JPS5847954B2 - Low hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coated arc welding rod, and more particularly to a low hydrogen-based coated arc welding rod that improves the fatigue strength of a welded part.

Currently, so-called low-hydrogen coated arc welding rods containing CaCO3, MgCO3, and CaF2 as main coating materials have excellent weldability and are widely used for welding thick mild steel plates and high-strength steel.

However, this type of low-hydrogen coated arc welding rod has poor workability, and in particular, the shape of the bead toe is poor as shown in Figure 1, so the stress concentration on the bead toe becomes large and the resistance to repeated loads increases. This causes a decrease in fatigue strength.

In other words, Fig. 1 shows the contact angle between the steel plate 1 and the bead 2 as θ, and the smaller the contact angle θ, the more a kind of notch effect occurs at the bead toe, and stress concentration occurs here. , fatigue strength decreases.

For example, Figure 3 shows the results of investigating the relationship between the contact angle θ and fatigue strength at the bead toe of a rib cruciform joint using HT 80 steel. It can be seen that the strength is significantly improved.

Therefore, the weld bead was welded using a welding rod that had the shape of the bead toe shown in Fig. 2, and the contact angle θ was set to l600.
By doing the above, the fatigue strength of the welded portion can be significantly improved.

Therefore, it is desired to develop a welding rod that is excellent in welding workability and can have a contact angle θ of 1600 or more at the weld toe.

As a result of various studies regarding the development of such a welding rod, the present inventors found that 1 to 6% of fluorotetrasilicon mica was added to the coating material.
By including it, the viscosity of the slag was increased, workability was improved, and the contact angle θ was successfully increased to 160° or more.

That is, Figure 4 shows CaCO355%, CaF23%, M
Fluorine tetrasilicon mica KMg2.5 (Si401o)F2 and similar fluorine to the coating material containing n 3%, SilO%, Fe I4 to 21%, 8% water glass in terms of solid content. Phlogopite KMIg 3 (
A I S l 3 01 o ) F 2 to 0, 0.
5, 1.0, 3.0, 60, and 7.0%, respectively, were prepared and fillet welded to a 20 mm thick high-tensile steel plate, and the toe of the resulting weld bead made contact. This figure shows the results obtained by measuring the angle θ and the viscosity (η) of the slag at 1450° C. using a rotation method.

As is clear from the figure, when fluorotetrasilicon mica is 1% or more, η increases, and θ becomes 160° or more, and the effect of fluorotetrasilicon mica can be seen.

However, if it exceeds 6%, the slag becomes too viscous and difficult to weld.
The disadvantage is that the beads are difficult to line up.

Further, even if fluorine phlogopite, which is similar to fluorine tetrasilicon mica, is added, it is not very effective and the contact angle θ cannot be improved to 160° or more.

This is probably related to the presence or absence of AI in the ingredients, and it can be seen that the addition of fluorotetrasilicon mica, which does not contain AI, is important.

In other words, it is thought that this is because the viscosity of the slag does not increase when a small amount of synthetic fluorinated mica containing AI is added.

Note that the welding rod using fluorine phlogopite is known as that described in Japanese Patent Application Laid-Open No. 52-70958, but as mentioned above, when added in small amounts, it tends to reduce the viscosity of the slag. As a result, the shape of the bead toe deteriorates, and no improvement in fatigue strength can be expected.

The present invention is a completely new low-hydrogen welding rod obtained based on such knowledge, and the shape of the toe of the weld bead is made extremely smooth as shown in Figure 2, thereby reducing fatigue in the welded part. This can significantly improve strength.

That is, in the present invention, 1 to 6% of fluorotetrasilicon mica is essential, and a total of 8 to 55% of one or both of CaCO3 and MgCO3, 23 to 22% of CaF, and 2 to 1% of Mn.
3%, one or both of Si and Ti, total 0.5~
A low hydrogen-based coated arc welding rod made by coating a mild steel core wire with a coating agent containing 11% Fe, 50% or less Fe, and 5 to 10% water glass as the solid content remaining after moisture is removed from the water glass. It is.

The present invention will be described in detail below.

First of all, the reason why the addition of fluorotetrasilicon mica, which is the most important essential component in the present invention, is set at I to 6% is as described above.If it is less than 1%, the addition effect is poor,
%, the slag viscosity becomes too high.

CaCO3 or MgCO3 is added as a slag forming agent or a gas generating agent, but if the total amount of either or both is less than 8%, pores are likely to occur in the weld metal, and conversely, if the total amount exceeds 55%, arcing is unstable and the bead shape is poor.

CaF2 is added to reduce the amount of hydrogen in the weld metal and as a slag forming agent, and if it is less than 3%, the slag fluidity will be poor.
In addition, pores are likely to occur in the weld metal, and conversely, if it exceeds 22%, the slag envelopment will be poor and the bead shape will be poor.

Mn is added as a deoxidizing agent and to improve weldability, and the addition form may be ferroalloy (Fe-Mn), but if it is outside the range of 2 to 13%, pores will occur in the weld metal and the toughness will deteriorate. to degrade.

Si and Ti are stronger deoxidizers than Mn, and by adding one or both in a total amount of 0.5 to 11%,
Better weldability can be obtained.

In addition, to add Si and Ti, alloy iron (Fe-S
i, Ee-Ti).

Fe is a general term for the Fe content contained in iron powder or ferroalloy, and is added to improve welding efficiency, and the more it is, the more the purpose is achieved, but if the total exceeds 50%, , 50% or less is appropriate because the arc blowing becomes weaker and the bead becomes convex.

Water glass has the role of a binder for coating and a lubricant during coating, and one type of ordinary soda water glass, potash water glass, or a mixture of both is used, but the amount depends on the solid content. 5 to 10% is appropriate.

The welding rod of the present invention is made by coating a mild steel core wire with a coating material having the following composition.
It represents a G3523 type 1, class 1 required wire, and can be coated using conventional methods such as extrusion machine coating, and is then dried and fired to form a welding rod.

The effects of the present invention will be illustrated in more detail by Examples below.

Table 1 shows the coating composition and test results.

In the same table, A-1 to A-10 are the present invention, and B-1 to B-
No. 10 is a normal low-hydrogen welding rod and a comparative welding rod outside the scope of the present invention.

As the core wire, a mild steel core wire with a diameter of 5.0 mm and a diameter of 550 mm was used.

The test is 1. Using 6 mm t HT80 steel, A-
1 to A-5 and B-1 to B-6 are 27OA downward fillet welding, A-6 to A-10 and B-7 to B-10 are 22OA.
Horizontal fillet welding was performed at 0A.

The contact angle θ of the obtained bead was measured, and fatigue test pieces of rib cross joints shown in FIG. 5 were cut out from the welded joints of these test materials and subjected to fatigue tests at 1200 cycles/min.

These results are also shown in Table 1.

As is clear from this table, all the beads obtained by the present invention had good workability and good contact angle θ and fatigue strength, whereas those welded using the comparison rod and the conventional rod had no contact The angle was less than 1600, and the fatigue test results were also poor.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic diagrams for explaining the contact angle of weld metal, and Figure 3 shows the relationship between the contact angle and fatigue strength of the weld bead toe of the fillet weld of HT 80 kg spun steel. Figure 4 is a diagram showing the relationship, Figure 4 is a diagram showing the influence of fluorine tetrasilicon mica and fluorine phlogopite on the viscosity and contact angle of slag, Figure 5
The figure is a diagram showing the dimensions and shape of a fatigue test piece. 1: steel plate, 2: bead, θ: contact angle.

Claims (1)

[Claims] 1 Fluorine tetrasilicon mica KMg2-5 (Si40t
o) F2l~6%, total of one or both of CaCO3 and MgCO3 8~55%, CaF23~22%, M
A low-hydrogen wire made by coating a mild steel core wire with a coating material containing n2 to 13%, a total of 0.5 to 11% of one or both of Si and Ti, 50% or less of Fe, and 5 to 10% of water glass as a solid content. Series coated arc welding rod.