Isothermal transformation behavior of acicular ferrite in a microalloy pipeline steel

The intermediate transformation behavior of a low carbon microalloy pipeline steel was studied by isothermal transformation on Gleeble1500D.The microstructure and transformation characteristics in the steel were investigated according to the results of both dilatometry measurements and microstructure observations.The results show that the acicular ferrite transformation of the steel is taken place about temperature of 550 ℃ and there are highly density dislocations and substructure in the base microstructure,the transformation behavior can be characterized as a two-stage reaction such as nucleation of acicular ferrite and acicular ferrite coarsening.