Duplex stainless steels (DSSS) have a microstructure composed of ferrite and austenite phases that gives them a very good combination of mechanical and corrosion properties. These steels are desirable for many applications in the chemical and petrochemical industries. In the present study, a type of stainless steel was cast, solution annealed at 1200°C for 60 min and then quenched in water. Initial microstructure was composed of about 51.8% ferrite and 48.1% austenite. The steel was then cold rolled about 90% and subsequent annealing at 800,850 and 900°C for different time were performed. Results showed that tensile strength of steel have been significantly improved. Austenite grain size of cast steel was refined through static recrystallization of the austenite occurred during post cold deformation annealing. Results show that yield strength of as-cast steel is increased from 552 to 1800 and its tensile strength increased from 672 to 2350 MPa as a result of large cold deformation. With increasing annealing time, sigma phase increases and this leads to decrease of elongation. Thus sigma phase can be expected to embitter the alloy. پرونده مقاله

Grain refinement improves the mechanical properties and formability of metals and alloys. So far, several different grain refinement methods have been proposed and studied. Severe plastic deformation is one of the most promising and efficient methods. Therefore, in the present study the possibility of imposing a two-step severe plastic deformation (Extrusion and Equal channel angular pressing) on AA7075 alloy using a special designed die is investigated. Using this method, a very coarse grained microstructure with grain size of 94µm is refined to grain size of 7.5µm. Also, microstructural developments during severe deformation with and without preheating are investigated. Plastic strain distribution and temperature variation inside deformed samples are predicted by the use of thermal coupled displacement 3D finite element method. Results of FEM simulations clearly showes that the plastic strain distribution and temperature is non-uniform in sample and this introduces inhomogeneity in the resultant microstructure of sample at different regions. پرونده مقاله