Abstract
	Influence of cooling conditions on ferrite and martensite formation was researched. Material used for experiments was (C-Mn-Si)-based steel produced by electric induction melting furnace, casting into ingots and then forged. Forging reduction was about 4. Laboratory controlled rolling and controlled cooling on air to holding temperature and followed by controlled cooling in furnace at holding temperature were made. Microstructural analysis was performed by optical microscopy. Final microstructure mostly consists of ferrite and martensite and in some cases also pearlite occurs. The largest ferrite fraction  about 65% was obtained at furnace holding temperature Th=570°C and longest furnace holding time th=240sec. Thermodynamic instability of austenite occurs at furnace holding temperature Th=740°C. Decrease of Th temperature generates heavy driving force for austenite to ferite transformation, whereby longer th time allows the diffusion of carbon from ferite to austenite. This leads to stabilisation of austenite. Long times and low temperatures give rise to pearlite creation in carbon-stabilised austenite, hence it came to decrease of carbon fraction in austenite. Vickers microhardness (HV 0,05) of martensite for selected samples was measured by Hanemann hardness tester. Next it was recalculated to HV hardness according to equations in [4,5]. In relation to results from these equations the carbide fraction in martensite was calculated. Measured microhardness reached the amount of 724 HV 0,05 and 810 HV 0,05; recalculated hardness reached the amount of 607 HV and 543 HV; and according to it the carbide fraction in martensite was in the range of (0,28-0,31)w.% and (0,35-0,39)w.% for selected samples.