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Austenitic Stainless Steel
Description of material
AMSL is a low-carbon austenitic stainless steel with a high Molybdenum content. It has good general / pitting corrosion resistance together with a good intergranular corrosion resistance after welding processes.
AMSL is suitable for the fabrication of many products such as flanges, valves, bolting, pump shafts, food /beverages industry equipment, pulp and paper equipment, heat exchangers, marine devices, storage tanks, offshore oil production, many products used in chemical processes, and rural applications. It is used when a better resistance to general and pitting corrosion, in comparison with APML, is necessary.
Argon Oxygen Decarburization
AMSL is resistant to fresh water, many organic chemicals and inorganic compounds, atmospheric corrosion, marine environments, and in contact with sterilizing solutions. In sea water, this grade is a more resistant to pitting than type 316 grades such as APML and similar. However, pitting and crevice corrosion may occur in environments if the chloride concentrations, pH and temperature are at determinate levels. As with other standard austenitic grades, AMSL suffers from stress corrosion cracking about fifty degrees (C°) above room temperature and above certain levels of stress and halogen concentrations. Very strain hardened structures increase the risk of stress corrosion cracking. Thanks to its low Carbon content AMSL offers a good intergranular corrosion resistance. It should be noted that this grade, as for every kind of stainless steel, surfaces should be free of contaminant and scale, heat tint, and passivated for optimum resistance to corrosion.
AMSL can be readily fabricated by cold working operations such as cold drawing and bending, and allows a good amount of cold heading and cold up setting thanks to its high Nickel and low Carbon content. Its structure after cold deformation is less hard than APML.
Machinists should know that Austenitic grades are different from Ferritic and Alloy steels and require more rigid and powerful machines in addition to the correct choice of tools, coating and cutting fluids. The Austenite structure is prone to transform in to α’Martensite caused by strain hardening of the tool on the surface of the machined piece. The knowledge of this behavior must be correctly considered when a piece requires two or several cutting steps to be finished. The layer of α’Martensite is very hard and, if the subsequent turning or milling processes work on this hardened layer, a rapid tool wear could happen. The tool must work under this layer. AMSL isn’t normally supplied with a micro re -sulphured structure and, therefore, doesn’t offer a good chip-ability.
No preheating or post welding are normally necessary. However, an annealing after welding should be done if the weld works in very aggressive environments. In the case of autogenous welding processes, there could be some risk of hot cracking in the fused zone due to a solidification mode from primary ferrite to primary austenite. This could be avoided only if the heat of supplied product has a chemical balance that allows a primary ferrite solidification mode or, alternatively, by use of a right filler metal and accurate welding procedures involving heat inputs and joint geometry.
AMSL has a good hot plasticity and is suitable for processing by hot extrusion or by upsetting with electric resistance heating. However, overheating must be always avoided. The choice of hot working temperature and process parameters must always evaluate the strain rate and the consequent increasing of temperature that is reached after hot deformation. High strain rates and temperature at the top end of the range during the extrusion and forging process, could generate internal bursts. Small forgings should be cooled rapidly in air or water quenched. However, the best corrosion resistance is obtained by annealing followed by quenching in water.