JPH03281765A - Production of zn-al alloy-plated steel wire excellent in corrosion resistance and fatigue resistance - Google Patents

Abstract

PURPOSE:To obtain the steel wire by specifying the thickness of an alloy layer after secondary plating in a method for applying hot-dip galvanizing as primary plating to a steel wire and subjecting this steel wire to immersion into an Al-containing Zn alloy bath as secondary plating. CONSTITUTION:A steel wire is subjected to primary plating and then to immersion, as secondary plating, into a bath of a Zn alloy containing 2-12% Al, by which a Zn-Al alloy-plated steel wire is obtained. In this method, the thickness of the alloy layer on the steel wire after secondary plating is regulated to 0.5-7mu. Although corrosion resistance can be improved by exerting hot-dip galvanizing as primary plating, a new alloy layer formed at this time contains a hard intermetallic compound and is hard and has strong preferential orientation in its growing direction. As a result, in the case where the origin of fatigue failure is formed in the new alloy layer, this failure is easily propagated and forms a crack having a size corresponding to the thickness of the alloy layer. Accordingly, it is desirable to minimize the thickness of the new alloy layer so long as it does not hinder corrosion resistance, and, by specifying the thickness as mentioned above, fatigue strength equal to that of conventional galvanized steel wire can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a Zn--Al alloy plated steel wire. The present invention relates to a method for manufacturing high-strength alloy-plated steel wire used for manufacturing ropes, steel stranded wires, cables for cable-stayed bridges, springs, etc.

[Conventional technology]

Many Zn-based alloy plating techniques have been developed for the purpose of improving the corrosion resistance of steel materials. For example, in Japanese Patent Publication No. 55-2G102, Z n-A I
, ZnA 1-Mg in Japanese Patent Publication No. 54-33223
, ZnAn-Minyu Metal in Japanese Patent Publication No. 24211, Zn-
Al2-Na etc. have been announced.

Alloy plating of steel sheets is performed by pre-treating the steel sheet using the oxidation-reduction method and then continuously immersing it in an alloy plating bath to deposit an alloy plating layer on the surface of the steel sheet with the same composition as the bath. ing. On the other hand, alloy plating of steel wire is generally carried out by ordinary hot-dip galvanizing or electrogalvanizing as the primary plating, and then continuously immersing the galvanized steel wire in the desired alloy bath. It is performed using the bath method.

[Problem to be solved by the invention]

Zn-Al alloy plated steel wire exhibits excellent corrosion resistance, but
Tensile strength 100kgf/wam2 made of high carbon steel
In the case of the above-mentioned high-strength steel wires, one drawback was that their fatigue strength was lower than that of ordinary galvanized steel wires.

In this regard, the present inventors have already conducted a lot of research, and
Patent Application No. 01-81262 and Patent Application No. 93037
The application has been filed as No. The former is 300 ~ after secondary plating
It is characterized by controlling the cooling rate in the range of 150°C to a range of 15 to 4°C/sec, thereby preventing cracking of the plating layer and improving fatigue properties. In the latter case, during the cooling process after secondary plating, the eutectoid transformation is completed while the steel wire temperature is high and the alloy has sufficient plastic deformability, and the shrinkage strain accompanying the eutectoid transformation is absorbed. This method aims to reduce tensile residual stress, and specifically, it is a method in which the steel wire after secondary plating is held in a temperature range of 250 to 100° C. for a predetermined period of time.

However, even with the above-described method, satisfactory fatigue characteristics may not always be obtained if the cooling conditions vary. Stable and high fatigue strength is particularly advantageous when the secondary plating is hot-dip galvanizing, when the steel wire is thin, or when the wire passing speed is increased to perform thick plating.

An object of the present invention is to solve the above-mentioned problems of the conventional method and to provide a method for producing a Zn-Al alloy plated steel wire having good corrosion resistance and stable high fatigue strength.

[Means to solve the problem]

In the present invention, after hot-dip galvanizing is applied to a steel wire as a primary plating, the steel wire is immersed in an alloy bath containing 2 to 12% Al as a secondary plating, with the remainder being essentially Zn. - A method for producing an Al alloy plated steel wire, characterized in that the thickness of the alloy layer of the steel wire after secondary plating is 0.5 μm or more and 7 μm or less. Zn with excellent corrosion resistance and fatigue resistance. This is a method for manufacturing an Al alloy plated steel wire.

[For production]

Hereinafter, the present invention will be explained in detail along with its operation.

According to the research conducted by the present inventors, in the production of ZnA6 alloy coated steel wire by the two-bath method, it is advantageous to use hot-dip galvanizing as the secondary plating to improve corrosion resistance. This is the inventor's "Tetsu to Hagane No. 75 No. 2" (Japan Iron and Steel Association)
As reported on page 298 (published on February 1, 1999) and disclosed in Japanese Patent Application Laid-open No. 134653/1983, Zn-Al! When a hot-dip galvanized steel wire is immersed in an alloy bath, the Al in the bath diffuses into the Zn-Fe alloy layer (for example, ζ phase or δ phase) of the hot-dip galvanized steel wire at high speed. Zn-Fe-Al new alloy layer containing % (
This is because an intermetallic compound layer) is formed, and the progress of corrosion is suppressed by the electrochemical action between the surface layer (the part with the same composition as the alloy bath) and the new alloy layer.

However, the above new alloy layer is made of F, which is a hard intermetallic compound.
e4-Al1. Because it is hard and has a strong preferred orientation in the growth direction, if a starting point of fatigue fracture is formed in the new alloy layer, the fracture will easily propagate and expand, creating a crack with a size equivalent to the thickness of the alloy layer. Form. Therefore, when fatigue resistance is required for alloy-plated steel wire,
The thinner the new alloy layer is, the better, as long as corrosion resistance is not affected.

As a result of many experiments, the inventors of the present invention have found that by suppressing the thickness of the new alloy layer to 7 μm or less, fatigue strength equivalent to that of conventional galvanized steel wire can be obtained. On the other hand, if the thickness is less than 0.5 μm, corrosion resistance decreases and red rust is likely to occur, so the lower limit is set to 0.5 μm.

-Al24 degree of the alloy plating bath is set to 2 to 12%.

If it is less than 2%, it takes a long time for -Al to diffuse and permeate, making it difficult to form a new alloy layer, making it impossible to achieve the desired corrosion resistance. An increase in Af concentration improves corrosion resistance, but on the other hand, it causes a decrease in steel wire strength due to an increase in plating temperature, so the upper limit is set at 12%.

Although the above description has been made regarding Zn-A based alloys, the present invention is not limited to this, and may be applied to cases where various alloys based on Zn to Al as shown in the above-mentioned prior art are used. can also exhibit similar effects.

〔Example〕

A method for producing a Zn-Al alloy plated steel wire to which the present invention is applied will be described below. The target m-line characteristics are a tensile strength of 150kg f/ffIm' or more, and a fatigue strength of 5.
0 kgf/mm2 or more, the corrosion resistance is more than three times that of ordinary hot-dip galvanized steel wire.

, diameter 2.3mm from IIS standard 5WRH72A wire
A steel wire was manufactured, and after degreasing and pickling, it was hot-dip galvanized as a secondary plating. −The steel wire after the next plating is Zn−
It was immersed in an An alloy bath and pulled up vertically.

The thickness of the new alloy layer was adjusted by controlling the ZnFe alloy layer thickness in the second plating, that is, by changing the bath temperature and immersion time. After alloy plating, all samples were slowly cooled by the method described in Japanese Patent Application No. 1-81262 to improve fatigue properties.

A Nakamura rotary bending fatigue tester was used for the fatigue test.
The stress that did not cause rupture after 7 repetitions was defined as fatigue strength.

Corrosion resistance was evaluated using salt spray test (JISZ 2371)
The red rust generation time was compared with that of hot-dip galvanized steel wire. The results were quantified as a corrosion resistance magnification defined by the following equation (1).

Occurrence time (br) Table 1 shows the manufacturing strip ('l) and steel wire characteristics of alloy-plated steel wire.

Nos. 1 to 5 show the relationship between the Al concentration of the plating bath and the characteristics of the alloy-plated steel wire. If the Al concentration is less than 2%, the target tactility will not be achieved. On the other hand, as the Ale temperature increases by 4 degrees, the corrosion resistance improves, but it is necessary to increase the plating temperature. As a result, the tensile strength of the steel wire decreases, and A
In No. 5 with a l concentration of 13.0%, the target tensile strength could not be obtained. From the above results, it is appropriate that the Al concentration of the alloy bath is 2 to 12%.

No. G to IO indicate that the thickness of the alloy layer does not affect the steel wire properties. For No. and G, the alloy layer thickness is 0.
Because it is thin at 3μ+11, its fatigue strength is at the same level as hot-dip galvanized steel wire, but di41'l! I! Gender is 1st; 1゛ (on°I: I can't add J.

No. 9 and No. 1O were manufactured by the following method;:'
L, in which case the thickness of the alloy layer is 8.0 and 1, respectively.
It is thick at 0.2 μm. All of these have good corrosion resistance, but the fatigue strength is less than the target of 50 kgf/+nm2. No. I1 has the lowest fatigue strength because it is almost the same method as the conventional method No. 9, or because slow cooling is not particularly performed after alloy plating. No. 12 is hot-dip galvanizing for comparison.As mentioned above, according to the method of the present invention,
It is possible to produce a ZnΔp alloy-plated steel wire that satisfies the targeted tensile strength and corrosion resistance and has a high fatigue strength that could not be achieved by conventional methods.

〔Effect of the invention〕

As explained above, according to the manufacturing method according to the present invention,
It is possible to produce high-strength Zn--Al alloy coated steel wire that not only exhibits excellent corrosion resistance and is three times heavier than ordinary hot-dip galvanized steel wire, but also has fatigue strength equivalent to that of galvanized steel wire. be.

Claims (1)

[Claims] After hot-dip galvanizing a steel wire as a primary plating, the steel wire is immersed in an alloy bath containing 2 to 12% Al, with the remainder essentially Zn, as a secondary plating.
- In a method for manufacturing an Al-based alloy plated steel wire, the thickness of the alloy layer of the steel wire after secondary plating is 0.5 μm or more and 7 μm.
A method for manufacturing a Zn-Al alloy plated steel wire having excellent corrosion resistance and fatigue resistance, which is characterized by the following steps.