Welding methods

When welding it is necessary to consider the difference between the physical properties of austenitic stainless steel and carbon steel. The specific electrical resistance of austenitic steel, alloyed with nickel and chromium is about 6 times higher, and thermal conductivity is much lower, the coefficient of thermal expansion along the length is 50% higher. Welding of austenitic steel can be accomplished by any method. Manual arc welding is usually used if the material thickness does not exceed 1.5 mm. Tungsten inert gas arc welding is suitable for joining pipes and thin sheets. For sheets with a thickness of 0.8 mm, pulsed arc welding with a fusion electrode in inert gas is suitable. Sheets with a thickness of 0.8 - 3 mm should be joined by spray arc welding. Arc welding with a melting electrode in an inert gas is characterized by high productivity. Sheets over 3 mm thick are best joined by this method. Submerged arc welding is used to weld constructions with thicknesses over 10 mm. Plasma welding is considered to be universal and is very widely used.

Seam processing

If I may say so, welding "foams" the metal, forming a porous oxide layer on the surface of the seam, depleted in chromium. It is because of the friability of such a layer makes the material vulnerable to corrosion. To avoid this it is necessary to heat treat the weld after welding.

Heat treatment

In our case heat treating is the dissolution of the friable layer at temperatures above 1000 °C. The weld is then smooth and less susceptible to corrosion.

Mechanical methods of final treatment

It must be remembered that only accessories that are designed for machining stainless steel must be used. These include grinding wheels, belts, as well as brushes, which are used for processing stainless steel. It is worth noting that carbon steel should not be machined with sand or steel grit.

Etching

This is the most effective way to treat welds on stainless steel. If done properly, pickling removes the loose oxide layer, which is depleted of chromium. The etching process is performed by either applying a paste or by immersing the steel in a special solution. In most cases, a mixture of acids is used for etching: 8 to 20% nitric acid and 0.5 to 5% hydrofluoric acid. How long it takes to pickle austenitic stainless steel depends on the acid concentration, scale thickness and temperature. In order for the weld to be of high quality, additional grinding or polishing is required, which greatly increases the resistance to corrosion.

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