KR20120099520A - Highly corrosion-resistant cold-rolled ferrite stainless steel sheet having excellent toughness, and process for production thereof - Google Patents

Abstract

An object of the present invention is to provide a highly corrosion-resistant ferritic stainless cold rolled steel sheet excellent in toughness, characterized in that the Charpy impact value at −50 ° C. at a plate thickness of 4 mm is 100 J / cm 2 or more. do. Specifically, in mass%, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.06% or less, S: 0.01% or less, Cr: 18.0-24.0%, Mo: 0.3% or less , Ti: 0.015% or less, Al: 0.20 to 0.40%, N: 0.020% or less, further 10 × (C + N) ≦ Nb ≦ 0.40%, and the component content satisfies the following formula (A), and the balance is Fe And high corrosion resistance ferritic stainless steel cold rolled steel sheet characterized by consisting of inevitable impurities.
Ti × N ≦ 8.00 × 10 ^-5 ‥‥ (A)

Description

Highly corrosion-resistant ferritic stainless steel cold rolled steel sheet and its manufacturing method {HIGHLY CORROSION-RESISTANT COLD-ROLLED FERRITE STAINLESS STEEL SHEET HAVING EXCELLENT TOUGHNESS, AND PROCESS FOR PRODUCTION THEREOF}

The present invention relates to a high-corrosion resistance cold rolled ferritic stainless steel sheet excellent in toughness or workability, and a manufacturing method.

Among stainless steels, due to its excellent corrosion resistance and toughness, SUS304 (18% Cr-8% Ni) (Austenitic stainless steel) (Japanese Industrial Standards, JIS G 4305) of austenitic stainless steel is widely used. However, this steel grade is expensive because it contains a large amount of Ni. In addition, in ferritic stainless steel that does not contain a large amount of Ni, SUS436L (18% Cr-1% Mo) (JIS G 4305) containing Mo is a type of steel having excellent corrosion resistance equivalent to SUS304. have. However, this is also an expensive element, so even a content of only 1% is a significant increase in cost. In addition, this SUS436L cannot be said to have sufficient toughness as a structural member. In addition, in the ferritic stainless steel containing no Mo, there is SUS430J1L (19% Cr-0.5% Cu-0.4% Nb) (JIS G 4305), but it is hard to say that it has sufficient toughness as a structural member.

In recent years, ferritic stainless steel cold rolled steel sheets excellent in low-temperature toughness applicable to structural member applications while having corrosion resistance equivalent to SUS430 and SUS304, which are general-purpose steel grades of stainless steel, are required.

In particular, in obtaining a cold rolled steel sheet excellent in low temperature toughness with a sheet thickness of more than 2 mm to 4 mm thick, in view of securing a rolling reduction of cold rolling, a hot rolled steel sheet having a sheet thickness of 6 mm or more ( hot rolled steel sheet). Ferritic stainless steels are inferior in toughness of hot rolled materials and cold rolled materials as compared to austenitic stainless steels. Hot-rolled sheet annealing is usually performed using a continuous annealing furnace. However, when the toughness of the hot rolled material is insufficient, the ferritic stainless steel hot rolled steel sheet is plated through a line of the continuous annealing process in a state in which tension is added to the hot rolled steel sheet. In other words, the thicker the plate thickness, the higher the probability of breaking. For this reason, conventionally, the board thickness of the ferritic stainless hot rolled sheet steel as a raw material for cold rolling is 4-5 mm. For this reason, the toughness improvement of the ferritic stainless hot-rolled steel sheet of 6 mm or more of plate | board thickness is calculated | required.

In addition, ferritic stainless steel is cheaper than austenitic stainless steel and has excellent corrosion resistance. Therefore, cold rolled steel sheet having a plate thickness of 2 mm or less is widely used for kitchen instruments, household electrical appliances, and the like. It is used. Recently, by improving the decarburizing and denitrogenation technology in the steel making process, a high-purity ferritic stainless cold rolled steel sheet having reduced C and N, which has further improved workability and corrosion resistance, has been developed. There are many opportunities for machining into complex geometries for a wider range of applications.

From this background, among the press workability of a ferritic stainless cold rolled sheet steel, the technique of improving especially deep drawability is desired. In the process which used the deep drawing element abundantly, it becomes important to improve the average r value of a raw material.

Increasing the cold rolling reduction rate is effective for improving the average r value, but in obtaining a cold rolled steel sheet having a sheet thickness of 2 mm or less, a hot rolled steel sheet having a sheet thickness of 6 mm or more is produced from the viewpoint of securing a higher cold rolling ratio. .

For this reason, in order to improve cold rolling reduction rate in order to improve average r value as mentioned above, the toughness improvement of the ferritic stainless steel hot rolled sheet steel of 6 mm or more of plate | board thickness is calculated | required.

On the other hand, as a technique of improving the toughness of ferritic stainless steel, in Patent Document 1, in mass%, C: 0.020% or less, Si: 0.30 to 1.00%, Mn: 1.00% or less, P: 0.040% or less, and S: 0.010 % Or less, Cr: 20.0-28.0%, Ni: 0.6% or less, Al: 0.03-0.15%, N: 0.020% or less, O: 0.0020-0.0150%, Mo: 0.3-1.5%, Nb: 0.25-0.60%, A ferritic stainless steel sheet for water heaters containing Ti: 0.05% or less, the balance being made of Fe and unavoidable impurities, and satisfying 25≤Cr + 3.3Mo≤30 and 0.35≤Si + Al≤0.85. Is disclosed.

Moreover, in patent document 2, in mass%, C: 0.1% or less, N: 0.003-0.05%, Si: 0.03-1.5%, Mn: 1.0% or less, P: 0.04% or less, S: 0.03% or less, Cr : 10-30%, Cu: 2% or less, Ni: 2% or less, Mo: 3% or less, V: 1% or less, Ti: 0.02-0.5%, O (oxygen): 0.001-0.005%, Nb: 0.8 % Or less, Al: 0.001-0.15%, Zr: 0.3% or less, B: 0.1% or less, Ca: 0.003% or less, Mg: less than 0.0005%, Ti x N: 0.0005 or more, and the balance is Fe and inevitable impurities The ferritic stainless steel with excellent workability and toughness in which a composite inclusion of Ti-containing inclusions and Ti-containing inclusions is dispersed in the steel with an Al and Mg ratio of 0.3 to 0.5 It is.

However, Patent Document 1, for the purpose of securing the productivity such as preventing the breakage of the steel strip at the time of hot-rolled sheet annealing or cold rolling, hot rolling with a sheet thickness of 4 mm at 0 ° C Since it is a technique which improves the toughness of a board and also contains a large amount of Mo element, the intermetallic compound etc. which reduce toughness are also easy to produce | generate. For this reason, it is thought that toughness is inadequate for the application to the use with thicker plate | board thickness which this invention aims at.

Moreover, also in patent document 2, dispersion control of Ti type interference | inclusion is difficult, toughness falls easily by coarsening, and sufficient toughness is not obtained.

Japanese Laid-Open Patent Publication No. 2008-190035 Japanese Laid-Open Patent Publication No. 2001-020046

As described above, in the method of containing Mo or Ti, the toughness improvement of the hot rolled sheet and the cold rolled sheet of ferritic stainless steel is not sufficiently achieved.

Therefore, the present invention significantly improves the toughness at the plate thickness of 6 mm or more of the ferritic stainless hot rolled steel sheet, so that the charpy impact value of −50 ° C. is achieved in the cold rolled steel sheet having a plate thickness of 4 mm or less. An object of the present invention is to provide a highly corrosion-resistant ferritic stainless cold rolled steel sheet excellent in toughness, characterized in that it is 100 J / cm 2 or more, and a manufacturing method thereof.

In addition, the present invention further provides a highly corrosion-resistant ferritic stainless cold rolled steel sheet having a toughness of −50 ° C. in a cold rolled steel sheet having a sheet thickness of 2 mm or less and further excellent toughness and workability, in particular, deep drawing property. It aims at providing the manufacturing method.

The inventors earnestly examined about the method of obtaining the Nb containing ferritic stainless cold rolled sheet steel which does not contain expensive Ni and Mo, and was excellent in corrosion resistance, toughness, or workability, in order to solve the above-mentioned subject.

First, the experimental result which led to discovering this invention is demonstrated. Hereinafter, unless otherwise indicated, all% display of a chemical component shall mean the mass%.

First, as a stabilizing element of ferritic stainless steel, in Ti-containing steel, coarse TiN precipitates produced from the solidification step are present in the steel, and the toughness is greatly reduced by the notch effect of the precipitates. Therefore, attention was paid to Al as a result of examining various alloy influences on the toughness of Nb-containing ferritic stainless steel without selecting Ti as much as possible and selecting Nb as a stabilizing element. 21% Cr-0.25% Nb-low C, N steel, the steel which contains 0.03-0.50% of Al, is heated, it is heated at 1200 degreeC, it hot-rolls, winding temperature is 450 degreeC, board | plate thickness A 7 mm hot rolled sheet was produced. A Charpy impact test at 0 ° C. of the obtained hot rolled sheet having a thickness of 7 mm was performed. The result is shown in FIG. The value of the vertical axis | shaft of FIG. 1 is the value converted into absorption energy per unit area (henceforth a Charpy impact value) by subtracting the value of the absorption energy obtained by a test from the cross-sectional area of the notch part of an impact test piece.

In addition, the inventors annealed the hot rolled steel sheet having a sheet thickness of 7 mm to produce a hot rolled and annealed steel sheet, and acid-cleaned and cold rolled to a plate thickness of 4 mm. Furthermore, the Charpy impact test at -50 degreeC of the cold-rolled annealing plate of 4 mm of plate | board thickness obtained by performing finish annealing at 980 degreeC was done. The results are shown in Fig.

The value of the vertical axis | shaft of FIG. 2 is the same as that of FIG.

1 and 2 show that the toughness of the hot rolled steel sheet with a plate thickness of 7 mm and the cold rolled annealing plate with a plate thickness of 4 mm is remarkably improved by containing Al in the range of 0.20 to 0.40%.

Although this reason is not certain, it is presumed that the amount of O in the steel decreases due to the inclusion of Al, and the inclusions decrease. In addition, the fall of toughness in the range exceeding 0.40% of Al is considered to be due to the increase of solid solution Al.

Next, in order to evaluate the influence of Ti and N on the toughness of the hot rolled sheet and the cold rolled annealing plate, the amount of Ti and N was changed in 21% Cr-0.25% Nb-0.25% Al-low CN steel shown in Table 1 The steel was melted, heated to 1200 ° C, hot rolling, the winding temperature was 450 ° C, and a hot rolled plate having a plate thickness of 7 mm was produced. The Charpy impact test at 0 degreeC of the obtained hot rolled sheet of 7 mm was performed. The result is shown in FIG. Further, the hot rolled sheet having a thickness of 7 mm was annealed to prepare a hot rolled annealed sheet, which was subjected to acid cleaning, followed by cold rolling to a plate thickness of 4 mm. Furthermore, by cold-annealing the cold-rolled sheet at 980 ° C, a cold-rolled annealing plate having a plate thickness of 4 mm was produced, and the Charpy impact test was conducted at -50 ° C. The result is shown in FIG. 3 and 4 represent the product of Ti (%) and N (%), and are values corresponding to solubility product constants (hereinafter referred to as "solubility product constants"). In the range where Ti (%) xN (%) exceeded ^{8.0x10 <-5>} from FIG. 3 and FIG. 4, toughness fell remarkably.

To investigate this cause, the sectional structures of the cold rolled and anneald steel sheets of Experiments 2-4 and 2-5 were polished and then corroded with aqua regalis. Samples were observed and analyzed with an electron scanning microscope (SEM) and an energy dispersive X-ray analyzer (EDX). In the steel of the sample of 2-4 (The solubility product constant of Ti and N is 8.00x10 <^-5> ), the fine spherical Nb carbide of diameter 200-300 nm was observed. On the other hand, in the steel of the sample of the low toughness experiment 2-5 (the solubility product constant of Ti and N is 9.52x10 <^-5> ) of a hot rolled sheet and a cold rolled annealing plate, the coarse rectangular parallelepiped whose diameter is 2-5 micrometers Numerous Ti nitrides of a rectangular solid like have been observed. In this regard, when the solubility product constant of Ti and N exceeds 8.00 × 10 ⁻⁵ , Ti nitride is precipitated and coarsened from the coagulation step, and the toughness is deteriorated due to the notch effect.

Moreover, the hot-rolled sheet plate thickness suitable for manufacturing the cold-rolled annealing plate of 4 mm of plate | board thickness was also examined. Using the steel of Experiment 2-2 of Table 1, four types of hot-rolled sheets of 5.0 mm, 5.7 mm, 6.8 mm, and 8.0 mm were prepared by hot rolling. Furthermore, after annealing and acid-cleaning a hot rolled sheet, it cold-rolled and finish annealing and produced the cold rolled annealing plate of 4 mm of plate | board thickness. The Charpy impact test at -50 degreeC of the obtained cold-rolled annealing board of 4 mm of thickness was done.

These results are shown in Table 2. Experiment 3-2 (plate thickness of hot rolled sheet 5.7 mm, cold rolling reduction rate 30%), Experiment 3-3 (plate thickness of hot rolled sheet 6.8 mm, cold rolling reduction rate 41%) and experiment 3-4 (plate thickness of hot rolled sheet) The Charpy impact value of -50 degreeC of the cold-rolled annealing plate of 8.0 mm and 50% of cold-rolling reduction rates was 100 J / cm <2> or more. On the other hand, the Charpy impact value at -50 ° C of the cold rolled annealing plate of Experiment 3-1 (plate thickness of 5.0 mm, cold rolling reduction rate 20%) was less than 100 J / cm 2. After polishing the cross-sectional structure of these cold-rolled annealing plates, the samples corroded with aqua regia were observed with an optical microscope. As a result, in the sample of Experiment 3-1, a band-shaped extended coarse recovery structure was observed in the rolling direction. . In this regard, when the cold rolling reduction rate is less than 30%, the accumulation of strain energy is insufficient, it is not sufficiently recrystallized by cold rolling annealing, it is considered to be a coarse recovery structure, and the toughness is deteriorated. .

From the above examination results, Cr content was made into 18.0-24.0% from the viewpoint of the corrosion resistance and manufacturability, and after containing an appropriate amount of Al, the solubility product constant [Ti%] x [N% of Ti and N contained in steel ] In an appropriate amount, suppresses the formation of coarse TiN precipitates precipitated from the molten steel stage that causes the toughness of the hot rolled sheet and the cold rolled annealing plate, and found that a highly corrosion-resistant ferritic stainless cold rolled steel sheet having excellent toughness is obtained. . This invention is made | formed based on these recognition.

Next, the influence of cold rolling reduction ratio was examined also aiming at the average r value of 1.30 or more of the cold rolling annealing board considered generally the index | index of which deep drawing property is favorable. The steel of Experiment 2-2 of Table 1 was heated to 1200 degreeC, hot rolling, the winding temperature was 450 degreeC, and plate | board thickness was 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 7.0 Seven types of hot rolled sheets of mm and 8.0 mm were manufactured. Furthermore, after annealing and acid-cleaning a hot rolled sheet, it cold-rolled and finish annealing and produced the cold rolled annealing plate of 2 mm of plate | board thickness. JIS 13B B test piece was cut out from the obtained cold-rolled annealing plate of 2 mm in thickness along the direction of a 45 degree with respect to a rolling direction, a rolling direction, and a 90 degree with respect to a rolling direction, and 15% tensile distortion was made to each test piece. After giving it, the average r value shown by following formula was calculated | required.

The average r value = (r _L + 2r _D + r _C ) / 4, where r _L , r _D , and r _C are the r values in the rolling direction, the 45 ° direction with respect to the rolling direction, and the 90 ° direction with respect to the rolling direction, respectively. . The larger the average r value, the better the deep drawability.

These results are shown in Table 3 and FIG. In the sample which cold-rolled the cold rolling reduction ratio to 65% or more, the target average r value obtained the characteristic of 1.30 or more.

This invention is made | formed based on these recognition.

That is, the structure of this invention is as follows.

(1) In mass%, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.06% or less, S: 0.01% or less, Cr: 18.0-24.0%, Mo: 0.3% or less, Ti: 0.015% or less, Al: 0.20 to 0.40%, N: 0.020% or less, further 10 × (C + N) ≦ Nb ≦ 0.40%, and the component content satisfies the following formula (A), with the balance being Fe and A high corrosion resistant ferritic stainless steel cold rolled steel sheet having excellent toughness, comprising inevitable impurities.

Ti x N? 8.00 x 10 ^-5 (A)

Here, each element symbol shows the component content (mass%) in steel.

(2) The ferritic stainless cold rolled steel sheet according to (1), wherein the mass is Si: 0.5% or less, Mn: 0.8% or less and Ti: 0.010% or less.

(3) The highly corrosion-resistant ferritic stainless cold rolled steel sheet excellent in toughness as described in (1) containing C: 0.015% or less and N: 0.015% or less by mass%.

(4) Furthermore, the highly corrosion-resistant ferritic stainless cold rolled steel sheet excellent in the toughness in any one of (1)-(3) containing at least 1 in the following group A or the group of B by mass%.

At least one selected from Group A: Cu: 0.3 to 0.8%, Ni: 1.0% or less, and Co: 1.0% or less

Group B: B: 0.0002-0.0020%

(5) The highly corrosion-resistant ferritic stainless steel cold rolled steel sheet having excellent toughness according to any one of (1) to (4), wherein the Charpy impact characteristic after the finish annealing of the cold rolled steel sheet is 100 J / cm 2 or more in the Charpy impact value at -50 ° C. .

(6) A ferritic stainless steel cold rolled steel sheet is produced by heating, hot rolling, hot rolled steel sheet annealing, acid washing, cold rolling, and finish annealing using a slab having the composition according to any one of the above (1) to (4). A method for producing a highly corrosion-resistant ferritic stainless steel cold rolled steel sheet having excellent toughness after the hot rolling and before the hot rolled steel sheet annealing is 6 mm or more.

(7) The method for producing a highly corrosion-resistant ferritic stainless cold rolled steel sheet according to (6), wherein the Charpy impact characteristic of the hot rolled steel sheet is 50 J / cm 2 or more at a Charpy impact value at 0 ° C.

(8) The manufacturing method of the highly corrosion-resistant ferritic stainless cold rolled sheet steel excellent in toughness as described in (6) or (7) characterized by making the rolling reduction rate of the said rolling in said cold rolling 30% or more.

According to the present invention, a highly corrosion-resistant ferritic stainless steel cold rolled steel sheet having excellent toughness, characterized in that the Charpy impact value at -50 ° C at a plate thickness of 4 mm is 100 J / cm 2 or more, more preferably 150 J / cm 2 or more. Can be.

In addition to the above improvement in toughness, a high corrosion resistant ferritic stainless cold rolled steel sheet excellent in workability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the effect of Al amount on the Charpy impact value of 0 degreeC.
It is a figure which shows the influence of Al amount on the Charpy impact value of -50 degreeC.
It is a figure which shows the influence of [Ti (%)] x [N (%)] on the Charpy impact value of 0 degreeC.
It is a figure which shows the influence of [Ti (%)] x [N (%)] on the Charpy impact value of -50 degreeC.
It is a figure which shows the relationship between a cold rolling reduction rate and an average r value.

(Mode for carrying out the invention)

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated in detail.

First, the reason for limitation of the component of the ferritic stainless steel of this invention is demonstrated.

C: 0.020% or less

Low C is preferable because C is easy to form Cr carbide in combination with Cr, and when Cr carbide is formed in a heat-affected zone during welding, it causes intergranular corrosion. . Therefore, C is 0.020% or less, More preferably, you may be 0.015% or less. Moreover, it is preferable to set it as 0.003 to 0.010% from a viewpoint of refining cost and the case where especially high intergranular corrosion prevention is calculated | required.

Si: 1.0% or less

Si is an element useful as a deoxidizing agent. In order to acquire this effect, 0.05% or more is preferable. However, when it contains a large amount, toughness will fall. Therefore, Si is made into 1.0% or less. More preferably, it is 0.5% or less, More preferably, it is 0.05 to 0.3% or less.

Mn: 1.0% or less

Mn combines with S present in the steel to form MnS, which is a fusible sulfide, to lower corrosion resistance. Therefore, Mn is made into 1.0% or less. More preferably, it is 0.8% or less. Moreover, especially when high corrosion resistance is calculated | required and a viewpoint of refining cost, More preferably, it is 0.05 to 0.6% or less.

P: 0.06% or less

Since P is an element harmful to corrosion resistance, it is preferable to reduce P as much as possible. Moreover, when it exceeds 0.06%, workability will fall by solid solution strengthening. Therefore, P is made into 0.06% or less. Moreover, when workability and toughness are considered, it is preferably 0.04% or less.

S: not more than 0.01%

Since S is an element harmful to corrosion resistance, it is preferable to reduce S as much as possible, and it is made into 0.01% or less. Moreover, in order to acquire high corrosion resistance, Preferably it is 0.006% or less.

Cr: 18.0-24.0%

Cr is an element which forms a passive film on the surface and improves corrosion resistance. If Cr content is less than 18.0%, sufficient corrosion resistance is not obtained. On the other hand, if it exceeds 24.0%, sigma phase embrittlement or brittleness at 475 DEG C tends to occur, and toughness tends to decrease. Therefore, Cr is made into 18.0-24.0%. Moreover, from a viewpoint of high corrosion resistance, Preferably it is 20.0-24.0%.

Mo: 0.3% or less

Mo contains the effect of improving the corrosion resistance of stainless steel. When contained excessively, coarse intermetallic compounds, such as a Laves phase, will be produced and toughness will fall. Therefore, Mo is made into 0.3% or less.

Nb: 10 × (C + N)? 0.40%

Nb has the effect of making C or N harmful to corrosion resistance harmless as Nb carbide, Nb nitride, or a precipitate in which these are mixed, and improving corrosion resistance. However, when the amount of Nb is less than 10 times the amount of (C + N), precipitation of Nb carbide, Nb nitride, or precipitates in which these are combined is insufficient, and Cr carbide, Cr nitride, or precipitates in which these are combined precipitates and corrosion resistance is lowered. do. Therefore, Nb is limited to 10x (C + N)% or more. On the other hand, when it contains excessively, coarse intermetallic compounds, such as a Laves phase, will be produced and toughness will fall. Therefore, Nb is made into 10x (C + N)-0.40%. Preferably it is 12 * (C + N)-0.30%.

Here, C and N have shown the content of each component by the mass%.

Ti: 0.015%

Ti forms coarse nitride and reduces toughness. Therefore, Ti is made into 0.015% or less. More preferably, you may be 0.010% or less. In addition, when a further high toughness is required, it is preferably 0.005% or less.

N: 0.020% or less

N forms toughness by forming nitride with Ti or Nb. In particular, when Ti coexists, coarse TiN precipitate produces | generates from the solidification step of molten steel, and a toughness falls remarkably by the notch effect. Therefore, N is made into 0.020% or less. Moreover, when especially high corrosion resistance is calculated | required, it is 0.015% or less, More preferably, it is 0.010% or less.

Al: 0.20 to 0.40%

Al is an important element in the present invention and has an effect of improving toughness. With respect to toughness aimed at the present invention, the effect is insufficient at less than 0.20%. Moreover, when it exceeds 0.40%, hot workability will fall. Therefore, Al is made into 0.20 to 0.40%. Moreover, when especially high toughness is calculated | required, it is preferable to set it as 0.20 to 0.30%.

Ti x N≤8.00 x 10 ^-5

As mentioned above, coarse TiN precipitate which becomes a factor of the toughness fall of a ferritic stainless steel is produced | generated from the solidification step. In order to suppress precipitation of this TiN, Ti and N are so preferable that they are small, and the solubility product constant of Ti * N is limited to 8.00 * 10 <^-5> or less. Preferably it is 5.00 * 10 <^-5> or less. Here, Ti and N have shown the content of each component by the mass%.

Remainder other than said chemical component is Fe and an unavoidable impurity. Moreover, as an unavoidable impurity, although Mg: 0.0020% or less, Ca: 0.0020% or less, V: 0.10% or less can be allowed, it is not limited to these elements, for example.

The ferritic stainless steel of the present invention can obtain desired properties from the above essential content elements, but may contain the following elements according to desired properties. However, as long as it is a range which does not impair the effect of this invention, containing of components other than the following is not rejected.

Cu: 0.3-0.8%

When contained, Cu is a useful element because it improves corrosion resistance, and it is an element especially effective in reducing crevice corrosion. In order to exhibit this effect, 0.3% or more of content is required. On the other hand, when it contains exceeding 0.8%, hot workability will fall. Therefore, Cu is made into 0.3 to 0.8%. Preferably it is 0.3 to 0.5%. However, especially when high corrosion resistance is not required, it is not necessary to contain Cu because it raises manufacturing cost and impairs economic efficiency.

Ni: 1.0% or less

When Ni contains, there exists an effect which prevents the fall of hot workability by Cu containing. It also has the effect of reducing inter-corrosion. In order to acquire this effect, 0.05% or more is preferable. However, in addition to being an expensive element, even if it contains exceeding 1.0%, these effects are saturated and rather, hot workability is reduced. Therefore, Ni is made into 1.0% or less. Preferably it is 0.05 to 0.4%.

Co: 1.0% or less

When Co contains, it is an element which contributes to the improvement of low-temperature toughness. In order to acquire this effect, 0.05% or more is preferable. However, excessive content reduces ductility. Therefore, Co is made into 1.0% or less.

B: 0.0002 to 0.0020%

When contained, B is an effective element in order to improve the resistance to cold-work embrittlement at the time of deep drawing molding. The effect is not obtained at less than 0.0002%. On the other hand, excessive content deteriorates hot workability and deep drawability. Therefore, when it contains B, the range of 0.0002 to 0.0020% is preferable.

In evaluating the toughness of the cold rolled and annealed steel sheet of the steel sheet of the present invention, the temperature of −50 ° C. was selected in the Charpy impact test, so that the steel of the present invention was constructed in the field of building materials in cold latitudes. It is because the environment used as a consideration was considered, and after finishing annealing of the cold rolled sheet steel, the Charpy impact value in the Charpy impact test in -50 degreeC evaluated 100 J / cm <2> or more as favorable. Moreover, 150 J / cm <2> or more evaluated as very favorable.

In addition, evaluation of the corrosion resistance of the steel plate was performed by measuring a pitting potential as described later in accordance with JIS G 0577, and made 180 kV vs SCE or more good and less than 180 kV vs SCE.

In addition, the processing characteristic after finish annealing of a cold rolled sheet steel evaluated with the average r value, as mentioned later, and made the case where the value is 1.30 or more favorable.

Next, the manufacturing method of the ferritic stainless steel of this invention is demonstrated.

In the efficient production method of the present invention, a continuous casting is performed on a slab, heated in a range of 1100 to 1300 ° C, hot rolling is performed to obtain a hot rolled coil. When the coil winding temperature in hot rolling exceeds 650 degreeC, carbides and an intermetallic compound will precipitate after winding, and toughness will fall. For this reason, it is preferable to make winding temperature into 650 degreeC or less, and when high toughness is calculated | required, it is preferable to make winding temperature into 450 degrees C or less. In addition, in order to manufacture the cold rolled annealing plate excellent in the toughness of 4 mm or less of plate | board thickness, or the cold rolled annealing plate excellent in the toughness and workability of 2 mm or less of plate | board thickness, a hot rolled sheet steel (simply a "hot rolled sheet" from a viewpoint of securing cold rolling reduction rate. Sheet thickness) is 6 mm or more. More preferably, it is 7 mm or more. The obtained hot rolled sheet is annealed and acid washed in the range of 900-1150 degreeC by a continuous annealing and an acid washing line. According to the continuous annealing line of the hot rolled sheet, since the line sheet is plated in a state where tension is applied to the hot rolled sheet, sheet fracture may occur when the toughness of the hot rolled sheet is insufficient, and thus, Charpy of the hot rolled sheet at 0 ° C. It is preferable that an impact value is 50 J / cm <2> or more.

Next, cold rolling and finish annealing are performed on the hot rolled annealing plate (steel sheet which annealed the hot rolled steel sheet) to obtain a cold rolled annealing plate.

In order to obtain a high toughness cold rolling annealing plate, it is preferable to secure 30% or more of the cold rolling reduction rate in cold rolling in total so that the coarse recovery structure extended in the rolling direction may not remain in the finish annealing.

In addition, in order to obtain a high toughness and high workability cold rolled annealing plate, it is preferable to secure a cold rolling reduction rate at 65% or more and to sufficiently store distortion energy.

In addition, it is preferable to anneal finish annealing at the temperature of 950 degreeC or more.

The manufacturing method of the ferritic stainless steel hot rolled sheet steel of this invention is not limited to the method described here, A well-known method is applicable.

Example 1

The ferritic stainless steel of the chemical component shown in Table 4-1 and Table 4-2 was melted, and it was set as the slab of 250 mm thickness by the continuous casting method. After heating these slabs to 1200 degreeC, it rough-rolls to 35 mm thickness, finish rolling starts at 1050 degreeC, finishes at 900 degreeC, winds up to 500 degreeC in coil shape, and cools. A hot-rolled sheet of 8 mm shall be used, and five test specimens (but the width shall be the plate thickness dimension) specified in JIS Z 2202 are taken for each of five pieces (the rolling direction is the collecting direction and the impact direction is the rolling width direction and the width of the test specimen). Silver plate thickness), and Charpy impact test was performed under the conditions of test temperature: 0 ° C in accordance with JIS Z 2242. The five Charpy impact values were averaged to make the case of 50 J / cm 2 or more good and the case of less than 50 J / cm 2 to be defective.

Furthermore, after holding a hot rolled sheet for 80 second (maximum temperature: 1100 degreeC) at 1050 degreeC or more, it annealed to cool and set it as the hot rolled annealing plate. After the obtained hot rolled annealing plate was acid-cleaned, it was cold rolled to the plate thickness shown in Table 5, and finish annealing was performed at 980 degreeC. From each of these cold-rolled annealing plates, four test specimens (but the width was set to 4 mm) specified in JIS Z 2202 were collected five times each (rolling direction is the sampling direction, impact direction is the rolling width direction, and test piece width is the plate thickness). In accordance with the provisions of JIS Z 2242, the Charpy impact test was conducted under the conditions of a test temperature of -50 ° C. Five Charpy impact values were averaged, and the case of 100 J / cm <2> or more was favorable and the case below 100 J / cm <2> was made defect. Moreover, the case where 150 J / cm <2> or more was made very favorable.

Moreover, about the test piece collected from the cold-rolled annealing plate, the pitting potential was measured in 3.5% NaCl solution and 30 degreeC according to JISG0577, and corrosion resistance was evaluated. More than 180 Hz vs SCE was good, and less than 180 Hz vs SCE was bad.

The obtained result is combined with Table 5 and shown. As shown in Table 5, steel sheet No. 4-7, 10-16, 18-21, 23-24, 26-34, 36 all have good toughness with a Charpy impact value of −50 ° C. of 100 J / cm 2 or more, and a corrosion resistance formula potential of 180 kV vs. It was favorable more than SCE. On the other hand, steel plate No. with little content of Nb. Steel plate No. 3 with less content of 3 and Cr 35 had a formal potential of less than 180 kV vs SCE, indicating poor corrosion resistance. In addition, steel sheet No. Since 1, 2, 8, 9, 17, 22, and 25 have the Charpy impact value of 0 degreeC of a hot rolled sheet less than 50 J / cm <2>, there exists a possibility of the plate breaking in the continuous annealing line mail box in tension addition, The subsequent evaluation is not performed. In addition, the solubility product constant of Ti and N was large, the plate | board thickness of the hot rolled sheet steel was 5 mm, and the steel plate No. 37 had a Charpy impact value of -50 ° C of less than 100 J / cm 2.

[Example 2]

Example 2 is the same as that of Example 1 except the cold rolling reduction rate of the cold rolled sheet steel of Example 1, and the plate thickness of a cold rolled annealing plate. Therefore, the steel No. of Table 6 of Example 2 is the same as the steel No. shown in Table 4-1, Table 4-2, and Table 5 of Example 1. FIG. That is, after acid-cleaning the hot rolled annealing plate of Example 1, it cold-rolled to the plate thickness shown in Table 6, and finish annealing was performed at 980 degreeC. JIS 13B test piece was cut out along the rolling direction of these cold-rolled annealing boards, 45 degrees with respect to a rolling direction, and 90 degrees with respect to a rolling direction, and after giving 15% tensile distortion to each test piece, the average r I got the value. The average r value made 1.30 or more good, and made less than 1.30 bad.

In addition, five specimens of No. 4 specified in JIS Z 2202 were collected (the rolling direction is the collecting direction, the impact direction is the rolling width direction, and the width of the test piece is the plate thickness), and the test was performed in accordance with the provisions of JIS Z 2242. Temperature: The Charpy impact test was performed on the conditions of -50 degreeC. Five Charpy impact values were averaged, and the case of 100 J / cm <2> or more was favorable and the case below 100 J / cm <2> was made defect. Moreover, the case where 150 J / cm <2> or more was made very favorable.

Moreover, about the test piece collected from the cold-rolled annealing plate, the formula electric potential was measured in 3.5% NaCl solution and 30 degreeC according to JISG0577, and corrosion resistance was evaluated. More than 180 Hz vs SCE was good, and less than 180 Hz vs SCE was bad.

The obtained result is combined with Table 6 and shown. As shown in Table 6, the cold rolling reduction rate is 65% or more. 44-47, 52-56, 58-61, 63-64, 66-74 have the average r value of 1.30 or more, and the Charpy impact value of -50 degreeC is also 100J / cm <2> or more, high toughness, and corrosion resistance formula The potential was good at 180 kV vs SCE or more.

On the other hand, the steel sheet No. 2 whose cold rolling reduction rate is less than 65%. 50-51 had an average r value of less than 1.30. In addition, steel sheet No. 41, 42, 48, 49, 57, 62, 65, since the Charpy impact value at 0 ° C. of the hot rolled sheet is less than 50 J / cm 2, there is a possibility of rupture of the sheet in the continuous annealing line plate in the tension addition, The subsequent evaluation is not performed. In addition, steel sheet No. with little content of Nb. Steel plate No. 43 with low content of 43 and Cr 75 had a formal potential of less than 180 kV vs SCE, and had poor corrosion resistance. In addition, the solubility product constant of Ti x N was large, the sheet thickness of the hot rolled steel sheet was 5 mm, and the steel sheet No. As for 77, the Charpy impact value of -50 degreeC became less than 100 J / cm <2>.

Ferritic stainless steel cold rolled steel sheet provided by the present invention is excellent in corrosion resistance and toughness, such as back of the truck, grating, various types of floor materials, and clasps. It is promising as a material for structural members such as civil engineering and construction.

Alternatively, the ferritic stainless steel cold rolled steel sheet provided by the present invention is not only excellent in workability but also excellent in toughness and corrosion resistance, and in addition to deep drawing applications such as kitchen appliances, transportation equipment such as home appliances and luggage compartments of trucks. It is also promising for materials such as various flooring materials such as gratings, civil engineering such as metal fittings, and structural members such as building applications.

[Table 1]

[Table 2]

[Table 3]

Table 4-1

Table 4-2

[Table 5]

TABLE 6

Claims (8)

In mass%, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.06% or less, S: 0.01% or less, Cr: 18.0-24.0%, Mo: 0.3% or less, Ti: 0.015 % Or less, N: 0.020% or less, Al: 0.20-0.40%, 10x (C + N) ≤ Nb ≤ 0.40%, and the component content satisfies the following formula (A), and the balance is Fe and inevitable Ferritic stainless steel cold rolled steel sheet composed of impurities.
Ti × N ≦ 8.0 × 10 ⁻⁵ ‥‥ (A)
Here, each element symbol shows the component content (mass%) in steel. The method of claim 1,
Further, a ferritic stainless cold rolled steel sheet containing, in mass%, Si: 0.5% or less, Mn: 0.8% or less, and Ti: 0.010% or less. The method of claim 1,
Moreover, the ferritic stainless cold rolled sheet steel containing C: 0.015% or less and N: 0.015% or less by mass%. 4. The method according to any one of claims 1 to 3,
Moreover, the ferritic stainless cold rolled sheet steel containing at least 1 in the following group A or the group of B by mass%.
At least one selected from Group A: Cu: 0.3 to 0.8%, Ni: 1.0% or less, and Co: 1.0% or less.
Group B: B: 0.0002-0.0020%. 5. The method according to any one of claims 1 to 4,
The ferritic stainless steel cold rolled steel sheet whose Charpy impact characteristic after finish annealing of the said cold rolled steel sheet is 100 J / cm <2> or more in Charpy impact value in -50 degreeC. A method for producing a ferritic stainless cold rolled steel sheet by heating, hot rolling, hot rolled steel sheet annealing, acid cleaning, cold rolling, and finishing annealing of the slab having the composition according to any one of claims 1 to 4, wherein A method for producing a ferritic stainless steel cold rolled steel sheet, the thickness of the hot rolled steel sheet after rolling and before the hot rolled steel sheet annealing. The method of claim 6,
A method for producing a ferritic stainless steel cold rolled steel sheet, wherein the Charpy impact characteristic of the hot rolled steel sheet is 50 J / cm 2 or more as the Charpy impact value at 0 ° C. 8. The method according to claim 6 or 7,
The manufacturing method of the ferritic stainless cold rolled sheet steel which makes 30% or more the rolling reduction rate of the said cold rolling.

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