JPH0770763A - Production of rust preventive steel sheet - Google Patents

Abstract

PURPOSE:To obtain a rust preventive steel sheet thin in coating weight and excellent in corrosion resistance by forming a Ni-P based alloy plated layer containing a specific quantity of P on the surface of the steel sheet, heat treating to form a diffused alloy zone mainly containing Fe-Ni-P on the boundary and further zinc electroplating. CONSTITUTION:The diffused alloy zone mainly containing Fe-Ni-P is formed on the boundary between the bare surface of the steel sheet and the plated layer by forming Ni-P based plated layer containing 8-15% P or a Ni-P based alloy plated layer containing <=15% one or more kind of W, Mo, Cu on at least one surface of the cold rolled steel sheet and heat treating the steel sheet in a non-oxidizing atmosphere. the steel sheet is zinc electroplated. As a result, the rust preventive steel sheet thin in coating weight and excellent in corrosion resistance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust preventive steel sheet suitable for automobiles and having a low weight and excellent corrosion resistance.

[0002]

2. Description of the Related Art Currently, rust-preventing steel plates are mainly used for automobile bodies in terms of reliability against long-term rust prevention. Generally, the zinc-based plated steel sheet is most often used among the rust-proof steel sheets, and among them is a zinc-nickel alloy electroplated steel sheet with a low weight and high corrosion resistance, or a slightly high basis weight, but a very high corrosion resistance. Alloyed hot-dip zinc-iron plated steel sheet, which has advantages and is cost-effective, is now the mainstream. However, in the case of alloying hot dip plating, there are cases where sufficient plating adhesion and workability cannot be secured depending on the composition of the steel sheet to be the base, which imposes restrictions on the component design of the base steel sheet. On the other hand, the electroplated steel sheet does not have such a restriction. In this respect, the electroplated steel sheet is superior. In recent years, the demand for low cost has increased, and in the case of electroplated steel sheets, it is particularly desirable to reduce the coating weight, but in order to prevent deterioration of corrosion resistance, electroplating is required to have low corrosion weight and high corrosion resistance. .

Conventionally, in order to improve the corrosion resistance of such electroplating, Japanese Patent Publication No. 1-24356 discloses Zn-Co-.
Composite plated steel sheet made of Cr-Al oxide, Japanese Patent Publication No. 2-
Japanese Patent No. 51996 discloses a Zn-Cr-based multi-layer plated steel sheet. The key to the corrosion resistance of these technologies is the sacrificial corrosion resistance of plating or the anticorrosion effect of the corrosion product of plating, and the effect is no longer significant after the plating layer in the corrosion process or the disappearance of the corrosion product of plating,
Corrosion of the base steel sheet progresses. As long as there is a premise of a low basis weight, it is difficult to meet the ever-increasing requirements for low cost and high corrosion resistance even with these plated steel sheets.

As a technique capable of solving this problem, Japanese Patent Publication No. 3-29877 discloses a technique of a zinc-based plated steel sheet on which a corrosion-resistant steel sheet having specified steel components is used as a base. However, this technique has the following problems.

Corrosion resistance is maintained by a stable rust layer formed on the surface of the corrosion-resistant steel plate during the corrosion process. Various additive components are required to form this stable rust layer, but in order to obtain a sufficient effect, a considerable amount must be added. However, what is utilized for forming the stable rust layer is limited to only those added in the total volume of the steel sheet which are added during the steelmaking and which are present in the surface layer portion. That is, in terms of corrosion resistance, it can be said that the components existing in the other inner layer portions are wasted. Therefore,
It cannot be said that the characteristics of the steel components that can contribute to corrosion resistance are fully exerted.

On the other hand, the components in the steel also have a role of controlling the mechanical properties of the steel plate, and in the corrosion-resistant steel plate, the combination of the mechanical property control component and the corrosion resistance improving component limits the component design. This point is the same as the problem with hot-dip galvanized steel sheets.

As a technique capable of overcoming these various problems, Japanese Patent Laid-Open No. 171692/1982 discloses a technique of Ni.
After applying the coating layer, heat it in a non-oxidizing atmosphere and add N to the steel.
A technique of forming an i diffusion layer and performing Zn—Ni alloy plating on the steel sheet is disclosed. However, the Ni-Fe diffusion layer certainly contributes to the improvement of the corrosion resistance after the plating layer or the corrosion product of the plating disappears in the corrosion process, but the effect is not sufficient. This is Ni-Fe
Although the starting point of corrosion is suppressed because the steel sheet surface state is stabilized by the presence of the diffusion layer, once the corrosion of the base iron begins, the density of the corrosion products is not high, so the water content that contributes to corrosion, Alternatively, it is considered that the permeation of oxygen and the like easily occurs and the progress of rust cannot be suppressed.

In Japanese Patent Publication No. 61-91414, one kind of metal plating selected from Zn, Ni, Sn, Cr or alloys containing these as main components is plated and heated in a non-oxidizing atmosphere. A technique of a highly corrosion-resistant surface-treated steel sheet is disclosed in which a diffusion layer of plated metal is formed in steel, and Zn-Ni alloy plating is further performed on the upper surface thereof. Also in this case, since the components such as Zn, Ni, Sn, and Cr do not contribute much to the densification of the corrosion product in the base iron corrosion,
Similar to the technique described above, the effect of improving the corrosion resistance is insufficient.

The thinner the plating applied to the upper layer, the shorter the period until the plating layer or the plating corrosion product disappears in the corrosion process, and the improvement of the corrosion resistance of the base steel sheet becomes a more important factor.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a galvanized steel sheet having a thin weight and good corrosion resistance.

[0011]

In order to solve the above-mentioned problems, the present invention provides a Ni-P alloy plating layer containing 8-15% by weight of P on at least one surface of a cold-rolled steel sheet, Alternatively, Ni-P containing one or more of W, Mo, Cr and Cu in a range of 15% by weight or less.
The step of forming the system alloy plating layer and the heat treatment of the steel sheet on which the alloy plating layer is formed in a non-oxidizing atmosphere to form a diffusion alloy region containing Fe-Ni-P as the main component at the interface between the steel sheet substrate and the plating layer. After the step of forming, after this step, Zn-based electroplating or Zn as a matrix, Ni, Fe,
A step of forming a zinc-based electroplated layer by performing zinc-based electroplating containing one or more of metals or oxides of Co, Cr, Mn, Ti, Mo, Si and Al as an alloy or dispersed particles. The present invention relates to a method for manufacturing a rust-preventing steel plate having a thin weight and high corrosion resistance.

[0012]

The steel sheet applied in the present invention is a cold rolled material, but the usefulness of the present invention is effectively exhibited when an extremely low carbon steel having particularly good mechanical properties is applied. That is, ultra-low carbon steel has a solute C content of several tens of ppm (usually 30 pp
m to 50 ppm) and the purity of the steel sheet is very high, so that its corrosion resistance tends to be inferior to that of ordinary low carbon steel. By the method of the present invention, such a weakness of the base steel can be compensated and a steel sheet having both good mechanical properties and high corrosion resistance can be obtained.

In the present invention, P is added to the cold rolled steel sheet to
A Ni-P alloy plating layer containing 15% by weight is formed. Ni-P alloy plating containing 8 to 15% by weight of P has a structure close to amorphous, and heat treatment of a steel sheet having such a plating layer results in a more uniform diffusion alloy than in the case of a general crystalline plating film. Layers are formed in a short period of time. Further, since P is contained in this diffusion layer, the corrosion product of iron formed after the corrosion of the base iron is started becomes very dense. As a result, it is possible to obtain excellent corrosion resistance that cannot be obtained by the conventional techniques.

8% by weight of P in the Ni-P alloy plating layer
When the amount is less than 1, the Ni-P alloy plating is crystalline and the P distribution is not uniform. For this reason, the composition of the diffusion alloy region formed when subjected to the heat treatment is not uniform, the contribution of the above-mentioned rust formed on the underlayer to the denseness is not sufficient, and excellent corrosion resistance cannot be obtained. On the other hand, if P exceeds 15% by weight, the Ni-P alloy plating becomes brittle and its adhesiveness deteriorates. Therefore, plating peeling is likely to occur during heat treatment or the like. From this, P of the plating layer formed on the steel sheet in the present invention is
The content rate was 8-15% by weight. The preferred range is 10-
It is 13% by weight.

A Ni-P alloy plating layer obtained by compounding Ni-P with one or more of W, Mo and Cu in an amount of 15% by weight or less is used as plating for post-rolling treatment. You can also Each of W, Mo, and Cu has an inhibitory role on steel corrosion, and at the same time, has a synergistic effect with Ni and P to further improve the denseness and stability of initial rust. The total content of W, Mo and Cu is preferably 15% by weight or less. Corrosion resistance improves with an increase in the total content of W, Mo, and Cu, but if the total value exceeds 15% by weight, the adhesion decreases, and thus plating peeling easily occurs in the subsequent process. Therefore, the total content of W, Mo and Cu is set to 15% by weight. In order to exert the effect of containing W, Mo and Cu, the lower limit is preferably 0.5% by weight.

The plating amount of this Ni-P alloy plating layer is not specified, but 0.1 g / m ² -8
A range of g / m ² is desirable. If the amount is too small, the effect of improving the corrosion resistance is not sufficient, and if the amount is too large, the cost increases with respect to the performance improvement, which is not practically efficient. Furthermore, the line speed must be slowed down to increase the plating amount, which is disadvantageous in terms of production efficiency.

Although various methods of forming the Ni-P alloy plating layer are conceivable, electroplating or electroless plating (chemical plating) is preferable in terms of simplicity and film quality to be obtained. Next, the steel sheet provided with the Ni-P alloy plating layer is heat-treated in a non-oxidizing atmosphere, and Fe-N is added to the interface between the steel sheet substrate and the plating layer.
A diffusion alloy region containing i-P as a main component is formed. The non-oxidizing atmosphere is preferably an argon atmosphere, an N ₂ atmosphere, or a reducing atmosphere containing a predetermined amount of H ₂ gas and the balance being an inert gas. The heat treatment for diffusion can be performed in a normal annealing equipment after cold rolling. In addition, at this time, the heat treatment can also be performed by performing normal annealing. The highest temperature reached at this time is preferably 500 ° C. or higher and 850 ° C. or lower. If it is less than 500 ° C, the diffusion layer between the Ni-P alloy plating layer and the steel surface is not sufficiently formed, and the dense rust formation during the corrosion process is not sufficient, so the effect of improving corrosion resistance is small. On the other hand, if the temperature exceeds 850 ° C., the plated metal is likely to be picked up by the roll in the heat treatment furnace, and as a result, surface scratches or the like are likely to occur. Further, the holding time at the maximum reached plate temperature varies depending on the temperature, but is preferably 1 second to 120 seconds. If it is too short, a sufficient diffusion region is not formed, so the effect of improving corrosion resistance does not appear, and if it is too long, this interface layer becomes brittle due to excessive diffusion alloying, and the adhesion and workability of the plating layer deteriorate. During the heat treatment, an overaging treatment may be performed at a temperature of about 300 to 400 ° C. for about several minutes. A suitable diffusion region formed by heat treatment has a depth of about 0.1-20 μm. When the Ni-P alloy plating layer is heat-treated, a part of the Ni-P alloy plating layer forms a diffusion alloy layer, which is steel plate / diffusion alloy region / N.
The present invention includes both the case of the i-P alloy plating layer and the case of forming the diffusion alloy layer entirely to form the steel plate / diffusion alloy region.

After the heat treatment for diffusion, temper rolling is performed under appropriate conditions if necessary. The steel sheet thus treated is further electroplated in an electroplating line. Regarding electroplating at this time, Zn-based electroplating or using Zn as a matrix, Ni, Fe, Co,
Zn-based electroplating containing one or more of the metals or oxides of Cr, Mn, Ti, Mo, Si and Al as an alloy or dispersed particles is effective. All of these platings contribute to the corrosion resistance in the plating corrosion process because the corrosion of the plating is inactive. However, even when the base is corroded, the components existing in the Zn matrix and Ni,
The synergistic effect with the diffusion layer component such as P is effective in stabilizing rust and densifying the base iron. In particular, in Zn-Cr plating, Cr in the film exerts a synergistic effect with components such as P in the diffusion-treated layer even after the plating disappears, and it is effective in stabilizing rust and densification of the base iron. Among the coatings, it has particularly excellent corrosion resistance.

The zinc adhesion amount of zinc-based electroplating is 1-30.
It is preferably g / m ² . If the adhered amount is too small, good corrosion resistance cannot be obtained, and if the adhered amount is too large, the workability of the plating amount is lowered and the cost is increased. As the zinc-based electroplating bath, a widely used sulfuric acid bath, chloride bath or the like can be used. The plating film obtained by applying these plating baths is a Zn film, a Zn-Ni film, a Zn-Cr film, a Zn-Fe film, a Zn-Cr-Ni film, a Zn-C film.
An r-Mo film and the like can be mentioned. The content of the alloy or dispersed particles present in the zinc-based electroplating layer is 1% by weight or more in total in order to effectively exert its effect, and
If the components other than the above are excessively contained, the adhesion control of the film becomes insufficient, so the total amount is preferably 70% by weight or less.

Further, when higher corrosion resistance is required, it is also possible to further subject the zinc-based electroplating layer to chromate treatment and to apply the organic composite resin thereon. At this time, as the chromate treatment method, any of reaction type, electrolytic type, and coating type can be applied. In the chromate film, organic substances such as acrylic resin, oxide colloids such as silica and alumina, acids such as molybdic acid, salts,
Other rust preventive strengthening components may be included. The organic resin film formed on the chromate film may use an epoxy resin or the like as a base resin, and further contains approximately 10-60% by weight of a rust preventive additive such as silica or chromate. desirable.

[0021]

EXAMPLES Examples of the present invention will be shown below. Each of these examples was carried out using a small test piece. After cold-rolled steel sheets having the components shown in Table 1 were subjected to Ni-P plating (hereinafter referred to as pre-plating) under the conditions shown in Table 2, under various conditions shown in Examples of Table 4 in a non-oxidizing atmosphere. Heat treatment was performed. After that, the usual plating pretreatment was performed and the plating shown in Table 3 was performed to prepare a test material. For a part of the comparison, a test piece was prepared in which some of the steel plates in Table 1 were annealed and plated without pre-plating. These test pieces were evaluated by the method described later. The results of Examples and Comparative Examples are shown in Table 4, Table 5, and
The results are shown in Table 6, Table 7 and Table 8.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

[Table 7]

[0029]

[Table 8]

As is apparent from the examples, the latter half of the corrosion resistance obtained by the method of the present invention is the same as the conventional corrosion-resistant steel plate (high P, Cr, Mo added) plated with Zn (Comparative Examples 22, 23, 24,25) is better. Also,
Regarding the types and compositions of pre-plating, Comparative Examples 6 to 1
8, the corrosion resistance of the present invention is better. It is considered that this is because the interfacial diffusion layer formed by “pre-plating” is superior to the conventional method in forming stable and dense initial rust.

[0031]

As described above, according to the present invention, it is possible to effectively manufacture a galvanized steel sheet having a thin weight and good corrosion resistance. Further, by adding a trace amount of the corrosion resistance enhancing component to the plating / steel plate interface, the corrosion resistance is significantly improved without adding a large amount of such a component to the steel plate. This gives a great advantage to the steel plate manufacturing cost, but its corrosion resistance is the same as that of conventional corrosion resistant steel plates (high P, C
It is better than the one in which Zn-based plating is applied to (r, Mo added). Further, regarding the type and composition of pre-plating, the steel sheet according to the method of the present invention has good corrosion resistance.

Front Page Continuation (72) Inventor Komitsu Shiobara 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A step of forming a Ni—P alloy plating layer containing 8 to 15% by weight of P on at least one surface of a cold rolled steel sheet, and heat treating the steel sheet in a non-oxidizing atmosphere, A step of forming a diffusion alloy region containing Fe-Ni-P as a main component at the interface between the steel sheet substrate and the plating layer, and a step of performing zinc-based electroplating to form a zinc-based electroplated layer after this step. A method of manufacturing a rust-preventing steel sheet having a thin weight and high corrosion resistance. 2. A cold-rolled steel sheet containing 8 to 15% by weight of P on at least one surface thereof, and containing W, Mo and Cu.
Forming a Ni-P alloy plating layer containing one or more of the above in a range of 15% by weight or less, heat treating the steel sheet in a non-oxidizing atmosphere, and Fe at the interface between the steel sheet substrate and the plating layer. -Ni-P having a high corrosion resistance with a low basis weight including a step of forming a diffusion alloy region having a main component, and a step of performing zinc-based electroplating to form a zinc-based electroplated layer after this step Manufacturing method of anti-corrosion steel sheet. 3. A step of forming a Ni—P alloy plating layer containing 8 to 15% by weight of P on at least one surface of the cold rolled steel sheet, and heat treating the steel sheet in a non-oxidizing atmosphere, A step of forming a diffusion alloy region containing Fe-Ni-P as a main component at the interface between the steel sheet substrate and the plating layer, and after this step, Zn is used as a matrix and Ni, Fe, Co, C
and a step of forming a zinc-based electroplating layer by performing zinc-based electroplating containing one or more of metals of r, Mn, Ti, Mo, Si, Al or oxides as an alloy or dispersed particles. A method for producing a rust-preventing steel sheet having a light weight and high corrosion resistance. 4. A cold-rolled steel sheet containing P in an amount of 8 to 15% by weight on at least one surface thereof, and containing W, Mo and Cu.
Forming a Ni-P alloy plating layer containing one or more of the above in a range of 15% by weight or less, heat treating the steel sheet in a non-oxidizing atmosphere, and Fe at the interface between the steel sheet substrate and the plating layer. A step of forming a diffusion alloy region containing -Ni-P as a main component and, after this step, using Zn as a matrix,
Ni, Fe, Co, Cr, Mn, Ti, Mo, Si, A
Rust-preventing steel plate having a thin weight and high corrosion resistance, which comprises a step of forming a zinc-based electroplated layer by subjecting zinc-based electroplating containing one or more metal or oxide of 1 as an alloy or dispersed particles Manufacturing method.