RU2279339C2 - Open electric arc welding method, welded seam and consumable welding electrode - Google Patents

Abstract

FIELD: welding by means of open electric arc with use of tubular consumable electrode.

SUBSTANCE: tubular consumable electrode contains in its core chrome, 17 - 30 mass % and nitrogen, up to 0.3 mass % or chrome, 17 -25 % and nitrogen, up to 0.3 mass %. Electrode wire or rod is used as tubular consumable electrode. Welded seam contains chrome in range 11 -15 mass %. Welded seam may have one or two layers, or several layers among which first and second layers are formed by means of electrode containing in core chrome in range 17 -30 mass %, nitrogen up to 0.3 mass % or containing chrome, 17 - 25 mass % and nitrogen up to 0.3 mass %. Some part of nitrogen of welded seam is absorbed out of environment air surrounding welding zone.

EFFECT: enhanced mechanical properties and improved corrosion resistance of welded seams without increased porosity.

12 cl, 3 dwg, 1 tbl, 1 ex

Description

The present invention relates to open arc welding using a tubular consumable welding electrode, such as an electrode wire or rod containing chromium and, optionally, nitrogen.

GB-A-2253804 describes tubular welding electrodes in the form of an electrode wire or rod containing chromium in an amount of 4-16 wt.%, Which, when using the appropriate open arc welding method, allows to obtain corrosion-resistant welds containing nitrogen absorbed from atmospheric air surrounding the electric welding arc at the welding site, and from nitrogen contained in the core of the electrode wire or rod.

The presence of a layer of chromium oxide formed during the welding process protects the weld metal from corrosion and oxidation. In addition, the presence of nitrogen improves the stability of the protective layer of chromium oxide and, in addition, helps to restore this layer in case of damage.

Another beneficial effect of nitrogen is that it reduces the softening of the weld metal at high temperatures. The weld metal containing chromium tends to soften rapidly in the presence of carbon caused by the formation of chromium carbides, but when nitrogen is replaced with a portion of the carbon, the formation of chromium carbides decreases, which leads to an improvement in the softening resistance of the weld metal.

Although chromium and nitrogen in the composition of the weld metal can form chromium nitrides, the reaction associated with the formation of chromium nitrides and the harmful effect on the microstructure and properties of the weld metal does not play a significant role.

The region adjacent to chromium carbides tends to decrease the chromium content, which leads to the rapid occurrence of intergranular corrosion.

Due to the favorable effect of nitrogen, a new generation of stainless steel castings has recently been used, and the solid electrode wire that is made from these castings is used in arc welding in protective atmospheres, when the welding arc is protected by a shielding gas. This gas protects the welding arc in order to ensure that the nitrogen present in the electrode wire does not cause porosity of the final weld metal. Pure argon and mixtures of argon and carbon dioxide, mixtures of argon and helium and other suitable gas mixtures are usually used as shielding gas.

Attempts have been made to increase the nitrogen content in the weld metal by adding gaseous nitrogen to the protective gas, but they have had limited success. Thus, there remains great interest in the production of high nitrogen steel stainless steel electrode wire designed to produce improved weld metal.

The aim of the present invention is to propose an improved method of open arc welding, which will eliminate or at least significantly reduce the disadvantages associated with the known methods discussed above.

Thus, the invention includes a method of open arc welding, which consists in feeding nitrogen and a tubular consumable welding electrode, such as an electrode wire or rod, containing 17-30 wt.% Chromium, preferably 17-25 wt.%, To the appropriate welding site.

The consumable electrode may contain nitrogen, in which case nitrogen can be introduced as a suitable nitrogen-containing substance in the core of the electrode.

Although the electrode may contain nitrogen, this gas may come fully or partially from atmospheric air surrounding the weld, in which case there is a deliberate addition of nitrogen to the final composition of the weld metal. In this case, and considering that the method that is the subject of the invention relates only to open arc welding, the need for additional gas protection is eliminated.

In fact, given that the amount of nitrogen absorbed by the weld metal at the weld point from ambient atmospheric air depends on the partial pressure of this gas at the weld point and, in addition, given that nitrogen accounts for approximately 78 vol% of atmospheric air, it is better to use open arc welding method to use such a nitrogen source with a high chromium content.

The weld metal may be applied in the form of a single or double layer surfacing containing nitrogen, fully or partially absorbed from the surrounding atmosphere during the hardening of the weld metal. Such a single-layer or two-layer surfacing can be used as a buffer layer for one or more subsequent layers of the same surfacing, such as multilayer depositions described in the aforementioned British patent.

Although consumable electrodes and corresponding welding methods described in GB-A-2253804, as discussed above, provide surfacing having acceptable integrity, strength, durability and corrosion resistance, as well as low porosity, tests have shown that an increase in chromium content in consumable electrodes up to 17-30 wt.% and, accordingly, the amount of nitrogen absorbed at the weld metal site, contributes to a significant improvement of these characteristics of the obtained weld deposits.

For a more complete understanding of the invention, an example of a preferred embodiment of an open arc welding method with a tubular consumable electrode will be described below with reference to the following example and the accompanying drawings, in which:

figure 1 shows a cross section of an electrode welding wire;

figure 2 shows a schematic cross section illustrating the effect of dilution of the electrode material, and

figure 3 shows a cross section of a multilayer weld bead.

As shown in figure 1, the electrode welding wire, indicated generally by the position 1, consists of a sheath of ferrous metal 2 and a core 3 containing chromium in an amount of 17-25 wt.% And a nitrogen-containing flux.

As shown in FIG. 2, the surfacing, indicated generally by 11, is superimposed on the substrate 12 and consists of an upper portion 13 and a lower portion 14.

Regarding this figure, the dilution of the electrode material is represented by the following ratio:

The magnitude of the molten lower part 14 is proportional to the welding conditions and, in general, the more heat is supplied during the welding process, the greater the magnitude of the molten lower part 14, which thus provides an increase in dilution of the electrode material.

Typical dilution values can vary between 10-50%. For example, if the electrode wire 1 contains 20 wt.% Chromium and if the dilution is about 30%, the chromium content in the final weld metal may be about 14%.

The dilution effect can be important in the presence of a substrate, as well as when two metals are joined together, since the level of dilution determines the chemical composition of the final weld.

The solubility of nitrogen, for example, in stainless steel is directly proportional to the amount of chromium coming from the consumable electrode. Thus, the higher the chromium content, the greater the potential solubility of nitrogen in the weld metal. For example, a chromium content of 17 wt.% Corresponds to an equilibrium nitrogen content in the range of 0.12-0.13 wt.%, While a chromium content of 25 wt.% Allows a nitrogen content of 0.25 wt.% .

According to the present invention, a welding electrode is used with a controlled chromium content in the range of 17-30 wt.%, Preferably 17-25 wt.%, Thus providing a controlled nitrogen content and one surfacing layer with the required chromium and nitrogen contents, which provide improved mechanical properties and corrosion resistance of the weld metal, but without significant porosity.

Example

Typical ranges of the chemical composition of the core of an tubular electrode wire or rod for open arc welding, intended for use in the method that is the subject of the present invention, are shown in the following table.

Table Element FROM N Mn Si Cr Mo Ni W V Co Fe Content, wt.% 0,0-0,50 0,0-0,3 0,0-4,0 0,0-2,0 17.0-30.0 0,0-5,0 0,0-8,0 0,0-5,0 0,0-3,0 0,0-5,0 Rest

Using the present invention, therefore, it becomes possible to obtain martensitic nitrogen-containing stainless steel deposited in one layer, while the weld metal contains chromium in the range of 11-15 wt.%, Using a tubular electrode wire containing chromium in the core in the range of 20-22 mass .%, taking into account dilution.

It is also possible to obtain martensitic stainless steel deposited in two layers by changing the chemical composition of the tubular consumable electrode, in particular the ratio of the content of chromium and nitrogen in it.

This can be a very useful tool, since in some cases overlapping two layers would be preferable.

The invention also provides the use of a tubular consumable electrode, such as an electrode wire or rod, in a method for producing multilayer clad substrates.

For example, most rolls used in ferrous metallurgy plants, such as continuous casting rolls used to support continuously cast slabs, or rolling rolls, are preferably made of low alloy steel with a chromium content of less than 2 wt.%, Since they are easily accessible and not expensive. However, when these grades of alloy steel are used in harsh environments where the rolls are exposed to very high temperatures and severe corrosion, the roll material suffers from premature failure. In order to solve this problem, these rolls are clad using consumable martensitic stainless steel consumables.

Thus, in order to achieve uniformity of the multilayer welds with respect to the chemical composition, in particular with respect to the chromium and nitrogen content, tubular consumable electrodes with a chromium content in the range of 17-30 wt.% For applying, by welding with an open arc, the first layer are possible on a substrate, in order to obtain a sufficient initial content of chromium and nitrogen. Subsequent weld layers, the number of which may not be limited, can then be superimposed on the first layer also using an electrode in accordance with the invention or using any other suitable welding material, for example, as described in the aforementioned British patent, namely welding alloys, containing up to 16 wt.% chromium.

Such multi-layer cladding 21 is shown in FIG. 3, on which the first layer 22 is applied to the substrate of the roll 23 in accordance with the present invention, and the subsequent layers 24 are made of any suitable welding material, for example, such as described in GB-A-2253804, containing chromium, as well as nitrogen.

Thus, the use of tubular consumable electrodes in the open arc welding method in accordance with the present invention, namely with a chromium content in the range of 17-30 wt.%, Can be used to create a buffer for multilayer cladding in order to obtain a uniform content of chromium and nitrogen.

As shown above, nitrogen can pass from atmospheric air surrounding the weld point and / or from nitrogen contained in the core material of the tubular electrode.

Thus, the invention provides a tubular consumable electrode for use in open arc welding with a chromium content in the core in the range of 17-30 wt.%, Preferably 17-25 wt.%, Along with a method for producing nitrogen-saturated welds in which nitrogen can be specially added from the ambient air in order to replace part of the carbon present, which contributes to both the improvement of corrosion resistance and the mechanical characteristics of the weld deposits.

It should be remembered that the improved stability of the microstructure of nitrogen-containing welds, especially with a low carbon content, also improves weld resistance to thermal fatigue, a property that is especially important when used at high temperatures, when the weld can be subsequently heated and cooled.

As mentioned above, a typical example of such an application is caster rolls, which are heated to more than 600 ° C due to contact with the hardened billet and then cooled to less than 100 ° C by directly cooling their surfaces with water.

A common weld material in this application is martensitic stainless steel, which usually contains 11-15 wt.% Chromium with the addition of nitrogen, as shown above.

Thus, the present invention provides for this purpose a convenient welding cladding by surfacing one or two layers using nitrogen-containing tubular welding electrodes with a chromium content in the range of 17-30 wt.% And / or with a weld metal that absorbs nitrogen from the ambient air in the process hardening of this metal.

In addition, there is no need for a shielding gas in the open arc welding method of the invention, wherein the nitrogen-saturated weld is obtained by absorbing nitrogen from the ambient air and with a consumable electrode containing at least 17% by weight of chromium. All these signs are combined, providing the beneficial use of nitrogen in the presence of an increased amount of chromium.

Claims (12)

1. A method of open arc welding, comprising feeding a tubular consumable electrode with a nitrogen-containing core to the weld site to produce a weld containing nitrogen, characterized in that an electrode is used with a chromium content in the core in the range of 17-30 wt.% And nitrogen up to 0.3 wt.%. 2. The method according to claim 1, characterized in that they use an electrode with a chromium content in the range of 17-25 wt.% And nitrogen up to 0.3 wt.%. 3. The method according to claim 1 or 2, characterized in that the electrode wire or rod is used as a tubular consumable electrode. 4. The method according to claim 1 or 2, characterized in that a weld is obtained in which at least part of the nitrogen is absorbed from the atmospheric air surrounding the weld site. 5. Weld, characterized in that it is made by the method according to claim 1. 6. The weld according to claim 5, characterized in that the chromium content in it is 11-15 wt.%. 7. The weld according to claim 5 or 6, characterized in that it is made in one or two layers. 8. The weld according to claim 5 or 6, characterized in that it is made multilayer. 9. The weld according to claim 8, characterized in that the first layer or the first and second layers are made by an electrode containing in the core 17-30 wt.% Chromium and up to 0.3 wt.% Nitrogen or 17-25 wt.% Chromium and up to 0.3 wt.% nitrogen. 10. Tubular consumable electrode for open arc welding, characterized in that the electrode core contains 17-30 wt.% Chromium and up to 0.3 wt.% Nitrogen. 11. The electrode of claim 10, characterized in that the core of the electrode contains 17-25 wt.% Chromium and up to 0.3 wt.% Nitrogen. 12. The electrode according to claim 10 or 11, characterized in that it is made in the form of an electrode wire or rod.

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