Mechanistic insights into the transformation processes in Z-phase strengthened 12% Cr steels

M. Rashidi; A. Golpayegani; S. Sheikh; S. Guo; H. O. Andrén; F. Liu

doi:10.1016/j.matdes.2018.08.006

Mechanistic insights into the transformation processes in Z-phase strengthened 12% Cr steels

M. Rashidi
, A. Golpayegani
, S. Sheikh
, S. Guo
, H. O. Andrén
, F. Liu

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

Compositionally complex Z-phase strengthened 12% Chromium steels are considered as potentially viable materials for components used in highly-demanding environments in steam power plants, operating at a target temperature of 650 °C. To date, however, the transformation processes of various phases into the desired precipitate, i.e., Z-phase CrTaN, are not fully understood. In this research, we first designed and produced three different alloys and then studied the microstructure in the as-tempered and aged conditions (for up to 10,000 h at 650 °C) using advanced electron microscopy, X-ray diffraction, and atom probe tomography. We report on the evolution of the densely distributed MX (Ta(C, N)) and M₂X ((Cr, Ta)₂N) precipitates into blade-like and bulky Z-phase, respectively. The blade-like precipitates benefit from a smaller size compared to the bulky ones, providing precipitation hardening for creep resistance. We discuss an interactive role of carbon and nitrogen content in the formation of the Z-phase. Our findings pave the way towards designing new alloys with improved properties to serve in harsh environments at 650 °C.

Original language	English
Pages (from-to)	237-247
Number of pages	11
Journal	Materials and Design
Volume	158
DOIs	https://doi.org/10.1016/j.matdes.2018.08.006
State	Published - Nov 15 2018
Externally published	Yes

Funding

Financial support from the Swedish Energy Agency (contract number: KME 710), the Research Foundation of VGB in Germany (contract number: 397), and the EU FP7 Z-ULTRA (contract number: 309916) is gratefully acknowledged. FL is partly funded via LIGHTer, a program financed within Strategic Innovation Areas, a mutual venture between VINNOVA, the Swedish Energy Agency, and Formas. Sandvik Materials Technology is acknowledged for performing the XRD measurements. John Hald at the Technical University of Denmark, and Lennart Johansson and Torsten Kern at Siemens are also gratefully thanked for fruitful discussions. Financial support from the Swedish Energy Agency (contract number: KME 710 ), the Research Foundation of VGB in Germany (contract number: 397 ), and the EU FP7 Z-ULTRA (contract number: 309916 ) is gratefully acknowledged. FL is partly funded via LIGHTer , a program financed within Strategic Innovation Areas , a mutual venture between VINNOVA , the Swedish Energy Agency , and Formas . Sandvik Materials Technology is acknowledged for performing the XRD measurements. John Hald at the Technical University of Denmark, and Lennart Johansson and Torsten Kern at Siemens are also gratefully thanked for fruitful discussions.

Keywords

Atom probe tomography
Creep
Electron microscopy
MN
MX
Precipitates

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10.1016/j.matdes.2018.08.006

Cite this

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title = "Mechanistic insights into the transformation processes in Z-phase strengthened 12\% Cr steels",

abstract = "Compositionally complex Z-phase strengthened 12\% Chromium steels are considered as potentially viable materials for components used in highly-demanding environments in steam power plants, operating at a target temperature of 650 °C. To date, however, the transformation processes of various phases into the desired precipitate, i.e., Z-phase CrTaN, are not fully understood. In this research, we first designed and produced three different alloys and then studied the microstructure in the as-tempered and aged conditions (for up to 10,000 h at 650 °C) using advanced electron microscopy, X-ray diffraction, and atom probe tomography. We report on the evolution of the densely distributed MX (Ta(C, N)) and M2X ((Cr, Ta)2N) precipitates into blade-like and bulky Z-phase, respectively. The blade-like precipitates benefit from a smaller size compared to the bulky ones, providing precipitation hardening for creep resistance. We discuss an interactive role of carbon and nitrogen content in the formation of the Z-phase. Our findings pave the way towards designing new alloys with improved properties to serve in harsh environments at 650 °C.",

keywords = "Atom probe tomography, Creep, Electron microscopy, MN, MX, Precipitates",

author = "M. Rashidi and A. Golpayegani and S. Sheikh and S. Guo and Andr{\'e}n, \{H. O.\} and F. Liu",

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doi = "10.1016/j.matdes.2018.08.006",

language = "English",

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AU - Rashidi, M.

AU - Golpayegani, A.

AU - Sheikh, S.

AU - Guo, S.

AU - Andrén, H. O.

AU - Liu, F.

PY - 2018/11/15

Y1 - 2018/11/15

N2 - Compositionally complex Z-phase strengthened 12% Chromium steels are considered as potentially viable materials for components used in highly-demanding environments in steam power plants, operating at a target temperature of 650 °C. To date, however, the transformation processes of various phases into the desired precipitate, i.e., Z-phase CrTaN, are not fully understood. In this research, we first designed and produced three different alloys and then studied the microstructure in the as-tempered and aged conditions (for up to 10,000 h at 650 °C) using advanced electron microscopy, X-ray diffraction, and atom probe tomography. We report on the evolution of the densely distributed MX (Ta(C, N)) and M2X ((Cr, Ta)2N) precipitates into blade-like and bulky Z-phase, respectively. The blade-like precipitates benefit from a smaller size compared to the bulky ones, providing precipitation hardening for creep resistance. We discuss an interactive role of carbon and nitrogen content in the formation of the Z-phase. Our findings pave the way towards designing new alloys with improved properties to serve in harsh environments at 650 °C.

AB - Compositionally complex Z-phase strengthened 12% Chromium steels are considered as potentially viable materials for components used in highly-demanding environments in steam power plants, operating at a target temperature of 650 °C. To date, however, the transformation processes of various phases into the desired precipitate, i.e., Z-phase CrTaN, are not fully understood. In this research, we first designed and produced three different alloys and then studied the microstructure in the as-tempered and aged conditions (for up to 10,000 h at 650 °C) using advanced electron microscopy, X-ray diffraction, and atom probe tomography. We report on the evolution of the densely distributed MX (Ta(C, N)) and M2X ((Cr, Ta)2N) precipitates into blade-like and bulky Z-phase, respectively. The blade-like precipitates benefit from a smaller size compared to the bulky ones, providing precipitation hardening for creep resistance. We discuss an interactive role of carbon and nitrogen content in the formation of the Z-phase. Our findings pave the way towards designing new alloys with improved properties to serve in harsh environments at 650 °C.

KW - Atom probe tomography

KW - Creep

KW - Electron microscopy

KW - MN

KW - MX

KW - Precipitates

UR - https://www.scopus.com/pages/publications/85052062998

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DO - 10.1016/j.matdes.2018.08.006

M3 - Article

AN - SCOPUS:85052062998

SN - 0264-1275

VL - 158

SP - 237

EP - 247

JO - Materials and Design

JF - Materials and Design

ER -

Mechanistic insights into the transformation processes in Z-phase strengthened 12% Cr steels

Abstract

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Keywords

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