JP2022105363A - Welded joint, and automobile member - Google Patents

Abstract

To provide a welded joint that has excellent fatigue characteristics at a toe of weld and also has high electrodeposition properties, and an automobile member.SOLUTION: The inventive welded joint according to one embodiment has two or more steel sheets, and a weld metal for joining the two or more steel sheets. The weld metal has a predetermined chemical composition. The weld metal has a Ceq of 0.450-0.950 mass%. The weld metal has a Vickers hardness of 300 HV or more. One or both of the two or more steel sheet has a plate thickness of 0.8 mm or more and 4.0 mm or less. Slag deposited on the welded joint has an Si content of 5.0 mass% or less. The largest value SiBM between the Si content SiWM in unit mass% of the weld metal and the Si content in unit mass% of the two or more steel sheets satisfies 2.5×{(SiWM/0.89)-0.6×SiBM}≤0.510.SELECTED DRAWING: Figure 1

Description

The present invention relates to welded joints and automobile members.

Mechanical structural parts having welded joints are usually structurally designed so that tensile stress is generated at the weld toe. Therefore, conventionally, improvement of the mechanical properties of the toe of the welded joint, particularly the fatigue strength, has been studied.

In Patent Document 1, C: 0.005% or more and 0.35% or less, Si: 2.0% or less, Mn: 0.10% or more and 3.0% or less, P: 0.20% or less, S: It is characterized by having a chemical component of 0.08% or less, Al: 0.01% or more and 0.10% or less, and (Ceq of steel plate)-(Ceq of weld metal part) <-0.1. A lap arc welded joint structure having excellent fatigue strength is disclosed.

In Patent Document 2, the first steel plate and the second steel plate, which are overlapped with each other and have a tensile strength of 950 MPa or more, respectively, and extend along the corner formed by the surface of the first steel plate and the end face of the second steel plate. A lap fillet arc welded joint provided with an existing weld metal, the Vickers hardness of the weld metal is 400 HV or less, and when viewed in a cross section orthogonal to the weld line of the weld metal, the first steel plate. The position of the fusion boundary existing on the surface is defined as point A, and the position 0.3 mm away from the point A toward the inside of the weld metal in the X direction parallel to the surface of the first steel plate is defined as point D. In the X direction, a position 0.4 mm away from the point A toward the inside of the weld metal is defined as a point C, a straight line passing through the point D and extending in the plate thickness direction of the first steel plate, and the surface of the weld metal. The point of intersection with the point B is defined as the point B, and the angle between the straight line connecting the point A and the point B and the straight line connecting the point A and the point D is defined as the toe angle β of the weld metal, and the point A is defined as the point A. The total number of recesses existing on the surface of the weld metal included in the range between the point C and the point C is defined as NA, and the number of recesses in which ferrite grains having a maximum particle size of 10 μm or more are in contact with the recesses is defined as NB. Then, the lap fillet arc welded joint is disclosed, wherein the weld metal satisfies the following conditional equations (1) and (2) at the same time.
0 ° <β <30 °… (1)
NB / NA ≤ 0.70 ... (2)
(However, NA is 20 or more)

Japanese Unexamined Patent Publication No. 6-340947 International Publication No. 2019/03549

In the manufacture of automobile members having welded joints (for example, lap fillet welded joints of thin plates), welded joints are required to have electrodeposition coating properties in addition to fatigue strength. In Neither Patent Documents 1 and 2, no consideration is given to the electrodeposition coating property, and no specific means for improving the electrodeposition coating property is disclosed. In addition, in the technique of Patent Document 2, it is aimed to reduce the carbon equivalent (Ceq) of the weld metal, and in this respect, it is considered that there is room for improvement in fatigue strength.

In view of the above circumstances, it is an object of the present invention to provide a welded joint having excellent fatigue characteristics of the toe and further having high electrodeposition coating property, and an automobile member.

The gist of the present invention is as follows.

(1) The welded joint according to one aspect of the present invention is a welded joint including two or more steel plates and a weld metal for joining two or more of the steel plates, and the chemical composition of the weld metal is a unit mass. %, C: 0.01 to 0.25%, Si: 0.01 to 1.00%, Mn: 0.80 to 2.50%, P: 0.0500% or less, S: 0.0100% Hereinafter, Ti: 0.020 to 0.120% and Zr: 0.001 to 0.050% are contained, the balance is composed of iron and impurities, and the Ceq of the weld metal calculated by the following formula 1 is 0. The weld metal has a Vickers hardness of 300 HV or more, and one or more of the two or more steel plates has a thickness of 0.8 mm or more and 4.0 mm or less. The Si content of the slag adhering to the welded joint is 5.0% by mass or less, and the Si content Si _WM in the unit mass% of the weld metal and the Si content in the unit mass% of 2 or more of the steel plate. The largest value, Si _BM , satisfies the following equation 2.
Ceq = C + Mn / 6 + Si / 24: Equation 1
2.5 × {(Si _WM / 0.89) -0.6 × Si _BM } ≦ 0.510: Equation 2
Here, the element symbol included in the formula 1 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in a unit mass%.
(2) In the welded joint according to (1) above, the largest value Ti among the Ti content Ti _WM in the unit mass% of the weld metal and the Ti content in the unit mass% of two or more steel sheets. _{The BM} may satisfy the following formula 3.
0.050 ≦ 2.5 × {(Ti _WM / 0.54) -0.6 × Ti _BM } ≦ 0.300: Equation 3
(3) In the welded joint according to (1) or (2) above, the Vickers hardness of the weld metal may be 80% or more of the HM calculated by the following formula 4.
HM = 884 × C × (1-0.3 × C ² ) +294: Equation 4
Here, the element symbol included in the formula 4 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in unit mass%.
(4) In the welded joint according to any one of (1) to (3) above, the total Ti content and Zr content of the slag may be 0.5% by mass or more.
(5) In the welded joint according to any one of (1) to (4) above, the toe angle at one or more toes of the weld metal may be more than 0 ° and less than 30 °.
(6) In the welded joint according to (5) above, two or more of the steel plates are a superposed first steel plate and a second steel plate, and the weld metal is the surface of the first steel plate and the said. The toe angle of the weld metal at the toe on the side of the first steel plate may be more than 0 ° and less than 30 ° by joining to the end face of the second steel plate.
(7) In the welded joint according to any one of (1) to (6) above, the chemical composition of the weld metal is replaced with a part of the iron in a unit mass%, and Al: 0. 12% or less, Ni: 3.00% or less, Cr: 1.20% or less, Mo: 1.00% or less, V: 0.30% or less, Nb: 0.10% or less, B: 0.0600% Hereinafter, the weld metal containing one or more selected from the group consisting of Mg: 0.01% or less, Cu: 1.00% or less, O: 0.0500% or less, and N: 0.0300% or less. The Ceq of the above may be calculated by the following formula 5.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 4: Equation 5
Here, the element symbol included in the formula 5 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in unit mass%.
(8) The automobile member according to another aspect of the present invention includes the welded joint according to any one of (1) to (7) above.

According to the present invention, it is possible to provide a welded joint having excellent fatigue characteristics of a toe and having a high electrodeposition coating property, and an automobile member.

It is sectional drawing of the welded joint which concerns on this embodiment. It is sectional drawing which explains the measurement point of the Vickers hardness of a weld metal. It is a schematic diagram explaining the welding target position.

The present inventors have diligently studied means for improving the fatigue characteristics of the toe and the electrodeposition coating property. As a result, the following became clear.

(1. Chemical composition and Ceq of weld metal, and hardness)
First, it is necessary to appropriately control the chemical composition and Ceq of the weld metal and further increase the hardness of the weld metal. This makes it possible to improve the fatigue strength of the weld metal.

(2. Si amount of slag)
Next, it is necessary to reduce the amount of Si in the slag adhering to the welded joint. As a result, the conductivity of the slag can be improved and the electrodeposition coating property can be improved.

(3. Relationship between Si content of steel sheet and Si content of weld metal)
Furthermore, it is necessary to optimize the relationship between the Si content of the steel sheet and the Si content of the weld metal. During arc welding, the steel plate, which is the base material, is also heated by heat conduction from the molten pool. Therefore, an oxide scale is generated on the surface of the heat-affected zone of the steel sheet. In addition, the weld fume may adhere to the surface of the heat-affected zone of the steel sheet. These deteriorate the electrodeposition coating property. By selecting the chemical composition of the welding material and the steel sheet so that the Si content of the steel sheet and the Si content of the weld metal satisfy the formulas described later, the above-mentioned phenomenon is suppressed and the electrodeposition coating property is further improved. be able to.

The welded joint according to the present embodiment obtained based on the above findings will be described below. Unless otherwise specified, the unit "%" relating to the chemical composition of the weld metal, the chemical composition of the steel sheet, and the chemical composition of the slag means% by mass.

The welded joint according to the present embodiment includes two or more steel plates and a weld metal for joining the two or more steel plates. The shape of the joint is not particularly limited, and various shapes such as a T-shaped fillet welded joint, a lap fillet welded joint, and a butt welded joint can be selected. First, the weld metal will be described.

(C: 0.01-0.25%)
C is an important element that affects the strength of the weld metal. If the C content of the weld metal is less than 0.01%, the strength of the weld metal is insufficient. On the other hand, if the C content of the weld metal is more than 0.25%, the toughness of the weld metal is impaired. Therefore, the C content of the weld metal is 0.01 to 0.25%. The C content of the weld metal may be 0.02% or more, 0.05% or more, or 0.10% or more. The C content of the weld metal may be 0.24% or less, 0.22% or less, or 0.20% or less.

(Si: 0.01-1.00%)
Si has the effect of deoxidizing the weld metal. Further, Si solidly dissolved in the weld metal also contributes to the improvement of the strength of the weld metal. If the Si content of the weld metal is less than 0.01%, these effects cannot be obtained. On the other hand, if the Si content of the weld metal is more than 1.00%, the toughness of the weld metal is impaired. Further, when the Si content of the weld metal is more than 1.00%, the amount of insulating slag increases and the electrodeposition coating property is impaired. Therefore, the Si content of the weld metal is 0.01 to 1.00%. The Si content of the weld metal may be 0.02% or more, 0.05% or more, or 0.10% or more. The Si content of the weld metal may be 0.90% or less, 0.80% or less, or 0.60% or less.

(Mn: 0.80 to 2.50%)
Mn is an important element that improves the hardenability of the weld metal. If the Mn content of the weld metal is less than 0.80%, the hardenability is insufficient and the strength of the weld metal is insufficient. On the other hand, if the Mn content of the weld metal is more than 2.50%, the toughness of the weld metal is impaired. Therefore, the Mn content of the weld metal is set to 0.80 to 2.50%. The Mn content of the weld metal may be 1.00% or more, 1.20% or more, or 1.50% or more. The Mn content of the weld metal may be 2.40% or less, 2.20% or less, or 2.00% or less.

(P: 0.0500% or less)
P is an impurity. When the P content of the weld metal is more than 0.0500%, P segregates at the grain boundaries of the weld metal, and the toughness of the weld metal is impaired. Therefore, the P content of the weld metal is 0.0500% or less. From the viewpoint of the characteristics of the welded joint, the smaller the P content is, the more preferable. Therefore, the lower limit of the P content is not set. The lower limit of the P content may be 0%. However, considering the manufacturing cost of the welded joint, it is permissible for the weld metal to contain P within the above range. The P content of the weld metal may be 0.0010% or more, 0.0050% or more, or 0.0100% or more. The P content of the weld metal may be 0.0400% or less, 0.0300% or less, or 0.0200% or less.

(S: 0.0100% or less)
S is an impurity. When the S content of the weld metal is more than 0.0100%, S segregates at the grain boundaries of the weld metal, and the toughness of the weld metal is impaired. Therefore, the S content of the weld metal is 0.0100% or less. From the viewpoint of the characteristics of the welded joint, the smaller the S content is, the more preferable. Therefore, the lower limit of the S content is not set. The lower limit of the S content may be 0%. However, considering the manufacturing cost of the welded joint, it is permissible for the weld metal to contain S within the above range. The S content of the weld metal may be 0.0010% or more, 0.0020% or more, or 0.0030% or more. The S content of the weld metal may be 0.0080% or less, 0.0070% or less, or 0.0050% or less.

(Ti: 0.020 to 0.120%)
Ti has the effect of deoxidizing the weld metal and the effect of miniaturizing the structure of the weld metal. Further, Ti forms a conductive slag that does not impair the electrodeposition coating property. Therefore, by modifying the slag component with Ti, the electrodeposition coating property of the welded joint can be improved. If the Ti content of the weld metal is less than 0.020%, these effects cannot be obtained. On the other hand, when the Ti content of the weld metal is more than 0.120%, coarse precipitates are formed in the weld metal and the toughness of the weld metal is impaired. Therefore, the Ti content of the weld metal is 0.020 to 0.120%. The Ti content of the weld metal may be 0.030% or more, 0.040% or more, or 0.050% or more. The Ti content of the weld metal may be 0.110% or less, 0.100% or less, or 0.080% or less.

(Zr: 0.001 to 0.050%)
Zr precipitates as fine nitrides in the weld metal and has the effect of improving the strength of the weld metal. Further, Zr forms a conductive slag that does not impair the electrodeposition coating property. Therefore, by modifying the slag component using Zr, the electrodeposition coating property of the welded joint can be improved. If the Zr content of the weld metal is less than 0.001%, these effects cannot be obtained. On the other hand, when the Zr content of the weld metal is more than 0.050%, coarse precipitates are formed in the weld metal and the toughness of the weld metal is impaired. Therefore, the Zr content of the weld metal is 0.001 to 0.050%. The Zr content of the weld metal may be 0.002% or more, 0.010% or more, or 0.015% or more. The Zr content of the weld metal may be 0.040% or less, 0.035% or less, or 0.030% or less.

(Remaining: iron and impurities)
The balance of the chemical composition of the weld metal contains iron and impurities. The impurities are components mixed by raw materials such as ore or scrap, or various factors in the manufacturing process, for example, when steel materials are industrially manufactured, and adversely affect the welded joint according to the present embodiment. It means something that is acceptable to the extent that it does not exist. Examples of impurities other than P and S described above are O and N. O and N are elements that are mixed into the weld metal from the atmosphere during welding. For example, by improving the welding environment so that the O content is 0.0500% or less and the N content is 0.0300% or less, the toughness of the weld metal is further improved.

Further, instead of a part of the remaining iron, the weld metal may contain, for example, one or more of the optional elements listed below. However, even when the optional element exemplified below is not contained in the weld metal, the welded joint according to the present embodiment can solve the problem. Therefore, the lower limit of each content of any element exemplified below is 0%.

(Al: preferably 0.12% or less)
Al has the effect of deoxidizing the weld metal. Therefore, Al may be contained in the weld metal. Further, when the Al content of the weld metal is 0.12% or less, it is possible to prevent an excessive amount of alumina-based oxide from precipitating in the weld metal and further improve the toughness of the weld metal.

(Ni: preferably 3.00% or less)
Ni has the effect of improving the low temperature toughness of the weld metal. Therefore, Ni may be contained in the weld metal. Further, setting the Ni content of the weld metal to 3.00% or less reduces the cost of the alloy and is economically advantageous.

(Cr: preferably 1.20% or less)
Cr is an element that improves the hardenability of the weld metal. Therefore, Cr may be contained in the weld metal. Further, setting the Cr content of the weld metal to 1.20% or less reduces the cost of the alloy and is economically advantageous. Further, by setting the Cr content of the weld metal to 1.20% or less, the toughness of the weld metal can be further improved.

(Mo: preferably 1.00% or less)
Mo is an element that improves the hardenability of weld metal. Therefore, Mo may be contained in the weld metal. Further, setting the Mo content of the weld metal to 1.00% or less reduces the cost of the alloy and is economically advantageous. Further, by setting the Mo content of the weld metal to 1.00% or less, the toughness of the weld metal can be further improved.

(V: preferably 0.30% or less)
V is an element that improves the hardenability of the weld metal. Therefore, V may be contained in the weld metal. Further, setting the V content of the weld metal to 0.30% or less reduces the cost of the alloy and is economically advantageous. Further, by setting the V content of the weld metal to 0.30% or less, the toughness of the weld metal can be further improved.

(Nb: preferably 0.10% or less)
A small amount of Nb forms a carbonitride in the weld metal and contributes to the miniaturization of the structure and the improvement of the strength of the weld metal. Therefore, Nb may be contained in the weld metal. Further, by setting the Nb content of the weld metal to 0.10% or less, the toughness of the weld metal can be further improved.

(B: preferably 0.0600% or less)
B improves the hardenability of the weld metal, even in trace amounts. Therefore, B may be contained in the weld metal. Further, by setting the B content of the weld metal to 0.0600% or less, the toughness of the weld metal can be further improved.

(Mg: preferably 0.01% or less)
Mg has the effect of deoxidizing the weld metal. Therefore, Mg may be contained in the weld metal. Further, when the Mg content of the weld metal is 0.01% or less, the toughness of the weld metal can be further improved.

(Cu: preferably 1.00% or less)
When Cu is plated on the surface of the welding wire, which is the material of the welding metal, the welding workability is improved. Cu also has the effect of improving the hardenability of the weld metal. Therefore, Cu may be contained in the weld metal. Further, when the Cu content of the weld metal is 1.00% or less, the toughness of the weld metal can be further improved.

The chemical composition of the weld metal is determined by taking a sample from the weld metal and performing a chemical analysis on it. The chemical composition of the weld metal can also be determined by performing QV (cantback) analysis on the weld metal. In any case, it is necessary to prevent the base steel sheet from being included in the analysis target.

(Ceq of weld metal: 0.450 to 0.950% by mass)
Ceq is called carbon equivalent, and is a numerical value obtained by converting the chemical composition contained in the steel material into carbon content. In the welded joint according to the present embodiment, Ceq is a value calculated by the following formula 1 or formula 5 shown by the Japan Welding Engineering Society (WES).
Ceq = C + Mn / 6 + Si / 24: Equation 1
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 4: Equation 5
Here, the element symbol contained in the formula 1 or the formula 5 is the content of the element corresponding to these element symbols in the chemical composition of the weld metal in the unit mass%. When the chemical composition of the weld metal does not contain the above-mentioned optional element, Ceq is calculated using the formula 1, and when the chemical composition of the weld metal contains the above-mentioned arbitrary element, the Ceq is calculated using the formula 5. ..

If the Ceq of the weld metal is less than 0.450%, the strength of the weld metal is insufficient. On the other hand, if the Ceq of the weld metal is more than 0.950%, the toughness of the weld metal is impaired. Therefore, the Ceq of the weld metal is 0.450 to 0.950%. The Ceq of the weld metal may be 0.500% or more, 0.550% or more, or 0.600% or more. The Ceq of the weld metal may be 0.900% or less, 0.850% or less, or 0.800% or less.

(Vickers hardness of weld metal: 300HV or more)
The greater the hardness of the weld metal, the better the fatigue strength of the welded joint. According to the study results of the present inventors, when the Vickers hardness of the weld metal is set to 300 HV or more, sufficient fatigue strength can be secured, for example, as an automobile member. Therefore, the Vickers hardness of the weld metal is set to 300 HV or more. The Vickers hardness of the weld metal may be 320 HV or more, 350 HV or more, or 380 HV or more.

The Vickers hardness of the weld metal is obtained by measuring the hardness of the weld metal in the cross section orthogonal to the weld line. In the cross section orthogonal to the welding line, Vickers hardness measurement is performed with a load of 0.2 kN or more for any 10 points or more inside the weld metal, and the average value of the measured values obtained by this is welded. Considered as the hardness of metal. The inside of the weld metal is a region separated by 0.1 mm or more from the outer edge of the weld metal (that is, the surface of the weld metal and the molten boundary which is the boundary between the weld metal and the steel plate) in the cross section orthogonal to the welding line (that is, the surface of the weld metal and the molten boundary which is the boundary between the weld metal and the steel plate). The area surrounded by the broken line in FIG. 2).

(Thickness of 1 or more of 2 or more steel plates: 0.8 mm or more and 4.0 mm or less)
Next, the steel plate will be described. One or both of two or more steel plates that are the base material of the welded joint are thin plates that are suitable as materials for, for example, automobile members. Specifically, the thickness of one or both of two or more steel plates is 0.8 mm or more and 4.0 mm or less. This makes it easy to apply the welded joint according to the present embodiment to an automobile member.

In general, the larger the plate thickness of the base metal, the smaller the influence of the weld metal structure on the fatigue strength tends to be. This is because the larger the plate thickness of the base metal, the larger the tensile residual stress introduced into the welded portion after welding. There is a correlation between the tensile residual stress of the weld and the fatigue strength, and the larger the tensile residual stress, the lower the fatigue characteristics tend to be. On the other hand, if it is a steel sheet in the above-mentioned plate thickness range, fatigue characteristics can be ensured by optimizing the composition and hardness of the weld metal. In a welded joint composed of two or more thick plates, the residual stress of the weld metal on the fatigue characteristics is dominant, and the components of the weld metal have almost no effect on the fatigue characteristics. Therefore, it is not expected that the above configuration will be adopted for the weld metal of the thick plate for the purpose of improving the fatigue characteristics.

If one of the two or more steel plates is a thin plate having a plate thickness of 0.8 mm or more and 4.0 mm or less, the thickness of the other is not limited. The thickness of one or more of the two or more steel plates may be 3.8 mm or less, 3.6 mm or less, or 3.2 mm. The thickness of one or more of the two or more steel plates may be 1.2 mm or more, 1.5 mm or more, or 1.6 mm or more.

(Si content of slag adhering to welded joints: 5.0% by mass or less)
Next, the slag adhering to the welded joint will be described. Si in the slag reduces the conductivity of the slag. Slag with low conductivity causes poor electrodeposition coating. Therefore, in order to further improve the electrodeposition coating property, it is effective to reduce the Si content of the slag adhering to the surface of the weld metal. Specifically, by setting the Si content of the slag adhering to the welded joint to 5.0% by mass or less, the electrodeposition coating property required for the welded joint can be ensured. The Si content of the slag attached to the welded joint may be 4.8% by mass or less, 4.5% by mass or less, or 4.0% by mass or less.

The method for measuring the Si content of the slag adhering to the welded joint is as follows. At the place where the slag is attached, the weld joint is cut so as to be orthogonal to the weld line of the weld metal. Before cutting, measures are taken to prevent the slag from falling off, such as applying a resin so as to cover the slag. Next, in the cross section, the chemical composition of the slag is analyzed using the EDS or WDS attached to the scanning electron microscope. The observation magnification is 500 to 1000 times. In addition, the analysis is performed at three locations in the slag, and the median value of the obtained measurement results is regarded as the chemical composition of the slag.

Also, when calculating the Si content of the slag, the measured value of oxygen mass is excluded. That is, the value obtained by dividing the measured value of the Si content by the total of the measured values of the contents of the components excluding oxygen is regarded as the Si content of the above-mentioned slag. For example, when the analysis result of slag shows O: 50% by mass, Fe: 40% by mass, and Si: 10% by mass, the Si content of the slag is considered to be 20% by mass (= 10 / (100-50)). .. This is because, in X-ray analysis such as EDS, the measured value of a light element represented by O has a large error. In the welded joint according to the present embodiment, the Si content of the slag is the ratio of the mass of Si to the mass of the slag excluding oxygen.

(Relationship between the Si content Si _WM in the unit mass% of the weld metal and the Si _BM having the largest Si content in the unit mass% of two or more steel sheets: Satisfyes Equation 2)
Next, the relationship between the chemical composition of the weld metal and the chemical composition of the steel sheet will be described. In the welded joint according to the present embodiment, the Si content Si _WM in the unit mass% of the weld metal measured by the above-mentioned means and the Si content in the unit mass% of two or more steel plates have the largest value Si. _BM satisfies the following equation 2.
2.5 × {(Si _WM / 0.89) -0.6 × Si _BM } ≦ 0.510: Equation 2
During welding (especially during arc welding), the steel plate, which is the base metal, is also heated by heat conduction from the molten pool. Then, an oxidation scale is generated on the surface of the heat-affected zone of the steel sheet. Welding fume generated by welding also adheres to the heat-affected zone of the steel sheet. These may deteriorate the electrodeposition coating property. On the other hand, according to the findings of the present inventors, it was found that the electrodeposition coating property of the heat-affected zone of the steel sheet is improved by selecting the components of the steel sheet and the welding material so as to satisfy the formula 2. In addition, 2.5 × {(Si _WM / 0.89) −0.6 × Si _BM } may be 0.500 or less, 0.400 or less, 0.300 or less, or 0.200 or less. Further, Si _BM is obtained by the same method as the method for measuring the chemical composition of the weld metal. That is, Si _BM is obtained by taking a sample from a steel plate and performing a chemical analysis on the sample. The chemical composition of the steel sheet can also be determined by performing QV (cantback) analysis on the steel sheet. The Ti _BM described later can also be obtained by the same method as the Si _BM .

As long as the above-mentioned requirements are satisfied, the welded joint according to the present embodiment can adopt various configurations depending on its use. On the other hand, by adopting the configuration exemplified below, various characteristics of the welded joint according to the present embodiment are further enhanced.

(Toe angle β at one or more toes of weld metal: preferably greater than 0 ° and less than 30 °)
It is preferable to smooth the shape of one or more toes of the weld metal. The toe is the point where the surface of the base metal and the surface of the weld bead intersect (JIS Z 3001-7: 2018), and the toe is the toe and its periphery. By smoothing the shape of the toe, stress concentration at the toe can be relaxed and fatigue strength can be further improved.
The toe angle β is a pinching angle formed by a line connecting the toe of the weld metal and the surface of the weld metal at a distance of 0.3 mm from the toe to the surface of the steel sheet. The toe angle is generally 0 ° or more and 60 ° or less, but in the weld metal of the welded joint according to the present embodiment, one or more toe portions may satisfy the following conditional expression.
0 ° <β <30 °
By satisfying the above conditional expression, the toe of the weld metal has a gentle shape, so that it is possible to further suppress the concentration of stress on the toe of the weld metal. The toe angle β may be 28 ° or less, 25 ° or less, or 20 ° or less. The toe angle β may be 12 ° or more, 14 ° or more, or 18 ° or more.

The method for measuring the toe angle β is as described below when the welded joint is a lap fillet welded joint. For convenience, of the two steel plates of the lap fillet welded joint, the steel plate whose surface (plate surface) is joined by the weld metal is referred to as the first steel plate 1, and the steel plate whose end face is joined by the weld metal is referred to as the second steel plate 2. It is called. As shown in FIG. 1, assuming that the position of the melting boundary existing on the surface 1a of the first steel plate 1 is point A, the weld metal 3 rises from point A with a toe angle β. Further, the weld metal 3 stands up with a flank angle θ from a position further closer to the side of the second steel plate 2 from the point A. The flank angle θ is generally used as a parameter representing the shape of the toe of the weld metal 3, but in the present embodiment, the toe angle β is used as a parameter representing the shape of the toe of the weld metal 3. Explaining with reference to FIG. 1, the toe angle β of the weld metal is a value defined as follows when viewed in a cross section orthogonal to the weld line of the weld metal.
-Point A: Melt boundary existing on the surface 1a of the first steel plate 1-Point C: 0.3 mm away from point A toward the inside of the weld metal 3 in the X direction parallel to the surface 1a of the first steel plate 1. Position ・ Point B: The intersection of the straight line passing through point C and extending in the plate thickness direction of the first steel plate 1 with the surface 3a of the weld metal 3 ・ The toe angle β of the weld metal: the straight line connecting points A and B And the angle between the straight line connecting points A and C

As described above, the molten boundary means the boundary between the weld metal and the steel plate. The melt boundary can be easily confirmed by corroding the cross section of the welded joint by a known method. The toe angle β can be measured by specifying points A, B, and C in the cross section where the melting boundary appears.

Further, in FIG. 1, for convenience of explanation, the surface 1a of the first steel plate 1 and the end surface 2a of the second steel plate 2 contained inside the weld metal 3 are represented by dotted lines in order to show the positions of the corners 4. However, in reality, the above dotted line portion is melted into the weld metal 3. Therefore, even if a cross-sectional photograph of the weld metal 3 is obtained using an optical microscope, the dotted line portion cannot be observed. Therefore, by specifying the three points A, B, and C defined as described above on the cross-sectional photograph of the weld metal 3, the toe angle β of the weld metal 3 can be obtained from the cross-sectional photograph of the weld metal 3. It can be easily obtained. As long as a photograph capable of identifying the toe angle β of the weld metal 3 can be obtained, the toe angle β is measured not only with an optical microscope but also with a scanning electron microscope (SEM) or a microscope. You may.

In the lap fillet welded joint, it is preferable that 0 ° <β <30 ° is satisfied at least at the toe portion on the side of the first steel plate 1. On the other hand, the toe angle β can also be specified at the toe on the second steel plate 2 side by the above method, and the toe on the first steel plate 1 side and the toe on the second steel plate 2 side. 0 ° <β <30 ° may be set in one or both.

Although the method of measuring the tongue angle β has been described above by taking a lap fillet welded joint as an example, the measurement can be similarly performed on a welded joint having other shapes such as a T joint and a butt joint. As described above, in the welded joint according to the present embodiment, it is preferable that the shape of one or more toes is gentle. When the weld metal has two or more toes, it is preferable to at least smooth the toes where fatigue cracks may occur. The toe where fatigue cracks may occur is, for example, a toe where stress tends to concentrate due to the structure of the member.
In the lap fillet welded joint, for example, the point where the surface of the lower plate and the surface of the weld bead intersect (the toe on the lower plate side) is the toe where fatigue cracks may occur.
In the case of a T-shaped joint (a joint in which the end face of one plate is placed on the surface of another plate and the end face is approximately right-angled in a T-shape), for example, a fatigue crack occurs at the toe on the main plate side (stress transmission side). It is a stop for concern. In the T-shaped joint, fatigue cracks are likely to occur in the order of the toe on the main plate side (stress transmission side), the toe on the side with a short weld leg length, and the toe on the side with a small throat thickness. Further, when the plate thickness of the steel base material is different, fatigue cracks are likely to occur from the toe on the base material side where the plate thickness is thin.
If the joint is a butt joint (a joint in which parts placed on the same plane face each other at 135 ° ≤ α ≤ 180 °) and the plate thickness of the steel base material is different, the stop on the steel plate side where the plate thickness is thin Fatigue cracks are likely to occur from the edges.
In consideration of the above circumstances, in the welded joint, only the shape of the toe portion where the above-mentioned fatigue crack may occur may be made gentle. On the other hand, the shape of all toes in the welded joint may be smoothed.

(Relationship between Ti _WM having Ti content in unit mass% of weld metal and Ti _BM having the largest Ti content in unit mass% of two or more steel sheets: preferably satisfying Equation 3)
In the welded joint according to the present embodiment, the Ti content Ti _WM in the unit mass% of the weld metal measured by the above-mentioned means and the Ti content in the unit mass% of two or more steel plates have the largest value Ti. The relationship with the _BM may satisfy Equation 3.
0.050 ≦ 2.5 × {(Ti _WM / 0.54) -0.6 × Ti _BM } ≦ 0.300: Equation 3
In the weld metal, the alloying elements are distributed almost evenly. However, the component of the weld metal near the toe tends to be easily affected by the component of the base metal. Here, the amount of Ti in the vicinity of the toe of the weld metal contributes to the miniaturization of the structure of the weld metal. Further, the amount of Ti in the vicinity of the toe of the weld metal also has a function of improving the conductivity of the slag generated in the vicinity of the toe and improving the electrodeposition coating property of the welded joint. Since slag tends to adhere to the toe, modification of the slag component at the toe is particularly effective for improving the electrodeposition coating property. When Ti _WM and Ti _BM satisfy Equation 3, the amount of Ti in the weld metal near the toe is preferably controlled, and the above-mentioned effect can be obtained. In addition, 2.5 × {(Ti _WM / 0.54) −0.6 × Ti _BM } may be 0.280 or less, 0.250 or less, or 0.200 or less. 2.5 × {(Ti _WM / 0.54) -0.6 × Ti _BM } may be 0.080 or more, 0.100 or more, or 0.150 or more. Further, Ti _WM is a value measured at a position sufficiently distant from the base metal (for example, at a position orthogonal to the welding line of the weld metal and at a distance of 0.1 mm or more from the melting boundary).

(Vickers hardness of weld metal: preferably 80% or more of HM)
In the welded joint according to the present embodiment, the Vickers hardness of the weld metal measured by the above-mentioned means may be 80% or more of the HM. HM is calculated by the following equation 4.
HM = 884 × C × (1-0.3 × C ² ) +294: Equation 4
Here, the element symbol included in the formula 4 is the content of the element corresponding to these element symbols in the chemical composition of the weld metal in the unit mass%.

The value HM calculated by Equation 4 is a value called 100% martensite hardness, and when the steel is quenched so that the entire structure becomes martensite (that is, when the maximum quench hardening is caused). It is an estimated value of hardness. The higher the ratio of actual hardness to HM, the higher the amount of martensite and the smaller the amount of soft structures such as ferrite that can be the origin of fatigue cracks. Therefore, the higher the ratio of the actual hardness to the HM, the more the origin of fatigue cracks can be reduced and the fatigue characteristics can be further improved. For the above reasons, the Vickers hardness of the weld metal is preferably 80% or more of the HM of the weld metal. The Vickers hardness of the weld metal may be 83% or more, 85% or more, or 90% or more of the HM of the weld metal. Since the HM of the weld metal is an estimated value of the hardness when the weld metal is maximally quenched and hardened, the hardness of the weld metal actually measured may exceed the HM.

(Total Ti content and Zr content of slag: preferably 0.5% by mass or more)
In the welded joint according to the present embodiment, the total Ti content and Zr content of the slag may be 0.5% by mass or more. As described above, Ti and Zr have a function of increasing the conductivity of slag and suppressing the occurrence of electrodeposition coating defects caused by slag. Therefore, the higher the Ti content and the Zr content in the slag, the better the electrodeposition coating property. The total Ti content and Zr content of the slag may be 0.6% by mass or more, 0.8% by mass or more, or 1.0% by mass or more. Here, the method for measuring the Ti content and the Zr content of the slag is a value measured by the same means as the Si content of the slag. In the welded joint according to the present embodiment, the Ti content and the Zr content of the slag are the ratio of the masses of Ti and Zr to the mass of the slag excluding oxygen.

In addition to or in place of the provision for the total Ti content and Zr content of the slag, the Ti content and Zr content of the slag may be specified individually. For example, the Ti content of the slag may be 0.4% by mass or more, 0.5% by mass or more, or 0.6% by mass or more. The Zr content of the slag may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

Next, a method for manufacturing a welded joint according to the present embodiment will be described. The method for manufacturing a welded joint according to the present embodiment includes a step of welding two or more steel plates using a filler metal. The type of welding is not particularly limited, but for example, arc welding, particularly gas shielded arc welding is preferable.

The chemical composition of the weld metal and Ceq, as well as the chemical composition of the slag, are determined by the chemical composition of the steel sheet to be welded, the chemical composition of the filler metal, and the transfer rate of the alloy components. For example, Si, Ti, Al and the like, which easily form oxides during welding, are partially discharged to the outside of the weld metal as slag. On the other hand, elements that do not easily form oxides tend to stay in the weld metal. Therefore, the chemical composition of the steel sheet and the chemical composition of the filler metal do not match the chemical composition of the weld metal. However, the chemical composition of the weld metal, Ceq, and the chemical composition of the slag can be within the above range by appropriately selecting the components of the steel sheet and the filler material while considering the characteristics of each alloying element.

The Vickers hardness of the weld metal is determined by the chemical composition and material structure of the weld metal. The hardenability of the weld metal depends on the Ceq of the weld metal, and the martensite structure hardness depends on the amount of C. Therefore, by setting the Ceq of the weld metal to the above-mentioned appropriate range, the weld metal formed by welding has a martensite structure, and the Vickers hardness of the weld metal and the ratio of the Vickers hardness of the weld metal to the HM are determined. , Can be within the above range. By optimizing the welding conditions at this time, the toe angle at one or more toes of the weld metal can be made to be more than 0 ° and less than 30 °.

The toe angle of the weld metal is affected by various welding conditions. For example, when the type of welding is arc welding, the higher the voltage, the wider the arc and the smaller the toe angle. Further, when the welding is fillet welding, the toe angle tends to become smaller as the welding target position is farther from the corner. Here, the welding target position is the intersection of the central axis of the welding torch and the surface of the lower plate. The lower plate is a plate whose surface is mainly welded. In the case of the lap welded joint exemplified in FIG. 1, the first steel plate 1 corresponds to the lower plate. In the case of a T-joint, the plate to which the end is welded corresponds to the upper plate, and the plate to which the upper plate is abutted corresponds to the lower plate.

The toe angle of the weld metal is also affected by the welding posture. The molten metal hangs down due to gravity. Therefore, the angle of the steel plate at the time of welding may be set so as to cause sagging that reduces the toe angle. For example, in the case of the lap welded joint exemplified in FIG. 1, the first steel plate 1 is welded with the first steel plate 1 and the second steel plate 2 standing upright so that the end surface 2a of the second steel plate 2 faces up. The stop angle of the toe on the side of 1 can be reduced.

However, if the arc is widened too much in order to reduce the toe angle, an undercut will occur at the toe and a sound welded joint cannot be obtained. Extreme welding postures can also adversely affect the overall shape of the weld metal. Under the above-mentioned guidelines, it is desirable to optimize the welding conditions while considering the type of welded joint, the material of the steel plate, the thickness of the steel plate, and the type and material of the filler metal.

Next, an automobile member according to another aspect of the present invention will be described. The automobile member according to another aspect of the present invention has the welded joint according to the above-described embodiment. As a result, the automobile parts according to the present embodiment are suppressed from electrodeposition coating defects and have better fatigue characteristics. The type of the automobile member is not particularly limited, but for example, the automobile member may be a front lower arm or a subframe.

(Example 1)
The effects of one embodiment of the present invention will be described more specifically by way of examples. However, the conditions in the examples are only one condition example adopted for confirming the feasibility and effect of the present invention. The present invention is not limited to this one-condition example. The present invention may adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Two steel plates having the plate thickness and chemical composition shown in Table 1 were superposed and welded by lap fillet. The rest of the chemical composition of these steel sheets was iron and impurities. In all the examples, the types of the two steel plates were the same, and the specific welding conditions were as follows. In the following description, t means the plate thickness of one steel plate.
・ Stacking allowance: 10 mm
-Welding current: 81 x t (A) in DC pulse mode
・ Welding speed: 0.8m / min ・ Shield gas type: Ar + 20% CO ₂

For various welded joints obtained by the above method, the total of the chemical composition of the weld metal, the Vickers hardness of the weld metal, the toe angle β, the Si content of the slag, the Ti content of the slag and the Zr content. The value was measured. The measurement method was as described above. The rest of the chemical composition of the weld metal was Fe and impurities.
Since most of Mg was discharged to the outside of the weld metal as slag, the amount of Mg detected in the weld metal was less than 0.0003%. In addition, the toe angle β was less than 30 ° in all welded joints.
Furthermore, the fatigue characteristics and electrodeposition coating properties of various welded joints obtained by the above method were evaluated.

Fatigue characteristic evaluation was carried out by the following procedure. A test piece having a width of 20 mm was collected from the welded joint in the direction of the weld line. The sampling was performed at a place where the weld bead was stable, and the start and end of the weld bead were not evaluated. Next, a flat bending fatigue test was performed on the test piece. The loading condition was displacement control of both swings with a stress ratio of -1. The breaking condition was set to the time when the bending moment acting on the test piece was 1 Nm or less. The fatigue limit σ _W was set to the stress amplitude (MPa) at the time of ¹⁰⁷ unbreaks. The stress standard was the maximum value of bending stress when the stress concentration at the weld toe in the center of the test piece was not taken into consideration. The maximum value of the above-mentioned bending stress calculated from the bending moment M (N · mm), the test piece width h (mm), and the plate thickness t (mm) is 6 × M / (h × t ² ) ( MPa).

The pass / fail criteria for fatigue characteristics are as follows. There is a plate thickness effect on the fatigue limit in bending loading. Therefore, considering the influence of the plate thickness, it is judged that the welded joint in which the fatigue limit σ _W (MPa) satisfying the relationship of the following formula A is obtained has a good fatigue limit, and the fatigue characteristic is set to “Δ”. evaluated. Further, the welded joint satisfying the relationship of the following formula B was judged to have a better fatigue limit and was evaluated as “◯”. Welded joints that do not satisfy the relationship of the following formula A were judged not to have a good fatigue limit and were evaluated as "x". A welded joint satisfying at least the relationship of the following formula A was judged to be acceptable in terms of fatigue characteristics.
σ _W ≧ 191 + 55.35 / t: Equation A
σ _W ≧ 200 + 57.99 / t: Equation B

The electrodeposition coating property evaluation was carried out by the following procedure. First, the welded joint was degreased and chemical-converted. Next, the welded joint was electrodeposited so that the film thickness was 20 μm. Then, a photograph of the weld bead portion after electrodeposition coating is taken, and the photograph is analyzed to measure the ratio of the area of the electrodeposition coating defective portion to the area of the weld bead, and this ratio is referred to as the coating defect area ratio. did. The length of the weld bead was 120 mm. 90 mm in length excluding the weld start end (region from the weld start side end of the weld bead to 15 mm) and the weld end (region from the weld end end of the weld bead to 15 mm) from this weld bead. The above-mentioned measurement was performed on the region of. A gray paint was used for electrodeposition coating. Since the yellowish brown slag is exposed in the electrodeposition coating defective portion, the electrodeposition coating defect portion can be easily identified by electrodeposition coating using a gray paint.

The pass / fail criteria for electrodeposition coating are as follows. A welded joint having a poor coating area ratio of 10% or less was judged to be a welded joint having excellent electrodeposition coating property, and was evaluated as "Δ". Welded joints with a poor coating area ratio of 5% or less were judged to be welded joints with particularly excellent electrodeposition coating properties, and were evaluated as "○". Welded joints with a poor coating area ratio of more than 10% were evaluated as "x". Welded joints with an evaluation of "Δ" or "○" were judged to pass the electrodeposition coating property.

The various evaluation results described above are shown in Table 2 and subsequent tables. In the table, values outside the scope of the invention are underlined. In addition, for the components that were not detected, the content thereof is indicated by "-" in the table.

In the table, "H _WM " indicates the Vickers hardness of the weld metal, and "base metal molten metal Si" indicates 2.5 × {(Si _WM / 0.89) -0.6 × Si _BM }. "Base metal molten metal Ti" indicates 2.5 x {(Ti _WM / 0.54) -0.6 x Ti _BM }, "slag Si%" indicates the Si content of slag, and "slag Ti + Zr%". "Shows the total Ti content and Zr content of the slag.

Weld metal composition, weld metal Ceq, weld metal Vickers hardness (welded metal HV), toe angle, slag Si content, and relationship between base metal Si amount and weld metal Si amount (base metal molten metal) Welds whose Si) is within the scope of the invention are excellent in both fatigue characteristics and electrodeposition coating properties. On the other hand, in the comparative example in which one or more of these were out of the scope of the invention, one or both of the fatigue characteristics and the electrodeposition coating property were inferior.

Welded joint No. In No. 4, the Ti content of the weld metal, the Ceq of the weld metal, and the Vickers hardness of the weld metal were insufficient. Therefore, the welded joint No. In 4, the fatigue characteristics were insufficient.
Welded joint No. In No. 5, the Ti content of the weld metal was insufficient. Therefore, the welded joint No. At 5, the fatigue characteristics were insufficient.
Welded joint No. At No. 10, the Si content of the slag was excessive (see “Slag Si%”), and Si _WM and Si _BM did not satisfy the formula 2 (see “Base metal melted Si”). Therefore, the welded joint No. At 10, the electrodeposition coating property was insufficient.
Welded joint No. In No. 12, the amount of Mn of the weld metal was excessive. Therefore, the welded joint No. At 12, the fatigue characteristics were insufficient.
Welded joint No. In No. 14, the Ceq of the weld metal and the Vickers hardness of the weld metal were insufficient. Therefore, the welded joint No. At 14, the fatigue characteristics were insufficient.
Welded joint No. In 17, the Ti content of the weld metal was insufficient. Therefore, the welded joint No. At 17, the fatigue characteristics were insufficient.
Welded joint No. In No. 19, the C content and V content of the weld metal and the Ceq of the weld metal were excessive. Therefore, the welded joint No. At 19, the fatigue characteristics were insufficient.
Welded joint No. At 20, the Mn content of the weld metal was insufficient. Therefore, the welded joint No. At 20, the fatigue characteristics were insufficient.
Welded joint No. In 22, Si _WM and Si _BM did not satisfy the formula 2 (see “Base metal molten metal Si”). Therefore, the welded joint No. At 22, the electrodeposition coating property was insufficient.
Welded joint No. In No. 23, the Zr content of the weld metal was insufficient. Therefore, the welded joint No. At 23, the fatigue characteristics were insufficient.
Welded joint No. In No. 26, the Ti content of the weld metal, the Ceq of the weld metal, and the Vickers hardness of the weld metal were insufficient. Therefore, the welded joint No. At 26, the fatigue characteristics were insufficient.

(Example 2)
In order to evaluate the effect of the toe shape, the experiments described below were performed.
Two steel plates A shown in Table 1 were superposed and welded by lap fillet. The welding wire, lap allowance, welding speed, and shield gas type used in the lap fillet welding were the same as those of the joint 1 in Table 2. Other welding conditions are as shown in Table 6. The numerical values listed in the "welding target position" column of Table 6 are the distances between the above-mentioned welding target position and the end face of the upper plate (second steel plate). As shown in FIG. 3, the closer the welding target position is to the upper plate (second steel plate), the larger the numerical value described in the “welding target position” column of Table 6. When the welding target position is arranged at a position that does not overlap with the lower surface of the upper plate (second steel plate), a negative value is described in the “welding target position” column of Table 6.
Similar to Example 1, the toe angle β was measured and the fatigue characteristics were evaluated for the various welded joints obtained by the above procedure, and the results are shown in Table 6. No. In the welded joints of 3 to 6, fatigue cracks were generated from the surface of the weld metal, and the fatigue strength was further enhanced.

1 1st steel plate 1a Surface of 1st steel plate 2 2nd steel plate 2a End face of 2nd steel plate 3 Welded metal 3a Surface of weld metal 4 Corner 10 Welded joint A Passing through the molten boundary B C point existing on the surface of the 1st steel plate Intersection point between the straight line extending in the plate thickness direction of the first steel plate and the surface of the weld metal C In the X direction parallel to the surface of the first steel plate, the position θ Frank separated from point A toward the inside of the weld metal by 0.3 mm. Angle β toe angle

Claims (8)

With 2 or more steel plates,
Welded metal that joins two or more steel plates,
It is a welded joint equipped with
The chemical composition of the weld metal is, in units of mass%,
C: 0.01-0.25%,
Si: 0.01-1.00%,
Mn: 0.80 to 2.50%,
P: 0.0500% or less,
S: 0.0100% or less,
Ti: 0.020 to 0.120%, and Zr: 0.001 to 0.050%
Containing, the balance consists of iron and impurities,
The Ceq of the weld metal calculated by the following formula 1 is 0.450 to 0.950% by mass.
The Vickers hardness of the weld metal is 300 HV or more, and the weld metal has a Vickers hardness of 300 HV or more.
The thickness of one or more of the two or more steel plates is 0.8 mm or more and 4.0 mm or less.
The Si content of the slag adhering to the welded joint is 5.0% by mass or less, and the slag has a Si content of 5.0% by mass or less.
A welded joint in which the Si content Si _WM in the unit mass% of the weld metal and the Si _BM having the largest value among the Si contents in the unit mass% of two or more of the steel sheets satisfy the following formula 2.
Ceq = C + Mn / 6 + Si / 24: Equation 1
2.5 × {(Si _WM / 0.89) -0.6 × Si _BM } ≦ 0.510: Equation 2
Here, the element symbol included in the formula 1 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in a unit mass%. The Ti content Ti _WM in the unit mass% of the weld metal and the Ti _BM having the largest value among the Ti contents in the unit mass% of two or more of the steel plates satisfy the following formula 3. The welded joint according to claim 1.
0.050 ≦ 2.5 × {(Ti _WM / 0.54) -0.6 × Ti _BM } ≦ 0.300: Equation 3 The welded joint according to claim 1 or 2, wherein the Vickers hardness of the weld metal is 80% or more of the HM calculated by the following formula 4.
HM = 884 × C × (1-0.3 × C ² ) +294: Equation 4
Here, the element symbol included in the formula 4 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in unit mass%. The welded joint according to any one of claims 1 to 3, wherein the total of the Ti content and the Zr content of the slag is 0.5% by mass or more. The welded joint according to any one of claims 1 to 4, wherein the toe angle at one or more toes of the weld metal is more than 0 ° and less than 30 °. The two or more steel plates are a superposed first steel plate and a second steel plate.
The weld metal joins the surface of the first steel sheet and the end face of the second steel sheet.
The welded joint according to claim 5, wherein the toe angle of the weld metal at the toe on the side of the first steel plate is more than 0 ° and less than 30 °. The chemical composition of the weld metal is, in units of mass%, in place of a portion of the iron.
Al: 0.12% or less,
Ni: 3.00% or less,
Cr: 1.20% or less,
Mo: 1.00% or less,
V: 0.30% or less,
Nb: 0.10% or less,
B: 0.0600% or less,
Mg: 0.01% or less,
Cu: 1.00% or less,
Contains one or more selected from the group consisting of O: 0.0500% or less and N: 0.0300% or less.
The welded joint according to any one of claims 1 to 6, wherein the Ceq of the weld metal is calculated by the following formula 5.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 4: Equation 5
Here, the element symbol included in the formula 5 is the content of the element corresponding to the element symbol in the chemical composition of the weld metal in unit mass%. An automobile member comprising the welded joint according to any one of claims 1 to 7.

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