ASME Grade 92 steel (Fe–9Cr–2W–0.5Mo, wt.%) is a creep strength-enhanced ferritic (CSEF) steel. The newer material is designed to have better creep rupture strength than, the former Gr.91 steel (9%Cr–1%Mo steel). Both steels are used in fossil-fuel-fired power and nuclear plants because of their suitability for continued long-term use in high-temperature, and high-pressure steam circulating environments. Due to the service application, the Grade 92 steel material components are regularly subjected to onsite welding, and steady degradation triggered by exposure to high-temperature service conditions. Hence, this material has a limited-service life and may fail in the heat-affected zone (HAZ) under creep conditions.
However, minimal research has been performed to examine the microstructure of Grade 92 steel welds in regions of the HAZ in reference to varied welding heat input. To improve inspection reliability and increase the effectiveness in the detection of unfavorable microstructures in applications of high steam temperatures and pressures, there is a need for an effective non-destructive evaluation (NDE) procedure that can detect weld HAZ microstructures based on the ultrasonic wave energy transmission and reflection principles.
This study explores the feasibility of an ultrasonic imaging procedure to reliably identify weld HAZ microstructures such as coarse-grain heat-affected zone (CGHAZ), fine-grain heat-affected zone (FGHAZ), weld metal (WM), and base metal (BM). This imaging technique can be further developed to be used in the field to improve the detectability of highly susceptible regions in weld microstructures of CSEF steels which, could potentially promote creep-type failures in welds manufactured using the traditional arc welding processes. Additionally, for this material, the fundamental relationships, and correlations are explored to showcase the differences in peak-to-peak amplitude, attenuation, and ultrasonic velocity caused by ultrasonic beam scattering patterns when the grains in WM, CGHAZ, FGHAZ, and BM interacted with 20-MHz ultrasonic wave.