JPH0699746B2 - Manufacturing method of ultra-high-strength steel wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an ultrafine high-strength steel wire of 0.5 mmφ or less, which has excellent wire drawability and excellent toughness after wire drawing. Is.

[Prior Art] Ultra-fine steel wire used for reinforcing automobile tires, various industrial belts, rubber hoses, etc. is manufactured from a hot-rolled steel wire material by wire drawing. Patenting is performed as a pretreatment for wire drawing. A fine pearlite structure that has high tensile strength by patenting and is suitable for wire drawing. High tensile strength of steel wire requires high tensile strength after patenting and good wire drawability. In order to utilize the cold work hardening effect of wire drawing as much as possible, it is necessary to increase the wire drawing strain. If there is no large hard inclusion such as 20 μm or more, the smaller the steel wire diameter, the more uniform the work becomes, the larger the wire drawing strain, and the higher the ultimate strength.

This can be seen by looking at the tensile strength of each wire diameter of the JIS G3522 piano wire. Conventionally, various types have been proposed as a component system for extra-fine steel wire rods, but Japanese Patent Publication No. 46-6702 has the highest strength. In Japanese Examined Patent Publication No. 46-6702, 0.076 mmφ with 492 kg / mm ²
Is possible.

However, Japanese Patent Publication No. 46-6702 requires patenting treatment before wire drawing.
It's done below 500 ℃. This is to increase the tensile strength of the patenting material and to make fine pearlite to increase strain in wire drawing. However, in this component system, the temperature of the nose in the pearlite transformation is around 550 ° C, so that the bainite structure is very likely to appear. Therefore, stable production of high-strength steel wire is difficult, and there is a high risk of poor toughness. Japanese Patent Publication No. 46-6702 has the expression that it has high tensile strength and toughness, but no concrete description of toughness is found in the examples.

At that time, when it came to high tensile strength, only strength was prioritized, and the applications were not as diverse as they are today. It cannot be put to practical use in reinforcing applications such as recent automobile tires, various industrial belts, and rubber hoses.

Therefore, it is the current situation that it has not been industrially used.

Recently, a method for manufacturing a high-strength steel wire using a duplex stainless steel has also been proposed. Abstracts of the Japan Institute of Metals (March 1988 issue, P55)
Introduces an ultra-high strength steel wire with a diameter of 25 to 100 μm and a weight of 400 to 475 kg / mm ² . However, this requires a wire drawing strain of 7 to 9 because the strength after heat treatment is low, which requires a great deal of labor for wire drawing.

In addition, the wire diameter is limited to 25 to 100 μmφ, which is extremely thin. The larger the diameter, the larger the starting wire diameter,
This is because uniform deformation becomes difficult. As mentioned above, it can be said that there is no ultra-fine high-strength steel wire that can be industrially used.

[Problems to be Solved by the Invention] The need for high-tensile steel wire is increasing year by year. This is especially noticeable in the field of ultrafine wires. The thinner the steel wire diameter, the more uniform the deformation becomes and the better the wire drawability. However, the presence of hard inclusions such as Al ₂ O ₃ and SiO ₂ causes wire breakage during wire drawing or twisting. In addition, the fatigue characteristics also deteriorate. Therefore, it is necessary to have a steel composition that does not easily generate hard inclusions. Further, in order to improve the wire drawing workability, it is necessary to make the pearlite structure fine and have a good consistency.

When bainite is generated during patenting, wire drawing cannot be performed, so a steel composition that easily undergoes pearlite transformation is required. Cold work hardening contributes significantly to the strengthening of steel wire, but the greater the wire drawing degree, the greater the number of dies during wire drawing, and the lower the productivity. Therefore, it is necessary that the tensile strength after patenting is high.

In the case of high strength steel wire, high tensile strength is an essential condition, but at the same time, toughness is required. Conventionally, as the toughness, the drawing and twisting properties have been used, but these are not sufficient for evaluation because of recent diversified applications, and fatigue and twisting properties are important. Fatigue characteristics are particularly important because they are factors that determine the design strength. Conventionally, very little data has been collected on the fatigue properties of ultrafine wires.

Since ultrafine wire is often used by twisting it rather than being used as a single wire, it is important for industrial use whether or not it can be twisted. Therefore, here, these required characteristics are collectively referred to as toughness.

The present invention has been made to solve these problems, and relates to a manufacturing method for stably supplying a high-strength steel wire having excellent toughness.

[Means and Actions for Solving Problems] That is, the present invention is C: 0.80 to 1.20%, Si: 0.70 to 1.50%, Mn: 0.20 to 0.70%, Cr: 0.30 to 1.00%, Co: 1.0 to 5.0%. , Ni: 0.10〜2.00%, O: 0.0015〜0.0045%, Al: 0.0005〜0.0050%, Steel wire rods consisting of balance iron and inevitable impurities 570〜630
After pearlite transformation at a temperature of ℃, wire drawing strain 3.5 ~
5.5 It is a manufacturing method of ultra-high-strength steel wire for ultra-fine wire, characterized by performing wire drawing of {drawing strain = ln (do / dn) ² , do: patenting wire diameter, dn: final wire drawing diameter} .

The inventors of the present invention have found that, by studying the alloying elements that affect the pearlite structure, it is possible to generate aligned fine pearlite by specifying the composition of the steel wire and to prevent hard inclusions. The present inventors have found conditions under which the heat-treated structure is further stabilized and toughness after wire drawing is secured, and the invention has been completed.

That is, the gist of the present invention is a combination of the following steps.

C: 0.80 to 1.20%, Si: 0.70 to 1.50%, Mn: 0.20 to 0.70%,
Cr: 0.30-1.00%, Co: 1.0-5.0%, Ni: 0.10-2.00%, O: 0.
0015 ~ 0.0045%, Al: 0.0005 ~ 0.0050%, use the steel wire consisting of balance iron and unavoidable impurities.

A fine pearlite structure in which the above-mentioned wire is pearlite-transformed at a temperature of 570 to 630 ° C to form a fine pearlite structure.

It is to maintain not only the strength but also the toughness by drawing the above heat-treated material in the strain of wire drawing of 3.5 to 5.5.

The reasons for limitation of the above will be described.

First of all, C is the most important element that increases the strength of steel. Therefore, use it as much as possible. If C is not more than 0.80%, the tensile strength after patenting will not exceed 150 kg / mm ² no matter how much other alloy elements are added, so the lower limit was made.
On the other hand, when the content is 1.20% or more, even if Co is added, the generation of coarse pro-eutectoid cementite cannot be suppressed, and it is not possible to suppress the cuppy breakage that is characteristic of wire drawing.

Si is conventionally known as a solid solution hardening element. To obtain a tensile strength of 150 kg / mm ² or more after patenting, Si is 0.70
% Or more is required. When Si is 1.50% or more, it becomes hard.
The appearance of inclusions of 20 μm or more cannot be prevented, and wire drawing to 0.5 mmφ or less cannot be performed.

Therefore, it is limited to 1.50% or less.

Mn delays pearlite transformation and makes it easy to generate bainite. Since Si, Cr, and Ni are also used in the present invention, the content of these elements is set to 0.70% or less in order to prevent bainite from being generated during patenting. Steel is hot-rolled into wire, but surface cracking cannot be prevented when Mn is 0.20% or less. If the wire has surface cracks, poor lubrication will occur during wire drawing, causing wire breakage and making it impossible to machine up to 0.5 mmφ or less. Therefore, it was set to 0.20% or more.

Cr is the most effective element for refining the pearlite lamellar structure. Tensile strength after patenting is 150kg / mm ²
To achieve the above, 0.30% or more must be added. On the other hand Cr
When the ratio is 1.00% or more, the cementite of the pearlite structure is divided into layers rather than layers, which hinders wire drawing workability and the pearlite transformation end time is 1 minute or more, which exceeds the allowable patenting time for industrial use. Will end up. Therefore, 1.00% or less.

Co is known as an element that promotes pearlite transformation. Even in the case of alloy steel, 1.0% or more is necessary to promote the pearlite transformation and keep the pearlite transformation ending time within 1 minute. When Si and Cr are added at the same time, 1.0% or more is necessary to make the pearlite lamellar shape uniform.

The effect becomes remarkable by adding Ni at the same time. Adding 5.0% or more of Co restricts industrial use from the viewpoint of cost, so the upper limit was defined.

Ni exhibits a pearlite lamellar alignment effect when added together with Co. Ni is required to be 0.10% or more in order to exert the pearlite lamellar alignment effect. Addition of 2.00% or more prolongs the pearlite transformation completion time and increases the pearlite colony size. The pearlite transformation completion time was kept within 1 minute, the pearlite colony size was reduced, and the squeezing after patenting was set to 30% or less, so that it was 2.00% or less.

O is a source of oxide inclusions because it does not form a solid solution in steel.
O can not be suppressed to less than 0.0001% by the current steelmaking technology, so oxide-based inclusions are generated. Therefore, it is necessary to soften it. By setting 0 to 0.0015% or more, the generation of hard inclusions disappears. The higher the O content, the larger the total amount of oxide-based inclusions. In order to prevent the stretched soft inclusions from affecting the twisting, fatigue, and twisting properties, it is necessary to keep O at 045% or less.
The hardest inclusion in steel is Al ₂ O ₃ alone.
However, in the case of complex inclusions, Al ₂ O ₃ has a function of melting into the oxide-based inclusions to lower the melting point and soften. in this case,
The optimum value varies depending on the addition of alloying elements. In the case of the present invention, if Al is 0.0005% or less, there is no softening action for oxide inclusions, so the content was made 0.0005% or more. When it becomes 0.0050% or more
Since Al ₂ O ₃ simple substance inclusions are generated, the content is limited to 0.0050% or less. This suppresses the appearance of hard inclusions and enables ultrafine wire drawing of 0.5 mmφ or less.

Next, regarding the pearlite transformation condition, if it is 570 ° C. or lower, local generation of bainite cannot be completely prevented. At 630 ° C or higher, the cementite shape becomes granular, so the temperature was set to 630 ° C or lower.
When the cementite shape is granulated, wire drawing with a wire drawing strain of 3 or more is impossible and high strength cannot be achieved.

In the case of an ultrafine wire having a wire drawing strain of 0.5 mm or less, the orientation of cementite in the pearlite structure in the wire drawing direction is completed with a wire drawing strain of 3.5 in the steel composition of the present invention. Therefore, the lower limit was set to 3.5. If the wire drawing strain is 3.5 or more, the toughness is stable and the strength is increased. However, the wire drawing strain
If it exceeds 5.5, peeling of the ferrite-cementite interface occurs and the toughness deteriorates rapidly. Therefore, the wire drawing strain is 5.
It was set to 5 or less.

According to the present invention, it is possible to stably manufacture a high-strength steel wire having a diameter of 0.5 mm or less and 350 kg / mm ² or more.

The present invention will be described below with reference to examples.

[Example] A steel having the components shown in Table 1 was melted using a 50 kg vacuum melting furnace. O was adjusted by the degassing time after vacuum melting.
Other alloying elements added pure metal. 5.5mm of these steels
After rolling into a φ wire material, wire drawing was performed. A 5.5 mmφ wire rod was drawn by a single-kama wire drawing machine and a continuous wiredrawing machine to obtain 2.0 to 0.30 mmφ steel wire.
This was subjected to lead patenting and then subjected to final wire drawing.

Table 2 shows the wire drawing conditions and the characteristic values of the obtained steel wire.

In Table 1, steel types A, X and Z are steels of the present invention. Steel type B is outside the lower limit of C, and D is outside the upper limit of C. E is out of the lower limit of Si, F is out of the upper limit of Si, G is out of the lower limit of Mn, H is out of the upper limit of Mn, I is out of the lower limit of Cr, J is out of the upper limit of Cr, and K is out of the upper limit of Cr.
Out of the lower limit of Co, L out of the lower limit of Ni, M out of the upper limit of Ni,
N is below the lower limit of O, Q is outside the upper limit of O. R is a steel type that is out of the lower limit of Al, and T is a steel type that is out of the upper limit of Al.

In Table 2, Test Nos. 1, 17, 18, 23, 24 and 25 are the present invention.

When using the current piano wire SWRS82A industrially used as extra-fine high-strength steel wire, the tensile strength of 0.30 mmφ is 340 kg / mm ² , and the fatigue life until fracture at a stress of 100 kg / mm ² is It is about 20,000 times, which is the highest strength and toughness level.

You can see how test No. 1 has high tensile strength and excellent toughness. No. 2 has low C, so both tensile strength and fatigue properties are low. Fatigue is comparable to conventional SWRS82A. Since No. 3 has a high C, it was broken during wire drawing due to the presence of mesh cementite. Since No. 4 has low Si, both tensile strength and fatigue properties are low as in No. 2. No. 5 has high Si, so 20 μm
The above hard SiO ₂ was generated and the wire was broken. Since No. 6 had a low Mn, surface cracks existed even after lead patenting, resulting in poor lubrication and disconnection. Since No. 7 had a high Mn, bainite was generated and the wire was broken. Since No. 8 has a low Cr content, both tensile strength and fatigue properties are low, similar to No. 2 and No. 4. No. 9 has high Cr, so 1
Partial granular cementite was generated and the wire was broken. No.1
Since 0 is low in Co and No. 11 is low in Ni, the alignment of the pearlite lamella is not good, so the twisting, twisting and fatigue properties after wire drawing are poor. Since No. 12 had a high Ni content, the pearlite colony size was too large, resulting in poor twisting, twisting, and fatigue properties. Nos. 13, 15, and 16 were all broken due to hard inclusions during wire drawing.

No. 14 had a tensile strength of 400 kg / mm ² or more, but due to the increase in the total amount of oxide inclusions, the twisting and fatigue properties were at a level inferior to SWRS82A.

No. 17 and 18 are the present invention, and the tensile strength is 400 kg / mm ² or more, and the toughness such as twisting is good. In No. 19, the pearlite transformation temperature was low, bainite was generated, and disconnection occurred during wire drawing. Since No. 20 had a high pearlite transformation temperature, part of the cementite was granulated, resulting in twisting and poor fatigue properties. N
o.21 has a short fatigue life due to small wire drawing strain
Not reached A level. No. 22 has a small twisting value because the wire drawing strain is too large, and the fatigue life is also extremely low. N
o.23, 24, 25 are the present invention, and have high tensile strength and good toughness.

From the above examples, it can be seen how the present invention is a method for producing a high-strength steel wire having excellent toughness.

[Effects of the Invention] As described above, according to the present invention, it is possible to manufacture an industrially stable high-strength steel wire for ultrafine wire by the present steelmaking technology, heat treatment technology, and wiredrawing technology.

Claims (1)

[Claims] 1. C: 0.80 to 1.20%, Si: 0.70 to 1.50%, Mn: 0.20 to 0.70%, Cr: 0.30 to 1.00%, Co: 1.0 to 5.0%, Ni: 0.10 to 2.00%, O: 0.0015 ~ 0.0045%, Al: 0.0005 ~ 0.0050%, 570 ~ 630 steel wire consisting of balance iron and unavoidable impurities
After pearlite transformation at a temperature of ℃, wire drawing strain 3.5 ~
5.5 {Drawing strain = ln (do / dn) ² , do: patenting wire diameter, dn: final wire drawing diameter}