Twinning-assisted ductile-to-brittle transition in single crystals of Fe-Mn-Al-C austenitic steels with different stacking fault energy

摘要

The paper is devoted to experimental investigation of ductile-to-brittle transition (DBT) and fracture peculiarities in austenitic high-carbon Fe-Mn-Al-C steels with different stacking fault energy. The DBT in Fe-13Mn-1.3C (Hadfield steel, Ⅰ), and Fe-13Mn-2.7Al-1.3C (Ⅱ) and Fe-28Mn-2.7Al-1.3C (Ⅲ) (wt. %) single crystals oriented along [001], [011], and [111] directions was investigated under tension. The tensile specimens were solution-treated at 1373 K for 1 hour and then water-quenched. Tensile tests were conducted in the temperature interval of 77 - 673 K at a strain rate of 4×10~(-4) s~(-1). For fracture and structural analysis, a scanning electron microscope and a transmission electron microscopy were utilized. In the present study single crystals were employed to exclude the contributions of the grain boundaries to work hardening and fracture. Moreover, the choice of specimens with the different tensile axes allowed to study fracture peculiarities under conditions where mechanical twinning dominates or suppressed, and also to change the number of twinning systems, which in turn provides information on the influence of multiplicity of shear on the fracture mechanism.