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Description of material
AISRU/2 is a low Carbon Cr-Ni-Cu austenitic stainless steel with a good general corrosion resistance as well as good intergranular corrosion resistance after welding processes. This grade has been designed in order to offer a good cold deforming and cold head ability thanks to an exact chemical balance of elements such as Carbon and Nitrogen but with a lower Nickel, but the same Copper content as AISRU/AISRUH.
AISRU/2 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.
AISRU/2 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, AISRU/2 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.
AISRU/2 offers a little bit higher cold working hardening factor compared to similar austenitic with high Nickel and Copper contents. These grades, such as AISRUH and AISRU, whose chemical balance provide a higher cold deformability, are the right choice if high cold heading performance were required. AISRU/1 has good polish-ability or mirror finishing capacity but it’s should be pointed out that these properties improve with a fine grain structure, harder than a fully annealed one. AISRU/2 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 coated 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.
AISRU/2 has a poor machinability due to a low Sulfur content but, however, a little bit better than high Nickel and Copper types such as AISRUH and AISRU. 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. 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 where cold heading, together a good machinability were required, but it shouldn’t be used for high polishability or mirror finishing processes.
AISRU/2 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.
AISRU/2 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 those typical of austenitic stainless steel. Small forgings 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.