Gas shielded welding wire, steel wire rod for gas shielded welding wire, and method for producing same

Abstract

The present invention discloses a gas-shielded welding wire, a steel wire rod for gas-shielded welding wire, and a method for producing the same. The steel wire rod for gas-shielded welding wire contains, in mass percent, the following chemical components: C 0.03-0.08%, Si 0.5-1.0%, Mn 1.4-1.8%, S 0.013-0.1%, P≦0.0015%, Ni≦0.8%, Cr≦0.4%, and Mo≦0.4%, with the balance being Fe and unavoidable impurities, and has a liquidus temperature T L =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T S =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T L -T S ≦45°C.

Description

[Technical field]

[0001] The present invention belongs to the technical field of welding materials, and relates to a gas-shielded welding wire, a steel wire rod for gas-shielded welding wire, and a method for producing the same. [Background technology]

[0002] Steel is the most widely used metallic material and is generally connected by welding, among which gas shielded welding is a commonly used welding method.

[0003] In welding, the welding performance depends on the quality of the welded joint, among which the mechanical performance and forming performance of the welded joint are important indexes for evaluating the quality of the welded joint, and one of the important factors affecting these two performances is the performance of the welding wire.

[0004] Currently, commercially available welding wires often have a problem during welding, especially when welding pipes and the like in all positions, where the weld seam metal at the 12 o'clock position, i.e., directly above the weld seam, flows down and falls, resulting in poor forming performance and uneven weld beads. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a gas shielded welding wire, a steel wire rod for gas shielded welding wire, and a manufacturing method thereof, thereby solving the problem that the welding seam metal at the 12 o'clock position flows downward during all-position welding, resulting in poor forming performance and uneven weld beads.

[0006] In order to achieve the object of the present invention, one embodiment of the present invention is a steel wire rod for gas shielded welding wire, which contains, in mass percent, the following chemical components: C 0.03-0.08%, Si 0.5-1.0%, Mn 1.4-1.8%, S 0.013-0.1%, P ≦0.0015%, Ni ≦0.8%, Cr ≦0.4%, Mo ≦0.4%, and the balance being Fe and unavoidable impurities, and the mass percents of C, Si, Mn, P, and S are less than or equal to a liquidus temperature T L =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T S =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T L -T S The present invention provides a steel wire material for gas-shielded welding wire, which satisfies the requirement of a temperature range of 45°C or less.

[0007] Among them, C is one of the important elements in steel wire for welding wire. It can reduce the average size of austenite grains, reduce pro-eutectoid ferrite, increase acicular ferrite, effectively improve the strength and hardness of the weld seam metal, improve the arc stability during welding, and improve the droplet transfer characteristics.

[0008] Silicon is a main deoxidizing and strengthening element in steel wire rods for welding wire, and is mainly dissolved in austenite and ferrite to achieve the effect of solid solution strengthening, thereby effectively improving the strength of welded seams.

[0009] Mn, as a deoxidizing element in the welding process, can form oxides during deoxidation to improve the strength and toughness of the weld seam, and can also improve the content of acicular ferrite in the weld seam metal, reduce pro-eutectoid ferrite and ferrite side plates, and refine acicular ferrite.

[0010] The content of S is within the range of 0.013 to 0.1%, which can improve the surface activity of the droplets, increase the fluidity of the weld seam metal, promote the formation of the weld seam, and avoid harm to the toughness of the weld seam.

[0011] P is an impurity element in steel wire rod for welding wire. If the content is too high, component segregation is likely to occur in the final stage of molten steel solidification, which is disadvantageous to wire rod drawing and to the low-temperature toughness of the welded seam.

[0012] Ni is an element that improves the strength and low-temperature impact toughness of a weld seam. Ni can refine the structure and promote the formation of acicular ferrite, and thus plays an important role in strengthening the weld seam metal.

[0013] Cr increases the content of acicular ferrite in the weld seam, and can improve the strength and low-temperature toughness of the weld seam.

[0014] Mo can lower the phase transformation temperature, inhibit the formation of proeutectoid ferrite, promote acicular ferrite transformation, and increase the proportion of acicular ferrite, which helps improve toughness.

[0015] In summary, the above elements and weight percentage ranges can be reasonably set to ensure the toughness of the weld seam metal and the smooth progress of the welding process. In addition, the mass percentages of C, Si, Mn, P, Ni, Cr, and Mo can be reasonably designed, and the S content can be controlled to make the droplets finer during the welding process, reduce the surface tension of the droplets, promote the flow of the weld metal, and improve the formability of the weld seam. In addition, the liquidus temperature and solidus temperature of the welding wire can be regulated to control the interval between the melting point and solidification point of the welding wire, and control the solidification speed of the weld seam metal, so that the fluidity of the weld seam metal can be increased and the weld molten pool can be solidified quickly, which solves the problem of the weld seam metal at the 12 o'clock position flowing down during all-position welding, and the surface of the weld seam can be made uniform and smooth during all-position welding, and the weld bead can be beautifully formed.

[0016] Preferably, the mass percentages of C, Mn, Ni, Cr, and Mo satisfy the following: austenite transformation start temperature Ar3=910-310[C]-80[Mn]-55[Ni]-15[Cr]-80[Mo], bainite transformation start temperature Bs=830-270[C]-90[Mn]-37[Ni]-70[Cr]-83[Mo], 30°C≦Ar3-Bs≦80°C. Through the rational design of each element composition and content, the austenite transformation start temperature and bainite transformation start temperature are adjusted and controlled to ensure the presence of sufficient ferrite in the weld seam metal, reduce the residual stress and deformation of the weld head, improve the weld forming performance, and the produced welding wire has a stable arc during welding, the surface of the weld seam is uniform and smooth during all-position welding, and the weld bead is beautifully formed.

[0017] In order to achieve the above object of the present invention, one embodiment of the present invention provides a gas-shielded welding wire manufactured using the above-mentioned steel wire material for gas-shielded welding wire as a base material. The above-mentioned steel wire material for gas-shielded welding wire is used as a base material and drawn into a gas-shielded welding wire having a diameter of 1.2 mm, and then subjected to Ar+20%CO 2 As a result of the deposition welding test, the welding process performance was excellent, and the tensile strength of the obtained weld seam metal was 770MPa or more, and the -40℃ impact energy was 98J or more. Not only that, but also the weld seam was beautifully formed.

[0018] In order to achieve the above object of the invention, one embodiment of the present invention comprises: A molten steel smelting process; The refining process, a steel billet casting process for casting the molten steel obtained by refining into a steel billet; a temperature-controlled heating step of heating the obtained steel billet in a heating furnace while controlling the temperature; a temperature-controlled rolling step in which the steel billet obtained in the temperature-controlled heating step is descaled with high-pressure water having a descaling water pressure of ≧18 MPa and rolled into a wire rod, and the wire rod is intensively cooled after the rolling is completed using an intermediate rolling mill having a machined rolling groove, and then wound after cooling; a Stelmor annealing process in which the wire rod obtained in the temperature controlled rolling process is annealed on a Stelmor annealing line at a cooling rate of ≦0.8° C. / s in the phase transformation temperature range of the wire rod with all heat-retaining covers and blower outlets closed; a production method for producing the steel wire rod for gas shielded welding wire, the production method including the steps of:

[0019] Through temperature controlled rolling and control over the Stelmor slow cooling, the scale on the surface of the steel billet can be effectively removed and the remaining scale can be prevented from being pressed deep into the wire structure during rolling into wire rod; the machined rolling groove can ensure the surface flatness of the wire rod and also prevent the increase of surface defects of the wire rod caused by the rolling groove with a rough surface, thereby ensuring the surface quality, structure and strength performance of the wire rod, and further benefiting drawing.

[0020] As a further improvement in one embodiment, on the Stelmor annealing line, the total length of all heat-insulating covers is >80m, the inlet roller table speed of the Stelmor annealing line is ≦0.18m / s, and the outlet roller table speed is ≦0.40m / s, thereby achieving a cooling rate of ≦0.8°C / s in the phase transformation temperature zone of the wire, extending the residence time in the phase transformation temperature zone, and rationally controlling the thickness and structure of scale on the wire surface to improve the mechanical peelability of the scale, improving the uniformity of the internal structure of the wire, and further facilitating drawing of the wire into welding wire.

[0021] As a further improvement of one embodiment, in the temperature controlled rolling step, the rolling start temperature is 970-1000°C, the finish rolling mill inlet temperature is ≦880°C, and the coiling temperature is 880-910°C. This makes it possible to effectively control the thickness and structure of scale on the wire rod surface, and the resulting scale thickness on the wire rod surface is 10 μm or more, resulting in the wire rod having excellent scale peelability.

[0022] In a further improvement of one embodiment, in the refining step, deoxidation and desulfurization are performed by forming white slag during refining, the refining time is ≥ 35 min, the white slag formation time is ≥ 15 min, the contents of other alloys are adjusted to meet the target range before the ferrotitanium wire is introduced, and the soft stirring time in the latter stage of refining is ≥ 15 min, and the molten steel obtained from the molten steel smelting step is refined in an LF furnace. By controlling the timing of introducing the ferrotitanium wire, it is possible to avoid the melting loss of titanium in the early stage of refining, improve the yield of titanium element, optimize the chemical composition of the final wire rod, effectively reduce production costs, ensure the structure, strength and welding performance of the produced wire rod, and also to improve the uniformity of the components in the molten steel by controlling the time during refining, thereby reducing the macro- and micro-segregation of the steel billet, improving the structure and strength of the final wire rod, and facilitating drawing into the welding wire.

[0023] As a further improvement of one embodiment, in the steel billet casting step, the molten steel superheat is set to 18-35°C, and the casting speed of the cast billet is kept constant at 2.5-2.7 m / min to perform full protection casting of the molten steel obtained from the refining step. By controlling each parameter in the casting step, it is possible to improve the homogenization of the molten steel, reduce the component segregation of the steel billet, improve the structure and strength of the finally obtained wire rod and welding wire, and improve the forming performance of the welding wire.

[0024] As a further improvement of one embodiment, in said temperature controlled heating step, the temperature of the heating zone is 960-1020°C and the temperature of the soaking zone is 1080-1120°C.

[0025] In a further improvement of one embodiment, in the molten steel smelting process, the smelting raw materials consisting of molten pig iron and steel scrap are smelted in a converter, the weight percentage of the molten pig iron in the smelting raw materials is >90%, and at 1 / 3 tapping, a ferrosilicon alloy, a silicomanganese alloy, a low carbon ferromanganese alloy, and lime are added to the molten steel in this order. In this way, by controlling the weight percentage of the molten pig iron and the timing of adding the various alloys and lime, it is possible to ensure high purity of the molten steel components, improve the structure and strength of the wire rod and the final welding wire, and further aid in drawing the wire rod into the welding wire, thereby improving the welding performance of the welding wire.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: The gas-shielded welding wire, the steel wire rod for gas-shielded welding wire and the production method thereof of the present invention, by rationally designing the composition and mass percentage thereof, not only can reduce the desulfurization cost in the steelmaking process, but also can achieve high fluidity of the weld seam metal, fast solidification rate of the weld molten pool, high formability of the weld seam, solve the problem of the weld seam metal at the 12 o'clock position flowing down during all-position welding, the surface of the weld seam is uniform and smooth during all-position welding, and the weld bead is beautifully formed; furthermore, by improving the uniformity and purity of the molten steel components, the macro-segregation and micro-segregation of the billet are reduced, the surface defect depth of the wire rod, the structure and strength of the entire wire rod are made uniform, and the mechanical peeling property and plasticity of the scale are improved, so that the wire rod finally obtained by using the production method can achieve a tensile strength of 650 MPa or more, has excellent drawing performance, can be drawn into a gas-shielded welding wire with a diameter of 1.2 mm, and ... by using Ar+20%CO 2 As a result of the deposition welding test, the welding process performance is excellent, and the tensile strength of the obtained weld seam metal is more than 770MPa, and the -40℃ impact energy is more than 98J. Not only that, but also the weld seam is beautifully formed. [Brief description of the drawings]

[0027] [Figure 1] 1 is a photograph of a welded seam portion in one embodiment of the present invention. [Diagram 2] 1 is a photograph of a welded seam portion in a comparative example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] An embodiment of the present invention provides a steel wire for gas shielded welding wire, a gas shielded welding wire, and a method for producing a steel wire for gas shielded welding wire.

[0029] The steel wire rod for gas-shielded welding wire of the present invention contains, in mass percent, the following chemical components: C 0.03-0.08%, Si 0.5-1.0%, Mn 1.4-1.8%, S 0.013-0.1%, P ≦0.0015%, Ni ≦0.8%, Cr ≦0.4%, Mo ≦0.4%, and the balance being Fe and unavoidable impurities. In addition, the mass percents of C, Si, Mn, P, and S are less than or equal to a liquidus temperature T L =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T S =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T L -T S The temperature must be ≦45°C.

[0030] Here, the liquidus temperature T L , solidus temperature T S In the formula, square brackets "[]" represent the mass percent of the element within, e.g., [C] represents the mass percent of C, and similarly for other elements.

[0031] Preferably, the mass percentages of C, Mn, Ni, Cr, and Mo satisfy the following: austenite transformation start temperature Ar3 = 910-310 [C] - 80 [Mn] - 55 [Ni] - 15 [Cr] - 80 [Mo], bainite transformation start temperature Bs = 830-270 [C] - 90 [Mn] - 37 [Ni] - 70 [Cr] - 83 [Mo], and 30°C ≦ Ar3 - Bs ≦ 80°C.

[0032] Similarly, in the formulas for the austenite transformation start temperature Ar3 and the bainite transformation start temperature Bs, the square brackets "[]" represent the mass percentage of the element therein, for example, [C] represents the mass percentage of C, and similarly for other elements.

[0033] The steel wire for gas-shielded welding wire can be used as a base material for producing gas-shielded welding wire.

[0034] In other words, one embodiment of the present invention further provides a gas-shielded welding wire manufactured using the steel wire material for gas-shielded welding wire as a base material. For example, the gas-shielded welding wire can be manufactured by further subjecting the steel wire material for gas-shielded welding wire to a drawing process. The gas-shielded welding wire has a diameter of 1.2 mm and is mixed with Ar+20%CO 2 As a result of the deposition welding test, the welding process performance is excellent, and the tensile strength of the obtained weld seam metal is more than 770MPa, and the -40℃ impact energy is more than 98J. Not only that, but also the weld seam is beautifully formed.

[0035] An embodiment of the present invention further provides a method for manufacturing the steel wire rod for gas shielded welding wire. As described above, the method for manufacturing the steel wire rod for gas shielded welding wire of the present invention is the result of a large amount of experimental research, and each step of the method for manufacturing the steel wire rod for gas shielded welding wire will be further described below.

[0036] (1) Molten steel smelting The raw materials consisting of molten iron and steel scrap are smelted in a converter, and the weight percentage of the raw materials in the molten iron is >90%, thereby ensuring the purity of the molten steel components. At the 1 / 3 tapping stage, ferrosilicon alloy, silicomanganese alloy, low carbon ferromanganese alloy, and lime are added to the molten steel in this order to adjust the composition content in the molten steel and turn it into slag, which effectively improves the purity of the molten steel and improves the structure and strength of the wire rod.

[0037] Here, the steel scrap is preferably high-quality steel scrap such as scrap from the head and tail ends of a billet cut during low-carbon steel smelting, but is of course not limited thereto. By using high-quality steel scrap with higher purity and fewer impurities, it is possible to reduce the difficulty of removing impurities in subsequent processes and increase the purity of molten steel.

[0038] (2) Refining The molten steel obtained from the molten steel smelting process is refined in an LF furnace. Here, deoxidation and desulfurization are performed by generating white slag during refining, the refining time is ≥ 35 min, the white slag generation time is ≥ 15 min, the contents of other alloys are adjusted to meet the target range before the ferro-titanium wire is introduced, and the soft stirring time in the later stage of refining is ≥ 15 min. By controlling the timing of introducing the ferro-titanium wire, the melting loss of titanium in the early stage of refining can be avoided, the yield of titanium element can be improved, the chemical composition of the final wire can be optimized, and the production cost can be effectively reduced. By controlling the time of various processes in refining, the homogenization of the molten steel can be greatly improved, the macro-segregation and micro-segregation of the resulting steel billet can be reduced, and the structure and strength of the final wire can be improved.

[0039] (3) Steel billet casting The molten steel obtained from the refining process is subjected to fully protected casting. Here, the molten steel superheat is set to 18-35°C, and the casting speed of the cast billet is kept constant at 2.5-2.7m / min. A steel billet with a cross-sectional size of 140mm x 140mm is obtained, and the size of the steel billet is not limited to this. Here, by controlling the parameters such as the superheat and the casting speed, the homogenization of the molten steel can be significantly improved, the component segregation of the steel billet can be reduced, and the structure and strength of the finally obtained wire rod can be improved.

[0040] (4) Temperature-controlled heating The obtained steel billet is heated in a heating furnace while controlling the temperature. Preferably, the temperature of the heating zone is 960 to 1020°C, and the temperature of the soaking zone is 1080 to 1120°C.

[0041] (5) Temperature-controlled rolling The steel billet obtained in the temperature-controlled heating step is descaled with high-pressure water and rolled into a wire rod. The wire rod has a chemical composition, in mass percent, of 0.03-0.08% C, 0.5-1.0% Si, 1.4-1.8% Mn, 0.013-0.1% S, P≦0.0015%, Ni≦0.8%, Cr≦0.4%, and Mo≦0.4%, with the balance being Fe and unavoidable impurities, and the mass percents of C, Si, Mn, P, and S are less than or equal to a liquidus temperature T L =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T S =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T L -T S ≦45℃. Thus, when the wire is drawn into a welding wire for welding, the toughness of the weld seam metal and the smooth progress of the welding process can be ensured, the droplets during the welding process can be made fine, the surface tension of the droplets can be reduced, the flow of the deposited metal can be facilitated, and the formability of the weld seam can be improved, while the desulfurization cost in the steelmaking process can be reduced. Furthermore, by controlling the liquidus temperature and solidus temperature of the welding wire, the interval between the melting point and the solidification point of the welding wire can be controlled to control the solidification rate of the weld seam metal, the fluidity of the weld seam metal can be increased, and the solidification rate of the weld molten pool can be increased, so that the problem of the weld seam metal at the 12 o'clock position flowing down during all-position welding can be solved, and the surface of the weld seam can be made uniform and smooth during all-position welding, and the weld bead can be beautifully formed.

[0042] Preferably, the mass percentages of C, Mn, Ni, Cr, and Mo in the chemical components of the wire rod further satisfy the austenite transformation start temperature Ar3=910-310[C]-80[Mn]-55[Ni]-15[Cr]-80[Mo], the bainite transformation start temperature Bs=830-270[C]-90[Mn]-37[Ni]-70[Cr]-83[Mo], and 30°C≦Ar3-Bs≦80°C, thereby ensuring the presence of sufficient ferrite in the weld seam metal, reducing the residual stress and deformation of the weld head, improving the weld forming performance, and the produced welding wire has a stable arc during welding, a uniform and smooth surface of the weld seam during all-position welding, and a beautiful weld bead is formed.

[0043] Here, the descaling water pressure is set to ≧18MPa, and an intermediate rolling mill with machined rolling grooves is used to intensively cool the wire rod after rolling, and then coil it after cooling. By controlling the descaling water pressure, the scale on the surface of the steel billet can be effectively removed, and the remaining scale can be prevented from being pressed deep into the wire rod structure during rolling into wire rod. The use of machined rolling grooves can ensure the flatness of the wire rod surface, and surface defects of the wire rod caused by rough rolling grooves can be improved.

[0044] Preferably, when the steel billet is rolled after high-pressure water descaling, the rolling start temperature is 970-1000° C., and the finishing mill inlet temperature is≦880° C. The low-temperature rolling can improve the plasticity of the rolled wire rod.

[0045] After the rolling, the wire is water-cooled and then wound, and the winding temperature is 880 to 910° C. In other words, water-cooling is performed between the rolling mill and the laying head.

[0046] Specifically, in this embodiment, at least three water-cooled tanks are arranged in sequence between the rolling mill and the laying head, and when the wire rod passes through the three water-cooled tanks after leaving the rolling mill, only a maximum of two water-cooled tanks close to the laying head are opened, and the remaining water-cooled tanks are closed. Of course, in other embodiments, the number of water-cooled tanks used is not limited to this.

[0047] (6) Stelmore Annealing The wire rod obtained in the temperature controlled rolling process is slowly cooled on a Stelmor slow cooling line at a cooling rate of ≦0.8°C / s in the phase transformation temperature range of the wire rod with all heat retaining covers and blower outlets closed, thereby extending the residence time of the wire rod in the phase transformation temperature range, realizing rational control of the thickness and structure of the scale on the wire rod surface, and improving the mechanical peelability of the scale.

[0048] In the Stelmor annealing line, the total length of all the insulation covers is >80m, the inlet roller table speed of the Stelmor annealing line is ≦0.18m / s, and the outlet roller table speed is ≦0.40m / s, so that the cooling rate of the wire in the phase transformation temperature range of ≦0.8℃ / s is realized, the residence time in the phase transformation temperature range is extended, and the thickness and structure of the scale on the wire surface are reasonably controlled to facilitate scale peeling, and the uniformity of the internal structure of the wire is improved, which is helpful for drawing the wire into welding wire.

[0049] Specific embodiments of the present invention will be described below with reference to five specific examples numbered 1 to 5, as well as three comparative examples numbered 6 to 8.

[0050] (1) Molten steel smelting The smelting raw materials consisting of molten pig iron and steel scrap are smelted in a 180 t converter, and at 1 / 3 of the tapping, ferrosilicon alloy, silicomanganese alloy, low carbon ferromanganese alloy, and lime are added to the molten steel in this order. Here, the mass percentage of S in the molten pig iron for each ladle is 0.03 to 0.18%, and the total amount of smelting raw materials charged, the weight percentage of the molten pig iron in the smelting raw materials, the smelting time, the mass percentage of C at the time of tapping, the tapping temperature, etc. for five examples and three comparative examples are as shown in Table 1. [Table 1]

[0051] Here, the steel scrap used in the five examples is head and tail scrap of billets produced by cutting low carbon steel, while the three comparative examples use general steel scrap.

[0052] (2) Refining The molten steel obtained from the molten steel smelting process is refined in an LF furnace, where deoxidation and desulfurization are performed by generating white slag during refining, the contents of other alloys are adjusted to meet the target range before the ferro-titanium wire is added, and soft stirring is performed in the later stage of refining, with the operation criterion being that the slag surface is gently shaking and the molten steel is not exposed.

[0053] The refining time, white slag generation time, soft stirring time, and tapping temperature for the five examples and three comparative examples are shown in Table 2. [Table 2]

[0054] (3) Steel billet casting The molten steel obtained from the refining process is cast with complete protection. That is, a large ladle long nozzle argon seal, tundish powder, and the entire nozzle are completely protected and argon sealed for casting. The casting speed of the cast billet is kept constant during casting, and the mold electromagnetic stirring current is controlled to 350A, frequency 4Hz, and the final electromagnetic stirring current is controlled to 480A, frequency 10Hz, and the billet is cast into a square billet with a cross-sectional size of 140mm x 140mm. The molten steel superheat and casting speed for the five examples and three comparative examples are as shown in Table 3. [Table 3]

[0055] (4) Temperature-controlled heating The obtained steel billet is heated in a heating furnace while controlling the temperature. The temperature of the heating zone, the temperature of the soaking zone, the air-fuel ratio of the soaking zone, and the heat retention time for five examples and three comparative examples are as shown in Table 4. [Table 4]

[0056] (5) Temperature-controlled rolling The steel billet obtained in the temperature-controlled heating process is descaled with high-pressure water and rolled into a wire rod. The descaling water pressure, the amount of molten steel passing through the carbide roller rings used in the last two passes of finish rolling, the rolling start temperature, the finish rolling mill inlet temperature, and the coiling temperature for the five examples and three comparative examples are as shown in Table 5. In addition, three tanks, numbered 5#, 6#, and 7#, are provided between the finish rolling mill of the last pass and the laying head, in that order from front to rear, and the open states of the three tanks in the five examples and three comparative examples are also as shown in Table 5. [Table 5]

[0057] (6) Stelmore Annealing The wire obtained in the temperature controlled rolling process is annealed on a Stelmor annealing line at a cooling rate of ≦0.8°C / s in the phase transformation temperature range of the wire with all heat-insulating covers and blower outlets closed. The total length of all heat-insulating covers, inlet roller table speed, outlet roller table speed, etc. of the Stelmor annealing lines of five examples and three comparative examples are as shown in Table 6.

[0058] Here, an infrared thermometer was used to measure the temperature of the wire between each heat-insulating cover, and the cooling rate of the wire in the phase transformation temperature range was calculated based on the temperature, and the cooling rates of the overlapping portion and the non-overlapping portion are shown in Table 6. The overlapping portion refers to the area where adjacent wires are in contact, and the non-overlapping portion refers to the area where different wires are not in contact with each other. [Table 6]

[0059] In the five examples and three comparative examples, the final wire products are manufactured according to the above-mentioned production method, and the obtained wire products are inspected.

[0060] Here, the chemical components and weight percentages (numerical unit %) of the finished wire rod are as shown in Table 7. Among them, the wire rods of five examples have the chemical components, in mass percent, of 0.03-0.08% C, 0.5-1.0% Si, 1.4-1.8% Mn, 0.013-0.1% S, P≦0.0015%, Ni≦0.8%, Cr≦0.4%, and Mo≦0.4%, with the balance being Fe and unavoidable impurities. In addition, the liquidus temperature T L =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T S =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T L -T S ≦45℃, and the austenite transformation start temperature Ar3 = 910-310[C]-80[Mn]-55[Ni]-15[Cr]-80[Mo], the bainite transformation start temperature Bs = 830-270[C]-90[Mn]-37[Ni]-70[Cr]-83[Mo], and 30℃≦Ar3-Bs≦80℃ are also satisfied. [Table 7]

[0061] The measured structure and mechanical properties of the wire are shown in Table 8. [Table 8]

[0062] (7) Withdrawal The wire obtained from the Stelmor annealing process was drawn into a welding wire having a diameter of 1.2 mm, and the welding wire was applied to gas-shielded welding using (Ar+20%CO 2 The welding test was carried out using 10 ... [Table 9]

[0063] In addition to the implementation verification, referring to Fig. 1 showing the photographs of the welded seams in some of the examples 1 to 5, it can be seen that the finished wire rods produced using the chemical composition and production method described in this embodiment in Examples 1 to 5 have excellent welding process performance when drawn into welding wire, and the surface of the welded seam is uniform and smooth when used in all-position welding, and the weld bead is beautifully formed. Referring to Fig. 2 showing the photographs of the welded seams in some of the examples of Comparative Examples 6 to 8, it can be seen that the contents of some elements and important production process parameters in Comparative Examples 6 to 8 are outside the scope of this embodiment, and the welding process performance is poor when drawn into welding wire, and the surface of the welded seam is rough and there are obvious drip marks when used in all-position welding.

[0064] The above-described examples are merely illustrative of specific embodiments of the present invention and should not be construed as limiting the scope of the present invention. Any modifications made by those skilled in the art based on the concept of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A steel wire rod for gas-shielded welding wire, comprising, in mass percent, 0.03-0.08% C, 0.5-1.0% Si, 1.4-1.8% Mn, 0.013-0.1% S, P≦0.0015%, Ni≦0.8%, Cr≦0.4%, Mo≦0.4%, and the balance being Fe and unavoidable impurities, wherein the mass percents of C, Si, Mn, P, and S are such that the liquidus temperature T Ｌ =1537-88[C]-8[Si]-5[Mn]-30[P]-25[S], solidus temperature T Ｓ =1536-415[C]-12[Si]-6.8[Mn]-125[P]-184[S], 25℃≦T Ｌ -T Ｓ 3. A steel wire material for gas-shielded welding wire, comprising:

2. 2. The steel wire rod for gas shielded welding wire according to claim 1, characterized in that the mass percentages of C, Mn, Ni, Cr, and Mo satisfy the following: austenite transformation start temperature Ar3 = 910 - 310 [C] - 80 [Mn] - 55 [Ni] - 15 [Cr] - 80 [Mo], bainite transformation start temperature Bs = 830 - 270 [C] - 90 [Mn] - 37 [Ni] - 70 [Cr] - 83 [Mo], and 30°C ≦ Ar3 - Bs ≦ 80°C.

3. A gas-shielded welding wire, characterized in that it is manufactured using the steel wire material for gas-shielded welding wire according to claim 1 as a base material.

4. A molten steel smelting process; The refining process, a steel billet casting process for casting the molten steel obtained by refining into a steel billet; a temperature-controlled heating step of heating the obtained steel billet in a heating furnace while controlling the temperature; a temperature-controlled rolling step in which the steel billet obtained in the temperature-controlled heating step is descaled with high-pressure water having a descaling water pressure of ≧18 MPa and rolled into a wire rod, and the wire rod is intensively cooled after the rolling is completed using an intermediate rolling mill having a machined rolling groove, and then coiled after cooling; a Stelmor annealing process in which the wire rod obtained in the temperature controlled rolling process is annealed on a Stelmor annealing line at a cooling rate of ≦0.8° C. / s in a phase transformation temperature range of the wire rod with all heat-retaining covers and blower outlets closed; 2. The method for producing a steel wire rod for gas shielded welding wire according to claim 1, comprising the steps of:

5. 5. The method for producing a steel wire rod for gas-shielded welding wire according to claim 4, characterized in that on the Stelmor annealing line, a total length of all heat-insulating covers is >80 m, the inlet roller table speed of the Stelmor annealing line is ≦0.18 m / s, and the outlet roller table speed thereof is ≦0.40 m / s.

6. 5. The method for producing a steel wire rod for gas shielded welding wire according to claim 4, characterized in that in the temperature controlled rolling process, the rolling start temperature is 970 to 1000°C, the finish rolling mill inlet temperature is ≦880°C, and the coiling temperature is 880 to 910°C.

7. 5. The method for producing a steel wire rod for gas shielded welding wire according to claim 4, characterized in that, in the refining step, deoxidation and desulfurization are performed by forming white slag during refining, the refining time is ≧35 min, the white slag formation time is ≧15 min, the contents of other alloys are adjusted to satisfy a target range before the ferrotitanium wire is charged, and the soft stirring time in the latter stage of refining is ≧15 min, and the molten steel obtained from the molten steel smelting step is refined in an LF furnace.

8. 5. The method for producing a steel wire rod for gas-shielded welding wire according to claim 4, characterized in that in the steel billet casting step, the molten steel superheat is set to 18 to 35°C, and the casting speed of the cast billet is kept constant at 2.5 to 2.7 m / min, thereby performing fully protected casting of the molten steel obtained from the refining step.

9. 5. The method for producing a steel wire rod for gas-shielded welding wire according to claim 4, characterized in that in the temperature-controlled heating step, the temperature of the heating part is set to 960 to 1020°C, and the temperature of the soaking part is set to 1080 to 1120°C.

10. 5. The method for producing a steel wire rod for gas shielded welding wire according to claim 4, characterized in that in the molten steel smelting step, raw materials consisting of molten pig iron and steel scrap are smelted in a converter, the weight percentage of the molten pig iron in the raw materials is >90%, and a ferrosilicon alloy, a silicomanganese alloy, a low carbon ferromanganese alloy, and lime are added to the molten steel in this order at 1 / 3 tapping.

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