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    A Comprehensive Model for Hardness Evaluation of Low-Alloy Steels Based on Carbon Content and Ultrasonic Wave Velocity
    (Amer Soc Nondestructive Test, 2017) Uzun, Fatih; Bilge, Ali Nezihi
    Ultrasonic techniques allow for the nondestructive investigation of material properties including hardness, but the requirement of correlation for each material, such as different alloys of steel, separately turns these tasks into a formidable process. This study aims to overcome this problem by proposing a new technique for hardness evaluation of low-alloy steels based on ultrasonic wave velocity and information about the weight percent of carbon content. For this purpose, carbon steel samples with different carbon content, less than 0.5 wt%, were selected. Samples were annealed at varying temperatures, and then an immersion ultrasonic technique was used to measure longitudinal ultrasonic wave velocity in each sample. The hardness of annealed samples was determined on the rockwell B scale. The relationship between ultrasonic wave velocity and hardness of annealed steel samples was investigated in terms of carbon content. A mathematical model was developed, based on carbon content and ultrasonic wave velocity, to predict hardness.
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    Application of ultrasonic waves in measurement of hardness of welded car bon steels
    (Elsevier Science BV, 2015-09) Bilge, Ali Nezihi; Uzun, Fatih
    The ultrasonic contact impedance technique and ultrasonic wave velocities have been widely used for non-destructive hardness measurement. Ultrasonic wave velocity shift provides through the thickness average hardness, however, the correlations are performed according to surface hardness. In order to accept this technique as a particular non-destructive method for determination of hardness, it is necessary to test it with industrial applications. A widely used joining (welding) technique is selected for this purpose. Samples of carbon steels with three different carbon contents, but similar composition, are annealed in order to obtain the softened samples with different hardness values. Rockwell B scale hardness of heat treated samples, which are assumed to be isotropic, are determined and correlated with ultrasonic wave velocity shifts. Effect of welding process on hardness is investigated using ultrasonic wave velocity shifts, and the results are verified with destructive hardness measurements. Copyright (C) 2015, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.
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    Ultrasonic Investigation of the Effect of Carbon Content in Carbon Steels on Bulk Residual Stress
    (Springer/Plenum Publishers, 2015) Uzun, Fatih; Bilge, Ali Nezihi
    Formation of residual stress as a result of welding process is a familiar fact, but its relation with material composition is unknown. This study aims to investigate the effect of carbon content on welding residual stress in carbon steels. For this purpose, samples of ultra-low carbon interstitial free, low carbon and medium carbon steels are selected. Welding is performed as a beam on plate in spite of a joining process. Weld grooves are prepared at center of the rectangular samples. Automated submerged arc technique is preferred for welding process in order to ensure same welding parameters at each sample. Ultrasonic sound waves are used to determine residual stress. This non-destructive technique provides bulk residual stress which is average of shear and normal stresses through thickness of a material. A new approach is practiced to verify experimentally determined bulk residual stress with finite element simulation results. The model geometry of numerical analysis is divided into equivalent parts and average of shear and normal stresses is calculated. Non-destructive ultrasonic technique seems to be in good agreement with finite element analysis.