JP3370441B2 - Duplex stainless steel sheet with excellent elongation characteristics and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duplex stainless steel sheet and a method for producing the same, and particularly to a duplex stainless steel sheet exhibiting excellent elongation characteristics and a method for producing the same.

[0002]

2. Description of the Related Art Duplex stainless steel is used as various chemical industrial devices and equipment because it has excellent corrosion resistance and high strength. As described above, the duplex stainless steel has excellent properties, but the SUS3
There is a problem that the elongation at room temperature is lower than that of general-purpose stainless steel such as 04 or SUS430. It is said that the elongation property of such duplex stainless steel is generally affected by the amount of austenite (γ). Incidentally, the conventional elongation property level is, for example, about 25% for a material having a γ amount of 40%, A value of about 28% was obtained with a material having an amount of 50%. Therefore, the conventional duplex stainless steel has low elongation and is inferior in formability and workability, so that it is difficult to apply it to a processed product having a complicated shape.

By the way, the focus of the research so far on the duplex stainless steel is rather to improve the corrosion resistance and the strength, and little attention has been paid to the workability as described above. Is the reality. Recently, workability, especially superplasticity, has been actively researched. However, since superplasticity is a phenomenon that occurs at a high temperature of about 1000 ° C in the first place, even if the superplasticity phenomenon is used for forming, it is necessary to maintain it at a high temperature during processing. This not only causes the price of the product to soar, but also is not suitable for mass production.

Therefore, if the formability and workability of the duplex stainless steel at room temperature can be improved, the advantages of the duplex stainless steel such as high corrosion resistance and high strength can be utilized and the conventional processing can be performed. Products that were difficult to manufacture can now be processed at low cost.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the processing cost of a product by enabling complex processing of a duplex stainless steel sheet at room temperature, and particularly at room temperature. The purpose is to provide a technique for improving the elongation characteristics of the. Another object of the present invention is to measure the elongation characteristics of a duplex stainless steel sheet at room temperature to 27% or more at a γ content of 40%,
It is to provide a manufacturing technique for increasing the amount of 50% to 30% or more.

[0006]

[Means for Solving the Problems] The inventors of the present invention focused on the influence of the texture and hot rolling conditions on the elongation characteristics of duplex stainless steel sheets at room temperature, and conducted earnest studies toward the achievement of the above object. It was As a result, the inventors have adopted the means of making the content described below into the gist configuration,
The inventors have obtained the knowledge that it is effective for solving the above-mentioned problems, and completed the method of the present invention.

That is, the present invention is: (1) C: 0.02 wt% or less, Si: 2.0 wt% or less, Mn:
3.0 wt% or less, Cr: 20.0-35.0 wt%, Ni: 3.0-
10.0wt%, Mo: 0.5-6.0wt%, B: 0.0005-0.01
wt%, N: 0.08 to 0.30 wt%, S: 0.005 wt% or less, and W: 0.03 to 2.0 wt%, V: 0.03 to 2.0 wt%
%, And the balance is Fe and inevitable impurities, and the (110) plane of the ferrite phase is oriented in the plate surface by 10% or more. It is a duplex stainless steel plate with excellent characteristics.

(2) C: 0.02 wt% or less, Si: 2.0 wt
% Or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt
%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%,
B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.
005 wt% or less, Cu: 2.0 wt% or less, and W:
0.03 to 2.0 wt%, V: 0.03 to 2.0 wt%, and any one or two kinds selected from the group consisting of Fe and unavoidable impurities.
10) A duplex stainless steel sheet having excellent elongation characteristics, characterized in that the faces are oriented by 10% or more.

(3) C: 0.02 wt% or less, Si: 2.0 wt
% Or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt
%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%,
B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.
005 wt% or less, and W: 0.03 to 2.0 wt%,
V: any one or two selected from 0.03 to 2.0 wt%
A steel slab containing seeds and the balance Fe and unavoidable impurities, hot rolling start temperature 1200 ~ 1270 ℃, rolling reduction 10 ~ 50% /
The hot-rolled sheet is annealed by hot rolling under the following conditions: pass, time between passes of 1 second or more, number of passes of 2 or more, total rolling reduction of 90% or more, and hot rolling end temperature of 850 to 1100 ° C. The method for producing a duplex stainless steel sheet is characterized in that cold rolling and cold rolled sheet annealing are performed.

(4) C: 0.02 wt% or less, Si: 2.0 wt
% Or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt
%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%,
B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.
005 wt% or less, Cu: 2.0 wt% or less, and W:
A steel slab containing one or two selected from 0.03 to 2.0 wt% and V: 0.03 to 2.0 wt% with the balance being Fe and inevitable impurities.
℃, reduction rate 10 to 50% / pass, time between passes 1 second or more, number of passes 2 passes or more, total reduction rate 90% or more and hot rolling end temperature 8
A method for producing a duplex stainless steel sheet is characterized in that hot rolling is performed under the condition of 50 to 1100 ° C, the obtained hot rolled sheet is annealed, and then cold rolling and cold rolled sheet annealing are performed.

(5) The manufacturing method according to the above (3) or (4), in which the hot-rolled sheet is annealed at 1000 to 1050 ° C and the cold-rolled sheet is annealed at 1000 to 1070 ° C.

[0012]

Now, as a result of detailed experiments conducted on the hot rolling conditions in the manufacturing process of the duplex stainless steel sheet, the inventors found that the elongation of the cold rolled steel sheet at room temperature was controlled by the hot rolling conditions. It is significantly improved, and the effect of such improvement is that the (110) texture of the ferrite formed in the stage of the hot rolled steel sheet finally leads to the development of the (110) texture of the cold rolled steel sheet. It was found that it was due to a thing. Fig. 1 shows C: 0.013 wt%,
Si: 0.63 wt%, Mn: 0.64 wt%, P: 0.026 wt%, S: 0.
001 wt%, Cr: 24.99 wt%, Ni: 6.24 wt%, Mo: 3.26 wt%
%, B: 0.0005 wt%, N: 0.108 wt%, Cu: 0.06 wt%,
W: 0.14 wt% steel slab was hot-rolled under various conditions, then annealed, cold-rolled and annealed, and the influence of (110) texture after cold rolling on the elongation of steel sheet was shown. It is a thing. From this, the elongation of the cold-rolled steel sheet has a strong relationship with the (110) surface strength after cold rolling, and the elongation of (1
10) It can be seen that it is improved by increasing the texture.

Next, in the present invention, the reason for limiting the manufacturing conditions of the duplex stainless steel sheet according to the above-mentioned essential constitution will be explained.

Hot rolling start temperature: 1200 to 1270 ° C. If the hot rolling start temperature is too low, it becomes difficult to secure hot workability in the post-rolling stage, and it is easy to cause edge cracking at the end. If it is too high, the rolled material will buckle during biting. Therefore, the hot rolling start temperature is 1200-1270 ℃
The range is.

Reduction ratio: 10 to 50% / reduction ratio per pass has an important role in promoting recrystallization during rolling. If the value is less than 10% / pass, recrystallization is insufficient. On the other hand, if it exceeds 50% / pass, the number of passes required for recrystallization cannot be secured, so the rolling reduction is 10 to 50% / Pass, preferably in the range of 20-40% / pass.

Time between passes: 1 second or more The time between passes is a necessary requirement for promoting recrystallization after processing. If the value is too small, recrystallization does not proceed sufficiently to make multiple passes. It makes no sense. Therefore, the time between passes is set to 1 second or longer, preferably 5 seconds or longer.

Number of passes: The number of passes of two or more is a requirement for obtaining a necessary crystal orientation by alternately causing processing and recrystallization. If the value is too small, processing-reproduction is performed. The rearrangement of crystals due to the repetition of crystals does not proceed sufficiently and a desired crystal orientation cannot be obtained. Therefore, the number of passes is 2 or more, preferably 5 to 1
The range is 0 pass.

Total rolling reduction: 90% or more The total rolling reduction is an important requirement from the point of view of uniformly processing the inside to obtain a homogeneous material, and if the value is too small, the material becomes uneven. Therefore, the total rolling reduction is set to 90% or more, preferably 95% or more.

Hot rolling end temperature: 850 to 1100 ° C. The hot rolling end temperature is a necessary requirement for determining the recrystallization behavior in the process recrystallization process. If the temperature is too low, recrystallization proceeds in a short time. On the other hand, if it is too high, the strength will be low and the operation will be difficult. Further, although the detailed cause is not clear, the tendency of crystal orientation changes and sufficient (110) plane orientation cannot be obtained. Therefore, the hot rolling end temperature is 850-11.
It shall be in the range of 00 ℃.

Annealing temperature of hot-rolled sheet: 1000 to 1070 ° C. Annealing of hot-rolled sheet is necessary for removing residual strain after hot rolling. If the temperature is too low, softening becomes insufficient,
Moreover, the σ phase may precipitate. On the other hand, if the temperature is too high, the strength is lowered, which makes the operation difficult, and the form of the scale changes, which easily causes flaws in the subsequent steps. Therefore, the annealing temperature of the hot rolled sheet is set in the range of 1000 to 1070 ° C.

Annealing of cold-rolled sheet is 1000 to 1050 ° C. The annealing temperature of the cold-rolled sheet is a necessary requirement for enabling cold working of the product. If the temperature is too low, a σ phase occurs,
On the other hand, if it is too high, the elongation decreases due to an increase in the ferrite phase. Therefore, the annealing temperature of cold-rolled sheet is 1000-1050.
It shall be in the range of ° C.

Further, the reasons for limiting the component composition necessary for applying the method of the present invention will be described. C: 0.02 wt% or less When the content of C exceeds 0.02 wt%, the intergranular corrosion susceptibility is increased, the pitting corrosion resistance is deteriorated, and the precipitation of carbide stabilizes the γ phase up to a high temperature range. Existing, it deteriorates hot workability. Moreover, the hardness increases during cold rolling, which makes subsequent processing difficult. Therefore, the C content is 0.02 wt% or less.

Si: 2.0 wt% or less Si is effective in improving the corrosion resistance, but if the amount of Si increases, σ
There is a concern that embrittlement due to phases may increase. Therefore, Si is
It should be 2.0 wt% or less, preferably 0.5 to 1.0 wt%.

Mn: 3.0 wt% or less Mn acts as a deoxidizing element during melting and refining, and
It is an element that combines with S to form a sulfide and is effective in preventing the occurrence of hot embrittlement, but if it exceeds 3.0 wt%, it is an element that deteriorates corrosion resistance and oxidation resistance. Therefore, Mn is 3.0 wt%
Hereafter, it is preferable that the content be 0.5 to 2.0 wt%.

Cr: 20.0-35.0 wt% Cr is a ferrite-forming element that contributes to the improvement of corrosion resistance, and is also a σ-phase constituent element. If the Cr content is less than 20.0 wt%, the corrosion resistance and oxidation resistance of the steel will be insufficient, while if the Cr content exceeds 35.0 wt%, the toughness of the steel will be deteriorated. Therefore, Cr is 20.0-35.0 wt%, preferably 23.0-27.0
Must be wt%.

Ni: 3.0-10.0 wt% Ni is an austenite forming element, and if it is less than 3.0 wt%, the ratio of γ phase is too small even if adjusted by other ferrite forming elements or austenite forming elements. If it exceeds 10 wt%, on the contrary, not only the γ phase ratio becomes more than the necessary amount but also the cost increases. Therefore, Ni
Must be 3.0-10.0 wt%.

Mo: 0.5-6.0 wt% Mo improves the corrosion resistance such as pitting corrosion resistance and crevice corrosion resistance.
It is also an element that contributes to solid solution strengthening. Mo content is
If it is less than 0.5% by weight, the effect is not obtained, while if it exceeds 6.0% by weight, the toughness is deteriorated and the manufacturing cost is increased. Therefore, the amount of Mo added is 0.5 to 6.0 wt%, preferably
It should be 1.0 to 4.0 wt%.

B: 0.0005 to 0.01 wt% B is an element which exists in the grain boundary of the alloy when added in a trace amount and improves hot workability. If the amount is less than 0.0005 wt%, the hot workability is not sufficient even if S or C is reduced. On the other hand, if the amount exceeds 0.01 wt%, the amount of grain boundary segregation becomes excessive and the hot workability is deteriorated. Cause deterioration. Therefore, the amount of B added is 0.00
05 to 0.01 wt%

N: 0.08 to 0.30 wt% N, like C, is an austenite forming element. Therefore, the N content must be determined from the structural balance in consideration of other ferrite forming elements. This N
Also has the effect of improving pitting corrosion resistance, and it is necessary to add at least 0.08 wt% of N.
If it exceeds 30 wt%, hot workability deteriorates, so 0.08 ~
It is limited to the range of 0.30wt%.

S: 0.005 wt% or less S is an element which precipitates at α / γ grain boundaries to deteriorate hot workability and also adversely affects corrosion resistance, and the lower the better. When the S content exceeds 0.005 wt%, the effect becomes particularly remarkable, so the S content must be suppressed to 0.005 wt% or less.

W: 0.03 to 2.0 wt%, V: 0.03 to 2.0 wt% Both W and V are ferrite-forming elements, which improve local corrosion resistance and prevent stable existence of γ phase at high temperature.
It is an element useful for improving hot workability. If both W and V are less than 0.03 wt%, the improvement effect is small, while if more than 2.0 wt%, deterioration of toughness reduces hot workability, which is disadvantageous in manufacturing cost. Therefore,
The amounts of W and V added are both 0.03 to 2.0 wt%, preferably 0.05 to 0.24 wt%.

Cu: 2.0 wt% or less Cu is an element that contributes to the improvement of corrosion resistance such as stress corrosion cracking resistance, general corrosion resistance and crevice corrosion resistance, but if too much is added, hot workability will be improved. Deteriorate. Therefore, if the above effect is expected, 2.0 wt% is added as the upper limit.
The preferable addition range is 1.0 to 2.0 wt%.

(110) Surface Strength: 10% or More The two-phase ferritic stainless steel sheet of the present invention requires that the strength of the (110) plane of the ferrite phase in the plate surface is 10% or more. As explained in FIG.
The elongation property at room temperature increases as the strength of the (110) plane increases, and especially when the strength of the (110) plane becomes 10% or more, the influence becomes remarkable, so that the (110)
The surface strength is 10% or more. Here, the (110) plane strength is (11) of the ferrite phase measured by the X-ray diffraction method.
0) It represents the relative ratio of the integrated value of the surface strength. This ratio corresponds to half the intensity of this diffraction peak at the diffraction position on the (110) plane of the diffraction chart.
An integrated intensity having upper and lower limits of two angles (2θ) sandwiching the diffraction angle, that is, an area (A) surrounded by two 2θ sandwiching the diffraction angle, a diffraction intensity curve and a reference line indicating the background intensity, Then, similarly, the angle (2θ): 20
Integrated intensity with upper and lower limits of ° and 100 °, that is, 2
θ: 20 °, 100 °, an area (B) surrounded by a diffraction intensity curve and a reference line indicating the background intensity,
It is calculated by (A / B) × 100.

[0034]

Example A stainless steel slab having the composition shown in Table 1 was hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 4 to 9 mm. Then, this hot rolled sheet is annealed (1 minute), further descaled, and then cold rolled,
Annealing (1 minute) was performed to produce a test steel plate having a plate thickness of 1.5 mm. Table 2 shows these hot rolling conditions and annealing temperatures. In the above manufacturing process, a sample for X-ray diffraction was sampled from a part of the cold-rolled sheet in parallel with the rolled surface, and the X-ray diffraction intensity of the central portion thereof was measured over 2θ: 20 ° to 100 °. From the resulting chart, we follow the definition above (11
0) Surface strength was determined. The test piece for measuring elongation was JIS Z2201 13B, and the tensile speed was 3 mm / min up to 0.2% proof stress, and then 30 mm / min.

The results obtained are also shown in Table 2. As is clear from the results shown in Table 2, when the duplex stainless steel produced according to the present invention is compared at the same level in the γ amount as compared with the superplastic duplex stainless steel produced by the conventional production method. It was found that the elongation was extremely large. Especially, when the γ amount is 40%, it is 27% or more, and the γ amount is 50%.
It was found that a high elongation of 30% or more can be obtained.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

As described above, according to the method of the present invention, the elongation characteristics of the duplex stainless steel sheet at room temperature are
It can be further improved. Furthermore, according to the method of the present invention, the elongation characteristics of the duplex stainless steel sheet at room temperature are
A γ content of 40% can be increased to 27% or more, and a γ content of 50% can be increased to 30% or more. Therefore, the method of the present invention makes it possible to reduce the cost of a processed product by performing complicated processing using a duplex stainless steel sheet at room temperature.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between elongation and (110) plane strength.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saito Fujiwara 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Yakin Kogyo Co., Ltd. Research and Development Headquarters Technical Research Center (56) Reference JP-A-7-278755 ( JP, A) JP 6-93380 (JP, A) JP 5-247592 (JP, A) JP 5-230600 (JP, A) JP 5-132741 (JP, A) JP Sho 62-180043 (JP, A) JP-A-1-100248 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (5)

(57) [Claims] 1. C: 0.02 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%, B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.005 wt% or less, and W: 0.03 to 2.0 wt%
%, V: 0.03 to 2.0 wt%, and the balance consists of Fe and unavoidable impurities. The (110) plane of the ferrite phase is 1 in the plate surface.
A duplex stainless steel sheet with excellent elongation characteristics characterized by being oriented by 0% or more. 2. C: 0.02 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%, B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.005 wt% or less, Cu: 2.0 wt% or less, and selected from W: 0.03 to 2.0 wt% and V: 0.03 to 2.0 wt% 1) or 2), and the balance is Fe and unavoidable impurities, and the (110) plane of the ferrite phase is oriented in the plate surface by 10% or more. Duplex stainless steel plate. 3. C: 0.02 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%, B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.005 wt% or less, and W: 0.03 to 2.0 wt%
%, V: 0.03 to 2.0 wt% selected from the group consisting of one or two kinds, and the balance being Fe and unavoidable impurities. A steel slab with a hot rolling start temperature of 1200 to 1270 ° C and a reduction rate of 10
-50% / pass, time between passes 1 second or more, number of passes 2 or more, total rolling reduction 90% or more and hot rolling end temperature 850-1100 ° C
Hot-rolled under the conditions consisting of, the obtained hot-rolled sheet is annealed,
Then, cold rolling and cold rolling sheet annealing are performed, The manufacturing method of the duplex stainless steel plate characterized by the above-mentioned. 4. C: 0.02 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Cr: 20.0 to 35.0 wt%, Ni: 3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%, B: 0.0005 to 0.01 wt%, N: 0.08 to 0.30 wt%, S: 0.005 wt% or less, Cu: 2.0 wt% or less, and selected from W: 0.03 to 2.0 wt% and V: 0.03 to 2.0 wt% A steel slab containing any one or two of the above, with the balance being Fe and inevitable impurities.
~ 1270 ° C, reduction rate 10-50% / pass, time between passes 1 second or more, number of passes 2 passes or more, total reduction rate 90% or more and hot rolling end temperature 850 ~ 1100 ° C A method for producing a duplex stainless steel sheet, which comprises annealing the obtained hot-rolled sheet, and then performing cold rolling and cold-rolled sheet annealing. 5. The method according to claim 3, wherein the hot-rolled sheet is annealed at 1000 to 1070 ° C. and the cold-rolled sheet is annealed at 1000 to 1050 ° C.