JPS62292298A - Coated electrode for fillet welding having excellent crack resistance - Google Patents

Abstract

PURPOSE:To develop a welding rod which can form a weld metal having excellent crack resistance by using a mixture composed of specific ratios of a metal carbonate, metal fluoride, metal oxide and iron powder as a coating material for a coated electrode for fillet welding. CONSTITUTION:The mixture composed of the compsn. consisting of 5-28wt% metal carbonate such as MgCO3 or CaCO2, 2-12wt% metal fluoride such as CaF2, 23-50wt% metal oxide such as MgO, TiO2, SiO2 or Al2O3 and 10-60wt% iron powder is coated on the outside periphery of a steel core wire as the coating material for the coated electrode for fillet welding at 38-55% ratio by the total weight of the welding rod. The compsn. over the entire part of the welding rod is so component-adjusted as to contain 0.005-0.05% C, <0.030% Si, 3.0-5.2% Mn, <0.006% S, and <0.25% Ni and to have >=600 Mn/S ratio. Further, <1.2% Ti+Zr and <0.8% Al+Mg are added as a deoxidizing agent and S fixing agent for the weld metal.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to existing steel structure bridges, offshore structures, etc.
The present invention relates to a coated arc welding rod for fillet welding that forms a weld metal with excellent cracking resistance even when welding in locations where fluctuating stress is repeatedly applied.

<Prior Art> Bridges are repeatedly subjected to fluctuating stress due to the passage of vehicles, etc., and when welding is performed during repair or remodeling work, the weld groove opening is naturally subject to displacement. As an example, the amount of displacement of the fillet weld groove opening when a vehicle passes through the bridge shown in FIG. 1 is shown.

When welding under such displacement, the weld metal is repeatedly tensed and compressed in a high temperature region where the weld metal does not have sufficient ductility, so cracks often occur immediately after welding. Furthermore, the current situation is that this crack starts as a starting point and further develops into a single crack during service, shortening the lifespan of structures such as bridges.

Conventionally, there were no coated arc welding rods that produced weld metal with excellent cracking resistance, so welding was carried out while restricting or stopping the passage of vehicles. ■ Perform welding after temporarily fixing the weld groove with a jig, etc. ■It is assumed that weld cracking is unavoidable, and design changes and service life are expected to be shortened. Currently, measures such as these are being taken.

<Problems to be Solved by the Invention> When conventional coated arc welding rods are used in welding at locations subject to repeated fluctuating stress, cracks are likely to occur in the weld metal. It was necessary to implement various measures during welding work and to make design changes.

The present invention aims to overcome these drawbacks.

This invention was made in order to provide a coated arc welding rod for fillet welding that does not cause weld cracking even when welding is performed under fluctuating stress at the groove opening, such as that caused by vehicle traffic on a bridge.

Means for Solving Problems〉 As a result of intensive research on weld cracking under fluctuating stress, the present inventors found that the relationship between this weld crack and the melting point of nonmetallic inclusions generated during the weld solidification process was determined by the present inventors. It was discovered that there is a close relationship between

In the present invention, metal carbonate = 5 to 28%, metal fluoride: 2 to 28%
12%, metal oxide: 23-50%, iron powder: 10-60
The coating material containing 38-55% based on the weight of the welding rod
% to the outer periphery of the steel core wire, and based on the total weight of the welding rod, C: 0.005 to 0.05%, Sl: 0
．． 30 or less, Mn: 3.0-5.2%, S: 0.0
6% or less, Ni: 0.25% or less, and
A coated arc welding rod for fillet welding with Mn/S of 600 or more, and Ti + Zr based on the total weight of the welding rod.
: 1.2% and/or Al + Na : 0.8%
The covered arc welding rod for fillet welding includes the following:

As mentioned above, there is a close relationship between weld cracking under fluctuating stress and the melting point of nonmetallic inclusions generated during the weld solidification process.
It has been found that C and C have a large effect on weld cracking. That is, if ■Mn/S is small, Fe-Fe
Low melting point inclusions of type 5 are generated and are present at metal grain boundaries, significantly deteriorating high temperature ductility and causing cracks. (2) When the Si content is high, inclusions of low-melting silicate (eg 5i-Un-0 system) are formed and cracks occur due to the same phenomenon as described above. Furthermore, C is one of the elements most likely to cause concentration segregation during solidification, and its high concentration at grain boundaries causes cracking immediately below solidification.

Based on these findings and the inventor's test research, the components and composition of the coated arc welding rod for fillet welding in the present invention were specified, and the basis thereof will be explained below.

First, in the present invention, metal carbonate in the coating material.

The reason for determining the content and coverage of metal fluorides and metal oxides is as follows.

Metal carbonate [Content in coating material (abbreviated below): 5-28%
] is less than 5%, the amount of CO gas generated by decomposition of carbonate is insufficient, and pores are generated in the weld bead.

On the other hand, if it exceeds 28%, the arc blowing force becomes too strong and the bead shape deteriorates.

If the metal fluoride (2 to 12%) is less than 2%, the viscosity of the molten slag becomes too high and welding workability deteriorates. on the other hand,
If it exceeds 12%, the viscosity of the molten slag becomes too low;
A satisfactory weld bead cannot be obtained.

If the content of metal oxides (23 to 50%) is less than 23%, the arc during welding becomes unstable, welding workability deteriorates, and the bead appearance also deteriorates significantly. On the other hand, if it exceeds 50%, the melting point of the molten slag becomes high and satisfactory welding workability cannot be obtained.

Iron powder (10-60%) is added in hopes of improving the welding efficiency of horizontal fillet welding and adjusting the bead shape.
If it is less than 10%, undercut will occur.
was set as the lower limit. On the other hand, if it is added in excess of 60%, the insulation properties of the coating will be impaired and current will leak (spark) from the sides of the welding rod, impairing safety.

If the coverage rate (38 to 55%; coverage rate is defined as the weight percent of the coating agent to the total weight of the welding rod) is less than 38%, the amount of molten slag will be insufficient, making it difficult to obtain a clean weld bead during horizontal fillet welding. I can't do it. on the other hand.

If it exceeds 55%, the amount of slag becomes too large, and defects such as slag entrainment are likely to occur in downward fillet welding.

Next, the essential elements to be contained in the above-mentioned welding rod, that is, either the coating material or the steel core wire, will be explained.

S [content rate based on the total weight of the welding rod (abbreviated below).

) :0.006% or less] is one of the most important elements in the present invention. S remains in the weld metal.

Most of it becomes sulfide and is generated as inclusions.

Among these, when forming low melting point eutectic inclusions such as Fe-Fe5, high temperature ductility at temperatures below 1000°C is significantly reduced. Therefore, the smaller S is, the better.

On the other hand, if it exceeds 0.006%, as will be described later.

Even if the addition of Mn, Ti, Zr, etc. is increased to the upper limit,
This is because the formation of low melting point inclusions of FeS cannot be prevented.

The upper limit was set at 0,006%.

Mn (3.0 to 5.2%) is present in Invention 1 along with S and C.
．． : It is one of the most important elements. The purpose of adding Mn to fillet welding rods is not only to act as a deoxidizing agent, but also to combine with S during welding to form high melting point MnS,
It is an essential component to prevent the generation of S, and contains 3.0%
If it is less than that, these cannot be satisfied. On the other hand, 5
．． When it exceeds 2%, the quench hardenability of the weld metal becomes large and the cracking resistance deteriorates.

In the fillet welding rod coating system of the present invention, since relatively acidic slag is generated, the deoxidizing ability of Si (0.30% or less) is relatively weak. It is not necessary to add it. on the other hand.

Adding more than 0.3% is bad because low melting point silicate inclusions (for example, SiMn03) are formed in the weld metal, reducing ductility.

C (0,005 to 0.05%) is retained in the weld metal and has the effect of suppressing the precipitation of coarse ferrite phase.

It must be contained in the welding rod at least 0.005%. However, if it is too large, high temperature ductility deteriorates, so it must be kept at 0.05% or less.

N1 (0.25% or less) is one of the austenite stabilizing elements, but it decreases the solid solution of S in prior austenite grains and makes it easier to cause S segregation at grain boundaries, so 0.2
The limit was set at 5%.

It was concluded that it is extremely effective to set Mn/S to 600 or more in order to ensure the ductility of the weld metal in the high temperature range and further effectively improve the cracking resistance. That is, Mn/
If S is less than 600, it is insufficient to precipitate most of the S in the weld metal as MnS, which is a high melting point inclusion, and FeS, which has a low melting point, is precipitated, which deteriorates high temperature ductility.

Although the present invention exhibits its effects within the above range, the effects are further enhanced by adding the following elements.

Ti + Zr (content based on the total weight of the welding rod (hereinafter abbreviated): 1.2% or less) is added for the purpose of deoxidizing the weld metal and generating sulfides, and is used to fix S (i.e. to prevent high-temperature ductility from decreasing). It is effective. If it exceeds 1.2%, nitride precipitation increases, which deteriorates mechanical performance at room temperature, which is bad.

Al+Mg (1.2% or less) is added for the purpose of deoxidizing the weld metal, and if added in excess of 1.2%.

During welding, Si increases in the coating due to reduction of 5IO3, leading to a decrease in high temperature ductility.

The present invention is composed of the alloy elements as described above, and by specifying the type and content of the alloy elements to be included in the coating material and the core wire, the present invention can be applied under varying stress (under a displacement of 20% or less). It is possible to obtain a coated arc welding rod for fillet welding that can be welded without cracking even in the welding of bridges, etc., and eliminates the previous limitations when welding to repair fatigue cracks that have occurred in bridges, etc., and welding for remodeling work. Since construction can be carried out regardless of the situation, quality has been significantly improved, construction time has been shortened, and economic benefits have been obtained.

The range of other elements currently added to the coated fillet arc welding rods for the HT60 class on the market is 0.4
It was also confirmed that Cr was 5% or less and Cr was 0.25% or less, but it was confirmed that there was no adverse effect on the scope of the present invention.

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

The coverage ratio is 38 to 55 on the outer periphery of the steel core wire (5.0 mm diameter).
%, and coated arc welding rods having the composition shown in Table 1 were manufactured. Using the obtained welding rod, the following tests were conducted to perform welding under fluctuating stress that is close to practical.

A test piece as shown in Figure 2 (a: 2, b: ll in the figure)
i.

c:20. Fillet welding (d: 1 GG, e: 600 mm) was performed using a fatigue testing machine (220 ^ITIII 2Qcm/
Immediately after the completion of welding, the test piece was removed, 10 cross sections of the welded part were cut out, and after polishing, the presence or absence of cracks was observed using a microscope. This was repeated twice. As a result of these tests, it was confirmed that none of the welding rods of the present invention (Nos. 2 to 9) produced cracks, but N.
In the comparison rods α1 and Aim 10 to 15, cracks due to insufficient high temperature ductility were observed.

That is, No. 1 is C, S, Ti+Zr, Mn/
S, No, 10 is C, Nl1lll is Si, No
, 12 is S, Mn/S, Na13 is Ni,
Na14 is S, Ti+Zr, Mn/S, No,
In No. 15, Mn was outside the range of the present invention, and cracks were observed in all cases due to insufficient high-temperature ductility. The results are summarized in Table 2.

In addition, the steel plate 5M-580 (thickness 116 mm) used at this time
) is shown in Table 3.

Table 2 Note) ○: No cracking ×: Cracking occurred Table 3 Eri <Effects of the invention> If the coated arc welding rod of the present invention is used, fluctuations in the groove opening caused by vehicle traffic on normal bridges will be reduced. Welding is possible without any weld cracking even under varying stress that gives rise to a large amount of stress (less than 20% when the root gap is 2). Therefore, there is no need to consider restrictions on vehicle traffic, installation of jigs, design changes, shortening of service life, etc. that occur when conventional welding rods are used.

[Brief explanation of the drawing]

Figure 1 (1) is a sectional view showing a corner weld of a bridge repair weld, and Figure 1 (2) is an explanation showing the relationship between displacement and time at both corner openings in Figure 1 (1). Figure 2 (1) is a plan view of a test piece for weld cracking test under varying stress. FIG. 2 (2) is a sectional view taken along line AA, and FIG. 2 (3) is a sectional view taken along line BB'. 1...Bridge flange material 2...Bridge web material 3...Welding opening

Claims (2)

[Claims] (1) Metal carbonate: 5 to 28% by weight (hereinafter abbreviated as %)
, metal fluoride: 2-12%, metal oxide: 23-50%
A coating material containing 10 to 60% of iron powder is applied to the outer periphery of the steel core wire in an amount of 38 to 55% based on the total weight of the welding rod, and a coating material containing C:0. 005~0
．． 05% Si: 0.30% or less Mn: 3.0 to 5.2% S: 0.006% or less Ni: 0.25% or less, and Mn/S is 600 or more. Covered arc welding rod for fillet welding. (2) The coated arc welding rod for fillet welding according to claim 1, which contains Ti+Zr: 1.2% or less and/or Al+Mg: 0.8% or less based on the total weight of the welding rod.