JPH07204726A - Wire rod with excellent mechanical descaling - Google Patents

Abstract

(57) [Summary] [Purpose] In mechanical wire drawing after mechanical descaling, prevent the occurrence of poor lubrication and die wear due to residual scale caught in the surface irregularities. [Structure] The ratio of the depth to the bottom of the recess of the surface of the cross section perpendicular to the length direction of the wire is 0.5 or less, and the depth from the entrance of the recess is 7 μm or less. A wire material having excellent mechanical descaling properties, which has surface irregularities, a scale thickness of 3 μm or more and 15 μm or less, and a FeO ratio of 65% or more in the scale composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolled wire having excellent mechanical descaling characteristics (hereinafter referred to as "wire").

[0002]

2. Description of the Related Art In recent years, in wire drawing of wire rods, from the viewpoint of pollution problems and cost reduction, batch pickling method is being replaced with mechanical descaling (hereinafter referred to as MD) method. For this reason, in wire rods, the development of wire rods having good MD scale properties is urgently needed.

Up to now, it has been possible to generally adjust the residual scale amount of the wire by controlling the scale thickness and scale composition. However, in the MD method, since the scale is dropped by applying bending strain to the wire or brushing the surface, unlike the pickling by the batch method, it is difficult to uniformly and stably treat the entire surface,
Residual scale may be generated linearly along the rolling direction of the wire rod, or scale powder finely crushed to a size of 0.1 mm or less may be scattered on the surface. In the MD method, the residual scale locally left behind causes problems such as flaws due to poor lubrication in the wire drawing process and deterioration of die life, so that it is not possible to manufacture a wire having good MD properties. It is a property that it is necessary to reduce the residual scale as much as possible, or to prevent peeling before wire drawing so as not to adversely affect wire drawing.

From such a background, the technology described in JP-A-5-123739, which reduces the decarburization of the billet, particularly the decarburization at the corners to make the growth of the secondary scale after hot rolling uniform, 90 kg / cm before hot rolling of billet
Descaling is performed using high-pressure water of ² or more so that the average surface roughness of the wire is 1.5 μm or less.
The technique described in Japanese Patent No. 4702 is disclosed. But,
As a result of many detailed investigations, the decarburization at the corner of the billet was not particularly large, and the position where the decarburization part and the residual scale were generated did not match. It is unlikely that the billet temperature will drop significantly when descaling with high-pressure water, so in actual operating conditions, the billet heating temperature in the heating furnace must be high, and the billet surface must have a sub-light such as firelight. The environment must be such that it is easy to scale, and when descaling with high-pressure water, the temperature of billet corners is particularly likely to drop, and the hardness inside the billet becomes uneven, causing uneven deformation during rolling. It was a cause of inducing coarsening of the surface irregularities. Further, since the average surface roughness cannot evaluate the shape of the irregularities on the surface of the wire material where scale is likely to remain, this index has not been able to obtain a sufficient effect.

[0005]

In view of the above situation, the inventors of the present invention reduce the residual scale as much as possible, or prevent peeling before wire drawing and adversely affecting wire drawing. We conducted a detailed study on the technology to be applied. In other words, not only was the control of the peeling ratio of the scale that was distorted with respect to the amount of scale on the entire surface of the wire rod carried out, but the detailed characteristics of the scale that remained after the strain was also investigated.

As a result, the peeling rate of the scale depends on the thickness and composition of the scale, but the peeling rate is 100.
Unless it is%, the residual scale is always a problem in the MD method. As a result of classifying the shape of the surface irregularities of the wire on which the scale easily remains and statistically organizing it, the residual scale exists on the irregularities of the wire surface, Observing the unevenness in a cross section perpendicular to the length direction of the wire, the ratio of the length of the entrance of the wire surface to the length from the entrance to the bottom of the recess is greater than 0.5,
And the length from the entrance of the wire surface to the bottom of the recess is 7 μm
It has been found that when the length is longer (for example, when the inlet length is 14 μm and the depth is deeper than 7 μm), the scale remains easily.

Further, as a result of detailed investigation on how this unevenness occurs at each rolling stage of the wire rod, when the billet is rolled, especially the biting of the scale of the corner portion into the billet and the cross section of the billet It was found that this was caused by the non-uniform deformation of the billet surface layer part during rolling due to the temperature unevenness and the like. An object of the present invention is to provide a wire rod having a small residual scale and excellent mechanical descaling properties.

[0008]

[Means for Solving the Problems] In order to eliminate surface unevenness where residual scale is likely to occur, the temperature of the corner portion of the billet is set to 10 degrees from the surface portion before leaving the heating furnace and rough rolling.
A wire rod manufactured by completely removing the scale attached to the surface, including the corners, without cooling at 0 ° C or more and rolling without causing non-uniform deformation is perpendicular to the length direction of the wire rod. It was found that the surface irregularities observed in the cross section had the following geometrical features.

That is, according to the present invention, the ratio of the depth to the bottom of the recess on the surface of the cross section perpendicular to the longitudinal direction of the wire is 0.5 or less, and the depth from the entrance of the recess is less than 0.5. Has a surface roughness of 7 μm or less and the thickness of the scale is 3 μm
A wire rod having an excellent mechanical descaling property, which has a FeO ratio of 65% or more in the composition of the scale of 15 μm or less, is a gist.

[0010]

The present invention clarifies the cross-sectional shape of a wire having a small residual scale. That is, while increasing the scale separation ratio due to tensile strain by controlling the thickness and composition of the scale, the scale residue, which is a problem in the MD method, is observed in a cross section perpendicular to the length direction of the wire and When the ratio between the length of the entrance and the length from the entrance to the bottom of the recess is greater than 0.5 and the length from the entrance of the wire surface to the bottom of the recess is longer than 7 μm (for example, if the entrance length is 14 μm It was found that scale remains easily when the depth is deeper than 7 μm.

The ratio of the depth to the bottom to the length of the entrance of the recess on the surface of the cross section perpendicular to the length direction of the wire is 0.5.
The reason for limiting to the following is that when the ratio is larger than 0.5, the scale is likely to remain in the concave portion in the MD method. In particular, if there is a recess having an acute angle of 1.0 or more, it becomes difficult to completely remove the scale even by a combination of methods such as bending, brushing, and shot blasting.

The reason why the depth from the entrance of the recess is limited to 7 μm or less is that if the depth is larger than 7 μm, the scale tends to remain in the recess. This is almost the same as the reason for limiting the depth ratio to 0.5 or less. In brushing and shot blasting used in the MD method, the scale is peeled off by directly applying an external force to the scale. , It is very difficult to sweep out the scale left on the bottom of the recess. If this depth is 7 μm or less, it is possible to open it by applying bending strain and sweep it out by brushing or the like.

[0013] Here, even if any one of the above-mentioned irregularities is confirmed in any cross section, it is about 500 at 1 ton.
Considering the total wire length of 0 m, it indicates that a sufficient amount of residual scale remains to deteriorate the die life during wire drawing. On the other hand, the surface roughness obtained by measuring the depth of the unevenness with a roughness meter or the like, for example, the index of the unevenness such as Rmax or Ra, does not accurately evaluate each unevenness in order to calculate the measured value. In addition, when the scale is clogged up to the surface of the wire in the recess, it is not possible to measure the presence of the scale or the roughness with a roughness meter, so the correlation between the index of the roughness and the MD property becomes extremely small. . Further, in the index of unevenness by a roughness meter, the unevenness in the depth direction has a sensitivity of several thousand times, so it is possible to measure up to the order of 1 μm, but the magnification in the length direction for the entrance of the recess is at most several. It is about 100 times, and the minute irregularities on the chart are measured on the actual wire having a plateau-like or basin-like length. Therefore, as in the present invention, the entrance length and depth are measured. The shape of the unevenness is completely different from the one in which MD is limited and does not serve as an index for evaluating MD property.

The reason why the thickness of the scale is limited to 3 μm or more and 15 μm or less is that if the thickness of the scale is thinner than 3 μm, even if bending is performed by bending or the like, the scale is not sufficiently distorted and residual scale is formed. This is because it becomes easier, and when the scale thickness is thicker than 15 μm, subscales such as firelite are generated, which may hinder the releasability.

The proportion of FeO in the scale composition is 65
% Is because the FeO fraction decreases and Fe ₂ O ₃ decreases.
This is because the ratio of the fine scale of Fe ₃ O ₄ and Fe ₃ O ₄ increases and the releasability deteriorates.

[0016]

EXAMPLE A wire rod according to the present invention is provided with a billet corner portion by adjusting the spray pressure and the water flow rate when the scale on the billet surface heated in a heating furnace is completely removed by a water jet. The temperature difference of the surface is 1
Perform hot rolling not to exceed 00 ° C, and at the rolling temperature of 1000 ° C or higher in the final pass,
It was manufactured by winding the wire at a temperature of 0 ° C. or lower and controlling the cooling rate after winding to 15 ° C./second or lower. In the comparative example, the wire material shown in Table 1 was manufactured by changing the temperature unevenness of the billet, the rolling temperature, the winding temperature, and the like.

One of the 2 ton wire rod coils
After bending the ton, the scale was removed with a wire brush. After that, the coil was cut every 100 m and sampling was performed from about 50 points. For each sample, the presence or absence of residual scale and the surface irregularities were confirmed from the cross section perpendicular to the length direction of the wire. The remaining 1to
n was used to investigate the scale characteristics of the wire. FIG. 1 is a photomicrograph showing the surface condition of a cross section of the wire rod according to the present invention, which is perpendicular to the longitudinal direction. No irregularities are observed at the boundary between the base metal and the scale, and a scale of about 3 μm is attached. ing. FIG. 2 is a micrograph showing a surface state of a cross section of a comparative material after MD, which is observed in a cross section perpendicular to the longitudinal direction,
In this example, unevenness is recognized on the surface and scale remains in it.

In Table 1, the scale thickness means the wire thickness.
Smell at 45 points on the circumference of the cross section perpendicular to the length direction at 45 ° intervals
The thickness of the scale was measured and calculated as the average value.
Scale composition is a scale with a length of 30 cm every 100 m
Sample the part that does not fall and use a torsion tester
The scale is peeled off, and FeO and Fe are analyzed by X-ray diffraction. ₂
O₃, Fe₃O_FourThe diffraction intensity of the
The ratio of the FeO diffraction intensity to be used was defined as the FeO ratio. Depth ratio
The number of irregularities of more than 0.5 means that the wire rod is cut every 100 m.
A cross-sectional sample perpendicular to the length direction is taken with a microscope (magnification 400
Of all surfaces observed on one cross-section
Enter the length from the entrance of the recess to the bottom of the recess in the unevenness.
If the value divided by the length of the mouthpiece exceeds 0.5, the depth ratio
It was counted as unevenness of more than 0.5. In addition to the depth ratio,
A recess with a length of more than 7 μm from the entrance to the bottom of the recess
Was counted as the number of irregularities having a depth of more than 7 μm.

[0019]

[Table 1]

Levels 1 to 5 are the wire rods of the examples of the present invention, and in this sample, no fine scale remained after MD. Levels 10 and 11 are obtained by changing the scale thickness of the coil. It can be seen that residual scale occurs when the scale thickness is thinner than 3 μm and thicker than 15 μm.

Level 12 is obtained by changing the scale composition. It can be seen that when the FeO ratio is smaller than 65%, the scale remains even after MD. Levels 6, 7, 8, 9
Shows the influence of the unevenness depth ratio of more than 0.5 and the number of unevennesses having a depth of more than 7 μm. These are 1 in 1 cross section
It is clear that if it is enough, the scale remains and it is important for the MD property to eliminate the surface irregularities.

Further, regarding the number of irregularities having a depth ratio of 0.5 or less and the number of irregularities having a depth of 7 μm or less, it is difficult to distinguish from the waviness on the surface of the wire material, and therefore a measurement error by a measurer may occur. Although it becomes large, the results of counting at 400 times magnification are as shown in Table 1. As is clear from this result, these are not related to the occurrence of residual scale, and in the case of the example of the present invention, it is understood that the number of these irregularities does not affect the MD property.

[0023]

EFFECTS OF THE INVENTION Since the wire rod according to the present invention has a good MD property, it is difficult to cause surface flaws on the wire rod and poor lubrication due to residual scale, and a stable wire drawing state can be obtained by a wire rod secondary maker, and quality of the wire rod can be improved. It has become possible to manufacture high steel wires.

[Brief description of drawings]

FIG. 1 is a micrograph showing a surface state of a cross section of a wire according to the present invention.

FIG. 2 is a micrograph showing a characteristic surface irregularity state after MD of a wire rod of a comparative example. A in the photograph is a depth ratio of 0.
5 is an example of irregularities having a depth of more than 7 μm. In each of the irregularities, the scale remains on the surface of the wire rod.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C21D 9/52 103

Claims (1)

[Claims] 1. The ratio of the depth to the bottom to the length of the entrance of the recess on the surface of the cross section perpendicular to the length direction of the wire is 0.
It is characterized by having a surface roughness of 5 or less and a depth from the entrance of the recess of 7 μm or less, a thickness of the scale of 3 μm or more and 15 μm or less, and a proportion of FeO in the composition of the scale of 65% or more. A wire rod with excellent mechanical descaling properties.