JP5716338B2 - High strength steel plate and manufacturing method thereof - Google Patents
High strength steel plate and manufacturing method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 121
- 239000010959 steel Substances 0.000 title claims description 121
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 238000000137 annealing Methods 0.000 claims description 39
- 238000010438 heat treatment Methods 0.000 claims description 33
- 229910052748 manganese Inorganic materials 0.000 claims description 28
- 229910052710 silicon Inorganic materials 0.000 claims description 23
- 239000002344 surface layer Substances 0.000 claims description 17
- 238000005554 pickling Methods 0.000 claims description 15
- 229910052742 iron Inorganic materials 0.000 claims description 13
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 12
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 8
- 229910052758 niobium Inorganic materials 0.000 claims description 8
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 229910021419 crystalline silicon Inorganic materials 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 229910052796 boron Inorganic materials 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 239000007864 aqueous solution Substances 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 239000000126 substance Substances 0.000 description 56
- 238000006243 chemical reaction Methods 0.000 description 55
- 238000011282 treatment Methods 0.000 description 36
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 34
- 230000003647 oxidation Effects 0.000 description 26
- 238000007254 oxidation reaction Methods 0.000 description 26
- 238000000034 method Methods 0.000 description 24
- 230000007797 corrosion Effects 0.000 description 21
- 238000005260 corrosion Methods 0.000 description 21
- 230000000694 effects Effects 0.000 description 21
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 19
- 229910052760 oxygen Inorganic materials 0.000 description 19
- 239000001301 oxygen Substances 0.000 description 19
- 239000011248 coating agent Substances 0.000 description 16
- 238000000576 coating method Methods 0.000 description 16
- 238000004070 electrodeposition Methods 0.000 description 16
- 239000000463 material Substances 0.000 description 12
- 230000001276 controlling effect Effects 0.000 description 9
- 230000009467 reduction Effects 0.000 description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 238000005868 electrolysis reaction Methods 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 239000010410 layer Substances 0.000 description 6
- 239000010960 cold rolled steel Substances 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910004298 SiO 2 Inorganic materials 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 238000005755 formation reaction Methods 0.000 description 4
- 230000001590 oxidative effect Effects 0.000 description 4
- 230000001737 promoting effect Effects 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 241000316887 Saissetia oleae Species 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005097 cold rolling Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 238000010301 surface-oxidation reaction Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000002950 deficient Effects 0.000 description 2
- 238000005238 degreasing Methods 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 238000009713 electroplating Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000010422 painting Methods 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000007739 conversion coating Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000005324 grain boundary diffusion Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Landscapes
- Heat Treatment Of Sheet Steel (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
Description
本発明は、Ｓｉの含有量が多い場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度鋼板およびその製造方法に関するものである。 The present invention relates to a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating even when the Si content is large, and a method for producing the same.
近年、自動車の燃費向上および自動車の衝突安全性向上の観点から、車体材料の高強度化によって薄肉化を図り、車体そのものを軽量化しかつ高強度化する要望が高まっている。そのために高強度鋼板の自動車への適用が促進されている。
一般に自動車用鋼板は塗装して使用されており、その塗装の前処理として、リン酸塩処理と呼ばれる化成処理が施される。鋼板の化成処理は塗装後の耐食性を確保するための重要な処理の一つである。
In recent years, from the viewpoint of improving the fuel efficiency of automobiles and improving the collision safety of automobiles, there is an increasing demand for reducing the thickness of the vehicle body by increasing the strength of the vehicle body material and reducing the weight of the vehicle body. Therefore, application of high-strength steel sheets to automobiles is being promoted.
In general, steel plates for automobiles are used after being coated, and as a pretreatment for the coating, a chemical conversion treatment called a phosphate treatment is performed. The chemical conversion treatment of the steel sheet is one of the important treatments for ensuring the corrosion resistance after painting.
鋼板の強度、延性を高めるためには、Ｓｉの添加が有効である。しかしながら、連続焼鈍の際に、ＳｉはＦｅの酸化が起こらない（Ｆｅ酸化物を還元する）還元性のＮ2＋Ｈ2ガス雰囲気で焼鈍を行った場合でも酸化し、鋼板最表層にＳｉ酸化物（ＳｉＯ2）を形成する。このＳｉＯ2が化成処理中の化成皮膜の生成反応を阻害するため、化成皮膜が生成されない微小領域（以後、スケと称することもある）が形成され、化成処理性が低下する。 In order to increase the strength and ductility of the steel plate, addition of Si is effective. However, during continuous annealing, Si is oxidized even when annealing is performed in a reducing N 2 + H 2 gas atmosphere in which Fe does not oxidize (reducing Fe oxide), and Si oxide is formed on the outermost layer of the steel sheet. (SiO 2 ) is formed. Since this SiO 2 inhibits the formation reaction of the chemical conversion film during the chemical conversion treatment, a minute region (hereinafter also referred to as “ske”) where the chemical conversion film is not formed is formed, and the chemical conversion treatment performance is lowered.
高Ｓｉ含有鋼板の化成処理性を改善する従来技術として、特許文献１では、２０〜１５００ｍｇ/ｍ２の鉄被覆層を電気めっき法を用いて鋼板上に形成する方法が開示されている。しかしながら、この方法では、電気めっき設備が別途必要となり工程が増加する分コストも増大するという問題がある。 As a prior art for improving the chemical conversion processability of a high Si content steel sheet, Patent Document 1 discloses a method of forming an iron coating layer of 20 to 1500 mg / m 2 on a steel sheet using an electroplating method. However, in this method, there is a problem that the cost is increased due to the additional steps required for the electroplating equipment.
また、特許文献２では、Ｍｎ/Ｓｉ比率を規定し、特許文献３ではＮｉを添加することによって、各々リン酸塩処理性を向上させている。しかしながら、その効果は鋼板中のＳｉ含有量に依存するものであり、Ｓｉ含有量の高い鋼板については更なる改善が必要であると考えられる。 Moreover, in patent document 2, Mn / Si ratio is prescribed | regulated, and patent document 3 is improving the phosphate processability by adding Ni, respectively. However, the effect depends on the Si content in the steel sheet, and it is considered that further improvement is necessary for the steel sheet having a high Si content.
更に、特許文献４では、焼鈍時の露点を−２５〜０℃にすることで、鋼板素地表面から深さ１μｍ以内にＳｉ含有酸化物からなる内部酸化層を形成し、鋼板表面長さ１０μｍに占めるＳｉ含有酸化物の割合を８０％以下にする方法が開示されている。しかしながら、特許文献４に記載の方法の場合、露点を制御するエリアが炉内全体を前提としたものであるため、露点の制御性が困難であり安定操業が困難である。また、不安定な露点制御のもとでの焼鈍を行った場合、鋼板に形成される内部酸化物の分布状態にバラツキが認められ、鋼板の長手方向や幅方向で化成処理性のムラ（全体または一部でスケ）が発生する懸念がある。さらに、化成処理性が向上した場合でも、化成処理皮膜の直下にＳｉ含有酸化物が存在することから電着塗装後の耐食性が悪いという問題がある。 Furthermore, in patent document 4, the dew point at the time of annealing is set to −25 to 0 ° C., thereby forming an internal oxide layer made of an Si-containing oxide within a depth of 1 μm from the surface of the steel sheet, and the steel sheet surface length is 10 μm. A method is disclosed in which the proportion of the Si-containing oxide is 80% or less. However, in the case of the method described in Patent Document 4, since the area for controlling the dew point is premised on the entire inside of the furnace, the controllability of the dew point is difficult and stable operation is difficult. In addition, when annealing was performed under unstable dew point control, variations were observed in the distribution of internal oxides formed on the steel sheet, and chemical conversion treatment unevenness in the longitudinal and width directions of the steel sheet (overall) Or there is a concern that a part of the scale may occur. Furthermore, even when the chemical conversion treatment property is improved, there is a problem that the corrosion resistance after electrodeposition coating is poor because the Si-containing oxide is present directly under the chemical conversion treatment film.
また、特許文献５では、酸化性雰囲気中で鋼板温度を３５０〜６５０℃に到達させて鋼板表面に酸化膜を形成させ、その後、還元性雰囲気中で再結晶温度まで加熱し冷却する方法が記載されている。しかしながらこの方法では、酸化する方法により鋼板表面に形成される酸化皮膜の厚みに差があり、十分に酸化が起こらなかったり、酸化皮膜が厚くなりすぎて、後の還元性雰囲気中での焼鈍において酸化膜の残留または剥離を生じ、表面性状が悪化する場合があった。実施例では、大気中で酸化する技術が記載されているが、大気中での酸化は酸化物が厚く生成してその後の還元が困難である、あるいは高水素濃度の還元雰囲気が必要である、等の問題がある。 Patent Document 5 describes a method in which a steel sheet temperature reaches 350 to 650 ° C. in an oxidizing atmosphere to form an oxide film on the steel sheet surface, and then heated and cooled to a recrystallization temperature in a reducing atmosphere. Has been. However, in this method, there is a difference in the thickness of the oxide film formed on the surface of the steel sheet due to the oxidation method, and sufficient oxidation does not occur, or the oxide film becomes too thick, and in subsequent annealing in a reducing atmosphere. Oxide film may remain or peel off, and surface properties may deteriorate. In the examples, a technique for oxidizing in the air is described, but oxidation in the air generates a thick oxide and subsequent reduction is difficult, or a reducing atmosphere with a high hydrogen concentration is required. There are problems such as.
さらに、特許文献６では、質量％でＳｉを０．１％以上、及び/または、Ｍｎを１．０％以上含有する冷延鋼板について、鋼板温度４００℃以上で鉄の酸化雰囲気下で鋼板表面に酸化膜を形成させ、その後、鉄の還元雰囲気下で前記鋼板表面の酸化膜を還元する方法が記載されている。具体的には、４００℃以上で空気比０．９３以上１．１０以下の直火バーナーを用いて鋼板表面のＦｅを酸化した後、Ｆｅ酸化物を還元するＮ２+Ｈ２ガス雰囲気で焼鈍することにより、化成処理性を劣化させるＳｉＯ２の最表面での酸化を抑制し、最表面にＦｅの酸化層を形成させる方法である。特許文献６には、直火バーナーの加熱温度が具体的に記載されていないが、Ｓｉを多く（概ね０．６％以上）含有する場合には、Ｆｅよりも酸化しやすいＳｉの酸化量が多くなってＦｅの酸化が抑制されたり、Ｆｅの酸化そのものが少なくなりすぎたりする。その結果、還元後の表面Ｆｅ還元層の形成が不十分であったり、還元後の鋼板表面にＳｉＯ２が存在し、化成皮膜のスケが発生する場合がある。 Further, in Patent Document 6, a cold rolled steel sheet containing Si by 0.1% by mass and / or Mn by 1.0% or more by mass%, the surface of the steel sheet in an iron oxidizing atmosphere at a steel sheet temperature of 400 ° C. or more. Describes a method in which an oxide film is formed, and then the oxide film on the surface of the steel sheet is reduced in an iron reducing atmosphere. Specifically, after oxidizing Fe on the surface of the steel sheet using a direct fire burner at 400 ° C. or higher and an air ratio of 0.93 or higher and 1.10 or lower, annealing is performed in an N 2 + H 2 gas atmosphere that reduces Fe oxide. This is a method of suppressing oxidation at the outermost surface of SiO 2 that deteriorates the chemical conversion property and forming an Fe oxide layer on the outermost surface. Patent Document 6 does not specifically describe the heating temperature of an open flame burner, but when it contains a large amount of Si (approximately 0.6% or more), the amount of oxidation of Si that is easier to oxidize than Fe. As a result, the oxidation of Fe is suppressed, and the oxidation of Fe itself becomes too small. As a result, the formation of the surface Fe reduction layer after reduction may be insufficient, or SiO 2 may be present on the steel sheet surface after reduction, resulting in the occurrence of a conversion coating.
本発明は、かかる事情に鑑みてなされたものであって、Ｓｉの含有量が多い場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度鋼板およびその製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and provides a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating, and a method for producing the same, even when the content of Si is large. With the goal.
従来は、単に焼鈍炉内全体の水蒸気分圧または酸素分圧を上昇させることで露点または酸素濃度を上げて過剰に鋼板の内部または外部を酸化させていたため、上述したように、露点または酸化制御性に問題があったり、化成処理性にムラが発生したり、電着塗装後の耐食性が劣化したりと、様々な問題が発生していた。そこで、本発明者らは、従来の考えにとらわれない新たな方法で課題を解決する方法を検討した。その結果、電着塗装後の耐食性劣化の起点になる可能性がある鋼板表層の組織、構造に対してより高度な制御を行うことで、化成処理性および電着塗装後の耐食性に優れる高強度鋼板が得られることを知見した。具体的には、加熱過程における加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域において、雰囲気中の露点を−４０℃以下、かつ、昇温速度を７℃/s以上に制御し、かつ、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の限定された温度域において、雰囲気中の露点を−１０℃以上となるように制御して焼鈍し化成処理を行う。このような処理を行うことによって、選択的表面酸化を抑制し、表面濃化を抑制することができ、化成処理性および電着塗装後の耐食性に優れる高強度鋼板が得られることになる。なお、化成処理性に優れるとは、化成処理後のスケ、ムラのない外観を有することを言う。 In the past, the dew point or oxygen concentration was raised by simply increasing the partial pressure of water vapor or oxygen in the entire annealing furnace to excessively oxidize the inside or outside of the steel sheet. Various problems have occurred, such as a problem in the properties, unevenness in the chemical conversion treatment property, and deterioration in corrosion resistance after electrodeposition coating. Therefore, the present inventors have studied a method for solving the problem by a new method not confined to the conventional idea. As a result, high strength with excellent chemical conversion treatment and corrosion resistance after electrodeposition coating by controlling the structure and structure of the steel sheet surface layer that may become the starting point of corrosion resistance degradation after electrodeposition coating It has been found that a steel plate can be obtained. Specifically, in the temperature range of the heating furnace in the heating process: 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780), the dew point in the atmosphere is −40 ° C. or less, and the heating rate is 7 The dew point in the atmosphere should be −10 ° C. or higher in a limited temperature range where the temperature is controlled to at least ° C./s and the temperature inside the heating furnace: A ° C. and B ° C. And controlled by annealing. By performing such treatment, selective surface oxidation can be suppressed, surface concentration can be suppressed, and a high-strength steel sheet excellent in chemical conversion treatment properties and corrosion resistance after electrodeposition coating can be obtained. In addition, having excellent chemical conversion property means having a non-scaling and uneven appearance after chemical conversion treatment.
そして、以上の方法により得られる高強度鋼板は、鋼板表面から１００μｍ以内の鋼板表層部にＦｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉの中から選ばれる少なくとも１種以上の酸化物を片面あたり０．０１０〜０．５０ｇ/m２形成し、鋼板表面から１０μｍまでの領域において、鋼板結晶粒界から１μm以内の粒内に結晶性Ｓｉ、Ｍｎ系酸化物が析出している組織、構造となる。これによって電着塗装後の耐食性の劣化が実現でき、化成処理性に優れることになる。 And the high-strength steel plate obtained by the above method has Fe, Si, Mn, Al, P, and also B, Nb, Ti, Cr, Mo, Cu, Ni on the steel plate surface layer portion within 100 μm from the steel plate surface. At least one oxide selected from the inside is formed in an amount of 0.010 to 0.50 g / m 2 per side, and in a region from the steel sheet surface to 10 μm, crystalline Si is present within the grain within 1 μm from the grain boundary of the steel sheet. The structure and structure in which Mn-based oxides are deposited are obtained. As a result, the deterioration of the corrosion resistance after electrodeposition coating can be realized and the chemical conversion processability is excellent.
本発明は上記知見に基づくものであり、特徴は以下の通りである。
［１］質量％で、Ｃ：０．０１〜０．１８％、Ｓｉ：０．４〜２．０％、Ｍｎ：１．０〜３．０％、Ａｌ：０．００１〜１．０％、Ｐ：０．００５〜０．０６０％、Ｓ≦０．０１％を含有し、残部がＦｅおよび不可避的不純物からなる鋼板に、連続焼鈍を施す際に、
加熱過程では、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域を雰囲気中の露点：−４０℃以下、かつ、昇温速度：７℃/s以上で、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域を雰囲気中の露点：−１０℃以上とすることを特徴とする高強度鋼板の製造方法。
［２］前記［１］において、前記鋼板は、成分組成として、質量％で、さらに、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％の中から選ばれる１種以上の元素を含有することを特徴とする高強度鋼板の製造方法。
［３］前記［１］または［２］において、前記連続焼鈍を行った後、硫酸を含む水溶液中で電解酸洗を行うことを特徴とする高強度鋼板の製造方法。
［４］前記［１］〜［３］に記載のいずれかの製造方法により製造され、鋼板表面から１００μm以内の鋼板表層部にＦｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉの中から選ばれる少なくとも１種以上の酸化物を、片面あたり０．０１０〜０．５０ｇ／ｍ2形成し、更に、鋼板表面から１０μm以内の領域において、鋼板結晶粒界から１μm以内の粒内に結晶性Ｓｉ、Ｍｎ系酸化物が存在していることを特徴とする高強度鋼板。
The present invention is based on the above findings, and features are as follows.
[1] By mass%, C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0% , P: 0.005 to 0.060%, S ≦ 0.01%, with the balance being subjected to continuous annealing on a steel plate made of Fe and inevitable impurities,
In the heating process, the temperature range in the heating furnace: 600 ° C. or higher and A ° C. or lower (A: 650 ≦ A ≦ 780) in the dew point of the atmosphere: −40 ° C. or lower, and the heating rate: 7 ° C./s or higher. A method for producing a high-strength steel sheet, characterized in that the temperature range in the heating furnace: A ° C. and B ° C. or less (B: 800 ≦ B ≦ 900) is the dew point in the atmosphere: −10 ° C. or more.
[2] In the above [1], the steel sheet is in mass% as a component composition, and further B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005. -0.05%, Cr: 0.001-1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0% A method for producing a high-strength steel sheet, comprising one or more elements selected from the inside.
[3] The method for producing a high-strength steel sheet according to [1] or [2], wherein after the continuous annealing, electrolytic pickling is performed in an aqueous solution containing sulfuric acid.
[4] Manufactured by any one of the production methods described in [1] to [3] above, Fe, Si, Mn, Al, P, B, Nb, Ti, Cr are formed on the steel sheet surface layer within 100 μm from the steel sheet surface. At least one oxide selected from Mo, Cu, and Ni is formed at 0.010 to 0.50 g / m 2 per side, and in the region within 10 μm from the steel plate surface, the grain boundary of the steel plate A high-strength steel sheet characterized by the presence of crystalline Si and Mn-based oxides in grains within 1 μm.
なお、本発明において、高強度とは、引張強度TＳが３４０ＭＰa以上である。また、本発明の高強度鋼板は、冷延鋼板、熱延鋼板のいずれも含むものである。 In the present invention, the high strength means that the tensile strength TS is 340 MPa or more. The high-strength steel sheet of the present invention includes both cold-rolled steel sheets and hot-rolled steel sheets.
本発明によれば、Ｓｉ含有量が多い場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度鋼板が得られる。 According to the present invention, even when the Si content is high, a high-strength steel sheet having excellent chemical conversion properties and corrosion resistance after electrodeposition coating can be obtained.
以下、本発明について具体的に説明する。なお、以下の説明において、鋼成分組成の各元素の含有量の単位は「質量％」であり、以下、特に断らない限り単に「％」で示す。 Hereinafter, the present invention will be specifically described. In the following description, the unit of the content of each element of the steel component composition is “mass%”, and hereinafter, simply indicated by “%” unless otherwise specified.
先ず、本発明で最も重要な要件である、鋼板表面の構造を決定する焼鈍雰囲気条件について説明する。
焼鈍炉内の加熱過程で、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域において、雰囲気中の露点を−４０℃以下、かつ、昇温速度を７℃/s以上に制御して焼鈍を行う。雰囲気中の露点を−４０℃以下に制御することで、鋼板表面の酸素ポテンシャルが低下し、選択的表面酸化（表面濃化）を抑制することが可能となる。しかし、酸素ポテンシャルの低下分のみでは化成処理時のスケやムラの発生を完全に抑制できる程度まで表面濃化を抑制しきれない場合がある。このため、雰囲気中の露点を−４０℃以下に制御することに加え、さらに昇温速度を７℃/ｓ以上に制御する。このように、雰囲気中の露点と昇温速度を制御することにより、表面濃化する温度域を極力早く通過させ、化成処理時にスケやムラが発生しない程度まで表面濃化をさらに抑制することが可能となる。昇温速度を７℃/ｓ以上とするには、ラジアントチューブおよび又はインダクションヒーターでの加熱が適用できる。
露点の下限は特には設けないが、−８０℃未満は効果が飽和し、コストが増大するため、−８０℃が望ましい。
昇温速度の上限は特には設けないが、５００℃/ｓ超えでは効果が飽和し、コストが増大するため、５００℃/ｓ以下が望ましい。
First, annealing atmosphere conditions that determine the structure of the steel sheet surface, which is the most important requirement in the present invention, will be described.
In the heating process in the annealing furnace, in the temperature range of the heating furnace temperature: 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780), the dew point in the atmosphere is −40 ° C. or less, and the heating rate is 7 Annealing is performed at a temperature of at least ° C / s. By controlling the dew point in the atmosphere to −40 ° C. or lower, the oxygen potential on the surface of the steel sheet is lowered, and selective surface oxidation (surface concentration) can be suppressed. However, there is a case where surface concentration cannot be suppressed to the extent that generation of scale and unevenness at the time of chemical conversion treatment can be completely suppressed only by a decrease in oxygen potential. For this reason, in addition to controlling the dew point in the atmosphere to −40 ° C. or lower, the temperature rising rate is further controlled to 7 ° C./s or higher. Thus, by controlling the dew point in the atmosphere and the heating rate, it is possible to pass the temperature region where the surface is concentrated as quickly as possible, and to further suppress the surface concentration to the extent that no scale or unevenness occurs during the chemical conversion treatment. It becomes possible. Heating with a radiant tube and / or an induction heater can be applied to increase the temperature rising rate to 7 ° C./s or more.
The lower limit of the dew point is not particularly set, but if it is less than −80 ° C., the effect is saturated and the cost increases, so −80 ° C. is desirable.
The upper limit of the rate of temperature rise is not particularly set, but if it exceeds 500 ° C./s, the effect is saturated and the cost increases.
６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）とする理由は以下の通りである。６００℃未満の温度域では、低温のため表面拡散するＳｉやＭｎ等の易酸化性元素の量が少ない。また、表面濃化がもともと少ない温度域であり、化成処理性が阻害されることがない。よって、６００℃以上とする。また、上限温度をＡ℃とした理由は、後述するように、Ａ℃を超える温度域では、雰囲気中の露点を−１０℃以上とすることにより、内部酸化が促進され、表面濃化が殆ど起こらなくなるためである。 The reason why the temperature is 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780) is as follows. In the temperature range below 600 ° C., the amount of easily oxidizable elements such as Si and Mn that diffuse on the surface is small because of the low temperature. Further, the temperature concentration is originally in a low temperature range, and the chemical conversion treatment property is not hindered. Therefore, it shall be 600 degreeC or more. The reason why the upper limit temperature is set to A ° C is that, as will be described later, in a temperature range exceeding A ° C, by setting the dew point in the atmosphere to -10 ° C or higher, internal oxidation is promoted and surface concentration is almost complete. This is because it will not happen.
焼鈍炉内の加熱過程で、加熱炉内温度：Ａ℃超えＢ℃以下（Ａ：６５０≦Ａ≦７８０、Ｂ：８００≦Ｂ≦９００）の限定された温度域において、雰囲気中の露点を−１０℃以上となるように制御して焼鈍処理することで、鋼板表層１０μm以内の内部に易酸化性元素（Ｓｉ、Ｍｎなど）の酸化物（以下、内部酸化と称する）を適量に存在させ、焼鈍後の化成処理性を劣化させる鋼中Ｓｉ、Ｍｎ等の鋼板表層における選択的表面酸化（以後、表面濃化と称する）を抑制することが可能となる。 In the heating process in the annealing furnace, the dew point in the atmosphere is-in the limited temperature range of the heating furnace temperature: A ° C. to B ° C. (A: 650 ≦ A ≦ 780, B: 800 ≦ B ≦ 900) By controlling the temperature to be 10 ° C. or higher and annealing, an appropriate amount of an oxide of an easily oxidizable element (Si, Mn, etc.) (hereinafter referred to as internal oxidation) is present inside the steel sheet surface layer within 10 μm, It is possible to suppress selective surface oxidation (hereinafter referred to as surface concentration) in the steel sheet surface layer of Si, Mn, etc. in steel, which deteriorates the chemical conversion treatment property after annealing.
下限温度Ａを６５０≦Ａ≦７８０とする理由は以下の通りである。６５０℃よりも低い温度域では、露点を−１０℃以上に制御しても、内部酸化が殆ど形成しない。６５０℃以上で内部酸化が起こり始める。また、露点を制御せず７８０℃を超える温度まで昇温した場合、表面濃化が多いため、酸素の内方拡散が阻害され、内部酸化が起こりにくくなる。従って、少なくとも７８０℃以下の温度域から−１０℃以上の露点に制御しなければならない。以上から、Ａの許容範囲はＡ：６５０≦Ａ≦７８０であり、上述した理由により、この範囲内においてＡはなるべく低い値であることが望ましい。 The reason why the lower limit temperature A is set to 650 ≦ A ≦ 780 is as follows. In the temperature range lower than 650 ° C., even if the dew point is controlled to be −10 ° C. or higher, almost no internal oxidation is formed. Internal oxidation begins to occur above 650 ° C. Further, when the temperature is raised to a temperature exceeding 780 ° C. without controlling the dew point, the surface is heavily concentrated, so that the inward diffusion of oxygen is inhibited and internal oxidation is less likely to occur. Therefore, the dew point must be controlled to at least −10 ° C. from the temperature range of at least 780 ° C. From the above, the allowable range of A is A: 650 ≦ A ≦ 780, and for the reason described above, it is desirable that A be as low as possible within this range.
上限温度Ｂを８００≦Ｂ≦９００とする理由は以下の通りである。表面濃化を抑制するメカニズムは、以下の通りである。内部酸化を形成することにより、鋼板表層１０μm以内の内部の易酸化性元素（Ｓｉ、Ｍｎなど）の固溶量を減少させた領域（以下、欠乏層と称する）を形成させ、鋼中からの易酸化性元素の表面拡散を抑制する。この内部酸化を形成し、表面濃化を抑制するために十分な欠乏層を形成させるためには、Ｂを８００≦Ｂ≦９００とする必要がある。８００℃を下回った場合、十分に内部酸化が形成されない。また、９００℃超えは内部酸化の形成量が過剰となり、電着塗装後の耐食性劣化の起点となってしまう。 The reason why the upper limit temperature B is set to 800 ≦ B ≦ 900 is as follows. The mechanism for suppressing surface concentration is as follows. By forming internal oxidation, a region (hereinafter referred to as a deficient layer) in which the solid solution amount of an easily oxidizable element (Si, Mn, etc.) within 10 μm of the steel sheet surface layer is reduced is formed. Suppresses surface diffusion of easily oxidizable elements. In order to form this internal oxidation and to form a deficient layer sufficient to suppress surface concentration, B needs to satisfy 800 ≦ B ≦ 900. When the temperature is lower than 800 ° C., sufficient internal oxidation is not formed. On the other hand, if the temperature exceeds 900 ° C., the amount of internal oxidation formed becomes excessive, which becomes a starting point for corrosion resistance deterioration after electrodeposition coating.
Ａ℃超えＢ℃以下の温度域における露点を−１０℃以上とする理由は以下の通りである。露点を上昇させることにより、Ｈ２Ｏの分解から生じるＯ２ポテンシャルを上昇させ、内部酸化を促進することが可能である。−１０℃を下回る温度域では、内部酸化の形成量が少ない。また、露点の上限については特に定めないが、９０℃を超えてくるとＦｅの酸化量が多くなり、焼鈍炉壁やロールの劣化が懸念されるため、９０℃以下が望ましい。 The reason why the dew point in the temperature range from A ° C. to B ° C. is −10 ° C. or higher is as follows. By increasing the dew point, it is possible to increase the O 2 potential resulting from the decomposition of H 2 O and promote internal oxidation. In the temperature range below −10 ° C., the amount of internal oxidation formed is small. The upper limit of the dew point is not particularly defined, but if it exceeds 90 ° C, the amount of Fe oxidation increases, and there is concern about deterioration of the annealing furnace wall and roll.
次いで、本発明の対象とする高強度鋼板の鋼成分組成について説明する。
Ｃ：０．０１〜０．１８％
Ｃは、鋼組織としてマルテンサイトなどを形成させることで加工性を向上させる。そのためには０．０１％以上必要である。一方、０．１８％を超えると伸びが低下し材質が劣化し、さらに溶接性が劣化する。したがって、Ｃ量は０．０１％以上０．１８％以下とする。
Next, the steel component composition of the high-strength steel sheet that is the subject of the present invention will be described.
C: 0.01 to 0.18%
C improves workability by forming martensite or the like as a steel structure. For that purpose, 0.01% or more is necessary. On the other hand, if it exceeds 0.18%, the elongation is reduced, the material is deteriorated, and the weldability is further deteriorated. Therefore, the C content is 0.01% or more and 0.18% or less.
Ｓｉ：０．４〜２．０％
Ｓｉは鋼を強化し伸びを向上させ良好な材質を得るのに有効な元素であり、本発明の目的とする強度を得るためには０．４％以上が必要である。Ｓｉが０．４％未満では本発明の適用範囲とする強度が得られず、化成処理性についても特に問題とならない。一方、２．０％を超えると鋼の強化能や伸び向上効果が飽和してくる。さらに、化成処理性の改善が困難になってくる。したがって、Ｓｉ量は０．４％以上２．０％以下とする。
Si: 0.4-2.0%
Si is an element effective for strengthening steel and improving elongation to obtain a good material, and 0.4% or more is necessary to obtain the intended strength of the present invention. If Si is less than 0.4%, the strength within the scope of the present invention cannot be obtained, and there is no particular problem with chemical conversion treatment. On the other hand, when it exceeds 2.0%, the steel strengthening ability and the effect of improving elongation become saturated. Furthermore, it becomes difficult to improve the chemical conversion processability. Therefore, the Si amount is set to 0.4% or more and 2.0% or less.
Ｍｎ：１．０〜３．０％
Ｍｎは鋼の高強度化に有効な元素である。機械特性や強度を確保するためは１．０％以上含有させることが必要である。一方、３．０％を超えると溶接性や、強度と延性のバランスの確保が困難になる。したがって、Ｍｎ量は１．０％以上３．０％以下とする。
Mn: 1.0-3.0%
Mn is an element effective for increasing the strength of steel. In order to ensure mechanical properties and strength, it is necessary to contain 1.0% or more. On the other hand, if it exceeds 3.0%, it becomes difficult to secure weldability and the balance between strength and ductility. Therefore, the Mn content is 1.0% or more and 3.0% or less.
Ａｌ：０．００１〜１．０％
Ａｌは溶鋼の脱酸を目的に添加される。溶鋼の脱酸の効果は０．００１％以上で得られる。一方、１．０％を超えるとコストアップになる。さらに、Ａｌの表面濃化が多くなり、化成処理性の改善が困難になってくる。したがって、Ａｌ量は０．００１％以上１．０％以下とする。
Al: 0.001 to 1.0%
Al is added for the purpose of deoxidizing molten steel. The effect of deoxidation of molten steel is obtained at 0.001% or more. On the other hand, if it exceeds 1.0%, the cost increases. Furthermore, the surface concentration of Al increases and it becomes difficult to improve chemical conversion properties. Therefore, the Al content is 0.001% or more and 1.0% or less.
Ｐ：０．００５〜０．０６０％以下
Ｐは不可避的に含有される元素のひとつであり、０．００５％未満にするためには、コストの増大が懸念されるため、０．００５％以上とする。一方、Ｐが０．０６０％を超えて含有されると溶接性が劣化する。さらに、化成処理性の劣化が激しくなり、本発明をもってしても化成処理性を向上させることが困難となる。したがって、Ｐ量は０．００５％以上０．０６０％以下とする。
P: 0.005 to 0.060% or less P is one of the elements inevitably contained, and in order to make it less than 0.005%, there is a concern about an increase in cost, so 0.005% or more And On the other hand, if P exceeds 0.060%, weldability deteriorates. Furthermore, the chemical conversion processability is greatly deteriorated, and even with the present invention, it is difficult to improve the chemical conversion processability. Therefore, the P content is 0.005% or more and 0.060% or less.
Ｓ≦０．０１％
Ｓは不可避的に含有される元素のひとつである。下限は規定しないが、多量に含有されると溶接性及び耐食性が劣化するため０．０１％以下とする。
S ≦ 0.01%
S is one of the elements inevitably contained. The lower limit is not specified, but if it is contained in a large amount, the weldability and corrosion resistance deteriorate, so the content is made 0.01% or less.
なお、強度と延性のバランスを制御するため、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％の中から選ばれる１種以上の元素を必要に応じて添加してもよい。
これらの元素を添加する場合における適正添加量の限定理由は以下の通りである。
In order to control the balance between strength and ductility, B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001 One or more elements selected from -1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0% are required. It may be added depending on.
The reason for limiting the appropriate addition amount in the case of adding these elements is as follows.
Ｂ：０．００１〜０．００５％
Ｂは０．００１％未満では焼き入れ促進効果が得られにくい。一方、０．００５％超えでは化成処理性が劣化する。よって、含有する場合、Ｂ量は０．００１％以上０．００５％以下とする。なお、機械的特性を改善する目的で添加する必要がない場合は添加する必要はない。
B: 0.001 to 0.005%
When B is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 0.005%, chemical conversion processability deteriorates. Therefore, when it contains, B amount shall be 0.001% or more and 0.005% or less. In addition, when it is not necessary to add for the purpose of improving a mechanical characteristic, it is not necessary to add.
Ｎｂ：０．００５〜０．０５％
Ｎｂは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えではコストアップを招く。よって、含有する場合、Ｎｂ量は０．００５％以上０．０５％以下とする。
Nb: 0.005 to 0.05%
If Nb is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when it contains, Nb amount shall be 0.005% or more and 0.05% or less.
Ｔｉ：０．００５〜０．０５％
Ｔｉは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えでは化成処理性の劣化を招く。よって、含有する場合、Ｔｉ量は０．００５％以上０．０５％以下とする。
Ti: 0.005 to 0.05%
If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, chemical conversion processability is deteriorated. Therefore, when it contains, Ti amount shall be 0.005% or more and 0.05% or less.
Ｃｒ：０．００１〜１．０％
Ｃｒは０．００１％未満では焼き入れ促進効果が得られにくい。一方、１．０％超えではＣｒが表面濃化するため、溶接性が劣化する。よって、含有する場合、Ｃｒ量は０．００１％以上１．０％以下とする。
Cr: 0.001 to 1.0%
When Cr is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 1.0%, the surface of Cr is concentrated, so that the weldability is deteriorated. Therefore, when it contains, Cr amount shall be 0.001% or more and 1.0% or less.
Ｍｏ：０．０５〜１．０％
Ｍｏは０．０５％未満では強度調整の効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｍｏ量は０．０５％以上１．０％以下とする。
Mo: 0.05-1.0%
If Mo is less than 0.05%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Mo content is 0.05% or more and 1.0% or less.
Ｃｕ：０．０５〜１．０％
Ｃｕは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｃｕ量は０．０５％以上１．０％以下とする。
Cu: 0.05 to 1.0%
If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Cu content is 0.05% or more and 1.0% or less.
Ｎｉ：０．０５〜１．０％
Ｎｉは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｎｉ量は０．０５％以上１．０％以下とする。
Ni: 0.05-1.0%
If Ni is less than 0.05%, the effect of promoting the formation of residual γ phase is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when it contains, Ni amount shall be 0.05% or more and 1.0% or less.
上記以外の残部はＦｅおよび不可避的不純物である。 The balance other than the above is Fe and inevitable impurities.
次に、本発明の高強度鋼板の製造方法とその限定理由について説明する。
例えば、上記化学成分を有する鋼を熱間圧延した後、冷間圧延し、次いで、連続式焼鈍設備において焼鈍を行った後、化成処理を行う。なお、この時、本発明においては、焼鈍時の加熱過程では、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域を雰囲気中の露点：−４０℃以下、かつ、昇温速度：７℃/ｓ以上で、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域を雰囲気中の露点：−１０℃以上とする。これは本発明において、最も重要な要件である。このように焼鈍工程において露点、すなわち雰囲気中酸素分圧を制御することで、酸素ポテンシャルを高め易酸化性元素であるＳｉやＭｎ等が化成処理直前に予め内部酸化し鋼板表層部におけるＳｉ、Ｍｎの活量が低下する。そして、これらの元素の外部酸化が抑制され、結果的に化成処理性が改善することになる。
上記において、熱間圧延終了後、冷間圧延を施さずに、そのまま焼鈍を行う場合もある。６００℃未満およびＢ℃超えの温度域の露点は通常の操業範囲である−４０℃超〜−１０℃でよい。
上記のように、通常の露点は−４０℃より高いので、炉内の水分を吸収剤で吸収除去する等により−４０℃以下の露点とする。逆に、−５℃以上の露点は炉内に水分を補充することで実現出来る。
Next, the manufacturing method of the high strength steel plate of the present invention and the reason for limitation will be described.
For example, the steel having the above chemical components is hot-rolled, cold-rolled, and then annealed in a continuous annealing facility, followed by chemical conversion treatment. At this time, in the present invention, in the heating process during annealing, the temperature range of the heating furnace temperature: 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780) is dew point in the atmosphere: −40 ° C. or less. In addition, the temperature range of the heating rate: 7 ° C./s or more and the temperature in the heating furnace: A ° C. and B ° C. or less (B: 800 ≦ B ≦ 900) is set to the dew point in the atmosphere: −10 ° C. This is the most important requirement in the present invention. In this way, by controlling the dew point, that is, the oxygen partial pressure in the atmosphere in the annealing process, the oxygen potential is increased and the easily oxidizable elements such as Si and Mn are internally oxidized in advance immediately before the chemical conversion treatment, and Si and Mn in the steel sheet surface layer portion. The activity of is reduced. And external oxidation of these elements is suppressed, and as a result, chemical conversion property improves.
In the above, after the hot rolling, annealing may be performed as it is without performing cold rolling. The dew point in the temperature range below 600 ° C. and above B ° C. may be from −40 ° C. to −10 ° C., which is the normal operating range.
As described above, since the normal dew point is higher than −40 ° C., the dew point is set to −40 ° C. or lower by absorbing and removing moisture in the furnace with an absorbent. Conversely, a dew point of −5 ° C. or higher can be achieved by replenishing the furnace with moisture.
熱間圧延
通常、行われる条件にて行うことができる。
Hot rolling Usually, it can be performed on the conditions performed.
酸洗
熱間圧延後は酸洗処理を行うのが好ましい。酸洗工程で表面に生成した黒皮スケールを除去し、しかる後冷間圧延する。なお、酸洗条件は特に限定しない。
It is preferable to perform a pickling treatment after hot pickling. The black scale formed on the surface in the pickling process is removed, and then cold-rolled. The pickling conditions are not particularly limited.
冷間圧延
４０％以上８０％以下の圧下率で行うことが好ましい。圧下率が４０％未満では再結晶温度が低温化するため、機械特性が劣化しやすい。一方、圧下率が８０％超えでは高強度鋼板であるため、圧延コストがアップするだけでなく、焼鈍時の表面濃化が増加するため、めっき特性が劣化する。
Cold rolling is preferably performed at a rolling reduction of 40% to 80%. If the rolling reduction is less than 40%, the recrystallization temperature is lowered, and the mechanical characteristics are likely to deteriorate. On the other hand, when the rolling reduction exceeds 80%, the steel sheet is a high-strength steel plate, so that not only the rolling cost is increased, but also the surface concentration during annealing is increased, so that the plating characteristics are deteriorated.
冷間圧延した鋼板もしくは熱間圧延した鋼板に対して、焼鈍し、次いで、化成処理を施す。
焼鈍炉では、前段の加熱帯で鋼板を所定温度まで加熱する加熱工程を行い、後段の均熱帯で所定温度に所定時間保持する均熱工程を行う。次いで、冷却工程を行う。
そして、上述したように、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域において、雰囲気中の露点が−４０℃以下、かつ、昇温速度が７℃/ｓ以上となるように制御し、かつ、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域において、雰囲気中の露点が−１０℃以上となるように制御して焼鈍を行う。上記露点を制御する領域以外の焼鈍炉内雰囲気中の露点は特に限定されないが、好ましくは−５０℃〜−１０℃の範囲が望ましい。
Cold-rolled steel sheets or hot-rolled steel sheets are annealed and then subjected to chemical conversion treatment.
In the annealing furnace, a heating process is performed in which the steel sheet is heated to a predetermined temperature in a preceding heating zone, and a soaking process is performed in which the temperature is maintained at a predetermined temperature for a predetermined time in a subsequent soaking zone. Next, a cooling process is performed.
As described above, in the temperature range of the heating furnace temperature: 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780), the dew point in the atmosphere is −40 ° C. or less, and the heating rate is 7 ° C. in a temperature range of A ° C. to B ° C. or less (B: 800 ≦ B ≦ 900), so that the dew point in the atmosphere is −10 ° C. or higher. Control and perform annealing. The dew point in the atmosphere in the annealing furnace other than the region where the dew point is controlled is not particularly limited, but is preferably in the range of −50 ° C. to −10 ° C.
焼鈍炉内の気体成分は、窒素、水素及び不可避的不純物からなる。本発明効果を損するものでなければ他の気体成分を含有してもよい。焼鈍炉内雰囲気の水素濃度が１ｖｏｌ％未満では還元による活性化効果が得られず化成処理性が劣化する。上限は特に規定しないが、５０ｖｏｌ％超えではコストアップし、かつ効果が飽和する。よって、水素濃度は１ｖｏｌ％以上５０ｖｏｌ％以下が好ましい。 The gas component in the annealing furnace consists of nitrogen, hydrogen and unavoidable impurities. Other gas components may be included as long as the effects of the present invention are not impaired. If the hydrogen concentration in the atmosphere in the annealing furnace is less than 1 vol%, the activation effect by reduction cannot be obtained and the chemical conversion treatment performance deteriorates. The upper limit is not particularly specified, but if it exceeds 50 vol%, the cost increases and the effect is saturated. Therefore, the hydrogen concentration is preferably 1 vol% or more and 50 vol% or less.
また、同一焼鈍条件で比較した場合、Ｓｉ、Ｍｎの表面濃化量は、鋼中Ｓｉ、Ｍｎ量に比例して大きくなる。また、同一鋼種の場合、比較的高い酸素ポテンシャル雰囲気では、鋼中Ｓｉ、Ｍｎが内部酸化に移行するため、雰囲気中酸素ポテンシャルの増加に伴い、表面濃化量も少なくなる。そのため、鋼中Ｓｉ、Ｍｎ量が多い場合、露点を上昇させることにより、雰囲気中酸素ポテンシャルを増加させる必要がある。 Further, when compared under the same annealing conditions, the surface enrichment amount of Si and Mn increases in proportion to the amount of Si and Mn in the steel. In the case of the same steel type, in a relatively high oxygen potential atmosphere, since Si and Mn in the steel move to internal oxidation, the amount of surface enrichment decreases as the oxygen potential in the atmosphere increases. Therefore, when the amount of Si and Mn in steel is large, it is necessary to increase the oxygen potential in the atmosphere by increasing the dew point.
７５０℃以上の温度域から冷却後、必要に応じて焼入れ、焼き戻しを行っても良い。この条件は特に限定しないが、焼き戻しは１５０〜４００℃の温度で行うのが望ましい。１５０℃未満では伸びが劣化する傾向にあり、４００℃超えでは硬度が低下する傾向にあるためである。 After cooling from a temperature range of 750 ° C. or higher, quenching and tempering may be performed as necessary. Although this condition is not particularly limited, tempering is desirably performed at a temperature of 150 to 400 ° C. This is because the elongation tends to deteriorate when the temperature is lower than 150 ° C., and the hardness tends to decrease when the temperature exceeds 400 ° C.
本発明においては、電解酸洗を実施しなくとも良好な化成処理性は確保可能であるが、焼鈍時に不可避的に発生する微量な表面濃化物を除去し、より良好な化成処理性を確保する目的で、電解酸洗を行うことが好ましい。
電解酸洗の条件は特に限定しないが、焼鈍後に形成された不可避的に表面濃化したＳｉやＭｎの酸化物を効率的に除去するため、電流密度が１Ａ/ｄｍ２以上の交番電解とすることが望ましい。交番電解とする理由は、鋼板を陰極に保持したままでは酸洗効果が小さく、逆に鋼板を陽極に保持したままでは電解時に溶出するＦｅが酸洗液中に蓄積し、酸洗液中のＦｅ濃度が増大してしまい、鋼板表面に付着すると乾き汚れ等の問題が発生してしまうためである。
In the present invention, good chemical conversion treatment can be ensured without carrying out electrolytic pickling, but a small amount of surface condensate inevitably generated during annealing is removed to ensure better chemical conversion treatment. For the purpose, it is preferable to perform electrolytic pickling.
The conditions for the electrolytic pickling are not particularly limited, but in order to efficiently remove the inevitably surface-enriched Si and Mn oxides formed after annealing, an alternating electrolysis with a current density of 1 A / dm 2 or more is used. It is desirable. The reason for alternating electrolysis is that the pickling effect is small when the steel plate is held at the cathode, and conversely, Fe that is eluted during electrolysis accumulates in the pickling solution while the steel plate is held at the anode. This is because if the Fe concentration increases and adheres to the surface of the steel sheet, problems such as dry dirt occur.
さらに、電解酸洗に用いる酸洗液は特に限定しないが、硝酸やフッ化水素酸は設備に対する腐食性が強く取り扱いに注意を要するため、好ましくない。また塩酸は陰極から塩素ガスを発生する可能性があり好ましくない。このため、腐食性や環境を考慮すると硫酸の使用が好ましい。硫酸濃度は５質量％以上２０質量％以下が好ましい。硫酸濃度が５質量％未満では導電率が低くなることから電解時の浴電圧が上昇し、電源負荷が大きくなってしまう場合がある。一方、２０質量％超えの場合は、ドラッグアウトによる損失が大きくコスト的に問題となる。 Furthermore, the pickling solution used for the electrolytic pickling is not particularly limited, but nitric acid and hydrofluoric acid are not preferable because they are highly corrosive to equipment and require careful handling. Hydrochloric acid is not preferred because it may generate chlorine gas from the cathode. For this reason, use of sulfuric acid is preferable in consideration of corrosivity and environment. The sulfuric acid concentration is preferably 5% by mass or more and 20% by mass or less. If the sulfuric acid concentration is less than 5% by mass, the electrical conductivity will be low, so that the bath voltage during electrolysis will rise and the power load may become large. On the other hand, if it exceeds 20% by mass, a loss due to drag-out is large, which causes a problem in cost.
電解液の温度は４０℃以上７０℃以下が好ましい。連続電解することによる発熱で浴温が上昇することから、４０℃未満では酸洗効果が低下する場合がある。また、４０℃未満に温度を維持することが困難な場合がある。また、電解槽のライニングの耐久性の観点から温度が７０℃を超えることは好ましくない。 The temperature of the electrolytic solution is preferably 40 ° C. or higher and 70 ° C. or lower. Since the bath temperature rises due to heat generated by continuous electrolysis, the pickling effect may be reduced at less than 40 ° C. Moreover, it may be difficult to maintain the temperature below 40 ° C. Moreover, it is not preferable that temperature exceeds 70 degreeC from a durable viewpoint of the lining of an electrolytic cell.
以上により、本発明の高強度鋼板が得られる。
そして、以下のように、鋼板表面の構造に特徴を有することになる。
鋼板表面から１００μｍ以内の鋼板表層部には、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃr、Ｍｏ、Ｃu、Ｎｉの中から選ばれる１種以上の酸化物が合計で片面あたり０．０１０〜０．５０ｇ/ｍ２形成される。また、鋼板表面から１０μｍまでの領域においては、粒界から１μｍ以内の地鉄粒内に結晶性Ｓｉ、Ｍｎ系酸化物が存在する。
鋼中にＳｉ及び多量のＭｎが添加された高強度鋼板において、電着塗装後の耐食性を満足させるためには腐食の割れなどの起点になる可能性がある鋼板表層の組織、構造をより高度に制御する必要がある。そこで、本発明では、まず、化成処理性を確保するために焼鈍工程において酸素ポテンシャルを高めるため、露点制御を上述のように行った。その結果、酸素ポテンシャルを高めることで易酸化性元素であるＳｉやＭｎ等が化成処理直前に予め内部酸化し鋼板表層部におけるＳｉ、Ｍｎの活量が低下する。そして、これらの元素の外部酸化が抑制され、結果的に化成処理性及び電着塗装後の耐食性が改善する。さらに、この改善効果は、鋼板表面から１００μｍ以内の鋼板表層部にＦｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃr、Ｍｏ、Ｃu、Ｎｉの中から選ばれる少なくとも１種以上の酸化物を片面あたり０．０１０ｇ/m２以上存在させることになる。一方、０．５０ｇ/ｍ２を超えて存在させた場合、腐食の割れの起点となる懸念があり、化成処理性向上効果は飽和するため、上限は０．５０ｇ/m２とする。
As described above, the high-strength steel sheet of the present invention is obtained.
And it has the characteristic in the structure of the steel plate surface as follows.
One or more oxides selected from Fe, Si, Mn, Al, P, and B, Nb, Ti, Cr, Mo, Cu, and Ni are present on the surface layer of the steel sheet within 100 μm from the steel sheet surface. A total of 0.010 to 0.50 g / m 2 is formed per side. In the region from the steel sheet surface to 10 μm, crystalline Si and Mn-based oxides exist in the ground iron grains within 1 μm from the grain boundary.
In high-strength steel sheets with Si and a large amount of Mn added to the steel, in order to satisfy the corrosion resistance after electrodeposition coating, the structure and structure of the steel sheet surface layer, which may be the starting point of corrosion cracking, is improved. Need to control. Therefore, in the present invention, first, the dew point control is performed as described above in order to increase the oxygen potential in the annealing process in order to ensure chemical conversion treatment. As a result, by increasing the oxygen potential, easily oxidizable elements such as Si and Mn are internally oxidized in advance immediately before the chemical conversion treatment, and the activities of Si and Mn in the steel sheet surface layer portion are lowered. And external oxidation of these elements is suppressed, and as a result, chemical conversion property and corrosion resistance after electrodeposition coating are improved. Furthermore, this improvement effect is at least one selected from Fe, Si, Mn, Al, P, and B, Nb, Ti, Cr, Mo, Cu, Ni on the steel sheet surface layer portion within 100 μm from the steel sheet surface. There will be 0.010 g / m 2 or more of the oxide of the seed or more per side. On the other hand, if it exceeds 0.50 g / m 2 , there is a concern that it may become a starting point of corrosion cracking, and the effect of improving chemical conversion treatment is saturated, so the upper limit is made 0.50 g / m 2 .
また、内部酸化物が粒界にのみ存在し、粒内に存在しない場合、鋼中易酸化性元素の粒界拡散は抑制できるが、粒内拡散は十分に抑制できない場合がある。したがって、本発明では、上述したように、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域を雰囲気中の露点：−４０℃以下、かつ、昇温速度：７℃/s以上で、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域を雰囲気中の露点：−１０℃以上となるように制御することで、粒界のみならず粒内でも内部酸化させる。具体的には、鋼板表層から１０μｍまでの領域において、粒界から１μｍ以内の地鉄粒内に結晶性Ｓｉ、Ｍｎ系酸化物を存在させることになる。地鉄粒内に酸化物が存在することで、酸化物近傍の地鉄粒内の固溶Ｓｉ、Ｍｎの量が減少する。その結果、Ｓｉ、Ｍｎの粒内拡散による表面への濃化を抑制することができる。 Moreover, when an internal oxide exists only in a grain boundary and does not exist in a grain, the grain boundary diffusion of an easily oxidizable element in steel can be suppressed, but the intragranular diffusion may not be sufficiently suppressed. Therefore, in the present invention, as described above, the temperature in the heating furnace: 600 ° C. or more and A ° C. or less (A: 650 ≦ A ≦ 780), and the dew point in the atmosphere: −40 ° C. or less and the rate of temperature increase By controlling the temperature range of 7 ° C./s or more and the temperature in the heating furnace: A ° C. and B ° C. or less (B: 800 ≦ B ≦ 900) to be a dew point of −10 ° C. Internal oxidation is performed not only at grain boundaries but also within grains. Specifically, in the region from the steel sheet surface layer to 10 μm, crystalline Si and Mn-based oxides are present in the ground iron grains within 1 μm from the grain boundary. The presence of oxide in the ground iron grains reduces the amount of solid solution Si and Mn in the ground iron grains near the oxide. As a result, concentration on the surface due to intragranular diffusion of Si and Mn can be suppressed.
なお、本発明の製造方法で得られる高強度鋼板の鋼板表面の構造は、上記の通りであるが、例えば、鋼板表面から１００μｍを超えた領域で前記酸化物が成長していても問題はない。また、鋼板表面から１０μｍを超えた領域おいて、鋼板結晶粒界から１μm以内の粒内に結晶性Ｓｉ、Ｍｎ系酸化物が存在させても問題はない。 The structure of the steel sheet surface of the high-strength steel sheet obtained by the production method of the present invention is as described above. For example, there is no problem even if the oxide grows in a region exceeding 100 μm from the steel sheet surface. . Further, in the region exceeding 10 μm from the steel plate surface, there is no problem even if crystalline Si or Mn-based oxides are present in grains within 1 μm from the steel plate crystal grain boundary.
以下、本発明を、実施例に基いて具体的に説明する。
表１に示す鋼組成からなる熱延鋼板を酸洗し、黒皮スケールを除去した後、冷間圧延し、厚さ１．０ｍｍの冷延鋼板を得た。なお、一部は冷間圧延を実施せず、黒皮スケール除去後の熱延鋼板（厚さ２．０ｍｍ）ままのものも用意した。
Hereinafter, the present invention will be specifically described based on examples.
The hot-rolled steel sheet having the steel composition shown in Table 1 was pickled, and after removing the black scale, it was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some did not carry out cold rolling, but prepared the hot-rolled steel plate (thickness 2.0 mm) after removing the black scale.
次いで、上記で得た冷延鋼板及び熱延鋼板を、連続式焼鈍設備に装入した。焼鈍設備では、表２に示す通り、加熱炉内温度と露点、昇温速度を制御して通板して焼鈍した後、水焼入れ後に３００℃×１４０ｓ間の焼き戻しを行った。引き続き、４０℃、５質量％の硫酸水溶液中、表２に示す電流密度条件にて、供試材を陽極、陰極の順に３秒ずつとする交番電解で電解酸洗を行い、供試材を得た。なお、上記露点を制御した領域以外の焼鈍炉の露点は−３５℃を基本とした。また、雰囲気の気体成分は窒素ガスと水素ガスおよび不可避的不純物気体からなり、−１０℃以上となる露点の制御については、窒素中に設置した水タンクを加熱して加湿した窒素ガスが流れる配管を予め別途設置し、加湿した窒素ガス中に水素ガスを導入して混合し、これを炉内に導入することで雰囲気中の露点を制御した。また、−４０℃以下の露点は雰囲気中の水分を吸収除去して制御した。雰囲気中の水素濃度は１０vol％を基本とした。 Next, the cold-rolled steel plate and hot-rolled steel plate obtained above were charged into a continuous annealing facility. In the annealing equipment, as shown in Table 2, the temperature inside the heating furnace, the dew point, and the heating rate were controlled and passed through the plate and annealed, and then tempered between 300 ° C. and 140 s after water quenching. Subsequently, electrolytic pickling was performed by alternating electrolysis in which the test material was in the order of anode and cathode for 3 seconds each in the order of the current density conditions shown in Table 2 in a sulfuric acid aqueous solution of 5% by mass at 40 ° C. Obtained. In addition, the dew point of the annealing furnace except the area | region which controlled the said dew point was based on -35 degreeC. The atmospheric gas components are nitrogen gas, hydrogen gas, and unavoidable impurity gas, and the dew point is controlled at -10 ° C or higher. Was separately installed, hydrogen gas was introduced into and mixed with humidified nitrogen gas, and the dew point in the atmosphere was controlled by introducing this into the furnace. Further, the dew point of −40 ° C. or lower was controlled by removing moisture in the atmosphere. The hydrogen concentration in the atmosphere was basically 10 vol%.
得られた供試材に対してJIS Z ２２４１ 金属材料引張試験方法に従い、ＴＳ、Ｅｌを測定した。また、得られた供試材に対して、化成処理性及び耐食性を調査した。鋼板表層直下の１００μｍまので鋼板表層部に存在する酸化物の量（内部酸化量）を測定した。測定方法および評価基準を下記に示す。 TS and El were measured with respect to the obtained test material in accordance with JIS Z 2241 metal material tensile test method. Moreover, the chemical conversion property and corrosion resistance were investigated with respect to the obtained test material. The amount of oxide (internal oxidation amount) present in the steel sheet surface layer up to 100 μm just below the steel sheet surface layer was measured. The measurement method and evaluation criteria are shown below.
化成処理性
化成処理性の評価方法を以下に記載する。
化成処理液は日本パーカライジング（株）製の化成処理液（パルボンドＬ３０８０（登録商標））を用い、下記方法で化成処理を施した。
日本パーカライジング（株）製の脱脂液ファインクリーナー（登録商標）で脱脂したのち、水洗し、次に日本パーカライジング（株）製の表面調整液プレパレンＺ（登録商標）で３０ｓ表面調整を行い、４３℃の化成処理液（パルボンドＬ３０８０）に１２０ｓ浸漬した後、水洗し、温風乾燥した。
化成処理後の供試材を走査型電子顕微鏡（ＳＥＭ）で倍率５００倍で無作為に５視野を観察し、化成処理皮膜のスケ面積率を画像処理により測定し、スケ面積率によって以下の評価を行った。○が合格レベルである。
○：１０％以下
×：１０％超
The chemical conversion property evaluation method of chemical conversion property is described below.
A chemical conversion treatment liquid (Palbond L3080 (registered trademark)) manufactured by Nihon Parkerizing Co., Ltd. was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed by the following method.
After degreasing with a degreasing liquid Fine Cleaner (registered trademark) manufactured by Nihon Parkerizing Co., Ltd., washing with water, and then adjusting the surface for 30 s with surface conditioning solution preparen Z (registered trademark) manufactured by Nihon Parkerizing Co., Ltd. After being immersed in a chemical conversion treatment solution (Palbond L3080) for 120 s, it was washed with water and dried with warm air.
The sample after the chemical conversion treatment was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, the scale area ratio of the chemical conversion film was measured by image processing, and the following evaluation was made based on the scale area ratio. Went. ○ is an acceptable level.
○: 10% or less ×: Over 10%
電着塗装後の耐食性
上記の方法で得られた化成処理を施した供試材より寸法７０ｍｍ×１５０ｍｍの試験片を切り出し、日本ペイント（株）製のＰＮ−１５０Ｇ（登録商標）でカチオン電着塗装（焼付け条件：１７０℃×２０分、膜厚２５μｍ）を行った。その後、端部と評価しない側の面をＡｌテープでシールし、カッターナイフにて地鉄に達するクロスカット（クロス角度６０°）を入れ、供試材とした。
次に、供試材を５質量％ＮａＣｌ水溶液（５５℃）中に、２４０時間浸漬後に取り出し、水洗、乾燥後にクロスカット部をテープ剥離し、剥離幅を測定し、以下の評価を行った。○が合格レベルである
○：剥離幅が片側２．５ｍｍ未満
×：剥離幅が片側２．５ｍｍ以上
Corrosion resistance after electrodeposition coating A test piece having a size of 70 mm x 150 mm was cut out from the test material subjected to chemical conversion treatment obtained by the above method, and cation electrodeposition was performed using PN-150G (registered trademark) manufactured by Nippon Paint Co., Ltd. Coating (baking conditions: 170 ° C. × 20 minutes, film thickness 25 μm) was performed. Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material.
Next, the test material was taken out after being immersed in a 5% by mass NaCl aqueous solution (55 ° C.) for 240 hours, washed with water and dried, and then the tape was peeled off, the peel width was measured, and the following evaluation was performed. ○ is an acceptable level ○: peeling width is less than 2.5 mm on one side ×: peeling width is 2.5 mm or more on one side
加工性
加工性は、試料から圧延方向に対して90°方向にJIS５号引張試験片を採取し、JIS Z 2241の規定に準拠してクロスヘッド速度10ｍｍ／ｍｉｎ一定で引張試験を行い、引張り強度（ＴＳ／ＭＰａ）と伸び（Ｅｌ％）を測定し、ＴＳが６５０ＭＰａ未満の場合は、ＴＳ×Ｅｌ≧２２０００のものを良好、ＴＳ×Ｅｌ＜２２０００のものを不良とした。ＴＳが６５０ＭＰａ以上９００ＭＰａの場合は、ＴＳ×Ｅｌ≧２００００のものを良好、ＴＳ×Ｅｌ＜２００００のものを不良とした。ＴＳが９００ＭＰａ以上の場合は、ＴＳ×Ｅｌ≧１８０００のものを良好、ＴＳ×Ｅｌ＜１８０００のものを不良とした。
Workability As for workability, a JIS No. 5 tensile test piece is taken from the sample in the 90 ° direction with respect to the rolling direction, and a tensile test is performed at a constant crosshead speed of 10 mm / min in accordance with the provisions of JIS Z 2241. (TS / MPa) and elongation (El%) were measured, and when TS was less than 650 MPa, TS × El ≧ 22000 was judged good and TS × El <22000 was judged poor. When TS was 650 MPa or more and 900 MPa, TS × El ≧ 20000 was judged good, and TS × El <20000 was judged poor. When TS was 900 MPa or more, TS × El ≧ 18000 was judged good, and TS × El <18000 was judged poor.
鋼板表層１００μmまでの領域における内部酸化量
内部酸化量は、「インパルス炉溶融−赤外線吸収法」により測定した。ただし、素材（すなわち焼鈍を施す前の高強度鋼板）に含まれる酸素量を差し引く必要があるので、本発明では、連続焼鈍後の高強度鋼板の両面の表層部を１００μｍ以上研磨して鋼中酸素濃度を測定し、その測定値を素材に含まれる酸素量ＯＨとし、また、連続焼鈍後の高強度鋼板の板厚方向全体での鋼中酸素濃度を測定して、その測定値を内部酸化後の酸素量ＯＩとした。このようにして得られた高強度鋼板の内部酸化後の酸素量ＯＩと、素材に含まれる酸素量ＯＨとを用いて、ＯＩとＯＨの差（＝ＯＩ−ＯＨ）を算出し、さらに片面単位面積（すなわち１m２）当たりの量に換算した値（ｇ／ｍ２）を内部酸化量とした。
The amount of internal oxidation in the region of the steel sheet surface layer up to 100 μm was measured by “impulse furnace melting-infrared absorption method”. However, since it is necessary to subtract the amount of oxygen contained in the material (that is, the high-strength steel plate before annealing), in the present invention, the surface layer portions on both surfaces of the high-strength steel plate after continuous annealing are polished by 100 μm or more in the steel. Measure the oxygen concentration, set the measured value as the amount of oxygen OH contained in the material, measure the oxygen concentration in the steel in the entire thickness direction of the high-strength steel sheet after continuous annealing, and measure the measured value internally. The subsequent oxygen amount OI was used. The difference between OI and OH (= OI-OH) is calculated using the oxygen amount OI after internal oxidation of the high-strength steel plate thus obtained and the oxygen amount OH contained in the material, and further, single-sided unit area (i.e. 1 m 2) value converted into the amount per (g / m 2) as an internal oxide amount.
以上により得られた結果を製造条件と併せて表２に示す。 The results obtained as described above are shown in Table 2 together with the production conditions.
表２から明らかなように、本発明法で製造された高強度鋼板は、Ｓｉ、Ｍｎ等の易酸化性元素を多量に含有する高強度鋼板であるにもかかわらず、化成処理性、電着塗装後の耐食性、加工性に優れることがわかる。
一方、比較例では、化成処理性、電着塗装後の耐食性、加工性のいずれか一つ以上が劣る。
As is apparent from Table 2, the high-strength steel sheet produced by the method of the present invention is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si and Mn, but the chemical conversion treatment property, electrodeposition It can be seen that it has excellent corrosion resistance and workability after painting.
On the other hand, in the comparative example, any one or more of chemical conversion property, corrosion resistance after electrodeposition coating, and workability is inferior.
本発明の高強度鋼板は、化成処理性、耐食性、加工性に優れ、自動車の車体そのものを軽量化かつ高強度化するための表面処理鋼板として利用することができる。また、自動車以外にも、素材鋼板に防錆性を付与した表面処理鋼板として、家電、建材の分野等、広範な分野で適用できる。 The high-strength steel sheet of the present invention is excellent in chemical conversion property, corrosion resistance, and workability, and can be used as a surface-treated steel sheet for reducing the weight and strength of the automobile body itself. In addition to automobiles, the steel sheet can be applied in a wide range of fields such as home appliances and building materials as a surface-treated steel sheet provided with rust prevention properties.
Claims (4)
加熱過程では、加熱炉内温度：６００℃以上Ａ℃以下（Ａ：６５０≦Ａ≦７８０）の温度域を雰囲気中の露点：−４０℃以下、かつ、昇温速度：７℃/s以上で、加熱炉内温度：Ａ℃超えＢ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域を雰囲気中の露点：−１０℃以上とし、前記加熱炉内温度：６００℃以上Ｂ℃以下（Ｂ：８００≦Ｂ≦９００）の温度域以外の雰囲気中の露点を−５０℃〜−１０℃とすることを特徴とする高強度鋼板の製造方法。 In mass%, C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0%, P: When steel sheet containing 0.005 to 0.060%, S ≦ 0.01%, the balance being Fe and inevitable impurities, is subjected to continuous annealing,
In the heating process, the temperature range in the heating furnace: 600 ° C. or higher and A ° C. or lower (A: 650 ≦ A ≦ 780) in the dew point of the atmosphere: −40 ° C. or lower, and the heating rate: 7 ° C./s or higher. In the heating furnace, the temperature range of more than A ° C and not more than B ° C (B: 800 ≦ B ≦ 900) is dew point in the atmosphere: −10 ° C. or more, and the temperature in the heating furnace: 600 ° C. or more and B ° C. or less ( B : The manufacturing method of the high strength steel plate characterized by making dew point in atmospheres other than the temperature range of 800 <= B <= 900 ) into -50 to -10 degreeC.
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