JP6529710B2 - Hot press-formed member having high strength and high corrosion resistance - Google Patents
Hot press-formed member having high strength and high corrosion resistance Download PDFInfo
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本発明は、加熱された鋼材をプレス加工して製造される熱間プレス成形部材、特に、自動車の足廻り部品や車体下部補強部材といった、高強度かつ高耐食性を求められる部品に用いられる熱間プレス成形部材に関する。 The present invention relates to a hot press-formed member manufactured by pressing a heated steel material, in particular, a hot press used for a part requiring a high strength and a high corrosion resistance, such as an undercarriage part of an automobile or a car body lower reinforcement member. The present invention relates to a press-formed member.
環境意識の高まりからＣＯ２の排出量の削減に大きく資する自動車の軽量化がより一層求められている。使用する鋼材の高強度化を図って鋼材の厚みを減らすことにより、自動車を軽量化する努力が続けられている。しかし、高強度化に伴って鋼材の成形性（以降の説明では鋼板のプレス加工性を例にとる）が低下するため、鋼板をプレス成形により所望の形状に加工する際における鋼板のカジリ，破断や、スプリングバック、さらには形状のばらつきといった様々な問題が発生する。 From the rise of environmental awareness, there is a further demand for weight reduction of vehicles which greatly contributes to the reduction of CO 2 emissions. Efforts are being made to reduce the weight of automobiles by reducing the thickness of steel by increasing the strength of the steel used. However, since the formability of the steel material (the pressability of the steel plate will be taken as an example in the following description) decreases as the strength is increased, the steel plate nicks and breaks when the steel plate is processed into a desired shape by press forming. There are various problems such as spring back, and even variations in shape.
近年、熱間プレス成形技術がこれらの問題の解決策として広く用いられる。熱間プレス成形技術とは、高炭素鋼板を高温に加熱した状態でプレス成形および急冷することにより、高強度鋼板における成形時の上記問題の発生を防ぎながら、焼入れによって所望の高強度を有する熱間プレス成形部材を製造する技術である。 In recent years, hot press forming techniques are widely used as a solution to these problems. In the hot press forming technology, heat generation having a desired high strength by quenching while preventing occurrence of the above-mentioned problems at the time of forming in a high strength steel sheet by performing press forming and quenching while heating a high carbon steel sheet to a high temperature. It is a technique of manufacturing an inter-press-formed member.
しかし、裸の鋼板ままでは加熱中に密着性が乏しい酸化物が鋼板表面に生成し、この酸化物が熱間プレス成形中に脱落することにより金型や鋼板の表面を損傷させることがあり、プレス金型の手入れを頻繁に行ったり、熱間プレス成形部材にショットブラスト処理といった酸化物除去処理を行う必要が生じ、熱間プレス成形部材の生産性を低下させる一因となる。さらに、このようにして製造された熱間プレス成形部材は、亜鉛めっき等の防錆処理を施されていないため、化成処理および電着塗装を施しても、特に自動車の足廻り部品や車体下部補強部材といった、高強度かつ高耐食性を求められる部品に要求される耐食性を満足できない。 However, in the case of a bare steel sheet, an oxide having poor adhesion is formed on the surface of the steel sheet during heating, and this oxide may fall off during hot press forming to damage the surface of the mold or the steel sheet. It is necessary to frequently carry out maintenance of the press die and to perform an oxide removing treatment such as a shot blasting treatment on the hot press-formed member, which contributes to a decrease in the productivity of the hot press-formed member. Furthermore, since the hot press-formed member manufactured in this manner is not subjected to anticorrosion treatment such as galvanization, it is particularly suitable for automobile footparts and lower vehicle body parts even when subjected to chemical conversion treatment and electrodeposition coating. It is not possible to satisfy the corrosion resistance required for parts requiring high strength and high corrosion resistance such as reinforcing members.
特許文献１には、熱間プレス成形用鋼板にアルミニウムめっきを施す技術が、このような密着性が乏しい酸化物の生成を抑制して熱間プレス成形部材の塗装後耐食性を確保する技術として、開示される。アルミニウムめっき皮膜は、優れた耐酸化性を示すために一部で実用化が進んでいるものの、犠牲防食性を有さないために上記の部品に適用することは難しく、亜鉛系めっきされた熱間プレス成形用鋼板に対する要望が強い。 In Patent Document 1, a technique of applying aluminum plating to a steel plate for hot press forming suppresses such formation of an oxide having poor adhesion to secure corrosion resistance after coating of a hot press formed member, Disclosed. Although the aluminum plating film has been commercialized in part to show excellent oxidation resistance, it is difficult to apply to the above-mentioned parts because it does not have sacrificial corrosion resistance, and zinc-plated thermal Demand for steel sheet for press forming is strong.
このような要望に応えるために亜鉛系めっきによる熱間プレス成形用鋼板の開発が進められている。しかし、亜鉛は融点４１９℃，沸点９０７℃であり、実際に熱間プレス成形が行われる温度域では液相または気相となるため、亜鉛めっき層の蒸散や酸化が発生し、残亜鉛量が低下して耐食性が著しく劣化したり、液相状態の亜鉛によりプレス成形時にめっき層の割れが誘発されるという問題がある。この問題を回避する方法が、特許文献２〜６に開示される。 In order to meet such a demand, development of a steel sheet for hot press forming by zinc-based plating is in progress. However, since zinc has a melting point of 419 ° C. and a boiling point of 907 ° C., it becomes a liquid phase or a gas phase in the temperature range where hot press forming is actually performed, so that evaporation and oxidation of the zinc plating layer occur and the residual zinc amount is There is a problem in that the corrosion resistance is significantly deteriorated and zinc in the liquid phase state causes cracking of the plating layer at the time of press forming. Methods to avoid this problem are disclosed in the patent documents 2-6.
特許文献２には、Ｃ：０．０８〜０．４５％（本明細書では化学組成に関する「％」は特に断りがない限り「質量％」を意味する）、ＭｎおよびＣｒの一方または双方：０．５〜３．０％を含有する鋼板に、Ｆｅ含有量が５〜８０％であるＦｅ−Ｚｎ合金からなるとともにＺｎ付着量が１０〜９０ｇ／ｍ２であるＺｎめっき層を有し、８００〜１０００℃に加熱されてＺｎＯ層を形成した後にプレスされる熱間プレス用鋼板が開示される。 In Patent Document 2, C: 0.08 to 0.45% (herein, “%” relating to the chemical composition means “% by mass” unless otherwise noted), one or both of Mn and Cr: A steel plate containing 0.5 to 3.0% has a Zn plating layer made of a Fe-Zn alloy having an Fe content of 5 to 80% and a Zn adhesion amount of 10 to 90 g / m 2 , A steel sheet for hot pressing is disclosed, which is heated to 800 to 1000 ° C. to form a ZnO layer and then pressed.
特許文献３には、Ｃ：０．１〜０．５％、Ｓｉ：０．０５〜０．５％、Ｍｎ：０．５〜３％を含有する鋼板に、めっき層断面が、素地鋼板界面近傍が層状でＦｅを５０〜８０％含有するＺｎ−Ｆｅ合金層からなり、それ以外の部分が、Ｆｅを１０〜３０％含有するＺｎ−Ｆｅ合金相マトリックス中にＦｅを５０〜８０％含有する球状の形態を有するＺｎ−Ｆｅ合金相が島状に分布するＺｎ−Ｆｅ合金めっき層があり、さらに、めっき層の表層に厚さが１０〜１００ｎｍでＦ元素を含有するＺｒ，Ｔｉ，Ｓｉの一種または二種以上の金属酸化物または金属水酸化物の一方または双方の皮膜がある熱間プレス鋼材が開示される。 Patent Document 3 discloses that a steel plate containing C: 0.1 to 0.5%, Si: 0.05 to 0.5%, and Mn: 0.5 to 3%, the cross section of the plating layer is an interface of the base steel plate. The neighborhood consists of a Zn-Fe alloy layer containing 50 to 80% of Fe, and the other part contains 50 to 80% of Fe in a Zn-Fe alloy phase matrix containing 10 to 30% of Fe. There is a Zn-Fe alloy plating layer in which a Zn-Fe alloy phase having a spherical form is distributed like islands, and further, Zr, Ti, Si containing F element and having a thickness of 10 to 100 nm on the surface layer of the plating layer Disclosed is a hot pressed steel having a coating of one or more of one or more metal oxides or metal hydroxides.
特許文献４には、表面に亜鉛または亜鉛を含むめっき層を設けた鋼板において、めっき層の上層として設けられた、Ｆｅ，ＮｉおよびＣｏからなる群から選んだ一種または二種以上の金属を主成分として含む金属あるいは合金からなるめっき層を有し、７００〜１０００℃に加熱されてプレスされる熱間プレス成形用鋼材が開示される。 Patent Document 4 discloses a steel plate provided with a zinc or zinc-containing plating layer on its surface, mainly comprising one or two or more metals selected from the group consisting of Fe, Ni and Co provided as an upper layer of the plating layer. Disclosed is a steel material for hot press-forming, which has a plated layer made of a metal or alloy containing as a component, and is heated and pressed at 700 to 1000 ° C.
特許文献５には、Ｃ：０．１〜０．８％、Ｍｎ：０．５〜３％を含有する鋼板表面に、Ｚｎ６０％以上を含有するＺｎ系めっきを有し、望ましくは、さらにその表面に、Ｎｉ，Ｃｕ，Ｃｒ，Ｓｎの１種または２種以上の元素を合計で８０％以上含有する層を有する熱間プレス用Ｚｎ系めっき鋼板が開示される。 Patent Document 5 has Zn-based plating containing 60% or more of Zn on the surface of a steel plate containing C: 0.1 to 0.8% and Mn: 0.5 to 3%, preferably, Disclosed is a Zn-based plated steel sheet for hot pressing, having a layer containing 80% or more in total of one or two or more elements of Ni, Cu, Cr, and Sn on the surface.
さらに、特許文献６には、鋼板表面に、順に、６０％以上のＮｉを含み、残部がＺｎおよび不可避的不純物からなり、付着量が０．０１〜５ｇ／ｍ２のめっき層Ｉと、１０〜２５％のＮｉを含み、残部がＺｎおよび不可避的不純物からなり、付着量が１０〜９０ｇ／ｍ２のめっき層ＩＩとを有する熱間プレス用鋼板が開示される。 Furthermore, according to Patent Document 6, a plated layer I containing 60% or more of Ni in order on the surface of the steel plate, the balance being Zn and unavoidable impurities, and the adhesion amount is 0.01 to 5 g / m 2 , Disclosed is a steel sheet for hot pressing, comprising: a plating layer II containing 25% Ni, the balance being Zn and unavoidable impurities, and having an adhesion amount of 10 to 90 g / m 2 .
特許文献２により開示される熱間プレス用鋼板によれば、Ｚｎ蒸散は抑制され、耐食性も良好であるとともに液相状態のＺｎによる割れを生じないＺｎめっき皮膜が得られるものの、適用する部品が高い耐食性を要求されるものである場合には耐食性が不足することがあり、さらなる耐食性の改善が求められる。 According to the steel plate for hot pressing disclosed by Patent Document 2, although the Zn evaporation is suppressed, the corrosion resistance is also good, and a Zn plating film which does not cause cracking due to Zn in a liquid phase state can be obtained, When high corrosion resistance is required, the corrosion resistance may be insufficient, and further improvement of the corrosion resistance is required.
特許文献３により開示される熱間プレス鋼材では、プレス成形時には熱間プレス成形用鋼板を７８０℃未満まで冷却する必要があるために生産性の低下が避けられず、プレス成形開始温度の高温化が求められる。 In the hot pressed steel disclosed in Patent Document 3, since it is necessary to cool the steel plate for hot press forming to less than 780 ° C. at the time of press forming, a decrease in productivity can not be avoided, and the press forming start temperature is increased. Is required.
特許文献４により開示される熱間プレス成形用鋼材や、特許文献５により開示される熱間プレス用Ｚｎ系めっき鋼板は、上層Ｎｉめっきによる改善効果が著しく、Ｚｎの蒸散を抑えることができ、耐食性が高く、高温での成形でも割れが生じないめっき皮膜を確かに得られるものの、特許文献２により開示される熱間プレス用鋼板と同様に、耐食性の要求が厳しい部品に適用すると、耐食性が不足したり、犠牲防食能を発揮せずに孔食となることがあり、性能の安定性に欠ける。 In the steel materials for hot press molding disclosed by Patent Document 4 and the Zn-based plated steel sheets for Hot Press disclosed by Patent Document 5, the improvement effect by the upper layer Ni plating is remarkable, and the transpiration of Zn can be suppressed. Although corrosion resistance is high and a plated film which does not form cracks even when molded at high temperatures is certainly obtained, when applied to parts with strict requirements for corrosion resistance as in the steel plate for hot pressing disclosed by Patent Document 2, the corrosion resistance In some cases, pitting may occur without exhibiting the ability to perform sacrificial corrosion protection, and the stability of performance is lacking.
さらに、特許文献６では、特許文献６により開示される熱間プレス用鋼板の穴あき耐食性は優れるとされるが、本発明者らが実際に確認試験を行なったところ、素地まで達する傷を与えた場合には孔食が誘発され、むしろ耐穴あき腐食性が劣る結果となった。 Furthermore, in Patent Document 6, although the perforated corrosion resistance of the steel plate for hot pressing disclosed by Patent Document 6 is considered to be excellent, when the present inventors actually conducted a confirmation test, a flaw reaching the substrate is given. In this case, pitting corrosion was induced, which resulted in poor resistance to pitting corrosion.
このように、特許文献２〜４ならびに特許文献６により開示された技術の課題は、高い耐食性の維持と、高温成形時の液相状態の亜鉛に起因する割れによるプロセスウィンドウの幅（加熱温度の許容範囲）の十分な確保とを両立できないことである。すなわち、高い耐食性、特に高い犠牲防食性を確保するためには亜鉛の蒸散を抑え、亜鉛主体のＦｅ−Ｚｎ合金相を残存させることが望ましいが、亜鉛主体のＦｅ−Ｚｎ合金相の融点は最高でも７８０℃であり、加熱温度の許容範囲が狭くなる（プロセスウィンドウの狭幅化）。一方、耐食性とプロセスウィンドウの確保の両立が可能な技術である上層Ｎｉめっき技術（特許文献５）は、性能の安定性に課題がある。 Thus, the problems of the techniques disclosed by Patent Documents 2 to 4 and Patent Document 6 are the maintenance of high corrosion resistance, the width of the process window due to cracking caused by liquid phase zinc during high temperature forming (heating temperature In this case, it is impossible to achieve both of securing sufficient tolerance. That is, in order to ensure high corrosion resistance, particularly high sacrificial corrosion resistance, it is desirable to suppress the transpiration of zinc and leave the Fe-Zn alloy phase mainly made of zinc, but the melting point of the Fe-Zn alloy phase mainly made of zinc is the highest Even at 780 ° C., the allowable range of heating temperature is narrowed (narrowing of process window). On the other hand, the upper layer Ni plating technology (patent document 5), which is a technology capable of achieving both corrosion resistance and securing of a process window, has a problem in the stability of performance.
本発明者らは、上記課題を解決するためには上層Ｎｉめっき技術による性能の安定化を図ることが最も有効であると考え、鋭意検討を重ねた結果、
（Ａ）合金めっき相の残存ならびに合金めっき相中のＦｅ，Ｎｉの濃度が、耐食性と高温成形時の割れに大きく影響すること、および
（Ｂ）固溶体層中のＮｉ濃度の抑制が、長期間の犠牲防食能と耐穴あき腐食性に大きく影響すること
を知見した。
In order to solve the above-mentioned problems, the present inventors believe that it is most effective to stabilize the performance by the upper layer Ni plating technology, and as a result of intensive studies,
(A) Fe remaining in the alloy plating phase and alloy plating phase, the concentration of Ni is, can significantly affect the cracking during corrosion resistance and high-temperature molding, and (B) inhibition of Ni concentration in the solid solution layer is, long term It has been found that it significantly affects the sacrificial corrosion resistance and resistance to pitting corrosion.
すなわち、Ｆｅ−Ｚｎ合金では７８０℃以上ではどの合金めっき相でも液相となるが、ここにＮｉを加えると新しい合金めっき相としてＦｅ−Ｎｉ−Ｚｎ合金めっき相が形成され、この合金めっき相の融点が７８０℃以上であることによりＦｅ−Ｚｎの二元系合金よりも高温まで液相が生成せず、Ｚｎが蒸散せずに残存するために耐食性が向上し、かつ高温で凝固するために高温成形時の割れが発生しない。従来の技術ではこの知見に基づき、Ｚｎめっき上にＮｉなどの金属または合金を少量めっき（フラッシュめっき）して表層のみ高融点化することが提案されていたが、素地鋼材における上層のめっき量のみに着目しており、下層のめっき層の組成や熱間プレス成形後の皮膜構造は考慮していないため、熱間プレス成形で所望の融点を備える合金めっき相を安定して形成することができず、Ｚｎ蒸散や液相の生成を十分に制御できなかったために性能が得られなかったと考えられる。 That is, in the case of an Fe-Zn alloy, any alloy plating phase becomes a liquid phase at 780 ° C. or higher, but if Ni is added here, a Fe-Ni-Zn alloy plating phase is formed as a new alloy plating phase. When the melting point is 780 ° C. or higher, the liquid phase does not form up to a higher temperature than the Fe—Zn binary alloy, and the corrosion resistance improves because Zn remains without transpiration, and it solidifies at a high temperature. No cracking occurs during high temperature molding. Based on this finding, it has been proposed in the prior art to increase the melting point only by plating a small amount of metal or alloy such as Ni on Zn plating (flash plating), but only the plating amount of the upper layer in base steel material Because the composition of the lower plating layer and the film structure after hot press forming are not considered, an alloy plating phase having a desired melting point can be stably formed by hot press forming. It is considered that the performance was not obtained because the Zn evaporation and the formation of the liquid phase could not be sufficiently controlled.
また、耐食性と高温成形時の割れの回避を望むあまりに上層Ｎｉめっき量を増やし過ぎた場合や、Ｎｉ濃度の高いＺｎ−Ｎｉ合金めっきを選択した場合、高価なＮｉを多量に使用することによりコスト的に不利になるばかりでなく、固溶体層のＮｉ濃度も高くなり、短期間は犠牲防食能を発揮するものの、Ｚｎの豊富な合金めっき相を消費し尽くした後にさらに腐食が進むにつれて孔食的となり、耐食性に劣る結果となると考えられる。これは、固溶体層中のＮｉ濃度が高くなることにより素地鋼材との電位差が小さくなり過ぎるために発生すると考えられる。このような腐食が進むにつれて孔食的となる傾向は、特許文献６により開示されるようなめっき層と鋼材界面にＮｉを多量の含む場合に特に見られる。 In addition, the cost is increased by using a large amount of expensive Ni when the amount of the upper layer Ni plating is increased too much in order to avoid corrosion resistance and cracking at high temperature molding, or when Zn-Ni alloy plating with high Ni concentration is selected. In addition to being disadvantageous, the Ni concentration in the solid solution layer is also high, and although it exhibits sacrificial corrosion ability for a short period of time, pitting corrosion occurs as the corrosion progresses further after consuming the Zn-rich alloy plating phase. It is believed that the result is poor corrosion resistance. It is considered that this occurs because the potential difference with the base steel material becomes too small due to the increase of the Ni concentration in the solid solution layer. Such a tendency toward pitting as the corrosion progresses is particularly observed when a large amount of Ni is contained in the plated layer-steel interface as disclosed by Patent Document 6.
図１は、カーケンダルボイドと呼ばれる拡散性の空隙が生成した状況を示す断面ＳＥＭ写真である。
他にも、上層Ｎｉめっき量を増やし過ぎた場合や、Ｎｉ濃度の高いＺｎ−Ｎｉ合金めっきを選択した場合には、固溶体層から素地鋼材中へのＺｎやＮｉの拡散速度と、素地鋼材から固溶体層へのＦｅの拡散速度と、固溶体層から合金めっき相へのＦｅの拡散速度と、合金めっき相から固溶体層へのＺｎやＮｉの拡散速度との間の差が大きくなり、図１の断面ＳＥＭ写真により示されるような、カーケンダルボイドと呼ばれる拡散性の空隙が生成し易くなる。このような空隙は、加工時に皮膜割れを起こす原因となり、空隙が多くなると合金めっき相の剥離をも引き起こし、卑な合金相を大きく失ってしまう。そのため、耐食性に劣る結果となると考えられる。
FIG. 1 is a cross-sectional SEM photograph showing a situation in which a diffusive void called a Kirkendall void is formed.
Besides, when the upper layer Ni plating amount is excessively increased, or when Zn-Ni alloy plating having a high Ni concentration is selected, the diffusion rate of Zn and Ni from the solid solution layer into the base steel and the base steel The difference between the diffusion rate of Fe to the solid solution layer, the diffusion rate of Fe from the solid solution layer to the alloy plating phase, and the diffusion rate of Zn and Ni from the alloy plating phase to the solid solution layer increases. As shown by the cross-sectional SEM photograph, a diffusive void called a Kirkendall void tends to be generated. Such voids cause film cracking during processing, and when there are many voids, exfoliation of the alloy plating phase also occurs, and the rough alloy phase is largely lost. Therefore, it is considered that the result is poor in corrosion resistance.
本発明者らは、熱間プレス成形の前後の合金めっき相中のＦｅ濃度とＮｉ濃度，ならびに熱間プレス成形後の固溶体層中のＮｉ濃度を制御することにより、耐食性とプロセスウィンドウの確保を高次元で両立でき、かつ安定して性能を発揮することができることを知見して、本発明を完成した。 The present inventors secured corrosion resistance and a process window by controlling the Fe concentration and Ni concentration in the alloy plating phase before and after hot press forming, and the Ni concentration in the solid solution layer after hot press forming. The present invention has been completed based on the finding that high-dimensional compatibility and stable performance can be exhibited.
本発明は、Ｚｎ含有量が１５％以上、望ましく３０％以上、Ｎｉ含有量が５％未満である固溶体層上または固溶体層内に形成された、質量％でＺｎ８５〜７０％含有し、ＮｉとＦｅの合計で１５〜３０％、望ましくは１７〜２４％、かつＮｉが３〜１２％、望ましくは５〜１２％となる亜鉛合金相を有する皮膜を、表層に有し、亜鉛合金相の一部または全部は、金属状態で存在するＡｌを０．０１％以上含有することを特徴とする熱間プレス成形部材である。 The present invention is formed on or in a solid solution layer having a Zn content of 15% or more, desirably 30% or more, and a Ni content of less than 5%, containing 85 to 70% by mass of Zn 15% to 30% in total of Fe, preferably 17-24%, and Ni 3 to 12% of the film desirably has a zinc alloy phase consisting 5 to 12% possess a surface layer of zinc alloy phase one The part or all is a hot press-formed member characterized in that it contains 0.01% or more of Al present in the metallic state .
本発明では、固溶体層中のＮｉ濃度は４．０％未満であることが望ましく、より望ましくは３．０％未満である。
なお、ＮｉとＦｅの合計で１５〜３０％となる亜鉛合金相は、Ｆｅ−Ｚｎ合金のΓ相とＮｉ−Ｚｎ合金のγ相の中間的な、両相とは異なる別の相であるが、格子間隔などが近いためにＸ線回折法などではこれら３相の区別は難しいため、断面からのＳＥＭ−ＥＤＸ分析などの組成分析可能な機器を使用することにより判別される。
In the present invention, the Ni concentration in the solid solution layer is desirably less than 4.0%, and more desirably less than 3.0%.
The zinc alloy phase, which is 15 to 30% of the total of Ni and Fe, is another phase different from both phases, which is intermediate between the Γ phase of the Fe-Zn alloy and the γ phase of the Ni-Zn alloy. Since it is difficult to distinguish these three phases by X-ray diffraction or the like because the lattice spacing is close, discrimination is made by using an apparatus capable of composition analysis such as SEM-EDX analysis from a cross section.
本発明では、亜鉛合金相の一部または全部が、金属状態で存在するＡｌを０．０１％以上含有する。Ａｌは、Ｎｉ，Ｚｎと親和性が高く、高融点の合金を形成するためにＺｎの蒸散抑制に効果がある。このようなＡｌは、合金相に金属状態で存在することが必要であるが、このことは断面からのＥＰＭＡ分析などによりＯ，Ａｌ，Ｆｅ，ＮｉやＺｎの存在位置を特定し、比較することにより判別される。 In the present invention, part or all of the zinc alloy phase contains 0.01% or more of Al present in the metallic state . Al has high affinity to Ni and Zn, and is effective in suppressing the transpiration of Zn to form a high melting point alloy. Such Al needs to be present in the metal phase in the alloy phase, which means that the locations of O, Al, Fe, Ni and Zn are identified and compared by EPMA analysis from the cross section, etc. It is determined by
本発明では、亜鉛合金相が、皮膜の厚み方向に分散して形成されることが望ましい。
このような皮膜を形成するための熱間プレス成形用鋼材としては、例えば鋼板上にめっき層全体としてＦｅとＮｉの合計で１２〜２５％、望ましくは１５〜２３％、かつＮｉ／Ｆｅ比が０．１５以上、望ましくは０．２〜１．５、より望ましくは０．２５〜１．０となる、Ｚｎを含むめっき層を設けたものが例示される。
In the present invention, it is desirable that the zinc alloy phase be formed to be dispersed in the thickness direction of the film.
As steel materials for hot press forming for forming such a film, for example, 12 to 25% in total of Fe and Ni as a whole plating layer on a steel plate, preferably 15 to 23%, and Ni / Fe ratio What provided the plating layer containing Zn which becomes 0.15 or more, preferably 0.2-1.5, more preferably 0.25-1.0 is illustrated.
特に、鋼板上に設けた皮膜がＦｅを含む亜鉛合金めっき層を下層とし、当該めっき層の上層として、Ｎｉを主成分として含む金属あるいは合金からなるめっき層を設けたものが、より望ましい。このような鋼材を使用し、通常の方法により熱間プレス成形を行えば上述の皮膜を有する熱間プレス成形部材を得ることができる。 In particular, it is more preferable that the coating provided on the steel sheet has a zinc alloy plating layer containing Fe as a lower layer, and a plating layer composed of a metal or alloy containing Ni as a main component is provided as the upper layer. By using such a steel material and performing hot press forming according to a conventional method, a hot press formed member having the above-mentioned film can be obtained.
以上のような鋼材を用い、前記皮膜を有する熱間プレス成形部材とすることにより、７８０℃以上の高温で熱間プレス成形を行っても割れが発生せず、腐食の厳しい部位に適用可能な高い耐食性を有する熱間プレス成形部材を安定して製造することができるようになる。 By using the above-described steel materials as a hot press-formed member having the above-mentioned film, cracking does not occur even if hot press forming is performed at a high temperature of 780 ° C. or higher, and application to severe corrosion is possible It becomes possible to stably manufacture a hot press-formed member having high corrosion resistance.
以下、本発明における各限定範囲について詳細に説明する。
１．熱間プレス成形部材の固溶体層
固溶体層は、ＦｅにＺｎが固溶した相であり、Ｚｎを主体とする後述の亜鉛合金相と全く同等ではないものの犠牲防食性を有する。この固溶体層にＮｉが含まれると、急激に貴化が進み、僅か数％の含有で素地のＦｅよりも貴な電位となり、孔食を誘発する。固溶体層中のＺｎの減少に伴ってより少量のＮｉでも貴化程度が大きくなるため、固溶体層中のＮｉ濃度は５．０％未満とし、４．０％未満であることがより望ましく、３．０％未満であることはさらに望ましい。
Hereinafter, each limitation in the present invention will be described in detail.
1. Solid Solution Layer of Hot-Press-Formed Member The solid solution layer is a phase in which Zn is solid-solved in Fe, and has sacrificial corrosion resistance although it is not completely equivalent to the later-described zinc alloy phase mainly composed of Zn. When Ni is contained in the solid solution layer, the noble metal rapidly proceeds to become nobler than Fe at a content of only a few percent, which induces pitting corrosion. The Ni concentration in the solid solution layer should be less than 5.0%, and more preferably less than 4.0%, because the degree of becoming noble increases even with a smaller amount of Ni as the Zn in the solid solution layer decreases. It is further desirable that it be less than 0%.
固溶体層中のＺｎ含有量が１５％未満では例えＮｉが含まれなくても素地のＦｅとの電位差がほぼ無くなるため、防食層としての固溶体層のＺｎ濃度は下限を１５％とする。本発明では固溶体層中にＮｉが不可避的に含まれるため、固溶体層のＺｎ濃度は２０％以上が好ましく、３０％以上がより望ましい。 If the Zn content in the solid solution layer is less than 15%, the potential difference with Fe in the base is almost eliminated even if Ni is not contained, for example, so the lower limit of the Zn concentration in the solid solution layer as the anticorrosion layer is 15%. In the present invention, since Ni is unavoidably contained in the solid solution layer, the Zn concentration of the solid solution layer is preferably 20% or more, and more preferably 30% or more.
ここで、防食層としての固溶体層のさらに下層にＺｎ濃度が１５％以下でＮｉを含まない固溶体層が形成されても本発明の効果を損なわれることはない。 Here, even if a solid solution layer containing no Zn at a Zn concentration of 15% or less is formed in the lower layer of the solid solution layer as the anticorrosive layer, the effect of the present invention is not impaired.
２．熱間プレス成形部材の亜鉛合金相
亜鉛合金相は、上述の固溶体層上または固溶体層内に存在する。亜鉛合金相は、皮膜の厚み方向に分散して形成されることが望ましい。卑な合金相が貴化した固溶体層を分断するように存在することによって腐食の経路を分散でき、より孔食を抑制することができる。亜鉛合金相中のＦｅ，Ｎｉ，Ｚｎの濃度比は、高温での成形性と耐食性に大きく影響する要素である。
2. Zinc Alloy Phase of Hot Press-formed Member The zinc alloy phase is present on or in the above solid solution layer. The zinc alloy phase is preferably dispersed in the thickness direction of the film. The existence of the base alloy phase so as to divide the noble solid solution layer can disperse the corrosion path and can further suppress pitting corrosion. The concentration ratio of Fe, Ni and Zn in the zinc alloy phase is a factor that greatly affects formability and corrosion resistance at high temperatures.
亜鉛合金相中のＮｉとＦｅの濃度の合計が１５％未満またはＮｉが３％未満では、亜鉛合金相の融点が７８０℃超に上昇せず、７８０℃以上では液体のままであるために熱間プレス成形時に割れを誘発する。一方、Ｎｉ濃度が高ければ高いほど融点は高くなるが、実際にプレス成形される際の温度で固相であればよく、また、亜鉛合金相中のＮｉとＦｅの濃度の合計が３０％を超えるか、あるいはＮｉ濃度が１５％を超えると効果が飽和し、コストの増加を招くだけとなる。さらに、Ｎｉ濃度が高いと上述のカーケンダルボイドと呼ばれる拡散性の空隙が発生し易くなるため、Ｎｉ濃度は所望の融点を備える中で可能な限り少ないほうが望ましい。 If the total concentration of Ni and Fe in the zinc alloy phase is less than 15% or Ni is less than 3%, the melting point of the zinc alloy phase does not rise above 780 ° C., and remains above 780 ° C. Induces cracking during press molding. On the other hand, the higher the Ni concentration, the higher the melting point, but it may be a solid phase at the temperature at which it is actually press-formed, and the total concentration of Ni and Fe in the zinc alloy phase is 30%. If it exceeds or the Ni concentration exceeds 15%, the effect is saturated and it only causes an increase in cost. Furthermore, since a high Ni concentration tends to cause the above-mentioned diffusible void called the Kirkendall void, it is desirable that the Ni concentration be as low as possible in the desired melting point.
そこで、亜鉛合金相におけるＮｉとＦｅの濃度の合計：１５〜３０％，Ｚｎ：８５〜７０％とする。
実際のプレス成形温度と耐食性の観点から、ＮｉとＦｅの濃度の合計：１７〜２４％，Ｎｉの濃度：５〜１２％，Ｚｎ：８３〜７６％となる亜鉛合金相であることがより望ましい。
Therefore, the total concentration of Ni and Fe in the zinc alloy phase: 15 to 30%, and Zn: 85 to 70%.
From the viewpoint of actual press forming temperature and corrosion resistance, it is more desirable that the zinc alloy phase be 17 to 24% in total concentration of Ni and Fe, 5 to 12% in Ni concentration, and 83 to 76% in Zn. .
このような範囲で融点が所望の温度となるように、Ｆｅ，Ｎｉの濃度を調整すればよい。
本発明に係る熱間プレス成形部材は、前記固溶体層上または固溶体層内に形成されたこの亜鉛合金相を有する皮膜を、表層に有するものである。
The concentrations of Fe and Ni may be adjusted so that the melting point becomes a desired temperature in such a range.
The hot press-formed member according to the present invention has, as a surface layer, a film having the zinc alloy phase formed on or in the solid solution layer.
３．亜鉛合金相のＡｌ
Ａｌは、Ｎｉ，Ｚｎと親和性が高く、高融点の合金を形成するために少量でもＺｎの蒸散抑制に効果がある。このようなＡｌは、亜鉛合金相に金属状態で存在することが必要であり、亜鉛合金相の一部または全部が、金属状態で存在するＡｌを０．０１％以上含有することが望ましい。一方、同じＡｌ化合物でも酸化物は化成処理性などに悪影響を与え、塗膜の密着性を劣化させるため、可能な限り存在しないことが望ましい。
3. Zinc alloy phase Al
Al has a high affinity to Ni and Zn, and is effective in suppressing the transpiration of Zn even in a small amount to form a high melting point alloy. Such Al is necessary to be present in a metallic state in the zinc alloy phase, some or all of the zinc alloy phase, the Al present in a metallic state desirably contains 0.01% or more. On the other hand, even with the same Al compound, the oxide adversely affects the chemical conversion treatment property and the like to deteriorate the adhesion of the coating film.
以上説明した亜鉛合金相や固溶体層の組成は、断面からのＳＥＭ−ＥＤＸ測定によるＢＳＥ測定と点分析との組み合わせや、断面からのＥＰＭＡ分析によるＺｎ，Ｎｉ，Ａｌ，Ｏの分布を比較すること等により確認される。 The composition of the zinc alloy phase or solid solution layer explained above is to compare the combination of BSE measurement by SEM-EDX measurement from cross section and point analysis, and the distribution of Zn, Ni, Al, O by EPMA analysis from cross section It is confirmed by etc.
４．熱間プレス用鋼材
（１）素地鋼材
本発明に係る熱間プレス成形部材を得るための、熱間プレス用鋼材について説明する。
4. Steel material for hot press (1) Base steel material The steel material for hot press for obtaining the hot press-formed member according to the present invention will be described.
熱間プレス用鋼材の素地鋼材は、溶融亜鉛系めっきを施す場合にはめっき時のめっき濡れ性，めっき後のめっき密着性が良好であれば特に限定を要さず、また、電気亜鉛系めっきを施す場合にはめっき後のめっき密着性が良好であれば特に限定を要さないが、熱間プレス成形の特性として、熱間でのプレス成形後に急冷して高強度，高硬度とする焼入れを行うため、焼入れ鋼、例えば高張力鋼板が実用上は特に望ましい。 The base steel of the steel for hot pressing does not need to be particularly limited if plating wettability during plating and plating adhesion after plating are good in the case of hot-dip galvanizing, and galvanizing In the case of applying a metal, it is not particularly limited as long as the plating adhesion after plating is good, but as a characteristic of hot press forming, quenching is performed after press forming with hot to make high strength and high hardness In practice, hardened steels, such as high tensile steel plates, are particularly desirable.
このような高張力鋼板ではＳｉを多量に含有する場合があり、ステンレス鋼などとともにめっき濡れ性やめっき密着性に問題がある鋼種であるが、そのようなめっき濡れ性やめっき密着性に問題がある鋼種であっても、プレめっき処理等の公知のめっき密着性向上手法を用いてめっき密着性を改善することにより、本発明に係る熱間プレス成形部材の素地鋼材として用いることができる。また、このような密着性向上手法を用いた場合でも、固溶体層のＮｉ濃度が５.０％未満であれば本発明の範囲内である。 Such high-tensile steel sheets may contain a large amount of Si, which is a type of steel that has problems with wettability and adhesion with plating as well as stainless steel etc. However, problems with such wettability and adhesion with plating occur. Even if it is a certain steel type, it can be used as a base steel material of the hot press-formed member concerning the present invention by improving plating adhesion using publicly known plating adhesion improvement methods, such as a pre-plating process. In addition, even in the case of using such an adhesion improving method, if the Ni concentration of the solid solution layer is less than 5.0%, it is within the scope of the present invention.
鋼板の焼入れ後の強度は、主として含有炭素（Ｃ）量によって決定されるため、高強度が必要な場合には、Ｃ含有量を０．１％以上とすることが望ましい。一方、Ｃ含有量が高くなり過ぎると熱間プレス成形部材の靭性が低下するおそれがあるため、Ｃ含有量は３．０％以下とすることが望ましい。 Since the strength after quenching of the steel sheet is mainly determined by the amount of carbon (C) contained, when high strength is required, it is desirable to make the C content 0.1% or more. On the other hand, if the C content is too high, the toughness of the hot press-formed member may be reduced, so the C content is preferably 3.0% or less.
その他、鋼板の焼入れ性を高め、かつ熱間プレス成形後の強度を安定して確保するために、Ｓｉ，Ｍｎ，Ｃｒ，Ｐ，Ｓ，Ｎｉ，Ｃｕ，Ｍｏ，Ｖ，Ｔｉ，Ｎｂ，Ａｌ，Ｎ等を必要に応じて含有してもよく、さらに脱酸剤としてＢを必要に応じて含有してもよい。 In addition, Si, Mn, Cr, P, S, Ni, Cu, Mo, V, Ti, Nb, Al, Si, Mn, Cr, P, S, Ni, Cu, Mo, V, Ti, Nb, Al, in order to increase the hardenability of the steel sheet and to stably secure the strength after hot press forming. N may be contained as necessary, and B may be further contained as a deoxidizing agent as necessary.
素材としての一般的なプレス成形用鋼材の形態は板材が主流であるが、本発明の対象としては鋼材の形状は特に問わず、棒材、線材、管材などを素材として用いてもよい。 Although a plate material is the mainstream in the form of a general steel material for press forming as a material, the shape of the steel material is not particularly limited as a target of the present invention, and a rod, a wire, a pipe or the like may be used as the material.
（２）めっき皮膜
本発明に係る熱間プレス成形部材を得るための素地鋼材の上に設けるめっき皮膜としては、熱間プレス成形後に前記組成を有する、亜鉛合金相および固溶体層を有する皮膜を形成できれば、特に限定しないが、熱間プレス成形工程における生産性を考慮すれば、めっき層全体としてＦｅとＮｉの濃度の合計で１２〜２５％かつＮｉ／Ｆｅ比が０．１５以上となる、Ｚｎを含んだ皮膜であることが望ましい。Ｎｉ／Ｆｅ比が０．１５未満では加熱中にＦｅの拡散が進んでも本発明に係る熱間プレス成形部材の組成とならず、ＦｅとＮｉの濃度の合計が１２％未満では長時間加熱しない限り本発明に係る熱間プレス成形部材の組成とならず、７８０℃以上の融点を備えないために７８０℃以上でのプレス成形時に割れが誘発される。一方、ＦｅとＮｉの濃度の合計が２５％を越えると高温での保持時間を長くしても熱間プレス成形後の固溶体層中のＮｉ濃度が高くなり過ぎるため、上限とした。より望ましい範囲はＦｅとＮｉの濃度の合計で１５〜２３％かつＮｉ／Ｆｅ比が０．２０〜１．５であり、さらに望ましくはＮｉ／Ｆｅ比が０．２５〜１．０である。
(2) Plating film As a plating film provided on a base steel material for obtaining a hot press-formed member according to the present invention, a film having a zinc alloy phase and a solid solution layer having the above composition after hot press forming is formed. If possible, it is not particularly limited, but in consideration of the productivity in the hot press forming step, the total concentration of Fe and Ni in the entire plating layer is 12 to 25% and the Ni / Fe ratio is 0.15 or more. It is desirable that the film contains If the Ni / Fe ratio is less than 0.15, even if diffusion of Fe proceeds during heating, the composition of the hot press-formed member according to the present invention does not become a composition, and if the total concentration of Fe and Ni is less than 12%, heating is not performed for a long time As long as it does not have the composition of the hot press-formed member according to the present invention, a crack is induced at the time of press forming at 780 ° C. or more because it does not have a melting point of 780 ° C. or more. On the other hand, when the total concentration of Fe and Ni exceeds 25%, the Ni concentration in the solid solution layer after hot press forming becomes too high even if the holding time at high temperature is prolonged, and therefore, it is set as the upper limit. A more desirable range is 15 to 23% in total of the concentration of Fe and Ni, the Ni / Fe ratio is 0.20 to 1.5, and more preferably, the Ni / Fe ratio is 0.25 to 1.0.
このような皮膜を設ける手法は特に限定しないが、例えば電気めっき法や溶融めっき法、ならびに両手法の組み合わせなどによって得ることができる。また、電気めっき法，溶融亜鉛めっき法ともに前記皮膜を単一の組成のめっき浴から形成してもよいが、製造のコストや浴の安定性や品質の安定性の観点からＦｅを含む亜鉛合金めっき層を下層とし、当該めっき層の上層として、Ｎｉを主成分として含む金属あるいは合金からなるめっき層を設けることが望ましい。特に下層のめっき層を合金化溶融亜鉛めっきとし、上層を電気めっき法で形成することはより望ましい。 Although the method of providing such a film | membrane is not specifically limited, For example, it can obtain by the electroplating method, the hot-dip plating method, the combination of both methods, etc. In addition, although both the electroplating method and the hot-dip galvanizing method may form the film from a plating bath of a single composition, a zinc alloy containing Fe from the viewpoint of manufacturing cost, bath stability and quality stability It is desirable to use a plating layer as a lower layer, and to provide a plating layer made of a metal or alloy containing Ni as a main component as an upper layer of the plating layer. In particular, it is more desirable to form the lower plating layer as alloyed hot-dip galvanizing and to form the upper layer by electroplating.
他方、下層にＮｉ濃度の高いめっきを施すことは、固溶体層のＮｉ濃度を高めることになるため、長時間の加熱保持などによって固溶体層のＮｉ濃度が本発明で規定している範囲内に入る場合を除き、望ましくない。 On the other hand, plating the lower layer with a high concentration of Ni increases the concentration of Ni in the solid solution layer, so the concentration of Ni in the solid solution layer falls within the range specified in the present invention due to heating and holding for a long time. It is not desirable except in cases.
ここで、合金化溶融亜鉛めっき皮膜の中にはＡｌ，Ｍｇ，Ｓｉ，Ｍｎ，Ｃｒ，Ｖ，Ｔｉ，Ｍｏ，Ｗなどが一種または二種以上を必要に応じて適宜添加しても本発明の効果はなんら損なわれることはなく、Ｎｉも上層めっきのＮｉと合わせて本発明で規定している範囲内であれば合金化溶融亜鉛めっき皮膜中に含まれていてもよい。 Here, Al, Mg, Si, Mn, Cr, V, Ti, Mo, W, etc. may be appropriately added to the alloyed galvanized film according to the present invention, if necessary. The effect is not impaired at all, and Ni may be included in the alloying galvanized coating as long as it is within the range specified in the present invention in combination with Ni of the upper layer plating.
上層のＮｉを主成分として含む金属または合金めっきとしてはＮｉ単体の他にＮｉ−Ｆｅ，Ｎｉ−Ｚｎ，Ｎｉ−Ｃｏ，Ｎｉ−Ｃｒなどがあり、Ｎｉ量が本発明の範囲内であれば同様の効果を発揮するが、コストと製造安定性の観点からＮｉ単体めっきであることが望ましい。 As metal or alloy plating containing Ni in the upper layer as a main component, there are Ni-Fe, Ni-Zn, Ni-Co, Ni-Cr, etc. in addition to Ni alone as long as the amount of Ni is within the range of the present invention It is desirable to use Ni single plating from the viewpoint of cost and manufacturing stability.
なお、下層，上層のめっきともに、上記の意図した添加元素の他に原料に含まれる不純物や製造工程において不可避的に混入する不純物が含まれることがあるが、本発明の効果は何ら損なわれることはない。 In addition, although the lower layer and the upper layer plating may contain impurities contained in the raw materials and impurities which are inevitably mixed in the manufacturing process in addition to the above intended added elements, the effect of the present invention is not impaired at all. There is no.
電気めっき浴としては塩化物浴，硫酸浴，スルファミン酸浴の他に、Ｎｉを効率よくめっきできる浴であれば特に制限はないが、工業的に扱い易い硫酸浴や、塩化物浴と硫酸浴の混合浴の使用が望ましい。また、電流密度，浴温，ｐＨ，流速などのその他のめっき条件についてはコゲが発生しない範囲で均一な皮膜が得られる条件を選べばよい。 The electroplating bath is not particularly limited as long as it can efficiently plate Ni, in addition to chloride bath, sulfuric acid bath and sulfamic acid bath, but industrially easy to handle sulfuric acid bath, chloride bath and sulfuric acid bath The use of a mixed bath is desirable. In addition, other plating conditions such as current density, bath temperature, pH, flow rate, etc. may be selected such that uniform coating can be obtained in the range where no kogation occurs.
これらめっき層の形成後、必要に応じて後処理を行ってもよい。本発明の範囲内であれば通常は塗膜の密着性にはなんら問題はないが、よりいっそうの密着性を求める場合や、熱間プレス成形前に予め部材に近い形状に成形するために潤滑性が要求される場合、さらには溶接性の改善が要求される場合、その他の場合に、それぞれの目的に応じた処理を行ったものであっても、めっき層が本発明の範囲内であれば効果が損なわれることはなく、本発明の範囲内である。 After formation of these plating layers, post-treatment may be performed as needed. Within the range of the present invention, there is usually no problem with the adhesion of the coating film, but when further adhesion is required, or before forming into a shape close to a member before hot press forming, lubrication is required. Whether the plating layer is within the scope of the present invention, even if the treatment according to the respective purpose is performed, if the weldability is required or if the weldability is required to be improved. The effect is not impaired and is within the scope of the present invention.
５．熱間プレス成形方法
本発明に係る熱間プレス成形部材の熱間プレス成形法は、特に制限はなく、通常行われているプレス成形を熱間で行えばよい。すなわち、鋼材を加熱し、Ａｃ３点以上の温度域から臨界冷却速度以上の速度でプレス成形する。
5. Hot Press Forming Method The hot press forming method of the hot press formed member according to the present invention is not particularly limited, and the press forming which is usually performed may be hot. That is, the steel material is heated and press-formed at a speed equal to or higher than the critical cooling rate from a temperature range of 3 or more Ac.
ここで、耐食性をより発揮するためには、亜鉛合金相が多く残存することが有効であるため、大気中または微酸化雰囲気中で加熱を行ない、昇温速度は速く、かつ熱間プレス部材に形成されるめっき層の融点以上の温度での保持時間は素地鋼材中のＣが完全に溶解するために必要な時間以上で短いことが望ましい。具体的には、昇温速度は１０℃／ｓｅｃ以上であることが望ましく、保持時間は３分間未満であることが望ましく、１分間未満であることがさらに望ましい。さらに、亜鉛合金相を皮膜の厚み方向に分散させるためには保持時間は１０秒間未満であることが望ましく、５秒間未満であることがさらに望ましい。 Here, since it is effective for the zinc alloy phase to remain in a large amount in order to further exhibit corrosion resistance, heating is performed in the atmosphere or in a slightly oxidized atmosphere, and the temperature rising rate is fast and the hot pressed member is The holding time at a temperature higher than the melting point of the plating layer to be formed is desirably shorter than the time necessary for complete dissolution of C in the base steel material. Specifically, the temperature rising rate is preferably 10 ° C./sec or more, the holding time is preferably less than 3 minutes, and more preferably less than 1 minute. Furthermore, in order to disperse the zinc alloy phase in the thickness direction of the film, the retention time is desirably less than 10 seconds, and more desirably less than 5 seconds.
プレス成形開始温度は、本発明に係る熱間プレス成形部材が備える亜鉛合金相の融点未満であれば如何なる温度でもよいが、本発明の効果をより享受するためには７８０℃以上でのプレス成形であることが望ましい。 The press forming start temperature may be any temperature as long as it is less than the melting point of the zinc alloy phase of the hot press-formed member according to the present invention, but in order to obtain the effects of the present invention more, press forming at 780 ° C. or higher Is desirable.
次に、実施例によって本発明の作用効果をさらに具体的に説明する。
素地鋼材として通常の熱延工程および冷延工程により製造された、鋼成分としてＣ：０．２１％，Ｓｉ：０．２％，Ｍｎ：１．３％，Ｐ：０．００５％，Ｓ：０．００１％，Ｃｒ：０．２％，Ｂ：０．００２％を含む冷延鋼板（板厚１．６ｍｍ）を用いた。
Next, the effects of the present invention will be more specifically described by way of examples.
C: 0.21%, Si: 0.2%, Mn: 1.3%, P: 0.005%, S: as a steel component manufactured as a base steel material by ordinary hot rolling process and cold rolling process A cold-rolled steel plate (plate thickness 1.6 mm) containing 0.001%, Cr: 0.2%, B: 0.002% was used.
実施例１〜２１についてはこの冷延鋼板上に下層として表１に示す付着量，組成となるように溶融亜鉛めっき又は合金化溶融亜鉛めっきを施し、そのうち、実施例１〜１４，１６〜１７については上層としてＮｉＳＯ４・６Ｈ２Ｏ＝２４０ｇ／Ｌ，ＮｉＣｌ２・６Ｈ２Ｏ＝４５ｇ／Ｌ，Ｈ３ＢＯ３＝３５ｇ／Ｌを含む電気Ｎｉめっき浴を用いて攪拌を十分に行いながら浴温４５℃，電流密度２０Ａ／ｄｍ２で表１に示す付着量となるように電気Ｎｉめっきを施した。 In Examples 1 to 21, hot-dip galvanizing or alloying galvanization is performed on the cold-rolled steel plate as the lower layer so that the adhesion amount and composition shown in Table 1 are obtained, and of those, Examples 1 to 14, 16 to 17 The bath is carried out using an electric Ni plating bath containing NiSO 4 · 6 H 2 O = 240 g / L, NiCl 2 · 6 H 2 O = 45 g / L, and H 3 BO 3 = 35 g / L as the upper layer. Electro Ni plating was applied so that the adhesion amount shown in Table 1 was obtained at a temperature of 45 ° C. and a current density of 20 A / dm 2 .
実施例１５と実施例２２では、上層めっきとしてＺｎ−Ｎｉ合金めっきを施した。Ｚｎ−Ｎｉ合金めっきは、ＺｎＳＯ４・７Ｈ２Ｏ＝８６ｇ／Ｌ，ＮｉＳＯ４・６Ｈ２Ｏ＝３１５ｇ／Ｌ、Ｎａ（ＳＯ４）２＝７５ｇ／Ｌを含むめっき浴を用いて相対流速１ｍ／ｓで流動を与えつつ、浴温５０℃，電流密度４０Ａ／ｄｍ２にて表１に示す付着量となるように施した。実施例２２の下層Ｎｉめっきは実施例１〜１４などと同条件で施した。 In Example 15 and Example 22, Zn-Ni alloy plating was performed as upper-layer plating. Zn-Ni alloy plating is carried out using a plating bath containing ZnSO 4 · 7H 2 O = 86 g / L, NiSO 4 · 6H 2 O = 315 g / L, Na (SO 4 ) 2 = 75 g / L, and the relative flow rate is 1 m / m. while providing flow at s, bath temperature 50 ° C., was subjected at a current density of 40A / dm 2 so that the adhesion amount shown in Table 1. The lower layer Ni plating of Example 22 was performed under the same conditions as in Examples 1-14.
得られためっき鋼板を空燃比１：１のガス炉または通電加熱により８８０℃に所定の平均昇温速度で加熱し、所定時間保持した後に取り出して７８０℃以上の所定の温度でプレス加工を行った。 The plated steel sheet thus obtained is heated at 880 ° C. at a predetermined average heating rate by an air-fuel ratio 1: 1 gas furnace or by electric heating, held for a predetermined time, taken out, and pressed at a predetermined temperature of 780 ° C. or higher The
このように作製した熱間プレス成形部材の一部を切り出してエポキシ系樹脂に埋め込んだ後に研磨し、断面観察用の試料を作製した。この断面観察用の試料について、合金相の有無，合金相中のＦｅ濃度およびＮｉ濃度，合金相中のＡｌの有無，固溶体層のＮｉ濃度についてはＳＥＭ−ＥＤＸ分析により、合金相中のＡｌについては断面からのＥＰＭＡ分析も併用して、確認を行った。結果を表１にまとめて示す。 A part of the hot press-formed member thus produced was cut out, embedded in an epoxy resin, and then polished to prepare a sample for cross-sectional observation. About this sample for cross-sectional observation, the presence or absence of the alloy phase, the concentration of Fe and Ni in the alloy phase, the presence or absence of Al in the alloy phase, and the concentration of Ni in the solid solution layer according to SEM-EDX analysis Confirmed using EPMA analysis from the cross section as well. The results are summarized in Table 1 below.
熱間プレス成形部材の割れ，電着塗装後の耐食性，腐食形態について評価を行った。評価方法を以下に列記するとともに、評価結果を表１にまとめて示す。 Evaluations were made on the cracking of the hot-pressed parts, the corrosion resistance after electrodeposition coating, and the form of corrosion. The evaluation method is listed below, and the evaluation results are summarized in Table 1.
（１）耐プレス割れ性試験（割れ）
熱間プレス成形部材の割れは、プレス加工の金型に９０度のＶ曲げ型のものを用い、プレス成形後の割れの有無を目視により評価した。成形開始温度は予め熱電対を付けた試料の、炉から取り出した後の時間による温度変化を測定しておき、所定の温度となる時間放冷することにより制御した。評価基準は、成形開始時の鋼板温度が８２０℃での成形で割れの観察されなかったものを◎とし、同じく８００℃の成形で割れの観察されなかったものを○とし、同じく８００℃の成形で割れが観察されたものを×とし、◎と○を合格とした。
(1) Press crack resistance test (cracking)
The cracks of the hot press formed member were evaluated by visually observing the presence or absence of cracks after press forming, using a 90 ° V-bending die for press working. The molding start temperature was controlled by measuring the temperature change of the sample attached with a thermocouple in advance after taking it out of the furnace and letting it cool for a predetermined temperature. The evaluation criteria are as follows: ◎ where no cracking was observed in the forming at a steel sheet temperature at the beginning of forming at 820 ° C., and 割 れ where no cracking was observed in the same forming at 800 ° C., also at 800 ° C. The thing in which the crack was observed was made into x, and it was set as ◎ and を.
（２）塗装後耐食性試験（耐食性）
塗装後の耐食性は、平板状のプレス金型を用い、炉から取り出した後に鋼板温度が８００℃に達したときにプレス金型で挟み込んで急冷して得られた部材に日本パーカラインジング（株）製ＰＢＬ−３０８０で通常の化成処理条件によりリン酸亜鉛処理した後、関西ペイント製電着塗料ＧＴ−１Ｏを電圧２００Ｖのスロープ通電で電着塗装し、焼付け温度１５０℃で２０分間の焼付けを行い、２０μｍの塗膜を得た。
(2) Post-painting corrosion resistance test (corrosion resistance)
The corrosion resistance after painting was determined using a flat press die and after taking it out of the furnace, when the steel plate temperature reached 800 ° C., Nippon Perca Ringing (stock) was obtained by sandwiching and quenching the press die. ) Zinc-treated with PBL-3080 under the usual chemical conversion treatment conditions, electrodeposited the electrodeposition paint GT-1O manufactured by Kansai Paint Co., Ltd. with a slope of 200 V, and baked for 20 minutes at a baking temperature of 150 ° C. Then, a coating of 20 μm was obtained.
得られた試験片の塗膜にカッターナイフで素地まで達するスクラッチ傷を入れ、ＪＩＳ Ｈ ８５０２に規定された中性塩水噴霧サイクル試験を３６０サイクル行った。傷部からの塗膜膨れ幅もしくは錆幅を測定し、塗装後耐食性の評価とした。評価基準は塗膜膨れ幅または錆幅のいずれか大きいほうの値が５ｍｍ未満を○とし、５ｍｍ以上を×とし、○を合格とした。 The coating film of the obtained test piece was scratched with a cutter knife to reach the substrate, and subjected to 360 cycles of a neutral salt spray cycle test specified in JIS H8502. The coating film swelling width or rust width from the flaw was measured to evaluate the corrosion resistance after coating. As the evaluation criteria, the larger value of either the coating film blister width or the rust width is less than 5 mm as ○, 5 mm or more as x, and ○ as pass.
（３）腐食形態観察（腐食形態）
腐食形態の評価は、前記の塗装後耐食性試験を行った後の試験片からスクラッチ部をスクラッチ傷に対して垂直に切り出し、エポキシ系樹脂に埋め込んだ後に研磨し、塗膜膨れ部もしくは錆部の先端を観察して行なった。
(3) Corrosion form observation (corrosion form)
For evaluation of the corrosion form, a scratched part is cut out perpendicular to a scratch from a test piece after the above-mentioned post-painting corrosion resistance test, embedded in an epoxy resin and then polished, and the coating bulge or rusted part It did by observing the tip.
評価基準は、図２の断面ＳＥＭ写真に示すような錆中に貴な固溶体層が見られない物を全面とし、図３の断面ＳＥＭ写真に示すような錆中に貴な固溶体層が腐食していない金属部と繋がって残存して貴な固溶体層の下部が腐食している物を孔食状とし、さらに、錆中に貴な固溶体層は存在するが腐食していない金属部と繋がっていない物をやや孔食状とし、全面ならびにやや孔食状の腐食形態を合格とした。 As the evaluation criteria, the noble solid solution layer is not seen in the rust as shown in the cross-sectional SEM photograph in FIG. 2 as the entire surface, and the noble solid solution layer is corroded in the rust as shown in the cross-sectional SEM photograph in FIG. The pitted part is formed by corroding the remaining lower part of the noble solid solution layer connected with the unpainted metal part, and further, the noble solid solution layer is present in the rust but connected to the non-corroded metal part Those not present were regarded as slightly pitted and all pits and pitted corrosion were accepted.
固溶体層中のＮｉ濃度が高くなり過ぎると素地鋼材の電位よりも貴となるため、固溶体層よりも先に素地鋼材が腐食され、孔食へと繋がることになる。そのため、金属部と繋がって残存して存在し、その下部が腐食している腐食形態は孔食発生有無の指針となる。 If the concentration of Ni in the solid solution layer is too high, the potential is higher than the potential of the base steel material, so that the base steel material is corroded earlier than the solid solution layer, leading to pitting. Therefore, the corrosion form in which the metal part is connected and remains and the lower part is corroded serves as a guideline for the occurrence of pitting.
本発明例である代符３〜６，１５〜２０，１７は耐プレス割れ性，塗装後耐食性，腐食形態がいずれも良好であった。
一方、熱間プレス成形後に合金相が存在しない代符１〜２，１５，２１は、塗装後耐食性が不合格である。合金相の組成が本発明の範囲から外れている代符１６，１８〜２０は、耐プレス割れ性が不合格である。熱間プレス成形後の固溶体層中Ｎｉ濃度が高過ぎる代符７〜８，２２は、腐食形態が孔食状である。このように、比較例には、耐プレス割れ性，塗装後耐食性，腐食形態の全てが合格レベルを満足するものは存在しなかった。
As for the marks 3 to 6, 15 to 20 and 17 which are examples of the present invention, all of the press crack resistance, the corrosion resistance after coating, and the corrosion form were good.
On the other hand, the corrosion resistance after coating is rejection of the marks 1 to 2, 15, 21 in which no alloy phase is present after hot press forming. The marks 16, 18 to 20 in which the composition of the alloy phase is out of the range of the present invention fail the press crack resistance. In the codes 7 to 8 and 22 in which the Ni concentration in the solid solution layer after hot press forming is too high, the corrosion form is pitted. Thus, in the comparative examples, none of the press cracking resistance, the corrosion resistance after coating, and the corrosion form satisfied the pass level.
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| JP7239059B2 (en) * | 2020-03-23 | 2023-03-14 | 日本製鉄株式会社 | hot stamped body |
| CN114981467B (en) * | 2020-03-23 | 2023-10-31 | 日本制铁株式会社 | Hot-stamped molded article |
| US11746434B2 (en) | 2021-07-21 | 2023-09-05 | Battelle Energy Alliance, Llc | Methods of forming a metal coated article |
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| JP3277816B2 (en) * | 1995-07-19 | 2002-04-22 | ユケン工業株式会社 | Ternary zinc alloy electroplating method |
| JP2002060978A (en) * | 2000-08-17 | 2002-02-28 | Nippon Steel Corp | Steel having metallic coating and excellent in corrosion resistance |
| JP4039548B2 (en) * | 2001-10-23 | 2008-01-30 | 住友金属工業株式会社 | Hot press molded products with excellent corrosion resistance |
| JP2004114052A (en) * | 2002-09-24 | 2004-04-15 | Nippon Steel Corp | High temperature press-forming method |
| JP4506128B2 (en) * | 2003-08-29 | 2010-07-21 | 住友金属工業株式会社 | Hot press-formed product and method for producing the same |
| ES2384135T3 (en) * | 2009-08-25 | 2012-06-29 | Thyssenkrupp Steel Europe Ag | Procedure for manufacturing a steel component provided with a corrosion protection metallic coating and steel component |
| KR101402503B1 (en) * | 2009-08-31 | 2014-06-03 | 신닛테츠스미킨 카부시키카이샤 | High-strength hot-dip galvanized steel sheet and process for producing same |
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