**4. Conclusions**

(1) A theoretical model for the phase transformation of USIBOR® 1500 high-strength steel was established. The initial phase transformation temperature of the high-strength steel phase was

calculated, and the ferrite, pearlite, and bainite transformation kinetic curves and TTT curves were plotted. An analysis of the curves showed that to ensure the martensite content of the final part, the cooling rate of quenching must be kept over 27 ◦C/s.

(2) The law of phase transformation of USIBOR® 1500 high-strength steel during hot stamping was studied by a simulation of the phase transformation process of the formed parts. For ensuring enhanced martensite content at the end of the final quenching, the best choice for the initial temperature of the sheet should be 850 ◦C.

**Author Contributions:** J.L. and P.Z. conceived and designed the experiments; L.Z. performed the experiments; C.X. analyzed the data; J.L. and P.Z. wrote the paper.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
