JP6493472B2 - Manufacturing method of hot press-formed member - Google Patents

Description

The present invention is a hot press-formed member produced by pressing a heated steel material, particularly hot parts used for parts that require high strength and high corrosion resistance, such as automobile undercarriage parts and lower body reinforcement members. The present invention relates to a method for manufacturing a press-formed member.

Due to increasing environmental awareness, there is a further demand for lighter automobiles that greatly contribute to the reduction of CO ₂ emissions. Efforts are being made to reduce the weight of automobiles by increasing the strength of the steel used and reducing the thickness of the steel. However, since the formability of steel materials (in the following explanation, taking the press workability of steel sheets as an example) decreases with increasing strength, the galling and fracture of steel sheets when processing steel sheets into the desired shape by press forming In addition, various problems such as springback and variation in shape occur.

  In recent years, hot press molding technology has been widely used as a solution to these problems. The hot press forming technology is a heat treatment with a desired high strength by quenching while preventing the occurrence of the above problems during forming in a high strength steel plate by press forming and quenching in a state where the high carbon steel plate is heated to a high temperature. This is a technique for producing an intermediate press-formed member.

  However, in the case of a bare steel plate, an oxide with poor adhesion is generated on the surface of the steel plate during heating, and this oxide may damage the surface of the mold and the steel plate by dropping during hot press forming, It is necessary to frequently care for the press mold or to perform an oxide removing process such as a shot blasting process on the hot press-formed member, which is a cause of reducing the productivity of the hot press-formed member. Furthermore, since the hot press-formed member produced in this way has not been subjected to rust prevention treatment such as galvanization, even if it has been subjected to chemical conversion treatment and electrodeposition coating, in particular, undercarriage parts of automobiles and lower parts of the vehicle body It cannot satisfy the corrosion resistance required for parts such as reinforcing members that require high strength and high corrosion resistance.

  In Patent Document 1, as a technology for ensuring the corrosion resistance after coating of a hot press-formed member by suppressing the formation of such an oxide having poor adhesion, the technology of applying aluminum plating to a hot press-formed steel plate, Disclosed. Aluminum plating film has been put into practical use in order to show excellent oxidation resistance, but it is difficult to apply to the above parts because it does not have sacrificial corrosion resistance. There is a strong demand for steel plates for hot press forming.

  In order to meet such a demand, development of a hot-press forming steel sheet by zinc-based plating is underway. However, since zinc has a melting point of 419 ° C. and a boiling point of 907 ° C. and is in the liquid phase or gas phase in the temperature range where hot press molding is actually performed, the galvanized layer is evaporated and oxidized, and the amount of residual zinc is There is a problem that the corrosion resistance is remarkably deteriorated due to lowering, or cracking of the plating layer is induced at the time of press molding by zinc in a liquid phase. Methods for avoiding this problem are disclosed in Patent Documents 2-6.

In Patent Document 2, C: 0.08 to 0.45% (in this specification, “%” relating to chemical composition means “% by mass” unless otherwise specified), one or both of Mn and Cr: a steel sheet containing 0.5 to 3.0%, has a Zn plating layer Zn deposition amount is 10~90g / ^{m 2} with Fe content is from Fe-Zn alloy is 5% to 80%, A steel sheet for hot pressing that is pressed after being heated to 800 to 1000 ° C. to form a ZnO layer is disclosed.

  Patent Document 3 discloses that a steel sheet containing C: 0.1 to 0.5%, Si: 0.05 to 0.5%, and Mn: 0.5 to 3% has a plating layer cross section of the base steel sheet interface. The vicinity is composed of a layered Zn-Fe alloy layer containing 50 to 80% Fe, and the other part contains 50 to 80% Fe in a Zn-Fe alloy phase matrix containing 10 to 30% Fe. There is a Zn-Fe alloy plating layer in which a Zn-Fe alloy phase having a spherical shape is distributed in an island shape, and the surface layer of the plating layer is made of Zr, Ti, Si having a thickness of 10 to 100 nm and containing F element Disclosed is a hot pressed steel having one or both coatings of one or more metal oxides or metal hydroxides.

  Patent Document 4 mainly uses one or more metals selected from the group consisting of Fe, Ni, and Co provided as an upper layer of a plating layer in a steel sheet having a zinc or zinc-containing plating layer on the surface. A hot press-forming steel material having a plating layer made of a metal or alloy contained as a component and heated and pressed at 700 to 1000 ° C. is disclosed.

  Patent Document 5 has a Zn-based plating containing Zn of 60% or more on a steel plate surface containing C: 0.1 to 0.8% and Mn: 0.5 to 3%. Disclosed is a Zn-plated steel sheet for hot pressing having a layer containing a total of 80% or more of one or more elements of Ni, Cu, Cr, and Sn on the surface.

Further, Patent Document 6 discloses that the steel plate surface contains 60% or more of Ni in order, the balance being Zn and inevitable impurities, and a plating layer I having an adhesion amount of 0.01 to 5 g / m ² and 10 A steel sheet for hot pressing is disclosed, which includes ˜25% Ni, the balance being Zn and inevitable impurities, and a plating layer II having an adhesion amount of 10 to 90 g / m ² .

JP 2000-38640 A Japanese Patent No. 3582512 Japanese Patent No. 4695459 Japanese Patent No. 3591501 JP 2004-124207 A Japanese Patent No. 4883240

  According to the hot-press steel sheet disclosed in Patent Document 2, Zn transpiration is suppressed, corrosion resistance is good, and a Zn plating film that does not cause cracking due to Zn in a liquid state is obtained, but the parts to be applied are When high corrosion resistance is required, the corrosion resistance may be insufficient, and further improvement in corrosion resistance is required.

  In the hot-pressed steel material disclosed in Patent Document 3, it is necessary to cool the hot-press-forming steel sheet to less than 780 ° C. during press forming, so a decrease in productivity is inevitable, and the press-forming start temperature is increased. Is required.

  The steel material for hot press forming disclosed in Patent Document 4 and the Zn-based plated steel sheet for hot pressing disclosed in Patent Document 5 are markedly improved by the upper Ni plating, and can suppress the transpiration of Zn. Although it is possible to obtain a plating film that has high corrosion resistance and does not crack even when molded at a high temperature, as with the hot-press steel sheet disclosed in Patent Document 2, when applied to parts that require strict corrosion resistance, the corrosion resistance is reduced. Insufficient or may exhibit pitting corrosion without exhibiting sacrificial anticorrosive ability, and lack performance stability.

  Furthermore, in Patent Document 6, it is said that the steel sheet for hot press disclosed in Patent Document 6 has excellent perforation corrosion resistance. However, when the present inventors actually conducted a confirmation test, they gave scratches that reached the substrate. In this case, pitting corrosion was induced, resulting in poor perforated corrosion resistance.

  As described above, the problems of the techniques disclosed in Patent Documents 2 to 4 and Patent Document 6 are the maintenance of high corrosion resistance and the width of the process window due to cracking due to zinc in the liquid phase during high temperature molding (heating temperature (Tolerable range) cannot be sufficiently secured. That is, in order to ensure high corrosion resistance, particularly high sacrificial corrosion resistance, it is desirable to suppress zinc transpiration and leave the zinc-based Fe—Zn alloy phase, but the zinc-based Fe—Zn alloy phase has the highest melting point. However, it is 780 ° C., and the allowable range of the heating temperature is narrowed (the process window is narrowed). On the other hand, the upper layer Ni plating technique (Patent Document 5), which is a technique capable of ensuring both corrosion resistance and a process window, has a problem in stability of performance.

The present inventors considered that it is most effective to stabilize the performance by upper layer Ni plating technology in order to solve the above-mentioned problems, and as a result of repeated earnest studies,
(A) The remaining of the alloy plating layer and the concentration of Fe and Ni in the alloy plating layer greatly affect the corrosion resistance and cracking during high temperature forming, and (B) the suppression of the Ni concentration in the solid solution layer is It has been found that the sacrificial anticorrosive ability and perforated corrosion resistance of the steel are greatly affected.

  That is, in an Fe—Zn alloy, any alloy plating phase becomes a liquid phase at 780 ° C. or higher, but when Ni is added here, an Fe—Ni—Zn alloy plating phase is formed as a new alloy plating phase. Because the melting point is 780 ° C. or higher, the liquid phase does not form up to a higher temperature than the binary alloy of Fe—Zn, the corrosion resistance is improved because Zn remains without evaporating, and it solidifies at a high temperature. No cracking during high temperature molding. Based on this knowledge, the conventional technology has proposed that a small amount of metal or alloy such as Ni is plated on Zn plating (flash plating) to increase the melting point of the surface layer only. Since the composition of the lower plating layer and the film structure after hot press forming are not taken into consideration, an alloy plating phase having a desired melting point can be stably formed by hot press forming. Therefore, it is considered that the performance could not be obtained because Zn evaporation or liquid phase generation could not be sufficiently controlled.

  In addition, if the amount of upper Ni plating is excessively increased and corrosion resistance and avoidance of cracking during high-temperature forming are desired, or if Zn-Ni alloy plating with a high Ni concentration is selected, the cost is increased by using a large amount of expensive Ni. In addition to being disadvantageous, the Ni concentration of the solid solution layer is also high and the sacrificial anticorrosive ability is exhibited for a short period of time. However, as the corrosion further progresses after consuming the Zn-rich alloy plating phase, It is considered that the result is inferior in corrosion resistance. This is considered to occur because the potential difference from the base steel material becomes too small due to the high Ni concentration in the solid solution layer. Such a tendency to become pitting corrosion as corrosion progresses is particularly seen when a large amount of Ni is contained in the plating layer and steel material interface as disclosed in Patent Document 6.

FIG. 1 is a cross-sectional SEM photograph showing a situation where diffusible voids called Kirkendall voids are generated.
In addition, when the amount of upper layer Ni plating is increased excessively or when Zn-Ni alloy plating with a high Ni concentration is selected, the diffusion rate of Zn or Ni from the solid solution layer into the base steel material, and the base steel material The difference between the diffusion rate of Fe into the solid solution layer, the diffusion rate of Fe from the solid solution layer into the alloy plating phase, and the diffusion rate of Zn and Ni from the alloy plating phase into the solid solution layer is increased, as shown in FIG. Diffusive voids called Kirkendall voids are easily generated as shown by the cross-sectional SEM photograph. Such voids cause film cracking during processing. If the voids increase, peeling of the alloy plating phase is caused and the base alloy phase is largely lost. Therefore, it is thought that it becomes a result inferior to corrosion resistance.

  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 inventors ensure corrosion resistance and process window. The present invention has been completed by finding out that it is possible to achieve both high dimensions and stably exhibit performance.

In the present invention, a zinc alloy plating layer containing Fe is provided on a steel plate, a plating layer made of a metal or alloy containing Ni as a main component is provided on the zinc alloy plating layer, and then hot pressing is performed on the steel plate. By performing molding,
The Zn content is 15% or more, desirably 30% or more, and the Ni content is less than 5%. The Ni content is formed on or in the solid solution layer , and the Zn content is 85 to 70% by mass. Manufacture a hot press-molded member having a coating layer with a zinc alloy layer of 15 to 30%, preferably 17 to 24%, and Ni of 3 to 15%, preferably 5 to 12% in total on the surface layer of Fe This is a method for producing a hot press-formed member.
In the present invention, the zinc alloy plating layer containing Fe and the plating layer made of a metal or alloy containing Ni as a main component as a whole have a total concentration of Fe and Ni of 12 to 25% and a Ni / Fe ratio of 0.1. It is desirable that the film contains Zn and is 15 or more.
In these inventions, the zinc alloy plating layer containing Fe is preferably an alloyed hot dip galvanizing layer, and the plating layer made of a metal or alloy containing Ni as a main component is preferably an electroplating layer.
In these present inventions, the hot press forming is performed by heating the steel sheet to a temperature range of Ac ₃ point or higher at a temperature increase rate of 10 ° C./sec or more and holding it in this temperature range for less than 3 minutes, and then the critical cooling rate. It is desirable to perform by pressing while cooling at the above speed. In this case, it is desirable that the press molding start temperature is 780 ° C. or higher and lower than the melting point of the zinc alloy plating layer containing Fe.

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%.
Note that the zinc alloy layer, which is 15 to 30% in total of Ni and Fe, is an intermediate phase between the Γ phase of the Fe—Zn alloy and the γ phase of the Ni—Zn alloy, but different from both phases. Since the lattice spacing and the like are close, it is difficult to distinguish these three phases by the X-ray diffraction method or the like. Therefore, the determination is made by using an instrument capable of composition analysis such as SEM-EDX analysis from a cross section.

  In the present invention, it is more desirable that a part or all of the zinc alloy layer contains 0.01% or more of Al present in a metallic state. Al has a high affinity with Ni and Zn, and is effective in suppressing the transpiration of Zn in order to form a high melting point alloy. Such Al needs to exist in a metal state in the alloy layer. This means that the location of O, Al, Fe, Ni and Zn is identified and compared by EPMA analysis from a cross section. Is determined.

In the present invention, it is desirable that the zinc alloy layer is formed dispersed in the thickness direction of the coating.
As a hot press forming steel material for forming such a film, for example, a total of 12 to 25%, preferably 15 to 23%, and a Ni / Fe ratio of Fe and Ni as a whole plating layer on a steel plate. Examples are provided with a plating layer containing Zn that is 0.15 or more, preferably 0.2 to 1.5, more preferably 0.25 to 1.0.

  In particular, it is more desirable that the coating provided on the steel sheet has a zinc alloy plating layer containing Fe as a lower layer and a plating layer made of a metal or alloy containing Ni as a main component as the upper layer of the plating layer. If such a steel material is used and hot press molding is performed by an ordinary method, a hot press molded member having the above-described film can be obtained.

  By using the steel material as described above and forming a hot press-molded member having the film, cracks do not occur even when hot press-molding is performed at a high temperature of 780 ° C. or higher, and can be applied to severely corroded parts. A hot press-formed member having high corrosion resistance can be stably produced.

FIG. 1 is a cross-sectional SEM photograph showing a situation where diffusible voids called Kirkendall voids are generated. FIG. 2 is a cross-sectional SEM photograph. FIG. 3 is a cross-sectional SEM photograph.

Hereinafter, each limited range in the present invention will be described in detail.
1. Solid solution layer of hot press-molded member The solid solution layer is a phase in which Zn is solid-solved in Fe, and has a sacrificial anticorrosive property although it is not completely equivalent to a zinc alloy phase described below mainly composed of Zn. When Ni is contained in this solid solution layer, nobleness rapidly progresses, and if it contains only a few%, it becomes a noble potential compared with Fe of the base, and induces pitting corrosion. As the Zn content in the solid solution layer decreases, the degree of preciousness increases even with a smaller amount of Ni. Therefore, the Ni concentration in the solid solution layer is preferably less than 5.0% and more preferably less than 4.0%. More preferably, it is less than 0.0%.

  If the Zn content in the solid solution layer is less than 15%, even if Ni is not included, the potential difference from the base Fe is almost eliminated. Therefore, the lower limit of the Zn concentration of the solid solution layer as the anticorrosion layer is 15%. In the present invention, since Ni is inevitably contained in the solid solution layer, the Zn concentration in the solid solution layer is preferably 20% or more, and more preferably 30% or more.

  Here, even if a solid solution layer containing 15% or less of Zn and containing no Ni is formed in a lower layer of the solid solution layer as the anticorrosion layer, the effect of the present invention is not impaired.

2. Zinc Alloy Phase of Hot Press-Molded Member The zinc alloy phase exists on or in the solid solution layer described above. The zinc alloy layer is desirably formed in a dispersed manner in the thickness direction of the coating. The presence 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 the formability and corrosion resistance at high temperatures.

  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 it remains liquid at 780 ° C. or higher. Induces cracks during press forming. On the other hand, the higher the Ni concentration is, the higher the melting point is. However, the solid phase may be used at the temperature at which the actual press forming is performed, and the total concentration of Ni and Fe in the zinc alloy phase is 30%. If the Ni concentration exceeds 15% or the Ni concentration exceeds 15%, the effect is saturated and only the cost is increased. Further, when the Ni concentration is high, the above-mentioned diffusive voids called Kirkendall voids are likely to be generated. Therefore, it is desirable that the Ni concentration is as low as possible while having a desired melting point.

Therefore, the total concentration of Ni and Fe in the zinc alloy phase is 15 to 30%, and Zn is 85 to 70%.
From the viewpoint of actual press molding temperature and corrosion resistance, it is more preferable that the zinc alloy layer has a total concentration of Ni and Fe: 17 to 24%, a concentration of Ni: 5 to 12%, and Zn: 83 to 76%. .

What is necessary is just to adjust the density | concentration of Fe and Ni so that melting | fusing point may become desired temperature in such a range.
The hot press-molded member has a film having the zinc alloy layer formed on or in the solid solution layer on the surface layer.

3. Al of zinc alloy layer
Al has a high affinity with Ni and Zn, and is effective in suppressing transpiration of Zn even in a small amount in order to form a high melting point alloy. Such Al needs to exist in a metallic state in the zinc alloy layer, and it is desirable that a part or all of the zinc alloy phase contains 0.01% or more of Al existing in the metallic state. On the other hand, even if the same Al compound is used, it is desirable that the oxide does not exist as much as possible because it adversely affects chemical conversion properties and degrades the adhesion of the coating.

  The composition of the zinc alloy phase and the solid solution layer described above is to compare the combination of BSE measurement by SEM-EDX measurement from the cross section and point analysis, and the distribution of Zn, Ni, Al, O by EPMA analysis from the cross section. Etc.

4). Hot press steel (1) Base steel
A steel material for hot press for obtaining a hot press-formed member will be described.

  The base steel for hot pressing steel is not particularly limited when hot dip galvanizing is applied, as long as the plating wettability during plating and the plating adhesion after plating are good. If the plating adhesion after plating is good, there is no particular limitation. However, as a characteristic of hot press forming, quenching is performed by rapidly cooling after hot press forming to high strength and high hardness. Therefore, hardened steel, for example, high-tensile steel sheet is particularly desirable in practice.

Such high-tensile steel sheet may contain a large amount of Si, and it is a steel type that has a problem in plating wettability and plating adhesion with stainless steel etc., but there is a problem in such plating wettability and plating adhesion. Even a certain steel type can be used as a base steel material for a hot press-formed member by improving the plating adhesion using a known plating adhesion improving method such as pre-plating treatment. Further, even when such an adhesion improving method is used, it is within the scope of the present invention if the Ni concentration of the solid solution layer is less than 5.0%.

  Since the strength after quenching of the steel sheet is mainly determined by the amount of carbon (C) contained, it is desirable that the C content be 0.1% or more when high strength is required. On the other hand, if the C content becomes too high, the toughness of the hot press-formed member may be lowered. Therefore, the C content is preferably 3.0% or less.

  In addition, Si, Mn, Cr, P, S, Ni, Cu, Mo, V, Ti, Nb, Al, in order to improve the hardenability of the steel sheet and ensure the strength after hot press forming stably. N or the like may be contained as necessary, and B may be contained as a deoxidizer as needed.

  A plate material is a main form of a general steel material for press forming as a material. However, the shape of the steel material is not particularly limited as an object of the present invention, and a bar material, a wire material, a pipe material, or the like may be used as a material.

(2) Plating film
The plating film provided on the base steel material for obtaining the hot press-formed member is not particularly limited as long as a film having the above composition after hot press forming and having a zinc alloy phase and a solid solution layer can be formed. Considering the productivity in the press molding process, it is desirable that the coating layer containing Zn has a total concentration of Fe and Ni of 12 to 25% and a Ni / Fe ratio of 0.15 or more as a whole plating layer. . The Ni / Fe ratio is less than 0.15 also progressed diffusion Fe during the heating not the composition of the hot press forming member, hot pressing as long as the sum of the concentrations of Fe and Ni is not prolonged heating is less than 12% Since it does not have the composition of the molded member and does not have a melting point of 780 ° C. or higher, cracks are induced during press molding at 780 ° C. or higher. On the other hand, if 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 a high temperature is increased, so the upper limit was set. A more desirable range is 15 to 23% in total of the concentration of Fe and Ni, and a Ni / Fe ratio is 0.20 to 1.5, and a Ni / Fe ratio is more preferably 0.25 to 1.0.

  Although the method of providing such a film is not particularly limited, it can be obtained by, for example, an electroplating method, a hot dipping method, a combination of both methods, or the like. In addition, both the electroplating method and the hot dip galvanizing method may form the coating from a plating bath having a single composition. However, a zinc alloy containing Fe from the viewpoint of manufacturing cost, bath stability, and quality stability. It is desirable to provide a plating layer made of a metal or an alloy containing Ni as a main component as a lower layer and a plating layer as an upper layer. In particular, it is more desirable that the lower plating layer is alloyed hot dip galvanizing and the upper layer is formed by electroplating.

  On the other hand, plating with a high Ni concentration on the lower layer increases the Ni concentration of the solid solution layer, so that the Ni concentration of the solid solution layer falls within the range defined by the present invention by holding for a long time. Except when not desirable.

  Here, in the alloyed hot-dip galvanized film, one or more of Al, Mg, Si, Mn, Cr, V, Ti, Mo, W, etc. may be appropriately added as required. The effect is not impaired at all, and Ni may be included in the alloyed hot-dip galvanized film as long as it is within the range specified in the present invention together with Ni of the upper plating.

  The metal or alloy plating containing Ni as a main component of the upper layer includes Ni—Fe, Ni—Zn, Ni—Co, Ni—Cr, etc. in addition to Ni alone, and the same if the amount of Ni is within the scope of the present invention. From the viewpoint of cost and manufacturing stability, Ni simple plating is desirable.

  Note that both the lower layer and upper layer plating may contain impurities contained in the raw material and impurities inevitably mixed in the manufacturing process in addition to the intended additive elements described above, but the effects of the present invention are impaired. There is no.

  The electroplating bath is not particularly limited as long as it is a bath capable of efficiently plating Ni in addition to a chloride bath, a sulfuric acid bath, and a sulfamic acid bath, but it is industrially easy to handle a sulfuric acid bath, a chloride bath and a sulfuric acid bath. It is desirable to use a mixed bath. In addition, as for other plating conditions such as current density, bath temperature, pH, and flow rate, conditions that can obtain a uniform film within a range in which kogation does not occur may be selected.

  After the formation of these plating layers, post treatment may be performed as necessary. Usually, there is no problem with the adhesion of the coating film within the scope of the present invention, but it is lubricated when further adhesion is required, or in order to form a shape close to the member in advance before hot press molding. If the weldability is required, further improvement of weldability is required, and other cases, the plating layer is within the scope of the present invention even if the treatment is performed according to each purpose. The effect is not impaired and is within the scope of the present invention.

5. Hot press forming method
The hot press forming method of the hot press formed member is not particularly limited, and the press forming that is usually performed may be performed hot. That is, the steel material is heated and press-molded at a speed equal to or higher than the critical cooling rate from a temperature range of Ac ₃ points or higher.

  Here, in order to further exhibit corrosion resistance, it is effective that a large amount of the zinc alloy phase remains, so heating is performed in the air or in a slightly oxidized atmosphere, the heating rate is high, and the hot press member is used. The holding time at a temperature equal to or higher than the melting point of the plating layer to be formed is preferably shorter than the time necessary for completely dissolving C in the base steel material. Specifically, the temperature rising rate is desirably 10 ° C./sec or more, the holding time is desirably less than 3 minutes, and more desirably less than 1 minute. Furthermore, in order to disperse the zinc alloy phase in the thickness direction of the film, the holding time is preferably less than 10 seconds, and more preferably less than 5 seconds.

The press molding start temperature may be any temperature as long as it is lower than the melting point of the zinc alloy layer included in the hot press molded member, but in order to further enjoy the effects of the present invention, the press molding must be performed at 780 ° C. or higher. desirable.

Next, the effects of the present invention will be described more specifically with reference to examples.
C: 0.21%, Si: 0.2%, Mn: 1.3%, P: 0.005%, S: Steel components manufactured by a normal hot rolling process and a cold rolling process as a base steel material A cold-rolled steel plate (plate thickness 1.6 mm) containing 0.001%, Cr: 0.2%, and B: 0.002% was used.

About Examples 1-21, hot-dip galvanization or alloying hot-dip galvanization was given so that it might become the adhesion amount and composition which are shown in Table 1 as this lower layer on this cold-rolled steel plate, Among them, Examples 1-14, 16-17 As for the upper layer, an electric Ni plating bath containing NiSO ₄ .6H ₂ O = 240 g / L, NiCl ₂ .6H ₂ O = 45 g / L, H ₃ BO ₃ = 35 g / L is used as the upper layer while sufficiently stirring. Electric 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 .

In Example 15 and Example 22, Zn—Ni alloy plating was applied as the upper layer plating. The Zn—Ni alloy plating uses 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 a relative flow rate of 1 m / L. The sample was applied at a bath temperature of 50 ° C. and a current density of 40 A / dm ² so as to achieve the adhesion amount shown in Table 1, while applying flow at s. The lower layer Ni plating of Example 22 was performed under the same conditions as in Examples 1-14.

  The obtained plated steel sheet is heated to 880 ° C. at a predetermined average temperature increase rate by a gas furnace having an air-fuel ratio of 1: 1 or energization heating, held for a predetermined time, taken out, and pressed at a predetermined temperature of 780 ° C. or higher. It was.

  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 cross-section observation sample, the presence or absence of the alloy phase, the Fe concentration and Ni concentration in the alloy phase, the presence or absence of Al in the alloy phase, and the Ni concentration in the solid solution layer were analyzed with respect to Al in the alloy phase by SEM-EDX analysis. Confirmed by using EPMA analysis from the cross section. The results are summarized in Table 1.

  We evaluated cracks in hot pressed parts, corrosion resistance after electrodeposition coating, and corrosion forms. The evaluation methods are listed below, and the evaluation results are summarized in Table 1.

(1) Press crack resistance test (crack)
The hot press-molded member was cracked by using a 90-degree V-bending die as a press working die, and visually evaluating the presence or absence of the crack after press molding. The molding start temperature was controlled by measuring the temperature change of the sample previously attached with a thermocouple over time after removal from the furnace and allowing to cool for a predetermined temperature. The evaluation criteria are ◎ when no crack was observed when the steel sheet temperature was 820 ° C at the start of forming, ○ when no crack was observed when forming at 800 ° C, and 800 ° C when forming. In the case where cracking was observed in the sample, x was given, and ◎ and ○ were accepted.

(2) Corrosion resistance test after coating (corrosion resistance)
Corrosion resistance after painting is determined by using Nihon Parker Rising Co., Ltd. to a member obtained by using a flat plate press mold and quickly cooling it after sandwiching it with a press mold when the steel plate temperature reaches 800 ° C. ) After zinc phosphate treatment with PBL-3080 made under normal chemical conversion conditions, electrodeposition paint GT-1O made by Kansai Paint was applied by slope energization with a voltage of 200 V and baked at a baking temperature of 150 ° C. for 20 minutes. And a 20 μm coating film was obtained.

  Scratch scratches reaching the substrate with a cutter knife were put into the coating film of the obtained test piece, and a neutral salt spray cycle test specified in JIS H8502 was conducted 360 cycles. The film swelling width or rust width from the scratch was measured to evaluate the corrosion resistance after painting. As the evaluation criteria, the larger of the swollen width of the coating film or the rust width was less than 5 mm, the x was 5 mm or more, and the mark was o.

(3) Corrosion morphology observation (corrosion morphology)
Corrosion form is evaluated by cutting the scratch part perpendicular to the scratches from the test piece after performing the above-mentioned post-coating corrosion resistance test, embedding it in an epoxy-based resin, polishing it, This was done by observing the tip.

  The evaluation criteria are such that no noble solid solution layer is seen in the rust as shown in the cross-sectional SEM photograph of FIG. 2, and the noble solid solution layer is corroded in the rust as shown in the cross-sectional SEM picture of FIG. The pitting corrosion is caused by the corrosion of the lower part of the noble solid solution layer that remains connected to the metal part that is not, and is connected to the metal part that is not corroded even though the noble solid solution layer exists in the rust. The thing which did not have it was made into a slightly pitting corrosion type, and the whole surface and the slightly pitting corrosion type were set as the pass.

  If the Ni concentration in the solid solution layer becomes too high, it becomes noble than the potential of the base steel material, so that the base steel material is corroded before the solid solution layer, leading to pitting corrosion. Therefore, the corrosion form that remains in connection with the metal part and corrodes the lower part serves as a guide for the presence or absence of pitting corrosion.

Samples 3-6, 15-20, and 17 as examples of the present invention were all good in press crack resistance, post-coating corrosion resistance, and corrosion form.
On the other hand, the symbols 1-2, 15, and 21 in which the alloy phase does not exist after hot press forming fail in the corrosion resistance after coating. The surrogate marks 16, 18 to 20 whose composition of the alloy phase is out of the scope of the present invention are unacceptable in the press crack resistance. In the solid marks 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 pitting corrosion. Thus, in the comparative examples, none of the press crack resistance, the post-coating corrosion resistance, and the corrosion form satisfied the acceptable level.

Claims (6)

A zinc alloy plating layer containing Fe is provided on a steel plate, and after providing a plating layer made of a metal or alloy containing Ni as a main component on the zinc alloy plating layer, the steel plate is subjected to 10 ° C./sec or more. The temperature is raised to a temperature range of Ac ₃ points or higher at a rate of temperature rise, held in the temperature range for 1 second or more and less than 3 minutes, and then press-formed while being cooled at a rate higher than the critical cooling rate. By
The Zn content is 15% or more and the Ni content is less than 5.0% by mass, formed on or in the solid solution layer, containing 85 to 70% Zn by mass, and the total of Ni and Fe. The manufacturing method of the hot press-molding member which manufactures the hot press-molding member which has a film | membrane which has a zinc alloy layer which becomes 15 to 30% and Ni becomes 3 to 15% in surface layer.   The zinc alloy plating layer containing Fe and the plating layer made of a metal or alloy containing Ni as a main component as a whole have a total concentration of Fe and Ni of 12 to 25% and a Ni / Fe ratio of 0.15 or more. The manufacturing method of the hot press-molded member according to claim 1, which is a coating film containing Zn.   The hot press according to claim 1 or 2, wherein the zinc alloy plating layer containing Fe is an alloyed hot dip galvanizing layer, and the plating layer made of a metal or alloy containing Ni as a main component is an electroplating layer. Manufacturing method of molded member. The method for producing a hot press-formed member according to any one of claims 1 to 3 , wherein a start temperature of the press forming is 780 ° C or higher and lower than a melting point of the zinc alloy plating layer containing Fe. The method for producing a hot press-formed member according to any one of claims 1 to 4 , wherein a part or all of the zinc alloy layer containing Fe contains 0.01% by mass or more of Al present in a metal state. The method for producing a hot press-formed member according to any one of claims 1 to 5 , wherein the zinc alloy layer containing Fe is formed dispersed in the thickness direction of the coating.

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