JPH08260043A - Production of ferritic stainless steel sheet excellent in formability - Google Patents

Abstract

PURPOSE: To produce a ferritic stainless steel sheet having excellent r-value, elongation, and formability even if hot rolled plate annealing is omitted, by subjecting a steel stock having a specific composition consisting of C, Si, Mn, Cr, S, O, N, and Fe to hot rolling under specific conditions and then to cold rolling. CONSTITUTION: A ferritic stainless steel stock, which has a composition consisting of, by weight, <=0.005% C, <=0.5% Si, 0.1-0.5% Mn, 10-35% Cr, <=0.0030% S, <=0.0040% O, <=0.005% N, and the balance Fe with inevitable impurities and satisfying (C+N)<=0.0060% and further containing, if necessary, 4(C+N) to 0.5% Ti or one or more kinds among <=3.0% Mo, <=0.2% Nb, and <=0.002% B or either or both of 0.0003-0.02% Se and 0.0005-0.01% Ca, is hot- rolled. Hot rolling conditions at this time are: rolling rate at the final pass, >=1000m/min; rolling finishing temp., >=800 deg.C; cumulative draft at final side 4 passes, >=70%; and coiling temp., >=600 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferritic stainless steel sheet (including steel strip) which exhibits excellent formability even if hot-rolled sheet annealing is omitted.

[0002]

2. Description of the Related Art Ferrite-based stainless steel sheets are widely used in various fields such as kitchen appliances and automobile parts because they are generally superior in stress corrosion cracking resistance and cheaper than austenitic stainless steel sheets.
In such a ferritic stainless steel sheet, the corrosion resistance is generally improved by increasing the amounts of Cr and Mo. However, while increasing the amount of Cr and Mo improves corrosion resistance, it hardens the steel sheet material and reduces formability. Therefore, in a ferritic stainless steel sheet, in order to improve both the corrosion resistance and the formability, it is not enough to simply increase the amount of Cr or Mo. As a countermeasure against this, impurity elements such as C, N, and S are added. Reducing is believed to be effective.

By the way, a ferritic stainless steel sheet is usually manufactured by heating a continuously cast slab and then performing steps of hot rolling, hot rolling annealing, pickling, cold rolling and finish annealing. The purpose of hot-rolled sheet annealing in the above process is (1) to remove rolling strain and improve cold rolling property.
(2) Formability, in particular, to improve deep drawability using the r value as an index. However, the hot-rolled sheet annealing step is not desirable from the viewpoint of energy saving, productivity improvement, etc., and a technique for omitting the hot-rolled sheet annealing step is disclosed in, for example, JP-A-57-35.
It is disclosed in Japanese Patent No. 634, etc.

[0004]

However, when the step of omitting the hot-rolled sheet annealing is applied to the above ferritic stainless steel having reduced C, N, and S, the crystal grains after hot-rolling become coarse, and As a result, there is a problem that the formability of the cold rolled annealed plate is deteriorated.

Therefore, a main object of the present invention is to establish a technique for producing a ferritic stainless steel sheet which does not cause the above-mentioned problems of the above-mentioned known techniques even if the hot-rolled sheet annealing is omitted. . Another object of the present invention is
Even if hot-rolled sheet annealing is omitted, r value: 1.0 or more, El: 33%
It is to provide a method for producing a ferritic stainless steel sheet having the above characteristics and excellent in formability.

[0006]

Means for Solving the Problems Now, as a result of earnest research aimed at realizing the above-mentioned object, the inventors have found that the rolling temperature, rolling speed, and rolling reduction in the finish rolling stage of hot rolling of ferritic stainless steel. By appropriately controlling the rolling rate and the winding temperature, a large rolling strain is applied in a short time to refine the structure and at the same time enhance the driving force for recrystallization, and complete the recrystallization while hot rolling. It has been found that excellent formability can be obtained even if hot-rolled sheet annealing is omitted, and the present invention has been completed.

The present invention has the gist of the following configuration embodying the above concept. (1) C: 0.005 wt% or less, Si: 0.5 wt% or less, M
n: 0.1-0.5 wt%, Cr: 10-35 wt%, S: 0.003
0 wt% or less, O: 0.0040 wt% or less, N: 0.005 wt
% Or less and the total amount of C and N: 0.0060 wt% or less, and the balance of Fe and unavoidable impurities in the ferritic stainless steel material, the final pass rolling speed: 1000 m / m
Forming characterized by hot rolling at in or above, rolling end temperature: 800 ℃ or more, cumulative rolling reduction of the last 4 passes: 70% or more, and winding temperature: 600 ℃ or more, and then cold rolling. A method for producing a ferritic stainless steel sheet having excellent properties.

(2) C: 0.005 wt% or less, Si: 0.5
wt% or less, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt
%, S: 0.0030 wt% or less, O: 0.0040 wt% or less,
N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
The following Ti: 4 (wt% C + wt% N) -0.5 wt% is contained, and the balance is Fe.
And the ferritic stainless steel material consisting of unavoidable impurities, the rolling speed of the final pass: 1000 m / min or more, the rolling end temperature: 800 ℃ or more, the cumulative rolling reduction of the last four passes: 70
% Or more and winding temperature: hot rolling at 600 ℃ or more,
Then, cold rolling is performed, The manufacturing method of the ferritic stainless steel sheet which is excellent in formability characterized by the above-mentioned.

(3) C: 0.005 wt% or less, Si: 0.5
wt% or less, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt
%, S: 0.0030 wt% or less, O: 0.0040 wt% or less,
N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
Including: Mo: 3.0 wt% or less, Nb: 0.2 wt%
% Or less and B: 0.002 wt% or less, and a ferritic stainless steel material containing at least one selected from the group consisting of Fe and unavoidable impurities, and the final pass rolling speed: 1000 m / min or more, rolling end temperature: 800 ℃ or more, cumulative rolling reduction of the last four passes: 70% or more, and winding temperature: 600 ℃ or more, and then cold rolling is performed. A method for producing a ferritic stainless steel sheet having excellent formability.

(4) C: 0.005 wt% or less, Si: 0.5
wt% or less, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt
%, S: 0.0030 wt% or less, O: 0.0040 wt% or less,
N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
The following Ti: 4 (wt% C + wt% N) to 0.5 wt% is included, and Mo:
3.0 wt% or less, Nb: 0.2 wt% or less and B: 0.
Any one or two selected from 002 wt% or less
A ferritic stainless steel material that contains more than one kind and the balance is Fe and unavoidable impurities, and the rolling speed of the final pass: 1000 m / min or more, the rolling end temperature: 800 ℃ or more, and the cumulative rolling reduction of the four passes on the final side. : 70% or more and winding temperature:
A method for producing a ferritic stainless steel sheet having excellent formability, which comprises hot rolling at 600 ° C or higher and then cold rolling.

(5) In addition to the steel composition described in any one of (1) to (2) above, Se: 0.0003 to 0.02 wt%,
Ca: 0.0005-0.01wt% of the steel material containing one or two kinds, the final pass rolling speed: 1000m / min or more, the rolling end temperature: 800 ° C or more, the cumulative rolling of the last four passes A method for producing a ferritic stainless steel sheet having excellent formability, which comprises hot rolling at a rate of 70% or more and a winding temperature of 600 ° C. or more, followed by cold rolling.

In the above inventions, other manufacturing conditions are recommended as follows. It is preferable that the slab heating temperature (rolling start temperature) is 1100 to 1300 ° C, the cold rolling reduction is 60% or more, particularly 70% or more, and the finish annealing (final annealing) temperature is 700 to 950 ° C.

[0013]

In the present invention, the reason why each condition is limited to the above-mentioned essential constitution will be described. C: 0.005 wt% or less C is an element that deteriorates the r value and the elongation property and is also harmful to the corrosion resistance. In particular, if it exceeds 0.005 wt%, the effect becomes remarkable, so 0.005 wt% or less is necessary. The range is preferably 0.003 wt% or less.

Si: 0.5 wt% or less Si is an effective element for deoxidation, but excessive addition causes deterioration of cold workability, so the addition range is 0.5 wt%.
Hereafter, it is preferably 0.35 wt% or less.

Mn: 0.1-0.5 wt% Mn is an element effective for precipitating and fixing S existing in steel and maintaining hot rolling property. However, excessive addition causes deterioration of corrosion resistance. The addition range is 0.1 to 0.5 wt%, preferably 0.1 to 0.35 wt%.

Cr: 10 to 35 wt% Cr is an essential element for maintaining the corrosion resistance as stainless steel. If the amount is less than 10 wt%, the corrosion resistance is insufficient, while if it exceeds 35 wt%, the formability is lowered and at the same time the recrystallization temperature rises, making it impossible to achieve the object of the invention. Therefore, the addition range is 10 ~ 35wt
%, Preferably 10 to 25 wt%.

S: 0.0030 wt% or less S is a harmful element that lowers the corrosion resistance. Especially,
If the content exceeds 0.0030 wt%, the effect becomes remarkable, so 0.0030 wt% or less, preferably 0.0015 wt% or less.

O: 0.0040 wt% or less O, like S, is a harmful element that lowers the corrosion resistance. Especially, when the content exceeds 0.0040 wt%, the effect becomes remarkable, so 0.0040 wt% or less, preferably 0.0030 wt% or less.
wt% or less.

N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt% or less N, like C, is an element that lowers the r value and elongation characteristics, and is also harmful to corrosion resistance. In particular, if it exceeds 0.005 wt%, the effect becomes remarkable, so 0.005 wt% or less is necessary. Preferably, the range is 0.004 wt% or less. Conventionally, although C and N have been contained in the range of several 100 ppm, if they are contained in a large amount as shown in FIG. 1, the recrystallization temperature rises, making it difficult to carry out recrystallization while hot rolling. Especially,
If the total amount of C and N exceeds 0.0060 wt%, the effect becomes remarkable, so 0.0060 wt% or less, preferably 0.0050 wt% or less is necessary.

Ti: 4 (wt% C + wt% N) to 0.5 wt% Ti is useful for depositing and fixing C and N, which are harmful to deep drawability, improving r-value and elongation characteristics, and enhancing formability. Is an element. The effect is not obtained below 4 (C + N) wt%, while 0.
These effects saturate even if added in excess of 5 wt% (see FIGS. 2 and 3). Therefore, the addition amount of Ti is 4 (C + N) ~
0.5 wt%, preferably 4 (C + N) to 0.25 wt%.

Mo: 3.0 wt% or less Mo is an element that is selectively added to enhance the corrosion resistance. However, the addition of more than 3.0 wt% raises the recrystallization temperature of the steel and the object of the present invention cannot be achieved. Therefore, the addition range is 3.0 wt% or less, preferably 2.0 wt%.
Below.

Nb: 0.2 wt% or less Nb is an element that is selectively added to precipitate and fix the solid solution C and N in the steel and enhance the formability. However, the addition of more than 0.2 wt% raises the recrystallization temperature of the steel, and the object of the present invention cannot be achieved.
The content is set to wt% or less, preferably 0.15 wt% or less.

B: 0.002 wt% or less B is an element that is selectively added to prevent the occurrence of cracks during secondary working of a steel sheet. However, since the addition of more than 0.002 wt% deteriorates the corrosion resistance of steel, the addition range is 0.002 wt% or less, preferably 0.001 wt% or less.

Se: 0.0003 to 0.02 wt%, Ca: 0.0005 to 0.01
Both wt% Se and Ca have the effects of increasing the fluidity of molten steel and suppressing nozzle clogging during continuous casting, and are elements added as necessary. The amount of Se and Ca added is 0.0003 each
If it is less than 0.005% by weight, its effect is poor. On the other hand, if it exceeds 0.02% and 0.01% by weight, the corrosion resistance is adversely affected. Therefore, the amounts of Se and Ca added are
0.0003 to 0.02 wt%, 0.0005 to 0.01 wt%, and preferably 0.0003 to 0.01 wt% and 0.0005 to 0.006 wt%, respectively.

(1) Rolling speed of final pass: 1000 m / min or more The rolling speed of the final pass is one of the important requirements in the present invention. That is, by increasing the rolling speed in the final pass, the effect of accumulating strain in hot rolling is exerted, the driving force for recrystallization is increased, and the structure is refined. Can be completed. The effect of such a rolling speed in the final pass is shown in FIG.
As shown in, less than 1000 m / min is insufficient. Therefore, the rolling speed in the final pass is 1000 m / min or more, preferably 1500 m / min or more.

(2) Rolling end temperature: 800 ° C. or higher The rolling end temperature is as shown in FIG.
If it is less than 800 ° C, the progress of recrystallization is insufficient even if the amount of accumulated strain is sufficient. Therefore, the rolling end temperature for completing the recrystallization is 800 ° C. or higher, preferably 850 ° C. or higher. Although the upper limit of the rolling end temperature is not specified,
It is preferably 1000 ° C or lower.

(3) Cumulative reduction rate of 4 passes on the final side: 70% or more The cumulative reduction rate of 4 passes on the final side is also an important factor for the progress of recrystallization. As shown in FIG. 5, when the cumulative rolling reduction is less than 70%, the accumulated strain during hot rolling is not sufficient, and recrystallization becomes insufficient if hot rolling is performed. Therefore, the cumulative rolling reduction of the final four passes is 70% or more, preferably 75% or more.

(4) Winding temperature: 600 ° C. or higher The winding temperature is also an important factor for the progress of recrystallization, like the above-mentioned conditions. As shown in FIG. 6, the recrystallization becomes insufficient when the coiling temperature is lower than 600 ° C. Therefore, the winding temperature should be above 600 ℃, preferably 650 ℃
That is all.

In the present invention, manufacturing conditions other than the above-mentioned processing conditions may be in accordance with ordinary methods. For example, in the production of ferritic stainless steel with reduced impurities, VI
A method such as M, EB or VOD may be adopted. Slab heating temperature (hot rolling start temperature) in hot rolling is 1100 to 13
It is desirable to set the temperature in the range of 00 ° C. The hot rolled steel sheet is usually subjected to descaling by pickling and then subjected to cold rolling in the next step. The pickling conditions are sulfuric acid concentration: 20 to 40 wt% and liquid temperature:
After 60 to 100 ° C., it is desirable that the liquid composition is 2 to 20 wt% nitric acid, 1 to 10 wt% hydrofluoric acid, and the liquid temperature is 40 to 70 ° C. Further, the cold rolling reduction is preferably 60% or more, and the finish annealing (final annealing) temperature of the cold rolled steel sheet is preferably in the range of 700 to 950 ° C. The surface finish of the product is HL, 2
The effect of the present invention is exhibited in any state such as D, 2B, BA, and polishing finish.

[0030]

Example Steels having the chemical compositions shown in Table 1 were melted in a high frequency vacuum melting furnace to form slabs. 1250 for steel D slabs in Table 1
After heating at .degree. C..times.1 h, hot rolling was performed to a plate thickness of 4.5 to 5 mm under each condition shown in Table 2, and the recrystallization rate of the hot rolled plate as it was wound was investigated. The results are also shown in Table 2. From this table, when any one of the conditions of the rolling end temperature, the rolling speed of the final pass, the cumulative rolling reduction of the final four passes, and the winding temperature is out of the range of the present invention, recrystallization of the hot rolled sheet is Turns out to be inadequate.

[0031]

[Table 1]

[0032]

[Table 2]

Next, after heating each of the steel slabs shown in Table 1, a rolling start temperature of 1225 ° C., a rolling end temperature of 850 ° C., a rolling speed of 1000 m / min in the final pass, a cumulative rolling reduction of 70% in the final pass, and winding Hot rolling was performed at a stripping temperature of 700 ° C to a plate thickness of 4 mm. This hot-rolled steel sheet was subjected to hot-rolled sheet annealing without being subjected to sulfuric acid concentration: 30.
wt%, liquid temperature: after treatment at 80 ° C, liquid composition: nitric acid 15
wt%, hydrofluoric acid 3 wt%, liquid temperature: pickled at 60 ° C, plate thickness 0.7 mm
After cold rolling, the cold rolled steel sheet was heated at 750 to 900 ° C. for 1 min and then air-cooled to finish annealing. The hot-rolled steel sheet obtained in this step was examined for recrystallization rate, and the cold-rolled steel sheet was examined for each characteristic value by a tensile test. Note that each of these characteristic values is X = (X _L +
2X _D + X _C ) / 4. However, _XL , _XD
And X _C are rolling direction and 45 with respect to the rolling direction, respectively.
The values in the direction of ° and the direction of 90 ° with respect to the rolling direction are shown.

The results obtained are shown in Table 3. It can be seen from Table 3 that the components corresponding to the components of the present invention have a sufficient recrystallization rate of the as-rolled hot-rolled steel sheet and excellent r-value and elongation characteristics of the cold-rolled steel sheet. On the contrary,
Outside the range of the present invention, too much C, N content, Cr content of 20
It can be seen that if the content exceeds%, the progress of recrystallization is insufficient.

[0035]

[Table 3]

[0036]

As described above, according to the method of the present invention, recrystallization sufficiently progresses in the stage of hot rolling-winding, and the cold rolling thereafter causes cold rolling excellent in r value and elongation characteristics. Steel sheets can be manufactured. Therefore, the present invention greatly contributes to energy saving, productivity improvement, etc. in the production of a cold rolled steel sheet having excellent formability.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of (C + N) and the recrystallization rate.

FIG. 2 is a graph showing the relationship between Ti amount and r value.

FIG. 3 is a graph showing the relationship between Ti amount and El.

FIG. 4 is a graph showing the relationship between the rolling speed in the final pass and the recrystallization rate.

FIG. 5 is a graph showing the relationship between the rolling reduction and the recrystallization rate of the final four passes.

FIG. 6 is a graph showing the relationship between the winding temperature and the recrystallization rate.

Claims (5)

[Claims] 1. C: 0.005 wt% or less, Si: 0.5 wt%
Below, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt%, S: 0.0030 wt% or less, O: 0.0040 wt% or less, N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
A ferritic stainless steel material containing the following, with the balance Fe and unavoidable impurities, in the final pass rolling speed: 1000 m / min or more, rolling end temperature: 800 ℃ or more, cumulative rolling reduction in the four passes on the final side: 70% or more and winding temperature:
A method for producing a ferritic stainless steel sheet having excellent formability, which comprises hot rolling at 600 ° C or higher and then cold rolling. 2. C: 0.005 wt% or less, Si: 0.5 wt%
Below, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt%, S: 0.0030 wt% or less, O: 0.0040 wt% or less, N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
The following Ti: 4 (wt% C + wt% N) -0.5 wt% is contained, and the balance is Fe.
And the ferritic stainless steel material consisting of unavoidable impurities, the rolling speed of the final pass: 1000 m / min or more, the rolling end temperature: 800 ℃ or more, the cumulative rolling reduction of the last four passes: 70
% Or more and winding temperature: hot rolling at 600 ℃ or more,
Then, cold rolling is performed, The manufacturing method of the ferritic stainless steel sheet which is excellent in formability characterized by the above-mentioned. 3. C: 0.005 wt% or less, Si: 0.5 wt%
Below, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt%, S: 0.0030 wt% or less, O: 0.0040 wt% or less, N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
Including: Mo: 3.0 wt% or less, Nb: 0.2 wt%
% Or less and B: 0.002 wt% or less, and a ferritic stainless steel material containing at least one selected from the group consisting of Fe and unavoidable impurities, and the final pass rolling speed: 1000 m / min or more, rolling end temperature: 800 ℃ or more, cumulative rolling reduction of the last four passes: 70% or more, and winding temperature: 600 ℃ or more, and then cold rolling is performed. A method for producing a ferritic stainless steel sheet having excellent formability. 4. C: 0.005 wt% or less, Si: 0.5 wt%
Below, Mn: 0.1 to 0.5 wt%, Cr: 10 to 35 wt%, S: 0.0030 wt% or less, O: 0.0040 wt% or less, N: 0.005 wt% or less, and the total amount of C and N: 0.0060 wt%
The following Ti: 4 (wt% C + wt% N) to 0.5 wt% is included, and Mo:
3.0 wt% or less, Nb: 0.2 wt% or less and B: 0.
Any one or two selected from 002 wt% or less
A ferritic stainless steel material that contains more than one kind and the balance is Fe and unavoidable impurities, and the rolling speed of the final pass: 1000 m / min or more, the rolling end temperature: 800 ℃ or more, and the cumulative rolling reduction of the four passes on the final side. : 70% or more and winding temperature:
A method for producing a ferritic stainless steel sheet having excellent formability, which comprises hot rolling at 600 ° C or higher and then cold rolling. 5. The steel composition according to claim 1, further comprising Se: 0.0003 to 0.02 wt%,
Ca: 0.0005-0.01wt% of the steel material containing one or two kinds, the final pass rolling speed: 1000m / min or more, the rolling end temperature: 800 ° C or more, the cumulative rolling of the last four passes A method for producing a ferritic stainless steel sheet having excellent formability, which comprises hot rolling at a rate of 70% or more and a winding temperature of 600 ° C. or more, followed by cold rolling.