The simulation test on controlling rolling and cooling process for Φ28 mm round billet of cold heading steel 10B21 (/% : 0. 20C

0. 20Si

0. 85Mn

0. 014P

0.005S

0. 001 8B) to be going to finishing rolling has been carried out by using Gleeble-1500 thermal simulation machine to study the effect of finishing rolling temperature- 850 ~ 1 000 °C with deformation rate 20 s

-1

and reduction- 65%

loop-laying temperature 820 〜940 ℃ and cooling rate in phase transformation range- 0. 2 〜1.0 °C/s on structure of steel. Results show that with increasing loop-laying temperature and cooling rate in phase transformation range the volume fraction of ferrite in steel increases obviously and with increasing cooling rate in phase transformation range the banded structure of steel is improved availably

. In order to get higher ferrite volume fraction

coarser ferrite grain and more homogeneous structure to increase the cold heading performance

the optimum controlling rolling and cooling process parameters are finishing temperature- 950°C

loop-laying temperature- 910°C and cooling rate in phase transformation range- 1. 0 °C/s.