Effect of Nb on phase transformation of the low carbon and low alloy steel

The phase transformation temperature was determined by Gleeble-1500 thermo-mechanical simulator with different Nb content for the low carbon and low alloy steel.The microstructure and hardness were studied,showing that under the same cooling rate,the austenite phase transformation temperature decreased with increasing Nb content,while the microstructure was long slip bainite ferrite and its hardness was also increasing.Under the same Nb content,the austenite phase transformation temperature decreased with increasing the cooling rate,and the microstructure became tiny fine while the big equiax ferrite grain changed into long lath bainite ferrite.