welding wire

Abstract

To provide a welding wire that can prevent the degradation of electrodeposition coating caused by slag, while also offering superior tensile strength, impact resistance and gap resistance.SOLUTION: A welding wire contains, in mass%, C: 0.01% to 0.15%, Si: more than 0% to 0.10% or less, Mn: 0.50% to 2.50%, P: 0.001% to 0.030%, S: 0.001% to 0.015%, Cu: 0.01% to 0.50%, Ti: 0.01% to 0.50%, Al: 0.001% to 0.15%, W: 0.01% to 0.50%, with the balance being Fe and inevitable impurities.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a welding wire, and more particularly to a welding wire capable of suppressing deterioration of electrodeposition coating properties caused by slag.

Background Art

[0002] In automobile chassis and the like, various high-strength plates are applied. After these are welded and assembled, electrodeposition coating for rust prevention is applied. However, if slag remains on the surface of the welded part (weld bead), the electrodeposition coating property deteriorates, and there are parts that are not coated, and corrosion progresses from those parts. In recent years, thinner steel plates have been increasingly used for weight reduction purposes, and there is a strong desire to solve the problem of corrosion due to inadequate electrodeposition coating in the welded part.

[0003] As a means to solve such problems, it is conceivable to reduce the content of deoxidizing elements in the welding wire and reduce the amount of slag generated in the welded part. However, in such a case, internal defects such as pits and blowholes are likely to occur due to insufficient deoxidation, and there is concern about a decrease in the strength of the welded part. In addition, a decrease in the amounts of Si and Mn as deoxidizing elements reduces the viscosity of the molten metal, so there is concern about a decrease in weldability (gap resistance) in a state where a predetermined gap exists between the base materials to be welded.

[0004] Incidentally, Patent Document 1 below discloses a technique related to the present invention. In this Patent Document 1, by suppressing the amount of Si in the welding wire and making the ratio of Si-based slag in the slag formed on the surface of the welded part below a predetermined value, an improvement in the electrodeposition coating property in the welded part is disclosed. However, the chemical composition of the welding wire of the present invention is not specifically disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Against the backdrop of the above circumstances, the present invention aims to provide a welding wire that can suppress the deterioration of electrodeposition coating properties caused by slag, and that also exhibits excellent tensile strength, impact properties, and gap resistance. [Means for solving the problem]

[0007] The inventors of this invention have conducted extensive research to solve the above problems and have arrived at the present invention as described below. The welding wire of the first aspect of the present invention is defined as follows: that is, The composition, in mass%, is as follows: C: 0.01-0.15%, Si: greater than 0-0.10%, Mn: 0.50-2.50%, P: 0.001-0.030%, S: 0.001-0.015%, Cu: 0.01-0.50%, Ti: 0.01-0.50%, Al: 0.001-0.15%, W: 0.01-0.50%, with the remainder being Fe and unavoidable impurities.

[0008] The welding wire of the second aspect of the present invention is defined as follows: that is, In the first phase, the specified welding wire further contains, by mass%, one or more of the following: B: greater than 0 to 0.010%, Mo: 0.01 to 0.50%, and satisfies the condition 0.01 ≤ Mo + 1 / 2W ≤ 0.50.

[0009] The welding wire of the third aspect of the present invention is defined as follows: that is, In the second phase, the specified welding wire further contains Ni: 0.01 to 2.00% by mass.

[0010] The welding wire of the fourth aspect of the present invention is defined as follows: That is, In the second phase, the specified welding wire further contains Cr: 0.05 to 0.70% by mass.

[0011] The welding wire of the fifth aspect of the present invention is defined as follows: In the first phase, the specified welding wire further contains Zr: 0.01 to 0.10% by mass.

[0012] The welding wire of the sixth aspect of the present invention is defined as follows: In the first phase, the specified welding wire further contains, by mass%, one or more of the following: Ba: 0.01-0.03%, Ca: 0.0005-0.0015%, Na: 0.01-0.03%, and Mg: 0.01-0.05%.

[0013] In the welding wire of the present invention as defined above, the content of deoxidizing elements Si and Mn, which form insulating oxides in the slag, is reduced, while predetermined amounts of other elements Ti and Al, which have a deoxidizing effect, are added to improve the conductivity of the slag generated during welding, thereby improving the electrodeposition coating properties. Furthermore, the decrease in viscosity of the molten metal caused by a reduction in Si and Mn content is suppressed by the addition of W, thereby improving gap resistance. In addition to these, the present invention takes into account the influence of each alloying element on tensile strength and impact properties, and by appropriately balancing the amount of each alloying element added, the overall effect ensures the target electrodeposition coating properties, gap resistance, tensile strength, and impact properties. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is an explanatory diagram regarding the evaluation of electrodeposition coating properties. [Figure 2] Figure 2 is an explanatory diagram regarding the evaluation of gap resistance. [Figure 3] Figure 3 is an explanatory diagram regarding the evaluation of tensile strength and impact properties. [Modes for carrying out the invention]

[0015] The welding wire according to an embodiment of the present invention contains C, Si, Mn, P, S, Cu, Ti, Al, and W, and the balance consists of Fe and inevitable impurities. Further, it may further contain B, Mo, Ni, Cr, Zr, Ba, Ca, Na, and Mg.

[0016] The reasons for limiting each chemical component in the welding wire of this embodiment will be described in detail below. In the following description, unless otherwise specified, “%” means “mass %”.

[0017] C: 0.01 to 0.15% C is an element added to ensure the strength of the welded metal part. In this embodiment, it is contained at 0.01% or more to obtain a predetermined strength. However, excessive addition causes embrittlement of the welded metal, so the upper limit is set to 0.15%. The preferred C content is 0.04 to 0.13%.

[0018] Si: More than 0 to 0.10% or less Si is an element that acts as a deoxidizer during welding. However, since insulating SiO2 is formed in the slag, significantly deteriorating the electrocoating property, the upper limit of Si in this embodiment is set to 0.10%. The preferred Si content is 0.001 to 0.08%.

[0019] Mn: 0.50 to 2.50% Mn acts as a deoxidizer during welding and has the effect of increasing the strength of the welded metal. In this embodiment, Mn is contained at 0.50% or more to suppress the occurrence of welding defects such as blowholes. However, excessive addition causes an increase in insulating MnO, deteriorating the electrocoating property, so the upper limit is set to 2.50%, preferably 2.10% or less.

[0020] P: 0.001 to 0.030% P is an element that is mixed into steel as an impurity. It may be contained at 0.001% or more. However, if the P content is excessive, welding cracks occur, so the upper limit is set to 0.030%.

[0021] S: 0.001~0.015% S is an element that is mixed into steel as an impurity. It may be present in amounts of 0.001% or more, but since excessive S content can cause welding cracks, the upper limit is set at 0.015%.

[0022] Cu: 0.01~0.50% Cu is included in the wire at a concentration of 0.01% or more, as it contributes to improving wire feeding performance and stabilizing electrical conductivity when applied to the wire as copper plating. However, since excessive Cu content can cause welding cracks, the upper limit is set at 0.50%.

[0023] Ti: 0.01~0.50% Ti is included at a concentration of 0.01% or more because it forms Ti-containing composite oxides that are more conductive than Si oxides, thereby improving electrodeposition coating properties. However, excessive Ti content reduces the elongation of the weld metal, leading to premature fracture under tensile load and a decrease in toughness. It also increases the amount of pure Ti oxide, which actually reduces electrodeposition coating properties. For this reason, the upper limit for Ti is set at 0.50%. The preferred Ti content is 0.03-0.30%.

[0024] Al: 0.001~0.15% Al is an effective element for ensuring the tensile strength of weld metal. Furthermore, it forms Al-containing composite oxides that are more conductive than Si oxides, improving electrodeposition properties; therefore, it should be included at a concentration of 0.001% or more. However, excessive Al content reduces the elongation of the weld metal, leading to premature fracture under tensile load and decreased toughness. It also increases the amount of pure Al oxide, which can actually reduce electrodeposition properties. For this reason, the upper limit for Al is set at 0.15%. A preferred Al content is 0.010-0.12%.

[0025] W: 0.01~0.50% W is an effective element for ensuring the tensile strength of the weld metal. It also has the effect of increasing the viscosity of the molten metal and improving gap resistance. To obtain these effects, in this embodiment, W is included at a concentration of 0.01% or more. However, since excessive W content can lead to a decrease in elongation and a decrease in impact properties due to excessive hardness, the upper limit is set at 0.50%. The preferred W content is 0.03 to 0.30%.

[0026] B: More than 0~0.010% or less B can be included as needed because it strengthens grain boundaries by segregating at them and reducing the amount of segregation of P and other elements, and also contributes to improved toughness by finely dispersing grain boundary carbides. However, if the amount of B is excessive, it will form Fe2B and cause red-hot brittleness. In addition, excess B oxides will be formed, leading to a decrease in electrodeposition coating properties, so the B content should be limited to 0.010% or less. The preferred B content is 0.001 to 0.006%.

[0027] Mo: 0.01~0.50% 0.01 ≤ Mo + 1 / 2W ≤ 0.50 Like W, Mo improves the tensile strength of the weld metal and increases the viscosity of the molten metal, thereby improving gap resistance. For this reason, Mo can be included in amounts of 0.01% or more as needed. However, excessive addition will lead to a decrease in elongation, so the upper limit should be 0.50%. The preferred Mo content is 0.03 to 0.20%. The amount of Mo required to obtain an effect equivalent to that of W is half the amount of W. When both W and Mo are added, the total amount of Mo and half the amount of W is specified as 0.01 to 0.50%. The preferred range for Mo + 1 / 2W is 0.03 to 0.30%.

[0028] Ni: 0.01~2.00% Ni has the effect of increasing the tensile strength and elongation of the weld metal, and can be included in amounts of 0.01% or more as needed. However, since excessive Ni content can cause welding cracks, the upper limit should be set at 2.00%. The preferred Ni content is 0.05 to 1.60%.

[0029] Cr: 0.05~0.70% Cr has the effect of increasing the tensile strength and hardness of the weld metal. It is also effective in increasing the viscosity of the molten metal and improving gap resistance, and can be included in amounts of 0.05% or more as needed. However, if the Cr content is excessive, the elongation of the weld metal will decrease, leading to premature fracture under tensile load and a decrease in toughness. In addition, insulating Cr oxides will be generated, which will reduce the electrodeposition coating properties. For this reason, the upper limit for Cr should be 0.70%. The preferred Cr content is 0.10 to 0.60%.

[0030] Zr: 0.01~0.10% Zr has the effect of improving electrodeposition coating properties by forming Zr-containing composite oxides that are more conductive than Si oxides. It is also effective in preventing the occurrence of white spots. To obtain these effects, the Zr content can be increased to 0.01% or more as needed. However, if the Zr content is excessive, insulating Zr oxides will be formed, which will conversely degrade the electrodeposition coating properties, so the upper limit should be 0.10%. The preferred Zr content is 0.05 to 0.07%.

[0031] Ba:0.01~0.03%, Ca:0.0005~0.0015%, Na:0.01~0.03%, Mg:0.01~0.05% Ba, Ca, Na, and Mg each form composite oxides that are more conductive than Si oxides, contributing to improved electrodeposition coating properties. Therefore, they can be included in predetermined amounts as needed. However, excessive content reduces the elongation of the weld metal, leading to premature fracture under tensile load and a decrease in toughness. Furthermore, an increase in the amount of insulating oxides can actually reduce electrodeposition coating properties. Therefore, the upper limit of the amount of each element added is limited as described above. [Examples]

[0032] Next, embodiments of the present invention will be described in detail. Here, test specimens were prepared using the welding wires of the embodiments and comparative examples shown in Tables 2 and 3 below, and their electrodeposition coating properties, gap resistance, tensile strength, and impact properties were evaluated. In the following, Examples 1, 4, 9, and 11 shall be read as Reference Examples 1, 4, 9, and 11, respectively.

[0033] <Electrodeposition coating properties> Alloys with the chemical compositions shown in Tables 2 and 3 below were melted, and the resulting ingots were subjected to hot working and cold working to produce welding wires with a diameter of φ1.2 mm. Next, using the steel plates shown in Table 1 as the base material, and as shown in Figure 1, the end of one steel plate (upper plate 2) was overlapped (without any gaps) onto the surface of the other steel plate (lower plate 3), and overlap fillet welding was performed using the welding wire described above to produce the overlap joint member 1. The length of the formed weld bead 4 is 220 mm. The welding conditions are as shown in Table 1 below.

[0034] [Table 1]

[0035] The overlapping joint member 1 thus prepared was degreased and chemically treated, then subjected to cationic electrodeposition coating (coating film thickness 20 μm) to obtain a test piece for evaluating the electrodeposition coating properties.

[0036] The weld beads on the obtained test specimens were photographed, and the paint defect area ratio (%), which is the ratio of the area of ​​paint defects to the area of ​​the weld bead, was calculated from the images to evaluate the electrodeposition coating performance. The criteria for evaluation were as follows: ○: Paint defect rate is 5% or less ×: Paint defect rate exceeds 5%

[0037] <Gap tolerance> As shown in Figure 2(A), overlap fillet welding was performed on overlap joint member 1, which was used to evaluate the electrodeposition coating properties described above, with a gap δ between steel plates 2 and 3 set to 1.0 mm, to prepare overlap joint member 1B as a test piece. The welding conditions were the same as those for overlap joint member 1. The weld bead 4 (220 mm in length) on the obtained test specimen 1B was observed to investigate whether there were any areas with insufficient weld weld. Here, "excess weld" refers to the portion of the fillet weld that rises above the upper surface 2a of the upper plate 2 (represented by the symbol 5 in the figure), as shown in Figure 2(B), while "insufficient weld" refers to the portion where excess weld 5 is not obtained, as shown in Figure 2(C). The criteria for determining gap resistance were as follows: ○: No areas with excess or insufficient filling. ×: Some areas have insufficient filling.

[0038] <Tensile strength and impact properties> As shown in Figure 3, a 20 mm thick steel plate (material SM490B) with a groove welded using the above-mentioned welding wire was used as the base material, and MAG welding was performed on the groove using the above-mentioned welding wire under the conditions shown below to form weld metal. Welding conditions: Welding current 250A, arc voltage 25.5V, welding speed 40cm / min. Interpass temperature 150-200°C, using Ar + 20% CO2 by volume as shielding gas.

[0039] Then, in accordance with JIS Z 3111, a tensile test specimen (JIS Z 2241 No. 14A) was taken so that the entire specimen consisted of weld metal along the direction of the weld line from the weld joint (weld metal). In addition, a Charpy impact test specimen (JIS Z 2242 V-notch test specimen) was taken so that the notched portion and the fracture portion consisted of the aforementioned weld metal.

[0040] The tensile strength was evaluated by performing a tensile test at room temperature using the above-mentioned tensile test specimens in accordance with JIS Z2241, and the obtained tensile strength was used for evaluation. The criteria for evaluation were as follows: ○: Tensile strength of 490 MPa or higher ×: Tensile strength less than 490 MPa

[0041] The impact properties were evaluated using the Charpy impact test specimens described above, performing Charpy impact tests at -20°C in accordance with JIS Z2242, and evaluating the average of the absorbed energy from three repeated tests. The criteria for evaluation were as follows: ○: Absorbed energy of 27J or more ×: Absorbed energy is less than 27J The evaluation results for electrodeposition coating properties, gap resistance, tensile strength, and impact properties obtained in this manner are shown in Tables 2 and 3 below.

[0042] [Table 2]

[0043] [Table 3]

[0044] The following can be seen from the evaluation results in Tables 2 and 3. Comparative Example 1 had an excessive amount of carbon added beyond the specified range, resulting in a "fail" rating for impact properties. It is believed that the excessive addition of carbon caused embrittlement, leading to a decrease in impact properties.

[0045] Comparative Example 2 had an excessive amount of Si added beyond the specified range, resulting in a "fail" rating for electrodeposition coating performance. This is thought to be due to the formation of insulating Si oxide, which led to a decrease in electrodeposition coating performance.

[0046] Comparative Example 3 is an example where Mn is less than the specified range, resulting in numerous internal defects (blowholes) due to insufficient deoxidation, and the evaluation of tensile strength and impact properties was "X".

[0047] Comparative Example 4 had an excessive amount of Mn added beyond the specified range, resulting in a "×" rating for electrodeposition coating performance. This is thought to be due to the formation of insulating Mn oxide, which led to a decrease in electrodeposition coating performance.

[0048] Comparative Example 5 is an example where P and S were added in excess beyond the specified range, and the tensile strength evaluation was "×". It is thought that the tensile strength decreased due to the occurrence of welding cracks inside the material.

[0049] Comparative Example 6 is an example where excessive amounts of Cu were added beyond the specified range, resulting in a "fail" (×) evaluation of tensile strength. Similar to Comparative Example 5, it is believed that the decrease in tensile strength was due to the occurrence of welding cracks.

[0050] Comparative Example 7 is an example where Ti was added in excess beyond the specified range, and the electrodeposition coating performance was evaluated as "×". This is thought to be due to the formation of elemental Ti oxide, resulting in a decrease in electrodeposition coating performance. Furthermore, the evaluation of tensile strength and impact properties was also "×". This is thought to be due to a decrease in elongation, resulting in a decrease in tensile strength and impact properties. Comparative Example 8, in which Al was added in excess beyond the specified range, yielded similar results.

[0051] Comparative Example 9 is an example where W was added in excess of the specified range, and the impact properties were evaluated as "×". This is thought to be due to excessive hardness caused by the excessive addition of W.

[0052] Comparative Example 10 is an example where B was added in excess beyond the specified range, and the electrodeposition coating performance was evaluated as "×". This is thought to be due to the formation of excess B oxides caused by the excessive addition of B, resulting in a decrease in electrodeposition coating performance.

[0053] Comparative Example 11 was an example where the total amount of Mo and half of W exceeded the specified range, and the impact properties were evaluated as "×". This is thought to be due to excessive hardness, similar to the case of Comparative Example 9. Comparative Example 12, in which Mo was added in excess beyond the specified range, yielded similar results.

[0054] Comparative Example 13 is an example where Ni was added in excess of the specified range, and the tensile strength evaluation was "×". It is thought that the tensile strength decreased due to the occurrence of welding cracks inside the material.

[0055] Comparative Example 14 is an example where Cr was added in excess beyond the specified range, and the electrodeposition coating performance was evaluated as "×". This is thought to be due to the formation of elemental Cr oxide, resulting in a decrease in electrodeposition coating performance. Furthermore, the evaluation of tensile strength and impact properties was also "×". This is thought to be due to a decrease in elongation, resulting in a decrease in tensile strength and impact properties.

[0056] Comparative Example 15 had an excessive amount of Zr added beyond the specified range, resulting in a "×" rating for electrodeposition coating performance. This is thought to be due to the formation of insulating elemental Zr oxide, leading to a decrease in electrodeposition coating performance.

[0057] Comparative Examples 16-20 are cases in which one or more of Ba, Ca, Na, and Mg were added in excess beyond the specified range. In all of these examples, the evaluation of tensile strength and impact properties was "×". The evaluation of electrodeposition coating properties was also "×".

[0058] As described above, in each comparative example, at least one of the following evaluations—electrodeposition coating properties, gap resistance, tensile properties, and impact properties—was marked as "×".

[0059] In contrast, Examples 1 to 34, in which the chemical composition of the welding wire is within the specified range, all received a "○" rating for electrodeposition coating properties, gap resistance, tensile properties, and impact properties, indicating that a balance of all four properties has been achieved.

[0060] Although embodiments and examples of the present invention have been described in detail above, the present invention is not limited thereto and can be implemented with various modifications without departing from its spirit.

Claims

1. by mass % C: 0.01-0.15% Si: more than 0 to 0.10% or less Mn: 0.50-2.50% P:0.001~0.030% S: 0.001-0.015% Cu: 0.01~0.50% Ti: 0.05-0.50% Al: 0.001-0.15% W: 0.01~0.50% A welding wire characterized by containing a certain substance, with the remainder being Fe and unavoidable impurities.

2. by mass% C: 0.01-0.15% Si: more than 0 to 0.10% or less Mn: 0.50-2.50% P:0.001~0.030% S: 0.001-0.015% Cu: 0.01~0.50% Ti: 0.01~0.50% Al: 0.001-0.15% W: 0.01~0.50% It contains, B: More than 0 to 0.010% or less Mo: 0.01~0.50% It further contains one or more of the following: 0.01% ≤ Mo + 1 / 2W ≤ 0.50% Satisfying the conditions, A welding wire characterized in that the remainder has a composition of Fe and unavoidable impurities.

3. In claim 2, by mass% Ni: 0.01-2.00% A welding wire characterized by further containing the following.

4. In claim 2, by mass% Cr: 0.05-0.70% A welding wire characterized by further containing the following.

5. by mass% C: 0.01-0.15% Si: more than 0 to 0.10% or less Mn: 0.50-2.50% P:0.001~0.030% S: 0.001-0.015% Cu: 0.01~0.50% Ti: 0.01~0.50% Al: 0.001-0.15% W: 0.01~0.50% Zr: 0.01~0.10% It contains, A welding wire characterized in that the remainder has a composition of Fe and unavoidable impurities.

6. by mass% C: 0.01-0.15% Si: more than 0 to 0.10% or less Mn: 0.50-2.50% P:0.001~0.030% S: 0.001-0.015% Cu: 0.01~0.50% Ti: 0.01~0.50% Al: 0.001-0.15% W: 0.01~0.50% It contains, Ba: 0.01~0.03% Ca: 0.0005-0.0015% Na: 0.01-0.03% Mg: 0.01-0.05% It further contains one or more of the following: A welding wire characterized in that the remainder has a composition of Fe and unavoidable impurities.

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