JPH07299586A - Wire for gas metal arc welding for austenite stainless steel - Google Patents

Abstract

PURPOSE:To improve arc stability in welding with a low oxygen contained Ar gas and to suppress generation of oxidized scale, blow holes and spatters, in the gas metal arc welding for austenite system stainless steel. CONSTITUTION:The welding wire is such that the quantities of C, Si, Mn, S, Al, Cr, Ni and Mo are stipulated, that Li: 0.001-0.01% and if necessary, Ti: 0.01-0.1% are contained, that O, Ca and Mg are regulated to be each specific quantity or less, and that the remainder is constituted of Fe and unavoidable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas metal arc welding wire having good welding workability even when a shield gas having a low oxygen content is used in gas shielded arc welding of austenitic stainless steel.

[0002]

2. Description of the Related Art In gas metal arc welding of stainless steel, a gas obtained by adding 1 to 5% oxygen to Ar gas is used as a shielding gas for the purpose of ensuring arc stability. In actual use, when 5% is added, oxide scale is remarkably generated on the weld bead, and in multi-layer welding, the oxide scale must be removed with a grinder or the like to perform welding, and work efficiency is significantly reduced. Furthermore, oxygen causes blowholes and causes welding defects.

Further, it is difficult to stabilize the arc with about 1% oxygen, and spatter is easily generated.
In many cases, the one containing the degree was used. However, this 2% oxygen-containing Ar gas also had problems such as the generation of oxide scale on the weld bead and the formation of blowholes similar to the case of 5%. To summarize the current situation, it is better to have a low oxygen content for high quality gas shielded arc welding, and it is better to have a high oxygen content for ensuring arc stability.

However, even if a shield gas having a high oxygen content is used, some wires have poor arc stability, and the oxygen content is not the only factor that determines arc stability. Currently, the reason why there is a difference in arc stability between wires of similar major components when welding is performed under the same conditions is that the arc stability deteriorates as the amount of trace components, especially Al, added increases. Is known. That is, it is described in the patent application of the welding wire for stainless steel of each welding material manufacturer that the arc stability is improved by controlling the addition amount of Al. Since Al is used as a deoxidizing agent when the material of the wire is made by melting, any amount of wire may be included.

A change in the amount of Al added has a great influence on the arc stability, particularly on the droplet transfer characteristics. FIG. 1 is a diagram showing a droplet transfer state at the tip of the welding wire, which is a case of a wire having a large amount of Al added and poor arc stability. As shown in FIG. 1, the droplet 2 becomes a teardrop shape and moves intermittently with respect to the pool 4 on the base material side, and when the droplet moves, spatter is generated with the momentum. The welding bead at this time is
Meandering is seen and the uniformity is lost. In the figure, 1 is a welding wire and 3 is an arc.

FIG. 2 is a view similar to FIG. 1, but shows the case of a wire in which the added amount of Al is small and the arc stability is good. The droplets 5 do not become teardrop-shaped, but flow down from the melting buckwheat to the pool 4 of the base material and perform stable transfer. Since the transfer is continuous, no spatter is generated and the weld bead is stable.

The reason why these differences occur will be described below.
In the case of stainless steel, a stable Cr oxide film is formed on the surface of the material, which serves as a protective film and exhibits high corrosion resistance. At the time of welding, this Cr oxide film has already been generated on the outermost surface of the molten wire melted by the arc by the shield gas containing oxygen, and causes surface tension on the surface of the molten wire. However, since it is not completely formed so as to cover the surface of the molten wire, it does not become teardrop-shaped and fluidity is secured. However, by adding a trace amount of Al, the protective film forms a strong film in a shorter time. For this reason, the surface tension of the surface of the droplet increases, and the droplet tends to be teardrop-shaped. This tendency becomes stronger as the added amount of Al increases.

[0008] Such a difference is a thin plate (thickness of 2 mm or less)
It has a great effect on welding in the short-circuit transition area, which is used for welding. In the case of a thin plate, the plate will melt down if welded at a high current, so the current is reduced (at least 150 A or less), the voltage is further reduced to shorten the arc length, and droplets are transferred to the base metal at a fine pitch to transfer to a short circuit. Weld. At this time, if an oxide film of Cr is formed on the surface of the droplet, the electrical conductivity of the oxide film deteriorates, arcing is less likely to occur, the arc state becomes unstable, and the droplet tip (if no arcing occurs, When the wire tip) contacts the base material, a spark is generated and a large amount of spatter is generated at this time. In the case of short-circuit transfer, this state is particularly serious, and the melted portion mainly composed of droplets is instantly blown off, and the arc may be interrupted.

[0009]

In view of the above circumstances, the present invention improves arc stability during welding with Ar gas containing a low oxygen content of 2% or less, and produces oxide scales, blowholes, and spatters. The purpose is to suppress.

[0010]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, and in% by weight, C: 0.015 to 0.1
5%, Si: 0.2 to 1.0%, Mn: 1.0 to 3.
0%, S: 0.004 to 0.015%, Al: 0.00
2 to 0.01%, Cr: 11 to 32%, Ni: 3.0 to
22.5%, Mo: 0.001 to 4%, Li: 0.00
1 to 0.01%, if necessary, Ti: 0.01 to 0.1
%, O: 0.01% or less, Ca: 0.005%
Hereinafter, the gas metal arc welding wire for austenitic stainless steel is characterized in that Mg is regulated to 0.005% or less and the balance is Fe and inevitable impurities.

[0011]

The present invention is characterized in that by controlling Al and adding Li, the surface tension and the electrical conductivity are controlled to improve the fluidity of droplets. That is, by adding the Li element, the generation rate of the Cr oxide film formed on the droplets when the wire was melted was controlled, the fluidity of the droplets was secured, and excellent workability was realized.

When the wire is melted into droplets, initial oxidation occurs first. This is an extremely thin oxide film generated on the outermost surface of the droplet, which blocks the outside air from the inside of the droplet. At this time, the surface tension is not so large as to affect the transfer state of the droplet. Subsequent oxidation is carried out by oxygen penetrating in the form of ions. Therefore, the oxygen partial pressure becomes low, and thereafter, the element that oxidizes at a low oxygen partial pressure is predominantly oxidized. Among the main components, Cr is selectively oxidized. When Li is added to this, it oxidizes at an oxygen partial pressure lower than that of Cr, so even if added in a small amount, the binding force with oxygen is large.

FIG. 3 is a diagram schematically showing an oxide film of Cr ₂ O ₃ . Further, FIG. 4 is a diagram schematically showing an oxide film of Cr ₂ O ₃ when Li is added. Li
In the case of no addition, dense and electrically balanced Cr ₂ O ₃ as shown in FIG. 3 is generated to form a strong oxide film and further oxidation is stopped. On the other hand, when Li is added, Li forms a solid solution with Cr ₂ O ₃ to form an oxide film, which impairs the electrical balance and delays the formation of a dense oxide film. Cr
The rate of oxidation is reduced and the complete formation of a coating over the droplet is delayed. As a result, the fluidity of the droplets is ensured, and the deterioration of the electric conductivity due to the formation of the Cr oxide film can be avoided.

The above effects will be emphasized when the oxygen partial pressure is further low and therefore the oxygen content in the shield gas is low. If a shielding gas with a low oxygen content can be used, welding with a metallic luster and few blow holes becomes possible. The action of each component of the wire of the present invention will be shown below.

C: C is 0.015% for increasing the strength.
Although the above is added, if too much is added, carbides are generated and the toughness is reduced. Therefore, it is set to 0.15% or less.

Si: 0.2% or more is added because it has the effect of suppressing the surface tension of the droplets, but it is liable to cause a decrease in the strength of the weld metal, and it is 1.0% or less.

Mn: 1.0% or more is added as a deoxidizing and desulfurizing agent, but if it is too much, corrosion resistance and oxidation resistance deteriorate, so it is made 3.0% or less.

S: There is an effect of lowering the surface tension of the droplet, but if it is less than 0.004%, the effect is small, and
If it exceeds 015%, sulfides may be generated at grain boundaries, so the content is made 0.004% to 0.015%.

Al: Although added as a deoxidizer, it has the greatest effect on the migration characteristics of the droplets, and the minimum amount of the deoxidizer is 0.
Even at about 002%, the oxide film of the droplet is strengthened to form a ball-shaped droplet. Too much addition impairs droplet transfer, so 0.01%
Below.

Cr: An essential component of stainless steel, which forms a passive film and improves oxidation resistance and corrosion resistance.
If it is less than%, the characteristics cannot be sufficiently retained, and if it exceeds 32%, sigma phase is likely to crystallize and workability deteriorates in the wire manufacturing process, so the content is made 11% to 32%.

Ni: 3.0% or more is added in order to stabilize austenite by an austenite forming element and improve corrosion resistance and toughness, but since workability deteriorates, 2
2.5% or less.

Mo: 0.001% or more is added in order to strengthen the structure and improve the corrosion resistance and creep strength.
If it exceeds 4%, the formation of sigma phase is promoted, the ductility decreases, and the workability deteriorates in the wire manufacturing process.
% Or less.

Li: Li enters between the oxide films of Cr,
Since the oxidation rate is reduced, the inhibition of droplet transfer due to the oxide film is suppressed, and the electric conductivity is improved by making the oxide film of Cr incomplete. However, if the addition amount is too large, the corrosion resistance due to the Cr oxide film is deteriorated, so the addition amount is limited, and the content is made 0.001 to 0.01%.

O: O is 0.01% or less in order to weaken the grain boundaries by forming inclusions and oxides at the grain boundaries.

Ca, Mg: Ca and Mg are strongly oxidative, and oxidize at the earliest point of the droplet to form slag, which makes the electrical conductivity of the droplet unstable. Therefore, each is made 0.005% or less.

Ti: An element added as required.
TiO ₂ is well known as a semiconductor oxide, which shows that it has good electrical conductivity when oxidized. Therefore, if Ti is added by 0.01% or more, this effect can be obtained.
Improves arc stability, spatter generation, and bead appearance. However, if it is too much, it affects the structure of the weld metal, so it is made 0.1% or less.

[0027]

EXAMPLE The wire of the component according to the present invention and the wire prepared as a comparative example were compared for welding workability by bead-on-plate. Table 1 shows the welding conditions at this time. In addition, in order to make the arc unstable easily, the shield gas used Ar + 0.5% O ₂ with a small oxygen content. In addition to normal conditions, current and voltage conditions
In order to investigate the short-circuit characteristics, the short-circuit transition condition was also implemented.

[0028]

[Table 1]

Table 2 shows the chemical composition of each wire, and Table 3 shows the evaluation of welding workability under the above-mentioned welding conditions. A1 to A6
Is a wire according to the invention.

[0030]

[Table 2]

[0031]

[Table 3]

The wire symbol A1 is a typical general-purpose brand component whose basic component is stainless steel, to which Li is added. Arc stability is good and no spatter is generated. As for the short-circuit characteristic, the droplet transfer state is stable. The bead appearance after welding has a metallic luster and is very good.

A2 is obtained by adding Ti to the Al component. Good arc stability, spatter generation, and bead appearance. In the case of this component, the short-circuit characteristic is very good, and the generation of spatter is further reduced as compared with Al.

A3 to A6 are different from each other in the main component range, and Li is added to each, and the arc stability is good, spatter is not generated at all, and the transition state at the time of short circuit is stable. The bead appearance was also metallic luster.

On the other hand, Comparative Example B1 is a general-purpose brand component in which Al is restricted. Compared to the present invention, the arc stability becomes worse and spatter is generated accordingly.
As for the short-circuit characteristics, the transition state becomes unstable and spatter becomes large. The bead appearance has a metallic luster.

B2 has a large content of Al as a general-purpose component. The arc is extremely unstable, has large vertical movements, and produces large spatters. The transitional state of the short-circuit characteristics is also very unstable, and large amounts of spatter are generated.
Overall, worse than B1. The bead appearance is metallic luster.

B3 is added with Li in an amount larger than that of the present invention, and has very good arc stability, spatter generation, and short-circuit characteristics. However, the bead appearance is oxidized to gray.
This is because the formation of the Cr oxide film was delayed and the protective effect was inferior.

[0038]

EFFECTS OF THE INVENTION By using the wire having the composition of the present invention, good arc stability can be obtained even when a shield gas having a small oxygen content is used, and short-circuit transfer welding with a small amount of spatter can be performed, which is effective. A bead with little oxide scale is obtained, and high-quality gas metal arc welding can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a droplet transfer state when a large amount of Al is added.

FIG. 2 is a diagram showing a droplet transfer state when the amount of Al added is small.

FIG. 3 is a diagram schematically showing a Cr ₂ O ₃ oxide film.

FIG. 4 is a diagram schematically showing an oxide film of Cr ₂ O ₃ when Li is added.

[Explanation of symbols]

 1 Welding wire 2,5 Droplet 3 Arc 4 Pool

Claims (2)

[Claims] 1. By weight%, C: 0.015 to 0.15% Si: 0.2 to 1.0% Mn: 1.0 to 3.0% S: 0.004 to 0.015% Al : 0.002 to 0.01% Cr: 11 to 32% Ni: 3.0 to 22.5% Mo: 0.001 to 4% Li: 0.001 to 0.01% contained, O: 0 0.01% or less Ca: 0.005% or less Mg: 0.005% or less, the balance being Fe and unavoidable impurities, the gas metal arc welding wire for austenitic stainless steel characterized by the above-mentioned. 2. The gas metal arc welding wire for austenitic stainless steel according to claim 1, further containing Ti: 0.01 to 0.1% by weight.