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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2009

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Effect of microstructure on impact toughness of duplex and superduplex stainless steels

Topolska S., Łabanowski J.

Journal of Achievements in Materials and Manufacturing Engineering

2009

Vol. 36, nr 2

142-149

Purpose: of this paper is to study the effect of heat treatments and resulting changes in microstructure on mechanical properties, mainly impact toughness, of commercial 2205 duplex stainless steel and higher alloy superduplex 2507 grade. Design/methodology/approach: Both steels were submitted to ageing treatments in the temperature range of 500-900 °C with exposure time periods 6 minutes, 1 hour and 10 hours. Light microscope examinations, hardness measurements and impact toughness tests were performed in order to reveal microstructure and changes in mechanical properties. Findings: Obtained results confirm that high temperature service of duplex stainless steels should be avoided. Precipitations of secondary phases (mainly ó phase) strongly deteriorate mechanical properties of steels but some amounts of these phases could be acceptable in the microstructure depending upon the application of the steel. Research limitations/implications: Presence of secondary phases in duplex stainless steel microstructure can be very harmful for its corrosion resistance. This phenomenon is not considered in this study. Practical implications: The accidents during exploitation and errors in processing of duplex stainless steels can result in undesired temperature growth over 500°C. Such events brings question whether the steel can be still exploited or not. The aim of present study is to reveal the effect of thermal cycles on structural changes and mechanical properties of duplex stainless steel and establish the highest acceptable time-temperature conditions for safe operation of the steel. Originality/value: Information available in literature does not clearly indicate what amount of secondary phases existing in duplex stainless steel microstructure can be acceptable. The current study shows that duplex 2205 steel affected by thermal cycles and containing about 10% of sigma phase still exhibit acceptable mechanical properties.