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Metals 2017, 7(9), 344; doi:10.3390/met7090344

Demonstrating the Effect of Precipitation on the Mechanical Stability of Fine-Grained Austenite in Reversion-Treated 301LN Stainless Steel

1
Kerttu Saalasti Institute, Future Manufacturing Technology Group, University of Oulu, Pajatie 5, FI-85500 Nivala, Finland
2
Centre for Advanced Steels Research, Materials and Production Engineering Unit, University of Oulu, P.O. Box 4200, FI-90014 Oulu, Finland
*
Author to whom correspondence should be addressed.
Received: 2 August 2017 / Revised: 28 August 2017 / Accepted: 31 August 2017 / Published: 4 September 2017
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Abstract

According to recent investigations, a huge difference exists in the mechanical stability of austenite between the grain-refined structure states obtained in reversion annealing at 800–700 °C or at 900 °C, in a 301LN type austenitic stainless steel. Precipitation of chromium nitride occurring at these lower temperatures has been argued to be the factor reducing the stability. To prove this argument, a fine-grained, very stable austenitic structure was created at 900 °C in 1 s, and subsequently annealed at lower temperatures between 850 and 750 °C, up to 1000 s. It was found that the subsequent annealing at 750 and 800 °C resulted in prominent gradual decrease of the mechanical stability under tensile straining, detectable after 10 s annealing duration and continued until 1000 s. Only minimal grain growth occurred, which decreased the stability very marginally. The degree of the stability drop followed the predicted kinetics of the Cr2N precipitation with regards as its dependence on annealing duration and temperature. Further, the tensile yield strength of the fine-grained structure increased slightly due to the annealing. The presence of nano-sized Cr2N particles was verified after 1000 s holding at 750 °C. These observations and predictions yield firm evidence for the imperative contribution of precipitation to the highly reduced mechanical stability of grain-refined austenite in this steel. View Full-Text
Keywords: austenitic stainless steel; refined grain size; austenite stability; annealing; precipitation; deformation induced martensite austenitic stainless steel; refined grain size; austenite stability; annealing; precipitation; deformation induced martensite
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Järvenpää, A.; Jaskari, M.; Juuti, T.; Karjalainen, P. Demonstrating the Effect of Precipitation on the Mechanical Stability of Fine-Grained Austenite in Reversion-Treated 301LN Stainless Steel. Metals 2017, 7, 344.

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