Mechanistic insights into the transformation processes in Z-phase strengthened 12% Cr steels
Journal article, 2018

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.

MX

Precipitates

M N 2

Electron microscopy

Creep

Atom probe tomography

Author

Masoud Rashidi

Chalmers, Industrial and Materials Science, Materials and manufacture

Ardeshir Golpayegani

Sandvik

Saad Ahmed Sheikh

Chalmers, Industrial and Materials Science, Materials and manufacture

Sheng Guo

Chalmers, Industrial and Materials Science, Materials and manufacture

Hans-Olof Andrén

Chalmers, Physics, Materials Microstructure

Fang Liu

Chalmers, Industrial and Materials Science, Materials and manufacture

Materials and Design

0264-1275 (ISSN)

Vol. 158 237-247

Z phase strengthened steels for ultra-supercritical power plants (Z-ULTRA)

European Commission (FP7), 2013-02-01 -- 2016-01-31.

Subject Categories

Inorganic Chemistry

Metallurgy and Metallic Materials

Corrosion Engineering

DOI

10.1016/j.matdes.2018.08.006

More information

Latest update

9/3/2018 2