Kinetics of Sigma Phase Precipitation in Niobium-Stabilized Austenitic Stainless Steel and Effect on the Mechanical Properties

Xavier Ledoux; Francois Buy; Aurélien Perron; Eric Suzon; José Farré; Bernard Marini; Thomas Guilbert; Pierre Wident; Gwénael Texier; Vincent Vignal; François Cortial; Philippe Petit

doi:10.4028/www.scientific.net/MSF.783-786.848

Paper Titles

Study on the Soaking Condition of High Carbon Chromium Bearing Steels
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Microstructure Evolution in a 304-Type Austenitic Stainless Steel during Multidirectional Forging at Ambient Temperature
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Mechanical and Corrosion Properties of a F138 Austenitic Stainless Steel after Deformation by Equal Channel Angular Pressing
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From Micro to Nano Scale Structure by Plastic Deformations
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Kinetics of Sigma Phase Precipitation in Niobium-Stabilized Austenitic Stainless Steel and Effect on the Mechanical Properties
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Optimization of Mechanical Properties of High Strength TRIP Steels
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Microstructure and Mechanical Properties of Extra High Strength Heavy Steel Plate for Bridge Application
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The Development and Application of High-Performance Ultra-High Strength Stainless Steel Subject to Marine Environment
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Effect of Martensite Fraction on Void Nucleation Behavior and Ductility in DP Steels
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Kinetics of Sigma Phase Precipitation in Niobium-Stabilized Austenitic Stainless Steel and Effect on the Mechanical Properties

Abstract:

Stabilized austenitic stainless steels are widely used in nuclear and oil industries. The 316 Nb steel grade presented in this study holds a small amount of delta ferrite in the austenitic matrix which tends to transform into sigma phase during prolonged exposures in the temperature range of 600-1000°C. Sigma phase is promoted by ferritic elements such as chromium, molybdenum, niobium and silicon. Time-Temperature-Transformation (TTT) diagram of the δ-ferrite evolution is established thanks to DSC experiments and quantitative metallographic analysis. It is observed that the highest sigma phase formation rate occurs between 800 and 900°C, and that the transformation of ferrite begins after a few minutes of exposure in this temperature range. The microstructure of transformed δ-ferrite is mostly dominated by the eutectoid mixture σ + γ₂. Tensile tests were performed for three different cooling conditions: a significant embrittlement attributed to the δ-ferrite transformation is measured by a ductility loss for the lowest cooling rate.