EFFECT OF AUSTENITIZATION AND COOLING MEDIUM ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 12 % MANGANESE STEEL

This study evaluates the mechanical properties of high manganese steel used in manufacturing hammers and grinding jaws, which reduce rocks into small particles. Four austenitization heat treatments (1025°C, 1050°C, 1075°C, and 1100°C) were applied, followed by quenching in water and ice water. Samples were characterized for microstructural and structural properties, as well as phase identification, using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Microhardness measurements revealed an increase in hardness from 436 HV0.2 for samples quenched in water at 1025°C to 680 HV0.2 for samples quenched in ice water at 1050°C. Impact resistance testing showed a resilience increase from 20 J cm-2 for samples treated at 1075°C in water to 161.27 J cm-2 for those treated at 1050°C in ice water. Tribological testing indicated a wear rate reduction from 6.23.10-4 mg m-1 for samples quenched in water to 0.3.10-4 mg m-1 for samples quenched in ice water. XRD results revealed an austenite solid solution phase across all samples, with additional martensitic and Mn7C3 - type carbide phases in those quenched in ice water. SEM analysis confirmed that manganese steel, austenitized for 45 min and quenched in water, shows coarse-grain carbide aggregates within an austenitic matrix. In contrast, samples quenched in ice water exhibit a compact matrix with fine-grain Mn7C3 - type carbides and martensite, resulting in enhanced mechanical performance. The 12 % Mn steel, austenitized at 1050°C and quenched in ice water, demonstrated the optimal combination of impact resistance and wear resistance.