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Description of material
BIOVAL® AISRUH is a very 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 has been designed in order to offer the best cold deforming and head ability thanks an exact chemical balance of elements such as Carbon, Nitrogen, Nickel and Copper.
BIOVAL® AISRUH is suitable for the fabrication of many products such as flanges, valves, bolting, screws, 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 great deal of cold working is required, and where type 304L group steels would not have the cold deformability sufficient for the final purpose.
BIOVAL® AISRUH is resistant to fresh water, many organic chemicals and inorganic compounds, atmospheric corrosion, rural applications and sterilizing solutions where the chloride content is 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, and even if this grade has a lower cold hardening capacity , BIOVAL® AISRUH suffers from stress corrosion cracking about forty/fifty degrees ( C°) above the room temperature and above certain levels of stress and halogen concentrations. Very Strain hardened structures increase the risk of stress corrosion cracking. Its intergranular corrosion resistance is very good. 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.
BIOVAL® AISRUH warrants a lower cold working hardening factor compared to similar other austenitic Copper or high Nickel alloyed grades thanks to its low Carbon and Nitrogen contents, together with a high Copper content. If lower cold heading performance were required, Valbruna produces other grades for these purposes such as AISRUB, AISRU/1/2 whose chemical balance provides a little bit lower cold deformability. MVAISRU (with Copper and Sulfur) could be used when both cold heading and machining are required. BIOVAL® AISRUH has good polish-ability or mirror finishing capacity but it should be pointed out that these properties improve with a fine grain structure, harder than a full annealed one. BIOVAL® AISRUH is usually supplied in different conditions such as : (1) annealed+ pickled (2) annealed + pickled and special mill coating (3) annealed + cold drawn with some kind of mill coating and ready to be entered in the header (4) annealed + cold drawn + protective atmosphere annealed + mill coating ready for cold heading, with or without sizing operations, before entering in the header. It should be noted that, as with all hot rolled wire rod surfaces, conditions (1) and (2) offer a higher surface roughness compared to other ones.
BIOVAL® AISRUH has a poor machinability due to its low Sulfur content. The best performance is obtained when employing the correct machining parameters while using multi - spindle and automatic screw machines. However, 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. This grade produces tough and stringy chips. The roughness of machined parts improves in the case of a harder structure than the full annealed one. MVAISRU (with Copper and Sulfur) could be used in the case of cold heading, together with a good machinability, were required, but it shouldn’t be used for high polishability or mirror finishing processes.
BIOVAL® AISRUH has a special chemical composition which helps to avoid solidification cracks in the fused-zone of autogenous welds due to a suitable Ferrite balance. Neither preheating nor post welding heat treatment is required. Nevertheless, in the case of aggressive environments, a post welding heat treatment is suggested. If welded or cold headed parts have to be heat treated, an annealing at 1020-1050°C and fast cooling should be done. But annealing with a long soaking between 500-850 °C must be avoided because the structure may suffer a certain level of embrittlement.
BIOVAL® AISRUH is usually supplied in wire or wire rod for cold heading processes. This grade can be easily hot headed, no preheating is required and forging temperatures are the typical ones of other austenitic stainless steels. Small forging must be rapid quenched in air or water cooled. In any case, slow cooling or heat treatments with long soaking in the temperature range between 500 - 850° C, must be avoided.