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    Evaluation of the mechanical properties and machinability of chromium and molybdenum-added powder metallurgy steels
    (Sage Publications Ltd, 2024) Vassouf, Abdul Rahman; Akgun, Mahir; Erden, Mehmet Akif
    The present study focuses on the microstructure, mechanical properties, and machining aspects of powder metallurgy (PM) steel containing different rates of chromium (Cr) and molybdenum (Mo). PM steel alloys were pressed at 700 MPa and sintered at 1400 degrees C in a mixture of nitrogen and hydrogen atmosphere for 1 hour. While the precipitates and fracture surfaces of the samples obtained were examined by scanning electron microscope (SEM) and EDS analyzes, the grain size and phase distributions were also examined with an optical microscope. Moreover, tensile and hardness measurement tests were carried out to determine the mechanical properties of the samples with different ratios of Cr and Mo content. The milling experiments were also performed without using coolant in a CNC milling machine at different cutting parameters. The surface roughness (Ra), tool wear (Vb), and wear mechanism were investigated under these conditions. The outcomes of this study reveal that the yield and tensile strength values of the samples with the addition of Cr and Mo increased but the elongation value decreased. The results also stated that the most effective process parameter for both Vb and Ra was the workpiece material and the regression models developed to estimate the output parameters (Vb and Ra) give successful results with high determination coefficients (R-2) of 98.05% and 98.11%, respectively.
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    INVESTIGATION OF THE EFFECT OF CR ADDITION ON THE MECHANICAL AND MACHINABILITY PROPERTIES OF CR-MO STEELS PRODUCED BY POWDER METALLURGY
    (2022-06) Vassouf, Abdul Rahman
    By using powder metallurgy (PM) techniques, materials with complex particle geometry can be produced with a relative lower cost compared to conventional steel production methods such as casting. In addition, the PM methods allow accurate preparation of various alloy compositions. The amount and type of alloying elements included in the steel composite play an important role in determining the mechanical and structural properties of steel, as they affect hardness, yield, strength and tensile strength. Thus, it directly affects the machinability. In powder metallurgy (PM), molybdenum, nickel, and copper are the most common alloying elements, because they are less sensitive to oxidation during sintering process. However, recently some studies on the oxidation of chromium during sintering process show that materials based on Cr-alloyed powders are less sensitive to sintering atmosphere compared to materials made from powder mixed with high chrome additives. Because of the good mechanical properties that result from the use of chromium as an alloying element, this has attracted the interest of some scientists and researchers in the field of biometals because this type of steel composites can be used in some biomedical applications. In this thesis work, chromium was added to Fe-Mo metal matrix composite (MMC) in different proportions, and an MMC was produced using PM method. In the production process, the powders were mixed with a three-axis (triaxial) mixer for about couple of hours while pressed at high pressing pressure, and then sintered at high temperature. The microstructures and surfaces of the steel samples produced were examined using an optical microscope and a scanning electron microscope (SEM). Density measurements were performed and porosity amounts were calculated. Tensile tests, corrosion tests and machinability tests were applied. After reviewing the results of mechanical and structural tests, the possibility of using Chromoly steels manufactured using powder metallurgy in biomedical applications was discussed.