By testing with a 80kg vacuum induction furnace and measuring continuous cooling transformation (CCT) curves by using Gleeble 3800 hot simulation machine the chemical composition of steel S2 (/%: 0.63~0.69C

1.00~1.20Si

0.40~0.60Mn

0.20~0.40Cr

0.40~0.50Mo

0.15~0.25V

0.10~0.30Ni

0.010~0.030Nb

≤0.015P

≤0.010S) has been designed

and the commercial production by 120t BOF-LF-VD-300mmx390mm bloom casting-breakdown-high speed wire rolling-Stelmor control cooling process has been carried out. With the process measures including hot metal dephosphorization

sulphur content in metal ≤0.010%

control of BOF end[C

]

0.10% ~0.30%

end[P

]

≤0.012%

liquid end temperature 1620~1660℃

using Si-Mn pre-deoxid

ation in BOF tapping

LF refining slag (/%: 8~10MgO

44~45CaO

5~10SiO

2

25~35Al

2

O

3

feeding calcium wire at end of LF refining

overheating extent of casting liquid ≤25℃，casting speed 0.65m/min

and controlling cooling after rolling

the cqil of alloy tool steel S2 is successfully developed. Examination results show that the each property index of Φ8mm hot-rolled coil meets the requirement of technical specification

including the austenite grain size rating 8.5~9.0

the depth of decarburization layer≤0.5%D

the HRC hardness value of hot-rolled coil 50 and the variation of HRC hardness value of same coil less than 6.