20th International Forgemasters Meeting - IFM 2017

The ultrasonic technique is the main non-destructive testing (NDT) method for the inspection of large forgings. With this technique, it is also possible to obtain information about microstructural features, which is very important because it gives the possibility to easily check the quality of processes during all the production cycle. In this paper, the relationship between some microstructural features of a medium carbon steel for forged components and the propagation of ultrasonic waves within the material is analyzed. The work focuses on the study of the relation between ultrasonic attenuation and mean grain dimension: this topic has attracted in the last years a renewed research interest since more accurate and fast measurements can be realized due to the evolution of digital instrumentation in the field of ultrasonic NDT [1-3]. In this paper, we compare different methods based on the use of linear and non-linear chirp signals, which allow an easy and fast analysis of the attenuation data. Moreover, by proper chirp design, also the non-linear ultrasonic response of the material can be analyzed [4]. Different microstructures obtained by means of different heat treatments were firstly realized on a pilot scale and characterized by means of light microscopy (LM). Afterwards, the ultrasonic attenuation of the various samples was measured in a wide range of frequencies by applying several measurement techniques and signal processing. In the full paper, a thorough analysis of these results will be given. [1] Sharma, Govind K., et al. "Short time Fourier transform analysis for understanding frequency dependent attenuation in austenitic stainless steel." NDT & E International 53 (2013): 1-7. [2] Du, Hualong, and Joseph A. Turner. "Ultrasonic attenuation in pearlitic steel." Ultrasonics 54, no. 3 (2014): 882-887. [3] Li, Min, et al."Material grain size characterization method based on energy attenuation coefficient spectrum and support vector regression." Ultrasonics 69 (2016): 1-10. [4] Matlack, K. H., et al. "Review of second harmonic generation measurement techniques for material state determination in metals." Journal of ND Evaluation 34.1 (2015): 1-23.