JPH0368747A - Alloying hot dip galvanized steel sheet - Google Patents

Abstract

PURPOSE:To produce an alloying hot dip galvanized steel sheet excellent in corrosion resistance by incorporating specific amounts of Al and Mg or further Cu and/or Co into a plating layer at the time of applying alloying hot dip galvanizing to the surface of a steel sheet. CONSTITUTION:At the time of producing an alloying hot dip galvanized steel sheet used for automobile body, building material, household electrical appliance, etc., hot dipping is carried out by passing a steel sheet through a hot dip galvanizing bath, as a hot dipping bath, containing prescribed amounts of Al, Mg, and Cu and/or Co. Subsequently, heating is applied to the resulting plated steel sheet, e.g. up to 500 deg.C to subject Fe in the steel sheet and Zn in the plating bath to mutual diffusion, by which an alloying hot dip galvanizing layer which has a composition containing, by weight, 7-20% Fe and also containing, in the case where the total content of Zn, Al, Mg, Cu, and Co, excluding Fe, is 100%, 0.1-2% Al, 0.2-2% Mg, 0.1-1% Cu and/or Co is formed. By this method, the alloying hot dip galvanized steel sheet having extremely superior corrosion resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface-treated steel sheet with excellent corrosion resistance, and more specifically, it relates to a surface-treated steel sheet with excellent corrosion resistance. #Relating to an alloyed hot-dip galvanized steel sheet suitable as a steel sheet.

(Prior Art) The rate of use of surface-treated steel sheets is increasing year by year in fields such as automobiles, building materials, and home appliances.

However, in recent years, the environment in which they are used in these fields has become increasingly harsh, and there has been a demand for further improvements in their antirust properties. In particular, there is a strong demand for improved rust prevention in surface-treated steel sheets for automobiles. For example, recently, surface-treated steel sheets for car bodies are required to have a 10-year guarantee against nail holes. This is because in cold regions such as North America, snow-melting salt is sprayed to prevent roads from freezing in the winter, and this causes pitting and corrosion of vehicle bodies, which is a problem.

Here, "porosity" refers to corrosion of a steel plate that progresses from a defective part of the coating, a defective or damaged part of the plating, or an insufficiently coated area, causing pitting corrosion in the steel plate, and in some cases, penetrating corrosion. A phenomenon that occurs.

Conventionally, Ni-Zn electroalloy plated steel sheets, Fe-Z
n Surface-treated steel sheets such as electro-alloy plated steel sheets or electro-galvanized steel sheets are used as anti-rust steel sheets for automobiles, but such anti-rust! # Steel plates are said to have insufficient rust prevention power to meet the 10-year guarantee for perforation resistance. These electroplated steel sheets generally have a coating weight of 20 to 30 g/
+ m" is often used, but in order to meet the requirements for a 10-year guarantee on perforation resistance, it is said that more than twice that amount of adhesion is required. However, in the case of electroplated steel sheets, the amount of adhesion is As the manufacturing cost increases significantly with the increase in quantity,
Its application is difficult from a cost standpoint.

On the other hand, hot-dip galvanized steel sheets are also used as antirust steel sheets for automobiles. In the case of this hot-dip galvanized steel sheet, from the viewpoint of weldability, the proportion of hot-dip galvanized steel sheets used as is is small, but alloyed hot-dip galvanized steel sheets that have been subjected to alloying treatment, such as alloyed steel sheets with a coating weight of about 45 g/m'' Hot-dip galvanized steel sheets have been widely used for a long time.In the case of alloyed hot-dip galvanized steel sheets, the cost increase due to an increase in coating weight is relatively small compared to electroplated steel sheets. There is also a movement to address the 10-year warranty on puncture resistance by increasing it to 60 g/m''.

However, alloyed hot-dip galvanized steel sheets have traditionally been considered to be a material with relatively many difficulties in press forming, and in fact,
There is a problem during molding, especially flaking and powdering, where the plating film peels off from the steel plate. This peeling of the plating film becomes more noticeable as the plating thickness increases.

Furthermore, an increase in the plating film thickness also reduces spot weldability.

On the other hand, as a method for improving the corrosion resistance of anticorrosive steel sheets for automobiles, there is also a method of further applying a chromate film and a thin resin film on the zinc or zinc alloy plating film to obtain an organic composite coated steel sheet.

In the case of this organic composite coated steel sheet, the plated steel sheet as the base material has a coating weight of 20 to 20%, which is generally said to have good corrosion resistance.
30g/m" Ni-Zn1i alloy plated steel sheets are often used and exhibit good performance overall. However, although the underlying Ni-Zn plating layer has excellent corrosion resistance, it has poor sacrificial corrosion protection. Therefore, the corrosion resistance at the end face is poor.This drawback can be improved by increasing the coating amount, but the cost will increase.Also, in order to improve the corrosion resistance at the end face, sacrificial coating is applied to the base metal plated steel sheet. It is conceivable to use alloyed hot-dip galvanized steel sheets, which have anti-corrosion properties and are relatively inexpensive, but it is also possible to use an alloyed hot-dip galvanized steel sheet, which has anti-corrosion properties and is relatively inexpensive. The reality is that corrosion resistance cannot be obtained.

In this way, increasing the thickness of the plating layer and using organic composite coated steel sheets are effective to some extent in improving corrosion resistance, but these measures are sufficiently satisfactory from a comprehensive standpoint, including sacrificial corrosion protection ability of the end face, formability, etc. It's hard to say.

(Intelligence B to be Solved by the Invention) The object of the present invention is to solve the above-mentioned problems in thickening the plating film and producing organic composite coated steel sheets, and to provide a surface treatment with high corrosion resistance and excellent economic efficiency. Our goal is to provide steel plates.

(Means for solving the problem) The above-mentioned alloyed hot-dip galvanized steel sheet is inexpensive and has sacrificial anticorrosion ability, so even if it is made into an organic composite coated steel sheet using this as a base material, the corrosion resistance of the end face can be ensured. I can do it.

However, it is inferior in corrosion resistance when compared to an organic composite coated steel sheet whose base material is a Ni-Zn electroalloy plated steel sheet. However,
The present inventors have discovered that corrosion resistance can be improved by improving the coating composition of this alloyed hot-dip galvanized steel sheet.

That is, the present inventors added Mg to the film and further added Cu.
We have found that when one or more types of Co or Co are added, corrosion resistance is significantly improved due to their synergistic effect, and that when this alloyed hot-dip galvanized steel sheet is used as a base material and an organic composite coated steel sheet is made, corrosion resistance is further improved. It is.

Here, the gist of the present invention is ``a plated steel sheet that has been subjected to an alloying treatment after hot-dipping, wherein Fe in the coating of the plated steel sheet is 7 to 20% by weight, and the composition of other components other than this Fe is as follows. An alloyed hot-dip galvanized steel sheet characterized by the following:

A? 0.1-2% by weight One or more of Cu and Co: 0.1-1% by weight Mg: 0.2
~2% by weight, Zn and unavoidable impurities: remainder However, the total of Al5Cu, Co, Mg, Zn and impurities is ioo%.

The above-mentioned alloyed hot-dip galvanized steel sheet of the present invention can be manufactured, for example, by the following method.

■A steel plate that has been subjected to normal pretreatment, such as oxidation/reduction pretreatment by the Sendzimer method, is prepared with Af:Q, Q3~2% by weight, Mg
: 0.2 to 2% by weight, 0.1% of one or more of Cu or CO
After immersion plating in a zinc plating bath containing ~1% by weight and adjusting the coating amount to a predetermined amount, alloying treatment is performed at a temperature of 300 to 700°C to reduce the Fe content in the film to 7 to 20% by weight.
How to do it.

■Cu and Co can be precipitated by electroplating, so after pre-plating a steel plate that has been pretreated with one or more of Cu or Co to a predetermined content, 0.08 ~2wt% Al and 0.2~2wt? Immersion plating in a galvanizing bath containing Ig,
Next, after adjusting the amount of adhesion in the same manner as described above, an alloying treatment is performed.

This method (2) is effective when using a galvanizing bath with a high Al concentration. When the Affi concentration in the bath becomes high, alloying tends to become uneven and the surface of the film after alloying becomes rough. However, by pre-plating Cu and Co on the steel sheet before hot-dipping, It is possible to suppress local semi-uniform formation of and form a uniform alloyed plating film.

In addition, polishing the steel plate surface with an abrasive-containing nylon brush after annealing before plating can also prevent the surface of the alloyed film from becoming rough, so use a galvanizing bath with a high degree of A. It is effective in some cases.

In addition, since Al tends to shrink slightly in the film,
Even if the A14 degree in the plating bath is 0.08 to 2% by weight, the Al content in the film will be 0.1 to 2% by weight.

Hereinafter, the reason for specifying the coating composition as described above for the alloyed hot-dip galvanized steel sheet of the present invention will be explained in detail.

In addition, "%" of the component is "weight percentage J" with respect to the entire film for Fe, and for Al, Cu, Co, Mg
For Zn and Zn, the film excluding Fe is 1
It is "weight percentage" when it is set as 00.

Fe: 1 to 20% by weight Fe in the film is Fe that flows into the film due to mutual diffusion between the base material and the film during alloying treatment. If the Fe content in the film is less than 7% by weight, the weldability and corrosion resistance will be poor, especially the corrosion resistance after painting. On the other hand, if the content exceeds 20% by weight, the anticorrosion properties of the notches or edges after painting will be significantly deteriorated.

AR: 0.1-2% by weight Al contributes to improving the toughness and corrosion resistance of the alloy layer (plating layer).However, if it is less than 0.1% by weight, these effects are poor, and due to coexistence with ig. The oxidation of the plating bath surface becomes significant. For example, even if plating is carried out in an atmosphere with a concentration of 0! or less than 50 pp-, oxidation cannot be sufficiently suppressed. In order to suppress
Since e and ^Lx tend to remain and form local batteries, reducing corrosion resistance, the upper limit is set to 2% by weight.

Mg: 0.2 to 2% by weight Mg has the effect of increasing corrosion resistance, but 0.2% by weight
If it is less than 2% by weight, the effect will be poor, and if it exceeds 2% by weight, the reaction between M and O (oxygen) will be intense, so 0°2 to 2% by weight.
If 0Mg exceeds 2% by weight, if more than 2% by weight is added, Mg,! :The abnormal reaction of O can be suppressed and normal plating bath characteristics can be ensured, but as mentioned above, if Al exceeds 2% by weight, the alloying reaction is suppressed.

Cu and Coa 1 or 2 types total 0.1 to 1% by weight
Cu and Co are unique elements that have a synergistic effect with Mg. Cu and Go themselves rather reduce corrosion resistance, or have almost no effect on corrosion resistance, but
When added in combination with Mg, it has the effect of further enhancing the corrosion resistance improvement effect of Mg. However, if Cu and Co are less than 0.1% by weight in total of type I or 2 types, the above effect will be poor; on the other hand, if the content of Cu and Co exceeds 1% by weight in total of 1 type or 2 types, Mg will be 2% by weight or less. In the range of , these synergistic effects not only reach saturation but also have a negative impact on corrosion resistance.

Note that the remainder is Zn and unavoidable impurities.

The alloyed hot-dip galvanized steel sheet of the present invention has an alloyed coating composed of the components described above.

This alloyed hot-dip galvanized steel sheet has excellent corrosion resistance as it is, but this film is further coated with a coating type chromate with a Cr content of 20 to 100 mg/l, and then acrylic or polyester is coated on top of this coating. Corrosion resistance is further improved by coating an organic composite coated steel sheet with 0.5 to 3 .mu.m of ether resin or the like.

Next, the present invention will be further explained with reference to Examples.

(Example 1) In weight%, C: 0.03%, Si: 0.01%,
'Mn: 0.21%, P: 0.01%, S: 0.01%
, Sol, ^j! : 0.021%, Ti: 0.
048%, including Nb: 0.010%, plate thickness: 0,
8■- extremely low C-I F tIi (Interstit
Using full hard material (unannealed material) of ial free steel, a test material of 100 cm width x 250 m + length was cut out from it, washed with an organic solvent, and further treated with NaxCOs.
+ After electrolytic cleaning in a Na0II solution, using a hot-dip plating simulator capable of hot-dip plating from a reducing atmosphere, heat reduction was performed under conditions of holding the temperature at 850° C. for 45 seconds, followed by hot-dip plating. After hot-dip plating, the coating weight was adjusted to 60 g/+w'', and alloying treatment was performed at a heating temperature of 500'C.

The sample materials subjected to alloying treatment were subjected to a salt spray test according to JIS Z 2867, and the time required for red rust to occur to reach 5% of the total surface area of the sample materials was determined. The results are shown in Table 1 along with the film composition after alloying.

(Hereinafter, blank spaces) As is clear from Table 1, the alloyed hot-dip galvanized steel sheets of the present invention are all superior in corrosion resistance compared to the alloyed hot-dip galvanized steel sheets of the comparative examples.

(Example 2) The same test material as in Example 1 was hot-dipped and alloyed in the same manner.

The sample materials after the alloying treatment were cleaned with Fine Cleaner 4336 (manufactured by Nippon Barcalizing Co., Ltd.), and then chromated and painted as described below.

[Chromate]

CrOx120g/j! The solution was reduced with ethylene glycol and Cr (h40g/j2 was added to the diluted chromate solution (Cr"/Cr"-273), which was mixed with colloidal silica 40g/l, glycerin 11.5g/l, citric acid 6.5g/IL, A suspension containing 15 g/l of T-glycidoxybrobyltrimethoxysilane was applied using a bar coater (the amount of Cr deposited was 60°C as total Cr).
1 g/l) and then baked at a temperature of 140'C for 30 seconds to form a chromate film.

〔Painting〕

Solid resin content: powdered polyhydroxy polyether resin (P manufactured by Union Carbide Co., Ltd.) was applied on the chromate film.
KHH) 20% by weight, inorganic filler: 5% by weight of colloidal silicate, medium: pure lohexane + cellosolve acetate (
A resin liquid consisting of a ratio of 1:IVoj2) was applied using a bar coater, and then baked at a temperature of 130°C. The finished coating thickness is 1.2 μm.

The organic composite coated steel sheet thus obtained was subjected to a tube drawing process with a punch bottom diameter of 50IIal as a flat plate, and then subjected to a salt spray test (5% NaCl, 35℃, 4 hours) → hot air drying (60℃ 'C2 hours) → Humidity (relative temperature 50
℃.

A drying test was conducted for 2,000 cycles in which one cycle was a 95% or more humid atmosphere for 4 hours, and the area ratio where red rust occurred was investigated. The results are shown in Table 2 along with the skin wA composition and adhesion amount after alloying.

(Hereafter, blank space) From Table 2, the alloyed hot-dip galvanized steel sheets of the present invention coated with organic composites (N117 to Nα13> are N.

It has excellent corrosion resistance similar to that of the Ni-Zn1i galvanized steel sheet shown in No. 15, which is coated with an organic composite. On the other hand, alloyed hot-dip galvanized steel sheets (kl to NcL6) and electrogalvanized steel sheets (
Organic composites of N1114) have poor corrosion resistance.

(Example 3) Hot-dip plating was performed in the same manner as in Example 1, and the coating amount was 4.
After adjusting to 3 to 65 g/s+'', alloying treatment was performed at a temperature of 500°C.

The sample material after the alloying treatment was subjected to a salt spray test according to JIS Z 2867, and the time required for red rust to occur to reach 5% of the total surface area of the sample material was determined. Furthermore, a cylindrical drawing test was conducted using a blank diameter of 9051 m and a punch diameter of 50 mm, and the powdering weight was measured from the weight difference before and after forming by forcibly taping after forming.

These results are shown in Table 3.

As is clear from Table 3, the examples of the present invention have excellent corrosion resistance and good powdering resistance even though the coating weight is as thin as approximately 40 to 45 g/+*''.

(Effects of the Invention) As explained above, the alloyed hot-dip galvanized steel sheet of the present invention has extremely good corrosion resistance. Therefore, this alloyed hot-dip galvanized steel sheet can withstand use even in severe corrosive environments as it is, but also If it is coated with an organic composite coating, corrosion resistance will be further improved.

Note that the alloyed hot-dip galvanized tR plate of the present invention is further coated with Fe.
system plating, for example, containing 10% by weight of zinc and the remainder being Fe.
Electrodeposition coating properties can be improved by applying Fe-based plating consisting of 3 to 5 g/2 of basis weight.

Claims (1)

[Claims] A plated steel sheet subjected to an alloying treatment after hot-dipping,
An alloyed hot-dip galvanized steel sheet characterized in that the Fe content in the coating of the galvanized steel sheet is 7 to 20% by weight, and the composition of other components other than Fe is as follows. Al: 0.1-2% by weight One or more of Cu and Co: 0.1-1% by weight Mg: 0.2-2% by weight, Zn and inevitable impurities: remainder