Sintered duplex stainless steels from premixes of 316L and 434L powders

doi:10.1016/S0254-0584(00)00477-6

Materials Chemistry and Physics

Volume 67, Issues 1–3, 15 January 2001, Pages 234-242

https://doi.org/10.1016/S0254-0584(00)00477-6 Get rights and content

Abstract

Duplex austenite–ferrite stainless steels were prepared from the premixes of 316L and 434L stainless steel atomized powders. Pronounced densification was observed after 1350°C sintering in hydrogen. 316L-60w/o 434L steel composition exhibited maximum transverse rupture strength, while 40 and 60w/o 434L containing compositions showed total immunity in 1N H₂SO₄ even after a exposure time of 360 h. Anodic polarization curves also suggest high-corrosion resistance of those two compositions. Magnetic coercivity decreased with increase in sintering temperature while magnetic saturation follows the reverse trend. Wear resistance of the duplex stainless steels under sliding condition was in between the straight steels.

Introduction

Duplex ferritic–austenitic stainless steels are characterized by an outstanding combination of strength, toughness and corrosion resistance. Ferritic steels have lower toughness and austenite steels have lower stress corrosion resistance, whereas duplex stainless steels have properties which are compromise between those two. Furthermore, due to lower nickel content duplex stainless steels are much cheaper than comparable austenite grades. They have therefore, found applications in off-shore constructions, heat-exchangers, gas and oil pipe lines as well as in the chemical industry. However, these steels posses considerable difficulties from the manufacturing point of view. This serves powder metallurgy an excellent alternative to produce this steel. Attempts have been made to introduce ferrite phase through the introduction of silicon powder in austenitic stainless steel [1], [2]. Another reported work is of Ruiz-Prieto et al. [3] who reported on such materials produced through powder metallurgy route based on straight stainless steel powder premixes.

In the present work powder metallurgical duplex stainless steels obtained from premixes of 316L and 434L powders are studied. The study includes mechanical, magnetic, microstructural and corrosion behaviors.

Section snippets

Experimental procedure

The investigation was carried out using water atomized and annealed 316L austenitic and 434L ferritic stainless steel powders supplied by AMETEK (Eighty Four, PA, USA). The chemical compositions and properties of two powders are shown in Table 1. This confirms that, apart from their compositions, all other characteristics of the steel powders are same.

Premixes of 316L and 434L were prepared in Turbula mixer, type 12C Nr921266 for half an hour. 434L content in different premixes were selected as

Results

Sintered density increases with increase in sintering temperature and the variation of sintered density with respect to temperature is shown in Fig. 1. With increase in sintering temperature porosity decreases leading to higher densification. However, the effect is not so visible after 1150 and 1250°C sintering.

Fig. 1 also shows variation of microhardness of steels with respect to composition for various sintering temperatures. In general, hardness decreases with increase in sintering

Discussion

It is well known fact that ferritic stainless steel increases yield strength and provides resistance to stress corrosion cracking, whereas austenitic steel imparts toughness along with good corrosion resistance. Keeping this in view, a mixed structure of ferrite and austenite would offer good corrosion resistance along with high-strengths and reasonable toughness. So far, the attention of stainless steel powder manufacturers has not yet turned to produce ferrite–austenite duplex stainless steel

Conclusions

1.
Densification increases with increasing sintering temperature for duplex stainless steels. Percentage porosity decreases with increase in 434L content only after 1350°C sintering.
2.
Ferrite–austenite two phase structure is observed for 40 and 60w/o 434L containing compositions after 1350°C sintering. Divergence of microhardness in 80w/o 434L containing alloy composition also suggests possibility of two phases.
3.
316L-60w/o 434L compositions exhibits maximum TRS value.
4.
Wear loss during sliding. Wear is

Acknowledgements

The authors are grateful to Ametek, Inc., Pennsylvania, USA for supplying the austenite and ferrite stainless steel powders.

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Mechanical properties and sigma phase precipitation of duplex stainless steels
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Sintered duplex stainless steels from premixes of 316L and 434L powders

Abstract

Introduction

Section snippets

Experimental procedure

Results

Discussion

Conclusions

Acknowledgements

Corrosion Sci.

Mechanical properties, corrosion resistance, and high temperature oxidation resistance of sintered duplex stainless steels

Powder Metall.

Mechanical properties and sigma phase precipitation of duplex stainless steels

Powder Metall. Int.