JP3731815B2

JP3731815B2 - Phosphor bronze and heat treatment method thereof

Info

Publication number: JP3731815B2
Application number: JP2002160056A
Authority: JP
Inventors: 太郎木村; 輝夫菅沼; 義輝西
Original assignee: 日鉱金属加工株式会社
Priority date: 2001-05-31
Filing date: 2002-05-31
Publication date: 2006-01-05
Anticipated expiration: 2022-05-31
Also published as: JP2003064459A

Description

【０００１】
【発明の属する技術分野】
本発明はりん青銅の熱処理に係り、特に、熱処理後の結晶粒を極めて微細にする技術に関する。
【０００２】
【従来の技術】
銅合金では結晶粒径が微細なほど高い降伏応力ないし耐力を得られることが知られている。たとえば、ホールペッチの関係によれば、結晶粒径の逆数の平方根と降伏応力ないし耐力とは比例関係にあることが知られている。
【０００３】
一般に、銅合金は、その製造工程で焼鈍が施され、再結晶を目的として行われる焼鈍（中間焼鈍）によって結晶粒径が決定される。再結晶によって得られる結晶粒径の大きさは焼鈍温度の影響を受け、焼鈍温度が高い程再結晶粒は大きく成長することが知られている。また、このような焼鈍によって再結晶粒が成長する温度は再結晶温度と呼ばれ、その材料の融点の概ね１／２程度の温度が採用される。
【０００４】
銅合金板条の工業的な製造プロセスでは、一般に、溶解鋳造工程および熱間圧延又は均質化焼鈍工程の後、必要に応じて圧延、焼鈍を繰り返して所定の素条をつくり、この素条に中間焼鈍によって再結晶処理を施した後、更に調質圧延、脱脂、調質焼鈍をして製品特性を付与している。
【０００５】
本発明では、中間焼鈍における再結晶の挙動に注目した。
一般に、再結晶処理を行うための熱処理は、材料の昇温と均熱保持からなり、その際得られる再結晶粒径は、均熱時の炉温と保持時間を選択することで調整されてきた。所定の再結晶粒径を得るための炉温と保持時間は、合金組成、加工前の結晶粒径等によって影響を受けることから、通常はそのような条件を加味して適宜選択される。
【０００６】
このような銅合金板条の再結晶焼鈍では、均熱時の炉温は５００℃以上に設定されることが多い。これは、これまで銅合金板条のすべての部分で再結晶組織を得るためと結晶粒を成長させるために、材料を高温で一定に保つことが必要と考えられたことが主な原因であり、未再結晶領域が残らないように高温領域で熱処理するように条件が設定されていたためと考えられる。
【０００７】
一方、材料の昇温は、均熱保持における熱処理を効率的に行うためのものとされ、材料の温度を速やかに均熱温度に昇温することぐらいにしか意識されていなかった。このため、再結晶粒径は、専ら均熱温度と保持時間によって制御されていた。
【０００８】
【発明が解決しようとする課題】
しかしながら、従来の熱処理方法で得られる再結晶粒径は数μｍ以上あるため、そのままでは耐力等が不充分であり、近年の小型化、薄肉化された電子部品における製品特性を満足することができなかった。また、従来の熱処理方法においては、再結晶を目的とする中間焼鈍工程の後、調質圧延、脱脂、焼鈍等を施すことで特性を調整し、これによって、製品に特性を付与することが必要であった。
【０００９】
本発明は、りん青銅の熱処理に関するものであり、特に、熱処理後のりん青銅板条の平均再結晶粒径を、０．９μｍ以下に微細化することを目的とするものである。また、本発明は、りん青銅板条の微細な結晶粒生成を熱処理によって実現することで、従来の製造工程の内、中間焼鈍よりも後の工程である調質圧延、脱脂、調質焼鈍等の工程を省略することを可能とし、低コストなりん青銅の板条を提供することを目的としている。
【００１０】
【課題を解決するための手段】
前述のように、焼鈍温度が高い程再結晶粒は大きく成長する。しかしながら、再結晶粒を細かくするために焼鈍温度を低く設定すると、材料が未再結晶のまま残留したり、再結晶が生じても部分的になってしまう。なお、本発明では、そのような完全に再結晶していない全ての組織状態を未再結晶と称する。本発明者等は、焼鈍の際の未再結晶の残留を防止すべく研究を重ねた結果、材料を急速加熱すると焼鈍（再結晶）に必要な処理温度が低下することを見い出した。また、本発明者等は、処理温度まで加熱した材料を急冷することにより、極めて短時間の内に微細な再結晶組織が得られることを見い出した。
【００１１】
本発明のりん青銅の熱処理方法は、上記知見に基づいてなされたもので、最終熱処理において錫を５．５〜１１．０質量％、りんを０．０３〜０．３５質量含有し、残部銅および不可避不純物からなるりん青銅を４０℃／秒以上の昇温速度で急速加熱することにより再結晶温度を低下させ、上記りん青銅が再結晶温度以上であって５６２℃以下の処理温度に達した直後に１５０℃／秒以上の冷却速度で急冷することにより再結晶してなる平均再結晶粒径を０．９μｍ以下にすることを特徴としている。
【００１２】
本発明によれば、再結晶のための処理温度が低温であるため、粒成長が遅く粗大化が防止される。また、材料が処理温度に達した後に急冷するから、結晶粒の粗大化がさらに阻まれる。したがって、本発明では極めて微細な再結晶粒を得ることができる。ここで、急冷とは、シリコーンオイルや焼入れ油等の液体冷媒、無酸化ガスの噴流等の気体冷媒もしくはそれらの混合ミスト、あるいはロール等の固体冷媒に材料を接触させて行う冷却をいう。その場合のりん青銅の冷却速度は、１５０℃／秒以上であることが望ましい。また、材料が処理温度に達したら、その温度で保持せずに間髪を入れずに急冷することが望ましい。材料が高温で保持されると結晶粒の成長が生じ、目的とする０．９μｍ以下の微細な再結晶粒径を得ることが困難となる。
【００１３】
材料を確実に再結晶させるには、りん青銅の加熱の到達温度（処理温度）と昇温速度が重要な因子である。到達温度が低い場合には昇温速度を速くする必要がある。本発明者等の検討によれば、急速加熱におけるりん青銅の昇温速度を４０℃／秒以上とすれば、到達温度が５００℃程度で再結晶がほぼ完全に生じることが判明している。よって、昇温速度は４０℃／秒以上とした。また、りん青銅の再結晶温度の範囲は、３５０〜５００℃であるが、昇温速度が６０℃／秒以上であればその温度範囲で確実に再結晶組織を生じさせることができ、さらに９０℃／秒以上であれば３００℃未満の到達温度であっても再結晶組織を得ることができる。
【００１４】
また、熱処理前の金属板条の加工度も重要な因子である。冷間加工によって再結晶の駆動力となる加工歪みを生じさせることで、再結晶の発生を促すためである。具体的には熱処理前に行われる加工の加工度は７０％以上であることが望ましい。このような強加工を行うことにより、再結晶の駆動力となる加工歪を大きくし、再結晶核の発生を促して結晶粒をさらに微細化することができる。また、これ以下の加工度では、加熱速度を高めても未再結晶部分が残留してしまい、従来のように高温で保持して結晶粒を成長させる必要が生じる。この場合には結果的に微細な結晶粒を得ることが困難となる。熱処理前に行われる加工の加工度は８０％以上であればさらに好適である。なお、この場合における加工度とは、加工前の板条の厚さをｔ_ｏ、加工後の板条の厚さをｔとし、（ｔ_ｏ−ｔ）／ｔ_ｏ×１００（％）である。また、上記加工度で行う加工は、最終の冷間加工である。
【００１５】
上記のような強加工による冷間加工前の平均再結晶粒径は、５μｍ以下であることが望ましい。最終の冷間加工前の再結晶粒径を微細化することにより、強加工に大きな歪と相俟って材料内部に蓄積されるエネルギーを増大させることができ、次の急速加熱および急速冷却によってさらに微細な結晶粒を均一に得ることができる。
【００１６】
以上のように、本発明では、上記のような熱処理方法を採用することによって、平均再結晶粒径が０．９μｍ以下という従来かつてなかった超微細結晶粒のりん青銅を得ることができる。図１はバネ用りん青銅における再結晶粒径と０．２％耐力との関係を示すものであり、図中の実線はホールペッチの関係を示す。図１（表１）に示すように、平均再結晶粒径が０．９μｍ以下の場合には、０．２％耐力が４００ＭＰａ以上、あるいは５００ＭＰａ以上という従来の焼鈍上がりのりん青銅では到底考えられなかった高い強度を示す。また、平均再結晶粒径を０．９μｍ以下にすることで、最小曲げ半径比が１以下の高曲げ性を実現することが可能である。
【００１７】
よって、本発明のりん青銅は、平均再結晶粒径が０．９μｍ以下であることを特徴とし、さらに好適には、０．２％耐力が４００ＭＰａ以上で、かつ最小曲げ半径比が１以下であることを特徴とするものである。なお、本発明において最小曲げ半径比（以下、ＭＢＲ／ｔと表記する）とは、Bad Way方向で９０°Ｗ曲げ試験を実施し、その際に試料表面から割れが発生しない最小の曲げ半径（ＭＢＲ）と、試料の板厚（ｔ）との比である。また、平均再結晶粒径は望ましくは０．５μｍ以下が良い。
【００１８】
本発明のりん青銅は、特に、錫を７．０〜９．０質量％、りんを０．０３〜０．３５質量含有し、残部銅および不可避不純物からなるものが望ましい。
【００１９】
図１において、実線は数式：「ＹＳ＝８．５／（ＧＳ）^１／２＋１５３」で表すことができ、種々の平均粒径を有する８質量％錫を含有するりん青銅の０．２％耐力を図１にプロットしたところ、いずれもホールペッチの関係を満足することが確認された。本発明のりん青銅の好ましい態様は、ホールペッチの関係に沿うものであり、図１における破線で囲まれた領域に入るものである。すなわち、本発明では、０．２％耐力をＹＳ（ＭＰａ）、平均再結晶粒径をＧＳ（ｍｍ）としたときに、下記式を満足することを好ましい態様としている。
【００２０】
【数２】
８．５／（ＧＳ）^１／２＋５３≦ＹＳ≦８．５／（ＧＳ）^１／２＋２５３
【００２１】
次に、本発明を実施するための熱処理装置としては、りん青銅を４０℃／秒以上の昇温速度で加熱する加熱手段と、加熱されたりん青銅を１５０℃／秒以上の冷却速度で冷却する冷却手段とを備えるものを用いることができる。このような熱処理装置によれば、極めて微細な結晶粒を有するりん青銅を製造することができるのは勿論のこと、急速加熱後に直ちに冷却するから、炉長の短いコンパクトな熱処理装置とすることができる。
【００２２】
本発明における加熱手段としては、誘導加熱、レーザー加熱、ロール加熱等の急速加熱に適した加熱方法を用いることが望ましい。ロール加熱とは、複数のロールで材料を挟み込み、ロール間に通電して材料自体のジュール熱で加熱する方法である。また、冷却手段としては、シリコーンオイルや焼入れ油等の液体冷媒を充填した冷却槽を用いたり、無酸化ガスの噴流等の気体冷媒、あるいはロール等の固体冷媒を利用することができる。この場合、必要に応じて、加熱手段によって加熱された材料を冷却槽に投入する搬送装置や、材料の温度を測定する温度検出装置、あるいは、液体冷媒を循環して冷却する循環手段を備えることができる。
【００２３】
【実施例】
［第１実施例］
以下、本発明の第１実施例を説明する。
Ｓｎ：８．０％（質量％、以下同じ）、Ｐ：０．０３〜０．３５％、Ｚｎ：０．２０％以下、Ｆｅ：０．１０％以下、Ｐｂ：０．０５％以下、残部：Ｃｕであって、Ｃｕ、Ｓｎ、およびＰを総量で９９．７％以上含有するりん青銅の加工前の平均再結晶粒径が５μｍ以下の条を作製した。これに焼鈍前加工として７４％以上で冷間加工を加えて厚さ０．３ｍｍの素条を得た。
【００２４】
この素条を、表１に示す到達温度と加熱速度で加熱し、材料が到達温度に達したら水ミストを噴射して急冷した。この熱処理を施すことにより得られた試験片について、組織に影響を与えないように電解研磨で薄膜化し、ＴＥＭ（Transmission Electron Microscope）観察によって組織を検鏡した。検鏡で得られた組織から切断法によって平均再結晶粒径を求めた。その結果を表１に示す。また、得られた試験片について引張試験を行い、その０．２％耐力を調査した。なお、この引張試験では、長さ：２０ｍｍ（標点間距離：１０ｍｍ）、幅：１．５ｍｍ、厚さ：０．３ｍｍの試験片を用い、この試験片を圧延方向と平行な方向に２ｍｍ／分の引張速度で引っ張った。また、Bad Way方向（曲げ軸が圧延方向に平行方向）で９０°Ｗ曲げ試験（ＪＩＳＨ３１１０）を行い、最小曲げ半径比ＭＢＲ／ｔ（割れの発生しない最小曲げ半径／試験片厚さ）を求めた。このＷ曲げ試験は、長さ：５０ｍｍ、幅：１０ｍｍ、板厚：０．３ｍｍの試験片を用い、５ｔｏｎの試験荷重で行った。それらの結果も併せて表１に示す。
【００２５】
【表１】

【００２６】
表１に示すように、本発明例では加熱速度が大きいため、平均再結晶粒径は全て０．９μｍ以下となった。また、図１は、数式：「ＹＳ＝８．５／（ＧＳ）^１／２＋１５３」の実線を引き、本発明例および比較例の０．２％耐力をプロットしたものであるが、図１から判るように、いずれもホールペッチの関係を満足し、本発明例では４００ＭＰａ以上の０．２％耐力を得ることができた。また、本発明例では最小曲げ半径比がいずれも１以下となった。
【００２７】
これに対して、比較例では加熱速度が小さいため、到達温度が低いものでは再結晶が不完全で未再結晶組織を呈した。また、未再結晶組織では延性が低く、このため最小曲げ半径比は２以上となった。到達温度が高い比較例では、再結晶は完全に行われたが、加熱速度が小さいために結晶粒が粗大化した。また、その結果、図１に示すように、ホールペッチの関係により０．２％耐力がいずれも小さくなった。さらに、表１に示す結果から以下の点が明らかとなった。
【００２８】
〔１〕これまで再結晶組織が得られなかった低い到達温度であっても、加熱速度を大きくすることで再結晶組織を得ることができる。
〔２〕小さい加熱速度で高温に到達させられる再結晶組織よりも、加熱速度が大きく到達温度が低い再結晶組織の方がより微細な結晶粒を得ることができる。
【００２９】
したがって、微細な再結晶組織を安定して得るためには、未再結晶組織である加工組織を再結晶組織に変化させる熱処理を、短時間の内に完了させることが必要である。また、生成した再結晶粒の成長を抑制してより微細な再結晶組織を得るために、到達温度を低くするとともに加熱速度を大きくすることが望ましい。
【００３０】
加えて、従来の熱処理方法では、再結晶焼鈍を施したままでは耐力等が低く、そのままでは製品特性を満足することができなかった。このため、従来では、図２（Ａ）に示すように、再結晶焼鈍の後に調質圧延、脱脂、調質焼鈍を行うことで製品に特性を付与することが必要であった。これに対して、上記実施例では、再結晶焼鈍を行うだけで耐力等の特性を付与することができるので、図２（Ｂ）に示すように、再結晶焼鈍以降の処理が不要となる。
【００３１】
［第２実施例］
第１実施例と同じ条件で厚さ０．３ｍｍの素条を作製し、この素条を、表２に示す到達温度と加熱速度で加熱し、材料が到達温度に達したら水ミストを噴射し、表２に示す冷却速度で冷却した。この熱処理を施すことにより得られた試験片について、組織に影響を与えないように電解研磨で薄膜化し、ＴＥＭ観察によって組織を検鏡した。検鏡で得られた平均再結晶粒径を表２に示す。表２に示すように、冷却速度が１５０℃／秒以上の場合には、０．９μｍ以下の平均粒径を得ることができた。以上により、到達温度に達した後の冷却速度は１５０℃／秒以上必要であることが確認された。
【００３２】
【表２】

【００３３】
［第３実施例］
最終の冷間加工を表３に示す加工度で行った以外は第１実施例と同じ条件で厚さ０．３ｍｍの素条を作製し、この素条を、表３に示す到達温度と加熱速度で加熱し、材料が到達温度に達したら水ミストを噴射し急冷した。この熱処理を施すことにより得られた試験片について、組織に影響を与えないように電解研磨で薄膜化し、ＴＥＭ観察によって組織を検鏡した。検鏡で得られた平均再結晶粒径を表３に示す。表３に示すように、到達温度が低いものでは未再結晶となり、到達温度が高いものでは結晶粒が粗大化した。この結果と第１実施例の結果から、最終の冷間加工の加工度は７０％以上が望ましいことが確認された。
【００３４】
【表３】

【００３５】
［第４実施例］
表４に示す最終の冷間加工前の平均再結晶粒径を有する条を用いた以外は第１実施例と同じ条件で厚さ０．３ｍｍの素条を作製し、この素条を、表４に示す到達温度と加熱速度で加熱し、材料が到達温度に達したら水ミストを噴射して急冷した。この熱処理を施すことにより得られた試験片について、組織に影響を与えないように電解研磨で薄膜化し、ＴＥＭ観察によって組織を検鏡した。検鏡で得られた平均再結晶粒径を表４に示す。表４に示すように、最終冷間加工前の平均再結晶粒径が５μｍ以下の場合には、０．９μｍ以下の平均再結晶粒径が得られた。これに対して、最終冷間加工前の再結晶粒径が５μｍを超える場合には、到達温度が低いと未再結晶となり、到達温度が高いと結晶粒が粗大化した。
【００３６】
【表４】

【００３７】
【発明の効果】
以上説明したように本発明によれば、再結晶粒径を０．９μｍ以下に微細化することが可能であり、強度等の特性に優れたりん青銅板条を得ることが可能となり、電子機器の小型化、薄肉化に大きく寄与することができるとともに、従来のりん青銅板条の製造工程における調質圧延以降の工程を省略することで低コスト化が可能となる。
【図面の簡単な説明】
【図１】再結晶粒径と０．２％耐力との関係を示す線図である。
【図２】（Ａ）は従来のりん青銅製品の製造工程を示す図、（Ｂ）は本発明を適用することで省略が可能となる製造工程を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to heat treatment of phosphor bronze , and more particularly to a technique for making crystal grains after heat treatment extremely fine.
[0002]
[Prior art]
It is known that a copper alloy can obtain higher yield stress or yield strength as the crystal grain size becomes finer. For example, according to the Hall Petch relationship, it is known that the square root of the reciprocal of the crystal grain size is proportional to the yield stress or proof stress.
[0003]
Generally, a copper alloy is annealed in the manufacturing process, and the crystal grain size is determined by annealing (intermediate annealing) performed for the purpose of recrystallization. It is known that the crystal grain size obtained by recrystallization is affected by the annealing temperature, and the higher the annealing temperature, the larger the recrystallized grains grow. In addition, the temperature at which recrystallized grains grow by such annealing is called the recrystallization temperature, and a temperature of about ½ of the melting point of the material is adopted.
[0004]
In an industrial manufacturing process for copper alloy strips, in general, after a melt casting process and hot rolling or homogenization annealing process, rolling and annealing are repeated as necessary to form a predetermined strip, After recrystallization treatment by intermediate annealing, product properties are imparted by temper rolling, degreasing, and temper annealing.
[0005]
In the present invention, attention is paid to the behavior of recrystallization in the intermediate annealing.
In general, the heat treatment for performing recrystallization treatment consists of raising the temperature of the material and holding the soaking, and the recrystallized grain size obtained at that time has been adjusted by selecting the furnace temperature and holding time during soaking. It was. Since the furnace temperature and holding time for obtaining a predetermined recrystallized grain size are affected by the alloy composition, crystal grain size before processing, and the like, they are usually selected as appropriate in consideration of such conditions.
[0006]
In such recrystallization annealing of copper alloy strips, the furnace temperature during soaking is often set to 500 ° C. or higher. This is mainly due to the fact that until now it was necessary to keep the material constant at high temperatures in order to obtain a recrystallized structure in all parts of the copper alloy sheet and to grow grains. This is presumably because the conditions were set so that the heat treatment was performed in the high temperature region so that no unrecrystallized region remained.
[0007]
On the other hand, the temperature rise of the material is intended to efficiently perform the heat treatment in the soaking, and it was only conscious of raising the temperature of the material to the soaking temperature quickly. For this reason, the recrystallized grain size was exclusively controlled by the soaking temperature and the holding time.
[0008]
[Problems to be solved by the invention]
However, since the recrystallized grain size obtained by the conventional heat treatment method is several μm or more, the proof stress is insufficient as it is, and the product characteristics in the recent downsized and thinned electronic parts can be satisfied. There wasn't. In addition, in the conventional heat treatment method, after the intermediate annealing step for recrystallization, it is necessary to adjust the properties by applying temper rolling, degreasing, annealing, etc., thereby imparting the properties to the product. Met.
[0009]
The present invention relates to heat treatment of phosphor bronze , and in particular, aims to reduce the average recrystallized grain size of the phosphor bronze strip after heat treatment to 0.9 μm or less. In addition, the present invention realizes fine crystal grain generation of phosphor bronze sheet strip by heat treatment, and in the conventional manufacturing process, temper rolling, degreasing, temper annealing, etc., which are steps after intermediate annealing, etc. The object of the present invention is to provide a low cost phosphor bronze strip.
[0010]
[Means for Solving the Problems]
As described above, the higher the annealing temperature, the larger the recrystallized grains grow. However, if the annealing temperature is set low in order to make the recrystallized grains fine, the material remains unrecrystallized or becomes partially even if recrystallization occurs. In the present invention, all such structural states that are not completely recrystallized are referred to as non-recrystallized. As a result of repeated studies to prevent the remaining of unrecrystallized during annealing, the present inventors have found that the processing temperature required for annealing (recrystallization) decreases when the material is rapidly heated. In addition, the present inventors have found that a fine recrystallized structure can be obtained within an extremely short time by rapidly cooling a material heated to a processing temperature.
[0011]
The heat treatment method for phosphor bronze according to the present invention was made based on the above findings, and contained 5.5 to 11.0 mass% tin and 0.03 to 0.35 mass phosphorus in the final heat treatment, and the remaining copper. The phosphor bronze composed of unavoidable impurities is rapidly heated at a temperature rising rate of 40 ° C./second or more to lower the recrystallization temperature, and the phosphor bronze reaches a processing temperature of 562 ° C. or less above the recrystallization temperature. Immediately after that, the average recrystallized grain size formed by recrystallization by quenching at a cooling rate of 150 ° C./second or more is set to 0.9 μm or less.
[0012]
According to the present invention, since the processing temperature for recrystallization is low, grain growth is slow and coarsening is prevented. Further, since the material is rapidly cooled after reaching the processing temperature, the coarsening of the crystal grains is further prevented. Therefore, in the present invention, extremely fine recrystallized grains can be obtained. Here, the rapid cooling means cooling performed by bringing a material into contact with a liquid refrigerant such as silicone oil or quenching oil, a gaseous refrigerant such as a jet of non-oxidizing gas or a mixed mist thereof, or a solid refrigerant such as a roll. In this case, the cooling rate of phosphor bronze is preferably 150 ° C./second or more. Also, when the material reaches the processing temperature, it is desirable to rapidly cool without holding it at that temperature and without putting in hair. When the material is held at a high temperature, crystal grains grow, making it difficult to obtain the desired fine recrystallized grain size of 0.9 μm or less.
[0013]
In order to reliably recrystallize the material, the ultimate temperature (treatment temperature) of the phosphor bronze heating and the heating rate are important factors. When the ultimate temperature is low, it is necessary to increase the heating rate. According to the study by the present inventors, it has been found that if the temperature rise rate of phosphor bronze in rapid heating is set to 40 ° C./second or more, recrystallization occurs almost completely at an ultimate temperature of about 500 ° C. Therefore, the temperature increase rate was set to 40 ° C./second or more. Further, the recrystallization temperature range of phosphor bronze is 350 to 500 ° C. However, if the rate of temperature rise is 60 ° C./second or more, a recrystallized structure can be reliably generated in that temperature range, and 90 ° C. A recrystallized structure can be obtained even at a temperature lower than 300 ° C. if it is at least ° C./second.
[0014]
The degree of processing of the metal strip before heat treatment is also an important factor. This is because the generation of recrystallization is promoted by generating a working strain that becomes a driving force for recrystallization by cold working. Specifically, the degree of processing performed before the heat treatment is desirably 70% or more. By performing such strong processing, it is possible to increase the processing strain that is the driving force for recrystallization, promote the generation of recrystallization nuclei, and further refine the crystal grains. Further, if the degree of processing is less than this, the non-recrystallized portion remains even if the heating rate is increased, and it is necessary to grow the crystal grains while maintaining at a high temperature as in the conventional case. In this case, it becomes difficult to obtain fine crystal grains as a result. More preferably, the degree of processing performed before the heat treatment is 80% or more. Note that the working ratio in this case, the thickness of _{t o} the sheet-metal strip prior to processing, the thickness of the sheet-metal strip after processing and _t, is _{(t o -t) / t o} × 100 (%) . In addition, the processing performed at the above processing degree is the final cold processing.
[0015]
It is desirable that the average recrystallized grain size before the cold working by the strong working as described above is 5 μm or less. By refining the recrystallized grain size before the final cold working, the energy accumulated inside the material can be increased in combination with large strains in strong working. Furthermore, fine crystal grains can be obtained uniformly.
[0016]
As described above, in the present invention, by adopting the heat treatment method as described above, it is possible to obtain phosphor bronze having an ultrafine crystal grain having an average recrystallized grain size of 0.9 μm or less, which has never been before. FIG. 1 shows the relationship between the recrystallized grain size and the 0.2% proof stress in phosphor bronze for springs, and the solid line in the drawing shows the relationship of Hall Petch. As shown in FIG. 1 (Table 1) , when the average recrystallized grain size is 0.9 μm or less, conventional phosphor bronze with 0.2% proof stress of 400 MPa or more, or 500 MPa or more is considered to be High strength that was not achieved. Further, by setting the average recrystallized grain size to 0.9 μm or less, it is possible to realize high bendability with a minimum bending radius ratio of 1 or less.
[0017]
Therefore, the phosphor bronze of the present invention is characterized in that the average recrystallization grain size is 0.9 μm or less, and more preferably, the 0.2% proof stress is 400 MPa or more and the minimum bending radius ratio is 1 or less. It is characterized by being. In the present invention, the minimum bend radius ratio (hereinafter referred to as MBR / t) is the minimum bend radius (in which a 90 ° W bend test is performed in the Bad Way direction and cracks do not occur from the sample surface at that time. It is the ratio between the MBR) and the plate thickness (t) of the sample. The average recrystallization grain size is desirably 0.5 μm or less.
[0018]
In particular, the phosphor bronze of the present invention preferably contains 7.0 to 9.0 % by mass of tin and 0.03 to 0.35% by mass of phosphorus, and is composed of the remaining copper and inevitable impurities .
[0019]
In FIG. 1, the solid line can be expressed by the formula: “YS = 8.5 / (GS) ^1/2 +153”, 0.2% of phosphor bronze containing 8% by mass tin having various average particle diameters. When the proof stress was plotted in FIG. 1, it was confirmed that all satisfied the Hall Petch relationship. A preferred embodiment of the phosphor bronze according to the present invention is in line with the Hall Petch relationship and enters the region surrounded by the broken line in FIG. That is, in the present invention, when the 0.2% proof stress is YS (MPa) and the average recrystallized grain size is GS (mm), it is preferable to satisfy the following formula.
[0020]
[Expression 2]
8.5 / (GS) ^1/2 + 53 ≦ YS ≦ 8.5 / (GS) ^1/2 +253
[0021]
Then, as a heat treatment apparatus for carrying out the present invention, a heating means for heating of phosphor bronze of 40 ° C. / sec or more heating rate, cooling at the heated phosphor bronze of 0.99 ° C. / sec or more cooling rate The thing provided with the cooling means to do can be used. According to such a heat treatment apparatus, it is possible to produce phosphor bronze having extremely fine crystal grains, as well as cooling immediately after rapid heating, so that a compact heat treatment apparatus with a short furnace length can be obtained. it can.
[0022]
As the heating means in the present invention, it is desirable to use a heating method suitable for rapid heating such as induction heating, laser heating, roll heating and the like. The roll heating is a method in which a material is sandwiched between a plurality of rolls and energized between the rolls to heat with the Joule heat of the material itself. As the cooling means, a cooling tank filled with a liquid refrigerant such as silicone oil or quenching oil, a gas refrigerant such as a jet of non-oxidizing gas, or a solid refrigerant such as a roll can be used. In this case, if necessary, it is provided with a conveying device for feeding the material heated by the heating means into the cooling tank, a temperature detecting device for measuring the temperature of the material, or a circulating means for circulating and cooling the liquid refrigerant. Can do.
[0023]
【Example】
[First embodiment]
The first embodiment of the present invention will be described below.
Sn: 8.0% (mass%, the same shall apply hereinafter), P: 0.03 to 0.35%, Zn: 0.20% or less, Fe: 0.10% or less, Pb: 0.05% or less, balance : A strip having an average recrystallized grain size before processing of phosphor bronze containing 99.7% or more of Cu, Sn, and P in a total amount was prepared. This was cold worked at 74% or more as a pre-annealing process to obtain a strip with a thickness of 0.3 mm.
[0024]
This strip was heated at the ultimate temperature and heating rate shown in Table 1, and when the material reached the ultimate temperature, water mist was jetted to quench. The test piece obtained by performing this heat treatment was thinned by electropolishing so as not to affect the structure, and the structure was examined by TEM (Transmission Electron Microscope) observation. The average recrystallized grain size was determined by a cutting method from the structure obtained with a microscope. The results are shown in Table 1. Moreover, the tensile test was done about the obtained test piece, and the 0.2% yield strength was investigated. In this tensile test, a test piece having a length of 20 mm (distance between gauge points: 10 mm), a width of 1.5 mm, and a thickness of 0.3 mm was used, and the test piece was 2 mm in a direction parallel to the rolling direction. It was pulled at a pulling speed of / min. In addition, a 90 ° W bending test (JIS H 3110) was performed in the Bad Way direction (the bending axis was parallel to the rolling direction), and the minimum bending radius ratio MBR / t (minimum bending radius at which cracks did not occur / test specimen thickness). Asked. This W bending test was performed using a test piece having a length of 50 mm, a width of 10 mm, and a plate thickness of 0.3 mm with a test load of 5 tons. The results are also shown in Table 1.
[0025]
[Table 1]

[0026]
As shown in Table 1, since the heating rate was high in the examples of the present invention, the average recrystallized grain size was all 0.9 μm or less. Further, FIG. 1 is a graph in which the solid line of the formula: “YS = 8.5 / (GS) ^1/2 +153” is drawn and the 0.2% proof stress of the present invention example and the comparative example is plotted. As can be seen from the graph, all satisfy the Hall Petch relationship, and in the present invention example, a 0.2% proof stress of 400 MPa or more could be obtained. In the examples of the present invention, the minimum bending radius ratio was 1 or less.
[0027]
On the other hand, in the comparative example, since the heating rate was low, recrystallization was incomplete and a non-recrystallized structure was exhibited at a low ultimate temperature. Further, the non-recrystallized structure has low ductility, and therefore the minimum bending radius ratio is 2 or more. In the comparative example having a high ultimate temperature, recrystallization was performed completely, but the crystal grains became coarse due to the low heating rate. As a result, as shown in FIG. 1, the 0.2% proof stress was reduced due to the Hall Petch relationship. Furthermore, the following points were clarified from the results shown in Table 1.
[0028]
[1] A recrystallized structure can be obtained by increasing the heating rate even at a low temperature that has not been obtained so far.
[2] Finer crystal grains can be obtained in a recrystallized structure having a higher heating rate and a lower reached temperature than a recrystallized structure that can reach a high temperature at a low heating rate.
[0029]
Therefore, in order to stably obtain a fine recrystallized structure, it is necessary to complete the heat treatment for changing the processed structure, which is an unrecrystallized structure, to a recrystallized structure within a short time. Moreover, in order to suppress the growth of the generated recrystallized grains and obtain a finer recrystallized structure, it is desirable to lower the ultimate temperature and increase the heating rate.
[0030]
In addition, in the conventional heat treatment method, the proof stress is low if recrystallization annealing is performed, and the product characteristics cannot be satisfied as it is. For this reason, conventionally, as shown in FIG. 2 (A), it has been necessary to impart characteristics to the product by performing temper rolling, degreasing, and temper annealing after recrystallization annealing. On the other hand, in the above-described embodiment, since characteristics such as proof stress can be imparted only by performing recrystallization annealing, as shown in FIG. 2B, processing after recrystallization annealing becomes unnecessary.
[0031]
[Second Embodiment]
A strip having a thickness of 0.3 mm was prepared under the same conditions as in the first example, and the strip was heated at the ultimate temperature and heating rate shown in Table 2, and water mist was injected when the material reached the ultimate temperature. Cooling was performed at a cooling rate shown in Table 2. The test piece obtained by performing this heat treatment was thinned by electrolytic polishing so as not to affect the structure, and the structure was examined by TEM observation. Table 2 shows the average recrystallized grain size obtained by the speculum. As shown in Table 2, when the cooling rate was 150 ° C./second or more, an average particle size of 0.9 μm or less could be obtained. From the above, it was confirmed that the cooling rate after reaching the ultimate temperature needs to be 150 ° C./second or more.
[0032]
[Table 2]

[0033]
[Third embodiment]
A strip with a thickness of 0.3 mm was prepared under the same conditions as in the first example except that the final cold working was performed at the working degree shown in Table 3, and this strip was heated to the ultimate temperature and heating shown in Table 3 Heating was performed at a speed, and when the material reached the ultimate temperature, water mist was sprayed to quench the material. The test piece obtained by performing this heat treatment was thinned by electrolytic polishing so as not to affect the structure, and the structure was examined by TEM observation. Table 3 shows the average recrystallized grain size obtained by the speculum. As shown in Table 3, when the temperature reached was low, it was not recrystallized, and when the temperature reached was high, the crystal grains became coarse. From this result and the result of the first example, it was confirmed that the final cold working degree is desirably 70% or more.
[0034]
[Table 3]

[0035]
[Fourth embodiment]
A strip having a thickness of 0.3 mm was prepared under the same conditions as in the first example except that strips having an average recrystallized grain size before the final cold working shown in Table 4 were used. Heating was performed at the ultimate temperature and heating rate shown in FIG. 4, and when the material reached the ultimate temperature, water mist was injected to quench the material. The test piece obtained by performing this heat treatment was thinned by electrolytic polishing so as not to affect the structure, and the structure was examined by TEM observation. Table 4 shows the average recrystallized grain size obtained by the speculum. As shown in Table 4, when the average recrystallized grain size before final cold working was 5 μm or less, an average recrystallized grain size of 0.9 μm or less was obtained. On the other hand, when the recrystallized grain size before the final cold working exceeds 5 μm, unrecrystallized when the ultimate temperature is low, and the crystal grains become coarse when the ultimate temperature is high.
[0036]
[Table 4]

[0037]
【The invention's effect】
As described above, according to the present invention, the recrystallized grain size can be reduced to 0.9 μm or less, and a phosphor bronze sheet having excellent properties such as strength can be obtained. It can greatly contribute to the downsizing and thinning of the equipment, and the cost can be reduced by omitting the steps after the temper rolling in the conventional manufacturing process of the phosphor bronze sheet strip.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between recrystallized grain size and 0.2% yield strength.
FIGS. 2A and 2B are diagrams showing a manufacturing process of a conventional phosphor bronze product, and FIG. 2B is a diagram showing a manufacturing process that can be omitted by applying the present invention.

Claims

In the final heat treatment, phosphor bronze containing 5.5 to 11.0 % by mass of tin, 0.03 to 0.35% by mass of phosphorus, and the balance copper and inevitable impurities is rapidly heated at a heating rate of 40 ° C./second or more. The phosphor bronze is recrystallized by quenching at a cooling rate of 150 ° C./second or more immediately after the phosphor bronze reaches a treatment temperature of 562 ° C. or less. A phosphor bronze heat treatment method characterized in that the average recrystallized grain size is 0.9 μm or less.

The phosphor bronze heat treatment method according to claim 1, wherein the temperature rise rate is 60 ° C./second or more, and the final temperature of the final heat treatment is 350 to 500 ° C.

2. The method for heat treating phosphor bronze according to claim 1, wherein the temperature rise rate is 90 ° C./second or more, and the final temperature of the final heat treatment is less than 300 ° C. 3.

The method for heat-treating phosphor bronze according to any one of claims 1 to 3, wherein the phosphor bronze is cold-worked at a working degree of 70% or more before the final heat treatment.

The method for producing phosphor bronze according to claim 4, wherein an average recrystallized grain size before cold working is set to 5 μm or less.

Phosphor bronze heat-treated by the heat treatment method according to claim 1.

7. The phosphor bronze according to claim 6, comprising 7.0 to 9.0% by mass of tin, 0.03 to 0.35% by mass of phosphorus, and remaining copper and inevitable impurities .

8. The phosphor bronze according to claim 6, wherein 0.2% proof stress is YS (MPa) and an average recrystallized grain size is GS (mm), and the following formula is satisfied.
[Expression 1]
8.5 / (GS) ^1/2 + 53 ≦ YS ≦ 8.5 / (GS) ^1/2 +253

The phosphor bronze according to claim 6 or 7, wherein a 0.2% proof stress is 400 MPa or more and a minimum bending radius ratio by W bending is 1 or less.