Measurement of Continuous Cooling Transformation Curve and Effect of Cooling Rate on the Inclusion and microstructure of DH36 Steels

The temperature-expansion curves under different of cooling rates of DH36 steels had been measured by high temperature phase transformation quenching instruments.The CCT curves of the steels had been determined by using the expansion method and observing the microstructure of the steels.The influence of different cooling rates on the inclusion size, quantity and microstructure had been studied.The results showed that the range of cooling rates for achieving acicular ferrite is 0.3~3℃/s and the optimum cooling rate is 1℃/s.With the increase of cooling rates, the number of the inclusions decreases first and then in-creases.The size of inclusion is mainly between 0~2 μm, and is suitable for inducing nucleation of acicular ferrite.The nucleation of acicular ferrite has not always been increased with the increase of inclusion num-ber.There is an optimal combination of number of inclusions and the nucleation of acicular ferrite.