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Title: Synchrotron Based Observations of Sigma Phase Formation and Dissolution in Duplex Stainless Steel

Abstract

The formation and growth of sigma ({sigma}) phase in 2205 duplex stainless steel was observed and measured in real time using synchrotron radiation during isothermal heat treating at temperatures between 700 C and 850 C. Synchrotron experiments were performed on this material at the Advanced Photon Source (APS) while isothermally holding the samples for times of up to 10 hr. During the isothermal hold, sigma formed in quantities up to 22% as the ferrite transformed to a mixture of sigma and austenite phases. In addition, sigma formed at 850 C was heated to 1000 C to observe its dissolution. The amounts of sigma that formed, and the dissolution temperature of sigma were compared to the results predicted by Thermocalc, showing differences between the calculated and measured values. The synchrotron data was further modeled using a modified Johnson-Mehl-Avrami analysis to determine kinetic parameters for sigma formation. The initial JMA exponent, n, at low fractions of sigma was found to be approximately 7.0, however, towards the end of the transformation, n decreased to values of approximately 0.75. Because of the variable value of n, it was not possible to determine reliable values for the activation energy and pre-exponential terms for the JMAmore » equation. During cooling to room temperature, the high temperature austenite partially transformed to ferrite, substantially increasing the ferrite content while the sigma phase kept its high temperature value.« less

Authors:
 [1];  [1];  [2]
  1. Lawrence Livermore National Laboratory (LLNL)
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1028144
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: Numerical Analyses of Weldability, Graz, Austria, 20060925, 20060927
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ACTIVATION ENERGY; AUSTENITE; DISSOLUTION; FERRITE; HEAT TREATMENTS; KINETICS; MIXTURES; PHASE DIAGRAMS; STAINLESS STEELS; SYNCHROTRON RADIATION; TEMPERATURE RANGE 1000-4000 K; WELDABILITY

Citation Formats

Elmer, J. W., Palmer, T. A., and Specht, Eliot D. Synchrotron Based Observations of Sigma Phase Formation and Dissolution in Duplex Stainless Steel. United States: N. p., 2007. Web.
Elmer, J. W., Palmer, T. A., & Specht, Eliot D. Synchrotron Based Observations of Sigma Phase Formation and Dissolution in Duplex Stainless Steel. United States.
Elmer, J. W., Palmer, T. A., and Specht, Eliot D. 2007. "Synchrotron Based Observations of Sigma Phase Formation and Dissolution in Duplex Stainless Steel". United States.
@article{osti_1028144,
title = {Synchrotron Based Observations of Sigma Phase Formation and Dissolution in Duplex Stainless Steel},
author = {Elmer, J. W. and Palmer, T. A. and Specht, Eliot D},
abstractNote = {The formation and growth of sigma ({sigma}) phase in 2205 duplex stainless steel was observed and measured in real time using synchrotron radiation during isothermal heat treating at temperatures between 700 C and 850 C. Synchrotron experiments were performed on this material at the Advanced Photon Source (APS) while isothermally holding the samples for times of up to 10 hr. During the isothermal hold, sigma formed in quantities up to 22% as the ferrite transformed to a mixture of sigma and austenite phases. In addition, sigma formed at 850 C was heated to 1000 C to observe its dissolution. The amounts of sigma that formed, and the dissolution temperature of sigma were compared to the results predicted by Thermocalc, showing differences between the calculated and measured values. The synchrotron data was further modeled using a modified Johnson-Mehl-Avrami analysis to determine kinetic parameters for sigma formation. The initial JMA exponent, n, at low fractions of sigma was found to be approximately 7.0, however, towards the end of the transformation, n decreased to values of approximately 0.75. Because of the variable value of n, it was not possible to determine reliable values for the activation energy and pre-exponential terms for the JMA equation. During cooling to room temperature, the high temperature austenite partially transformed to ferrite, substantially increasing the ferrite content while the sigma phase kept its high temperature value.},
doi = {},
url = {https://www.osti.gov/biblio/1028144}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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