Showing papers by "Anish Kumar published in 2000"

Ultrasonic spectral analysis for microstructural characterization of austenitic and ferritic steels

Abstract: The paper discusses the use of ultrasonic spectral analysis for microstructural characterization in AISI type 316 stainless steel and modified 9Cr–1Mo ferritic steel (T91/P91). Several specimens of AISI type 316 stainless steel have been heat treated at different temperatures varying from 1373 to 1623K. for different time durations (from 15 to 120min) to obtain specimens with different grain sizes. Spectral analysis has been carried out on the rf signal corresponding to the first back-wall echo obtained with a 25 MHz delay line longitudinal beam transducer. The shift in the peak frequency and the change in the full width at half-maximum of the autopower spectrum have been correlated with the average grain size and yield stress. Various specimens of modified 9Cr–1Mo ferritic steel have also been subjected to a series of heat treatments consisting of soaking for 5min at different temperatures in the range 1073–1623K followed by oil quenching. These treatments were given to obtain different microstr...

Characterization of microstructures in austenitic stainless steels by ultrasonics

Abstract: Recently, many nondestructive techniques have been considered for microstructural characterization of materials to enable in-situ component assessment for pre-service quality and in-service performance. Ultrasonic parameters have been used for estimation of average grain size, evaluation of recrystallization after cold working, and characterization of Cr2N precipitation during thermal aging in different grades of austenitic stainless steels. Ultrasonic first back wall echo signals were obtained from several specimens of AISI type 316 stainless steel with different grain sizes. Shift in the spectral peak frequency and the change in the full width at half maximum of the autopower spectrum of the first back wall echo are correlated with the grain size in the range 30–150 microns. The advantages of this method are: (i) independence of variation in couplant conditions, (ii) applicable even to highly attenuating materials, (iii) direct correlation of the ultrasonic parameters with yield strength and (iv) suitab...