EFFECTS OF ANNEALING HEAT TREATMENT ON THE MECHANICAL AND MICROSTRUCTURAL CHARACTERISTICS OF MEDIUM CARBON STEEL.

The mechanical behavior and performance of medium carbon steel can be profoundly modified through thermal processing. This study investigates the effect of annealing temperature on the mechanical and microstructural behaviour of medium carbon steel. Test specimens were subjected to full annealing at various temperatures ranging from 600 °C to 850 °C, followed by controlled furnace cooling. Mechanical properties such as tensile strength, yield strength, hardness, elongation, and impact toughness, were evaluated according to ASTM standards, while microstructural evolution was examined using optical microscopy. Results showed that annealing temperature had a profound influence on material behavior. Tensile and yield strengths decreased initially with rising temperature, reaching a minimum at 650 °C, but recovered progressively at higher temperatures. Elongation and impact energy improved significantly with temperature up to an optimum point (700–750 °C), beyond which ductility and toughness declined, suggesting over-annealing effects. Hardness followed a similar trend, with initial softening and subsequent partial recovery. Microstructural analysis revealed a transformation from fine pearlite-ferrite in the as-received condition to coarser ferrite grains with spheroidized carbides at higher annealing temperatures. These findings underscore the critical role of annealing temperature in optimizing the balance between strength and ductility for enhanced processability and structural performance of medium carbon steel