The cold heading cracked samples and Φ 12 mm hot-rolled wire rods of SWRCH35K steel are inspected by optical microscope. Analysis results show that the reason for cold heading cracking is full decarburized layer exist on the surface of hot-rolled wire rod

led to decrease of strength

resulting in stress cracking of the surface layer during the cold upsetting process. By decreasing billet heating temperature from original 1 000 〜1 150 °C  to 950 〜1 050 °C

controlling air-fuel ratio 0. 4 ~0. 6

and decreasing billet total heating time from original 95 ~212 min to 95 ~ 158 min

the full decarburized layer of SWRCH35K steel hot-rolled wire rod is effectively eliminated

and the cold heading cracking in the production process of bolts and nuts is avoided.