The Effect of Tempering Holding Time in Rapid Heat Treatment on The Mechanical Properties and Microstructure of Medium Carbon Steel

Rapid heat treatment sustainably optimizes steel strength and toughness through precise control of phase kinetics and grain refinement. Rapid heat treatment with an induction furnace consisting of austenitization held for 25 s reaching a temperature of 900℃ followed by oil quench, and tempering with holding times of 5, 8, and 10 s reaching a temperature of 150℃, 250℃, and 300℃ respectively, and results were compared with conventional heat treatment. The research results show that the variation of holding time in rapid tempering has a significant effect on mechanical properties, where impact energy (30.6 J/cm²), yield strength (1430 MPa), tensile strength (1768.79 MPa), and percent elongation (12.32%) reached their peak values at a holding time of 8 s, while hardness values tended to be linear and stable. Microstructurally, this treatment produced a martensite phase with heterogeneous laths, bainite structure, undissolved carbide, and a mixed fracture morphology of quasi-cleavage and dimples.