JPH0579732B2

JPH0579732B2 -

Info

Publication number: JPH0579732B2
Application number: JP62318381A
Authority: JP
Inventors: Sadao Hasuno
Original assignee: Kawasaki Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1987-12-16
Filing date: 1987-12-16
Publication date: 1993-11-04
Also published as: JPH01159319A

Description

[Detailed description of the invention]

〈産業上の利用分野〉本発明は、自動車外装部品あるいは各種装飾用
素材として用いられるフエライト系ステンレス鋼
の製造方法に係り、特に成形性、製造時の強靭性
に優れた高耐食フエライト系ステンレス鋼の製造
方法に関する。〈従来技術およびその問題点〉 SUS430に代表されるフエライト系ステンレス
鋼は、安価で耐応力腐食割れ性にも優れている
が、ニツケルを多量に含むオーステナイト系ステ
ンレス鋼と比較すると塩素イオンを含む水溶液に
おける耐銹性をはじめとする一般耐食性でかなり
劣つている。近年、ステンレス鋼溶製技術の進歩に伴ない、
特開昭52−30715号に開示されているように、極
低Ｃ，Ｎの高Crフエライト系ステンレス鋼の製
造が可能となり、耐食性の点では著しく改善され
たフエライト系ステンレス鋼が開発されている。ところが、高クロムフエライト鋼ではＣおよび
ＮがCrと炭窒化物を形成し、耐食性が逆に低下
し、熱延焼鈍板での靭性が低下し、最終製品にお
いては強度の上昇と、ｒ値の低下を招く。従つて、高クロムフエライト鋼はＣ、Ｎを0.01
％以下と厳しく制限されるため、製造コストが上
昇し、価格はオーステナイト系ステンレス鋼より
高く設定されている。Ｃ、Ｎが0.01％以上でも、耐食性、製造時の強
靭性、加工性の優れた高クロムフエライト系ステ
ンレス鋼の開発が望まれている。〈発明の目的〉本発明の目的は上述した従来の技術の問題点を
解決しようとするもので、加工性、製造時の強靭
性、耐食性の優れたフエライト系ステンレス鋼の
製造方法を提供しようとするものである。〈発明の構成〉本発明はＣ；0.015〜0.03重量％、Si；0.1〜１
重量％、Mn；１重量％以下、Ｓ；0.01重量％以
下、Cr；20〜25重量％、Mo；0.3〜1.0重量％、
Ni；0.2〜1.5重量％、Cu；0.04〜0.5重量％、Ｎ；
0.015〜0.03重量％、Nb；８（Ｃ＋Ｎ）〜20（Ｃ＋
Ｎ）重量％、Tiおよび／またはZrが（Ti＋Zr／
２）の総量として；0.02〜0.1重量％を含有し、
残部は鉄および不可避的不純物からなるフエライ
ト系ステンレス鋼板を熱間圧延した後、350℃以
下で巻取り、その後、［800＋1250×（Ti＋Zr／
２）］±25℃の温度域で母板焼鈍を行なうことを特
徴とする成形性の優れた高耐食フエライト系ステ
ンレス鋼の製造方法を提供するものである。以下に本発明を更に詳細に説明する。本発明に用いるフエライト系ステンレス鋼の組
成は、Ｃ；0.015〜0.03重量％、Si；0.1〜１重量
％、Mn；１重量％以下、Ｓ；0.01重量％以下、
Cr；20〜25重量％、Mo；0.3〜1.0重量％、Ni；
0.2〜1.5重量％、Cu；0.04〜0.5重量％、Ｎ；
0.015〜0.03重量％、Nb；８（Ｃ＋Ｎ）〜20（Ｃ＋
Ｎ）重量％、Tiおよび／またはZrが（Ti＋Zr／
２）の総量として；0.02〜0.1重量％を含有し、
残部は鉄および不可避的不純物である。Ｃが0.03重量％を越えるときは、クロム炭化物
を形成し、フエライト系ステンレス鋼の耐食性、
製造時の強靭性を劣化させる。Ｃが0.015重量％
未満のときは、溶製するのにコストがかかる。 Siが１重量％を越えるときは、成形性に有害で
あり、0.1重量％未満のときは、脱酸作用が十分
でない。 Mnは脱硫、脱酸作用のある元素であるが、１
重量％を越えるときは、フエライト系ステンレス
鋼の耐食性が低下する。Ｓは0.01重量％を越えるときは、フエライト系
ステンレス鋼の耐食性が低下する。 Crは耐食性を決定する中心元素であり、オー
ステナイト系ステンレス鋼と同等の耐食性を得る
ためには20重量％以上でなければならない。Cr
が25重量％超のときはCrの炭窒化物が粒界に生
成し、得られるフエライト系ステンレス鋼の製造
時の靭性が低下し、製造が困難となる。 Moが0.3重量％未満のときは、耐食性が劣化
し、1.0重量％を越えるときは、Moが高価なた
め、製造コストが高くなる。 Niが0.2重量％未満のときは、耐食性、靭性が
劣化し、1.5重量％を越えるときは、Niが高価な
ため、製造コストが高くなる。 Cuが0.04重量％未満のときは、大気中における
耐銹性が劣化し、0.5重量％を越えるときは、熱
間圧延時に表面割れが発生する。Ｎが0.03重量％以上のときは、Cr窒化物を生成
し、製造時に靭性が低下する。 0.015重量％未満のときは、製造コストが著し
く上昇する。 Nbは炭窒化物生成傾向が大きく、Crの炭窒化
物生成を抑制するために添加するが、Ｃ＋Ｎの総
量の８倍未満のときは、上記Crの炭窒化物生成
を抑制する効果が十分ではなく、Ｃ＋Ｎの総量の
20倍を越えるときは、上記Crの炭窒化物生成を
抑制する効果が飽和し、強度を著しく増大させ、
成形性をそこなう。 TiおよびZrはNbより炭窒化物生成傾向が大き
く、Crの炭窒化物生成を抑制する効果が大きな
元素である。Ti＋Zr／２の総量が0.02重量％未満
のときは、上記Crの炭窒化物生成の抑制効果が
十分でなく、0.1重量％を越えるときは、粗大な
TiおよびZrの窒化物を生成し、表面清浄を著し
く低下させる。 Ti＋Zr／２の総量が0.1重量％以下と制限され
るため、Crの炭窒化物の生成を抑制するには
Nb、およびTiおよび／またはZrの複合添加が不
可欠である。上記の組成のフエライト系ステンレス鋼を以下
の条件で製造し、成形性の優れた高耐食フエライ
ト系ステンレス鋼を得ることができる。上記組成のフエライト系ステンレス鋼をスラブ
となし、熱間圧延後350℃以下の低温巻取りを行
なう。巻取り温度を350℃以下とすることにより、Ｃ
およびＮを固溶状態に存在させ、Crの炭窒化物
の生成を抑制し、得られるフエライト系ステンレ
ス鋼の耐食性、製造時に必要な強靭性を低下させ
ない。その後、上記巻取りを行つた熱延鋼板を［800
＋1250×（Ti＋Zr／２）］±25℃の温度域で母板焼
鈍を行ない、成形性の優れた高耐食フエライト系
ステンレス鋼を製造することができる。第１ａ図にTi＋Zr／２の総量と最適焼鈍温度
の関係を示す。第２図に、表１に示すTi添加量の異なるNo.２，
３，９の化学組成のステンレス鋼についての焼鈍
温度と衝撃試験による吸収エネルギーとの関係を
示す。第２図からわかるように、衝撃試験での吸収エ
ネルギーの焼鈍温度依存性は、焼鈍温度が高すぎ
ても、低すぎても吸収エネルギーは低くなり、吸
収エネルギーの高い適度な温度域が存在する。こ
の適度な温度域の中心温度を最適焼鈍温度と言
う。吸収エネルギーの高い温度域は最適焼鈍温度
±25℃の領域である。最適焼鈍温度とTi＋Zr／２の総量は、第１ａ
図に示すように直線関係にあり、Ti＋Zr／２の
総量が増加すると最適焼鈍温度も上昇し、最適焼
鈍温度は 800＋1250（Ti＋Zr／２）で表わされる。フエライト系ステンレス鋼を上記最適焼鈍温度
±25℃で母材焼鈍することにより、製造時の強靭
性に悪影響をおよぼすCrの炭窒化物の形成を抑
制し、加工性の良好なオーステナイト系ステンレ
ス鋼と同等の耐食性を有するフエライト系ステン
レス鋼とすることができる。本発明により製造されたフエライト系ステンレ
ス鋼は酸洗後冷間圧延し、その後、焼鈍・酸洗
（あるいは光輝焼鈍）を行なうことにより、冷間
圧延鋼帯として使用される。〈実施例〉本発明を実施例を用いて具体的に説明する。（実施例） TiおよびZr量の異なる表１に示す組成の鋼を
真空溶解炉にて溶製し、厚さ180mmのスラブを製
造した。No.１〜No.８は本発明鋼であり、No.９〜No.
13は、Ti＋Zr／２の総量が0.02〜0.1重量％の範
囲からはずれている比較鋼である。No.14およびNo.
15はNb量が８（Ｃ＋Ｎ）〜20（Ｃ＋Ｎ）重量％の
範囲から外れている比較鋼である。上記スラブを1250℃に加熱し、圧延終了温度
850℃で板厚４mmまで熱間圧延し、表２に示す温
度で巻取つた。その後、上記熱延鋼板を［800＋1250×（Ti＋
Zr／２）］±25℃の温度域（表２に焼鈍温度を示
す）で母材焼鈍を行ない、母材焼鈍温度に２分間
保持した後、急冷した。得られた熱延鋼板に対して、２mmＶノツチ付シ
ヤルビー衝撃試験を行なつた。結果を表２に示し、また、本発明例No.１〜No.８
および比較例No.９〜No.13の結果を第１ｂ図に示
す。なお、本発明例No.１〜No.８は、それぞれ表１
に示す本発明鋼No.１〜No.８を本発明法に従つて製
造した結果を示し、比較例No.7′は、本発明鋼No.７
の巻取温度が350℃以下の範囲から外れている結
果を示し、比較例No.8′は、本発明鋼No.８の母材焼
鈍温度が［800＋1250×（Ti＋Zr／２）］±25℃の
範囲から外れている結果を示し、比較例No.９〜No.
15は、それぞれ表１に示す比較鋼No.９〜No.15を本
発明の限定範囲内の温度で巻取り、母材焼鈍した
結果を示すものである。得られた熱延鋼板を酸洗後、厚さ２mmに冷間圧
延し、その後、母材焼鈍と同一条件で焼鈍した。さらに、上記冷延鋼板を酸洗し、厚さ0.4mmに
冷間圧延し、950℃×２分間の大気焼鈍を行なつ
た後に、酸洗を行ない最終製品の冷延鋼板を得
た。得られた冷延鋼板に対して引張試験を行ない、
0.2％耐力、引張強さを測定した。結果を表２に示し、本発明No.１〜No.８および比
較例No.９〜No.13の結果を第３ｂ図および第３ｃ図
に示した。さらに、得られた冷延鋼板のランクフオード値
（ｒ値）を測定した。結果を表２に示し、また、本発明No.１〜No.８お
よび比較例No.９〜No.13の結果を第３ａ図に示し
た。本発明例においては、0.2％耐力が32〜34Kg
ｆ／mm²の範囲にあり、引張強さは48〜50Kgｆ／mm²
の範囲にあり、ｒ値は1.9〜2.1の範囲にあり、加
工性は良好であつた。比較鋼においては、Ti＋Zr／２の総量が0.02重
量％未満のときは0.2％耐力、引張強さは高く、
ｒ値は低く、加工性は劣化していた。Ti＋Zr／
２の総量が0.1重量％を超えるときは、加工性は
本発明例と同様であつたが、鋼中の介在物に起因
する表面清浄が劣化していた。また、Nbの量が
８（Ｃ＋Ｎ）重量％未満では、ｒ値は低く、20（Ｃ
＋Ｎ）重量％を超えるときは、0.2％耐力、引張
強さは高く、ｒ値は低く、加工性は劣化してい
た。さらに、比較例No.7′およびNo.8′のように巻取
温度が350℃より高いときおよび母材焼鈍温度が
本発明の限定範囲から外れているときは、0.2％
耐力、引張強さは高く、ｒ値は低く、加工性は劣
化していた。また、JIS G0577に従つて測定した孔食電位を
表２に示す。SUS304の孔食電位0.32（V_VSSCE）
に比べて本発明例はいづれも高い値を示してい
る。 <Industrial Application Field> The present invention relates to a method for manufacturing ferritic stainless steel used as automobile exterior parts or various decorative materials, and in particular, highly corrosion-resistant ferritic stainless steel with excellent formability and toughness during manufacturing. Relating to a manufacturing method. <Prior art and its problems> Ferritic stainless steel, represented by SUS430, is inexpensive and has excellent stress corrosion cracking resistance, but compared to austenitic stainless steel containing a large amount of nickel, it is less susceptible to aqueous solutions containing chloride ions. It is considerably inferior in general corrosion resistance, including rust resistance. In recent years, with the advancement of stainless steel melting technology,
As disclosed in JP-A No. 52-30715, it has become possible to produce high Cr ferritic stainless steel with extremely low C and N, and ferritic stainless steel with significantly improved corrosion resistance has been developed. . However, in high chromium ferritic steel, C and N form carbonitrides with Cr, resulting in a decrease in corrosion resistance and a decrease in toughness in hot-rolled annealed sheets, resulting in an increase in strength and an increase in r-value in the final product. causing a decline. Therefore, high chromium ferrite steel has C and N of 0.01
% or less, production costs rise and the price is set higher than that of austenitic stainless steel. It is desired to develop a high chromium ferritic stainless steel that has excellent corrosion resistance, toughness during manufacturing, and workability even when C and N are 0.01% or more. <Objective of the Invention> The object of the present invention is to solve the above-mentioned problems of the conventional technology, and to provide a method for producing ferritic stainless steel with excellent workability, toughness during production, and corrosion resistance. It is something to do. <Structure of the invention> The present invention comprises C: 0.015 to 0.03% by weight, Si: 0.1 to 1
Weight%, Mn: 1% by weight or less, S: 0.01% by weight or less, Cr: 20-25% by weight, Mo: 0.3-1.0% by weight,
Ni; 0.2-1.5% by weight, Cu; 0.04-0.5% by weight, N;
0.015-0.03% by weight, Nb; 8(C+N)-20(C+
N) wt%, Ti and/or Zr are (Ti+Zr/
Contains 0.02 to 0.1% by weight as the total amount of 2);
After hot rolling a ferritic stainless steel sheet, the remainder of which consists of iron and unavoidable impurities, it is wound at 350°C or less, and then [800+1250×(Ti+Zr/
2)] The present invention provides a method for producing highly corrosion-resistant ferritic stainless steel with excellent formability, which is characterized by annealing the mother plate in a temperature range of ±25°C. The present invention will be explained in more detail below. The composition of the ferritic stainless steel used in the present invention is: C: 0.015 to 0.03% by weight, Si: 0.1 to 1% by weight, Mn: 1% by weight or less, S: 0.01% by weight or less,
Cr; 20-25% by weight, Mo; 0.3-1.0% by weight, Ni;
0.2-1.5% by weight, Cu; 0.04-0.5% by weight, N;
0.015-0.03% by weight, Nb; 8(C+N)-20(C+
N) wt%, Ti and/or Zr are (Ti+Zr/
Contains 0.02 to 0.1% by weight as the total amount of 2);
The remainder is iron and unavoidable impurities. When C exceeds 0.03% by weight, chromium carbide is formed, which reduces the corrosion resistance of ferritic stainless steel.
Deteriorates toughness during manufacturing. C is 0.015% by weight
If it is less than 20%, it will be costly to melt it. When Si exceeds 1% by weight, it is harmful to moldability, and when it is less than 0.1% by weight, the deoxidizing effect is insufficient. Mn is an element that has desulfurization and deoxidizing effects, but 1
When the content exceeds % by weight, the corrosion resistance of the ferritic stainless steel decreases. When S exceeds 0.01% by weight, the corrosion resistance of the ferritic stainless steel decreases. Cr is a central element that determines corrosion resistance, and in order to obtain corrosion resistance equivalent to austenitic stainless steel, it must be at least 20% by weight. Cr
When the content exceeds 25% by weight, Cr carbonitrides are formed at grain boundaries, and the toughness of the resulting ferritic stainless steel during production decreases, making production difficult. When Mo is less than 0.3% by weight, corrosion resistance deteriorates, and when it exceeds 1.0% by weight, Mo is expensive and manufacturing costs increase. When Ni is less than 0.2% by weight, corrosion resistance and toughness deteriorate, and when it exceeds 1.5% by weight, Ni is expensive and manufacturing costs increase. When Cu is less than 0.04% by weight, rust resistance in the atmosphere deteriorates, and when it exceeds 0.5% by weight, surface cracks occur during hot rolling. When N is 0.03% by weight or more, Cr nitrides are produced and the toughness decreases during manufacturing. When it is less than 0.015% by weight, manufacturing costs increase significantly. Nb has a strong tendency to form carbonitrides, and is added to suppress the formation of carbonitrides in Cr. However, when the amount is less than 8 times the total amount of C+N, the effect of suppressing the formation of carbonitrides in Cr is not sufficient. of the total amount of C+N.
When it exceeds 20 times, the above-mentioned effect of suppressing carbonitride formation of Cr is saturated, and the strength increases significantly,
Detracts from moldability. Ti and Zr have a greater tendency to form carbonitrides than Nb, and are elements that have a greater effect of suppressing the formation of carbonitrides in Cr. When the total amount of Ti + Zr/2 is less than 0.02% by weight, the above-mentioned effect of suppressing the carbonitride formation of Cr is insufficient, and when it exceeds 0.1% by weight, coarse
Forms Ti and Zr nitrides, significantly reducing surface cleanliness. Since the total amount of Ti + Zr/2 is limited to 0.1% by weight or less, it is necessary to suppress the formation of Cr carbonitrides.
Combined addition of Nb and Ti and/or Zr is essential. A ferritic stainless steel having the above composition can be produced under the following conditions to obtain a highly corrosion-resistant ferritic stainless steel with excellent formability. The ferritic stainless steel having the above composition is made into a slab, and after hot rolling, it is rolled up at a low temperature of 350°C or less. By keeping the winding temperature below 350℃, C
and N in a solid solution state to suppress the formation of carbonitrides of Cr, and do not reduce the corrosion resistance of the resulting ferritic stainless steel and the toughness required during production. After that, the hot-rolled steel sheet that had been wound above was heated to [800
+1250×(Ti+Zr/2)] By annealing the mother plate in a temperature range of ±25°C, it is possible to produce highly corrosion-resistant ferritic stainless steel with excellent formability. Figure 1a shows the relationship between the total amount of Ti+Zr/2 and the optimum annealing temperature. Figure 2 shows No. 2 with different amounts of Ti added shown in Table 1,
The relationship between the annealing temperature and the energy absorbed by the impact test for stainless steels with chemical compositions No. 3 and 9 is shown. As can be seen from Figure 2, the dependence of the absorbed energy on the annealing temperature in the impact test shows that even if the annealing temperature is too high or too low, the absorbed energy decreases, and there is a moderate temperature range where the absorbed energy is high. . The center temperature of this moderate temperature range is called the optimum annealing temperature. The temperature range with high absorbed energy is the range of the optimum annealing temperature ±25°C. The optimum annealing temperature and total amount of Ti + Zr/2 are 1a
As shown in the figure, there is a linear relationship, and as the total amount of Ti + Zr/2 increases, the optimum annealing temperature also increases, and the optimum annealing temperature is expressed as 800 + 1250 (Ti + Zr / 2). By annealing the base material of ferritic stainless steel at the above optimum annealing temperature of ±25°C, the formation of Cr carbonitrides that adversely affect the toughness during manufacturing is suppressed, and it is made into an austenitic stainless steel with good workability. Ferritic stainless steel having equivalent corrosion resistance can be used. The ferritic stainless steel produced according to the present invention is pickled, cold rolled, and then annealed and pickled (or bright annealed) to be used as a cold rolled steel strip. <Examples> The present invention will be specifically described using examples. (Example) Steels having compositions shown in Table 1 with different amounts of Ti and Zr were melted in a vacuum melting furnace to produce slabs with a thickness of 180 mm. No. 1 to No. 8 are steels of the present invention, and No. 9 to No. 8 are steels of the present invention.
No. 13 is a comparative steel in which the total amount of Ti+Zr/2 is outside the range of 0.02 to 0.1% by weight. No.14 and No.
Steel No. 15 is a comparative steel in which the amount of Nb is outside the range of 8 (C+N) to 20 (C+N) weight %. The above slab is heated to 1250℃, and the rolling end temperature is
It was hot-rolled at 850°C to a thickness of 4 mm and wound at the temperatures shown in Table 2. After that, the above hot-rolled steel plate was
Zr/2)] The base metal was annealed in a temperature range of ±25°C (annealing temperatures are shown in Table 2), and after being maintained at the base metal annealing temperature for 2 minutes, it was rapidly cooled. The obtained hot rolled steel sheet was subjected to a 2 mm V-notched sialby impact test. The results are shown in Table 2, and invention examples No. 1 to No. 8
The results of Comparative Examples No. 9 to No. 13 are shown in FIG. 1b. In addition, examples No. 1 to No. 8 of the present invention are shown in Table 1, respectively.
Comparative Example No. 7' shows the results of manufacturing inventive steels No. 1 to No. 8 according to the inventive method, and Comparative Example No. 7'
Comparative Example No. 8' shows that the coiling temperature of Inventive Steel No. 8 is outside the range of 350°C or lower, and the base material annealing temperature of Invention Steel No. 8 is [800+1250×(Ti+Zr/2)] ±25°C. Comparative Examples No. 9 to No.
No. 15 shows the results of comparative steels No. 9 to No. 15 shown in Table 1, respectively, wound at a temperature within the limited range of the present invention and base metal annealed. The obtained hot rolled steel sheet was pickled, cold rolled to a thickness of 2 mm, and then annealed under the same conditions as the base material annealing. Further, the cold-rolled steel sheet was pickled, cold-rolled to a thickness of 0.4 mm, annealed in the atmosphere at 950° C. for 2 minutes, and then pickled to obtain a final cold-rolled steel sheet. A tensile test was conducted on the obtained cold rolled steel sheet,
0.2% proof stress and tensile strength were measured. The results are shown in Table 2, and the results for Invention Nos. 1 to 8 and Comparative Examples No. 9 to No. 13 are shown in Figures 3b and 3c. Furthermore, the Rankford value (r value) of the obtained cold rolled steel sheet was measured. The results are shown in Table 2, and the results of Invention Nos. 1 to 8 and Comparative Examples Nos. 9 to 13 are shown in FIG. 3a. In the example of the present invention, the 0.2% yield strength is 32 to 34 kg
f/ ^mm2 , tensile strength is 48~50Kgf/ ^mm2
The r value was in the range of 1.9 to 2.1, and the processability was good. In comparison steel, when the total amount of Ti + Zr / 2 is less than 0.02% by weight, the yield strength is 0.2%, the tensile strength is high,
The r value was low and the workability was degraded. Ti＋Zr／
When the total amount of 2 exceeds 0.1% by weight, the workability was similar to the example of the present invention, but the surface cleanliness due to inclusions in the steel was deteriorated. Furthermore, when the amount of Nb is less than 8 (C+N) weight%, the r value is low and 20 (C
+N) wt%, 0.2% proof stress and tensile strength were high, r value was low, and workability was deteriorated. Furthermore, when the coiling temperature is higher than 350°C or when the base material annealing temperature is outside the limited range of the present invention, as in Comparative Examples No. 7' and No. 8', 0.2%
The proof stress and tensile strength were high, the r value was low, and the workability was deteriorated. In addition, Table 2 shows the pitting corrosion potential measured according to JIS G0577. Pitting potential of SUS304 0.32 (V _VS SCE)
All of the examples of the present invention show higher values than .

【表】 (注) ＊は本発明の限定範囲から外れていることを示
す。
[Table] (Note) * indicates outside the limited range of the present invention.

【表】じである。＊は本発明の限定範囲から外れているこ
とを示す。
〈発明の効果〉本発明の方法によれば、Crより炭窒化物の生
成傾向の大きなNbおよびTiおよび／またはZrを
適量含有させた高Crフエライト系ステンレス鋼
を熱間圧延後低温捲取りし、その後適当な温度で
母材焼鈍をすることにより、NbおよびTiおよ
び／またはZrが炭窒化物を生成し、Crの炭窒化
物の生成を抑制することにより、オーステナイト
系ステンレス鋼程度の耐食性を有し、製造時の強
靭性に優れた、加工性の良好なフエライト系ステ
ンレス鋼を得ることができる。[Table] Same. * indicates outside the limited range of the present invention.
<Effects of the Invention> According to the method of the present invention, high Cr ferritic stainless steel containing an appropriate amount of Nb, Ti and/or Zr, which has a greater tendency to form carbonitrides than Cr, is hot rolled and then cold rolled. Then, by annealing the base material at an appropriate temperature, Nb, Ti, and/or Zr form carbonitrides, and by suppressing the formation of carbonitrides of Cr, the corrosion resistance is comparable to that of austenitic stainless steel. It is possible to obtain a ferritic stainless steel having excellent toughness during production and good workability.

[Brief explanation of the drawing]

第１ａ図はTi＋Zr／２の総量と最適焼鈍温度
の関係を示す図である。第１ｂ図は母材焼鈍を行
なつた熱延鋼板のTi＋Zr／２の総量と吸収エネ
ルギーの関係を示す図である。第２図は母材焼鈍
温度と母材焼鈍を行なつた熱延鋼板の吸収エネル
ギーの関係を示す図である。第３ａ図は実施例で
得られた冷延鋼板のTi＋Zr／２の総量とランク
フオード値（ｒ値）の関係を示す図である。第３
ｂ図は実施例で得られた冷延鋼板のTi＋Zr／２
の総量と引張強さの関係を示す図である。第３ｃ
図は実施例で得られた冷延鋼板のTi＋Zr／２の
総量と0.2％耐力の関係を示す図である。 FIG. 1a is a diagram showing the relationship between the total amount of Ti+Zr/2 and the optimum annealing temperature. FIG. 1b is a diagram showing the relationship between the total amount of Ti+Zr/2 and absorbed energy in a hot rolled steel sheet subjected to base metal annealing. FIG. 2 is a diagram showing the relationship between base metal annealing temperature and absorbed energy of a hot rolled steel sheet that has undergone base metal annealing. FIG. 3a is a diagram showing the relationship between the total amount of Ti+Zr/2 and the Rankford value (r value) of the cold rolled steel sheets obtained in the examples. Third
Figure b shows Ti+Zr/2 of the cold-rolled steel sheet obtained in the example.
It is a figure showing the relationship between the total amount of and tensile strength. 3rd c
The figure shows the relationship between the total amount of Ti+Zr/2 and 0.2% yield strength of the cold rolled steel sheets obtained in the examples.

Claims

[Claims]

1 C; 0.015 to 0.03% by weight, Si; 0.1 to 1% by weight,
Mn; 1% by weight or less, S; 0.01% by weight or less, Cr;
20~25% by weight, Mo; 0.3~1.0% by weight, Ni; 0.2~
1.5% by weight, Cu; 0.04~0.5% by weight, N; 0.015~
0.03% by weight, Nb; 8(C+N) to 20(C+N)% by weight, Ti and/or Zr as the total amount of (Ti+Zr/2); 0.02 to 0.1% by weight, the remainder from iron and unavoidable impurities. After hot rolling a ferritic stainless steel plate, it is wound at 350℃ or less, and then [800+1250×(Ti+Zr/2)]±25
A method for manufacturing highly corrosion-resistant ferritic stainless steel with excellent formability, which is characterized by annealing the base plate in a temperature range of ℃.