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3715099 
Journal Article 
TRANSFORMATION-INDUCED PLASTICITY IN STEEL FOR HOT STAMPING 
Masek, B; Stadler, C; Jirkova, H; Feuser, P; Selig, M 
2014 
1 
Materiali in Tehnologije
ISSN: 1580-2949 
48 
4 
555-557 
WOS:000341068600018 
The hot-stamping process for manufacturing car-body components was patented in 1977. Its main advantages include the precision of the product shape, the reduced spring-back effect and the resulting high strength of steel parts upon hardening. Boron- and manganese-alloyed steels have been specially developed for this process. The 22MnB5 grade is a typical representative of this group with its strength up to 1500 MPa. For the desired mechanical properties to be achieved, the final microstructure should consist primarily of martensite without any substantial amounts of other phases. Further development of press hardening, therefore, requires all the phenomena associated with the phase transformations during the cooling between dies to be well mapped. Significant parameters, in this respect, include phase-transformation temperatures and the data on a number of additional phenomena, including transformation-induced plasticity. Transformation-induced plasticity is manifested when a part held between dies undergoes a phase transformation, typically, when being under stress. In the course of a lattice rearrangement, this stress causes the atoms to occupy more favourable positions in terms of energy. At the macro-level, this can be detected as a change in the dimensions, which, at the same time, significantly relieves the stress, therefore, eliminating the spring back. Despite a profound importance of this phenomenon for the press-hardening process, it has not been explored in detail up to now. For these reasons, a 22MnB5 steel grade was employed in this project. The impacts of the tensile and compressive stresses occurring during phase transformations, upon the changes in the expansion of the sheet specimens, were explored using the schedules that simulated real-world hot-stamping and press-hardening processes. 
press hardening; hot stamping; spring-back effect; 22MnB5; transformation-induced plasticity