RU2309829C2 - Melt flux for powered welding of low alloy steel - Google Patents

Abstract

FIELD: production of welding flux used for powered welding of modern vessels of nuclear reactors and other high pressure vessel in power machine engineering and petro-chemistry.

SUBSTANCE: melt flux contains next relation of ingredients, mass %: SiO₂, 20 - 27; CaO, 12 - 18; Al₂ O₃, 13 - 18; CaF, 2O - 33; MnO, 7 - 13; TiO₂, 3 - 10; K₂ O, 1 - 5; Fe₂O₃ as impurities no more than 1.5; S, no more than 0.01; P, no more than 0.01; while 0.15 < TiO₂/SiO₂ < 0.40. Flux provides enhanced reliability and resource of made equipment due to lowered temperature of brittle-viscous transition (Tko) of seam metal. Flux allows perform welding at rate higher than 28m/h.

EFFECT: lowered labor consumption of process for making welded structures.

2 cl, 4 tbl

Description

The invention relates to the field of production of welding flux used for mechanized welding of modern cases of atomic reactors and other pressure vessels in power engineering and petrochemicals.

At present, flux grade ФЦ-16А (OST 24.948.02-99, table 1) is widely used for mechanized arc welding of low alloy steels in nuclear power engineering.

Flux FTs-16A contains SiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, MgO, NaF in its composition in the following ratio, wt.%

SiO ₂ 26-32 CaO 15-21 Al ₂ About ₃ 17-21 CaF ₂ 12-18 MnO 3-6 MgO 6-9 NaF 3-8 impurities Fe ₂ O ₃ no more than 1,0 S no more than 0,01 R no more than 0,01

The flux has good welding and technological properties, however, its use leads to an increased content of diffusion-mobile hydrogen in the weld metal - 4.6-5.0 cm ³ with the required - not more than 3.0 cm ³ per 100 g of weld metal. This leads to pore formation and the risk of cold cracks in the weld metal. This drawback is due to the increased content of basic oxides and components of CaO, CaF ₂ , MnO, MgO, NaF relative to the content of acidic oxides SiO ₂ , Al ₂ O ₃ in the flux composition and its low oxidizing ability.

The flux SU 1754377 A1 B23K 35/362 contains SiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, MgO, Fe ₂ O ₃ , TiO ₂ , K ₂ O and / or Na ₂ O in its composition in the following ratio of components , wt.%:

SiO ₂ 16-28 CaO 2-7 Al ₂ About ₃ 14-22 CaF ₂ 2-8 MnO 10-20 TiO ₂ 16-21 MgO 11-16 Fe ₂ O ₃ 2-6 K ₂ O and / or Na ₂ O 0.5-4

in this case, the ratio: K ₂ O + Na ₂ O / CaF ₂ ≥0.11 should be satisfied.

Due to the presence of components that increase the oxidizing ability of the flux, such as TiO ₂ and Fe ₂ O ₃ , the flux allows you to get welds without pores and with a hydrogen content of not more than 3.0 cm ³ per 100 g of weld metal.

The disadvantage of flux is the high content of MnO. A manganese content of more than 13-15% leads to an increase in MnO activity, due to which reaction 2 (MnO) ↔2 [Mn] +2 {O} is developing. The reaction restores manganese, which passes into the weld metal, thereby reducing the resistance of the metal to thermal embrittlement.

Also known is welding flux SU 1754378 A1, taken as a prototype, containing SiO ₂ , TiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, Cr ₂ O ₃ , Fe ₂ O ₃ , S, P in its composition in the following the ratio of components, wt.%

SiO ₂ 20-25 CaO 13-18 Al ₂ About ₃ 13-18 CaF ₂ 20-30 MnO 7-13 TiO ₂ 3-10 Cr ₂ O ₃ 0.3-4 Fe ₂ O ₃ 0.4-0.9 S 0.01-0.005 R 0.01-0.005

in this case, the ratio should be satisfied: 1.1≤SiO ₂ + Cr ₂ O ₃ / CaO≤2.2.

Flux allows you to provide good quality metal with high mechanical properties with satisfactory separability of the slag crust.

The disadvantages of flux include the following:

- poor formation of weld metal during welding at speeds above 28 m / h due to a significant deterioration in the stability of the arc process with an increase in welding speed;

- the lack of stability in obtaining satisfactory technological properties when welding seams with a thickness of more than 50 mm and an angle of opening of the edges of less than 8 ° (The content of TiO ₂ on the upper aisle, while the content of SiO ₂ on the lower one, leads to the appearance of pores when surfacing the beads located above the weld height above 50 mm, the Content of TiO ₂ on the lower aisle, while the content of SiO ₂ on the upper side, leads to poor separation of the slag crust when welding in the groove with an opening angle of less than 8 °.);

- the presence of Cr ₂ O ₃ in the flux leads to the formation of highly toxic aerosols (chromic anhydrite, chromates, dichromates) in the air during the manufacture and use of the flux. These substances have 1 hazard class. In the manufacture and use of this flux, the content in the air of these aerosols significantly exceeds the MPC (0.01 mg / m ³ ).

The technical result of the invention is:

- ensuring good formation of the weld metal at welding speeds above 28 m / h, when welding in the groove with an opening angle of less than 8 °;

- stability of producing deposited metal without pores with a weld thickness of more than 50 mm;

- ensuring sanitary and hygienic standards for MPC of harmful substances in the air of the working area during the manufacture and use of flux.

The technical result is achieved in that the fused flux for mechanized welding of low alloy steel containing SiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, TiO ₂ and having impurity restrictions, according to the invention additionally contains K ₂ O in the following ratio of components, wt.%:

SiO ₂ 20-27 Cao 12-18 Al ₂ About ₃ 13-18 CaF ₂ 20-33 MnO 7-13 TiO ₂ 3-10 K ₂ O 1-5 impurities Fe ₂ About ₃ no more than 1,5 S no more than 0,01 R no more than 0,01

in this case, the ratio: 0.15≤TiO ₂ / SiO ₂ ≤0.40.

The addition of K ₂ O to the flux improves the ionization and stability of the arc burning, thereby ensuring a good formation of weld metal at welding speeds above 28 m / h. A decrease in the K ₂ O content of less than 1% leads to unsatisfactory formation of the weld metal during welding at speeds above 28 m / h due to a significant deterioration in the stability of the arc process due to a decrease in the number of easily ionized potassium atoms. On the other hand, an increase in the K ₂ O content of more than 5% leads to porosity of the weld metal.

The established ratio of 0.15≤TiO ₂ / SiO ₂ ≤0.40 allows us to guarantee good technological properties of flux during welding with an opening angle of edges less than 8 ° and the thickness of the welded parts more than 50 mm. When the value of the specified ratio is below 0.15, the slag becomes more viscous and “long”, which leads to a deterioration in the separability of the slag crust, this is especially true when welding in narrow grooves (the angle of the edges is less than 8 °). When this ratio is exceeded more than 0.40, pores are observed in the deposited rollers located along the seam height above 50 mm. This is due to the fact that a decrease in the content of SiO ₂ while increasing the content of TiO ₂ reduces the resistance of the flux against hydration, thereby increasing the concentration of hydrogen in the weld metal.

Chromium oxide is excluded in order to ensure sanitary and hygienic standards for maximum permissible concentration of harmful substances in the air of the working area during the manufacture and use of flux.

It was experimentally established that the content of Fe ₂ O ₃ up to 1.5% does not lead to the burning of alloying metal components in amounts that affect the physicomechanical properties of the deposited metal. The lower limit of the content of Fe ₂ O _{3 is} excluded due to the fact that good separability of the slag crust is provided by the ratio of 0.15≤TiO ₂ / SiO ₂ .

The flux is made by the method used for the manufacture of fused welding fluxes, i.e. fusion of the feedstock (marble, fluorspar, quartz sand, alumina, manganese, rutile and potash) in flux-smelting furnaces, followed by granulation of the melt with water.

For laboratory tests, 6 experimental flux melts were made with different contents of the main components: SiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, TiO ₂ , K ₂ O (Table 1). Welding of plates made of steel grade 15X2MFA (TU 108.131-86) was performed by wire grade Sv-10KhMFTU ⌀4 mm (TU 14-1-4818-90) (chemical composition in Table 2) in the following modes:

Isv = 550-600A, Ud = 30-34V, Vsv = 28-34 m / h.

The angle of the opening of the edges was 2 ° ± 30 ^/ .

The thickness of the welded plates is 90 mm.

During the tests, the following parameters were evaluated:

- chemical composition of the weld metal;

- formation of a weld bead;

- separability of the slag crust;

- the presence of pores in the weld metal;

- concentration of Cr compounds in the air of the working area.

Tables 1, 2 and 3 show the results of comparative tests of pilot flux and prototype melts when welding with a Sv-10KhMFTU grade wire in narrow cutting.

The results confirm the deterioration of the separability of the slag crust at 0.15> TiO ₂ / SiO ₂ and the appearance of pores at TiO ₂ / SiO ₂ > 0.4. With the introduction of K ₂ O into the flux, the formation of the weld metal becomes satisfactory at a welding speed above 28 m / h.

The optimal limits of the content of the components of the fused flux of the claimed composition, as well as their ratio, were determined by the technological properties and results of determining the chemical composition of the deposited metal. The test results confirmed the high technological properties of the claimed flux when welding at high speeds of large thicknesses.

Thus, the proposed fused flux for mechanized welding of pearlite-grade steels allows welding at increased speeds with an opening angle of less than 8 ° at thicknesses above 50 mm. The technical and economic effect when using the proposed flux is expressed in the reduction of labor costs due to:

- reducing the mass of weld metal by reducing the angle of cutting;

- reducing the complexity when cleaning the seam and correcting defects (removing pores), as well as by reducing the cost of labor protection (ventilation).

Table 3
The chemical composition of the weld metal Sample number The content of elements in the weld metal FROM Si Mn Cr V Ti Mo R S Cu one 0.04 0.32 0.85 1,52 0.16 0.01 0.45 0.011 0.012 0,07 2 0.06 0.24 0.72 1.65 0.20 0.02 0.44 0.010 0.011 0,07 3 0,07 0.26 0.68 1,63 0.20 0,03 0.43 0.012 0.010 0,07 four 0.05 0.28 0.70 1.65 0.19 0,03 0.45 0.011 0.009 0,07 5 0.06 0.21 0.70 1,63 0.20 0,03 0.45 0.010 0.010 0,07 6 0.05 0.25 0.71 1,63 0.19 0,03 0.44 0.010 0.010 0,07 Prototype 0.04 0.33 0.92 1.46 0.15 0.01 0.44 0.014 0.011 0,07

Table 4
The content in the air of the working zone of aerosols of chromium compounds No. of swimming trunks the content in the air of the working zone of aerosols of chromium compounds (chromic anhydrite, chromates, dichromates in terms of Cr ₂ O ₃ ) in the manufacture of flux when using flux mg / m ³ Experienced pl. one 0,086 0.013 Experienced pl. 2 0,079 0,021 Experienced pl. 3 0,085 0.015 Experienced pl. four 0,091 0.011 Experienced pl. 5 0,085 0.016 Experienced pl. 6 0,083 0.013 SU1754378 A1 (prototype) 4,785 1,670

Claims (2)

1. Fused flux for mechanized welding of low alloy steel, containing SiO ₂ , CaO, Al ₂ O ₃ , CaF ₂ , MnO, TiO ₂ , characterized in that it additionally contains K ₂ O in the following ratio of components, wt.%: SiO ₂ 20-27 CaO 12-18 Al ₂ O ₃ 13-18 CaF ₂ 20-33 MnO 7-13 TiO ₂ 3-10 K ₂ O 1-5 and impurities no more than 1,52, wherein 0.15 T TiO ₂ / SiO ₂ 0 0.40. 2. The fused flux according to claim 1, characterized in that it contains impurities in the following ratio, wt%: Fe ₂ O ₃ no more than 1,5 S no more than 0,010 R no more than 0,010