JPH0853743A - Production of high strength and high toughness hot-dip plated steel wire - Google Patents

Abstract

PURPOSE:To produce a hot-dip plated steel wire applicable even to pure galvanizing, in a producing method in which a high carbon steel wire rod is subjected to patenting treatment and is thereafter subjected to wire drawing, by specifying the componental compsn. in the steel wire and executing the wire drawing under optimum producing conditions. CONSTITUTION:A high carbon steel wire contg., by weight, 0.7 to 1.2% C, 0.5 to 2.0% Si, 0.2 to 1.0% Mn, 0.02 to 0.07% Al and 0.003 to 0.015% N is subjected to hot rolling and is directly, or after reaustenitization, subjected to patenting treatment to produce a steel wire having a structure essentially consisting of fine pearlite. This steel wire is subjected to cold wire drawing, is thereafter applied with galvanizing or Zn-Al plating, is next subjected to wire drawing at 4 to 15% reduction rate of area and is moreover subjected to modifying. The same steel wire may furthermore be incorporated with specified amounts of Cu, Cr, Ni, Co and W and moreover with V, Nb and Ti.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength, high-toughness hot-dip galvanized steel wire having excellent corrosion resistance, which is useful for PC steel wire, galvanized steel stranded wire, spring steel wire, suspension bridge cable and the like. Is.

[0002]

2. Description of the Related Art When manufacturing high-strength wires such as PC steel wires and cables for suspension bridges, which are required to have corrosion resistance, high carbon steel wires having a certain diameter are subjected to patenting treatment to a predetermined wire diameter. In general, wire drawing is performed, and then hot dip Zn plating for imparting corrosion resistance is performed. However, with this method, 400 ° C after wire drawing
Since the hot-dip galvanizing process is performed at the above-mentioned high temperature, there is a problem that the strength of the wire material improved by the wire drawing is reduced again. Further, the higher the degree of wire drawing and the higher the strength, the greater the decrease in strength due to the plating treatment. Therefore, it was difficult to increase the strength of the plated steel wire by this method.

Therefore, increasing the C content of the high carbon steel wire rod to improve the strength has been studied as an industrially desirable method because it is inexpensive and has a great effect. However, in the hyper-eutectoid region where the C content is 0.9% or more, brittle pro-eutectoid cementite forms along the austenite grain boundaries during patenting in the form of a network. Disconnection occurs,
A new problem has arisen that wire drawability deteriorates.

On the other hand, Si has the effect of increasing the strength of the steel wire after patenting and improving the strength of the steel wire after drawing, and the effect of improving the hardenability of the steel wire and suppressing the precipitation of pro-eutectoid cementite. It is an element that has. In addition to these effects, it also has the effect of suppressing the strength reduction due to plating treatment, and it is a very effective element for increasing the strength of hot dip plated steel wire, but excessive addition causes toughness of the steel wire. It is also known to reduce ductility.

Therefore, several proposals have been made to obtain a steel wire having high strength and high toughness by subjecting a high carbon steel wire material containing Si to hot-dip plating, and then applying working and heat. For example, Japanese Patent Application Laid-Open No. 4-246125 discloses a method of performing a straightening process and a bluing process after performing a hot dip Zn-Al plating. However, these treatments are intended to compensate for the decrease in creep property due to the increase in the yield strength of the plated steel wire, and are not intended to increase the strength or recover the elongation of the steel wire. In addition, Japanese Patent Laid-Open Nos. 4-236756 and 4-236742 disclose that
Although a method of performing wire drawing and heat treatment after performing hot dipping Zn-Al plating is disclosed, these techniques can only perform Zn-Al plating because the wire drawing rate after plating is large. That is, pure Z that is generally mass-produced
The n-plating causes cracks in the Fe—Zn alloy plated layer, which causes a problem that corrosion resistance and fatigue characteristics are deteriorated.

[0006]

Therefore, in the present invention, in order to obtain a steel wire having high strength and high toughness, the optimum chemical conditions of the steel wire are grasped and the optimum manufacturing conditions applicable to pure Zn plating are also set. The purpose is to find out.

[0007]

The method for producing a high-strength and high-toughness hot-dip galvanized steel wire according to the present invention, which has solved the above-mentioned problems, comprises: C: 0.7-1.2% Si: 0.5-2.0% Mn: 0.2 to 1.0% Al: 0.02 to 0.07% N: 0.003 to 0.015% After hot rolling a high carbon steel wire, directly or after reaustenization. A patenting treatment is performed to obtain a steel wire having a structure mainly composed of fine pearlite, the steel wire is cold-drawn, then hot-dip Zn or Zn-Al plating is applied, and then the area reduction ratio of 4 to It has the gist of performing 15% wire drawing and further straightening. Moreover, in the steel wire of this invention, Cu: 0.05-0.5% Cr: 0.05-1.0% Ni: 0.05-1.0% Co: 0.05-1.0% W: 0.05 to 1.0% or more, or V: 0.05 to 0.5% Nb: 0.01 to 0.2% Ti: 0.01 to 0.2% 1 It may contain one or more species.

[0008]

First, the reason for limiting the optimum chemical composition of the high carbon steel wire of the present invention will be explained. Other than the chemical components shown below, the balance is Fe
And unavoidable impurities. C: 0.7 to 1.2% C is an element effective for increasing the strength of the steel wire and is economical. If the C content is less than 0.7%, it is insufficient to exert the effect of improving the strength of the steel wire. But,
If the C content exceeds 1.2%, the ductility of the steel wire will be significantly reduced.

Si: 0.5 to 2.0% Si acts as a deoxidizing agent, and has the effect of forming a solid solution with ferrite to remarkably increase the strength of the solid solution. Further, Si in the ferrite has an effect of reducing the strength reduction during hot dipping performed after wire drawing. These effects are recognized when the steel wire contains Si, but the more remarkable effect is when Si is 0.5% or more. But Si
However, since the ductility of the steel wire after wire drawing is deteriorated, the upper limit of the amount of Si was set to 2.0%.

Mn: 0.2 to 1.0% Mn has an effect as a deoxidizing agent and an effect of improving the hardenability of the steel wire and improving the uniformity of the structure in the cross section of the steel wire.
However, if Mn is excessively added, a supercooled structure such as martensite or bainite is generated in the segregated portion of Mn to deteriorate the wire drawing workability. Therefore, the upper limit of the content is set to 1.0%.

Al: 0.02 to 0.07% Al is effective as a deoxidizing agent, and is effective in preventing coarsening of the austenite grain size by adding N together. However, if the added amount is less than 0.02%, this effect is insufficiently expressed, and if added excessively, the amount of nitride increases excessively and the wire drawability deteriorates. I won't.

N: 0.0030 to 0.0150% N forms a nitride of Al in the steel wire and is effective in preventing coarsening of the austenite grain size during heating. 0.00 0.00
If it is less than 30%, this effect is not sufficiently exhibited. Also, if added in excess of 0.0150%, not only does Al nitride increase too much, which adversely affects the wire drawability, but also solid solution N
May accelerate aging during wire drawing, so the upper limit is 0.0
It was set to 150%.

The high carbon steel wire applied to the method of the present invention has the above-mentioned essential components and the balance Fe and unavoidable impurities. However, the following chemical components, namely Cu,
The present invention also relates to a steel type in which one or more kinds selected from the group consisting of Cr, Ni, Co and W, or further, one or more kinds of chemical components selected from the group consisting of V, Nb and Ti are positively added. The method can be preferably used.

Cu: 0.05 to 0.5% Cu improves the strength of the steel wire by the precipitation hardening action, but if the addition amount is less than 0.05%, the effect is too small. However, if it is added excessively, not only the strength improving effect is saturated, but also grain boundary embrittlement is caused, and the ingot surface may be cracked during hot rolling, so the upper limit was made 0.5%.

Cr: 0.05 to 1.0% Cr improves the strength and drawability of steel wire. This is because Cr reduces the lamellar spacing in pearlite. This effect is observed at 0.05
%, But when added in excess of 1.0%, the transformation end time becomes too long, which is not preferable from the viewpoint of productivity.

Ni: 0.05 to 1.0% Ni does not contribute so much to the strength improvement of the steel wire, but has the effect of increasing the toughness of the drawn wire. This effect is recognized when the addition amount is 0.05% or more, but if the addition amount exceeds 1.0%, the transformation end time becomes too long,
It is not preferable in terms of productivity.

Co: 0.05 to 1.0% Addition of 0.05% or more of Co suppresses the precipitation of pro-eutectoid cementite. However, even if added over 1.0%, the effect is saturated and it is uneconomical, so the upper limit was made 1.0%.

W: 0.05 to 1.0% W is added in an amount of 0.05% or more and has the effect of improving the strength of the steel wire. However, even if added over 1.0%, the effect is saturated and conversely causes a decrease in ductility, so the upper limit was made 1.0%.

V: 0.05 to 0.5%, Nb: 0.01
.About.0.2%, Ti: 0.01 to 0.2% These elements form fine carbonitrides in the steel wire, improve the strength of the steel wire by precipitation hardening, and increase the austenite during heating. Helps prevent coarsening of particle size. This effect is not observed when the amount added is less than the above lower limit. On the other hand, if the amount exceeds the upper limit, the amount of carbonitrides increases too much and the particle size of the carbonitride itself becomes too large, resulting in poor ductility.

Next, the optimum manufacturing conditions in the method of the present invention will be described. In the method of the present invention, the high-carbon steel wire having the optimum chemical composition is hot-rolled → directly or after reaustenizing, patenting → cold-drawing → molten Zn or Zn-
High-strength and high-toughness hot-dip galvanized steel wire is obtained through a process of Al plating → drawing with a surface reduction rate of 4 to 15% → straightening. The point of the manufacturing conditions of the present invention is to draw wire after plating. The area reduction rate in the process is specified to be 4 to 15%.

Since hot-dip galvanizing is performed at a high temperature, the strength of the steel wire improved in cold drawing before hot-dip galvanizing is reduced in this plating step. Therefore, wire drawing is performed again after plating so that a steel wire having a target strength and wire diameter is obtained. In the method of the present invention, the area reduction rate of this wire drawing must be 4 to 15%. If the area reduction rate is lower than 4%, the strength improving effect by wire drawing is too small. Further, wire-drawing of less than 4% is an unstable region, and the strength may be decreased conversely depending on the shape of the die (Nishioka Tasaburo, The Japan Institute of Metals, vol. 22,
Therefore, the lower limit was set to 4%. However, if the wire drawing exceeds 15%, the ductility deteriorates, and even if an attempt is made to recover the ductility by a straightening process after wire drawing,
It becomes irrecoverable. In addition, especially in pure Zn-plated steel wire, F
Since cracks occur in the e-Zn alloy plated layer, the upper limit value was set to 15%.

In the present invention, the conditions for cold wire drawing before plating may be set in consideration of the area reduction rate in this wire drawing step. Other steps may be performed according to a conventional method, and the conditions are not particularly limited.

[0023]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
All modifications and implementations that do not depart from the spirit of the description below are included in the technical scope of the present invention.

In Table 1, the chemical composition of the steel used in the examples is shown in% by weight. P and S are unavoidable impurities, and the balance is Fe. The steels shown in Table 1 were first hot-rolled to a wire diameter of 7.5 to 14 mm and then subjected to lead patenting treatment (reheating: 950 ° C. × 5 minutes, isothermal transformation:
540 ° C. × 4 minutes). After that, the wire rod was cooled at the exit of the die and was drawn to a target wire diameter while being kept at 170 ° C or lower. Next, hot-dip Zn plating was applied in the experiments shown in Tables 2 to 4, and hot-dip Zn-Al plating was applied in the experiment shown in Table 5. The steel wire properties after plating are shown in Tables 2-5. Further, with the area reduction ratios shown in Tables 2 to 5, the wire diameter was 5 mm in the experiments of Tables 2, 3 and 5 and 3 mm and 7 mm in the experiment of Table 4.
Was drawn. Finally, straightening was performed, and the characteristics of the obtained steel wire are shown in Tables 2-5.

The criterion for the determination is that the strength of the steel wire after plating is T
S ₀ , TS ₀ -TS when the straightened steel wire strength is TS
(ΔTS) is 4 kgf / cm ² or more, or ΔTS /
TS ₀ is 2% or more, TS is 205 kgf / cm ²
And the steel wire after straightening having an elongation of 4% or more is marked with ◯.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

[Table 5]

From the above experimental example, the following was found. Experiment Nos. 1 to 23 are experiments investigating the influence of the difference in the composition of the steel on the steel wire characteristics (Tables 1 to 3). No. 1 uses steel type A with a small amount of C, so its strength is low. No. 2 is
The present invention steel B is used, but the increase in strength is small because the area reduction rate in the wire drawing process after plating is low, and No. 4 is too large in area reduction due to wire drawing, and the elongation is reduced. It did not recover even after processing. No. 3 uses steel type B, and No. 5
Since steel type C was used and wire drawing was performed at a surface reduction ratio within the range of the present invention, the steel had high strength and excellent elongation.

Since C of steel type D exceeds the upper limit value, in No. 6 using this steel, a large amount of pro-eutectoid cementite was precipitated and the wire drawability was deteriorated, and wire breakage occurred during cold wire drawing. No. 7 is Si
Since steel type E, which is too much, was used, the ductility deteriorated and the wire breakage occurred frequently. In addition, No. 8 is a steel type F with low Mn
Although the wire could be drawn, the strength of the steel wire after straightening was insufficient. Steel type G has a large amount of Mn and therefore has a poor drawability due to the presence of a supercooled structure (No. 9), and steel type I has a large amount of Al and is incapable of being drawn (No. 1).
1). In addition, No. 10 using the steel type H with less Al
Since the crystal grain size became coarse, the wire drawability was inferior.

Since No. 16 uses the steel type L in which Cr exceeds the upper limit value, the transformation time becomes long, and under the present patenting conditions, the transformation did not end within the time, so that the supercooled structure was It exists and has many disconnections. In No. 23, since the steel type S in which N exceeds the upper limit value was used, the age hardening action during wire drawing was too strong and the wire was broken. No. 12, 14, and 17 to 22 all use the steel of the present invention to perform wire drawing at a surface reduction rate within the specified range of the present invention, so that a steel wire having excellent strength and elongation is obtained. . However, No. 13 has a low area reduction rate in the wire drawing process after plating, so the increase in strength is small, and No. 15 has an excessively large wire area reduction rate, resulting in a decrease in elongation. Also did not recover.

Experiment Nos. 31 to 36 are the results of examining the influence of the area reduction rate when the wire diameter of the final steel wire is set to 3 mm and when it is set to 7 mm. From Table 4, it can be seen that if the wire drawing is not performed at an appropriate area reduction rate, the strength and the elongation will be insufficient.

Experiment Nos. 41 to 46 are the experimental results of the steel wire plated with the hot dip Zn-Al. However, as in the case of Table 5, when the area reduction rate is low, the strength improving effect is not recognized, It is also understood that if the area reduction rate is too low, the elongation will be significantly reduced.

From the above experimental results, in order to obtain a plated steel wire excellent in both strength and elongation characteristics, it is necessary to use a steel having the optimum chemical composition specified by the method of the present invention and perform wire drawing under optimum manufacturing conditions. It is clear that there is.

[0037]

The present invention is configured as described above,
It has become possible to obtain hot-dip galvanized steel wire with high strength and high toughness. INDUSTRIAL APPLICABILITY The method of the present invention is applicable to steel wire applications such as PC steel wire, galvanized steel wire, spring steel wire, suspension bridge cable, and plated steel wire for ACSR (strengthening wire for power transmission line cable) requiring high strength. This is the most suitable method for producing plated steel wire.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI technical display location C22C 38/52 C23C 2/06 2/38 (72) Inventor Katsuji Mizutani Nadahama, Nada-ku, Kobe-shi, Hyogo 2 Higashimachi Stock Company Kobe Steel Works Kobe Steel Works (72) Inventor Kenji Ochiai 2 Nadahama Higashicho, Nada-ku, Kobe City, Hyogo Prefecture Koshi Works Kobe Steel Works (72) Inventor Yukio Yamaoka 10 Nakahama, Amagasaki City Address 1 Shinko Steel Wire Industrial Co., Ltd. (72) Inventor Masaru Kodama 10-1 Nakahama-cho, Amagasaki City Shinko Steel Wire Industrial Co., Ltd.

Claims (3)

[Claims] 1. C: 0.7 to 1.2% (weight%, the same applies hereinafter) Si: 0.5 to 2.0% Mn: 0.2 to 1.0% Al: 0.02 to 0. High carbon steel wire containing 07% N: 0.003 to 0.015% is hot-rolled, and then directly or after reaustenizing, a patenting treatment is applied to the steel wire having a structure mainly composed of fine pearlite. Obtained by cold-drawing the steel wire, followed by hot-dip Zn or Zn-Al plating, then wire drawing with a surface reduction rate of 4 to 15%, and further straightening. Method for producing high strength and high toughness hot-dip galvanized steel wire. 2. The high carbon steel wire according to claim 1, further comprising: Cu: 0.05 to 0.5% Cr: 0.05 to 1.0% Ni: 0.05 to 1.0% Co. : 0.05-1.0% W: The manufacturing method of Claim 1 containing 0.05-1.0% of 1 type or more. 3. The high carbon steel wire according to claim 2, further comprising: V: 0.05 to 0.5% Nb: 0.01 to 0.2% Ti: 0.01 to 0.2%. The manufacturing method according to claim 2, which contains one or more kinds.