Wire rod for electrode and method for manufacturing the same

Abstract

Provided are a wire for welding electrode and a method for manufacturing the same. One aspect of the present disclosure provides a wire for welding electrode and a method for manufacturing the same. Preferably, one preferred aspect of the present disclosure provides a wire for welding electrode and a method for manufacturing the same, which have excellent strength and wire drawing workability while having excellent economic feasibility.

Description

Technical Field

[0001] This disclosure relates to welding electrode wires and their manufacturing methods. Background Technology

[0002] In the case of welding electrode wire, a wire with a diameter of about 5.5 mm is processed into a diameter of about 2.2 mm by a first wire drawing, and then subjected to wire drawing heat treatment and plating process, and then manufactured into a welding electrode with a final diameter of 0.8 mm to 1.6 mm by a second wire drawing.

[0003] In this paper, in the case of conventional ultra-high strength wire, in order to ensure the wire drawing processability, a preheating treatment is performed in the step before the first wire drawing, which leads to increased production costs and reduced productivity.

[0004] Meanwhile, in the case of conventional welding electrode wire, in order to ensure the low-temperature impact physical properties required during multi-layer welding of thick plates, expensive Ni is included in an amount of about 2% to 3%, and when it is applied to the automotive industry, the increased manufacturing cost becomes an obstacle to expanding industrial applications.

[0005] Technologies related to wire for welding electrodes include patent documents 1 and 2.

[0006] Patent document 1 discloses a special welding electrode wire containing, by weight: 0.03% to 0.13% C, 1.5% to 2.5% Mn, 0.5% to 1.2% Si, 0.2% to 0.4% Mo, 0.1% to 0.3% Ti, 70 ppm or less N, 0.03% or less S, the balance being Fe and other unavoidable impurities, wherein the average grain size is 10 μm to 30 μm.

[0007] Patent document 2 discloses a wire for welding electrodes, comprising, by weight: 0.01% to 0.15% C, 0.001% to 0.15% Si, 0.5% to 3.0% Mn, greater than 0% and 0.03% or less P, greater than 0% and 0.03% or less S, greater than 0% and 0.5% or less Cu, 0.05% to 0.9% Ni, 0.001% to 0.1% Cr, and 0.001% to 0. The wire material contains at least one or more of the following: 0.5% Mo, 0.001% to 0.05% Al, 0.0005% to 0.01% B, 0.001% to 0.01% N, and V, Nb and Ti (0.05% to 0.2% V, 0.005% to 0.1% Nb, and 0.05% to 0.3% Ti), with the balance being Fe and unavoidable impurities, wherein the tensile strength of the wire material is up to 700 MPa, with a deviation of 40 MPa or less.

[0008] However, the tensile strength of patent documents 1 and 2 is low, and they are difficult to apply to welding steel used for gigabit steel.

[0009] [Related Technical Documents]

[0010] (Patent Document 1) Korean Patent Registration Publication No. 1060785

[0011] (Patent Document 2) Korean Patent Publication No. 2024-0063539 Summary of the Invention

[0012] Technical issues

[0013] One aspect of this disclosure provides wire for welding electrodes and a method for manufacturing the same.

[0014] A preferred aspect of this disclosure provides a welding electrode wire with excellent strength and wire drawing processability, as well as excellent economic feasibility, and a method for manufacturing the same.

[0015] The purpose of this disclosure is not limited to the above description. Other purposes of this disclosure will be readily apparent to those skilled in the art based on the general description herein.

[0016] Technical solution

[0017] According to one aspect of this disclosure, the welding electrode wire, by weight, comprises: 0.050% to 0.160% C, 0.0010% to 0.250% Si, 1.0% to 2.50% Mn, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.40% to 6.0% Cr, 0.10% to 0.650% Mo, 0.20% or less (excluding 0%) Al, 0.40% or less (excluding 0%) Ni, 0.20% or less (excluding 0%) Ti, 0.10% or less (excluding 0%) Nb, with the balance being Fe and other unavoidable impurities, wherein the microstructure comprises bainitic ferrite having a minimum effective grain size of 0.50 μm or greater, and bainitic ferrite having a minimum effective grain size of 20.0 μm. Maximum effective grain size of μm or smaller.

[0018] The wire may also contain one or more of 0.20% or less V, 0.10% or less Zr, and 0.010% or less B.

[0019] The wire may also contain 0.50% or less Cu.

[0020] The microstructure may contain 0.50% or less (including 0%) of retained austenite and the balance of bainitic ferrite by area.

[0021] The average effective grain size of bainitic ferrite can be 10 μm or smaller.

[0022] The tensile strength of the wire can range from 840 MPa to 1000 MPa.

[0023] The reduction of area (RA) of the wire can be 60% to 75%.

[0024] According to another aspect of this disclosure, a method for manufacturing wire for welding electrodes includes: preparing a steel billet, said steel billet comprising, by weight: 0.050% to 0.160% C, 0.0010% to 0.250% Si, 1.0% to 2.50% Mn, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.40% to 6.0% Cr, 0.10% to 0.650% Mo, 0.20% or less (excluding 0%) Al, 0.4%... 0% or less (excluding 0%) of Ni, 0.20% or less (excluding 0%) of Ti, 0.10% or less (excluding 0%) of Nb, the balance of Fe and other unavoidable impurities; reheating the billet at 1050°C to 1250°C; removing the reheated billet at 1050°C to 1150°C and then rolling it into wire to obtain wire; coiling the wire at 860°C to 940°C; and cooling the wire on a Steyrmo cooling conveyor at a cooling rate of 2.0°C / sec to 3.0°C / sec.

[0025] The billet may also contain one or more of 0.20% or less V, 0.10% or less Zr, and 0.010% or less B.

[0026] The billet may also contain 0.50% or less Cu.

[0027] Beneficial effects

[0028] According to one aspect of this disclosure, wire for welding electrodes and a method for manufacturing the same may be provided.

[0029] According to a preferred aspect of this disclosure, a welding electrode wire and a method thereof can be provided that have excellent strength and wire drawing processability while also having excellent economic feasibility. Attached Figure Description

[0030] Figure 1 To observe the image quality (IQ) and inverse pole figure (IPF) photographs of Invention Example 2 using EBSD.

[0031] Figure 2 To observe the image quality (IQ) and inverse pole figure (IPF) images of Comparative Example 3 using EBSD.

[0032] Figure 3 To observe the image quality (IQ) and inverse pole figure (IPF) images of Comparative Example 7 using EBSD. Detailed Implementation

[0033] Preferred embodiments of this disclosure will be described below. However, embodiments of this disclosure can be modified in many different forms, and the scope of this disclosure should not be limited to the embodiments set forth herein.

[0034] Furthermore, the implementation of this disclosure is provided so that this disclosure will be comprehensive and complete, and will fully convey the concept of this disclosure to those skilled in the art.

[0035] In describing embodiments of this specification, detailed descriptions of known techniques related to this disclosure will be omitted where it is determined that such detailed descriptions may unnecessarily obscure the main points of this disclosure. Furthermore, the following terms are defined in consideration of the functionality within this disclosure and may vary depending on the intent, conventions, etc., of the user and operator. Therefore, the terms should be defined based on the content throughout this specification. The terms used in the detailed description are for describing exemplary embodiments of this disclosure and should not be limiting. Unless expressly used otherwise, the singular form includes the meaning of the plural form.

[0036] Expressions such as “comprising” or “provided” in this specification are used to refer to certain features, quantities, steps, actions, elements, or parts or combinations thereof, and should not be construed as excluding the presence or possibility of one or more other features, quantities, steps, actions, elements, or parts or combinations thereof other than those described herein.

[0037] Unless otherwise defined in the description of this disclosure, % refers to weight.

[0038] The present disclosure will be described in detail below through various embodiments or examples. It should be noted that the embodiments or examples described in this specification are not only intended to describe one embodiment or example, but also to be combined with other embodiments or examples. Therefore, references to the claims are merely examples of embodiments and should not be construed as simply combining the technical concept of the present disclosure with the referenced claims; various combinations with the claims are also included within the scope of the technical concept of the present disclosure.

[0039] The following describes a welding electrode wire according to one embodiment of this disclosure. First, the alloy composition of this disclosure will be described. Unless otherwise specified, the alloy composition described below is in weight percent.

[0040] C: 0.050% to 0.160%

[0041] Carbon (C) is an element that helps ensure the strength of the weld zone by improving hardenability. When the C content is 0.050% or less, it may be difficult to impart sufficient strength to the weld metal when welding ultra-high strength steel with a tensile strength of 1 GPa or greater. When the C content is greater than 0.160%, the viscosity of the molten metal decreases during arc welding, resulting in a deterioration of the weld bead shape, and the weld metal also becomes over-hardened, increasing brittleness. Therefore, the C content can be in the range of 0.050% to 0.160%. The lower limit of the C content is more preferably 0.055%, even more preferably 0.060%, and most preferably 0.065%. The upper limit of the C content is more preferably 0.155%, even more preferably 0.150%, and most preferably 0.145%.

[0042] Si: 0.0010% to 0.250%

[0043] Si is an element that promotes deoxidation of molten metal during arc welding, and it is beneficial for ensuring the strength of the weld zone due to its ability to suppress pore defects such as porosity. When the Si content is less than 0.0010%, pore defects such as porosity easily occur in the weld zone due to insufficient deoxidation capacity. When the Si content is greater than 0.250%, non-conductive slag appears significantly, thus deteriorating the electrodeposition paintability of the weld zone. Therefore, the Si content can be in the range of 0.0010% to 0.250%. The lower limit of the Si content can be more preferably 0.0025%, even more preferably 0.0050%, and most preferably 0.010%. The upper limit of the Si content is more preferably 0.18%, even more preferably 0.16%, and most preferably 0.14%.

[0044] Mn: 1.0% to 2.50%

[0045] Mn is a deoxidizing element, and because it has the effect of suppressing pore defects such as porosity by promoting deoxidation of the molten metal during arc welding, it is beneficial for ensuring the strength of the weld zone. When the Mn content is less than 1.0%, deoxidation is insufficient within a suitable Si content range, and pore defects such as porosity may easily occur in the weld zone. When the Mn content is greater than 2.50%, the viscosity of the molten metal increases excessively, and when the welding speed is high, the molten metal cannot be properly introduced into the weld, thus forming a raised weld bead, which may easily lead to weld bead shape defects. Therefore, the Mn content can be in the range of 1.0% to 2.50%. The lower limit of the Mn content is more preferably 1.1%, even more preferably 1.2%, and most preferably 1.3%. The upper limit of the Mn content is more preferably 2.45%, even more preferably 2.40%, and most preferably 2.35%.

[0046] P: 0.030% or less (excluding 0%)

[0047] P is an impurity element contained in steel, and when the P content is greater than 0.030%, the weld metal may be susceptible to cracking at high temperatures. While it is advantageous to exclude P from the steel if possible, considering that P is inevitably included during the manufacturing process, excluding 0% is preferable. Therefore, a P content of 0.030% or less (excluding 0%) is preferred. A P content of 0.025% or less is more preferred, even more preferred is 0.020% or less, and most preferably is 0.015% or less.

[0048] S: 0.030% or less (excluding 0%)

[0049] Sulfur (S) is an impurity element contained in steel, and when the S content is greater than 0.030%, it may impair the toughness of the weld metal. While it is advantageous for the steel to be free of S if possible, considering that S is inevitably included during the manufacturing process, 0% is excluded. Therefore, it is preferable that the S content is 0.030% or less (excluding 0%). More preferably, the S content is 0.025% or less, even more preferably 0.020% or less, and most preferably 0.015% or less.

[0050] Cr: 0.40% to 6.0%

[0051] Cr is a ferrite stabilizing element and a hardenable element that helps ensure the strength of weld metal. When the Cr content is less than 0.40%, it may be difficult to impart sufficient strength to the weld metal when welding ultra-high strength steel with a tensile strength of 1 GPa or greater. When the Cr content is greater than 6.0%, δ-ferrite structure may form, or excessive precipitation of chromium carbides may occur in the structure, leading to embrittlement of the weld metal, i.e., reduced toughness. Therefore, the Cr content can be in the range of 0.40% to 6.0%. The lower limit of the Cr content is more preferably 0.70%, even more preferably 1.0%, and most preferably 1.20%. The upper limit of the Cr content is more preferably 5.5%, even more preferably 5.0%, and most preferably 4.5%.

[0052] Mo: 0.10% to 0.650%

[0053] Mo is a ferrite stabilizing element and a hardenable element that helps ensure the strength of weld metal. When the Mo content is less than 0.10%, it may be difficult to impart sufficient strength to the weld metal when welding ultra-high strength steel with a tensile strength of 1 GPa or greater. When the Mo content is greater than 0.650%, the toughness of the weld metal may decrease. Therefore, the Mo content can be in the range of 0.10% to 0.650%. The lower limit of the Mo content is more preferably 0.15%, even more preferably 0.20%, and most preferably 0.25%. The upper limit of the Mo content is more preferably 0.63%, even more preferably 0.61%, and most preferably 0.59%.

[0054] Al: 0.20% or less (excluding 0%)

[0055] Al is a deoxidizing element, and even in trace amounts during arc welding, it contributes to ensuring the strength of the weld metal by promoting the deoxidation of the molten metal. To ensure the above effect, the lower limit of Al content is not 0%. However, for example, during the welding of galvanized steel sheets, Al interferes with the oxidation reaction of Zn (as a deoxidizing effect), thereby promoting the occurrence of porosity defects in the weld zone due to increased zinc vapor and arc instability. When the Al content is greater than 0.20%, the generation of Al-based oxides increases, and in some cases, the strength and toughness of the weld metal decrease, and electrodeposition coating defects in the weld zone due to non-conductive oxides become more sensitive. Therefore, the Al content can be 0.20% or less (excluding 0%). The lower limit of Al content is more preferably 0.001%, even more preferably 0.002%, and most preferably 0.003%. The upper limit of Al content is more preferably 0.19%, even more preferably 0.18%, and most preferably 0.17%.

[0056] Ni: 0.40% or less (excluding 0%)

[0057] Ni is an element that helps ensure the strength and toughness of weld metal. To ensure these effects, the lower limit of Ni content is excluding 0%. When the Ni content is greater than 0.40%, susceptibility to cracking occurs. Therefore, the Ni content can be 0.40% or less (excluding 0%). The lower limit of Ni content is more preferably 0.001%, even more preferably 0.002%, and most preferably 0.003%. The upper limit of Ni content is more preferably 0.39%, even more preferably 0.38%, and most preferably 0.37%.

[0058] Ti: 0.20% or less (excluding 0%)

[0059] Ti is a carbonic acid element and, even in trace amounts, it contributes to improving the strength of the weld metal by promoting the carburization of the molten metal during arc welding. Furthermore, it promotes the development of acicular ferrite, which improves the toughness of the weld zone. To ensure these effects, the lower limit of Ti content is excluding 0%. When the Ti content exceeds 0.20%, the formation of Ti-based oxides increases, and in some cases, the strength and toughness of the weld metal decrease. Therefore, the Ti content can be 0.20% or less (excluding 0%). The lower limit of Ti content is more preferably 0.001%, even more preferably 0.002%, and most preferably 0.003%. The upper limit of Ti content is more preferably 0.19%, even more preferably 0.18%, and most preferably 0.17%.

[0060] Nb: 0.10% or less (excluding 0%)

[0061] Nitrogen (Nb) is an element that improves hardenability and densifies the microstructure, thus contributing to improved strength and toughness of weld metals. Furthermore, it improves metal flow and stabilizes the arc during arc welding. To ensure these effects, the lower limit of Nb content is excluding 0%. When the Nb content exceeds 0.10%, low-melting-point compounds form at grain boundaries, making high-temperature cracking more likely. Therefore, the Nb content can be 0.10% or less (excluding 0%). The lower limit of Nb content is more preferably 0.001%, even more preferably 0.002%, and most preferably 0.003%. The upper limit of Nb content is more preferably 0.09%, even more preferably 0.08%, and most preferably 0.07%.

[0062] The remaining component is iron (Fe). However, since unintended impurities may inevitably be introduced from raw materials or the surrounding environment during ordinary manufacturing processes, this component cannot be excluded. Since these impurities are known to those skilled in the art during ordinary manufacturing processes, not all of them are specifically mentioned in this specification.

[0063] The wires disclosed herein may also contain one or more of 0.20% or less V, 0.10% or less Zr, and 0.01% or less B.

[0064] V: 0.20% or less

[0065] V is a precipitation strengthening element that can generate carbonitrides to improve the strength of weld metal, and it also benefits the strength and toughness of weld metal by improving hardenability and densifying the microstructure. When the V content is greater than 0.20%, excessive precipitates are generated, and therefore, in some cases, the toughness of the weld metal may be reduced due to excessive strength. Therefore, the V content can be 0.20% or less. The V content is more preferably 0.19% or less, even more preferably 0.18% or less, and most preferably 0.17% or less. Furthermore, in this disclosure, there is no particular limitation on the lower limit of the V content, but as an example, the lower limit can be 0.0001%.

[0066] Zr: 0.10% or less

[0067] Zr is an element that promotes deoxidation of molten metal during arc welding and is beneficial in suppressing pore defects such as porosity. When the Zr content is greater than 0.10%, the electrodeposition coating properties of the weld zone may decrease. Therefore, the Zr content can be 0.10% or less. More preferably, the Zr content is 0.09% or less, even more preferably 0.08% or less, and most preferably 0.07% or less. Furthermore, in this disclosure, there is no particular limitation on the lower limit of the Zr content, but as an example, the lower limit can be 0.0001%.

[0068] B: 0.010% or less

[0069] Boolean (B) is an element that improves the strength of weld metal by increasing hardenability. When the B content is greater than 0.010%, in some cases, the toughness of the weld metal may be reduced due to excessive hardenability. Therefore, the B content can be 0.010% or less. More preferably, the B content is 0.009% or less, even more preferably 0.008% or less, and most preferably 0.007% or less. Furthermore, in this disclosure, there is no particular limitation on the lower limit of the B content, but as an example, the lower limit can be 0.0001%.

[0070] The wires disclosed herein may also contain 0.50% or less Cu.

[0071] Cu: 0.50% or less

[0072] Cu is an element that is beneficial for improving corrosion resistance. When the Cu content is greater than 0.50%, the crack susceptibility of the weld metal may increase. Therefore, the Cu content can be 0.50% or less. More preferably, the Cu content is 0.45% or less, even more preferably 0.40% or less, and most preferably 0.35% or less. Meanwhile, in this disclosure, there is no particular limitation on the lower limit of the Cu content, but as an example, the lower limit can be 0.0001%.

[0073] The microstructure of the wire disclosed herein may comprise bainitic ferrite. The bainitic ferrite may have a minimum effective grain size of 0.50 μm or greater. When the minimum effective grain size of the bainitic ferrite is less than 0.50 μm, the strength of the wire increases excessively, thereby relatively reducing the elongation. The minimum effective grain size of the bainitic ferrite may more preferably be 1.0 μm or greater, even more preferably 1.5 μm or greater, and most preferably 2.0 μm or greater. In this disclosure, there is no particular upper limit to the minimum effective grain size of the bainitic ferrite, but as an example, it may be 3.0 μm.

[0074] Bainitic ferrite can have a minimum effective grain size of 20.0 μm or less. When the maximum effective grain size of bainitic ferrite is greater than 20.0 μm, the strength of the wire may be relatively insufficient. The maximum effective grain size of bainitic ferrite can more preferably be 19.0 μm or less, even more preferably 18.0 μm or less, and most preferably 17.0 μm or less. In this disclosure, there is no particular limitation on the lower limit of the maximum effective grain size of bainitic ferrite, but as an example, it can be 15.0 μm.

[0075] Meanwhile, the effective grain size can be defined according to the standard ASTM E2627 as the average grain size converted from the number of grains per unit area. While not specifically limited, for example, to obtain the effective grain size, at least 10 and at most 50 measurements can be performed at random points. Among the effective grain sizes obtained herein, the smallest value is defined as the minimum effective grain size, and the largest value can be defined as the maximum effective grain size. Furthermore, while not specifically limited, for example, to obtain the effective average grain size, it can be defined as the average of the effective grain sizes obtained by performing at least 10 and at most 50 measurements at different points on the wire.

[0076] The average effective grain size of bainitic ferrite can be 10 μm or less. When the average effective grain size of bainitic ferrite is greater than 10 μm, it may be difficult to obtain sufficient strength and elongation of the wire according to the Hall-Petch relationship. The average effective grain size of bainitic ferrite can more preferably be 9 μm or less, even more preferably 8 μm or less, and most preferably 7 μm or less.

[0077] The microstructure of the wire of this disclosure may contain 0.50% or less (inclusive) of retained austenite and the balance of bainitic ferrite by area. Bainitic ferrite is a microstructure that is beneficial in ensuring the strength and elongation of the wire. Meanwhile, retained austenite is an impurity that is unavoidably included during the manufacturing process. Since it is preferred to contain as little retained austenite as possible, its fraction is advantageously 0%. However, considering that retained austenite may inevitably be included in this disclosure, the upper limit may be limited to 0.5%. When the fraction is greater than 0.50%, some dimensional change occurs during the transformation of retained austenite to martensite during wire drawing, and therefore, in some cases, the dimensional accuracy of the drawn wire may decrease during the transformation process.

[0078] The wire of this disclosure, as described above, has a tensile strength ranging from 840 MPa to 1000 MPa. Furthermore, the reduction of area (RA) of the wire of this disclosure can be from 60% to 75%. Moreover, even if the preheating process prior to the first wire drawing is omitted during electrode manufacturing, the wire of this disclosure can ensure a first wire drawing speed of 300 m / min or greater and a second wire drawing speed of 250 m / min or greater. Furthermore, it can be manufactured at low cost and is preferably used as a welding electrode for steels such as gigabit-grade vehicle steels.

[0079] The following describes a method for manufacturing wire for welding electrodes according to one embodiment of the present disclosure.

[0080] First, a steel billet satisfying the above alloy composition is prepared. In this disclosure, there are no particular limitations on the method for preparing the steel billet, and any method used in the art can be used.

[0081] Subsequently, the billet is reheated at 1050°C to 1250°C. The temperature range referred to herein refers to the preheating zone, heating zone, and cracking zone within the reheating section. That is, the temperature is maintained at a relatively low level in the heating zone and gradually increased from the heating zone to the cracking zone. When the reheating temperature is below 1050°C, the interior and exterior of the billet are not uniformly heated, and the subsequent rolling temperature of the billet decreases, potentially causing deformation of the material shape during rolling, which may become an obstacle during the rolling process. When the reheating temperature of the billet is above 1250°C, bending of the material occurs, which may cause problems when removing it by heating. The lower limit of the reheating temperature of the billet is more preferably 1060°C, even more preferably 1070°C, and most preferably 1080°C. The upper limit of the reheating temperature of the billet is more preferably 1240°C, even more preferably 1220°C, and most preferably 1200°C.

[0082] The reheated billet is then removed at 1050°C to 1150°C and subsequently wire-rolled to obtain wire. When the billet removal temperature is below 1050°C, the rolling load on the billet is too high, thus overloading the rolling equipment and potentially causing obstacles during the rolling process. When the billet removal temperature is above 1150°C, the rolls become sensitive to heat damage at high temperatures, and the excessively high temperature during rolling can lead to a deterioration in the billet shape. The lower limit of the billet removal temperature is more preferably 1060°C, even more preferably 1070°C, and most preferably 1080°C. The upper limit of the billet removal temperature is more preferably 1140°C, even more preferably 1130°C, and most preferably 1120°C. In this document, the removal temperature may not exceed the reheating temperature.

[0083] Subsequently, the wire is wound at a temperature between 860°C and 940°C. When the winding temperature is below 860°C, the elongation of the wire decreases, and the winding shape may deteriorate. When the winding temperature is above 940°C, deviations in the material and mechanical properties of the wire are adversely affected, and excessive oxide scale may form on the surface of the wire. The lower limit of the winding temperature is more preferably 870°C, even more preferably 880°C, and most preferably 890°C. The upper limit of the winding temperature is more preferably 930°C, even more preferably 920°C, and most preferably 910°C.

[0084] The wound wire is then cooled on a Steyrmo cooling conveyor at a cooling rate of 2.0°C / s to 3.0°C / s. When the cooling rate is less than 2.0°C / s, the material properties of the wire soften, and in some cases, coil sagging may occur, leading to winding defects. When the cooling rate is greater than 3.0°C / s, the material of the wire hardens, reducing its processability, and therefore preheating is required during wire drawing, increasing manufacturing costs. The lower limit of the cooling rate is more preferably 2.1°C / s, even more preferably 2.2°C / s, and most preferably 2.3°C / s. The upper limit of the cooling rate is more preferably 2.9°C / s, even more preferably 2.8°C / s, and most preferably 2.7°C / s.

[0085] Invention Embodiments

[0086] The present disclosure will be described in detail below by way of examples. However, it should be noted that the examples described below are merely illustrative and are not intended to limit the scope of the present disclosure. This is because the scope of the present disclosure is determined by the matters described in the claims and those reasonably inferred therefrom.

[0087] (Example)

[0088] Steel billets with the alloy compositions described in Tables 1 and 2 were prepared, and then the billets were reheated, rolled, coiled, and cooled under the conditions described in Table 3 to produce wire rods. The microstructure, mechanical properties, etc., of the wire rods thus produced were measured, and the results are shown in Table 4 below. Furthermore, the produced wire rods were subjected to a first wire drawing and a second wire drawing without a preheating process to produce welding electrodes, and the first and second wire drawing speeds were measured, and the results are shown in Table 4 below.

[0089] Microstructure and effective grain size were obtained by collecting samples from wire, grinding the cross-sectional microstructure of the samples, etching with nitric acid ethanol solution (Nital), and observing under an optical microscope. Furthermore, image quality (IQ) and inverse pole figure (IPF) plots were obtained to visualize grain interfaces and grain orientation information by analyzing the Kikuchi pattern via electron backscatter diffraction (EBSD). Subsequently, grains were classified based on the aforementioned EBSD IQ and IPF plots and the microstructure photographs observed under an optical microscope. The effective grain size, converted from the number of grains per unit area, was calculated, and at least 10 and at most 50 such measurements were performed at other points to measure the average effective grain size.

[0090] In mechanical properties, tensile strength is measured using the test method described in ASTM A370.

[0091] In mechanical properties, reduction of area is measured using the test method described in ASTM A 370 and is shown as a percentage of the value obtained by dividing the difference between the initial diameter of the wire and the diameter at which it breaks by the initial diameter of the wire.

[0092] [Table 1]

[0093]

[0094] [Table 2]

[0095]

[0096] [Table 3]

[0097]

[0098] [Table 4]

[0099]

[0100] Figure 1 To observe the image quality (IQ) and inverse pole figure (IPF) photographs of Invention Example 2 using EBSD. Figure 2 To observe the image quality (IQ) and inverse pole figure (IPF) images of Comparative Example 3 using EBSD. Figure 3 To observe the image quality (IQ) and inverse pole figure (IPF) of Comparative Example 7 using EBSD. See Tables 1 to 4 and... Figures 1 to 3 It can be seen that, since the alloy composition and manufacturing conditions of Examples 1 to 4 satisfy the microstructure, the minimum and maximum effective grain sizes of bainitic ferrite, and the average effective grain size of bainitic ferrite, they ensure the tensile strength and reduction of area desired by the present disclosure. Furthermore, it was found that even if the preheating process prior to the first wire drawing during electrode manufacturing is omitted, the first and second wire drawing speeds remain at high levels.

[0101] Comparative Examples 1 to 4, whose alloy compositions do not meet the requirements of this disclosure, failed to ensure the microstructure proposed in this disclosure, or failed to meet the minimum or maximum effective grain size of bainitic ferrite or the average effective grain size of bainitic ferrite. Therefore, it was found that the tensile strength or reduction of area desired in this disclosure could not be guaranteed. Furthermore, it was found that the first or second wire drawing speed during electrode manufacturing was at a low level.

[0102] Comparative Examples 5 to 12, which do not meet the manufacturing conditions of this disclosure, do not meet the minimum or maximum effective grain size or the average effective grain size of bainitic ferrite as proposed in this disclosure. Therefore, it was found that the tensile strength or reduction of area desired in this disclosure could not be ensured. Furthermore, it was found that the first or second wire drawing speed during electrode manufacturing was at a low level.

Claims

1. A welding electrode wire, comprising, by weight: 0.050% to 0.160% C, 0.0010% to 0.250% Si, 1.0% to 2.50% Mn, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.40% to 6.0% Cr, 0.10% to 0.650% Mo, 0.20% or less (excluding 0%) Al, 0.40% or less (excluding 0%) Ni, 0.20% or less (excluding 0%) Ti, 0.10% or less (excluding 0%) Nb, with the balance being Fe and other unavoidable impurities. The microstructure contains bainitic ferrite. The bainitic ferrite has a minimum effective grain size of 0.50 μm or greater, and The bainitic ferrite has a maximum effective grain size of 20.0 μm or less.

2. The welding electrode wire according to claim 1, wherein the wire further comprises: 0.20% or less V, 0.10% or less Zr and 0.010% or less B.

3. The welding electrode wire according to claim 1, wherein the wire further comprises 0.50% or less Cu.

4. The welding electrode wire according to claim 1, wherein the microstructure comprises, by area: 0.50% or less (including 0%) of retained austenite and the balance of bainitic ferrite.

5. The welding electrode wire according to claim 1, wherein the average effective grain size of the bainitic ferrite is 10 μm or less.

6. The welding electrode wire according to claim 1, wherein the tensile strength of the wire is from 840 MPa to 1000 MPa.

7. The welding electrode wire according to claim 1, wherein the reduction of area (RA) of the wire is 60% to 75%.

8. A method for manufacturing wire for welding electrodes, the method comprising: Prepare a steel billet, the steel billet comprising, by weight: 0.050% to 0.160% C, 0.0010% to 0.250% Si, 1.0% to 2.50% Mn, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.40% to 6.0% Cr, 0.10% to 0.650% Mo, 0.20% or less (excluding 0%) Al, 0.40% or less (excluding 0%) Ni, 0.20% or less (excluding 0%) Ti, 0.10% or less (excluding 0%) Nb, the balance being Fe and other unavoidable impurities; The steel billet is reheated at 1050°C to 1250°C; The reheated steel billet is taken out at 1050°C to 1150°C and then rolled into wire to obtain wire. The wire is wound at 860°C to 940°C; and The wire is cooled on a Steyrmo cooling conveyor at a cooling rate of 2.0°C / sec to 3.0°C / sec.

9. The method for manufacturing wire for welding electrodes according to claim 8, wherein the steel billet further comprises one or more of 0.20% or less V, 0.10% or less Zr, and 0.010% or less B.

10. The method for manufacturing wire for welding electrodes according to claim 8, wherein the steel billet further comprises 0.50% or less Cu.

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