JP3267833B2 - High-strength extra-fine steel wire with excellent fatigue properties 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 ultrafine steel wire which is used as a strand of steel tire cords, steel belt cords and the like, has a wire diameter of 0.05 to 0.4 mm, and has excellent fatigue properties. It relates to a manufacturing method.

[0002]

2. Description of the Related Art The demand for higher strength of ultrafine steel wires for weight reduction and the like is increasing more and more. Conventionally, ultra-fine steel wires used for reinforcement of automobile tires, industrial belts, etc. are made from hot-rolled high-carbon steel wire,
After the patenting process is repeatedly performed to a predetermined wire diameter, a final patenting process is performed, a plating process is performed to improve the wire drawing processability and the adhesion to rubber, and wet drawing is performed to a predetermined wire diameter. Is done. For example, a steel tire cord is manufactured by finally twisting a strand manufactured as described above using a twisting machine such as a double twister.

In the above-described manufacturing process, in order to increase the strength of the ultrafine steel wire, it is necessary to increase the wire strength after the final patenting process or to increase the final drawing strain. However, even if the strength of the ultrafine steel wire is increased by increasing the wire strength or drawing strain after the final patenting process, the fatigue characteristics of the ultrafine steel wire do not improve, but rather deteriorate. This was one of the factors that hindered the strengthening of ultrafine steel wires.

On the other hand, as a means for improving the fatigue characteristics of an ultrafine steel wire, for example, Japanese Patent Application Laid-Open No. 2-179333 discloses a technique in which shot peening is applied to an ultrafine steel wire. There has been proposed a method for improving the tensile residual stress of steel to a compressive residual stress to produce an ultrafine steel wire having high fatigue resistance. According to the present inventors' detailed tests, it is possible to improve the tensile residual stress on the surface of ultrafine steel wire to compressive residual stress by shot peening, but to convert it to compressive residual stress, a very strong shot Peening is required. When such a shot peening treatment is performed, the brass plating layer on the surface layer of the ultrafine steel wire, which has become extremely thin due to the wire drawing, is peeled off, resulting in a problem that the adhesion to rubber is deteriorated. There are limits to improving the fatigue properties of steel. Further, Japanese Patent Application Laid-Open No. Hei 5-195457 discloses a method of controlling the distribution of minute non-uniform strain in a very fine line, which is disclosed in Japanese Patent Application Laid-Open No. Hei 6-18496.
No. 2 discloses a technique for improving the fatigue properties of the ultrafine steel wire by controlling the difference in strength between the surface layer and the inside of the ultrafine steel wire, but according to the detailed research of the present inventors, Even if such a technique is applied, there is a limit to the high fatigue strengthening of ultrafine steel wires.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned situation, and has been developed in view of the fatigue generated when producing an ultrafine steel wire having a wire diameter of 0.05 to 0.4 mm by wire drawing. It is an object of the present invention to prevent the deterioration of the properties, to realize a high-strength ultrafine steel wire having excellent fatigue properties, and to provide a manufacturing method thereof.

[0006]

Means for Solving the Problems First, the present inventors first examined the chemical composition of a steel wire, the conditions of heat treatment for patenting, the shape of a die used for wire drawing, the strain of wire drawing, the bending after wire drawing, and the like. The dominant factors of the fatigue properties were analyzed in detail using various samples in which the tensile strength and the yield ratio of the ultrafine steel wire were changed by changing. As a result, it was found that, besides the residual stress on the surface layer of the ultrafine steel wire, the yield ratio of the steel wire significantly affects the fatigue of the high-strength ultrafine steel wire.
Therefore, the effects of yield ratio and residual stress for improving the fatigue strength of high-strength ultrafine steel wire were quantitatively studied.
Furthermore, as a means for controlling the yield ratio and the residual stress, it was clarified that a die shape used in wire drawing and bending after wire drawing were extremely effective.

[0007] Based on the above study results, used for wire drawing
Die shape and bending conditions after wire drawing are limited
By doing so, the yield ratio of ultrafine steel wire and residual stress on the surface layer
Optimum control is possible, and high fatigue characteristics
We concluded that we could manufacture high-strength ultrafine steel wire, and
It was done. The present invention has been made based on the above findings.
The main point is that in weight%, C: 0.8 to 1.1%, Si: 0.1 to 0.5
%, Mn: 0.2-0.7%, Al: 0.005% or less
Or Cr or 0.05 to 0.5%, Ni: 0.1 to 1.0
%, V: one or more of 0.05 to 0.3%, with the balance being Fe and inevitable
Consist of natural impuritiesIntermediate wire drawing from hot rolled wire rods, patente
After repeating the printing process to the specified wire diameter,
And then plating, 0.05 ~
Wet wire drawing to 0.4mm wire diameterIn steel wire,
After the final patenting treatment of the steel wire rod, Die approach angle: 8-12 ° Die bearing length: 0.2 ~ 0.5D (D: Die
Diameter) Wire drawing using a die that satisfies the conditions of
10% or more of the tensile breaking load of the steel wire
While passing between multiple rolls at a bending angle of 15 to 30 °
Manufactured by 3702MPa tensile strength
As described above, the yield ratio is 0.93 or more, and the residual stress of the surface layer is +2.
Excellent fatigue properties characterized by being less than 00MPa
A high-strength ultrafine steel wire and a method for manufacturing the same.

[0008]

The present invention will be described below in detail. First, the reasons for limiting the chemical components of the steel targeted by the present invention will be described. C : C has the effect of increasing the tensile strength after the patenting treatment and increasing the drawing work hardening rate, and can increase the tensile strength of the ultrafine steel wire with less drawing strain. 0.
If it is less than 8%, even if an alloy element is added, the tensile strength after the patenting treatment is low, and the wire work hardening rate is also small, so that a high-strength ultrafine steel wire cannot be finally obtained, so the lower limit is 0.8.
%. On the other hand, if it exceeds 1.1%, proeutectoid cementite precipitates at the austenite grain boundaries during the patenting treatment, deteriorating the wire drawing workability, and frequently causes wire breakage in the wire drawing step or the stranded wire processing step. .1%.

[0009] Si : Si is an effective element for strengthening ferrite in pearlite and for deoxidizing steel.
If it is less than 0.1%, the above effect cannot be expected.
%, The effect is saturated.
Limited to the range of ~ 0.5%. Mn : Mn is an element effective not only for deoxidation and desulfurization but also for improving the hardenability of steel and increasing the tensile strength after patenting, but is less than 0.2% If the above effect is not obtained, on the other hand, if it exceeds 0.7%, the above effect is saturated, and the processing time for completing the pearlite transformation at the time of the patenting process becomes too long, thereby lowering the productivity. It was limited to the range of 0.2 to 0.7%.

[0010]Al: Al exceeds 0.005% in steel
Al hardest among inclusions_TwoO _ThreeSystem inclusions
Wire breakage during wire drawing or stranded wire processing
Therefore, the content was limited to 0.005% or less. In the present invention
In the case of high-strength extra-fine steel wire with excellent fatigue characteristics
In addition to the elements, Cr: 0.05-0.5%, N
i: 0.1-1.0%, V: 0.05-0.3%
May be used alone or in combination of two or more.

Cr : Cr has the effect of making the cementite spacing of pearlite finer, increasing the tensile strength after the patenting treatment, and particularly improving the wire drawing work hardening rate,
It is an effective element for increasing the strength of ultrafine steel wires. 0.
If it is less than 005%, the effect of the above effect is small, while
%, The finish time of the pearlite transformation during the patenting process becomes longer and the productivity is reduced.
The range was limited to 0.5%.

Ni : Ni has the effect of improving the drawability of the pearlite generated during transformation during the patenting process and further improving the corrosion fatigue strength. However, if it is less than 0.1%, the above effects can be obtained. However, even if the content exceeds 1.0%, the effect corresponding to the added amount is small, so that the upper limit was set. V : V has the effect of reducing the pearlite cementite spacing and increasing the tensile strength after patenting. 0.
If it is less than 05%, the effect cannot be expected, while 0.3%
Is exceeded, the effect saturates, so the range is limited to 0.05 to 0.3%.

The other elements are not particularly limited, but P: 0.0
15% or less, S: 0.015% or less, N: 0.005%
The following are desirable ranges. Next, the reasons for limiting the yield ratio of the steel wire and the residual stress in the surface layer, which are extremely effective in increasing the fatigue strength of the high-strength ultrafine steel wire, which are the objectives of the present invention, will be described. FIG.
Fig. 1 shows an example of analysis of the relationship between the yield ratio of steel wires and the fatigue limit of 0.2 mm steel wires. Here, the yield ratio indicates a ratio between 0.2% proof stress and tensile strength. The yield ratio of the steel wire when wire drawing is performed normally is about 0.90.
90 indicates that the fatigue limit is low. On the other hand, when the yield ratio is 0.93 or more, the fatigue limit is greatly improved. Therefore, the yield ratio of the ultrafine steel wire is limited to 0.93 or more.
In addition, since a remarkable effect is obtained in a region of 0.95 or more, a preferable condition is 0.95 or more. FIG. 2 shows an example in which the relationship between the residual stress in the surface layer of the ultrafine steel wire and the fatigue limit is analyzed. When the residual stress of the surface layer is +200 MPa or less and the fatigue limit of the steel wire is significantly improved, the residual stress of the surface layer is reduced by +200 MPa.
It was limited to 200MPa or less. In addition, in the conventional knowledge, there are many reports that there is no effect unless the residual stress of the surface layer is on the compression side, but in the present invention, since the effect of the yield ratio is large,
It is characterized that the residual stress is significantly improved on the fatigue side even on the tensile side.

Next, a method for reducing the yield ratio to 0.93 or more and the residual stress in the surface layer to 200 MPa or less will be described. Here, the bending conditions after wire drawing have an effect on the yield ratio of the steel wire, and the bending angle and the approach angle and bearing length of the die used for wire drawing have an effect on the residual stress. Exert. First, regarding the residual stress, FIG. 3 shows an example in which the approach angle of the die and the residual stress of the ultrafine steel wire are analyzed. In the figure,
○ marks are examples where bending was not performed after wire drawing.
The mark ● indicates an example of bending. It can be seen that the residual stress decreases as the approach angle decreases, but it does not become less than 200 MPa unless bending is performed after wire drawing. Further, even if bending is performed, if the approach angle exceeds 12 °, it is difficult to reduce the residual stress to 200 MPa or less, so the upper limit of the approach angle is limited to 12 °. On the other hand, although the residual stress can be reduced to 200 MPa or less even when the approach angle is less than 8 °, the lower limit is set to 8 ° because the drawing force during wire drawing increases.
Similarly, when the bearing length exceeds 0.5D (D: die diameter), the residual stress is reduced to 200 even if proper bending is performed.
Since it is difficult to reduce the pressure to MPa or less, the upper limit of the bearing length is limited to 0.5D. If the bearing length is less than 0.2D, the linearity of the ultrafine steel wire will deteriorate,
The lower limit was limited to 0.2D.

Next, the bending conditions which affect the yield ratio and residual stress of the steel wire will be described. FIG. 4 shows an example of analyzing the effect of tension on the yield ratio of a steel wire. It is understood that the yield ratio does not become 0.93 or more unless a tension of 10% or more of the tensile breaking load is applied. In addition, the residual stress of the surface layer can be reduced to 200 MPa by using the above-described die.
Since it is difficult to reduce the tension below, the lower limit of the tension during bending is limited to 10% of the tensile breaking load. On the other hand, even if a tension exceeding 50% of the tensile breaking load is applied, the amount of improvement in the fatigue limit of the ultrafine steel wire is small and the risk of disconnection increases, so the upper limit was limited to 50%. The bending can be performed using a jig having five or more rolls as shown in FIG. If the bending angle is less than 15 °, it is difficult to increase the yield ratio to 0.93 or more and to reduce the residual stress to 200 MPa even when the tension is in an appropriate range.
Since the angle cannot be reduced below, the lower limit of the bending angle is limited to 15 °. On the other hand, the effect is saturated even if it is performed beyond 30 °, and the linearity of the steel wire after bending is deteriorated.
°.

[0016]

EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples. Table 1 shows the chemical composition of the test materials.

[0017]

[Table 1]

These test materials were hot-rolled to a wire diameter of 5.
It was set to 5 mm and subjected to primary drawing, primary patenting, and secondary drawing. Thereafter, a final patenting treatment (austenitizing temperature: 950 ° C., lead bath temperature: 560)
〜600 ° C.), followed by brass plating, and wet drawing at a drawing speed of 600 m / min. Table 2
The die shape used during wire drawing and the bending conditions after wire drawing are shown in FIG. Table 3 shows the mechanical properties such as the yield ratio, residual stress, and fatigue strength of the ultrafine steel wire processed under the drawing and bending conditions shown in Table 2. The fatigue strength (1
0 ⁷ cycles), temperature: 20~25 ℃, Humidity: 50
This is a result of performing the test under a condition of 60% and evaluating by a rotating bending fatigue test.

[0019]

[Table 2]

[0020]

[Table 3]

In the table, test No. (1), (4),
(5), (7), (9), (12), (13), (1
4) is an example of the present invention, and the others are comparative examples. As can be seen from Table 3, all of the examples of the present invention have a tensile strength of 3702 MPa or less.
Above, the yield ratio of the ultrafine steel wire is 0.93 or more, and the residual stress of the surface layer is 200 MPa or less. As a result, an ultrafine steel wire with high fatigue strength is realized.

On the other hand, the comparative example No. 2,11,
In No. 15, the residual stress of the surface layer could not be reduced to 200 MPa or less even if proper bending was performed after the wire drawing because the die shape at the time of wire drawing was inappropriate, and the fatigue strength was not improved. It is an example. That is, No. In Nos. 2 and 14, the approach angle exceeded 12 °. 11 has a residual stress exceeding 200 MPa because the bearing length exceeds 0.5D.

In addition, No. Nos. 3 and 8 are examples in which the bending process was not performed after the wire drawing process, so that the yield ratio was less than 0.93 and the residual stress could not be reduced to 200 MPa or less. As a result, the fatigue strength is also significantly inferior to the examples of the present invention. Further, in Comparative Example No. 6,10,
Reference numeral 16 denotes an example in which the bending conditions after the wire drawing are inappropriate.
That is, No. 6: bending angle is too low and residual stress is 200MP
a. In No. 10, the yield ratio was less than 0.93 because no tension was applied during bending. No. No. 16 is an example in which the yield ratio could not be increased because the tension was too low. As a result, none of them has achieved improvement in fatigue strength.

[0024]

As is clear from the above embodiments, the present invention shows that an increase in the yield ratio is extremely effective for improving the fatigue strength of a high-strength ultrafine steel wire, in addition to controlling the residual stress in the surface layer. In addition to finding out, it is possible to control the yield ratio and residual stress if the die shape during wire drawing and the bending conditions after wire drawing are optimally selected.
This realizes a high-strength ultrafine steel wire with excellent fatigue characteristics, and has extremely remarkable industrial effects.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of analyzing the effect of the yield ratio on the fatigue strength of a high-strength ultrafine steel wire.

FIG. 2 is a diagram showing an example of analyzing the effect of residual stress on the fatigue strength of a high-strength ultrafine steel wire.

FIG. 3 is a diagram showing an example in which the influence of a die approach angle and bending on the residual stress of an ultrafine steel wire is analyzed.

FIG. 4 is a diagram showing an example in which the relationship between the yield ratio of ultrafine steel wires and the tension during bending is analyzed.

FIG. 5 is a diagram showing an example of a jig for bending a high-strength ultrafine steel wire.

[Explanation of symbols]

 1 ... roll 2 ... steel wire

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI D07B 1/06 D07B 1/06 A (56) References JP-A-2-217421 (JP, A) JP-A-6-158225 (JP, A JP-A-6-346190 (JP, A) JP-A-8-27539 (JP, A) JP-A-6-254647 (JP, A) JP-A-6-312209 (JP, A) 1027 (JP, A) JP 50-19512 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21F 1/00-1/06 C22C 38/00-38/60 B21C 1/00 D06B 1/02

Claims (4)

(57) [Claims] C .: 0.8 to 1.1% by weight, Si: 0.1 to 0.5% by weight
%, Mn: 0.2-0.7%, Al: 0.005% or less
Below, with the balance being Fe and unavoidable impuritiesHot
Repeated intermediate drawing and patenting from rolled wire
After the specified wire diameter, perform the final patenting process,
Plating process, wet type up to 0.05-0.4mm wire diameter
Wire-drawnIn steel wire,The steel wire rod is applied to the final patent
After the Die approach angle: 8-12 ° Die bearing length: 0.2 ~ 0.5D (D: Die
Diameter) Wire drawing using a die that satisfies the conditions of
10% or more of the tensile breaking load of the steel wire
While passing between multiple rolls at a bending angle of 15 to 30 °
Manufactured by 3702MPa tensile strength
As described above, the yield ratio is 0.93 or more, and the residual stress of the surface layer is +2.
Excellent fatigue properties characterized by being less than 00MPa
High strength extra fine steel wire. 2. The method according to claim 1, wherein one or more of Cr: 0.05 to 0.5%, Ni: 0.1 to 1.0%, and V: 0.05 to 0.3% are contained in% by weight. High strength ultra-fine steel wire with excellent fatigue properties. In wherein wt%, C: 0.8~1.1%, Si : 0.1~0.5%, Mn: 0.2~0.7%, Al: 0.005% or less, containing the balance between heat consisting of Fe and unavoidable impurities
Repeated intermediate drawing and patenting from rolled wire
After the specified wire diameter, perform the final patenting process,
Plating treatment and wet drawing to 0.05-0.4mm wire diameter
In this method, a steel wire rod is subjected to the final patenting process, and a die approach angle: 8 to 12 mm. A die bearing length: 0.2 to 0.5 D (D: die diameter) is used. The steel wire is passed through a plurality of rolls at a bending angle of 15 to 30 ° while applying a tension of 10% or more of the tensile breaking load of the steel wire to the steel wire .
Tensile strength is 3702MPa or more, yield ratio is 0.93 or more,
Excellent process for producing a high-strength ultra-fine steel wire fatigue residual stress characterized that you produce steel wire is less than + 200 MPa. 4. The method according to claim 3, further comprising one or more of Cr: 0.05 to 0.5%, Ni: 0.1 to 1.0%, and V: 0.05 to 0.3% by weight%. Method for producing high-strength ultrafine steel wire with excellent fatigue characteristics.