Studio dell'effetto delle fasi secondarie della tenacita' a frattura in un 2205 DSS

It is well known that the fracture toughness of DSS is strongly reduced by the precipitation of various inter- metallic phases occurring in the temperature range 600-1000°C. A large decrease in impact fracture toughness occurs even at room temperature for volume fractions of intermetallic phases lower than 1%, when only small and rare particles are present. In the present investigation, the influence of the intermetallic phases on the impact fracture behaviour of a 2205 grade DSS has been investigated. Samples containing different amounts of the intermetallic phases have been obtained by isothermal aging treatments in the range 800-950°C. The results of the impact tests confirm that the dangerous phase content determine both the toughness and the fracture behaviour of the DSS examined. At content lower than 1%, when precipitates are rare and small, their effect is a reduction of the absorbed energy for the ductile fracture. But the 1% appears as the critical content, when some particles became large enough to operate the nucleation of the brittle fracture. Indeed, at higher content, a number of large particles are present, well sufficient to induce a general brittle fracture. The obtained results allow correlating the absorbed energy values with the intermetallic phases content and dimensions.