The effect of cooling rate 100-10 °C/min from 1150 °C to 500 °C on attribute of inclusions and behavior of inducing intragranular ferrite nucleation in 0.45C steel casting billet has been studied by using high temperature confocal superpower laser-beam microscope to control cooling rate combined with optical

scanning electron microscope and energy dispersive spectrometer. Results show that with decreasing cooling rate the high melting-point inclusions in steel basically no-change while the low melting-point inclusions size and amount in steel trend towards increasing

especially the amount of vanadium carbo-nitride increases obviously; with decreasing cooling rate the amount of precipitated intragranular ferrite increases

the average grain size increases and the ferrite ratio first increases and afterwards decreases. As continuous cooling with 30 Y/min

the ratio of size of inclusions in steel less than 10 μm is up to 93%

the average size of ferrite is 9.2 μm and the dimensions ratio of ferrite is 30.2%.