The metallurgical flowsheet for developed cold heading steel QB3O wire-rod (/% ： 0. 27 〜0. 32C

≤0. 20Si

0. 90 ~ 1. lOMn

≤0. 020P

≤ 0. 020S) is hot metal pre-desulphurization- 80 t BOF- LF- RH vacuum degassing- 4 strands 280 mm x 325 mm bloom casting- stacking cooling- blooming- grinding- high speed wire rolling process. With the process measures including using BOF high catch carbon reblow practice

controlling BOF end [C] 0. 07% ~0. 15% and [P]≤ 0. 013%

hot metal [P] ≤0. 095% and [S]≤ 0. 03%

controlling LF refining slag basicity R = 4~10 and (FeO + MnO) ≤l. 0%

and RH vacuum ≤90 Pa

of φ18 mm wire coil of steel QB30 the tensile strength is 591 MPa

elongation is 29% and reduction of area is 60%

the nitrogen content and total oxygen content in steel respectively are 0.004 0% and 0.001 8%

and the rating of non-metal inclusions in steel is 0 ~ 1. 5 to meet the requirement of user.