242 KB13 KB200020242014Feuser, PeterJirková, HanaMašek, BohuslavSelig, MikeŠtádler, Ctiborštevilka:4letnik:48str. 555-557COBISSID:1074090ISSN:1580-2949URN:URN:NBN:SI:doc-7FA0B1BGenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijeheat treatmenthot stampinglegirano jekloplastičnostpress hardeningspring-back effecttoplotna obdelavatransformation-induced plasticityutrjevanje s stiskanjemvroče štancanjevzmetni učinekTransformation-induced plasticity in steel for hot stamping| Vpliv pretvorbe na plastičnost jekla za vroče štancanje|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 processesPostopek vročega štancanja za izdelavo komponent karoserije avtomobilov je bil patentiran leta 1977. Njegove glavne prednosti so natančnost oblike izdelka, zmanjšan vzmetni učinek in visoka trdnost jeklenih delov po toplotni obdelavi. Posebno za ta postopek so bila razvita jekla, legirana z borom in manganom. Značilen predstavnik te skupine je jeklo 22MnB5 s trdnostjo do 1500 MPa. Za doseganje želenih mehanskih lastnosti mora biti končna mikrostruktura martenzitna, brez večjih deležev drugih faz. Nadaljnji razvoj utrjevanja pri stiskanju zahteva, da se obvladajo vsi pojavi, ki so povezani s faznimi premenami med ohlajanjem v orodju. S tega vidika so pomembni parametri, ki vključujejo temperature faznih premen in podatki o številnih drugih pojavih, vključno z vplivom fazne premene na plastičnost. Vpliv fazne premene na plastičnost se pokaže, ko se v delu med orodjema zgodi fazna premena, navadno pod tlakom. Med preureditvijo mreže napetosti povzročijo, da atomi zasedejo energijsko bolj ugodne položaje. Na makronivoju se to kaže kot sprememba dimenzij, ki istočasno zmanjšajo napetosti in odpravijo učinek vzmeti. Kljub pomembnosti ta pojav utrjevanja pri stiskanju do sedaj še ni bil podrobno raziskan. Zato je bilo v tej raziskavi uporabljeno jeklo 22MnB5. Raziskani so bili učinki nateznih in tlačnih napetosti, ki se pojavijo med fazno premeno pri spremembi širjenja vzorcev pločevine, s simulacijo realnega vročega štancanja in procesa utrjevanja s stiskanjemTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije