Influence of Microstructural Length Scale on the Strength and Annealing Behavior of Pearlite, Bainite, and Martensite

A medium carbon steel containing 0.4 pct C, 2.9 pct Mn, and 1.9 pct Si (wt. pct) was heat treated to produce pearlitic, bainitic, and martensitic microstructures. The three microstructures were cold rolled to large strains in order to investigate the change in strength/hardness as a result of the refinement of the microstructural length scale due to plastic deformation. The results show that the hardness does not saturate in any of the above microstructures, implying that geometric strengthening plays an important role not only in lamellar microstructures such as pearlite, but also in lath-type microstructures such as bainite and martensite. Low temperature annealing of the deformed microstructures revealed that they are very resistant to recrystallization.