ANÁLISE EM CONDIÇÕES NÃO ISOTÉRMICAS DE UM AÇO INOXIDÁVEL SUPERDUPLEX ASTM A182 – F53 VIA DILATOMETRIA
ANALYSIS IN NON-ISOTHERMAL CONDITIONS OF SUPERDUPLEX STAINLESS STEEL ASTM A182 – F53 BY DILATOMETRY
Camila dos Santos Pinto, Gabrielle Cristine Lemos Duarte Freitas, Isabele Cristina Abreu de Sá, Gláucio Soares da Fonseca, Luciano Pessanha Moreira, Paulo Rangel Rios
Resumo
O aço ASTM A182 – F53, comercialmente SAF 2507, conhecido como superduplex, é frequentemente utilizado em indústrias offshore, de papel e celulose, devido a suas ótimas propriedades mecânicas e de resistência à corrosão, em função da estrutura balanceada de ferrita e austenita. Quando submetido a elevadas temperaturas, este balanço entre as fases pode ser comprometido e fases intermetálicas que degradam suas propriedades e limitam a sua utilização podem precipitar. A principal fase intermetálica é a fase sigma que nucleia e cresce no aço inoxidável e como consequência degrada as suas propriedades mecânicas e de resistência à corrosão. Os principais estudos na área simulam situações de envelhecimento, mantendo o material em um patamar isotérmico, para propiciar a formação desta fase e resfriamento rápido para posterior caracterização da fase sigma. Neste trabalho, as amostras sofreram ciclos térmicos (CT) de resfriamento sob taxas controladas em condições não isotérmicas em um simulador termomecânico Gleeble. A caracterização microestrutural após os CT foi realizada via microscopia ótica e eletrônica de varredura acoplada com detector de espectro de energia dispersiva. Como resultado, a ferrita se transforma em austenita secundária e fase sigma. O que é confirmado pela microscopia/EDS e pelos picos de temperaturas indicando a transformação de ferrita em fase sigma nas curvas dilatométricas.
Palavras-chave
Abstract
The Steel ASTM A182 – F53, commercially SAF 2507, known as superduplex, is widely used in offshore, pulp and paper industries due to its excellent mechanical properties and corrosion resistance, depending on the balanced structure of ferrite and austenite. When subjected to high temperatures, this balance between phases can be compromised, and intermetallic phases that degrade their properties and limit their use may precipitate. The main intermetallic phase is the sigma phase that nucleates and grows in stainless steel and therefore degrades its mechanical properties and corrosion resistance. The main studies in the area simulate aging situations, keeping the material in an isothermal level, to provide the formation of this phase and rapid cooling for later characterization of the sigma phase. In this work, the samples were submitted to thermal cooling cycles (TC) under controlled rates in non-isothermal conditions in a Gleeble thermomechanical simulator. Microstructural characterization after TC was performed by optical microscopy and scanning electron microscopy coupled to a dispersive energy spectrum detector. As a result, the ferrite turns into secondary austenite and sigma phase. That is confirmed by microscopy/EDS and temperature peaks indicating the transformation of ferrite into sigma phase in the dilatometric curves.
Keywords
Referências
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