Development of a nanostructured bainitic steel

Visoko trdnostna bainitna jekla brez karbidov, so v novejšem času bila deležna velike pozornosti, saj lahko zgolj z fazno transformacijo, dosegajo ugodne kombinacije mehanskih lastnosti. Če poteče bainitna premena pri dovolj nizkih temperaturah se debelina ploščic bainitnega ferita giblje med 20 in 60 nm. Po mnenju nekaterih zato lahko smatramo kot prvi masovni nanomaterijal. Žal zahteva doseganje tako fine mikrostrukture zelo dolge čase izotermnega žarjenja (vsaj 10 dni), v primerih da se ne poslužimo dragih legirnih elementov, kot sta Co in Ni. Posledično so ta jekla komercialno manj zanimiva, razen v določenih nišah (zobniki pri formuli 1, gredi za letalske motorje). V magistrskem delu bo predstavljen lasten razvoj visokotrdnostnega nanostrukturnega bainitnega jekla brez karbidov, s kinetiko transformacije ki je vsaj za dva velikostna razreda hitrejša, v temperaturno primerljivem področju.Ultra hight strength carbide free bainitic steels, have recently been giving much attention, due to the outstanding combinations of mechanical properties obtainable in this alloys, by means of phase transformation alone. Of special interest are the microstructures obtained by isothermal holding at sufficiently low temperatures, where the thickness of individual bainitic ferrite plates lies within the range of just 20 to 60 nm. According to certain experts the later qualifies them as the the first bulk nanostructured material. The low transformation temperature however, has as a consequence that the times of isothermal holding become very long (at least 10 days), unless expensive alloying elements like cobalt andare used. Rendering them quite unappealing, and therefore limited only to specific applications, like F1 gearboxes, and aircraft engine shafts. In the following work, the independent development of a new kind of carbide free bainitic steel is presented, in which the transformation kinetics are at least 2 hours of magnitude faster in the same temperature region