Yield Strength Enhancement by Carbon Trapping in Ferrite of the Quenching and Partitioning Steel

The split quenching and partitioning (S-QP) process allows researchers to investigate microstructure and properties separately, i.e., before and after partitioning. After the partitioning process, the yield strength increases by approximately 300 MPa in the ferrite-bearing delta-quenching and partitioning (delta-QP) steel. We propose that carbon trapping in dislocations at the ferrite grain boundaries during partitioning process is responsible for the yield strength enhancement of ferrite. Combined transmission electron microscopy and 3D atom probe tomography observations demonstrate carbon atoms segregating in dislocations. The mechanisms for the high yield strength of ferrite presented QP steels are clarified for the first time in this research. (C) The Minerals, Metals & Materials Society and ASM International 2017