Correlation Between Microstructure and Micromechanism of Quasi-Cleavage Fracture of 33Mn2V Dual-Phase Steel

Abstract

As oil exploration expands into deep-sea and cold regions, improving the low-temperature toughness of oil casings is crucial, and dual-phase (DP) heat treatment has shown potential as an effective method to enhance this property. In this study, the relationship between the microstructure and low-temperature fracture mechanism of 33Mn2V steel is investigated under various heat-treatment conditions. Intercritical quenching and tempering treatments produced DP steels with varying martensite fractions, analyzed using optical microscope, scanning electron microscopy, and electron backscatter diffraction. In the results, it is shown that quenching at 800 °C achieves the best impact toughness (40.5 J cm⁻² at −120 °C), which is attributed to the combined effects of cooperative deformation between martensite and ferrite, effective surface energy (36.1 J m⁻²), and the maximum plastic deformation area (871 μm²) during crack propagation. In these findings, the role of microstructural evolution, including the optimal martensite fraction, in influencing fracture behavior and quasi-cleavage mechanisms is highlighted.