The  effect  of cooling rate

reduction

original  austenite  grain  size  and  strain rate  of0.05C-0. 13Nb  steel  af- ter  single  pass-reduction  40%  with  2  s

-1

at   1000  ℃  or  two  pass-reduction  40%  with 2 s

-1

at   1000℃+  reduction  40%  with 5 s

-1

at 980 ℃ on structure and microhardness HV has been studied by Thermecmastor-Z thermal simulation test ma- chine.Results indicated that with increasing cooling rate the granular bainite gradually increased

of which the content was up  to93%  as  cooling  rate  was  to 5  ℃/s

and  the  HV  value  obviously  increased

while  cooling  rate  was  more  than  5  ℃/s the morphology of bainite island structure was changed and the HV value increased little; with decreasing original austenite grain size and increasing reduction the HV value decreased; but the effiect of strain rate on HV value was not appreciab

le.