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The notch sensitivity of a material is a measure of how sensitive a material is to notches or geometric discontinuities. Notch sensitivity is influenced by many parameters such as notch geometry. Three types of notch geometries, V-shape, U-shape and -shape notches of various sizes are considered in this investigation. Two steel alloys of high and low strength (designated by HS-steel and LS-steel) are used in this work. Stress concentration is obtained by numerical simulation and the literature and fatigue reduction factor is determined by experiment using rotating bending fatigue device, Moore. The results show that the notch geometry has profound effect on fatigue life of materials. For HSsteel this reduction is roughly about 50%. For LS-steel alloy, however, the reduction depends on fatigue life and varies from 20% for low cycle fatigue tests up to 75% for high cycles fatigue tests. The maximum and minimum fatigue life reduction occurs for the V-shape and U-shape notches, respectively. The Equations proposed by Hardrath and Peterson underestimate the fatigue reduction parameters, q and K f and it seems that they are not adequate for prediction of notch sensitivity and they must be used with care.

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Thermal reactive diffusion coating of vanadium carbide on DIN 2714 steel substrate was performed in a molten borax bath at 950-1050 o C. The coating formed on the surface of the substrate had uniform thickness (1-12 µm) all over the surface and the coating layer was hard (2430-2700 HV), dense, smooth and compact. The influence of the kinetics parameters, temperature and time, has been investigated. Vanadium carbide coating was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction analysis (XRD). The corrosion resistance of the coating was evaluated by potentiodynamic polarization in 3.5% NaCl solution. The results obtained showed that decrease of coating microhardness following increasing time and temperature is owing to the coarsening of carbides and coating grain size.