LOW AND HIGH TEMPERATURE EMBRITTLEMENT OF Ti-Nb MICROALLOYED STEEL SLAB

The aim of this work was to analyze the morphology of fractures after notch impact toughness tests at room temperature and fractures after hot torsion plastometry tests in the temperature range from 600 to 1250[degrees]C for a TiNb microalloyed steel slab. It was found that the slab cast at the real...

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Bibliographic Details
Published in:Powder Metallurgy Progress 2015-01, Vol.15, p.61-72
Main Authors: Longauerova, M, Bekec, P, Konradyova, J, Vojtko, M, Boruta, A
Format: Article
Language:English
Subjects:
Austenite
Embrittlement
Ferrite
Fracture mechanics
High strength low alloy steels
Intermetallics
Microstructure
Morphology
Slabs
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Summary:The aim of this work was to analyze the morphology of fractures after notch impact toughness tests at room temperature and fractures after hot torsion plastometry tests in the temperature range from 600 to 1250[degrees]C for a TiNb microalloyed steel slab. It was found that the slab cast at the real pulling rate 1.03 m/min had mostly low toughness practically over the whole width of the slab at room temperature. This was also reflected in the fracture morphology, which consisted predominantly of transcrystalline cleavage facets, sporadically smooth facets of intercrystalline decohesion and ductile transcrystalline failure with dimples. Embrittlement at high temperatures was found in the area of stable austenite at 1140[degrees]C and near to the area of phase transformation temperature alpha/gamma austenite at 900[degrees]C. Intergranular facets manifested the embrittlement, and at high temperatures there were also signs of melting. While embrittlement at room temperature under the given test conditions was due to microstructure factors (ferrite, pearlite, size of ferrite or austenite grains, precipitates), the high temperature ductility loss was also dependent on the type of microstructure at the test temperature (austenite, ferrite and austenite), but also on the phase transformation temperature and accompanying precipitation. Comparison of fracture surfaces obtained after impact tests at room temperature with those obtained from the hot plastometry torsion tests confirmed some signs of heredity pointing to types of particles and types of facets in the fracture surfaces.
ISSN:1335-8987