JPH0787998B2 - Gas shielded arc welding wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is resistant to cracking even when welding is performed at a place where fluctuating stress is repeatedly applied, such as in an existing steel structure bridge or offshore structure. The present invention relates to a gas shielded arc welding wire capable of forming an excellent weld.

(Prior art) Although bridges are repeatedly subjected to fluctuating stress during passage of vehicles, etc., when welding during repair or remodeling of bridges in such a state, the welding groove opening is naturally displaced. receive.
Fig. 1b shows the route gap displacement amount of the welding groove opening when the vehicle passes through the bridge having the welding groove opening (root gap a = 2 mm) as shown in Fig. 1a.

In FIG. 1a, 1 is a base material and 2 is a root.

During welding under such a displacement, the weld metal often undergoes cracking immediately after welding due to repeated tension and compression in a high temperature region where ductility is not sufficient, and thus, during welding, this Starting from the crack, the crack further develops,
In some cases, the life of the bridge as a structure is shortened.

In the past, there was no gas-shielded arc welding wire with excellent crack resistance that was suitable for welding under such varying stresses.Therefore, welding is restricted by restricting the passage of vehicles and welding. Only the measures were taken such as temporarily fixing the parts with a jig etc. and then performing welding, arguing that welding cracks are unavoidable, design changes and expected short service life.

(Problems to be solved by the invention) When welding a conventional gas shielded arc welding wire during welding work at a place where repeated stress is repeatedly applied to a bridge or offshore structure, cracks are generated in the weld metal. Since it is likely to occur, it left a problem where it was unavoidable to implement various measures and design changes during welding work as described above.

The present invention advantageously solves the above-mentioned problems. Even when welding is performed under fluctuating stress of a groove opening such as that caused by vehicle passage in a bridge, in other words, even when welding is performed under opening displacement, weld cracking occurs. It is an object of the present invention to propose a wire for gas shielded arc welding, which does not generate

(Means for Solving Problems) First, the process of clarifying the present invention will be described.

Now, as a result of repeated studies to clarify the cause of the occurrence of welding cracks under fluctuating stress, the inventors found that such welding cracks were
It has a close relationship with the melting point of non-metallic inclusions formed during the welding and solidification process, especially when low-melting non-metallic inclusions are formed, weld cracking is likely to occur. , Mn, Si and C have been found to have a particularly large effect on weld cracking.

That is, i) when Mn / S is small, Fe-FeS-based low-melting-point inclusions are generated, which intervene in the metal grain boundaries to remarkably deteriorate high-temperature ductility and induce cracking. When it is high, for example, Si-Mn-O-based low-melting point silicate inclusions are generated, and cracking occurs due to the same phenomenon as i) above. Iii) C is one of the elements most likely to cause concentration segregation during solidification. Then, it was clarified that cracking occurs just under solidification due to high-concentration segregation at grain boundaries.

The present invention is based on the above findings.

That is, the present invention provides C: 0.005 to 0.05 wt% (hereinafter simply referred to as%), Si: 0.25% or less, Mn: 1.00 to 2.70%, P: 0.015% or less and S: 0.004% or less of Mn / S. The ratio is contained in the range of 350 or more, and if necessary, at least one of Ni: 0.25% or less or Al: 0.40% or less and (Ti + Zr): 0.40% or less, and further Ni: 0.25% or less and Al: 0.40% or less and (Ti + Z
r): A gas shielded arc welding wire containing at least one of 0.40% or less and the balance being substantially Fe.

(Operation) The reason why the composition of the wire in the present invention is limited to the above range is as follows.

C: 0.005 to 0.05% C has the effect of suppressing the precipitation of coarse ferrite phase by forming a solid solution in the weld metal, and at least 0.005 in the welding wire.
% Must be included.

However, if it is too large, the high temperature ductility of the weld metal is deteriorated, so the upper limit was made 0.05%.

Si: 0.25% or less Si is a low-melting silicate inclusion (SiMn
O ₃ ) is easily generated and the ductility of the weld metal is reduced.
The amount added is 25% or less (preferably 0.01% or more).

Mn: 1.00 to 2.70% Mn is one of the most noteworthy elements in the present invention together with S. In addition to contributing to deoxidation, Mn combines with S during welding to form MnS having a high melting point and effectively suppresses the generation of FeS having a low melting point. However, if the Mn content is less than 1.00%, the effect of addition is poor, while if it exceeds 2.70%, the quench hardening of the molten metal becomes large, so the range was limited to 1.00 to 2.70%.

P: 0.015% or less P forms a low melting point intermetallic compound,
Since the ductility of the weld metal up to about ℃ is significantly reduced, it is desirable to reduce it as much as possible, but 0.015% or less is acceptable.

S: 0.004% or less S is one of the most noteworthy elements in the present invention as described above, and when S is contained in the weld metal, most of it becomes a sulfide and a non-metallic inclusion is present in the grain boundary. Generate as. Particularly, when a low melting point inclusion such as Fe-FeS is formed, the high temperature ductility from the solidification temperature to about 1000 ° C is significantly reduced. Therefore, as with P, it is desirable to reduce it as much as possible, but it is allowable within a range of 0.004% or less.

Also, if Mn / S is less than 350, it is not enough to precipitate most of S in the weld metal as MnS which is a high melting point inclusion,
FeS, which is a low-melting point inclusion, precipitates, leading to a decrease in ductility in the high temperature range.

Therefore, it is especially important to set Mn / S to 350 or more in order to prevent cracks during welding under variable stress.

Although the basic components have been described above, the present invention may further contain at least one selected from Ni, Al, and (Ti + Zr).

Ni: 0.25% or less Ni is an austenite stabilizing element and effectively contributes to enhancing impact resistance performance.However, when the content exceeds 0.25%, solid solution of P and S in the former austenite crystal grains occurs. Since Ni tends to decrease and segregation of P and S to grain boundaries easily occurs, Ni is 0.25
It is necessary to add it in less than%.

Al: 0.40% or less and / or (Ti + Zr): 0.40% or less Al, (Ti + Zr) not only contributes effectively to deoxidation of the weld metal, but by preferentially combining with S or N, It is a useful element that effectively prevents the formation of low-melting inclusions such as FeS and the generation of pores due to nitrogen. However, if too much is added, the amount of carbon / nitride precipitation will increase and the mechanical properties will deteriorate, so Al was made 0.40% or less. Ti and Zr are the same substances (Ti + Zr) 0.
It was added within the range of 40% or less.

The wire for gas shielded arc welding according to the present invention is composed of the above alloy elements, and by specifying the type and content thereof, cracks are generated even in welding under fluctuating stress (displacement amount of 1 mm or less). Thus, gas shielded arc welding that can perform welding without the need for welding is realized.

In addition, other elements such as Mo, Cr, Ca and B are contained in the wire.
And Cu may be contained, but the content of these elements is in the range that is added to the currently marketed wire for gas shielded arc welding below HT60 class, that is, Mo0.45%, Cr0 If the content was about .50%, Ca0.0010%, B0.0090% and Cu0.50% (including Cu plating), no adverse effect on the effect of the present invention was observed.

(Examples) Using gas shielded arc welding wire having a diameter of 1.2 mm and having various component compositions shown in Table 1, the component compositions shown in Table 2 were obtained, and as shown in Fig. 2a. Depth 10m
m, width: 40 to 50 mm, grooved plate thickness: 16 mm, with respect to the grooved test piece 3, only CO ₂ gas as a shielding gas and Ar: 80
~90vol%, CO _2: using 10～20Vol% of the gas mixture, after having been subjected to buildup welding, as shown in FIG. 2 b Thickness: 12m
It was cut into m, width: 150 mm, and length: 350 mm to obtain Balestlane test piece 4.

For each of the obtained test pieces, the bending strain of the plate surface was changed from 4% to 9%.
Table 3 shows the results of an examination of the occurrence of cracks when the ballast lane test was performed in the state of being changed up to%.

As is clear from the results shown in Table 3, when the wires W1 to W5 according to the present invention were used, no cracking occurred at all, regardless of the kind of shield gas and strain amount.

On the other hand, when W6 to 9 in which any of C, Si, S and Mn / S deviated from the proper range of the present invention was used, cracking occurred under all conditions. Note that W10 is a case where Si alone exceeds the proper range of this invention to some extent, but cracks did not occur when CO ₂ gas was used as a shield gas, but strain amount under (Ar + CO ₂ ) mixed gas shield Cracking occurred in both cases of 4% and 9%.

Next, using W1 to 5 and W10, a welding test was conducted in the following manner in order to investigate the weldability under a varying stress close to that of an actual bridge.

Fatigue test pieces having the composition shown in Table 2 and the shape and dimensions shown in FIG. 3 (a = 2 mm, b = 30 mm, c in the figure)
= 150mm, d = 300mm, e = 12mm, g = 2mm, α = 60 °)
After making and setting this test piece in the fatigue tester,
Fluctuation cycle as shown in Fig. 1a (displacement is ± 0.2m
m), welding current: 170 A, welding voltage: 24 V, welding speed: 15 cm / min, shielding gas: CO ₂ gas or (Ar + C)
Welding was performed under the condition of O ₂ ) mixed gas.

Immediately after such welding, the test piece was removed, 10 cross-sections of the welded portion were polished, and the presence or absence of cracks was examined with a microscope.

As a result, when any of the wires W1 to W5 according to the present invention was used, no cracking occurred at all.

In contrast, when using the W10 wire, (Ar + C
O ₂ ) Cracking was observed under the mixed gas shield.

Regarding W6 to W8, cracking occurred in the previous Balestlane test, and therefore, it was predicted from experience so far that cracking would naturally occur in a more severe fatigue test, so no particular test was performed.

(Effects of the Invention) Thus, when the gas shielded arc welding wire according to the present invention is used, welding cracks are generated at all even under a fluctuating stress that gives a fluctuating amount of a groove opening caused by vehicle passage in a normal bridge. Welding can be carried out without using any wire. Therefore, there is no need to consider traffic restrictions of vehicles and the like, attachment of jigs, design changes, shortening of service life, etc., as in the case of using conventional wires.

[Brief description of drawings]

1a is a sectional view of the weld groove portion, FIG. 1b is a view showing the relationship between the displacement amount and time in the weld groove portion shown in FIG. 1a, and FIG. Fig. 3 is a perspective view of a grooved test piece, Fig. 3b is a perspective view of a ballest lane test piece, and Fig. 3 is a front view of a fatigue test piece.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Noboru Nishiyama, No. 1 Kawasaki-cho, Chiba-shi, Chiba, Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Yasumasa Nakanishi No. 1 Shin-Nakahara-cho, Isogo-ku, Yokohama, Kanagawa (72) ) Inventor Takesuke Kono 1-1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Yoshitaka Nakamura 3-1-15-1 Toyosu, Koto-ku, Tokyo (72) Inventor Keiichi Sakai 3--1 Toyosu, Koto-ku, Tokyo No. 15 (56) Reference JP 61-67593 (JP, A) JP 48-103047 (JP, A) JP 61-165294 (JP, A)

Claims (4)

[Claims] 1. C: 0.005 to 0.05 wt%, Si: 0.25 wt% or less, Mn: 1.00 to 2.70 wt%, P: 0.015 wt% or less, and S: 0.004 wt% or less with a Mn / S ratio of 350. A gas shielded arc welding wire which is contained in the above range and the balance is substantially Fe composition. 2. C: 0.005 to 0.05 wt%, Si: 0.25 wt% or less, Mn: 1.00 to 2.70 wt%, P: 0.015 wt% or less and S: 0.004 wt% or less with a Mn / S ratio of 350. A gas shielded arc welding wire containing in the above range and containing Ni: 0.25 wt% or less, with the balance being substantially Fe composition. 3. C: 0.005 to 0.05 wt%, Si: 0.25 wt% or less, Mn: 1.00 to 2.70 wt%, P: 0.015 wt% or less and S: 0.004 wt% or less, and the ratio of Mn / S is 350. A wire for gas shield arc welding, which is contained in the above range and contains at least one of Al: 0.40 wt% or less and (Ti + Zr): 0.40 wt% or less, and the balance being substantially Fe composition. 4. C: 0.005 to 0.05 wt%, Si: 0.25 wt% or less, Mn: 1.00 to 2.70 wt%, P: 0.015 wt% or less, and S: 0.004 wt% or less with a Mn / S ratio of 350. A gas shield containing in the above range and containing at least one of Ni: 0.25 wt% or less, Al: 0.40 wt% or less and (Ti + Zr): 0.40 wt% or less, and the balance being substantially Fe composition. Arc welding wire.