JPS6320196A - Cored wire for non-shielded arc welding for repair welding - Google Patents

Abstract

PURPOSE:To form a weld metal having excellent crack resistance even in the case of welding a groove formed of steel sheets under oscillation by specifying the content of C in a sheath metal and specifying the contents of C, Mn, etc., by the total weight of a welding rod. CONSTITUTION:This cored wire for non-shielded arc welding contains <0.04% C in the heath metal 3 and contains <=0.05% C, 1.0-4.0% Mn, <=0.2% Al, and <=0.005% S by the total weight of the welding rod. Welding is thereby executed without generating weld cracks even under the fluctuating stresses which are generated by vehicle traffic on a bridge and fluctuate the opening rate of the groove.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to welding of grooves formed by mutually vibrating steel plates, such as in bridges of existing steel structures (hereinafter abbreviated as welding under fluctuating stress). ) also relates to an uncoated arc welding rod that can form weld metal with excellent crack resistance.

<Conventional technology> Bridges are repeatedly subjected to fluctuating stress due to the passage of vehicles, etc., and during welding during repair and remodeling work.

The weld groove opening is naturally subject to displacement. Figure 1 (a:2
mm,) shows the amount of displacement of the weld groove opening when a vehicle passes through the bridge.

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 during service, this crack starts as a starting point and further develops into a single crack, shortening the lifespan of the bridge as a structure.

Conventionally, there was no arc welding rod that could form a weld metal with excellent crack resistance during welding under such fluctuating stress, 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.

Therefore, the development of welding materials that can form welds with excellent crack resistance even when welding under fluctuating stress has great social significance from the perspective of bridge safety and smooth traffic flow. .

<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 was done in order to provide an arc welding rod that does not cause weld cracks even when welding is performed under fluctuating stress at the groove opening, such as that caused by vehicle traffic on a bridge.

As a result of extensive research into weld cracking under fluctuating stress, the present inventors have found that cracking occurs only in high temperature ranges, and that craters are particularly susceptible to cracking. picture.

This discovery was made based on this knowledge.

The present invention is characterized in that C in the outer skin metal is less than 0.04%, C: 0.05% or less with respect to the total weight of the welding rod, and λln: 1.0
~4.0%, Al: 0.2% or less, s: 0.00
It is a cored wire for unencapsulated arc welding with a Mg content of 0.2% to 2.5% or less based on the total weight of the welding rod.
0%, metal fluoride = 4.0% to 10.0%.

An investigation into cracking phenomena under varying stress revealed that cracks occur in high temperature ranges, and cracks do not develop when the temperature drops to low temperatures.

It was also found that craters are particularly susceptible to cracking. Therefore, as a welding rod with strong cracking resistance under fluctuating stress, it is essential that it has excellent high-temperature sidewall resistance, ■ reduces craters during continuous welding, and ■ requires on-site welding.
The condition is that it has excellent wind resistance.

Welding with covered rods produces many craters because it is not continuous welding. ! , I I G , λIAG welding is not suitable for outdoor work because the shield is disturbed by wind, so unencapsulated arc welding using cored wire is most suitable for the above conditions.

However, in a wire in which 0.6% or more of A1 is added to stabilize the arc and fix nitrogen in the weld metal, as shown in JP-A-61-1498,
Since Al is a strong ferrite former, unless a large amount of austenite former is added to the wire,
During the cooling process, the weld metal does not change to the austenite phase but instead remains in the ferrite phase, which causes the structure of the weld metal to become coarse and reduce its toughness. For this purpose, a C source such as graphite or high carbon ferroman is generally added to the flux, but C itself promotes hot cracking and is therefore not preferred as a welding material used under fluctuating stress.

Methods for investigating the high-temperature ductility of weld metal include the high-temperature tensile test (Greeple test) and the palestrain test, but these simply apply tensile displacement, and the tension and compression applied by varying stress cannot reproduce the repeated state. Therefore, even if the relationship between wire composition and cracking is investigated, a qualitative evaluation can be made, but a quantitative evaluation of the composition is not possible. Therefore, we investigated the composition required for the wire by welding it to a groove that was subjected to repeated displacement that faithfully reproduced the actual environment. Sunawa°
First, the groove shown in Figure 2 (a: 2 mm, b in the figure)
A fatigue testing machine reproduced the displacement with a vibration period of 0.2 seconds, vibrating between 1.9 mm and 2.1 mm around a root gap a of 2 mm, with a vibration period of 0.2 seconds (see Figure 1). (See (2)). In the cracking test, welding was performed while vibrating, and after cooling to room temperature, the material was cut perpendicular to the welding direction to examine cracks. The composition of the steel plate used is shown in Table 1.

As a result, in order to prevent single cracking during welding under fluctuating stress, it is necessary to first reduce the amount of C1S contained in the core bead wire, and add an appropriate amount of Mn. It has been found that in some cases, the combination of Mg addition and fluoride addition is effective.

Based on these findings and research conducted by the inventors, three components of the core wire for non-encapsulated arc welding according to the present invention have been identified, and the basis thereof will be explained below.

C: As mentioned above, it promotes hot cracking, so a lower value is better. In order to prevent cracking, the content must be 0.05% or less. To this end, it is not enough to not add graphite or to reduce the C content of metal elements such as iron powder and Mn in the flux as low as possible;
Keep it below 4%. Consideration must be taken such as limiting the amount of lubricant applied to wire 1 (3 g or less per 1 kg (the amount of C in the lubricant is 10 to 30%)).

If Al:C is within the above range, if A1 exceeds 0.2%, the weld metal will not undergo transformation during the cooling process, and the toughness of the weld metal will deteriorate.

S: A typical element that promotes high-temperature cracking.

The lower the better, and in the above experiment it was 0.
When it exceeded 0.005%, cracking occurred.

The S of the entire flux depends on the raw materials that make up the flux.
Although the amount varies, as long as ordinary industrial raw materials are used, the flux inevitably contains an average S amount of 20 to 39 ppm. When the inclusion ratio of flux is 20%, the amount of S in the flux is 0.0004 to 0.0004 o, oo to the entire wire.
It accounts for o6%.

Assuming that 3 g of lubricant is applied per 10 kg of wire, and that the lubricant contains 5% S (teributene sulfide is usually added as an extreme pressure agent).

The S content in the lubricant is 0.0015% for the wire as a whole, and the sum of these amounts alone is close to 0.002%, and the S content for the entire wire is 0.0015%. In order to achieve QQ5X or lower, it is necessary to lower the S content in the outer skin to about 0.003%. Therefore, in order to keep it below 0.005% in the entire wire,
Use a lubricant that does not contain S to reduce the S content of the outer metal to 0.
．． 0.004% or less is economical, and it is not a good idea to use a skin metal with an extremely low S content.

Mn:Al must be limited to a low value, so! , I
n is important as a deoxidizing element and also has a desulfurizing effect.

If Mn is not added in an amount of 1.0% or more, cracks will occur, and if it exceeds 4%, the weld metal will harden due to the hardenability of Mn, impairing its toughness.

If the above conditions are met, a normal steel plate with an S content of 0.020% or less will not crack even under fluctuating stress, and the mechanical performance of the weld metal will be ensured, but if the S content of the steel plate is 0.020% or less, If the cracking resistance is exceeded, the above measures are insufficient and it is necessary to further improve the cracking resistance.

As a countermeasure to this, it is possible to further lower the C and S content in the wire, but as discussed in each item, it is uneconomical to further reduce the C and S content of the outer sheath metal. To prevent cracking, it is sufficient to reduce the S content of the weld metal, so it is more effective to desulfurize by adding Mg and fluoride.

11g: Mg has the effect of converting S into MgS and removing it as slag during welding, and also has the effect of rendering S in the weld metal harmless by converting it to MgS. If S is 0.005% or less, this effect can be obtained by adding 0.2% or more, but if it exceeds 2%, it is not practical due to the amount of fume.

Metal fluoride: Fluoride also has a desulfurization effect, and the above 1.1g shows a strong desulfurization effect at a relatively early stage of the reaction, but the effect of fluoride lasts until the late stage of the reaction when the slag-metal reaction is the main reaction. Therefore, it is desirable to use it together with Mg, and it is effective when added in an amount of 4% or more; if it exceeds 10%, the melting point of the slag becomes too low and the slag does not cover the bead, resulting in poor bead shape and is not practical.

Since the wire of the present invention does not substantially contain Al,
Due to the lack of arc stability and poor denitrification effect, pores may be formed in the weld metal. Regarding nitrogen absorption, if you use it with DC reverse polarity, the amount of nitrogen absorption itself will be reduced, so there is no need to add ^1, and for arc stability, it seems that arc is likely to occur from the center of the wire. A double structure in which a conductive metal element is mainly arranged in the center of the wire may be used, and a typical cross-sectional shape thereof is shown in FIG. 3(2). In this case, the distribution of the metal elements between the inside and the outside does not necessarily require that all of the metal elements be placed inside, but it is sufficient that 70% or more of one metal element be placed inside.

<Example> The method of carrying out the present invention will be described below by giving specific examples.

While continuously shaping a steel strip with the ingredients shown in Table 2, flux was added to create a long cylinder of 4 mmφ, and the wire was drawn to 1.8+n+nφ using a die to create a flux-cored wire. did. In the final wire drawing process, apply lubricating oil containing C and S listed in Table 3 to the surface at a rate of 2 per 10 kg of wire.
g was applied. The flux composition calculated from the blended amount is the fourth
As shown in the table, for C9S, the total amount of impurities in the raw materials is shown. Furthermore, C was not added because it hardly stops yielding in carbonates. Using this wire, prepare the bevel shown in Fig. 2 on the base material listed in Table 1 above, and the root gap a is 1.9 ml to 2.
A fatigue testing machine applied a displacement of 1 mm with a period of 0.2 seconds, and welding was performed while vibrating to perform a 1-crack test. To detect cracks, the bead was cut perpendicular to the welding direction and examined under 10x magnification. The cracking test results and the Charpy test absorbed energy values of all weld metals were
Shown in the table. Examples 1 to 6.

This is a case where the present invention was implemented, and good results were obtained in all cases. In comparison, cracks occurred in Comparative Example 7 due to the high C content of the outer skin metal, and in Comparative Example 9 due to the high S content. Further, in Comparative Example 8 in which 0.3% of A1 was added, no cracking occurred, but the mechanical performance of 9 was inferior to that of the Example. In Comparative Example 10, M
Cracking occurred in the case where n was low, while in Comparative Example 11 in which Mn was added in excess, the hardenability was too good and the absorbed energy was low.

Next, a similar experiment was conducted using a steel plate with a high S content of 0.022% as shown in Table 5. As shown in Table 6, if the S of the steel plate is this high, the steel plate with S = 0.010% in Example 2 will not crack even if the wire has the same composition as in Comparative Example 14. It will break. For such severe conditions, addition of Mg and fluoride, which have desulfurization power, is recommended in Example 1.
It is valid as shown in 2.13.

Can prevent cracking.

In the above experiments, the welding conditions were 200A, 20V, 30cm.
/min with reverse polarity (on the electrode). In terms of welding workability, it can be used as is, but the arc can be further stabilized by improving the wire cross-sectional shape and flux composition. Examples are shown below.

A cored wire having a cross-sectional shape shown in FIG. 3 was prepared using a strip electrode having a composition of N011 shown in Table 2. The wire diameter is 1. Ij-mmφ. The center and the outside (internal capsule).

It is an outer package. ) The flux composition was as shown in Table 7. When the inner and outer fluxes are added, this flux becomes that of Example 1 in Table 4 and that of Example 12 in Table 6. Note that No. 1 in Table 3 was used as the lubricant.

Table 8 shows the cracking test results and workability with varying welding polarity. It has become clear that arc stability can be greatly improved by welding a wire with metal components mainly on the inside using an electrode.

Table 8 <Effects of the Invention> If the coated arc welding rod of the present invention is used, no weld cracks will occur even under the varying stress that causes the groove opening to fluctuate due to vehicle traffic on a normal bridge. It is possible to weld without any need for welding.

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 cross-sectional view of the bridge welding groove, Figure 1 (2)
FIG. 2 is a cross-sectional view of a crack test piece, and FIG. 3 is a cross-sectional view of an example of the cored wire of the present invention. 1... Base material 4... Flux 2... Root End... Outer envelope flux 3... Outer shell metal 6
...Internal flux, mass Fig. 1 +0.1 0 -0.1 Displacement (mm) Fig. 2 (1) No. 3' (2) 6 Inclusive flux

Claims (2)

[Claims] (1) C in the outer skin metal is less than 0.04% by weight, and based on the total weight of the welding rod, C: 0.05% or less Mn: 1.0% to 4.0% Al: 0.2% or less A cored wire for non-encapsulated arc welding, characterized in that S: is limited to 0.005% or less. (2) The unencapsulated arc according to claim 1, which contains Mg: 0.2% to 2.0% and metal fluoride: 4.0% to 10.0% based on the total weight of the welding rod. Cored wire for welding.