In the last decades several investigations have been conducted with the objective of studying the microstructural characteristics and mechanical properties in low carbon microalloyed steel [1,2]. These steels contain a polyphase microstructure, with complex mixture of bainite, MA constituent (martensite-austenite residual), pearlite, ferrite and martensite. They are often used in the automobile industry, in the production pipelines for the transport of gas and oil in areas of sub-zero temperature and in the naval ship construction, because they possess high strength, high toughness at low temperature and good weldability.