Title

MICROSTRUCTURAL CHANGES IN THE HAZ OF A SAF 2205 DUPLEX STAINLESS STEEL, AFTER LONG AGING AT 380°C

MICROSTRUCTURAL CHANGES IN THE HAZ OF A SAF 2205 DUPLEX STAINLESS STEEL, AFTER LONG AGING AT 380°C

Authorship

FERRANTE, MAURIZIO; MELLO, MARCELO DE; LESKO, ANDREJ

FERRANTE, MAURIZIO

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MELLO, MARCELO DE

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LESKO, ANDREJ

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DOI

10.5151/2594-5327-C00073-1132-1144

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Abstract

The present investigation was performed on the HAZ of a SAF 2205 Duplex stainless steel plate. Welding was carried out using the TIC technique; subsequently, the samples were kept at 380°C during long periods of time, up to 3000 h. Metallographic investigations consisted of optical microscopy plus scanning and transmission electron microscopy on thin foils and replicas, besides EDS microanalysis. The microhardness of the weld joint (base metal, HAZ and weld deposit) was performed on the ferrite and results show a continuous increase with time of that property, particularly on the HAZ. Transmission electron microscopy showed extensive precipitation, already in as-welded state, identified by microanalysis and diffraction ring patterns as complex carbonitrides, containing Fe, Cr and Fe in a 2:1:1 proportion. Also, a modulated contrast on the as-welded ferritic matrix suggests the onset of spinodal decomposition, and observation of such contrast in aged samples showed that it becomes sharper with time, implying continuation of the decomposition. Finally a combined analysis of precipitation, spinodal decomposition and microhardness evolution concluded that the decomposition is the main responsible for properties degradation of long term aged samples, up to 3000 h.

The present investigation was performed on the HAZ of a SAF 2205 Duplex stainless steel plate. Welding was carried out using the TIC technique; subsequently, the samples were kept at 380°C during long periods of time, up to 3000 h. Metallographic investigations consisted of optical microscopy plus scanning and transmission electron microscopy on thin foils and replicas, besides EDS microanalysis. The microhardness of the weld joint (base metal, HAZ and weld deposit) was performed on the ferrite and results show a continuous increase with time of that property, particularly on the HAZ. Transmission electron microscopy showed extensive precipitation, already in as-welded state, identified by microanalysis and diffraction ring patterns as complex carbonitrides, containing Fe, Cr and Fe in a 2:1:1 proportion. Also, a modulated contrast on the as-welded ferritic matrix suggests the onset of spinodal decomposition, and observation of such contrast in aged samples showed that it becomes sharper with time, implying continuation of the decomposition. Finally a combined analysis of precipitation, spinodal decomposition and microhardness evolution concluded that the decomposition is the main responsible for properties degradation of long term aged samples, up to 3000 h.

Keywords

Duplex Stainless Steel, HAZ, Precipitation

Duplex Stainless Steel, HAZ, Precipitation