JP2002120084A - Hot rolled wire for solid wire for arc welding and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a hot-rolled wire that the feedability is improved and the generation of spatter is decreased without adding any process in a manufacturing process of a solid wire used for an arc welding. SOLUTION: The hot rolled wire for the solid wire used for the arc welding is characterized by that the diameter of the hot rolled wire is 3 to 6 mm, the depth of the intercrystalline oxidation is 3 to <12 μm, and further dG/ε is in the range of 1.3 to <4.5, where dG μm stands for the depth of intercrystalline oxidation of the hot rolled wire, ε (ε=2×ln(d0/d)) stands for the real strain occurring in a working process where the diameter of the hot rolled wire is reduced to the diameter of the solid wire, d0 mm stands for the diameter of the hot rolled wire, and d mm stands for the diameter of the solid wire. The method for manufacturing the hot rolled wire for the solid wire used for the arc welding is characterized by that the heating index HI which is derived from the heating history after rolling the wire and calculated by the equation shown below is controlled in the range from 700 to 4000. HI=1/2×(maximum temperature of wire deg.C-600)×holding time (min) under 600 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hot rolling for producing a solid wire which is excellent in feedability in a conduit tube during welding operation with a solid wire and with little welding spatter during welding. The present invention relates to a wire and a method for manufacturing the wire.

[0002]

2. Description of the Related Art Gas shielded arc welding is a large-scale steel mainly used in buildings and bridges because it has high welding, has good penetration into a base material, has a high degree of freedom in welding position, and has a highly reliable welding joint. It is widely used in the manufacture of structures and sheet steel structures for transportation equipment such as automobiles.

Solid wires for gas shielded arc welding are not only used for welding mild steel, but also 490 N / mm ² class, 590
It can be widely applied to welding of high-strength steel of N / mm ² class or higher or alloy steel such as Cr-Mo steel, and CO ₂ , Ar-CO ₂ ,
_{Ar-O 2, CO 2 -O} 2, Ar-CO 2 -O 2, Ar, H
It can be used in combination with various shielding gases such as e.

[0004] During an arc welding operation using a solid wire, a feeding roller of a wire feeding device is inserted through a tubular body containing a helically formed flexible tube (hereinafter referred to as a conduit tube) inside a conduit cable. 6m long conduit cable and welding torch contact tip connected to it (current-carrying part)
It is used in a method in which an arc is melted in a shield gas atmosphere while a wire is continuously sent out from the furnace. In welding, a long conduit cable is often bent up and down or left and right to adjust the distance from a welding power source to a welding site, or wound around a loop to adjust the length.

[0005] When used in such a situation, the wire passing through the conduit cable has an increased frictional contact with the surface inside the spiral conduit tube, increasing the feeding resistance and allowing the wire to be fed smoothly. It becomes difficult. As a result, various welding defects such as instability of the welding arc, irregularity of the bead shape, poor fusion, and occurrence of undercut occur.

[0006] Recently, as the welding operation has become complicated, high-speed, and widespread, the frictional resistance with the inner surface of the conduit tube has been small, the feeding has been smooth and stable, and the welding wire which is always fed at a constant speed, ie, the feeding wire has been developed. There is a strong demand for a welding wire with excellent feedability.

[0007] For this reason, various devices have been conventionally devised in order to improve the wire feedability in the production of welding wires.

For example, Japanese Unexamined Patent Publication (Kokai) No. 61-27198 discloses a method in which fine irregularities are formed on the surface of a wire, and an average particle diameter of 50 to 50 mm is applied to the surface of the wire in order to attach a lubricant to the irregularities.
A method has been proposed in which shot blasting is performed for 2 seconds or less using a 750 μm shot, and a lubricant such as a vegetable oil, a mineral oil, or an animal oil is used alone or in combination. Further, when the use condition is severe, Mo
A method has been proposed in which a solid lubricant such as S ₂ and graphite powder is suspended in lubricating oil and applied to the surface of a wire.

Japanese Patent Application Laid-Open No. Hei 7-223087 specifies the shape and number of grooves formed on the outer peripheral surface of the welding wire. Japanese Patent Application Laid-Open No. Hei 5-21674 discloses that the average grain boundary oxidation depth and the average crystal grain size are determined. One with a limited ratio has been proposed. These solid wire manufacturing methods improve the feedability by accelerating grain boundary oxidation by heat treatment during the manufacturing process to form grooves on the surface of the wire and holding a lubricant inside the grooves. It is.

However, shot blasting is also used as a method of forming irregularities on the surface of a solid wire.
In the case where grooves are formed on the surface by performing heat treatment, it is necessary to add a shot blasting step and a heat treatment step in the manufacturing process, so that equipment needs to be installed, and there is a problem that manufacturing costs increase due to an increase in the number of steps.

As a method of forming a groove on the surface of a wire in addition to the grain boundary oxidation, Japanese Patent Laid-Open No. 1-15356 discloses a method in which the surface of the wire is covered with a porous copper plating layer and the plating layer contains a lubricant. However, Japanese Unexamined Patent Publication (Kokai) No. 2-42593 proposes a welding wire in which a natural potential is controlled, a large number of fine ground irons are exposed, and a copper plating is applied to hold a lubricant.

[0012] As described above, the method of controlling the surface condition of the plating to form the unevenness to retain the lubricant in the concave portion and improve the feedability is based on the fact that the ground iron is locally exposed, so that the rust during storage is low. It is necessary to strengthen the management so that rust does not occur between production and use, and an increase in cost is inevitable.

[0013] In addition to the feedability, the occurrence of spatter is a factor that reduces the welding workability. In a region where the current is relatively low, an instantaneous short circuit occurs without the transfer of the droplet at the tip of the wire to the molten pool, and the more the number of short circuits, the better the welding becomes. Conversely, if the arc is unstable or a short circuit is poorly generated, spatter is generated, and good welding work cannot be performed. Generally, there is a clear relationship between the number of short circuits and the occurrence of spatter, and the spatter is reduced by increasing the number of short circuits. Since the number of short circuits during welding often occurs when the oxygen concentration of the wire is high, it is possible to improve welding workability by increasing the oxygen concentration.

In view of the above, there has been proposed a technique in which the oxygen concentration is limited in order to suppress the occurrence of sputtering.

For example, Japanese Patent Application Laid-Open No. 60-231590 discloses that the oxygen concentration in the surface layer up to 2.5% of the diameter is 1100.
There has been proposed a wire in which resputtering is reduced by setting the content to 8000 ppm and a fine crack is formed on the surface.

However, in order to increase the oxygen concentration in the surface layer, it is necessary to perform a heat treatment in the solid wire manufacturing process to promote oxidation of the wire surface layer.
There is a problem that manufacturing costs increase due to an increase in operating costs.

[0017]

As described above, in the prior art, the feedability or the generation of spatter is improved by using some equipment and adding a process.
All of these techniques have resulted in an increase in the cost of solid wires.

In view of the above situation, the present invention has been made in view of the above circumstances, and has no problem in adding a special process or processing in a solid wire manufacturing process. It is an object of the present invention to provide a rolled wire and a method for manufacturing the same.

[0019]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have developed a novel process in which a solid wire having excellent feedability and less occurrence of spatter is directly produced from a hot-rolled wire rod into a current production process. A method of manufacturing without adding a layer was studied.

As a result, when a solid wire is manufactured from a hot-rolled wire, if no heat treatment is performed, the wire surface becomes smooth, no groove capable of holding a lubricating component is formed, and the wire is directly formed from the hot-rolled wire. It was found that the produced solid wire could not improve the feedability. However, when a solid wire is manufactured from a hot-rolled wire rod having a diameter within a range in which grain boundary oxidation of the surface layer is promoted by performing slow cooling treatment after hot rolling, a groove is formed on the surface of the solid wire. Was found.

When the surface during wire drawing was observed in detail, it was found that there was a state of grain boundary oxidation and a degree of work of the hot-rolled wire which could stably form a groove on the wire surface. Based on the above findings, we conducted various studies on the effect of groove formation on the surface of the solid wire that is affected by the wire diameter, grain boundary oxidation depth and workability of the hot-rolled wire rod. The inventors have found the depth of oxidation and have accomplished the present invention.

Furthermore, since a deep grain boundary oxide layer is formed on the surface layer of the hot-rolled wire and internal oxidized particles can be generated in the grains and the oxygen concentration in the surface layer can be increased, the hot-rolled wire can be used. It was also found that the use of this material can improve the feedability and suppress the generation of spatter, enabling the production of a low-cost, high-performance solid wire.

The present invention has been made based on the above detailed examination, and the gist thereof is as follows.

(1) A hot-rolled wire for an arc-welded solid wire having a wire diameter of 3 mm or more and 6 mm or less, having a grain boundary oxidation depth of 3 μm or more and less than 12 μm continuous from the surface layer of the hot rolled wire.

(2) The diameter of the hot-rolled wire is d ₀ mm,
When the wire diameter of the solid wire is dmm, the processing true strain from the hot-rolled wire to the solid wire diameter is ε, and the grain boundary oxidation depth of the hot-rolled wire is dGμm, dG / ε is 1.3 or more.
The hot-rolled wire for an arc-welded solid wire according to the above (1), wherein the value is less than 4.5. Where true strain ε
Is represented by the following equation. ε = 2 × ln (d ₀ / d)

(3) The hot-rolled wire for an arc-welded solid wire according to the above (1), wherein internal oxide particles are present in the vicinity of the surface layer where the grain boundary oxide layer is present.

(4) An arc welding solid characterized by controlling a temperature history after hot rolling of a wire rod having a wire diameter of 3 mm or more and 6 mm or less to a heating index HI shown in the following equation within a range of 700 to 4000. A method for producing a hot-rolled wire for a wire. HI = 1/2 x (maximum temperature of wire rod-600) x 600
Holding time over min (° C)

The depth of the grain boundary oxidation of the present invention is a continuous oxide layer formed along the crystal grain boundary, and is actually continuous in the direction of the grain boundary. Defined the depth as a value measured perpendicular to the surface.

Further, since grain boundary oxidation is continuously generated from the surface, it is necessary to remove the surface by pickling treatment such as pre-treatment for plating to enhance the adhesion of the plating. In the case of iron oxides, those mainly composed of FeO and Fe ₃ O ₄ are preferably those having a composition that can be easily dissolved in an acid, and other Mn, Si, and Ti oxides have the same properties. Is more preferable. However, the oxide composition is not particularly limited as long as it is an oxide having a composition that does not inhibit the adhesion of plating.

When the grain boundary oxide has been removed, it is difficult to maintain a high oxygen concentration in the surface layer.

On the other hand, the internal oxide particles are not removed even by the pickling treatment and are present near the surface layer, so that the oxygen concentration in the surface layer can be increased. The internal oxide particles are, for example, F
Oxide compositions having a high oxygen concentration, such as e ₂ O ₃ , MnO ₂ , TiO ₂ , and SiO ₂ , are preferred, but are not particularly limited to these components and compositions.

Means for controlling the temperature history of the wire after hot rolling is not particularly limited, but for example, a continuous tunnel furnace for maintaining a high temperature can be used.
There is no particular limitation on the heating means or the heat retention form, but other means such as an electric heater, a gas burner, and a radiant tube, and other means such as direct energization can be applied, and the surface of the rolled wire can be coated with an oxidation promoter or the like.

The HI defined as the heating index can be controlled by the finishing temperature and the winding temperature of the hot-rolled wire, the atmosphere temperature in the continuous furnace, and the transfer time, and the finishing temperature, the winding temperature and the furnace temperature can be increased. By lowering the transfer speed in the furnace, the HI can be increased, and deeper grain boundary oxidation can be obtained.

[0034]

Embodiments of the present invention will be described below in detail.

First, the reasons for limiting the grain boundary oxidation depth and the wire diameter of the hot-rolled wire according to the present invention will be described. FIG. 1 is a diagram schematically showing the state of formation of grain boundary oxidation, and shows a state in which oxides of Si, Mn, Fe and Ti are formed along crystal grain boundaries. The figure also shows a state in which internal oxide particles are also formed in the crystal grains.

Grain boundary oxidation depth: This is the starting point for forming a groove by the tensile stress acting on the surface layer in the grain boundary oxidation depth processing step, and is the most important thing of the present invention. Since the grain boundary oxidation is present on the surface of the hot rolled wire, an opening is formed on the surface starting from the grain boundary oxidation, and this portion is formed as a groove on the surface of the solid wire. In order to stably form grooves on the surface formed at the time of this processing, the grain boundary oxidation depth of the surface of the hot rolled wire is required to be at least 3 μm or more from the detailed experimental results of the present inventors, so that it is 3 μm. The lower limit was the grain boundary oxidation depth. However, if too deep grain boundary oxidation is formed, a deep grain boundary oxide layer remains on the surface of the processed solid wire.
When welding is performed using a solid wire having such a deep grain boundary oxide layer, copper plating containing ground iron is peeled on the surface of the solid wire due to bending stress etc. when passing through the conduit tube. Occurs and exfoliation powder accumulates in the conduit tube, resulting in poor feedability. For this reason, the upper limit of the grain boundary oxidation depth is set to less than 12 μm.

More preferably, the grain boundary oxidation depth is from 4 μm to 1 μm.
0 μm.

Wire diameter: In the present invention, since no heat treatment is performed during the processing of the solid wire, the wire diameter of the hot-rolled wire directly affects the working ratio. That is, when the wire diameter of the hot-rolled wire is large, the working ratio for manufacturing a solid wire having the same wire diameter increases. In order to form a groove on the surface of a solid wire, certain processing is required so that a tensile stress acts on the surface of the wire. From this, the wire diameter of the solid wire specified in JIS is 0.6 mm to 2 mm.
Therefore, the lower limit of the wire diameter of the hot-rolled wire was set to 3 mm. On the other hand, when the wire diameter is large, a large processing is performed, but when the processing degree is large, the groove formed on the surface is crushed once and disappears, and the process becomes longer and the productivity is deteriorated. For this reason, the upper limit of the wire diameter of the hot-rolled wire was set to 6 mm or less.

Relation with solid wire linear shape: The wire diameter of the solid wire is 0.6 mm as specified in JIS.
When a solid wire is manufactured from a hot-rolled wire having the same grain boundary oxidation depth and the same wire diameter, the workability varies depending on the wire diameter of the solid wire. If the degree of processing is large, the grooves on the surface will disappear due to strong processing,
Conversely, when the degree of processing is small, no groove is formed. From this, it is expected that there is an optimum working degree for the wire diameter of the solid wire. Therefore, in the present invention, the wire diameter and grain boundary oxidation depth of a hot-rolled wire rod in which grooves are formed stably in the range of 0.6 mm to 2 mm, which is the wire diameter of a solid wire, were further studied.

In order to form a groove on the surface of the solid wire, when the grain boundary oxidation depth of the hot-rolled wire is large, a larger process can be performed. Conversely, when the grain boundary oxidation depth is small, the processing is large. A groove is not formed unless the degree of processing is reduced.
From this, it is considered that a certain ratio exists between the grain boundary oxidation depth and the workability.

Then, when the wire diameter of the hot-rolled wire is d ₀ mm, the wire diameter of the solid wire is dmm, and the grain boundary oxidation depth is dG μm, the working ratio is expressed as ε = 2 × ln ( d ₀ / d) The relationship between the grain boundary oxidation depth and the true strain ratio (dG / ε) and the formation of grooves on the surface of the solid wire was investigated in detail.

As a result, FIG. 2 shows a mapping of the groove formation for hot-rolled wire rods having a wire diameter of 3 mm to 6 mm and a grain boundary oxidation depth of 3 μm to 12 μm.

In this figure, ○ indicates a region where a groove is formed, X indicates a region where no groove is formed, and ● indicates a region where peeling occurs from a grain boundary oxidized portion.

As shown in FIG. In the region smaller than 3, the wire diameter of the hot-rolled wire is large, the wire diameter of the solid wire is small, and strong working is performed, or the grain boundary oxidation depth of the hot-rolled wire is small. Therefore, dG / ε was limited to 1.3 or more because an effective groove was not easily formed on the surface of the solid wire, and a lubricating component could not be held on the wire surface.

Conversely, in the region where dG / ε is 4.5 or more, the wire diameter of the hot-rolled wire is small or the wire diameter of the solid wire is large.
When the degree of work is small or when the grain boundary oxidation depth of the hot-rolled wire is deep, the grain boundary oxidation depth remaining on the surface of the solid wire becomes large. If deep grain boundary oxidation occurs on the solid wire surface, stress acts on the solid wire during feeding, causing surface peeling of the plating containing ground iron from the grain boundary oxidation part, and peeling powder in the conduit tube. Accumulates and becomes a resistance when the solid wire is moved, so that it is impossible to secure a stable feeding property. For this reason, the value of dG / ε was set to less than 4.5.

More preferably, dG / ε is 2 or more and less than 4.

Internal oxide particles: In the present invention, even when the diameter of the hot-rolled wire is small or large, the depth of grain boundary oxidation remaining on the surface of the solid wire is controlled to a certain depth or more. In addition, internal oxide particles formed on the surface of the solid wire are also left on the surface of the solid wire together with the grain boundary oxide layer having a certain depth, and the oxygen concentration on the surface of the solid wire is increased.

FIG. 3 shows a change in the surface oxygen concentration ratio of the wire of the present invention with respect to a hot-rolled wire having almost no grain boundary oxidation without any slow cooling treatment in the hot rolling process. As is apparent from this figure, the surface oxygen concentration of the solid wire of the present invention is increased by about 2 to 3 times as compared with the comparative example having no grain boundary oxidation. At this time, the oxygen concentration in the range of 1 μm in the surface layer of the solid wire of the present invention was 1000 ppm or more, and the average oxygen concentration up to the depth of 10 μm was 100 ppm or more.

The internal oxide particles in the surface layer are not removed even by pickling or the like in the pretreatment for plating and remain in the surface layer, so that the oxygen concentration in the surface layer increases and the generation of spatter during solid wire welding is suppressed. As a result, the solid wire of the present invention can improve the feeding property and also suppress the spatter.

Next, the reasons for limiting the manufacturing method of the present invention will be described.

The production conditions of the present invention are as follows:
By utilizing the sensible heat brought in by the hot-rolled material, the cooling rate is reduced, and the material is held at a high temperature for as long as possible so that grain boundary oxidation is formed stably and deeply over the wire, the entire circumference and the entire length.

For this reason, the hot-rolled material manufacturing method of the present invention is to promote the grain boundary oxidation of the wire rod immediately after rolling by passing the hot-rolled material through a continuous processing furnace controlled to a high temperature atmosphere.

Operating conditions that affect the state of formation of grain boundary oxidation include the finishing temperature during rolling, the temperature of the wire rod when introduced into the lehr, the transport time in the furnace, and the temperature in the furnace. The grain boundary oxidation depth can be controlled.

Therefore, in the present invention, the production conditions which are clearly related to the grain boundary oxidation depth are indexed and limited so that an appropriate dG / ε can be obtained.

From the temperature change of the hot-rolled wire, it was found that the holding area of the high-temperature portion at 600 ° C. or more had a clear relationship with the grain boundary oxidation depth. The portion related to the area of the high-temperature region of 600 ° C. or more from the temperature is indexed, and the high-temperature index is defined as HI (Heat In).
dex) is defined by the following equation, and this value is limited.

HI = １ ／ × (maximum temperature of wire rod ℃ -60
0) Holding time of 600 ° C or more (min)

When the HI is high, it is sufficient to keep the temperature at 600 ° C. or higher for a long time or to cool from a higher temperature state, so that the oxidation reaction on the surface of the wire is accelerated and deeper grain boundary oxidation is formed. The HI index can be increased by increasing the winding temperature after finish rolling, increasing the temperature of the continuous furnace, and decreasing the moving speed of the wire rod in the continuous furnace. On the other hand, the HI index decreases due to a decrease in the finishing temperature, a decrease in the continuous furnace temperature, and an increase in the furnace transfer speed.

As shown in FIG. 3, a very good correspondence is obtained between the high temperature index (HI) and the grain boundary oxidation depth on the surface of the hot-rolled wire. From this, in order to obtain a hot-rolled wire rod according to the present invention in which the ratio between the grain boundary oxidation depth and the true strain for forming a clear groove on the surface of the solid wire is 1.3 to 5 within the range of the present invention. The appropriate HI value was determined from the experimental results and limited.

When the HI index is less than 700, only a grain boundary oxidation depth of less than 3 μm is obtained. Even if a solid wire is formed from this hot-rolled wire, no clear groove is formed on the surface. Was set as the lower limit.

On the other hand, when the HI index is increased, a deeper grain boundary oxidation can be obtained, but the copper plating peels off together with the base iron at the time of processing, so that the feedability decreases and spatters occur. And

More preferably, the HI index is 1000 to 30.
00 range.

[0062]

EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

Using a steel material having the composition shown in Table 1, the rolling wire diameter was 3 to 7 mm, and the rolling conditions were adjusted to control the HI index to make the grain boundary oxidation depth in the range of 0.6 to about 14 μm. .

The hot-rolled wire was subjected to a pretreatment of degreasing and pickling, followed by a continuous copper electroplating treatment, and the hot-rolled wire was directly subjected to 0.1 mm.
Processed into 8mm ~ 2mm solid wire, surface condition,
The feedability during passage through the conduit tube and the occurrence of spatter during welding were investigated. In addition, as a comparative example, the feedability and spatter generation were investigated for a solid wire processed to a thickness of 1.2 mm after performing batch annealing and electrolytic copper plating at 2.45 mm during processing, which is the current manufacturing condition.

The welding conditions for the investigation of the solid wire feedability and the spatter generation state are shown below. Test steel plate: JIS G310 SM490 Shielding gas: 100% CO ₂ flow rate 25 l / min Welding current: 180 A Welding speed: 5 m / min Wire protrusion length: 15 mm Welding polarity: DCEP (DC reverse polarity) Welding posture: Downward bead-on-plate welding Conduit situation: 80φ 1 turn Length of conduit tube: 3m

The evaluation of the feeding property was made by measuring the current value of the motor at the time of feeding, and evaluated as feeding resistance. In other words, the higher the current value, the higher the feed resistance and the worse the feedability.

When the current value is 1 or less, it is regarded as extremely good.
1 to 2 as O, and 2 to 3 as △, 3
The above is indicated by x as bad.

The spatter generation condition is that the spatter generation amount is 3
In the case of 00 mg / min or less, it is marked as ◎ as extremely excellent, and in the case of 300 mg / min or more and less than 500 mg / min, as O, it is 500 mg / min.
As described above, in the case of less than 700 mg / min,
In the case of 700 mg / min or more, it was indicated by x as bad.

[0069]

[Table 1]

Table 2 summarizes the surface roughness of the solid wires manufactured under the respective manufacturing conditions, the results of the investigation of the weldability, and the superiority of the manufacturing costs.

[0071]

[Table 2]

No. Nos. 1 to 28 have a wire diameter and a grain boundary oxidation depth within the range of the present invention, and have dG / ε of less than 1.3 to 4.5. 1 to 8 have a wire diameter of 3 mm and N
o. Nos. 9 to 22 have a wire diameter of 4 mm. Nos. 23 to 26 have a wire diameter of 5.5 mm. Nos. 27 to 28 are obtained by manufacturing solid wires having different wire diameters from a hot-rolled wire having a wire diameter of 6 mm. Solid wire manufactured from any wire diameter is manufactured directly without heat treatment in the middle of processing, but has good feedability and good spatter generation, especially dG / ε in the range of 2 to 4. Is an extremely good feeding property and spatter generation. The HI index was 730 to 3950 to produce a hot-rolled wire rod according to the present invention. The surface of the solid wire of the present invention is shown in FIG.
The groove as shown in (1) was formed stably over almost the entire circumference, and good feedability was obtained by holding a lubricating component in this groove.

The feedability and spatter generation state of the solid wire of the present invention are shown in Comparative Example No. 1 where annealing was performed during the processing. This is equivalent to the solid wire of No. 29, and in the case of the present invention, it is not necessary to perform annealing in the middle of the processing, and the improvement of the productivity and the reduction of the cost can be achieved by omitting the steps.

No. of Comparative Example 30 to 39 have a wire diameter of 4 mm
Any of a wire diameter of about 7 mm, a grain boundary oxidation depth of 3 μm or less or 12 μm or more, and a grain boundary oxidation depth are out of the range of the present invention. Here, No. 3 having a grain boundary oxidation depth of less than 3 μm. 3
0, 32, 34, and 38 are cases where a solid wire having a wire diameter of 1.2 to 1.6 mm has a dG / ε of less than 1.3 and a HI index of 680 or less. Among them, No. No. 32 has a true strain of 3 or more and is strongly processed. The dG / ε is as small as 0.2 and no clear groove is formed on the surface of the solid wire as shown in FIG. Inferior, and because the grain boundary oxidation is shallow, the oxygen concentration in the surface layer is low, and the occurrence of sputtering is increased. No. 31, 33, 3
5, 36, 37, and 39 are manufactured under the condition that the HI index is 4200 or more, the grain boundary oxidation depth is 12 µm or more, and the dG / ε is 4.5 or more. In this case, since deep grain boundary oxidation is formed, the surface properties when a solid wire is manufactured are as shown in FIG. 4 (c). Is recognized. The peeled portion is a portion where the copper plating is peeled from a part of the grain boundary oxidized portion as a starting point due to the action of strain such as bending on the solid wire. The result of the evaluation of the weldability of such a solid wire was that peeling powder was deposited in the conduit tube, the feed resistance was increased, and the feedability was poor. In some cases, the occurrence of spatter was good in some cases. However, the spatter increased in the portion where the surface was peeled off, and the overall deterioration was worse. This is because the high oxygen portion where the internal oxide particles in the surface layer together with the exfoliated powder are present is subjected to strain such as bending in the conduit tube and is exfoliated and removed, and the oxygen concentration in the surface layer is reduced.

As described above, the shape of the hot-rolled wire is 3 mm or more and 6 mm or less, the grain boundary oxidation depth is 3 μm or more and less than 12 μm, and the surface grain boundary oxidation depth dG
μm and the ratio of true strain ε for processing to a solid wire diameter is d
By controlling G / ε within the range of 1.3 to less than 4.5, the solid wire can be directly formed on the surface of the solid wire even if a solid wire is directly manufactured without performing annealing or processing for surface modification during processing. A turtle-shaped groove can be formed, and feed resistance due to contact with the conduit tube during welding is reduced by holding a lubricant such as oil that improves lubrication performance in this groove,
It becomes possible to feed smoothly. In addition, since internal oxide particles are present in the grain boundary oxidized portion, the generation of spatter is reduced due to an increase in the oxygen concentration in the surface layer portion, and a stable welding operation is performed.

Further, when producing the hot-rolled wire of the present invention, the surface oxidation reaction proceeds by controlling the heating index HI determined from the heat history after the finish rolling to 700 to 4000, and the hot-rolled wire is heated. A grain boundary oxide layer having an appropriate depth was formed on the surface.

[0077]

As described above, the solid wire manufactured by using the hot-rolled wire rod for arc welding solid wire of the present invention can be manufactured without any heat treatment or surface quality improvement during the processing. Even though it has excellent feedability and spatterability, it is extremely useful in industry because stable welding workability is ensured at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state of generation of grain boundary oxidation.

FIG. 2 dG / ε in which a groove is formed on the surface of a solid wire
FIG.

FIG. 3 is a diagram showing an oxygen concentration increase ratio on a solid wire surface according to the present invention and a comparative example.

FIG. 4 is a diagram showing a relationship between a heating index HI and a grain boundary oxidation depth.

FIG. 5 is a view showing a groove formation state on the surface of a solid wire according to the present invention and a comparative example.

[Explanation of symbols]

 a Grain boundary oxide layer b Internal oxide particles c Grain boundary d Grain boundary oxidation depth

Claims (4)

[Claims] 1. A continuous 3 μm from a surface layer of a hot-rolled wire rod.
A hot-rolled wire for an arc-welded solid wire having a wire diameter of 3 mm or more and 6 mm or less, which has a grain boundary oxidation depth of at least 12 μm. Wherein the wire diameter of the hot-rolled wire rod d ₀ mm, dmm the diameter of the solid wire, a machining true strain from hot rolled wire rod until solid wire wire diameter epsilon, grain boundary oxidation of the hot rolled wire rod When the depth is dG μm, dG / ε is 1.3 or more and 4.5.
2. The hot-rolled wire for arc-welded solid wire according to claim 1, wherein Here, the true strain ε is represented by the following equation. ε = 2 × ln (d ₀ / d) 3. The hot-rolled wire for an arc-welded solid wire according to claim 1, wherein internal oxide particles are present in the vicinity of the surface layer where the grain boundary oxide layer is present. 4. A heating index HI represented by the following equation, which shows a temperature history after hot-rolled wire rods having a wire diameter of 3 mm or more and 6 mm or less.
Is controlled in the range of 700 to 4000. HI = 1/2 x (maximum temperature of wire rod-600) x 600
Holding time over min (° C)