Abstract
	The purpose of this work is to quantitative evaluate precipitation in Nb-V microalloyed steel and to investigate the effect of holding time at rolling temperature on the precipitate parameters, austenite recrystallization and mechanical properties. The specimens were heat treated at 1200oC for 30 min and hot rolled at 1150oC by deformation 45%. Then followed rolling at the temperature 900oC by deformation 30%. The samples were hold at rolling temperature 900oC for times 1s up 1000s, followed by water quenching. For experimental procedure were used: dilatation test, hardness test, tensile test, Charpy impact test, light microscopy and electron microscopy of extraction carbon replicas. Precipitate parameters were evaluated by the method of 3 step statistic. The total evaluated area of precipitation was 4,2-6,0 ?m. It is shown that very fine strain-induced particles Nb(CN) occured after rolling by deformation 30% at the temperature 900oC. The mean particle size 2 increases linearly with holding time at rolling temperature and proportionately the mean particle number on unit area  decreases. The Nb(CN) particles start to form clusters or coagulated particles after holding time 100s and 1000s. Strain-induced particles cause the significant retardation of austenite recrystallization and hardening of steel. The austenite recrystallization was retarded until 100s after deformation at 900oC and maximum steel hardening occured in quench state without holding time after rolling.