JP3226723B2 - Wire with excellent mechanical descaling - Google Patents

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 (hereinafter referred to as a wire) having excellent mechanical descaling characteristics and having a scale which can be easily removed by mechanical descaling.

[0002]

2. Description of the Related Art A scale is formed on the surface of a wire manufactured by hot rolling, and it is necessary to remove the scale formed prior to wire drawing or the like in secondary processing of the wire. 2. Description of the Related Art In recent years, in wire drawing of a wire rod, from the viewpoint of pollution problems and cost reduction, a batch pickling method is being replaced with a mechanical descaling (hereinafter, referred to as MD) method. Therefore, it is desired to develop a wire having a good MD property and a scale property.

In view of such a background, Japanese Patent Laid-Open No.
Increase the thickness of the scale as described in -10829,
A method of increasing the FeO ratio of the scale and reducing the residual scale amount of the wire is disclosed in Japanese Patent Application Laid-Open No. HEI 5-123739 by applying a decarburizing prevention material to the billet to reduce the decarburization of the billet, particularly the corner portion. A method for making the growth of the secondary scale after hot rolling uniform, and a method disclosed in JP-A-61-15470.
As described in the publication 2, 90 kg / c before hot rolling of billet
A method is disclosed in which high-pressure water of m ² or more is jetted to perform descaling to reduce the average surface roughness of the wire to 1.5 μm or less.

However, such a conventional technique has the following problems and cannot be said to be a sufficient method. JP-A-52-1
In the method according to No. 0829, it is difficult to completely remove the scale even when the wire is subjected to bending strain by the MD method and the surface is further brushed because the scale is formed thickly, which causes a decrease in the yield in the stretching step. Yes,
Unlike pickling by batch, it is difficult to remove the scale uniformly and stably over the entire surface, and finely crushed scale powder of 0.1 mm or less may be scattered on the surface of the wire. An increase in the amount of the residual scale locally left causes problems such as generation of defects due to poor lubrication in the wire drawing step and deterioration of the die life, and is not always a sufficient method.

Further, the technique of applying a decarburization preventing material to a corner of a billet requires a work step of applying the decarburizing preventing material to the billet before heating, which increases the work load and further increases the work space. There is a problem that costs increase, such as securing of This technique improves scale releasability by preventing decarburization. Therefore, this technique is limited to the application to steel types having a relatively high carbon content of 0.4% or more and cannot be applied to low-carbon steel wire rods.

In the descaling method using high-pressure water, the billet temperature in the heating furnace must be increased in actual operating conditions because the billet temperature is greatly reduced. In addition, a thick sub-scale is likely to be formed during heating, and the scale loss of the steel material is large, leading to a decrease in yield, and there are problems in quality and cost.
On the other hand, when descaling with high-pressure water, the temperature of the billet corner is particularly easy to decrease, the load on the rolling equipment increases, and this may cause rolling trouble, and the hardness in the billet becomes uneven, and There is a problem that surface unevenness is coarsened due to uneven deformation at the time.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention relates to a scale having an excellent peeling property which minimizes residual scale even by the MD method and has no adverse effect upon drawing. Detailed examination of properties and peelability by MD was performed to clarify scale characteristics that are easily peeled by the MD method. It has been conventionally known that the peeling ratio of the scale by the MD method is higher when the scale is thicker. However, when the scale is thicker, the iron portion of the steel material is peeled off as a scale, resulting in a loss and lowering the yield. . Therefore, the present invention provides a thinner wire having a scale with good peelability and excellent mechadism.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the gist of the present invention is that pores existing in the oxide scale on the surface of the wire have a diameter of 15 mm.
Wire material excellent in mechanical descaling property of volume% or more. Alternatively, there is provided a wire excellent in mechanical descaling, characterized in that the average diameter of pores in the oxide scale on the surface of the wire is 100 μm or less.

[0009]

The MD method is a method of forming a crack in the scale or at the interface between the wire and the scale by applying a strain to the wire and separating the wire. If the strength of the scale can be reduced, the crack can be easily generated in the scale. In addition, the growth of the crack can be promoted more easily.

As the physical properties of the conventional scale, the thickness of the scale and the FeO ratio as the scale composition are controlled. This is the strength of FeO as shown in Table 1 Fe ₂ O
₃ , more FeO than Fe ₃ O ₄
This is because a scale composition having the following is considered to be advantageous.
However, in order to increase the FeO ratio, it is generally necessary to form a secondary scale at a high temperature, and the scale becomes thick. For this reason, it has been difficult to achieve a thin, high-FeO ratio scale property with contradictory properties.

[0011]

[Table 1]

On the other hand, if the strength of the scale can be further reduced, the scale properties can be made thin and have good releasability irrespective of the FeO ratio. Therefore, means for reducing the strength of the scale are studied in detail. Was. The present inventor has investigated in detail the porosity of many scales having different manufacturing conditions, and the pores in the scale have a great effect on the improvement of the releasability of the scale by the MD method. It has been found that the peeling rate of the flakes increases and the residual scale is greatly reduced, and the present invention has been completed.

Most of the scale formed on the surface of the wire is a secondary scale generated in a cooling process after rolling. As shown schematically in FIG. 1, the structure and composition of the scale cooled to room temperature after rolling are FeO, Fe ₃ O ₄ , and F from the interface between the wire and the scale (inside the scale layer).
It is layered with e ₂ O ₃ . The scale generated at a high temperature generates cracks in the scale part having weak strength due to the generation of thermal stress due to the difference in thermal expansion coefficient between the wire and the scale during the cooling process.

In the MD method, a strain is applied to the wire after cooling, and a large crack is generated in the scale. The scale is broken and the wire is separated from the wire. At this time, if there is a crack in the scale in advance, it is easier to crack and peel more easily, furthermore, the strength of the scale is low, and if the crack generated in the scale has scale physical properties that are easy to develop, it is even smaller. The scale easily peels off even with strain. When the strain rate is constant, the scale can be peeled more efficiently, and the residual scale can be reduced.

Although the relationship between the pores in the scale and the MD method has hardly been studied, according to the study of the present inventors, the pores in the scale are one of the controlling factors of the peelability of the scale. As the porosity present in the increases, more scale will delaminate under the same strain. In addition, it has been found that the scale can be easily peeled off by applying less strain in order to obtain the same residual ratio of the scale as the conventional wire rod.

The mechanism of the influence of the fine pores present in the scale is not always clear, but the increase in porosity promotes the reduction of the strength of the scale and the development of cracks. It is estimated to improve When a large number of pores of an appropriate size that reduce the scale strength and promote the crack growth are distributed, the cracks easily and continuously grow with small stress, and the peelability of the scale is improved. . However, if the pores are too large, the cracks that have developed due to the application of strain, when the cracks reach the pores, the stress is relaxed, the cracks stagnate, and the scale can be peeled off the wire without breaking the scale. become unable. For this reason, it is effective to introduce a large number of pores in an appropriate size into the scale in order to improve the peelability of the scale.

The reason for limiting the numerical values of the present invention will be described below. The method for measuring the porosity of the present invention is not particularly limited as long as the method can determine the volume ratio of the pores present in the scale as a numerical value. For example, the measurement of the porosity is performed by using a mercury intrusion-type commercially available porosimeter to determine the distribution of the pore size in the scale, a method of obtaining the porosity from the result, and analyzing the image of the scale by microscopic observation, A method of calculating the porosity by determining the size and area ratio of the pores, actually measuring the density of the scale using a densitometer after mechanically peeling the scale from the wire, and scaling the scale from the scale composition ratio and the theoretical density of each scale composition The average theoretical density of the whole is calculated, and the porosity can be measured from the true density and the measured density by a method of obtaining the porosity according to the following equation (1). Porosity (volume%) = (1−measured density / average theoretical density) × 100 (1) A measurement method considering the simplicity of measurement is the simplest and easiest method. The following porosity will be described using values measured by the method described below.

FIG. 2 shows the relationship between the porosity of the scale peeled from the wire and the scale remaining in the wire after a tensile strain of 6% was applied to the wire. As can be seen from this figure, the residual scale decreases due to an apparent increase in the porosity of the scale, and the residual scale decreases significantly with an increase in the porosity up to a porosity of 15%. However, when the porosity is further increased, the residual scale tends to slightly decrease, but there is no significant improvement effect. In the present invention, the porosity in the scale is limited to 15% by volume or more.

FIG. 2 also shows the effect of pore size.
Shown along with. It is considered that the average pore diameter is preferably smaller as estimated from the fracture mechanism. However, according to the measured results, even when the average pore diameter is larger than 100 μm, the residual scale at a porosity of 15% by volume or more is reduced, and the scale is reduced. Although the releasability is improved, the residual scale increases as compared with a scale having an average pore size of 100 μm or less. When the average pore diameter of the scale is 100 μm or less, by setting the porosity of the scale to 15% or more, the residual scale is significantly reduced, and the peelability of the scale is further improved. For this reason, the average pore diameter together with the porosity of the scale is 100 μm or less, and more preferably 50 μm or less, so that the releasability by the MD method is greatly improved, so that the average pore diameter in the present invention is 100 μm or less. And

[0020]

The present invention will be specifically described below with reference to examples. (Example 1) A wire rod according to the present invention is obtained by heating a 122 mm square billet of SWRH82A in a heating furnace with a wire diameter of 5.5.
mm, the winding temperature is adjusted in the range of 750 to 950 ° C., and the degree of opening of the wind blower for cooling the wound wire is reduced to 0 on the rolled steermore.
% To 100%, and the cooling rate was adjusted to cool to room temperature. As a result, the thickness of the scale formed on the surface of the obtained wire was 7.5 μm to 18.0 μm,
The eO ratio greatly changed in the range of 22% to 78%. The scale thickness of the surface of the wire was measured at right angles to the longitudinal direction of the wire, polished and then divided equally into eight parts in the circumferential direction by a microscope. The scale composition gives strain to the wire, and after the scale attached to the wire surface is completely peeled off, FeO, Fe ₂ O is obtained by X-ray diffraction.
₃ , the respective ratios were determined from the peak intensity ratios of Fe ₃ O ₄ .

After the wires having different scale thicknesses and FeO ratios are cut to a length of 250 mm, a tensile load is applied to the cross head at a distance of 200 mm (6%) up to a displacement of 12 mm (6%). A wind is blown on the sample to blow off the scale on the surface of the wire, cut into a length of 200 mm, and weighed (W
1) The sample was immersed in hydrochloric acid to completely remove the scale adhering to the wire surface, and the weight was measured again (W2). The residual scale was determined from the weight measurement by the following equation (2). Residual scale (% by weight) = (W1−W2) / W2 × 100 (2)

The porosity of the scale is defined as the change in helium gas pressure when the peeled scale is filled in a specified container and hermetically sealed, helium gas is filled up to a certain pressure, and the container volume in the gas filling path is changed. Calculate the volume of the filled scale based on the equation of state of the gas, measure the volume of the scale using a multi-volume densitometer, divide by the weight of the scale to obtain the measured density of the scale, and the theoretical density of the scale is ASTM 5.92 FeO from the card
7, Fe ₂ O ₃ is 5.287, Fe ₃ O ₄ is 5.193
And the theoretical density of each of the scales was multiplied from the actual measured value of the scale composition to obtain the average theoretical density of the scale.
The measured density, the average theoretical density, and the porosity were determined from the above equation (1).

The average size of the pores was measured by observation with a scanning electron microscope. As a result, the relationship between the porosity of the scale and the residual scale is shown in FIG. 2 for each average pore diameter. As can be seen from this figure, the residual scale is sharply reduced at a scale having a porosity of 15% by volume or more in the range of the present invention, and there is no large change in the residual scale even when the porosity increases to about 20% by volume. In the case of coarse pores having an average pore diameter of more than 100 μm, the effect of reducing residual scale is also recognized. However, when the average pore diameter is as small as 100 μm or less, the porosity is 15% by volume or more, and the residual scale reduction effect is obtained. Is large.

As described above, when the wire rod according to the present invention having a scale having a porosity of 15% by volume or more was drawn on an actual drawing line, it could be drawn from 5.5 mm to 2 mm without any trouble. . However, when the porosity in the scale was less than 15% and there were many residual scales, frequent flaws due to the remaining scale, disconnection, and abrasion of the dies due to poor lubrication caused severe troubles after drawing. SWRM
As a result of investigating the same relationship in Fig. 8, even if the steel type is a low carbon steel wire, the porosity in the scale is 15% by volume or more, the residual scale by the MD method is significantly reduced, and the average pore diameter is 1%.
The effect of improving the residual scale by the MD method when the thickness is not more than 00 μm is also large, which confirms that the wire having the scale of the present invention has excellent descaling properties regardless of the type of steel.

(Embodiment 2) SWRH8 similar to Embodiment 1
The porosity of the present invention was changed by changing the value of the strain applied to the wire at the time of measuring the residual scale using 2A in the range of 2% to 7%.
The remaining scale of the wire rod having a scale of not less than% by volume and an average pore diameter of not more than 100 μm and the remaining scale of the wire rod outside the range of the present invention were measured. The result is shown in FIG. From this result, when the porosity in the scale is 15% by volume or more, even when 4% strain is applied, the residual scale with 6% strain applied when the scale porosity is out of the range of the present invention is almost the same value. In the wire of the present invention, a sufficient descaling property was obtained by applying less strain.

[0026]

According to the wire rod of the present invention, the mechanical descaling property is improved by increasing the porosity of the scale. Since the mechanical descaling property is favorable regardless of the thickness and composition of the scale, the scale can be thinned and the peeling property can be improved. And the yield can be kept high. Furthermore, since the scale is easily peeled off, the descaling device is simple and sufficient peelability can be secured, and wire surface flaws and poor lubrication due to scale residue are unlikely to occur. Is obtained, and a high-quality steel wire can be manufactured, which is an industrially very useful invention.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a scale formed on a wire rod surface.

FIG. 2 shows porosity, average pore diameter, and 6 of SWRH82A wire rod.
Diagram showing the relationship of residual scale due to% strain

FIG. 3 is a diagram showing the influence of the strain imparting rate of the SWRH82A wire rod of the scale having porosity of the present invention and the wire rod having a porosity outside the range of the present invention on the residual scale.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-10829 (JP, A) JP-A-54-46118 (JP, A) JP-A-58-81929 (JP, A) JP-A-59-819 30404 (JP, A) JP-A-61-154702 (JP, A) JP-A-62-21245 (JP, A) JP-A-3-62890 (JP, A) JP-A-55-110727 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 8/14 B21C 1/00 B21C 9/00 B21C 43/04 C21D 1/82

Claims (2)

(57) [Claims] 1. A wire excellent in mechanical descaling, characterized in that pores present in an oxide scale on the surface of the wire are 15% by volume or more. 2. An average diameter of pores in an oxide scale on the surface of a wire is 100 μm or less.
A wire with excellent mechanical descaling properties as described.