JP3120929B2 - Welding method for galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding galvanized steel sheet, which is suitable for, for example, lap fillet welding of galvanized steel sheet.

[0002]

2. Description of the Related Art Conventionally, in lap fillet welding of a galvanized steel sheet, gas generated from a plated portion by heat at the time of welding blows out from a lap portion into a molten pool, so that the gas is contained in a weld metal after solidification. There is a problem that defects such as pits (openings) in which pits are formed on the surface of the weld metal due to the residual blowholes and the gas easily occur. For this reason, conventionally, in lap fillet welding of galvanized steel sheets, a welding wire whose composition has been adjusted so that the viscosity of the molten pool becomes high and gas growth is suppressed, and droplet transfer is stable. By setting welding conditions such that the number of blow holes and pits is reduced.

[0003]

However, in the conventional method for lap fillet welding of galvanized steel sheet, the effect of suppressing blowholes and pits is not sufficient. Therefore, there is a demand for a galvanized steel sheet welding method that can further reduce defects such as blowholes and pits.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for welding a galvanized steel sheet that can reduce defects such as blowholes and pits.

[0005]

SUMMARY OF THE INVENTION A method for welding a galvanized steel sheet according to the present invention is a method for welding a galvanized steel sheet by welding a galvanized steel sheet by energizing a welding wire through an energizing electrode while shielding a welding portion with a shielding gas. In the welding method, the amount of deposited metal per cm of the weld bead is x (g / c
m) and the amount of heat applied per cm of the weld bead is y (J /
cm), the relationship between the amount x of deposited metal and the amount of heat y satisfies the following expression. 3000x + 150 ≦ y ≦ 4680x-200

[0006]

The present inventors conducted various experimental studies to suppress defects such as blowholes and pits in welding galvanized steel sheets. As a result, in order to suppress defects such as blowholes and pits, the amount of heat applied to the base material during welding is reduced to reduce the area of the plated part heated to the gas generation temperature and reduce the amount of gas generated To do
It has been found that it is effective to reduce the amount of heat applied to the molten pool and solidify the molten pool before the pores generated in the molten pool grow. The present invention has been made based on such experimental results.

In the present invention, the amount of deposited metal per cm of the weld bead is x (g / cm), and the amount of heat applied per cm of the weld bead (hereinafter also referred to as heat input) is y (J / c).
m), the amount x of the deposited metal and the heat input y are set so that x and y satisfy the following equation (1).

[0008]

## EQU1 ## 3000x + 150 ≦ y ≦ 4680x−200

However, the heat input y is equal to the total amount of energy applied by welding, and the current is I (A) and the voltage is E
(V), assuming that the welding speed is v (cm / sec), y = I
E / v.

[0010] If the heat input y is less than 3000x + 150, the bead shapes become irregular, and it is difficult to stably obtain a bead having a good shape. On the other hand, when the heat input y is 46
If it exceeds 80x-200, the effect of preventing blow holes and pits is reduced. Therefore, it is necessary to set the amount x of the deposited metal and the heat input y so as to satisfy Equation (1).

For example, when x is 0.5 (g / cm), the lower limit of the heat input y is 3000 × 0.5 + 150 = 1.
650 (J / cm) = 1.65 (kJ / cm),
The upper limit of the heat input y is 4680 × 0.5−200 = 214.
0 (J / cm) = 2.14 (kJ / cm). Therefore, the current and the voltage may be set so that the heat input y is in the range of 1.65 to 2.14 (kJ / cm). Conventionally, when the amount of deposited metal is around 0.5 (g / cm), the heat input for welding has been 2.3 to 2.7 (kJ / cm). According to the present invention, welding heat input is lower than before.

By reducing the heat input in this way,
The area of the plated part heated to the gas generation temperature during welding is reduced and the amount of gas generated can be reduced, and the amount of heat applied to the molten pool is reduced, so that the pores generated in the molten pool melt before growing. The pond solidifies. This allows
Defects such as blow holes and pits can be suppressed.

In order to perform good welding while reducing the heat input y, there are the following methods.

(1) The length of the current-carrying portion of the welding wire is set to 20
To 50 mm. That is, between the electrode (current-carrying tip) that supplies current to the welding wire and the tip of the arc (ie,
At the wire protruding portion), a current flows through the welding wire, and Joule heat W is generated. This Joule heat W is represented by the following equation, where I is the current, and R is the resistance value of the wire protrusion.
I ² × R. In other words, the longer the wire protrusion length, the greater the resistance value R, and the wire protrusion is heated by Joule heat, and the welding arc current required for melting the wire can be reduced. In this case, when the protrusion length of the welding wire is less than 20 mm, the above-mentioned effects cannot be sufficiently obtained. Also, the protrusion length of the welding wire is 5
If it exceeds 0 mm, welding becomes unstable and inconveniences such as poor shielding occur. Therefore, the length of the current-carrying portion of the welding wire is preferably 20 to 50 mm.

(2) As the shielding gas, a gas containing 50% by volume or more of argon and / or helium and the balance being carbon dioxide is used. That is, by increasing the ratio of argon and / or helium in the shielding gas, the diameter of the droplet immediately before transfer to the base material is reduced. Therefore, the welding voltage can be reduced and the arc length can be shortened. If the content of argon and / or helium in the shielding gas is less than 50% by volume, such effects cannot be sufficiently obtained. Therefore, the content of argon and / or helium in the shielding gas is preferably 50% by volume or more.

(3) Si content is 0.5 to 4% by weight,
Mn content of 0.01 to 2% by weight, C content of 0.0
A welding wire having a content of 8% by weight or less and a balance of Fe and inevitable impurities is used. That is, for welding a galvanized steel sheet, a welding wire containing Fe as a main component is usually used. By adding Si to the welding wire, the electric resistance of the welding wire increases. For this reason, Joule heat generated in the current-carrying portion of the welding wire increases, and the wire protruding portion is heated in advance, so that the welding arc current required for melting the wire can be reduced. Further, by adding Mn and C to the welding wire, the welding transfer is stabilized and the mechanical performance of the welded portion is improved.

In this case, if the Si content is less than 0.5% by weight, the above effects cannot be sufficiently obtained.
On the other hand, if the Si content exceeds 4% by weight, the performance of the deposited metal deteriorates. In particular, the reduction of the Charpy impact absorption energy becomes remarkable. If the Mn content is less than 0.01% by weight, pore defects due to insufficient deoxidation are likely to occur. On the other hand, if the Mn content exceeds 2% by weight, the strength of the welded portion becomes too high, so that the Charpy impact absorption energy is reduced and the elongation and the draw deformation are reduced. Further, when the C content exceeds 0.08% by weight, welding cracks are likely to occur. For this reason, the welding wire has a Si content of 0.1.
5-4% by weight, Mn content 0.01-2% by weight,
It is preferable that the C content is 0.08% by weight or less, and the balance consists of Fe and inevitable impurities.

(4) The ratio (Iavg / Ieff) between the average value Iavg of the welding current and the effective value Ieff of the welding current is reduced.
The average value Iavg and the effective value Ieff of the welding current are represented by the following equations (2) and (3), respectively.

[0019]

## EQU2 ## Iavg = [∫I (t) dt] / t

[0020]

## EQU3 ## Ieff = {[{I ² (t) dt] / t} ^1/2

The effective value Ieff of the welding current is proportional to the melting amount of the welding wire, and the average value Iavg is proportional to the welding heat input. Therefore, if welding is performed using a welding current waveform that reduces the ratio (Iavg / Ieff) of both, it is possible to reduce the heat input while maintaining the amount of deposited metal constant. In the case of short-circuit transfer welding, for example, as shown in FIG. 12, the current is controlled in synchronization with the occurrence of an arc and the short-circuit transfer of a droplet. In this case, the arc current at the time of arc generation is represented by Iab in the figure.
And the average value of the arc current Iav
The ratio (Iavg / Ieff) between g and the effective value Ieff is set to 0.93 or less. In pulse welding for supplying a pulsed arc current to the welding wire at a predetermined cycle, the ratio (Iavg / Ieff) between the average value Iavg of the arc current and the effective value Ieff is set to 0.8 or less. Thus, the average value of the arc current Iav
By setting the ratio of g to the effective value Ieff (Iavg / Ieff), it is possible to reduce the heat input while keeping the amount of the deposited metal constant.

By the methods shown in (1) to (4) and the combinations thereof, the heat input y can be made to fall within the range shown by the above-mentioned formula 1, so that blow holes and pits at the time of welding a galvanized steel sheet can be obtained. Defects can be suppressed.

[0023]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings. In the method for welding a galvanized steel sheet according to the embodiment of the present invention, the welding heat input is set according to the amount of the deposited metal. That is, as shown in FIG. 1, when the amount of deposited metal is x (g / cm), the welding heat input y (J / cm) is
It is set to be 3000x + 150 or more and 4680x-200 or less. For example, assume that the diameter of the welding wire is 1.2 mm, the density of the welding wire is 7.9 g / cm ³ , the welding speed is 120 cm / min, and the wire feed rate is 7 m / min. Then, the amount x of the deposited metal becomes
As shown in the figure, it is 0.52 (g / cm).

[0024]

X = π × (0.12 (cm) / 2) ² × 700 (cm / min) × 7.9 (g / cm ³ ) / 120 (cm / min) = 0.52 (g / cm)

Therefore, the lower limit of the heat input y is 3000
× 0.52 + 150 (J / cm) = 1.71 (kJ / c)
m) and the upper limit is 4680 × 0.52-200 (J /
cm) = 2.23 (kJ / cm) and may be set between the lower limit and the upper limit. Conventionally, when a galvanized steel sheet is welded under the above conditions, the heat input is about 2.3 to 2.7.
(KJ / cm), the heat input is set lower in this embodiment than in the prior art. FIG. 2 shows the welding heat input on the horizontal axis and the number of blow holes on the vertical axis,
It is a graph which shows the relationship between both. As shown in FIG. 2, by setting the welding heat input low, it is possible to obtain a welded portion having few defects such as blowholes and pits.

By the way, the heat input y is equal to the total amount of energy applied by welding. If the current is I (A), the voltage is E (V), and the welding speed is v (cm / min), y
= IE / (v / 60). That is, it is understood that at least one or both of the welding current I and the welding voltage V should be controlled in order to control the heat input y.

FIG. 3 is a graph showing the relationship between the protrusion length on the horizontal axis and the welding current on the vertical axis. However, for other welding conditions, the welding speed was 120 cm.
/ Min, welding wire is YGW17 (wire diameter: 1.2m
m, density: about 7.9 g / cm ³ ), wire feed rate is 7 m
/ Min, fillet facing downward with welding posture, shielding gas Ar-20% CO ₂ , shielding gas supply 20 liter / m
in, the voltage is 20V.

At the projecting portion of the welding wire, Joule heat W is generated because electricity passes through the welding wire. Assuming that the current is I and the resistance value of the protruding portion of the welding wire is R, the Joule heat W is W = I ² R. That is, by increasing the protruding length of the welding wire, Joule heat increases, and the protruding portion of the welding wire is heated in advance, so that the welding arc current required for melting the welding wire can be reduced. In other words, by increasing the protrusion length of the welding wire, heat input can be reduced while maintaining a favorable welding state.

FIG. 4 shows the case where welding heat input is changed by changing the protrusion length and welding current by taking the welding heat input on the horizontal axis and the number of blowholes having a width of 1 mm or more on the vertical axis. FIG. 4 is a graph showing the relationship between welding heat input and the number of blow holes. As is clear from FIG. 4, as the welding heat input increases, the number of blow holes also increases. When the welding heat input is 2.23 kJ / cm or less, the number of blowholes generated is as small as 40 or less.

FIG. 5 is a graph showing the relationship between the ratio (volume%) of CO ₂ in the shielding gas on the horizontal axis and the welding voltage on the vertical axis. However, other welding conditions are as follows: welding speed is 120 cm / min, welding wire is YGW
17 (wire diameter: 1.2 mm, density: about 7.9 g / cm
³ ) The wire feed rate is 7 m / min, the welding position is the downward fillet, and the protrusion length is 15 mm.

As is apparent from FIG. 5, by increasing the ratio of argon and / or helium in the shielding gas, the diameter of the droplet immediately before transfer to the base material is reduced. Therefore, welding in which the welding voltage is reduced and the arc length is shortened becomes possible. That is, by reducing the CO ₂ ratio in the shielding gas, the welding voltage can be reduced while maintaining a favorable welding state.

FIG. 6 is a graph showing the welding heat input on the horizontal axis and the number of blow holes having a width of 1 mm or more on the vertical axis.
It is a graph which shows the relationship between the welding heat input and the number of blow holes when changing the welding heat input by changing the argon ratio and the welding voltage in the carbon dioxide shielding gas. As is apparent from FIG. 6, the welding heat input was 2.2 k.
In the range of J / cm or more, the number of blowholes increases with an increase in welding heat input. Heat input of 2.23 kJ /
cm or less, the number of blow holes generated is about 10 or less, which is extremely small.

FIG. 7 is a graph showing the relationship between the Si content on the horizontal axis and the welding current on the vertical axis.
However, for other welding conditions, the welding speed is 120 cm / mi.
n, welding wire feed rate is 7m / min, welding position is downward fillet, protrusion length is 15mm, shielding gas is Ar
-20% CO ₂ , shield gas supply 20 l / min.

[0034] Increasing the amount of silicon added to the welding wire increases the electrical resistance of the wire. For this reason,
As the Joule heat increases and the wire is pre-heated, the welding arc current required to melt the wire can be reduced.

FIG. 8 shows the welding heat input by changing the Si content and welding current of the welding wire by taking the welding heat input on the horizontal axis and the number of blowholes having a width of 1 mm or more on the vertical axis. It is a graph which shows the relationship between welding heat input at the time of changing, and the number of blow holes. As is clear from FIG. 8, the number of blow holes increases by increasing the welding heat input. When the welding heat input is 2.23 (kJ / cm) or less, the number of blow holes generated is as small as about 40 or less.

FIG. 9 shows the welding current on the vertical axis, the conventional standard method (std.) And the effective value Ieff of the arc current.
FIG. 7 is a graph showing two methods A and B in which the average value Iavg of the arc current is reduced by making the method substantially the same as the conventional standard method. In the conventional standard method, the effective value Ieff of the welding current and the average value Iavg are substantially equal. On the other hand, in the methods A and B, the ratio (Iavg / Ieff) between the average value Iavg and the effective value Ieff of the welding current is set to about 0.9 and 0.75 by changing the welding current waveform. did. However, other welding conditions are as follows: welding speed is 120 cm / min, welding wire is YGW17 (wire diameter: 1.2 mm, density: about 7.9 g / cm ³ ), wire feeding amount is 7 m / min, and welding posture is Downward fillet, 15mm overhang length, Ar-20 shielding gas
% CO ₂ , shielding gas supply amount 20 liter / min, welding voltage 20V. FIGS. 11A to 11C respectively show std. FIG. 7 is a graph showing current waveforms in the methods indicated by A, B and B. In the conventional method (std.), When a short circuit occurs, a large current is supplied to promote the regeneration of the arc, and control is performed so that the welding voltage becomes constant when the arc occurs. Further, in the method indicated by A in FIG. 9, the current is forcibly reduced after a predetermined time has passed after the occurrence of the arc, and is maintained at a constant current value. Further, in the method shown by B in FIG. 9, the welding current was changed rectangularly. As described above, by changing the waveform of the welding current, it is possible to reduce the average value while maintaining the effective value of the welding current constant. In other words, by changing the waveform of the welding current, it is possible to reduce the heat input while maintaining the amount of the deposited metal constant.

FIG. 10 shows the average value Iavg of the welding current and the effective value Ieff by changing the welding current waveform by taking the welding heat input on the horizontal axis and the number of blowholes having a width of 1 mm or more on the vertical axis. FIG. 4 is a graph showing a relationship between welding heat input and the number of blow holes when the ratio (Iavg / Ieff) of the welding is changed. Also in this case, when the welding heat input increases, the number of blow holes increases. When the welding penetration value is 2.23 kJ / cm or less, the number of blowholes is as extremely small as about 25 or less.

As is apparent from FIGS. 4, 6, 8, and 10, the blow holes are reduced by reducing the heat input. Although the tendency is slightly different depending on the means for reducing the heat input, in the above embodiment, the heat input was 2.23 kJ /
cm or less, the generation of blow holes can be suppressed. However, the heat input was 1.71 (kJ / c)
In the case of less than m), the bead shape becomes irregular in any case, and a bead having a good shape cannot be stably obtained.

[0039]

As described above, in the galvanized steel sheet welding method according to the present invention, the amount of heat applied per 1 cm of the weld bead is set within a predetermined range according to the amount of the deposited metal per cm of the weld bead. The generation of blow holes and pits can be suppressed, and a good weld bead can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a set range of a deposited metal amount and welding heat input in an example of the present invention.

FIG. 2 is a graph showing the relationship between welding heat input and blow holes.

FIG. 3 is a graph showing a relationship between a protrusion length and a welding current.

FIG. 4 is a graph showing the relationship between welding heat input and the number of blow holes when welding heat input is changed by changing the protrusion length and welding current.

FIG. 5 is a graph showing a relationship between a ratio of CO _{2 in} a shielding gas and a welding voltage.

FIG. 6 is a graph showing the relationship between the welding heat input and the number of blow holes when the welding heat input is changed by changing the ratio of argon in the shielding gas and the welding voltage.

FIG. 7 is a graph showing a relationship between a Si content in a welding wire and a welding current.

FIG. 8 is a graph showing the relationship between the welding heat input and the number of blow holes when the welding heat input is changed by changing the Si content in the welding wire and the welding current.

FIG. 9 is a graph showing an effective value Ieff and an average value Iavg of the welding current.

FIG. 10 is a graph showing the relationship between the welding heat input and the number of blow holes when the welding heat input is changed by changing the ratio between the effective value Ieff of the welding current and the average value Iavg.

FIGS. 11A to 11C respectively show std. , A
6A and 6B are graphs showing current waveforms in the methods shown by B and B.

FIG. 12 is a waveform chart showing an example of a welding current waveform in droplet transfer welding.

────────────────────────────────────────────────── ⁷ Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B23K 35/30 320 B23K 35/30 320A (56) References JP-A-4-143076 (JP, A) JP-A-6-210490 (JP, A) JP-A-5-42387 (JP, A) JP-A-4-1388893 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 9/23 B23K 9 / 095 B23K 9/16 B23K 9/173 B23K 35/30

Claims (6)

(57) [Claims] In a method for welding a galvanized steel sheet by energizing a welding wire through a current-carrying electrode while welding a welded portion with a shielding gas to weld the galvanized steel sheet, the amount of deposited metal per 1 cm of a weld bead is x (g). / Cm),
The amount of heat applied per 1 cm of weld bead is y (J / cm)
Then, the relationship between the amount x of deposited metal and the amount of heat y is expressed by the following (1).
A method for welding galvanized steel sheet, characterized by satisfying the formula. 3000x + 150 ≦ y ≦ 4680x−200 (1) 2. The method for welding galvanized steel sheet according to claim 1, wherein the protrusion length of the welding wire is 20 to 50 mm. 3. The method for welding a galvanized steel sheet according to claim 1, wherein the shielding gas contains 50% by volume or more of argon and / or helium, and the remainder consists of carbon dioxide gas. 4. The welding wire according to claim 1, wherein the Si content is 0.5.
-4% by weight, Mn content 0.01-2% by weight, C
The content is 0.08% by weight or less, and the balance consists of Fe and unavoidable impurities.
The method for welding a galvanized steel sheet according to any one of the above. 5. A method for welding galvanized steel sheet in which droplets are transferred to a short circuit, wherein a ratio (Iavg / Ieff) between an average value Iavg and an effective value Ieff of an arc current at the time of arc generation is 0.93.
The method for welding a galvanized steel sheet according to any one of claims 1 to 4, wherein: 6. A welding method for a galvanized steel sheet for supplying a pulsed arc current to the welding wire at a predetermined cycle, wherein a ratio (Iavg / Ieff) between an average value Iavg of the arc current and an effective value Ieff is 0. The method for welding a galvanized steel sheet according to any one of claims 1 to 4, wherein the value is 0.8 or less.