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Title:
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A microstructural study of F82H-MOD: plate, powder HIP and EB and TIG weldments
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Author(s):
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Published by:
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Publication date:
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ECN
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1998
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ECN report number:
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Document type:
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ECN-R--98-013
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Other
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Number of pages:
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Full text:
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68
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Download PDF
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Abstract:
F82H is the heat identification number of a ferritic/martensitic steel.The steel has a chemical composition resulting in low activation after
neutron irradiation. At ECN a microstructural study was conducted on plates
of F82H (73, 15 and 25mm thick), a bar of HIPped F82H and EB and TIG welds in
F82H plates. The investigation was aimed to characterise the microstructures
for reference in irradiation experiments. The F82H mod. plates have a
martensitic matrix with carbide precipitation on the prior austenite grain
boundaries and the martensite laths. The carbide precipitation is most
pronounced on the prior austenite grain boundaries. The PAG is comparable for
the three plate thicknesses investigated. In two plates faint segregation
bands were found with a denser carbide precipitation and 8-ferrite. Further
Ta, Ti and Zr containing oxides are present. Hardness measurements show a
higher overall hardness in the 25mm plate investigated compared to the 7.5
and 15mm plates. The F82H HIP bar shows a homogeneous PAG throughout the
diameter. The microstructure shows a zone starting at about 1 mm below the
surface with a width of 14mm, with a relatively high concentration of low
precipitation density ferritic like fields, which corresponds to a zone with
a 15HV5 lower hardness with respect to the rest of the bar. This zone is
expected to be related to the HIP process. Further in the microstructure a
circular pattern of W and Ta enriched inclusions is found, which mark the
original HIP-powder grain boundaries. The EB-welds were manufactured by two
manufactures and differ mostly in the heat input, resulting in differences in
HAZ-width and the width of the weld cap. The F82H EB welds show comparable
microstructures in the weld pool, with a martensitic microstructure free of
carbides. All EB-welds contain 8-ferrite in concentrations of 0.1-1%. In the
heat affected zone (HAZ), the coarse grained HAZ (CGHAZ) is free of carbide
precipitation, whereas the fine grained HAZ (FGHAZ) shows a dense carbide
precipitation. At the transition from FGHAZ to unaffected base material,
non-transformed ferritic phases enriched in W are present. The TIG weld was
post weld heat treated which resulted in a lower hardness than the EB welds
and a dense carbide precipitation. The hardness measurements of the EB and
the TIG welds show a hardness dip on the transitions FGHAZ to the
'unaffected' base material. 3 refs.
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