JP3806186B2 - Method for producing ferritic stainless steel with excellent anti-roping properties - Google Patents

Description

【００１４】
またγｐに関しては、γｐが高いほどロ−ピングは改善されるがγｐが３５を超えるように成分を規定すると本発明の熱延板焼鈍省略プロセスでは、冷延時の耳割れや、また冷延性が悪化するとともに冷延後の焼鈍のみではγ相が消えずに焼鈍時の粒成長を阻害し、また強度が高くなり加工性が低下するなど表面特性以外の製造性、材質で悪影響がでるためにγｐは３５％以下とした。
【００１５】
加熱条件としては、加熱時にγ相量が最大となるように加熱温度を設定するとγ相活用の点で不利であり、粗圧延中にγ相が析出または増加するように加熱温度を設定することが重要である。γp が２０％以上でもγ相が熱延途中で減少しないようにするには、加熱時にはむしろある程度γ相が減少する温度にすることが必要であり、１１００℃以上で４０％以上の累積圧下を取ることを考慮すると加熱温度として１１５０℃以上が必要である。しかし、１３００℃を超えて加熱すると表層部が脱炭により異常粒成長をおこし疵の原因となるため、加熱温度の上限は１３００℃とした。
【００１６】
上記の観点で、成分、加熱条件を満足し、γ相と熱延条件の関係は１１００℃以上での累積圧下率を４０％以上とすることで、冷延時のロ−ピングは低減できることが判明した。１１００℃以上での圧下率を４０％以上としたのは、γ相を加工後微細に分散させるために必要であるためであり、これ以下では粒界へのγ析出が主体となるためである。また累積圧下率が４０％を確保できても、γｐが２０％未満ではγ相の分散が均一でなくなり粗大粒が熱延板に残存し、ロ−ピングを不良とする。
１１００℃以上の圧延に関しては、１パスあたりの圧下率が高いほど好ましいが、数パスに分けて実施しても効果があり、また仕上圧延に関しては高速圧延−高温仕上げが望ましい。
【００１７】
熱延後の捲取温度は６００℃以下で４５０℃より高温とする。６００℃より高温ではγ相がフェライトと炭化物に分解してしまい、ロ−ピングの改善傾向が減少する。また４５０℃以下の低温ではマルテンサイトに変態してしまい、本発明のようにγ相を微細に分散させ、かつ熱延板焼鈍を省略したプロセスを前提とした場合、冷延後の熱処理時にマルテンサイトが逆変態するまでにフェライト粒の成長を阻害し降伏点が高くなるため、著しい低温捲取はロ−ピング特性は改善するが材質を硬質にするため捲取温度の下限は４５０℃を超える温度とした。
【００１８】
そして、成分範囲について検討した結果、上記のロ−ピング低減方法は、
質量％で、
Ｃ：０．０２５〜０．０５５％、Ｎ：０．００１〜０．０１５％、Ｃｒ：１５．０〜１８．０％、Ｓ：０．０１０％以下、Ｐ：０．０４％以下、Ｔｉ：０．００５〜０．１０％、Ｍｎ：０．０１〜１．０％、Ｓｉ：０．０１〜１．０％、Ｎｉ：０．５％以下、Ｃｕ：０．５％以下、Ｍｏ：０．２％以下、Ａｌ：０．０１５〜０．０２５％、Ｏ：０．０１０％以下、
さらに必要に応じて、
Ｂ：０．００５％以下、Ｖ：０．０５％以下の１種以上を含有し、
残部がＦｅ及び不可避的不純物からなるフェライト系ステンレス鋼において成り立つことが判明した。
【００１９】
以下に成分の限定理由を述べる。
Ｃ：Ｃは耐食性の点では有害であり特に溶接部の耐食性に悪影響を与えるが、強度およびγ相量を適正に確保するためにはある程度は必要である。γ相の観点からは０．０２５％未満ではγ量が不足しフェライト粒が粗大化する、また０．０５５％を超えて添加すると加工性、延性が劣化するためにＣは０．０２５〜０．０５５％とした。
【００２０】
Ｎ：ＮはＣと同様に含有量が少ないほど耐食性、加工性が好ましいが０．００１％未満にすることは工業的には困難であり、また０．０１５％を超えて添加すると高強度となり加工性が劣化するためにＮは０．００１〜０．０１５％の範囲で添加する。
【００２１】
Ｃｒ：Ｃｒは本発明のフェライト系ステンレス鋼の主要元素であり、耐食性を確保するためには１５％以上添加する必要がある。しかし、１８％を超えて添加しても食性は向上するが、γ量を確保するためのＣ、Ｎ、Ｍｎ量が増加し加工性や靭性が化するのでＣｒの上限は１８％とした。
【００２２】
Ｓ：Ｓは延性、靭性等を劣化させ、また耐食性の観点からも有害であるため、０．０１０％以下とする。
Ｐ：Ｐは加工性や靭性また耐食性の点でも有害でありその含有量は少ないほど望ましく０．０４０％以下とする。
【００２３】
Ｔｉ：本発明においては加工性の観点からＮを固定するために必要な元素であり、０．００５％以上添加する。しかし、過剰に添加するとＮの固定効果は向上するもの価格が高くなることや、Ｔｉ自身が強力なフェライト形成元素であるためγ安定化元素を多量に添加する必要性が生じるなど上限は０．１％以下である。ロ−ピングの観点からは０．０５％以下、とすることが望ましい。
【００２４】
Ｍｎ：Ｍｎは脱酸元素として添加するが、０．０１％未満では効果が十分ではなく、１％を超えて添加してもその効果が飽和するため０．０１〜１．０％で添加する。
【００２５】
Ｓｉ：Ｓｉは脱酸剤として使用されるが０．０１％未満では十分な効果がなく、また１％を超えて添加すると脆化を著しく促進させ延性、靭性を劣化させるので０．０１〜１．０％で添加する。
【００２６】
Ｎｉ：Ｎｉはγ相安定化元素として使用できる。但し多量に添加するとγ相が著しく安定化するため、γ相がその後の熱処理中に分解できず加工性が劣化するため０．５％以下で添加する。
Ｃｕ：Ｃｕはγ相安定化元素として使用できる。但し多量に添加するとＣｕによって強度が著しく上昇するため０．５％以下で添加する。
Ｍｏ：Ｍｏはフェライト相安定化元素として使用できる。但し、多量に添加すると強度が上昇し、加工性が劣化するため０．２％以下で使用する。
【００２７】
Ａｌ：Ａｌは脱酸元素として使用され、またＮの固定にも使用できる０．０１５％以上とすることが必要である。またＡｌは強力なフェライト安定化元素であり、多量に含有させるとγ量を減少させるため０．０２５％以下とした。
Ｏ：Ｏは熱延板の靭性を劣化させたり鋳造時のノズル詰まりやキズ発生また熱延板の靭性劣化の原因となるため、本発明においては０．０１％以下、とした。
【００２８】
本発明では必要に応じてＢ、Ｖの１種以上を含有させることができる。
Ｂ：ＢはＮを固定するため、加工性を改善することができる。しかし過剰に添加してもその効果は飽和するため、０．００５％以下とした。
Ｖ：ＶはＣやＮを固定し、加工性を改善できるため選択元素として０．０５％以下で添加できる。
【００２９】
【実施例】
表１に示す成分のフェライト系ステンレス鋼をラボの真空溶解で溶製し、厚み１００ｍｍの５０ｋｇ鋼塊を製造した。この後、表２に示す条件で加熱後、粗圧延を５パスで２０ｍｍまで実施し、仕上熱延を２０ｍｍから５〜３ｍｍまで６パスで実施し、そのまま熱延板を７５０〜３５０℃の炉に挿入し１時間保持後炉冷して捲取をシミュレ−トした。表中の捲取温度はこのシミュレ−トの保持温度である。この後、硫酸で酸洗後、厚み２．０〜０．４ｍｍまで冷間圧延率を変えて冷延し、ロ−ピング高さを評価した。
【００３０】
ロ−ピングは、上記熱延板を酸洗後、０．４ｍｍまで冷延を行い、冷延方向に対して直角方向に１０ｍｍ長さについて粗度計で測定し、うねり高さの最大値を持ってロ−ピング高さとした。この測定を３箇所実施し、その平均値でロ−ピングを評価した。評価は、３箇所のロ−ピング最大高さの平均が０．１５μｍ未満をＡランク、０．１５μｍ以上０．２５μｍ未満をＢランク、０．２５μｍ以上〜０．３５μｍ未満をＣランク、０．３５μｍ以上をＤランクとして評価した。表面品位の点からはＡ，Ｂランクであれば問題となることはない。
表２に示すように、本発明材はいずれもロ−ピング高さが０．２５μｍ未満と小さく、優れた表面特性を示した。
【００３１】
【表１】

【００３２】
【表２】

【００３３】
【発明の効果】
上記のように、本発明はフェライト系ステンレス鋼の表面特性の問題点である冷延時のロ−ピングを熱延板焼鈍省略プロセスにて低減でき、低コストで表面特性の改善に寄与する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a ferritic stainless steel thin plate that has small surface undulation (loping) that occurs during cold rolling in a ferritic stainless steel production process and is excellent in surface properties.
[0002]
[Prior art]
Ferritic stainless steel is widely used including kitchen appliances because it has a lower Ni content and is less expensive than austenitic stainless steel. In this case, since the surface needs to be beautiful, it is required for the ferritic stainless steel to improve the surface characteristics.
[0003]
However, it is known that ferritic stainless steel is prone to surface irregularities called ridging during molding as a product. This ridging is unevenness having a height of 5 to 50 μm generated during processing.
Various methods for improving the ridging of ferritic stainless steel have been studied conventionally. For example, iron and steel 76 (1990) p. As described in 1520, the generation mechanism is also examined.
[0004]
Until now, the above-mentioned ridging has been regarded as a problem as a surface defect. However, recently, when the hot rolled sheet of ferritic stainless steel is cold-rolled, not at the time of product forming, the minute undulations that occur on the surface of the cold-rolled sheet remain until the final product has been sought after. It is a problem that the surface quality cannot be satisfied and the value as a product is impaired. This minute undulation is a undulation extending in the rolling direction at a height of about 0.2 μm to 0.5 μm on the surface of the cold-rolled sheet, and this undulation is called roping to distinguish it from ridging that occurs during the molding process of the product. It is.
[0005]
In addition, SUS430 steel, which is a typical steel type of ferritic stainless steel, requires SUS304, which is a typical steel type of austenitic stainless steel in terms of manufacturability, such as requiring box annealing that requires several tens of hours after hot rolling. The reality is that it is inferior. In order to simplify the manufacturing process of SUS430 from this point of view, many studies have been made on continuous annealing technology for hot-rolled sheet annealing and a process for omitting hot-rolled sheet annealing. In either case, the components of normal SUS430 steel are used. It is a component system characterized by a high pure flight system with a low C, low N and high Ti and high Al, and is established in a normal component system based on low Ti and low Al. Absent.
[0006]
[Problems to be solved by the invention]
Until now, roping was considered to be the same phenomenon as ridging, but it cannot be said that there is always a good response to ridging during forming and roping during cold rolling. The higher the rate, the higher the height, while the lower the rolling height, the lower the cold rolling reduction rate, and the rupture generation mechanism is not clear. Therefore, it has become necessary to establish a manufacturing method that can reduce roping.
[0007]
Adding a new process to the conventional process to reduce the roping is likely to lose the merit of inexpensive ferritic stainless steel, and the roping occurs in the process of omitting hot-rolled sheet annealing, which is the most advanced process Can be reduced, ferritic stainless steel having excellent surface characteristics can be provided at a lower cost. Accordingly, an object of the present invention, without increasing the process, b - is to provide a method of manufacturing a ferritic stainless steel occurs and excellent low surface characteristics of the ping.
[0008]
[Means for Solving the Problems]
The present inventors have studied various methods for reducing the roping in the manufacturing process in which the hot rolled sheet annealing of ferritic stainless steel is omitted. As a result, it was found that by controlling a series of process conditions of components, heating conditions, hot rolling conditions, and cutting conditions consistently, the roping can be reduced even in a process in which hot-rolled sheet annealing is omitted.
[0009]
The present invention is not based on independent control of components and hot rolling conditions, but requires a configuration for controlling the following series of process conditions.
[0010]
That is, the present invention
In mass%, C: 0.025~0.055%, N : 0.001~0.015%, Cr: 15.0~18.0%, S: 0.010% or less, P: 0. 04% or less, Ti: 0.005 to 0.10%, Mn: 0.01 to 1.0%, Si: 0.01 to 1.0%, Ni: 0.5% or less, Cu: 0.5 %: Mo: 0.2% or less, Al: 0.015-0.025%, O: 0.010% or less,
If necessary,
B: containing at least one of 0.005% or less, V: 0.05% or less,
The ferritic stainless steel whose balance is made of Fe and inevitable impurities and γp expressed by the following formula is 20 to 35% is hot-rolled at a heating temperature of 1150 ° C. or higher and 1300 ° C. or lower, and rough rolling is 1100 ° C. the cumulative rolling reduction of at least a 40%, continuing the coiling temperature by carrying out finish rolling and 450 ° C. ultra 600 ° C. or less, pickled without performing the subsequent hot rolled sheet annealing, cold rolling, final annealing This is a method for producing a ferritic stainless steel having excellent anti-roping characteristics.
γp = 420 × C + 470 × N + 23 × Ni + 12 × Cu + 7 × Mn-11.5 × Cr-11.5 × Si-11 × Mo-52 × Al-49 × Ti + 189
[0011]
Embodiment
Embodiments of the present invention will be described below.
The present inventors conducted an experiment for the purpose of reducing the roping generated during cold rolling of ferritic stainless steel, and examined the experimental result in detail.
As a result, it was found that it is important to promote the dispersion of the γ phase during hot rolling in order to omit hot-rolled sheet annealing and improve the rolling. In this case, it was found that the γ phase can be further dispersed by precipitating in the middle of hot rolling rather than precipitating during heating, and the roping can be improved by increasing the amount of γ phase to 15% or more. did.
[0012]
Therefore, as the component, a component system in which the γ phase precipitates or increases during hot rolling is good, and it is clear that the roping cannot be improved by a component system in which the volume fraction of the γ phase decreases during rough hot rolling. It became. When the amount of γ during rough hot rolling is 15% or more and the cumulative rolling reduction at 1100 ° C. or more exceeds 40%, the roping can be improved. In addition, in a component system in which the γ phase is reduced to 15% or less during rough hot rolling, recrystallization is likely to occur during hot rolling. It was also found that it was not allowed.
[0013]
From the above viewpoint, the component needs to be adjusted so that the amount of γ is 15% or more during rough hot rolling, and the amount of γ can be coarse if γp represented by the following formula is 20% or more. It was also revealed that the necessary amount of γ can be secured during rolling.

[0014]
Regarding γp, the higher the γp, the better the roping, but if the component is specified so that the γp exceeds 35, the process of omitting the hot-rolled sheet annealing of the present invention will prevent the ear cracking during cold rolling and the cold rolling property. As it deteriorates and only after annealing after cold rolling, the γ phase does not disappear and hinders grain growth during annealing, and the strength increases and the workability deteriorates. γp was set to 35% or less.
[0015]
As heating conditions, setting the heating temperature so that the amount of γ phase is maximized during heating is disadvantageous in terms of utilization of the γ phase, and setting the heating temperature so that the γ phase precipitates or increases during rough rolling. is important. In order to prevent the γ phase from decreasing during hot rolling even if γp is 20% or more, it is necessary to set the temperature so that the γ phase is reduced to some extent during heating, and a cumulative reduction of 40% or more at 1100 ° C. or higher is required. Considering taking it, 1150 degreeC or more is required as heating temperature. However, if the heating exceeds 1300 ° C., the surface layer part grows abnormally due to decarburization and causes wrinkles, so the upper limit of the heating temperature is 1300 ° C.
[0016]
From the above viewpoints, the components and heating conditions are satisfied, and the relationship between the γ phase and the hot rolling conditions is found to be able to reduce the rolling during cold rolling by setting the cumulative rolling reduction at 1100 ° C. or higher to 40% or higher. did. The reason why the rolling reduction at 1100 ° C. or higher is 40% or higher is that it is necessary for finely dispersing the γ phase after processing, and below this, γ precipitation at the grain boundaries is the main component. . Even if the cumulative rolling reduction is 40%, if γp is less than 20%, the dispersion of the γ phase is not uniform and coarse grains remain in the hot-rolled sheet, resulting in poor rolling .
For rolling at 1100 ° C. or higher, the higher the rolling reduction per pass, the better. However, it is also effective to divide into several passes, and for finish rolling, high speed rolling-high temperature finishing is desirable.
[0017]
The coiling temperature after hot rolling is 600 ° C. or lower and higher than 450 ° C. When the temperature is higher than 600 ° C., the γ phase is decomposed into ferrite and carbide, and the tendency to improve the roping is reduced. Further, when the temperature is lower than 450 ° C., it transforms into martensite, and assuming a process in which the γ phase is finely dispersed and the hot-rolled sheet annealing is omitted as in the present invention , the martensite is subjected to heat treatment after cold rolling. Since the ferrite grain growth is inhibited before the site undergoes reverse transformation and the yield point becomes high, the low temperature cutting improves the rolling characteristics but makes the material hard, so the lower limit of the cutting temperature exceeds 450 ° C. It was temperature.
[0018]
And as a result of examining the component range, the above-mentioned roping reduction method is
In mass%,
C: 0.025 to 0.055%, N: 0.001 to 0.015%, Cr: 15.0 to 18.0%, S: 0.010% or less, P: 0.04% or less, Ti : 0.005-0.10%, Mn: 0.01-1.0%, Si: 0.01-1.0%, Ni: 0.5% or less, Cu: 0.5% or less, Mo: 0.2% or less, Al: 0.015-0.025%, O: 0.010% or less,
If necessary,
B: containing at least one of 0.005% or less, V: 0.05% or less,
It has been found that the balance is established in ferritic stainless steel composed of Fe and inevitable impurities .
[0019]
The reasons for limiting the components are described below.
C: C is harmful in terms of corrosion resistance and adversely affects the corrosion resistance of the welded portion. However, it is necessary to some extent to ensure the strength and the amount of γ phase. From the viewpoint of the γ phase, if less than 0.025%, the amount of γ is insufficient and the ferrite grains become coarse, and if added over 0.055%, the workability and ductility deteriorate, so C is 0.025-0. 0.055%.
[0020]
N: N is the corrosion resistance smaller the content as with C, and preferably workability but be Rukoto below 0.001% is difficult for industrial and high when added in excess of 0.015% strength N is added in the range of 0.001 to 0.015% because processability is deteriorated.
[0021]
Cr: Cr is a main element of the ferritic stainless steel of the present invention , and it is necessary to add 15% or more in order to ensure corrosion resistance. However, even if added over 18%, the food property is improved, but the amount of C, N, and Mn for securing the amount of γ is increased and the workability and toughness are improved, so the upper limit of Cr was made 18%.
[0022]
S: Since S deteriorates ductility, toughness and the like and is also harmful from the viewpoint of corrosion resistance, it is set to 0.010% or less.
P: P is also harmful in terms of workability, toughness, and corrosion resistance. The smaller the content thereof, the more desirable it is to be 0.040% or less.
[0023]
Ti: In the present invention, it is an element necessary for fixing N from the viewpoint of workability, and 0.005% or more is added. However, if added excessively, the fixing effect of N is improved, but the price is increased, and since Ti itself is a strong ferrite-forming element, it is necessary to add a large amount of γ-stabilizing element. 1% or less. From the viewpoint of loping, it is desirable to be 0.05% or less.
[0024]
Mn: Mn is added as a deoxidizing element, but if less than 0.01%, the effect is not sufficient, and even if added over 1%, the effect is saturated, so 0.01 to 1.0% is added. .
[0025]
Si: Si is used as a deoxidizer, but if it is less than 0.01%, there is no sufficient effect, and if added over 1%, embrittlement is remarkably promoted and ductility and toughness are deteriorated. Add at 0.0%.
[0026]
Ni: Ni can be used as a γ-phase stabilizing element. However, since the γ phase is remarkably stabilized when added in a large amount, the γ phase cannot be decomposed during the subsequent heat treatment and the workability is deteriorated.
Cu: Cu can be used as a γ-phase stabilizing element. However, if added in a large amount, the strength is remarkably increased by Cu, so 0.5% or less is added.
Mo: Mo can be used as a ferrite phase stabilizing element. However, if added in a large amount, the strength increases and the workability deteriorates.
[0027]
Al: Al is used as a deoxidizing element and needs to be 0.015% or more, which can also be used for fixing N. Moreover, Al is a strong ferrite stabilizing element, and if it is contained in a large amount, the amount of γ is reduced, so that the content was made 0.025% or less.
O: O is to become a cause of deterioration of toughness of hot-rolled sheet toughness nozzle clogging and scratches occur also hot-rolled sheet at the time of casting or deteriorate, and 0.01% or less in the present invention, and the.
[0028]
In this invention, 1 or more types of B and V can be contained as needed.
B: Since B fixes N, workability can be improved. However, even if added excessively, the effect is saturated, so the content was made 0.005% or less.
V: V fixes C and N and improves workability, so it can be added as a selective element at 0.05% or less.
[0029]
【Example】
Ferritic stainless steel having the components shown in Table 1 was melted by vacuum melting in a laboratory to produce a 50 kg steel ingot having a thickness of 100 mm. Thereafter, after heating under the conditions shown in Table 2, a rough rolling was carried out in five passes to 20mm, a final hot rolling was carried out in six passes from 20mm to 5～3Mm, the or or hot rolled sheet seven hundred fifty to three hundred fifty ° C. the furnace insert and cooled 1 hour hold after furnace coiling simulator - was collected. Coiling temperature in the table is the simulator - a capital of hold temperature. Then, after pickling with sulfuric acid, the cold rolling ratio was changed to a thickness of 2.0 to 0.4 mm and cold rolled to evaluate the rolling height.
[0030]
For the rolling, the hot-rolled sheet is pickled, cold-rolled to 0.4 mm, measured with a roughness meter for a length of 10 mm in a direction perpendicular to the cold-rolling direction, and the maximum waviness height is determined. I took it as a roping height. This measurement was performed at three places, and the roping was evaluated by the average value. In the evaluation, the average of the three maximum rolling heights is less than 0.15 μm, A rank, 0.15 μm or more and less than 0.25 μm is B rank, 0.25 μm or more to less than 0.35 μm is C rank, 35 μm or more was evaluated as D rank. From the viewpoint of surface quality, there is no problem if it is A or B rank.
As shown in Table 2, all of the materials of the present invention had a low roping height of less than 0.25 μm and exhibited excellent surface characteristics.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
【The invention's effect】
As described above, the present invention can reduce the rolling during cold rolling, which is a problem of the surface characteristics of ferritic stainless steel, by a process of omitting hot-rolled sheet annealing, and contributes to the improvement of the surface characteristics at a low cost.

Claims (2)

% By mass
C: 0.025 to 0.055%,
N: 0.001 to 0.015%,
Cr: 15.0 to 18.0%,
S: 0.010% or less,
P: 0.04% or less,
Ti: 0.005 to 0.10%,
Mn: 0.01 to 1.0%
Si: 0.01 to 1.0%,
Ni: 0.5% or less,
Cu: 0.5% or less,
Mo: 0.2% or less,
Al: 0.015-0.025%,
O: containing 0.010% or less, the balance being Fe and unavoidable impurities, the ferritic stainless steel γp of the following formula is 20 to 35% and when the hot rolling, pressing heat temperature Is 1150 ° C. or higher and 1300 ° C. or lower, the cumulative rolling reduction at 1100 ° C. or higher in rough rolling is 40% or higher, and finish rolling is performed to set the milling temperature above 450 ° C. to 600 ° C. or lower. pickled without performing, cold rolling, which comprises carrying out the final annealing method for producing a superior ferritic stainless steel resistant roping characteristics.
γp = 420 × C + 470 × N + 23 × Ni + 12 × Cu + 7 × Mn-11.5 × Cr-11.5 × Si-11 × Mo-52 × Al-49 × Ti + 189 Furthermore, in mass%,
B : 0.005% or less,
V: 0.05% or less under
1 you characterized by containing on or more kinds,請 Motomeko 1 method for producing superior ferritic stainless steel resistant roping properties described in.