JPS58117890A - Highly corrosion resistant surface treated steel plate - Google Patents

Abstract

PURPOSE:To obtain a titled steel plate having good corrosion resistance, paintability, and weldability by carrying out electroplating of metals (alloys) of Zn, Ni, etc. on the surface of a steel plate and forming a diffusion layer of said metals (alloys) by heating in the steel then carrying out plating of a Zn-Ni alloy on the surface of the steel plate. CONSTITUTION:Metallic plating of Zn, Ni, Sn, Cr or consisting essentially of these metals is carried out thinly on both front and rear surfaces of a steel plate. The plating in this case is carried out preferably at 0.5-20g/m<2> per one side. The steel plate after the plating is heated in a nonoxidative atmosphere to diffuse said plating metal thoroughly into the steel. Zn-Ni alloy plating is carried out on at least one surface of the steel plate formed with the diffused layer, whereby the intended surface treated steel plate having high corrosion resistance is obtained. The Zn-Ni alloy plating has a sacrificial effect of preventing corrosion when the content of Ni is 10-20wt% and is the range where the corrosion resistance is high.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a highly corrosion-resistant surface-treated steel sheet, which is coated with a Zn-Ni alloy that has been improved to provide corrosion resistance, paintability, and km-worthiness for the interior and exterior surfaces of vehicle bodies as a corrosion-resistant material for automobiles. These are 6 items related to steel plates.

Recently, the use of surface-treated steel sheets, in which steel sheets are subjected to chemical conversion treatment or further painting treatment, has expanded, and as a result, a high degree of corrosion resistance is required to match surface characteristics such as paintability, weldability, and other processability. Now it is strongly 1IIdI.

In particular, the corrosive environment of automobile bodies has become increasingly severe, and body corrosion has become a major problem. Recently, laws and regulations have been enacted regarding the corrosion protection of automobiles. For example, in Canada, 1981 handcarts are required to have a one-and-a-half year guarantee against surface rust and a five-year guarantee against pitting and rot.

Spraying antifreeze rock salt on highways has made the corrosive environment even more severe on the inside of the car body, accelerating corrosion, and there is a need for countermeasures against pitting corrosion. On the other hand, corrosion on the outside of the car body is caused by damage (chipping) that reaches the base material when the Q paint is hit by pebbles, sand, rock salt, etc. thrown up from the road surface sprayed with antifreeze while driving. Moisture infiltrates from the damaged area and salt acts on it, causing -C corrosion to progress.

As a countermeasure against corrosion from the inside and outside of the car body, it is possible to use a steel plate with thick galvanizing on both sides. However, double-sided galvanized steel sheet C is coated M J) 1
Because the adhesion is not good, the outer surface of the car body is prone to peeling of the paint film due to stone splashes mentioned above, and even blisters due to spoilage. The coating significantly impairs weldability.For this reason, single-sided anti-corrosion treated steel plates are being used extensively, with consideration given to ensuring the rust-proofing properties of the inner surface of the car body, and corrosion resistance is required. By using a 114ilVc anti-corrosion treated surface on the inside of the vehicle body, weldability is ensured by using a non-rubbed surface on the outside.

However, this single-sided anti-corrosion treated steel plate has insufficient rust-prevention properties on the exterior surface of the car body.
There is.

・Problems related to painting steel machines for automobile exterior panels, such as those described by inventors + Ih? As a result of intensive research to solve the problem, we found that the surface or both sides of the steel plate, Zn, Ni, Sn, Cr.
Or, if these are the main components (the inner part of the alloy), the free metal 4
Apply a thin layer of air plating and heat it in a non-oxidizing atmosphere to coat the steel! It has been found that by forming a metal diffusion layer of ``Ll-'' and applying Zn--Ni alloy plating on at least one side of the steel sheet, the desired result can be achieved in an advantageous manner.

In other words, the surface of a steel plate that has been thinly metal-plated and then metal-diffused has good temporary rust prevention properties, as well as good coating properties, as well as good resistance after coating. . Therefore, Zn-Ni is suitable for the Ni degree corrosion resistance requirement on the inner surface of the car body.
Alloy plating is applied to the outer surface of the car body, which requires paintability and corrosion resistance after painting, using Zn, Ni,
An alloy containing Sn, Cr, ', i, etc. as its main components)) 1 type (by applying thin plating and diffusion treatment to the surface of the steel plate, it is extremely convenient as a protective plate for automobiles. Surface-treated steel sheets are available.

In the present invention, m f is applied to the surface or both the front and back surfaces of the steel plate.
Zn, Ni, Sn, Cr or this
The alloy plating, which is the main component of the coating, is infiltrated into the steel by heat treatment, forming a diffusion layer and creating a new steel plate surface condition, thereby creating gaseous contact between the steel plate surface and the diffusion layer. J) Q
These metals can be easily coated on the surface of a plate by the known one-layer plating method. In particular, the present invention is determined in accordance with the requirements of the surface of the surface of the lid, and the diffusion treatment is carried out with the surface of a single plate, Ni, Sn, Cr.
Alternatively, it is preferable that a sliding joint containing these as main components has a range of 0.5 P/rrl or more and 20 P/- or less on one side. The reason is that if the film is thin enough to be less than 20 jE /
If it exceeds nl, there will be problems in weldability and economy, so cb
Ru. Furthermore, in the case of Cr plating, the same effect as range C can be obtained in areas below 0.05 P/wl and below 2 y/m''.

Next, for the permeation and diffusion treatment into the steel by heating the plated metal, the conventional heating method in a non-oxidizing atmosphere is suitable as is, and the continuous method used for annealing after cold rolling is suitable. Annealing or box annealing can also be used:
Colander. When continuous annealing is used, conditions of VC and Z are preferred in order to effectively diffuse the plating metal or alloy.

Temperature 300-800C 1 hour 5 seconds-3 minutes. In case 1 where box type annealing is used, the temperature is preferably 250 to 800C and the time is 1 to 12 hours, depending on the type of plated metal and the thickness of the plating. T"a? Select this and perform sufficient penetration diffusion 2 into the steel.

Z performed on at least the yield strength J) surface of the steel plate on which the diffusion layer has been formed
Although n-Ni alloy plating is not particularly limited, according to the research carried out by the present inventors, there is a range Q in which Ni plating of 20 to 20 wt 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 crawling flow density and good conductivity.
, &tAf, kidney level 10 A/dm' or higher, liquid flow rate 1
0m/- or less hQJ)dL solution is practically desirable.

41: The invention is described above.) Applying anti-corrosion treatment to the front and back surfaces of the steel plate - [The environment in which it is used: ICC gives performance τ, especially on the outside of the vehicle body.] Painting J) Improved corrosion resistance, inner surface of vehicle body Q) Provides a surface-treated steel sheet that not only improves corrosion resistance but also has excellent weldability.

The surface-treated steel sheets of the present invention are obtained in the first to fourth embodiments (4 aspects J as shown in C). In lJ, l is a steel plate, 2 is a metal diffusion layer, and 3 is a Zn-Ni alloy plating layer. Here, the metal diffusion layer refers to the above-mentioned Zn, Ni, Sn, Cr.
Alternatively, it refers to a heat-penetration diffusion layer of a metal or alloy plated layer selected from alloys containing these as main components.

Next, regarding the surface characteristics of the surface-treated steel sheet with different anti-corrosion treatments on the front and back sides according to the present invention, the surface of the steel sheet with the metal diffusion layer has better paintability than the conventional cold-rolled steel sheet r%v. and Q, which improves corrosion resistance after painting, and improves paintability, corrosion resistance after painting, and droplet resistance compared to conventional double-sided Zn-Ni alloy plated steel sheets. Furthermore, the other side, which has a metal diffusion layer as a base and is plated with Zn Nu gold, has improved corrosion resistance compared to conventional Zn-Ni alloy plates, and a corresponding reduction in the amount of adhesion. Therefore, the anti-inflammatory effect of ffI contact can also be expected.

The surface properties of the surface-treated steel sheet according to the present invention, particularly on the surface having a metal diffusion layer, were compared with conventional cold-rolled steel sheets and Zn-Ni alloy plated steel sheets, and the results are shown in Table 1. In Table 1, C1 paint adhesion is t? / Prite 3114 (manufactured by Nippon Parker Co., Ltd. / acid treatment agent) was sprayed at a liquid temperature of 50°C for 150 seconds, and then various steel plates were electrocoated with a 20 μm thick anionic paint using Dupont impact coating. Test (500PX50cm) and 5 (Good) (+
A 5-grade evaluation of 1 (poor) was given, and the corrosion resistance after painting was expressed by the appearance after 720 hours of salt spray test after DuPont impact processing.

6 As is clear from Table 1, the steel plate surface with the metal diffusion treatment layer of the present invention has excellent paint adhesion and post-painting corrosion resistance compared to conventional cold-rolled steel plates and Zn-Ni alloy plated steel plates. Extremely excellent as an outer panel for automobile bodies.

Hereinafter, the present invention will be explained with reference to embodiments.

[Example j Material 5 pcc, plate thickness 0.7 mm, width IQQas, length 2
After degreasing and pickling a 00Peng cold-rolled steel plate, how many times should it be exposed to a reduced-acid zinc bath? Using a tIl flow density of 20A/drrI2 and a bath temperature of 50''C, ZnY was applied to both sides at a temperature of 3.5 and lOy/2, respectively.
It was plated so that it would adhere to tn. After that, H
, lO4, N2 Q plate temperature 650'C in 90% reducing atmosphere
(Heating was performed for 1 to 30 seconds to perform Zn diffusion. This sample was further treated with a tlLfIl of 30 A/dm' using a healthy acid bath.

At a bath temperature of 50'C and a bath temperature of 50'C, the Zn--Ni alloy was coated with a coating weight of 20y/cm on one side.

The following tests were carried out on the surface-treated steel sheet of the present invention, the conventional//) Zn--Ni alloy plated steel sheet, and the cold-rolled steel sheet obtained by this method. The results are shown in Table 2.

Corrosion resistance salt spray test of uncoated Q (JIS Z 2371) Number of days (2) Corrosion resistance salt spray test after layered coating (1 (lItm) cross cut) Paint film blistering from part 41
! (intestine), 3) Corrosion resistance after 3-coat painting Salt spray test 3-coat painting after 90 days (eta-
+ Medium chain length + l: cIlisu) Paint film bulge from cross-cut area (m) (4) Adhesion salt water spray test after 3 coats! From the test results in Table 2, the surface-treated steel sheet according to the present invention has no peeling amount compared to the conventional one. It is clear that the corrosion resistance of the paint, the corrosion resistance after painting, and the adhesion of the paint film are significantly improved.
The steel plate coated with an alloy plating layer shows excellent corrosion resistance, and the Zn-N4 plated steel plate shows excellent corrosion resistance. Giving 1. ! : Even with a steel plate having only a dark Zn diffusion layer, the electrodeposition coating is 1st; the corrosion resistance after 3 coats is extremely excellent. In particular, the corrosion resistance and coating properties after 3 coats are better than conventional Zn-Ni coatings. It can be seen that this is significantly superior to alloy plated and cold rolled steel sheets.

[Brief explanation of drawings]

Figures 1, 2.3 and 4 are sectional views C showing four embodiments of the surface-treated steel sheet according to the present invention. Explanation of symbols 1... Steel plate, 2... Metal diffusion layer, 3... Zn −
Ni Alloy Plating Layer Patent Applicant Kawasaki Steel Corporation Agent Nozomu Watanabe Nozomi Watanabe 1 Figure 3 ゝ Hot Mouse 2 Figure 2 ! jF, Figure 4, , 73 \ ″′2

Claims (1)

[Claims] Zn, Ni%Sn on at least one surface of the steel plate. Cr or one type of metal selected from alloys containing these metals as main components is applied with vapor plating, and heated in a non-oxidizing atmosphere to form a diffusion layer of the plating metal in the steel. A highly corrosion-resistant surface-treated steel sheet, characterized in that at least one surface of the treated steel sheet having a metal diffusion layer is plated with a KZn-Ni alloy.