JP4708517B2

JP4708517B2 - Cylindrical member made of austenitic stainless steel and manufacturing method thereof

Info

Publication number: JP4708517B2
Application number: JP06475599A
Authority: JP
Inventors: 聡杉山; 不二男大久保
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1999-03-11
Filing date: 1999-03-11
Publication date: 2011-06-22
Anticipated expiration: 2019-03-11
Also published as: JP2000263180A

Description

【０００１】
【技術分野】
本発明は，例えば磁性材料として用いることができるステンレス鋼よりなる円筒部材およびその製造方法に関する。
【０００２】
【従来技術】
例えば，電磁弁等の磁気回路を有する装置においては，オーステナイト系ステンレス鋼よりなる円筒部材を磁性材料として用いる場合がある。
オーステナイト系のステンレス鋼は，元来非磁性体であるが，冷間加工を加えると誘起マルテンサイトが発生し，これにより強磁性体となるという特徴を有している。そのため，オーステナイト系ステンレス鋼を用いて，冷間加工，溶体化処理等に工夫を加え，オーステナイトよりなる非磁性部とマルテンサイトよりなる強磁性部とを一体的に併せ持つ複合磁性部材も開発されている。
【０００３】
かかるオーステナイト系ステンレス鋼よりなる円筒部材を製造するに当たっては，通常，円筒形状の中間材を作製した後，絞り加工等を複数回加えて所定寸法に加工する。また，この絞り加工等の条件を調整することにより，誘起マルテンサイトを発生させることができ，円筒部材を全体的に強磁性化させることができる。
【０００４】
【解決しようとする課題】
しかしながら，上記従来のステンレス鋼よりなる円筒部材の製造方法には，次の問題がある。
即ち，上記絞り加工を加えて得られた円筒部材には，引張残留応力が残る。このとき，円筒部材の開口端部に小さなキズなどの応力集中部が存在する場合には，開口端部から縦方向に時期割れが生じる場合がある。
【０００５】
一方，この時期割れ防止には，ショットピーニングにより上記引張残留応力を低減する方法が有効である。しかしながら，絞り加工後ショットピーニングを施すまでの時間が長い場合には，対策をとる前に時期割れが生じてしまう場合もある。
【０００６】
また，開口端部を滑らかな面に加工することも時期割れ対策に有効である。しかしながら，この場合も，開口端部の加工時期が遅い場合には，上記と同様に対策前に時期割れが生じてしまう場合がある。さらに，開口端部の加工工程の増加により製造コストの増加を招いてしまう。
【０００７】
また，絞り加工後にしごき加工を加えて引張残留応力を低減する方法もある。しかしながら，引張残留応力が大きい場合には，しごき率を大きく設定しても，引張残留応力を十分に低減することができない。
【０００８】
本発明は，かかる従来の問題点に鑑みてなされたもので，円筒部材の成形後における時期割れを確実に防止することができる，ステンレス鋼よりなる円筒部材およびその製造方法を提供しようとするものである。
【０００９】
【課題の解決手段】
請求項１の発明は，オーステナイト系ステンレス鋼よりなる素材を用いて円筒形状の中間材を作製し，次いで，該中間材に，絞り加工，しごき加工又はＤＩ加工を加えて円筒部材を成形するに当たり，
少なくとも最後の加工ではＤＩ加工を行い，該最後の加工においては，上記中間材の開口端部の加工完了直前で加工を止めることにより，該開口端部に本体部よりも大径に拡開され，少なくともその端部の断面形状が内側に向けて凸状の形状である曲面形状の端部として形成された拡径部を形成して該拡径部を圧縮残留応力状態とし，
上記本体部から開口端部までの間に形成される上記拡径部の高さは０．５〜５．０ｍｍに設定し，
かつ，上記拡径部の厚さが０．１〜２．０ｍｍとなるようにＤＩ加工を行うことを特徴とするオーステナイト系ステンレス鋼よりなる円筒部材の製造方法にある。
【００１０】
本発明において最も注目すべきことは，上記最後の絞り加工又はしごき加工（以下，最終加工という）において，上記開口端部の加工完了直前で加工を止めることにより，上記拡径部を形成することである。
【００１１】
上記拡径部は，少なくとも上記最終加工において形成する。なお，絞り加工又はしごき加工を複数回行う場合には，最終加工よりも前の加工工程においても拡径部を形成してもよい。但し，この場合にも，最終加工においては必ず上記拡径部を形成する。
【００１２】
上記拡径部は，上記のごとく，本体部よりも大径に拡開させて設ける。
この拡径部の形成は，上記最終加工を開口端部の加工完了直前で止めることにより行う。具体的には，上記最終加工としての絞り加工あるいはしごき加工を行うダイとして，加工前の中間材の外径よりも小さい内径を有するダイを用いる。そして，上記のごとく，開口端部の加工が完了する直前，即ち，開口端部の加工途中で最終加工を止める。これにより，最終加工が完了した本体部よりも，最終加工が施されない開口端部を大径に維持することができる。
【００１３】
また，上記拡径部は，圧縮残留応力状態となるように設ける。これは，上記絞り加工又はしごき加工における加工途中部分が圧縮残留応力状態にあることを利用し，かつ，上記のごとく開口端部を未加工状態に維持することにより実現することができる（実施形態例参照）。
【００１４】
上記中間材としては，一端部に底部を有する有底円筒形状であっても，両端部を開口させた円筒形状であってもよい。
但し，上記有底円筒形状の方が，絞り加工又はしごき加工を行う場合の作業性に優れる。
【００１５】
また，素材として用いるオーステナイト系ステンレス鋼としては，例えばＣｒ−Ｎｉ系のステンレス鋼がある。
また，素材形状としては，板状，棒状，筒状等，少なくとも円筒形状の中間材を形成できればいずれの形状でもよい。例えば板状の場合には，これをプレスで打ち抜くと共に絞り加工して得ることができる。
【００１６】
次に，本発明の作用につき説明する。
本発明においては，上記最後の絞り加工又はしごき加工において，上記のごとく，開口端部に上記拡径部を形成する。この拡径部の存在により，上記円筒部材は時期割れを確実に回避することができる。
【００１７】
この理由は次のように考えられる。
即ち，上記拡径部は，上記のごとく，最終加工の加工完了直前で止めることにより形成している。一方，絞り加工あるいはしごき加工においては，加工途中の材料内部は全体的に圧縮残留応力が発生した状態とすることができる。そのため，加工完了直前で加工を中止された上記拡径部は，全体的に圧縮残留応力を有するものとなる。
【００１８】
そのため，たとえ円筒部材の開口端部（拡径部の端部）に小さなキズのような応力集中部が存在する場合においても，拡径部が圧縮残留応力状態にあるので割れの発生を十分に抑制することができる。
それ故，円筒部材を長期間放置しても，該円筒部材は時期割れすることなく健全な状態に維持される。
なお，上記拡径部は，その後にショットピーニング処理等の時期割れ対策を施した後削除することもできるし，そのまま残すことも可能である。
【００１９】
このように，本発明によれば，円筒部材の成形後における時期割れを確実に防止することができる，ステンレス鋼よりなる円筒部材の製造方法を提供することができる。
【００２０】
次に，請求項２の発明のように，上記拡径部は，少なくともその端部が上記円筒部材の外側に曲率中心を有する曲面形状の端部として形成されていることが好ましい。即ち，上記拡径部の少なくともその端部は，内側に向けて凸状の形状とし，水平面状あるいは外側に向けて凸状となるような形状には設けない。これにより，上記拡径部の圧縮残留応力状態を高めることができる。
【００２１】
さらに，請求項３の発明のように，上記拡径部の縦断面形状は，上記拡径部の全体に渡って，上記円筒部材の外側に曲率中心を有する曲面状に設けることが好ましい。即ち，上記拡径部の断面形状は，その全体に渡って内側に向けて凸状の形状とし，水平面状あるいは外側に向けて凸状となるような形状には設けない。これにより，上記拡径部の圧縮残留応力状態をさらに高めることができる。
【００２２】
また，請求項４の発明のように，上記最後の絞り加工又はしごき加工は，絞り加工としごき加工とを同時に行うＤＩ（Drawing Ironing）加工であることが好ましい。この場合には，しごき加工により，円筒部材全体の引張残留応力を軽減することができ，上記拡径部による時期割れ防止効果をさらに高めることができる。
【００２３】
また，請求項４の発明のように，上記円筒部材は，上記絞り加工，しごき加工又はＤＩ加工によって，誘起マルテンサイト変態させて強磁性体とすることができる。この場合には，オーステナイト相からマルテンサイト相への変態による体積膨張が発生し，通常は時期割れを生じやすい状態となる。しかしながら，この場合にも上記拡径部を設けることにより十分に時期割れの発生を防止することができる。
【００２４】
また，上記請求項１の発明では，上記本体部から開口端部までの間に形成される上記拡径部の高さは０．５〜５．０ｍｍに設定される。この場合には，拡径部の残留応力を容易に圧縮状態とすることができる。一方，拡径部の高さが０．５ｍｍ未満の場合には，拡径部の領域が小さすぎて本体部の引張残留応力に対向しきれないという問題があり，また，５．０ｍｍを越える場合には，端部側が引張残留応力に変化してくるという問題がある。
【００２５】
また，上記拡径部の厚さが０．１〜２．０ｍｍとなるように絞り加工又はしごき加工を行う。この場合には，上記拡径部の高さを上記範囲内に設定することにより，拡径部の残留応力をさらに容易に圧縮状態とすることができる。
【００２６】
次に，請求項５の発明は，オーステナイト系ステンレス鋼よりなる円筒部材であって，該円筒部材の開口端部には，本体部よりも大径に拡開され，少なくともその端部の断面形状が内側に向けて凸状の形状である曲面形状の端部として形成されてなると共に圧縮残留応力状態に設けられた拡径部を有しており，
上記本体部から開口端部までの間に形成される上記拡径部の高さは０．５〜５．０ｍｍに設定されており，
かつ，上記拡径部の厚さが０．１〜２．０ｍｍとなるようにＤＩ加工されていることを特徴とするオーステナイト系ステンレス鋼よりなる円筒部材にある。
【００２７】
本発明の円筒部材において最も注目すべきことは，上記開口端部には，上記拡径部を設けてあり，かつ，該拡径部を圧縮残留応力状態としてあることである。
上記拡径部の形成方法としては，例えば，上述した製造方法に示したごとく，絞り加工又はしごき加工を途中で止めることにより形成する方法がある。
【００２８】
本発明においては，この拡径部が圧縮残留応力状態にある。そのため，たとえ円筒部材の開口端部（拡径部の端部）に小さなキズのような応力集中部が存在する場合においても，割れの発生を十分に抑制することができる。
それ故，本発明の円筒部材を長期間放置しても，該円筒部材は時期割れすることなく健全な状態に維持される。
【００２９】
また，請求項６の発明のように，上記拡径部の縦断面形状は，上記円筒部材の外方に曲率中心を有する曲面状であることが好ましい。この場合には，上記のごとく，上記拡径部の圧縮残留応力状態をさらに高めることができる。
【００３０】
【発明の実施の形態】
実施形態例１
本発明の実施形態例にかかるオーステナイト系ステンレス鋼よりなる円筒部材およびその製造方法につき，図１，図２を用いて説明する。
本発明のオーステナイト系ステンレス鋼よりなる円筒部材１は，図１，図２に示すごとく，その開口端部には，本体部１０よりも大径に拡開されていると共に圧縮残留応力状態に設けられた拡径部２を有している。
また，この拡径部２の縦断面形状は，上記円筒部材１の外方に曲率中心を有する曲面状，即ち，内側に向けて凸状に設けられている。
【００３１】
この円筒部材１を製造するに当たっては，図１に示すごとく，まず，オーステナイト系ステンレス鋼よりなる素材８１を用いて円筒形状の中間材８を作製する。次いで，該中間材８に絞り加工又はしごき加工を加えて円筒部材１を成形する。
そして，少なくとも最後の絞り加工又はしごき加工においては，上記中間材８の開口端部の加工完了直前で加工を止めることにより，上記拡径部２を形成する。
【００３２】
以下，この製造方法につき詳説する。
本例においては，図１（ａ）に示すごとく，オーステナイト系ステンレス鋼よりなる素材として，板材８１を準備した。これを円盤状のブランク材に打ち抜き，絞り加工を施して有底円柱形状の中間材８を形成した（同図（ｂ））。この第１回目の絞り加工は端面部も含めて全体的に絞り加工を施した。
【００３３】
次に，中間材８に対して，同図（ｃ）に示すごとく，複数回の絞り加工を施して，誘起マルテンサイトを発生させて全体を強磁性化した。このときの複数回の絞り加工は，通常の絞り加工と同様に端面部も含めて加工を施した。
次に，同図（ｄ）に示すごとく，強磁性化した中間材８にＤＩ加工を２回施した。１回目のＤＩ加工は開口端部も含めて全体的に加工を施した。最後のＤＩ加工においては，中間材８の開口端部の加工完了直前で加工を止めた。そして，開口端部に本体部１０よりも大径に拡開された拡径部２を形成した。
【００３４】
この拡径部２の縦断面形状は，図２に示すごとく，ＤＩ加工用ダイの断面形状の影響により，円筒部材１の外方に曲率中心を有する曲面状に設けられた。即ち，拡径部２の断面形状は，内側に向けて凸状の形状とした。
この拡径部２の応力状態は，Ｘ線による測定の結果，圧縮残留応力状態にあることが確認された。
【００３５】
次に，本例の作用につき説明する。
本例においては，上記最後のＤＩ加工において，上記のごとく，開口端部に上記拡径部２を形成する。また，この拡径部２は，上記のごとく圧縮応力状態にある。そのため，上記円筒部材１は時期割れを確実に回避することができる。
【００３６】
即ち，たとえ円筒部材１の開口端部に応力集中部が存在する場合においても，拡径部２が圧縮残留応力状態にあるので割れの発生を十分に抑制することができる。
それ故，円筒部材１を長期間放置しても，該円筒部材１は時期割れすることなく健全な状態に維持される。
【００３７】
実施形態例２
本例は，図３に示すごとく，実施形態例１における最初の絞り加工を除き，複数回の絞り加工（同図（ｃ））と２回のＤＩ加工のすべて（同図（ｄ））において拡径部２を形成した。即ち，上記中間材８の絞り加工においては，中間材８の開口端部の加工完了直前で加工を止めた。また，２回のＤＩ加工においても，同様に，中間材８の開口端部の加工完了直前で加工を止めた。
【００３８】
これにより，各途中段階の中間材８においても，その開口端部に本体部よりも大径に拡開された拡径部２を形成した。また，各拡径部２の縦断面形状は，各中間材８の外方に曲率中心を有する曲面状に設けた。この断面形状は，絞り加工又はＤＩ加工に用いるダイの断面形状の影響により得ることができた。
【００３９】
この場合には，最後のＤＩ加工を施す前の中間段階においても，時期割れの発生を十分に防止することができる。例えば，絞り加工とＤＩ加工との間のように，比較的長時間放置される可能性がある場合には特に有効である。
その他は実施形態例１と同様の作用効果が得られる。
【００４０】
なお，製品の種類によっては，上記拡径部２を取り除く必要がある場合もある。この場合には，上記拡径部２を備えたまま円筒部材１にショットピーニング等の時期割れ防止策を施した後，上記拡径部２を削除することもできる。また，拡径部２を残せる場合であっても，ショットピーニング処理を施して時期割れ防止効果をさらに高めることも勿論可能である。
【００４１】
実施形態例３
本例においては，実施形態例２の製造方法により作製した円筒部材の効果を評価すべく，比較例の製造方法により作製した円筒部材と共に時期割れの発生状況を確認するテストを行った。
比較例の製造方法は，図４に示すごとく，オーステナイト系ステンレス鋼よりなる素材として，板材９８１を準備した。そして，これを円盤状のブランク材に打ち抜き，絞り加工を施して有底円柱形状の中間材９８を形成した（同図（ｂ））。
【００４２】
次に，中間材９８に対して，同図（ｃ）に示すごとく，複数回の絞り加工を施して，誘起マルテンサイトを発生させて全体を強磁性化すると共に，所望寸法の円筒部材９に仕上げた。上記絞り加工においては，開口端部も含めて全体に加工を施した。
【００４３】
次に，上記実施形態例２の製造方法により作製した円筒部材１と，比較例の製造方法により作製した円筒部材９をそれぞれ８７個，３ヶ月間放置した。そして，放置後に時期割れ発生状況を調べた。
このテストの結果，比較例の方法による場合には，８７個中４５個（５２％）に時期割れが発生した。一方，実施形態例２にかかる円筒部材１には，まったく時期割れが発生しなかった。
以上の結果から，本発明にかかる円筒部材は時期割れが非常に起こりにくい優れた材料であることが分かる。
【００４４】
実施形態例４
本例では，上記拡径部２による時期割れ防止のメカニズムをさらに明確にすべく，実験的に絞り加工を行い，各加工段階での残留応力状態を測定した。
具体的には，図５に示すごとく，ダイ７１とパンチ７２とを用いて板材８８に絞り加工を施した。また，この絞り加工は，ダイ７１を通過していない開口端部を十分に残して途中で止めた。
【００４５】
そして，図６に示すごとく，開口端部付近における，曲げ加工開始前のフランジ部Ａ，曲げ加工中の曲げ加工部Ｂ，曲げ加工が完了した加工完了部Ｃの各部分をリング状に輪切りした。そして切り出したリングの一部を切断して，この切断部が口開き状態あるいは口閉じ状態のいずれになるかを観察した。
【００４６】
その結果を模式的に示したものが図６である。同図に示すごとく，上記フランジ部Ａおよび加工完了部Ｃは，いずれも最初の外径Ｄ₁，Ｄ₃がＤ₁₂，Ｄ₃₂に拡大して口開き状態となり，引張残留応力状態にあることが分かる。一方，上記曲げ加工部Ｂは，最初の外径Ｄ₂がＤ₂₂に縮小して口閉じ状態（スプリングゴー状態）となり，圧縮残留応力状態にあることが分かる。
【００４７】
これらのことから，絞り加工又はしごき加工あるいはＤＩ加工において，図７に示すごとく，開口端部が上記曲げ加工部Ｂの位置において止まるように加工を施すことにより，拡径部２の応力状態を確実に圧縮残留応力状態にすることができるということが分かる。
【００４８】
また，上記実施形態例１のように，拡径部２の縦断面形状を上記円筒部材１の外方に曲率中心を有する曲面状，即ち，内側に向けて凸状とすることにより，拡径部２を上記の曲げ加工部Ｂの状態にすることができる。そして，これにより，拡径部２を容易に圧縮残留応力状態とすることができることが分かる。
【００４９】
なお，上記各実施形態例により得られたオーステナイト系ステンレス鋼よりなる円筒部材を複合磁性部材の素材として利用することも勿論可能である。即ち，得られた円筒部材の一部に熱処理を加えてオーステナイト化し，マルテンサイト相よりなる強磁性部とオーステナイト相よりなる非磁性部とからなう複合磁性部材を得ることができる。
【００５０】
実施形態例５
本例では，上記拡径部２の残留応力状態を，拡径部の高さと厚みの面から評価した。
即ち，実施形態例１に示した製造工程において，最後のＤＩ加工における拡径部２の形成状態を変更し，得られた拡径部の残留応力を測定した。具体的には，拡径部の厚み（板厚）が１．２ｍｍの場合と２．０ｍｍの場合について，拡径部の高さを０〜５．３ｍｍの範囲で変更し，得られた拡径部の残留応力を測定した。
【００５１】
残留応力の測定結果を図８に示す。同図は，横軸に拡径部の高さ（端面残し量Ｌ（ｍｍ：図７参照））を，縦軸に端面の円周方向の残留応力（ＭＰａ）をとった。このとき残留応力が０より大きければ引張状態であることを意味し，０より小さければ圧縮状態であることを意味する。また，厚みが１．２ｍｍの場合を実線Ｅ１，２．０ｍｍの場合を実線Ｅ２により示した。さらに比較のために，拡径部を設けない場合（Ｌ＝０）において，最終加工が絞り加工の場合の残留応力を符号Ｃ１，ＤＩ加工の場合の残留応力を符号Ｃ２により示した。
【００５２】
同図より知られるごとく，拡径部の厚さが２．０ｍｍの場合にはその高さが０．５〜５．０ｍｍの範囲において，拡径部の厚さが１．２ｍｍの場合にはその高さが０．６〜２．８ｍｍの範囲において，圧縮残留応力状態を実現できた。
また，拡径部を設けない場合（Ｃ１，Ｃ２）には，最終加工が絞り加工であってもＤＩ加工であっても残留応力を圧縮状態とすることが困難であることも分かった。
【００５３】
以上のことから，板厚が１．２〜２．０ｍｍの場合には，拡径部の高さを０．５〜５．０ｍｍの範囲から選択することにより，拡径部を所望の圧縮残留応力状態とすることができるということが分かる。
なお，拡径部の板厚の加工範囲としては，０．１〜２．０ｍｍ程度である。上述したように，拡径部の高さの適性範囲は，その板厚に応じて変動するので，最終的に得られる拡径部の板厚に応じて拡径部の高さを適切に選択することが必要である。
【００５４】
【発明の効果】
上述のごとく，本発明によれば，円筒部材の成形後における時期割れを確実に防止することができる，ステンレス鋼よりなる円筒部材およびその製造方法を提供することができる。
【図面の簡単な説明】
【図１】実施形態例１における，円筒部材の製造工程を示す説明図。
【図２】実施形態例１における，円筒部材の断面図。
【図３】実施形態例２における，円筒部材の製造工程を示す説明図。
【図４】実施形態例３の比較例における，円筒部材の製造工程を示す説明図。
【図５】実施形態例４における，試験方法を示す説明図。
【図６】実施形態例４における，残留応力状態を示す説明図。
【図７】実施形態例４における，円筒部材の形状を示す説明図。
【図８】実施形態例５における，端面残し量と端面残留応力との関係を示す説明図。
【符号の説明】
１．．．円筒部材，
１０．．．本体部，
２．．．拡径部，
８．．．中間材，[0001]
【Technical field】
The present invention relates to a cylindrical member made of stainless steel that can be used as a magnetic material, for example, and a method for manufacturing the same.
[0002]
[Prior art]
For example, in a device having a magnetic circuit such as a solenoid valve, a cylindrical member made of austenitic stainless steel may be used as a magnetic material.
Austenitic stainless steel is originally a non-magnetic material, but when cold-worked, induced martensite is generated, which makes it a ferromagnetic material. Therefore, using austenitic stainless steel, we devised cold working, solution treatment, etc., and developed a composite magnetic member that has both a nonmagnetic part made of austenite and a ferromagnetic part made of martensite. Yes.
[0003]
In manufacturing a cylindrical member made of such austenitic stainless steel, usually, a cylindrical intermediate material is manufactured, and then drawing or the like is applied a plurality of times to process to a predetermined dimension. In addition, by adjusting the conditions such as drawing, induced martensite can be generated, and the cylindrical member can be made ferromagnetic as a whole.
[0004]
[Problems to be solved]
However, the conventional method for manufacturing a cylindrical member made of stainless steel has the following problems.
That is, a tensile residual stress remains in the cylindrical member obtained by applying the drawing process. At this time, if there is a stress concentrating portion such as a small scratch at the opening end of the cylindrical member, a time crack may occur in the vertical direction from the opening end.
[0005]
On the other hand, a method of reducing the above-mentioned tensile residual stress by shot peening is effective for preventing this period cracking. However, if it takes a long time to perform shot peening after drawing, there may be a case where time cracking occurs before taking countermeasures.
[0006]
In addition, machining the open end to a smooth surface is also effective as a countermeasure against time cracking. However, in this case as well, if the processing time of the opening end is late, there may be a case where a time crack occurs before the countermeasure is taken as described above. Furthermore, an increase in the manufacturing process of the opening end portion causes an increase in manufacturing cost.
[0007]
There is also a method of reducing the tensile residual stress by adding ironing after drawing. However, if the tensile residual stress is large, the tensile residual stress cannot be reduced sufficiently even if the ironing rate is set large.
[0008]
The present invention has been made in view of such conventional problems, and intends to provide a cylindrical member made of stainless steel and a method for manufacturing the same, which can reliably prevent the time cracking of the cylindrical member after molding. It is.
[0009]
[Means for solving problems]
The invention of claim 1, to produce an intermediate material of a cylindrical shape using a material made of austenitic stainless steel, then the intermediate member, drawing, when forming the cylindrical member by adding ironing or DI processing ,
At least in the last machining, DI machining is performed, and in the last machining, the machining is stopped immediately before completion of machining of the opening end of the intermediate material, so that the opening end is expanded to a larger diameter than the main body. , Forming a widened portion formed as an end portion of a curved surface that is a convex shape in which at least the end portion has a cross-sectional shape inward, and the expanded diameter portion is brought into a compressive residual stress state,
The height of the enlarged diameter portion formed between the main body portion and the opening end is set to 0.5 to 5.0 mm,
And it exists in the manufacturing method of the cylindrical member which consists of austenitic stainless steel characterized by performing DI process so that the thickness of the said enlarged diameter part may be set to 0.1-2.0 mm.
[0010]
The most notable aspect of the present invention is that, in the final drawing or ironing process (hereinafter referred to as final process), the diameter-enlarged portion is formed by stopping the process immediately before the end of the opening end. It is.
[0011]
The enlarged diameter portion is formed at least in the final processing. In the case where the drawing process or the ironing process is performed a plurality of times, the diameter-enlarged portion may be formed also in the machining process prior to the final machining. However, also in this case, the above-mentioned enlarged diameter portion is always formed in the final machining.
[0012]
As described above, the enlarged diameter portion is provided so as to expand to a larger diameter than the main body portion.
The formation of the enlarged diameter portion is performed by stopping the final processing just before the end of the opening end is completed. Specifically, a die having an inner diameter smaller than the outer diameter of the intermediate material before processing is used as the die for performing drawing or ironing as the final processing. Then, as described above, the final processing is stopped immediately before the processing of the opening end is completed, that is, during the processing of the opening end. Thereby, the opening end part which is not subjected to final processing can be maintained at a larger diameter than the main body portion where final processing is completed.
[0013]
Moreover, the said enlarged diameter part is provided so that it may become a compressive residual stress state. This can be realized by utilizing the fact that the part in the middle of the drawing or ironing process is in a compressive residual stress state and maintaining the open end in an unprocessed state as described above (embodiment). See example).
[0014]
The intermediate material may be a bottomed cylindrical shape having a bottom portion at one end or a cylindrical shape having both ends opened.
However, the bottomed cylindrical shape is superior in workability when drawing or ironing.
[0015]
As an austenitic stainless steel used as a material, for example, there is a Cr-Ni stainless steel.
The material shape may be any shape as long as at least a cylindrical intermediate material can be formed, such as a plate shape, a rod shape, or a cylindrical shape. For example, in the case of a plate shape, this can be obtained by punching with a press and drawing.
[0016]
Next, the operation of the present invention will be described.
In the present invention, in the final drawing process or ironing process, as described above, the enlarged diameter portion is formed at the opening end. Due to the presence of the enlarged diameter portion, the cylindrical member can surely avoid the time cracking.
[0017]
The reason is considered as follows.
That is, the expanded diameter portion is formed by stopping immediately before the completion of the final processing as described above. On the other hand, in drawing or ironing, the inside of the material being processed can be in a state where compressive residual stress is generated as a whole. For this reason, the above-mentioned enlarged diameter portion whose processing has been stopped immediately before the completion of processing has a compressive residual stress as a whole.
[0018]
For this reason, even if there is a stress-concentrated part such as a small scratch at the open end of the cylindrical member (end of the enlarged diameter part), the enlarged diameter part is in a compressive residual stress state, so that cracks are sufficiently generated. Can be suppressed.
Therefore, even if the cylindrical member is left for a long period of time, the cylindrical member is maintained in a healthy state without being cracked.
The diameter-enlarged portion can be deleted after taking measures against time cracking such as shot peening after that, or can be left as it is.
[0019]
Thus, according to this invention, the manufacturing method of the cylindrical member which consists of stainless steel which can prevent the time crack after the shaping | molding of a cylindrical member reliably can be provided.
[0020]
According to a second aspect of the present invention, it is preferable that at least the end portion of the enlarged diameter portion is formed as a curved end portion having a center of curvature outside the cylindrical member. That is, at least the end portion of the enlarged diameter portion has a convex shape toward the inner side, and is not provided in a horizontal plane shape or a convex shape toward the outer side. Thereby, the compressive residual stress state of the said enlarged diameter part can be raised.
[0021]
Further, as in a third aspect of the invention, it is preferable that the longitudinal cross-sectional shape of the enlarged diameter portion is provided in a curved shape having a center of curvature outside the cylindrical member over the entire enlarged diameter portion. That is, the cross-sectional shape of the enlarged diameter portion is a convex shape toward the inside over the whole, and is not provided in a shape that is a horizontal surface or a convex shape toward the outside. Thereby, the compressive residual stress state of the said enlarged diameter part can further be raised.
[0022]
As in the invention of claim 4, the last drawing or ironing is preferably a DI (Drawing Ironing) process in which drawing and ironing are performed simultaneously. In this case, the tensile residual stress of the entire cylindrical member can be reduced by ironing, and the effect of preventing the time cracking by the enlarged diameter portion can be further enhanced.
[0023]
According to a fourth aspect of the present invention, the cylindrical member can be transformed into an induced martensite by the drawing process , the ironing process, or the DI process to form a ferromagnetic material. In this case, volume expansion occurs due to the transformation from the austenite phase to the martensite phase, and usually it is in a state where it is likely to cause time cracking. However, in this case as well, the occurrence of time cracking can be sufficiently prevented by providing the above-mentioned enlarged diameter portion.
[0024]
In the first aspect of the present invention, the height of the enlarged diameter portion formed between the main body portion and the opening end is set to 0.5 to 5.0 mm . In this case, the residual stress in the enlarged diameter portion can be easily compressed. On the other hand, when the height of the enlarged diameter portion is less than 0.5 mm, there is a problem that the area of the enlarged diameter portion is too small to completely face the tensile residual stress of the main body, and exceeds 5.0 mm. In this case, there is a problem that the end side changes to a tensile residual stress.
[0025]
The thickness of the enlarged diameter portion performs drawing or ironing so as to be 0.1 to 2.0 mm. In this case, by setting the height of the enlarged diameter portion within the above range, the residual stress in the enlarged diameter portion can be more easily compressed.
[0026]
Next, the invention of claim 5 is a cylindrical member made of austenitic stainless steel, the opening end of the cylindrical member is expanded to have a larger diameter than the main body, and at least the cross-sectional shape of the end Is formed as an end of a curved surface that is convex toward the inside, and has a diameter-enlarged portion provided in a compressive residual stress state,
The height of the enlarged diameter portion formed between the main body portion and the opening end is set to 0.5 to 5.0 mm,
And it exists in the cylindrical member which consists of austenitic stainless steel characterized by carrying out DI process so that the thickness of the said enlarged diameter part may be set to 0.1-2.0 mm.
[0027]
What should be noted most in the cylindrical member of the present invention is that the enlarged diameter portion is provided at the opening end portion and the enlarged diameter portion is in a compressive residual stress state.
As a method for forming the enlarged diameter portion, for example, as shown in the manufacturing method described above, there is a method of forming by stopping drawing or ironing on the way.
[0028]
In the present invention, this enlarged diameter portion is in a compressive residual stress state. Therefore, even when a stress concentrating portion such as a small scratch exists at the opening end portion (end portion of the enlarged diameter portion) of the cylindrical member, the occurrence of cracks can be sufficiently suppressed.
Therefore, even if the cylindrical member of the present invention is left for a long period of time, the cylindrical member is maintained in a healthy state without being cracked.
[0029]
According to a sixth aspect of the present invention, the longitudinal cross-sectional shape of the enlarged-diameter portion is preferably a curved surface having a center of curvature outside the cylindrical member. In this case, as described above, the compressive residual stress state of the enlarged diameter portion can be further increased.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A cylindrical member made of austenitic stainless steel according to an embodiment of the present invention and a manufacturing method thereof will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the cylindrical member 1 made of austenitic stainless steel according to the present invention has a larger opening diameter than that of the main body 10 and is provided in a compressive residual stress state. The enlarged diameter portion 2 is provided.
Moreover, the longitudinal cross-sectional shape of this enlarged diameter part 2 is provided in the curved surface shape which has a curvature center in the outer side of the said cylindrical member 1, ie, the convex shape toward the inner side.
[0031]
In producing this cylindrical member 1, as shown in FIG. 1, first, a cylindrical intermediate member 8 is produced using a material 81 made of austenitic stainless steel. Next, the intermediate member 8 is drawn or ironed to form the cylindrical member 1.
In at least the final drawing or ironing, the diameter-enlarged portion 2 is formed by stopping the processing immediately before the end of the opening of the intermediate member 8 is completed.
[0032]
Hereinafter, this manufacturing method will be described in detail.
In this example, as shown in FIG. 1A, a plate material 81 was prepared as a material made of austenitic stainless steel. This was punched out into a disk-shaped blank, and subjected to drawing to form a bottomed cylindrical intermediate material 8 (FIG. 2B). In the first drawing process, the drawing process was performed as a whole including the end face part.
[0033]
Next, as shown in FIG. 2C, the intermediate material 8 was subjected to drawing processing a plurality of times to generate induced martensite to make the whole ferromagnetic. In this case, the drawing was performed a plurality of times, including the end face, in the same manner as in the normal drawing.
Next, as shown in FIG. 4D, the DI processing was performed twice on the ferromagnetized intermediate material 8. The first DI processing was performed entirely including the opening end. In the last DI processing, the processing was stopped immediately before the processing of the opening end portion of the intermediate member 8 was completed. And the enlarged diameter part 2 expanded by larger diameter than the main-body part 10 was formed in the opening edge part.
[0034]
As shown in FIG. 2, the longitudinal cross-sectional shape of the enlarged diameter portion 2 was provided in a curved shape having a center of curvature outside the cylindrical member 1 due to the influence of the cross-sectional shape of the DI processing die. That is, the cross-sectional shape of the enlarged diameter portion 2 is a convex shape toward the inside.
As a result of measurement by X-ray, it was confirmed that the stress state of the expanded diameter portion 2 is in a compressive residual stress state.
[0035]
Next, the operation of this example will be described.
In this example, in the final DI processing, as described above, the enlarged diameter portion 2 is formed at the opening end portion. Further, the enlarged diameter portion 2 is in a compressive stress state as described above. Therefore, the cylindrical member 1 can reliably avoid the time cracking.
[0036]
That is, even when a stress concentration portion exists at the opening end portion of the cylindrical member 1, since the enlarged diameter portion 2 is in a compressive residual stress state, occurrence of cracks can be sufficiently suppressed.
Therefore, even if the cylindrical member 1 is left for a long period of time, the cylindrical member 1 is maintained in a healthy state without being cracked.
[0037]
Embodiment 2
In this example, as shown in FIG. 3, except for the first drawing process in the first embodiment, all of the multiple drawing processes (FIG. (C)) and the two DI processes (FIG. (D)). The enlarged diameter part 2 was formed. That is, in the drawing process of the intermediate material 8, the process was stopped immediately before the end of the opening of the intermediate material 8 was completed. Similarly, in the two DI processes, the process was stopped just before the opening end of the intermediate member 8 was completed.
[0038]
Thereby, also in the intermediate material 8 of each intermediate | middle stage, the enlarged diameter part 2 expanded more largely than the main-body part was formed in the opening edge part. Moreover, the longitudinal cross-sectional shape of each enlarged diameter part 2 was provided in the curved surface shape which has the center of curvature in the outward of each intermediate material 8. As shown in FIG. This cross-sectional shape could be obtained due to the influence of the cross-sectional shape of the die used for drawing or DI processing.
[0039]
In this case, the occurrence of time cracking can be sufficiently prevented even in the intermediate stage before the final DI processing. For example, this is particularly effective when there is a possibility of being left for a relatively long time, such as between drawing and DI processing.
In other respects, the same effects as those of the first embodiment can be obtained.
[0040]
Depending on the type of product, it may be necessary to remove the enlarged diameter portion 2. In this case, the diameter-enlarged portion 2 can be deleted after the cylindrical member 1 is provided with a measure for preventing cracking such as shot peening while the diameter-enlarged portion 2 is provided. Further, even when the enlarged diameter portion 2 can be left, it is of course possible to further enhance the effect of preventing the time cracking by performing shot peening.
[0041]
Embodiment 3
In this example, in order to evaluate the effect of the cylindrical member manufactured by the manufacturing method of the second embodiment, a test for confirming the occurrence of time cracking was performed together with the cylindrical member manufactured by the manufacturing method of the comparative example.
As shown in FIG. 4, the manufacturing method of the comparative example prepared a plate material 981 as a material made of austenitic stainless steel. Then, this was punched out into a disk-shaped blank and subjected to drawing to form a bottomed cylindrical intermediate member 98 ((b) in the figure).
[0042]
Next, as shown in FIG. 5C, the intermediate member 98 is subjected to drawing processing a plurality of times to generate induced martensite to ferromagnetize the whole, and to the cylindrical member 9 having a desired size. Finished. In the above drawing processing, the entire processing was performed including the opening end.
[0043]
Next, 87 cylindrical members 1 manufactured by the manufacturing method of the second embodiment and the cylindrical member 9 manufactured by the manufacturing method of the comparative example were left for 3 months, respectively. Then, after leaving it, the occurrence of cracking was investigated.
As a result of this test, in the case of the method of the comparative example, time cracking occurred in 45 (87%) of 87 pieces. On the other hand, no cracking occurred at all in the cylindrical member 1 according to the second embodiment.
From the above results, it can be seen that the cylindrical member according to the present invention is an excellent material in which time cracking is hardly caused.
[0044]
Embodiment 4
In this example, in order to further clarify the mechanism for preventing the time cracking by the enlarged diameter portion 2, the drawing was experimentally performed, and the residual stress state at each processing stage was measured.
Specifically, as shown in FIG. 5, the plate material 88 was drawn using a die 71 and a punch 72. Further, this drawing process was stopped halfway leaving a sufficient open end that did not pass through the die 71.
[0045]
Then, as shown in FIG. 6, in the vicinity of the opening end, each part of the flange part A before the bending process, the bending part B during the bending process, and the processing completed part C where the bending process is completed is cut into a ring shape. . Then, a part of the cut-out ring was cut, and it was observed whether the cut portion was in the mouth open state or the mouth closed state.
[0046]
FIG. 6 schematically shows the result. As shown in the figure, both the flange part A and the machining completion part C are in the state of tensile residual stress, with the initial outer diameters D ₁ and D ₃ expanding to D ₁₂ and D ₃₂ to open the mouth. I understand. On the other hand, it can be seen that the bent portion B is in a compressive residual stress state because the initial outer diameter D ₂ is reduced to D ₂₂ and the mouth is closed (spring go state).
[0047]
From these facts, in drawing processing, ironing processing or DI processing, as shown in FIG. 7, by performing processing so that the opening end portion stops at the position of the bending portion B, the stress state of the enlarged diameter portion 2 is changed. It can be seen that the compression residual stress state can be surely obtained.
[0048]
Further, as in the first embodiment, the enlarged diameter portion 2 has a longitudinal cross-sectional shape that is a curved surface having a center of curvature on the outside of the cylindrical member 1, that is, a convex shape toward the inside. The part 2 can be in the state of the bending part B described above. As a result, it can be seen that the expanded diameter portion 2 can be easily brought into a compressive residual stress state.
[0049]
Of course, a cylindrical member made of austenitic stainless steel obtained by the above embodiments can be used as a material of the composite magnetic member. That is, it is possible to obtain a composite magnetic member composed of a ferromagnetic portion made of martensite phase and a nonmagnetic portion made of austenite phase by applying heat treatment to a part of the obtained cylindrical member.
[0050]
Embodiment 5
In this example, the residual stress state of the expanded diameter portion 2 was evaluated in terms of the height and thickness of the expanded diameter portion.
That is, in the manufacturing process shown in Embodiment 1, the formation state of the enlarged diameter portion 2 in the last DI processing was changed, and the residual stress of the obtained enlarged diameter portion was measured. Specifically, in the case where the thickness (plate thickness) of the enlarged diameter portion is 1.2 mm and 2.0 mm, the height of the enlarged diameter portion is changed within the range of 0 to 5.3 mm, and the obtained enlarged diameter is obtained. The residual stress in the diameter portion was measured.
[0051]
The measurement result of the residual stress is shown in FIG. In the figure, the horizontal axis represents the height of the enlarged diameter portion (end face remaining amount L (mm: see FIG. 7)), and the vertical axis represents the residual stress (MPa) in the circumferential direction of the end face. At this time, if the residual stress is larger than 0, it means that it is in a tensile state, and if it is smaller than 0, it means that it is in a compressed state. The case where the thickness is 1.2 mm is indicated by the solid line E1, and the case where the thickness is 2.0 mm is indicated by the solid line E2. Further, for comparison, in the case where the enlarged diameter portion is not provided (L = 0), the residual stress when the final processing is drawing is indicated by reference symbol C1, and the residual stress when DI processing is indicated by reference symbol C2.
[0052]
As can be seen from the figure, when the diameter of the enlarged diameter portion is 2.0 mm, the height is in the range of 0.5 to 5.0 mm, and when the thickness of the enlarged diameter portion is 1.2 mm, In the range of 0.6 to 2.8 mm in height, a compressive residual stress state could be realized.
Further, it was also found that in the case where the diameter-expanded portion is not provided (C1, C2), it is difficult to make the residual stress in a compressed state regardless of whether the final processing is drawing processing or DI processing.
[0053]
From the above, when the plate thickness is 1.2 to 2.0 mm, the diameter of the enlarged portion is selected from the range of 0.5 to 5.0 mm so that the enlarged portion can be compressed to a desired level. It turns out that it can be set as a stress state.
In addition, as a processing range of the plate | board thickness of an enlarged diameter part, it is about 0.1-2.0 mm. As described above, the appropriate range of the height of the expanded portion varies depending on the thickness of the expanded portion, so the height of the expanded portion is appropriately selected according to the thickness of the expanded portion finally obtained. It is necessary to.
[0054]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a cylindrical member made of stainless steel and a method for manufacturing the same, which can reliably prevent the time cracking after the cylindrical member is molded.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a manufacturing process of a cylindrical member in Embodiment 1;
2 is a cross-sectional view of a cylindrical member in Embodiment 1. FIG.
3 is an explanatory view showing a manufacturing process of a cylindrical member in Embodiment 2. FIG.
4 is an explanatory view showing a manufacturing process of a cylindrical member in a comparative example of Embodiment 3; FIG.
FIG. 5 is an explanatory diagram showing a test method in Embodiment Example 4;
6 is an explanatory diagram showing a residual stress state in Embodiment Example 4. FIG.
7 is an explanatory diagram showing the shape of a cylindrical member in Embodiment 4. FIG.
FIG. 8 is an explanatory diagram showing a relationship between an end face remaining amount and an end face residual stress in Embodiment 5;
[Explanation of symbols]
1. . . Cylindrical member,
10. . . Body part,
2. . . Expanded part,
8). . . Intermediate material,

Claims

To produce an intermediate material of a cylindrical shape using a material made of austenitic stainless steel, then the intermediate member, drawing, when forming the cylindrical member by adding ironing or DI processing,
At least in the last machining, DI machining is performed, and in the last machining, the machining is stopped immediately before completion of machining of the opening end of the intermediate material, so that the opening end is expanded to a larger diameter than the main body. , Forming a widened portion formed as an end portion of a curved surface that is a convex shape in which at least the end portion has a cross-sectional shape inward, and the expanded diameter portion is brought into a compressive residual stress state,
The height of the enlarged diameter portion formed between the main body portion and the opening end is set to 0.5 to 5.0 mm,
And the manufacturing method of the cylindrical member which consists of austenitic stainless steel characterized by performing DI process so that the thickness of the said enlarged diameter part may be set to 0.1-2.0 mm.

The cylindrical member made of austenitic stainless steel according to claim 1, wherein the enlarged diameter portion is formed as a curved end portion having a center of curvature at least at an end portion of the cylindrical member. Production method.

3. The austenitic stainless steel according to claim 1, wherein a longitudinal cross-sectional shape of the enlarged diameter portion is provided in a curved shape having a center of curvature outside the cylindrical member over the entire enlarged diameter portion. A method for producing a cylindrical member.

The cylindrical member according to any one of claims 1 to 3, wherein the cylindrical member is made of an austenitic stainless steel that is induced martensitic transformed into a ferromagnetic material by the drawing, ironing, or DI processing. Manufacturing method of cylindrical member.

  A cylindrical member made of austenitic stainless steel, the opening end of the cylindrical member having a larger diameter than the main body, and at least the cross-sectional shape of the end is convex inward. It is formed as an end of a curved surface and has an enlarged diameter portion provided in a compressive residual stress state.
  The height of the enlarged diameter portion formed between the main body portion and the opening end is set to 0.5 to 5.0 mm,
  A cylindrical member made of austenitic stainless steel, which is DI processed so that the thickness of the expanded diameter portion is 0.1 to 2.0 mm.

6. The cylindrical member made of austenitic stainless steel according to claim 5, wherein a longitudinal cross-sectional shape of the enlarged diameter portion is a curved surface having a center of curvature outward of the cylindrical member.