JP2986645B2 - High Fatigue Strength Low Relaxation Galvanized PC Steel Strand and Method for Producing the Same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, low-relaxation galvanized PC steel strand and a method for producing the same.

[0002]

2. Description of the Related Art When the fatigue limit is evaluated by the rotational bending fatigue of a galvanized PC steel strand, the rotational bending fatigue limit of a conventional galvanized PC strand is 30 to 45 kgf / m.
m ² . As a galvanized PC steel strand, a strand having even higher fatigue strength and low relaxation is desired.

[0003]

In such a high fatigue strength, low relaxation zinc-coated PC steel stranded wire, the suppression of the plating alloy layer, particularly the composition of the alloy layer, is an important factor. As well as the time limit, rapid heating in the tempering process is important. For this purpose, high-frequency heating is performed in a tempering step after the stranding.
However, when high-frequency heating is performed on a galvanized PC steel strand, there is a problem in that the temperature varies along the wire length direction.

The present invention has been developed to provide a high-strength, low-relaxation galvanized PC steel stranded wire and a method for producing the same, which solve the above problems.

[0005]

SUMMARY OF THE INVENTION The present invention provides a high-strength, low-relaxation galvanized PC in which a wire has a rotary bending fatigue strength of 50 to 55 kgf / mm ^2.
It is a steel strand. The method for producing such high fatigue strength low relaxation zinc-coated PC steel wires is to heat-treat, wire-draw, apply plating, after-draw, and coat the surface with an electrical insulating film of 1 g / m ² or more. After wearing
It is characterized by stranding and hot stretching at a tempering temperature.

[0006]

According to the present invention, hot stretching is performed during tempering heating in order to reduce relaxation. In this case, the fatigue strength can be improved by suppressing the development of the alloy layer. Then, in order to suppress the development of the plating alloy layer, in addition to the temperature and time restrictions in the plating step, tempering is performed by high-speed heating with high frequency.

[0007] However, when high-frequency heating of a plated steel strand was carried out, the temperature varied greatly in the length direction. This is presumed to be due to unevenness of the induced current flow. In order to prevent this phenomenon, it has been found that it is sufficient that the electric insulating film such as the wire drawing lubricant is 1 g / m ² or more over the entire length of each strand.

FIG. 1 shows a phenomenon by the present inventors when a PC steel stranded wire is heated at a high frequency, when an electrical insulating film such as a wire drawing lubricant is applied to the surface of the strand. P
It shows the variation of the temperature in the length direction of the C wire. If the electric insulating film is less than 1 g / m ² , the temperature variation is large, and if it is 1 g / m ² or more, the variation is within 10 ° C. The application of the electric insulating film may be performed by applying a lubricant or the like after the final drawing, but it is most efficient to perform the afterdraw including the effect of obtaining the roundness.

When the fatigue strength is evaluated by the rotational bending fatigue of the strand, the conventional level has a fatigue limit of 30 to 45 kgf / mm ² . In order to obtain a material having a fatigue limit of 50 kgf / mm ² or more, the iron-zinc alloy layer needs to be composed of a ζ layer (FeZn ₁₃ ) and a δ layer (FeZn ₉ ).
However, even when the δ ₁ layer (FeZn ₇ ) exists, the thickness is 5 μm.
It turned out that the following should suffice. Figure 2 shows the relationship between the thickness and the fatigue limit of [delta] ₁ layer of the alloy layer indicates this. δ
_If the thickness of _one layer is 5 μm or less, the fatigue limit is 50 kgf
/ Mm ² .

In the above description, hot-dip galvanizing has been assumed as a plating method. Alternatively, electro-galvanizing or hot-dip zinc-aluminum (mesh metal added) plating may be considered. Such plating is also effective for suppressing the development of the alloy layer. JI as a wire rod
It is preferable to use a high carbon steel material specified in SG35063502. C: 0.75 to 0.95 as a wire component
%, Si: 0.12-1.0%, Mn: 0.30-0.
90%, with the balance being Fe and unavoidable impurities. As an additional component, Al: 0.015 to 0.0
Preferably, it contains 60% and / or Ti: 0.05 to 0.060%, and more preferably contains Cr: 0.10 to 0.50% and / or V: 0.02 to 0.20%. is there. (P + S) < 0.015%, (N + O)
A small amount of unavoidable impurities, such as < 60 ppm, is effective in increasing the fatigue strength. It is more preferable to use a material in which the central segregation represented by C is C / Co ≦ 1 (C: analysis value of C in the central portion, Co: ladle analysis value) by continuous forging.

The total amount of wire drawing after the heat treatment is 80 in terms of area reduction.
The range is preferably within ± 5%, more preferably 80 ± 2%. The tensile strength including the plating layer is 180kgf / m
m ² or more is preferable.

[0012]

[Example] Twisted wire diameter 15.2mm and tensile strength 190kg
A high-strength galvanized PC steel wire of f / mm ² class (JIS class B equivalent) was produced. A wire (diameter: 12 mm) subjected to continuous forging treatment having the chemical composition shown in Table 1 was patented and then pre-drawn to a diameter of 7.50 mm, which was subjected to bluing (400 ° C. × 5 seconds) and hot-dip galvanizing ( 4
Was 50 ° C. × 5 seconds), so as not to produce a [delta] ₁ layer in galvanized alloy layer to obtain a galvanized steel wire.

Next, wire drawing is performed using a wire drawing lubricant (calcium stearate-based lubricant containing molybdenum disulfide).
A steel wire with a diameter of 5.20 mm and a surface adhesion amount of 4 g / m ² ,
The number of strands is increased to 7 by a stranding machine, rapidly heated to 370 ° C. by high-frequency heating, hot stretched during tempering, the rotational bending fatigue strength of the strand is 53 kgf / mm ² , and the thickness of the alloy layer δ ₁ is 2 μm. Was produced from a galvanized PC steel wire.

In the relaxation, the initial load is set at 0.2.
A low relaxation galvanized PC steel strand having a relaxation value of 0.50% at a holding time of 10 hours was obtained at a minimum value of 80% of the load with respect to the% permanent elongation. The property results are shown in Table 2 together with the property results of products manufactured by the conventional method. The production method according to the conventional method is a method in which a wire having a diameter of 12 mm is patented, finish-drawn, hot-dip galvanized, and then subjected to ordinary bluing after wire drawing. The thickness of the alloy layer δ ₁ was 13 μm.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

According to the present invention, it is possible to provide a high-strength, low-relaxation galvanized PC steel strand.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an electric insulating film thickness due to high-frequency heating and a variation in temperature.

FIG. 2 is a graph showing the effect of the embodiment.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI E04C 5/08 E04C 5/08 // B21C 9/00 B21C 9/00 AK E04C 5/08 (72) Inventor Shigeo Shoji Chiba 1 Kawahama Techno Wire Co., Ltd., Chuo-ku, Chuo-ku, Japan (72) Kimio Mine Inventor 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawasaki Steel Corporation Tokyo Headquarters 2-3 2-3 Uchisaiwai-cho Kawasaki Steel Corp. Tokyo Head Office (72) Inventor Wataru Ohashi 12nd-cho, Chiyoda-ku, Tokyo SE Inn Co., Ltd. (56) References JP-A-59-20427 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 30/00

Claims (2)

(57) [Claims] 1. The wire has a rotational bending fatigue strength of 50 to 55 k.
gf / mm ² , high fatigue strength low relaxation galvanized PC steel strand. 2. After the wire is heat-treated, drawn, plated, after-drawn, and coated with an electric insulating film of 1 g / m ² or more on the surface thereof, and then twisted and hot-pressed at a tempering temperature. A method for producing a high-strength, low-relaxation galvanized PC steel strand, characterized by stretching.