The production flowsheet of Φ35 mm bar of non-quenching-tempering steel C70S6 (/% ： 0.72C

0.20Si

0.58Mn

0.015P，0.065S，0.12Cr，0.05Ni， 0.035V， 0.008Al) is 60 t UHP EAF-LF-VD-240 mm x240 mm bloom casting-rolling process. The analysis on structure

fracture and shearing technology of cracking bar during shearing process is carried out. It is obtained that the structure and hardness of cracking bar are no-obvious different to the non-cracking bar during shearing

and during shearing process by shearing stress action the shift of bar along horizontal plane occurs led to increasing the interval between flat cutter and round cutter

the deformation of bar shearing plane curving and deforming

finally causing crack at end of bar. With the measures including decreasing the interval between cutters from 0.5 mm to 0.3 mm

increasing clamping force from 3 t to 3.5 t and carried out spraying water on steel bar to enlarge coefficient of wear as installing cutters

the results of cutting 30 t steel C70S6 Φ35 mm bar products show that the rate of cutting cracking decreases to 0 from original 10% .