JP3939534B2 - Duplex stainless steel sheet and manufacturing method thereof - Google Patents

Description

【００３３】
【表２】

【００３４】
【表３】

【００３５】
【表４】

【００３６】
試験結果を表１〜表４に示すように、板厚中心領域のフェライト相Ｘ線強度比｛１００｝／｛１１１｝が２以下の２相ステンレス鋼板は伸びが２５％以上と良好である。
【００３７】
また、本発明による成分、スラブ加熱温度、熱延板焼鈍温度によって製造された２相ステンレス鋼板は従来材よりも伸びが向上している。よって、本発明により、加工性に優れた２相ステンレス鋼板の製造が可能である。
【００３８】
尚、本発明の効果は、冷間圧延−焼鈍を２回繰り返す２回冷延法においても有効である。また、研磨仕上げなどの各種表面仕上材に対しても有効である。
【００３９】
【発明の効果】
以上の説明から明らかなように、本発明によれば加工性特に伸びが高い２相ステンレス鋼板を特別な新規設備を必要とせずに提供することができる。そして、プレス成型時の割れなどが防止でき、加工時にも特別な手段を用いることなく良好なプレス成形性が得られる。
【図面の簡単な説明】
【図１】製品板の｛１００｝／｛１１１｝強度比と伸びの関係を示す図である。
【図２】スラブ加熱時のフェライト相比率と製品伸びの関係を示す図である。
【図３】熱延板焼鈍時のフェライト相比率と製品伸びの関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a duplex stainless steel sheet comprising a ferrite phase and an austenite phase excellent in workability.
[0002]
[Prior art]
Duplex stainless steel sheet consisting of ferrite phase and austenite phase has excellent corrosion resistance, high strength and fatigue resistance, so it is widely used in chemical plants, etc., but its ductility is austenitic stainless steel Therefore, cracking may occur during press molding, and improvement in workability is desired.
[0003]
In the duplex stainless steel, the ratio of the ferrite phase to the austenite phase changes depending on the heat treatment temperature, so that the structure control is important. Among prior arts, Japanese Patent Application Laid-Open No. 11-50143 discloses that elongation is improved by heating to a ferrite single-phase region during heating in hot rolling.
[0004]
However, the conventional technique of heating to the ferrite single phase region is not easy to manufacture because the steel sheet is remarkably softened during heating, and the ratio of γ phase precipitated in the cooling process becomes unstable and the product elongation may not improve. there were. Therefore, it has been difficult to provide a duplex stainless steel excellent in workability with the prior art.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to control the texture of the product plate by controlling the α and γ phase ratios during hot rolling slab heating and hot-rolled sheet annealing in order to solve the problems of the prior art. The basic technical idea is to provide a ferritic phase and austenitic duplex stainless steel sheet with excellent workability.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted detailed studies on the improvement of elongation of a duplex stainless steel sheet from the viewpoint of the metal structure and texture.
[0007]
The present invention
(1) In a duplex stainless steel sheet composed of a ferrite phase and an austenite phase, the ferrite phase X-ray intensity ratio {100} / {111} in the center region of the sheet thickness is 2 or less, and the chemical component of the duplex stainless steel sheet is % By mass, C ≦ 0.05%, Si ≦ 1.0%, Mn ≦ 2.0%, P ≦ 0.03%, S ≦ 0.01%, Ni: 5 to 10%, Cr: A duplex stainless steel sheet containing 20 to 30%, N: 0.05 to 0.20%, the balance being Fe and inevitable impurities .
( 2 ) Further, the chemical component of the duplex stainless steel sheet contains one or two or more of Mo: 1.0 to 5.0% and Cu: 0.5 to 3.0% as described in ( 1 ). Phase stainless steel sheet.
( 3 ) Further, the chemical component of the duplex stainless steel sheet is one or two of Al: 0.05 to 0.5%, Ca: 0.001 to 0.005%, Mg: 0.0002 to 0.002%. The duplex stainless steel sheet according to ( 1 ) or ( 2 ), which contains at least seeds.
( 4 ) Further, the chemical components of the duplex stainless steel plate are V: 0.01 to 1.0%, B: 0.0005 to 0.005%, Ti: 0.01 to 0.3%, Nb: 0.00. The duplex stainless steel sheet according to any one of ( 1 ) to ( 3 ), containing one or more of 01 to 0.3%.
( 5 ) The heating temperature of the duplex stainless steel slab is heated to a temperature at which the ferrite phase ratio becomes 70% to 95% and hot-rolled to form a hot-rolled sheet, and then the hot-rolled sheet has a ferrite phase ratio of 70. % To 95% hot-rolled sheet annealing, followed by cold rolling, followed by cold-rolled sheet annealing to obtain the ferrite phase X-ray intensity ratio {100} / {111} in the center region of the sheet thickness. a method of manufacturing a two-phase stainless steel, characterized by 2 or less, the chemical components of the two-phase stainless steel sheet, C ≦ 0.05%, Si ≦ 1.0%, Mn ≦ 2.0% P ≦ 0.03%, S ≦ 0.01%, Ni: 5 to 10%, Cr: 20 to 30%, N: 0.05 to 0.20%, the balance being Fe and inevitable For producing a duplex stainless steel sheet made of mechanical impurities .
( 6 ) Further, the chemical components of the duplex stainless steel sheet contain one or more of Mo: 1.0 to 5.0%, Cu: 0.5 to 3.0%, the balance being Fe and inevitable The method for producing a duplex stainless steel sheet according to ( 5 ), comprising impurities.
( 7 ) Further, the chemical components of the duplex stainless steel sheet are Al: 0.05 to 0.5%, Ca: 0.001 to 0.005%, Mg: 0.0002 to 0.002%, or one or two. The manufacturing method of the duplex stainless steel sheet as described in ( 5 ) or ( 6 ) which contains seed | species or more.
( 8 ) Further, the chemical components of the duplex stainless steel sheet are V: 0.01 to 1.0%, B: 0.0005 to 0.005%, Ti: 0.01 to 0.3%, Nb: 0.00. The manufacturing method of the duplex stainless steel sheet in any one of ( 5 )-( 7 ) which contains 01-0.3% 1 type or 2 types or more, and remainder consists of Fe and an unavoidable impurity.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The reason for limitation of the present invention will be described below.
In the present invention, it has been found that the elongation is improved by setting the X-ray integral intensity ratio {100} / {111} in the center region of the plate thickness to 2 or less in the texture of the product plate. The duplex stainless steel sheet develops the rolling orientation of the ferrite phase ({100} <011>, {111} <011>, etc.) during hot rolling. In these rolling orientations, the {100} oriented crystal grains are remarkably easily constricted in the thickness direction, so that the elongation is deteriorated. This crystal orientation is remarkably developed during hot rolling, and hardly changes in orientation even by recrystallization annealing, so that it remains up to the product plate and causes a reduction in the elongation of the product. FIG. 1 shows the relationship between the X-ray integral intensity ratio {100} / {111} and elongation in the center region of the thickness of a product plate having a thickness of 1.5 mm. From this, {100} / {111} is 2 or less and the elongation is 25% or more, which is favorable. As described above, the elongation of the entire steel sheet is improved by reducing the {100} <011> -oriented crystal grains that are easily constricted in the thickness direction and have a low elongation. Here, the X-ray integral intensity is calculated from the intensity ratio with the non-directional sample by measuring the X-ray reflection intensity for each crystal plane in the center region of the thickness of the product plate. In addition, the elongation was evaluated by taking a JIS No. 13 B test piece in parallel with the rolling direction and carrying out a tensile test by the method specified in JISZ2201.
[0009]
Duplex stainless steel has a feature that the ratio of two phases of a ferrite phase and an austenite phase varies depending on the heat treatment temperature. The present invention is characterized in that the ferrite phase ratio is 70 to 95% during slab heating when hot rolling duplex stainless steel. FIG. 2 shows the relationship between the ferrite phase ratio and product elongation during slab heating. Accordingly, when the ferrite phase is precipitated by 70% or more, the elongation becomes 25% or more. This is because by setting the ferrite phase ratio to 70% or more, the ferrite phase becomes coarse, and strain is easily introduced into the ferrite phase during subsequent rolling, thereby promoting recrystallization of the ferrite phase. When the ferrite phase ratio is less than 70%, a large amount of austenite phase is precipitated, so that recrystallization of the ferrite phase is delayed, and the rolling orientation of the ferrite phase ({100} <011>, {111} <011>, etc.) develops. To do. Further, when the ferrite phase becomes 95% or more during slab heating, the ferrite phase becomes extremely soft and deformation of the slab occurs in the heating furnace, so 95% was made the upper limit. Desirably, the ferrite phase ratio during slab heating is 75 to 85%.
[0010]
Here, for the ferrite phase ratio at the time of heating, the steel sheet heated to a specific temperature is cooled by water cooling or air cooling, and the structure of the central region of the plate thickness is revealed by, for example, oxalic acid electrolytic etching, via an optical microscope. By image analysis, the area ratio of the ferrite phase or austenite phase was measured and used as the ratio of each phase. The same applies to the ferrite phase ratio during the following hot-rolled sheet annealing.
[0011]
The two stainless steel hot-rolled sheets are in a two-phase state of a ferrite phase and an austenite phase. The ferrite phase is a stretched structure with a rolled texture developed. The rolling texture developed at the hot-rolled sheet stage causes a reduction in the elongation of the product sheet. Therefore, it is necessary to promote recrystallization in the steps after the hot-rolled sheet annealing, but since these orientations are remarkably stable, it is difficult to reduce at the time of hot-rolled sheet annealing. In this invention, it discovered that the elongation of a product board improved by making the ferrite phase ratio at the time of hot-rolled sheet annealing 70 to 95%. FIG. 3 shows the relationship between the ferrite phase ratio and the elongation of the product plate during hot-rolled sheet annealing. Thus, when 70% or more of the ferrite phase is precipitated, the elongation is good at 25% or more. This is because the ferrite phase becomes coarser by setting the ferrite phase ratio to 70% or more, so that when it is cold-rolled, strain is easily accumulated in the ferrite grains, and it is difficult to recrystallize during cold-rolled sheet annealing. This is because recrystallization of the rolling direction of the phase is promoted. If the ferrite phase becomes 95% or more during hot-rolled sheet annealing, the ferrite phase becomes extremely soft and the steel sheet is deformed in the heating furnace, causing troubles such as sheet breakage, so 95% was made the upper limit. Desirably, the ferrite phase ratio at the time of hot-rolled sheet annealing is 75 to 85%.
[0012]
As described above, in the present invention, in order to obtain an elongation of 25% or more, the slab heating temperature and the hot-rolled sheet annealing temperature are set to temperatures at which the ferrite phase ratio becomes 70 to 95%. In addition, in the case of the said steel component, it is preferable that slab heating temperature shall be 1150-1300 degreeC and hot-rolled sheet annealing temperature shall be 1100-1250 degreeC.
[0013]
Although the steel component of this invention should just be common duplex stainless steel, the said component is especially preferable. The following steel composition will be described.
[0014]
C is an element that deteriorates corrosion resistance and workability, and deteriorates manufacturability. However, excessive reduction leads to an increase in refining costs and it becomes difficult to adjust the phase balance between the ferrite phase and the austenite phase. It was as follows. Preferably, it is 0.02% or less.
[0015]
Si improves oxidation resistance and is also added as a deoxidizing material. However, excessive addition promotes precipitation of intermetallic compounds that degrade manufacturability and causes embrittlement, so it is made 1.0% or less. . Desirably, it is 0.6% or less.
[0016]
Although Mn may be added as a deoxidizing element, it is an element that deteriorates workability and corrosion resistance. Desirably, it is 0.8% or less.
[0017]
P deteriorates corrosion resistance and workability, but excessive reduction leads to an increase in refining cost, so 0.03% or less is preferable. Desirably, it is 0.02% or less.
[0018]
S is not more than 0.01% because it segregates at the grain boundaries to deteriorate the hot workability and the corrosion resistance. Desirably, 0.001% or less is good.
[0019]
Ni is an austenite-generating element in addition to improving oxidation resistance, and needs to be 5% or more. However, if it is 10% or more, the phase ratio cannot be controlled. Therefore, Ni is preferably 5 to 10%, and preferably 6 to 8%.
[0020]
Cr needs to be added in an amount of 20% or more in order to improve corrosion resistance and high-temperature oxidation resistance. However, addition of 30% or more causes deterioration of toughness and deteriorates manufacturability. Therefore, the Cr range is 20-30%. Furthermore, 22 to 28% is desirable from the viewpoint of ensuring corrosion resistance and workability.
[0021]
Mo is an element that contributes to improving the corrosion resistance, and 1.0% or more is necessary. However, if it exceeds 5.0%, the raw material cost is increased and manufacturability is deteriorated. Desirably, the content is 2.0 to 4.0%.
[0022]
Cu is an element that contributes to the improvement of corrosion resistance and needs to be added in an amount of 0.5% or more, but if added over 3.0%, the hot workability deteriorates, so that it is 3.0% or less. did. Desirably, it is 0.8 to 2.0% or less.
[0023]
N is an element that improves the corrosion resistance and is determined by controlling the ferrite phase ratio. However, excessive addition deteriorates the hot workability, so 0.05 to 0.20%. Desirably, 0.08 to 0.12% is good.
[0024]
Al is a deoxidizing element and may be added to improve oxidation resistance and workability. The effect can be obtained at 0.05% or more. The ductility is reduced. Therefore, the Al range is set to 0.05 to 0.5%. Furthermore, if considering manufacturability, 0.07 to 0.2% is desirable.
[0025]
When Ca is added in an amount of 0.001% or more, it combines with S to improve hot ductility, but if it exceeds 0.005%, the effect is saturated and the corrosion resistance deteriorates. Therefore, it was 0.001 to 0.005%. Furthermore, if considering the manufacturability and cost, 0.002 to 0.004% is desirable.
[0026]
Mg acts as a deoxidizing element when added in an amount of 0.0002% or more. However, if over 0.002%, the deoxidation effect is saturated, so the content was made 0.0002 to 0.002%. Considering the refining cost and corrosion resistance, 0.0005 to 0.001% or less is desirable.
[0027]
V increases the workability by generating nitride by adding 0.01% or more, but if it exceeds 1.0%, it causes a decrease in hot workability. did. Furthermore, if considering the manufacturability, 0.1 to 0.5% is desirable.
[0028]
B is an element that improves the hot workability because it promotes austenite / ferrite transformation and softens, and the effect is produced by addition of 0.0005% or more, but conversely if added over 0.005%. In order to deteriorate the properties and corrosion resistance, the content was made 0.0005 to 0.005%. Furthermore, if considering cost and corrosion resistance, 0.0007 to 0.002% is desirable.
[0029]
Ti forms nitride TiN or carbide TiC by addition of 0.01% or more and improves workability. However, if it exceeds 0.3%, ductility decreases conversely, so 0.01 to 0.3% It was. Furthermore, if considering the manufacturing cost and castability, 0.05 to 0.1% or less is desirable.
[0030]
Nb forms nitride NbN and carbide NbC by addition of 0.01% or more as in the case of Ti, and improves the workability. However, if it exceeds 0.3%, the ductility is reduced, so 0.01 to 0.3%. Furthermore, if considering the manufacturing cost and castability, 0.05 to 0.1% or less is desirable.
[0031]
【Example】
Two-phase stainless steels having the component compositions shown in Tables 1 to 4 were melted and cast into 250 mm thick slabs. Thereafter, the slab is hot rolled to form a 5.0 mm thick hot rolled sheet, followed by annealing the hot rolled sheet, followed by cold rolling to a 1.5 mm sheet thickness, and annealing the cold rolled sheet at 1080 ° C. A product plate having a thickness of 1.5 mm was obtained. Elongation was evaluated by taking a JIS No. 13 B test piece in parallel with the rolling direction and carrying out a tensile test by the method defined in JISZ2201.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
[Table 3]

[0035]
[Table 4]

[0036]
As the test results are shown in Tables 1 to 4, the duplex stainless steel sheet having a ferrite phase X-ray intensity ratio {100} / {111} in the center region of the plate thickness of 2 or less has a good elongation of 25% or more.
[0037]
Moreover, the elongation of the duplex stainless steel sheet produced by the component according to the present invention, the slab heating temperature, and the hot-rolled sheet annealing temperature is improved as compared with the conventional material. Therefore, according to the present invention, it is possible to produce a duplex stainless steel sheet having excellent workability.
[0038]
In addition, the effect of this invention is effective also in the double cold rolling method which repeats cold rolling-annealing twice. It is also effective for various surface finishing materials such as polishing finish.
[0039]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to provide a duplex stainless steel sheet having high workability, particularly high elongation, without requiring special new equipment. And the crack at the time of press molding can be prevented, and favorable press moldability is obtained without using a special means also at the time of processing.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the {100} / {111} strength ratio and elongation of a product plate.
FIG. 2 is a graph showing the relationship between ferrite phase ratio and product elongation during slab heating.
FIG. 3 is a diagram showing the relationship between the ferrite phase ratio and product elongation during hot-rolled sheet annealing.

Claims (8)

In a duplex stainless steel sheet (hereinafter simply referred to as a duplex stainless steel sheet) composed of a ferrite phase and an austenite phase, the ferrite phase X-ray intensity ratio {100} / {111} in the sheet thickness center region is 2 or less ,
The chemical component of the duplex stainless steel sheet is
% By mass
C ≦ 0.05%,
Si ≦ 1.0%,
Mn ≦ 2.0%,
P ≦ 0.03%,
S ≦ 0.01%,
Ni: 5 to 10%
Cr: 20-30%,
N: A duplex stainless steel sheet containing 0.05 to 0.20%, the balance being Fe and inevitable impurities . Furthermore, the chemical composition of the duplex stainless steel sheet
Mo: 1.0-5.0%,
The duplex stainless steel sheet according to claim 1 , containing one or more of Cu: 0.5 to 3.0%. Furthermore, the chemical composition of the duplex stainless steel sheet
Al: 0.05-0.5%
Ca: 0.001 to 0.005%,
The duplex stainless steel sheet according to claim 1 or 2 , characterized by containing one or more of Mg: 0.0002 to 0.002%. Furthermore, the chemical composition of the duplex stainless steel sheet
V: 0.01-1.0%
B: 0.0005 to 0.005%,
Ti: 0.01 to 0.3%,
The duplex stainless steel sheet according to any one of claims 1 to 3, wherein Nb is contained in one or more of 0.01 to 0.3%. The heating temperature of the duplex stainless steel slab is heated to a temperature at which the ferrite phase ratio becomes 70% to 95% and hot-rolled to form a hot rolled sheet, and then the hot rolled sheet has a ferrite phase ratio of 70% to 95%. % Of the ferrite phase X-ray intensity ratio {100} / {111} in the center region of the plate thickness is 2 or less by performing hot-rolled sheet annealing at a temperature of%, followed by cold rolling, followed by cold-rolled sheet annealing. A method for producing a duplex stainless steel sheet, characterized in that
The chemical component of the duplex stainless steel sheet is
In mass%
C ≦ 0.05%,
Si ≦ 1.0%,
Mn ≦ 2.0%,
P ≦ 0.03%,
S ≦ 0.01%,
Ni: 5 to 10%
Cr: 20-30%,
N: A method for producing a duplex stainless steel sheet containing 0.05 to 0.20%, with the balance being Fe and inevitable impurities . Furthermore, the chemical composition of the duplex stainless steel sheet
Mo: 1.0-5.0%,
The method for producing a duplex stainless steel sheet according to claim 5 , comprising one or more Cu: 0.5 to 3.0%. Furthermore, the chemical composition of the duplex stainless steel sheet
Al: 0.05-0.5%
Ca: 0.001 to 0.005%,
The method for producing a duplex stainless steel sheet according to claim 5 or 6 , wherein Mg: 0.0002 to 0.002% is contained in one kind or two or more kinds. Furthermore, the chemical composition of the duplex stainless steel sheet
V: 0.01-1.0%
B: 0.0005 to 0.005%,
Ti: 0.01 to 0.3%,
Nb: 0.01-0.3% of 1 type or 2 types or more are contained, The manufacturing method of the duplex stainless steel plate in any one of the Claims 5 thru | or 7 characterized by the above-mentioned.

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