Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Grain Boundary Strengthening Mechanism of Tungsten Containing 9 to 12% Chromium Ferritic Heat Resistant Steels at 650°C
Yasushi HASEGAWAMasahiro OHGAMITaro MURAKI
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2003 Volume 52 Issue 7 Pages 843-850

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Abstract

Creep strengthening mechanism of tungsten containing 9 to 12% chromium steels for high temperature application was experimentally extracted and discussed from the view point of grain boundary shielding by Fe2W type Laves phase and M23C6 type carbide during the creep exposure at 650°C. Increase of tungsten content from 1.8mass% for ASME Gr. 92 to 2.5mass% for model alloys resulted in the abrupt creep rupture strength deterioration for about 1000 hours creep time. Increase of chromium from 9mass% to 11mass% or more also affected the creep rupture curve. Excess tungsten and chromium almost precipitated grain boundary, and a grain boundary shielding ratio by the precipitates explained the creep rupture behavior, bending of the curves, in tungsten or chromium increased model alloys according to the analyze by thin foil observation through the Transmission Electron Microscope (TEM) with Energy Dispersive X-ray Spectroscopy. Grain boundary shielding possibly delayed the recovery of dislocation substructure by rigid grain structure. Grain boundary shieldng ratio f0/f expressed the creep curves of model alloys based on the dislocation density degradation at 650°C. Species of precipitates did not seem to affect the dynamic recrystalization of a grain boundary.

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