JPH02274394A - Low hydrogen type coated electrode for fillet welding of steel having excellent refractoriness - Google Patents

Abstract

PURPOSE:To obtain the coated electrode having excellent refractory performance, weatherability and welding workability by coating a steel core wire with a coating material having a specific compsn. CONSTITUTION:The steel core wire is coated with the coating material contg., by weight, 5 to 30% SiO2 15 to 35% TiO2, 5 to 30% MgCO3, 0.5 to 8% MgO, 10 to 45% iron powder, 1 to 10% Mn, 0.1 to 0.4% water of crystallization released by heating to >=400 deg.C, 0.05 to 2% Ni, 0.02 to 0.1% Nb, 0.5 to 3% Mo, 0.4 to 0.9% (0.5Mo+10Nb), and 0.1 to 3% total of one or two kinds of Cu and Cr and consisting of the balance a slag forming agent, arc stabilizer and binder. This coating material comprises adding slight ratios of the Nb and Mo in combination to the coating material and limiting the sum of (0.5Mo+10Nb) to 0.4 to 0.9%. The coated electrode which exhibits the high-temp. yield point equal to or higher than the yield point of steel products, etc., is exhibited and the impact toughness is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a low-hydrogen coating for fillet welding of steel with excellent fire resistance for use in various buildings in the fields of architecture, civil engineering, marine structures, etc. This relates to arc welding rods.

[Conventional technology]

As is well known, as coated arc welding rods for welding various structures in the fields of architecture, civil engineering, marine structures, etc., there are coated arc welding rods for mild steel (JIS Z3211), coated arc welding rods for high tensile steel (JIS Z3212), Covered arc welding rods for low-alloy high-strength steel (JIS Z3213), coated arc welding rods for weathering steel (JIS Z3214), and the like are widely used.

For example, JP-A-55-40064 and JP-A-5
6-80391 discloses a coated arc welding rod with improved bit resistance and welding workability.

By the way, when constructing buildings using the above-mentioned coated arc welding rods, such as buildings, offices, and residences that are closely connected to daily life, it is necessary to apply sufficient fireproof coating to ensure safety in the event of a fire. Construction-related laws and regulations stipulate that the temperature of steel materials and welded parts should not exceed 350'C in the event of a fire. This is 3
This is because the yield strength decreases to 60 to 70% of that at room temperature at about 50°C, which may cause the building to collapse. For this reason, in addition to spreading spraying material or felt based on slag wool, rock wool, glass wool, asbestos, etc. on the surface of steel materials and welded parts, there are also methods of covering with fireproof mortar and the above-mentioned insulation layer. In addition, a fireproof coating is carefully applied, such as a thin metal plate, such as aluminum or stainless steel plate, to prevent thermal damage in the event of a fire.

As a result, travel costs for fireproof coatings become high compared to the price of welding materials, and it is unavoidable that construction costs will rise significantly.

[Problem to be solved by the invention]

As mentioned above, when using well-known coated arc welding rods for buildings, they are cheap, but because of their poor high-temperature properties, they cannot be used with a light liquid layer or no coating on the surface of steel materials or welded parts, and are relatively expensive. Since fireproof coatings must be applied, there are problems in that the construction cost is increased and the usable space of the building is narrowed, reducing economic efficiency. On the other hand, JP-A No. 62-224493 and JP-A No. 63-14079
According to the coated arc welding rod for low-alloy heat-resistant steel disclosed in Publication No. 7, it is effective when used for welding heat-resistant steel, but the price is very high and it is particularly suitable for the construction field where economic efficiency is important. The reality is that it is extremely difficult to use, and is almost never used.

In addition, as buildings have become increasingly high-rise in recent years, fire-resistant design has been reviewed due to improvements in design technology and high reliability, and in 1988, a new fire-resistant design law for buildings was enacted. As a result, steel materials,
The high-temperature strength of the weld and the actual loads applied to the building now determine the capacity of the fireproof coating, and in some cases it is now possible to use it without coating.

However, a coated arc welding rod for obtaining a weld metal with excellent fire resistance does not currently exist.

An object of the present invention is to provide a coated arc welding rod that has excellent high-temperature properties at 600°C, weather resistance, and welding workability.

[Means to solve problems,]

The present invention overcomes the aforementioned problems and achieves the objectives.
The specific means is 5iOz5-30%, T
i0215~35%, MgC015~30%, MgO0
．． 5-8%, iron powder 10-45%, M11-10%, 40
Crystal water released by heating above 0'C 0.1~
0.4%, Ni0.05-2%, Nb0.02-0, 1
%, Mo 0.5-3%, (0.5Mo+10Nb
) is 0, 4 to 0.9%, one or two of Cu, Cr
A steel with excellent fire resistance, characterized in that the steel core wire is coated with a coating agent consisting of a total of 0.1 to 3% of seeds, and the remainder consisting of a slag forming agent, an arc stabilizer, and a binder. Low hydrogen coated arc welding rod for fillet welding.

[For production]

According to the results of the research conducted by the present inventors on the strength of welded metal in the event of a fire, when uncoated use is targeted, the maximum temperature reached in the event of a fire is approximately 1000°C, so at this temperature 70% of the room temperature proof strength In order to provide the above-mentioned yield strength, it is necessary to add a large amount of expensive metal elements to the well-known coated arc welding rod. However, such welding rods cannot be practically used due to economical reasons.

Therefore, steel materials currently being developed with excellent fire resistance are designed and manufactured so that their high temperature yield strength at 600° C. is 70% or more of that at room temperature.

Therefore, if the welded part also has a high-temperature yield strength higher than that of this highly fire-resistant steel material, it will be safe and economical from the perspective of the entire building, reduce the amount of expensive additive elements, and further improve the fire resistance of the welded part. We have developed a coated arc welding rod with excellent fire resistance that allows the coating to be made thinner and can be used without coating when the fire load is small.

The feature of the present invention is that a small amount of Nb and Mo are added in combination, (0,
5Mo-1-10Nb) is limited to 0.4 to 0.9%.

Next, characteristic component elements related to the present invention and their addition amounts will be explained.

Nb and Mo form fine carbonitrides, and Mo increases high-temperature strength through solid solution strengthening, but M.

When added alone, it is difficult to obtain sufficient yield strength in the high temperature range of 600°C.

As a result of test research using various prototype welding rods, the present inventors found that
It has been found that the combined addition of Nb and Mo is extremely effective in increasing the yield strength in the high temperature range. However, if too much Nb or Mol is present, the toughness of the weld metal will deteriorate, and the cracking resistance will further deteriorate, so the upper limit of the Nb and Mo contents is each 0.1%.

It is necessary to set the content to 3%, and the lower limit is 0.02% and 0.5%, respectively, as the minimum amount to obtain a composite effect.

Furthermore, Nb, Mail is within the range mentioned above,
The sum of (0.5Mo+10Nb) is 0.4 to 0.9%
In the case of
The sum of (0,5Mo+10Nb) was limited to a range of 0.4 to 0.9%.

The use of Mo in order to increase high-temperature strength is known in conventional coated arc welding rods for heat-resistant steel; There is no known low-hydrogen coated arc welding rod for fillet welding of steel with excellent fire resistance.

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

5iOz is effective as a slag former and viscosity modifier and is usually added in the form of a silicate. If it is less than 5%, the slag easily flows and does not cover the bead well, resulting in a convex bead shape. If it exceeds 30%, the viscosity of the slag will be too high, resulting in poor welding workability, and the slag will adhere firmly to the bead, resulting in poor slag removability.

TiO□ has the same effect as SiO□ as a slag forming agent, viscosity modifier, and arc stabilizer, and is added from among rutile, iron sand, and illuminite. If it is less than 15%, the stability of the arc and the shape of the bead toe deteriorate, resulting in non-uniform beads. If it exceeds 35%, the slag removability deteriorates or burns occur.

MgC (h acts as a gas generating agent, i.e.
It decomposes due to arc heat and generates CO2 gas, which has the effect of protecting weld metal from the atmosphere and is effective in preventing cracking caused by hydrogen. Usually added from magnesite or dolomite. If it is less than 5%, the effect as a gas generating agent is insufficient, blowholes and pits are likely to occur, and oxygen and nitrogen increase in the weld metal, deteriorating the mechanical properties of the weld metal.

If it exceeds 30%, the stability of the arc deteriorates and there is a lot of spatter (and undercuts are likely to occur).

MgO is a slag forming agent and a viscosity modifier, and improves slag removability. It also improves the basicity of the slag and helps improve the mechanical properties of the weld metal, and is added as a magnesia clinker. If it is less than 0.5%, the above effect will not be exhibited significantly, and if it exceeds 8%, arc stability will deteriorate, spatter will increase, and undercuts will increase.

Iron powder is added to improve 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 will become unstable, and if the amount of slag is too large, it will cause bead formation. I'm disgusted. When it exceeds 45%, the amount of slag becomes insufficient and the bead shape becomes convex.

Mn is effective as a deoxidizing agent and an alloying agent.

It is also effective as a reslag generator due to the action of MnO produced as a deoxidation product. If it is less than 1%, deoxidation is insufficient and blowholes and bits are likely to occur. 10%
If it exceeds this, the Mn content in the weld metal becomes excessive, and the weld metal is hardened significantly and its mechanical properties deteriorate.

Crystal water acts as a hydrogen source, mica, and cruzi.

It is added from kaolin, sericite, etc. However, for low-hydrogen coated arc welding rods, after applying the coating material,
Since the water glass is fired at a temperature of approximately 0.degree. The water of crystallization here is released by heating at 400 to 1000°C, and the hydrogen released under welding conditions is
Bit resistance 1 Improves arc stability. If it is less than 0.1%, bits will occur due to hydrogen deficiency, and the arc will spread poorly, resulting in convex beads. If it exceeds 0.4%, the amount of diffusible hydrogen in the weld metal increases and cracking resistance decreases.

Ni improves the mechanical properties of weld metal as well as Nb and M.

It is necessary to exhibit the effect of addition, and 0.05%
If it is less than that, it will be difficult to ensure strength and the effect of adding Nb and Mo will be diminished. If it exceeds 2%, the weld metal will be hardened significantly and its mechanical properties will deteriorate.

Furthermore, Cu or Cr is effective in improving weather resistance; if the total amount of one or both is less than 0.1%, the effect is weak, and if it is added in excess of 3%, the weather resistance effect is maintained, but This is unsuitable because the cracking resistance of the weld metal deteriorates.

The composition of the coating material used in the present invention is such that, in addition to the above-mentioned components, an arc stabilizer, a slag forming agent, and water glass as a binder are added in the same manner as in ordinary coated arc welding rods.

Furthermore, the composition of the steel core wire to be coated is normally shown in the coated arc welding rod core wire (JTS G3523). In addition, in order to increase the strength of the weld metal, St.

Steel core wires to which Mn and other alloying elements have been added may also be used.

〔Example〕

Table 1 shows the composition of typical steel wires with excellent fire resistance used in the test, Table 2 shows the chemical composition of the steel core wire used in the prototype coated arc welding rod, and Table 3 shows the wire used in the test. The invention coated arc welding rod and the comparative coated arc welding rod are shown.

A steel plate with a thickness of 25ffII11 having the steel components shown in Table 1 was prepared with a groove shape shown in Fig. 1 (T=25mm, D=10
mm, φ-45゛), welded joints were prepared using the coated arc welding rods shown in Table 3 and the welding conditions shown in Table 4, and their room temperature strength, high temperature strength, and corrosion resistance were examined.

The 6 most important factors when evaluating the mechanical performance of weld metal
The yield strength at 00℃ is 33kg, which is the minimum yield point at room temperature of 5M50 steel specified in JIS G3106 type 2.
The goal was to secure 70% or more of f/-. In other words, regarding the yield strength of weld metal at 600'C,
It was determined that 23 kgf/- or more was applicable.

In addition, a plate-shaped corrosion test piece with a thickness of 3InII+1 and a width of 501 Tlffl in the direction of the weld line and a length of 150 mm with the welded part in the center was taken from the surface of the steel plate after welding.1. lr
According to the salt spray test method specified in S Z 2371,
Corrosion tests were conducted on welded parts.

Corrosion resistance evaluation showed that there was no pitting corrosion and the rust area ratio was 50.
% or less was rated as good.

The corrosion test conditions were as follows: 4% NaCl aqueous solution was applied to the above test piece placed in the exposure zone at 35°C at a rate of 2.0 cm per 80 c+ft.
It was sprayed for 48 hours at a rate of mf/hr.

A 25 mm thick steel plate having the steel components shown in Table 1 has a joint shape shown in FIG. 2 (T+ ・Tg = 25 mm).

V=100mm, F=100mm, L-100
Welded joints were prepared under the welding conditions shown in Table 4 under the 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 the coated arc welding rods according to the present invention have good strength at room temperature and high temperature, as well as excellent welding workability and corrosion resistance, whereas all the comparative coated arc welding rods have good strength at room temperature and high temperature. It is unsuitable as a welding material for fire-resistant construction because its strength is too high or its high-temperature strength is insufficient, and its welding workability and corrosion resistance are poor.

Table 1 [Effects of the Invention] The coated arc welding rod of the present invention has excellent high-temperature strength characteristics and corrosion resistance, and has good welding workability, and can significantly reduce the cost of fireproofing welded parts. be.

[Brief explanation of drawings]

FIG. 1 is a front sectional view showing the groove shape used in the example. FIG. 2 is a sketch showing the shape of the joint used in the example.

Claims (1)

[Claims] In terms of weight ratio, SiO_25-30%, TiO_215-35%, MgCO_35-30%, MgO 0.5-8%, iron powder 10-45%, Mn 1-10%, by heating at 400°C or higher. Crystal water released from 0.1 to
0.4% Ni0.05-2% Nb0.02-0.1% Mo0.5-3% (0.5Mo+10Nb) is 0.4-0.9%,
The steel core wire is coated with a coating material containing one or two of Cu and Cr, with the remainder consisting of a slag forming agent, an arc stabilizer, and a binder. A low-hydrogen coated arc welding rod for fillet welding of steel with excellent fire resistance.