JPS58120794A - Highly corrosion resistance surface treated steel plate - Google Patents

Abstract

PURPOSE:To provide a highly corrosion resistant surface treated steel plate which is improved in paintability, corrosion resistance after painting and weldability by providing two layers of plating films of an Ni-Fe alloy and a Zn-Ni alloy on the surface of the steel plate. CONSTITUTION:A highly corrosion resistant surface treated steel plate wherein the double films consisting of an Ni-Fe alloy plating layer as the 1st layer and a Zn-Ni alloy plating layer as the 2nd layer are provided on at least one surface of a steel plate for outside plate of automotive bodies, etc. In this stage, the coated weight of the Zn-Ni alloy plating is made preferably 5-50g/m<2> and the coated weight of the Ni-Fe alloy 1/50-1/2 of the coated weight of the Zn-Ni alloy plating. The film compsn. of Zn-Ni is made about 10-20wt% in terms of content of Ni and the film compsn. of the Ni-Fe about 5-90% in terms of content of Fe. If the double layered films are provided on one surface of the steel plate and the Ni-Fe plating layer is provided on the other surface, the performance suited for use environment is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface-treated steel sheet with excellent corrosion resistance, paintability, and weldability.

There is a growing trend toward durability from the perspective of resource and energy conservation.
Surface-treated steel sheets with excellent durability are required, and the number of cases where they are used under harsh conditions is increasing.In particular, the corrosive environment of automobile bodies is becoming increasingly severe, and car body corrosion has become a major problem. There is.

Recently, laws and regulations have been enacted regarding corrosion protection for automobiles.
For example, in Canada, 1981 cars are required to come with a five-year warranty for no surface rust, no pitting, and no corrosion.

Therefore, in addition to corrosion from the inner surface of the vehicle body, corrosion from the outer surface of the vehicle body becomes a serious problem. This corrosion on the exterior surface is caused by the paint film being hit by pebbles, sand, rock salt, etc. thrown up from the road surface sprayed with antifreeze while driving, causing damage to the base material (chipping). The high humidity (moisture) and antifreeze agents (salt) in winter in cold regions act on the damaged parts, causing significant corrosion.

As a countermeasure against corrosion from the outside of the car body, for example,
Double-sided galvanized steel sheets can be considered.However, the adhesion of the coating film on the galvanized surface is not necessarily good, and the I! ! It has the disadvantage that it is prone to blistering due to film peeling and corrosion, and has poor weldability because both sides are coated with zinc.

As a result of intensive research with the aim of solving various problems in automobile exterior steel sheets as described above, the authors have found that a Nt-h alloy plating layer is applied as the first layer on at least one side of the steel sheet, and a second layer is coated with Nt-h alloy on at least one side of the steel sheet. The desired purpose can be achieved by forming a Zn-Ni alloy plating layer as a layer, or by forming the above two alloy plating films on one side and a Ni-Fe alloy plating layer on the other side. This is what we have found to achieve the following: 〇 Regarding internal corrosion of automobile steel sheets, Ni content of 10
~20 vtJ ((D) Although Zn-Ni alloy plating exhibits superior corrosion resistance to zinc plating, it is not necessarily satisfactory under the severe conditions described above.The present invention attempts to further improve this corrosion resistance. , a Ni-pe gold alloy plating layer as a first layer on at least one side of the steel plate, aI2
A surface-treated steel sheet having a Zn-Ni alloy plating layer as a layer, and the two layers of alloy plating film on one side and Ni on the other side.
This invention provides a surface-treated steel sheet coated with a -Fe alloy plating layer, and the steel sheet has the embodiments shown in FIGS. 1 to 3.

The one shown in FIG. 1 has an N1-Fe alloy plating layer 2 and the Zn-Ni alloy plating layer 3 formed on both sides of the base steel 1, and the one shown in FIG. A layer 2 with Ni-)'e gold alloy is formed on the surface, and Z is formed on one side of the layer 2.
n-Ni alloy plating layer 3 is formed, and the third
What is shown in the figure is one in which a Ni-Fe alloy plating layer 2 and a Zn-Ni alloy plating layer 3 are formed on one side of a base steel 1. The plating layer is formed as a base layer, and the purpose of adopting Ni--Fe alloy plating as the base plating is as follows.

(1) Another corrosion-resistant film is applied between the Zn-Ni alloy plating and the base steel, and 72-Ni with the same plating thickness is applied.
It has better corrosion resistance than the alloy plated layer, and also has better corrosion resistance than the N1-pe plated layer.
The objective is to create a stable steel plate surface condition even on the single plated surface, improve the corrosion resistance of both unpainted and painted surfaces, and improve the secondary adhesion of the coating film.

■ Zn-Ni alloy and base steel (Fe) are in contact with dissimilar metals, but by using Ni-Fe alloy as a base, Fe, Ni, and Zn components are layered in stages from the base steel to the outermost surface. This is intended to improve the adhesion of the Ni alloy on the top surface and to alleviate the sticking strain.

(2) Even if the base steel is damaged, the Fe-Ni alloy, which is at fault, will preferentially form a couple with the Zn-Ni alloy on the outermost surface, which has a large potential difference, rather than the base steel or Zn-Ni alloy. The purpose of this invention is to further suppress the corrosion of the base steel by delaying the corrosion of the base steel and depositing corrosion products on the stable Ni--Fe alloy plating layer.

The exterior surface of an automobile body (exterior panel) is generally coated with electrodeposition coating, intermediate coating, top coating, etc., and requires corrosion resistance in the above-mentioned severe corrosive environment.On the other hand, for example, zinc-based The use of plating may be considered, but painted galvanized steel sheets may develop filamentous rust in areas that have been chipped.
Eventually, red rust develops. When using galvanized steel sheets, there are many changes in color tone (color unevenness) after painting, which makes them difficult to use, and generally cold-rolled steel sheets or single-sided surface-treated steel sheets are used. As described above, the present invention can significantly improve the paintability of the outer panels of such automobile bodies and the corrosion resistance after painting.

The present invention is characterized by imparting performance suitable for the usage environment as described above (when the front and back sides of a steel plate are used in different environments, the present invention has the effect of improving corrosion resistance of the Ni-Fe alloy plating layer formed in the present invention). The Zn--Ni alloy plating layer can be reduced, which has the advantage of saving energy and resources, as well as improving weldability.

Although the type and dimensions of the steel plate used in the present invention are not particularly limited, the amount of Ni-Pc alloy deposited is 0.1 f/
s/or more is desirable o Ni-Fe adhesion amount is 0.1f
If it is less than /-, there is no improvement in corrosion resistance either alone or as a Zn-Ni underlayer. Moreover, the optimum adhesion amount is the corresponding Zn
It is determined by the thickness of the -Ni layer, and is preferably 1/50 to 1/2 the thickness of the Zn--Ni layer. Also, Ni −
The Fe content of the Fe layer is 10 to 50 from the viewpoint of workability.
Although wtX is preferable, it is not limited to this and is effective from 5 vtX to 90 vtX depending on the purpose.

The amount of Za-Ni alloy plating applied to at least one surface of the steel plate on which the Ni-Fe alloy plating layer is formed is 5 to 5.
50 f/glI is preferable; if it is less than 5 f/d, high corrosion resistance cannot be obtained, and if it exceeds 50 f/glI, it will be economically disadvantageous. Further, according to research by the present inventors, the N1 content of the zn-Ni layer is in the range of 10 to 20 vtX, which has a sacrificial corrosion prevention effect and is excellent in corrosion resistance.

It is desirable that the plating bath used in the present invention has a high current density and good electrical conductivity.From this point of view, a sulfur salt bath, a chloride bath, or a mixed bath thereof is used, and a current density of 10 A/dsd or higher, liquid flow rate lO course/
Electrolysis at sII or higher is practically desirable. Hereinafter, the present invention will be explained with reference to examples.

[Example 1] Material 5PCC, plate thickness 0.7am - width 100mm, length 20mm
0. After electrolytically degreasing and pickling cold-rolled steel sheets, the following N
Using an i-Fe alloy plating bath, N1-Fe alloy plating was applied to both surfaces at a current density of 15 A/P and a bath temperature of 60° C. to a coating weight of 2 f/- on each side. This sample was further coated at 30A/30A using the following Zn-Ni alloy plating bath.
-＼16 f/ml on the surface and 8 on the back at a bath temperature of 50℃
Zn--Ni alloy plating was performed with a difference in thickness between the front and back surfaces so that the coating amount was f/d.

■　Ni　-)’e Bath with gold alloy NlSO4・6L0 105 f/l.

NIC1, 6Hz0 60 f/l.

Fe5Oa 20t/1HsBO
z 50 f/lPH3 (2) Zn-Ni alloy plating bath ¥4 136 f/LNicz2/6
Ht0 236 t/l■4C160f/l pH4 Various tests as described below were conducted on the surface-treated steel sheet of the present invention thus obtained, the conventional Zn-Ni alloy plated steel sheet, and the cold-sagi steel sheet. The results are shown in Table 1.

■ Number of days until red rust occurs in unpainted corrosion resistance salt spray test (JIS Z 2371) (2) Corrosion resistance salt water spray test after electrodeposition coating 30 days after cationic electrodeposition coating (1)
0 μIR) Width of paint film bulge from the scut part (m ) @ Corrosion resistance salt spray test after 3 coats Painting after 90 days (electrodeposition + 10 intermediate coats) The width of the paint film bulge from the scut part (W
) Adhesion after 3-coat painting (secondary adhesion) Amount of paint film peeled off by 7μ tape peeling method from 3-coat F coated cross-cut part after 90 days of salt spray test Based on the test results in Table 1, It is clear that the surface-treated steel sheet according to the present invention has significantly improved corrosion resistance without painting, corrosion resistance after painting, and paint film adhesion as compared to conventional steel sheets.

Table 1 [Example 2] A cold-rolled steel plate with a material of 5 pcc, a plate thickness of 17 rin% @ lOO layer, and a length of 200 was electrolytically degreased in the same manner as in Example 1.
After pickling, using the Ni-1i'e alloy plating bath below, Ni
Fe-plated. Furthermore, only one side of this sample was coated with a 50A plating bath using the Zn-Ni alloy plating bath described in ① of Example 1.
Zn--Ni alloy plating was performed at a current density of /di and a bath temperature of 45° C. to a coating weight of 15 f/lel.

■ Ni -Fe alloy plating bath p'ectx・4X0 300 f/1Ni
(::L2・6dan+0 401/1CaC
41g 0 f /j pH 1,0 The surface-treated steel sheet of the present invention thus obtained, the conventional ZN-Ni alloy plated steel sheet, and the cold-rolled steel sheet were subjected to various tests and weldability tests similar to those in Example 1. C went
The results are shown in Table @2. In the weldability test, the surface-treated steel sheets of the present invention were combined as shown in FIG. 4, continuous spot welding was performed, and the number of consecutive welds was evaluated. The welding current was 9000A, the pressure was 22 (it), the welding time was 12
It's a cycle.

From the test results in Table 2, Z
The steel plate with n-Ni alloy plating showed excellent corrosion resistance as in Example 1, and the steel plate with only Ni-Fe alloy plating without Zn-lft alloy plating was also resistant to electrodeposition coating and 3-suite coating. It can be seen that the corrosion resistance after painting is extremely excellent, and in particular, the corrosion-resistant window and paint adhesion after 3-coat painting are significantly superior to conventional Zn--Ni alloy plating and cold-rolled steel sheets. Moreover, the single-sided Zn-Ni alloy plated steel plate in this example has a greater weldability improvement effect than the double-sided Zn-Ni alloy plated steel plate.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are cross-sectional views showing aspects of the surface-treated steel sheet according to the present invention, and Figure 4 is a diagrammatic cross-sectional view (2) showing the overlapping state of the steel sheets in a spot welding test. be. Explanation of symbols 1... Steel plate, 2-Ni-Pa alloy plating layer, 3-Zn
-Ni alloy plating layer, 4--electrode guide pin for spot welding Applicant: Kawasaki Tentetsu Co., Ltd.

Claims (1)

[Claims] ■ Ni-Fe as the first layer on at least one side of the steel plate.
A highly corrosion-resistant surface-treated steel sheet having a two-layer coating consisting of an alloy plating layer and a Zn-Ni alloy plating layer as the second layer. ■ The scope of claims characterized in that the adhesion i of Zn-Ni alloy plating is 5 to 50 f/i, and the amount of adhesion of Ni-Fe alloy plating is 140 to 1/2 of the amount of Zn-Ni alloy plating. The highly corrosion-resistant surface-treated steel sheet according to item 1. Claim 1, characterized in that the film composition of Zn-Ni alloy plating is 10-20 wtK in terms of Ni content, and the film composition of Ni-Fe alloy plating is 5-90 wtX in terms of PE content. or the highly corrosion-resistant surface-treated steel sheet 0 (I) described in Item 2, having a two-layer coating on one side of the steel sheet consisting of a Ni-Fe alloy plating layer as the first layer and a Zn-Ni alloy plating layer as the second layer. , a highly corrosion-resistant surface-treated steel sheet characterized by having a Ni-Fe alloy plating layer on the other surface.
The highly corrosion-resistant surface-treated steel sheet according to claim 4, wherein the coating amount of the Ni-Fe alloy plating is 1150 to V2 of the Zn-N1 alloy plating amount. (6) The film composition of the Zn-Ni alloy plating has a Ni content of ZO~20 wtNs, and the film composition of the Nt-Fe alloy plating has a Fe content of 5~904X. Highly corrosion-resistant surface-treated steel sheet according to item 4 or 5.