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Austenitic Stainless Steel
Description of material
MVAISRU is a low-carbon Cr-Ni-Cu austenitic stainless steel with good general corrosion resistance as well as good intergranular corrosion resistance after welding processes. This grade is a Copper alloyed steel with a precise micro-resulphured structure. This results in lower tool wear, higher chip-breaking and very good cold heading and deformability.
MVAISRU is suitable for the fabrication of many products such as flanges, valves, bolting, pumps shafts, food /beverages industry equipment, storage tanks, many organic chemicals and parts working in mild to medium corrosive environments. This grade should be considered when a type 304 group steel needs to be cold deformed, together with a suitable machining or severe cold heading application, including making bolts and machined screws.
MVAISRU is resistant to fresh water, many organic chemicals and inorganic compounds, atmospheric corrosion, rural applications and sterilizing solutions where chloride levels are very low. Pitting and crevice corrosion may occur in chloride environments if concentration, pH and temperature are at determinate levels. As with other standard austenitic grades, MVAISRU suffers from stress corrosion cracking about fifty degrees ( C°) above room temperature and above certain levels of stress and halogen concentration. Strain hardened structures increase the risk of stress corrosion cracking but it is however useful to pointed out that MVAISRU doesn’t generate an austenitic structure as hard as MVAISL reducing the risk of stress corrosion. 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.
MVAISRU is readily fabricated by cold working such as cold drawing and bending and allows a good amount of cold heading thanks to its Copper content. Its structure after cold deformation is less hard than standard type 304L. If a heavy cold heading performance was required, Valbruna produces other grades for these purposes, such as AISRUH whose chemical balance provides the highest cold deformability and the lowest CWHF. This grade has a poor machinability due to a low Sulphur content. The experience is that MVAISRU (alloyed with Copper and Sulphur) is required for its good machinability and low strain hardening properties.
MVAISRU is not a Free Machining grade (FM) but rather an alloy with enhanced machinability characteristics due to Copper content and micro resulphurized structure. In terms of machinability, MVAISRU stands in an intermediate position between standard and Free Machining grades but cannot compete with FM (such as AISI 303, EN 1.4305). MVAISRU offers a lot of advantages in terms of productivity when compared to type 304 standard grades. The best performance is obtained when employing the correct machining parameters while using multi - spindle and automatic screw machines. However, 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 work piece. Even if MVAISRU has a hardening factor lower than MVAISL, 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 of MVAISRU is less hard than type 304 , but 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. MVAISRU shouldn’t be used for high polishability or mirror finishing processes.
MVAISRU has a special chemical composition which helps to avoid solidification cracks in the fused-zone of autogenous welds due to a special Ferrite balance. Because this grade has a low carbon content the choice of filler metal should be carefully evaluated to maintain the corrosion resistance of the weld zone. In solid state joining such as Friction Welding, MVAISRU could provide a very poor quality bond line or no joining.
MVAISRU is not specifically designed for hot working and is usually supplied as cold finished round, hexagonal, flat and square bars for machining processes. However, when open die forging of large ingots and shapes, MVAISRU has a good hot plasticity if suitable soaking and the right temperature are applied. No preheating is required and long term soaking and overheating must be avoided. Small forgings can be cooled rapidly in air or water.