JPH05293595A - Production of ferritic stainless steel cast strip - Google Patents

Abstract

PURPOSE:To produce a cast strip having excellent toughness at the time of continuously casting an Nb-containing ferritic stainless steel. CONSTITUTION:The ferritic stainless steel composed of <=0.03wt% C, <=1.0% Si, <=1.0% Mn, <=0.040% P, <=0.030% S, 10.0-35.0% Cr, 0.1-1.0% Nb and <=0.03% N and if necessary, containing one or more kinds of 0.3-5.0% Ni, 0.1-5.0% Mo, 0.2-1.0% Cu, 0.1-1.0% Ti, 0.05-1.0% Al, 0.1-1.0% V and 0.0003-0.0030% B and the balance Fe with inevitable impurities and satisfying gamma'p (gam-mer potential) <=0 is continuously cast. Successively, this cast strip is coiled in the temp. range of 700-200 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 thin cast piece.

[0002]

2. Description of the Related Art Heretofore, Japanese Patent Application Laid-Open No. 64-4458 has been disclosed as a technique for producing a ferritic stainless steel having excellent toughness by using a ribbon casting method by rapid solidification. In particular, the slab of ferritic stainless steel containing Nb has poor toughness, and cracks are generated during cold rolling.
The above technique suppresses C and N, which have a bad influence on toughness, to 0.03% or less in each of the components of ferritic stainless steel, and controls the rapidly solidified structure of the columnar crystal by controlling the pouring temperature during casting. The ratio is adjusted to 70% or more to improve the toughness.

[0003]

However, according to the findings of the present inventors, most of the solidification structure of the Nb-containing ferritic stainless steel has a columnar structure in order to improve the toughness. In addition, the adjusting means for making the columnar crystals 70% or more causes a problem in productivity.

An object of the present invention is to solve the problems of the prior art and to provide a method which can be achieved more reliably and in an advantageous state in terms of productivity.

[0005]

As a factor affecting the toughness of thin cast slabs of ferritic stainless steel containing Nb, the present invention is the precipitation of FeNb, Fe ₂ Nb, Fe ₃ Nb ₃ C, and other Lar base phases in the slabs. Was found to play an important role. That is, the present invention is first, as chemical components gamma potential (hereinafter gamma 'referred to as _p) values martensite to slab of preventing the produced during cooling of the slab by regulating below 0% To improve the toughness and further prevent the precipitation of the Larbase phase by cooling the temperature range of at least 700 ° C. lower than the solidification temperature of the slab and then winding the slab in the temperature range of 700 to 200 ° C. Is characterized by.

That is, the present invention, in% by weight, is C: 0.03.
% Or less, Si: 1.0% or less, Mn: 1.0% or less,
P: 0.040% or less, S: 0.030% or less, Cr:
Contains 10.0 to 35.0%, Nb: 0.1 to 1.0% and N: 0.03% or less, and Ni: 0.3 if necessary.
~ 5.0%, Mo: 0.1-5.0%, Cu: 0.2-
1.0%, Ti: 0.1 to 1.0%, Al: 0.05 to
1.0%, V: 0.1 to 1.0% and B: 0.0003
~ 0.0030% of one or more, with the balance Fe
And unavoidable impurities, and γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% + 179≤ A ferritic stainless steel satisfying 0 is continuously cast, the cast slab after cooling is cooled from the solidification temperature to at least 700 ° C., and then the slab is wound in a temperature range of 700 to 200 ° C. It is intended to provide a method for producing an excellent thin slab of ferritic stainless steel.

The present invention will be described in detail below.

[0008]

First, the reason why the chemical composition of steel is limited as described above in the present invention will be explained. C adversely affects 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, their contents are 1.0% or less. If it exceeds 1%, the mechanical properties deteriorate. Cr requires a minimum of 10.0% to improve corrosion resistance and high temperature oxidation resistance, and if it exceeds 35%, toughness deteriorates and manufacturing becomes extremely difficult.
The range is 35%.

Nb has the property of combining with C and N to prevent grain boundary precipitation of Cr carbide and improve grain boundary corrosion resistance.
If the content is less than 0.1%, the above properties cannot be obtained, and if it exceeds 1.0%, the above properties are saturated and the workability deteriorates. Therefore, the range is 0.1 to 1.0%. N
Like C, it deteriorates the workability and toughness of steel, so the upper limit of the content is made 0.03%.

In order to further improve the characteristics such as toughness, corrosion resistance, and workability, in addition to the above chemical components, the following components are appropriately selected and contained. Ni is effective for improving the toughness of high Cr materials, but if its content is less than 0.3%, its characteristics disappear, and if it exceeds 5.0%, gamma (γ) is generated in the high temperature range and the toughness is increased. Is deteriorated and the stress corrosion resistance is deteriorated, so the range is 0.3 to 5.0%.

To improve the corrosion resistance, Mo, Cu, Ti, A
1 and V are effective, and one or more kinds are selected and contained. That is, since Mo has a remarkable effect of improving the corrosion resistance, Mo is contained in the range of 0.1 to 5.0%.
If it exceeds the upper limit, the workability deteriorates and the cost increases. C
u is contained in the range of 0.2 to 1.0% in order to improve the corrosion resistance. If it exceeds the upper limit, γ is generated in the high temperature range and the toughness is deteriorated.

Ti improves not only intergranular corrosion resistance but also pressability, but if it is less than 0.1%, its characteristics cannot be obtained, and if it exceeds 1.0%, these characteristics are saturated and workability is deteriorated. to degrade. Al has similar characteristics to Ti, so 0.0
It is contained in the range of 5 to 1.0%.

Since V has characteristics similar to Ti, it is 0.1
Contained in the range of 1.0%. B is effective in improving the grain boundary cracking property in hot and cold working, but 0.00
If it is less than 03%, the property cannot be obtained, and it is 0.0030.
If it exceeds%, the characteristics are saturated and the hot workability is deteriorated. Therefore, the content range is 0.0003 to 0.003.
0%

[0015] The present invention has been regulated so that the value of gamma _'P represented further by the following formula or chemical components is less than 0%. That is, if γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% + 179≤0, It is possible to prevent the formation of martensite during cooling and improve the toughness of the cast slab.

Next, the winding temperature, which is another feature of the present invention, will be described. The inventors of the present invention have conducted various studies on factors affecting the toughness of the cast slab, and found that in Nb-containing ferritic stainless steel, the La-base phase (FeN
b, Fe ₂ Nb, Fe ₃ Nb ₃ C, and other Fe-Nb-based precipitation phases) precipitate during cooling, especially during cooling of coiled slabs wound at high temperatures, and this precipitation phase deteriorates the toughness. I have made sure that it is.

It was found that the Larbase phase precipitates in the temperature range from the solidification temperature (about 1500 ° C.) of the cast slab to 700 ° C. In order to prevent this precipitation, this temperature range is rapidly cooled to 700 ° C. It turns out that the following may be taken up. It is preferable that the winding temperature is low, but if it is less than 200 ° C, it will be difficult in terms of equipment. Therefore, 700 ℃ to 200 ℃
It may be wound in the temperature range up to.

In order to keep the coiling temperature at 700 ° C. or lower, for example, in the twin-drum type casting system, an air-cooled or water-cooled cooling device is installed between the cooling drum and the winder, and if necessary. Forced cooling may be performed. This is the Charpy impact value at 20 ℃ (kgfm / cm) that represents the winding temperature and toughness.
² ) is shown in Fig. 1.

FIG. 1 is obtained by the following experiment. Chemical composition: C 0.013%, Si 0.49%, Mn
0.26%, P 0.024%, S 0.001%,
Ni 0.27%, Cr 19.15%, Cu 0.44
%, Nb 0.50%, Al 0.003%, N 0.
A slab having a thickness of 3.0 mm was cast from a molten steel consisting of 0185%, balance Fe and unavoidable impurities, and regulated to γ ′ _P = −44.4% by a twin drum casting method.

The cast slab is wound up at a winding temperature of 200 to 100.
It was wound while changing between 0 ° C. Then, the Charpy impact value at 20 ° C. at each winding temperature was measured, and this was measured as shown in FIG.
Displayed on. Each such slab was pickled and cold rolled at room temperature to a thickness of 0.5 mm. As a result, 700 ℃ ~ 2
No slabs rolled at a temperature of 00 ° C produced any cracks during rolling, but any slabs rolled at 800 to 1000 ° C had a Charpy impact value of 20 ° C, which is a standard for cold rolling. Was 5 kgfm / cm ² or less, and fracture occurred during cold rolling.

That is, it was confirmed that when rolled over 700 ° C., a large amount of the Larbase phase was precipitated in the slab and deteriorated the toughness. As described above, by suppressing the formation of martensite in the slab immediately after casting and suppressing the precipitation of the La-base phase, the toughness of the ferritic stainless steel thin slab is improved, and as a result, it is annealed before cold rolling. It is possible to roll to a predetermined thickness in a stable state without applying the above.

[0022]

Example A ferritic stainless steel having the chemical composition shown in Table 1 was melted, cast into a thin cast piece having a thickness of 3.0 mm by a twin drum method, and wound at a predetermined temperature of 450 to 900 ° C. Then, the coil is descaled by shot blasting and sulfuric acid pickling, cold rolled to 0.5 mm, and 950 ° C.
Final annealing for 30 seconds was carried out and pickling (salt + nitric acid electrolysis) was performed to obtain a 2B finished product plate.

In each of the examples of the present invention, a product sheet could be obtained without cracks during rolling, but sample No. 11 had a low impact value due to the formation of martensite, and fracture occurred during cold rolling. Since No. 12 and No. 13 had high coiling temperatures of 900 ° C. and 800 ° C., both had low impact values and cracks occurred during cold rolling and did not become product sheets.

[0024]

[Table 1]

[0025]

As described above in detail, the ferritic stainless steel thin cast piece obtained by the present invention is cold-rolled without fear of rolling cracks even if hot rolling and hot-rolled sheet annealing are omitted. Because it is possible, it has a lot of industrial benefits.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a winding temperature of a continuously cast thin slab of ferritic stainless steel and a Charpy impact value at 20 ° C.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Arai 3434 Shimada, Hitsu-shi, Yamaguchi Pref., Nippon Steel Corporation Hikari Works (72) Inventor Shuichi Inoue 3434, Shimada, Hikari-shi, Yamaguchi Prefecture Made in Japan Inside the Kogaku Steel Works

Claims (7)

[Claims] 1. By weight%, 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%, Nb: 0.1 to 1.0% and N: 0.03% or less, the balance Fe and unavoidable impurities, and γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% + 179≤0 Continuously cast ferritic stainless steel, and then the cast slab at 700-200 ° C. A method for producing a thin slab of ferritic stainless steel, characterized by winding in a temperature range. 2. 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%, Nb: 0.1 to 1.0%, N: 0.03% or less and Ni: 0.3 to 5.0%, balance Fe and unavoidable impurities, and γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% +179 continuously ferritic stainless steel satisfying 0, Next, a method for producing a ferritic stainless steel thin-walled slab, which comprises winding the slab in a temperature range of 700 to 200 ° C. 3. By weight%, 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%, Nb: 0.1 to 1.0% and N: 0.03% or less, and Mo: 0.1 to 5.0%, Cu: 0.2
~ 1.0%, Ti: 0.1-1.0%, Al: 0.05
To 1.0%, and V: 0.1 to 1.0% of 1 or 2
More than one species, the balance Fe and unavoidable impurities,
_{And, γ 'P = 420C% +} 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% + 179 ferritic stainless steel satisfying ≦ 0 A method for producing a ferritic stainless steel thin-walled slab, which comprises continuously casting a steel and then winding the slab in a temperature range of 700 to 200 ° C. 4. 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%, Nb: 0.1 to 1.0%, N: 0.03% or less and Ni: 0.3 to 5.0%, and Mo: 0.1.
~ 5.0%, Cu: 0.2-1.0%, Ti: 0.1
1.0%, Al: 0.05 to 1.0% and V: 0.1
It comprises one or more of 1.0%, and the balance Fe and unavoidable impurities, _{and, γ 'P = 420C% +} 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% - 12Mo% -23V% -47Nb% -49Ti% -52Al% + 179≤0 Continuously cast ferritic stainless steel, and the cast slab is then wound in a temperature range of 700 to 200 ° C. Method for producing thin cast slab of stainless steel. 5. By weight%, 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%, Nb: 0.1 to 1.0%, N: 0.03% or less and B: 0.0003 to 0.0030%, balance Fe
And unavoidable impurities, and γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb% -49Ti% -52Al% + 179≤ A method for producing a thin slab of ferritic stainless steel, comprising continuously casting a ferritic stainless steel satisfying 0 and then winding the slab in a temperature range of 700 to 200 ° C. 6. 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%, Nb: 0.1 to 1.0%, N: 0.03% or less,
Ni: 0.3 to 5.0% and B: 0.0003 to 0.0
030%, balance Fe and unavoidable impurities, and γ ′ _P = 420C% + 470N% + 23Ni% + 9Cu% + 7Mn% -11.5Cr% -11.5Si% -12Mo% -23V% -47Nb%- Ferrite stainless steel satisfying 49 Ti% -52 Al% + 179 ≦ 0 is continuously cast, and the cast piece is then wound in a temperature range of 700 to 200 ° C. .. 7. In weight%, 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%, Nb: 0.1 to 1.0%, N: 0.03% or less,
Ni: 0.3 to 5.0% and B: 0.0003 to 0.0
030%, Mo: 0.1-5.0%, C
u: 0.2 to 1.0%, Ti: 0.1 to 1.0%, A
1: 0.05-1.0% and V: 0.1-1.0% of 1
1 or 2 or more, and balance Fe and unavoidable impurities, and γ ′ _P = 420 C% + 470 N% + 23 Ni% + 9 Cu% + 7 Mn% −11.5 Cr% −11.5 Si% -12 Mo% -23 V% − Ferrite-based stainless steel satisfying 47Nb% -49Ti% -52Al% + 179 ≦ 0 is continuously cast, and then the cast piece is wound in a temperature range of 700 to 200 ° C. Manufacturing method.