JP3739485B2

JP3739485B2 - Heat treatment method for metal strip

Info

Publication number: JP3739485B2
Application number: JP14098696A
Authority: JP
Inventors: 次夫皆川; 圭祐八色
Original assignee: Dai Ichi High Frequency Co Ltd
Current assignee: Dai Ichi High Frequency Co Ltd
Priority date: 1996-05-10
Filing date: 1996-05-10
Publication date: 2006-01-25
Anticipated expiration: 2016-05-10
Also published as: JPH09302416A

Description

【０００１】
【発明の属する技術分野】
本発明は、Ｈ形鋼、Ｉ形鋼、鋼管、板材等の金属条材の熱処理方法に関し、特に長手方向に肉厚の異なる部分が混在する金属条材の熱処理方法に関する。
【０００２】
【従来の技術】
従来、熱間曲げ加工などを行った金属条材に対して、延性、靱性等の機械的特性を回復させるための熱処理を行うことが知られており、また、その熱処理方法として、金属条材の長手方向の小領域を局部的に加熱して加熱部を形成する加熱手段（例えば、誘導加熱用コイル）とその加熱部の一端を冷却する冷却手段（例えば、冷却水噴射器）とを、金属条材に対して長手方向に相対的に且つ加熱手段を冷却手段の前側に配して移動させ、前記金属条材を連続的に加熱冷却して熱処理する方法が知られている。
【０００３】
【発明が解決しようとする課題】
ネジ接続して使用する鋼管等の管端部に熱間据込み加工を施した場合にも、該加工により形成された厚肉部及びその近傍の熱影響部に上記機械的特性を回復するための熱処理が必要となる場合があり、その方法として上記した熱処理方法を用いることが考えられる。そこで、図６及び後述する比較例に示すように、平板状の金属条材の長手方向の一部領域を据込み加工し、元の厚みのままの薄肉部１ａ（厚さ１０ｍｍ）と、テーパ部１ｂと、厚肉部１ｃ（厚さ２０ｍｍ）とを有する金属条材１（材質ＳＳ４００）を用意し、この金属条材１を取り囲むように、誘導加熱用コイルからなる加熱手段２と、冷却水３を噴射する冷却水噴射器からなる冷却手段４とをセットし、加熱手段２で金属条材１の小領域を約１０００°Ｃに加熱して加熱部５としながら、その加熱手段２と冷却手段４を金属条材１に対して、１．５ｍｍ／ｓで相対的に移動させ、且つ冷却水量を３リットル／ｍｉｎ／ｃｍに保持して、熱処理を行った。そして、その熱処理前と熱処理後の金属条材１の機械的特性（横断面の平均硬度、引張強さ及び伸び）を測定した。
【０００４】
ところが、測定結果は図６のグラフに示した通りであって、熱処理前にはほぼ同一の機械的特性を持っていた薄肉部１ａと厚肉部１ｃとを同一条件で熱処理したにも係わらず、熱処理後の機械的特性は薄肉部１ａと厚肉部１ｃとで大きく変化してしまい、特に薄肉部１ａでは硬度が逆に増加し、伸びが低下してしまうという問題点のあることが判明した。
【０００５】
本発明はかかる問題点に鑑みてなされたもので、薄肉部と厚肉部を有するような金属条材に対して、薄肉部と厚肉部の機械的特性がほぼ均一となるように熱処理することの可能な金属条材の熱処理方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者等は、図６のグラフ内の線７、８、９で示すように、金属条材１の薄肉部と厚肉部とを同一熱処理条件（同一温度、同一送り速度、同一冷却水量）で熱処理したにもかかわらず、機械的特性が異なってしまう原因を検討した結果、これが加熱部の温度降下速度に起因していることを見出した。すなわち、図７に示すように、条材１を、その条材１に沿って一定速度Ｖで移動する加熱手段２で局部的に加熱して加熱部５とし、その後ろ側を冷却手段４からの冷却媒体即ち冷却水３で冷却してゆく場合において、或る瞬間における金属条材の長手方向の温度分布を測定したところ、薄肉部１ａの温度分布は線１０で、厚肉部１ｃの温度分布は線１１で示すようになっており、厚肉部１ｃの方がゆるやかに温度が低下していたことが判明した。これは、厚肉部１ｃの方が加熱部５から冷却されている部分へ移動する熱量Ｑが多いためと思われる。線１０、１１に示す温度分布から、金属条材１の或る位置における温度変化をグラフ化すると、加熱部５の移動速度が一定であるので、結局、図７の下側のグラフに示すように、薄肉部では線１２、厚肉部では線１３となり、それぞれ、温度分布の線１０、１１と同様な曲線となる。従って、厚肉部ではゆるやかに温度が降下しているが、薄肉部では急激に温度が降下している。金属の熱処理、特に鋼材の熱処理において、温度降下速度は機械的特性に影響しており、この温度降下速度が早いほど、引張強さ及び硬度が大きくなり、伸びが小さくなる傾向がある。このため、薄肉部と厚肉部とに対して一定の条件で熱処理を行ったにもかかわらず、熱処理後の機械的特性が異なっていたと思われる。
【０００７】
本発明はかかる知見に基づいてなされたもので、薄肉部と厚肉部を有する金属条材に対して、加熱手段と冷却手段を相対的に移動させて熱処理するに際し、熱処理後における前記金属条材の機械的特性を長手方向にほぼ均一とするように、前記加熱手段及び冷却手段が金属条材に加える熱処理条件を、金属条材の肉厚に応じて変化させることを特徴とし、これにより、薄肉部と厚肉部を、ほぼ均一な機械的特性となるように熱処理することが可能となる。
【０００８】
本発明において、熱処理後における前記金属条材の機械的特性を長手方向にほぼ均一とするように、金属条材の肉厚に応じて変化させる熱処理条件としては、熱処理時における前記加熱手段及び冷却手段の金属条材に対する相対的移動速度を挙げることができ、この相対的移動速度を、金属条材の肉厚の薄い領域では厚い領域よりも遅くすることが、機械的特性の均一化に有効である。
【０００９】
【００１０】
また、金属条材の肉厚に応じて変化させる熱処理条件として、加熱温度を挙げることもでき、熱処理時に前記加熱手段により形成される加熱部の到達温度を、金属条材の肉厚の薄い領域では厚い領域よりも低くすることが、機械的特性の均一化に有効である。
【００１１】
以上に述べた加熱手段及び冷却手段の金属条材に対する相対的移動速度、前記加熱手段により形成される加熱部の到達温度などの熱処理条件は、それぞれを単独で変化させることで機械的特性の均一化を図ってもよいし、必要に応じ、これらの熱処理条件を適宜組み合わせて変化させることにより機械的特性の均一化を図ってもよい。なお、金属条材の肉厚に応じて変化させる熱処理条件として、熱処理時における前記冷却手段による冷却熱量を挙げることもでき、この冷却熱量を、金属条材の肉厚の薄い領域では厚い領域よりも小さくすることが、機械的特性の均一化に有効である。従って、上記した相対的移動速度による熱処理条件或いは加熱部の到達温度による熱処理条件に、冷却手段の冷却熱量による熱処理条件を組み合わせてもよい。
【００１２】
【発明の実施の形態】
以下、図面を参照して本発明を更に詳細に説明する。
本発明の熱処理方法は、図１に示すように、金属条材１の長手方向の小領域を局部的に加熱して加熱部５を形成する加熱手段２と、その加熱手段２による加熱部５の一端を冷却する冷却手段４とを、熱処理すべき金属条材１に対して長手方向に相対的に且つ加熱手段２を冷却手段４よりも前側に配して移動させ、金属条材１を連続的に加熱冷却して熱処理することを基本とする。
【００１３】
ここで使用する加熱手段２としては、金属条材を局部的に所望温度に加熱しうる任意のものを使用しうるが、なかでも電磁コイルを配して行う誘導加熱法が、金属条材を敏速に且つ局部的に高温に加熱することができるので好適である。冷却手段４としては、加熱部５に対して冷却媒体３を吹き付けることで冷却しうるものが使用される。その冷却媒体としては、水、油等の液体、空気、窒素ガス等の気体等任意であるが、水を用いることが冷却熱量が大きく、しかも取り扱いが容易で且つ安価であるので、好ましい。加熱手段２の幅ないしはこれにより形成される加熱部５の長さは、加熱手段２を条材１に対して相対的に移動させながら、加熱部５の最高温度を熱処理に要求される所望温度まで昇温させることができるように定めればよい。なお、たとえば、基本構成として必要な上記冷却手段４の他に、加熱部長さの調整を補助する目的で加熱手段２の前側に補助冷却手段（図示を省略）を配備するなどの付随的な措置は、本発明の目的に沿った範囲で適宜行われてよい。加熱手段２と冷却手段４とを金属条材１に対して相対的に移動させるには、金属条材１を定位置に固定し、加熱手段２と冷却手段４とを移動させる方法、加熱手段２と冷却手段４とを定位置に固定し、金属条材１を移動させる方法、加熱手段２と冷却手段４及び金属条材１をそれぞれ移動させる方法のいずれをも採用しうる。
【００１４】
図１に示す本発明の実施の１形態では、薄肉部１ａ、テーパ部１ｂ、厚肉部１ｃ等を有する金属条材１に対して上記した方法で熱処理を行うに当たって、加熱手段２及び冷却手段４の金属条材１に対する相対的移動速度を、金属条材の肉厚の薄い領域では厚い領域よりも遅くしている。すなわち、図１のグラフに線７で示すように、加熱手段２及び冷却手段４の金属条材１に対する相対的な移動速度（送り速度）を、薄肉部１ａでは低い一定の速度Ｖ_a に、テーパ部１ｂでは徐々に増加する速度Ｖ_b に、厚肉部１ｃでは高い一定の速度Ｖｃとするものである。なお、温度及び冷却水量はそれぞれ線８、９で示すように一定としておく。
【００１５】
移動速度にこのような変化を与えると、加熱手段２による加熱部５の到達温度（最高温度）及び冷却水量（冷却熱量）を線８、９で示すように一定とした熱処理を行った場合において、加熱中の或る瞬間における金属条材１の加熱部５及びその後ろの冷却部分での温度分布は、図２に示す線１５、線１６のようになる。ここで、線１５は薄肉部１ａの加熱冷却時における温度分布を、線１６は厚肉部１ｃの温度分布を示している。もし、薄肉部１ａにおける移動速度を厚肉部１ｃにおける移動速度と同一とすると、薄肉部１ａにおける温度分布は線１５′のように、急激に温度が低下したものとなるが、本発明では移動速度を遅くしたことにより、線１５のように温度低下がややゆるやかとなる。ただし、厚肉部１ｃにおける曲線１６よりは幾分急である。この温度分布を元に、横軸を時間軸として書き直すと（すなわち、金属条材１の１点における温度変化曲線として書き直すと）、図２の下側のグラフに示す線１７、１８のようになり、両者はほぼ重なる。すなわち、薄肉部１ａの温度降下がゆるやかとなって厚肉部１ｃとほぼ等しくなる。これにより、薄肉部１ａも厚肉部１ｃとほぼ等しく熱処理され、図１の下側のグラフに示すように機械的特性が均一となる。
【００１６】
以上に、移動速度を変化させることにより、薄肉部１ａ、厚肉部１ｃがほぼ等しく熱処理され、機械的特性が均一となる理由を説明したが、実際の操業に当たっては、実験によって、薄肉部１ａ及び厚肉部１ｃのそれぞれの移動速度を定めればよい。また、図１において、中間のテーパ部１ｂにおける移動速度Ｖ_b は、その前後の速度Ｖ_a 、Ｖｃを結ぶ直線となるように変化させればよいが、このように速度変化させることが困難な場合には、二点鎖線７′で示すように、テーパ部１ｂ内の適当な位置で、速度をＶ_a からＶｃに変化させるようにしてもよい。通常、薄肉部１ａと厚肉部１ｃの間に位置するテーパ部１ｂは短いので、この部分は多少ラフな制御を行っても機械的物性にさほど大きい影響を与えることがなく、支障はない。
【００１７】
なお、冷却手段４による冷却熱量を、金属条材の肉厚の薄い領域では厚い領域よりも小さくすることでも機械的物性の改善を図ることができる。移動速度を一定として熱処理を行った場合、冷却熱量が一定であると、薄肉部１ａと厚肉部１ｃとの温度分布はそれぞれ、図２に線１５′、線１６で示すようになり、薄肉部１ａでは温度分布が急激となる。これに対し、薄肉部１ａにおける冷却熱量を減少させると、温度がゆるやかに低下し、温度分布は線１５′から線１５に接近した状態となる。これにより、薄肉部１ａについても厚肉部１ｃと同様の熱処理が行われ、機械的物性がほぼ均一となる。この現象は移動速度を変化させた場合にも生じるので、前記した移動速度を変化させる構成とした実施の形態に、或いは後述する加熱部の到達温度を変化させる構成とした実施の形態に、冷却熱量を変化させる技術を組み合わせ、機械的物性の均一化を図ることもできる。冷却手段４による冷却熱量を変化させるには、冷却手段４が条材１に噴射する冷却媒体３の噴射量を変化させればよい。なお、この冷却手段４の冷却媒体噴射量を変化させる量も実験的に定めればよい。また、薄肉部１ａと厚肉部１ｃの間にあるテーパ部１ｂにおける冷却熱量は、徐々に変化するようにしてもよいし、或いはテーパ部１ｂ内の適当な位置で、急激に変化させるようにしてもよい。
【００１８】
本発明の更に他の実施の形態は、加熱手段２が昇温させる加熱部５の到達温度を、金属条材の肉厚の薄い領域では厚い領域よりも低くするものである。図７で説明したように、薄肉部１ａと厚肉部１ｃを同一温度に加熱し且つ同一の移動速度、同一の冷却熱量で熱処理した場合、薄肉部１ａでは温度が急激に低下し、その結果、硬度が増加し、伸びが低下した特性となってしまう。ところで、本発明者等が加熱部５の到達温度（最高温度）を変化させ、その他の条件を一定として熱処理テストを行ったところ、図３に示すように、到達温度を高めると、硬度が増加することが判明した。従って、図４のグラフに線８で示すように、薄肉部１ａは低い到達温度とし、厚肉部１ｃは高い到達温度とすることにより、薄肉部１ａと厚肉部１ｃとを、図４のグラフに示すようにほぼ同じ機械的特性となるように熱処理できる。なお、この場合における到達温度条件も、実験的に求めて定めればよい。また、薄肉部１ａと厚肉部１ｃの間にあるテーパ部１ｂにおける到達温度は、徐々に変化するようにしてもよいし、或いはテーパ部１ｂ内の適当な位置で、急激に変化させるようにしてもよい。
【００１９】
以上の説明では、薄肉部と厚肉部で移動速度のみを変えたり、到達温度のみを変えたりしている。しかしながら、本発明はこの場合に限らず、これらの特性を適宜組み合わせて変化させる形態で実施することも可能である。例えば、薄肉部では厚肉部に比べて、移動速度を低くし且つ処理温度を低くするとか、更に冷却熱量を減少させる等の組み合わせを行うことも可能である。
【００２０】
本発明の熱処理の対象とする金属条材の材質は、熱処理が有効なものであれば任意であり、通常は鋼である。また金属条材の形状は、細長い板状のもの、断面Ｈ形、Ｉ形、Ｌ形、円筒形、角筒形のものなど任意である。
【００２１】
【実施例】
以下実施例及び比較例を説明する。
【００２２】
〔実施例１〕
(1) 供試条材１
材質ＳＳ４００の板材（厚さ１０ｍｍ、幅２００ｍｍ、長さ１ｍ）の長手方向の一端側に据込み加工を施して、図１に示すように、長さ約３５ｍｍのテーパ部１ｂと、長さ約２００ｍｍ、厚さ２０ｍｍの厚肉部１ｃを形成し、供試条材１とした。この条材１の各部の機械的特性は表１に示す通りであった。なお、表１における数値は、３個の供試条材の平均値である。
【００２３】
【表１】

【００２４】
(2) 熱処理装置
加熱手段２：誘導加熱コイル（加熱幅Ｗ３０ｍｍ）
印加周波数６ｋＨｚ
冷却手段４：水噴射方式
【００２５】
(3) 熱処理
図１に示すように、条材１の薄肉部１ａに加熱手段２及び冷却手段４をセットし、その加熱手段２及び冷却手段４を作動させた状態で条材１に沿って厚肉部１ｃに向かって移動させ、熱処理を行った。この時、到達温度（加熱部５の最高温度）はほぼ１０００°Ｃに保持し、冷却水量もほぼ３リットル／ｍｉｎ／ｃｍに保持し、移動速度のみを薄肉部１ａでは１．０ｍｍ／ｓ、厚肉部１ｃでは１．５ｍｍ／ｓ、テーパ部１ｂでは、薄肉部１ａにおける速度から厚肉部１ｃにおける速度になるようになだらかに変化させた。
【００２６】
(4) 結果
熱処理後の条材１の機械的物性を測定したところ、表２に示し且つ図１のグラフに示すようになっており、薄肉部１ａ、厚肉部１ｃでほぼ均一となっていた。なお、表２における数値は、３個の条材１の平均値である。
【００２７】
【表２】

【００２８】
【００２９】
【００３０】
【００３１】
【００３２】
〔実施例２〕
(1) 供試条材１
実施例１と同じ
(2) 熱処理装置
実施例１と同じ
【００３３】
(3) 熱処理
図４に示すように、条材１の薄肉部１ａに加熱手段２及び冷却手段４をセットし、その加熱手段２及び冷却手段４を作動させた状態で条材１に沿って厚肉部１ｃに向かって移動させ、熱処理を行った。この時、到達温度（加熱部５の最高温度）のみを薄肉部１ａでの９５０°Ｃから厚肉部１ｃでの１０５０°Ｃまで変化させ、移動速度はほぼ１．５ｍｍ／ｓで一定に保持し、冷却水量もほぼ２．５リットル／ｍｉｎ／ｃｍで一定に保持した。
【００３４】
(4) 結果
熱処理後の条材１の機械的物性を測定したところ、表３及び図４のグラフに示すようになっており、薄肉部１ａ、厚肉部１ｃでほほ均一となっていた。なお、表３における数値も、３個の条材１の平均値である。
【００３５】
【表３】

【００３６】
〔実施例３〕
(1) 供試条材１
実施例１と同じ
(2) 熱処理装置
実施例１と同じ
【００３７】
(3) 熱処理
図５に示すように、条材１の薄肉部１ａに加熱手段２及び冷却手段４をセットし、その加熱手段２及び冷却手段４を作動させた状態で条材１に沿って厚肉部１ｃに向かって移動させ、熱処理を行った。この時、到達温度（加熱部５の最高温度）を薄肉部１ａでの９２５°Ｃから厚肉部１ｃでの１０００°Ｃまで変化させ、移動速度も薄肉部１ａでの１．２５ｍｍ／ｓから厚肉部１ｃでの１．５ｍｍ／ｓまで変化させ、冷却水量のみをほぼ３リットル／ｍｉｎ／ｃｍで一定に保持した。
【００３８】
(4) 結果
熱処理後の条材１の機械的物性を測定したところ、表４及び図５のグラフに示すようになっており、薄肉部１ａ、厚肉部１ｃでほぼ均一となっていた。なお、表４における数値も、３個の条材１の平均値である。
【００３９】
【表４】

【００４０】
〔比較例１〕
(1) 供試条材１
実施例１と同じ
(2) 熱処理装置
実施例１と同じ
【００４１】
(3) 熱処理
図６に示すように、条材１の薄肉部１ａに加熱手段２及び冷却手段４をセットし、その加熱手段２及び冷却手段４を作動させた状態で条材１に沿って厚肉部１ｃに向かって移動させ、熱処理を行った。この時、薄肉部１ａから厚肉部１ｃまで到達温度（加熱部５の最高温度）は１０００°Ｃで一定に保ち、移動速度も１．５ｍｍ／ｓで一定に保ち、冷却水量も３リットル／ｍｉｎ／ｃｍで一定に保った。
【００４２】
(4) 結果
熱処理後の条材１の機械的物性を測定したところ、表５及び図６のグラフに示すように、厚肉部１ｃでは硬度が低下し、伸びが高くなって、良好な靱性が確保されていたが、薄肉部１ａでは硬度が増加し、伸びが低下していた。なお、表５における数値も、３個の条材１の平均値である。
【００４３】
【表５】

【００４４】
【発明の効果】
以上に説明したように、本発明は、薄肉部と厚肉部を有する金属条材に対して、加熱手段と冷却手段を相対的に移動させて熱処理するに際し、熱処理後における前記金属条材の機械的特性を長手方向にほぼ均一とするように、前記加熱手段及び冷却手段が金属条材に加える熱処理条件、例えば、加熱手段及び冷却手段の金属条材に対する相対的移動速度、加熱手段による加熱温度などを、金属条材の肉厚に応じて変化させるように構成したことにより、１回の熱処理操作によって薄肉部と厚肉部を、ほぼ均一な機械的特性となるように熱処理することができ、金属条材の薄肉部、厚肉部を共に、所望の機械的特性とすることができるという効果を有している。
【図面の簡単な説明】
【図１】本発明の実施の一形態を示すもので、金属条材を熱処理する状態を示す概略断面図及びその時の熱処理条件と得られた機械的特性を示すグラフ
【図２】金属条材を熱処理する状態を示す概略断面図及び図１に示す熱処理条件で金属条材を処理する時の温度分布及び温度変化を示すグラフ
【図３】熱処理時の処理温度と硬度の関係を示すグラフ
【図４】本発明の実施の他の形態を示すもので、金属条材を熱処理する状態を示す概略断面図及びその時の熱処理条件と得られた機械的特性を示すグラフ
【図５】本発明の実施の更に他の形態を示すもので、金属条材を熱処理する状態を示す概略断面図及びその時の熱処理条件と得られた機械的特性を示すグラフ
【図６】従来の方法を適用して金属条材を熱処理する状態を示す概略断面図及びその時の熱処理条件と得られた機械的特性を示すグラフ
【図７】金属条材を熱処理する状態を示す概略断面図及び図６に示す熱処理条件で金属条材を処理する時の温度分布及び温度変化を示すグラフ
【符号の説明】
１金属条材
１ａ薄肉部
１ｂテーパ部
１ｃ厚肉部
２加熱手段
３冷却媒体
４冷却手段
５加熱部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat treatment method for metal strips such as H-section steel, I-shape steel, steel pipe, and plate material, and more particularly to a heat treatment method for metal strips in which portions having different thicknesses are mixed in the longitudinal direction.
[0002]
[Prior art]
Conventionally, it has been known to perform heat treatment for recovering mechanical properties such as ductility and toughness on a metal strip that has been subjected to hot bending or the like. A heating means (for example, an induction heating coil) that locally heats a small region in the longitudinal direction of the heating portion and a cooling means (for example, a cooling water injector) that cools one end of the heating portion, A method is known in which a heating means is disposed relative to the metal strip in the longitudinal direction and moved to the front side of the cooling means, and the metal strip is continuously heated and cooled to perform heat treatment.
[0003]
[Problems to be solved by the invention]
In order to restore the above mechanical properties to the thick wall part formed by the processing and the heat affected part in the vicinity even when the pipe end part of a steel pipe or the like used by screw connection is subjected to hot upsetting process. It may be necessary to use the heat treatment method described above as the method. Therefore, as shown in FIG. 6 and a comparative example which will be described later, a partial region in the longitudinal direction of the flat metal strip is upset, and the thin portion 1a (thickness: 10 mm) with the original thickness and a taper are formed. A metal strip 1 (material SS400) having a portion 1b and a thick portion 1c (thickness 20 mm) is prepared, and a heating means 2 including an induction heating coil and a cooling unit are provided so as to surround the metal strip 1 The cooling means 4 composed of a cooling water injector for jetting water 3 is set, and the heating means 2 is used to heat the small area of the metal strip 1 to about 1000 ° C. with the heating means 2, The cooling means 4 was moved relative to the metal strip 1 at 1.5 mm / s, and the amount of cooling water was maintained at 3 liters / min / cm to perform heat treatment. The mechanical properties (average hardness, tensile strength and elongation of the cross section) of the metal strip 1 before and after the heat treatment were measured.
[0004]
However, the measurement results are as shown in the graph of FIG. 6 , and the thin-walled portion 1a and the thick-walled portion 1c, which had almost the same mechanical properties before the heat treatment, were heat-treated under the same conditions. The mechanical properties after the heat treatment are greatly changed between the thin portion 1a and the thick portion 1c, and in particular, the thin portion 1a has a problem that the hardness increases conversely and the elongation decreases. did.
[0005]
The present invention has been made in view of such problems, and heat-treats a metal strip having a thin portion and a thick portion so that the mechanical properties of the thin portion and the thick portion are substantially uniform. An object of the present invention is to provide a heat treatment method for a metal strip that can be used.
[0006]
[Means for Solving the Problems]
As shown by the

lines

7, 8, and 9 in the graph of FIG. 6 , the present inventors apply the same heat treatment conditions (the same temperature, the same feed rate, the same amount of cooling water) to the thin portion and the thick portion of the metal strip 1. As a result of investigating the cause of the difference in mechanical properties despite the heat treatment in (1), it was found that this was due to the temperature drop rate of the heating section. That is, as shown in FIG. 7 , the strip 1 is locally heated by the heating means 2 that moves along the strip 1 at a constant speed V to form the heating section 5, and the rear side thereof from the cooling means 4. When the temperature distribution in the longitudinal direction of the metal strip at a certain moment is measured, the temperature distribution of the thin portion 1a is a line 10 and the temperature of the thick portion 1c is measured. The distribution is as shown by the line 11, and it was found that the temperature of the thick portion 1c was gradually decreased. This is probably because the thick part 1c has a larger amount of heat Q that moves from the heating part 5 to the cooled part. From the temperature distribution shown in the

lines

10 and 11, when the temperature change at a certain position of the metal strip 1 is graphed, the moving speed of the heating unit 5 is constant, and as a result, as shown in the lower graph of FIG. In addition, the line 12 is formed in the thin part and the line 13 is formed in the thick part, and the curves are similar to the

lines

10 and 11 of the temperature distribution, respectively. Therefore, the temperature gradually decreases in the thick portion, but the temperature rapidly decreases in the thin portion. In the heat treatment of metals, particularly the heat treatment of steel materials, the temperature drop rate has an influence on the mechanical properties. The higher the temperature drop rate, the greater the tensile strength and hardness, and the smaller the elongation. For this reason, it seems that the mechanical properties after the heat treatment were different from each other even though the thin-walled portion and the thick-walled portion were heat-treated under certain conditions.
[0007]
The present invention has been made based on such knowledge, and when the metal strip having a thin portion and a thick portion is heat-treated by relatively moving the heating means and the cooling means, the metal strip after the heat treatment is obtained. In order to make the mechanical properties of the material substantially uniform in the longitudinal direction, the heat treatment condition applied to the metal strip by the heating means and the cooling means is changed according to the thickness of the metal strip, thereby The thin part and the thick part can be heat-treated so as to have substantially uniform mechanical properties.
[0008]
In the present invention, the heat treatment conditions that change according to the thickness of the metal strip so that the mechanical properties of the metal strip after the heat treatment are substantially uniform in the longitudinal direction are the heating means and cooling during the heat treatment. The relative movement speed of the means with respect to the metal strip can be mentioned, and it is effective to make the relative mechanical speed uniform in the thin region of the metal strip than in the thick region. It is.
[0009]
[0010]
In addition, as a heat treatment condition to be changed according to the thickness of the metal strip, the heating temperature can also be mentioned, and the ultimate temperature of the heating part formed by the heating means at the time of the heat treatment is a region where the thickness of the metal strip is thin. Thus, lowering the thickness than the thick region is effective for making the mechanical characteristics uniform.
[0011]
Mechanical properties to the relative movement speed with respect to the metal strip material of the heating means and cooling means described, heat treatment conditions, such as reaching the temperature of the heating portion which is formed by the front Symbol heating means, varying the singly or it may work to the homogenization, if necessary, but it may also be made uniform mechanical properties by changing a combination of these heat treatment conditions appropriately. In addition, as the heat treatment condition to be changed according to the thickness of the metal strip, the amount of cooling heat by the cooling means at the time of heat treatment can also be mentioned, and this cooling heat amount is smaller than the thick region in the thin region of the metal strip. It is effective to make the mechanical characteristics uniform. Therefore, the heat treatment conditions based on the cooling heat amount of the cooling means may be combined with the heat treatment conditions based on the relative moving speed or the heat treatment conditions based on the temperature reached by the heating unit .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
As shown in FIG. 1, the heat treatment method of the present invention includes a heating unit 2 that locally heats a small region in the longitudinal direction of the metal strip 1 to form a heating unit 5, and a heating unit 5 by the heating unit 2. The cooling means 4 for cooling one end of the metal strip 1 is moved relative to the metal strip 1 to be heat-treated relative to the longitudinal direction and the heating means 2 in front of the cooling means 4 to move the metal strip 1 Basically, heat treatment is performed by continuously heating and cooling.
[0013]
As the heating means 2 used here, any one capable of locally heating the metal strip to a desired temperature can be used. Among them, an induction heating method in which an electromagnetic coil is arranged is used for the metal strip. It is preferable because it can be heated quickly and locally at a high temperature. As the cooling means 4, one that can be cooled by spraying the cooling medium 3 on the heating unit 5 is used. As the cooling medium, water, liquid such as oil, gas such as air, nitrogen gas and the like are arbitrary, but it is preferable to use water because it has a large amount of heat for cooling, is easy to handle and is inexpensive. The width of the heating means 2 or the length of the heating part 5 formed thereby is the desired temperature required for the heat treatment while the heating means 2 is moved relative to the strip 1 while the maximum temperature of the heating part 5 is required. The temperature may be determined so that the temperature can be raised to the maximum. For example, in addition to the cooling means 4 necessary as a basic configuration, an auxiliary cooling means (not shown) is provided on the front side of the heating means 2 for the purpose of assisting the adjustment of the heating unit length. May be performed as appropriate within the scope of the object of the present invention. In order to move the heating means 2 and the cooling means 4 relative to the metal strip 1, a method of fixing the metal strip 1 at a fixed position and moving the heating means 2 and the cooling means 4, heating means 2 and the cooling means 4 are fixed at fixed positions, and either the method of moving the metal strip 1 or the method of moving the heating means 2, the cooling means 4 and the metal strip 1 can be employed.
[0014]
In the embodiment of the present invention shown in FIG. 1, when the heat treatment is performed on the metal strip 1 having the thin portion 1a, the tapered portion 1b, the thick portion 1c and the like by the above-described method, the heating means 2 and the cooling means. The relative moving speed of 4 with respect to the metal strip 1 is set to be slower in the thin region of the metal strip than in the thick region. That is, as shown by the line 7 in the graph of FIG. 1, the relative movement speed with respect to the metal strip material 1 of the heating means 2 and the cooling means 4 (feed speed), the the thin portion 1a low constant speed V _a, The taper portion 1b has a gradually increasing speed _Vb , and the thick portion 1c has a high constant speed Vc. The temperature and the amount of cooling water are fixed as shown by lines 8 and 9, respectively.
[0015]
When such a change is given to the moving speed, in the case of performing heat treatment in which the reached temperature (maximum temperature) and the amount of cooling water (cooling heat amount) of the heating unit 5 by the heating means 2 are made constant as shown by lines 8 and 9. The temperature distribution in the heating part 5 of the metal strip 1 and the cooling part behind it at a certain moment during heating is as shown by the

lines

15 and 16 shown in FIG. Here, the line 15 shows the temperature distribution during heating and cooling of the thin part 1a, and the line 16 shows the temperature distribution of the thick part 1c. If the moving speed in the thin wall portion 1a is the same as the moving speed in the thick wall portion 1c, the temperature distribution in the thin wall portion 1a is suddenly lowered as shown by the line 15 '. By reducing the speed, the temperature drop is slightly gentle as shown by the line 15. However, it is somewhat steeper than the curve 16 in the thick part 1c. Based on this temperature distribution, if the horizontal axis is rewritten as the time axis (that is, rewritten as a temperature change curve at one point of the metal strip 1), as shown by

lines

17 and 18 in the lower graph of FIG. And both overlap. That is, the temperature drop of the thin portion 1a is gradual and becomes almost equal to the thick portion 1c. As a result, the thin part 1a is also heat-treated substantially equally with the thick part 1c, and the mechanical characteristics become uniform as shown in the lower graph of FIG.
[0016]
As described above, the reason why the thin wall portion 1a and the thick wall portion 1c are almost equally heat-treated and the mechanical characteristics are uniform by changing the moving speed has been described. In actual operation, the thin wall portion 1a is experimentally measured. And the moving speed of each thick part 1c may be determined. In FIG. 1, the moving speed V _b in the intermediate taper portion 1b may be changed so as to be a straight line connecting the preceding and succeeding speeds V _a and Vc, but it is difficult to change the speed in this way. in this case, as indicated by the chain line 7 'two points, at the appropriate position within the tapered section 1b, and the speed may be changed from V _a to Vc. Usually, since the taper portion 1b located between the thin portion 1a and the thick portion 1c is short, this portion does not have a great influence on mechanical properties even if somewhat rough control is performed.
[0017]
The mechanical properties can also be improved by reducing the amount of heat of cooling by the cooling means 4 in the thin region of the metal strip material than in the thick region . When heat treatment is performed at a constant moving speed, if the amount of cooling heat is constant, the temperature distribution of the thin portion 1a and the thick portion 1c is as shown by lines 15 'and 16 in FIG. In the part 1a, the temperature distribution becomes abrupt. In contrast, when the Ru reduces cooling heat in thin walled portion 1a, the temperature is lowered gradually, the temperature distribution is in a state of approaching from line 15 'to line 15. Thereby, the heat treatment similar to that of the thick portion 1c is performed on the thin portion 1a, and the mechanical properties are substantially uniform. Since this phenomenon also occurs when the moving speed is changed, the cooling is performed in the embodiment in which the moving speed is changed or in the embodiment in which the temperature reached by the heating unit described later is changed. It is also possible to achieve uniform mechanical properties by combining techniques for changing the amount of heat. In order to change the amount of heat of cooling by the cooling means 4, the amount of cooling medium 3 injected by the cooling means 4 onto the strip 1 may be changed. The amount by which the cooling medium injection amount of the cooling means 4 is changed may be determined experimentally. Further, the amount of cooling heat in the tapered portion 1b between the thin portion 1a and the thick portion 1c may be changed gradually, or may be changed rapidly at an appropriate position in the tapered portion 1b. May be.
[0018]
In still another embodiment of the present invention, the temperature reached by the heating unit 5 raised by the heating means 2 is lower in the thin region of the metal strip than in the thick region. As described in FIG. 7 , when the thin portion 1a and the thick portion 1c are heated to the same temperature and heat-treated at the same moving speed and the same amount of cooling heat, the temperature rapidly decreases in the thin portion 1a. The hardness increases and the elongation decreases. By the way, when the inventors changed the ultimate temperature (maximum temperature) of the heating unit 5 and performed a heat treatment test with other conditions being constant, as shown in FIG. 3, when the ultimate temperature was increased, the hardness increased. Turned out to be. Therefore, as shown by the line 8 in the graph of FIG. 4 , the thin portion 1a and the thick portion 1c are made to have a low reached temperature and the thick portion 1c is set to a high reached temperature . As shown in the graph, heat treatment can be performed so as to have substantially the same mechanical characteristics. The ultimate temperature condition in this case may be determined experimentally. Further, the temperature reached at the tapered portion 1b between the thin portion 1a and the thick portion 1c may be gradually changed, or may be changed suddenly at an appropriate position in the tapered portion 1b. May be.
[0019]
In the above description, Ri was changed only the movement speed in the thin-walled portion and the thick portion, are changing the only arrival our temperature. However, the present invention is not limited to this case, and can be carried out in a form in which these characteristics are appropriately combined and changed. For example, in the thin portion, it is possible to perform a combination such as lowering the moving speed and lowering the processing temperature or further reducing the amount of cooling heat compared to the thick portion.
[0020]
The material of the metal strip to be heat-treated according to the present invention is arbitrary as long as the heat treatment is effective, and is usually steel. The shape of the metal strip is arbitrary, such as an elongated plate shape, a cross-sectional H shape, an I shape, an L shape, a cylindrical shape, or a rectangular tube shape.
[0021]
【Example】
Examples and comparative examples will be described below.
[0022]
[Example 1]
(1) Test strip 1
A plate material (thickness 10 mm, width 200 mm, length 1 m) of the material SS400 is subjected to upsetting on one end side in the longitudinal direction, and as shown in FIG. 1, a taper portion 1b having a length of about 35 mm and a length of about A thick part 1c having a thickness of 200 mm and a thickness of 20 mm was formed as a test strip material 1. The mechanical properties of each part of the strip 1 were as shown in Table 1. In addition, the numerical value in Table 1 is an average value of three test strip materials.
[0023]
[Table 1]

[0024]
(2) Heat treatment device Heating means 2: induction heating coil (heating width W 30 mm)
Applied frequency 6 kHz
Cooling means 4: water injection method
(3) Heat treatment As shown in FIG. 1, the heating means 2 and the cooling means 4 are set in the thin portion 1 a of the strip 1, and the heating means 2 and the cooling means 4 are operated along the strip 1. It moved toward the thick part 1c and heat-processed. At this time, the ultimate temperature (maximum temperature of the heating unit 5) is maintained at approximately 1000 ° C., the amount of cooling water is also maintained at approximately 3 liters / min / cm, and only the moving speed is 1.0 mm / s in the thin-walled portion 1a The thick portion 1c was gently changed to 1.5 mm / s, and the tapered portion 1b was gradually changed from the speed of the thin portion 1a to the speed of the thick portion 1c.
[0026]
(4) Result When the mechanical properties of the strip 1 after heat treatment were measured, it was as shown in Table 2 and shown in the graph of FIG. 1, and was almost uniform in the thin portion 1a and the thick portion 1c. It was. In addition, the numerical value in Table 2 is an average value of the three strips 1.
[0027]
[Table 2]

[0028]
[0029]
[0030]
[0031]
[0032]
[Example 2 ]
(1) Test strip 1
Same as Example 1
(2) Heat treatment device Same as Example 1 [0033]
(3) Heat treatment
As shown in FIG. 4 , the heating means 2 and the cooling means 4 are set on the thin portion 1 a of the strip 1, and the thick portion 1 c along the strip 1 with the heating means 2 and the cooling means 4 being operated. And moved to heat treatment. At this time, only the ultimate temperature (maximum temperature of the heating part 5) is changed from 950 ° C. in the thin part 1a to 1050 ° C. in the thick part 1c, and the moving speed is kept constant at approximately 1.5 mm / s. The amount of cooling water was also kept constant at approximately 2.5 liters / min / cm.
[0034]
(4) Results When the mechanical properties of the strip 1 after the heat treatment were measured, it was as shown in the graphs of Table 3 and FIG. 4 and was almost uniform in the thin portion 1a and the thick portion 1c. In addition, the numerical value in Table 3 is also an average value of the three strips 1.
[0035]
[Table 3]

[0036]
[Example 3 ]
(1) Test strip 1
Same as Example 1
(2) Heat treatment device Same as Example 1 [0037]
(3) Heat treatment
As shown in FIG. 5 , the heating means 2 and the cooling means 4 are set on the thin portion 1 a of the strip 1, and the thick portion 1 c along the strip 1 in a state where the heating means 2 and the cooling means 4 are operated. And moved to heat treatment. At this time, the ultimate temperature (maximum temperature of the heating part 5) is changed from 925 ° C. in the thin part 1a to 1000 ° C. in the thick part 1c, and the moving speed is from 1.25 mm / s in the thin part 1a. The thickness was changed to 1.5 mm / s at the thick portion 1c, and only the cooling water amount was kept constant at approximately 3 liters / min / cm.
[0038]
(4) Results When the mechanical properties of the strip 1 after heat treatment were measured, it was as shown in the graphs of Table 4 and FIG. 5 , and was almost uniform in the thin portion 1a and the thick portion 1c. In addition, the numerical value in Table 4 is also an average value of the three strips 1.
[0039]
[Table 4]

[0040]
[Comparative Example 1]
(1) Test strip 1
Same as Example 1
(2) Heat treatment apparatus Same as Example 1 [0041]
(3) Heat treatment
As shown in FIG. 6 , the heating means 2 and the cooling means 4 are set on the thin portion 1 a of the strip 1, and the thick portion 1 c along the strip 1 with the heating means 2 and the cooling means 4 being operated. And moved to heat treatment. At this time, the temperature reached from the thin part 1a to the thick part 1c (maximum temperature of the heating part 5) is kept constant at 1000 ° C., the moving speed is kept constant at 1.5 mm / s, and the amount of cooling water is 3 liters / second. It was kept constant at min / cm.
[0042]
(4) Results When the mechanical properties of the strip 1 after the heat treatment were measured, as shown in the graphs of Table 5 and FIG. 6 , the hardness in the thick portion 1c decreased, the elongation increased, and good toughness. However, in the thin portion 1a, the hardness increased and the elongation decreased. In addition, the numerical value in Table 5 is also an average value of the three strips 1.
[0043]
[Table 5]

[0044]
【The invention's effect】
As described above, in the present invention, when the heat treatment is performed by moving the heating means and the cooling means relative to the metal strip material having the thin wall portion and the thick wall portion, as substantially uniform mechanical properties in the longitudinal direction, the heating means and the heat treatment conditions that the cooling means applied to the metal strip material, for example, the relative movement speed with respect to the metal strip material of the heating means and cooling means, pressurizing heat means By configuring the heating temperature by changing according to the thickness of the metal strip, heat treatment is performed so that the thin wall portion and the thick wall portion have substantially uniform mechanical characteristics by one heat treatment operation. It has the effect that both the thin part and the thick part of the metal strip can have desired mechanical characteristics.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention, and is a schematic cross-sectional view showing a state of heat-treating a metal strip, and a graph showing heat treatment conditions and the obtained mechanical properties. A schematic cross-sectional view showing the state of heat treatment and a graph showing the temperature distribution and temperature change when the metal strip is processed under the heat treatment conditions shown in FIG. 1 [FIG. 3] A graph showing the relationship between the treatment temperature and hardness during heat treatment [ FIG. 4 shows another embodiment of the present invention, and is a schematic cross-sectional view showing a state of heat-treating a metal strip, and a graph showing the heat treatment conditions and the obtained mechanical characteristics. shows still another embodiment, the metal is applied to the graph 6 conventional method shows the mechanical properties obtained with the heat treatment conditions when schematic sectional view and a showing a state of heat treating the metal cord member Schematic sectional view showing the state of heat treatment of strip material Temperature distribution and when treating a metal strip material in beauty heat treatment conditions shown in the schematic cross-sectional view and FIG. 6 shows a state of heat-treating the

graph

7 metal strip material showing the mechanical properties obtained with the heat treatment conditions at the time Graph showing temperature change 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Metal strip 1a Thin part 1b Tapered part 1c Thick part 2 Heating means 3 Cooling medium 4 Cooling means 5 Heating part

Claims

A heating unit that locally heats a small region in the longitudinal direction of the metal strip to form a heating unit and a cooling unit that cools one end of the heating unit relative to the metal strip in the longitudinal direction. In addition, in the method in which the heating means is arranged and moved to the front side of the cooling means, and the metal strip material is continuously heated and cooled to heat-treat, the metal strip material includes portions having different thicknesses in the longitudinal direction. It is a metal strip, and the heat treatment conditions applied to the metal strip by the heating means and the cooling means are set so that the mechanical properties of the metal strip after heat treatment are substantially uniform in the longitudinal direction. In order to change the heat treatment conditions, the relative moving speed of the heating means and the cooling means during the heat treatment with respect to the metal strip is set to be smaller in the thin region of the metal strip than in the thick region. and characterized in that the slow Heat treatment method of that metal strip material.

A heating unit that locally heats a small region in the longitudinal direction of the metal strip to form a heating unit and a cooling unit that cools one end of the heating unit relative to the metal strip in the longitudinal direction. In addition, in the method in which the heating means is arranged and moved to the front side of the cooling means, and the metal strip material is continuously heated and cooled to heat-treat, the metal strip material includes portions having different thicknesses in the longitudinal direction. It is a metal strip, and the heat treatment conditions applied to the metal strip by the heating means and the cooling means are set so that the mechanical properties of the metal strip after heat treatment are substantially uniform in the longitudinal direction. In order to change the heat treatment conditions, the ultimate temperature of the heating part formed by the heating means during the heat treatment should be lower in the thin region of the metal strip than in the thick region. Netsusho of the metal strip material, characterized Method.

The heat treatment method for a metal strip according to claim 1 or 2, wherein the heat of cooling by the cooling means during heat treatment is made smaller in a thin region of the metal strip than in a thick region .