JPH0947886A - Non-consumable nozzle type electroslag welding method for fire resisting steel for construction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of elongation at a high temperature of a non- consumable nozzle type electroslag welding metal of a B-contained fire resisting for construction. SOLUTION: Such fire resisting steels 1, 2 for construction as containing 0.0003-0.0025% B are welded by non-consumable nozzle type electroslag welding with the oxygen partial pressure 0.35 or above for the atmosphere with which a welding slag 6 comes into contact in welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-consumable nozzle type electroslag welding method for refractory steel used in construction.

[0002]

2. Description of the Related Art A non-consumable nozzle type electroslag welding method shown in FIG. 1 is often used for diaphragm attachment welding when manufacturing a prism of a building. In this welding method, a welding wire 4 which also serves as an electrode is inserted between the steel plates 1 and 2 and the contact plate 5, and at the start of welding, a molten slag 6 having a thickness of 30 to 40 mm is produced by arc welding. 6 is a method of melting and welding the steel plates 1 and 2 and the wire 4 by Joule heat. This welding method is used because welding can be performed if only the upper side is open.

On the other hand, as a steel material for construction, a steel called a refractory steel has been developed which has improved strength at high temperature when a fire or the like occurs. For example, JP-A-5-279735,
JP-A-5-339632 and JP-A-5-33963.
Japanese Unexamined Patent Publication (Kokai) No. 3 describes various steel material components and a method for producing the same, and the steel described in Japanese Unexamined Patent Publication (Kokai) No. 2-250940 contains B: 0.0003 to 0.0025%. B is used because it has high hardenability and can reduce the amount of expensive alloy used.

Welding of B-containing steels has been reported to have reduced elongation at elevated temperatures. Therefore, for example, JP-A-3-174978 discloses a submerged arc welding method for B-containing refractory steel, and JP-A-6-262387 describes an electroslag welding wire. These promote the oxidation of B by using a welding material with a high oxygen content, and B in the weld metal
To improve elongation at high temperature.

[0005]

However, although the welding material for submerge can be produced with high oxygen relatively easily,
Electroslag welding, especially non-consumable nozzle electroslag welding, requires high oxygen wires and is difficult to manufacture. There is a wire in which an oxidant is enclosed, but this is also complicated to manufacture. Further, in the non-consumable nozzle type electro slag welding, when an oxidant is used, the molten slag becomes gradually excessive or the fluidity deteriorates, so that a long welding length may not be welded. Therefore, the present invention provides a non-consumable nozzle type electroslag welding method for preventing a decrease in elongation at high temperature of welding of B-containing refractory steel for construction without using a high-oxygen welding wire.

[0006]

The present invention provides B: 0.00
In a non-consumable nozzle type electroslag welding method for building refractory steel containing 03 to 0.0025%, the oxygen partial pressure of the atmosphere in contact with the molten slag during welding is set to 0.35 or more. It is a non-consumable nozzle type electroslag welding method for refractory steel.

[0007]

The present invention is intended to improve the elongation of a welded portion at high temperature in a non-consumable nozzle type electroslag welding method of B-containing refractory steel for construction. If the B content of the refractory steel is less than 0.0003% by weight, the quenching effect of B is not sufficiently exerted, and if it is more than 0.0025% by weight, there is a problem that the hardenability becomes too high and the toughness decreases.
B: 0.0003 to 0.0025% of refractory steel.

Usually, the atmosphere of electroslag welding is not controlled, and it is performed in an air atmosphere. When the oxygen partial pressure in this atmosphere is 0.35 or more, the effect of improving the elongation of the weld metal at high temperature is recognized. This is because when the atmospheric oxygen partial pressure is increased, the oxygen partial pressure of the molten slag is increased, the oxygen partial pressure of the weld metal is also increased, and the oxidation of B is promoted. When the atmospheric oxygen partial pressure is less than 0.35, no difference from the air atmosphere is observed.

The oxygen partial pressure in the atmosphere in contact with the molten slag in electroslag welding can be easily increased by blowing a gas having a high oxygen partial pressure from above because the welding is performed in the enclosed space as shown in FIG. it can. As the gas having a high oxygen partial pressure, oxygen or a mixed gas of oxygen and one or more of air, nitrogen, argon, carbon dioxide, helium, and the like, and a gas having a higher oxygen partial pressure than air is used. Also, the water content of the gas should be as low as possible. This is because in a high moisture atmosphere, moisture migrates into the molten slag, which increases the diffusible hydrogen of the weld metal and increases the risk of hydrogen cracking.

Although electroslag welding is roughly classified into a consumable nozzle type and a non-consumable nozzle type, it is limited to the non-consumable nozzle type electroslag welding. This is because the consumable nozzle type can add an oxidant to the coating of the consumable nozzle, has little advantage of atmosphere control, and the molten slag is consumed and replaced as the welding progresses.

[0011]

EXAMPLES Steel sheets 1 and 2 were welded as shown in FIG. 1, and a tensile test at 600 ° C. and JIS were conducted on a test piece having a diameter of 10 mm.
The No. 4 test piece was subjected to a Charpy impact test at 0 ° C. to investigate its material. In addition, the stability of welding and the occurrence of defects were also investigated. Steel plates 1 and 2 are 50 mm thick, C: 0.09%, Si: 0.16%, Mn: 1.4
%, Mo + Nb + V: 0.2% as a main component, B:
It contained 0.0001 to 0.003%. MnO-Ca
The flux of O-SiO ₂ composition system is melted slag thickness 35-
40 mm was used as the target. JIS for welding wire 4
A 1.6 mm diameter material corresponding to Z 3312 YGW14 was used. Nozzle 3 is a copper tube with water cooling.
Welding was performed by supplying power of 80 A and voltage of 48 to 52V.
Regarding the atmospheric oxygen partial pressure, a gas pipe 7 is provided at a position close to the molten slag 6, and a gas with a high oxygen partial pressure is blown in to adjust the partial pressure.
The sample was collected with a syringe-type gas sampler and measured by a gas chromatography method.

Table 1 shows the outline of the implementation.

[0013]

[Table 1]

In Example 1, the steel sheet was B: 0.002% refractory steel and was welded while blowing oxygen gas at a flow rate of 10 l / min. The oxygen partial pressure of the atmosphere at this time was 0.74. Welding has no problem, elongation at 600 ℃ is 21%,
The absorbed energy at 0 ° C. was 51 J, which was a good value.

In Example 2, the steel sheet had a B content of 0.0004%.
No. 1 refractory steel was welded while blowing a gas of an equal mixture of oxygen and nitrogen at a rate of 15 l / min. The atmospheric oxygen partial pressure was 0.38. Welding is flawless and elongation at 600 ℃ is 2
It was a good value with an absorbed energy of 61 J at 3% and 0 ° C.

In Comparative Example 3, the steel sheet had a B content of 0.0001%.
Welded with ordinary steel plate without controlling the atmosphere. The oxygen partial pressure at this time was 0.28. It can be welded without any problems, and since B is originally low in ordinary steel, it has an elongation of 600 ° C 22
%, And the absorbed energy at 0 ° C. was 72 J, which was a good value.
However, since it is not a refractory steel, there is a problem that the high temperature strength of the steel sheet is insufficient.

In Comparative Example 4, the steel sheet was B: 0.003% high B steel and was welded by flowing oxygen gas at a rate of 15 l / min. The atmospheric oxygen partial pressure was 0.85, but the elongation at 600 ° C was a low value of 17%, and the absorbed energy at 0 ° C was a low value of 29J.

In Comparative Example 5, B: 0.002% refractory steel was welded while blowing a mixed gas of oxygen and carbon dioxide gas at a rate of 10 l / min. The oxygen partial pressure at this time was 0.31. As a result, the elongation at 600 ° C was as low as 16%,
The absorbed energy at 0 ° C was a low value of 20J.

[0019]

According to the present invention, B: 0.0003 to 0.00
Even with refractory steel for construction containing 25%, non-consumable nozzle type electroslag welding with good elongation at 600 ° C can be performed. In particular, the fact that welding can be performed without using a welding material considering the content of B enables not only higher quality but also higher price of the molten material and reduction of the load of the molten material management.

[Brief description of drawings]

FIG. 1 is a diagram showing a non-consumable nozzle type electroslag welding method.

[Explanation of symbols]

 1 Steel plate 2 Steel plate 3 Nozzle 4 Welding wire 5 Patch plate 6 Molten slag 7 Gas pipe

Claims (1)

[Claims] 1. A non-consumable nozzle type electroslag welding method for building refractory steel containing B: 0.0003 to 0.0025%, wherein the oxygen partial pressure of the atmosphere in contact with the molten slag at the time of welding is 0.35 or more. A non-consumable nozzle type electroslag welding method for building refractory steel, characterized by the following.