JP3067892B2 - Manufacturing method of ferritic stainless steel sheet with excellent surface properties and deep drawability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has good surface properties, and r
The present invention relates to a method for producing a ferritic stainless steel sheet having a high value.

[0002]

2. Description of the Related Art As a prior art, in order to obtain a product with improved surface defects such as ridging and roping from a ferritic stainless steel slab thinly cast to a thickness of 60 mm or less,
A method of hot rolling a thin cast piece cast by a twin belt method, a belt caster method or the like, followed by annealing, cold rolling and finish annealing (Japanese Patent Application Laid-Open No. 60-180648), or after casting the thin cast piece A method in which heat is kept in a temperature range of 900 to 1150 ° C. for 5 minutes or more, followed by hot rolling at a rolling end temperature of 800 to 1100 ° C., and thereafter, annealing, pickling, cold rolling and finish annealing are performed according to a conventional method. (JP-A-62-1
36526) and the like.

[0003]

However, in any of the above-mentioned techniques, the method of improving the ridging characteristics is to make the columnar grain size of the thin-walled slab fine by hot rolling. It is necessary to hot-roll the material using a thin cast slab set to 60 mm or less as a starting material, and further, to perform cold rolling, hot-rolled sheet annealing is required.

As a result, the most important effect of the thin casting technique of casting a slab close to the final product thickness is lost. The present invention provides a method for improving ridging characteristics as a thin slab having a slab thickness of 10 mm or less,
It is an improvement over the prior art.

[0005]

That is, the present invention improves the toughness of a slab by limiting the gamma potential (hereinafter referred to as γp ') based on the chemical composition of ferritic stainless steel to 0% or less to improve the toughness of the slab. In order to make it possible to omit omission and to further improve ridging and roping characteristics,
It adopts the stage cold rolling method, the gist of which is% by weight, C:
0.03% or less, Si: 1.0% or less, Mn: 1.0%
Hereinafter, P: 0.040% or less, S: 0.030% or less,
Cr: 10.0 to 35.0%, N: 0.03% or less, Ni: 0.3 to 5.0%, and Mo: 0.1 to 5.0%, if necessary. Cu: 0.2 to 1.0
%, Ti: 0.1 to 1.0%, Al: 0.05 to 1.0
%, Nb: 0.1 to 1.0%, V: 0.1 to 1.0%, and if necessary, B: 0.0% or more.
003-0.0030%, the balance being Fe and unavoidable impurities, and γp ′ = 420C% + 470N% + 23Ni% + 9Cu
% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23
V% -47Nb% -49Ti% -52Al% + 179 ≦ 0 A ferritic stainless steel satisfying the following condition is continuously cast into a thin cast slab and wound up.
The first stage cold rolling of 0% or more is performed, the second stage cold rolling of 40% or more after the intermediate annealing is performed to obtain a desired thickness, and then the final annealing is performed.

Hereinafter, the present invention will be described in detail.

[0007]

First, the reason why the chemical components of steel are limited as described above in the present invention will be described. C has an adverse effect on the workability and toughness of steel, so the content is made 0.03% or less.

Since Si and Mn are effective as deoxidizing agents for steel, each of them contains 1.0% or less. If it exceeds 1%, the mechanical properties deteriorate. Cr requires at least 10.0% to improve corrosion resistance and high-temperature oxidation resistance, and if it exceeds 35%, toughness deteriorates and production becomes extremely difficult.
35% is in the range.

Since N deteriorates the workability and toughness of steel like C, the upper limit of the content is set to 0.03%. Furthermore, in order to further improve the properties such as toughness, corrosion resistance, and workability, in addition to the above chemical components, the components are appropriately selected from the following components. Ni is effective in improving the toughness of a high Cr material. However, if its content is less than 0.3%, its characteristics are lost, and if it exceeds 5.0%, gamma (γ) is generated in a high temperature region and toughness is increased. Deteriorates the stress corrosion resistance.
The range is 0.3 to 5.0%.

[0010] To improve the corrosion resistance, Mo, Cu, Ti, A
Addition of l, Nb, and V is effective, and one or two or more kinds are selected and contained. Mo has a remarkable effect of improving corrosion resistance, and is therefore contained in the range of 0.1 to 5.0%. If the upper limit is exceeded, the workability will deteriorate and the cost will increase. Cu
Is contained in the range of 0.2 to 1.0% in order to improve corrosion resistance. If the upper limit is exceeded, γ is formed in a high temperature range to deteriorate toughness.

[0011] Ti improves the intergranular corrosion resistance and pressability as well as Nb, but if its content is less than 0.1%, its characteristics cannot be obtained. If it exceeds 1.0%, these characteristics are saturated.
Workability deteriorates. Al has the same properties as Ti, so it is contained in the range of 0.05 to 1.0%.

Nb has the property of bonding with C and N to prevent grain boundary precipitation of Cr carbide and to improve intergranular corrosion resistance.
If the content is less than 0.1%, the above characteristics cannot be obtained, and if it exceeds 1.0%, the above characteristics are saturated and workability is deteriorated. Therefore, the range is 0.1 to 1.0%. V
Has the same properties as Ti, so is contained in the range of 0.1 to 1.0%.

Further, B is effective for improving the intergranular cracking properties in hot and cold working. However, if it is less than 0.0003%, its properties cannot be obtained, and if it exceeds 0.0030%, it is not effective. The properties are saturated and the hot workability deteriorates. Therefore, the content range is set to 0.0003 to 0.0030%.
In the present invention, the above chemical components are further converted to γp ′ represented by the following formula:
Is regulated to be 0% or less. γp ′ is: γp ′ = 420 C% + 470 N% + 23Ni% + 9Cu
% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23
V% −47Nb% −49Ti% −52Al% + 179 ≦ 0 , and is a value defined by heating at 1100 ° C.
This is an equation for estimating the maximum value of the amount of austenite from the components.
In thin-wall continuous casting process, slab crystal grains are
Coarser than the grains of the hot-rolled annealed sheet
Therefore, if γp ′ exceeds 0, austenite
Precipitates at the grain boundaries and the toughness of the slab at room temperature is remarkably high.
In the worst case, the slab coil cannot be rewound.
You. In the process of cooling the slab, γp ′ exceeds 0
Austenite goes to martensite in case of quenching,
On the other hand, in the case of slow cooling, it transforms into ferrite and carbide.
However, both phases cause a decrease in toughness. Therefore, γ
It is necessary to make p '0 or less.

Next, the cold rolling condition, which is a main feature of the present invention, will be described. The present inventors have found that to produce a product of 1~0.1mm thickness about from 10mm or less thick thin cast strip of ferritic stainless steel, the product re di ring height and r
The target values were set to 10 μm or less (there is no problem as a product at this height), and 1.20 or more. It has been found that cold rolling is extremely effective.

The above fact was determined by the following experiment.
Chemical components: C: 0.015%, Si: 0.55%, M
n: 0.24%, P: 0.020%, S: 0.001
%, Ni: 0.15%, Cr: 19.03%, Cu:
0.40%, Nb: 0.48%, Al: 0.008%,
N: 0.0166%, the balance being Fe and unavoidable impurities, and casting a 3.0 mm thick cast piece of molten steel regulated by γp '=-46.3% by a twin drum casting method. After the pieces were pickled with sulfuric acid, they were subjected to a first-stage cold rolling at a rolling ratio of 10 to 90% to form a 2.7-0.3 mm thick rolled plate, and then at 950 ° C. for 1 minute. After the intermediate annealing, electrolytic pickling with an aqueous solution of salt and nitric acid is performed, and the second-stage cold rolling at a rolling reduction of 50% is performed, and 1.35 to 0.1
A 5 mm thin rolled plate was formed. Subsequently, 900
Final annealing was performed at 30 ° C. for 30 seconds, followed by electrolytic pickling in the same manner as described above (Step A), and the ridging and r value of each obtained product were measured.

Next, under the same conditions as above, except that the rolling reduction of the first-stage cold rolling was fixed at 50% and the rolling reduction of the second-stage cold rolling was changed to 5-90%. Each product was obtained (Step B), and its ridging and r value were measured. The ridging and r value obtained in each of the above steps are summarized in FIG.
And FIG.

As shown in FIG. 1, the ridging height which does not affect the product is about 10 μm.
The rolling reduction of the stage is 30% or more (process A), the rolling ratio of the second stage is 40% or more (process B), and the r value at which deep drawing pressing is possible is about 1.2. The rolling reduction in the first stage, which exceeds the value, is 20% or more (Step A), and the rolling reduction in the second stage is 30% or more (Step B).

Therefore, it was confirmed that the cold rolling reduction satisfying both of the above characteristics was 30% or more in the first-stage cold rolling and 40% or more in the second-stage cold rolling. That is, the slab obtained by the thin-wall casting method is subjected to the first-stage rolling at a cold rolling ratio of 30% or more to break the slab structure, and further subjected to a second-stage cold rolling ratio of 40% or more after intermediate annealing. By performing the rolling, the above-mentioned excellent characteristics were able to be obtained by performing the destruction of the colonies of the rolled slab and the sizing.

The intermediate annealing is preferably performed at a temperature in the range of 900 to 1000 ° C.

[0020]

EXAMPLE A molten steel of ferritic stainless steel having a chemical composition shown in Table 1 was poured into a pool of a twin-drum casting apparatus, and a thin cast slab having a thickness of 3.0 mm was cast.
850 ° C for 1,2,3,4,5,8,9, and
No. In the case of 6, 7, 10, and 11, it was wound at 600 ° C.
Next, these coils were descaled by a combination of shot blasting and sulfuric acid pickling, and were subjected to cold rolling under the conditions shown in Table 2.

The annealing and pickling conditions between the first stage cold rolling and the second stage cold rolling are 970 ° C. and salt + nitric acid electrolysis, respectively, and the final annealing and pickling conditions are 930 ° C. and salt + This is a nitric acid electrolytic treatment.

[0022]

[Table 1]

[0023]

[Table 2]

The ridging and r of the product obtained in the above process
The values are shown in Table 1. In Nos. 1 to 8 of the present invention, the ridging had a target value of 10 μm or less, and the r value had a target value of 1.2.
No. 9 of Comparative Example was 1 while 0 or more was indicated.
No. 10 has a low rolling reduction of No. 10 and the cold rolling rate of the No. 2 rolling is low and the ridging is poor. No. 11 has a low rolling reduction of the No. 1 and No. 2 rolling. , Ridging and r
Both values were poor.

[0025]

According to the present invention, as described above, a deep drawn product having particularly excellent surface properties can be manufactured from a ferritic stainless steel slab obtained by a thin strip casting method. It is.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between cold rolling reduction and ridging in two-stage rolling of thin cast slabs.

FIG. 2 is a diagram showing a relationship between a cold rolling reduction and an r value in two-stage rolling of a thin cast slab.

Continuation of front page (56) References JP-A-62-176649 (JP, A) JP-A-2-258931 (JP, A) JP-A-62-247027 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) C21D 9 / 48,8 / 04 C22C 38/00-38/18

Claims (4)

(57) [Claims] 1. The method according to claim 1, wherein C: 0.03% or less, Si:
1.0% or less, Mn: 1.0% or less, P: 0.040%
Hereinafter, S: 0.030% or less, Cr: 10.0 to 35.
0% and N: 0.03% or less, and γp ′ = 420C% + 470N% + 23Ni% + 9Cu
% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23
The V% -47Nb% -49Ti% -52Al% + 179 ≦ 0 ferritic stainless steels that satisfy the sheet thickness 10mm
The following thin-walled slabs are continuously wound up, the surface of the slabs is descaled, first-stage cold rolling of 30% or more is performed, and second-stage cold rolling of 40% or more is performed after intermediate annealing. A method for producing a ferritic stainless steel sheet having excellent surface properties and deep drawability, wherein the sheet is subjected to final annealing after having a desired thickness. 2. The method for producing a ferritic stainless steel sheet according to claim 1, further comprising 0.3 to 5.0% by weight of Ni. 3. Mo: 0.1 to 5.0% by weight,
Cu: 0.2-1.0%, Ti: 0.1-1.0%, A
3. The surface texture according to claim 1, wherein 1 or 2 or more of 1: 0.05 to 1.0%, Nb: 0.1 to 1.0% and V: 0.1 to 1.0% are contained. A method for producing ferritic stainless steel sheets with excellent deep drawability. 4. The method for producing a ferritic stainless steel sheet having excellent surface properties and deep drawability according to claim 1, further comprising B in an amount of 0.0003 to 0.0030% by weight.