KR950003538B1 - Method of manufacturing arc welding bar wire - Google Patents

Abstract

The method improves drawability of wire rods for CO2 gas arc welding electrodes without annealing treatment by controlling the amound of bainite and martensite. The method comprises; (A) hot rolling a billet with 0.07-0.1% C, 0.85-0.95% Si, 1.45-1.65% Mn, after homogenization treatment at 1050-1100 deg.C for 2 hours; (B) quenching to 820-840 deg.C by water injecting; (C) coiling and cooling to 760 deg.C with cooling rate of 2.3 deg.C per second; (D) slow cooling to 635 deg.C with cooling rate of 0.74 deg.C per second; and (E) air cooling to room temperature.

Description

Method for manufacturing wire rod for carbon dioxide arc welding rod

1 (a) and 1 (b) are continuous cooling curves when the cooling start temperatures are 880 ° C and 830 ° C, respectively.

2 is a schematic representation of a controlled cooling system used to practice the method of the present invention.

3 is a photograph of the structure of the wire rod of the present invention and the comparative material.

4 is a tissue photograph after the first drawing of the comparative material other than the present invention.

5 is a photograph after the final drawing of the wire rod prepared according to the method of the present invention.

6 is a tissue photograph of the site which was disconnected at the time of freshness in a comparative material.

* Explanation of symbols for main parts of the drawings

1: heating furnace 2: horizontal ball rolling stand

3: water cooling zone 4: winder

5: Conveyer

The present invention relates to a method for producing a carbon dioxide arc welding rod wire, and more particularly, to a method for producing a carbon dioxide arc welding rod wire.

Carbon dioxide welding rod wire (hereinafter referred to simply as "welding rod wire") is widely used as a material for welding of steel or steel or fostering welding of high-strength steel and surface hardened steel, and for improving the electrical conductivity and supply efficiency of the wire without coating material It is a copper plating, semi-automatic welding wire that is wound in a spool state and welded using carbon dioxide as a protective gas.

This carbon dioxide welding rod wire is usually wired with a diameter of 5.5mm in the primary drawing, first annealing after the annealing treatment, and after the second drawing, the secondary copper plating is used to make the third drawing. It is usually used freshly in two sizes of 0.8mm and 1.2mm in diameter.

However, such a welding bar (diameter 5.5 mm) has a low temperature during wire rod production due to the influence of alloying elements added in wire rod cooling after hot rolling in manufacturing, for example, high manganese (1.5% Mn) and high silicon (0.9% Si). Tissues (bainite + martensite) are produced, and in the case of the Stelmor facility, it is impossible to completely suppress the formation of such low temperature tissues. The formation of low-temperature tissues causes stress due to the concentration of stress around the low-temperature tissues during the drawing process, and it is not possible to obtain good freshness unless the fraction of the low-temperature tissues is controlled to 5% or less in the wire rod state.

In order to improve the freshness, the annealing heat treatment is performed before or after the primary processing, depending on the occurrence of low temperature structure according to the degree of cooling during wire rod cooling.However, the annealing heat treatment is performed in terms of energy saving and manufacturing cost. It is preferable to omit it. Therefore, it is required to secure a fine ferrite + perlite structure having a low temperature tissue fraction of 5% or less by performing proper fresh processing without annealing heat treatment.

Conventional techniques for suppressing the formation of low-temperature structure, the control cooling method by the austenite grain refining method due to the addition of a small amount of titanium (Ti) to ordinary carbon dioxide arc welding rod steel due to titanium carbide and nitride precipitation However, in this case, there is a problem of deterioration of weldability due to the addition of titanium, and the conventional stealmo method is hot-rolled in a wire state at high speed and then rapidly cooled to 880 ° C. and wound up in a coil state to average cooling at 0.8 ° C./sec. The air is cooled by cooling slowly to the finishing temperature of 720 ℃, but at such cooling temperature and cooling rate, the transformation finish time is not transformed due to the lack of transformation finishing time when austerite is transformed from ferrite to ferrite due to the ability of the Stelmore facility during wire rod cooling. Austenitic is transformed into low-temperature structure (bainite + martensite) during air cooling of wire rod It is difficult to secure the ferrite + perlite structure and it is almost impossible to suppress the fraction of the low temperature structure (bainite + martensite) to 5% or less, and thus, there is a problem in that freshness is lowered without annealing heat treatment.

Accordingly, an object of the present invention is to provide a method for producing a carbon dioxide arc welding rod wire rod that solves the conventional problems as described above.

Furthermore, an object of the present invention is to provide a method for producing a carbon dioxide arc welding rod wire having excellent fresh workability without annealing heat treatment.

Another object of the present invention is to control the cooling of the wire rod only in the Stelmor cooling facility without the miniaturization of the austenite particles by the addition of the trace alloy element, so that the low temperature structure (bainite + martensite) The present invention provides a method for producing a carbon dioxide arc welding rod wire which suppresses the annealing heat treatment during the drawing process by suppressing the production to 5% or less.

According to the present invention, carbon 0.07-0.10% by weight (hereinafter referred to simply as '%'), silicon 0.85-0.95%, manganese 1.45-1.65%, phosphorus 0.02% or less, sulfur 0.01% or less, aluminum 0.015% or less, titanium 0.003 Billet of steel grade containing -0.015%, calcium 30ppm or less is maintained at 1050-1100 ℃ for 2 hours, then rolled in hot state, and immediately cold rolled up to 820-840 ℃ by water spray immediately after rolling After, 2.3 After cooling to 760 ± 30 ° C at a cooling rate of 1.0 ° C, again 0.74 Provided is a method for producing a carbon dioxide arc welding rod wire which is cooled slowly to 635 ± 45 ° C. at a cooling rate of 0.1 ° C./sec and air cooled to room temperature.

According to the method of the present invention as described above, the fraction of the low-temperature structure is 5% or less, excellent wire workability without annealing heat treatment at the wire diameter of 5.5mm wire, and can be drawn directly to a line of 0.8mm diameter.

Hereinafter, the present invention will be described in detail.

The reason for limiting the chemical composition of the material used in the present invention is as follows.

The reason why the carbon content is 0.07-0.10% is that it is difficult to secure sufficient strength of the material at 0.07% or less, and at 0.10% or more, it decreases the ductility and toughness according to the increase in strength, and in particular, the weldability. .

The Si content of 0.85-0.95% is due to the fact that silicon (Si) is dissolved in the ferrite at 0.85% or less, and the effect of strengthening the strength of the base material is not sufficient. This is because bubbles generated by carbon monoxide decomposed in the high temperature arc of carbon dioxide gas, which is a protective gas, and inadequate deoxidation reaction during welding.

Manganese (Mn) content of 1.45-1.65% is not enough to secure the strength and toughness of the electrode at 1.45% or less, but also to secure the strength of the weld metal after welding due to the lack of hardenability and the restriction of carbon harmful to weldability. This is because the toughness and cold workability are lowered at 1.65% or more.

It is preferable to limit the upper limit to 0.02% because phosphorus (P) is segregated at grain boundaries and lowers toughness. Sulfur (S) lowers toughness and forms an emulsion, which has a detrimental effect on cold workability. It is desirable to limit.

Aluminum (Al): 0.015% or less, Titanium (Ti): 0.003-0.015%, Calcium (Ca): 30ppm or less because the weldability and fresh workability of the non-metallic inclusions decrease, and the calcium It decreases the surface tension of the drop to increase the size and increase the incidence of the sputter, especially the high vapor pressure pushes up the volume of the welding wire during welding to prevent uniform melting. In addition, if the amount of titanium is large, TiO ₂ remains on the weld bead (bead) surface to impair the paintability of the surface and to reduce the amount of sputter.

Continuous cooling curve according to the cooling start temperature for welding wire (diameter 5.5mm) is the same as the first (a) and the first (b), and the completion curve of the perlite transformation on the cooling curve does not appear. This is because the completion point of metamorphosis is shifted in a considerably long time direction. For this reason, the microstructure of the welding rod wire is mainly composed of ferrite + perlite structure, but because of the cooling ability of the Stelmoir facility, it contains some low temperature structure (bainite + martensite), so it is best to keep it at a temperature above 620 ℃ for a long time. It is preferable, but such a condition is almost impossible in terms of equipment capacity, so it is preferable to minimize the formation of low temperature tissue. In the case of the first (a) degree with the cooling start temperature of 880 ° C, the target structure can be obtained when the cooling rate is 1 ° C / sec. If the cooling rate is increased to 2 ° C / sec, the formation of the fraction of the low temperature tissue is 5%. More than expected.

However, when the cooling start temperature is 830 ° C., the formation rate of the low temperature tissue is suppressed under the same cooling rate condition. As described above, the inventors of the present invention confirmed that the lowering of the cooling start temperature is effective in suppressing the formation of low-temperature tissue.

In the case of cooling multiple coils, two cooling conditions with different cooling speeds can be applied to one cooling condition because the temperature history of the coils in the air cooling zone, that is, the overlapping and central parts, is very different. Consideration should be given to That is, it is preferable that the cooling pattern that can be normally operated when the proper cooling pattern is set has a wide width so as to form a band. The upper limit of the band should be higher than the temperature measured at the overlapping portion of the wire coil, and the lower limit of the band should be lower than the temperature at the center of the coil so that the cooled wire coil has a normal structure.

According to the present invention, after high-speed hot rolling in a wire rod state, rapid cooling is performed to 820-840 ° C by water spraying. This temperature range is able to maintain fine austenite grains in the austenite single-phase zone and the hardenability of the material decreases because the transformation start temperature and time move in the direction of high temperature and short time compared to the cooling start temperature of 880 ° C in the continuous cooling curve. It is advantageous to suppress the possibility of low temperature tissue. On the other hand, immediately after rolling, it is rapidly cooled to 820-840 ℃ by the water spray and wound in a coil form. Cool to 1.0 ° C./sec.

Here, the range of cooling temperature and cooling rate is ± 30 ℃ and The range of 1.0 ° C / sec is a range that considers the difference in the degree of cooling of the wire rod integrated state on the conveyor, that is, the overlapping and non-overlapping areas after the wire is wound in the form of a coil. On the other hand, 2.3 up to 760 ± 30 ℃ 0.74 ± 45 ° C after cooling to 1.0 ° C / sec After slow cooling at 0.1 ℃ / sec and air cooling to room temperature, the range of cooling temperature and cooling rate is ± 45 ℃ and The range of 0.1 deg. C / sec is a range considering the integrated state of the wire rod as in the case of the cooling condition. The conditions of the cooling temperature and the cooling rate are to secure the fine ferrite + perlite structure and the low temperature structure of 5% or less with good freshness. 2.3 When cooling to a temperature of 760 ± 30 ℃ or higher at a cooling rate of 1.0 ℃ / sec, the appropriate transformation time in the cooling zone is insufficient, which leads to a high possibility of low temperature tissues. The possibility of low temperature tissue is very high. Then 0.74 to 635 ± 45 ℃ In case of slow cooling at 0.1 ° C / sec, the cooling temperature of 635 ± 45 ° C is higher than this temperature range, which is highly likely to cause 5% or more of low-temperature tissues during air cooling due to the presence of large amounts of unmodified austenite. Cooling rate 0.74 Since the cooling rate is 0.1 ° C / sec or more, it is almost impossible to secure ferrite + perlite tissue and a low temperature tissue of less than 5%. In addition, the slow cooling rate is an appropriate cooling rate range in consideration of the cooling capacity and workability of the Stallmore facility. It was 0.1 degreeC / sec. On the other hand, if it is cooled to 635 ± 45 ℃ or more above this cooling rate, low-temperature structure is more likely to occur at 5% or more. It is difficult to produce low temperature tissue by more than 5%. On the other hand, air cooling after 635 ± 45 ° C does not have a detrimental effect on the freshness of the cold tissue produced by air cooling because the amount of untransformed residual austenite is 5% or less even if the perlite transformation is incomplete.

Hereinafter, the present invention will be described in more detail according to embodiments.

EXAMPLE

Carbon: 0.07-0.10%, Silicon: 0.85-0.95%, Manganese: 1.45-1.65%, Phosphorus: 0.02% or less, Sulfur: 0.01% or less, Aluminum: 0.015% or less, Titanium: 0.003-0.015%, Calcium: 30 ppm or less After holding the billet (billet, 160sq.) Of steel grade for 2 hours at 1100 ℃, high-speed rolling with 5.5mm diameter wire rod, and rapidly rolling the rolled 5.5mm diameter wire rod product to 830 ℃ by water spray It was cooled to 2.3 ℃ / sec to 790 ℃ and slow cooled to 0.74 ℃ / sec to 635 ℃ and then air cooled to room temperature. On the other hand, the comparative material maintained the billet (160sq.) Of steel grades containing the same chemical composition at 1100 ℃ for 2 hours, and then rolled the 5.5mm diameter wire rod product which was rolled after high speed rolling with 5.5mm diameter wire rod at 880 ℃ by water spraying. After the rapid cooling until then, the coil was wound up, and then cooled slowly to the vicinity of 720 ° C. which is the average cooling finish temperature at an average cooling rate of 0.8 ° C./sec and air cooled.

In the drawing process, the wire rod having a diameter of 5.5 mm was drawn without heat-annealing at a final drawing speed of 500 m / min for the present invention and the comparative material under the same conditions.

1 is a continuous cooling curve according to the cooling start temperature when the first (a) is a cooling start temperature of 880 ℃, the first (b) is 830 ℃ and the austenite grain size is ASTM No. It was ten. Symbol F: Ferrite transformation zone, P: Perlite transformation zone, B: Bainite transformation zone, Ms: Martensite transformation starting point.

2 is a top schematic view of a device suitable for practicing the present invention.

The microstructure in the wire state prepared by the method of the present invention is as shown in Figure 3, compared to the comparative material fine ferrite + 5% or less of the low-temperature tissue (bainite or martensite) in the matrix structure It was a pearlite organization.

The fraction of the low temperature structure of the carbon dioxide arc welding rod wire manufactured by the method of the present invention was measured and the results are shown in Table 1. M is martensite and B is bainite. The fraction of cold tissue was measured using an image analyzer.

4 is a structure photograph of the wire direction after the primary drawing of the present invention and the comparative material, Figure 5 is a microstructure of the wire drawn up to 0.8mm dia without preheating heat treatment of the wire produced by the present invention.

FIG. 6 is a tissue photograph of a site where a disconnection is generated in the step of drawing a comparative material manufactured by a conventional method to a diameter of 1.18 mm during the third drawing without heat treatment, and is lower than that of the present invention (FIG. 5). It can be seen that the size and distribution of the tissues are large, and cracks are generated and propagated at the interface between the low-temperature tissues and the matrix tissues.

As described above, the wire 5.5 mm diameter wire product manufactured according to the present invention was drawn to a diameter of 0.8 mm, and thus wire drawing was possible without the occurrence of disconnection and carbon dioxide arc welding rods could be manufactured.

TABLE 1

Claims (1)

By weight, carbon: 0.07-0.10%, silicon: 0.85-0.95%, manganese: 1.45-1.65%, phosphorus: 0.02% or less, sulfur: 0.01% or less, aluminum: 0.015% or less, titanium: 0.003-0.015%, Calcium: Bilwe of steel grades containing 30ppm or less is kept at 1050-1100 ℃ for 2 hours and then rolled in hot state. Immediately after rolling, it is rapidly cooled to 820-840 ℃ by water spray and wound up to 760 ± 30 ℃. Cool to 1.0 ℃ / sec and 0.74 to 635 ± 45 ℃ A method of producing a carbon dioxide arc welding rod wire, including cooling slowly at room temperature to 0.1 ° C./sec.