JP3770522B2 - Method and apparatus for measuring internal temperature of steel material - Google Patents

Description

ただし、ｔは超音波伝播時間（往復）、ｄは鋼材の厚み、Ｈは変態率で０〜１の値 ( ０の時は全領域ＦＣＣ、１の時は全領域ＢＣＣ ) 、Ｃ _B （Ｔ）はＢＣＣ領域での温度Ｔのときの音速、Ｃ _F （Ｔ）はＦＣＣ領域での温度Ｔのときの音速、ｘは鋼材の厚み方向の位置を表す。また、Ｔ（ｘ）はｘの位置での鋼材の温度である。
【００１４】
鋼材のＢＣＣ領域での音速、ＦＣＣ領域での音速は、それぞれ温度の関数として予め測定により求めることができる。よって、鋼材の変態率、鋼材の内部温度（表面温度を含む）分布、鋼材の厚さがわかれば、鋼材中の厚み方向への超音波伝播時間を計算することができる。
【００１５】
本手段においては、鋼材内部の温度分布を、鋼材表面温度と他の１つのパラメータで決定される関数形で近似する。測定に際しては、鋼材の表面温度と鋼材の厚みを測定や推定により求め、鋼材中の厚み方向への超音波伝播時間を測定する。次に、鋼材の内部温度分布を変化させて繰り返し計算を行い、計算した超音波伝播時間と実測した超音波伝播時間が一致するようにする。そして、一致した時点で計算に使用されていた鋼材の内部温度分布を、求める鋼材の内部温度分布とする。
【００１６】
鋼材内部の温度分布は、鋼材表面温度と他の１つのパラメータで決定される関数形で近似されているので、当該パラメータを決定すれば、鋼材内部の温度分布は一義的に決定される。よって、前記計算は、当該パラメータを求めるような計算とすることが最も好ましい。
【００１７】
なお、本手段においては、鋼材の変態率を予め知る必要があるが、鋼材の変態率の測定には、特開平５−１２６７９８号公報に開示されるような公知の手段が使用できる。
【００１８】
以上のように、本手段では、鋼材内部の温度分布を、鋼材表面温度と他の１つのパラメータで決定される関数形で近似した上で、ＢＣＣ領域での音速の温度依存性とＦＣＣ領域での温度依存性の二つの音速カーブ、変態率を考慮することにより、変態温度がどのように変わっても温度分布を求められるようにしているので、冷却速度がダイナミックに変化するようなプロセスにおいても内部温度を測定することができるようになる。また、一つの未知数を求めるようにしているため、超音波は縦波と横波の二つを用いる必要がなく、どちらか一方（特に縦波）のみで良いので、超音波装置を簡素化できるという特長も有する。
【００１９】
又、本手段において、鋼材の内部温度を求める方法は、下記方程式またはその近似方程式を解くことにより、鋼材内部の温度分布を求めるものである。
【００２０】
【数５】

【００２１】
ただし、ｔは超音波伝播時間（往復）、ｄは鋼材の厚み、Ｈは変態率で０〜１の値(０の時は全領域ＦＣＣ、１の時は全領域ＢＣＣ)、Ｃ_B（Ｔ）はＢＣＣ領域での温度Ｔのときの音速、Ｃ_F（Ｔ）はＦＣＣ領域での温度Ｔのときの音速、ｘは鋼材の厚み方向の位置を表す。また、Ｔ（ｘ）はｘの位置での鋼材の温度である。
【００２２】
本手段においては、ＢＣＣ領域での音速の温度依存性Ｃ_B（Ｔ）と、ＦＣＣ領域での音速の温度依存性Ｃ_F（Ｔ）とを予め実験により求めておく。
変態が外側から進行するとすると、変態が完了した範囲の音速はＢＣＣ領域での音速の温度依存性Ｃ_B（Ｔ）と内部温度分布Ｔ（ｘ）から定まり、変態が完了していない範囲の音速はＦＣＣ領域での音速の温度依存性Ｃ_F（Ｔ）と内部温度分布Ｔ（ｘ）から定まることとなる。ここに、ｘは厚み方向の位置である。この時、鋼材の厚みｄを考慮すると、超音波の伝播時間ｔは下式から求められる。ただし、変態率Ｈは、０〜１の値(０の時は全領域ＦＣＣ、１の時は全領域ＢＣＣ)をとるものとする。
【００２３】
【数６】

【００２４】
式(1)の未知数は、鋼材の厚み方向の内部温度分布Ｔ(ｘ)（実際は、この関数を決める未知の一つのパラメータ）のみであるため、鋼材のＢＣＣ領域での音速温度依存性Ｃ_B（Ｔ）と、ＦＣＣ領域での音速温度依存性Ｃ_F（Ｔ）と、鋼材の厚み方向の内部温度分布Ｔ（ｘ）と、鋼材の厚みｄと、鋼材中の厚み方向への超音波伝播時間の測定値ｔとから、繰り返し計算によりこの式を満足する鋼材の厚み方向の内部温度分布Ｔ(ｘ)を求めることができる。
【００２５】
前記課題を解決するための第２の手段は、鋼材内部の温度分布を、鋼材表面温度と他の１つのパラメータで決定される関数形で近似し、鋼材のＢＣＣ領域での音速と、ＦＣＣ領域での音速と、鋼材の変態率と、鋼材の表面温度と、鋼材の厚みと、鋼材中の厚み方向への超音波伝播時間の測定値とから、下記方程式またはその近似方程式を解くことにより、鋼材内部の温度分布を求める鋼材の内部温度の測定方法であって、下記の式により、いくつかの鋼材の変態率と、鋼材の表面温度と、鋼材の厚みと、鋼材の温度分布の組み合わせ毎に、鋼材の厚み方向への超音波伝播時間を計算して記憶しておき、鋼材中の厚み方向の超音波伝播時間を実測し、与えられた鋼材の変態率と、鋼材の表面温度と、鋼材の厚みにおいて実測値に一番近い値を有する鋼材の温度分布を、鋼材の温度分布として採用することを特徴とする鋼材の内部温度の測定方法（請求項２）である。
【００２６】
【数７】

【００２７】
ただし、ｔは超音波伝播時間（往復）、ｄは鋼材の厚み、Ｈは変態率で０〜１の値(０の時は全領域ＦＣＣ、１の時は全領域ＢＣＣ)、Ｃ_B（Ｔ）はＢＣＣ領域での温度Ｔのときの音速、Ｃ_F（Ｔ）はＦＣＣ領域での温度Ｔのときの音速、ｘは鋼材の厚み方向の位置を表す。また、Ｔ（ｘ）はｘの位置での鋼材の温度である。
【００２８】
前記(1)の方程式は、積分を含むため、解析的に解を求めることは難しい。そこで、本手段においては、鋼材の変態率Ｈと、鋼材の表面温度Ｔ_sと、鋼材の厚みｄと温度分布Ｔ（ｘ）（実際には、この関数を決定する未知の一つのパラメータ）を、それぞれあるピッチで変化させて、それらの組み合わせにおける(1)式の右辺の値を求めることにより、温度分布Ｔ（ｘ）と超音波伝搬時間計算値との近似式を作成しておき、与えられた鋼材の変態率Ｈと、鋼材の表面温度Ｔ_sと、鋼材の厚みｄの条件において、その式の超音波伝搬時間計算値に超音波伝搬時間実測値を代入することによって、すなわち近似方程式を解くことによって、鋼材内部の温度分布Ｔ（ｘ）を求める。これにより、鋼材内部の温度分布Ｔ（ｘ）を簡単に求めることができる。
【００２９】
前記課題を解決するための第３の手段は、前記第１の手段又は第２の手段であって、鋼材の内部温度分布を、以下の式で近似したことを特徴とするもの（請求項３）である。
T(x) = a₂・x²+a₁・x+a₀ … (2)
ここに、a₂、a_１、a₀は定数である。
【００３０】
一次元の熱伝導方程式を解いた場合には、鋼材内部の温度分布は、鋼材中心を軸とする２次関数になることが分かっているので、鋼材内部温度を前記(2)式で表すと精度の良い近似ができる。鋼材中心温度をＴ_c、表面温度をＴ_sとすると、(2)式の係数は、a₂=-4/d²・(T_c-T_s)、a₁=4/d・(T_c-T_s)、a₀=T_sと表される。よって、表面温度Ｔ_sが分かっていれば、(2)式を(1)式に代入することにより、未知数は中心温度Ｔ_cのみとなるため、比較的簡単に(1)式を解くことができる。特に、前記第３の手段に本手段を応用することにより、積分方程式を解くことなく中心温度Ｔ_cを求めることができ、これを(2)式に代入することにより鋼材内部の温度分布Ｔ（ｘ）を求めることができる。
【００３１】
また、本手段において、鋼材内部の温度分布Ｔ（ｘ）を近似的に求めるために、非線形最小二乗法を使うこともできる。すなわち、式(1)における計算値と測定値の差を評価関数とおき、それが最も小さくなるようにパラメータである中心温度を決定する。このとき、評価関数は、(1)式におけるｔの測定値をｔ_m、計算値をｔ(Ｔ_c)とすると、
S = (t(T_c)-t_m)² …(3)
となり、ｔ(Ｔ_c)をテーラー展開して一次の項までを考慮すると、
【００３２】
【数８】

【００３３】
となる。ここで、Ｔ_c0は初期値、ΔＴ_c＝Ｔ_c−Ｔ_c0である。評価関数の最小条件は、
【００３４】
【数９】

【００３５】
であるから、最小二乗法によりΔＴ_cを容易に求めることができ、数回の繰り返しによって中心温度Ｔ_cを求めることができる。
【００３６】
前記課題を解決するための第４の手段は、鋼材のＢＣＣ領域での音速温度依存性を記憶しておく第１の音速記憶手段と、ＦＣＣ領域での音速温度依存性を記憶しておく第２の音速記憶手段と、鋼材の変態率を推定する変態率推定手段と、鋼材の表面温度を推定する表面温度推定手段と、鋼材の厚みを測定する厚み測定手段と、鋼材の厚み方向への超音波伝播時間を測定する超音波測定手段と、前記各手段により得られた値とから、下記方程式またはその近似方程式を解くことにより、鋼材の内部温度を求める演算手段とを備えたことを特徴とする鋼材の内部温度の測定装置（請求項４）である。
【数１０】

ただし、ｔは超音波伝播時間（往復）、ｄは鋼材の厚み、Ｈは変態率で０〜１の値 ( ０の時は全領域ＦＣＣ、１の時は全領域ＢＣＣ ) 、Ｃ _B （Ｔ）はＢＣＣ領域での温度Ｔのときの音速、Ｃ _F （Ｔ）はＦＣＣ領域での温度Ｔのときの音速、ｘは鋼材の厚み方向の位置を表す。また、Ｔ（ｘ）はｘの位置での鋼材の温度である。
【００３７】
鋼材のＢＣＣ領域での音速の温度依存性Ｃ_B（Ｔ）と、ＦＣＣ領域での音速の温度依存性Ｃ_F（Ｔ）とを、それぞれ第１の音速記憶手段と第２の音速記憶手段に記憶しておく。鋼材の変態率は、変態率推定手段（特開平５−１２６７９８号公報に開示されるようなもの）により測定する。表面温度推定手段は、実測した表面温度と実測した時点からの経過時間より、熱伝導方程式等を使用して表面温度を推定する。表面温度推定手段としては、公知のものを使用することができる。そして、厚み測定手段により鋼材の厚みｄを測定すると共に、超音波測定手段により、鋼材の厚み方向への超音波伝播時間ｔを測定する。
【００３８】
演算手段は、これらの実測値や推定値を利用して、鋼材の内部温度を求める。鋼材の内部温度を求める具体的なアルゴリズムとしては、前記第２の手段から第４の手段で説明した方法を採用することができる。表示手段は、求められた温度分布そのもの、又はその一部である鋼材の中心温度を表示する。
【００３９】
【発明の実施の形態】
以下、本発明の実施の形態の例を図を用いて説明する。図１は、本発明の実施の形態の一例である鋼材の内部温度測定装置を示すブロック図である。
【００４０】
被検体１は、圧延を終了した後の冷却プロセスにある厚板であり、図には示されていない水冷装置により表裏面から冷却されている。２、３はそれぞれＢＣＣ領域での音速の温度依存性と、ＦＣＣ領域での音速の温度依存性を記憶する手段であり、具体的には図３に示される線を多項式で最小二乗近似し、その係数を記憶することにより、ある温度の時の音速が容易に求められるようにしている。すなわち、Ｃ_B(Ｔ)、Ｃ_F(Ｔ)を多項式で表し、その係数を記憶している。
【００４１】
４は変態率推定手段であり、ここでは変態率測定装置を用いている。これは特開平５−１２６７９８号公報に開示されるように磁気を利用したものであり、鋼材の一方面に磁束を発生する磁化器を、鋼材を挟んだ反対側に一対の磁気センサを備え、この磁気センサ同士の減算値から、鋼材を透過した磁束量を求め、その値から変態率を求めるものである。この他、変態率推定手段としては、連続冷却変態線図いわゆるＣＣＴ線図を用いて計算により変態率を求めるようにしたものを使用できる。また、加熱炉抽出後のスラブのように全く変態していない場合や、冷却が進み明らかに変態が完了している場合には、変態率Ｈを０ないしは１とみなして扱っても本発明の実施は可能である。
【００４２】
５は表面温度推定手段であり、ここでは放射温度計を用いている。冷却水の影響を受けないように、光路をシールドし、被検体１表面と温度計の間をエアパージしながら測定するようにしている。６は厚み測定手段であり、ここではγ線厚み計を用いている。
【００４３】
７は超音波測定手段であり、ここでは冷却中であることを利用し、圧電探触子から水柱により材料に音響カップリングしている。冷却水によって沸騰膜を除去するようにしているので、この方法でも測定が可能である。伝播時間は、材料の表面からのＳエコーと底面からのＢエコーとの時間差から求めるようにしている。なお、復熱時に測定する際には、表面温度が高くなるため、電磁超音波やレーザー超音波など、非接触で超音波測定できる手段を使用する。
【００４４】
超音波測定手段での測定位置と、放射温度計設置位置とが異なる場合には、表面温度推定手段５に温度推定機能を持たせ、超音波での測定中の被検体１の表面温度を推定可能とする。また、厚み測定手段６の位置での被検体１の表面温度と超音波での測定中の被検体１の表面温度が異なる場合には、熱膨張補正を行って、超音波で測定中の被検体の厚みを計算に用いる。
【００４５】
８は中心温度演算手段であり、本実施の形態では図２に示す構成としている。すなわち、中心温度ー伝播時間演算手段１０は、被検体１の中心温度、表面温度、厚み、変態率を変数として、各変数について離散的な代表値を定め、これらの代表値の組み合わせについて、(2)式より被検体１内部の温度分布を求め、これを(1)式に代入して超音波の伝播時間を各々求めている。そして、これらをテーブル化し、中心温度ー伝播時間演算手段１０内に格納している。たとえば、中心温度については200℃から800℃の間を50℃毎に分割して、計算を行っている。
【００４６】
また、テーブル化を行う代わりに、被検体１の中心温度と、表面温度、厚み、変態率と超音波の伝播時間との関係を多項式近似し、その係数を記憶しておくようにしてもよい。
【００４７】
次に、中心温度演算手段１１は、超音波測定手段７で得た伝播時間測定値を、前記被検体１の厚み、表面温度、変態率と共に、前記テーブルに当てはめ、伝播時間測定値に一番近い伝播時間計算値を有する中心温度を、求める中心温度とする。または、超音波測定手段７で得た伝播時間測定値を、前記被検体１の厚み、表面温度、変態率と共に、前記多項式に当てはめ、伝播時間と中心温度との関係式に入力して、被検体１の中心温度を求めるようにしてもよい。中心温度が求まれば、(2)式により、被検体１内部の温度分布を求めることができる。９は温度分布表示手段であり、式(2)に基づいた温度分布を表示するためのＣＲＴや、中心温度の推移を表示するアナログ記録計である。
【００４８】
中心温度演算手段８の動作としては、前述した最小二乗法を用いて、中心温度を求めるようにしてもよい。なお、本実施の形態においては、被検体１の内部温度の分布として(2)式を仮定したが、本発明における被検体１の内部温度の分布の仮定としては、表面温度と他の一つのパラメータで決定されるものであれば、これに限らず、適当なものを選択して使用することができる。
【００４９】
また、本実施の形態においては、以上の構成要素の内、第１の音速温度依存性記憶手段２、第１の音速温度依存性記憶手段３、中心温度演算手段８については、コンピュータを用いて構成している。
【００５０】
【実施例】
以下、前記の本発明の実施の形態である鋼材内部の温度測定方法を用いた、具体的な測定例について説明する。
測定に用いた材料は厚さ23.39mmの炭素鋼鋼板で、900℃の均熱状態から連続的に10℃/s程度の冷却速度で冷却し、冷却開始40秒後に測定した。この時の変態率推定結果は83％、表面温度は196℃であった。これを用い、式(1)、(2)に基づいて、ある中心温度と式(1)、(2)とから求められる超音波伝播時間との関係をいくつかの中心温度で計算する。例えば、中心温度400℃、500℃、600℃、700℃の時の音速分布は図４のようになるから、式(1)に基づいて伝播時間を計算することができる。
【００５１】
図５はその結果であり、中心温度が高くなるに従って伝播時間が増えていくことが分かる。この測定を行なった時の実際の伝播時間は8.383μsであったので、このときの中心温度は図５から容易に求められ、513℃となった。このとき、鋼材の厚みの中心に埋め込んだ熱電対温度計の値は520℃であり、両者は良く一致した。図６はこの時の温度分布の表示例であり、式(2)を基に計算される。
【００５２】
【発明の効果】
以上説明したように、本発明においては、鋼材内部の温度分布を、鋼材表面温度と他の１つのパラメータで決定される関数形で近似し、鋼材内部の温度分布を、鋼材表面温度と他の１つのパラメータで決定される関数形で近似し、鋼材のＢＣＣ領域での音速と、ＦＣＣ領域での音速と、鋼材の変態率と、鋼材の表面温度と、鋼材の厚みと、鋼材中の厚み方向への超音波伝播時間の測定値とから、鋼材内部の温度分布を求めているので、変態温度がどのように変わっても温度分布を求められるようにしているので、冷却速度がダイナミックに変化するようなプロセスにおいても内部温度を測定することができるようになる。また、一つの未知数を求めるようにしているため、超音波は縦波と横波の二つを用いる必要がなく、どちらか一方（特に縦波）のみの測定で良いので、超音波装置を簡素化できる。
【図面の簡単な説明】
【図１】本発明の実施の形態の一例である鋼材の内部温度測定装置を示すブロック図である。
【図２】中心温度演算手段の構成の例を示すブロック図である。
【図３】縦波音速の温度依存性を示す図である。
【図４】鋼材の中心温度と厚み方向音速との関係の例を示す図である。
【図５】鋼材の中心温度と超音波伝播時間との関係の例を示す図である。
【図６】測定により求められた鋼材中の温度分布を示す図である。
【図７】従来の鋼材内部の温度測定装置の一例を示すブロック図である。
【図８】鋼材温度と超音波の縦波、横波の音速の関係を示す図である。
【図９】材料温度と、超音波の縦波と横波の速度比との関係を示す図である。
【図１０】従来の鋼材内部の温度測定装置の他の例を示すブロック図である。
【符号の説明】
１… 被検体
２… 第１の音速温度依存性記憶手段
３… 第２の音速温度依存性記憶手段
４… 変態率推定手段
５… 表面温度推定手段
６… 厚み測定手段
７… 超音波測定手段
８… 中心温度演算手段
９… 温度分布表示手段
１０… 中心温度ー伝播時間演算手段
１１… 中心温度演算手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring the internal temperature of a steel material in a cooling process of the steel material, and more particularly to a method and apparatus for measuring the internal temperature of a steel material capable of measuring the distribution of the internal temperature of the steel material.
[0002]
[Prior art]
In the steel cooling process, estimating the internal temperature of the steel is very important for controlling the structure and the material. Currently, the most commonly used method is to measure the surface temperature using a radiation thermometer in a state that can be considered to be approximately equal to the temperature before cooling, and calculate heat conduction from the capacity of the cooling device and the cooling time. Is used to estimate the transition of the internal temperature. In the case of this method, it is inevitable that a certain degree of error is caused by factors such as the measurement accuracy of the surface temperature being influenced by the scale and the like and the estimation accuracy of the cooling capacity of the cooling device.
[0003]
For this reason, a method for directly measuring the internal temperature of a steel material has been developed for some time, and a method for measuring the internal temperature using the temperature dependence of the ultrasonic velocity has been proposed. A typical example is that the propagation speed of ultrasonic waves varies depending on the temperature of the steel material and its crystal structure, FCC (Face Center Cubic) and BCC (Body Center Cubic). It is what you use. As an example, what is described in Japanese Patent Publication No. 2-16874 will be described with reference to FIGS.
[0004]
This method simultaneously obtains the temperature distribution inside the steel material and the transformation rate of the steel material (the ratio of FCC and BCC takes a value of 0 to 1, where 0 is the entire region is FCC, and 1 is the entire region is BCC). , and the like shown in FIG. 8, keep the relationship between the temperature and the ultrasonic longitudinal wave sound velocity v _l and shear wave velocity v _s is stored in the storage device 51 to the steel type. The electromagnetic ultrasonic longitudinal wave and transverse wave propagation time measuring device 52 measures the longitudinal wave round-trip propagation time T _l and the transverse wave round-trip propagation time T _s inside the steel sheet, and inputs them to the comparison unit 55. Further, the plate thickness is measured by the X-ray thickness meter 53 and input to the calculation unit 54. The temperature distribution inside the steel plate is assumed to be a quadratic function.
[0005]
Assuming initial values of the surface temperature θ _s and the center temperature θ _c , an internal temperature distribution is obtained from the initial values by the calculation unit 54, and from the sound velocity distribution and thickness D derived from the internal temperature distribution, The ultrasonic round-trip propagation time (T ₁ , T _s ) is obtained and compared with the actual measured propagation time. If the actual value and the calculated value are different, change the surface temperature θ _s and the center temperature θ _c and repeat until the calculated propagation time (T _l , T _s ) matches the actual measured value. Determine the temperature distribution.
[0006]
The determined surface temperature θ _s and center temperature θ _c enter the transformation rate calculation unit 56. Here, the temperature distribution in the thickness direction of the steel sheet is calculated from the surface temperature θ _s and the center temperature θ _c and displayed on the display device 57. Further, the transformation temperature θ _p for each steel type is stored in advance, the thickness of the region where the transformation temperature is θ _p or less is obtained, and the transformation rate is obtained from the ratio to the total thickness. According to this method, the internal temperature distribution can be obtained simultaneously with the transformation rate.
[0007]
Japanese Laid-Open Patent Publication No. 5-215617 discloses a method for obtaining an average temperature of a steel material by utilizing the fact that the sound velocity ratio of the longitudinal wave and the transverse wave of the ultrasonic wave in the steel material varies depending on the temperature of the steel material. This is because, as shown in FIG. 9, the sound velocity ratio of the longitudinal wave and the transverse wave with respect to the material temperature is obtained in advance, the ultrasonic wave is actually incident on the steel material, the sound velocity of the longitudinal wave and the transverse wave is measured, and the ratio is calculated from the ratio. The average temperature of the steel material is measured using FIG.
[0008]
Furthermore, as a method for measuring the temperature distribution in the thickness direction of the steel surface layer portion, a method using the propagation velocity of ultrasonic surface waves is described in JP-A-7-77465. An outline of this method is shown in FIG. An ultrasonic pulser 62 is driven from a computer 61 and ultrasonic waves are incident on a steel material 64 from an ultrasonic probe 63 to generate surface waves. Then, the surface wave propagating on the surface of the steel material 64 is received by another probe 65 and input to the computer 61 via the amplifier 66. The computer 61 calculates the propagation time of the ultrasonic surface wave from these input / output signals. This measurement is performed a plurality of times while changing the frequency of the ultrasonic wave, and the thickness direction temperature distribution of the steel material surface layer portion is measured from these values. In addition, 67 is a contact-type thermometer, 68 is a radiation thermometer, and measures the temperature of the steel material 64 and uses it for calculation.
[0009]
[Problems to be solved by the invention]
However, these methods also have the following problems.
That is, the method described in Japanese Patent Publication No. 2-16874 and the method described in Japanese Patent Application Laid-Open No. 5-215617 require measurement of longitudinal and transverse waves and two sound velocities. However, especially for the transverse wave, since it is easily affected by acoustic anisotropy, there is a problem that the sound speed varies greatly depending on the plane of polarization of the ultrasonic wave. As a result, accurate measurement is difficult. In addition, the measurement apparatus becomes complicated because two measurements of the longitudinal wave and the transverse wave are required.
[0010]
A further problem is that the temperature dependence of the sound speed is measured in advance in these conventional techniques, but the temperature dependence of the sound speed differs depending on the cooling rate. In addition to temperature, the crystal structure has a great influence on the temperature dependence of the sound speed. However, in a ferritic steel material, the sound speed greatly changes at the transformation point as shown in FIG. This transformation temperature is a temperature determined by the equilibrium diagram when the cooling rate is extremely slow, and is constant. However, as the cooling rate increases, a supercooling phenomenon occurs and becomes lower than the transformation temperature in the equilibrium state.
[0011]
The inventors focused on this phenomenon and investigated the relationship between the cooling speed and the sound speed in detail. As a result, the temperature dependence of the sound speed is a temperature at which the sound speed changes discontinuously as the cooling speed increases as shown in FIG. It has been clarified that becomes lower. It is considered that the transformation is proceeding in the temperature range where the sound velocity changes discontinuously. From FIG. 3, it can be seen that the temperature dependence of the sound velocity of the ultrasonic waves cannot be expressed in a fixed relationship. As a result, the prior art can only be used under a certain cooling rate, and it can be used at all times under conditions where the cooling rate is dynamically changed as necessary, as in an actual process. Can not.
Moreover, the technique described in Japanese Patent Application Laid-Open No. 7-77465 has a problem that only a temperature at a depth near the surface of the steel material can be measured.
[0012]
This invention is made in view of such a situation, and makes it a subject to provide the method which can measure the temperature distribution inside steel materials accurately.
[0013]
[Means for Solving the Problems]
The first means for solving the above-mentioned problem is to approximate the temperature distribution inside the steel material in a function form determined by the steel material surface temperature and another parameter, the sound velocity in the BCC region of the steel material, and the FCC region. From the measured sound velocity, steel transformation rate, steel surface temperature, steel thickness, and ultrasonic propagation time in the thickness direction of the steel , solve the following equation or its approximate equation: A method for measuring the internal temperature of a steel product, characterized in that a temperature distribution inside the steel product is obtained.
[Expression 4]

Where t is the ultrasonic propagation time (reciprocation), d is the thickness of the steel material, H is the transformation rate and is a value from 0 to 1 ( 0 for the entire region FCC, 1 for the entire region BCC ) , C _B (T ) Is the speed of sound at the temperature T in the BCC region, C _F (T) is the speed of sound at the temperature T in the FCC region, and x is the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x.
[0014]
The sound velocity in the BCC region and the sound velocity in the FCC region of the steel material can be obtained by measurement in advance as a function of temperature. Therefore, if the transformation rate of the steel material, the distribution of the internal temperature (including the surface temperature) of the steel material, and the thickness of the steel material are known, the ultrasonic propagation time in the thickness direction in the steel material can be calculated.
[0015]
In this means, the temperature distribution inside the steel material is approximated in a function form determined by the steel material surface temperature and another parameter. In the measurement, the surface temperature of the steel material and the thickness of the steel material are obtained by measurement or estimation, and the ultrasonic propagation time in the thickness direction in the steel material is measured. Next, the calculation is repeated by changing the internal temperature distribution of the steel material so that the calculated ultrasonic propagation time and the actually measured ultrasonic propagation time coincide with each other. And let the internal temperature distribution of the steel materials used for calculation at the time of matching be the internal temperature distribution of the steel materials to obtain.
[0016]
Since the temperature distribution inside the steel material is approximated by a function form determined by the steel material surface temperature and another one parameter, the temperature distribution inside the steel material is uniquely determined by determining the parameter. Therefore, the calculation is most preferably a calculation for obtaining the parameter.
[0017]
In this means, it is necessary to know the transformation rate of the steel material in advance, but known means as disclosed in JP-A-5-126798 can be used for measuring the transformation rate of the steel material.
[0018]
As described above, in this means, the temperature distribution inside the steel material is approximated by a function determined by the steel material surface temperature and one other parameter, and then the temperature dependence of the sound velocity in the BCC region and the FCC region. By considering the two sound velocity curves and the transformation rate, the temperature distribution can be obtained no matter how the transformation temperature changes, so even in a process where the cooling rate changes dynamically. The internal temperature can be measured. In addition, since one unknown is obtained, it is not necessary to use two longitudinal waves and two transverse waves, and only one of them (particularly the longitudinal wave) may be used, so that the ultrasonic apparatus can be simplified. It also has features.
[0019]
In this means, the method for obtaining the internal temperature of the steel material is to obtain the temperature distribution inside the steel material by solving the following equation or its approximate equation .
[0020]
[Equation 5]

[0021]
Where t is the ultrasonic wave propagation time (reciprocating), d is the thickness of the steel material, H is the transformation rate and is a value of 0 to 1 (0 for all regions FCC, 1 for all regions BCC), C _B (T ) Is the speed of sound at the temperature T in the BCC region, C _F (T) is the speed of sound at the temperature T in the FCC region, and x is the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x.
[0022]
In this means, the temperature dependence C _B (T) of the sound speed in the BCC region and the temperature dependence C _F (T) of the sound speed in the FCC region are obtained in advance by experiments.
When the transformation proceeds from the outside, the sound velocity in the range where the transformation is completed is determined from the temperature dependence C _B (T) of the sound velocity in the BCC region and the internal temperature distribution T (x), and the sound velocity in the range where the transformation is not completed. Is determined from the temperature dependence C _F (T) of the sound velocity in the FCC region and the internal temperature distribution T (x). Here, x is a position in the thickness direction. At this time, in consideration of the thickness d of the steel material, the ultrasonic wave propagation time t can be obtained from the following equation. However, the transformation rate H takes a value of 0 to 1 (when the value is 0, the entire area FCC, and when it is 1, the entire area BCC).
[0023]
[Formula 6]

[0024]
Since the unknown in equation (1) is only the internal temperature distribution T (x) in the thickness direction of the steel material (actually, one unknown parameter that determines this function), the sonic temperature dependence C _{B in} the BCC region of the steel material (T), sonic temperature dependence C _F (T) in the FCC region, internal temperature distribution T (x) in the thickness direction of the steel material, thickness d of the steel material, and ultrasonic wave propagation in the thickness direction in the steel material From the measurement value t of time, the internal temperature distribution T (x) in the thickness direction of the steel material satisfying this equation can be obtained by repeated calculation.
[0025]
The second means for solving the above-mentioned problem is to approximate the temperature distribution inside the steel material in a function form determined by the steel material surface temperature and another parameter, the sound velocity in the BCC region of the steel material, and the FCC region. From the measured sound velocity, steel transformation rate, steel surface temperature, steel thickness, and ultrasonic propagation time in the thickness direction of the steel, solve the following equation or its approximate equation: This is a method for measuring the internal temperature of a steel material to obtain the temperature distribution inside the steel material, and for each combination of the transformation rate of several steel materials, the surface temperature of the steel material, the thickness of the steel material, and the temperature distribution of the steel material by In addition, the ultrasonic propagation time in the thickness direction of the steel material is calculated and stored, the ultrasonic propagation time in the thickness direction in the steel material is measured, the transformation rate of the given steel material, the surface temperature of the steel material, Has the closest value to the actual measured value for the thickness of steel. That the temperature distribution of the steel material, a method of measuring the internal temperature of the steel material characterized by employing as the temperature distribution of the steel material (claim 2).
[0026]
[Expression 7]

[0027]
Where t is the ultrasonic wave propagation time (reciprocating), d is the thickness of the steel material, H is the transformation rate and is a value of 0 to 1 (0 for all regions FCC, 1 for all regions BCC), C _B (T ) Is the speed of sound at the temperature T in the BCC region, C _F (T) is the speed of sound at the temperature T in the FCC region, and x is the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x.
[0028]
Since the equation (1) includes integration, it is difficult to obtain a solution analytically. Therefore, in this means, the transformation rate H of the steel material, the surface temperature T _s of the steel material, the thickness d of the steel material and the temperature distribution T (x) (actually one unknown parameter that determines this function) Approximating the temperature distribution T (x) and the calculated ultrasonic propagation time by obtaining the value of the right side of the formula (1) for each combination by changing at a certain pitch, By substituting the measured ultrasonic propagation time value into the calculated ultrasonic propagation time value under the conditions of the transformation rate H of the steel material, the surface temperature T _s of the steel material, and the thickness d of the steel material, that is, an approximate equation To obtain the temperature distribution T (x) inside the steel material. Thereby, the temperature distribution T (x) inside the steel material can be easily obtained.
[0029]
The third means for solving the problem is the first means or the second means , wherein the internal temperature distribution of the steel material is approximated by the following expression (claim 3). ) .
T (x) = a ₂・ x ² + a ₁・ x + a ₀ … (2)
Here, a ₂ , a ₁ and a ₀ are constants.
[0030]
When the one-dimensional heat conduction equation is solved, the temperature distribution inside the steel is known to be a quadratic function centered on the steel center. Accurate approximation is possible. Assuming that the steel center temperature is T _c and the surface temperature is T _s , the coefficients of the formula (2) are a ₂ = −4 / d ² · (T _c -T _s ), a ₁ = 4 / d · (T _c -T _s ), a ₀ = T _s . Therefore, if the surface temperature T _s is known, by substituting equation (2) into equation (1), the unknown is only the center temperature T _c , so equation (1) can be solved relatively easily. it can. In particular, by applying this means to the third means, the center temperature T _c can be obtained without solving the integral equation, and by substituting this into the equation (2), the temperature distribution T ( x) can be determined.
[0031]
Moreover, in this means, in order to approximately obtain the temperature distribution T (x) inside the steel material, a nonlinear least square method can be used. That is, the difference between the calculated value and the measured value in Equation (1) is set as an evaluation function, and the central temperature as a parameter is determined so that it becomes the smallest. At this time, the evaluation function is expressed as follows, assuming that the measured value of t in equation (1) is t _m and the calculated value is t (T _c ).
S = (t (T _c ) -t _m ) ² … (3)
When t (T _c ) is Taylor-expanded and the first order terms are considered,
[0032]
[Equation 8]

[0033]
It becomes. Here, T _c0 is an initial value, ΔT _c = T _c −T _c0 . The minimum condition of the evaluation function is
[0034]
[Equation 9]

[0035]
Therefore, ΔT _c can be easily obtained by the least square method, and the center temperature T _c can be obtained by repeating several times.
[0036]
The fourth means for solving the above-mentioned problem is a first sonic speed storage means for storing the sonic temperature dependency in the BCC region of the steel material, and a sonic temperature dependency in the FCC region. 2 sound speed storage means, transformation rate estimation means for estimating the transformation rate of the steel material, surface temperature estimation means for estimating the surface temperature of the steel material, thickness measurement means for measuring the thickness of the steel material, and the thickness direction of the steel material Ultrasonic measurement means for measuring ultrasonic propagation time, and an arithmetic means for obtaining the internal temperature of the steel material by solving the following equation or its approximate equation from the values obtained by the respective means: An apparatus for measuring the internal temperature of a steel material ( claim 4 ).
[Expression 10]

Where t is the ultrasonic propagation time (reciprocation), d is the thickness of the steel material, H is the transformation rate and is a value from 0 to 1 ( 0 for the entire region FCC, 1 for the entire region BCC ) , C _B (T ) Is the speed of sound at the temperature T in the BCC region, C _F (T) is the speed of sound at the temperature T in the FCC region, and x is the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x.
[0037]
The temperature dependence C _B (T) of the sound speed in the BCC region of the steel material and the temperature dependence C _F (T) of the sound speed in the FCC region are respectively stored in the first sound speed storage means and the second sound speed storage means. Remember. The transformation rate of the steel material is measured by transformation rate estimation means (as disclosed in JP-A-5-126798). The surface temperature estimation means estimates the surface temperature using the heat conduction equation or the like from the measured surface temperature and the elapsed time from the measured time. A well-known thing can be used as a surface temperature estimation means. And while measuring the thickness d of steel materials with a thickness measurement means, the ultrasonic propagation time t to the thickness direction of steel materials is measured with an ultrasonic measurement means.
[0038]
The calculation means obtains the internal temperature of the steel material using these actually measured values and estimated values. As a specific algorithm for obtaining the internal temperature of the steel material, the method described in the second to fourth means can be employed. The display means displays the obtained temperature distribution itself, or the center temperature of the steel material that is a part thereof.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an internal temperature measuring device for steel as an example of an embodiment of the present invention.
[0040]
The subject 1 is a thick plate in the cooling process after the rolling is finished, and is cooled from the front and back surfaces by a water cooling device not shown in the drawing. 2 and 3 are means for storing the temperature dependence of the sound velocity in the BCC region and the temperature dependence of the sound velocity in the FCC region, respectively. Specifically, the line shown in FIG. By storing the coefficient, the speed of sound at a certain temperature is easily obtained. That is, C _B (T) and C _F (T) are expressed by polynomials and their coefficients are stored.
[0041]
Reference numeral 4 denotes transformation rate estimation means, which uses a transformation rate measuring device. This uses magnetism as disclosed in JP-A-5-126798, and includes a magnetizer that generates magnetic flux on one surface of a steel material, and a pair of magnetic sensors on the opposite side of the steel material, The amount of magnetic flux transmitted through the steel material is obtained from the subtraction value between the magnetic sensors, and the transformation rate is obtained from the value. In addition, as the transformation rate estimating means, a transformation rate can be obtained by calculation using a continuous cooling transformation diagram so-called CCT diagram. Further, when the transformation is not performed at all like the slab after extraction from the heating furnace, or when the transformation is clearly completed due to the cooling, the transformation rate H can be regarded as 0 or 1 even if treated. Implementation is possible.
[0042]
Reference numeral 5 denotes surface temperature estimation means, and here, a radiation thermometer is used. The optical path is shielded so as not to be affected by the cooling water, and measurement is performed while air purging between the surface of the subject 1 and the thermometer. Reference numeral 6 denotes a thickness measuring means, which uses a γ-ray thickness meter.
[0043]
Reference numeral 7 denotes an ultrasonic measurement means, which utilizes the fact that it is being cooled, and acoustically couples the material from the piezoelectric probe to the material by a water column. Since the boiling film is removed by cooling water, measurement can be performed by this method. The propagation time is obtained from the time difference between the S echo from the surface of the material and the B echo from the bottom surface. Note that when measuring at the time of recuperation, since the surface temperature becomes high, a means capable of non-contact ultrasonic measurement such as electromagnetic ultrasonic waves and laser ultrasonic waves is used.
[0044]
When the measurement position of the ultrasonic measurement means is different from the position where the radiation thermometer is installed, the surface temperature estimation means 5 is provided with a temperature estimation function to estimate the surface temperature of the subject 1 during measurement with ultrasonic waves. Make it possible. If the surface temperature of the subject 1 at the position of the thickness measuring means 6 is different from the surface temperature of the subject 1 being measured with ultrasonic waves, thermal expansion correction is performed, and the object being measured with ultrasonic waves is corrected. The thickness of the specimen is used for calculation.
[0045]
Reference numeral 8 denotes a central temperature calculation means, which is configured as shown in FIG. 2 in the present embodiment. That is, the center temperature-propagation time calculation means 10 determines the discrete representative values for each variable, using the center temperature, surface temperature, thickness, and transformation rate of the subject 1 as variables, and for combinations of these representative values, ( The temperature distribution inside the subject 1 is obtained from the equation (2), and this is substituted into the equation (1) to obtain the ultrasonic propagation time. These are tabulated and stored in the center temperature-propagation time calculation means 10. For example, the center temperature is calculated by dividing between 200 ° C. and 800 ° C. every 50 ° C.
[0046]
Instead of performing table formation, the relationship between the center temperature of the subject 1, the surface temperature, the thickness, the transformation rate, and the ultrasonic propagation time may be approximated by a polynomial, and the coefficients may be stored. .
[0047]
Next, the center temperature calculation means 11 applies the propagation time measurement value obtained by the ultrasonic measurement means 7 together with the thickness, surface temperature, and transformation rate of the subject 1 to the table, so that the propagation time measurement value is the best. The center temperature having a close calculated propagation time is taken as the center temperature to be obtained. Alternatively, the propagation time measurement value obtained by the ultrasonic measurement means 7 is applied to the polynomial together with the thickness, surface temperature, and transformation rate of the subject 1 and input to the relational expression between the propagation time and the center temperature, The center temperature of the specimen 1 may be obtained. If the center temperature is obtained, the temperature distribution inside the subject 1 can be obtained from the equation (2). Reference numeral 9 denotes a temperature distribution display means, which is a CRT for displaying the temperature distribution based on the expression (2) or an analog recorder for displaying the transition of the center temperature.
[0048]
As the operation of the center temperature calculation means 8, the center temperature may be obtained using the above-mentioned least square method. In the present embodiment, Equation (2) is assumed as the internal temperature distribution of the subject 1, but the assumption of the internal temperature distribution of the subject 1 in the present invention is the surface temperature and another one. As long as it is determined by parameters, not limited to this, an appropriate one can be selected and used.
[0049]
In the present embodiment, among the above-described components, the first sonic temperature dependency storage unit 2, the first sonic temperature dependency storage unit 3, and the central temperature calculation unit 8 are used by using a computer. It is composed.
[0050]
【Example】
Hereinafter, a specific measurement example using the temperature measuring method inside the steel material according to the embodiment of the present invention will be described.
The material used for the measurement was a carbon steel plate having a thickness of 23.39 mm, which was continuously cooled from a soaking state of 900 ° C. at a cooling rate of about 10 ° C./s and measured 40 seconds after the start of cooling. At this time, the transformation rate was estimated to be 83%, and the surface temperature was 196 ° C. Using this, the relationship between a certain center temperature and the ultrasonic propagation time obtained from the expressions (1) and (2) is calculated at several center temperatures based on the expressions (1) and (2). For example, since the sound speed distribution at the center temperatures of 400 ° C., 500 ° C., 600 ° C., and 700 ° C. is as shown in FIG. 4, the propagation time can be calculated based on the equation (1).
[0051]
FIG. 5 shows the result, and it can be seen that the propagation time increases as the center temperature increases. Since the actual propagation time when this measurement was performed was 8.383 μs, the center temperature at this time was easily obtained from FIG. 5 and was 513 ° C. At this time, the value of the thermocouple thermometer embedded in the center of the thickness of the steel material was 520 ° C., and both agreed well. FIG. 6 is a display example of the temperature distribution at this time, and is calculated based on the equation (2).
[0052]
【The invention's effect】
As described above, in the present invention, the temperature distribution inside the steel material is approximated by a function form determined by the steel material surface temperature and another parameter, and the temperature distribution inside the steel material is approximated by the steel surface temperature and the other surface temperature. It is approximated by a function determined by one parameter, and the sound speed in the BCC region of steel, the sound speed in the FCC region, the transformation rate of the steel, the surface temperature of the steel, the thickness of the steel, and the thickness in the steel Since the temperature distribution inside the steel material is obtained from the measured value of the ultrasonic propagation time in the direction, the temperature distribution can be obtained no matter how the transformation temperature changes, so the cooling rate changes dynamically. Even in such a process, the internal temperature can be measured. In addition, since one unknown is obtained, it is not necessary to use two longitudinal waves and transverse waves, and only one of them (especially longitudinal waves) can be measured. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an internal temperature measuring device for steel as an example of an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an example of a configuration of a center temperature calculation unit.
FIG. 3 is a diagram showing temperature dependency of longitudinal wave sound velocity.
FIG. 4 is a diagram showing an example of the relationship between the center temperature of the steel material and the sound velocity in the thickness direction.
FIG. 5 is a diagram showing an example of the relationship between the center temperature of a steel material and the ultrasonic wave propagation time.
FIG. 6 is a diagram showing a temperature distribution in a steel material obtained by measurement.
FIG. 7 is a block diagram showing an example of a conventional temperature measuring device inside a steel material.
FIG. 8 is a diagram showing the relationship between the steel material temperature and the ultrasonic velocity of longitudinal and transverse waves.
FIG. 9 is a diagram illustrating a relationship between a material temperature and a velocity ratio between a longitudinal wave and a transverse wave of ultrasonic waves.
FIG. 10 is a block diagram showing another example of a conventional temperature measuring device inside a steel material.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Subject 2 ... 1st sound speed temperature dependence storage means 3 ... 2nd sound speed temperature dependence storage means 4 ... Transformation rate estimation means 5 ... Surface temperature estimation means 6 ... Thickness measurement means 7 ... Ultrasonic measurement means 8 ... center temperature calculation means 9 ... temperature distribution display means 10 ... center temperature-propagation time calculation means 11 ... center temperature calculation means

Claims (4)

The temperature distribution inside the steel material is approximated by a function determined by the steel surface temperature and one other parameter. The sound velocity in the BCC region, the sound velocity in the FCC region, the transformation rate of the steel material, and the steel material A steel material characterized in that the temperature distribution inside the steel material is obtained by solving the following equation or its approximate equation from the surface temperature, the thickness of the steel material, and the measured value of the ultrasonic propagation time in the thickness direction in the steel material. To measure the internal temperature of

Where t is the ultrasonic propagation time (reciprocation), d is the thickness of the steel material, H is the transformation rate and is a value from 0 to 1 ( 0 for the entire region FCC, 1 for the entire region BCC ) , C _B (T ) Represents the sound velocity at the temperature T in the BCC region, C _F (T) represents the sound velocity at the temperature T in the FCC region, and x represents the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x. The temperature distribution inside the steel material is approximated by a function determined by the steel surface temperature and one other parameter. The sound velocity in the BCC region, the sound velocity in the FCC region, the transformation rate of the steel material, and the steel material Measurement of the internal temperature of the steel to obtain the temperature distribution inside the steel by solving the following equation or its approximate equation from the surface temperature, the thickness of the steel, and the measured ultrasonic propagation time in the thickness direction in the steel The ultrasonic propagation time in the thickness direction of the steel material is calculated for each combination of the transformation rate of several steel materials, the surface temperature of the steel material, the thickness of the steel material, and the temperature distribution of the steel material by the following formula. Calculate and store, measure the ultrasonic propagation time in the thickness direction in the steel, and have the closest value to the measured value in the transformation rate of the given steel, the surface temperature of the steel, and the thickness of the steel The temperature distribution of steel material is the same as the temperature distribution of steel material. Method of measuring the internal temperature of the steel material, characterized by employing Te.

Where t is the ultrasonic wave propagation time (reciprocating), d is the thickness of the steel material, H is the transformation rate and is a value of 0 to 1 (0 for all regions FCC, 1 for all regions BCC), C _B (T ) Represents the sound velocity at the temperature T in the BCC region, C _F (T) represents the sound velocity at the temperature T in the FCC region, and x represents the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x. The method for measuring the internal temperature of a steel material according to claim 1 or 2 , wherein the internal temperature distribution of the steel material is approximated by the following equation.
T (x) = a ₂・ x ² + a ₁・ x + a ₀ … (2)
Here, a ₂ , a ₁ and a ₀ are constants. The first sonic speed storage means for storing the sonic temperature dependence in the BCC region of the steel material, the second sonic speed storage means for storing the sonic temperature dependence in the FCC area, and the transformation rate of the steel material are estimated. Transformation rate estimation means, surface temperature estimation means for estimating the surface temperature of the steel material, thickness measurement means for measuring the thickness of the steel material, ultrasonic measurement means for measuring the ultrasonic propagation time in the thickness direction of the steel material, An apparatus for measuring the internal temperature of a steel material, comprising: an arithmetic means for obtaining an internal temperature of the steel material by solving the following equation or an approximate equation thereof from the values obtained by the respective means.

Where t is the ultrasonic propagation time (reciprocation), d is the thickness of the steel material, H is the transformation rate and is a value from 0 to 1 ( 0 for the entire region FCC, 1 for the entire region BCC ) , C _B (T ) Represents the sound velocity at the temperature T in the BCC region, C _F (T) represents the sound velocity at the temperature T in the FCC region, and x represents the position in the thickness direction of the steel material. T (x) is the temperature of the steel material at the position x.

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