JPS5944157B2 - Flux for low temperature steel submerged arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flux for submerged arc welding of low-temperature steel that exhibits excellent welding workability and ensures high quality welded joints.

Ni-containing low-temperature steel such as 9% Ni steel has strength comparable to 7Okl first class high-strength steel, and also exhibits good toughness even at extremely low temperatures of, for example, -196°C, so it can be used at extremely low temperatures such as liquefied natural gas. It is extremely important as a construction material for liquid storage tanks and the like.V) As the demand for liquefied natural gas as an energy source increases, its consumption is expected to increase further in the future.

In addition, when welding construction using such low-temperature steel, the welded joints are required to have the same strength and low-temperature toughness as the base metal, so conventionally covered arc welding with a high Ni alloy as the core material was used. Manual welding methods and semi-automatic welding methods using rods with relatively low heat input were the mainstream.

However, automatic welding, which generally requires a large amount of heat input, is likely to cause hot cracking, making repair welding extremely complicated and causing serious accidents due to joint defects. However, recently, welding wires containing a large amount of Mo and having excellent hot cracking resistance have been developed (for example, the
-39453, 51-14976, 49-27
No. 732, No. 51-29104, etc.), and by using these wires, automatic welding of 9% Ni steel, etc. has become possible. However, while the above-mentioned high Mo wire provides a weld metal with excellent cracking resistance, when multi-layer welding is performed by latent arc welding in a horizontal position, the weld metal is reheated due to repeated thermal history. Microcracks are likely to occur, and bending performance is significantly reduced.

This is because low melting point Mo oxides and Ni
This is thought to be due to segregation of sulfides, etc. The present inventors have focused on the above-mentioned circumstances, and have developed a method to prevent the reheat micro-cracking and improve cracking resistance, particularly when high heat input welding is performed using a high-Ni welding wire containing Mo. Research has been progressing with the aim of developing a method that can simultaneously improve bending performance and bending performance.

As a result of these efforts, the inventors realized that the above object could be successfully achieved by using a flux with a specific composition containing rare earth elements, etc., for arc welding, and thus completed the present invention. That is, the structure of the flux for low-temperature steel submerged arc welding according to the present invention is as follows:
The metal fluoride is 10 to 30 qf (in terms of fluorine) (weight%; the same applies hereinafter), the Al is 0.5 to 5 q1), and the rare earth element is 0.
1-2#) The gist exists where it is included.

As mentioned above, the flux of the present invention is a MO-containing high Ni welding wire suitable for high heat input welding of low-temperature steels such as 9% Ni steel (particularly those containing 50% or more Ni and 10% or more MO).
It exhibits excellent characteristics when combined with
While retaining the characteristics of MO-containing high-Ni wire (excellent low-temperature strength, low-temperature toughness, hot cracking resistance, etc.), it prevents reheat micro-cracks caused by segregation of MO oxides, etc., and can be used as welded. Excellent quality weld metal can be obtained.

The functions of the essential components of the flux according to the present invention and the reason for setting the content will be clarified below.

Metal fluoride; 10 to 30% in terms of fluorine. Promotes deoxidation and desulfurization reactions during welding, and supports Al as described below.
It promotes the deoxidizing and desulfurizing effects of rare earth elements and prevents reheat microcracks in weld metal.

Since the slag-metal reaction during welding is extremely short-lived, if the amount of metal fluoride is too small, deoxidation and desulfurization will be insufficient and V) the effects of A1 and rare earth elements will not be effectively exhibited. Therefore, metal fluoride contains at least 10 qf in terms of fluorine.
) or more is required.If it exceeds 30%, welding workability deteriorates, such as poor slag viscosity and deterioration of beep shape. The most common metal fluorides are fluorite, barium fluoride, sodium fluoride, etc., and these can be used singly or in combination.
More than one species can be used in combination. Al; 0.5
~5% It is an essential component as a deoxidizing agent. It prevents the segregation of oxides at the grain boundaries in selective weld metal, improves bending performance, improves blowhole resistance, and further improves the desulfurization effect of rare earth elements as described below. It has a promoting effect.

However, if the amount of oxygen in the weld metal is large, the rare earth elements will be oxidized and consumed, weakening the desulfurization effect. In order to effectively exhibit these effects, a force of 0.5 (fl) or more is required. If the force ζ is too large, the amount of AI in the weld metal becomes excessive, the impact value at -196°C decreases, and ductility is insufficient. Since the bending performance deteriorates due to The most preferable method for adding Al is Fe-Al alloy (for example, F
Of course, the method is not limited to this, but it can be added in any form such as Al powder or an alloy with other metals. Rare earth elements;
When used in combination with 0.1 to 2% Al, it exhibits excellent desulfurization performance, prevents segregation of sulfides at grain boundaries in weld metal, and improves microcracking resistance.

If it is less than 0.1%, these effects will not be effectively exhibited, while if it exceeds 2(f), the low-temperature toughness of the weld metal will be significantly reduced.

Rare earth elements include lanthanum, cerium, praseodymium, etc. Lanthanum and cerium are the most common from the viewpoint of economy. In addition to being added as a single element, the rare earth element can also be added as a mixture with calcium-silicon or the like (for example, rare earth calcium silicon). In addition, the flux of the present invention may contain an appropriate amount of oxides such as silica sand, alumina, and limestone as slag forming agents, and may also contain an appropriate amount of alloy components to compensate for the missing components in the welding wire.

However, care must be taken because if the amount of alloy components in the flux exceeds 40%, the beep becomes convex and the slag removability decreases. The present invention is generally constructed as described above. 1. In particular, by incorporating appropriate amounts of metal fluoride, Al, and rare earth elements into flux for submerged arc welding, low-temperature steel using MO-containing high-Ni welding wire can be produced. The performance of welded parts can be significantly improved.

Next, examples of the present invention will be shown.

Example Using a welding wire with the composition shown in Table 1 and a flux with the composition shown in Table 2, welded 9#)Ni under the conditions shown in Table 3.
Multi-layer submerged arc welding of steel (JISG3l27SL9N6O) was performed.

The groove shape and build-up shape were D as shown in FIG. 1, and after welding on the front side, the root portion was arc air gouged, and then welding on the back side was performed. Table 4 shows the performance of the obtained welds.

However, the test piece should be taken from the position indicated by the broken line in Figure 2, and the test method would be as follows. The above results can be considered as follows.

Flux Shop 2: Welding workability is poor due to too much fluorine content, and micro-cracks frequently occur on the bead surface and bent surface because rare earth elements are not included. flux black 4
: The impact value is low due to too much Al content, and the bending performance is also poor due to insufficient ductility.

Flux black 5: The impact value is low because the amount of rare earth elements is too large.

Flux Black 9: Since it does not contain Al and has a small amount of fluorine, microcracks occur frequently on the surface of the pipe and the surface of the bent portion.

Flux Black 10: The amounts of Al and rare earth elements are within the specified range, but due to the insufficient amount of fluorine, microcracks occur frequently on the bead surface and the surface of the bent portion.

Flux black 11: Due to insufficient Al content, microcracks occur on the beep surface and the bent surface. Flux shop 1.
3.6.7, 8, and 12: All satisfy the requirements of the present invention, and have good welding workability, joint strength, and low-temperature toughness, and have almost no microcracks on the pipe surface and the bent surface. It is possible to obtain extremely high quality welded joints without causing any damage.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the groove shape and build-up procedure of submerged arc welding employed in the example, and FIG. 2 is an explanatory diagram showing the sampling position of physical property test pieces of the welded part.

Claims (1)

[Claims] 1. A flux for low-temperature steel submerged arc welding, characterized in that it contains 10 to 30% by weight of metal fluoride, 0.5 to 5% by weight of Al, and 0.1 to 2% by weight of rare earth elements.