JP2003096544A - Wire for high strength high carbon steel wire, and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire for a high strength high carbon steel wire which has suppressed delamination, and has excellent ductility, and to provide a technique of realizing the production method therefor at a low cost. SOLUTION: In the wire for a high strength high carbon steel wire, when tensile strain of 1 to 2% is applied to a hot-rolled wire rod having a composition containing, by mass, 0.8 to 1.1% C, 0.05 to 2% Si, and 0.2 to 2% Mn or further, containing one or more metals selected from 0.0001 to 0.002% Mg and 0.0001 to 0.002% Zr, and the balance Fe with inevitable impurities, and, successively, aging treatment is performed thereto at 150 to 300 deg.C, the amount of proof stress to be increased before and after the aging treatment is <=200 MPa, and, the content solid solution C is <=25 ppm. In the method of producing the high strength high carbon steel wire, after hot rolling, without performing reheating, patenting is directly performed under the condition of 450 to 650 deg.C, and, successively, cooling is performed at a rate of 1 to 8 deg.C/sec, or, after the patenting treatment, successively, the temperature is held at 150 to 300 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a steel wire for a bridge, a PC.
Steel wire, steel wire for reinforcement of transmission line (ACSR), steel wire for springs,
The present invention relates to a high-strength wire material for high-carbon steel wire, which is widely used in various wire ropes, steel tire cords, and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A high carbon steel wire obtained by strengthening a high carbon steel wire having a pearlite structure by wire drawing has been required to have higher strength in order to reduce the weight or shorten the construction period. Normally, high carbon steel wires such as bridge steel wires and PC steel wires are
After performing a patenting treatment to reheat the hot-rolled high-carbon steel wire rod, cold wire drawing is performed, and finally hot-dip Zn plating, hot-dip Zn-Al for ensuring corrosion resistance.
It is manufactured in the process of plating or bluing. The steel cord is manufactured in a process of performing brass plating after patenting treatment and performing wet drawing.

The greatest problem in achieving high strength of these high-carbon steel wires is the ductility of the steel wire, and in particular, the longitudinal direction that occurs in the longitudinal direction of the steel wire in the torsion test, which is one of the evaluation methods of the ductility. This is a technique for suppressing the occurrence of cracks (hereinafter referred to as delamination).

As a technique for suppressing delamination in a high carbon steel wire or a technique for preventing deterioration of ductility, Japanese Patent Application Laid-Open No. 7-179994 discloses a technique for controlling the pearlite nodule size after patenting treatment.
-292443 discloses a technique for controlling the amount of Si and Al added, and JP-A-8-53737 discloses a technique for controlling the surface hardness of a hot-dip steel wire.
Japanese Patent Laid-Open No. 7-87803 proposes a technique for controlling the average particle size of cementite, and Japanese Patent Laid-Open No. 9-87803 proposes a technique for controlling the amount of solute N. In addition, JP-A-60-
204865, JP-A-63-24046, Japanese Patent Publication No. 3
No. 23674, C, Si, Mn,
A high-strength, high-ductility, high-carbon steel wire for ultrafine steel wire in which chemical components such as Cr have been regulated has been proposed. Furthermore, JP-A-6-14
Japanese Patent No. 5895 discloses a high strength and high toughness steel wire rod in which the chemical composition, the composition of non-metallic inclusions and the area fraction of proeutectoid cementite are controlled. A method for producing a high-strength, high-toughness ductile extra-fine steel wire with controlled rate is disclosed.

However, the above-mentioned technique has a drawback in that the strength of the high carbon steel wire is limited, and the manufacturing cost is high.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and includes steel wire for bridge, PC steel wire, steel wire for reinforcement of transmission line (ACSR), steel wire for spring, A technology that suppresses delamination that occurs during a torsion test in high carbon steel wires that are widely used for various wire ropes, steel tire cords, etc., and realizes a high carbon steel wire with excellent ductility and a manufacturing method thereof at low cost. It is intended to provide.

[0007]

[Means for Solving the Problems] The present inventors have conducted various analyzes on the controlling factors of delamination, which is a factor inhibiting the strengthening of high carbon steel wires. As a result, it has been found that the solid solution C in the patented wire material significantly affects the occurrence of delamination. That is, it was found that the structure after patenting treatment is fine pearlite composed of a layered structure of ferrite and cementite, but the occurrence frequency of delamination remarkably increases when the amount of solute C in ferrite is large. . Furthermore, investigations have been advanced on means for controlling the amount of solid solution C in ferrite at low cost. As a result, it has been found that fine oxides and sulfides containing Mg and Zr or their composites have the effect of reducing the amount of solid solution C as a means for solving the problems from the steel material side. Also, the optimum cooling rate after patenting treatment,
Alternatively, a technology has been established that can control the amount of solute C by low temperature annealing after the patenting treatment.

Based on the above new findings, it was concluded that if the amount of solid solution C in ferrite in the patented wire can be controlled, the occurrence of delamination can be prevented in a high strength high carbon steel wire. It has reached the present invention.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) C: 0.8 to 1.1 by mass%
%, Si: 0.05 to 2%, Mn: 0.2 to 2%, the balance being a hot-rolled wire consisting of Fe and unavoidable impurities. A wire rod for a high-strength high-carbon steel wire, which is characterized in that an increase in proof stress before and after aging treatment is 200 MPa or less when a tensile strain is applied and subsequently subjected to aging treatment at 150 to 300 ° C.

(2) In mass%, Mg: 0.0001 to
The wire rod for high-strength steel wire according to (1) above, which contains one or two of 0.002% and Zr: 0.0001 to 0.002%.

(3) Cr: 0.05 to 1 in mass%
%, Mo: 0.05 to 0.5%, Ni: 0.05 to 1
%, V: 0.01 to 0.5% of one kind or two or more kinds contained therein, the wire material for high strength and high carbon steel wire according to the above (1) or (2).

(4) Al: 0.005% by mass
0.1%, Ti: 0.002-0.1%, Nb: 0.0
02-0.1% 1 type (s) or 2 or more types are contained, The high-strength high carbon steel wire rod wire of said (1), (2) or (3) characterized by the above-mentioned.

(5) The amount of solute C in ferrite is 25 p
The wire rod for high-strength and high-carbon steel wire according to any one of (1) to (4) above, which is pm or less.

(6) A method for manufacturing the wire rod according to any one of (1) to (5), which comprises:
After hot-rolling the steel consisting of the component described in any one of (4), patenting is performed at 450 to 650 ° C. without reheating, and subsequently cooling is performed at 1 to 8 ° C./second. A method for producing a wire rod for a high-strength high-carbon steel wire, which is characterized.

(7) A method for manufacturing the wire rod according to any one of (1) to (5) above, which comprises:
After hot-rolling the steel composed of the component according to any one of (4), patenting is performed at 450 to 650 ° C. without reheating, and then retained in a temperature range of 150 to 300 ° C. A method for manufacturing a wire rod for high-strength and high-carbon steel wire.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

First, the reasons for limiting the components of the present invention will be described.

C: C has the effect of increasing the tensile strength after patenting and increasing the wire drawing work hardening rate, and can increase the tensile strength of a high carbon steel wire with less wire drawing strain. When C is less than 0.8%, it is difficult to realize the high-strength high-carbon steel wire targeted by the present invention, while
If it exceeds 1.1%, pro-eutectoid cementite precipitates at the austenite grain boundaries during patenting, wire drawability deteriorates, and wire breakage frequently occurs during wire drawing, so C is 0.8 to 0.8.
It was limited to the range of 1.1%.

Si: Si is an effective element for strengthening ferrite in pearlite and for deoxidizing steel.
If less than 0.05%, the above effect cannot be expected, while 2%
If it exceeds 1.0, hard SiO ₂ inclusions harmful to wire drawing workability are likely to be generated, so the range is limited to 0.05 to 2%.

Mn: Mn is an element effective not only for deoxidation and desulfurization but also for improving the hardenability of steel and the tensile strength after patenting treatment.
If it is less than 0.2%, the above effect cannot be obtained. On the other hand, if it exceeds 2%, the above effect is saturated, and further, the processing time for completing the pearlite transformation during the patenting process is too long and the productivity is increased. Since it decreases, it was limited to the range of 0.2 to 2%.

Mg: When Mg is added, fine Mg oxides and sulfides or their composites are formed. Mg
The presence of system oxides and sulfides in ferrite has the effect of reducing the amount of solid solution C after patenting treatment.
It was found that it is an extremely effective element for preventing delamination. If Mg is less than 0.0001%, the above effect cannot be exhibited, and if added in excess of 0.002%, the effect is saturated and the manufacturing cost becomes high.
It was limited to 01 to 0.002%.

Zr: Zr, like Mg, also produces fine oxides and sulfides of Zr or their composites. Z
The presence of r-based oxides and sulfides in ferrite has the effect of reducing the amount of solid solution C after patenting treatment, and is clearly an extremely effective element for preventing delamination. became. Zr is 0.0001
If less than%, the above effect cannot be exhibited, and 0.002%
If added in excess, the effect will be saturated and the manufacturing cost will increase, so the content was limited to 0.0001 to 0.002%. In addition,
When both Mg and Zr are added, composite oxides and sulfides of Mg and Zr are produced, but even composite oxides and sulfides have the effect of reducing the amount of solid solution C.

Cr: Cr is an effective element that refines the cementite spacing of pearlite to increase the tensile strength after patenting treatment and especially to improve the wire work hardening rate. Less effective,
On the other hand, if it exceeds 1%, the pearlite transformation end time at the time of patenting treatment becomes long and the productivity is lowered.
The range is limited to 5 to 1%.

Mo: Mo has the effect of increasing the hardenability during the patenting treatment and increasing the tensile strength after the patenting treatment. If it is less than 0.05%, the above effect cannot be exhibited, while if it is added over 0.5%, the effect is saturated, so the range is limited to 0.05 to 0.5%.

Ni: Ni has the effect of making pearlite, which is transformed during the patenting treatment, have good wire drawability, but if it is less than 0.05%, the above effect cannot be obtained, and if it exceeds 1%. However, since the effect corresponding to the addition amount is small, this is the upper limit.

V: V has the effect of refining the cementite spacing of pearlite and increasing the tensile strength after patenting treatment, but this effect is insufficient at less than 0.01%, while exceeding 0.5%. Since the effect is saturated with 0.0
The range was limited to 1 to 0.5%.

Al: Al is effective for preventing coarsening of austenite crystal grains by denitrification and by forming a nitride. If the added amount of Al is less than 0.005%, the above effect is not sufficient, so the lower limit is limited to 0.005%. On the other hand, the effect is saturated even if added over 0.1%, so the upper limit was limited to 0.1%.

Ti: Ti has the effect of preventing coarsening of austenite crystal grains by deoxidizing and forming carbonitrides, but if it is less than 0.002%, these effects are not exhibited. The effect is saturated even if added in excess of 0.1%, so the range was limited to 0.002 to 0.1%.

Nb: Nb is an element effective for refining crystal grains by forming carbonitrides like Ti, but if it is less than 0.002%, its effect is insufficient, while 0 If the content exceeds 0.1%, this effect is saturated, so the content is limited to 0.002 to 0.1%.

Other elements are not particularly limited, but P: 0.02% or less, S: 0.
A desirable range is 02% or less and N; 0.007% or less.

Next, the amount of solute C in ferrite, which is extremely important for preventing the occurrence of delamination in the high-strength, high-carbon steel wire of the present invention, will be described.

In the present invention, the ductility of the high carbon steel wire is evaluated by the torsion test by the presence or absence of delamination. Here, it means that the steel wire in which delamination occurs has low ductility. Further, the amount of solute C in ferrite of the wire rod can be accurately measured by using an atom probe field ion microscope. However, since it takes a long time to prepare and analyze the sample for analysis, the present invention employs a method capable of simply evaluating the magnitude of the amount of solute C in ferrite. That is, the wire rod after patenting treatment is straightened by straightening, and then a tensile strain of 1 to 2% is applied to the wire rod by a tensile tester. The value obtained by dividing the load when a tensile strain of 1 to 2% is applied to the wire rod by the cross-sectional area of the wire rod is the yield strength before aging. After applying strain, the load is removed, 150-30
Aging treatment is performed for 60 to 300 seconds in an oil bath at 0 ° C., and a tensile test is performed again. This process is shown in FIG. In the figure, proof stress increases when aging treatment is performed after applying strain. The proof stress after aging is defined as the proof stress after aging. The value obtained by subtracting the proof stress before aging from the proof stress after aging is the amount of increase in proof stress before and after aging limited in the present invention. Here, the larger the amount of solute C in the wire, the larger the increase in yield strength before and after aging. This is a phenomenon that occurs when dislocation is introduced into ferrite when strain is applied and then solid solution C fixes the dislocation when aging treatment is performed. FIG. 2 shows an example of analysis of the relationship between the increase in proof stress before and after aging of a patented wire, that is, the amount of solid solution C and the occurrence of delamination in a high carbon steel wire. High carbon steel wire has a wire diameter of 0.4 m
The tensile strength at m is around 3850 MPa. As is clear from the figure, the increase in proof stress before and after aging is 200
It can be seen that delamination occurs when the pressure exceeds MPa. When the amount of increase in proof stress before and after aging ΔY exceeded 200 MPa, the amount of solid solution C in the wire rod was 25 ppm. Further, FIG. 3 is an example of a high carbon steel wire having a wire diameter of 7 mm and a tensile strength of about 1950 MPa. Similar to the results shown in FIG. 2, it can be seen that delamination does not occur when the amount of increase in proof stress before and after aging is 200 MPa or less. Solid solution C of wire when the increase ΔY in proof stress before and after aging exceeds 200 MPa
The amount was 25 ppm. From the above, the increase in yield strength before and after the aging treatment was limited to 200 MPa or less. A more preferable condition for obtaining high strength and delamination resistance is 180 MPa or less. Further, the reason why the tensile strain is limited to 1 to 2% is that it is difficult to control the strain accurately if it is less than 1%, and if the strain is applied to the wire rod in excess of 2%, there is a possibility of breakage. For,
It was limited to the range of 1-2%. If the aging temperature after straining is less than 150 ° C, the diffusion rate of C becomes slow,
It takes a long time for the treatment, and if the temperature exceeds 300 ° C., the pearlite structure itself may change.
Limited to 0 ° C.

From the above, the amount of solid solution C of the wire is set to 25 ppm or less.

Next, the reasons for limiting the manufacturing method of the wire for high strength and high carbon steel wire will be described.

In the present invention, after carrying out ordinary hot rolling, patenting is directly carried out at 450 to 650 ° C. without reheating. Direct patenting has higher tensile strength after patenting treatment than conventional patenting performed after cooling and reheating the hot-rolled material, which is advantageous for high strength and low cost. This is because high-strength, high-carbon steel wire can be manufactured. If the direct patenting temperature is lower than 450 ° C., bainite, which is harmful to the wire drawing workability, is likely to occur, so the lower limit was limited to 450 ° C. On the other hand, when the temperature exceeds 650 ° C, a coarse pearlite structure having poor wire drawability is formed, and proeutectoid cementite is easily generated in a steel having a high C content. Therefore, the upper limit of the patenting treatment temperature is limited to 650 ° C. .

The cooling rate after the patenting treatment is 8 ° C.
If it exceeds / sec, the increase in proof stress before and after strain aging is 20
Since it exceeds 0 MPa and delamination easily occurs, it is limited to 8 ° C./second or less. A more preferable cooling rate is 5 ° C./second or less. On the other hand, if the cooling rate is slower than 1 ° C / sec, the productivity decreases, so the lower limit of the cooling rate is 1
C / sec.

The cooling end temperature after the patenting treatment is
Less than 150 ° C is a preferred condition. In addition, in the manufacturing method of the present invention, after the patenting treatment, 1
There is no problem even if it is held in the temperature range of 50 to 300 ° C. Here, if the temperature is lower than 150 ° C., it is difficult to control the increase amount of the proof stress before and after the aging treatment to 200 MPa.
If the temperature is maintained above 00 ° C, the pearlite structure changes and the wire drawing workability tends to deteriorate.
Limited to the temperature range. The holding time is not particularly limited, but 2 to 60 minutes is a preferable condition.

[0039]

EXAMPLES The effects of the present invention will be described more specifically below with reference to examples.

Table 1 shows the chemical composition of the test materials. These test materials were hot-rolled into various wire diameters and then directly patented. The patenting bath is molten lead,
It carried out on 3 conditions, a molten salt and air. In air patenting, the patenting temperature was controlled by adjusting the amount of air blown onto the hot-rolled wire. In the case of continuous retention after the direct patenting treatment, the retention time was set to 30 minutes. The solute C content of these patenting wire rods was measured using an atom probe field ion microscope. The amount of increase in proof stress of the patented wire before and after aging was examined under conditions of a tensile strain of 1.5%, an aging temperature of 250 ° C and an aging time of 90 seconds. Then, using these patenting wire rods, wire drawing was performed to a predetermined wire diameter, and bluing treatment or hot dip plating was performed depending on the application. The bluing temperature is 300-500 ℃
Under the conditions, hot dip galvanizing was performed at 450 ° C.
Further, according to the end use, after the patenting treatment, copper plating or brass plating was applied, and then wire drawing was performed. Tensile tests and twist tests were performed on these high carbon steel wires. The presence or absence of delamination was judged by a torsion test.

[0041]

[Table 1]

Table 2 shows the types of test materials, manufacturing conditions, tensile strength, presence / absence of delamination, etc. In the table, test Nos. 1, 3, 5, 8, 10, 12,
15, 17, 19, 22, 24, 26, 28, 30, 3
2, 34, 36 and 38 are examples of the present invention, and others are comparative examples. As can be seen from the table, the high-carbon steel wire rods of the examples of the present invention each had an increase in yield strength before and after the aging treatment of 200.
The amount of solid solution C in the wire is controlled to 25 ppm or less. As a result, in the high-carbon steel wire that has been subjected to the wire drawing work, despite its high strength, delamination does not occur in the torsion test, and high ductility can be realized.

On the other hand, comparative examples No. 7 and 21
Are examples where the chemical composition of steel is inappropriate. That is,
No. 7 is an example in which high strength cannot be achieved because the C content is as low as 0.72%. No. 21 is an example in which proeutectoid cementite was precipitated during the patenting treatment because the C content was too high. As a result, the wire drawability deteriorates, and wire breakage frequently occurs during wire drawing.

Test Nos. 14 and 40, which are comparative examples, are examples in which the direct patenting treatment temperature is inappropriate. No. 14 is an example in which, because the patenting treatment temperature was too high, a coarse pearlite structure was formed, proeutectoid cementite was precipitated, and wire breakage frequently occurred during wire drawing. No. 40 is an example in which bainite, which deteriorates the wire drawing workability, was generated because the patenting treatment temperature was too low, and as a result, wire breakage occurred during wire drawing.

Test Nos. 2, 4, 6, 9, which are comparative examples
11, 13, 16, 18, 25, 29, 31, 33, 3
Nos. 5, 37, and 39 are examples in which the cooling rate after the patenting treatment was too fast, and thus the increase in yield strength before and after the aging treatment exceeded 200 MPa. As a result, delamination occurred in the twist test after wire drawing.

Further, test Nos. 20 and 2 which are comparative examples.
Nos. 3 and 27 are examples in which the holding temperature after the patenting process is inappropriate. That is, the retention temperature is 150 in both cases.
This is an example in which the increase in yield strength before and after the aging treatment exceeded 200 MPa because the temperature was less than 0 ° C, resulting in delamination.

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

As is clear from the above examples, the present invention is extremely effective in reducing the amount of solid solution C in high carbon steel wire rods for preventing delamination in high strength high carbon steel wire rods. In addition, it was clarified that delamination can be prevented if the increase amount of proof stress before and after aging treatment is 200 MPa or less, and a wire rod for high carbon steel wire with high strength was realized. The above effect is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of obtaining an increase amount of proof stress before and after aging treatment in a high carbon steel wire rod.

FIG. 2 is a diagram showing an example of an analysis of the relationship between the increase amount of proof stress before and after aging treatment in a high carbon steel wire and the presence or absence of delamination in a high carbon steel wire having a wire diameter of 0.4 mm.

FIG. 3 is a diagram showing an example of an analysis of the relationship between the increase amount of proof stress before and after aging treatment in a high carbon steel wire and the presence or absence of delamination in a high carbon steel wire having a wire diameter of 7 mm.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaharu Oka             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters F-term (reference) 4K032 AA01 AA06 AA07 AA11 AA19                       AA22 AA23 AA31 AA32 AA35                       AA36 AA39 BA02                 4K043 AA02 AB01 AB05 AB06 AB10                       AB15 AB18 AB21 AB22 AB27                       AB28 AB29 AB30 AB32

Claims (7)

[Claims] 1. In mass%, C: 0.8 to 1.1%, S
i: 0.05 to 2%, Mn: 0.2 to 2%, the balance being a hot-rolled wire consisting of Fe and unavoidable impurities, wherein the wire has a tensile strain of 1 to 2%. And a continuous aging treatment at 150 to 300 ° C., the increase in yield strength before and after the aging treatment is 200 MPa or less. 2. In mass%, Mg: 0.0001 to 0.0
02%, Zr: 0.0001-0.002% 1 type or 2 types are contained, The high-strength steel wire wire rod of Claim 1 characterized by the above-mentioned. 3. In mass%, Cr: 0.05-1%, M
o: 0.05 to 0.5%, Ni: 0.05 to 1%, V
: 0.01-0.5% of 1 type (s) or 2 or more types, The high-strength high carbon steel wire rod wire of Claim 1 or 2 characterized by the above-mentioned. 4. In mass%, Al: 0.005 to 0.1
%, Ti: 0.002-0.1%, Nb: 0.002-
The high-strength, high-carbon steel wire rod according to claim 1, 2 or 3, containing 0.1% of one or more kinds. 5. The wire rod for high-strength and high-carbon steel wire according to claim 1, wherein the amount of solute C in the ferrite is 25 ppm or less. 6. A method for producing the wire rod according to any one of claims 1 to 5, which is obtained by hot rolling steel made of the component according to any one of claims 1 to 4. , Patenting at 450-650 ° C without reheating,
A method for producing a wire rod for high-strength high-carbon steel wire, which comprises cooling at 1 to 8 ° C./second. 7. A method for producing the wire rod according to any one of claims 1 to 5, which is obtained by hot rolling a steel comprising the component according to any one of claims 1 to 4. , Patenting at 450-650 ° C without reheating,
A method for producing a wire rod for a high-strength high-carbon steel wire, which comprises holding at 150 to 300 ° C.