JP3433891B2 - Gas shielded arc welding wire for P-added sheet steel and MAG welding method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is 0.06% by weight.
In gas shielded arc welding of P-added thin steel sheet containing 0.15% of P, gas shielded arc welding that prevents weld cracks that are likely to occur during solidification of weld metal and that produces weld metal with excellent gap resistance The present invention relates to a MAG welding method for a wire and a P-added thin steel sheet.

[0002]

2. Description of the Related Art Conventionally, welded structures or automobiles, machines,
In electric parts and the like, a surface-treated steel sheet on which a surface of a cold-rolled or hot-rolled steel sheet has been subjected to a rust-preventive treatment such as coating with a zinc-based paint or galvanization is often used as a means for compensating for the rust-prone defect of steel members. Furthermore, the development of surface-treated steel sheets in which the thickness of the plating is increased for the purpose of improving the corrosion resistance and various plating compositions are devised is under way.

However, in recent years, porosity defects caused by zinc vapor are less likely to occur during welding of galvanized steel sheets,
High-P steel materials, which have better corrosion resistance than galvanized steel sheets, have been developed and are being put to practical use.

This P-added steel material means P: 0.06-0.
It is a Si-Mn-based ultra-low carbon steel containing 15% and Cu, which is superior in corrosion resistance compared to ordinary steel and is unlikely to cause porosity defects due to zinc vapor during welding like galvanized steel sheets. Instead of the conventionally used galvanized steel sheet, it is used for welding structures such as automobiles, machines and electric parts.

However, when a P-added thin plate is welded, a low melting point alloy of P in the weld metal and other weld metal components is formed, hot cracking easily occurs, and a sound weld is obtained. I couldn't do it.

On the other hand, automation has developed in the welding method,
The welding method by gas shield arc welding by a welding robot is often adopted.

Particularly, for thin steel products such as thin steel plates and electric resistance welded pipes manufactured from thin steel plates, gas shielded arc welding with Ar-CO ₂ gas is excellent in efficiency, low spattering property and burn-through resistance, Since stable quality welding can be performed, S
Various wires centering on the i-Mn system and welding methods have been proposed and put to practical use.

In the welding of such a thin plate, the welding current may be set low in order to prevent burn-through and the like, and the welding speed may be 1 m / min or more for the purpose of improving the productivity of welding. In many cases, the welding condition range with respect to the gap between the members is narrowed, and it is also required to satisfy the gap resistance and to perform stable welding.

The above problems tend to become more apparent as a factor that hinders automation, and it is strongly desired to solve these problems.

In the welding of a P-added thin steel sheet, a low-melting-point alloy component of P, which is a low-melting-point element, and other weld metal components is formed, and hot cracking may occur, so that a sound weld part may not be obtained. It was

Particularly when a thin steel plate or a steel pipe material is subjected to gas shield arc welding, the welding heat input per unit thickness is large and the deformation amount of the welded portion is large as compared with the thick plate, so that high temperature cracking is caused. Outbreaks were also increasing.

On the other hand, also in gas shield arc welding, in order to improve the productivity of welding, automation by a welding robot is often used, and the welding speed is often set to a high speed of 1 m / min or more. The range of welding conditions for the wire gap (gap) becomes narrower, making it difficult to stably form good weld metal with members with large gaps.
At the same time, it is required to satisfy the gap resistance.

Further, since welding of thin steel plates requires welding current to be set low in order to prevent burn-through and the like, the present condition is that the proper welding condition range is further tightened, and the gap resistance It is difficult to secure it.

[0014]

The present invention has been made in order to solve the above problems, and solves the problem of hot cracking that occurs during the welding of P-added thin steel sheets, and a good weld metal can be obtained. Furthermore, the present invention provides a wire for gas shielded arc welding and a welding method that secures gap resistance even in high-speed welding.

[0015]

SUMMARY OF THE INVENTION The gist of the present invention is the weight%
C: 0.04 to 0.16%, Si: 0.5 to 1.2
%, Mn; 1.0 to 2.0%, P; 0.015% or less,
S: 0.005% or less, O: 0.005 to 0.03%, containing 0.005 to 0.2% in total of one or more of La, Ce, Zr, and Ti, The balance is Fe
And a gas shield arc welding wire for P-added thin steel sheet, which is composed of unavoidable impurities, and a CO ₂ gas mixed with Ar gas as a shielding gas, and further, a mixed gas of O ₂ gas, if necessary. A MAG welding method characterized in that a gas shielded arc welding wire for P-added thin steel sheet is used.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above in the gas shielded arc welding, the inventors of the present invention also have an influence of S, which is a low melting point impurity, particularly in welding such as an added steel plate in which P is increased to improve corrosion resistance. Since the influence on the occurrence of hot cracking becomes large, it is possible to suppress the occurrence of hot cracking by lowering the S content of the wire and fixing S by La, Ce, Zr, and Ti which are sulfide-forming elements. I thought it was effective. Further, even in such high-speed welding of thin steel sheets, Si, which is a deoxidizing element, may increase or decrease the bead width in order to secure the gap resistance. From this viewpoint, the wire composition was investigated and the present invention was investigated. Came to ensure the composition of.

The reasons for limiting the components of the wire of the present invention will be described below.

C is an element that secures the strength of the weld metal, but it has a great effect on hot cracking of the weld metal during the welding of P-added thin steel sheets. If C is added in excess of 0.16%, the primary crystal during solidification becomes an austenite (γ) phase, and hot cracking is likely to occur. Further, when the content of C is suppressed to a low level, the short-circuit transferability of the molten metal during arc welding tends to decrease, the arc state tends to become unstable, and in order to secure a stable and good arc state, its addition The amount should be 0.04% or more.

Although Si is added as a deoxidizing agent, it is an element that induces high temperature cracking, and it is better that the amount is small, but if it is less than 0.5%, the gap resistance cannot be ensured, so the lower limit was made 0.5%. Further, if it exceeds 1.2%, the crack resistance deteriorates, so the content was made 0.5 to 1.2%.

Like Mn, Mn is also added as a deoxidizing agent, but in gas shielded arc welding, less than 1.0% is insufficient for deoxidizing and a healthy weld bead cannot be formed, and a weld crack inducing element. And S have the effect of forming a compound of MnS and improving the crack resistance,
The effect is obtained when the percentage is over. On the other hand, if it exceeds 2.0%, the strength of the weld metal increases and the crack resistance deteriorates, and the workability deteriorates due to an increase in the amount of slag. Furthermore, since the strength increases at the stage of processing into a wire, the wire drawability deteriorates, so the upper limit was made 2.0%.

P is an element that inhibits crack resistance, and in a steel sheet containing a large amount of P for improving corrosion resistance as in the present invention, the amount of P in the welding wire is reduced and the amount of P in the weld metal is reduced. Need to consider. Since P forms a compound such as Fe ₃ P having a low melting point and deteriorates crack resistance, it is particularly preferable that Si,
In the wire of the present invention containing a large amount of Mn, it is preferable to suppress it as much as possible, and if it is 0.015% or less, the purpose is achieved.

When S forms a compound having a low melting point such as FeS and segregates, it causes cracking in the weld metal solidification stage. Further, in a steel plate to which a large amount of P is added to improve the corrosion resistance, the cracking property of the weld metal becomes remarkable, so it is necessary to keep it particularly low, and the addition amount is 0.005% or less.

La, Ce, Zr and Ti are sulfide forming elements and form sulfides such as La ₂ S ₃ , CeS, ZrS and TiS. These sulfides are stable, have a freezing point higher than that of Fe, can remove or fix S, and are elements that reduce cracking by S. La, Ce, Zr, and Ti are 0.005% in total of one kind or two or more kinds. The above effect is obtained, but if it exceeds 0.2%, the short-circuit transfer characteristics during welding are inferior, the arc becomes unstable, and good bead formation cannot be performed.
05 to 0.2%.

O has the effect of stabilizing the arc, reducing the amount of spatter, smoothing the bead, and ensuring the bead width, and is required to be 0.005% or more. The upper limit was set to 0.03% because the arc becomes unstable and frequent spatter occurs and the amount of slag generated on the bead surface increases.

In the present invention, the structure is as described above, and by using the wire having the composition as described above, the shielding gas used for arc welding is mixed with Ar gas and CO ₂ gas for high speed welding. Even in this case, a stable arc state and low spatter can be welded, and the range of CO ₂ gas is preferably 5 to 40 Vol%. Further, by using a mixed gas of O ₂ gas, the penetration depth and the bead width can be secured. The preferred range of this O ₂ gas is 7 Vo
It is 1% or less.

As described above, even when the high P-added thin plate is gas shielded by arc welding, welding cracks, particularly high temperature cracks, are extremely small, and stable welding is possible even with respect to the gap of the welding line of the member to be welded. Since a weld metal having an excellent bead appearance is obtained, the welded portion is sufficiently satisfactory for a structure.

The effects of the present invention will be specifically described below with reference to examples.

[0028]

[Examples] First, 2.3 mm of P-added thin steel plate shown in Table 3
Using a wire having a chemical composition shown in Table 1 (diameter: 1.2 mm) having a width of t, a width of 40 mm, and a length of 330 mm, the test beads were bead-on-plate-welded by the test method shown in Table 4 as if there were excess in FIG. After that, the excess of this bead was deleted and a Varestraint weld cracking test piece was produced.

A Varestraint weld cracking test by TIG welding was performed on the upper surface of the test piece from which the excess was removed by the method of FIG. In addition, 1 in FIG. 2 is a P-added steel plate with the extra reinforcement removed,
2 is a die block, the bending radius is 62.5 mm, the strain amount is 1.84%, 3 is a test piece holding jig, 6 is a ram descending position, and the descending speed is 500 mm / sec.
Indicates a TIG test start position, and 5 indicates a TIG welding end position. The test method is the bead longitudinal bending test shown in Table 4, and the Barestrain test is performed. After the weld crack test, the total of weld crack lengths generated on the bead surface as shown in FIG. 3 is measured with a high-power microscope up to 500 times. Table 1 shows the results of the total of the crack lengths measured and evaluated. In FIG. 3, 1 is a P-added steel plate, 7 is a test bead, 8 is a TIG weld bead, 9 is a crater portion of the TIG weld, and 10 is a weld crack cracked by the Varestrain weld crack test.

As for the gap resistance, the SPCC polished steel plate shown in Table 3 is used, the downward butt joint is used as the joint shape of FIG. 4, and the gap is 0 mm to 4 mm. Is measured
The results are also shown in Table 1. Furthermore, it was confirmed that, during gas shielded arc welding with the shield gas composition shown in Table 2, weld cracking characteristics, a weldable gap with respect to a gap, stable welding and good weld beads could be obtained.

In Table 1, the wire No. 1 to 10 are wires of the present invention, C is 0.04 to 0.16%, Si is 0.5
~ 1.2%, Mn 1.0-2.0%, P 0.015
% Or less, S is 0.005% or less, and O is 0.005 to 0.
It is 03% and is in the range of 0.005 to 0.2% in total of one or more of La, Ce, Zr and Ti.
In addition, No. Reference numerals 11 to 16 represent comparative wires.

No. With the wires 1 to 10 of the present invention, high-temperature cracking does not occur, and a sound weld metal having good gap resistance and bead appearance is obtained.

On the other hand, Nos. In which the amounts of P and S are above the range of the present invention. In No. 11, many high temperature cracks occurred, and No. In No. 12 as well, since the amount of C exceeds the range of the present invention, the occurrence of cracks increases.

Further, in the case of No. 3 whose Si content is less than that of the present invention 1
3 and No. No. 14 is inferior in the gap resistance because the bead width is less secured. Furthermore, No. In No. 14, since the amount of C and the amount of Si are small, the arc state becomes unstable and the gap resistance cannot be secured. No. 15 is La, Ce, Zr, T added to improve the crack resistance.
Since i was excessively large, the amount of slag produced increased and the short-circuit transfer characteristics deteriorated, and the weldability tended to be significantly inferior.

Further, when the amount of Mn exceeds the range of the present invention, N
o. No. 16 also had an increased slag generation amount and deteriorated short-circuit transfer characteristics, resulting in poor weldability, and further, the bead cracked and the bead appearance was poor.

Further, in Table 2, No. 1 of the method of the present invention is used. 1
7-No. In No. 22 of the comparative example, there is no hot cracking, and good weldable gap and bead appearance are obtained. 23-No. In No. 26, it was difficult to secure high-speed weldability, and the weldability tended to be poor. In addition, the shield gas composition C
In the weld metal containing a large amount of O ₂ or O ₂ gas, crack resistance was also deteriorated and cracks were generated in the Varestraint test for evaluating high temperature cracks.

As described above, the wire of the present invention and the shielding gas provide a sound weld metal portion having no cracks in welding even if the steel material of the P-added steel sheet is MAG welded, and has good gap resistance and bead appearance. It is clear.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

As described above, with the wire and the shielding gas of the present invention, even when MAG welding is performed on a steel material such as a steel sheet with P added for the purpose of corrosion resistance, no welding cracks, particularly high temperature cracks, are generated. A good weld metal part with excellent gap resistance and good bead appearance can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a weld crack test piece.

FIG. 2 is a view showing a Varestraint weld cracking test by TIG welding.

FIG. 3 is a view showing welding cracks generated on a bead surface.

FIG. 4 is a view showing a joint shape.

[Explanation of symbols] 1 P-added steel plate 2 blocks 3 Test piece holding jig 4 TIG welding torch 5 TIG welding torch 6 Ram down position 7 test beads 8 TIG welding beads 9 Crater section 10 Weld crack w Board width G gap t plate thickness L plate length

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-281439 (JP, A) JP-A-9-52192 (JP, A) JP-A-9-122970 (JP, A) JP-A-10- 34379 (JP, A) JP-A-10-43883 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 35/30

Claims (2)

(57) [Claims] 1. C, 0.04 to 0.16%, Si; 0.5 to 1.2%, Mn; 1.0 to 2.0%, P; 0.015% or less, S in weight%. 0.005% or less, O; 0.005 to 0.03%, and 0.005 to 0.2% in total of one or more of La, Ce, Zr, and Ti, and the balance. A gas shielded arc welding wire for P-containing thin steel sheet, characterized in that is composed of Fe and inevitable impurities. 2. A gas shield arc welding wire for P-added thin steel sheet according to claim 1, wherein a shield gas prepared by mixing Ar gas with CO ₂ gas and optionally O ₂ gas is used as the shield gas. MA characterized by
G welding method.