JP2566631B2 - Low-hydrogen coated arc welding rod for fillet welding of steel with excellent fire resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a low hydrogen coating for fillet welding of steel having excellent fire resistance used for various structures in the fields of construction, civil engineering, marine structures and the like. It relates to an arc welding rod.

[Prior Art] As is well known, as a coated arc welding rod for various structures in the fields of construction, civil engineering and marine structures, a coated arc welding rod for mild steel (JIS Z3211), a coated arc welding rod for high strength steel Rods (JIS Z3212), coated arc welding rods for low alloy high strength steel (JIS Z3213), coated arc welding rods for weather resistant steel (JIS Z3214), etc. are widely used.

For example, Japanese Patent Application Laid-Open Nos. 55-40064 and 56-803.
Japanese Patent No. 91 discloses a covered arc welding rod having improved pit resistance and welding workability.

By the way, in the case of constructing a building, an office, a house, etc., which are closely related to daily life, using the covered arc welding rod among various kinds of buildings, a sufficient fireproof coating is required to ensure safety in a fire. It is obligatory to apply it, and under various building-related laws and regulations, the temperature of steel materials and welds is
It is regulated not to exceed 350 ℃. This is because the proof stress at about 350 ° C is reduced to 60 to 70% of that at normal temperature, which may cause the building to collapse.

For this reason, steel materials, slag wool, rock wool, glass wool, asbestos-based spraying material and felt spread on the surface of the welded portion, a method of covering fire mortar and the heat insulating material layer, Furthermore, a fireproof coating such as a method of protecting with a metal thin plate, that is, an aluminum or stainless steel thin plate is carefully applied to prevent thermal damage in the event of a fire.

Therefore, the fireproof coating construction cost becomes higher than the welding material price, and it is unavoidable that the construction cost rises significantly.

[Problems to be Solved by the Invention] When using a well-known coated arc welding rod for a building as described above, the surface of a steel material or a welded portion is used as a light coating or an uncoated surface because of its low price but low high-temperature characteristics. Since it is not possible to do so and expensive fireproof coating must be applied, there is a problem that the construction cost is increased and the space used for the building is narrowed, and the economic efficiency is reduced.

On the other hand, JP-A-62-224493 and JP-A-63-1407
According to the coated arc welding rod for low alloy heat-resistant steel disclosed in Japanese Patent Publication No. 97, the high temperature characteristics are good, but the price is very high and it is very difficult to use it for welding work.

In addition, with the recent rise in the height of buildings, the refractory design was reviewed due to the improvement of design technology and its high reliability, and the new fireproof design method for buildings was enacted in 1987. , It is possible to determine the fireproof coating capacity by the high temperature strength of steel materials and welds and the weight actually applied to the building, without depending on the temperature limit of 350 ° C mentioned above. In some cases, use it without coating. Is also possible.

However, there is currently no coated arc welding rod for obtaining a weld metal having excellent fire resistance.

An object of the present invention is to provide a coated arc welding rod which has excellent high temperature characteristics at 600 ° C and excellent welding workability.

[Means for Solving the Problems] The present invention is to achieve the object by overcoming the above-mentioned problems, and the specific means is SiO ₂ 5 to 30% by weight ratio and TiO ₂ 1
5 to 35%, MgCO ₃ 5 to 30%, MgO 0.5 to 8%, iron powder 10 to 45
%, Mn 1-10%, water of crystallization 0.1-0.4%, Ni0.05-3%, Nb0.02-0.1%, Mo0.5 released by heating above 400 ° C
~ 4%, (0.5Mo + 10Nb) is 0.5-2.0%, and the balance consists of coating the steel core wire with a coating consisting of slag generator, arc stabilizer and binder. A low-hydrogen coated arc welding rod for fillet welding of steel with excellent properties.

[Operation] As a result of a study on the strength of weld metal during a fire, the inventors of the present invention found that the maximum temperature reached during a fire was about 1000 ° C. when the uncoated use was the target, and therefore the room temperature yield strength of 70 In order to have a yield strength of not less than%, it is necessary to add a large amount of an expensive metal element to a known coated arc welding rod, which cannot be practically used.

Therefore, what is currently being developed as a steel material with excellent fire resistance is designed and manufactured so that the high temperature proof stress at 600 ° C is 70% or more of that at room temperature.

For this reason, if the welded part also has the high temperature proof strength of the steel material with excellent fire resistance, it is safe and economical from the perspective of the entire building, the amount of expensive additional elements is reduced, and the fire resistance of the welded part is reduced. We have developed a coated arc welding rod with excellent fire resistance that enables thin coatings and can be used uncoated when the fire load is small.

The feature of the present invention is that a small amount of Nb and Mo are added together, and (0.5Mo
It is to limit the sum of +10 Nb) to 0.5 to 2.0%.

Next, the characteristic component elements according to the present invention and the addition amounts thereof will be described.

Nb and Mo form fine carbonitrides, and Mo increases the high temperature strength by solid solution strengthening, but it is difficult to obtain sufficient proof stress in the high temperature region of 600 ° C by adding Mo alone.

The present inventors have found from the results of test studies using various trial welding rods that the combined addition of Nb and Mo is extremely effective in increasing the yield strength in the high temperature region. However, if the Nb and Mo contents are too large, the toughness of the weld metal deteriorates and the crack resistance deteriorates, so the upper limits of the Nb and Mo contents must be 0.1% and 4%, respectively. 0.02% and 0.5% are included as the minimum amount to obtain the effect.

Furthermore, the amounts of Nb and Mo are within the range as described above,
When the sum of (0.5Mo + 10Nb) is 0.5 to 2.0%, the high temperature proof stress at 600 ° C shows strength equal to or higher than that of steel material and the impact toughness becomes good, so the sum of (0.5Mo + 10Nb) becomes 0.5
Limited to ~ 2.0%.

Incidentally, in order to increase the high temperature strength, the use of Mo is known in the conventional coated arc welding rod for heat-resistant steel, but it is a small amount as a coated arc welding rod used for construction.
There is no known low-hydrogen coated arc welding rod for fillet welding of steel with excellent fire resistance in which Mo is added to Nb.

Next, the reasons for limiting the components other than Nb and Mo in the present invention will be described in detail.

SiO ₂ has an effect as a slag generator and a viscosity modifier, and is usually added in the form of silicate. If it is less than 5%, the slag tends to flow and the beads are not well encapsulated, so the bead shape becomes convex. If it exceeds 30%, the viscosity of the slag is too high, which deteriorates the welding workability, and the slag is hard and adheres to the bead, resulting in poor slag removability.

Similar to SiO ₂ , TiO ₂ has an effect as a slag generator, a viscosity modifier, and an arc stabilizer, and is added from rutile, iron sand, and illuminite. If it is less than 15%, the stability of the arc and the shape of the toe of the bead are deteriorated, and the bead becomes uneven. If it exceeds 35%, the slag removability deteriorates and stick burning occurs.

MgCO ₃ acts as a gas generant. That is, it has the effect of decomposing by the arc heat to generate CO ₂ gas and protecting the weld metal from the atmosphere, and is effective in preventing cracking due to hydrogen. Usually added from magnesite or dolomite. If it is less than 5%, the effect as a gas generating agent is insufficient and blowholes and pits are easily generated, and oxygen and nitrogen increase in the weld metal to deteriorate the mechanical properties of the weld metal. If it exceeds 30%, the stability of the arc deteriorates, the amount of spatter increases, and undercut easily occurs.

MgO is a slag-forming agent and a viscosity modifier, and has good slag releasability. Further, the basicity of the slag is improved, which helps improve the mechanical properties of the weld metal, and it is added as a magnesia clinker. If it is less than 0.5%, the above effect is not significantly exhibited, and if it exceeds 8%, the stability of the arc is deteriorated, the spatter increases, and the undercut also increases.

Iron powder is added to improve the welding efficiency by increasing the amount of deposited metal, stabilize the arc and adjust the amount of slag.If it is less than 10%, the arc becomes unstable and beads with too much slag are generated. Drool. If it exceeds 45%, the amount of slag is insufficient and the bead shape becomes convex.

Mn has an effect as a deoxidizing agent and an alloying agent. Also,
The action of MnO produced as a deoxidation product is also effective as a slag producing agent. If it is less than 1%, deoxidation becomes insufficient and blow holes and pits are likely to occur. If it exceeds 10%, the Mn in the weld metal becomes excessively large, and the weld metal is significantly hardened to deteriorate the mechanical properties.

The water of crystallization acts as a hydrogen source and is added from mica, talc, kaolin, sericite and the like. However, since the low-hydrogen coated arc welding rod is fired at about 400 ° C. after applying the coating agent, the water content or the like in the water glass evaporated in this step is not shown in the present invention.

The water of crystallization here is released by heating at 400 to 1000 ° C., and the hydrogen released under welding conditions improves pit resistance and arc stability. 0.1
If it is less than%, pits are generated due to lack of hydrogen, and the arc spreads poorly, resulting in a convex bead. If it exceeds 0.4%, the amount of diffusible hydrogen in the weld metal increases and crack resistance decreases.

Ni is necessary to improve the mechanical properties of the weld metal and to exert the effect of adding Nb and Mo. If it is less than 0.05%, it is difficult to secure the strength and the effect of adding Nb and Mo is weakened. If it exceeds 3%, the weld metal is significantly hardened and the mechanical properties are deteriorated.

The composition of the coating agent used in the present invention is the same as that of the conventional coated arc welding rod of the above-described components, with the addition of an arc stabilizer, a slag generator and water glass as a binder.

As the composition of the steel core wire to be further coated, that shown in the core wire for a coated arc welding rod (JIS G3523) is usually used.
Further, in order to increase the strength of the weld metal, a steel core wire to which Si, Mn and other alloy elements are added may be used.

[Examples] Table 1 shows typical steel materials with excellent fire resistance used in the test.
Table 2 shows the composition of the steel core wire used in the trial production of the covered arc welding rod,
Table 3 shows the coating material of the present invention and the comparative coating material used in the test.

After processing the steel plate shown in Table 1 with a plate thickness of 25 mm into the groove shape (T = 25 mm, D = 10, Φ = 45 °) shown in Fig. 1, the steel core wire shown in Table 2 was used in Table 3 A welded joint was prepared under the conditions shown in Table 4 and the coated arc welding rod coated with the coating material shown in
The room temperature strength and high temperature strength were investigated.

In addition, the joint shape shown in Fig. 2 for the steel plate shown in Table 1 with a plate thickness of 25 m (T ₁ · T ₂ = 25 mm, V = 100 mm, F = 100 mm, L = 1000 mm)
A welding joint was prepared under the welding conditions shown in Table 4 and the welding workability was investigated.

 The results of these tests are shown in Table 5.

As is clear from Table 5, all of the coated arc welding rods according to the present invention have good room temperature and high temperature strength and also have excellent welding workability. Is too strong,
Alternatively, it lacks high-temperature strength and poor welding workability, and is unsuitable as a fire-resistant construction welding material.

[Advantages of the Invention] The coated arc welding rod according to the present invention is excellent in high-temperature special properties, has good welding workability, and can significantly reduce the cost required for fireproofing the welded portion.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a groove shape used in the embodiment, and FIG. 2 is a perspective view showing a joint shape used in the embodiment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihide Yamane 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Inside Nippon Steel Co., Ltd. 2nd Technical Research Institute (56) References Japanese Patent Publication No. 4-55794 (JP, B2)

Claims (1)

(57) [Claims] 1. By weight%, SiO ₂ 5-30%, TiO ₂ 15-35%, MgCO ₃ 5-30%, MgO 0.5-8%, iron powder 10-45%, Mn 1-10%, 400 Water of crystallization released by heating above ℃ 0.1-0.4%, Ni 0.05-3%, Nb 0.02-0.1%, Mo 0.5-4%, (0.5Mo + 10Nb) 0.5-2.0% The balance is slag generator, arc A low-hydrogen coated arc welding rod for fillet welding of steel having excellent fire resistance, characterized in that a steel core wire is coated with a coating material comprising a stabilizer and a binder.