Ultrasonic Testing of ML80 and Grade 483 Q&T Steel

Abstract

ML80 and Grade 483 are heat treatable steels, produced by a quench and temper process, that are used in the oil and gas industry. The development of the microstructure during heat treatment is important to ensure that the correct properties are achieved for these steels. However, a real-time monitoring method to ensure that the proper microstructure has been formed is not available at this time. Ultrasonic testing has the possibility of being used to measure the microstructure of steels after heat treatment. The purpose of this research is to investigate the connection between ultrasonic parameters and the martensite microstructure fraction in heat treated steel. Ultrasonic measurements are conducted in pulse-echo mode, using longitudinal and shear wave modes. Using ultrasonic velocity and attenuation measurements, this research analyzes the relationship between the ultrasonic parameters, steel hardness measurements, and microstructure fraction measurements. These measurements are taken at varying distances along the axial direction of Jominy end quench specimens of ML80 and Grade 483 Q&T steel. Lower ultrasonic longitudinal velocity is measured for steel materials with higher hardness, and lower velocity is correlated with higher martensite fractions for both steel types examined. Ultrasonic attenuation is found to be highest in martensite for both steel types. Ultrasonic wave energy loss (ultrasonic energy attenuation) is measured using a Fourier transform method and is observed to obey the same trend seen in attenuation, with martensitic microstructures showing increased energy loss. Calculation of Poisson’s ratio from ultrasonic measurements is examined as an alternative to ultrasonic velocity calculations.