Cold welding of cast iron with simple electrodes designed for welding cast iron hot, does not provide positive results, since at high cooling rates, corresponding to the given conditions of welding, a structure of white cast iron in the weld and heat affected zone of high-temperature region, and is a sharp hardening of the metal base stations heat-affected zone, heated in the welding process temperature above Ac 3 . The resulting strain with the ability to exceed the deformation of the weld metal and heat affected zone, resulting in cracks.
To prevent bleaching is necessary to provide such a composition of the weld metal, for which these conditions will be obtained structure of gray cast iron with the most favorable form of graphite inclusions. This can be achieved by introducing into the weld metal is sufficiently large amount of iron and alloying grafitizatorov elements contributing to the spheroidization of carbides (magnesium). An example of such electrodes can serve as electrodes EMCH brands, the rod which is iron with a high (up to 5.2%) silicon content, covering a two-layer: first layer - dopant, the second - provides gas and slag protection:
1st layer
Graphite - 41%
Silikomagny - 40%
Iron scale - 14%
Aluminum (powdered) - 5%
2nd layer
Marble - 50%
Fluorspar - 50%
(The relative weight of each layer - 15-20%)
When these electrodes welding of cast iron parts with wall thickness up to 12 mm without preheating can get the seams and weld zone without bleaching and quenching. Slow the rate of cooling at the eutectic temperature promotes the reaction between iron powder and aluminum dross, which flows with heat release. When welding electrodes, these massive parts for defect-free welds have to warm up to a temperature of 400 ° C depending on the thickness and hardness of cast iron products. To improve the workability and the slight increase in ductility of the weld metal using electrodes made of nickel-iron, such as Ni-resist or nikrosilalya.. composition of the electrode rods of nickel pig iron,%
The electrodes are made of nickel iron joints ensure receipt, having a good workability. Coating applied to the rods of nickel pig iron is recommended the following composition: 55% of silicon carbide, barium carbonate 23.7%, 21.3% sodium silicate. The coating thickness should be 0.5-0.8 mm in the direction of the use of rods with a diameter of 7-8 mm. Welding is performed in several layers, with the reciprocating movement of the electrode. The main drawback of the nickel-iron electrodes - an increased tendency to hot cracking.
Get in the weld metal and weld metal can be cast iron, using special welding materials, which provide a doping electrode surface. Examples of such materials can serve as electrodes, which rod is made of low carbon wire, such as stamps, or CB-08 CB-08A in accordance with GOST 2246-70, and the dopant coating contains a sufficient number of elements grafitizatorov - carbon and silicon. The most characteristic mark EMCHS electrodes, the core of which consists of a low-carbon electrode wire and the coating of three layers:
1st layer
Graphite - 50% Silikomagny - 41% Hematite - 6% Aluminum (powder) - 1.5% Bentonite - 1.5%
2nd layer:
Marble - 50% of fluorspar - Bentonite 47.5% - 2.5%
Third layer
Graphite - 100%
The electrodes are made by sequential deposition coating, zameshennoy liquid glass, the thickness of each layer should provide the relative weight of 1st layer of 25 - 30% of 2 - and third - 10-15%. As can be seen from the above coating composition, the 1st layer is the alloying, 2nd slag and gaseous, 3rd - gas protection. Graphite and silikomagny belonging to the 1st layer are grafitizatorami, and magnesium, to some extent contributes to spheroidization of graphite, hematite, and aluminum, engaging in interaction, contribute to some reduction in the rate of cooling at the eutectic temperature, thereby obtaining the structure in the weld cast iron.
The application of these electrodes for welding of cast iron products with a relatively small thickness of the welded metal (up to 8 - 10 mm) allows to obtain high quality welds without preheating of the product; at large thicknesses should be used for semi welding. And cold welding of cast iron for semi automatic, semiautomatic and mainly use a special flux cored wires to ensure getting in the seam of gray cast iron. For cold-welding products with relatively small wall thickness (in place of welding) wire is recommended brands HRE-1, the welding-wire for semi CFR-2.
Mechanized welding flux cored wire produces weld metal and weld metal, similar in composition and structure of welded cast iron. When tea leaves large defects in iron castings, which is necessary to fix a large amount of metal afloat, as well as in the manufacture of large bulky items from high-strength cast iron with nodular graphite can be used electroslag welding plate electrodes, representing a cast iron plate with the contents of the corresponding elements grafitizatorov ( carbon and silicon) is equal to the last content in the electrode rods grades A and B, and 0,04 - 0,08% Mg.
In electroslag welding of cast iron used fluoride and non-oxidative desulfurizing flux. Slow cooling of the weld metal and heat affected zone, which is characteristic for electroslag welding produces welds with no bleached and hardened areas, cracks, pores and other defects. Electroslag welding provides a satisfactory mechanical properties of welded joints of cast iron and its good workability.
In addition to the total heat applied during welding for semi variety of ways, in some cases, when the rigidity of the product is relatively small, we can restrict ourselves to local heating to the desired temperature. During the welding process is necessary to pay attention to the fact that the product is not in the weld cooled below the set temperature heating.
Cold welding electrodes, cast iron, provides in low-carbon steel weld metal
If you run surfacing on cast iron electrodes designed for welding of carbon or low alloy structural steels, the 1-m layer, even with a relatively small percentage of participation of the base metal will high-carbon steel, which is at cooling rates that occur in welding without preheating the product, acquires sharp hardening. Therefore, the metal 1 layer will have a high hardness, low deformation capacity and will be prone to the formation of cold cracks and porosity. In the 2nd layer, of course, the share of iron is reduced, but the carbon content in it will be still at a high level, which will also lead to hardening and eventual cracking. Subsequent layers of the share of iron to be insignificant, and the weld metal will have a certain level of plasticity.
In connection with the foregoing, such steel electrodes can be used only for decorative welding of the small size of defects, if the weld is not subject to requirements to ensure the strength, density and workability of the cutting tool. In order to reduce the stake of the base metal in the weld and heat affected zone sizes, including the areas of bleaching and quenching, small diameter electrodes are used (for the 1st layer of 3 mm, for the 2nd and subsequent 3-4 mm) at low currents [Isv = (20-25) de, without overheating the base metal.
First performed facing the 1st layer. Welding is performed in short segments, ridges small sections [F = (6-8) de] randomly at intervals to cool the weld and heat affected zone to a temperature of 50-60 ° C. In a second layer applied to the 2nd transverse ridges, then 3 - First, after the third layer can be applied to multiple modes of higher energy per unit length, but also with interruptions to the heating zone was a small iron. To reduce the stresses are useful in forging middle-class.
When welding low-carbon iron electrodes the most general weak spot weld - the weld zone at the fusion boundary. The fragility of this area and the presence of cracks in it often leads to peeling of the seam of the base metal. To increase the strength of the welded joint, when it is not imposed on other requirements (such as repairing frames, frames, brackets and other load-bearing elements of thick-walled structures), used steel studs, which are partially unload the weakest part of the weld - a line of fusion.
Studs are threaded, they vvertyvayut the body part to be welded. Size of studs are usually dependent on the thickness of the workpiece. Practice, the following recommendations: diameter 0.3-0.4 stud thickness of parts, but not exceeding 12 mm, depth 1.5 diameter rods vvertyvaniya them, but no more than half the thickness of the workpiece, the height of the protruding part of 0,75-1,2 diameter studs. Studs are placed in a checkerboard pattern on the beveled edges of the parts in a row on the surface of the part on each side of the junction, the distance between them must be equal to 6.4 diameters of the pins.
Welding is performed in the following order. First scald each pin and the surface of the veneer edges electrodes 3 mm in diameter at low currents. Then, on the edge of the first hairpin coated bead and fill in a breaker, as in the previous case. To reduce the carbon content in the weld metal invited to perform welding on a layer of flux containing 30% iron scale (eg, borax 50%, 20% caustic soda, iron dross 30%). Carbon entering the weld pool, in the high part of it is actively oxidized and removed from it in the form of carbon monoxide, are not soluble in the metal. As a result, the concentration of carbon at the time of solidification of the weld pool is reduced. Hardness of weld metal decreases, the deformation capacity increases.
However, for more complete burning of the effect of carbon is necessary to use welding regimes, characterized by relatively high energy per unit length, which, however, affects the heat-affected zone: it formed a significant-sized areas of bleaching and quenching, leading to the formation of cracks. When welding cast iron with a fairly high content of elements grafitizatorov with a small wall thickness of welded parts can get positive results.
More successful was the other way. In the weld metal is introduced strong karbidoobrazovatel - vanadium. In this case, the carbides are formed mainly of the element does not dissolve in iron and having a non-solid form of fine particles. Metal base in this case is decarburized and enough plastic. An example is the mark electrodes TSCH-4 with a rod of low carbon wire marks, or CB-08 CB-08A and cover the following composition: 12% of marble, fluorspar 16%, 66% ferrovanadium, ferrosilicon 4% and 2% potash, liquid glass 30 % by weight of dry mixture. The metal deposited by these electrodes have the following composition: 0.15% C, up to 0,6% Si; 0,5% Mn; 8,5-10,5% V; sulfur and phosphorus to 0.04% each. These electrodes first veneer edge at low currents [Isv = (20-25) de]. Welding is performed by parallel ridges with overlapping each previous half its width. After a 2-layer current strength increased by 15-20%, a breaker completely filled electrodes UONI-13/45.
Scope of the electrodes - Welding of damaged parts and welding defects in castings from gray and ductile iron. If necessary, you can also weld connections of gray and ductile cast iron to steel. Welds made these electrodes have satisfactory workability, density and relatively high strength. By ways of ensuring the receipt of the weld metal of low carbon steel may also include mechanized welding short sections of the electrode wire Sv-08GS marks, or St-08G2S diameter of 0,8-1 mm in carbon dioxide. Welding current of 50-75 A, arc voltage 18-21 V, welding speed 10-12 m / h
See also:
Welding of Cast Iron
Composition and Properties of Iron
Marking of Iron
Basic Information on Weldability and Technological Advice
Structural Transformations in the Heat Affected Zone during Welding of Cast Iron
Effect of Cooling Rate on the Structure of the Weld Metal and Heat Affected Zone
The Technological Process of Hot Welding
Cold Welding of Cast Iron with Simple Electrodes
Cold Welding Electrodes, Cast Iron, Providing the Receipt of the Weld Metal Color
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