Akademik Veri Yönetim Sistemi
JOURNAL OF THE BALKAN TRIBOLOGICAL ASSOCIATION, cilt.16, sa.3, ss.340-352, 2010 (SCI-Expanded)
In this study, fatigue fracture surface morphology of the nitrided and non-nitrided AISI H13 hot work tool steel has been comparatively analysed. In this analysis, metallographic and fractographic characteristics of fracture surface have been assessed together. Fatigue samples were prepared in hourglass shape and nitrided in salt bath (NaCN - KCN) at 570 degrees C for 2 h. Experiments have been conducted on a fatigue experiment device which applied cyclic stress with rotational bending principle at 95 Hz. Nitrided and non-nitrided samples have been tested under the same circumstances and the results have been analysed comparatively. At the end of the experiment, metallographic and EDX analyses of the cross-sections of the samples have been conducted under scanning electron microscope (SEM). The hardness profile of the nitrided case was determined by a microhardness tester. Sample fracture surfaces have been analysed also under SEM, and surface fracture characteristics have been determined. As a result of nitriding, a compound layer with 2-3 mu m thickness and 800 HV(0.03) hardness and a diffusion layer with 70-75 mu M thick have been formed on the surface. Fatigue strength of the nitrided samples has increased by 23% when compared to non-nitrided samples. Mechanical and metallurgical compositions of the fracture surface have been analysed. Fatigue crack initiated at surface for non-nitrided specimen while fatigue crack initiated at the subsurface for nitrided specimen. In the nitrided specimen, fish-eye type crack initiation mechanism developing around a local inclusion is the effective fatigue crack initiation mechanism.