Experimental and theoretical investigation of precipitate coarsening rate in Z-phase strengthened steels

Masoud Rashidi; Joakim Odqvist; Lennart Johansson; John Hald; Hans-Olof Andrén; Fang Liu

doi:10.1016/j.mtla.2018.09.024

Experimental and theoretical investigation of precipitate coarsening rate in Z-phase strengthened steels

Masoud Rashidi^*, Joakim Odqvist, Lennart Johansson, John Hald, Hans-Olof Andrén, Fang Liu

^*Corresponding author for this work

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Abstract

Two Z-phase strengthened 12% Cr steels were investigated: they are similar in composition, however one steel contains Nb and the other contains Ta. Z-phase precipitates (CrMN, M = Nb or Ta) provide precipitation hardening for creep resistance at 650 °C in these steels. Experimental data based on the transmission electron microscopy in- vestigation of the size evolution of Z-phase precipitates during isothermal ageing at 650 °C show that the Ta-based Z-phase benefits from a five times smaller coarsening constant compared to the Nb-based Z-phase. Theoretical calculations show that this is attributed to the smaller diffusivity of Ta compared to Nb in the steel matrix. Be- sides, comparing the size of the Ta-based Z-phase precipitates in the gauge and head portion of a crept specimen, it is shown that Z-phase coarsens faster under stress.

Original language	English
Journal	Acta Materialia
Volume	4
Pages (from-to)	247-254
ISSN	1359-6454
DOIs	https://doi.org/10.1016/j.mtla.2018.09.024
Publication status	Published - 2018

Keywords

Precipitate
Coarsening rate
Creep
Electron microscopy
Diffusivity

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Postscript Maosud RashidiAccepted author manuscript, 0.98 MB

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title = "Experimental and theoretical investigation of precipitate coarsening rate in Z-phase strengthened steels",

abstract = "Two Z-phase strengthened 12% Cr steels were investigated: they are similar in composition, however one steel contains Nb and the other contains Ta. Z-phase precipitates (CrMN, M = Nb or Ta) provide precipitation hardening for creep resistance at 650 °C in these steels. Experimental data based on the transmission electron microscopy in- vestigation of the size evolution of Z-phase precipitates during isothermal ageing at 650 °C show that the Ta-based Z-phase benefits from a five times smaller coarsening constant compared to the Nb-based Z-phase. Theoretical calculations show that this is attributed to the smaller diffusivity of Ta compared to Nb in the steel matrix. Be- sides, comparing the size of the Ta-based Z-phase precipitates in the gauge and head portion of a crept specimen, it is shown that Z-phase coarsens faster under stress.",

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T1 - Experimental and theoretical investigation of precipitate coarsening rate in Z-phase strengthened steels

AU - Rashidi, Masoud

AU - Odqvist, Joakim

AU - Johansson, Lennart

AU - Hald, John

AU - Andrén, Hans-Olof

AU - Liu, Fang

PY - 2018

Y1 - 2018

N2 - Two Z-phase strengthened 12% Cr steels were investigated: they are similar in composition, however one steel contains Nb and the other contains Ta. Z-phase precipitates (CrMN, M = Nb or Ta) provide precipitation hardening for creep resistance at 650 °C in these steels. Experimental data based on the transmission electron microscopy in- vestigation of the size evolution of Z-phase precipitates during isothermal ageing at 650 °C show that the Ta-based Z-phase benefits from a five times smaller coarsening constant compared to the Nb-based Z-phase. Theoretical calculations show that this is attributed to the smaller diffusivity of Ta compared to Nb in the steel matrix. Be- sides, comparing the size of the Ta-based Z-phase precipitates in the gauge and head portion of a crept specimen, it is shown that Z-phase coarsens faster under stress.

AB - Two Z-phase strengthened 12% Cr steels were investigated: they are similar in composition, however one steel contains Nb and the other contains Ta. Z-phase precipitates (CrMN, M = Nb or Ta) provide precipitation hardening for creep resistance at 650 °C in these steels. Experimental data based on the transmission electron microscopy in- vestigation of the size evolution of Z-phase precipitates during isothermal ageing at 650 °C show that the Ta-based Z-phase benefits from a five times smaller coarsening constant compared to the Nb-based Z-phase. Theoretical calculations show that this is attributed to the smaller diffusivity of Ta compared to Nb in the steel matrix. Be- sides, comparing the size of the Ta-based Z-phase precipitates in the gauge and head portion of a crept specimen, it is shown that Z-phase coarsens faster under stress.

KW - Precipitate

KW - Coarsening rate

KW - Creep

KW - Electron microscopy

KW - Diffusivity

U2 - 10.1016/j.mtla.2018.09.024

DO - 10.1016/j.mtla.2018.09.024

M3 - Journal article

SN - 1359-6454

VL - 4

SP - 247

EP - 254

JO - Acta Materialia

JF - Acta Materialia

ER -

Experimental and theoretical investigation of precipitate coarsening rate in Z-phase strengthened steels

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Keywords

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