JP4325442B2 - Method for producing hot dip galvanized steel - Google Patents
Method for producing hot dip galvanized steel Download PDFInfo
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- JP4325442B2 JP4325442B2 JP2004070749A JP2004070749A JP4325442B2 JP 4325442 B2 JP4325442 B2 JP 4325442B2 JP 2004070749 A JP2004070749 A JP 2004070749A JP 2004070749 A JP2004070749 A JP 2004070749A JP 4325442 B2 JP4325442 B2 JP 4325442B2
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- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 28
- 239000008397 galvanized steel Substances 0.000 title claims description 28
- 238000004519 manufacturing process Methods 0.000 title claims description 25
- 229910000831 Steel Inorganic materials 0.000 claims description 91
- 239000010959 steel Substances 0.000 claims description 91
- 238000007747 plating Methods 0.000 claims description 53
- 239000000463 material Substances 0.000 claims description 51
- 238000010438 heat treatment Methods 0.000 claims description 46
- 238000005275 alloying Methods 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 24
- 239000007788 liquid Substances 0.000 claims description 21
- 238000010791 quenching Methods 0.000 claims description 18
- 230000000171 quenching effect Effects 0.000 claims description 17
- 238000000465 moulding Methods 0.000 claims description 15
- 238000007598 dipping method Methods 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- 150000003377 silicon compounds Chemical class 0.000 claims description 6
- 239000011701 zinc Substances 0.000 description 21
- 230000000694 effects Effects 0.000 description 16
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 15
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 14
- 239000002585 base Substances 0.000 description 14
- 229910052725 zinc Inorganic materials 0.000 description 14
- 238000004140 cleaning Methods 0.000 description 12
- 238000005246 galvanizing Methods 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 239000007864 aqueous solution Substances 0.000 description 9
- 229910000765 intermetallic Inorganic materials 0.000 description 9
- 230000000087 stabilizing effect Effects 0.000 description 9
- POWFTOSLLWLEBN-UHFFFAOYSA-N tetrasodium;silicate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-][Si]([O-])([O-])[O-] POWFTOSLLWLEBN-UHFFFAOYSA-N 0.000 description 9
- 238000005238 degreasing Methods 0.000 description 8
- 238000009792 diffusion process Methods 0.000 description 8
- 230000007547 defect Effects 0.000 description 6
- 238000005096 rolling process Methods 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 5
- 238000007731 hot pressing Methods 0.000 description 5
- 239000012778 molding material Substances 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 229910001297 Zn alloy Inorganic materials 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 229910052761 rare earth metal Inorganic materials 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910052910 alkali metal silicate Inorganic materials 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 230000002708 enhancing effect Effects 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 230000003746 surface roughness Effects 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- 229910000838 Al alloy Inorganic materials 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 2
- 239000004115 Sodium Silicate Substances 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
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- 238000007654 immersion Methods 0.000 description 2
- 210000003205 muscle Anatomy 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 229910052911 sodium silicate Inorganic materials 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910018137 Al-Zn Inorganic materials 0.000 description 1
- 229910018573 Al—Zn Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 101000993059 Homo sapiens Hereditary hemochromatosis protein Proteins 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
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- 230000006698 induction Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052914 metal silicate Inorganic materials 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 229910052913 potassium silicate Inorganic materials 0.000 description 1
- 235000019353 potassium silicate Nutrition 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- -1 silicate compound Chemical class 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 235000019795 sodium metasilicate Nutrition 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- RLQWHDODQVOVKU-UHFFFAOYSA-N tetrapotassium;silicate Chemical compound [K+].[K+].[K+].[K+].[O-][Si]([O-])([O-])[O-] RLQWHDODQVOVKU-UHFFFAOYSA-N 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
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Description
本発明は、溶融亜鉛系めっき鋼材、特に合金化溶融亜鉛めっき鋼材に関する発明である。より具体的には、本発明は、自動車用の足廻り、シャーシ、補強部品などとして使用される熱間プレス成形品の素材として好適な溶融亜鉛めっき鋼材の製造方法に関する。 The present invention relates to a hot dip galvanized steel material, particularly an alloyed hot dip galvanized steel material. More specifically, the present invention relates to a method for producing a hot-dip galvanized steel material suitable as a material for hot press-formed products used as automobile suspensions, chassis, reinforcing parts and the like.
近年、自動車の軽量化のため、鋼材の高強度化を図り、使用する鋼材の厚みを減ずる努力が進んでいる。このため、高強度鋼板等の難成形材料をプレス成形する技術として、成形すべき材料を予め鋼材の再結晶温度以上に加熱して成形する熱間プレス技術が採用されている。さらに、熱間プレス用材料として、母材鋼表面の酸化抑制および／またはプレス成形品の耐食性向上を目的として、亜鉛系またはアルミニウム系めっきで被覆した鋼板を使用することが提案されている。熱間成形に亜鉛系めっき鋼板を用いた従来技術の例としては、特開2001−353548号公報、特開2003−73774 号公報、特開2003−126921号公報、特開2003−147499号公報等が挙げられる。 In recent years, in order to reduce the weight of automobiles, efforts have been made to increase the strength of steel materials and reduce the thickness of steel materials used. For this reason, as a technique for press-forming a difficult-to-form material such as a high-strength steel plate, a hot press technique is adopted in which the material to be formed is preliminarily heated to the recrystallization temperature or higher of the steel material. Furthermore, it has been proposed to use a steel sheet coated with zinc-based or aluminum-based plating as a hot pressing material for the purpose of suppressing oxidation of the base steel surface and / or improving the corrosion resistance of the press-formed product. Examples of conventional techniques using galvanized steel sheets for hot forming include JP 2001-353548 A, JP 2003-73774 A, JP 2003-126921 A, JP 2003-147499 A, etc. Is mentioned.
溶融亜鉛系めっき鋼材、中でも溶融亜鉛めっき後に加熱によるめっき皮膜を合金化する処理が施された合金化溶融亜鉛めっき鋼材（以下、ＧＡ鋼材または単にＧＡと略すことがある）、を熱間プレス成形する場合、成形前に通常は700 ℃以上の高温に加熱されるが、この加熱により、加熱前には見られない筋状の表面欠陥（以下、筋ムラという）が見られることがあった。この欠陥は肉眼で見ても目立つため、成形品の商品価値を著しく損なう。前述した特許文献１〜４にはこの筋ムラについての記載がなく、筋ムラ解消のための有効な対策はこれまで知られていなかった。 Hot-press forming hot-dip galvanized steel, especially alloyed hot-dip galvanized steel (hereinafter sometimes abbreviated as “GA steel” or simply “GA”), which has been subjected to a process of alloying a plating film by heating after hot-dip galvanization. In this case, the material is usually heated to a high temperature of 700 ° C. or higher before molding. However, due to this heating, streak-like surface defects (hereinafter referred to as streak unevenness) that are not seen before heating may be observed. Since this defect is conspicuous even with the naked eye, the commercial value of the molded product is significantly impaired. Patent Documents 1 to 4 described above do not describe this stripe unevenness, and no effective measures for eliminating the stripe unevenness have been known so far.
従って、本発明は、このような筋ムラの発生を著しく抑制ないし防止することができる、熱間プレス成形に適した溶融亜鉛系めっき鋼材を提供することを課題とする。 Therefore, an object of the present invention is to provide a hot dip galvanized steel material suitable for hot press forming, which can remarkably suppress or prevent the occurrence of such stripe unevenness.
熱間プレス前の加熱により上記の筋ムラが発生した部位の溶融亜鉛系めっき鋼材の断面を顕微鏡で観察したところ、ムラ部では他の部位と比較して、加熱中に生成した表面のFe−Zn合金層 (Zn−Fe金属間化合物相＋αFe中にZnが固溶した固溶相) の厚みが厚いことがわかった。筋ムラ発生の原因をさらに調査するため、加熱前の合金化溶融亜鉛めっき鋼板の観察結果と比べたところ、加熱により筋ムラが発生した部位は、程度はごく僅かであるが、他の部位よりめっき皮膜が厚くなっていることがあった。 When the cross section of the hot dip galvanized steel material at the site where the streak unevenness occurred due to heating before hot pressing was observed with a microscope, the surface of the Fe- It was found that the thickness of the Zn alloy layer (Zn—Fe intermetallic compound phase + solid solution phase in which Zn was dissolved in αFe) was thick. Compared with the observation results of the galvannealed steel sheet before heating to further investigate the cause of streak unevenness, the part where streak unevenness was caused by heating was very slight, but it was less than other parts. The plating film was sometimes thick.
前述のような観察結果から、筋ムラの発生機構を以下のように推定した。即ち、めっき皮膜の合金化処理時の加熱および／または熱間プレス成形前の加熱における亜鉛の拡散挙動は、鋼板の全面においてでは均一でない。その不均一さが局部的に顕著になると、筋ムラとして肉眼で見えるようになる。 From the observation results as described above, the generation mechanism of the unevenness of muscle was estimated as follows. That is, the diffusion behavior of zinc in the heating during the alloying treatment of the plating film and / or the heating before hot press forming is not uniform over the entire surface of the steel sheet. When the non-uniformity becomes noticeable locally, it becomes visible to the naked eye as streaks.
このような推定から、亜鉛の拡散挙動の不均一さが生じる原因は、めっきの基材となる鋼板の表面状態にも原因があると考えた。しかし、基材鋼板自体の圧延以前の製造条件から、問題となる表面状態を生み出す要因を特定し、これを解決するのは必ずしも容易でない。そこで、基材鋼板の圧延以降の工程で筋ムラを解決することを検討した結果、溶融めっき前の特定の前処理により解決できることを見出した。 From such an estimation, it was considered that the cause of the non-uniformity of the zinc diffusion behavior was also due to the surface state of the steel sheet used as the base material for plating. However, it is not always easy to identify and solve the factor that produces a problematic surface state from the manufacturing conditions before rolling the base steel sheet itself. Then, as a result of investigating solving the stripe unevenness in the process after rolling the base steel sheet, it was found that the problem can be solved by a specific pretreatment before hot dipping.
本発明は、水溶性の珪素化合物を含む処理液で鋼材表面にＳｉを付着させる工程を実施後、該工程により表面にＳｉが付着した鋼材を還元雰囲気で焼鈍して溶融めっきする溶融めっき工程を行うことを特徴とする、溶融亜鉛系めっき鋼材の製造方法である。 The present invention includes a hot dipping process in which after the step of attaching Si to the surface of a steel material with a treatment liquid containing a water-soluble silicon compound, the steel material with Si attached to the surface by the step is annealed in a reducing atmosphere to perform hot dipping. It is a manufacturing method of the hot dip galvanized steel material characterized by performing .
好適態様においては、溶融めっき工程に引き続き、合金化のための加熱工程を含む。即ち、合金化溶融亜鉛めっき鋼材の製造方法である。また、製造された溶融亜鉛系めっき鋼材は、製造後に700 ℃以上の温度に曝される用途、例えば、熱間プレス成形用途、に使用することが好ましい。従って、本発明によれば、鋼材の熱間プレス成形による成形品の製造方法であって、鋼材が上記方法により製造された溶融亜鉛系めっき鋼材であることを特徴とする、成形品の製造方法も提供される。 In a preferred embodiment, subsequent to the hot dipping process, a heating process for alloying is included. That is, it is a manufacturing method of alloyed hot-dip galvanized steel. Moreover, it is preferable to use the manufactured hot dip galvanized steel material for the use exposed to the temperature of 700 degreeC or more after manufacture, for example, a hot press molding use. Therefore, according to the present invention, there is provided a method for producing a molded product by hot press forming of a steel material, wherein the steel material is a hot dip galvanized steel material produced by the above method. Is also provided.
本発明の方法に従うと、簡単で低コストの前処理によって、溶融亜鉛系めっき鋼材を熱間温度に加熱する際に見られた筋ムラを抑制することができる。従って、本発明の方法により製造された溶融亜鉛系めっき鋼材は、特に自動車の高強度部品等の熱間プレス成形技術により製造される部品の素材として好適であり、筋ムラ発生による商品価値の低下を防ぐことができる。 According to the method of the present invention, streak unevenness observed when heating a hot-dip galvanized steel material to a hot temperature can be suppressed by a simple and low-cost pretreatment. Therefore, the hot dip galvanized steel manufactured by the method of the present invention is suitable as a material for parts manufactured by hot press forming technology such as high strength parts of automobiles in particular, and the commercial value is reduced due to the occurrence of streaks. Can be prevented.
次に、本発明のめっき鋼材の製造方法について説明する。なお、本明細書において、鋼組成およびめっき組成を規定する「％」は、断らない限り「質量％」である。また、鋼材の形態は、後述するように鋼板に限られないが、以下では、主として鋼板を対象として説明する。 Next, the manufacturing method of the plated steel material of this invention is demonstrated. In the present specification, “%” defining the steel composition and the plating composition is “mass%” unless otherwise specified. Further, the form of the steel material is not limited to the steel plate as described later, but the following description will mainly be made on the steel plate.
[めっき前処理]
本発明における亜鉛系めっき鋼板の製造方法では、めっき工程の前の基材鋼板に対して、珪素化合物を含有する処理液 (以下、Si含有液ともいう) を鋼板表面と接触させる処理を行う。Si含有液は、水溶性の珪素化合物を水に溶解させた水溶液であることが好ましい。本発明で使用するのに適した珪素化合物は、水溶性のアルカリ金属珪酸塩、例えば、オルト珪酸ナトリウム (オルソ珪酸ソーダ) 、オルト珪酸カリウム、メタ珪酸ナトリウム、メタ珪酸カリウムである。
[Plating pretreatment]
In the method for producing a zinc-based plated steel sheet according to the present invention, a treatment liquid containing a silicon compound (hereinafter also referred to as Si-containing liquid) is brought into contact with the steel sheet surface with respect to the base steel sheet before the plating step. The Si-containing liquid is preferably an aqueous solution in which a water-soluble silicon compound is dissolved in water. Suitable silicon compounds for use in the present invention are water-soluble alkali metal silicates such as sodium orthosilicate (orthosilicate sodium), potassium orthosilicate, sodium metasilicate, and potassium metasilicate.
Si含有液の濃度は、特に制限されるものではないが、質量％で好ましくは 0.5〜10％、より好ましくは１〜５％である。Si含有液と鋼板表面との接触は、他の方法も可能であるが、スプレーまたは浸漬により行うことが簡便で好ましい。珪素化合物は、鋼板表面に付着すればよいので、浸漬処理の場合でも数秒〜十数秒といったごく短時間の浸漬 (接触時間) でよい。もちろん、より長い接触時間をとることも可能である。Si含有液の温度も特に制限されないが、常温で十分である。 The concentration of the Si-containing liquid is not particularly limited, but is preferably 0.5 to 10% by mass%, more preferably 1 to 5%. Although other methods are possible for the contact between the Si-containing liquid and the steel sheet surface, it is convenient and preferable to carry out by spraying or dipping. Since the silicon compound only needs to adhere to the surface of the steel sheet, even in the case of immersion treatment, immersion (contact time) in a very short time such as several seconds to several tens of seconds is sufficient. Of course, longer contact times are possible. The temperature of the Si-containing liquid is not particularly limited, but normal temperature is sufficient.
たとえば、めっき工程が鋼板の連続溶融めっきラインにおいて行われる場合、上記のSi含有液によるめっき前処理は、めっき基材の脱脂・洗浄工程に使用するアルカリ性洗浄液として、オルト珪酸ナトリウム処理液または他のアルカリ金属珪酸塩の処理液を使用することにより実施することができる。 For example, when the plating process is performed in a continuous hot dipping line for steel sheets, the above-mentioned plating pretreatment with the Si-containing liquid is an ortho-sodium silicate treatment liquid or other alkaline washing liquid used for the degreasing / cleaning process of the plating substrate. It can implement by using the processing liquid of an alkali metal silicate.
オルト珪酸ナトリウム処理液を用いた脱脂・洗浄は、電気亜鉛めっき前の鋼板の前処理としては広く利用されているが、溶融亜鉛めっきの場合には、めっき濡れ性に影響を及ぼし、ピンホール状のめっき欠陥が発生し易くなるので、一般に利用されていなかった。しかし、本発明が対象とするような、溶融亜鉛めっき後に700 ℃以上に加熱される用途に使用する場合には、この加熱時にピンホールは解消するので、めっき皮膜にピンホールが発生していても構わない。この点に着目して、本発明では、ピンホールを発生し易いために溶融亜鉛めっきには敬遠されてきたオルト珪酸ナトリウム等のアルカリ金属珪酸塩による処理を、加熱時の筋ムラ解消のために、あえて採用する。 Degreasing / cleaning using sodium orthosilicate treatment solution is widely used as a pretreatment for steel sheets before electrogalvanization, but in the case of hot dip galvanization, it affects the wettability of the plating and has a pinhole shape. In general, it has not been used because it tends to cause plating defects. However, when used in applications that are heated to 700 ° C. or higher after hot dip galvanizing as the object of the present invention, pinholes are eliminated during this heating, so pinholes are generated in the plating film. It doesn't matter. Focusing on this point, in the present invention, the treatment with alkali metal silicates such as sodium orthosilicate, which has been avoided in hot dip galvanizing because it is easy to generate pinholes, eliminates unevenness in heating. Adopt it.
連続めっきラインでの脱脂・洗浄液として珪酸塩処理液を用いたくない場合には、ライン外の別の洗浄工程（例えば洗浄ライン）において、オルト珪酸ナトリウム処理液を洗浄液に使用して洗浄することにより、Si含有液による前処理を実施してもよい。その場合、洗浄工程に続いて連続めっきライン等でめっきされる際に、その前処理として、通常行われる水酸化ナトリウム水溶液等による洗浄・脱脂をしてもよい。 If you do not want to use a silicate treatment solution as a degreasing / cleaning solution in a continuous plating line, use a sodium orthosilicate treatment solution as a cleaning solution in another cleaning process (for example, a cleaning line) outside the line. A pretreatment with a Si-containing liquid may be performed. In that case, when plating is performed on a continuous plating line or the like following the cleaning step, as a pretreatment, cleaning and degreasing with a sodium hydroxide aqueous solution or the like that is usually performed may be performed.
このように、本発明に従って行うSi含有液によるめっき前処理は、従来の溶融めっきラインにおける脱脂・洗浄工程において、或いはライン外の洗浄工程において、単に洗浄液としてオルト珪酸ナトリウム処理液 (または他のアルカリ金属珪酸塩処理液) を用いることにより実施できる。従って、本発明によれば、この前処理のための工程を付加することなく、コストをかけずに、加熱時の筋ムラ発生が防止された溶融亜鉛系めっき鋼板を製造することができる。 As described above, the plating pretreatment with the Si-containing liquid performed in accordance with the present invention is simply performed in a degreasing / cleaning process in a conventional hot dipping plating line, or in a cleaning process outside the line, as a sodium orthosilicate treatment liquid (or other alkali solution as a cleaning liquid). It can be carried out by using a metal silicate treatment solution. Therefore, according to the present invention, it is possible to manufacture a hot-dip galvanized steel sheet in which streak unevenness during heating is prevented without adding a step for the pretreatment and without cost.
めっき前にSi含有液で前処理することにより、熱間プレス成形で発生する筋ムラが改善される理由については必ずしも明確ではないが、実験結果等から例えば以下のような機構が考えられる。 The reason why unevenness in hot press molding is improved by pretreatment with a Si-containing solution before plating is not necessarily clear, but the following mechanism can be considered from experimental results and the like.
Si含有液で浸漬処理またはスプレー処理した鋼板表面を分析すると、このような処理をしない鋼板表面と比較して、Siの検出値が大きかった。その後、これらの鋼板を、溶融亜鉛系めっき前に通常行われるように、還元雰囲気で焼鈍すると、Si含有液で処理した鋼板表面の方が逆にSiの検出値が小さかった。この結果から、Si含有液の処理によって鋼板表面にSiを付着させることにより、焼鈍時の鋼中のSiの表面濃化がかえって抑えられたと考えられる。Siの表面濃化は、たとえば偏析や介在物等により不均一になる可能性があるのに対し、Si含有液の処理は鋼板表面にほぼ均一にSiを付着させることができる。そのため、鋼中Siの不均一な表面濃化を抑えることができ、合金化処理時や熱間プレス成形時の加熱によるめっき皮膜から鋼への亜鉛の拡散が均一になって、筋ムラが抑制される。 When the steel plate surface immersed or sprayed with the Si-containing liquid was analyzed, the detected value of Si was larger than that of the steel plate surface not subjected to such treatment. Thereafter, when these steel sheets were annealed in a reducing atmosphere as is usually done before hot dip galvanizing, the detected value of Si was smaller on the steel sheet surface treated with the Si-containing liquid. From this result, it is considered that the surface concentration of Si in the steel during annealing was suppressed by attaching Si to the steel sheet surface by the treatment of the Si-containing liquid. The surface concentration of Si may become non-uniform due to segregation or inclusions, for example, whereas the treatment of the Si-containing liquid can adhere Si substantially uniformly to the steel sheet surface. Therefore, non-uniform surface concentration of Si in the steel can be suppressed, and the diffusion of zinc from the plating film to the steel due to heating during alloying treatment or hot press forming becomes uniform, thereby suppressing streaking unevenness. Is done.
[溶融めっきと合金化処理]
本発明では、前述のようなSi含有液での処理をした鋼板に、溶融亜鉛系めっきを施す。この溶融めっきは、溶融亜鉛めっきでよいが、溶融５％Al−Zn合金めっきといった亜鉛合金めっきとすることも可能である。以下では、溶融亜鉛めっきについて説明する。
[Hot plating and alloying]
In the present invention, hot dip galvanizing is performed on the steel sheet treated with the Si-containing liquid as described above. The hot dip galvanizing may be performed by hot dip galvanization, but may be zinc alloy plating such as hot dip 5% Al-Zn alloy plating. Below, hot dip galvanization is demonstrated.
本発明の好適態様では、溶融亜鉛めっきに引き続いて加熱による合金化処理を施して、合金化溶融亜鉛めっき鋼板（ＧＡ鋼板）とする。
めっき浴中のAl量は0.10〜0.20％程度が好ましい。めっき浴中に少量のAlを含有させることで、溶融めっき時にめっき／母材界面にFe−Al合金層が形成される。この合金層中のAlが多すぎたり、Fe−Al合金層が厚すぎる場合、合金化処理時や熱間プレス成形時の加熱による亜鉛の拡散が遅れ、結果として、後述するような熱間プレス成形時の加熱後に金属間化合物相が残りやすくなる。
In a preferred embodiment of the present invention, an alloying treatment by heating is performed subsequent to hot dip galvanizing to obtain an galvannealed steel plate (GA steel plate).
The amount of Al in the plating bath is preferably about 0.10 to 0.20%. By including a small amount of Al in the plating bath, an Fe—Al alloy layer is formed at the plating / base metal interface during hot-dip plating. If there is too much Al in this alloy layer, or if the Fe-Al alloy layer is too thick, the diffusion of zinc due to heating during alloying treatment or hot press forming will be delayed, resulting in hot pressing as described later. The intermetallic compound phase tends to remain after heating during molding.
鋼板をめっき浴から引上げて、ガスワイピング等で付着量を制御した後、好ましくは直ちに加熱して合金化処理を施し、めっき皮膜をZn−Fe合金とする。合金化処理の加熱温度は500 ℃以上とすることが望ましい。合金化処理の加熱温度が500 ℃未満では、合金化速度が遅いため、ライン速度が低下し、生産性を阻害したり、合金化炉を長くするなどの設備対応が必要となる。合金化処理の加熱温度が高くなるほど、合金化速度が速くなり、生産性が向上するが、合金化温度を上げる加熱バーナー等の設備強化が必要なので、好ましい範囲は 550〜650 ℃である。 After the steel sheet is pulled up from the plating bath and the amount of adhesion is controlled by gas wiping or the like, it is preferably heated immediately and subjected to an alloying treatment to make the plating film a Zn-Fe alloy. The heating temperature for the alloying treatment is desirably 500 ° C. or higher. When the heating temperature for the alloying treatment is less than 500 ° C., the alloying speed is slow, so the line speed decreases, and it is necessary to deal with facilities such as inhibiting productivity and lengthening the alloying furnace. The higher the heating temperature of the alloying treatment, the faster the alloying speed and the higher the productivity. However, it is necessary to strengthen equipment such as a heating burner that raises the alloying temperature, so the preferred range is 550 to 650 ° C.
ＧＡ鋼板の場合、めっき皮膜中のFe濃度は８〜25％の範囲が望ましい。合金化度が８％未満の場合、表面に融点の低い純亜鉛相が残りやすいため、熱間成形前の加熱時に亜鉛が蒸発して、製品の表面欠陥や金型の汚染が生じやすい。ＧＡ鋼板のめっき皮膜のFe濃度は好ましくは10％以上、さらに好ましくは13％以上である。このように高いFe濃度の方が好ましいのは、純亜鉛相が残りにくくなるだけでなく、次に述べる効果も期待できるためである。 In the case of a GA steel sheet, the Fe concentration in the plating film is desirably in the range of 8 to 25%. When the degree of alloying is less than 8%, a pure zinc phase having a low melting point tends to remain on the surface, so that zinc evaporates during heating before hot forming, and product surface defects and mold contamination are likely to occur. The Fe concentration in the plating film of the GA steel sheet is preferably 10% or more, more preferably 13% or more. The reason why such a high Fe concentration is preferable is that not only the pure zinc phase hardly remains, but also the following effects can be expected.
前述のように、熱間プレス成形時の加熱により、めっき皮膜中の亜鉛が鋼中に拡散して、Fe−Zn合金層が生成する。この拡散が進行するにつれて、Fe−Zn合金層は、Fe−Zn金属間化合物相から、α−Fe中にZnが固溶した固溶相に変化する。従って、加熱中の拡散が不十分であると、加熱後もFe−Zn金属間化合物相が残る。この金属間化合物相は、一般に硬く脆いため、引き続くプレス成形時に、金型の損傷や成形品表面の割れの原因となりやすい。そこで、表面にFe−Zn金属間化合物相が残存しない（いいかえると、実質的にFe中にZnが固溶した固溶相のみが認められる）程度まで拡散が進行していることが好ましい。それには、めっき皮膜中のFe％を予め高くしておくほうが、短時間で金属間化合物相が消失するため有利である。一方、めっき皮膜のFe濃度が25％より高いと、めっきが既に脆くなっているため、熱間プレス成形前のブランク加工時に、鋼板搬入時などにめっき割れの発生や脱落が発生しやすくなる。このような観点からは、めっき皮膜中のFe濃度は、好ましくは10％〜20％、更に好ましくは13〜17％である。 As described above, by heating during hot press forming, zinc in the plating film diffuses into the steel, and an Fe—Zn alloy layer is generated. As this diffusion proceeds, the Fe—Zn alloy layer changes from a Fe—Zn intermetallic compound phase to a solid solution phase in which Zn is dissolved in α-Fe. Therefore, if the diffusion during heating is insufficient, the Fe-Zn intermetallic compound phase remains even after heating. Since this intermetallic compound phase is generally hard and brittle, it tends to cause damage to the mold and cracking of the surface of the molded product during subsequent press molding. Therefore, it is preferable that the diffusion progresses to the extent that no Fe—Zn intermetallic compound phase remains on the surface (in other words, only a solid solution phase in which Zn is dissolved in Fe is substantially observed). For this purpose, it is advantageous to increase the Fe% in the plating film in advance because the intermetallic compound phase disappears in a short time. On the other hand, if the Fe concentration in the plating film is higher than 25%, the plating is already brittle, and therefore, plating cracking or dropout is likely to occur at the time of blanking before hot press forming or when carrying a steel plate. From such a viewpoint, the Fe concentration in the plating film is preferably 10% to 20%, more preferably 13 to 17%.
めっき付着量は、求められる耐食性に応じて主に決定されればよいが、亜鉛として30〜70 g/m2 程度が好ましい。亜鉛の付着量が多すぎると、上述したような加熱後の金属間化合物相が残りやすくなるからである。 The plating adhesion amount may be mainly determined according to the required corrosion resistance, but is preferably about 30 to 70 g / m 2 as zinc. This is because if the amount of zinc deposited is too large, the intermetallic compound phase after heating tends to remain.
[調質圧延]
溶融めっき（または合金化処理）後に、機械特性や表面粗さの調整の目的で、調質圧延を施すことが多い。このとき、通常はある程度の粗さ（例えば、調質圧延後のＲａで約１μm 以上）の表面となるように調質圧延されることが多いので、例えば、合金化処理後に前述したようなごく軽い筋状の欠陥があったとしても、欠陥は表面粗さの中に埋没するので、ほとんど問題になることはない。しかし、そのように調質圧延しても、熱間プレス成形や他の目的で700 ℃以上に加熱されると、筋ムラが改めて目立つようになる。従って、本発明の製造方法は、溶融亜鉛めっき後に調質圧延した溶融亜鉛系めっき鋼板にも非常に有用である。
[Temper rolling]
After hot dip plating (or alloying treatment), temper rolling is often performed for the purpose of adjusting mechanical properties and surface roughness. At this time, since the surface is usually temper-rolled so as to have a certain degree of roughness (for example, Ra after temper rolling is about 1 μm or more), for example, as described above after the alloying treatment. Even if there is a light streak defect, the defect is buried in the surface roughness and is hardly a problem. However, even with such temper rolling, streaks become more noticeable when heated to 700 ° C or higher for hot press forming or other purposes. Therefore, the production method of the present invention is very useful for a hot dip galvanized steel sheet that has been temper-rolled after hot dip galvanizing.
[熱間プレス]
上述の製造方法により得られた溶融亜鉛めっき鋼板や合金化溶融亜鉛めっき鋼板は、製造後に700 ℃以上の温度に加熱される用途に有用であり、そのような加熱により従来は発生していた筋ムラの発生が著しく抑制される。従って、この溶融亜鉛系めっき鋼板は、熱間プレス成形用途に特に有用であるが、プレス成形せずに、例えば、700 ℃以上で熱処理だけを受ける用途、例えば、高強度化を図るために焼入れが行われるような用途にも有用である。
[Hot press]
Hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets obtained by the above-described production methods are useful in applications where the steel is heated to a temperature of 700 ° C. or higher after production. The occurrence of unevenness is remarkably suppressed. Therefore, although this hot dip galvanized steel sheet is particularly useful for hot press forming applications, it is not subjected to press forming, for example, only subjected to heat treatment at 700 ° C. or higher, for example, quenching to increase strength. It is also useful for applications where
以下には熱間プレス成形工程の一例を説明する。
通常、熱間プレス成形工程では、鋼材をオーステナイト領域（通常 700〜1000℃程度）に加熱し、続いてプレス成形を行う。鋼板の種類（組成）、あるいは、成形品として要求される強度によっては、もう少し低い温度の加熱で良い場合もある。加熱方法としては、電気炉やガス炉等による加熱、火炎加熱、通電加熱、高周波加熱、誘導加熱などが挙げられる。
Below, an example of a hot press molding process is demonstrated.
Usually, in a hot press forming process, a steel material is heated to an austenite region (usually about 700 to 1000 ° C.), and then press forming is performed. Depending on the type (composition) of the steel sheet or the strength required for the molded product, heating at a slightly lower temperature may be sufficient. Examples of the heating method include heating with an electric furnace or a gas furnace, flame heating, energization heating, high-frequency heating, induction heating, and the like.
また熱間プレス成形工程を利用して、焼入れも達成したい場合には、目標の硬度となるよう焼入れ温度に材料を加熱し、その温度で通常一定時間（数分程度）を保持し、引き続き高温のままプレス成形し、プレス成形と実質的に同時またはプレス成形後直ちに急冷する。例えば、水冷金型を用いてプレス成形を行うと、金型との接触により急冷することができる。また、プレス金型を所定温度に加熱しておいて、その後直ちに急冷する方法も可能である。熱間プレス後の成形品が所定の性能をみたすように、焼入れ温度あるいは冷却速度を適宜変化させることができる。 If you want to achieve quenching using the hot press forming process, heat the material to the quenching temperature to achieve the target hardness, hold the temperature for a certain period of time (several minutes), and continue with high temperatures. Press molding is performed as it is, and quenching is performed substantially simultaneously with press molding or immediately after press molding. For example, when press molding is performed using a water-cooled mold, it can be rapidly cooled by contact with the mold. In addition, a method in which the press mold is heated to a predetermined temperature and then immediately cooled is possible. The quenching temperature or the cooling rate can be appropriately changed so that the molded product after hot pressing exhibits a predetermined performance.
上述したように、熱間プレス成形時の加熱 (および、場合により温度保持) の際に、前述しためっき皮膜中の亜鉛の母材鋼への拡散が生じる。このときの亜鉛の拡散による金属間化合物相の消失（固溶相の形成）までの時間が短いほど、加熱および／または保持の時間が短くてすみ、生産性の面からも有利である。 As described above, the zinc in the plating film diffuses into the base steel during the heating (and in some cases, the temperature is maintained) during hot press forming. At this time, the shorter the time until the disappearance of the intermetallic compound phase due to the diffusion of zinc (formation of the solid solution phase), the shorter the time for heating and / or holding, which is advantageous from the viewpoint of productivity.
[その他]
(1)基材の形態
本発明では、自動車用や家電用にプレス成形されて使用されるような薄鋼板を主な対象とするものであるが、これ以外に、例えば拡管、孔広げされるような鋼管や、その他成形形態によっては、線材や棒材などであってもよい。本明細書では、鋼板を対象に説明しているが、鋼板以外の形態の溶融亜鉛系めっき鋼材に対しても本発明を適用できる。
[Other]
(1) Form of base material In the present invention, the main object is a thin steel plate that is used by being press-molded for automobiles and home appliances. Depending on such steel pipes and other forming forms, wire rods and rods may be used. In this specification, although it demonstrated to the steel plate object, this invention is applicable also to hot dip galvanized steel materials of forms other than a steel plate.
(2)基材の鋼の組成および金属組織
基材の鋼組成や金属組織は、特に限定されない。ただし、熱間成形時の焼き入れ性その他を考慮した場合、好ましい組成等は以下の通りである。
(2) Steel composition and metal structure of base material The steel composition and metal structure of the base material are not particularly limited. However, when considering the hardenability and the like at the time of hot forming, preferred compositions and the like are as follows.
・鋼中Ｃ濃度：0.15％以上、好ましくは3.0 ％以下
熱間成形は、材料を加熱することで軟質化させ、成形しやすくすることが一つの特色であるが、あわせてプレス金型等で急冷することによって鋼を焼き入れし、より高強度の成形品を得ることができる。鋼の焼き入れ後の強度は主に含有炭素（Ｃ）量によって決まるため、求める強度に応じてＣ濃度を設定する。高強度の成形品が必要な場合には、Ｃ濃度を0.15％以上にすることが更に望ましい。Ｃを過剰に含む場合には、成形品の靱性が低下する恐れがあるため、3.0 ％以下とするのが望ましい。さらに好ましくは0.20％〜0.5 ％Ｃであり、靱性劣化の少ない高強度成形品が得ることができる。
-C concentration in steel: 0.15% or more, preferably 3.0% or less Hot forming is one of the features of softening the material by heating and making it easy to form. By quenching the steel, the steel can be quenched and a molded product with higher strength can be obtained. Since the strength after quenching of steel is mainly determined by the amount of carbon (C) contained, the C concentration is set according to the required strength. When a high-strength molded product is required, the C concentration is more preferably 0.15% or more. When C is excessively contained, the toughness of the molded product may be lowered, so that the content is desirably 3.0% or less. More preferably, it is 0.20% to 0.5% C, and a high-strength molded product with little toughness deterioration can be obtained.
・鋼中Si濃度0.01〜2.0 ％、Al濃度 0.005〜2.0 ％以下、
SiおよびAlは、鋼板の焼き入れ性を高め、かつ焼き入れ後の強度の安定効果をさらに高める重要な元素である。しかし、これらの元素はフェライト安定化元素であり、加熱中のオーステナイト化を図るために、加熱温度を上昇させなくてはならず、加熱コスト・製造コストの観点からそれぞれ2.0 ％を上限とする。また、SiならびにAlは鋼中の脱酸材と使用され、その効果を発揮させるにはSiは0.01％、Alは0.005 ％の添加が必要である。
・ Si concentration in steel: 0.01-2.0%, Al concentration: 0.005-2.0% or less,
Si and Al are important elements that enhance the hardenability of the steel sheet and further enhance the strength stabilizing effect after quenching. However, these elements are ferrite stabilizing elements, and in order to achieve austenite during heating, the heating temperature must be increased, and the upper limit is set to 2.0% from the viewpoint of heating cost and manufacturing cost. Si and Al are used as deoxidizers in steel, and in order to exert their effects, Si needs to be added by 0.01% and Al by 0.005%.
・鋼中Mn濃度 0.3〜3.5 ％、
Mnは、鋼板の焼入れ性を高め、かつ焼き入れ後に強度を安定して確保するために非常に効果のある元素である。しかし、Mn濃度が0.3 ％未満ではその効果は十分ではなく、一方、Mn濃度が3.5 ％を越えるとその効果は飽和し、更に焼き入れ部の靱性劣化を招く。より望ましいMn濃度は 0.8〜3.0 ％である。
・ Mn concentration in steel: 0.3-3.5%
Mn is an element that is very effective for enhancing the hardenability of the steel sheet and ensuring a stable strength after quenching. However, if the Mn concentration is less than 0.3%, the effect is not sufficient. On the other hand, if the Mn concentration exceeds 3.5%, the effect is saturated, and the toughness of the quenched portion is further deteriorated. A more desirable Mn concentration is 0.8 to 3.0%.
・鋼中Ｐ濃度0.10％以下、Ｓ濃度：0.05％以下、Ｎ濃度0.01％以下
Ｐ、Ｓ、Ｎも、それぞれ0.10％以下、0.05％以下、0.01％以下含有させた場合に、鋼板の焼入れ性を高め、かつ焼入れ後強度の安定効果をさらに高める効果を有する。一方、これらは、不純物の１種としても含有されるが、下限としてＰ：0.005 ％以上、Ｓ：0.0005％以上、Ｎ：0.001 ％以上が望ましい。それより少なくすると製造コストを上昇させるためである。
-P concentration in steel 0.10% or less, S concentration: 0.05% or less, N concentration 0.01% or less P, S, N hardenability of steel sheet when 0.10%, 0.05% or less, 0.01% or less, respectively. And has the effect of further enhancing the effect of stabilizing the strength after quenching. On the other hand, these are also contained as one kind of impurities, but the lower limit is preferably P: 0.005% or more, S: 0.0005% or more, and N: 0.001% or more. If it is less, the manufacturing cost will increase.
・鋼中Ti濃度 0.2％以下、Nb濃度 0.1％以下、Ｖ濃度 0.2％以下
Ti，Nb、Ｖも、それぞれ0.2 ％以下、0.1 ％以下、0.2 ％以下含有させた場合に、鋼板の焼入れ性を高め、かつ焼入れ後強度の安定効果をさらに高める効果を有するので、場合によりこれらの１種または２種以上を添加してもよい。この量を超えて含有させても鋼板の焼入れ性、焼入れ後強度の安定効果は飽和し、コスト増を招く。一方、下限としてTi：0.01％未満、Nb：0.005 ％未満、Ｖ：0.005 ％未満の含有では、効果は十分でない。
-Ti concentration in steel 0.2% or less, Nb concentration 0.1% or less, V concentration 0.2% or less
When Ti, Nb, and V are contained in amounts of 0.2% or less, 0.1% or less, and 0.2% or less, respectively, they have the effect of enhancing the hardenability of the steel sheet and further improving the strength stabilizing effect after quenching. One or two or more of these may be added. Even if the content exceeds this amount, the effect of stabilizing the hardenability of the steel sheet and the strength after quenching is saturated, resulting in an increase in cost. On the other hand, if the content of Ti is less than 0.01%, Nb is less than 0.005%, and V is less than 0.005%, the effect is not sufficient.
・鋼中Mo濃度1.0 ％以下、Ni濃度1.0 ％以下、Cu濃度1.0 ％以下
Mo、Ni、Cuも、それぞれ1.0 ％以下、1.0 ％以下、1.0 ％以下含有させた場合に、鋼板の焼入れ性を高め、かつ焼入れ後強度の安定効果をさらに高める効果を有するので、場合によりこれらの１種または２種以上を添加してもよい。この量を超えて含有させても、鋼板の焼入れ性、焼入れ後強度の安定効果は飽和し、コスト増を招く。一方、下限として、Mo：0.02％未満、Ni：0.02％未満、Cu：0.02％未満の含有では、効果は十分でない。
・ Mo concentration in steel: 1.0% or less, Ni concentration: 1.0% or less, Cu concentration: 1.0% or less
When Mo, Ni, and Cu are added in amounts of 1.0% or less, 1.0% or less, or 1.0% or less, respectively, the hardenability of the steel sheet is enhanced and the strength stabilizing effect after quenching is further enhanced. One or two or more of these may be added. Even if the content exceeds this amount, the effect of stabilizing the hardenability and post-quenching strength of the steel plate is saturated, resulting in an increase in cost. On the other hand, when the content is less than Mo: less than 0.02%, Ni: less than 0.02%, and Cu: less than 0.02%, the effect is not sufficient.
・鋼中Cr濃度1.0 ％以下、Ｂ濃度0.005 ％以下
Cr、Ｂも、それぞれ1.0 ％以下、0.005 ％以下含有させた場合に、鋼板の焼入れ性を高め、かつ焼入れ後強度の安定効果をさらに高めることができるので、場合によりこれらの１種または２種を添加してもよい。この量を超えて含有させても鋼板の焼入れ性、焼入れ後強度の安定効果は飽和し、コスト増を招く。一方、下限として、Cr：0.02％未満、Ｂ：0.0003％未満の含有では、その効果は十分でない。
・ Cr concentration in steel: 1.0% or less, B concentration: 0.005% or less
When Cr and B are contained in amounts of 1.0% or less and 0.005% or less, respectively, the hardenability of the steel sheet can be improved and the effect of stabilizing the strength after quenching can be further enhanced. May be added. Even if the content exceeds this amount, the effect of stabilizing the hardenability of the steel sheet and the strength after quenching is saturated, resulting in an increase in cost. On the other hand, as the lower limit, if Cr is less than 0.02% and B is less than 0.0003%, the effect is not sufficient.
・鋼中Ca濃度0.01％以下、Mg濃度0.01％以下、希土類元素濃度0.01％以下
Ca、Mg、希土類元素も、それぞれCa0.01％以下、Mg0.01％以下、希土類元素0.01％以下含有させた場合に、鋼中の介在物の形態を微細化し、介在物による熱間プレス時の割れを防止する効果があるので、場合によりこれらの１種または２種以上を添加してもよい。この量を超えて含有させても、鋼中の介在物の形態を微細化効果は飽和する。一方、下限として、Ca：0.0005％未満、Mg：0.0005％未満、希土類元素：0.0005％未満の含有では、その効果は十分でない。
・ Ca concentration in steel 0.01% or less, Mg concentration 0.01% or less, rare earth element concentration 0.01% or less
When Ca, Mg, and rare earth elements are also contained in each of Ca 0.01% or less, Mg 0.01% or less, and rare earth elements 0.01% or less, the inclusions in the steel are refined in the form of hot pressing with inclusions. Since these are effective in preventing cracking, one or more of these may be added in some cases. Even if it contains exceeding this amount, the refinement | miniaturization effect is saturated with the form of the inclusion in steel. On the other hand, as the lower limit, if Ca is less than 0.0005%, Mg is less than 0.0005%, and the rare earth element is less than 0.0005%, the effect is not sufficient.
(3)鋼材の製造方法、鋼の金属組織
本発明で使用する鋼材については、特に熱間成形により焼入れを目的とする場合、加熱前の機械的性質は重要でない。そこで、加熱前の金属組織については必ずしも限定されない。また、コストや求められる板厚およびその精度等、状況に応じて熱延鋼板または冷延鋼板を用いればよい。
(3) Manufacturing method of steel material, metal structure of steel For the steel material used in the present invention, the mechanical properties before heating are not important particularly for the purpose of quenching by hot forming. Therefore, the metal structure before heating is not necessarily limited. Moreover, what is necessary is just to use a hot-rolled steel plate or a cold-rolled steel plate according to conditions, such as cost, the required plate | board thickness, and its precision.
本例では、実験用の溶融亜鉛めっき設備を利用して、表１のＡ〜Ｃに示す組成をもつ冷延鋼板 (いずれも板厚1.6 mm) からなるめっき基材に対して、下記の前処理を施した後、合金化溶融亜鉛めっきを行った。溶融亜鉛めっき条件は、浴温460 ℃、浴中Al濃度0.12〜0.15％、片面あたりのめっき付着量：Znとして30〜70 g/m2 の範囲内であった。合金化処理は、溶融めっき処理後、 500〜650 ℃の温度で処理時間を変更して実施した。形成されたＧＡめっき皮膜中の合金化度（Fe％）は12〜17％であった。 In this example, using the experimental hot dip galvanizing equipment, a plating base made of a cold-rolled steel sheet having a composition shown in A to C in Table 1 (each having a thickness of 1.6 mm) After the treatment, alloying hot dip galvanizing was performed. The hot dip galvanizing conditions were such that the bath temperature was 460 ° C., the Al concentration in the bath was 0.12 to 0.15%, and the plating adhesion amount per side: Zn was in the range of 30 to 70 g / m 2 . The alloying treatment was performed after changing the treatment time at a temperature of 500 to 650 ° C. after the hot dipping treatment. The degree of alloying (Fe%) in the formed GA plating film was 12 to 17%.
基材１は、上記鋼板を、本発明に従って、温度50℃にした3.0 ％オルト珪酸ナトリウム水溶液に10秒間浸漬する処理を行い、その後に乾燥することにより、めっき前処理を行ったものである。 In accordance with the present invention, the base material 1 is subjected to a pretreatment for plating by performing a treatment for immersing in a 3.0% sodium orthosilicate aqueous solution at a temperature of 50 ° C. for 10 seconds and then drying.
基材２は、上記鋼板を、本発明に従って、温度50℃にした3.0 ％オルト珪酸ナトリウム水溶液に10秒間浸漬する処理を行い、自然乾燥した後、更に、温度50℃にした３％水酸化ナトリウム水溶液に６秒間浸漬する前洗浄・脱脂を行い、その後に水洗し、乾燥したものである。 The base material 2 was subjected to a treatment of immersing the steel sheet in a 3.0% sodium orthosilicate aqueous solution at a temperature of 50 ° C. for 10 seconds in accordance with the present invention, naturally dried, and further 3% sodium hydroxide at a temperature of 50 ° C. Before washing and degreasing for 6 seconds in an aqueous solution, washing with water and drying are performed.
比較のために、オルト珪酸ナトリウム水溶液に浸漬しない基材（比較材１、上記鋼板を水洗だけして、溶融亜鉛めっきしたもの）、オルト珪酸ナトリウム水溶液に浸漬しないが、水酸化ナトリウム水溶液により前洗浄・脱脂し、水洗した基材（比較材２）についても、溶融亜鉛めっきとその後の合金化処理を上記の条件で実施した。 For comparison, a base material that is not immersed in a sodium orthosilicate aqueous solution (Comparative Material 1, the above steel sheet is washed with water and hot-dip galvanized), is not immersed in a sodium orthosilicate aqueous solution, but is pre-cleaned with a sodium hydroxide aqueous solution. -Also about the base material (comparative material 2) which degreased and washed with water, the hot dip galvanization and the subsequent alloying process were implemented on said conditions.
いずれのめっきサンプルも、合金化処理後に調質圧延を実施し、めっき表面粗さがRaで約1.0 μｍとなるようにした。この状態では、いずれのサンプルも目視では筋ムラが認められなかった。 All plating samples were temper-rolled after alloying treatment so that the plating surface roughness was about 1.0 μm in terms of Ra. In this state, no streak unevenness was visually observed in any of the samples.
次に、これらのサンプルについて、試験片サイズ長さ500 mm×幅200 mmの供試材を、鋼組成とめっき前処理が同一であるグループ毎に30枚ずつ作成し、大気雰囲気の加熱炉内で950 ℃×５分間の加熱を行った。その後、加熱炉から取り出し、高温状態のままで、図１に示す曲げ形状の熱間プレス成形を行った。 Next, for each of these samples, 30 specimens with a specimen size of length 500 mm x width 200 mm were prepared for each group with the same steel composition and pre-plating treatment, and the sample was placed in a heating furnace in an air atmosphere. Was heated at 950 ° C. for 5 minutes. Then, it took out from the heating furnace, and the hot press molding of the bending shape shown in FIG. 1 was performed in the high temperature state.
この成形材（図２）について、成形材表面の表裏における筋ムラの発生状況を調査した。筋ムラの発生状況は目視で確認し、グループ毎の筋ムラ発生率を次式により求めた。
筋ムラ発生率(%)＝(筋ムラが発生した成形材の個数／調査した成形材の個数)×100
表２に、めっき前処理条件と試験結果を示す。
About this molding material (FIG. 2), the generation | occurrence | production situation of the stripe unevenness in the front and back of the molding material surface was investigated. The occurrence of streak unevenness was confirmed visually, and the streak unevenness occurrence rate for each group was determined by the following equation.
Streak unevenness occurrence rate (%) = (number of molding materials with streak unevenness / number of investigated molding materials) x 100
Table 2 shows plating pretreatment conditions and test results.
本発明の方法に従って製造した試験番号１〜６の合金化溶融亜鉛めっき鋼板を熱間プレス成形した成形材については、筋ムラの発生は無かった。それに対し、比較例である試験番号７〜12については、成形材に筋ムラが70〜80％発生した。 There was no occurrence of streak unevenness in the molded material obtained by hot press-forming the alloyed hot-dip galvanized steel sheets of test numbers 1 to 6 produced according to the method of the present invention. On the other hand, for test numbers 7 to 12, which are comparative examples, 70-80% of streak irregularities occurred in the molded material.
即ち、水酸化ナトリウム水溶液による前洗浄・脱脂では筋ムラの発生が起こるのに対し、本発明に従って、珪酸化合物の水溶液を用いてめっき前処理を行うと、その後の水酸化ナトリウム水溶液の脱脂の有無にかかわらず、筋ムラの発生を防止することができた。 That is, streak unevenness occurs in pre-cleaning and degreasing with an aqueous sodium hydroxide solution, whereas when pre-plating is performed using an aqueous solution of a silicate compound according to the present invention, the presence or absence of subsequent degreasing of the aqueous sodium hydroxide solution Regardless of this, it was possible to prevent the occurrence of muscle unevenness.
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| KR102264726B1 (en) * | 2018-11-30 | 2021-06-16 | 주식회사 포스코 | STEEL SHEET PLATED WITH Al-Fe ALLOY FOR HOT PRESS FORMING HAVING EXCELLENT CORROSION RESISTANCE, HOT PRESS FORMED PART, AND HEAT RESISTANCE, AND MANUFACTURING METHOD THE SAME |
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