JPS62112766A - Zinc alloy for zinc hot dip coating and method for using said alloy - Google Patents

Abstract

PURPOSE:To provide the titled zinc alloy forming a plating film which exhibits substantial corrosion resistance even under severe conditions and has high hardness to withstand the contact and impact during handling by incorporating a specific ratio of Mg therein an controlling the contents of inevitable impurities such as Pb, Cd, Fe or Sn etc., and comprising the alloy of the balance Zn. CONSTITUTION:The zinc alloy for zinc hot dip coating of this invention contains 0.03-0.8wt% Mg and 0.01wt% in total of inevitable impurities suchas Pb, Cd, Fe or Sn, etc. The Mg component in the zinc hot dip coating bath combines with Zn to solutionize as the intermetallic compd. in the form of MbZn2 or Mg2Zn3. The alloying reaction of Zn-Fe, therefore, progresses preferentially when steel products are immersed in said plating bath. A Zn-Ma alloy layer is formed on the Zn-Fe alloy layer on the steel products pulled up from the bath. The alloy layer is harder than the plating film of the steel plated with Zn alone and decreases the damages on the plating film in the stage of the above-mentioned contact and impact. The plating on the iron and steel products at 440-480 deg.C bath temp. is possible when the Zn alloy of this invention is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zinc alloy for hot-dip galvanizing used to produce hot-dip galvanized steel for membrane structures and a method for using the same.

Conventional Dan Keketsu! Hot-dip galvanized steel is used as a corrosion-resistant material for various structures and facilities in a wide range of fields such as architecture, civil engineering, electric power, transportation, agriculture, and fisheries. However, when the hot-dip galvanized steel is used as mentioned above, the plating film of the galvanized steel often becomes bl(1!i) due to contact and impact during handling such as transportation, construction, and storage. There is a need to provide hot-dip galvanized steel with very high hardness.

In addition, hot-dip galvanized steel, which is used as a material for structures and facilities in harsh environments such as industrial areas, ocean areas, and areas affected by springs, has a 172% - Since the life span is on the order of ~173 - high corrosion resistance is required.

Incidentally, conventionally, as a countermeasure against H4 scratches on the plating film that occur when handling hot-dip galvanized steel, if the damage is at the level of abrasion, it should be used as is, and if the plating layer has peeled off, it should be re-plated or treated with zinc powder. Currently, measures such as applying a so-called zinc-rich paint containing a high concentration and replacing the plated steel with new plated steel in some cases are taken depending on the degree of damage mentioned above and the requirements of the user's inspection standards. be.

Therefore, the only way to prevent damage when handling hot-dip galvanized steel is to rely on the operator's caution, and this point is considered to be a disadvantage in terms of the properties of the above-mentioned galvanized steel.

The lifespan of hot-dip galvanized steel is proportional to the amount of plating deposited, and in order to extend the life span, it is necessary to increase the amount of plating deposited, which increases the weight of the galvanized steel. The relationship between weight reduction at the design stage of steel towers, bridges, etc. and lifetime guarantees has become an issue.

■I'm trying to do it. The present invention was developed in view of the above-mentioned problems found in conventional hot-dip galvanized steel, and it exhibits sufficient corrosion resistance even under the above-mentioned harsh environments, and is resistant to contact and impact during handling. The object of the present invention is to provide a zinc alloy for hot-dip galvanizing that forms a plating film with high durability and hardness, and a method for using the same.

The present invention will be explained in detail below.

The characteristics of the light plate raw bottom of the present invention are as follows: Mg 0.03-0.8%, pb
A zinc alloy for hot-dip galvanizing in which the total amount of unavoidable impurities such as Cd, Fe or Sn is less than 0.01% by weight, and the balance is Zn, and the zinc alloy is used at a bath temperature of 440°C to 480°C. The purpose is to plate steel materials. It should be noted that the plating of the steel material herein refers to hot-dip galvanizing, also called gutter immersion plating, which is performed in the atmosphere, and refers to hot-dip galvanizing particularly intended for large steel materials.

The zinc alloy for hot-dip galvanizing according to the present invention has Mg of 0.0
It is important to contain Mg in an amount of 3 to 0.8% by weight, and Mg has the following functions when galvanizing steel.

The Mg component in the hot-dip galvanizing bath combines with Zn to form MgZ
Zn − is dissolved as a solid solution in the form of a gold intermetallic compound in the form of n2 or MgλZn3, so when a steel material is immersed in the plating bath, Zn −
The alloying reaction of Fe proceeds preferentially, and a Zn-Mg alloy layer is formed on the Zn-Fe alloy layer when the steel material is pulled up from the bath. In addition, the Zn-Mg alloy layer that forms the surface layer of the plated layer is harder than the plated film of Zn-only plated steel, which is a great advantage for plated steel fertilizers! ll, reduces the tf'i (g) of the plating film due to contact and impact caused during handling such as construction and storage. Also, in the surface layer of the plating layer, Mg becomes an oxide and protects the protective film of the plating layer. Since it forms, it also has the effect of improving the corrosion resistance of plated steel.

The Mg content in the zinc alloy for hot-dip galvanizing is 0.
It is necessary that the amount is 03 to 0.8fftff1%, and if the amount is more than o, sl amount%, a large amount of oxides will be generated on the plating bath, and the plating wettability with the plated steel material will decrease. On the other hand, if it is less than 0.03% by weight, the formation of l'1g oxide on the surface layer of the plating layer will be premature, making it impossible to obtain the above-mentioned corrosion-resistant effect.

Furthermore, the zinc alloy for hot-dip galvanizing according to the present invention has Pb
The total content of impurities such as , Cd, Fe or Sn is less than 0.01% by weight, but these total impurities are Z
It is unavoidably contained in trace amounts in n. therefore,
The total amount of the above impurities in the zinc alloy for hot dip galvanizing is reduced to 0.
．． In order to make the amount of Tfi less than 0.01% by weight, it is preferable to use zinc whose total amount of impurities is less than 0.01% by weight. Such zinc has a zinc purity higher than special zinc in the zinc ingot specified by JI32107, and the impurity content contained in the zinc ingot is, for example, PbO,01
CdO,0010% by weight or less.

Next, a method of plating a steel material using the zinc alloy for hot-dip galvanizing of the present invention will be described.

In order to carry out the plating method according to the present invention, the above-mentioned zinc alloy is melted in a plating bath using a conventional method, and the steel material that has been pretreated by degreasing, hot water washing, etc. is immersed in the melt. The composition of the plating bath is hg 0.03-0.8 m
A zinc alloy bath containing less than 0.01% by weight of unavoidable impurities derived from zinc base metal such as fJ%, Pb, Cd, and Sn, and 03 to 0.1% by weight of FeO, which is eluted from steel materials and the plating bath pot. becomes.

The bath temperature of the plating bath during the above plating is 440℃~4
It is necessary to adjust the temperature within the range of 80°C; if the bath temperature is lower than 440°C, the viscosity of the plating bath will increase and the thickness of the plating formed will be uneven, while if it is higher than 480°C, the plating will become uneven. This is not preferable since the amount of oxides produced on the bath surface increases, causing problems such as a decrease in plating wettability with plated steel materials and a decrease in yield.

Note that the immersion time of the steel material in the plating bath and the rate of pulling the plated steel material out of the plating bath may be appropriately selected in consideration of the steel type, the thickness and shape of the Sr1 material, etc.

According to the present invention, the Zn-Mg alloy plated steel obtained by plating the steel material by dipping it in the plating bath and pulling it up using the zinc alloy for hot-dip galvanizing as described above is different from the conventional hot-dip galvanized steel. It has the following advantages compared to

The hardness of the plating film is approximately doubled, so there is no need to worry about any contact that may occur during transportation, installation, or storage of the product.
Damage to the plating film due to impact can be prevented or significantly reduced.

(b) Since the corrosion resistance of plated steel is improved approximately three times, the service life can be significantly extended in harsh environments such as industrial areas, marine areas, and visitor areas without increasing the amount of coating.

Therefore, according to the present invention, problems such as damage to the plating film that occurs during handling and shortened life under harsh conditions, which have been considered disadvantages of hot-dip galvanized steel that has been used in a wide range of fields, can be solved. Since the problem can be effectively solved, it can be said that it is extremely beneficial for the use of the plated steel.

The above-mentioned effects of the present invention will be specifically explained below with reference to Examples.

Example board middle 50mm x board length 100mm X board J! J3.2m
An SS 41 Sl plate with dimensions of m was immersed in an alkaline bath at a temperature of 80°C for 30 minutes to degrease it, then washed with hot water, and then immersed in a 10% solution of hydrochloric acid (at room temperature) for 30 minutes to remove rust. After removing and washing with hot water, add 1 to ZnCl2-NkC+ solution (80℃).
Flux treatment was performed by immersing it for a minute.

Each i! that has been preprocessed as described above. The il slope was immersed in each of the plating baths shown in the table below at a bath temperature of 460° C. for 1 minute, and then pulled out of the plating bath at a rate of 1 m/mm. After being pulled up from the plating bath, it was cooled with warm water (60°C).

For each of the plated steel sheets obtained as described above, the plating film hardness and corrosion loss after 240 hours of SST (salt spray test) were measured.

The results are shown in the table below.

As seen in the above table, according to the present invention, the hardness and corrosion resistance of the plating film are significantly improved compared to the conventional method.

Claims (2)

[Claims] (1) Mg0.03-0.8% by weight, Pb, Cd, Fe
Or a zinc alloy for hot-dip galvanizing, which has a total amount of unavoidable impurities such as Sn of less than 0.01% by weight, and the balance is Zn, and has excellent corrosion resistance and the ability to form a plating film with high hardness. (2) Mg0.03-0.8% by weight, Pb, Cd, Fe
Alternatively, a method of plating a steel material at a bath temperature of 440° C. to 480° C. using a zinc alloy for hot-dip galvanizing in which the total amount of unavoidable impurities such as Sn is less than 0.01% by weight, and the balance is Zn.