The production flowsheet for non-quenched and tempered steel F45MnVS is 50 t UHP EAF-LF-VD-260 mm x300 mm and 180 mm x 220 mm billet casting-rolling to Φ20-Φ160 mm products. According to analysis on microstructure of steel

the hot heading crack is caused by block and lamella MnS and attached with Al

2

O

3

-MnO-FeO compound oxide. With using the process measures including controlling Al content in steel 0.010%-0.030%

EAF end [C

]

≥0.20% and end [P

]

≤0.025%

[Mn

]

/[S

]

＞20

LF refining slag basicity ≥3.0

after VD soft argon blowing for ≥ 12 min

ensuring homogeneous distribution of sulfur in steel

superheating extent of liquid in tundish 20-30 °C

controlling casting speed to prevent MnS segregation

and controlling finishing rolling temperature 850-1000 °C and cooling rate after rolling 2

-4℃/s

the main inclusions in steel is long lath MnS

the hot heading test is all qualified without crack and other defects.