J Integral Fracture Toughness of a Twinning-Induced Plasticity Steel Fe-Mn-C-Cr: Effect of Cr content

This study investigates the influence of chromium on the fracture behavior of TWIP steels with a base chemical composition of Fe-22Mn-0.6C (wt.%), and with chromium contents of 5 wt.% Cr and 10 wt.% Cr. Tensile tests were conducted at room temperature showed that the yield strength increased with Cr content, from 320 MPa (0 wt.% Cr) to 520 MPa (10 wt.% Cr), while ductility dropped significantly for the highest Cr alloy. Fracture toughness was quantified using the J-integral parameter following the ASTM E1820 standard. Due to the exceptionally high damage tolerance of the 0 wt.% and 5 wt.% Cr alloys, their initiation toughness exceeded the geometric validity limits of the specimens and are conservatively reported as provisional J Q values of 764.3 kJ/m 2 and 892.2 kJ/m 2 , respectively. In contrast, the 10 wt.% Cr alloy yielded a valid size-independent J IC of 79.2 kJ/m 2 . Fractographic and microstructural analyses using FEG-SEM-EBSD revealed that the 0 wt.% and 5 wt.% Cr steels exhibited intense mechanical twinning (Twinned Grain Fractions of 77.1% and 66.9%, respectively) and predominantly ductile fracture modes with stretch zone widths (SZW) of 160 μm and 200 μm. Conversely, the 10 wt.% Cr alloy showed significantly reduced twinning (29.1% TGF) and a fracture surface dominated by intergranular and quasi-cleavage features. The stretch zone width (SZW) was measured and analyzed as an additional indicator of fracture toughness of the material.