This work produced high-strength quenching and tempering medium carbon steels via fast induction heating to achieve an optimal combination of strength and ductility. The achieved yield strength, tensile strength, and total elongation were 2103 MPa, 2301 MPa, and 8.26%, respectively. Compared to conventional heating, fast induction heating results in finer martensite blocks and a much higher density of dislocations. The contribution of dislocation strengthening is found to be dominant, exceeding 1000 MPa, rather than boundary strengthening as commonly considered. With a proper raising of tempering temperature, the dislocations interact and partially annihilate, leading to a fallback in strength but an increment in ductility. Thus, it can be concluded that fast induction heating is a feasible technique to balance ultrahigh strength and high ductility in medium carbon steels.