Abstract
The AISI 317L grade is an austenitic stainless steel with high Mo content (3.0 wt% min.). Due to the higher pitting resistance, this grade has replaced AISI 316L steel in many applications where the corrosion resistance is a critical property. However, the high Mo can induce phase transformations in high temperature services. In modern oil refinaries and petrochemical industries AISI 317L has been selected for temperatures as high as 550 °C. The goal of this work was to analyze the microstructural evolution and corrosion resistance of base and weld metal of AISI 317L stainless steel. The welded joints were produced by friction stir welding (FSW). The effect of prolonged exposure at 550 °C was investigated in specimens aged for 200h, 300h and 400h. After each aging treatment microstructural characterization was performed by scanning electron microscopy (SEM). Double loop electrochemical polarization reactivation tests (DL-EPR) were performed to evaluate the degree of sensitization of the samples. The results indicated that the increase of the exposure time at 550 °C promotes the formation of intermetallic phases, which causes corrosion decay of the weld metal.
Highlights
IntroductionAustenitic stainless steels are usually selected to high temperature services due to the high creep and oxidation resistance
The optimization of the structural integrity of the equipment applied in the petrochemical industry motivates the analysis and validation of alternative materials and welding processes, seeking to ensure better metallurgical properties under severe service conditions.Austenitic stainless steels are usually selected to high temperature services due to the high creep and oxidation resistance
The images were obtained in the scanning electron microscopy (SEM) operating in the backscattered electron mode (BSE)
Summary
Austenitic stainless steels are usually selected to high temperature services due to the high creep and oxidation resistance. Microstructural changes may take place during service. “H” grades are often selected for high temperature services because Cr carbides enhance creep resistance[2]. If sensitization by chromium carbide precipitation is considered a problem in services were corrosion resistance must be maintained, Nb or Ti-stabilized steels can be used (grades AISI 347 or AISI 321). These steels are susceptible to sigma (σ) phase formation in long term aging[3,4]
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