Welding wire for high-strength steel

Abstract

A welding wire for high-strength steel for improving slag coagulation includes a combination of Carbon, Manganese, Silicon, Aluminum, Sulfur, and Selenium. With use of the welding wire, the generation of slag is minimized, and the slag is allowed to induce the generation of crystalline oxides having a low surface energy, so that the slag is easily removed, and the flow of a molten pool to the center in a width direction of a weld bead do that the slag is coagulated.

Claims

1. A welding wire for high-strength steel for improving slag coagulation, the welding wire essentially consisting of: in terms of weight percent relative to the total weight thereof, 0.09-0.11% C, 0.2-0.4% Mn, 0.3-0.65% Si, 0.03-0.04% Al, 0.05-0.07% S, 0.005-0.01% Se, and a remainder composed of Fe and impurities whereas such effects of narrowing ranges of a combination of elements improves slag coagulation.

2. The welding wire of claim 1, wherein the weight ratio of Mn:Al:Si is 3:2:3.

3. The welding wire of claim 1, wherein an AlMnSi-based crystalline oxide is generated as slag resulting from a welding process.

4. The welding wire of claim 3, wherein the AlMnSi-based crystalline oxide is Mn3Al2Si3O12.

5. The welding wire of claim 1, further forms a molten pool during a welding process, the pool flowing to a center portion in a width direction of a weld bead, thereby allowing a generated slag to be concentrated on the center portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features, and advantages of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a diagram illustrating slag remaining between a weld bead and a base material after welding;

(3) FIG. 2 provides diagrams comparing arc welding using a conventional welding wire and arc welding using a welding wire for high-strength steel according to various examples of the present disclosure;

(4) FIG. 3 is a graph comparing surface energy among various crystalline oxides;

(5) FIG. 4 provides images showing the formation of weld bands at the time of welding in various examples and comparative examples in table 1; and

(6) FIG. 5 is a diagram comparing paintability according to the selenium (Se) content.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure is not restricted or limited to the embodiments. For reference, like numerals substantially refer to like elements throughout the present specification, and can be described with reference to contents described in other drawings in the following description, and the contents that are determined to be apparent to those skilled in the art or that are repeated may be omitted.

(8) The welding wire for high-strength steel according to an embodiment of the present disclosure is characterized in that, while the generation of slag is minimized, the slag is allowed to induce the generation of crystalline oxides having a low surface energy so that the slag is easily removed, and the flow of a molten pool to the center in a width direction of a weld bead so that the slag is coagulated.

(9) FIG. 2 provides diagrams comparing arc welding using a conventional general welding wire and arc welding using a welding wire for high-strength steel according to various examples of the present disclosure. FIG. 3 is a graph comparing surface energy among various crystalline oxides.

(10) As shown in FIGS. 2 and 3, in the conventional art, it was advantageous to minimize the contents of manganese (Mn) and silicon (Si) in order to minimize slag, but this led to a deterioration of strength and viscosity of a welded portion. However, when manganese (Mn) and silicon (Si) are limited to the ranges according to the examples of the present disclosure, the generation of slag can be minimized. Further, the flow of a molten pool is induced to the center in a width direction of the weld bead using Marangoni convection. Thus, when the slag coagulated on the center of the weld bead, it can be easily removed using a brush or a similar device.

(11) Hereinafter, the composition of the present disclosure will be described in detail. The contents of respective components were expressed by weight percent (wt %) relative to the total weight of the welding wire.

(12) The content of carbon (C) is preferably 0.09-0.11%.

(13) Carbon (C) is an essential component for securing the strength and welding curability of a welded portion. The addition of less than 0.09% of carbon (C) makes it difficult to secure physical properties of the welded portion. The addition of more than 0.11% of carbon (C) causes significant deterioration of weldability and remarkably reduces impact toughness. Therefore, the content of carbon (C) is preferably delimited within the above range.

(14) The content of manganese (Mn) is preferably 0.2-0.40.

(15) Manganese (Mn) is an element that is effective in the improvement of a deacidification action and strength and improves a molten pool flow changing effect. If the content of manganese (Mn) is more than 0.4%, the molten pool flow changing effect is slight, which leads to inhibiting the remaining of slag between a base material and a weld bead, that is, on a toe portion. If the content of manganese (Mn) is less than 0.2%, crystalline oxides having a low surface energy are not smoothly generated, and thus the removal of slag becomes difficult. Therefore, the content of manganese (Mn) is delimited within the above range.

(16) The content of silicon (Si) is preferably 0.3-0.65%.

(17) Silicon (Si), together with manganese (Mn), is an element that generates crystalline oxides having low surface energy. As the content of silicon (Si) is lower, the viscosity of the molten pool decreases, and thus the molten pool flow changing effect is improved. More than 0.65% of silicon (S) increases the viscosity of a molten pool, thus reducing the molten pool flow changing effect. Therefore, the content of manganese (Mn) is delimited within the above range.

(18) The content of aluminum (Al) is preferably 0.03-0.04%.

(19) Aluminum (Al), together with manganese (Mn) and silicon (Si), is an element that generates AlMnSi-based crystalline oxides having relatively low surface energy. If the content of aluminum (Al) is less than 0.03%, Mn.sub.3Al.sub.2Si.sub.3O.sub.12 having the lowest surface energy, as shown in FIG. 3, is not smoothly generated, and thus, a desired effect is difficult to attain. If the content of aluminum (Al) is more than 0.04%, the generated crystalline oxides have a low coefficient of thermal expansion, and thus the removal of slag is difficult. Therefore, the content of aluminum (Al) is delimited within the above range.

(20) Here, the welding wire for high-strength steel according to an embodiment of the present disclosure is preferable when the weight ratio of manganese (Mn), aluminum (Al), and silicon (Si) is 3:2:3. With this weight ratio, slag is used to maximize the generation of Mn.sub.3Al.sub.2Si.sub.3O.sub.12 among AlMnSi-based crystalline oxides, and thereafter, the removal of slag can be easily conducted.

(21) The content of selenium (Se) is preferably 0.005-0.01%.

(22) Selenium (Se) is one of surface activation elements that reduces the surface energy of a molten pool and improves slag coagulation by changing the Gibbs free energy per particle, that is, chemical potential. If the content of selenium (Se) is less than 0.005%, the surface energy reducing effect of the molten pool is slight, causing surface tearing. If the content of selenium (Se) is more than 0.01%, the coagulated slag is stuck together, and thus the effects of the slag are difficult to exert and painting adhesion is degraded.

(23) The content of sulfur (S) is preferably 0.05-0.07%.

(24) If the content of sulfur (S) is more than 0.07%, an intermediate such as FeS is generated, causing the deterioration of physical properties, such as mechanical strength, of a welded portion. If the content of sulfur (S) is less than 0.05%, the surface tension changing effect of a molten pool is slight. Therefore, the content of sulfur (S) is delimited within the above range.

(25) TABLE-US-00001 TABLE 1 Presence of slag in toe Slag Classification C Mn Si Al Se S Fe portion evauation Example 1 0.1 0.39 0.55 0.035 0.0088 0.05 rem. x pass Example 2 0.1 0.33 0.53 0.036 0.0075 0.05 rem. x pass Comparative 0.88 0.35 0.48 0.033 0.0077 0.05 rem. fail Example 1 Comparative 0.115 0.30 0.57 0.034 0.0080 0.05 rem. fail Example 2 Comparative 0.1 0.15 0.5 0.035 0.0075 0.05 rem. fail Example 3 Comparative 0.1 0.45 0.5 0.035 0.0075 0.05 rem. fail Example 4 Comparative 0.1 0.3 0.35 0.035 0.0075 0.05 rem. fail Example 5 Comparative 0.1 0.3 0.7 0.035 0.0075 0.05 rem. fail Example 6 Comparative 0.1 0.3 0.5 0.025 0.0075 0.05 rem. fail Example 7 Comparative 0.1 0.3 0.5 0.045 0.0075 0.05 rem. fail Example 8 Comparative 0.1 0.3 0.5 0.035 0.0045 0.05 rem. fail Example 9 Comparative 0.1 0.3 0.5 0.035 0.0105 0.05 rem. fail Example 10

(26) Table 1 above shows the presence of slag in a toe portion and slag evaluation results in various examples and comparative examples according to an embodiment of the present disclosure. FIG. 4 provides images showing the formation of weld bands at the time of welding in various examples and comparative examples in Table 1.

(27) As can be seen from Table 1 and FIG. 4, when the composition range of the present disclosure is satisfied, the surface energy of slag was low, and thus the slag was easily removed and the slag did not remain in the toe portion. In the comparative examples, the slag remained in the toe portion to form slag bands. Further, comparative examples 4 to 10, excluding comparative examples 1 and 2, did not satisfy the reference values of the present disclosure since the surface energy of slag was high.

(28) FIG. 5 provides images showing an external appearance of a welded portion after the welded portion was painted and the painting adhesion evaluation results in example 1 and comparative examples 9 and 10.

(29) The painting adhesion evaluation was conducted in the following manner: an adhesive tape, such as a cellophane adhesive tape, was attached to the painted welded portion; the same force was then applied thereto at an angle of 45 to remove the adhesive tape; and thereafter, the area of the paint on the adhesive tape was measured.

(30) As shown in FIG. 5, in comparative example 10 in which the content of selenium (Se) was more than 0.01 wt %, the amount of slag was excessively increased to form a new layer composed of silicone (Si) and aluminum (Al) compounds and had a negative influence on painting adhesion, resulting in significant deterioration of painting adhesion. In case that the content of selenium (Se) was less than 0.005 wt %, the amount of slag was too slight to form a new layer. However, as shown in comparative example 9, in case that the content of selenium (Se) was less than 0.005 wt %, the amount of slag causes interlayer separation between welding bead and Fe oxide layer.

(31) Thus, it can be seen that the paintability was improved when the content of selenium (Se) was in the range of 0.005-0.01 wt %.

(32) As described above, when arc welding is conducted using a welding wire according to an embodiment of the present disclosure, the surface energy of the slag is lowered. Thus, the amount of slag remaining in the toe portion is reduced by about 80%, as compared with a welded portion formed using arc welding using a general welding wire in the conventional art. As a result, a slag band with a band shape is not formed, thereby improving paintability of the welded portion and anti-corrosive performance of the toe portion and, further, increasing the lifetime of the manufactured products.

(33) Although the preferred embodiment of the present disclosure has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.