JPS61279372A - Gas shielded arc welding method - Google Patents

Abstract

PURPOSE:To increase the high temp. crack resistance of a welding metal by welding an austenite group stainless steel by using the shielded gas adding N2 in Ar, He or Ar + He gas. CONSTITUTION:The stainless steel 1 of a base metal is welded with feeding a shielded gas 10 from a shielded gas nozzle 7 with feeding a welding wire 3 via a welding wire feeding roll 8. The shielded gas is fed after mixing uniformly by a mixer, etc. in advance 2-30% N2 in either Ar, He, or Ar + He inert gas. The welding head consisting of a welding torch 5 and shielded gas nozzle 7 is made in flat shape so as to come into a narrow groove. For melting sufficiently both sides of the groove the oscillating device by the magnetic deviation, etc. of the arc and the mechanism forming a bending habit to the wire 3 are installed. The high temp. crack resistance of the welding metal can thus be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gas-shielded arc welding method such as νXa welding of austenitic stainless steel.

(Prior art) Austenitic stainless steel is often used when the working atmosphere is extremely low temperature and high pressure to ensure safety against brittle fracture. In particular, when using the MrG welding method, the following five requirements must be met in order to obtain a high quality weld.

The first point is the stability of the arc during welding work in order to prevent welding defects.For this purpose, in the past, approximately 2% oxygen was added to an inert gas such as Ar, and oxides were formed on the surface of the molten pool. The formation of K provides a multistable cathode spot and stabilizes the arc.

The second point is the excellent low-temperature toughness of the weld metal, and for this purpose it is necessary to reduce the amount of oxygen and 6-ferrite in the weld metal as much as possible.

The third point is to improve the high temperature resistance of the weld metal, and for this purpose, in addition to reducing impurity elements such as p and s, conventionally it is necessary to reduce the impurity elements such as p and s, and to add δ7 elite to the entire weld metal, which can dissolve more of these elements. By containing several percent of Ni, segregation to these grain boundaries is suppressed and hot cracking is prevented.

However, the 1 to 5 requirements are contradictory, and no MIG welding method that satisfies them all at the same time has been realized to date. In other words, in order to improve the second point of low-temperature toughness, it is necessary to reduce the amount of oxygen and 17-elite in the weld metal, or because most of this oxygen is mixed in with the shielding gas, 6j) Ar is used as the shielding gas. The conventional method using +2%02 etc. was unable to reduce the level of damage from the viewpoint of arc stability. Furthermore, it has been impossible to reduce δ ferrite beyond a certain level from the viewpoint of hot cracking resistance.

Therefore, in order to solve these eight problems, we developed rare earth elements (La.

A wire (so-called activated wire) to which a small amount of (Os, etc.) is added has appeared in New Nine.

According to the MIG welding method using this wire, the amount of oxygen in the weld metal is equal to that of conventional methods. Evening low temperature toughness improves to a certain degree. However, even with this method, from the viewpoint of hot cracking resistance, it is not possible to reduce sita ferrite f to a level below that of the steel, and there is a limit to this improvement in low temperature toughness.

Furthermore, if pure argon is used as the shielding gas in this welding method, the stability of the arc is poor and welding defects often occur. Currently, in order to obtain excellent arc stability, it is necessary to use argon with several 10% helium added as a shielding gas, which also poses a problem in terms of cost.

(Problems to be Solved by the Invention) The present invention aims to improve the stability of the arc during welding during welding in the process of manufacturing a utensils made of austenitic stainless steel that are used at extremely low temperatures and under high pressure. The purpose is to provide a MIG welding method that provides excellent performance in all aspects, including low-temperature toughness and hot cracking resistance of the weld metal.

(Means for solving the problem) That is, the present invention provides an inert gas (Ar1H6+hr+
This is a shielded arc # welding method for austenitic stainless steel, which is characterized by using 2 to 30% of 'm2)'t- added to austenitic stainless steel as a shielding gas.

The characteristics of the method of the present invention include the following.

By adding nitrogen to the re-shielding gas, there is no adverse effect on the stability of the arc in a normal wire, and the arc is more stable in an activated wire than in the case of pure argon.

2) In both types of wires, nitrogen in the shielding gas is dissolved in the weld metal, improving the low-temperature toughness and hot cracking resistance of the weld metal by reducing the amount of δ ferrite and making the crystal grains finer.

The method of the present invention is applicable to various chemical aIs in which austenitic stainless steel is used! It can be advantageously applied to the production of general welded structures such as nuclear power equipment, nuclear power equipment, and space equipment.

Hereinafter, one embodiment of the method of the present invention will be described in detail with reference to FIG.

(composition) FIG. 1 shows the configuration of one embodiment of the present invention.

In Fig. 1, (kl shows the A-A cross section of (bJ. 1 is the base material stainless steel, 2 is the welding metal, 5 is the welding wire, 4 is the welding current feeding tip, 5 is the welding torch, 6 is the arc, 7 is a shielding gas nozzle, 8 is a welding wire feed roll, 9 is a welding power source, and 10 is a shielding gas.

Here, a welding head consisting of a welding torch 5 and a shield gas nozzle 7 has a flat shape so as to fit into a narrow gap (Min, 9.0 degrees). Furthermore, it has the advantage of sufficiently melting both gJUt of the groove, a mechanism for bending the welding wire, and an oscillation device that magnetically deflects the arc. Note that the welding power source 9 is a DC pulse MrG welding power source. The shielding gas 10 is an inert gas (Ar, He, Ar+H6
) and nitrogen (N2) are uniformly mixed in advance in a mixer, etc., and then fed.

Although the 19th article describes MIG welding, it can be applied to all gas-shielded arc welding such as TIG welding.

(Functions and Effects) The effects of adding nitrogen (N2)' to the shielding gas will be described. Figure 2 shows all the effects of the amount of N2 in the shielding gas on the amount of pN2 in the weld metal and the amount of N2 in the weld metal on the amount of δ ferrite in the weld metal. Oblique ff1A
ta+, (bl, (cl and (dl) are each 9% of J ferrite when the amount of N2 in the shielding gas is 0%.
, 7%, 5% and 2%.

As the amount of N2 in the shielding gas increases, the amount of N2 in the weld metal increases and the amount of δ ferrite in the weld metal decreases. If the amount of N2 in the shielding gas exceeds 30%, the arc becomes unstable and scale forms on the bead surface, making it impractical. Figure 5 shows the influence of the amount of δ ferrite in the weld metal on the toughness and hot cracking rate of the weld metal.

Normally, as the amount of δ ferrite increases, toughness decreases, but hot cracking resistance improves. However, when all N2 is added, the hot cracking resistance is good even if the amount of δ ferrite is small.

Therefore, 2 to 30% of government (N2) is added to the shielding gas.
%, it is possible to improve both toughness and hot cracking resistance. Furthermore, if 0.05% or less of Ti is added to the weld metal, the above effects will be further enhanced by the fixation of N2 and the desulfurization effect by TiS. Conversely, when T1>0°05%, the toughness decreases.

Example 5US31, a glaze of austenitic stainless steel
In the 6L MIG welding method, various performances were compared when an activated wire with all rare elements added was used and the shielding gas was changed to pure Ar and Ar+5%N2.

(Structure) A test specimen with a groove as shown in Fig. 4 was made using SUS316L steel plate 1 and M fillet 1-1, and narrow groove MIG welding was performed for 1 bus/1 layer using activated wire. Weld metal 2 was obtained.

The shielding gas was the same during welding of one specimen; in this case, pure Ar and Ar+5%N2 were used for the two specimens, respectively.

Table 1 shows the chemical composition, gas composition, and δ of the two weld metals and steel sheets.
tli-indicated. Here, the amount of δ ferrite is determined using chemical components, gas components, and Shibu-Tang's phase diagram, and the amount measured by Vermas;
! It showed the kind.

Table 2 shows the welding conditions □ Table 2 Welding conditions (function and effect) Re-arc stability comparison table 3 Shows the results of a radiographic test according to KJIS Z3104. This is Ar -1-5% as a dishield gas.
It was found that the arc was more stable when N2 was used than when pure Ar was used.

Table 3 Radiographic test results 2) Comparison of low-temperature toughness of weld metal
It shows the energy absorbed by a 2111V notched pylon impact test at a test temperature of -196C for weld metal when X6hr, 730CX6hr)i.

This allows the shielding gas to contain Ar+ under any conditions.
It was found that the low-temperature toughness of the weld metal using 5% N2 was superior to that using pure Art.

Considering the effects of nitrogen, it is thought that the eight elements in the shielding gas form a solid solution in the weld metal and have the function of reducing the amount of δ ferrite, thereby completely improving the low-temperature toughness of the weld metal. At the same time, the solid-solved nine-fold stabilizes the austenite phase and suppresses stress-induced martensitic deformation 114 at low temperatures, which is considered to improve the low-temperature toughness.

3) Comparison of hot cracking resistance of weld metals Figure 6 shows the results of a transpare strain test, which is a type of hot cracking testing method, in which hot cracking was forcibly generated.

As a result, it was found that the hot cracking resistance of the weld metal is better when Ar + 5% N2 is used as the shielding gas than when pure Ar is used, no matter which parameter is compared.

Considering the effect of nitrogen, it is found that when nitrogen exists in a large amount in weld metal, it has a sudden effect on high temperature machining resistance by reducing the amount of δ-ferrite, but if it exists to a certain extent, Since the effect of making T-fine grains is stronger, it is thought that the propagation of hot cracking was suppressed and the hot cracking resistance was improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the configuration of one embodiment of the present invention, and Fig. 2 shows the effect of the amount of N2 in the shielding gas on the amount of N2 in the weld metal and the effect of the amount of δ ferrite in the weld metal on the amount of δ ferrite in the weld metal. Figure 5 is a diagram showing the influence of N2 i, Figure 5 is a diagram showing the influence of the amount of 5 ferrite in weld metal on the toughness and hot cracking rate of weld metal, and Figure 4 is a diagram showing a preferred test piece in an example of the present invention. , FIG. 5 is a chart showing the low-temperature toughness effect of the weld metal of the test piece of FIG. 4, and FIG. 6 is a chart showing the effect of hot cracking resistance of the weld metal of the test piece of FIG. 4. Sub-Agent 1) Meifuku Agent Ryo Hagiwara - Sub-Agent Atsushi Anzai Figure 6

Claims (1)

[Claims] A gas-shielded arc welding method for austenitic stainless steel characterized by using Ar and/or He with 2 to 30% N_2 added as a shielding gas.