JPH11199980A - High strength extra fine steel wire - Google Patents

Abstract

(57) [Problem] To provide a high-strength ultrafine steel wire having a tensile strength of 4200 MPa or more and excellent ductility. SOLUTION: C: 0.85 to 1.1%, Si: 0.0
Contains 5 to 2.0%, Mn: 0.2 to 2.0%,
Alternatively, Cr: 0.05 to 1.0%, Ni: 0.1
-1.0%, V: 0.01-0.5%, Nb: 0.00
A steel wire containing 1 to 0.1% of one or more kinds and the balance being Fe and unavoidable impurities has a drawn pearlite structure and a C concentration of 1.5% in ferrite. High-strength ultrafine steel wire characterized by being at most atomic%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is used as a strand for steel tire cords, steel belt cords and the like.
The present invention relates to a high-strength ultrafine steel wire having excellent ductility and a tensile strength of 4200 MPa or more.

[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 strength of the wire 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 treatment, if the strength exceeds 4200 MPa, the ductility is significantly reduced, and it is extremely difficult to put it to practical use. It will be difficult.

[0004] On the other hand, as a conventional finding of means for increasing the strength with less decrease in ductility, for example, Japanese Patent Application Laid-Open No. 60-204 discloses
865, JP-A-63-24046, JP-B-3-23
No. 674 proposes a high-strength, high-ductility, high-carbon wire rod for ultrafine wires in which chemical components such as C, Si, Mn, and Cr are regulated. However, as can be seen from the examples disclosed in these publications, the tensile strength of the steel wire is 3500 to 3600 MPa at the maximum, and there is a limit in increasing the strength of the ultrafine steel wire. In addition, Japanese Patent Application Laid-Open No. 6-14589
No. 5 proposes a high-strength and high-toughness steel wire in which the chemical composition, the composition of nonmetallic inclusions, and the area fraction of proeutectoid cementite are controlled. Furthermore, Japanese Patent Application Laid-Open No. Hei 7-113119 discloses a method for manufacturing a high-strength, high-toughness ductile ultrafine steel wire that controls the chemical composition of steel and the reduction in area in the final die. However, it was difficult to realize an ultrafine steel wire having a tensile strength of 4200 MPa or more and a high ductility by any of the techniques.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has a wire diameter of 0.05 to 0.5 mm.
An object of the present invention is to provide a high-strength ultra-fine steel wire having a strength of 4200 MPa or more and having excellent ductility while preventing a decrease in ductility which is a problem when increasing the strength of a 4 mm ultra-fine steel wire.

[0006]

Means for Solving the Problems The inventors of the present invention have analyzed the controlling factors of the ductility of a high-strength steel wire in various ways. Have been found to have an effect. That is, the inventors have found a completely new fact that when the drawing strain increases, cementite is decomposed, the C concentration in ferrite increases, and the ductility of the high-strength steel wire decreases.

Based on the above-mentioned new findings, the present inventors have concluded that it is possible to prevent a decrease in ductility of a high-strength ultrafine steel wire by controlling the C concentration in the ferrite of the pearlite structure which has been strongly worked, and have made the present invention. Things.

[0008] The present invention has been made based on the above findings, and the gist of the present invention is that in weight%, C: 0.85 to 1.1% Si: 0.05 to 2.0% Mn: 0.2 to 2.0%, or Cr: 0.05 to 1.0% Ni: 0.1 to 1.0% V: 0.01 to 0.5% Nb: 0 The steel wire contains 0.001 to 0.1% of one or more kinds and the balance is Fe and unavoidable impurities. The steel wire has a drawn pearlite structure, and the C concentration in ferrite is 1.0%.
A high-strength ultrafine steel wire characterized by being at most 5 atomic%.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

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 the patenting treatment and increasing the hardening rate of the wire drawing work, and can increase the tensile strength of the ultrafine steel wire with less drawing strain. If C is less than 0.85%, 4
It becomes difficult to produce a high-strength ultrafine steel wire of 200 MPa or more. On the other hand, if it exceeds 1.1%, proeutectoid cementite precipitates at austenite grain boundaries during the patenting treatment, and wire drawing workability is deteriorated and wire drawing becomes poor C is 0.85 to 1.1% because disconnection frequently occurs in the processing step or the stranded wire processing step.
Limited to the range.

Si: Si is an effective element for strengthening ferrite in pearlite and for deoxidizing steel.
If it is less than 0.05%, the above effect cannot be expected, while 2.
If it exceeds 0%, hard SiO which is harmful to drawability
_{For 2} inclusions are likely to occur, 0.05-2.0
% Range.

Mn: Mn is an element not only required for deoxidation and desulfurization but also effective for improving the hardenability of steel and increasing the tensile strength after patenting.
If it is less than 0.2%, the above effects cannot be obtained.
Exceeds 0.2%, the above effect is saturated, and the processing time for completing the pearlite transformation during the patenting process becomes too long, and the productivity is reduced.
Limited to the range.

In the high-strength ultrafine steel wire according to the present invention,
In addition to the above elements, Cr: 0.05 to 2.0%,
Ni: 0.1 to 1.0%, V: 0.01 to 0.5%, N
b: One or more kinds can be contained in the range of 0.001 to 0.1%.

Cr: Cr is an effective element for refining the cementite spacing of pearlite, increasing the tensile strength after the patenting treatment, and particularly improving the drawing hardening rate. Less effective,
On the other hand, if it exceeds 2.0%, the pearlite transformation end time during the patenting process becomes longer, and the productivity decreases.
It was limited to the range of 0.05 to 2.0%.

Ni: Ni has the effect of improving the drawability of pearlite generated during transformation during patenting. However, if it is less than 0.1%, the above effect cannot be obtained. Even if it exceeds, there is little effect corresponding to the added amount, so this is set as the upper limit.

V: V has the effect of refining the cementite spacing of pearlite and increasing the tensile strength after patenting, but this effect is insufficient at less than 0.01%, while exceeding 0.5%. And the effect saturates to 0.0
Restricted to the range of 1-0.5%.

Nb: Like V, Nb has the effect of refining the cementite spacing of pearlite and increasing the tensile strength after patenting, but less than 0.001% is insufficient, while 0.1% Even if added in excess, the effect saturates, so the content is limited to the range of 0.001 to 0.1%.

Other elements are not particularly limited, but P: 0.015% or less, S:
Desirable ranges are 0.015% or less and N: 0.007% or less. On the other hand, if the content of Al exceeds 0.005%, the hardest Al ₂ O ₃ -based inclusion among the inclusions in the steel is likely to be generated, which causes a disconnection in wire drawing or stranded wire processing. , 0.005% or less is a preferable range.

Next, the reason for limiting the C concentration in the ferrite in the pearlite structure, which is extremely important in preventing the decrease in ductility of the high-strength ultrafine steel wire intended in the present invention, will be described.

In the present invention, the ductility of a steel wire is evaluated by the number of twists up to breaking using a torsion test. FIG. 1 shows that the wire diameter is 0.15 mm obtained by performing a strong processing of 4 or more with a true strain of wire drawing.
1 is an example in which the relationship between the C concentration in ferrite and the number of times of torsion of an ultrafine steel wire is analyzed. The tensile strength of extra fine steel wire is
The steel composition was adjusted to about 4500 MPa by changing the chemical composition and strain of wire drawing. As is clear from the figure, the number of twists decreases as the C concentration in the ferrite in the pearlite structure that has undergone heavy working increases. In particular, when the C concentration in the ferrite exceeds 1.5 atomic%, the number of twists is significantly reduced, and the ductility is deteriorated. Since exactly the same results can be obtained when the wire diameter and strength of the ultrafine steel wire are variously changed, the C concentration in the ferrite is limited to 1.5 atomic% or less. From the viewpoint of achieving both high strength and high ductility of the ultrafine steel wire, the C concentration in the ferrite is preferably 1.2 atomic% or less.

Here, in order to control the C concentration in ferrite in the pearlite structure of the strongly processed ultrafine steel wire to 1.5 atomic% or less, the following A to G in the manufacturing process after the final patenting treatment. Manufacturing methods can be adopted, and it is important to combine them not alone. Among the following production methods A to G, A, B, C,
D, E, and G are particularly important technologies. For this reason, in order to produce an ultrafine steel wire having a C concentration of 1.5 atomic% or less,
Of the methods A, B, C, D, E, F and G, two or more, preferably three or more methods may be combined.

A: The strength of the patenting material is increased to 1450 MPa or more by optimizing the chemical composition of the steel and the final patenting treatment conditions. It is important that the patenting process is performed at a temperature at which bainite is not generated.

B: Wire drawing is performed using a die having an approach angle of 8 to 12 ° and a bearing length of 0.2 to 0.5 D (D: die diameter).

C: A diamond die is used instead of a conventional carbide die.

D: Suppression of heat generation due to wire drawing. Preferably, the wire drawing is performed while controlling the temperature of the drawn material to 50 ° C. or less.

E: Use a lubricant having a high lubricating ability. Preferably, a lubricant having a friction coefficient of 0.1 or less between the die and the drawn wire is used.

F: Wire drawing In the initial stage of wire drawing up to 1 with true strain, the area reduction rate per die is set to 20% or more.

G: After drawing, heat to a temperature of 200 to 500 ° C.

The C concentration in ferrite can be easily and accurately measured by using an atom probe field ion microscope. In the present invention, the C concentration X in the ferrite is determined by the following equation when the total number of detected ions is Y (total) and the number of detected ions of C is Y (carbon) from analysis by an atom probe field ion microscope.

X = [Y (carbon) / Y (total)] × 100 (atomic%)

[0032]

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

Table 1 shows the chemical compositions of the test materials. Using these test materials, ultrafine steel wires having a brass plating with a wire diameter of 0.12 to 0.35 mm were prototyped. Table 2 shows the manufacturing conditions and tensile strength of ultrafine steel wire, the C concentration in ferrite, and the number of twists. In the table, symbols B to
G is the content described above. In the torsion test, both ends of the test piece were fixed at an interval of a grip 100 times the wire diameter, and the number of torsion until breaking was measured.

In Table 2, test no. 1 to 8 are examples of the present invention, and others are comparative examples. As can be seen from the table, all of the examples of the present invention have a tensile strength of 4200 MPa or more and a C concentration in the ferrite of 1.5 at% or less. As a result, despite the high strength, a very fine steel wire having a high number of twists and a high ductility has been realized.

On the other hand, the comparative example No. 9, 1
Nos. 6 and 17 are examples in which the chemical composition of steel is inappropriate. That is, No. 9 is 4 because C content is as low as 0.72%.
High strength of 200 MPa or more has not been achieved. In addition, No. No. 16 is SiO ₂ because the Si content is too high.
This is an example in which the number of system inclusions increased and the disconnection frequently occurred during drawing. In addition, No. No. 17 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 drawing workability was deteriorated, and the wire was frequently broken during the wire drawing.

Further, in any of the ultrafine steel wires of Comparative Examples 10 to 15, the C concentration in the ferrite exceeds 1.5 atomic%, so that the number of twists is lower than that of the present invention. Significant ductility deterioration.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

As is clear from the above examples, the present invention controls the concentration of C in ferrite in order to prevent a decrease in ductility of a high-strength ultrafine steel wire having a tensile strength of 4200 MPa or more. It is extremely effective and realizes a high-strength ultra-fine steel wire with high ductility, and the industrial effect is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of analyzing a relationship between a C concentration in ferrite of an ultrafine steel wire and the number of twists.

Claims (2)

[Claims] C .: 0.85 to 1.1% Si: 0.05 to 2.0% Mn: 0.2 to 2.0% by weight% Steel wire consisting of Fe and inevitable impurities 3. The high-strength ultrafine steel wire according to claim 1, which has a drawn pearlite structure and a C concentration in ferrite of 1.5 atomic% or less. 2. Further, by weight%, Cr: 0.05 to 2.0% Ni: 0.1 to 1.0% V: 0.01 to 0.5% Nb: 0.001 to 0.1 The high-strength ultrafine steel wire according to claim 1, which contains one or more of the following.