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Austenitic Stainless Steel
Description of material
APMT is an austenitic stainless steel, Titanium-stabilized, and also with added Molybdenum, which has good general and pitting corrosion resistance as well as good intergranular corrosion resistance after welding processes.
APMT is suitable for the fabrication of many products such as flanges, valves, bolting, pump shafts, food/beverages industry equipment, storage tanks, and parts working in mild to medium corrosive environments. This grade is chosen in the case of welding processes and in applications where intermittent heating up to 870 C° can happen.
Argon Oxygen Decarburization
APMT is resistant to fresh water, many organic chemicals and inorganic compounds, atmospheric corrosion, marine environments, many products used in chemical processes, paper production equipment, and rural applications and sterilizing solutions. In sea water, this grade is more resistant to pitting than type 304/304L steels such as AISL 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, APMT suffers from stress corrosion cracking about forty degrees (C°) above room temperature and above certain levels of stress and halogen concentrations. Strain hardened structures increase the risk of stress corrosion cracking. 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.
APMT can be readily fabricated by cold working operations such as cold drawing and bending but should only be used for a moderate amount of cold heading or cold upsetting.
Austenitic grades are different from Ferritic and Alloy steels and require more rigid and powerful machines in addition to the correct choice of tools, coatings and cutting fluids. The Austenite structure is prone to transform into 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. APMT has a chemical balance for a suitable machining thanks to its micro-resulphured structure.
APMT has a special chemical composition which helps to avoid solidification cracks in the fused-zone of autogenous welds due to a special Ferrite balance. In case of filler metal welding, E /ER 316L group could be used. PWHT is generally not necessary. Its composition prevents Chromium-Carbide precipitation on the grain boundaries at temperature between 500 and 850°C. However, a stabilization heat treatment should be carried out in case of high temperature applications.
Long products of APMT are not specifically designed for hot working and are usually supplied as cold finished round, hexagonal, flat and square bars for machining processes or general use. Other grade such as APMTF1 is recommended for forging quality billets and large ingots thanks to a special composition with low ferrite content. No preheating is required. Small forgings can be cooled rapidly in air or water.