JPH0460757B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing composite wire, and in particular, by specifying the physical properties of the steel sheath before wire drawing, wire breakage accidents during forming and wire drawing can be eliminated, and quality can be improved. The present invention relates to a method for manufacturing stable composite wires with high productivity. [Prior art] As is well known, composite wire is obtained by filling the inside of a metal sheath with granular flux and then drawing it, and it has a self-shielding effect and is suitable for automatic welding. Since it is a thing,
The demand is rapidly increasing. Various methods for manufacturing composite wire have been proposed, but
The following methods are currently most commonly used. (1) A wide cold-rolled coil is slit to form a hoop for pipe making. At this point, the width and thickness of the hoop are determined in consideration of the area reduction rate during pipe forming and wire drawing. (2) Connect (weld) the hoops longitudinally. (3) Fill the inside of the hoop with powdery flux while curving it in the width direction to form a tubular shape. In this case, the abutting portions of both side edges of the hoop may be seam welded to seal the joint. (4) The cross-sectional dimensions of the product (5.0 to 1.2 mm) are
〓) Wire drawing process is performed. In this case, the total area reduction rate is 90% or more in most cases. By the way, as the outer skin material used for manufacturing the composite wire, a soft drawing steel plate, which has excellent press workability among cold-rolled coils, is used. The processing properties of cold-rolled steel coils include tensile strength, yield value, elongation, bending strength, Erichsen value,
There are conical cup values, hardness, etc., and by comprehensively evaluating these values, it is possible to know whether the workability is good or bad. From this point of view, when selecting a steel material for the outer sheath of a composite wire, the above-mentioned machining characteristic values are used as criteria for appropriate judgment. [Problems to be solved by the invention] However, even when using a steel material for the outer skin selected based on the processing characteristic values as described above,
Wire breakage accidents often occur during forming and drawing of composite wires. The present invention aims to provide a technology that can prevent such wire breakage accidents and manufacture composite wires of stable quality with high productivity. [Means for Solving the Problems] The method for manufacturing a composite wire according to the present invention is to fill the constituent outer sheath with powdery flux and further wire-draw the same to manufacture the composite wire. The front steel shell has a tensile strength of at least 29Kg/
mm ² or more, the ferrite crystal grain size specified by JIS G 0552 is 7 to 9, and the plastic strain ratio (value) determined by the following formula []
The gist is that it satisfies each condition of 1.2 or higher. = (r _L + r ₉₀ + 2r ₄₅ )/4...(1) However, r _L : Plastic strain ratio when strain below the uniform elongation limit is applied in the rolling direction r ₉₀ : Uniform elongation in the direction perpendicular to the rolling direction Plastic strain ratio when applying a strain below the limit r ₄₅ : Plastic strain ratio when applying a strain below the uniform elongation limit in a direction intersecting the rolling direction at a 45 degree angle, each of the following: A value determined by a calculation formula. = (W/W ₀ )/(t/t ₀ ) W ₀ : Plate width before deformation W: Plate width after deformation t ₀ : Plate thickness before deformation t: Plate thickness after deformation [Function] Hereinafter, the present invention The effect of the present invention will be explained by clarifying the reason for specifying the physical properties of the outer skin steel used in the following. First, the causes of wire breakage accidents that occur when manufacturing composite wires using the conventional method as described above can be considered as follows. In other words, it is recognized that the above-mentioned processing characteristic values, which are used as criteria for selecting outer skin steel materials, are sufficiently appropriate as general judgment criteria for press workability, as explained above. It is considered that it would be unreasonable to try to judge suitability by directly applying the above-mentioned standard of processing characteristic values to a wire-drawn material in which the extensibility in the rolling direction (lengthwise direction) is particularly important. In other words, in order to understand the characteristics of steel materials for outer skins, for which extensibility in the rolling direction is most important, it is necessary to establish a material testing method that can more accurately determine the superiority or inferiority of extensibility. Based on this idea, we conducted various studies in search of material testing methods that more accurately reflected the suitability of steel materials for outer skins. As a result, we found that the plastic strain ratio (value) expressed by the above formula [] We found that it accurately reflects the The value is determined as follows. That is, for example, as shown in FIG. 1, (a) steel strip for outer skin 1
(b) a direction perpendicular to the rolling direction, and (c) a direction intersecting at a 45 degree angle to the rolling direction, using JIS standard tensile test pieces No. 5 or 13, respectively.
From the ratio of the change in plate width and plate thickness when a strain below the uniform elongation limit is applied to each test piece, r _L , r ₉₀ and r ₄₅ are calculated using the following formula, and = (W/W ₀ )/(t/t ₀ ) (However, W ₀ , W, t ₀ , and t are as described above) The plastic strain ratio obtained by substituting each obtained value into the formula [] is called the value. ing. It has become clear that this value has a close correlation with the frequency of wire breakage accidents during wire drawing. It was confirmed that wire breakage accidents could be prevented as much as possible by using a steel strip with this value of 1.2 or more as the outer skin. However, even when using steel for the outer skin with a value of 1.2 or higher,
If the tensile strength of the steel material becomes lower than the pulling force applied during wire drawing, a wire breakage accident will naturally occur. Therefore, it is necessary to set a lower limit for the tensile strength of steel materials, but as a result of conducting experiments from this point of view, the lower limit for the tensile strength was set at 29 kg/
It became clear that the standard should be mm ² . By the way, when manufacturing a composite wire using the method described above, the processing rate must be considerably high in order to eliminate leakage of the filling flux when the wire is drawn continuously after being curved into a tubular shape and filled with granular flux. Therefore, the pulling force must be increased accordingly, but in order to avoid wire breakage accidents under such pulling force, the tensile strength must be at least 29 kg/mm ² . If the outer skin steel material has a tensile strength less than this value, even if the value is appropriate, frequent occurrence of wire breakage accidents cannot be prevented. In addition, properties that affect the malleability of steel materials,
There is a ferrite crystal grain size specified in JIS G0552, but experimental results show that those with a coarse grain structure with a crystal grain size of less than 7 generally have poor strength, and because the surface roughness of the outer steel material during wire drawing is significant, it is difficult to use ferrite in dies. It was found that the coefficient of friction during passage increased rapidly, making wire breakage more likely to occur. However, if a material with a microstructure with a ferrite crystal grain size exceeding 9 is used, the surface of the outer skin becomes mirror-like during wire drawing, resulting in excessive flatness, and the amount of wire drawing lubricant brought in is drastically reduced, making seizure more likely. , die roughness becomes significant and wire breakage becomes more likely to occur. For this reason, the ferrite crystal grain size was limited to a range of 7 to 9. In this way, in the present invention, the plastic strain ratio (value), tensile strength, and ferrite grain size of the outer steel material are strictly specified, but these physical properties are determined by considering the malleability during wire drawing. This is specified as the physical properties before wire processing, and as long as a skin steel material that satisfies these physical properties is used, it can be applied to any manufacturing method for composite wire. In other words, the method for manufacturing composite wire is to bend a steel strip into a tubular shape as described above, fill the inside with granular flux (in some cases, seam weld the joints of the steel strips), and then wire-draw the steel strip. In addition to this method, there is a method in which powdery flux is filled into a steel pipe for the outer skin that has been formed into a tubular shape in advance, and then wire-drawn to a predetermined cross-sectional dimension. It can be applied in exactly the same way. [Example] As shown below, the plate thickness and chemical composition of the steel strip are kept constant, and the manufacturing conditions of the steel strip (rolling end temperature, coiling temperature, annealing temperature and annealing time that affect the precipitation of Al and N, etc.) are changed. As a result, eight types of steel hoops for outer shells having different r values were manufactured as shown in Table 1. Table 1 also includes the Erichsen value (Japanese Unexamined Patent Publication No. 110148/1983), which has been proposed as a characteristic value for evaluating the wire drawability of steel hoops for outer skins, and shows the correlation with wire drawability. Examined. (Thickness and chemical composition of steel strip) Plate thickness: 0.95mm Chemical composition (weight%): C...0.001, Mn...0.20, Si
…0.01, P…0.020, S…0.020, sol.Al…0.025,
N…0.0060, remainder Fe

[Table] Using each test hoop obtained, the conventional method [(1)
The wire drawing process was carried out according to the method of passing through the steps of (4) to (4) (the wire drawing speed was 500 or 1000 m/min), and the frequency of occurrence of wire breakage was investigated. The results are shown in Figure 2, and the wire drawing speed is
Looking at experimental examples at 500 m/min, wires with a value of less than 1.2 frequently break and the operating rate of the wire drawing equipment is below 70%. The number of disconnections is drastically reduced and an operating rate of over 90% can be achieved. In addition, if a wire with a value of 1.2 or higher is used, an operating rate of 80% or higher is guaranteed even when the wire drawing speed is increased to 1000 m/min.
If the value is less than 1.2, the drawing speed is 1000m/min.
If the voltage is increased to a high level, the number of disconnections will increase dramatically, making continuous operation impossible. As is clear from comparing the Erichsen values in Table 1 and the experimental data in Figure 2, the Erichsen values do not have a particular correlation with the frequency of wire breakage during wire drawing. It cannot necessarily be used as a guideline for wire drawability. In the above experiment, only the value of the steel material for the outer skin was taken up to investigate the relationship with wire drawability, but in addition to the value,
In order to clarify the relationship between tensile strength, yield point, elongation, and the frequency of wire breakage, including the relationship with the ferrite grain size, we conducted wire drawing experiments using a number of outer hoops with different physical properties. . The results are summarized in Table 2,
For coarse-grained materials with a tensile strength of less than 29 Kg/ ^mm2 and a ferrite crystal grain size of less than 6, the effects of insufficient strength and increased drawing resistance due to rough skin during wire drawing are noticeable, leading to frequent wire breakage accidents and The surface of the product wire is also noticeably rough. Furthermore, in the case of fine-grained materials with a ferrite crystal grain size exceeding 9, the surface of the outer skin becomes mirror-like during wire drawing, reducing the amount of lubricant carried in, resulting in significant die roughness, and wire breakage accidents also occur frequently. On the other hand, in embodiments in which the values, tensile strength, and ferrite grain size are all within the specified ranges, composite wires with less breakage during wire drawing and less surface roughness can be efficiently produced.

[Table] [Effects of the Invention] The present invention is constructed as described above, and in particular, by strictly specifying the value, tensile strength, and ferrite crystal grain size of the outer steel material, the frequency of wire breakage during wire drawing can be reduced. As a result, production efficiency can be greatly increased. Furthermore, the resulting composite wire has a beautiful appearance without roughness or seizure, and its quality can also be improved.

[Brief explanation of the drawing]

Figure 1 is a sketch to explain the direction in which specimens are taken to calculate the values, Figure 2 is a graph showing the relationship between the values obtained in the experiment and the frequency of wire breakage, and Figures 3 to 5 are the diagrams used in the experiment. It is a micrograph substituted for a drawing showing the metallographic structure of a test hoop.

Claims (1)

[Scope of Claims] 1. When manufacturing a composite wire by filling a steel sheath with granular flux and drawing the flux, the steel sheath before wire drawing has a tensile strength of at least 29 kg/mm. ² or more, the ferrite crystal grain size specified by JIS G 0552 is 7 to 9, and the plastic strain ratio (value) determined by the following formula:
A method for manufacturing a composite wire, characterized in that the ratio satisfies each condition of 1.2 or more. = (r _L + r ₉₀ + 2r ₄₅ ) / 4 where r _L : Plastic strain ratio when applying strain below the uniform elongation limit in the rolling direction r ₉₀ : Strain below the uniform elongation limit in the direction perpendicular to the rolling direction Plastic strain ratio when given r ₄₅ : Plastic strain ratio when a strain below the uniform elongation limit is given in a direction intersecting the rolling direction at an angle of 45 degrees, and is calculated using the following formula, respectively. It is sought after. = (W/W ₀ )/(t/t ₀ ) W ₀ : Plate width before deformation W: Plate width after deformation t ₀ : Plate thickness before deformation t: Plate thickness after deformation