Mechanical properties and microstructural characterization of medium carbon non-quenched and tempered steel: Microalloying behavior

Microalloying behavior in medium carbon non-quenched and tempered steel was investigated in this paper. The mechanical properties and microstructures in steels with different V, Ti, Nb and V contents were carefully compared and analyzed. The results showed that V and N largely reduced the average size of network ferrite and increased the volume fraction of intragranular ferrite (IGF) and ferrite. Ti, and Nb had the same effect as V and N while the effect was weaker. Ti and Nb could further increase the IGF content by increasing the size of the IGF nuclei (V, Ti)(C, N) and (V, Ti, Nb)(C, N). The precipitation strengthening of V-N steel was the highest. The precipitation strengthening of other steels was weaker due to the larger size of the particles. The highest elongation of the microalloying elements free steel can be attributed to the lack of precipitation strengthening in the steel. The relatively lower elongation of V-N steel can be ascribed to the larger grain size of steel. The V(C, N) and (V, Ti)(C, N) particles decreased the impact energy of V-N steel and V-Ti-N steel. The highest impact energy of V-Ti-Nb-N steel resulted from the refinement of the grain size. The comprehensive mechanical properties can be obtained in V-Ti-Nb-N steel as: the yield strength was 509.7 MPa, the elongation was 19.2% and the impact energy AkU was 55.4 J.