The experimental data of 400 heats of steel produced by 110 t EAF + LF/VD refining + continuous casting + hoi rolling in a special steel plant are statistically analyzed. The hardenability [at (920 ± 10) °C for 50 min and then air cooling to room temperature

followed by holding at (880 ±5) °C for 30 min water quenching

]

and chemical composition of 20CrMnTiH steel are obtained by means of Jominy test and spectral analysis to get a linear relationship between the hardenability and the content of residual boron. By each steelmaking practice analysis it is found that the main source of B in steel is EAF tapping slag. The content of B in steel can be effectively controlled by controlling the amount of tapping slag in EAF tapping. In addition

when the amount of Al

2

O

3

in the refining slag decreases from 30 % to 15% ~20%

the content of B in steel can be controlled below 0.

000 2%.