JP3923485B2 - Manufacturing method of ferritic single-phase stainless steel with excellent deep drawability - Google Patents
Manufacturing method of ferritic single-phase stainless steel with excellent deep drawability Download PDFInfo
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Description
本発明は、高度の深絞り加工を施しても加工割れの発生が少ないフェライト単相系ステンレス鋼を製造する方法に関する。 The present invention relates to a method for producing a ferritic single-phase stainless steel that is less prone to processing cracks even after high-level deep drawing.
SUS430，SUS430LXに代表されるフェライト系ステンレス鋼は、耐食性に優れ、高価なＮｉを含まないので安価な耐食性材料として種々の用途に使用されている。しかし、体心立方格子の結晶構造をもち、面心立方格子のオーステナイト系ステンレス鋼に比較して加工性に劣る。厨房機器，家具調度品，各種内装材等の用途では、過酷な深絞り加工で製品形状に成形されることが多く、これらの用途にフェライト系ステンレス鋼を使用する上では延性，深絞り性の改善が必要である。 Ferritic stainless steel represented by SUS430 and SUS430LX is excellent in corrosion resistance and does not contain expensive Ni, so it is used in various applications as an inexpensive corrosion resistant material. However, it has a body-centered cubic lattice crystal structure and is inferior in workability as compared to a face-centered cubic lattice austenitic stainless steel. In applications such as kitchen equipment, furniture, and various interior materials, it is often formed into product shapes by severe deep drawing, and when using ferritic stainless steel for these applications, ductility and deep drawability Improvement is needed.
フェライト系ステンレス鋼板の深絞り性改善に関し、従来から種々の研究結果が報告されている。代表的な手法では、Ｔｉ，Ｎｂの複合添加で固溶Ｃ，Ｎを析出物として固定し、マトリックスのＣ，Ｎ濃度を低減している。たとえば、特許文献１では、Ｔｉ，Ｎｂの複合添加に熱延条件の制御を組み合わせて深絞り性の評価指標であるランクフォード値を向上させている。また、特許文献２では、熱延板をバッチ焼鈍した後、冷間圧延，焼鈍をそれぞれ２回施すことにより深絞り性を改善している。
製品形状の複雑化に伴い、現行のＴｉ，Ｎｂを単独又は複合添加したフェライト単相系ステンレス鋼では深絞り性が不十分であり、更なる改善が求められている。
バッチ焼鈍した熱延板を２回冷延・２回焼鈍する方法では、Ｔｉ，Ｎｂ等の添加を要しないため鋼材コストの上昇を招くことなく深絞り性等の加工性が改善されるものの、高度の深絞り加工では依然として割れ，波打ち等の加工欠陥が散見される。しかも、冷間圧延に先立つ熱延板焼鈍に生産性の低いバッチ焼鈍を採用しているため、生産性に劣る。
As the product shape becomes more complex, the ferrite single-phase stainless steel to which current Ti and Nb are added alone or in combination has insufficient deep drawability, and further improvement is required.
In the method of cold-rolling and twice-annealing hot-rolled sheets that have been batch-annealed, workability such as deep drawability is improved without incurring an increase in steel material costs because it does not require the addition of Ti, Nb, etc. Processing defects such as cracks and waviness are still found in advanced deep drawing. And since batch annealing with low productivity is employ | adopted for the hot-rolled sheet annealing prior to cold rolling, it is inferior to productivity.
本発明は、このような問題を解消すべく案出されたものであり、Ｎｂ系析出物のピンニング作用を利用して再結晶粒の微細化を促進させ、熱延板焼鈍に生産性の高い連続焼鈍の適用を可能とし、しかも深絞り加工性の異方性を改善したフェライト単相系ステンレス鋼を提供することを目的とする。 The present invention has been devised to solve such problems, and promotes refinement of recrystallized grains by utilizing the pinning action of Nb-based precipitates, and is highly productive in hot-rolled sheet annealing. An object of the present invention is to provide a ferritic single-phase stainless steel that can be continuously annealed and has improved deep drawing workability anisotropy.
本発明の製造方法は、Ｃ：０.０１５質量％以下，Ｓｉ：０.８質量％以下，Ｍｎ：１.５質量％以下，Ｃｒ：１１〜２３質量％，Ｎ：０.０２質量％以下，Ｎｂ：０.１〜０.５質量％を含み、更に必要に応じてＴｉ：０.３５質量％以下，Ｍｏ：３.０質量％以下，Ｂ：０.０１質量％以下の１種又は２種以上を含み、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のスラブを使用する。スラブを常法に従って鍛造，熱間圧延した後、７００〜９００℃の温度域で均熱する連続焼鈍でＮｂ系析出物を析出させる。 The production method of the present invention is as follows: C: 0.015 mass% or less, Si: 0.8 mass% or less, Mn: 1.5 mass% or less, Cr: 11-23 mass%, N: 0.02 mass% or less , Nb: 0.1 to 0.5% by mass, and if necessary, Ti: 0.35% by mass or less, Mo: 3.0% by mass or less, B: 0.01% by mass or less, or A ferritic stainless steel slab containing at least two types and the balance being Fe and inevitable impurities is used. The slab is forged and hot-rolled according to a conventional method, and then Nb-based precipitates are deposited by continuous annealing soaking in a temperature range of 700 to 900 ° C.
熱延焼鈍板は、中間圧延→中間焼鈍→仕上げ圧延→仕上げ焼鈍の２回冷延・２回焼鈍で製品鋼板に製造される。中間焼鈍では、(再結晶完了温度)〜(再結晶完了温度＋５０℃)の温度域にステンレス鋼帯を加熱することにより、平均結晶粒径３０μｍ以下，各結晶粒の平均アスペクト比１.５以下の再結晶組織に調質する。中間焼鈍時に残存した結晶粒及び析出物を圧下率５０％以上の仕上げ圧延で微細化した後、仕上げ焼鈍する。 A hot-rolled annealed sheet is produced into a product steel sheet by two cold rolling and two annealing steps of intermediate rolling → intermediate annealing → finish rolling → finish annealing. In the intermediate annealing, the stainless steel strip is heated to a temperature range of (recrystallization completion temperature) to (recrystallization completion temperature + 50 ° C.), so that the average crystal grain size is 30 μm or less and the average aspect ratio of each crystal grain is 1.5 or less. Temper to a recrystallized structure. The crystal grains and precipitates remaining during the intermediate annealing are refined by finish rolling with a reduction rate of 50% or more, and then finish annealing.
本発明では、図１のヒートパターンに示すように連続焼鈍された熱延板を２回冷延・２回焼鈍している。
熱延板焼鈍では、Ｎｂ系析出物を生成させるため７００〜９００℃の温度域に熱延板を均熱するが、熱延板のＣ，Ｎ，Ｎｂ含有量それぞれをＣ：０.０１５質量％以下，Ｎ：０.０２質量％以下，Ｎｂ：０.１〜０.５質量％の範囲に調整しているので１分以内の短時間加熱でも後工程の中間焼鈍工程で必要なピンニング作用を呈するＮｂ系析出物が生成する。Ｎｂ系析出物は、ＮｂＣ，ＮｂＮ等であり、Ｎｂ，Ｔｉを複合添加した鋼種ではＮｂ，Ｔｉの複合した析出物も生成する。なお、熱延板焼鈍時に一部のＮｂ系析出物が再固溶する。Ｎｂ系析出物を十分生成させる上で７００℃以上の均熱温度が必要であるが、９００℃を超える均熱温度では結晶粒が粗大に成長する。
In this invention, as shown in the heat pattern of FIG. 1, the hot-rolled sheet continuously annealed is cold-rolled twice and annealed twice.
In hot-rolled sheet annealing, the hot-rolled sheet is soaked in a temperature range of 700 to 900 ° C. in order to generate Nb-based precipitates, but the C, N, and Nb contents of the hot-rolled sheet are each C: 0.015 mass. % Or less, N: 0.02 mass% or less, Nb: 0.1 to 0.5 mass%, so the pinning action required in the intermediate annealing process of the subsequent process is possible even for short heating within 1 minute Nb-based precipitates exhibiting Nb-based precipitates are NbC, NbN, and the like. In a steel type in which Nb and Ti are added in combination, Nb and Ti composite precipitates are also generated. In addition, a part of Nb-based precipitate is re-dissolved during hot-rolled sheet annealing. A soaking temperature of 700 ° C. or higher is necessary to sufficiently generate Nb-based precipitates, but crystal grains grow coarsely at a soaking temperature exceeding 900 ° C.
Ｎｂ系析出物が析出した熱延板に中間圧延，中間焼鈍を施すと、圧延時の歪み蓄積にＮｂ系析出物のピンニング作用が重畳し、中間焼鈍終了時点で平均粒径：３０μｍ以下，平均アスペクト比：１.５以下の微細な再結晶粒が生成する。圧延率が小さすぎると歪み蓄積が不足し、中間焼鈍によって微細な再結晶粒が得られないため、３０％以上の圧延率で中間圧延することが好ましい。中間焼鈍の温度域は、再結晶を進行させるため再結晶完了温度以上に設定されるが、高すぎる加熱温度では生成した再結晶粒の成長が加速されるため、中間焼鈍の均熱温度を(再結晶完了温度＋５０℃)以下に規制する。 When intermediate rolling and intermediate annealing are performed on a hot-rolled sheet on which Nb-based precipitates are deposited, the pinning action of the Nb-based precipitates is superimposed on the strain accumulation during rolling, and the average particle size is 30 μm or less at the end of the intermediate annealing. Fine recrystallized grains having an aspect ratio of 1.5 or less are generated. If the rolling rate is too small, strain accumulation is insufficient, and fine recrystallized grains cannot be obtained by intermediate annealing. Therefore, it is preferable to perform intermediate rolling at a rolling rate of 30% or more. The temperature range of the intermediate annealing is set to be higher than the recrystallization completion temperature in order to advance the recrystallization, but if the heating temperature is too high, the growth of the recrystallized grains generated is accelerated. Recrystallization completion temperature + 50 ° C) or less.
中間焼鈍終了時点の再結晶粒が微細であると、再結晶粒の粒界三重点が仕上げ圧延時に不均一変形領域となって{１１１}面の再結晶サイトとなりやすく、後続する仕上げ圧延，仕上げ焼鈍を経て{１１１}面の占有率が高く深絞り性に優れた再結晶組織が得られる。中間焼鈍終了時点における再結晶粒の微細化は、予めＮｂ系析出物を析出させる熱延板焼鈍によって達成される。微細化による作用を効果的に発現させる上で、中間焼鈍終了時点における再結晶粒の平均結晶粒径を３０μｍ以下に規制している。また、中間焼鈍終了時点における再結晶粒のアスペクト比が大きすぎると耐リジング性や異方性が悪化するので、平均アスペクト比を１.５以下に規制している。 If the recrystallized grains at the end of the intermediate annealing are fine, the grain boundary triple points of the recrystallized grains become non-uniformly deformed regions during finish rolling, and tend to become recrystallized sites on the {111} plane, followed by finish rolling and finishing. Through annealing, a recrystallized structure with a high {111} plane occupancy and excellent deep drawability can be obtained. The refinement of recrystallized grains at the end of the intermediate annealing is achieved by hot-rolled sheet annealing in which Nb-based precipitates are preliminarily deposited. In order to effectively express the effect of miniaturization, the average crystal grain size of the recrystallized grains at the end of the intermediate annealing is regulated to 30 μm or less. In addition, when the aspect ratio of the recrystallized grains at the end of the intermediate annealing is too large, ridging resistance and anisotropy deteriorate, so the average aspect ratio is regulated to 1.5 or less.
平均結晶粒径：３０μｍ以下，平均アスペクト比：１.５以下に調質されたステンレス鋼帯は、５０％以上の冷延率で製品板厚まで仕上げ圧延される。仕上げ圧延中に粒界三重点が不均一変形領域となる。熱延板焼鈍で析出したＮｂ系析出物も、中間焼鈍時に一部固溶するが、残存した析出物周囲が不均一変形領域になる。不均一変形領域は、仕上げ焼鈍時に{１１１}面の優先的な再結晶サイトになると推察される。仕上げ圧延は、{１１１}面の優先的な再結晶サイトとなる不均一変形領域を発達させるため５０％以上の圧延率が必要である。圧延率の上限は特に規制されるものではなく、圧延機の能力に応じて適宜定められる。 A stainless steel strip tempered to have an average grain size of 30 μm or less and an average aspect ratio of 1.5 or less is finish-rolled to a product thickness at a cold rolling rate of 50% or more. The grain boundary triple point becomes a non-uniform deformation region during finish rolling. Nb-based precipitates precipitated by hot-rolled sheet annealing also partially dissolve at the time of intermediate annealing, but the periphery of the remaining precipitates becomes a nonuniform deformation region. It is inferred that the non-uniform deformation region becomes a preferential recrystallization site of the {111} plane during finish annealing. The finish rolling requires a rolling rate of 50% or more in order to develop a non-uniform deformation region that becomes a preferential recrystallization site of the {111} plane. The upper limit of the rolling rate is not particularly limited, and is appropriately determined according to the capability of the rolling mill.
仕上げ圧延されたステンレス鋼帯は、次いで仕上げ焼鈍される。仕上げ圧延時に導入された歪みが仕上げ焼鈍で解放され、深絞り性に優れたステンレス鋼帯が得られる。常法に従った仕上げ焼鈍条件を採用できるが、歪みを十分に解放し軟質化を図る上で再結晶を十分に進行させ、また深絞り加工後の肌荒れを防ぐために結晶粒の粗大化を防止することが好ましい。 The finish-rolled stainless steel strip is then finish annealed. The strain introduced during finish rolling is released by finish annealing, and a stainless steel strip excellent in deep drawability is obtained. Finish annealing conditions in accordance with the usual method can be adopted, but recrystallization is sufficiently advanced to sufficiently release strain and soften, and also prevent coarsening of grains to prevent rough skin after deep drawing. It is preferable to do.
このように、熱延板焼鈍時にＮｂ系析出物をマトリックスに分散析出させ、中間圧延，中間焼鈍を施し、Ｎｂ系析出物のピンニング作用を利用して中間焼鈍終了時点で微細でアスペクト比の小さな金属組織に調整すると、仕上げ圧延時に粒界三重点やＮｂ系析出物の周辺に不均一変形領域が形成され、仕上げ焼鈍時に{１１１}面の占有率が高く深絞り性に優れた再結晶組織が得られる。加工性に及ぼすＮｂの影響は０.１質量％以上のＮｂ添加でみられるが、０.５質量％を超える過剰添加は過剰量のＮｂ系析出物を析出させ、材料の硬質化，再結晶温度の上昇をもたらすので好ましくない。 In this way, Nb-based precipitates are dispersed and precipitated in the matrix during hot-rolled sheet annealing, subjected to intermediate rolling and intermediate annealing, and are fine and have a small aspect ratio at the end of intermediate annealing using the pinning action of the Nb-based precipitates. When adjusted to a metal structure, non-uniform deformation regions are formed around grain boundary triple points and Nb-based precipitates during finish rolling, and a recrystallized structure with a high {111} face occupancy and excellent deep drawability during finish annealing. Is obtained. The effect of Nb on workability is observed when Nb is added in an amount of 0.1% by mass or more. However, excessive addition exceeding 0.5% by mass causes an excessive amount of Nb-based precipitates to be precipitated, hardening the material, and recrystallization. This is not preferable because it causes an increase in temperature.
本発明で使用するフェライト系ステンレス鋼は、{１１１}面の高い再結晶組織を得る上でＮｂ：０.１〜０.５質量％を必須とするが、Ｎｂの外にもＣｒ，Ｃ，ＮをそれぞれＣｒ：１１〜２３質量％，Ｃ：０.０１５質量％以下，Ｎ：０.０２質量％以下に規制している。Ｃｒは、ステンレス鋼としての耐食性に必要な合金成分であり、１１質量％以上の含有量で耐食性改善効果がみられるが、Ｃｒ含有量が多くなるに応じて加工性が低下するので上限を２３質量％に規制した。Ｃ，Ｎは、冷延板焼鈍後の強度を高める成分であり、過剰に含まれるとステンレス鋼帯の延性を低下させるので、上限をそれぞれＣ：０.０１５質量％，Ｎ：０.０２質量％に規制した。 The ferritic stainless steel used in the present invention requires Nb: 0.1 to 0.5% by mass in order to obtain a recrystallized structure with a high {111} plane, but besides Nb, Cr, C, N is restricted to Cr: 11 to 23 mass%, C: 0.015 mass% or less, and N: 0.02 mass% or less, respectively. Cr is an alloy component necessary for corrosion resistance as stainless steel, and an effect of improving corrosion resistance is seen at a content of 11% by mass or more. However, as the Cr content increases, the workability decreases, so the upper limit is 23. Restricted to mass%. C and N are components that increase the strength after cold-rolled sheet annealing, and if included excessively, the ductility of the stainless steel strip is lowered, so the upper limits are C: 0.015% by mass and N: 0.02%, respectively. % Regulated.
他の合金成分として、Ｔｉ，Ｍｏ，Ｂを必要に応じて添加しても良い。Ｔｉは、Ｃ，Ｎを固定し加工性，耐食性を向上させる合金成分であるが、０.３５質量％を超える過剰量のＴｉを添加するとＴｉ系介在物起因の表面欠陥が発生しやすくなる。Ｍｏは、耐食性の改善に有効な合金成分であるが、３.０質量％以下を超える過剰添加は熱間加工性を低下させる。Ｂは、Ｎの固定，耐食性，加工性の改善に有効な成分であるが、０.０１質量％を超える過剰添加は熱間加工性，溶接性等に悪影響を及ぼす。 Ti, Mo, and B may be added as necessary as other alloy components. Ti is an alloy component that fixes C and N and improves workability and corrosion resistance. However, when an excessive amount of Ti exceeding 0.35% by mass is added, surface defects due to Ti inclusions are likely to occur. Mo is an alloy component effective for improving the corrosion resistance, but excessive addition exceeding 3.0% by mass lowers hot workability. B is an effective component for fixing N, improving corrosion resistance, and workability. However, excessive addition exceeding 0.01 mass% adversely affects hot workability, weldability, and the like.
フェライト系ステンレス鋼に通常含まれる成分のうち、脱酸剤として添加されるＳｉは材質硬化，延性低下を来さないように０.８質量％（好ましくは０.５質量％）に上限を規制することが好ましい。Ｍｎは、ヒューム発生等の製造上の問題から１.５質量％以下に規制することが好ましい。偏析によって結晶粒界を脆化させる有害不純物であるＳは、上限を０.０１質量％に規制することで悪影響が抑えられる。 Of the components normally contained in ferritic stainless steel, the upper limit of Si added as a deoxidizer is restricted to 0.8 mass% (preferably 0.5 mass%) so as not to cause material hardening and ductility deterioration. It is preferable to do. Mn is preferably regulated to 1.5% by mass or less because of manufacturing problems such as generation of fume. The adverse effect of S, which is a harmful impurity that embrittles the grain boundaries by segregation, can be suppressed by limiting the upper limit to 0.01% by mass.
表１の組成をもつステンレス鋼を溶製し、連鋳，鍛造，熱延を経て板厚４.５ｍｍの熱延板を製造した。表中、Ａ１〜Ａ１０が０.１〜０.５質量％の範囲でＮｂを添加した基本系のステンレス鋼であり、Ｂ１〜５が更にＴｉ，Ｍｏ，Ｂ等を添加したステンレス鋼である。比較のため、Ｎｂ含有量が不足する鋼Ａ11，過剰量のＮｂを含む鋼Ａ12，SUS430に相当する鋼Ｃ１からも同様に板厚４.５ｍｍの熱延板を製造した。 Stainless steel having the composition shown in Table 1 was melted, and a hot rolled sheet having a thickness of 4.5 mm was manufactured through continuous casting, forging, and hot rolling. In the table, A1 to A10 are basic stainless steels to which Nb is added in the range of 0.1 to 0.5% by mass, and B1 to 5 are stainless steels to which Ti, Mo, B, etc. are further added. For comparison, a hot-rolled sheet having a thickness of 4.5 mm was similarly produced from steel A11 having a short Nb content, steel A12 containing excessive Nb, and steel C1 corresponding to SUS430.
各熱延鋼帯を８００℃×均熱５０秒で連続焼鈍した後、室温まで冷却した熱延焼鈍板の金属組織を調査したところ、０.１〜０.５質量％の範囲でＮｂを含むＡ１〜Ａ４，Ｂ１〜Ｂ５では、Ｎｂラーベス相、ＮｂＮ等のＮｂ系析出物が検出された。Ｎｂ含有量が不足するＡ11ではＮｂ系析出物の生成が極僅かに留まり、過剰量のＮｂを含むＡ12では過剰量のＮｂ系析出物が分散していた。Ｎｂを含まないＣ１には、Ｎｂ系析出物に相当する析出物が検出されなかった。 Each hot-rolled steel strip was subjected to continuous annealing at 800 ° C. × soaking for 50 seconds, and then the metal structure of the hot-rolled annealed plate cooled to room temperature was examined. Nb was included in the range of 0.1 to 0.5 mass%. In A1 to A4 and B1 to B5, Nb-based precipitates such as Nb Laves phase and NbN were detected. In A11 where the Nb content is insufficient, the formation of Nb-based precipitates remained very little, and in A12 containing an excessive amount of Nb, an excessive amount of Nb-based precipitates was dispersed. No precipitate corresponding to the Nb-based precipitate was detected in C1 containing no Nb.
熱延焼鈍板を圧下率４０％で板厚２.０ｍｍまで中間圧延し、次いで（各鋼種の再結晶完了温度＋１０℃）×均熱５０秒の中間焼鈍を施し、圧下率６５％で板厚０.９５ｍｍに仕上げ圧延し、仕上げ焼鈍として１１００℃に均熱５０秒加熱した。ただし、鋼種Ａ12は１０５０℃×均熱５０秒，鋼種Ｃ１は８００℃×均熱５０秒でそれぞれ加熱した。
この過程で、中間焼鈍が終了したステンレス鋼帯をサンプリングし、再結晶粒の平均結晶粒径及び平均アスペクト比を求めた。平均結晶粒径は圧延方向に平行な板厚断面について切断法で測定し、任意に選択した５０個の結晶粒の圧延方向長さと板厚方向の長さの比を算出することにより平均アスペクト比を求めた。
The hot-rolled annealed sheet is intermediate-rolled to a sheet thickness of 2.0 mm at a rolling reduction of 40%, then subjected to intermediate annealing (recrystallization completion temperature of each steel type + 10 ° C.) × soaking for 50 seconds, and the sheet thickness is reduced to 65%. It was finish-rolled to 0.95 mm and heated to 1100 ° C. for 50 seconds soaking as finish annealing. Steel type A12 was heated at 1050 ° C. × soaking for 50 seconds, and steel type C1 was heated at 800 ° C. × soaking for 50 seconds.
In this process, the stainless steel strip after the intermediate annealing was sampled, and the average crystal grain size and average aspect ratio of the recrystallized grains were obtained. The average crystal grain size is measured by a cutting method on a plate thickness section parallel to the rolling direction, and the average aspect ratio is calculated by calculating the ratio of the length in the rolling direction to the length in the plate thickness direction of 50 arbitrarily selected crystal grains. Asked.
表２の調査結果にみられるように、Ｎｂ含有量を０.１〜０.５質量％の範囲に規制した鋼Ａ１〜Ａ４，Ｂ１〜Ｂ５，過剰量のＮｂを含むＡ12は、再結晶粒が平均結晶粒径：３０μｍ以下と細粒化しており、圧延集合組織が解消された平均アスペクト比：１.５以下の再結晶組織となっていた。Ｎｂが不足する鋼Ａ11では、平均結晶粒径が約６０μｍと大きく、混粒を呈しており、平均アスペクト比も２.０を超え圧延方向に伸びた再結晶粒が検出された。この対比から、０.１〜０.５質量％の範囲でＮｂ添加した鋼種では、Ｎｂ系析出物のピンニング作用により再結晶粒が細粒化されることが確認された。 As can be seen from the results of the investigation in Table 2, the steels A1 to A4, B1 to B5, and A12 containing an excessive amount of Nb whose Nb content is regulated within the range of 0.1 to 0.5% by mass are recrystallized grains. However, the average crystal grain size was reduced to 30 μm or less, and the recrystallized structure had an average aspect ratio of 1.5 or less, which eliminates the rolling texture. Steel A11 lacking Nb had a large average crystal grain size of about 60 μm, mixed grains, and recrystallized grains having an average aspect ratio exceeding 2.0 and extending in the rolling direction were detected. From this comparison, it was confirmed that the recrystallized grains were refined by the pinning action of the Nb-based precipitates in the steel type added with Nb in the range of 0.1 to 0.5 mass%.
更に、仕上げ焼鈍後のステンレス鋼板についてランクフォード値を測定し、ｒ-〔=(ｒL＋２ｒD＋ｒT)／４〕及びΔｒ〔=(ｒL−２ｒD＋ｒT)／２〕を求めた。ただし、ｒL，ｒD，ｒTは、それぞれ圧延方向，圧延方向に対して４５度方向，圧延方向に直交する方向のｒ値を示す。ｒ値の測定結果を示す表３にみられるように、Ｎｂ含有量を０.１〜０.５質量%の範囲に規制した鋼Ａ１〜Ａ４，Ｂ１〜Ｂ５は、ｒ-が２.０以上でΔｒも０.５以下になっており、優れた深絞り性を有していた。一方、Ｎｂが不足する鋼Ａ11、過剰にＮｂを含む鋼Ａ12，SUS430に相当する鋼Ｃ１では、ｒ-が１.５以下の低い値であった。 Further, the Rankford value was measured for the stainless steel plate after the finish annealing, and r-[= (r L + 2r D + r T ) / 4] and Δr [= (r L −2r D + r T ) / 2] were obtained. . However, r L , r D , and r T indicate the r value in the rolling direction, the 45 ° direction with respect to the rolling direction, and the direction perpendicular to the rolling direction, respectively. As can be seen in Table 3 showing the measurement results of the r value, the steels A1 to A4 and B1 to B5 in which the Nb content is regulated to a range of 0.1 to 0.5 mass% have an r- of 2.0 or more. Δr was 0.5 or less, and the film had excellent deep drawability. On the other hand, in steel A11 in which Nb is insufficient, steel A12 in which Nb is excessively contained, and steel C1 corresponding to SUS430, r − was a low value of 1.5 or less.
ｒ値は、中間焼鈍時の結晶粒径，平均アスペクト比の低下に応じて高くなっており、仕上げ圧延時の歪導入によって不均一変形した粒界三重点及びＮｂ系析出物が{１１１}面の再結晶サイトとして働き、{１１１}面の占有率が上がったため向上したと考えられる。
Ｎｂが不足する鋼Ａ11では、中間焼鈍時の結晶粒が粗大で圧延方向に伸びており、Ｎｂ系析出物のピンニング作用が発現しなかったと考えられる。逆に、過剰量のＮｂを含む鋼Ａ12では、中間焼鈍後に粒径が小さく平均アスペクト比も１に近い組織になっているが、仕上げ焼鈍の際に過剰量の析出物が生成するため再結晶が阻害され、{１１１}面の占有率が減少しており、結果としてｒ値の低下になっていると考えられる。
The r value increases as the crystal grain size and average aspect ratio decrease during intermediate annealing, and the grain boundary triple points and Nb-based precipitates deformed non-uniformly by the introduction of strain during finish rolling are {111} planes. It is thought that it improved because the occupancy of the {111} plane increased.
In steel A11 in which Nb is insufficient, the crystal grains during intermediate annealing are coarse and extend in the rolling direction, and it is considered that the pinning action of Nb-based precipitates did not appear. On the contrary, in the steel A12 containing an excessive amount of Nb, the grain size is small and the average aspect ratio is close to 1 after the intermediate annealing, but an excessive amount of precipitates are generated during the final annealing, so that recrystallization occurs. Is inhibited, and the occupancy ratio of the {111} plane is reduced, and as a result, the r value is considered to be lowered.
次に、鋼種Ａ１，Ｂ１の熱延板を用い、表４に示す製造条件で板厚：０.９５ｍｍのステンレス鋼板を製造した。この過程で、中問焼鈍が終了したステンレス鋼板をサンプリングし、同様に再結晶粒の平均結晶粒径，平均アスペクト比，ｒ-，Δｒを求めた。
表５の調査結果にみられるように、温度域：７００〜９００℃の熱延板焼鈍，温度域：(再結晶完了温度)〜(再結晶完了温度+５０℃)の中間焼鈍を経るとき、中間焼鈍後に平均結晶粒径：３０μｍ以下，平均アスペクト比：１.５以下の再結晶組織が得られた。この中間焼鈍されたステンレス鋼帯を圧延率：５０％以上で仕上げ圧延した後、仕上げ焼鈍することにより製造された仕上げ焼鈍板は、ｒ-が２を超えΔｒが０.５以下の優れた深絞り性を備えていた。
Next, a stainless steel plate having a thickness of 0.95 mm was manufactured under the manufacturing conditions shown in Table 4 using hot rolled sheets of steel types A1 and B1. In this process, the stainless steel plate after intermediate annealing was sampled, and the average crystal grain size, average aspect ratio, r −, and Δr of the recrystallized grains were similarly determined.
As seen in the investigation results in Table 5, when the temperature range: 700 to 900 ° C hot-rolled sheet annealing, the temperature range: (recrystallization completion temperature) to (recrystallization completion temperature + 50 ° C) intermediate annealing, After the intermediate annealing, a recrystallized structure having an average crystal grain size of 30 μm or less and an average aspect ratio of 1.5 or less was obtained. This intermediate annealed stainless steel strip is finish-rolled at a rolling reduction ratio of 50% or more, and then finish-annealed. The finished annealed plate has an excellent depth of r− exceeding 2 and Δr not exceeding 0.5. It had squeezability.
中間焼鈍，仕上げ焼鈍の一方でも特定した条件を外れると、中間焼鈍後の再結晶組織が平均結晶粒径：３０μｍ以下，平均アスペクト比：１.５以下の何れかを満足せず、続く仕上げ圧延，仕上げ焼鈍で十分な{１１１}集合組織の発達がなく、ランクフォード値が低い値を示した。また、特定条件下の熱延板焼鈍，中間焼鈍を施し、中間焼鈍後の再結晶組織を平均結晶粒径：３０μｍ以下，平均アスペクト比：１.５以下に調整しても、仕上げ圧延の圧延率が５０％未満では{１１１}集合組織が十分に発達せず、同様に低いランクフォード値であった。 If one of the intermediate annealing and finish annealing is outside the specified conditions, the recrystallized structure after the intermediate annealing does not satisfy either the average grain size: 30 μm or less and the average aspect ratio: 1.5 or less, and the subsequent finish rolling , Finish annealing did not develop enough {111} texture, and showed a low Rankford value. Moreover, even if hot-rolled sheet annealing and intermediate annealing under specific conditions are performed and the recrystallized structure after the intermediate annealing is adjusted to an average crystal grain size of 30 μm or less and an average aspect ratio of 1.5 or less, rolling in finish rolling When the rate was less than 50%, {111} texture did not develop sufficiently, and the Rankford value was low as well.
以上に説明したように、Ｎｂ含有量を０.１〜０.５質量％の範囲に調整したフェライト系ステンレス鋼の熱延板を７００〜９００℃の温度域で連続焼鈍した後、中間圧延，中間焼鈍すると平均結晶粒径：３０μｍ以下，平均アスペクト比：１.５以下の微細な再結晶組織が発現する。このステンレス鋼帯は、仕上げ圧延，仕上げ焼鈍後にランクフォード値ｒが高く、Δｒが小さいため、高度の深絞り加工を施しても割れの発生がなく、肉厚が安定した深絞り製品となる。そのため、従来では加工性に難点があったことから複雑形状の厨房機器，，家具調度品，各種内装材等の用途に適用可能なフェライト単相系ステンレス鋼板として使用される。 As explained above, after hot annealing a hot rolled sheet of ferritic stainless steel whose Nb content is adjusted to a range of 0.1 to 0.5 mass% in a temperature range of 700 to 900 ° C., intermediate rolling, When the intermediate annealing is performed, a fine recrystallized structure having an average crystal grain size of 30 μm or less and an average aspect ratio of 1.5 or less appears. Since this stainless steel strip has a high Rankford value r and a small Δr after finish rolling and finish annealing, it does not generate cracks even if it is subjected to high-level deep drawing, and becomes a deep drawn product with a stable wall thickness. For this reason, since there has been a difficulty in workability in the past, it is used as a ferritic single-phase stainless steel sheet that can be used for applications such as complex-shaped kitchen equipment, furniture furnishings, and various interior materials.
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