JP2847846B2 - Multi-layer plated steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to, for example, adhesion durability, chemical conversion treatment, coating film adhesion, and
The present invention relates to a multilayer plated steel material excellent in corrosion resistance after painting and spot weldability.

(Prior art) The requirements for surface-treated materials are more diverse than before. For example, as surface-treated steel sheets for automobiles, improvements and improvements in chemical conversion properties, coating film adhesion, post-paint corrosion resistance, spot weldability, etc. are particularly required. Have been.

By the way, the application of various anticorrosion plated steel sheets has been actively promoted particularly for automobile bodies used under severe corrosive environments. At present, the most common anti-corrosion plated steel sheets include Zn-based or Zn-Ni-based, Zn-Fe-based, Zn-Al-based Zn
A steel sheet having an alloy plating film is generally known.

However, such a corrosion-resistant plated steel sheet has insufficient chemical conversion treatment performance, which is a base treatment for coating, and therefore has insufficient coating film adhesion. In order to solve such a problem, it has been proposed to increase the number of plating layers. For example, JP-A-56-142885 discloses a two-layer plated material having a sacrificial anti-corrosion coating as a lower layer, a Fe-based continuous coating as an upper layer, and JP-A-59-129797 and JP-A-59-129797.
In Japanese Patent No. 182988, a sacrificial anti-corrosion coating is used as a lower layer, a Ni or Ni-based alloy coating is used as an intermediate layer, and
Three-layer plated materials having a coating of Fe or an Fe-based alloy have been proposed, and these multilayer plated materials can solve the above problem.

(Problems to be Solved by the Invention) These multi-layer plated materials can satisfy the above-mentioned performances required for, for example, a steel sheet for automobiles, namely, chemical conversion treatment, coating film adhesion, and post-coating corrosion resistance. However, performances other than these performances, such as spot weldability and adhesion durability described later, could not be sufficiently satisfied.

In other words, in order to meet the demands of users for even higher corrosion resistance, it is conceivable to increase the thickness of the lower sacrificial anticorrosion coating layer in this multilayer plated material, but in this case, deterioration of spot weldability becomes a problem. .

It is also thought that the increase in the rate of dissolution of the lower sacrificial anticorrosive coating layer increases the progress of corrosion in the surface direction of the steel material. Occurs.

The adhesion durability is, for example, a bonding portion in the initial stage of bonding when surface-treated materials such as steel used for automobiles, home appliances, building materials, and the like, or when the surface-treated material is bonded to another metal material or the like. The term "adhesion strength at the interface (ie, initial adhesion)" and "adhesion strength at the bonding interface in a corrosive environment (i.e., adhesion durability)." This is a performance that has attracted attention in recent years because it is impossible, difficult to apply to material types and members, and further, from the viewpoint of improving the appearance (welding marks are generated by welding).

In particular, various tests and studies have been performed on the adhesion durability of the surface-treated steel sheet in recent years.

For example, as a surface-treated steel sheet, electro-galvanized steel sheet,
By using a hot-dip galvanized steel sheet and further a surface-treated steel sheet such as an alloyed hot-dip galvanized steel sheet and joining them with an adhesive, by performing a composite corrosion test in parallel and measuring the shear stress of the bonded part as needed, Tests were conducted to investigate the initial adhesion and adhesion durability of the surface-treated steel sheet,
The results show that the hot-dip galvanized steel sheet shows consistently stronger initial adhesion than the other galvanized steel sheets at the start of the corrosion test, and that other galvanized materials are equivalent to cold-rolled steel sheets in the early stages of corrosion. Alternatively, it has been shown that the adhesive strength is slightly inferior (initial adhesiveness), but as corrosion progresses, the adhesive strength is superior to that of cold-rolled steel sheets, and the adhesive durability is excellent.

However, this test result is a test result under a severe corrosion test under severe corrosion conditions.Corrosion progresses slowly under a mild corrosion cycle and environment such as actual use conditions. In other galvanized materials other than galvanized materials, regarding the adhesive strength, the period during which the cold-rolled steel sheet shows superiority over the galvanized material continues for a long time, and the merits of using the galvanized material under actual use conditions are small. Has become.

In addition, even though the use of galvanized material shows superiority in initial adhesion and adhesion durability in a corrosive environment, this means that it is relatively superior to cold-rolled steel sheets. Since the absolute value of the adhesive strength of a plated material also decreases with the progress of corrosion, it has been difficult to say that the adhesive durability in actual use is sufficient.

By the way, as described above, the reason why the initial adhesion of the plated material is inferior to that of the cold-rolled steel sheet can be considered as follows. That is, a brittle substance in the plating film, for example, a Γ phase in the alloyed hot-dip galvanized coating film, a 電 気 phase in the alloyed Zn—Ni plating film, and δ ₁ in the alloyed Zn—Fe plating film
It is considered that the presence of a phase, a Γ phase, or the like, results in peeling at the site during shearing and pulling, resulting in apparently low adhesive strength.

Therefore, with respect to such a material, in the hot-dip plating or the like, it is possible to increase the tensile strength by reducing the generation of the brittle body as much as possible, for example, by controlling the heat treatment conditions, and to improve the initial adhesiveness. .

However, with such means, as the corrosion progresses,
It is not possible to solve the problem of the deterioration of the bonding strength, that is, to improve the bonding durability.

In recent years, some means for using a plating material as a material have been proposed as a means for solving the problem of the deterioration of the adhesive durability. However, the level of the adhesive strength improved by such means is still insufficient. I could not say that.

As described above, the problem of deterioration in spot weldability when the thickness of the sacrificial anti-corrosion coating layer below the multilayer plated material is increased for the purpose of imparting high corrosion resistance, and further improvement in adhesion durability. Until now, there has been no means that can achieve both the tasks.

Here, the object of the present invention is to solve the above problems and problems, for example, suitable for use in automobiles, home appliances, building materials, etc., while being excellent in chemical conversion treatment, coating film adhesion, corrosion resistance after painting, An object of the present invention is to provide a multilayer plated steel material having excellent spot weldability and adhesive durability.

(Means for Solving the Problems) In order to achieve the above-mentioned object, in order to solve the above-mentioned problems, the present inventors have found that not only the initial adhesiveness but also the strength with the passage of time in a corrosive environment is small with little change with time. We first conducted a thorough study, recognizing that the most important thing was to develop a plated steel material with excellent durability.

Among the factors affecting the initial adhesiveness of the steel material, the factors resulting from the steel material include the shape of the coating surface of the steel material (surface roughness of the coating, etc.), compatibility with the adhesive, and the like.
The present inventors have thought. In addition, the present inventors considered that factors that particularly affect the adhesion durability of the steel material may be due to the progress of corrosion, and in particular, the progress of corrosion in the surface direction may have an adverse effect.

Based on such knowledge, the present inventors have further studied, as a result, the surface of the steel material to be treated, as a lower layer is subjected to alloying hot-dip plating of Zn or a Zn-based alloy having a sacrificial anti-corrosion effect, Cr, Cr-based alloy, A
l, obtained by applying a coating of one metal or alloy selected from the group consisting of Al-based alloys, Co-based alloys and Ni-based alloys, and further applying an Fe-based alloy as an upper layer.
By using the plated steel material of the plating film structure of the layer,
With the knowledge that it is possible to provide a multi-layer plated steel material that is excellent not only in chemical conversion treatment, coating film adhesion and corrosion resistance after painting, but also in spot weldability and adhesion durability,
The present invention has been completed.

Here, the gist of the present invention is that at least a lower layer on the surface: an alloyed hot-dip galvanized layer having an average Fe content of 5 to 20% by weight and a surface roughness Ra of 0.3 μm or more; Intermediate layer: a coating layer of the following metal or alloy having an adhesion amount of 0.01 to 10 g / m ² , metal: Cr, Al alloy: one selected from the group consisting of Cr, Al, Co and Ni, and Zn, Mn And an alloy having at least one selected from the group consisting of Fe and an upper layer: the coating amount is 0.01 to 10 g / m ² , and the Fe composition is 90 to
A multi-layer plated steel material comprising 99.9999% by weight and having a coating layer of an Fe-based alloy having at least one element selected from the group consisting of Ni, Co, Mn, B, S and P.

In the present invention, "steel material" refers to a member used for, for example, an automobile, a home appliance, a building material, and the like, and specifically includes, for example, an automobile body, a building material inner / outer plate, a home appliance main body, and the like.

In the present invention, the method of coating the intermediate layer or the upper layer is not particularly limited, and the intermediate layer is, for example, an electroplating method or a dry plating method, and the upper layer is, for example, an electroplating method, an electroless plating method, or a dry method. The coating may be performed using a plating method or the like.

Further, in the present invention, "excellent in adhesive durability" means that the combined tensile strength of the adhesive portion is determined based on the T-peel test based on the peel tensile strength specified by JIS K 6854 in combination with the composite corrosion test. Occurs almost all over the peeled surface,
That is, it means that the interfacial adhesion between the base material-plating layer, the plating layer-plating layer, and the plating layer-adhesive has a performance stronger than the cohesive failure of the adhesive.

Further, the present invention is not limited to an embodiment having only three layers of the lower layer, the intermediate layer, and the upper layer. For example, the adhesive durability between the lower layer and the intermediate layer and / or the intermediate layer and the upper layer may be improved. It is good also as a plating steel material which has a coating layer which does not deteriorate property, and has a coating of a multilayer structure of four or five or more layers in total. In the present invention, “at least” is used to clarify that such an embodiment is included.

Further, in the present invention, the three layers may be formed on the entire surface or a part of the steel material (especially when the steel material is a steel plate, on both surfaces or one surface).

(Operation) Hereinafter, the configuration and operation and effect of the present invention will be described. In this specification, “%” means “% by weight” unless otherwise specified.

The configuration of the present invention has, as a brief description, an alloyed hot-dip galvanized layer having a sacrificial anticorrosive action as a lower layer, and a Cr, Cr-based alloy, Al, Al-based alloy, Co-based alloy, or Ni-based as an intermediate layer. A plated steel material having a coating layer of at least a three-layer structure, having a coating layer of an alloy, and further having a coating layer of an Fe-based alloy as an upper layer.

First, the lower layer of the multilayer plated steel material according to the present invention will be described.

The addition of the galvannealed layer as the lower layer
This is because the alloyed hot-dip galvanized layer has a sacrificial anticorrosion effect. This is because a coating having no sacrificial anticorrosion effect causes significant progress of corrosion on the base material side and cannot prevent significant deterioration in adhesion durability. Furthermore, among the coatings having a sacrificial anti-corrosion effect, only the alloyed hot-dip galvanized layer was limited.
The reason is unclear, but it is still not possible to prevent a remarkable decrease in adhesion durability with a coating having many sacrificial anticorrosive actions.

The alloying degree of this galvannealed layer is averaged.
The reason why the Fe content is limited to 5% or more and 20% or less will be described. That is, as a result of studying the coating composition and surface morphology of the alloyed hot-dip galvanized steel sheet, which is the lower layer, using samples in which the coating composition and surface morphology were variously changed, the average Fe content was 5%. Not less than 20%
It has been found that when the surface roughness is in the range of 0.3 μm or more, it is most effective in improving the adhesion durability. In addition, taking into account errors in manufacturing conditions, etc., a more desirable average
The Fe content is 7% or more and 14% or less.

Although the details of this action mechanism are unknown, one of the reasons is the anchor effect due to the surface morphology of the steel material, that is, the difference in adhesion between the plating film layers and the plating film-adhesive interface. . It is also conceivable that the abundance of the brittle body is affected by the coating composition. The upper limit of the surface roughness is not particularly limited with respect to the operation and effect of the present invention, but in consideration of the sharpness of the surface of the overcoated film when performing electrodeposition coating, intermediate coating, and overcoating, The thickness is desirably 1.8 μm or less, and more desirably 1.5 μm or less.

Further, as alloying elements of the lower alloyed hot-dip galvanized layer, other than Zn, Fe and Al added in the plating bath, for example, Si, Nb, Mn, Mg, Mo, Ta, Cu, Ni, Co , S
n, Sb, Ti, Cr, Cd, Pb, Tl, In, V, W, La, P,
It may contain a trace amount of one or more elements selected from the group consisting of S, B, etc., and has no effect on the effects of the present invention.

In order to apply the alloyed hot-dip galvanized layer as a lower layer of the steel material, a well-known means currently used may be used. For example, in a strip stage which is a stage before processing into a steel material, continuous hot-dip galvanizing is performed. It is sufficient that the amount of zinc deposited is adjusted on the plating elution side of the line, and the zinc is immediately introduced into a heating furnace maintained at 500 to 650 ° C., and no limitation is required.
Adjustment of the average Fe content (degree of alloying) may be managed by means conventionally used, and no limitation is required.

Next, the intermediate layer and the upper layer of the plated steel material having excellent adhesion durability according to the present invention will be described.

The reason why the intermediate layer and the upper layer are coated on the surface of the plated steel material having the lower layer to form at least a three-layer structure is that the intermediate layers are Cr, Cr-based alloy, Al, Al-based alloy, Co-based alloy, and Ni-based alloy. Only the coating layer of one kind of metal or alloy selected from the group consisting of the base alloys, or the coating layer of the upper Fe-based alloy alone is not enough to prevent the significant progress of corrosion. This is because it is considered that a satisfactory adhesion durability can be obtained by the interaction (synergistic effect) of having the coating layer. The reason considered in this way is that the effect of inhibiting the progress of the corrosion described above greatly changes due to the difference in the amount of adhesion between the coating layers, particularly the difference in the amount of adhesion between the upper layer and the intermediate layer.

The components of the coating of the intermediate layer include Cr, Cr-based alloy, Al, Al
Any metal or alloy selected from the group consisting of a base alloy, a Co base alloy, and a Ni base alloy may be used. That is, an object of the present invention is to improve the adhesion durability of a steel material while sufficiently ensuring the spot weldability of the steel material as described above. In order to ensure sufficient spot weldability of the steel material, for example, damage (seizure, wear, etc.) on the electrode tip of the welder may be suppressed as much as possible. For the purpose of suppressing the occurrence of chromium, one of Cr or a Cr-based alloy, Al or an Al-based alloy, a Co-based alloy, or a Ni-based alloy is applied as an intermediate layer.

As the alloy element, it is necessary to use one or more elements selected from the group consisting of Zn, Mn and Fe. Although a detailed study has not been conducted, it is considered that the addition of an excessive amount of a noble metal layer to the base material cold-rolled steel sheet is because the progress of corrosion of the base material is accelerated and thus the bonding durability is deteriorated. As alloying elements other than the above, elements exhibiting a lower potential than the material to be plated, for example, Mg, Pb, Cd, Ta, Ti, Nd, V, W,
One or two selected from the group consisting of Sb, P, B, S, etc.
It may contain more than one element.

Further, the adhesion amount of the intermediate layer film is required to be 0.01 g / m ² or more in order to exhibit its performance,
If it exceeds g / m ² , the adhesion durability of the entire coating film is deteriorated. Accordingly, the adhesion amount was limited and 0.01 to 10 g / m ^2. In addition, stable performance is exhibited irrespective of the manufacturing conditions, while considering the high cost due to the thick plating and the saturation of the performance, more preferably 0.05 to 6 g / m ² .

There is no particular limitation on the method of coating the intermediate layer. For example, (i) a so-called electroplating method, or (ii) a CVD method in which a gas serving as a raw material is supplied to the surface of a plated steel material having the lower layer, and a chemical reaction is caused to cause the gas to adhere thereto, or the Cr, Cr Alloy, Al, Al alloy, Co alloy, and
One type of metal or alloy selected from the group consisting of Ni-based alloys is heated and evaporated in a vacuum by an appropriate method, and this vapor is deposited on the surface of the plated steel material having the lower layer by a vacuum evaporation method, glow discharge. Ar ions made into plasma are converted to Cr, Cr
Alloys, Al, Al-based alloys, Co-based alloys, and Ni-based alloys, which collide with a target plate of one metal or alloy at high speed to repel atoms and ions of the target plate (sputter) , Which is deposited on the surface of the plated steel material having the lower layer by sputtering, and further, ionizes low-pressure Ar and converts Ar ⁺ into the Cr, Cr-based alloy, Al, Al-based alloy, C
When the evaporation source is heated after the surface is purified by colliding with a plate of one metal or alloy selected from the group consisting of o-based alloys and Ni-based alloys, the evaporated metal collides with Ar ⁺ It may be performed by a so-called dry plating method such as a PVD method such as an ion plating method or the like, which becomes ions and is electrostatically attracted to and deposited on the surface of the plated steel material having the lower layer.

Next, the components of the upper layer coating are Ni,
Fe-based alloy containing one or more of Co, Mn, P, S, B, etc. Fe composition 90% or more and 99.9999%
The following may be sufficient. It is for improving the coating film adhesion and the chemical conversion treatment which greatly contributes to this performance among the above various performances. By forming the coating layer of the Fe-based alloy as the upper layer, the phosphate phosphatized crystal formed on the surface of the steel material during the chemical conversion treatment before painting becomes dense, and good performance can be obtained. Although the cause is unknown, it is necessary to include one or more of Ni, Co, Mn, P, S, and B as an alloy component in order to improve the chemical conversion treatment property and the adhesion durability. It turned out to be.

In addition, Zn, Al, T
a, Cu, Sn, Sb, Cr, Cd, Pb, Tl, 1n, V, W, N, and the like may be included, and the effect of the present invention does not cause any problem.

Next, the coating amount of the coating layer of the upper layer of the Fe alloy was determined to be 0.
01G / m ² or more 10 g / m ² or less reason for limiting the described. If the content is less than 0.01 g / m ² , the effect of preventing the deterioration of the adhesion durability due to the deterioration of the corrosion resistance is not recognized, and if the content is 0.01 g / m ² or more, this effect appears. On the other hand, in the case of 10 g / m ² greater than the performance of the effect is what is on the decline in saturated or conversely, results in cost increase problem with increasing the film was further subjected to a plating of only the upper layer without an intermediate The performance is degraded to almost the same level as in the case. Therefore, in the present invention, the adhesion amount of the upper layer coating is limited to 0.01 g / m ² or more and 10 g / m ² or less. In addition, regardless of the variation in the manufacturing conditions, while exhibiting stable performance, considering the high cost and saturation in terms of performance due to thick plating, the adhesion amount of the upper layer is 0.05 g / m ² or more 6 g / m ² or less is more desirable.

The method of coating is not particularly limited. In addition to the above-mentioned (i) electroplating method and (ii) dry plating method, (iii) the intermediate layer is formed from a metal salt solution. An example is an electroless plating method that precipitates on the surface of the plated steel material that has been applied.

Further, in the multi-layer plated steel material according to the present invention,
The layers need not necessarily be formed on both sides of the steel. For example, I. Cover only one side of the steel with these three layers and leave the other side bare, or II. Cover only one side of the steel with these three layers and the other side The desired performance required for the steel material may be obtained by appropriately using a coating layer having a configuration different from the three layers, for example, a configuration including only the plating layer.

As described above, the multi-plated steel material according to the present invention having the three layers described above has adhesive durability, chemical conversion treatment, coating film adhesion,
It has excellent corrosion resistance and spot weldability after painting, and is suitable for use in, for example, automobiles, home appliances, building materials, and the like.

That is, the multilayer plated steel material according to the present invention is particularly excellent in adhesion durability. As mentioned above, the factors of the base material that affect the initial adhesion and the adhesion durability of the plated steel material include, as described above, the initial adhesion, the shape of the coating surface, compatibility with the adhesive, and the like. It is considered that the deterioration of the adhesion durability in the above has adverse effects on the progress of corrosion, particularly the progress of corrosion in the surface direction of the steel material.

The multilayer plated steel material according to the present invention satisfies these performances, but the reason why these performances are satisfied by the present invention is not exactly known. However, the present inventors have confirmed that these factors have been solved by the present invention, and in particular, regarding the deterioration of adhesion durability caused by the progress of corrosion, as described above, the present invention has Having a galvannealed layer as the lower layer, imparts a sacrificial anticorrosion effect to the steel material, and is selected from the group consisting of Cr, Cr-based alloy, Al, Al-based alloy, Co-based alloy, and Ni-based alloy as the intermediate layer A single metal or alloy coating layer, and a coating layer of an Fe-based alloy containing one or more of the alloy components Ni, Co, Mn, B, S and P as an upper layer. Thereby, (a) chemical conversion treatment property becomes good, and accordingly, coating film adhesion becomes good.

(B) Spot weldability is improved.

(C) The adhesion durability can be improved by slowing down the corrosion rate and suppressing the spread of the corroded portion in the surface direction.

It is considered something.

Further, the present invention will be described in detail with reference to examples, but this is merely an example of the present invention, and the present invention is not limited thereto.

Example A cold-rolled steel sheet having a thickness of 0.8 mm was subjected to pretreatment, hot-dip galvanizing, and alloying heat treatment by a conventional method to obtain a lower alloyed hot-dip galvanized layer.

Pretreatment and hot-dip galvanizing were performed by a conventional method to obtain a hot-dip galvanized layer as a lower layer.

Electrogalvanizing was performed by a conventional method.

In addition, the composition, surface roughness and plating adhesion amount of this lower layer were measured, and the results are shown in Table 1. The composition is indicated by the numeral (% by weight) before each element.

As shown in Table 1, electroplating (EL), electroless plating (N
E) and the dry plating method (DP) as appropriate to form an intermediate layer and an upper layer having the composition and the coating amount shown in Table 1, and to prepare Sample No. 1 to Sample No. 44 (Example of the present invention) and Sample No. No.45
Or sample No. 64 (Comparative example, sample No. 63 and sample
No. 64 has no lower layer). In Table 1, G
A indicates the galvannealing method, and GI indicates the galvanizing method.

The plating conditions of the intermediate layer and the lower layer, which are more used in this example, are shown below.

I. [Electroplating conditions] (i) Intermediate layer plating conditions Plating is performed based on a pyrophosphoric acid bath, a sulfuric acid bath, a Watts bath, or a sargent bath. , Sulfate, acetate,
The plating was performed by adding carbonate, molybdate, pyrophosphate, hypophosphite, an organic metal salt, a metal previously dissolved in an acid, or the like to the plating bath so as to obtain a target composition. The ion concentration in the bath of the deposited metal is 1 to
2M /.

(Ii) an upper layer plating conditions _{FeSO 4 · 7H 2 O: 250g} / Na 2 SO 4 or (NH 4) 2 SO 4: based on the constant and the plating bath at 100 g /, the addition of alloying elements to the alloy plating Is added to the plating bath such that a sulfate, an acetate, a carbonate, a molybdate, a hypophosphite, an organic metal salt, a metal previously dissolved in an acid or the like has a target composition. It was done by doing. The conditions at the time of electroplating were as follows.

Current density: 40 to 150 A / dm ² pH: 1 to 2 Bath temperature: 50 to 60 ° C. Liquid flow rate: 1 to 3 m / s For electroplating from a molten salt bath, chloride molten salt is used. The test was performed at a temperature of 200 ± 10 ° C. Also,
Other conditions were the same as the above-mentioned plating conditions for the intermediate layer.

II. [Electroless plating conditions] Using a commercially available bath containing a reducing agent or a bath that chemically substitutes and precipitates, immersion treatment is performed at a bath temperature of 30 to 80 ° C. Adjusted by changing.

III. [Dry plating conditions] Zn, Al or Ti, and an alloy containing these as a main component were coated by a PVD method or a CVD method. The processing was performed under known conditions.

Obtained in this way, the width is 25 mm and the length is 120 m
With respect to Sample No. 1 to Sample No. m, the adhesive durability of the coating layer, the chemical conversion property, the secondary adhesion of the coating film, the corrosion resistance after coating, and the spot weldability were evaluated by the following means.

(Adhesion durability evaluation)

In order to evaluate the adhesiveness of the obtained sample, the two samples were laminated with an adhesive, heated and dried at 175 ° C. × 30 min, and then dried as shown in FIG. 1 (a) and FIG. As shown in (b), a T-shaped peel test was performed. Further, the same sample was subjected to the following composite corrosion test, and a sample was taken out every 10 cycles and subjected to a T-peel test to examine the adhesion durability. The pulling speed was 50 mm / min.

The adhesive used was a one-pack type epoxy araldite XB3062 (manufactured by Nippon Ciba-Gaikey) and had a thickness of 100 μm.
m. The bonding area was set to width × 100 mm.

The evaluation of the adhesiveness is performed based on the area ratio of a portion of the peeled surface where the adhesive is cohesively broken, and the larger the value, the better the adhesiveness.

The results are shown in Table 1. The evaluation criteria in Table 1 are summarized below.

In the evaluation of the adhesion durability, the corrosion cycle shown below was defined as one cycle, and the composite corrosion test was performed in combination. (1 cycle) Adhesion durability results for 0 cycle, 10 cycle and 20 cycle
The cycles are summarized in Table 1.

The bending fatigue test was carried out by repeatedly holding the sample as shown in FIG. 2 and bending it alternately in the direction of the arrow.

(Chemical conversion treatment evaluation)

After degreased with a degreasing agent FC4326-TA (manufactured by Nippon Parkerizing Co., Ltd.) and surface-adjusted with PZT (manufactured by Nippon Parkerizing Co., Ltd.), a chemical conversion treatment was performed under predetermined conditions using PB-L3080 (manufactured by Nippon Parkerizing Co., Ltd.). .

With respect to the conversion crystals in the chemical conversion coating film thus obtained, the (100) plane strength (P) of phosphophyllite and the (020) plane strength (H) of Hopeite were detected by X-ray analysis.
The crystal structure was investigated by calculating the P / (P + H) ratio (P value).

 The results are shown in Table 1.

According to this evaluation method, the larger the P value, the better the chemical conversion treatment.

[Coating film secondary adhesion production] After carrying out cationic electrodeposition coating (film thickness 20 µm) on the steel sheet subjected to the chemical conversion treatment, a melamine alkyd resin-based intermediate coating and a top coating are further performed, and the same as an automobile outer panel. Coating was performed with a total dry film thickness of 80 μm.

The sample thus obtained was immersed in ion-exchanged water at 50 ° C. for 10 days.
Gobang eyes were put so that I could do it. Then, an adhesive tape was stuck on the stitches, and the coating film remaining rate after peeling off the tape was examined. As the evaluation, x was obtained when 5 or more portions of the above-mentioned rust-coated film were peeled by 50% or more, を was obtained for 4 to 1 of the same, and 同 じ く was obtained for none at all.

(Corrosion resistance after painting)

After the chemical conversion treatment and the electrodeposition coating with kaotin, a crosscut reaching the substrate was inserted, and a salt water spray test was performed for 30 days. After the test, the occurrence of red rust in the crosscut portion was examined.

The results are shown in Table 1. In Table 1, there was no red rust: O, and there was red rust: X.

[Spot weldability]

The two samples were overlapped, and spot welding was continuously performed. The number of hit points maintaining the above (t: plate thickness) was investigated.

The results are shown in Table 1. In Table 1, the number of hit points was evaluated as 5000 when the number of hit points was 5000 or more, and evaluated as x when the number of hit points was less than 5000. The welding conditions are shown below.

Pressing force: 200kgf Current: 10KA Squeeze time: 28 cycles Energizing time: 12 cycles Electrode material: Cu-Cr (commonly used) Electrode shape: truncated cone, diameter 6.0mm Test results are shown in Table 1. Shown together.

As is clear from Table 1, the present invention example (Sample No. 1 to Sample No. 44) is compared with Comparative Example (Sample No. 45 to Sample No. 64) using the same lower plating material. The same or better initial adhesion,
And with the progress of the corrosion cycle, the adhesiveness of the comparative example was remarkably reduced, while that of the present invention was not so reduced, and the adhesive durability was much better. It can be seen that the film adhesion and the corrosion resistance after painting are good, and that the spot sacrificial anticorrosion layer as well as the lower one has good spot weldability even if it is thick.

On the other hand, as shown in Sample Nos. 45 to 46, when only the lower plating layer is applied, all the performances are deteriorated.

Further, in a sample such as Sample No. 47 or Sample No. 49 in which the adhesion amount of the intermediate layer is smaller than the range of the present invention, the chemical conversion treatment property and the coating film secondary adhesion are improved, but not sufficient. And other performances were also inadequate.

Further, in samples such as Sample No. 48 or Sample No. 50 in which the amount of adhesion of the upper layer is smaller than the range of the present invention, the spot weldability and the initial adhesion are improved, but the adhesion durability is particularly insufficient. But also the other performances were inadequate.

Further, in Sample No. 51, in which the upper adhesion layer is excessive, the adhesive durability was deteriorated, and the advantage of thickening was lost.

Thus, when the balance between the middle layer and the upper layer is lost,
It is considered that the performance of the steel material is reduced, and particularly regarding the adhesive durability, various synergistic effects are produced between the intermediate layer and the upper layer, so that various performances of the steel material are improved.

Further, when an upper plating material outside the scope of the present invention is used, as in Sample Nos. 52 to 54, even if the amount of adhesion falls within the scope of the present invention, the chemical conversion property is reduced and the adhesion is also reduced. It can be seen that the durability is deteriorated.

In addition, when an intermediate layer that shows a higher potential than that of the base material to be plated is used, as in Sample No. 55 and Sample No. 56, it is considered that corrosion progresses in the surface direction faster, The property is deteriorated. In addition, spot weldability also deteriorates depending on the plating base material.

Further, when a lower layer outside the scope of the present invention is used as in Sample Nos. 57 to 62, the adhesion durability and the corrosion resistance after painting are deteriorated.

Further, all the performances of Sample No. 63 and Sample No. 64 having no lower layer are deteriorated.

As described above, in the present invention, the effect of having three multilayer coating layers is clear.

(Effects of the Invention) Since the present invention is configured as described above,
By using the multilayer plated steel material according to the present invention, it is possible to improve the initial adhesiveness and to minimize the deterioration of the adhesive durability under a corrosive environment.

Furthermore, the multi-layer plated steel material according to the present invention is excellent in chemical conversion treatment, coating film adhesion, corrosion resistance after painting, and spot weldability, and is extremely suitable for use in, for example, automobiles, home appliances, building materials, and the like. It is a suitable plated steel material.

Thus, the significance of the present invention, which has high industrial utility value, is extremely remarkable.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are schematic explanatory views each showing the appearance of a sample used in an adhesion durability evaluation test performed in an example of the present invention for a multilayer plated steel material according to the present invention. And FIG. 2 is a schematic explanatory view showing a bending fatigue test state in a composite corrosion test performed in an example of the present invention.

Claims (1)

(57) [Claims] 1. An underlayer having an average Fe content of 5 to 20% by weight and a surface roughness of at least
Alloyed hot-dip galvanized layer with Ra of 0.3 μm or more, Intermediate layer: Coating layer of the following metal or alloy with an adhesion amount of 0.01 to 10 g / m ² , Metal: Cr, Al Alloy: Cr, Al, Co and Ni An alloy having one selected from the group consisting of Zn and Mn and one or more selected from the group consisting of Fe Upper layer: an adhesion amount of 0.01 to 10 g / m ² and an Fe content of 90 ~
A multi-layer plated steel material comprising 99.9999% by weight of a Fe-based alloy containing at least one selected from the group consisting of Ni, Co, Mn, B, S and P.