Influence of Microstructure on the Corrosion Resistance of AISI 317L (UNS S31703)

Abstract

The AISI 317L stainless steel is an austenitic grade with at least 3%Mo. Recently, this steel has replaced AISI 316L in many applications in chemical and petrochemical industries, due to its higher pitting corrosion resistance. The microstructure of the hot rolled and annealed material studied in this work consists of austenitic grains and 4.0% of delta ferrite (δ) with elongated islands morphology. This microstructure was modified by three processes: cold rolling with 87% of reduction, aging at 450 o C for 400 h, and welding by gas tungsten arc welding (GTAW) process. The corrosion resistance was evaluated by anodic polarization tests (ASTM G-61) and critical pitting temperature tests (ASTM G-150). Cold rolling produced a microstructure consisting of elongated grains of austenite and martensite α', high dislocation density and the elongated islands of delta ferrite present in the annealed material. Welding produced a dendritic microstructure with 7.0% of delta ferrite and some σ precipitated in the ferrite. Finally, the aging at 450 o C for 400 h provoked the decomposition of ferrite. The results show that these microstructural changes affected the pitting corrosion resistance, as detected by ASTM G-61 and ASTM G-150 tests.

Mechanical Properties of a Thermally-aged Cast Duplex Stainless Steel by in Situ Tensile Test at the Service Temperature

“…It has been reported that the thermal aging embrittlement in CDSS was caused by the precipitation that formed in the ferrite phase after long-term thermal aging, e.g., the G-phase precipitates and the spinodal decomposition during which the ferrite phase decomposes into a Fe-rich α-phase and a Cr-rich α'-phase [10,11,[13][14][15]. Many researchers have found that the mechanical properties of CDSS are strongly dependent on the strength of each individual phase [16,17] and their microstructures, e.g., the volume fraction and the morphology of the ferrite phase, have meaningful influence on the fracture toughness, thermal aging embrittlement, high-temperature ductility, impact properties and corrosion resistance of duplex stainless steel [18][19][20][21][22][23][24].…”

Three-Dimensional (3D) Microstructure-Based Modeling of a Thermally-Aged Cast Duplex Stainless Steel Based on X-ray Microtomography, Nanoindentation and Micropillar Compression

“…It has been reported that the morphology and the volume fraction of the ferrite phase in duplex steel has an extensive influence on the mechanical performance such as the corrosion resistance [14], the fracture toughness [15,16] and the thermal aging embrittlement [17][18][19][20]. Tavares [14] conducted electrochemical corrosion tests on AISI 317L stainless steel with different microstructures and ferrite contents, which showed that that the microstructural changes affected the pitting corrosion resistance. Li [21] investigated duplex stainless steels equipped with ferrite of different contents through different aging conditions.…”

Estudo da estabilidade microestrutural e das propriedades magnéticas do aço inoxidável austenítico AISI 317L laminado a frio

“…Nos últimos anos a utilização do aço inoxidável austenítico AISI 317L nas indústrias químicas e petroquímicas tem aumentado devido à sua elevada resistência à corrosão. Essa propriedade advém principalmente do teor de molibdênio dessa classe de aços, a qual é no mínimo de 3% (em peso) (FARNEZE et al, 2016;TAVARES et al, 2017).…”

“…Como o aço AISI 317L é do tipo austenítico, ele é suscetível à formação de martensita induzida por deformação. Ou seja, ele sofre uma transformação da fase austenítica (cfc) para martensítica (ccc ou hc), dependendo do grau de deformação e temperatura (TAVARES et al, 2017). Além disso, a martensita induzida por deformação pode ser revertida mediante tratamento térmico MIRAGLIA, 2000;RIOS, 2003;SOUZA FILHO et al, 2016).…”

“…Em um aço inoxidável austenítico é muito comum a presença de ferrita delta, uma fase residual aprisionada na solidificação. No caso do aço 317L, o alto teor de molibdênio o torna suscetível à precipitação de fases intermetálicas quando exposto às altas temperaturas, o que ocorre preferencialmente nas ilhas de ferrita delta (FARNEZE et al, 2014(FARNEZE et al, , 2016TAVARES et al, 2017). A ferrita delta é ferromagnética e essas fases intermetálicas que se formam em razão da decomposição da ferrita são paramagnéticas.…”