Department of Metallurgical and Materials Engineering
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Browsing Department of Metallurgical and Materials Engineering by Author "Arslan, Ebru"
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Item NONDESTRUCTIVE CHARACTERIZATION OF BEARING STEELS BY MAGNETIC BARKHAUSEN NOISE TECHNIQUE(2017-06-02) Arslan, Ebru; Davut, Kemal; Şimşir, CanerOne of the most popular type of bearing steels is 100Cr6. The strength, toughness, hardness, fatigue life, wear resistance of it can be improved by heat treatment applications which also changes the microstructure. For controlling the microstructure, traditional metallographic and XRD- based methods, that involve taking representative specimens from lots, are used. Magnetic Barkhausen noise (MBN) technique may provide an alternative nondestructive, fast and practical measurement method to those traditional techniques. This study aims at investigating the possibility of nondestructive characterization of microstructure of heat treated 100Cr6 bearing steels by using the MBN technique. For that purpose, 100Cr6 steel specimens were heat treated in a quenching dilatometer under different austenitization conditions and then quenched to room temperature and to -130°C, in order to generate variations in their microstructures. After heat treatment applications, microstructural properties of the specimens including the fraction and distribution of carbides, amount of retained austenite and also hardness were determined by metallographic and XRD analysis. Moreover, MBN measurements were performed and then the results were correlated to the microstructural parameters. MBN signals correlate with the microstructure variations in the 100Cr6 steel samples via simple linear relations; however, the prediction bands were quite wide and the MBN technique was not sufficiently sensitive, for direct characterization of hardness, retained austenite and carbide fraction of the specimens that were quenched to room temperature. In order to characterize these interdependent microstructural parameters via MBN technique, non-linear relations based on carbide dissolution kinetics are needed. On the other hand, the MBN measurement results of the sub-zero treated specimens showed that; elimination of retained austenite significantly improved the goodness of fit of on those linear relations. Although coefficient of determinations of both carbide fractions and hardness were acceptable, it can be improved by developing a newer non-linear model. Nevertheless, all of the results were promising for the future applications of MBN technique on nondestructive characterization of microstructure variations in 100Cr6 steels.