ABSTRACT:
The strength and fatigue resistance of components subjected to cyclic and alternating loading, such as crankshafts and gears, are enhanced through diffusion surface hardening processes. Determining the hardened case depth is one of the essential quality control procedures that is typically required after the hardening process. Therefore, this study investigates the measurement of this important control parameter using a non-destructive ultrasonic technique. The ultrasonic method employed in this research is the immersion ultrasonic backscatter technique, in which a 25 MHz transducer is used to measure the depth of thin hardened layers. The hardened specimen is made of DIN 1.7131 steel and has undergone a carburizing heat treatment. The acquired ultrasonic signals are analyzed using signal processing techniques, including noise reduction and detection of the echo reflected from the hardened-layer boundary. The obtained results are then compared with the case depth measured using the conventional destructive method. The results obtained from measurements at 96 locations showed that the hardened case depth of the investigated specimen ranged from 0.76 to 1.24 mm, while the effective case depth determined by the destructive test was approximately 0.867mm, demonstrating good agreement with the ultrasonic measurements. Furthermore, the use of the 25 MHz transducer enabled the detection of the echo reflected from the interface between the martensitic case and the ferrite–pearlite core, making it possible to non-destructively measure hardened layers thinner than 1 mm with satisfactory accuracy. Therefore, the proposed method can be employed as an efficient quality control technique for surface-hardened components in various industrial applications. ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‍‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌‌‌‌‌‌‌‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌ ‌