JP2011137210A - Steel sheet for hot stamp and method of producing the same - Google Patents
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本発明は、ホットスタンプ用鋼板及びその製造方法に関し、特に、塗装後耐食性及び生産性に優れるホットスタンプ用めっき鋼板及びその製造方法に関する。 The present invention relates to a steel sheet for hot stamping and a method for producing the same, and more particularly to a plated steel sheet for hot stamping having excellent post-painting corrosion resistance and productivity and a method for producing the same.
近年、自動車用鋼板の用途(例えば、自動車のピラー、ドアインパクトビーム、バンパービーム等)などにおいて、高強度と高成形性を両立する鋼板が望まれており、これに対応するものの1つとして、残留オーステナイトのマルテンサイト変態を利用したTRIP(Transformation Induced Plasticity)鋼がある。このTRIP鋼により、成形性の優れた1000MPa級程度の強度を有する高強度鋼板を製造することは可能であるが、さらに高強度、例えば1500MPa以上といった超高強度鋼で成形性を確保することは困難である。 In recent years, in steel plate applications for automobiles (for example, automobile pillars, door impact beams, bumper beams, etc.) and the like, steel plates that have both high strength and high formability have been desired. There is TRIP (Transformation Induced Plasticity) steel using martensitic transformation of retained austenite. With this TRIP steel, it is possible to produce a high-strength steel sheet having excellent formability and a strength of about 1000 MPa, but it is possible to secure formability with ultra-high-strength steel with higher strength, for example, 1500 MPa or more Have difficulty.
このような状況で、高強度及び高成形性を両立するものとして最近注目を浴びているのが、ホットスタンプ(熱間プレス、ホットプレス、ダイクエンチ、プレスクエンチ等とも呼称される。)である。このホットスタンプは、鋼板を800℃以上のオーステナイト域で加熱した後に熱間で成形することにより高強度鋼板の成形性を向上させ、成形後の冷却により焼きを入れて所望の材質を得るというものである。 Under such circumstances, hot stamping (also referred to as hot pressing, hot pressing, die quenching, press quenching, etc.) has recently attracted attention as being compatible with both high strength and high formability. This hot stamping improves the formability of a high-strength steel sheet by heating it in an austenite region at 800 ° C. or higher and then forming it hot, and it is baked by cooling after forming to obtain a desired material. It is.
ホットスタンプは、超高強度の部材を成形する方法として有望であるが、通常は大気中で鋼板を加熱する工程を有しており、この際、鋼板表面に酸化物(スケール)が生成するため、スケールを除去する工程が必要であった。ところが、このような後工程には、スケールの除去能や環境負荷等の観点からの対応策の必要性等の問題があった。 Hot stamping is promising as a method for forming ultra-high strength members, but usually has a step of heating a steel plate in the atmosphere, and at this time, oxide (scale) is generated on the surface of the steel plate. The process of removing the scale was necessary. However, such post-processes have problems such as the necessity of countermeasures from the viewpoints of scale removal ability and environmental load.
これを改善する技術として、ホットスタンプ用の鋼板としてAlめっき鋼板を使用することにより、加熱時のスケールの生成を抑制する技術が提案されている(例えば、特許文献1〜3を参照)。更にホットスタンプの加熱時にAlめっきが溶融して寄り(垂れとも称呼される)を生じるために、加熱時に融点以下の温度で保定することで寄りを回避する技術についても開示されている(特許文献4を参照)。 As a technique for improving this, there has been proposed a technique for suppressing the generation of scale during heating by using an Al-plated steel sheet as a steel sheet for hot stamping (see, for example, Patent Documents 1 to 3). Furthermore, since the Al plating melts and is shifted (also referred to as sagging) when the hot stamp is heated, a technique for avoiding the shift by holding at a temperature below the melting point during heating is also disclosed (Patent Document). 4).
上記特許文献1〜3に記載された技術は、炉加熱のような昇温速度が緩やかな加熱条件を前提としている。炉加熱の場合には通常常温から900℃程度まで昇温する際の平均昇温速度は3〜5℃/秒のため、加熱するまでに180〜290秒が必要で、熱間プレスにより成形可能な部品は2〜4個/分程度であり非常に生産性が低かった。 The techniques described in Patent Documents 1 to 3 are premised on heating conditions such as furnace heating where the rate of temperature rise is moderate. In the case of furnace heating, the average rate of temperature increase from normal temperature to about 900 ° C is 3 to 5 ° C / second, so 180 to 290 seconds are required before heating and molding is possible by hot pressing. The number of parts was about 2-4 pieces / minute, and the productivity was very low.
特許文献4は、約20℃/秒という、比較的早い昇温であり、このようなときには溶融したメタルが寄るという課題が示されている。これを解決するために融点以下の温度で緩やかに昇温させてこの間に合金化(めっきと鋼板が反応して金属間化合物へと変化する現象をこう呼ぶ)を進行させることでめっきの融点を上昇させることが示されている。しかしこの場合も例えば30μm厚みのめっき層では60秒の緩やかな加熱が必要とされており、合計加熱時間は100秒必要となっている。従って生産性向上という観点からはまだ改善の余地があった。 Patent Document 4 shows a relatively fast temperature increase of about 20 ° C./second. In such a case, a problem that molten metal approaches is shown. In order to solve this problem, the temperature of the plating is lowered at a temperature lower than the melting point, and alloying (the phenomenon in which the plating and the steel plate react to change to an intermetallic compound) is advanced during this time, thereby reducing the melting point of the plating. It has been shown to rise. However, in this case as well, for example, a 30 μm thick plating layer requires gentle heating for 60 seconds, and the total heating time is 100 seconds. Therefore, there was still room for improvement from the viewpoint of improving productivity.
ホットスタンプの生産性を向上させるためには通電加熱や誘導加熱等のような電気を使用する加熱方式で急速加熱を行うことが有効である。しかし急速に加熱すると特許文献4にも記載されている寄り(或いは垂れ)が発生して局部的にめっき厚みが厚くなるなど、めっき厚みが不均一になる、という問題があった。寄りの本質的な原因は、加熱過程でめっきが合金化する前に溶融することにある。すなわち合金化すると、融点が上昇するためこのような現象は起こらないが、急速に昇温するとAlの融点である660℃以上でめっきが溶解し、重力や電磁力で移動する現象が観察される。このようなめっき厚みが不均一なめっき鋼板は、プレス時に型に噛みこんだり、凝着したりするため、生産性を大きく阻害する。すなわちこの寄り現象を克服することで生産性向上を達成することが可能となる。 In order to improve the productivity of hot stamping, it is effective to perform rapid heating by a heating method using electricity such as energization heating or induction heating. However, when heated rapidly, there has been a problem that the plating thickness becomes non-uniform, for example, a shift (or sagging) described in Patent Document 4 occurs and the plating thickness locally increases. The essential cause of the deviation is that the plating melts before alloying during the heating process. That is, when the alloy is formed, such a phenomenon does not occur because the melting point rises. However, when the temperature is rapidly raised, the plating dissolves at a melting point of Al of 660 ° C. or higher, and a phenomenon of moving by gravity or electromagnetic force is observed. . Such a plated steel sheet with a non-uniform plating thickness bites into or adheres to the mold at the time of pressing, which greatly impedes productivity. That is, productivity improvement can be achieved by overcoming this shift phenomenon.
更に急速加熱技術として、上記の電気を使用する方法に加えて、輻射加熱を利用して急速加熱する技術も今日では得られている。すなわち、近赤外線のようなエネルギー密度の高い放射線を鋼板に照射することで急速加熱することも可能である。電気加熱は一般にブランク材の形状制約があるが、輻射加熱はその制約が少ないという利点がある。ところが輻射加熱を使用してAlめっき鋼板を急速加熱すると、めっきが溶融した時点で表面が鏡面となり、熱の吸収効率が低下して例えば非めっき材と比べて昇温速度が小さくなるという課題もあった。 Furthermore, as a rapid heating technique, in addition to the above-described method using electricity, a technique of rapid heating using radiant heating has been obtained today. That is, rapid heating is possible by irradiating the steel sheet with radiation having a high energy density such as near infrared rays. Although electric heating generally has a shape restriction on the blank material, radiant heating has an advantage that the restriction is small. However, when the Al-plated steel sheet is rapidly heated using radiant heating, the surface becomes a mirror surface when the plating is melted, and the heat absorption efficiency is lowered, for example, the heating rate is lower than that of the non-plated material. there were.
そこで、本発明は、このような問題に鑑みてなされたもので、Alめっき鋼板のAlめっき層をAl−Fe合金化する過程で、めっきが剥離する現象を回避して表面まで合金化させてAlめっき層の寄りを防止したホットスタンプ用めっき鋼板及びその製造方法を提供することで、生産性を向上させることを目的とする。 Therefore, the present invention has been made in view of such problems. In the process of forming an Al plating layer of an Al-plated steel sheet into an Al-Fe alloy, the phenomenon of plating peeling is avoided and alloyed to the surface. It aims at improving productivity by providing the plated steel plate for hot stamps which prevented the shift | offset | difference of Al plating layer, and its manufacturing method.
本発明者らは、上記課題を解決するために鋭意研究を重ねた結果、急速加熱によるAlめっき鋼板のめっきの寄りを完全に防止できるホットスタンプ用めっき鋼板を実現させた。 As a result of intensive studies to solve the above-described problems, the present inventors have realized a hot stamped plated steel sheet that can completely prevent the plating of the Al plated steel sheet from being rapidly heated.
すなわち、本発明者らは、優れた耐食性と優れた生産性を兼ね備える急速加熱ホットスタンプ用めっき鋼板を得るために鋭意検討を行った結果、表面まで合金化させることが有効との知見を得た。そして、優れた塗装後耐食性を得るためには、一定以上の付着量が必要となるが、一定以上の付着量を有するAlめっき鋼板をコイル状態で合金化させるとめっきが剥離するとの現象が観察された。そこで、Alめっき鋼鈑のAlめっき層をボックス焼鈍によりAl−Fe合金化する際に、適正な合金化条件として、焼鈍条件(温度、時間、雰囲気等)および鋼成分を特定することで、この剥離現象を回避できることを見出し、本発明を完成した。 That is, as a result of intensive studies to obtain a plated steel sheet for rapid heating hot stamping that has both excellent corrosion resistance and excellent productivity, the present inventors have obtained knowledge that alloying to the surface is effective. . In order to obtain excellent post-painting corrosion resistance, a certain amount of adhesion is required, but the phenomenon of plating peeling is observed when an Al-plated steel sheet having a certain amount of adhesion is alloyed in a coil state. It was done. Therefore, when the Al-plated layer of the Al-plated steel sheet is formed into an Al-Fe alloy by box annealing, as an appropriate alloying condition, the annealing condition (temperature, time, atmosphere, etc.) and the steel component are specified, and this The present inventors have found that the peeling phenomenon can be avoided and completed the present invention.
本発明の要旨とするところは、次の通りである。 The gist of the present invention is as follows.
(1) 鋼成分として質量%で、
C:0.1〜0.5%、
Si:0.01〜0.7%、
Mn:0.5〜2.5%、
Cr:0.4%超〜3%、
P:0.001〜0.1%、
S:0.001〜0.1%、
Al:0.1%以下、
N:0.01%以下
を含有し、残部がFe及び不可避的不純物より成る鋼板の表面に、厚みが10〜45μmのFe:42〜88%を含有し、残部Al及び不可避的不純物より成るAl−Fe合金層を有し、該Al−Fe合金層表面のAlN量が0.01〜1g/m2であることを特徴とする、ホットスタンプ用鋼板。
(1) By mass% as a steel component,
C: 0.1 to 0.5%
Si: 0.01 to 0.7%,
Mn: 0.5 to 2.5%
Cr: more than 0.4% to 3%,
P: 0.001 to 0.1%,
S: 0.001 to 0.1%,
Al: 0.1% or less,
N: 0.01% or less, balance of Fe and unavoidable impurities on the surface of the steel sheet, 10 to 45 μm of Fe: 42 to 88% of the thickness, balance Al and Al of unavoidable impurities A steel sheet for hot stamping, comprising a Fe alloy layer, wherein the AlN amount on the surface of the Al—Fe alloy layer is 0.01 to 1 g / m 2 .
(2) 鋼成分として質量%で、
C:0.1〜0.5%、
Si:0.01〜0.7%、
Mn:0.5〜2.5%、
Cr:0.2〜3%、
Mo:0.005〜0.5%、
P:0.001〜0.1%、
S:0.001〜0.1%、
Al:0.1%以下、
N:0.01%以下
を含有し、残部がFe及び不可避的不純物より成る鋼板の表面に、厚みが10〜45μmのFe:42〜88%を含有し、残部Al及び不可避的不純物より成るAl−Fe合金層を有し、該Al−Fe合金層表面のAlN量が0.01〜1g/m2であることを特徴とする、ホットスタンプ用鋼板。
(2) By mass% as a steel component
C: 0.1 to 0.5%
Si: 0.01 to 0.7%,
Mn: 0.5 to 2.5%
Cr: 0.2-3%,
Mo: 0.005 to 0.5%,
P: 0.001 to 0.1%,
S: 0.001 to 0.1%,
Al: 0.1% or less,
N: 0.01% or less, balance of Fe and unavoidable impurities on the surface of the steel sheet, 10 to 45 μm of Fe: 42 to 88% of the thickness, balance Al and Al of unavoidable impurities A steel sheet for hot stamping, comprising a Fe alloy layer, wherein the AlN amount on the surface of the Al—Fe alloy layer is 0.01 to 1 g / m 2 .
(3) 上記鋼成分が、さらに質量%で、
B:0.0001〜0.01%、
W:0.01〜3%、
V:0.01〜2%、
Ti:0.005〜0.5%、
Nb:0.01〜1%
の内の1種又は2種以上を含有することを特徴とする、上記(1)または(2)に記載のホットスタンプ用鋼板。
(3) The steel component is further mass%,
B: 0.0001 to 0.01%
W: 0.01 to 3%
V: 0.01-2%
Ti: 0.005 to 0.5%,
Nb: 0.01 to 1%
The steel sheet for hot stamping according to (1) or (2) above, comprising one or more of the above.
(4) 上記Al−Fe合金層が、さらに質量%で、
Si:3〜15%
を含有することを特徴とする、上記(1)〜(3)のいずれか1項に記載のホットスタンプ用鋼板。
(4) The Al-Fe alloy layer is further in mass%,
Si: 3 to 15%
The steel sheet for hot stamping according to any one of the above (1) to (3), comprising:
(5) 上記Al−Fe合金層が、さらに質量%で、
Mn:0.05〜1%、
Mg:0.05〜1%、
Cr:0.05〜0.5%、
Mo:0.05〜0.5%
の内の1種又は2種以上を含有することを特徴とする、上記(1)〜(4)のいずれか1項に記載のホットスタンプ用鋼板。
(5) The Al—Fe alloy layer is further mass%,
Mn: 0.05 to 1%
Mg: 0.05 to 1%,
Cr: 0.05 to 0.5%,
Mo: 0.05-0.5%
The steel sheet for hot stamping according to any one of (1) to (4) above, comprising one or more of the above.
(6) 上記(1)〜(3)のいずれかに記載の鋼成分の鋼板に付着量が片面当たり30〜100g/m2となるようにAlめっき浴を用いてAlめっきを施してAlめっき鋼板とし、該Alめっき鋼板コイルをボックス焼鈍炉内で、その保定時間、温度をそれぞれX軸、Y軸とし、X軸を対数表示した時に、(600℃、5時間)、(600℃、200時間)、(630℃、1時間)、(750℃、1時間)、(750℃、4時間)の5点で囲まれる内部となるような温度並びに保定時間で焼鈍することでAlめっきと鋼板を合金化させ、鋼板の表面に、厚みが10〜45μmのFe:42〜88%を含有し残部Al及び不可避不純物からなるAl−Fe合金層を形成し、該Al−Fe合金層表面のAlN量を0.01〜1g/m2に抑制することを特徴とする、ホットスタンプ用鋼板の製造方法。 (6) Al plating is performed by using an Al plating bath so that the adhesion amount of the steel component steel sheet according to any one of (1) to (3) is 30 to 100 g / m 2 per side. When a steel plate is used, and the Al-plated steel plate coil is kept in a box annealing furnace, the holding time and temperature are X-axis and Y-axis, respectively, and the X-axis is logarithmically expressed (600 ° C, 5 hours), (600 ° C, 200 ° C) Time), (630 ° C., 1 hour), (750 ° C., 1 hour), and (750 ° C., 4 hours). Is formed on the surface of the steel sheet to form an Al—Fe alloy layer containing 10 to 45 μm of Fe: 42 to 88% and the balance Al and unavoidable impurities, and AlN on the surface of the Al—Fe alloy layer. inhibiting amount 0.01 to 1 g / m 2 Characterized Rukoto method of hot stamping steel plate.
(7) 上記合金化させた後に、圧下率3%以下のスキンパス圧延を行なうことを特徴とする、上記(6)に記載のホットスタンプ用鋼板の製造方法。 (7) The method for producing a steel sheet for hot stamping according to (6) above, wherein after the alloying, skin pass rolling is performed at a rolling reduction of 3% or less.
(8) 前記Alめっき浴が、Siを3〜15質量%含有することを特徴とする、上記(6)または(7)に記載のホットスタンプ用めっき鋼板の製造方法。 (8) The method for producing a plated steel sheet for hot stamping according to (6) or (7), wherein the Al plating bath contains 3 to 15% by mass of Si.
(9) 前記Alめっき浴が、さらに質量%で、
Mn:0.05〜1%、
Mg:0.05〜1%、
Cr:0.05〜0.5%、
Mo:0.05〜0.5%
の内の1種又は2種以上を含有することを特徴とする、上記(8)に記載のホットスタンプ用めっき鋼板の製造方法。
(9) The Al plating bath is further mass%,
Mn: 0.05 to 1%
Mg: 0.05 to 1%,
Cr: 0.05 to 0.5%,
Mo: 0.05-0.5%
1 type or 2 types or more are contained, The manufacturing method of the plated steel plate for hot stamps as described in said (8) characterized by the above-mentioned.
本発明によれば、ホットスタンプ用めっき鋼板を製造方法するにあたり、Alめっき鋼鈑のめっき層をボックス焼鈍によりAl−Fe合金化する際に、適正な合金化条件として、焼鈍条件(温度、時間、雰囲気)および鋼成分を特定することで、めっきの剥離現象を回避して、表面まで合金化させることができるので、ホットスタンプ用めっき鋼板を急速加熱しても寄りの発生を無くすことが可能となり、生産性を向上させることが可能となるなど、産業上有用な著しい効果を奏する。 According to the present invention, when producing a hot stamped plated steel sheet, when the Al-Fe alloy is formed by box annealing the plated layer of the Al-plated steel sheet, the annealing conditions (temperature, time) By specifying the steel atmosphere and the steel components, it is possible to avoid the peeling phenomenon of the plating and to alloy it to the surface. Thus, it is possible to improve the productivity, and there are significant industrially useful effects.
以下、本発明の好適な実施の形態について詳細に説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail.
上述したように、上記特許文献1〜3に記載された技術では、加熱に約200秒以上を掛けるような低生産性プロセスであった。ホットスタンプの生産性を向上させるために、通電加熱等により急速加熱を行うと、特許文献4に記載されているように鋼板表面に溶融しためっきの寄りが発生するという問題もあった。ここで電気を用いた加熱方法における寄りについて述べる。高周波加熱、通電加熱のいずれも、鋼板を電流が流れることで鋼板の抵抗発熱を利用した加熱方法である。 As described above, the techniques described in Patent Documents 1 to 3 described above are low productivity processes in which heating takes about 200 seconds or more. When rapid heating is performed by energization heating or the like in order to improve the productivity of hot stamping, there is a problem that a molten plating shift occurs on the steel sheet surface as described in Patent Document 4. Here, the shift in the heating method using electricity will be described. Both high-frequency heating and energization heating are heating methods that utilize the resistance heat generation of a steel sheet by passing a current through the steel sheet.
ところが、図1に示すように、鋼板1に電流2が流れると、磁場3が生じ、電流と磁界との相互作用で溶融Alに加わる力(ピンチ力)4が生じる。この力(ピンチ力)のために溶融した金属が中央移動して寄り(或いは垂れ)が生じる。加熱方法により電流の方向は様々に変わるため一概には言えず、鋼板の中央部が厚くなる場合や、逆に鋼板の端部が厚くなる場合がありうる。またピンチ力が加わらなくとも、ブランク材を縦置きにして加熱した場合、重力が働いてブランク下部のめっきが厚くなる場合もある。 However, as shown in FIG. 1, when a current 2 flows through the steel plate 1, a magnetic field 3 is generated, and a force (pinch force) 4 applied to the molten Al is generated by the interaction between the current and the magnetic field. Due to this force (pinch force), the melted metal moves to the center and shifts (or droops). Since the direction of the current varies depending on the heating method, it cannot be said unconditionally, and the central portion of the steel plate may be thick, or conversely, the end portion of the steel plate may be thick. Even if the pinch force is not applied, if the blank is heated in a vertical position, gravity may work and the plating at the bottom of the blank may become thick.
本発明者らの検討の結果によれば、この加熱時に生じるめっきの寄りを防止するためには、めっき付着量を減らせば良いことがわかっている。例えば、図2のAlめっき鋼板を加熱した際の寄り高さへの付着量、昇温速度の影響を示す図で明らかにしているように、Alめっき鋼板を使用して昇温速度を30℃/秒および100℃/秒で昇温温度900〜1200℃とした場合を比較すると、昇温速度を30℃/秒の場合ではめっき付着量が片面で50g/m2以下では、めっきの寄りが発生せずに平滑な表面となるが、それ以上のめっき付着量では、めっきの寄りが発生する。また、昇温速度を100℃/秒の場合ではめっき付着量が片面で47g/m2以下では、めっきの寄りが発生せずに平滑な表面となるが、それ以上のめっき付着量では、めっきの寄りが発生するという実験例が得られている。 According to the results of the study by the present inventors, it is known that the amount of plating adhesion may be reduced in order to prevent the deviation of the plating that occurs during heating. For example, as shown in the figure showing the influence of the amount of adhesion on the height when the Al-plated steel sheet is heated in FIG. 2 and the temperature rise rate, the temperature rise rate is 30 ° C. using the Al-plated steel sheet. When the temperature rising rate is 900 to 1200 ° C. at 100 ° C./second and 100 ° C./second, when the temperature rising rate is 30 ° C./second, the plating adhesion is less than 50 g / m 2 on one side. The surface becomes smooth without being generated, but when the amount of plating is larger than that, plating shift occurs. Further, when the rate of temperature increase is 100 ° C./second, if the amount of plating adhesion is 47 g / m 2 or less on one side, the surface becomes smooth without shifting of the plating. An experimental example has been obtained that the deviation occurs.
したがって、めっきの寄りを防止するためには、昇温速度を低く設定し融点に到達する前に合金化すれば良いが長時間の合金化時間が必要となり、生産性向上のためには現実的でない。また、めっきの寄りを防止するために、めっき付着量を減らすと良いが、十分な塗装後耐食性を確保することができないという問題がある。すなわち、生産性の向上と耐食性の確保とはトレードオフの関係にあるため、従来は、優れた耐食性と優れた生産性を兼ね備える急速加熱ホットスタンプ用めっき鋼板は得られていなかった。 Therefore, in order to prevent shifting of the plating, it is sufficient to set the heating rate low and alloy before reaching the melting point. However, a long alloying time is required, which is realistic for improving productivity. Not. Moreover, in order to prevent the shift | offset | difference of plating, although it is good to reduce the amount of plating adhesion, there exists a problem that sufficient corrosion resistance after coating cannot be ensured. That is, since the improvement in productivity and the securing of corrosion resistance are in a trade-off relationship, conventionally, a rapid heating hot stamping plated steel sheet having both excellent corrosion resistance and excellent productivity has not been obtained.
そこで、本発明者らは、優れた耐食性と優れた生産性を兼ね備える急速加熱ホットスタンプ用めっき鋼板を得るために鋭意検討を行った結果、めっきの寄りを抑制するためにはAlめっき層を表面までAl−Fe合金化させ融点を高めることが有効との知見を得た。優れた塗装後耐食性を得るためには、一定以上の付着量が必要となる。ところが一定以上の付着量を有するAlめっき鋼板をコイル状態でボックス焼鈍して合金化させるとめっきが剥離するとの現象が観察された。この剥離現象を回避するための適正な加熱条件(焼鈍条件)および鋼板成分を見出すことで本発明は完成された。 Therefore, as a result of intensive studies to obtain a plated steel sheet for rapid heating hot stamping that has both excellent corrosion resistance and excellent productivity, the present inventors have found that an Al plating layer is formed on the surface in order to suppress the deviation of plating. It was found that it was effective to increase the melting point by forming an Al—Fe alloy. In order to obtain excellent post-painting corrosion resistance, a certain amount of adhesion is required. However, it was observed that when an Al-plated steel sheet having a certain amount of adhesion was box-annealed and alloyed in a coil state, the plating peeled off. The present invention was completed by finding appropriate heating conditions (annealing conditions) and steel plate components to avoid this peeling phenomenon.
例えば、付着量が片面60g/m2以上のAlめっき鋼板のめっき層を合金化させるためには、温度を600℃以上に昇温させるか、あるいは600℃未満で数十時間加熱する必要がある。600℃以上に昇温する際には特に異常な現象は認められない。しかし、通常の連続AlめっきラインでAlめっき後このような高温まで昇温することは困難であるので、コイルをボックス焼鈍する方が容易である。ところが、コイルをボックス焼鈍する際に、幾つかの課題がある。1つは通常用いられているAlめっきでのAl−10%Siの融点は約600℃のため、融点近傍ではAlめっきが軟化して、コイルの鋼板同志が溶着する懸念がある。温度を低下させるとこの懸念は無くなるが、例えば520℃では72時間加熱しても表面まで合金化しないため、非常に長時間の加熱が必要となる。更に、窒素雰囲気や、窒素−水素の混合雰囲気中で加熱すると、Al部が剥離してしまう現象が生じた。 For example, in order to alloy a plated layer of an Al-plated steel sheet having an adhesion amount of 60 g / m 2 or more on one side, it is necessary to raise the temperature to 600 ° C. or higher, or to heat at less than 600 ° C. for several tens of hours. . No unusual phenomenon is observed when the temperature is raised to 600 ° C. or higher. However, since it is difficult to raise the temperature to such a high temperature after Al plating in a normal continuous Al plating line, it is easier to box anneal the coil. However, there are some problems when the coil is subjected to box annealing. One is that Al-10% Si has a melting point of about 600 ° C. in the Al plating that is usually used, so there is a concern that the Al plating softens near the melting point and the steel plates of the coils are welded. When the temperature is lowered, this concern disappears. However, for example, at 520 ° C., even when heated for 72 hours, the surface is not alloyed. Furthermore, when heated in a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen, a phenomenon that the Al portion peeled occurred.
そこで、ボックス焼鈍(BAF焼鈍)でめっき層が剥離する原因について調査したところ、めっき層内部にAlNが生成して、これがめっき剥離の原因となっていることがわかった。その原因は次の通りと推察される。 Then, when the cause which a plating layer peeled by box annealing (BAF annealing) was investigated, it turned out that AlN produces | generates inside a plating layer and this causes a plating peeling. The reason is presumed as follows.
図3は、Alめっき鋼板をN2雰囲気中でボックス焼鈍した場合に剥離の原因となるAlNがめっき層に生成する状態を示す図である。 FIG. 3 is a diagram illustrating a state in which AlN that causes peeling is generated in the plating layer when the Al-plated steel sheet is subjected to box annealing in an N 2 atmosphere.
加熱前の溶融Alめっき鋼板は、図3(a)に示すように、溶融Alめっきと鋼板1母材との界面にFe−Al合金層7が形成されていて、Siを含有させたAlめっきではめっき層中にSi8が存在するめっき層6となっている。このAlめっき鋼板をN2雰囲気中で焼鈍すると、(b)に示すように合金層とめっき層の界面にAlN9が生成し、時間の経過と共に(c)に示すようにAlN9が成長して行き、そして、(d)に示すように厚く成長することで、めっきの剥離を引き起こす。さらに時間の経過が進むと、(e)に示すようにめっきは全てAlN9となり、黒化してしまい、これにホットブレスを実施すると黒化したAlNが破砕して耐食性の劣化を引き起こす。 As shown in FIG. 3 (a), the molten Al-plated steel sheet before heating has an Fe-Al alloy layer 7 formed at the interface between the molten Al plating and the steel sheet 1 base material, and contains Al. Then, it is the plating layer 6 in which Si8 exists in the plating layer. When this Al plated steel sheet is annealed in an N 2 atmosphere, AlN9 is formed at the interface between the alloy layer and the plated layer as shown in (b), and AlN9 grows as time passes (c). And, as shown in (d), it grows thick and causes peeling of the plating. As time elapses further, as shown in (e), all the plating becomes AlN9 and becomes black. When hot breathing is performed on this, the blackened AlN is crushed to cause deterioration of corrosion resistance.
この現象を防止するために、ボックス焼鈍の焼鈍雰囲気について鋭意研究し、焼鈍雰囲気としては、焼鈍雰囲気中に酸素を3体積%以上含有させることが重要であることを見出した。このような雰囲気では、酸素が存在するために、図4(a)に示すように、めっき層表面にはアルミナ11が生成して、(b)に示すように焼鈍中にN2がめっき層に進入することを抑制するので、めっき剥離の原因となるAlNを生成しないで合金化が達成されるものと推察される。酸素3体積%未満の焼鈍雰囲気では、アルミナの生成が不十分となり、N2がめっき層に進入することを抑制できず、めっき剥離の原因となるAlNが生成する。このような酸素を3体積%以上含有する雰囲気としては、酸素を約21体積%含有する大気を雰囲気として使用するのが簡便である。酸素含有量の上限は特に限定するものではないが、雰囲気中に酸素含有量をあまり多くしても、効果が飽和するので、上限を30体積%とすることが好ましい。 In order to prevent this phenomenon, intensive research was conducted on the annealing atmosphere of box annealing, and it was found that it is important to contain 3% by volume or more of oxygen in the annealing atmosphere as the annealing atmosphere. In such an atmosphere, since oxygen is present, alumina 11 is formed on the surface of the plating layer as shown in FIG. 4A, and N 2 is plated during annealing as shown in FIG. 4B. Therefore, it is presumed that alloying can be achieved without producing AlN that causes plating peeling. In an annealing atmosphere of less than 3% by volume of oxygen, generation of alumina becomes insufficient, and N 2 cannot be prevented from entering the plating layer, and AlN that causes plating peeling is generated. As an atmosphere containing 3% by volume or more of oxygen, it is convenient to use air containing about 21% by volume of oxygen as the atmosphere. The upper limit of the oxygen content is not particularly limited, but even if the oxygen content is excessively increased in the atmosphere, the effect is saturated, so the upper limit is preferably set to 30% by volume.
ついで、Alめっき鋼板を加熱合金化(Fe−Al合金化)するための温度条件について説明する。 Next, temperature conditions for heating alloying (Fe—Al alloying) of the Al-plated steel sheet will be described.
特開平09−195021号公報に鋼中に固溶Nを残存させた鋼成分において、鋼板の固溶Nと合金層から供給されるAlが鋼板−合金層界面にAlNを生成して570℃程度で焼鈍した時のFe−Al合金化を抑制する事例が示されている。しかし、焼鈍温度が580℃以上となると、AlNはFe−Al合金化を抑制できなくなることも示されている。つまり、この温度域では、Al−N、Al−Fe反応が競争し、580℃以上ではAl−Fe反応が優勢となり、AlN皮膜が存在していてもAl−Fe合金化が可能となるものと考えられる。 In Japanese Patent Laid-Open No. 09-195021, in a steel component in which solid solution N remains in steel, Al supplied from the solid solution N of the steel plate and the alloy layer generates AlN at the steel plate-alloy layer interface to about 570 ° C. The example which suppresses Fe-Al alloying at the time of annealing with is shown. However, it has also been shown that when the annealing temperature is 580 ° C. or higher, AlN cannot suppress Fe—Al alloying. That is, in this temperature range, Al—N and Al—Fe reactions compete, and at 580 ° C. or higher, the Al—Fe reaction becomes dominant, and even if an AlN film is present, Al—Fe alloying is possible. Conceivable.
したがって、本発明は固溶Nを残存させる鋼成分系ではないものの、大気中のNと合金層中のAlが反応してAlめっき−合金層界面にAlNが生成しており、このAlNが生成してもAl−Fe合金化反応が進めるためには600℃以上の焼鈍温度をとることが有効と推察して焼鈍試験を実施した。焼鈍試験では、図5に示すように、Alめっき鋼板(試験材)11を重ね合わせて、大気雰囲気中で、600℃で8時間及び650℃で5時間の焼鈍条件で焼鈍し、鋼板の併せ部を観察する焼鈍試験を実施した。焼鈍後の鋼板の断面写真を図6に示した。図6(a)は600℃で8時間の焼鈍板の断面写真であり、図6(b)は650℃で5時間の焼鈍板の断面写真である。焼鈍試験の結果は、図6に示すように、600℃以上の焼鈍温度で、焼鈍を実施すると、Al−Fe反応が進行して、健全に合金化が達成されていた。ただし、表面にやや着色があり、AlNが生成していることが認められた。そこで、更にこのAlNの発生を抑制することについて研究し、特定の鋼成分が有効であることを見出した。 Accordingly, although the present invention is not a steel component system in which solid solution N remains, Al in the atmosphere reacts with Al in the alloy layer to produce AlN at the Al plating-alloy layer interface. Even if the Al—Fe alloying reaction was advanced, it was assumed that it was effective to take an annealing temperature of 600 ° C. or higher, and an annealing test was conducted. In the annealing test, as shown in FIG. 5, the Al-plated steel sheet (test material) 11 is superposed and annealed in an air atmosphere at 600 ° C. for 8 hours and at 650 ° C. for 5 hours. An annealing test was performed to observe the part. A cross-sectional photograph of the steel sheet after annealing is shown in FIG. 6A is a cross-sectional photograph of the annealed plate at 600 ° C. for 8 hours, and FIG. 6B is a cross-sectional photograph of the annealed plate at 650 ° C. for 5 hours. As a result of the annealing test, as shown in FIG. 6, when annealing was performed at an annealing temperature of 600 ° C. or higher, the Al—Fe reaction progressed and the alloying was soundly achieved. However, it was recognized that the surface was slightly colored and AlN was generated. Therefore, further study was made to suppress the generation of AlN, and it was found that a specific steel component was effective.
すなわち、AlNの発生を抑制できる鋼成分としては、Crが特に有効で、めっき層と鋼板母材との界面に生成するめっき層剥離の原因となるAlNの生成を抑制する効果がある。そして、Cr:質量0.4%超の添加からAlNの生成を抑制する効果が発揮されることを見出した。また、MoもCrほどではないが、同様にAlNの生成を抑制する効果があり、Mo:0.005質量%以上でAlNの生成を抑制する効果が発揮されていた。MoとCrとを同時に添加する場合には、Cr:0.2質量%以上でAlNの生成を抑制する効果が認められた。 That is, as a steel component capable of suppressing the generation of AlN, Cr is particularly effective, and has an effect of suppressing the generation of AlN that causes the peeling of the plating layer generated at the interface between the plating layer and the steel plate base material. And it discovered that the effect which suppresses the production | generation of AlN from the addition of Cr: mass more than 0.4% is exhibited. Moreover, although Mo is not as much as Cr, it has the effect which suppresses the production | generation of AlN similarly, and the effect which suppresses the production | generation of AlN by Mo: 0.005 mass% or more was exhibited. When Mo and Cr were added simultaneously, the effect of suppressing the formation of AlN was observed with Cr: 0.2% by mass or more.
したがって、本発明では鋼板の成分設計として、AlN生成を抑制するCrまたはCrとMoを添加することを限定した。 Therefore, in the present invention, the addition of Cr or Cr and Mo that suppresses the formation of AlN is limited as a component design of the steel sheet.
なお、焼鈍温度が、Alめっきの融点(600℃)を超える温度で焼鈍すると、めっき層が溶融してめっき鋼板が溶着することが懸念されたが、めっき鋼板の溶着は認められなかった。 In addition, when annealing was performed at a temperature exceeding the melting point (600 ° C.) of Al plating, there was a concern that the plated layer melted and the plated steel sheet was welded, but no welding of the plated steel sheet was observed.
本発明のAl−Fe合金層は、母材の鋼板中のFeがAlめっき中に拡散して形成されるものであるから、めっき層の鋼板側ではFe濃度(99〜85質量%)が高く、めっき層の表面側に向かってFe濃度(42〜50質量%)が低下するFe濃度分布を有している。Al−Fe合金層中のFe含有量は全体で、42〜88質量%とすることが好ましい。なお、好ましくは、42〜60%である。Fe含有量が42%未満であると、融点の高い合金化めっき層が得られず、一方、88質量%を超えるとFe成分が多くなりすぎて耐食性に優れた合金化めっき層が得られないからである。 Since the Al—Fe alloy layer of the present invention is formed by diffusion of Fe in the base steel plate during Al plating, the Fe concentration (99 to 85 mass%) is high on the steel plate side of the plating layer. The Fe concentration distribution is such that the Fe concentration (42 to 50% by mass) decreases toward the surface side of the plating layer. The total Fe content in the Al—Fe alloy layer is preferably 42 to 88% by mass. In addition, Preferably, it is 42 to 60%. If the Fe content is less than 42%, an alloyed plating layer having a high melting point cannot be obtained. On the other hand, if the Fe content exceeds 88% by mass, the Fe component is excessive and an alloyed plating layer having excellent corrosion resistance cannot be obtained. Because.
また、合金化めっき層の表面に生成するAlNは少ないほうが理想的であるが、窒素を含有する雰囲気で焼鈍する以上、AlNの生成は避けることができない。100%水素中で焼鈍すると、鋼板中に水素が取り込まれ、ホットスタンプ後の遅れ破壊特性が低下するため好ましくない。従ってAlNを完全に回避する手段は現段階では工業的に得られない。本発明においては、Al−Fe合金層表面に0.01〜1g/m2のAlNは生成する。しかし、この範囲のAlNの生成は本発明の効果を損なうものでない。 Further, although it is ideal that less AlN is generated on the surface of the alloyed plating layer, generation of AlN cannot be avoided as long as annealing is performed in an atmosphere containing nitrogen. Annealing in 100% hydrogen is not preferable because hydrogen is taken into the steel sheet and delayed fracture characteristics after hot stamping are reduced. Therefore, means for completely avoiding AlN cannot be obtained industrially at this stage. In the present invention, 0.01 to 1 g / m 2 of AlN is generated on the surface of the Al—Fe alloy layer. However, the production of AlN in this range does not impair the effects of the present invention.
以下、上述したような被覆層を有する急速加熱ホットスタンプ用めっき鋼板の製造に用いられる本発明に係るAlめっき鋼板の構成について詳細に説明する。
(鋼板について)
ホットスタンプが金型によるプレスと焼入を同時に行うものであることから、本発明に係る急速加熱ホットスタンプ用めっき鋼板としては、焼入されやすい成分である必要がある。また、Alめっき鋼板を焼鈍する時にAlNの生成を抑制する成分を含有することが重要である。これらの観点から鋼板の成分設計をした。
Hereinafter, the configuration of the Al-plated steel sheet according to the present invention used for the production of the rapidly heated hot stamped plated steel sheet having the coating layer as described above will be described in detail.
(About steel plate)
Since hot stamping is performed simultaneously with pressing and quenching with a mold, the plated steel sheet for rapid heating hot stamping according to the present invention needs to be a component that is easily quenched. Moreover, it is important to contain the component which suppresses the production | generation of AlN when annealing an Al plating steel plate. The components of the steel sheet were designed from these viewpoints.
以下本発明での鋼板成分を限定した理由について説明する。なお、成分についての%は質量%を意味する。 The reason why the steel plate components in the present invention are limited will be described below. In addition,% about a component means the mass%.
C:0.1〜0.5%、
本発明は成型後に1000MPa以上の高強度を有する製品とするものであり、ホットスタンプ後に急冷してマルテンサイトを主体とする組織に変態させることが要求される。そのためには焼入性の向上という観点からC量0.1%が必要である。一方、C量が多過ぎると鋼板の靭性の低下が著しくなるため、加工性を低下させる。そのため、上限は0.5%以下である。
C: 0.1 to 0.5%
The present invention is a product having a high strength of 1000 MPa or more after molding, and is required to be rapidly cooled after hot stamping and transformed into a structure mainly composed of martensite. For this purpose, a C content of 0.1% is necessary from the viewpoint of improving hardenability. On the other hand, if the amount of C is too large, the toughness of the steel sheet is significantly reduced, so that workability is reduced. Therefore, the upper limit is 0.5% or less.
Si:0.01〜0.7%、
SiはめっきのAlとFe間の反応を促進して鋼板の耐熱性を向上させる効果を有する。しかし、Siは再結晶焼鈍中に安定な酸化皮膜を鋼板表面に形成し、アルミめっき性を阻害する元素でもある。この意味からSiの上限を0.7%とする。しかし、0.01%未満とすると疲労特性が劣るため好ましくない。このため、Siは0.01〜0.7%とした。好ましくは0.2〜0.6%である。
Si: 0.01 to 0.7%,
Si has the effect of promoting the reaction between Al and Fe in the plating to improve the heat resistance of the steel sheet. However, Si is also an element that forms a stable oxide film on the surface of the steel sheet during recrystallization annealing and inhibits aluminum plating properties. In this sense, the upper limit of Si is set to 0.7%. However, if it is less than 0.01%, the fatigue properties are inferior. For this reason, Si was made into 0.01 to 0.7%. Preferably it is 0.2 to 0.6%.
Mn:0.5〜2.5%、
Mnは、鋼板の焼入れ性を高める元素としてよく知られている。また、不可避的に混入するSに起因する熱間脆性を防ぐために必要な元素でもある。この理由から0.5%以上の添加が必要である。また、Mnはアルミめっき後の耐熱性も向上させる。しかし、2.5%を超えてMnを添加すると焼入れ後の衝撃特性が低下するためここを上限とする。
Mn: 0.5 to 2.5%
Mn is well known as an element that enhances the hardenability of the steel sheet. It is also an element necessary for preventing hot brittleness due to S unavoidably mixed. For this reason, addition of 0.5% or more is necessary. Mn also improves heat resistance after aluminum plating. However, if Mn is added in excess of 2.5%, the impact properties after quenching are lowered, so this is the upper limit.
Cr:0.4%超〜3%(請求項1)、
Crは本発明においては重要な元素であり、Alめっき鋼板のめっきの合金化のために、ボックス焼鈍を行う際、めっき層と鋼板母材との界面に生成するめっき層剥離の原因となるAlNの生成を抑制する効果があり、また、焼入れ性の観点から有用な元素である。それらの効果を得るためにはCr0.4%超必要である。しかし、3%を超えて添加しても効果は飽和し、またコストも上昇するので上限を3%としたが、好ましくは2%である。CrのAlN生成抑制作用について、完全に判明している訳ではないが、先述したようにAlNはAlめっきと合金層の界面に生成する。窒素は雰囲気に由来するもので、AlはAlめっき層に多量に存在するため、本来AlNはAlめっき層表面に生成してもよいが、実際にはAlめっき層と合金層の界面に生成する。これは合金層がAlN生成の触媒作用を有しているものと推察しており、鋼中にCrを添加することで合金層中にもCrが含有され、この触媒作用を弱めているものと考えている。
Cr: more than 0.4% to 3% (Claim 1),
Cr is an important element in the present invention, and AlN causes peeling of the plating layer generated at the interface between the plating layer and the steel plate base material when box annealing is performed for alloying the plating of the Al-plated steel plate. It is an element that has the effect of suppressing the formation of and is useful from the viewpoint of hardenability. In order to obtain these effects, Cr needs to exceed 0.4%. However, even if added over 3%, the effect is saturated and the cost increases, so the upper limit was made 3%, but preferably 2%. Although the AlN formation suppressing action of Cr is not completely known, as described above, AlN is generated at the interface between the Al plating and the alloy layer. Nitrogen originates from the atmosphere, and since Al is present in a large amount in the Al plating layer, AlN may be originally generated on the surface of the Al plating layer, but in reality, it is generated at the interface between the Al plating layer and the alloy layer. . This is presumed that the alloy layer has a catalytic action of generating AlN, and Cr is contained in the alloy layer by adding Cr to the steel, and this catalytic action is weakened. thinking.
Mo:0.005〜0.5%、Cr:0.2〜3%(請求項2)、
MoもCrと同様に本発明においては重要な元素であり、Alめっき鋼板のめっきの合金化のために、ボックス焼鈍を行う際、めっき層と鋼板母材との界面に生成するめっき層剥離の原因となるAlNの生成を抑制する効果があり、また、焼入れ性の観点から有用な元素である。それらの効果を得るためにはMo0.005%必要である。しかし、0.5%を超えて添加しても効果は飽和し、またコストも上昇するので上限を0.5%とした。
Mo: 0.005 to 0.5%, Cr: 0.2 to 3% (Claim 2),
Mo is also an important element in the present invention like Cr, and when the box annealing is performed for alloying the plating of the Al-plated steel sheet, the plating layer peeling generated at the interface between the plating layer and the steel sheet base material It has the effect of suppressing the generation of AlN causing it, and is a useful element from the viewpoint of hardenability. To obtain these effects, Mo 0.005% is necessary. However, even if added over 0.5%, the effect is saturated and the cost increases, so the upper limit was made 0.5%.
MoはCrと同様な効果を奏する元素であるので、Moを添加する場合にはCrの添加量の下限を低下させることができる。したがって、Moを添加する場合のCr量は0.2〜3%の範囲とすることができる。 Since Mo is an element having the same effect as Cr, when adding Mo, the lower limit of the amount of Cr added can be reduced. Therefore, the Cr amount in the case of adding Mo can be in the range of 0.2 to 3%.
P:0.001〜0.1%、
Pは不可避的に含有される元素であるが、固溶強化元素であり、比較的安価に鋼板の強度を上昇させることができるが、経済的な精錬限界から下限を0.001%とした。好ましくは0.005%である。ただし、添加量がむやみに増加すると高強度材での靭性を低下させるなどの悪影響が出るため上限を0.1%とした。
P: 0.001 to 0.1%,
P is an element that is unavoidably contained, but is a solid solution strengthening element and can increase the strength of the steel sheet relatively inexpensively. However, the lower limit is set to 0.001% from the economical refining limit. Preferably it is 0.005%. However, if the amount added is increased excessively, adverse effects such as lowering the toughness of the high-strength material will occur, so the upper limit was made 0.1%.
S:0.001〜0.1%、
Sは不可避的に含まれる元素であり、MnSとして鋼中の介在物になり、MnSが多いと破壊の起点となり、延性、靭性を阻害し、加工性劣化の要因となるため、低いほど望ましく、上限を0.1%以下としたが、Sを低下させるには製造コストから望ましくないので、下限を0.001%とした。好ましくは0.005%である。
S: 0.001 to 0.1%,
S is an element inevitably contained, and becomes an inclusion in the steel as MnS, and if MnS is large, it becomes a starting point of fracture, impairs ductility and toughness, and causes deterioration of workability. Although the upper limit was made 0.1% or less, it is undesirable from the manufacturing cost to lower S, so the lower limit was made 0.001%. Preferably it is 0.005%.
Al:0.1%以下、
Alは脱酸剤として鋼中に含有される成分であるが、Alはめっき性阻害元素であるため、上限を0.1%とした。好ましくは0.05%である。そして、下限は特に限定するものではないが、経済的な精錬限界から下限を0.001%とすることが好ましい。さらに好ましくは0.005%である。
Al: 0.1% or less,
Al is a component contained in steel as a deoxidizer, but since Al is a plating-inhibiting element, the upper limit was made 0.1%. Preferably it is 0.05%. And although a minimum is not specifically limited, it is preferable to make a minimum into 0.001% from an economical refining limit. More preferably, it is 0.005%.
N:0.01%以下
Nは不可避的に含まれる元素であり、特性の安定化の観点からは固定することが望ましく、Ti、Nb、Al等にて固定可能であるが、N量が増加すると固定用に添加する元素が多量となり、コストアップを招くことになるため、その上限を0.01%とした。
N: 0.01% or less N is an element inevitably contained, and is preferably fixed from the viewpoint of stabilization of characteristics, and can be fixed with Ti, Nb, Al, etc., but the amount of N increases. Then, the amount of elements to be added for fixing becomes large, leading to an increase in cost, so the upper limit was made 0.01%.
次に、鋼中に選択的に含有させることができる成分について説明する。 Next, components that can be selectively contained in steel will be described.
B:0.0001〜0.01%
Bも焼入れ性の観点から有用な元素であり、0.0001%以上の添加が必要である。但し、0.005%を超えて添加しても効果は飽和し、また鋳造欠陥や熱間圧延時の割れを生じさせるなど製造性を低下させるので、上限を0.01%とした。好ましくは、0.0003〜0.005%である。
B: 0.0001 to 0.01%
B is also a useful element from the viewpoint of hardenability, and 0.0001% or more must be added. However, even if added over 0.005%, the effect is saturated and manufacturability is reduced by causing casting defects and cracking during hot rolling, so the upper limit was made 0.01%. Preferably, it is 0.0003 to 0.005%.
W:0.01〜3%
Wは焼入れ性の観点から有用な元素であり、0.1%以上にて効果を発揮する。但し、3%を超えて添加しても効果は飽和し、またコストも上昇するので上限を3%とした。
W: 0.01 to 3%
W is a useful element from the viewpoint of hardenability and exhibits an effect at 0.1% or more. However, even if added over 3%, the effect is saturated and the cost increases, so the upper limit was made 3%.
V:0.01〜2%
Vは焼入れ性の観点から有用な元素であり、0.1%以上にて効果を発揮する。但し、2%を超えて添加しても効果は飽和し、またコストも上昇するので上限を2%とした。
V: 0.01-2%
V is a useful element from the viewpoint of hardenability and exhibits an effect at 0.1% or more. However, even if added over 2%, the effect is saturated and the cost increases, so the upper limit was made 2%.
Ti:0.005〜0.5%
TiはN固定の観点から添加することができ、質量%にてNの約3.4倍添加することが必要であるが、Nは低減しても10ppm程度であるので、下限を0.005%とした。またTiを過剰に添加しても焼入れ性を低下させ、また強度も低下させるためその上限を0.5%とした。
Ti: 0.005 to 0.5%
Ti can be added from the viewpoint of N fixation, and it is necessary to add about 3.4 times as much as N in mass%. However, since N is about 10 ppm even if it is reduced, the lower limit is set to 0.005. %. Further, even if Ti is added excessively, the hardenability is lowered and the strength is also lowered, so the upper limit was made 0.5%.
Nb:0.01〜1%
NbはN固定の観点から添加することができ、質量%にてNの約6.6倍添加することが必要であるが、Nは低減しても10ppm程度であるので、下限を0.01%とした。またNbを過剰に添加しても焼入れ性を低下させ、また強度も低下させるためその上限を0.5%とした。
Nb: 0.01 to 1%
Nb can be added from the viewpoint of N fixation, and it is necessary to add about 6.6 times as much as N in mass%. However, since N is about 10 ppm even if it is reduced, the lower limit is set to 0.01. %. Moreover, even if Nb is added excessively, the hardenability is lowered and the strength is also lowered, so the upper limit was made 0.5%.
また鋼板中の成分として、他にNi、Cu、Sn、Sb等を含有しても本発明の効果を阻害しない。また、Niは焼入れ性に加え、耐衝撃特性改善に繋がる低温靭性の観点で有用な元素であり、0.1%以上にて効果を発揮する。但し、5%を超えて添加しても効果は飽和し、またコストも上昇するので0.01〜5%の範囲で添加しても良い。Cuも焼入れ性に加え、靭性の観点で有用な元素であり、0.1%以上にて効果を発揮する。但し、3%を超えて添加しても効果は飽和し、またコストを上昇させるばかりでなく鋳片性状の劣化や熱間圧延時の割れや疵発生を生じさせるため0.01〜3%の範囲で添加しても良い。さらに、Sn、Sbはいずれもめっきの濡れ性や密着性を向上させるのに有効な元素であり、0.005%〜0.1%で添加できる。いずれも0.005%未満では効果が認められず、0.1%を超えて添加すると製造時の疵が発生しやすくなったり、また靭性の低下を引き起こしたりするため上限を0.1%とした。 Moreover, even if it contains Ni, Cu, Sn, Sb, etc. in addition as a component in a steel plate, the effect of this invention is not inhibited. Ni is a useful element from the viewpoint of low temperature toughness leading to improvement in impact resistance in addition to hardenability, and exhibits an effect at 0.1% or more. However, even if added over 5%, the effect is saturated and the cost increases, so it may be added in the range of 0.01 to 5%. Cu is an element useful from the viewpoint of toughness in addition to hardenability, and exhibits an effect at 0.1% or more. However, even if added over 3%, the effect is saturated, and not only increases the cost, but also causes deterioration of the slab properties and generation of cracks and flaws during hot rolling. You may add in the range. Furthermore, both Sn and Sb are effective elements for improving the wettability and adhesion of plating, and can be added at 0.005% to 0.1%. In any case, if less than 0.005%, the effect is not recognized, and if added over 0.1%, wrinkles at the time of production are likely to occur or the toughness is lowered, so the upper limit is 0.1%. did.
また、その他の成分については特に規定しないが、Zr、As等の元素がスクラップから混入する場合があるが、通常の範囲であれば本発明鋼の特性には影響しない。
(Alめっきについて)
本発明に係る急速加熱ホットスタンプ用めっき鋼板は、鋼板表面にAlめっきが施されたAlめっき鋼板において、Alめっき層を表面まで合金化処理することにより製造されるが、本発明における鋼板へのAlめっきの方法については特に限定するものでなく、溶融めっき法を初めとして電気めっき法、真空蒸着法、クラッド法等が可能であるが、溶融めっきが好ましい。
Further, other components are not particularly defined, but elements such as Zr and As may be mixed from scrap, but within the normal range, the characteristics of the steel of the present invention are not affected.
(About Al plating)
The rapid heating hot stamped plated steel sheet according to the present invention is manufactured by alloying the Al plating layer up to the surface in the Al plated steel sheet with the Al plating applied to the steel sheet surface. The method of Al plating is not particularly limited, and electroplating, vacuum deposition, cladding, and the like including hot dipping are possible, but hot dipping is preferable.
現在工業的に最も普及しているのは溶融めっき法であり、Al単独のめっき浴を用いることができるが、通常、めっき浴として、Alに3質量%〜15質量%のSiを含有するものを使用することが好ましい。SiはAlめっき時の合金層成長を抑制する働きがある。ホットスタンプ用途に限れば合金層成長を抑制する必然性は小さいが、溶融めっき法においては、1つの浴で種々の用途の製品を製造するため、Alめっきの加工性を要求される用途においては合金層成長を抑制する必要がある。Si量が3質量%未満においては、合金層が成長するため、Alめっき鋼板としての加工性が低下する。一方、Si量が多すぎるとめっき層中に粗大結晶として晶出し、耐食性やめっきの加工性を阻害する。このため15%質量以下が好ましい。 Currently, the most widely used industrially is the hot dipping method, and a plating bath of Al alone can be used. Usually, the plating bath contains 3% by mass to 15% by mass of Si. Is preferably used. Si has a function of suppressing alloy layer growth during Al plating. In the hot stamping application, the necessity for suppressing the growth of the alloy layer is small. However, in the hot dipping process, products for various uses are manufactured in one bath, and therefore, in applications that require the workability of Al plating. It is necessary to suppress layer growth. When the amount of Si is less than 3% by mass, the alloy layer grows, so that the workability as an Al-plated steel sheet is lowered. On the other hand, if the amount of Si is too large, it will crystallize out as coarse crystals in the plating layer, impairing corrosion resistance and plating workability. For this reason, 15% or less is preferable.
これに不可避的不純物として鋼板から溶出したFe等が混入している。これ以外の添加元素として、Mn、Cr、Mg、Ti、Zn、Sb、Sn、Cu、Ni、Co、In、Bi、Mo、ミッシュメタル等があり得るが、めっき層がAlを主体とする限り、適用可能である。特に耐食性向上に効果のある元素がMn、Cr、Mo、Mgであり、これらの元素を少量添加することもできる。 Fe and the like eluted from the steel sheet are mixed in as unavoidable impurities. Other additive elements may be Mn, Cr, Mg, Ti, Zn, Sb, Sn, Cu, Ni, Co, In, Bi, Mo, Misch metal, etc., as long as the plating layer is mainly Al. Applicable. Elements that are particularly effective in improving corrosion resistance are Mn, Cr, Mo, and Mg, and these elements can be added in a small amount.
Mn:0.05〜1%、Mg:0.05〜1%、
これらの元素は耐食性向上に有効な元素で、それぞれ0.05%以上の合金層に添加されることでその効果を奏する。しかしAl浴へのMnの過剰な添加は浴温増大、ドロス量の増大となり操業性が低下する。Mgの過剰な添加もAl浴表面の酸化膜を厚くし、めっき外観が低下する。このためそれぞれ上限を1%とする。
Mn: 0.05 to 1%, Mg: 0.05 to 1%,
These elements are effective elements for improving the corrosion resistance, and exert their effects when added to an alloy layer of 0.05% or more. However, excessive addition of Mn to the Al bath increases the bath temperature and the dross amount, resulting in a decrease in operability. Excessive addition of Mg also increases the thickness of the oxide film on the surface of the Al bath and degrades the plating appearance. For this reason, the upper limit is set to 1%.
Cr:0.05〜0.5%、Mo:0.05〜0.5%、
これらの元素も耐食性を向上させる元素であり、それぞれ0.05%以上で有効となる。しかしこれら元素はAlへの溶解度が小さいので、それぞれ上限を0.5%とする。
Cr: 0.05-0.5%, Mo: 0.05-0.5%,
These elements are also elements that improve the corrosion resistance, and are effective at 0.05% or more, respectively. However, since these elements have low solubility in Al, the upper limit is 0.5%.
また、本発明において、Alめっきのめっき前処理、後処理等については特に限定するものではない。めっき前処理としてNi、Cu、Cr、Feプレめっき等もありうるが、これも適用可能である。また、めっき後処理としては一次防錆、潤滑性を目的としてクロメート処理、樹脂被覆処理等を施してもよい。ただし、クロメート処理については、近年の6価クロム規制を考慮すると、電解クロメート等の3価の処理皮膜が好ましい。その他、無機系のクロメート以外の後処理も適用可能である。潤滑性を付与するため、アルミナ、シリカ、MoS2等を用いて予め表面処理することも可能である。 Moreover, in this invention, it does not specifically limit about the plating pre-processing and post-processing of Al plating. Ni, Cu, Cr, Fe pre-plating and the like may be used as the plating pretreatment, but this is also applicable. Further, as a post-plating treatment, chromate treatment, resin coating treatment, or the like may be performed for the purpose of primary rust prevention and lubricity. However, with regard to the chromate treatment, a trivalent treatment film such as electrolytic chromate is preferable in consideration of recent hexavalent chromium regulations. In addition, post-treatment other than inorganic chromate is also applicable. In order to impart lubricity, it is also possible to perform surface treatment in advance using alumina, silica, MoS 2 or the like.
本発明に係るめっき鋼板は、表面にAlめっきを施した鋼板を焼鈍することにより、めっき層と母材鋼板の界面に合金化したAl−Fe合金層を有する。このときAl−Fe合金層の厚みは10〜45μmとする。Al−Fe合金層の厚みが10μm以上であれば、加熱工程後に、急速加熱ホットスタンプ用めっき鋼板として十分な塗装後耐食性を確保できるため好ましい。厚みが大きいほど耐食性上は優位に働くが、一方、Alめっき層の厚みとFe−Al合金層の厚みの和が大きいほど、被覆層がホットスタンプ加工時に欠落し易くなるため、被覆層の厚みは45μm以下であることが好ましい。合金層の厚みは、焼鈍温度、焼鈍時間を調整することによって制御することができる。 The plated steel sheet according to the present invention has an Al—Fe alloy layer alloyed at the interface between the plating layer and the base steel sheet by annealing the steel sheet with Al plating on the surface. At this time, the thickness of the Al—Fe alloy layer is 10 to 45 μm. If the thickness of the Al—Fe alloy layer is 10 μm or more, it is preferable since sufficient post-coating corrosion resistance can be secured as a plated steel sheet for rapid heating hot stamping after the heating step. The larger the thickness, the better the corrosion resistance. On the other hand, the larger the sum of the thickness of the Al plating layer and the thickness of the Fe-Al alloy layer, the more easily the coating layer is lost during hot stamping. Is preferably 45 μm or less. The thickness of the alloy layer can be controlled by adjusting the annealing temperature and the annealing time.
また、Al−Fe合金層表面には、合金化のためのボックス焼鈍を施すため、必然的にAlNが0.01g/m2以上生成するが、加熱条件および鋼成分を特定することで1g/m2以下に抑制することができる。AlNは存在しないことが好ましいが、1g/m2以下であれば耐食性、スポット溶接性等の特性への影響が殆どないので1g/m2以下とした。このときのAlNはFe−Alの表面に生成しており、そのAl−Fe合金層表面のAlN量の測定は簡便には質量法による。すなわち鋼板を20%苛性ソーダに浸漬し、Fe−Alの表面を20g/m2溶解させる。このときAlNは溶解しないため、沈殿した粉末の質量を測定することでAlN量を測定できる。この粉末には厳密にはAl2O3を含有されているが、BAF後のFe−Al表面はAl2O3に比べてAlNの量が多いため、概ねの量はこの方法で知ることができる。より厳密に分析するには、こうして得られた粉末を酸で溶解してICP等でN量を求めるとよい。 In addition, in order to perform box annealing for alloying on the surface of the Al—Fe alloy layer, AlN is inevitably produced in an amount of 0.01 g / m 2 or more, but by specifying the heating conditions and the steel components, 1 g / It can be suppressed to m 2 or less. AlN is preferably not present, but if it is 1 g / m 2 or less, there is almost no influence on properties such as corrosion resistance and spot weldability, so it was 1 g / m 2 or less. AlN at this time is generated on the surface of Fe—Al, and the measurement of the amount of AlN on the surface of the Al—Fe alloy layer is simply performed by a mass method. That is, the steel sheet is immersed in 20% caustic soda to dissolve the surface of Fe—Al at 20 g / m 2 . Since AlN does not dissolve at this time, the amount of AlN can be measured by measuring the mass of the precipitated powder. Strictly speaking, this powder contains Al 2 O 3 , but since the Fe—Al surface after BAF has a larger amount of AlN than Al 2 O 3 , the approximate amount can be known by this method. it can. In order to perform a more rigorous analysis, it is advisable to dissolve the powder obtained in this way with an acid and determine the N content by ICP or the like.
以上、本発明に係る急速加熱ホットスタンプ用めっき鋼板の構成について詳細に説明したが、続いて、このような構成を有する本発明に係る急速加熱ホットスタンプ用めっき鋼板の製造方法について詳細に説明する。 As mentioned above, although the structure of the galvanized steel sheet for rapid heating hot stamps concerning this invention was demonstrated in detail, continually, the manufacturing method of the galvanized steel sheet for rapid heating hot stamps concerning this invention which has such a structure is demonstrated in detail. .
本発明に係る急速加熱ホットスタンプ用めっき鋼板は、鋼成分として、上述した成分の鋼に付着量が片面当り30〜100g/m2となるようにAlめっきが施されたAlめっき鋼板を、50℃/時間〜500℃/時間の昇温速度で600℃〜800℃まで昇温した後に、50℃/時間〜500℃/時間の冷却速度で冷却する合金化処理を行うことにより製造する。この合金化処理により、Alめっき層が母材中のFeと合金化して、Al−Fe合金層とする。 The rapid heating hot stamped plated steel sheet according to the present invention is an Al plated steel sheet obtained by applying Al plating so that the amount of adhesion is 30 to 100 g / m 2 per side of the above-described steel. The temperature is increased from 600 ° C. to 800 ° C. at a temperature increase rate of from 500 ° C./hour to 500 ° C./hour, and then subjected to an alloying treatment for cooling at a cooling rate of 50 ° C./hour to 500 ° C./hour. By this alloying treatment, the Al plating layer is alloyed with Fe in the base material to form an Al—Fe alloy layer.
また、上記合金化処理は、ボックス焼鈍(BAF焼鈍)で実施することが好ましい。合金化処理を行う場合には、焼鈍条件、すなわち、昇温速度、最高到達板温等の諸条件を調整する。 Moreover, it is preferable to implement the said alloying process by box annealing (BAF annealing). When the alloying treatment is performed, the annealing conditions, that is, various conditions such as the rate of temperature increase and the maximum plate temperature are adjusted.
BAF焼鈍の条件について説明する。付着量が片面当たり30〜100g/m2となるようにAlめっき浴を用いてAlめっきを施してAlめっき鋼板とし、該Alめっき鋼板コイルをボックス焼鈍炉内で、図7に示すように、その保定時間、温度をそれぞれX軸、Y軸とし、X軸を対数表示した時に、(600℃、5時間)、(600℃、200時間)、(630℃、1時間)、(750℃、1時間)、(750℃、4時間)の5点で囲まれる内部となるような温度並びに保定時間で焼鈍することでAlめっきと鋼板を合金化させることが好ましい。この5点で囲まれる内部であれば所定の厚みの良好な合金化が得られるからである。 The conditions for BAF annealing will be described. As shown in FIG. 7, in the box annealing furnace, the Al-plated steel sheet coil is subjected to Al plating using an Al plating bath so that the adhesion amount is 30 to 100 g / m 2 per side. When the holding time and temperature are X-axis and Y-axis, respectively, and the X-axis is logarithmically displayed, (600 ° C., 5 hours), (600 ° C., 200 hours), (630 ° C., 1 hour), (750 ° C., 1 hour), (750 ° C., 4 hours) It is preferable to alloy the Al plating and the steel sheet by annealing at a temperature and holding time surrounded by five points. This is because if the interior is surrounded by these five points, good alloying with a predetermined thickness can be obtained.
これらの設定理由は以下である。まず温度下限600℃は、前述したようにAlNを生成させずにAlめっきを合金化させるのに必須の条件である。Alめっきを焼鈍した際にめっき中のAlは鋼板のFe、大気中のNと反応することができ、これは競争反応である。600℃未満の温度においてはAlNの生成が主となり、結果としてAlとFeとの反応が抑制される。しかし600℃超ではAl−Fe反応が優勢となり、AlN生成は抑制される。これはそれぞれの反応の温度依存性が異なることからこうなるものと解釈できる。 The reasons for these settings are as follows. First, the lower temperature limit of 600 ° C. is an essential condition for alloying Al plating without generating AlN as described above. When Al plating is annealed, Al during plating can react with Fe in the steel sheet and N in the atmosphere, which is a competitive reaction. At a temperature lower than 600 ° C., AlN is mainly generated, and as a result, the reaction between Al and Fe is suppressed. However, when the temperature exceeds 600 ° C., the Al—Fe reaction becomes dominant and the generation of AlN is suppressed. This can be interpreted as such because the temperature dependence of each reaction is different.
また温度上限は750℃であり、これはコイルで焼鈍した際のAl同士の融着を抑制するために必要である。すなわち、750℃超の高温で溶融したAl同士が接触すると容易に接合してしまい、コイルを展開することが困難となる。750℃以下の焼鈍温度とすることで融着を抑制でき、合金化されたコイルを得ることができる。 The upper temperature limit is 750 ° C., which is necessary to suppress the fusion of Al when annealed by a coil. That is, when Al melted at a high temperature exceeding 750 ° C. comes into contact with each other, they are easily joined, making it difficult to deploy the coil. By setting the annealing temperature to 750 ° C. or lower, fusion can be suppressed, and an alloyed coil can be obtained.
次に時間については1時間が下限となる。これはボックス焼鈍においてこれ以下の時間では安定した焼鈍ができないためである。 Next, about time, 1 hour becomes a lower limit. This is because in the box annealing, stable annealing cannot be performed at a time shorter than this.
図7に示す(600℃、5時間)、(630℃、1時間)を結ぶ線はほぼ表面まで合金化する条件に対応し、(600℃、200時間)、(750℃、4時間)を結ぶ線はほぼ良好な塗装後耐食性を得られる線に対応する。図7において右上に行くほど高温、長時間保定となり合金化が進行することを意味する。合金化程度として表面まで合金化しないと輻射加熱における昇温速度が低下し、また通電加熱等で垂れが発生する。また合金化しすぎると表面のAl濃度が低下し、塗装後耐食性が低下する傾向にある。現行の耐食材料であるGA同等の塗装後耐食性を確保するためには(600℃、200時間)、(750℃、4時間)を結ぶ線よりも左側(低温、短時間側)で焼鈍することが望ましい。 The line connecting (600 ° C., 5 hours) and (630 ° C., 1 hour) shown in FIG. 7 corresponds to the condition of alloying almost to the surface, and (600 ° C., 200 hours), (750 ° C., 4 hours) The connecting line corresponds to a line that can obtain almost good corrosion resistance after painting. In FIG. 7, the higher the temperature is, the higher the temperature and the longer the retention, which means that alloying proceeds. If the surface is not alloyed as the degree of alloying, the rate of temperature rise in radiant heating is reduced, and sagging occurs due to current heating or the like. Further, when alloyed too much, the Al concentration on the surface is lowered, and the corrosion resistance after coating tends to be lowered. In order to ensure the post-painting corrosion resistance equivalent to GA, which is the current corrosion resistant material (600 ° C, 200 hours), anneal to the left (low temperature, short time side) from the line connecting (750 ° C, 4 hours). Is desirable.
なお、ボックス焼鈍条件は付着量も影響し、付着量が少ないと低温でも表面まで合金化可能であるが、付着量が多いと高温あるいは長時間の条件が必要となる。 The box annealing condition also affects the adhesion amount. If the adhesion amount is small, the surface can be alloyed even at a low temperature, but if the adhesion amount is large, a high temperature or a long time condition is required.
鋼板へのめっき付着量が片面当り30g/m2未満の付着量であると、良好な塗装後耐食性を得ることが困難で、100g/m2超の付着量ではホットスタンプした際のAl−Fe合金層の剥離と金型への付着が問題となる。600℃未満の温度で合金化させるためには、200時間を越える時間が必要で工業的な実施が困難で、一方、800℃超まで加熱すると、合金化が進行しすぎて塗装後耐食性が低下する。 When the coating amount on the steel sheet is less than 30 g / m 2 per side, it is difficult to obtain good post-coating corrosion resistance. If the amount exceeds 100 g / m 2 , Al-Fe when hot stamping is performed. The peeling of the alloy layer and the adhesion to the mold become a problem. In order to alloy at a temperature of less than 600 ° C, it takes a time exceeding 200 hours, and industrial implementation is difficult. On the other hand, when heated to over 800 ° C, alloying progresses too much and the corrosion resistance after coating decreases. To do.
また、BAF焼鈍後には、鋼板のそりの矯正や表面平滑性を確保するために、従来と同様なスキンパス圧延(調質圧延)を実施することが望ましい。そして、その際の圧下率は3%以下とする。圧下率が3%を超えると合金層が割れ、耐食性を劣化させる可能性があるので、スキンパス圧下率を3%以下とした。なお、圧下率の下限については1%以上であることがスキンパスの効果を得るためには好ましい。
(ホットスタンプ前の加熱工程について)
なお、上述したようにして得られたAlめっき鋼板は、その後のホットスタンプ工程において合金層の構造を主に律すると考えられる600℃から最高到達板温より10℃低い温度までの温度域において、50℃/秒以上の昇温速度で急速加熱されることができる。加熱方式については特に限定せず、通常の炉加熱や輻射熱を用いる近赤外線方式の加熱方式を使用することも可能であるが、昇温速度50℃/秒以上の急速加熱を行うことが可能な、通電加熱や高周波誘導加熱等の電気を用いる加熱方式を使用することがより好ましい。
Further, after BAF annealing, it is desirable to perform skin pass rolling (temper rolling) similar to the conventional one in order to correct warpage of the steel sheet and ensure surface smoothness. And the rolling reduction in that case shall be 3% or less. If the rolling reduction exceeds 3%, the alloy layer may crack and the corrosion resistance may be deteriorated, so the skin pass rolling reduction was set to 3% or less. In order to obtain the skin pass effect, the lower limit of the rolling reduction is preferably 1% or more.
(About the heating process before hot stamping)
In addition, the Al plated steel sheet obtained as described above is in a temperature range from 600 ° C. considered to mainly govern the structure of the alloy layer in the subsequent hot stamping process to a temperature 10 ° C. lower than the maximum attained plate temperature, It can be rapidly heated at a heating rate of 50 ° C./second or more. The heating method is not particularly limited, and it is possible to use a normal infrared heating method using a furnace or radiant heat, but rapid heating at a heating rate of 50 ° C./second or more is possible. It is more preferable to use a heating method using electricity such as energization heating or high frequency induction heating.
昇温速度の上限は特に規定しないが、上記の通電加熱や高周波誘導加熱等の加熱方式を使用する場合には、その装置の性能上、300℃/秒程度が上限となる。 The upper limit of the rate of temperature rise is not particularly specified, but when using the heating method such as the above-described current heating or high frequency induction heating, the upper limit is about 300 ° C./second due to the performance of the apparatus.
また、この加熱工程において、最高到達板温を850℃以上とすることが好ましい。最高到達板温をこの温度とするのは、鋼板をオーステナイト域まで加熱するとともに、表面まで十分に合金化を進行させるためである。 Moreover, in this heating process, it is preferable to make the maximum reach | attainment board temperature into 850 degreeC or more. The reason why the maximum attainable plate temperature is set to this temperature is that the steel plate is heated to the austenite region and the alloying is sufficiently advanced to the surface.
ホットスタンプ後の鋼板は、溶接、化成処理、電着塗装等を経て最終製品となる。通常は、カチオン電着塗装が用いられることが多く、その膜厚は1〜30μm程度である。電着塗装の後に中塗り、上塗り等の塗装が施されることもある。 The steel sheet after hot stamping becomes a final product through welding, chemical conversion treatment, electrodeposition coating, and the like. Usually, cationic electrodeposition coating is often used, and the film thickness is about 1 to 30 μm. After electrodeposition coating, coating such as intermediate coating and top coating may be applied.
以下、実施例を用いて本発明をさらに具体的に説明する。
(実施例1)
通常の熱延工程及び冷延工程を経た、表1に示すような鋼成分の冷延鋼板(板厚1.2mm)を供試材料として、溶融Alめっきを行った。溶融Alめっきは無酸化炉−還元炉タイプのラインを使用し、めっき後ガスワイピング法でめっき付着量を片面約80g/m2となるように調節し、その後冷却した。この際のめっき浴組成としてはAl−9%Si−2%Feであった。浴中のFeは、浴中のめっき機器やストリップから供給される不可避のものである。めっき外観は概ね不めっき等がなく良好であったが、一部に不めっき発生が認められた。
Hereinafter, the present invention will be described more specifically with reference to examples.
(Example 1)
Using a cold-rolled steel sheet having a steel component as shown in Table 1 (thickness 1.2 mm) that has undergone a normal hot-rolling process and a cold-rolling process, molten Al plating was performed. For the molten Al plating, a non-oxidation furnace-reduction furnace type line was used, and after plating, the amount of plating adhered was adjusted to about 80 g / m 2 on one side by a gas wiping method, and then cooled. The plating bath composition at this time was Al-9% Si-2% Fe. Fe in the bath is inevitable supplied from plating equipment or strips in the bath. The plating appearance was good with almost no unplating or the like, but some unplating was observed.
次に、この鋼板をコイル状態でボックス焼鈍で加熱した。ボックス焼鈍条件は大気雰囲気、620℃、15時間とした。ボックス焼鈍後、AlNによるめっき剥離の有無を目視判定し、20%苛性ソーダ中でFe−Al合金層の表面を剥離して重量法でAlN量を測定した。 Next, this steel plate was heated in a coil state by box annealing. The box annealing conditions were an air atmosphere, 620 ° C., and 15 hours. After box annealing, the presence or absence of plating peeling by AlN was visually determined, the surface of the Fe—Al alloy layer was peeled in 20% caustic soda, and the amount of AlN was measured by a gravimetric method.
こうして作成した試料の焼入後硬度(Hv)及び塗装後耐食性(mm)を評価した。ホットスタンプは急速加熱に相当する条件として、通電加熱を用い、昇温速度は約100℃/秒であった。大気中で200×200mm大の試験片を950℃狙いで加熱し、約700℃の温度まで大気中で冷却して、その後、厚さ50mmの金型間で圧着することで急冷した。このとき金型表面に断熱材を薄く引いて冷却速度が30〜40℃/秒となるように調節した。 The samples thus prepared were evaluated for hardness after quenching (Hv) and corrosion resistance after coating (mm). The hot stamping used heating as a condition corresponding to rapid heating, and the heating rate was about 100 ° C./second. A test piece 200 × 200 mm in size was heated with the aim of 950 ° C. in the air, cooled to a temperature of about 700 ° C. in the air, and then rapidly cooled by pressure bonding between molds having a thickness of 50 mm. At this time, the heat insulating material was thinly drawn on the mold surface, and the cooling rate was adjusted to 30 to 40 ° C./second.
断面硬度を荷重10kgfのビッカース硬度計で求め、塗装後耐食性を以下の手順で評価した。70×150mmに剪断した試験片を用いて日本パーカライジング(株)製化成処理液PB−SX35Tで化成処理を施し、その後、日本ペイント(株)製カチオン電着塗料パワーニクス110を約20μm厚みで塗装した。その後、カッターで塗膜にクロスカットを入れ、自動車技術会で定めた複合腐食試験(JASO M610−92)を180サイクル(60日)行ない、クロスカットからの膨れ幅(片側最大膨れ幅)を測定した。このときGA(付着量片面45g/m2)の膨れ幅は5mmであった。 The cross-sectional hardness was determined with a Vickers hardness tester with a load of 10 kgf, and the corrosion resistance after coating was evaluated by the following procedure. Using a test piece sheared to 70 × 150 mm, a chemical conversion treatment solution PB-SX35T manufactured by Nippon Parkerizing Co., Ltd. was applied, and then Cationic Electrodeposition Paint Powernics 110 manufactured by Nippon Paint Co., Ltd. was applied to a thickness of about 20 μm. did. After that, a cross-cut is put into the coating film with a cutter, and a composite corrosion test (JASO M610-92) determined by the Automotive Engineering Society is performed for 180 cycles (60 days), and the swollen width from the cross-cut (maximum swollen width on one side) is measured. did. At this time, the swollen width of GA (attached amount on one side: 45 g / m 2 ) was 5 mm.
表2に、加熱条件と組織並びに特性評価結果をまとめた。 Table 2 summarizes the heating conditions, structure, and property evaluation results.
鋼中Si量が多すぎるような場合(番号12)、Si酸化に伴う不めっきが発生して、それ以降の評価は不可能であった。鋼中Cr,Mo量が少ない場合(番号1、6)にはこの温度で焼鈍してもAlNの生成を完全には抑制できず、1g/m2以上のAlNが生成し、塗装後耐食性も比較材のGA以下に低下する傾向が認められた。鋼中C量やMn量が低い場合には(番号9、13)、焼入性が低下して十分な硬度が得られなかった。鋼成分を適正化した他の条件においては、焼入後硬度、塗装後耐食性共に良好となり、このときのAlN量は1g/m2以下であった。
(実施例2)
表1のCに示した鋼成分を持つ冷延鋼板(板厚1.2mm)に実施例1と同じ要領で溶融Alめっきを施した。めっき付着量は片面20〜100g/m2とした。こうして製造したAlめっき鋼板を、ボックス焼鈍を用いて種々の条件で焼鈍した。
When the amount of Si in the steel was too large (No. 12), non-plating accompanied with Si oxidation occurred, and subsequent evaluation was impossible. When the amount of Cr and Mo in the steel is small (Nos. 1 and 6), the formation of AlN cannot be completely suppressed even if annealing is performed at this temperature, and 1 g / m 2 or more of AlN is generated, and the corrosion resistance after coating is also good. A tendency to fall below the GA of the comparative material was observed. When the amount of C and the amount of Mn in steel were low (Nos. 9 and 13), the hardenability was lowered and sufficient hardness was not obtained. Under other conditions in which the steel components were optimized, both the hardness after quenching and the corrosion resistance after coating were good, and the amount of AlN at this time was 1 g / m 2 or less.
(Example 2)
In the same manner as in Example 1, hot-dip Al plating was performed on a cold-rolled steel sheet (plate thickness: 1.2 mm) having the steel components shown in Table 1C. The amount of plating adhesion was 20 to 100 g / m 2 on one side. The thus-prepared Al-plated steel sheet was annealed under various conditions using box annealing.
ホットスタンプ前の加熱は通電加熱に加えて近赤外線も用いた。このときの昇温速度は通電加熱で約150℃/秒、近赤外線加熱で約40℃/秒であった。また合金化の不十分な場合にはめっきの寄り、垂れが認められたため、加熱前後の板厚変化(最大値をそれぞれ測定)を測定し、板厚変化として評価した。板厚変化0.1mmというのは、加熱後の最大板厚が0.1mm増大していることを意味し、これはAlめっきが局部的に凝集しているためである。 For heating before hot stamping, near infrared rays were used in addition to energization heating. The rate of temperature rise at this time was about 150 ° C./second for electric heating and about 40 ° C./second for near infrared heating. In addition, when the alloying was insufficient, since a shift or sagging of the plating was observed, the plate thickness change before and after heating (the maximum value was measured respectively) was measured and evaluated as the plate thickness change. The plate thickness change of 0.1 mm means that the maximum plate thickness after heating is increased by 0.1 mm because the Al plating is locally aggregated.
条件と評価結果を第3表にまとめた。Alめっきの付着量が少ない場合(番号1)には、十分な塗装後耐食性が得られなかった。ボックス焼鈍の条件が表面まで合金化まで至らないと(番号16)、Alが残存していた。このときには垂れが発生し、局部的に板厚が0.2mm程度厚くなり、耐食性評価ができなかった。またバッチ焼鈍での温度が高すぎると、コイルが溶着してしまい(番号13)、一方温度が低すぎると先述したAlNの生成が起こり、表面のめっきが剥離したり、粉状物が付着したりした(番号6、7、8、9)。保定時間が長すぎるような条件(番号14、15)ではボックス焼鈍で合金化が進行しすぎて塗装後耐食性の低下が認められた。また番号17はボックス焼鈍を施していない場合に相当するが、このときには垂れが発生した。一方、付着量に見合った条件で加熱した水準においては合金化が表面まで進行し、塗装後耐食性は良好で、板厚変化も認められなかった。
(実施例3)
表1のQの鋼成分を有する冷延鋼板(板厚1.6mm)を用いて実施例1と同様の方法で片面80g/m2のAlめっきを施した。その後ZnO微粒子懸濁液(シーアイ化成(株)社製nanotek slurry)に水溶性のウレタン樹脂をZnOに対して重量比で20%添加した液をZnとして1.5g/m2となるように塗布し、80℃で乾燥させた。この材料を用いてバッチ焼鈍条件:630℃、保定7時間で焼鈍し、表面まで合金化させた。
Table 3 summarizes the conditions and evaluation results. When the adhesion amount of Al plating was small (No. 1), sufficient post-coating corrosion resistance was not obtained. If the box annealing condition did not reach alloying to the surface (No. 16), Al remained. At this time, sagging occurred, the plate thickness locally increased by about 0.2 mm, and corrosion resistance evaluation could not be performed. If the temperature in batch annealing is too high, the coil is welded (No. 13). If the temperature is too low, the above-described generation of AlN occurs, and the plating on the surface is peeled off or the powder is adhered. (Numbers 6, 7, 8, 9). Under conditions where the holding time was too long (numbers 14 and 15), alloying progressed too much during box annealing, and a decrease in corrosion resistance after coating was observed. Reference numeral 17 corresponds to the case where the box annealing is not performed, but sagging occurred at this time. On the other hand, at the level heated under conditions suitable for the amount of adhesion, alloying progressed to the surface, the post-coating corrosion resistance was good, and no change in plate thickness was observed.
(Example 3)
Using a cold-rolled steel sheet (plate thickness 1.6 mm) having a steel component of Q in Table 1, Al plating of 80 g / m 2 on one side was performed in the same manner as in Example 1. Thereafter, a solution obtained by adding 20% by weight of a water-soluble urethane resin to ZnO fine particle suspension (Canochemical Slurry, manufactured by CI Kasei Co., Ltd.) by weight with respect to ZnO was applied to 1.5 g / m 2 as Zn. And dried at 80 ° C. Using this material, batch annealing conditions: 630 ° C., annealing for 7 hours, and alloyed to the surface.
この試料を用いて通電加熱法で950℃まで昇温し、保定時間はとらずに金型で急冷した。このときの平均昇温速度は60℃/秒であった。こうして製造した材料の塗装後耐食性を実施例1と同様の方法で評価したところ、膨れ幅は1mmであった。この条件とほぼ同様の条件が表3の番号4に相当するが、これと比較しても極めて優れた耐食性を示した。このことからAlめっき表面にZnOを含有する処理を施すことで塗装後耐食性の更なる向上が図れると考えられた。
(実施例4)
表1のGの鋼成分を有する冷延鋼板(板厚2.0mm)を用いてAlめっきを施した。このときAl−9%Si−2%Feめっき浴にMn、Cr、Mg、Moを添加してその効果を評価した。めっき付着量は片面約80g/m2、ボックス焼鈍条件は650℃、保定10時間、ホットスタンプ前の加熱は近赤外線加熱で、昇温速度約30℃/秒、昇温温度930℃とした。このときの塗装後耐食性を評価した結果を表4に示す。
Using this sample, the temperature was raised to 950 ° C. by an electric heating method, and the sample was quenched with a mold without taking a holding time. The average temperature increase rate at this time was 60 ° C./second. When the corrosion resistance after painting of the material thus produced was evaluated in the same manner as in Example 1, the swollen width was 1 mm. A condition substantially similar to this condition corresponds to No. 4 in Table 3, but extremely excellent corrosion resistance was exhibited as compared with this. From this, it was thought that the post-coating corrosion resistance could be further improved by applying a treatment containing ZnO to the Al plating surface.
Example 4
Al plating was performed using a cold-rolled steel sheet (thickness 2.0 mm) having the steel component G in Table 1. At this time, Mn, Cr, Mg, and Mo were added to the Al-9% Si-2% Fe plating bath to evaluate the effect. The amount of plating was about 80 g / m 2 on one side, the box annealing condition was 650 ° C., the holding time was 10 hours, the heating before hot stamping was near infrared heating, the temperature rising rate was about 30 ° C./second, and the temperature rising temperature was 930 ° C. Table 4 shows the results of evaluation of post-coating corrosion resistance at this time.
浴へこれらのMn、Cr、Mg、Moの元素を添加することによる耐食性向上効果が認められた。浴温を保ったままでは、Mn、Cr、Moは上記の濃度しか添加することができなかった。 The effect of improving the corrosion resistance by adding these elements of Mn, Cr, Mg and Mo to the bath was recognized. While maintaining the bath temperature, Mn, Cr and Mo could only be added at the above concentrations.
(実施例5)
表1のGの鋼成分を有する冷延鋼板(板厚1.2mm)を用いてAlめっきを施した。めっき付着量は片面約80g/m2、ボックス焼鈍条件は650℃、保定10時間であり、ボックス焼鈍後、圧下率0.5〜5%のスキンパスを付与した。スキンパス圧延を施すことにより鋼板の反りが矯正され、表面平滑性が改良されていた。この試料を用いて通電加熱法で950℃まで昇温し、保定時間はとらずに金型で急冷した。このときの平均昇温速度は60℃/秒であった。こうして製造した材料の塗装後耐食性を実施例1と同じ方法で評価した。その結果、以下の表5に示す結果となった。この結果よりスキンパスでの圧下率を上げると塗装後耐食性が低下する傾向が認められた。これはスキンパスにより合金化しためっき層にクラックが入り、続く加熱工程においてその部位より鉄が酸化したものと推定される。スキンパス圧下率は3%以下とすることが好ましい。
(Example 5)
Al plating was performed using a cold-rolled steel sheet (thickness 1.2 mm) having the steel component G in Table 1. The plating adhesion amount was about 80 g / m 2 on one side, the box annealing conditions were 650 ° C. and the holding time was 10 hours, and after the box annealing, a skin pass with a rolling reduction of 0.5 to 5% was applied. By applying the skin pass rolling, the warpage of the steel sheet was corrected and the surface smoothness was improved. Using this sample, the temperature was raised to 950 ° C. by an electric heating method, and the sample was quenched with a mold without taking a holding time. The average temperature increase rate at this time was 60 ° C./second. The post-coating corrosion resistance of the material thus produced was evaluated in the same manner as in Example 1. As a result, the results shown in Table 5 below were obtained. From this result, it was found that the corrosion resistance after painting tended to decrease when the rolling reduction ratio in the skin pass was increased. This is presumed that the plating layer alloyed by the skin pass cracked, and iron was oxidized from that portion in the subsequent heating process. The skin pass reduction ratio is preferably 3% or less.
以上、添付図面を参照しながら本発明の好適な実施形態について説明したが、本発明はかかる例に限定されないことは言うまでもない。当業者であれば、特許請求の範囲に記載された範疇内において、各種の変更例または修正例に想到し得ることは明らかであり、それらについても当然に本発明の技術的範囲に属するものと了解される。 As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.
1 鋼板
2 電流
3 磁場
4 溶融Alに加わる力
5 寄り
6 Alめっき
7 合金層
8 Si
9 AlN
10 アルミナ
11 Alめっき鋼板(試験材)
DESCRIPTION OF SYMBOLS 1 Steel plate 2 Current 3 Magnetic field 4 Force applied to molten Al 5 Near 6 Al plating 7 Alloy layer 8 Si
9 AlN
10 Alumina 11 Al plated steel sheet (test material)
Claims (9)
C:0.1〜0.5%、
Si:0.01〜0.7%、
Mn:0.5〜2.5%、
Cr:0.4%超〜3%、
P:0.001〜0.1%、
S:0.001〜0.1%、
Al:0.1%以下、
N:0.01%以下、
を含有し、残部がFe及び不可避的不純物より成る鋼板の表面に、厚みが10〜45μmのFe:42〜88%を含有し、残部Al及び不可避的不純物より成るAl−Fe合金層を有し、該Al−Fe合金層表面のAlN量が0.01〜1g/m2であることを特徴とする、ホットスタンプ用鋼板。 As a steel component in mass%,
C: 0.1 to 0.5%
Si: 0.01 to 0.7%,
Mn: 0.5 to 2.5%
Cr: more than 0.4% to 3%,
P: 0.001 to 0.1%,
S: 0.001 to 0.1%,
Al: 0.1% or less,
N: 0.01% or less,
A balance of Fe and unavoidable impurities on the surface of the steel sheet, and a thickness of 10 to 45 μm Fe: 42 to 88%, the balance Al and an inevitable impurity Al-Fe alloy layer , wherein the AlN amount of the Al-Fe alloy layer surface is 0.01 to 1 g / m 2, the steel sheet for hot stamping.
C:0.1〜0.5%、
Si:0.01〜0.7%、
Mn:0.5〜2.5%、
Cr:0.2〜3%、
Mo:0.005〜0.5%、
P:0.001〜0.1%、
S:0.001〜0.1%、
Al:0.1%以下、
N:0.01%以下、
を含有し、残部がFe及び不可避的不純物より成る鋼板の表面に、厚みが10〜45μmのFe:42〜88%を含有し、残部Al及び不可避的不純物より成るAl−Fe合金層を有し、該Al−Fe合金層表面のAlN量が0.01〜1g/m2であることを特徴とする、ホットスタンプ用鋼板。 As a steel component in mass%,
C: 0.1 to 0.5%
Si: 0.01 to 0.7%,
Mn: 0.5 to 2.5%
Cr: 0.2-3%,
Mo: 0.005 to 0.5%,
P: 0.001 to 0.1%,
S: 0.001 to 0.1%,
Al: 0.1% or less,
N: 0.01% or less,
A balance of Fe and unavoidable impurities on the surface of the steel sheet, and a thickness of 10 to 45 μm Fe: 42 to 88%, the balance Al and an inevitable impurity Al-Fe alloy layer , wherein the AlN amount of the Al-Fe alloy layer surface is 0.01 to 1 g / m 2, the steel sheet for hot stamping.
B:0.0001〜0.01%、
W:0.01〜3%、
V:0.01〜2%、
Ti:0.005〜0.5%、
Nb:0.01〜1%
の内の1種又は2種以上を含有することを特徴とする、請求項1または2に記載のホットスタンプ用鋼板。 The steel component is further mass%,
B: 0.0001 to 0.01%
W: 0.01 to 3%
V: 0.01-2%
Ti: 0.005 to 0.5%,
Nb: 0.01 to 1%
The steel sheet for hot stamping according to claim 1, comprising one or more of the above.
Si:3〜15%
を含有することを特徴とする、請求項1〜3のいずれか1項に記載のホットスタンプ用鋼板。 The Al-Fe alloy layer is further mass%,
Si: 3 to 15%
The steel sheet for hot stamping according to any one of claims 1 to 3, wherein the steel sheet for hot stamping is contained.
Mn:0.05〜1%、
Mg:0.05〜1%、
Cr:0.05〜0.5%、
Mo:0.05〜0.5%
の内の1種又は2種以上を含有することを特徴とする、請求項1〜4のいずれか1項に記載のホットスタンプ用鋼板。 The Al-Fe alloy layer is further mass%,
Mn: 0.05 to 1%
Mg: 0.05 to 1%,
Cr: 0.05 to 0.5%,
Mo: 0.05-0.5%
The hot stamping steel plate according to any one of claims 1 to 4, comprising one or more of the above.
請求項6に記載のホットスタンプ用鋼板の製造方法。 After the alloying, skin pass rolling with a rolling reduction of 3% or less is performed.
The manufacturing method of the steel plate for hot stamping of Claim 6.
Mn:0.05〜1%、
Mg:0.05〜1%、
Cr:0.05〜0.5%、
Mo:0.05〜0.5%
の内の1種又は2種以上を含有することを特徴とする、請求項8に記載のホットスタンプ用めっき鋼板の製造方法。 The Al plating bath is further mass%,
Mn: 0.05 to 1%
Mg: 0.05 to 1%,
Cr: 0.05 to 0.5%,
Mo: 0.05-0.5%
The manufacturing method of the hot-stamped steel plate of Claim 8 characterized by including 1 type (s) or 2 or more types of these.
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