Transition from carbon clusters to ε, θ-carbides in a quenched and aged low-carbon ferritic steel

Enhancing Mechanical Properties of Carbon–Silicon Steel through Two‐Stage Quenching and Partitioning with Bainitic Transformation: Ultimate Tensile Strength of 1875 MPa and Total Elongation of 8.03%

“…During the second partitioning stage at 400 °C, the observed change in dilation can be attributed to a combination of phase transformations, precipitation hardening, carbon depletion in martensite (which reduces the c / a or tetragonality index), and a sequence of carbide transitions during tempering. This sequence begins with the formation of a supersaturated solid solution of carbon, followed by Zener‐ordering of carbon atoms, leading to the formation of Zener‐ordered Fe 8 C. Subsequently, fine ε‐carbide precipitation occurs, resulting in the clustering of ε‐carbide rods and ultimately leading to the precipitation of θ‐carbides, as suggested by Kawahara et al [ 35 ] Moreover, studies by Ning et al [ 36 ] on carbide precipitation and coarsening kinetics in carbon steel during quenching and subsequent tempering reveal the formation of nanosized, plate‐like, autotempered transition‐iron‐ε’ carbide and cementite within coarse lath martensite. Zhang et al [ 37 ] showed the competitive reactions during partitioning/tempering, which include carbon segregation to dislocations and transition carbide precipitation, significantly impacting the microstructures and dimensional changes.…”