JP3487956B2 - Wire material with excellent descaling properties - 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 carbon steel wire rod having excellent wire drawability and mechanical descaling.

[0002]

2. Description of the Related Art Conventionally, high-carbon steel wire rods are hot-rolled and then subjected to an in-line heat treatment process to obtain wire rods, which are then pickled or mechanically descaled to remove scale adhering to the steel surface. It is used by repeatedly drawing wire by drawing wire and intermediate heat treatment to form a thin wire diameter, and then performing final patenting treatment to obtain a high strength wire by drawing wire.

Therefore, in manufacturing the final product,
The better the workability of the wire rod after hot rolling, the easier the intermediate heat treatment step can be omitted, and thus the easier it is to reduce the manufacturing cost.

As a method for adjusting the mechanical properties of the hot rolled wire rod, there are a Stelmore method by blast cooling and a method using a molten salt as a cooling medium. There is Japanese Patent Publication No. 59-37725, which uses a molten salt, but it is a direct heat treatment method capable of obtaining high strength equivalent to lead patenting by improving workability.

Further, bainite is used in Japanese Patent Laid-Open Nos. 6-17190, 6-17191 and 6-19.
Although -17192 and the like are disclosed, these are steel wire rods having excellent workability, which are characterized by having a bainite structure of 80% or more and adjusting to a predetermined strength and ductility. However, there is a problem that it is extremely difficult to set the bainite ratio shown in this publication to 80% or more with a wire diameter of 5.0 mmφ or more.

[0006] In the case of a steel wire rod which is further excellent in workability, the scale characteristics of the steel surface are an important factor for carrying out multi-step processing continuously, and wire drawing is only performed by controlling the structure after heat treatment as in the past. Sex cannot be well controlled.

[0007] There are a pickling method and a mechanical descaling method as a method for removing the scale of the steel wire. The pickling method is widely used because it can sufficiently remove the scale, but since an acid is used, problems such as pollution may occur, and the mechanical descaling method is often applied.

On the other hand, the mechanical descaling method is a method of removing the scale by bending the wire material with multiple rolls, and its scale removal ability is greatly affected by the surface texture.

For this reason, in Japanese Patent Laid-Open No. 52-10829, the wire is hot-rolled and then kept or heated at 700 ° C. or more to increase the scale amount to 0.6% or more and to produce a scale containing a large amount of FeO. Is proposed. However, in the case of a steel wire having excellent workability, the initial strength is low and the ductility is high, so that the adhesion of the scale is improved and residual scale is likely to occur. Therefore, the mechanical descaling property cannot be sufficiently controlled only by the conventional method.

[0010]

In the present invention, C
In the field of high carbon steel whose content is 0.6% by weight or more, when the mechanical descaling method is used to remove the scale of the steel material, the scale is sufficiently removed, and further wire drawing using a drawing die. The wire diameter is 3.0
An object of the present invention is to provide a wire rod having a workability of 3.7 or more in true strain in a wire diameter of mmφ or more, which is excellent in wire drawing workability and mechanical descaling property.

[0011]

The workability of a wire is greatly affected by the form of cementite in the wire. The shorter the length of cementite observed in the cross section of the wire, the better the drawability because the growth of dislocations introduced during working is suppressed.

Similarly, the larger the average spacing of cementite observed in the cross section of the wire, the more suppressed the growth of dislocations introduced during working, and the better the drawability.

Further, when mechanical descaling is performed, scale peeling is caused by propagation of cracks generated at the interface between the wire and the scale. The propagation of this crack depends on the irregularities on the surface of the wire, and the smaller the interface irregularities, the easier the crack propagates. In addition, in the scale portion remaining after mechanical descaling, unevenness is seen at the interface between the wire rod and the scale.

[0014] Therefore the object of the present invention, the amount of C obtained by hot rolling on a 0.6% or more by weight%, bainite
In a steel wire rod having a gauze structure, a pearlite structure, or a mixed structure thereof, the cementite existing in the cross section of the wire has a specified shape, and the steel-scale interface roughness of the wire in the cross section of the wire is within the specified range. It is solved by providing a wire rod for descaling which is excellent in wire drawability.

[0015] That is the amount of C where the gist obtained by rolling (1) heat of the present invention in weight percent 0.6
% On more than, bainite, pearlite or child
In the steel wire rods of these mixed structures, the shape of cementite existing in the cross section of the wire rod has the following characteristics, the average length of cementite is 0.7 μm or less, the average interval of cementite is 900 Å or more, and the steel of the wire rod in the cross section of the wire rod A wire material having excellent descaling properties, characterized by having 50% or more of a region having a maximum scale interface roughness of 10 μm or less and having excellent wire drawability.

(2) The steel composition is characterized by containing C: 0.6 to 1.5% Si: 0.1 to 2.0% Mn: 0.1 to 2.0% by weight. A wire rod excellent in descaling property according to (1) above.

(3) A wire rod excellent in descaling property according to the above (2), characterized in that one or more of the following steel components are added. Cr: 0.1 to 2.0% Ni: 0.1 to 2.0% Cu: 0.1 to 2.0% Mo: 0.1 to 2.0% Co: 0.01 to 2.0% .

(4) The wire rod excellent in descaling property according to (2) or (3), characterized in that one or more of the following steel components are added. Ti: 0.005-0.03% Nb: 0.005-0.03% V: 0.005-0.03% Al: 0.005-0.03% B: 0.0001-0.003% .

(5) The steel composition is P: 0.02% or less and S: 0.02% or less, which is excellent in descaling property according to the above (2), (3) or (4). wire.

[0020]

The reason for limiting the constituent features of the present invention will be described.
The reasons for limiting the chemical components are as follows. C is an economical and effective strengthening element. In order to secure the required strength as a steel wire, C must be at least 0.6% or more. If it is too high, the ductility decreases, so the upper limit is made 1.5%.

Si is an element necessary for deoxidizing steel. Therefore, when the content is too small, the deoxidizing effect becomes insufficient, so the lower limit is made 0.1%. Also, Si
Is a solid solution in the ferrite phase in the pearlite formed after heat treatment to increase the strength after patenting, but on the other hand reduces the ductility of ferrite, so the upper limit was 2.0%, which does not adversely affect the wire drawability. .

Mn is added in order to secure the hardenability of steel.
Add 1% or more. However, addition of a large amount of Mn causes segregation, and a supercooled structure such as bainite and martensite is generated during patenting, which impairs the subsequent wire drawability, so the upper limit was made 2.0%.

If S is contained in a large amount, the ductility of the wire is impaired, so the content is preferably 0.02% or less.
If P is contained in a large amount, the ductility of the wire is impaired, so the content is preferably made 0.02% or less.

Cr has the effect of suppressing the appearance of abnormal portions of cementite and further refining pearlite. However, a large amount of addition increases the dislocation density in the ferrite after heat treatment, and therefore the ductility of the ultrafine wire after drawing is significantly deteriorated. Therefore, the addition amount of Cr is set to 0.1% or more where the effect can be expected, and the upper limit is set to 2.0% or less which increases the dislocation density in ferrite and does not deteriorate ductility.

Since Ni has the same effect as Cr, if necessary, 0.1% or more is added to exhibit the effect. If Ni is added too much, the ductility of the ferrite phase deteriorates, so the upper limit is made 2.0%.

Cu is an element that improves the corrosion fatigue properties of the wire, so if necessary, 0.1% to exert its effect.
It is desirable to add the above. If Cu is added too much, the ductility of the ferrite phase deteriorates, so the upper limit is made 2.0%.

Mo is an element added in order to improve the hardenability of the wire rod, and if necessary, it exerts its effect.
% Or more is desirable. If Mo is added too much, the hardenability will be improved and micro martensite will be precipitated in the segregated portion, so the upper limit is made 2.0%.

Co is an element added to improve the ductility of the wire, and if necessary 0.01% to exert its effect.
It is desirable to add the above. If the addition amount of Co is too large, the hardenability is increased and micro martensite is likely to be precipitated in the segregated portion, so the upper limit is made 2.0%.

Ti, Nb, V, and Al can make the γ grain size fine and the microstructure unit formed thereafter to make the toughness value improved, so that 0.005 is effective.
% Or more, and the upper limit is 0.03% or less, which does not adversely affect other properties.

B is added to improve the hardenability, and 0.0001% or more, which is effective, is added. The upper limit of the hardenability is too high, so that the treatment becomes difficult.
003% or less.

The workability of the wire is greatly affected by the form of cementite in the wire. The shorter the length of cementite observed in the cross section of the wire, the more the growth of dislocations introduced during processing is suppressed. Therefore, the average length of cementite must be at least 0.7 μm or less. Fig. 1 shows the relationship between the average length of cementite and wire drawability.

Similarly, the larger the average spacing of cementite observed in the cross section of the wire, the more the growth of dislocations introduced during processing is suppressed. Therefore, the average spacing of cementite must be at least 900Å or more. Fig. 2 shows the relationship between the average cementite spacing and wire drawability.

If the cementite can be adjusted to the above-mentioned form, the initial strength of the wire rod can be lowered and the work hardening rate during wire drawing can be lowered, so that the wire rod having excellent workability can be obtained.

Further, the steel-scale interface roughness of the wire in the transverse section in the rolling direction of the wire is an important factor affecting the scale peeling property during mechanical descaling. If the interface roughness is large, crack propagation is less likely to occur, and the scale remains after mechanical descaling. A wire rod having excellent wire drawing workability has a large aperture value as compared with a conventional wire rod, is likely to be locally deformed on the surface of the wire rod, and requires further improvement in descaling property. As shown in FIG. 3, the residual scale amount, which hinders the processing in the subsequent process, is usually 0.
It is set to 050% or less, and therefore, the upper limit of the interface roughness is 1 as the limit at which the amount of residual scale does not hinder the subsequent process.
It was set to 0 μm.

[0035]

EXAMPLES In the present invention, wire rods were manufactured by a method of adjusting the morphology of cementite by separately producing a bainite structure, a pearlite structure and a mixed structure thereof by adjusting cooling after rolling.

Table 1 shows the chemical composition of the test steel. After these test steels were manufactured into billets of 122 mm square, they were hot-rolled to 4.5 to 16.0 mmφ and adjusted and cooled to obtain wire rods having the structures shown in Table 2.

The drawability test of these test steels was carried out using dry drawing. The wire drawing was carried out so that the area reduction rate in each pass was between 15 and 20%.
For raw drawability, processing is performed up to the wire drawing limit, and the true strain is 3.8.
When the above processing was possible, it is shown in Table 2, and when it cannot be processed, it is shown in Table 2.

In the evaluation of mechanical descaling (MD) property, the scale was removed by applying a tensile strain of 6% and the scale amount was expressed as a percentage of the sample weight.

Regarding the steel-scale interface roughness of the wire in the transverse section in the rolling direction of the wire, the maximum height was measured by microscopic observation of the section according to the method of JIS B0601.

In Table 3, 1-45 are examples of the steels of the present invention, and 46-51 are examples of comparative steels. In each of the examples of the present invention, the cementite shape is adjusted according to the present invention, and the steel-scale interface roughness of the cross section in the wire rolling direction is 10 μm or less at the maximum height. The residual scale amount of No. 2 is low, and both are suppressed to 0.050% or less.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

Comparative steels 46 and 47 differ from the present invention in that the cementite length is as long as more than 0.7 μm. Comparative steel 4
8 and 49 differ from the present invention in that the cementite spacing is as small as less than 900Å. In the comparative steels 50 and 51, the roughness of the steel-scale interface in the cross section in the wire rolling direction is 10 μm or more at the maximum height, and the residual scale amount after mechanical descaling is 0.050% or more, which is a high value. The points shown are different from the present invention. As described above, the comparative steels are all different from the present invention, and it is difficult to apply them as a wire rod for mechanical descaling having excellent wire drawability.

[0045]

As described above, the wire produced according to the method of the present invention has a much improved descaling property as compared with the conventional method, which results in 3 after hot rolling.
In the wire rod of mmφ to 16 mmφ, it is possible to obtain a wire rod for mechanical descaling which is more excellent in wire drawing workability than the conventional method, the intermediate heat treatment step can be omitted, and the manufacturing cost can be easily reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the length of cementite and the critical strain for wire drawing.

FIG. 2 is a diagram showing a relationship between an average interval of cementite and a wire drawing limit.

FIG. 3 is a diagram showing a relationship between residual scale amount and steel-scale interface roughness.

Claims (5)

(57) [Claims] 1. A C amount obtained by hot rolling on a 0.6% or more by weight%, bainite is pearlite structure
Or , in steel wire rods of these mixed structures, the shape of cementite existing in the wire rod cross section has the following characteristics, the average length of cementite is 0.7 μm or less, and the average interval of cementite is 900 Å or more. A wire rod having an excellent descaling property, which has a steel-scale interface roughness with a maximum height of 10 μm or less and has an excellent wire drawability. 2. A steel composition containing C: 0.6 to 1.5% Si: 0.1 to 2.0% Mn: 0.1 to 2.0% by weight. Item 1. A wire rod having excellent descaling properties according to item 1. 3. A wire rod having excellent descaling properties according to claim 2, wherein one or more of the following steel components are added. Cr: 0.1 to 2.0% Ni: 0.1 to 2.0% Cu: 0.1 to 2.0% Mo: 0.1 to 2.0% Co: 0.01 to 2.0% 4. A wire rod having excellent descaling properties according to claim 2, wherein one or more of the following steel components are added. Ti: 0.005-0.03% Nb: 0.005-0.03% V: 0.005-0.03% Al: 0.005-0.03% B: 0.0001-0.003% 5. The wire rod excellent in descaling property according to claim 2, 3 or 4, wherein the steel component is P: 0.02% or less and S: 0.02% or less.