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    Effect of Various Spheroidizing Methods on Microstructure-Mechanical Properties and Wear Performance of PM High-Carbon Steel
    (Springer India, 2022) Gokmese, Hakan; Karadag, Hakan Burak; Tasdogen, Hacer
    In high-carbon unalloyed steels produced by the powder metallurgy method, the effect of different spheroidizing heat treatments on microstructure, mechanical properties, and wear performance was studied. For this purpose, 1.2 wt% graphite powders were added to Fe powders, and a powder composition was formed. The prepared powder mixtures were pressed at room temperature under 850 MPa and then sintered at 1180 degrees C for 20 min. After sintering, sample phase compositions were determined by the XRD analysis. Then, three different spheroidizing heat treatments were applied. First, the conventional spheroidizing was used for 5-10-20-40 h at a constant temperature of 700 degrees C. Secondly, for 5-10-20-40 h, cyclical spheroidizing was involved in the temperature range of 700 degrees C and 740 degrees C. A third heat treatment (post-quenching spheroidizing), which represented the study's original aspect and was an alternative to these known spheroidizing methods, was applied. Fully austenitized work-pieces were quenched in water at room temperature. Consequently, the martensitic structure was formed. These samples were over-annealed for 5-10-20 h at 700 degrees C. Even after a short period, such as 5 h, homogeneous and fine spherical cementite was formed in the microstructure. Depending on the spherical cementite morphology and distribution, impact toughness and hardness values were evaluated. Besides, steels' wear characteristics were determined using the block-on disc device, and three-dimensional worn surface morphologies were examined with the profilometer device. With the scanning electron microscope (SEM), microstructures formed due to different heat treatments were displayed. Also, the fractured and worn surfaces of the samples were examined. It was determined that with the post-quenching spheroidizing treatment, which may be an alternative to known and widely used spheroidizing treatments, the desired microstructure and properties such as machinability and ductility could be achieved in a much shorter period.