JP6242247B2 - Manufacturing method of Si-added cold-rolled steel sheet - Google Patents
Manufacturing method of Si-added cold-rolled steel sheet Download PDFInfo
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Description
本発明は、Ｓｉの添加によって高い強度と優れた加工性を備えた高強度冷延鋼板であるＳｉ添加冷延鋼板の製造方法に関し、例えば、リン酸塩処理等の化成処理を施して使用される自動車用高強度冷延鋼板の製造方法に関する。 The present invention relates to a method for producing a Si-added cold-rolled steel sheet, which is a high-strength cold-rolled steel sheet having high strength and excellent workability due to the addition of Si. For example, the present invention is used after chemical conversion treatment such as phosphate treatment. The present invention relates to a method for producing a high-strength cold-rolled steel sheet for automobiles.
高強度鋼板の優れた機械的特性の確保、すなわち高強度と高加工性を両立するための手段としては「Ｓｉ(ケイ素)添加」が有効であることが知られている。しかし、添加されたＳｉは、冷間圧延後に鋼板の金属組織を作り込む焼鈍工程において、酸化物（Ｓｉ酸化物）として鋼板表層に濃化する。
鋼板表層のＳｉ酸化物は、焼鈍後に行われるリン酸塩処理等による化成皮膜の生成（化成処理）を著しく阻害するので、連続焼鈍工程においては、従来から、焼鈍後の鋼板表層を酸洗除去する方法（後酸洗）で対応している。また、この酸洗に代わるものとして、「直火炉・還元炉を利用した酸化還元法」によって化成処理性を確保する試みもなされている。このような化成処理を阻害する鋼板表層のＳｉ酸化物に対処する技術として、以下の特許文献に開示される技術が存在する。
It is known that “Si (silicon) addition” is effective as a means for ensuring the excellent mechanical properties of a high-strength steel sheet, that is, for achieving both high strength and high workability. However, the added Si is concentrated on the steel sheet surface layer as an oxide (Si oxide) in an annealing process in which the metal structure of the steel sheet is formed after cold rolling.
Since the Si oxide on the steel sheet surface layer significantly inhibits the formation of a chemical conversion film (chemical conversion treatment) by phosphate treatment, etc. performed after annealing, the steel sheet surface layer after annealing has been conventionally pickled and removed in the continuous annealing process. It corresponds by the method to do (post pickling). As an alternative to this pickling, an attempt has been made to ensure chemical conversion processability by an “oxidation-reduction method using a direct furnace / reduction furnace”. As a technique for dealing with such Si oxide on the steel sheet surface layer that hinders the chemical conversion treatment, there is a technique disclosed in the following patent document.
特許文献１は、連続焼鈍設備における直火式加熱炉を開示している。特許文献１に開示の直火式加熱炉は、全有効炉長に亘って複数の加熱バーナを配置し、これら加熱バーナのうち、有効炉長に対し、複数の鋼帯温度、還元速度、酸化速度及び加熱速度を考慮して求められる割合以上の炉出側炉長部分の加熱バーナを、火炎中に焼成中間生成物を有し且つ遊離酸素を有しない非平衡領域を形成し、火炎が鋼帯に対し略直角にしかもその非平衡領域で鋼帯面に衝突するよう配置される還元型加熱バーナとし、残炉長部分の加熱バーナを、非還元型加熱バーナとしたことを特徴とする。 Patent Literature 1 discloses a direct-fired heating furnace in a continuous annealing facility. The direct-fired heating furnace disclosed in Patent Document 1 has a plurality of heating burners arranged over the entire effective furnace length, and among these heating burners, a plurality of steel strip temperatures, reduction rates, oxidations The heating burner of the furnace length side of the furnace outlet side that exceeds the ratio required in consideration of the speed and the heating speed forms a non-equilibrium region having a calcined intermediate product and no free oxygen in the flame. The reduction heating burner is arranged so as to collide with the steel strip surface in the non-equilibrium region at a substantially right angle with respect to the strip, and the heating burner in the remaining furnace length is a non-reduction heating burner.
また、特許文献２は、連続焼鈍方法を開示している。特許文献２に開示の連続焼鈍方法は、帯状の被加熱材を、予熱帯および加熱帯に連続通板させて焼鈍する連続焼鈍方法であって、加熱帯では蓄熱燃焼切替型バーナにより燃焼させるとともに、被加熱材の表面近傍に燃料を分散供給して低空気比で燃焼させ、予熱帯では加熱帯における前記バーナの吸引排ガスを燃焼させることを特徴とする。 Patent Document 2 discloses a continuous annealing method. The continuous annealing method disclosed in Patent Document 2 is a continuous annealing method in which a band-shaped material to be heated is annealed by continuously passing through a pre-tropical zone and a heating zone, and in the heating zone, the material is burned by a regenerative combustion switching burner. The fuel is dispersedly supplied near the surface of the material to be heated and burned at a low air ratio. In the pre-tropical zone, the exhaust gas exhausted from the burner in the heating zone is burned.
上述の各特許文献は、いずれも直火を用いた直火炉出側における鋼板表面の酸化を抑制するものであるが、これら特許文献の技術を、Ｓｉが添加された高強度鋼板に対して用いても、焼鈍工程において鋼板表層にはＳｉ酸化物が生成されてしまう。
従って、鋼板の表面品質を安定して確保するためには、各特許文献の酸化還元法の適用に関わらず、焼鈍後の後酸洗によってＳｉ酸化物を除去しなくてはならないというのが実情である。しかも、Ｓｉの添加量（Ｓｉの含有量）が多いほど鋼板表層にＳｉ酸化物が多く生成されるので、焼鈍後の後酸洗で除去しなくてはならない鋼板表層の厚み（これを、必要除去量という）が大きくなる。
Each of the above-mentioned patent documents suppresses oxidation of the steel sheet surface on the direct-fired furnace exit side using direct fire, but the techniques of these patent documents are used for high-strength steel sheets to which Si is added. However, Si oxide will be produced | generated by the steel plate surface layer in an annealing process.
Therefore, in order to stably secure the surface quality of the steel sheet, the actual situation is that the Si oxide must be removed by post pickling after annealing, regardless of the application of the redox method of each patent document. It is. Moreover, as the amount of Si added (Si content) increases, more Si oxide is generated on the steel sheet surface layer, so the thickness of the steel sheet surface layer that must be removed by post-annealing after annealing (this is necessary) The amount of removal) increases.
Ｓｉの含有量が多い近年の高強度鋼板ではこの必要除去量が非常に大きいので、後酸洗における酸洗原単位（酸洗の負荷）が大きくなってしまい、ひいては連続焼鈍工程における生産性や製造コスト（酸洗原単位）を悪化させている。
本発明は、上述の問題に鑑みてなされたものであって、Ｓｉ添加冷延鋼板の焼鈍後に行われる酸洗の負荷を低減することができるＳｉ添加冷延鋼板の製造方法を提供することを目的とする。
In recent high-strength steel sheets with a high Si content, this necessary removal amount is very large, so that the basic unit of pickling in the post pickling (load of pickling) becomes large, and as a result, productivity in the continuous annealing process and Manufacturing costs (pickling basic unit) are exacerbated.
This invention is made in view of the above-mentioned problem, Comprising: It provides the manufacturing method of Si addition cold-rolled steel plate which can reduce the load of the pickling performed after annealing of Si addition cold-rolled steel plate. Objective.
上記課題を達成するために、本発明は、以下の技術的手段を採用した。
本発明に係るＳｉ添加冷延鋼板の製造方法は、冷延鋼板のエッジ側に前記冷延鋼板を加熱するための酸化バーナを有する直火炉、及び還元性雰囲気の均熱炉を用いて、Ｓｉ含有量が０.５重量％以上の冷延鋼板を焼鈍してＳｉ添加冷延鋼板を製造するに際し、前記直火炉において、前記酸化バーナの燃焼空気比を１.１５以上１.３５以下とし、前記酸化バーナによって前記冷延鋼板を加熱して４５０℃以上６２０℃以下の温度範囲にまで昇温する昇温工程と、前記還元性雰囲気の均熱炉において、前記昇温工程で加熱された冷延鋼板を、７５０℃以上９５０℃以下の温度範囲で均熱焼鈍する焼鈍工程と、前記焼鈍工程で均熱焼鈍された冷延鋼板を酸洗処理する酸洗工程と、を備えることを特徴とする。
In order to achieve the above object, the present invention employs the following technical means.
The method for producing a Si-added cold-rolled steel sheet according to the present invention uses a direct-fired furnace having an oxidation burner for heating the cold-rolled steel sheet on the edge side of the cold-rolled steel sheet, and a soaking furnace in a reducing atmosphere. When manufacturing a Si-added cold-rolled steel sheet by annealing a cold-rolled steel sheet having a content of 0.5% by weight or more, the combustion air ratio of the oxidation burner is set to 1.15 or more and 1.35 or less in the direct-fired furnace, In the heating step of heating the cold-rolled steel sheet by the oxidation burner and raising the temperature to a temperature range of 450 ° C. or more and 620 ° C. or less, and in the soaking furnace in the reducing atmosphere, the cooling heated in the heating step An annealing process of soaking annealing a rolled steel sheet in a temperature range of 750 ° C. or more and 950 ° C. or less, and a pickling process of pickling the cold-rolled steel sheet soaked in the annealing process, To do.
ここで、前記直火炉の酸化バーナが、前記酸化バーナの火炎噴出方向軸線が前記鋼板の表面と交わらないように配置されているとよい。
なお、本発明の最も好ましい形態は、冷延鋼板のエッジ側に前記冷延鋼板を加熱するための酸化バーナを有する直火炉、及び還元性雰囲気の均熱炉を用いて、Ｓｉ含有量が０.５重量％以上の冷延鋼板を焼鈍してＳｉ添加冷延鋼板を製造するに際し、前記直火炉において、前記酸化バーナの燃焼空気比を１.１５以上１.３５以下とし、前記酸化バーナによって前記冷延鋼板を加熱して４５０℃以上６２０℃以下の温度範囲にまで昇温する昇温工程と、前記還元性雰囲気の均熱炉において、前記昇温工程で加熱された冷延鋼板を、７５０℃以上９５０℃以下の温度範囲で均熱焼鈍する焼鈍工程と、前記焼鈍工程で均熱焼鈍された冷延鋼板を酸洗処理する酸洗工程と、を備えるものであって、前記直火炉の酸化バーナが、前記酸化バーナの火炎噴出方向軸線が前記鋼板の表面と交わらないように配置されていることを特徴とする。
Here, the oxidation burner of the direct-fired furnace may be arranged so that the flame ejection direction axis of the oxidation burner does not intersect the surface of the steel plate.
The most preferable embodiment of the present invention uses a direct-fired furnace having an oxidation burner for heating the cold-rolled steel sheet on the edge side of the cold-rolled steel sheet and a soaking furnace in a reducing atmosphere, and has a Si content of 0. When producing a Si-added cold-rolled steel sheet by annealing a cold-rolled steel sheet of 0.5% by weight or more, the combustion air ratio of the oxidation burner is set to 1.15 or more and 1.35 or less in the direct-fired furnace. In the temperature raising step of heating the cold-rolled steel plate to a temperature range of 450 ° C. or higher and 620 ° C. or lower, and the soaking furnace in the reducing atmosphere, the cold-rolled steel plate heated in the temperature raising step, An annealing process for soaking in a temperature range of 750 ° C. or more and 950 ° C. or less, and a pickling process for pickling the cold-rolled steel sheet soaked in the annealing process, the direct furnace Oxidizing burner is a flame jet of the oxidizing burner Wherein the direction axis is arranged so as not to intersect with the surface of the steel sheet.
本発明のＳｉ添加冷延鋼板の製造方法によれば、Ｓｉ添加冷延鋼板の焼鈍後に行われる酸洗の負荷を低減することができる。 According to the method for producing a Si-added cold-rolled steel sheet of the present invention, it is possible to reduce the load of pickling performed after annealing the Si-added cold-rolled steel sheet.
以下、図面を参照しながら、本発明の実施形態を説明する。
なお、以下に説明する実施形態は、本発明を具体化した例示であって、その具体例をもって本発明の構成を限定するものではない。従って、本発明の技術的範囲は、以下の実施形態に開示の内容だけに限定されるものではない。
図１〜図３を参照しつつ、本実施形態によるＳｉ(ケイ素)添加冷延鋼板の製造方法について説明する。図１は、Ｓｉ添加冷延鋼板の製造方法における各工程を示すブロック図である。図２は、焼鈍工程における直火炉の構成を模式的に示す模式図である。図３は、Ｓｉ添加冷延鋼板の鋼板表層の変化を模式的に示す図である。
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In addition, embodiment described below is the illustration which actualized this invention, Comprising: The structure of this invention is not limited with the specific example. Therefore, the technical scope of the present invention is not limited to the contents disclosed in the following embodiments.
The manufacturing method of the Si (silicon) -added cold rolled steel sheet according to the present embodiment will be described with reference to FIGS. FIG. 1 is a block diagram showing each step in the method for producing a Si-added cold-rolled steel sheet. FIG. 2 is a schematic view schematically showing the configuration of the direct furnace in the annealing process. FIG. 3 is a diagram schematically showing changes in the steel sheet surface layer of the Si-added cold-rolled steel sheet.
まず、図１のブロック図に示すように、Ｓｉ添加冷延鋼板の製造方法は、例えば、Ｓｉを０.５重量％以上含有する高Ｓｉスラブを熱間圧延する熱延工程１、熱延工程１によって圧延された高Ｓｉ圧延材を酸性溶液に漬けて洗い（酸洗し）、表面のスケールを除去する前酸洗工程２、及び前酸洗工程２で酸洗された高Ｓｉ圧延材を冷間圧延してＳｉ含有量が０.５重量％以上のＳｉ添加冷延鋼板である冷延鋼板Ｗを製造する冷延工程３を備えている。 First, as shown in the block diagram of FIG. 1, a method for producing a Si-added cold-rolled steel sheet includes, for example, a hot-rolling process 1 and a hot-rolling process in which a high Si slab containing 0.5% by weight or more of Si is hot-rolled. The high Si rolled material rolled by 1 is dipped in an acidic solution and washed (pickling), the pre-pickling step 2 for removing the surface scale, and the high-Si rolled material pickled in the pre-pickling step 2 There is provided a cold rolling step 3 for producing a cold rolled steel sheet W which is a cold rolled steel sheet with Si added and having a Si content of 0.5% by weight or more by cold rolling.
しかし、Ｓｉ添加冷延鋼板の製造方法は冷延工程３で終わりではなく、冷延工程３で製造された冷延鋼板Ｗがめっき材に適用される場合は、冷延鋼板Ｗの金属組織を作り込む焼鈍工程４、及び焼鈍工程４に続いて冷延鋼板Ｗの表面にめっき処理を施しＳｉ添加冷延鋼
板として仕上げる（製造する）めっき工程５を備えている。また、冷延工程３で製造された冷延鋼板Ｗが冷延材に適用される場合、Ｓｉ添加冷延鋼板の製造方法は、冷延工程３の後に、冷延鋼板Ｗの金属組織を作り込む焼鈍工程６、焼鈍工程６で冷延鋼板Ｗの表層（以下、単に鋼板表層という）に生成したＳｉ酸化物を除去するために、当該冷延鋼板Ｗを酸洗し鋼板表層を除去する後酸洗工程７、及び後酸洗工程７で鋼板表層が除去された冷延鋼板Ｗにリン酸塩処理等の化成処理を施してＳｉ添加冷延鋼板として仕上げる（製造する）化成処理工程８を備えている。
However, the manufacturing method of the Si-added cold-rolled steel sheet does not end with the cold-rolling process 3, and when the cold-rolled steel sheet W manufactured in the cold-rolling process 3 is applied to a plating material, the metal structure of the cold-rolled steel sheet W is changed. Following the annealing step 4 to be formed and the annealing step 4, the surface of the cold-rolled steel sheet W is plated to finish (manufacture) it as a Si-added cold-rolled steel sheet. When the cold-rolled steel sheet W manufactured in the cold rolling process 3 is applied to a cold-rolled material, the Si-added cold-rolled steel sheet manufacturing method creates a metal structure of the cold-rolled steel sheet W after the cold rolling process 3. In order to remove the Si oxide generated in the surface layer of the cold-rolled steel sheet W (hereinafter simply referred to as the steel sheet surface layer) in the annealing process 6 and the annealing process 6, the cold-rolled steel sheet W is pickled and the steel sheet surface layer is removed. The cold-rolled steel sheet W from which the steel sheet surface layer has been removed in the pickling process 7 and the post-pickling process 7 is subjected to chemical conversion treatment such as phosphate treatment to finish (manufacture) the chemical conversion treatment process 8 as a Si-added cold-rolled steel sheet. I have.
本実施形態によるＳｉ添加冷延鋼板の製造方法は、冷延鋼板Ｗをめっき材として仕上げる場合においても冷延材として仕上げる場合においても、焼鈍工程に特徴を有するものである。以下、冷延鋼板Ｗを冷延材として仕上げる場合を例として、焼鈍工程６について詳しく説明する。焼鈍工程６は、めっき材として仕上げる場合の焼鈍工程４とほぼ同内容の工程である。 The manufacturing method of the Si-added cold-rolled steel sheet according to the present embodiment is characterized by the annealing process both when the cold-rolled steel sheet W is finished as a plated material and when it is finished as a cold-rolled material. Hereinafter, the annealing step 6 will be described in detail by taking as an example the case where the cold rolled steel sheet W is finished as a cold rolled material. The annealing process 6 is substantially the same process as the annealing process 4 in the case of finishing as a plating material.
尚、本実施形態において冷延鋼板ＷのＳｉ含有量が０.５重量％以上であると説明しているが、これは、本実施形態によるＳｉ添加冷延鋼板の製造方法が、Ｓｉ添加量の多い冷延鋼板Ｗを対象としているからである。
冷延鋼板ＷにおけるＳｉ含有量が０.５重量％以上であれば、焼鈍工程６の後に後述するＳｉ濃化層が形成されやすいので、後酸洗工程７での酸洗無しでは冷延鋼板Ｗに対する化成処理性を確保することが困難になる。このように、Ｓｉ含有量について０.５重量％以上の水準にある冷延鋼板Ｗは、焼鈍工程６の後に後酸洗工程７が必要となる。そこで、冷延鋼板Ｗは、酸洗量を低減することができるなど、後酸洗工程７の負荷を軽減することができる本実施形態によるＳｉ添加冷延鋼板の製造方法の対象となる。ここで、Ｓｉ含有量の上限は特に定めないが、３.０重量％を超えて過剰に添加すると加工性の劣化を招く。
In the present embodiment, the Si content of the cold-rolled steel sheet W is explained to be 0.5% by weight or more. This is because the Si-added cold-rolled steel sheet manufacturing method according to the present embodiment is the same as the Si content. This is because the cold-rolled steel sheet W having a large amount is targeted.
If the Si content in the cold-rolled steel sheet W is 0.5% by weight or more, a Si-concentrated layer, which will be described later, is easily formed after the annealing step 6, and therefore the cold-rolled steel plate without the pickling in the post-pickling step 7 is performed. It becomes difficult to ensure the chemical conversion processability for W. Thus, the cold-rolled steel sheet W at a level of 0.5% by weight or more with respect to the Si content requires the post pickling process 7 after the annealing process 6. Therefore, the cold-rolled steel sheet W is an object of the method for manufacturing the Si-added cold-rolled steel sheet according to the present embodiment, which can reduce the load of the post-pickling process 7 such as reducing the pickling amount. Here, the upper limit of the Si content is not particularly defined, but if it is added in excess of 3.0% by weight, workability is deteriorated.
焼鈍工程６は、冷延工程３を終えて長尺且つ平板となった冷延鋼板Ｗを、後述する直火炉１０及び還元炉（図示せず）の内部に連続的に通過させることで、Ｓｉ添加冷延鋼板の金属組織を作り込む連続焼鈍を行う工程である。
図２を参照して、焼鈍工程６で用いられる直火炉１０は、内部を通過する冷延鋼板Ｗを加熱して第１の所定温度にまで上昇させる予熱炉であり、当該内部を通過する冷延鋼板Ｗの幅方向における端部（エッジ）側の炉壁に、火炎を噴出して当該冷延鋼板Ｗを加熱するためのバーナ１１を複数有する。直火炉１０が有するバーナ１１は、火炎として酸化炎Ｆを噴出する酸化バーナであり、直火炉１０内において酸化バーナの酸化炎Ｆで加熱された冷延鋼板Ｗの表面には、主にＦｅ（鉄）の酸化物からなる酸化層が生成する。以下、バーナ１１を酸化バーナ１１と記すことがある。
In the annealing process 6, the cold-rolled steel sheet W that has become a long and flat plate after finishing the cold-rolling process 3 is continuously passed through the inside of a direct-fired furnace 10 and a reduction furnace (not shown) described later. This is a step of performing continuous annealing to create a metal structure of the added cold-rolled steel sheet.
Referring to FIG. 2, the direct-fired furnace 10 used in the annealing process 6 is a preheating furnace that heats the cold-rolled steel sheet W passing through the interior to a first predetermined temperature, and cools the interior through the interior. A plurality of burners 11 for jetting a flame and heating the cold-rolled steel sheet W are provided on the furnace wall on the end (edge) side in the width direction of the rolled steel sheet W. The burner 11 included in the direct-fired furnace 10 is an oxidation burner that ejects an oxidation flame F as a flame. The surface of the cold-rolled steel sheet W heated by the oxidation flame F of the oxidation burner in the direct-fired furnace 10 mainly contains Fe ( An oxide layer made of an oxide of (iron) is formed. Hereinafter, the burner 11 may be referred to as an oxidation burner 11.
酸化バーナ１１は、冷延鋼板Ｗの幅方向における両方のエッジ側の炉壁に複数設けられている。これら複数の酸化バーナ１１は、冷延鋼板Ｗの長手方向に沿ってほぼ等間隔（等ピッチ）に配置されている。冷延鋼板Ｗの一方のエッジ側に配置された酸化バーナ１１の配置位置と他方のエッジ側に配置された酸化バーナ１１の配置位置は、冷延鋼板Ｗの長手方向においてほぼ半ピッチ（１／２ピッチ）分異なっており、冷延鋼板Ｗの長手方向における同一位置には配置されていない。つまり、酸化バーナ１１は、冷延鋼板Ｗの長手方向に沿って見たときに、一方のエッジ側と他方のエッジ側に交互に配置されている。 A plurality of oxide burners 11 are provided on the furnace walls on both edges in the width direction of the cold-rolled steel sheet W. The plurality of burners 11 are arranged at substantially equal intervals (equal pitch) along the longitudinal direction of the cold-rolled steel sheet W. The arrangement position of the oxidation burner 11 arranged on one edge side of the cold-rolled steel sheet W and the arrangement position of the oxidation burner 11 arranged on the other edge side are substantially a half pitch (1 / 2 pitch) and are not arranged at the same position in the longitudinal direction of the cold-rolled steel sheet W. That is, when viewed along the longitudinal direction of the cold-rolled steel sheet W, the oxide burners 11 are alternately arranged on one edge side and the other edge side.
この冷延鋼板Ｗの長手方向に沿ってほぼ等間隔に配置された複数の酸化バーナ１１は、当該平板状の冷延鋼板Ｗの両面である一方の平板面側と他方の平板面側のそれぞれに設けられている。
さらに、各酸化バーナ１１は、当該酸化バーナ１１から噴出する酸化炎Ｆが冷延鋼板Ｗの一方のエッジ側から他方のエッジ側に向かって噴出するように設けられる。これに加えて各酸化バーナ１１は、図２に示すように、この酸化炎Ｆの噴出方向に沿った酸化炎Ｆの軸心線であり一点鎖線で示す火炎噴出方向軸線Ｘ（つまり、酸化バーナ１１の火炎噴出方向軸線Ｘ）が、冷延鋼板Ｗの一方の平板面と他方の平板面、つまり冷延鋼板Ｗの両表面と交わらないように配置されている。
The plurality of burners 11 arranged at substantially equal intervals along the longitudinal direction of the cold-rolled steel sheet W are respectively provided on one flat plate surface side and the other flat plate surface side which are both surfaces of the flat cold-rolled steel plate W. Is provided.
Further, each oxidation burner 11 is provided such that the oxidation flame F ejected from the oxidation burner 11 is ejected from one edge side of the cold-rolled steel sheet W toward the other edge side. In addition to this, as shown in FIG. 2, each oxidation burner 11 is a flame ejection direction axis X (that is, an oxidation burner) that is an axial center line of the oxidation flame F along the ejection direction of the oxidation flame F and indicated by a one-dot chain line. 11 is arranged so as not to intersect one flat surface of the cold rolled steel sheet W and the other flat surface, that is, both surfaces of the cold rolled steel sheet W.
各酸化バーナ１１の火炎噴出方向軸線Ｘは、冷延鋼板Ｗの平板面に対する平行面上に位
置すれば好ましい。また、火炎噴出方向軸線Ｘと酸化バーナ１１が設けられた炉壁との角度は、垂直に限定されず、冷延鋼板Ｗの幅方向の温度むらを大きく生じない程度の範囲の角度であっても構わない。
上述の配置で各酸化バーナ１１を設けることによって、例えば、各酸化バーナ１１から噴出される酸化炎Ｆが、各酸化バーナ１１の配置に従ってほぼ等間隔となると共に、各酸化炎Ｆの向きが冷延鋼板Ｗの表面に対してほぼ平行となる。このとき、各酸化バーナ１１は、酸化バーナ１１から噴出される酸化炎Ｆが冷延鋼板Ｗの表面に触れない位置に配置されていることが望ましい。酸化炎Ｆが冷延鋼板Ｗの表面に触れると、当該酸化炎Ｆが触れる部分と酸化炎Ｆが触れない部分とで温度差が生じやすくなり、冷延鋼板Ｗの表面に温度むらを生じてしまう。この冷延鋼板Ｗの温度むらは、冷延鋼板Ｗ全体の均一な加熱を困難にするだけでなく、冷延鋼板Ｗの表面に生成する酸化層の厚みにむらを生じさせて、冷延鋼板Ｗ全体の均一な酸化を困難にする。
The flame jetting direction axis X of each oxidation burner 11 is preferably located on a plane parallel to the flat plate surface of the cold-rolled steel sheet W. Further, the angle between the flame jetting direction axis X and the furnace wall provided with the oxidation burner 11 is not limited to a vertical angle, and is an angle in a range that does not cause large temperature unevenness in the width direction of the cold-rolled steel sheet W. It doesn't matter.
By providing each oxidation burner 11 in the above-described arrangement, for example, the oxidation flames F ejected from each oxidation burner 11 are substantially equally spaced according to the arrangement of each oxidation burner 11, and the direction of each oxidation flame F is cold. It becomes substantially parallel to the surface of the rolled steel sheet W. At this time, each oxidation burner 11 is desirably arranged at a position where the oxidation flame F ejected from the oxidation burner 11 does not touch the surface of the cold-rolled steel sheet W. When the oxidation flame F touches the surface of the cold-rolled steel sheet W, a temperature difference is likely to occur between the portion where the oxidation flame F touches and the portion where the oxidation flame F does not touch, and temperature unevenness occurs on the surface of the cold-rolled steel plate W. End up. The uneven temperature of the cold-rolled steel sheet W not only makes it difficult to uniformly heat the entire cold-rolled steel sheet W, but also causes unevenness in the thickness of the oxide layer formed on the surface of the cold-rolled steel sheet W. Makes uniform oxidation of the entire W difficult.
例えば、図８に比較例として示す直火炉１００のように、酸化バーナ１１０の火炎噴出方向軸線Ｘを冷延鋼板Ｗの表面にほぼ垂直に向けることで、酸化炎Ｆを冷延鋼板Ｗにあてる場合、冷延鋼板Ｗの温度むらが大きくなり易く、冷延鋼板Ｗ全体の均一な加熱及び酸化が一層困難となる。
図２に示す本実施形態による直火炉１０（焼鈍工程６で用いられる直火炉１０）において、各酸化バーナ１１は、以下に説明する条件で燃焼して酸化炎Ｆを噴出し、冷延鋼板Ｗを加熱する。
For example, like the direct-fired furnace 100 shown as a comparative example in FIG. 8, the flame ejection direction axis X of the oxidation burner 110 is directed substantially perpendicular to the surface of the cold-rolled steel sheet W, so that the oxide flame F is applied to the cold-rolled steel sheet W. In this case, the temperature unevenness of the cold-rolled steel sheet W tends to increase, and uniform heating and oxidation of the entire cold-rolled steel sheet W become more difficult.
In the direct-fired furnace 10 (direct-fired furnace 10 used in the annealing step 6) according to the present embodiment shown in FIG. 2, each oxidation burner 11 burns under the conditions described below and ejects an oxidation flame F, and cold-rolled steel sheet W Heat.
各酸化バーナ１１は、コークス炉ガス（ＣＯＧ）や液化天然ガス（ＬＮＧ）等のガス燃料と空気の混合気体を燃焼させて火炎を噴出し、冷延鋼板Ｗを加熱する。このとき、ガス燃料に対して空気比が１以上と高くなるように酸素を混合して燃焼させることで、酸化バーナ１１から未燃酸素が存在する酸化炎Ｆを噴出させて直火炉１０内に未燃酸素を送り、冷延鋼板Ｗの酸化を促進する。 Each oxidation burner 11 burns a mixed gas of gas fuel such as coke oven gas (COG) or liquefied natural gas (LNG) and air, and jets a flame to heat the cold-rolled steel sheet W. At this time, oxygen is mixed and burned so that the air ratio becomes higher than 1 with respect to the gas fuel, and thereby the oxidation flame F in which unburned oxygen is present is ejected from the oxidation burner 11 to enter the direct-fired furnace 10. Unburned oxygen is sent to promote oxidation of the cold-rolled steel sheet W.
具体的に、酸化バーナ１１の酸化炎Ｆを冷延鋼板Ｗにあてずに必要な酸化膜の厚みを得るには、空気比は、少なくとも１.１５以上必要であり、１.１５〜１.３５の範囲にあることが好ましい。この空気比が１.２０〜１.３０の範囲にあるとさらに好ましい。後に詳しく説明するが、空気比が１.１５未満では、必要な酸化膜の厚みを得ることが困難となる。逆に空気比が１.３５を超えると、燃焼効率の低下が顕著となり酸化促進への寄与は少なくなる。 Specifically, in order to obtain the necessary oxide film thickness without applying the oxidation flame F of the oxidation burner 11 to the cold-rolled steel sheet W, the air ratio is required to be at least 1.15, and 1.15 to 1. It is preferable to be in the range of 35. More preferably, the air ratio is in the range of 1.20 to 1.30. As will be described in detail later, when the air ratio is less than 1.15, it is difficult to obtain a necessary thickness of the oxide film. On the other hand, if the air ratio exceeds 1.35, the reduction in combustion efficiency becomes remarkable and the contribution to the promotion of oxidation decreases.
このような空気比で燃焼する酸化バーナ１１の酸化炎Ｆによって、冷延鋼板Ｗの表面に生成する酸化膜の厚みは、少なくとも０.０３μｍ以上必要であり、０.０５μｍ以上あれば好ましい。
このような好ましい厚みの酸化膜を生成するために、直火炉１０は、前述の空気比にて酸化バーナ１１を燃焼させた上で、上述の第１の所定温度として、冷延鋼板Ｗの温度を４５０〜６２０℃に到達するまで昇温する。必要な酸化膜の厚みを得るには、冷延鋼板Ｗの温度は少なくとも４５０℃以上でなくてはならず、好ましくは５００〜６００℃の範囲にある必要がある。冷延鋼板Ｗの温度が４５０℃未満では、空気比が高くとも必要な酸化膜の厚みを得ることが困難となる。逆に、冷延鋼板Ｗの温度が６２０℃を超えると酸化が過度となって「焼鈍炉内ロールへのピックアップ」発生リスクを増加させてしまい、連続焼鈍の生産性を低下させる可能性がある。
The thickness of the oxide film formed on the surface of the cold-rolled steel sheet W by the oxidation flame F of the oxidation burner 11 that burns at such an air ratio needs to be at least 0.03 μm, preferably 0.05 μm or more.
In order to generate an oxide film having such a preferable thickness, the direct-fired furnace 10 burns the oxidation burner 11 at the air ratio described above, and then sets the temperature of the cold-rolled steel sheet W as the first predetermined temperature. Until the temperature reaches 450 to 620 ° C. In order to obtain the required thickness of the oxide film, the temperature of the cold-rolled steel sheet W must be at least 450 ° C. or higher, and preferably in the range of 500 to 600 ° C. When the temperature of the cold-rolled steel sheet W is less than 450 ° C., it is difficult to obtain a necessary oxide film thickness even if the air ratio is high. Conversely, if the temperature of the cold-rolled steel sheet W exceeds 620 ° C., oxidation may become excessive, increasing the risk of “pickup to the roll in the annealing furnace” and reducing the productivity of continuous annealing. .
なお、直火炉１０における冷延鋼板Ｗの加熱時間（昇温時間）は、一般的な鋼帯の連続焼鈍設備に付随する直火炉１０で冷延鋼板Ｗの温度が４５０〜６２０℃に到達するまでの所要時間（数秒〜数十秒）の範囲であればよい。冷延鋼板Ｗの表面の酸化量は鋼板温度と空気比によってほぼ決まるものであり、当該温度を維持する時間による影響は小さい。直火炉１０の前段には直火炉１０を含む加熱炉の排ガスによる予備加熱を行ってもよい。 In addition, the heating time (temperature rising time) of the cold-rolled steel sheet W in the direct-fired furnace 10 is such that the temperature of the cold-rolled steel sheet W reaches 450 to 620 ° C. in the direct-fired furnace 10 associated with a general steel strip continuous annealing facility. It may be in the range of required time (several seconds to several tens of seconds). The amount of oxidation on the surface of the cold-rolled steel sheet W is substantially determined by the steel sheet temperature and the air ratio, and the influence of the time for maintaining the temperature is small. You may perform the preliminary heating by the waste gas of the heating furnace containing the direct-fired furnace 10 in the front | former stage of the direct-fired furnace 10. FIG.
以上の説明をまとめると、本実施形態による直火炉１０は、当該直火炉１０において、酸化バーナ１１の燃焼空気比を１.１５以上１.３５以下とし、この酸化バーナ１１によって冷延鋼板Ｗを加熱して４５０℃以上６２０℃以下の温度範囲にまで昇温する昇温処理（昇温工程）を行うものであるといえる。
次に、焼鈍工程６で用いられる還元炉は、雰囲気ガスとして水素(Ｈ２)ガスや窒素(Ｎ２)ガスを用いた還元性雰囲気の均熱炉であり、直火炉１０で予熱された冷延鋼板Ｗを還元性雰囲気で第２の所定温度にまで加熱して保持するバーナとして、ラジアントチューブバーナを備えている。
In summary, the direct-fired furnace 10 according to the present embodiment has a combustion air ratio of the oxidation burner 11 of 1.15 or more and 1.35 or less in the direct-fired furnace 10, and the cold-rolled steel sheet W is formed by the oxidation burner 11. It can be said that a heating process (heating process) for heating to a temperature range of 450 ° C. to 620 ° C. is performed.
Next, the reducing furnace used in the annealing step 6 is a soaking furnace having a reducing atmosphere using hydrogen (H 2 ) gas or nitrogen (N 2 ) gas as the atmospheric gas, and the cold furnace preheated in the direct furnace 10. A radiant tube burner is provided as a burner that heats and holds the rolled steel sheet W to a second predetermined temperature in a reducing atmosphere.
還元炉内の雰囲気ガスは、水素(Ｈ２)ガスと窒素(Ｎ２)ガスの混合気体であり、１〜１０vol％Ｈ２ガスを含有し残りはＮ２ガスである。Ｈ２ガスの含有率が１vol％未満では、冷延鋼板Ｗの表面の酸化物を還元するには不十分であり、１０vol％を超えても還元作用は飽和し無駄となるＨ２ガスが生じる。
このとき、均熱炉である還元炉は、上述の第２の所定温度として、７５０〜９５０℃の温度範囲で冷延鋼板Ｗを均熱焼鈍する。均熱焼鈍において７５０℃未満では、材質特性を得るためのオーステナイト変態が不十分となり、また鋼板表面の酸化物を還元するにも不十分となる。また、９５０℃超であっても、材質特性の確保や酸化物の還元の面でメリットは少なく、高温を保つためのエネルギーが無駄となる。ここで、冷延鋼板Ｗを上述の温度範囲に保つ均熱時間は、３０秒から１０分の間が好ましい。
The atmosphere gas in the reduction furnace is a mixed gas of hydrogen (H 2 ) gas and nitrogen (N 2 ) gas, contains 1 to 10 vol% H 2 gas, and the rest is N 2 gas. If the H 2 gas content is less than 1 vol%, it is insufficient to reduce the oxide on the surface of the cold-rolled steel sheet W, and even if it exceeds 10 vol%, the reducing action is saturated and wasteful H 2 gas is generated. .
At this time, the reduction furnace which is a soaking furnace anneals the cold-rolled steel sheet W in the temperature range of 750 to 950 ° C. as the second predetermined temperature. If it is less than 750 ° C. in soaking, the austenite transformation for obtaining material properties becomes insufficient, and it becomes insufficient for reducing oxides on the surface of the steel sheet. Even if it exceeds 950 ° C., there are few advantages in terms of securing material properties and reducing oxides, and energy for maintaining a high temperature is wasted. Here, the soaking time for keeping the cold-rolled steel sheet W in the above temperature range is preferably between 30 seconds and 10 minutes.
以上の説明をまとめると、本実施形態による還元炉は、還元性雰囲気の均熱炉であって、当該均熱炉において、直火炉１０による昇温処理で加熱された冷延鋼板Ｗを、７５０℃以上９５０℃以下の温度範囲で均熱焼鈍する焼鈍処理を行うものであるといえる。
この焼鈍処理の後にガスや液体等を用いて冷延鋼板Ｗを冷却し、その後必要に応じて冷延鋼板Ｗの加工性を向上させるために焼き戻し処理を施してもよい。冷却条件と焼き戻し条件については特に限定されるものではなく、所望の機械的特性を得る上で必要な処理を施すことができる。ただし、焼き戻し処理は、均熱焼鈍と同様に還元性雰囲気炉にて行うものとする。
To summarize the above description, the reduction furnace according to the present embodiment is a soaking furnace with a reducing atmosphere, and in the soaking furnace, a cold-rolled steel sheet W heated by a temperature raising process by the direct-fired furnace 10 is 750. It can be said that the annealing treatment is performed soaking in the temperature range of 950C to 950C.
After this annealing treatment, the cold-rolled steel sheet W may be cooled using a gas, a liquid, or the like, and then tempered to improve the workability of the cold-rolled steel sheet W as necessary. The cooling condition and the tempering condition are not particularly limited, and a treatment necessary for obtaining desired mechanical characteristics can be performed. However, the tempering treatment is performed in a reducing atmosphere furnace as in the soaking annealing.
この還元炉における焼鈍処理において、直火炉１０で生成した冷延鋼板Ｗ表面のＦｅ酸化物などが還元されるが、その際還元反応によってＦｅと分離した酸素や還元雰囲気に含まれる微量の酸素などが冷延鋼板Ｗ（母材）の内部にも拡散し、母材中のＳｉと反応することでＳｉの内部酸化が生じる。このＳｉ酸化物は、冷延鋼板Ｗの最表面で生じ、Ｓｉ酸化物によるＳｉ濃化層を生じる。 In the annealing treatment in the reduction furnace, the Fe oxide on the surface of the cold-rolled steel sheet W generated in the direct-fired furnace 10 is reduced. At that time, oxygen separated from Fe by the reduction reaction, a small amount of oxygen contained in the reducing atmosphere, etc. Is diffused into the cold-rolled steel sheet W (base material) and reacts with Si in the base material to cause internal oxidation of Si. This Si oxide is generated on the outermost surface of the cold-rolled steel sheet W, and a Si concentrated layer is formed by the Si oxide.
上述の還元炉によって焼鈍処理を行っても、Ｓｉを多く含んだ冷延鋼板Ｗでは均熱処理後の最表面にＳｉ酸化物によるＳｉ濃化層の生成を完全に防止することは困難であり、また均熱焼鈍後の冷却でも冷延鋼板Ｗの表面は少なからず酸化することがあるため、一連の焼鈍処理後には、冷延鋼板Ｗを酸洗する必要がある。
上述の直火炉１０及び還元炉による焼鈍工程６の後、後酸洗工程７が行われる。後酸洗工程７は、冷延鋼板Ｗの表面に生成した上述のＳｉ濃化層を除去するために、当該冷延鋼板Ｗを酸洗する工程である。この酸洗工程は、冷延工程３の前に行われる酸洗工程を前酸洗工程２と呼ぶのに対応して、後酸洗工程７と呼ぶ。
Even if the annealing treatment is performed by the above-described reduction furnace, it is difficult to completely prevent the formation of a Si concentrated layer by Si oxide on the outermost surface after soaking in the cold-rolled steel sheet W containing a large amount of Si. Further, even after cooling after soaking, the surface of the cold-rolled steel sheet W may be oxidized to some extent. Therefore, the cold-rolled steel sheet W needs to be pickled after a series of annealing treatments.
After the above-described annealing process 6 using the direct-fired furnace 10 and the reduction furnace, a post pickling process 7 is performed. The post-pickling step 7 is a step of pickling the cold-rolled steel sheet W in order to remove the Si-enriched layer generated on the surface of the cold-rolled steel sheet W. This pickling step is referred to as a post-pickling step 7 correspondingly to the pickling step performed before the cold rolling step 3 being referred to as the pre-pickling step 2.
後酸洗工程７では、塩酸や硫酸などの酸性溶液を用いた酸洗を行い、冷延鋼板Ｗの表面に生成したＳｉ濃化層を除去する。冷延鋼板Ｗの表面１ｍ２あたりの酸洗で溶解する鋼材の量（重量）を示す酸洗量は、少なくとも１ｇ／ｍ２である。この酸洗量は、冷延鋼板Ｗに添加されたＳｉの添加量に影響されるものの、１ｇ／ｍ２未満の酸洗量では、冷延鋼板Ｗの表面にＳｉ濃化層が残留してしまい、後酸洗工程７に続く化成処理工程８における化成処理性の確保が困難となる。ここで、酸洗量は、３ｇ／ｍ２以上であれば好ましい。 In the post pickling step 7, pickling using an acidic solution such as hydrochloric acid or sulfuric acid is performed to remove the Si concentrated layer formed on the surface of the cold rolled steel sheet W. The pickling amount indicating the amount (weight) of the steel material dissolved by pickling per 1 m 2 of the surface of the cold rolled steel sheet W is at least 1 g / m 2 . Although this pickling amount is affected by the amount of Si added to the cold-rolled steel sheet W, an Si-concentrated layer remains on the surface of the cold-rolled steel sheet W when the pickling amount is less than 1 g / m 2. Therefore, it becomes difficult to ensure the chemical conversion treatment in the chemical conversion treatment step 8 following the post pickling step 7. Here, the pickling amount is preferably 3 g / m 2 or more.
まず、図３及び図９を参照して、本実施形態による焼鈍工程６によって得られる効果について説明する。図３及び図９は、共に焼鈍工程と後酸洗工程におけるＳｉ添加冷延鋼板の鋼板表層の変化を模式的に示す図であるが、図３が本実施形態による鋼板表層の変化を示すのに対して、図９は図３との対比に用いられる図であり、従来技術による鋼板表層の変化を示す。 First, with reference to FIG.3 and FIG.9, the effect acquired by the annealing process 6 by this embodiment is demonstrated. 3 and 9 are diagrams schematically showing changes in the steel sheet surface layer of the Si-added cold-rolled steel sheet in both the annealing step and the post pickling process. FIG. 3 shows the change in the steel sheet surface layer according to this embodiment. On the other hand, FIG. 9 is a diagram used for comparison with FIG. 3 and shows the change of the steel sheet surface layer according to the prior art.
図９を参照して、従来技術による焼鈍工程では、直火炉での予熱において冷延鋼板Ｗの表面を極力酸化させないように加熱が行われており、直火炉内で冷延鋼板Ｗの表面に酸化層はほとんど形成されない。表面に酸化層がほとんど存在しない冷延鋼板Ｗを還元炉で焼鈍処理すると、本実施形態による焼鈍工程６と対比して比較的厚いＳｉ濃化層Ｌ１が形成
される。冷延鋼板Ｗに厚いＳｉ濃化層Ｌ１が形成されると、続く後酸洗工程において大きな酸洗量で冷延鋼板Ｗを酸洗しなくてはならず、酸洗に要するコストや時間といった酸洗の負荷が大きい。
Referring to FIG. 9, in the annealing process according to the prior art, heating is performed so as not to oxidize the surface of the cold-rolled steel sheet W as much as possible in the preheating in the direct-fired furnace. An oxide layer is hardly formed. When the cold-rolled steel sheet W having almost no oxide layer on the surface is annealed in a reduction furnace, a relatively thick Si concentrated layer L1 is formed as compared with the annealing step 6 according to the present embodiment. When the thick Si-concentrated layer L1 is formed on the cold-rolled steel sheet W, the cold-rolled steel sheet W must be pickled with a large amount of pickling in the subsequent post-pickling process, and the cost and time required for pickling The load of pickling is large.
これに対して、図３を参照すると、本実施形態による焼鈍工程６では、直火炉１０での予熱において冷延鋼板Ｗの表面に酸化層Ｌ２を形成するように加熱している。このような表面に酸化層Ｌ２が形成された冷延鋼板Ｗを還元炉で焼鈍処理すると、酸化層Ｌ２が消滅して代わりにＳｉ濃化層Ｌ１が形成される。このＳｉ濃化層Ｌ１の厚みは、図９に示す従来技術によるＳｉ濃化層Ｌ１の厚みと対比して比較的薄い層であり、その厚みの減少は、還元炉での焼鈍処理の前に予め冷延鋼板Ｗの表面に酸化層Ｌ２を形成したことによる効果であると考えられる。冷延鋼板Ｗに形成されるＳｉ濃化層Ｌ１が薄ければ、後酸洗工程７における酸洗量は小さくて済み、酸洗に要するコストや時間といった酸洗の負荷が小さくなるので、Ｓｉ添加冷延鋼板の製造効率が向上する。 On the other hand, referring to FIG. 3, in the annealing process 6 according to the present embodiment, heating is performed so as to form an oxide layer L <b> 2 on the surface of the cold-rolled steel sheet W in the preheating in the direct-fired furnace 10. When the cold-rolled steel sheet W having the oxide layer L2 formed on such a surface is annealed in a reduction furnace, the oxide layer L2 disappears and a Si concentrated layer L1 is formed instead. The thickness of the Si concentrated layer L1 is a relatively thin layer as compared with the thickness of the Si concentrated layer L1 according to the prior art shown in FIG. 9, and the thickness reduction is performed before the annealing treatment in the reduction furnace. This is considered to be an effect obtained by forming the oxide layer L2 on the surface of the cold-rolled steel sheet W in advance. If the Si concentrated layer L1 formed on the cold-rolled steel sheet W is thin, the amount of pickling in the post pickling process 7 is small, and the pickling load such as cost and time required for pickling becomes small. The production efficiency of the added cold-rolled steel sheet is improved.
以上に説明した直火炉１０及び還元炉による焼鈍工程６、及びこの焼鈍工程６に続く後酸洗工程７の特徴を、本実施形態によるＳｉ添加冷延鋼板の製造方法の特徴として以下にまとめる。
まず、焼鈍工程６における昇温処理によって、冷延鋼板Ｗのエッジ側の炉壁に配置された酸化バーナ１１から冷延鋼板Ｗの平板面に対して平行に酸化炎Ｆを噴出する直火炉１０内で、酸化バーナ１１からの酸化炎Ｆが冷延鋼板Ｗに触れないようにすることで、当該冷延鋼板Ｗを温度むらのないようにほぼ均一に加熱する。この加熱によって、冷延鋼板Ｗの表面に、厚みにむらのないほぼ均一な酸化膜を形成する。
The characteristics of the annealing process 6 using the direct-fired furnace 10 and the reduction furnace described above, and the post pickling process 7 subsequent to the annealing process 6 are summarized as the characteristics of the method for manufacturing the Si-added cold-rolled steel sheet according to the present embodiment.
First, a direct-fired furnace 10 in which an oxidizing flame F is jetted in parallel to the flat plate surface of the cold-rolled steel sheet W from the oxidation burner 11 disposed on the furnace wall on the edge side of the cold-rolled steel sheet W by the temperature raising process in the annealing process 6. In the inside, by preventing the oxidation flame F from the oxidation burner 11 from touching the cold-rolled steel sheet W, the cold-rolled steel sheet W is heated almost uniformly so as not to cause temperature unevenness. By this heating, a substantially uniform oxide film having no thickness unevenness is formed on the surface of the cold-rolled steel sheet W.
この昇温処理において、酸化バーナ１１の燃焼空気比は１.１５〜１.３５であり、冷延鋼板Ｗの温度を４５０〜６２０℃に到達するまで昇温し予熱する。
昇温処理に続く焼鈍処理によって、予熱された冷延鋼板Ｗを、還元性雰囲気の還元炉にて７５０〜９５０℃の温度範囲で均熱焼鈍し、冷延鋼板Ｗとしての材質特性の確保と、直火炉１０による昇温処理で形成された酸化層Ｌ２を還元する。その結果、冷延鋼板Ｗの表面には、Ｓｉ濃化層Ｌ１が形成される。
In this temperature raising process, the combustion air ratio of the oxidation burner 11 is 1.15 to 1.35, and the temperature of the cold-rolled steel sheet W is raised until it reaches 450 to 620 ° C. and preheated.
The pre-heated cold-rolled steel sheet W is annealed in a reducing furnace in a reducing atmosphere at a temperature range of 750 to 950 ° C. by the annealing process subsequent to the temperature raising process, thereby ensuring the material properties as the cold-rolled steel sheet W. Then, the oxide layer L2 formed by the temperature raising process by the direct furnace 10 is reduced. As a result, a Si concentrated layer L1 is formed on the surface of the cold-rolled steel sheet W.
上述の昇温処理及び焼鈍処理を含む焼鈍工程６に続く後酸洗工程７において、冷延鋼板Ｗの表層に生じたＳｉ酸化物からなるＳｉ濃化層Ｌ１を除去し、当該冷延鋼板Ｗの化成処理性を確保する。
このように、本実施形態によるＳｉ添加冷延鋼板の製造方法は、昇温処理によって冷延鋼板Ｗの表面にほぼ均一な厚みの酸化層Ｌ２を形成するので、続く焼鈍処理によって冷延鋼板Ｗの表面に形成されるＳｉ濃化層Ｌ１の厚みをほぼ均一に小さく抑制することができる。その結果、冷延鋼板Ｗの化成処理性を確保するためのＳｉ濃化層Ｌ１の除去に必要とされる酸洗量を低減することができるので、連続焼鈍におけるＳｉ添加冷延鋼板の生産性向上と表面品質（化成処理性）確保の両立が容易に可能となる。
（実施例）
以下に、本実施形態によるＳｉ添加冷延鋼板の製造方法の実施例について説明する。
In the post pickling process 7 subsequent to the annealing process 6 including the temperature raising process and the annealing process described above, the Si concentrated layer L1 made of Si oxide generated on the surface layer of the cold rolled steel sheet W is removed, and the cold rolled steel sheet W is removed. Ensure chemical conversion processability.
Thus, since the manufacturing method of the Si-added cold-rolled steel sheet according to the present embodiment forms the oxide layer L2 having a substantially uniform thickness on the surface of the cold-rolled steel sheet W by the temperature raising process, the cold-rolled steel sheet W is obtained by the subsequent annealing process. The thickness of the Si concentrated layer L1 formed on the surface can be reduced almost uniformly. As a result, it is possible to reduce the amount of pickling required for removing the Si-concentrated layer L1 for ensuring chemical conversion treatment of the cold-rolled steel sheet W, so the productivity of the Si-added cold-rolled steel sheet in continuous annealing is reduced. Both improvement and securing of surface quality (chemical conversion processability) can be easily achieved.
(Example)
Below, the Example of the manufacturing method of the Si addition cold-rolled steel plate by this embodiment is described.
まず、下の表１に示す化学成分を有する３種の高Ｓｉスラブ（鋼種Ａ〜Ｃ）を熱間圧延、酸洗（前酸洗）、冷間圧延し、厚さ１.２ｍｍの冷延鋼板Ｗを製造した。 First, three types of high Si slabs (steel types A to C) having chemical components shown in Table 1 below are hot-rolled, pickled (pre-pickled), cold-rolled, and cold-rolled with a thickness of 1.2 mm. A steel plate W was manufactured.
鋼種Ａ〜Ｃは、それぞれＳｉ含有量が０.５重量％以上であり、０.６８〜１.８２重量％の範囲にある。これら鋼種Ａ〜Ｃから製造された冷延鋼板ＷもＳｉ含有量が０.５重量％以上である。
表１に示す鋼種から製造された冷延鋼板Ｗを、酸化バーナ１１を備える酸化性雰囲気の直火炉１０、還元性雰囲気の還元炉（均熱炉）、及び冷却帯を備える焼鈍・冷却設備に通
し、焼鈍された冷延鋼板Ｗを得た。
Steel types A to C each have a Si content of 0.5% by weight or more and are in the range of 0.68 to 1.82% by weight. The cold-rolled steel sheet W manufactured from these steel types A to C also has a Si content of 0.5% by weight or more.
The cold-rolled steel sheet W manufactured from the steel types shown in Table 1 is applied to an annealing / cooling facility equipped with a direct-fired furnace 10 with an oxidizing atmosphere provided with an oxidation burner 11, a reducing furnace with a reducing atmosphere (soaking furnace), and a cooling zone. The cold-rolled steel sheet W annealed was obtained.
まずは、冷延鋼板Ｗを直火炉１０で加熱した後、均熱焼鈍の前にＮ２ガスを用いて平均冷却速度５０〜６０℃／ｓｅｃで常温まで冷却した。直火炉１０の酸化バーナ１１には燃料としてＣＯＧを使用し、空気比を種々変更して異なる条件で直火炉１０における加熱を行った。
直火炉１０での加熱条件を次の表２に示す。
First, after the cold-rolled steel sheet W was heated in the direct-fired furnace 10, it was cooled to room temperature at an average cooling rate of 50 to 60 ° C./sec using N 2 gas before soaking. COG was used as fuel for the oxidation burner 11 of the direct furnace 10, and the direct furnace 10 was heated under different conditions by variously changing the air ratio.
The heating conditions in the direct furnace 10 are shown in Table 2 below.
表２によれば、実験Ｎｏ.１〜Ｎｏ.７として示す鋼種Ａの冷延鋼板Ｗは、空気比が１.１２〜１.３４の範囲であり、実験Ｎｏ.８,Ｎｏ.９として示す鋼種Ｂの冷延鋼板Ｗは、空気比が１.３２と１.１１の範囲であり、実験Ｎｏ.１０,Ｎｏ.１１として示す鋼種Ｃの冷延鋼板Ｗは、空気比が０.９０と１.１６の範囲である。実験Ｎｏ.１〜実験Ｎｏ.１１について、直火炉１０における加熱温度も様々に変えて冷延鋼板Ｗを昇温し、直火炉１０の出側において冷延鋼板Ｗの温度を測定した。また、実験Ｎｏ.７以外では、図２に示すような、酸化炎Ｆが冷延鋼板Ｗの平板面に触れずほぼ平行に噴出される直火炉１０を用い、実験Ｎｏ.７では、図８に示すような、酸化炎Ｆが冷延鋼板Ｗの平板面に対してほぼ垂直に噴出される直火炉１００を用いた。 According to Table 2, the cold rolled steel sheet W of steel type A shown as Experiment No. 1 to No. 7 has an air ratio in the range of 1.12 to 1.34, and is shown as Experiment No. 8 and No. 9. The cold rolled steel sheet W of steel type B has an air ratio in the range of 1.32 and 1.11, and the cold rolled steel sheet W of steel type C shown as Experiment No. 10 and No. 11 has an air ratio of 0.90. The range is 1.16. Regarding Experiment No. 1 to Experiment No. 11, the heating temperature in the direct furnace 10 was also changed in various ways to raise the temperature of the cold rolled steel sheet W, and the temperature of the cold rolled steel sheet W was measured on the exit side of the direct furnace 10. In addition to Experiment No. 7, a direct-fired furnace 10 in which the oxidation flame F is jetted substantially in parallel without touching the flat plate surface of the cold-rolled steel sheet W as shown in FIG. The direct-fired furnace 100 in which the oxidation flame F is ejected substantially perpendicularly to the flat plate surface of the cold-rolled steel sheet W as shown in FIG.
このような直火炉１０及び直火炉１００による冷延鋼板Ｗの昇温を行った後、均熱焼鈍の前にＮ２ガスを用いて平均冷却速度５０〜６０℃／ｓｅｃで常温まで冷却した冷延鋼板Ｗについて、グロー放電分光分析(ＧＤＳ)で表層部分の元素ＦｅとＯの量を調査した。ＧＤＳ分析は実験Ｎｏ.１〜実験Ｎｏ.１１の１サンプルごとにランダムな５ヵ所でおこない、表層部分のＦｅ酸化層（酸化層Ｌ２）の厚みについて平均値と偏差（最大値と最小値の差異）を求めた。 After the temperature of the cold-rolled steel sheet W is increased in such a direct-fired furnace 10 and the direct-fired furnace 100, it is cooled to room temperature with an average cooling rate of 50 to 60 ° C./sec using N 2 gas before soaking annealing. For the rolled steel sheet W, the amount of elements Fe and O in the surface layer portion was examined by glow discharge spectroscopic analysis (GDS). GDS analysis is performed at random five locations for each sample of Experiment No. 1 to Experiment No. 11, and the average value and deviation (difference between maximum value and minimum value) of the thickness of the Fe oxide layer (oxide layer L2) in the surface layer portion. )
冷延鋼板Ｗの表層部分をＧＤＳ分析によって調査した後、還元炉において均熱焼鈍をおこなった。均熱条件は、還元炉の炉内雰囲気として５vol％Ｈ２、残りをＮ２とし、均熱温度を９００℃、均熱時間を１４０秒とした。還元炉における加熱開始から均熱温度まで到達する間の加熱速度を平均７℃／ｓｅｃとした。均熱焼鈍後の冷却は、再びＮ２ガスを用いて平均冷却速度５０〜６０℃／ｓｅｃで常温まで冷却した。 After the surface layer portion of the cold rolled steel sheet W was examined by GDS analysis, soaking was performed in a reduction furnace. The soaking conditions were 5 vol% H 2 as the furnace atmosphere of the reduction furnace, the rest was N 2 , the soaking temperature was 900 ° C., and the soaking time was 140 seconds. The heating rate while reaching the soaking temperature from the start of heating in the reduction furnace was set to 7 ° C./sec on average. Cooling after soaking was performed by using N 2 gas again and cooling to room temperature at an average cooling rate of 50 to 60 ° C./sec.
冷却後の冷延鋼板Ｗについては、酸洗無しも含む種々の条件（酸洗量）で酸洗した後、各々の冷延鋼板Ｗを化成処理し、化成皮膜の付着性を評価することで化成処理性を確保可能な必要酸洗量（ｇ／ｍ２）を求めた。酸洗条件については、塩酸を使用し、酸濃度１０〜２０％、液温度８０℃、酸洗時間０〜２０ｓｅｃで行い、酸洗量を０〜１０ｇ／ｍ２とした。 About the cold-rolled steel sheet W after cooling, after pickling under various conditions (pickling amount) including no pickling, each cold-rolled steel sheet W is subjected to chemical conversion treatment to evaluate the adhesion of the chemical conversion film. The required pickling amount (g / m 2 ) capable of ensuring chemical conversion treatment was determined. About pickling conditions, hydrochloric acid was used, the acid concentration was 10 to 20%, the liquid temperature was 80 ° C., the pickling time was 0 to 20 sec, and the pickling amount was 0 to 10 g / m 2 .
化成処理性の評価については、まず冷延鋼板Ｗの表面を脱脂した後に水洗し、次に、水洗いした冷延鋼板Ｗの表面を日本パーカライジング社製の表面調整液「プレパレンＰＬ−Ｘ」で調整した後、当該冷延鋼板Ｗを化成処理液である同社製「パルポンドＬ３０６５」に１２０ｓｅｃ浸漬した後、水洗し温風乾燥した。冷延鋼板Ｗの表面に付着させた化成皮膜について、走査型電子顕微鏡にて倍率１５００倍で観察し、化成皮膜の付着率を測定し、付着率が９５％以上であれば化成処理性が確保されている（合格）とした。 Regarding the evaluation of chemical conversion treatment, first the surface of the cold-rolled steel sheet W is degreased and then washed with water, and then the surface of the washed cold-rolled steel sheet W is adjusted with a surface conditioning solution “preparene PL-X” manufactured by Nihon Parkerizing Co., Ltd. After that, the cold-rolled steel sheet W was immersed in “Palpond L3065” manufactured by the company, which is a chemical conversion treatment solution, for 120 seconds, washed with water and dried with warm air. The chemical conversion film adhered to the surface of the cold-rolled steel sheet W is observed with a scanning electron microscope at a magnification of 1500 times, the adhesion rate of the chemical conversion film is measured, and if the adhesion rate is 95% or more, chemical conversion treatment performance is ensured. (Passed).
今一度、表２に示す結果をみれば、直火炉１０において、酸化バーナ１１の燃焼空気比を１.１５以上１.３５以下とし、冷延鋼板Ｗを４５０℃以上６２０℃以下の温度範囲にまで昇温し、且つ、冷延鋼板Ｗに対する酸化炎Ｆの向きを冷延鋼板Ｗに平板面に対してほぼ
平行にした実験Ｎｏ.１〜３（鋼種Ａ）、実験Ｎｏ.８（鋼種Ｂ）及び実験Ｎｏ.１０（鋼種Ｃ）に示す実施例では、他の実験Ｎｏが付された同一鋼種についての比較例と比べて明らかに必要酸洗量が少なくなって半分程度になっている。
If the results shown in Table 2 are observed once more, in the direct-fired furnace 10, the combustion air ratio of the oxidation burner 11 is set to 1.15 to 1.35, and the cold-rolled steel sheet W is set to a temperature range of 450 ° C. to 620 ° C. Experiment Nos. 1 to 3 (steel type A) and experiment No. 8 (steel type B) in which the direction of the oxidation flame F with respect to the cold-rolled steel sheet W was substantially parallel to the cold-rolled steel sheet W with respect to the flat plate surface. ) And Experiment No. 10 (steel type C), the required pickling amount is clearly reduced to about half compared to the comparative example for the same steel type to which other experiment Nos. Are attached.
図４〜図６は、表２に示す結果に基づいて、鋼種Ａ〜Ｃについて、直火炉１０の条件を様々に変化させたときの必要酸洗量を比較したグラフを示す図である。図４は、鋼種Ａについての必要酸洗量を棒グラフで示し、図５は、鋼種Ｂについての必要酸洗量を棒グラフで示し、図６は、鋼種Ｃについての必要酸洗量を棒グラフで示す。これら図４〜図６によっても、実験Ｎｏ.１〜３（鋼種Ａ）、実験Ｎｏ.８（鋼種Ｂ）及び実験Ｎｏ.１０（鋼種Ｃ）に示す実施例では、同一鋼種の比較例と比べて明らかに必要酸洗量が少なくなって半分程度になっていることがわかる。 4-6 is a figure which shows the graph which compared the required pickling amount when changing the conditions of the direct-fired furnace 10 variously about steel types AC based on the result shown in Table 2. FIG. 4 shows the necessary pickling amount for steel type A in a bar graph, FIG. 5 shows the necessary pickling amount for steel type B in a bar graph, and FIG. 6 shows the necessary pickling amount for steel type C in a bar graph. . 4 to 6, the Examples shown in Experiment Nos. 1 to 3 (Steel Type A), Experiment No. 8 (Steel Type B), and Experiment No. 10 (Steel Type C) are compared with Comparative Examples of the same steel type. It is clear that the required amount of pickling is reduced to about half.
これら表２及び図４〜図６に示す結果は、実施例における後酸洗工程７の負荷が、比較例における後酸洗工程の負荷よりも軽減されたことを示している。
また、図７を参照して、酸化バーナ１１の空気比の範囲、及び直火炉１０における冷延鋼板Ｗの加熱温度（図２における、炉出側の鋼板温度）の範囲について検討する。図７は、３種類の鋼種Ａ〜Ｃの実験Ｎｏ.１〜実験Ｎｏ.１１について、表２に示す結果を空気比と鋼板温度によってまとめたグラフを示す図である。
The results shown in Table 2 and FIGS. 4 to 6 indicate that the load of the post-pickling step 7 in the example was reduced than the load of the post-pickling step in the comparative example.
Moreover, with reference to FIG. 7, the range of the air ratio of the oxidation burner 11 and the range of the heating temperature of the cold-rolled steel sheet W in the direct-fired furnace 10 (steel temperature on the furnace exit side in FIG. 2) will be examined. FIG. 7 is a diagram showing a graph in which the results shown in Table 2 are summarized according to the air ratio and the steel plate temperature for Experiment No. 1 to Experiment No. 11 of three types of steel types A to C.
図７に示すグラフにおいて、記号「○」で示す結果は実施例を表し、記号「×」で示す結果は比較例を表す。図７のグラフにおいて、実施例の結果が含まれる領域（好ましい範囲）が破線で囲まれており、この破線で囲まれる領域の上限と下限を、空気比及び鋼板温度について読み取ると、酸化バーナ１１の燃焼空気比は１.１５〜１.３５であり、冷延鋼板Ｗの加熱温度は４５０〜６２０℃である。 In the graph shown in FIG. 7, a result indicated by a symbol “◯” represents an example, and a result indicated by a symbol “x” represents a comparative example. In the graph of FIG. 7, a region (preferable range) including the result of the example is surrounded by a broken line, and the upper and lower limits of the region surrounded by the broken line are read with respect to the air ratio and the steel plate temperature. The combustion air ratio is 1.15 to 1.35, and the heating temperature of the cold-rolled steel sheet W is 450 to 620 ° C.
尚、図７において破線で囲まれる好ましい範囲に記号「×」で示す比較例が含まれているが、この比較例は実験Ｎｏ.７に対応するものである。実験Ｎｏ.７は、空気比及び鋼板温度が好ましい範囲にあるものの、空気比及び鋼板温度以外の条件である酸化炎Ｆの向きが垂直になっているため必要酸洗量が大きく比較例となっている。
以上に説明したように、本実施形態によるＳｉ添加冷延鋼板の製造方法は、焼鈍処理後の後酸洗無しでは化成処理性確保が困難なＳｉ添加冷延鋼板の製造において、冷延鋼板Ｗの表面全体を均一に酸化することができる。その結果、還元性雰囲気炉にて均熱焼鈍中にＳｉ濃化層Ｌ１として形成されるＳｉ酸化物の量を冷延鋼板Ｗ全体にわたって均一に抑制し、焼鈍した冷延鋼板Ｗの化成処理性確保に必要な表層の酸洗除去量を従来の半分程度に低減することができる。これによって、連続焼鈍工程においてＳｉ添加冷延鋼板の表面品質（化成処理性）確保を確保しつつ、生産性と製造コストを低減することができる。
In addition, although the comparative example shown by symbol "x" is included in the preferable range enclosed with a broken line in FIG. 7, this comparative example respond | corresponds to experiment No.7. In Experiment No. 7, although the air ratio and the steel plate temperature are in the preferable ranges, the required pickling amount is large because the direction of the oxidation flame F, which is a condition other than the air ratio and the steel plate temperature, is vertical. ing.
As described above, the manufacturing method of the Si-added cold-rolled steel sheet according to the present embodiment is the cold-rolled steel sheet W in the manufacture of the Si-added cold-rolled steel sheet that is difficult to ensure the chemical conversion treatment without post-annealing after the annealing treatment. The entire surface of the film can be uniformly oxidized. As a result, the amount of Si oxide formed as the Si concentrated layer L1 during the soaking annealing in the reducing atmosphere furnace is uniformly suppressed over the entire cold-rolled steel sheet W, and the chemical conversion treatment property of the annealed cold-rolled steel sheet W is achieved. The pickling removal amount of the surface layer necessary for securing can be reduced to about half of the conventional amount. Thereby, productivity and manufacturing cost can be reduced while ensuring the surface quality (chemical conversion property) of the Si-added cold-rolled steel sheet in the continuous annealing process.
ところで、今回開示された実施形態はすべての点で例示であって制限的なものではないと考えられるべきである。特に、今回開示された実施形態において、明示的に開示されていない事項、例えば、動作条件や測定条件、各種パラメータ、構成物の寸法、重量、体積などは、当業者が通常実施する範囲を逸脱するものではなく、通常の当業者であれば、容易に想定することが可能な値を採用している。 By the way, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, such as operating conditions and measurement conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that is normally implemented by those skilled in the art. Instead, values that can be easily assumed by those skilled in the art are employed.
例えば、Ｓｉ以外の鋼成分については本発明において特に限定するものではないが、高強度冷延鋼板を製造するにあたり次に示す範囲内で適宜添加しても構わない。
炭素Ｃを０.０５〜０.３０重量％添加してもよい。Ｃは冷延鋼板Ｗの低温変態生成物の量や特性を変えることで強度や加工性に大きな影響を与える元素であるため、０.０５〜０.３０重量％の範囲とする。０.０５重量％未満では十分な強度が得られず、一方０.３０重量％を超えて過剰になると加工性や溶接性の低下を招く。
For example, although steel components other than Si are not particularly limited in the present invention, they may be added as appropriate within the following range in producing a high-strength cold-rolled steel sheet.
Carbon C may be added in an amount of 0.05 to 0.30% by weight. C is an element that greatly affects the strength and workability by changing the amount and characteristics of the low-temperature transformation product of the cold-rolled steel sheet W, and is therefore in the range of 0.05 to 0.30% by weight. If it is less than 0.05% by weight, sufficient strength cannot be obtained. On the other hand, if it exceeds 0.30% by weight, workability and weldability are deteriorated.
マンガンＭｎを１.０〜３.０重量％添加してもよい。Ｍｎは冷延鋼板Ｗの強度を確保する上で重要な元素であり、１.０〜３.０重量％の範囲とする。１.０重量％未満では十分な強度が得られず、一方で３.０重量％を超えて過剰になると加工性や溶接性の低下を招く。
リンＰを０.１０重量％以下添加してもよい。Ｐは冷延鋼板Ｗの強度を高める作用があるが、０.１０重量％を超えて過剰になると加工性の劣化が大きくなる。好ましくは０.０５重量％以下にするのが良い。
Manganese Mn may be added in an amount of 1.0 to 3.0% by weight. Mn is an important element for securing the strength of the cold-rolled steel sheet W, and is in the range of 1.0 to 3.0% by weight. If it is less than 1.0% by weight, sufficient strength cannot be obtained. On the other hand, if it exceeds 3.0% by weight, workability and weldability are deteriorated.
Phosphorus P may be added up to 0.10% by weight. P has the effect of increasing the strength of the cold-rolled steel sheet W, but if it exceeds 0.10% by weight and becomes excessive, deterioration of workability becomes large. Preferably it is 0.05% by weight or less.
硫黄Ｓを０.０３重量％以下に抑制するのが好ましい。Ｓは熱間圧延時の割れの原因となったり、加工性や溶接性を損なったりする元素であるため、上限値を０.０３重量％に止める必要がある。好ましくは０.０１重量％以下にするのが良い。
アルミニウムＡｌを０.０１〜０.１０重量％添加してもよい。Ａｌは脱酸のときに必要な元素であるため、０.０１〜０.１０重量％必要である。０.０１重量％未満では十分な脱酸効果が得られず、一方で０.１０重量％を超えて過剰になると加工性劣化を招く。
It is preferable to suppress sulfur S to 0.03 wt% or less. Since S is an element that causes cracking during hot rolling, or impairs workability and weldability, the upper limit value needs to be limited to 0.03 wt%. Preferably, the content is 0.01% by weight or less.
Aluminum Al may be added in an amount of 0.01 to 0.10% by weight. Since Al is an element necessary for deoxidation, 0.01 to 0.10% by weight is necessary. If the amount is less than 0.01% by weight, a sufficient deoxidizing effect cannot be obtained. On the other hand, if it exceeds 0.10% by weight, workability is deteriorated.
クロムＣｒを１.０重量％以下添加してもよい。Ｃｒは冷延鋼板Ｗの焼入れ性を高め、強度を得る上で有効な元素であるが、含有量が１.０重量％を超えても効果が飽和するばかりでなく、コスト面でも不利となるため、上限値を１.０重量％とする。
モリブデンＭｏを０.５重量％以下添加してもよい。Ｍｏは冷延鋼板Ｗの焼入れ性を高めるとともに、固溶強化により強度を得る上で有効な元素であるが、含有量が０.５重量％を超えると製造コストの大幅な悪化を招くため、上限値を０.５重量％とする。
You may add 1.0 weight% or less of chromium Cr. Cr is an element effective in improving the hardenability of the cold-rolled steel sheet W and obtaining strength, but not only when the content exceeds 1.0% by weight, the effect is saturated, but also in terms of cost. Therefore, the upper limit is set to 1.0% by weight.
Molybdenum Mo may be added in an amount of 0.5% by weight or less. Mo is an element effective for improving the hardenability of the cold-rolled steel sheet W and obtaining strength by solid solution strengthening, but if the content exceeds 0.5% by weight, the manufacturing cost is greatly deteriorated. The upper limit value is 0.5% by weight.
銅Ｃｕ及びニッケルＮｉを、それぞれ０.５重量％以下添加してもよい。ＣｕおよびＮｉは冷延鋼板Ｗの強度を高める上で有効な元素であるが、過剰な添加は加工性を劣化させ、経済性にも見合わなくなるため上限値を０.５重量％とする。
ニオブＮｂ、チタンＴｉ及びバナジウムＶを、それぞれ０.５重量％以下添加してもよい。Ｎｂ、ＴｉおよびＶはいずれも炭化物を形成し、冷延鋼板Ｗの強度を高める上で有効な元素であるが、過剰な添加は加工性を劣化させ、経済性にも見合わなくなるため上限値を０.５重量％とする。
Copper Cu and nickel Ni may be added in an amount of 0.5% by weight or less. Cu and Ni are effective elements for increasing the strength of the cold-rolled steel sheet W. However, excessive addition deteriorates workability and is not suitable for economy, so the upper limit is set to 0.5% by weight.
Niobium Nb, titanium Ti, and vanadium V may be added in an amount of 0.5% by weight or less. Nb, Ti, and V are all elements that form carbides and are effective in increasing the strength of the cold-rolled steel sheet W. However, excessive addition deteriorates workability and is not suitable for economic efficiency, so the upper limit value is set. Is 0.5% by weight.
ホウ素Ｂを０.００５重量％以下添加してもよい。Ｂは冷延鋼板Ｗの焼入れ性を高める上で有効な元素であるが、含有量が０.００５重量％を超えると効果が飽和するだけでなく、加工性を劣化させるため上限値を０.００５重量％とする。
カルシウムＣａを０.００５重量％以下添加してもよい。Ｃａは冷延鋼板Ｗ中の介在物の形態を制御することで加工性を向上させる元素であるが、含有量が０.００５重量％を超えて過剰になると介在物が増加し加工性の劣化を招くため、上限値を０.００５重量％とする。
Boron B may be added in an amount of 0.005% by weight or less. B is an element effective in enhancing the hardenability of the cold-rolled steel sheet W. However, when the content exceeds 0.005% by weight, not only the effect is saturated, but also the workability is deteriorated, so the upper limit value is set to 0.0. 005 wt%.
You may add 0.005 weight% or less of calcium Ca. Ca is an element that improves the workability by controlling the form of inclusions in the cold-rolled steel sheet W, but if the content exceeds 0.005% by weight, the inclusions increase and the workability deteriorates. Therefore, the upper limit is set to 0.005% by weight.
１ 熱延工程
２ 前酸洗工程
３ 冷延工程
４，６ 焼鈍工程
５ めっき工程
７ 後酸洗工程
８ 化成処理工程
１０ 直火炉
１１，１１０ 酸化バーナ（バーナ）
１０，１００ 直火炉
Ｗ 冷延鋼板
Ｆ 酸化炎
Ｘ 火炎噴出方向軸線
Ｌ１ Ｓｉ濃化層
Ｌ２ 酸化層
DESCRIPTION OF SYMBOLS 1 Hot rolling process 2 Pre pickling process 3 Cold rolling process 4,6 Annealing process 5 Plating process 7 Post pickling process 8 Chemical conversion treatment process 10 Direct furnace 11,110 Oxidation burner (burner)
10,100 Direct-fired furnace W Cold-rolled steel sheet F Oxidation flame X Flame ejection direction axis L1 Si concentrated layer L2 Oxidation layer
Claims (1)
前記直火炉において、前記酸化バーナの燃焼空気比を１.１５以上１.３５以下とし、前記酸化バーナによって前記冷延鋼板を加熱して４５０℃以上６２０℃以下の温度範囲にまで昇温する昇温工程と、
前記還元性雰囲気の均熱炉において、前記昇温工程で加熱された冷延鋼板を、７５０℃以上９５０℃以下の温度範囲で均熱焼鈍する焼鈍工程と、
前記焼鈍工程で均熱焼鈍された冷延鋼板を酸洗処理する酸洗工程と、を備えるものであって、
前記直火炉の酸化バーナが、前記酸化バーナの火炎噴出方向軸線が前記鋼板の表面と交わらないように配置されている
ことを特徴とするＳｉ添加冷延鋼板の製造方法。 Using a direct-fired furnace having an oxidation burner for heating the cold-rolled steel sheet on the edge side of the cold-rolled steel sheet and a soaking furnace in a reducing atmosphere, a cold-rolled steel sheet having a Si content of 0.5% by weight or more is obtained. When manufacturing Si-added cold-rolled steel sheet by annealing,
In the direct-fired furnace, the combustion air ratio of the oxidation burner is set to 1.15 or more and 1.35 or less, and the cold-rolled steel sheet is heated by the oxidation burner to be raised to a temperature range of 450 ° C. or more and 620 ° C. or less. Temperature process,
In the soaking furnace in the reducing atmosphere, an annealing step of soaking the cold-rolled steel sheet heated in the temperature raising step in a temperature range of 750 ° C. or more and 950 ° C. or less;
A pickling process for pickling the cold-rolled steel sheet annealed in the annealing process ,
The method for producing a Si-added cold-rolled steel sheet, characterized in that the oxidation burner of the direct-fired furnace is arranged such that the flame jetting direction axis of the oxidation burner does not intersect the surface of the steel sheet.
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