The effect of 0. 03% —0. 21% Si on structure and properties of 10B21 cold heading steel of containig boron (/% ：0.20C

0.03 〜0

21Si

0. 82 ~0. 83Mn

0

009 〜0. 013S

0. 015 〜0. 016P

0.0019 ~ 0.0020B)Φ34 mm hot- rolled coil has been analyzed and studied. The end-rolling temperature of hot-rolling coil is 900℃

slow-cooling. Results show that with increasing Si content in 10B21 steel from 0. 03% to 0. 21%

the tensile strength of coil increasing from 480 MPa to 489 MPa

i. e. that increases by 9 MPa; the HRB hardness value increases by 5. 3 ； the size of ferrite groups in structure of steel reduces from 52μm; to 42 μm； the size and quantity of non-metallic inclusions has no obvious change ； and the hardenability of steel improves.