Experimental Study on Effect of Tempered Microstructure on Ultrasonic Signal of 30CrMnSiA Steel

30CrMnSiA steel, with high strength and good toughness, is an important stressed component of aircraft structure and is often used under tempering conditions of different temperatures after being quenched. In this study, the quenched 30CrMnSiA steel was tempered between 200 ℃ and 700 ℃ to observe its metallographic structure, and the ultrasonic testing method was used to detect the different tempered structures, the relationship between ultrasonic propagation characteristics (longitudinal wave speed, sound attenuation coefficient, bottom wave frequency shift) and tempering temperature and microstructure changes was analyzed. The results showed that with the increase of tempering temperature, the 30CrMnSiA microstructure was tempered martensite, tempered troostite, tempered sorbite, ferrite + pearlite in turn, and the hardness decreases gradually; Because of the influence of tempering brittleness, the ultrasonic testing characteristic parameters of tempered troostite tempered between 540 ℃ to 620 ℃ fluctuated greatly. The ultrasonic velocity increased and the bottom wave frequency shift decreased with the increase of tempering temperature when the others tempered microstructure were tested.