© Copyright by International OCSCO World Press. All rights reserved. 2007 VOLUME 24 ISSUE 2 October 2007 Research paper 11 of Achievements in Materials and Manufacturing Engineering of Achievements in Materials and Manufacturing Engineering Sinter-hardening process applicable to stainless steels L.A. Dobrzański a, *, Z. Brytan a , M. Rosso b a Division of Materials Processing Technology, Management and Computer Techniques in Materials Science, Institute of Engineering Materials and Biomaterials, Silesian University of Technology, ul. Konarskiego 18a, 44-100 Gliwice, Poland b Politecnico di Torino, Alessandria Campus, Viale T.Michel 5, 15100, Italy * Corresponding author: E-mail address: leszek.dobrzanski@polsl.pl Received 12.04.2007; published in revised form 01.10.2007 Manufacturing and processing AbstrAct Purpose: of this paper was to describe sintered duplex stainless steels manufactured in sinter-hardening process and its usability in field of stainless steels. Design/methodology/approach: In presented study duplex stainless steels were obtained through powder metallurgy starting from austenitic, ferritic base powders by controlled addition of alloying elements, such as Cr, Ni, Mo and Cu. In the studies apart from 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°C to 1285°C 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. Findings: Obtained microstructure and mechanical properties of sintered duplex stainless steel strictly depend on the density and the pore morphology present in the microstructure and especially on cooling rate directly from sintering temperature in sinter-hardening process. The lowest cooling rate - applied gas pressure, the mechanical properties and corrosion resistance decrease due to precipitation of sigma phase. Proper bi-physic microstructure was obtained using nitrogen under pressure of 0.6 and 0.2 MPa. 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 its influence on corrosion properties. Originality/value: The utilization of sinter-hardening process combined with use of elemental powders added to a stainless steel base powder shows its potentialities in terms of good microstructural homogeneity and especially working with cycles possible to introduce in industrial practice. Keywords: Sintering; Sinter-hardening; Powder metallurgy; Duplex stainless steel 1. Introduction Application of powder metallurgy as a highly cost effective and high performance and possibility of manufacturing products with dimensional stability and shape reproducibility, created chances to manufacture duplex stainless steels witch controlled mechanical properties and corrosion resistance. Stainless steels made by powder metallurgy mainly single-phase stainless steels, austenitic and ferritic with desired mechanical properties – ferritic stainless steels and high corrosion resistance – austenitic one, for many years have stable position on market of sintered components. The powder metallurgy stainless steels, especially ferritic grades, have found applications in mounting brackets for the rear view mirrors, the tone wheels for the antilock brake systems and also in automotive exhaust applications like exhaust flanges and mounting unit of HEGOS. The automotive market introduces newly designed sintered parts in large amounts in 1. Introduction