Martensite content effect on fatigue crack growth and fracture energy in dual-phase steels

The effect of different microstructural factors on crack growth and fatigue fracture mechanisms in dual-phase (DP) steels has yet to be fully understood. The present research examines the relationship between crack growth, microstructure, and fracture mechanisms. The samples were intercritically annealed at different temperatures to produce three different martensite volume fractions (MVFs). The results show that the mechanical incompatibility of ferrite and martensite promotes continuous crack tip deflection. MVF increases are associated with elevated fracture tortuosity, more significant fracture energy surface formation, and higher Paris law exponent m values. The interaction of the microstructure with the crack tip, the strain energy density, and the softening caused by secondary microcrack propagation are all illustrated by Electron backscatter diffraction (EBSD) maps. Increasing MVF promotes slow crack growth and a fracture energy increase of 22.9% between the as-received and heat-treated steels. Martensite content in dual-phase steels generate greater crack propagation resistance.Martensite volume increase produces a more significant number and extension of secondary microcracks.Differences in ferrite and martensite phases promote continuous crack tip deflection.