JPH0225998B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electrically alloy plated steel sheet that has excellent adhesion and corrosion resistance and can be used for various purposes, such as steel sheets for automobiles. [Prior Art and Problems] Application of various galvanized steel plates is being studied and promoted to solve the problem of corrosion of automobile bodies due to rock salt sprayed to prevent roads from freezing during winter in cold regions. Corrosion on the exterior of the car body occurs when the car is hit by pebbles or scattered rock salt thrown up from the road surface while driving on the road (this phenomenon is called chipping). (The impact force is extremely high at 150 km/h.), the paint on the car body surface peels off, and scratches reach the base steel plate, which are accelerated by the action of water from melting snow and sprayed salt. For example, Zn-plated steel plates are used as a countermeasure against corrosion on the outside of the car body. Due to its strong sacrificial anticorrosion effect, Zn plating has the ability to sufficiently prevent corrosion of steel plates even if scratches reach the base steel plate, but when used as a coating such as on the outside of a car body, a coating film called blister occurs. It has the disadvantage of being prone to blistering and rust. Therefore, recently Zn-Ni, Zn-Fe, Zn
−Co, Zn−Fe−Cr, Zn−Ni−Co, Zn−Cr, Zn
−Mn, Zn−Ti, Zn−Sn, Zn−Cu, Zn−Cd,
Electroplating of Zn-based alloys such as Zn-Pb and multi-layered plating of these (that is, Zn with different components and compositions)
Steel sheets have been developed that have been subjected to plating (with stacked plating layers of plating alloys) and plating with gradient concentration (that is, plating in which the composition changes in the direction of the thickness of the plating layer).
It has been recognized for its good blister resistance and is beginning to be put into practical use. However, these Zn-based alloy electroplating
The internal stress of the plating film is higher than that of electroplating using Zn alone, and therefore the adhesion of the plating layer to the steel sheet base is weaker than that of Zn plating. (Hereinafter, the adhesion that plating has to the steel plate directly to the steel plate will be referred to as road adhesion.) In addition, cationic electrodeposition coating,
Approximately 3 coats of paint, intermediate coat and top coat.
It is generally done to a thickness of 100μ or more, and the shrinkage stress during baking acts on the plating layer, causing
Adhesion to the substrate is lower than when unpainted.
Furthermore, in cold regions during the winter, the temperature drops to around -50°C, and the shrinkage of the coating film progresses, so the stress acting on the plating layer also increases, and the adhesion to the substrate is even lower. When subjected to the above-mentioned chipping under such conditions where the adhesion to the substrate is further reduced, the plated layer of the Zn-based alloy electroplated steel sheet has the disadvantage of peeling off. As a measure to increase the plating adhesion of Zn-based alloy electroplated steel sheets (hereinafter, the adhesion of plating to the steel sheet is referred to as plating adhesion, regardless of whether it is in direct contact with the steel sheet base or not). , for example, Cr, Mn, Fe, Co, as in JP-A No. 59-200789,
A method is disclosed in which a coating layer made of one or more of Ni, Cu, In, Zn, Cd, and Pb is provided between a Zn-based alloy plating and a base steel sheet. However, this method involves extrusion molding in an unpainted state at room temperature (5
Adhesion has been confirmed under mild conditions (mm Eriksen overhang), but it is useless under severe conditions such as cold regions, 3-coat painting, and chipping as mentioned above. Also, in Tetsu to Hagane 71 (1985) s1273
A method is disclosed in which a thin coating layer consisting of one of Fe, Zn, Ni, Cu, and Sn is provided between the Zn-based alloy plating and the base steel sheet, and the conditions of two-coat painting, freezing point, and Dupont impact test are disclosed. Although it has been reported that sufficient plating adhesion can be obtained under the above-mentioned three-coat coating and chipping conditions, insufficient effects are obtained. [Means for Solving the Problems] The present invention provides Cr, P on at least one side of a steel plate.
Each component concentration is 0.1% or more and the upper limit is Cr
A Fe-Cr-P alloy electroplated layer with a total concentration of 20% and P, with Fe component occupying the balance, is formed at 0.1 g/m ² or more, and furthermore, a 5 g/m ² or more electroplated layer is formed on the electroplated layer. , Fe, Ni, Co, Cr, Mn, Ti, Sn, Cu,
Plating adhesion characterized by forming one or more Zn-based alloy electroplated layers containing Cd and Pb alone or in combination at a total concentration of 5wt% to 90wt%, with the balance being Zn. It is a multi-layer plated steel plate with excellent corrosion resistance after painting. In view of the above-mentioned circumstances, the present inventors conducted various experiments with the aim of obtaining good plating adhesion even when a Zn-based alloy coated steel sheet coated with an automotive three-coat coating is subjected to chipping at low temperatures. A ternary alloy plating layer consisting of Fe-Cr-P is applied to the surface of the steel sheet.
It was confirmed that by depositing 0.1 g/m ² or more and then applying Zn-based alloy plating on the plating layer, the desired plating adhesion under severe conditions could be obtained. In other words, if Zn-based alloy plating is applied directly to a crystalline material such as the surface of a steel plate, the
Since Zn-based alloy plating precipitates continuously with the steel plate,
It attempts to have the same crystal structure as steel crystals. As a result, the Zn-based alloy has to adopt a crystal structure different from that of the original plating, resulting in large distortions at the interface with the steel plate, which is a factor that inhibits plating adhesion. . Zn alloy plating is particularly susceptible to this because its structure is more complex than Zn plating or other single metal plating.
The present inventors confirmed that in order for the Zn-based alloy plating to have the original crystal structure from the initial precipitation, it is necessary to provide an amorphous layer between the Zn-based alloy plating and the base steel sheet. However, among these, it was discovered that a ternary alloy of Fe, Cr, and P is industrially optimal, and the present invention was developed. [Function] Hereinafter, the present invention will be explained in detail using the drawings. Figure 1 shows a steel plate coated with non-Zn-based electroplating or non-Zn-based alloy electroplating as a lower layer plating, and then 50 g/m ² of 50 g/m 2 applied as an upper layer on the plating layer.
Multi-layer plated steel plate with Zn-based alloy electroplating.
This shows how the plating adhesion of the upper layer plating, Zn-based alloy electroplating, changes when the amount of non-Zn-based electroplating or non-Zn-based alloy electroplating, which is the lower layer plating, changes. FIG.
In Figure 1, A is Fe-only electroplating, B
is Fe-P alloy electroplating in which Fe contains 1% P, C is Fe-Cr in which Fe contains 1% each of Cr and P.
- When P alloy electroplating is applied as the lower layer plating, we showed how the plating adhesion of the Zn alloy electroplating, which is the upper layer plating, changes as the amount of the lower layer plating changes. It is a correlation curve. Figure 2 shows 0.1g/m ² as the lower layer plating on the steel plate.
This is a multi-layer plated steel sheet which has been electroplated with a Fe-Cr-P ^alloy of FIG. 2 is a diagram showing the relationship between the content range of Cr and P and the electroplating adhesion of the Zn-based alloy, which is the upper layer plating. In FIG. 2, each frame indicates the range of plating adhesion of Zn-based alloy electroplating, which is the upper layer plating. When Fe is used as the sole underlayer plating to improve the adhesion of Zn-based alloy electroplating, as shown by curve A in Figure 1, the plating adhesion of Zn-based alloy electroplating also improves as the amount of Fe deposit increases. do. However, in order to obtain good plating adhesion with lower layer plating using only Fe,
The thickness must be 20g/m2 or ^more .
As an effect of the Fe underlayer plating, it is thought that electroplating of Fe alone is more likely to undergo plastic deformation than steel, which alleviates the impact force of chipping. However, as mentioned above, Fe is used as a base material for Zn-based alloy electroplating.
When using a crystalline material such as electroplating, distortion occurs at the interface between the base layer and Zn-based alloy electroplating, which reduces plating adhesion.
It is presumed that in order to obtain good results with lower layer plating using only Fe, it is necessary to increase the amount of deposited material and further reduce the impact force. When plating the lower layer of an Fe-P alloy containing 1% P in Fe for the purpose of improving the plating adhesion of Zn-based alloy electroplating, the Fe-P The plating adhesion of Zn-based alloy electroplating also improves as the amount of adhesion increases. Fe-P
In the case of lower layer plating of alloys, the same effect can be obtained with a lower coating amount than that of Fe alone, but in order to obtain good plating adhesion, the coating amount must be 5 g/m ² or more. However, it has little industrial practicality. Since the lower layer plating of this Fe-P alloy is amorphous, even if the upper layer is electroplated with a Zn-based alloy, no distortion will occur at the interface between the two platings.
It is thought that the same effect was obtained with a lower coating amount than when Fe was used alone for lower layer plating. However, with less than 5 g/m ² of Fe-P alloy plating, the surface of the steel sheet cannot be uniformly covered, and good plating adhesion cannot be obtained. Fe-Cr-, which contains Fe with 1% each of Cr and P for the purpose of improving the plating adhesion of Zn-based alloy electroplating.
When plating the lower layer of P alloy electroplating, as shown by curve C in Fig. 1, the plating adhesion of Zn-based alloy electroplating increases as well as the amount of Fe-Cr-P deposited, and as shown by curve C in Fig. Demonstrates good plating adhesion with a trace amount of P0.1g/ ^m2 . According to the findings of the present inventors, by adding Cr, the Fe-P alloy plating can uniformly cover the steel plate surface even if it is thin, and the Fe-P alloy plating can coat the surface of the steel sheet uniformly even if it is thin.
This is to create Cr-P alloy plating. In Figure 2, if the Cr and P component concentrations in the Fe-Cr-P alloy lower plating layer are each 0.1% or more,
The plating adhesion of Zn-based alloy electroplating is good, and the total concentration of Cr and P is 20% or less, and Zn
It was shown that the plating adhesion of electroplating based alloy was good. If the Cr and P component concentrations are each less than 0.1%, both components will not exhibit the above-mentioned effects. In addition, Fe easily alloys with Cr and P.
Although it is optimal as a base metal, if the total concentration of Cr and P exceeds 20%, the plating layer becomes brittle and the adhesion between the steel plates and the substrate deteriorates. The Fe-Cr-P alloy electroplating related to the present invention is
5g/m2 or ^more of Fe, Ni, Co, Cr, Mn, Ti,
The plating layer contains Sn, Cu−, Cd, and Pb alone or in combination at a total concentration of 5wt% to 90wt%, with the remainder being
Zn-based alloy electroplated layer (Zn−Ni, Zn−
Fe, Zn−Co, Zn−Fe−Cr, Zn−Ni−Co, Zn−
Cr, Zn-Mn, Zn-Ti, Zn-Sn, Zn-Cu, Zn
- Electroplating of Zn-based alloys such as Cd and Zn-Pb, multi-layered plating of these (that is, stacking of Zn-based alloy plating layers with different components and compositions), and gradient-based plating (that is, plating of Zn-based alloys with different compositions) , plating that varies in the thickness direction of the plating layer), and furthermore, those containing small amounts of Al, Mg, In, etc.). The reason why the amount of the Zn-based alloy electroplated layer described above is set to 5 g/m ² or more in the present invention is that if the amount is less than that, no anticorrosive effect on the steel plate can be obtained. or,
Fe in the above-mentioned Zn-based alloy electroplated layer in the present invention,
The reason why the content of Ni, Co, Cr, Mn, Ti, Sn, Cu, Cd, and Pb was set to 5wt% to 90wt% is that in this range, these elements form intermetallic compounds with Zn, and this intermetallic compound plating occurs. This is because the layer exhibits excellent blister resistance. Fe, Ni, Co, Cr, Mn, Ti, Sn,
When the content of Cu, Cd, and Pb is less than 5%, Zn has a structure in which these elements are solidified, and the properties of Zn become stronger.
If the content exceeds 90 wt%, Zn will be solidified in these, resulting in stronger properties and poorer blister resistance, so this range was set. The multi-layer plated steel sheet of the present invention can be prepared by conventional degreasing (degreasing agents such as strong alkali, weak alkali, and solvents and degreasing methods such as immersion, spraying, counterflow, and electrolysis), and by ordinary pickling (degreasing using sulfuric acid, hydrochloric acid, etc.). After applying Fe-Cr-P alloy electroplating to a steel plate that has been pretreated with pickling methods such as pickling detergent and pickling methods such as dipping, spraying, counterflow, and electrolysis, Zn
Obtained by electroplating a series alloy. Fe-Cr-P alloy electroplating is performed using a Fe-Cr-P alloy electroplating bath (Fe ²⁺ chloride or sulfate, Cr ³⁺
The main components are chlorides or sulfates, phosphites or hypophosphites of non-metals such as K, Na, NH ₄ , etc.
PH with chlorides, sulfates, or borates such as K, Na, NH ₄ , Mg, and Al as subcomponents and acids such as sulfuric acid and hydrochloric acid, or carbonates such as Na, Mg, and Sr as PH regulators.
It is obtained by electroplating at a current density of 10 to 300 A/dm ² and a flow rate of 10 to 300 m/min in a plating bath with a temperature of 30 to 70° C. and a temperature of 30 to 70° C. Fe ²⁺ is the main component in the bath,
The total concentration of Cr ³⁺ and P is 30 to 100 g/, and by changing the ratio of each, Fe, Cr, and P in the plating layer can be adjusted.
The alloy electroplating ratio can be changed. The structure of the plating tank can be either vertical or horizontal. In addition, the power source for plating is not limited to direct current, but may also be a pulse power source with a high cathode electrolysis ratio or a DC/AC superimposed power source without any particular problem. Zn-based alloy electroplating is performed using a Zn-based alloy electroplating bath (Zn ²⁺ , Fe ²⁺ , Co ²⁺ , Cr ⁶⁺ , Cr ³⁺ , Mn ²⁺ , Ti ²⁺ ,
Bath temperature 20~20~ with PH0.5~13.5 mainly composed of Sn ²⁺ , Cu ²⁺ , Cd ²⁺ , Pb ²⁺ chloride, sulfate, borofluoride, sulfamate, or chelate salt such as citric acid. Current density 10~ in plating bath (70℃)
It is obtained by electroplating at 300 A/dm ² and a flow rate of 10 to 300 m/min. The main components in the bath are Zn ²⁺ , Fe ²⁺ ,
Ni ²⁺ , Co ²⁺ , Cr ⁶⁺ , Cr ³⁺ , Mn ²⁺ , Ti ²⁺ , Sn ²⁺ ,
The total concentration of Cu ²⁺ , Cd ²⁺ , and Pb ²⁺ is 30 to 100 g/
By changing the ratio of each, the plating layer
Zn ²⁺ , Fe ²⁺ , Ni ²⁺ , Co ²⁺ , Cr ⁶⁺ , Cr ³⁺ , Mn ²⁺ ,
The alloy electroplating ratio of Ti ²⁺ , Sn ²⁺ , Cu ²⁺ , Cd ²⁺ , Pb ²⁺ can be changed. The structure of the plating tank can be either vertical or horizontal. In addition, the plating power source is not limited to direct current, but may also be a pulsed power source with a high cathode electrolysis ratio or a DC/AC superimposed power source without any particular problem.
In addition, when forming these layers into multiple layers, baths with different concentration ratios of the main components are separately settled for each layer, and the layers are sequentially plated in plating tanks for each layer. In addition, when forming plating with a gradient in concentration, it is possible to combine the above-mentioned multilayer method and the method of changing the current density for each plating bath. The multi-layer plating of the present invention does not need to be applied to both sides of a steel plate; depending on the application, it may be plated on only one side, and the other side may be left as the steel plate surface, or may be coated with Zn or Zn-based alloy. may be applied. The base steel plate to which the present invention is applied is usually a mild steel plate that has been subjected to dull finish rolling, but it can also be applied to mild steel plates that have been subjected to bright finish rolling or high-strength steel plates that contain large amounts of Mn, S, P, etc. as steel components. . Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples. [Example] Various multi-layer plated steel sheets according to the present invention and plated steel sheets other than the present invention were tested for evaluation of plating adhesion by chipping at low temperature after 3-coat coating for automobiles, as well as red rust resistance and blister resistance. A post-painting corrosion resistance evaluation test was conducted mainly for evaluation. Table 1 shows coating conditions, test conditions, and evaluation criteria. Table 2 shows the upper layer plating using alloy electroplating in which Ni is added to Zn alone, and Table 3 shows
When the upper layer is electroplated with an alloy in which Fe is added alone to Zn, Table 4 shows that Fe, Ni,
Examples of single-layer plating and multi-layer plating when the upper layer is electroplated alloy containing Co, Cr, Mn, Ti, Sn, Cu, Cd, and Pb added singly or in combination are shown below. . Sample No. 2-1, 2-2, 2-5, 2-6, 2-
10, 2-11, 2-16, 2-17, 2-18, 2-19,
2-20, 2-21, 2-23, 2-25, 3-1, 3-
2, 3-5, 3-6, 3-10, 3-11, 3-16,
3-17, 3-18, 3-19, 3-20, 3-21, 3-
23 and 3-25 are comparative examples, and sample Nos. 2-3 and 2-
4, 2-7, 2-8, 2-9, 2-12, 2-13,
2-14, 2-15, 2-22, 2-24, 3-3, 3-
4, 3-7, 3-8, 3-9, 3-12, 3-13,
3-14, 3-15, 3-22, 3-24, 4-1 to 4-
25 is an example of the present invention. Comparative Examples 2-1 and 3-1 had poor plating adhesion because the lower layer was not plated, and inevitably the corrosion resistance after painting was also poor. In Comparative Examples 2-2 and 3-2, the plating adhesion of the lower layer was small, so the plating adhesion was somewhat poor, and as a result, the corrosion resistance after painting was also slightly poor. Comparative Examples 2-5 and 3-5 are
Since there is no Cr, plating adhesion is poor, and corrosion resistance after painting is inevitably poor. In Comparative Examples 2-6 and 3-6, the plating adhesion was somewhat poor because the Cr content in the lower layer plating was low, and as a result, the corrosion resistance after painting was also slightly poor. Comparative Examples 2-10 and 3
-10 has poor plating adhesion due to the lack of P in the lower layer plating, which inevitably results in poor corrosion resistance after painting. In Comparative Examples 2-11 and 3-11, the plating adhesion was slightly poor because the P content in the lower layer plating was small.
Naturally, the corrosion resistance after painting also deteriorated a little. In Comparative Examples 2-16 and 3-16, the total content of Cr and P in the lower layer plating was a little high, so the plating adhesion was somewhat poor, and the corrosion resistance after painting was inevitably also slightly poor. In Comparative Examples 2-17 and 3-17, the total content of Cr and P in the lower layer plating was high, resulting in poor plating adhesion and, inevitably, poor corrosion resistance after painting. Comparative Examples 2-18 and 3-18 had a small amount of upper layer plating, so Comparative Examples 2-19, 3-19, and 2-
20 and 3-20, the components of the upper layer plating were outside the range required by the present invention, so the plating adhesion was good, but the corrosion resistance after painting was slightly poor. Comparative Examples 2-21 and 3-21 have two layers of upper plating, Comparative Examples 2-23 and 3-23 have a sloped upper plating layer, and Comparative Examples 2-25 and 3-25.
has three upper plating layers, but since the lower plating layer is not applied, the plating adhesion is poor, and the corrosion resistance after painting is also inevitably poor. In contrast, the multi-layer plated steel sheets of the examples of the present invention clearly have better plating adhesion and post-painting corrosion resistance.

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〔Effect of the invention〕

As described above, the multilayer plated steel sheet of the present invention is a high-performance steel sheet with excellent plating adhesion and post-painting corrosion resistance, and its practical value is truly great.

[Brief explanation of drawings]

Figure 1 shows a steel plate coated with non-Zn-based electroplating or non-Zn-based alloy electroplating as a lower layer plating, and then 50 g/m ² of 50 g/m 2 applied as an upper layer on the plating layer.
Multi-layer plated steel plate with Zn-based alloy electroplating.
FIG. 3 is a correlation diagram between changes in the amount of plating of the lower layer and plating adhesion of the upper layer. Figure 2 shows a steel plate coated with 0.1 g/m ² of Fe-Cr-P alloy electroplating as a lower layer plating, and then 50 g/m ² of Zn-based alloy electroplating as an upper layer on the plating layer. FIG. 2 is a diagram showing the relationship between the content range of Cr and P in the lower plating layer and the plating adhesion of the upper plating layer in a multi-layer plated steel sheet.

Claims (1)

[Claims] 1. At least one side of the steel plate has a Fe-concentration of Cr and P components each of 0.1% or more, and the upper limit is 20% for the total concentration of Cr and P, with Fe component accounting for the remainder.
Forming a Cr-P alloy electroplated layer of 0.1 g/m ² or more,
Further, on the electroplated layer, 5 g/m ² or more of Fe,
Ni, Co, Cr, Mn, Ti, Sn, Cu, Cd, Pb alone or in combination at a total concentration of 5wt% or more in the plating layer
A multilayer plated steel sheet with excellent plating adhesion and post-painting corrosion resistance, characterized by forming one or more Zn-based alloy electroplated layers containing 90wt% and the balance being Zn.