SU1685660A1 - Fused low-silicon welding flux - Google Patents

Abstract

The invention relates to the production of welding materials and can be used in electric arc welding of low- and medium-alloyed steels by multilayer seams. The purpose of the invention is to increase the welding-technological properties, reduce the content of harmful impurities in the directional metal, increase the resistance of the weld metal to the formation of pores and cracks and the physicomechanical properties of welded joints. The components of the flux are taken in the following ratio, wt.%: The amount of iron oxides is 2.0 ... 4.0, silica 9.0. .12.0, calcium oxide 18.0 ... 24.0, alumina 36.0 ... 48.0, margarine oxide 5.0 .. 7.0, magnesium oxide 5.0 ... 7.0, calcium fluoride 5.0 .. 8.0, the amount of oxides of sodium and potassium 1.0 ... 2.5, sodium fluoride 1.5 2.5. The mass ratio of silicon oxide, calcium oxide and aluminum oxide is 5102: CaO: A1203 1.24, and the ratio of phosphorus to the amount of iron oxides is not more than 0.004 of the table. k

Description

The invention relates to welding materials and can be used in narrow-cut electric arc welding of low-alloyed and medium-alloyed body steels used for the manufacture of critical products of atomic and power engineering, shipbuilding, heavy engineering and other industries.

The aim of the invention is to create a flux with good welding and technological properties, providing enhanced resistance of the weld metal against the formation of cold cracks and pores, a decrease in the phosphorus content in the weld metal and an improvement in the physicomechanical properties of welded joints of low and medium alloyed steels.

When building a slag system for the proposed flux with enhanced oxidizing properties, the flux should have a low content of SI02 and MpO since these oxides impair its metallurgical properties from the point of view of the repair process during welding and the adverse chemical composition of the weld metal, and also increased contamination by its non-metallic inclusions. Flux should provide good

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welding and technological properties of slag when welding thick metal in a narrow cutting. To ensure good welding and technological properties of slag with a limited silica content, it is necessary to have a sufficiently high alumina content. The deterioration of the formation of seams caused by a decrease in the content of SI02 in the flux can be compensated for by the content of A1203. This is due to the ability (like SI02) to impart viscosity to the flux. With the introduction of large amounts of SI02 into the flux, its chemical activity with respect to the weld pool metal decreases, the contamination of the weld metal with non-metallic inclusions decreases, and its mechanical properties are improved. An increase in the oxidative properties of the flux can be achieved by additionally adding iron oxides to the slag. The introduction of iron oxides into the low-silicon fluxes contributes to a significant improvement in the mechanical properties of the weld metal on low-alloyed steel x. Braking the passage of silicon and manganese-reducing processes, increases the oxidative capacity of the flux and thereby reduces the amount of hydrogen in the weld metal, improves the welding and technological properties of the flux, increases the resistance of welds against the formation of cold cracks, reduces the content of harmful impurities (S and P) in the weld metal. Flux should provide a low content of harmful impurities (phosphorus and sulfur) in the weld metal.

Based on these considerations, the alumina base of the proposed flux is taken. Based on experimental studies, it was established that the content of SI02 in the flux should be 9-12 wt.%. This ensures the minimum oxygen content in the weld metal and the optimal content of SI and Mn in the weld metal.

To obtain good welding and technological properties in the proposed flux, the SI02 / AI203 ratio should be 1/4. When determining the CaO content in the flux, it is assumed that with increasing CaO / SI02 ratio, the impact toughness of the weld metal increases, however, this results in deterioration of the technological properties of the flux. The arc stability and the formation of seams depend on the content of CaO and CaFz in the flux. The stabilizing properties of CaO increase with increasing and reach an optimum level with a content of about 20%. Empirically set the ratio of Si02 / CaO 1: 2.

Thus, in the selected slag system to obtain a good formation of seams of easy separability of the silk crust of stable arc burning, low content of nonmetallic inclusions in the weld metal, the ratio of sv2: CaO: A120z components in the proposed

The flux should be 1: 2: 4.

As additives, a certain amount of CaF2, MgO, NazO + + K20, MpO and NaF is introduced into the flux.

It is experimentally established that for

To ensure the high stabilizing properties of the arc, 5.0–8.0 wt.% CaF2 should be introduced into the flux. This amount of CaF2 in the chosen flux base is sufficient to ensure the stability of the seams.

0 against the formation of pores and cold cracks,

To improve the arc stability, compounds characterized by a low ionization potential are introduced into the flux.

5 These primarily include "20, Na20 and to some extent CaO. The introduction of 1.0–3.0 wt.% C20 and Na20 into the flux makes it possible to significantly improve the formation of welds in narrow flux prospecting with a low content of SIO2 and MpO.

Additives of MpO to the flux increase the basicity of the flux, and the brake is silicon regenerative. process and improve the formation of seams. At the same time, the introduction of a significant amount of MpO into the flux in the form of manganese ore introduces phosphorus into the weld metal. Therefore, in the proposed flux, the content of MpO is limited to 5.0-7.0 wt.%.

0 To increase the flux basicity, which in the presence of deoxidizing agents, reduces the content of sulfur in the metal and some phosphorus, as well as increases the purity of non-metallic inclusions,

5 flux injected 5.0-7.0 wt.% MgO.

To slow down the silicon recovery process during welding, which makes it possible to reduce oxygen and reduce the content of oxide silicate inclusions, the flux is introduced to 4 wt.% NaF.

To impart oxidative properties, iron oxides 2 FeO are introduced in the amount of 2.0-5.0 wt.%, In such amount as used in oxidizing fluxes for

5 welding low alloy steels. The introduction of iron oxides in such an amount changes not only the nature of the metallurgical processes, but also has a positive effect on the welding-technological properties, makes it possible to obtain a directional metal with a low content of diffuse hydrogen, low oxygen concentrations when using wires with deoxidizing agents, and also contributes to sulphurization and dephosphorization of metal welds.

Desulfurization is associated with the burning of sulfur as it increases in flux. The phosphorus of the liquid metal bath is associated with the initial oxidation of phosphorus and the subsequent transfer of its oxides to slag. The possibility of phosphorus oxidation in a liquid metal due to oxygen or ferrous inclusions dissolved in it is limited. The effort of dephosphorization of a liquid metal contributes to the development of the process of phosphorus oxidation at the slag-metal interface:

 + + +. ( one)

The absorption capacity of slag in relation to phosphorus is determined by the content of calcium oxides in the slag, which is not due to some selective means for phosphoric anhydride, but follows from the structure of Fe2 + Ca2 ions. O2, PCM. The P043 ion is almost equal in size to the ion (2.76 and 2.79 A, respectively), but its charge is less than the charge of the simplest silica-oxygen complex. Therefore, in a system containing ions Fe2 +, Ca2 +. O2 and PCm, slag micro-uniformity is largely manifested. The bonding forces of anions O with Ca2 cations are much weaker than with Fe2 + cations. In the presence of PCm3 ions, the latter are pushed aside to Ca2 ions, which are not capable of holding O2 ions to the same extent as iron ions hold. Consequently, both the oxidation process during welding and the selected slag composition contribute to the dephosphorization of the weld metal.

To increase the service life of power plants, it is necessary to ensure uniform strength of the welded joint to the base metal, low initial critical temperature of brittleness and its minimum shift during operation of nuclear power plants from neutron irradiation and prolonged thermal loads, the phosphorus content in the weld metal should not exceed 0.01 wt. .%. To provide such a phosphorus content in the weld metal, as established empirically, the ratio of the phosphorus impurity content in the flux to the total iron oxide content in it should not exceed 0.004.

This dependence is maintained within the content of total iron oxides in the flux of 2–4 May. % The transfer of phosphorus from flux to metal depends on the degree of oxidation of the flux melt, which in this case is mainly determined by the content of iron oxides in it. The equilibrium distribution of phosphorus between the metal and slag is determined by equation (1). Constant

equilibrium phosphorus distribution

(FeO) (PO3.) 2

(2)

largely depends on the content of iron oxides in the slag and the ratio between the content of phosphorus in the slag and iron oxides.

The flux provides a high stability of the arc in the welding process, good formation of the weld metal, easy separation of the slag crust, including when welding in a narrow deep cutting

joints of high thickness, obtaining seams with a minimum amount of slag inclusions, without pores and cracks, high mechanical properties of the weld and welded joints of low-alloyed medium-alloyed steels at low and high temperatures, low initial critical temperature of brittleness and low diffusion hydrogen content in the weld metal.

Thus, the flux has good welding and technological properties, provides increased resistance of the weld metal against the formation of cold cracks and pores, low phosphorus content

in the weld metal and high physicomechanical properties of welded joints of low- and medium-alloyed steels, which contributes to improving the quality and reliability of welded nodes of

products of nuclear and power engineering, i.e. has new properties that are not inherent in previously known solutions.

Example. The weighed initial components of the charge for smelting the proposed flux (AN-48) - alumina, manganese concentrate, quartz sand, fluorite concentrate, marble, magnesite, feldspar are loaded into a flux arc furnace with a water-cooled chill mold. After complete melting of the charge from the special technology, iron oxides (hematite or mill scale) are additionally introduced into the liquid slag, then wet granulation of the flux is carried out.}

The economic effect of using the proposed flux is obtained by ensuring high quality of welded joints and their increased operational reliability with an extended time resource.

To test the properties of the flux (known as AN-48) in experimental batches, a number of heats are made, from which compositions are selected with a content of components around the middle of the proposed intervals, at their boundaries and overseas areas.

The chemical composition of the melted fluxes is presented in table. one.

These fluxes are subjected to welding and technological tests.

These fluxes are tested during welding of 15H2MFA grade steel steel with a Sv-YUHMFTU wire with a diameter of 3 mm. Welding mode: ICB 420-450 A, Ug 36-38 V. VCB 21 m / h at direct current of reverse polarity.

Resistance to pore formation is determined by the Lubawski method by filling the grooves on the steel plate with various amounts of rust per 100 mm length.

The test results are shown in table 2.

As can be seen from the table. 2 data, sufficient resistance to the formation of pores (above 0.5 g / 100 mm weld) have melting 2, 3 and 4, 6.

The content of harmful impurities of sulfur and phosphorus in the weld metal is determined at different levels of the multilayer weld when welding 60 mm thick body steels.

These experiments are given in table. 3. As can be seen from the table. 3, the content of sulfur and phosphorus in the welds welded to fluxes 1 and 5 exceeds the permissible limit - 0.01 wt.%.

The content of diffusible hydrogen in the weld metal is determined by pencil samples using the glycerol method. The fluxes after smelting, granulation and calcination were kept for 2 months in an open container. After that, welding and determination of the content of diffusible hydrogen in the weld metal was carried out. The data are given in table. four.

As can be seen from the table. 4 data, in the seams welded under the flux of melting 5, the permissible hydrogen content is 3 ml / 100 g.

The critical temperature of brittleness is determined, which is determined by the value of viscosity (on average, 15.9 J / cm2 with a content of fiber

Charpy samples at least 50%). Data on impact toughness at various temperatures and critical brittleness temperature of welds after the required heat treatment are given in Table. five.

The critical temperature of brittleness (TCO) is one of the main indicators of the tendency of metal to brittle fracture. Therefore, reducing it even by 1 ° C

It is a significant contribution to the service life of welded joints of the hull equipment of nuclear power plants. As can be seen from the table. 4, seams welded under the fluxes of heats 2, Zi4 have a critical brittleness temperature below -5 ° C. 6

Thus, from the foregoing, it can be seen that the requirements for the welding and technological properties of the flux AN-48 are satisfied by melting 2, 3, 4 and 6 in their chemical composition.

To obtain a comprehensive assessment of the tendency of welded joints to the formation of cold cracks when welding under

The proposed flux is used for quantitative assessment of crack resistance (according to the Implant method) and testing of technological samples (Lehai test). Testing of samples of welded joints

15Kh2MFA steel during AN-48 submerged-arc welding. Welding is performed using Sv-10Kh2GMFTAA wire. Tests are carried out in non-preheated and pre-heated welding. The test results of the insert samples (according to the Implant method) show that when welding with the proposed flux without heating, resistance to the formation of cold cracks increases. In this case, significant

the difference in the critical stress level for samples during welding under the proposed flux, which is acre. 260 MPa against OCD 150MPa for flux welding AN-42M. In the first

In this case, the maximum time before the destruction of the samples with strained, slightly exceeding the critical, is about 2 hours, in the second - no more than 1 hour, which indicates a greater resistance of the samples. When welding specimens with preheating to 300 ° C, the critical stresses for the case of welding under the proposed 7Kr flux of 500 MPa. At stresses exceeding the critical, the maximum duration before the destruction of the specimens after loading in both cases is about 6 hours.

Tests of technological samples of the Lehai type show that to prevent the formation of cold cracks when welding steel 15X2MFA, it is possible to limit preheating to 250 ° C. Lowering the preheat temperature is a very significant factor in terms of improving the resistance of welded joints against cracking.

Thus, the assessment of the fracture toughness of welded joints shows that welding with a new flux provides higher critical stresses for delayed failure of welded joints, and also eliminates the formation of cold cracks at a lower preheating temperature.

Claims (1)

Claims of the Invention Fused welding low-silicon flux for welding low- and medium-alloyed steels containing silica, alumina, calcium oxide, manganese oxide, calcium fluoride, the amount of potassium oxides and sodium, sodium fluoride, 0 five 0 five iron oxides, phosphorus, characterized in that, in order to increase the resistance of welded joints to the formation of cracks and pores, reduce the content of harmful impurities in the weld metal and enhance the physical and mechanical properties of welded joints, in multilayer welding, the flux contains components in the following ratio, wt.%: Iron oxides2-4 Silica 9-12 Calcium Oxide 18-24 Aluminum oxide 36-48 Manganese oxide5-7 Magnesia 5-7 Calcium Fluoride5-8 The amount of oxides of potassium and sodium 1, -2.5 Sodium fluoride1.0-2.5 Phosphorus0,007-0,010 the mass ratio of silicon oxide, calcium and aluminum is 1: 2: 4, and the ratio of phosphorus to the amount of iron oxides is less than 0.004. Table 1 table 2 Table 3 Table 4 Table 5