JP5691371B2 - Manufacturing method of high Si content high strength steel sheet with excellent chemical conversion - Google Patents
Manufacturing method of high Si content high strength steel sheet with excellent chemical conversion Download PDFInfo
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本発明は、優れた化成処理性が要求される高張力鋼板、特に自動車用部材として好適に用いられる高張力鋼板に係り、多くのSiを含有するにも拘らず優れた化成処理性を有する高張力鋼板の製造方法に関する。 The present invention relates to a high-tensile steel sheet that is required to have excellent chemical conversion properties, in particular, a high-tensile steel plate that is suitably used as a member for automobiles, and has high chemical conversion property even though it contains a large amount of Si. The present invention relates to a method for manufacturing a tension steel sheet.
近年、地球環境問題の高まりから、所望の強度を確保しつつ自動車車体を軽量化して燃費の向上を図ることが重要課題とされている。そして、このような課題を解決するうえでは自動車部品の素材を高強度化かつ薄肉化することが有効であるため、自動車部品の素材には高強度であり且つ板厚の薄い高張力鋼板が積極的に用いられている。 In recent years, due to the growing global environmental problems, it has been an important issue to improve fuel efficiency by reducing the weight of an automobile body while ensuring a desired strength. In order to solve these problems, it is effective to increase the strength and thickness of automobile parts. Therefore, high-strength steel sheets with high strength and thin thickness are actively used for automobile parts. Has been used.
また、上記のような高張力鋼板を素材として用いて自動車部品を製造するに際し、鋼板は通常、プレス加工等の複雑な加工が施されることにより所望の部品形状に成形される。そのため、自動車部品の素材として用いられる高張力鋼板には、高強度であることに加えて優れた延性等の加工性を有することも要求される。 Moreover, when manufacturing an automotive part using the above-described high-tensile steel plate as a raw material, the steel plate is usually formed into a desired part shape by performing complicated processing such as press working. Therefore, high-tensile steel plates used as materials for automobile parts are required to have excellent workability such as ductility in addition to high strength.
そこで、高張力鋼板ではC、Si、Mn等の元素を添加し、これらの元素の含有量を調整することにより鋼板に所望の強度および加工性を付与している。また、これらの元素のうち固溶強化元素であるSiは、安価であり且つ鋼板の延性を低下させることなく鋼板強度の上昇に寄与する元素であるため特に重要な元素であり、優れた強度と加工性が要求されるような高張力鋼板にはSiが積極的に添加されている。 Therefore, in a high-tensile steel plate, elements such as C, Si, and Mn are added, and desired strength and workability are imparted to the steel plate by adjusting the content of these elements. Of these elements, Si, which is a solid solution strengthening element, is a particularly important element because it is an element that contributes to an increase in steel sheet strength without lowering the ductility of the steel sheet. Si is positively added to high-tensile steel sheets that require workability.
ところで、鋼板をプレス加工等により所望の形状に成形して得られた自動車部品は組立・塗装されるが、この塗装の際の塗膜密着性を向上させるため、塗装に先立ち、鋼板には化成処理（リン酸塩皮膜処理）が施される。化成処理では、鋼板表面に均一、かつ、微細なリン酸塩の結晶を形成させることにより鋼板の塗膜密着性を向上させるが、リン酸塩結晶が部分的に欠落したり、あるいは、粗大な結晶になると、鋼板の塗膜密着性が低下し、塗装後の自動車部品の耐食性が悪くなる。このため、自動車部品の素材として用いられる高張力鋼板には、高強度であり且つ優れた加工性を有することに加え、優れた化成処理性を有することが必要不可欠である。 By the way, automobile parts obtained by forming a steel sheet into a desired shape by pressing or the like are assembled and painted, but in order to improve the adhesion of the coating film during the coating, the steel sheet is formed before the coating. Treatment (phosphate film treatment) is performed. In the chemical conversion treatment, the coating film adhesion of the steel sheet is improved by forming uniform and fine phosphate crystals on the surface of the steel sheet, but the phosphate crystals are partially missing or coarse. When it becomes crystal, the coating film adhesion of the steel sheet is lowered, and the corrosion resistance of the automobile parts after painting is deteriorated. For this reason, in addition to having high strength and excellent workability, it is indispensable for a high-tensile steel sheet used as a material for automobile parts to have excellent chemical conversion treatment properties.
しかしながら、高強度化および加工性の向上に有効な元素であるとして高張力鋼板に積極的に添加されているSiは、化成処理性を劣化させる元素である。冷延後の鋼板は、還元雰囲気で再結晶焼鈍されたのち、化成処理が施されるが、再結晶焼鈍の際、Siは易酸化元素であるため優先的に酸化され、鋼板表面に酸化物として濃化する。化成処理の際、鋼板表面にSi酸化物が濃化していると、濡れ性、反応性が悪くなり、リン酸塩結晶が形成され難くなる。このため、Siを多く含んだ高張力鋼板は再結晶焼鈍後の化成処理性が低下するという問題を有する。 However, Si that is positively added to high-tensile steel sheets as an element effective for increasing the strength and improving the workability is an element that deteriorates the chemical conversion processability. The steel sheet after cold rolling is recrystallized and annealed in a reducing atmosphere, and then undergoes chemical conversion treatment, but during recrystallization annealing, Si is preferentially oxidized because it is an easily oxidizable element, and the surface of the steel sheet is oxidized. As it thickens. If the Si oxide is concentrated on the surface of the steel sheet during the chemical conversion treatment, the wettability and reactivity deteriorate, and phosphate crystals are difficult to form. For this reason, the high-tensile steel sheet containing a large amount of Si has a problem that the chemical conversion property after recrystallization annealing is lowered.
以上のような問題を解決する方法としては、焼鈍後、鋼板表面に濃化したSi酸化物を除去する方法が知られている。このように、化成処理性の低下を招くSi酸化物を除去しておけば、高Si含有高張力鋼板に所望の化成処理性を付与することが可能となる。
ここで、焼鈍後の鋼板表面に生じた酸化物を除去する方法としては様々なものがあり、例えば特許文献１に開示されているように、連続焼鈍後の鋼板表面を酸洗する化学的方法や、この化学的方法に代えて鋼板表面にショットブラスト等を施す機械的方法がある。また、鋼板表面に生じた酸化物を機械的に除去する手段としては、例えば特許文献２で提案されたブラシロールを用いて鋼板表面をブラシ研削する手段が知られている。
As a method for solving the above problems, a method of removing Si oxide concentrated on the steel sheet surface after annealing is known. Thus, if the Si oxide that causes a decrease in chemical conversion property is removed, it becomes possible to impart desired chemical conversion property to the high-Si content high-tensile steel sheet.
Here, there are various methods for removing oxides generated on the surface of the steel sheet after annealing. For example, as disclosed in Patent Document 1, a chemical method for pickling the steel sheet surface after continuous annealing. Alternatively, there is a mechanical method in which shot blasting or the like is applied to the steel sheet surface instead of this chemical method. Further, as means for mechanically removing oxides generated on the steel sheet surface, for example, means for brush grinding the steel sheet surface using a brush roll proposed in Patent Document 2 is known.
しかしながら、特許文献１に開示された方法を、質量％で1.5％以上のSiを含有する高Si含有高張力鋼板に適用しても、Si酸化物を除去することはできない。連続焼鈍後の高Si含有高張力鋼板に形成されたSi酸化物は、鋼板表面に極めて強固に密着している。そのため、特許文献１で開示されているように、酸洗やショットブラスト等を各々単独で適用しても、高Si含有高張力鋼板の表面に形成されたSi酸化物を除去することはできない。また、特許文献２で提案されたようなブラシロールを用いたブラシ研削を単独で適用しても、やはり高Si含有高張力鋼板の表面に形成されたSi酸化物を除去することはできない。 However, even if the method disclosed in Patent Document 1 is applied to a high-Si content high-tensile steel sheet containing 1.5% or more of Si by mass%, the Si oxide cannot be removed. The Si oxide formed on the high-Si content high-tensile steel plate after the continuous annealing is extremely firmly adhered to the steel plate surface. Therefore, as disclosed in Patent Document 1, even if pickling, shot blasting, or the like is applied alone, the Si oxide formed on the surface of the high-Si containing high-tensile steel sheet cannot be removed. Moreover, even if brush grinding using a brush roll as proposed in Patent Document 2 is applied alone, it is still impossible to remove Si oxide formed on the surface of a high-strength steel sheet with high Si content.
一方、特許文献３では、焼鈍後の高Si含有高張力鋼板に、ブラシ研削と塩酸酸洗を組み合わせた酸化膜除去処理を施す方法が提案されている。そして、特許文献３で提案された方法によると、ブラシ研削量を2.0g/m2以上とすることにより、焼鈍後の高Si含有高張力鋼板表面に形成されたSi含有酸化物を効果的に除去することが可能であるとされている。また、特許文献３で提案された方法では、Si含有酸化物を完全に除去するには、塩酸酸洗で用いる塩酸濃度を3％以上とすることが好ましいとされている。 On the other hand, Patent Document 3 proposes a method of subjecting a high-Si containing high-tensile steel sheet after annealing to an oxide film removal process that combines brush grinding and hydrochloric acid pickling. And according to the method proposed in Patent Document 3, the Si-containing oxide formed on the surface of the high-Si containing high-tensile steel sheet after annealing is effectively obtained by setting the brush grinding amount to 2.0 g / m 2 or more. It can be removed. In addition, in the method proposed in Patent Document 3, it is preferable that the hydrochloric acid concentration used in hydrochloric acid pickling is preferably 3% or more in order to completely remove the Si-containing oxide.
しかしながら、特許文献３で提案された方法では、ブラシ研削量を2g/m2以上とすることを必須としており、このように大きな研削量のブラシ研削を施すことに起因した幾つかの問題点が見られる。まず、ブラシ研削量を2g/m2以上と大きくすると、鋼板表面にブラシ研削目が残存してしまう。そして、鋼板表面にブラシ研削目が残存すると、その後に行われる化成処理や塗装処理に悪影響を及ぼすとともに、最終製品の外観を損なう。また、ブラシ研削量を2g/m2以上と大きくすると、ブラシ研削コストが過大になる。 However, in the method proposed in Patent Document 3, it is essential to set the brush grinding amount to 2 g / m 2 or more, and there are some problems caused by performing brush grinding with such a large grinding amount. It can be seen. First, when the brush grinding amount is increased to 2 g / m 2 or more, brush grinding marks remain on the steel plate surface. If the brush grinding marks remain on the surface of the steel sheet, it adversely affects the chemical conversion treatment and coating treatment performed thereafter, and impairs the appearance of the final product. Further, if the brush grinding amount is increased to 2 g / m 2 or more, the brush grinding cost becomes excessive.
ところで、化成処理に関しても、鋼板と化成処理液の反応の際、副産物であるスラッジの発生が環境負荷の観点から問題となっており、スラッジ低減のために化成処理温度の低温化が進みつつある。化成処理温度が低温化すると、均一で微細なリン酸塩結晶を得ることが難しくなるため、ますます、化成処理性に対する要望が強くなっている。言い換えれば、優れた化成処理性を有する鋼板であれば、化成処理温度を低温化できるため、化成処理工程でのスラッジ低減などに寄与できるのである。 By the way, regarding the chemical conversion treatment, generation of sludge as a by-product has become a problem from the viewpoint of environmental load during the reaction between the steel sheet and the chemical conversion treatment liquid, and the temperature of chemical conversion treatment is being lowered to reduce sludge. . When the chemical conversion treatment temperature is lowered, it becomes difficult to obtain uniform and fine phosphate crystals, so that there is an increasing demand for chemical conversion treatment. In other words, a steel sheet having excellent chemical conversion property can contribute to the reduction of sludge in the chemical conversion treatment process because the chemical conversion treatment temperature can be lowered.
以上のような背景の下、本発明の目的は、化成処理性に優れた、高Si含有高張力鋼板を製造するに際し、焼鈍時に形成されるSi酸化物を効率的に除去する方法を提供することを目的とする。 Under the background as described above, an object of the present invention is to provide a method for efficiently removing Si oxide formed at the time of annealing when producing a high-Si containing high-tensile steel sheet excellent in chemical conversion treatment. For the purpose.
上記課題を解決すべく、本発明者らは、連続焼鈍によって高Si含有高張力鋼板表面に形成されたSiを含む酸化物を除去する方法に関し、高Si含有高張力鋼板の化成処理性に及ぼすブラシ研削条件および塩酸酸洗条件の影響について鋭意検討した。その結果、以下の知見を得た。 In order to solve the above-mentioned problems, the present inventors relate to a method of removing oxides containing Si formed on the surface of a high-strength steel sheet with high Si content by continuous annealing, and affect the chemical conversion treatment properties of the high-strength steel sheet with high Si content The effects of brush grinding conditions and hydrochloric acid pickling conditions were studied intensively. As a result, the following knowledge was obtained.
ａ）ブラシ研削量が増加すると、ブラシ研削時の加工発熱が大きくなり、この加工発熱に起因して鋼板表面に酸化物が生成してしまうこと。
ｂ）加工発熱に起因した上記酸化物が、後工程の化成処理時に均一微細な化成結晶の形成を阻害すること。
ｃ）塩酸濃度が過剰に高くなると、酸液の酸化力が強くなるため、鋼板表面の活性度が低くなり、均一微細な化成結晶が生成し難くなること。
ｄ）ブラシ研削量・塩酸濃度をともに所定量に低減すれば、ブラシ研削時の加工発熱および酸液の酸化力が適度に低減され、化成処理時に均一微細な化成結晶が形成されること。
a) When the amount of brush grinding increases, the processing heat generated during brush grinding increases, and oxides are generated on the surface of the steel sheet due to the processing heat generation.
b) The oxide resulting from the processing heat generation inhibits the formation of uniform fine chemical crystals during the chemical conversion treatment in the subsequent step.
c) When the concentration of hydrochloric acid is excessively high, the oxidizing power of the acid solution becomes strong, so that the activity on the surface of the steel sheet is lowered and it becomes difficult to form uniform fine chemical crystals.
d) If both the brush grinding amount and the hydrochloric acid concentration are reduced to a predetermined amount, the processing heat generated during brush grinding and the oxidizing power of the acid solution are moderately reduced, and uniform fine chemical crystals are formed during the chemical conversion treatment.
本発明は、これらの知見に基づきなされたものであり、その要旨は次のとおりである。
［１］質量％で、
Ｃ：0.03％以上0.20％以下、 Si：0.5％以上1.8％以下、
Mn：1.5％以上3.5％以下、 Ｐ：0.01％以上0.04％以下、
Ｓ：0.001％以上0.01％以下
を含有し、残部Feおよび不可避的不純物からなる組成を有する鋼板に、冷間圧延および連続焼鈍を施して高張力鋼板を製造するに際し、前記連続焼鈍後の鋼板の表面に研削量0.5g/m2以上1.0 g/m2未満のブラシ研削を施し、次いで濃度が1.0％超3.0％未満の塩酸を用いた塩酸酸洗を施すことを特徴とする、化成処理性に優れた高Si含有高張力鋼板の製造方法。
The present invention has been made based on these findings, and the gist thereof is as follows.
[1] By mass%
C: 0.03% to 0.20%, Si: 0.5% to 1.8%,
Mn: 1.5% to 3.5%, P: 0.01% to 0.04%,
S: A steel sheet containing 0.001% or more and 0.01% or less and having the balance Fe and inevitable impurities is subjected to cold rolling and continuous annealing to produce a high-strength steel sheet. Chemical conversion processability, characterized in that the surface is subjected to brush grinding with a grinding amount of 0.5 g / m 2 or more and less than 1.0 g / m 2 , followed by hydrochloric acid pickling using hydrochloric acid with a concentration of more than 1.0% and less than 3.0% For producing high-strength steel sheets with high Si content that excel in resistance.
［２］前記［１］において、前記鋼板が、前記組成に加えてさらに質量％で、Nb：0.OO1％以上0.15％以下、Ti：0.001％以上0.15％以下、Al：0.02％以上0.04％以下、Ｎ：0.001％以上0.005％以下、Cu：0.001％以上0.03％以下、Ni：0.001％以上0.03％以下、Cr：0.001％以上0.2％以下、Ｖ：0.001％以上0.2％以下、Mo：0.001％以上0.20％以下から選択される１種または２種以上を含有することを特徴とする、化成処理性に優れた高Si含有高張力鋼板の製造方法。 [2] In the above [1], in addition to the composition, the steel sheet is further in mass%, Nb: 0.001% to 0.15%, Ti: 0.001% to 0.15%, Al: 0.02% to 0.04% N: 0.001% to 0.005%, Cu: 0.001% to 0.03%, Ni: 0.001% to 0.03%, Cr: 0.001% to 0.2%, V: 0.001% to 0.2%, Mo: 0.001 The manufacturing method of the high Si content high-tensile steel plate excellent in chemical conversion property characterized by containing 1 type, or 2 or more types selected from% to 0.20%.
［３］前記［１］または［２］において、前記ブラシ研削を、＃120以下の砥粒を含有するブラシを用いて研削することを特徴とする、化成処理性に優れた高Si含有高張力鋼板の製造方法。 [3] In the above [1] or [2], the brush grinding is performed using a brush containing abrasive grains of # 120 or less, and high Si content and high tension excellent in chemical conversion processability A method of manufacturing a steel sheet.
以上に示したように、本発明を用いることにより、質量％で0.5％以上のSiを含有する高張力鋼板の場合も、ブラシロール、塩酸原単位を低減した上で、Si酸化物を効果的に除去でき、優れた化成処理性を得ることができる。これにより、安価で強度と加工性を両立する自動車用鋼板を製造でき、成形加工後の塗装も良好に行うことができる。 As described above, by using the present invention, even in the case of a high-tensile steel sheet containing 0.5% or more by mass of Si, the brush roll and hydrochloric acid basic unit are reduced, and the Si oxide is effectively used. And excellent chemical conversion processability can be obtained. This makes it possible to produce an automotive steel sheet that is inexpensive and has both strength and workability, and can be well coated after forming.
以下、本発明について詳細に説明する。
まず、本発明の知見に至った、化成処理性に及ぼすブラシ研削条件、塩酸酸洗条件の影響を評価した実験について述べる。実験には、表１に示す化学成分の質量％で1.5％のSiを含有する鋼板を、圧下率75％で冷間圧延した後、露点−40〜−42℃、H2ガス5％の雰囲気中、800℃の条件で30sec.焼鈍した、1.6mm厚の鋼板を用いた。そして、このようにして得られた鋼板に、表２に示す種々の条件でブラシ研削および塩酸酸洗を施した。
Hereinafter, the present invention will be described in detail.
First, an experiment for evaluating the influence of brush grinding conditions and hydrochloric acid pickling conditions on chemical conversion treatment properties, which led to the knowledge of the present invention, will be described. In the experiment, a steel sheet containing 1.5% Si by mass% of the chemical components shown in Table 1 was cold-rolled at a reduction rate of 75%, and then an atmosphere with a dew point of −40 to −42 ° C. and H 2 gas of 5%. A 1.6 mm thick steel plate annealed for 30 sec at 800 ° C. was used. Then, the steel plate thus obtained was subjected to brush grinding and hydrochloric acid pickling under various conditions shown in Table 2.
ブラシ研削は、特許文献２に開示されているような、砥粒を含有する、直径400mmのブラシロールを用いて行った。ブラシロールを1000rpmで鋼板通板方向と逆方向に回転させ、圧下量3mm、鋼板通板速度100mpmの条件でブラシ研削を行った。この際、ブラシロールの砥粒の大きさや研削パス回数を種々変更した。ブラシ研削に続く酸洗は、濃度0.1％〜10.0％の種々の濃度の塩酸を用いて、50℃で10秒間の酸洗を行った。ブラシ研削、塩酸酸洗の前後に、鋼板の重量測定を行い、その重量差から、ブラシ研削量、酸洗溶解量を求めた。また、ブラシ研削および塩酸酸洗を施した後の鋼板について、Si酸化物の除去を同定するためにグロー放電発光分光分析装置（GDS）による分析を行い、得られた発光強度値に基づき鋼板表面から深さ方向0.1μmまでのSiとFeの積分強度比（Si/Fe）を求めた。Si/Feが高いほど、鋼板表層にSi酸化物が残存していることになる。 The brush grinding was performed using a brush roll having a diameter of 400 mm containing abrasive grains as disclosed in Patent Document 2. The brush roll was rotated at 1000 rpm in the direction opposite to the steel plate passing direction, and brush grinding was performed under the conditions of a reduction of 3 mm and a steel plate passing speed of 100 mpm. At this time, the size of the abrasive grains of the brush roll and the number of grinding passes were variously changed. The pickling following brush grinding was performed at 50 ° C. for 10 seconds using hydrochloric acid having various concentrations of 0.1% to 10.0%. Before and after brush grinding and hydrochloric acid pickling, the steel sheet was weighed, and the brush grinding amount and the pickling dissolution amount were determined from the weight difference. In addition, the steel plate after brush grinding and hydrochloric acid pickling was analyzed by a glow discharge optical emission spectrometer (GDS) to identify the removal of Si oxide, and the surface of the steel plate was determined based on the obtained emission intensity value. The integrated intensity ratio (Si / Fe) of Si and Fe from 0.1 to 0.1 μm in depth was obtained. The higher the Si / Fe, the more Si oxide remains on the steel sheet surface layer.
更に、鋼板の化成処理性を評価するため、以下の化成処理評価を行った。ブラシ研削および塩酸酸洗を施した後の鋼板表面を、日本パーカライジング社製の脱脂液ファインクリーナ(登録商標)で脱脂した後、水洗し、次いで日本パーカライジング社製の表面調整液プレパレンZ(登録商標)で30秒表面調整を行い、35℃の日本パーカライジング社製の化成処理液(パルボンドL3080;登録商標)に120秒浸漬した後、水洗し、温風で乾燥させた。得られた化成処理後鋼板の表面を走査型電子顕微鏡（SEM）（倍率：1000倍）にて120μm×80μmの視野を4視野観察し、化成結晶が生成していない面積率(スケ面積率)および化成結晶サイズを求めた。スケ面積率１％未満を○、スケ面積率１％以上５％未満を△、スケ面積率５％以上を×とし、スケ面積率１％未満かつ化成結晶サイズ3μm以下を良好な化成処理性の基準とした。
以上の評価結果を表２に示す。
Furthermore, in order to evaluate the chemical conversion property of a steel plate, the following chemical conversion treatment evaluation was performed. The steel plate surface after brush grinding and hydrochloric acid pickling was degreased with a degreasing fine cleaner (registered trademark) manufactured by Nihon Parkerizing Co., Ltd. ) For 30 seconds, immersed in a chemical conversion treatment liquid (Palbond L3080; registered trademark) manufactured by Nippon Parkerizing Co., Ltd. at 35 ° C. for 120 seconds, washed with water, and dried with warm air. The surface of the resulting steel sheet after chemical conversion treatment is observed with a scanning electron microscope (SEM) (magnification: 1000 times) in four fields of 120 μm x 80 μm, and the area ratio where no conversion crystals are formed (skelet area ratio) And the chemical crystal size was determined. The scale area ratio is less than 1%, the scale area ratio is 1% or more and less than 5%, and the scale area ratio is 5% or more. The scale area ratio is less than 1% and the chemical conversion crystal size is 3μm or less. Standard.
The above evaluation results are shown in Table 2.
表２に示すとおり、ブラシ研削量を0.5g/m2以上として、濃度1.0％超の塩酸で酸洗処理することにより、前記Si/Feを低減することができた。また、これらの条件では、スケなく化成結晶が形成された。一方、結晶サイズに関しては、塩酸濃度の影響が大きく、3μm以下の微細な化成結晶が得られたのは、ブラシ研削量が0.5g/m2以上1.0 g/m2未満であり、かつ、塩酸濃度が1.0％超3.0％未満の場合に限られる。 As shown in Table 2, the Si / Fe could be reduced by pickling with a hydrochloric acid having a concentration exceeding 1.0% with a brush grinding amount of 0.5 g / m 2 or more. Also, under these conditions, chemical conversion crystals were formed without scaling. On the other hand, regarding the crystal size, the influence of hydrochloric acid concentration is large. Fine chemical crystals of 3 μm or less were obtained because the brush grinding amount was 0.5 g / m 2 or more and less than 1.0 g / m 2 and hydrochloric acid Only when the concentration is more than 1.0% and less than 3.0%.
また、図１〜図３にブラシ研削および塩酸酸洗を施し化成処理した後のSEM観察結果を示す。図１は「ブラシ研削量：0.5g/m2、塩酸濃度：1.6％」、図２は「ブラシ研削量：0.9g/m2、塩酸濃度：10.0％」、図３は「ブラシ研削量：2.4g/m2、塩酸濃度：10.0％」とした場合のSEM観察結果である。なお、図４はブラシ研削および酸洗を施さない場合のSEM観察結果である。図２と図３の比較から、ブラシ研削量が多い方がスケ面積率は少なくなるものの、化成結晶は粗粒となる傾向が確認される。しかしながら、図１と図２の比較から明らかであるように、塩酸濃度を3.0g/m2未満に低減した場合には、研削量を1.0 g/m2未満と極めて少なくすることにより、スケ面積率が少ないうえに化成結晶サイズも3μmと極めて小さくなる。 Moreover, the SEM observation result after performing brush grinding and hydrochloric acid pickling and chemical conversion treatment is shown in FIGS. Fig. 1 shows "Brush grinding amount: 0.5 g / m 2 , hydrochloric acid concentration: 1.6%", Fig. 2 shows "Brush grinding amount: 0.9 g / m 2 , hydrochloric acid concentration: 10.0%", and Fig. 3 shows "Brush grinding amount: SEM observation results when 2.4 g / m 2 , hydrochloric acid concentration: 10.0% ”. FIG. 4 shows SEM observation results when brush grinding and pickling are not performed. From the comparison between FIG. 2 and FIG. 3, it is confirmed that the larger the amount of brush grinding, the smaller the scale area ratio, but the tendency for the chemical conversion crystals to become coarse grains. However, as is clear from the comparison between FIG. 1 and FIG. 2, when the hydrochloric acid concentration is reduced to less than 3.0 g / m 2 , the grinding area can be reduced to an extremely low level of less than 1.0 g / m 2, thereby reducing the scale area. In addition to the low rate, the chemical conversion crystal size is as small as 3 μm.
以上の結果から、本発明者らは、ブラシ研削量を0.5g/m2以上1.0 g/m2未満とし、続いて行う塩酸酸洗で用いる塩酸濃度を1.0％超3.0％未満とすることが、高Si含有高張力鋼板の化成処理性を改善するうえで極めて有効であることを知見した。なお、このようにブラシ研削量と塩酸濃度をともに低減化することによりスケ面積率・化成結晶サイズについて良好な結果が得られる理由については定かではないが、次のように推測される。 From the above results, the present inventors may set the brush grinding amount to 0.5 g / m 2 or more and less than 1.0 g / m 2, and the hydrochloric acid concentration used in the subsequent hydrochloric acid pickling to more than 1.0% and less than 3.0%. It was found that it is extremely effective in improving the chemical conversion of high-strength steel sheets with high Si content. In addition, it is not certain why the brush ground amount and the hydrochloric acid concentration are reduced in this way, but good results are obtained with respect to the skelet area ratio and the chemical conversion crystal size, but it is presumed as follows.
ブラシ研削量が増加すると、ブラシ研削時の加工発熱が大きくなり、この加工発熱に起因して鋼板表面に酸化物が生成してしまう。そしてこの酸化物が、後工程の化成処理時に均一微細な化成結晶の形成を阻害する。また、塩酸濃度が過剰に高くなると、酸液の酸化力が強くなるため、鋼板表面の活性度が低くなり、均一微細な化成結晶が生成し難くなる。一方、ブラシ研削量・塩酸濃度をともに所定量に低減すれば、ブラシ研削時の加工発熱および酸液の酸化力が適度に低減され、化成処理時に均一微細な化成結晶が形成されるものと推測される。 When the amount of brush grinding increases, processing heat generation during brush grinding increases, and oxides are generated on the surface of the steel sheet due to the processing heat generation. This oxide inhibits the formation of uniform and fine chemical crystals during the chemical conversion treatment in the subsequent step. Further, when the hydrochloric acid concentration is excessively high, the oxidizing power of the acid solution becomes strong, so that the activity on the surface of the steel sheet is lowered and it becomes difficult to form uniform fine chemical crystals. On the other hand, if both the brush grinding amount and hydrochloric acid concentration are reduced to the prescribed amount, the heat generated during brush grinding and the oxidizing power of the acid solution are moderately reduced, and it is assumed that uniform and fine chemical crystals are formed during the chemical conversion treatment. Is done.
次に、本発明が対象とする鋼板について説明する。
本発明では質量％でSiを0.5％以上含有する鋼板を対象とする。これは、上述したように、Siが安価であり、強度と加工性を両立する上で重要な元素であるからである。質量％でSiが0.5％未満であれば、通常の焼鈍ままの場合も、良好な化成処理性が得られるため、本発明を適用する必要はない。なお、Si含有量は、溶接性、割れ性などの観点から、質量％で1.8％を上限とすることが好ましい。C、Mnなどの元素は、要求される強度、加工性に応じ、必要量を添加すれば良く、また、Ti、Nb、Moなどを添加することも本発明を妨げるものではない。
Next, the steel plate targeted by the present invention will be described.
In the present invention, steel sheets containing 0.5% or more of Si by mass% are targeted. This is because, as described above, Si is an inexpensive element and is an important element in achieving both strength and workability. If Si is less than 0.5% by mass%, it is not necessary to apply the present invention because good chemical conversion treatment properties can be obtained even with normal annealing. The Si content is preferably 1.8% by mass in terms of weldability and crackability. The elements such as C and Mn may be added in a required amount according to the required strength and workability, and addition of Ti, Nb, Mo and the like does not hinder the present invention.
以下に、本発明鋼板の成分組成の限定理由について説明する。なお、以下の成分組成を表す％は、特に断らない限り質量％を意味するものとする。
C :0.03％以上0.20％以下
C は、鋼の強度を増加させる元素であり、所望の高強度を確保するために、0.03％以上含有することが望ましい。一方、0.20％を超える含有は、鋼板の溶接性を著しく劣化させる。このため、0.03％以上0.20％以下の含有が好ましい。より好ましくは0.04％以上0.08％以下である。
Below, the reason for limitation of the component composition of this invention steel plate is demonstrated. In addition,% showing the following component composition shall mean the mass% unless there is particular notice.
C: 0.03% to 0.20%
C 2 is an element that increases the strength of steel, and is desirably contained in an amount of 0.03% or more in order to ensure a desired high strength. On the other hand, a content exceeding 0.20% significantly deteriorates the weldability of the steel sheet. Therefore, the content is preferably 0.03% or more and 0.20% or less. More preferably, it is 0.04% or more and 0.08% or less.
Si:0.5％以上1.8％以下
Siは、Cと同様に鋼の強度を向上させる元素であるとともに、安価であり、加工性の向上にも有効な元素であるため、0.5％以上含有することが望ましい。一方、1.8％を超える含有は、鋼板の低温脆性を著しく劣化させる。このため、0.5％以上1.8％以下の含有が好ましい。より好ましくは0.9％以上1.5％以下である。
Si: 0.5% to 1.8%
Si, like C, is an element that improves the strength of steel, and is an inexpensive element that is also effective for improving workability, so it is desirable to contain 0.5% or more. On the other hand, a content exceeding 1.8% significantly deteriorates the low temperature brittleness of the steel sheet. For this reason, the content of 0.5% or more and 1.8% or less is preferable. More preferably, it is 0.9% or more and 1.5% or less.
Mn:1.5％以上3.5％以下
Mnも、CおよびSiと同様に、鋼の強度を向上させる元素であるとともに安価であるため、1.5％以上含有することが望ましい。一方、3.5％を超える含有は、鋼板の溶接性を著しく劣化させる。このため、1.5％以上3.5％以下の含有が好ましい。より好ましくは1.5％以上2.5％以下である。
Mn: 1.5% to 3.5%
Mn, like C and Si, is an element that improves the strength of steel and is inexpensive, so it is desirable to contain Mn in an amount of 1.5% or more. On the other hand, a content exceeding 3.5% significantly deteriorates the weldability of the steel sheet. For this reason, content of 1.5% or more and 3.5% or less is preferable. More preferably, it is 1.5% or more and 2.5% or less.
P :0.01％以上0.04％以下
S :0.001％以上0.01％以下
P、Sは、いずれも低温靭性に悪影響を及ぼす元素である。このため、これらの元素はできるだけ低減することが好ましいが、過度の低減は、製造コストの増大を招く。以上の理由により、P、S各々の含有量は、製造コストが増大しない程度の範囲、すなわち、Pは0.01％以上0.04％以下、Sは0.001％以上0.01％以下の含有が好ましい。
P: 0.01% or more and 0.04% or less
S: 0.001% to 0.01%
P and S are both elements that adversely affect low temperature toughness. For this reason, it is preferable to reduce these elements as much as possible, but excessive reduction leads to an increase in manufacturing cost. For these reasons, it is preferable that the contents of P and S are such that the manufacturing cost does not increase, that is, P is 0.01% or more and 0.04% or less, and S is 0.001% or more and 0.01% or less.
以上が、本発明の鋼板の基本成分であるが、強度の更なる向上を目的として、上記に加えて以下の元素を選択して含有することができる。
Nb:0.001％以上0.15％以下、Ti:0.001％以上0.15％以下
Nb、Tiは、いずれも析出強化により鋼の強度向上に寄与する元素であり、必要に応じ選択して含有することができる。いずれの元素も、析出強化を得るためには0.001％以上の含有が望ましいが、0.15％を超えて含有しても、含有量に見合う効果が得られない。このため、Nb、Tiともに、0.001％以上0.15％以下の含有が好ましい。より好ましくは、Nb:0.01％以上0.03％以下、Ti:0.01％以上0.03％以下である。
The above are the basic components of the steel sheet of the present invention. For the purpose of further improving the strength, the following elements can be selected and contained in addition to the above.
Nb: 0.001% to 0.15%, Ti: 0.001% to 0.15%
Nb and Ti are elements that contribute to improving the strength of the steel by precipitation strengthening, and can be selected and contained as necessary. In order to obtain precipitation strengthening, any element is preferably contained in an amount of 0.001% or more, but even if it exceeds 0.15%, an effect commensurate with the content cannot be obtained. For this reason, the content of Nb and Ti is preferably 0.001% or more and 0.15% or less. More preferably, Nb: 0.01% or more and 0.03% or less, Ti: 0.01% or more and 0.03% or less.
A1：0.02％以上0.04％以下
Alは、脱酸剤として作用するとともに、A1Nを形成することで高温における結晶粒の粗大化を抑制する元素であり、必要に応じて含有することができる。上記の効果を得るためには、0.02％以上含有することが好ましい。一方、0.04％を超える含有は、鋼の清浄度を低下させるおそれがある。このため、0.02％以上0.04％以下の含有が好ましい。
A1: 0.02% to 0.04%
Al is an element that acts as a deoxidizer and suppresses the coarsening of crystal grains at a high temperature by forming A1N, and can be contained as necessary. In order to acquire said effect, it is preferable to contain 0.02% or more. On the other hand, if it exceeds 0.04%, the cleanliness of the steel may be reduced. Therefore, the content is preferably 0.02% or more and 0.04% or less.
N ：0.001％以上0.005％以下
Nは、固溶強化による強度確保に有効であり、0.001％以上の含有が好ましい。一方、0.005％を超える含有は、溶接性の低下を招く。このため、0.001％以上0.005％以下の含有が好ましい。
N: 0.001% or more and 0.005% or less
N is effective for securing strength by solid solution strengthening, and is preferably contained in an amount of 0.001% or more. On the other hand, a content exceeding 0.005% causes a decrease in weldability. Therefore, the content is preferably 0.001% or more and 0.005% or less.
Cu：0.001％以上0.03％以下、Ni：0.001％以上0.03％以下、Cr：0.001％以上0.2％以下、V ：0.001％以上0.2％以下、Mo：0.001％以上0.20％以下
Cu、Ni、Cr、V、Moは、固溶強化を介して鋼の強度上昇に寄与する元素であり、必要に応じて選択して含有することができる。上記の効果を得るためには、各元素とも0.00l％以上の含有が望ましい。一方、Cuであれば0.03％、Niであれば0.03％、Crであれば0.2％、Vであれば0.2％、Moであれば0.20％をそれぞれ超えて含有しても、強度上昇効果が飽和し、含有量に見合う効果が期待できなくなる。このため、Cu：0.001％以上0.03％以下、Ni：0.001％以上0.03％以下、Cr：0.001％以上0.2％以下、V：0.001％以上0.2％以下、Mo：0.001％以上0.20％以下含有することが好ましい。より好ましくは、Cu：0.01％以上0.02％以下、Ni：0.01％以上0.02％以下、Cr：0.01％以上0.1％以下、V ：0.01％以上0.1％以下、Mo：0.01％以上0.1％以下である。
Cu: 0.001% to 0.03%, Ni: 0.001% to 0.03%, Cr: 0.001% to 0.2%, V: 0.001% to 0.2%, Mo: 0.001% to 0.20%
Cu, Ni, Cr, V, and Mo are elements that contribute to an increase in steel strength through solid solution strengthening, and can be selected and contained as necessary. In order to obtain the above effect, each element preferably contains 0.001% or more. On the other hand, even if the content exceeds 0.03% for Cu, 0.03% for Ni, 0.2% for Cr, 0.2% for V, and 0.20% for Mo, the effect of increasing the strength is saturated. However, an effect commensurate with the content cannot be expected. Therefore, Cu: 0.001% to 0.03%, Ni: 0.001% to 0.03%, Cr: 0.001% to 0.2%, V: 0.001% to 0.2%, Mo: 0.001% to 0.20% Is preferred. More preferably, Cu: 0.01% to 0.02%, Ni: 0.01% to 0.02%, Cr: 0.01% to 0.1%, V: 0.01% to 0.1%, Mo: 0.01% to 0.1% .
本発明の鋼板において上記以外の成分は、Feおよび不可避的不純物である。なお、不可避的不純物としては、B などが挙げられる。これらは0.01％以下の含有が許容されるが、好ましくは0.005％以下である。 Components other than the above in the steel sheet of the present invention are Fe and inevitable impurities. Inevitable impurities include B and the like. These are allowed to contain 0.01% or less, but preferably 0.005% or less.
本発明は、上記組成を有する鋼板に、冷間圧延および連続焼鈍を施して高張力鋼板を製造するに際し、前記連続焼鈍後の鋼板の表面に研削量0.5g/m2以上1.0 g/m2未満のブラシ研削を施し、次いで濃度が1.0％超3.0％未満の塩酸を用いた塩酸酸洗を施すことにより、前記連続焼鈍後の鋼板の表面に濃化したSi酸化物を除去する。 The present invention provides a steel sheet having the above composition by cold rolling and continuous annealing to produce a high-strength steel sheet, and the surface of the steel sheet after the continuous annealing has a grinding amount of 0.5 g / m 2 or more and 1.0 g / m 2. The concentrated Si oxide is removed from the surface of the steel plate after the continuous annealing by performing brush grinding of less than 1.0% and then performing hydrochloric acid pickling using hydrochloric acid having a concentration of more than 1.0% and less than 3.0%.
本発明において、冷間圧延を施す前の鋼板を製造する方法については特に限定されず、従前公知の方法により製造することができる。また、冷間圧延条件についても特に限定されない。
なお、本発明が対象とする高Si含有高張力鋼板（Siを0.5％以上含有する鋼板）を製造するに際しては通常の条件により熱延板とし、必要に応じて酸洗したのち、圧下率40〜70％程度の冷間圧延が施される。
冷間圧延後の鋼板の板厚は1.0〜2.0mm程度である。
In this invention, it does not specifically limit about the method of manufacturing the steel plate before performing cold rolling, It can manufacture by a conventionally well-known method. Further, the cold rolling conditions are not particularly limited.
In addition, when manufacturing a high Si content high strength steel sheet (a steel sheet containing 0.5% or more of Si) which is a subject of the present invention, a hot rolled sheet is used under normal conditions, and after pickling as necessary, a reduction rate of 40 About 70% cold rolling is applied.
The thickness of the steel sheet after cold rolling is about 1.0 to 2.0 mm.
本発明が対象とする高Si含有高張力鋼板（Siを0.5％以上含有する鋼板）の場合、冷間圧延後の鋼板を、露点−30〜−45℃、H2ガス5〜10％程度の還元雰囲気中、750〜900℃の温度域で10〜60sec.程度保持して焼鈍されるのが一般的である。また、これらの焼鈍条件は、焼鈍ラインの設備能力、生産性、鋼板の成分や要求される強度・伸びなどによって、適宜、決定される。そして、このような条件下で焼鈍が施されることにより、高Si含有高張力鋼板の表面には極めて強固に密着したSi酸化物が形成される。 In the case of the high Si content high strength steel sheet (the steel sheet containing 0.5% or more of Si) targeted by the present invention, the steel sheet after the cold rolling has a dew point of −30 to −45 ° C. and H 2 gas of about 5 to 10%. In a reducing atmosphere, it is generally annealed while being held at a temperature range of 750 to 900 ° C. for about 10 to 60 seconds. Further, these annealing conditions are appropriately determined depending on the equipment capacity of the annealing line, productivity, steel plate components, required strength and elongation, and the like. And annealing is performed under such conditions, thereby forming a Si oxide that adheres very firmly to the surface of the high-Si containing high-tensile steel plate.
なお、露点を−50℃以下に低下させること、或いは焼鈍温度を700℃以下に低下させることができれば、高Si含有高張力鋼板であってもその表面にSi酸化物が生成されず、優れた化成処理性が得られることが知られている。しかしながら、設備能力・生産性の問題や、材質確保の観点からこのような焼鈍条件を適用することは現状では困難である。そのため、本発明では、連続焼鈍後の鋼板にブラシ研削および塩酸酸洗を施すことにより、連続焼鈍時、高Si含有高張力鋼板の表面に生じたSi酸化物を除去することとする。 If the dew point can be lowered to -50 ° C or lower, or the annealing temperature can be lowered to 700 ° C or lower, even if it is a high-strength steel sheet with high Si content, Si oxide is not generated on the surface, which is excellent. It is known that chemical conversion properties can be obtained. However, it is difficult to apply such annealing conditions from the viewpoints of facility capacity and productivity and securing the material. Therefore, in the present invention, by performing brush grinding and hydrochloric acid pickling on the steel plate after continuous annealing, Si oxide generated on the surface of the high-Si containing high-tensile steel plate is removed during continuous annealing.
ブラシ研削の研削量：0.5g/m2以上1.0 g/m2未満
連続焼鈍時、鋼板の表面に生じたSi酸化物は、塩酸には溶解しないため、塩酸酸洗のみではSi酸化物を除去することが困難である。したがって、本発明ではブラシ研削を必須とする。ブラシ研削の効果は、機械的にSi酸化物を除去することに加えて、表面酸化物に研削目により亀裂を導入して酸の浸透を促進することにある。亀裂導入により酸がSi酸化物−母相（鋼板素地）界面に浸透すると、後述する塩酸酸洗において母相（鋼板素地）が溶解する。そして、母相（鋼板素地）の溶解に伴いSi酸化物が除去される。
Grinding amount of brush grinding: 0.5g / m 2 or more and less than 1.0 g / m 2 During continuous annealing, Si oxide generated on the surface of the steel sheet does not dissolve in hydrochloric acid, so Si oxide can be removed only by hydrochloric acid pickling. Difficult to do. Therefore, brush grinding is essential in the present invention. The effect of brush grinding is not only to mechanically remove Si oxide, but also to promote cracking of the acid by introducing cracks in the surface oxide through the grinding lines. When the acid penetrates into the Si oxide-matrix (steel base) interface by introducing cracks, the mother phase (steel base) is dissolved in hydrochloric acid pickling described later. And Si oxide is removed with melt | dissolution of a mother phase (steel plate base).
ブラシ研削量が0.5g/m2未満の場合、亀裂導入効果が小さくなる結果、酸浸透を促進することができず、Si酸化物−母相（鋼板素地）界面に酸液を十分に浸透させることができない。一方、ブラシ研削量が1.Og/m2以上になると、研削時の加工発熱が大きくなるため、鋼板表面に酸化物が生成してしまい、これが均一微細な化成結晶の形成を阻害する場合がある。またブラシ研削で1.Og/m2以上研削するためには、ブラシ研削コストが多大になるため好ましくない。以上の理由により、ブラシ研削量を0.5g/m2以上1.0 g/m2未満に規定した。 When the brush grinding amount is less than 0.5 g / m 2 , the effect of introducing cracks is reduced. As a result, the acid penetration cannot be promoted, and the acid solution is sufficiently penetrated into the Si oxide-matrix (steel base) interface. I can't. On the other hand, if the amount of brush grinding is 1.Og / m 2 or more, the heat generated during processing increases, and oxides are generated on the surface of the steel sheet, which may hinder the formation of uniform fine chemical crystals. is there. Further, it is not preferable to perform grinding at 1.Og / m 2 or more by brush grinding because the brush grinding cost becomes high. For the above reasons, the brush grinding amount was set to 0.5 g / m 2 or more and less than 1.0 g / m 2 .
以上のように、本発明では焼鈍後の鋼板にブラシ研削を施し、鋼板表面から機械的にSi酸化物を除去するが、鋼板表面には通常、深さ2μm以上の凹凸があり、鋼板の凹み部の底に存在するSi酸化物をブラシ研削で安定して研削除去することは事実上困難である。このため、本発明ではブラシ研削後の塩酸酸洗による化学的な溶解を必須とする。 As described above, in the present invention, the annealed steel sheet is subjected to brush grinding, and the Si oxide is mechanically removed from the steel sheet surface.However, the steel sheet surface usually has irregularities with a depth of 2 μm or more, and the steel sheet has dents. It is practically difficult to stably remove the Si oxide present at the bottom of the part by brush grinding. For this reason, in the present invention, chemical dissolution by hydrochloric acid pickling after brush grinding is essential.
塩酸酸洗に用いる塩酸濃度：1.0％超3.0％未満
本発明においては、ブラシ研削を施すことにより、鋼板表面に亀裂が導入されている。このような亀裂が導入された鋼板表面に対して酸洗を施すと、酸液がSi酸化物−母相（鋼板素地）界面に浸透して母相（鋼板素地）を溶解する。そして母相（鋼板素地）の溶解に付随してSi酸化膜が除去されるのである。
Hydrochloric acid concentration used for hydrochloric acid pickling: more than 1.0% and less than 3.0% In the present invention, cracks are introduced into the steel sheet surface by brush grinding. When pickling is performed on the surface of the steel sheet in which such cracks are introduced, the acid solution penetrates into the Si oxide-matrix (steel base) interface and dissolves the matrix (steel base). The Si oxide film is removed along with the dissolution of the matrix (steel plate substrate).
酸洗時の塩酸濃度が1.0％以下である場合、母相（鋼板素地）の溶解によるSi酸化物の除去効果が不十分となる。一方、酸洗時の塩酸濃度が3.0％以上であると、酸液の酸化力が強くなり、鋼板表面の活性度が低くなることが推測され、均一微細な化成結晶が生成し難くなる。なお、塩酸濃度が3.0％以上で化成処理性が劣化する原因は必ずしも定かではないが、前述の実験結果に示すように塩酸濃度の影響は明瞭である。 When the hydrochloric acid concentration at the time of pickling is 1.0% or less, the effect of removing the Si oxide due to the dissolution of the matrix (steel plate body) becomes insufficient. On the other hand, when the hydrochloric acid concentration during pickling is 3.0% or more, it is presumed that the oxidizing power of the acid solution becomes strong and the activity on the surface of the steel sheet is lowered, and it becomes difficult to form uniform fine chemical crystals. The reason why the chemical conversion treatment performance deteriorates when the hydrochloric acid concentration is 3.0% or more is not necessarily clear, but the influence of the hydrochloric acid concentration is clear as shown in the above experimental results.
また、上記のブラシ研削は、JIS R6001(1998)に規定された粒度で＃120以下の砥粒を含有するブラシを用いて研削することが、研削量を確保する観点から好ましい。 In addition, the above-mentioned brush grinding is preferably performed from the viewpoint of securing a grinding amount by using a brush containing abrasive grains of # 120 or less with a grain size defined in JIS R6001 (1998).
従来、Si酸化物を除去するためには、ブラシ研削量、塩酸溶解量ともに大きい方が好ましいと考えられてきた。しかしながら、本発明者らは、ブラシ研削量を多くすることによりスケ面積率の低減効果が得られるものの、化成結晶は粗粒となり化成処理性に悪影響を及ぼすことを知見した。そして、塩酸酸洗に用いる塩酸の濃度を低減することが化成処理性改善に有効であること、及び、塩酸の濃度を3.0％未満に低減した場合、ブラシによる研削量は1.Og/m2未満、更には0.5g/m2程度でも十分であることを知見した。また、本発明は、優れた化成処理性を得ることだけでなく、ブラシ研削に必要なパス数を大幅に削減でき、ブラシロールや塩酸の原単位削減にも有効である。 Conventionally, in order to remove Si oxide, it has been considered that a larger amount of brush grinding and hydrochloric acid dissolution is preferable. However, the present inventors have found that although the effect of reducing the scale area ratio can be obtained by increasing the amount of brush grinding, the chemical conversion crystals become coarse grains and adversely affect the chemical conversion processability. And reducing the concentration of hydrochloric acid used for hydrochloric acid pickling is effective in improving chemical conversion treatment, and when the concentration of hydrochloric acid is reduced to less than 3.0%, the grinding amount with a brush is 1.Og / m 2 It was found that even less than about 0.5 g / m 2 is sufficient. The present invention not only provides excellent chemical conversion properties, but can greatly reduce the number of passes required for brush grinding, and is effective in reducing the basic unit of brush rolls and hydrochloric acid.
表３に示す、種々の組成の冷延鋼板を、連続焼鈍ラインにて露点−37〜−39℃、H2ガス5〜6％の雰囲気中、800〜870℃の温度で20〜35sec.保持する焼鈍処理を施し、室温まで冷却した。引き続き、ブラシ研削と塩酸酸洗を施してSi酸化物の除去処理を行った。ブラシ研削は、＃100砥粒を含有する直径450mmのブラシロールを具えた特許文献２に記載の如きブラシ研削設備を使用し、2〜4パスの研削とした。また、ブラシ研削は、ブラシロールを1200rpmの回転速度で鋼板通板方向と逆方向に回転させ、圧下量を2〜3mmの範囲で制御し、鋼板通板速度を80〜100mpmとする条件で行った。塩酸酸洗は、温度45℃で10sec.間の酸洗処理とした。ここで、従来例としては、４パスのブラシ研削(研削量：2.3〜2.7g/m2)を行い、4％の塩酸で酸洗を行った。また、本発明例としては、２パスのブラシ研削(研削量は0.7〜0.9g/m2)を行い、１％の塩酸で酸洗を行った。また、比較例を、4％での塩酸酸洗のみの条件とした。 Cold-rolled steel sheets with various compositions shown in Table 3 are held for 20 to 35 seconds at a temperature of 800 to 870 ° C. in an atmosphere with a dew point of −37 to −39 ° C. and H 2 gas of 5 to 6% in a continuous annealing line. An annealing treatment was performed and cooled to room temperature. Subsequently, brush grinding and hydrochloric acid pickling were performed to remove Si oxide. The brush grinding was performed in 2 to 4 passes using a brush grinding facility as described in Patent Document 2 including a brush roll having a diameter of 450 mm containing # 100 abrasive grains. Brush grinding is performed under the condition that the brush roll is rotated in the direction opposite to the sheet passing direction at a rotation speed of 1200 rpm, the reduction amount is controlled in the range of 2 to 3 mm, and the sheet passing speed is 80 to 100 mpm. It was. The hydrochloric acid pickling was performed at a temperature of 45 ° C. for 10 seconds. Here, as a conventional example, 4-pass brush grinding (grinding amount: 2.3 to 2.7 g / m 2 ) was performed, and pickling was performed with 4% hydrochloric acid. In addition, as an example of the present invention, two-pass brush grinding (grinding amount was 0.7 to 0.9 g / m 2 ) was performed, and pickling was performed with 1% hydrochloric acid. Moreover, the comparative example was made into the conditions of only 4% hydrochloric acid pickling.
得られた鋼板に対し、前述と同様の条件で、化成処理を施し、化成処理性を評価した。評価結果を表４に示す。比較例、従来例に比べ、本発明例により製造した冷延鋼板の化成処理性が優れていることが確認された。 The obtained steel sheet was subjected to chemical conversion treatment under the same conditions as described above, and the chemical conversion treatment property was evaluated. The evaluation results are shown in Table 4. Compared with the comparative example and the conventional example, it was confirmed that the chemical conversion property of the cold-rolled steel sheet produced by the example of the present invention was excellent.
Claims (3)
Ｃ：0.03％以上0.20％以下、 Si：0.5％以上1.8％以下、
Mn：1.5％以上3.5％以下、 Ｐ：0.01％以上0.04％以下、
Ｓ：0.001％以上0.01％以下
を含有し、残部Feおよび不可避的不純物からなる組成を有する鋼板に、冷間圧延および連続焼鈍を施して高張力鋼板を製造するに際し、前記連続焼鈍後の鋼板の表面に研削量0.5g/m2以上1.0 g/m2未満のブラシ研削を施し、次いで濃度が1.0％超3.0％未満の塩酸を用いた塩酸酸洗を施すことを特徴とする、化成処理性に優れた高Si含有高張力鋼板の製造方法。 % By mass
C: 0.03% to 0.20%, Si: 0.5% to 1.8%,
Mn: 1.5% to 3.5%, P: 0.01% to 0.04%,
S: A steel sheet containing 0.001% or more and 0.01% or less and having the balance Fe and inevitable impurities is subjected to cold rolling and continuous annealing to produce a high-strength steel sheet. Chemical conversion processability, characterized in that the surface is subjected to brush grinding with a grinding amount of 0.5 g / m 2 or more and less than 1.0 g / m 2 , followed by hydrochloric acid pickling using hydrochloric acid with a concentration of more than 1.0% and less than 3.0% For producing high-strength steel sheets with high Si content that excel in resistance.
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