Non destructive Characterization of Prior Austenite Structure of AISI D2 Tool Steel by Magnetic Barkhausen Noise Technique

Davut, Kemal
Kılıçlı, Volkan
Murathan, Ömer Faruk
Şimşir, Caner
Heat treatment operations of steels usually start with austenitization. The properties of the heat treated products, therefore, are strongly influenced by the prior austenite grain structure. The present study aims at investigating the possibility of using magnetic Barkhausen noise (MBN) technique to evaluate the prior austenitic grain structure. For that purpose air quenched AISI D2 cold work tool steel samples were used. In order to obtain samples having different prior austenitic structure, the samples were austenitized between 1000 ⁰C and 1150 ⁰C for 30 minutes. Afterwards all the samples were air quenched. Formation of the desired microstructures was ensured by metallographic examinations. The Barkhausen activity of the samples were evaluated by MBN fingerprints and the root-mean-square value of the noise signal. The results show that with increasing prior austenite grain size, the Barkhausen activity increases due to the enhancement of domain wall displacement. This enhancement is mainly caused by the reduction of prior austenite grain boundary area per unit volume. Apart from the martensitic matrix, the prior austenite grain boundaries act as an additional obstacle to domain wall motion; due to the presence of non-magnetic precipitates at these regions. Moreover; the increase of austenite grain size is accomplished by higher austenitizing temperatures; which in turn reduces the density of alloy carbides by dissolving them. Since the alloy carbides can also restrict domain wall motion, lower density alloy carbides also contribute to higher MBN response of the samples austenitized at a higher temperature. The results indicate that the MBN technique, with a proper calibration, can non-destructively characterize the prior austenitic structure of tool steels.
Citation Formats
K. Davut, V. Kılıçlı, Ö. F. Murathan, and C. Şimşir, “Non destructive Characterization of Prior Austenite Structure of AISI D2 Tool Steel by Magnetic Barkhausen Noise Technique,” presented at the 11th Int Conf on Barkhausen Noise Micromagnetic Testing (ICBM 11), (18 - 20 Haziran 2015), İzmir, Türkiye, 2015, Accessed: 00, 2021. [Online]. Available: