JPH0630832B2 - Coated arc welding rod with excellent crack resistance - 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 covered arc welding rod capable of forming an excellent welding part.

<Prior art> Although bridges are repeatedly subjected to fluctuating stress during the passage of vehicles, the welding groove opening is naturally displaced during welding during repair and remodeling work. In Fig. 1 (a: 2 mm.),
The amount of displacement of the weld groove opening when the vehicle passes through the bridge is shown.

During welding under such displacement, the weld metal is often subjected to repeated tension and compression in a high temperature region where the ductility of the weld metal is insufficient, so that cracks often occur immediately after welding. In addition, the cracks further develop from this crack during service, and the life of the bridge structure is shortened.

Conventionally, there has been no covered arc welding rod that forms weld metal with excellent crack resistance in welding under such variable stress, so welding is performed with the passage of vehicles and the like restricted and stopped.
Welding is performed after the welding groove is temporarily fixed with a jig or the like.
We assume that weld cracking is unavoidable, and anticipate design changes and shortened service life. It was the current situation that we were taking such a convenient route.

<Problems to be solved by the invention> When a conventional covered arc welding rod is used for welding at a place where repeated fluctuating stress is applied, cracks are easily generated in the weld metal. It was necessary to implement various measures and design changes that were made during welding.

In order to overcome such drawbacks, the present invention is a coating that does not cause welding cracks even when welding is performed under variable stress of a groove opening (displacement of the opening), which is caused by vehicle passage in a bridge. It was made to provide an arc welding rod.

<Means for Solving Problems> As a result of intensive studies on weld cracks under fluctuating stress, the present inventors have found that between these weld cracks and the melting point of non-metallic inclusions generated in the weld solidification process. The present invention has been completed based on this finding.

The present invention, metal carbonate: 40-60%, metal fluoride: 10-25
%, Metal oxide: 4 to 25% of the coating material is 24 to the total weight of the welding rod including the weight of the coating material and the steel core wire.
It is applied to the outer circumference of the steel core wire in the range of 32%, and C: 0.005 to 0.05%, Si: 0.1 to 1.1% of the total weight of the welding rod.
%, Mn: 1.5 to 2.5%, S: 0.007% or less, Ni: 0.25%
It is a covered arc welding rod with Mn / S of 350 or more and Ti + Zr: 1.2% based on the total weight of the welding rod.
And / or Al + Mg: 1.2% or less of the coated arc welding rod.

As described above, there is a close relationship between weld cracking under variable stress and the melting point of non-metallic inclusions formed during the weld solidification process. In particular, among the chemical components of weld metal, S, Mn, Si and It was found that C has a large effect on weld cracking. That is, when Mn / S is small, Fe-FeS-based low-melting inclusions are generated and intervene in the metal grain boundaries, which significantly deteriorates high temperature ductility and causes cracking. When Si is high, silicate (eg Si-Mn-O based) inclusions with a low melting point are generated and cracks are generated by the same phenomenon as described above. Further, C is one of the elements most likely to cause concentration segregation during solidification, and cracks occur just below solidification due to high concentration segregation at grain boundaries.

The components and composition of the coated arc welding rod in the present invention were identified based on these findings and the inventor's test and research. The grounds for this will be described below.

First, the reason why the contents of metal carbonate, metal fluoride and metal oxide in the coating agent and the coating rate are determined in the present invention is as follows.

Metal carbonate (content in coating agent (abbreviated below): 40-60%)
If it is less than 40%, the viscosity of the molten slag becomes high, and the slag is likely to precede, degrading the welding workability. In addition, the amount of shielding gas generated is insufficient and porosity occurs in the weld metal.

On the other hand, if it exceeds 60%, the viscosity of the molten slag is insufficient, the slag coverability deteriorates, and the bead shape deteriorates.

If the content of metal fluoride (10 to 25%) is less than 10%, the viscosity of the molten slag becomes too high, and the welding workability deteriorates especially in vertical welding. On the other hand, if it exceeds 25%, the viscosity of the molten slab becomes too low, and the downward welding workability deteriorates.

If the metal oxide content (14 to 25%) is less than 14%, the welding workability deteriorates and the bead appearance remarkably deteriorates. On the other hand, 25
%, The viscosity of the molten slag increases, and satisfactory welding workability cannot be obtained.

If the coverage (24 to 32%, the coverage is defined as the weight% of the coating agent relative to the total weight of the welding rod) is less than 24%, the protective cylinder is not sufficiently formed and spatter increases, and the generated slag is generated. The bead appearance also deteriorates due to the lack of. On the other hand, if it exceeds 32%, the amount of slag becomes too large, and defects such as slag entrainment are likely to occur especially during welding in the groove.

Next, the basis for setting the component composition of the above-mentioned welding rod, that is, the essential element contained in either the coating material or the steel core wire will be described.

S [content rate with respect to the total weight of the welding rod (abbreviated below): 0.00
7% or less] is one of the most noteworthy elements in the present invention, but S is retained in the weld metal, and most of it becomes a sulfide and is formed as a non-metal inclusion in the grain boundary. .
In particular, when low-melting eutectic inclusions such as Fe-FeS are formed, the ductility at high temperature from solidification to about 1000 ° C is significantly reduced. Therefore, it is desirable to keep it within the range where it is mixed as an unavoidable component. On the other hand, if it exceeds 0.007%, as will be described later, even if the addition amount of Mn, Ti, Zr, etc. is increased to the upper limit, the formation of FeS low melting point inclusions cannot be prevented, so 0.007% is set as the upper limit. did.

Mn (1.5 to 2.5%), together with S, is one of the most noteworthy elements in the present invention. Mn is a high melting point MnS that binds to S during welding and is an indispensable component to prevent the formation of low melting point FeS. If less than 1.5%, these cannot be satisfied. On the other hand, if it exceeds 2.5%, the quench hardenability of the weld metal becomes large and the crack resistance deteriorates.

Si (0.1 to 1.1%) is mainly used for deoxidation in the molten metal. If the content of Si in the welding rod is less than 0.1%, deoxidation will be insufficient and porosity will occur in the weld metal. On the other hand, if it exceeds 1.1%, low melting point silicate inclusions (SiMnO ₃ ) are formed and the ductility of the weld metal deteriorates.

C (0.005 to 0.05%) has a result that it is retained in the molten metal and suppresses the precipitation of coarse ferrite phase. Therefore, at least 0.005% or more must be contained in the welding rod. However, if too much, the hot ductility of the weld metal deteriorates, so
Must be kept below 0.05%.

Ni (0.25% or less) is one of the austenite stabilizing elements, but it is not always necessary to add it. However, when the addition amount is large, the solid solution of S in the old austenite crystal grains is lowered, and S segregation at the grain boundaries is likely to occur, so 0.25% was made the limit.

If Mn / S (350 or more) 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, and it precipitates as FeS of a low melting point inclusion.
Reduces ductility in high temperature range. Therefore, Mn / S is 3
A value of 50 or more is under fluctuating stress (root gap 2 mm
It was found that it is extremely effective in preventing cracks in welding work with fluctuations of 20% or less).

The present invention exerts its effect in the above component composition range, but the effect of the present invention is further exerted by adding an appropriate amount of the following elements.

Ti + Zr [content of the total weight of the welding rod (abbreviated below):
1.2% or less] is for adding deoxidation of molten metal (auxiliary deoxidation accompanying Si reduction) for the purpose of nitriding and sulfurization. The order of strength of the reaction is nitriding>sulfurization> carbonization. It is effective in preventing the deterioration of hot ductility), but if it exceeds 1.2%, the precipitation of carbides increases and the mechanical performance at room temperature deteriorates.

Al + Mg (1.2 or less) is added for the purpose of deoxidizing molten metal (auxiliary deoxidation accompanying Si reduction). If added in excess of 1.2%, Si due to reduction of SiO _{2 in} the coating agent increases. ， Induced reduction of hot ductility.

The covered arc welding rod according to the present invention is composed of the above alloying elements, and by specifying the type and content thereof, cracking occurs even under welding under fluctuating stress (when fluctuating amount is 20% or less). It was possible to obtain a welding rod that can be welded without causing any.

Other elements include Mo, Cr, B, etc., which are currently added to commercially available HT60 class covered arc welding rods (in the entire welding rod) Mo ≤ 0.45% Cr ≤ 0.50% B or B oxide B conversion An examination was also made for ≤0.15%, but within the above range, no effect on the effect of the present invention was observed.

<Examples> Next, the present invention will be specifically described with reference to Examples.

A coating agent was applied to the outer circumference of the steel core wire (4 mm diameter) so that the coverage was 24 to 32%, and a coated arc welding rod having the composition shown in Table 1 was manufactured. Using the obtained welding rod, as shown in FIG. 2 (1), the inside of the groove of the steel plate (the components are shown in Table 3) was welded and raised, and then cut out to obtain a test piece. (Second
(2) Refer to Fig. 4) This test piece has a bending strain of 4 to 15% on the plate surface.
The value was varied within the range of, and the test was conducted by the Balestraint test method.

As is clear from Table 1 and Table 2, the welds obtained by using the welding rods (No. 2 to 8) satisfying the requirements of the present invention are
No cracks occur at all even in a strain restraint test in which a strain amount of 4 to 15% is applied.

On the other hand, No. 1 which is close to the conventional rod is C, Si, Mn, S and M.
n / S is out of the range of the present invention, and cracking occurs even with a bending strain amount of 4%. In addition, Nos. 9 to 14 are comparative examples, but N
o.9 is C, Si, S and Mn / S within the scope of the present invention, and No. 10 is Si.
However, since it is out of the range of the present invention, cracking occurs at a bending strain amount of 4% or 10% or more. Furthermore, No. 11 is C, Si, Mn, N
i, Mn / S, No. 12 is C, Si, Mn, S, Mn / S, No. 13 is Si, M
In n, S, Ni, Mn / S, and No. 14, C was outside the scope of the present invention, and therefore the occurrence of cracking could not be prevented with a bending strain amount of 4%.

Furthermore, the following tests were conducted using these welding rods in order to weld under varying stress close to that of an actual bridge.

Test pieces as shown in FIGS. 3 and 4 (b: 30 in the figure,
c: 150, d: 300, e: 16 mm α: 60 °. ) Is set during the fatigue test, and the welding cycle (welding condition: horizontal direction, welding amount: ± 0.2 mm during the test) is applied while giving the fluctuation cycle as shown in Fig. 1 (2). 170Amp, 24-25
(Volt, 15 cm / min), and immediately after welding was completed, the test piece was removed, and after cutting and polishing 10 cross sections of the weld,
The presence or absence of cracks was observed with a microscope. The results of these tests,
When the welding rods (No. 2 to 8) according to the present invention were used, it was confirmed that no cracks occurred at all. In contrast, it was confirmed that when the comparative welding rods of No. 1, No. 9 and No. 10 were used, many cracks were generated due to insufficient hot ductility.

Table 3 shows the chemical composition of the steel sheet SM-58Q (16 mmt) used at this time.

<Effects of the Invention> By using the coated arc welding rod according to the present invention, even under a fluctuating stress which gives a variation amount (20% or less when the root gap is 2 mm) of the groove opening portion generated by vehicle traveling in a normal bridge. ， Welding is possible without any weld cracking. Therefore, it is no longer necessary to take into consideration the traffic restrictions of vehicles, jig attachment, design changes and shortening of the service life when using conventional welding rods.

[Brief description of drawings]

Figure 1 (1) is a cross-sectional view of the weld groove, and Figure 1 (2) is the first
Fig. 1 (1) is an explanatory view showing the relationship between displacement and time at the weld groove opening, Fig. 2 (1) is a perspective view of a grooved test piece for vale restraint, and Fig. 2 (2) is barre FIG. 3 is a perspective view of the strain test piece, FIG. 3 is a plan view of the test piece set in the fatigue test, and FIG. 4 is an enlarged view of the AA ′ section of FIG. 1 …… Base material 2 …… Route 3 …… Grooved test piece 4 …… Multilayer weld metal 5 …… Test piece

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noboru Nishiyama 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division

Claims (4)

[Claims] 1. Metal carbonate: 40 to 60% by weight (hereinafter abbreviated as%), metal fluoride: 10 to 25%, metal oxide: 4 to 25%
The coating material containing is applied to the outer circumference of the steel core wire in the range of 24 to 32% with respect to the total weight of the welding wire, which is the total weight of the coating material and the steel core wire. C: 0.005 to 0.05% Si: 0.1 to 1.1% Mn: 1.5 to 2.5% S: 0.007% or less Ni: 0.25% or less and a covered arc welding rod having Mn / S of 350 or more. 2. Metal carbonate: 40-60% by weight (hereinafter abbreviated as%), metal fluoride: 10-25%, metal oxide: 4-25%
The coating material containing is applied to the outer circumference of the steel core wire in the range of 24 to 32% with respect to the total weight of the welding wire, which is the total weight of the coating material and the steel core wire. C: 0.005 to 0.05% Si: 0.1 to 1.1% Mn: 1.5 to 2.5% S: 0.007% or less Ni: 0.25% or less Ti + Zr: 1.2% or less and Mn / S is 350 or more covered arc welding rod . 3. Metal carbonate: 40-60% by weight (hereinafter abbreviated as%), metal fluoride: 10-25%, metal oxide: 4-25%
The coating material containing is applied to the outer circumference of the steel core wire in the range of 24 to 32% with respect to the total weight of the welding wire, which is the total weight of the coating material and the steel core wire. C: 0.005 to 0.05% Si: 0.1 to 1.1% Mn: 1.5 to 2.5% S: 0.007% or less Ni: 0.25% or less Al + Mg: 1.2% or less and Mn / S is 350 or more covered arc welding rod . 4. Metal carbonate: 40-60% by weight (hereinafter abbreviated as%), metal fluoride: 10-25%, metal oxide: 4-25%
The coating material containing is applied to the outer circumference of the steel core wire in the range of 24 to 32% with respect to the total weight of the welding wire, which is the total weight of the coating material and the steel core wire. C: 0.005 to 0.05% Si: 0.1 to 1.1% Mn: 1.5 to 2.5% S: 0.007% or less Ni: 0.25% or less Ti + Zr: 1.2% or less Al + Mg: 1.2% or less and Mn / S is 350 or more A coated arc welding rod.