The dynamic (deforming 50% at 950 °C with deformation rate 5 s

-1

cooling to ambient) and static (nondeforming

880 °C

cooling to ambient) continuous cooling transformation (CCT) curves with cooling rate 0. 5 ~20 °C/s of non-quenching-and-tempering steel C38N2 (/%: 0. 38C

0. 55Si

1.42Mn

0. 011P

0. 047S

0. 03Nb

0. 015Ti

0. 022Al

0. 020N) have been tested and studied with using Gleeble-1500 thermal simulation machine by thermal expansion dilation method and metallographic examination. Results show that for non-deforming steel

with cooling rate 0. 5 °C/s

the structure of non-quenching-and-tempering steel C38N2 is ferrite-pearlite

as cooling rate is 3. 0 °C/s its structure is bainite + ferrite-pearlite

with cooling rate >3. 0 ~ 11 °C/s the steel has bainite + martensite structure and

with 15 ^C/s the structure of steel is martensite； as cooling rate ≤11℃/s

all the phase transformation initial temperature of dynamic CCT is larger than that of static CCT.