Isothermal versus non-isothermal hot compression process: A comparative study on phase transformations and structure–property relationships

It is known that the direct hot stamping process in which the specimen is deformed and quenched simultaneously results in a high-strength product without the occurrence of springback. In the current work, the effects of isothermal and non-isothermal thermo-mechanical processes on the phase transformations and the resultant microstructure and mechanical properties of 22MnB5 steel are investigated. For the non-isothermal processing route which is similar to direct hot stamping, the specimens were simultaneously compressed and quenched, while in the isothermal route, the specimens were isothermally deformed and subsequently quenched. The results indicated that higher forming loads as well as Ms and Mf temperatures are the characteristics of the former process over the latter one. Additionally, following the isothermal compression process by quenching resulted in a fully martensitic microstructure.

► Fully martensitic microstructure resulted after isothermal hot compression process.
► Isothermally compressed specimen has lower Ms. and Mf temperatures.
► Implementation of non-isothermal hot compressing process demands higher force.
► Application of isothermal hot deformation process is recommended.