ABSTRACT Samples of the Al 7075 naturally and artificially aged were processed by conventional and asymmetrical rolling with 5% of thickness reduction. The rolling processes were evaluated under room temperature and under warm condition (130°C). Mechanical properties were evaluated by uniaxial tensile and Vickers microhardness tests. Microstructure evolutions were followed by optical microscopy analysis. Naturally aged samples showed better yield strengthening under warm processing. Greater ultimate stress and ductility under room temperature processing was also noticed in naturally aged specimens. Artificially aged samples showed better mechanical properties under room temperature, softening under warm processing due to grain recovery process. Microhardness tests showed expected results for both rolling types, especially on asymmetrical rolling with the higher predictions were observed. Micrographs have shown no expressive grain changes or refinement although its flattening was observed. Precipitates were analyzed by EDS/SEM revealing the presence of MgZn2 and CuMgAl along the matrix that provides plastic strengthening.

Stainless steels are well known by their corrosion resistance. The austenitic types, in particular, are also applied as structural components in engineering systems operating at high temperatures such as nuclear reactors, petrochemical furnaces and turbines. For these applications operational temperatures may go up to 800ºC. Under constant load applications the main mechanism of failure, which would limit the material's life, is creep. In the present work creep parameters were evaluated in the high temperature interval of 600 to 800ºC for an AISI 316 austenitic stainless steel. Dislocation substructures were observed by transmission electron microscopy in creep ruptured specimens. Two distinct mechanisms of dynamic strain aging and dynamic recovery associated with different values for the power law exponent n and the Arrhenius activation energy Q for creep were verified below and above 700ºC, respectively.

Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.