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Title: Crystallography and structural evolution during reverse transformation in an Fe-17Cr-0.5C tempered martensite

Abstract

The mechanism and the crystallography of austenite and {delta}-ferrite formation from tempered martensite at temperatures of 900-1,200 C have been studied by means of transmission electron microscopy in an Fe-17Cr-0.55C alloy. It was found that austenite nucleates within ferrite at low angle, high angle and twin-related lath boundaries as well as at high angle equiaxed grain boundaries in contact with M{sub 23}C{sub 6} grain/lath boundary carbides. The austenite grains are in a cube-cube relationship with the M{sub 23}C{sub 6} carbide particles and bear the Kurdjumov-Sachs orientation relationship with at least one of the adjacent ferrite grains. They are often in the Kurdjumov-Sachs relationship with both ferrite laths separated by a high angle boundary as far as the laths had formed from the same austenite. The {l_brace}111{r_brace}{sub A} close packed plane of {gamma} precipitate is parallel to the {l_brace}110{r_brace}{sub F} plane most parallel to the grain boundary. The close packed planes of some austenite grains nuclearing at the high angle lath boundaries are parallel to the close packed planes of both ferrite laths. These crystallographic features often result in a single variant of austenite orientation at a grain boundary. After nuclearion, the austenite grains grow by the migration of both semicoherentmore » and incoherent interfaces. These results demonstrate that a specific orientation relationship is preferred for the austenite nucleation, but is not necessary for the subsequent growth. The kinetics of austenite growth are controlled by chromium diffusion. The {delta}-ferrite particles precipitate at high temperatures as a non-equilibrium phase. No rational orientation relationship between {delta}-ferrite and retained austenite was found. The experimental results are discussed qualitatively in terms of the thermodynamic predictions using the soft-water ThermoCalc, assuming local equilibrium at the moving interfaces.« less

Authors:
; ;
Publication Date:
Research Org.:
Ehime Univ., Matsuyama (JP)
OSTI Identifier:
20075925
Resource Type:
Journal Article
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 48; Journal Issue: 8; Other Information: PBD: 11 May 2000; Journal ID: ISSN 1359-6454
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTAL-PHASE TRANSFORMATIONS; IRON ALLOYS; CHROMIUM ALLOYS; CARBON ADDITIONS; AUSTENITE; FERRITE; MARTENSITE; TEMPERATURE RANGE 1000-4000 K; NUCLEATION; KINETICS

Citation Formats

Shtansky, D.V., Nakai, K., and Ohmori, Y. Crystallography and structural evolution during reverse transformation in an Fe-17Cr-0.5C tempered martensite. United States: N. p., 2000. Web. doi:10.1016/S1359-6454(00)00015-X.
Shtansky, D.V., Nakai, K., & Ohmori, Y. Crystallography and structural evolution during reverse transformation in an Fe-17Cr-0.5C tempered martensite. United States. doi:10.1016/S1359-6454(00)00015-X.
Shtansky, D.V., Nakai, K., and Ohmori, Y. Thu . "Crystallography and structural evolution during reverse transformation in an Fe-17Cr-0.5C tempered martensite". United States. doi:10.1016/S1359-6454(00)00015-X.
@article{osti_20075925,
title = {Crystallography and structural evolution during reverse transformation in an Fe-17Cr-0.5C tempered martensite},
author = {Shtansky, D.V. and Nakai, K. and Ohmori, Y.},
abstractNote = {The mechanism and the crystallography of austenite and {delta}-ferrite formation from tempered martensite at temperatures of 900-1,200 C have been studied by means of transmission electron microscopy in an Fe-17Cr-0.55C alloy. It was found that austenite nucleates within ferrite at low angle, high angle and twin-related lath boundaries as well as at high angle equiaxed grain boundaries in contact with M{sub 23}C{sub 6} grain/lath boundary carbides. The austenite grains are in a cube-cube relationship with the M{sub 23}C{sub 6} carbide particles and bear the Kurdjumov-Sachs orientation relationship with at least one of the adjacent ferrite grains. They are often in the Kurdjumov-Sachs relationship with both ferrite laths separated by a high angle boundary as far as the laths had formed from the same austenite. The {l_brace}111{r_brace}{sub A} close packed plane of {gamma} precipitate is parallel to the {l_brace}110{r_brace}{sub F} plane most parallel to the grain boundary. The close packed planes of some austenite grains nuclearing at the high angle lath boundaries are parallel to the close packed planes of both ferrite laths. These crystallographic features often result in a single variant of austenite orientation at a grain boundary. After nuclearion, the austenite grains grow by the migration of both semicoherent and incoherent interfaces. These results demonstrate that a specific orientation relationship is preferred for the austenite nucleation, but is not necessary for the subsequent growth. The kinetics of austenite growth are controlled by chromium diffusion. The {delta}-ferrite particles precipitate at high temperatures as a non-equilibrium phase. No rational orientation relationship between {delta}-ferrite and retained austenite was found. The experimental results are discussed qualitatively in terms of the thermodynamic predictions using the soft-water ThermoCalc, assuming local equilibrium at the moving interfaces.},
doi = {10.1016/S1359-6454(00)00015-X},
journal = {Acta Materialia},
issn = {1359-6454},
number = 8,
volume = 48,
place = {United States},
year = {2000},
month = {5}
}