RU2325983C2 - Electrode for underwater welding - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention can be used for underwater manual welding of higher strength low-carbon and low-alloyed steels, in particular, in repair of vital metal structures, for example, pipelines operated underwater. The electrode steel core is alloyed, mainly, with nickel and chromium. The content of the said metals is limited by 19...32% and 21...33%, respectively. The coating components content is as follows, percent by weight i.e. fluorite 22.0-31.0, rutile concentrate 22.0-37.0, iron oxide 15.0-31.0, feldspar 8.0-13.0, metallurgical magnesite 4.0-9.0, ferrosilicon 0.5-2.0, carboxymethyl cellulose 1.5-2.0. the coating weight factor makes 22-25%. The electrode allows in welding in any spatial position a high-quality weld formation, resistance of welded joints to the cold fracture formation in the low-alloyed steel thermal effects zone, higher strength and weld metal properties not worse than those of the base metal.

EFFECT: increased strength and improved weld metal mechanical properties not worse than those of the base metal.

1 dwg, 5 tbl

Description

The invention relates to the field of fusion arc welding, in particular to the development of welding materials for manual underwater wet welding of low-carbon and low-alloy steels of increased strength. It can be used in gas and other industries.

The problem of welding underwater metal structures for critical purposes has not yet been resolved. The mechanical properties of welded joints, primarily plasticity, do not correspond to the level of properties of the base metal. In addition, when welding low-alloy steels of increased strength in the heat-affected zone (HAZ), cold cracks occur, which makes it impossible to operate metal structures ("On the assessment of weldability of low-alloy steels taking into account rapid cooling in underwater welding." Avtomat. Welding, 1988, No. 12 p. 48-50). This result is caused by two main factors due to the presence of an aqueous medium - high cooling rates and a high hydrogen content. To combat cold cracks, electrodes have been developed that provide austenitic weld metal with high mechanical properties and avoid the formation of cold cracks. But the slag coating system of such electrodes allows to obtain high-quality formation of the weld metal only in the lower position. When welding on a vertical plane and especially in the ceiling position, the welding and technological properties of the electrodes deteriorate, since the physical properties of the slag formed during the melting of the electrode coating do not provide reliable protection of the molten metal, do not prevent it from dripping, as well as the formation of undercuts and sag. As a result, the formation of deposited metal becomes unsatisfactory, the mechanical properties of such joints are sharply reduced. At the same time, the majority of work in the repair of underwater metal structures (the underwater part of the ship’s hull, pipelines, vertical platform supports and walls of port facilities) must be performed in spatial positions other than the lower one. Therefore, the possibility of welding in all spatial positions is one of the key issues in the creation of electrode materials, the development or improvement of the underwater welding process.

Known electrode (USSR Author's Certificate No. 1540992 of 02/07/90, bull. No. 5) with a rod of high-alloy wire St.-07X25H12G2T, the coating of which contains (wt.%):

Marble 10-14 Fluorspar 18-22 Feldspar 2-4 Ferromanganese 7-10 Ferrotitanium 3-6 Ferrosilicon 3-6 Potash 0.5-1.5 Titanium powder 4.7-7.7 Titanium dioxide rest

The disadvantage of an electrode with such a coating is too much slag formed during its melting. Although this provides reliable protection of the weld pool metal and the seam from the aquatic environment, it makes welding impossible in spatial positions other than the lower one. In addition, as a result of an insufficient supply of austeniticity, brittle layers appear in the weld metal near the fusion line, prone to the formation of cold cracks.

Also known is an electrode (RF Patent No. 2071895, IPC V23K 35/365) with a rod of high-alloy wire St.-10X16H25AM6, the coating of which contains (wt.%):

Fluorspar 36-40 Quartz sand 17-21 Ferromanganese 8-12 Ferrotitanium 4-6 Ferrosilicon 4-6 Potash 1-3 Chromium oxide 1-3 Titanium dioxide 9-29

With this ratio of CaF ₂ and TiO _{2, the} transfer of molten metal has a pronounced large droplet character, which significantly impairs the stability of arc burning. The high content of SiO ₂ leads to an increase in slag viscosity, as a result of which it does not completely cover the deposited metal, the formation of the weld deteriorates, which makes it impossible to weld in spatial positions other than the lower one. This is confirmed by the results of tests of welding and technological properties conducted by the developers of the electrode (Welding, No. 11, 2000).

Both of these electrodes make it possible to obtain welded joints with a level of mechanical properties that corresponds to the level of properties of the base metal and to avoid the formation of cold cracks in the HAZ of low alloy steels of increased strength. But their welding and technological properties do not meet the requirements.

As a prototype, we chose an electrode (USSR Author's Certificate 1549706 dated 03.15.90, bull. No. 10), the coating of which contains (wt.%):

Marble 14-16 Fluorspar 24-26 Feldspar 3-5 Ferromanganese 9-11 Ferrotitanium 4-6 Ferrosilicon 4-6 Potash 0.5-1.5 Titanium dioxide rest

The electrode rods are high-alloy steel wire, which contains chromium and nickel in an amount of at least 13.5 and 22%, respectively.

In our experience in the study of slag systems, the range of TiO ₂ / CaF ₂ ratios used in the prototype is not optimal for the high-quality formation of welds under water, and the introduction of marble in amounts that exceed 10% into this system also worsens the welding and technological properties electrode coating. This does not allow their use for high-quality welding in all spatial positions. In addition, the introduction of marble is not justified due to the fact that a slight (up to 5%) decrease in the hydrogen content in the deposited metal when the atmosphere of the arc gap is diluted with gaseous decomposition products of marble is practically irrelevant due to the austenitic structure of the weld metal.

The objective of the invention is the provision in welding in all spatial positions of the qualitative formation of the weld metal, the resistance of welded joints against the formation of cold cracks in the HAZ low-alloy steels of increased strength and mechanical properties of the weld metal at the level of the properties of the base metal.

The problem is solved in that the electrode for underwater welding, including a rod of high alloy steel and a coating containing rutile concentrate, feldspar, fluorite and ferrosilicon, differs from the known ones in that the values of nickel and chromium equivalents of the rod are limited by the following values: Ni _eq. 19 ... 32%, Cr _equiv. 21 ... 33%, and the coating contains iron oxide, metallurgical magnesite and carboxymethyl cellulose in the following ratio of components, wt.%:

fluorite 22.0-31.0 rutile concentrate 22.0-37.0 iron oxide 15.0-31.0 feldspar 8.0-13.0 metallurgical magnesite 4.0-9.0 ferrosilicon 0.5-2.0 carboxymethyl cellulose 1.5-2.0

while the coating mass coefficient is 22 ... 25%.

A decrease in the hardening temperature of the slag, its elongation, as well as an increase in the wetting angle of the main metal with molten metal were achieved by introducing a balanced amount of fluorite and iron oxide into the coating. The introduction of a significant amount of fluorides provides a decrease in the hydrogen content in the weld metal, desulfurization of the molten metal, a high degree of assimilation of easily oxidizable elements, and together with feldspar, contributes to the formation of a slag crust, which reliably protects the joint from the environment, and to obtain a good formation. This technical solution is the result of a thorough study of the influence of the components of the CaF ₂ -TiO ₂ -FeO ternary system on the welding and technological properties of electrodes for underwater wet welding. The use of a high-alloy wire as a core guarantees the production of an austenitic-type weld metal, which eliminates the formation of cold cracks in the HAZ of low-alloy steels of increased strength.

The essence of the experiments is illustrated in the drawing, where the concentration triangle qualitatively reproduces the nature of the influence of the ratio of the ingredients of the CaF ₂ -TiO ₂ -FeO system on the welding and technological properties of the electrodes. Here, A is the region of optimal electrode coating compositions for performing wet underwater welding in all spatial positions of multipass butt welds.

Direction 1 - with such a change in the ratios of ingredients, the tendency to form weld beads of a triangular shape, the formation of a solid ceramic slag crust with a tendency to jam during multilayer welding of butt joints, an increase in the coefficient of reinforcement of joints, coarsening of flakes, the formation of defects in the form of undercuts, slag inclusions during welding increases multipass seams.

Direction 2 - with such a change in the ratios of the ingredients, the tendency to form a solid ceramic slag crust, high uneven coarse scaly crusts, and finally rounded cast rollers, worsens the separation of the slag crust, large drops appear next to the seam, the arc voltage increases, the mode becomes unstable.

Direction 3 - with such a change in the ratios of the ingredients, the tendency to form rollers with a low gain, a finely scaly surface and a smooth transition to the surface of the base metal or pre-welded rollers increases, the transfer of molten metal becomes small-droplet, the formation of an amorphous slag coating of deposited rollers is observed, which is easily removed with a brush, the possibility of high-quality welding in spatial positions other than the lower ogre ichivaetsya.

Thus border content fluorite, rutile concentrate and iron oxide, as well as their relation to the electrode surface, which serves as the invention defined in the study of the slag system CaF ₂ -TiO ₂ -FeO and correspond to the values optimal area A formulation system.

In order to improve the stabilization of the arc gap and ensure stable arc burning both on the direct and reverse polarity, as well as a certain increase in the shape factor, magnesite (in the form of metallurgical magnesite) is introduced into the coating, which also practically prevents spatter. The introduction of magnesite in an amount that exceeds the accepted limit leads to coarsening of the scaly shape of the rollers and their unevenness in height.

Iron oxide, when CaF ₂ -TiO _{2 is} introduced into the slag system, reduces its melting temperature and the surface tension coefficient, which leads to the droplet transfer of the molten metal and the formation of rollers with a finely scaly surface and a smooth transition to the base metal or the metal of the previously deposited rollers. The introduction of the coating of the proposed electrode FeO in an amount less than stated, leads to the formation of "hump" rollers. Exceeding the amount of FeO over the proposed limit contributes to the formation of low-melting slag, which makes it impossible to qualitatively form vertical and ceiling joints. The introduction of FeO in the proposed amount in the presence of calcium fluoride causes the formation of iron fluorides, which also provide an additional reduction of diffuse hydrogen in the weld metal.

The introduction of feldspar at the indicated boundaries causes the formation of a sufficiently dense slag crust and, together with magnesite, stabilizes the arc gap. An increase in the content of feldspar over the specified limit leads to the formation of more fluid slags of large mass, which complicates the welding in spatial positions.

Ferrosilicon facilitates the transition of the required amount of manganese from the rod to the weld metal. But an increase in its content above the proposed limit leads to an increase in intracrystalline segregation in the metal of austenitic joints, as a result of which silicon enriches the boundary layers of dendrites. This reduces the critical rate of deformation of the austenitic weld metal and their resistance to the formation of hot cracks.

The composition of the welding wire was selected from the following considerations. An insufficient doping level (Ni _equiv. <19% and Cr _equiv. <21%) leads to the formation in the weld metal near the fusion line of a brittle martensitic layer affected by cold cracks. When using wires with excessive doping levels, there is a risk of hot cracking, which can be reduced by introducing molybdenum. This allows you to set the upper limit of alloying at the level of Ni _equiv. = 32% and Cr _eq. = 33%.

For experimental verification of the proposed technical solution, 5 batches of electrodes with a diameter of 4 mm were made with rods made of St.-10X16H25AM6 wire with a nickel equivalent of 28.81% and a chromium equivalent of 21.8%, the coating composition of which is shown in Table 1.

Table 1 The coating composition of the electrodes, wt.% Coating
Components one 2 3 four 5 fluorite twenty 22 26 31 34 rutile concentrate 39 37 29th 22 eighteen iron oxide eleven fifteen 22 31 34 magnesite eleven 9 8 four 3 feldspar fifteen 13 eleven 8 7 ferrosilicon 2 2 2 2 2 carboxymethyl cellulose 2 2 2 2 2

To evaluate the welding and technological properties, a diver-welder in the laboratory pool at a depth of 2 m in all spatial positions welded butt samples of steel St3 14 mm thick. The formation of the deposited metal was evaluated using a three-point system taking into account the appearance, separability of the slag, the nature of the slag crust, spatter, combustion stability, etc., table 2. Analysis of the results allows us to conclude that the electrodes coated with the proposed composition provide satisfactory formation of multilayer welds in all spatial positions.

In the manufacture of electrodes for further testing, coating No. 3 was used, table 1.

Tests of the manufactured electrodes included welding and metallographic studies of technological samples of the Tekken type and welding of butt joints in the lower, vertical and ceiling positions to determine the mechanical properties. As the base metal, 17G1S steel was used, which was predisposed to the formation of cold cracks in the HAZ.

To determine the crack resistance of welded joints, experimental wires with alloying within Ni _{equiv were} used as rods _. = 19 ... 32% and Cr _equiv. = 21 ... 33%, table 3. The test results are shown in table 4.

Thus, the use of rods of wires with a doping level of Ni _equiv. = 19 ... 32% and Cr _equiv. = 21 ... 33% provides welded joints without cracks.

To determine the mechanical properties of the weld metal, electrodes with rods made of St.-10X16H25AM6 wire were made. The test results are shown in table 5. Their analysis allows us to draw the following conclusions. The electrodes of the proposed composition ensure the absence of cracks both in the weld metal and in the heat affected zone and the level of mechanical properties that exceeds the level of mechanical properties of 17G1S steel.

Table 5 Test results of electrodes with rods made of St. 10X16H25AM6 wire Spatial position Mechanical properties of weld metal Tekken Test Tests σ _t , MPa σ _b , MPa δ,% Lower 420 590 32 no cracks Vertical 390 570 32 Ceiling 380 570 thirty

Thus, the proposed electrode makes it possible to obtain a high-quality welded joint in all spatial positions with the necessary level of mechanical properties when welding low-alloy steel of increased strength without cold cracks in the heat-affected zone under water and can be recommended for use in the repair of underwater pipelines.

Claims (1)

The electrode for underwater welding, which includes a rod of high alloy steel, and a coating containing rutile concentrate, feldspar, fluorite and ferrosilicon, characterized in that the values of nickel and chromium equivalents of the rod are limited to the following values, wt.%: Ni _eq. 19-32 Cr _eq. 21-33 and the coating additionally contains iron oxide, metallurgical magnesite and carboxymethyl cellulose in the following ratio of components, wt.%: fluorite 22.0-31.0 rutile concentrate 22.0-37.0 iron oxide 15.0-31.0 feldspar 8.0-13.0 metallurgical magnesite 4.0-9.0 ferrosilicon 0.5-2.0 carboxymethyl cellulose 1.5-2.0 while the coating mass coefficient is 22-25%.