JP2018126755A - Method for pulse mag welding of thin steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for pulse MAG welding of a thin steel plate which can obtain a weld zone which makes little slag remain on a bead surface, generates little sputter from stable arc, and has little welding defect from a favorable bead shape.SOLUTION: In a method for welding pulse MAG of a thin sheet plate, a solid wire, by mass% to the wire total mass, with 0.03-0.11% of C, 0.50-0.90% of Si, 1.40-1.90% of Mn, 0.15-0.35% of Ti, and an A value represented by the below (1), 0.55-0.85, 0.08-0.45% of Cu, and 0.006-0.020% of S is used for welding by adding pulses the pulse peak current (Ip) and the pulse peak time (Tp) of which satisfy the following formula (2) pulse current (Ip) being 440-600A and pulse base current (Ib) being 30-80A. A=0.33Si+0.15Mn+Ti...(1), 415≤Ip(A)×Tp(msec)≤780...(2).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pulse MAG welding method for a thin steel plate, and in particular, when welding a lap joint portion or a T joint portion of a thin steel plate having a thickness of 1.2 to 6 mm, there is little slag remaining on the bead surface and the arc is stabilized. In particular, the present invention relates to a pulse MAG welding method for a thin steel sheet suitable for obtaining a high-efficiency and high-quality welded part such as a low spatter generation amount, a good bead shape, and no welding defects.

The undercarriage member of an automobile is mostly a thin steel plate having a thickness of 1.2 to 6 mm, and is usually electrodeposited with a paint for rust prevention and aesthetic appearance after welding.
The purpose of welding undercarriage members of thin steel sheets for automobiles is to reduce the amount of spatter generated by using solid wire for gas shielded arc welding and to reduce the amount of spatter generated from the aspect of quality characteristics of the joints, and at high speed. Ar gas as a main component as the shielding gas from the viewpoint of weldability secure, the mixing CO ₂ gas thereto, further the pulse MAG welding method using a mixed gas of O ₂ gas is increased in recent years. The pulse MAG welding method can weld with a low average current, so it can improve the melt-off resistance when welding thin steel plates, and it can be applied under high-speed welding conditions, so it is highly productive and has good quality. Is obtained.

Pulse MAG welding is a welding method in which a peak current that is higher than the average current value as a welding current and a base current that is lower than the average current value are periodically passed. As a result, the welding wire, which is constantly fed during the peak current period, is melted into a droplet state by an action such as an electromagnetic pinch force, and this droplet is stably transferred to the molten pool during the base current period. The droplets can be smoothly transferred to the molten pool without short-circuiting with the molten pool during high-speed welding.

In this way, by applying the pulse welding power source, the droplet generation amount for each wire feeding amount corresponding to the melting energy consisting of the product of peak current, peak time, and arc voltage in pulse MAG welding is obtained. That is, by forming a single droplet at the time of one pulse peak current and setting a pulse condition of 1 pulse-1 drop transition that regularly transfers the droplet to the molten pool during the base current period, The amount of spatter generated is reduced by smoothly moving to the molten pool. For this reason, the welding power source can change the frequency of the pulse from about several tens of Hz to about 300 Hz corresponding to the feeding speed of the welding wire.

As a wire for pulse MAG welding of thin steel plate welding, for example, JP-A-8-99175 (
Patent Document 1) welds thin high-strength steel sheets with limited wire components, shielding gas composition and pulse application conditions to improve the mechanical properties of the weld metal and reduce the amount of spatter generated. A technique having excellent properties is disclosed. However, even with the technique disclosed in Patent Document 1, it is impossible to obtain a weld metal with a stable arc and a good bead shape. Furthermore, there was a problem that the amount of slag generation increased and the paint was peeled off together with the slag after the paint was applied.

In addition, Japanese Patent Laid-Open No. 9-239583 (Patent Document 2), Japanese Patent Laid-Open No. 2001-321985 (Patent Document 3) and Japanese Patent Laid-Open No. 2009-166066 (Patent Document 4) describe a solid wire for pulse MAG welding. There is disclosure. However, even in the pulse MAG welding using the welding solid wire described in Patent Documents 2 to 4, there is a problem that the amount of slag generated is large and the paint is peeled off together with the slag after coating.

On the other hand, in JP-A-2006-203247 (Patent Document 5), welding of thin steel sheets is performed by containing at least one of silicon oxide, chromium oxide and nickel oxide in a flux-cored wire for gas shield arc welding. In addition, there is a disclosure of a technique in which an oxide film layer is formed on the bead surface to prevent peeling after coating. However, when the bead surface oxide film layer disclosed in Patent Document 5 is applied to a body structure member of an automobile, it is oxidized with a weld metal due to a temperature difference in an environment in which the automobile is used, such as seasonal changes, cold regions and warm regions. There is a problem that the oxide film layer is peeled off together with the paint due to a difference in thermal expansion from the film layer.

JP-A-8-99175 Japanese Patent Laid-Open No. 9-239583 JP 2001-321985 A JP 2009-166066 A JP, 2006-203247, A

Therefore, the present invention has been devised in view of the above-described problems, and has a thickness of 1.2 to 6 m.
High efficiency, such as when there are few slags remaining on the bead surface when welding lap joints and T joints of thin steel plates of m, the arc is stable and the amount of spatter is small, the bead shape is good and there are no welding defects Another object of the present invention is to provide a pulse MAG welding method for a thin steel plate that can obtain a high-quality weld.

The gist of the present invention is a pulse MAG welding method of a thin steel plate having a thickness of 1.2 to 6 mm.
% By mass with respect to the total mass of the wire, C: 0.04 to 0.11%, Si: 0.50 to 0.90%, Mn: 1.40 to 1.90%, Ti: 0.15 to 0.35 %, And A value shown in the following (1): 0.55 to 0.85, Cu: 0.08 to 0.45%, S: 0.006 to 0.020%, P: 0.00. 02% or less, the remainder using a solid wire made of Fe and inevitable impurities, pulse peak current (Ip): 440-600A, pulse base current (Ib): 30-80A, the pulse peak current (Ip) And a pulse MAG welding method for a thin steel sheet, characterized in that welding is performed by applying a pulse whose pulse peak time (Tp) satisfies the following formula (2).
A = 0.33Si + 0.15Mn + Ti (1)
(However, Si, Mn, and Ti are mass% with respect to the total mass of the wire)
415 ≦ Ip (A) × Tp (msec) ≦ 780 (2)

  According to the pulse MAG welding method of a thin steel plate of the present invention, when welding a lap joint portion or a T joint portion of a thin steel plate having a thickness of 1.2 to 6 mm, there is little slag remaining on the bead surface, and the arc is stabilized. As a result, the spatter generation amount is small, the bead shape is good and there are no welding defects, and a high-quality welded portion can be obtained with high efficiency.

It is a graph shown about the relationship between A value and the slag area rate on a bead surface. It is a figure which shows the wire aim position of the lap fillet joint welding used for the Example of this invention.

In order to solve the above-mentioned problems, the present inventors made thin steel plates into a fillet joint, and welded at a welding speed of 0.8 m / min or more under various pulse conditions using solid wires of various components. As a result of detailed examination of the amount of slag remaining on the bead surface, the stability of the arc, the occurrence of spatter, the bead shape and the presence or absence of welding defects, the following knowledge was obtained.

  (1) Although the wire composition was able to reduce the slag generation amount by making the Si content, the Mn content, the Ti content, and the S content appropriate, it can be sufficiently improved. could not. Therefore, as a result of further studies, the content of Si, Mn, Ti is appropriate, and the A value determined by the content of Si, Mn, Ti is within an appropriate range to suppress the slag generation amount It was found that the effect was sufficiently obtained. Further, by making the C content, Ti content, and Cu content appropriate, the arc was stabilized and welding with less spatter generation was achieved.

  (2) By using the wire having the above-described composition and making the region where the pulse condition is 1 pulse-1 drop droplet transfer, the arc is stabilized by high-speed welding at 80 cm / min or more, and the amount of spatter generated is reduced. Less bead shape can be obtained.

Hereinafter, the reason for limitation of the pulse MAG welding method of the thin steel plate of this invention is demonstrated.
First, the wire component composition will be described. In addition, the content rate of each component shall be represented by the mass% with respect to the total mass of a wire, and the description regarding the mass% is only described as%.

[C: 0.03-0.11%]
C has the effect of stabilizing the arc and making the droplets fine. If C is less than 0.03%, it is difficult to make the droplets finer, the arc becomes unstable, and the amount of spatter generated increases. On the other hand, if C exceeds 0.11%, the viscosity of the molten metal becomes low and the bead shape becomes poor, and the weld metal is hardened and crack resistance deteriorates. Therefore, C is 0.03 to 0.11%.

[Si: 0.50-0.90%]
Si is an element (deoxidation element) that promotes deoxidation of molten metal during arc welding, and is effective in suppressing the generation of blowholes. However, if Si is contained excessively, the generation of slag is suppressed. It is also a remarkable element. When Si is less than 0.50%, deoxidation is insufficient, and blow holes are likely to occur. On the other hand, when Si exceeds 0.90%, the amount of slag generation increases. Therefore, Si is 0.50 to 0.90%.

[Mn: 1.40 to 1.90%]
Mn is an important element as a deoxidizing element. If Mn is less than 1.40%, pits are likely to be generated particularly under high-speed welding conditions. On the other hand, when Mn exceeds 1.90%, spatter generation amount and slag generation amount increase. Therefore, Mn is 1.40 to 1.90%.

[Ti: 0.15-0.35%]
Ti has the effect of stabilizing the arc, and is also a deoxidizing element, so it is effective in suppressing blowholes. If Ti is less than 0.15%, these effects cannot be obtained, the arc becomes unstable, and blow holes are likely to occur. On the other hand, when Ti exceeds 0.35%, the amount of slag generation in which the slag generation reaction is promoted increases. Therefore, Ti is set to 0.15 to 0.35%.

[A value: 0.55 to 0.85]
It has been found that the A value obtained by the content of Si, Mn, and Ti as deoxidizing elements by the following formula (1) has a great influence on the state of slag generation. In particular, as a component contained in the solid wire, not only the individual content of each element is specified, but also when the A value is in the range of 0.55 to 0.85, the effect of suppressing the amount of slag generation is sufficient can get. This will be described with reference to experiments described later.
A = 0.33Si + 0.15Mn + Ti (1)
(However, Si, Mn, and Ti are mass% with respect to the total mass of the wire)

[Experiment]
A part of the result of the experiment is shown in FIG. In this experiment, ingots having various steel compositions were melted, hot-rolled, drawn, annealed, copper-plated, and further drawn to produce a 1.2 mm solid wire. The composition of the solid wire including the plating layer is as follows: C: 0.03 to 0.11%, Si: 0.50 to 0.90%, Mn: 1.40 to 1.90%, Ti: 0.15 -0.35%, S: 0.006-0.020%. Using a solid wire, Ar-20% CO ₂ gas as a shielding gas, and a thin steel plate having a thickness of 3.2 mm, pulse welding conditions are as follows: pulse peak current (Ip): 480 A, pulse base current (Ib) : 50 A, pulse peak time (Tp): Bead-on-plate welding was carried out for a length of 400 mm at 1.4 msec. And the slag area rate shown to following (3) Formula was computed.

FIG. 1 is a plot of the above experimental results with the vertical axis representing the slag area ratio and the horizontal axis representing the A value of each solid wire. As apparent from FIG. 1, it was found that the slag area ratio was suppressed to a low value of 10% or less when the value of A was in the range of 0.55 to 0.85. Here, when the slag rate is 10% or less, a coating defect does not substantially occur when the surface of the weld metal using the solid wire is coated. On the other hand, when the A value is less than 0.55, the slag area ratio increases rapidly to 20% or more, and when the A value exceeds 0.85, the slag area ratio increases to 20% or more. did. Therefore, the A value is set to 0.55 to 0.85.
Slag area ratio (%) = total of slag area ÷ total image area × 100 (%) (3)

[Cu: 0.08 to 0.45%]
Cu is contained in steel in an amount of about 0.02% as an inevitable impurity, but Cu of the present invention mainly refers to copper plating applied to the wire surface. In general, copper plating is a surface treatment method that is extremely important for stabilizing the wire feeding property and the current carrying property. If the copper plating thickness is thin, tip wear during welding becomes severe, and wire feedability and electrical conductivity deteriorate during welding, resulting in an unstable arc. If the Cu content is less than 0.08%, the required wire feedability and electrical conductivity cannot be obtained and the arc becomes unstable. On the other hand, if Cu exceeds 0.45%, the crack resistance of the weld metal deteriorates. Therefore, Cu is made 0.08 to 0.45%. In addition, it is preferable that the copper plating thickness of the wire surface is 0.2-1.0 micrometer from chip | tip wear resistance and electrical conductivity.

[S: 0.006 to 0.020%]
S has the effect of reducing the amount of slag remaining on the bead surface by floating a small amount of slag generated during welding to the surface of the molten pool and carrying it to the crater portion. When S is less than 0.006%, the effect of floating the generated slag on the surface of the molten pool and transporting it to the crater portion is reduced, and the slag remains on the bead surface. On the other hand, when S exceeds 0.020%, the crack resistance of the weld metal deteriorates. Therefore, S is made 0.006 to 0.020%.

[P: 0.02% or less]
P is an impurity, and an increase in P causes cracks in the weld metal. Preferably it is 0.015% or less.
Furthermore, as a result of examining the optimum pulse MAG condition range in which the arc is stable under the high-speed welding conditions of 80 cm / min or more, the amount of spatter generation is small, and the bead shape is good, the pulse peak which is one pulse-1 drop region In the region of the current Ip and the pulse peak time Tp, the optimum pulse MAG condition range in which a short-circuit is difficult to occur, the arc is stable, the amount of spatter generation is small, and a good bead shape is obtained was found.

[Pulse peak current (Ip): 440 to 600 A]
When the pulse peak current (Ip) is less than 440 A, the generation and separation of droplets due to the electromagnetic pinch effect are not smoothly performed, resulting in uneven convex beads. Also, the arc is unstable and the amount of spatter generated increases. On the other hand, when the pulse peak current (Ip) exceeds 600 A, the amount of spatter generated increases due to the arc force. Therefore, the pulse peak current (Ip) is set to 440 to 600A.

[Pulse base current (Ib): 30-80A]
The pulse base current (Ib) requires a current value that can hold the arc in the base period. If the pulse base current (Ib) is less than 30 A, the arc becomes unstable, the amount of spatter generated is large, and the bead shape deteriorates. On the other hand, when the pulse base current (Ib) exceeds 80 A, the droplets are not released quickly, the arc is unstable, and the amount of spatter generated increases. Therefore, the pulse base current (Ib) is 30 to 80A.

[415 ≦ Ip (A) × Tp (msec) ≦ 780]
Even when the arc voltage is high in the region where the peak time is short, by limiting the value obtained by the product (Ip × Tp) of the pulse current (Ip) and the pulse peak time (Tp) represented by the following formula (1), A short circuit of the droplets occurs moderately at the peak and at the base, and a good bead shape is obtained. If the product (Ip × Tp) of the pulse peak current (Ip) and the pulse peak time (Tp) is less than 415, the energy for forming the droplet is insufficient during the peak current period, and sufficient droplet formation is not possible. It becomes a convex bead. On the other hand, if the product of the pulse peak current (Ip) and the pulse peak time (Tp) exceeds 780, the excessively grown droplets are likely to be short-circuited, and the molten ground is blown away by the arc force at the time of re-ignition. Is unstable and the amount of spatter is increased. Therefore, Ip × Tp is set to a range represented by the following formula (1).
415 ≦ Ip (A) × Tp (msec) ≦ 780 (1)

Hereinafter, the effects of the present invention will be described more specifically with reference to examples.
First, Table 1 shows the chemical composition of the prototype wire in which the raw steel was vacuum melted, forged, rolled, drawn, annealed and copper plated, drawn to a wire diameter of 1.2 mm and wound on a spool.

Wires W1 to W9 shown in Table 1 are examples of the present invention, and wires W10 to W18 are comparative examples.

Using the prototype wire shown in Table 1, a steel plate having a thickness of 3.2 mm shown in Table 2 is converted into an upper plate 1 shown in FIG.
A weld length of 400 mm was welded between the end of the plate and the surface of the lower plate 2 under the pulse MAG welding conditions shown in Tables 3 and 4. The target position of the wire was the corner portion of the lap joint, and the angle θ of the welding torch 2 was 60 °. In the welding test, slag generation on the bead surface, arc stability, spatter generation amount, bead shape, and presence / absence of welding defects were evaluated.

In addition, the slag generation | occurrence | production condition of the bead surface was evaluated by the slag area rate. That is, with respect to a bead having a length of 300 mm at the center excluding a portion having a length of 50 mm from the beginning of the weld bead 400 mm, an image is taken by taking a photograph of the bead surface, marking a portion in the image, and a slag area ratio Was calculated.
Slag area ratio (%) = total of slag area ÷ total image area × 100 (%) (3)

  About the slag generation | occurrence | production situation, the reference value of slag area rate was set to 10%, the slag area rate determined with 10% or less as the pass, and the thing exceeding 10% was determined with the failure. In addition, the stability of the arc, the amount of spatter, the bead shape, and the presence or absence of welding defects were evaluated visually. The results are summarized in Table 4.

Test No. in Table 4 1-No. 10 is an example of the present invention, test no. 11-No. 20 is a comparative example.

  Test No. which is an example of the present invention. 1-No. No. 10, the wire symbols W1 to W9 are within the respective component ranges defined in the present invention, and the pulse MAG welding conditions are appropriate, so the amount of slag generated on the bead surface is small, the arc is stable, and the amount of spatter generated is small. The bead shape was good, there were no weld defects, and the results were extremely satisfactory.

Test No. in the comparative example. In No. 11, since the C of the wire symbol W10 was small, the arc was unstable and the amount of spatter generated was large. Moreover, since the A value was low, the slag area ratio was high. Test No. No. 12 had a lot of C in the wire symbol W11, so the bead shape was poor and crater cracking occurred. Moreover, since there was much Si, the slag area rate was high. Test No. In No. 13, blow hole was generated because the Si of the wire symbol W12 was small. Further, since the pulse peak current (Ip) was low, the arc was unstable, the amount of spatter was large, and a convex bead was formed.

Test No. No. 14 had pits because the Mn of the wire symbol W13 was small. Also,
Since the pulse base current (Ib) was low, the arc was unstable, the amount of spatter generated was large, and the bead shape was poor. Test No. No. 15 had a high Mn of the wire symbol W14, so the slag area ratio was high and the amount of spatter generated was also large. Moreover, since there is much S, the crater crack also generate | occur | produced. Test No. In No. 16, since the Ti of the wire symbol W15 is small, the arc is unstable and blow holes are also generated. Further, since the product Ip × Tp of the pulse peak current Ip and the peak time Tp was low, a convex bead was formed.

Test No. No. 17 had a high slag area ratio because there was much Ti of the wire symbol W16. Moreover, since there was much Cu, the crater crack generate | occur | produced. Furthermore, since the pulse peak current (Ip) was high, the amount of spatter generated was large. Test No. No. 18 had a high slag area ratio because the A value of the wire symbol W17 was high. Further, since the pulse base current (Ib) is high, the arc becomes unstable and the amount of spatter generated is large.

Test No. No. 19 had an unstable arc because there was less Cu in the wire symbol W18.
Moreover, since there was little S, the slag area rate was high. Test No. No. 20 is within the component ranges defined by the wire symbol W8 in the present invention, but the product Ip × Tp of the pulse peak current Ip and the peak time Tp is high, so the arc becomes unstable and the amount of spatter generated is large.

1 Upper plate 2 Lower plate 3 Welding torch θ Torch angle


Patent Applicant Nippon Steel & Sumikin Welding Industry Co., Ltd.
Attorney Attorney Shiina and others 1

Claims (1)

In the pulse MAG welding method of a thin steel plate having a plate thickness of 1.2 to 6 mm,
% By mass relative to the total mass of the wire
C: 0.03-0.11%,
Si: 0.50-0.90%,
Mn: 1.40 to 1.90%,
Ti: 0.15-0.35%,
And A value shown by following (1) formula: 0.55-0.85,
Cu: 0.08 to 0.45%
S: 0.006 to 0.020% is contained,
P: 0.02% or less,
The remainder uses a solid wire made of Fe and inevitable impurities,
Pulse peak current (Ip): 440 to 600 A,
Pulse base current (Ib): 30-80A,
A pulse MAG welding method for a thin steel sheet, wherein the pulse peak current (Ip) and the pulse peak time (Tp) are welded by applying a pulse satisfying the following formula (2).
A = 0.33Si + 0.15Mn + Ti (1)
(However, Si, Mn, and Ti are mass% with respect to the total mass of the wire)
415 ≦ Ip (A) × Tp (msec) ≦ 780 (2)