The Effect of Intercritical Annealing Temperature on the Microstructure and Mechanical Properties of Dual-Phase Cast Steel

In this research, a steel specimen with the new chemical compositions of 0.3 C, 2.5 Si, 1.8 Mn, and 0.5 Cr (wt. percent) was cast. Intercritical annealing (IA) heat treatment was performed at three temperatures(i.e., 825, 850, 875°C) on these samples in 26 minutes to achieve the dual-phase steel. To determine the effect of intercritical annealing (IA) temperature, optical (OM) and scanning electron microscopy (SEM) microstructures were studied, as well as mechanical properties via hardness, micro-hardness, and tensile testing. The results indicated that intercritical annealing temperature increased, martensite volume, hardness, and yield strength increased. Also, the tensile strength initially increased and then decreased. However, the sample intercritical annealed at 850°C showed maximum tensile strength (1532 MPa), and the sample intercritical annealed at 825°C showed maximum elongation (18.52 %), and strength–elongation balance (UTS×UE). This dual-phase steel showed two stages of hardening, with the increase of martensite, the slope of the second stage decreased, and the strain at the beginning of the second stage of hardening was transferred to lower strains.