Gas-shielded welding wire, steel wire rod for gas-shielded welding wire, and method for producing the 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 joined by welding, with gas shielded welding being 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 indicators for evaluating the quality of the welded joint. 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 with the weld seam metal flowing down at the 12 o'clock position, i.e., directly above the weld seam, during welding, particularly in all-position welding of pipes, etc., 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 provides a gas-shielded welding wire, a steel wire rod for gas-shielded welding wire, and a method for producing the same, which solve the problem of poor forming performance and uneven weld beads caused by the weld seam metal flowing downward at the 12 o'clock position during all-position welding.

[0006] In order to achieve the object of the 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 compositions: C 0.03 to 0.08%, Si 0.5 to 1.0%, Mn 1.4 to 1.8%, S 0.013 to 0.1%, 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 ... 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 rod for gas-shielded welding wire that satisfies the requirement of a temperature range of 45°C or less.

[0007] Among these, C is one of the important elements in steel wire rods 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 arc stability during welding, and improve droplet transfer properties.

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

[0009] Mn acts as a deoxidizing element during the welding process, forming oxides during deoxidation to improve the strength and toughness of the weld seam. It can also increase the content of acicular ferrite in the weld seam metal, reduce the amount of pro-eutectoid ferrite and ferrite side plates, and refine the 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 rods for welding wire. If the content is too high, elemental segregation is likely to occur in the final stage of molten steel solidification, which is disadvantageous for wire drawing and for the low-temperature toughness of the welded seam.

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

[0013] Cr can increase the content of acicular ferrite in the weld seam, thereby improving 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, by rationally setting the above elements and weight percentage ranges, it is possible to ensure the toughness of the weld seam metal and the smooth progress of the welding process. Furthermore, by rationally designing the mass percentages of C, Si, Mn, P, Ni, Cr, and Mo and controlling the S content, it is possible 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. It also reduces the desulfurization costs in the steelmaking process. Furthermore, by regulating the liquidus temperature and solidus temperature of the welding wire, it is possible to control the interval between the melting point and solidification point of the welding wire and control the solidification rate of the weld seam metal, thereby increasing the fluidity of the weld seam metal and allowing the weld molten pool to solidify quickly, thereby solving the problem of the weld seam metal flowing down at the 12 o'clock position during all-position welding. This ensures that the weld seam surface is uniform and smooth during all-position welding, and that the weld bead is 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], and 30°C ≤ Ar3 - Bs ≤ 80°C. Rational design of the element composition and content allows the austenite transformation start temperature and bainite transformation start temperature to be adjusted and controlled, ensuring sufficient ferrite in the weld seam metal, reducing residual stress and deformation in the weld head, and improving weld forming performance. The resulting welding wire has a stable arc during welding, a uniform and smooth weld seam surface during all-position welding, and a beautifully formed weld bead.

[0017] To achieve the above object, one embodiment of the present invention provides a gas-shielded welding wire manufactured using the above-mentioned steel wire rod for gas-shielded welding wire as a base material. The steel wire rod for gas-shielded welding wire was used as a base material and drawn into a gas-shielded welding wire with a diameter of 1.2 mm. A deposition welding test was conducted using Ar+20%CO2 as a shielding gas, a welding current of 220-230A, and a welding voltage of 25V. The results showed excellent welding process performance, with the resulting weld seam metal having a tensile strength of 770MPa or more and a -40°C impact energy of 98J or more, and the weld seam also being 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 in which the molten steel obtained by the refining is cast into a steel billet; a temperature-controlled heating step of heating the obtained steel billet in a heating furnace while controlling the temperature; The steel billet obtained in the temperature-controlled heating process is descaled with high-pressure water at a descaling water pressure of 18 MPa or higher and rolled into a wire rod. After the wire rod is rolled, it is intensively cooled using an intermediate rolling mill with machined rolling grooves, and then coiled after cooling. pressure Extension process (Hereinafter, this may be referred to as the temperature-controlled rolling process.) and, a Stelmor slow cooling step in which the wire rod obtained in the temperature controlled rolling step 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 of the heat insulating covers and the air blower outlets closed; a production method for producing the steel wire rod for gas shield welding wire, the production method comprising the steps of:

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

[0020] In a further improvement of one embodiment, the total length of all insulation covers on the Stelmor annealing line is greater than 80 m, the inlet roller table speed of the Stelmor annealing line is ≦0.18 m / s, and the outlet roller table speed is ≦0.40 m / s, thereby achieving a cooling rate of ≦0.8°C / s in the phase transformation temperature range of the wire, extending the residence time in the phase transformation temperature range, rationally controlling the thickness and structure of the 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] In a further improvement of one embodiment, in the temperature-controlled rolling step, 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. 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 refinement of one embodiment, the refining process includes deoxidizing and desulfurizing the molten steel by forming a white slag during refining, setting the refining time to ≥ 35 min and the white slag formation time to ≥ 15 min, adjusting the contents of other alloys to meet target ranges before adding the ferrotitanium wire, and setting the soft stirring time in the later stage of refining to ≥ 15 min, and refining the molten steel in an LF furnace. Controlling the timing of adding the ferrotitanium wire avoids titanium melting in the early stage of refining, improves the yield of titanium element, optimizes the chemical composition of the final wire rod, effectively reduces production costs, and ensures the structure, strength, and welding performance of the produced wire rod. Furthermore, time management during refining improves the uniformity of the components in the molten steel, reducing macro- and microsegregation in the steel billet, improving the structure and strength of the final wire rod and facilitating drawing into welding wire.

[0023] In a further improvement of one embodiment, 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 maintained constant at 2.5 to 2.7 m / min, thereby performing 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 element 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] In a further improvement of one embodiment, in the temperature-controlled heating step, the temperature of the heating zone is set to 960 to 1020°C, and the temperature of the soaking zone is set to 1080 to 1120°C.

[0025] In a further refinement of one embodiment, the molten steel smelting process comprises smelting raw materials consisting of molten pig iron and steel scrap in a converter, the weight percentage of the molten pig iron in the raw materials being greater than 90%, and adding a ferrosilicon alloy, a silicomanganese alloy, a low-carbon ferromanganese alloy, and lime to the molten steel in this order at the one-third tapping stage. In this manner, controlling the weight percentage of the molten pig iron and the timing of adding the various alloys and lime ensures high purity of the molten steel components, improves the structure and strength of the wire rod and the final welding wire, and further aids in drawing the wire rod into 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 method for producing the same of the present invention, by rationally designing the composition and mass percentage thereof, not only reduce the desulfurization cost in the steelmaking process, but also improve the fluidity of the weld seam metal, the solidification rate of the weld molten pool, and the formability of the weld seam, solving the problem of the weld seam metal at the 12 o'clock position flowing downward during all-position welding, ensuring a uniform and smooth surface of the weld seam during all-position welding, and beautifully forming the weld bead; furthermore, by improving the uniformity and purity of the molten steel components, the macro- and micro-segregation of the billet can be reduced, and the depth of surface defects in the wire rod can be reduced. By making the structure and strength of the entire wire uniform and improving the mechanical peelability and plasticity of the scale, the wire finally obtained using this production method can achieve a tensile strength of 650 MPa or more, has excellent drawability, and can be drawn into a gas-shielded welding wire with a diameter of 1.2 mm. When a deposition welding test was conducted using Ar+20% CO2 as the shielding gas, with a welding current of 220-230 A and a welding voltage of 25 V, it was found to have excellent welding process performance, with the resulting weld seam metal having a tensile strength of 770 MPa or more and a -40°C impact energy of 98 J or more, and the weld seam being beautifully formed. [Brief explanation of the drawings]

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

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

[0029] The steel wire rod for gas-shielded welding wire of the present invention contains, in mass percent, the chemical compositions of C 0.03 to 0.08%, Si 0.5 to 1.0%, Mn 1.4 to 1.8%, S 0.013 to 0.1%, 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 such that the mass percentages 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 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, 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 rod 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 rod 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 rod for gas-shielded welding wire to a drawing process. The gas-shielded welding wire has a diameter of 1.2 mm, and when subjected to a deposition welding test using Ar+20%CO2 as a shielding gas, a welding current of 220-230A, and a welding voltage of 25V, the gas-shielded welding wire has excellent welding process performance, with the resulting weld seam metal having a tensile strength of 770MPa or more and a -40°C impact energy of 98J or more, and the weld seam being 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 extensive testing and 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 pig iron and steel scrap, are smelted in a converter, and the weight percentage of the raw materials in the molten pig iron is greater than 90%. This ensures 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 of the molten steel and form slagging, effectively improving the purity of the molten steel and 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 billets cut during low-carbon steel smelting, but is not limited thereto. Using high-quality steel scrap with higher purity and fewer impurities reduces the difficulty of removing impurities in subsequent processes, and can increase the purity of molten steel.

[0038] (2) Refining The molten steel obtained from the smelting process is refined in an LF furnace. During the refining process, deoxidation and desulfurization are performed by generating white slag. The refining time is ≥ 35 min, with the white slag generation time ≥ 15 min. The contents of other alloys are adjusted to meet target ranges before the ferrotitanium wire is added, and the soft stirring time in the later stages of refining is ≥ 15 min. Controlling the timing of the ferrotitanium wire addition prevents titanium loss in the early stages of refining, improves titanium yield, optimizes the chemical composition of the final wire rod, and effectively reduces production costs. Managing the time of various refining processes significantly improves the homogenization of the molten steel, reduces macro- and microsegregation in the resulting steel billet, and improves the structure and strength of the final wire rod.

[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 to 35°C, and the casting speed of the cast billet is maintained constant at 2.5 to 2.7 m / min. A steel billet with a cross-sectional size of 140 mm x 140 mm is obtained, although the size of the steel billet is not limited to this. Here, by controlling parameters such as the superheat and casting speed, the homogenization of the molten steel can be significantly improved, and the elemental segregation of the steel billet can be reduced, resulting in improved structure and strength of the final wire rod obtained.

[0040] (4) Temperature-controlled heating The obtained steel billet is heated in a heating furnace while controlling the temperature. Preferably, the temperature in the heating zone is 960 to 1020°C, and the temperature in 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 having 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 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 ≦45℃。 Therefore, when the wire is drawn into a welding wire and used for welding, it is possible to ensure the toughness of the weld seam metal and the smooth progress of the welding process, to make the droplets finer during the welding process, to reduce the surface tension of the droplets, to facilitate the flow of the deposited metal, and to improve the formability of the weld seam, and it is also possible to reduce the desulfurization cost in the steelmaking process. Furthermore, by controlling the liquidus temperature and solidus temperature of the welding wire, the interval between the melting point and solidification point of the welding wire is controlled, which controls the solidification rate of the weld seam metal, improves the fluidity of the weld seam metal, and speeds up the solidification rate of the weld molten pool, thereby solving the problem of the weld seam metal at the 12 o'clock position flowing down during all-position welding, and it is possible to ensure a uniform and smooth surface of the weld seam and beautifully form the weld bead during all-position welding.

[0042] Preferably, the mass percentages of C, Mn, Ni, Cr, and Mo in the chemical components of the wire rod further 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. This ensures sufficient ferrite in the weld seam metal, reduces residual stress and deformation in the weld head, improves weld forming performance, and the produced welding wire has a stable arc during welding, a uniform and smooth weld seam surface during all-position welding, and produces a beautifully formed weld bead.

[0043] Here, the descaling water pressure is set to ≥ 18 MPa, 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, 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 ensures the flatness of the wire rod surface and also improves surface defects of the wire rod caused by rough rolling grooves.

[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. Low-temperature rolling can improve the plasticity of the rolled wire rod.

[0045] After the rolling, the wire rod is water-cooled and then coiled, and the coiling temperature is 880 to 910° C. That is, 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 closest 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 the heat insulating cover and the air blower outlets all 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] The total length of all insulation covers on the Stelmor annealing line is more than 80m, and the inlet roller table speed of the Stelmor annealing line is ≦0.18m / s and the outlet roller table speed is ≦0.40m / s, which achieves a cooling rate of ≦0.8℃ / s in the phase transformation temperature range of the wire, extends the residence time in the phase transformation temperature range, and rationally controls the thickness and structure of the scale on the wire surface, making it easier to peel off the scale and improving the uniformity of the internal structure of the wire, which is beneficial for drawing the wire into welding wire.

[0049] Specific embodiments of the present invention will be described below using 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 were smelted in a 180 ton converter, and at the 1 / 3 tapping stage, a ferrosilicon alloy, a silicomanganese alloy, a low-carbon ferromanganese alloy, and lime were added to the molten steel in this order. The mass percentage of S in the molten pig iron for each ladle was 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, and the tapping temperature for five examples and three comparative examples are shown in Table 1. [Table 1]

[0051] Here, the steel scrap used in the five examples is scrap from the head and tail ends of billets cut from 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 latter stage of refining, with the soft stirring being performed so that the slag surface is gently shaking without exposing the molten steel.

[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 was cast with complete protection. Specifically, a large ladle long nozzle was sealed with argon, and the tundish powder and nozzle were completely protected and sealed with argon. The casting speed of the cast billet was maintained constant during casting, and the mold electromagnetic stirring current was controlled at 350 A and a frequency of 4 Hz, and the final electromagnetic stirring current was controlled at 480 A and a frequency of 10 Hz. The molten steel superheat and casting speed for the five examples and three comparative examples are shown in Table 3. [Table 3]

[0055] (4) Temperature-controlled heating The obtained steel billet was 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 the 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 wire rod. The descaling water pressure, the amount of molten steel passing through the carbide roller rings used in the final 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. Three tanks, numbered 5, 6, and 7, were installed between the finish rolling mill of the final pass and the laying head, and the opening 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 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 with all heat insulating covers and air blower outlets closed. The total length of all heat insulating covers, inlet roller table speed, outlet roller table speed, etc. of the Stelmor slow cooling lines of the five examples and three comparative examples are as shown in Table 6.

[0058] Here, the temperature of the wire between each insulation cover was measured using an infrared thermometer, and the cooling rate of the wire in the phase transformation temperature range was calculated based on the temperature. 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 contact each other, and the non-overlapping portion refers to the area where wires do not contact each other. [Table 6]

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

[0060] The chemical components and weight percentages (unit: %) of the finished wire rods are shown in Table 7. Of these, the wire rods of five examples satisfy the following chemical components in mass percentage: 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%, with the balance being Fe and unavoidable impurities. 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 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℃≦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) Pulling out The wire obtained from the Stelmor slow cooling process was drawn into a welding wire with a diameter of 1.2 mm, and the welding wire was applied to gas-shielded welding, and a deposition welding test was carried out using (Ar + 20% CO2) as the shielding gas. As a result, the tensile strength and -40°C impact energy of the weld seam metal measured at a welding current of 220 to 230 A and a welding voltage of 25 V are shown in Table 9. [Table 9]

[0063] 1, which shows photographs of weld seams in some of Examples 1 to 5, it can be seen that the finished wires produced using the chemical compositions and production methods described in this embodiment in Examples 1 to 5 have excellent welding process performance when drawn into welding wire, and when used in all-position welding, the weld seam surfaces are uniform and smooth, and the weld beads are beautifully formed. FIG. 2, which shows photographs of weld seams in some of Comparative Examples 6 to 8, shows that the contents of some elements and key production process parameters in Comparative Examples 6 to 8 are outside the ranges of this embodiment, and therefore have poor welding process performance when drawn into welding wire, and when used in all-position welding, the weld seam surfaces are rough and have obvious drip marks.

[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 containing, in mass percent, the following chemical compositions: C 0.03 to 0.08%, Si 0.5 to 1.0%, Mn 1.4 to 1.8%, S 0.013 to 0.1%, 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 1. A steel wire rod for gas-shielded welding wire, characterized in that it satisfies the condition that the temperature of the welding wire is ≦45°C.

2. 2. The steel wire rod for gas-shielded welding wire according to claim 1, wherein 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 containing, in mass percent, the following chemical compositions: 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, wherein the mass percents of C, Si, Mn, P, and S are such that the wire 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 1. A gas-shielded welding wire, characterized in that it satisfies the requirement of ≦45°C.

4. a molten steel smelting process; The refining process, a steel billet casting process in which the molten steel obtained by the refining is cast into a steel billet; a temperature-controlled heating step of heating the obtained steel billet in a heating furnace while controlling the temperature; a 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 rolling using an intermediate rolling mill having machined rolling grooves, and then coiled after cooling; a Stelmor annealing step in which the wire rod obtained in the rolling step 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 of the heat-insulating covers and the air blower outlets closed; 2. The method for producing a steel wire rod for gas shield 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, wherein the total length of all heat insulating covers on the Stelmor annealing line is greater than 80 m, the speed of the roller table at the entrance of the Stelmor annealing line is ≦0.18 m / s, and the speed of the roller table at the exit of the Stelmor annealing line is ≦0.40 m / s.

6. 5. The method for producing a steel wire rod for gas-shielded welding wire according to claim 4, wherein in the rolling step, a rolling start temperature is 970 to 1000°C, a finish rolling mill inlet temperature ≦880°C, and a 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, wherein in the refining step, deoxidation and desulfurization are performed by generating white slag during refining, the refining time is set to ≥ 35 min, the white slag generation time is set to ≥ 15 min, the contents of other alloys are adjusted to satisfy target ranges before the ferro-titanium wire is introduced, and the soft stirring time in the latter stage of refining is set to ≥ 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, wherein 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 in the refining step.

9. 5. The method for producing a steel wire rod for gas-shielded welding wire according to claim 4, wherein in the temperature-controlled heating step, the temperature of the heating zone is set to 960 to 1020°C, and the temperature of the soaking zone 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, wherein 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 greater than 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 one-third of the tapping stage.

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