Effect of thermal regime on the microstructure and microhardness of steels microalloyed with Nb and V

Microalloying of high strength steels with elements, such as Nb, Ti and V, having high affinity to carbon and nitrogen, contribute to a significant improvement of its mechanical properties. Microalloying of steel using these elements allows the obtainment of mechanical strength and good toughness at low cost as compared with conventional alloyed steels. If the metallurgical processes for obtaining (steelmaking and refining) and thermo-mechanical processing (rolling, forging etc.) are appropriate, precipitates may act within the material by blocking the movement of grain boundaries, which allows the increasing of toughness and thermal stability characteristics at high temperatures. To study the effect of thermal regime on the microstructure and microhardness of steels microalloyed with niobium and vanadium were made several charges, with different chemical composition, using two types of metallurgical units: a Balzers type vacuum induction furnace VIM and vacuum arc remelting equipment - VAR. In order to estimate the effect that the applied thermal regime have on the steel microstructure and hardness characteristics, samples of steel microalloyed with Nb and V were normalized at 950...970 degrees C for 20 minutes, after which they were cooled in air. Microstructure analysis and microhardness measurements were performed. It was found that after applying the heat treatment, for most analyzed steel samples, the microhardness has decreased with different values, depending on the chemical composition.