EP3282033A1

EP3282033A1 - Zinc-aluminum-alloy-coated shaped steel wire with superior corrosion resistance and method for producing same

Info

Publication number: EP3282033A1
Application number: EP15887848.8A
Authority: EP
Inventors: Jae Up SONG; Jin Young Jung
Original assignee: Kiswire Ltd
Current assignee: Kiswire Ltd
Priority date: 2015-04-02
Filing date: 2015-05-18
Publication date: 2018-02-14
Also published as: CN107406956A; KR101632900B1; EP3282033A4; JP2018511704A; WO2016159438A1

Abstract

The present invention relates to a wire for wrapping which is wound spirally on the outer circumference of a main cable in which a plurality of metal wires are compactly arranged in parallel, wherein the wire for wrapping is a zinc-aluminum-alloy-coated shaped steel wire with superior corrosion resistance which has an S-shaped cross section coated with a zinc-aluminum alloy and has a thickness of coating layer of at least 20µm at any part of the outer circumference of the S-shaped cross section. A method of producing a zinc-aluminum-alloy-coated shaped steel wire according to the present invention comprises the steps of: primarily rolling a material wire rod; performing stress-relief heat treatment for the primarily rolled wire at a temperature of 300-500°C; coating the heat-treated primarily rolled wire with a zinc-aluminum alloy; and secondarily rolling the coated primarily rolled wire at a rolling quantity of 5-40% to obtain the shaped steel wire of the S-shaped cross section.

Description

Technical Field

The present invention relates to a wrapping wire which is spirally wound around an outer circumferential surface of a main cable of a suspension bridge and, more specifically, to a zinc-aluminum alloy-plated deformed steel wire with excellent corrosion resistance, wherein a stress relief heat treatment operation and a zinc-aluminum alloy plating operation are performed during a shape rolling process and then an extra shape rolling operation is performed, so that a plating layer with excellent corrosion resistance is finally formed to have a uniform thickness on all regions of the outer circumferential part of an "S"-shaped cross-sectional steel wire, and to a method for manufacturing the same.

Background Art

A main cable used in a suspension bridge is generally configured such that, while a plurality of metal wires are densely arranged in parallel with each other, a wrapping wire is wound tightly without gaps and spirally around an outer circumferential surface of the main cable, thereby preventing the penetration of water and the like into the main cable.
In cases where a circular-shaped cross-sectional wire is used as the wrapping wire for a wrapping wire, gaps are generated between contact portions of the wrapping wire due to a change in the load applied to the main cable and repetitive expansion and contraction caused by thermal expansion, whereby rainwater or the like permeates through the gaps or through cracks of a thick coating outside the wrapping wire, the cracks accompanying the gaps, causing a deterioration in anticorrosive performance.
Therefore, a deformed cross-sectional wire, deviating from a circular cross-sectional wire, has been used as a main cable wrapping wire of a suspension bridge. Representative deformed cross-sectional wires may be Z- and C-shaped cross-sectional wires.
Japanese Patent No. 2986288 discloses a Z-shaped wrapping wire. As shown in FIG. 1, when a Z-shaped cross-sectional wrapping wire 2 is spirally wound around an outer circumferential surface of a cylindrical metal wire bundle composed of a plurality of metal wires 1 densely arranged in parallel with each other, wrapping is conducted such that adjacent wrapping wire portions partially overlap each other, so that a surface and a bottom surface of the wrapping wire make flat surfaces in a completed state, thereby eliminating the generation of gaps between adjacent wrapping wire portions 2.
In addition, Korean Patent No. 10-1396764 discloses a C-shaped cross-sectional wrapping wire. As shown in FIG. 2, when C-type cross-sectional wrapping wires 2' are spirally wound around an outer circumferential surface of a cylindrical metal wire bundle composed of a plurality of metal wires 1', wrapping is conducted on the outer circumferential surface of the main cable such that curved surface portions of the wrapping wires 2', which have different pitches, are combined oppositely to interlock each other.
In general, the conventional Z-shaped or C-shaped cross-sectional wrapping wire is molded by rolling a circular cross-sectional wire rod to have a predetermined deformed cross section, and in a step prior to the molding into such a deformed cross section, zinc plating is carried out on a surface of a material steel wire in a way to give corrosion resistance.
However, in the process where a zinc-plated steel wire is molded to have a C-shaped or Z-shaped cross section, which corresponds to a complicated cross-sectional shape, the thickness of the plating layer formed on a surface of the wire is inevitably changed due to a difference in the load applied to respective cross-sectional regions and a difference in the amount of process in respective cross-sectional regions. In other words, even though a zinc-plated layer with a uniform thickness is formed on a surface of a material steel wire before rolling, there is a difference in the thickness of the plating layer due to a difference in the load applied and a difference in the amount of process in the process of rolling into a complicated shape. In some cases, the plating layer may become very thinned or partially peeled off at corner portions where processing is relatively focused.
As such, when the zinc plating layer becomes very thinned or peeled off, the corrosion resistance of the wrapping wire is degraded, and thus, the wrapping function with respect to the main cable cannot be property exerted.

Detailed Description of the Invention

Technical Problem

The present invention has been made in view of the above-mentioned problems of a conventional deformed cross-sectional wrapping wire, and an aspect of the present invention is to provide a zinc-aluminum alloy deformed steel wire, which is an S-shaped cross-sectional wrapping wire plated with a zinc-aluminum alloy having excellent corrosion resistance compared with existing zinc, wherein a zinc-aluminum plating layer with a sufficient thickness is provided on all regions of an outer circumferential part of the S-shaped cross-sectional wire without any region where the plating layer is especially thin, thereby exerting excellent corrosion resistance.
Another aspect of the present invention is to provide a method for manufacturing an S-shaped cross-sectional wrapping wire, wherein when a deformed cross-sectional wrapping wire is manufactured by rolling a material steel wire to mold the material steel wire to have an S-shaped cross section, stress relief heat treatment is performed and then a zinc-aluminum alloy plating layer is formed during the rolling process, and thereafter, an extra rolling operation is performed, so that a plating layer with a uniform thickness is formed on all regions of the outer circumferential surface of the S-shaped cross-sectional wrapping wire.

Technical Solution

In accordance with an aspect of the present invention, there is provided a zinc-aluminum plated deformed steel wire with excellent corrosion resistance, which is an S-shaped cross-sectional wrapping wire plated with a zinc-aluminum alloy, wherein the thickness of a zinc-aluminum plating layer is at least 20µm on all regions of an outer circumferential part of the S-shaped cross-sectional wire, and wherein the amount of zinc-aluminum plated is 250 g/m² or more.
FIG. 3 is a cross-sectional view of an S-shaped cross-sectional deformed steel wire of the present invention. As shown in the drawing, the deformed steel wire 10 having an overall S-shape has a zinc-aluminum plating layer 11 formed on an entire outer circumferential surface thereof. Here, the zinc-aluminum plating layer 11 may become very thinned or peeled off at corner regions (indicated by arrows in the drawing) of the deformed steel wire 10 where a large amount of processing is focused during a rolling process. However, the deformed steel wire 10 of the present invention shows a thickness of at least 20µm even at such corner regions.
A method for manufacturing a zinc-aluminum alloy plate deformed steel wire with excellent corrosion resistance of the present invention includes: drawing a wire rod to prepare a steel wire; performing primary rolling on the steel wire; performing heat treatment on a primarily rolled wire at 300-500°C; plating the heat-treated wire with a zinc-aluminum alloy; and performing secondary rolling on the plated wire at an amount of rolling of 5-40% to obtain an S-shaped cross-sectional wrapping wire.
The chemical composition of the deformed steel wire according to the present invention includes, by wt%, 0.06-0.15% of C, 0.15-0.25% of Si, 0.4-0.6% of Mn, 0.015% or less of S, 0.015% or less of P, and the balance Fe and inevitable impurities.
The wire rod having the above composition is drawn to prepare a steel wire, which is then supplied to a rolling apparatus to be subjected to primary shape rolling. The deformed rolled wire in an immediate state after the primary rolling has been ended is subjected to heat treatment using a heat treatment apparatus to relieve the stress generated inside the wire through the primary rolling process.
The temperature for such stress relief heat treatment is preferably 300-500°C. Therefore, if the temperature for heat treatment is below 300°C, aging hardening occurs in the internal structure due to primary rolling processing, thus reducing the ductility of the material wire, causing the generation of cracks during secondary rolling. If the temperature for heat treatment is above 500°C, the spheroidization of cementite occurs in the primarily rolled material wire, thereby causing wire softening, thus reducing tensile strength during secondary rolling.
Meanwhile, through the stress relief heat treatment in which the temperature for heat treatment is maintained at 300-500°C and the time for heat treatment is set to 30 seconds, wire linearity can be ensured, thereby improving the plating quality during zinc-aluminum plating as a subsequent process and securing necessary ductility while appropriate tensile strength is maintained during secondary rolling.
Then, a zinc-aluminum plating process is performed on the primarily rolled steel wire after the stress relief heat treatment has been completed. For the plating of the primarily rolled steel wire, the primarily rolled steel wire is first acid-pickled and pretreated (chlorine film formation after chlorination + drying), followed by molten zinc plating, and subsequently, the resultant wire is immersed in a molten zinc-aluminum composite plating bath, thereby finally performing zinc-aluminum plating.
Here, the plating amount with respect to the primarily rolled steel wire is preferably in the range of 400-430 g/m².
Upon completion of the zinc-aluminum alloy plating, secondary plating as a subsequent process is performed on the plated primarily rolled steel wire. Through such secondary rolling, a final S-shaped cross-sectional wrapping wire is obtained.
Here, the amount of rolling in the secondary rolling is preferably in the range of 5-40%. If the amount of rolling is below 5%, the cross-sectional shape or dimension of the final wire may not be secured, and if the amount of rolling is above 40%, the plating layer may become very thinned or peeled off at corner regions where rolling processing is relatively focused. Therefore, the amount of rolling needs to be maintained in the range of 5-40%.
In the final S-shaped cross-sectional wrapping wire obtained after the secondary rolling, the thickness of the zinc-aluminum alloy plating layer is at least 20µm at any region of the outer circumferential part of the S-shaped cross section and the amount of plated is 250 g/m² or more.

Advantageous Effects

The zinc-aluminum alloy plated deformed steel wire of the present invention, compared with an existing zinc-plated wrapping wire, can primarily improve corrosion resistance by carrying out the plating of the wrapping wire using a zinc-aluminum alloy with excellent corrosion resistance, and in addition, can secondarily improve corrosion resistance by maintaining a thickness of the zinc-aluminum plating layer of at least 20µm even at regions of the S-shaped cross-sectional steel wire, including corners, where rolling processing is relatively focused.
Furthermore, in the zinc-aluminum alloy plated deformed steel wire of the present invention, during the shape rolling process for a material wire, stress relieft heat treatment is performed and appropriate ductility is provided in a state in which tensile strength with a required range is maintained, so that a secondary rolling process as a subsequent finishing process can be smoothly performed without causing damage or deformation to the rolled steel wire or the rolling die, and the quality characteristics of the plating layer of the final product and the tensile strength of the wrapping wire can be secured.

Brief Description of the Drawings

FIG. 1 is a perspective view of a main cable employing a conventional Z-shaped wrapping wire.
FIG. 2 is a perspective view of a main cable employing a conventional C-shaped wrapping wire.
FIG. 3 is a cross-sectional view of an S-shaped deformed steel wire according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view of an S-shaped deformed steel wire sample.

Best Mode for Carrying Out the Invention

Specific manufacturing methods, including the foregoing technical objects and other features of the present invention, will be more apparently understood through the following examples.
First, a wire rod composed of, by wt%, 0.10% of C, 0.17% of Si, 0.5% of Mn, 0.00176% of P, 0.00086% of S, and the balance Fe and inevitable impurities was prepared.
The material rod was primarily drawn, and then subjected to primary rolling and high-frequency treatment. Then, the primarily rolled wire subjected to stress relief was acid-pickled and pretreated, followed by molten zinc plating, and subsequently, the resultant wire was immersed in a molten zinc-aluminum composite plating bath, thereby finally forming a zinc-aluminum plating layer. As such, the primarily rolled wire with a plating layer was subjected to secondary rolling to give a final S-shaped cross-sectional deformed steel wire.
In the manufacturing of a deformed steel wire through the above process, the amount of primary rolling, the temperature for stress relieft heat treatment, and the amount of secondary rolling were changed to evaluate the plating layer thickness and the behaviors of corrosion characteristics. The evaluation results are shown in Table 1 below.

Meanwhile, the plating layer thickness by region in the S-shaped deformed steel wire was measured. T1 to T4 shown in Table 1 below indicate respective T1 to T4 regions shown on the cross-sectional view of the S-shaped deformed steel wire sample in FIG. 4.

[Table 1] Evaluation results of plating characteristics according to amount of rolling and temperature for heat treatment

	Temperature for stress relief after primary rolling (°C)	Time for stress relief after primary rolling (s)	Amount of rolling after zinc plating (%)	Type of plating	Amount of plated (g/m²)	Plating thickness				Salt spray test (Hours)	Workability
	Temperature for stress relief after primary rolling (°C)	Time for stress relief after primary rolling (s)	Amount of rolling after zinc plating (%)	Type of plating	Amount of plated (g/m²)	T1	T2	T3	T4	Salt spray test (Hours)	Workability
Comparative Example 1	450	30	3	Zn-Al	420	58	56	58	61	1450	Dimension defect
Comparative Example 2	250	30	30	Zn-Al	330	42	43	28	45	1300	Rolling crack
Comparative Example 3	600	30	30	Zn-Al	310	45	42	32	39	1350	Strength resistance
Comparative Example 4	450	30	50	Zn-Al	240	29	31	15	28	700	Peeling off of edge plating layer
Conventional Example 1	450	30	30	Al	350	52	48	40	50	300	Corrosion resistance degradation
Example 1	450	30	5	Zn-Al	348	51	50	48	53	1460	Favorable
Example 2	450	30	10	Zn-Al	373	55	51	42	53	1430	Favorable
Example 3	450	30	20	Zn-Al	351	51	49	38	49	1450	Favorable
Example 4	300	30	30	Zn-Al	312	46	42	35	42	1320	Favorable
Example 5	450	30	30	Zn-Al	320	41	39	32	43	1290	Favorable
Example 6	500	30	30	Zn-Al	300	38	43	31	41	1320	Favorable
Example 7	450	30	30	Zn-Al	280	37	38	27	41	1280	Favorable
Example 8	450	30	40	Zn-Al	260	32	34	23	31	1150	Favorable

As shown in Table 1 above, when the temperature for stress relief after primary rolling was below 300°C, cracks occurred during secondary rolling, resulting in a deterioration in workability (Comparative Example 2), and when the temperature for stress relief was 600°C or above, tensile strength was lowered to a required level or less (Comparative Example 3).
In addition, an amount of secondary rolling of less than 5% made it difficult to match exact dimensions of the S-shaped cross-sectional shape (Comparative Example 1); and in a case of above 40% (45%) as in Comparative Example 4, the plating layer thickness at T3 region was 15µm or less, and the plating layer was peeled off at some corner regions, and the corrosion resistance were remarkably degraded (700 hours) in a salt spray test.
Meanwhile, in a sample of Conventional Example 1 in which the plating layer was formed of only existing zinc, rust was observed from the elapse of 300 hours in the salt spray test. Whereas, samples of Examples 1 to 8 showed a rusting time of 1300 hours or more, confirming excellent corrosion resistance.

Claims

A zinc-aluminum alloy plated deformed steel wire with excellent corrosion resistance, wherein a wrapping wire, which is spirally wound around an outer circumference of a main cable having a plurality of metal wires densely arranged in parallel with each other, has an S-shaped cross section and is plated with a zinc-aluminum alloy, and wherein the thickness of a plating layer is at least 20µm at any region of an outer circumferential part of the S-shaped cross section.
The zinc-aluminum alloy plated deformed steel wire of claim 1, wherein the amount of zinc-aluminum alloy plated is 250g/m² or more.
A method for manufacturing a wrapping wire spirally wound on an outer circumference of a main cable having a plurality of metal wires densely arranged in parallel with each other, the method comprising:
drawing a wire rod to prepare a steel wire;

performing primary rolling on the steel wire;

performing stress relief heat treatment on a primarily rolled wire at 300-500°C;

plating the heat-treated primarily rolled wire with a zinc-aluminum alloy; and

performing secondary rolling on the plated primarily rolled wire at an amount of rolling of 5-40% to obtain an S-shaped cross-sectional deformed steel wire.
The method of claim 3, wherein the chemical composition of the wire rod comprises, by wt%, 0.06-0.15% of C, 0.15-0.25% of Si, 0.4-0.6% of Mn, 0.015% or less of S, 0.015% or less of P, and the balance Fe and inevitable impurities.
The method of claim 3, wherein the thickness of a plating layer is at least 20µm at any region of an outer circumferential part of the S-shaped cross section that is finally molded through secondary rolling.
The method of claim 3, wherein in the S-shaped cross section that is finally molded through secondary rolling, the amount of zinc-aluminum alloy plated is 250g/m² or more.