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    THE EFFECT OF NI ON THE MICROSTRUCTURE, WEAR AND CORROSION BEHAVIORS OF MICROALLOYED STEELS PRODUCED BY POWDER METALLURGY
    (2023-02) Ahssi, Mohamed Ahmed Mohamed
    Microalloyed steels can be stated as low-alloyed high-strength steels that improve the mechanical properties of the carbide, nitride and carbonitride formed by the addition of carbide and nitride-forming elements such as titanium, niobium and vanadium, which are added below 0.2% by weight. The formation and dissolution temperatures of carbon nitrides formed in microalloy steels must be calculated very well. Otherwise, incorrectly designed casting method, rolling temperature and cooling rate may cause carbonitrides not to form or to form and overgrow. The production of microalloyed steels produced by rolling, controlled cooling and casting methods has also been carried out by powder metallurgy method in recent years. Powder metallurgy is one of the independent production methods that is used in the manufacture of parts used in many sectors such as implant materials, gears, tortoiseshells, bushings, which cannot be produced with other production methods such as tungsten filament used in electric lamps, including small precision parts that are difficult to manufacture. The element nickel added in this study is an austenite stabilizer and widens the austenite area as well as narrowing the ferrite area in iron chromium carbon alloys. Nickel increases corrosion resistance against oxidation at high temperatures. It prevents scale formation on the material surface. In addition, nickel, which has a grain reduction effect, increases the toughness and strength of the material. It increases the hardness, ductility, high fatigue resistance of the material and decreases the critical cooling rate by using it with chromium. Compared to many elements such as carbon, copper and molybdenum, the nickel element diffuses slowly in iron because its diffusion coefficient value is lower. In this study, alloy steel with nine different compositions was produced by adding graphite, Nb, V and Ni in different proportions into Fe powders. Characterization of alloy steel samples containing different amounts of Nickel was carried out by corrosion test, wear test, hardness test, optical microscope, XRD, SEM Mapping and SEM EDS analyses.
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    The Effect of Nickel on the Microstructure, Mechanical Properties and Corrosion Properties of Niobium-Vanadium Microalloyed Powder Metallurgy Steels
    (Mdpi, 2020) Ahssi, Mohamed Ahmed Mohamed; Erden, Mehmet Akif; Acarer, Mustafa; Cug, Harun
    In this study, the effects of adding Ni in different ratios to Fe-matrix material containing C-Nb-V produced by powder metallurgy on microstructure, tensile strength, hardness and corrosion behaviors were investigated. Fe-C and Fe-C-Nb-V powders containing 5%, 10%, 13%, 15%, 20%, 30% and 40% nickel were pressed at 700 MPa and then sintered in an Ar atmosphere at 1400 degrees C. Microstructures of the samples were characterized with optical microscope, scanning electron microscope (SEM) and XRD. Corrosion behaviors were investigated by obtaining Tafel curves in an aqueous solution containing 3.5% NaCl. Mechanical properties were determined by hardness and tensile testing. While Fe-C alloy and Fe-C-Nb-V microalloyed steel without Ni typically have a ferrite-pearlite microstructure, the austenite phase has been observed in the microstructures of the alloys with 10% nickel and further. Yield and tensile strength increased with nickel content and reached the highest strength values with 13% Ni content. The addition of more nickel led to decrease the strength. Analysis of Tafel curves showed that corrosion resistance of alloys increased with increasing nickel concentration.