Cast iron is known to be an alloy of iron and carbon. In this case, the content of the latter should exceed two percent. Depending on the state in which the carbon is in the alloy, gray and white types of cast iron are distinguished. In the first form, carbon is in the form of graphite, in a free state, which leads to its good machinability. Since this element is in a bound state in white cast iron, it is almost impossible to weld it. The material is light in color when broken.
How is cast iron welded? To begin with, this material is not the most suitable for this type of processing. When welding, it is deformed and cracks easily form in it. This is due to the special structure of carbon in its fracture. Oiled cast irons, as well as those that have been exposed to various aggressive environments, cannot be welded. However, species with a fine-grained structure and a light gray color are optimally suited for this. Welding cast iron has the following side effects: bleaching and, as a result, the appearance of a layer of white cast iron at the welding site, which cannot be processed in any way; as already mentioned, the formation of cracks; increase in voltage in the welding zone; weld pool metalbecome porous due to the burning of carbon with the simultaneous formation of carbon dioxide. So, this process causes a lot of difficulties. Nevertheless, welding of cast iron is used quite widely. It has three main ways: cold, semi-hot and hot.
The first is the lack of preheating. Cold welding of cast iron is carried out with steel, cast iron and electrodes made of non-ferrous metals and alloys. The main thing is to avoid strong heating in the heat-affected zone. To do this, when using steel electrodes, the first layer is applied with electrodes of small diameter with a low carbon content, a thin coating. The current strength at this stage of work should not exceed 90 amperes. Subsequent layers are applied with electrodes of a larger diameter, the coating can be either thin or thick.
One important rule is that metal seams should be applied with short breaks so that the temperature in the heat-affected zone does not exceed sixty degrees.
If welding needs to be carried out on critical products, then special devices can be used. These are the so-called screws - special studs that are made of mild steel. Their purpose is to connect the weld metal with cast iron. Welding is performed first around them, and then in the usual manner. When it is necessary to weld any casting defects, cracks and other weak points, electrodes made of nickel-based or copper-based alloys are often used. Contributinggraphitization, they prevent the appearance of a wide bleaching zone. Welding cast iron at home is mainly done in a cold way. In this case, any of the types of electrodes listed above can be used.
Hot welding of cast iron involves heating the workpiece before starting work with it. This method reduces the stress of the metal structure. The semi-hot method is a modified hot method. It consists in metal graphitization and general or local heating to a certain temperature. These methods are applied in different ways.
If it is necessary to weld individual parts made of cast iron, then in this case a cold welding method is used. If the work is carried out at the enterprise, on an industrial scale, the hot method is used.
