Relative influence of microsegregation and structural unit size on the strength-impact toughness properties of an armor grade steel

Abstract

The present study highlights the comparative interplay between microsegregation of alloying elements and structural unit size on the strength and impact toughness properties of a medium carbon low alloy armor grade steel. Interestingly, despite possessing finer substructural unit (Bain width), the sample austenitized at a lower temperature (800 °C) exhibits inferior impact toughness. This emanates from centerline fissure cracking assisted by severe segregation-induced tensile residual stress at the mid-thickness region. On the other hand, coarse Bain width reduces toughness at the higher temperature (1200 °C). Therefore, austenitization at an intermediate temperature (1000 °C) imparts excellent impact toughness (∼ 45 J at – 40 °C) combined with a commendable yield strength (∼ 1090 MPa). This is attributed to the fine Bain width along with moderate segregation, indicating the significance of austenitization temperature to get an optimized microstructure for achieving a striking balance between strength and impact toughness in a chemically inhomogeneous armor steel structure.