Microstructural Evaluation of High-strength Bainitic Steel by Nondestructive Techniques

Phase transformation in 28Cr3SiNiWMoV steel was studied by utilizing different techniques. Appropriate heat treatment cycles were employed to understand the microstructural changes within the high-strength steel. It was observed that the austenite formation started at 1073 K (800 degrees C) and completed at approximately 1123 K (850 degrees C). Further, on cooling in the furnace from the austenitic range, it was noted that the resultant structure was bainitic, having hardness greater than 450 Hv. Nondestructive analysis of the samples treated at different heat treatment temperatures revealed that there is a good correlation between the metallurgical changes and the ultrasonic longitudinal velocity. This study can be used to evaluate the hardness of the material without any destructive testing.