When choosing a stainless steel sheet for welded structures, not only the alloy composition is taken into account, but also the technological features of the welding process, the influence of thermal effects, the material's tendency to deformation and the corrosion resistance of the seam. If you buy a stainless steel sheet of the wrong thickness or grade, it is fraught with low structural strength, deterioration of corrosion properties and problems with the welded joint.
Which stainless steel is suitable for welding
The most common alloys are austenitic steels AISI 304, 321, 316, which are well welded by all methods and have high ductility. For structures operating in aggressive environments (for example, in the chemical industry), AISI 316L with a low carbon content is chosen, which reduces the risk of intercrystalline corrosion in the zone of thermal influence. If it is necessary to avoid heat treatment after welding, stabilized AISI 321 alloys are used, where the presence of titanium prevents carbides from falling out.
Ferritic steels (AISI 430) are more difficult to weld because they are sensitive to overheating and can become brittle due to grain growth in the heat affected zone. Soft welding modes with minimal heat input are selected for them. Duplex steels (AISI 2205) are used for structures operating at high temperatures and loads, which have good strength combined with high corrosion resistance, but the cooling rate needs to be controlled during the welding process in order to maintain the balance of austenite and ferrite.
Thickness of the welding sheet
The thickness of the stainless sheet affects the choice of welding method, the modes of heat input and the behavior of the metal during the joining process.
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Thin sheets (0.5–2 mm) require minimal heat exposure, otherwise burns and warping are possible. TIG welding (argon arc welding) is most often used, which gives a narrow and neat seam with a minimal zone of thermal influence. When welding with a semi-automatic MIG (in an inert gas environment), it is important to adjust the current and wire feed rate correctly to avoid overheating.
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Sheets of medium thickness (3-6 mm) can be welded by any method, including manual arc welding (MMA), if appropriate stainless steel electrodes are used. When using a semi-automatic machine, it is important to select a wire with an alloy similar to the base metal.
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Thick sheets (8 mm or more) require cutting edges, preheating and thermal expansion control to avoid deformation and the appearance of internal stresses. In such cases, multi-pass welding with temperature control between passes is often used.
