JPS59166382A - Welding method of joint formed of different materials - Google Patents

Abstract

PURPOSE:To prevent generation of stress corrosion cracking in a weld zone in the stage of welding an austenitic stainless steel and a carbon steel by beveling much the edge on the austenitic stainless steel side. CONSTITUTION:The edge on an austenitic stainless steel side is beveled much and welding is so accomplished that the angle theta (acute angleABB') at the junction point B of a carbon steel 2 and a deposited metal 3 attains <=90 deg. in the stage of welding different metallic materials such as the steel 1 and the carbon steel 2 from one side by using a welding rod of an austenitic stainless steel or an inconel welding rod. The stress corrosion cracking in the joint part between the austenitic stainless steel and the carbon steel is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method for dissimilar materials such as carbon steel and austenitic stainless steel, and particularly to a welding method that can prevent stress corrosion cracking.

When welding a combination of carbon steel and austenitic stainless steel from one side using an austenitic stainless steel welding rod or an Inconel welding rod, weld with a bevel only on the carbon steel side as shown in Figure 1 for ease of workability. was often done.

In Fig. 1, 1 is austenitic stainless steel;
2 is carbon steel and 3 is weld metal.

In the above-mentioned groove shape, if there is a root gap, the weld root portion may form insufficient penetration in the form of a sharp notch on the austenitic stainless steel 1 side, as shown in FIG. Stresses such as welding residual stress, thermal stress during equipment operation, and internal pressure act, and when C/- is present in the fluid on the root side, stress corrosion cracking often occurs from the notch.

In the case of such a combination of dissimilar materials, an electrical circuit is formed in the meat, carbon steel is corroded, austenitic stainless steel is cathodically protected, and stress corrosion cracking is generally not likely to occur.

However, the root shape as shown in Fig. 1 above, that is, a sharp notch is formed at the junction A of the austenitic stainless steel 1 and the weld metal 3, and moreover, the corrosion protection current from the carbon steel 2 is difficult to flow into this part. If the root shape forms a relative spatial position, no corrosion protection effect will be obtained, and the root shape will be extremely disadvantageous in terms of longevity against stress corrosion cracking.In other words, the weld root shape will be highly susceptible to stress corrosion cracking. I can say it.

The present invention has the following advantages:
This paper proposes a dissimilar metal joint welding method that can reduce stress corrosion cracking susceptibility by using an improved notch shape and cathodic corrosion protection effect depending on the relative spatial position of the material. .

That is, in the present invention, when welding a combination of carbon steel and austenitic stainless steel with an austenitic stainless steel welding rod or an Inconel welding rod,
The present invention relates to a dissimilar metal joint welding method characterized in that the welding is performed so that the austenitic stainless steel side has a large groove and the angle at the joining point between the carbon steel and the weld metal is 90° or less.

Hereinafter, the method of the present invention will be explained in detail using the accompanying drawings.

FIG. 2 is a schematic diagram showing a joint shape in an embodiment of the method of the present invention. In FIG. 2, the same symbols as in FIG. 1 have the same meanings as in FIG.
In the figure, if the surface on the austenitic stainless steel 1 side passing through the junction A is P, and the surface on the carbon steel 2 side passing through the junction B is BB', then /ABB'=6.

The angle 0 is determined by the austenitic stainless steel 1. as shown in FIG. 1.2. It changes depending on the amount of groove to be removed from the carbon steel 2. That is, in Fig. 1, the groove on the carbon steel 2 side is larger than on the austenitic stainless steel 1 side, and the weld root shape in this case is e>qa as shown in the figure.
On the other hand, in FIG. 2, there are more grooves on the peaustenitic stainless steel 1 side than on the carbon steel 2 side, and the weld root shape becomes θ<90°.

The relationship between the magnitude of this - and stress corrosion cracking susceptibility is explained in the third section.
Shown in Figure (A). Note that the meaning of the data in Figure 3) is as shown in Figure 5 (B).

The data in Figure 5 (5) is 5EI41 and 5US
A 504 plate was welded from one side with a D609 welding rod, and the welding groove shape was changed to change the 0. The test piece was a 3-point bending test method with the root part as the bending surface. Measurements were taken by applying stress and using a 42% Mg, O/2 boiling aqueous solution as a corrosive liquid.

From Figure 3), it can be seen that cracks at the joint point A no longer occur when θ is 90°. The reason for this is that as θ decreases, the shape factor of junction A becomes smaller.
In other words, since the notch shape formed at the joint point becomes gentler, it is thought that the cracking susceptibility is naturally lowered due to a decrease in stress concentration. By the way, 0=120
' and junction point A at 135° and 6=6D.

Since the joint point B at 0-60° and 45° has the same notch shape, the sensitivity and degree of cracking due to stress concentration are the same.
The cracking life at θ-120° and 135° is clearly greater.

In the case of e>90°, as mentioned above, the junction point A
The notch shape becomes sharp, and the anti-corrosion current from the carbon steel 2 does not flow into the joint A part, and the cathodic corrosion protection effect cannot be obtained. This shows that the corrosion protection current from the carbon steel 2 flows into the junction point A, and cathodic corrosion protection is achieved. Since the ratio of surface BB' on the anode side (carbon steel 2) to surface AA'+AB is larger than that in Figure 1, the current density flowing into the cand side is higher in Figure 2 than in Figure 1. , it is easy for the water to flow to the junction point A.

As described above, according to the method of the present invention, the following effects are achieved,
Significantly reduces stress corrosion cracking susceptibility.

(1) When the shape factor of the joint point A is small, stress concentration is relaxed and cracking susceptibility is reduced.

(2) The thickness of the welded metal 3 in the cross section including the junction point A increases, and the applied stress at the junction point A decreases.

(3) The cathode side (of the surface of the anode side (carbon steel)
Since the ratio of the austenitic stainless steel and weld metal to the surface is larger than that in the conventional case, the density of the corrosion protection current flowing from the carbon steel to the austenitic stainless steel and the weld metal is larger than that in the conventional case. .

(4) Due to the shape, corrosion protection current from the carbon steel (., anomad side) easily flows into the junction A.

(5) Junction B forms a notch with the same shape as junction M in FIG. 1, but the anticorrosion current from the anode side tends to flow through junction P.

Note that Figure 4 is shown for reference, and the steam jacket (carbon steel) 2 side is beveled and the stay (SU
B304) This is a schematic diagram showing the state of stress corrosion cracking that occurred after about 3 years of use when welded with 1, and racks as shown in 4 had occurred.

As explained above, when welding austenitic stainless steel and carbon steel from one side with an austenitic stainless steel welding rod or an Inconel welding rod, the method of the present invention has a notch shape that has extremely low susceptibility to cracking due to stress concentration, and an art material. By using a weld root shape that overlaps the cathodic corrosion protection effect depending on the relative spatial position of the question, stress corrosion cracking at the joint between austenitic stainless steel and carbon steel can be prevented, and the service life in actual use can be reduced. can be significantly extended.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of weld route shapes in dissimilar metal joints, where FIG. 1 is a conventional welding route and FIG. 2 is an embodiment of the method of the present invention. Figure 3) is a diagram showing experimental data to show the effects of the present invention in comparison with the conventional method, Figure 3 middle) is an explanatory diagram of the data in Figure 3 (4), and Figure 4 is a diagram showing the conventional mode. FIG. 2 is a schematic diagram showing the state of stress corrosion cracking that occurred in a steam jacket and a stay after welding and using an actual machine for about three years. Sub-agent 1) Meikoku agent Ryo Hagiwara - , 8-1 Figure 2 A B'

Claims (1)

[Claims] When welding a combination of carbon steel and austenitic stainless steel from one side with an austenitic stainless steel welding rod or an Inconel welding rod, the angle at the joining point of the carbon steel and weld metal is 900 by making a large groove on the austenitic stainless steel side. A dissimilar metal joint welding method characterized by welding as follows.