Influence of sintering parameters on the properties of duplex stainless steel

Purpose: of this paper was to examine the influence of sintering parameters like time, temperature, atmosphere and gas pressure under cooling stage on the mechanical properties of duplex stainless steels. Design/methodology/approach: In presented study duplex stainless steels were obtained through powder metallurgy starting from austenitic, martensitic base powders by controlled addition of alloying elements, such as Cr, Ni, Mo and Cu. In the studies behind the preparation of mixes, Schaeffler's diagram was taken into consideration. Prepared mixes have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at temperatures from 1200 to 1285 degrees centigrade for 0,5, 1 and 2 h. After sintering different cooling cycles were applied using nitrogen under pressure from 0.6 MPa to 0.002 MPa in argon atmosphere. Produced duplex stainless steels have been studied by scanning and optical microscopy and EDS chemical analysis of microstructure components. Mechanical properties have been studied through tensile test. Findings: Mechanical properties of sintered stainless steels are strictly connected with the density and the pore morphology present in the microstructure too and especially of cooling rate directly from sintering temperature. The lowest cooling rate - applied gas pressure, the mechanical properties decrease due to precipitation of sigma phase. Mechanical properties of studied steels depends on austenite/ferrite ratio in the microstructure and elements partitioning between phases too. Research limitations/implications: Applied fast cooling rate seems to be a good compromise for mechanical properties and obtained microstructures, nevertheless further tests should be carried out in order to examine it influence on corrosion properties. Originality/value: The use of elemental powders added to a stainless steel base showed its potentialities, in terms of fair compressibility and final sintered density. In addition a good microstructural homogeneity and first of all good mechanical properties was achieved, also working with cycles possible for industries.