Effect of ageing on phase evolution and mechanical properties of a high tungsten super-duplex stainless steel

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The effect of ageing temperature and holding time on the precipitation of secondary phases and the mechanical properties of a 25Cr-6.7Ni-0.32N-3.0Mo-2.5 W super duplex stainless steel is examined. The ageing temperature was varied from 600 to 900 °C and the holding time was varied from 1 to 240 minutes. Two types of Cr and Mo enriched intermetallic phases, sigma (s) and chi (¿), were found to precipitate preferentially at the ferrite/austenite interface and within the ferrite grain. The precipitation of the ¿-phase occurred preferentially before the s-phase. The concentration of these secondary phases, which was quantified by a combination of microscopy and image analysis, increases with increasing ageing temperature and holding time, leading to significant reduction in the uniform strain and enhancement of the modulus, hardness and yield and tensile strengths. The measured concentration of the precipitated sigma phase is in agreement with the prediction by the Johnson-Mehl-Avrami kinetic model.
Original languageEnglish
Pages (from-to)281-289
Number of pages9
JournalMaterials Science and Engineering A
Early online date27 Dec 2011
Publication statusPublished - 15 Feb 2012



  • electron microscopy
  • mechanical characterisation
  • hardness measurement
  • stainlless steel
  • intermetallics
  • isothermal ageing
  • phase transformation
  • precipitation
  • hardness
  • failure
  • strength

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