TECHNOLOGICAL PROPERTIES OF AGGLOMERATED FLUXES IN COMPARISON WITH FUSED FLUXES

ABSTRACT

This article provides an analysis of agglomerated (ceramic) and fused fluxes by various technological parameters. The change in the basicity index of ceramic fluxes over a wide range makes the use of these fluxes relevant for welding particularly important structures. Also, manufacturers of agglomerated (ceramic) fluxes have achieved a decrease in the hygroscopicity of welding materials in recent years.

АННОТАЦИЯ

В этой статье приводится анализ агломерированных (керамических) и плавленных флюсов по различным технологическим параметрам. Изменение индекса основности керамических флюсов в широких пределах делает актуальной применение этих флюсов для сварки особо ответственных конструкций. А также производители агломерированных (керамических) флюсов за последние годы добились снижения гигроскопичности сварочных материалов.

Keywords: flux, ceramic, fused, agglomerated

Ключевые слова: флюс, керамический, плавленый, агломерированный

Introduction. The use of new cold-resistant low-alloy steels in the production of welded structures for critical purposes requires an increase in the impact toughness of the weld metal on samples with a sharp notch at a test temperature of - 15°C of more than 60 J/cm². This requirement can be met by creating new welding materials: fused and agglomerated fluxes with a low content of harmful impurities - sulfur and phosphorus.

The aim of this work is to create a comprehensive technology for the production of agglomerated fluxes, which would combine the advantages of agglomerated and fused fluxes, while eliminating their disadvantages. This technology will not be so dependent on high-quality raw materials with harmful impurities, which will generally allow the creation of competitive production of agglomerated fluxes in the Republic of Uzbekistan. The creation of modern agglomerated fluxes for welding pipes and pipe products from low-alloy steels of increased strength is possible on the basis of fundamental research into the physical and chemical properties of slag melts.

According to the production method, welding fluxes are divided into fused, ceramic and fused-ceramic.

Fused fluxes are produced by melting components followed by granulation or crushing of the solidified mass. Ceramic ones are produced by mixing dry flux components, adding a binding element (liquid glass) to the resulting mixture and then granulating it. The production process of fused ceramic fluxes includes both manufacturing methods. To compare the properties, fused flux of the AН-348 brand and agglomerated flux of the OK Flux 10.71 brand were chosen.

Alloying a weld using flux. Fluxes are divided into alloying (active) and passive.

Passive fluxes: have higher mechanical characteristics of the weld; more suitable for multi-pass welding, since they allow maintaining an almost constant chemical composition of the seam; have restrictions on use due to rust and scale.

Active fluxes: have lower susceptibility to rust and scale; are characterized by better slag separation; have the potential danger of uneven alloying of the seam during multi-pass welding.

Fused fluxes, as a rule, are only passive, since the components of the flux, through which alloying can be carried out, begin to enter into chemical reactions during melting during the production process.

Ceramic fluxes are developed as both active and passive, which allows for more narrow specialization of different brands of fluxes. As a result, optimal combinations of various properties of the welded joint required for a given design are achieved.

Mechanical properties of deposited metal. The plastic properties of the deposited metal at negative temperatures very much depend on the basicity index Bi of the flux used (Fig. 1), which, for example, can be calculated using the Boneshevsky formula, which determines the ratio of basic and acidic oxides in the flux composition:

Depending on this index, fluxes are divided into:

acidic - B_i < 0,9; neutral - B_i = 0,9 - 1,2; main - B_i = 1,2 -2,0; highly basic - B_i > 2,0.

Figure 1. Dependence of the cold brittleness threshold temperature on the basicity  index of the flux used

Physically, this is due to the fact that during crystallization of the weld pool, oxygen inclusions remain between the dendrites. They are the microscopic concentrators that reduce the plastic properties of the weld. Typical values ​​of oxygen content in the deposited metal depending on the basicity of the flux:

sour - more than 750 ppm; neutral - 550 - 750 ppm; main – 300 - 550 ppm; highly basic - less than 300 ppm.

Due to the fact that during the production of fused fluxes the molten components begin to interact with each other, it is usually not possible to achieve a basicity index B_i of more than 1,4 (the most common fused fluxes have a B_i less than 1,2).

For ceramic fluxes, this index can be obtained within very wide limits. In the range of ceramic fluxes for welding carbon and low-alloy steels, there are fluxes with B_i  equal to 0,6 (high-speed fluxes) to 3,2 for particularly critical structures operating at temperatures of 60°C and below. In connection with the above, ceramic fluxes are of particular relevance for welding critical structures operating under alternating loads and at low ambient temperatures.

Melting temperature of slag. The slag produced by submerged arc welding, like any amorphous substance, does not have a specific melting point. Therefore, the melting temperature is taken to be the temperature range of transition of slag from a viscous to a fluid state. There is a fairly clear relationship between the basicity index and the temperature of this transition:

sour - 1100 - 1300°C; neutral – 1300 - 1500°C; basic and highly basic – above 1500°C.

Taking into account the fact that the liquidus temperature for carbon steels is about 1535°C [3], it is necessary to obtain a situation where the slag crust of basic and highly basic fluxes will harden until the weld pool crystallizes. It was believed that the most optimal solidification temperature of slag should be 200...300°C lower than the crystallization temperature of the metal [1]. This looks quite logical for a quasi-stationary process. However, the submerged arc welding process proceeds quite quickly, and due to more intense heat removal, the weld pool still crystallizes before the slag crust hardens. In this case, the slag located in the molten metal has time to harden and float to the surface.

Thanks to this, the number of microscopic slag inclusions in the weld, which subsequently serve as stress concentrators, is significantly reduced. Therefore, seams welded using ceramic fluxes have a denser and more uniform structure, which has a positive effect on their performance properties.

Bulk density of fluxes. If we compare the consumption of different fluxes, made in the same modes, per kilogram of deposited metal, it becomes obvious that almost the same volume is consumed per meter of weld.

Fused fluxes are divided into glassy and pumice-like. The average bulk density of the former is about 1,8 kg/dm³, of the latter - about 1,2 kg/dm³. At the same time, glassy fluxes make up about 90% of all volumes of fused fluxes used. The bulk density of agglomerated fluxes is 1,0 – 1,2 kg/dm³. Based on the foregoing, it is obvious that the consumption of glassy fused fluxes is 30 - 45% higher than that of pumice and ceramic ones. At the same time, due to the higher strength of the granules, fused fluxes are destroyed somewhat more slowly during recycling. However, this also has a negative side in the form of faster wear of the flux recirculation system of the equipment used.

Hygroscopicity of fluxes. It is known how much the humidity of the welding materials used affects the quality of the welded joint. In practice, most regulatory documents require calcination of welding fluxes before their use. The undeniable advantage of glassy fused fluxes is their lower tendency to absorb moisture from the atmosphere, and due to the less developed surface of the granules, the calcination temperature of fused fluxes is 150 - 250°C compared to 275 - 325°C for ceramic ones.

However, this disadvantage of agglomerated fluxes is quite easily eliminated as a result of their packaging in sealed packages of small volume, which allow, subject to the required storage conditions and maintaining the integrity of the packaging, these fluxes can be used within six months after the release date without preliminary calcination before use.

It should also be noted that manufacturers of ceramic fluxes have done a lot of work over the past 20 years to reduce the hygroscopicity of the welding materials they produce.

Granulometric composition of fluxes. Many fused fluxes must be separated by granule size using screens of specific mesh sizes to achieve optimal welding results. Flux with small granules is used for welding in forced modes and for multi-arc welding. High-speed welding requires good wettability of the molten slag with the edge of the metal being welded. Flux with normal granule size is used for single-arc welding using soft modes.

Ceramic fluxes have all granules of the same size (0,2 - 1,6 mm) for all welding current values. This makes it possible to reduce the range of welding materials used for various conditions.

Figure 2. Alloying abilities of flux:

Alloying of the weld metal with silicon (a) and manganese (b) depending on its content in the welding wire and welding current. Ud = 30 V; vst = 35 m/u

Agglomerated welding flux OK Flux 10.71 is a universal ceramic flux for general technical purposes. This welding material was developed and released onto the world market in the 90s of the last century. On the one hand, it can be considered a modern development, on the other, enough time has passed and it is necessary to optimize its characteristics by analyzing the various results of its use in real production. OK Flux 10.71 is an aluminate-basic agglomerated flux (basicity index B_i = 1,5), intended for welding critical structures made of carbon and low-alloy steels of the pearlitic class with a tensile strength of up to 750 MPa in mechanical engineering, shipbuilding, energy, bridge construction, welding of pipelines and beam structures. With a sufficiently high basicity, it has very good welding and technological characteristics.

Welding and technological testing of agglomerated fluxes of the OK flux series showed that the OK Flux 10.71 flux has better performance than the fused flux AN-348 for automatic welding of low-carbon and low-alloy steels of increased strength.

Thus, by increasing the sintering temperature and the holding time at this temperature, it is possible to significantly reduce the hygroscopicity of highly basic welding agglomerated fluxes. This flux can be used in combination with welding wires from various manufacturers.

Conclusion. This flux is intended for single- and multi-pass welding with one or more arcs of butt and fillet welds on both direct and alternating current. It allows welding at relatively forced conditions, comparable to AН-348 flux, while maintaining a low content of slag inclusions in the deposited metal, thereby ensuring high mechanical characteristics of the weld at negative temperatures (up to – 40° C and below) and good detachability of the slag crust. High mechanical properties of the deposited metal are also ensured due to the low content of diffusion hydrogen. Provided that it is transported and stored correctly, the hydrogen content is no more than 5 ml/100 g of deposited metal. The flux is slightly sensitive to rust and scale on the surface of the products being welded.

From the point of view of activity, it can be classified as a Mn - Si low-alloying flux. The alloying properties of the flux are shown in Fig. 4. Bulk density is in the range of 1,05 - 1,20 kg/dm³, granulometric composition is 0,2 - 1,6 mm [4]. According to the European standard EN 760, the flux is classified as SAAB 1 67 AC H5. TУ 5929-201-53304740 - 2007 has been developed for flux. The chemical composition of OK Flux 10,71 flux is given in table. 1 [4].

Table 1.

Composition of the slag base of the agglomerated flux

References:

1. Сварочные материалы для дуговой сварки. Т. 1. / Под ред. Н. Н. Потапова. — М.: Машиностроение, 1989. - С. 83 -108.
2. Houldcroft P., John R. Welding and cutting. A guide to fusion welding and associated cutting processes. Cambridge: Woodhead-Faulkner Ltd., 1988. - 128 p.
3. Muzaffar Abralov Nurilla Khudaykulov. On the question of use of agglomered welding flux in the formation of weld metal during arc welding of low-alloyed high-strength steels. Universum: технические науки: 2023. 3(108). URL: https://7universum.com/ru/tech/archive/item/15146
4. М.А. Абралов и др. Влияние состава шлакообразующей основы на десулфурирующую способность некоторых флюсов. Проблемы механики, № 4, 2020, Ташкент.
5. Хренов К.К., Кушнерев Д.М. Керамические флюсы для автоматической сварки и наплавки. Москва. Машиностроение.: 1989. -  263с.
6. Власов С.А. Восстановление гребней колесных пар подвижного состава электродуговой наплавкой // Universum: технические науки: 2023. 6(111). URL: 7universum.com/ru/tech/archive/item/15677
7. Khudaykulov N.Z., Abralov M.M., Yusupov B.D. Investigation and Selection of a Surface Electrode with Improved Properties for Restoration of Worn Parts of Machines from Steel 110G13L// International Journal Of Advanced Research in Science, Engineering and Technology - India, 2023. – Vol.10, № 5 (May). – pp. 20645 – 20648.
8. Dunyashin N.S., Khudoyorov S.S., Zairkulov E.Y., Valuev D.V., Karlina Antonina Igorevna. Study of the Effect of K₂O, Na₂O, MgO, Al₂O₃ Oxide Additions on Density, Viscosity, Separability and Covering Capacity of CaO–MnO–SiO₂ System Slag in Low Carbon Steel Automatic Submerged Arc Welding // Metallurgist, 2023