JP2000107861A - Pulse mag welding method for corrosion-resisting steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse MAG welding method by which the weld crack of the deposited metal on a corrosion-resisting steel sheet for automotive use is prevented, moreover the generation of spatter is reduced and good appearance of a bead is obtained even at welding in all positions. SOLUTION: In the pulse MAG welding method of a corrosion-resisting steel sheet containing 0.04-0.12 wt.% P and having the thicknness of 0.8-3.6 mm, a wire consisting of C, Si, Mn and S, <=0.015 wt.% P which is controlled and the balance Fe is used. When the content of C and content of S in a wire are respectively expressed by Cw and Sw and the content of C and content of S in the base metal respectively by Cbm and Sbm, they satisfy 2×Cw+ Cbm<=0.16, 2×Sw+Sbm<=0.044. And, a gaseous mixture which is an inert gas in which oxygen or carbon dioxide of 2-30 vol.% is mixed is used. A pulse current having a peak current of 430-500A and peak period of 0.9-1.5 msec is supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas shielded arc welding method which is particularly suitable for welding corrosion-resistant steel sheets for automobiles containing 0.04 to 0.12% by weight of P and has excellent cracking resistance. The present invention relates to a preferred pulse mag welding method for a corrosion-resistant steel sheet.

[0002]

2. Description of the Related Art Steel sheets used for automobile parts include:
Conventionally, surface-treated steel sheets such as galvanized steel sheets have been used in order to enhance the corrosion resistance. Recently, however, corrosion-resistant steel sheets that suppress the growth of rust due to the chemical composition of the steel sheets themselves have been used.

[0003] Compared to conventional galvanized steel sheet, this corrosion-resistant steel sheet contains a large amount of P and Cu, and while improving corrosion resistance, is caused by zinc as in the case of welding a conventional galvanized steel sheet. Problems such as generation of pore defects can be solved.

However, it has been found that when this corrosion-resistant steel sheet is welded with a conventional welding wire, cracks tend to occur in the weld metal at the welded portion. Therefore, in order to prevent welding cracks generated during welding of the corrosion-resistant steel sheet, for example, Japanese Unexamined Patent Application Publication No.
JP-A-281439, JP-A-9-52192 or JP-A-9-122970 are disclosed.

[0005]

However, Japanese Patent Application Laid-Open No. Hei 8-281439 discloses that Si, P, S
And the value of a predetermined mathematical expression based on the Nb content is set to be equal to or less than a predetermined value. However, since the content of P greatly changes due to the dilution of the base material, in order to satisfy the restrictions of the mathematical expression with a margin, It is necessary to use welding conditions that do not allow the base metal to melt.In the case of welding automotive parts that have various conditions such as various groove shapes, gaps, and welding positions in thin press-formed products, welding is required. It is easy to cause welding defects such as poor penetration.

Japanese Patent Application Laid-Open No. 9-52192 specifies the range of alloy components such as C, Si, Mn, O, P and S in the composition of a welding wire.
Or YGW ・ 15, YCW ・ 1 used for MAG welding
In particular, the content of Si is suppressed to be lower than that of 6 etc.
Deoxidation failure occurs when using a shielding gas containing a large amount of oxidizing gas such as oxygen or carbon dioxide, and in the case of vertical bead welding, etc., a bead appearance such as dripping of molten metal or insufficient throat thickness is caused. There is.

Further, in Japanese Unexamined Patent Publication No. 9-122970, the maximum content of Si in the welding wire is 1.0% by weight, but for this purpose, Mo must be added. However, the addition of Mo to the wire leads to an increase in manufacturing cost due to poor drawability of the welding wire, and the strength of the weld metal becomes too high due to the hardness of the weld metal, and the strength balance with the base metal is reduced. It is not preferable because it collapses.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in welding a corrosion-resistant steel sheet for an automobile, welding cracks of a weld metal generated at a welded portion are prevented, the amount of spatter generated is small, and all postures are obtained. It is an object of the present invention to provide a pulse mag welding method for a corrosion-resistant steel sheet which can obtain a good bead appearance even when welding.

[0009]

According to the present invention, there is provided a method for pulse mag welding of a corrosion-resistant steel sheet according to the present invention.
In a pulse mag welding method for a corrosion-resistant steel sheet having a thickness of 0.8 to 3.6 mm and containing P, the chemical composition is C: 0.
02 to 0.06% by weight, Si: 0.55 to 1.0% by weight, Mn: 0.8 to 1.8% by weight, and S: 0.00
3 to 0.012% by weight, and the C content and the S content in the wire are Cw and Sw, respectively.
When the content and the S content are Cbm and Sbm, respectively, 2 × Cw + Cbm ≦ 0.16 2 × Sw + Sbm ≦ 0.044 is satisfied, and a solid welding wire consisting of iron and unavoidable impurities is used as a balance, As a shielding gas, a mixed gas obtained by mixing at least one kind of oxidizing gas of oxygen and carbon dioxide in an inert gas at 2 to 30% by volume is used.

[0010] In the pulse mag welding method for a corrosion-resistant steel sheet, the solid wire for welding may have a P content of 0.015% by weight or less, and a peak current: 430 to 500 A, and a peak period:
A pulse current of 0.9 to 1.5 msec can be supplied.

The present inventors first investigated cracks generated along columnar crystals in the weld metal structure of a corrosion-resistant steel sheet welded using a conventional commercial welding wire. As a result, it was found that impurities such as S mainly exist in a concentrated state near the position where the cracks occurred.
tron Probe Micro Analyzer). For this reason, as a cause of cracking, impurities or compounds such as S having a lower melting point than steel are concentrated in the liquid phase in the solidification process of the molten pool and are left behind in the final solidified portion, and accompanying the solidification of the weld metal. An impurity thickening castle with low strength due to shrinkage stress opens,
It was speculated that the weld metal was cracked.

The inventors of the present invention devised a crack test method described below, and investigated the effect of the composition of the welding wire on the crack of the welded portion of the corrosion-resistant steel sheet.

It has also been found that not only weld cracking, but also the appearance of the bead can be improved, and the welding wire composition and the working conditions that minimize spatter generation can be satisfied simultaneously.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure of the present invention will be described in more detail. In the present invention, the reason for defining the composition of each component of the welding wire, the shielding gas composition, and the welding conditions will be described.

The reasons for defining the composition of the welding wire are as follows. (1) C: 0.02 to 0.06% by Weight C is an essential element for securing the strength of the weld metal, but is conventionally known as an element for increasing the hot cracking sensitivity. Further, it is an element that greatly affects the solidification temperature range of the molten metal, and as the content increases, the solidification temperature range also increases. As described above, impurities and compounds such as S are concentrated in the liquid phase during the solidification process of the molten pool and are left behind in the final solidified portion as a possible cause of the cracks generated in the welded portion of the corrosion-resistant steel plate. Therefore, when the solidification temperature range of the molten metal is large, impurities are more likely to be concentrated in the liquid phase, and therefore, the C content that affects the solidification temperature range is important.

If the C content exceeds 0.06% by weight, cracking becomes remarkable in a crack resistance evaluation test of a corrosion-resistant steel sheet weld described below, and the C content is less than 0.02% by weight. In this case, the strength of the weld is insufficient.

(2) Si: 0.55 to 1.0% by Weight Si has a deoxidizing effect in a molten metal and improves the appearance of a weld bead. On the other hand, Si is a factor that causes the bead to sag in the vertical welding posture. 0.55 Si content
If the content is less than the weight percentage, the deoxidizing action is small, and the appearance of the weld bead is deteriorated. On the other hand, when the Si content exceeds 1.0% by weight,
Since the productivity in the wire drawing of the welding wire is deteriorated, a large amount of slag is generated, and the bead sags, the S
The upper limit of the i content is 1.0% by weight.

(3) Mn: 0.8 to 1.8% by weight Mn is added to deoxidize a molten metal, secure the strength of a welded part, and improve the appearance of a weld bead. Mn is 0.8
If the content is less than the weight percentage, the bead appearance deteriorates due to insufficient deoxidation. When Mn exceeds 1.8% by weight, drawing of the welding wire becomes difficult. Therefore, when Mn is contained, its content is set to 0.8 to 1.8% by weight.

(4) S: 0.003 to 0.012 weight
The amount% As described above, S is therefore causes hot cracking, but its content is preferably lower, the S content is less than 0.003 wt%, fluidity of the molten metal is deteriorated, the welding The affinity between the bead and the base material deteriorates. On the other hand, when the S content exceeds 0.012% by weight, the occurrence of hot cracks becomes remarkable.

(5) 2 × Cw + Cbm ≦ 0.16, and
2 × Sw + Sbm ≦ 0.044 It is as described above that C and S in the welding wire have an effect on hot cracking resistance, and the content thereof is regulated as described above. C and S are also diluted, so that the P content of the base material is 0.04 to 0.12% by weight.
In the welding of the corrosion-resistant steel sheet, it is necessary to limit the content including the C content and the S content of the base material.

Regarding the influence of C, when the value of 2 × Cw + Cbm exceeds 0.16% by weight, even if the C content of the welding wire satisfies the range described in the above (1), the rate of occurrence of cracks Becomes higher, the upper limit of 2 × Cw + Cbm is set to 0.1.
6% by weight. Also, regarding the influence of S, 2 × Sw
If the value of + Sbm exceeds 0.044% by weight, the rate of occurrence of cracks increases even if the S content of the welding wire satisfies the range described in the above (3), so the upper limit of 2 × Sw + Sbm is set. 0.044% by weight.

Next, the reasons for limiting the composition of the shielding gas are as follows. Mixing at least one oxidizing gas of oxygen or carbon dioxide with argon as an inert gas is essential for stabilizing the welding work.

(6) Oxidizing gas: 2 to 30% by volume If the oxidizing gas is less than 2% by volume in the mixed gas, droplets during welding are large and unstable, and the oxidizing gas is 30% by volume. If it exceeds, the amount of spatter generated will increase. For this reason, the oxidizing gas is set to 2 to 30% by volume.

Thus, the composition of the solid wire for welding can further restrict P to a predetermined value or less in addition to the above-mentioned component composition.

(7) P: 0.015% by weight or less P is used for concentrating impurity elements such as S in the final solidified portion,
Since the element itself is an impurity element, it is concentrated and causes high-temperature cracking. Therefore, the content is preferably as small as possible. P is 0.01
If it exceeds 5% by weight, the crack resistance deteriorates. For this reason,
The content of P is regulated to 0.015% by weight or less.

The reasons for limiting the output waveform of the welding power source in addition to the reasons for limiting the welding wire composition and the shielding gas composition are as follows. In pulse mag welding, pulse parameters, that is, a pulse peak current and a pulse peak time, need to be set according to physical properties of a droplet determined by a welding wire composition and a shielding gas composition in order to obtain a stable droplet transfer. A desirable droplet transfer form in pulsed mag welding is to form a droplet at the wire tip during a pulse period and to make the droplet move freely during a base period. Indispensable for. Unless a pulse parameter corresponding to the physical properties of the droplet is output, the droplet is not transferred unless a plurality of pulses are supplied, which causes spatter.

(8) Pulse peak current: 430 to 50
If the 0 A pulse peak current is less than 430 A, the time required for the droplet to separate from the wire tip becomes longer, and the droplet formed at the wire tip also becomes large. It causes spatter. If the pulse peak current exceeds 500 A, the energy of the pulse current is high, and the droplet formed at the tip of the wire is blown off to generate spatter. Therefore, the pulse peak current is 43
It is preferably 0 to 500A.

(9) Pulse peak period: 0.9 to 1.
If the 5 msec pulse peak period is less than 0.9 msec, a droplet of a sufficient size cannot be formed at the tip of the wire by one pulse. It causes spatter. If the pulse peak feedback exceeds 1.5 msec, the droplet may become large and short-circuit with the molten pool, or may be blown off from the wire tip by pulse energy.
For this reason, the pulse peak period is 0.9 to 1.5 msec.
It is preferably c.

[0029]

EXAMPLES Next, in order to demonstrate the effects of the present invention, examples of the present invention and comparative examples that fall outside the scope of the present invention will be described.
The crack resistance of the weld was evaluated. This evaluation method is newly developed by the present inventors. Conventionally, as a method for evaluating the crack resistance of a welded portion, particularly a hot crack to be solved in the present application, a C-type jig restrained butt welding crack test method (JIS Z3155) and a T-type crack test method (JIS
Z3153), and a special test method such as a balest train test. However, any of these methods is an evaluation method that targets a thick plate or requires a special device, and is used for welding automobiles and vehicles. 0.8mm to 3.6mm thick
It is not suitable for a weld crack evaluation test of a steel sheet of a certain degree. Therefore,
In the following evaluation tests, evaluation was made by an original test method.

That is, for a corrosion-resistant steel plate having a thickness of 2.6 mm,
After tack welding with a gap of 6 mm, the jig is fixed to a jig, and the crack occurrence rate is calculated from the length of the cracks generated in the nugget observed after arc spot welding for about 1.2 seconds, whereby the resistance of the welded portion is calculated. A method for evaluating the crackability was devised.

Then, solid wires of various compositions were trial-produced, and the influence of each element on the crack resistance was investigated, and conditions for solving the problem of weld cracking of the corrosion-resistant steel sheet were determined. In the following Examples and Comparative Examples, the crack occurrence rate is a numerical value obtained by the test method of FIG. FIG. 1 (a)
As shown in FIG. 2, two corrosion-resistant steel plates 1 and 2 are butt-welded, and the distance between the plates 1 and 2 is L in the nugget 3 of the welded portion. If the length of 5 is a and b respectively, the cracking rate is 10
It was calculated as 0 × (a + b) / L.

The appearance of the weld bead and the evaluation of spatter were evaluated by performing a welding test using a flare joint as shown in FIG. Table 1 below shows various welding conditions such as a crack resistance evaluation test and a bead appearance test. Table 2 below shows the wire compositions and composition parameters of Examples and Comparative Examples.
Tables 5 to 7 show the shielding gas composition and pulse parameters, and the crack ratio, spatter amount, and bead appearance of the obtained welds. The evaluation criteria for the amount of spatter fused to both sides of the weld bead (weld length 100 mm) of the flare joint are as follows. Minimum: 0 to 2 Small: 3 to 5 Medium: 6 to 10 Many: 10 or more

In Tables 5 to 7, the pulse parameters Ip indicate the peak current, and Tp indicates the peak period. Further, A, B, C, and D in parentheses in the composition parameter column
Represents a combined base material.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

[Table 7]

No. 1 to 4 show the effect of the C content in the welding wire.
Therefore, it is possible to obtain a beautiful weld bead with less spatter and less clean bead.

No. Nos. 5 to 7 show the effect of the Si content in the welding wire. Although only 5 had cracks, the ratio was extremely small.

No. 8 to 10 show the effect of the S content in the welding wire, and the cracking rate is extremely small in all the welding wires.

No. Nos. 11 to 15 show the effects of the C content and the S content of the base material. 11 and 12 used a base material (B, see Table 1) having a higher C content than a commercially available corrosion-resistant steel sheet. If a welding wire is selected so as to satisfy 2 × Sw + Sbm ≦ 0.044 and 2 × Cw + Cbm ≦ 0.16, the rate of occurrence of cracks is small even when the C content of the base material is high. No. 13 and 14 used a base material (C, see Table 1) having a higher S content than a commercially available corrosion-resistant steel plate. As described above, if the welding wire is selected so as to satisfy 2 × Cw + Cbm ≦ 0.16 and 2 × Sw + Sbm ≦ 0.044, the rate of occurrence of cracks is small. In addition, No. No. 15 used a base material (D, see Table 1) having a higher C content and S content than a commercially available corrosion-resistant steel sheet. 2 × Cw + Cbm ≦ 0.16 and 2 × Sw + Sbm ≦
If the welding wire is selected so as to satisfy 0.044, the rate of occurrence of cracks is small.

No. 16 to 18 are Mn in the welding wire
In view of the effect of the content, the crack rate is 0 for all welding wires, and it is possible to obtain a clean welding bead with less spatter.

No. Nos. 19 and 20 show the effect of the P content in the welding wire. All of the welding wires have a crack rate of 0, and it is possible to obtain a clean welding bead with little spatter.

No. 21 to 30 show the effects of the shielding gas composition and the pulse parameters on the selection of one welding wire from the examples.
o. 24, no. In the case of No. 25, a slight increase in slag was observed, but the crack rate was 0 for all the welding wires, and a clean welding bead was obtained.

No. Nos. 31 to 33 show the effect of the C content in the welding wire as a comparative example. In No. 31, since the content of both C and S was small, no cracking was observed, but the strength of the weld metal was reduced. No. 32 and N
o. No. 33 has a high cracking rate.

No. 34-36 are Si in the welding wire
The effect of the content was observed. 34 and No. 34. 35
Is not glossy on the bead surface due to insufficient deoxidation, and wrinkles are observed. Conversely, No. In No. 36, since the amount of Si is large, a large amount of slag is generated on the surface of the weld bead.

No. 37 and no. No. 38 shows the effect of the S content in the welding wire. No. 37 is a weld bead in which cracks do not occur but the end of the bead and the base material are not easily compatible. No. No. 38 has a very large crack.

No. 39 to 43 show the influence of the C content and the S content of the base material. No. 39 uses a base material having a higher C content than a commercially available corrosion-resistant steel sheet.
Even if the C content of the welding wire is within individual limits,
The relational expression 2 × Cw + Cbm with the C content of the base material is 0.16.
If the ratio is more than 1, the crack generation rate increases. No. Reference numerals 40 and 41 use a base material having a higher S content than a commercially available corrosion-resistant steel sheet. If the relational expression 2 × Sw + Sbm exceeds 0.044, the rate of occurrence of cracks is high. In addition, No. Reference numerals 42 and 43 each use a base material having a higher C content and a higher S content than a commercially available corrosion-resistant steel sheet.
If any of them exceeds the limit, the incidence of cracking is very high.

No. 44 and no. No. 45 shows the effect of the Mn content in the welding wire. In No. 44, wrinkles occurred on the weld bead surface due to insufficient deoxidation, while N
o. No. 45 was inferior in workability, for example, in the process of making the welding wire itself, for example, the drawing speed had to be reduced.

No. Reference numeral 46 indicates a case where a large amount of P was contained in the welding wire, but the cracking rate was high.

Nos. 47 and 47. No. 48 shows the effect of the shielding gas composition. In No. 47, the ratio of argon was too high and the formation of droplets at the tip of the wire became unstable, resulting in large spatters adhering around the weld bead. No.
Reference numeral 48 indicates a case where the amount of CO ₂ was large, and the transfer of droplets by pulse welding was not stable, and large spatters adhered to the periphery of the weld bead.

No. Nos. 49 to 52 show the effects of the pulse parameters. 49 indicates a case where the peak current is low. When observing the droplet transfer phenomenon, a droplet large enough to transfer by one pulse is not formed, and one droplet is transferred by two or three pulses. . For this reason, the regularity of the transfer is broken, and a short circuit occurs between the droplet and the molten pool, and spatter occurs. No. Reference numeral 50 denotes a case where the peak current is too high, and the droplet formed at the tip of the wire is blown off with high peak current energy and sputtered. No. No. 51 is when the peak time is too short. As in the case of 49, the droplets shift to a plurality of pulses and a spatter is generated. Also, N
o. Reference numeral 52 denotes a case in which the peak period is too long, which is separated from the tip of the droplet wire during the peak period, but is blown off due to the peak current and becomes sputter.

[0056]

As described above, according to the welding method of the present invention, it is possible to prevent cracks at the contact portions in welding a corrosion-resistant steel sheet containing 0.04 to 0.12% by weight of P and to reduce spatter. Welding is possible and the quality of the weld is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a crack evaluation test method.

FIG. 2 is a diagram showing a welding test method for a flare joint.

[Explanation of symbols]

 1: Corrosion resistant steel plate 3: Nugget 4, 5: Crack

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) C22C 38/04 C22C 38/04 (72) Inventor Masaharu Sato 100-1 Urakawachi Miyamae, Fujisawa-shi, Kanagawa Kobe Co., Ltd. F term in the Fujisawa Works of Steel Works (reference) 4E001 AA03 BB06 BB08 CA07 DC01 DD01 DD04 DD05 DE04 EA01 EA05 EA10

Claims (3)

[Claims] 1. A pulse mag welding method for a corrosion-resistant steel sheet having a thickness of 0.8 to 3.6 mm containing 0.04 to 0.12% by weight of P, wherein the chemical composition is C: 0.02 to 0.06. % By weight, Si: 0.55 to 1.0% by weight, M
n: 0.8 to 1.8% by weight and S: 0.003 to 0.012% by weight, and the C content and S content in the wire are Cw and Sw, respectively. When the content and the S content are Cbm and Sbm, respectively, 2 × Cw + Cbm ≦ 0.16 2 × Sw + Sbm ≦ 0.044 is satisfied, and a solid welding wire consisting of iron and unavoidable impurities is used as a balance, A pulse mag welding method for a corrosion-resistant steel sheet, comprising using, as a shielding gas, a mixed gas in which at least one oxidizing gas of oxygen and carbon dioxide is mixed in an amount of 2 to 30% by volume with an inert gas. 2. The welding solid wire according to claim 1, wherein P: 0.
2. The method according to claim 1, wherein the content is restricted to 015% by weight or less.
2. A pulse mag welding method for a corrosion-resistant steel sheet according to claim 1. 3. A pulse current having a peak current of 430 to 500 A and a peak period of 0.9 to 1.5 msec is supplied as a welding current.
2. A pulse mag welding method for a corrosion-resistant steel sheet according to claim 1.