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Innovative PM duplex stainless steels obtained basing on the Schaeffler diagram

Dobrzański L., Brytan Z., Actis Grande M., Rosso M.

Archives of Materials Science and Engineering

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2008

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Vol. 30, nr 1

49-52

EN

Purpose: The purpose of this paper was to describe the sintered duplex stainless steels manufactured in sinterhardening process and its usability in field of stainless steels and moreover using computer software to calculate the powder mix composition. Design/methodology/approach: In presented paper duplex stainless steels were obtained through powder metallurgy starting from austenitic or ferritic base powders by controlled addition of alloying elements powder. In the studies besides the preparation of powder mixes, computer software based on Schaeffler’s diagram was studied. Findings: It has been demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition and sintering cycle. Research limitations/implications: According to the alloys characteristic applied cooling rate and powder mix composition seems to be a good compromise to obtain balanced duplex stainless steel microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and sintering parameters. Practical implications: Applied producing method of sintered duplex steels and used sintering cycle as well as developed computer software to calculating powder mix composition proves his advantage in case of obtained microstructures and additionally it seem to be very promising for obtaining a balanced duplex structure, also working with cycles easy to be introduced in industries. Originality/value: The utilization of sinter-hardening process combined with use of elemental powders added to a stainless steel base powder shows its advantages in terms of good microstructural homogeneity and especially working with cycles possible to introduce in industrial practice.

2

Sinter-hardening process applicable to stainless steels

Dobrzański L. A., Brytan Z., Rosso M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 2

11-18

EN

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 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. 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.

3

Microstructural characteristic and mechanical properties of Ni-Mo-(W) steels

Dobrzański L. A., Otręba J., Actis Grande M., Rosso M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

347--350

EN

Purpose: Purpose of this paper was to examine the role of tungsten on properties of two different carbon levels pre-alloyed steel powders. Microstructural characteristic and mechanical properties of sinter-hardened Ni-Mo steels with increasing amount of tungsten (from 0 to 0.3% wt.) were taken under consideration. Design/methodology/approach: Powder mixes (Ni-Mo, Ni-Mo-W) have been compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at 1120°C for 60 minutes. Rapid cooling has been applied with an average cooling rate of 2.5°C/s. Obtained samples were analyzed by scanning microscopy with Energy dispersive spectroscopy (EDS) for phase distribution and mapping and light optical microscopy for observations of the microstructure. Charpy impact test, three-point bending, microhardness and pin-on-disk tests were used. Findings: The effect of chemical composition and applied vacuum sintering with rapid cooling were studied in terms of mechanical properties, focusing in particular on impact energy, hardness and wear resistance. The results achieved after the investigation of Ni-Mo and Ni-Mo-W sinter-hardened steels with low and high carbon content proved that applied process of sintering under vacuum and rapid cooling brought expected outcome. Research limitations/implications: According to the powders characteristic, the applied cooling rate seems to be a good compromise for mechanical properties and microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and parameters of tempering process. Originality/value: The effect of small additions of W and WC to low alloyed steels, especially in terms of hardenability and wear resistance, was investigated.