Start Date

2016 12:00 AM

Description

Austenitic stainless steels have a wide range of applications in the energy industry. However, these stainless steels can be susceptible to stress corrosion cracking (SCC) under normal operating environments. Of particular concern is weld sensitization, a process by which chromium carbide precipitates are formed at the grain boundaries in the heat affected zone. Sensitization reduces the resistance of stainless steels to SCC by local depletion of chromium content in the sensitized material.

This research uses nonlinear Rayleigh waves to quantitatively track the sensitization of AISI 304 and AISI 304L stainless steels which were exposed to a temperature of 675 °C with variable time. The effect of the carbon contents of the alloys (AISI 304 versus AISI 304L) to the sensitization process and the measured nonlinearity parameters are investigated. Note that an initiallymonochromatic propagating Rayleigh wave interacts with the grain-boundary precipitates due to the sensitization and generates higher harmonics.

A set of laboratory specimens were created with different degrees of sensitization and varying precipitate sizes and contents using heat treatments at 675 °C in for varying heat treatment times. The acoustic nonlinearity parameter was determined from the first and second harmonic Rayleigh waves measured in the propagation direction. This acoustic nonlinearity parameter is directly related to the evolution of the grain boundary precipitates. Furthermore, we evaluated the degree of sensitization in these specimens with the electrochemical reactivation (EPR) test and used microscopy to quantify the average size, location, and content of the chromium carbide precipitates. The results show that the acoustic nonlinearity parameter is sensitive to the presence of M23C6 precipitates.

Language

en

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Jan 1st, 12:00 AM

Evaluation of Sensitization in AISI 304 and AISI 304L Stainless Steel with Nonlinear Ultrasonic Rayleigh Wave Measurements

Austenitic stainless steels have a wide range of applications in the energy industry. However, these stainless steels can be susceptible to stress corrosion cracking (SCC) under normal operating environments. Of particular concern is weld sensitization, a process by which chromium carbide precipitates are formed at the grain boundaries in the heat affected zone. Sensitization reduces the resistance of stainless steels to SCC by local depletion of chromium content in the sensitized material.

This research uses nonlinear Rayleigh waves to quantitatively track the sensitization of AISI 304 and AISI 304L stainless steels which were exposed to a temperature of 675 °C with variable time. The effect of the carbon contents of the alloys (AISI 304 versus AISI 304L) to the sensitization process and the measured nonlinearity parameters are investigated. Note that an initiallymonochromatic propagating Rayleigh wave interacts with the grain-boundary precipitates due to the sensitization and generates higher harmonics.

A set of laboratory specimens were created with different degrees of sensitization and varying precipitate sizes and contents using heat treatments at 675 °C in for varying heat treatment times. The acoustic nonlinearity parameter was determined from the first and second harmonic Rayleigh waves measured in the propagation direction. This acoustic nonlinearity parameter is directly related to the evolution of the grain boundary precipitates. Furthermore, we evaluated the degree of sensitization in these specimens with the electrochemical reactivation (EPR) test and used microscopy to quantify the average size, location, and content of the chromium carbide precipitates. The results show that the acoustic nonlinearity parameter is sensitive to the presence of M23C6 precipitates.