in ductility. Therefore, the Co content is 0.50 mass% or less. The amount of Co is preferably 0.1 mass% or less. In order to stably obtain the effect of Co, the amount of Co is preferably 0.005 mass% or more, and more preferably 0.01 mass% or more.

(V, W: 0.50 mass% or less)

V and W, like Ti, combine with C to form a carbide. If the addition amount of V or W exceeds 0.50 mass%, precipitation of TiN is promoted and scratches on the surface of the steel sheet are caused. Therefore, when V and W are added, the amount is preferably 0.50 mass% or less, more preferably 0.10 mass% or less, and further preferably 0.05 mass% or less. In order to stably obtain the effect of V and W, the amounts of V and W are preferably 0.005 mass% or more, and more preferably 0.01 mass% or more.

(Mg: 0.01 mass% or less)

Mg is a component added as a deoxidizer. However, when added in a large amount, it is precipitated as MgO, which is a cause of clogging of the nozzle at the time of steelmaking. Therefore, in the present embodiment, the amount of Mg is 0.01 mass% or less, more preferably 0.002 mass% or less. In order to stably obtain the effect of Mg, the amount of Mg is preferably 0.0001 mass% or more, and more preferably 0.0003 mass% or more.

(Ca: 0.01 mass% or less)

Ca is a component added as a deoxidizer. However, when Ca is added in a large amount, it precipitates as CaO or CaS, which causes rust. Therefore, in the present embodiment, Ca is set to 0.01 mass% or less. In order to stably obtain the effect of Ca, the amount of Ca is preferably 0.0001 mass% or more, and more preferably 0.0003 mass% or more.

(Zr: 0.30 mass% or less)

Zr, like Nb and Ti, forms carbonitride to inhibit the formation of Cr carbonitride and improve corrosion resistance, so that Zr is added at 0.01% by mass or more, if necessary. If the amount of the additive is more than 0.30 mass%, the effect is saturated, which may cause surface scratches due to formation of a large oxide, and therefore, the additive is added in an amount of 0.01 to 0.30 mass%. The upper limit value is more preferably 0.20 mass%. Ti, and Nb, it is preferably 0.02 mass% to 0.05 mass% in view of the production cost.

[REM (rare earth metal): 0.02 mass% or less]

REM (rare-earth metal) is an element for increasing the grain boundary strength like B and stabilizes the end face property at the time of punching, but its action saturates to 0.02 mass%. Therefore, the amount of REM (total amount of rare earth metals) is set to 0.02 mass% or less. It is preferable to set the lower limit of the REM amount to 0.002 mass%. REM (rare earth element) refers to a generic term of 15 elements (lanthanoids) from scandium (Sc) and yttrium (Y) and lanthanum (La) to lutetium (Lu) according to a general definition. May be added singly or in a mixture.

(Ta: 0.50 mass% or less)

Ta is an element which improves high temperature strength and can be added as needed. However, the addition of an excessive amount of Ta leads to a decrease in the ductility at room temperature and a decrease in toughness, so 0.50% by mass is made the upper limit of the amount of Ta. In order to achieve both high temperature strength and softness and toughness, the amount of Ta is preferably 0.05 mass% or more and 0.5 mass% or less.

(Sb: 0.001 to 0.3% by mass)

Sb is effective for improving the corrosion resistance, and may be added in an amount of 0.3 mass% or less, if necessary. In particular, the lower limit of the amount of Sb is set to 0.001 mass% from the viewpoint of the gap corrosion resistance. Also, from the viewpoints of production and cost, it is preferable that the amount of Sb is 0.01 mass% or more. From the viewpoint of cost, the upper limit of the amount of Sb is preferably 0.1% by mass.

(Ga: 0.0002 to 0.1% by mass)

Ga may be added in an amount of 0.1 mass% or less for the purpose of improving corrosion resistance and suppressing hydrogen embrittlement. The lower limit of the amount of Ga is set to 0.0002 mass% from the viewpoint of formation of sulfides and hydrides. From the viewpoint of production and cost, the amount of Ga is preferably 0.0020 mass% or more.

Other components are not specifically defined in the present embodiment, but in this embodiment, Hf, Bi and the like may be added in an amount of 0.001 to 0.1 mass%, if necessary. In addition, it is preferable that the amount of generally harmful elements such as As, Pb and the like is reduced as much as possible.

In the ferritic stainless steel sheet of the present embodiment, the balance parts other than the above components are Fe and inevitable impurities.

Next, the Cu concentration and the ferrite grain size on the surface of the ferritic stainless steel sheet according to the present embodiment will be described.

(The Cu concentration on the surface of the steel sheet is 15% or more in terms of the cation fraction)

It has been found that the surface Cu concentration of the ferritic stainless steel sheet has an important function of reducing the coefficient of friction with the tool at the time of punching, suppressing occurrence of burrs and suppressing tool abrasion. When Cu is concentrated on the surface, Cu is present as a built-up edge at the tip of the tool when contacted with the punching tool, thereby suppressing abrasion of the tool. Moreover, since Cu has excellent thermal conductivity, diffusion of the processing heat accumulated in the tool is suppressed, softening due to the temperature rise of the steel sheet is suppressed, and the burr on the end face is reduced. In order to exhibit this effect, it is necessary that at least Cu is concentrated so that the Cu concentration in the surface layer of the steel sheet is converted into a cation fraction and is at least 15%. Below this, the coefficient of friction between the steel plate and the tool rises, which increases the burr and promotes tool wear. In order to concentrate Cu on the surface of the product, the amount of Cu added as the alloy element is preferably large. However, since Cu coexists with Sn, it has become clear that Cu is concentrated on the surface even at a low Cu concentration. The addition of an excessive amount of Sn or Cu promotes the embrittlement of the ferritic stainless steel, so that it is necessary to exhibit the effect with a small addition amount. In order to concentrate Cu so that the Cu concentration on the surface is 15% or more in the range of Cu content of 0.1 to 0.5%, Sn of 0.01% or more is required.

1 is a diagram showing the relationship between the Cu concentration in the surface layer and the burr height. In Fig. 1, the plotted points in the white circles represent examples in which the ferrite grain size is 30 mu m or less. The plotted points in the black circles represent an example of more than 30 [mu] m. The test example shown in Fig. 1 is the same as that of the first embodiment shown in Fig. 1 except that the steel of the present embodiment (steels 1-1, 1-6 and 1-9 in the first embodiment) , And the cold-rolled sheet is manufactured by changing the heat treatment conditions. The ferrite grain size was controlled to be 30 占 퐉 or less under the processing heat treatment conditions and the Cu concentration on the surface of the steel material was changed under the conditions of combination of the atmosphere for annealing the cold rolled sheet, the cooling rate and the pickling conditions. As a result, if the Cu concentration on the surface of the steel sheet is 15% or more, the burr height can be stably set to 50 탆 or less. Even when the ferrite grain size is 35 占 퐉 and the Cu concentration on the surface of the steel sheet is less than 15%, the burr height may be 50 占 퐉 or less. However, the 20th burr height in this example is out of the range of 50 占 퐉 or less.

(Ferrite particle diameter: 30 탆 or less)

If the ferrite particle size is large, the deformation amount of each ferrite particle occurring at the time of punching becomes large, so that the burr becomes large. Therefore, it is necessary to set the ferrite grain size to 30 탆 or less. The ferrite grain size is preferably 25 占 퐉 or less, and more preferably 20 占 퐉 or less.

2 is a diagram showing the relationship between the ferrite grain size and the 20th burr height. 2, the plotted points in the white circles are examples in which the Cu concentration on the surface of the steel sheet is at least 15% in terms of the cation fraction, and the plotted points in the black circle are examples in which the Cu concentration on the surface of the steel sheet is less than 15% in cation fraction. When these steels (the steels Nos. 1-1, 1-6 and 1-9 of the first embodiment) according to the present embodiment are produced in accordance with the production method of the present embodiment, This is an example in which annealing conditions are changed. The Cu concentration on the surface of the steel material was controlled to be not less than 15% and less than 15% in accordance with the combination of the annealing atmosphere of the cold-rolled sheet and the pickling conditions, and the ferrite grain size was changed under the annealing conditions of the hot and cold rolled plates. When the Cu concentration on the surface of the steel sheet is as high as 15% or more, the burr height at the 20th time can be roughly controlled by the ferrite grain size. The smaller the particle diameter, the smaller the burr height. In addition, when the Cu concentration on the surface of the steel sheet is as low as less than 15%, the burr height increases even if the ferrite grain size is small.

Next, a method of manufacturing the ferritic stainless steel sheet according to the present embodiment will be described.

As described below, the manufacturing method according to the present embodiment is a method in which hot rolled and rolled at a relatively low temperature, hot rolled sheet annealing is performed at a relatively low temperature, and the cooling rate after final annealing is increased. Thereby, dissolved Cu is secured by avoiding precipitation of? -Cup. According to the manufacturing method of the present embodiment, it is possible to appropriately concentrate Cu on the surface of the steel sheet, and further reduce the ferrite grain size to 30 mu m or less. The manufacturing process will be described below.

The steel slab to be the base of the ferritic stainless steel sheet of the present embodiment can be produced by a commonly known method. For example, the steel is dissolved in a converter, an electric furnace, etc., and if necessary, secondary refining is performed with an RH degassing apparatus, AOD, VOD, etc., and the composition is adjusted to the above composition. Thereafter, slabs are preferably formed by a continuous casting method or a bar-rolling mill method.

The subsequent hot rolling should be performed under the following conditions.

(Slab heating temperature: 1100 DEG C or more)

The heating temperature of the slab prior to hot rolling is required to be 1100 DEG C or higher. If the heating temperature is lower than 1100 ° C, the hot-rolled structure tends to remain on the hot-rolled sheet. As a result, the ferrite particles are easy to expand in the rolling direction, and burrs are enlarged.

(Finishing rolling finish temperature: 900 DEG C or more)

The finishing rolling finishing temperature in hot rolling must be 900 캜 or higher. When the finish temperature of finish rolling is less than 900 캜, the material is hardly recrystallized during hot rolling, and as a result, the ferrite particles are liable to expand.

(Coiling temperature: 450 to 600 DEG C)

The coiling temperature after hot rolling is important for grain boundary segregation and control of precipitates in the hot rolled steel sheet, and it is necessary to set the coiling temperature to 600 占 폚 or less. If the coiling temperature exceeds 600 ° C, Cu precipitates as an epsilon-Cu phase, and the Cu concentration effective on the surface is lowered. On the other hand, when the coiling temperature is less than 450 캜, the increase of the hardness of the steel sheet is remarkable due to the influence of Cu or Sn, which causes a bad scratch of the wound shape at the time of winding. For this reason, the coiling temperature is set to 450 DEG C or higher. The coiling temperature is preferably in the range of 500 to 550 占 폚.

The hot-rolled sheet thus obtained is subjected to hot-rolled sheet annealing, pickling and cold rolling. Thereafter, final annealing for recrystallization is performed. The annealing temperature and the final annealing temperature of the hot-rolled sheet at this time are in the following ranges.

(Annealing temperature of hot rolled sheet: 800 to 950 DEG C)

The annealing temperature of the hot-rolled sheet is preferably in the range of 800 to 950 캜. When the annealing temperature of the hot-rolled sheet is less than 800 ° C, the recrystallization of the hot-rolled sheet is insufficient and the ferrite particles are renewed. When the annealing temperature of the hot-rolled sheet is 800 DEG C or higher, the epsilon-Cu phase is dissolved and the amount of Cu concentrated on the surface after final annealing of the cold-rolled sheet can be secured. On the other hand, when the annealing temperature of the hot-rolled sheet exceeds 950 DEG C, the coarsening of the ferrite particles is promoted and the ferrite particles of the product are coarsened. For this reason, it is necessary to set the temperature to 950 占 폚 or lower.

(Final annealing temperature: 820 to 950 DEG C or less)

The final annealing temperature after cold rolling is 820 캜 or higher. If the final annealing temperature is lower than 820 占 폚, the cold rolled structure stretched in the rolling direction is liable to remain and the burr becomes larger. Further, precipitation of the epsilon-Cu phase starts, the amount of solute Cu becomes insufficient, and the surface Cu concentration becomes low. On the other hand, when the final annealing temperature exceeds 950 占 폚, the coarsening of the ferrite particles proceeds and the ferrite grain size exceeds 30 占 퐉. The preferred final annealing temperature ranges from 850 to 920 占 폚.

(Atmosphere of final annealing: oxygen concentration 1% or more)

Further, since the oxidation state of the surface of the steel sheet affects the Cu concentration on the product surface, the oxygen concentration in the atmosphere at the final annealing is 1% or more. When a scale is formed by Mn oxide or Fe oxide together with Cr oxide, the number of elements forming an oxide in the vicinity of the surface layer is reduced. As a result, the amount of Cu increases as compared with the upper limit. Generally, in descale, since the steel sheet core is dissolved together with the oxide scale by the acid solution, the concentration of the surface together with Cu concentrated on the surface is promoted by the diffusion during the final annealing. Also, the final annealing may be performed in the atmosphere. That is, the oxygen concentration in the atmosphere (about 21%) may be set as the upper limit of the oxygen concentration in the atmosphere.

(Cooling rate to 600 占 폚: 30 占 폚 / s or more)

Cu precipitates as ε-Cu phase upon cooling after the final annealing. Once the ε-Cu phase is precipitated, it is not redissolved in subsequent steps. In order to concentrate Cu on the surface layer, precipitation must be suppressed. For this purpose, it is necessary to cool at a cooling rate of 30 ° C / s or higher in a temperature range of up to 600 ° C. If the cooling rate is high, the precipitation behavior can be suppressed, but there is a problem that the shape defect is likely to occur. Therefore, the cooling rate is preferably in the range of 35 to 60 DEG C / s.

The cold-rolled sheet after the final annealing is subjected to descaling by pickling. Subsequently, the product may be left as it is, and after that, temper rolling may be carried out if necessary. At this time, it is preferable that the rough reduction ratio is in the range of 0.3 to 1.2%.

(Second Embodiment)

The composition of the ferritic stainless steel sheet according to the second embodiment will be described.

(C: 0.020 mass% or less)

C forms Cr carbide and causes sensitization. Therefore, in the present embodiment, Ti or Nb is added to form a carbide, and C is fixed. TiC has a function of promoting work hardening by precipitation strengthening of steel finely. However, if the content of C exceeds 0.020 mass%, it is necessary to add a large amount of Ti or Nb, and therefore the content of C is 0.020 mass% or less. It is preferably 0.012 mass% or less. From the viewpoint of avoiding deterioration of corrosion resistance and the like caused by C, the content is preferably as small as possible, but excessive reduction leads to an increase in refining cost, and therefore, it is preferably 0.001% by mass or more. In consideration of the production cost and the like, the content is preferably 0.005 mass% to 0.010 mass%.

(Si: 0.80 mass% or less)

Si is a solid solution strengthening element, hardens the steel and lowers the ductility. When the ductility is lowered, the deforming ability at the time of punching breakage is lowered. As a result, the area of the punching condition in which the burr property is stable is narrow, and the punching condition is deviated from the stable area due to the increase in the number of punching, and the burr height becomes large. Therefore, in the present embodiment, the Si content needs to be 0.80 mass% or less. The amount of Si is preferably 0.30 mass% or less, and more preferably 0.25 mass% or less. In addition, Si is an element which may be added as a deoxidizing element. In view of production costs and the like, the amount of Si is preferably set to 0.01 mass% or more.

(Mn: 1.0 mass% or less)

Mn is an element which deteriorates corrosion resistance and is also an element constituting MnS. A large amount of MnS is precipitated, or MnS is coarsened, and punching workability is deteriorated. MnS is precipitated in a ferrite grain boundaries to form ferrite grains as expansion grains, thereby increasing burrs during punching processing. Therefore, in the present embodiment, it is necessary to make the Mn content 1.0 mass% or less. It is preferably 0.50 mass% or less. More preferably, it is 0.30 mass% or less. Further, Mn is an element which may be added as a deoxidizing element, and it is preferable to set it to 0.01% by mass or more in view of production cost and the like.

(P: 0.010 to 0.035% by mass)

P has the action of forming FeTiP to promote the occurrence and progress of cracking during punching, and to reduce the height of burrs. This effect is exhibited by containing P in an amount of 0.010 mass% or more.

However, if it is added in an amount exceeding 0.035% by mass, it will result in embrittlement of the material, so that it is made 0.035% by mass or less. And preferably 0.020 to 0.025 mass%.

(S: 0.005 mass% or less)

S forms MnS or TiS so as to suppress the ferrite particles from being equalized, and promotes new telephone calls, thereby promoting occurrence of burrs. In order to prevent this phenomenon, the S content is required to be 0.005 mass% or less. It is preferably 0.003 mass% or less. However, an excessive reduction leads to an increase in refining cost, and therefore, it is preferable to be 0.0001 mass% or more.

(Al: 0.50 mass% or less)

Al is a component to be added as a deoxidizer, and in order to improve the cleanliness of steel, it is preferable to add Al in an amount of 0.02 mass% or more. However, when Al is added in a large amount, AlN precipitates to promote the softening of the ferrite particles, and also to cause the ferrite particles to expand in the rolling direction. Therefore, in the present embodiment, the Al content is 0.50 mass% or less. It is preferably 0.10 mass% or less. In addition, Al may be added as a deoxidizing element in some cases, and the high-temperature strength and oxidation resistance are improved. Since the action is expressed at 0.01 mass%, the amount of Al is preferably 0.01 mass% or more.

(N: 0.020 mass% or less)

N is an element that tends to form TiN by binding with Ti. In particular, when the N content exceeds 0.020 mass%, a large amount of coarse rectangular TiN is precipitated in the steel to cause surface scratches of the steel sheet. Therefore, the N content is set to 0.020 mass% or less. It is preferably 0.07 to 0.012 mass%.

(Cr: 15.6 to 17.5% by mass)

Cr is an important element for forming a passive film on the surface of stainless steel and improving the corrosion resistance. In order to maintain the corrosion resistance of the end face, it is necessary to contain not less than 15.6 mass%. However, if it exceeds 17.5 mass%, the hardening by Cr becomes remarkable, the work hardening coefficient is lowered, and the ferrite particles are liable to elongate in the punching direction, so that the burr becomes larger. Therefore, the Cr content is set to 17.5 mass% or less. Preferably, it is in the range of 16.0 to 17.3 mass%.

(Cu: 0.50 to 2.00% by mass)

Cu acts to reduce the friction with the punching tool by concentrating on the surface of the steel sheet, and thus plays an important role in this embodiment. By adding Sn at 0.50 mass% or more, Cu concentration on the surface of the steel sheet is stabilized, burr is reduced, and tool wear is suppressed. On the other hand, if it is added in an amount exceeding 2.00 mass%, hardness is increased due to solid solution strengthening, and Cu is precipitated by intergranular precipitation, so that ferrite particles tend to become brittle. Further, precipitation of the epsilon-Cu phase is caused, and an increase in hardness due to dispersion strengthening promotes tool wear. Therefore, the upper limit of Cu is set to 2.00 mass%. Preferably, it is more than 0.50 mass% and 2.00 mass% or less, and more preferably 0.8 to 1.2 mass% or less.

(Sn: 0.001 to 0.1% by mass)

Sn is an important element in this embodiment because it exerts an effect of accelerating the concentration of Cu on the surface of the steel sheet when it coexists with Cu. The effect of promoting the surface enrichment of Cu by the coexistence of Sn and Cu is exhibited by adding Sn at a content of 0.001 mass% or more, and a remarkable effect is manifested at a content of 0.01 mass% or more. Practically, it may be 0.003 mass% or more. However, Sn is also an element of employment hardening. Therefore, if the excess amount is added, the work hardening constant is increased, so that the amount of Sn is 0.1 mass% or less. Sn is also an element that improves corrosion resistance. The effect of improving the corrosion resistance is exhibited at not less than 0.01 mass%, and the effect is remarkably exerted at not less than 0.03 mass%. Therefore, in order to accelerate surface enrichment of Cu by Sn, it is preferably 0.003 to 0.01 mass%.

When an effect of improving the corrosion resistance is also required, Sn is preferably set in a range of 0.03 to 0.08 mass%. More preferably, it is in the range of 0.04 to 0.06 mass%.

The steel sheet of the present embodiment further contains at least one selected from 0.05 to 0.30 mass% of Ti, 0.05 to 0.40 mass% of Nb, and 0.05 to 0.50 mass% of Ni.

(Ti: 0.05 to 0.30 mass%)

Ti combines with C, N, and S to form carbides, nitrides, and sulfides. Ti content is 0.05 mass% or more, and the effect of fixing these elements is exhibited. Therefore, it is necessary to add Ti at 0.05 mass% or more. On the other hand, when the amount of Ti exceeds 0.30 mass%, a large amount of TiN precipitates and scratches on the surface of the steel sheet occur. Therefore, the amount of Ti is set to 0.30 mass% or less. Preferably, the amount of Ti is in the range of 0.15 to 0.25 mass%.

(Nb: 0.05 to 0.40 mass%)

Nb is an element improving moldability and corrosion resistance. Moldability and corrosion resistance are improved by adding 0.05 mass% or more of Nb. On the other hand, excessive addition of Nb causes problems such as surface scratches and gloss unevenness, and deterioration of ductility. Therefore, Nb is set in the range of 0.05 to 0.40 mass%. Also, considering the preparation and ductility, the amount of Nb is preferably in the range of 0.07 to 0.20 mass%.

(Ni: 0.05 to 0.50% by mass)

Ni is an element improving the corrosion resistance, and the effect is exhibited by addition of 0.05 mass% or more. On the other hand, when added in a large amount, the steel becomes hard and causes deterioration in ductility. Therefore, the Ni content is 0.50 mass or less. It is preferably 0.25 mass% or less.

In the present embodiment, if necessary, the following elements may be contained.

(B: 0.001 mass% or less)

B is an element segregating at grain boundaries to increase the grain boundary strength, and stabilizes the end face property at the time of punching. However, the addition of an excessive amount of B forms a low-melting point boride and remarkably lowers the hot workability. Therefore, the amount of B is set to 0.001 mass% or less. In order to stably obtain the effect of B, the amount of B is preferably 0.0002 mass% or more, and more preferably 0.0003 mass% or more.

(Co: 0.50 mass% or less)

Co, like Ni, is an element that improves corrosion resistance, but when added in a large amount, it hardens the steel and causes deterioration in ductility. Therefore, the Co content is 0.50 mass% or less. The amount of Co is preferably 0.10 mass% or less. In order to stably obtain the effect of Co, the amount of Co is preferably 0.005 mass% or more, and more preferably 0.01 mass% or more.

(Mo: 0.01 to 0.50% by mass)

Mo is an element that improves corrosion resistance and is added in applications where corrosion resistance is required. By adding Mo in an amount of 0.01 mass% or more, an effect of improving corrosion resistance is developed. On the other hand, an excessive amount of Mo causes deterioration of moldability, particularly ductility. Therefore, it is preferable that the content is in the range of 0.01 to 0.50 mass%. And more preferably 0.30 mass% as the upper limit. Further, in consideration of the composition and strength, it is more preferable to set the range of 0.05 to 0.20 mass%. More preferably, it is 0.05 to 0.15 mass%.

(V, W: 0.50 mass% or less)

V and W, like Ti, combine with C to form a carbide. If the addition amount of V or W exceeds 0.50% by mass, precipitation of TiN is promoted and scratches on the surface of the steel sheet are caused. Therefore, when V or W is added, the amount is preferably 0.50 mass% or less, more preferably 0.10 mass% or less, and further preferably 0.05 mass% or less. In order to stably obtain the effect of V and W, the amounts of V and W are preferably 0.005 mass% or more, and more preferably 0.01 mass% or more.

(Mg: 0.01 mass% or less)

Mg is a component added as a deoxidizer. However, if it is added in a large amount, it is precipitated as MgO, which may cause nozzle clogging at the time of steelmaking. Therefore, in the present embodiment, the amount of Mg is 0.01 mass% or less, more preferably 0.002 mass% or less. In order to stably obtain the effect of Mg, the amount of Mg is preferably 0.0001 mass% or more, and more preferably 0.0003 mass% or more.

(Ca: 0.003 mass% or less)

Ca is a component added as a deoxidizer. However, if it is added in a large amount, CaO or CaS may be precipitated to cause rust. Therefore, in the present embodiment, Ca is set to 0.003 mass% or less. In order to stably obtain the effect of Ca, the amount of Ca is preferably 0.0001 mass% or more, and more preferably 0.0003 mass% or more.

[REM (rare earth metal): 0.02 mass% or less]

REM (rare-earth metal) is an element for increasing the grain boundary strength like B and stabilizes the end face property at the time of punching, but its action saturates to 0.02 mass%. Therefore, the amount of REM (total amount of rare earth metals) is set to 0.02 mass% or less. It is preferable to set the lower limit of the REM amount to 0.002 mass%. REM (rare earth element) refers to a generic term of 15 elements (lanthanoids) from scandium (Sc) and yttrium (Y) and lanthanum (La) to lutetium (Lu) according to a general definition. May be added singly or in a mixture.

(Ta: 0.50 mass% or less)

Ta is an element which improves high temperature strength and can be added as needed. However, the addition of an excessive amount of Ta leads to a decrease in ductility at room temperature and a decrease in toughness, so 0.50% by mass is made the upper limit of the amount of Ta. In order to achieve both high temperature strength and softness and toughness, the amount of Ta is preferably 0.05 mass% or more and 0.5 mass% or less.

(Sb: 0.001 to 0.3% by mass)

Sb is effective for improving the corrosion resistance, and may be added in an amount of 0.3 mass% or less, if necessary. In particular, the lower limit of the amount of Sb is set to 0.001 mass% from the viewpoint of the gap corrosion resistance. Also, from the viewpoints of production and cost, it is preferable that the amount of Sb is 0.01 mass% or more. From the viewpoint of cost, the upper limit of the amount of Sb is preferably 0.1% by mass.

(Ga: 0.0002 to 0.1% by mass)

Ga may be added in an amount of 0.1 mass% or less for the purpose of improving corrosion resistance and suppressing hydrogen embrittlement. The lower limit of the amount of Ga is set to 0.0002 mass% from the viewpoint of formation of sulfides and hydrides. From the viewpoint of production and cost, the amount of Ga is preferably 0.0020 mass% or more.

(Zr: 0.30 mass% or less)

Zr, like Nb and Ti, is added in an amount of 0.01% by mass or more, if necessary, in order to form a carbonitride to inhibit the formation of Cr carbonitride and improve the corrosion resistance. If it is added in an amount exceeding 0.30 mass%, the effect is saturated, and it may cause surface scratches due to the formation of a large oxide. Therefore, it is added in an amount of 0.01 to 0.30 mass%. More preferably, it is 0.20 mass% or less. Zr is an expensive element as compared with Ti and Nb, and is preferably 0.02 mass% to 0.05 mass% in consideration of production cost.

Other components are not specifically defined in the present embodiment, but in this embodiment, Hf, Bi and the like may be added in an amount of 0.001 to 0.1 mass%, if necessary. In addition, it is preferable that the amount of generally harmful elements such as As, Pb and the like is reduced as much as possible.

In the ferritic stainless steel sheet of the present embodiment, the balance parts other than the above components are Fe and inevitable impurities.

Next, the surface Cu concentration and the ferrite grain size in the ferritic stainless steel sheet according to the present embodiment will be described.

(The Cu concentration on the surface of the steel sheet is 15% or more in terms of the cation fraction)

It has been found that the surface Cu concentration of the ferritic stainless steel sheet has an important function of reducing the coefficient of friction with the tool at the time of punching, suppressing occurrence of burrs and suppressing tool wear. When Cu is concentrated on the surface, Cu is present as a constituent wire at the tip of the tool when contacted with the punching tool, thereby suppressing the wear of the tool. Moreover, since Cu has excellent thermal conductivity, diffusion of the processing heat accumulated in the tool is suppressed, softening due to the temperature rise of the steel sheet is suppressed, and the burr on the end face is reduced. In order to exhibit this effect, Cu must be concentrated so that the Cu concentration in the surface layer of the steel sheet is at least 15% in terms of the cation fraction. Below this, the coefficient of friction between the steel plate and the tool rises, which increases the burr and promotes tool wear. In order to concentrate Cu on the surface of the product, the amount of Cu added as an alloying element is preferably as large as possible. By inclusion of Cu in an amount of 0.5% or more, Cu tends to be thickened so that the surface Cu concentration is 15% or more. However, it was confirmed that the surface Cu concentration was less than 15% according to the production conditions. As a result, the concentration of Cu on the surface is stabilized by adding Sn which is likely to coexist with Cu. In order to stabilize the Cu concentration on the surface by 15% or more, it is necessary to add 0.001% or more of Sn.

4 is a diagram showing the relationship between the Cu concentration in the surface layer and the burr height at the 20th time. When the Cu concentration in the surface layer exceeds 15%, the burr height is stabilized, and the burr height at the 20th time is 50 탆 or less. In Fig. 4, even if the surface Cu concentration is 15% or more, the burr height may exceed 50 탆, and then the replenishment is performed. The black circle plot points in the figure show examples where the ferrite grain size is 30 탆 or less, but the surface hardness is less than 140 or more than 180. The plot points of the white triangles represent examples where the particle diameter is more than 30 占 퐉. These were produced by changing the heat treatment conditions of the cold rolled steel sheet in accordance with the manufacturing method of the present embodiment with respect to the steels having the component compositions of the present embodiment (steels 2-1 and 2-7 of the second embodiment) Yes. The Cu concentration on the surface of the steel material was changed under the condition of controlling the ferrite grain size to 30 占 퐉 or less and the surface hardness to 140 to 180 under the processing heat treatment conditions and combining the heat treatment atmosphere of the cold rolled sheet and the acid cleaning condition. As a result, when the Cu concentration on the surface of the steel sheet is 15% or more, the burr height can be stably set to 50 탆 or less.

(Ferrite particle diameter: 30 탆 or less)

If the ferrite particle size is large, the deformation amount of each ferrite particle occurring at the time of punching becomes large, so that the burr becomes large. Therefore, it is necessary to set the ferrite grain size to 30 탆 or less. The ferrite grain size is preferably 25 占 퐉 or less, and more preferably 20 占 퐉 or less.

5 is a diagram showing the relationship between the ferrite grain size and the 20th burr height. 5, the white triangulated plot point is an example in which the Cu concentration on the surface of the steel sheet is 15% or more at the cation fraction, but the surface hardness is less than 140 or more than 180. Plot points in the black circles are examples where the Cu concentration is less than 15%. These are examples in which the conditions of the hot-rolled sheet and the cold-rolled sheet annealing were changed when the steels having the component compositions of the present embodiment (steels 1 and 7 in the examples) were produced in accordance with the production method of this embodiment. The Cu concentration on the surface of the steel material was controlled to be not less than 15% and the surface hardness was controlled to be in the range of 140 to 180 under the combination of the atmosphere of cold rolling annealing and the pickling condition of the cold rolled steel sheet, . When the Cu concentration on the surface of the steel sheet is 15% or more, the burr height at the 20th time can be controlled by the ferrite grain size, and the smaller the grain size, the smaller the burr height. Further, when the surface layer Cu concentration is low, the burr height at the 20th time is high even though the particle diameter is small.

(Surface hardness 140 to 180)

The surface hardness is an important factor affecting deformation and tool life in punching. If the hardness is high, it is difficult to deform but is retreated, and the ratio of the shear wavefront to the soft wavefront is changed. So that it is effective to reduce the burr height. However, the tool life is remarkably lowered. Therefore, the upper limit of the surface hardness was set at 180. On the other hand, when the surface hardness is low, sagging easily occurs, and deformation accompanying sagging increases the height. Particularly, in the case where the surface hardness is low, the increase in the burr height becomes remarkable, so that the surface hardness is a standard. In addition, there is a correlation between the crystal grain size and the surface hardness, and grain coarsening of the crystal grains is effective means for lowering the surface hardness.

In order to stably satisfy the crystal grain size of 30 占 퐉 or less, the surface hardness is set to 140 or more. The surface hardness in the present embodiment is Vickers hardness.

Next, a method of manufacturing the ferritic stainless steel sheet according to the present embodiment will be described.

As described below, the production method of the present embodiment is such that the hot rolling is performed at a relatively low temperature, followed by hot rolled sheet annealing at a relatively low temperature, and at the same time, the cooling rate after the final annealing is increased. By this, ∈-Cu is prevented from being precipitated to secure solidified Cu, and the crystal grain size and the hardness of the material are controlled. According to the manufacturing method of the present embodiment, it is possible to appropriately concentrate Cu on the surface of the steel sheet, and further reduce the ferrite grain size to 30 mu m or less. The manufacturing process will be described below.

The steel slab to be the base of the ferritic stainless steel sheet of the present embodiment can be produced by a commonly known method. For example, the steel is dissolved in a converter, an electric furnace, etc., and if necessary, secondary refining is performed with an RH degassing apparatus, AOD, VOD, etc., and the composition is adjusted to the above composition. Thereafter, slabs are preferably formed by a continuous casting method or a bar-rolling mill method.

The subsequent hot rolling must be performed under the following conditions.

(Slab heating temperature: 1100 DEG C or more)

The heating temperature of the slab prior to hot rolling is required to be 1100 DEG C or higher. When the heating temperature of the slab is less than 1100 ° C, the hot-rolled structure tends to remain on the hot-rolled steel sheet. As a result, the ferrite particles are easy to expand in the rolling direction, and burrs are enlarged.

(Rolling rate at finishing rolling: 80 to 90%)

The finish rolling ratio in hot rolling should be in the range of 80 to 90%. When the rolling rate is less than 80%, the cast structure can not be completely crushed. As a result, problems such as ridging due to coarse solidification structure occur in the surface properties of the final product. In addition, when the rolling rate exceeds 90%, the temperature of the judging unit is remarkably lowered, and there is a high possibility that problems such as scap and edge cracks will occur.

(Finishing rolling finish temperature: 900 DEG C or more)

The finishing rolling finishing temperature in hot rolling must be 900 캜 or higher. When the finish temperature of finish rolling is less than 900 캜, the material is hardly recrystallized during hot rolling, and as a result, the ferrite particles are liable to expand. The expanded ferrite particles cause coarse grain structure including coarse particles, and hardness tends to become unstable, and strict management is required.

(Coiling temperature: 400 to 500 DEG C)

The coiling temperature after hot rolling is important for grain boundary segregation in the hot rolled steel sheet and control of the precipitates, and it is necessary to set the coiling temperature to 500 deg. In the amount of Cu in the steel of the present invention, when the coiling temperature exceeds 500 캜, Cu begins to precipitate as an ε-Cu phase. In order to ensure the amount of Cu solubilized in the Cu concentration on the surface, the deposition amount should be as small as possible. On the other hand, when the coiling temperature is less than 400 캜, the increase in hardness of the steel sheet is remarkable due to the effect of solidifying Cu or Sn, which is a cause of defective scratches in the winding shape at the time of winding. The coiling temperature is preferably in the range of 450 to 500 占 폚.

The hot-rolled sheet thus obtained is subjected to hot-rolled sheet annealing, pickling and cold rolling. Thereafter, final annealing for recrystallization is performed. The annealing temperature and the final annealing temperature of the hot-rolled sheet at this time are in the following ranges.

(Annealing temperature of hot rolled sheet: 850 to 950 DEG C)

The annealing temperature of the hot-rolled sheet is preferably in the range of 850 to 950 ° C. When the annealing temperature of the hot-rolled sheet is less than 850 ° C, the recrystallization of the hot-rolled sheet is insufficient and the ferrite particles are renewed. When the annealing temperature is 850 DEG C or higher, the epsilon-Cu phase is dissolved, and the amount of Cu concentrated on the surface after final annealing of the cold-rolled sheet can be secured. On the other hand, when the annealing temperature exceeds 950 占 폚, the coarsening of the ferrite particles is promoted, and the ferrite particles of the product are coarsened. For this reason, it is necessary to set the temperature to 950 占 폚 or lower.

(Final annealing temperature: 850 to 950 DEG C or less)

The final annealing temperature after cold rolling is 850 ° C or higher. If the final annealing temperature is lower than 850 占 폚, the cold rolled structure stretched in the rolling direction tends to remain and the burr becomes larger. Further, precipitation of the epsilon-Cu phase starts, the amount of solute Cu becomes insufficient, and the surface Cu concentration becomes low. On the other hand, when the final annealing temperature exceeds 950 占 폚, the coarsening of the ferrite particles proceeds and the ferrite grain size exceeds 30 占 퐉. The preferred final annealing temperature is in the range of 880 to 920 占 폚.

(Atmosphere of final annealing: oxygen concentration 1% or more)

Further, since the oxidation state of the surface of the steel sheet affects the Cu concentration on the product surface, the oxygen concentration in the atmosphere at the final annealing is 1% or more. When a scale is formed by Mn oxide or Fe oxide together with Cr oxide, the number of elements forming an oxide in the vicinity of the surface layer is reduced. As a result, the amount of Cu increases as compared with the upper limit. Generally, in descale, since the steel sheet core is dissolved together with the oxide scale by the acid solution, the concentration of the surface together with Cu concentrated on the surface is promoted by the diffusion during the final annealing. Also, the final annealing may be performed in the atmosphere. That is, the oxygen concentration in the atmosphere (about 21%) may be set to the upper limit of the oxygen concentration in the atmosphere.

(Cooling rate up to 500 DEG C: 50 DEG C / s or more)

Cu precipitates as ε-Cu phase upon cooling after the final annealing. Once the ε-Cu phase is precipitated, it is not redissolved in subsequent steps. In addition, fine dispersion causes an increase in hardness. It is necessary to control the precipitation state in order to concentrate Cu in the surface layer and suppress the rise of hardness. For this purpose, it is necessary to cool at a cooling rate of 50 DEG C / s or higher in a temperature range up to 500 DEG C. If the cooling rate is high, the precipitation behavior can be suppressed, but there is a problem that the shape defect is likely to occur. Therefore, the cooling rate is preferably in the range of 55 to 65 占 폚 / s.

The cold-rolled sheet after the final annealing is subjected to descaling by pickling. Subsequently, the product may be left as it is, and after that, temper rolling may be carried out if necessary. At this time, it is preferable that the rough reduction ratio is in the range of 0.3 to 1.2%.

Example

(Embodiment 1)

Hereinafter, examples corresponding to the ferritic stainless steel sheet of the first embodiment are shown below.

The components Nos. 1-1 to 1-38 having the component compositions shown in Tables 1A and 1B were dissolved in a solvent to form a steel ingot. Subsequently, hot rolling was performed under the conditions shown in Tables 2A, 2B, and 2D to obtain a hot rolled sheet having a thickness of 4 mm. This hot-rolled sheet was subjected to hot-rolled sheet annealing by continuous annealing at 890 캜. After acid cleaning, cold-rolling was performed to obtain a cold-rolled sheet having a thickness of 1 mm.

Subsequently, the cold-rolled sheet was subjected to final annealing and cold-rolling annealing at the temperatures shown in Tables 2A, 2B and 2D. The thus obtained cold-rolled annealing plate was subjected to the following test.

(Evaluation of Punching Property)

The cold-rolled annealing plate was punched to form a hole having a clearance of 10% and 12 mm, and the height of the burr of the front end surface was measured. This punching test was repeated, and the burr height after punching 50 times in succession was measured. The burr height at the time of continuous punching depends on the contact with the tool at the beginning of the punching process. Therefore, it has been found that stable burr heights are maintained unless large burrs are generated by 20 to 30 times of machining. Therefore, the punching property was evaluated at the 20th burr height as an index that does not impair the productivity. The first burr height was also evaluated.

(Measurement of ferrite crystal grain size)

In the plate thickness section parallel to the rolling direction of the cold annealing plate, the central portion of the plate thickness was mirror-polished and corroded with aqua regia to reveal the structure. The ASTM nominal grain size of the ferrite particles was measured by the cutting method specified in JIS G0552. The particle diameters were measured in the following order. Five line segments having an actual length of 800 占 퐉 were drawn on the photograph in the sheet thickness direction, and five lines were drawn in the rolling direction. The intersections of these line segments and the ferrite grain boundaries were counted. The total length of the line segments in the plate thickness direction was divided by the number of the intersections, and the average length of the line segments cut into the ferrite grain boundaries in the plate thickness direction was determined. Similarly, the average length of the cut line segments in the rolling direction was also determined. ASTM nominal particle size was obtained by multiplying them again by a mean of 1.13.

(Measurement of Cu concentration on the surface of the steel sheet)

A square specimen having a side length of 20 mm was cut out from the cold annealing plate. The concentration of Cu in the depth direction was measured while using Ar gas sputtering from the surface using a Rigaku Spectruma GDA750 / Glow Discharge Emission Spectrometer (GDS) under the conditions of an analysis diameter of 4 mm, a measurement pitch of 2.5 mm / min, and an analysis time of 20 seconds. Were continuously measured. From the measurement results, the cation element was extracted, and the amount of the cation element was converted into the existing ratio, and the concentration profile inside the outermost layer was determined. From the obtained profile, the Cu concentration at the 5 nm portion from the outermost layer was determined as the surface Cu concentration. 3 is a diagram showing an example of measurement of the surface layer Cu concentration. As shown in Fig. 3, Cu is remarkably concentrated in the vicinity of the surface layer.

The measurement results are shown in Tables 2C and 2E. From Table 1A, Table 1B, and Table 2A to Table 2E, the following can be known.

In the steel sheets of Test Nos. 1-1 to 1-30, the steel sheet (Test Nos. 1-6, 1-7, 1-10, 1-14, 1-15, 1-17, 1-22, 1-24, 1-25, 1-27, 1-29, 1-30), the burr height at the punching test was 50 Mu] m or the burr height at the 20th time exceeded 50 mu m.

Test Nos. 1-1 to 1-5, 1-8, 1-9, 1-11 to 1-13, 1-16, 1-18 to 1-21, 1-23, 1-26, 1-28 , 1-30-1 and 1-30-2, all the conditions satisfied the range of the present embodiment, and the burr height at the initial stage of the punching test and the burr height at the 20th time were all satisfactory at 50 μm or less.

Since the steel sheets of Test Nos. 1-31 to 1-51 did not satisfy the range of the present embodiment, the burr height at the 20th time was large.

In Test Nos. 1-6, 1-7, 1-14, 1-17, and 1-24, the hot rolling conditions are changed to components that satisfy the range of the present embodiment.

In Test No. 1-6, the rolling finish temperature at the time of hot rolling was out of the range of the present embodiment. As a result, the ferrite grain size exceeded 30 占 퐉 and the burr height at the 20th time was increased.

In Test No. 1-14, the rolling finish temperature was low and the coiling temperature was high in the hot rolling, which was outside the scope of the present embodiment. As a result, the Cu concentration in the surface layer was low and the ferrite grain size was large, and the burr height at the beginning of the punching test and the burr height at the twentieth time were increased.

In Test Nos. 1-7 and 1-17, the coiling temperature of the hot rolling was high, which was beyond the scope of the present embodiment. As a result, the Cu concentration in the surface layer of the steel sheet was lowered, and the burr height at the beginning of the punching test and the burr height at the 20th time were increased.

In Test No. 1-24, the rolling finish temperature was low and the final annealing temperature of the cold-rolled steel sheet was high, which was outside the scope of the present embodiment. As a result, the ferrite grain size was large and the burr height at the beginning of the punching test was low, but the burr height was increased in the 20th punching test.

Test Nos. 1 to 10 and 1 to 30 are examples in which the annealing temperature of the hot-rolled steel sheet whose composition is suitable for the present embodiment is changed.

In Test Nos. 1-10, the annealing temperature of the hot-rolled sheet is low and the Cu concentration in the surface layer is low. This increased the burr height at the beginning of the punching test and the burr height at the 20th time.

In Test No. 1 to 30, since the annealing temperature of the hot-rolled sheet was high, the surface Cu concentration was less than 15%. This increased the burr height at the beginning of the punching test and the burr height at the 20th time.

Test Nos. 1-22 and 1-25 are examples in which the final annealing temperature of the cold-rolled sheet of the steel whose composition is suitable for this embodiment is changed.

In Test No. 1-12, the final annealing temperature is low and the Cu concentration in the surface layer is low. This increased the burr height at the beginning of the punching test and the burr height at the 20th time.

In Test Nos. 1 to 25, since the final annealing temperature was high, the ferrite grains coarsely grown. As a result, the burr height at the 20th time was increased.

Test No. 1-27 is an example in which the cooling rate at the final annealing of the steel whose composition is suitable for the present embodiment is changed. In Test Nos. 1 to 27, Cu was precipitated because the cooling rate was slow. As a result, the Cu concentration in the surface layer was lowered. Also, due to the effect of the high annealing temperature, the ferrite grain size became large. As a result, the burr height at the beginning of the punching test and the burr height at the 20th time were both increased.

Test No. 1-29 is an example in which the oxygen concentration at the final annealing of the steel whose composition is suitable for the present embodiment is changed. In Test Nos. 1 to 29, since the oxygen concentration at the final annealing was low, the oxidation scale was thin and the Cr oxide was the main material. As a result, the elemental change in the vicinity of the surface layer became slight, and the Cu concentration became small. Therefore, the burr height at the beginning of the punching test and the burr height at the 20th time were increased.

[Table 1A]

[Table 1B]

[Table 2A]

[Table 2B]

[Table 2C]

[Table 2D]

[Table 2E]

(Second Embodiment)

Hereinafter, examples corresponding to the ferritic stainless steel sheet of the second embodiment are shown below.

The components Nos. 2-1 to 2-36 having the component compositions shown in Tables 3A and 3B were dissolved in a solvent to form a steel ingot. Subsequently, hot rolling was performed under the conditions shown in Tables 4A, 4B, and 4D to obtain a hot rolled sheet having a thickness of 4 mm. This hot-rolled sheet was subjected to hot-rolled sheet annealing by continuous annealing. After acid cleaning, cold-rolling was performed to obtain a cold-rolled sheet having a thickness of 1 mm.

Subsequently, the cold-rolled sheet was finally annealed under the conditions shown in Tables 4A, 4B and 4D to obtain a cold-rolled annealed sheet. The thus obtained cold-rolled annealing plate was subjected to the following test.

(1) Evaluation of punching property

The cold-rolled annealing plate was punched to form a hole having a clearance of 10% and 12 mm, and the height of the burr of the front end surface was measured. This punching test was repeated, and the burr height after punching 20 times in succession was measured. The burr height at the time of continuous punching depends on the contact with the tool at the beginning of the punching process. As a result, stable burr heights are maintained unless large burrs are produced by 20 to 30 machining operations. Therefore, the 20th burr height was measured as an index that does not impair the productivity.

(2) Measurement of ferrite crystal grain size

In the plate thickness cross-section parallel to the rolling direction of the cold-annealed plate, the central portion of the plate thickness was mirror-polished and corroded with aqua regia to reveal the structure. The ASTM nominal grain size of the ferrite particles was measured by the cutting method specified in JIS G0552. The particle diameters were measured in the following order. Five line segments having an actual length of 800 占 퐉 were drawn on the photograph in the sheet thickness direction and five sheets were drawn in the rolling direction. The intersections of these line segments and the ferrite grain boundaries were counted. The total length of the line segments in the plate thickness direction was divided by the number of the intersections, and the average length of the line segments cut into the ferrite grain boundaries in the plate thickness direction was determined. Similarly, the average length of the cut line segments in the rolling direction was also determined. ASTM nominal particle size was obtained by multiplying them again by a mean of 1.13.

(3) Measurement of surface hardness

The surface of the cold-rolled annealing plate was polished with # 600 and the surface hardness was measured by the method specified in JIS Z 2244 using a Vickers hardness meter. The test force at the time of measurement was 9.807 N. Five points were measured, and the average value was taken as the surface hardness.

(4) Measurement of cation fraction of Cu concentration on the steel sheet surface

A square specimen having a side length of 20 mm was cut out from the cold annealing plate. The concentration of Cu in the depth direction while sputtering Ar from the surface was measured using a Rigaku Spectruma GDA750 / Glow Discharge Emission Spectrometer (GDS) under the conditions of an analysis diameter of 4 mm, a measurement pitch of 2.5 mm / min, and an analysis time of 20 sec. Were continuously measured. From the measurement results, the cation element was extracted, and the amount of the cation element was converted into the existing ratio, and the concentration profile inside the outermost layer was determined. From the obtained profile, it is assumed that the Cu concentration at the 5 nm portion from the outermost layer is the surface Cu concentration. 6 is a diagram showing an example of measurement of the surface layer Cu concentration. It can be seen that Cu is remarkably concentrated in the vicinity of the surface layer.

The measurement results are shown in Tables 4C and 4E. From Table 3A, Table 3B, and Table 4A to Table 4E, the following can be found.

In the steel sheets of Test Nos. 2-1 to 2-25, the composition range satisfies the conditions relating to the composition of the present embodiment, but in the steel sheet which does not satisfy the other conditions, the burr height at the 20th punching test is 50 Mu m. The steel sheets of Test Nos. 2-1, 2-5 to 2-8, 2-10, 2-11, 2-13 to 2-15, 2-17 to 2-19, 2-22, All conditions satisfy the range of the present embodiment, and the burr height is preferably 50 占 퐉 or less.

In Test Nos. 2-2, 2-9, 2-12, 2-16, and 2-20, the hot rolling conditions are changed to components that satisfy the range of the present embodiment.

In Test Nos. 2-2 and 2-9, since the finish rolling ratio at the time of hot rolling is out of the range of this embodiment, the burr is large.

In Test No. 2-12, the rolling finish temperature is low in the hot rolling and is outside the scope of the present embodiment. As a result, the Cu concentration in the surface layer is low and the burr height is large.

In Test Nos. 2-16 and 2-20, the coiling temperature of hot rolling is out of the range of the present embodiment. As a result, in Test No. 2-16, the Cu concentration in the surface layer of the steel sheet was lowered, and in Test No. 2-20, the ferrite grain size exceeded 30 탆. The burr height is large on both sides.

Test Nos. 2-3, 2-4, 2-21 and 2-23 are examples in which the conditions of the cold-rolled sheet annealing of the steel according to the present embodiment are changed.

In Test No. 2-3, since the cooling rate after the annealing of the cold-rolled sheet was slow, the ferrite particles coarsely gravitated and the ε-Cu phase precipitated. As a result, the Cu concentration in the surface layer is lowered, and the 20th burr is large.

In Test No. 2-4, the annealing temperature is low. As a result, the surface Cu concentration and the ferrite grain size satisfy the range of the embodiment, but the surface hardness is high. Due to this, the burr is large.

In Test No. 2-21, the cooling rate after cold-rolled sheet annealing was slow, and an ε-Cu phase precipitated. As a result, the concentration of Cu in the surface layer is lowered and the burr of the 20th time is large.

In Test No. 2-23, since the final annealing temperature of the cold-rolled sheet is high, the surface hardness is lowered, and the 20th burr is large.

Test No. 2-25 is an example in which the oxygen concentration at the final annealing of the steel whose composition is suitable for the present embodiment is changed. Since the oxygen concentration is low, the oxide scale is thin and the Cr oxide is the main body. As a result, elemental changes in the vicinity of the surface layer are slight, and Cu concentration is reduced. Therefore, the burr is large.

Since the steel sheets of Test Nos. 2-26 to 2-46 do not satisfy the range of the present embodiment, the burr height is large.

[Table 3A]

[Table 3B]

[Table 4A]

[Table 4B]

[Table 4C]

[Table 4D]

[Table 4E]

The ferritic stainless steel sheet of the first embodiment is excellent in corrosion resistance and can reduce burrs during punching. Therefore, the ferritic stainless steel sheet of the first embodiment can be applied to the fields of kitchens, household electric appliances, utensils, containers, medical instruments, and low-water machines.

The ferritic stainless steel sheet of the second embodiment is excellent in corrosion resistance and can reduce burrs during punching processing. Therefore, the ferritic stainless steel sheet of the second embodiment can be applied to the fields of medical instruments and building hardware.

Claims (3)

C: not more than 0.02 mass% of C, not more than 0.80 mass% of Si, not more than 0.80 mass% of Mn, not more than 1.0 mass% of P, not more than 0.010 mass% By mass or more, more than 0.50% by mass of Al: O, 0.50 to 2.00% by mass of Sn, and 0.001 to 0.1% by mass of Sn, ,
Further, it is preferable that the steel sheet contains at least one selected from Ti: 0.05 to 0.30 mass% or less, Nb: 0.05 to 0.40 mass%, and Ni: 0.05 to 0.50 mass%
The balance being Fe and inevitable impurities,
A ferritic stainless steel sheet excellent in punching workability, wherein the Cu concentration on the surface of the steel sheet is 15% or more at the cation fraction, the ferrite grain size is 30 占 퐉 or less, and the surface hardness is 140 to 180. The steel according to any one of claims 1 to 3, further comprising, by mass%, Mo: 0.01 to 0.50 mass%, B: 0.001 mass% or less, V: 0.50 mass% or less, W: 0.50 mass% By mass, Ca: not more than 0.003 mass%, Zr: not more than 0.30 mass%, REM (rare earth metal): not more than 0.02 mass%, Ta: not more than 0.5 mass%, Sb: 0.001 to 0.3 mass% %, Based on the total weight of the ferritic stainless steel sheet. A steel slab comprising the composition according to claim 1 or 2 is heated to a temperature of 1100 占 폚 or higher and subsequently subjected to hot rolling under the conditions of a rolling rate of 80 to 90% at the finish rolling and a finish temperature of 900 占 폚 or more, Rolled sheet is obtained at 400 to 500 ° C, and then the hot rolled sheet is annealed, pickled, cold-rolled, and finally annealed at a temperature of 850 ° C to 950 ° C and in an atmosphere of 1% or more of oxygen concentration , And then cooling is performed at a cooling rate of 50 占 폚 / s or more in a temperature range of up to 500 占 폚, thereby producing a ferritic stainless steel sheet excellent in punching workability.

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