JPH08295992A - Descaling wire - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a high carbon steel wire rod for descaling, which is excellent in wire drawability. [Structure] In a steel wire rod having a C content of 0.6% by weight or more by hot rolling, the true stress-true strain curve in a tensile test has the following characteristics, and the maximum deformation stress is 800 MPa or more and 1200 MPa or less. more than 20% yield ratio σ _{0 2} / σ _uts 0.5 or more (where sigma _{0 2} 0.2% proof stress, sigma _uts is the maximum deformation stress.) further the steel wire rod in the wire rod cross section -. scale A wire material for descaling with excellent wire drawability, which has a maximum interface roughness of 10 μm or less. [Effect] According to the method of the present invention, the descaling property is further improved as compared with the conventional method, and it is possible to obtain a descaling wire rod excellent in wire drawing workability in a wire rod of 3 mmφ to 16 mmφ after hot rolling. Therefore, the intermediate treatment process can be omitted, and the manufacturing cost can be easily reduced.

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 for descaling which is excellent in wire drawability.

[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.

Therefore, in Japanese Patent Laid-Open No. 52-10829, it is proposed to heat or heat the wire rod at 700 ° C. or higher after hot rolling to increase the scale amount to 0.6% or more and to prepare a scale containing a large amount of FeO. Has been done. 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 scale removal of steel materials is performed by the mechanical descaling method, the scale is sufficiently removed and wire drawing using a drawing die is performed. The wire diameter is 3.0
An object of the present invention is to provide a wire rod for descaling, which has a workability of 3.7 or more in true strain in a wire diameter of mmφ or more and is excellent in wire drawing workability.

[0011]

[Means for Solving the Problems] In order to improve the workability of a wire, the workability of the wire can be improved by adjusting the maximum deformation stress, total elongation and yield ratio of a stress-strain curve obtained from a tensile test. .

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 the cracks is related to the irregularities on the surface of the wire, and the smaller the interface irregularities, the easier the cracks propagate. In addition, in the scale portion remaining after mechanical descaling, unevenness is seen at the interface between the wire rod and the scale.

The object of the present invention is to provide a steel wire having a C content of 0.6% by weight or more, which is obtained by hot rolling, and has a property that a true stress-true strain curve in a tensile test is defined. Further, it is solved by providing a wire rod for descaling excellent in drawability, characterized in that a steel-scale interface roughness of the wire rod in a cross section of the wire rod is within a specified range.

That is, the gist of the present invention is: (1) The amount of C obtained by hot rolling is 0.6% by weight.
% Of steel wires, the true stress-true strain curve in the tensile test has the following characteristics, the maximum deformation stress is 800 MPa or more and 1200 MPa or less, the total elongation is 20% or more, and the yield ratio σ _0.2 / σ _uts is 0.5 or more ( However, σ _0.2 is 0.2% proof stress, and σ _uts is the maximum deformation stress. Furthermore, the maximum height of the steel-scale interface roughness of the wire in the cross section of the wire is 10 μm or less. Excellent descaling wire.

(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. The wire rod for descaling according to (1) above.

(3) The wire material for descaling according to (2) above, 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) The wire material for descaling according to (2) or (3) above, 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 descaling wire according to (2), (3) or (4), wherein the steel composition is P: 0.02% or less and S: 0.02% or less.

[0019]

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, if 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 an amount of 0. 1 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 its 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, 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 0.01% to exert its effect if necessary.
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 finer and the structure units formed thereafter finer to improve the toughness value, 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 in which the effect is recognized is added. The upper limit of the hardenability is too high, which makes the treatment difficult.
003% or less.

The maximum deformation stress in the true stress-true strain curve corresponds to the degree of refinement of the material structure. Therefore, at least 800 MPa or more of strength is required for uniform and stable deformation, and 1200 is required for reducing work hardening.
It is necessary to adjust to MPa or less. The relationship between tensile strength and wire drawing limit is shown in FIG. However, the wire drawing limit is true strain.

The total elongation in the true stress-true strain curve is an index of the uniformity of the material, and in order to secure the true strain of 3.8 or more, it is necessary to secure the workability of at least 20% or more. is there. The relationship between total elongation and wire drawing limit is shown in FIG.

The yield ratio in the true stress-true strain curve depends on the shape of cementite, and the yield ratio decreases as the cementite is divided. In order to reduce the work hardening rate, it is better that the cementite is divided, so it is necessary to adjust the yield ratio to at least 0.5 or more. Fig. 3 shows the relationship between the yield ratio and the wire drawing limit.

As a method of achieving such characteristics of the true stress-true strain curve, any of a pearlite structure, a bainite structure and a mixed structure thereof obtained by controlled cooling after rolling may be used.

Further, the structure obtained by performing controlled cooling after rolling may be tempered and annealed to satisfy the characteristics of the true stress-true strain curve.

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 larger aperture value than that of a conventional wire rod, is likely to be locally deformed on the surface of the wire rod, and requires further improvement in descaling. As shown in Fig. 4, the amount of residual scale, which hinders the processing in the subsequent process, is usually 0.050.
% Or less, and the upper limit was set to 10 μm as the limit at which the amount of residual scale does not hinder the subsequent steps.

[0035]

EXAMPLE In the present invention, wire rods were manufactured by a method of adjusting the morphology of cementite by separately forming 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.

These wire rods after hot rolling were processed by G. L. = 2
The test was carried out at 00 mm to obtain a true stress-true strain curve. Maximum deformation stress obtained from this true stress-true strain curve. Table 2 shows the total elongation and the yield ratio.

The pullability 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), the scale was removed by applying a tensile strain of 6%, and the scale amount was expressed as a percentage of the sample weight.

The steel-scale interface roughness of the wire in the transverse section in the rolling direction of the wire is determined by the method of JIS B0601.
The maximum height was measured by microscopic observation of the cross section.

1 to 45 shown in Table 3 are examples of the steels of the present invention, and 46 to 50 are examples of comparative steels.

In the examples of the present invention, the maximum deformation stress, the total elongation, and the yield ratio all satisfy the conditions according to the present invention, and the maximum height of the steel-scale interface roughness of the cross section in the rolling direction of the wire rod is 10 μm.
Since it is less than m, it has excellent raw drawability, and the residual scale amount after mechanical descaling is low.
It is held below. A typical example of the true stress-true strain curve is shown in FIG.

Comparative steels 46 and 47 have high maximum deformation stress,
The low total elongation is different from the present invention. Comparative steel 48 differs from the present invention in that the yield ratio is low. Comparative steel 49 is tempered, but differs from the present invention in that the total elongation is low due to inappropriate treatment conditions.

In Comparative Steel 50, the maximum height of the steel-scale interface roughness of the cross section in the wire rolling direction is 10 μm or more, and the residual scale amount after mechanical descaling is all.
This is different from the present invention in that it shows a high value of 0.050% or more.

As described above, each of the comparative steels is different from the present invention, and it is difficult to apply it as a descaling wire having excellent wire drawability.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

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, the wire rod for descaling which is more excellent in wire drawing workability than the conventional method can be obtained, 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 a relationship between tensile strength and working limit strain.

FIG. 2 is a diagram showing the relationship between total elongation and critical strain for wire drawing.

FIG. 3 is a diagram showing a relationship between a yield ratio and a wire drawing limit.

FIG. 4 is a diagram showing a relationship between a residual scale amount and a steel-scale interface roughness.

FIG. 5 is a diagram showing a true stress-true strain curve.

Claims (5)

[Claims] 1. A steel wire rod having a C content of 0.6% by weight or more obtained by hot rolling has the following characteristics in a true stress-true strain curve in a tensile test and a maximum deformation stress of 800 MPa or more and 1200 MPa. The total elongation is 20% or more. Yield ratio σ _0.2 / σ _uts is 0.5 or more (where σ _0.2 is 0.2% proof stress, σ _uts is the maximum deformation stress). A wire material for descaling with excellent wire drawability, which has a maximum interface roughness of 10 μm or less. 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. The wire rod for descaling according to Item 1. 3. The wire material for descaling 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. The wire material for descaling 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 material for descaling according to claim 2, wherein the steel composition is P: 0.02% or less and S: 0.02% or less.