JPH0237833B2 - SABUMAAJIAAKUYOSETSUYOSHOSEIFURATSUKUSU - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is a hygroscopic material that is commonly used for welding steels such as mild steel, high-strength steel, low-alloy steel, or stainless steel. The present invention relates to a sintered flux for submerged arc welding that can keep the temperature low. (Prior Art) Submerged arc welding is currently widely used as an automatic welding method for steel. This flux for submerged arc welding (hereinafter referred to as flux)
There are so-called molten fluxes, which are made by melting various raw materials in an electric furnace, cooling them, crushing them, and granulating them.
Various fine grain raw materials are granulated with water glass and heated to 400℃~
There is a so-called fired flux that is fired at a temperature of 900°C. Of these, calcined fluxes meet the recent demands for improved quality, with the following advantages: a highly basic composition can be easily obtained, and low hydrogenation can be achieved by incorporating carbonate into the raw material;
Furthermore, it has a great degree of freedom in terms of composition, such as the ability to easily add deoxidizers and alloying agents, and is becoming widely used. However, the biggest problem with this calcined flux is the use of water glass as a sticking agent for granulation. Conventionally, fluxes that are granulated with water glass and then fired at 400°C to 600°C lose moisture when they are sealed in cans, opened during welding, and left in the atmosphere. If the moisture absorption is significant and it is left in the atmosphere for more than 10 hours, for example, 1
The amount of moisture absorbed is approximately % by weight. In such a case, if welding is continued as is, problems such as pits or blowholes will occur in the welded area due to the absorbed moisture, or hydrogen cracking will occur in the welded area due to an increase in the amount of diffusible hydrogen. This moisture absorption phenomenon is clearly based on the hygroscopicity of water glass, and in order to reduce this hygroscopicity as much as possible, conventional methods such as (SiO ₂ /alkali oxide) as seen in JP-A-55-133899 have been used. Studies have been conducted on water glass compositions that limit the molar ratio (K ₂ O / Na ₂ O + K ₂ O), but sufficient effects have not been obtained, and in reality, it is difficult to manage the moisture absorption of flux during use. Currently, a great deal of attention is being paid to (Problems to be Solved by the Invention) The present invention provides a fired flux in which the amount of water glass added to the fired flux using water glass as a fixing agent can be significantly reduced, and as a result, the hygroscopicity of the flux is extremely reduced. I will provide a. (Means for Solving Problems) The gist of the present invention is that, in a fired flux for submerged arc welding containing 50% by weight or less of alumina, 3% by weight or more of fine-grained alumina with a particle size of 10 μm or less is added to the raw material before firing. The fired flux for submerged arc welding is characterized in that the content of coarse-grained alumina having an average particle diameter of 40 to 100 μm is 15% by weight or less. (Function) Hereinafter, the present invention will be explained in detail. The present inventors have found that alumina, which is commonly used for welding high-strength steel, low-temperature steel, and even high-alloy steel, is contained in an amount of 3 to 50% by weight, and in addition, SiO ₂ is contained in an amount of 5 to 40% by weight. , TiO ₂ 0-35% by weight, CaO 10-50% by weight, MgO 15-50% by weight, BaO 0-25% by weight, alkali metal oxide 2-10% by weight, CO ₂ 0-20% by weight, metal fluoride In order to reduce the amount of moisture absorbed by using a Henschel high-speed granulator, which has propeller-like blades that rotate at high speed in a cylinder, for the fired flux containing 3 to 60% by weight of chemical compounds and 0 to 50% by weight of metal powder, Various studies were conducted, mainly regarding the particle size structure of the raw materials, in order to find out how to reduce the amount of water glass for granulation and maintain a high particle strength after firing. As a result, by using fine-grained alumina as an alumina raw material instead of the conventionally used standard-grained alumina, the amount of water glass added can be significantly reduced, and the particle strength after firing can also be improved. It became clear that this would be sufficient. This has made it possible to reduce the amount of moisture absorbed by the fired flux to about half that of the conventional method. Alumina is a white powder crystal produced by firing aluminum hydroxide, and when observed under a microscope, it can be seen as agglomerated particles of many fine α-crystal grains (corundum). What has traditionally been used for welding flux is coarse-grained alumina, in which many α-crystal grains of several μm are aggregated, and the average particle diameter is 40 to 100 μm.
This is porous, so to speak, and has a large specific surface area compared to the average particle size, and although a large amount of water glass is required during granulation, it is not sufficient for agglomeration (granulation) of flux particles. is considered not to work effectively. On the other hand, fine-grained alumina in the present invention has a small average particle size, 1 to 10 μm, which is close to the α crystal grain size.
This means that the α-crystal grains themselves are alumina particles, which means that the porous state is reduced, and the specific surface area does not change much and is in a fine-grained state. Therefore, the cohesive force of the flux particles when water glass is added increases due to the finer alumina particles, and since the water glass works effectively, it becomes easier to granulate the flux particles even if the amount added is very small. After granulation and firing, the flux was subjected to a pulverization test and the particle strength of the flux was measured, and it was found that the particle strength of the flux did not deteriorate because the water glass was working effectively in granulation. The reasons for the numerical limitations are listed below. As mentioned above, alumina is produced as an aggregate of stable α-alumina crystal grains by firing aluminum hydroxide at high temperatures, but generally both the apparent particle size (agglomerated grains of α-crystals) and the size of the α-alumina crystal grains are Controlled by manufacturing conditions. Among these, the size of the α crystal grains varies depending on the firing temperature and time, but is usually 10 μm or less. The reason why the alumina particle size is set to 10 μm or less in the present invention is to reduce porosity as much as possible by loosening the agglomerated α crystal grains by crushing and making the alumina particle size as close to the α alumina crystal grain size as possible. This results in the effect of reducing the amount of water glass added. Furthermore, since fine alumina particles of 10 μm or less are mixed with other flux raw materials, most of which have particle diameters of 10 μm or more, granulation performance is good when granulation is attempted by adding water glass. In addition, the amount of water glass can be further reduced. The effect becomes clear when the content of fine alumina in the flux is 3% by weight or more.
The effect is that the alumina tested by the present inventors is 50%
It was also effective when the entire amount of the flux was replaced with this fine-grained alumina. However, the content of coarse alumina in this case must be 15% by weight or less. As mentioned above, coarse-grained alumina is porous, and if it is contained in an amount exceeding 15% by weight, the amount of water glass added during granulation increases, and the amount of moisture absorbed by the flux is reduced by pits, blowholes, or It becomes difficult to reduce the content to 1% by weight or less, which is necessary to prevent hydrogen cracking and the like. Note that the present invention reduces hygroscopicity by reducing the amount of water glass added, and the composition of water glass can be freely adjusted depending on the purpose, and of course it is also possible to use Li ₂ O-based water glass with low hygroscopicity. . (Example) Fluxes with four compositions (No. 1, No.
5, No. 7, and No. 10) in which the alumina was partially or completely replaced with fine-grained alumina, water glass was added to the raw materials and granulated. The required amount of water glass required for granulation at that time was recorded in the rightmost column of the same table. The standard grain alumina used has a grain size of 74 μm.
32% or more, 77% of 44μm or more, and 3% of 10μm or less (representative values of average particle size are 60μm and alpha grain size of 3μm), and fine grain alumina has a grain size of 10μm or less95 %, 86% of 4 μm or less, 55% of 2 μm or less (representative of average particle diameter is 2 μm, and α crystal grain size is presented as 0.3 to 3 μm). Water glass used as a fixing agent for granulation
It is of 40 Baume, consisting of SiO ₂ 28, Na ₂ O 10, K ₂ O4 ratio. Granulation was performed using a high-speed rotating Henschel mixer, and the granulation time was approximately 1 to 2 minutes. After granulation, these fluxes No. 1 to No. 11 were dried in a rotary kiln at 250°C for a short time, then fired at 480°C to 500°C for 1 hour, and then formed into 12 × 100 meshes (1410 μm to 149 μm). It was grainy. These fluxes were subjected to moisture absorption tests and dusting (particle strength) tests. Moisture absorption test is conducted with an atmosphere of 30
The test was carried out with a flux thickness of 20 mm in a constant temperature and humidity oven at 80% relative humidity and the weight of absorbed moisture was measured after 24 hours. In addition, in the powdering test, 50 g of flux was placed in a cylindrical container with an inner diameter of 40 mm and a length of 300 mm together with nine iron balls of 8 mm in diameter, and a cylindrical tube was passed through the center at a point 150 mm in the axial direction from the center of both ends of the container. After rotating for 30 minutes around a line perpendicular to the axis at a rotation speed of 30 revolutions/minute, the increase in the amount of particles smaller than 149 μm (% by weight) was measured, and this was taken as the particle strength. The results of these tests are shown in Table 2 and FIG. As shown in Table 2, the addition of fine alumina reduced the amount of water glass added. No.2,
3, 4 (Base No. 1), No. 6 (Base No. 5), No. 8
,
The moisture absorption amount of No. 9 (Base No. 7) and No. 11 (Base No. 10) decreased in proportion to the amount of water glass added compared to those of each base, and the amount of moisture absorbed by No. 9 (Base No. 7) and No. 11 (Base No. 10) decreased in proportion to the amount of water glass added. Approximately 50% less than those that are not used
It was possible to reduce it to Moreover, the amount of powdering is small regardless of the difference in the amount of water glass, and it is clear that there is no problem in either case. Note that FIG. 1 shows the influence of the content of fine alumina and the content of coarse alumina on the amount of moisture absorbed by the flux for each flux in Examples. When the amount of fine alumina is 3% by weight or more and the amount of coarse alumina is 15% by weight or less, the amount of moisture absorbed by the flux can be reduced to 1% by weight or less.

【table】

[Table] (Effects of the invention) As is clear from the above results, the use of the fluxes of the present invention makes it possible to significantly reduce the hygroscopicity caused by water glass, and the use of these fluxes makes it possible to reduce the hygroscopicity during on-site use. Moisture absorption management becomes easier, and it becomes possible to prevent the occurrence of pits and blowholes due to moisture absorption during welding, as well as hydrogen cracking.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results of a moisture absorption test on flux in Examples.

Claims (1)

[Claims] 1 In the fired flux for submerged arc welding containing 50% by weight or less of alumina, the raw material before firing contains 3% by weight or more of fine-grained alumina with a particle size of 10 μm or less, and the average particle size is 40 to 100 μm.
A fired flux for submerged arc welding, characterized in that the content of coarse-grained alumina is 15% by weight or less.