JPS5914315B2 - Low hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-hydrogen coated arc welding rod that has excellent welding workability and joint performance.

There is an increasing demand for 50 kg/md class high tensile strength steel plates as steel plates for ship hull structures. In welding this type of steel plate, a low-hydrogen welding rod is used to prevent delayed cracking caused by diffusible hydrogen. However, when using a low hydrogen welding rod,
Joint performance, especially paint resistance (prevention of pits, etc.) and weldability are poor, and it is often subject to rework 10 welding.
On the other hand, low-hydrogen welding rods with improved joint performance (paint resistance) have been developed, but they have drawbacks such as a convex bead, which worsens the appearance, and stress concentration at the upper end of the bead. . 15 The present invention was made in view of the above-mentioned circumstances, and provides a low-hydrogen coated arc welding rod that can improve the appearance of the bead and the stress concentration at the upper end while maintaining excellent joint performance. The purpose is to provide.

In addition, arc stability, undercut resistance, and 0 slabs
The present invention aims to provide a low hydrogen-based coated arc welding rod with excellent peelability. However, the low hydrogen-based coated arc welding rod according to the present invention includes MgO: 5 to 24%, TiO
2: 6-25%, SiO2: 3-20%, metal fluoride: 3-2515%, CO2 in the form of MgCO3, MgC
5 to 25% in terms of 03, oxides of Fe and/or Mn: 2 to 10%, one or more elements selected from Si, Mg, Al and Ti: 0.5 to 8%, Mn: 2-1
0%, respectively, and the content of (Fe oxide and Mn acid 90ide) is Y%, [(Si, Mg, Al, Ti) + 1
15Mn] content is X%, the relationship between X and Y satisfies the following formula: (X/2-1)≦Y≦(X/
2+6)? 5 It is made by coating a steel core wire.

That is, in the present invention, the above-mentioned object has been achieved by specifying the composition of the coating material, and by kneading this with a water glass-based binder and applying it to the steel core wire, high-tensile steel sheets can be formed. A low hydrogen-based coated arc welding rod with excellent performance for practical use is obtained.

The basis for setting the numerical range in the present invention will be described below. 1M
g0: 5-24% MgO acts as a slag forming agent and a viscosity modifier and improves the encapsulation properties of the slag.

Also, since it is a basic oxide, other acidic equivalent substances (Si
There is no risk of deteriorating the mechanical properties of the weld metal unlike O2, TiO2, etc.).

If it is less than 5%, the above-mentioned effects will not be exhibited significantly, and undercuts will occur frequently due to insufficient viscosity of the slag, or the basicity of the slag will decrease, resulting in deterioration of the mechanical properties of the weld metal.

On the other hand, if it exceeds 24%, the viscosity of the slag will increase, the encapsulation will deteriorate, and the beads will become convex. Note that MgO sources include dolomite, MgCO3, and the like in addition to clinker and silicates. 2Ti02: 6 to 25% It functions as a slag forming agent and a viscosity modifier to improve slag envelopment.If it is less than 6%, slag becomes insufficient and becomes convex beads, undercuts are likely to occur, and slag removability is reduced. to degrade.

On the other hand, if it exceeds 25%, the fluidity of the slag increases and the slag tends to take the lead and form a two-stage bead.In addition, the apparent amount of slag increases, the appropriate welding current value increases, and undercuts due to stick burn occur. and pits occur frequently. 3Si
02: 3 to 20% It acts as a slag forming agent and a viscosity modifier, and is a component that has a particularly large effect on viscosity.If it is less than 3%, the fluid state of the slag becomes unstable and the appearance of the bead deteriorates. If it exceeds 20%, the slag becomes so hard that it becomes extremely difficult to peel it off.Also, since it is an acidic oxide, the toughness of the weld metal deteriorates.

4-metal fluoride: 3-15% Specific examples include CaF2, AlF3, MgF2, NaF
These may be used alone or in combination of two or more types.

These have the function of reducing the amount of diffusible hydrogen in the weld metal and improving cracking resistance, as well as preventing the formation of pits and blowholes caused by rust, oil, fat, paint, etc. attached to the surface of the base metal. If it is less than 3%, the above-mentioned functions will not be exhibited significantly, and cracking resistance will decrease due to an increase in the amount of diffusible hydrogen, and pits and blowholes due to rust, oil, paint, etc. will be likely to occur.

On the other hand, if it exceeds 15%, the fluidity of the slag increases, making it easy to form convex beads and impairing isopodal properties. 5MgC03:5
~25% MgCO3 acts as a gas generating agent and is a component for protecting the weld metal from the atmosphere.

MgO transferred to slag after decomposition due to arc heat does not deteriorate workability. If MgCO3 is less than 5%, the amount of CO2 gas generated is too small, causing shield failure and causing repeat pits, and the toughness of the weld metal deteriorates due to absorption of nitrogen gas. On the other hand, if it exceeds 25%, the amount of CO2 gas generated is sufficient, but the arc becomes unstable and arc breakage occurs frequently, joint defects such as undercuts are likely to occur, and the viscosity of the slag increases. The encapsulation property decreases and the bead becomes convex. DFe and/or Mn oxide: 2 to 10% Specific examples include FeO, . Fe2O3, M
nOlMnO2, etc., and since all of these have the same effect, they can be used alone or in an appropriate combination of two or more.

Oxygen contained in these oxides generates CO gas or CO2 gas by reaction with carbon in the molten metal, producing porous molten slag, and therefore these are hereinafter referred to as oxidizing oxides. As a result, the apparent volume of the slag increases, the encapsulation of the slag is greatly improved, and a beautiful bead shape is guaranteed. In order to exhibit these effects significantly, it is necessary to add 2% or more; if it is less than 2%, convex beads are likely to be formed due to a lack of apparent slag amount, and underfilling may occur due to a decrease in encapsulation. It becomes easy to cause cuts, etc. On the other hand 10
If it exceeds %, the apparent amount of slag increases too much, causing problems of leading slag and two-stage beads, and excess oxygen, leading to the generation of blowholes due to insufficient deoxidation. cormorant
Mn: 2-10% Mn is blended as metal Mn or ferromanganese, and has both the function as a deoxidizing agent and the function as an alloying element.

However, in the case of a low-hydrogen welding rod for high-strength steel welding as in the present invention, it plays a strong role as an alloying element for improving the mechanical properties of the weld metal. If it is less than 2%, the mechanical properties (impact strength, elongation, squeezing properties, etc.) of the weld metal cannot be sufficiently improved, and the suitability for welding high-strength steel cannot be satisfied.

On the other hand, if it exceeds 10%, hot cracking properties will decrease. 8Si.
Mg. One or more of A1 and Ti: 0.5 to 8% It is blended as metal powder or alloy powder such as ferroalloy, and has a strong deoxidizing effect.

Since the deoxidizing effect is stronger than that of Mn, these elements act as deoxidizing agents when coexisting with Mn, increasing the yield of Mn in the weld metal. If it is less than 0.5%, blowholes tend to occur due to insufficient deoxidation, and the yield of Mn in the weld metal also decreases.

On the other hand, if it exceeds 8%, oxygen for generating CO and CO2 gas will be consumed, the apparent amount of slag will be insufficient, the encapsulation will deteriorate, and undercuts will likely occur. In addition, it is preferable to incorporate an appropriate amount of iron powder into the coating material, if necessary, because it improves arc stability and increases welding efficiency by increasing the amount of deposited metal.

However, if the amount of iron powder is too large, the spread of the arc and the blowing strength will deteriorate, and the encapsulation of the slag will decrease, making it easier to form convex beads, so it should be kept at 60% or less.
By the way, in the present invention, as explained in 6, 7, and 8 above, an oxidizing oxide (Fe.Mn oxide) and a deoxidizing component (Si.Mn oxide) are used.
g. Although it is essential to specify the content of Al, Ti, and some of Mn), it is necessary to balance the amount of oxygen in the oxidizing oxide and the deoxidizing component to ensure a proper bead shape. It was confirmed that this should be considered. In other words, if the deoxidizing component is relatively too small and there is an excess of oxygen, the apparent amount of slag becomes too large and two-stage convex beads are likely to be formed.On the other hand, if there is a lack of oxygen, the apparent amount of slag It becomes insufficient and a simple convex bead is formed. Therefore, in order to ensure an appropriate range of quantitative balance between the oxidizing oxide and the deoxidizing component, the following confirmation experiment was conducted. That is, since almost all of the oxides of Fe and Mn act as oxidizing oxides, the content of oxidizing oxides (Y) is set at a certain level, and among the deoxidizing components, Si, . Mg,. Al,. Almost all of Ti acts as a deoxidizing agent, and 4/5 of Mn is retained in the weld metal and 1/5 is consumed as a deoxidizing agent.
X) was used to examine the effects of X and Y in the coating on the bead shape.

The results are shown in Figure 1.

However, the experimental conditions and criteria were as follows. [Experimental conditions] Other coating components: (mixing ratio) Core wire: Mild steel, 5.5 mm (I) x 7 OO mml Coverage rate:
Approximately 43% test board: 12t x 100W x 7501 (M77
! ), SM5OA (C=0.39%) 20 μ of wash primer applied to the surface Joint shape: See Figure 2 Welding method: Gravity welding, rod operation ratio 1.2 times Welding current:
A. C. 24OA [Judgment Criteria] ○: Flat and good bead (see Figure 3)
(See figure) △: Intermediate shape between the above ○ and × As is clear from the results in Fig. 1, X. ! l:. Even if each value of Y satisfies the requirements of the present invention, the Y value is (X/2
If the value exceeds +6), the bead shape will deteriorate;
Even if the value is less than 2-1), a consistently good bead shape cannot be obtained.

However, by setting the blending amount so that the Y value falls within the range of (X/2+6) and (X/2-1), it is possible to reliably obtain a beautiful bead that is flat and has excellent isopodal properties. The present invention is roughly constructed as described above, and by specifying the component composition of the coating material as described above, it is possible to ensure excellent welding workability (arc stability, slag removability, etc.) and This makes it possible to prevent defects such as blowholes, pits, and undercuts as much as possible. Furthermore, by using the welding rod of the present invention, the mechanical properties of the weld metal itself are improved, and a weld bead with excellent flat and isolateral properties can be reliably obtained. Its practical value as an arc welding rod is extremely large. Next, examples of the present invention will be shown.

Example A coating material raw material having the composition shown in Table 1 was kneaded with an appropriate amount of water glass binder, and this was mixed into a 5.5 mm (!) x 7 OO mm.
A coated arc welding rod is manufactured by coating a mild steel core wire of 1 or 4.0 mmφ x 400 mm 1, and each welding rod is tested for welding workability (arc stability, slag encapsulation, bead shape, undercut) and paint resistance. (Pitt), diffusible hydrogen amount and cracking resistance were tested.

The paint resistance, diffusible hydrogen content, and cracking resistance were tested using the following methods. [Paint resistance] Test bar: 5.5mmφ x 700mu1 Test plate: 12t x 100W x 7501 (Mm), SM5
OA (C=0.39%) Apply 20μ of wash primer to the surface. Joint shape: See Figure 2. Paint resistance determined by bead on second side. Welding current: A. C. 24OA Welding method: gravity welding, rod operation ratio 1.2 times (n-3)
[Diffusible hydrogen amount]...JIS-Z-31
13 Test rod: 4.0m71L(!)X4OOm7! Ll
Welding current: A. C. 175A welding method: Manual welding Rod operation ratio: Bead length 115 mm / Rod length used 150 mm [Crack resistance] (JIS-Z-3157, U-type slit weld cracking test) Test rod: 4.0 mm (!) x 4 OO mml Welding current :A. C. 18OA Welding method: Manual welding Rod operation ratio: Bead length 60mm/Used rod length 75 gates 1 test plate:
19t x 150W x 2001 (M7!t), SM5OA
(C-0.41%) Test temperature: R. T. (about 26-30
℃) The results are shown in Table 2.

From Tables 1 and 2, the following considerations can be made.

(1) A6. 1 and 2 are representative examples of commercially available low-hydrogen-based coated arc welding rods for fillet welding.The one with good welding workability (A6.1) has poor joint performance, and the one with improved joint performance (A6. 2) has poor weldability. (2) /
F61O-21 are comparative examples that lack any of the requirements defined by the present invention, and cannot achieve the purpose of the present invention as shown below.

Corrosion 10: Due to insufficient amount of MgCO3, shield failure occurs and the number of pits increases.

Corrosion 11: The lack of MgCO3 was supplemented with CacO3, but the slag encapsulation was poor and the bead shape deteriorated (convex bead).

Waterfall 12: Arc stability deteriorates due to too large amount of MgCO3, and workability deteriorates due to arc breakage.

Waterfall 13: Due to insufficient amount of SiO2, the fluidity of the slag becomes unstable and convex beads are formed. Waterfall 14: Due to insufficient amount of metal fluoride, paint resistance and cracking resistance cannot be satisfied.

．． /F6. 15: An example in which the amount of metal fluoride is too large, and although paint resistance and cracking resistance are good, welding workability is poor.

．． /F6. 16: Because the amount of SiO2 is too large, welding workability is poor and slag removability is also poor.

Waterfall 17: Because the amount of oxides of Fe and Mn is too large, the apparent amount of slag increases, and stable slag envelopment cannot be obtained, causing problems in terms of bead shape and undercut.

Waste 18: Due to too much deoxidizing agent, the apparent amount of slag is small, and the bead becomes slightly convex due to a decrease in slag envelopment.

滉19: Since the amount of oxidizing oxides is small, the apparent amount of slag cannot be sufficiently increased, and the beads become convex.

A62O: Comparative example in which the content of each compounded component satisfies the requirements of the present invention, but the above-mentioned Y value exceeds (X/2+6) value [
Y=8.5%, (X/2+6)-8.1%], the balance between oxidizing oxide and deoxidizing agent is poor, and the apparent amount of slag is too large, resulting in a two-stage convex bead. become.

Waterfall 21: Comparative example where the Y value is less than the (X/2-1) value [Y
= 2.5%, (X/2-1) = 3.3%], a simple convex bead is formed because the apparent slag amount is insufficient.

(3) Polishing Nos. 3 to 9 are all examples that satisfy the requirements of the present invention, and are extremely excellent in both welding workability and joint performance.

[Brief explanation of the drawing]

Figure 1 shows the effect of oxidizing oxide content (Y
) and deoxidizing component content (X), Figure 2 is a sketch of the main parts showing the joint shape adopted in the paint resistance test, and Figures 3 to 5 are schematic diagrams showing the criteria for determining bead shape. It is a diagram.

Claims (1)

[Claims] 1 MgO: 5-24%, TiO_2: 6-25%, S
iO_2: 3-20%, metal fluoride: 3-15%, C
Converting O_2 to MgCO_3 in the form of MgCO_3 is 5
~25%, Fe and/or Mn oxide: 2-10
%, one or more elements selected from Si, Mg, Al and Ti: 0.5 to 8%, Mn: 2 to 10%, respectively,
And the content of (Fe oxide and Mn oxide) is Y%, [
When the content given by (Si, Mg, Al, Ti) + 1/5Mn] is set to X%, the relationship between X and Y satisfies the following formula: (X/2-1)≦Y≦ (X/2+6) A low hydrogen-based coated arc welding rod, which is kneaded with a fixing agent and applied to a steel core wire.