Precipitação de fases intermetálicas e austenita secundária na ZAC de soldagens multipasse de aços inoxidáveis duplex. / Intermetallic phases and secondary austenite precipitation at the multipass welding HAZ of duplex stainless steels.

AUTOR(ES)

Antonio José Ramírez Londoño

DATA DE PUBLICAÇÃO

2001

RESUMO

Duplex stainless steels (DSS) have excellent mechanical and corrosion properties. Many researches have been developed regarding the weldability of these alloys. There are some phase transformations that take place during the welding process, which may impair the welded joint behavior. High temperature heat-affected zone (HTHAZ) microstructures were simulated using a proposed heat flow model. Fundamental aspects of the secondary austenite and chromium nitride precipitation, and its interactions in the HTHAZ of multipass welds, were studied. In addition, toughness and corrosion tests were done to evaluate the influence of the studied phase transformations on the weld behavior. A GleebleÒ system was used to do the heat treatments and HTHAZ simulations. The microstructures were analyzed by means of optic and electron microscopy. Along with the electron microscopy it was done chemical microanalysis of the studied phases. Based on results, it was verified that not all DSSs can be ferritized. This fact has a strong influence on metallurgical behavior and weldability of these alloys. Regarding to the metallurgical fundamental aspects of these steels, it was observed a remarkable interaction between secondary austenite and chromium nitride precipitation. Thus, it was proposed a mechanism of intragranular secondary austenite precipitation from chromium nitrides. It was also verified, how the deleterious effect of intragranular secondary austenite in the corrosion resistance can be avoided by means of appropriate welding procedures.

ASSUNTO(S)

secondary austenite heat-affected zone (haz) austenita secundária chromium nitride zona afetada pelo calor (zac) multipass welding duplex stainless steel aço inoxidável duplex nitreto de cromo soldagem multipasse

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